-------
ION
TORS NO. 1,2 4 3
earn
Chlorine
SECONDARY
SEPARATOR
EDC
'YROLYSIS
•TJRNACE QUENCH
COLUMN
DISTILLATION
COLUMN
sposal
EDC
RECYCLE
VCM
DISTILLATION
COLUMN
EDC
iRMAL DEHYDROCHLORINATION
SECTION
VCM PURIFICATION SECTION
F1GURE2.4
STAUFFER BALANCED PROCESS FOR THE MANUFACTU
VINYL CHLORIDE MONOMER (VCM) AND
ETHYLENE DICHLORIDE (EDC) BY DIRECT
CHLORINAT10N AND OXYCHLORINATION OF ETHYLE^
EDC FOLLOWED BYTHERMAL DEHYDROCHLORINATION
27
-------
The oxychlorination section combines HC1 from the EDC thermal
dehydrochlorination section with fresh ethylene and air in three
tubular fixed-bed catalytic reactors operating in series. The tem-
perature is '.maintained below 325°C, generally in.a range of 225-
325°C. Pressures of 1 to 15 atmospheres are used. The catalyst
generally -consists of cupric chloride and sodium or potassium chlo-
ride deposited on alumina. The three reactors are packed with cata-
lyst of increasing activity from reactor No. 1 to reactor No. 3 to
achieve better temperature control. In the Stauffer process, ethy-
lene and air are fed in excess of stoichiometric requirements to
assure high HC1 conversion. The heat of reaction is removed by gen-
eration of steam on the shell side of each reactor.
The effluent from reactor No. 3 is cooled to condense the EDC.
The unreacted ethylene gas is separated from the EDC in a phase
separator. The ethylene flows into a chlorination reactor where-it
is combined with chlorine to produce more EDC. The off-gas stream
from the chlorination reactor is cooled with plant cooling water and
.refrigeration, and passed through a primary and secondary separator
before exiting the process. This process reduces the residual
ethylene concentration in the vent gas to as low as 10 ppm. EDC
recovered from the primary and secondary separators is sent to the
EDC purification section.
EDC used to make vinyl chloride by dehydrochlorination must be
of high purity, normally greater than 99.5 percent, since the thermal
29
-------
dehydrochlorination process is susceptible to inhibition and fouling
by trace amounts of impurities. EDC from three sources is combined
for purification: EDC from direct chlorination, EDC from oxychlori-
nation, and EDC recovered from the thermal dehydrochlorination step.
I
The combined EDC streams are fed to a washer where ferric chloride
may be removed with a water wash. Chloral and other water extract-
able impurities are removed by washing with a caustic solution.
Effluent from the washer is fed. to a light ends distillation
column where low boiling impurities and water are removed as an over-
hea-d stream. The bottoms from the light ends column are fed to a
heavy ends distillation column where pure dry EDC is taken off over-
head. At this point EDC may be' recovered as product for sale or sent
%
to the thermal dehydrochlorination section. The bottoms*'from the
heavy ends column are sent to-another column where useful heavy ends,
e.g., perchloroethylene, are separated from tars which go to waste
disposal.
The purified EDC is preheated in the economizer section of the
pyrolysis furnace, and then vaporized with steam. EDC vapor is
heated to dissociation temperature in the tubes of the pyrolysis fur-
nace to give a mixture of vinyl chloride and hydrogen chloride. Fur-
nace temperature and pressure are normally maintained at 500-550°C
and 25 to 30 atmospheres respectively. Residence time is between 2
and 30 seconds. EDC conversion levels of 50 to 55 percent are
achieved, with selectivities to VCM of 96 to 99 percent.
30
-------
The exit stream from the pyrolysis furnace is sent to a quench
column where it is cooled by vaporization of a liquid mixture of EDC
and VCM. Rapid cooling or quenching of the reaction mixture is
important because if the cooling is done too slowly, there are
substantial yield losses to heavy ends and tarsi The exit stream
from the quench column flows through a condenser and into a phase
separator. The exit streams from the phase separator are sent to the
HC1 distillation column where HC1 gas is separated overhead and sent
to the oxychlorination section. A portion of the liquid stream from
the phase separator is used as quench in the quench column. The
bottoms from the HC1 distillation column are sent to the VCM distil-
lation column. Purified VCM is taken overhead and condensed to give
VCM product. VCM is easily liquified and is usually handled as a
liquid under 5 to- 8 atmospheres pressure. The bottoms from the VCM
column are sent to the EDC purification section.
2.5 Manufacture of Chlorophenols
The commercial process for the chlorination of phenol to
chlorophenols is a semi-batch process. Figure 2.5 is a schematic
illustration of the process. At the beginning of the reaction,
phenol is charged into two batch reactors—a primary reactor and a
secondary scrubber reactor. Chlorine is added only to the primary
reactor.
The temperature of the phenol in the primary reactor at the
start of chlorination is in the range of 65-130°C (generally 105°C).
31
-------
LO
N>
Anhydrous
Aluminum
Chloride
W.i i or
Chlorine
IIC1
| UKILIIX
J DIUIN
uct
ol
lorophenol
lorophenol
Dlchlorophenol
1
[— *~
CA
z
1 ABSORPTIO:
-*- VC'II
<
2 ,'i ,(>-Trli lilorophenol
2,3,^,6-Tetrachlorophcnol
X
Conccntrntetl
Hydrochloric
Ac 1.1
HEOYCLE
PUMP
Hot Cons To
Unsce Disposal
FIGURE 2.5
CHLORINATION PROCESS FOB MANUFACTURE OF
CHLOHOPHENOLS
-------
The reactor pressure is maintained at about 1.3 atmospheres. A small
amount of anhydrous aluminum chloride is added as catalyst to the
primary reactor when chlorination has .proceeded to the dichlorophenol
stage, as determined by analysis. If 2,4,6- trich^lorophenol and
2,3,4,6-tetrachlorophenol are desired as products, the reaction is
stopped when the melting point of the reactor contents reaches 95 °C
(about 2 t'o 3 hours). At that point, the reactor contents are sent
to a batch vacuum distillation column for separation of the two prod-'
ucts.
If pentachlorophenol is the desired product, the chlorination is
continued and the reaction temperature is progressively increased to
maintain a. differential temperature of 10°C over the product melting
point. The total period of chlorination is generally 8-10 hours.
Chlorination' is stopped when the reactor contents have a melting
point of at least 174°C and contain at least 95 percent of chlori-
nated phenols. For technical grade pentachlorophenol, no further
purification is required.
The off-gas from the primary reactor, consisting of unreacted
chlorine and hydrogen chloride, is passed into a scrubber reactor
where sufficient phenol is present to ensure complete reaction of the
chlorine. Catalyst is not used in the scrubber reactor. The scrub—
ber reactor is used to manufacture monochlorophenol and dichloro-
phenol. The reactor operates at about 1.3 atmospheres pressure.
33
-------
For production of raonochlorophenols, the temperature in the
scrubber reactor is maintained at about 70°C. When one atom of chlo-
rine has combined with one molecule of phenol, as determined by
analysis, the reactor contents are charged to a batch vacuum distil-
lation column for separation of o-chlorophenol and p-chlorophenol.
When 2,A-dichlorophenol is the desired product the scrubber
reactor is operated at a higher temperature, between 90° and 120°C.
After two atoms of chlorine have combined with one atom of phenol,
as shown by analysis, the reactor contents are charged to two batch
vacuum distillation columns operated in series for separation of the
reactor product components.
The off-gas from the scrubber reactor consists mainly of hydro-
gen chloride with entrained phenols and chlorinated phenols. The gas
is passed through a condensing trap where the entrained phenols and
chlorinated phenols separate from the gas stream and are returned'' to
the scrubber reactor. The hydrogen chloride gas flows to an absorp-
tion tower where it is absorbed in water. Hydrochloric acid is taken
off from the lower portion of the tower, and recirculated by means of
a pump until hydrochloric acid of the desired concentration is ob-
tained. The acid is directly suitable for commercial use. The vent
from the absorption tower releases water vapor containing traces of
hydrogen chloride. The operation of the batch vacuum distillation
columns proceeds as follows:
34
-------
Batch distillation column number 1 receives the contents of the
scrubber reactor. The components of the reactor contents are removed
sequentially. The column is operated at about 110 mm Hg pressure.
If the reactor contents are monochlorophenol, opthochlorophenol is
taken overhead first at about 104°C, and condensed and recovered as
product. Unchlorinated phenol is then recovered at about 111°C and
recycled to the reactors as needed. The third overhead stream is
p-chlorophenol, which distills at about 145°C. It is condensed and
recovered as product.
