Environmental Protection Technology Series
FUEL CONTAMINANTS:
Volume 1. Chemistry
Industrial Environmental Research Laboratory
Office of Research and Development
U.S. Environmental Protection Agency
Research Triangle Park, North Carolina 27711
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RESEARCH REPORTING SERIES
Research reports of the Office of Research and Development, U.S. Environmental
Protection Agency, have been grouped into five series. These five broad
categories were established to facilitate further development and application of
environmental technology. Elimination of traditional grouping was consciously
planned to foster technology transfer and a maximum interface in related fields.
The five series are:
1. Environmental Health Effects Research
2. Environmental Protection Technology
3. Ecological Research
4. Environmental Monitoring
5. Socioeconomic Environmental Studies
This report has been assigned to the ENVIRONMENTAL PROTECTION
TECHNOLOGY series. This series describes research performed to develop and
demonstrate instrumentation, equipment, and methodology to repair or prevent
environmental degradation from point and non-point sources of pollution. This
work provides the new or improved technology required for the control and
treatment of pollution sources to meet environmental quality standards.
EPA REVIEW NOTICE
This report has been reviewed by the U. S. Environmental
Protection Agency, and approved for publication. Approval
does not signify that the contents.necessarily reflect the
views and policy of the Agency, nor does mention of trade
names or commercial products constitute endorsement or
recommendation for use.
this document is available to the public through the National Technical Informa-
tion Service, Springfield, Virginia 22161.
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EPA-600/2-76-177a
July 1976
FUEL
CONTAMINANTS
VOLUME 1. CHEMISTRY
by
E.J. Mezey, Surjit Singh, and D. W. Hissong
Battelle-Columbus Laboratories
505 King Avenue
Columbus, Ohio 43201
Contract No. 68-02-2112
Program Element No. EHB529
EPA Project Officer: William J. Rhodes
Industrial Environmental Research Laboratory
Office of Energy, Minerals, and Industry
Research Triangle Park, NC 27711
Prepared for
U.S. ENVIRONMENTAL PROTECTION AGENCY
Office of Research and Development
Washington, DC 20460
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ABSTRACT
Volume I of this two-volume report reviews information on the
characteristics of solid and liquid fuels. Specifically, this volume
deals with the chemical and physical characteristics of components of
the fuel which are sources of sulfur, nitrogen, and trace element
pollutants when these fuels are utilized.
This review suggests that at least part of the sulfur and most
of the nitrogen originate from compounds common to the fuels reviewed, i.e.,
coal, petroleum, tar sand oil, and shale oil. These are primarily organic
sulfur and organic nitrogen compounds. For liquid fuels, it was concluded
that intrinsic centers of sulfur and nitrogen contamination are found in
the colloidal suspensions commonly known as asphaltenes and the more soluble
resins. Trace elements are present as oil soluble compounds in petroleum,
tar sand oil, and shale oil. In coal, it was concluded that the nitrogen
contaminants are present as organic compounds and that the sulfur in coal
is present both as organic and inorganic compounds. The organic sulfur and
nitrogen contaminants are part of the three-dimensional carbon skeletal
structure that makes up the organic part of coal. The major sources of
inorganic sulfur are pyrites and sulfates. Trace elements in coal were
categorized into those found principally with the organic matter of coal
and those found present principally in the mineral matter associated with
coal. Upon conversion of coal to a coal liquid, most of the organic sulfur
and nitrogen originally present in the coal remain in the coal liquid.
Most of the trace elements associated with the mineral matter remain
insoluble. Such characterizations were done in part to facilitate the
review of methods of removal of contaminants prior to combustion of the fuel
reported in Volume II.
iii
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TABLE OF CONTENTS
Page
ABSTRACT iii
1. INTRODUCTION 1
1.1. Technical Objectives 1
1.2. Approach 1
1.3. Background 2
1.3.1. Characteristics of Coal 6
1.3.2. Characteristics of Petroleum or Crude Oils . 14
1.3.3. Characteristics of Tar Sands . 15
1.3.4. Characteristics of Shale Oil 17
2. CHARACTERIZATION OF CONTAMINANTS IN FUELS 25
2.1. Sulfur Contaminants in Fuels 25
2.1.1. Sulfur Contaminants in Coal/Coal Liquids . . 25
2.1.2. Sulfur Contaminants in Petroleum or
Crude Oils . 31
2.1.3. Sulfur Contaminants in Tar Sand Oil 34
2.1.4. Sulfur Contaminants in Shale Oil 35
2.2. Chemical and Physical Characteristics of Organic
Sulfur Contaminants in Fuels 35
2.2.1. Mercaptans (Thiols) 38
2.2.2. Sulfides . . 41
2.2.3. Disulfides 44
2.2.4. Heterocyclic (Thiophene) 47
2.3. Nitrogen Contaminants in Fuels 52
2.3.1. Nitrogen Contaminants in Coal/Coal Liquids . 52
2.3.2. Nitrogen Contaminants in Petroleum 56
2.3.3. Nitrogen Contaminants in (U.S.) Tar
Sand/Oil 60
2.3.4. Nitrogen Contaminants in Shale Oil 60
2.4. Chemical and Physical Characteristics of Organic
Nitrogen Contaminants in Fuels 64
2.4.1. Pyrroles 66
2.4.2. Indole 67
2.4.3. Carbazoles 67
2.4.4. Benzonitriles. 68
iv
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TABLE OF CONTENTS (Continued)
Page
2.4.5. Benzamide 6g
2.4.6. Phenazine 6g
2.4.7. Acridine 69
2.4.8. Amines 69
2.5. Characteristics of Trace-Element Contaminants in
Coal/Coal Liquids 72
2.5.1. Trace Elements Identified in Coal 75
2.5.2. Trace Elements Associated With Mineral
Matter in Coal 83
2.5.3. Trace Elements Associated With Organic
Matter in Coal 92
2.5.4. Characteristics of Nonmetallic Trace
Elements in Coal 98
2.6. Characteristics of Trace Elements in Liquid Fuels
(i.e., Petroleum, Tar Sand Oils, and Shale Oils). . . 106
2.6.1. Trace Elements Identified in the Liquid
Fuels 107
2.6.2. Trace Elements Associated with Petroleum
Mineral Matter 115
2.6.3. Trace Elements Associated with Petroleum
Organic Matter 117
2.6.4. Trace Elements in Tar Sand Oils and
Shale Oils 139
3. CONCLUSIONS 144
3.1. Contaminants in Solid Fuels 144
3.2. Contaminants in Liquid Fuels 146
3.3. Distribution of Contaminants in Fuels 148
3.3.1. Sulfur and Nitrogen Contaminants 148
3.3.2. Trace Elements 150
3.4 Potential for Removal of Contaminants 153
3.4.1. Contaminants Present as Discrete Phases. . f . 153
3.4.2. Contaminants Present as Part of
Fuel Structure 155
4. REFERENCES
4.1. Fuel and Fuel Contaminant Characterization 156
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LIST OF TABLES
Page
Table 1. Search Terms and Strategy 3
Table 2. Results of Electronic Data Base Literature Search. . . 4
Table 3. Classification of Coal by Rank 10
Table 4. Analysis of Some Representative Crude Oils 14
Table 5. Elemental Analysis of Some Tar Sands 16
Table 6. Chemical Analysis and Molecular Weights of Tar Sands
Bitumen, Coal Liquids, and Their Fractions 18
Table 7. Composition of Colorado Shale Oil 19
Table 8. Mineral Matter of Oil Shales 21
Table 9. Percentage of Colorado Oil Shale as Minor Elements . . 22
Table 10. Typical Ultimate Analysis of Oil-Shale Kerogen .... 22
Table 11. Some Organic Sulfur Compounds Present in Coal
Products 27
Table 12. Estimates of the Sulfur Content in Eastern and
Western Coal Reserves 30
Table 13. Sulfur Present as Constituents Indicated in
Crude Oils 32
Table 14. Sulfur Compounds in Tar Sand Oils 34
Table 15. Average Distribution of Sulfur in Colorado
Mineable-Bed Oil Shales 36
Table 16. Sulfur-Type Compounds in Colorado Shale Oil Naphtha. . 36
Table 17. Boiling Point, Density, and Solubility in Water
of Various Mercaptans 39
Table 18. Boiling Point and Density of Alkyl Sulfides 42
Table 19. Boiling Point and Density of Various Disulfides. ... 45
Table 20. Boiling Point, Density, and Freezing Point of
Thiophene and Some Derivatives 48
Table 21. Nitrogen Content of U.S. Coals 53
Table 22. Bituminous Coal Treatment and Determination of
Nitrogen Bond Types 54
Table 23. Nitrogen Compounds and Building Blocks in Tars .... 54
Table 24. Nitrogen Compounds in Creosote Oil and Coal
Tar Pitch 57
Table 25. Distribution of Nitrogen in Crude Oil 59
Table 26. Nitrogen Compounds in Petroleum 59
vi
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LIST OF TABLES (Continued)
iauj-c £./ .
Table 28. _
Table 29.
Table 30.
Table 31.
Table 32.
Table 33.
Table 34.
Table 35.
Table 36.
Table 37.
Table 38.
Table 39.
Table 40.
Table 41.
Table 42.
Table 43.
Table 44.
Table 45.
Table 46.
Table 47.
Table 48.
Table 49.
Table 50.
Nonhydrocarbon Concentrate P.R. SPRINGS BITUMEN. . . .
Nitrogen Type Analysis of Shale Oil Distillate ....
Physical Properties of Some Amines Found in Fuels. . .
Elemental Composition of NBS-EPA Coal and Fly Ash
Distribution of Trace Elements in Coal Seams and
Correlation of Trace Element Distribution in
Average Organic Affinity of Some Metals
Determined by Float-Sink Methods
Affinity of Elements for Pure Coal and Mineral
Minerals Associated with British Bituminous Coals. . .
Trace Element--Coal Mineral Species Correlations . . .
Forms of Binding of Germanium in Solid Fuels
Ratio of Na + K to Cl in Coal and Solubilized
Ratios of Cl, Br, and I Found in Coal
Distribution of 28 Trace Metals in Ashes of
24 Crude Oils
Summary of the Analysis of Oil-Soluble Ash in
Trace-Element Contents of Four Crude Oils
Obtained by Neutron-Activation Analysis
Detection Limits for Different Elements in a
"Typical" Crude Oil Matrix in PPB
Typical Salt Contents of Crude Oils
ox
62
63
63
65
70
77
78
80
82
84
85
86
90
91
95
102
105
108.
109
111
112
116
vii
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LIST OF TABLES (Continued)
Page
Table 51. Distribution of Percentage of Total Nitrogen
of Crude in Resins and Asphaltenes 126
Table 52. Distribution of Trace Elements in Components of
a California Crude Oil 128
Table 53. Distribution of Molecular-Weight Fractions of
Oil Compounds 130
Table 54. Distribution of Trace Elements in Asphaltenes 131
Table 55. Distribution of Trace Elements in Resins. . . 132
Table 56. Distribution of Trace Elements in Methanol-
Soluble Fractions .. ..... 133
Table 57. Distribution of Nickel and Nickel Porphyrin in
Asphaltenes and Resins from a California
Tertiary Oil 135
Table 58. Resins and Asphaltene Content of Tar Sand Oils,
Shale Oil Fractions, and Coal Liquids .... 140
Table 59. Porphyrin and Trace-Metal Contents of Certain
Asphaltic Oils . 142
Table 60. Elemental Analysis of Typical Fuels . . 145
Table 61. Distribution of S and N Contaminants in Fuels 149
Table 62. Trace Elements Associated with Mineral Matter in
Solid and Liquid Fuels 151
Table 63. Trace Elements Associated with Organic Matter of
Solid and Liquid Fuels 152
Table 64. Metal Contaminants Associated with Organic Matter
in Coal and Compared to their Presence in Petroleum . . 154
viii
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LIST OF FIGURES
Page
Figure 1. Tomkeieffs Classification of Carbonaceous
substances . . , 5
Figure 2. Coal Structures with Probable Sulfur and Nitrogen
Compounds 12
Figure 3. Building Blocks of Coal (Wander) 13
Figure 4. Arrangement of Tar Sand Particles and Bitumen 16
Figure 5. Generalized Structure of Kerogen from Colorado and
Products from Thermal Fragmentation of Kerogen . . . .' 23
Figure 6. Nitrogen Compounds Extracted from Coal Precursors,
e.g., Humic Acids, Peat 55
Figure 7. Representative Basic and Nonbasic Nitrogen Compounds
in Petroleum Products 58
Figure 8. Occurrence Frequency of Elements in 13 Raw Coals as
Determined by Spark-Source Mass Spectrometry 76
Figure 9. Concentration Range of Elements in 13 Raw Coals
Analyzed by Spark-Source Mass Spectrometry 76
Figure 10. Relation of Organic Affinity and Ionic Potential
of the Elements. 97
Figure 11. Trace Elements Identified in Petroleum and Shale Oils.
Figure 12. The Porphin Structure and Well Known Porphyrins
Containing the Structure 120
Figure 13. Tetradentate Metal Complexes of Nickel and
Vanadium with Mixed Ligand Atoms 122
Figure 14. Model Defect Site (or Gaps) in an Aromatic Sheet of
the Asphaltene Structure 122
Figure 15. Effect of Asphaltenes Content on Sulfur and Metals
in Six Fractions of Ultracentrifuged Oil 124
ix
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I. INTRODUCTION
1.1. Technical Objectives
The overall objective of this study is to identify by means of a
literature survey possible future environmental control techniques for
potential pollutants in solid and liquid fuels which use as their approach
the removal of such contaminants from the fuels before combustion. The
program included a survey and subsequent evaluation of techniques both past
and present plus evaluation of potential new and unique techniques based on
detailed basic studies of the fuel-contaminant chemistry and potential
removal mechanisms that may be applicable to fuels. Primary emphasis is on
the removal of sulfur and nitrogen, but removal of other contaminants such
as trace elements and their compounds which are potential pollutants of
interest or concern are also considered. These include, but are not linked
to, the following which are listed in a tentative order of priority: Hg, Be,
Cd, As, Pb, Cu, V, Ni, Se, Mn, Sn, F, Cl, Ga, Co, Cr, Ge, Te, B, Br, Mo, Zn,
Zr, and P.
1.2. Approach
The approach used to fulfill these objectives was to identify the
chemical and physical nature of general groups of contaminants and specific
contaminants through a literature survey. In addition, the problems of
removing such contaminants from fuels were discussed. The literature survey
was to identify contaminant-removal methods which have been successfully used
in the past and/or are currently being utilized and also to look at
techniques which were previously unsuccessful but in today's world might be.
These removal methods were systematically categorized according to the
mechanism for removal and the contaminant(s) removed. The nature of the
removal process, what it achieved, and how it achieved the removal were
analyzed and are discussed in a separate volume.
-------
An electronic search of the literature was made by the EPA
Library at Research Triangle Park and the Battelle Energy Information
Center using the search terms and strategy given in Table 1. The output
from these searches produced over 8,000 citations from the data bases given
in Table 2, which were then hand sorted and placed into a keysort infor-
mation storage, and retrieval system. Additional search of the literature
to identify older contaminant removal methods was done by hand using
Chemical Abstracts. To cover the intervening periods, extensive use of
the review articles and books was made.
This report is divided into two volumes. The first volume
covers the identification and characterization of sulfur, nitrogen, and
trace-element contaminants in coal, coal liquids, petroleum, tar sand oils,
and shale oils. The second volume lists and discusses methods for
contaminant removal under five or six broad categories of methods used
for these fuels.
1.3. Background
In order to better understand the characteristics of the sulfur,
nitrogen, and trace-element contaminants in solid and liquid fuels, a brief
review of these fuels seems appropriate.
The carbonaceous fuels that will be discussed here were classified
by Tomkeieff^ as shown in Figure 1. In this figure the fuels are further
subdivided into liptobiolites, coals, and bitumens. The liptobiolites
consist primarily of resins, waxes, and spores and represent the more
stable residues of decomposed land plants. The coals are subdivided into
the humic series, the humic-sapropelic series, and the sapropelic series.
The humic coals are the common coals (lignite to anthracite) formed from peat
swamp type deposits. The sapropelic coals were formed in stagnant water
from the remains of aquatic organisms that were primarily plantonic. The
humic-sapropelic type coal was formed by a combination of the conditions
that produced the humic and sapropelic coals. The bitumens are naturally
occurring hydrocarbons (including petroleum, asphalt-like material, and
* References are cited at the end of this report.
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TABLE 1. SEARCH TERMS AND STRATEGY
Fuel
Coal (Bituminous Coal) (Lignite) (Subbituminous Coal)
Oil (Crude) (Crude Oil) (Petroleum) (Oils) (Crude Oils)
Shale Oil (Oil Shale) (Kerogen)
Tar Sands
Coal Liquids
Processes
i
Cleaning
Washing
Leaching
Chemical Treatment
Hydrogenation
Desulfurization }>- Coal
Hydrodesulfurization
Sulfur Removal (not stack or flue gas)
Preparation
Beneficiation
Liquefaction
Deashing
Desalting
Washing
Deasphalting
Asphaltene Removal
II { Demetallization > Oils
Metal Removal
Denitrification
Nitrogen Removal
Hydrodesulfurization
Deashing
Contaminants
Sulfur
Nitrogen
Mineral (s)
Asphaltene
Halides
Halogens
Contaminant
Contamination
Trace Element(s)
Trace Metal(s)
" Metal (s) et al
Nickel
Mercury
Cadmium
Arsenic
Lead
Copper
Vanadium
Selenium
Manganese
» Tin
Fluorine
Chlorine
Gallium
Cobalt
Chromium
Germanium
Boron
Molybdenum
Zinc
Zirconium
Phosphorus
Berylium
Tellurium
Bromine
Coal, Oils
Search Procedure
Combine Fuels and Equivalents
Separate
Coal
Oils
Coal Liquids
Combine Processes
Separate
I
II
Combine Contaminants
Search Strategy
Coal and I but not Flue/Stack Gas
Coal and Contaminants but not Flue/Stack Gas
Coal Liquids and II
Coal Liquids and Contaminants
Oils and II
Oils and Contaminants
Suggested Data Bases to be Searched
Chem Abs
NTIS
Engineering Index
ERDA-Recon
Energy Research and Development
Coal Data Base
NSA(?)
APIC
Physics Index Abstracts
Geological Reference File
Pollution Abstracts
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TABLE 2. RESULTS OF ELECTRONIC DATA BASE LITERATURE SEARCH
Data Base
Battelle Energy Information
Center (Basis 70)
American Petroleum
Institute
Smithsonian Science
Information Exchange
(Currently Funded Projects)
Geological Reference File
National Technical
Information Service
Engineering Index
Chemical Abstracts Service
(Chem 70-71)
(CHEMCON)
Coverage
Subject
Coal, Petroleum
Shale Oil, Tar Sands
Petroleum
Coal Cleaning Research
Fossil Fuels
(Minus Coal)
Coal
Petroleum
Coal
Petroleum
Petroleum
Coal
Coal
Petroleum Contaminants
Pet. Contain. Removal
Petroleum Contaminants
Pet. Contain. Removal
Total Citations
Years
1932-present
1972-1975
?
?
19 67- present
1964-present
19 64- present
1964-present
1969-present
1970-present
1970-present
1970-1971
1970-1971
1972-present
1972-present
Citations
Printed (a)
576
941
76
170
476
229
382
104
694
186
1511
449
335
625
1548
8302
(a) The number of citations are for as-received outputs with no screening of
relevant articles or titles.
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CARBONACEOUS SUBSTANCES
1
Living
corbonoceous
substances
(Parts of plants and
1
LIPTOBIOLITES
1
HUMIC
SERIES
Humic peat
Brown coal
Bitumious
coal
Anthracite
animals)
1
Fossil
carbonaceous
substances
|
COALS
HUMIC-
SAPROPELIC
SERIES
SAPROPELIC
SERIES
Pollen and resin peat
Subcannel
*
coal
Cannel coal
Canneloid
Pyropissite
Torbanite
1
BITUMENS
Natural gas,
petroleum, ens
ozokerite
Maltha and
elaterite
asphalt
Pyrobitumen
Anihroxolite
shungite
FIGURE I. TOMKEIEFF'S CLASSIFICATION
OF CARBONACEOUS SUBSTANCES
(1)
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oil shale) and are soluble in carbon disulfide. The coals of the humic
series are discussed in the next section. Cannel coal, which has a dark
grey color.is a rare coal that occurs in nonbanded massive structures and
usually breaks with a concoidal fracture. Cannel coal burns readily with
a bright flame. The canneloid coal is like cannel coal in some respects
but contains less volatile matter. Pyropissite and torbanite are two kinds
of sapropelic coals. Pyropissite is like lignite (brown coal) and is a
source for montan wax. Torbanite coal was formed from algal mass. Among
the bitumens, ozokerite is a hard, waxy, jet black hydrocarbon that is
soluble in turpentine and chloroform. Ozokerite is finely disseminated
in the rock unlike gilsonite which occurs as veins. Maltha and elatenite
are viscous tar-like materials. The Pyrobitumen and anthroxolite are types
of heavy (tar-like) bitumen.
" - . '
Summaries of the physical and chemical characteristics of coal,
coal liquids, petroleum, tar sand oil, and shale oil are given in the
following sections.
1.3.1. Characteristics of Coal
Physical Characteristics. Coal has been defined appropriately
as an organic rock and as such it is not a homogeneous substance in either
chemical composition or physical appearance. Most coals with ranks from
lignites to anthracites appear to consist of alternating bands of bright
and dull material. These bands vary in width from a few millimeters to
several centimeters. In some coals, the bright layers comprise by far the
larger part, while in others they make up only a small portion of the
cross section or are entirely absent. In banded bituminous coal, the bands
are discontinuous and appear to be embedded in a continuous mass. These
bands of heterogeneity in the physical aggregation of coal provide paths
and channels into coal for diffusion of appropriate desulfurizing and
denitrification reagents.
The bands differ greatly in color, texture, and luster. The
bright bands are homogeneous, compact, jet black, and often glossy in
appearance. The duller material is grayish and more granular in appearance,
-------
and the surface is irregular and rough. The macroscopic components found
in coal are commonly referred to as lithotypes (rock types). These
lithotypes are further described in the "European System" as:
(1) Vitrain, a uniform bright material, referred to as
anthraxylon in the U.S. Bureau of Mines classification
of coal.
(2) Clarain, which has a surface luster that is inherently
banded. It contains considerable amounts of translucent
material, as well as large proportions of voids, resin,
and opaque material.
(3) Durain, which has a hard, granular appearance. It is
practically structureless and dull black in color.
There is no equivalent of clarain and durain in the
Bureau of Mines classification system but the term
attritus describes the dull bands that consist of
plant debris.
(4) Fusain, which occurs as patches, consists of powdery,
readily detachable, fibrous strands and is often
referred to as "mineral charcoal". The term is also
used in the Bureau of Mines classification.
The lithotypes are further subdivided into homogeneous microscopic
constituents which are called macerals. The most common macerals
specially relevant to U.S. coals are:
(1) Vitrinite, the principal coal maceral and the primary
constituent of bright coal. This is readily soluble
in a range of organic solvents, including polycyclic
aromatics (anthracene oil).
(2) Fusinite, the maceral found in fossil charcoal. This
does not swell, soften, or cake on heating, and
particles of fusinite can still be recognized as such
under the microscope after pyrolysis.
(3) Sporinite, the fossil remains of spores. This becomes
extremely fluid on heating to 400-450 C, and at these
temperatures yields large amounts of the volatile matter.
-------
8
(4) Micrinite, the maceral, which is completely structureless.
This was probably derived from humic mud. It is a majur
ingredient of dull coal. Like fusinite, this maceral is
inert.
These macerals can be removed from coal by techniques developed
(2)
by Kroger, Van Krevelen, and othersv ' (the order c£ densities among
macerals from any one coal is fusinite > micrinite > vitrinite > sporinite).
By similar separation of appropriate lithotypes, high concentrates of
micrinites and fusinites can also be obtained from some coals.
Pores and Capillaries of Coal. The presence of naturally occurring
pores, capillaries, and channels in coal plays a prominent role in making
the internal part of coal accessible to solvents and gaseous reagents. The
rank of coal is basically an indication of the carbon content and is also a
good indicator of the pores in coal. High-rank coal approaches a graphite
lattice structure. Some of the openings in bituminous coals are ultrafine,
just a few angstroms wide, while others are as large as 100 A. In addition,
there are cracks which are larger and contribute from 20 to 50 percent of
(2)
the total internal free volume. The surface area can be measured by heat
of wetting of methanol or by adsorption of inert gases. Discrepancies in
the surface area observed at low temperatures (liquid nitrogen) have been
attributed to the cecrease in molecular diffusion and collapse of capillaries
(3)
at low temperatures. Walkerv ' has shown that for American coals the
surface area as measured at 77 K and 298 K using nitrogen and carbon dioxide,
respectively, indicate fine microporosity in the 4 to 5 A range. Both the
low-rank coals (<70 percent carbon) and high-rank coals (90 percent carbon)
2
have a large surface area (300 to 400 m /g), whereas for coals of intermediate
rank (78 percent carbon), the amount of surface area is at a minimum. Large
voids of up to 30,000 A are present in most coals. Smaller voids of 12 to
300 A are called transitional pores. There exists no clear relationship
between total surface area and coal rank, but lower tank coals generally
have a larger percentage of their total surface area due to larger pores.
-------
The value measured for the surface area of coal depends largely
on the reagent and temperature used in the determination. While processing
coal to remove contaminants, the temperature or the reagent selected could
be crucial in utilizing the inherent surface area of coal. Bituminous coals
are known to become plastic or fluid-like between 400 to 430 C, so that at
this temperature the surface areas would be at a minimum. As most coals are
heated to higher temperatures, there occur physical and chemical changes
leading to increases in surface area. The treatment of coal with reactive
reagents, e.g., benzene or pyridine, begins to dissolve the coal particle
starting from the surface of contact. In such a case, the fine capillaries
in the structure would serve no purpose, but the large voids could promote
faster penetration. In the case of high temperatures (400 to 450 C) and
with coal-derived solvents (anthracene oil, a polynuclear aromatic mixture),
the surface area loses all significance as a pathway for diffusion processes
as at this temperature coal is solubilized.
Types of Coal. In the standard ASTM classification of coal,
coal is ranked according to fixed-carbon content, volatile matter content,
and heating value. There is no sharp line of demarcation between the
properties of coals of different ranks, but each merges gradually into
those of the adjacent group. The coal classification by rank is shown in
Table 3. Wide variations may be encountered in the analysis, not only for
each rank of coal, but also for those from each seam and from each
individual mine.
The bituminous and subbituminous coals are also classified, in the
U.S. System, as to type according to the relative amounts of the petrographic
constituents, anthraxylon, and the finely divided attritus matter, both
translucent and opaque. The banded coals are divided into three types:
(1) bright coals, (2) semisplint coal, and (3) splint coal. The bright coals
consist principally of anthraxylon and attritus, with the translucent type
predominating. The semisplint coals are also made up of anthraxylon and
attritus but in about the same relative proportions. Most of the U.S. coals
are bright coals. The splint and semisplint coals seldom occur by
themselves, but are usually associated with bright coals in the bed. The
splint coals are harder than bright coals, and more solid and less friable
than the bright and semisplint coals.
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10
TABLE 3. CLASSIFICATION OF COAL BY RANK
(a)
Class
Anthracitic
Bituminous
Subbituminous
Llgnitic
Croup
Meta-arithracite . ........
Semianthracite*
Low-volatile bituminous coal ....
Medium-volatile bituminous coal . .
High-volatile A bituminous coal . .
High-volatile B bituminous coal . .
High-volatile C bituminous coal . .
Subbituminous B coal
Subbituminous O coal
Lignite A .
Lignite fl
Fixed
carbon
limits, %
(dry m.m.f.
basis)
Equal or
greater
than
98
92
86
78
69
...
Less
than
98
92
86
78
69
Volatile
matter
limits, %
(dry m.m.f.
basis)
Greater
than
2
8
14
22
31
Equal or
less
than
2
8
14
22
31
::: (
Calorific
value limits,
B.t.u./lb.
(moist11 m.m.f.
basis)
Equal or
greater
than
14,000*
13,000"
11,500
10,500
10,500
9,500
8,300
6,300
Less
than
14,000
13,000
11,500
11,500
10,500
9,500
8,300
6,300
Agglomerating character
I Non-agglomerating
1 Commonly agglom-
erating*
Agglomerating
\ Non-agglomerating
A.S.T.M. Designation D 388-36. Data from U.S. Bureau of Mines. This classification does not include a few coals, principally non-banded varieties,
which have unusual physical and chemical properties and which come within the limits of fixed carbon or calorific value of the high-volatile bituminous and
Subbituminous ranks. All these coals either contain less than 48% dry m.m.f. fixed carbon or have more than 15,500 moist m.m.f. B.t.u./lb.
*Moist refers to coal containing its natural inherent moisture but not including visible water on the surface of the coal.
clf agglomerating, classify in low-volatile group of the bituminous class.
'Coals having 69% or more fixed carbon on the dry m.m.f. basis are classified according to fixed carbon, regardless of calorific value.
'There may be non-agglomerating varieties in these groups of the bituminous class, and there are notable exceptions in the high-volatile C bituminous
group.
(a) Source: Chem. Eng. Handbook. Perry (1973).
-------
11
Chemical Characteristics. For a detailed characterization of
contaminants in coal, and to have a better understanding of the removal
methods, it is relevant to define coal in terms of its chemical composition
and the important concepts of its molecular structure.
Coal consists mainly of carbon, hydrogen, oxygen, sulfur, and
nitrogen. The nitrogen content may be considered as constant and amounts
to 1 to 1.5 percent. Coals are predominantly aromatic in structure;
60 to 90 percent of the carbon in vitrinites is present as aromatic rings,
and the percentage increases with coal rank. Chakrabaty and Berkowitz have
recently suggested an adamantane-based structure for coal, but this
hypothesis has received little acceptance to date with the limited evidence
they have presented. ' Cartz and Hirsch^ ' showed in an X-ray diffraction
study on vitrains that the structural units in bituminous coals consist of
small condensed aromatic ring systems, probably 1 to 3 rings for low rank
vitrains and 2 to 5 rings for vitrains with 90 percent carbon. These
aromatic layers are linked to each other by C-C linkages and aliphatic
groups (or possibly also by ether linkages) to form imperfect sheets which
are buckled (through the presence of hydroaromatic groups) or in which
adjacent aromatic-ring systems are rotated relative to each other owing
to the presence of a five-membered ring. The rings and aliphatic groups
form a three-dimensional array. The hydroaromatic character of coal
decreases with increasing rank. The infrared spectra of bituminous
vitrinites show intense bands due to aliphatic C-H vibrations and the
aliphatic character of the material has also been confirmed by NMR.
