Thermodynamic study of CO₂ hydrogenation to methanol with integrated water removal

CO 2 hydrogenation to methanol (CH 3 OH) was investigated through a comprehensive thermodynamic analysis to identify favourable operating windows within a reaction network that includes competing pathways, notably the reverse water–gas shift (RWGS). Equilibrium simulations were performed in Aspen Plus® v14 and post-processed in Matlab® to generate heat-map visualizations across different temperature (150–600 °C), pressure (20, 40, 60, 80 and 100 bar), and H 2 /CO 2 molar ratio (2:1, 3:1, 4:1 and 5:1). The selected pressure range reflects conditions relevant to power-to-liquid applications, excluding values below 20 bar (due to reduced conversion) and above 100 bar (for a limited additional thermodynamic benefit relative to cost). Initially, the system was modelled as a single equilibrium stage, representative of a conventional once-through reactor operated at fixed temperature and pressure. Subsequently, selective H 2 O removal (varied from 0% to 99%) was investigated via equilibrium thermodynamic simulations to emulate sorption-enhanced and membrane-assisted concepts, thereby shifting equilibrium according to Le Chatelier’s principle. The intensified configuration was represented as a cascade of N + 1 equilibrium reactor stages in series, with an intermediate separation block placed between adjacent stages to remove a fraction of the produced water. The results show that increasing pressure strongly enhances CO 2 conversion. Water removal further promotes methanol production, leading to a higher methanol yield despite a slight increase in CO selectivity, of about 2 % points, associated with the growth of the RWGS pathway contribution. Overall, the gain in methanol production outweighs this limited selectivity penalty, indicating that water removal remains an effective process-intensification strategy. Water removal also increases the overall exothermicity of the system, although this effect becomes less pronounced at high pressure, where conversion is already strongly favored. Overall, the analysis provides design-relevant thermodynamic insights and clarifies the key conversion-selectivity trade-offs associated with water-management strategies in CO 2 -to-methanol processes.