Assessment of Acid Gas Adsorption Selectivities in MIL-125-NH₂

Abstract

Robust, stable, and selective adsorption materials have the potential to enhance the performance of biogas recovery systems. Here, we explore the binary adsorption behavior of MIL-125-NH2 when challenged with CO2/H2S mixtures. Under dry H2S exposure, MIL-125-NH2 retained its crystallinity and single-component CO2 and CH4 uptakes. It was hypothesized that the presence of H2S resulted in a slight decrease in pore volume and weaker binding of condensable gases. To investigate possible defect formation during H2S exposure and handling in ambient air, defect formation energies of the Metal–organic framework (MOF) after H2S exposure were calculated from first principles. The model suggests that the MOF is stable under dry H2S exposure. We find that there is a complete lack of binary CO2/H2S isotherm data on MOFs in the open literature. Our binary experiments reveal that the MOF is selective for H2S over CO2 beyond what is predicted by molecular models and the ideal adsorbed solution theory. The chemical stability of MIL-125-NH2 is advantageous for adsorption in mixtures containing trace H2S, and the experimental H2S/CO2 selectivities around 9 within the biogas composition range suggest that MIL-125-NH2 can be a promising candidate for H2S removal in biogas.