Synthesis Of Dimethyl Carbonate By Gas-Phase Oxidative Carbonylation Of Methanol

Dimethyl carbonate(DMC) is an environmental-friendly chemical product which possesses wide application prospect in solvent,dopes,drugs manufacture and fuel additives and so on, and is known as organic synthesis new benign in the new century. Its green process of synthesis has been a "hot" pot recently. At present, the major disadvantage of the current production method by using the vapor phase oxidative carbonylation of methanol is the low conversion of methanol and the rapid catalyst deactivation. Pd and Cu catalysts are prepared by using template method synthesis mesoporous materials as the supports, and are used in the synthesis of DMC by methanol. At the same time, support, promoter and active component were investigated to study the catalyst to the synthesis of DMC by methanol. The results are summarized as follows:1. The synthesis of mesoporous materials and the reactivity of Pd-Cu bimetallic catalyst which is loaded on mesoporous materials. The mesoporous carbon material is synthesized with the SBA-15 as template and with sucrose as cabon source. The test results of SEM,XRD and N2 physisorption show that the mesoporous carbon is rod-shaped, its texture is loose , its degree of order is well, its surface area is large, its pore canal distribution is well-distributed and its pore diameter is around 4nm. The synthetic mesoporous carbon material is applied to the reaction of gas-phase oxidative carbonylation as the carrier. The results of activity rating show that the initial rate of conversion of methanol is high ,it can reach to 27%; the selectivity of product to methanol is on the low side, about 7%; the rate of conversion drops gradually to 18%; the selectivity of DMC to methanol increases to 30% in 6 hours and it remains stable in the latter testing period .We can know that the change of pore structure of carrier and the aggrandizemen of pore diameter cann't raise the reactivity worth of catalyst effectively by contrasting with the reactivity worth of catalyst loaded on active carbon. It indicates that the mass transfer resistance of this reaction is less and the degree of dispersion of metal active spice affects the reactivity worth of catalyst mostly.2. The effects of promoters on performance of catalysts for synthesis of dimethyl carbonate by gas-phase oxidative carbonylation of methanol were studied. The catalysts using polyhydroxy compounds as promoter were characterized by means of XRD, SEM and TEM. Active evaluation results show: when promoter was not added, the conversion of methanol is only 15%, while moderate glycerol was added, the conversion of methanol can lead to 27.5%, the selection also achieve 92.1%.3. The catalysts using CuCl₂, CuO, Cu₂(OH)₂CO₃ as active components were tested for synthesis of dimethyl carbonate by gas-phase oxidative carbonylation of methanol. Active evaluation results show that the catalysts using CuO or Cu₂(OH)₂CO₃ as active components showed higher catalytic activity, when use Cu₂(OH)₂CO₃ as active component, the highest conversion of methanol can achieve 32%, the selection also can reach 90%.4. The effects on the catalyst by different methods of activated carbon pretreatment were investigated and found that the activated carbon treated with nitric acid treatment (0.5M) received the best performance, the highest conversion of methanol was more than 30%, when catalyst remains stable the conversion can also achieve 25%. Characterization results show that nitric acid treatment can obviously improve the carbon surface oxygen groups, makes the metal active components were easily dispersible. With the increase of nitric acid concentration, high levels of nitric acid can oxidate the unstable carbon molecules of carbon surface, make the oxygen groups of carbon surface be destroyed, thereby the activity of the catalyst was reduced.