Preparation method of hexafluorodianhydride

A preparation method of hexafluorodianhydride comprises the following steps: S1, mixing hexafluoroacetone trihydrate with methylcyclohexane, and carrying out an oxidation reaction with thionyl chloride to prepare hexafluorodianhydride monohydrate; s2, under the action of a trifluoromethanesulfonic acid catalyst, the hexafluorodianhydride monohydrate and o-xylene are subjected to a coupling reaction, and a hexafluorodianhydride crude product is prepared; and S3, carrying out water washing, neutralization, primary concentration and primary crystallization on the hexafluorodianhydride crude product. And finally preparing a hexafluorodianhydride refined product through the processes of chromatographic column decoloration, secondary concentration, secondary crystallization, drying and the like. O-xylene is adopted as the solvent and the coupling agent, the defect that other solvents are added to reduce the reaction effect is overcome, the reaction time is shortened, the conversion rate of the raw materials is incr