Given has proposed a structure for bituminous vitrinite, and
Wiser, in his hypothetical coal model, has shown the structures of sulfur
/Q\
and nitrogen compounds (see Figure 2). Wenderv ' prefers to consider coals
as consisting of different building blocks, as shown in Figure 3. The
lignite (Coal D in Figure 3), as shown, contains fewer aromatic structures
than bituminous coals contain. As a consequence, the sulfur and nitrogen
compounds in lignite and lower rank coals would not exist as part of large
(3 to 4 rings), condensed aromatic or heterocyclic compounds.
-------
12
HO
OH
Bituminous Vitrinite (Given)
Bituminous Coal Structure (Wiser)
FIGURE 2. COAL STRUCTURES WITH PROBABLE SULFUR AND NITROGEN COMPOUNDS
-------
13
COAL A
Low-volotile
bituminous
COAL B
High-volatile A
bituminout
PouhontM No. 3 tea, W. V*. (Ivb)
Pittsburgh ted (hvab)
c
K
0
M
S
Volatile Hatter
Btu per pound
4.2
2.6
1.2
0.6
7.6
17.3
»0.7
4.6
2.S
1.3
0.6
It.7
15,660
C
R
O
N
S
Aah
Volatile utter
Btu per pound
77.1
5.1
6.4
1.5
1.5
S.4
36.5
84.2
5.6
6.9
1.6
1.7
15,040
CH,-
COAL C
Subbituminou* cool
(ed. Wyo. (Subbltualnoui A)
drj ..{
COAL O
Lignite
Lignite, Beul«h-Z«p 1*4, M. D.
is. ssi
e
B
0
II
S
Afh
Volatile Hatter
Itu per pound
72,
5,
14,
1,
0,
4,
41,
76.
5.
15.
1.
0.
43.6
13,490
FIGURE 3. BUILDING BLOCKS OF COAL (WENDER)
-------
14
The oxygen content of coal varies over a wide range, from up to
30 percent in low-rank coals (lignites) to about 1.5 percent in anthracite.
The oxygen, besides decreasing the heating value of coal, forms a range of
functional groups, e.g., -COOH, -OCH3, and -OH. The phenolic hydroxyl group
is the most important oxygen-containing functional group present in all ranks
of coal and the only one found in bituminous coals. Coals that contain more
than a few percent of oxygen are generally more reactive than coals with
lesser amounts of oxygen. The reactivity is observed, e.g., in high rates of
gasification, solvent extraction, and hydrogenation. Oxygen that cannot be
accounted for in any other way is assumed to be in ether links or in
(9)
heterocyclic systems.
1.3.2. Characteristics of Petroleum or Crude Oils
Crude oil is a liquid consisting chiefly of hydrocarbons with
traces of sulfur, nitrogen, oxygen, and a few impurities, such as water,
sediments, and trace elements. The chemical analyses of representative
American crudes from various states are shown in Table 4.
TABLE 4. ANALYSIS OF SOME REPRESENTATIVE CRUDE OILS
(10)
Percent by Weight
Source
Pennsylvania
West Virginia
Ohio
California
Texas
Carbon
85
84
84
82
85
Hydrogen
14
13
13
10
11
Impurities
(include S,0,N)
1
3
3
8
4
These data show that the percentages of carbon and hydrogen present in the
crudes from all these sources are essentially the same. However, such an
analysis is in a way misleading since two crudes with similar carbon and
hydrogen contents could contain different hydrocarbons, e.g., Pennsylvania
crude is principally paraffinic, while California crudes contain large
amounts of naphthenic compounds. Some generalizations on compounds found
-------
15
in crudes have been made^ and those relevant to sulfur and nitrogen
contaminants in crude are: (1) all crudes contain substantially the same
general structural features as the hydrocarbons, the ring systems of the
hydrocarbons being replaced by hetero-ring systems.
There are two portions of petroleum crudes, the resins and
asphaltenes, which are important as a source of sulfur and nitrogen
contaminants. The nitrogen, sulfur, and oxygen contents of resins indicate
that one or more atoms of one or more of these elements is present in each
molecule. In the case of asphaltenes, the sulfur, nitrogen, and oxygen
occur in concentrations equivalent to one or more heteroatom per molecule.
1.3.3. Characteristics of Tar Sands
Physical Characteristics. Tar sands should technically be called
bituminous sands as the hydrocarbon which the sands contain is a bitumen
(i.e., a carbon disulfide-soluble oil). ' ' Bitumen has been classified
with coal and petroleum crude as shown in Figure 1. The Athabasca tar sand
is a mixture of sand, water, and bitumen, as shown in Figure 4, where the
larger sand particles are coated with water and fines which in turn are
coated with the bitumen film. The balance of the void volume is filled
with connate water, and at times, methane or air is also present. The sand
grains are packed to a void volume of about 35 percent. This corresponds
to a tar-sand mixture of roughly 83 weight percent sand; the balance is
bitumen and water.
The tar sands are found in Utah and in other parts of the U.S. are
known by specific names, e.g., asphalt deposits, gilsonite, and grahamite.
The bitumen present in these deposits has certain characteristics, appearances,
and properties. The asphalts vary in consistency from plastic material to
hard and brittle solids. Gilsonite is a bright, black hydrocarbon resembling
glossy asphalt. The Gilsonite occurs in pure form as veins ranging from
(9)
thin sheets to a maximum thickness of 2000 feet. ' Gilsonite is
hydraulically mined and transported by pipe to be converted to gasoline and
asphalt. Grahamite (characterized by a low solubility in carbon disulfide)
is found at many locations in the United States.
The elemental analysis of Utah asphalts, gilsonite, and Athabasca
tar sands is given in Table 5.
-------
16
Sand
particle
Water
^""envelope
Bitumen
film
Sand
particle
Sand
particle
FIGURE 4. ARRANGEMENT OF TAR SAND
PARTICLES AND BITUMEN(12)
TABLE 5. ELEMENTAL ANALYSIS OF SOME TAR SANDS
(1,12)
Weight Percent
Deposit
Carbon Hydrogen Sulfur Nitrogen
Utah asphalt 82 11 2 2-2.5
Gilsonite, m.p. 121-177 C 85-86 8.5-10 0.3-0.5 2.0-2.8
Athabasca 83.4 10.4 4.5 0.5
(a) Remainder oxygen.
-------
17
Chemical Characteristics. There is paucity of information on the
chemical characterization of U.S. tar sands, but the hydrocarbon constituent
has been defined as bitumen. In the case of Athabasca tar sands (bitumen),
each fraction of the bitumen contains large proportions of saturated carbon
atoms (50 percent in solid asphalt to 75 percent in oils). Of the saturated
carbon atoms within each fraction, more than 50 percent are paraffinic. The
amount of naphthenic carbon in the fractions is low. In the absence of
evidence for free paraffins in the bitumen, saturated constituents of the
low-molecular-weight fractions appear to be single aromatic or naphthenic
rings with long-chain alkyl groups. The aromatic constituents in the
bituminous fractions are condensed aromatic systems ranging from 1 to 2 rings
to greater than 40 rings per molecule in the asphaltenes. The asphaltenes
have greater than 4 aromatic sheets containing 10 or more rings each
joined by one or more alkyl rings. The asphaltene (pentane-insoluble
material) constitutes about 17 percent by weight (mmf) of the bitumen. '
It appears that the asphaltenes are due not only to chemical bonding but
(14)
also to electrostatic association between the individual units. The
chemical analysis of Athabasca tar sands is compared with that of a coal
liquid in Table 6. Some constituents of the coal liquid have lower molecular
weight than the corresponding constituents in tar sand bitumen.
1.3.4. Characteristics of Shale Oil
Shale oil as obtained by the pyrolysis of oil shale in a vertical
retort is a dark, viscous, organic liquid. This liquid has less than 3 percent
straight-run gasoline fraction and only one-half of the total oil is
distillable below 300 C at 400-mm pressure. The API gravity will be
approximately 20 and the pour point around 26.7 C. This shale oil liquid
as shown in Table 7 is similar in some respects to petroleum in that the
refining steps and the end-use products are generally the same.^ ' However,
certain contaminants, e.g., nitrogen compounds, are found in larger quantities
in shale oil than in most petroleum crudes, and the ratio of the olefins to
paraffins is higher in shale oil. The contaminants that are finally found
in processed fuels would depend on the characteristics of the source of shale
-------
18
TABLE 6. CHEMICAL ANALYSIS AND MOLECULAR WEIGHTS OF TAR SANDS
BITUMEN, COAL LIQUIDS, AND THEIR FRACTIONS(15>
Tar Sands Bitumen
Saturates
Aromatics
Monoaromatics
Di- + Trtaromatics
Polyaromattcs
Resins
Asphaltenes
Big Horn Coal Liquids
Saturates
Aromatics
Monoaromatics
Di- + Triaromatics
Polyaromatics
Resins
Asphaltenes
Benzene Insolubles
Mol.
Wt.
_
365
460
360
365
1,400
1,300
5,100
-
300
222
285
220
-
380
-
_
c,
Wt. %
82.98
86.00
--
88.55
85.04
79.36
81.15
78.84
89.18
86.12
88.09
92.38
84.19
83.84
87.37
.
H,
Wt. %
10.42
14.00
--
11.36
9.45
9.57
9.04
7.80
8.97
13.65
10.10
7.13
6.60
7.09
6.06
* _
N,
Wt. %
0.42
--
0.02
0.42
1.34
1.19
0.40
--
--
0.06
0.01
0.20
1.62
1.25
.
0
Wt. %
1.15
__
1.14
3.40
3.35
4.53
1.03
--
--
1.82
0.80
7.80
7.15
4.92
<-
s,
Wt. %
4.60
--
--
--
3.80
6.89
5.31
8.46
0.04
--
--
0.00
0.15
0.97
0.30
0.62
-------
TABLE 7. COMPOSITION OF EQUAL WEIGHT FRACTIONS DISTILLED FROM COLORADO SHALE
Fraction Composition, Percent
Component, percent
Polycyclic aromatics
Monocyclic aromatics
Branched olefins and cycloolefins
Straight-chain olefins
Branched paraffins and naphthenes
Straight-chain paraffins
Oxygen compounds
Sulfur compounds
Nitrogen compounds
190-270^
9
6
15
26
7
8
12
5
12
, 20
3'270-310
9
8.5
24.5
9
6
8
17
4
14
30
310-350
9
6
19
11
4
8.5
17.5
4.5
20.5
40
350-380
10
6.5
14
10.5
3
8.5
17
5
25.5
50
380-410
7.5
4.5
12.5
8.5
3
12
14
5.5
32.5
60
410-440
2
2
6
2.5
4.5
3.5
21.5
7
51
70
440-470
2
2
6
2.5
4.5
3.5
21.5
7
51
80
470-485
2
2
6
2.5
4.5
3.5
21.5
7
51
(a) Numbers represent equal and sequential weight percent of oil removed overhead as obtained in
routine distillation.
(b) Boiling point ranges of fraction, C.
VO
-------
20
oil. The source is a somewhat vaguely defined material known as oil shale, a
term applied to a wide variety of laminated sedimentary rocks containing
organic matter. The Colorado oil shale of the Green River Formation contains
about 16 percent insoluble organic matter, the so-called "kerogen" (a term
first used in relation with Scottish shales).^ ' This represents about
80 percent of the total organic matter present. The remaining 20 percent
/I Q\
soluble organic matter represents the "soluble bitumen". ' Attempts have
been made to remove the organic matter by solvents, but the yields are low
because of the insolubility of kerogen; this insolubility permits one to
distinguish oil shale from tar sands, which are rocks or sand formations
actually impregnated with oil. The oil shales generally contain over one-third
mineral matter, as shown in Table 8, and are thus distinguished from coal.
Mineral constituents of Colorado oil shale, for example, include dolomite,
35 percent; calcite, 15 percent; quartz, 15 percent; feldspar, 25 percent;
clay, 5 percent; pyrite, 10 percent; and minor elements listed in Table 9.
A structural model of kerogen as proposed by Yen has the
following features:
(1) There is little or no aromatic carbon skeleton
in kerogen
(2) The bulk of the carbon structure is naphthenic,
containing 3 to 4 rings. It is possible that
there are clusters of rings linked by heterocyclic
atoms and short-chain bridges.
(3) There are no free-end and flexible long-chain linear
polymethylene structures, but polycycloparaffins
could exist.
(4) The C/0 atomic ratio is 18. The crosslink sites are
anticipated to be largely oxygen.
(5) The difference between the structures of bitumen and
kerogen is one of degree and not of kind.
(6) The structure of kerogen is a multipolymer consisting
of monomers which are molecules so far identified from
bitumen, as shown in Figure 5. These molecules in
bitumen are steranes, triterpanes, and isoprenoids of
C40 size* The monomers as obtained from mild oxidation
are mono- and dicarboxylic acids. The ultimate analysis
of kerogen is given in Table 10.
-------
21
(19)
TABLE 8. MINERAL MATTER OF OIL SHALES
Analysis, percent
Chemical
Constituent
Raw Shale:
S102
Fe203
A1203
CaO
MgO
sc3
Na20
K20
Spent Shale:
S102
Fe2°3
A1203
& w
CaO
MgO
Very Low-
Grade Shale
(10.5 Gal/Ton)
40.9
4.3
9.4
11.0
5.4
0.1
1.8
3.4
53.27
5.64
12.28
14.82
7.00
Medium Hlgh-Grade Very Hlgh-
Grade Shale Shale Grade Shale
(26.7 Gal/Ton) (36.3 Gal/Ton) (61.8 Gal/Ton)
26.1
2.6
6.5
17.5
5.3
0.6
2.6
1.0
41.90
4.10
10.53
28.11
8.53
25.5
2.9
6.3
14.2
5.6
1.2
2.7
1.9
42.36
4.74
10.46
23.54
9,30
26.4
3.1
7.0
8.3
4.5
1.4
1.9
1.0
49.19
5.87
13.13
15.40
8.35
-------
22
TABLE 9. PERCENTAGE OF COLORADO OIL SHALE
AS MINOR ELEMENTS
As
Cu
Pb
Mn
Ag
Ti
0.005
.008
.09
.08
.001
.06
Ba
Cr
Li
P
Sr
V
0.03
.007
.05
.4
.08
.06
B
Au
Mo
Se
Tl
Zn
0.003
.001
.001
.001
.7
.1
TABLE 10. TYPICAL ULTIMATE ANALYSIS OF
OIL-SHALE KEROGEN(16)
Carbon
Hydrogen
Nitrogen
Sulfur
Oxygen
Weight
Percent
80.3
10.4
2.3
1.1
5.9
-------
23
Principal Fragmentation Products From , .
Controlled Pyrolysis of Kerogen Concentrate^
No.
Name
I Formula
I Aliphatic Hydrocarbons n-Cio to n-Cj4
b<,o
2 Alicyclic Hydrocarbons
Cyclohexane
Decattru
3 Hydroaromatlc Hydrocarbons
Dialkyltetralini
Hexahydro-
phenanthrenes
4 Dhlkylbenzena
5 DiaDcyliuphthaleiKS
6 Alkylphcnanthrerws
Jn
Generalized structure of kerogen
of the Green River Formation
(a) Subunits of kerogen identified
by techniques employing micro-
pyrolysis with pyrochromatography
and mass spectrotnetry (MPGM method)
FIGURE 5. GENERALIZED STRUCTURE OF KEROGEN FROM COLORADO AND
PRODUCTS FROM THERMAL FRAGMENTATION OF KEROGENC18)
-------
24
(7) Inter- and intramolecular hydrogen bondings as well as
charge-transfer bonding play an important role in the
structure. The kerogen is comparable in nature to a
molecular sieve and it can retain small molecules
present in bitumen due to van der Waals molecular
forces.
Oil shale is a highly consolidated organic-inorganic system with
no significant micropore structure or internal surface. The inorganic
part consists of essentially nonspherical particles. The organic matter
is distributed essentially interparticle rather than intraparticle and is
between the particles with only a small amount of the organic matter chemically
or directly bonded to the mineral constituents. The porphyrins in the
kerogen may be chelated with some of the minerals. A typical kerogen molecule
may be considered as a polymer with a molecular weight of well over 3000.
The structure of this complex molecule consists of saturated condensed
polycyclic rings with closely associated aromatic, nitrogen, and sulfur
heterocyclic ring compounds that are randomly distributed.^ ' This model
of shale oil is consistent with the one proposed by Yen. Some kerogens
show definite evidence of a benzenoid structure similar to that found in coals.
-------
25
2. CHARACTERIZATION OF CONTAMINANTS IN FUELS
Characterization of sulfur, nitrogen, and trace-element contam-
inants in the solid and liquid fuels considered was undertaken to identify
the sources of these contaminants in the fuels. After the sources of the
contaminants were identified, their chemical and physical characteristics
were developed relevant to contaminant removal reactions. In the case of
organic sulfur and nitrogen, the discussions do not differentiate between
the fuel origin of the contaminants, but instead treat them on the basis
of the characteristics of either their functional groupings or parent
heterocyclic compounds. In most cases, the organic sulfur and organic
nitrogen contaminants are common to all of the fuels or the modified fuels
(e.g., coal liquids).
2.1. Sulfur Contaminants in Fuels
The sulfur contaminants in fuels fall into two broad categories:
(1) organic sulfur compounds which are found in all of the fuels and
(2) inorganic sulfur compounds which are more typically found in the solid
fuels, such as coal and oil shale.
2.1.1. Sulfur Contaminants in Coal/Coal Liquids
Coal contains both types of sulfur contamination. The organic
sulfur is inherently bound in the organic structure of coal. The inorganic
forms of sulfur are usually present outside of the coal structure as occluded
mineral matter, although their distribution may be so finely disseminated
that distinct phases are difficult to detect and physical separation is
difficult to accomplish.
-------
26
Organic Sulfur. The products from coal pyrolysis, e.g., gas,
liquid, and char, all contain sulfur compounds, some of which seem to be
fragments of parent compounds in coal. The organic sulfur in coal, therefore,
can be considered as part of the aromatic or the aliphatic molecular
structure of coal. Thus, to completely desulfurize coal, a chemical
treatment is necessary. If the coal is to remain a solid, the treatment
would be complicated by transport limitations that exist during reactions
between a solid (coal) and gaseous or liquid reagents. The organic sulfur
(21)
in coal is considered to exist in one of the following four forms:
(1) Mercaptan or thiol (RSH)
(2) Sulfide or thioether (RSR1)
(3) Disulfide (RSSR')
(4) Thiophene-based compounds.
There are also cyclic derivatives of these types of sulfur compounds,
(e.g., R and R' may be alkyl or aryl groups; types (2) and (3) may be part
of one ring system). The important organic sulfur compounds obtained from
coal by pyrolysis or hydrogenation are listed in Table 11.
Inorganic Forms of Sulfur in Coal. Classical characterization of
sulfur in coal differentiates between the amount of sulfur present in coal
as pyrite (or sulfide) and sulfate contaminants. Organic sulfur is deter-
mined as the difference between the total sulfur value and the sum of the
pyritic (or sulfide) and sulfate values. ''
j>u.1Jl.t§_sJjLfyr.c Sulfate sulfur is usually present in coal as a
result of oxidation through weathering of pyrites. Therefore, major
amounts occur as iron (II) sulfate. Calcium sulfate is also known to be
present as gypsum. Both are soluble in water and their concentrations in
coal beds vary accordingly. Insoluble sulfate salts such as those of
strontium and barium are present in coals adjacent to shales at the bottom
(25)
and top of coal seams. Typically they are present as cleat filling
-------
27
TABLE 11. SOME ORGANIC SULFUR COMPOUNDS
PRESENT IN COAL PRODUCTS
Formula
MERCAPTANS
C6H6S
C14H10S
SULFIDES
W
C4H10S
DISULFIDES
C2H6S2
C4H4S2
THIOPHENE
W
C5H6S
C6H8S
C7H10S
C8H12S
C8H6S2
Name Structure
THIOLS (RSH)
Ethanethiol ^ H r S H
Benzethiol C^~S H
Anthrathiol LI jT lT
THIOETHER (RSR1)
Methylsulfide (CH3>2S
Ethylsulfide (C0He)0S
JL *> /
(RSSR1)
Methyldisulfide CH3'S
-------
28
TABLE 11. (Continued)
Formula
W
C8H6°S
C9H8S
C12H8S
C12H8S
C16H10S
Name Structure
Benzofb] thiophene ff^t\ [)
(thianaphlthene) Wx^vC/
4-Thianaphthenol (T JFj
OH
2-Methylbenzo[b]
thiophene
Dibenzothiophene f ]T T 1
Naphtho [2,3,6] tfl
thiophene ff^C**\
Benzo [b ] naphtho
B.P., Occurrence in
C Coal Product
(22)
L.T. tar, crude
7 naphthalene, coal
oil, lignite tar
Tar
240 H.T. tar
331 H.T. tar, coal
330 H.T. tar
oil
Naphtho [1,2-b]
thianaphthene
429
H.T. tar
CYCLIC SULFUR COMPOUNDS OF LESS IMPORTANCE
C_H,S
5 o
C5H4SO
(C6H5)S
C13H10S
Vs08
C12H8 S2
Thiopyran(e)
Thiopyrone
Phenylsulfide
Thioxanthene
Thioxanthone
Thianthrene
H?
030 C/12 mm Coal tar
n
Cl"^~C j 364 Coal tar
i^V^j^ 340 Coal tar
*^fc JV.^r j/J*~ *£)
^^^ ^3 ^^^ Q
1)
fPi^^T^ii 371 Coal tar
^**^ S&**^f+ jSL^^ jJ
f^V^V^i
Is^JL^A^J 296 Coal tar
(a) H.T. tar = high-temperature tar.
(b) L.T. tar = low-temperature tar.
-------
29
/oc\
minerals. For freshly mined coals, the sulfate sulfur level in raw coal
is usually less than 0.1 percent. In the analysis of a large number of coals,
the mean value for sulfate sulfur was 0.10 percent, with minimum and maximum
values of 0.01 and 1.06 percent, respectively.^23^
.Pyritic £pr Julfide)_Sulfur. In some raw coals, when the total
sulfur is near 0.5 percent, essentially all of the sulfur is present as
organic sulfur. Values greater than this are largely attributed to the
presence of pyritic sulfur, although as the amount of pyritic sulfur increases
(23 25)
so does the organic sulfur content. ' Organic sulfur and pyritic sulfur
comprise essentially all of the sulfur in coal.' ' Analysis of various coals
of the world for total and pyritic sulfur was reported by Yancey and Greer
and the value for total sulfur ranged from 0.44 to 9.01 percent. However,
isolated higher values exist, e.g., 12 percent in an Iowa coal. The amount
of pyritic sulfur ranges from 2.9 to 88.6 percent of the total sulfur pre-
(27)
sent. In American coals, the amount of pyritic sulfur ranged from 16.4
percent to 79.1 percent of the total sulfur and the mean value was 48.8
(28)
percent. The reserve base of U.S. coals by sulfur content has been es-
timated for the eastern and western states (i.e., east and west of the
(29 30)
Mississippi River). ' It includes both the strippable and deep mine
reserves. In the eastern states the reserve base was estimated to be about
203.3 billion short tons and for the western states about 234.3 billion short
tons. Estimates of the sulfur content of these reserves are given in Table
12 which clearly shows that the largest reserves of low sulfur coal exist in
the western states. The data did not differentiate between inorganic and
organic sulfur content of these reserves but suggested that coals containing
a higher percentage of an inorganic sulfur facilitated easier removal of sulfur
as a percentage of total sulfur.
Pyrites is the term used to describe the iron sulfides present as
marcasite or pyrite geomorphs in coal. They are characterized by extreme
(25)
variations in their morphology, size, and mode occurrence.v Those formed
during the formation of the peat swamps, are considered to be syngenetic, and
are the origin of the submicron-size particles closely associated with the
organic matter of coal. However, nodules up to 1 meter in diameter can have
similar origin. The pyrite formed subsequent to coalification (epigenetic)
is present along vertical fractures and cleats and exists in a range of sizes.
-------
30
TABLE 12. ESTIMATES OF THE SULFUR CONTENT JN EASTERN
AND WESTERN COAL RESERVES * ' '
"nl fur Pnntrmt Percentage of the Reserve
Percent East West
< 1 16.2 71.4
1.1 - 3.0 27.4 16.0
>3.0 40.3 4.8
Unknown 16.1 7.8
Combined
43.8
21.7
22.6
12.3
(a) Calculated from data from Eastern and Western Reserves.
-------
31
The larger pieces of pyrite are amenable to removal from the coal
by physical means such as size reduction and gravity separation. The
fraction of pyrite closely associated with coal is microscopic and is dis-
seminated extensively. This form requires extensive size reduction to
liberate it. Moreover, once liberated, the micron-size pyrite is often too
small for gravity separation, and thus other methods, either physical or
( 28)
chemical, are needed to remove it from the coal. A number of sulfide
minerals have been reported in coals, but these occur only in small
(28)
amounts. They are discussed in the section on trace-element contamina-
tion in coal.
Sulfur in Coal Liquids. The coal-derived liquids obtained from
a process using catalytic or noncatalytic hydrogenation refining of coal
(31 32)
contain less than 1 percent sulfur. ' When coal was liquefied without
E catalyst, 14 sulfur compounds were identified; one was a disulfide and the
(33)
rest were thiophene derivatives. The sulfur compounds in coal-derived
liquids are of an organic nature, and the pyrite sulfur present in the feed
coal is readily converted to hydrogen sulfide and FeS during hydrogenation.
The FeS is in suspension along with other minerals and undissolved matter
and is removed with them.
2.1.2. Sulfur Contaminants in Petroleum or Crude Oils
Crudes being used today contain sulfur in varying amounts. The
Pennsylvania and some mid-continent crudes contain 0.1 to 0.2 percent sulfur,
while heavier California, Wyoming, and southern crudes, as shown in Table 13,
(34)
contain 3 to 5 percent sulfur.v ' The mean sulfur content of all U.S.
(35)
production in 1966 was 0.67 percent. ' Crudes with a very high sulfur
content exist (e.g., 7.47 percent in Oxnard, California crude or 13.96 percent
in Rozel Point seepage in Utah). This wide variation in the amount of sulfur
in crude is expected because of the vastly different history of the petroleum
formations. The sulfur present in crude oils occurs as numerous types of
organic compounds, as shown in Table 13, and also as hydrogen sulfide and
f 36)
elemental sulfur.^ The concentration of sulfur compounds usually varies
-------
TABLE 13. SULFUR PRESENT AS CONSTITUENTS INDICATED IN CRUDE
Distribution of Sulfur in Crude
Field
Heidelberg
Hawkins
Rangely
Oregon Basin
Wilmington
Midway-Sunset
Schuler
Agha Jari
Santa Maria
Elk Basin
Was son
Slaughter
Velma
Kirkuk
Deep River
Yates
Goldsmith
Loca-
tion
Miss.
Texas
Colo.
Wyo.
Calif.
Calif.
Ark.
Iran
Calif.
Wyo.
Texas
Texas
Okla.
Iraq
Mich.
Texas
Texas
Wt. %
Sulfur
in Crude
Oils
3.75
2.41
0.76
3.25
1.39
0.88
1.55
1.36
4.99
1.95
1.85
2.01
1.36
1.93
0.58
2.79
2.17
Residual
Sulfur
(Thiophene
Derivatives)
80.3
73.8
72.0
68.2
66.7
66.5
66.4
65.7
58.2
54.9
52.6
48.8
43.9
41.0
28.6
20.5
17.3
R-S-R
(R=Aromatic
Thiophene
Sul fides)
11.7
14.6
20.3
13.5
19.9
26.0
22.7
9.6
35.5
25.1
13.0
22.5
41.5
24.7
3.0
20.1
11.6
R-S-R
(R=Aliphatic
Sul fides)
7.8
11.1
7.7
15.0
12.7
7.3
9.3
12.8
6.1
1.4
11.6
7.5
12.4
20.9
0.0
9.2
9.6
Oil, Percent of Total Sulfur
R-S-H
(Mercaptan)
0.0
0.3
0.0
1.7
0.3
0.2
0.6
8.5
0.2
11.3
15.3
10.8
1.1
7.9
45.9
7.5
10.6
R-S-S-R
(Disulfide)
0.2
0.3
0.0
1.3
0.5
0.0
1.0
3.4
0.0
7.2
7.4
9.2
0.7
5.5
22.5
6.9
8.4
Ele-
c mental
V S
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
1.2
0.0
0.0
0.0
0.0
0.3
0.0
OO
0.0 *>
0.0
0.0
0.0
0.1
0.1
1.2
0.4
0.0
0.0
34.6
42.5
-------
33
directly with the molecular weight or boiling range of the fraction of
petroleum being investigated. As the molecular weight of a given crude
increases, the concentration of sulfur compounds increases. In many oils,
the heavier fractions contain sufficient sulfur to account for at least one
atom of sulfur per molecule. Although some molecular types containing two
atoms of sulfur have been identified, most of the sulfur compounds in
petroleum seem to contain a single sulfur atom. Thus, these heavier fractions
actually consist of sulfur compounds rather than hydrocarbons.
The various types of sulfur compounds which have been positively
identified in crude oils are:
(1) Mercaptans (Thiols) . Alkyl thiols with both normal
and branched alkyl groups, and with the thiol group in
a primary, secondary, or tertiary position, have been
identified. Cycloalkyl thiols containing cyclopentane
rings or cyclohexane rings are also present. Aromatic
thiols are not common, but benzenethiol has been iden-
tified.
