Design Of The Catalytic Distillation Process For The Preparation Of Dimethyl Carbonate By The Alcoholysis Of Urea

Dimethyl carbonate (DMC) is an attractive green chemical due to its wide application. In the last decade, world DMC yield has increased more than 20 times. In 1992, DMC is registered in Europe as a non-toxic chemical, which greatly promoted DMC application procedure. In this thesis, which is based on the research result of DMC synthesis by means of urea methanolysis from Chinese Academy Shanxi Coal Chemical Research Institute, the electric charge distribution of methanol and urea is calculated via molecular modeling, the reaction mechanism and possibility of synthesis of DMC from urea and methanol under the catalysis of solid base catalysis is analyzed and proved. The equilibrium constants and conversion calculated with Benson method showed that methyl carbamate (MC) could be synthesized easily by the reaction of urea and methanol in first step, but it was difficult to convert into DMC in second step in thermodynamics. According to pilot experiment data, the overall process design is configured for DMC synthesis by means of urea methanolysis. The whole process consists of such sections as urea solution, catalytic distillation, atmospheric concentration, pressurized distillation, atmospheric distillation, ammonia recover, methanol recover and crystal treatment. In this thesis, a study on the key section—catalytic distillation as well as a comparison and optimization between pilot experiment and operation conditions are made with modified catalyst, theoretic analysis and discussion for problems appeared in pilot experiment is made so that the industrialized design philosophy is put forward, which includes adopting a compound reaction section combining two reactors with different structures, discharging co-boiling DMC and methanol on the side, extending residence time of the downcomer, cooling with hot water, increasing the condensation temperature of the condenser so as to extend operation period, etc. Simulation and calculation for the whole process shows that it complies well with the pilot experiment data, which means the process of synthesizing DMC from urea and methanol under solid base catalyst and separating DMC through atmospheric distillation—pressurized distillation—atmospheric distillation is feasible.