ATMOSPHERIC EMISSIONS
FROM CHLOR-ALKALI
MANUFACTURE
ENVIRONMENTAL PROTECTION AGENCY
-------
ATMOSPHERIC EMISSIONS
FROM
CHLOR-ALKALI MANUFACTURE
Cooperative Study Project
Manufacturing Chemists' Association, Inc.
and
Public Health Service
ENVIRONMENTAL PROTECTION AGENCY
Air Pollution Control Office
Research Triangle Park, North Carolina
January 1971
For sale by the Superintendent of Documents, U.S. Government Printing Office
Washington, D.C., 20402 - Price 55 cents
-------
The AP series of reports is issued by the Air Pollution Control Office to
report the results of scientific and engineering studies, and information
of general interest in the field of air pollution. Information reported in
this series includes coverage of APCO intramural activities and of coop-
erative studies conducted in conjunction with state and local agencies,
research institutes, and industrial organizations. Copies of AP reports
are available free of charge to APCO staff members, current contractors
and grantees, and nonprofit organizations - as supplies permit - from the
Office of Technical Information and Publications, Air Pollution Control
Office, Environmental Protection Agency, Research Triangle Park, North
Carolina 27709.
Air Pollution Control Office Publication No. AP-80
-------
PREFACE
To provide reliable information on the nature and quantity of emissions to
the atmosphere from chemical manufacturing, the National Air Pollution
Control Administration (NAPCA) of the United States Department of Health,
Education, and Welfare, and the Manufacturing Chemists' Association, Inc.,
(MCA), entered into an agreement on October 29, 1962, to study emissions
from selected chemical manufacturing processes and to publish information
that would be helpful to air pollution control and planning agencies and to
chemical industry management. Direction of these studies is vested in an
MCA-NAPCA Steering Committee, presently constituted as follows:
Representing NAPCA Representing MCA
Stanley T. Cuffe* Willard F. Bixby*
Robert L. Harris, Jr. Louis W. Roznoy
Dario R. Monti Clifton R. Walbridge
Raymond Smith Elmer P. Wheeler
Information included in these reports describes the range of emissions under
normal operating conditions and the performance of established methods and
devices employed to limit and control these emissions. Interpretation of emission
values in terms of ground-level concentrations and assessment of potential effects
produced by the emissions are both outside the scope of this program.
Reports published to date in this series are:
Atmospheric Emissions from Sulfuric
Acid Manufacturing Processes PHS Publication No. 999-AP-l 3
Atmospheric Emissions from Nitric
Acid Manufacturing Processes PHS Publication No. 999-AP-27
Atmospheric Emissions from Ther-
mal-Process Phosphoric Acid Manu-
facture PHS Publication No. 999-AP-48
Atmospheric Emissions from Hydro-
chloric Acid Manufacturing Processes NAPCA Publication No. AP-54
Atmospheric Emissions from Wet-
Process Phosphoric Acid Manufac-
ture NAPCA Publication No. AP-57
*Principal representative.
Ill
-------
USE AND LIMITATIONS OF THIS REPORT
This report, one of a series concerning atmospheric emissions from chemical
manufacturing processes, has been prepared to provide information on
atmospheric emissions from the manufacture of chlorine and caustic. The
manufacture of chlorine and related products is generally known as the
chlor-akali industry. Although the report centers around the electrolytic
production of chlorine and caustic from brine, it also touches upon the use of
fused-salt cells for the manufacture of sodium and chlorine, minor chemical
processes for the manufacture of chlorine, and the lime-soda method for
caustic manufacture. For the purposes of this report, only processes directly
involved in the manufacture of chlorine and caustic have been examined.
Background information is included to define the importance of the
chlor-alkali industry in the United States. Basic characteristics of the industry
are discussed, including growth rate in recent years, manufacturing processes,
uses for the products, and the number and location of production sites.
A description is given of the electrolytic process. Process information
includes the discussion of normal process variables that affect the range and
quantities of emissions and methods of controlling or reducing emissions.
Supplemental material provides detailed emission-sampling and analytical
methods.
This report provides information on the range of emissions that occur under
normal operating conditions and with the use of established methods and
devices employed to limit or control emissions from the manufacture of
chlorine and caustic. The emissions and operating data in Appendix A are
results from approximately 15 percent of present establishments,* representing
a broad range of plant capacities and both diaphragm and mercury cells. Most
of these data have been gathered from production records of chlorine and
caustic manufacturers. Stack tests from four plants conducted during 1967 by
the National Air Pollution Control Administration show results consistent with
the data received from industry sources.
The production of chlorine and caustic, a basic industry in the United States
for 50 years, involves well-established manufacturing procedures. Since the
industry is growing at a rate double that of the economy, a review of the
information in this report will be desirable within the next 5 to 10 years.
*An establishment is defined as a works having one or more chlor-alkali plants or units,
each of which is a complete production entity.
IV
-------
Although this report has been prepared as an industry review primarily for
public officials concerned with the control of air pollution, the information
may also be helpful to chemical plant management and technical staffs. It may
be helpful as well to engineering students, medical personnel, and other
professional people interested in emissions from chlor-alkali plants.
ACKNOWLEDGMENTS
Many companies and individuals in the chlorine industry have been helpful
in promoting this study; for their contributions, the project sponsors extend
their sincere gratitude.
Special thanks are due the following operating companies for their participa-
tion in a program of stack sampling specifically for this study:
Hooker Chemical Company
Olin Corporation
Wyandotte Chemical Corporation
The Chlorine Institute, Inc., New York, New York, supplied statistics on the
industry.
James C. Knudson and George Crane of the National Air Pollution Control
Administration and Raymond S. Briggs of Hooker Chemical Co., subsidiary of
Occidental Petroleum Corporation, were the investigators and are the principal
authors of this report. The sponsors acknowledge the contribution of the
Hooker Chemical Company in providing the services of Mr. Briggs, whose
extensive experience in the chlorine industry has proved invaluable.
-------
TABLES
1.
2.
3.
4.
5.
6.
7
8.
A-l.
A-2.
A-3.
A-4.
C-l.
C-2.
D-l.
D-2.
E-l.
E-2.
Estimated 1969 End-Use Distribution of Chlorine . .
Estimated 1969 End-Use Distribution of Caustic Soda
Typical Diaphragm-Cell Gas Analysis
Chlorine Emissions From Liquefaction Blow Gases in
Diaphragm- and Mercury-Cell Plants
Treatment of Chlorine from Air Blowing of Depleted Brine
Carbon Dioxide Before Blow-Gas Treatment in Diaphragm-
Cell Plant (Plant 30) . .
Processing of Blow-Gas Chlorine
Effect of Liquid-Gas Ratio Upon Chlorine Absorption
Efficiency ....
Emission and Operating Data from Chlor-Alkali Establish-
ments Using Blow-Gas Treatment
Questionnaire Emission Data from Chlor-Alkali Plants with
Blow-Gas Treatment Equipment
Questionnaire Data On Handling of Chlorine from Shipping-
Container Vents During Loading . .... . .
Chlorine in Air Vents from Transfer of Liquid Chlorine in
Storage
Solubility of Chlorine in Water as a Function of Partial
Pressure and Temperature
Specific Gravity of Caustic Soda Solutions at 60° F Based
on Dilution of 50% Standard-Grade Caustic
Chlorine Plants in United States ...
Summary of Chlorine-Producing Plants ....
Tests of Blow-Gas Absorber Efficiency
Water and Steam Needed to Increase Absorber Efficiency
vi
8
9
16
19
22
73
C)C
38
48
49
50
59
75
81
87
90
94
. 94
-------
FIGURES
1. Chlorine Production in United States by Cell Type 7
2. Caustic Soda Production in United States : . 8
3. Vertical Section through Typical Diaphragm Cell 13
4. Horizontal Section through Typical Diaphragm Cell 14
5. Flow Diagram of a Typical Diaphragm-Cell Chlor-Alkali
Installation 15
6. Typical Mercury-Cathode Cell : . . . 17
7. Manufacture of Sodium by the Downs Fused-Salt Process ... 26
8. Downs Fused-Salt Electrolytic Cell 27
9. Flow Diagram of Lime-Soda Plant with Countercurrent
Decantation 32
10. Recovery of Blow-Glas Chlorine by Water Absorption .. ..38
11. Recovery of Blow-Gas Chlorine by Carbon Tetrachloride
Absorption 40
A-1. Chlorine in Vent Gas from Air-Padded Liquid Chlorine Tank . 51
A-2. Nomograph for Determining Chlorine in Blow Gas with No
Dilution Air and No Recycle of Chlorine in Blow Gas .... 53
A-3. Chlorine in Blow Gas versus Chlorine in Main Gas and Blow
Gas with No Dilution Air and No Recycle of Chlorine in Blow
Gas 54
A-4. Lower Explosive Limits for Hydrogen-Chlorine Mixtures
at 3.0 Atmospheres (Absolute) 54
A-5. Relationship of Chlorine and Inerts in Cell Gas and Blow
Gas (with No Air Dilution) 55
A-6. Hydrogen in Vent from Blow-Gas Absorber 56
vii
-------
A-7. Dilution Air Required (per 100 tons/day Chlorine as Cell
Gas) to Reduce Hydrogen in Blow-Gas Absorber Vent to
A-8.
B-l.
B-2.
B-3.
B-4.
B-5.
B-6.
C-l.
C-2.
C-3.
C-4.
C-5.
C-6.
C-l.
C-8.
C-9.
C-10.
D-l.
E-l.
5% by Volume .... . ....
Effect of Air Dilution on Chlorine Loss with Blow Gas .
Three-Way Stopcock, "L", and Flask .
Chlorine-Sampling Apparatus . ...
Probe for Sampling Chlorine . .
Burette for Adding NaOH
Datasheet . . . . ... ....
Apparatus for Determination of Carbon Dioxide in Presence
of Chlorine ... ... .
Density of Liquid Chlorine .
Effect of Temperature on Corrosion of Mild Steel by Chlorine
Solubility of Chlorine in Selected Solvents at Atmospheric
Pressure ....
Vapor Pressure of Liquid Chlorine
Percent Chlorine in Air by Volume versus Percent by Weight
and Weight of Gas Mixture at Standard Conditions
Freezing Points of Caustic Soda Solutions
Viscosity of Caustic Soda Solutions . .
Vapor Pressure of Caustic Soda Solutions
Caustic Soda Dilution Nomograph
Relationship of Vapor Pressure and Temperature of
Liquid Sodium . . . ...
United States Chlorine and Alkali Producers, January 1,
1970
Water and Steam Required to Increase Blow-Gas Absorber
Efficiency
57
58
62
63
64
65
66
71
73
76
77
79
80
82
83
84
85
86
91
95
Vlll
-------
CONTENTS
SUMMARY ............................... 1
Production of Chlorine and Caustic .................... 1
Description of Processes .......................... 1
Emissions .................................. 2
Control of Emissions ....................... . . 3
Emission Guidelines ................................. 3
CHLOR-ALKALI INDUSTRY ...................... 5
Historical Background ............................ 5
Growth of Industry . ................... 6
Future Trends ....... ..................... 7
CHLORINE AND CAUSTIC MANUFACTURE BY DIAPHRAGM
AND MERCURY CELLS .............................. 1 1
Process Description ............................. 11
Raw Materials ............................... 11
Brine Treatment ............................... 12
Diaphragm Cells ............................. 12
Mercury Cells ........................... 12
Cell Description and Operation .................... 13
Diaphragm Cells ............................. 13
Mercury Cells ................................ 16
Sources and Quantities of Emission .................. 18
Chlorine Emissions ............................. 18
Blow Gas ................................... 18
Vents from Returned Tank Cars, Ton Containers, and
Cylinders ................................... 20
Vents from Storage Tanks, Process Transfer Tanks, and Tank
Cars During Handling and Loading of Liquid Chlorine ..... 20
Water Removal from Chlorine Gas ................... 21
Emergency Vents ............................. 21
Air Blowing of Depleted Brine in Mercury-Cell Plants ....... 21
Mercury-Cell End Boxes ......................... 22
Other Emissions ................................ 22
Carbon Dioxide .............................. 22
Carbon Monoxide ............................. 23
Mercury ..................................... 23
ix
-------
MINOR METHODS OF CHLORINE MANUFACTURE . • • • 25
Fused-Salt Cell . 2S
Process Description .... . - 25
Sources and Quantities of Emissions . . 25
Minor Chemical Methods . . ... . 28
Salt Process 28
Process Description 28
Sources and Quantities of Emissions .. • • 29
Electrolysis of Hydrochloric Acid 29
Process Description .... 29
Sources and Quantities of Emissions . . 29
CAUSTIC MANUFACTURE BY THE LIME-SODA PROCESS . 31
Process Description 31
Sources and Quantities of Emissions ... .32
CONTROL OF EMISSIONS 35
In-Plant Use ... 36
Alkaline Scrubbing Systems 36
Absorbers . .37
Water . 37
Carbon Tetrachloride 39
Sulfur Monochloride 39
Other Absorption Systems 39
Adsorption Systems . . . . . 39
GLOSSARY OF TERMS 41
Abbreviations ... . . ^1
Chemical Symbols . ... ... . . . . . 42
Definitions . . . . .... ^3
APPENDIX A. EMISSIONS FROM CHLOR-ALKALI PLANTS . 47
Field Test of Potential Chlorine Emissions Using Air for Liquid
Chlorine Transfer .... . 47
Calculated Potential Chlorine Emissions from Blow Gas . . 47
APPENDIX B. SAMPLING AND ANALYTICAL TECHNIQUES . . . . 59
Determination of Chlorine in Stack Gas . 59
Reagents ..... ' S9
Water .-..'.'..''.'..'..'..'. 59
Nitrobenzene ... CQ
-------
Ferric Indicator 59
Nitric Acid (8 N) 60
Sodium Chloride Solution (0.1 N) (Primary Standard) 60
Standard Silver Nitrate Solution (0.1 N) 60
Ammonium Thiocyanate (0.1 N) 60
Sodium Arsenite (20%) 60
Sodium Hydroxide (10%) 60
Sodium Hydroxide (IN) 60
Ortho-Tolidine Dihydrochloride Solution (0.134%) 60
Apparatus 61
Flasks 61
Vacuum System 61
Thermometer 61
Probe 61
Glass "L" 61
Variable Transformer 61
Glass Wool 61
Dispenser (NaOH) 61
Burettes (50 ml) 61
Spectrophotometer 61
Analytical Procedures 61
Collection of Samples 61
Sample Preparation 65
Analysis 65
Discussion of Procedures 69
Determination of Carbon Dioxide in the Presence of Chlorine 69
Reagents 70
Water 70
Sodium Hydroxide (10%) 70
Sodium Arsenite (20%) 70
Ascarite (8 to 20 mesh) ... . 70
Apparatus 70
Drying Tube 70
Evolution Apparatus 70
Sampling Equipment 70
Analytical Procedures 70
Collection of Samples 70
Cleanup 70
Analysis 72
Discussion of Procedures 72
APPENDIX C. PHYSICAL DATA 73
Chlorine 73
Purity of Commercial Chlorine 74
Atomic and Molecular Properties 74
Chemical Properties 76
Physical Properties 77
XI
-------
Boiling Point .... 77
Critical Properties ... . 77
Density .... . • 78
Latent Heat of Vaporization .... 78
Melting Point . . ... ... 78
Specific Gravity . . . .... 78
Specific Heat . ... 78
Specific Volume 78
Vapor Pressure ... . . . 78
Viscosity . ... 79
Volume in Air . ... 79
Caustic Soda . . .... .79
Caustic Potash 80
Sodium . . . 81
APPENDIX D. CHLORINE-CAUSTIC, FUSED-SALT, AND LIME-
SODA ESTABLISHMENTS IN UNITED STATES, JANUARY
1970 ... ... . . . 87
APPENDIX E. FIELD TEST OF ABSORPTION EFFICIENCY OF
BLOW-GAS ABSORBER ... 93
REFERENCES ... ... . 97
SUBJECT INDEX ... .101
XII
-------
ATMOSPHERIC EMISSIONS
FROM CHLOR-ALKALI
MANUFACTURE
SUMMARY
PRODUCTION OF CHLORINE AND CAUSTIC
During 1969, 9.4 million tons of chlorine and 10 million tons of caustic
soda were produced in the United States. The annual rate of production has
been increasing at about 8 percent per year. More than 99.5 percent of the
chlorine and 94 percent of the caustic soda made in 1969 were produced
electrolytically. Less than 0.5 percent of the chlorine was produced chemically.
The remaining 6 percent of caustic soda was produced by the lime-soda
process. In 1968, diaphragm cells accounted for about 68 percent of chlorine
production, mercury cells for about 29 percent, and fused-salt cells for
approximately 3 percent.
DESCRIPTION OF PROCESSES
Chlorine and caustic are produced concurrently in electrolytic cells. An
electric current decomposes a chloride salt that is usually fed to the cell as a
water solution. Chlorine gas is produced at the anode of the cell. In one type of
cell, hydrogen is liberated at the cathode and a diaphragm is used to prevent
contact of the chlorine produced with the hydrogen or the alkali hydroxide
that is formed simultaneously. In another type of cell, liquid mercury is used as
the cathode and forms an amalgam with the alkali metal. The amalgam is
removed from the cell and is reacted with water in a separate chamber called a
denuder to form alkali hydroxide and hydrogen. In another version of the
electrolytic process, molten salts are used in place of aqueous solutions.
Both chlorine and hydrogen are produced in the electrolytic cell. Hydrogen
gas saturated with water vapor leaves the cell at the top of the cathode
compartment, usually with a purity above 99.9 percent (dry basis). In most
-------
plants it is cooled to condense moisture, compressed, and used as process
hydrogen or fuel. Chlorine gas leaving the cells is saturated with water vapor
and cooled to condense some of the water. In diaphragm cell operation, the
cooling may be done indirectly or by direct contact with cold water as in a
blow-gas absorber. Chlorine gas from mercury cells is usually cooled indirectly
with cold water. After water cooling, the gas is further dried by direct contact
with strong sulfuric acid. The dry chlorine gas is then compressed for in-plant
use or is cooled further by means of refrigeration to liquefy the chlorine.
Approximately half of the total chlorine in the United States is produced as
liquid chlorine.
The caustic produced in diaphragm-cell plants leaves the cell as a dilute
solution along with unreacted brine. The solution is evaporated to increase the
concentration to 50 or 73 percent, so that most of the residual salt is
precipitated and removed by filtration. In mercury-cell plants, high-purity
caustic can be produced in any desired strength and needs no concentration.
EMISSIONS
Emissions to the atmosphere from diaphragm- and mercury-cell chlorine
plants include chlorine gas (C12), carbon dioxide (C02), and hydrogen (H2).
Gaseous chlorine is present in the blow gas from liquefaction from vents in
tank cars, ton containers, and cylinders during loading and unloading and from
storage- and process-transfer tanks. The chlorine content of blow-gas streams
normally ranges from 2,000 to 10,000 pounds per 100 tons of chlorine
produced for diaphragm cells and from 4,000 to 16,000 pounds for mercury
cells. Methods of removing chlorine from these streams are summarized in the
next section, Control of Emissions.
The venting of returned tank cars yields about 450 pounds of chlorine per
55-ton tank car. In addition, the handling and loading of shipping containers
generates an average of 1,700 pounds per 100 tons of chlorine liquefied. These
quantities are from venting and loading operations without controls. Most of
this gas is returned to the liquefaction system or controlled by means of
scrubbing systems.
Carbon dioxide is generated in mercury-cell and diaphragm-cell chlorine
plants. Tests of blow gas in a diaphragm-cell plant before treatment showed
C02 gas in amounts of 3,100 to 4,480 pounds per 100 tons of chlorine produced.
Carbon monoxide in the cell gas amounts to about 0.02 percent by volume.
Other emissions include mercury vapor from mercury-cathode cells; chlorine
from compressor seals, header seals, and storage tank vents; and air blowing of
depleted brine in mercury-cell plants.
Chlorine emissions from the Downs cell are of the order noted from
mercury and diaphragm cells. The Downs cell itself is a source of metal oxide
fume during startup.
2 CHLOR-ALKALI EMISSIONS
-------
Emissions from the lime-soda process consist of soda particulate from
lime-reburning kilns from the handling of soda-ash before solution. Carbon
dioxide is also emitted from the lime kiln. Particulate loss from lime-reburning
kilns has been measured at 980 to 1,880 pounds per day for a 120-ton-per-day
lime kiln at collection efficiencies of 86 to 97 percent. Other tests have yielded
a figure of 335 to 1,346 pounds per day from a 290-ton-per-day kiln at 98 to
98.7 percent control efficiency.
Carbon dioxide is evolved from lime burning in stoichiometric quantities of
0.785 ton of C02 per ton of lime.
CONTROL OF EMISSIONS
Chlorine emissions from chlor-alkali plants may be controlled by the
following three general methods: (1) use of dilute gas streams in other plant
processes, (2) neutralization in alkaline scrubbers, and (3) recovery of chlorine
from effluent gas streams.
Waste chlorine can be used to synthesize chlorinated hydrocarbons, bleach,
hydrochloric acid, and sulfur monochloride. It has also been used for
chlorination of plant cooling water.
When plant effluent gas streams contain less than 1 percent chlorine,
recovery of chlorine is not economical. Current practice involves scrubbing
with alkaline solutions to neutralize chlorine-producing hypochlorites. The
scrubbing is accomplished by using sodium or calcium hydroxide solution in
packed, plate, or spray towers. Efficiencies of more than 99 percent have been
obtained.
Waste gas streams, generally containing more than 10 percent chlorine, lend
themselves to the recovery of chlorine by absorption of the gas in water or a
carbon tetrachloride solution through the use of spray or packed towers.
Chlorine is subsequently stripped from the absorbing medium in a distillation
tower, thus regenerating the absorption medium for recycle. Absorption by
sulfur monochloride is also used, though less commonly. Sulfur monochloride
contacts gaseous chlorine to form sulfur dichloride, from which chlorine is
then distilled. Some absorption systems employing stannic chloride, ethylene
dichloride, etc., although patented, are not commercially significant. Chlorine
can also be removed from effluent gases by adsorption onto silica gel or
activated carbon. These methods are not used commercially either.
