FINAL REPORT
WASTES RESULTING FROM CHLORINATED AROMATIC
HYDROCARBON MANUFACTURE: CHLOROBENZENES
Prepared by
Lowenbach and Schlesinger Associates, Inc.
Rosslyn, Virginia 22209
Under Subcontract to
Acurex Corporation
Mountain View, CA. 94042
Contract No. 68-03-2567, TESC Task 4024
ENVIRONMENTAL PROTECTION AGENCY
Office of Solid Waste
Washington DC 20460
December 15, 1979
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TABLE OF CONTENTS
PAGE
SECTION I
INTRODUCTION 1-1
OVERVIEW OF THE MANUFACTURE OF CHLOROBENZENES 1-2
PHYSICOCHEMICAL PROPERTIES 1-2
Process Technology 1-5
Market Outlook 1-8
SECTION II
MANUFACTURE OF CHLOROBENZENES II-l
FEEDSTOCK COMPOSITION 11-2
REACTION MECHANISM 11-4
BY-PRODUCT FORMATION 11-10
Significant Side Reactions 11-12
By-Products from Feedstock Impurities - 11-16
PROCESS CONFIGURATION FOR PRODUCTION OF CHLOROBENZENES . . . 11-18
POLYCHLOROBENZENES 11-24
Oichlorobenzenes 11-25
Trichlorobenzenes 11-25
Tetrachlorobenzenes 11-28
Pentachlorobenzene and Hexachlorobenzene 11-28
SECTION III
TREATMENT OF PROCESS WASTES III-l
Process Wastes 111-3
PROBABLE FATE OF PRINCIPLE SPECIES 111-6
SECTION IV
SUMMARY AND CONCLUSIONS IV-1
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LIST OF TABLES AND FIGURES
TABLES PAGE
I PHYSICAL PROPERTIES OF CHLOROBENZENES 1-3, 1-4
II WATER SOLUBILITIES AND PARTITION COEFFICIENTS
OF SELECTED CHLORINATED BENZENES 1-6
III CONSUMPTION PATTERN OF SELECTED CHLOROBENZENES 1-9
IV ANALYSIS OF PURE GRADE BENZENE II-3
V COMPOSITION OF MONOCHLOROBENZENE 11-13
VI SUMMARY OF POLLUTANTS FROM MANUFACTURE OF
CHLOROBENZENES 11-19
VII PRODUCT DISTRIBUTION OF A CHLOROBENZENE
BATCH REACTION 11-24
VIII ESTIMATED LOSS OF MATERIAL DURING CHLOROBEN-
ZENE MANUFACTURE (BATCH PROCESS) II1-3
IX ESTIMATED EMISSIONS FROM CHLOROBENZENE
MANUFACTURE: Chiorination of Benzene II1-4
FIGURES
1 SEQUENTIAL REACTIONS SHOWING RELATIVE RATES
IN THE LIQUID PHASE CHLORINATION OF BENZENE 11-9
2 CONTINUOUS PRODUCTION OF CHLOROBENZENE 11-21
3 BATCH PRODUCTION OF CHLOROBENZENES 11-23
4 PRODUCTION OF HIGHER"CHLOROBENZENES 11-26
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SECTION I
*
INTRODUCTION
The objective of this task is to provide EPA, Office of Solid Waste, with
background data on chlorinated hydrocarbons in support of Section 250.14,
Hazardous Waste Lists (see Federal Register 43 (243) and 44 (164)) proposed
rules. As such, potential constituents of waste streams from the manufacture of
chlorinated hydrocarbons will be provided together with identification of the
unit operation from which they originate. Docunentation will include a brief
discussion of the reaction mechanism and process conditions, typical feedstocks,
resultant by-products and process wastes, and, where readily available, -the typical
fate or treatment of by-products and wastes.
Information has been gathered and generated in the following manner:
(1) Through a thorough search of the chemical literature, the reaction
mechanism (and thus the reaction intermediates) for the formation of a
given product is identified. From this knowledge of the reaction inter-
mediates, significant by-products formed during manufacture of a given
product may be predicted. Additionally, the effect of feedstock impurities
are considered using the same analysis. (2) From an extensive patent search,
a generic process configuration for the manufacture of a given product has
been formulated. Included in this process description are specific point
sources for various process operations. In general, pollutant discharges
are considered from a multi-media viewpoint and are not restricted solely
to solid waste discharges. (3) Current solid waste and wastewater'treat-
ment and disposal practices, where available, will be identified
1-1
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OVERVIEW OF THE MANUFACTURE OF CHL0R0BEN2ENES
Although chlorobenzenes had been synthesized about the middle of the
Nineteenth Century, direct chlorination of benzene was not reported until 1905.
Commercial production began in England in 1909 and by 1915 two U.S. companies,
the Dow Chemical Company and the Hooker Electrochemical Company, had begun
production.
Direct chlorination of benzene is always a multiple product process;
production of one isomer (for example, monochlorobenzene) may be favored, but
never to the total exclusion of all other isomers. There are twelve chlorinated
benzene isomers; in commercial practice, however, only nine are accessible
by direct chlorination.
Multiple product mixtures are separated by distillation and crystallization.
Monochlorobenzene has been and remains the dominant commercial product and
production rates of the other chlorobenzenes are controlled to meet market
demands. As a class, chlorobenzenes are used largely as solvents and as inter-
mediates for dyes and agricultural chemicals.
PHYSICOCHEMICAL PROPERTIES
The physicochemical properties of chlorobenzenes are shown in Table I.
Monochlorobenzene is a colorless, mobile, volatile liquid possessing a pleasant
odor. Three polychlorinated benzenes (1,2-dichlorobenzene; 1,3-dichlorobenzene;
and 1,2,4-trichlorobenzene) are also liquids, the remaining chlorobenzenes
are white crystaline solids. While the isomeric dichlorobenzenes have nearly
the same boiling points, the para isomer has a melting point some 70 degrees
higher than the ortho or meta isomer. The higher melting para isomer is ialso
generally less soluble than the ortho isomer in a given solvent; thus purification
1-2
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TABLE I
PHYSICAL PROPERTIES OF CHLOROBENZENES
mol wt
mp
bp, 760 mm Hg
Antoine constants1
A
B
C
vapor pressure,
inm Hg 20°C
liq. density, kg/1
viscosity, mP
a-s(=cP)
heat capacity .
for liquid, J/g
heat of fusion,
J/gb
heat of vapor-
ization, J/gb
refractive index
of liquid, nQ^
dielectric con-
stant of liquid
Chloro-
benzene
1.2,-DI-
chloro-
benzene
1,3-Di-
chloro-
benzene
1 ,4-Di-
chloro-
benzene
1.2,3-
Trichloro-
benzene
1,2,4-
Trichloro-
benzene
112.56
-45.34
131.7
147.005
-16.97
180.4
147.005
-24.76
173.0
147.005
53.04
174.1
181.45
53.5
218.5
181.45
17.15
213.8
7.046324
1482.156
224.115
9.44
1.10118
0.756
1.339
90.33
331.1
1.5219
5.621
7.143024
1703.916
219.352
1.06
1.3022
1.3018
1.159
86.11
311.0
1.5492
9.93
7.072644
1629.811
215.821
1.45
1.2828
1.0254
85.98
296.8
1.54337
5.04
7.002424
1578.149
208.84
1.28
1.2475
1.188
123.8
297.4
1.52849
(55°C)
2.41
7.136684
1790.267
206.283
0.17
1.44829
1.008
85.78
280.0
1.56933
2.24
The Antoine equation is: log]QP-A-B/(C+t) where P is the vapor pressure of the compound in mm of mercury and
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TABLE I
(Concluded)
PHYSICAL PROPERTIES OF CHLOROBENZENES
1,3,5-Tri
chloro-
benzene
1,2,3,4-
Tetra-
chloro-
benzene
1,2,3,5-
Tetra-
chloro-
benzene
1,2,4,5-
Tetra-
chloro-
benzene
Penta-
chloro-
benzene
Hexa-
chloro-
benzene
mol wt 181.45
215.90
215.9
215.9
250.35
284.80
mp 63.5
46.0
51.