(2) Alkyl Sulfides. These compounds have been found with
either straight or branched structures. Cyclic sulfides
having four or five carbon atoms in their ring structure
are present in petroleum, but none containing less than
four or more than five carbon atoms in the rings are
found. The mixed alkyl-cycloalkyl sulfides and alkyl-
aryl sulfides are present in low concentrations.
(3) Heterocyclic. These compounds include thiophenes,
thiaindans, and thienothiophenes as the basic building
blocks for sulfur contaminants found in high-boiling-
point (84 to 450 C) fractions of crude. The thiophenes
are the most important , but the thienothiophenes are
(35)
not quantitatively important., In the case of Wasson
crude, for the 200 to 250 C boiling range, 46 sulfur
compounds were identified; these included 2 thienothio-
phenes, 18 thianindans, 4 alkyl sulfides, and 22 benzo[g]
(35)
thiophenes.
-------
34
2.1.3. Sulfur Contaminants in Tar Sand Oil
Ritzma, in his discussion of oil-impregnated rock deposits of
Utah, considered their sulfur content as the most significant characteristic.
The sulfur content of the oils in Unita Basin was found to be between 0.19
and 0.82 percent. The deposits of central-southeastern Utah were found to
have a sulfur content of 1.64 to 6.27 percent.
Clugston^36^ has identified sulfur compounds in Athabasca tar sands,
as shown in Table 14. The oils were distilled to obtain four fractions:
saturates, 37 to 69 percent; monoaromatics, 13 to 21.3 percent; diaromatics,
7.1 to 15.1 percent; and polyaromatics, 10.3 to 25.6 percent. The sulfur
compounds were identified in these fractions, as shown in Table 14.
(37)
TABLE 14. SULFUR COMPOUNDS IN TAR SAND OILS
(38)
Oil Fraction
Total Sulfur
(0.8 to 2.9 wt. %)
Mercaptan
Sulfide
Thiophene
Derivative
Saturates Trace
Monoaromatics Small
Diaromatics Large
Polyaromatics Large
Polar-polyaromatic Large
Alkyl sulfide
Alkyl sulfide
Thiophene
Alkyl(methyl)
cyclo-alkyl
Alkyl-
dibenzo-
thiophene
Alkyl-dibenzo-
thiophene
(alkyl-small-
chain; methyl
abundant)
The sulfur compounds found in tar sand bitumen are thus similar to those
found in coal liquids and shale oil but their concentration is higher.
-------
35
2.1.4. Sulfur Contaminants in Shale Oil
It has been shown that a typical Colorado shale oil consists of
39 percent hydrocarbons (many of which are unsaturated) and 61 percent hetero-
hydrocarbons containing oxygen, nitrogen, and sulfur. Because only 14 per-
cent, by weight, of the original raw oil shale is valuable organic matter and
only two-thirds of that is recovered, only about 10 percent of the original
raw oil shale is obtained as shale oil. ' The sulfur contaminants in raw
oil shale are organic and inorganic in nature, as shown in Table 15. The
total sulfur content of raw oil shale minerals from Colorado is less than 1
percent, and 33 percent of this is organic sulfur.
(1) The organic sulfur compounds to be found in shale
oil would be those that withstand the retorting
temperatures (500 to 700 C) of the initial recovery
method. The predominant sulfur types reported are
(a) heterocyclic (thiophene based) and (b) sulfides;
small amounts are found as mercaptans and disulfides,
(39)
as shown in Table 16. '
(2) Inorganic sulfur, occurs as pyrites and marcasite
sulfates such as CaSO,, FeSO,, MgSO. in the raw shale.
4 44
After retorting the oil shale the spent shale contains
up to 66 percent of the raw shale sulfur as shown in
Table 15. Some entrainment of spent shale and its
inorganic sulfur contaminants occurs during retorting
(40 41)
and must be separated from the recovered liquids. '
2.2. Chemical and Physical Characteristics of
Organic Su1fur Contaminants in
The similarities in the types of organic sulfur compounds in the
four fuel types suggest that the chemical and physical characteristics of
these contaminants can be discussed as a unit rather than separately for
each fuel type. The discussions relate to contaminant-removal reactions
-------
36
TABLE 15. AVERAGE DISTRIBUTION OF SULFUR IN1
COLORADO MINEABLE-BED OIL SHALES
Type of Sulfur Compound in Raw Shale
Sulfide sulfur
Organic sulfur
Sulfate sulfur
Total
Distribution of Raw Shale Sulfur in
Assay Products
Spent shale
Oil
Gas plus water by difference
Total
Percent
67
33
Remarks
66
H
23
100
As pyrite and marcasite,
Trace As CaSO^, FeSO^, and
100
As FeS2, FeS, CaS, and MgS
with minor amounts of organic
and sulfate sulfur
As H2S and possibly some SOo
or S0 z
(a) Data Source: Stanfield, K.E., et al., U.S. Bureau of Mines RI 4825 (1951),
Reference 41.
TABLE 16. SULFUR-TYPE COMPOUNDS IN COLORADO
SHALE OIL NAPHTHA
Sulfur Type
Weight Percent
Elemental
Thio
Disulfide
Sulfide
Sulfide residual
(including thiophene)
0
4
2
19
75
-------
37
and do not attempt to differentiate between the sources of the compounds
but instead treat them on the basis of their functional groupings or parent
heterocyclic compounds. However, the actual treatments used will differ
depending on which constituents are present and their concentrations in each
fuel type.
The processing conditions required in the conventional desulfurizing
of fuels are quite severe. This could be due to the inherent stability of
the C-S bond in the organic compounds. It was recognized long ago that
sulfur behaved like oxygen and formed compounds such as CS-, COS, and those
equivalent to ethers and phenols. The divalent sulfur, because of the
available unshared electrons, is capable of releasing electrons in conju-
gative interactions with electron-deficient groups or with electron with-
drawing unsaturated groups as shown:
0 «
R - S - C -
-------
38
2.2.1. Mercaptans (Thiols)
General Formula; R-SH. The mercaptans could be naturally
occurring in fuels. They can also be synthesized while the fuel is being
processed. The reaction between hydrogen sulfide and an olefin gives
mercaptans:
R-H-C - CH-R y y R-H-C-CH0-R
^ j 2
SH
Catalysts that have been found effective are the sulfides of metals like
cobalt and nickel. These are the catalysts used in the conversion of coal
or crude bottoms to more useful clean fuels. A mercaptan could also be
synthesized during fuel processing by:
(1) Decomposition of a disulfide
RSSR *2RSH
(2) Reaction between a phenol, alcohol, and hydrogen
sulfide (commercial process, methanol to methyl
mercaptan) .
ROH + H2S CatalyS> RSH + H20
(3) Carbon disulfide hydrogenation
Physical Characteristics. The physical characteristics of mercaptans
have been studied and compared with those of alcohols. The heat of formatidn
of C-S bond is greater in the (alkyl) sulfides than in the corresponding
mercaptans and is still greater in carbon disulfide. ^2^ The surface
tension of ethyl mercaptan is less than that of alcohol. In the infrared,
mercaptans have a well-defined absorption band at 3.8 to 3.85 microns.
There are distinct ultraviolet bands and frequency shifts in Raman spectra.
The ionization constant of mercaptans is on the order of 10"11. Azeotropes
have been used in the separation of mercaptans and alcohols. The boiling
points, densities, and solubility in water for some mercaptans are given
in Table 17.
-------
39
TABLE 17. BOILING POINT, DNESITY, AND SOLUBILITY
IN WATER OF VARIOUS MERCAPTANS(41)
Me re apt an
Methyl
Ethyl
Propyl
Butyl
Octyl
B.P., C
5.96
34.7
67.5
98.0
199.1
d°4
0.8948
0.8617
0.8617
0.8601
0.8500
s*
23.3
6.76
1.96
0.57
0.004
* S = solubility, g/1, at 20 C.
-------
40
Reactions and Properties. The mercaptans, besides being con-
taminants, are largely responsible for equipment corrosion, catalyst poisoning,
and unpleasant odors. The presence of sulfur compounds in gasoline is
objectionable because of odor, gum formation, corrosion, and the formation
of deposits in engines. Most often sited are the mercaptans and their
reaction products, alkyl disulfides and polysulfides, Mercaptans are much
more acidic than corresponding alcohols.
They form addition compounds with water, nitric oxide, AlCl^,
TiCl,, BF,. HF, and urea. Ethane thiol forms a hydrate that is stable at
4> 4» »
low temperatures.
JDecomDpsition._ An extensive review of mercaptan decomposition is
given by Reid.^ ' The significant methods are:
(1) Light - Ethane thiol decomposes to ethyl disulfide,
hydrogen, ethylene and higher olefins.
(2) Radiation - In an aqueous solution, the mercaptans
are decomposed to a disulfide by X-ray,
beta rays, and gamma rays.
(3) Thermal Cracking - Primary and secondary mercaptans
decompose readily above 300 C to hydrogen
sulfide and the corresponding olefin. The
tertiary mercaptans decompose at lower tem-
peratures .
(4) Catalytic Cracking - A silica alumina cracking catalyst
will decompose decane thiol at 250 C to decyl
sulfide and an olefin, but at 300 C, decomposition
is to an olefin and hydrogen sulfide.
Aromatic thiols are more difficult to decom-
pose and at 300 C, thiophenol decomposes to
give benzene and thianthrene. Some other
effective catalysts proposed are phosphoric
acid, sulfides of cadmium, zinc, tin, bismuth,
aluminum, and iron.
-------
41
(5) Use of Additives - Various compounds such as cresol,
furfural, terpenes, asphalt, petroleum
residue, calcium cyanamide, and sodium
compounds of multiring aromatics when
added to petroleum promote the decom-
position of the mercaptans.
(6) Catalytic Hydrogenation - With catalysts like
cobalt -mo lybdate and nickel and molybdenum
sulfides, the organic sulfur is converted
to hydrogen sulfides during hydrogenation.
Oxidation. Mercaptans react with oxygen to form disulfides. The
reaction below is promoted by the addition of sodium or ammonium hydroxide
to the reaction mixture:
3C2H5SH + NaOH + C>2 * C^SSC^ + H20 + C^SC^Na .
Other common oxidizing agents are iodine, hydrogen peroxide, ozone, nitric
acid, potassium permanganate, sulfur dioxide, and sulfuric acid.
Mercaptans form heavy -metal complexes with mercury, copper,
antimony, bismuth, and lead. The sodium and lead plumbites have been used
for sweetening of sour gasolines (i.e., those that contain mercaptans).
2.2.2. Sulfides
General Formula; RSR. The alkyl sulfides are the analogues of
ethers, RORC The sulfides are widely distributed in nature, while mercaptans
are comparatively rare. Sulfides are found in crude petroleum and distil-
C35)
lates. Sulfides have been isolated from shale oil and low-temperature
tar, and the presence of organic sulfides in coal is indicated by certain
specific reactions, e.g., with methyl iodide.
-------
42
The sulfides found in partially treated crudes or synthetic crudes
(shale oil, coal liquids) could result from the following reactions:
(1) Reaction of tnercaptan and olefin
RSH + RCH : CH2
(oxygen favors the reaction)
(2) Reaction of sulfur and hydrocarbons
Paraffin + S heat> olefin + H2S
Olefin + H S ^ mercaptan
Mercaptan + olefin ^alkyl sulfide
(3) Reaction of alcohols with hydrogen sulfide
2ROH + H2S catalyst R2S + 2H20
(4) Reaction between aldehyde and a mercaptan in hydrogen
RCHO H- RSH + H
Physical Characteristics. The resemblance of sulfides to ethers
is closer than that of mercaptans to alcohols. The ultraviolet and infrared
absorption of sulfides has been studied. The bond energy for C « S, C - S,
and S - H, is 177.8, 59.2, and 87.1 kcal/mole, respectively. Entropy, free
energy, and heat capacities of methyl and ethyl sulfides have been deter-
mined over a wide temperature range. The alkyl sulfides form azeotropes
with paraffins, olefins, and alcohols. The boiling points and densities
of some sulfides are given in Table 18. The alkyl sulfides are not soluble
in water.
TABLE 18. BOILING POINT AND. DENSITY OF
ALKYL SULFIDES (43)
Sulfide
Dimethyl
Methyl ethyl
Diethyl
Methyl propyl
Ethyl propyl
Methyl butyl
B.P.,C
37.3
66.6
92.0
95.6
118.5
122.5
d 20/4
0.8483
0.8422
0.8363
0.8424
0.8370
0.8427
-------
43
Reactions and Properties. Alkyl sulfides are more reactive than
ethers and readily react with many reagents.
Addition_Compo_unds_. Methyl sulfide and boron hydride form an
addition compound that melts at -38 C. Ethyl sulfide dissolves in anhydrous
hydrofluoric acid, forming a type of sulfonium salt, and the sulfide can be
recovered by the addition of water. Methyl sulfide reacts similarly with
hydriodic and hydrobromic acid. Methyl sulfoxide is an excellent solvent
for sulfur dioxide. Alkyl sulfides form crystalline adducts with urea.
The primary product from the reaction of chlorine and bromine with alkyl
sulfides and aryl sulfides is an addition compound. The aryl sulfides do
not take up the halogen readily. The oxidation of sulfides to sulfoxides
occurs with chlorine in the presence of water. Alkyl sulfides form addition
compounds with salts of the heavy metals, e.g., platinum and mercury com-
pounds are most numerous.
De_cqmpjos_itiqn. This usually involves the breaking of the C-S
bonds. Kekiile showed that thiophene results when ethyl sulfide is passed
through a hot tube. Ethyl sulfide begins to decompose at 400 C, and at
496 C, the decomposition of i-amyl sulfide, ^..-.H^S, is complete. Phenyl
sulfide, (C,HC)0S, gives dibenzothiophene, benzene, and hydrogen sulfide.
o 5 2
The t-butyl sulfide is converted by hydrogen sulfide into two molecules of
the mercaptan. The addition compound of a sulfide, e.g., methyl sulfide
with hydrogen iodide, when heated, produces a mercaptan, sulfonium iodide,
and hydrogen iodide. At temperatures below 250 C under 1500 psig of
hydrogen in the presence of a catalyst, the alkyl sulfide is split into a
mercaptan and a hydrocarbon. Catalysts like Raney nickel and cobalt molybdate
remove the sulfur as hydrogen sulfide. The cleavage of an alkyl sulfide
occurs in the presence of sodium in liquid ammonia. A sulfide is decomposed
by the addition of an alkyl halide; methyl iodide is most active:
RSR + CH3I->RRCH3SI >RI + RSCH.J.
-------
44
(hcidatipn,. The indirect oxidation by bromine and chlorine is an
addition reaction, and occurs in two stages as follows:
Sulfide »-Sulfoxide ^Sulfone .
(R2S) (R2SO)
-------
45
bond is restricted and that dimethyl disulfide exists in cis and trans forms.
Data on vapor pressure, latent heat of vaporization, heats of formation, and
specific heats are available. The alkyl disulfides have been shown by
diamagnetic susceptibilities to have the structure RS'SR and not R_S:S.
Solutions of thiols and disulfides in concentrated sulfuric acid are strongly
colored. The disulfides form azeotropes with hydrocarbons, e.g., 27.5 percent
dimethyl sulfide and hexane, the azeotrope boiling at 96.4 C/' The boiling
points and densities of some disulfides are given in Table 19.
(43)
TABLE 19. BOILING POINT AND DENSITY--
OF VARIOUS DISULFIDES
Disulfide
Methyl
Ethyl
Propyl
Butyl
Cyclopentyl
Biphenyl
B.P., C
109.75
152.00
193.00
230.00
105.50
310.00
d 20/4
1.0647
0.9882
0.9599
0.9383
1.0617
1.3530
Reactions and Properties. Disulfides, besides undergoing thermal
decomposition and oxidation, are reduced and undergo hydrolysis. '^)
Decomposition. The S-S bond in a disulfide is reactive. Aryl
disulfides can be decomposed by ultraviolet light. Like the peroxides, the
disulfides generate free radicals. The aliphatic disulfides are not as
efficient as the aryl disulfides in this respect. Benzyliodide combines with
benzyl disulfide and mercuric iodide to give (C6H5°CH2)3SI-HgI. Ethyl
disulfide gives a sulfonium salt. These reactions suggest that the S-S
bond is broken.
-------
46
Aliphatic disulfides are unstable at high temperatures, and the
product of pyrolysis will be a mixture of mercaptan, monosulfide, and
hydrogen sulfide. Aromatic disulfides are more stable, and one of the
products on thermal decomposition is a mercaptan. In the case of diphenyl
sulfide decomposition, many products have been reported, e.g.,
970 300 C
Diphenyl disulfide . » monosulfide, dibenzothiophene,
thiophenol, thianthrene
In general, the aromatic disulfides when decomposed by metal salts (e.g., aluminum
chloride) or by a metal (e.g., copper) form other aromatic derivatives
that include the thiophene structure. Decomposition can also be achieved
by using microorganisms.
Red_uctJ.on. The disulfides can be completely reduced to a mercaptan.
A mixture of a disulfide and mercaptan can be considered as an oxidation-
reduction buffer, analogous to the well-known acid-base buffers. Some
reagents which convert sulfides to mercaptans are sodium hydrosulfide, sulfide,
disulfide, or polysulfide. Higher alkali polysulfides may convert mercaptans
to disulfides and even add sulfur to the alkyl disulfide. The presence of
a mercaptide is believed to act as a catalyst. Reduction can also be
achieved with glucose, sodium arsenite, or lithium aluminum hydride, or by
hydrogenation over a molybdenum sulfide.
Oxidation.. A disulfide is an intermediate in the oxidation of a
mercaptan and on further oxidation produces acids. The common oxidants used
are nitric or sulfuric acid, chromate, permanganate, hydrogen peroxide, and
oxygen containing nitrogen oxides. Chlorine forms sulfuryl chlorides which
can be separated from other hydrocarbons by a hot alkali wash. In the
presence of bromine, a disulfide appears to form an addition product.
. The disulfides are split during alkaline hydrolysis:
(CH3)2S2 + 2NaOH->CH3S Na + CH3SO Na -f H.O.
-------
47
Some disulfides, e.g., t-butyl are not affected by alkali. Thus, cleavage
seems to depend on the presence of a hydrogen atom on the carbon linked to
the sulfur.
2ther_Reactiqns_. Disulfides form complexes with salts of platinum,
mercury, gold, silver, and indium. Copper napthanate reacts with disulfides
to form complexes. Mercuric chloride forms mercuric compounds with some
aromatic disulfides.
2.2.4. Heterocyclic (Thiophene)
Sulfur forms many heterocyclic compounds that consist of three-,
four-, or five-member rings. The large size of the sulfur atom may account
for the fact that ring compounds with five members are more common than
those with six members. When considering fuel contaminants, the five-member
ring compound thiophene and its derivatives are the most important. Thiophene
was discovered in coal tar in 1883.^ ' In 1899, Charistschoff reported that
Grosny crude contained 1 ppm thiophene. The inherent stability of thiophene
(43) (44)
makes its removal a challenge. Reidv and Hartough have extensively
discussed the basic chemistry of thiophenes. The resonance energy of thio-
phene is 31 kcal/mole and that of benzene is 36 kcal/mole, which helps explain
its aromaticity.
The synthesis of thiophene during fuel processing is accomplished
by ring-closure reactions that could occur by
(1) Joining a C, alkane unit at the 1,4-carbons by a
sulfur atom
(2) Reactions akin to the production synthesis of thio-
phene, e.g., by the reaction of butane and sulfur at
high temperatures
(3) Reaction of an olefin and sulfur at 600 C
(4) Decomposition and cyclization of a disulfide.
-------
48
Physical Characteristics of Thiophene. Thiophene is a colorless
liquid, insoluble in water, having an odor somewhat like benzene when highly
purified. In general, the derivatives of thiophene have odors fairly similar
to those of their benzene isologues, i.e., 2-thiobenzaldehyde and benzaldehyde.
The monosubstituted thiophene derivatives usually boil at higher temperatures
than the corresponding benzene derivatives. The thiophene compounds, however,
are usually not as thermally stable as benzene. The molecular structure and
spectroscopy of thiophene and its derivatives was published in API Project
44 reports. ' Some physical properties of thiophene and methyl thiophene
that are related to contaminant removal are given in Table 20.
TABLE 20. BOILING POINT, DENSITY, AND FREEZING POINT
OF THIOPHENE AND SOME DERIVATIVES^)
Compound
Thiophene
2-methyl-
3-methyl-
JU
B.P. , C/900mm Hg d. Freezing Point, C
89.7
118.4
121.3
1.0542
1.0086
1.0110
-38.30
-63.50
-68.9
Reactions and Properties. Thiophene and its derivatives exhibit
(43 44)
certain characteristic chemical reactions. ' It is unnecessary to draw
a chemical distinction between thiophene and benzene other than to say that
they are distinct chemical compounds to be compared only because both happen
to be aromatic compounds. Thiophene cannot easily be compared with pyrrole
and furan since there are many reactions of these that fail with the thio-
phenes. The following reactions may be used to remove thiophenes from fuels.
r_o^ejioJvsis_. Thiophene poisoning
of hydrogenation catalysts for benzene was first mentioned in 1912 when
benzene containing 0.01 mg of thiophene per gram of benzene could not be
(44)
hydrogenated over platinum. Thiophene can be successfully hydrogenated
-------
49
to tetrahydrothiophene without the breakage of the C-S bond. The commonly
used catalysts are cobalt molybdate or sul fides of cobalt and molybdenum.
Molybdenum disulfide at 200 C and 200 atm of hydrogen pressure promotes the
hydrogenation of thiophene to the tetrahydrothiophene in yields of 52 percent.
The other products are butyl sulfide (11 percent) and butyl mercaptan (6
percent).^ ' Higher temperatures bring about the breakage of C-S bond, and
catalysts like nickel-tungsten sulfide, cobalt tetracarbonyl, and rhenium
sulfide have been used. In this case, the sulfur is removed as hydrogen
sulfide and butane is produced.
D_ecomp_qsit^qri. Chemically, thiophene is less stable than benzene.
Ring rupture with evolution of hydrogen sulfide begins to take place at about
200 C in the presence of silica-alumina-type cracking catalysts. In the
presence of 100 percent orthophosphoric acid, some ring rupture is observed
at the boiling point, and with sulfuric acid, polymerization occurs with
evolution of sulfur dioxide. Thallous hydroxide decomposes thiophene to
give thallous succinate and thallous sulfide. Potassium causes ring rupture
and potassium sulfide is formed, while sodium is inactive. Ozone, when
bubbled through a suspension of thiophene in water, forms an ozonide. Thio-
phene undergoes autoxidation in light and is decomposed to sulfuric and oxalic
acids.
oii. Chlorination of thiophene in a
liquid phase can be carried out at low temperatures, ranging from -30 C to
84 C. Both substituion and addition to the thiophene nucleus take place.
In general, the polychlorothiacyclopentanes (polychloro-thiophenes) are stable
below 150 C and can be distilled under vacuum without decomposition. These
compounds can be decomposed by pyrolysis, alcoholic caustic, solid potassium
hydroxide, hot potassium carbonate, or zinc dust in water and alcohol. The
bromothiophenes undergo mercuration, metallization with sodium, nitration,
sulfonation, acylation, and typical Grignard reactions. The iodination of
thiophene can also be accomplished by using iodine and mercuric oxide.
-------
50
Alkylation. Direct alkylation of thiophene can be accomplished
easily by reaction of certain branched-chain olefins with thiophene in the
presence of mineral acids. Isobutylene and thiophene react to form butyl-
thiophenes and di- tertbutylthiophenes. With activated clays, dilute
sulfuric acid, and phosphoric acid, thiophene polymerizes to a trimer and a
pentamer. The trimer has been shown to have the structure
Concentrated sulfuric acid and aluminum chloride produce amorphous red poly-
mers of high molecular weight. Alcohols can also be used as the source of
alkyl groups if stannous chloride is used as a catalyst:
Qnfl
C,H,-CKLOH + thiophene ... 2* 2 benzyl thiophene
6 ^ L 2,5 dibenzylthiophene.
Aldehydes, especially formaldehyde, react with thiophene in the 2,5 positions
to produce polymers when the reaction is catalyzed by strong mineral acids.
Some aldehydes such as benzaldehyde can be condensed with thiophene in the
presence of activated clays.
Oxidation_. Thiophene and hydrogen peroxide form a sulfane as the
intermediate product and then ring rupture occurs to give fumeric acid
(HOOCHCHCOOH) . The highly substituted and condensed thiophenes form stable
sul fanes.
^^^^ti??.' Selective sulfonation of thiophene with 96 percent
sulfuric acid was the method first used to show the presence of thiophene
in coal tar. For the purpose of identification and isolation of thiophene,
the sulfonic acid obtained was converted to the lead salt and thiophene was
then recovered. However, sulfonation can lead to polymerization as well.
-------
51
MetaHj.za.tjLcm. The reaction of mercuric compounds, e.g., mercuric
chloride and mercuric acetate, with thiophene occurs readily. These salts
have been used for the concentration and purification of thiophenes, since
the highly insoluble mercury salts can be separated easily. Lithium and
sodium derivatives are easily prepared. Most lithium and sodium derivatives
are prepared by a transmetallization reaction involving thiophene or a sub-
stituted thiophene and an alkyl or aryl lithium or sodium. While lithium does
not react with 2-chlorothiophene dissolved in ether or benzene, sodium reacts
at 60 to 80 C to give a sodium derivative, and at 20 to 30 C, gives a 5-chloro-
2-sodium derivative:
Cl
n
-------
52
2.3. Nitrogen Contaminants in Fuels
The nitrogen contaminants in fuels have not been characterized as
well as the sulfur contaminants. In general, the nitrogen is considered to
be of organic origin. Inorganic-nitrogen sources outside of some rare
instances do not apparently exist.
2.3.1. Nitrogen Contaminants in Coal/Coal Liquids
Coal contains nitrogen in the form of organic compounds which are
part of its organic structure. Traces of inorganic nitrogen have been found,
as nitrates, in the low-temperature ashes of some western coals, but its
origin is postulated as part of the ashing process, and is not believed to
be in the raw coal.
It is quite difficult to describe the state of organic nitrogen
in coal. Hauck' ' reiterates that "little is known with certainty about
the nitrogen forms in coal". In the process of identification of the nitrogen
compounds in coal, the compounds are altered by thermal or chemical effects
used in their isolation, so that the nitrogen compounds ultimately deter-
mined may not be representative of the original compounds in coal. Use of
a mild selective solvent extraction has partially circumvented this problem.
This technique has been carried out, but some coal pretreatment is
also involved. In another approach, the nitrogen compounds are identified
in coal degradation products (e.g., coal tars). Then, on the basis of the
nitrogen compounds identified in the products, postulates are made as to
the type of nitrogen compound originally in coal.
In 1925, Francis and Wheeler^ concluded that nitrogen in coal
was aromatic in nature. This was proved conclusively when, by coal/nitrogen
analysis, it was shown that nitrogen occurred in pyridine, picoline, quino-
line, and nicotine structures. The nitrogen content of U.S. coals of
different ranks is given in Table 21.
-------
53
TABLE 21. NITROGEN CONTENT OF U.S. COALS(50)
Coal Maf coal, percent
Lignite ifQ
Subbituminous 12-17
High volatile C bituminous 1.6 - 2.1
High volatile B bituminous 1.7
High volatile A bituminous 1.6 - 1.9
Coals contain 10 to 30 times the amount of nitrogen present in
wood. It has been shown in numerous studies that soil humus, humic acid,
and peat, i.e., precursors of coal, contain the nitrogen compounds shown in
Figure 6. Thus, some complicated mechanisms concentrate the nitrogen of
the wood to the levels found in coal, since the nitrogen content of younger
coal (peat) is less than that of bituminous coal, as shown in Table 21.
Coals that are treated with hydrochloric or sulfuric acid produce
an extract that contains up to 78.5 percent of the nitrogen present in
young coals (peat), but only 2.64 percent of that in anthracite. Thus it
is concluded that in older coals (anthracite), the nitrogen compounds are
neither basic nor are they present as reactive species, but instead are
linked to other groups. '
Another scheme for the determination of the distribution of the
nitrogen bond types is given in Table 22. ' The nitrogen bond types
isolated in water and chloroform extracts and in the residue were determined.
A reductive pretreatment with hydrogen iodide and phosphorus was carried out
to enhance coal extraction, but this pretreatment could alter the coal
constituents, and in this specific study, a gas was produced which contained
26 percent of the coal nitrogen.
Nitrogen compounds isolated in the tarlike products of coal
pyrolysis have been identified by many workers. The nitrogen com-
pounds are aromatic in nature and could be derivatives of those shown in
Table 23. The derivatives could fce alkyl substituted or combinations of
the compounds in Table 23 to give aza coronene, nitrites, quinoline, and
indole structures. Other compounds, e.g., acetonitrile and benzonitrile,
-------
54
TABLE 22. BITUMINOUS COAL TREATMENT AND DETERMINATION
OF NITROGEN BOND TYPES ^'
Gas
Coal
Pretreatment with Hydrogen
Iodide and Phosphorus
Treated Coal
Chloroform
Extract
Water
Phase
Residue
Extract
Nitrogen Bond Types
Percent N in Coal
Water
Water
Water
Chloroform
Purine bases, urea
structures, aminoacids,
peptides
Carbazole structures
Cyclic bases, phenylamines
Nonbasic N-compounds,
fatty amines, hydrophobic
basis
Residual nitrogen
Nitrogen in gas on pretreatment
Total
35
10
3
23
3
-26
100
TABLE 23. NITROGEN COMPOUNDS AS BUILDING
BLOCKS FOUND IN COAL TARS
Pyrroles
Pyridines
Anilines
Indoles
Quinolines
Fluoranthene
Carbazoles
Acridines
Perylenes
Coronene
-------
55
PROTEIN
AMINOACIDS
CHITIN
NUCLEIC ACIDS
AMIDES
AMINES
-NH
PURINES
PYRIMIDES
PYRIDINE
FIGURE 6. NITROGEN COMPOUNDS EXTRACTED FROM /51)
COAL PRECURSORS (Humic Acids, Peat)
-------
56
have also been identified which probably were produced from the degradation
of larger aromatic compounds. Compounds identified in coal tar have a
molecular-weight range of 167 to 301, as shown in Table 24.(53) In a more
recent study twice as many of the structural types than previously reported
in literature have been determined, but the nitrogen compounds identified
all fall into the type of compounds shown in Table 24.
