Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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~043;~59
DEHYOR(~CHI.ORINATION OF 1, 2 DIC]-ILOROETJ~ANE
This invention relates to the production of vinyl chloride,
and more particularly, to improved dehydrochlorination of 1, 2 -dichlo-
roethane to vinyl chloride.
A process for dehydrochlorinating 1,2-dichloroethane to vinyl
chloride by the use of molten salts is known in the art. In accordance
with such a process, 1, 2 -dichloroethane is dehydrochlorinated by direct
contact with a melt containing the higher and lower valent forms of a
multivalent metal chloride, with the meU optionally including the
corresponding oxychloride, at high conversion and higher selectivity.
I0 It has been recently found that in the case where the melt includes the
oxychloride, the selectivity to vinyl chloride is lower than the case in
which the melt does not include the oxychloride. Furthermore, in many
cases, the 1, 2-dichloroethane employed as feed is recovered from the
chlorination effluent produced in an overall process for the production
of vinyl chloride, as described in British Patent Specification No.
1,213,202. The recovered 1,2-dichloroethane may include unsaturated
chlorinated hydrocarbons, such as trichloroethylene, which may
function as dehydrochlorination inhibitors and thereby decrease select-
Lvity to vinyl chloride.
In accordance with the present invention, 1, 2 -dichloro -
ethane is dehydrochlorinated by direct contact with a molten salt con-
taining a multivalent metal chloride in its higher and lower valence
state the contacting being effected in the presence of ethane in that the
presence of ethane has been found to improve the overall selectivity
to vinyl chl-)ride.
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More particularly, the ethane is prescnt in an amount to
provide a weight ratio of ethane to 1,2-dichloroethane from 0.0l:l to
0.15:1, and preferably from 0. 0l5:l to O. lO:l. The use of ethane in
amounts lower than those hereinabove described does not provide the
desired improvement in selectivity to vinyl chloride, and the use of
ethane in amounts greater than those hereinabove described results
in a decrease in vinyl chloride selectivity and/or 1, 2 -dichloroethane
convers ion.
Although the present invention is not bound by any theory,
it is believed that the addition of ethane functions to reduce substitutive
chlorination of dichloroethane which results in an increase selectivity
to vinyl chloride. It is further believed that the addition of ethane
functions, in part, to inhibit the increase of cupric chloride concentra-
tion of the melt through the dehydrochlorination reaction zone which
I5 could result from interaction between any oxychloride present in the
melt and hydrogen chloride released during the dehydrochlorination.
The melts employed in the dehydrochlorination include the
higher and lower valent forms of a chloride of a multivalent metal; i, e.,
a metal having more than one positive valence state, such as manga-
nese, iron, copper, cobalt and chromium, preferably copper. In the
cases of higher melting multivalent metal chlorides, such as copper
chlorides, a metal salt melting point depressant which is non-volatile
and resistant to the action of oxygen at the process conditions, such as
a chloride of a univalent metal; i. e., a metal having only one positive
valence state, is added to the multivalent metal chloride to form a
molten salt mixture having a reduced melting point. The univalent
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metal chlorides, are preferably alkali metal chlorides, such as potas-
sium and lithium chlorides 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. The metal chloride meLting point depressant is added in an
amount sufficient to maintain the salt mixture as a melt at the reaction
temperatures, and is generally added in an amount sufficient to adjust
the melting point of the molten salt mixture to a temperature of below
500DF. In the case of a salt mixture of copper chlorides and potassium
chloride, the composition of the melt ranges between 20~1C to 40~c, pre-
ferably 30~1c, by weight, potassium chloride, wUh the remainder being
copper chlorides. It is to be understood, however, that in some cases
the catalyst melt may have a melting point higher than 500F, provided
the catalyst remains in the form of the melt throughout the processing
steps. It is further to be understood that the melt may contain a mix-
ture of multivalent metal chlorides or other reaction promoters. It
is also to be understood that in some cases, metal chloride may be
maintained in molten form without a melting point depressant.
In accordance with a preferred embodiment, the molten
salt used in the dehydrochlorination further includes the oxychloride
of the multivalent metal in that the oxychloride reacts with the hydro-
gen chloride liberated during the dehydrochlorination, as represented
by the following equation using copper oxychloride as a representative
2 5 oxychloride:
(1) Cu O. C~ C12 ~ IICl ~ 2 Cu ~'~2 + lI2O
104;~;~S9
In this manner, the effluent will have reduced amounts of hydrogen
chloride (the effluent includes equilibrium amounts of hydrogen chloride~.
