Note: Descriptions are shown in the official language in which they were submitted.
BACKGROUND OF THE INVENTION
This invention relates to a process for the production of
hexachlorocyclopentadiene.
The chemical literature is replete with processes for the
preparation of chlorinated hydrocarbon compounds. Many of the
known processes are used commercially for the preparation of
specific chlorinated hydrocarbons. The development of a suitable
process for the preparation of a particular chlorinated hydro-
carbon depends on a variety of factors, including for example,
1~ the chemical and physical properties of available starting
materials, the chemical and physical properties of the chlor-
inated compound to be prepared, the economic factors relative to
utilization of materials and energy involved in the process, and
the environmental impact of the process. It is known, for example,
15 that hexachlorocyclopentadiene may be produced in low yields by
the chlorination of cyclopentadiene at elevated temperatures
using C12 as the chlorinating agent. However, at the high tem-
peratures required for the reaction, cyclopentadiene exhibits a
strong tendency to polymerize, resulting in the production of
20 dimeric and polymeric compounds as well as substankial amounts
of other undesired side products, especially octachlorocyclo-
pentene. To avoid the problem of polymerization, a process,
disclosed in U. S. Patent 3,637,479, provides for a two stage
chlorination wherein cyclopentad~ene is first reacted with
25 chlorine at lower temperatures such as below about 110 Celsiusg
to form a poly chlorinated product having a composition approxi-
mating tetrachlorocyclopentane, and then photo chlorinated to
produce hexachlorocyclopentane. The product may then be sub-
iected to catalytic vapor phase dehydrochlorination at elevated
30 temperatures to form hexachlorocyclopentadiene. In the vapor
phase process about 20% excess of the stoichiometric amount of
-," `~
chlorine is employed. Thus, this route of preparation involves
three separate steps or stages each requiring substantially dif-
ferent conditions.
A single s~age thermal chlorination process is disclosed in
U.S. Patent 3,649,699. In accordance with the disclosure of that
patent, normal penta~e and chlorine are reacted at 275 to 400
Celsius in the presence of a catalyst comprising alumina h~ving
a low surface ~rea to produce hexachlorocyclopentadiene. In
another single stage process disclosed in U.S. Patents 3,364,269
10 hexachlorocyclopentadiene is prepared by a single stage catalytic
process employing a fluidi~ed bed of catalytically activated carbon.
It will be appreciated that although a variety of processes
are known and used for the production of hexachlorocylcopentadiene,
a need continues to ex;st for the development of a process pro-
15 viding improvemen~s in efficiency of the utilization of reactantsand energy and the elimination or minimization of waste products.
Accordingly, it is an object of the present invention to
provide a novel and improved process for the preparation of hexa-
chlorocyclopentadiene from cyclopentadiene starting material. A
20 further object of the present invention is to provide a process
for the production of hexachlorocyclopentadiene wherein the use
of excess amounts of chlorine is avoided.
SUMMARY OF THE INVENTION
In accordance with this invention there is provided a process
for the preparation of hexachlorocyclopentadiene comprising si-
multaneously introducing, in the vapor phase, chlorine and a
polychlorinated c~clopentane of the formula C5H8 xC12+x, where
x is Q to 4, into a pool of molten salt comprising a mixture of
copper chlorides, preferably maintained at a temperature of about
3Q 250 to about 500 and most preferably about 250 to about 350
Celsius.
" f~ ,,
. ~
The polychlorinated cyclopentane and chlorine may be fed as
separate streams into a reactor containing the molten salt. In
a preferred form, the polychlorinated cyclopentane is vaporized,
mixed with chlorine and the reactant mixture fed into a pool oF
molten copper chl~ride salts.
Typically, the vaporized mixture may be sparyed into the
bottom of a bubble reactor containing the molten salt. To assure
a uniform feed rate to the reactor, it is preferred to employ an
inert gas, such as nitrogen or HCl in admixture with either of
10 the vaporized reactants or mixture thereof. The inert gas may
be mixed with the gaseous reactants prior to entering the molten
salt reactor. The amount of inert gas may vary considerably but
is preferably in the range of about 10 to about 50 weight percent
of the entire gaseous mixture. The rate of feed of the vaporized
mixture, expressed as reciprocal space velocity may vary consider-
ably, but will typically be in the range of about 2 to about 20
seconds. At low values of reciprocal space velocity, that is
faster feed rate, complete conversion may be achieved. A~ higher
values the formation of dimers or over-chlorinated products, such
20 as octachlorocyclopentene is likely to increase.