If the reactor contents are primarily dichlorophenol, the dis-
tillation column is operated to recover monochlorophenols first, then
2,4-dichlorophenol at 1508C.
The bottoms from column 1 consist of 2,6-dichlorophenol and
2,4,6-trichlorophenol. This stream is sent to column 2 along with
the trichlorophenol and tetrachlorophenol mixture from the primary re-
actor. Column 2 operates at 60 mm Hg. In column 2, 2,6-dichloropher
nol is removed as an overhead stream at 135°C, condensed, and re-
cycled to the primary reactor for further chlorination. 2,4,6-
trichlorophenol is recovered next at about 160°C and collected as
product. The final overhead stream is 2,3,4,6-tetrachlorophenol,
which distills at about 190°C. It is condensed and collected as
product. The bottoms from column 2 consist of a mixture of penta-
chlorophenol and polynuclear polychlorinated tars. This mixture is
disposed of as waste.
35
-------
2.6 Manufacture of Allyl Chloride (Shell Process)
A flow diagram of a commercial scale allyl chlorile plant, as
developed by the Shell Chemical Company, is illustrated in Figure 2.6
(Fairbairn, Cheney, and Cherniavsky, 1947; Pilorz, 1964). Wet pro-
pylene from storage is chilled by passage through a bayonet type
cooler immersed in dry propylene. The chilling causes condensation
of water which is subsequently removed in a coalescer. The separated
water is periodically drawn off. :The propylene then passes through a
drier packed with activated alumina where residual water is removed.
The drier system includes two driers which operate alternately so
that one is being regenerated while the other is operating. The dried
propylene then flows to the dry propylene storage tank.
\
In the dry storage tank the pjropylene is vaporized in the pro-
cess of providing refrigeration for chilling the wet propylene. The
gaseous propylene flows through a heater prior to mixing with gaseous
chlorine and entering the reactor. Normally the feed will contain
about 4 moles of propylene per mole of chlorine. The reaction tem-
perature is maintained at between 500 and 510°C and the pressure in
the reactor is about 1 atmosphere gauge pressure. Residence time is
a few seconds. Because carbonaceous material accumulates in the re-
i
actor, it is necessary to clean the reactor about once every two
weeks. Therefore, two reactors are commonly provided so 'that one is
in operation while the other is being cleaned.
36
-------
LIQUID
KNOCK-OUT
POT
LIQUID
PROPYLENE
STORAGE
WET PROPYLENE
STORAGE
DRY PROPYLENE
STORAGE
o o
LIQUID
CHLORINE
TANK CAR
CHLORINE
VAPORIZER
PUMP
-------
HYDROGEN
CHLORIDE
ABSORBER
• Water
20° Be
Hydrochloric
Acid
REBOILER
CONDENSER
o
REFLUX
DRUM
REBOILER
REFLUX
DRUM
Allyl
Chloride
To
Storage
REBOILER
P RETRACTIONATOR
DISTILLATION
COLUMN NO. 1
DISTILLATION
COLUMN NO. 2
Heavy
Ends
To
Storage
FIGURE2.6
CHLORINAT10N PROCESS FOR THE MANUFACTURE OF
ALLYL CHLORIDE FROM PROPYLENE
37
-------
The reaction product is cooled and fed directly to a prefrac-
tionator where excess propylene and byproduct hydrogen chloride is
separated as an overhead product from the organic chlorides. Liquid
propylene, cooled to -408C by self-vaporization in a propylene flash
drum, is used as reflux in the prefractionator.
The propylene and hydrogen chloride mixture from the prefrac-
cionator flows through an absorber where commercial strength hydro-
chloric acid is produced. Liquid propylene is used to-remove the
heac of absorption in this process. The propylene leaving the ab-
sorber is scrubbed with caustic to remove residual hydrogen chloride.
It then passes through a liquid knockout pot to remove entrained
water before being compressed, liquified, and returned to wet propy-
lene storage. Gaseous, propylene generated in the propylene flash *
drum and during regeneration of the driers is also recycled through
the compressor to wet propylene storage.
The organic chlorides from the bottom of the prefractionator are
refined in two distillation columns operating in series. In the
'first distillation column, residual propylene and light ends such as
isopropyl chloride and 2-chloropropene are removed as overhead prod-
uct. The bottoms from the first column are fractionated in the
second column where allyl chloride is removed as the overhead prod-
uct. The bottoms from the second column consist primarily of dichlo-
ropropene and dichloropropane.
39
-------
2.7 Manufacture of Mono- and Dichlorobenzenes
Monochlorobenzenes and dichlorobenzenes are produced commer-
cially by a continuous process in which liquid benzene is chlorinated
with chlorine in the presence of anhydrous ferric chloride catalyst.
The production of monochlorobenzene is favored by maintaining the
reaction temperature below 50°C.
Figure 2.7 is a schematic diagram of the process. Chlorine, an-
hydrous ferric chloride, and dry benzene are continuously fed to a
reactor. The reaction temperature is maintained at between 308C and
50°C, partly by circulating the reactor contents through a cooler,
and partly by vaporizing some of the reactant mixture. The vapor
*
stream from the reactor consists of hydrogen chloride, unreacted
chlorine, inerts, benzene, and some chlorinated benzene. T^e =treani
is first scrubbed with a refrigerated stream of chlorinated benzenes
in an organic absorber to recover the benzene and chlorobenzenes.'1 It
is then scrubbed with water in a hydrogen chloride absorber system.
The hydrogen chloride absorber system consists of a hydrogen chloride
absorber, a tail gas scrubber, and a residual gas neutralizer. In
the hydrogen chloride absorber, the gas stream is scrubbed with a
dilute hydrochloric acid stream, and commercial strength hydrochloric
acid is produced. The inert gas stream from the absorber (tail gas)
containing unabsorbed hydrogen chloride, passes through a tail-gas
scrubber which removes most of the remaining hydrogen chloride in the
gas stream. The hydrogen chloride solution from the tail gas
40
-------
Make-up —
Water
CW~~'
Chlorine
FeCl3
Catalyst
ORGANIC
ABSORBER
HC1
ABSORBER
water
Caustic Wash
Wash
CRUDE
CHLOROBENZENE
DISTILLATION
COLUMN
Ref
Cooler or Condenser
Using Cooling Water
Refrigerated Cooler
Reboiler
Reflux Drum
J C Ejector Pump
-------
Make-up
Caustic
Organics
for Recycle
Salt +
Caustic
Solution
to Waste
Treatment
p-DICHLOROBENZENE
CRYSTALLIZATION
p-dichlorobenzene
Crytals to Recovery
and Packaging
Solvent grade
o,p-Dichlorobenzene
to Separation
and Recovery
Hydrochloric
Acid to
Storage
VENT
Monochlorobenzene
to Storage
MDNOCHLOROBENZENE
RECOVERY COLUMN
To o-dichlorobenzene
Storage
DICHLOROBENZENE-
ISOMER SEPARATION
COLUMN
Trichlorobenzene
Isomers and
Heavier Compounds
To Storage
Wastewater
FIGURE 2.7
MANUFACTURE OF MONO- ANO DICHLOROBE
CHLORINAT10N OF BENZENE
41
-------
scrubber flows into a settler in which condensed organic compounds
are separated and recovered for recycle. Part of the dilute acid
solution from the separator is used as the scrubber .medium in the
hydrogen chloride absorber and the remainder is mixed with fresh
make-up water and used as the scrubber medium in the tail-gas scrub-
ber. The inert gas stream from the tail-gas scrubber contains traces
of hydrogen chloride. It is scrubbed with a caustic solution before
discharge to the atmosphere.
The liquid stream from the reactor (crude chlorobenzene) con-
tains chlorinated benzenes, unreacted benzene, dissolved hydrogen
chlqride, and spent catalyst. The stream is distilled in a crude
dichlorobenzene vacuum distillation column. The benzene, hydrogen
chloride, and most of the monochlorobenzene and dichlorobenzenes are
removed overhead in the column. The column bottoms contain the cat-
alyst, some dichlorobenzene, and the more highly chlorinated benzena.
The bottom stream is washed with caustic and water to separate the
organics from the catalyst. The organics are dried and fed to the
dichlorobenzene isomer separation column and the spent caustic and
wash water streams containing catalyst salts are disposed of.
