I
Industrial Manufacturing Process Quality Control
Evaluation Series • 01/79-04
Toxic Pollutant
Identification:
NITROBENZENE/ANILINE MANUFACTURING
U.S. ENVIRONMENTAL PROTECTION AGENCY
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EPA - IMPQCE Series
TOXIC POLLUTANT IDENTIFICATION:
NITROBENZENE/ANILINE MANUFACTURING
Ol/fS-04
January 1979
by
W. LOWENBACH
J. SCHLESINGER
J. KING
The MITRE Corporation
METREK Division
McLean, Virginia 22101
Grant No. 805620 \
Technical Advisor: Paul E. desRosiers
Project Officer: David R. Watkins, IERL-CI
U.S. ENVIRONMENTAL PROTECTION AGENCY
INDUSTRIAL AND EXTRACTIVE PROCESSES DIVISION
OFFICE OF ENERGY, MINERALS AND INDUSTRY
OFFICE OF RESEARCH AND DEVELOPMENT
WASHINGTON, D.C. 20460
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ABSTRACT
A detailed description of nitrobenzene/aniline manufacture and
pollution control technology is presented. Included is a compre-
hensive discussion of the reaction mechanism, with a summary of
potential pollutants generated from feedstock impurities and
significant side reactions. A generic process configuration is
formulated, from which specific point source discharges are identi-
fied. From this perspective, current wastewater treatment and
disposal practices, as well as alternative methods of treatment,
are reviewed and potential treatment options recommended.
iii
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TABLE OF CONTENTS
LIST OF FIGURES
LIST OF TABLES
EXECUTIVE SUMMARY x
I. INTRODUCTION 1
Legislative and Regulatory Background 1
Objectives and Approach 4
Overview of Nitrobenzene/Aniline Manufacture 8
Process Technology 8
Market Outlook 10
II. NITROBENZENE/ANILINE MANUFACTURE 14
Reaction Conditions 14
Feedstock Composition 16
Reaction Mechanisms 21
Nitration of Benzene 22
Hydrogenation of Nitrobenzene 25
Catalytic Hydrogenation 30
Dissolving Metal Reductions 34
Mechanism of Catalysis 37
By-Product Formation 42
Significant Side Reactions 44
By-Products from Feedstock Impurities 57
Process Configuration for Nitrobenzene/Aniline
Manufacture 65
Generic Nitration Processes 65
Generic Nitrobenzene Reduction Processes 73
Catalytic Processes 73
Batch Processes 79
III. INDUSTRIAL WASTEWATER MANAGEMENT 83
Introduction 83
Current Treatment of Wastewater from Nitrobenzene/
Aniline Manufacture 86
Wastewater Characteristics 86
Federal and State Discharge Requirements 88
Current Industrial Practices 93
Future Regulatory Concerns 96
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TABLE OF CONTENTS (Concluded)
Page
IV. METHODS OF WASTEWATER TREATMENT 99
Introduction 99
Biological Treatment 101
Physical Pretreatment and Separation Practices 107
Liquid-Liquid Extraction 107
Theory and Process Description 108
Application to Nitrobenzene/Aniline Manufacture 110
Gas Liquid Operations 112
Steam Stripping 113
Adsorption on Granular Activated Carbon 115
Theory and Process Description 115
Waste Stream Applications 122
Adsorption on Synthetic Resins 125
Membrane Processes 129
Dialysis 131
Reverse Osmosis (RO) 135
Combination and Alternative Techniques 137
V. RECOMMENDED TREATMENT ALTERNATIVES 143
Introduction 143
Point Sources of Potential Pollutants 144
Nitration of Benzene 144
Point No. 1 144
Point No. 2 145
Point No. 3 145
Point No. 4 146
Point No. 5 146
Reduction of Nitrobenzene 148
Point No. 6 148
Point No. 7 149
Point No. 8 ' 149
Point No. 9 149
VI. SUMMARY AND CONCLUSIONS 151
REFERENCES 155
BIBLIOGRAPHY 169
vi
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LIST OF FIGURES
Figure Number Page
1 Nitrobenzene and Aniline Markets 12
2 Proposed Reaction Mechanism for the Hydro-
genation of Nitrobenzene Over Copper Catalysts 32
3 Proposed Mechanism for Dissolving Metal
Reduction of Nitrobenzene 35
4 Continuous Liquid Phase Nitration of
Benzene 68
5 Tubular Reactor for Nitrobenzene Manufacture 71
\
6 Continuous Vapor Phase Production of Aniline 74
7 Continuous Liquid Phase Production of
Aniline 78
8 Batch Production of Aniline 80
9 Significant Pollutants from Nitrobenzene/
Aniline Manufacture 82
10 Aniline Wastewater Treatment by Steam
Stripping 114
j
11 Typical Carbon Adsorption Column Configur-
ation 118
12 Primary Adsorption Zone and Resulting Break-
through Curve 120
13 Adsorption of Nitrobenzene and Aniline on
Carbon as a Function of Influent
Concentration 124
14 Adsorption of p-Nitrophenol as a Function
of pH 128
15 Potential Treatment Options for Nitro-
benzene/Aniline Wastewaters by Point
Sources 153
vii
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LIST OF TABLES
Table Number
I
II
III
IV
VI
VII
VIII
IX
XI
XII
XIII
XIV
Page
Consumption Pattern of Aniline 11
Analysis of Pure Grade Benzene 17
Product Specifications for Sulfuric and
Nitric Acids 18
Typical Compositions of Various Hydrogen
Feed and Product Streams 20
Organic By-Product Yield From Mononitration
of Aromatic Hydrocarbons 45
Composition of Acidic Organic By-Products
From Nitration of Toluene 60
Summary of Pollutants From Nitrobenzene/
Aniline Manufacture 66
Characterization of Raw Waste Loading From
Nitrobenzene/Aniline Manufacture 87
BPT Effluent Limitations and New Source
Standards of Performance for Aniline
Manufacture 91
Major U.S. Nitrobenzene/Aniline
Manufacturers 94
Biological Studies of Nitrophenols, Nitro-
benzenes, and Aniline-Containing
Wastewater 102
Efficiency of Organic Solvents in Removing
Phenolic Nitration By-Products 111
Aniline Sorption by Ion Exchange Resins 130
Aniline and Water Transport Through
Polymeric Membranes 133
viii
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LIST OF TABLES (Concluded)
Table Number Page
XV Pervaporation Study: Nitrobenzene
Permeability Coefficients 134
XVI Summary of Foreign Applications of
Physical-Chemical Treatment to Waste-
waters Containing Nitrophenols, Nitro-
benzenes, and Aniline 142
ix
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EXECUTIVE SUMMARY
The discharge of a toxic substance by an organic chemical
manufacturer, may have irreversible effects on the environment. The
extent of such effects will depend on the persistence and mobility of
the compound. Under the Clean Water Act of 1977, the Environmental
Protection Agency (EPA) must establish effluent limitations for 65
toxic pollutants (and/or classes of pollutants) in terms of the best
available technology. As the Clean Water Act of 1977 does not
preclude consideration of other pollutants, the EPA is currently
working from a list of 129 chemicals (see Appendix III).) However,
the establishment of such standards that are not only equitable to
industrial manufacturers, but more importantly that will prevent
further deterioration of the environment, is an exceedingly difficult
task. As a first step, EPA must thoroughly understand the manufactur-
ing process and available control technologies so that, ultimately,
attainable standards may be set.
Because nitrobenzene and aniline are major organic intermediates
(the annual nameplate production capacities for aniline and nitroben-
zene are 730 and 1010 million pounds, respectively) and in light of
current toxicity data, their manufacture potentially represents a
significant hazard to both man and his environment. For the above
reasons, this study is specifically directed toward the assessment of
toxic pollutant generation from the manufacture of nitrobenzene/aniline
and possible methods of control.
Currently, nitrobenzene production throughout the world is based
on nitration of benzene in the liquid phase with a mixture of nitric
and sulfuric acid:
HN03
H2S04
The bulk of aniline production is based upon nitrobenzene
reduction, generally by one of three methods: catalytic hydrogena-
tion.in the vapor phase, catalytic hydrogenation in the liquid phase,
and by dissolving metal reduction. Of these methods, vapor phase
catalytic hydrogenation is most commonly used:
N02 NH2
Catalyst f^^
+ 3 H2 + 2 H20
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Current domestic producers of nitrobenzene/aniline are American
Cyanamid Company (Bound Brook, New Jersey, and Willow Island, West
Virginia), E.I. duPont de Nemours & Company (Beaumont, Texas, and
Gibbstown, New Jersey), First Mississippi Corporation, a subsidiary of
First Chemical Corporation (Pascagoula, Mississippi), Mobay Chemical
Corporation (New Martinsville, West Virginia), Rubicon Chemical
Corporation (Geismar, Louisiana), and Mallinkrodt, Inc. (aniline
only—Raleigh, North Carolina).
In Section II, a detailed description of nitrobenzene/aniline
manufacture has been presented. Included is a comprehensive discus-
sion of the reaction mechanism, with a summary of potential pollutants
generated from feedstock impurities and significant side reactions.
The liquid phase nitration of benzene involves generation and
the subsequent attack of the nitronium ion to form the benzenonium
ion. This species reacts further with any base present to form
nitrobenzene and the protonated base. Alternatively, the benzenonium
ion may react with water to form nitrophenols. Catalytic reduction
of nitrobenzene involves adsorption on the catalyst surface through
both oxygen atoms; by hydrogen addition to an oxygen atom to yield,
in a series of rapid steps, water and nitrosobenzene; a second
addition of hydrogen to yield an adsorbed nitrene and water; and
finally, reaction of the nitrene with hydrogen to yield aniline.
Alternatively, intermediate species may react to form azepins,
azoxybenzene, azobenzene, N-phenylaniline, and complex nitrogen-
containing polymers.
A generic process configuration for nitrobenzene/aniline manu-
facture has been formulated, identifying a total of nine point source
discharges. Specifically, two maj'or process waste streams are
generated; the column overhead product from sulfuric acid recovery
during nitrobenzene manufacture and the extraction column bottoms
during aniline manufacture. Other significant point sources include
the still bottoms from nitrobenzene purification, nitrobenzene wash
water, and the still bottoms from aniline purification.
A review of current wastewater treatment and disposal practices
is presented in Section III, with regard to current discharge require-
ments and future regulatory concerns. At this time, there are no
effluent limitations specific to point source discharge from nitroben-
zene/aniline manufacture. As a result, a wide variety of treatment
techniques are applied to the treatment of .nitrobenzene/aniline
manufacturing wastes. First Mississippi Corporation, a subsidiary of
First Chemical Corporation, completed installation of both steam
stripping (allowing for counter-current extraction) and granular
activated carbon columns during 1977. Carbon adsorption is also
employed in combination with biological treatment by both duPont
xi
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(Beaumont, Texas, facility) and Mobay Chemical Corporation for
removal of dissolved organics. At their Gibbstown, New Jersey,
facility, duPont provides both organic extraction and stripping
units, while American Cyanamid and Mallinkrodt rely on biological
treatment for removal of organic pollutants. Only Rubicon Chemicals
practices deep well disposal of nitrobenzene/aniline process waste
streams.
Section IV consists of a detailed discussion of pollution abate-
ment alternatives for nitrobenzene/aniline manufacture. Typically,
the treatability of a waste stream is evaluated in terms of its
biodegradability. However, as the nature of the organic waste load
from nitrobenzene/aniline manufacture is conducive to physical
treatment (i.e., activated carbon adsorption, liquid-liquid extrac-
tion, steam stripping), Section IV is divided into three major subsec-
tions: (1) biological treatment; (2) physical treatment; and (3)
combinations of selected treatment technologies.
Section V presents a point source-by-point-source summary of
potential pollutants from nitrobenzene/aniline manufacture and
recommends treatment alternatives for each stream. Major recommenda-
tions (which are based solely on the efficiency of a process to treat
a waste stream, and exclude any analyses of capital, operation and
maintenance, and energy costs) are directed toward the cleanup of
the column overhead product from sulfuric acid recovery during
nitrobenzene manufacture and the extraction column bottoms during
aniline manufacture. Whatever method is used for acid purification,
the toxic effluent stream is best treated by activated carbon adsorp-
tion. The aniline water is best treated by a counter-current extrac-
tion with nitrobenzene. Alternatively, the organic contaminants
could be recovered by steam stripping techniques. In either case,
the final effluent stream should receive further purification by
adsorption on activated carbon.
In summary, this report outlines some of the steps that must be
taken before BAT effluent limitations can be rationally promulgated
for nitrobenzene/aniline wastewaters.
Recommendations for further studies include:
• EPA verification, from sampling of actual process wastewaters,
of all pollutant predictions and concentrations.
• Extension of this pollution prediction and abatement method-
ology to additional compounds exemplifying other unit proces-
ses such as amination, chlorination, oxidation, etc.
xii
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EPA funding of pilot scale studies for determination of the
technical practicability of the recommended treatment alterna-
tives.
An economic analysis of viable treatment alternatives (with
regard to best available technology economically achievable).
Demonstration of BAT in an EPA-industry jointly funded proj-
ect.
xiii
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SECTION I
INTRODUCTION
LEGISLATIVE AND REGULATORY BACKGROUND
While the hazards of certain toxic water pollutants have long
been recognized, the Environmental Protection Agency has histori-
cally placed priority on controlling conventional water quality para-
meters such as pH, suspended solids and biochemical oxygen demand.
Yet specific waterborne pollutants are coining increasingly into
prominence; headlines tell of widespread Kepone contamination of
the James River in Virginia, carbon tetrachloride spills in the Ohio
River,.and contamination of the Hudson River from dumping of poly-
chlorinated biphenyls. Furthermore, seventy-eight cities have found
significant quantities of industrial chemicals such as PCB's, cyanides,
phenols, and carcinogenic chlorinated hydrocarbons in drinking water
supplies (Becker, 1977).
There is no single comprehensive water pollution control statute;
indeed, toxic substances are generally regulated under no less than
nine different federal laws - the Clean Water Act of 1977 (PL 95-217*);
the Safe Drinking Water Act (PL 93-523); the Marine Protection, Re-
search, and Sanctuaries Act (PL 92-532, also known as the Ocean
Dumping Act); the Resource Conservation and Recovery Act (PL 94-580,
also known as the Solid Waste Act); the Federal Insecticide, Fungi-
cide, and Rodenticide Act (PL 92-516); the Toxic Substances Control
*
This act supercedes the Federal Water Pollution Control Act of
1972, PL 92-500.
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Act (PL 94-469); the Hazardous Materials Transportation Act (PL 93-
633); the Ports and Waterways Safety Act (PL 92-340); and the Atomic
Energy Act of 1954 (PL 83-703). Thus, there is a complex inter-
relationship of federal statutes dealing with various aspects of
toxic substance control. More significant, perhaps, is that because
each of these laws takes a somewhat different approach to regulation
of water quality, areas of jurisdiction often overlap or intersect.
Undoubtedly, the Federal Water Pollution Control Act (PL 92-500)
was initially intended as EPA's primary regulatory tool for control
of toxic discharges to the aquatic environment. Section 307(a)
specifically required that a list of toxic pollutants be published
and limits for the discharge of those pollutants be established,
taking only into account the substance's impact on the environment.
However, nearly four years after the passage of the Act, Section
307(a) had yet to be implemented. Thus, in June of 1976 as a result
of civil actions brought by three environmental interest groups,
the EPA signed a consent agreement which required the immediate
establishment of Section 307(a) limitations for six particularly
toxic chemicals (four pesticides - aldrin/dieldrin, DDT/DDD/DDE,
endrin, and toxaphene, plus benzidine and polychlorinated biphenyls).
Additionally the EPA agreed to write effluent limitations for 65
other chemicals (and/or classes of chemicals) into best available
technology (BAT) effluent guidelines for NPDES* permits (authorized
*
National Pollutant Discharge Elimination System
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under Section 302 and 304 of PL 92-500) for 21 industries (see
Appendices I and II); these limitations were to have gone into
effect by 1983.
As a result of the shortcomings of PL 92-500 for the control
of toxic discharges to public waters,* Congress has sought to correct
these deficiencies by the Clean Water Act of 1977 which embodies the
major points of the consent agreement. Specifically under Section 307
of this legislation, the Administrator must establish effluent
limitations for 65 toxic pollutants in terms of the best available
technology economically achievable for the applicable category or
class of point sources established in accordance with sections 301(b)
(2)(A) and 304(b)(2) as soon as practicable, but no later than July
1, 1980 (see Appendices I and II for the list of toxic pollutants and
applicable categories respectively). In seeking to provide a rea-
sonable amount of flexibility for the protection of the environment
from new and unforseen hazards, Section 307 does not, however, pre-
clude consideration of other pollutants. Thus, the EPA is currently
working from a list of 129 chemicals (see Appendix III). Irrespective
of the number of pollutants, to be able to promulgate these regulations
the Environmental Protection Agency must at a minimum:
• Predict or otherwise measure discharge rates for each
pollutant;
• Provide supporting data on each pollutant's health and
ecological effects;
For a brief review of the difficulties encountered by EPA in im-
plementing Section 307(a) of PL 92-500, see Ward (1977).
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• Evaluate control technology capabilities; and
• Recommend ambient water quality criteria levels.
OBJECTIVES AND APPROACH
Much of the information required by the EPA for promulgation
of practicable regulations in accordance with the Clean Water Act
of 1977 does not yet exist. Pollutant discharge rates for each of
the hundreds of processes in the 21 targeted industries is not
readily available; indeed, general analytical protocols have yet
to be developed for a substantial number of the specified pollutants.
Moreover, effective methods of wastewater treatment for each of
the 65 pollutants have yet to be defined, much less demonstrated as
BAT.
Thus, the first task in meeting the requirements of the Clean
Water Act of 1977 is to develop the data necessary to promulgate
practicable regulations. Nonetheless, any data gathering system,
whether it is a complex sampling and analysis program or simply a
collection of existing wastewater data must be designed, within the
existing budgetary constraints, to be both cost and information
effective. The current procedures for collecting this pollutant
information focus on the list of 65 classes or compounds known to
i
be hazardous to the environment and, as such, involve only a cursory
review of manufacturing processes. While this method is probably
cost effective, the risk of bypassing unsuspected hazardous materials
is rather high. An alternate solution is to directly analyze, and
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evaluate in some manner, each stream individually within a manufac-
turing process without any a priori assumptions as to its composition .
Though this scheme is obviously information effective, it is also
likely to be prohibitively expensive.
Yet another approach to this problem, which represents a com-
promise between the above extremes is to -identify! prior to sampling
and analysis in the field, which species are likely to occur at each
point source within a process from consideration of the reactants and
reaction pathway. Thus the advantages of working from a limited list
of discrete species is retained in addition to examining, in detail,
each process for potentially toxic emissions to the environment.
Because toxic species formation is derived solely from the reaction
chemistry (and feedstock impurities), this method represents a multi-
media approach to this problem.
Aniline, the simplest of the primary aromatic amines, is a
clear to pale yellow flammable liquid which has a boiling point of
184 C at atmospheric pressure, a vapor pressure of 0.4 mm Hg at 20°C,
and a solubility of 3.7 grams/liter at 30 C. Aniline is regarded as
a highly toxic chemical. Whether the exposure route is via inhalation,
ingestion, or absorption through the skin, the acute toxic effects
are the same: decrease or loss of oxygen transport by the blood
(cyanosis). More significant, perhaps, are the chronic health effects
of aniline exposure: though carcinogenic studies are inconclusive,
aniline has been identified as a tumorgenic agent (Brown et al., 1975).
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Nitrobenzene, the immediate precursor of aniline,* is a pale
yellow flammable liquid which has a boiling point of 211°C at
atmospheric pressure, a vapor pressure of 0.3 mm Hg at 25 C, and a
solubility of approximately 1 gram/liter at 20°C. Nitrobenzene is
also regarded as an extremely toxic chemical, with acute effects
similar to those of aniline. It has been shown to affect the blood
(causing methemoglobinemia), central nervous system, body
metabolism, and cause local skin irritation. Though there are no
data regarding the carcinogenicity or mutagenicity of nitrobenzene,
it has produced teratogenic changes in rats. Moreover, it is
relatively persistent in the environment and may bioaccumulate.
Thus the Interagency Testing Committee (as established under Section
4 of the Toxic Substances Control Act, PL 94-469) has recommended
nitrobenzene be tested for carcinogenicity, mutagenicity, and en-
vironmental effects**.
Because both chemicals are major chemical intermediates (the
annual nameplate production capacities for aniline and nitrobenzene
are 730 and 1010 million pounds respectively) and in light of the
above toxicity data, nitrobenzene/aniline manufacture potentially
represents a significant hazard to both man and his environment.
*Although aniline may be manufactured from other chemical intermediates
(e.g., phenol), production in the United States is based solely on the
reduction of nitrobenzene.
**For complete details see the Federal Register, 4_3_(21) , 4073, January
31, 1978 and the Federal Register 42_(197) , Part IV, October 12, 1977.
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Therefore, this- study is specifically directed to the assessment of
toxic pollutant generation within the manufacture of nitrobenzene/
aniline and possible methods of control. As such, the objectives
are fivefold:
• Identify the toxic chemicals likely to be present in
the aqueous effluent from each process;
• Identify the point sources of these pollutants;
• Identify current treatment practices;
• Survey alternate treatment technologies;
• Indicate practicable methods of pollutant reduction
where current treatment has been deemed inadequate.
Information has been gathered and generated in the following
manner:
(1) Through a thorough search of the chemical literature,
the reaction mechanism (and thus the reaction inter-
mediates) for the formation of nitrobenzene and aniline
have been identified. From a knowledge of the reaction
intermediates, significant by-products formed during
nitrobenzene/aniline manufacture have been predicted.
Additionally, the effect of feedstock impurities has
been considered.
(2) From an extensive patent search, a generic process
configuration for nitrobenzene/aniline manufacture has
been formulated. Included in this process description
are specific point sources for various process opera-
tions. In general, pollutant discharges are considered
from a multimedia viewpoint and are not restricted solely
to aqueous effluents.
(3) The EPA Office of Effluent Guidelines has provided
summaries of current wastewater treatment and discharge
practices of nitrobenzene/aniline manufacturers, from
information gathered under Section 308 of PL 92-500.
In addition to these summaries, relevant supplementary
information has been provided.
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(4) From a thorough literature review, "state-of-the-art"
wastewater treatment technology for nitrobenzene/aniline
manufacture has been, identified. Both patented tech-
nologies and relevant theoretical studies have' been
included in this review.
OVERVIEW OF NITROBENZENE/ANILINE MANUFACTURE
Process Technology
Nitrobenzene is manufactured exclusively by nitration of
benzene, •2
HNOo
H2S04
although there are numerous process variations. Virtually all
capacity (greater than 97 percent) is captive to aniline manufacture
and indeed, each aniline producer (with the exception of Mallinkrodt,
Inc.) manufactures nitrobenzene at the same facilities.
Although there are numerous procedures which might conceivably
be used for the manufacture of aniline, relatively few have proved
to be of commercial interest. These process include:
• Vapor phase, catalytic reduction of nitrobenzene in either
a fluidized or fixed bed reactor using a variety of
catalysts,
vapor phase
catalyst
2H20
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• Liquid phase, catalytic reduction of nitrobenzene
using a variety of catalysts,
N02 NH2
Liquid phase
Ammonolysis of phenol using an aluminum catalyst,
QH
• Liquid phase reduction of nitrobenzene with metals
in mineral acids, e.g.,
N02 NH2
+ 9Fe +4H20
• Ammonolysis of chlorobenzene using a copper (I)
chloride catalyst,
* 1
I + NH3, x
U 3(aq)
+ HC1
Though each of the first three (and perhaps the fourth) processes
are currently being used to produce aniline on a commercial scale,
manufacture in the United States is based predominantly on the
continuous, vapor phase, catalytic reduction of nitrobenzene. A
small, but significant amount (approximately 8 percent based on name-
plate capacity) is manufactured by Rubicon Chemicals, Inc., using a
liquid phase catalytic reduction process. A smaller amount still is
manufactured by Mallinkrodt, Inc., by a liquid phase, batch process.
