Abstract:
Disclosed is a process for the making chlorotrifluoroethylene. The process comprises the step of reacting 1,1,2-trichlorotrifluoroethane with a reducing metal in the presence of a polar aprotic solvent under conditions sufficient to form chlorotrifluoroethylene.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The present application is a continuation of application Ser. No. 12/537,805 filed Aug. 7, 2009, now U.S. Pat. No. 7,723,552. The &#39;552 patent claims domestic priority from U.S. Provisional Application No. 61/087,482, filed Aug. 8, 2008. The disclosures of these applications are hereby incorporated herein by reference in their entirety. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to a process for the making chlorotrifluoro-ethylene (CFO-1113) from 1,1,2-trichlorotrifluoroethane (CFC-113). 
     BACKGROUND OF THE INVENTION 
     Chlorotrifluoroethylene (CFO-1113) is currently manufactured commercially by dechlorinating 1,1,2-trichlorotrifluoroethane (CFC-113) via reaction with zinc in the presence of methanol as a solvent. A major drawback with this process is the formation of 1,2-dichloro-1,1,2-trifluoroethane (HCFC-123a) as a major byproduct, which greatly reduces the yield of CFO-1113 and is costly to dispose of. 
     It would be desirable to have an improved process for making CFO-1113 from CFC-113. 
     SUMMARY OF THE INVENTION 
     According to the present invention there is provided a process for the making chlorotrifluoroethylene. In one embodiment, the method has the step of reacting 1,1,2-trichlorotrifluoroethane (CFC-113) with a reducing metal in the presence of one or more polar aprotic solvents under conditions sufficient to form chlorotrifluoroethylene (CFO-1113). 
     In certain embodiments, the one or more polar aprotic solvents is selected from the group consisting of aldehydes, ketones, dimethyl sulfoxide, dimethyl formamide, and combinations thereof. In certain embodiments, the aldehydes have the formula R—CHO, wherein R is an alkyl group having from 1 to 4 carbon atoms. In certain embodiments, the ketones have the formula R—CO—R′, wherein R and R′ are alkyl groups, each independently having from 1 to 4 carbon atoms. 
     In certain embodiments, the one or more polar aprotic solvents is selected from the group consisting of ethyl ether, ethyl acetate, acetone, methyl ethyl ketone, and combinations thereof. 
     In certain embodiments, the polar aprotic solvent comprises ethyl ether. In certain embodiments, the polar aprotic solvent comprises ethyl acetate. In other embodiments, the polar aprotic solvent comprises acetone. In other embodiments, the polar aprotic solvent comprises methyl ethyl ketone. 
     In certain embodiments, the reducing metal is selected from the group consisting of zinc, magnesium, aluminum, and tin. In certain embodiments, the reducing metal comprises zinc. In certain embodiments, the reducing metal comprises magnesium. In certain embodiments, the reducing metal comprises aluminum. In certain embodiments, the reducing metal comprises tin. 
     In certain embodiments, the reaction is carried out at a temperature of from about 50° C. to about 100° C. In certain embodiments, the reaction is carried out at a temperature of from about 60° C. to about 90° C. In certain embodiments, the reaction is carried out at a temperature of from about 60° C. to about 85° C. 
     In certain embodiments, the reaction is carried out in batch mode. In certain embodiments, the reaction is carried out in continuous mode. 
     It should be appreciated by those persons having ordinary skill in the art(s) to which the present invention relates that any of the features described herein in respect of any particular aspect and/or embodiment of the present invention can be combined with one or more of any of the other features of any other aspects and/or embodiments of the present invention described herein, with modifications as appropriate to ensure compatibility of the combinations. Such combinations are considered to be part of the present invention contemplated by this disclosure. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The process of the present invention has the following reaction sequence:
 
CFCl 2 —CF 2 Cl+M→CF 2 ═CFCl+MCl x  
 
(CFC-113) (CFO-1113+metal chloride)
 
wherein M is a reducing metal and wherein the dechlorination reaction is carried out in the presence of a polar aprotic solvent. When M is zinc, the reaction sequence is the following:
 
CFCl 2 —CF 2 Cl+Zn→CF 2 ═CFCl+ZnCl 2  
 
(CFC-113) (CFO-1113+zinc chloride)
 