The overhead stream from the crude distillation column is passed
through a hydrogen chloride stripper where dissolved hydrogen chlo-
ride is boiled off. The hydrogen chloride stream from the stripper
contains some organics. It is mixed and processed with the gas
stream from the reactor. The organic absorber bottoms stream is also
43
-------
processed through the hydrogen chloride stripper to remove dissolved
hydrogen chloride.
The hydrogen chloride free bottoms-stream from the hydrogen
chloride stripper is then processed through a series of distillation
columns to recover benzene and the product chlorinated benzenes.
Benzene is recovered as an overhead product from the benzene recovery
column and recycled to the reactor.
The bottoms from the benzene recovery column consist of mixed
chlorobenzenes. The stream is distilled in a monochlorobenzene re-
covery column where monochlorobenzene is recovered as an overhead
product. The bottoms from the monochlorobenzene recovery column are
distilled in a dichlorobenzene isomer separation column.
The overhead product fron the isomer separation column consists
primarily- of para-dichlorobenzene and some ortho- and meta-dichloro-
benzene. Purified para-dichlorobenzene is recovered from this stream
by fractional crystallization. Residual liquid from the crystalliza-
tion process consists of a mixture of ortho-, para- and meta-dichlo-
robenzene which is separated by distillation into solvent grades of
ortho-and para-dichlorobenzene.
The bottoms from the isomer separation column are separated by
distillation into an ortho-dichlorobenzene product stream and a
stream containing a mixture of trichlorobenzene isomers and more
highly chlorinated benzene compounds.
44
-------
3.0 IDENTIFICATION OF CONTAMINANTS FORMED IN CHLORINATTON AND RE-
LATED UNIT PROCESSES
In this section, contaminants that may be formed during the man-
ufacturing processes described in Section 2 are identified on the
basis of the process chemistry. Details of the process chemistry
were obtained from the open literature and from personal knowledge
and experience. In predicting possible contaminants, considera-
tion was given to the presence of impurities in the raw materials,
process operating conditions, the stability of the compounds on
exposure to the environment, and the use of additives.
Four unit processes are described,*as follows:
• Direct chlorination, in which chlorine reacts directly with a
hydrocarbon
• Hydrochlorination of alcohol, in which chlorine from hydrogen
chloride replaces the hydroxyl group on the alcohol
• Oxychlorination, in which hydrogen chloride is catalytically
oxidized, making the chlorine atom available for addition to
the hydrocarbon
• Dehydrochlorination, in which hydrogen chloride is removed
from a chlorinated hydrocarbon to make an unsaturated
compound
3.1 Direct Chlorinatipn •
Six of the manufacturing processes described in section 2
involve the unit process of direct chlorination: chlorination of
methane, manufacture of carbon tetrachloride and perchloroethylene,
manufacture of vinyl chloride monomer and ethylene dichloride,
manufacture of chlorophenols, manufacture of allyl chloride and
45
-------
manufacture of chlorobenzenes. The chemistry of these processes can
be characterized by the following three types of chlorination
reactions:
• Free radical chain reactions
• Electrophilic aromatic substitution reactions
• Addition reaction to a double bond
In the first two types of reactions, a chlorine atom replaces a
hydrogen atom on the hydrocarbon, and hydrogen chloride is formed as
a by-product. In the third type of reaction, both chlorine atoms of
the chlorine molecule are added to the hydrocarbon fo-rming a
saturated chlorohydrocarbon.
3.1.1 Chlorination of Methane
The direct chlorination of methane proceeds by a free radical
chain reaction involving an initiation reaction, propagation re-
actions, and termination reactions. In the initiation reaction,
chlorine molecules break, apart under the influence of heat or light
into chlorine radicals.
Cl - Cl -£— 2 Cl- (1)
Propagation reactions consist of the reaction of a chlorine radical
with methane or a chloromethane to generate hydrogen chloride and a
methyl radical or a chloromethyl radical, and the reaction of a
methyl radical or a chloromethyl radical with chlorine to form a
methyl chloride and a chlorine radical.
CH4 + Cl- HC1 + CH3 (2)
CH3 + Cl - Cl CH3C1 + Cl- (3)
46
-------
CH3C1 + Cl- HC1 + CH2C1 (4)
CH2C1 + Cl - Cl CH2C12 H- Cl- (5)
CH2C12 + Cl- HC1 + CHC12 (6)
CHC12 + Cl - Cl CHC13 + Cl- (7)
CHC13 + Cl- HC1 + CC13 (8)
CC13-+ Cl - Cl CC14 + Cl- (9)
Termination involves the reaction of two free radicals. Termination
reaction products include Cl,, CH-jCl, CH?C12, CHC13> CC14, CH3 - CH3,
CH3 - CH9C1, CH3 - CHC1,,*, CH3 - CC13, CH2C1 - CHnCL*. CH,C1 -
CHCi.,, Qi?Cl - CC13, CHC1, -CHC12, CHCl^ -CC13> and CCl-j - CClj.
To a much lesser extent, the two-carbon termination products can
themselves act as reactants and occasionally undergo terminations to
form longer chain carbon compounds.
Chlorinated methanes are somewhat unstable when exposed to air
and water. Decomposition products include carbon dioxide, hydrogen
chloride, phosgene, methanol, and chlorine. In hot water (180°C),
methylene chloride forms carbon monoxide and formic acid. In the
presence of iron and water, chloroform reacts with oxygen to produce
hydrogen peroxide, phosgene, and hydrogen chloride (Hardie, 1974):
+H20
CHC13 + 02 Fe_ C13COOH C13COH + H202 (10)
C13COH COC12 + HC1 (11)
*This compound is a precursor of vinyl chloride (CH2 = CHC1). It
is possible that at high temperatures, a very small amount of vinyl
chloride will form.
-------
The above reaction is accelerated by the presence of base. In
wate-r, phosgene (COC^) decomposes rapidly into carbon dioxide and
hydrogen chloride. Carbon tetrachloride forms hexachloroethanes,
perchloroethylene, and chloromethanes when exposed to high tempera-
ture steam.
Stabilizers are commonly added to the chloromethanes to inhibit
decomposition. Phenolic compounds or amines are used in methylene
chloride. Stabilizers for chloroform include absolute alcohol,
methylated spirits, thymol, t-butyl phenol, and n-octyl phenol.
Stabilizers for carbon tetrachloride are alkyl cyanamides, diphenyl
amines, ethyl acetate, ethyl cyanide, fatty acid derivatives,
hexamethylene tetramine, resins and amines, thiocarbamide, and
guanidine (Hardie, 1964).
3.1.2 Chlorination of Mixed Hydrocarbons and Chlorohydrocarbons
The direct chlorination of mixed hydrocarbons and chloro-
•»
hydrocarbons is used to manufacture perchloroethylene (tetrachloro-
ethylene, 1,1,2,2-tetrachloroethylene) and carbon tetrachloride. The
feedstock for the process consists of a mixture of aliphatic hydro-
carbons ranging from methanes to butanes. The process operates at
pyrolytic or near pyrolytic temperature (500-650°C), which is high
enough to pyrolyze the Chlorohydrocarbons formed. The chemical
process can be analyzed in two stages. In the first stage the feed-
stock hydrocarbons are completely chlorinated (perchlorinated) in a
free radical chain reaction. In the second stage, chlorinated com-
pounds are partially pyrolyzed to yield the final product.
48
-------
A generalized reaction sequence for Che first stag-; is as fol-
lows:
1. C1-C1 2 Cl-
Heat
Initiation
2. R-C-H + Cl- H-C1 + R-C
3. R-C- + C1-C1 R-C-C1 + Cl-
Propagation
C1-C1
. R
R' - R"
6, R'. -r Cl-
R' - Cl
Termination
Specific examples of reactions which may occur are:
CH4 + , C12
Heat
CC14 -I- 4HC1
C4H6C14 •(• 6 C12 C4C110 + 6HC1
Heat
(12)
(13)
NOTE: R' and R" are any hydrocarbon or chlorohydrocarbon radi-
cals. Steps 2 and 3 together form a cycle which can generate hun-
dreds or thousands of product molecules, depending upon the process
conditions. A termination step halts two chains simultaneously.