EMISSION GUIDELINES
Inert gases purged from chlorine plant operations contain substantial
quantities of chlorine gas and constitute the largest potential source of chlorine
emissions. In many cases, the chlorine can be recovered for use either by
diverting the inert gas that contains it to other plant processes or by absorbing
the chlorine from the gas and subsequently regenerating it. In other cases,
chlorine in the inert gases can be neutralized by caustic soda or lime.
Summary 3
-------
A properly designed and operated water scrubber may be expected to
operate at efficiencies of 97 percent or greater, with exit-stream chlorine
concentrations of less than 0.5 percent, representing a chlorine loss of less than
100 pounds per 100 tons of chlorine produced. Chlorine recovery efficiencies
with carbon tetrachloride absorbers are reputed to be essentially complete,
although no quantitative data on this type of system are available for either
chlorine or carbon tetrachloride emissions.
Alkaline scrubbers that react caustic or lime with dilute concentrations of
chlorine in inert gas streams are very effective, with an absorption efficiency
approaching 99.9 percent for a well-operated unit. Exit-stream chlorine con-
centrations can be expected to be less than 10 ppm.
Carbon dioxide is generated in chlorine cells by oxidation of the graphite
anodes. Approximately 2,000 pounds per 100 tons of chlorine are produced in
mercury-cell plants and 4,000 pounds per 100 tons of chlorine in diaphragm-
cell plants. This may comprise 15 percent or more of the blow gas emitted to
the atmosphere. Carbon monoxide is also produced from graphite electrodes
and may amount to 0.4 percent of the blow gas by volume.
Losses of mercury in the form of vapor from mercury-cell plants are small
and proper building ventilation reduces mercury concentrations inside to
negligible levels.
Submerged pumps, if used for transfer of liquid chlorine, eliminate the loss
of chlorine attendant with air padding. To minimize emergency venting when
maintenance and repairs are required for such pumps, small pump tanks should
be used that can be isolated from storage tanks during servicing.
CHLOR-ALKALI EMISSIONS
-------
CHLOR-AKALI INDUSTRY
HISTORICAL BACKGROUND
Karl Wilhelm Scheele, a Swedish chemist, discovered chlorine in 1774 while
working on the analysis of manganese dioxide. Although chlorine was not
generally believed to be an element until 40 years after its discovery, Sir
Humphrey Davy, in 1810, substantially verified Scheele's theory that chlorine
was "dephlogisticated marine acid" and named the chemical "chlorine." It was
not until 1815, through extensive work by Joseph Louis Gay-Lussac, that
chlorine was generally accepted as an element. Chlorine gas was first used for
bleaching in 1785, but it did not find acceptance because of its corrosive action
on metals and the discomfort it caused workmen. Chlorine water was next
tried and, in 1789, chlorine was absorbed in potassium hydroxide to form a
potassium hypochlorite solution which proved to be successful as a bleaching
agent. The potassium hydroxide was replaced by milk of lime in 1798, by G.
Tennent of Glasgow, who was granted a patent that year for his new bleaching
solution. It achieved immediate success in bleaching linen and cotton and, soon
after, in bleaching paper.
Chlorine was first produced commercially by the Deacon process, in which
hydrochloric acid is oxidized by air to chlorine using either Mn02 orCu2C02
as a catalyst. The overall reaction of that process is:
4 HC1 + 02 *- 2C12 + 2H2 0
Commercial production of chlorine in the United States was started in 1892
at Rumford Falls, Maine, where the Electro-Chemical Company developed a
bell-jar-type electrolytic cell.1 The plant was moved to Berlin, New Hampshire,
in 1898 and until its recent shutdown was operated by the Brown Paper
Company. Other companies—S. D. Warren, Olin, and Dow-followed in quick
succession. Roberts Chemical Company started producing electrolytic chlorine
in 1901, followed by the Developing and Funding Company in 1905. Other
pioneer manufacturers were Pennsylvania Salt Manufacturing Company in
1903, Warner-Klipstein Company in 1915, and pulp manufacturers, including
the New York and Pennsylvania Company and the West Virginia Pulp and
Paper Company.
One of the earliest uses of chlorine in the United States was in the
manufacture of bleaching powder, which was produced by passing chlorine gas
over beds of hydrated lime. The Niagara Alkali Company, Niagara Falls, New
York, first liquefied chlorine gas in 1909.2 This proved to be a turning point
-------
in the industry, so that by 1910 there were 11 plants in the United States
producing liquid chlorine, with a total installed capacity of about 200 tons per
day. By 1920 the capacity had increased to 600 tons per day; in 1940 the total
installed capacity was nearly 2,000 tons per day and by the end of 1969 was in
excess of 28,000 tons per day.
The original electrolytic chlorine cell was of bell-jar design. The develop-
ment of diaphragm-type cells in the United States was favored by the existence
of underground sodium chloride brine and the easy extraction of underground
solid salt deposits as brine. Since the mercury-cathode or mercury-type cell
requires solid salt for resaturation of the depleted brine from the cells, the
growth of the industry in Europe, where salt was generally more available in
solid form, favored the mercury cell.
A recent trend toward mercury cells in the United States is the result of
increased demands for high-purity caustic, which can be produced directly in
this type of cell. Most of the diaphragm-cell caustic soda is sold as standard
grade containing about 1 percent sodium chloride. Processes have been
developed, however, to reduce the salt content to meet the specifications
required for rayon manufacture and for other special uses.
GROWTH OF INDUSTRY
Since the start of the chlor-alkali industry in the United States at the turn of
the century, the growth of the electrolytic chlor-alkali industry has been rapid.
Although chlorine was first produced chemically, production by chemical
means is now less than 0.5 percent of the total production. Within the last 35
years, production of chlorine in the United States has increased 25-fold.
Production at the beginning of 1970 was at a rate in excess of 30,000 tons per
day with an anticipated growth in 1970 of about 6 percent. Nearly 50 percent
of all chlorine produced in this country is liquefied.
Electrolytic production of chlorine from sodium chloride brine will
theoretically release 1.13 tons of sodium hydroxide per ton of chlorine
produced. The market growth rate for caustic soda has not kept pace, however,
with the increased demands for chlorine. Consequently, as electrolytic chlorine
production has increased, caustic soda produced by chemical means has been
replaced by caustic soda produced electrolytically. There were no known
lime-soda plants in operation as of January 1970. Figure 1 shows the growth of
chlorine production in the United States by years and the amount that has
been produced with diaphragm and with mercury cells.
There were approximately 70 chlorine establishments in the United States
as of January 1970, most of which are located in the eastern part of the
country because of the availability of salt and a proximity to skilled labor and
markets. Plants west of the Rocky Mountains are concentrated in the
Northwest in proximity to paper mills. Most of the chlorine plants in the
United States have a captive market for all or part of their chlorine.
CHLOR-ALKALI EMISSIONS
-------
I I
TOTAL PRODUCTION
DIAPHRAGM CELLS
MERCURY CELLS
FUSED SALT AND NON-ELECTROLYTIC
-f""'-r--i — i ...... r-"T
1946 1948 1950 1952 1954 1956 1958 1960 1962 1964 1966 1968 1970
YEAR
Figure 1. Chlorine production in United States by cell
type.3 (Percentage of production by respective cell type
not available for 1947 to 1955 or 1957 to 1961.)
Figure 2 shows caustic soda production by years and the amount produced
by the electrolytic and lime-soda processes. The distribution by use of chlorine
and caustic soda is summarized in Tables 1 and 2, respectively.
FUTURE TRENDS
Chlorine, caustic, and related products are expected to maintain a healthy
growth pattern for a number of years ahead. Estimated rate of growth for the
next 5 years or so is 6 percent per year for chlorine, 5.5 for caustic soda, and 3
for caustic potash. No major technological changes are anticipated in the next
10 years that will seriously affect either the total demand for these products or
their relationship to each other.
In an attempt to compensate for the slower growth of demand for caustic
compared with that for chlorine, many studies have been conducted on ways
to produce chlorine without producing caustic. Efforts have also been made to
Industry
-------
100,000
10,000 —
1930
Figure 2. Caustic soda production in United States.4
diversify and expand the uses of caustic. None of these efforts have been
particularly successful. The electrolytic processing of sodium and magnesium in
molten-salt cells produces chlorine without caustic soda, but the market
requirements for these metals have not been sufficient to correct the imbalance
in demands for chlorine and caustic. An electrolytic process to decompose
by-product hydrochloric acid is available and may be economically justified
whenever excess acid might otherwise constitute a disposal problem.
Table 1. ESTIMATED 1969 END-USE DISTRIBUTION OF CHLORINE3
End use
Organic chemicals
Pulp and paper
Inorganic chemicals
Water treatment
Miscellaneous
Total
Percent of total
64.5
11.6
10.7
3.6
9.6
100.0
CHLOR-ALKALI EMISSIONS
-------
Table 2. ESTIMATED 1969 END-USE DISTRIBUTION OF
CAUSTIC SODA3
End use
Chemicals
Pulp and paper
Rayon
Aluminum
Textiles
Petroleum
Soap and detergents
Cellophane
Export
Miscellaneous
Total
Percent of total
42.5
13.6
5.4
7.4
3.9
3.8
4.8
2.1
1.3
15.2
100.0
Industry
-------
CHLORINE AND CAUSTIC MANUFACTURE BY
DIAPHRAGM AND MERCURY CELLS
PROCESS DESCRIPTION
As of January 1970, more than 97 percent of the chlorine and nearly all of
the caustic produced in the United States were made by electrolytic cells of the
diaphragm or mercury type. Although diaphragm cells account for slightly over
two-thirds of the present production, about half the plants under construction
in 1968 had mercury cells. This reflects an increased demand for the
higher-purity caustic produced by mercury cells.
Chlorine and caustic are produced concurrently in both types of cells. Both
types use the same basic raw materials, employ electrolysis, and are similar in
the generation and treatment of waste gases; however, there are differences in
the design and operation of and emissions from the two types of cells. The raw
materials and brine treatment used, the design and operation of the cells, and
the sources and emissions of air pollutants for both types are described in
subsequent sections of this report.
Raw Materials
An aqueous solution of sodium chloride is usually employed as the
electrolyte in electrolytic cells. Other metal chlorides such as potassium
chloride are also used, but to a much smaller extent. Generally, sodium
chloride is obtained either from brine wells, underground deposits of solid salt,
or ocean water. Salt derived from these sources is 95 percent or more pure and
contains small amounts of calcium (usually as calcium sulfate), magnesium,
iron, and clay. Before its use, raw brine is treated to remove some of the
impurities.
Salt used in mercury plants requires more extensive treatment to produce a
higher purity brine than that necessary for diaphragm cells. The high-purity salt
produced from caustic evaporation usually practiced in diaphragm-cell plants
can be used as raw material for mercury cells.* In some mercury-cell plants
*Based on the assumptions of approximately 52 percent decomposition of brine feed for
diaphragm-cell operation and 20 percent of the salt return required for resaturation,
including salt losses, a 100-ton-per-day diaphragm-cell plant would be able to produce
sufficient purified solid salt beyond its own needs to supply a 75-ton-per-day mer-
cury-cell plant.
11
-------
jerground salt
depleted brine from the cells is resaturated by pumping it to un
deposits that serve as subsurface resaturators.
Brine Treatment
Diaphragm Cells
Since calcium and magnesium salts tend to build up on diaphragms, raw
brine is treated with soda ash and caustic and is then filtered to reduce these
elements to reasonable levels. Sulfates must also be kept under control since
sulfate ions decrease graphite life. The practice of providing for the rapid
solution of salt with prompt removal of the brine leaves much of the calcium
sulfate undissolved and thus minimizes brine purification costs. Recycled brine
may also be high in sulfates. In plants where salt costs are low, sulfates in the
feed brine are usually controlled by discarding or purging high-sulfate brine
returned from the caustic evaporation process. This brine, or "transfer liquor,"
as well as the first warm-water wash of the returned salt, may contain about
175 to 200 pounds of sodium sulfate per 1,000 pounds of sodium chloride.
Where salt costs are high, the first warm-water wash of the returned salt, or a
portion of the transfer liquor, may be refrigerated to crystallize sodium sulfate
as the decahydrate (Na2S04 • 10H20), which is then discarded.
Mercury Cells
In most mercury-cell plants about 10 to 15 percent of the sodium chloride
is decomposed as the brine passes through the cell. Depleted brine must usually
be dechlorinated before recycle. Depleted brine leaving the electrolyzer is first
sent to a storage tank, is usually acidified with hydrochloric acid, and is then
reacted with hypochlorite in the brine, forming some free chlorine. The brine is
then subjected to vacuum or is air blown, or both, to remove most of the
chlorine. This gas is usually piped to the cell header. When high vacuum is used,
the air-blowing step is sometimes omitted. Brine is dechlorinated before
resaturation for the following reasons:
1. Control of iron removal is difficult in the presence of hypochlorite ion.
2. Hypochlorous acid, if not removed, will be converted to chlorate,
resulting in rapid graphite attack.
3. Workmen are caused less discomfort by this process.
Dechlorinated brine contains about 260 to 280 grams of NaCl per liter and
is usually at a temperature of about 50 to 80° C. It is made neutral or alkaline
before resaturation.
After dechlorination, the brine is resaturated. Some operators prefer to
purchase or manufacture a "mercury-cell grade" of salt for use in resaturating
the brine because no further purification is then needed. Others prefe t
lower grade of salt. The brine must then be purified to remove iro d th
metals since small traces of vanadium, chromium, and molvhria ,
uryoaenum deposit
12
CHLOR-ALKAUEM1SSIONS
-------
out, form a film on the mercury, and thereby increase the cathode overvoltage.
This increases the breakdown of the amalgam with an increase of hydrogen in
the chlorine. These impurities are usually removed by adding caustic soda, soda
ash, and/or barium carbonate or barium chloride, followed by settling,
filtration, or both, to remove precipitated metallic compounds.
Cell Description and Operation
Diaphragm Cells
Diaphragm cells consist essentially of three parts: the anode compartment,
the cathode compartment, and the diaphragm separating the two. This
comprises a unit cell. During the past 10 years all new diaphragm cells have
been of two basic types. One type consists of a filter press or box structure
that contains as many as 50 unit cells. The cells are arranged in the building so
that a maximum of four such assemblies may be operated in series, making as
many as 200 unit cells in the series.
The second type consists of a single-unit cell. This cell is also connected in
series to feed into common chlorine and hydrogen collection systems. Both
types of cells have vertical graphite anodes, steel screen cathodes, and
deposited asbestos diaphragms.
The Hooker cell (Figures 3 and 4) is an example of the single-unit cell type.
The anode section consists of a concrete bottom holding an assembly of closely
spaced graphite blades cast in lead. Extending through the side of the bottom
are copper bus bars to conduct current into the lead. The cathode section rests
on the concrete bottom and is constructed of steel plate with fingers of wire
screen coated on the anode side with an asbestos diaphragm. A concrete top is
sealed to the cathode section.
CONCRETE
CELL TOP
ANOLYTE (BRINE)
CHLORINE
OUTLET
HYDROGEN'
OUTLET
CATHODE
BUS BAR +_
A
GRAPHITE ANODE
CONCRETE
CELL BOTTOM
LEAD POUR
JOINING ANODES
ASBESTOS-COVERED
CATHODE FINGER
BRINE INLET
(ORIFICE FEED)
MANOMETER
f^-
CATHODE
FRAME
CELL LIQUOR
OUTLET
y/ A
MASTIC SEALER
'AND INSULATOR
SANODE BUS BAR
INSULATOR
Figure 3. Vertical section through typical diaphragm
cell (cells connected electrically in series).
Manufacture
13
-------
r l
CftTHODE
BUS BAR
GRAPHITE ANODE
ANODE BUS BAR
CELL LIQUOR
OUTLET
Figure 4. Horizontal section through typical dia-
phragm cell (cross section at A-A (Figure 3» to
indicate arrangement of anodes and cathode fingers.
Electrical connections from one cell to the next are made with L-shaped
copper connector bars. Cells can be removed from this circuit individually for
renewal by using a portable jumper switch. The jumper is applied without the
interruption of current to the circuit.
The Dow dipolar cell is the only type of filter-press cell now in use for
chlorine production. Current passes through approximately 50 cells in series
without electrical connectors between successive cells. Concrete frames are
pressed together, with each unit connected electrically to the next cell within
the frame. Graphite plates form a tight, vertical partition across the concrete
frame, and graphite anode plates are set into this portion in vertical rows. The
cathode, which is a steel wire screen bolted to the concrete frame, has vertical,
hollow fins spaced to form pockets between the rows of anode plates. Asbestos
fiber is deposited on the side facing the anodes.
Figure 5 is a flow diagram of a typical chlor-alkali diaphragm-cell
installation. The overall reaction effected by the electrical current when
sodium chloride brine is used is as follows:
2NaCl + 2H2 0
(sodium chloride + water
-*- 2NaOH + C12 + H2 (2)
caustic soda + chlorine + hydrogen)
Potassium chloride may be used in place of sodium chloride in diaphragm
cells, in which case potassium hydroxide is produced. Market demand for
potassium hydroxide is very small, however, compared with that for caustic
soda.
Anodic reaction- In most diaphragm cells, hot, purified, saturated brine is fed
continuously to the anode compartment. Brine in the anode compartment,
known as anolyte, is in direct contact with graphite anodes. Chlorine gas is
evolved at the anode and leaves the cell saturated with water vapor. This gas is
cooled in direct or indirect water coolers to condense most of the water and is
then dried in direct-contact sulfuric acid drying towers. Some plants employ
mist eliminators after the coolers and use sulfuric acid towers to remove liquid
14
CHLOR-ALKALI EMISSIONS
-------
S3
o
TRANSFORMERS \-»\ RECTIFIERS
POWER
16% Nad
11.5% NaOH
(TYPICAL
ANALYSIS)
V SLUDGE 50"*
TO DISPOSAL CAUSTIC
ECOVERED SALT | ^TANtP
CAUSTIC
Figure 5. Flow diagram of a typical diaphragm-cell chlor-alkali installation.
-------
condensable vapors, and solid impurities.5 The chlorine is coirlpreSS^hlorine
or part of it may be further cooled by refrigeration to produce hqui c •
Chlorine is shipped as a liquefied gas under pressure in tank cars, tame irucKs,
barges, 1-ton containers, or cylinders. Chlorine gas is also shipped by pipeline
over distances of several miles from one plant to another.
Small amounts of oxygen, carbon dioxide, carbon monoxide, and hydrogen
are produced within the cells because of side reactions (current efficiency is
normally 95 to 96 percent). These gases, along with a small amount of air
leakage into the chlorine system, usually represent 4 to 6 percent by volume of
the main chlorine gas stream. A typical chlorine-cell gas analysis is given in
Table 3.
Table 3. TYPICAL DIAPHRAGM-CELL GAS ANALYSIS
Component
CI2
C02
N2
02
H2
CO
Volume, %
96.28
1.61
1.27
0.66
0.12
0.02
Cathodic reaction—The anolyte passes from the anode section into the cathode
section by gravity flow through a porous asbestos diaphragm. The liquor
leaving the cathode compartment contains about 11 percent caustic and 15
percent salt. It is sent to evaporators where it is concentrated to 50 percent or,
sometimes, to 73 percent caustic. During the evaporation step excess salt
precipitates out. This salt is filtered, washed, and returned as a slurry to the
brine system.
Mercury Cells
A mercury cell consists of two sections, the electrolyzer and the denuder.
The electrolyzer has a chlorine outlet, graphite anodes, and a mercury cathode
(Figure 6). It is generally constructed with a flat-bottomed steel trough in
which mercury and brine flow uniformly. The anodes are usually horizontal
graphite plates that hang on insulated rods from the top of the cell. The anodes
are close and parallel to the mercury-brine interface, with a space of several
millimeters between them that allows the chlorine to get to the outlet. Mercury
cells generally have greater current-carrying capacity (100,000 to 200,000
amperes) than diaphragm cells (30,000 to 60,000 amperes).
The denuder is usually a steel duct mounted below or alongside the
electrolyzer. It has a mercury-amalgam anode and iron or graphite cathodes
No electrical power is applied to the denuder. Design variations in mercury
16 CHLOR-ALKALI EMISSIONS
-------
1. HYDROGEN EXIT PIPE (FROM SODA
CELL)
2. CHLORINE EXIT PIPE (FROM BRINE
CELL)
3. ELECTRIC MOTOR DRIVING SCREW
PUMP
4. BRINE FEED PIPE
5. ARCHIMEDEAN SCREW PUMP RAISING
DENUDED MERCURY FROM SODA CELL
TO BRINE CELL
6. BARRIER ACROSS BRINE CELL PER-
MITTING MERCURY TO FLOW BELOW
IT AND PREVENTING BRINE FROM
PASSING BACK INTO MERCURY PUMP
7. DENUDED MERCURY FROM SODA CELL
8. WATER FEED PIPE TO SODA CELL
9. IRON (OR GRAPHITE) GRIDS PRO.
MOTING DECOMPOSITION OF SODIUM
AMALGAM
10. ELECTRICAL CONNECTION TO
PLATE IN BASE OF THE BRINE CELL
(seo 11)
II. ELECTRICAL CONTACT PLATE OVER
WHICH MERCURY CATHODE FLOWS
12. SODIUM AMALGAM FLOWING ALONG
SODA CELL
13. PIPE THROUGH WHICH AMALGAM
PASSES FROM BRINE CELL TO SODA
CELL
14. CAUSTIC LIQUOR EXIT PIPE
15. BRINE EXIT PIPE
16. BARRIER ACROSS BRINE CELL
PERMITTING AMALGAM TO
FLOW BELOW IT AND PREVENT-
ING BRINE FROM PASSING INTO
SODA CELL
17. ELECTRICAL CONNECTION TO
ANODES
18. ANODE BLOCK
19. MERCURY CATHODE
20. CHLORINE GAS PASSING ALONG
BRINE CELL IN SPACE BETWEEN
CELL COVER AND BRINE
21. WATER FEED PIPE TO COOLING
JACKET OF CHLORINE EXIT PIPE
Figure 6. Typical mercury-cathode cell.
cells include cathode and anode orientation for both the electrolyzer and
denuder, type of mercury flow, and construction of the cell parts.
The reaction in each section of the cell can be shown as follows:
In the electrolyzer:
NaCl + Hg »~ Na(Hg) + 1/2 C12
In the denuder:
Na(Hg) + H2 0 *- NaOh + 1/2 H2 + Hg
The net reaction is the same as that for diaphragm cells:
2NaCl + 2H20-
(sodium chloride + water —
-*• 2NaOH + C12 + H2
- caustic soda + chlorine + hydrogen)
(3)
(4)
(5)
Electrolyzer reaction-Brine and liquid-mercury cathode are fed continuously
into the electrolyzer section. Chlorine evolves from the surface of the anodes
and passes out of an opening at the top of the cell. The chlorine is cooled,
dried, and liquefied in the same manner as that from diaphragm cells.