     Polar aprotic solvents are solvents that have similar dissolving power to protic solvents, but without the presence of an acidic hydrogen. Useful polar aprotic solvents include, but are not limited to, aldehydes (R—CHO), ketones (R—CO—R′), dimethyl sulfoxide (DMSO) (CH 3 —SO—CH 3 ), dimethyl formamide (DMF) (H—CO—N(CH 3 ) 2 ), and combinations thereof wherein R and R′ are alkyl groups having 1 to about 4 carbon atoms. Additional examples of useful polar aprotic solvents include ethyl ether, ethyl acetate, acetone, and methyl ethyl ketone. Aprotic solvents have the advantage of producing lower amounts of byproducts. More particularly, polar aprotic solvents have the advantage of producing lower amounts or none of the byproduct HCFC-123a. 
     Although not wishing to be bound by any particular theory, it is conjectured that protic solvents (e.g., methanol) cause the formation of HCFC-123a by losing an acidic hydrogen to a reaction intermediate. Use of polar aprotic solvents will reduce or eliminate the formation of hydrogen-containing byproducts. 
     Useful polar aprotic solvents are those capable of dissolving the reactant and the reaction products, i.e., CFC-113, CFO-1113 and MCl x , i.e., a chloride of the reducing metal. A polar aprotic solvent is preferably used in an amount sufficient to substantially dissolve the reactant and the reaction products. 
     The solvent system may be made up substantially or entirely of a polar aprotic solvent(s) or combinations of a polar aprotic solvent(s) and a protic solvent(s). In the instance of combinations, the amount of protic co-solvent can range from about 1 wt. % to about 80 wt. % and more preferably about 5 wt. % to about 40 wt. % based on the total weight of the polar aprotic solvent(s) and the protic co-solvent(s). 
     Protic co-solvents useful in combination with the aprotic solvents include methanol, ethanol, propanol, isopropanol, and water. 
     Useful examples of suitable reducing metals include zinc, magnesium, aluminum, and tin. A preferred reducing metal is zinc. 
     The dechlorination reaction is carried out under conditions sufficient to form chlorotrifluoroethylene. The reaction is preferably carried out at a temperature of about 50° C. to about 100° C., more preferably about 60° C. to about 90° C., and most preferably about 60° C. to about 85° C. The reaction can be carried under vacuum, atmospheric, or superatmospheric pressure conditions. The reaction vessel is preferably an agitated pressure vessel. The process can be either batch or continuous. 
     The following are examples of the present invention, and are not to be construed as limiting. 
     EXAMPLES 
     Examples of the process of the invention and a comparative example were tested for conversion. 
     Comparative Example 
     In a plant operation test, only a protic solvent, MeOH, was used. Starting materials of 1.08 liters of methanol and 0.32 kilogram of zinc per kilogram of CFC-113 were charged into a batch reactor equipped with agitation. The reaction was carried out at about 73° C. The conversion of CFC-113 and selectivity to CFO-1113 were 92.4% and 94.1%, respectively. 
     Example 1 
     This is an example that demonstrates using only an aprotic solvent. Here, 65 grams of zinc powder was charged into a one-liter agitated pressure vessel. The vessel was then sealed, pressure checked, and evacuated. Approximately 175-250 milliliters of acetone were charged into the reactor on top of the zinc followed by an addition of 200 grams of CFC-113. The vessel was heated to a temperature necessary to run the reaction, approximately 60° C. to 85° C. with agitation. The reaction was run for 220 minutes after the temperature was stabilized at the desired setting. During the reaction, the pressure rose to 150 psig. After the run was completed, the volatile reaction products were transferred to a chilled and evacuated product collection cylinder by venting the pressure from the reactor down to atmospheric. The collected material was analyzed using Gas Chromatography (GC) which revealed that conversion of CFC-113 was 88.6%, while selectivity to CFO-1113 was 99.8%. 
     Example 2 
     The process of Example 2 was run substantially as described in Example 1 except that a mixture of acetone and methanol (80:20) was used as the solvent instead of acetone alone. Conversion of CFC-113 and selectivity to CFO-1113 were 99.4% and 99.6%, respectively. The presence of methanol had the effect of increasing conversion and the presence of the polar aprotic solvent, acetone, improved selectivity to CFO-1113. 
     It should be understood that the foregoing description is only illustrative of the present invention. Various alternatives and modifications can be devised by those skilled in the art without departing from the invention. Accordingly, the present invention is intended to embrace all such alternatives, modifications and variances that fall within the scope of the appended claims.