Process for producing 1,1,1,2,2-pentafluoroethane

Details Process for producing 1,1,1,2,2-pentafluoroethane Process for producing 1,1,1,2,2-pentafluoroethane

2000-04-05

2002-05-21

Siegel, Alan (Department: 1621)

Organic compounds -- part of the class 532-570 series

Organic compounds

Halogen containing

C570S165000, C570S166000, C570S167000, C570S168000, C570S169000

Reexamination Certificate

active

06392106

ABSTRACT:

TECHNICAL FIELD
The present invention relates to a process for producing 1,1,1,2,2-pentafluoroethane (HFC-125).
BACKGROUND ART
1,1,1,2,2-pentafluoroethane (HFC-125), which is a useful hydrofluorocarbon compound for its zero ozone depleting potential, is used in applications such as refrigerant, foaming agent, solvent, propellant and dry-etchant.
Among known processes for producing HFC-125, U.S. Pat. No. 3,755,477 discloses a process comprising fluorinating perchloroethylene or 2,2-dichloro-1,1,1-trifluoroethane (HCFC-123), and U.S. Pat. No. 5,334,787 discloses a process comprising fluorinating 2,2-dichloro-1,1,1-trifluoroethane (HCFC-123) or 2-chloro-1,1,1,2-tetrafluoroethane (HCFC-124).
These processes produce, in addition to the target HFC-125, various compounds as impurities including chlorofluoroethanes (CFCs) such as 1,2,2-trichrolo-1,1,2-trifluoroethane (CFC-113), 2,2,2-trichrolo-1,1,1-trifluoroethane (CFC-113a), 1,2-dichrolo-1,1,2,2-tetrafluoroethane (CFC-114), 2,2-dichrolo-1,1,1,2-tetrafluoroethane (CFC-114a), 2-chrolo-1,1,1,2,2-pentafluoroethane (CFC-115), etc.; 2-chrolo-1,1,1-trifluoroethane (HCFC-133a) and 1,1,1,2-tetrafluoroethane (HFC-134a). Further, when HCFC-123 is used as a starting material, part of HCFC-123 is fluorinated to form HCFC-124. Whereas, when HCFC-124 is used as a starting material, HC1 produced therein as a by-product reacts with the unreacted HCFC-124 to produce HCFC-123.
Among these compounds, HCFC-123 and HCFC-124 can be converted into the target HFC-125 by fluorination; therefore, in the case where a single gas-phase reactor is used for fluorination, they are economically recycled together with the unreacted HF, and fed to the reactor to be reused as starting materials together with newly added HCFC-123 or HCFC-124.
On the other hand, among the impurities, CFC-115 and HFC-134a respectively have a boiling point close to that of the target HFC-125; therefore, they are prone to be contained in HFC-125 when separating HFC-125 from the reaction mixture. HFC-125 needs to be highly purified in order to be used in the above-mentioned applications; however, the separation of CFC-115 is difficult in the subsequent purifying process of HFC-125, and the separation can not be achieved by way of a usual distillation process, whereby disadvantageously causing purity degradation and low yield of HFC-125. It is necessary to conduct a special distillation process such as an extractive distillation to effect sharp separation of CFC-115 from HFC-125 (Japanese Unexamined Pat. Publication No. 3082/1996). The separation of CFC-115 thus necessitates additional apparatuses for extractive distillation and the like, which leads to increased costs of equipment and production.
Furthermore, in the case of reusing HCFC-123, HCFC-124, HF and the like as the feedstocks, CFCs such as CFC-113, 113a, 114 and 114a are contained in the feedstocks and converted to CFC-115 as a result of a further fluorination in a reactor, thereby increasing the amount of CFC-115 contained in the reaction products.
Among known processes for the preparation of HFC-125 by using HCFC-124 as a starting material with reduced production of CFCs, U.S. Pat. No. 5,475,167 discloses a process which uses Cr
2
O
3
as a catalyst, whereby the amount of CFC-115 relative to HFC-125 is regulated to about 0.1-0.5%. However, since the process employs particular Cr
2
O
3
catalyst pre-treated with CO, H
2
or H
2
O, the pretreatment of catalyst is necessarily conducted to cause the process to be complicated. Moreover, HCFC-124 and HF in the process continuously flow and react together in the reactor and HCFC-123, HCFC-124, HF and the like are not reused as feedstocks; therefore, if the reaction products are recycled, fluorination of CFCs contained in the reaction products would be promoted to increase the production ratio of CFC-115.