Denuder reaction—On electrolysis, the sodium forms an amalgam with
mercury, the mercury containing about 0.1 to 0.3 percent sodium. The
amalgam flows to a denuder where it becomes the anode to a short-circuited
iron or graphite cathode. Hydrogen, caustic, and mercury are the products
when the ?;-a.algam reacts with water.
Manufacture
17
-------
r similar to that used
The hydrogen gas is cooled and compressed in a manner M1 of mercury
with diaphragm cells. Hydrogen from mercury cells contains t ^ ^ CQndenseJ[.
vapor most of which is removed in a direct-contact scrubber
so that the resulting gas is approximately 99.9 percent H2 on a ary and
contains 20 to 30 milligrams of mercury per cubic meter. In some cases the
gas is further purified by deep cooling and by filtering through activated
adsorbents to remove the remaining traces of mercury.
Caustic produced in a mercury cell is unusually pure because there is no
direct connection between the brine solution in the electrolyzer and the caustic
solution in the denuder. Moreover, a mercury cell usually produces 50 percent
caustic liquor in comparison with the 11 percent caustic produced in a
diaphragm cell. This pure, concentrated caustic normally requires no further
processing other than filtration.
Investment and operating costs are higher for mercury cells because of the
cost of mercury, mercury losses, and higher energy requirements (15 percent)
per ton of product.
SOURCES AND QUANTITIES OF EMISSIONS
Atmospheric emissions of chlorine, carbon dioxide, carbon monoxide, and
hydrogen occur from diaphragm- and mercury-cell plants in amounts that
depend largely upon plant design and operation. If liquid chlorine is not
produced (as in a paper mill plant), the plant will have no blow gas resulting
from liquefaction and will have, therefore, no chlorine emissions from this
source. Where liquid chlorine is produced, emissions vary according to the
waste treatment system employed and the chlorine content of the blow gas.
Chlorine Emissions
Blow Gas
When a chlorine-cell gas such as that described in Table 3 is compressed and
cooled to produce liquid chlorine, noncondensable gases saturated with
chlorine vapor are produced at the discharge of the condenser. These gases are
commonly called blow gas, sniff gas, or tail gas. The amount of chlorine
emitted to the atmosphere from blow gas varies with operating conditions and
the type of recovery equipment through which the stream is processed. It
varies with plant capacity, concentration of chlorine in the blow gas,
percentage of inerts in the cell gas, and according to whether air is injected
before the chlorine condenser to prevent an explosive mixture in the vent gas
(Appendix A).
Table 4 shows ranges of concentrations and the amounts of chlorine that
may be emitted if these emissions are uncontrolled and when various types of
scrubbers are used to remove chlorine.
18 CHLOR-ALKALI EMISSIONS
-------
Table 4. CHLORINE EMISSIONS FROM LIQUEFACTION BLOW GASES
IN DIAPHRAGM- AND MERCURY-CELL PLANTS
Type
of
control
None
Water absorber
Caustic or lime scrubber
Chlorine concen-
trations in
exhaust, vol %
20 to 50
0.1 to 4.5
0.0001
Emission factor,
1bchlorine/100tons
chlorine liquefied
2,000 to 16,000
25 to 1,090
1
A typical range for the diaphragm cells is 2,000 to 10,000 pounds of
chlorine in the blow gas per 100 tons liquefied. Mercury-cell installations
usually require more air dilution because more hydrogen is contained in the
cell gas. The usual range of chlorine in the blow gas is 4,000 to 16,000 pounds
of chlorine per 100 tons of chlorine liquefied.
It is common practice to operate at condensing pressures and temperatures
that represent an economic optimum. When there is no use for chlorine in the
blow gas and chlorine must be neutralized, it becomes economical to condense
at higher pressures or lower temperatures, or both, to reduce the chlorine in
the blow gas. If useful by-products can be made, or if the chlorine in the blow
gas is recycled or recovered in some other manner, it will usually be more
economical to allow the percentage chlorine in the blow gas to increase in lieu
of operating at relatively high pressures or low temperatures, or both.
The high operating costs encountered when chlorine in the blow gas must be
neutralized and discarded have directed considerable attention to methods of
recycle or recovery. This is particularly true for gas streams with large
concentrations of carbon dioxide since this compound also reacts with alkali.
Abnormal operating conditions that increase the quantities of chlorine in
the blow gas are given below.
Operating above rated capacity-Cell manufacturers specify for a particular cell
an upper current limit or cell load that determines the rate of chlorine, caustic,
and hydrogen production. As technical and operating improvements have been
made, cell ratings for both new and existing cells have increased. If existing
chlorine-condensing facilities are inadequate for the expanded plant production
resulting from such improvements, the percentage of chlorine in the blow gas
will increase and positive pressure may occur in the cell headers, resulting in
chlorine emissions in the cell room.
Startup and shutdown-During chlorine plant startup, air is present in chlorine
lines and equipment and liquefaction efficiencies are low, so that large amounts
of blow gas are generated. A new cell circuit may require 8 to 24 hours to
attain steady operating conditions at full load. Normally when a cell circuit is
started up, every effort is made to maintain continuous operation; at times,
Manufacture-Emissions 19
-------
- . 0;,c or for economic
however, entire circuits may be shut down for major repairs u
reasons. To minimize the excess air in the chlorine system at s v, 4
chlorine is frequently evaporated into the chlorine headers.
Vents from Returned Tank Cars, Ton Containers, and Cylinders
Occasionally water and other liquids are present in returned tank cars. In
order to ensure an empty and clean car before reloading, it is common practice
to apply suction to returned tank cars, as well as to cylinders and ton
containers, to remove any liquid chlorine remaining in the vessel before
inspection and cleaning. The amount of chlorine thus removed varies
considerably but averages about 450 pounds for a 55-ton tank car.3 The
recovered chlorine is usually sent to the chlorine-handling system although
some plants send the chlorine to a caustic scrubber to avoid upsetting their cell
operation.
Vents from Storage Tanks, Process Transfer Tanks, and Tank Cars
During Handling and Loading of Liquid Chlorine
A common method of transferring chlorine involves the use of air padding.
After the transfer it is necessary to vent the air, which now contains a relatively
small concentration of chlorine, because the transfer is normally completed
before equilibrium conditions can be reached. The amount of chlorine in the
vented air varies considerably and is greater at higher temperatures. It depends
also upon the shape of the vessel, the time required for transfer, and the
number of transfers made.
Quantities of chlorine are flushed out with the padding air during the
loading of shipping containers with liquid chlorine. Data from 19 plants, given
in response to a questionnaire for this study, show that the chlorine flushed
out varied from 110 to 6,000 pounds per 100 tons of chlorine liquefied, with
an average of 1,700 pounds. In all cases except two, chlorine removed during
tank-car loading operations was transferred to other plant uses, returned to the
process, or treated in a scrubber. In the two exceptions, the scrubber collection
was not complete, and 10 to 140 pounds, respectively, of chlorine were vented
per day. This represents a chlorine emission rate of 7.2 and 100.8 pounds of
chlorine, respectively, per 100 tons of chlorine liquefied.
In many newer plants, submerged pumps are used for the transfer of liquid
chlorine. Although pumps eliminate the loss of chlorine attendant with air
padding, emergency venting is necessary for pump repair and general
maintenance. These emergency vents are usually connected to a caustic
scrubber. It is good practice to use small pump tanks that can be isolated from
large storage tanks for servicing. This practice greatly reduces emissions during
pump repair.
Another method of transfer is to apply suction on the receiver or vessel to
which a transfer is to be made and connect the discharge from the comnressor
to the vessel containing the chlorine that is to be transferred. This is <=r,™ ,h,t
similar to transfer by means of air, except that neither tank re SS m
, re m
20
-------
Water Removal from Chlorine Gas
Chlorine gas is normally cooled to condense water vapor and then is further
dried in concentrated-sulfuric acid scrubbers. The loss of chlorine with the
water that condenses from cell gas varies from 400 to 1,200 pounds of chlorine
per 100 tons liquefied, depending on the type of cell, cell temperature, and
location of drip connections in the chlorine gas system. Usually this condensate
is flushed to the sewer. Care must be taken that such liquid streams are not
discharged into a ditch or sewer that also receives strong acid wastes since this
could result in the release of chlorine.7 The sulfuric acid used for chlorine
drying has a low solubility for chlorine, and loss of chlorine is, therefore,
negligible when spent acid is discarded.
Emergency Vents
Chlorine seals and other sources of infrequent emissions are usually
connected to an emergency scrubber, although in other cases these emissions
are vented to the atmosphere. In either case, alarms and electrical tie-in
connections are usually provided to permit prompt shutdown or changes in
operating procedures to limit the duration of the emission.
Cell room chlorine header seals—Seals on chlorine headers, provided to prevent
backpressure at the cells, are usually vented to the cell house or to the outside
atmosphere. Although in an emergency they must handle the full capacity of
the cells connected to the header, the seals blow infrequently and for short
periods. In certain locations seals are piped to a lime or caustic scrubber
designed to absorb all the cell chlorine produced.
Compressor seals—The shaft seals on liquid-seal chlorine compressors are
usually piped so that a stream of sulfuric acid is fed into the compressor.
Carbon-ring reciprocal compressors usually have a double stuffing box vented
to a caustic scrubber or to the suction of the compressor. This effectively
prevents emissions to the atmosphere.
Storage tanks—The tank vent line is usually connected to a disposal scrubber.
The relief connection from the safety valves may be vented to the atmosphere
or to an emergency scrubber.
Air Blowing of Depleted Brine in Mercury-Cell Plants
Recycled brine in mercury-cell plants is saturated with chlorine. This brine is
usually vacuum-treated, air-blown, or both, to remove residual chlorine before
resaturation. Concentrations of chlorine encountered in the vent gas are usually
low* and economic recovery in a water or carbon tetrachloride absorber
cannot be obtained. Consequently, such gases are normally used for in-plant
purposes such as water chlorination, or they are sent to lime or caustic
*From practical solubility data it can be shown that if brine is depleted by 10 percent in
passing through the cell, approximately 1.5 percent of the chlorine produced is present in
the depleted brine. If vacuum treatment of the depleted brine at 22.5 inches of Hg
Manufacture-Emissions 21
-------
scrubbers for disposal or vented to the atmosphere. Although air blowing of
depleted brine is common, it is by no means universal. For example, certain
plants air-blow and re-treat only a 5 to 10 percent side-stream, and several
plants dispense with this procedure entirely. The questionnaire responses of 11
plants indicating treatment of chlorine from brine blowing are given in Table 5.
Table 5. TREATMENT OF CHLORINE FROM AIR BLOWING
OF DEPLETED BRINE3
Treatment
Used for in-plant processes
Sent to scrubbers
Vented to atmosphere
Number
7
3
Ib
following vacuum degassing
^Fifty-six pounds of emissions per 100-tons chlorine produced.
Note: Since about 540 pounds corresponds to 75 percent vacu-
um, 56 pounds residual indicates that an almost complete vacuum
was used.
Mercury-Cell End Boxes
On certain mercury cells the discharge end box is constructed with a
removable cover for servicing. End boxes are connected to a common suction
header to prevent chlorine gas from entering the cell room when the covers of
the end boxes are opened. Chlorine in the exhaust header is usually neutralized
with lime or caustic.
Other Emissions
Carbon Dioxide
Carbon dioxide is generated in both diaphragm and mercury cells by
oxidation of the graphite anodes.8 In addition, carbonates present in the cold
feed brine are decomposed during acidification, freeing carbon dioxide that is
evolved as the electrolytic cell heats the feed brine to,operating cell
temperature. Typical cell gas contains 1 to 2 percent carbon dioxide.9
Condensation of chlorine from the cell gas increases carbon dioxide concentra-
tions in the blow gas to more than 15 percent.1 °
suction (75 percent of full vacuum) is assumed, the vacuum treatment at equilibrium will
recover 2,250 pounds (0.75 X 1.5 X 2,000) of chlorine per 100 tons produced. This
corresponds to a reduction in chlorine content of hot brine from about 0.024 to 0.006
percent. Air blowing reduces the residual chlorine in the brine to 0.001 to 0.003 percent,
depending on the quantity of air used. On the assumption that 0.02 gram per liter
(0.00167 percent) chlorine remains in the depleted brine after air blowing, the air blow
in this example will contain 0.27 ton (540 Ib) of chlorine per 100 tons of chlorine
produced, or about 500 ppm chlorine in the effluent airstream.
22 CHLOR-ALKALI EMISSIONS
-------
Analysis of one blow-gas stream before treatment reveals the carbon dioxide
production rate shown in Table 6.
Table 6. CARBON DIOXIDE BEFORE BLOW-GAS TREATMENT
IN DIAPHRAGM-CELL (PLANT 30)
Test
1
2
3
4
Inlet, Ib C02/100 tons
CI2 produced
3,100
4,280
4,340
4,480
Since less graphite is consumed in mercury cells,11'12 carbon dioxide
generated in mercury-cell plants is correspondingly lower and has been
calculated to be about 2,000 pounds per 100 tons of chlorine produced. Like
chlorine, carbon dioxide emissions to the atmosphere depend upon the
blow-gas scrubber employed.
Carbon Monoxide
As shown in Table 3, carbon monoxide forms a small part of the inerts in
the cell gas, amounting to 0.02 percent by volume and appearing in the same
relative amounts in the blow gas. Assuming a 20-fold increase in carbon
monoxide concentrations because of liquefaction of the chlorine, the carbon
monoxide concentration in the blow gas would be 0.40 percent by volume.
Mercury
The use of mercury in mercury-cathode cells produces some mercury vapor,
which is emitted during cell operations. The trend toward the use of
higher-strength amalgams and, therefore, lower mercury requirements has
minimized mercury-vapor emissions. Modern cells with steeper bottom slope,
vertical decomposers, higher-strength amalgam, and increased current densities
have reduced mercury inventory to slightly less than 90,000 pounds for a
100-ton-per-day chlorine plant, about half that required by older plants. With
the newer cells, daily mercury losses have decreased from 0.6 pound to less
than 0.3 pound per ton of installed daily chlorine capacity.13 The usual range
of mercury losses for typical plants in the United States has been given as 30 to
40 pounds per 100 tons of chlorine produced.11 European sources13 indicate
that some 3 percent of the mercury lost is emitted to the surrounding
atmosphere.
Manfacture-Emissions 23
-------
MINOR METHODS OF CHLORINE
MANUFACTURE
FUSED-SALT CELL
Approximately 3 percent of the chlorine manufactured in this country is
produced as a by-product of the Downs fused-salt process.
Process Description
Figure 7 is a flow diagram of the Downs fused-salt process. The process can
be divided into four main steps: (1) preparation of dry sodium chloride and
calcium chloride feed streams, (2) electrolysis, (3) treatment of gaseous
chlorine by-products, and (4) purification of molten sodium.
In the salt preparation stage, a pure sodium chloride brine is obtained by
dissolving raw salt in water and treating with sodium hydroxide and ferric and
barium chlorides to remove impurities that would interfere with electrolysis.
The pure brine is evaporated, filtered, and dried, and then fed to the Downs
electrolytic cell along with dry calcium chloride.
Electrolysis of a molten salt bath occurs in the Downs cell (Figure 8) at a
temperature of about 550° C, producing molten elemental sodium and gaseous
chlorine.
The lower density sodium and the chlorine percolate separately through the
molten salt bath to a submerged conical collection dome, where an outer
annular ring and inner nickel dome remove the molten sodium and hot gaseous
chlorine, respectively. A cell cover enclosing the collection dome reduces heat
losses from the salt bath and minimizes contact with the atmosphere. An
opening in the cover is provided for the salt feed. A vertical riser pipe, fitted
with cooling coils at its upper end, continuously removes and cools the molten
sodium so that dissolved metallic calcium precipitates and settles back into the
bath. From the riser pipe, the crude sodium flows into a collector tank and
then to a scale tank at 100° C, where a screen filter removes any remaining
calcium and sodium impurities.
Sources and Quantities of Emissions
Chlorine emissions from the liquefaction and handling of Downs-cell
chlorine are of the same magnitude as reported earlier for mercury- and
diaphragm-cell processes. Chlorine blow-gas emissions may be prevented by:
25
-------
BAR UM CHLORIDE
SODIUM HYDROXIDE
FERRIC CHLORIDE
RAW.SALT
TO
PROCESS
CHLORINATION
CHLORINE
BLOW-GAS
EMISSIONS
SALT AEROSOL
EMISSIONS
SALT
SETTLER
OISSOLVER^c7
PURIFICATION
EVAPORATION RAW
CALCIUM
SALT PREPARATION CHLORIDE
O
a
Ł
r
*•*
w
en
STORAGE
OR
TANK CAR
TO OTHER
SODIUM-CONSUMING
PROCESSES
SCREEN
FILTER
SODIUM I SODIUM
STORAGE T TANK CARS
TO BRICK OR
DRUM MOLDING
-------
SALT FEED
TO CHLORINE PURIFICATION
SODIUM
RISER
PjPE | k-CHLCRINE COLLECTION DOME
SODIUM COLLECTION RING -
CYLINDRICAL
STEEL CATHODE
/ REFRACTORY BOTTOM
• COOLING-WATER
OUTLET
WATER-COOLED
ANODE
CONNECTION
FigureS. Downsfused-salt electrolytic cell (Source: U.S.
Patent 2,913,381).
(1) the use of absorbers or scrubbers employing water, caustic soda, slaked
lime, or carbon tetrachloride or (2) the use of blow-gas chloride directly for
in-plant processes such as chlorination of organics.
In some sodium-producing plants, including two that responded to the
questionnaire used in this study, all the gaseous chlorine is used within the
plant for chlorination, a practice that eliminates the liquefaction blow gas and
its disposal. Emergency caustic or lime tanks are usually available to absorb
gaseous chlorine in case the chlorination process is-stopped temporarily and the
Downs cells continue to operate.
The Downs cell itself is a source of metal fume emission during startup and
diaphragm replacement, which occur at 350- and 20-day intervals, respective-
ly.14
The cell startup procedure15 involves the use of graphite starter blocks,
which are wedged between the anode and cathode to serve as current
"bridges." After the sodium chloride-calcium chloride mixture is packed
around the graphite blocks, current is passed between the electrodes, heating
the blocks and melting the surrounding bath. While the electrolyte is melting
and the collection dome has not yet been inserted into the electrolyte bath,
emissions of calcium and sodium oxides16 and sodium chloride17 occur,
requiring ventilation hoods directly over the cell to remove the fumes from the
cell room. When the bath is sufficiently molten to allow free current flow, the
graphite wedges are removed and the collection dome is swung into place. More
frequently, the collection dome must be removed to replace the steel
diaphragm, although cell shutdown is not required.
The dense white fume formed during cell startup is, in part, sodium oxide
that is formed when sodium vapor combines with atmospheric oxygen.
Minor Methods
27
-------
Sittie 1S writing about the oxidation reaction, reports that sodium peroxide
(Na262) is probably the initial product which reacts with any excess sodium to
give sodium monoxide (Na2O)." Sodium vapor also combines with chlorine
to form \white sodium chloride fume during cell startup and diaphragm
replacement.
No source sampling of Downs-cell emissions during startup and diaphragm
replacement was undertaken for this study and no data on the magnitude of
sodium and calcium oxide and sodium chloride emissions are available in the
literature. The only reference to the collection of Downs-cell emissions is by
McFadyen and Buterbaugh,1 5 who state that cell startup fumes may be sent to
caustic scrubbers for collection, a practice indicating that the caustic liquor
may aid in controlling chlorine emissions.
Sodium oxide fumes may also be emitted during cleaning operations when
sodium and salt residues, scraped from cell parts, storage drums, and other
equipment, are burned with kerosene. The dense metal oxide fumes from
either can be collected by medium-pressure-drop water scrubbers.
Sources of salt emissions during raw material preparation are the primary
and secondary salt driers. These can also be controlled by water scrubbers.
MINOR CHEMICAL METHODS
Other methods of chlorine production include the salt process and the
electrolysis of hydrochloric acid to form elemental hydrogen and chlorine.
These processes are currently operated on a commercial scale in two separate
plants in the United States.
Salt Process
Process Description
In the salt process, potassium chloride reacts with nitric acid and oxygen to
form potassium nitrate, chlorine gas, and water. The potassium nitrate is a
valuable by-product and is dried for use in fertilizers.
The overall reaction is:
12KC1 + 12HNO3 + 302 -* ^ 12KNO3 + 6C12 + 6H2 0
Intermediate steps regenerate nitric acid as illustrated by the following
equations:
12KC1 + 16HN03 -«—*- 12KN03 + 4NOC1 + 4C12 + 8H2 O (6)
4NOC1 + 8HN03 ^—^ 12N02 + 2C12 + 4H2 O (7)
12NO2 + 6H2O + 3O2-« *- 12HNO3 /-g)
28 CHLOR-ALKALI EMISSIONS
-------
Sources and Quantities of Emissions
Emissions of potassium nitrate dust can be expected from drying and
prilling operations. The emission of oxide in the absorption process (Equation
A),8 and of acid mist from the handling and storage of nitric acid are also
possible.
Electrolysis of Hydrochloric Acid
Process Description
The electrolytic cell is comprised of vertical bipolar graphite electrodes and
polyvinyl chloride diaphragms. Hydrochloric acid feed is introduced into the
cell at 150° F. The chlorine that comes off at the anode is scrubbed to remove
entrained hydrochloric acid and water and dried with sulfuric acid to provide a
gaseous chlorine of 99.8 percent purity. The chlorine is then sent to process or
liquefaction using the same equipment used in a conventional chlorine plant.
Sources and Quantities of Emissions
Emissions of chlorinated organics and inerts arise from the absorption of
process hydrogen chloride in the acid scrubber. The magnitude of those
emissions depends upon the yield of the side reactions that occur during
chlorination and upon scrubber operating conditions.
Minor Methods 29
-------
CAUSTIC MANUFACTURE BY THE
LIME-SODA PROCESS
Some caustic soda was previously produced by the lime-soda process, which
consists of reacting soda ash with lime to produce sodium hydroxide and
calcium carbonate. This process is of historical significance only, since there
were no lime-soda plants known to be operating in the United States at the end
of 1969. This situation is primarily the result of the construction of
electrolytic chlorine plants that produce caustic as a co-product.
