(814e) Performance and Stability of RTIL-Membranes for Dehumidification of Methane

The biogas production from organic waste—animal, sewage, landfill material - could be a valuable renewable fuel.  Before this biogas—predominately bio-methane—can be converted to fuel, it must be dehumidified. Typically membrane-based gas dehumidification uses hydrophilic polymer membrane materials, such as polydimethylsiloxane (PDMS) and cellulose acetate (CA).  The main problems with polymer dehumidification membranes are methane loss and the susceptibility of polymer materials to plasticization by H₂O.  Room temperature ionic liquid membranes (RTIL-membranes), according to recent literature, are not plasticized by water and have large water/CH₄ selectivities.  In our paper, we will build on the initial literature RTIL-dehumidification data by looking at a series of ammonium and imidazolium-based ionic liquids.  One membrane based on the trifluoromethanesulfonate [TfO] anion had a water permeance of 2000 GPUs with a H₂O/CH₄ selectivity of 12 000.  With such high water permeances, boundary layer and support structures might significantly contribute to the overall water transport resistance, we will, therefore, present our work to measure and minimize this effect in our data.  Of greater interest to the membrane community, however, will be our finding that there is an impact on some of the RTIL-membranes from the water vapor in the feed. This impact appears to be an increase in membrane mechanical stability and H₂O/CH₄ selectivity with increasing feed gas relative humidity.  In an attempt to explain these phenomena we will explore the impact of the Feed rH the on surface tension of the stabilized RTIL.