超临界CO2萃取反应合成碳酸二甲酯

实验测定了不同条件下碳酸二甲酯(DMC)、甲醇、乙二醇(EG)、碳酸乙烯酯(EC)在超临界相和液相中的分配系数，计算了DMC相对于其他组分的分离因子. DMC相对于甲醇的分离因子随EC浓度的升高而降低，随DMC和EG含量增加而升高，随压力增加而增大，随温度升高而变小. 这种变化规律表明利用超临界萃取与反应耦合提高酯交换反应转化率的前提是：(1) 反应体系中DMC的浓度要高，即进料中环氧乙烷(EO)的浓度要高，且EC转化率要高；(2) 低的反应温度和高的反应压力. 在160℃和5~20 MPa下，以环氧乙烷、甲醇和CO2为原料，考察了超临界CO2萃取与反应相耦合提高酯交换反应转化率的可行性. 研究结果表明，DMC与甲醇间的分离因子是影响超临界萃取反应操作过程中DMC收率的关键因素. 采用耦合技术可以提高DMC的单级收率约4%以上.

Continuous Synthesis of Dimethyl Carbonate by Supercritical CO2 Extractive Reaction

Dimethyl carbonate (DMC) is an important green chemical. The distribution coefficients of DMC, methanol, ethylene glycol (EG) and ethylene carbonate (EC) between the supercritical CO2 phase and the liquid phase in the one-pot synthesis of DMC were determined under various conditions, and the separation factors of DMC corresponding to methanol, EG and EC were calculated. The experimental results showed that DMC-methanol separation factor decreased with EC content in the mixture，increased with the contents of DMC and EG, enhanced with pressure and declined with temperature. These results indicated that the prerequisites of supercritical extractive reaction to promote the transesterification conversion were: (1) keeping high DMC concentration in the reaction mixture, namely, relatively high EO/methanol ratio in the feed solution and high EC conversion rate; (2) low reaction temperature and high reaction pressure. The feasibility of one-pot continuous synthesis of DMC by supercritical extractive reaction was explored using EO, methanol and CO2 as raw materials at 160℃ in the pressure range of 5~20 MPa. Both the experimental results and process analysis showed that DMC-methanol separation factor is a key factor which affects DMC yield in the supercritical extractive reaction. Supercritical extractive reaction could get more than 4% DMC yield in single-stage compared with that without supercritical extraction.