139.5
85.
228.7
bp, 760 mm Hg 208.5
254.9
246.
248.0
276
319.3
Antoine constants*
A
B
C
7.159274
1930.023
196.213
7.284164
2003.495
207.038
6.66747
1654.17
117.536
vapor pressure,
mm Hg at 20 C
0.017
0.029
4.37 x 10"6
liquid density, kg/1
1.70
1*833(s)
1.596
viscosity, mP
a-s(=cP)
3.37
heat capacity
for liquid, J/gb
1,259
1.142
heat of fusion,
J/9
64.52
112.2
89.62
heat of vapor-
ization, J/g
268.9
221.8
190.8
*
The Antoine equation is: logioP=A-B/(C+t) where P is the vapor pressure of the compound in
where t is the temperature in degrees centigrade.
mm of mercury and
Source: Kao and Poffenberger in Kirk-Othmer, 1978.
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of the para isomer is feasible by recrystallization. However, ortho-
dichlorobenzene, contaminated with the para isomer, is difficult to purify
by recrystallization (Morrison and Boyd, 1967).
Chlorobenzenes are not appreciably soluble in water and- have notably
high partition coefficients (see Table II) indicating a high lipid solubility
and potential for bioaccumulation. Chlorobenzenes are appreciably volatile
and under suitable conditions may vaporize and disperse in the atmosphere.
Further, characterized by their low reactivity in the environment, chlorobenzenes
are generally resistant to biodegradation (Ware and West, 1977).
Process Technology
Chlorobenzene, dichlorobenzenes, and higher chlorinated benzenes are
produced in batch and continuous processes by direct chlorination of benzene
in the presence of a Friedel-Craft catalyst, such as ferric chloride.
Because higher chlorinated benzenes always result from the di-rect chlorination of
benzene, chlorobenzene production is a multiple product operation. Product ratios
are influenced by temperature, mole ratios of the feedstocks, residence time,
and the catalyst. Additionally, the crude reaction product of a continuous
process may be recycled to the process to achieve the desired final product
mixture. Depending on the final product mixture, chlorobenzenes are purified
by fractional distillation and/or crystallization. Hydrogen chloride, a
CI
CI
(1.1)
1-5
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TABLE II
WATER SOLUBILITIES AND PARTITION COEFFICIENTS OF SELECTED CHLORINATED BENZENES
Compound
Water
Solubility
ppm
Log
Partition
Coefficient
Partition
Coefficient
References
Monochlorobenzene
100
2.18
,150
Lu and Metcalf, 1975
o-Dichlorobenzene
0 to 1450/1
3.38
2,399
Brown et al., 1975
p-Dichlorobenzene^
800
3.39
2,455
Brown et al., 1975
Hexachlorobenzene
0.006
4.13
13,560
Lu and Metcalf, 1975
^Neely et al. have reported a somewhat different value of log P = 3.38
Source: Ware and West, 1977.
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reaction by-product, is either recovered as an anhydrous product or scrubbed
and recovered as hydrochloric acid. Continuous chlorination processes, in
contrast to batch processes, minimize the amount of higher chlorinated
products, thereby maximizing chlorobenzene yields (Kao and Poffenberger, 1979;
Hatch and Matar, 1978; and Lowenheim and Moran, 1975).
The Raschig-Hooker process for production of chlorobenzenes involves
vapor phase chlorination of benzenes using air and HC1 .for in situ generation
of chlorine:
2HC1 + CL + 2CcHc 2CcHcCl + 2Ho0 (1-2)
c 0 0 0 3 c
However, because of high energy costs, this process is no longer used commercially
(Kao and Poffenberger, 1979; Hatch and Matar, 1978).
In 1978, monochlorobenzene production was approximately 134,000 metric tons.
Total production of o-dichlorobenzene and p-dichlorobenzene for 1978 were
estimated as 19,000 metric tons each (.USITC, 1979). Production of 1,2,4-
trichlorobenzene was reported as approximately 13,000 metric tons in 1973
(USITC, 1973) and estimated to be. in the same range in 1977 (EPA, 1979).. Statis-
tics for production of the other chlorobenzenes are unavailable, as these by-
products are produced in limited quantities. Major producers of chlorobenzenes
in the United States include: Allied Chemical Corporation (Syracuse, New
York); Dow Chemical Company (Midland, Michigan); Monsanto Company (Sauget,
Illinois); Montrose Chemical Corporation of California (Henderson, Nevada);
PPG Industries, Inc. (Natrium, West Virginia); Specialty Organics, Inc.
(Irwindale, California); and Standard Chlorine Chemical Company, Inc. (Delaware
City, Delaware); (SRI International, 1979).
1-7
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Market Outlook
Chlorobenzenes are used primarily by the organic chemical industry as
solvents, or as intermediates for pesticide and dye manufacture, Use patterns
for monochlorobenzene, ortho- and para-dichlorobenzenes are presented in
Table III. The textile industry uses 1,2,4-trichlorobenzene as a dye carrier
and 1,2,4,5-tetrachlorobenzene is used as raw material in the production of
agricultural products and disinfectants. Other applications of the ch1o.ro-
benzene isomers are not of industrial significance (Kao and Poffenberger, 1979)..
Historically, chlorobenzene production has been tied to its use in the
manufacture of phenol, aniline and DDT, Restrictions on DDT production and
large scale use of^cumene and nitrobenzene in the manufacture of phenol and
aniline manufacture, respectively, have led to sharp declines in chlorobenzene
demand from an estimated 275,000 metric tons in 1960 to 133,000 metric tons
in 1977. Current demand for chlorobenzene is estimated as 50 to 50 percent of
reported production capacity. Furthermore, production of higher chlorinated
benzenes must be carefully controlled to meet demand, or unused by-products
must be disposed of by the manufacturer. However, with the decreasing market
for monochlorobenzene, producers have been moving in the direction of maximizing
dichlorobenzene and trichlorobenzene capacity (Kao and Poffenberger, 1979).
1-8
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Table III
CONSUMPTION PATTERN OF SELECTED CHLOROBENZENES
Compound Market Consumption
(Percent)
Monochlorobenzene Production of o- and p-nltrochlorobenzenes 50
Solvent 20
Miscellaneous 20
Phenol 10
o-Dichlorobenzene Organic synthesis, mainly for pesticides 53
Toluene dlisocyanate process solvent 20
Solvent, Including paint removers and 15
engine cleaners
Dye manufacture 8
Miscellaneous 4
p-Dichlorobenzene Space odorant 50
Moth control 40
Miscellaneous 10
Source: Lowenheim and Moran, 1975
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SECTION II
MANUFACTURE OF CHLOROBENZENES
Chlorobenzenes are produced by the direct chlorination of benzene in the
presence of a catalyst*: r, ri r
o- -«*-6
The most common catalyst is ferric chloride, either as such or generated in
situ by conducting the chlonnation in the present of iron. With the exception
of hexachlorobenzene, each chlorobenzene can be further chlorinated-, thus, the
reaction product is necessarily a mixture of isomers which must be purified by
distillation and crystallization.