PROCESS DESCRIPTION
The production of sodium hydroxide from soda ash and lime proceeds
according to the following reaction:
NaC03 + Ca(OH)2 *- 2NaOH + CaC03 (9)
Lime for the process is obtained by calcining quarry limestone or the
calcium carbonate mud that is produced by the process when lime recycle is
practiced. Soda ash is usually supplied by an adjacent plant or from natural
deposits of trona (Na3H(C03)2 • 2H20). A typical flowsheet for a plant using
mud recycle is shown in Figure 9.
To recover lime, it is necessary to wash the precipitated calcium carbonate
thoroughly in order to achieve efficient recovery of caustic and unreacted soda
ash. Either countercurrent decantation or multistage vacuum filtration has
been used to accomplish this.
In countercurrent decantation a series of decanters performs the caustic
extraction by washing the carbonate slurry with successively weaker caustic
solutions. Water is used for the final wash. The strong caustic stream from the
first decanter is sent to a caustic settler to remove traces of solids. The thick
carbonate slurry from the last decanter is fed to the reburning kiln for recovery
of the lime or it is lagooned and not recycled.
Where vacuum filtering is employed, repulping and washing of the filter
cake recover caustic and soda ash from the thick carbonate muds. As in
countercurrent washing, caustic-rich filtrates are sent to the caustic settler,
while the washed muds are returned to the mud-reburning kiln or lagooned.
31
-------
SODA ASH EMISSIONS
DUST-LADEN
EXHAUST GASES
Figure 9. Flow diagram of lime-soda plant with counter-
current decantation.
A rotary kiln is used to roast carbonate mud cake or quarry limestone,
producing calcium oxide and carbon dioxide. Mud reburning eliminates the
mud disposal problem and produces a relatively pure grade of calcium oxide.
Carbon dioxide may be recovered for the manufacture of soda ash in some
integrated plants, or it may be vented to the atmosphere.
SOURCES AND QUANTITIES OF EMISSIONS
Emissions from lime-reburning kilns may be controlled by the use of venturi
scrubbers. Stuart and Bailey18 report efficiencies of from 98 to 98.7 percent
and losses of 335 to 1,346 pounds per day for a venturi scrubber serving a kiln
producing 200 to 292 tons of calcine per day. Collins19 also performed
emission tests on venturi scrubbers controlling kiln emissions and found 0.49
to 0.94 ton per day particulate emissions for a 120-ton-per-day kiln at
collection efficiencies of 86 to 97 percent. Collins also found that most of the
uncollected particulate was the fine soda fume; thus, thorough washing of the
carbonate muds to remove alkali residues will prevent excessive small-particle
emissions in lime-reburning kilns. Improved mud washing also prevents
excessive ring and ball formation within the kiln.
32
CHLOR-ALKALI EMISSIONS
-------
Kilns also emit carbon dioxide in stoichiometric quantities (0.785 ton of
C02 per ton of lime, excluding the C02 contributed by fuels) if it is not
recovered from soda ash manufacture.
Soda ash handling before solution may be a source of particulate emissions
from soda lime manufacturing. No figures are available on the quantities or
types of control for soda ash emissions. Kayloor20 reports, however, that soda
ash handling (conveyor transfer points, elevators, screens, and storage bins) for
a dense soda ash operation created a general housekeeping dust problem that
was adequately controlled by a 25,000 cubic feet per minute reverse-jet-type
tubular bag collector. Collected soda ash amounted to 6 tons per day.
In another soda ash-handling operation described by Kaylor, dry cyclones
and washers collected nearly 2 tons of soda per day, although the reported
collection efficiency was only 80 to 90 percent.
Sodium hydroxide fumes, mists, or dusts from the concentration of 50
percent to 73 percent caustic or to fused caustic are the same as those
produced by the electrolytic caustic concentration process.
Lime-Soda 33
-------
CONTROL OF EMISSIONS
In the chlor-alkali industry, the significant contaminant from the standpoint
of emission control is chlorine. Other contaminants include carbon dioxide and
carbon monoxide, which are present in cell gas in small quantities, averaging 1
to 2 percent for C02 and about 0.02 percent for CO.9 The following sections
deal with the current practices for controlling chlorine emissions in the
chlor-alkali industry.
Emissions of chlorine originating from blow gases, tank-car blowdowns, air
blowing of mercury-cell brine, and air padding of liquid-chlorine storage tanks
can be prevented or controlled by:
1. Using the chlorine so produced for chemical requirements within the
plant.
2. Neutralizing the chlorine in alkaline scrubbing units to form disposable,
non-volatile substances such as calcium or sodium hypochlorites.
3. Scrubbing the chlorine from the gas streams with a suitable solvent, such
as water, alkaline brine, or carbon tetrachloride, with subsequent
recovery of the chlorine.
Table 7 summarizes present practices for the treatment of chlorine in blow
gas as reported in 24 questionnaire responses.
Table 7. PROCESSING OF BLOW-GAS CHLORINE3
Process used
Sent to alkaline scrubbing equipment
Sent to absorptive scrubbing equipment
Vented to atmosphere
Sent to in-plant processes
Not indicated
Total
Number of plants
7
4
0
11
_2
24
aData from 24 questionnaire responses
35
-------
IN-PLANT USE
Waste chlorine has been used to manufacture chlorobenzene,2 ' hydro-
chloric acid,22 sulfur monochloride,23 or bleach.24 Waste chlorine has also
been used to chlorinate river water to prevent algae buildup in cooling towers
and to treat waste water before discharge. Eleven of 24 plant questionnaires
indicated the use of blow-gas chlorine within the plant.
ALKALINE SCRUBBING SYSTEMS
., Alkaline scrubbers, employing caustic or lime to react with the waste
chlorine.to form salt and hypochlorite, are suited for dilute tail gases (less than
1 percent chlorine). (When chlorine concentrations are higher — in the range of
several percent — other control methods permitting recovery of pure chlorine
are more attractive economically.) Absorption efficiences of nearly 100
percent (Appendix A) are attainable at modest equipment costs. Operating
costs can be minimized if the plant produces excess caustic liquor, because the
liquor can be used for scrubbing. Waste chlorine in the blow gas from the
liquefaction system and that originating from the air blowing of depleted brine
and other sources are generally combined and sent to a countercurrent packed
tower using caustic liquor or a spray tower using a lime slurry ."As the blow gas
proceeds through the scrubbing system, one of the following reactions takes
place as chlorine is removed from the waste-gas stream:
2NaOH + C12 - +• NaCl + NaOCl + H20 (10)
2Ca(OH)2 .+ 2C12 -«-— »~ Ca(OCl)2 + CaCl2 + 2H20
Both reactions are exothermic, proceed rapidly to completion, and are
irreversible over a wide range of concentrations, if high temperatures and low
pH are avoided.25 Any carbon dioxide in the gas stream will consume alkali.
The consumption of alkali can be reduced by controlling the temperature and
pH so that some bicarbonate is formed.
Packed towers usually employ Raschig rings or ceramic packings to increase
contact with the waste chlorine and caustic. Milk-of-lime scrubbers use sprays,
cascade baffles, or falling films to avoid clogging and disintegration of the
packing.
The chlorine content of waste gases sent to the alkaline scrubbers varies
from 0.1 to 30 percent (Appendix A, Tables A-l and A-2), depending upon the
sources of waste chlorine and the amount of dilution air present.
Air blowing of depleted brine produces chlorine concentrations of about
500 ppm whereas concentrations in vent gases from liquefaction systems are
usually greater than 10 percent by volume.
Seven of the 24 plants responding to die questionnaires use alkaline
scrubbers to control blow-gas emissions. Three of these plants use lime slurry as
36 CHLOR-ALKALI EMISSIONS
-------
the scrubbing agent, three use caustic solution, and one uses a mixture of
caustic, sodium carbonate, and sodium bicarbonate. One of the plants using
lime employs vats for scrubbing waste chlorine. Absorption efficiencies
exceeding 99 percent were given for all plants. Source tests were performed on
two lime scrubbers and one caustic scrubber. Absorption efficiencies of 99.9
percent or higher and exit chlorine concentrations of less than 10 ppm in the
vents were found in all three cases.
ABSORBERS
In contrast to scrubbing systems involving neutralization and disposal of
chlorine, various absorption techniques can be used to recover waste chlorine.
This is especially useful where high chlorine concentrations (greater than 10
percent) favor economic recovery of chlorine. Such systems contain an
absorber to remove chlorine from the gas stream and a stripper to recover the
absorbed chlorine from the rich absorbing liquor. Collection efficiencies will
generally be better than 90 percent.
Water
Blow-gas columns using water for absorption (Figure 10) are particularly
useful in some diaphragm-cell chlorine plants. A cooler-stripper is integrated
into the main cell chlorine purification system. Cold water is passed
countercurrent to the chlorine-containing gas stream in an absorption tower
filled with ceramic packing. Overhead gases, too low in chlorine for its
economical recovery, can be sent to alkaline scrubbers or discharged to the
atmosphere. Bottoms from the tower, rich in dissolved chlorine, are sent to a
desorption tower consisting of a direct-contact cooler and a steam-stripping
section. Hot chlorine cell gas is used to strip the chlorine partially from the
cold water while the cell gas is simultaneously cooled. The remaining chlorine
is removed by direct contact with live steam. Two plants responding to the
questionnaire indicated that water absorbers are used to control blow-gas
emissions. One of these, having exit chlorine concentrations of 3 percent,
directs vent gases to a caustic scrubber that virtually eliminates chlorine
emissions to the atmosphere. The other plant uses an absorber designed to give
an absorption efficiency of 97 percent, corresponding to an exit chlorine
concentration of 0.3 percent. Normally a blow-gas water absorber is operated
at 95 to 97 percent absorption efficiency and the unabsorbed chlorine is
vented to the atmosphere. If such vent gases are considered to contain chlorine
in excess of allowable limits, absorption efficiencies as high as 99.4 percent can
be obtained at a somewhat higher cost, the cost of the steam used in stripping.
As an alternative, a secondary water scrubber can be used, with the water
effluent sent to the sewer. In any event, it is good practice to provide an
alkaline scrubber for emergency use in case the chlorine in the vent gases
should become excessive.
Stack tests performed in one plant for this study found chlorine absorption
efficiencies ranging from 72.5 to 99.4 percent. The efficiency of 72.5 percent,
which is unusually low, was obtained when the scrubber was operating under
foaming conditions caused by the experimental use of amines for treating the
Control of Emissions 37
-------
AUXI
WA
CHLORINE
CELL GAS >
STEAM Q
LIARY
TER
1!
COOLED
GAS
DIRECT-
CONTACT
COOLER
SECTION
STEANI
STRIPPING
SECTION
DRYING,
CONlPRhoolUN,
AND LIQUEFACTION
\
LIQUEFIER VENT GASE
, VENT
1 GASES
JL, WATER
LIQUID
CHLORINE
ABSORPTION
TOWER
WATER SATURATED
WITH
i
f
^^ GASES
" DISSOLVED CHLORINE GAS
STRIPPED
WATER
Figure 10. Recovery of blow-gas chlorine by water absorption (Source: U.S.
Patent 2,750,002).
scrubber water. Mass chlorine efficiencies are dependent upon gas-to-liquid
ratios, the effects of which are shown in Table 8.
Table 8. EFFECT OF LIQUID-GAS RATIO UPON CHLORINE
ABSORPTION EFFICIENCY3
Inlet gas
flow, scfmb
191
184
163
139
Water flow,
gal/min
115
112
112
112
L/G ratio,
gal/scfm
0.60
0.61
0.69
0.81
Mass chlorine
efficiency, %
72.5C
91.0
97.4
99.4
These data, from Plant 30, are used in Appendix E to cal-
culate the economical optimum operation of a blow-gas water
absorber.
bAt32°F, 1 atm, wet.
Foaming in scrubber caused by experimental amine treatment
of cooling water. At the liquid-gas (L/G) ratio used, the ex-
pected efficiency would be in the range of 90 percent.
38
CHLOR-ALKALI EMISSIONS
-------
Carbon Tetrachloride2 6
Another type of blow-gas absorber uses carbon tetrachloride as the solvent
to recover chlorine from gas streams. Carbon tetrachloride contacts the waste
chlorine in a packed tower and releases it in a steam-heated stripper.
The chlorine-containing gas stream is compressed and cooled to condense
part of the chlorine before it is fed to the absorber. The chlorine-rich carbon
tetrachloride solution is stripped of chlorine in a recovery tower consisting of a
stripping section and a rectifying section (Figure 11).
Literature references and one questionnaire indicate that chlorine recovery
in the absorber is essentially 100 percent. No stack tests were made, however,
in plants using carbon tetrachloride absorbers.
Sulfur Monochloride
A third and less common absorption system uses sulfur monochloride to
recover waste chlorine according to the following reaction:
C12+S2C12- -2SC12 (12)
Sulfur monochloride contacts chlorine-rich blow gas in an absorber, forming
sulfur dichloride. Chlorine is then distilled from the dichloride and is recovered
while the resulting monochloride is recycled to the absorption tower. A
variation of the process reacts chlorine with sulfur monochloride. The resulting
mixture of mono- and dichlorides is marketed by some plants. The process is
unpatented, however, and is not reported in the literature.
Other Absorption Systems
Other patented systems include those using alkaline brine,26 stannic
chloride,27 hexachlorobutadiene,28 and ethylene dichloride.29 The alkaline
brine system is used in mercury-cell plants to some extent; however, the other
three systems have no commercial significance.
ADSORPTION SYSTEMS
A patented recovery system uses silica gel to adsorb chlorine from waste
streams.30 Recovery efficiencies of 90 to 98 percent are claimed. Chlorine can
also be removed from very dilute gas streams by means of activated carbon.
The carbon can be reactivated by hydrogen gas at nominal pressures and
temperatures, forming hydrochloric acid, which can be readily absorbed in
water.3
Control of Emissions
-------
VENT GASES
TO ATMOSPHERE
GASEOUS CHLORINE
TO PROCESS
s
s
ya
w
2
O
z
ABSORBER
BLOW GAS
• | !•
c
COMPRESSOR
1
WATER REFRIGERATED
COOLER COOLER
1
D
T WATER
^COOLER
LEAN
SOLVENT
k2
RICH SOLVENT
±
\ \
H
(tf CONDENSER
STRIPPER
&
^REBOILER
i
BOTTOMS
Figure 11. Recovery of blow-gas chlorine by carbon tetrachloride absorption (Source: U.S. Patent
2,765,873).
-------
GLOSSARY OF TERMS
ABBREVIATIONS
abs Absolute
amps Amperes
atm Atmosphere
"Be Degrees Baume
145
Btu British thermal units
cal Calories
cc Cubic centimeter
cfm Cubic feet per minute
"C Degrees centigrade
ft3 Cubic feet
°F Degrees Fahrenheit
gal Gallons
gal/min Gallons per minute
g Grams
gr Grains (1 grain = 64.8
milligrams)
ID Inside diameter
in. H2 0 Inches of water
in. Hg Inches of mercury
kcal Kilocalorie
1.
Ib
L/G
m
mg
ml
mm
mol
N
OD
ppm
psia
psig
scf
Liter
Pounds
Liquid to gas ratio in
mass units
Meters
Milligram
Milliliter
Millimeter
Mole
Normal
Outside diameter
Parts per million
Pounds per square
absolute
Pounds per square
gauge
Standard cubic feet
inch
inch
mea-
scfm
sec
sp. gr.
V
41
sured at 0 C
(32° F) and 760 mm
(29.92 in.) Hg
Standard cubic feet per
minute
Second
Specific gravity
Volts
-------
Ba
BaCl2
BaC03
C
Ca
CHEMICAL SYMBOLS
AgCl Silver chloride
AgNO3 Silver nitrate
Barium
Barium chloride
Barium carbonate
Carbon
Calcium
CaCO3 Calcium carbonate
CaSO4 Calcium sulfate
Chlorine
Carbon monoxide
Carbon dioxide
Carbon tetrachloride
Chromium
Iron
Ferric chloride
Hydrogen
Water
Hydrogen chloride
Mercury
C12
CO
CO2
CC14
Cr
Fe
FeCl3
H2
H20
HC1
Hg
HNO3
H2S04
KC1
KOH
Mg
MgCl2
Mo
N2
Na
Na20
Na202
NaCl
Na2C03
NaS04
NH4CNS
02
SC12
S2C12
Ti
V
Nitric acid
Sulfuric acid
Potassium chloride
Potassium hydroxide
Magnesium
Magnesium chloride
Molybdenum
Nitrogen
Sodium
Sodium monoxide
Sodium peroxide
Sodium chloride
Sodium carbonate
Sodium sulfate
Ammonium thiocyanate
Oxygen
Sulfur dichloride
Sulfur monochloride
Titanium
Vanadium
42
CHLOR-ALKALI EMISSIONS
-------
DEFINITIONS
Absorber Within the context of this report, a tower in which a falling
liquid absorbs a gas, such as a blow-gas absorber that prefer-
entially removes chlorine from a chlorine-air mixture. It may
be packed, spray, or bubble cap in design.
Air blowing Passing air upward through a liquid to remove dissolved gases.
Air padding Use of compressed air above the surface of a liquid to transfer
the liquid to another vessel.
Amalgam An alloy of mercury with another metal such as sodium or
potassium.
Anode The positive pole of an electrolytic cell.
Blow gas Chlorine-inert gas mixture separated from liquid chlorine; also
known as sniff gas or tail gas.
Cathode The negative pole of an electrolytic cell.
Cell gas Chlorine gas from an electrolytic cell.
Contact cooler A tower in which a liquid is used to cool a gas by direct
contact.
Diaphragm A porous asbestos coating over the cathode screen of a dia-
phragm-type cell that separates the chlorine gas evolved at the
anode from the hydrogen gas evolved at the cathode.
Denuder The section of mercury-cathode cell where the sodium or po-
tassium amalgam is reacted with water to form caustic and
hydrogen.
Effluent Exit gas or liquid stream containing pollutants.
Electrolyzer The section of a mercury-cathode cell where electrolytic de-
composition of brine takes place.
Emission Any gas stream emitted to the atmosphere.
Establishment A plant or manufacturing unit.
Explosion disc See frangible disc.
Frangible disc A disc, installed between pipe flanges, designed to fail at a
predetermined pressure.
"Gunk" Liquid or solid impurities, or both, present in gaseous or
liquid chlorine.
Glossary
43
-------
Header A pipe into which several other pipes are connected.
Heel Residual liquid left in a vessel after a portion of its contents
has been discharged.
Padding See air padding.
Safety valve A valve designed to open at a predetermined pressure
Safety disc See frangible disc.
Stripper Within the context of this report, a tower in which chlorine
-rich solvent is heated to recover chlorine as gas.
44
CHLOR-ALKALI EMISSIONS
-------
APPENDICES
A. EMISSIONS FROM CHLOR-ALKALI PLANTS
B. SAMPLING AND ANALYTICAL TECHNIQUES
C. PHYSICAL DATA
D. CHLORINE-CAUSTIC, FUSED-SALT, AND LIME-SODA ESTABLISH-
MENTS IN UNITED STATES, JANUARY 1970
E. FIELD TEST OF ABSORPTION EFFICIENCY OF BLOW-GAS AB-
SORBER
45
-------
APPENDIX A: EMISSIONS FROM
CHLOR-ALKALI PLANTS
Most of the emission and operating data (Table A-l) in Appendix A were
supplied by the manufacturers of chlorine and caustic. The emission data repre-
sent results obtained from questionnaires sent to 39 chlorine establishments and
from stack-sampling programs conducted jointly by the Manufacturing Chem-
ists' Association and the Public Health Service (Tables A-2 and A-3).
Following the emission and operating data are a field test of potential
chlorine emissions using air for liquid chlorine transfer (Table A-4, Figure A-l),
and the calculated potential chlorine emissions from blow gas.
FIELD TEST OF POTENTIAL CHLORINE EMISSIONS, USING
AIR FOR LIQUID CHLORINE TRANSFER
The test data in Table A-4 (also shown in Figure A-l), supplied by Hooker
Chemical Corporation, relate the increase in chlorine in the vent gas of a
"padded" liquid chlorine tank as the pressure in the tanks is released and that
present after the liquid chlorine has been transferred. The tank was air padded
at 125 pounds gauge for 4 hours prior to the transfer, which required an
additional 5.25 hours. A 5-ton "heel" of residual chlorine was present in the
tank during the venting period.
CALCULATED POTENTIAL CHLORINE EMISSIONS FROM
BLOW GAS
As stated in the chapter on diaphragm and mercury cells, the principal
emission from chlorine manufacture is the chlorine present in the so-called
inerts that are separated from the liquid chlorine during liquefaction.
This gaseous mixture, along with blow gas, may be returned or recycled to
the chlorine system for chlorine recovery; it may be absorbed in water or other
absorbants for chlorine recovery or manufacture of useful by-products, or
both; or it may be neutralized to minimize or prevent emissions to the at-
mosphere. Under some circumstances the blow gas may be vented, in which
case the potential emissions become actual emissions. Even with chlorine recov-
ery or neutralizing systems, the efficiency is less than 100 percent and some
chlorine is emitted to the atmosphere.
The amount of chlorine in the blow gas is a function of operating conditions
and can be calculated from the partial pressure of chlorine in the blow gas. A
fraction of a percent of hydrogen is present in the inert gases. In some cases the
47
-------
Table A-1. EMISSION AND OPERATING DATA FROM CHLOR-ALKALI ESTABLISHMENTS USING BLOW-GAS TREATMENT3
Plant number
1
: 28
Chlorine production, tons/day
Liquid chlorine capacity, tons/day
Cell typed
Description of control equipment
Tower diameter, in. OD
Height of packing, ft
Type of packing
Materials of tower construction
Sources of inlet chlorine
490
370
M and D
Two milk-of-lime
falling film towers
56
30.5f
None; 4-in. standard
pipe launderer
Concrete sections
29
140
140
M
Two caustic-packed
towers in parallel
52C
6.83
2-in. Intalox saddles and
ceramic tiles
Titanium-lined steel
Blow gas, process i Blow gas, brine blowing.
j blowdown, tank car process blowdown, tank
| ventina car ventina
Scrubbing liquor and strength at test, % by
wt
Liquor circulation rate, gal/min
Liquor temperature, °F
Scrubber pressure drop, in. H20
Scrubber
Inlet gas rate, scfm at 32° F, 1 atm wet
Outlet gas rate, scfm at 32° F, 1 atm wet
Inlet chlorine concentration, vol %, wet
Outlet chlorine concentration, vol %, wet
Inlet carbon dioxide concn., vol %, wet
Outlet carbon dioxide concn., vol %, wet
Chlorine mass efficiency, %
Chlorine emitted, Ib/day
Chlorine emission factor, Ib chlorine/100 tons
chlorine liquefied
Ca(OH)2 NaOH
17 4 and 17
550 75
N.M.h
2.5
N.M.