2.3.2. Nitrogen Contaminants in Petroleum
Nitrogen contaminants in petroleum occur in amounts ranging from
a trace up to slightly less than 1 percent, and are primarily organic com-
pounds. The nitrogen compounds found in crude oil fall into two main
categories, basic and nonbasic, as shown in Figure 7. The significance of
the basic and nonbasic nature is discussed later in the section on processing
of nitrogen-rich fuels. The nitrogen compounds are generally concentrated
in the heaviest portion of crude oil, as shown in Table 25. When a
petroleum is separated into oils, resins, and asphaltenes, the nitrogen
compounds are found to be concentrated in the latter two classes. The
types of nitrogen compounds found in petroleum are shown in Table 26.
The nitrogen compounds found in shale oil and coal tar may suggest
compounds likely to be found in petroleum. Compounds like pyridine, quino-
line, isoquinoline, dihydropyridine, pyrroles, and nitriles which have been
found in shale oil and carbazoles, indoles, benzonitrile, amides, and others
which have been found in coal tar, are also reported in petroleum crudes. '
Porphyrins, another class of nitrogen-containing compound, are
also associated with the high-boiling portion of crude oil. They also include
nickel or vanadium in their structure. The structure of a vanadium prophyrin
is shown in Figure 7,
-------
57
TABLE 24. NITROGEN COMPOUNDS IN CREOSOTE OIL
AND COAL TAR PITCH(52>
Structural Types
Nitrogen Compounds
Carbazole
Acridine
4H-Benzo[def ]carbazole
Dibenz[cd, g]indole
llH-Benzo [a] carbazole
Benz[c]acridine
lH-Anthra[2,l,9-cde]indole
Indeno [ 7 , 1-ab ] acrid ine
Dibenz[b,h]acridine
9H-Phenathro[4,5-abc]carbazole
X-Azabenzo (ghi) f luoranthene
Z-Azabenzo (ghi)perylene
Anthra(l,9-ab)carbazole
X-Azacoronene
Total
Molecular
Weight
167
179
191
203
217
229
241
253
279
291
227
277
303
301
Total
Weight }a)
percent
4.6
2.5
1.6
1.6
3.6
1.3
0.7
.6
.1
Trace
--
--
IsTo
Totaln^
Weight y>t
. percent
0.1
0.8
0.6
1.6
1.6
1.0
--
1.4
0.5
--
0.6
0.6
0.4
0.1
777
(a) Creosote oil.
(b) High-temperature coal tar.
-------
58
3-METHYlPYHIOINE
Shuchn
BO.IC
H
HC C-CH3
I ll
HC CH
Found l«
4,6-DIMETHYL (2,6,6-
niMETHnCYCLOHEXVU H2C
PYXIDINE
H, CH3 HC ^CH
.C CH [
^ fc_C Id
.A**
11 r
HC_ C. ,)
Not (bund
(POBibl.1,
kewln.)
GnM
Norn
2-QUINOI.OI>«
2-THIOQUINOtONE
BENZ-2-QUINOLONE
SlniGhin
Nonbotle-ConHnu.j
H H .
I || 1
Hi
H H H
"f M r
"yw
Fowl In
Got «U
«"
I || I Go.1l
H H H
6o><"
COjH C02H
FIGURE 7. REPRESENTATIVE BASIC AND NONBASIC NITROGEN
COMPOUNDS IN PETROLEUM PRODUCTS (55)
-------
59
TABLE 25. DISTRIBUTION OF NITROGEN IN CRUDE
Field
Schuler, Ark.
Heidelberg, Miss.
Deep River, Mich.
Midway-Sunset, Calif.
Wilmington, Calif.
Velma, Okla.
Yates, Texas
Chromo, Colo.
Dallas, Wyo.
Derby, Wyo.
Pilot Butte, Wyo.
Keri, Greece
Circle Ridge, Wyo.
Winkleman Dome, Wyo.
Sage Creek, Wyo.
Steamboat Butte, Wyo.
Nitrogen in
Crude Oil,
percent by
weight
0.06
0.11
0.12
0.58
0.65
0.27
0.16
0.03
0.28
0.25
0.22
0.17
0.23
0.23
0.28
0.16
Percentage of
Nitrogen in
Residuum
88
106
91
85
86
89
88
100
96
96
95
94
96
91
93
88
TABLE 26. NITROGEN COMPOUNDS IN PETROLEUM
(54)
Types of Nitrogen Compounds Found
In Crude Oil
By Identifying
Individual
Compounds
Carbazoles
Pyridines
Quinolines
Tetrahydroquinolines
Dihydropyridines
Benz oqu ino1ines
Only as
Type
Identification
Pyrroles
Indoles
Isoquinolines
Acridines
Porphyrins
Only in
Processed
Fractions
Anilines
Phenazines
Nitriles
-------
60
2.3.3
Nitrogen Contaminants in (U.S.) Tar Sand/Oil
A detailed characterization of the tar sands has shown that the
tar sand oils can be separated into acids, bases, nonbasic nitrogen, and
(58)
saturated and aromatic fractions. ' The elemental analysis of tar sands
is given in Table 5, which shows that Utah asphalt and gilsonite have a
nitrogen content of 2 to 2.5 and 2 to 2.8 weight percent, respectively,
compared to 0.5 weight percent for Athabasca tar sands.
The elemental analysis of bitumen from P. R. Springs, Utah, is
given in Table 27. The samples have the carbon-hydrogen atomic ratio of
0.637 which suggests that the bitumen is of average composition and the
i
sulfur-nitrogen weight ratios are less than 1,which is similar to petroleum
crudes. The oxygen content (2.59 percent) is high compared with that of
other fuels.
A gross comparison of the composition of P.R. Springs bitumen
with petroleum residues is shown in Table 28 where the nonhydrocarbon
content (includes acids, bases, and nonbasic nitrogen) of the P. R. Springs
bitumen is high (46.2 percent), second only to Gach Saran residue. Also
it is known that the P. R. Springs bitumen contains 30 to 50 percent
material in the 275 to 500 C boiling range which is absent in the petroleum
residues. This suggests that a comparable initial-boiling-point residue
of the P. R. Springs bitumen with that of petroleum residues would have an
unusually high content of nonhydrocarbons.
The analysis of the nonhydrocarbon (46.2 percent) content of
P. R. Springs is shown in Table 29. The bitumen acid fraction consists
of carbazoles (pyrrolic N-H) that are common with coal liquids and petroleum
residues. The amide fraction is greater than that in other fuels.
2.3.4. Nitrogen Contaminants in Shale Oil
A characteristic of shale oil is its high nitrogen content as
compared with that of petroleum. The nitrogen contents of the distillation
fractions of a Colorado shale oil containing about 1.6 total weight percent
nitrogen are given in Table 30. The data in the table show that the nitrogen
of the distillate fraction increases with the temperature of the cut. The
residuum fraction (b.p. > 430 C) contains 62 percent of the total nitrogen.
-------
61
TABLE 27. P. R. SPRINGS, UTAH, BITUMENS (TAR SAND OILS)
(58)
Sample
B
E
This Main
S tudy Canyon
(Core) SeeP
Core Core
79 to 137 to
83 ft 141 ft
Outcrop Outcrop
Sample No. Sample No.
69-13E 67-1A
Specific gravity 60/60
API gravity
Elemental analysis,
weight percent
Carbon
Hydrogen
Sulfur
Nitrogen
Oxygen (a)
C/H (atomic ratio)
S/N (weight ratio)
0.998
10.3
84.44
11.05
0.75
1.00
2.59
0.637
0.75
0.974
13.8
0.34
0.77
0.44
0.995
10.7
0.33
0.88
0.38
1.004
9.4
0.40
1.08
0.37
1.016
8.3
80.0
9.5
0.45
1.0
0.702
0.45
0.969
14.5
86.0
10.9
0.36
0.67
0.657
0.54
(a) Determined by difference.
TABLE 28. GROSS COMPOSITION OF SELECTED BITUMEN (TAR SAND OIL, CRUDE OILS)^58'
Components of Residue Sample. Percent
Components
Acids
Bases
Nonbasic nitrogen
Saturated
hydrocarbons
Aromatic
hydrocarbons
Recovery
P.R.
Spring,
>225 C^a
15.4
12.3
18.5
25.7
24.9
96.8
Wil-
v mington
' >485 C
10.7
13.3
20.4
18.4
35.1
97.9
Red
Wash
>545 C
6.0
10.2
10.8
51.8
10.9
94.4
Recluse
>750 C
5.9
8.3
17.4
40.8
24.8
97.2
Gach
Saran
>675 C
12.1
14.2
23.2
25.6
18.7
93.8
Prudhoe
Bay
>675 C
10.0
15.7
12.6
32.9
23.4
94.6
(a) Boiling point of the residue sample.
-------
62
TABLE 29. NONHYDROCARBQN CONCENTRATE
P.R. SPRINGS BITUMEN
(58)
Fraction
Acids I
II
III
IV
Bases I
II
III
Nonbasic
nitrogen I
II
Weight %
of
Bitumen
4.8
2.2
4.0
4.4
2.0
1.5
8.8
10.3
8.2
Weight
Percent of
Molecular Carbolic
Weight Acids
1240 4
1161 28
853 60
(850 est.) 39
855
(900 est.)
952
982
(982 est.)
Phenols
9
20
6
4
- .
Weight
Carbazoles
34
18
7
17
trace
32
17
Percent of
Fraction
Unidentified
Amides
40
33
10
9
67
55
17
55
51
Bitumen
by IR
13
1
17
31
33
45
83
13
32
Total
46.2
4.9
1.3 7.7 20.1
12.2
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63
TABLE 30. NITROGEN DISTRIBUTION IN SHALE-OIL FRACTIONS
Boiling Range,
Fraction
Naphtha
Light distillate
Heavy distillate
Residuum
C
Below 200
200-310
310-430
Above 430
Amount in Shale Oil, Nitrogen in Fraction,
volume percent
3
16
34
47
weight percent
1.17
1.24
1.60
2.04
Poulson^ ' has reviewed the characterization of shale oils and
concludes that the principal nitrogen-containing species are pyridine- and
pyrrole-type compounds. In shale oils with a boiling range of 329 to
583 C, a nitrogen concentrate containing 3.79 percent nitrogen was obtained.'
This oil contained compounds having about 15 to 30 carbon atoms, and about
half of the compounds contained nitrogen. The nitrogen compounds consist-
ing of pyridines, dihydropyridines, indoles, and quinolines comprised over
half the nitrogen compounds in this oil. Much of the remainder consisted
of compounds having one or more saturated rings condensed with these com-
pounds. In addition, smaller quantities of compounds having three or more
aromatic rings were present. The multiring compounds contain a greater
number of substituents, e.g., OH and alkyl. About twice as many pyridines
as dihydropyridines, indoles, and quinolines were found. Pyrroles were
present in small amounts in the heavier fractions. The pyrroles could have
been lost due to the high temperature of retorting. The distribution of
nitrogen-ring compounds in shale oil is given in Table 31. About 40 percent
are multiring compounds.
TABLE 31. NITROGEN COMPOUNDS IN
SHALE OIL (59)
Percent
One-ring compounds 35
Two-ring compounds 25
Multiring compounds 40
-------
64
The nitrogen in the different distillate fractions of shale oil
is evenly distributed. The decrease in the carbon-hydrogen ratio is such
that the relationship of these elements in the average molecule for each of
the cuts is about C En ,, Thus the increase in molecular weight is due
n Zn-11
principally to the addition of methylene groups to the aromatic heterocycllc
nucleus. In shale oil with a boiling range of 329-593 C, the alkyl and
cycloalkyl pyridines comprise 35 percent of the nitrogen compounds in the
oil based on single-ring aromatics in the molecule. The bicyclic, e.g.,
indoles and quinolines, make up 25 percent, and the remaining are multiring
(61)
compounds, many of which also contain oxygen.
When chlorophyllin was used as a kerogen model compound to study
the probable precursors for pyrroles in shale oil pyrolysis, the distri-
(59)
bution of nitrogen compounds formed was comparable to that in shale oil.
A shale-oil light fraction with a boiling range of 204 to 316 C
was found to contain over 43 percent of its nitrogen compounds as alkyl
pyridines and only 4 percent as pyrroles and indoles, as shown in Table 32.
The nitrogen compounds were classified as weak bases, very weak bases, and
nonbasic (pyrroles).
Other nitrogen compounds that occur in small amounts in shale oil
are the amides, arylamides, and nitriles.^ ' 63~65)
Porphyrins, another source of nitrogen contaminants which have
been extracted from shale oils undergo pyrolysis similar to chloraphyllin.
They are discussed in more detail in the section on trace elements.
2.4. Chemical and Physical Characteristics
of Organic Nitrogen Contaminants in Fuels
The similarities in the kinds of organic nitrogen compounds in
the four fuel types suggest that the chemical and physical characteristics
of these contaminants can be discussed as a unit rather than separately
for each fuel type. The discussions relate to contaminant-removal reactions
and do not attempt to differentiate between the sources of the compounds,
but rather treat them on the basis of their functional groupings or parent
heterocyclic compounds.
The nitrogen contaminants concentrate in the heavier fractions of
liquid fuels. Nitrogen removal from the lighter fractions of petroleum
-------
65
TABLE 32. NITROGEN TYPE ANALYSIS OF SHALE OIL
DISTILLATE (204 TO 316 C)(63)
Percent of
Nitrogen Type Total Nitrogen
Weak bases (pKa = +8 to +2)
Alkylpyridines 43
Alkylquinolines 22
Very weak bases (pKa = +2 to -2)
Alkypyrroles (N-H) 10
Alkylindoles (N-H) 9
Cyclicamides (pyridones, quinolones) 3
Anil ides 2
Unclassified 7
Nonbasic (pKa < -2) corrected
for pyrroles and indoles 4
(a) pKa is the log of 1/Ka where Ka is the dissociation
constant of the compound.
-------
66
crudes is rapid at mild conditions, whereas, under conventional hydrogen
treatment procedures, extreme pressures and temperatures are required to
remove the nitrogen from residues.
Nitrogen, which has five-valence electrons, forms heterocyclic
compounds analogous to cyclohexane. Two valence electrons are involved in
the formation of covalent bonds to the adjacent carbon atoms in the ring;
one valence electron is involved in the bond to a hydrogen atom or an alkyl
or alkyl group, and two electrons (the "lone pair" electrons) are not
involved in bond formation. Like ammonia, which is saturated with respect
to hydrogen, but not to hydrogen ions, the organic nitrogen compounds can
thus form an ammonium ion by the addition of a proton. Saturated nitrogen
heterocyclic compounds (e.g., piperidine) show similar characteristics.
The most abundant nitrogen compounds fall into the following
(22)
two categories, basic or nonbasic (see Figures 6 and 7 for structures) ':
Basic Nonbasic
Methylamine Pyrroles
Pyridine Indoles
Quinoline Carbazoles
Piperidine Phenazines
Indole-quinoline Benzonitriles
Acridine Benzamides
The properties of these compounds are discussed with emphasis on
breakage of the C-N bond, the removal of nitrogen from the molecule or of
the nitrogen-containing molecule as a complex. Many individual nitrogen
compounds have been identified in fuels. Over 130 individual nitrogen-base
hydrocarbons have been identified in low-temperature bituminous coal tar,
but they are all derivatives of the compounds listed above. ' In the
following, the more important characterisitics of these compounds are covered
under each parent compound. The pKa values are also given for aqueous solutions
at 20 C. (pKa equals minus the logrithm of the equilibrium dissociation constant;
pKa = log[l/Ka].)
2.4.1 Pyrroles (B.P. 130 C)
Pyrrole has an aromatic structure, is a reative compound, and is
f (\ 7 f\ R ^
a weak base. ' The alkyl-substituted pyrroles have greater basic
-------
67
strength, and, in some cases, relatively stable salts with hydrochloric acid
have been obtained (e.g., 3-ethyl-2;4 dimethyl pyrrole has a pKa of 2.84). The
weakly basic properties of pyrrole are masked by the fact that it readily
polymerizes under the influence of mineral acid. Pyrrole has acidic
properties but is a weaker acid than phenol and reacts with potassium (but
not sodium) to liberate hydrogen to form a salt.
The nitrogen atom in pyrrole (unlike that in ammonia) has no "lone pair"
of electrons not involved in bond formation. Pyrrole can form a salt only at
the expense of its aromatic character, a fact that explains not only its
weakly basic nature, but also its tendency to resinify when treated with
strong acids. Because of the localization tendency of the ff-electrons,
reagents may attack pyrrole at different positions. The infrared absorption
spectra of pyrrole show two types of NH bonds.
2.4.2. Indole (B.P. 254 C)
Indole is a benzo derivative of pyrrole and has similar electronic
structure.* ' ' It can be obtained by heating pyrroles in the presence
of zinc salts. Like pyrrole, indole is an extremely weak base and a weak
acid. The resonance energy is 47 to 54 kcal/mole. As in pyrrole, the
carbon atoms acquire some negative charge (particularly at the 3 position).
Indole can be synthesized by the cyclization of two carbon chains in
o-aminophenyl compounds, and the amino derivative is prepared via the
corresponding o-nitro compound.
The substitution of halogen and nitro or nitroso groups on the
benzene ring of indole does not occur.
2.4.3. Carbazoles (B.P. 355 C)
Carbazole is similar to pyrrole^ ' , but has a greater
resonance energy (74 to 91 kcal/mole). The hydrogenated carbazoles become
more basic. Carbazole dissolves in sulfuric acid to give a colorless
solution. In oxidation reactions of tetrahydrocarbazole, an indole-
carboxylic acid is obtained, i.e., the saturated benzene ring is destroyed.
The oxidation (e.g., with sodium dichromate or silver oxide) of
carbazole forms dicarbazyls (two carbazoles linked at the nitrogen). Oxidation
-------
68
with potassium permanganate at 100 C is slowest compared with that for
(68)
bituminous coal, pyrene, and naphthacene.
The catalytic hydrogenation of pure carbazole over nickel does
not occur even at 260 C and 450 psi, whereas substituted carbazoles are
readily reduced. The outer ring is saturated with hydrogen and then cracks,
leaving an indole. The mechanism of hydrocracking is discussed in a
separate volume in a section on the kinetics of hydrodenitrification (HDN)
reactions. Contrasted with other nitrogen heterocycles such as acridine,
indole, and phenylpyrrole, carbazole is much more resistant to catalytic
hydrogenation, and the tendency for hydrogen addition decreases in that order.
2~.4.4. Benzonitriles (B.P. 190 C)
The removal of nitrogen from nitriles involves the breakage of
the C=N bond.^ ' The carbon-nitrogen triple bond is stronger than the
carbon-carbon triple bond (212 kcal vs 200 kcal) and is much more polar.
The nitriles (-CN) can be reduced to amines (-CN-NH-) under controlled
conditions with lithium-aluminum hydride. An aldehyde is formed from
nitriles with an imine lithium salt. Hydrolysis of nitriles yields amides.
2.4.5. Benzamide (B.P. 290 C)
The amide (-CONH2) group is reasonably polar and the lower-molecular
weight amides are high melting and water soluble.(69) Amides with N-H bonds
*
are weakly acidic but much more acidic than ammonia. Many cyclic amides
undergo the Hofmann degradation (treatment with alkali). The unsubstituted
amides are easily converted to carboxylic acids by treatment with nitrous
acid; however, the disubstituted amides do not react.
2.4.6. Phenazine (B.P. >360 C)
This heterocyclic system is analogous to anthracene. Phenazine is
a weak base (pKa 1.2), which is relatively resistant to electrophilic sub-
stitution. Nevertheless, it can be chlorinated and sulfonated provided the
conditions are sufficiently rigorous. Monosulfonation, for example, can be
-------
69
effected with oleum and mercuric sulfate at 160 to 170 C. The major product
is 2-phenazine sulfonic acid.
Oxidation with hydrogen peroxide gives phenazine-5,10-dioxide.
Reduction with lithium aluminum hydride gives 5-10-dihydrophenazine
which in turn can be oxidized to phenazine.
2.4.7. Acridine (B.P. 345-346 C)
Acridine and its derivatives are highly conjugated and chemically
/£Q\
stable aromatic compounds. Acridine is a base with about the same
strength as pyridine and aniline (pKa of 5.6). Its strength is lowered by
electron-attracting substituents. Amino groups in the 2 or 5 position
make acridine as basic as aliphatic amines. It remains unchanged after
heating to 280 C with concentrated HCl or KOH. Hydrogenation is possible
with Raney nickel to form acridan, but with sodium amalgum, a diacridyl is
formed and formation of polyacridines is also possible. The best method
of oxidation is to heat the acridine with sulfur in a sealed tube at 190 C
and treat the thioacridone with sodium hypochlorite. A certain amount of
addition occurs at the middle ring, e.g., halogen atom. Acridine hydro-
chlorite, nitrate, acid sulfate, dichromate, mercuric chloride, and picrate
can be prepared. The properties of substituted acridines do not differ from
those of acridine.
2.4.8. Amines
The physical properties of aliphatic and ring aromatic amines
that occur in fuels are given in Table 33. The properties of amines depend
on the degree of substitution on the nitrogen. Tertiary amines have no
N-H bonds. Hydrogen bonding is weaker in amines than in alcohol systems.
Amines can act as bases by accepting protons and the primary and secondary
amines can act like weak acids as well. Complexes are formed with trimethyl
boron, boron trichloride, and similar compounds.
Hydrogenolysis of pyridine is possible using hydrogen and a catalyst
at high temperatures or with hydriodic acid. Electrophilic reagents attack
pyridine with difficulty and are thus not attached in Friedel-Crafts reaction.
-------
70
TABLE 33. PHYSICAL PROPERTIES OF SOME AMINES FOUND IN FUELS
Amine
NH3
CH3NH2
cn3CE2m2
(CH3)3CNH2
(Cl^CH^NH
(CH3CH2)3N
(CH3CH2CH2CH2
OH
/~\
\_/
{3*H2
f^>NH2
^NCi^CI^NI^
00
<^rr~
Name
Ammonia
Methy lamine
Ethy lamine
t-butylamine
Die thy lamine
Triethylamine
,) N Tri-n-buty lamine
Piperidine
Pyridine
Cyc lohexy lamine
Aniline
Ethy lened iamine
Quinoline
^| Acridine
B.P.,
C
-33
-6.5
16.6
46
55.5
89.5
214
106
115
134
184.4
116
237.7
346
Water
M.P., Solubility
C g/100 ml
-77.7 90
-92.5 1156
-80.6
-67.5
-50 v. sol.
-115 1.5
si. sol.
-9
-42
si. sol.
-6.2 3.4
8.5 sol.
-19.5 6
108 v. si. s.
-------
71
In halogenation, substitution occurs on the ring. Peracids are able to
oxidize pyridine forming pyridine-N-oxide (-N-0) which can act as electron
attracting or electron-donating group. Mercuration of the pyridine-N-oxide
is possible.
Quinoline is stable and is used as a high boiling solvent. It is
oxidized by potassium permanganate to give pyridine dicarboxylic acid, i.e.,
the ring in the quinoline not containing nitrogen is destroyed. Hydrogenation
first saturates the nitrogen containing ring. Saturation of the nitrogen
containing ring has been determined as a fast step compared to the ring
cracking and ammonia evolution.
Acridine has a very stable ring system. The middle ring hydro-
genates readily. With sodium hypochlorite oxidation leads to acridone.
In general the ring amines are more stable with respect to ring
breakage and removal of nitrogen than aliphatic amines.
-------
72
2.5 Characteristics of Trace-Element
Contaminants in Coal/Coal Liquids
Volatile materials and fine participate matter emitted into the
atmosphere, or the disposal of such matter isolated in emission control
systems, during coal combustion are considered potential environmental
hazards. Major chemical constituents retained in fly ash, bottom ash, or
other coal combustion residues may constitute long-term disposal hazards,
particularly if they become soluble and enter groundwater or surface
waters. With the advent of new analytical techniques, significant gains
have been made in the knowledge relating to elements, other than C, H, S,
N, and 0, present in coal only in minor and trace amounts. Some of these
trace elements in coal are known to be toxic to plant and animal life at
relatively low concentrations and are potential pollutants. The concern
over trace elements in coal has gone beyond their potential for environmental
effects with development of large-scale coal-conversion operations. Certain
trace elements, which may not even be classified as toxic, shorten the life
of catalysts (catalyst poisons) used in liquefaction and gasification
processes which are important in coal-derived fuel manufacture.
Minor and trace elements in coal as well as in coal that has under-
gone chemical modification to become coal liquids have their origin in the
plant systems that made up the coal seams, the water and soils that isolated
and surrounded the seams, the groundwater that flowed through the seams, and
adjacent mineral beds during and after maturation of the coal. The final
state of these elements was influenced by the chemical reactions that took
place during maturation processes that converted the organic matter to the
various coal ranks (lignite to anthracite). The residues from syngenetic
processes of plants and the residues of microbial life left during transforma-
tion of plants to coal (which accounted for the part of the nitrogen and
sulfur impurities in coal) also contributed to the retention of trace
elements and the nature of their occurrence in the matured coals.
Identification of the minor elements and their quantitative deter-
mination in coal ash have been done for years. The composition of coal ash
has been the subject of reviews. ' ' Trace-element analyses of high-
temperature (450 to 500 C) ash from thousands of coals have been reported/72
-------
73
Such determinations provide a measure of the oxides of these elements that
are retained by the ash because of their refractory characteristics, low
volatility, or the chemical compounds formed during ashing. However, such
determinations did not account for the trace elements in the raw, whole
coal that are volatile at the high ashing temperatures. Recent advances
in low-temperature ashing procedures and in the analysis of whole coal by
neutron-activation analysis have been employed to overcome these short-
comings .
The utility of the low-temperature ashing technique as described
by Gluskoter,(77) O'Gorman and Walker,(78) and Ruch et al(79'80) lies in the
fact that coal and coal-like materials can be removed from a sample without
grossly altering the mineral-matter composition as it existed in the raw
coal. Analyses of such a low-temperature ash by X-ray diffraction and scanning
electron microscopy have enabled the identification of unaltered mineral
phases in coal and thereby the characterization of the occurrence of part of
the trace elements in coal. Such mineral phases in coal have been postulated
for many years and have been grouped into (a) epigenetic substances, or
those added during coal formation, and (b) syngenetic substances, or those
originating from the swamp biomass. Another system used more frequently by
workers in coal research for differentiating the noncombustible components
in coal is to characterize the mineral matter as either "inherent" or
(78 81)
"extrinsic, extraneous, or adventitious". ' Inherent mineral matter
usually is defined as that portion of mineral matter originally combined
with coal. It cannot be detected petrographically or separated by physical
methods. This form of "mineral matter" consists of elements assimilated by
growing plants, e.g., Si, Na, Mn, and Al or those essential to proper plant
(82)
growth which Sprunk and O'Donnel reported to be the elements Fe, P, S,
Ca, K, and Mg. Extrinsic or adventitious mineral matter is readily detected
petrographically and readily separated from coal. It may have originated
during coal formation (syngenetic) or after the coal had formed
(epigenetic).(78)
-------
74
Analysis of whole coal by means of neutron-activation analysis
(NAA) has provided the means by which trace and minor elements can be detected
and quantitatively determined as they exist in whole coal. It provides a
means of analysis for elements normally lost during high- and low-temperature
ashing and those difficult to determine by other techniques (e.g., Hg, Sb,
Se, As, Ga, Mn, Na).(79>80)
In coal utilization, exclusion of mineral matter in coal, including
the trace elements, is desirable. In combustion, gasification, liquefaction,
or carbonization processes, reduction of these materials to a minimum by
proper coal cleaning and beneficiation is also desirable and perhaps even
essential. Utilization of the wastes from cleaning operations and improving
the separation procedures both require thorough understanding of the char-
acteristics of minerals in coal and their role in coal and coal utilization.
Part of this knowledge already exists in the vast number of experiments docu-
mented in the literature. The existing knowledge can be summarized by saying
that mineral matter in coal is not uniformly distributed within a coal seam,
but occurs as extensive layers of grains and rock fragments and as localized,
thin, lenslike layers, grains, and rock fragments. Other noncombustible
material classed as mineral matter occurs such that it is almost an integral
part of the organic substance of coal itself. In this form, the elements
normally are not released until coal structure itself is altered or
(81)
destroyed.
In processes using coal, the ultimate behavior of the coal is
dependent to some extent on the amount and character of the noncombustible
material present at the time the coal enters the process. In coal combustion,
it influences the extent of boiler tube fouling and the fly-ash particle
size distribution. In coal-conversion processes, ash-forming minerals
have exhibited catalytic activity for gasification and liquefaction. There-
fore, knowledge of the amount and character of the mineral matter or noncom-
bustible portion of coal can provide a basis for intelligent selection of a
coal for utilization in a particular process. Control and/or removal of
trace elements is essential to limiting the pollution inherent to these trace
-------
75
elements in large-scale coal-utilization operations. Detailed character-
ization of these trace elements should provide a better understanding of the
development of control methods and the possible limits of existing control
methods.
2.5.1. Trace Elements Identified in Coal
Of 73 elements of the periodic table analyzed for in 13 raw (whole)
coal, 44 elements were found in all the coals, 12 elements were found in >75
percent of the coals, 8 elements were found in about 50 percent of the coals,
and 9 elements were sought but not detected in any of the coals. The concen-
(83)
trations ranged from 0.01 to 41,000 ppm. The results of spark-source
mass spectrometric analysis of 13 coals are summarized in Figures 8 and 9.
Figure 8 shows the frequency of occurrence in these 13 coals. Figure 9 shows
the ranges of the concentrations found in these same coals. This information,
(83)
in the periodic-table format, was taken from Sharkey, et al.
