Study On Synthesis Of Dimethyl Carbonate In Supercritical Carobn Dioxide

The synthesis of dimethyl carbonate(DMC) in supercritical carbon dioxide which is significant to the resourcization of carbon dioxide and green chemical synthesis, can bring environmental benefits, social benefits and economic benefits. The application status of supercritical fluid technology and the production technology of dimethyl carbonate, especially the research progress on synthesis of dimethyl carbonate in supercritical carbon dioxide, were reviewed, based on which the study was carried out.Dimethyl carbonate known as a green chemical was synthetized by useing carbon dioxide, propylene oxide and methanol in the supercritical condition. Several factors were studied, including types of catalyst and dehydration agent, dosage of catalyst (2%～6%) and dehydration agent (0.1～0.9g), material ratio (VCH3OH:VPO=1～12), mixing speed (0～500r/min), pressure (5.0～10.0MPa), temperature (110～190℃) and reaction time (0.25～3.0h). In addition, a possible reaction mechanism was proposed.The results showed that the existence of K+could promote the reaction rate effectively and inhibit the formation of by-products, potassium methoxide(CH3OK) was the proper catalyst of one-pot synthesis of dimethyl carbonate. Dehydration agents, among which the calcium chloride (CaCl2) showed the best effect, could improve the yield of DMC. The yield of DMC could be affected by the dosing quantity of catalyst and dehydration agent.The yield of DMC increased gradually with the increase of VCH3OH:VPO. In consideration of conversion, the best result was VCH3OH:VPO=10:1. Mixing speed was an important factor that could influence the uniform dispersion of catalyst and dehydration agent, the appropriate mixing speed might be300r/min. High pressure was benefit for reaction, but the relative concentration of reactants, such as methanol, reduced with the increasing of CO2, the proper pressure was7.0MPa. The reaction rate was low at low temperature and DMC would decompose or carbonize at high temperature, the appropriate temperature was140℃. Transesterification reaction was the speed-limit reaction, the yield of DMC could reach45.5%under the optimum reaction conditions (VCH3OH-VPO=10:1, mixing speed300r/min, pressure7.0Mpa, temperature140℃, reaction time1h).