Highly Selective Gas-phase Synthesis Of Dimethyl Carbonate And Integrated Process Optimization

The gas-phase oxidative carbonylation of methanol is an economic and environmentalfriendly route for dimethyl carbonate synthesis. In this paper, a macro-integrated system ofmethanol oxidative carbonylation with transesterification was built by introducingbio-derived epichlorohydrin into the reactor in order to solve the existing problems of lowmethanol conversation and low selcetivity of DMC to CO, poor catalytic stability, unsafeprocess, and so on. By so doing, the industrialization of the direct synthesis of dimethylcarbonate by gas-phase oxidative carbonylation of methanol could be promoted.In order to increase the atom utilization and save energy, two kinds of the complexreaction systems were proposed. One is the macro-integrated system mentioned above, andthe other one is sequential production of dimethyl carbonate, methylal and dimethyl ether.The thermodynamics of the above complex reaction systems were analyzed and the resultsshowed that the conversion of H2O, CO2and other by-product into organic compounds andthe dramatic increase of the equilibrium methanol conversion were feasible.PdCl2–CuCl2–KOAc/AC was treated by both Al2O3and dilute hydrochloric acid toobtain a novel efficient composite catalyst PdCl2–CuCl2–KOAc/AC@Al2O3in this work.The treatment brought about not only the higher activity but also the better stability andselectivity:98%of DMC selectivity to methanol,70%of DMC selectivity to CO, andspace-time yield of DMC ranging from600to700g·L-cat-1·h-1. Simultaneously, thethermal effect of reaction was small.PdCl2–CuCl2–KOAc/AC@Al2O3was characterized and the results showed that itpossessed enlarged specific surface area, enriched active components and Cl-on the surface,decreased KCl crystalline and new Cu2O crystalline phase formed, as coMPared withPdCl2–CuCl2–KOAc/AC. On the basis of activity evaluation and characterization, thecatalytic reaction mechanism is proposed. The new formed Cu2O not only acted as anactive species for the synthesis of DMC, maitaining a proper ratio of Cu2+/Cu+, but also could be converted to more active CuCl. The loss of Cl-and the blockage of pore were themain reason of the catalyst deactivation.The effect of some organic chlorides on the catalytic selectivity and stability wasstudied. The results showed that epichlorohydrin can improve the catalytic selectivity andcatalyst service life. Almost100%selectivity of DMC to methanol,70~80%selectivity ofDMC to CO, and space-time yield of DMC above500g·L-cat-1·h-1within the runtime of300h were achieved under the conditions of molar ratio of O2, CO and methanol of1:2.3:3.6, the gas hourly space velocity of7100h-1, the temperature of160°C, the pressureof0.3MPa and the concentration of epichlorohydrin of0.2wt%.A novel and highly selective route to synthesizing glycerol dimethyl ether fromepichlorohydrin and methanol was proposed. The acidic ionic liquid[HSO3-b-N(CH3)3]HSO4exhibited the highest activity and selectivity:100%conversion ofepichlorohydrin and99%selectivity of2,3-dimethoxy-1-propanol at a reaction temperatureof120°C, an initial pressure of0.1MPa, a reaction time of10h and a molar ratio ofcatalyst/ECH/methanol=0.01/1/5. The ionic liquid could be reused.The synthesis of dimethyl carbonate from epichlorohydrin, methanol and CO2over thealkaline catalysts was studied and the results showed that the yield of dimethyl carbonatereached to25.2%when the mixtures of n-Bu4NBr and NaHCO3were used as the catalyst.