Black and Dams' ' using neutron-activation analyses on whole coal
reported on 43 elements in coal. Emission spectroscopy has been used
primarily on ash from coal samples to identify the 36 elements. Most work
on determination of trace elements in whole coal is fairly recent. The
accuracy of the analytical techniques, especially those newly developed, has
been open to question because of the lack of standards and lack of knowledge
of the range of concentrations for many trace elements in coal. Methods of
analysis of an NBS-EPA round-robin coal sample have been evaluated by various
laboratories. These programs were aimed at developing coal standards through
the means of the round-robin program. The 43 elements and their mean concen-
tration (in ppm) in the round-robin coal sample, determined by NAA at the
/pr\
Lewis Research Center of the NASA, are given in Table 34. ' Another set
of determinations by NAA, done at Battelle's Pacific Northwest Laboratories,
/OC\
are presented in Table 35 for comparison.v ' Only four of the participating
laboratories reported mercury, and in all but one, the values on the whole
coal were greater than those on the samples analyzed by destructive methods.
-------
76
H
NO
Li
100
No
100
K
100
Rb
100
c*
100
Fr
NO
6t
100
M«
100
Co
100
S'
too
Bo
100
Ro
NO
Sc
100
Y
100
LO
100
AC
NO
Ti
100
Zr
100
HI
46
Ct
100
Th
92
V
100
Nb
100
To
62
ft
100
Pfl
NO
Cr
100
Mo
100
W
69
N«
100
U
92
MA
100
Te
Nd
R*
0
Pm
NO
Fl
100
Mu
0
Oi
0
Sm
100
Co
100
Rk
0
Ir
0
E»
too
Ni
too
Pd
0
PI
0
Gd
65
Cu
100
Ag
92
Au
0
Tb
as
Zn
too
Cd
92
H«
38
oy
OS
B
100
At
100
Go
100
In
Stood-
ord
TI
31
Ho
77
C
NO
SI
100
G*
too
Sn
100
Pb
100
Er
77
N
NO
P
100
At
100
Sb
92
B!
31
Tm
0
0
NO
S
100
S*
too
T«
85
Po
NO
Yb
62
F
100
Cl
too
8f
100
I
85
At
ND
Lti
36
FIGURE 8. OCCURRENCE FREQUENCY OF ELEMENTS IN 13 RAW COALS AS
DETERMINED BY SPARK-SOURCE MASS SPECTROMETRY. ALL
QUANTITIES IN PERCENT. ND _=..NOT DETERMINED. 0 =
CHECKED BUT NOT DETECTED.(83)
H
NO
Li
4-163
No
100-
1000
K
300-
6,500
Rb
1-150
Cl
0.8-9
Fr
NO
B«
0.4-
3
Mo.
500-
3£00
Co
800-
MOO
Sr
17-
WOO
60
20-
l£00
Ro
NO
Sc
3-30
Y
3-25
10
0.3-
29
Ac
NO
Ti
200-
1,800
Zr
28-300
Hf
<0 3-
4
Cl
1-30
Th
<0.l-
5
V
2-77
Nb
5-41
To
<0.l-
8
Pr
1-8
Pa
NO
Cr
26-
400
Mo
1-5
W
<0.l-
0.4
Nd
4-36
U
<0.l-
1
Mn
5-240
Tc
ND
Ri
<0.2
Pm
ND
Fl
1400-
2,000
Rv
-------
77
TABLE 34. PRECISION ON NBS-EPA ROUND-ROBIN COAL SAMPLE
Element
Al
As
Au
Br
Ba
Ca
Ce
Cl
Co
Cr
Cs
Cu
Dy
Eu
Fe
Ga
Ge
Hf
Hg
I
In
Ir
K
La
Lu
Mg
Mn
Na
Nd
Rb
Sb
Se
Sm
Sn
Sr
Ta
Tb
Th
Ti
U
V
W
Yb
Mean,
ppm
15,700
5.9
0.146
20
337
4,070
17.340
750
5.48
19
2.55
14.1
0.85
0.312
7,517
5.4
70
0.92
0.95
2.78
0.04
2.48
3,500
11.3
0.416
980
38.0
370
6.4
19
6.4
3.8
1.3
125
93
0.360
0.03
3.1
1,312
0.980
36
1.9
0.55
± 1*»
ppm
1,550
0.5
0.048
3
42
560
0.089
75
0.15
0.8
0.06
0.9
0.06
0.037
119
0.8
5
0.05
0.09
0.38
0.01
0.27
360
3.3
0.017
250
2.6
33
1.5
1.9
1.6
0.51
0.19
20
9.2
0.028
0
0.2
150
0.078
4
0.8
0.04
Standard
Deviation, percent
9
9
33
15
12
14
2
10
3
4
2.3
6
7
12
2
14
7
6
10
14
25
11
10
30
4
26
7
9
24
10
24
13
15
16
10
8
0
8
12
8
11
40
8
(a) Analysis performed by NASA Lewis Research Center.
-------
78
TABLE 35. ELEMENTAL COMPOSITION OF(
NBS-EPA COAL STANDARDS
(PPM Except as Noted) <-a)
Element
Al (percent)
Ag
As
Au
Ba (percent)
Br
Cd
Cl (percent)
Co
Cr
Cs
Cu (percent)
Eu
Fe (percent)
Hf
Hg
K (percent)
La
Mg (percent)
Mn
Na (percent)
Ni
Rb
Sb
Sc
Se
Sm
Sr (percent)
Ta
Tb
Tb
Ti (percent)
D
V
Yb
Coal*
1.78 + 0.08
0.06 + 0.03
5.7 + 0.5
< 0.03
0.039 +. 0.002
17 i 2
< 2.1
0.08 +. 0.02
5.2 + 0.4
19 + 2
1.4 t 0.1
< 0.007
0.28 + 0.01
0.81 +. 0.07
0.97 + 0.10
0.28 + 0.01
(0.284~+ 0.008)
10.5 + 0.5
0.23 + 0.07
41+6
0.042 + 0.003
16+4
19 + 2
3.7 1 2.0
3.4 1 0.3
3.3 + 0.4
1.7 + 0.3
0.017 + 0.001
0.46 + 0.05
0.23 + 0.06
3.4 + 0.6
(3.45~+ 0.10)
0.11 i 0.02
(1.41 j; 0.07)
33+4
--
* Average and standard deviation of 6 determinations.
( ) - Number from Na I (Tl) multidimensional
y-ray spectrometry.
(a) Analysis performed by Battelle Pacific Northwest Laboratories.
-------
79
Extensive data on the amount of trace elements in coal and on their
mode of occurrence have been published by the staff at Illinois State Geolo-
(79 80}
gical Survey (ISGS). ' The authors reviewed work on coal trace-element
characterization and provided new information on the J:race elements in 101
coals, especially as it related to whole coal analysis. The study has shown
that when high-temperature ashing techniques are used in sample preparation,
part of the trace elements are volatilized. Some trace elements are lost
even with low-temperature ashing. In particular, the study showed that the
elements Hg, Br, F, and Sb are volatilized at 150 C (Hg ~ 90 percent, Br ~ 100
percent, Sb ~ 50 per cent, F presumed 100 percent), while Ga, Se, and As are
volatilized at 450 to 500 C. Molybdenum and vanadium are partially lost
during 450 to 500 C ashing. Therefore, only the most recent values from
whole-coal analysis or from the analyses of low-temperature plasma ash would
appear to be providing an accurate measure of all the trace elements reported
on in whole coal. The residues from low-temperature ashing also provide the
best form in which to identify mineral matter in coal.
The mean analytical values of elements for which determinations
were made in the 101 coals are given in Table 36 A statistical analysis of
the large amount of data generated from the analytical results for 101 whole-
(80)
coal samples provided some important general relationships. These are:
A near normal distribution of analytical values with
small standard deviations and ranges was found for
the elements Al, Fe, F, Ga, Br, B, Cr, Cu, K, Ni,
Si, Ti, Se, and V (always present).
Of the group of elements consisting of Cd, Zn, P,
As, Sb, Pb, Sn, Cl, Ge, and Hg, each exhibited a
highly skewed distribution with large standard
deviations and ranges (presence varies).
Positive correlation coefficients existed for Zn
and Cd, for the group As, Co, Cu, Ni, Pb, and Sb
(known chalcophiles), for the group Si, Al, Ti,
and K (known lithophiles), for Mn and Ca (known
carbonates), and for Na and Cl (brines).
-------
80
TABLE 36. MEAN ANALYTICAL VALUES FOR 101 COALS
(805
Constituent
Aa
B
Be
&Jw
Br
JJi
Cd
Co
Cr
Cu
F
Ga
Ge
Hg
Mn
Mo
Ni
P
Pb
Sb
Se
So
V
Zn
Zr
Al
Ca
Cl
Fe
K
Mg
Na
Si
Ti
ORS
PYS
SUS
TOS
SXRF
ADL
MOIS
VOL
FIXC
ASH
BTU/LB
C
H
N
0
HTA
LXA
Mean
14.02
102.21
1.61
15.42
2.52
9.57
13.75
15.16
60.94
3.12
6.59
0.20
49.40
7.54
21.07
71.10
34.78
1.26
2.08
4.79
32.71
272.29
72.46
1.29
0.77
0.14
1.92
0.16
0.05
0.05
2.49
0.07
1.41
1.76
0.10
3.27
2.91
7.70
9.05
39.70
48.82
11.44
12748.91
70.28
4.95
1.30
8.68
11.41
15.28
Unit
PPM
PPM
PPM
PPM
PPM
PPM
PPM
PPM
PPM
PPM
PPM
PPM
PPM
PPM
PPM
PPM
PPM
PPM
PPM
PPM
PPM
PPM
PPM
Percent
Percent
Percent
Percent
Percent
Percent
Percent
Percent
Percent
Percent
Percent
Percent
Percent
Percent
Percent
Percent
Percent
Percent
Percent
Percent
Percent
Percent
Percent
Percent
Percent
STD
17.70
54.65
0.82
5.92
7.60
7.26
7.26
8.12
20.99
1.06
6.71
0.20
40.15
5.96
12.35
72.81
43.69
1.32
1.10
6.15
12.03
694.23
57.76
0.45
0.55
0.14
0.79
0.06
0.04
0.04
0.80
0.02
0.65
0.86
0.19
1.35
1.24
3.47
5.05
4.27
4.95
2.89
465.50
3.87
0.31
0.22
2.44
2.95
4.04
MIN
0.50
5.00
0.20
4.00
0.10
1.00
4.00
5.00
25.00
1.10
1.00
0.02
6.00
1.00
3.00
5.00
4.00
0.20
0.45
1.00
11.00
6.00
8.00
0.43
0.05 .
0.01
0.34
0.02
0.01
0.00
0.58
0.02
0.31
0.06
0.01
0.42 '
0.54
1.40
0.01
18.90
34.60
2.20
11562.50
55.23
4.03
0.78
4.15
3.28
3.82
MAX
93.00
224.00
4.00
52.00
65.00
43.00
54.00
61.00
143.00
7.50
43.00
1.60
181.00
30.00
80.00
400.00
218.00
8.90
7.70
51.00
78.00
5350.00
133.00
3.04
2.67
0.54
4.32
0.43
0.25
0.20
6.09
0.15
3.09
3.78
1.06
6.47
5.40
16.70
20.70
52.70
65.40
25.80
14362.00
80.14
5.79
1.84
16.03
25.85
31.70
Note: Abbreviations other than standard chemical symbols: organic sulfur (ORS),
pyritic sulfur (PYS), sulfate sulfur (SUS), total sulfur (TOS), sulfur by
X-ray fluorescence (SXRF), air-dry loss (ADL), moisture (MOIS), volatile
matter (VOL), fixed carbon (FIXC), high-temperature ash (HTA), low-temper-
ature ash (LTA).
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81
Only the elements Cd, B, and Se were found to be
enriched in coal to values greater than the average
composition of the earth's crust. The elements F,
Mn, and P were found to be depleted to values below
the average composition of the earth's crust.
The last relationship, which reflects refinements in analytical procedures,
is considerably different from that presented by earlier workers whose
comparisons of values with those of the earth's crust were made from coal-
ash analyses (Reference 80 for example).
Extensive work has been reported on the variation of trace elements
in columns of coal taken from the full height of the seams throughout the
United States. To compile such information and present a generalized char-
acterization of all coals would be difficult. However, some of the general-
izations made on the occurrence of the trace elements in large numbers of
coal seams provides additional bases for understanding the nature of their
occurrence in coal. A typically thorough study is the work done on the
distribution of 35 elements in West Virginia coals.^ ' A summary on the
mechanism of retention and the occurrence of trace elements is given in
Table 37. (Secondary mineralization implies chemical changes that occurred
after the organic mass of the coal bed was in place.)
The analysis of coal fractions separated by specific gravity
differences (i.e., washed coals or float-sink fractions separated by means
of specific gravity differences) provides information on the distribution of
trace elements in coal more relevant to establishing their occurrence and
to their potential for removal from coal. A correlation of the trace-element
(79 80}
concentrations in such fractions has been reported. ' ' From the analyses
of 8 fractions from 4 coals, the trace elements were classified into four
groups as follow:
1. The elements in the first group, Ge, Be, and B, have the
greatest affinity for the organic phase and tend to be
concentrated in the coal fractions isolated in the lower
specific-gravity range (1.28 to 1.31), i.e., the clean
coal fractions.
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82
TABLE 37. DISTRIBUTION OF TRACE ELEMENTS IN COAL SEAMS
AND PROBABLE MODE OF MINERALIZATION(81)
Element
Distribution or Mode of Mineralization
As Distribution in coal seam suggests that arsenic is not
concentrated by secondary mineralization.
B Distribution in coal seam suggests secondary mineraliza-
tion process for its presence; trend is reverse of
germanuim and antimony concentration.
Be Present in low- and high-ash coals, indicating origin from
secondary mineralization processes; highest values at
top and bottom of seams.
Bi No evidence for secondary mineralization; associated with
high-ash coals.
Co Secondary mineralization may or may not be the cause of
high-cobalt regions.
Cr No evidence for secondary mineralization; uniformly
distributed between coals and shales near bottom of seam.
Cu Distributions are uniform; in low-ash coals, random
higher values are due to secondary mineralization.
Ga High values appear in low-ash coals, usually in top and
bottom of coal seam.
Ge Appears to be in the organic matter rather than associated
with mineral matter; absorbed by the coal from water
carrying germanuim salts in solution and most concentrated
in top and bottom of seam.
Hg No evidence for secondary mineralization.
Mn Wide range of distribution due to secondary mineralization.
Mo Random distribution due to secondary mineralization.
Ni Variable distribution in coal seam suggesting some
secondary mineralization.
P High phosphorous values occur in regular intervals and
independent of ash content. (Exclusion of such intervals
during mining would produce low-phosphorus coal for
metallurgical purposes.)
Pb Distribution varies with region and suggests secondary
mineralization.
Sb Similar to Ge; highest concentration at top and bottom of
seam.
Sn Most high values are-in coals with low ash < 3 percent;
high tin associated with low inherent ash; secondary
mineralization suggested by distribution in coal seams.
V Distribution random but quite uniform; shales have the
same concentrations as coal ashes.
Zn Shale and ash have similar values and the maximum is just
slightly greater than median concentation, suggesting that
no secondary mineralization occurs.
Zr Has uniform symetrical distribution in coal seam.
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83
2. The elements in the second group are those with the
least organic affinity and are found concentrated in
the mineral matter in coal. The elements in this
group are Hg, Zr, Zn, Cd, As, Pb, Mn, and Mo.
3. The elements in the third group, P, Ga, Ti, Sb, and V,
are assumed to be associated with both organic and
inorganic materials in coal but are more closely tied
to the elements with the highest organic affinity,
i.e., Ge, Be, and B.
4. The elements in the fourth group, Co, Ni, Cr, Se,
and Cu, were also found to be associated with organic
and inorganic materials in coal. However, they are
more closely tied to the elements known to be inorgan-
ically related, i.e., Group 2 above.
These correlations are summarized in Table 38.
Development of correlations of the occurrence of trace metals with
the organic phase of coals as determined in five different density fractions
(87)
has been a subject of a review by Zubovic.^ ' The results of such a corre-
lation in which the distribution of the elements with organic and inorganic
matter were ranked are given in Table 39. There is general agreement between
trends reported in the table and those summarized in more recent work (Table
40^(80,88) Similar studies on lignites have shown that Na, Ca, and Mg,
although minor elements rather than trace elements, report to the float
fraction (sp gr < 1.59), while Fe, S, Si, Al, and Cu report to the sink
fraction/89^ The distribution of these metals in fractions with other
specific gravities was not reported in this study.
2.5.2. Trace Elements Associated With
Mineral Matter in Coal
The meaning of the term mineral matter in coal has generally been
accepted to include all inorganic, noncoal material present in coal as
mineral phases and all elements in coal that are considered inorganic (i.e. ,
-------
TABLE 38i. CORRELATION OF TRACE ELEMENT DISTRIBUTION IN WASHED COAL FRACTIONS
Clean Coal
Organic Matrix
Coals Only « »
Mineral Matter
Decrease in Organic Content ^ Inorganic Matrix
r" '" -^
Clays and Coal Combination « « Partly as Sulfides « » Sulfides and Carbonates
P0>) Co Hg
Ga ~v Ni Zn
Ti'' ; Cr . Zr
V Se^ ' ,, ,. Cd (Sulfides)
Sb Cu(b> As
Pb
Mo
Mn (Carbonates)
Fractions from Wash Media of Specific Gravity
< 1.29 1.31 1.40 1-60 2.89 > 2.9
(a) Mostly in organic phase but also present in heavier inorganic fractions.
(b) Mostly in inorganic phase but also present in organic.
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85
TABLE 39. AVERAGE ORGANIC AFFINITY OF SOME METALS
DETERMINED BY FLOAT-SINK METHODS(87)
Element
Percent Organic
Association(21)
Germanium
Beryllium
Gallium
Titanium
Boron
Vanadium
Nickel
Chromium
Cobalt
Yttrium
Molybdenum
Copper
Tin
Lanthanum
Zinc
87
82
79
78
77
76
59
55
53
53
40
34
27
3
0
100
75-100
75-100
75-100
75-100
100
0-75
0-100
25-50
N.D/a>
50-75
25-50
0
N.D.
50
(a) N.D. - not determined.
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86
TABLE 40. AFFINITY OF ELEMENTS FOR PURE COAL AND MINERAL
MATTER AS DETERMINED FROM FLOAT-SINK DATA(88)
Davis
Coal
DeKoven
Coal
Colchester
(No. 2)
Coal
Herrin
(No. 6)
Coal
Clean coal - lightest specific
gravity fraction (elements
in "organic combination")
A
V
Mineral matter - specific
gravity greater than 1.60
(elements in "inorganic
combination")
B
Ge
Be
Ti
Ga
P
V
Cr
Sb
Se
Co
Cu
Ni
Mn
Zr
Mo
Cd
Hg
Pb
Zn
As
Ge
Ga
Be
Ti
Sb
Co
P
Ni
Cu
Se
Cr
Mn
Zn
Zr
V
Mo
Pb
Hg
As
Ge
B
P
Be
Sb
Ti
Co
Se
Ga
V
Ni
Pb
Cu
Hg
Zr
Cr
Mn
As
Mo
Cd
Zn
Ge
B
Be
Sb
V
Mo
Ga
P
Se
Ni
Cr
Co
Cu
Ti
Zr
Pb
Mn
As
Cd
Zn
Hg
-------
87
other than C, H, N, 0, S). Of course, carbon is also found as carbonates;
hydrogen as water of hydration or crystallization; oxygen as oxides, sulfates,
and silicates in addition to those above; and sulfur as sulfides or as
i ,. .. (78-80)
sulfate.
Analysis of a very large number of coals for their mineral-matter
content has given a range of 9.05 to 32.26 percent mineral matter in coal
with 15 percent being a reasonable estimate of the average value for coals
in North America.
The total mineral matter contained in whole coal has, until recently,
been a value estimated from the coal-ash analysis and various formulas.(70>77»78)
More recently, with development of low-temperature ashing techniques, precise
mineral-content determinations for coal have been made. ^ This has
permitted calculation of mineral-to-ash ratios for a large number of coals.
The average ratio is about 1.10, with a range of values from 0.97 to 1.32.
About 80 percent of the ratios fall between 1.02 and 1.17 for the coals
studied. ' Ratios less than unity are possible if the mineral matter
gained weight during ashing, e.g., oxide going to carbonate or sulfide to
sulfate. The assumption made in the development of this ratio was that the
values obtained after low-temperature ashing were identical with the mineral
matter in coal. Except for a few elements that volatilize during low-
temperature ashing, this is about as close as researchers have been able to
come to an absolute mineral-matter determination.
The importance of the characterization of mineral matter in coal
and its constituents is to provide a more thorough knowledge of their concen-
trations, distribution in coals, their volatility, and their potential effects
on the environment during combustion or coal conversion. Their role in the
conversion of coal to gases, liquids, and clean fuels has become increasingly
important and greater knowledge of their characteristics should aid in
solving the problems of their removal and disposal.
A recent review on the subject of mineral matter and trace elements
(88)
in coal categorized the major minerals in coal into four groups.
1. Aluminosilicates - Clav Minerals. Most commonly
occurring minerals are illite [K^Sig-Alp (OH^Al^],
kaolinite [SiOOlO], and an illite-montmorillonite
-------
88
mixture. Their amount in coal varies but a mean
value of 52 percent of the mineral matter in coal
has been reported for Illinois coals. ' Other
investigations have obtained similar results for
other U.S. coals.^78)
2. Sulfides and Sulfates. Pyrite and its dimorph, marc-
asite, are the major sulfides (FeS_). Other sulfides
identified are sphalerite (ZnS) and galena (PbS).
Sulfates are not common and often are not present in
fresh unweathered coal. The salts are the various
hydrates of ferrous sulfate and ferric-ferrous sulfate
mixtures. In Illinois coals, the sulfides and sulfates
make up about 25 percent of the mineral-matter content.
In low-sulfur coals, the contribution of the sulfide
minerals to the total mineral matter is much less since
only a small amount of the total sulfur present is due
to pyritic sulfur.
3. Carbonates. Carbonate minerals, because of the potential
for solid-solution formation of calcium, magnesium,
iron, and manganese, vary in composition. Pure calcite
(CaC03) and siderite (FeCOg) have been reported. The
most frequent minerals are dolomite (CaCO-«MgCO_) and
J J
ankerite (2CaCO,-MgCO,»FeCO,). Carbonate minerals make
(90)
up 9 percent of Illinois coals. The mineral phase
varies with regions.
4. Silica (Quartz). Illinois coals average about 15 percent
silica. Values of 1 to 20 percent have been found in
other U.S. coals.(78)
In addition to the minerals cited above, apatite has been definitely isolated
and identified [Ca5(P04)3(FC03>].
-------
89
Older categorizations covered in reviews are not appreciably
different (see Table 41>.<'°> Analyses of coals from numerous worldwide
regions have identified minerals from the identical groups. Studies on
lignite residues in which low-temperature ashing was employed have indicated
that nitrates of sodium and the alkaline earth were present. (78'91) (There
is some question as to whether or not the nitrate may have been formed from
_ nitrogen gas dissociates during low^temPeMture_asjiing .in^t
.^^
highly energetic radio frequency plasma.) Other studies with lignites from
the northern great plains coal provinces have shown that the minerals nacrite
[Al2Si205(OH)4] and barite (8aS04> are also present in coals. (89) It is the
general conclusion that the major types of mineral matter present in coal are
kaolinite, illite-montmorillinite, and quartz. (70»78'88) For high-sulfur
coals, pyrites are included in the list.^88^
As in all mineral systems, the substitution in the mineral lattice
of one element for another occurs frequently and is not unexpected. This is
especially true when metals with the same oxidation state (ionic charge) or
similar size (ionic radii) are involved. Therefore, positive correlations
of various trace elements with the host mineral elements is not unexpected.
Such a correlation was developed for the minerals identified in a recent
study. (79»8°) The results are given in Table 42, which shows the mineral
phase and the principal elements of which it is composed. Opposite each
mineral listed in Table 42 are the elements found to have a positive corre-
lation with this mineral phase. Those elements in parentheses in the right-
hand column were not detected as such in the mineral.
Physical Characteristics of Mineral Matter in Coal. O1 Gorman and
Walker in their studies on the amounts of major minerals present in four
coals of different rank found wide differences in mineral-matter composition.
Physical characterization of the products from low-temperature ashing were
performed and this included surface area measurements by low-temperature
absorption techniques and true density measurements. The surface area varied
-------
90
TABLE 41. MINERALS ASSOCIATED WITH
BRITISH BITUMINOUS COALS
Group Species
Shales Muscovite Bravasite
Hydromuscovite Montmorillonite
Illite
Kaolins Kaolinite Metahalloysite
Livesite
Sulfides Pyrite Marcasite
Carbonates Ankerite Ankeritic dolomite
Ankeritic calcite Ankeritic chalybite
Chlorides Sylvine Halite
Accessory Quartz Prochlorite
Minerals Feldspar Diaspore
Garnet Lepidocrocite
Hornblende Magnetite
Gypsum Kyanite
Apatite Staurolite
Zicron Topaz
Epidote Tourmaline
Biotite Hermatite
Augite Penninite
-------
91
TABLE 42. TRACE ELEMENTCOAL MINERAL SPECIES CORRELATIONS
(80)
Mineral Group, Element With Positive^8)
Principal Elements - Correlation With Mineral
Sphalerite, ZnS zn, Cd, (Hg, B)
Galena, PbS pb (Hg)
Apatite, Ca5(P04)3(F,C03) Ca, P, F
Pyrite, FeS2 Ni, Cu (As, Be, Sb)
Kaolinite, aluminosilicate si, Al, Ti, K, (B, Cu, F, Hg, Sn, V)
Quartz, SiO (B, Cr, Mn, Cd, Mo, Se, V, Zn)
Calcite, CaC03 Mn (B, Cd, Mo, Se, V)
(a) Elements in parentheses in this column have not been detected in
specific mineral phases; however, a positive correlation existed.
-------
92
2 3
from 5.1 to 14.3 m /g and the densities varied from 2.79 to 3.39 g/cm .
The densities agreed closely with those calculated from the mineral-matter
compositions and known true densities of individual minerals. (Both of
these physical characteristics will affect the ease of their separation from
coal when physical methods are used.)
Handbook values of the specific gravities of the mineral phases
identified by Ruch, et al' ' are given below:
Mineral Specific Gravity Range
Sphalerite 3.90 - 4.11
Galena 7.3 - 7.6
Apatite 3.15 - 3.27
Pyrite 4.95 - 5.17
Kaolinite 2.60 - 2.63
Quartz 2.59 - 2.66
Calcite 2.71
Dolomite (Ankerite) 2.80 - 2.99
Siderite 3.0 - 3.88
The characteristic property of most clay and shale associated with
coal is disintegration in water to smaller particle sizes. Such behavior
affects washery-water clarification, dewatering, and drying of the fine
sizes of coal, contamination and increased viscosity of dense-medium
suspensions, filtration of froth-flotation-cleaned coal, and the refuse
and the handling and disposal of fine refuse. Clay and shale swell in
particle size to such an extent that the specific gravity is decreased
from 2.1 for dry material to less than 1.60. When this happens, shale
and clay may be discharged along with the washed coal. '
2.5.3. Trace Metals Associated With
Organic Matter in Coal
The behavior of the elements Ge, Be, B, and sometimes Ti and U
during coal cleaning or coal-conversion processes and the differences in
the distribution of these trace elements in specific-gravity fractions of
-------
93
younger (lignites and brown coals) and older coals suggest that the nature
of their occurrence in coal is tied more closely to the organic matter in
coal and less with the mineral matter.
Germanium in Coal. Early reports on the distribution of germanium
in coal have shown that bituminous coal fractions with a specific gravity of
<1.31 contained most of the germanium. ' In lignites, germanium could be
found only in association with the mineral matter, even though both uranium
and arsenic were found only in the organic matter. ^94' (In this case the
arsenic was assumed to have originated from the oxidation of arsenopyrite
during aging and was captured by the organic matter as oxidized arsenic
compounds.) Other lignites are reported to contain germanium, which during
low-temperature charring exhibits little or no loss of the element during
the process (as contrasted to the losses during combustion and concentra-
(95)
tion in the fly ash). Germanium also could not be detected in coal
washing refuse indicating low levels in mineral matter. Typically, higher
germanium concentrations are found in low-ash coals, and the regions of
maximum accumulation were in the vicinity of zinc and lead ore deposits. '
Germanium is usually concentrated near the top and bottom of coal seams.
These regions also have high concentrations of Be, Ca, Cr, and Ni. The same
research group noted that the vitrinites (wood portion) contained absorbed
water-soluble germanium and acid-soluble germanium combined with iron hydroxides
and sulfides, and suggested that a considerable part of the germanium in
coal was found in free inorganic matter, chiefly in the form of pyrites
(Ge"1"*" + Fe"1"1" have similar ionic radii). In contrast, workers in Russia
have shown that germanium is bound in coal by functional groups in the coal
structure and is partially in a relatively mobile form. (98) The mobile
portion was extracted from known coals and lignites with complexing reagents
such as pyrocatechol and tartaric acid (removed < 35 percent of germanium
present). This suggested that germanium was bound to the coal functional
groups by ionic and coordination bonds. The more tightly bound germanium can
be solubilized only by decomposition of the coal structure binding it.
-------
94
The forms of binding of germanium in solid fuels have been the
subject of a recent study which demonstrated, by selective reactivity with
reagents, that three types of binding hold germanium in coal and that their
(99)
proportions are related to the coal types being investigated.v ' Complex
humate salts of germanium form 0-Ge-O bonds which are readily hydrolyzed by
strong acids such as hydrochloric acid. The germanium-organic compounds
which have a Ge-C bond are resistant to acid treatment and require oxidation
at 300 C before the acid treatment is effective in the removal of the
germanium. The germanium untouched by either of these processes is that
present as silica-germanates or a solid solution of Ge02 in Si02- The
proportion of these types of germanium compounds in solid fuels is given in
Table 43.(99)
Titanium in Coal. Titanium is found in all coal seams, in concen-
trations varying from about 0.3 to 0.15 percent Ti02 in coal ash. The concen-
tration does not appear to be related to rank of the coal nor geographic
location. The primary distinction of titanium in coal is its wide variability
(97)
even though some removal can be accomplished by gravity separation.
