A comprehensive review of metal-organic frameworks sorbents and their mixed-matrix membranes composites for biogas cleaning and CO2/ CH4 separation

Metal-organic framework (MOF) sorbent materials have recently gained considerable attention in gas separation technology. This is because of their unique structural properties, such as high gas permeability and selectivity promoted by large porosity and high surface areas. Integrating MOF fillers with polymer membranes to construct mixed-matrix membranes (MMMs) has enhanced gas separation and capture performance and stability. This review provides a comprehensive current status development in MOFs and their integrated MMMs composites with focused applications in biogas cleaning for the removal of common trace impurities such as hydrogen sulfide (H2S), ammonia (NH3), siloxanes, and moisture and upgrading of the subsequent carbon dioxide/methane (CO2/CH4) mixture to bio-methane and biogenic CO2. We highlight the structural properties and descriptors critical for designing MOF sorbents and MOF-based MMMs to improve their adsorption capacities and separation efficiency in biogas cleaning and upgrading. The tuneable surface modifications of MOFs boasted by the surfaceendowed basic-acidic sites and coordinated open metal sites effectively provide high adsorption capacities and separation selectivities in biogas processing. The combination of MOFs and membranes offers high separation efficiencies of biogas-derived CO2 and CH4 for their diverse potential downstream utilisation. Future perspectives on advancing further developments in MOF sorbents and MOFs-based MMMs for biogas cleaning and upgrading to access sustainable and green derivatives with fewer carbon footprints while beneficiating wastes for adopting a circular economy are highlighted to provide solutions to the shortcomings.