The above representation does not, in any manner, however, account for
reaction by-products which occur during manufacture of chlorinated benzenes.
Such by-products, while produced in relatively small quantities as compared to
the product, are an important facet of the "environmental acceptability" of
a process. Properly managed, such by-products present no special risk; improperly
controlled, such by-products might have significant health effects upon a given
population. Only from careful consideration of (1) reaction conditions, (2) feed-
stock composition, (3) the reaction mechanism, and (4) the most probable manu-
facturing configuration, can formation of such by-products be logically explained
and the environmental impact adequately assessed.
Though in general any Friedel Crafts catalyst can be used for the manufac-
ture of chlorinated benienes, only iron(III) chloride appears to be used
*1,3 Oichlorobenzene, 1,3,5 trichlorobenzene, and 1,2,3,5 tetrachloro-
benzene are not produced by this method.
II-l
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commercially, other suggested catalysts include derivatives of first group
transition metals, of second group transition metals (in particular zinc
chloride), and of third group transition metals, such as boron or aluminum.
Catalytic activity is suggested to be simply a function of their Lewis
acidity, i.e., catalysis of molecular halogenation by solvation through
overlap of a metal orbital with an electron pair of the halogen atom.
Stronger Lewis acids, such as aluminum chlorides, however, favor poly-
chlorination over monochlorination. Monochlorobenzene, however, is produced
in far greater quantity than other chlorinated benzenes (monochlorobenzene
represents about 33% of all chlorobenzene production) and the remaining chloro-
benzenes (mainly o- and p-dichlorobenzene) are commercially produced as by-
products during monochlorobenzene manufacture. Thus, the following discussion
is applicable to chlorobenzenes in general, but directed primarily to the
production of monochlorobenzene in the liquid phase using a ferric chloride
catalyst.
FEEDSTOCK. COMPOSITION
Accurate prediction of the formation of reaction by-products from chloro-
benzene manufacture necessarily requires identification of significant (in terms
of chemical reactivity, potential toxicity, and quantity present) impurities in
all starting materials (benzene and chlorine). Unfortunately, a truly re-
presentative analysis of benzene is difficult to obtain because of varying
sources* (thus leading to potentially different impurities). A typical benzene
*Benzene is currently derived from four principal sources: coke ovens,
reformate, crackers, and toluene hydrodealkylation. Based on nameplate capacity
only, their relative market shares in 1976 were approximately 8, 47, 14, and 31%,
respectively. In the near future, however, this pattern is expected to alter
considerably, the largest orowth occurring in production of benzene from crackers.
Thus, SchoeffeT-, and Dmuchovsky (1977) predict the following market* in 1981 (again
based on nameplate capacity): coke ovens - 5%, reformate - 40%, crackers - 24%,
and toluene hydrodealkylation - 31%.
11-2
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feedstock, however, is likely to contain toluene and ethyl benzene with smaller
amounts of xylenes, cycloalkanes, cycloalkenes, and straight chain alkenes
as shown in Table IV.
TABLE IV
ANALYSIS OF PURE GRADE BENZENE
COMPONENT PERCENT BY WEIGHT
Benzene 99.8
Toluene , 0.1
Ethyl benzene 0.1
1-Pentenes
2-Methyl-l-butene
2-Methyl-2-butene
Cyclopentane reported impurities
Cyclopentene but not measured
Cyclohexane
Cyclohexene
Vaken to include isomeric xylenes
Source: Mellan, 1977
Though concentrations are not specified for the majority of impurities shown,
their presence should not be precluded; indeed these and similar compounds have
been identified in a less pure benzene* CGlick et al., 1960). For the purpose
of this study (and consistent with the accuracy of the above data), it is
assumed that the sum of these impurities is less than one tenth of 1 percent.
Similarly, impurities in feedstock chlorine are difficult to specify.
Chlorine is produced exclusively by electrolysis of brine solutions and is avail-
*Glick and co-workers have identified 20 specific compounds in conventional!,
acidvwashed, lo coke oven benzene of 99.30 mole percent purity.
11-3
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able in several grades ranging from technical to ultrapure, Typical impurities
found in chlorine include bromine (100-200 ppm), oxygen, nitrogen, hexachloro-
benzene, and hexachlorobutadiene (Hanna and Strom, 1953; Mumma and Lawless,
1975). With regard to the latter contaminants, hexachlorobenzene and hexa-
chlorobutadiene are known (and significant) byrproducts of chlorine manufacture
by electrolysis of sodium chloride in cells with carbon electrodes. Presumably,
additional chlorinated hydrocarbons may result from attack of either atomic
or molecular chlorine on the graphite electrode or hydrocarbon oil used to coat
the electrode:
C + 4C1 »¦ C Cl4 (2.2)
Such impurities, which might include carbon tetrachloride, perch]oroethylene,
etc., are referred to as heavy ends and are removed from chlorine by distillation.
The efficiency of this purification step is unknown, however, and contaminant
concentrations cannot be estimated without further information.
REACTION MECHANISM
An understanding of the reaction mechanism, specifically the identification
of those reactive intermediates which describe the reaction pathway, results in
a complete, although qualitative, description of by-products.* Only a limited
number of by-products has been explicitly associated with or identified from
manufacture of chlorobenzsnes in the chemical literature, though a large number
of species has been suggested to arise from such processes (for example, see
Dryden et al., 1979, pp. 43-65). Known by-products of monochlorobenzene
manufacture include hydrochloric acid, 2,4-dichlorobenzene, 1,2-dichlorobenzene,
trichlorobenzenes, tetrachlorobenzenes, and highly chlorinated, heavy organic
*By-products,within the context of this report, are defined as all chemical
specves other than the manufactured product which result from manufacture of that
product. Thus, this definition includes both by-products recovered for reuse/
resale as well as species found in process wastes.
11-4
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polymers. A detailed examination of the reaction mechanism will provide an
indication of which minor side reactions may generate other hazardous or toxic
compounds.
Chlorination of organic compounds has been much studied, due to both
the theoretical and practical value of halogenation reactions and their products.
Industrially, it was among the first unit processes to be operated on a large
scale. Of the several chlorination processes known, heterogeneous catalytic
chlorination is most important industrially; typically, the catalyst is a Lewis
acid, such as aluminum chloride or ferric chloride. Indeed, there is a strong
analogy between these reactions and the reaction of a hydrocarbon with an
alky! oracyl halides in the presence of a Lewis acid; accordingly, the term
"Friedel-Crafts chlorination" is often used to describe chlorination over
metal catalysts, A useful representation of liquid phase aromatic chlorination
is shown in equation 1;
ArH + X-Y + M ArH-X--Y* -M ArX + HY + M (1)
where ArH is an aromatic hydrocarbon, X-Y a halogenating agent where at least
X is a halogen, and M is a suitable catalyst (Olah, 1964). Although reactions
vary in terms of homogeneity and heterogeneity and in degree of ionization of
chlorine prior to attack on the hydrocarbon, there are a number of common points.
Carbon-hydrogen bond breaking has not made appreciable progress in the rate deter-
mining transition state. The reaction rate is dependent upon chlorine, catalyst,
(in the case of benzene, at least) aromatic hydrocarbon concentration. The
role of the catalyst is to aid polarization and ionization of the chlorine
molecule; thus, chlorination processes do not depend on action between the
catalyst and substrate, but rather betv/een substrate and chlorine and/or chlorine
11-5
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and catalyst. The catalytic range encompasses, at one extreme, compounds
which produce a catimic species which then attacks the hydrocarbon and at the
other extreme, catalysts which have only a slight effect on the ionization of
the addition compound.