49
-------
Hie generalized reaction sequence for partial pyrolysis is
CC13 - CC12 - R R- 4- CC13 - CC12 (14)
Heat
R- + CC13 - CC12 R-C1 4- CC12 - CC12 (15)
ific examples of partial pyrolysis reactions which may occur are
cci3K:ci2^;ci3 cci4 + cciz = cci2 (16)
2 CC13-CC13 2 CC14 4- CC12 = CC12 (17)
cci3K:ci2-<:ci2-<:ci3 cci3K:ci3 4- cci2 = cci2 (is)
Other possible combinations exist, all of which ultimately lead
CC14 and C2Cl/f. All of these reactions stem from fragmenta-
)ti of Che intermediates to yield CC13 - CC13 which then reacts
"yield the final products (equation 17). Molecules which fail to
•rolyze completely, ultimately end up as the "heavy ends.
3.1.3 High Temperature Propylene Chlorination
Propylene will react with chlorine to produce a number of dif-
erent compounds. The predominant reaction at 500°C is the free
'adical reaction which results in the production of allyl chloride:
"12 = CHCH3'+ C12 CK2 = CHCH2C1 4- HC1 (19)
The allyl chloride may'also be chlorinated to 1,3-dichloropropene
(Hearne, 1953).
m
At temperatures too low for free radical formation (below
200°C), the chlorine will add across the double bond to produce
50
-------
1,2-dichloropropane unless a free radical-producing catalyst has been
added. Even at 500°C or above, this reaction takes place to an
appreciable degree (Fairbairn et al., 1947). Similarly, the HC1
present may add across the double bond to produce isopropyl chloride
(Fairbairn et al. , 1947).
A'likely reaction pathway to allyl chloride at high (500°C)
temperatures is:
C1-C1 2 Cl- Initiation (1)
Heat
Cl- + CH2 - CH-CH3 HC1 + CH2 = CH-CH2
C1-C1 + CH2 - CH-CH2 Cl- + CH2 = CH-CH2
Cl
and termination^of the chains shown in 20a and b.
Propagation
(20a)
(20b)
A process which probably takes place simultaneously is as fol-
lows :
CH2 = CH-CH3 + C12 - CH2-^H-CH3 (21)
Cl Cl
CH2-CH-CH3 - Cl- + CH2-CH-CH3 (22)
Cl Cl Cl
Cl- + CH2-CH-CH3 - ^HCl + CH2-CH = CH2 (23)
Cl ' Cl
The former (chain) mechanism can lead to the formation of
products larger than butanes in a manner analogous to that described
earlier for chlorination of methanes and mixed hydrocarbons.
51
-------
The major side reactions are:
CH2 » CH-CH3 + HC1 CH3-CH-CH3+ CH3CH2CH2C1 (24)
Cl
PH-I— CU—/*"- - tri-M _L /"
-------
A pathway to benzene formation is as follows:
2 CII2 - CH-CH2 CH2 - CH-CH2-CH2-CH = CH2
(27)
CH2
CHo
CH-CH2-CH2-CH = CH2 + 1/2 C12
CH2 = CH-CH-CH2-CH = CH2 +^HC1
Cl
CH-CH-CH2-CH =• CH2 CH2 - CH-CH = CH-CH
Cl
+ HC1
CH2
(28)
(29)
\\ //
F\
'(30)
+ h Cl,
+ HC1
(31)
cr
HCl
(.32)
Cl
Propylene is commercially available as a highly purified com-
pound, but it may contain detectable quantities of propane, ethane,
ethylene, and carbonyl sulfide. The hydrocarbon impurities will be
chlorinated in a free radical reaction to yield the respective
chlorohydrocarbons. Ethylene will also undergo a chlorine addition
reaction. Thus, all the mono- and dichlorinated isomers of these
hydrocarbons are likely to be present in the process streams,
although in very small quantities.
53
-------
Carbonyl sulfide (COS) is likely to be present only in trace
quantities. COS is a relatively stable compound but at 500°C there
nay be enough dissociation for its reaction with chlorine to reach
equilibrium:
2 COS + 3 C12 " 2 COC12 + S2C12 (33)
On the.basis of free energy considerations, it is expected that the
equilibrium proceeds toward the right at low temperatures, and to the
i
left at the high temperatures of the allyl chloride production
process. However, even if some phosgene and sulfur chloride were
formed when che temperature is dropped during the quench, they would
be destroyed by water in the scrubber. Therefore, phosgene or sulfur
chloride are not expected to be found in process streams downstream
of the scrubber.
Following che chlorination step, the reaction products are
scrubbed with water to recover HC1 as hydrochloric (muriatic) acid.N-.
None of che other products (with the exception of phosgene, if
present) is broken down or removed by water. The final caustic
scrubber removes traces of HC1, producing NaCl.
Allyl chloride may also be produced by a low temperature
(200°C) catalytic process (Rust, 1942). It is not expected that the
substances present in the catalytic process will be different from
chose in the high temperature process except for the addition of
catalyst fragments. Among the different catalysts which may be used
are organo metallic compounds, azo compounds, organic peroxides, and
organic free radical compounds.
54
-------
3'1«4 Ethylene Chlorination
The direct chlorination of ethylene is an addition reaction in
which chlorine adds to the double bond of ethylene to form a
saturated dichloride (ethylene dichloride). The reaction proceeds
with the aid of a Lewis acid catalyst, as follows:
- - -—• d .. - & Q
:C1 - Cl: FeGl3 :C1 - Cl - FeCl3 (34)
.. .. S 0
:C1 - Cl - FeCl3 H2C - CH2 + FeCl4 (35)
© ©
• CH2 -
Cl" • Cl" Cl"
(36)
Under noraal reaction conditions, Che yield of ethylene
..-.•.-ride is greater than 99 percent.
Impurities in the ethylene feedstock include methane and ethane
••..lc>. should pass through the system unchanged.
3.1.5 Chlorobenzenes
The direct chlorination of benzene is an electrophilic aromatic
substitution reaction. Benzene is a source of electrons and thus
reacts with electron seeking reagents (electrophilic reagents). The
reaction is believed co proceed as follows:
1. Chlorine is polarized by a Lewis acid catalyst:
..' V - -© ©
•Cl - Cl: FeCl3 'Cl - Cl - FeCl3 (34)
— •* j •• *• w
55
-------
.e positive chlorine (electrophile) reacts with the benzene
:arbonium ion:
+ :Cl-Cl-FeCl3 f| *| + Feci, (37)
\ hydrogen ion is subsequently abstracted from the carbonium
negative chloride ion to form hydrogen chloride and
;e the ferric chloride:
H Cl
/-v ^^
(38)
ie remaining hydrogen atoms on the ring can be sequentially
jted by chlorine forming a total of twelve chlorinated
ds: monochlorobenzene, three dichlorobenzenes, three
(robenzenes, three tetrachlorobenzenes, pentachlorobenzene, and
Lorobenzene. The extent to which polychlorinated compounds are
depends on the reaction temperature, the molar ratio of
ie to chlorine, the catalyst used, and the reactor residence
Low temperature, short residence time, and high mole ratio of
ne to chlorine favor'the production of monochlorobenzene.
:hlorobenzene is the preferred product at 40-45°C. Poly-
robenzenes are produced in more abundance at 75-858C (Brunjes,
). The use of Fuller's earth (Hardie, 1964) or magnesium iron
linum silicate (Darragh, 1949) as a catalyst reduces the pro-
tion of dichlorobenzenes. However, it is not possible to entirely
initiate polychlorinated benzene byproducts (Hardie, 1964).
56
-------
The presence of chlorine on the benzene ring influences the
:f subsequent chlorination and the attachment position of the
quent chlorine atoms on the ring. The chlorine inhibits sub-
>nt reaction and is orVho-para directing. Thus, the products of
lorination are principally ortho- and para-dichlorobenzene with
' minor -amounts of meta dichlorobenzene :
ci ci ci ci
3 r . "cl ^ (39)
Para CI Ortho Meta
2,4-trichlorobenzene is the predominant trichlorination product.
. also is present in only minor amounts.
Impurities in benzene are usually less than 0.5 percent
Hancock, 1975). The impurities are mostly toluene' and aliphatics
such as n-heptane, with boiling points close to that of benzene.
Thiophene is also often present as an impurity (Hancock, 1975).
Toluene can be chlorinated under the conditions of the reaction in a
manner similar to that of benzene. Toluene, in fact, is more re-
active than benzene towards electrophilic substitution. It is not
expected that the methyl group of the toluene would be chlorinated.
The heptane and other aliphatic impurities in the benzene are ex-
pected to go through the reaction unchanged. Thiophene reacts with
chlorine but does not alter the course of the main reaction:
s
57
-------
Downstream processing of the reactor product includes a caustic
wash and a water wash of a mixture of catalyst and polychlorinated
benzenes. It is anticipated that reactions could take place between
hydroxide ion and dichlorobenzene to a limited extent, producing
phenols, polyhydroxy benzenes, chlorophenols, and related compounds.