456
19.7
0.0009
N.M.
N.M.
99.9
1.16
0.314
Stack plume opacity, % j 80
N.M.
2
30
180b
180b
170C
170C
D
Packed-tower water
pressure
42
29
Alternately stacked
149C
149C
119C
119C
absorbed under
1- and
1-1/2 in.
Intalox saddles
Rubber-lined steel
Blow gas only
H2O
115
52
3
N.M.
4,140'
0.325
N.D.k
N.M.
N.M.
>99.9
None
None
40
191
1711
14.4
4.461
18.0
19.6
72.5'
2,130
1.090
N.0.°
112
75
4
184
1511
14.1
1.55
22.4
21.6
91.0
659
388
N.O.
112
75
4
163
127'
13.9
31
316
316
M
Two milk-of-lime cascade
baffle towers in parallel
60
_4T
12'
None; 3-ft overlapping
baffles
Hetron, glass-matte rein-
forced
iBIowgas.a cell end boxes,
tanK car verub
; CalUHh
0 0
1 3'2
112 | 200
75 I 109
3.5 2
i
139
j N.M.
106i i 1,120'
13.1 ! 1.41
0.44 0.1 ! 0.0008
22.4
18.6
97.4
158
106
N.O.
22.3 I N.D.
15. 2m ! N.D.
99.4 j >99.9
29.6 ! 0.284
24.9
I 0.095
i
I
N.O. i
O
o
tn
CO
Ł2
o
aBased on sampling by the Public Health Service.
^Actual liquid production at time of test was 195 tons/'
^5 day. Production changed to 180 tons/day to agree
total chlorine in blow gas/100 tons chlorine liquefied for
tests 2, 3, and 4 performed at a later date.
cLiquid production based upon absorber chlorine load.
dD = diaphragm; IV! = mercury.
e Inside diameter.
*Weight of towers, no packing
9After scrubbing in alkaline brine.
hNot measured.
'Combined exhaust rate from both stacks.
'Calculated by material balance.
kNot detected.
'Foaming present in scrubber.
m Determined by extrapolation.
"Exhaust sent to powerhouse stack.
-------
Table A-2. QUESTIONNAIRE EMISSION DATA FROM CHLOR-ALKALI PLANTS WITH BLOW-GAS TREATMENT EQUIPMENT
s
a.
Type of cell
Rated capacity, tons/day
Scrubbing liquor
Liquor flow, gal/min
Inlet liquor conditions
Nominal Ci Concn., g/liter
Temperature, °C
Outlet liquor conditions
Nominal Cl concn., g/liter
Temperature, °C
Tower diameter, in.
Height of packing, ft
Type of packing
Materials of construction
Inlet gas temp., °C
pressure, psig
chlorine, vol. %
Outlet gas temp., °C
pressure, psig
chlorine, vol. %
Outlet gas flow, scfm
Efficiency of scrubber, %
Plant number
1
DO
240
5% NaOH
25
4
D
50C
5% NaOH
10
60 ; 1
21 20
120
2
21 22
30 | 10
17 20
2-in.
Raschig
rings
1-in.
Raschig
rings
Rubber-lined Rubber-lined
steel steel
4 -60
2
2
21
0
0
0.1
0.1
-10
0
0
1,078 8
100 >99
Total chlorine emitted, 1
tons/day j nil
<0.1
Lb chlorine emitted solidus j
100 tons of liquid
chlorine
-
<400
7
D
65
H20
80
0
g
D
50
Ca(OH)2e
N.A.a
N.A.
20 N.A.
? N.A.
20 N.A.
24 N.A.
30 N.A.
1.5-in.
Intalox
saddles
Rubber-lined
steel
25
N.A.
N.A.
35
35 35
26 7
20
34.66 0
3 0
14.5 ' 180
1 >99
0 ! N.A.
- . -
10
M
230
Ca(OH)2
2
0
30
150
30
72
32
Spray
tower
Concrete
20
0.5
9
25
0
0
390
100
N.D.
-
12 13
M M
260 130
Ca(OH)2 Na(OH)
600 j 73
I
10 0
30 28
20
32
72
32
Raschig
rings
Concrete
40
33
40
72
20
Chemical
stoneware
rings
Concrete
3
0.14 ! 15
1 15
32 40
0 ; 0
o ; o
600 : 120
100 ; 100
N.D. N.D.
'
14
M
112
Waste
alkali'
50
0
30
?
35
72
40
8-x 12-in.
clay
tile
Concrete
35 to 40
18
M
262
CCI4
17
22 25a
M D
180C
—
-
0.01 h
-18
9.4h
10
42'
29'
50)
50'
Platesi
1-in.
Raschig'
Steel
100
35 95
7 30
30 to 35 i 30
0
40
N.D.k t 0
370
>99
N.D.
-
—
100
nil
-
—
-
—
—
38
20
3-in.
ceramic
partition
rings
Rubber-lined
steel
-10
5
5.2
20
0
0.5
510
90
0.4
<400
458d
H2O
550
0
32.2
1.23
32.2
48
20
2-in.
ceramic
Berl saddles
Rubber-lined
steel
-38
35
11
32.2
35.0
0.3a
202
97
0.084
54
8Design data.
bD = diaphragm; M = mercury.
cAll output is liquid CI2.
d Liquid CI2 product = 308 tons/day.
eReported use of vats containing Ca(OH)2 slurry.
fNaOH,NaHCO3,Na2C03.
9Not applicable.
hMole%.
'Stripper.
^Absorber.
kNot detectable by odor.
'Water absorber vented to caustic scrubber; chlorine emissions reported as zero.
-------
en
O
Table A-3. QUESTIONNAIRE DATA ON HANDLING OF CHLORINE FROM SHIPPING-CONTAINER VENTS DURING LOADING
1 2 j 3 ' 4
Rated capacity.
tons/day | 240 180
Liquid capacity, j
tons/day CI2 i 240 a
Quantities of CI2,
from tank car
loading, tons/day 2 0.1
150 : 50
i
a
50
0.1
j
Frequency of tank >
car loading, j •
no. /day
Tons of chlorine
evolved/55-ton
3 | 2b
tank car loading j 0.67
Tons of chlorine
0.35
0.2
1 1
0.1 | 0.2
evolved/100 tons j i
of chlorine
liquefied 0.84 0.055
Treatment of tank
car waste chlorine:
Scrubber
In-plant
Vent
>
x
-
—
x
0.067 0.4
x x
- ! -
6
70
a
<0.1
c
-
<0.14
x
-
1
Plant number
7 8 ' 9 10 11 12
i ' '
65
69
<1.0
180 50
i
a I a
i
2.0 0.25 to
! • 0.50
j
|
a
a : 1
j |
- - • 0.25 to
I 0.50
|
j
230
230
0.2
d
-
79
a
1 to 2
e
260
250
1
1
!
- i 1.0
<1.45 1.1 0.5 to
!
0.087 1.3 to > 0.40
1 1.0 , 2.5 •
x
X XIX
x
— ; x
— [ X r —
; !
13 : 14
130
100
3.0
e
-
112
112
2.0
f
-
!
3.0 . 1.8
,
x x
- i -
!
15 : 19
254 222
a a
1.0 1.0
2 1
i
0.5 i 1.0
20
21
I
138 190
a
1.0
a
243
22
25
i
180 I 458
100 308
0.3
5.6
[
i
d | g
i
25
- ! - 0.01
i
i
0.39 0.45
0.72
i
(
— x
1.28
i
—
X , X X X
h i
0.167
x
-
g
-
1.22
x
-
— —
O
5
70
—
O
C/5
aUnknown.
bPer week.
cRare.
dlntermittent.
e8-hr day.
'6-hr day.
SDaily.
h0.5% vented = 10 Ib/day.
'140 Ib/day vented.
-------
130
120
110
100
I 1 1
NOTE:
50-ton TANK; 47.5 tons CONTENTS
AIR PADDED TO 125 Ib (gauge)
AFTER 4 hr, 42.5 tons TRANSFER-
RED TO SECOND TANK KEPT AT
ATMOSPHERIC PRESSURE (5-ton
heel, 5.25 hr required for transfer)
50-ton TANK KEPT AT 125 Ib
PRESSURE AND -21° C FOR 19 min.,
THEN VENTED TO LINE KEPT AT
ATMOSPHERIC PRESSURE FOR 71
min.
SOURCE: HOOKER CHEMICAL CORP.
ABSOLUTE VAPOR PRESSURE
OFCl2AT-21°C,TOTAL
ABSOLUTE PRESSURE
MEASURED CHLORINE
THEORETICAL CHLORINE
(ASSUMING PERFECT MIXING
OF PADDING AIR AND CHLORINE)
j I | L
20 30 40
CHLORINE IN VENT GAS, % by vol
50
Figure A-1. Chlorine in vent gas from air-padded
liquid chlorine tank.
hydrogen content may be sufficiently large to form an explosive mixture in or
at the exit of the chlorine liquefier. To prevent this, it is common practice to
admit dry air to the chlorine system prior to the condenser. Any additional air
at this point acts as inerts and increases the potential chlorine emissions. Calcu-
lations of the chlorine present in the blow gas from both diaphragm and
mercury cells can be explained best by an example.
Let us assume the following plant operating conditions:
Main chlorine gas from cells (after drying and compressing):
95% chlorine by volume
0.5% hydrogen by volume (0.2 to 0.3% normal range)
4.5% inerts by volume (other than H2)
Appendix A
51
-------
Table A-4 CHLORINE IN AIR VENTS FROM TRANSFER
OF LIQUID CHLORINE IN STORAGE
Tank pressure,
psig
125
110
100
90
80
70
60
53
41
39
Chlorine in vent gas,
vol %
Trace3
Trace3
Trace3
Trace3
2.0
3.0
5.75
5.0
6.25
11.0
Air padding intake and sampling nozzle at top of tank,
along with the greater density of chlorine gas with respect
to air, result in comparatively little mixing of the padding
air with the chlorine gas above the liquid contents. To cal-
culate the pounds of chlorine lost in each incremental
pressure drop, the following expression was employed:
fib/day CI2 1 + (CVT • AP") 71
L JAP R/
(A-1)
V
T
P
T
Where: C = concentration of chlorine over the pres-
sure interval, vol %
= volume of the tank, 1,155 ft3
= increment at pressure, psi
= temperature of chlorine, -21 °C
(psi) (ft3)
R =19.3 5—
Clbmole) ( K)
The total chlorine emitted during the venting is obtained
by adding all the increments.
Such a calculation for the data given in Table A-4 reveals
that a total of 33.7 pounds of chlorine is released in trans-
ferring 42.5 tons of liquid chlorine. If three transfers
of chlorine are assumed, then
3 x 33.7
2,000
100
42.5
= 0.119 ton/100 tons of liquid
chlorine would be vented to the caustic scrubber, or to the
atmosphere, as the case may be.
52
CHLOR-ALKALI EMISSIONS
-------
Blow gas (at purge trap):
30 psig
-11° F (same temperature as liquid chlorine)
No recycle of chlorine to the main chlorine system.
From the vapor pressure curve for chlorine (Figure C-4, Appendix C) the vapor
pressure of liquid chlorine at -11° F equals 7.65 psig. Thus the percentage of
chlorine in the blow gas, on the assumption that there is no air dilution to
lower the hydrogen percentage in the vent, is
( 7.65 + 14.7) absolute vapor pressure
*—*- = 50%
(30 + 14.7) absolute total pressure
This relationship of percentage of chlorine in blow gas versus liquid chlorine
temperature and pressure is shown in the nomograph, Figure A-2. In addition,
if the percentage chlorine in the main gas and that in the blow gas are known,
one can compute the potential loss of chlorine in the blow gas as tons per 100
tons of chlorine liquefied. For example, let us assume that the blow gas goes to
an absorber where all the chlorine is absorbed to make a useful by-product or
to be neutralized and wasted. As chlorine is condensed, the inerts in the main
gas, originally 5 percent by volume, will remain unliquefied and will be concen-
trated in the blow gas to 50 percent by volume. Since the chlorine in the blow
gas is also 50 percent by volume, the weight ratio of chlorine will be 5/95
(100), or 5.26 tons per 100 tons of chlorine as cell gas. We have assumed that
the chlorine in the blow gas is not recycled back into the chlorine system;
therefore, the chlorine in the blow gas equals 5.26/(100-5.26), or 5.55 tons per
BLOW-GAS
PRESSURE,
psig
10:
-3
-4.7 J
CHLORINE IN
BLOW GAS (NOT
INCLUDING C02), %
rlOO
CHLORINE IN BLOW GAS,
tons/100 tons CHLORINE
LIQUEFIED
CHLORINE IN
CELL GAS (NOT
INCLUDING C02), %
EXAMPLE:
ASSUME:
30-pslg BLOW-GAS PRESSURE
-20°F LIQUID CHLORINE TEMPERATURE
FROM® CHLORINE IN BLOW GAS = 41%
ASSUME:
95% CHLORINE IN CELL GAS
FROM® CHLORINE IN BLOW GAS, tons/100
tons LIQUEFIED = 3.9
NOTE: PERFECT GAS IS ASSUMED AND
SLIGHT SOLUBILITY OF INERTS IN LIQUID
CHLORINE IS NEGLECTED
ANALYSIS: % BY VOLUME, DRY BASIS
Figure A-2. Nomograph for determining chlorine in blow gas
with no air dilution and no recycle of chlorine in blow gas.
Appendix A
53
-------
CHLORINE IN BLOW GAS, tons/100 tons SENT TO LIQUEFACTION SYSTEM
12345 6 7
1 2 3 4 5 6 7 8 9 10
CHLORINE IN BLOW GAS, tons/100 tons CHLORINE LIQUEFIED
Figure A-3. Chlorine in blow gas versus chlorine in main gas and blow gas
with no dilution air and no recycle of chlorine in blow gas.
O 14.3X 02; 38.3% C02I 48.2* N2
* 20.9* 0Z; 79.1% N2 (AIR)
—EXPLOSIVE
100« Cl2
Figure A-4. Lower explosive limits for hydrogen-chlorine
mixtures at 3.0 atmospheres (absolute).
54
CHLOR-ALKALI EMISSIONS
-------
100 tons liquefied. This relationship, shown in Figures A-2 and A-3, represents
the chlorine used to make a by-product or the loss of product if the chlorine in
the blow gas is neutralized or vented to the atmosphere. It also represents the
actual emissions to the atmosphere in the event that a blow-gas absorber is not
used or becomes inoperative. Figure A-4 indicates the lower explosive limit of
hydrogen in the presence of chlorine and in the normal composition of cell gas
inerts. A safe upper limit of hydrogen in cell gas inerts is about 5 percent. In
the example above, the inerts in the cell gas were 5 percent by volume, which
included 0.5 percent hydrogen. The inerts entering the blow-gas absorber will
therefore contain 50/5 (0.5) or 5 percent hydrogen.
The relationship of chlorine in cell gas and blow gas to inerts in cell gas and
blow gas is shown in Figure A-5. In the preceding example, 50 percent of the
blow gas was chlorine. Since the hydrogen content at the entrance to the
blow-gas absorber is 5 percent, the hydrogen content of the exit gas after
scrubbing out the chlorine will be 2 times 5, or 10 percent. The relationship of
chlorine and hydrogen in the main gas to hydrogen at the exit from the
blow-gas absorber is shown in Figure A-6.
In the preceding example, note that 10 percent hydrogen in the blow-gas
absorber vent is above the lower explosive limit. If the inerts are doubled by
adding dilution air at or before the exit of the blow-gas absorber, the hydrogen
at the absorber vent will be reduced from 10 to 5 percent, which is considered
a safe limit. The inerts in the main gas were 5 cubic feet per 95 cubic feet of
INERT GAS IN BLOW GAS, % by vol
EXAMPLE:
ASSUME
96% CHLORINE IN CELL GAS
42% CHLORINE IN BLOW GAS
0.33% HYDROGEN IN CELL GAS-
FROMCD®®®®
HYDROGEN IN BLOW GAS = 4.8%
FOR OTHER INERTS MULTIPLY
INERT GAS BY APPROPRIATE
NOTE: FACTOR-
CHLORINE ANALYSIS MAY BE Cl2 ALONE
OR Cl5 + C02 FOR BOTH CELL GAS
AND BLOW GAS.
ASSUME PERFECT GAS AND
NEGLECT SOLUBILITY OF INERTS
IN LIQUID Cl2.
I I
10 20 "30 40 50 60 70 80 90 100
CHLORINE IN BLOW GAS, % by vol
Figure A-5. Relationship of chlorine and inerts in cell gas
and blow gas (with no air dilution).
Appendix A
55
-------
0.2 0.3 0.4 0.5
HYDROGEN IN CELL GAS, % by vol
0.7
Figure A-6. Hydrogen in vent from blow-gas absorber
(with no air dilution).
chlorine. By doubling the inerts, an additional 5 cubic feet of air is added to
the chlorine system. Cell gas at a rate of 100 tons per day represents (100)
(2000)(5.06)/1440 = 703 scfm. The dilution air required is thus 5/95 times
703, or 37 scfm per 100 tons per day of chlorine as cell gas. The dilution air
required for various percentages of chlorine and hydrogen in the cell gas to
reduce the hydrogen in the vent to 5 percent, or a safe limit, is shown in Figure
A-7.
The heat capacity of the dilution air is small compared with that of the
chlorine and it is therefore assumed that the dilution air has no measurable
effect on the temperature or pressure of the chlorine system. The point of
entrance of the dilution air does, however, have an effect on the amount of
chlorine in the blow gas. If the dilution air is added at or before the entrance to
the final condenser such that equilibrium conditions can be assumed, doubling
the inerts by adding dilution air will double the weight of chlorine in the blow
gas (the percentage of chlorine will be unchanged). The weight of chlorine in
the blow gas will increase but will not be quite doubled as is the case, for
example, if the dilution air is added at or just before the exit of the final
56
CHLOR-ALKALI EMISSIONS
-------
0.2
0.4 0.6 0.8 1.0
HYDROGEN IN CELL GAS, % by vol
Figure A-7. Dilution air required (per 100 tons/day
chlorine as cell gas) to reduce hydrogen in blow-gas
absorber vent to 5% by volume (assume 0° C and
14.696 psia).
condenser. There will be no increase in chlorine if dilution air is added at the
inlet to the blow-gas absorber. These variables in operating conditions have
been included in one curve of Figure A-8, showing the chlorine that occurs in
the blow gas with the various amounts of air dilution required to limit hydro-
gen in the absorber vent to 5 percent. Equilibrium conditions have been
assumed in Figure A-8 but, as previously stated, the chlorine in the blow gas
will be somewhat less if it is added just before the exit-of the final condenser
rather than at or before the entrance to the final condenser.
The percentage of chlorine in blow gas will vary considerably with operating
conditions as noted. An average range is 20 to 50 percent.
The rate of potential or actual chlorine emissions in the blow gas will also
vary with operating conditions. The potential emissions as weight per day will
increase with percentage of chlorine in the blow gas, percentage of inerts in the
cell gas, air dilution if added before the exit of the final condenser, and plant
capacity. An average range for diaphragm cells is 1 to 5 tons of chlorine in
blow gas per 100 tons of chlorine liquefied. Similarly, the average range for
mercury cells is 2 to 8 tons of chlorine in blow gas per 100 tons liquefied.
Appendix A
57
-------
EflSSM«EE95 5% Clz AND 0 4% H2 IN CELL GAS AND 25% CI2 IN BLOW GAS. FROM©® DILUTION AIR TO REDUCE H2 IN BLOW-GAS
ABSORBER VENT TO 5% IS 26 sdm/100 tons CI2 AS CELL GAS AND C12 IN BLOVI GAS BECOMES 1.75 ORIGINAL WEIGHT; FROM®®
CI2 IN BLOW GAS WITHOUT AIR DILUTION = 1.6 tons; WITH AIR DILUTION, 1.75 x 1.6 = 2.8 tons.
DILUTION AIR REQUIRED TO REDUCE H2 IN BLOW-GAS ABSORBER CHLORINE IN BLOW GAS, tons/100 tons LIQUEFIED WITH NO
VENT TO W, (seta/100 tons CI2 AS CELL GAS) AIR DILUTION AND NO RECYCLE
ISO Ho !0o 30 S/J ?o So So 10 30 !p 10 0 j
1 0
1.0 0.9 0.8 0.7 0.6 0.5 0.4 0.3 0.2 0.1 0
HYDROGEN IN CELL GAS (DRY BASIS), » by vol
Figure A-8. Effect of air dilution on chlorine loss with blow gas (assume no
chlorine recycle).
58
CHLOR-ALKALI EMISSIONS
-------
APPENDIX B. SAMPLING AND ANALYTICAL
TECHNIQUES
The sampling and analytical techniques described were used by the National
Air Pollution Control Administration to conduct source tests on four chlor-
alkali plants. The analytical procedures are based on methods described in the
literature and by manufacturers of chlorine and caustic.
DETERMINATION OF CHLORINE IN STACK GAS
This method is intended for the determination of gaseous chlorine in stack-
gas samples. Chlorine is collected in an evacuated 2-liter flask and reacted with
sodium hydroxide to form sodium hypochlorite. Because of the large variation
in chlorine concentration in stack gas before and after scrubbers, two methods
of analysis are used. Samples collected before the scrubber usually contain
percentage quantities of chlorine and are analyzed by the Volhard Titration
following reduction of the hypochlorite to chlorine by sodium arsenite. This
method can be used to analyze for chlorine from percentage quantities down
to about 5,000 ppm when 0.1 N reagents are used. Outlet samples after the
scrubber usually contain ppm quantities and are analyzed by the ortho-tolidine
method. Chlorine reacts under acid conditions (optimum pH 1.2) with ortho-
tolidine to form the yellow holoquinone of ortho-tolidine dihydrochloride and
is determined spectrophotometrically at 490 mp.. The color developed is pro-
portional to the amount of chlorine present, and Beers' law is obeyed in the
concentration range of 0 to 7 mg chlorine per liter.
