Note: Descriptions are shown in the official language in which they were submitted.
107~Z38
PU~GING OF TARS AND CARBON FROM
CHLORINATED HYDROCARBON EFFLUENT
This invention relates to the treatment of an
effluent containing chlorinated hydrocarbons, and more particu-
larly, to a new and improved process for purging tars and carbon
from an effluent containing chlorinated hydrocarbons.
In the chlorination of a hydrocarbon, or partially
chlorinated hydrocarbon, the chlorination effluent generally
includes tars and carbon which are carried into the separation
and recovery system for separating and recovering the various
components of the chlorination effluent. In such processes,
the tar and carbon materials may cause difficulties in the
separation and recovery system. In addition, processing steps
must be effected to purge the system of such tars and carbon.
In accordance with the present invention, tars and
carbon are separated from an effluent containing chlorinated
hydrocarbons, withdrawn from a melt chlorination and/or dehydro-
chlorination reaction zone, and the separated tars and carbon
are directly contacted with a molten mixture, containing the
higher and lower valent chlorides of a multivalent metal and the
oxychloride of the metal to effect oxidation of the tars and
carbon. In this manner, the tars and carbon are effectively
purged from the system without being passed through the separa-
tion and recovery system for recovering the various chlorinated
hydrocarbons.
Thus, in accordance with the present teachings,
an improved process is provided for producing a chlorinated
hydrocarbon by contacting in a chlorinated hydrocarbon production
zone a member selected from the group consisting of a hydrocarbon,
chlorinated hydrocarbon and mixtures thereof with a molten salt
mixture containing the higher and lower valent chlorides of a
multivalent metal selected from the group consisting of copper,
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1071Z38
iron, cobalt, chromium and manganese and the oxychloride of the
multivalent metals. The process comprises withdrawing from the
chlorinated hydrocarbon production zone a gaseous chlorinated
hydrocarbon effluent which contains carbon and tars, cooling the
effluent to condense a portion of the chlorinated hydrocarbon
with the condensed portion containing carbon and tars present in
the effluent and introducing at least a portion of the condensed
chlorinated hydrocarbon into the chlorinated hydrocarbon production
zone to contact the molten salt mixture to oxidize the carbon
and tars.
The effluent, containing chlorinated hydrocarbons,
carbon and tars, is generally one produced by contacting, in
a chlorination (oxychlorination) zone, a hydrocarbon or partially
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chlorinated hydrocarbon with chlorine and/or hydrogen chloride,
and a melt containing the higher and lower valent chlorides
of a multivalent metal and the oxychloride of the multivalent
metal. Accordingly, the separated tars and carbon may be
conveniently oxidized by introducing the separated tars and
carbon into the chlorination ~oxychlorination) reaction zone.
It is to be understood, however, that oxidation of separated
tars and carbon by direct contact with the hereinabove
described molten salt could be effected in a separate reaction
zone designed and operated for the purpose of oxidizing such
separated tars or in a reaction zone other than the chlorination
reaction zone, in which there is present the hereinabove
described molten salt,
The hydrocarbon or partially chlorinated hydrocarbon
employed as feed to the chlorination reaction zone may be:
an aromatic hydrocarbon, such as benzene; an aliphatic hydro-
carbon (gaturated or olefinically unsaturated), preferably
a Cl to C4 aliphatic hydrocarbon; or a partially chlorinated
derivative of such aromatic and aliphatic hydrocarbons,
The most preferred feeds are: ethane, ethylene, methane
and the partially chlorinated C2 hydrocarbons.
The process of the present invention is also
applicable to the treatment of an effluent containing chlorinated
hydrocarbons produced by the dehydrochlorination of a
chlorinated hydrocarbon by direct contact with a molten salt
mixture, containing the higher and lower valent chlorides of
a multivalent metal, which may further include the oxychloride
of the multivalent metal.
The chlorides of the multivalent metals used in forming
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the melt employed in the present invention are generally the
chlorides of manganese, iron, copper, cobalt or chromium,
preferably copper. The molten mixture generally also includes
a metal salt melting point depressant which is non-volatile
and resistant to oxygen at the process conditions, such as
chloride of a univalent metal; i.e., a metal having only one
positive valence state, to provide a salt mixture having
a reduced melting point. The univalent metal chlorides are
preferably alkali metal chlorides, such as potassium and lithium
chloride, in particular, but it is to be understood that other
metal chlorides and mixtures thereof, such as the heavy
metal chlorides; i.e, heavier than copper, of Groups I, II,
III and IV of the Periodic Table; e.g., zinc, silver and thallium
chloride, may also be employed. A preferred composition is
formed from copper chlorides and potassium chloride with the
potassium chlorlde comprising from about 20% to about 40%, by
weight, of the composition with the remainder being copper
chlorides.