World demand for aniline has been estimated at 1.2 billion pounds
in 1976 of which 730 million pounds were manufactured in the United
States; by 1980 world demand is anticipated to reach as high as 2.3
9
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billion pounds per year with U.S. aniline capacity rising to 1 billion
pounds per year (Chemical Week, July 20, 1977). Current domestic pro-
ducers of nitrobenzene/aniline are American Cyanamid Company (Bound
Brook, New Jersey and Willow Island, West Virginia), E.I. duPont
de Nemours & Company (Beaumont, Texas and Gibbstown, New Jersey),
First Mississippi Corporation a subsidiary of First Chemical Corpor-
ation (Pascagoula, Mississippi), Mobay Chemical Corporation (New
Martinsville, West Virginia), Rubicon Chemical Corporation (Geismar,
Louisiana), and Mallinkrodt, Inc. (aniline only - Raleigh, North
Carolina).
*
Market Outlook
The backbone of aniline demand lies in the production of
methylene diisocyanates, an intermediate used in manufacture of
urethanes (see Table 1 and Figure 1). Growth in urethane markets
has long been forecast, but slow in developing. The most promising
markets are in insulation products and reaction-injection-molded (RIM)
auto parts. Urethane insulation products are regarded as being
particularly attractive because of their superior insulation qualities
(one anticipated use is urethane board for construction). The same
forecast suggests that use of aniline for RIM materials could rise
from 20 million pounds in 1976 to 80 million pounds in 1980 and 160
million pounds in 1985. Other markets, however, are expected to do
*
As stated previously 97 percent of nitrobenzene production is captive
to aniline manufacture. To avoid the redundancy of considering both
nitrobenzene and aniline markets, only aniline is discussed in the
following section. Nitrobenzene market outlets are, however, shown
in Figure 1.
10
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TABLE I
CONSUMPTION PATTERN OF ANILINE
MARKET
CONSUMPTION
(Percent)
Isocyanates (4,4*-methylenediphenyl
isocyanate and polymethylene poly-
phenylisocyanate)
Rubber Chemicals
Dyes and Dye Intermediates
Hydroquinone
Drugs
Miscellaneous Applications
40
35
6
6
4
9
Source: Lawler, 1977.
11
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ro
NITROBENZENE
ORGANIC SYNTHESIS
UBBER COMPOUNDING AGENT
3 , 3-DICHLOROBENZ IDINE
0-CHLOROANILINE
0-AN1SIDINE
2,4-DINITROCHLOROBENZENE
O-D I CHLOROBENZEHE
DIANISID1NE
DYES
RUBBER CHEMICALS (e.g., TUIAZOLE)
PHOTOGRAPHIC CBEHICALS
(e.g.. HYDROQUINONE)
P-UTTPA..1T1 »TO^
o-Sulfonlc Acid
RUBBER CHEMICALS
DYE INTERMEDIATE
OTDROQUINONE »
DYES
CELLULOSE ESTER STABILIZER
HYDROGEN PEROXIDE PRESERVATIVE
RUBBER CHEMICALS
DIPHENYLMETHANE DIISOCYANATE— — *•
:DYES
PHOTOGRAPHIC CHEMICALS
ANTIOXIDANTS
DYES
HEDICINALS
POLYUKETHAilE
PHARMACEUTICALS
AHTIOXIDANT
DYES
PHOTOGRAPHIC CHEMICAL
PHENACETIN tffiDICINALS (ANALGESIC)
DYES
DYES
RUBBER ACCELERATORS AND
ANTIOXIDANTS
Source: Chemical Origin! and Markets. SSI, 1977.
FIGURE 1
NITROBENZENE AND ANILINE MARKETS
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no more than match the performance of the general economy.
Several U.S. manufacturers have already or are expected to ex-
pand in response to anticipated demand. First Mississippi Corpora-
tion has recently added 150 million pounds per year capacity which
increases capacity of the Pascagoula, Mississippi plant to 250 million
pounds per year; an additional 50 million pounds could be provided
by increasing the output of the older unit to that of the new unit.
Rubicon Chemical Corporation is currently adding a 220 million
pounds per year plant which will increase the capacity of the existing
Geismar, Louisiana facility to 280 million pounds per year when on-
stream in 1978. American Cyanamid is also reactivating an existing
plant in Bound Brook, New Jersey. On standby since 1974 and due to
come online in 1978, the plant's nameplate capacity was 60 million
pounds per year, but with refurbishing the capacity may be somewhat
higher. DuPont will add about 15 percent by mid-1978 to its 360
million pounds per year capacity in Beaumont, Texas and Gibbstown,
New Jersey. Finally, Mobay Chemical Corporation, will increase
capacity by 40 million pounds per year as a by-product when its new
pigments plant in New Martinsville, West Virginia comes online in 1981.
13
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SECTION II
NITROBENZENE/ANILINE MANUFACTURE
REACTION CONDITIONS
The stoichiometric equations describing the reaction of benzene
with nitric acid to produce nitrobenzene, and the subsequent reaction
with hydrogen to yield aniline,
N02
H2S04
HN03
3
50-90C
+H°
are too often regarded as sufficient description of the industrial
synthesis of nitrobenzene/aniline. Yet, any reaction in which a
large number of bonds are broken will necessarily require passage
through a number of distinct intermediates. Thus, the above equations
do not, in any way, account for observed reaction by-products such as
nitrophenols (in the case of nitration) or diphenyl hydrazine (in the
case of nitrobenzene reduction). Only from careful consideration of
(1) reaction conditions, (2) feedstock composition, (3) the reaction
mechanisms, and (4) the most probable manufacturing configuration,
can formation of such by-products be logically explained and the
environmental impact adequately assessed.
14
-------
The previous section provided a brief overview of the industrial
synthesis of nitrobenzene and aniline. While there is only one
procedure for nitrobenzene manufacture (in terms of process chemistry
only), there are three separate and distinct procedures* in current
use for the reduction of nitrobenzene to aniline, which require
separate discussion. Specifically, the following reactions will be
considered:
(1) The heterogeneous nitration of benzene with mixed acid (15 mole
percent nitric acid, 30 mole percent sulfuric acid, and 55 mole
percent water - see reaction (1));
(2) the gas phase heterogeneous catalytic reduction of nitrobenzene
using a copper catalyst,
270-475°C
~ 1 atm
Copper on
Silica
2H20
(3)
(3) the liquid phase heterogeneous catalytic reduction of nitroben-
zene using a nickel catalyst,
+ 3H
atm
2 Nickel on
Kieselguhr
+ 2H20
(4)
*A fourth procedure, the amination of phenol to yield aniline, is not
in current use by U.S. aniline manufacturers, for this reason, this
procedure will not be discussed further.
15
-------
and (4) the liquid phase heterogeneous catalytic reduction of nitro
benzene with iron in acid solution,
However, because nitrobenzene and aniline are manufactured at the
same site (with the exception of Mallinkrodt which does not produce
nitrobenzene), all process chemistry will be discussed prior to
introduction of any process configuration description.
FEEDSTOCK COMPOSITION
Accurate prediction of the formation of reaction by-products
from nitrobenzene/aniline manufacture necessarily requires identifi-
cation of significant (in terms of chemical reactivity, potential
toxicity, and quantity present) impurities in all starting materials
(benzene, nitric acid, and sulfuric acid). Unfortunately, a truly
representative analysis of benzene is difficult to obtain because
of varying sources* (thus leading to potentially different impuri-
ties). A typical benzene feedstock, however, is likely to contain
*Benzene is currently derived from four principal sources: coke
ovens, reformate, crackers, and toluene hydrodealkylation. Based on
nameplate capacity only, their relative market shares in 1976 were
approximately 8, 47, 14, and 31 percent, respectively. In the near
future, however, this pattern is expected to alter considerably, the
largest growths occurring in production of benzene from crackers and
by toluene hydrodealkylation. Thus, Schoeffel and Dmuchovsky (1977)
predict the following market in 1981 (again based on nameplate
capacity): coke ovens - 5 percent, reformate - 40 percent, crackers
- 24 percent, and toluene hydrodealkylation - 31 percent.
16
-------
reported impurities
but not measured
toluene and ethylbenzene with smaller amounts of xylenes, cycloal-
kanes, cycloalkenes, and straight chain alkenes as shown in Table II,
TABLE II
ANALYSIS OF PURE GRADE BENZENE
COMPONENT PERCENT BY WEIGHT
Benzene 99.8
Toluene 0.1
Ethylbenzene ^ 0.1
1-Pentenes
2-Pentenes
2-Methyl-l-butene
2-Methyl-2-butene
Cyclopentane
Cyclopentene
Cyclohexane
Cyclohexene
Taken to include isomeric xylenes.
SOURCE: Mellan, 1977
Though concentrations are not specified for the majority of impuri-
ties shown, their presence should not be precluded; indeed these and
similar compounds have been identified in a less pure benzene* (Click
et al., 1960). For the purpose of this study (and consistent with
the accuracy of the above data), it is assumed that the sum of these
impurities is less than one tenth of 1 percent.
*Glick and co-workers have identified 20 specific compounds in con-
ventionally acid washed, 1° coke oven benzene of 99.30 mole percent
purity.
17
-------
Similarly, impurities in the,other feedstocks are difficult to
specify. In general sulfuric and nitric acid are both available in
sufficiently pure commercial grades sp as to preclude significant
contribution (in terms of impurities present in these acids) to
pollutant emissions, although each are polluting species in their own
right. Product specifications of commercial grades of sulfuric acid
and nitric acid are shown in Table III.
TABLE III
PRODUCT SPECIFICATIONS FO^
SULFURIC AND NITRIC ACIDS
IMPURITY
Hydrogen chloride
Nitric acid
Sulfur dioxide
Ammonia
Arsenic
Iron
Lead
Sulfate
SULFURIC
99%
5
5
150
10
0.5
150
50
ACID
140%
5
5
150
0.5
200
50
NITRIC
69-71%.
50
0.1
0.2
0.5
1
ACID
>90%
0.7
0.3
2
5
5
All concentrations are in mg/1.
SOURCE: Kirk-Othmer Encyclopedia of Chemical Technology, 2nd Edi-
tion, 1966; Reagent Chemicals, 4th Edition; American
Chemical Society, 1968.
18
-------
Though the concentrations shown are only generic rather than specific
to a given manufacturer's product, these values are probably applic-
able to commercial grades because of competitive conditions within
the industry.
Feedstocks for aniline production are nitrobenzene and hydrogen.
By-products of nitrobenzene manufacture (and thus, possible contami-
nants of nitrobenzene) will be extensively considered in following
sections of this report and will not be discussed further at this
point. Hydrogen, required for the industrial manufacture of aniline,
in tonnage quantities is obtained from a variety of sources which
include (1) natural gas via steam reforming, (2) petroleum via
partial oxidation, (3) refinery tail gas, and (4) coke oven gas. The
impurities present in hydrogen will be at least somewhat dependent on
its source but may be divided into two groups depending upon their
boiling point. Low boiling contaminants are nitrogen, carbon monoxide,
argon, and methane. Impurities belonging to the high boiling group
include acetylene,carbon dioxide, paraffinic and olefinic hydrocarbons,
hydrogen sulfide, carbonyl sulfide, mereaptans, and water. Of these
two groups, generally only the low boiling contaminants present
purification problems. Table IV illustrates typical compositions of
several feed and product streams.
From the information presented above, the principal impurities
most likely to occur in feedstock hydrogen, regardless of its source,
are methane, carbon monoxide, and nitrogen. There are no specifica-
tions stated in the patent literature regarding hydrogen other than a
19
-------
TABLE IV
TYPICAL COMPOSITIONS OF VARIOUS HYDROGEN FEED AND PRODUCT STREAMS2
ro
o
COMPONENT
Hydrogen
Nitrogen
Carbon
Monoxide
Argon
Oxygen
Methane
Carbon
Dioxide
Ethane
Ethylene
Acetylene
Hydrogen
Sulfide
Other
FEED STREAMS
PARTIAL COKE
REFORMER OXIDATION OVEN REFINERY
GAS GAS GAS GAS
95.6 96.6 55.9 40.0
0.4 0.6 4.4 1.5
1.7 2.0 6.8 1.0
_ n •> — __ .__
»_«w U • £ ..«.»
0.7
2.3 0.6 26.8 55
200ppm 200ppm 1.8 AOOppm
— _ ft /. 1 /
_ — ...._ U. *» i. <\
2.8 0.7
600ppm 0.1
0.2
0.2 0.3
PRODUCT STREAMS2
METHANE PROPENE
ABSORBER ABSORBER PRODUCT
98.99 99.99
30ppm 30ppm
lOppm lOppm
1.0 60ppm
99.9999
• < Ippm
All concentrations are percent by weight unless otherwise noted.
2
Purification is via cryogenic procedures.
Source: Baker and Paul, 1963.
-------
purity of greater than 90 percent (Karkalits et al., 1959; Sperber
and Poehler, 1964); however, considering the low sulfur specification
for nitrobenzene (Karkalits, 1959), it is not unlikely that a similar
requirement exists for hydrogen. Other impurities, for example
methane and carbon monoxide, though not necessarily inhibitory, may
also be detrimental to the yield of aniline and should probably be
kept to a minimum. Thus, for the purposes of this document all
impurities shown in Table IV are assumed to be present in hydrogen
(to a greater or lesser extent) used for aniline manufacture.
REACTION MECHANISMS
An understanding of the reaction mechanism, specifically the
identification of those reactive intermediates which describe the
reaction pathway, results in a complete, although qualitative,
description of by-products.* Only a limited number of by-products
have been explicitly associated with or identified from nitrobenzene/
aniline manufacture in the chemical literature, though a large number
of species have been found in the wastewater at such facilities.
Known by-products of nitrobenzene/aniline manufacture include p-nitro-
phenol, 2,4-dinitrophenol, 1,3-dinitrobenzene, azobenzene, phenylene-
diamine, nitrates, and sulfates. A detailed examination of the
reaction mechanism will provide an indication of which minor side
reactions may generate other hazardous or toxic compounds.
*This is actually the reverse of a more traditional approach, where
the existence of minor products is used to validate a mechanism.
21
-------
Nitration of Benzene
Nitration chemistry occupies a unique position in organic chem-
istry. Industrially, it was among the first unit processes to be
operated on a large scale. Equally important has been its role in
developing our understanding of reaction mechanisms, in particular
offering an ideal example of electrophilic substitution (see Ingold
et al., 1950). Yet despite a relatively long history of industrial
application and extensive mechanistic investigations, answers to
fundamental questions, especially those which relate to the reaction
conditions of industrial nitrations, remain elusive.
Before discussing nitration mechanisms per se, it is important
to recognize that aromatic nitration as practiced by industry is a
heterogeneous reaction, that is the organic substrate and nitro pro-
duct form a separate phase from the aqueous acid. The nitration
reactions certainly must occur in the acid phase or at least at the
interface between the phases. Thus the organic substrate must be
transferred either to acid phase or interface. Depending on reac-
tion conditions, either the intrinsic chemical kinetics or the mass
transer process may be rate limiting. The intent here, however, is
not to discuss the various mathematical models describing mass trans-
fer with chemical reaction*, but rather to indicate only the signifi-
cant intermediates of the reaction pathway. That the former may be
*For a thorough discussion of such models as applicable to'nitration
see Schiefferle et al., 1976; Giles et al., 1976; and.Strachan,
1976.
22
-------
important in terms of pollutant formation is acknowledged, but such
considerations have more effect on reactor design and remain beyond
the scope of this document.
In 1950 Ingold and his co-workers first proposed what is now
widely accepted as the scheme for the mechanism of aromatic nitration
with nitric acid/sulfuric acid systems: initial formation of the
nitronium ion, NCL , followed by attack of this species upon the
aromatic substrate. Yet when the nitronium ion was used as the rea-
gent (e.g., nitronium tetrafluoroborate), anomalous results (in terms
of partial rate factors) were obtained. In 1968, Coombes and co-
workers proposed the following mechanism as the simplest explanation
consistent with all observed data:
H
(6)
NO* + ArH « * [ArHN02]*
[ArHN02]
(7)
(8)
+ Base
N02 + Base-H
(9)
where the species enclosed in brackets is described as an encounter
complex. The principal difference between this mechanism and that of
23
-------
Ingold is the formal existence of the encounter complex. For suffi-
ciently reactive substrates (e.g., xylenes), it may be shown that
formation of the encounter complex may be rate limiting; for less
reactive compounds, for example benzene and toluene, formation of
the benzenonium ion (reaction 7) is rate limiting. An additional
point of the mechanism which is open to question is the formal
existence of the nitric acidium ion, H«NO_ , a known precursor of the
nitronium ion. Yet the latter question may be largely one of seman-*
tics in that the nitronium ion in aqueous solution must certainly be
HN03 + H* =^=± H2N03+ (fast) (10)
(11)
hydrated to some extent; thus, as Hanson (1976) has pointed out, the
differences in the expected kinetics of a hydrated nitronium ion and
the nitric acidium ion will depend on the degree of bonding between
water and the nitronium ion and the moment in the reaction process at
which water is lost. For the purposes of this document, the formal
existence of the nitric acidium ion will not be assumed.
Of considerable interest, however, is the effect of water on
the rate and order of a heterogeneous reaction system. In homogeneous
systems (i.e., in the absence of water) formation of the nitronium
24
-------
•ion (reaction 11 or 6) is rate controlling and is independent of the
concentration and nature of the aromatic substrate. This results
from reaction (7) being faster than the reverse of reaction (6);
in other words, nitronium ions react with the substrate as fast as
they are produced. In the presence of water the reaction rate is
decreased with the eventual result that reaction (8) is rate con-
trolling (Hughes et al., 1958, and Hanson et al., 1976). This
effect is attributed to water reacting with the nitronium ion, the
rate of which becomes comparable or greater than the rate of reaction
with the aromatic substrate. Thus, the reactivity of the substrate
becomes important and the rate of formation of the nitro product
involves both the concentration of the substrate and nitronium ion.
In the industrial nitration of benzene, where water is present in
high concentration, the rate limiting step is formation of the
benzenonium ion, the principal reactive intermediate.
Hydrogenation of Nitrobenzene
To facilitate the discussion of the hydrogenation of nitroben-
zene, it is useful to first consider the general relationships
existing in heterogeneous processes in the gas or vapor phase over
solid catalysts. Whereas simple gas phase reactions are characterized
by radical rather than ionic mechanisms, heterogeneous reactions
(i.e., reactions occurring in more than one phase), such as those
which take place partly in the gas phase and partly on a solid
surface, are considerably more complex. In the latter case, radical
25
-------
species need not exist explicitly and indeed, neither ionic nor
radical species may predominate at the solid-gas interface. Regard-
less of the specific species involved, a reaction occurring on a
surface may usually be regarded as involving the following five
consecutive steps:
1. Diffusion of the reacting molecules to the surface;
2. Adsorption of the gases on the surface;
3. Reaction on the surface;
4. Desorption of the products;
5. Diffusion of the desorbed products into the main body of
the gas.
For reactions such as the gas phase hydrogenation of nitroben-
zene which occur over porous catalysts, the diffusion process, 1, may
be the slowest process and, thus, the rate determining step. General-
ly, however, either adsorption or desorption, is likely to be rate
determining' since both commonly have appreciable activation energies.
Desorption energies are particularly high and may, for a large number
of reactions, be the slow step. In practice, separation of steps 3
and 4 is difficult since product desorption rates are not generally
known; therefore, the reaction on the surface, giving the gaseous
products, is most often regarded as a single step.
Turn now from consideration of any heterogeneous reactions to
the main features of hydrogenation reactions from the standpoint of
reaction kinetics. As pointed out previously, hydrogenation reac-
tions can only be explained by passage through a series of distinct
26
-------
intermediates. Were such reactions to proceed through a single step,
the catalyst surface would participate with its free valence electrons
in both the formation and decomposition of a single activated complex;
not only is this extremely unlikely from a purely theoretical view-
point, but also contradicted by a large body of experimental evidence
(Kiperman, 1978). Moreover, hydrogenation reactions are further
complicated by the possibilities of more than one reaction pathway.
Such reactions may proceed under steady-state conditions in indepen-
dent directions of which some represent different reaction routes to
identical products, while others lead to formation of different
products. The latter pathways are of paramount importance to the
consideration of reaction selectivity and must be considered in any
kinetic analysis. Thus,.any kinetic model which is formulated to
take the above features into account, will necessarily be quite
complex.
Certainly the same general features of a reaction occurring on a
surface must also apply to liquid phase heterogeneous catalysis:
diffusion of reactants to the surface; adsorption of the reactants on
the surface; reaction on the surface; desorption of the products;
diffusion of desorbed products into the main body of the reaction
medium. Less clear, however, are their relationships from the
standpoint of reaction kinetics. In particular,diffusion (step 1
and/or step 5) in the liquid phase may well be rate limiting as
diffusion coefficients are three to five orders of magnitude lower
27
-------
than those in the gas phase. (Diffusion is defined as before and
includes both external, as well as internal diffusion processes; the
latter are rarely taken into account in liquid phase reactions and
may be of some importance with small catalyst particles.)
Not surprisingly, the kinetics of liquid phase reactions are
considerably more complex than the general case of vapor phase
hydrogenation. This results for the ..following reasons:
• The effects of both the solvent and the liquid reactants them-
selves are both diverse and complex. Thus, not only solvation
effects for the reactants, catalyst, and activated complex,
but also hydrogen bonding, cage effects, as well as ion and
dipole interaction must be considered. The influence of such
factors is extremely difficult to assess quantitatively;
• The same reactant, for example hydrogen, may exist in differ-
ent adsorbed states of differing reactivity. Such behavior
effects the homogeneity of the surface layer (tending to make
the surface heterogeneous), and consequently influences the
reaction process;
• The three phase system (interfaces between liquid, solid,
and gas) requires that hydrodynamics and transport between
these phases be considered.
Discussion of the reaction kinetics of a hydrogenation system
provides a formal framework in which all reactions may be considered
and reconciled with a reaction mechanism. It is more useful, however,
for the purposes of this document, to defer such a discussion to a
later section and to first identify the reaction intermediates which
lead to the formation of products and by-products. With regard to
the latter, though the nature of the reacting species is difficult to
ascertain with absolute certainty, available experimental evidence is
best accounted for in terms of several radical-like intermediates
28
-------
derived from nitrobenzene. Less attention has been given to the
nature of the adsorbed hydrogen in these particular hydrogenation
systems; however, hydrogen adsorption on the thin metallic films
(nickel in particular) has been studied extensively. In the case of
nickel hydrogen is present in three distinct states, ranging from
adsorption in the atomic form to adsorption in the molecular form.
Where the specific identity of adsorbed hydrogen is not known, such
species shall be identified only as [H] but are assumed to exist in
atomic form (i.e., as a radical).
So that the following discussion of the reaction mechanism will
be intelligible to a reader with a limited knowledge of organic
chemistry, the basic features of the reaction mechanism which lead to
the formation of important reaction intermediates (i.e., lead directly
to nitrobenzene or significant by-products) are outlined first. Two
separate mechanisms, which are directly applicable to all known
commercial procedures for nitrobenzene reduction in the United
States, are considered: catalytic hydrogenation over copper or
nickel.catalysts in either the gas or the liquid phase and reduction
with elemental iron in the liquid phase. The more difficult question
of the specific mode of catalysis is discussed in a separate subsec-
tion entitled "Mechanism of Catalysis" and may be omitted without
serious loss of continuity.
29
-------
Catalytic Hydrogenation
Few data are available concerning the catalytic hydrogenation
of nitrobenzene to aniline. This situation is no doubt due to the
extreme difficulty of considering any heterogeneous reaction system
by reaction kinetics alone. Generally, such studies are greatly
complicated by a variety of surface effects. In recent years new
research and analytical techniques have made the direct.study of the
events on a catalyst surface possible, thus eliminating the necessity
of drawing conclusions about a mechanism indirectly. Though such
techniques have yet to be applied to nitrobenzene/aniline, such
studies should firmly establish the mechanism of catalysis in this
system.
Keeping the above points in mind, it is pertinent to note that a
small number of kinetic investigations have, been made using commer-
cial, supported catalysts, generally with the addition of a promoter.*
Unfortunately, the,majority of investigations performed to date have
suffered from serious procedural defects: lack of isothermal condi-
tions in the catalyst bed; the use of an integral reactor; and the
probable effects of diffusional factors on the reaction kinetics.