Reagents
All chemicals used must be ACS analytical-reagent grade.
Water
Doubly distilled or deionized-distilled water.
Nitrobenzene
ACS reagent grade.
Ferric Indicator
Dissolve 28 grams of ferric ammonium sulfate, FeNH4(SO4)2-12H2O, in 90
ml of hot water. Cool, filter, add 10 ml of concentrated nitric acid, and dilute
to 100 ml in a volumetric flask. Use 1 to 3 ml of indicator per titration.
59
-------
Nitric Acid (8 N)
Prepare NOx-free nitric acid by adding 50 ml of concentrated nitric acid to
50 ml of distilled water and boil in a conical flask until the solution is colorless.
Sodium Chloride Solution (0.1 N) (Primary Standard)
Prepare a 0.1 N solution of sodium chloride by accurately weighing 5.846
grams of reagent-grade NaCl that has been dried at 120° C for 2 hours. Dissolve
in distilled water and dilute to 1 liter in a volumetric flask.
Standard Silver Nitrate Solution (0.1 N)
Dissolve 17.0 grams of dried AgN03 in distilled water that has been tested
for the presence of chlorides and dilute to 1 liter. Transfer the solution to an
amber glass-stoppered bottle. Protect the solution from exposure to direct
sunlight when not in use. Standardize the silver nitrate solution against 30 to
40 ml of the 0.1 NaCl solution, according to the Volhard Titration as described
under the analytical section. From the net volume of AgN03 used in the
titration and the weight of chloride present in the 30- to 40-ml sample used in
standardization, compute the chlorine titer of the'solution. One ml of 0.1 silver
nitrate is equal to 0.003545 gram of chlorine or chloride.
Ammonium Thiocyanate (0.1 N)
Dissolve 8 grams of ammonium thiocyanate in 500 ml of distilled water and
dilute to 1 liter in a volumetric flask. Determine the titer of NH4CNS solution
as related to the AgN03 solution by: (1) measuring 30 to 40 ml of the 0.1 N
AgN03 solution; (2) adding 2 ml of ferric ammonium sulfate indicator and 5
ml of nitric acid (1:1); and (3) titrating with the NH4CNS solution until the
reddish-brown endpoint appears. Shake vigorously during titration. The
NH4CNS titer must be determined before the AgN03 is standardized.
Sodium Arsenite (20%)
Dissolve 20 grams of sodium arsenite in 100 ml of distilled water. Store in a
glass-stoppered reagent bottle.
Sodium Hydroxide (10%)
Dissolve 10 grams of sodium hydroxide in 100 ml of distilled water. Store in
a tightly closed polyethylene bottle.
Sodium Hydroxide (1 N)
Dissolve 40 grams of sodium hydroxide in 1 liter of distilled water. Store in
a tightly closed polyethylene bottle. Use when ppm concentrations of chlorine
and C02 are expected.
Ortho-Tolidine Dihydrochloride Solution (0.134%)
Dissolve 1.34 grams of ortho-tolidine dihydrochloride in 500 ml of distilled
water. Add this solution, with constant stirring, to 500 ml of a mixture of
60 CHLOR-ALKALI EMISSIONS
-------
distilled water (350 ml) and concentrated HC1 (150 ml). Store in an amber
glass-stoppered bottle. This reagent is stable for 6 months.2 8
Apparatus
Flasks
Two-liter, pyrex, round-bottom flasks with sleeve and accompanying three-
way stopcock with T-bore. The T-bore has a cone for the vertical leg and a ball
and socket for the horizontal legs (Figure B-l).
Vacuum System
The vacuum system consists of a vacuum pump capable of pumping 0.1 cfm
at 27 in. Hg vacuum, or more, connected by a quick connect to a vacuum
gauge capable of measuring vacuum pressure with an accuracy of 0.25 in.Hg
(Figure B-2).
Thermometer
Weston thermometer, range 25 to 125° F, 5-in. stem.
Probe
(See Figure B-3).
Glass "L"
Connects three-way stopcock to probe (Figure B-l).
Variable Transformer
Rated at 7.5 amps, 0 to 135 volts.
Glass Wool
One-fourth pound fine glass wool.
Dispenser (NaOH)
A 100-ml round-bottom flask, modified with a Teflon stopcock and ball-
joint extension (Figure B-4).
Burettes
50ml.
Spectrophotometer
This instrument should be capable of measuring optical density at 490 mM
in 0.5-in. absorbance cells, or at 440 mju in 1-in. absorbance cells.
Analytical Procedures
Collection of Samples
Emission sources containing chlorine are sampled in quadruplicate by a
grab-sampling technique using an evacuated 2-liter flask. The equipment devel-
oped and used by the Public Health Service is shown in Figure B-l.
Appendix B 61
-------
1. GROUND-GLASS SOCKETS-5 NO. 12/5, PYREX.
2. STOPCOCK-THREE-WAY, T-BORE, J, PYREX,
2-mm BORE, 8-mmOD
3. GROUND-GLASS SOCKET-5 NO. 12/5.
4. GROUND-GLASS CONES-STANDARD TAPER, §"
SLEEVE NO. 24/40.
r~r ~/^
J L
' -s
X N
V
/ \
1 \
1 \
1
'
\ ;
\ 1/4 in. /
^ L '
^^JL^-"
f
t*T In W
.f |p_ ^
i
C
^
0
1. BOILING FLASK - 2-liter, ROUND-BOTTOM, SHORT-
NECK, WITH I SLEEVE NO. 24/40.
2. URETHANE FOAM ENCASEMENT.
Figure B-1. Three-way stopcock, "L", and flask.
62
CHLOR-ALKALI EMISSIONS
-------
THREE-WAY STOPCOCK -
FEMALE BALL JOINT FOR
EASY CONNECTION TO
THREE-HAY STOPCOCK
FLASK IN
URETHANE
FOAM
VACUUM
GAUGE
GLASS "L"
VACUUM HOSE iNaOH TRAP CAN BE
INSERTED IN THIS LINE WHEN
NECESSARY TO PROTECT PUMP
FROM CORROSIVE GASESi
TYGON TUBE CONNECTS
VACUUM GAUGE TO
THREE-WAY STOPCOCK
VARIABLE
TRANSFORMER
PLYWOOD BOX HOLDS
SAMPLING TRAIN COMPONENTS
Figure B-2. Chlorine-sampling apparatus.
A 2-liter round-bottom flask encased in urethane foam and equipped with a
three-way stopcock is connected to the probe via a glass "L". A wad of glass
wool is inserted into the probe to minimize the amount of particulates entering
the flask. A 500-ml wash bottle filled with a saturated caustic solution is placed
in the line before the vacuum pump to protect it from corrosive gases (not
shown in Figure B-2). The stem of a dial thermometer is inserted into the
urethane foam adjacent to the flask.
The following procedure is used for the collection of samples. Connect the
female ball-joint of the stopcock to the vacuum gauge and pump. Insert the
sampling probe into the stack, turn on the vacuum pump, and purge stack gas
through the stopcock. If condensation is observed in the stopcock, heat the
probe by applying sufficient voltage to the probe heating element with the
variable transformer. Turn the stopcock so that the vacuum pump and vacuum
gauge are connected with the flask. Evacuate the flask to at least 25 inches of
mercury vacuum. Disconnect the vacuum pump line at the quick disconnect
(i.e., close the line to the vacuum gauge) and accurately measure the vacuum in
the flask. Turn the three-way stopcock so that the flask is connected to the
probe and vacuum gauge. Allow the flask to fill with a sample of stack gas until
there is little or no vacuum left; however, avoid pressurizing the flask, a condi-
tion that is possible if stack pressure exceeds atmospheric pressure. If the flask
takes longer than 15 seconds to fill, the glass wool filter is plugging and should
be replaced. Measure precisely the final vacuum in the flask. Turn the three-
way stopcock so that the flask is closed. Record the flask temperature indi-
cated by the dial thermometer. Disconnect the flask and attach the burette to
Appendix B
63
-------
n
I
jo
GLASS WOOL-
-PYREX GLASS, 10 mm
l-in.-OD ,0.035-in.-WALL
STEEL TUBE
CORK
BALL JOINT
Figure B-3. Probe for sampling chlorine.
w
2
o
-------
100-ml CAPACITY
TEFLON STOPCOCK
5 NO. 12/5
Figure B-4. Burette for adding NaOH.
the female ball-joint of the stopcock. Add approximately 50 ml of 10 percent
sodium hydroxide to the burette when chlorine and carbon dioxide concentra-
tions are expected to exceed 1 percent, and 50 ml of IN NaOH for 1 percent
or less. Open the burette stopcock, and slowly open the three-way stopcock to
the burette. Because the NaOH solution readily absorbs chlorine, there is no
difficulty in adding sufficient reagent to absorb all the chlorine present. The
quantity and strength of NaOH should be adjusted to the amount of chlorine
and C02 anticipated in the stack gas. Turn the stopcock so that the flask is
closed. Shake the flask for 1 minute to ensure complete reaction of the NaOH
with the chlorine. Record the data taken on a sheet such as that shown in
Figure B-5.
Sample Preparation
Transfer the sample solution from the collection flask into a graduated
cylinder. Wash the flasks three times with distilled water and add to the gradu-
ated cylinder. Adjust the solution to a known volume and transfer to a poly-
ethylene container.
Analysis
Since there are two procedures for analyzing chlorine in stack-gas samples
(i.e., for C12 concentrations 0.5 percent or more and for C12 concentrations
less than 0.5 percent), each analytical method will be described separately.
Appendix B
65
-------
Date_
Plant.
Operating conditions.
Sample collected by
Run number
Field data
Flask number
Volume of flask less correction (Vf), S.
Pressure before sampling (Pj), in. of Hg
Pressure after sampling (Pf), in. of Hg
Flask temperature (Tf), °R
Stack gas flow rate (Q), scfm
Remarks
Figure B-5. Data sheet.
Method A: modified Volhard Titration for C12 concentrations of 0.5 per-
cent or more-Pipet an aliquot of the hypochlorite solution into a 250-ml
Erlenmeyer flask. Add 50 ml of distilled water and 5 ml sodium arsenite
solution. Swirl to mix and add 5 ml of nitric acid solution (1:1). Mix
thoroughly. Omit this step when standardizing the silver nitrate against the
standard sodium chloride solution.
66
CHLOR-ALKALI EMISSIONS
-------
add 5 ml of AgNOa m excess. Add 1 to 3 ml nitrobenzene to form an oily coat
on the particles of AgCl and prevent reaction with the thiocyanate or aUer-
nately, filter off the AgCl precipitate. Add 2 ml of indicator solution swirl to
mix, and titrate with thiocyanate until the first appearance of the'reddish
brown [Fe(CNS)6]- complex. The color should last at least 1 minute with
vigorous shaking. Determine the net volume of AgNO3 consumed.
Calculations.
Compute the number of grams of chlorine present in the sample by the
following equation:
X = mlAgN03(T)(F) (B-l)
where
T = chlorine titer of standard AgN03
X = grams of chlorine
total volume of sample, ml
F =
aliquot volume, ml
Calculate the liters of chlorine in the sample by the following equations:
gClX 22.4 liters/mole
liters chlorine =:
71 g/mole (B-2)
71 = molecular weight C12
22.4 liters/mole = gram-molecular volume at 32° F
Calculate the ppm chlorine in the sample by the following equation:
liters of chlorine X 106
ppm chlorine =
liters of gas sampled (B-3)
V1 f , (530°R)Vf(Pf-Pi)
Volume ot gas samples =
29.92in.Hg(Tf)
Vf = flask volume, liters
Pf = final flask pressure, in. Hg
Pi = initial flask pressure, in. Hg
Tf = flask temperature, °R
Appendk B 67
-------
Method B: Ortho-tolidine The ortho-tolidine method is used to analyze
scrubber outlet samples, in which ppm concentrations of chlorine are encount-
ered. Pipet an aliquot of the sample into a 100-ml volumetric flask, neutralize
with nitric acid, add 2 ml of ortho-tolidine reagent, and dilute to the mark with
distilled water. Prepare a blank consisting of 2 ml of ortho-tolidine reagent and
distilled water in a 100-ml volumetric flask. Using the blank, set the spectro-
photometer at zero absorbance at 440 m/u. Read the absorbance of the sample
in 0.5-inch absorbance cells within 5 minutes after the addition of the ortho-
tolidine reagent.
Read the number of milligrams of chlorine present from a previously pre-
pared calibration curve made by plotting absorbance versus milligrams of chlo-
rine. Calculate the concentration of chlorine in ppm in the same manner as
previously stated.
Preparation of Calibration Curve- Hypochlorite solutions for calibration
purposes can be prepared by bubbling chlorine gas through 0.1 N NaOH.
Certain commercial solutions of hypochlorite can also be used, such as Zonite
(Zonite Products Corporation).* Zonite contains approximately 1 percent
available chlorine.31 Standardize the hypochlorite solution by adding an
aliquot of the solution to an acid solution of potassium iodide. Titrate the
equivalent amount of iodine released with standard sodium thiosulfate, using
starch as an indicator.
Prepare a hypochlorite solution in which 1 ml contains approximately 1.0
mg available chlorine. Dilute 10 ml of this solution to 1 liter in a volumetric
flask with distilled-deionized water. Standardize this solution by titrating as
given above. Adjust the hypochlorite solution to contain 0.01 mg of chlorine
per ml.
Pipet exactly 1, 5, 10, 20, 50, and 75 ml of the 0.01 mg/ml hypochlorite
solution into 100-ml volumetric flasks, so that the solution will contain, respec-
tively, 0.1, 0.5, 1.0, 2.0, 5.0, and 7.5 mg of chlorine per liter. Add 2 ml of the
o-tolidine reagent to each flask and dilute to 100 ml with distilled-deionized
water. Within 5 minutes after addition of the o-tolidine reagent, read the
absorbance of the solution at 490 m^ in 0.5-inch absorbance cells, or at 440
mid in 1-inch cells.
To prepare standards in the range of 0.01 mg/liter, dilute 100 ml of the
original 0.01 mg/ml solution to 1 liter in a volumetric flask. This solution
contains 0.001 mg/ml, or 1 mg/liter. Pipet 1, 5, 10, 20, 50, and 75 ml of this
solution into 100-ml volumetric flasks, so that the flasks will contain,
respectively, 0.01, 0.05, 0.1, 0.2, 0.5, and 0.75 mg of chlorine per liter. Add 2
ml of the o-tolidine reagent to each flask and dilute to 100 ml with
distilled-deionized water. Within 5 minutes after addition of the o-tolidine
*Mention of commercial products or company names does not constitute endorsement by
the Air Pollution Control Office or the Environmental Protection Agency.
68 CHLOR-ALKALI EMISSIONS
-------
orato
, or at ^vu m^ m 0.5-inch absorbance cells.
Prepare a calibration curve by plotting absorbance versus concentration on
rectangular graph paper.
Discussion of Procedures
The estimated error for the combined sampling and analytical procedure
using the Volhard Titration is ± 7 percent for samples containing more than
0.05 percent chlorine. The precision of the analytical method is ±2 percent on
standard samples containing NaCl.
The usual volumetric errors are encountered with this method. Prema-
ture endpoints may occur if the NH4CNS is not added dropwise near the
equivalence point and the solution shaken before the next addition. The
necessity of removing silver chloride by filtering or coating the precipitate
(AgCl) with nitrobenzene has been emphasized. Interferring substances that
form insoluble silver salts, and bivalent mercury, which forms a stable complex
with the thiocyanate, must be absent from the sample.
The estimated error for combined sampling and analysis using the o-tolidine
method is ± 7 percent in the concentration range of 1 to 7 mg/liter. Analyses
of samples containing more than 7 mg chlorine/liter may be performed by
taking an appropriate aliquot of the sample. Precision and accuracy of the
o-tolidine method are greatest for samples containing about 1 mg/liter.
Distilled-deionized water free of chlorine should be used in all procedures
where water is used. Nitrites and ferric compounds, when present, interfere
with the analysis. For best results, the pH of the solution must be 1.3 during
the contact time, and the chlorine concentration must not exceed 10
mg/liter.23 Extreme care is required in preparing standards from hypochlorite
solutions. Color comparisons should be made at the time of maximum color
development. If the sample contains predominantly free chlorine as the
hypochlorite, the maximum color appears almost instantaneously and begins to
fade.32 Samples containing combined chlorine (i.e., chloroamines) develop
their maximum color within 3 minutes at 25° C and should be allowed to
develop color in the dark.32 If it can be shown that maximum color
development occurs instantly, the absorbance of the samples and standards
should be read either as quickly as possible or at a designated time following
addition of the o-tolidine reagent. Absorbance readings can be taken within 5
minutes after addition of the o-tolidine reagent with no apparent color fading.
DETERMINATION OF CARBON DIOXIDE IN THE PRESENCE
OF CHLORINE
Carbon dioxide and chlorine can be collected simultaneously in a 2-liter
evacuated flask, reacted with sodium hydroxide to form sodium carbonate and
sodium hypochlorite, and analyzed separately. Chlorine is determined by
Appendix 6
-------
using the Volhard Titration of chloride, following reduction of the hypochlo-
rite to chloride with sodium arsenite. Carbon dioxide, evolved from sodium
carbonate upon acidification, is collected on ascarite and then determined
gravimetrically. Carbonate-free reagents (sodium hydroxide, sodium arsenite)
must be used if analyses for both chlorine and carbon dioxide are performed.
The gravimetric method is applicable to the determination of carbon dioxide in
the range of 0.3 to 25 percent by volume in stack gases in the presence of
chlorine.
Reagents
All chemicals must be ACS analytical-reagent grade.
Water
Distilled-deionized water.
Sodium hydroxide (10%)
Prepare carbonate-free sodium hydroxide by dissolving 100 grams of NaOH
in freshly boiled and cooled water and diluting to 1 liter.
Sodium arsenite (20%)
Dissolve 20 grams of carbonate-free sodium arsenite (NaAs02) in 100 ml
of water or prepare from primary-standard-grade arsenic trioxide.
Ascarite
Eight to 20 mesh.
Apparatus
Drying tube
Glass drying tube with two ground-glass stopcocks. The tube is filled with
ascarite and several grams of drierite.
Evolution apparatus
See Figure B-6.
Sampling equipment
Same as for chlorine.
Analytical Procedures
Collection of samples
Same as for chlorine
Cleanup
Same as for chlorine.
70 CHLOR-ALKALI EMISSIONS
-------
ATMOSPHERE
VACUUM
"S
•o
ROTANIETER
DRIERITE
DRIERITE
ASCARITE
GLASS DRYING TUBE
ASCARITE
DRYING TUBE
SEPARATORY
FUNNEL
RUBBER STOPPER
SAMPLE SOLUTION
MIDGET IMPINGER
MAGNETIC STIRRER
Figure B-6. Apparatus for determination of carbon dioxide in presence of chlorine.
-------
Analysis
Transfer an aliquot of the sample to a 100-ml Erlenmeyer flask and add 10
ml of sodium arsenite (carbon-free) for prescrubber samples and 2 ml for outlet
samples. Set up the apparatus as shown in Figure B-6. Place 20 ml of 1:1 HC1
in the separatory funnel along with 5 drops of 0.1 percent methyl-red indicator
and start the magnetic stirrer. Preweigh the glass drying tube containing
ascarite and drierite to the nearest 0.1 mg and insert into the sampling line.
Open the stopcocks to the drying tube, turn on the vacuum source, and open
the separatory funnel stopcock. Adjust the flow to approximately 200 cc/min.
and run the sample for 15 minutes. Shut off the vacuum and the drying tube
stopcocks and remove the drying tube from the line. Carefully weigh the
drying tube and determine the amount of C02 collected on the ascarite by
subtracting the tare weight of the tube. A blank should also be run to
determine the background C02 in the reagents. Using the aliquot factor,
calculate the total weight of C02 in the sample.
Discussion of Procedures
The evolution of carbon dioxide from sodium carbonate solutions has been
applied to the measurement of C02 in stack gases containing large concentra-
tions of chlorine. Reduction of the hypochlorite to chloride with arsenite
prevents the formation of volatile hypochlorous acid upon acidification. The
pH of the solution upon acidification should be less than 2 to ensure complete
evolution of C02 . Water vapor is removed in the sulfuric acid impinger and in
the drierite drying tube and does not enter the glass drying tube. When
exhausted, as indicated by the formation of white sodium carbonate, the
ascarite should be replaced. Standard samples of sodium carbonate result in 99
percent recovery of C02 with no interference from the presence of chlorides
produced from the reduction of hypochlorite.
72 CHLOR-ALKALI EMISSIONS
-------
APPENDIX C. PHYSICAL DATA
Some physical and chemical properties of chlorine, caustic soda, caustic
potash, and sodium are given in Appendix C.
CHLORINE
Liquid chlorine is a clear amber-colored liquid about 1.5 times the density
of water (see Figure C-l). At atmospheric pressure it has a boiling point of
-29.29° F and is usually shipped in steel containers as a liquid under pressure.
Wet chlorine gas or liquid is quite corrosive to all common metals. Gold, silver,
platinum, and tantalum resist both wet and dry chlorine at temperatures less
than 300° F. Titanium resists wet chlorine but is attacked by dry. In the
manufacture of chlorine the wet gas is usually handled in chemical stoneware,
97.57
95.77
94.80
92.85
90.85
88.79
86.64
84.25
82.09
79.65
77.06
74.31
71.31
67.98
TEMPERATURE, °F
Figure C-1. Density of liquid chlorine.33
73
-------
glass, porcelain, and certain plastics such as Haveg and polyesters. After the gas
is dried it is compressed, liquefied, and stored in steel equipment. The use of
steel for handling dry chlorine is usually limited to temperatures of about 212°
F and less. Nickel, Hastelloy C, Monel, and types 304 and 316 stainless steel
may be used at temperatures higher than this.
Minor leaks of gaseous or liquid chlorine are potentially hazardous.
Expansion of the liquid or gas in the vicinity of the leak will condense moisture
from the air, rapidly increase the corrosion rate, and thereby increase the
extent of leakage to the atmosphere. One pound of the liquid will rapidly
expand to about 460 times its liquid volume, occupying 5 cubic feet. The gas is
greenish-yellow and about 2.5 times as heavy as air. It tends, therefore, to flow
to the floor or lower levels of a building.
