Atomistic investigation of porous amorphous materials for CH₄/H₂ separation

Revealing the gas separation capabilities of amorphous porous materials remains a critical challenge in the materials community for their development as novel adsorbents. This work aims to unlock the potential of amorphous materials for adsorption-based CH4/H-2 separation at pressure swing adsorption (PSA) condition using grand canonical Monte Carlo (GCMC) simulations. Several adsorbent performance evaluation metrics, including adsorption selectivity, working capacity, adsorbent performance score (APS) and regenerability (R%) were computed at 298 K for polymers of intrinsic microporosity (PIMs), amorphous carbons, kerogens, and amorphous zeolitic imidazole frameworks (ZIFs). The CH4/H-2 selectivities and CH4 working capacities of the amorphous materials were estimated to be 9-62 and 0.1-5 mol/kg under PSA condition. Kerogens exhibited the highest APS, and most of the structures provided high R%>80 %. However, none of the materials could reach the maximum APS (802 mol/kg) of crystalline MOFs. Diffraction pattern analysis of crystalline and amorphous ZIF-4 was also performed, and the structural changes were monitored to independently confirm the amorphization. Although crystalline ZIFs exhibited higher adsorption selectivities for CH4/H-2 separation than amorphous ZIFs, their R% were significantly lower. Gas mixture adsorption isotherms of promising amorphous materials were also computed to reveal gas adsorption mechanism. The developed computational approach will be useful in predicting the performance of amorphous materials for CH4/H-2 separation under industrial conditions and monitoring amorphization by diffraction analysis during mass production.