Process to produce vinylidene chloride using phase transfer catalyst

The invention concerns a process for producing unsaturated compounds from chlorinated alkanes by dehydrochlorination wherein a phase transfer catalyst is used during reaction of chlorinated alkane with aqueous base. After dehydrochlorination, the products are distilled or flashed off. Then, the phase transfer catalyst is recovered and reused by extracting the catalyst from spent aqueous base with fresh chlorinated alkane and using the mixture of chlorinated alkane and catalyst from the extraction as feedstock.

BACKGROUND OF INVENTION 
This invention concerns the production of unsaturated compounds from 
chlorinated compounds using phase transfer catalysts in combination with a 
base. 
Various methods are known to dehydrohalogenate halogenated hydrocarbons 
using a base and a phase transfer catalyst. For instance, U.S. Pat. No. 
3,664,966 describes such a process wherein an aqueous base in conjunction 
with an organic quaternary salt. In the examples, 1,1-dichloroethylene 
(vinylidene chloride) is produced from 1,1,2-trichloroethane. The 
advantages of the phase transfer catalyst is an increase in reaction rate 
while allowing the reaction to be conducted at lower temperatures. 
A similar process is described in U.S. Pat. No. 3,754,044. In this patent, 
a quaternary ammonium compound and a phosphate ester are utilized in 
combination as the phase transfer catalyst system. The phosphate ester is 
taught to act as a promoter. 
While the processes described above produce enhanced reaction rates, such 
methods have generally not been used on a commercial scale because the 
phase transfer catalysts are expensive and lost during the process. Thus, 
such processes do not produce the desired products in a cost effective 
manner. 
There followed U.S. Pat. No. 4,418,232 which describes an improved 
dehydrohalogenation process wherein a phase transfer catalyst is used. In 
this process, a cascade arrangement of reactors is described such that 
partially spent alkali solution from the first reactor is recycled back to 
a stage reactor prior to the primary reactor where fresh caustic solution 
is introduced. While this process recycles the caustic, the phase transfer 
catalyst is in large part not recycled because the phase transfer 
catalysts have greater solubility in the organic phase than in the aqueous 
phase. 
More recently, U.S. Pat. No. 4,605,800 describes an improved 
dehydrohalogenation process to produce chloroprene from 
3,4-dichlorobutene-1 using a phase transfer catalyst and caustic. In this 
process, the reactor effluent is sent to a decanter where the organic 
phase is separated from the aqueous phase. The organic phase is then sent 
to a steam-stripper whereby product is recovered and the heels from the 
stripper are returned to the reactor. However, since contaminants are 
present in the heels which would build-up if continuously recycled, from 2 
to 20 percent of the heels are purged to prevent contaminant build-up. 
Moreover, it is know that phase transfer catalysts in general will 
decompose to some extent at temperatures greater than 130.degree. C. When 
this is done, catalyst is also purged. In addition, catalyst is lost in 
the decanter as well as the steam-stripper. Hence, make up catalyst must 
be added to the heels to maintain the proper amount of catalyst in the 
reaction. 
It is apparent that new and improved processes are desirable in 
dehydrohalogenation processes using phase transfer catalyst to provide 
more cost effective methods of production. 
SUMMARY OF INVENTION 
This invention, in one respect, is a process for producing unsaturated 
compounds which comprises: 
(A) contacting a chlorinated alkane with an aqueous base solution in the 
presence of a phase transfer catalyst to form an unsaturated compound; 
(B) distilling the unsaturated compound to make a bottoms mixture 
containing the residual of the aqueous basic solution and phase transfer 
catalyst; 
(C) adding chlorinated alkane to the bottoms mixture from Step B and mixing 
the resulting admixture so that the phase transfer catalyst is extracted 
into the chlorinated alkane to form an organic solution of chlorinated 
alkane and phase transfer catalyst; and 
(D) using the organic solution from Step C as at least a portion of the 
chlorinated alkane and phase transfer catalyst employed in Step A. 