Chlorine is nonexplosive, noncombustible, and a nonconductor of elec-
tricity. When chlorine is dissolved in pure water, weak solutions of hydro-
chloric and hypochlorous acid are formed. The water solution is an oxidizing
agent of moderate strength. The maximum solubility of chlorine is approxi-
mately 1 percent at 49.3° F; it is insoluble in boiling water. For the solubility
of chlorine in water, see Table C-l. At temperatures below 49.3° F, chlorine
hydrate (C12 -8H20), usually referred to as "chlorine ice," may crystallize.
Purity of Commercial Chlorine
Commercial liquid chlorine averages about 99.4 percent chlorine and
contains in solution solid, liquid, and gaseous impurities in small amounts. The
following are approximate:
1. Gaseous impurities (largely due to air padding of tank cars): C02 = 0.5
to 0.7 percent by volume; 02 = 0.04 to 0.1 percent by volume; and N2 =
0.07 to 0.3 percent by volume.
2. Liquid impurities: 40 ppm total, largely carbon tetrachloride, chloro-
form, and chloroethanes; and 40 ppm bromine, usually not considered
an impurity since it reacts chemically very much like chlorine.
3. Solid impurities: 100 ppm total, largely hexachloroethane and ferric
chloride.
Solid impurities may be troublesome since they tend to deposit in orifices,
valves, and control instruments. When chlorine is used at low rates, thus
requiring small mechanical clearances or orifices, as in water purification, glass
wool filters are commonly used to remove a considerable amount of the solid
impurities. Moreover, higher purity chlorine is frequently used. By fractional
distillation of commercial chlorine, solid impurities can be reduced to about 25
ppm.
Atomic and Molecular Properties
Atomic symbol: Cl
Atomic weight: 35.457
74 CHLOR-ALKALI EMISSIONS
-------
I
g.
Table C-1. SOLUBILITY OF CHLORINE IN WATER AS A FUNCTION OF PARTIAL PRESSURE AND
TEMPERATURE34
Partial
pressure
of C12,
mm Hg
5
10
30
50
100
150
200
250
300
350
400
450
500
550
600
650
700
750
800
900
1000
1200
1500
,2000
2500
3000
3500
4000
4500
5000
0°C
0.488
0.679
1.221
1.717
2.79
3.81
4.78
5.71
-
-
-
—
—
-
—
—
—
-
—
—
—
CI2-8
separ
-
—
-
-
—
-
—
-
10° C
0.451
0.603
1.024
1.354
2.08
2.73
3.35
3.95
4.54
5.13
5.71
6.26
6.85
7.39
7.97
8.52
9.09
9.65
10.21
—
H2O
ates
—
_
-
—
—
-
--
-
20° C
0.438
0.575
0.937
1.210
1.773
2.27
2.74
3.19
3.63
4.06
4.48
4.88
5.29
5.71
6.12
6.52
6.90
7.29
7.69
8.46
9.27
10.84
13.23
17.07
21.0
_
_
-
—
-
30° C
0.424
0.553
0.873
1.106
1.573
1.966
2.34
2.69
3.03
3.35
3.69
3.98
4.30
4.60
4.91
5.21
5.50
5.80
6.08
6.68
7.27
8.42
10.14
13.02
15.84
18.73
21.7
24.7
27.7
30.8
;
40° C
0.412
0.532
0.821
1.025
1.424
1.754
2.05
2.34
2.61
2.86
3.11
3.36
3.61
3.84
4.08
4.32
4.54
4.77
4.99
5.44
5.89
6.81
8.05
10.22
12.32
14.47
16.62
18.84
20.7
23.3
Solubility
50° C
0.398
0.512
0.781
0.962
1.313
1.599
1.856
2.09
2,31
2.53
2.74
2.94
3.14
3.33
3.52
3.71
3.89
4.07
4.27
4.62
4.97
5.67
6.70
8.38
10.03
11.70
13.38
15.04
16.75
18.46
got C12/
60° C
0.383
0.492
0.743
! 0.912
! 1.228
1.482
1.706
1.914
2.10
2.28
2.47
2.64
2.80
2.97
3.13
3.29
3.44
3.59
3.75
4.04
4.36
4.92
5.76
7.14
8.48
9.83
11.22
12.54
13.88
15.26
liter
! 70° C
0.369
0.470
0.704
0.863
, 1.149
1 .382
[ 1 .580
! 1.764
! 1.932
, 2.10
2.25
2.41
: 2.55
' 2.69
2.83
2.97
3.10
3.23
3.37
3.63
3.88
j 4.37
(
5.09
6.26
7.40
8.52
9.65
10.76
11.91
13.01
! 80° C
0.351
0.447
': 0.67 1
i 0.815
1 .085
1.294
1.479
1.642
1.793
1.940
2.08
2.22
2.35
2.47
2.59
j 2.72
2.84 ;
2.96 i
3.08 I
3.30 '
3.53 |
3.95
4.58
5.63
6.61 ,
7.54 ,
8.53 i
9.52 !
10.46 j
1 1 .42 :
90° C
0.339
0.431
0.642
0.781
1.034
1.227
1.396
1.553
1.700
1.931
1.965
2.09
2.21
2.32
2.43 j
2.55 I
2.66 !
2.76 I
2.87 1
3.08 :
3.28 i
3.67
|
4.23 >
5.17 ;
6.05
6.92 i
7.79
8.65 | '
9.49 j t
0.35 | Ł
100°C
0.326
0.415
0.627
0.747
0.987
1.174
1.333
1.480
1.610
1.736
1.854
1.972
2.08
2.19
2.29
2.41
2.50
260
2.69
2.89
3.07
3.43
3.95
4.78
5.59
5.38
7.16
J.94
.72
.48
: 110°C
0.316
0.402
i 0.598
0.722
]' 0.950
1.137
1.276
1.413
1.542
' 1.661
1.773
. 1.880
' 1.986
:2.09
12.19
J 2.28
: 2.37
2.47
2.56
2.74
2.91
3.25
3.74
4.49
5.25
5.97
6.72
7.42
8.13
8.84
-------
290 330 370
TEMPERATURE, °F
450
Figure C-2. Effect of temperature on corrosion of mild
steel by chlorine.35
17 (Number of protons within the atomic nucleus.)
C12
70.906
Atomic number:
Molecular symbol:
Molecular weight:
Chemical Properties
Valence: Usually forms univalent compounds but can combine with a
valence of 3,4, 5, or 7.
Chemical Reactions: Nonflammable; like oxygen, however, it is capable of
supporting the combustion of certain substances. Many organic chemicals
react readily with chlorine, sometimes with explosive violence.
The rate of chlorine corrosion of most metals increases rapidly with
temperature, particularly if the metal is finely divided or is in wire, powder, or
sponge form. Dry chlorine reacts with aluminum, arsenic, gold, mercury,
selenium, tellurium, tin, and titanium. Potassium and sodium will burn in
chlorine at most temperatures, and steel will ignite at 483° F (see Figure C-2).
When in finely divided form, antimony, arsenic, bismuth, boron, copper,
iron, phosphorus, and certain of their alloys will ignite spontaneously in
chlorine. Mixtures of chlorine and hydrogen can react with explosive violence,
the lower limit being about 5 percent H2 (see Figure A-4). Chlorine removes
hydrogen from some of its compounds, as in its reaction with hydrogen sulfide
to form hydrochloric acid and sulfur. It reacts with ammonia and ammonium
compounds to form various chloroamines. Under proper conditions nitrogen
trichloride, which is highly explosive, is formed.
The reactions of chlorine with organic compounds are similar to those with
inorganic compounds, with hydrogen chloride and chlorinated derivatives being
76
CHLOR-ALKAL1 EMISSIONS
-------
formed. Some of these reactions, including those with hydrocarbons, alcohols
and ethers, can be explosive, and care should be used in selecting the propel
methods and procedures for these reactions. For the solubility of chlorine in
selected solvents, see Figure C-3.
TEBPERATURE, °C
Figure C-3. Solubility of chlorine in selected solvents at
atmospheric pressure.34
Physical Properties 35
Boiling point
-29.29° F at 1 atmosphere pressure (14.696 psia)
Critical properties
Critical density: 35.77 lb/ft3 or 0.573 g/cc. Mass of unit volume of chlorine
at the critical pressure and temperature.
Critical pressure: 1,118.4 psia (76.1 atm). Pressure at critical temperatures.
Critical temperature: 291.2° F (144° C). Temperature above which chlorine
exists as a gas regardless of increase in pressure.
Critical volume: 0.02796 ft3/lb (1-745 cc/g). Volume of unit mass of
chlorine at the critical pressure and temperature.
Appendix C
77
-------
Density
Dry gas: 0.2003 lb/ft3 (0.003209 g/cc) at standard conditions.*
Saturated gas: 0.7537 lb/ft3 (12.07 g/liter at 32° F (0° C).**
Liquid: 91.67 lb/ft3 (1.468 g/liter at 32° F (0° C) (see Figure C-l).
Liquid: 88.79 lb/ft3 (11.87 Ib/gal) at 60° F (15.6° C). Pressure of liquid
chlorine at 60° F is 85.61 psia.
Latent heat of vaporization
123.7 Btu/lb (68.7 gcal/g) at the boiling point of-29.29°F.
Melting point
-149.76°F (-100.98°C), temperature at which solid chlorine melts or liquid
chlorine solidifies under 1 atmosphere pressure (14.696 psia).
Specific gravity
Gas: 2.482 (air = 1).
Liquid: 1.418 (at 0° C).
Specific heat*
Dry gas at constant pressure: 0.115 Btu/lb-° F at 15 psia between 50° F and
100° F. (C 8.28 + 0.0056T, where C is m cal/degree mol and T is in ° K
for the range 273 to 2,000 K.
Dry gas at constant volume: 0.0848 Btu/lb-° F at 15 psia between 50° F
and 100° F.
Liquid: 0.236 Btu/lb-° F at equilibrium between 0° F and 100° F.
Cp/Cy = 1.355; ratio of gas specific heat at constant pressure to specific heat
at constant volume at 1 atm and 15° C.
Specific volume*
Dry gas: 4.992 ft3/lb at standard conditions.*
Saturated gas: 1.327 ft3/lb at 32° F.**
Liquid: 0.01091 ft3/lb at 32° F.**
Vapor pressure*
At 32°F, vapor pressure is 3.617 atm, or 53.155 psia (see Figure C-4).
*Standard conditions are 32° F (0° C) and 14.696 psia (1 atm).
"Pressure of saturated gas and liquid chlorine at 32° F (0° F) is 53.155 psia(3.617 atm).
78 CHLOR-ALKALI EMISSIONS
-------
-100 -90 -80 -70 -60 -50 -40 -30 -20 -10 0 10 20 30 40 50
TEMPERATURE, °F
70 80 90
Figure C-4. Vapor pressure of liquid chlorine.35
Viscosity
Gas at 20°C, 1.4 x 1CT4 poises.
Volume in air
See Figure C-5.
36
CAUSTIC SODA
Anhydrous caustic soda is a white, translucent solid having a crystalline
structure. It is deliquescent and also absorbs carbon dioxide from the air, with
the formation of sodium carbonate. It dissolves readily in water, with evolution
of heat, to form a colorless solution. Viscosity increases rapidly with
concentration.
Caustic soda, or sodium hydroxide, has the chemical formula, NaOH, a
molecular weight of 40, and a specific gravity of 2.1345'5. It melts at 3.8° C
and has a boiling point of 1,390° C. The latent heat of fusion is 40 cal/g and
the heat of solution is 10.3 kcal/g mol at 22° C (463 Btu/lb). The solubility is
42g/100 ml of water at 0° C and 347 g/100 ml of water at 100° C.
Freezing points of caustic soda solutions are shown in Figure C-6.
Viscosities of solutions at various temperatures are shown in Figure C-7, and
vapor pressures of solutions at various temperatures are shown in Figure C-8.
Specific gravities of caustic solutions are shown in Table C-2.
Commercial caustic soda is most frequently shipped as a 50 percent
solution, or it may be further concentrated to 73 percent. A dilution
nomograph for caustic soda is given in Figure C-9. Solid caustic may be
shipped in drums as such or as flake. Rayon-grade caustic may be made by
Appendix C
79
-------
NOTE: AT STANDARD CONDITIONS (0 °C AND 760 mm Hg),
VOLUME OF CHLORINE = 5.06 It3/lb AND VOLUME
OF AIR =12.38 R3/lb
40 50 60
CHLORINE IN AIR, « by wl
100
Figure C-5. Percent chlorine in air by volume versus
percent by weight and weight of gas mixture at standard
conditions.
further reducing the small content of salt and other impurities present in
standard-grade caustic. High purity 50 percent caustic is produced in mercury
cells directly without evaporation or purification.
CAUSTIC POTASH
Anhydrous caustic potash or potassium hydroxide is a white, translucent,
crystalline solid with properties somewhat similar to those of caustic soda. In
reaction with other chemicals, the products formed frequently differ from the
properties of similar sodium chemicals. Caustic potash is therefore used in
special cases for soaps, glass, textiles, and chemicals where the particular
property of the product cannot be obtained by the use of the lower-priced
caustic soda.
Potassium hydroxide (KOH) has a molecular weight of 56.1 and a density of
2.04445 '5 It has a melting point of 360.4 to 367° C and a boiling point of
1,320 to 1,324° C. The heat of solution is 12.95 kcal/g mol at 21° C. The
solubility is 97 g/100 ml of water at 0° C and 178 g/100 ml at 100° C.
The standard-grade caustic potash contains 90 percent KOH. A product
having low iron and salt is produced having 85 percent KOH. Liquid grades
80
CHLOR-ALKALI EMISSIONS
-------
CAT «SnP°EcC'FIC GRAVITY OF RUSTIC SODA SOLUTIONS
AT 60 F BASED ON DILUTION OF 50 PERCENT
5TANDARD-GRADE CAUSTIC37
by wt.
2
4
6
8
10
12
14
16
18
20
22
24
26
28
30
32
34
36
38
40
42
44
46
48
50
52
%Na2O
1.55
3.10
4.65
6.20
7.75
9.30
10.85
12.40
13.95
15.50
17.05
18.60
20.15
21.70
23.25
24.80
26.35
27.90
29.45
31.00
32.55
34.10
35.65
37.20
38.75
40.30
Sp. gr.,
60° F/60° F
1.023
1.045
1,067
1.090
1.111
1.130
1.156
1.178
1.201
1.223
1.245
1.267
1.289
1.311
1.332
1.356
1.378
1.400
1.420
1.438
1.457
1.476
1.495
1.514
1.532
1.552
"Be
3.3
6.2
9.1
12.0
14.6
17.1
19.6
21.9
24.3
26.4
28.5
30.6
32.5
34.4
36.1
38.1
39.8
41.5
42.9
44.3
45.6 ..
46.7
48.0
49.3
50.3
51.6
°Twaddell
4.6
9.0
13.6
18.0
22.4
26.8
31.2
35.8
40.2
44.6
49.0
53.4
57.8
62.0
66.4
71.2
75.6
79.9
84.0
87.6
91.4
95.1
98.9
103.0
106.3
110.3
NaOH,
g/liter
20.5
41.8
63.9
87.2
111.1
135.6
161.8
188.5
216.2
244.5
274.0
304.0
335.0
367.0
399.5
434.0
468.0
504.0
540.0
576.0
612.0
649.0
688.0
727.0
767.0
807.0
NaOH,
Ib/gal
0.17
0.35
0.53
0.73
0.93
1.13
1.35
1.57
1.80
2.04
2.28
2.53
2.79
3.06
3.34
3.62
3.91
4.20
4.50
4.80
5.11
5.42
5.74
6.07
6.39
6.73
contain 45 to 52 percent KOH, the lower strength product being more
desirable for shipment in cold weather.
SODIUM
Sodium is a waxy, bright, silvery metal readily cut by a knife. In moist air it
rapidly tarnishes, becoming dull grey. When sodium is exposed to the
atmosphere over a long period, an amorphous skin of hygroscopic oxide forms
on the metal. In atmospheric air the metal ignites at 115° C, but in very dry air
ignition does not occur until the metal is near its boiling point. The flame^of
burning sodium has a characteristic yellow color. Pure sodium melts at 97.8° C
and boils at 892° C. The density at 20° C is 0.971; a cubic foot of sodium
weighs about 60.5 pounds. Sodium is soluble in liquid ammonia (26.6% at 22°
C), molten caustic soda (6.5% at 800° C), fused sodium chloride (4.2% at 88°
C), and in mixtures of sodium and calcium chlorides.
81
Appendix C
-------
1 I
SOLID PHASE EQUILIBRIUhl
1 to 2 NaOH 7 K20
2 lo 3 NaOH 5 H20
3 lo 4 NaOH 4H20
4 to 5 NaOH 3!i
5 to 6 HaOH Z H20
S to 7 NaOH 1 H20
7 to 8 NaOH
Figure C-6. Freezing points of caustic soda
solutions.37
The vapor pressures of molten sodium solutions, taken from reference 15,
are shown in Figure C-10.
82
CHLOR-ALKAL1 EMISSIONS
-------
TEMPERATURE,°F
Figure C-7. Viscosity of caustic soda solutions.37
Appendix C
83
-------
200 300
TEMPERATURE.^
Figure C-8. Vapor pressure of caustic soda solutions.37
84
CHLOR-ALKALI EMISSIONS
-------
1.7
1.6
1.5
S 1.4
SNaOH
INITIAL FINAL
1.1
1.0
EXAMPLE:
TO DILUTE 50% CAUSTIC SODA (NaOH) TO 30%
DRAW A STRAIGHT LINE FROM 50% ON INITIAL
SCALE THROUGH 30% ON FINAL SCALE TO
GALLONAGE. NaOH OF 30% CAN BE OBTAINED
BY DILUTING 0.96 gal 50% NaOH WITH 1 gal
WATER.
il ...... l,,,,,.,,,l ......... I, ........ I,,I\,I.M. ,1,1.1.1 ....... 1,,., ..Mil ......... I ......... I
0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0
GALLONS NaOH/GALLON DILUTION H20
Figure C-9. Caustic soda dilution nomograph.
37
Appendix C
85
-------
1,000
A
- ./
- /
500 600 700 800
TEMPERATURE. °C
900
Figure C-1U. Relationship of vapor pressure and
temperature of liquid sodium.15
86
CHLOR-ALKALI EMISSIONS
-------
APPENDIX D. CHLORINE-CAUSTIC,
FUSED-SALT, AND LIME-SODA
ESTABLISHMENTS IN UNITED STATES,
JANUARY 1970
87
-------
Table D-l. CHLORINE PLANTS IN UNITED STATES3
Location
Alabama
Huntsville
Le Moyne
Mclntosh
Mobile
Muscle Shoals
Arkansas
Pine Bluff
California
Dominguez
Pitts burg
Delaware
Delaware City
Georgia
Augusta
Brunswick
Brunswick
Illinois
East St. Louis
Kansas
Wichita
Kentucky
Calvert City
Calvert City
Louisiana
Baton Rouge
Baton Rouge
Geismar
Gramercy
Lake Charles
Plaquemine
Taft
Maine
Ornngton
Rumford
Michigan
Midland
Montague
Wyandotte
Wyandotte
Mississippi
Vicksburg
Producer
Stauffer Chemical Co.
(leased from U.S. Government)
Stauffer Chemical Co.
Olin Corp.
Diamond Shamrock Chemical Co.
Diamond Shamrock Chemical Co.
(U.S. Government)
Stauffer Chemical Co.
The Dow Chemical Co.
Diamond Shamrock Chemical Co.
Olin Corp.
Allied Chemical Corp.
Brunswick Chemical Co.
Monsanto Co.
Vulcan Materials Co.
B.F Goodrich Chemical Corp.
Pennwalt Corp.
Ethyl Corp.
Allied Chemical Corp.
Wyandotte Chemicals Corp.
Kaiser Aluminum and Chemical Corp.
PPG Industries Inc.
The Dow Chemical Co.
Hooker Chemical Corp.
IMCChlor-Alkali Inc.
Ethyl Corp. (Oxford Paper Div.)
The Dow Chemical Co.
Hooker Chemical Corp.
Pennwalt Corp.
Wyandotte Chemicals Corp.
Southwest Potash Corp.
Yeoi
built"
1943
1965
1952
1964
1952
1943
1963
1917
1965
1965
1957
1967
1922
1952
1966
1953
1938
1937
1959
1958
1947
1958
1966
1967
1916
1897
1954
1898
1938
1962
Cells**
HookerS (D)
De Nora 22 x 5 (M)
Olin E8 (M)
DeNora (M)
De Nora 24 x 2M (M)
HookerS (D)
BASF (M)
Dow (D), Dow (M)
DeNora 18 x 4 (M)
Olin E11F (M)
Solvay V-100 (M)
Hooker S4 (D)
De Nora 18 x 6 (M) (1962)
HookerS, S3A.S3B (D)
DeNora24H5 (M)
Olin E11F (1967) (M)
Downs (fused salt),
Hooker S3D (D)
Allen-Moore (modified) (D),
(Hooker S4 (D) (1968)
Diamond D3 (D), Uhde 30 m2
(M) (1964), Hooker S4 (D)
(1969)
Hooker S3B (D)
Columbia N 1, Hooker S3A (D),
DeNora48H5 (M) (1969)
Dow (D),
Solvay V-200 (M) (1963)
Hooker S4 (D)
De Nora24H5 (M)
Sorensen (M)
Dow (D)
Hooker S3A (D)
Diamond D3 (D) (1960)
Hooker S3B (D),
Wyandotte (M)
None
CHLOR-ALKALI EMISSIONS
-------
Nevada
Henderson
New Jersey
Elizabeth
Linden
Newark
New York
Niagara Falls
Niagara Falls
Niagara Falls
Niagara Falls
Niagara Falls
Syracuse
North Carolina
Acme
Canton
Pisgah Forest
Ohio
Ashtabula
Ashtabula
Barberton
Painesville
Stauffer Chemical Co. of Nevada Inc. 1942 Hooker S (D)
Maquite Corp. 1964
GAF Corp. 195g
Vulcan Materials Co. 1961
E.I. du Pont de Nemours and Co., Inc. 1898
Hooker Chemical Corp. 1898
Int'l. Minerals and Chemical Corp. 1916
Olin Corp. 1897
Stauffer Chemical Co. 1898
Allied Chemical Corp. 1927
Allied Chemical Corp. 1963
U.S. Plywood-Champion Papers, Inc. 1916
Olin, Ecusta Operations 1947
Detrex Chemical Industries, Inc. 1963
Reactive Metals, Inc. 1949
PPG Industries Inc. 1936
Diamond Shamrock Chemical Co. 1928
Maquite (M)
Krebs (M) (1963); Mod. BASF-Krebs
(1969)
Hooker S (D), Hooker S4 (1968)
Downs (fused salt)
Hooker S, S3A, Gibbs (modified)
(D), Uhde20 m2 (M)
(1961)
HookerS (D)
Olin E11F (M) (1960)
Hooker S, S3M (D)
Allen-Moore (modified) (D),
Solvay Process SD12 (M) (1946),
Solvay S60 (M) (1953),
Hooker S4 (D) (1968)
Solvay V-200 (M)
HookerS (D)
Sorensen (M)
Olin E11F (M)
Downs (fused salt)
Columbia (D)
Diamond D3 (D) (1959)
Oregon
Portland
Pennwalt Corp.