Because of the above factors, interpretation of kinetic results from
such studies (which typically have been confusing and contradictory)
has been difficult. Moreover, the use of promoters in catalysts
*A promoter may be defined as a substance, which when added to a
catalyst in small amounts, enhances (promotes) the reaction selec-
tivity or yield.
30
-------
would make the validity of extending the kinetic processes to pure
copper doubtful in any case.
There are no data in the literature concerning the adsorption of
nitrobenzene (or any aromatic nitro compound for that matter) on
copper surfaces; however, it is not unreasonable to assume that, upon
adsorption, a molecule of nitrobenzene bonds to two atoms of copper
through oxygen. Taking into account that molecular hydrogen is not
effectively adsorbed below 300°C, together with empirical evidence,
Pogorelov (1976) suggests a variation of an impact mechanism similar
to that proposed by Twigg (1950). This.variation is shown in Figure
2. Formally, this mechanism may be expressed by the following
reactions:
M<|>N02 + H2 —- M<|>NOOH . mH (13)
M4>NOOH . mH —> M<|>NO + H20 (14)
MNO + H2 MNOH . mH (15)
M4>NOH . mH M<|>N + H20 (16)
MN + H2 —— M4>NH . mH (17)
M4>NH , mH —- M + NH ' (18)
31
-------
8
2Cu
A
/Cu Cu
f I 11 I I I
9JV
.fc. /Cu Cu-H
^ r I 11 I i 11 I
/Cu Cu
11111111
H
U)
N)
;-OH
uCu-H
f I H H H i
H
M-H
u Cu-H
LJ
'
/Cu Cu
1 1 1 1 1 1 1 1
FIGURE 2
PROPOSED REACTION MECHANISM FOR THE HYDROGENATIOIM
OF NITROBENZENE OVER COPPER CATALYSTS
-------
where M equals 2m denotes an adsorption center consisting of two
surface atoms of copper, denoted as m. If the rate limiting step
is reaction (13) and nitrobenzene adsorption (reaction 12) is at
equilibrium, then the rate equation may be expressed as:
k K P
K13*l *
V =
where k , is the rate constant for reaction 13 and KI the adsorption
coefficient for nitrobenzene. It is pertinent to note that where
K.P. is large (i.e., where P.Nn is large) this equation reduces
to
v - k,, Pu (20)
1J H-
in accordance with experimental data. This, together with the experi-
mental value of the pre-exponential factor of the rate constant for
reaction (13) and the large value of K- lend further credence to this
mechanism.
In summary, the mechanism of catalytic hydrogenation of nitroben-
zene to aniline has yet to be conclusively demonstrated, though the
scheme proposed by Pogorelov et al., 1976, is the most rational inter-
pretation of existing data. For the purposes of this document (i.e.,
pollutant prediction), the general mechanism as shown in Figure 2 is
33
-------
assumed to be applicable to both the vapor and liquid phase hydrogen-
ation processes over copper and nickel catalysts. This assumption
should not be interpreted to mean that the preceding processes
(reactions 12 through 17) have equal importance in alternate systems,
but rather that the same reactive intermediates are suggested to
exist and play a greater or lesser role depending on the specific
system. By further examination of these intermediates, i.e., NOOH,
NOH, and <|>N, together with consideration of their subsequent
reactions, additional by-products may be predicted.
Dissolving Metal Reductions
Not unlike gas and liquid phase hydrogenation processes, dis-
solving metal reductions of aromatic nitro compounds have not been
extensively studied despite their wide usage in synthetic organic
chemistry. Again, this is no doubt due to the extreme difficulties
(as discussed at the beginning of the previous subsection) of studying
liquid phase heterogeneous reactions.
Nonetheless there is, from electron spin resonance (ESR) studies
with aromatic nitro compounds and other observations (chiefly electro-
chemical - see, for example, Wagniere, 1969), general belief in the
mechanism shown in Figure 3 as proposed by House (1972). As such, it
is useful to identify this mechanism in terms of the following
reactions:
Fe° * -
4>NO, • 9 NO. (21)
34
-------
Fec
H+
;,,°H Fe
N=0)
Fe
N-OI
H+
u>
Oi
Fe
R-OH
N-OH
H
Fe
H+
NH
FIGURES
PROPOSED MECHANISM FOR DISSOLVING METAL
REDUCTION OF NITROBENZENE
-------
- +
NO + H * 4>NO H . (22)
2
Fe
(23)
_
<|>N02H + H »-NO + H20 (24)
4>NO e - $ NO" (25)
+ *
H — <|>NOH (26)
- Fe -
(27)
4>NOH~ + H «-4>NHOH . (28)
<(>NHOH + H"*"—— ^ 9NH + H0 (29)
The key intermediate step in this mechanism is the formation of stable
aromatic radical ions. The protonation of this intermediate with
subsequent reduction by the metal (iron) leads first to a nitroso
intermediate followed by a hydroxylamine intermediate. Though these
intermediates have not been isolated in this particular system
(iron/nitrobenzene/hydrochloric acid), their existence is well
established in other systems (e.g., zinc and tin). Notably the
36
-------
oxidation state of iron is not indicated other than at the outset
2+ 3+
(Fe°), and at the end of the reaction scheme (Fe /Fe ), as this
electron transfer process is not well understood at this time.
Furthermore, because there do not appear to have been any rigorous
kinetic studies of this system, identification of the rate limiting
step is speculative; however, proton transfer reactions are generally
very rapid. Therefore an electron transfer step, perhaps the
first, might reasonably be suggested as being rate controlling.
Again, as before, the purpose of proposing this mechanism has
been solely to provide a rational framework for identification of
reactive intermediates which have bearing on by-product formation via
significant side reactions. Thus, by further examination of these
intermediates, i.e., the benzonitroyl radical anion, nitrosobenzene,
and hydroxylamine, together with their subsequent reactions, forma-
tion of significant pollutants may be predicted in the following
sections.
Mechanism of Catalysis (Optional Section)
By further examining the reactive intermediates at the catalyst
surface, a mechanism for the catalytic hydrogenation of nitrobenzene
over copper and nickel may be postulated. To do this, however,
necessitates detailed consideration of the bonding between metallic
(i.e., copper or nickel), inorganic (i.e., hydrogen), and organic
species. Though this bonding is best considered in terms of molecular
orbital theory, studies to date have been limited solely to hydrogen
37
-------
absorption on copper and nickel (itoh, 1976; Fassaert et al., 1972;
Barclay, 1973, and Takasu and Matsuda, 1976). Thus, the reactive
intermediates discussed previously have been identified by kinetic
evidence, that is, an indirect method. Because such results, i.e.,
rate laws, are mathematical descriptions of a physical process,
totally different mechanisms may, in fact, be consistent with such
descriptions. Physico-chemical methods (e.g., ESR, NMR, IR, UV, low
energy electron diffraction (LEED), and mass spectroscopy) which
generally allow selection of the authentic varient of the mathematical
description, have yet to be applied to elucidation of this mechanism.
Kinetic results and a corresponding mechanism for the catalytic
reduction of nitrobenzene to aniline in the vapor phase ( 300°C) over
a tin (ll) oxide were first reported by Tsutsumi and Terada in 1951.
Their kinetic investigation suggested that the presence of two
alternate reaction pathways depending on the hydrogen concentration at
the catalyst surface. The first pathway, thought to be dominant at
low surface concentrations of hydrogen, involves phenylnitrene as the
principal reactive intermediate. The second pathway, occurring at
high surface concentrations of hydrogen, proceeds through a phenyl-
aminyl radical. Thus, catalysis of this reduction process apparently
occurs at various oxidative levels. A reasonable interpretation of
these results is the initial oxidation of the catalyst by the nitro
group, hydrogen addition to the nitrogen atom, and subsequent reduction
of the catalyst'by hydrogen.
38
-------
Two kinetic studies have been reported- concerning reduction of
nitrobenzene to aniline in packed beds with various copper catalysts.
Rihani et al., 1965, while not successful in elucidating the reaction
mechanisms, noted that the reaction velocity could be empirically
expressed as:
1/5
(30)
where v is the reaction velocity and PtM_ , PH are the partial
™NU* ti-
pressures of nitrobenzene and hydrogen, respectively. This equation,
however, is applicable only over the temperature range of 275 to
350°C and for a specific catalyst: 20 percent copper/nickel alloy
(1:1 by weight) on asbestos with cadmium as a promoter (15 percent
by weight of copper/nickel alloy). Gharda and Sliepcevich (1960) in
a separate study, derived a similar relationship and indicated the
difficulty of visualizing the rate controlling step as being the
surface reaction between molecularly adsorbed hydrogen and nitroben-
zene dissociated on two active centers. This difficulty notwith-
standing, three general mechanisms have been considered by both
groups: the adsorption of reactants is rate controlling; the surface
reaction is rate controlling; and desorption of products is rate
controlling. Additionally, several other combinations based on
hydrogen and nitrobenzene dissociating, and either hydrogen or
nitrobenzene not being adsorbed were examined.
39
-------
While none of these mechanisms (as derived by Rihani) were con-
sistent with the empirical data, a surface reaction may still be rate
controlling (based on observed heats of adsorption together with the
reversible deactivation of the copper catalyst by dinitrobenzene) if
surface heterogeneity (in terms of energy) and diffusivity of the
reactants are considered. Regarded from this viewpoint, the above
empirical data may be interpretable in terms of a simpler pathway
than a surface reaction between molecularly adsorbed hydrogen and
nitrobenzene dissociated on two active centers. In this regard,
Halsey (1949) has shown that a reaction which obeys the rate law as
defined by Langmuir adsorption on a homogeneous surface,
1 + K
P
where v is the volume of gas adsorbed, K the adsorption equilibrium
constant, and p the pressure of the gas, may obey
P
<32)
on an energetically nonuniform surface. This result is particularly
interesting, as it may shed light upon the fractional orders found by
Garda et al., 1960.
40
-------
Many of the questions which the previous studies cited have been
recently answered by Pogorelov et al., 1976. Though surface species
are not explicitly identified, the design of the experiment (in terms
of catalyst purity and identity, variation of the partial pressures
of the reactants, and the addition of reaction products to the
reaction zone) is excellent. In contrast to the earlier studies,
Pogorelev and coworkers found that the rate of reaction does not
depend on the partial pressure of nitrobenzene (over the range of
_4 -2
8 x 10 to 2.5 x 10 atm at 260°C) but is directly proportional to
the partial pressure of hydrogen. Moreover, addition of water and
aniline (varied from approximately 0.002 to 0.06 and 0.002 to 0.02
atm., respectively) to the reaction mixture was without effect indi-
cating the lack of inhibition of the reaction by reaction products.
Though the reaction rate at low nitrobenzene concentrations (i.e.,
partial pressures-) is dependent only on the partial pressure of
hydrogen
v - k^ P^ (20)
when variation of all reagent concentrations is taken into account,
the kinetics may be more generally described in the following form:
p
PH.
(33)
P4>NO
41
-------
2
where v is the reaction rate in moles aniline/M hr, K1, K" are con-
stants; and ?.„_ and Ptl are the partial pressures of nitrobenzene
^2 2
and hydrogen, respectively.
BY-PRODUCT FORMATION
Two possible pathways leading to by-product formation (and
hence to process emissions) have been identified*: by-products from
alternate reaction routes; and reaction, by either the main or
alternate reaction route, of feedstock impurities. With regard to
the latter, it is important to realize that, even though a feedstock
impurity may be inert under a given set of reaction conditions, the
direct discharge of such an impurity to the environment may still
represent a significant effluent. Additionally, the identity and
quantity of such impurities are difficult to ascertain in many cases
because feedstock sources may vary from day to day regardless of the
supplier.
Clearly, prediction of pollutant formation via either pathway is
necessarily of a qualitative rather than quantitative nature; though
reactive intermediates may be identified without extensive kinetic
measurements, their rate of formation (and thus quantities produced)
are impossible to predict without kinetic measurements. Other quanti-
tative approaches, for example detailed calculation of an equilibrium
*There is, of course, a third possibility: direct discharge of a
reaction mixture to the environment due to a major process upset.
Such events, while worthy of serious consideration, are however
beyond the scope of the present document.
42
-------
composition by minimization of the free energy of a system, require
complete specification of all species to be considered. Because such
methods necessarily assume equilibrium, the concentrations generated
by such methods represent only trends or, perhaps at best, concentra-
tion ratios. Thus, qualitative predictions are extremely useful
(if not essential) for initial assessment of environmental hazards
associated with a given manufacturing process, development of
a rational sampling and analysis program, and identification or
design of suitable effluent control technologies, all in a cost
effective manner.
The following discussion is broken into two general sections;
the first will consider by-products which form as a result of alter-
nate reaction pathways while the second will consider the effect of
feedstock impurities. Moreover, as there is obvious overlap between
the two sections, the following differentiations are made: (1) no
formal distinction is made between by-products arising from nitroben-
zene production and aniline production; that is to say, that while
relevant reactive intermediates are considered sequentially, there
is but one overall process; (2) by-products which result from alter-
nate reaction pathways are considered from the viewpoint of reactive
intermediates identified as defined in the previous subsection,
Reaction Mechansims; (3) regardless of the source of compound (i.e.,
whether a feedstock impurity or reaction product), once introduced,
the entire reaction course of that compound is considered in that
43
-------
subsection; (4) only those impurities identified and defined in the
previous subsection, Feedstock Composition, will be considered
initially.
Significant Side Reactions
•
Examination of intermediate species (0NCL, <{)NOOH, N:,etc.)
together with consideration of the subsequent reactions of these
initial products, provides a logical basis for prediction of addi-
tional by—products. However, this discussion is based on probable
rather than demonstrated reaction pathways and, as such, the exist-
ence of predicted pollutant species must be verified experimentally.
Side reactions during aromatic nitration are well documented in
the literature (Ross and Kirahen, 1976; Titov, 1952; and Bennett and
Youle, 1938). The most relevant and comprehensive discussion, how-
ever, is that of Hanson and coworkers (1976), who not only charac-
terize by-products formed during aromatic nitration, but also consider
the rate and extent of formation of such by-products as a function of
reaction conditions. In particular, though side reactions of nitro-
benzene are minimal, those of other aromatic compounds are not. The
average yield of by-products, as compared to the corresponding
mononitro compound, is shown in Table V.
44
-------
TABLE V
ORGANIC BY-PRODUCT YIELD
'FROM MONONITRATION OF AROMATIC HYDROCARBONS
Weight % Organic
Hydrocarbon By-Products
Benzene 0.018
Toluene 1.72
Ethylbenzene 1.63
o-Xylene 6.19
p-Xylene 3.13
m-Xylene 0.77
Source: Hanson, 1976.
The most obvious side reaction of aromatic nitration is simply
that of dinitration:
HN03 t f -j| HN03
H2S04 L JJ H2S04 ' "
The extent of this reaction is unknown, but is likely to be small in
that the first nitro group significantly deactivates the aromatic
ring.
Less obvious is the formation of nitrophenols during the nitra-
tion of benzene. Though a number of mechanisms have been suggested
to account for the occurrence of nitrophenols, only two merit serious
consideration. The first, suggested by Bennett (1943; 1945) presup-
poses that a nitronium ion becomes attached to the aromatic ring
45
-------
through one of the two oxygen atoms instead of the normal nitrogen
atom to form an aryl nitrite. This then decomposes to a phenol and a
nitrosyl ion:
ONO
(35)
A phenol so formed will be rapidly nitrated to form either a mono-,
di-, or trinitrated phenol.
OH
(36)
The NO ion formed in reaction (35) ultimately yields nitrous acid
by either of the following pathways:
(37)
N0+ + NO
HN03 + HN02
(38)
NO N02
The experimental observation that one mole of nitrous acid is pro-
duced for each mole of organic acid by-products (Hanson, 1976) is in
accordance with this mechanism, though there is no evidence which
suggests that a nitronium ion may react with benzene in this manner.
Hanson and coworkers (1976) believe the following mechanism, also -
consistent with experimental evidence, to be a more likely explanation:
46
-------
initial attack of the nitronium ion, followed by attack of water, with
subsequent elimination of nitrous acid.
+NO-
HN0
(39)
Again, the phenol so formed will be rapidly nitrated to form either
a mono-, di-, or trinitro phenol (see reaction 35).
Hydrogenation of such by-products is relatively straight-
forward, although there is a question of the extent of such reductions
(Rihani, 1965). Thus, dinitrobenzene is reduced to m-phenylenediamine
(presumably through a nitroso intermediate),
N02 NO NH2
s!P^ xi^X
(40)
while polynitrophenols are reduced to polyaminophenols (again pre-
sumably through a nitroso intermediate).
N02
+ 3H-
+ 6H
(41)
OH OH OH
Though the reactions shown above indicate complete reduction of all
nitro groups, this need not necessarily occur; indeed, it is likely
that partially reduced species such as the following may predominate:
NO2 NO? NHr
+3H2
(42)
47
-------
The thermal decomposition of liquid nitric acid may be important
in nitrobenzene manufacture since it does decompose at the tempera-
tures used in the liquid phase reactions and yields potential oxi-
dizers as products. While a single mechanism has not been agreed
upon, there is general agreement that formation of dinitrogen pentox-
ide is the rate determining step in the decomposition. A reasonable
mechanism* would be (Ross and Kirshen, 1976):
(43)
(44)
The net reaction is simply the equilibrium for production of nitric
acid from nitrogen dioxide, water, and oxygen:
2HN03 * 1/2 02 + H20 + N02 (45)
Nitrogen dioxide evolved in the above sequence is probably the active
oxidizer in mixed acid systems. Although such a discussion is some-
what premature, a simplified mechanism of oxidation following nitrogen
dioxide generation via reaction (45) would be:
*Cordes et al., 1958, have suggested an alternative sequence involving
the step:
HN03 *-*N02 '+ HO*
Ross and Kirshen, however, point out that such a step would be far
too slow to be consistent with the observed rates of decomposition.
48
-------
RH + *N02 • R* + HN02 (46)
R- + o-'O - RO-0* (47)
RO-0* + RH •- R-OOH + R* (48)
R-OOH »- Decomposition products (49)
In mixed acid systems nitrous acid formed is rapidly protonated
and the resulting product dissociates, forming NO :
HN02 + H+ NO* + H20 (50)
Aside from formation of oxidized by-products, the above mechanism
may be of greater environmental significance regarding nitrosamine
formation.*
*While aniline is certain to be present in. wastewaters at facilities
manufacturing nitrobenzene (recall that 97 percent of nitrobenzene
production is captive to aniline manufacture), reaction with nitrous
acid yields the reactive benzenediazonium cation; this intermediate
may either decompose to benzene and nitrogen or further react with
other nucleophiles present (e.g., 1^0 to yield phenol). Amines other
than aniline (most importantly secondary amines), however, may be
present in the wastewater of such facilities. An appropriate
mechanism for nitrosamine formation is (EPA, 1976):
2HN02 „ N203 + H20
R'R"NH + N203 - - R'R"N-N=0 +
where R1 and R" may represent either alkyl or aryl groups.
49
-------
While it is clear that the principal intermediates formed during
reduction of nitrobenzene -<(>NOOH, 4>NOH, N: during catalytic hydro-
genation and 4>NCL , <}>NO, 4>NHOH during dissolving metal reduction -
lead to aniline, other reaction pathways for each of the above species
do exist. Perhaps the easiest and most general deviation from the
course of the main reaction, is that of partial reduction (cf, reac-
H2—L I +H2 — L I
(51)
This type of by-product formation may be most important for dissolving
metal reductions. Alternatively, reduction of nitrobenzene may not
stop at reduction of the nitro group; thus cyclohexylamine, cyclohex-
enyl amine (various isomers), and cyclohexadienylamine may be formed.
Formation of reduced by-products via this scheme, known to be impor-
tant during liquid phase catalytic reduction (Cooke and Thurlow, 1966),
is probably important in the vapor phase process as well.
NH2 NH2 NH2
+ H
+ H
(52)
Nitrosobenzene and the immediate precursor of phenyl hydroxyl amine,
NOH may undergo an aldol-like condensation on the catalyst surface
to yield azoxybenzene:
50
-------
-NOH'
.fc. * i ^^ i —-
(53)
Potentially*, the most reactive, Tnd "thus the most interesting
proposed intermediate during catalytic hydrogenation, is an adsorbed
phenylnitrene species, [N:]. While the properties of such an
adsorbed species no doubt differ significantly from that of a "free"
nitrene, it is not unreasonable, within the context of this document,
to assume an adsorbed phenylnitrene reacts in a manner similar
(though not necessarily to the same extent or rate) to that of a free
nitrene. Thus, additions to multiple bonds and insertion reactions
are assumed to typify the reactions of an adsorbed phenylnitrene.*
Certainly the most prevalent molecules present during catalytic
hydrogenation, aside from hydrogen, are aniline and nitrobenzene which
may react, via insertion reactions, in the following ways:
^
• ii • •• • ••
(54)
(55)
(56)
*For a cogent discussion of the reactions of nitrenes, the reader
is referred to Lwowski, 1963.
51
-------
Subsequent reduction of N-nitrobenzene substituted anilines may
reasonably lead to the formation of complex nitrogen-containing
N:
polymers: NO.
H.
N
(57)
Were the'substitued nitrene to react at any point along this pathway
with aniline (either by C-H or N-H insertion) the reaction would termi-
nate; though this pathway apparently does not occur to a large extent
during catalytic hydrogentation, such a mechanism does rationally
explain the formation of organic tar during the vapor phase process
(Karkalits, 1959). In an analogous manner, an insertion reaction
may occur intramolecularly:
(58)
Nitrenes can also add to aromatic rings to give substitued
azepins as ring expansion products:
N -
(59)
where R represents either an araino or a nitro group. If this sub-
stituent is a nitro group, further reduction and subsequent reaction
52
-------
may in a manner similar to that shown in reaction 57, lead to com-
plex nitrogen-containing polymers:
-O-(OfO
Q-C
>.NV
-"
02
(60)
As before, polymer termination occurs upon reaction of the nitrene
with aniline or a similarly unreactive substrate. Worth noting, is
that neither insertion nor addition reactions are mutually exclusive;
in fact, any polymer formation is likely to result from both insertion
and addition reactions.
Another reaction which is likely to be significant during
catalytic reduction is dimerization to azo products; arylnitrenes
sometimes have sufficient lifetimes for the preparation of mixed
azo species. Diazobenzene thus formed,
N:
(61)
may be subsequently reduced to hydrazobenzene:
N-N
H H
(62)
53
-------
Other reactions similar to the above may also occur by reac-
tion of impurities which are present in the nitrobenzene feedstock.
In general, the interest is not so much that these impurities intro-
duce similar compounds to those shown in reactions (55) through (64)
but rather that these impurities may react with an absorbed phenyl
nitrene to form new products. Thus nitrotoluene (and other nitroalkyl
benzenes), and nitrophenol may react in the following manner (cf
reaction 54):
(63)
and
(64)
Another type of reaction, of interest in that oxygenated deriv-
atives may be formed, is as follows (cf reaction 22):
H2O
(65)
In tfie presence of suitable acid (or perhaps catalyst), a dienone
may rearrange to yield a phenol:
*The small amounts of impurities present together with the minor
extent of the above reactions must certainly lead to even smaller
amounts of products.
54
-------
(66)
This type of reaction is probably most prevalent in liquid phase
catalytic hydrogenation processes. Though the above reactions are
assumed to apply to liquid phase catalytic reduction, it is important
to note that by-products obtained in liquid phase catalytic processes
may be different than those in vapor phase processes for the follow-
ing reasons: (1) lower temperatures for reduction; (2) different
catalysts; and (3) formation of two liquid phases, if water is
not removed as it is formed. Preferential solubility of the product
and by-products in one phase may be quite important.
Based on the sequence of reactions (25) through (33), generally
generally similar side reactions may reasonably be expected to occur
during dissolving metal reduction. Nitrosobenzene and phenyl-
hydroxylamine are both reactive intermediates in this scheme and
under suitable conditions (i.e. in the presence of a base) react via
an aldol-like condensation to yield azoxybenzenes:
NO N(OH)H
f^XrN=N^X,
(67)
The oxygen can be removed relatively easily to yield azobenzne, which
»
in turn, can add hydrogen and form hydrazobenzene. Further reduction of
this system yields aniline:
55
-------
(68)
Under acidic conditions, phenylhydroxylamine rearranges intromolecu-
larly in aqueous solution to p-aminophenol; the rearrangement involves
nucleophilic attack and the following mechanism has been proposed
(Fieser and Fieser, 1961):
NHOH
H +
OH
(69)
Where nucleophiles other than hydroxide predominate in the reaction
media, p-aminophenols are not formed; in the presence of chloride,
for example, p-chloroaniline is formed.