The oxychloride is preferably present in an amount to react with essen-
tially all of the hydrogen chloride produced in the dehydrochlorination.
The ethane which is present during the dehydrochlorination
reaction may be chlorinated in part or in its entirety to chlorinated
hydrocarbons (vinyl chloride, ethyl chloride, dichloroethanes, etc. )
as a result of the chlorinating abilUy of the molten salt.
The dehydrochlorination is generally effected at tempera-
tures from 700F to 1200F, preferably from 750F to 1000F, although
the temperatures could be as low as 575F, and at pressures from 1
to 20 atmospheres. The contacting of feed and melt is generally effec-
ted in a countercurrent fashion, preferably with the feed as a continuous
vapor phase, at residence times from 1 to 60 seconds, although longer
residence times may be employed.
The dehydrochlorination process of the present invention
is preferably employed as part of an overall process for producing
vinyl chloride from ethane and/or ethylene by the use of molten salts.
More particularly, ethane and/or ethylene is contacted with a melt
containing the multivalent metal chloride in its higher and lower valence
state, with the molten salt mixture preferably also containing the oxy-
chloride of the metal, with the contacting preferably also being effected
with hydrogen chloride and/or chlorine to produce an effluent containing
vinyl chtoride and 1,2-dichloroethane, The vinyl chloride is recovered
as product and the 1, 2-dichloroethane is dehydrochlorinated by direct
contact u~ 'h the molten salt containing the higher and lower valent
~043359
metal chloride, and preferably also including the oxychloride of the
multivalent metal, in the presence of ethane as hereinabove described,
to produce a dehydrochlorination effluent containing vinyl chloride.
In accordance with a preferreù embodiment of the present
invention, a molten salt mixture containing copper chlorides and a
melting point depressant (preferably in an amount from 20 to 40 weight
percent of the melt with the melting point depressant being preferably
potassium chloride, with the remainder of the melt being copper chlo-
rides) is contacted in a first reaction zone with molecular oxygen to
produce copper oxychloride. The cupric chloride content of the melt
is generally at least 16~c, by weight, of the melt, and generally from
18~c to 50~c, by weight, in order to provide sufficient cupric chloride
for the subsequent chlorination and dehydrochlorination reactions. It
is to be understood, however, that lower amounts of cupric chloride
may also be employed by increasing salt circulation rates and residence
times. As a result of the various reactions which occur during the
chlorination and dehydrochlorination steps, the cupric chloride content
of the melt does not significantly vary through the various reaction
zones. The molecular oxygen is preferably introduced in an amount,
and at a rate, to provide a molten salt mixture containing from 0. 5~1c
to 5. 5~c, preferably from 15~ to 3~c, all by weight, of copper oxychloride.
It is to be understood that minor amounts of chlorine and/or hydrogen
chloride could also be introduced into the first reaction zone, but in
accordance with this preferred embodiment, the major portion of the
chlorine and/or hydrogen chloride is added to the chlorination zone.
The m?~ten salt mixture, now containing copper oxychLoridc,
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is circulated to a second reaction zone (chlorination zone) wherein the
molten salt is contacted with ethane and/or ethylene, preferably
ethane, and chlorine and/or hydrogen chloride as fresh feed, in
addition to recycle unconverted ethane (if employed as feed) and
recycle ethyl chloride and unreacted ethylene or that generated as
reaction intermediate. The recycle, may also include l,l-dichloro-
ethane and/or dichloroethylene.
The effluent from the second zone includes vinyl chloride,
1,2-dichloroethane, ethyl chloride, ethane, ethylene, and heavier
chlorinated hydrocarbons; for example, one or more of the following:
trichloroethylene, tetrachloroethylene, trichloroethanes and tetra-
- chloroethane. The effluent also includes water vapor and equilibrium
amounts of hydrogen chloride.
The reaction effluent is passed to a separation and reco-
very zone wherein various components are recovered. Ethyl chloride,
ethane and ethylene are recovered for ultimate cor~ersion to vinyl
chloride. The recovered 1,2-dichloroethane is introduced into a dehy-
drochlorination zone (third reaction %one) wherein the 1,2-dichloro-
ethane is contacted with molten salt from the first (the salt includes
oxychloride?, the second zone or both zones in the presence of ethane
to effect dehydrochlorination of 1,2-dichloroethane to vinyl chloride.