1947
Gibbs (modified) (D)
Diamond (D) 1957)
Tennessee
Charleston
Memphis
Memphis
Olin Corp. 1962
E.I. du Pont de Nemours and Co., Inc. 1958
Velsicol Chemical Corp. 1943
Olin E11F, E812 (M)
Downs (fused salt)
Hooker S4 (D) (1969)
Texas
Corpus Christ!
Denver City
Freeport
Houston
Deer Park
(Houston)
Houston
Houston
Point Comfort
Port Neches
Snyder
Virginia
Hopewell
Saltville
Washington
Bellingham
Longview
Tacoma
Tacoma
PPG Industries Inc. 1938
Vulcan Materials Co. 1947
The Dow Chemical Co. 1940
U.S. Plywood-Champion Papers, Inc. 1936
Diamond Shamrock Chemical Co. 1938
Ethyl Corp. 1952
Shell Chemical Co. 1966
Aluminum Co. of America 1966
Jefferson Chemical Co., Inc. 1959
American Magnesium Co. 1969
Hercules, Inc. 1939
Olin Corp. 1951
Georgia-Pacific Corp. 1965
Weyerhaeuser Co. 1957
Hooker Chemical Corp. 1929
Pennwalt Corp. 1929
Columbia N1, N3 (D)
HookerS (D)
Dow (D)
Hooker S'(D)
Diamond (D),
De Nora 18SGL (M)
Downs (fused salt)
Hooker S4 (D)
De Nora 24x5 (M)
Hooker S3B (D)
Hooker S3 (D)
Olin E8(M)
De Nora 18x4 (M)
De Nora 14 TGL & 24 H5 (M) (1967)
Hooker S3 (D)
Gibbs (modified) (D)
Appendix C
89
-------
West Virginia
Moundsville Allied Chemical Corp.
New Martmsville PPG Industries, Inc.
So. Charleston
Wisconsin
Green Bay
Port Edwards
FMC Corp.
Fort Howard Paper Co.
Wyandotte Chemicals Corp.
1953 Solvay S60 (M)
1943 Columbia N1, N3, N6 (D),
Uhde 20m2 (D) (1958)
1916 Hooker S3B (D) (1957),
Hooker S4 (D) (1967)
1968 Hooker S4 (D)
1967 De Nora 24H5 (M)
aRefers to year chlorine production started at location.
bD = diaphragm cells; M - mercury cells.
Table D-2. SUMMARY OF CHLORINE-PRODUCING PLANTS3
Type of plant
Chlorine producers3'
Companies
Plants
Pulp mills producing chlorine3
(included in A)
Companies
Plants
Chlorine repackagers
Companies
Plants
Cells
Diaphragm-cell plants
Mercury-cell plants
Diaphragm- and Mercury-cell plants
Fused-salt cell plants
Non-electrolytic plants
Diaphragm- and fused-salt cell plants
Magnesium-cell plants
Number of
plants
35
69
6
7
45
91
27
25
10
4
1
1
1
aOnly those in operation.
Daily capacity of 27,494 tons of gas as of November 1, 1969.
90
CHLOR-ALKALI EMISSIONS
-------
13
•O
n
CL
Figure D-1. United States chlorine and alkali producers, January 1, 1970.
-------
\o
K)
n
o
fd
2
1
o
C/5
CHLORINE AND SODA ASH 32.
33.
1. GEORGIA-PACIFIC-Bellingham, Wash. 34.
2. HOOKER-Tacoma, Wash. 35.
3. PENNWALT-Tacoma, Wash. 36.
4. WEYERHAEUSER-Longview, Wash. 37.
5. PENNWALT-Portland, Oregon 38.
6. DOW-Pittsburg, Calif. 39.
7. STAUFFER-Henderson, Nevada
8. VULCAN-Wichita, Kansas 40.
9. VULCAN-Denver City, Texas
10. PPG-Lake Charles, La. 41.
11. JEFFERSON-PortNeches, Texas 42.
12. DIAMOND-Houston, Texas 43.
13. U.S. PLYWOOD-CHAMPION-Houston, 44.
Texas 45.
14. SHELL-Houston, Texas 4$.
15. ALCOA—Pt. Comfort, Texas 47
16. FT. HOWARD-Green Bay, Wis. 43.
17. WYANDOTTE-Port Edwards, Wis. 49.
18. MONSANTO-East St. Louis, III. 50.
19. GOODRICH-Calvert City, Ky. 51.
20. PENNWALT-CalvertCity, Ky. 52.
21. VELSICOL-Memphis, Tenn. 53.
22. DIAMOND-Muscle Shoals, Ala.
23. OLIN-Mclntosh, Ala. SODA ASH
24. DIAMOND-Mobile, Ala.
25. DOW-Plaquemine, La. 54.
26. WYANDOTTE-Geismar, La.
27. KAISER-ALUMINUM-Gramercy, La. 55.
28. HOOKER-Taft, La. 56.
29. STAUFFER-Lemoyne, Ala. 57.
30. OLIN—Charleston, Tenn. 58.
31. PENNWALT-Wyandotte, Mich. 59.
HOOKER—Montague, Mich.
DOW-Midland, Mich.
DOW-Sarnia, Ont., Canada
ALLIED-Moundsville, Ohio
PPG—New Martinsville, W. Va.
DETREX-Ashtabula, Ohio
FMC CORP.-South Charleston, W. Va.
U. S. PLYWOOD-CHAMPION-Canton,
N.C.
ECUSTA OPERATIONS, OLIN-Pisgah
Forest, N. C.
OLIN-Augusta, Ga.
ALLIED—Brunswick, Ga.
BRUNSWICK CHEM.-Brunswick, Ga.
ALLIED-Acme, N. C.
HERCULES-Hopewell, Va.
DIAMOND-Delaware City, Del.
MAQUITE-Elizabeth, N. J.
GAF-Linden, N. J.
VULCAN-Newark, N. J.
ETHYL-Rumford, Me.
HOOKER-Niagara Falls, N. Y.
OLIN-Niagara Falls, N. Y.
STAUFFER-Niagara Falls, N. Y.
AMERICAN POTASH AND CHEM.-
Trona, Calif.
STAUFFER-West End, Calif.
ALLIED—Green River, Wyo.
STAUFFER-Green River, Wyo.
FMC CORP.—Green River, Wyo.
ALLIED—Amherstburg, Ont., Canada
60. OLIN-Lake Charles, La.
CHLORINE, CAUSTIC SODA, SODA ASH
61. DOW-Freeport, Texas
62. PPG—Corpus Christi, Texas
63. ALLIED—Baton Rouge, La.
64. WYANDOTTE-Wyandotte, Mich.
65. DIAMOND-Painesville, Ohio
66. PPG-Barberton, Ohio
67. OLIIM-Saltville, Va.
68. ALLIED-Syracuse, N. Y.
69. ETHYL-Baton Rouge, La.
CHLORINE
70. SOUTHWEST POTASH-Vicksburg, Miss.
CHLORINE AND CAUSTIC POTASH
71. INT. MIN. AND CHEM.-Niagara Falls,
N. Y.
CHLORINE AND SODIUM
72. DUPONT-Niagara Falls, N. Y.
73. ETHYL-Houston, Texas
74. REACTIVE METALS-Ashtabula, Ohio
75. DUPONT-Memphis, Tenn.
CHLORINE AND MAGNESIUM
76. AMERICAN MAGNESIUM-Snyder,
Texas
-------
APPENDIX E. FIELD TEST OF ABSORPTION
EFFICIENCY OF BLOW-GAS ABSORBER
Plant 30, a diaphragm-cell plant (see Tables 6 and D-l), was operated under
several sets of conditions to permit calculation of absorption efficiencies of the
water absorber at several different simulated plant operating rates. This was
accomplished by keeping the water circulation constant at the maximum
practical rate and varying the amount of blow gas fed into the scrubber, thus
changing the liquid/gas ratio in order to determine its effects on absorption
efficiency. Table E-l was developed from the test data obtained.
The blow-gas absorber in this plant is part of an integrated system having
the dual purpose of cooling cell gas and recovering chlorine from blow gas. The
main factors in the operation are the quantity of water circulated and the
quantity of steam required to complete stripping of the chlorine to the desired
level in the discarded water stream (Figure 10). Since at a constant plant
capacity (e.g., 100 tons per day) the blow-gas rate may be expected to be
constant, and, therefore, to impose a constant-heat load on the system, the
incremental quantities of steam required to heat water to stripping tempera-
tures at various water rates can be easily calculated as follows:
First, reduce the test data to a constant production rate of 100 tons per
day.
Test
1234
Chlorine absorbed, Ib/hr 129.4 164.5 176.1 180.5
Residual chlorine in vent, Ib/hr 51.7 16.1 4.43 1.034
Absorption efficiency, % 72.5 91.0 97.4 99.4
Absorber water rate, 1000 Ib/hr 32.1 33.1 37.8 47.3
Second, from the data above, calculate: (1) the additional water required
for Test 2 as compared with Test 1: 33,100 - 32,100 = 1000 Ib/hr; (2) simi-
larly, for Test 3 with respect to Test 2: 37,800 - 33,100 = 4700 Ib/hr; and
(3) for Test 4 with respect to Test 3: 47,300 - 37,800 = 9500 Ib/hr.
Similarly, calculate the incremental amounts of chlorine absorbed: (1) Test
2 - Test 1 = 164.5 129.4 = 35.1 Ib/hr; (2) Test 3 - Test 2 = 176.1 164.5 =
11.6 Ib/hr; and (3) Test 4 -Test 3 = 180.5 176.1 =4.4 Ib/hr.
The incremental amount of water required to recover an incremental
amount of chlorine can now be calculated: (1) Test 2 - Test 1 = 1000/35.1 =
93
-------
Table E-1. TESTS OF BLOW-GAS ABSORBER EFFICIENCY
Equivalent plant capacity, tons
CI2/day (based on total pounds
1
180.0
of chlorine to absorber) |
Chlorine in blow gas, Ib/hr 326.0
Chlorine absorbed, Ib/hr
Residual chlorine in vent, Ib/hr
233.0
93.0
Absorption efficiency, % 72.5
Water rate to absorber, 1000 Ib/hr
57.8
Water/chlorine ratio, Ib/lb chlorine 248.1
absorbed
2
170.0
307.0
279.6
27.4
91.0
56.3
201.4
3
149.0
269.0
262.4
6.6
97.4
56.3
214.6
4
119.0
216.0
214.77
1.23
99.4
56.3
262.1
28.5 Ib of water/lb of chlorine; (2) Test 3 Test 2 = 4700/11.6 = 405 Ib of
water/lb of chlorine; and (3) Test 4 Test 3 = 9500/4.4 = 2159 Ib of water/lb
of chlorine.
The amount of steam required to heat the incremental quantities of water
from feed temperature (24.5° C) to stripping temperature (97° C) can be easily
calculated as follows:
(97 - 24.5)(9/5)
1000
= 0.1305 Ib steam/lb water circulated.
Although additional steam is also required to vaporize the incremental
pound of chlorine in removing it from the water solution, the latent heat of
chlorine is so small in relation to that of steam (about 1:10) that this can be
neglected in the calculation. Results can be summarized as shown in Table E-2.
These results are also plotted in Figure E-1.
Determination of the point at which it is no longer economical to recover
further chlorine can easily be calculated from these values by assigning values
Table E-2. WATER AND STEAM NEEDED TO INCREASE
ABSORBER EFFICIENCY
To increase efficiency
From,
%
72.5
91.0
97.4
To,
%
91.0
97.4
99.4
Lb additional water
needed/lb chlorine
recovered
28.5
405.0
2159.0
Lb additional steam
needed/lb chlorine
recovered
3.72
52.9
282.0
94
CHLOR-ALKALI EMISSIONS
-------
for the cost of water, steam, and chlorine. When the cost of incremental water
and steam is equivalent to the value of the chlorine recovered, the optimum
operating point has been reached. Obviously, a water absorber can be operated
above the economical optimum to reduce a pollution problem. Consideration
of values similar to those noted in this example will permit the selection of
desirable operating conditions.
It is also possible to scrub vent gas from the main water absorber in a second
unit from which the water is discarded. This requires no additional steam and
chlorine absorbed in the waste water is sufficiently dilute that usually no
problem with liquid waste disposal is encountered. This method is generally
preferable to passing vent gases to a caustic scrubber where the carbon dioxide
in the vent gas will consume a large amount of additional caustic.
) 92 94 96 97 98 99 99.5 99.7 99.8 99.9
ABSORBER EFFICIENCY, %
Figure E-1. Water and steam required to increase blow-gas
absorber efficiency.
Appendix E
95
-------
REFERENCES
1. Sheltmire, W. H. Chlorinated Bleaches and Sanitizing Agents: In:
Chlorine, Its Manufacture, Properties, and Uses, Sconce, J. S. (ed.)- New
York, Reinhold Publishing Corp., 1962. p. 512-542.
2. Taylor, D. L. Production and Use Patterns. In: Chlorine, Its Manufacture,
Properties, and Uses, Sconce, J. S. (ed.). New York, Reinhold Publishing
Corp, 1962, p. 10-20.
3. Private Communication with Hooker Chemical Co.
4. Chlorine Summary Statistics—United States and Canada. The Chlorine
Institute. Pamphlet No. 11. May 17,1967.
5. Nichols, J. H. and J. A. Brink, Jr. Fiber Filters Now Clean Chlorine.
Chem. Eng. 77:221-222, June 8, 1964.
6. MacMullin, R. B. Electrolysis of Brines in Mercury Cells. In: Chlorine, Its
Manufacture, Properties, and Uses, Sconce, J. S. (ed.). New York,
Reinhold Publishing Corp., 1962. p. 127-199.
7. Chemical Industry Committee, Tl-2. Manufacture of Chlorine and Sodium
Hydroxide. J. Air Pollution Control Assoc. 14:88-90, March 1964.
8. Kircher, M. S. Electrolysis of Brines in Diaphragm Cells. In: Chlorine, Its
Manufacture, Properties, and Uses, Sconce, J. S. (ed.). New York,
Reinhold Publishing Corp., 1962. p. 81-126.
9. Kircher, M. S. Electrolysis of Brines in Diaphragm Cells. In: Chlorine, Its
Manufacture, Properties, and Uses, Sconse, J. S. (ed.). New York,
Reinhold Publishing Corp., 1962. p. 81-126.
10. Bryson, H. W. Recovery of Chlorine from Chlorine Plant Vent Cases.
Proceedings of the Eleventh Pacific Northwest Industrial Waste Con-
ference 1963. Engineering Experimental Station, Oregon State University,
Corvallis, Oregon. Circular Number 29:146-149. September 1963.
11. MacMullin, R. B. Electrolysis of Brines in Mercury Cells. In: Chlorine, Its
Manufacture, Properties, and Uses, Sconse, J. S. (ed.). New York,
Reinhold Publishing Corp., 1962. p. 127-199.
12. MacMullin, R. B. Electrolysis of Brines in Mercury Cells. In: Chlorine, Its
Manufacture, Properties, and Uses, Sconce, J. S. (ed.). New York,
Reinhold Publishing Corp., 1962. p. 127-199.
97
-------
13. Nichols, J. H. Ventilation in Mercury Cell Rooms. Monsanto Co., St.
Louis. Presented at the 8th Meeting of the Chlorine Plant Managers.
Decembers, 1963.
14. Mantell, C. L. Electrochemical Engineering, 4th ed. New York, McGraw-
Hill, Inc., 1960. p. 190.
15. Sittig, M. Sodium, Its Manufacture, Properties, and Uses. New York,
Reinhold Publishing Corp., 1956. p. 190-201.
16. McFadyen, W. F. and C. E. Buterbaugh. Start Up Method for Fused Salt
Electrolytic Cells (U. S. 2,913,381). Official Gazette U. S. Patent Office
748:115, November 17, 1959.
17. Hardie, D. W. F. Electrolytic Manufacture of Chemicals from Salt.
London, Oxford University Press, 1959. p. 33.
18. Stuart, H. H. and R. E. Bailey. Performance Study of a Lime Kiln and
Scrubber Installation. Tappi. 45:104A-108A, May 1965.
19. Collins, T. T., Jr. The Venturi-Scrubber on Lime Kiln Stack Gases. Tappi.
42:9-13, January 1959.
20. Kaylor, F B. Air Pollution Abatement of a Chemical Processing Industry.
J. Air Pollution Control Assoc. 15:65-61, February 1965.
21. For Chlorine Recovery, Take Your Choice. Chem. Eng. 64:154, 156. June
1957.
22. Bryson, H. W. Recovery of Chlorine from Chlorine Plant Vent Gases.
Proceedings of the Eleventh Pacific Northwest Industrial Waste Con-
ference. 1963. Engineering Experimental Station, Oregon State Univer-
sity, Corvallis, Oregon. Circular Number 29:146-149. September 1963.
23. Sutter, R. C. Recovery of Chlorine from Air-Chlorine Mixtures. J. Air
Pollution Control Assoc. 7(1):30-31, May 1957.
24. Kenyon, R. L. and G. Patrizio. Chlorine and Caustic in Italy; Amalgam
Cell Production. Ind. Eng. Chem. 45:1162-1172, June 1953.
25. Gasauswurfbegrenzung, Chlor. Verein Deutscher Ingenieure, VDI-Kom-
mission Reinhaltung der Luft. Germany. VDI 2103. January 1961. 6p.
26. Chlorine Recovery System. Diamond Alkali Company, Cleveland, Ohio.
Brochure E2-17. January 1963. p. 8.
27. Hulme, R. E. Method of Purifying Chlorine (U. S. 2,765,873). Official
Gazette U. S. Patent Office 7J7(2):285, October 9, 1956.
28. Redniss, A. HC1 Oxidation Processes. In: Chlorine, Its Manufacture,
Properties, and Uses, Sconce, J. S. (ed.). New York, Reinhold Publishing
Corp., 1962. p. 250-272.
98 CHLOR-ALKALI EMISSIONS
-------
29. Karpiuk, R. S. Recovery of Chlorine (U. S. 2,881,054). Official Gazette
U. S. Patent Office 747(1):188, April 7, 1959.
30. Wynkopp, R. Chlorine Recovery (U. S. 2,800,197). Official Gazette U. S.
Patent Office 72tf(4):759, July 23, 1957.
31. Jacobs, M. B. The Chemical Analysis of Air Pollutants. Vol. 10. New
York, Interscience Publishers, 1960. p. 195-197.
32. Standard Methods for the Examination of Water and Waste Water, 12th
Ed. New York, American Public Health Assoc., Inc., 1965. p. 93-100.
33. Kapoor, R. M. and J. J. Martin. Thermodynamic Properties of Chlorine.
Ann Arbor, Mich., Univ. of Mich. Press, 1957. 39p.
34. Redniss, A. HCL Oxidation Processes. In: Chlorine, Its Manufacture,
Properties, and Uses, Sconce, J. S. (ed.). New York, Reinhold Publishing
Corp., 1962, p. 250-272.
35. Laubusch, E. J. Physical and Chemical Properties of Chlorine. In:
Chlorine, Its Manufacture, Properties, and Uses, Sconce, J. S. (ed.). New
York, Reinhold Publishing Corporation, 1962. p. 2145.
36. Pittsburgh Plate Glass Company. Bulletin Form M, A-500, Rev. 9-52-10M.
1952.
37. Hooker Chemical Co. Hooker Caustic Soda Bulletin Number 115. Niagara
Falls, N. Y.
References
-------
SUBJECT INDEX
Absorbers, 33
Carbon tetrachloride, 35
Other absorption systems, 35
Sulfur monochloride, 35
Water absorbers, 33
Adsorption systems, 35
Analytical techniques, 54-67
D
Definitions, 39
Diaphragm cell
Anodic reaction, 13
Brine treatment, 11
Cathodic reaction, 15
Description, 12
Caustic potash, 75
Caustic soda
Freezing point, 77
Lime-soda process, 28
Physical properties, 74
Plants in U.S., 86,87
Production, 8
Specific gravity, 76
Vapor pressure, 79
Viscosity, 78
Chemical symbols, 38
Chlor-alkali industry
Future trends, 7
Growth, 6
Historical background, 5
Raw materials, 10
Chlorine
Density, 73
Minor methods of manufacture, 23-27
Electrolytic process, 27
Fused-salt cell, 23
Salt process, 26
Physical properties, 68,72
Plants in U.S., 83-87
Solubility, 70
Vapor pressure, 73
Control methods, 3,31
Absorbers, 33
Adsorption systems, 35
Alkaline scrubbing, 32
In-plant use, 32
Types, 31
Electrolytic process, 27
Emissions
Carbon dioxide, 21
Carbon monoxide, 22
Chlorine, 17
Air blowing, 20
Blow gas, 17
Compressor seals, 20
End boxes, 21
Header seals, 20
Storage tanks, 20
Vents, 19
Water removal, 20
Mercury, 22
Sources and quantities, 17
Summary of, 2-4
Fused-salt cell
Emissions, 23
Process description, 23
Start-up, 25
Glossary, 37
Lime-soda process
Emissions, 29
Process description, 28
101
-------
M
Mercury-cathode cell
Denude: reaction, 16
Description, 15
Electrolyzer reaction, 16
S
Salt process, 26
Sodium, 76
Vapor pressure, 81
102 CHLOR-ALKALI EMISSIONS
------- |