Study on Synthesis of Dimethyl Carbonate in Supercritical Carbon Dioxide
|School||Zhejiang University of Technology|
|Keywords||supercritical carbon dioxide dimethyl cabonate metal acetates one-pot synthesis catalytic synthesis|
Study on organic synthesis reactions involved supercritical CO2 （CO2 could be not only a reagent but also a solvent）, which could expand the possible ways of CO2 utilization and could be the direction of green synthesis. The study on one-pot synthesis of dimethyl carbonate in supercritical CO2 is carried out, using propylene oxide（PO） and methanol as raw materials and metal acetate formulated with K2CO3 and KI as a catalyst.The results showed that: Zn（CH3COO）2 had outstanding catalytic effect in the reaction. Appropriate increase in the dosage of catalyst played a role in speeding up the reaction and in promoting the production of DMC, and the most appropriate dosage of reaction catalyst was 4% of the reactants amount（PO+CH3OH）. Excess of methanol could be properly help to improve the yield of DMC, VCH3OH:VPO = 8 was appropriate in one-pot DMC synthesis in supercritical CO2. The yields gradually increased with reaction temperature rising, higher than 443K, the product was easily color changed because of carbonation, and thus the suitable reaction temperature is 433K. When the pressure was controlled at the vicinity of supercritical point, the yield of DMC got best. DMC yield increased with reaction time gradually increased, then remained stable after more than 4h, and the highest yield was 54.3%. The best reaction conditions catalyzed by zinc acetate composite catalysts in one-step synthesis of DMC in supercritical CO2 was: K2CO3: KI: Zn（CH3COO）2 = 1:1:2, dosage 4%, reaction ratio VCH3OH:VPO=8, reaction temperature 433K, reaction pressure 7.5Mpa, reaction time 4h. By analyzing the products, the possible reaction mechanism and kinetics were proposed, and the activation energy was Ea=89.81kJ/mol.Propylene glycol（PG） is a major by-product in the one-pot synthesis of DMC, its conversion in CO2 would play an important role in the further development of the synthesis of DMC. Using propylene glycol as raw materials in supercritical CO2, the conversion of propylene glycol into propylene carbonate （PC） was studied. It showed that only in the case of acetonitrile as solvent and absorbent ,the catalysts such as K2CO3, Zn（CH3COO）2 or Ni（CH3COO）2 can be conducted, but the yield of propylene carbonate was small. By contrast, K2CO3 showed the best catalysis. With temperature increasing, yield of PC first increased then decreased, in the 433K, the yield reached the highest. When carbon dioxide pressure kept 7.5MPa, PC reached the maximum yield of 8.91%. Adding PO as coupling agent could effectively enhance the effect PG conversing into PC in supercritical CO2, and PC yield can increased to 50.9%.