Carbon nanofibers with gas selective layer containing rich and accessible ultramicropores for methane/nitrogen separation

Abstract

The adsorption separation and purification of coalbed methane (CH4) has attracted global interest as an important technique for the utilization of unconventional natural gas. The success for this method relies on the development of adsorbent materials that can selectively enrich CH4. Toward this goal, we report a facile in-situ growth method to prepare carbon nanofibers with ultramicroporous gas selective layer as adsorbent for CH4/N2 separation. The thickness of gas selective layer can be precisely tuned from 90 nm to 525 nm. The optimal carbon nanofibers exhibited a high CH4/N2 selectivity of 6.8 with the CH4 uptake reaching 0.97 mmol g−1 as well as two orders of magnitude faster CH4 diffusion kinetics than the commercial activated carbon adsorbent. The high accessibility to the adsorption sites and short diffusion path of the nanofibers facilitate the rapid mass transfer and intensify the dynamic CH4/N2 separation. Pressure swing adsorption simulations indicated the recovery and productivity over the carbon nanofibers with 90 nm-thick gas selective layer increased by 40 % and 20 %, respectively, as compared to the 525 nm-thick counterparts. This work offers a new insight for designing high-performance CH4/N2 adsorbents through suitable combination between rich ultramicropores and short diffusion path.