WO95/16654 discloses a process for producing HFC-125 which comprises the steps of fluorinating perchloroethylene to produce HCFC-122, HCFC-123 or HCFC-124, removing CFCs such as CFC-112, 113 and 114 from the reaction product, and then further fluorinating the reaction product. However, since, according to this process, HFC-125 is produced by two-step fluorination of perchloroethylene used as the starting material, it is impossible to know how to reduce the production of CFC-115 in a process wherein a single gas-phase reactor is used for fluorination and the reaction products are recycled.
DISCLOSURE OF INVENTION
A primary object of the present invention is to provide a process for producing HFC-125 by fluorinating HFCF-123 and/or HCFC-124 as a starting material with HF and reusing CFC-123, HCFC-124 and HF in the reaction mixture as feedstocks for fluorination, wherein the production of CFC-115, which is a product difficult to be separated from HFC-125, can be reduced.
The inventors conducted an extensive study considering the above-mentioned problems in the prior art. As a result, the inventors found that, in the process for producing HFC-125 by fluorinating HCFC-123 and/or HCFC-124 as a starting material with HF and recycling HCFC-123, HCFC-124 and HF as feedstocks for fluorination, the impurities such as CFCs including CFC-113, 113a, 114, 114a and the like are mostly isomerized or fluorinated products of CFC-113a which is formed as a result of dismutation of HCFC-123, and that, because CFC-113, CFC-113a and the like among the impurities are very quickly fluorinated, most of the CFCs turn to CFC-114a when a steady state is reached, i.e., when the composition of reaction mixture is substantially fixed during the continuous reaction. The inventors also found that the amount of CFCs present in the recycled materials can be effectively decreased by separating the fluorinated reaction mixture into a portion mainly containing HFC-125 and a portion mainly containing HCFC-123, HCFC-124 and HF, removing a fraction mainly containing CFC-114a from the latter portion, and recycling the residual part of the latter portion as part of feedstocks for the continuous fluorinating reaction. Based on the above findings, the present invention was accomplished, which is capable of remarkably reducing the amount of CFC-115 contained in the target HFC-125.
Thus, the invention provides a process for producing 1,1,1,2,2-pentafluoroethane as described below.
(1) a process for producing 1,1,1,2,2-pentafluoroethane (HFC-125) by fluorinating with hydrogen fluoride at least one of 2,2-dichloro-1,1,1-trifluoroetahne (HCFC-123) and 2-chloro-1,1,1,2-tetrafluoroethane (HCFC-124) as a starting material, the process being characterized by
separating the reaction mixture resulting from the fluorination into a product portion A mainly containing 1,1,1,2,2-pentafluoroethane (HFC-125) and a product portion B mainly containing 2,2-dichloro-1,1,1-trifluoroethane (HCFC-123), 2-chloro-1,1,1,2-tetrafluoroethane (HFCF-124) and hydrogen fluoride (HF), removing a fraction mainly containing 2,2-dichloro-1,1,1,2-tetrafluoroethane (CFC-114a) from the product portion B, and recycling the rest of the product portion B as part of feedstocks for fluorination.
(2) a process according to the item 1, wherein the method of separating the reaction mixture resulting from the fluorination into the product portion A mainly containing 1,1,1,2,2-pentafluoroethane and the product portion B mainly containing 2,2-dichloror-1,1,1-trifluoroethane, 2-chloro-1,1,1,2-tetrafluoroethane and hydrogen fluoride is a partial condensation of the reaction mixture, using a heat exchanger, for giving a non-condensate mainly containing 1,1,1,2,2-pentafluoroethane and a condensate mainly containing 2,2-dichloro-1,1,1-trifluoroethane, 2-chloro-1,1,1,2-tetrafluoroethane and hydrogen fluoride.
(3) a process according to the item 1 or 2, wherein the method of removing the fraction mainly containing 2,2-dichloro-1,1,1,2-tetrafluoroethane from the product portion B is a method of distilling the product portion B and withdrawing the fraction from the middle section of a distillation column.
(4) a process according to the item 2 or 3, wherein the product portion B is introduced

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