(550c) Hydrogen Sulfide Removal from Biogas on "Molecular Basket" Sorbents

Biogas is a sustainable energy source which can be used as an alternative fuel. However, hydrogen sulfide (H₂S) in biogas (formed from the decomposition of organic materials) limits the application of biogas due to its corrosivity and sulfur-toxicity. Recently, “Molecular basket” sorbents (MBS) for acid gas adsorption developed in our group could achieve H₂S sorption/desorption at ambient conditions. Nevertheless, the large amount of CO₂ in biogas strongly inhibits H₂S sorption on conventional MBS. Therefore, the objective of this work is to selectively remove H₂S from biogas which contains a high-level concentration of CO₂. In this work, a series of tertiary-amine-based “Molecular Basket” sorbents were prepared and applied in H₂S removal from the gas mixture containing a high concentration of CO₂. Poly allylamine (PA), polyethylenimine (PEI), and tetramthyl hexanediamine (TMHDA) were loaded on SBA-15 to compare the H₂S sorption performance in the absence and presence of CO₂. In the presence of CO₂, the H₂S sorption dropped dramatically on PA/SBA-15 and PEI/SBA-15, whereas the selectivity of TMHDA/SBA-15 for H₂S sorption remained stable. The inlet concentration (H₂S and CO₂), the regenerability, as well as the effects of CH₄ and moisture were studied. The H₂S sorption capacity was increased with increasing inlet H₂S concentration, and the sorption on TMHDA/SBA-15 was fitted to Langmuir adsorption isotherm. However, the H₂S sorption capacity was slightly decreased with the increase of inlet CO₂ concentration. The regenerability was good under mild regeneration conditions. In addition, other components in biogas, such as CH₄ and moisture, showed little effect on the H₂S sorption performance over MBS. This work demonstrated that tertiary-amine-based MBS is selective for the H₂S removal from biogas.