尿素醇解法催化合成碳酸二甲酯连续反应工艺研究

以金属氧化物为催化剂,采用间歇操作和连续操作两种不同方式,对尿素醇解法合成碳酸二甲酯的工艺条件进行系统研究,探索提高碳酸二甲酯收率的有效方法研究结果表明,尿素的醇解反应分两步进行,第一步醇解较易实现,在无催化剂存在时,190℃下一步醇解产物氨基甲酸甲酯的收率可达73.4%;第二步醇解较难发生,是合成碳酸二甲酯的控制步骤,需要催化剂的作用。ZnO对两步醇解反应都能起到催化作用,但ZnO-La2O3较ZnO更能有效促进第二步醇解反应的进行。在所确定的适宜条件下,由氨基甲酸甲酯合成碳酸二甲酯的收率最高达到55.4%,同时碳酸二甲酯的选择性达到73.5%研究了连续操作条件下由尿素一步合成碳酸二甲酯的反应,以ZnO-La2O3作催化剂,在尿素与甲醇的摩尔比为1/20、反应温度170℃、催化剂占尿素质量的27%的条件下,碳酸二甲酯收率达到45.8%

Continuous Synthesis of Dimethyl Carbonate by Catalytic Alcoholysis of Urea

Dimethyl carbonate(DMC)was prepared by alcoholysis of urea using metal oxides as catalysts. To find an effective way of raising the yield of DMC, and since alcoholysis of urea proceeded in two steps, the reaction conditions were systemetically studied for both batch and continuous processes. The first - step alcoholysis of urea to methyl carbamate(MC)could easily carried out without the use of catalyst. The yield of MC was 73.4% at 190 ℃. ZnO-La2O3 catalyst was found to be more efficient than ZnO in promoting the second-step of alcoholysis from MC to DMC. Under proper conditions,the yield of DMC reached 55 .4% based on MC, while the selectivity to DMC was as high as 73.5% . In the continuous direct synthesis of DMC from urea with ZnO-La2O3 as catalyst,the yield of DMC reached 45.8%.