Hydrazobenzene, in the presence of a mineral acid, undergoes
a double side-chain-to-nucleus rearrangement to form benzidine as
a major product:
(70)
Minor
Products:
56
-------
Usually the 4,4'-diaminobiaryl is the principal product except when
one or both of the para positions are substituted; however, such
substitution does not preclude formation of the 4,4'-diamine. The
2,2'-diaminobiaryl and p-semidine are formed in smaller amounts
than the other two side products. Another side reaction which may
occur under similar conditions is disproportionation (March, 1977):
N = N
(71)
By-Products From Feedstock Impurities
From consideration of the feedstock analyses presented in
Tables II through IV, it is readily apparent that the bulk of contam-
inants are found in benzene; moreover, those impurities which are
present in sulfuric acid, nitric acid and hydrogen may reasonably be
expected to be inert. Therefore, only impurities present in benzene
will be considered in the following discussion.
Contaminants present in the benzene used for production of
nitrobenzene have been previously identified, in approximate order
of significance, as toluene, ethylbenzene (and probably the isomeric
xylenes), various acyclic pentenes, cyclopentane, cyclopentene,
cyclohexane, and cyclohexene; though aliphatic species may be present
in smaller quantities than aromatic impurities, their presence may
nonetheless be important. However, of the eleven species shown in
57
-------
Table II (see page ) toluene, ethylbenzene and isomeric xylenes,
are of particular importance with regard to by-product formation, in
that (on a mole basis) these compounds produce approximately ninety
to three hundred times the amount of side products as does benzene.
The most obvious reaction of feedstock impurities is that of
simple mono-nitration (cf reaction 1):
NOJ"
(72)
Though shown only for toluene, the reaction is equally applicable
to ethylbenzene and o,m-xylenes. Equally obvious is the dinitration
of such substrates (again shown only for toluene, but equally appli-
cable to other aromatic substrates; cf reaction 34):
(73)
Other by-products result from both oxidation and water addition to
such substrates (cf reactions 39 and 48):
COOH
(74)
58
-------
HNO3
H2S04
HNO-j
H2S04
N02+
N°2 02N
OH OH
(75)
(76)
The above reactions (72-76) must be regarded as being archetypal
rather than comprehensive; the two types of reactions, oxidation and
electrophilic substitution—together with both the number of attacking
species and positions susceptible to attack—lead to a large number
of possible compounds.
The composition of organic by-products from the mono-nitration
of toluene as presented in Table VI, may, however, indicate the
relative importance of such side reactions. Thus, while space
does not permit delineation of the generally similar reactions of
ethylbenzene and xylenes, such as reaction products are included
in the pollutant summary.
59
-------
TABLE VI
COMPOSITION OF ACIDIC ORGANIC BY-PRODUCTS FROM
NITRATION OF TOLUENE*>2
COMPOUND PERCENT BY WEIGHT
2,6 dinitro p-cresol 79.6
4,6 dinitro o-creosol 10.3
2,4 dinitrophenol 1.4
p-nitrophenol and mono-nitrocresol 4.3
3 nitro 4 hydroxy benzoic acid 3.3
Extraction with 2N NaOH; thus, dinitrotoluene would not be
recovered by such a procedure.
2
Mixed acid composition: 30 mole percent sulfuric acid, 15
percent nitric acid, and 55 mole percent water.
Source: Hanson et al., 1976.
Aliphatic impurities present in benzene are presumed to react
via a free radical mechanism, to yield either oxidized or nitrated
aliphatic species; however, the conditions required for significant
free radical production are considerably different and more severe
(generally in the vapor phase at higher temperature and pressures)
than the conditions found during nitration of benzene. As such,
the formation of species predicted via this scheme, though not
necessarily insignificant, must be considered with due caution.
The following mechanism has been proposed as being predominant
for nitration of aliphatic species by Lee et al., (1976):
60
-------
HNO HO* + *N02 (77)
RH + *OH •- R* + H20 . (78)
R* + HON02 — RN02 + HO* (79)
It should be noted that the first step of this mechanism is in
direct contradiction to that proposed by Ross and Kirschen (1976)
in reactions (46) to (49). This contradiction, though of theoretical
interest, is not germane to the question at hand; it is enough that
both mechanisms indicate a resonable pathway for radical formation.
Thus, aliphatic nitrates of the following type may be produced:
N02
(80)
o ^- o
C - CH - CH -HC - C -
During such free radical processes, oxidation steps also occur
and carbon-carbon bonds may be broken. Therefore, not only may
oxygenated by-products be produced,
61
-------
HNO3
(CH2)
and
CH
HC=C-CH
HNO
HOOC [ CH2 1 COOH
4
COOH
(82)
(83)
but conceivably low molecular weight nitrated products (e.g., nitro-
propane) as well.
Pollutant formation from hydrogenation of the products (i.e.,
reactions 72-83) which are presumed to be present* in nitrobenzene
is relatively straight forward, if somewhat laborious. Thus, the
+ 3H-
(84)
CH3 (85)
3H-
following types of products are expected (again shown only for
toluene by-products; cf reaction 40 to 42):
*Impurities such as those shown in Table VI can be removed by
extraction with a base (e.g, Na2CO_); however, only a small
portion of nitrobenzene (that which is not used for aniline
production) is so treated.
62
-------
CH*.
(86)
(87)
OH
>H
The extent of hydrogenation of the above compounds is unknown;
however, it is not unreasonable to assume that the nitro group may
be reduced only partially as shown below:
CH3 CH,
(88)
NO
Furthermore, there is evidence (Rihani et al., 1965) that dinitroben-
zene rapidly deactivates copper catalysts rather than being reduced
to phenylenediamine. Thus, such byproducts may never appear as
effluents because of adsorption on, and subsequent regeneration of,
the catalyst.
Again, via a pathway an analogous to that of reaction (55), the
aromatic nucleus may be either partially or completely reduced; thus
the following types of by-products may reasonably be expected (again
shown only for p-nitrotoluene):
63
-------
+ 4H2
(89)
The hydrogenation of aliphatic nitro compounds are well known
and lead to fonna'tion of primary amines (or if reduction is incom-
plete, nitroso derivatives):
NO; NH2
3H-
(90)
CH2N02.
-[.
3C-CH-CH2CH3
]-
CH2NH2
H C-CH-
(91)
From the foregoing discussion, by-products from the manufacture
of nitrobenzene/aniline have been predicted. The intent of this
section, despite the- large number of reactions presented, has not
been- to imply that aniline manufacture results in excessive discharge
of environmentally hazardous pollutants, but rather to account for
the seemingly infinite number of species which are typically found
in process wastewaters. Thus, the reactions shown must be considered
exemplary of possible reaction types, rather inclusive of all possible
64
-------
reactions. From this standpoint, those pollutants which pose serious
environmental threats may be quantified and the requisite control
technology designed. To this end, by-products from the preceding
reactions, together with feedstock impurities, are summarized in
Table VII.
PROCESS CONFIGURATION FOR NITROBENZENE/ANILINE MANUFACTURE
Although a large number of different process configurations
are described in the patent literature, only the general features
of nitration processes and three reduction processes—catalytic
vapor phase, catalytic liquid phase, and dissolving metal—will
be considered explicity. However, it is important to note that
any process description derived from the patent literature is
likely to be somewhat different than that used in actual practice,
and therefore, the following configurations must be regarded as
generic rather than specific to any given plant.
Generic Nitration Processes
Nitrobenzene was first manufactured commercially in England
in 1856, and thus was one of the first industrial chemicals to
become available on a large scale. This early batch manufacture—
practiced in five gallon reactors (a glass carboy) cooled with ice—
reflects more the relative ease of aromatic nitration rather than
a prior existing need. Currently, however, batch reactors (1000 to
1500 Ib capacity—2 to 4 hour cycle) are uneconomical for large
scale nitrations, as compared to continuous operations. Moreover,
65
-------
TABLE VII
SUMMARY OF POLLUTANTS FROM NITROBENZENE/ANILINE
MANUFACTURE
Pollutant
Reaction
Number1
Acridine
Alkyl nitrates
Amino cresols
Amino phenols
Amino polymers
Aniline
Azobenzene
Azoxybenzene
Benzene
Benzidine (and related semidines)
Benzoic acid
Carbon monoxide
Copper salts
Cyclohexane
Cyclohexene
Cyclopentane
Cyclohexadienone
Cyclohexadienylamine
Cyclohexenylamine
Cyc lohexylamine
Diaminotoluene
Dinitrpbenzene
61
82
89
40,72
.60,63
P
64,74,71
56
F
72
77
F
C
68
55,56
88
33
Dinitrotoluene
Ifi.
Diphenylhydrazine
Diphenylhydroxylamine
Ethanolamine
Ethylbenzene
Hydroxylamine
Methane
Me thyIdiphenylamine
N-substituted anilines
N-substituted nitrosamines
N-phenyl azepin
Nickel salts
Nitric Acid
Nitrobenzene
57,65
67
F
F
54,70
F
66
59
52
62
C
F
P
66
-------
TABLE VII (Continued)
Reaction
Pollutant Number*
Nitrogen oxides
Nitrous acid
Nitro cresols
Nitro phenols
""Nilroaubem.ene —
Pentenes
Phenol
Phenvlenediamine
Picric acid
Polycarboxylic acids
Sulfuric Acid
Toluene
Toluidine
Xylenes
43,1
36,38
78
35,37
55
F
50,67
39
35
85
F
87
F
The following notations are used for brevity:
F = feedstock impurities v
C = species results from catalyst attrition
I = species results from incineration of waste products
P = product
67
-------
Drown Tank
Steam«
ncy
k ^
From Reactor
Absorber
.
-
Denitrating Tower
-
(1
A M
U 01
<3 3
To Wastewater
Treatment
Source: Process Research, Inc., 1972.
•H 4-1
C
c
3 O
• Steam
Sulfuric Acid
(98%)
To Reactor
FIGURE 4
CONTINUOUS LIQUID PHASE NITRATION OF BENZENE
68
-------
because few process changes have been made in batch processes in
recent years, and descriptions of such processes have been presented
by Groggins (1958) and Urbanski (1964) in considerable detail, only
continuous processes are discussed further. Benzene may, in fact, be
nitrated directly in either the liquid or vapor phase. The following
discussion, however, is predicated upon the prevalence of liquid
phase processes.
In the most common continuous phase process (Albright, 1966),
benzene is nitrated with an aqueous mixture of sulfuric acid (53 to
60 mole percent) and nitric acid (39 to 32 mole percent) at atmos-
pheric pressure and temperatures between 45 to 90°C. Yields are
typically better than 98 percent. This process (see Figure 4) is
carried out in vented stainless steel vessels equipped with high
speed agitators and cooling coils. Average residence time is ap-
proximately 8 to 10 minutes. Nitrobenzene is continuously drawn from
the side of the reactor and separated in a decanter. Once separated,
this "crude" nitrobenzene is reportedly used directly in the manufac-
ture of aniline. If pure nitrobenzene is required, the product is
washed first with water and subsequently with an alkaline solution
(generally either a sodium carbonate or sodium hydroxide solution) in
small vessels similar to the nitration vessel (i.e., equipped with
high speed mechanical agitators) and then distilled.
Alternatively, a tubular reactor may be used for production
of nitrobenzene. Advantages of such systems are somewhat shorter
69
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residence times, high spaces velocities (pounds of product per hour
per gallon of reactor capacity), and lower capital, maintenance, and
operating costs. In this sytem, benzene and the mixed acid (as defined
for the above system) are rapidly emulsified by impinging the two
streams and pumped to the reactor (see Figure 5). The reaction tem-
perature is controlled by circulating cold water about the outside
reactor shell. Products are removed from the top of the reactor to a
surge tank equipped with a vent. By controlling the recycle ratio
from this tank, benzene is nitrated to nitrobenzene in yields better
than 99 percent. Nitrobenzene is continuously withdrawn from the surge
tank and purified, as described previously and shown in Figure 4.
Whatever type of reactor is used for nitrobenzene manufacture,
recovery of spent acid is essential, both from the standpoint of eco-
nomical operation and pollution. Generally, unreacted nitric acid is
extracted from the spent acid by steam stripping (denitrating tower).
The bottom products, dilute sulfuric acid (-60 percent by weight), is
then concentrated by distillation (sulfuric acid concentrator) and
recycled to the reactor as shown, or used in other manufacturing
operations. Nitric acid removed overhead from the denitrating tower
is bleached with air to remove nitrogen oxides and subsequently
recycled to the reactor. The overhead nitrogen oxides from the
bleacher are scrubbed with water and recycled to the denitrating
tower. Nitrogen oxides generated from the reactor are oxidized with
air and water scrubbed, prior to recovery in the denitrating tower.
70
-------
Vent
>l
M
o
o
CO
0)
§
H
-------
Another approach to spent acid recovery is the use of feed
benzene for nitric acid extraction (Dubois et al., 1956, and Buchanan
1958). In this method benzene, rather than steam is used to strip
nitric acid from spent acid in the denitrating tower (see Figure 4).
The nitric acid is thus dissolved in the benzene and fed to the
reactor. The remaining sulfuric acid is concentrated as before.
Advantages of such a system include the elimination of a bleaching
tower and a large absorption tower; presumably recovery of nitrobenzene
is also enhanced. Disadvantages, however, include: indiscriminant
extraction of all reaction impurities present in the spent acid
which necessitates a bleed stream to prevent buildup of such im-
purities; and more importantly, introduction of perhaps significant
amounts of benzene into the sulfuric acid to be concentrated.
Though relatively few process modifications have been suggested
for reduction of effluents during nitrobenzene manufacture, Hanson
(1976) has shown that organic by-product is a function of the sul-
furic acid concentration in mixed acid systems. Additionally, the
rate of aromatic nitration is known to increase with increasing
sulfuric acid concentration. Of greater significance, perhaps, is
the decrease in both organic by-product and nitrous acid formation
with increasing sulfuric acid concentration. Based on studies of the
mono-nitration of toluene, if the proportion of sulfuric acid is
increased towards the limit of about 37 mole percent sulfuric acid,
15 mole percent nitric acid, and 48 mole percent water, organic
by-product formation is decreased by over 25 percent.
72
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Generic Nitrobenzene Reduction Processes
Not suprisingly, aniline, like it's immediate precursor nitro-
benzene, was among the first organic chemicals to be manufactured
on an industrial scale. Traditionally this was a batch process
using agitated reactors, in which iron (generally in the form of
turnings), water and 30 percent hydrochloric acid reduced the
nitrobenzene to aniline in 90 to 95 percent yield. Drawbacks of
this process include: (1) large quantities of iron (II) and iron
(III) hydroxides are generated which must be disposed of in an
environmentally acceptable way; and (2) high labor requirements.
Interestingly enough, though largely replaced by continuous catalytic
hydrogenation processes, the above method is now used for production
of piment grade iron oxides with aniline as a by-product. Thus,
three manufacturing configurations will be. considered: vapor phase
catalytic processes; liquid phase catalytic processes; and the
Bechamp process (batch).
Catalytic Processes
The major portion of the United State aniline capacity is
based upon continous vapor phase processes. Typically, nitrobenzene
(containing less than 10 ppm thiophene) is vaporized in a stream
of hydrogen and introduced into the fluidized bed reactor (see
Figure 6). The catalyst, 10 to 20 percent copper by weight on
silica, is made by spray-drying a silicic acid matrix (20 to 150 p.m)
with a cuprammonium compound and activated in situ with hydrogen at
73
-------
6A
Purge
Hydrogen
Nitrobenzene.
7A
Volatile
Impurities
Aniline
c
O
a
co
w
o
u
9A
To Wastewater
Treatment
^—Nitrobenzene
Source: Karkalits, 1959.
FIGURES
CONTINUOUS VAPOR PHASE PRODUCTION OF ANILINE
74
-------
250°C. The nitrobenzene vapor-hydrogen mixture (300 percent excess
hydrogen) is fed through a porous distribution plate at the bottom of
the fluidized bed reactor. Actual reaction conditions have not been
publicized but the basic patent (Karkalits, 1959) claims operation at
270°C and 1.5 atm with a contact time of several seconds between
catalyst and reaction mixture. The reaction is highly exothermic and
heat is removed by circulating a cool fluid (most probably nitroben-
zene) through tubes suspended in the fluidized bed. Catalyst fines
are removed from the product gas with porous stainless steel filters
in the top of the reactor.
The crude product mixture (aniline, hydrogen, and water) leaving
the reactor is condensed and separated from the gas stream (3.5 per-
cent water, 0.5 percent aniline, balance hydrogen); most of this gas
stream is compressed and recycled to the reactor, but a small portion
is vented to prevent buildup of gaseous impurities introduced with
the hydrogen feed.
The aqueous and organic phases are separated in a decanter. The
organic phase (lower layer), consisting principally of aniline, up
to 0.5 percent nitrobenzene, and 5 percent water is purified by two
stage distillation. In the crude still, aniline and water are removed
overhead, while higher boiling organic impurities, such as nitro-
benzene, remain in the still bottoms. The overhead product from the
first column, is purified in a finishing still; water is withdrawn
75
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from the top of the column while aniline is withdrawn in a side-
stream near the bottom of the column. The bottom product is recycled
to the crude aniline still. Obviously other separation processes
are possible: water may first be removed by distillation from the
organic material; this may then be distilled to produce aniline
as an overhead product. The waste streams from this separation
process are similar to those described previously.
Sulfur compounds (e.g., thiophenes) irreversibly poison the
catalyst by forming copper sulfide; in addition, dinitrobenzenes are
also reported to decrease catalyst activity (Gharda and Sliepcevich,
1960). Since commercial production of aniline is reported to be 1500
grams of aniline per gram of catalyst, deactivation via these mecha-
nisms does not appear to be serious. By burning off the organic
materials which deposit during normal operation, the catalyst may be
reactivated to near initial activity. Presumably, this regeneration
is done in situ, and probably not more than several times a year.
Recovery of aniline from the aqueous phase (approximately 3
percent by weight) of the decanter, if not economically justified,
is required to meet current water quality standards. Aniline may be
recovered from this phase by countercurrent extraction with nitro-
benzene, for which an extraction efficiency of 98 percent is claimed
(Sittig, 1974). An alternative technique is to concentrate aniline
from this stream using a stream stripper and to then incinerate the
enriched aniline water mixture (EPA, 1972).
76
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Further variants of nitrobenzene reduction processes have been
described in the patent literature. Among these are a fixed bed
process which uses a nickel sulfide catalyst deposited on alumina
(Winstrom, 1958, 1959) and liquid phase processes using supported
palladium (Thelen et.al., 1975), rhodium (iqbal, 1976), or nickel
catalysts (Cooke, 1966). Of these liquid phase processes, only the
nickel catalyst system is used commercially in the United States and
therefore is the only configuration to be considered in the following
discussion.
The reactor, equipped with suitable heat exchanger and an agitator
capable of dispersing hydrogen at high rates, is charged initially
with aniline, ethanolamine, and a supported nickel catalyst (both 5
percent by weight based on aniline). As illustrated in Figure 7,
nitrobenzene (containing less than lOppm of thiophene) is continuously
fed, together with hydrogen, to the reactor at such a rate that the
concentration of aniline (by weight) in the liquid phase is 95 percent
or greater; product aniline and water are removed as a vapor. The
reaction proceeds at temperatures of 160 to 180°C under pressures of 1
to 2 atmospheres. The temperature of the reaction is controlled by
circulating a coolant (generally water or low pressure steam) through
heat exchangers (which remove approximately 65 percent of the heat of
the reaction) and by evaporation of aniline and water from the reactor.
The product mixture (hydrogen, aniline, and water) is cooled
and separated in a binary separator. Because the reaction is strongly
77
-------
6B
Purge
Hydrogen-
Catalyst -
Nitrobenzene
7B
Volatile Impurities
• Aniline
Still Bottoms
e
o
4J O
X O
w
9B
To Wastewater
Treatment
•Nitrobenzene
FIGURE?
CONTINUOUS LIQUID PHASE PRODUCTION OF ANILINE
78
-------
exothermic, generally more aniline is evaporated from the reactor
than is produced by reduction of nitrobenzene; therefore a portion
of the condensed aniline is returned to the reactor. Hydrogen is
also recycled from the separator to the reactor, although about 5
percent of this stream is purged to prevent accumulation of volatile
impurities. Though the purification procedures are not specified in
the basic patent (Cooke, 1966), a process similar to that shown in
Figure 6 is assumed.
Batch Processes
The final configuration to be considered is the Bechamp process
(see Figure 8). Crude nitrobenzene is charged to a reactor fitted
with an efficient reflux condenser and agitator. Cast iron, water,
and dilute (30 percent) hydrochloric acid are gradually added to the
nitrobenzene. Typically 10 to 20 percent of the total iron is added
initially and the mixture heated to reflux temperature ( 200°C). The
remaining iron is added at such a rate so as to maintain reflux
conditions.
'The water used in the reaction is generally in the form of
aniline water recovered from the separator. Not only does this
procedure minimize effluent discharges, but the catalytically active
iron salts are also recycled. The weight ratio of reactants is
approximately 115 parts of iron, 0.27 part of hydrogen chloride and
60 parts of water per 100 parts of nitrobenezene.
79
-------
Water/
Hydrochloric
Acid
Iron
Nitrobenzene
7C
Volatile Impurities
oo
o
Aniline
Sludge
/ X
8C
Still Bottoms
11
To Wastewater
Treatment
Fe3°4
Steam
10
To Wastewater
Treatment
FIGURES
BATCH PRODUCTION OF ANILINE
-------
At the end of the reaction ( 10 hour for a 2270 kg charge),
aniline may be separated from the resulting sludge by any number
of methods including steam distillation, vacuum distillation, fil-
tration, centrifugation, or syphoning. Typically the product is
neutralized with sodium carbonate and allowed to separate. Aniline,
along with some reaction water, is decanted; the remaining aniline
may be separated from the sludge by steam distillation. After
drying, this sludge may be used in pigment manufacture. The water-
aniline mixture is purified as discussed previously and shown in
Figures 6 and 7.
Effluent species have been previously identified and summarized
in Table VII. This information, together with a generic process
configuration of nitrobenzene and aniline manufacture previously
formulated, is presented in Figure 9.
*
Three process configurations have been formulated for aniline
manufacture. Because of process similarities and to avoid
duplication, only the generic process for vapor phase hydro-
genation of aniline is presented.
81
-------
NITROBENZENE MANUFACTURE
ANILINE MANUFACTURE
6
Purge
0
1 — »r 3 \* AIr "yd
1 ^-T-' Cat
Benzene M K 7 r «
Sulfurlc J S fs
^cZdi \\) v-
Add ^ |_V 1)a2C03.
A
Vent
1 1 .-.A
00 POINT 1 * J /rf~\ 1 S
KJ BENZENE CJ o foil A
NITROALKANES g H 1 * M 1 1» o
NITROBENZENE a 1 " » 1 5
NITROGEN OXIDES 1 J° 1 5
POINT 2 Steam — > ^v_X ^V^
NITROALKANES T
NITROBENZENE Nitric Acid
NITROGEN OXIDES (Recycle to
POINT 3 Reactor)
BEN ZOIL ACID
ruHHriYvi ir anns .. __
M J U^Ta Wastewater I
1 -g 1 Treatment 1
•\3/ « r 1
Y PuvrUrf 1
p-> Nitrobenzene
x*^>v Product
( ° \
•H
1 S|
•H O
4-1 U
00
L-^ Still Bottoms to
Wastewater
Treatment
§ -Ho Wastevater
u g Treatment
NITRATES ' ^ "S
NITRITES " <->
NITROBENZENE Steam— •+ ™
NITROPHENOL \f J
Sulfurlc Acid ^-T^
POINT 4 (Recycle to < 1
OINITROBENZENE leactor?
NITROBENZENE Reactor)
alyst— J § I
1 at \ o
._ fcl " \ Q
,_!_,
g
•H
*-> g
O B
« 3
\* •-«
*J O
a5
|~1 I » Volatile
1 ^^^ Impurities
/ I c 1
/ 5 -*• Aniline
' a
^^31
4J •-!
