Preparation And Activity Study On Catalysts For Direct Synthesis Of Dimethyl Ether From Carbon Dioxide Hydrogenation

As we all know, with the sharp increase in the world’s population, as well as economic development and the expanding degree of industrialization, excess CO2 emitted into the atmosphere, which is the main cause of greenhouse effect. Meanwhile, CO2 can be the carbon source of C1 compound. Make “the twenty-first century clean fule”dimethyl ether by carbon dioxide hydrogenation, can not only solve the environmental problem but also produce certain economic benefits.One-step synthesis of dimethyl ether by carbon dioxide hydrogenation is a complex chemical process, including the synthesis of methanol by CO2 hydrogenation, dehydration of methanol to dimethyl ether and the reversed water-gas shift reaction. In this paper, thermodynamics, kinetics, reaction mechanism for the reaction system were analyzed firstly, and catalyst reserch were aslo reviewed, then the following works were done:The bifunctional hybrid catalyst which were prepared by the mechanical mixing of CuO-ZnO-Al2O3(as methanol synthesis catalyst)and HZSM-5(as dehydration catalyst) is used for one-step synthesis of dimethyl ether by carbon dioxide hydrogenation. And the effects of reaction conditions including temperature, pressure and space velocity on the reactivity over the hybrid catalyst were also tested on a high-temperature and high-pressure fixed-bed reactor-gas chromatographic apparatus combined equipment. Through the experimental results, the feasible reaction conditions were suggested. Then, the effects of promoters, the Si/Al ratio of HZSM-5 zeolite, calcination temperatures and ultrasonic processing on the physico-chemical and catalytic paoperties of the hybrid catalysts were systemically investigated, using the technologies of XRD、BET、H2-TPR、NH3-TPD and activity evaluation on a laboratory fixde-bed reactor. Under the the optimum reaction conditions of temperature at 250 ℃, pressure at 3 MPa, space velocity at 2400 ml·gcat-1·h-1, the result shows that the performance of catalytic reaction were respectively improved when the promoters is Zr O2, the Si/Al ratio of HZSM-5 zeolite is 25, calcination temperature is 350℃. The hybrid catalyst showed the best catalytic performance when ultrasonic processing was used in the preparation of the catalysts,and the conversion of CO2 can be reached to 23.80%, the selectivity of dimethyl ether is 68.87%, the total yield of dimethyl ether and methanol can be reached to 16.96%.The bifunctional hybrid catalyst CuO-ZnO-ZrO2/HZSM-5 was prepared when we used Zr O2 as carrier instead of Al2O3, the effects of the ratio and different composite methods of hydrogenation component(CuO-ZnO-Zr O2) and dehydration components(HZSM-5) of the hybrid catalysts were investigated, using the technologies of XRD、BET、H2-TPR、NH3-TPD and activity evaluation on a laboratory fixde-bed reactor. The result shows that, under the the optimum reaction conditions,the performance of catalytic reaction is better when the preperation method is coprecipitation-impregnation and the ratio of hydrogenation component and dehydration components is 3. And the conversion of CO2 can be reached to 22.46%, the selectivity of dimethyl ether is 65.18%, the total yield of dimethyl ether and methanol can be reached to 15.04%.