The molten salt mixture employed is a mixture of copper chlor-
ides comprising cupric chloride, and cuprous chloride and a minor
proportion of a metal salt melting point depressant which is sub-
skantially non-volatile. Suitable melting point depressants are
25 salts, preferably chlorides, of a metal having only one positive
valence state. Metal salts, known to be useful for this purpose,
include for example the heavy metal chlorides of ~roups 1, II,
III and IV of the Periodic Table, including for example, zinc
chloride, silver chloride, thallium chloride and the like or
30 mixtures thereof. The preferred melting point depressants are
the alkali metal chlorides, preferably potassium and/or lithium
chloride. The amount of metal chloride melting point depressant
present in the copper chloride mixture may vary considerably but
should be an amount sufficient to lower the melting point of the
copper chloride mixture to a temperature below the lowest process
temperature contemplated and preferably to a mel~ing point below
about 250 Celsius. The proportions of the components of the
molten salt mixture may vary considerably. The preferred com-
positions for this purpose are mixtures containing about 10 to
about 40 percent and preferably about 10 to about 20 percent by
weight of cupric chloride; about 30 to about 65 percent and pre~
10 ferably about 50 to about 60 percent by weight of cuprous chloridei :~
and about 20 to about 50 percent by weight of a melting point de~
pressant, preferably an alkali metal chloride, most prefer~bly,
potassium chloride. In addition, copper oxychloride may be
present in the molten salts, in amounts, for example of ~bout
15 0.5 to about 5.5 percent by weight.
Cyclopentadiene - a starting material for the formation of
hexachlorocyclopentadiene in some processes of the prior art -
is not employed directly in the molten salt chlorination of this
invention since the required temperatures result in the formation
20 of undesired volatile chlorornethanes and polymeric materials.
However, cyclopentadiene may be chlorinated readily in a simple
low temperature chlorination to ~form a polychlorinated cyclo-
pentane having the approximate composition C5H8 xC12~x, where
x is 0 to ~. The polychlorinated product formed in this manner
is well-suited for chlorination in the hereinabove-described molten
salt chlorination to prepare a hexachlorocyclopentadiene product.
Thus, a preferred embodiment of the present invention provides a
two-stage chlorination process for the production of hexachloro-
cyclopentadiene which comprises the steps of:
a) reacting chlorine with cyclopentadiene in the l~quid
phase at a temperature of below 110C to produce a polychlorinated
cyclopentane product having an approximate composition of
5~
C5H8 xC12+x, where x is O to ~;
b) heating the polychlorinated cyclopentane product to form
vapors thereof;
c) feeding the vapors of polychlorinated cyclopentane to-
gether with chlorine gas into a molten salt comprising a mixture
of copper chlorides maintained at a temperature of about 250 to
about S00Ci and
d) recovering hexachlorocyclopentadiene therefrom.
In the first stage, that is the low temperature chlorination
step, cyclopentadiene is reacted with chlorine at a temperature of
about 0 to about 110 Celsius and preferably about 30 to about
80 Celsius. The chlorination is preferably carried out at atmos-
pheric pressure although subatmospheric or super-atmospheric pres-
sures may be employed iF desired.
Typically, in the low temperature liquid phase chlorination
step chlorine gas and liquid cyclopentadiene are fed separately into
a temperature-controlled reaction vessel, preferably at a molar ratio
of about 2 to about ~ moles of chlorine gas per mole of cyclopenta-
diene, and liquid polychlorocyclopentane having a composi~ion as
20 set forth hereinabove is withdrawn. The reaction may be efFected
in the presence of an inert liquid diluent such as carbon tetra-
chloride, or preferably a portion of the polychlorinated cyclo
pentane product may be recirculated as a diluent for the process.
