Selective Preparation And Reaction Kinetics Of Dimethyl Carbonate From Alcoholysis Of Methyl Carbamate With Methanol Over Composite Metal Oxides

In this paper,the composite metal oxides Zn Al-LDO and Zn Al M-LDO catalysts,which was prepared from calcinating Zn Al-LDHs and Zn Al M-LDHs at a certain temperature as the precursor,has been evaluated for the synthesis of dimethyl carbonate by MC alcoholysis.In the binary composite metal oxide(Zn Al-LDO)catalytic system,the catalytic reaction conditions have been investigated and optimized in the previous work,in this paper,the catalytic reaction system has been further investigated.The carbon balance analysis of the reaction system showed that sum of the selectivity of DMC and the by-product NMMC in the Zn Al-LDO catalytic system under the optimal catalytic reaction conditions was not 100%because of the self-decomposition reaction of MC and DMC.The Zn Al-LDO before and after catalytic reaction were characterized and analyzed to determine the influence of physical and chemical properties of the catalysts on the catalytic stability,the results showed that the selectivity of DMC decreased when Zn Al-LDO participated in the catalytic cycle reaction.The reason for this phenomenon is that the Zn contained in the catalyst partially dissolves in the reaction system,resulting in the loss of the active metal.Based on the discussion of the reaction process existing in the reaction system,the reaction rate equations was modified,the reaction kinetics model was established,and the kinetic parameters were calculated by Arrhenius equation.The results shows that there is little difference in the total average relative deviation of the three kinetics models,however,the Power-rate law kinetic model based on nonelementary reactions requires the least reaction rate constants to fit and is the easiest to apply,so this model is chosen as the optimal kinetic model.The kinetic parameters(pre-exponential factor and activation energy)of MC and methanol synthesis DMC were 4.57?1018 and 177.63 k J/mol,respectively.In the catalytic system of terpolymer metal oxide(Zn/Al/M-LDO),the optimal catalyst was selected as(3:1:0.9)Zn Al La-LDO-700/6 through single factor experiment,and the reaction conditions of MC and methanol reaction to synthesize DMC were optimized.The results showed that under the optimal reaction conditions(the reaction temperature was 170 ℃,the reaction time was9 h,the catalyst dosage was 0.8 wt.%,and the MC to methanol molar ratio was1:20),the selectivity of DMC can reach 92.40 %,and the MC conversion was33.52 %,the selectivity of byproduct NMMC was 6.18 %.The effects of physical and chemical properties on catalytic performance of(3:1:0.9)Zn Al LaLDO-700/6 were characterized and analyzed,and the catalytic stability of catalyst was analyzed,the results showed that the catalyst displayed the same change trend as Zn Al-LDO before and after catalytic reaction.The decrease of catalytic activity of(3:1:0.9)Zn Al La-LDO-700/6 catalyst can also be attributed to the dissolution of the active metal Zn in the catalyst.The kinetic model of the catalytic system was established and the kinetic parameters of the main reaction were calculated.Similar to Zn Al-LDO catalytic system,the Power-rate law kinetic model based on non-elementary reactions is chosen as the optimal model,the kinetic parameters(pre-exponential factor and activation energy)of MC and methanol synthesis DMC were 5.77?107 and 77.60 k J/mol,respectively.