A commercially scalable MOF adsorbent Cu-BTC for helium recovery from natural gas: performance and mechanism studies at room temperature and lower temperatures

Abstract

The performance and mechanism of the adsorptive separation of some helium-based gas mixtures in a metal–organic framework (MOF) Cu-BTC at room and lower temperature were studied for helium recovery from natural gas. Both GCMC simulations and experimental tests were used to obtain adsorption isotherms for Cu-BTC with CO₂, CH₄, N₂, and He adsorbates. The ideal adsorbed solution theory (IAST) and GCMC simulations were applied to calculate the CO₂/He, CH₄/He, and N₂/He selective adsorption coefficients respectively. Additionally, adsorption breakthrough experiments were conducted to test the adsorption breakthrough curves of CO₂/He, CH₄/He, N₂/He, and CH₄/N₂/He gas mixtures on Cu-BTC. The study found that Cu-BTC exhibited a favorable separation effect for CO₂/He, CH₄/He, and N₂/He gas mixtures, with the separation efficiency at room temperature following the order of CO₂/He > CH₄/He > N₂/He. Further investigations revealed that lowering the temperature significantly improved the adsorptive selectivity of Cu-BTC for CH₄/He and N₂/He mixtures, as well as the separation efficiency for the CH₄/N₂/He ternary gas mixture. Based on simulation data, the study also calculated the isosteric heat of adsorption, adsorption energy distribution, adsorbate density distribution, and binding energy to analyze the mechanism of competitive adsorption of the studied helium-based gas mixtures on Cu-BTC.