(351m) Measuring Intrinsic Membrane Permeability Using in Situ FTIR

Membranes enable low energy separations in a variety of applications ranging from water purification to alternative energy devices. Membranes achieve solute separation because solutes transport across the membrane at different rates. Thus, accurate determination of membrane permeability, the intrinsic property that quantifies solute transport through the membrane, is essential to predicting membrane performance. Organic solute transport through a polymer electrolyte membrane is important in applications including artificial photosynthesis and direct methanol fuel cells. Permeation studies of organic solutes through commercial polymer electrolyte membranes have been conducted in aqueous diffusion cells equipped with in situ ATR-FTIR. In situ ATR-FTIR provides chemical specificity within multicomponent systems without the labor and complications of isolating samples for analysis. In these experiments, time-resolved concentration data on the downstream side of the membrane are collected, and by fitting a solution to the flux equation to this experimental data, the membrane permeability can be determined. Herein, we develop the methodology and data analysis utilized in in situ ATR-FTIR aqueous permeation experiments to account for boundary layers and determine the intrinsic membrane permeability. We demonstrate that the experimental conditions used herein are such that the apparent permeability is equivalent to the intrinsic membrane permeability. The development of this methodology improves our knowledge of a fundamental membrane property and could enable the study of higher complexity membrane systems in the future.