Molecular simulation of helium-light hydrocarbon separation using a metal-organic framework and its derivative at ambient and lower temperatures

This study uses molecular simulations to examine the adsorptive separation of helium-light hydrocarbon mixtures by the metal-organic framework (MOF) UPC-66 and its activated form UPC-66a. Grand canonical Monte Carlo (GCMC) simulations were conducted to obtain single-component adsorption isotherms of CH 4 , C 2 H 2 , C 2 H 4 , C 2 H 6 , and He at 298 K and 220 K. The ideal adsorbed solution theory (IAST) was applied to predict selective adsorption coefficients, and its accuracy was evaluated by comparison with direct GCMC-calculated selectivities for UPC-66a. Multicomponent GCMC simulations were further performed for a five-component gas mixture. To clarify competitive adsorption mechanisms, isosteric heats of adsorption were determined using the Clausius-Clapeyron relation and GCMC simulations, while adsorption energy distributions, adsorbate probability density distributions, and binding energies were analyzed. The results show that both MOFs can effectively extract helium from light hydrocarbon mixtures, with separation performance significantly enhanced at lower temperatures. The observed selectivity mainly arises from the stronger binding interactions between the adsorption sites and light hydrocarbon molecules compared with helium. • Simulations assess UPC-66 and UPC-66a for removing hydrocarbons in crude helium. • GCMC and DFT are used to study MOFs' separation at room and lower temperatures. • Lower temperature markedly improves He recovery by UPC-66 and UPC-66a. • Activated UPC-66a outperforms the parent UPC-66 in He separation. • Many factors such as affinity, adsorbate size, and adsorbent flexibility affect selectivity.