Optimal adsorbent selection for synthetic biogas: Adsorption in static conditions on activated biochars and activated carbons of CNR-115 family

This study investigates the adsorption properties of activated biochars (Cabosse-A-700, Bamboo-A-900) and activated carbons from the CNR-115 family (CNR-115, CNR-115-ox, and CNR-115-ox-am) for CO 2 /CH 4 separation using a synthetic 40%/60% CO 2 /CH 4 gas mixture under dry static conditions. The effects of activation conditions and chemical modifications on adsorption behavior were analyzed. CNR-115, synthesized from renewable precursors via phosphoric acid activation, exhibited the highest BET surface area (1714 m 2 g −1 ) and micropore volume (0.64 cm 3 g −1 ), making it ideal for gas adsorption. However, oxidation and ammonia treatment reduced its porosity while increasing surface basicity, enhancing CO 2 selectivity. Bamboo-A-900, with a BET surface area of 1220 m 2 g −1 , showed a well-balanced micro- and mesoporous structure, while Cabosse-A-700, with a lower surface area (97 m 2 g −1 ), remained a more sustainable and cost-effective alternative. Adsorption results indicated that CO 2 was preferentially adsorbed over CH 4 due to stronger surface interactions with the adsorbent surface. At 2 MPa, CNR-115-ox-am demonstrated the highest selectivity ( S C O 2 / C H 4 ≈ 37) and API (10.12±0.11), driven by its nitrogen functionalities. CNR-115 had an API of 8.08 ± 0.09, with moderate selectivity (5.7 ± 0.3), while CNR-115-ox reached a selectivity of 9.3 ± 0.1 and API of 4.96 ± 0.06. In contrast, the activated biochars (Bamboo-A-900 and Cabosse-A-700) showed lower selectivities (2.2 ± 0.2 and 1.5 ± 0.1) and API values (1.07 ± 0.03 and 0.15 ± 0.02), respectively. However, at 0.1 MPa, API values were similar across all materials ( 0.007–0.04), with Cabosse-A-700 standing out as the most sustainable due to its low activation temperature (700 °C) and biomass origin. These results confirm that API is a reliable indicator of adsorbent performance in biogas upgrading. • Static CO 2 /CH 4 adsorption on activated biochars and modified CNR-115 carbons. • Chemical treatment improved CO 2 selectivity of CNR-115-ox-am via nitrogen surface. • Cabosse-A-700 showed good performance at 0.1 MPa with low-cost production. • CNR-115-ox-am had the highest API at 2 MPa due to nitrogen functionalities. • API effectively evaluates adsorbent performance in biogas purification.