Sub-nanopore orifice control on carbonaceous adsorbent boosting N2/CH4 inverse separation with ultra-high selectivity

Abstract

Selective capture of nitrogen (N₂) to upgrade natural gas is of both environmental significance and economic benefit. The realization of carbons with superior N₂-selectivity and adsorption capacity is highly desirable but rarely reported. Herein, polydopamine-derived carbonaceous adsorbent is reported to realize the reverse adsorption separation of N₂/CH₄ with ultra-high selectivity of 11 and N₂ capacity of 47 cm³g^-1 under ambient conditions, as well as impressive separation factor of 7.7 at adsorption-desorption pressure of 20 and 1 bar. The sub-nanopore orifice of carbon as low as 0.36–0.38 nm is finely tuned by controlling the sp²C/sp³C ratio of precursors with optimized ethanol/dopamine ratio. A mathematic linear model is built between gas diffusion rates and the ratio of Ln/Md in the confined sub-nanopores of carbon. Dynamic breakthrough performances at ambient and higher pressures, as well as the exceptional cyclic stability and mild regeneration, further confirm its potential for industrial pressure-swing adsorption processes.