(396i) Co-Permeation of Alcohols in Hydrated Polymer Membranes

Membrane transport of aqueous solutes is critically important for a range of membrane separations and fuel cell operation and is commonly investigated experimentally using diffusion cell experiments. The transport of solutes through dense, hydrated polymer membranes is described by the well-known solution diffusion model, <P_i> = <Ki> <Di>, where <P_i> is the apparent permeability of the membrane to component i, <K_i> is the solubility of component i in the membrane, and <D_i> is the apparent diffusivity of component i in the membrane. Traditionally, techniques to measure permeation through a membrane require aliquot sampling with analysis of solution composition ex situ. Here, we utilize in-situ ATR FTIR spectroscopy to quantify solution concentrations, preempting the need for aliquotic sampling and ex situ analysis. We apply this technique towards understanding how the presence of co-permeants impact solute uptake and permeability in hydrated, dense polymer membranes. In particular, we examine the permeation of a series of single and multicomponent mixtures of alcohols through Nafion. Membrane permeabilities extracted from in situ monitored diffusion cell experiments are coupled with solute solubility measurements to fully describe the permeability, solubility and diffusivity in these systems. Focusing on the interactions in binary mixtures we find in some instances substantial differences in selectivity as calculated from single solute permeabilities compared to binary diffusion cell experiments. This illustrates the limitations involved in attempting to predict membrane separations from single solute permeabilities and the need for investigations into the impact of co-permeants on transport.