Utilizing zeolitic imidazolate framework-8 for enhanced carbon dioxide/methane separation and improved carbon dioxide methanation performance.

Zeolitic imidazolate framework-8 (ZIF-8) has been widely employed for carbon dioxide (CO2) and methane (CH4) separation, and CO2 adsorption and storage owing to its high porosity and tunable pore structure. However, its potential to enhance CO2-to-CH4 conversion by grasping CO2 in hydrogenotrophic methanogenic systems, thereby increasing CH4 percentage in biogas, remains unexplored. This study synthesized ZIF-8 material and applied it in a biological biogas upgrading system. The results indicated that the CO2-to-CH4 conversion rate was maximized in the system with 0.75 g/L of ZIF-8 added. Over a single reaction cycle (5 days), the CH4 proportion increased from 60 % to 97 %. Furthermore, in continuous operation over three reaction cycles, the ultimate CH4 proportion in this reactor consistently exceeded 95 %, meeting the standards of biomethane. The pathway analysis revealed that the ZIF-8 introducing could increase abundance of hydrogenotrophic methanogens and facilitated the transition of metabolic pathway from acetotrophic to hydrogenotrophic methanogenesis.