There is disagreement as to the exact mechanism of aromatic halogenation.*
Generally, it was assumed that the rate determining transition state is the
formation of a sigma or sigma-type of bond with the nuclear carbon atom on
which displacement occurs by attack of the electrophilic part of the chlorine
molecule (I).
The octet of the bonded halogen is expanded and stabilization is achieved con-
jugatively by positive charge distribution on the ring. The stabilities of the
aromatic hydrocarbon-halogen Brg > I2 (McCaulay, 1951). This
effectively rules out bond formation to be rate controlling. In contrast, the
subsequent step, breaking of the halogen-halogen bond by an ionization of a
halogen atom, is in accord with observed halogen reactivity. Ionization may
proceed via an ion pair. Keefer and Andrews (1950; 1951) suggest that with
chlorine, an ion pair [ArHCl *][ CI" ] is formed immediately to avoid the placing
of ten electrons on the central halogen atom. Whatever the exact nature of the
ionization process, bond breaking results in a positively charged species:
*For the purposes of. this document only the salient features of the
mechanism will be discussed.
ArH - X - X
[ArHX]+ + X' (2.3)
I
II-6
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Loss of hydrogen from I is fast and kinetically not significant (i.e., absence
of a hydrogen isotope effect). Thus, Braendlin and McBee 0964} suggest that
cation I is a discrete
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unselective free radical chlorination. Under vapor phase conditions (i.e..,
the Rashig process), free radical chlorination predominates.
At higher temperatures in the presence of Lewis acid catalysis, the
product distribution of polychlorobenzenes is controlled to some extent by
isomerization. Intramolecular chlorine migration, which is analogous to
alkyl-benzene isomerization, does not occur at normal reaction temperatures.
o-Oich.lorobenzene in the presence of aluminum chloride at temperatures
around 150°C yields all three isomers, but mainly m-dichlorobenzene.
Other reaction variables include chlorine and catalyst concentration.
In general, monochlorination is favored at a high chlorine and catalyst
concentration coupled with a short reaction time. Low catalyst concentrations,
together with low reaction temperatures, favor formation of p-dichlorobenzene.
Batch chlorination, in contrast to continuous chlorination processes, is
more selective for para chlorination.
The most common catalyst, as noted previously, is ferric chloride. There
has been some dispute as to the nature of this catalyst. In continuous processes,
this catalyst is formed in situ in the reaction column from chlorine and iron
rings. Generally, it is known that no water should be present in this reaction
(Braendlin and McBee, 1965); therefore, in industrial processes, benzene and
chlorine are dried. On the other hand, Olah (1964) notes that the presence of
small quantities of h^O increases the reaction rate in non-aqueous solvents.
The effect of water has been investigated- by Berg and Westerink (1976) who
provide convincing evidence that the monocomplex FeCl-j-f^O is the active cata-
lyst in the chlorination of benzene. Anhydrous ferric chloride is practically
11-8
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CI CI CI
FIGURE 1
SEQUENTIAL REACTIONS SHOWING RELATIVE RATES
IN THE LIQUID PHASE CHLORINATION OF BENZENE
Source:Kao and Poffqnberger, 1979.
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insoluble in dry benzene; only the monohydrate has appreciable solubility.
The presence of hydrogen chloride also increases the solubility of ferric
chloride. In the presence of water, the attendant increase of FeCl3 solubility
with HC1 is also larger.
A generalized rate expression for chlorination of benzene is:
r = k [C12]a [FeCl3]" [C6H6]c
Generally, the reaction is recognized being first order in all reactants
(i.e., a=b=c=l}, The reaction does not, of course, stop at monochlorobenzene;
polychlorinated benzenes are also produced. The possible reactions are shown
in Figure 1 with, available rate constants indicated. The rate constant for
the first step, chlorination of benzene to monochlorobenzene, has arbitrarily
been set at unity, and other rate constants are relative. The kinetics of
sequential reactions are, in general, quite complex; Bourion (1920) has
considered the ratio of the reaction rate constants of the first and second
steps (through dichlorobenzene). McMullin (1948) has extended this analysis
through the third step.
In theory, the availability of rate constants such as those shown in Figure
1 allows for the calculation of product distribution. Such quantitative
modeling, while useful for maximizing chlorobenzene or dichlorobenzene production,
are probably of limited utility for minor products. More useful pefhaps, are
simple qualitative estimates of the relative ratios of by-products.
BY-PRODUCT FORMATION
Two possible pathways leading to by-product.formation (andhence to
11-10
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process emissions) have been identified*; by-products from alternate
reactions routes; and reaction, by either the main or alternate reaction
route, of feedstock impurities. With regard to the latter, it is important
to realize that, even though a feedstock impurity may be inert under a given set
of reaction conditions, the direct discharge of such an impurity to the
environment may still represent a significant effluent. Additionally, the
identity and quantity of such impurities are difficult to ascertain in many
cases because" feedstock sources may vary from day to day regardless of the
supplier.
Clearly,.prediction of pollutant formation via either pathway is nec-
essarily of a qualitative rather than quantitative nature; thougjr-reactive
intermediates may be identified without extensive kinetic measurements, their
rate of formation Cand thus quantities produced) are impossible to predict
without kinetic measurements. Other quantitative approaches, for example
detailed calculation of an equilibrium composition by minimization of the free
energy of a system, require complete specification of all species to be consi-
dered. Because such methods necessarily assume equilibrium, the concentrations
generated by such methods represent only trends' or, perhaps at best, concen-
tration ratios. Thus, qualitative predictions are extremely useful (if not
essential) for initial assessment of environmental hazards associated with
a given manufacturing process, development of a rational sampling and analysis
program, and identification or design of suitable effluent control technologies,
all in a cost effective manner,
*There is, of course, a third possibility: direct discharge of a reaction
mixture to the environment due to a major process upset. Such events, while
worthy of serious consideration, are however, beyond the scope of the present
document,
11-11
-------
The following discussion is broken into general sections; the first will
consider by-products which form as a result of alternate reaction pathways
while the second will consider the effect of feedstock impurities. Moreover,
as there is obvious overlap between the two sections, the following differen-
tiations are made: (1) no formal distinction is made between by-products arising
from monochlorobenzene production and the remaining chlorobenzenes; that is to
say, that while relevant reactive intermediates are considered sequentially,
there is but one overall process; (2) by-products which result from alternate
reaction pathways are considered from the viewpoint of reactive intermediates
identified as defined in the previous subsection, Reaction Mechanisms; (3) re-
gardless of the source of compounds (i.e., whether a feedstock impurity or reaction
product), once introduced, the entire reaction course of that compound is con-
sidered in that subsection; (4) only those impurities identified and defined
in the previous subsection, Feedstock Composition, will be considered initially.
Significant Side Reactions
Examination of intermediate species together with consideration of the
subsequent reactions of these initial products provides a logical basis for
prediction of additional by-products. However, this discussion is based on
probable rather than demonstrated reaction pathways, and, as such, the existence
of predicted pollutant species must be verified experimentally. Side reactions
during aromatic chlorination are not well documented in the open chemical lit-
erature. Most analytical efforts have been directed to analysis of the isomer
distribution of the chlorination reaction product. By-product information, where
available, is derived largely from process information contained in patents.
The composition of a crude chlorobenzene is shown in Table V.