A-very minor side reaction could occur between hydroxide ion
and a chlorobenzene as follows:
Cl
OH
4- NaOH
NaCl-
Dichlorobenzenes may react as follows:
Cl
Cl
NaOH
OH
NaCl
(41)
(42)
Cl
Cl
4- 2 NaOH
OH
(43)
NaOH
NaCl
(44)
4- 2NaOH
4- 2NaCl
(45)
53
-------
If phenol gets recycled to the "reactor, chlorophenols will
result, as follows:
OH
+ 3C1.
Further products are:
OH ci
Cl 1 OH
3HC1
(46)
Cl
Cl
Cl
0
Cl
Cl
Cl
Cl
OH
OH
(47)
Cl ^ 'Cl
Cl
OH Cl
The hydrolysis of chlorobenzene with caustic to produce phenol
is normally a high pressure, high temperature reaction. Thus, it is
not expected that very much phenol or other oxygenated compounds will
form under the conditions encountered in the caustic and water wash
steps.
The ferric chloride will react with the caustic and water to N •>
produce ferric hydroxide and sodium chloride. Metal impurities
present in the ferric chloride will also react to form metallic
hydroxides.
3.1.6 Chlorophenols
The direct chlorination of phenol,' like that of benzene, is an
electrophilic, aromatic substitution reaction. The hydroxyl group is
rate-enhancing relative to benzene, and is a strong ortho-para
director. Thus the chlorination of phenol yields ortho- and para-
chlorophenols. The rate of chlorination of phenol is 1.1 x 10^
times the rate of benzene chlorination (Reiche et al., 1975).
59
-------
The direct chlorinaticm of phenol with chlorine proceeds in
steps and can lead to seven chlorinated phenols, as shown below:
OH
OH
OH
C1
70°C
C12 70°C
OH
Cl
+ HC1
ortho-Chlorphenol
HC1
Cl
para-Chlorophenol
OH OH
,C1 C
(48)
(49)
2HC1
(50)
Cl
ortho-Chlorophenol 2,4-Dichlorophenol 2,6-Dichlorophenol
OH
C1
Cl
para-Chlorophenol
90°C
OH
Cl
HC1
(51)
Cl
2,4-Dichlorphenol
60
-------
,
2 105°C
2 ,4-Dichlorophenol
2 ,6-Dichlorophenol
Cl, A1^3
2 130°C-
OH
Cl
Cl
HC1
Cl
2,4,6-Trichlorophenol
HC1
Cl
2,4,6-Trichlorophenol
2,4,6-Trichloropheno1
+ HC1
2,3,4,6-Trichlorophenol
OH
Cl
Cl,
'Cl
A1C13
2 130^185°C
2 ,3 ,4,6-Tetrachlorophenol-
+. HC1
Pentachlorophenol
(52)
(53)
(54)
(55)
As seen in equations (48) and (49), phenol chlorinates at 70°C
<*
to both-ortho-chlorophenol and para-chlorophenol. On further chlori-
nation at 90°C, ortho-chlorophenol yields both 2,4- and 2,6-dichloro-
phenol (equation 50), while para-chlorophenol yields mainly 2,4-di-
chlorophenol (equation 51). "To chlorinate beyond the dichlorophenol
' 61
-------
stage at an acceptable rate, anhydrous aluminum chloride is added as
catalyst, For commercial chlorinations a preferred amount of cata-
lyst is 0.0075 mole of aluminum chloride per mole of phenol. Both
2,4- and 2,6-dichlorophenol yield 2,4,6-trichlorophenol on chlorina-.
tion at 105°C in the presence of aluminum chloride catalyst (equa-
tions 52 and 53). The temperature is increased from 1058C to 130°C
for the chlorination of 2,4,6-trichlorophenol to 2,3,4,6-tetrachloro-
phenol (equation 54).
To obtain pentachlorophenol, the temperature is increased pro-
gressively (from about 130°C to 185°C) to maintain a differential
temperature of 10°C over the product melting point (equation 55).
The action of aluminum chloride in the synthesis of
"*•-,-
2,4,6-trichlorophenol from 2,4-dichlorophenol is shown in equations
56 to 59 as follows:
A1C1
6+ 6-
C1-C1 A1C13
(56)
OH
Cl 6+
+ C1--C1 -
- (57)
Cl ,°H Cl
(58)
62
-------
(A1C1.)~ +--H+ ^. A1CL, + HC1 (59)
4/ r-** ^ 3
The high temperatures used in the manufacture of the higher
chlorinated phenols result in side reactions that produce many
contaminants. Most of the available information pertains to penta-
chlorophenol. Commercial technical grade pentachlorophenol contains
4 to 10 percent 2,3,4,6-tetrachlorophenol, traces of 2,4,6-triehioro-
phenol, chlorinated dibenzo-p-dioxins, chlorinated dibenzofurans,
chlorophenoxy chlorophenols, chlorodiphenyl ethers, and chlorohydroxy-
diphenyl ethers. Analyses of pentachlorophenol have revealed that
•v,^
the principal chlorodioxin and chlorodibenzofuran contaminants are
*
those containing six to eight chlorine atoms. The highly toxic
2,3,7,8-tetrachlarodibenzo-p-dioxin (TCDD) has not been identified in
any sample of pentachlorophenol that has been analyzed (U.S. EFA,
1978).
Analysis results for a commercial-grade pentachlorophenol
(Dowicide 7, Sample 9522 A) produced by the Dow Chemical Company in
June 1970, and a purified grade of pentachlorophenol, prepared by dis-
tillation of Dowicide 7, are given in Table III (U.S EPA, 1978).
Chlorodioxins may result from condensation reactions of ortho-
subs tituted chlorophenoxy radicals (Kulka, 1961). Chlorophenoxy
radicals are produced from decomposition of polychlorocyclohexa-
dienone (2,3,4,4,5,6-hexachlorocyclohexa-2,5-dien-l-one) which is
63
-------
TABLE
COMPOSITION OF COMMERCIAL-GRADE AND
PURIFIED-GRADE PENTACHLOROPHENOL (PGP)
ANALYTICAL RESULTS
COMPONENT
Pen tachlorophenol
2,3 ,4., 6-Tetrachlorophenol
2 ,4,6-Trichlorophenol
Chlorinated phenoxyphenols
Octachlorodioxins
Hep cachlcrodioxins
Hexachlorodioxins
Octachlorodibenzofurans
Hep tachlorodibenzo f-urans
Hexac hlo ro dibenz o f tirans
Commercial
(Dowicide 7)
88.4%
4.4%
0.1%
6.2%
2500 ppm
125 ppm
4 ppm
80 ppm
80 ppm
30 ppm
Purifiedb
(Dowicide EC-7)
89.8%
10.1%
0.1%
15 . 1 ppm
6 . 5 ppm
1.0 ppm
1,0 ppm
1.8 ppm
1 . 0 ppm
Sample 9522 A, 1970
Technical-grade PC? purified by distillation
SOURCE: U.S. EPA, 1978
64
-------
produced by overchlorination of tri-, tetra- or pentachlorophenol
(see equation 60 below). The chlorophenoxy radical (an electrophile)
attacks electronegative sites (ortho or para positions) on a poly-
chlorophenol molecule to form chlorophenoxy chlorophenols (see equa-
tion 61 below) which undergo further reaction to form chlorodioxins
(see equation 62 below) (U.S. EPA, 1978).
0
C1-
heat
Pentachlorophenol
9
2,3,4,5,6-
ci
Chlorophenoxy
hexachlorocyclohexa- radical
2,5-dien-l-one
PH PI C.1
a chlorophenoxy chlorophenol
(61)
1,2,3,4,6,7,8,9-octachlorodibenzo-p-dioxin
Similar reactions may be written starting with 2,4,6-trichloro-
phenol and 2,3,4,6-tetrachlorophenol.
3.2 Hydrochlorination of Methanol
The reaction of a~n alcohol with hydrogen chloride involves
substitution in which the chloride group replaces the OH group on the
alcohol:
R - C - OH
H
HCl
R - C - Cl + H20
(63)
65
-------
The reaction is catalyzed by Lewis acids such as alumina, cuprous
chloride, or zinc chloride. The process for manufacturing methyl
chloride from methanol is represented by:
catalyst
CH3 - OH + HC1 CH3 - Cl + H20 (64)
heat
The reaction produces no organic side products. Methanol of
greater than 99.9 percent purity is commercially available (Hardie,
1964). Possible impurities include methyl ether and acetone. If the
methyl chloride is used to make more highly chlorinated methanes by
direct chlorination, any acetone in the methyl chloride can react to
fora chloroketones. The methyl ether can react with chlorine to form
chloroethers.
