Hydrogen sulfide mix gas permeation in Aquivion® perfluorosulfonic acid (PFSA) ionomer membranes for natural gas sweetening

Permeation tests of CO2/CH4 and H2S/CH4 mixtures in a commercial Perfluorosulfonic acid membrane, Aquivion® E87-12S, were carried out at different temperatures, namely 27, 35 and 50 °C, and at relative humidity (RH) ranging from 20 to 95%. A purposely modified experimental set up was used to allow mixture testing in a fixed volume variable pressure permeometer. The results confirmed the major influence of water content on the gas permeation behavior in PFSA as permeability strongly increased with RH. CO2 and CH4 results confirmed experimental data already available in the open literature, while, for H2S, permeability increased from a value of 17 Barrer measured at 27 °C and 20%RH up to 450 Barrer at the same temperature but at 95%RH. The selectivity with respect to methane also increased with RH, going from 7 to 36 at the same temperature and in the same RH range. The temperature's increase also improved H2S permeability, which reached 512 Barrer at 50 °C and 85%RH, but slightly decreased selectivity towards methane which in the same conditions was limited to 23. A simple model, already used to describe the permeation behavior of other different gases in PFSA, also proved to be able to fit experimental data of H2S with slight changes of the adjustable parameters.