Uranium in Coal. There are sizable amounts of uranium in the low-
rank coals of the western United States, and in certain locations its concen-
tration approaches or exceeds ore-grade specifications for uranium. Lignites
contain the highest concentrations. The fact that coals with the highest
uranium levels do not show individual minerals of uranium (autunite, carno-
tite, etc.) suggest that it is held in the coal as an organo-uranium complex
which is soluble (decomposes) at pH less than 2.18. Recovery from coal,
however, usually is done after combustion, using acid leaching of the ash
(lignite ash is alkaline in character due to the sodium and calcium
(97)
associated with it).
Chemistry of Metals Associated with Organic Matter. The affinity
of some metals for the organic phase, determined on float-sink fractions,
(87)
was summarized by Zubovic and was presented earlier in Table 39. To
explain these trends, Zubovic postulated that these metals are present in
the most stable complex possible, i.e., as chelated metal-organic com-
plexes forming 5- and 6-member rings with the metal. Metal ions with a
-------
95
TABLE 43. FORMS OF BINDING OF GERMANIUM IN SOLID FUELS
Bound Germanium in Percent of Initial Sample
In the Form In the Form of As Silicoger-
Type of of Complex Germanium- manates or Solid
Solid Fuel Humates Organic Compounds Solutions
Peat 21 16 63
Brown coal (lignite) 58 15 27
Brown coal (lignite) 90 none 10
High-volatile bitumi- 18 none 82
nous coal
-------
96
high ratio of ionic charge to ion radius would be the preferred species
undergoing complex formation. The stability of chelated complexes of bivalent
metal ions prepared in the laboratory is on the order of Be>Cu>Ni>Co>Zn>Fe.
For tervalent ions, the stability trend is Ga>Y>La. Strikingly, this is the
same order of affinity (except for copper) for organics given in Table 39.
Zubovic postulated, on the basis of this observed organic affinity and the
stability of the complexes of these metals, that portions of the Ga, Y, La,
Be, Ni, Co, and Zn bonded to organic matter in coal are held as chelated
complexes. In the light of more recent data, even the metals Ge, B, Ti, and
V, for which adequate experimental data could not be found by Zubovic to
support the existence of complex formation, can now be included in the list.
The relationships developed in this work are summarized in Figure 10, In
Figure 10, the plot of the percentage of metal associated with organic
material versus the order of decreasing affinity produces three sets of trend
lines. A similar pattern, shown in Figure 10, is obtained when the affinity
is plotted against the ratio of the ion charge to ion radii (ionic potential).
Ligand Effect. The nature of the donor atom in the organic molecule
or ligand making the complex (0, N or S) plays an important role in stability
of the complexes formed with metals. More stable complexes are formed when
the metal bonds to preferred atoms. For example, complexes of Ga, Ge, Ti, Sn,
V(IV), V(V), and Co all prefer oxygen to nitrogen. Complexes of Cu(Il),
Cu(I), V(III), and Ni(II) ions prefer nitrogen to oxygen. Ge, Cr, Fe, and
Be form complexes of equal stability with either oxygen- or nitrogen-containing
organic molecules.
(Q~J\
Such considerations suggested to Zubovic that complex-forming
ligands present in decomposing plant remains which could form metal chelates
could include chlorophyl (porphyrin), amino acids, and lignin derivatives.
He postulated that V(III), Ni, Cu, and Fe would be chelated by the nitrogen
donor atoms in porphyrin and the amino acids systems. The oxygen in lignin
derivatives would form complexes with Be, Ge, Ga, Ti, Ca, Al, and Si.
In the former set, preservation of amino acids in carbonaceous
materials could be related to very stable complex formations through chelation
or ring formation with the metal atoms. The vanadium or nickel porphyrin
complexes in petroleum have been well characterized (see section on trace
-------
9T
Ge Be Go Ti B V Ni Cr Co Y Mo Cu Sn La I \
Decreasing Affinity for theOrganic Matter of Coal
10
o
-------
98
metals in petroleum) and the stability of these nitrogen chelate complexes
explains their survival throughout maturation processes forming the fossil
fuel.
The oxygen in lignin derivatives such as those formed by depoly-
merization and degradation form complexes usually through carboxylic acid
or phenolic functional groups. Some proposed systems are:
coniferal alcohol sinapyl alcohol g-isopropyltropolone catechol
More likely, partially depolymerized lignin can also provide sufficient
functionality to form complexes of unusual stability and low solubility.
Compounding these trends in the affinity of certain metals for
the organic constituents in coal are the secondary mineralization processes
going on during maturation,, For example, low levels of copper found in
organic matter, despite the demonstrated stability of copper complexes
prepared in the laboratory, can readily be attributed to the formation of
the even more stable copper sulfide formed from sulfides generated under
the reducing conditions present during coal formation,
2.5.4. Characteristics of Nonmetallic
Trace Elements in Coal
In the previous sections, the major emphasis of contaminant char-
acterization has been on the trace metals associated with coal. Of those
trace nonmetallic elements important to this study, only As, Se, P, and F
have been discussed and related to their possible occurrence in coal or the
mineral matter in coal through correlation analysis. The elements P, F,
Cl, Se, Te, and Br, however, have not been discussed in detail. A summary
of the literature on the characteristics of the occurrence of these elements
in coal is presented in the following discussions.
-------
99
Phosphorus and Fluorine in Coal. Phosphorus in coal has been
recognized as the source of phosphate-bonded deposits in superheater and
reheater sections of boilers. (100) The origin of phosphorus is principally
the mineral fluorapatite [Ca F (PO ) ] which readily loses HF when heated
(101 102} to
in moist air. ' It also accounts for a major portion of fluorine in
coal. Under reducing conditions and at temperatures >1590 C, elemental
phosphorus is evolved which under boiler coalitions is oxidized to pyro-
phosphoric acid, H^Oy. Reaction with fly-ash minerals produces crystalline
phosphate deposits.
(79)
Ruch, et al. ' have isolated, photographed, and identified calcium
phosphate minerals in the low-temperature ash of coals from Colorado and
Illinois. Those coals, with high levels of fluorine as well as phosphorus,
are considered to have the fluorapatite mineral present as well as the apatite
(fluorine free) mineral. Data from analytical determinations on washed coal
fractions placed phosphorus in the group of trace elements which are appar-
ently associated both organically and inorganically in coals but are more
closely allied to the elements with the higher organic affinity (along with
Ga, Ti, Sb, and V). Ruch, et al^7 , Abernathy and Gibson(103', and other
researchers^ ' could not show a strong correlation between phosphorus and
fluorine in coals, but it is generally observed that coals with high phos-
phorus levels had high fluorine levels as well. The ratio of phosphorus to
fluorine usually exceeded the weight ratio of 1.5 that would be expected for
the pure fluorapatite compound, Ca1()F2(P04)6. The reason suggested was that
the phosphorus may be present as the hydroxyapatite mineral or some other
phosphate minerals such as A1P04« (104) The phosphate in coal is believed to
be of plant origin. Mineralization yielding fluorapatite was in all proba-
bility due to fluoride diffusion from the surrounding shale coverings of the
(102)
coal seam (shales are generally higher in fluorine than coal). The
apatite mineral is given the general formula (R04)g X2 M^, where the R is
usually phosphorus but occasionally may be arsenic or vanadium. The X is
usually OH or fluorine but might be chlorine or C03= ion. The M usually
is calcium but may be manganese or cerium. Therefore, these trace elements
may be associated with this mineral phase as well.
-------
100
Coal washing was effective in reducing phosphorus in coal by 67
percent while simultaneously reducing the ash content 47 to 63 percent. ^ 5'
However, the process was successful for only two of the seven coal beds tried
For the other five coals examined, the phosphorus was associated with the
"clean" coal rather than the impurities, which strongly suggests that some
of the phosphorus is inherent and may be bound to the organic portion of coal.
Compounds of this type have not been characterized. Similar conclusions were
obtained from studies on the phosphorus content of various specific-gravity
fractions separated from coals ' and from a study on the action of sulfuric
acid on phosphorus in coal. No organo-f luorine compounds are considered
to be present in coal, but minerals such as fluorite (CaF-), although not
identified as such, may contribute to the overall fluorine content of some
coals.
Chlorine in Coal. There has been a continuous concern about the
presence of chlorine (primarily as chloride ion) in coal because of inherent
corrosion-related problems in steam-generation facilities associated with
the element. A value for chlorine in coal from 0.15 to less than 0.40 percent
is generally acceptable and should provide trouble-free operation. The
chlorine content^ along with the ash and sulfur contents of coals, plays an
interacting role in boiler-component corrosion.
Occurrence . The manner of the occurrence of chlorine in coal has
been a subject of several investigations in the United States and Europe.
Two schools of thought on the subject have been cited:
The manner of the occurrence of chlorine in coal has been a subject
of several investigations in the United States and Europe. Two schools of
thought on the subject have been cited . '
(1) One school postulates that the chlorine is present
almost entirely as inorganic chlorides such as the
salts of sodium, potassium, and calcium, and in some
instances as magnesium and iron chloride. (108-111)
(2) The second school postulates that the chlorine occurs
C\ 1 2-
partially in combination with the organic matter in coal.
The second school bases its argument on the fact that not all the chlorine
can be removed with water and that chlorine can be driven off as HC1 by
-------
101
heating coal in air at 200 C. The resistance to removal by water and the
imbalance between soluble alkali and soluble chloride suggested that the
chloride ion is attached to the coal through an ion-exchange-type association.
It was also postulated that loss of chlorine below the temperature of
vaporization and decomposition of inorganic chlorides could occur through
organic intermediates.
Gluskoter and Rees^ 07) have shown experimentally that the
volatilization of chlorine from NaCl could be promoted by the presence of
iron pyrite (FeS2) both in undried and dried air at temperatures below 500 C.
Heating NaCl with carbon (lampblack), with clays, or alone did not produce
a volatile chloride under the same conditions. Addition of NaCl to raw coal
gave stronger tests for chlorine evolution than when coal was heated alone
in an air stream. Strong tests were also obtained when iron pyrites and salt
were heated together in air. The authors proposed that the volatilization
occurred through sulfur-compound intermediates such as S09 and S0_ and that
there was no evidence for organically combined chlorine.
In the same study, it was found that the amount of water-soluble
chlorine could not be made to equal the total chlorine contained in the coal,
even with further grinding and prolonged leaching with fresh water (7 days).
The reasoning given to explain this behavior was that the chloride salts
were present in the very small pores in coal (most frequent size pores were
near 40 angstroms in diameter), and grinding even to 5-micron particle size,
although enhancing the amount of salt dissolved in water, could not produce
total access to water. It was also substantiated that the established
correlation used in coal analysis of relating total alkali metal to the
chlorine found in coal could be used as a valid approximation. If all of
the chlorine in coal were present as chlorides of sodium and potassium, the
mole ratio of Na + K to Cl would be one. Ratios of 1.527 to 0.787 were
found for various coals. A ratio greater than unity would mean an excess
of Na and K was present. A ratio less than unity would mean a deficiency of
Na and K. To explain these observations, it was suggested that other
cations were associated with chlorine. The presence of Na and K ions in
silicates accounts for the ratios greater than unity. The distribution
-------
102
ratio in the water-soluble portion of chlorides did not always agree with
that found in the coal, as shown in Table 44.
TABLE 44. RATIO OF Na + K TO Cl IN COAL AND
SOLUBILIZED CHLORIDE SALTS '(107)
Illinois Coal
Illinois Coal
Illinois Coal
1
2
3
Ratio of
Total
Chlorine
1.5268
0.9302
0.7866
Na + K to Cl
Water-Soluble
Chlorine
0.8541
0.1476
0.5959
The ratios less than unity were claimed to be due to the presence of metal
ions other than sodium or potassium. The presence of metal ions in salts
such as Mg(OH)Cl and Ca(OH)Cl and minerals such as chlorapatite [Cair.(PO.) ,ClJ
CllSI 462
has been suggested, in addition to MgCl- and CaCl-. ' Organic chlorine
hydrolyzable in hot water, acid, or alkali was also postulated as a source of
chloride ion. Experimental programs to prove or disprove the presence of
organic chlorine in coal have been inconclusive.
A direct correlation (0.93 correlation coefficient) of the chlorine
in coal versus the chlorine in groundwater has been calculated for coals of
the Illinois basin.* ' This fact supported the hypothesis that the chlorine
content of the coals is controlled by the composition of the groundwater in
contact with the coal. A good correlation has been demonstrated between the
increase in saline content of groundwater with depth and the chlorine in
coals. This concept has been used to explain the trends in chlorine content
of European coal beds at various depths above salt beds. There is another
opinion that relates the salt content of coal to the extent that inorganic
chlorides were absorbed by the plants that produced the coal prior to coal
formation. The existence of chlorinated organic compounds in coal has been
all but ruled out.
-------
103
Removal £f_CttLorine from_C£a.L. Washing of coal has been suggested
as a method for the removal of chlorine from coals. It has been shown on a
laboratory scale and also in field trials that only a small but variable
percentage of chlorine can be readily extracted with water.^107^ in a coal-
washing segment of a preparation plant, fresh water with a dissolved solids
content of 0.03 percent by weight was used for a period of 2 weeks. After
48 hours, the dissolved-solids level reached 0.23 percent and remained at
this equilibrium level. During the operation, the chlorine in the washed
coal was unaltered and identical to that in the unwashed coal. The extent of
chlorine removal by washing varied for different coals. A final freshwater
flushing of the washed coal reduced the chlorine content slightly, and this
certainly is applicable only in those cases where the dissolved salts in the
water are at low levels. Therefore, use of water recycled from settling
ponds would not be effective since the dissolved salt levels would be high.
It has been suggested that the practice of adding CaCl2 or NaCl to prevent
freezing during transportation could shift a marginal chloride level in
coal to levels that may cause corrosion problems.
The experiments cited by Gluskoter and Rees did suggest that during
pyrolysis or gasification (air), the chlorine content in the coal might be
reduced through the formation of volatile chloride compounds in the presence
of sulfur oxides. The characteristics of these volatile chloride compounds
were not described.
In a study cited by Rear, et al, ^ the use of tetralin (a known
hydrogen-transfer agent for coal liquefaction) produced an appreciable amount
of HC1 during the extraction of a high-chlorine British coal. The conclusion
was that hydrogenation of chlorides that normally are insoluble had occurred.
It did not necessarily mean that an organic chloride had been decomposed.
However, regardless of the source of chlorine, the corrosive effects of HCl
formed during any hydrogenation process involving chlorine-containing coals
would have to be dealt with.
-------
104
Selenium and Tellurium in Coal. Selenium is one of the elements
that is found to be enriched in coals over that found in the earth's crust.
This was true not only for coals of the Illinois basin but also for coals
/QA
from the eastern and western United States. ' Analysis of four specific-
gravity fractions for selenium suggests that it is contained in both the
organic and inorganic components in coal. It has been suggested that the
portion in organic matter is there as an inherent selenium that was concen-
trated during plant growth. However, that portion associated with the
sulfide and polysulfide impurities suggests that a major amount is found in
the inorganic phase.
Tellurium was found to be present in 85 percent of the coals
analyzed by spark-source mass spectrometry in the range of <0.1 to 0.4 ppm
( 83)
by weight. It was not reported in the 101-coal study, even though it
is suited to neutron-activation analysis and flameless atomic adsorption
(80)
spectroscopy.
To our knowledge, the exact nature of the occurrence of tellurium
in coal has not been reported. Since the ranges of selenium and tellurium
levels in coal are similar, as are their chemistry, it might be expected
to be distributed in the same way in which selenium is. Their dual occurrence
in the residues from electrolytic copper refining muds suggests their close
association with chalcopyrite (sulfide) minerals.
Bromine and Iodine in Coals. Bromine has been determined in coals
by X-ray fluorescence and neutron-activation analysis, while iodine has been
(80 8S 86 117 11A^
found by neutron activation. >»>»-> Ttie nature of their occurrence
in coal has not been described. However, the occurrence of bromine and
iodine in deposits of NaCl or brines, in seawater, and in salt-lake brines is
well known. The uniformity of the ratio of chlorine to bromine and chlorine
to iodine in coals shown in Table 45 suggests that their origin may be the
same as that of chlorine. There does not appear to be good correlation to
the ratios observed in seawater or salt-lake brines; however, there is
reasonable correlation in the ratio of chlorine to bromine in salt deposits.
One might speculate that bromine and iodine are present principally as impur-
ities in the inorganic chloride salts present in coal.
-------
TABLE 45. RATIOS OF Cl, Br, AND I FOUND IN COAL AND HALIDE SOURCES
Number
of Coal
Samples
13
101
RR
RR
48
Halide Sources
Salt brines
Lake brines
Seawater
Range of Concentration, ppm
Cl
8-1,500
100-5,400
750
800
320-1,400
60.6 (c>
1 141, 000- 155, 000
19,000
Br I
0.1-23 0.1-4
4-52
20 2.8
17
8.2-24(b) 1.4-4.1
0.05-0.30
100-160
65 0.06
Ratios of Minimum
and Maximum Values
Cl/Br Cl/I
Min. Max. Min. Max.
80 65 80 375
25 103
38 - 268
47 ...
39 58 228 341
1,210 202
1,410 968
292 - 1,083
Reference
Cited
82
80
85
86
117
_
_
*
(a) RR = NBS-EPA round-robin sample.
(b) Bromine concentrations of 6,900 and 5,800 ppm were found in two coal samples from Belgium.
(c) Values in percentage of salt (NaCl) in Michigan brines.
-------
106
2.6. Characteristics of Trace Elements in Liquid Fuels
(i.e.. Petroleum. Tar Sand Oils, and Shale Oils)
Liquid fuels and the characterization of the trace elements they
contain are limited in this study to the liquids to be used as a feedstock
to refineries and the liquids recovered from tar sands during bitumen
separation or from oil shale during retorting. Therefore, in the case of
petroleum, the trace elements in the crude oil as it comes from the ground
are characterized. For tar sand oils, the trace elements in only the raw
bitumen feedstock are characterized here. Finally, for shale oil only the
trace elements prior to refining are characterized here. Similarities that
exist in the characteristics of nitrogen and sulfur contaminants in the
three liquid fuels are also true for the characteristics of the trace
elements they contain.
As they are removed from the ground, the differences in the amount
of inorganic matter associated with the fuels have been amply documented.
Petroleum contains inorganic matter that is measured by its ash content.
The major effort has been centered on the oil-soluble inorganic constituents,
usually metals, even though the water associated with the crude contains
dissolved salts. Contaminants are also introduced during well drilling and
transport of the oil. Typically the range of ash content is from 0.001 to
0.130 percent and has been reported for 25 petroleums.(119»12°)
Tar sands typically contain about 11 percent oil and 5 percent
water by weight, with mineral matter making up the remainder. The mineral
matter, which is mostly quartz sand and clays, contains numerous other
mineral constituents that range in particle size up to 99.9 percent finer
than 1000 microns. Particles as fine as 2 microns are also present. 12»120»123)
An 85 to 90 percent recovery of bitumen from the tar sands is common practice."'
Canadian tar sands are better characterized than are the deposits in the
United States.
Oil shale is a term that refers to a wide variety of laminated sedi-
mentary rocks containing organic matter than can be released only by destructive
distillation. The mineral content of oil shale is inversely proportional to
the organic matter it contains and ranges from 67 to 92 percent. The major
minerals (95 percent of the total minerals) are dolomite, calcite, quartz, and
-------
107
_ ., (41,124)
feldspars. ^"J^f mineral constituents are clay minerals, pyrite,
and analcite. ' ' 'The mineral matter is extremely finely divided
(90 percent <44 microns)/124) Typically, about 66 percent of the organic
matter is obtainable as liquid or shale oil, regardless of the retorting
procedure. ' About 9 percent ends up as gaseous hydrocarbons.
Contact between the organic matter (kerogen) and the inorganic mineral
matter is limited to the external particle surface, and micropore structure
is considered insignificant.(16) Kerogen, the major organic constituent of
oil shale, has been concentrated by centrifugation after removing the
inorganic material. Organic sulfur and nitrogen compounds were found to be
only weakly bound to the mineral constituents. Oxygen compounds were more
closely associated with the kerogen and not with the mineral matter. Iron
compounds other than pyrites were found to be closely associated with the
organic material.
2,6.1. Trace Elements Identified
in the Liquid Fuels
This section will point out the influence that new analytical
techniques have had on identifying trace elements in liquid fuels. Major
emphasis has been put on the elements associated in petroleum, primarily
those considered to be oil soluble. Efforts to identify trace elements in
the bitumin extracted from tar sands and the liquids retorted from shale
oil have not been as extensive as those for petroleum.
Trace Elements in Petroleum. Most analyses for trace elements in
petroleum have been done on the ash obtained from the oxidation of petroleum
samples and each constituent is usually reported as the percentage in ash.
Early spectral analyses were semiquantitative at best, except for the elements
V Ni Cu and U.^120^ Chemical analysis of ash provided quantitative values
* ' ' (119)
for Ni, Na, Si, V, Fe, Al, Ca, and Mo (S03 values were also determined).
Typical values obtained for 24 petroleums using spectrographic analysis are
given in Table 46.. ^120^ Chemical analysis of the ash from 25 other petroleums
exhibited a wide range of values and are reported as percentage of oxides in
the ash in Table 4
-------
108
TABLE 46. DISTRIBUTION OF 28 TRACE METALS IN ASHES OF 24 CRUDE OILS (12°)
Occurrence in Concentration ...
Percent of Range in Ash£a' Concentration Range
Metal
Al
Fe
Ti
Mn
Ca
Mg
Na
K
Ag
As
B
Ba
Ce
Co
Cr
Cu
Ga
La
Mo
Nd
Ni
Pb
Sn
Sr
V
Zn
Zr
U
Samples
100
100
50
96
100
100
88
8
17
21
17
100
33
100
100
100
67
38
83
8
100
96
38
92
100
58
33
100
Percent Percent of Ash ppm in Crude
0.001 - 10
0.01 - >10
0.001 - 1.0
0.001 - 1.0
0.01 - >10
0.1 - 10
0.1 - >10
1-10
0.1 - 1
0.001 - 1
0.001 - 1
0.001 - 1
0.01 - 1
0.001 - 1
0.001 - 0.1
0.001 - >10 13 - 0.007 1.7 - 0.03
0.0001 - 0.01
0.001 - 1
0.001 - 1
0.1 - 1
0.01 - >10 16 - 0.1 35 - 0.03
0.001 - 1.0
0.001 - 1.0
0.0001 - 1.0
0.001 - >10 46 - 0.41 106 - 0.002
0.01 - 10
0.001 - 1.0
0.0001 - 0.01 0.0075-0.001 0.013-0.00012
(a) Semiquantitative values.
(b) Quantitative values.
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109
TABLE 47. SUMMARY OF THE ANALYSIS OF OIL-
SOLUBLE ASH IN 25 CRUDE OILS ^11!
(Range of Ash, wt % « 0.005 to 0.0388)
(a)
Ash Chemical Analysis,
weight percent
NiO
SiOn
V2°5
Fe2°3
CaO
S00
(a)
0.1 to 17.9
3.0 to 46.5
0.9 to 11.7
0.1 to 64.9
0.3 to 29.0
0.5 to 12.1
1.1 to 33.2
0.2 to 59.6
(a) Na_0 and Fe?0- were found in all samples.
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110
Other methods such as X-ray fluorescence, atomic adsorption,
electron paramagnetic resonance, and plasma arcs have been used for trace-
element analysis. The limited sensitivities of these methods require concen-
tration of the samples (usually by ashing) before analysis. Such treatment
creates the situation where potential contamination of samples or volatil-
ization of compounds and elements such as Cl, Br, S, Se, As, and Hg might
occur. In addition, analysis of the whole petroleum or petroleum fractions
without altering the sample by concentration provides added latitude in the
characterization of these trace elements in their unaltered state. With the
development of neutron-activation analysis using high-resolution spectrometry
(INAA), a rapid nondestructive analysis for Na, S, Cl, K, Ca, V, Mn, Cu8 Ga,
Br, Sc, Cr, Ni, Co, Zn, Se, As, Sb, Eu, Au, Hg, and U is now readily made.
/TO A\
Special techniques permit the INAA determination of cadmium. Others
(129)
have expanded the technique to include analysis for In, La, and Sm.
Less sophisticated nuclear-activation techniques require radiochemical separ-
ation for the determination of only one element at a time, but have been
used to characterize the trace elements in petroleum fractions and develop
contaminant correlations. It should be noted here that neutron-activation
analysis provides the means for the analysis of nonmetallic elements as well
as metals.^ ' ' The results of INAA analyses performed on four crude
oils are given in Table 48. The detection limits in parts per billion (ppb)
for 22 elements are given in Table 49.
Germanium, although capable of being detected by INAA, has not
been reported in oil using the activation method. However, germanium has
been reported in oils in the USSR and its behavior has been characterized.
Rhenium has also been reported to be present in both oils and heavy oils,
in bitumins, and in oil shale of the USSR in the range of 5 to 200 ppb for
the oils and 5 to 800 ppb for bitumens. ' Fluorine has been reported to
be present in ten crudes. The range of fluorine in oils is 0". 14 ppm for Iranian
heavy crude to 1.1 ppm for Alaskan crude. Forty-two crude oils representing
90 percent of the oils used in West Germany were found to contain less than
the detection limit of 0.03 ppm fluorine (ion selective electrode).
-------
Ill
TABLE 48. TRACE-ELEMENT CONTENTS OF FOUR CRUDE OILS
OBTAINED BY NEUTRON-ACTIVATION ANALYSIS^128)
Concentration
Element
V
Cl
I
S
Na
K
Mn
Cu
Ga
As
Br
Mo
Cr
Fe
Hg
Se
Sb
Ni
Co
Zn
Sc
U
California
(Tertiary)
7.5
1.47
-
9.90
13.2
-
1.20
0.93
0.30
0.655
0.29
m»
0.640
68.9
23.1
0.364
0.056
98.4
13.5
9.76
8.8
_
Libya
8.2
1.81
-
4694
13.0
4.93
0.79
0.19
0.01
0.077
1.33
-
0.0023
4.94
-
1.10
0.055
49.1
0.032
62.9
0.282
0.015
in Crude Oil
Venezuela
(Boscan)
1100
-
-
-
20.3
-
0.21
0.21
-
0.284
-
7.85
0.430
4.77
0.027
0.369
0.303
117
0.178
0.692
4.4
-
(a)
Alberta
(Cretaceous)
0.682
25.5
-
1450
2.92
-
0.048
-
-
0.0024
0.072
*
<*
0.696
0.084
0.0094
.
0.609
0.0027
0.670
-
-
. ._ -«^~-===S=SZ ' i n
(a) Values in ppm, except for scandium which is given in ppb,
-------
112
TABLE 49. DETECTION LIMITS FOR DIFFERENT ELEMENTS
IN A "TYPICAL" CRUDE OIL MATRIX IN PPfiC128)
Element
Cl
S
V
Na
As
Ca
Mn
Cu
Ga
Br
I
Detection Limit
10
1000
2
20
6
4000
15
100
25
1.5
5
Element
Ni
Co
Se
Hg
Zn
Cr
Fe
Sb
Sc
U
Mo
Detection Limit
30
0.02
23
4 (a)
90
23
400
1.0
0.1
100
500
(a) Assumes selenium absent.
-------
113
Of the elements cited for this study, analytical values for Te, P,
and Be have not been reported for petroleum. A summary of the 42 trace
elements found in petroleum is given in Figure 11. Similar compilations
made on the basis of much earlier work mentioned other elements, e.g., Li,
Be, P, Pb, Y, Tl, and Bi but did not include any of the halogens/135^
Trace Elements in Tar Sand Oils. Tar sand oils (or the raw bitumin
before it undergoes upgrading) contain various amounts of ash which appear
to vary with the bitumen-recovery process. Typically the ash content can
/-| Q£ -I O"5\
range from 0.65 percent by weight (700 C) to as high as 3.5 percent. '
Much of the ash is due to residual concentration of clay and silt. The
concentration of nickel and vanadium in the bitumen with a low ash content
was 68 and 189 ppm, respectively, while the concentration levels of these
elements in the bitumen with the high ash content were 70 and 180 ppm, which
suggests that the residual clays and silt only contribute ash without
affecting the nickel and vanadium concentrations. Trace elements attributed
to the mineral matter associated with tar sands are assumed present. Copper
concentration in the Athabasca bitumen is about 5 ppm. Utah tar and oils
contain 10 ppm of vanadium and 88 ppm nickel.
Trace Elements in Shale Oil. Shale oil which has been recovered
after retorting has a small amount of entrained shale mineral matter, Sedi-
(19)
ments of the order of 0.04 weight percent have been reported. Elements
present in the shale mineral matter are also present in the crude shale oil.
Trace amounts of nickel (4-6 ppm), vanadium (1.5 to 6.0 ppm), and iron (55-
108 ppm) have been found in Colorado crude shale oils from three retorting
processes. Recently, arsenic has been reported in shale oil at a concentration
of 40 ppm/138^ The same study identified the following oil-soluble elements
in shale oil: Sb, Be, B, Cd, Ca, Cr, Co, Cu, F, Ge, Pb, Mg, Mn, Hg, Mo, K,
Se, Ag, Na, Sr, Te, Ti, V, Y, and Zn.
-------
114
Li
By Chemical Determination
By Emission Spectroscopy and Others
By Inst. Nuclear Activation Analysis
Reported for Shale Oils Only
ci\
'
'Mn'^F. /
Fe
/Co
>Cu
Ge
/*
^
^
^^
S^
Rb
Nb
!/Mo
Tc
Ru
Rh
Pd
SbN
^^
= Te =
Cs
Hf
To
W
Re
Os
Ir
Pt
v\
Tl
Po
At
Fr
Ro
Ac
/Ce '
Pr
Pm
Eu
Gd
Tb
Dy
Ho
Er
Tm
Yb
Lu
Th
Pa
FIGURE 11. TRACE ELEMENTS IDENTIFIED IN PETROLEUM AND SHALE OILS
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115
2.6.2. Trace Elements Associated
with Petroleum Mineral Matter
Except for petroleum which inherently has low mineral content
(except for the associated brines), the two other principal liquid fuels,
tar sand oils (bitumins) and shale oils, have been separated from their
host minerals. However, residues and entrained minerals contribute to the
overall trace-element concentrations. This is also true in the case of
petroleum. The water commonly associated with petroleum contains dissolved
salts. Portions of the Ca, Mg, and Na values found in the ash from petroleum
have their origin as NaCl, CaCl2, and MgCl2 dissolved in the water. In
addition, emulsified water present in the crude contributes to the overall
(119 139 140)
contaminant level. ' * ' The determination in crude oils of 1.5 to
25 ppm chlorine along with bromine (0.12 to 1.5 ppm) and iodine (0.12 to
1.5 ppm) by neutron-activation analysis supports this possibility. '
Brine is associated with crude oil both as a fine suspension of
droplets and as more permanent emulsions. The demarcation line between these
two types is not always clear, but, generally, the less stable mixtures can
be separated by simple settling methods, whereas the more permanent mixtures
require chemical or electrical methods.
