(583bd) Dehydrofluorination of 1,1,1,2,3,3-Hexafluoropropane to 1,2,3,3,3-Pentafluoropropene for the Production of a Refrigerant 2,3,3,3-Tetrafluoropropene

While the protection of ozone layer has been successfully achieved by banning the manufacture of refrigerants chlorofluorocarbons (CFCs) containing chlorines, the recent interest to the climate change resulting in global warming urged the current ozone-safe but highly global warming refrigerants hydrofluorocarbons (HCFCs), such as 1,1,1,2-tetrafluoroethane (HFC-134a), with the environmentally-friendly refrigerants such as 2,3,3,3-tetrafluoropropene (HFO-1234yf) with the lower global warming potient. HFO-1234yf can be obtained by consecutive hydrogenation and dehydrofluorination purocesses using hexafluoropropene. In the process to obtain HFO-1234yf from 1,1,2,3,3,3-hexafluoropropene (HFP), hydrogenation of HFP to 1,1,1,2,3,3-hexafluoropropane (HFC-236ea) is performed then hydrogenated HFC-236ea is dehydrofluorinated to produce 1,2,3,3,3-pentafluoropropene (HFO-1225ye). HFO-1225ye is further hydrogenated to 1,1,1,2,3-pentafluoropropane (HFC-245eb) then dehydrofluorinated to the final refrigerant product 2,3,3,3-tetrafluoropropene (HFO-1234yf). In this study, we described the catalytic dehydrofluorination of HFC-236ea to HFO-1225ye, which must be similar to the dehydrofluorination of HFC-245eb to HFO-1234yf. Catalysts including commercially available AlF₃, MgF₂-supported Cr (Cr/MgF₂), commercially available Cr₂O₃ powder, and fluorinated CrO_xF_y were used for the dehydrofluorination. While non-fluorinated metal oxides had a negligible catalytic activity of dehydrofluorination, metal fluorides and fluorinated catalysts exhibited good catalytic activity. With a very low BET surface area (< 10 m²/g) calculated by N₂-physisorption results of fluorinated catalysts, the high dispersion of catalytic active sites does not seem to be the reason for the improved catalytic activity. The observations on the acidity and fluorine modification using XPS, XRD, and SEM strongly indicated that the metal fluorides on the catalyst surface are responsible to the improved catalytic activity.