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The present work studied the simultaneous separation of H2S and CO2 from biogas by gas–liquid membrane contactor (GLMC) using single and mixed absorbents. The synthetic biogas contained 300 to 900 ppm of H2S, 30% to 50% CO2 and CH4. To better understand the effects of different absorbents on simultaneous separation of H2S and CO2 from biogas, water, monoethanolamine (MEA, primary amine), potassium carbonate (K2CO3, inorganic salt), potassium hydroxide (KOH, inorganic salt), and potassium sarcosine (PS, organic salt) were applied as absorbent solutions. Poly­(vinylidene fluoride) (PVDF) hollow fiber membrane was used in the membrane contactor modules. The simultaneous absorption performance of CO2 and H2S into single and mixed absorbents was investigated. In addition, the effects of liquid and gas velocities, absorbent concentration, acid gas content of the feed gas, and gas pressure on the absorption performance and the analysis of mass transfer coefficients were investigated. The results indicated that the highest H2S absorption flux was obtained when KOH and K2CO3 were used as single absorbents, and the highest CO2 flux was obtained using PS as the single absorbent. The use of promoted K2CO3 with PS solutions could simultaneously improve the absorption flux of H2S and CO2. Increasing the liquid flow rate and absorbent concentration led to an increase in the CO2 absorption flux, while increasing the gas flow rate led to a significant increase in H2S absorption; The change of liquid flow rate has little effect on H2S absorption flux. A long-term stability test revealed that partial wetting of membrane could reduce the CO2 absorption flux but has little effect on H2S absorption flux. The detailed analysis of the mass transfer coefficients showed that liquid side resistance was negligible in comparison with membrane and gas side resistances for H2S absorption. On the contrary, the mass transfer process of CO2 was controlled by liquid mass transfer resistance.

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