The present invention provides a process for preparing 1234yf, comprising: (i) contacting 1233xf with hydrogen fluoride HF in gas phase in the presence of a fluorination catalyst under conditions sufficient to produce a reaction mixture; (ii) separating the reaction mixture into a first stream comprising HCl, 1234yf and a second stream comprising HF, unreacted 1233xf and 245cb; (iii) recycling at least a part of the second stream at least in part back to step (i). The present invention also provides a process for preparing 1234yf, comprising: (i) contacting 1233xf with hydrogen fluoride HF in gas phase in the presence of a fluorination catalyst under conditions sufficient to produce a reaction mixture; (ii) separating the reaction mixture into HCl and a stream containing the fluorinated products; (iii) separating said stream containing the fluorinated products into a first stream comprising 1234yf and a second stream comprising HF, unreacted 1233xf and 245cb; (iv) recycling at least a part of the second stream at least in part back to step (i).