11-12
-------
The following discussion, is broken into "general sections; the first will
consider by-products which form as a result of alternate reaction pathways
while the second will consider the effect of feedstock impurities. Moreover,
as there is obvious overlap between the two sections, the following differen-
tiations are made: (1) no formal distinction is made between by-products arising
from monochlorobenzene production and the remaining chlorobenzenes; that is to
say, that while relevant reactive intermediates are considered sequentially,
there is but one overall process; (2) by-products which result from alternate
t
reaction pathways are considered from the viewpoint of reactive intermediates
identified as defined in the previous subsection, Reaction Mechanisms; (3) re-
gardless of the source of compounds (i.e., whether a feedstock impurity or reaction
product), once introduced, the entire reaction course of that compound is con-
sidered in that subsection; (4) only those impurities identified and defined
in the previous subsection, Feedstock Composition, will be considered initially.
Significant Side Reactions
Examination of intermediate species together with consideration of the
subsequent reactions of these initial products provides a logical basis for
prediction of additional by-products. However, this discussion is based on
probable rather than demonstrated reaction pathways, and, as such, the existence
of predicted pollutant species must be verified experimentally. Side reactions
during aromatic chlorination are not well documented in the open chemical lit-
erature. Most analytical efforts have been directed to analysis of the isomer
distribution of the chlorination reaction product. By-product information, where
available, is derived largely from process information contained in patents.
The composition of a crude chlorobenzene is shown in Table V.
11-12
-------
TABLE V
COMPOSITION OF MONOCHLOROBENZENE
Component
% by weight
Trichloroethylene
Perchloroethylene
Benzene
Monochlorobenzene
Hexachlorobenzene
Pentachloroethane
Dichlorobenzenes
0.21
0.50
0.027
96.73
1.31
1.2
0.019
Sourcfc: Robata and Whelan, 1978
The most obvious side reactions are those of polychlorination:
CI CI
+ Cl2 FeC13
n (2.4)
n=l-5
The extent of this reaction under monochlorination conditions is unknown, but
is likely to be small in that the chloro group deactivates the aromatic ring.
Where dichloro, trichloro, and tetrachlorobenzenes are desired products,
pentachloro and hexachlorobenzene are likely to be major by-products.
Based on the analogy of nitrophenol formation during nitration of benzene
(Hanson, 1976) there exists the remote possibility of chlorophenol formation
directly (.as opposed to subsequent hydrolysis of polychlorobenzenes) during
chlorination of benzene. Attack of chlorine results in a positively charged
intermediate:
H CI H OH OH
+C1.
FeCl.
H^0
H OH
hXci
(2.5)
11-13
-------
In the presence of water, phenol could be formed. A phenol so formed would be
rapjidly chlorinated to yield a mono, di, or trichlorophenol. Alternatively,
attack on benzene would yield a chlorinated biphenyl.
OH
Cl,
+C1,
FeCl.
* I I!
OH
OH
CI,
0
CI
CI,
clArci
V
(2.6)
„ /"VTV"
(2.7)
Chlorophenols can also result from hydrolysis of substituted chloro-
benzenfes. Hydrolysis of chlorobenzene occurs only under extreme conditions
(200-300 atm, 300°C) but
Q01
OH
o
(2.8)
200-300 atm.
300 °C
was a commercial method of phenol manufacture. Other chlorobenzenes hydrolyze
under milder conditions. 1,2,4-Trichlorophenol, for example, yields 2,5-di-
chlorophenol at temperatures as low as 200°C (Dryden et al., 1979).
rt CI OH
°H
CI OH
200 °C
- kJ •
cl
(2.9)
Tetrachlorobenzenes are presumed to undergo similar reactions:
Cl
OH
aV
Cl
OH
ci V
(2.10)
11-14
-------
The resulting chlorophenols are known precursors of dioxins (Cadogan et al., 1974):
0
(2.11)
CI
Ajcl C1 iTy v^r°I (2-12)
Trichlorophenols are known precursors of 2,3,7,8-tetrachlorodibenzodioxins:
0" 0" 0"
^\jC1
CI
CI
(2.13)
Perhaps the most significant side reaction occurring during chlorination of
benzene is that of chlorinolysis. Excess chlorine in high temperature chlorinatior
can cleave carbon-carbon bonds to give chlorinated derivatives of shorter chain
length. Chlorinalysis is, in fact, a well-known commercial process for production
of carbon tetrachloride and tetrachloroethylene, using up to a feedstock,
temperatures in the range of 600-900°C, in the absence of a catalyst.
Benzene; is known to undergo chlorinalysis; at sufficiently high temperatures
benzene may be oxidized to carbon and hydrogen chloride.
+ 3C12 6C + 6HC1
(2.14)
This reaction is extreme and would presumably occur only during a major process
upset. Yet chlorinalysis does apparently occur during monochlorobenzene productic
based on the presence of perch!oroethylene (Robata and Whelan, 1978).
(f^l
- c2ci4
(2.15
11-15
-------
Presumably other degradation products such as trichloroethylene, perchloro-
ethane, chloromethanes, chlorobutene and butanes are possible as well.
By-Products from Feedstock Impurities
From consideration of feedstocks, it is apparent that the bulk of con-
taminants are found in benzene. The extent of chlorocarbon contamination in
feedstock chlorine is unknown; however, based on the differences in boiling
points (CI2 bp 1S -34°'C) impurities (if indeed present) are likely to be the
low molecular weight chlorocarbons such as chloroform. Hexachlorobenzene is a
known by-product of chlorine product, but the extent to which it may be found in
chlorine is unknown.
Contaminants present in henzene used for production of chlorobenzene have
been previously identified, in approximate order of significance, as toluene,
ethyl benzene (and possibly isomeric xylenes), various acyclic pentenes, cyclo-.
pentane, cyclohexane, and cyclohexene; though aliphatic species may be. present
in smaller quantities than aromatic impurities, their presence is nonetheless
important.
The most obvious side reaction of impurities is chlorination. Alkyl groups
are weakly activating and ortho, para directors.
CH3 CH3 CH
C12.
Catalyst ^yCl
(2.16)
CI
Chlorination of aliphatic impurities occurs by a radical mechanism. Radicals can
be formed either thermally, photolytically, or from initiators.
CI2 2C1' k = 4.8 x 10~16 , 600°K ^*17^
11-16
-------
cr
+ ci.
(2.18)
+ cr
Chlorinated derivatives of this type may be important in that dehydrochlorination
may occur during distillation of chlorobenzene products resulting in severe
corrosion in the distillation train (Hanna and Strom, 1953).
cih2c - ch2ci
300-515 C
HC=CHC1 + HC1
(2.19)
Toluene may react via a free radical mechanism to yield i»,ar, a - trichloro-
toluene. Under alkaline conditions, these
CC1
CI,
OH
(2.20)
species hydrolyze to benzoic acid.
Addition reactions may also be carried out catalytically in the l'tquid
phase. The mechanism of such reactions is similar to that of chlorination of
benzene.
+ CI, catalyst,
(2.21)
Addition of hydrogen chloride (produced on an equimolar basis with chloro-
benzene) to olefinic impurities may also occur during chlorobenzene manufacture.
In the presence of a catalyst such as ferric chloride, the mechanism of such
reactions are electrophilic and similar to that of the chlorination of benzene.
+ HC1
catalyst
50-100°C
¦>
(2.22)
11-17
-------
Bromine is a significant impurity found in feedstock chlorine. Like
chlorine, bromine reacts with benzene to form bromobenzene. Bromine is a less
reactive Br
OFeCl,
reagent than chlorine; bromobenzene is presumed to be the dominant reaction
product based on benzene and bromine concentration.
