Intrinsic Kinetics of Hydrogenation of CO₂ towards Methanol on a Cu/ZnO/Al₂O₃ Modified Catalyst

Since the industrial revolution, the use of fossil fuels has led to a sharp increase in CO₂ emissions, which has caused a series of environmental problems. Therefore, the conversion and utilization of CO₂ have become one of the most important green chemistry research topics. Among them, the preparation of methanol from CO₂ is considered as a promising resource utilization way. The effects of operating conditions on the hydrogenation of CO₂ towards methanol were investigated in an isothermal integral reactor. The experimental results show that under the experimental conditions, higher conversion of CO₂ and yield of methanol can be obtained at a reaction temperature of 240.0 ℃, higher reaction pressure and ratio of hydrogen to CO₂. Meanwhile, the intrinsic kinetics of hydrogenation of CO₂ towards methanol was studied on a Cu/ZnO/Al₂O₃ modified catalyst with 80—100 meshes （150—180 μm） under the condition of 240.0—280.0 ℃, 4.00—8.00 MPa and 3.0—3.4 of feed gas n(H₂)/n(CO₂). Orthogonal method was used to design experiments and measure the kinetic data. A double-rate intrinsic kinetic model expressed by the fugacity of each component was deduced by taking the hydrogenation of formate as the rate control step, and its kinetic parameters were estimated by the maximum inheritance method. The statistical test, physicochemical meaning analysis and residual analysis results of the models show that both the kinetic models are applicable, and the relative error of the proposed double-rate kinetic model is smaller than that of the model of CO generation by direct dissociation and adsorption of CO₂ in the literature.