Using ligand regulation, metal replacement, and ligand doping strategies on Zr-FUM to improve methane separation from coalbed gas.

Abstract

Developing adsorbents suitable for industrial applications that can effectively enhance the separation of methane (CH₄) from nitrogen (N₂) in coalbed gas is crucial to improve energy recovery and mitigate greenhouse gas emissions. In this study, three modification strategies were implemented on Zr-FUM, including ligand regulation, metal replacement, and ligand doping, to synthesize Zr-FDCA, Al-FUM, and Zr-FUM-FA, with the aim of improving the performance of CH₄/N₂ separation under humid conditions. The results demonstrated that the promotion of robust orbital overlap and strengthened electrovalent bonding on adsorbents can selectively enhance CH₄ adsorption. As a result, Zr-FUM-FA achieved a saturated CH₄ adsorption capacity of 1.37 mmol/g, a CH₄ working window of 307 s, and a CH₄/N₂ sorbent selection parameter (Ssp) of 47.31, exceeding the performance of most reported adsorbents. Analyses of the pore structure, surface morphology, and functional groups revealed that the presence of an ultramicropore proximity to CH₄, reduced static resistance, and enhanced electrovalent bond were key factors for CH₄ separation. Grand Canonical Monte Carlo and Density Functional Theory studies indicated that the introduction of -C-H- in FA played a crucial role in enhancing CH₄ adsorption. Optimization of adsorption parameters using the Aspen adsorption package showed that in a dual-adsorbent bed system, the recovery and purity of CH₄ in Zr-FUM-FA reach 99.5% and 97.3%, respectively, providing important theoretical support for the improvement of CH₄ recovery in the pressure swing adsorption process from coalbed gas.