Relatively little has been published on the amount of salt contained
in crude oils, and little consistency in values is evident because the brine
which contains the salt tends to settle from the crude oil during handling.
Thus, the salt content of oil at the field is higher than the salt content
at the pipeline or at the refinery. Neither crude oil gravity nor bottom
sediment and water content appear to be related to salt content except when
in a particular field or region. Some typical salt contents of crude oils
from various regions are shown in Table 50.
The removal of brine from crude oil is important because the salt
can leave deposits on processing equipment, thus leading to fouling or
plugging of heat exchangers. The salt also increases the coking rate when
the crude oil is heated, such as in the initial distillation operations.
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116
TABLE 50. TYPICAL SALT CONTENTS OF CRUDE OILS^
Region
Pennsylvania
Wyoming
Middle East
Venezuela
East Texas
Gulf Coast
Pipelines (U.S.)
Oklahoma and Kansas
Canada
West Texas
Lb Salt Per
Average ^-J
1
5
8
11
28
35
65
78
200
2.10.)
1000 Bbl
Range
--
1-13
1-1,085
0-63
9-44
2-70
22-200
7-305
10-8,250
4-2,580
Number of
Samples
6
8
9
124
5
11
12
15
14
173
(a) Very high samples omitted from average.
(b) Most samples taken at field.
-------
117
Also, the chloride salts (particularly MgClp tend to decompose during
processing of the oil, thereby liberating HC1 and contributing to corrosion
problems. The combination of HC1 and H2S is particularly troublesome in
this regard. Reduction of the salt content to 15 to 30 g/1000 liters (5 to
10 pounds per 1000 bbl) of crude oil greatly reduces corrosion problems.
2.6.3. Trace Elements Associated^
with Petroleum Organic Matter
Shale oil and more so tar sand oils are similar to petroleum in
that the major portion of the trace elements associated with them are present
in the organic phase. In other words, the contaminants are oil soluble or
in oil suspension. The following constituents are present in minor amounts
in the three liquid-fuel types:
Heterocyclic organic compounds containing sulfur,
nitrogen, and oxygen (i.e., nonhydrocarbons)
Inorganic substances such as silica, salts, and metals
High-molecular-weight asphaltic molecules.
Despite their low concentrations, these constituents are the source of environ-
mental pollutants and the cause of corrosion of equipment and poisoning of
catalysts. In the refining process, the raw fuel is treated to eliminate
these constituents, usually by chemical conversion and upgrading. The
processes of desulfurization, denitrification, and demetallization ensure
a clean final fuel. Reductive cleavage of the heterbcycles removes the
heteroatoms by the splitting of the heteroatom-carbon bonds into H2S, NH3,
and H.O. The asphatenes are usually depolymerized during the hydrodesul-
furization process. Removal of metallic impurities can be done by acid
(139)
treatment or by a process that employs a slurry of asphaltenes.v In the
area of trace-element contaminants in petroleum, major emphasis has been
placed on the characterization of the trace metals.
-------
118
Background on the Characterization of Trace Metals in Petroleum,
Petroleum, although it consists predominantly of hydrocarbons, also contains
measurable quantities of metals. Nickel and vanadium are commonly most
abundant. In addition, Fe, Zn, Cr, Cu, Mn, Co, and others are almost always
(139)
present in concentrations from less than 1 ppb to more than 100 ppm.
Characterization based on groups of metals present in crudes and ratios of
metal concentrations have been made to aid in correlation of the age and
depth of oil deposits and in some cases their countries of origin. Much work
has been done in the interpretation of trace-element data for development of
valid geochemical interpretations. To do this it is necessary to know in
what forms trace elements occur. Except for nickel and vanadium, such infor-
mation is lacking. It is a generally accepted fact that metals may be present
in crude oil as inorganic particulate matter (such as mineral grains, or
absorbed on clay minerals), in emulsified formation waters, introduced in
drilling fluids and corrosion inhibitors, or present in oil solution as metal
complexes of organic ligands. The characterization here deals only with the
oil-soluble forms of metals.
Significant amounts of nickel and vanadium cannot be accounted for
by free metalloporphyrins in crude oils. Both vanadium and nickel concen-
trations increase with asphaltic content of the oil (API gravity), and lighter
oils contain less metals. Usually, the vanadium concentration is higher
(139)
than the nickel concentration but this is not always the case.
Yen classified metal components in petroleum into the following
categories:^139^
(1) Metalloporphyrin chelates
(a) Compounds with heterocyclics containing
nitrogen, e.g., vanadyl and nickel porphyrins.
(b) Chlorophyl a_ and other hydroporphyrins.
(c) Highly aromatic porphyrin chelates.
(d) Porphyrin decomposition ligands.
-------
119
(2) Transition metal complexes* such as those of V, Ni,
Fe, Cu, Co, and Cr of tetradentate** mixed ligands
(a) Simple complexes from resin molecules
(b) Chelates** from asphaltene sheets
(3) For organometallic compounds of such elements as Hg, Sb,
and As, both alkyl and aryl types are possible as are
Tr-complexes.
(4) Carboxylic acid salts of polar functional groups of
the resin component with elements like molybdenum
or germanium in coal. Complexes of a-dihydroxyl
groups of catechol, thiocarboxylic acids, and
N-containing ligands are possible.
(5) Colloidal minerals such as NaCl or silica carried over
by water during formation and other fluids introduced
during oil recovery.
The two major classes of metals considered to be important are
the porphyrin metals and nonporphyrin metals. Porphyrin metals have been
studied widely. Nonporphyrin metals have not been as extensively charac-
terized, and typically in these compounds, the porphin skeleton has lost
(139)
its true porphyrin characteristics as reviewed by Yen. As seen in
Figure 12, the basic porphin structure with uninterrupted conjugation is
repeated in chlorophyl-a and the deoxyphylloerthroetioporphyrin (DPEP)
and etioporphyrin-III forms of vanadyl complexes (nickel complexes are
similar). Porphyrin systems vary extensively because of substituents,
isomers, and symmetry differences as well as with the central metal atoms
they contain. Altered or modified porphyrins such as hydroporphyrin, aryl-
porphyrin, and degraded porphyrin products all fall under the nonporphyrin
systems containing complexed metals.
The other major class of nonporphyrin metals comprises the com-
pounds forming complexes of the tetradentates type with mixed ligands usually
* Complexes refer to compounds with more than one ligand molecule to one
metal atom.
** Chelates refer to compounds in which one ligand satisfies the coordin-
ation sites (£2<6) of one central metal atom, e.g., tetradentate liqand
provides 4 coordination sites per molecule.
-------
CHLOROPHYLL a
porphin
CH
OPEP
ETIO (ETIOPORPNYRIN m)
CH,
CJ.HS
FIGURE 12. THE PORPHIN STRUCTURE AND WELL KNOWN PORPHYRINS CONTAINING THE STRUCTURE
(139)
-------
121
containing a combination of N, S, and 0 heteroatoms. Some of these are
shown in Figure 13. Smaller molecular systems are usually formed from the
resin molecules and larger systems are formed from the asphaltic sheets
that are known to contain these heteroatoms. Yen^ has given supporting
evidence for the existence of tetradentate ligand-metal complexes in both
the resin and asphaltene components of oil.
During the genesis of asphaltenes, it has been postulated that the
graphitization process is interrupted owing to the presence of nitrogen,
(139)
sulfur, and oxygen atoms. ' Therefore, a structure consisting mostly of
fused benzene rings exists; however, holes or gaps in the hexagonal array
are formed where these heteroatoms are located. This is represented graph-
ically in Figure 14. ' Such holes or gaps provide sites for metal-complex
formation and metals held as these complexes cannot be removed by aqueous
acid washing. Metals can be removed from the tetradentate complexes present
in the resin component of oil under slightly acid conditions.
Characterization of Trace-Metal Contaminants by Physical Separation.
A physical separation of petroleum into various fractions has been done by
ultracentrifugation in an attempt to characterize the colloidal nature of
petroleum. This method of separation provided a means to limit the
amount of polar molecules normally removed with the asphaltene component of
petroleum by n-propane precipitation (as described later). Therefore, metal
constituents, salts, water, and other metals, including those normally dis-
solved in oil (yet polar), are not precipitated and may be better correlated
to their true existence in petroleum. The following findings were cited as
important in characterizing the trace-element contaminants in petroleum,
especially as it relates to the colloidal material.*
Most metals were found to be associated with the colloidal
material. The colloids are rich in asphaltenes, vanadium,
nickel, and nitrogen. The bottom one-third of the centri-
fuged sample contained 10 percent asphaltene and 42 percent
nonhydrocarbon (feed: ~7 percent asphaltene).
-------
122
FIGURE 13. TETRADENTATE METAL COMPLEXES OF NICKEL AND
VANADIUM WITH MIXED LIGAND ATOMS C139)
FIGURE 14. MODEL DEFECT SITE (OR GAPS) IN AN
SHEET OF THE ASPHALTENE STRUCTURE
.TIC
-------
123
Sulfur (and nitrogen) correlates well with asphaltene
content; metals show a linear relationship (see Figure 15)
The authors suggested that if oil were freed of
asphaltene, only 2 ppm metals would exist in true
solution. Sulfur does not exhibit a linear relationship
to asphaltene content as the metals do. This was
attributed to the high solubility of some sulfur organic
components not present in the asphaltenes.
Although this technique showed that metal, sulfur, and nitrogen
contaminants could be partitioned, sample sizes were too small for
characterizations that are possible by solvent precipitation techniques.
The results do lend support to Yen's concepts and reasons for the
investigation of a centrifugal process for metal removal.
Effect of Filtration and Water Washing on Crude-Oil Metal
Content. Filtration of benzene-diluted crude yielded black deposits that
exhibited only background levels of trace elements. Analysis of unfiltered
and filtered crudes from California and Venezuela showed significant
decreases in arsenic and sodium, and mercury, iron, arsenic, and sodium,
respectively, after filtration. An aqueous phase separated from the
California oil contained 2800 ppm sodium, 21.3 ppm iron, and 18.2 arsenic
and appeared to be residual water retained by the crude. Negligible amounts
of other elements could be ascribed to the aqueous phase.
Distilled-water extraction of California oil indicated that 92
percent of the sodium, 37.5 percent of the arsenic, and 22.5 percent of
the antimony were extracted, but other elements were not affected. Repeated
extractions did not alter the sodium, arsenic, and antimony levels remaining
in the oil. This and related data supported Filby's conclusion that the
sodium in these oils was there as an oil-soluble compound or one that is
readily hydrolyzed (sodium salt of petroleum acid)/ In addition, some
of the arsenic and antimony appears to be present as soluble or readily
hydrolyzable compounds.
-------
124
ULTRACENTRIFUGATION FRACTIONS
"0 02 0.4 0.6 0.8 1.0 12 1.4 1.6
ASPHALTENES CONC., WT.
1.3
FIGURE 15. EFFECT OF ASPHALTENES CONTENT ON SULFUR AND
METALS IN SIX FRACTIONS OF ULTRACENTRIFUGED
OIL'140*
-------
125
Characterization of Trace-Metal Contaminants by Solvent
Precipitation. The liquid fuels, especially petroleum, have been
characterized by separation into their components based on the solubility
of each component in a series of solvents. Several approaches have been used,
but one that appears to be well suited to trace-element characterization is
the following scheme and definitions:<143-145)
n - pentane insoluble = asphaltenes
n - pentane soluble but methanol insoluble = resins
methanol soluble = methanol solubles.
Further separation of each of the components and chemical
characterization of these isolated fractions have been done for the purpose
of locating the centers of contaminant concentration. For example, both the
resins and the asphaltenes are minor components in oil, yet they contain a
proportionately large fraction of the nitrogen and sulfur contents of crude
(139 143-145)
oils (10 to 50 percent), as shown in Table 51. ' In addition,
the distribution of metal contaminants in each of the components of petroleum
as complexes of organic molecules called porphyrins or as nonporphyrin compounds
have also been determined. Recent publications on the subject have drawn
extensively on review of past work and provide an up-to-date interpretation of
the characteristics of trace metals in petroleum. Much of the information that
follows is covered in articles by Filby and Yen.
A California tertiary crude oil, which has high trace-metal concen-
trations, has been characterized as to the distribution of the trace metals
within each component of petroleum and the distribution of the metals within
various molecular-weight fractions of each component. The capability of
neutron-activation analysis to determine metal concentrations on small (0.1
to 1.0 g) samples was fundamental to this study by Filby.^ The distri-
bution of V, Go, Hg, Fe, Zn, Cr, As, Sb, Na, and Cd was determined in the
asphaltene, resin, and methanol-soluble components of petroleum. Further
separation of these three components into fractions with four molecular-weight
-------
TABLE 51. DISTRIBUTION OF PERCENTAGE OF TOTAL NITROGEN
OF CRUDE IN RESINS AND ASPHALTENES^139'
Crudes
Mara- La Lune
Oficina
Ragusa
Wilmington
North Belridge
Boscan
Sandhills
Abel 1- El lenburger
South Waddell
Keystone
South Ward
Hiseville
Athabasca
Percent
Resin
9.1
3.9
9.2
14.2
18.0
29.4
4.4
4.2
3,9
2.2
1.2
0.97
24.2
of Crude
Asphaltenes
4.1
1.1
0.28
5.1
5.1
18.0
0.44
0.24
0.39
0.22
0.80
0.19
19.4
Percent
in Resins
30.0
18.3
30.5
25.8
20.4
8.5
39.3
50.0
40.0
14.4
53.0
21.8
Nitrogen
in Asphaltenes
27.5
12.8
48.2
15.6
14.8
41.0
3.2
3.1
10.0
10.0
3.9
4.1
49.7
Percent
in Resins
20.5
33.3
--
22.9
23.9
35.1
9.1
33.8
17.4
15.1
6.7
12.2
28.2
Sulfur
in Asphaltenes
10.5
13.8
24.3
8.5
7.8
23.0
3.1
3.9
3.1
0.34
2.3
0.7
28.5
ro
-------
127
ranges was accomplished by gel-permeation chromotography (GPC). Liquid
chromotography was also used to separate porphyrin concentrates in an attempt
to determine whether metal porphyrins other than those of nickel and vana-
dium existed. Several other crude oils with high (>5 percent) asphaltene
content as well as high trace-metal concentrations were among those selected
for study.
Eflect of Filtration and Water Washing on Crude-Oil Metal Content.
Filtration of benzene-diluted crude yielded black deposits that exhibited only
background levels of trace elements. Analysis of unfiltered and filtered
crudes from California and Venezuela showed significant decreases in arsenic
and sodium, and mercury, iron, arsenic and sodium, respectively, after filtra-
tion. An aqueous phase separated from the California oil contained 2800 ppm
sodium, 21.3 ppm iron, and 18.2 ppm arsenic and appeared to be residual water
retained by the crude. Negligible amounts of other elements could be ascribed
to the aqueous phase.
Distilled-water extraction of California oil indicated that 92
percent of the sodium, 37.5 percent of the arsenic, and 22.5 percent of the
antimony were extracted, but other elements were not affected. Repeated
extractions did not alter the sodium, arsenic, and antimony levels remaining
in the oil. This and related data supported Filby's conclusion that the
sodium in these oils was there as an oil-soluble compound or one that is
readily hydrolyzed (sodium salt of petroleum acid). In addition, some
of the arsenic and antimony appears to be present as soluble or readily
hydrolyzable compounds.
Distribution of Metals in the Three Isolated Petroleum Components.
Analyses of the asphaltene component revealed that it contained the highest
concentrations of all elements, and that the combined resin and asphaltene
fractions (i.e., the asphaltic components) account for the major portion of
the trace elements V, Ni, Co, Fe, Hg, Zn, Cr, and Sb in California oil.
Table 52 shows the distribution of the trace elements among the three com-
ponents separated from this crude oil, and the ratios of the asphaltene to
-------
TABLE 52. DISTRIBUTION OF TRACE ELEMENTS IN
COMPONENTS OF A CALIFORNIA CRUDE OIL
(143)
Trace Element Concentration,
Trace Element
Crude Oil , percent
V
Ni
Ni/V ratio
Co
Fe
Hg
Cr
Zn
Sb
As
1
Crude Oil
100.0
7.5
93.5
12.47
12.7
73.1
21.2
0.634
9.32
0.0517
0.656
Methanol
Soluble
57.5
0.82
7.21
8.8
0.8
1.95
0.686
0.300
0.74
0.0033
0.546
Resins
37.5
12.4
147.0
11.9
10.7
66.4
29.6
0.894
8.86
0.0130
0.290
ppm
Asphaltenes
4.99
61.6
852.0
13.8
122.0
895.0
140.0
7.540
109.
1.22
2.25
Ratio of
Trace Element
Concentrations
R/C(a>
1.65
1.57
0.84
0.91
1.40
1.41
0.95
0.25
0.44
A/C
8.2
9.1
9.6
12.2
6.6
11.9
11.7
23.6
3.4
ts3
00
(a) R/C = ratio of concentration in resins to that in crude.
(b) A/C - ratio of concentration in asphaltenes to that in crude.
-------
129
crude oil (A/G) and resin to crude oil (R/C). Of particular importance is
the observation that 48 percent of the arsenic is present in the methanol-
soluble fraction and suggests the presence of low-molecular-weight compounds,
possibly as alkyl or aryl arsines. The elements Ni, V, Co, Fe, Cr, Hg, and
Zn are enriched in the asphaltene phase. (Since it is well established that
the asphaltenes and resins exist in the oil as a colloidal dispersion, the
crude oil may be considered as a system of the polar aromatic micelles of
asphaltenes and less-polar resins in the major, nonpolar-hydrocarbon phase
, fc. . ., , (140,143)
of the crude oil.) ' '
In the separation scheme used to isolate the three oil components,
the trace-element constituents enriched in the asphaltene may have their
origin from the presence of small (low molecular weight), highly polar
molecules which could precipitate with the asphaltenes when a non-polar
solvent such as n-pentane is used. On the other hand, the metal ions might
be complexed in the asphaltene sheet structure at sites bounded by hetero-
atoms of sulfur, nitrogen, or oxygen.
Studies by Filby ' using gel-permeation chromotography showed
the molecular-weight-fraction distribution for the three petroleum components
to be that given in Table 53. The similarity of the resin and asphaltene
molecular-weight distribution suggested similarity in the makeup of these
two fractions. Therefore, the difference in solubility behavior in n-pentane
was attributed to the greater polarity of the asphaltenes rather than to
molecular-weight differences. The presence of 11 percent material with a
molecular weight of 300 to 1000 suggested that small polar molecules are
isolated with the asphaltene micelles during precipitation of the n-pentane-
insoluble components.
The distribution of trace elements found in the various asphaltene
and resin molecular-weight fractions is shown in Tables 54 and 55. These
can be compared with the distribution for the methanol-soluble fractions
given in Table 56. The following observations were made by Filby for the
asphaltenes fractions:
-------
130
TABLE 53. DISTRIBUTION OF MOLECULAR-WEIGHT
FRACTIONS OF OIL COMPOUNDS (143)
Molecular -Weight
Fraction
300-1,000
1,000-4,000
4,000-8,000
8,000-22,000
Total
Percentage of
Methanol Soluble (a)
93.8
6.2
--
100.0
Fraction
Resins
29.4
21.2
49.4
0
100.0
Asphaltenes
11.0
23.2
50.6
15.2
100.0
(a) The higher-molecular-weight component of the methanol fraction
was not separated into smaller fractions.
-------
TABLE 54. DISTRIBUTION OF TRACE ELEMENTS IN ASPHALTENES
)
Molecular-Weight
Fraction (GPC):
Fraction, percent:
Ni
Co
Fe
Hg
Cr
Zn
Cu
Sb
As
300-1,000
11.0
1327.0(a)
2.67
480.0
72.0
0.77
112.00
0.34
11.0
0.850
1,000-4,000
23.2
189.0
30.00
368.0
20.9
4.80
52.00
1.50
0.9100
0.620
4,000-8,000
50.6
984.0
167.00
867.0
90.0
9.12
103.00
4.00
0.3500
1.900
8,000-22,000
15.2
1060.0
176.00
1934.0
350.0
19.6
225.00
7.20
0.1040
6.600
Total
100.0
852.0
122.00
895.0
140.0
7.540
109.00
3.02
1.2200
2. 250
(a) All values in ppm.
-------
TABLE 55. DISTRIBUTION OF TRACE ELEMENTS IN RESINS^
(143)
Molecular-Weight
Fraction (GPC):
Fraction, percent:
Ni
Co
Fe
Hg
Cr
Zn
Cu
Sb
As
300-1,000
29.4
206.0
4.37
30.1
22.0
0.310
3.31
<0.20
0.0430
0.407
1,000-4,000
21.2
110.0
10.00
24.0
44.0
0.800
11.00
<0.50
0.0026
0.200
4,000-8,000
49.4
80.2
24.90
236.0
72.0
2.960
27.00
1.30
0.0054
0.200
8,000-22,000 Total
0 100.0
147.0
10.70
66.4
29.6
0.894
8.86
0.32
0.0130
0.290
to
N5
(a) All values in ppm.
-------
TABLE 56. DISTRIBUTION OF TRACE ELEMENTS IN METHANOL-SOLUBLE FRACTIONS
(143)
Molecular Weight
Fraction
300-1,000
> 1,600
Total,
percent
93.8
6.2
Concentration,
Ni
11.00
< 1.00
Co
0.73
2.61
Fe
< 1.00
9.90
Hg
0.410
7.130
Cr
--
--
ppm
Zn Cu
< 1.00
3.50
Sb
0.0046
<0.0020
As
0.340
5.000
Total
100.0
7.21 0.80
1.95 0.886 < 0.3
0.74 < 0.5 0.0033
0.564
to
CO
-------
134
The highest trace-element concentrations (except
nickel and antimony) were found in the highest-
molecular-weight fraction.
The highest nickel concentration was found in the
300 to 1000 molecular-weight fraction (entirely
nickel porphyrins associated with asphaltenes).
Sb concentration was highest in lowest-molecular- ,.
weight fraction and decreased with increasing
molecular weight of the asphaltene component.
Cr, Gu, and Co show increasing concentration with
increasing molecular weight of the asphaltene
fractions.
Fe, Hg, Zn, and As show highest concentration in
the highest-molecular-weight asphaltene fraction.
The possible existence of porphyrin derivatives of
these metals was surmised by the fact that their
concentration was greater in the 300 to 1000 fraction
than in the 1000 to 4000 fraction.
The resin fractions show trace-element patterns similar to those
of the asphaltenes; however, their concentrations were much lower. In the
methanol-soluble component, only nickel and antimony are present in greater
concentration in the low-molecular-weight fraction (nickel as porphyrin and
antimony as low-molecular-weight organoantimony compounds). The existence
of Fe, Hg, Zn, and Co as porphyrins in the low-molecular-weight fraction
was not ruled out, but their exact character is not known.
Filby^143^ has shown that about 50 percent of the nickel in the higher-
molecular-weight asphaltenes is present as nonporphyrin compounds, the
percentage increasing with the molecular weight of the fraction. The results
of the study are given in Table 57. The same trend was observed for the
(146)
resin component of crude oil. Similar trends have been observed for vanadium.
Data on Fe, Co, Zn, Cr, and Hg suggested that they occur as nonporphyrins in
oil and that their behavior is similar to that of nonporphyrin nickel.
-------
135
TABLE 57. DISTRIBUTION OF NICKEL AND NICKEL PORPHYRIN IN
ASPHALTENES AND RESINS FROM A CALIFORNIA TERTIARY OIL(143)
Molecular-Weight
Fraction (GPC)
Asphaltenes
or Resins,
percent
Nickel As
Nickel
Porphyrin,
percent
Nonporphyrin
Nickel,
percent
Asphaltenes
300-1,000
1,000-4,000
4,000-8,000
8,000-22,000
Total
300-1,000
1,000-4,000
4,000-8,000
8,000-22,000
Total
1.1.2
23.2
50.6
15.2
100.0
Resins
29.4
21*2
49.4
0
100.0
100.0
49.0
34.5
22.9
49.2
100.0
38.6
32.0
«
64.0
0
5.1.0
65.5
72.1
50.8
0
61.4
68.0
-
36.0
-------
136
Conclusions made by Filby on the basis of his work and the review
of the work of others are as follows:
Oil-soluble compounds of Ni, V, Fe, Co, Cr, Hg, Zn,
As, Sb, Cu, and Na are present in California tertiary
crude oil.
Nickel is present in the oil as nickel porphyrin and
nonporphyrin nickel. The porphyrin compounds, which
are found to be present in all fractions of crude oil,
accounted for 100 percent of the nickel in the low-
molecular-weight fractions of the three oil components.
The proportion of nickel in the resins and asphaltenes
increased with molecular weight.
The elements Fe, Co, Zn, Hg, Cr, and Cu occur in a
nonporphyrin form in the oil. Porphyrin complexes of
these metals were not observed. These elements are
incorporated into the asphaltene sheet structure through
complexing at holes bordered by nitrogen, sulfur, and
oxygen atoms.
Arsenic and antimony appear to be present as low-molecular-
weight compounds such as alkyl or aryl arsines and stibines.
The antimony compounds are also associated with the asphal-
tenes.
The origin of the Fe, Co, Hg, Zn, Cr, and Cu in asphaltenes
may involve complexing from an aqueous or solid phase
(rocks) during maturation of the petroleum.
The characteristics of the nature of vanadium compound's contained
(142 144 147-150
in petroleum have been the subject of numerous studies and reviews. J '
These studies conclude that there are a number of types of vanadium compounds
in petroleum and virtually all are complexes. Since they are readily separated
by extraction, much work has been directed toward detecting their presence.
The commonest of these are the porphyrins. Other types of complexes exist
such as the tetradentate mixed ligands containing nitrogen, sulfur, and
oxygen donor atoms, and pseudoaromatic and highly aromatic porphyrins.
-------
137
(Association with asphaltenes through TT-electron bonding has been postulated.)(150)
These latter complexes are held tightly in the organic matrix and as a result
exert a strong influence on the properties of petroleum samples. Vanadium's
adverse effects in refining and on health are also well documented.
Mechanisms for Trace-Metal Removal from Petroleum. The removal of
trace metals from petroleum is complicated by the following facts:
Metals are chelated or complexed by ligands that are
compatible in petroleum (separation is made difficult).
The amount of metals usually ranges from 1 to 100,000 ppb
(these small amounts also make separation difficult).
Metals are associated with the heterocyclic organic
molecules and the asphaltic fraction.
Metals removal may enhance petroleum refining catalyst
life, but their removal may alter the reaction path
from a more favored one when the metals are present.
In order to explain the common belief that porphyrin metal
complexes in petroleum had their origin from chlorophylls, some process
must exist by which the magnesium in chlorophyll is removed and thep replaced
i *y J_O
by other metal ions such as Ni and VO . The reaction to describe this
(39)
process can be generalized as follows:
H- 4"2
2H + metal porphyrin a* porphyrin'2H 4- metal
The forward reaction, which is demetallization, produces the porphyrin'2H
base and the metal ion by reacting with an acid. The reverse reaction, of
course, is metallization. The strength of acid systems required to promote
the demetallization reaction is also a measure of the chemical stability
of the porphyrins. The following generalizations on their stability were
(139)
presented by YenN ':
Acid System Metal Ions Removed From Porphyrin Complexes
Water Ag(I), K(I), Na(I), Pb(II), Hg(II)
Dil HCI Zn(II), Cd(II), Mg(II), Fe(II)
Conc H SO Cu(II), Mn(II), Co(II), Ni(II), Fe(III)
HBr-acetic acid VO(IV)
Trichloroacetic acid VO(IV)
-------
138
The best method for demetallization has been the acid treatment.
Glacial acetic acid-HBr is a traditional method (The Groenning Process).
Methansulfonic acid, p-toluene sulfonic acid, sulfuric acid, and phosphoric
acid all can be used for demetallization of porphyrins. Unsuccessful methods
cited by Yen include the use of ion exchange, electron discharge, and
dialysis.(139)
Erdman and Harju have shown that asphaltenes are under-
saturated with respect to metal ions and that sites in sheets are available
for holding metal ions by complexing. This was demonstrated by the observed
takeup of vanadium, nickel, and copper ions from aqueous solutions by asphal-
tenes. Similar behavior would be expected for Fe, Zn, Co, Cr, and Hg.
Gulyaeva and Lositskaya ' found that uptake of vanadium occurred only
when asphaltenes were present in the crude oil and that it was inhibited by
high concentrations of NaCl and in solutions with pH >7. Filby substantiated
(143
such behavior by observing the uptake of copper from solutions by asphaltenes.