In accordance with the present invention, the effluent
withdrawn from the melt chlorination zone is at a temperature
from about 700 F to about 1200 F, with the specific temperature
being dependent upon the feed being chlorinated and the products
desired. The chlorination effluent, containing tars and
carbon, is then cooled to a temperature at which a portion of
the chlorinated hydrocarbon stream, including tars and carbon,
i8 condensed. In general, the chlorinated hydrocarbon effluent
i8 cooled to a temperature of from about 100 F to about 300F,
preferably a temperature of from about 150F to about 280F,
and mo9t preferably, a temperature of from about 180F. to
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about 240F, at which temperature a portion of the chlorinated
hydrocarbon stream, including the tars and carbon, is condensed.
In general, such condensation is effected at a pressure from
about 0 to about lO0 psig, preferably from about 25 to about
60 psig. The cooling of the effluent to effect such condensation
is preferably effected by direct contact quenching with a suit-
able quench liquid, such as a chlorinated hydrocarbon (the
chlorinated hydrocarbon quench is preferably one or more of the
chlorinated hydrocarbons recovered from the effluent).
The chlorinated hydrocarbon effluent condensate,
containing tars and carbon, is then oxidized by direct contact
with a molten salt mixture, containing the higher and lower
valent chlorides of a multivalent metal and the oxychloride
of the multivalent metal with the oxidation as hereinabove des-
cribed, preferably being effected by introducing the condensate
into the melt chlorination zone. The oxidation of the separated
tars and carbon is effected at a temperature of at least 700F,
generally a temperature from 700 F to 1200F, and preferably
a temperature from 800 F to 900F. The tars and carbon are
combusted to carbon oxide(s) and water, and any chlorinated
hydrocarbons present release chloride values as hydrogen
chloride and/or chlorine.
In some cases, the condensate separated from the
chlorination effluent, containing separated tars and carbon,
is introduced into a stripping zone to strip chlorinated hydro-
carbon therefrom, and provide a bottom of tar and carbon dis-
persed in a sufficient amount of chlorinated hydrocarbon to
maintain a flowable stream. In this manner, the total
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amount of chlorinated hydrocarbon passed to the tar and
carbon oxidation steps can be controlled.
The invention will be further described with respect
to the accompanying drawing which is a simplified schematic
flow diagram of a process for producing vinyl chloride which
incorporates the process of the present invention.
Referring now to the drawing, a molten chloride salt,
such as a mixture of potassium chloride, cupric and cuprous
chloride in line 201 is introduced into the top of an oxidation -
vessel 202, maintained at a pressure from about 1 to about 20
atm. and at a temperature of from 600 F to 900 F. A compressed
oxygen-containing gas, such as air, introduced through line 203
countercurrently contacts the descending salt to produce copper
oxychloride. The feed to reactor 202 may also include chlorine
and/or hydrogen chloride (aqueous and/or gaseous) recovered
in the process and introduced into reactor 202 to recover
chlorine values by generation of cupric chloride.
A gaseous stream is withdrawn, from reactor 202 through
line 211 for further processing as required. The molten salt,
now containing copper oxychloride, is withdrawn from the bottom
of vessel 202 through line 321 and introduced into the top
of the reaction vessel 233. The reaction vessel 233 is divided
into two reaction sections 233a and 233b, with reaction section
233a functioning as a chlorination Rection and section 233b as
a dehydrochlorination section. The molten salt in line 234
is introduced into both sections 233a and 233b.
Fresh feed chlorine and/or hydrogen chloride ls
introduced into the bottom of section 233a through line 241,
and fre9h feed ethane and/or ethylene, preferably ethane is
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107~238
introduced in line 242 and is combined with a recycle stream
comprised of ethyl chloride, ethane and ethylene in line 245
for introduction into the bottom of reaction section 233a.
A liquid chlorinated hydrocarbon stream, containing tars and
carbon separated from the chlorination-dehydrochlorination
effluent, obtained as hereinafter described, is also introduced
into section 233a through line 244.
The reaction section 233a is operated at a
temperature of 700 F to 1200F and a pressure of from 1 to 20
atm. to effect chlorination, dehydrogenation and dehydrochlorin-
ation of the fresh feed and recycle by direct countercurrent
contact of the feed and recycle with the descending molten salt.
