HFC-125 (C2HF5), HFC-32 (CH2F2) and like alternative refrigerants are widely used as vital alternatives for CFCs, HCFCs, etc., which deplete the ozone layer. However, these alternative refrigerants exhibit strong greenhouse effects, and their diffusion may enhance the effects of global warming. As a countermeasure, HFC-125 (C2HF5), HFC-32 (CH2F2), etc., are recovered after use, but it is impossible to recover them completely. In addition, the diffusion thereof due to leakage, etc., cannot be ignored. The use of CO2 or hydrocarbon-based materials as an alternative is also under consideration. However, because CO2 refrigerants are inefficient, equipment using such refrigerants inevitably becomes large, causing problems in the comprehensive reduction of greenhouse gas emissions when energy consumption is also considered. Hydrocarbon-based materials are highly combustible and therefore pose safety problems.
2,3,3,3-Tetrafluoropropene (HFO-1234yf, CF3CF═CH2), which is an olefinic HFC having a low global warming potential, is currently attracting public attention as a substance that can solve these problems.
HFO-1234yf can be produced by using 1,1,1,2,3-pentafluoropropane (HFC-245eb) as a starting material and subjecting the material to dehydrofluorination in the presence of a catalyst. This is the predominant method for obtaining HFO-1234yf at a high yield. Patent Literature (PLT) 1 listed below, for example, discloses a process for preparing 2,3,3,3-tetrafluoropropene (HFO-1234yf), wherein HFC-245eb is subjected to dehydrofluorination in the presence of an alumina catalyst.
However, when HFC-245eb is subjected to the dehydrofluorination reaction, 1,3,3,3-tetrafluoropropene (HFO-1234ze), 1,1,1,3,3-pentafluoropropane (HFC-245fa) and like by-products are produced in addition to the objective 2,3,3,3-tetrafluoropropene (HFO-1234yf), and unreacted HFC-245eb may also remain. Therefore, in order to economically produce 2,3,3,3-tetrafluoropropene (HFO-1234yf), the effective use of these components is desired.