453
v° /
T 8
' > Still Bottoms
to Wastewater
Treatment
' > To Wastewater
Treatment
POINT 6 POINTS
ANILINE AMINOPHENOLS
CARBON MONOXIDE AZEPIN
HYDROGEN OIPHENYLAMINE
METHENE NITROBENZENE
NITROBENZENE PHENYLENEDIAMINE
NITROGEN CONTAINING HIGH
POINT 7 MOLECULAR WEIGHT POLYMERS
CYCLOHEXYLAMINE
VOLATILE AMINES POINTS
WATER AMINOPHENOL
ANILINE
NITROBENZENE
PHENYLENEDIAMINE
WATER SOLUBLE AMINES
NITROPHENOL
NITROGEN CONTAINING
HIGH MOLECULAR WEIGHT POLYMERS
POLYCAR8OXYLIC ACID
POINT 5
NITROBENZENE
NITROPHENOL
POLYCARBOXYLIC ACID
NITROGEN CONTAINING HIGH
MOLECULAR WEIGHT POLYMERS
FIGURES
SIGNIFICANT POLLUTANTS FROM
NITROBENZENE/ANILINE MANUFACTURE
-------
SECTION III
INDUSTRIAL WASTEWATER MANAGEMENT
INTRODUCTION
In the first half of this report, potential pollutants from the
manufacture of nitrobenzene/aniline were identified. The remainder
of the report will discuss specific industrial wastewater practices
for handling those waste streams identified, and evaluate alternative
treatment practices for removing toxic contaminants from the process
effluents prior to discharge to the environment.
INDUSTRIAL WASTEWATER TREATMENT PRACTICES
In selecting the appropriate mode of treatment for an industrial
waste stream, factors other than just the simple reduction of standard
wastewater parameters should be examined. Specifically, the following
areas merit consideration:
• The origin of toxic pollutants, in terms of both
reaction chemistry and process configuration;
• The identification of inhibitory or refractory
components of the waste stream;
• The acceptability of current treatment practices; and
• The compatability of treatment processes in
achieving the effluent requirements.
Wastewater management of toxic effluent streams involves both
in-plant control technology and end-of-pipe treatment practices.
Procedures to reduce the strength and volume of the final effluent
stream may include improved housekeeping practices, waste stream
83
-------
segregation, and reuse or recycle of process streams. End-of-pipe
treatment technology which, for purposes of this report, refers to
both pretreatment and final treatment practices, may involve physical-
chemical treatment techniques, biological treatment, or a combination
of the above. Waste disposal by subsurface injection, although widely
accepted in the past, is being more closely regulated by Federal and
State agencies, and is generally discouraged when alternate treatment
and disposal systems are available.
The selection of the mode of treatment is largely dependent on
the volume of waste to be treated and the pollutants present.
Traditionally, the efficiency of a treatment method is measured by
the percent removal of 5-day biochemical oxygen demand (BOD ) and
total suspended solids (TSS). Chemical oxygen demand (COD), or total
organic carbon (TOO are used to measure the strength of industrial
waste. Discharge standards commonly include specific restrictions on
the pH range, effluent color, level of ammonia-nitrogen, and total
Kjeldahl nitrogen (TKN). Where applicable, other wastewater constit-
uents, such as free cyanide, heavy metal, or phenol concentrations
may be monitored and controlled. A brief, general review of biolog-
ical and physical treatment methods used by industrial dischargers
follows.
Biological treatment involves the breakdown and stabilization of
organic material by aerobic or anaerobic microorganisms. Treatment
processes available for industrial application include: variations
84
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of the activated sludge process, aerated lagoon systems, oxidation or
contact stabilization ponds, trickling filters, rotating biological
discs, and anaerobic lagoons or digesters. Historically, the acti-
vated sludge process, in which aerobic microorganisms are mixed with
the influent wastewater and subsequently removed as a sludge, has had
the broadest application to industrial wastes. Detention periods and
process configurations may be modified to achieve the desired level
of BOD removal, nitrification, and in some cases, denitrification.
The toxicity of the waste, the biodegradability of the waste (typically
judged by the BOD/COD ratio), and the metabolic rate of the micro-
organisms (i.e., the effective removal rate) all influence process
efficiency.
Physical-chemical treatment techniques may be used alone or in
combination with biological processes to achieve effluent standards.
Neutralization and equalization, for example, are commonly used as
pretreatment steps prior to activated sludge treatment. Soluble
organic compounds not effectively removed by biological treatment may
be separated from waste streams by adsorption (generally on either
carbon or an ion exchange resin), stripping techniques, distillation,
solvent extraction, or membrane processes (i.e., ultrafiltration,
reverse osmosis, electrodialysis). Oxidation, acid or alkaline
hydrolysis, photolysis, chlorinolysis, or incineration have also been
used to degrade organic species in process wastewater streams.
85
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The selected mode of treatment is determined by the availability
of different treatment operations and processes to economically
achieve the desired effluent. The design criteria for a specific
treatment facility will vary with the strength and volume of the
wastewater stream and the final means of effluent disposal. In each
case, the process configuration and plant layout should be examined
to identify point source discharges and pollutant loadings. Where
possible, in-process changes, stream segregation, and solvent reuse
should be implemented to reduce the process waste load.
CURRENT TREATMENT OF WASTEWATER FROM NITROBENZENE/ANILINE MANUFACTURE
Wastewater Characteristics
Major process waste streams generated during the manufacture of
nitrobenzene/aniline include: the nitrobenzene wash water (Point
No. 3), the nitrobenzene distillation column overhead (Point No. 5)
and the aniline recovery column purge (Point No. 8) (See Figure 9).
Major pollutants include aniline, nitrobenzene, aminophenols, nitro-
phenols, carboxylic acids, water soluble amines, nitrates, and
nitrites. Table VIII lists typical concentrations of selected
pollutants found in nitrobenzene/aniline waste streams, as reported
by two manufacturers. A point source-by-point source summary, of all
significant pollutants predicted from the manufacturing process are
presented in Figure 9.
86
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TABLE VIII
Characterization of Raw Waste Loading From
Nitrobenzene/Aniline Manufacture*> 2
oo
Nitrobenzene
Av. Min.
Flow
PH
COD
TOC
TSS
Aniline
Benzene
Nitrobenzene
170-897
1.8
5.8
1.6-3.5
0.09
-
-
^
110-501
0.6-1.7
3.8
0.6-0.9
0.04
-
-
^
Process Lines
Max . Av .
220-1840
5.2-2.1
8.6
2.2-11.7
0.18
-
-
*~
73-787
8.4
7
7.6
-
0.067
0.005
0.002
Aniline
Min.
23-471
5.7-7
-
1.8
-
0.005
0
0
Max.
110-1040
, 10.2-10.5
-
27.5
-
0.49
0.031
0.012
Data reported in units of lb/1000 Ib of - product, with the exception of pH.
"Compiliation of data reported by two manufacturers.
Source: EPA Organics and Plastics 1976 308 Response BPT Master File Listing.
-------
Data characterizing the combined waste load from an nitrobenzene/
aniline manufacturing facility have been previously published by EPA
as part of support material for the development of effluent limita-
tions (Train, 1975). However, as those effluent limitations were
remanded in 1976 (questionable procedures were claimed to have been
used for the measurement of wastewater parameters), these data are
not provided within this report.
Federal and State Discharge Requirements
The major objective of the Federal Water Pollution Control Act,
as amended*, is to restore and maintain the chemical, physical, and
biological integrity of the Nation's waters. Among the goals and
policies set forth by the Act, the following address industrial point
source discharges to navigable streams:
• It is the national goal that the discharge of pollutants into
the navigable waters be eliminated by 1985.
• It is the national goal that wherever attainable, an interim
goal of water quality which provides for the protection and
propagation of fish, shellfish, and wildlife and provides for
recreation in and on the water be achieved by July 1, 1983.
• It is the national policy that the discharge of toxic pollu-
tants in toxic amounts be prohibited.
• It is the national policy that a major research and demonstra-
tion effort be made to develop technology necessary to elimi-
nate the discharge of pollutants into the navigable waters,
waters of the contiguous zone, and the oceans.
*The Federal Water Pollution Control Act Amendments of 1972 (PL 92-500)
further extended the scope of the Federal Water Pollution Control Act
of 1965, as previously amended in 1966 and 1970. New amendments to
this legislation, The Clean Water Act of 1977 (PL 92-217), were signed
into law in December, 1977.
88
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In committing the nation to meeting these goals and policies, the Act
established an implementation schedule for compliance. To this end,
Section 301(b) of the Act mandates the following:
• Not later than July 1, 1977, effluent limitations for point
sources, other than publicly owned treatment works, shall
require the implementation of the best practicable control
technology currently available (BPT) as defined by Section
304.* Those discharges to publicly owned treatment works
shall comply with any applicable pretreatment standards
defined under Section 307 of the Act.
• Not later than July 1, 1984 effluent limitations for cate-
gories and classes of point sources, other than publicly
owned treatment works will require application of the best
available technology economically achievable (BAT) for the 65
toxic pollutants (as listed in Appendix I), which will result
in reasonable further progress toward the national goal of
eliminating pollutant discharge.** In the case of the
discharges of a pollutant into a publicly owned treatment
work, compliance with applicable pretreatment standards is
required.
• Compliance within 1 to 3 years of issuance for any toxic
standard established under Section 307(a).
• Not later than July 1, 1984, effluent limitations for point
sources, other than publicly owned treatment works, shall
require application of best conventional pollutant control
technology (BCT).
• Not later than 3 years after the date such limitations are
established, but in no case later than July 1, 1987, com-
pliance with effluent limitations for all unconventional
pollutants (i.e., those pollutants not included under toxic
regulations or BCT).***
*An estimated 85 percent of industrial dischargers met this deadline.
For those dischargers that have acted "in good faith" the compliance
schedule has been extended to April 1, 1979 (Barrett, 1978).
**Industry must comply within 3 years of issuance of BAT regulations
for any chemical added to the list.
***Under Section 304(a) the EPA Administrators directed to publish a
list identifying a list of conventional pollutants. The list, which
is to be revised as deemed appropriate, shall include, but is not
limited to, BOD, suspended solids, fecal coliform, and pH.
89
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Additionally, the Administrator of the EPA, under Section 304(b)
of the Act, is directed to promulgate regulations which identify in
terms of wastewater characteristics, the degree of effluent reduction
attainable through the application of BPT, BCT, and BAT for classes
and categories of point sources (other than publicly owned treatment
works). These regulations, or effluent limitation guidelines, are
to specify those factors related to the establishment of BPT, BCT,
and BAT control measures and practices, such as, the process employed,
the age of equipment, process changes, the engineering aspects of the
application of various types of control techniques, non-water quality
impacts, and the cost of achieving such effluent reduction.
The organic chemicals industry is highly complex, covering two
Standard Industrial Classification (SIC) Groups in which 260 product-
process segments have been identified. Thus, for the purpose of
developing effluent regulations, the EPA has categorized selected
segments of the industry into two phases. On April 25, 1974, Part
414 was added to Title 40 of the Code of Federal Regulations, estab-
lishing final effluent limitations for existing sources in 40 product-
process segments (Phase I). Additionally, performance and pretreat-
ment standards for new sources in the organic chemical manufacturing
point source category were defined. Interim final regulations for -
Phase II were published on January 5, 1976, amending 40 CFR to include
27 additional product-process segments and a new subcategory.
Chemicals were grouped within four subcategories on the basis of
90
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similarities of process operations. The manufacture of nitrobenzene/
aniline by the nitration of benzene and its subsequent hydrogenation
is included as part of "Subcategory C - Aqueous Liquid Phase Reaction
Systems."
In establishing Phase I and Phase II regulations, the Agency
acknowledged the toxicity of certain organic chemical manufacturing
wastewaters and the potential hazard to the environment; however,
faced with a mammoth task and rapidly approaching deadlines, effluent
limitations were written in terms of the conventional parameters of
BOD,, TSS, COD, and pH. Furthermore, since biological treatment was
the identified BPT for the organic chemicals point source category,
effluent limitations were established for specific pollutants known
to be inhibitory to biological treatment and detected in significant
concentrations in given waste streams. Table IX presents the BPT
regulations and standards of performance for new point sources for
•
aniline manufacture.
TABLE IX
BPT Effluent Limitations and New Source Standards
of Performance for Aniline Manufacture
Effluent
Characteristic
BOD5
TSS
pH
Effluent Limitations kg/kkg (lb/1000 Ib) of Product
BPT New Source
Daily
Maximum
1.15
0.15
6.0-9.0
30-Day
Average
0.51
0.68
. -
Daily
Maximum-
0.94
0.76
6.0-9.0
30-Day
Average
0.42
0.34
-
Source: Federal Register, Vol. 39, No. 81, April 25, 1974.
91
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As part of the rule making process, the EPA is required to
gather information and comments pertinent to proposed and established
regulations. Strong opposition to the sampling and analytical tech-
niques used by the EPA contractor in developing effluent limitations
led to court action in 1976 (after issuance of Phase II regulations
oh January 5, 1976). As a result, the EPA eventually concluded that
the contractor retained by the Agency had used procedures to measure
certain parameters of the industry wastewaters "which may have been,
in certain instances, faulty" (Federal Register, April 1, 1976).
Thus, in accordance with a decision by the U.S. Court of Appeals, the
EPA revoked all of 40 CFR 414 regulations concerning organic chemicals
with the exception of those concerning butadiene manufacture. At this
time, there are no existing federal regulations under Title III of the
Federal Water Pollution Control Act governing the point source dis-
charges from the manufacture of nitrobenzene/aniline.
Under Title IV of PL 92-500, however, any discharger to navigable
waters must be certified by the State in which the discharge originates
and issued a permit under the National Pollutant Discharge Elimination
System (NPDES). Each NPDES permit defines effluent limitations and
monitoring requirements, as well as a schedule of compliance. In the
absence of effluent limitation regulations, discharge limitations have
been established on a case-by-case basis, as authorized by the State
agency and approved by the Regional Water Enforcement Board of the
EPA. NPDES permits are to be "revised or modified in accordance with
92
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toxic effluent standards or prohibition" under Section 307(a) of the
Act.
While injection wells are not specifically addressed by the NPDES
legislation, EPA has established rules and regulations governing waste
disposal wells within the framework of the NPDES system. Industrial
dischargers are typically required to monitor flow rate, injection
and annulus pressure for each well; moreover, no new wells may be put
into operation without re-application and subsequent NPDES permit
modification. Deep well disposal is no longer considered to be a
viable disposal method by EPA (Federal Register, January 6, 1977).*
Current Industrial Practices
There are five U.S. manufacturers of nitrobenzene/aniline with
facilities currently in operation at six locations; a sixth manufac-
turer, Mallinckrodt, Inc. produces aniline from a supplier delivered
nitrobenzene feedstock.** Table X presents a listing of these manu-
facturers, indicating nameplate capacities and current wastewater
treatment practices. As will be discussed in Section IV, there are
several practicable methods by which wastewaters containing nitro-
phenols, nitrobenzenes, and aniline may be treated. However, as most
*In an effort to control such practices (though short of out-
lawing deep well injection), the EPA has required permit holders to
submit engineering summaries of disposal practices and "practicable
alternatives" to subsurface disposal including evaluation of: (1)
process changes and in-plant reductions to alter the nature of the
wastes; (2) incineration; (3) biological treatment methods; (4)
physical-chemical treatment methods, and (5) combinations of the
above.
**American Cyanamid's production facilities in Bound Brook, New
Jersey, reported to be on stand-by since 1974, are to be reacti-
vated in mid 1978.
93
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TABLE X
MAJOR U.S. NITROBENZENE/ANILINE MANUFACTURERS
MANUFACTURER
First Mississippi Corporation
Fascagoula, Mississippi
American Cyanamid
Willow Island, West Virginia
E.I. duFont de Nemours & Co.
Beaumont, Texas
E.I. duFont de Nemours & Co.
Glbbstovn, Mew Jersey
MalllnckrodC, Inc.
Raleigh, North Carolina
Mobay Chemical Corporation
New Martinsville, West Virginia
Rubicon Chemical, Inc.
Geismar, Louisiana
NAME PLATE CAPACITY
NITROBENZENE ANILINE
(Million pounds/year)
135 100
60 50
310 230
200 130
4
135 100
75 60
•>
NPDES NO.
MS 0001791
WV 0000787
TX 0004669
NJ 0004219
NC 0003538
WV 0005169
LA 0000892
MEANS OF WASTEWATER
TREATMENT2
Neutralization, equal-
ization, stripping,
activated carbon adsorp-
tion.
Aerated lagoon, biologi-
cal contact, clarification,
sludge handling.
Equalization, aerated
lagoon, activated sludge
activated carbon
adsorption.
Organic extraction.
stripping, neutralization,
equalization, clarification.
Equalization, stabiliza-
tion pond, activated sludge,
clarification, chemical
treatment (odor control) ,
stabilization pond, land
application.
Neutralization, clarifica-
tion, equalization, activated
sludge, activated carbon
adsorption.
Subsurface disposal.
Chemical Marketing Reporter, January 7, 1974, May 24, 1971, August 30, 1976 and communications with Industry;
as cited In Directory of Chemical Producers - U.S.A.
Data collected from EPA Organics and Plastics 308 Response (1976), BPT Master File Listing. Note: This listing
represents all unit treatment processes in use for all nitrobenzene/aniline manufacturing effluents, however, it
is not the intention of this listing to necessarily imply an ordering of unit processes. Furthermore, segregated
process streams are typically combined with other manufacturing wastes at each facility, making a detailed descrip-
tion of wastewater treatment facilities from publicly available information impossible.
American Cyanamid facility in Bound Brook, New Jersey has been on stand-by since 1974; nitrobenzene capacity:
85 million pounds/year; and aniline capacity: 60 million pounds/year. This plant is due to come on-line in 1978.
f,
Production figures are unavailable for this aniline manufacturer. Note: Nitrobenzene is not produced at this
facility..
94
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manufacturers produce numerous chemical compounds at a particular
manufacturing site and historically, have combined product waste
lines prior to treatment, it is impossible to assess the efficiency
of a treatment scheme specific to nitrobenzene/aniline wastes. Fur-
thermore, data resulting from treatability studies on segregated
streams have been classified by manufacturers as confidential, and
therefore, are unavailable for reference.
At this time, a wide variety of treatment techniques are being
applied to nitrobenzene/aniline manufacturing wastewaters. First
Mississippi Corporation, a subsidiary of First Chemical Corporation,
completed installation of both steam stripping columns and granular
activated carbon columns at their Pascagoula, Mississippi plant in
1977. This exemplary operation was designed to achieve zero pollutant
discharge; however, wastewater treatment data (e.g., influent/effluent
analyses) are not publicly available at this time (desRosiers, 1978).
Carbon adsorption is also employed by both duPont (at their Beaumont,
Texas facility) and Mobay Chemical Corporation for removal of dis-
solved organics, following pretreatment and activated sludge treat-
ment of the waste streams.* At their Gibbstown, New Jersey facility,
duPont provides organic extraction and stripping units, while American
Cyanamid and Mallinckrodt rely on biological treatment for removal of
*0nly limited information is publicly available indicating the manner
in which waste streams are segregated (and/or mixed with waste
streams from other process operations) at a particular manufacturing
site.
95
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organic pollutants. Only Rubicon Chemicals, Inc. practices deep well
disposal of nitrobenzene/aniline process streams.*
Future Regulatory Concerns
In recent years, through court and congressional action, tighter
restrictions have been placed on the discharge of hazardous or toxic
materials. The four laws which directly affect the manufacture of
nitrobenzene/aniline are: (1) The Clean Air Act; (2) The Toxic Sub-
stances Control Act; (3) The Resource Recovery and Conservation Act;
and (4) The Clean Water Act of 1977.
• The Clean Air Act, PL 91-604 (passed in 1970, and subsequently
amended in 1977) requires regulation of specific pollutants
under a permit system for point source emissions. Air
emissions resulting from nitrobenzene manufacture have been
studied in detail (Process Research, Inc., 1972).
» The Toxic Substances Control Act (TOSCA), PL 94-469, which
was signed into law in October of 1976, authorizes the EPA to
regulate the manufacturing, processing, distribution, use,
and disposal of chemical substances or mixtures deemed to
represent an "unreasonable risk of injury to health or the
environment." The Administrator is directed to control
hazardous emissions or discharges to the environment under
the Clean Air Act and Federal Water Pollution Control
Act, as necessary, unless, it is in the public interest
to enforce additional protective measures under TOSCA.
**In general, proper site selection (i.e., geological conditions suit-
able for the emplacement of fluids), well design, and construction
techniques used in injection well systems, make contamination of
fresh water aquifers remote. However, deep well disposal is not
without hazards for extremely toxic and persistent wastes. A
serious threat to nearby groundwater supplies is potentially posed
by either the failure of the well system or migrations of the
wastes. Specifically, in the case of deep well disposal of nitro-
benzene/aniline waste streams, nitrobenzene and nitrophenol are
deemed "hazardous for deep well injection in any system" (Reeder,
et al., 1977 and Water Pollution Control Federation, 1977).
96
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• The Resource Recovery and Conservation Act (PL 94-580) signed
into law in October of 1976, will control the transportation
and disposal of solid wastes designated as toxic or hazardous.
• The Clean Water Act of 1977 (PL 95-217) which embodies the
major points of the "consent agreement" (signed in 1976 by
EPA and environmental interest groups), requires stricter
regulation of toxic discharges. Aside from establishing
effluent limitations for 65 toxic pollutants in terms of
BAT, pretreatment standards are required for wastes dis-
charged to publicly owned treatment works (POTW). However,
if the treatment by such POTW removes all or any part of the
toxic pollutant in question (and discharge of the pollutant
does not prevent sludge use or disposal), the pre-treatment
requirements for the sources may now be so modified as to
reflect the removal rate achieved by the POTW.
Although the Safe Drinking Water Act (PL 93-523) enacted in 1974
is not explicitly directed toward point source discharges, the EPA is
empowered by this legislation "to promulgate regulations which contain
minimum requirements for effective programs to prevent underground
injection practices which endanger potential or present drinking water
sources" (Federal Register, August 31, 1976). The responsibility of
enforcement is left to State agencies under a federally approved per-
mit program. Thus, the proposed regulations are intended to give
maximum flexibility to the States in designing underground injection
control programs, in recognition of the large degree of variation in
geological conditions, groundwater use, and existing deep well injec-
tion operations. While key provisions of this Act have yet to be
defined, regulations will, at the very least, require the routine
monitoring and inspection of subsurface injection systems (Federal
Register, August 1976).
97
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However, as was the case with Section 307(a) of PL 92-500 and
the resulting "consent agreement," judicial interpretation of the
laws will undoubtedly play a major role in their enforcement. It
is clear, however, that with the passage of The Clean Water Act of
1977, effluent guidelines promulgated by EPA will strike a balance
between controlling the classic water quality parameters (i.e., BOD,.,
TSSj pH) and specific toxic pollutants.
98
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SECTION IV
METHODS OF WASTEWATER TREATMENT
INTRODUCTION
The quantity and quality of the pollutant waste load from a manu-
facturing facility is dependent on the degree of product purification,
by-product separation and recovery, solvent reuse and recycle, and
stream segregation practiced. Ideally, the treatment system best
suited for a particular manufacturing operation should be approached
on an individual basis, point source-by-point source. However, from
a historical perspective, treatment of industrial effluents has been
limited, in most cases, to the application of "end-of-pipe" technolo-
gies to combined waste streams.*
Typically, the treatability of a waste stream is described in
terms of its biodegradability, as biological treatment usually
provides the most cost-effective means of treating a high volume,
high (organic) strength industrial waste (i.e., minimum capital and
operating costs). Furthermore, biodegradability serves as an impor-
tant indicator of the toxic nature of the waste load upon discharge to
the environment. However, as indicated in Section III, the nature of
the organic waste load from nitrobenzene/aniline manufacture is
conducive to physical treatment (i.e., activated carbon adsorption,
liquid-liquid extraction, steam stripping). Thus, in presenting a
*In practice, waste streams from not only a specific manufacturing
process, but also from several product lines, may be combined, prior
to treatment and discharge.
