Oxygen/nitrogen co-doped flexible ultramicroporous carbon monolith with a high CH4 adsorption capacity for CH4/N2 separation from low-concentration coalbed methane

Developing novel carbon adsorbents with high CH4 adsorption capacity for CH4/N-2 separation is always an imperative and challenging process, which could effectively mitigate global warming and fully utilizes low-concentration coalbed methane (CBM). Herein, a green and effective method is proposed to synthesize flexible porous carbon monolith without using binder and toxic/corrosive agents. Melamine sponge is selected as carbon source and nitrogen source, simultaneously as a three-dimensional flexible supporting framework, and glucose is used as second carbon source. The environment-friendly chemical agent potassium oxalate monohydrate (K2C2O4<middle dot>H2O) is used as activator to control the ultramicroporous structure and O&N co-doped property via changing the activation temperature and the amount of K2C2O4<middle dot>H2O. The optimal sample exhibits a record-high CH4 adsorption capacity of 1.95 mmol/g and a good IAST CH4/N-2 selectivity of 5.58 at 25 degrees C and 1.0 bar, outperforming many other adsorbents. Above results originate from the synergistic effect of its high ultramicropore volume (0.26 cm(3) g(-1)), suitable ultramicropore size (centered at 0.55 nm), abundant -OH groups and a certain amount of -COOH groups, as well as N-6 and N-5 species. Dynamic breakthrough experiments further approve that CH4/N-2 mixture can be well separated on this carbon material under realistic condition. This work introduces a new pathway to prepare O&N co-doped flexible ultramicroporous carbon monolith adsorbent for efficient capture of CH4 from low-concentration CBM.