The Study Of Gas-phase Carbonylation Synthesis Of Dimethyl Carbonate From Methanol

Gas-phase oxidative carbonylation synthesis from methanol and direct synthesis from carbon dioxide and methanol are two potential synthesis routes for dimethyl carbonate (DMC) at present. In this paper, the methods of catalysts preparation and the conditions of reactions for two synthesis routes were investigated, and the reactions mechanism were discussed. Meanwhile, in order to accomplish the matching of the temperatures between the hydrolysis of dimethyl ether (DME) and the carbonylation of methanol, the hydrolysis of DME on zeolites was researched roundly. The results were shown as follows:(1) The study of DMC synthesis by gas-phase oxidative carbonylation of methanol showed that the PdCl₂-CuCl₂-TBAB/AC catalyst, which was prepared by two-step impregnation with NH₃ ? H₂O solution, exhibited higher activity. When the loading of Pd% was 0.5% and Pd/Cu mole ratio was 1/14 in the PdCl₂-CuCl₂-TBAB/AC catalyst, the highest space time yield (STY) of DMC, 159.7 g/L-cat ? h, was obtained. The reaction of DMC synthesis by gas-phase oxidative carbonylation of methanol over PdCl₂-CuCl₂-TBAB/AC catalyst was impressible by temperature. The optimal reaction temperature was 140℃-150℃.(2) The study of DMC direct synthesis from carbon dioxide and methanol showed that the Cu-Ni/ZrO₂ catalyst, which was prepared by impregnation, exhibited higher activity. After the catalyst was modified by H3PO4, the conversion of methanol and the selectivity of DMC toward methanol were increased, presumably due to the improvement of cooperation between surface acidic site and activity site on ZrO₂. The optimal reaction condition was following: the temperature was 130℃-150℃, the pressure was 0.6 MPa, the hourly space velocity was 1440h^-1 and the n(CH₃OH)/n(CO₂) mole ratio was 2.(3) MCM-22 zeolite with high crystallization was prepared by the hydrothermal synthesis method. NH3-TPD showed that the acid sites was similar to ZSM-5, the difference was the distribution of acid sites on the zeolites. On the MCM-22 zeolite, the acid sites are distributed inside 12-rings super cages and 10-rings channels, while the acid sites are distributed in 10-rings channels on HZSM-5 zeolites. The results of low-temperature hydrolysis of DME over zeolite catalyst showed that the acid sites on the zeolites were actual catalytic active sites for the reaction, and the hydrolysis activity was determined by the amount of the acid. The catalytic...