Hydrofluorocarbons (HFC) and in particular hydrofluoro-olefins such as 2,3,3,3-tetrafluoro-1-propene (HFO 1234yf) are compounds that are known for their properties as refrigerants and heat exchangers, extinguishers, propellants, foaming agents, swelling agents, dielectric gases, polymerization or monomer medium, support fluids, abrasive agents, drying agents and fluids for power production units. Unlike CSCs and HCFCs, which are potentially hazardous to the ozone layer, HFOs do not contain chlorine and therefore pose no problem to the ozone layer.
Several processes for manufacturing 1234yf are known.
WO 2008/002 499 describes a process for producing a mixture of 2,3,3,3-tetrafluoro-1-propene (HFO 1234yf) and 1,3,3,3-tetrafluoro-1-propene (HFO 1234ze) by pyrolysis of 1,1,1,2,3-pentafluoropropane (HFC 245eb).
WO 2008/002 500 describes a process for producing a mixture of 2,3,3,3-tetrafluoro-1-propene (HFO 1234yf) and 1,3,3,3-tetrafluoro-1-propene (HFO 1234ze) via catalytic conversion of 1,1,1,2,3-pentafluoropropane (HFC 245eb) on a dehydrofluorination catalyst.
These two abovementioned patent applications are thus directed toward the production of a mixture containing a substantial portion of the product 1234ze.
WO 2007/056 194 describes the preparation of 1234yf by dehydrofluorination of 245eb, especially on a catalyst based on nickel, carbon or a combination of the two.
The document Knunyants et al., Journal of the USSR Academy of Sciences, Chemistry Department, “Reactions of fluoro-olefins”, report 13, “Catalytic hydrogenation of perfluoro-olefins”, 1960, distinctly describes various chemical reactions on fluorine compounds. Said document describes the substantially quantitative hydrogenation of HFP on a platinum-supported palladium-based catalyst, the temperature rising from 20° C. to 50° C., and then being maintained at this value. Said document describes the dehydrofluorination of 1,1,1,2,3,3-hexafluoropropane (236ea) via passage through a suspension of KOH, to produce 1,2,3,3,3-pentafluoro-1-propene (1225ye). Said document describes the hydrogenation of 1,2,3,3,3-pentafluoro-1-propene (1225ye) to 1,1,1,2,3-pentafluoropropane (245eb) on an alumina-supported palladium catalyst. During this hydrogenation, a hydrogenolysis reaction also takes place, a significant amount of 1,1,1,2-tetrafluoropropane being produced. Said document describes the dehydrofluorination of 1,1,1,2,3-pentafluoropropane (245eb) to 2,3,3,3-tetrafluoro-1-propene (HFO 1234yf) via passage through a suspension of KOH. These reactions are described independently of each other, although it is indicated that it is possible to combine them to synthesize a range of ethylene, propylene and isobutylene derivatives containing variable amounts of fluorine.
Document U.S. Pat. No. 5,396,000 describes the preparation of 1,1,1,2,3-pentafluoropropane by catalytic dehydrofluorination of 1,1,1,2,3,3-hexafluoropropane (236ea) to 1,2,3,3,3-pentafluoro-1-propene (1225ye), followed by hydrogenation to produce the desired compound. The dehydrohalogenation of 236ea to 1225ye is performed in the gas phase, the reaction product being, in one example, sent directly to the next reactor in which the hydrogenation of the compound 1225ye to the compound 245eb takes place. It is also indicated in that document that the compound 236ea may be obtained by hydrogenation of hexafluoropropylene (HFP), making reference to the abovementioned Knunyants et al. document.
Document U.S. Pat. No. 5,679,875 describes the preparation of 1,1,1,2,3-pentafluoropropane by catalytic dehydrofluorination of 1,1,1,2,3,3-hexafluoropropane (236ea) to 1,2,3,3,3-pentafluoro-1-propene (1225ye), followed by a hydrogenation to produce the desired compound. The reactions are performed in the gas phase. It is also indicated in that document that the compound 236ea may be obtained by hydrogenation of hexafluoropropylene (HFP), making reference, inter alia, to the abovementioned Knunyants et al. document.
There is a need for a process for preparing 1234yf from a readily accessible starting material, and which leads to the desired product in high selectivity, and advantageously in high yield.