In Situ N-Doped Low-Corrosion Porous Carbon Derived from Biomass for Efficient CH4/N2 Separation

The separation of CH4and N2is essential for the effective use of low-concentration coalbed methane (CBM). In this study, a series of nitrogen-doped porous carbons were synthesized using an in situ nitrogen doping method combined with K2CO3activation. The study systematically examined how changes in the physical structure and surface properties of the porous carbons affected their CH4/N2separation performance. The results revealed that in situ nitrogen doping not only effectively adjusts the pore structure and alters the reaction of K2CO3on the carbon matrix, but also introduces nitrogen and oxygen functional groups that significantly enhance the adsorption capabilities of the materials. In particular, sample S3Y6−800 demonstrated the highest methane adsorption capacity of 2.23 mmol/g at 273 K and 1 bar, outperforming most other porous carbons. This exceptional performance is attributed to the introduction of N-5, N-6, C-O, and COOH functional groups, as well as a narrower pore-size distribution (0.5–0.7 nm) and the formation of carbon nanotube structures. The introduction of heteroatoms also provides additional adsorption sites for the porous carbon, thus improving its methane adsorption capacity. Furthermore, dynamic breakthrough experiments confirmed that all samples effectively separated methane and nitrogen. The Toth model accurately described the CH4adsorption behavior on S3Y6−800 at 298 K, suggesting that the adsorption process follows a sub-monolayer coverage mechanism within the microporous regions. This study provides a mild and environmentally friendly preparation method of porous carbons for CH4/N2separation.