Preparation of 1,1,1,3-tetrafluoropropene( 1234ze )

Abstract: Disclosed is a process for the preparation of cis/trans 1,1,1,3-tetrafluoro-2-propene (1234 ze) which comprises (a) contacting 1,1,1,3,3-pentafluoropropane (245fa) with an alkaline solution, preferably an aqueous or alcoholic solution of a base such as KOH, NaOH, Ca(OH) 2 or Mg(OH) 2 , or with a chromium-based catalyst, such as fluorided Cr 2 O 3 or fluorided Cr/Ni/Alf 3 , and (b) recovering cis/trans 1,1,1,3-tetrafluoro-2-propene from the reaction mixture.

Description: This invention relates to preparation of cis/trans 1,1,1,3-tetrafluoropropene ("1234ze"), a monomer useful for the preparation of various homopolymers and copolymers, particularly to processes for the dehydrofluorination of 1,1,1,3,3-pentafluoropropane ("245fa"), a known blowing agent, to 1234ze using a chromium-based catalyst. While the prior art, R. N. Haszeldine, J. Chem. Soc., 1952 (3490), describes the synthesis of cis/trans 1,1,1,3-tetrafluoropropene by fluorination of 1,1,1-trifluoro-2-propyne, this latter feed stock material is not available commercially. Knunyants et al, in Bulletin of the Academy of Sciences of the USSR, Division of Chemical Sciences 1960 pages 1312 to 1317, incidentally describe a conversion of 1,1,1,3,3-pentafluoropropane to 1234ze using KOH powder suspended in ether. We propose herein a process for the preparation of 1234ze by contacting 245fa with a chromium-based catalyst and recovering cis/trans 1,1,1,3-tetrafluoro-2-propene from the resulting reaction mixture. In the prior art, WO96/05157 proposes a Cr 2 O 3 catalyst for use in dehydrofluorination reactions, exemplified by the preparation of trifluoroethylene from 1,1,1,2-tetrafluoroethane. Other chromium catalyst disclosures include EP234002, which uses chromium oxyfluoride to convert 1,1,1-trifluoro compounds to 1,1-difluoro compounds, and WO96/41679 and JP-A-54/130507, which use a fluorided Cr 2 O 3 catalyst to convert 1,1-difluoroethane to vinyl fluoride and vinylidene fluoride respectively. The process of the present invention comprises a process for the preparation of cis/trans 1,1,1,3-tetrafluoro-2-propene which comprises (a) contacting 1,1,1,3,3-pentafluoropropane with an oxygen-containing gas in the presence of a fluorided catalyst selected from Cr 2 O 3 and Cr/Ni/AlF 3 , and (b) recovering cis/trans 1,1,1,3-tetrafluoro-2-propene from the resulting reaction mixture. The catalyzed process is preferably carried out in the gas phase. Use of the oxygen-containing gas such as air is to extend the catalyst lifetime, the level of oxygen generally being from about 1 to about 10 volume percent (preferably about 2 to 5%), based on the volume of the organic feed. Temperatures of from about 100°C. to about 600°C. are typically used, preferably from about 300°C. to about 400°C. The pressure can be atmospheric. Contact time (total flow rate per catalyst volume) is typically from about 1 to about 60 seconds, preferably from about 20 to 50 seconds. The catalyst is a fluorided chromium-based catalyst such as fluorided chromium oxide, Cr 2 O 3 , which chromium-based catalyst is either unsupported or supported on a support such as activated carbon, graphite, fluorided graphite or fluorided alumina, the chromium catalyst being used alone or in the presence of a co-catalyst selected from a nickel, cobalt, manganese or zinc salt. Two such preferred chromium catalysts are high surface area chromium oxide and chromium/nickel on fluorided alumina (Cr/Ni/AlF 3 ), preparation of this latter catalyst being taught, for example, in European Patent 486333. The chromium-based catalysts are preferably activated before use, typically by a procedure wherein the catalyst bed is heated to about 370°-380°C. (normally with a continuous flow of nitrogen), after which a mixture of approximately equal volumes of HF and air or nitrogen (preferably nitrogen) are fed over the catalyst bed for about 18 hours. The following examples are illustrative. Example 1. 52.4 Grams of a high surface area Cr 2 O 3 catalyst was activated by first feeding 30 ccm of nitrogen for 2 hours at 370°C, followed by cofeeding 30 ccm of HF and 30 ccm of nitrogen for 18 hours at 370°C. Subsequently, a mixture of 20 ccm of 245fa and 3 ccm of air (equal to about 3 volume % of oxygen, based on the 245fa volume) was fed over the catalyst bed at 400°C for a contact time of 45 seconds. Conversion was 96.2%. Selectivity for the desired (1234ze) product was about 96.3% (about 18.5% cis, about 77.8% trans). Performance of the catalyst was steady for 360 hours. Example 2. Example 1 was repeated using Cr/Ni/AlF 3 catalyst (activated at 370°C. using a cofeed of 30 ccm of nitrogen and 30 ccm of HF for 18 hours) in a series of 3 tests, using the same temperature and air/245fa feed ratio, but with the contact time between 26 and 39 seconds. Conversions ranged from 88 to 94.5%. Selectivity for the desired (1234ze) product ranged from 96.2 to 98.5% (17.7 to 20.5% cis, 77 to 80.5% trans).

Claims: A process for the preparation of cis/trans 1,1,1,3-tetrafluoro-2-propene which comprises (a) contacting 1,1,1,3,3-pentafluoropropane with an oxygen-containing gas in the presence of a fluorided catalyst selected from Cr 2 O 3 and Cr/Ni/AlF 3 , and (b) recovering cis/trans 1,1,1,3-tetrafluoro-2-propene from the resulting reaction mixture. A process as in Claim 1 wherein the catalyst is fluorided Cr 2 O 3 . A process as in Claim 1 wherein the catalyst is fluorided Cr/Ni/AlF 3 . A process as in any one of claims 1 to 3 in which the oxygen-containing gas is air. A process as in any of the preceding claims in which the level of oxygen in an organic feed to the catalyst is from 1 to 10vol% based on the volume of the organic feed. A process as in claim 5 in which said level of oxygen is from 2 to 5vol%. A process as in any one of the preceding claims in which the temperature is from 300°C to 400°C. A process as in any one of the preceding claims in which the contact time, defined as total rate of flow divided by volume of catalyst, is from 20 to 50s. A process as in any one of the preceding claims in which the fluorided catalyst is activated before use.

Inventors: ELSHEIKH MAHER YOUSEF, FELLENGER PAUL DAVID, ELSHEIKH, MAHER YOUSEF, FELLENGER, PAUL DAVID
Applicants: ATOFINA CHEM INC, ATOFINA CHEMICALS, INC.
Application year: 1999
Main classification: C07C17
IPC codes: C07C17, C07B61, B01J27, C07C21, B01J23