99
-------
general discussion and literature review of wastewater treatment from
nitrobenzene/aniline manufacture, this section of the report is
divided into three major subsections: (1) biological treatment; (2)
physical treatment; and (3) combinations of selected treatment
technologies. Furthermore, with the exception of specific treatment
processes, such as counter-current extraction of aniline with nitro-
benzene, this section will not be specific to individual process
waste streams.
Of the several hundred potential pollutants from nitrobenzene/
aniline manufacture (see Table VII), 10 compounds* are EPA priority
pollutants (see Appendix III). In addition, many other pollutants
(e.g., acridine, azepins, diphenylamine, to name but.a few) represent
toxic discharges to the environment. However, only those pollutants
that were repeatedly cited in the literature as contributing to the
refractory, inhibitory, or toxic nature of the waste load (that is
nitrobenzene, dinitrobenzene, aniline, nitrophenols, and soluble
amines) are considered explicitly in evaluating wastewater treatment
alternatives. This decision was based on two major considerations:
(1) It is impractical from an engineering standpoint to discuss
treatment options on a pollutant-by-pollutant basis.
Treatment operations and processes are selected on the
basis of their effectiveness in treating a particular
wastewater, with many constituents.
(2) Without laboratory or pilot test data, a ranking of each
treatment operation and process, based on its ability to
remove each of the pollutants potentially present, would
be speculative.
*Benzene, benzidine, nitrobenzene, 2-nitrophenol, 4-nitrophenol, 2,4-
dinitrophenol, 2,4-dinitrotoluene, 2,6-dinitrotoluene, phenol, and
toluene.
100
-------
It is not unreasonable to assume, however, that a treatment method
capable of removing nitrobenzene, dinitrobenzene, nitrophenols, and
aniline from wastewater, might also be effective for the treatment of
other toxic pollutants present in low, or trace concentrations.
BIOLOGICAL TREATMENT
Water and soil organisms naturally found in the environment
have only a limited ability to assimilate synthetic organic chemicals
found in an industrial waste stream. However certain compounds
which may appear to be resistant to biological degradation in natural
waters, may, in fact, be readily oxidized by a microbial population
adapted to the waste. Thus, the successful application of biological
processes to the treatment of hazardous organic wastes is largely
dependent on: (l) the ability to acclimate biological organisms to
the waste stream (e.g., activated sludge); (2) the operation of the
treatment system at a practicable removal rate (throughout seasonal
changes); and (3) the stability of the treatment system during
variations in the waste loading (i.e., operation near toxic or
inhibitory concentrations).
Table XI presents a summary of those studies pertinent to the
biological degradation and treatment of nitrobenzene/aniline waste-
waters. Although many of the citations are specific to the degrada-
tion pathways (in microbial systems) of pesticide-derived substituted
anilines and nitrophenols, these data do provide valuable informa-
tion as to the susceptibility of such compounds to biochemical
transformation. Furthermore, while only one biological study on
101
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Table XI
Biological Studies of Nitrophenob, Nitrobenzene*, and Aniline-Containing Wastewattn
Investigator
Alexander and
Luetigmon,
1966
Azlm and
Mohyuddin
Barnhart and
Campbell,
1972
"
Bollag and
Russel. 1976
Bordeleau
and Bartha,
1972
Brlngmann
and Kuehn,
1971
Cartwrlght
and Cain,
1959
Chambers et
al., 1963
Chudoba and
Pitter, 1976
Germanler and
Wuhrmann,
1963
Type of Treatment/
Study
Degradation by a mixed
population of soil
mi croor ganlsms
genoua compounds by
Azotobacter vinelandii
sludge
Metabolism of chlor-
inated anilines by a
Paracoccus sp. under
aerobic and anaerobic
conditions.
Biochemical oxidation
of substituted
anilines by fungal
enzymes.
2-stage model purifier
consisting of an
aerator Inoculated
with Azobacter agilis,
and a second stage
overflow basin contain-
ing activated sludge.
Degradation by Mocardia
and a strain of
Paeudoaonas fluorescens
Oxidation by a phenol-
adapted mixed culture
of several bacterial
species, pseudomonads
predominating.
Biological treatment of
nitrobenzene manufac-
turing wastes.
Aerobic degradation by
N.. Alba and several
,—-..•
Substrate
(Concentration)
Substituted benzenes,
Including aniline and
nitrobenzene, in con- .
cent rations of 10 ug/ml
and 5 ug/ml respective-
benzene at concentra-
tions ranging from
10~4M to 10- 2M.
in concentrations of
100 mg/1 as COD, were
mixed with 100 mg/1 as
COD of synthetic waste
(i.e., readily de-
gradable organic com-
pounds and inorganic
nutrients).
Aniline
14 C- labeled 4-
chloro aniline
Synthetic wastewater
containing nitroben-
zene In concentrations
of 118 to 146 mg/1 vas
continuously added.
Nitrobenzene, 2,4-
dinitrophenol, and
2 , 5-dini t rophenol
Substances tested In-
cluded: amlnophanols
(100 mg/1), nitro-
pheaols (100 mg/1) ,
dinltrophenols (60
mg/1), trlnlt rophenol
(100 mg/1). bentene
(100 mg/1) , nitroben-
zene (100 mg/1) .
dinltrobenzenes (100
mg/1) , and aniline
(100 mg/1).
Nitrobenzene, dinltro-
phenols, and dinitro-
benzene.
Nitropbenols , dinltro-
phenols as sola carbon
and nitrogen sources.
Degradation Pathway/
Detention Period
Four day decomposition period for
aniline, greater than 64 days for
nitrobenzene.
determined by colorimetric tests.
aniline test, either aniline or a
degradation product remains.
Ace ty let ion of aniline noted (i.e..
acetylanilideHn two day old growth
medium.
Aniline subjected to Geotrichum
candidum peroxidase and aniline
oxidaae resulted in formation of
polymers.
No reduction products detected.
Reduction of the nit to group to the
corresponding amino moiety.
Oxygen consumption monitored during
Warburg run and compared to an
endogenous control for a period of
up to 240 minutes.
Nitrobenzene and 2,4-dinitrophenol
removed at rates of 3.7 to 4.7 and
7.0 to 7.5 mg~1g"1hr~l, respective-
ly-
Nitrophenols hydroxylated to
resorclnol and 1,2,4-benezenetriol.
Comments
Soil organisms exhibited a pre-
ference to certain ring subati-
tuencs. Many shortcomings in
test conditions cited by authors.
nitrobenzene was insignificant.
Test periods undefined.
Accumulation of the acetylated
aniline was much greater under
aerobic conditions.
Aniline susceptibility to trans-
formation is related to electron
density at the amino groups; the
substituents increases yield of
higher polymers rather than azo-
benzenes .
Nitrobenzene was almost com-
pletely removed in the aeration
stage
Postulated to proceed in Nj,
ervthropolls via the corres-
ponding nleroso- and hydroxyl-
aminobenzoic acid.
Addition of a nltro group to the
phenol ring tends to increase
resistance to oxidation. The
resistance of the nitrobenzene*
to degradation seemed to de-
crease as the number of nltro
groupa increased. Aniline was
oxidized to a limited extant.
50 percent of COD non-biodegrad-
able; reflects presence of m- and
p-dlnltrobenzene, 2,5- and 2-6-
dinltropnenol.
102
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Table XI. {Continued)
Investigator
Hermann, 1959
Hockenbury
and Crady,
1977
Holder and
Wlllox. 1973
Hooper and
Tarry. 1972
Horakova, M.
1976
Joal and
Crady. 197?
Malanay, 1960
Malaney and
McKlnney,
1966
KcCormick at
al.. 1976
Munneck. and
H.ieh, 1974
Pitter, 1976
Typa of Treatment/
Study
Toxlcity Index for in-
dustrial va«te«, util-
izing the standard BODj
teat.
Inhibition of nitrif-
ication by nitrogen -
containing organic
compounds.
Nitrobenzene reduction
in two species of
Arachnlda.
Inhibition of ammonia
oxidation in Nitro-
somonaa.
Haatavatar treatment
by anaerobic digestion.
Inhibition of nitrif-
ication in o«npletely
mixed activated sludge
(CMAS; and fill and
draw activated sludge
(i.e., plug-Clow).
Oxidation of selected
compounds by aniline -
acclimated activated
sludge (Warburg Teat).
Oxidation of selected "
compounds by benzene-
acclimated activated
sludge (Warburg teac) .
Tranaf oration of
nitroaromatic con-
pounds by Veillonella
alkalaacena extracts*
Hicrobial degradation
of p-oicroph«nol (by
isolates from a mixed
culture adapted to
parathion) .
Biological oxidation
by adapted activated
aludge.
Substrate
(Concentration)
Nitrobenzene tested at
varying concentration*
Aniline (100 mg/1)
14 C-nitrobenzene
2,4-dinitrophenol
(2 x 10-4M)
Hitrophenols
Aniline (600 mg/1 aa
COD) feed to CMAS and
fill and draw reactors
500 mg/1 teat sub-
strate-
Nitrobenzene, 1,3-di-
nitrobenzene, 1,4-
dinltrobenzene. and
aniline individually
tested in SOO mg/1
concent rat ions .
Nitrobenzene, nitro-
toluenes, nitrophenole.
and dlnitrobenzenes.
P-nitrophenol (PNP)
varying concentration*.
up to 3.24mM.
All blodegradability
teats were on batch
runs, with the initial
concentration of the
test compound 200 mg/1
COD.
Degradation Pathway/
Detention Period
Toxic concentration SO (TC-.) equal
to 630 ag/1 (i.e., concentration
required to obtain SO percent inhi-
bition of oxygen utilization).
Caused > 75 percent inhibition of
Nitrosomonaa ap., inhibitory effects
Increase as the concentration of
NH. - N increases. At concentra-
tions <1 mg/1* 50 percent inhibition
reported .
Nitrobenzene reduction to aniline
reported .
Rate of HN02 syntheala (fro a NH*
substrate) 27 percent of control.
Negative effect on anaerobic pro-
cess.
CMAS reduced COD to 25 + 3 mg/1 in
effluent; aniline degradation and
nitrification occurred simultaneous-
ly at a solid* retention tine (SET)
of 7 days. SRT had no significant
effect on degradation under plug-
flow conditions; however, at SRT 'a
of 7. 10, and 13 day* aniline re-
moval and nitrification occur
sequent lonally.
Incubation for 120 to 192 hours.
Nitrobenzene poorly oxidized.
Nitro compounds resistant to bio-
oxidation by acclimated sludge
during 192 hour teat (i.e., oxygen
uptake less than control).
Initial conversion of nitro groups
to hydroxyl groups.
Lag period for growth on PNP is
directly proportional to its con-
centration in the medium.
Stoichlooetric release of nitrite
noted.
After 120 hours, the percent COD re-
moved was aa follow*: aniline -
94.5; nitrobenzene - 98.0; o-, o-.
P - nitrophenol - 95.0 to 97.0;
o-, m-, p - aminoptienol - 87. 0 to
95.0; 1,3-dinltrobenzcne -0; 1,4-
dinltrobenzene -0; and 0-, or-,
p - nitro toluene - 98.0 to 98.5.
Comments
Inhibitory "dip" noted at
50 mg/1 nitrobenzene.
Review of organic compounds
that inhibit ammonia and
nitrite oxidation.
In tick experiments, aromatic
hydroxylation of nitrobenzene
to nitrophenols waa of signif-
icance.
Reported uncoupler and inhibitor
of electron transport.
Detoxification achieved by re-
duction of nitro group*.
Study did not examine shock
loading.
1
Substitution of a nitro group
on the benzene ring of aniline
resulted in marked resistance
to biological oxidation.
Amino moiety (e.g., aniline)
greatly increuea resistance
to biological oxidation.
Reactivity of nitro groups ap-
pears to depend not only on
other subetituents, but also on
the position of the nitro groups
relative to these substituents.
Hypothesized nitro group removal
before aromatic ring fisaioa.
Rate of biodegradation in
mg CODg~l hr"1 reported.
103
-------
Table XI. (Concluded)
Investigator
Pltt«r ec
al.. 1974
Fitter and
Rlchtrova,
1974
Rabech and
Frit ache.
1977
Raymond and
Alexander ,
1971
Smith and
Roaazza. 1974
Sudhakar-
Barlk et
al.. 1976
Tlachler and
Eckenf alder.
1969
Tonlinaon
at al.. 1966
Walkar and
Harria,
1969
Type of Treatment/
Study
Blodagradatlon of
aromatic nltro deriva-
tives by adapted acti-
vated aludge.
Biodegradatlon of
aromatic nltro deriva-
tives by adapted acti-
vated aludge
Aniline degradation by
Achronobacter Ir 2.
Metabolism and cometa-
bolism of nitrophenols
(by a p-nltrophenol
utilizing bacterium)
Hydroxylation of aroma-
tic aubatrataa by 11
selected mlcroorganlsma
Matabollam of nltro-
phenols by Paeudomonas
and Bacillus species.
Substrate removal In an
acclimated activated
sludge (both fila-
mentous and non- fila-
mentous aludge) - batch
and contlnuoua nma.
Inhibitory effecta of
specific coapounda on
ammonia oxidation by
activated aludge.
Oxygen uptake by
paeudomonas grown with
aniline aa ita sola
carbon aource
Substrate
(Concentration)
Trinltrophenol,
dlnltrophenola
Aniline (150 to
200 mg/1 aa COO)
Aniline at concentra-
tions of 0.5 to 3.0
mg/1 - ;" •
p-nltrophenol
nr-nitrophenol
Aniline, benzene, and
nitrobenzene
Nitrophenols,
2,4-dlnltrophenol
Influent aniline con-
centrations ranging
from 29 to 184 mg/1;
or 0.2 to 2.5 Kg COD/
Kg MLVSS-day.
Aniline (7.7 mg/1).
2,4-dinitrophenol
(460 mg/1).
2 or 3 u molea of
aniline/3 ml of solu-
tion.
Degradation Pathway/
Detention Period
2-4,6-Trinitrophenol and 3,5-dinitro-
b«nzolc acid resistant to blodagra-
dation. 2,4-dinitrophenol readily
degraded.
Aniline was readily degraded.
Range 0.5;to'1.25 mg/1 dry wt. pro-
duction followed log-growth after a
short lag-phase. At concentrations
>1.S mg/1, inhibition was observed.
Complete inhibition at 3.0 mg/1.
Nitrite formed In stolchlometric
amounts; nr-nltrophenol oxidized to
nltrohydroqulnone.
Aniline was converted to 2-hydroxy
acetanilide, 4-hydroxyaniline ,
acetanlllde, and 2 unidentified
phenolic product. Benzene was
hydroxylated to phenol and two un-
known phenols. Nitrobenzene was
not hydroxylated.
CO 2 and nitrite were identified aa
end products from p-nltrophenol
degradation by both bacteria.
Paeudomonaa produced alt rite from
2,4-dinitrophenol after a lag.
but not fron O-. and m~nltrophenola.
o-nitrophenol and 2,4-dlnltrophenol
were resistant to Bacillus.
Substrate removal (measured aa COD)
was zero order. Variations of
initial concentrations of each com-
pound had no effect on removal rate.
Concentrations given for each coo-
pound Inhibit oxidation of amoDnla
by 75 percent.
Recovery of ammonia in the bacterial
oxidation of aniline nitrogen
reported.
Comments
Law degree of degradation of
2,6- and 2,4-dinitrophenola
observed.
Aniline only source of carbon.
Degradation activity was
200 ug/mg dry wt./houx.
p-nltrophenol incubated with
chloroform treated cells yielded
4-nitrocatechol.
Relative hydroxylase activities
of the selected microorganism*
are presented.
•
m-nltrophenol, noted for resis-
tance to biodegradatlon, was
decomposed to phenol and nitrite
by Bacillus.
Removal rate was found to be
directly proportional to the
biological solids concentration
(MLVSS) for both sludges.
2.3 mg/1 of aniline reduced
ammonia oxidation by 46 percent,
as compared to a control.
Aniline conversion to catechol
with liberation of ammonia
postulated.
104
-------
actual manufacturing wastes has been cited (see Chudoba and Fitter,
1976), the biodegradability and removal rate of nitrobenzenes, nitro-
phenols, and aniline in acclimated systems have been examined. Thus,
Table XI serves as a useful reference point for determination of an
optimal treatment scheme for nitrobenzene/aniline manufacturing wastes.
As indicated, microbial degradation of nitrobenzene has been
reported by Alexander and Lustigman (1966) but neither the pathway
nor the degradation products were identified. Cartwright and Cain
reported reduction of the nitro group of substituted benzenes (nitro-
benzoic acids) to the amino moiety. On the other hand, reduction of
p-nitrophenol to nitrite was reported by Raymond and Alexander (1971).
Environmental degradation of aniline appears to be somewhat
better understood than nitrobenzene. Bordeleau and Bartha (1972)
studied the susceptibility of substituted anilines to enzymatic
transformation by the soil fungus Geotrichum candidum. This research,
which was designed to determine molecular configurations of substi-
tuted anilines that are conducive to efficient biochemical trans-
formation, found azobenzene and high molecular weight amino
polymers to be the principal products of degradation. Furthermore,
as electron-density of the amino group increases, the yield of
amino polymers increases relative to azobenzene.
Aniline utilization by a soil pseudomonad has been reported by
Walker and Harris (1969). While the degradation pathway was not
determined, ammonia was identified as a product of the bacterial
105
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oxidation. A possible pathway, however, is direct conversion of
aniline to catechol with the liberation of ammonia. In support of
this hypothesis, catechol is a well established intermediate in the
breakdown of many aromatic substances, which is immediately oxidized
by aniline grown* pseudomonads.
Malaney (1960) observed that acclimated activated sludge is
able to use aniline as a sole source of carbon. Although the ability
of the aniline-acclimated activated sludge to oxidize N-substituted
anilines and nitroanilines was greatly reduced in. Warburg tests,
Malaney concluded that the sludge could be adapted to a great variety
of compounds related in chemical structure to aniline (e.g., phenyl-
diamines, aminophenols, aminobenzoic acids, and aliphatic amines).
Furthermore-, removal of nitrobenzene and nitrophenols was 98 percent
and 95 to 97 percent complete, respectively, in biodegradability
studies with adapted, activated sludge. However, the non-biodegrad-
ability of dinitrobenzenes, dinitrophenols and trinitrophenols has
been documented (Fitter, 1976; Fitter et al., 1974; and Chudoba and
Fitter, 1976). These research results are not intended to suggest
that effluents suitable for direct discharge to navigable waterways
may be achieved solely by biological treatment.**
*Pseudomonads grown on aniline as its sole source of carbon.
**Potential drawbacks include limited efficiency in the removal
of toxic organic compounds (as compared to physical separation
processes) and possible inhibition of nitrification by degradation
products (see Tomlinson et al., 1966; Hockenbury and Grady, 1977;
and Joel and Grady, 1977).
106
-------
Currently, four manufacturers are utilizing biological processes
to treat nitrobenzene/aniline manufacturing wastes (see Table X)
duPont (at their Beaumont, Texas facility) and Mobay Chemical employ
biological treatment in combination with activated carbon adsorption;
whereas, American Cyanamid and Mallinkrodt combine biological
treatment with physical-chemical pretreatment.
PHYSICAL PRETREATMENT AND SEPARATION PRACTICES
Physical unit operations are commonly used by industrial manu-
facturers as in-process purification steps, for separation of streams
(e.g., a decanter), or for removal of constituents from liquid phases
for recovery or disposal. Such unit operations include: solvent
extraction, stripping, aeration, absorption on silica, alumina, a
synthetic resin or activated carbon, and azeotropic or extractive
distillation. These techniques may be combined or repeated in
sequence, as required, to achieve the desired level of treatment of
the waste effluent; such separation processes prove most effective
when applied to a waste stream at its most concentrated point.
Wherever practical, materials such as solvents or adsorption
resins are recovered for reuse within the treatment process.
Liquid-Liquid Extraction
Liquid-liquid extraction, often referred to as solvent extrac-
tion, is a mass transfer operation allowing for the preferential
separation of solutes from one solvent to another. Employed by the
107
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organic and petro-chemicals industries for the separation of aromatic
and aliphatic compounds, liquid-liquid extraction has proved useful
for removal of phenols from petroleum refinery and coke-oven plant
wastewaters. In general, solvent extraction is economically competi-
tive with, and often preferable to steam stripping (see subsection on
Gas-Liquid Operations) for the treatment of high strength wastewaters
(i.e., with solute concentrations of several percent).* Solvent
(and/or solute) recovery, which is usually vital to the economics of
the operation, is typically accomplished by distillation or stripping
practices (Hanson, 1968; Lyman, 1976a; and Kiezyk and Mackay, 1971).
Theory and Process Description
Liquid-liquid extraction is based on the principle that when a
partially miscible or immiscible liquid is added to a solution of
a solute(s), the solute will equilibrate between the two phases.
The concentration of a solute, A, within each phase depends upon
its relative affinity for the two solvents and may be defined as
follows:
y
D = — (92)
A x.
A
where, D is the distribution coefficient;
x is the concentration of solute remaining in the raffinate,
(treated stream); and
y is the concentration of the solute in the extract.
*0ther factors influencing the selection of the treatment operation
include: molecular weight of the organic species, energy require-
ments, volatility of the solute(s) and the potential for azeotrope
formation.
108
-------
Preferably, the extracted solute has a distribution coefficient, D. ,
A
that is greater than one.
Although often considered in terms of removing a single solute,
liquid-liquid extraction may be applied to a mixture of species. The
ease with which two solutes may be extracted from solutions is
measured by the separation factor, & , which under equilibrium condi-
tions is defined as:
. . -°i- . %_=* (,3)
AB DB <*A "B
where, <* is the ratio of the two contaminants between the two
solvents;
Q.* is the activity coefficient in the extract phase; and
o is the activity coefficient in the raffinate phase.
The phase ratio, or the relative amounts of the phases used, together
with the separation factor, will determine the maximum separation
that can be accomplished between two species in any one equilibra-
tion.
The application of liquid-liquid extraction to an industrial
wastewater requires bench scale or pilot plant testing to properly
select a suitable solvent (i.e., high extraction efficiency, easily
recoverable, non-reactive, practical to use from an economic stand-
point, and low toxicity) and determine optimum operating conditions
(Sandall et al., 1974). In practice, one phase is dispersed in the
109
-------
other liquid (continuous) phase; mass transfer rates may be improved
by effective mixing or agitation.*
After the extraction is complete, the solute is separated from
the solvent for disposal and, in most cases, the solvent is re-
covered. Solvent recovery is often accomplished by distillation,
but stripping or adsorption processes may be required. In certain
instances, where the solute-containing solvent may be used as a
feedstock for an industrial manufacturing process (e.g., nitrobenzene
extraction of the solute, aniline), the costs of recovery are elimi- .
nated.
Application to Nitrobenzene/Aniline Manufacture
Nitrophenols and nitrous acids, which are formed during the
nitration of aromatic hydrocarbons, may be removed -from process
wastes by liquid-liquid extraction techniques. Typically the ni-
trated product is washed first with water and subsequently with
dilute sodium hydroxide to remove the free acids. Approximately 60
to 80 percent of the phenols present in this alkaline wash are
recovered (for subsequent disposal) by neutralization with a strong
acid. A practical modification to this approach, suggested by Hanson
et al., (1976), is to acidify the aqueous wash liquor (after alkaline
extraction), extract the phenols with an organic solvent, and recover
the solvent by distillation. Suitable organic solvents are shown in
*For a discussion of mass transfer kinetics and design requirement,
the reader is referred to Treybal, 1963; Hanson, 1968; and Bailes et
al., 1976.
110
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Table XII; of these, methyl isobutyl ketone is most efficient for
removal of phenolic by-products.
TABLE XII
Efficiency of Organic Solvents in Removing
Phenolic Nitration By-Products
Solvent Extraction Efficiency (%)
Benzene 88
Carbon tetrachloride 79
Chloroform 70
Cyclohexane 57
Dichloroethane . 78
Diethyl ether 92
Methyl isobutyl ketone 98
Toluene 82
Source: Hanson et al., 1976.
An alternative treatment process, dissociation extraction,
involves contacting the organic phase containing the acidic phenols
with a weakly basic solution of phosphate salt (Hanson, 1976). The
phenols are extracted into the aqueous phase as the conjugate base:
4>OH + P0~ - - <|>0~ + HPO~ (94)
or
0~ + HPO~ (95)
In the next step, the aqueous phase is extracted with a suitable
organic solvent. Although several countercurrent contact stages may
be required to achieve the predetermined level of treatment, the
organic phase may be distilled to recover the phenols and subsequently
recycled.
