Preparation of methyl isocyanate Methylamine and phosgene are directly subjected to gas chromatography reaction at high temperature, and the reactor is a pipeline. The reaction temperature is higher than 400°C, and the material of the reactor is steel-lined graphite. The prevention of by-products and the elimination of reactor clogging are key in production. The main equipment of the methyl isocyanate separation and purification system is a dephosgenation tower, and the purified methyl isocyanate tower is a valve tower with 90 trays, all of which are made of high-nickel alloy steel materials.
The synthesis reaction of Carbaryl Dust is carried out in the presence of a solvent at a temperature of 60-80°C and a slight negative pressure. The resulting mixed solution is distilled, and the excess methyl isocyanate is distilled off from the top of the distillation column together with part of the solvent, and then reused. Carnavale is refined in solution to obtain pure product.
Preparation of naphthyl chloroformate Dissolve 100kg of naphthol and 200kg of toluene, pump into a reactor containing 600kg of toluene, stir, cool down to below -10°C, stop stirring, and introduce about 224kg of phosgene, and pass through in 4 hours. Begin to add alkali dropwise, control the temperature below 0°C, drip 400-500kg 20% lye solution in about 2 hours, make the pH of the brine layer = 6, drain off the salt water, and wash the naphthyl chloroformate twice with water, the general ester content is 14% to 15%.
The synthesis temperature of carbaryl is kept at 10～20℃, about 80kg of 40% monomethylamine is added dropwise at about 40min, then 120kg of 20% liquid caustic soda is added dropwise at about 10℃ in about 20min, stirred for 10min, and added dropwise to 30 % hydrochloric acid 80kg, the measured pH value is 5-6. The product is obtained after separation, washing and drying.
carbamoyl chloride method
Preparation of methylcarbamoyl chloride Methylcarbamoyl chloride was synthesized by chloroformylation of methylamine. The liquid-phase method and the gas-phase method are commonly used in industry, among which the gas-phase method has a higher yield and is easy to be continuous. The gas phase method is to heat methylamine to above 200 °C and phosgene to above 150 °C. After the two gases are mixed, they pass through a pipeline reactor at 240 to 300 °C. Or carbon tetrachloride cycle absorption. The main process conditions are: the ratio of monomethylamine and phosgene is 1:1.3 (volume ratio), the preheating temperature of methylamine and phosgene is 220-240°C, the reaction temperature is 280-300°C, and the absorption temperature is 0-20°C .
The synthesis of carnaphthalene is to prepare sodium naphthol with dilute lye, and add methylcarbamoyl chloride dropwise when the temperature reaches 0 to 5°C. During the dropwise addition, the lye should be continuously supplemented until the pH value reaches 7.5. When ~8.0, the reaction reaches the end point, and the reaction time is about 30-40 min. Centrifugation, washing and drying to obtain the finished product with a content of more than 90%.
The synthesis of Carbaryl Dust can also be produced by a solvent method or a solvent-free method.