Selective Removal of H₂S from Biogas Using Solid Amine-Based "molecular Basket" Sorbent

Biogas is an important renewable energy source, but its ppm-level hydrogen sulfide (H₂S) component must be removed from the gas mixture dominated by CO₂ and CH₄. In this work, a tertiary-amine-based "molecular basket" sorbent with a mesoporous silica as support was found to be effective for the selective hydrogen sulfide (H₂S) removal from gas mixtures simulating biogas with a high CO₂ concentration up to 40 vol %. Polyallylamine (PA), polyethylenimine (PEI), and tetramethyl hexanediamine (TMHDA) were used as primary, secondary, and tertiary amines to prepare the SBA-15 supported sorbents, respectively, and their H₂S sorption performances were evaluated in a flow system in the absence and presence of CO₂. The tertiary-amine-based sorbent, TMHDA/SBA-15, can selectively remove H₂S in the presence of CO₂, and the highest sorption capacity was achieved at 15 wt % TMHDA loading which is close to its monolayer coverage on the surface. More importantly, about 90% of the capacity could be maintained on TMHDA/SBA-15 even with the CO₂ concentration as high as 40 vol %. The H₂S sorption on TMHDA/SBA-15 fitted with the Langmuir adsorption isotherm well although the estimated adsorption heat with the van't Hoff equation is relatively low. Characterization using N₂ physisorption, FT-IR, and XPS demonstrated that the TMHDA is dispersed within the pore channels through the interaction between amine and silanol groups on the surface of SBA-15. The TMHDA/SBA-15 sorbents showed a good regenerability under a mild regeneration condition (e.g., 110 °C), the capacity of which was not impeded by other components in biogas such as CH₄ and H₂O.