Real-Time Quantification of Sorption-Enhanced CO2 Hydrogenation to Methanol over Zeolite 4A

Sorption enhanced reaction processes (SERP) were successfully evaluated in the CO2 hydrogenation reaction, by leveraging the sorption benefits to enhance the formation of methanol. In this work, a dedicated experimental protocol and an analytical setup were developed to quantitatively investigate the coupling between reaction and sorption during the transient regime. This system enables the direct quantification of all molecules at the reactor outlet, including methanol and water, thus allowing an accurate real-time mass balance analysis and improved understanding of the phenomena occurring during sorption-enhanced operation. Experiments performed at 230°C and 30 bar using a Cu / ZnO / Al2O3 commercial catalyst combined with LTA zeolite (4A) demonstrated that sorption significantly enhances methanol production beyond the thermodynamic equilibrium predicted for a conventional reactor, while the impact on CO production remains limited. Substantial adsorption of both water and methanol within the zeolite framework was assessed. Indeed, the LTA sorbent exhibited a methanol sorption selectivity of 31%, which significantly enhanced the total methanol production during the sorption-enhanced effect. Indeed, 56% of the total methanol formed was temporarily retained within the zeolite, highlighting the key role of the methanol sorption in promoting CO2 hydrogenation with respect to the reverse water-gas shift reaction (RWGS), while water removal influences both reactions. As a result of this sorption-enhanced effect, the quantities of methanol and CO produced increased by 168% and 55%, respectively, compared with the reference experiment for a 60 min period. Structural characterization (XRD and 27Al MAS NMR) confirmed that the LTA zeolite framework remained stable after the experiment despite the harsh conditions of high pressure and temperature in the presence of steam.