In another respect, this invention is a process for producing vinylidene 
chloride which comprises: 
(A) contacting 1,1,2-trichloroethane with an aqueous sodium hydroxide 
solution in the presence of a phase transfer catalyst to form vinylidene 
chloride at a temperature such that the vinylidene chloride is distilled 
off from the aqueous base solution and a spent aqueous base solution 
containing phase transfer catalyst is formed; 
(B) adding 1,1,2-trichloroethane to the spent aqueous sodium hydroxide 
solution containing phase transfer catalyst and mixing the resulting 
admixture so that the phase transfer catalyst is extracted into the 
1,1,2-trichloroethane to form an organic solution of 1,1,2-trichloroethane 
and phase transfer catalyst; and 
(C) using the organic solution from Step B as at least a portion of the 
1,1,2-trichloroethane and phase transfer catalyst employed in Step A. 
The processes of this invention recover and recycle a high percentage of 
phase transfer catalyst. Consequently, this invention provides 
commercially desirable methods of producing unsaturated compounds from 
chlorinated alkanes with efficient recovery and recycle of phase transfer 
catalyst.

DETAILED DESCRIPTION OF INVENTION 
In the practice of this invention, the starting compounds to be 
dehydrochlorinated are any chlorinated alkanes which may be 
dehydrochlorinated in the process of this invention. Preferably, the 
starting compounds include chlorinated ethanes, propanes, and butanes that 
have at least one hydrogen. More preferably, the starting compounds are 
chlorinated ethanes that have at least one hydrogen. Preferred chlorinated 
ethanes are chloroethane, 1,1-dichloroethane, 1,2-dichloroethane, 
1,1,1-trichloroethane, and 1,1,2-trichloroethane. The products of the 
process are unsaturated. Preferred products include vinyl chloride and 
1,1-dichloroethene (vinylidene chloride). 
The chlorinated alkane is contacted with an aqueous base solution. The 
aqueous base solution can be based on the hydroxides and carbonates of 
alkali and alkaline earth metals. Preferred aqueous base solutions are 
aqueous solutions of sodium or potassium hydroxides. The concentration of 
the aqueous solutions is not critical, but generally is 0.1N to 10N. 
Likewise, the amount of base is not critical, but a slight molar excess 
relative to the chlorinated ethane is generally used. Typically, the mole 
ratio of base to chlorinated solvent is 1:2 to 2:1. 
The phase transfer catalysts which can be used in this invention include 
any compounds which catalyze the process of this invention to make 
unsaturated products from chlorinated alkanes. Classes of such phase 
transfer catalysts include quaternary ammonium salts, quaternary 
phosphonium salts, quaternary sulfonium salts, cyclic ethers (crown 
ethers), ether-alcohols, and betaines. Preferably, the phase transfer 
catalyst is a quaternary ammonium salt. The preferred quaternary ammonium 
salts are of the formula R.sub.4 NX wherein R is independently in each 
occurrence is a C.sub.1-20 alkyl, C.sub.2-20 alkenyl, or C.sub.7-20 
aralkyl and wherein X is Cl, Br, I or F. X is preferably Cl. Generally, 
longer alkyl groups in the quaternary ammonium salts perform better in the 
process of this invention. Examples of preferred quaternary ammonium salts 
include benzyltrimethylammonium chloride, benzyltriethylammonium chloride, 
and benzyltributylammonium chloride with benzyltributylammonium chloride 
being most preferred in this group. The amount of the quaternary ammonium 
salts is 0.001 to 10 weight percent based on chlorinated ethane starting 
material with 0.1 to 0.5 weight percent being preferred. 
The contacting of the reactants can occur at any temperature which will 
convert at least a portion of the chlorinated ethane to product. 
Generally, the temperature will be from 0.degree. to 150.degree. C. 
Pressure is sufficient to maintain substantially liquid conditions of 
reactants. The contacting typically occurs under strong agitation or 
circulation as practiced by those skilled in the art, such as by 
introducing the reactants in or near a pump. This strong circulation is 
employed to provide maximum contact of aqueous solution and organic 
starting material, the organic starting material being sparingly soluble 
in the aqueous solution. 
The contacting can be carried out using conventional equipment designed for 
such purpose. The process can be run batch-wise or continuously. 
After the contacting has proceeded to the desired level, the product is 
distilled off or flashes off during the process to leave the residual of 
the aqueous base solution which contains phase transfer catalyst. The 
residual leaves the reactor. The distillation temperature will vary 
depending on the chlorinated alkane and reaction products. Reduced 
pressure can be used to hasten distillation. The distillation can be 
performed using conventional equipment and techniques. In addition, the 
products can be further purified by well known methods such as additional 
distillation steps. 