The composition oF the product, that iS9 the degree of chlorination
25 may be varied by varying the time of reaction and/or the proportion
of chlorine reactant to cyclopentadiene reactant. The preparation
of higher chlorinated cyclopentanes, such as C5H8 xC12~x, where x
is greater than about 3, by low temperature chlorination is diffi-
cult and becomes increasingly less efficient from the standpoint
30 of chlorine utilization due to the need of excess chlorine gas
reactant. On the other hand, the molten salt chlorination of
lower chlorinated cyclopentanes becomes increasingly less effi-
cient, from the standpoint of chlorine utilization as the aforesaid
~lZ050~
value of x decreases, especially at values where x is less than
about 2. Thus it is preferred to carry out the low temperature
chlorination to a degree sufficient to provide a polychlorinated
cyclopentane product having an approximate composition of C5H8 x~
C12+x, where x is about 0 to about 3, and most preferably about
1.5 to about 2.5, a product having an average composition approxi-
mating that of tetrachlorocyclopentane and to utilize such poly-
chlorinated cyclopentanes as reactants in the subsequent molten
salt chlorination step to prepare hexachlorocyclopentadiene.
10 Polychlorinated cyclopentanes prepared in this manner by low temp-
erature chlorination are generally a mixture of chlorinated cyclo-
pentanes. Thus, a polychlorinated cyclopentane having a compo-
sition of C5H8 xC12+x, where x is between 1.5 and about 2.5, will
generally be a mixture wherein the predominant components are
15 C5H5C15, C5H6C14, and C5H7C13. Although the preferred starting
material for the preparation of the polychlorinated cyclopentane
by low temperature chlorination is cyclopentadiene, other five
membered hydrocarbon ring compounds, in particular cyclopentene,
may be employed.
In the molten salt chlorination, when a polychlorinated
cyclopentane having a composition characterized by the formula
C5H8 xC12+x. where x is about 1.5 to about 2.5 is employed, it
has been found that hexachlorocyclopentadiene is advantageously
produced with less than the stoichiometric amount of chlorine
25 gas reactant than is required for the chlorination and dehydro-
chlorination reactions involved. During the reaction additional
chlorine atoms are contributed by the conversion of cupric
chloride to cuprous chloride in the molten salt. The depletion
of the cupric chloride may be compensated for by replacement of
30 the molten salt or periodic additions of cupric chloride thereto.
Alternatively, when the cupric chloride component is depleted
the molten salt may be regenerated by addition of chlorine values,
O~
preferably utilizing waste chlorine values from the low temp-
erature chlorination step.
The following specific examples are provided to further
illuskrate this inven-tion and the manner in which it may be
carried out. It will be understood that the specific details
given in the examples have been chosen for purpose of illustration
and are not to be construed as a limitation of the invention. In
the examples, unless otherwise indicated, all parts and percentages
are by weight and all temperatures are in degrees Celsius.
EXAMPLE I
A) Low temperature chlorination of cyclopentadiene
Six hundred parts of cyclopentadiene and 1930 parts of chlorine
gas were fed continuously in separate streams over a period of six
hours into a reactor containing a pool of about 300 parts of a poly-
chlorinated cyclopentane having an average composition approximately
corresponding to tetrachlorocyclopentane. The reactor contents were
continuously circulated through an external cooler to maintain a
reactor temperature of about 40C. The chlorine feed was main-tained
at about 50% excess of the stoichiometric amount. A polychlorinated
20 cyclopentane product having an approximate average composition of
C5H6 16C13 ~4 was conkinuously wi-thdrawn from the bot-tom of -the
reactor.
B) Molten salt chlo nation of polychlorinated cyclopentane
Polychlorinated cyclopentane, prepared as in I-A, above,
having an approximate average composition of C5~l6 16C13 84 was
heated to about 300C and the resultant vapors mixed with chlorine
gas and nitrogen in a proportion of about 1.42 par-ts of polychlor-
inated cyclopentane to about 1.5 parts of chlorine gas (about 77
percent of the stoichiometric amount of chlorine required for the
production of hexachlorocyclopentadiene) and 0.05 parts of nitrogen.
The mixture was continuously bubbled over a period of ~ hours into
~ - ,
a molten salt pool comprising 300 parts of a mixture of 15l CuC12,
60% CuCl, and 25% KCl. The molten salt w~s maintained at a tem-
perature of about 350C and the reactant mixture was allowed to
bubble through the molten salt with an approximate reciprocal
space velocity of about 11 seconds. Product vapors were withdrawn,
condensed, and analyzed using gas chromatographic techniques, every
15 minutes for the first two hours and every 30 minutes there~fter
for the total 4 hour reaction period. The product thus obtained
was found to contain greater than 94% hexachlorocyclopentadiene,
10 the remainder being primarily octachlorocyclopentene.
