Simultaneous absorption of CO 2 and H 2S from biogas by capillary membrane contactor

Abstract

This work presents the study on the simultaneous absorption of H 2S and CO 2 from biogas using a capillary membrane contactor. The synthetic biogas contained 250–1000 ppm H 2S, 20–40% CO 2 and CH 4. 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 H 2S 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 CO 2 and H 2S compared to water. The absorption flux of H 2S significantly increased with increasing gas flow rate and slightly increased with liquid velocity and MEA concentration, while the absorption flux of CO 2 moderately increased with liquid velocity and was highly enhanced with increasing MEA concentration. The increase in CO 2 concentration obviously decreased the H 2S flux. The results of H 2S 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 H 2S. The opposite was found for the mass transfer of CO 2, i.e., the liquid phase resistance controlled the mass transfer. For the partially wetted mode, the wetted membrane resistance controlled the CO 2 absorption. On the contrary, for H 2S absorption, the wetted membrane resistance was insignificant and the gas phase resistance controlled the mass transfer. The observation of CO 2 and H 2S flux for a period of 6 h in order to investigate the effect of membrane wetting showed that the CO 2 flux dropped approximately 7.6%, while change of H 2S flux was negligible.