Complex Solute Transport through a Cation Exchange Membrane Via in Situ ATR FTIR Spectroscopy

Polymeric membranes are utilized for a wide variety of applications, from fuel cells to dialysis to water treatment. The mechanisms behind the transport through dense polymeric membranes, however, are not well understood, especially in the case of multiple simultaneous solutes. Generally, to quantify solute concentration in downstream solutions, aliquots are taken at defined intervals and characterized by ex situ techniques. This methodology, however, is arduous due to the numerous samples and added complexity due to the constantly decreasing downstream volume. Nafion^® 117 is a commercially utilized membrane and has been significantly studied over the last several decades. In this work, we employ an in situ Attenuated Total Reflectance Fourier-Transform Infrared (ATR FTIR) spectrometer to determine single and multi-component transport of similar species through Nafion^® 117 membranes using a custom-built diffusion cell. We find significant differences in permeability for solutes in single and multicomponent systems. These differences are important for characterizing membranes for application to separations as membrane selectivities calculated from single component diffusion experiments and multicomponent diffusion experiments differ up to 25%. These experiments demonstrate the complexity of transport with multiple solutes and motivates the performance of multicomponent diffusion experiments towards understanding transport behavior in real systems.