Modeling and simulation of a steam-selective membrane reactor for power-to-methanol

Abstract

The hydrogenation of CO2 to methanol is currently receiving increased attention following the deployment of Power-to-X processes. In this exothermic reversible reaction, the CO2 conversion is strongly limited by the thermodynamic equilibrium and the offer of commercial catalysts is mostly limited to Cu-based materials. Therefore, available options for improving methanol production consider either process design and optimization and/or using multifunctional reactors that provide advantageous features compared to conventional reactors, despite additional complexity. In this work we have modeled and simulated a membrane reactor (MR) featuring steam removal for shifting the reaction equilibrium to the products side and thus not only improving the CO2 conversion but also contributing to the increase of catalyst life span and representing a reliable alternative for heat removal. For this purpose, the proposed model for the MR considered the properties of a hydrophilic sodalite (SOD) membrane and the kinetics of a Cu/ZnO/Al2O3 catalyst. A split feed strategy has been devised to tackle poor membrane selectivity in the temperature range of interest. At 270 °C and 50 atm, the split feed allowed increasing the methanol yield up to 18%, while an ideal membrane (i.e., infinitely selective to steam) up to 31% (both in relative terms), when compared to a traditional reactor. Moreover, using the MR with the SOD membrane in the referred conditions it was obtained a permeate outlet stream containing only reactants and steam, therefore easily recyclable.