Can Gas Absorption be Tuned in a Multifunctional Ionic Liquid?

The challenge of CO separation and management in biogas upgrading processes is addressed, which remains a critical bottleneck when considering biomethane as a competitive and sustainable alternative to natural gas. Ionic liquids offer a promising alternative to existing sorbents due to their negligible volatility and their tunable properties. Herein, a multifunctional phosphonium triazolate ionic liquid capable of reacting reversibly with CO without loss of fluidity through both cation and anion is presented. Using a combination of experiments and reaction models the interplay of different absorption mechanisms is demonstrated at varying temperatures and pressures, which lead to high capacity for CO absorption and excellent selectivity for CO over CH. The multifunctional phosphonium triazolate can be used to prepare a porous ionic liquid with enhanced physical gas absorption by dispersing up to 10% w/w of ZIF-8. The stability and porosity are maintained after CH absorption but are lost upon prolonged exposure to CO due to dissolution of the porous solid. These findings provide crucial insights for the development and modeling of ionic liquid-based absorbents, paving the way for biogas upgrading technologies with reduced carbon footprint.