Enhanced CO2/CH4 separation by solvent-based pressure swing absorption: Effects of solvent composition and concentration in ternary system

Abstract

Global warming, largely driven by greenhouse gases such as carbon dioxide (CO2), necessitates efficient strategies for CO2 mitigation. This study investigated solvent-based pressure-swing absorption techniques to selectively separate CO2 from methane (CH4) in anaerobic digester (AD) biogas mixtures. Water, used as the reference solvent, exhibited selective CO2 absorption with over 90 % CO2 purity upon degassing at varying pressures (5, 10, and 15 bar). Artificial seawater tests revealed minimal reductions in CO2 absorption capacity at moderate salt concentrations (∼36,000 ppm), while salt addition notably improved CO2 selectivity due to the salting-out effect. Among pure solvents tested, acetone emerged as most effective, significantly increasing the dissolved gas ratio (∼40 %) and yielding up to 80 % CH4 purity in residual gases. Introducing sodium iodide (NaI, 20 wt%) into acetone solutions enhanced degassed gas CO2 concentrations from 60 % to approximately 70 %. Further, the ternary NaI-water-acetone system substantially improved CO2 selectivity, with optimized compositions (20 wt% NaI, 10 wt% water, and 70 wt% acetone) achieving degassed gas compositions of up to 77 % CO2. These findings highlight the effectiveness of this ternary solvent system for selective CO2 recovery, providing promising potential for practical greenhouse gas mitigation applications.