Performance Assessment of a Membrane Gas Absorption (MGA) Process for Biogas Upgrading with Potassium-Based Solvents

Global energy instability has increased interest in biomethane production through biogas upgrading as a renewable alternative to natural gas. This study experimentally investigated membrane gas absorption (MGA) for CO₂ capture using aqueous potassium hydroxide (KOH) and potassium carbonate (K₂CO₃) in a hydrophobic polypropylene hollow fiber membrane contactor under once-through and recycle operating modes. KOH demonstrated faster reaction kinetics and superior mass transfer performance, whereas K₂CO₃ exhibited slower but steadier CO₂ absorption behavior. Under recycle mode operation, both absorbents reached a comparable saturation capacity of approximately 1 mol of CO₂ per mol of absorbent despite their different absorption profiles. The membrane showed no measurable performance decline or morphological changes, confirming good membrane stability and compatibility with both solvents. The results demonstrate the potential of MGA as an effective and flexible approach for small- to medium-scale decentralized biogas upgrading using alkaline solvents with improved chemical stability, lower toxicity, and potential economic advantages over conventional amine-based absorbents.