Effect of Amines on MIL-101(Cr) for Simultaneous H₂S/CO₂ Removal from Biogas

Production of biomethane from raw biogas requires the removal of impurities, such as CO₂ and H₂S. To accommodate the variety of biogas sources, a modular separation design with a small footprint is desired. In this work, we report three diamine-impregnated metal-organic frameworks (MOFs), MIL-101(Cr) (diamines: diethylethylenediamine, ee-2; 2,2-dimethyl-1,3-propanediamine, dmpn; <i>N</i>-methylethylenediamine, m-2) for simultaneous removal of H₂S and CO₂ from simulated binary and ternary biogas mixtures. The H₂S and CO₂ separation performance and regeneration conditions were investigated by dynamic column breakthrough and temperature-programmed desorption experiments. While all three diamine-impregnated MIL-101(Cr) samples were H₂S-selective over CO₂ in the mixture compositions studied, MIL-101(Cr)-ee-2 displayed the highest H₂S/CO₂ adsorption selectivity of ∼7. Also, it showed distinct desorption temperatures for H₂S and CO₂ that allows for concentrated H₂S collection during adsorbent regeneration, which can potentially simplify the biogas separation process to achieve concentrated biomethane and H₂S collection using the same adsorption module.