Study On The Technology Of Dimethyl Carbonate Production By Transesterification

Dimethyl carbonate (DMC)is one of the most important chemicals in chemical industry. It is a methylating agent, carbonylating agent, methoxylating agent and methylolating agent with active chemical properties. It has being expected as new fuel additive in the new century. The transesterification process was studied in detail based on the background of 10000t/a DMC production process in the JinXi Petroleum Processing & Chemical Plant. Dimethyl carbonate is synthesized through transesterification between methanol and propylene carbonate (PC). PC can be produced from liquid CO2 and propylend oxide. Transesterification is reversible reaction and reaction distillation was used to increase the yield of DMC, reaction distillation removes react productions in time, makes the conversion ration of raw materials improved. Pressure fractionation is suitable for separating dimethyl carbonate and methanol azeotropic mixture. By increasing pressure,the azeotropic temperature to changed, which helps to purify DMC from the mixture that DMC and methanol azeotrope .The catalyst was studied and the result shows that the catalyst CH3ONa has very good activity and high selectivity, but very sensitive to water and carbon dioxide in raw material. From the kinetics of DMC synthesis reaction,it was found that the reaction rate is dependent upon PC concentration with first-order,while to be independent of methanol concentration。 Through analyzing and optimizing the operation parameters, we get the following optimum parameters :(1) In reaction distillation tower, the mole ratio of methanol to PC is 4/1, the reflux ratio is 3-4, (2)The reflux ratio of pressurized tower is 1.5-2.5, the operation pressure is 0.64-0.66MPa,(3)Temperature at the bottom of methanol restoring tower is 140-155℃,(4) The reflux ratio of methanol distillation tower is 1.5-2.5,(5) In DMC batch distillation tower, complete cycle is 9500-10500 kg/h, the reflux ratio is 9-11 in transition stage and 1.5-2.5 in product stage . which are consistent with actual production conditions. The result is helpful for improving the production and operating state, optimizing the process condition and decrease production costs。...