Preparation of 5,5-Dimethylhydantoin

Method 1:

a. Add 600-800 parts of ammonium bicarbonate and 500-700 parts of acetone cyanohydrin to water, stir and fully dissolve, heat to 10°C and seal;

b. Add 30-50 parts of ammonia gas to the substance obtained in step a, slowly heat to 50-65°C, keep constant temperature for 1-2 hours, and stir;

c. Heat the substance obtained in step b to 75-85°C, induce air for 30-50 minutes, and then cool to room temperature After filtering, crude dimethyl hydantoin and mother liquor are obtained;

d. Add 950-1150 parts of crude dimethyl hydantoin obtained in step c to a mixture of 150-300 parts of water and 700-900 parts of mother liquor, stir while adding, heat to 80-98°C, add 3-8 parts of activated carbon, decolorize for 20-40 minutes, filter to remove activated carbon, cool and crystallize, centrifuge and dry, and obtain finished dimethyl hydantoin.

Method 2:

(1) Weigh 30 parts of water, 25 parts of ammonium bicarbonate and 35 parts of acetone cyanohydrin respectively; first put the weighed water and ammonium bicarbonate into a reactor, stir until completely dissolved, the stirring rate is 50 rpm, then add the weighed acetone cyanohydrin, react in the reactor at 40°C and 0.1MPa pressure for 8 hours, then cool the materials in the reactor to 35 for 6 hours to obtain 5,5-dimethylhydantoin crude product; the total volume of water and ammonium bicarbonate in step (1) accounts for 50% of the total volume of the reactor.

(2) Weigh 50 parts by weight of the crude 5,5-dimethylhydantoin obtained in step (1) and 40 parts by weight of water and add them to the second reactor to stir and dissolve. When the material in the second reactor is heated to 40°C, add 0.3 parts by weight of activated carbon to the second reactor. Continue to heat the second reactor. When the temperature of the material in the second reactor reaches 80°C, decolorize and keep warm for 30 minutes.

Then the material in the second reactor is filtered through a titanium rod microporous filter and a microporous bag filter in turn, and then pressed into a third reactor at a pressure of 0.1MPa. The material in the third reactor is kept at 70°C. After keeping warm for 10 minutes, it is pressed into a cationic resin column and an anionic resin column in turn at a pressure of 0.3MPa for filtration. After filtration, the filtrate is pressed into a crystallization kettle at a pressure of 0.1MPa, and cooled at an ambient temperature below 30°C for recrystallization;

In step (2), the total volume of the crude 5,5-dimethylhydantoin and water accounts for 70% of the total volume of the second reactor. In step (2), the titanium rod microporous filter model is T-17, with an outer size of 620mm×850mm, a theoretical pore size of 0.1um-30um, and a theoretical flow rate of 5.0-7.0T/h; the microporous bag filter model is DL-5P2S, with 5 filter bags, a filtration area of 2.5 square meters, a flow rate of 175 cubic meters/hour, and a working pressure of 0.5MPa. The cationic resin column uses cationic resins such as 001×4, 001×7, and the anionic resin column uses anionic resins such as 201×4, 201×7.

(3) When the material temperature in the crystallization kettle drops to 35°C, the material in the crystallization kettle is deliquated in a centrifuge at a speed of 950 rpm. The centrifuged material is dried at a drying temperature of 150°C for 4 hours.

Method 3:

Use the tail gas containing ammonia and carbon dioxide and raw materials produced in the industrial production process of melamine, sodium cyanate and nitrogen fertilizer, and continuously pass them into the bubbling reactor at a reaction system of 95-100℃ and pH=7.5-8.5 to produce 5,5-dimethylhydantoin; the raw material is a mixed solution of acetone cyanohydrin and water.

Further, the tail gas containing carbon dioxide and ammonia first enters the cyclone separator, removes the solid particles, and then enters the gas-liquid bubbling reactor. The mixed solution of acetone cyanohydrin and water is used as the raw material to enter from the top of the gas-liquid bubbling reactor, so that the gas phase is highly dispersed in the liquid phase, with a large liquid holding capacity and interphase contact surface, high mass transfer and heat transfer efficiency, control the reaction temperature at 95-100℃, and control the liquid material to stay in the tower for 20-30 minutes; after the reaction material flows out from the bottom of the tower, it is cooled and crystallized, and centrifuged to obtain 5,5-dimethylhydantoin.

The filtrate mainly contains water and the product 5,5-dimethylhydantoin. The filtrate is re-added to the reactor from the top of the bubbling reactor to recycle the water.