Preparation of N- and O-doped microporous carbon granules for effective CH4 adsorption and separation from low-concentration coal-bed methane

Abstract

Developing novel granular carbon adsorbents for CH₄ adsorption and CH₄/N₂ separation has always been a great challenge in the utilization of low-concentration coal-bed methane (CBM). Herein, N- and O-doped microporous carbon granules are prepared from corn kernels via a facile and effective method. Notably, neither a binding agent nor KOH is used in the preparation process. The resulting optimal corn-kernel-based carbon granule (CKCG) adsorbent CKCGs-900-1 exhibits a high CH₄ adsorption capacity of 1.31 mmol g⁻¹ and IAST selectivity value of 17.62 (CH₄/N₂ = 10/90 v/v) at 25 °C and 1 bar, making it superior or comparable to most of the reported powdery and shaped adsorbents. The above-mentioned properties result from the synergistic effect of the microporous structure (micropores concentrated at 0.55 nm), functional groups (C–OH and COOH) and surface species (N-5 and N-6). Dynamic breakthrough experiments prove that CH₄/N₂ mixtures can be separated under ambient conditions. Kinetics study shows that CH₄ adsorption on CKCGs-900-1 conforms to the Bangham model, indicating a pore diffusion process. This work provides a useful strategy for developing potential materials for recovering CH₄ from low-concentration CBM.