Study On Synthesis Of Dimethyl Carbonate From Urea And Methanol

The alcoholysis of urea for producing dimethyl carbonate is a new process developed recently. The method greatly reduces the synthesis cost of dimethyl carbonate due to the facile and low-cost material. The reaction process is secure and controlled easily, and the by-products have lower pollution than the other methods. Moreover, it has vital significance on enhancing the competitiveness of the methanol industry in China, reducing the production cost of synthetic ammonia and urea, and promoting the vigorous development of coal chemical industry in our country. So it is an environment friendly and sustainable synthetic route.The urea is decomposed easily at the high temperature, however, it becomes more urgent to solve the problem for how to implement the directional activation of carbonyl carbon in urea and improve the balance of urea conversion rate under the premise of limited by thermodynamic equilibrium conversion rate. In this paper, the preparation of dimethyl carbonate by the alcoholysis of urea is studied by using urea and methanol as raw materials through laboratory and pilot experiment. The main research contents are as follows:1) In the laboratory research stage, the experiment was carried out at different temperatures, with materials of different ratio, catalysts of different quantities, and for different stirring speed and time so as to acquire their effects on the yield of DMC and found the suitable condition of the reaction: the optimal temperature was 170℃,the optimal urea/methanol ratio was 1:15, catalyst quantities of 3.5g, the stirring speed of 600 r/min and the best reaction time was 7h.2) Under the certain reaction condition, the study on the catalytic effect of catalysts was carried, such as HY、HZSM-5、ZnO、Fe2O3、PbO、Fe2O3/HY、ZnO/HZSM-5 and Fe2O3/HZSM-5. The results show that: the catalytic effect was best with Fe2O3/HZSM-5 catalyst, the yield of target product was 18.4%, and after four reproducibility experiments the immobilized catalyst stability was well. After taking off the extractive and vacuum distillation we got the product with purity of 99.5%.3) In the 500 t/a pilot experimental study, the appropriate operating conditions was determined. The optimal conditions were as follows: the temperature of the reaction tower was 165℃~175℃,the mole ratio of urea/methanol in the ingredients kettle was 1:13~1:15, the temperature of the decarburization tower was 24℃~ 28℃, the yield of target product was 19.5% and the purity was 99.5%~99.7%.4) The economic benefit analysis of the whole process of pilot was investigated, the cost reduce more than 30% compared with the industrialized technology, production products 120 tons, the net profit of 150000. At the same time, it had the very good social and environmental benefits because of its high-efficient clean process.