Preparation method of 4,4'-diphenylmethane diisocyanate

The invention relates to a preparation method of 4,4'-diphenylmethane diisocyanate. The method comprises the steps of adding a catalyst polyoxometallate and a solvent into a reaction vessel; adding araw material 4,4'-diaminodiphenylmethane, phenylsilane, an acid-binding agent and a dehydrating agent into the reaction vessel; uniformly mixing the materials, finally adding gaseous carbon dioxide into the reaction vessel, and magnetically stirring the mixture for a thorough reaction at a certain temperature to obtain a product. According to the method, M-Anderson type heteropoly acid is used asthe catalyst, and the catalyst only needs mild reaction conditions and is high in specific selectivity, recyclable and environmentally friendly; the cleanliness of an industrial reaction is improved,the economy of the process is improved, the manufacturing cost and the generation of three wastes are reduced, the environmental protection pressure is reduced, and industrial production is facilitated. 本发明涉及一种4,4'二苯基甲烷二异氰酸酯的制备