Study On The Cu-Si-Ti Based Catalysts For Liquid Phase Oxidative Carbonylation Of Methanol To Dimethyl Carbonate

Dimethyl carbonate (DMC) has been considered as a green chemical raw material due to its lower toxicity and quick biodegradation. It passed the registration of non-toxic chemical products in Europe in 1992. DMC molecule contains several active basic groups, such as CH3-, CH3O-CO-, and -CO-; therefore, it has good reactivity and has been used as an important intermediate in organic synthesis. Hence, it is regarded as a so called environmentally benign building Block. Furthermore, DMC has also show bright future in the non-reactive fields, it can be used as an additive to gasoline and a green solvent in medicine, pesticide, dyestuff, flavoring agent of foodstuff and electronic chemical, thus DMC synthesis has attracted more attention for its growing market.The oxidative carbonylation of methanol route is one of the earliest phosgene-free synthetic routes of DMC, and it also contains the virtue of low cost which made it more economical. But in oxidative carbonylation of methanol route Cl- will be easily lost from the CuCl catalyst and leads to activity declines, this is the main reason which has slowed the development of the oxidative carbonylation of methanol route.The sol-gel process has been known as a common technique in preparation of catalysts. It has many advantages, such as brief handle, inexpensive equipment, and the components can be mixed uniformly and easily changed. Via sol-gel method we can obtain materials with large specific surface, narrow aperture distributing, more elements and many other novel structures and functions. In order to solve the problems of catalyst deactivation and corrosion, the Cu-SiO2-TiO2 catalysts have been prepared by sol-gel method. CuCl2 has been sucdessfully mixed with SiO2-TiO2 in the sol-gel process, and the Cl- has been removed during the heat treatment. Microwave irradiation is characteristic in its selective, which can disperse the active species on the support materials uniformly in a short time; hence microwave is gaining increasing importance in the catalysts preparation. It is known that CuCl is a good microwave adsorbing material, which can be quickly heated by microwave and then dispersed onto the surface of support. In this study, the microwave irradiation is used to disperse CuCl on to SiO2-TiO2 mixed oxides and advance the strong interaction between CuCl and support, thus the stability of catalyst can be improved.The Cu-Si-Ti cogelled oxerogel catalysts were prepared by sol-gel method for DMC synthesis form methanol via oxidative carbonylation route. The results show that the catalytic activities of sol-gel derived catalysts are largely influenced by the source of copper and the Si/Ti ratios. The most promosing precursor of copper is CuCl2 and the suitable Si/Ti ratio is 10. Under optimum reaction conditions, the catalyst with 12.5 mol% of Cu loading exhibits the highest activity and selectivity. The conversion of methanol and selectivity of DMC reach 13.0% and 96.7%, respectively, higher than those obtained over the commercial cuprous chloride catalyst. The analytical result showed that about 90% Cl is removed from the cogelled xerogel catalysts, resulting in a lower corrosion as compared with the CuCl catalyst.CuCl/SiO2-TiO2 catalysts have been prepared by microwave irradiation and conventional heating; the characterization results show that microwave can quickly disperse CuCl onto the surface of support in a lower temperature than conventional heating method. Furthermore, it is found that there is more strong interaction between CuCl and support in the catalyst prepared by microwave irradiation than by conventional heating, leading to the formation of more copper species that has higher CO adsorption capacity and is more easily reduced. The catalytic test results indicated that under identical reaction conditions, the conversion of CH3OH over the catalyst prepared by microwave heating reached 11.7% and the selectivity of DMC was 96.5% in the synthesis of DMC via liquid-phase oxidative carbonylation of methanol, higher than the catalyst prepared by conventional heating.