Studies On Heterogeneous Catalytic Systems For Direct Synthesis Of Dimethyl Carbonate From Methanol And Carbon Dioxide

DMC is one of the fastest growing environmentally benign chemical product. It cansubstitute substances such as phosgene, dimethyl sulfate（DMS）, halogenated methaneand methyl chloroformate in methylation reaction, carbonylation reaction and methylesterification reaction. So DMC is called as the "new foundation" of the future world.CO₂and methanol directly synthesis of DMC is a green and sustainable developmentroute for cheap and non-posionous raw materials and little by-product.Screening of active catalysts and dehydrating agents, copper nickel supportedcatalysts, CuO-NiO and Fe-Zr-O showed a good catalytic activity, using4A molecularsieve as the dehydrating agent.The component ratio, roasting temperature and activation time of copper-nickelcatalyst was studied by orthogonal experiment. The results show that the catalyst activityis low and not stable; Study of different carriers on copper-nickel catalysts, the resultsshow that, zirconium oxide carrier prepared by sol-gel method has a higher activity,150℃,10h, initial pressure of5MPa（room temperature）, the yield of DMC is0.042%.In this article, effect of the different mole ratio, activation temperature, elementdoping, phosphorus modification on catalyst active were investigated. The results showedthat1:5zirconium to iron mole ratio and500℃activation temperature are the bestreaction conditions. Element doping results: Doping Zn can improve the activity，doping K and Ce have an opposite effect; Phosphorus modification on different catalystsshow that the activation of zirconium-iron1:5catalyst is decreased and1:2is improved.The Fe-Zr-O catalyst was characterized by X-ray power diffraction（XRD）,Temperature programmed desorption（TPD）, Infrared spectrum（IR）, Scanning electronmicroscopy with X-ray microanalysis（SEM-EDS） and Specific surface area（BET）. Theresults show that no solid solution is found in iron-zirconium catalysts. Iron oxide is sixcrystal type, zirconia is tetragonal crystal type; Iron in ZrO₂catalyst increases thequantity of surface acidic and basic sites;1:5zirconium to iron mole ratio catalyst has thelargest specific surface area and it is48.73m²/g.The experiment has been looked for the optimum conditions of1:5catalyst. Theyield of DMC is increased with time an pressure and it is increased obviously when thepressure is higher than16MPa.Finally，the reaction mechanism is also briefly discussed.