Preparation method of cellulose acetate propionate mixed ester with high propionyl content

The invention relates to a preparation method of cellulose acetate propionate mixed ester with high propionyl content. Cellulose is prepared from the following components in parts by weight: 650g of wood pulp, 2630g of propionic acid, 40g of acetic anhydride, 2070g of propionic anhydride and 19.5-52g of a catalyst, wherein the ratio of a liquid acid catalyst to heteropolyacid catalyst is 4:6 to 6:4. The preparation method comprises the steps of activating, carrying out esterification reaction, mixing, adding a magnesium acetate solution, hydrolyzing and carrying out chromatography; and then, sequentially carrying out conventional filtration, washing and drying to obtain a finished product. The preparation method has the advantages that the finished product of cellulose acetate propionate, prepared by using the method, contains more than or equal to 46% of propionyl content and less than or equal to 2% of acetyl and is stable in performance; the catalyst is a mixture of liquid acid and heteropolyacid, so that the consumption of sulfuric acid is reduced, furthermore, corrosion to process equipment and environment pollution can be reduced, and the process safety can be improved; and meanwhile the heteropolyacid is additionally applied, so that the esterification reaction is accelerated, and hydrolysis reaction is more precise and controllable.