From the foregoing discussion, by-products from the manufacture of.chloro-
benzene have been predicted. The intent of this section, despite the large
number of reactions presented, has not been to imply that production of chloro-
benzenes results in excessive discharge of environmentally hazardous pollutants,
but rather to account for the seemingly infinite number of species which are
typically found in process wastes. Thus, the reactions shown must be considered
exemplary of possible reaction types, rather inclusive of all possible reactions.
From this standpoint, those pollutants which pose serious environmental threats
may be quantified from sampling studies and appropriate regulatory action taken.
To this end, by-products from the preceding reactions, together with feedstock
impurities, are summarized in Table VI.
PROCESS CONFIGURATION FOR PROOUCTION OF CHLOROBENZENES
The production of any chlorinated benzene is a multiple product operation;
any chlorobenzene manufacturing facility necessarily produces hydrogen chloride
and polysubstituted chlorobenzenes. To a certain extent, product distribution
can be controlled by maintaining low residence times in a reactor. Maximizing
monochlorobenzene production in this manner is at the expense of the energy
required to recycle unreacted benzene.
11-18
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TABLE VI
SUMMARY OF POLLUTANTS FROM MANUFACTURE.OF CHLOROBENZENES
Pollutant Reaction
Number
Benzene F
Benzoic Acid 2.20
Bromobenzene 2.23
Chlorinated Biphenyl 2.7
Chlorobenzene P
Dichlorobenzenes (o&p) 2.1
Dichlcrodibenzodioxins 2.11, 2.12
Dichlorophenols (o&p) 2.9
Chlorinated aliphatic compounds:
tetrachloroethene 2.15
trichloroethene 2.15
chlorocyclohexane 2.18
chlorohexane F
Hydrogen chloride 2.1
Iron III salts C
Iron HI hydroxide C
Tetrachlorooenzenes 2.4
2,3,7,8-Tetrachlorodibenzodioxin 2.13
Trichlorobenzenes 2.4
Trichlorophenols 2.10
Vhe following notations are used for brevity:
F - feedstock impurity
C - species results from catalyst carryover
P - product
11-19
-------
Chloroberizenes can be produced by either batch or continuous methods.
Monochlorobenzene is produced largely from continuous reactors (Berg and
Westerink, 1976); batch chlorination may be reserved more for production of poly-
substituted chlorobenzenes. Both processes, however, will be described.
In a typical continuous process for production of chlorobenzenes
(Hunter, 1968], anhydrous benzene and chlorine are introduced into a reactor
operating at a bottom temperature of 90-125°C and a top temperature of 30-50°C.
Benzene is introduced near the top of the column (see Figure 2); an equimolar
amount of chlorine near the midpoint of the reactor. A variety of catalysts
may be used including Rashig rings, pall rings, ferric chloride impregnated on
a suitable carrier, etc.
Overhead vapor, consisting largely of hydrogen chloride and benzene* is
recovered by passing the gas through a scrubber tower over a reaction
mixture containing chlorination catalyst, thereby removing unreacted chlorine.
Hydrogen chloride is then passed through one or more towers in which the
high boiling chlorobenzenes are used to remove organic contaminants. The hydrogen
chloride may be recovered as either an anhydrous product or as a 30-40% aqueous
solution. If the hydrogen chloride must meet a low organic specification, a
carbon column may be used prior to or after absorption water. If anhydrous HC1 is
produced, the product may be distilled and the bottom product recirculated to
the reactor. Any noncondensible gas present in the HC1 stream is vented and
scrubbed with water (Kao and Poffenberger, 1979).
To maximize monochlorobenzene production, a high recycle rate of benzene
is maintained (y 20:1). Clilorobenzene is withdrawn at a rate similar to that at
which benzene is fed and fractionally distilled. The fractionating column is
11-20
-------
VENT
I
ro
HEAVY TARS
FIGURE 2
CONTINUOUS PRODUCTION OF CHLOROBENZENE
-------
reported to operate-at a bottom temperature of approximately 190°C and top
temperature of 140°C, Higher boiling products (mostly dichlorobenzenes) are
continuously bled at approximately 2% of the product feed. If high purity
chlorobenzene is required, perchloroethylene can be removed by distillation
in a high efficiency column at high reflux ratios. Alternatively, perchloro-
ethylene may be photolytically converted to hexachloroethylene which may then
be removed by conventional distillation (Robata and Wheian, 1978).
Chlorobenzenes may also be manufactured by a batch process as shown in
Figure 3 (Lowenheim and Moran, 1975). Dry benzene is charged into a glass or
lead lined stirred tank reactor. Either iron turnings or anhydrous ferric
chloride are used as a catalyst and remain in the chlorinator after each batch.
Chlorine is added to the reactor at a rate to keep the temperature between
40° to 60°C. If monochlorobenzene is the desired product, the reaction temper-
ature is maintained at approximately 40°C and about 60 percent of the
stoichiometeric requirement of chlorine used. If poly-substituted chloro-
benzenes are desired in addition to monochlorobenzene, the reaction is run at
a temperature of 55 to 60°C for approximately six hours.
Hydrogen chloride is recovered in a manner similar to that of continuous
processes by scrubbing with chlorobenzene to remove organic .contaminants and
absorbing the product gas in a suitable absorption system to give hydrochloric
acid. The chlorobenzene product is washed in a stirred reactor with an
aqueous solution of sodium hydroxide (.10 percent by weight). A sludge rich
in dichlorobenzenes settles and is withdrawn for subsequent distillation.
After separation of the aqueous layer, the crude reaction product is distilled.
A product distribution is shown for a fully chlorinated (i.e., 100 percent of
the theoretical amount of the requirement- for monochlorobenzene) in Table VII.
11-22
-------
VENT
FIGURE 3
¦S
BATCH PRODUCTION OF CHLOROBENZENES
Source: Lowenheim and Moran,1975.
-------
TABLE VII
PRODUCT DISTRIBUTION OF A CHLOROBENZENE BATCH REACTION
Component % by weight
Benzene and water 3
Benzene and chlorobenzene 10
Chlorobenzene 75
Chlorobenzene and dichlorobenzene 10
Tar 2
Source: Lowenheim and Moran, 1975
The first two fractions are returned to the reactor for further reaction.
The fourth fraction may be distilled to yield p-dichlorobenzene in the distillate
and o-dichlorobenzene, contaminated with some para isomer and polychlorobenzenes
(principally 1,2,4-trichlorobenzene) in the residue. The relative proportions
of the products obtained vary according to reaction conditions—reaction temp-
erature, degree of chlorination, and the catalyst used. A 100 percent cfiTor-
ination run at 40°C using a ferric chloride catalyst yields approximately
80 percent chlorobenzene, 15 percent p-dichlorobenzene, and 5 percent dichloro-
benzene.
POLYCHLOROBENZENES
As noted previously, aromatic chlorination is a multiple product process;
most polychlorobenzenes can be produced via similar processes to those described
above. Reaction conditions are, however,!ikely to be somewhat different.
Stronger catalysts (.in the sense of Lewis Acids, e.g., aluminum chloride),
higher reaction temperatures, and longer reaction times are likely modifications.
11-24
-------
A process configuration for production of polychlorobenzenes is shown in
Figure 4,
Dichlorobenzenes
Dichlorobenzenes, for example, which are produced at 150° to 190°C using a
ferric chloride catalyst such as benzene sulfonic acid or p-methlybenzene
sulfonic acid, increase the yield of p-dichlorobenzene up to 86 percent.