As a result of the chlorinating ability of the molten salt all or a por-
tion of the ethane is converted to chlorinated products, as dcscribed
with reference to the second reaction zone, The effluent from the
dehydrochlorination reaction zone is introduccd into a separation and
recovery zcne ~D recover vinyl chloride r eaction product and other
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components for ultimate utilization thereof for the production of vinyl
chlor ide .
The ethane utilized in tlle dehydrochlorination reaction
zone may be either fresh feed or recycle ethane recovered from the
chlorination (second reaction zone) effluent or a combination thereof.
It is to be understood that the source of ethane is immaterial to the
present invention, provided the ethane is employed for the dehydro-
chlorination as hereinabove described.
The chlorination in the presence of the melt (second
reaction zone) may be effected at conditions, as hereinabove described
with reference to the dehydrochlorination in the presence of molten
saU. The production of oxychloride is generally effected at temper-
atures of 600DF to 900DF, although higher temperatures may be
employed. The preferred oxychloride production temperature is
from 750F to 870F,
The overall process for producing vinyl chloride from
ethane and/or ethylene by the use of molten salts, including dehydro-
chlorination of 1, 2-dichloroethane by the use of molten salts, is
described in British Patent Specification No. 1, 213, 202 . The present
invention is an improvement with respect to such a process in that
dehydrochlorination selectivity to vinyl chloride is improved by use
of ethane in the dehydrochlorination zone, as hereinabove described.
Although the invention is particularly applicable to an
embodiment in which oxychloride is present in the melt employed in
the dehydrochlorination reaction zone, the present invention may
also be employed in cases where there is no oxyctlloride present in
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that the 1,2-dichLo!~oethane feed to the dehydrochlorination reaction
zone, in SUCil a case, -may include a àehydrochlorination inhibitor,
such as trichloroethylene, The addition of ethane to the dehydrochlo-
rination reaction zone, as hereinabove described, minimizes the
adverse effect on selectivity to vinyl chloride which could result from
the presence of a dehydrochlorination inhibitor.
The invention will be further described with respect to the
following example.
EXAMPLE I
A molten salt comprised of 17.1 wt. ~c cupric chloride; 51. 8
wt.~c cuprous chloride; 0.2 wt.~c copper oxychloride; and 30.9 wt.%
potassium chloride is countercurrently contacted with a feed comprised
of 90. 6 mole ~c of a l, 2-dichloroethane blend and 9. 4 mole percent of
ethane, at a temperature of 849~F and a residence time of 8. 7 seccnds.
The 1,2-dichloroethane blend has the following composition:
DCE blend mole ~'lc
1, l, l C2H3Cl3 0. 6
CCl4 l' 3
l,2 C2H4Cl2 78. 3
C2HCl3 11.1
1,1, 2 C2 H3C13 4' 5
C2C14 4. 2
100. 0
The vinyl chloride selectivity is 90. 4 mole percent, and the l, 2-
dichloroethane conversion is 80 mole percent, notwithstanding the
presence of oxychloride intlle melt and the use of a high propor~ion
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of trichloroetllylene in the feed which would be expected to inhibit
dehydrochlorination.
EXAMP LE II
~ molten salt comprised of 16. 5 wt. ~c cupric chloride;
52. 6 wt. ~ cuprous chloride; 0. 2 wt. '~c copper oxychloride; and 30. 7
wt. ~lc potassium chloride is countercurrently contacted with a feed
comprised of 84. 5~c mole ~c of the 1, 2-dichloroethane blend of Example
I and 15. 5 mole percent of ethane, at a temperature of 850F and a
residence time of 7 seconds. The vinyl chloride selectivity is 91. 8
mole percent, and the 1, 2-dichloroethane conversion is 79. 7 mole
per cent .
The present invention is particularly advantageous in that
1 2-dichloroethane can be dehydrochlorinated to vinyl chloride at
corv ersions in excess of 70 percent while maintaining selectivity to
vinyl chloride of at least about 80 percent, (and generally selectivities
of greater than 90~c can be achieved), notwithstanding the presence of
oxychloride in the melt and/or the presence of a dehydrochlorination
inhibitor, such as trichloroethylene, in the 1, 2 -dichloroethane feed.
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