Hydrodesulfurization of petroleum not only depolymerizes some asphal-
(139 153 154}
tenes but a porportional removal of metal is also observed. ' ' It
has been demonstrated that when aryl or alkyl derivatives of Sb, Bi, Sn, and
As are hydrogenated, the products are the metal and the saturated hydrocarbon
with no apparent side reactions. Similar behavior was observed for the cyclo-
pentadiene ir-complexes of nickel and iron (ferrocene-type compounds). '
Characteristics of Trace-Nonmetal Contaminants in Petroleum. Of
the trace elements of interest in this study, As, Se, Te, P, F, Cl, and Br
have been categorized as nonmetals. No values for the concentration of
phosphorus or tellurium in petroleum were found; therefore, their compounds
could not be characterized. Arsenic has been considered in the previous
sections and is assumed to be present partially as readily hydrolyzable
compounds and as alkyl or aryl arsines. The concentrations of Se, Cl, Br,
and I in petroleum have been cited previously. Citations characterizing the
selenium compounds could not be found. Of the halogens, the presence of
fluorine in crude oils appears to be questionable since; in one case it was
found and in another it was not. ' Chlorine, bromine, and iodine
are believed to be present in oils as suspensions of metal salts rather than
organic molecules. The behavior of iodine during distillation suggests
-------
139
that it forms, or is present as, volatile compounds that appear to be isolated
in the 80-170 C fraction. No report of similar behavior for bromine was
(130)
noted. During distillation at 200 to 300 C, hydrogen chloride gas, HC1,
is evolved; the amount is dependent on the chlorine content but was found
to increase with increasing nitrogen content. This suggested to the authors
that organic nitrogen complexes of NiCl2 were the source of the correlation.^56^
Correlation in the occurrence of the halogens with other trace
elements suggests their mode of occurrence but does not truly characterize
the nature of their compounds. It has been determined that the bromine con-
centration generally follows the nickel and vanadium concentrations but not
always, and it even varies in different parts of the oil field. ' The
same authors showed that the chlorine concentration is related to the con-
centration of Na, K, Al, and Mn and suggest that chloride salts are the source
of chlorine in petroleum. In a comparison of the concentrations of 25
elements in petroleum with those found in living organisms, bromine was in
the group of elements whose concentrations were lower than those in organisms,
while iodine was present in concentrations equal to those found in organisms.
2.6.4. Trace Elements in
Tar Sand Oils and Shale Oils
Tar sand oils (or raw bitumen) and shale oils have been charac-
terized primarily for their trace-metal content. Since tar sand oils are
considered to be geologically younger petroleum, intercomparisons of their
trace-metal content have been made. Also, since a major portion of the
metal contaminant in petroleum can be located in the resin and asphaltene
component of petroleum, a comparison of the resin and asphaltene content of
tar sand oils should give some measure of the amounts of trace metals that
would be expected in each of the liquid fuels. The amounts of resin and
asphaltene isolated from tar sand oils, shale-oil fractions, and two coal
liquids have been reported, and the results are summarized in Table 58.^
The component separation was done by the procedure developed for the study
and is similar to those employed in the petroleum trace-metal character-
ization studies/ '
-------
TABLE 58. RESINS AND ASPHALTENE CONTENT OF TAR SAND OILS,
SHALE OIL FRACTIONS, AND COAL LIQUIDS^15)
Content, weight percent
Coal Liquids
Isolated
Component
Resin (nonhydrocarbons)
Asphaltene
Benzene insoluble
Tar Sand
Oils
25.9
9.8
< 0.1
Big Horn
Coal
8.3
1.5
< 0.1
Pitt Seam
Coal
11.1
20.3
5.5
B.P. of
60-282 C
12.1
0.7
< 0.1
Shale Oil Cuts
282-360 C
38.6
0.8
< 0.1
> 360 C
68.6
3.3
< 0.1
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141
The data in Table 58 show that the tar sand oils are very high in
resins and asphaltenes. The asphaltene content in shale oil varies with
the boiling range of the shale-oil fractions from very low to that comparable
to the content in some crude oils (< 5 percent). The resin content ranges
from less than that present in crude oils (~35 percent) to almost twice as
much. These facts, along with the data on trace-metal characterization reported
earlier, suggest that the trace metals in tar sand oils and shale oils exist
in the same form as they do in petroleum.
A comparison of the nickel and vanadium in known asphaltic oils,
given in Table 59, supports this relationship between petroleum and tar sand
oils (Athabasca).*1 ' The similarity in the excess of vanadium and nickel
to porphyrin content also suggests similarities in the types of trace-element
compounds that are present in petroleum. The nickel and vanadium concentrations
appear to be independent of ash content of the recovered tar sand oils/ ^
However, the metals and their concentrations will depend on the characteristics
of host rocks. For example, Athabasca tar sand oil contains anomalously high
concentrations of Mo, Dy, and Eu which may be related to the presence of
minerals such as molybdenite in the sand. The molybdenum concentration
in several oils and tar sand oils has been found to range from less than
0.4 ppm (the detection limit of the analytical method) up to 10 ppm.
Thirty-five percent was found in the heptane-soluble fraction of the tar
sand oil and 42 percent in the insoluble fraction (77 percent accountability).
Iron and copper have also been found at concentrations of 75 and 5 ppm,
respectively.^12'137^ Vanadyl and nickel porphyrins have been isolated
from various other tar sand oils and solid hydrocarbons such as those from
Utah and California deposits. In Utah, the oils contain more nickel than
vanadium. ^148^ Virtually all of the metals remain in the coke from the
delayed-coking operations used to recover the volatile portions from raw
. (122)
bitumen (tar sand oil).
With respect to the volatile shale-oil fractions, the small amount
of asphaltenes is not surprising and larger fractions would not be expected
since they are products of retorting.(15) Regardless of this fact, crude
shale oils contain 4 to 6 ppm nickel, 1.5 to 6 PPm vanadium, and 55 to 100
ppm iron.(19) All oil shales contain porphyrins principally as metal complexes
-------
TABLE 59. PORPHYRIN AND TRACE-METAL CONTENTS OF CERTAIN ASPHALTIC
Vanadium, ppm
Nickel , ppm
Vanadium ,
Nickel '
Porphyrin aggregate, ppm
Total V + Ni .mole ratio
Total Porphyrin
Tat urns
110
55
2.3
165
9.1
(a}
Athabasca
180
80
2.6
260
9.0
S.M. Valley
280
130
2.5
300
12.2
N. Belrdige
23
83
0.3
390
2.3
Colesville
94
32
3.4
110
10.4
(a) Tar sand oil
-------
143
with vanadyl and nickel cations, with some iron porphyrin being present as
well. The retorted oil contains alkyl porphyrins of the etio series. Since
such complexes are stable, some survive the retorting and codistill with the
oil products and organic nitrogen derivatives. Iron compounds other
than pyrites are closely associated with the kerogen (organic) in the oil
shale.<125)
Quantitative determinations have shown that arsenic is present at
(138}
a 40-ppm concentration in crude shale oil. In addition to arsenic, the
following trace elements have been found in shale oil: Sb, Be, B, Cd, Ca,
Cr, Co, Cu, F, Ge, Pb, Mg, Mn, Hg, Mo, K, Se, Ag, Na, Sr, Te, Ti, V, Y, and
Zn. These trace elements are dissolved in various forms in the oil and
differ from the form of the fine suspended solids entrained during oil
pyrolysis. Their origin, however, may have been closely related to the
mineral matter. The trace elements can be concentrated in the heavy end.
Arsenic, however, is distributed throughout the boiling range (probably
as various organo-arsine derivatives, as shown below.
Fraction, Arsenic
Boiling Range. C volume percent Content. ppm
IBP-204 18 10
204-482 58 52
482+ 24 38
The nature of the compounds of the other trace elements dissolved
in shale oil has not been defined.
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144
3. CONCLUSIONS
The detailed characterization of the sources of sulfur, nitrogen,
and trace element contaminants in fuels, such as coal, coal liquids,
petroleum, shale oil, and tar sand oil, can best be done with an understanding
of the characteristics of and the differences in these fuels. As shown in
Table 60, typical fuel types considered in this review exhibit marked
differences in the amount of ash forming matter they contain and in the
elemental composition of their combustible part. Coals have a much higher
ash content than do petroleum crudes. Coals also have the lowest value
for the H/C ratio and are considered in a state of unsaturation with respect
to hydrogen. To approach petroleum crude in character, hydrogen must be
added to coals or coal liquids (obtained by coal pyrolysis). The ratio for
shale oil and tar sand oil fall between coal and petroleum. Formation of
coal liquids by hydrogenation of coal increases the H/C ratio. Such
processes also significantly reduce the amount of sulfur and nitrogen
remaining in the fuel.
The review of the characteristics of the components of coal,
petroleum, tar sand oil, and shale oil which are the sources of sulfur
nitrogen, and trace element pollutants when these fuels are utilized
suggests that at least part of the sulfur and most of the nitrogen originate
from compounds common to all of these fuels. These compounds are primarily
organic sulfur and nitrogen compounds. The principal difference between
the solid and liquid fuels is the way in which these compounds are combined
in the fuel. The noncombustible matter associated with coal distinguishes
it from the liquid fuels and is the source of inorganic sulfur and most of
the trace elements. In liquid fuels the trace elements are present
primarily as oil soluble compounds or associated with the colloidal
suspensions commonly present in them.
3.1. Contaminants in Solid Fuels
In coal, the nitrogen contaminants are present primarily as
organic compounds which are part of the three-dimensional carbon skeletal
-------
145
TABLE 60. ELEMENTAL ANALYSIS OF TYPICAL FUELS
Weight Percent
Coal (mf)
Subbituminous
(Big Horn)
Bituminous
(Pittsburgh)
Coal Liquids
(Big Horn)
(Pittsburgh)
Shale Oil
Utah Asphalt
Petroleum Crude
C
69.2
78.7
89.2
89.1
80.3
82
85
H
4.7
5.0
8.9
8.2
10.4
11
14
0
17.8
6.3
1.03
1.5
5.9
3
1
N S Ash
1.2 0.7 6.5
1.6 1.7 6.9
0.4 0.04 >1
0.8 0.2 >1
2.3 1.1
2 2
1 1 <1
H/C
(Atomic)
0.81
0.76
1.20
1.10
1.55
1.61
1.98
(Pennsylvania)
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146
structure that makes up the organic matter of coal. Indirect evidence
suggests that the nitrogen compounds exist as both alkyl and aryl
derivatives of amines, quinolines, and carbazoles. The sulfur in coal is
present both as organic and inorganic compounds. The organic sulfur
compounds are also part of the carbon skeleton of coal and consist of both
alkyl and aryl derivatives of thiols, thioether, disulfides, and thiophene.
The major sources of inorganic sulfur in coal are the pyrites and the
sulfate salts. Neither of these sources are part of the organic portion
of coal. Pyrites and other mineral matter exist in raw coal as discrete
phases ranging in size from gross inclusions in the coal seam to micron-size
particles disseminated throughout the organic matter of coal. Trace
elements that exist in raw coal can be categorized into those found
principally with the organic matter of coal and those present principally
in the mineral matter associated with coal. However, there are some trace
elements that exhibit a dual role and are found in both components. Trace
metals and metalloids exist as complexes of the organic oxygen, nitrogen,
and sulfur compounds or as crystal-lattice impurities in the mineral matter
associated with coal seams. Nonmetallic trace elements are found primarily
as part of the inorganic mineral impurities. Some, such as phosphorus,
are found also in the organic part of coal.
It can be concluded that nonuniform distribution of impurities
exists not only from one coal seam to another but also within the coal seam.
Despite this limitation, intrinsic centers of sulfur and nitrogen contamination
have been identified. The organic sulfur and nitrogen compounds are uniformly
distributed in the organic part of the coal, as are the trace elements
associated with it. Inorganic sulfur and the trace elements associated
with the mineral matter in the coal are considered to be variable with the
source of coal. However, with the use of modern mining and coal-preparation
techniques, a more uniform product is available for use.
3.2. Contaminants in Liquid Fuels
In petroleum and tar sand oil, and to some extent in shale oil,
the majority of the organic sulfur and nitrogen compounds found in the
asphaltene and resin fractions are similar to those found in coal. In
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147
petroleum nearly 50 percent of these fractions consist of molecules in
the 4,000 to 8,000 molecular-weight range. Between 10 and 50 percent of
the nitrogen and 3 and 35 percent of the sulfur in petroleum are found in
these fractions. Similar distributions are indicated for tar sand oils.
However, shale oil, because it is formed by thermal degradation of the
kerogen in oil shale during retorting, contains much less asphaltenes
than either petroleum or tar sand oil. As a result, the organic sulfur
and nitrogen contaminants are found mostly in the resin fraction of shale
oil. Although coal liquids are known to contain resin and asphaltene
fractions, the liquefaction process by the addition of hydrogen to coal
also reduces the sulfur content (and at times the nitrogen content) to
low levels. The contaminants in coal liquids remaining after removal of
the solids are present as organic sulfur and nitrogen compounds that are
difficult to remove and are usually found in the higher molecular-weight
asphaltene and resin fractions of coal liquids.
It can be concluded that in the liquid fuels, the intrinsic centers
of sulfur and nitrogen contamination are found in the colloidal suspensions,
otherwise known as asphaltenes, and in the more soluble resins, both of
which make up anywhere from 1 to 43 percent (but more commonly less than
6 percent) of the petroleum, about 37 percent of tar sand; oils that have
been characterized, 13 to 71 percent of the shale oil, and 10 to 30 percent
of the coal liquids. However, the molecular weights of the asphaltenes and
resins in petroleum crudes are greater than those in synthetic crudes, as
shown in Tables 6 and 53. Trace elements in petroleum, tar sand oil, and
shale oil are present as oil soluble compounds (usually as porphyrin or
porphyrin-like complexes) and adducts to molecules making up the resins
and asphaltene fractions. Alkyl and aryl derivatives of the metal or
metalloid elements that do not exist as complexes or salts of organic acids
make up the other group of oil soluble compounds. Nonmetallic trace elements
such as chlorine and bromine are present usually as suspension materials in
the oil.
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148
3.3. Distribution of Contaminants in Fuels
3.3.1. Sulfur and Nitrogen Contaminants
The distribution of sulfur and nitrogen contaminants in the fuel
types is shown in Table 61. Large variations in the total sulfur and
nitrogen content exist between the fuels and within a fuel type. Coal is
unique with respect to the other fuels in that sulfur is also present in
the form of pyrites. The organic sources of sulfur in coal have been
determined indirectly primarily from studies on depolymerized coal. The
exact nature of organic sulfur in solid coal can only be surmised from
these studies. There is strong evidence that mercaptans, sulfides, and
disulfides are present in the coal structure. The same type of compounds
are usually present in tar sand oils and petroleum but not in coal liquids
and shale oils. Thiophenes and benzothiophenes are known to be present in
coal liquids and shale oil as well as in tar sand oil and petroleum.
The amount of total nitrogen contained in fuels is the highest
in coal and shale oil. Little is known for certain about the types of
nitrogen compounds contained in coal. The characterization of the nitrogen
compounds in coal has been determined indirectly from studies on coal tars
or depolymerized coal. There is good evidence that pyridine, quinoline,
acridine, indole, carbazole, and porphyrins or their derivatives acccount
for the nitrogen in solid coal. Thus, it may be concluded that the
nitrogen in coal is present as aromatic compounds. Quinolines, pyrroles,
indoles, carbazoles, acridines, and porphyrins are present in coal liquids,
shale oil, tar sand oil, and petroleum. Benzamides have been found in
shale oil and petroleum. The porphyrin compounds may contain trace metals
as coordination compounds.
Values for the amount of each type of organic sulfur and nitrogen
compound are available for only a limited number of fuels and then for only
a few sources of the fuel type (e.g., petroleum). Others have not yet been
characterized or are in the process of being characterized (e.g., coal
liquids, shale oils, and tar sand oils). Until additional data are made
available, a quantitative comparison would be difficult. But it has been
-------
TABLE 61. DISTRIBUTION OF S AND N CONTAMINANTS IN FUELS
Fuel
Contaminants
Parent
Type and Source Structure
Sulfur, Total
Inorganic
Pyrites FeS,
Organic
Mercaptans R-SIP6'
Sulf ides R-S-R^
, .
Thiophenes l^jJl
Benzothiophenes ^j) f^i
Nitrogen. Total
Basic
^^sz^.
Qu inclines kj*s\r
Acridines (^If^f*)
Nonbasic
Pyrroles ^tir
Indoles ^>r
Carbazoles UsJL^JL^
Benzamides Q-CONHZ
(a) Colorado shale oil.
(b) Tar sands including Utah tar sands.
(c) 48 percent of total sulfur, a mean
value for U.S. coals.
Coal
0.4-13%
x(c,d)
x(f)
x(f)
(f\
xw
x(f)
1-2 . 1%
(f\
X1 }
(f)
xw
x(f)
x(f)
x(f)
x(f)
x(c,f)
Coal
Liquids Shale
Primary Oil(a
<1% 1.1%
X X
X X
>1% 2.3%
X
X X
X
X X
X X
X X
X X
(d) Represents the
contaminant in
(e) R is an alkyl
(f) Inferred from
Tar
. Sand, .
Oil^
0.2-6.3%
X
X
X
X
<1%
X
X
X
X
X
presence of the
the fuels.
or aryl group.
studies on coal
Petroleum
Crude
0.1-5%
X
X
X
X
«1%
X
X
X
X
X
X
tar,
VO
depolymerized coal, and liquefied
coal.
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150
determined that the total nitrogen content of U.S. coals (maf) varies in
the range of 1 to 1.9 weight percent for lignite and high volatile
bituminous coal, respectively. Though this amount of nitrogen appears
small, the nitrogen is present as an integral part of the chemical structure
of coal.
3.3.2. Trace Elements
The trace elements in the fuels covered in this review can be
categorized as to their association either with the organic matter making
up the fuel or the mineral matter associated with it. As shown in Table 62,
coal, by virtue of its large mineral matter content, has most of the trace
elements closely associated with these minerals. Petroleum and tar sand
oils by comparison contain much less mineral matter and hence less trace
elements associated with them (e.g., those elements commonly associated with
brines and suspended sands and clays). Shale oils contain finely divided
shale minerals carried over during retorting and contain trace elements
found in the shale minerals. In the case of the formation of liquids from
coal, the trace elements associated with the mineral matter in coal remain
insoluble and are removed along with the mineral matter.
The trace elements more closely associated with the organic
matter in coal are shown in Table 63. These trace elements in coal are
held in the organic matrix as complexes of organic compounds (containing
oxygen, sulfur, or nitrogen), porphyrins or amino acids, or as alkyl- or
aryl-derivatives. Most of the trace metals found in petroleum and tar
sand oils are found in the organic phase as oil soluble compounds. They
exist primarily as complexes, organic acid salts, and alkyl- and aryl-
derivatives. Shale oil also contains a large number of oil soluble trace
elements which may have formed during retorting. Coal liquids would be
expected to contain in solution those elements most closely associated with
the organic part of coal or those that enter into solution during the
liquefaction process.
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151
TABLE 62. TRACE ELEMENTS ASSOCIATED WITH MINERAL MATTER
IN SOLID AND LIQUID FUELS
Mineral (Percent of Total)
Trace Elements
Coal
Shales, Kaolins (52)
Sulfides, Pyrites (25)
Carbonates (9)
Chlorides (0.1)
Quartz (1-20)
Apatite
Sulfates
Petroleum (Tar Sand Oils)
Chloride (Trace)
Quartz (Trace)
Shales, Kaolins (Trace)
Shale Oils
Shale Minerals
Coal Liquids (Speculation)
Removed with
Mineral Matter
Si, Al, Ti, K (B, Cu, F, Hg, Sn, V)
(a)
Fe, Zn, Cd, Pb, Ni, Cu (Hg, B, As, Be,
Sb, Ge)(a)
Ca, Mg, Mn (B, Cd, Mo, Se, V) (a)
Na, K, Cl (Br, I, Mg, Ca) ^
Si (B, Cr, Mn, Cd, Mo, Ge, Se, V, Zn)
Ca, P, F (As, V, Cl, Mn, Ce) ^
Fe, Ca, (Mn)
(a)
(a)
Na, K, Mg, Ca, Cl, Br, I (Mn)
Si
Si, Al, K
As, Ba, B, Cu, Cr, Pb, Li, Mo, Mn
P, Se, Sr, Tl, Ti, V, Zn, Ag, Au
Hg, Zn, Zr, Cd, As, Pb, Mo, Mn
(Co, Ni, Cr, Se, Cu, Sb, V, Ti, Ga, P)
(b)
(a) Elements in parentheses are known to have high correlation with minerals
but not necessarily detected with minerals.
(b) The elements in parentheses are more commonly found with mineral matter but
are also found in organic portion of coal.
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152
TABLE 63. TRACE ELEMENTS ASSOCIATED WITH ORGANIC MATTER
OF SOLID AND LIQUID FUELS
Derivative
Trace Elements
Coal
Complexes of 0,N,S Ligands i
and Organic Acid Salts
Porphyrin , Amino Acids
Alkyl- or Aryl-
Petroleum (Tar Sand Oils)
Porphyrin
Nonporphyrin
Tetradentate Complexes (S,N,0)
Alkyl-or Aryl-
Organic Acid Salts
Unknown
Shale Oils
Oil Soluble
Coal Liquids (Speculation)
Liquid Soluble (?)
> 50 percent Organic Affinity
Ge, Be, B, Ti, U (Ga, Y, La, Ni, Co,
Zn, V, Ca, Al, Si, P) W
V, Ni, Cu, Fe
Ge (P, Se)(a)
Ni, V
Ni, V, Fe, Co, Zn, Hg, Cr, Cu
V, Ni, Fe, Cu, Co, Cr (Cl)
Hg, Sb, As
Na, As, Hg, Fe, Sb (Mo)
Se, I
(b)
Sb, Be, B, Cd, Ca, Cr, Co, Cu,
', Ge, Pb, Mg, Mn, Hg, Mn, Mo
:, Se, Na, Sr, Te, Ti, V, Y, Zn
Ge, Be, Ga, B, Ti (P, U, V, Sb, Co, Ni,
Cr, Se, Cu) (c>
(a) Elements forming compounds to a lesser extent are in parentheses.
(b) Cl" suggested as counter ion.
(c) Elements in parentheses are more closely associated with organic part of
coal but are also present in mineral matter.
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153
Of the trace metals known to be present in coal, V, Ni, Ge, Be,
B, Ti, Ga, and Sb have been shown to be closely associated with organic
part of coal. Of these elements, only Ni, V, B, Ti, Ga, and Sb have been
reported in the crude oils for which analyses were given. Table 64
presents a correlation of the trace elements with their organic affinity
in coal and with their occurrence in petroleum. Germanium and berylium
(and perhaps phosphorus), which have strong organic affinities in coal,
are not reported in many of the world petroleums. Conversely, the number
of trace elements found dissolved in petroleum far exceeds those closely
associated with the organic part of coal. Arsenic is a good example. In
some oils, it is present as oil soluble compounds, some of which are water
hydrolyzable, while in coal arsenic exists predominantly with mineral matter
(close to zero organic affinity). In shale oil, arsenic is present as an
oil soluble and volatile compound. Other metals such as Na, Cu, Co, Fe, Hg,
and Cr follow a similar distribution pattern in petroleum and coal as arsenic
does.
3.4. Potential for Removal of Contaminants
3.4.1. Contaminants Present as Discrete Phases
The potential for the removal of contaminants that are present
as a discrete phase such as pyrites and other mineral matter in coal or
brine in petroleum is technically and economically feasible. In the case
of coal, size reduction is needed to free the mineral occlusions. However,
since the pyrite in some coals is present in the micron size range, there
would appear to be a practical limit in the size that coal can be pulverized to
expose the pyrite. Density differences should provide a means for their
separation. Similar reasoning might apply to other mineral phases dispersed
in the coal. Pyrite might also be removed by selective chemical attack.
Separation of brine end water soluble salts from petroleum would require the
addition of water and separation of the two phases.
-------
TABLE 64. METAL CONTAMINANTS ASSOCIATED WITH ORGANIC MATTER IN
COAL AND COMPARED TO THEIR PRESENCE IN PETROLEUM
Occurrence in Percent^3)
of 13 Coals
EPA Sample (a) ppm
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155
3.4.2. Contaminants Present as Part of Fuel Structure
Sulfur, nitrogen, and trace elements that are present in the
fuel as part of the organic structure will require severe methods for their
selective removal. The potential for their removal from a liquid fuel would
be greater than from a solid fuel because of contact problems between a
reagent and solid fuel. One alternative might be to remove the molecules
containing the sulfur, nitrogen, or trace element by reaction with a
reagent and subsequent removal from the fuel. For simple alkyl compounds
this would seem practical as the weight of sulfur or nitrogen removed would
be comparable to the.weight of the original compound.- However, for
compounds such as dibenzothiophene or carbazole the sulfur and nitrogen
contaminant is only 17 and 8 percent, respectively, of the compound weight
and the associated fuel carbon losses would not make the approach practical.
Such an approach would first require the conversion of coal to a liquid
either by hydrogenation or pyrolysis. Another alternative might be to
disrupt the molecular structure of the molecules containing the sulfur
and/or nitrogen by (1) hydrogenation to release the sulfur and nitrogen
as H_S or NIL., (2) selective chemical attach and subsequent liberation of
the contaminant, or (3) partial oxidation and gasification followed by gas
purification. Such approaches would appear to be suited for both solid and
liquid fuels.
The choice of the approach to remove sulfur and nitrogen contained
in organic compounds from solid or liquid fuels would thus depend on
whether the desired clean final product is to be a liquid or a gas. Removal
of these same impurities to yield a clean solid fuel would be highly desirable
yet appears to be difficult to accomplish.
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156
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(121) Bowman, C. W., "Molecular and Interfacial Properties of Athabasca Tar
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(123) Kaminsky, V. P., and Nagy, E., "Athabasca Oil Sands: Recovery Methods",
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(125) Thomas, R. D., and Lorenz, P. B., "Use of Centrifugal Separation to
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(126) Shah, K. R., Filby, R. H., and Haller, W. A., "Determination of Trace
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(127) Ibid., Part II, p. 413 (1970).
(128) Filby, R. H., and Shah, K. R., "Neutron Activation Methods for Trace
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(130) Ordogh, M., Belazs, A., Reti, S., and Szabo, E.. "Determination of I,
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(131) Gordon, S. A., Menkovskii, M. A., and Kler V R »
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Geokhimiya 9, p 1399 (1974), CA82, r 61491A (1975).
(133) Wilson, TT^Kczewskl, C. Z., a~nd Jones, P., "Determination of Fluorine
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(145) Helm, R. V., Latham, D. R., Ferrin, C. R., and Ball, J. S., "Distribution
of Nitrogen Compounds in Wilmington, Ca. Petroleum", Ind. Eng. Chem.,
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(146) Sugihara, J. M., Branthaver, J. F., Wu, G. Y., and Weatherbee, C.,
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(148) Hodgson, G. W., Baker, B. L., and Peake, E., "The Role of Porphyrins
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(149) Dwiggins, Jr., C. W., Willcox, K. W., Doughty, D. A., and Heemstra, R. J.,
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(150) Yen, T. F., "Vanadium and Its Bonding", in Reference 126, p 167.
(151) Erdman, J. G., and Harju, P. H., "Capacity of Petroleum Asphaltenes
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(153) Ebel, R. H., "Recent Advances in Fuel Desulfurization Technology",
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(154) Drushel, H. V., "Analytical Characterization of Residual and Hydrotreated
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(155) Thompson, C. J., et al., "Characterization of Non-hydrocarbon Constituents
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(156) Sapiro, M. D., Stomenko, A. E., and Kulik, A. P., "Determination of
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(157) Al-Shahristani, H., and Al-Attiya, M. J., "Trace Elements in Iragi Oils
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108149 s (1974).
(158) Gulyaeva, L. A., and Pumanova, S. A., "Petroleum Trace Elements, Relics
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(159) Champlin, J. B. F., and Dunning, H. N., "Geochemical Investigation
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(160) Gleim, W. K. T., Gastsis, J. G., and Perry, C. J., "Occurrence of
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168
TECHNICAL REPORT DATA
(Please read Instructions on the reverse before completing)
1. REPORT NO. 2."
EPA-600/2-76-ma
4. TITLE AND SUBTITLE
Fuel Contaminants: Volume 1. Chemistry
7. AUTHORIS)
I E . J. Mezey , Sur jit Singh , and D. W. Hissong
9. PERFORMING ORGANIZATION NAME AND ADDRESS
Battelle- Columbus Laboratories
505 King Avenue
Columbus, Ohio 43201
12. SPONSORING AGENCY NAME AND ADDRESS
EPA, Office of Research and Development
Industrial Environmental Research Laboratory
Research Triangle Park, NC 27711
3. RECIPIENT'S ACCESSION NO.
5. REPORT DATE
July 1976
6. PERFORMING ORGANIZATION CODE
8. PERFORMING ORGANIZATION REPORT NO.
10. PROGRAM ELEMENT NO.
EHB529
11. CONTRACT/GRANT NO.
68-02-2112
13. TYPE Of REPORT AND PERIOD COVERED
Task Final; 6/75-2/76
14. SPONSORING AGENCY CODE
EPA-ORD
is. SUPPLEMENTARY NOTES Project officer for this report is W.J.Rhodes, mail drop 61,
919/549-8411, ext 2851.
reviews information on the characteristics of solid and liquid
fuels. Specifically, it deals with the chemical and physical characteristics of compo-
nents of the fuel which are sources of sulfur, nitrogen, and trace element pollutants
when that fuel is utilized. The review suggests that at least part of the sulfur and
most of the nitrogen originate from compounds common to the fuels reviewed (coal,
petroleum, tar sand oil, and shale oil). These are primarily organic sulfur and
organic nitrogen compounds. For liquid fuels, it was concluded that intrinsic_qenters
of sulfur and nitrogen contamination are found in the colloidal suspensions commonly
known as asphaltenes and the more soluble resins. Trace elements are present as
oil-soluble compounds in petroleum, tar sand oil, and shale oil. In coal, it was
concluded that the nitrogen contaminants are present as organic compounds and that-'
the sulfur is present both as organic and inorganic compounds. Trace elements in
coal were categorized into those found principally with the organic matter of coal
and those found present principally in the mineral matter associated with coal.
J17. KEY WORDS AND DOCUMENT ANALYSIS
(a. DESCRIPTORS
Pollution Sulfur
1 Fuels Nitrogen
Contaminants Trace Elements
Chemistry
I Chemical Properties
Physical Properties
|18. DISTRIBUTION STATEMENT
Unlimited
b.lDENTIFIERS/OPEN ENDED TERMS
Pollution Control
Stationary Sources
Solid Fuels
Liquid Fuels
19. SECURITY CLASS (This Report)
Unclassified
20. SECURITY CLASS (This page)
Unclassified
c. COSATI Field/Group -
13B 07B
21D
06A,06P
07
07D
21. NO. OF PAGES
177
22. PRICE
EPA Form 2220-1 (S-73)
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