Ill
-------
According to the "Development Document for Proposed Effluent
Limitations Guidelines and New Source Performance Standards for the
Major Organic Products Segment of the Organic Chemicals Manufacturing
Point Source Category" (EPA, 1973a) aniline is also commonly recovered
from the aqueous phase of the separator by extraction with either
nitrobenzene or benzene. Specifically, an extraction efficiency of
98 percent has been reported for countercurrent extraction with
nitrobenzene. As shown in Figure 9, the solvent stream (containing
extracted aniline) may be recycled to the process, thus avoiding
solvent recovery costs.
Ohkawa and Sawaguri (1976), in a patent assigned to the Sumitomo
Chemical Company, report that organic nitro compounds and phenols may
be extracted from acidic waste streams by a water immiscible organic
solvent solution containing at least one tertiary dibenzylamine. The
organic extract is then washed with an aqueous alkali solution to
remove acidic compounds; the amine is recovered as the organic
solution. The concentrated wastewater can then be disposed of by
incineration.
Gas-Liquid Operations
Gas-liquid operations are based on the diffusional interchange
which occurs when a gas and liquid phase are contacted. Primary
examples of such operations are distillation and steam stripping,
both widely used by organic (and petro) chemical manufacturers for
separating volatile organic compounds from aqueous waste streams.
Whereas distillation is a means of seoarating the components
112
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of a solution by creating a new phase (by vaporization or condensa-
tion), stripping is a form of gas desorption in which the new phase
is introduced in the form of a gas, for example, steam or air.
Steam Stripping
A type of fractional distillation, steam stripping is a means
of removing volatile organic contaminants from a dilute solution.
As is the case with any mass-transfer operation (cf, liquid-liquid
extraction), the objective in designing a stripping tower is to
maximize the rate of diffusion between the two phases, and is general-
ly accomplished by increasing the interfacial surfaces. Commonly
employed industrial contactors include bubble-cap tray towers or a
packed tower in which stepwise countercurrent contact of gas and
liquid phases takes place (Treybal, 1963).
Two nitrobenzene/aniline manufacturers, First Mississippi and
duPont (at their Gibbstown, New Jersey, facility) report the use of
stripping techniques in treating process wastewaters. The aqueous
phase from the product separator (see Figure 9) which contains
approximately 3 percent aniline by weight, may be sent to an aniline
stripper, as shown in Figure 10.* The overhead product from the
stripper, containing 50 percent aniline by weight, would be inciner-
ated leaving a bottom product (0.2 percent aniline by weight)
a
*EPA reports a 10 Ib/yr aniline plant requires a 2.5' x 40'
stripping tower with a feed rate of 17 gpm (EPA, 1973a).
113
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Aniline/Water
to Incineration
Aniline Water
from Separator-
Steam-
to
r-l
O
u
Aniline/Water
• to Wastewater
Treatment
Source: EPA, 1973a.
FIGURE 10
ANILINE WASTEWATER TREATMENT BY STEAM STRIPPING
114
-------
requiring additional treatment.* For a discussion of aniline
stripper economics, see EPA (1973a).
Adsorption on Granular Activated Carbon
Adsorption on granular activated carbon** is an effective and,
moreover, commercially established means of removing dissolved
organic species from aqueous waste streams. Contaminants are removed
from solution by a three-step process involving (1) transport to the
exterior of the carbon; (2) diffusion within the pores of the activa-
ted carbon; and finally (3) adsorption on the interior surfaces
bounding the pore and capillary spaces of the activated carbon.
Eventually the surface of the carbon will become saturated, requiring
replacement of the adsorber system with fresh carbon (i.e., virgin or
reactivated). Thus, the development of a high surface area carbon
that could be reactivated made commercial application of this adsorp-
tion process economically practical (Rizzo and Shepherd, 1977 and
EPA, 1973b).***
Theory and Process Description
The effectiveness of granular carbon in removing a given waste
from solution is typically discussed in terms of its adsorption
isotherm. The adsorption isotherm illustrates the relationship, at
constant temperature, between the amount of solute adsorbed per unit
weight of adsorbent and its concentration in bulk solution. In
*The type of additional treatment would depend on the plant facili-
ties; ideally, the stream would undergo adsorption on activated
carbon.
**Treatment of industrial wastewaters with powered activated carbon
will be discussed in the subsection, Combination and Alternative.
Techniques.
***There were an estimated 100 large-scale industrial/municipal waste-
water treatment systems in the United States in 1976 (Lyman, 1976b).
115
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theory, a point must be reached, where the concentration of the
solute remaining in solution and the concentration of the solute
adsorbed on the surface of the carbon are in equilibrium. The
position of the equilibrium (i.e., the distribution ratio) is de-
picted by the adsorption isotherm, which for dilute solutions,
can be expressed mathematically by the Freundlich equation:
\
X _ ,c 1/n \J ' (96)
M " kC
where X is the amount of contaminant adsorbed on the carbon;
M is the weight of the system carbon; and
C is the residual contaminant concentration
and, k and n are constants.
By taking the log of both sides, one obtains the linear relation-
ship:
log X/M = log k + — log C (97)
where — is the slope of the straight line isotherm whose inter-
cept is k at C = 1. By definition, X/M (where C is equal to
0 °
the influent concentration of C) represents the maximum amount of
contaminant adsorbed per unit weight of carbon at equilibrium
conditions. Thus, from this expression, the theoretical carbon
demand of the system can be estimated, (in dealing with complex
waste streams with nonlinear isotherms, a theoretical carbon demand
can be calculated for each identifiable component of the wastewater,
and summed together.)
116
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The adsorption capacity of the activated carbon is a function
of several factors, including the nature of the organic contaminant
and the nature of the solution. In general, adsorptivity increases
with the molecular weight of the solute, and decreases with solute
polarity, solubility, and branching. Furthermore, adsorption is
maximized at a solution pH corresponding to the minimum ionization of
functional groups, vary with the concentration and mixture of con-
taminants present. However, in practice, to realize optimum
operating conditions, consideration must be given to the type of
carbon selected, the contacting system, and the mode of operation
(EPA, 1973b and Rizzo and Shepherd, 1977).
As shown in Figure 11, granular activated carbon systems are
commonly designed in one of four major adsorber configurations:
moving bed, fixed beds in series, fixed beds in parallel, and upflow
expanded beds in series. The objective, in any application, is to
design a system in which the most economical, yet practicable carbon
exhaustion rates can be achieved*. The actual selection of the
adsorber configuration is, however, dependent on the required carbon
dosage and contact time, requiring bench and/or pilot scale testing
to determine the rate of adsorption. By dynamic column testing over
a range of contact times, the concentration of solute (contaminant)
*The carbon exhaustion rate can be defined as the pounds of carbon
used per unit volume of wastewater treated (Rizzo and Shepard,
1977).
117
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Moving Bed
oo
Effluent
Down Flow in Series
Influent
Influent
Carbon to
Regeneration
Requires suspended
solids pretreatment,
but provides counter-
current carbon use
for smaller volume
systems.
Source: Hager, 1974.
Effluent
Down Flow in Parallel
Influent
Effluent
Provides counter-
current efficiency,
suitable for large
volume systems; each
carbon bed is replaced
as a separate unit.
Upflow-Expanded
in Series
Effluent
t
Influent
Suitable for large
volume systems re-
quiring both filtration
and adsorption capabil-
ities; allows for
blending of effluents.
Requires minimum
pretreatment with
minimum headless,
provides counter-
current carbon use
with expanded bed
capacity.
FIGURE 11
TYPICAL CARBON ADSORPTION COLUMN CONFIGURATION
-------
remaining in solution (C/C ) can be plotted versus volume of solution
(wastewater) through the column to give the breakthrough curve.
Depending on the complexity of the wastewater, the shape of the
breakthrough curve may vary but, as shown in Figure 12, it is char-
acteristically "S-shaped." The breakpoint represents the point on
the curve at which the column is in equilibrium with the influent
wastewater, and little additional removal of the contaminant(s) will
occur. The movement of the primary adsorption zone along the column
in the direction of the flow (see Figure 12) influences the slope of
the breakthrough curve and the position of the breakpoint. Generally,
time to breakpoint may be extended by increasing the carbon bed depth
and lowering the flow rate; however, several other factors, such as:
the characteristics and concentration of the solute, the pH of the
solution, and the characteristics of the carbon selected influence
the overall capacity of the adsorption system (i.e., height and rate
of movement of the mass transfer zone, capacity of adsorbent, etc.).
For further details concerning process design, see EPA, 1973b; Rizzo
and Shepherd, 1977, and Zogorski and Faust, 1976.
Another major consideration in the design and operation of a
carbon adsorption system is the means of replacing exhausted carbon.
This may be accomplished by removing the carbon from the adsorber
for permanent disposal (i.e., throwaway carbon), or more typically,
for reactivation. Reactivation is any means by which the carbon is
restored to its original adsorptive capacity. Organic impurities may
119
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Influent
Adsorption
Zone
1
M-l
O
g
•H 4J
iJ fl
efl iu
ij 3
4J iH
C M-l
-------
be removed by thermal, alkaline acid, hot gas (steam), solvent, or
biological regeneration. However, in treating wastewaters containing
a mixture of organics, thermal regeneration of the carbon in either
multihearth or rotary tube furnaces provides the most reliable
reactivation process and, thus, is the most widely applied. Thermal
regeneration may be carried out on-site or off-site: according to
Hutchins (1975) if carbon regeneration requirements are less than 580
Ibs/day, off-site regeneration is more economical. As a result of
handling and reactivation, attrition losses, requiring fresh make-up
carbon, will typically range from 5 to 15 percent by weight (Hutchins,
1975; and Rizzo and Shepherd, 1977).
Under certain conditions (e.g., the presence of biodegradable
organics, favorable pH ranges, etc.) biological activity may occur in
the carbon adsorption column. In general, anaerobic growth not only
results in H S production, but reduces the adsorption capacity of
the column and therefore should be discouraged. Aerobic bacterial
activity, depending on the concentration and composition of the waste
loading, may enhance treatment efficiency. In certain cases, biologi-
cal degradation of organic contaminants complements the adsorption
process, increasing adsorption capacity and providing partial
regeneration of the carbon (Argaman and Eckenfelder, 1976).*
*A discussion of the advantages and disadvantages of combining pow-
dered activated carbon with biological treatment can be found in the
subsection entitled Combination and Alternative Techniques.
121
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Waste Stream Applications
Carbon has long been recognized as a means of reducing BOD,
COD, suspended solids and color at physical-chemical treatment plants
receiving municipal wastes (or combination municipal/industrial
wastes), and as a means of polishing secondary effluent from a
municipal .treatment plant. In recent years, the number of industrial
applications has increased as attention focuses on the removal of
toxic organic pollutants from waste streams. Granular activated
carbon systems are currently being used for removal of a wide variety
of organic compounds including nitrophenols, phenol, nitrosamines,
benzene, toluene, cresol, cyanide, resorcinols (Lyman, 1976b; Hager,
1976; and EPA, 1977). Thus, it was not surprising that the BAT for
the organic chemicals manufacturing category was designated as
biological treatment followed by adsorption with activated carbon
(Federal Register, January 5, 1976). (These proposed effluent
limitations and guidelines were later remanded by EPA, see Federal
Register, April 1, 1976.)
As discussed in the previous section, many factors enter into
the design of a carbon adsorption system. In treating waste streams
from nitrobenzene/aniline manufacture, the principal pollutants
targeted for removal include: nitrobenzene, aniline, dinitrobenzenes,
nitrophenols, nitrotoluenes, phenylenediamine, cyclohexylamine, and
nitros amines.. Through bench scale/pilot testing (i.e., selection of
carbon, system configuration, hydraulic loading, operating pH, etc.,
122
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the optimum conditions for treatment of the combined wasteload can be
determined. In any industrial application of carbon adsorption
systems, however, it is essential to recognize the vast difference
between the treatment of a synthetic wastewater (e.g., a given carbon
isotherm for an aniline solution at a known concentration) and a
complex waste containing many competing species. Thus, theoretical
studies of the surface chemistry of activated carbon and its capacity
for adsorption of nitrobenzene and nitrophenols (see Cough1in et al.,
1968, and Mattson et al., 1969), in addition to typical Freundlich
isotherm constants for aniline and nitrobenzene plotted in Figure 13
(Rizzo and Shepherd, 1977) must be regarded only as background
information for laboratory studies.
Thus, the feasibility of treating the product/process raw waste
lines from a particular facility individually, or as a combined
waste load, should be evaluated on a plant-by-plant basis. In some
cases, segregation of certain waste streams may be required to
optimize treatment conditions. For instance, the adsorption capacity
of activated carbon for nitrophenol decreases significantly with
increasing pH.* Other wastewater constituents, such as soluble
amines or specifically nitrosamines, however, are best treated at
higher pH's (MacNaughton and Stauffer, 1976). Another fundamental
*This is partially a result of an increase in the repulsive forces
between neighboring anionic species of the sorbate, nitrophenol, and
the negatively charged carbon surfaces, see Snoeyink et al., (1969).
123
-------
•o
-------
example of waste stream segregation involves the separation of
nitration wastes from amination wastes, wherever possible, to avoid
secondary reactions and formation of nitrosamines.
Currently, three nitrobenzene/aniline manufacturers employ
carbon adsorption in conjunction with other treatment techniques
to remove organic contaminants from waste effluent (see Table X).
However, data on treatment efficiency (on a stream-by-stream basis),
as well as process design, and operation and maintenance are not
publicly available. Thus, at this time, no further attempt will be
made to evaluate the effectiveness of activated carbon adsorption
treatment on nitrobenzene/aniline wastewater.
Adsorption on Synthetic Resins
As an alternative to adsorption on activated carbon, soluble
organic species may be removed from aqueous solution by macroreticu-
lar polymeric adsorbents or ion exchange resins. Advances in macrore-
ticular polymerization techniques, allowing for the manufacture of
microporous molecular sieves with a predetermined (average) pore
size, pore size distribution, and surface area enable the selection
of a synthetic resin with specific adsorption selectivity. For
example, nonionic organic compounds are removed from aqueous solutions
by nonpolar or intermediate polarity resins (e.g., hydrophobic
molecules are attracted to hydrophobic surfaces).* Synthetic resins
*The polarity of a particular adsorbent is typically classified by
the dipole moment of its surface functional group(s).
125
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may be regenerated by a basic or acidic solution, or an organic sol-
vent such as methanol, water, or steam, depending on the adsorption
characteristics of the solute; in many cases, recovery of the solute
is also practiced (Simpson, 1972; Kim et al., 1976; Breck, 1977; and
Lyman, 1976c).
Prior to any application of adsorption on synthetic resins to
nitrobenzene/aniline manufacture, laboratory and/or pilot tests would
be required to screen resins and study, for purposes of design, those
parameters which affect adsorptive capacity (i.e., wastewater composi-
tion, flow rate, pH, and bed volume). The selection of a. regenerant
requires examination of stoichiometric requirements, elutant patterns,
and regeneration cycles.
Burnham et al., (1972) removed aniline (4.0 ppm influent)
from an aqueous solution with 100 percent efficiency in a laboratory
study utilizing Amberlite XAD-7 resin.* Complete recovery of p-
nitrophenol (0.2 ppm) from solution was achieved employing the
polystyrene Amberlite XAD-2 (100 to 150 mesh; 1.25 gpm/cu ft).
Experimental isotherms for p-nitrophenol adsorption on Duolite
A-7** at varying pH values and concentrations were determined by Kim
et al.., (1977); the effect of pH on adsorption capacity at the
-4
equilibrium concentration (10 M) is graphically presented in
*XAD-7 is an acrylic base resin with no ion-exchange functional
groups.
**Duolite A-7 is a phenol-formaldehyde resin with amine functional
groups.
126
-------
Figure 14. As shown, the maximum adsorption capacity is reached in
the pH region of 5 to 5.4, a range in which the resin is most likely
present as a free base. Therefore, the authors hypothesize that
adsorption is taking place predominantly through formation of a
hydrogen bond between the free amino group on the resin and the
p-nitrophenol hydroxyl group:
H H
R - N + HO - M — R - N HO - M (98)
R •'. •' : R
where R. is the resin matrix, R is a hydrogen or alkyl group, and
HO-M is p-nitrophenol. Thus, as the pH is lowered and the amine
group becomes protonated, the adsorption capacity decreases dramat-
ically. The significant decrease in-capacity as the pH is increased
may be attributed to the increased solubility of p-nitrophenol. For
comparison, the variation in adsorption capacity of activated carbon
and the nonionic Amberlite XAD-7 are also presented in Figure 14.
Under optimum pH conditions, the Duolite A-7 resin capacity approxi-
mated that of a common granular activated carbon. In general, however,
the adsorption of weak organic acids on the weak base resin is much
more sensitive to pH (Kim et al., 1976).
As part of a study on .the recovery of amines from aqueous so-
lutions, Sargent (1964) tested aniline sorption on various anion
exchange resins. At, or prior to aniline breakthrough, the resin was .
washed with a mineral acid to elute the aniline salt. (Aniline may
127
-------
60
*^
(0
e
o
nt
M
4-1
§
O
c
o
0)
o
t«
4-1
M
10
-2
10
-3
10
10
-5
10
-6
PNP on Activated
Carbon
I
1 3 57 9 . 11 13
pH
15
Source: Kim et al., 1976.
FIGURE 14
ADSORPTION OF p-NITROPHENOL AS A FUNCTION OF pH
128
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then be recovered from the regeneration solution by distillation,
crystallization,'or extraction practices.) From the test results,
presented in Table XIII, there are a number of anion exchange resins
which have rather high distribution ratios and would be effective for
the sorption of aniline and other amines. However, the overall prac-
ticability of the process has yet to be demonstrated on nitrobenzene/
aniline manufacturing wastes.
Membrane Processes
Molecular or ionic species may be separated from an aqueous
stream by a selective membrane, which has high permeability for some
species and low permeability for others. The principal driving force
across a membrane in terms of thermodynamics, is a function of the
free-energy potential. The major membrane processes, electrodialy-
sis, reverse osmosis, and ultrafiltration have had varied and large-
scale applications to water and wastewater treatment, principally in
the desalting of brackish water (in the case of the former two proces-
ses), and in the concentration and purification of single phase
industrial wastes. With recent advances in the development of
synthetic membranes which provide improved selectivity and uniformity
of performance, new applications of membrane processes are being
investigated (Lacey, 1972; Smith et al., 1976; and Arthur D. Little, .
1976). Specifically, the practicability of using dialysis and
reverse osmosis for the treatment of nitrobenzene/or aniline-contain-
ing wastes has been examined.
129
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TABLE XIII
ANILINE SOSPTION BY ION EXCHANGE RESINS
1.2
TYPE OF RESIN
Poly(vinylbenzyl trimethyl ammonium chloride)
PolyCvlnylbenzyl trlmethyl ammonium chloride)
PolyCvinylbenzyl Crioethyl ammonium chloride)
Poly(vinylbenzyl trlmethyl ammonium chloride)
Poly(vlnylbenzyl trimethyl ammonium chloride)
Dowex 1-X2 resin
PolyCvinylbenzyl trlmethyl ammonium chloride)
PolyCvinylbenzyl trlmethyl ammonium chloride)
Poly(vinylbenzyl dimethyl ethanolammonium chloride)
Dowex 2-X8 resin
Foly(vinylbenzyl polyalkylene polyamlne)
Dowex 3-X4 resin
CROSSLINKAGE
(Weight
Percent)
1
2
2
2
2
2
4
8
2
8
2
4
CAPACITY
(Meq./dry g.)
0.76
0.64
1.23
1.61
2.59
4.28
1.4S
0.94
1.43
3.59
4.67
5.50
WATER
CONTENT
(Percent)
36.5
30.2
37.6
47.3
59.7
75.0
31.5
19.6
39.0
36.5
20.0
36.8
EQUILIBRIUM
SORPTION
(mg/wet g.)
5.74
5.82
5.18
4.54
4.12
2.67
5.75
(5.52)
5.03
4.23
(4.48)
4.84
DISTRIBUTION
RATIO, Kd3
(100 Min)
116
126
89.8
36.7
23.8
6.43
122
(>256)
45.5
36.9
(>58.5)
47.8
^ests performed on 0.1 percent aniline solutions.
Values in parentheses were not at equilibrium at 100 minutes.
Distribution ratio is equal to the molarlty of aniline in the water inside the resin bead plus the molarlty of aniline in the
external solution at equilibrium.
Source: Sargent, 1964.
-------
Dialysis
Dialysis is a diffusion process in which a solution containing
two solutes (or permeating species) is separated from a solvent in an
adjacent compartment by a membrane, thereby establishing a difference
in the chemical potential of the permeant in each compartment. The
rate of transport across the membrane (per unit area) can be described
in terms of:
F = Ldc/dx (99)
where F is the rate of transport;
L is the permeability coefficient, which is a function
of the diffusion and partition coefficient of the given
solute; and
dc/dx is the concentration gradient, which represents the driving
force in terms of entropy production.
Therefore by definition, the rate of transport, F, is directly propor-
tional to dc/dx and L at steady state.
Thus, in applying conventional dialysis to industrial waste
problems, where toxic pollutants may be present in low concentrations,
it is essential that the driving force be maximized. This may be
accomplished (without necessitating a continual supply of a pure
receiving solvent) by contaminant removal downstream of the selective
membrane, employing conjugation and pervaporation techniques devel-
oped and demonstrated by Smith et al., (1976).
Aniline can be effectively removed from solution by combining
dialysis through hydrophobic membranes with conjugation downstream of
the membrane. The theory behind this practical application is
131
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simple: the concentration of aniline in the receiving compartment is
reduced to a minimum by formation of a nonpermeating conjugate on the
downstream side, thereby maximizing the rate of transport. Smith et
al., (1976) studied an aniline system to illustrate the practicability
of conjugation in treating dilute waste streams;* as shown in Table
XIV, the specific permeability, L, reported for Kraton and XD-7
(polycarbonate-co-silicone) films are "the same order of magnitude as
those found in other commercial dialyzing processes and in reverse
osmosis." By neutralizing the conjugate acid, recovery of aniline
can be accomplished.
Pervaporation,-or activated diffusion, is based on a vapor-
phase sink downstream of a permselective hydrophobic film, and has
been applied to the separation of hydrocarbons and azeotropic mix-
tures. This process involves (1) adsorption of the contaminant at
the liquid-membrane interface, (2) diffusion through the permselec-
tive membrane; and (3) removal of the contaminant from the downstream
surface of the permselective membrane by evaporation. As the trans-
port rate is proportional to the membrane area and vapor pressure of
the solute, pervaporation appears feasible when the contaminant to be
removed from solution has a relatively high vapor pressure. Nitro-
benzene with a solubility of 0.20 wt percent and vapor pressure of
*Initial upstream concentration: 2.98 wt percent aniline; initial
downstream concentration 5.33 wt percent sulfuric acid.
132
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TABLE XIV
ANILINE AND WATER TRANSPORT THROUGH POLYMERIC MEMBRANES
MEMBRANE
Polyethylene A
Polyethylene B
Kraton 1101
XD-7
THICKNESS
L (microns)
20.0
13.6
Uq
35.7
68.3
SPECIFIC PERMEABILITY, L2
WATER ANILINE*
1.16 x 10~10 0.44 x 10~7
2.32 x 10"11 0.15 x 10~7
5 o i
-------
0.4 iranHg (at 25°C) was screened in a pervaporation study at a concen-
tration of 600 mg/1; permeability coefficients are presented in Table
XV. From experimental tests, the authors concluded that in order to
optimize conditions in a commercial application of the pervaporation
scheme, (1) membrane thickness should be 25 microns or less, in order
to minimize boundary layer resistance; (2) the feed velocity should
be maximized, as membrane permeability is directly related to flow
rate; and (3) feed temperatures should be elevated to increase feed
solute vapor pressure and decrease viscosity (Smith et al., 1976).
TABLE XV
Pervaporation Study:. Nitrobenzene
Permeability Coefficients*
Membrane
Polyethylene (low density)
Saran
Kraton 1101
Pliolite
Adiprene
Polyethylene. (Plasticized)
Thickness
(Microns)
14.7
19.4
25.0
38.0
59.0
24.4
L x 107
(cm2/sec)
6.85
6.42
9.6
10.7
.13
7.7
Liquid Flow: 0.75 1/min; Air Flow: 12.0 1/min.
