Process of separating pentafluoroethane and process of producing

Details Process of separating pentafluoroethane and process of producing Process of separating pentafluoroethane and process of producing

1997-07-02

1998-12-15

Manoharan, Virginia

Distillation: processes, separatory

With fractional condensation of vapor outside still

62115, 95 39, 203 29, 203 39, 203 91, 570177, 570178, B01D 300, C07C 17383, C07C 1908

Patent

active

058491600

DESCRIPTION:

BRIEF SUMMARY
DESCRIPTION

1. Techincal Field
The present invention relates to a process of producing 1,1,1,2,2-pentafluoroethane (which is also referred to as "HFC-125" or "pentafluoroethane" herein and the attached claims). Particularly, the present invention relates to a process of effectively separating pentafluoroethane out of a reaction mixture comprising pentafluoroethane and a process of producing pentafluoroethane using such a separation process.
2. Background Art
Pentafluoroethane is prepared by reacting perchloroethylene (which is also referred to as "PCE" herein and the attached claims) and excessive hydrogen fluoride (which is also referred to as "HF" herein and the attached claims) (see U.S. Pat. No. 4,766,260). In that reaction, the following compounds are formed as by-products: 1,1-dichloro-2,2,2-trifluoroethane and 1,2-dichloro-1,1,2-trifluoroethane (which are also referred to as "dichlorotrifluoroethane" or "HFC-123" together as herein and the attached claims), 1,2,2,2-tetrafluoro-1-chloroethane and 1,1,2,2-tetrafluoro-1-chloroethane (which are also referred to as "tetrafluorochloroethane" or "HFC-124" together as herein and the attached claims) and hydrogen chloride (which is also referred to as "HCl" herein and the attached claims). Therefore, it is necessary to remove products except HFC-125.
As to separation of HFC-123 and HFC-124 out of HF, for example, a process has been known in which azeotropic distillation is used (see U.S. Pat. Nos. 5,094,773 and 4,944,846). An alternative process of separating produced HFC-123 and HFC-124 out of HF excessively present, a process has been known in which a mixture gas containing those components are condensed and divided into a liquid phase rich in HF and another liquid phase rich in HFC-123 and HFC-124, then the latter phase is subjected to distill off HFC-123 and HFC-124 as azeotrope mixtures with HF and remaining pure HFC-123 and HFC-124 are obtained (see U.S. Pat. No. 4,911,792). This process is characterized in that an organic phase as a lower layer (which corresponds to the phase rich in HFC-123 and HFC-124) contains HF of less than 15% by mole and an HF phase as an upper layer contains HF of not less than 93% by mole.
When the separation process as described above is applied to a reaction gas contains a large amount of HFC-125 as in the case of the production of HFC-125, a relatively large amount of HFC-125 is distributed in both of the upper and the lower layers. In order to recover HFC-125 from the gas mixture, the upper and lower layers separated into immiscible liquid phases should be subjected to distillation. Thus, a process including the liquid separation and the azeotropic distillation is not economical since facilities thereof are so complicated so that a capital cost is increased.
Thus, it has been desired to develop a process in which HFC-125 is separated and refined effectively, particularly in a simpler manner from a reaction mixture in the production of HFC-125.


DISCLOSURE OF INVENTION

The present inventors have found that a liquid mixture containing perchloroethylene, pentafluoroethane, hydrogen chloride and hydrogen fluoride has a composition range in which the mixture does not separate into immiscible liquid phases within an industrially operative temperature range, for example -30.degree. to 90.degree. C. (the composition range depends on a temperature a little, and is for example a composition range of which PCE concentration is not larger than about 3% by mole), and then reached the present invention.
That is, the first aspect of the present invention provides a process of separating pentafluoroethane out of a gas mixture which contains at least perchloroethylene, pentafluoroethane, hydrogen chloride and hydrogen fluoride, characterized in that the process comprises the steps of: the first liquid phase which contains, as a main component, perchloroethylene contained in the gas mixture and the first vapor phase which contains the rest of the gas mixture, obtain the second vapor phase which contains pentafluoroethane and hydrogen ch

REFERENCES:
patent: 4766260 (1988-08-01), Manzer et al.
patent: 4911792 (1990-03-01), Manzer et al.
patent: 4944846 (1990-07-01), Manzer et al.
patent: 5094773 (1992-03-01), Manzer et al.
patent: 5453551 (1995-09-01), Lacroix et al.
patent: 5569794 (1996-10-01), Tang

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