Method for reducing grain size of AC foaming agent

The invention relates to a method for effectively reducing the grain size of an AC foaming agent. In the invention, hydrazine hydrate and urea are used as raw materials, an alkaline method is used for synthesizing biurea which is the intermediate of the AC foaming agent, and the biurea is oxidized to form the AC foaming agent. In the method, the biurea is formed by using the alkaline method, a mother solution is used constantly and circularly to reduce the grain size of the biurea to make the oxidation reaction more complete, and a certain amount of solution of dimethyl sulfoxide or N,N-dimethylformamide is added during the oxidation reaction to control the grain size of the AC foaming agent. Due to the circular use of the washing and filtering water and the addition of amount of the solution of the dimethyl sulfoxide or N,N-dimethylformamide during the oxidation reaction, the produced AC foaming agent has the characteristics of fine and uniform grain size, light equipment corrosion, a little amount of waste