Study On The Catalyst For Methanol Synthesis By Carbon Dioxide Hydrogenation

The domestic and international demand for methanol,the research of carbon dioxide hydrogenation catalyst for methanol and the modified method of Cu-based catalysts were analyzed. On the basis of the conventional catalyst Cu/Zn/Al₂O₃,The catalyst support for methanol catalysts was studied.Changing the carrier of the catalyst, Cu, Zn and other active component were loaded onto TiO₂. Changing the content of CuO and ZnO,the strueture and surface properties of the catalysts were characterized by BET,TPRand XRD.The impact of different content of CuO and ZnO on catalystic activity were studied. In a certain load case, the process of post-processing and reaction conditions on catalystic properties were studied. Through orthogonal experimental,different reaction conditions on catalyst activity were studied, the reaction temperature is between 240℃～340℃, operation pressure 2.0 MPa～5.0MPa, space velocity of 2000 h-1～5000h-1, the optimum reaction conditions for methanol synthesis were explored. The effects of different rate of materials on the reaction were studied and the change of the structures after reaction were compared.Among different prapared methods, the catalyst by infusing TiO₂from sol-gel method has the best performance. At the temperature of 300℃, pressure of 4MPa and airspeed of 5000h^-1, the methanol yield was 5.68%. The catalysts by coprecipitation method has higher conversion rate of CO₂, but less selectivity of methanol. By infesing TiO₂ calcining metatitanic acid, the catalyst has the worst catalytic properties.Comparing the catalyst of different content of CuO and ZnO through infusing TiO₂ from sol-gel method, when the content reaches 15%, the catalytic activity reached a maximum.Continuing to increase the content , the activity of catalyst decreased slightly.With the increase of calcining temperature, conversion rate of CO₂ increased first and then decreased, calcining at 350℃, CO₂ conversion rate is highest, and the calcining temperature at 300℃or 400℃were better than at 250℃. When the reaction temperature is low, the selectivity of methanol was 100%, and there were no other effects occurred.When the temperature is higher than 280℃, the selectivity of methanol reduced dramatically.Compared with the catalyst deoxidized for12h, CuO deoxidized more thoroughly under the catalyst deoxided for 24h, and the conversion rate of CO₂ and the selectivity of CH₃OH were higher, which indicated that the extension of deoxidized time will help to raise the yield of methanol.The conversion rate of CO₂ is not very different at different deoxidizing temperature, the conversion rate of CO₂ declined slightly at 300℃.With the increase of deoxidizing temperature, the selectivity of CH₃OH increased.The increase of reaction temperatures conduced to improving the conversion rate of CO₂, but the selectivity of CH₃OH decreased.The yield of methanol has a maximum of 6.63% at 280℃. As the pressure increases, the conversion rate of CO₂ and the selectivity of CH₃OH gradually increased.When the pressure was 5MPa, the yield of methanol reached 7.38%. As the airspeed increases, the conversion rate of CO₂ decreased, and the selectivity of CH₃OH fluctuated between 97% and 99%.Through the orthogonal design of catalysts,the descending order of the effect on catalystic activity shows as follows: reaction pressure> reaction temperature> reaction airspeed. The best conditions for methanol synthesis is temperature of 280℃, pressure of 5MPa and airspeed of 2000h^-1.