Hydrolysis of polymaleic anhydride is a polycarboxylic acid type scale inhibitor and dispersant, its preparation is carried out in two steps, first in the solution to polymerize maleic anhydride to obtain polymaleic anhydride, and then hydrolyzed polymaleic anhydride can be obtained.

(1) Hydrolysis of polymaleic anhydride The stoichiometric maleic anhydride is dissolved in an appropriate amount of toluene and added to the polymerization reactor equipped with an electric stirrer, a reflux condenser, a dripping funnel and a thermometer, and then the metered dibenzoyl peroxide is dissolved in an appropriate amount of toluene to prepare a dilute solution and placed in the drop funnel on the polymerization reactor. Start stirring and raise the temperature to toluene reflux temperature. At this time, open the nitrogen protective air flow, and slowly add toluene solution dissolved with benzoyl peroxide dropwise. The reaction was carried out under the protection of nitrogen from beginning to end, and as the reaction progressed, polymaleic anhydride products were gradually precipitated from toluene. When dibenzoyl peroxide is added within 3~4h, continue to maintain the reflux temperature reaction for 1h. Separation of polymerization products to obtain brownish-yellow viscous solid polymaleic anhydride. Add metered deionized water to the polymerization product polymaleic anhydride, stir and hydrolyze at 85~100 °C for 1h, or saponify polymaleic anhydride with industrial caustic soda aqueous solution to obtain hydrolyzed sodium salt of polymaleic anhydride.

(2) Preparation of hydrolyzed polymaleic anhydride by aqueous solution method A certain proportion of deionized water is added to the reactor equipped with an electric stirrer, a reflux condenser, and a dripping funnel, and then metered ferric chloride is added, and the stirring is started, and the temperature of the water in the reactor is raised to 90~95 °C. The quantitative maleic anhydride was added to the reactor in batches, stirred thoroughly and kept the water temperature in the reactor at 95~100 °C. After the maleic anhydride in the reactor is completely dissolved, the weighing of hydrogen peroxide aqueous solution is slowly added dropwise to the reaction solution in the reactor under stirring, and the drop acceleration is controlled to maintain the temperature of the polymerization reaction between 95~100 °C, and the whole reaction process takes about 3~4h. The product is a brownish-yellow aqueous solution.