The Synthesis Of Methanol And Dimethyl Ether Vis The Hydrolysis Of Methyl Bromide Over MO/SiO₂-γ-Al₂O₃ Catalyst

Methanol and dimethyl ether (DME) are two important feed stocks in chemical industry. Traditionally, methanol and DME are mainly synthesized via the synthesis gas process.However, reforming of methane to syngas needs high temperature, which would cause energy-wasting, not to mention the enormous emissions of carbon dioxide. It is a promising pathway that methyl bromide and methylene bromide was used to prepare corresponding chemicals instead of syngas. In this paper, we prepared two excellent catalysts, CuO/SiO2-γ-Al2O3 and ZnO/SiO2-γ-Al2O3, studies hydrolysis of methyl bromide reaction systematically and obtained satisfactory results, which are described as follows:First of all, the catalysts CuO/SiO2-γ-Al2O3 were prepared via sol-gel method. Of which the component, sturcture, morphology were characterized BET, DTG, XRD, SEM, XPS, et al. In the self-developed fixed-bed reactor, the effects of carriers, mole ratio of silicate to aluminum and loading weight of CuO on the catalyst activity were studied. The research results showed that activity of supported catalysts was higher than that of pure carriers, and 50wt%-CuO/SiO2-γ-Al2O3showed best catalytic activity. Under the optimal reaction condition, hydrolysis of methyl bromide was carried out 170℃ with H2O/CH3Br molar ratio of 0.9 and V(CH3Br)=8ml/min over 50wt%-CuO/SiO2-γ-Al2O3 (2.5wt%Al2O3) catalyst. The methyl bromide conversion reached 99.3% with DME selectivity of 52%, carbon dioxide selectivity of 14.4%, methanol selectivity of 34%. At the same time, the reasons of deactivation were analyzed by the modern technology. Some useful conclusions were obtained.The second, to decrease the selectivity of carbon dioxide, metal oxides include main group metal oxides, rare earth metal oxides, first transition metal oxides, second transition metal oxides were added to CuO/SiO2-γ-Al2O3. Catalytic performance of them showed that the presence of ZnO decreased carbon dioxide selectivity. In order eliminate production of CO2 in the conversion of methyl bromide, catalysts ZnO/SiO2-γ-Al2O3 were prepared via sol-gel method and applied to methyl bromide hydrolysis. Under the optimal reaction condition, hydrolysis of methyl bromide was carried out at 170℃ with H2O/CH3Br molar ratio of 1.2 and V(CH3Br)=9ml/min over20wt%-ZnO/SiO2-γ-Al2O3 (2.5wt%Al2O3) catalyst. The methyl bromide conversion reached 88.4% with DME selectivity of 67.4%, and methanol selectivity of 32.6%. No carbon dioxide to produce, this means that the raw materials has been completely fully utilized.In addition, recycling of the catalysts was investigated through DTG analysis. The deactivated catalysts were regenerated by calcination in oxygen, at the same time, bromine was recycled. Finally based on our research conclusions and the results reported in literatures, the possible reaction mechanism of methyl bromide hydrolysis over CuO/SiO2-γ-Al2O3 and ZnO/SiO2-γ-Al2O3was proposed.In summary, two kinds of catalysts with outstanding performance were prepared. Methanol and DME can be produced at low temperature and normal pressure over these catalysts. What’s more, the whole process is of less energy consumption, high utilization rate of raw materialsand, environmentally friendly.