The bottoms from the distillation next go to a liquid/liquid extractor 
wherein fresh chlorinated alkane is added. During the extraction, the 
volume ratio of aqueous to organic phase can vary widely, but generally is 
from about 10:1 to about 1:10 based on weight, preferably 1:2 to 2:1. 
After addition of the chlorinated alkane, the entire mixture is mixed so 
that the aqueous and organic phases make intimate contact so that a 
substantial portion of the phase transfer catalyst is extracted into the 
organic phase. Preferably, greater than 95 percent of the phase transfer 
catalyst is extracted into the organic phase. The phases are then allowed 
to separate and the organic phase is recovered with the aqueous phase 
being disposed of or steam stripped to recover the saturated organics. 
The organic phase, which comprises chlorinated alkane and phase transfer 
catalyst, is next recycled back to the primary reactor wherein the 
contacting occurs. Due to the slight loss of phase transfer catalyst, an 
appropriate amount of phase transfer catalyst can be added when desired to 
the primary reactor. Higher ratios of organic phase to aqueous phase will 
generally enable a greater amount of phase transfer catalyst being 
extracted. In the extraction, the temperature can be from 0.degree. to 
150.degree. C., preferably from 20.degree. C. to 100.degree. C. Higher 
temperatures tend to decompose the phase transfer catalysts. Pressures can 
be up to about 300 psig during the extraction. The amount of time needed 
for the extraction can vary depending on the conditions, but generally is 
from 1 minute to 4 hours. Additional extraction stages can be utilized to 
further increase recovery of phase transfer catalyst. 
The process of this invention can be understood by referring to FIG. 1. 
Aqueous sodium hydroxide, 1,1,2-trichloroethane, and benzyltributylammonium 
chloride (BTBAC) are introduced into reactor 10 through line 11. In 
reactor 10 the 1,1,2-trichloroethane is dehydrochlorinated to form 
1,1-dichloroethene (vinylidene chloride) which flashes off and exists 
reactor 10 through line 12. The spent aqueous sodium hydroxide solution 
which contains BTBAC exits reactor 10 through line 13 and enters 
liquid/liquid extractor 20. Fresh 1,1,2-trichloroethane enters 
liquid/liquid extractor 20 through line 21. In liquid/liquid extractor 20 
the fresh 1,1,2-trichloroethane and spent aqueous sodium hydroxide 
solution are circulated to extract the BTBAC into the 
1,1,2-trichloroethane. The extracted spent sodium hydroxide solution exits 
liquid/liquid extractor 20 through line 22. 1,1,2-trichloroethane which 
contains BTBAC exits liquid/liquid extractor 20 though line 23 and is then 
introduced into line 11 wherein sufficient make up BTBAC is added along 
with fresh aqueous sodium hydroxide and any needed 1,1,2-trichloroethane. 
While FIG. 1 shows a single liquid/liquid extractor, additional 
liquid/liquid extractors can be employed to increase phase transfer 
catalyst recovery. 
The invention is now illustrated by the following example which should not 
to be construed to limit the scope of the invention or claims. 
EXAMPLE 1 
An aqueous sodium hydroxide solution was prepared that had a composition 
similar to that of spent solution from a commercial process used to make 
vinylidene chloride. The aqueous sodium hydroxide solution contained 0.3 
weight percent NaOH and 21 NaCl to which was added 5,000 ppm of 
benzyltributylammonium chloride (BTBAC). Portions of the spent aqueous 
sodium hydroxide solution were contacted with fresh 1,1,2-trichloroethane 
in weight ratios denoted below in Table 2 (as "O/A", meaning organic to 
aqueous ratio). The mixture of organic and aqueous phases were thoroughly 
mixed and then the amount of BTBAC in the organic layer determined by gas 
chromatography. The results are reported below in Table 1. 
TABLE 1 
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O/A w/p % BTBAC Recovered 
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1:1 98.6 
1:2 97.5 
1:3 93.4 
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The mixture of 1,1,2-trichloroethane and BTBAC could be recycled back to a 
primary reactor in a process to make vinylidene chloride wherein aqueous 
sodium hydroxide is contacted with 1,1,2-trichloroethane in the presence 
of a quaternary ammonium salt such as BTBAC.