Organic compounds -- part of the class 532-570 series – Organic compounds – Halogen containing
Patent
1996-04-29
1998-10-20
Killos, Paul J.
Organic compounds -- part of the class 532-570 series
Organic compounds
Halogen containing
570151, C07C 1700
Patent
active
058248285
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND
Tetrachlorodifluoroethanes are readily converted to trichlorotrifluoroethanes (C.sub.2 Cl.sub.3 F.sub.3) by using conventional fluorination. The C.sub.2 Cl.sub.3 F.sub.3 product typically contains greater than 98% of the more symmetrical isomer, CCl.sub.2 FCClF.sub.2 (CFC-113). CFC-113 can be readily isomerized to its more unsymmetrical isomer, CCl.sub.3 CF.sub.3 (CFC-113a) using aluminum trihalide catalyst. CFC-113a can in turn be converted to 1,1-dichlorotetrafluoroethane (i.e., CCl.sub.2 FCF.sub.3 or CFC-114a) by conventional fluorination. CCl.sub.2 FCF.sub.3 is of interest as an intermediate to 1,1,1,2-tetrafluoroethane (i.e., CF.sub.3 CH.sub.2 F or HFC-134a) which can be obtained via catalytic hydrogenolysis of its carbon-chlorine bonds using a supported metal hydrogenation catalyst (see e.g., C. Gervasutti et al., J. Fluorine Chem., 1981/82, 19, pgs. 1-20). HFC-134a is an environmentally acceptable potential replacement for chlorofluorocarbon (i.e., CFC) refrigerants, blowing agents, aerosol propellants and sterilants that are being viewed with concern in connection with the destruction of stratospheric ozone. It is highly desired that the 1,1-dichlorotetrafluoroethane employed in the hydrogenolysis route to HFC-134a has as low a content of 1,2-dichlorotetrafluoroethane (i.e., CClF.sub.2 CClF.sub.2 or CFC-114) as practicable since the presence of CFC-114 during hydrogenolysis can lead to formation of 1,1,2,2-tetrafluoroethane (i.e., CHF.sub.2 CHF.sub.2 or HFC-134; see e.g., J. L. Bitner et al., U.S. Dep. Comm. Off. Tech. Serv. Rep. 136732, (1958), p. 25). HFC-134 mixed in HFC-134a may be objectionable for some applications depending on concentration and, since the two isomers boil only 7.degree. C. apart, separation of the isomers in high purity is difficult.
There remains a need for processes which facilitate the production of CFC-114a substantially free of its isomer, particularly processes which may employ conventional vapor-phase fluorination techniques. This includes processes for producing trichlorotrifluoroethane without producing 1,2-dichlorotetrafluoroethane.
SUMMARY OF THE INVENTION
A process is provided in accordance with this invention for producing a reaction product comprising C.sub.2 Cl.sub.3 F.sub.3 substantially free of 1,2-dichlorotetrafluoroethane. The process comprises the steps of (i) contacting a feed mixture consisting essentially of compounds of the formula C.sub.2 Cl.sub.4-x F.sub.2+x (where x is 0 or 1) wherein the C.sub.2 Cl.sub.4 F.sub.2 content is between about 10 mole percent and 90 mole percent of said C.sub.2 Cl.sub.4-x F.sub.2+x and wherein the mole ratio of the total amount of CCl.sub.2 FCCl.sub.2 F and CCl.sub.2 FCClF.sub.2 (i.e., the more symmetric C.sub.2 Cl.sub.4-x F.sub.2+x isomers) to the total amount of CCl.sub.3 CClF.sub.2 and CCl.sub.3 CF.sub.3 (i.e., the more unsymmetric C.sub.2 Cl.sub.4-x F.sub.2+x isomers) is at least about 1:9, with an isomerization catalyst to produce isomerization product wherein there is less than about 50,000 parts by weight total CCl.sub.2 FCCl.sub.2 F and CCl.sub.2 FCClF.sub.2 per million parts by weight total of CCl.sub.3 CClF.sub.2 and CCl.sub.3 CF.sub.3 ; (ii) contacting the isomerization product with HF in the vapor phase in the presence of a fluorination catalyst comprising trivalent chromium at an elevated temperature below 400.degree. C. selected to provide a fluorination product containing C.sub.2 Cl.sub.2 F.sub.4, C.sub.2 Cl.sub.3 F.sub.3 and between about 10 and 90 percent of the C.sub.2 Cl.sub.4 F.sub.2 from the isomerization product, wherein the ratio of CCl.sub.2 FCCl.sub.2 F to CCl.sub.3 CClF.sub.2 and the ratio of CCl.sub.2 FCClF.sub.2 to CCl.sub.3 CF.sub.3 are both greater than the ratios thereof in the isomerization product and wherein the molar ratio of CClF.sub.2 CClF.sub.2 to CCl.sub.2 FCClF.sub.2 is less than about 1:9; (iii) recovering the C.sub.2 Cl.sub.2 F.sub.4 and a first portion of the C.sub.2 Cl.sub.3 F.sub.3 from the fluorination product; and (iv) recycling C.sub.2 Cl.sub.4 F.sub.2 and a
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Gervasutti, C. et al., J. Fluorine Chem., 19, 1-20, 1981/82.
Bitner, J.L. et al., U.S. Dept. Comm. Off. Tech. Serv. Rep. 136732, 25-27, 1958.
E. I. Du Pont de Nemours and Company
Killos Paul J.
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