Direct hydrogenation of carbon dioxide to methanol: Systematic generation of multi-stage designs

Abstract

Commercial methanol catalysts based on Cu/ZnO/Al2O3 are less effective applied to direct hydrogenation of CO2 to methanol. The main reason is that the catalyst deactivation increases with the water pressure and temperature, and from stoichiometry, water formation is equal to the CO2 consumption. Here, the focus is on how the process can be designed to reduce this problem. Multi-stage reactor designs with inter-condensation of water and methanol will reduce the water pressure. Several optimal designs are generated with the use of a path optimization method to maximize the methanol production per pass with the use of the least possible reaction volume and hydrogen. Based on a published kinetic model, the optimal volume stage distribution, coolant temperature, and fluid mixing are found. Two configurations of the tail gas treatment are investigated, a once-though and a recycle configuration. A three-stage reactor design with recycling of the tail gas is found to be the better configuration. High CO2-conversion per pass and a low recycle ratio are obtained. Rigorous process simulations of the most promising designs are made to verify that the pressure drop, temperature peaks, and water pressure are good. The maximum water pressure is low. A shell and tube boiling water type reactor design is selected. For a 10 t h− 1 plant, all tubes of all three stages can be located in the same shell.