3.3 Oxychlorination
The overall equation for the oxychlorination of ethylene is:
catalyst
2 CH2 = CH2' + 02 + 4 HC1 2CH2 " ?H2 + 2H20 (65)
Cl Cl
Either air or pure oxygen may be used as the source of oxygen. The
reaction catalyst is commonly copper chloride and sodium or potassium
chloride deposited on alumina or other suitable support media. Other
catalysts that have been described in- the patent literature are rare
earth metal chlorides, sulfate salts, and ferric- chloride (McPherson,
66
-------
1979). The reaction mechanism is still unclear at this time. The
following pathway has been suggested (Rothon, 1972):
CH2 - CH2 + 2 CuCl2 CH2 - CH2 + 2 CuCl (66)
Cl Cl
2 CuCl + 1/2 02 CuOCuCl2 (67)
CuOCuCl2 + 2HC1 2 CuCl2 + H20 (68)
A number of side reactions can occur leading to the formation of
ethyl chloride ('by addition of HC1 to ethylene), polychlorinated
hydrocarbons, and vinyl chloride:
•
CH2 = CH2 + HC1 CH3 - CH2C1 (69)
CH3 - CH2C1 CuCl2 Higher-chlorinated products, e.g., (70)
CH3 - CHC12, CH2C1 - CHC1, also, smaller
products, e.g., CC14 by fragmentation.
heat
5
Cl"
CH2 - CH2 HC1 + CH2 = CHC1 (71)
Cl
Other unsaturated chlorohydrocarbons are also possible, e.g.,
CH3 - CC13 ^I±l HC1 + CH2 = CC12 (72)
Aldehydes can also be formed by reaction of chlorinated and
unchlorinated hydrocarbons with oxygen.
67
-------
R - CH + 1/2 02 R - <2 - H (73)
Chloral (CC13 - C - H) and acetaldehyde (CH3 - C - H)
in particular have been identified as present in the process streams.
The sodium or potassium chloride serves to increase the yield of
ethylene dichloride by inhibiting the formation of ethyl chloride
(Rothon, 1972). Byproduct formation can also be minimized by main-
taining the temperature below 3259C.
The hydrogen chloride used in the oxychlqrination process may
contain acetylene as an impurity as a result of being generated from
downstream dehydrochlorination of ethylene chloride to make vinyl
chloride. The acetylene can react to form highly chlorinated by-
products. Sorae companies selectively hydrogenate the acetylene to
ethylene and ethane in order to minimize this occurrence (McPherson,
1979).
3.4 Dehydrochlorination (Pyrolysis) of Ethylene Dichloride
The dehydrochlorination of ethylene dichloride operates at py-
rolytic (500°C) temperatures to produce vinyl chloride:
CH2 - CH2 CH2 --CHC1 + HC1 (74)
6l Cl heat
The reaction proceeds by a free radical mechanism, e.g.,
Cl Cl Cl
CH- - CH2 CH2C1 - CH + H- Initiation
Cl
CH2C1 - CH2 + H- HC1 + CH2C1 - CH2 Propagation
63
-------
CH2C1 ~ CH2 CH = CH2 + H- Propagation
Cl
R- + R1 R-R Termination
where R-and R'. are any two free radicals.
By-products from the pyrolysis reaction include acetylene,
ethylene, chloroprene, vinylidene chloride, 1,1-dichloroethane,-
chlorofo'na, carbon tetrachloride, 1,1,1-trichloroethane , and other
compounds (McPherson, 1979).
69
-------
4.0 COMPARISON OF CONTAMINANTS AND WASTE DISCHARGES FOR CHLORINATIOH
PROCESSES
In this section, the manufacturing processes described in this
report are compared with respect to the nature of the substances pre-
sent in the process streams and the types of wastes generated.
4.1 Comparison of Chlorination Processes with Respect to Process
Stream Contaminants
The kinds of substances that are likely to be found in the
process streams associated with the manufacture of chlorinated organic
compounds depends on the composition of the feedstock naterials, the
types of reactions that can occur at the operating conditions, and the
nature of product recovery and purification steps. In section 3., the
•
likely process stream constituents for each of the product/processes
were identified on the basis of the known process chemistry. Table IV
lists these process stream constituents by generic name for each
product/process. Table V identifies those reaction products that are-.
on the U.S. Environmental Protection Agency list of priority
pollutants.
All of the desired products of the processes are on the list of
priority pollutants. However, most of the processes produce, as
by-products or contaminants and waste products, several additional
compounds that are on the list. Ethylene dichloride produced by the
direct chlorination of ethylene is an exception. Under the usual
conditions of the reaction it is not expected to produce any by-
products. However, if more severe reaction conditions are imposed
71
-------
I AHI.F I V
LISTIN' OF SUUSTAN"tS PilLStNl IN CIILOMINAIION I'KIICI.SS SVKhANS
llvilrnrlilorl | Onvclilorl- |llrliy<
Proceua Stream Conatl tueiita
Chlor lut
Hydro... cklorld.
Saturated hydrocarbons
llnsaturatcd hydrocarbon*'
Ararat Ic hydrocarbona
A 1 echo la
A Idt-livdea and kcton«a
t-.ihera
Phunola
Carbon dioxide
Carbon monoxide
but unit ed cUlorohydro-
carbona
Cli 1 or liinr r»l
-------
TAIILF. IV )
U)
Proceaa Scream ConetItuenta /
llvdrnclilnrt Oxyclilorl- HrhvJrot
iia i ion I nai Ion I r ln.it I
CMorlnafrd ethers
Cli lor Inai ed pit c no Is
Q,,.no,«.
<:ti loroqulnonea
Cli 1 orod loxina
Cli lor tnarud ptieny lei tiers
Cltlor Inal ed b«iicofuran
Ca rhony 1 «ulf Ide
S.il f>irlc acid
C.....I.-
Hianl Salia
K
M
K
k
«
H
K
K
K
X
K
«
•
H
X
~~
X
X
X
K
.
K
X
X
M
M
K
-------
1AIII.F V
I'HIOHITV POLLUTANTS FKOM'CIILOK INA IKK PHOCLSSES
. . ,
Dlii-ci Milor la.i; in
7
7 Sulni II ni lun
/ Hi-ncllon
Ox ycli Iff! - IK*liv
X
K
K
•
K
/ -C*
/ /
X
X
X
K
K
M
K
X
X
K
X
K
X
X
/ -»
/ ^
«
X
X
K
X
K
K
K
X
K
K
K
K
-
/
-------
TAIIII V «:,il Ion
ltly.Jrcirlil.irl-]
1 M.ll Illll |
Oxyclilnr 1 -
flat Ion
lldiy.lro.liln
r 1 n.i 1 Ion
free Kadlc.il ftetictloa
/ SuliNi Jtut Joti
/ HCACIIon
,
-------
TABLE V (CONCUIDHI)
o\
IHrfct Chloi liuit Ion
Free HuJIc.l
React Ion
//s,ii.«i a,.i i,
/ Heactlui.
Priority Pollutant*
Phenols
Plienol
2 CUlorophenol
2,^ Dl chloropltcaol
Peacachlorophenol
2,4.6 Tclclilorophenol
Met.l.
Copper
Zinc
/ -?
/ tf
/ /
/ ^"
/ />A
/ /
X
X
«
K
X
X
K
•f
/ /
_•_
*
H
X
X
X
X
/ /
It
X
/ /
X
/ ^
-------
e'S«> higher reaction temperatures, free radical reactions will take
place and result in the formation of numerous saturated and unsatu-
rated hydrocarbons of various molecular weights with and without
chlorine attached, this is observed in the case of allyl chloride
production where an olefin, propylene, is chlorinated .under conditions
favorable to free radical formation so that an unsaturated chloro-
hydrocarbon, allyl chloride, is produced. The nature of free radical
reactions is such that polychlorinated hydrocarbons are formed. Free
radical reactions involving olefins also tend to result in the forma-
tion of aromatic compounds, e.g., benzenes and chlorobenzenes (see
section 3.1.3). Also, although the free radical reaction of olefinic
hydrocarbons predominates at the higher temperatures, the addition
reaction proceeds to a limited extent so that saturated chlorinat-d
compounds' will be produced as by-products.
