Study On The Reaction Kinetics And Catalyst Of Carbon Dioxide To Methanol

CO2 is not only the main component of greenhouse gases,but also a cheap and readily available carbon resource.Hydrogenation of CO2 to methanol is of great significance to the solutions of environmental damage and energy crisis.The operating conditions,catalyst modification and intrinsic kinetics of hydrogenation of CO2 to methanol were studied in a fixed-bed reactor based on Cu/ZnO/Al2O3 catalyst.The effects of reaction temperature,reaction pressure,nH2/nCO2,GHSV,reduction temperature and reduction time on the catalytic performance of CO2 hydrogenation to methanol were investigated.Increasing reaction temperature can increase the conversion of CO2 but decrease the selectivity of methanol.Higher catalytic performance can be obtained under high pressure,high nH2/nCO2 and low GHSV.The effect of reduction temperature on catalyst activity and product selectivity is small,and the suitable constant temperature reduction time makes the bed temperature distribution more uniform,which is conducive to improving catalyst performance.The optimum operating conditions are as follows:reaction temperature 240.0 C,reaction pressure 5.00 MPa,nH2/nCO2 3.5-4.0,GHSV 9000 h-1,reduction temperature 230.0?240.0? and constant temperature reduction time 2 h.The effect of additives on the heat resistance of Cu-based catalysts for CO2 hydrogenation to methanol was studied with BET,XRD,H2-TPR and CO2-TPD characterization and experiments by isovolumetric impregnation method.The results show that the additives(Zr,Mn,Ce)have a certain degree of improvement on the catalytic performance and heat resistance of the catalyst.The introduction of Ce can make the pore size distribution of the catalyst more uniform,increase the number of active sites and adjust the strength of alkaline sites,and thus has a better modification effect.And the optimum Ce content was 1.5%wt.According to the Langmuir-Hinshellwood-Hougen-Watson theory,a kinetic model was established with the hydrogenation of formate as the rate-determing step(rds)for both reactions.The parameters of it and another model in literature in which CO2 directly adsorbed and dissociated to CO as RWGS reaction's rds were estimated and tested(statistical test,physical and chemical significance test and residual analysis)based on the orthogonal experimental data.The results show that both models are reliable and the deviation of the former is smaller.