Production of green methane by carbon dioxide capture from landfill biogas via pressure swing adsorption mediated by MOF ZIF-8

The growing interest in biomethane (bioCH4) as a sustainable replacement for conventional fossil fuels highlights the urgency to develop efficient CO2 capture methods from raw biogas, thereby enhancing the value of this renewable fuel source. This study investigates the efficacy of ZIF-8 as an adsorbent for CO2 capture through pressure swing adsorption (PSA) under non-isothermal conditions. ZIF-8 was synthesized and characterized using SEM, BET, FTIR, and XRD to understand and confirm its microstructures. A computational model was developed to simulate the dynamic behavior of ZIF-8 during adsorption, incorporating insights from its characterization. The model, based on the extended Langmuir model for multicomponent adsorption, also accounted for adjustments in the adsorption bed geometry. Dynamic simulations were performed employing the Aspen Adsorption platform to assess the impact of key parameters such as the CH4/CO2 ratio, length/diameter ratio, and adsorption time on bioCH4 purity. Utilizing the Design of Experiments framework, central composite design (CCD), and desirability functions, the interplay of these parameters was optimized to enhance bioCH4 purity and recovery rates. The optimized PSA system, utilizing ZIF-8, demonstrated impressive purity of 99.93% and recovery of 96.5% at CH4/CO2 ratio of 2.06, a length/diameter ratio of 2.76, and an adsorption time of 115 s. These results meet stringent quality criteria for vehicle fuel, aligning with the most rigorous emission standards. For future investigations, it is crucial to explore the long-term stability and regeneration capabilities of ZIF-8 in large-scale applications. Understanding its practical feasibility and sustainability as an adsorbent for biogas upgrading will provide valuable insights for further advancements in this field.