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°C 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.