The effect of hydrogen sulfide, carbon monoxide and water on the performance of a PDMS membrane in carbon dioxide/nitrogen separation

Rubbery polymeric membranes demonstrate potential in gas separation as they can be selective for carbon dioxide over less condensable gases such as hydrogen. In many industrial processes where these membranes are applicable, minor gas components such as carbon monoxide, hydrogen sulfide and water are present. Here, the effect of these minor components on the performance of a polydimethyl siloxane rubbery membrane in CO2/N2 separation is experimentally determined. The permeability of CO2 through PDMS is reduced upon exposure to CO, H2S and water, due to competitive sorption of these gases into the polymeric matrix. Similar behavior is observed for N2; however the presence of H2S gives rise to an observed increase in N2 permeability. Extension of the Flory–Huggins theory to a quaternary system allows the relevant interaction parameters for this system to be determined. Upon exposure to a wet feed, CO2 and N2 permeability decrease due to water occupying free volume within PDMS, with the Flory–Huggins interaction parameters indicating mixing of CO2 or N2 with water within PDMS is highly unfavorable. Quantitative analysis of the change in permeability of CO2 and N2 in PDMS in the presence of these minor components enables more accurate prediction of membrane performance in industrial applications to be undertaken.