Method for preparing hexahydrophthalic anhydride

The invention provides a method for preparing hexahydrophthalic anhydride, belonging to the field of synthesis of fine chemicals. The method comprises the steps: phthalic anhydride is heated to 50 DEG C and injected into a phthalic anhydride dissolving tower, the phthalic anhydride is dissolved with a solvent, the temperature of the dissolving tower is 50-70 DEG C, the dissolved phthalic anhydride solution is pressurized and injected into a constant-pressure reaction kettle or a fixed bed reactor filled with a selective hydrogenation catalyst to carry out selective hydrogenation reaction, the product directly enters a solvent recovery column after hydrogenation reaction, the solvent is distilled off at the tower top, the materials at the tower bottom enter a hexahydrophthalic anhydride rectifying tower, the hexahydrophthalic anhydride is obtained at the tower bottom, and a mixture of phthalide, o-toluic acid and o-methyl cyclohexanecarboxylic acid is obtained at the tower top; and the mixture obtained at the top of the rectifying tower is recrystallized to crystallize phthalide. The method has the advantages of simple operation, favorable economic benefit and industrial application prospects.