Source: Smith et al., (1976).
134
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Reverse Osmosis (RO)
In reverse osmosis, a semipermeable membrane is utilized to
transfer solvent (water) from a more concentrated solution to a more
dilute solution, thereby purifying the solvent. Whereas, in dialysis
the concentration gradient is the driving force, the driving force
for this separation process is pressure. For ideal solutions,
osmotic pressure, TT , is defined as:
RT P,
TT= — In ^=- (100)
P2
where P and P are the solvent vapor pressure in the solutions on
either, side of the membrane, R is the gas constant, T is absolute
temperature (Kelvin), and v is the molar volume of the solvent. By
definition, "reverse" osmosis occurs when the pressure is greater
than on the (concentrated) solution side of the membrane, and the
liquid flow (which is normally from the more dilute solution to the
more concentrated), reverses. The actual mechanism by which solute
separation takes place is still unclear, but the most widely accepted
theory is that of a preferential sorption-capillary flow. The theory
suggests that both the chemical nature and the microporous structure
of the membrane surface are related to solute separation (Birkett,
1977; Weber, 1972; and Fang and Chian, 1976).
In the actual design and operation of a reverse osmosis unit,
major considerations include: (1) the module design, which is
intended to minimize concentration polarization of the solute on the
135
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membrane surface while maximizing solvent flux; (2) membrane selec-
tion; and (3) membrane susceptibility to chemical attack or fouling
by the wastewater. Prior to scale-up, laboratory or pilot studies
should be carried out to fully evaluate membrane selection, module
configuration, optimum feed rates, pretreatment requirements (e.g.,
filtration) and potential problems associated with fouling of the
membrane (Birkett, 1976).
In 1975, there were nearly 300 large-scale reverse osmosis
plants in operation throughout the world, purifying brackish or
saline water for both domestic and municipal use (Birkett, 1976).
In the treatment of industrial wastewaters, where reuse and/or
recovery of materials is desirable (e.g., electroplating industry), RO
becomes both a practical and economic process.
However, the practicability of applying RO to industrial waste-
waters, specifically nitrobenzene/aniline process streams, would be
largely dependent on the degree of solute(s) separation achieved, or
the efficiency of the process.* To this end, Fang and Chian studied
the potential of 12 reverse osmosis membranes to separate polar
organic compounds from aqueous waste solutions. Each membrane was
characterized by testing with sodium chloride solutions under
*RO is ideally suited for the treatment of brine solutions with up
to 34»000 ppm IDS (i.e.,, seawater). As the IDS level of nitroben-
zene/aniline manufacturing waste is more typically in the range of
500 ppm (see Table XIII) the advantages of employing this separation
technique may be overridden by energy costs.
136
-------
standardized conditions. Aniline solution results showed 75 percent
or greater solute separation with a cross-linked polyethylenimine
membrane (flat sheet and tube configuration) or with a NS-200 membrane
(flat sheet). The test data, according to the authors, should
represent a conservative assessment of the treatment effectiveness.
In treatment of actual wastewaters, the steric and polar effect of
the solute would yield a higher degree of separation. Thus, while
reverse osmosis remains a potential treatment alternative, the
practicability of this process in treating nitrobenzene/aniline wastes
has yet to be demonstrated.
COMBINATION AND ALTERNATIVE TECHNIQUES
From the preceding review of biological processes and physical
separation techniques, it is likely that no single treatment opera-
tion or process is ideally suited and/or could achieve the reduction
in'total pollutant loading from nitrobenzene/aniline waste streams
necessary for discharge to navigable waters. Thus, the next step in
evaluating this wastewater problem is to assess the technical feasi-
bility of combining certain treatment techniques for application to
combined and/or segregated waste streams.
In theory, there are many different approaches in which treatment
techniques may be selected and combined to attain the desired level •
of pollutant reduction. As was discussed, in the section on Current
Industrial Practices, physical separation techniques, such as coun-
tercurrent extraction of aniline by nitrobenzene and adsorption on
137
-------
activated carbon, are combined in practice as part of an overall
treatment scheme for the wastewater. However, certain portions of
the total waste load, depending on its strength and biodegradability,
might be more appropriately treated by biological processes. As
specific recommendations will be presented in Section V, the re-
mainder of. this chapter will be limited to a general discussion of
alternative or combination treatment schemes that are either patented
inventions or in commercial use.
A treatment method for reducing wastes, such as chromophoric
compounds, heavy metals, and nitrobenzene, from the manufacture of
synthetic dyestuffs and related intermediate chemicals has been
patented by Sweeny (1977). The pretreatment procedure involves
equalization, chemical treatment to remove heavy metal impurities,
addition of a flocculating agent, subsequent clarification, and a
second equalization treatment. The mixture is then passed through a
carbon adsorption column to lower the nitrobenzene concentration and
remove colored constituents from the wastes. Finally, the effluent
is treated with activated sludge containing microorganisms acclimated
to the waste* Reviewing the treatment procedure, the patent is a
logical application of demonstrated treatment technologies. Chemical
pretreatment of the effluent reduces excessive column pressure as a
result of sludge accumulation. The activated carbon treatment reduces
the nitrobenzene levels in the effluent prior to biological treatment.
As noted in the patent, very low levels of nitrobenzene increase the
138
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respiration rate of bacteria; concentrations over 12.0 tng/1 however,
are toxic to the bacteria. Thus, the carbon effectively lowers the
nitrobenzene concentration in the effluent to a level below which is
toxic to the microorganisms.
Eli Lilly has patented a pretreatment process for removing
nitrophenols and nitroaniline (trifluralin) from manufacturing
wastewater (Howe, 1969). The waste stream is acidified to a pH less
than 3 and a decolorizing material is added; the preferred adsor-
bent is an activated or. digested sludge. The following step involves
neutralization of the mixture by the addition of a metallic oxide or
hydroxide (e.g., calcium hydroxide). After separation of the re-
sulting sludge (or foam), the effluent may undergo conventional
biological treatment for further reduction of organic loading. Ac-
cording to the patent, the phenol content of a waste stream (2000 to
2800 ppm) was reduced to a trace amount by these treatment procedures.
Alternatively, an organic waste stream may be subjected to bio-
logical treatment in the presence of powdered activated carbon (PAC).
The powdered carbon is added to the aeration contact basin to enhance
bio-oxidation (by removing adsorbable toxic, inhibitory and refractory
substances) and reduce color and odor. Furthermore, addition of PAC
may improve floe formation, sludge settling, and sludge dewatering. •
For a more complete process description, including commercial applica-
tions of the process and regeneration schemes the reader is referred
to: DeWalle and Chian, 1977; Davis, 1977; Hutton and Robertaccio,
139
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1978; Grulich et al., 1972; Wilhelmi and Ely, 1976; Pradt, 1976; and
Environmental Science and Technology (February), 1977.
A treatability and design study performed by Zimpro, Inc. on a
high flow waste stream known to be difficult to treat biologically
(high organic, as well as a high dissolved solids content) serves to
compare conventional activated sludge systems, to the biophysical
(carbon/wet-ox) system.* Nitrification was found to be enhanced in
the latter system, with a 95.5 percent total Kjeldahl nitrogen (TKN)
removal, as opposed to 13.8 percent for the activated sludge.
Furthermore, with some modifications and the judicious addition of a
carbon source (e.g., methanol, molasses), denitrification of the
waste will occur (Frohlich et. al., 1976).
H + 6H+ + 6N0~ — *• 5C0 + 3N + 13H<) ' (101)
A critical factor in adopting any treatment practice is the
economics of the operation. Although an economic analysis of each
alternative treatment scheme (e.g., a comparison of capital invest-
ment, operation and maintenance costs, materials, and energy re-
quirements) is beyond the scope of this report, it is, nevertheless,
important to acknowledge that activated carbon adsorption was pre-
viously selected by EPA as an "economically achievable technology"
for the treatment of organic chemicals manufacturing process wastes
*Wet-ox, or wet-oxidation, is a means of detoxifying organic wastes
in aqueous solution at high pressures and temperatures.
140
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(Federal Register, January 6, 1976). However, the final selection of
any treatment operation, or processes, would be largely dependent
on dilution prior to discharge (many plants are capable of combining
treated streams with non-contact cooling water, etc.) and binding
effluent limitation requirements. A summary of alternative treat-
ment systems investigated by foreign researchers appears in Table
XVI, a more detailed discussion of practicable alternatives follows
in Section V, Recommended Treatment Alternatives.
141
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TABLE XVI
SUMMARY OF FOREIGN APPLICATIONS OF PHYSICAL-CHEMICAL TREATMENT TO UASTEUATERS
CONTAINING NITROPHENOLS, NITROBENZENES, AND ANILINE
Investigators
Treatment Process/
Description
.U
IO
Bellefontaine and
Koehncke, 1971
Del Manclno et al.
1974
Korenman et al.,
1977
Korenman et al.,
1977
Korenman et al.,
1977
Verlinskaya and
Shutter, 1977
Purification of nltrophenol-
containing alkaline wash waters
from nitrobenzene manufacture*
Reactivation of carbon used for
the treatment of aniline-con**
taining wastewaters.
Extraction of nitrophenols
from aqueous saline solutions.
Extraction of nitrophenols from
aqueous solutions at various
temperatures.
Molecular complexes of dinltro-
phenols with solvotroplc sub-
stances.
Sorption of aromatic amines on
carbon black
Nltrophenol-containing alkaline wastewater was purified by
reduction with formaldehyde, mixed with iron oxide sludge,
filtered, washed and calcined to give a red iron pigment and
a wash water free of amlnophenols.
Reactivation of carbon bed with hot air at ^220 C was Incom-
plete.
Salting-out coefficients for sodium and potassium salts in the
extraction of nitrophenols by Immiscible solvents (e.g.,
octane and benzene) were studied.
Partition coefficients for the extraction of 4-nitrophenol,
2,4-dlnitrophenol, 2,4,6-trinitrophenol, and 2,4-dinitro-6-
amlnophenol from strong acid to n-amyl acetate and toluene
are reported at various temperatures.
Extraction of dlnltrophenols from aqueous solutions with n-amyl
acetate, benzene, and n-hexane was studied as a function of the
concentration of selected solvotropic substances in the extrac-
tant (e.g., camphor, dimethyl phthalate).
Aniline may be extracted with dilute HC1.
are discussed.
Sorption mechanisms
-------
SECTION V
RECOMMENDED TREATMENT ALTERNATIVES
INTRODUCTION
As was discussed in Section I, the major objective of this
study is to assess pollution control practices from the manufacture
of nitrobenzene/aniline with regard to toxic pollutant generation.
Whereas Section II provided the process chemistry and manufacturing
configuration necessary for the prediction of toxic pollutants
(identifying point source discharges of specific pollutants), Sections .
Ill and IV reviewed current wastewater practices and alternative
control technologies largely in terms of the combined waste load from
nitrobenzene/aniline manufacture. Thus, it is the purpose of this
section to examine the treatability of the process wastewater in
terms of segregated point source discharges. As shown in Figure 9,
the most refractory of the waste streams generated during nitrobenzene
manufacture is Point No. 5, characterized.by high loadings of nitro-
phenols, nitrobenzenes, organic acids and heavy polymeric material.
In the course of aniline manufacture, the most refractory stream is
Point No. 8, characterized by significant concentrations of nitro-
benzene, aniline, and other organic compounds. Also important during
aniline manufacture is the disposition of the still bottoms from the '
aniline distillation column. Detoxification of these streams repre-
sent the major obstacles to successful treatment of nitrobenzene/
aniline wastewaters and must be the focal point of any future treat-
ability study.
143
-------
The discussion that follows will: (1) present a point source-
by-point source summary of potential pollutants from nitrobenzene/
aniline manufacture using the generic processes previously formulated;
and (2) recommend treatment alternatives for each stream. Recommenda-
tions will be based solely on the efficiency of a process to treat a
waste stream, and exclude any analyses of capital, operation and
maintenance, and energy costs. Thus, included in this section are
treatment options whose practical application may be only to new
sources (i.e., existing facilities might require extensive repiping
in order to implement a recommended treatment). Furthermore, it is
assumed throughout the section that conventional treatment practices
(e.g., equalization, neutralization, separation) will be employed, as
required..
POINT SOURCES OF POTENTIAL POLLUTANTS
The following remarks are directed to nitrobenzene manufacture
and refer to Figure 9.
Nitration of Benzene
Point No. 1
The nitration vessel most probably requires venting. Dinitrogen
pentoxide, dinitrogen trioxide, nitric oxide, benzene, and nitroben-
zene represent the major components of this vent stream. Depending
on the volume of this discharge, either wet scrubbing or adsorption
with silica ,gel, activated carbon, etc. is required for control
of atmospheric emissions. In the case of wet scrubbing, the effluent
144
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is combined and treated with the spent acid (the disposition of
solid adsorbents is unknown although regeneration may be feasible).
Nitrogen oxides, together with benzene and nitrobenzene, are the
potentially significant emissions from this point source. Therefore,
current control technology (i.e., wet scrubbers) appears adequate.
Point No. 2
The nitrogen oxides (principally nitrogen dioxide and dinitro-
gen tetroxide) produced in the bleaching tower are extracted with
water and recycled to the denitrating tower. Those gases which are
not extracted during this process are vented to the atmosphere. As
such, the composition of this stream is presumed to be qualitatively
similar to that of point number 1; potential contaminants include:
dinitrogen pentoxide, dinitrogen tetroxide, dinitrogen trioxide,
nitrogen dioxide, nitric oxide, benzene, and nitrobenzene. Though
emissions of nitrogen oxides are likely to be minimal, benzene
and nitrobenzene may conceivably be vented in environmentally
significant amounts from this point. Further study of emissions
from this point may be warranted.
Point No. 3
Prior to distillation, crude nitrobenzene is washed first with
water, then a dilute solution of aqueous base (Na CO, or NaOH), and •
finally water once again. To reduce the volume of aqueous effluent,
recycle of this water may be assumed; however, even with efficient
water reuse, this point may still represent a major discharge point
145
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within the process. Nitrophenols and carboxylic acids together with
nitrates and nitrites comprise the major portion of toxic effluents
from this stream. This stream would be best treated by activated
carbon adsorption.
v
Point No. 4
While most nitrobenzene is used directly for aniline production,
small amounts are further purified by distillation. This stream is
likely to be rather small, but may be toxicologically significant.
Nitrobenzene, nitrophenol, dinitrobenzenes, polycarboxylic acids,
and high molecular weight polymers, are the principal components of
this stream. This stream would also be best treated by activated
carbon adsorption.
Point No. 5
Purification of spent acid (a mixture of sulfuric and nitric
acid) for reuse, is not only the most practical method for mini-
mization of environmental impact but also economically justified.
A number of processes have been used successfully by industry for
recovery of dilute sulfuric acid. Conventional methods for removal
of volatile impurities such as nitrogen oxides, benzene, nitro-
benzene, and dinitrobenzene, entail heating the spent acid to its
boiling point and stripping the acid with hot gases such as steam
or air (De La Mater and Milligan, 1974). These compounds may then
be removed from the resulting 'gas stream using conventional scrubbing
systems, the aqueous effluent going to wastewater treatment. This
146
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procedure, while effective in removing essentially all of the
volatile organic and inorganic impurities, yields a product which
requires further treatment: the stripped acid must be either
fortified with oleum or otherwise concentrated (e.g. distilled)
prior to reuse.* Furthermore, these processes necessarily concentrate
nonvolatile organic impurities, primarily nitrophenols and various
organic acids (cf Table VI), and inorganic impurities which must be
continually removed; concentrations of 200 .ppm or greater within this
stream are reported under steady state conditions. This stream
obviously presents a waste disposal problem and represents a poten-
tially significant environmental hazard.
While direct disposal of this stream is possible, other treat-
ment methods have been suggested which may result in lower aqueous
emissions of toxic substances. Briefly, one procedure involves
continuous, in situ oxidation of nonvolatile organic species with
strong oxidants such as ozone, hydrogen peroxide, chlorates, or
peroxydisulfates at temperatures between 130 to 230°C (De La Mater
and Milligan, 1974). An alternative technique is reported by von
Plessen et al. (1976, 1977): initial concentration of the spent
acid (60 to 70 percent by weight) using the Pauling process**
*This, of course, assumes that the market for dilute sulfuric acid
is small; this acid could, in fact, be used for phosphoric acid
or fertilizer manufacture.
**The Pauling process is a counter-current extraction method in
which impure dilute acid is added to the top of a fractionating
column under reflux; concentrated (96 percent by weight) acid is
withdrawn from the bottom; the distillate, principally water,
with only traces of acid, is discarded.
147
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and then distilling the concentrated, still contaminated acid a
second time. Organic impurities are generally degraded in the first
concentration step to carbon dioxide, nitrogen oxides, and water;
the nitrogen oxides are presumed to be removed by conventional
means, i.e., scrubbing. As with any distillation procedure however,
there remains a small, concentrated, highly contaminated acid stream
which must be disposed of.
Whatever method is used for acid purification, it is apparent
that a relatively small, but toxic effluent stream must be treated.
Likely contaminants include nitrobenzene, nitrophenols, polycarboxy-
lic acids, and high-molecular weight nitrogen containing organic
polymers. This stream would be best treated by activated carbon
adsorption.
Reduction of Nitrobenzene
The following point sources have been identified for generic
processes for the catalytic reduction of nitrobenzene to aniline
as shown in Figure 9.
Point No. 6
The crude mixture of aniline after leaving the reactor is
condensed and separated from the gas stream. The gas stream,
which is principally hydrogen but also contains about 3.5 percent
and 0.05 percent of water and aniline respectively, is compressed
and recycled to the reactor. A small portion of this stream must
be vented to prevent buildup of gaseous impurities. Hydrogen,
148
-------
together with aniline, nitrobenzene, and water, represent the major
components of this purge stream. If a.less pure grade of hydrogen is
used as a feedstock, carbon monoxide, methane, and ethane may be also
present (see Table III). Air emissions may be best controlled by
combustion in a properly designed flare.
Point No. 7
This point is comprised of the volatile components removed
overhead from the distillation column. The major components of this
stream are presumed to be cyclohexylamine, cyclohexenyl amine, other
volatile amines, and water. This stream would probably be amenable
to dilution and biological treatment; however, incineration of this
stream may also be practicable.
Point No. 8
A variety of configurations for the distillation of aniline
may be envisioned; all processes will however have a purge to
prevent accumulation of high boiling products. Aminophenols,
nitrobenzene, phenylenediamine, diphenylamine, azepins, and high
molecular weight aminopolymers are likely components of this stream.
Because of the high organic content of this stream, disposal by
incineration is recommended.
Point No. 9
Water saturated with aniline is obtained from the separator
and possibly as a top product from the distillation column. Recovery,
even if not economically justified, will be required to prevent
149
-------
serious degradation of water quality. Again, a wide variety of
configurations for aniline recovery are possible; shown in Figure 9
is a scheme based on counter-current extraction with nitrobenzene.
Compounds of interest in this stream include aniline, nitrobenzene,
aminophenols, phenylenediamine, and other water soluble amines.
The aniline water is best treated by a counter-current extrac-
tion with nitrobenzene. Alternatively, the organic contaminants
could be recovered by steam stripping techniques. In either case,
the final effluent stream should receive further purification by
adsorption on activated carbon.
In order for the treatment process to effectively reduce
the potential formation of nitrosamines, nitration wastes should
remain segregated from amine-containing streams. Furthermore,
because the ability of activated carbon to remove specific species
is pH dependent, the waste streams are most likely treated by carbon
columns in series, with pH adjustments as required. A U.S. Air
Force study on the treatment of nitrosamine contaminated waste with
activated carbon demonstrated higher removal efficiencies in caustic
solutions (MacNaughton and Stauffer, 1976). However, as discussed
in the subsection on Adsorption on Activated Carbon, the removal of
color (e.g., nitroanilines and nitrophenols) is favored under acidic
conditions (Howe, 1969; Snoeyink et al., 1969).
150
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SECTION VI
SUMMARY AND CONCLUSIONS
The discharge of a toxic substance to the environment by an
organic chemical manufacturer, depending on the persistence and
mobility of the compound, may have irreversible effects on the
environment. Under the Clean Water Act of 1977, EPA must regulate
such industrial discharges by the establishment of effluent limita-
tions, defined in terms of the best available technology economi-
cally achievable. However, the establishment of such standards for
specific toxic species that are not only equitable to industrial
manufacturers, but more importantly that will prevent further dete-
rioration of the environment, is an exceedingly difficult task.
As a first step, EPA must thoroughly understand the manufacturing
process and available control technologies so that, ultimately,
attainable standards may be set.
To this end, a detailed description of nitrobenzene/aniline
manufacture and pollution control technology has been presented.
Included is a comprehensive discussion of the reaction mechanism,
with a summary of potential pollutants generated from feedstock
impurities and significant side reactions. Additionally, a generic
process configuration for nitrobenzene/aniline manufacture has been
formulated, identifying specific point source discharges (see Fig-
ure 10). From this information, current wastewater treatment and
151
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disposal practices, as well as alternative methods of treatment,
were reviewed.
Currently, there are no effluent limitations specific to the
point source discharge from nitrobenzene/aniline manufacture. As
summarized in Table 10, U.S. manufacturers use a variety of waste-
water treatment techniques, as in most cases the process wastes
are combined with other product lines. However, it is important to
note, that despite the vast number of potential pollutants generated
from the manufacture of nitrobenzene/aniline, this is basically a
"clean" process (that is, the process streams are highly treatable,
as compared to the manufacture of other organic compounds). Addition-
ally, the wastewater treatment techniques currently employed by
certain manufacturers are commendable. Nevertheless, in light of
future regulatory concerns, a complete review of alternate treatment
technologies (without industry bias) is appropriate.
As discussed in detail in Section V, pollution abatement from
nitrobenzene/aniline manufacture may be accomplished by in-process
modifications or end-of-pipe technologies. Practicable methods for
pollutant reduction are best examined with regard to the treatability
of segregated waste streams, as presented in Figure 15. An economic
analysis of the costs of implementing such in-process changes or
wastewater treatment options, has not been performed, and furthermore,
remains beyond the scope of this report.
152
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NITBOBEHZENE MANUFACTURE
I
Vent
tn
co
POINT 1
SCRUBBER
POINT 2
SCRUBBER
POINT 3
CARBON ADSORPTION
POINT 4
CARBON ADSORPTION
POINT 5
CARBON ADSORPTION
Nitric Acid
(Recycle to
Reactor)
Steam
'o Uastewater
Treatment
'Nitrobenzene
Product
Still Bottoms to
Wastewater
Treatment
p*To Uastewater
Treatment
Sulfurlc Acid
(Recycle to
Reactor)
ANILINE MANUFACTURE
Hydrogen
Catalyst
Still Bottoms
to Uastewater
Treatment
»To Uastewater
Treatment
POINT 6
INCINERATION
POINT 7
INCINERATION OR
DILUTION AND BIOLOGICAL TREATMENT
POINT a
INCINERATION
POINTS
COUNTER-CURRENT EXTRACTION WITH
NITROBENZENE OR
STEAM STRIPPING
FOLLOWED BY CARBON ADSORPTION
FIGURE IB
POTENTIAL TREATMENT OPTIONS FOR
NITROBENZENE/ANILINE WASTEWATERS
BY POINT SOURCE
-------
This study has provided, however, a framework for approaching a
difficult industrial wastewater treatment problem. As such, it has
outlined some of the steps that must be taken before BAT effluent
limitations can be rationally promulgated for nitrobenzene/aniline
containing wastewaters. Recommendations for further studies (to
validate the conclusions reached in Section V) include:
• EPA verification, from sampling of actual process waste-
waters, of all pollutant predictions and concentrations.
• Extension of this pollution prediction and abatement metho-
dology to additional compounds exemplifying other unit pro-
cesses such as amination, chlorination, oxidation, etc.
• EPA funding of pilot scale studies for determination of
the technical practicability of the recommended treat-
ment alternatives.
• An economic analysis of viable treatment alternatives
(with regard to best available technology economically
achievable).
• Demonstration of BAT in an EPA-industry jointly funded
project.
154
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