EXAMPLE 2
A) Low temperature chlorination
Dichlorocyclopentane was prepared by low temperature chlori-
nation reaction of cyclopentene with approximately stoichiometric
15 amoun~s of chlorine. Cyclopentene vapor and chlorine were fed
simultaneously (feed rates about 2 mls/minute and 1.6 g/minute,
respectively) into the upper portion of a tubular reactor packed
with 0.5 inch Berl saddles. The reactor was maintained at a tem-
perature of about 35C by external cooling and the dichlorocyclo-
20 pen~ane produced was continuously condensed and collected inquantitive amounts at the bottom of the reactor. Analysis o~ the
dichlorocyclopentane product indicated a chlorine content of 55.4
weight percent (~heoretical value, approximately 51 weight percent).
B) Molten salt chlorination
A reactor containing about 300 parts of a mixture of 15%
CuC12, 60% CuCl and 25% KCl was heated to about 280C and chlorine
gas was fed into the molten salt, to saturate the salt with chlorine.
Dichlorocyclopentane~ prepared as in Example 2A, was heated to about
170C and the resultant vapors continuously mixed with chlorine gas
30 and nitrogen and ~he mixture continuously-fed into -the molten salt
in a manner similar to that of Example lB. The process was con-
tinued over a period of about 4 hours during which the molten salt
~24~5~
10 --
was maintained a~ a temper~ture about 280C. The reactants were
mixed and fed into the molten salt at an initial rate of about 4.5
parts/minute of dichlorocyclopentane to about 0.25 parts/minute of
chlorjne and the quantities gradually increased to the final rate
of about 7.0 parts/minute of dichlorocyclopentane to about 5.0 parts/
minute of chlorine. The product vapors were continuously withdrawn,
condensed and analyzed using gas chromatographic techniques. Init-
ially the product obtained represented approximately 75% conversion
of the dichlorocyclopentane to hexachlorocyclopentadiene. When the
10 chlorine feed rate WAS increased to approximately double the stoichio-
metric amount, a conversion of about 96% to hexachlorocyclopentadiene
and octachlurocyclopentene was achieved.
EXAMPLE 3
Molten salt chlorination of hexachlorocyclopentane
Hexachlorocyclopentane was continuously mixed with chlorine
gas and minor proportions of nitrogen and the vapor mixture fed
into a reactor containing a pool of 300 parts of chlorides (15%
Cu~12, 6q% CuCl, and 25% KCl) following the general procedure oF
Example lB. During the reaction, the temperature of the molten
20 salt was maintained at between about 310 and 375C. The reaction
was run over a period of 4 hours and 34 minutes, with an average
feed rate of about l.l9 parts/minute of hexachlorocyclopentane
to about 0.4 parts/minute of chlorine yas. The proportions of
hexachlorocyclopentane and chlorine reactants was varied during
25 the reaction period. Ini-tially, chlorine was added -to the mixture
at a rate equivalent to about 36 percent of the stoichiometric
amount required for complete conversion of hexachlorocyclopentane
to hexachlorocyclopentadiene. At this proportion, product analy-
sis indicated 91.8% hexachlorocyclopentadiene and minor amounts
30 of hexachlorocyclopentanone and octachlorocyclopentene. When the
chlorine feed rate was increased to about ~6% of the stoichiometric
amount, the product analysis indicated greater than 98% hexachloro-
cyclopentadiene with very minor amounts of hexachlorocyclopentanone
s~
and octachlorocyclopentene. Similar r~sults, i.e. 98% hexachloro-
cyclopentadiene, were achieived when the chlorine feed rate was
~urther increased to 45 to 52% of the stoichiometric amount.
In a number of experiments utilizing different polychlor-
inated cyclopentane starting materials, it was found that for a
given molten salt composition, the chlorine efficiency, that is,
the percent of chlorine, based on the stoichiometric amount,
varied inversely with the chlorine content of the polychlorinated
cyclopentane. Thus, when the starting material for the molten
10 salt chlorination step was dichlorocyclopentane, essentially
quantitative conversion to hexachlorocyclopentadiene required
about double the stoichiometric amount of chlorine gas reactant
required for the chlorination and dehydrochlorination reaction.
When the starting m~terial composition was approximately that
15 of tetrachlorocyclopentane, essentially quantitative conversion
to hexachlorocyclopentadiene required about 75% of the stoichio-
metric amount of chlorine gas reactant. About 50% of the stoichio-
metric amount of chlorine gas reactant was required for essentially
quantitative conversion of hexachlorocyclopentane to hexachloro-
20 cyclopentadiene.
