Computational screening of hydrophobic metal–organic frameworks for the separation of H2S and CO2 from natural gas

Abstract

Natural gas is an environmentally friendly energy resource and it is of central importance to remove acid gases (e.g. H₂S and CO₂) from natural gas. In this study, we computationally screen 6013 metal–organic frameworks (MOFs) for the simultaneous separation of H₂S and CO₂ from natural gas under humid conditions (represented by a six-component CH₄/C₂H₆/C₃H₈/H₂S/CO₂/H₂O gas mixture). To minimize the competitive adsorption of H₂O, 606 hydrophobic MOFs are first selected on the basis of the Henry constants of H₂O and subsequently assessed for the adsorption capacity of H₂S + CO₂ (N_H2S+CO2) and the selectivity of H₂S + CO₂ over C₁–C₃ (S_{H2S+CO2/C1–C3}). Structure–performance relationships are established between MOF descriptors (the largest cavity diameter, surface area, void fraction and isosteric heat) and performance metrics (N_H2S+CO2 and S_{H2S+CO2/C1–C3}). Moreover, a new performance metric (TSN, the trade-off between N_H2S+CO2 and S_{H2S+CO2/C1–C3}) is proposed. From the Pearson correlation technique, it is revealed that the TSN has strong correlations with the MOF descriptors. Finally, the best MOFs are identified. Interestingly, most of the best MOFs contain N-rich organic linkers (e.g. pyridine and azoles), which are recommended for the design of functional MOFs for H₂S and CO₂ separation. The microscopic insights and guidelines provided by this computational study are useful toward the development of new MOFs for the efficient upgrading of natural gas.