Toward predictive permeabilities: Experimental measurements and multiscale simulation of methanol transport in Nafion

Abstract

A polymer membrane's permeability to solutes determines its suitability for various applications: a permeability value is essential for predicting performance in diverse contexts. Using aqueous methanol permeation through Nafion as an example, we describe a methodology for determining membrane permeability that accounts for boundary layer effects and the possibility of swelling. For the materials and apparatus used herein, analysis of a permeance measurement and computational fluid dynamics simulations show that the

Transport and co‐transport of carboxylate ions and alcohols in cation exchange membranes

“…Previously, our group has performed a series of investigations to gain a fundamental understanding of the cotransport behavior of an alcohol (MeOH) and a carboxylate anion (either OFm À or OAc À ) in CEMs (with bound sulfonate). 13,15,17 In Nafion ® 117, we observed increases in both OFm À and OAc À permeability in co-permeation with MeOH, where we conjectured that electrostatic repulsions between bound sulfonate and mobile carboxylate ions might be interfered with by the co-permeating MeOH molecules. 13 Next, we prepared a series of chargeneutral crosslinked poly(ethylene glycol) diacrylate (PEGDA, n = 13, where n represents the number of ethylene oxide repeating units [18][19][20][21][22][23] ) films at varied fractional free volume (FFV), where we observed OAc À permeability increases in co-permeation with MeOH and that the differences between permeability in single solute and co-permeation increased with increasing FFV.…”

“…Previously, our group has performed a series of investigations to gain a fundamental understanding of the co‐transport behavior of an alcohol (MeOH) and a carboxylate anion (either OFm − or OAc − ) in CEMs (with bound sulfonate) 13,15,17 . In Nafion® 117, we observed increases in both OFm − and OAc − permeability in co‐permeation with MeOH, where we conjectured that electrostatic repulsions between bound sulfonate and mobile carboxylate ions might be interfered with by the co‐permeating MeOH molecules 13 .…”

“…where P i is the permeability to solute i, D i is the diffusivity to solute i, and K i is the solubility to solute i, for an alcohol (MeOH 17,32,34,36,41 or EtOH 10,15 ) or a carboxylate anion (OFm À or OAc À13,42,43 ) in single and co-transport between an alcohol and a carboxylate (MeOH-OFm À , MeOH-OAc À , EtOH-OFm À , and EtOH-OAc À ). Permeabilities are measured by diffusion cell experiments coupled with in situ Attenuated total reflectance-Fourier transform infrared (ATR-FTIR) 13 spectroscopy, solubilities are measured by sorption-desorption experiments coupled with a high-performance liquid chromatography (HPLC), 33 and diffusivities by calculation using the Equation (1).…”

“…We determine all components of the solution‐diffusion model, assuming the pressure in the membrane is uniform, such that the chemical potential gradient is expressed as a concentration gradient 29 . The model (Equation ) describes the overall solute permeation to be dependent on solute sorption 30–35 into the membrane and diffusion (Fickian) 32,36–39 through the fractional free volume 18–20,40 within the polymer matrix: where is the permeability to solute i , is the diffusivity to solute i , and is the solubility to solute i , for an alcohol (MeOH 17,32,34,36,41 or EtOH 10,15 ) or a carboxylate anion (OFm − or OAc − 13,42,43 ) in single and co‐transport between an alcohol and a carboxylate (MeOH‐OFm − , MeOH‐OAc − , EtOH‐OFm − , and EtOH‐OAc − ). Permeabilities are measured by diffusion cell experiments coupled with in situ Attenuated total reflectance–Fourier transform infrared (ATR‐FTIR) 13 spectroscopy, solubilities are measured by sorption–desorption experiments coupled with a high‐performance liquid chromatography (HPLC), 33 and diffusivities by calculation using the Equation ().…”

Modeling Electrokinetic Flows with the Discrete Ion Stochastic Continuum Overdamped Solvent Algorithm

“…Although a range of properties of bulk electrolytes can be studied using triply-periodic domains, as discussed above, many physical systems of interest feature confining boundaries. Aside from those mentioned above, this also includes metal electroplating [31], and systems utilizing electrodialysis [32,33] such as desalinization [34] and the utilization of solar energy to produce fuels [35,36]. In this article we extend the DISCOS method to include flows in the presence of confining boundaries, including slip and no-slip walls, and where each location on a wall is held at a specified electric potential or treated as weakly polarizable dielectric with a specified surface charge density.…”