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 (CO 2 ) and methane (CH 4 ) separation, and CO 2 adsorption and storage owing to its high porosity and tunable pore structure. However, its potential to enhance CO 2 -to-CH 4 conversion by grasping CO 2 in hydrogenotrophic methanogenic systems, thereby increasing CH 4 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 CO 2 -to-CH 4 conversion rate was maximized in the system with 0.75 g/L of ZIF-8 added. Over a single reaction cycle (5 days), the CH 4 proportion increased from 60 % to 97 %. Furthermore, in continuous operation over three reaction cycles, the ultimate CH 4 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.