Recycle dichloroethane, preferably 1,2-dichloroethane,
in line 250 is introduced into reaction section 233b and is
countercurrently contacted with the molten salt to effect
dehydrochlorination thereof to vinyl chloride.
The effluents from each of the sections 233a and
233b, each containing equilibrium amounts of hydrogen chloride,
are combined in the top portion of reactor 233.
An effluent gas, containing vinyl chloride, ethyl
chloride, dichloroethane, other chlorinated hydrocarbons (one
or more of the following: dichloroethylenes, trichloroethylene,
tetrachloroethylene, trichloroethane and tetrachloroethane),
ethane, ethylene, water vapor, some hydrogen chloride, (the
ma~or portion of the hydrogen chloride produced from dichloro-
ethane reacts with the oxychloride of the salt) carbon and
tars, rlses into the top of the vessel 233 wherein the effluent
107~Z38
gas is directly contacted with a spray of quench liquid, in
particular one or more of the chlorinated hydrocarbons produced
in reactor 233, introduced through line 246 to cool the effluent
gas and thereby eliminate any vaporized and entrained salts
therefrom. The effluent gas is cooled to a temperature at which
the salt mixture remains in molten salt form to permit the
molten salt to flow back into the reactor 233,
The effluent gas, now containing vaporized quench
liquid, is withdrawn from vessel 233 through line 247 and intro-
duced into a quench vessel 248 wherein the effluent gas iscontacted with chlorinated hydrocarbon quench liquid in line
249 to further cool the gas and thereby separate carbon, tars
and any remainin~ entrained salts. The gas is cooled to a
temperature at which tars and carbon are separated from the
effluent, with essentially no aqueous hydrogen chloride being
condensed therefrom. A liquid chlorinated hydrocarbon
stream,containing separated tars and carbon is recycled to reactor
233 through line 244, wherein the tars are purged from the system
by oxidation. Alternatively, in order to reduce the quantity
of chlorinated hydrocarbon returned to reactor 233, all or a
portion of the condensate in line 244 is introduced through
line 272 into a stripping zone 271 to strip chlorinated
hydrocarbons therefrom and provide a flowable bottoms con-
taining separated carbon and tar, which is introduced into
reactor 233 through line~ 273 and 244. The stripped overhead
in line 274 is combined in line 251 with gaseous effluent from
quench vessel 248.
Molten salt is withdrawn from the bottom of reactor 233
~07123~
through line 201 and introduced into vessel 202, for oxidation
thereof, as hereinabove described.
The reaction effluent in line 251 is introduced into a
separation and recovery zone 261 to separate and recover various
components thereof. In particular, hydrogen chloride may be re-
covered from the effluent as aqueous hydrogen chloride, and re-
cycled to the oxidation reactor 202 to recover the chlorine values.
Heavier chlorinated hydrocarbons are also recovered from the
effluent and employed as quench liquid in lines 246 and 249.
Vinyl chloride is recovered as reaction product from
separation and recovery section 261. Ethane, ethylene chloride -
recovered in separation and recovery section 261 are recycled to
reactor 233 through line 245 for ultimate conversion to vinyl
chloride. Dichloroethane, prefer-ably only 1,2-dichloroethane,
produced in chlorination section 233a is recovered in separation
and recovery section 261 and recycled through line 25 to section
233b.
Other chlorinated hydrocarbons comprised of one or more
of the following chlorinated hydrocarbons: dichloroethylenes,
trichloroethylene, tetrachloroethylene, trichloroethanes and tetra-
chloroethanes recovered in separation and recover section 261 can
be combusted, with the gaseous chlorine values of the combustion
effluent being recovered in oxidation reactor 202.
Although the present invention has been particularly des-
cribed with respect to the production of vinyl chloride in asystem employing two reactors, the chlorination and dehydrochlor-
ination could be effected in a single zone. Similarly, separate
reactors could be used for effecting the dehydrochlorination and
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chlorination reactions. Furthermore, the effluents from de-
hydrochlorination and chlorination may be separately quenched
to separate tars and carbon.
Similarly, the separated tars and carbon could be directly
contacted with molten salt in a separate reactor designed and
operated for such a purpose.
As a further modification, separated tars and carbon could
be combusted in the oxidation vessel.
It is also to be understood that the present invention is
also applicable to the chlorination of hydrocarbons other than
ethane and/or ethylene. Thus, for example, the hereinabove des-
cribed embodiment is also suitable for the chlorination of methane,
with reaction 233 being comprised of a single reaction section
for chlorination (oxychlorination) of fresh methane feed, recycle
methane and chlorinated methane recycle, if any.
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