Separation of o- and p-dichlorobenzene is difficult by fractional distillation
Gibp - 60C). Alternatives are crystallization of the para isomer in methanol,
treating the mixed isomers with chlorosulfonic acid and separating p-dichloro-
benzene from o-dichlorobenzenesulfonicacid by distillation, or further chlor-
ination of the reaction mixture. In the case of the latter, o-dichlorobenzene
reacts more rapidly than does the para isomer. The resultant 1,2,4-trichloro-
benzene may be easily separated from p-dichlorobenzene by distillation (Abp--30°C).
m-Dichlorobenzene may be prepared by either isomerization of o-and-. p-dichloro-
benzene at 120°C and 45 atm in the presence of catalysts such as aluminum
chloride or hydrogen chloride. Alternatively, higher chlorinated derivatives
may be catalytically dechlorinated using molybdenum oxide, chromium oxide, or
nickel chloride to yield the m-isomer. In particular, 1,3,5-trichlorobenzene
can be reduced exclusively to the meta isomer (Rucker, 1960). The practicality
of the latter method is limited, however, by the availability of the 1,3,5-isomer.
Trichlorobenzenes
As noted previously, both 1,2,4-and 1,2,3-trichlorobenzene are produced
via catalytic chlorination of benzene. Isomers may be separated by fractional
crystal 1ization.
11-25
-------
VENT
FIGURE 4
PRODUCTION OF HIGHER CHLOROBENZENES
Source: Mumroa and Lawless, 1975.
-------
Tetrachlorobenzenes
There are three isomeric tetrachlorobenzenes: 1,2,3,4-tetrachlorobenzene;
1,2,3,5-tetrachlorobenzene; and 1,2,4,5-tetrachlorobenzene. Of these isomers,
the 1,2,4,5- isomer is a chemical and pesticide intermediate (hexachlorophene,
Isobac 20, Ronnel, Silvex, and 2,4,5-T). Each isomer is accessible via
catalytic chlorination using an aluminum chloride catalyst. 1,2,4,5-Tetra-
chlorobenzene may also be produced via the Sandmeyer reaction:
HNO.
rV-
ll^j HoS0
CI
CI
Reduction
h2n
CI
HNO,
CuCl
2 CI
.CI
CI
(2.23)
Pentachlorobenzene and Hexachlorobenzene
Pentachlorobenzenes are formed by chlorination of benzene in the presence
of ferric or aluminum chloride at temperatures of 150 to 200°C, or by chlorin-
ation of any of the lower chlorobenzenes. Hexachl orobenzene is reported not to
be produced via chlorination of benzene, although a certain amount must be
produced as a by-product. Hexachlorobenzene (which has limited uses) is
recovered as a by-product during perchloroethylene production (Mumma and
Lawless, 1975; Gruber, 1975).
11-28
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SECTION III
TREATMENT OF PROCESS WASTES
INTRODUCTION
In Section II of this report, potential pollutants from the manu-
facture of 1,2-dichloroethane were identified. Section III will discuss
specific industrial waste treatment and disposal practices for handling
those waste streams identified. In considering the appropriate mode of
treatment for an industrial waste stream, factors other than just the
simple reduction of standard parameters should be examined. Specifically,
the following areas merit consideration.
o The origin of toxic pollutants, in terms of both reaction
chemistry and process configuration;
o The identification of inhibitory (or refractory) and
hazardous components of the waste stream;
o The acceptability of current treatment and disposal
practices; and
o The compatability of treatment processes in achieving
the discharge requirements.
Waste management of toxic effluent streams involves both in-plant
control technology and end-of-pipe treatment practices. Procedures to
reduce the strength and volume of the final effluent stream may include
improved housekeeping practices, waste stream segregation, and reuse
or recycle of process streams. End-of-pipe treatment technology refers
to both pretreatment and final treatment practices, may involve physical
chemical treatment techniques, biological treatment, or a combination of
III-l
-------
the above. For example, biodegradable wastewaters may be subjected
to activated sludge followed by treatment with activated carbon,
while concentrated streams that are toxic in nature are commonly dis-
posed of by thermal oxidation or incineration. Waste disposal by
sub-surface injection, although widely accepted in the past, is being
more closely regulated by Federal and State agencies, and is generally
discouraged when alternate treatment and disposal systems are available.
The selection of the mode of treatment is largely dependent on the volume
of waste to be treated and the pollutants present.
The selected mode of treatment is determined by the availability
of different treatment operations and processes to economically achieve
the desired effluent. The design criteria for a specific treatment
facility will vary with the strength and volume of the wastewater
stream and the final means of waste disposal.* In each case, the pro-'
cess configuration and plant layout should .be examined to identify
point source discharges and pollutant loadings. Where possible, in-
process changes, stream segregation, and solvent reuse should be imple-
mented to reduce the process waste load.
*The quantity and quality of the pollutant waste load from a manufactur-
ing facility is dependent on the degree of product purification, by-product
separation and recovery, solvent reuse and recycle, and stream segregation
practiced.
111-2
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Process Wastes
Wastes from chlorobenzene manufacture, together with estimates of
waste loads for batch and continuous processes, are presented in Tables VIII
and IX. Distillation residues containing a mixture of chlorobenzene isomers
and other chlorinated aromatic resinous materials are the major sources of
toxic discharge. These polychlorinated wastes have in the past been disposed
of at both on-site and off-site (i.e., contract) industrial landfills, as well
as at sanitary landfills. Alternatively, the toxic components of the waste
have been destroyed by incineration. Incineration of chlorobenzene manufacturing
waste may be carried out with or without by-product recovery. For example,
Dow Chemical reduces waste loads by reclaiming dichlorobenzenes from process
wastes prior to incineration. Major emissions include carbon oxides, chlorine,
water; hydrogen chloride is scrubbed and recovered. Finally, deepwell disposal
of chlorinated solvents has been practiced in the past; however, the tar-like
consistency of the waste would require pretreatment to reduce clogging and
plugging problems (Gruber, 1975; West and Ware, 1977; Quinlivan et'al., 1976).
TABLE VIII
ESTIMATED LOSS OF MATERIALS DURING CHL0R08ENZENE MANUFACTURE
(.BATCH PROCESS)
Chemical
Source
Quantity Produci
(kg/kg monochloroben
Hydrogen Chloride
Monochlorobenzene
Hot scrubber vent
Dichlorobenzene column
0.0014
0.00088
0.0037
0.004
0.0001
0.044
Dichlorobenzenes (isomers not specified)
M
Monochlorobenzene
Dichlorobenzenes
Fractionating towers
u
Polychlorinated Sludge
Distillation residues
Source: Gruber, 1975.
111-3
-------
TABLE IX
ESTIMATED EMISSIONS FROM CHLOROBENZENE MANUFACTURE: Chlorination of Benzene
EMISSIONS kg/Mg
Species
Air
Aqueous
Solid
Benzene
1.6
Chlorobenzene
1.0
Polychlorlnated benzenes
(as trichlorobenzene)
31
33.6
Source: Hunter, 1968.
