Simultaneous Removal of CO₂ and H₂S from Biogas by Blending Amine Absorbents: A Performance Comparison Study

Greenhouse gas treatment is urgently needed because of the impact of climate change caused by greenhouse gas emissions after global economic growth. In this study, postcombustion capture was carried out to screen absorbents for simultaneous absorption and regeneration of CO₂ and H₂S byproducts of biogas using N-methyldiethanolamine (MDEA)-based additives. Twelve different absorbents were selected and compared according to the types of the amine group and the alcohol group. The mixture gas of 35 vol % CH₄, 15 vol % CO₂, and 50 ppm H₂S balanced by N₂ was used for absorption and regeneration. Absorption and regeneration were carried out at 35 and 80 °C, respectively. The absorbent concentration was fixed at 4.5 wt % for MDEA and 0.5 wt % for additives. In the continuous absorption and regeneration experiments, rich loading, lean loading, cyclic loading, absorption rate, and desorption rate were measured according to the loading values of CO₂ and H₂S using MDEA/additive mixed absorbent. CO₂-rich loading was excellent in MDEA/diethylenetriamine (DETA), and CO₂ cyclic capacity was excellent in MDEA/bis(3-aminopropyl)amine (APA). H₂S-rich loading was superior in MDEA/APA, and H₂S cyclic capacity was superior in MDEA/DETA. The CO₂ absorption and regeneration rates were excellent in MDEA/piperazine (PZ), and the H₂S absorption and regeneration rates were excellent in MDEA/2-amino-2-methyl-1-propanol. MDEA-based blending absorbent showed better absorption and regeneration performance than MDEA, and MDEA/PZ showed good performance for CO₂ but very poor performance for H₂S. It was confirmed that MDEA/APA was superior for gas composition in the simultaneous absorption and regeneration of CO₂ and H₂S.