Overcoming the equilibrium barriers of CO2 hydrogenation to methanol via water sorption: A thermodynamic analysis

In this work, a detailed thermodynamic analysis and simulation of an intensified process for CO2 hydrogenation to methanol with in-situ water sorption is presented. The study focused on the effect of different operating parameters, such as temperature, pressure, H-2/CO2 molar ratio and adsorbent volume capacity, on the reactor performance with the aim to define the optimum operating window. The analysis was also performed for the conventional process as benchmark. The continuous removal of H2O shifts the thermodynamic equilibrium and drives the reactions of CO2 to completion under the entire investigated parameter range. In temperatures and pressures of interest for practical application (220 degrees C-270 degrees C and 50-70 bar), the methanol yield is up to 130% higher in the sorption-enhanced process compared to direct hydrogenation. The only negative aspect was the decrease of CH3OH selectivity in favor of CO production. Despite this, the benefits of water sorption are indisputable and overcome the slight decrease in selectivity. The simulation of the complete process, including gas recycle, showed that with in-situ water removal 15% higher methanol productivity can be attained, with very high once-through CO2 conversion and CH3OH yield and very low gas recycle. This has important implications on the economics of the process, as it decreases the size of the reactor and the auxiliary equipment and practically eliminates the need for downstream methanol-water separation via distillation, leading to substantial process intensification and reduction of capital and operating costs.