Commercial feedstocks contain impurities. In the case of ethy-
lene, the major impurities are methane and ethane. These saturated
hydrocarbons do not undergo addition reactions and therefore would
pass through the reaction unchanged. However, under conditions favor-
able to free radical formation, they will react to form saturated
chlorohydrocarbons and higher molecular weight saturated hydrocarbons.
Higher molecular weight olefin impurities will react similarly to the
ethylene.
Hydrogen chloride is not a by-product of the addition reaction
but will be formed if free radical reactions take place.
77
-------
The hydrochlorination of methanol to form methyl chloride is also
a. process that is relatively clean, producing a small amount of by-
products. The priority pollutants that are present in the process, in
addition to the product methyl chloride, are heavy metals from the
catalyst used. The methanol feedstock may contain oxygenated organics
as impurities, e.g., methyl ether and acetone. These compounds are
inert in the hydrochlorination process. However, if they are present
in the product methyl chloride, and the methyl chloride is subse-
quently chlorinated to make more highly chlorinated methanes, the
methyl ether and acetone will also chlorinate to form chloromethyl
ethers and chloroketones, respectively.
The direct chlorination of methane and mixed hydrocarbons and the
dehydrochlorination of ethylene dichloride to produce vinyl chloride
are fres radical reactions. The processes produce numerous by-
products with various,degrees of chlorination, various molecular
weights, and various levels of unsaturation. All of the processes
liberate hydrogen chloride as a major product. The chlorination of
the mixed hydrocarbons to produce perchloroethylene and carbon
tetrachloride, and the' dehydrochlorination of ethylene dichloride to
produce vinyl chloride take place at pyrolytic temperatures. The high
temperatures promote the fragmentation of molecules to smaller mole-
cules and unsaturated compounds. Thus, in the chlorination of mixed
\
hydrocarbons, molecules such as octachloropropane break down into
78
-------
carbon tetrachloride and perchloroethylene. In the dehydrochlorina-
ti.on of ethylene dichloride, acetylene, carbon tetrachloride, and
methyl chloride are among the by-products of the reaction. The
unsaturated compounds present in these processes will also have a
tendency to combine to form aromatic compounds as described earlier
for the-high temperature chlorination of propylene.
The chlorination of aromatic compounds by a substitution re-
action results in the formation of each of the possible chlorinated
aromatic compounds and hydrogen chloride. The amount of each of the
chlorinated compounds formed depends on the reaction conditions
(e.g., higher degrees of chlorination are favored by high tempera-
tures) , and high chlorine to aromatic mole ratio. Also some loca-
tions of the aromatic ring may be more susceptible to substitution
than others, (e.g., the presence of the hydroxyl group on the phenol
molecule promotes the substitution of chlorine in an ortho or para
position). The nature- of the aromatic feedstock compound influences
the nature of the side reactions that may occur- Alkyl substituted
benzenes (e.g., toluene, which may be an impurity in benzene), can
be chlorinated on the alkyl group by a free radical mechanism under
conditions that promote free radical formation. This would not be
an expected occurrence under the reaction conditions described in
this report for production of mono and dichlorobenzenes. Chlorinated
phenols tend to form chlorinated benzo-p-dioxins, chlorinated diben-
zofurans , chlorophenoxy chlorophenols, and chlorodiphenyl ethers.
79
-------
The oxychlorination process can result in the formation of a wide
variety of chlorinated hydrocarbons, saturated and unsaturated, and of
various molecular weights. The presence of oxygen in the process also
promotes the formation of oxygenated compounds (e.g., chloral and
acetaldehyde). Some carbon dioxide and carbon monoxide is also
formed.
Product recovery and purification steps in the manufacture of
chlorinated hydrocarbons almost always include a washing step using
water or caustic. Because 'chlorinated compounds could possibly under-
go hydrolysis reactions, particularly at elevated temperatures, the
washing step can cause the formation of additional contaminants..
Crude chlorobenzene,. for example, is washed with caustic. 1,2,4-
Trichlorobenzene that may be present in the crude stream can react
with caustic to. form a chlorinated phenolic compound. Less chlori-
nated benzenes requi're more severe conditions (e.g., higher tempera-
tures) to form phenols.
Several of the processes use catalysts. In some cases the cata-
lyst is in a fixed or fluidized bed and is only minimally present as a
contaminant in the process streams (e.g., the copper catalyst in oxy-
chlorination of ethylene).. In other cases, the catalyst is spent dur-
ing the process and must be separated from the reactor product stream
(e.g., ferric chloride in chlorobenzene manufacture). The catalyst in
this case presents a continuous disposal problem.
80
-------
Additional substances may be found in process or waste streams
as the result of the use of additives to stabilize the product (e.g.,
phenol may be added to vinyl chloride to inhibit polymerization during
storage).
The chlorine and caustic used in the process may contain contami-
nants that end up-in process and/or waste streams. Mercury can be a
contaminant if the chlorine and caustic were derived from a mercury
cell. Carbon tetrachloride and other chlorinated organic substances
may be present as contaminants in chlorine made with graphite anodes
(Edwards, 1968). Metallic anodes do not cause such impurities
(Lowenheim and Moran, 1975).
4.2 Pollutant Discharges from Chlorination Processes
4.2.1 Emissions to the Atmosphere
The direct chlorination processes for chloromethanes, perchloro-
ethylene and carbon tetrachloride, vinyl chloride, allyl chloride,
chlorophenol, and chlorobenzene produce hydrogen chloride gas as a "- >
aajor by-product. The hydrogen chloride gas is usually scrubbed with
water and recovered as a water solution for subsequent sale. The
hydrogen chloride gas contains some non-water-soluble and nonconden-
sible gases which will be'vented from the scrubber system. This emis-
sion will usually contain residual low-molecular weight hydrocarbons,
unreacted chlorine, hydrogen chloride, and inert gases and air that
enter with the raw materials or become entrained during processing ?
The oxychlorination process has a gaseous emission due to the
use of air or oxygen in the process. When air is used, nitrogen from
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the air straam is vented and will carry residual lew molecular weight
hydrocarbons. When oxygen is used, the unreacted oxygen is recycled
to the reactor; however, a small, portion of this recycle stream is
continuously purged to prevent a buildup of inerts. This stream will
also carry residual low molecular weight hydrocarbons; however, since
the stream volume is smaller than for the air based process, the pol-
lutant discharge is correspondingly less.
Emissions to the air also occur from distillation column vents
and from storage tanks. The manufacture of pentachlorophenol may
result in particulate emissions during the processing and packaging of
solid pentachlorophenol.
4.2.2 Wastewater Discharges
A caustic and/or water-washing step is used to remove catalyst
and/or impurities from process streams in the processes for man-
ufacture of chloromethanes, allyl chloride,'et'hylene dichloride (both
processes), vinyl chloride, methyl chloride bv hydrochlorination. and
chlorobenzenes. Thus, in these processes a spent caustic and waste
water will be generated which will contain dissolved organics, metal
salts from catalysts, sodium chloride, and chlorine as hypochlorite.
In addition, hydrolysis products of the chlorohydrocarbons will be
present, such as phenols in the chlorobenzene wash, and methanol and
formic acid in the chloromethane wash.
An intermittent wastewater discharge is likely to occur from the
chlorination processes which produce hydrogen chloride as a
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by-product. During start-up, shut down, or process upsets, an off-
grade hydrochloric acid solution may be produced which is not saleable
and must be disposed of. • The hydrochloric acid is often neutralized
by passage through a bed of•limestone, oyster shells, clam shells, or
I
in a neutralization system employing lime as the neutralizing reagent
and discharged. The neutralized effluent will contain dissolved salts
of the heavy metal impurities in the neutralizing reagent [e.g.,
FeCl3, PbCl2, AlCla].
4.2.3 Liauid Orzanic Wastes
A distillation residue consisting of polychlorinated compounds
and high molecular weight organic compounds is produced in all pro-
»
cesses except the hydrochlorination of methanol. The direct chlo-
rination of ethylene should not produce any appreciable amount of
residue unless the reaction temperature goes out of control and some
free radical reactions occur- The distillation residue from penta-
chlorophenol production will contain spent catalyst.
4.2.4 Solid Waste and Sludges
The processes involving catalysts are likely to generate solid
wastes and/or sludges that must be disposed of. In the case of the
direct chlorination of ethylene and the direct chlorination of ben-
zene, the catalyst is washed from the product with caustic. Treatment
of the spent caustic will produce a sludge containing metal salts.
