Simultaneous absorption of CO2 and H2S from biogas by capillary membrane contactor

This work presents the study on the simultaneous absorption of H2S and CO2 from biogas using a capillary membrane contactor. The synthetic biogas contained 250–1000 ppm H2S, 20–40% CO2 and CH4. The absorbents used were water and monoethanolamine (MEA) solution. The effects of liquid and gas velocities, gas composition, on the absorption performance and selectivity of H2S were investigated together with the detailed analysis of the mass transfer resistances of the membrane contactor system.The use of MEA solution gave much higher absorption fluxes of both CO2 and H2S compared to water. The absorption flux of H2S significantly increased with increasing gas flow rate and slightly increased with liquid velocity and MEA concentration, while the absorption flux of CO2 moderately increased with liquid velocity and was highly enhanced with increasing MEA concentration. The increase in CO2 concentration obviously decreased the H2S flux. The results of H2S selectivity and the mass transfer resistance analysis of the non-wetted mode showed that the gas phase resistance played the important role on the mass transfer of H2S. The opposite was found for the mass transfer of CO2, i.e., the liquid phase resistance controlled the mass transfer. For the partially wetted mode, the wetted membrane resistance controlled the CO2 absorption. On the contrary, for H2S absorption, the wetted membrane resistance was insignificant and the gas phase resistance controlled the mass transfer. The observation of CO2 and H2S flux for a period of 6 h in order to investigate the effect of membrane wetting showed that the CO2 flux dropped approximately 7.6%, while change of H2S flux was negligible.

► A capillary membrane contactor was applied for CO2 and H2S removal from biogas.
► The results include experimental data and analysis of mass transfer.
► The resistance in liquid phase played the important role to the CO2 absorption.
► H2S absorption was strongly influenced by the resistance in gas phase.
► Membrane wetting affected the overall mass transfer coefficient of CO2 more than H2S.