Organic compounds -- part of the class 532-570 series – Organic compounds – Halogen containing
Patent
1995-02-17
1997-02-04
Evans, Joseph E.
Organic compounds -- part of the class 532-570 series
Organic compounds
Halogen containing
C07C 17389, C07C 1908
Patent
active
056000405
DESCRIPTION:
BRIEF SUMMARY
This application represents the U.S. national filing (371) of International Application No. PCT/US92/05851 filed Jul. 17, 1992 and published as WO94/02440 Feb. 3, 1994.
FIELD OF THE INVENTION
This invention relates to the separation of fluorocarbon products, more particularly to the separation of the isomers of tetrafluoroethane, CHF.sub.2 CHF.sub.2 (HFC-134) and CF.sub.3 CH.sub.2 F (HFC-134a).
BACKGROUND
Isomers of C.sub.2 H.sub.2 F.sub.4 (HFC-134s) are used as refrigeration fluids for a number of applications. HFC-134s can also be used as starting materials for producing various other halogenated hydrocarbons. Products containing isomers of C.sub.2 H.sub.2 F.sub.4 are produced in various degrees of isomer purity. One method of producing HFC-134s is by the hydrogenolysis of C.sub.2 C.sub.12 F.sub.4 isomers (CFC-114s). In the manufacture of C.sub.2 Cl.sub.2 F.sub.4 by the chlorofluorination of perchloroethylene the product typically consists of a mixture of the isomers, CClF.sub.2 CClF.sub.2 (CFC-114) and CF.sub.3 CCl.sub.2 F (CFC-114a) (see e.g., U.S. Pat. No. 4,605,798). If the CFC-114s are then used to produce CHF.sub.2 CClF.sub.2 (HCFC-124a), CF.sub.3 CHClF (HCFC-124), HFC-134 or HFC-134a by hydrodehalogenation, the products often consist of a mixture of C.sub.2 HClF.sub.4 and C.sub.2 H.sub.2 F.sub.4 isomers (see e.g., GB 1,578,933).
It has been found that for many applications, the presence of the second isomer of the isomer pair can significantly alter the physical and chemical properties of the desired isomer. For example, variation in the HFC-134/HFC-134a ratio in the product can result in dramatic variability in the thermodynamic properties critical for use in refrigeration applications. For use as a raw material feed, the presence of the unwanted isomer can result in yield loss due to increased side reactions. As a result, there has been a continually increasing demand for high isomer purity materials. Consequently, the separation of HFC-134 isomers represents a significant aspect of preparing these compounds for various applications.
Purification of halogenated hydrocarbon products has been the subject of considerable research. Of particular interest are the challenges presented in separating desired halogenated hydrocarbon products from materials such as impurities in the starting materials used to produce the halogenated hydrocarbon, excess reactants, and reaction by-products and/or reaction co-products which are difficult to remove by standard separation methods such as distillation. Selective sorbents such as carbons and zeolites have been proposed for various separations. The effectiveness of separation using such sorbents varies with the chemical components and the sorbents involved. The successful design of sorbent based systems is considered highly dependent upon experimental determination of whether the relative sorbencies of the particular compounds are suitable for such systems.
HFC-134 has a boiling point of -23.degree. C. and HFC-134a has a boiling point of -26.5.degree. C. Distillation is consequently relatively inefficient as a means for separating these two compounds.
SUMMARY OF THE INVENTION
We have found that mixtures of the isomers of C.sub.2 H.sub.2 F.sub.4 (i.e., CHF.sub.2 CHF.sub.2 and CF.sub.3 CH.sub.2 F) can be substantially separated by using a sorbent for CHF.sub.2 CHF.sub.2 selected from the group consisting of (i) inorganic molecular sieves (e.g., zeolites) having greater intermediate electronegativities than Zeolite Na-X, and (ii) activated carbons. The present invention provides a process for separating a mixture of CHF.sub.2 CHF.sub.2 and CF.sub.3 CH.sub.2 F to provide a product wherein the mole ratio of CF.sub.3 CH.sub.2 F relative to CHF.sub.2 CHF.sub.2 is increased which comprises contacting said mixture with said sorbent at a temperature within the range of -20.degree. C. to 300.degree. C. and a pressure within the range of 10 kPa to 3000 kPa and for a period of time sufficient to remove a substantial amount of the CHF.sub.2 CHF.sub.2. As a result, the
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Hiromoto, Ono et al, "Purification of 1,1,1,2-tetrafluoroethane", Chemical Abstracts, 115(17), Oct. 18, 1991, Abstract No. 182607b.
Corbin David R.
Mahler Barry A.
E. I. Du Pont de Nemours and Company
Evans Joseph E.
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