The catalyst for the oxychlorination process and the hydrochlorination
process is in a fixed bed. Some of the catalyst may be carried out in
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the reactor product stream as a result of attrition and will end up in
the subsequent caustic wash streams. The catalyst bed does, however,
have a finite life and must be replaced periodically. The spent cata-
lyst must then be disposed of.
4.2.5 Other Wastes
»
Gulfuric acid is used to dry process streams in the manufacturing
processes for methyl chloride by hydrochlorinatioa and for chlorome-
thanes by direct chlorination. A spent acid stream containing organic
compounds is thus generated by these processes.
Periodic cleaning of process equipment also results in a resi-
»
due that must be disposed of. The reactors in the allyl chloride
process must be cleaned of an accumulation of carbonaceous residue
biweekly. Other processes are .likely to generate a similar residue.
although the rate of accumulation of such residue varies from process
.!»»»• >^V3>">'- . .
to process. Distillation equipment is also likely to accumulate such
residues, particularly in the reboiler and bottom section of the col-
umn.
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5.0 CONCLUSIONS
This study of f0ur unit processes used to produce chlorinated
hydrocarbons, shows that the unit process of direct chlorination can
be subdivided into three distinct groups with regard to the types of
by-products and/or contaminants present in the process and waste
streams-. The groupings, based on the reaction type, are as follows:
• Free radical reactions
• Electrophilic aromatic substitution reaction
• Addition reaction to a double bond
The high temperature, uncatalyzed dehydrochlorination unit process is
a free radical reaction. By-products and/or contaminants in the
process and waste streams from the manufacture of products by
uncatalyzed, high temperature dehydrochlorination are similar t« those
produced in the free radical direct chlorination unit process.
The processes of hydrochlorination and oxychlorination each have
their own unique characteristics with regard to byproduct and con-
taminant generation.
The characteristics of each unit process and subgroup of a unit
process is described below.
5.1' Direct Chlorination and Dehydrochlorination
5.1.1 Free Radical Reactions including Dehydrochlorination
The compounds discussed in this report that are produced by a
free radical reaction are chloromethanes, carbon tetrachloride,
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perchloroethylene, allyl chloride, and vinyl chloride. In free radi-
cal chlorination processes, side reactions occur Chat can result in
the formation of a wide assortment of chlorinated and unchlorinated
hydrocarbons. The amount of any particular compound that will be
formed is determined by the reaction conditions. Polychlorinated com-
pounds and high molecular weight compounds are favored by increased
reaction temperature; however, at pyrolytic temperatures, cracking
will occur producing smaller molecules, unsaturated compounds, and
aromatic compounds. The major by-product of free radical chlorina-
tions is hydrogen chloride. For each chlorine atom added to a hydro-
carbon molecule by a free radical reaction, one molecule of hydrogen
chloride is produced. The hydrogen chloride may be absorbed in water
to make a commercial grade muriatic (hydrochloric) acid, collected as
•
an anhydrous product, used directly in an associated .process such as
hydrochlorination or oxychlorination, or neutralized and disposed of
with wastewater.
Waste discharges from free radical chlorinations usually include
an inert gas purge stream from the hydrogen chloride recovery opera-
tion; a spent caustic and/or wastewater stream from washing steps
designed to remove acid and soluble impurities from process streams; a
speit sulfuric acid waste from process stream drying operations; and a
distillation column residue. Accumulations of carbonaceous material
from reactors and distillation column reboilers are periodical!/ re-
moved and disposed of. A wastewater stream may also be produced as a
result of the need to dispose of unmarketable hydrochloric acid.
36
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The inert gas purge stream may contain unreacted feedstock
materials (low molecular weight hydrocarbons and chlorine), hydrogen
chloride, and low molecular weight chlorohydrocarbons. The spent
caustic and wastewater may contain hydrocarbons, chlorohydrocarbons,
chloride salts, and products of the hydrolysis of chlorohydrocarbons
(e.g., methanol, formic acid, phenols). The neutralized waste hydro-
chloric acid stream may contain salts of heavy metals. The spent acid
may contain hydrocarbons and chlorohydrocarbons. The distillation
column residue will consist primarily Of high molecular weight and •
polychlorinated hydrocarbons.
5.1.2 Eleetrophilic Aromatic Substitution Reactions
The ring chlorination of phenol and benzene are electrophilic
aromatic substitution reactions. The ring chlorination of aromatic
compounds is promoted by a Lewis acid catalyst and relatively low
temperatures. All possible ring-chlorinated compounds of the feed
compound are likely to be present in the process and waste streams,
although the quantity of any particular compound depends on the
.reaction conditions. Hydrogen chloride is the major by-product of
this process. For each atom of chlorine added to the aromatic ring,
one molecule of hydrogen chloride is formed. Substituent groups on
the feedstock aromatic compound may participate in reactions that form
additional byproducts. Chlorinated phenols, for example, form
benzofurans, quinones, and dioxins.
Waste streams from ring chlorination of aromatic compounds
usually include an inert gas purge stream from the hydrogen chloride
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recovery operation, wastewater from a caustic wash or acid neutrali-
zation operation, and_a distillation column residue. Accumulations of
carbonaceous material from reactors and distillation column reboilers
may also be periodically removed and disposed of. A wastewater stream
nay also be^produced as a result, of the need to_dispase__of__unmarket-
able hydrochloric acid.
The -inert gas purge stream may contain unreacted aromatic hy-
drocarbons, chlorine, hydrogen chloride, and volatile chlorinated
aromatic compounds. The wastewater will contain some of these same
compounds, plus inorganic salts from neutralization and/or spent cata-
lyst residue, and products of hydrolysis of the chlorinated hydrocar-
bons, e.g., phenols, and quinones. The neutralized waste hydrochloric
acid stream may contain salts of heavy metals. The distillation
column residue will contain polychlorinated aromatic compounds, and
other reaction side products (e.g., residues from chlorophenol manu-
facture may contain benzofurans and dioxins). It may also contain
catalyst residue not previously removed.
5.1.3 Addition Reaction to a Double Bond
The direct chlorination of ethylene is the addition process de-
scribed in this report. In the addition reaction, two chlorine atoms
add to the olefin compound at the double bond to form a saturated
chlorohydrocarbon. The addition reaction occurs under relatively mild
conditions in the presence of a Lewis acid catalyst and does not re-
sult in the formation of by-products. However, a spent catalyst waste
88
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is generated in the process. At high temperatures, olefins can react
with chlorine to form unsaturated chlorides by a free radical reac-
tion. Both the addition reaction and the free radical reaction will
occur at the high temperatures, with the free radical reaction be-
coming increasingly dominant as the temperature increases. The main
waste discharge from this process is a spent caustic solution which
will contain hydrocarbons, chlorohydrocarbons, hydrolysis products of
*
chlorohydrocarbons, and spent catalyst residues.
5.2 Hydrochlorination
The hydrochlorination of methanol with hydrogen chloride in the
presence of a catalyst (e.g., zinc chloride), is described in this ee-
port. The only by-product of this reaction is water;
•
The wastes from this process include the water generated by the
reaction, and a spent caustic solution which was used to remove resi-
'HffifT'-actcP'an'd impurities from the product stream. The waste will
contain some feedstock and product, hydrolysis products of the chloro-
hydrocarbon product, and probably some catalyst residues. The cata-
lyst in this process does not require continuous renewal; however, it
is anticipated that it will be replaced periodically, and therefore
there will periodically be a spent catalyst waste from the process.
5.3 Oxychlorination
The oxychlorination of ethylene to make ethylene dichloride is
described in this report. The by-products of the oxychlorination of
olefins are primarily chlorinated derivatives of the olefin and their
39
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breakdown products, and oxygenated hydrocarbons and chlorohydrocarbons
sucTi as acetaldehyde and chloral. Some carbon monoxide and carbon
dioxide is also produced.
Waste discharges from this process are a gaseous emission of
inert gases, a spent caustic waste, and a distillation column residue.
The amount of gaseous emission depends on whether air or oxygen
is used. The inert gas will contain some volatile hydrocarbons and
chlorohydrocarbons, and unreacted hydrogen chloride. The spent
caustic will contain organics including aldehydes and chlorinated
aldehydes, some catalyst residue, and hydrolysis products of the
chlorinated hydrocarbons. The distillation column residue will con-
sist primarily of polychlorinated hydrocarbon derivatives of the
feedstock.
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