Study On Catalytic Hydrogenation Of Carbon Dioxide For Direct Synthesis Of Dimethyl Ether

Direct synthesis of dimethyl ether (DME) from carbon dioxide catalytic hydrogenation is of great economical and environmental importance, not only to synthesize the useful chemical products, which will utilize carbon dioxide more efficiently, but also to reduce the greenhouse effect resulted from carbon dioxide.Direct synthesis of DME is rather complicated, which consists of three independent reactions, i.e., methanol synthesis from carbon dioxide hydrogenation, methanol dehydration to dimethyl ether and reverse water-gas shift reaction. In order to obtain the information about the reaction, the thermodynamical analysis for direct synthesis of DME was first carried out. Because the reaction was a two-step one, the composite catalyst consisted of methanol synthesis component and methanol dehydration component was necessary. In the present work, Cu-based catalyst prepared by co-precipitation method was selected as methanol synthesis catalyst, and HZSM-5 zeolite was selected as methanol dehydration catalyst. The effects of precipitation temperatures, precipitation methods, precipitation sequences, Cu/Zn ratios, compound methods, calcination conditions and modifications on the physico-chemical and catalytic properties of the composite catalysts were systemically investigated, using the technologies of nitrogen adsorption-desorption (BET), X-ray diffraction (XRD), thermal gravimetry (TG), temperature programmed reduction (TPR), hydrogen temperature programmed desorption (H2-TPD), ammonia temperature programmed desorption (NH3-TPD), X-ray photoelectron spectra (XPS), infrared spectroscopy (IR) and activity evaluation on a laboratory fixed-bed reactor.In the thermodynamic analysis of balanceable reaction system for the hydrogenation of carbon dioxide to dimethyl ether, the effect of gas pressure on the thermodynamic parameters was corrected with fugacity coefficient. Through computer simulation, the equilibrium compositions and their relations with reaction conditions, such as temperature, pressure and the molar ratio of H₂ to CO₂ in the reaction system were analyzed. Under the reaction conditions of 533 K,3 MPa and the molar ratio of H₂ to CO₂ 3:1, the equilibrium conversion of CO₂ and the equilibrium yield of DME were 26.5% and 14.9%, respectively.