Ultramicroporous carbon granules with narrow pore size distribution for efficient CH4 separation from coal-bed gases

The adsorptive separation of CH4 from low-grade coal-bed gas can be performed at decentralized and remote coal mines, and it uses more energy- and is cost-efficient than the traditional cryogenic distillation process. Herein, we present a facile method to prepare ultramicroporous carbon granules with a narrow pore-size distribution at 0.5-0.6 nm. To our knowledge, such centered and uniform pore-size distribution in carbon granules has never been reported. The carbon granules can be directly utilized in adsorption columns without a granulation or pelletization process. The granular oil-tea-shell-derived porous carbon (GOC-2) exhibited a record-high CH4 uptake of 1.82 mmol/g and CH4/N-2 selectivity of 5.8 at 1.0 bar and 298 K among carbon granules. The excellent CH4/N-2 separation performances were confirmed from the results of dynamic breakthrough experiments and pressure swing adsorption simulations. This work provides a novel strategy for developing ultramicroporous carbon granules and guides the future design of efficient CH4/N-2 separation adsorbents.