Synthesis Of Dimethyl Carbonate By Gas-phase Oxidative Carbonylation Of Co-feeding Methanol With Dimethyl Ether

Dimethyl carbonate (DMC), a green chemical intermediate, has considerable potential fororganic synthesis. It is currently produced by the oxidative carbonylation of methanol. Theco-product water in this reaction, however, often induces catalyst deactivation and equipmentcorrosion. In light of the reversible reaction (CH₃OCH₃+H₂O(?)2CH₃OH), the aboveproblems may be diminished somewhat if the dimethyl ether (DME) is introduced as a co-feedgas to the methanol carbonylation reaction. From the thermodynamic point of view, partialconsumption of the produced water via the hydrolysis of DME can also increase the yield ofDMC.In the present thesis, the hydrolysis performance of dimethyl ether at low temperature wasinvestigated to develop a catalyst for DME hydrolysis with high activity at low temperature.Furthermore, the catalytic performance in the co-feeding system over the bi-functional catalysts,which were prepared by mixing the hydrolysis catalyst with carbonization catalyst, was alsostudied. The results are summarized as follows:1. The effect of the types of zeolites, silicon aluminum mole ratio, Cu and Pd modificationon the hydrolysis activity of dimethyl ether at low temperature over the zeolite catalysts wasinvestigated. The acidity of the catalysts was characterized by Py-IR. The results show that theperformance of the catalysts was dependent on the structure and acidity of the zeolites. TheMCM-22 zeolite with super-cage structure showed better hydrolysis activity of DME. Thehydrolysis activity of the MCM-22 catalysts modified by Cu and Pd was further enhanced. At150℃, the conversion of dimethyl ether increased by 3.9ï¼…to 14.0ï¼…when compared with theunmodified MCM-22 catalysts. Based on the above results, the problem of reaction temperaturematching for the coupling DME hydrolysis with methanol oxidative carbonylation was resolvedeffectively.2. The structure and the acidity of MCM-22 zeolite, which was home-made according to themethod in reference, were characterized by SEM,XRD,FT-IR,NH₃-TPD and Py-IR. The resultsindicated that the MCM-22 zeolite has high crystallization, and there are two kind of acid site, i.e.the strong-acidic site and the weak-acidic site, in this zeolite. 3. The space time yield of DMC over the mixed catalysts of Cu-Pd-TBAB/AC and Cu-Pd/MCM-22 can be improved effectively after the dimethyl ether was introduced to the reactionsystem. The addition of Ce to the catalysts further enhanced the catalytic performance. When theflux of DME is 5mL/min, the conversion of methanol, the selectivity of DMC to methanol andspace time yield of DMC were 17.9ï¼…,99.8ï¼…and 10.18 mmol·(g-cat·h)^-1, respectively. Theresults of life-time evaluation indicate that the introduction of DME in the reaction system ofoxidative carbonylation could increase the stability of the catalysts. This is because that thehydrolysis of dimethyl ether can consume some of the water produced in the oxidativecarbonylation of methanol, which, to some extent, resolves the problem of dramatic deactivationof the catalysts due to the water produced in the oxidative carbonylation of methanol. Theconversion of methanol decreased to the half of the highest value after running for 55h.