-------
Aqueous waste discharges originate from the didilorobenzene column waste
stream, In 1978, wastewater treatment at one producer of chlorinated benzenes
consisted of settling to remove heavy organics and iron precipitates Cor catalyst
fines) and neutralization to maintain pH in the range of 6,5 to 8.5, Wroniewicz
(.1978) investigated four possible treatment schemes for upgrading these manu-
facturing wastewaters to meet secondary treatment effluent limitations:
biological treatment, air stripping, steam distillation,and treatment with
activated carbon preceeded by sand filtration. As would be expected, the
volatile aromatic compounds were easily removed by air stripping. However, the
resulting air pollution problems were deemed unacceptable. Biological treatment
was also found to be inappropriate, as the required dilution and detention time we
impractical, the system was intolerant of waste variation, and considerable
quantities of organic sludges accumulated in the reactor tanks. Both steam
distillation and the sand fitter/activated carbon alternatives provided acceptable
levels of treatment. While steam distillation did provide the advantage of
product recovery, uncertainties remained as to the effectiveness of distillation
for dichlorobenzene and trichlorobenzene separation. As the economics of
activated carbon adsorption are acceptable to most manufacturers (and carbon
towers may already be present at the plant site for treatment of other process
wastes or for by-product purification (e.g., HC1), activated carbon was the most
logical treatment option.
In the selected treatment scheme, influent from the existing settling and
neutralization facilities would be sent through a sand filter and on to activated
carbon columns. By monitoring effluent with a gas-liquid chromatograph (GLC),
a standby column may be placed on line as the second in a series when required.
Backwash water from sand filtration operation and the carbon columns would be
111-5
-------
recycled back to the primary settling tanks. After completing full scale tests,
final selection of a method for carbon regeneration will be made. If dichloro-
benzene and trichlorobenzene are found amenable to steam stripping (i.e.,
recovery), steam regeneration would become a viable option (in combination
with or entirely eliminating thermal regeneration (Wroniewicz, 1978).
Air emissions from chlorobenzene manufacture are controlled by scrubbing
vent gas. By-product hydrogen chloride may be scrubbed with benzene or chloro-
benzene to remove organic contaminants, and absorbed in water to produce a
30 to 40 percent hydrochloric acid solution (Gruber, 1975; Kao and Poffenberger,
1979).
PROBABLE FATE OF PRINCIPLE SPECIES'
Industrial discharges (largely from the textile industry) and pesticide
use release chlorobenzenes to the environment. As a result of their resistance
to degradation and their potential for bioaccumulation, numerous researchers
have studied their contamination of wildlife and aquatic ecosystems. An
overview of chlorobenzenes in the environment is presented in the Third Report
of the TSCA Interagency Testing Committee to the Administrator, Environmental
Protection Agency (January, 1979).
The biodegradability of chlorobenzenes is largely a function of the
number of chlorine substituents and their position on the benzene ring; in
general, the more chlorinated compounds are more resistant to degradation.
Mulaney and McKinney (1966) have documented the limited ability of benzene-
acclimated activated sludge to degrade chlorobenzenes. As Simmons et al.,
(1976) showed, the rate of biological degradation of 1,2,4-trichlorobenzene
increases once the previously unacclimated microbial population becomes adapted
to the waste. However, from the jstudies by Simmons et al., (1976) and others,
111-6
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it ts apparent that several factors influence the biodegradability of di.chloro-
benzenes; Cl) prior exposure of the microbial population to the compound; (2)
residence time; (3) aeration rate; and (41 the volatility of the compounds
(West and Ware, 1977].*
Monochlorobenzene is oxidized to 3-chlorocatechol by Pseudomonas putida
grown on toluene as a sole source of carbon (Gibson et al., 1968).
Ballschmiter et al., (1977) investigated the microbial transformation of
chlorobenzenes to chlorophenols by mixed cultures of soil bacteria. The hydrox-
ylation exhibited structural specificity, whereby all chloroohenols up to
3,4-dichloro- and 3,4,5-trichlorophenol are formed by attack at the ortho
position to the chlorine of a -CC1=CH group.
In a model aquatic ecosystem, Lu andMetcalf (197$) studied the environ-
mental distribution and metabolic fate of selected benzene derivatives,
including monochlorobenzene and hexachlorobenzene. Both compounds were found
to bioaccumulate and to be highly persistent. Ecological magnification (EM),
which is the ratio of the concentration of the chemical in an organism to the
water concentration, was found in the mosquito fish for monochlorobenzene
and hexachlorobenzene to be 645 and 1166, respectively. The hydroxylated
compounds, o- and p- chlorophenol and 4-chlorocatechol were identified as
degradation products of monochlorobenzene. The only identified degradation
product of hexachlorobenzene was pentachlorophenol. The biodegradability
index of monochlorobenzene in mosquito fish was reported as 0.014 (cf. a
measured value of 0.012 for DDT).
The observed rate of biodegradation and percent removal in laboratory tests
is often difficult to interpret. Experimental results are completely dependent
on the design of the test system and sampling procedures. Results must account
for possible air stripping of volatile contaminants and removal by adsorption on
settled sludge of the test compound (e.g., Simmons et al.,(1976) found trichloro-
benzene adsorbed on solids).
111 - 7
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Chlorobenzenes volatilize (or codistill with water) into the atmosphere
where they may be subject to hydrozyl radical attack, Dichlorobenzenes and
1,2,4-trichlorobenzene are reported to be susceptible to such hydroxy!ation,
with estimated half-lives of several days (See Brown et al.,1975, Simmons et al,,
1976 j West and Ware, 1977), However, further study is required before the
atmospheric persistence and distribution of chlorobenzenes is fully understood.
There is no clear evidence that chlorinated benzenes undergo environmental
hydrolysis. However, West and Ware (1977) note that if environmental hydrolysis
does occur, because of the limited solubility of chlorobenzenes, the formation of
mono and polyhydric phenolic compounds would be a very slow process.
Ill-8
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SECTION IV
SUMMARY AND CONCLUSIONS
Improper management of wastes which emanate from chemical manufacture
pose a real and serious threat to the environment. Chlorobenzenes have been
found to be moderately toxic during acute exposure ; one isomer, hexachloro-
benzene, has been found to be carcinogenic. Moreover, chlorobenzenes are
relatively mobile, likely to persist in the environment for long periods,
and bioaccumulate to a high degree. Wastes from manufacture of chlorobenzenes,
which necessarily contain chlorobenzenes, must be regarded as hazardous.
Properly controlled, these wastes present no special risk to the envir-
onment. In general, incineration at high temperatures (~ 1200°C) together
with adequate retention times (~ 2 sec.) provide a viable means of disposal.
Only amounts (ppt typically) of hexachloropentadiene, octachloropentadiene,
and hexachlorobenzene are found in incineration scrubber waters (Steiner;, et
al., 1978). Improper combustion, however, may result in formation of combustion
products which are significantly more toxic than the original wastes (e.g.,
dioxins).
Manufacture of chlorobenzenes does result in generation of significant
amounts (~ 0.05 kg waste/kg of chlorobenzene) of solid waste based on analysis
of batch reactions; amounts of wastes which result from the continuous manu-
facture are unknown. Therefore, the following points should be addressed in a
sampling and analytical effort:
IV-1
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Reliable emission factors for batch and continuous process
waste streams should be determined;
Waste streams should be sampled for chlorinated phenols and
dioxins, in addition to chlorobenzenes. Formation of the
latter compounds is probably minimal for continuous processes
but may be significant for batch process where alkaline
wastes are used;
If incineration is used as a means of waste disposal, all
process effluents including scrubber water, stack emissions
and incineration residues should be monitored for toxic
species. Incineration residues, in fact, may be the most
hazardous portion of the process waste load if species such
as dioxins and dibenzofurans are present.
Where process wastewaters are treated by carbon absorption,
carbon regeneraton (most likely thermal regeneration) should
be monitored for toxic emissions.
IV-2
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