The Analysis And Optimization Of The Synthesis Of Dimethyl Carbonate By Transesterification

Dimethy Carbonate (DMC) is a basic raw material for green chemical industry, which has very extensive application now and in the future. 10,000 t/a DMC production in Jinxi Petroleum Process & Chemical Complex (JPPCC) was taken as an example, the operating parameters of the main processes such as the reaction rectifying tower and pressure rectifying tower were analyzed and optimized. The transesterification of propylene carbonate ester with methanol to DMC is a reversible reaction. Reaction rectification technology was adopted to promote reaction going on toward DMC production and improve DMC yield. Since the reaction and rectification take place at the same time, rectifying helps removing the products in time, which forces the reaction balance moving toward DMC production and increases the conversion ratio of raw materials. Sodium methoxide was used as the catalyst in reaction rectifying process and exhibited very good activity and high selectivity. Increasing the concentration of the methanol in reflecting section is favorable for DMC production. In order to separate DMC from the azeotropic mixture of DMC and methanol, pressure rectification technology was used to enhance the yield of DMC. By increasing pressure of rectification tower, the azeotropic temperature of DMC and methanol changed and the separation of DMC and methanol was achieved successfully. It overcomes the drawback of DMC low yield in traditional technology, raises the output of the product DMC and decreases the consumption of energy. Another product, 1.2-dihydroxypropane was purified in a batch rectification process at total-reflux operation condition. By analyzing and optimizing the reaction rectifying process, the optimum operation parameters were obtained as following: mole ratio of methanol to propylene carbonate ester is 4:1, reflux ratio is 3-5, pressure is 1.6-1.8 KPa and temperature in rectifying section is 65 ～ 67℃. At this condition, the yield of DMC and 1.2-dihydroxypropane was maximum. The suitable operation conditions in the pressure rectifying tower is: material entering at bubble point state with flowrate of 11t/h and DMC content 26-27%, pressure 0.64~0.66MPa, temperature 120-130℃, reflux ratio of 2.5-3.5. These are in consistent with actual production conditions. There is no corrosive materials in the whole process, which is an environmentally process and has important strategic meaning in environmental protection.