Monitoring multicomponent transport using in situ ATR FTIR spectroscopy

Abstract

Membranes are a critical component of many energy generation and storage technologies, including artificial photosynthesis systems that reduce atmospheric CO 2 to high-value products. In this study, we used in situ ATR FTIR spectroscopy to monitor the crossover of three commonly-reported CO 2 reduction products-methanol, sodium formate and sodium acetatethrough Nafion ® 117, a common cation exchange membrane. Measurement errors for the permeation of mixtures of solutes are discussed. Permeabilities from one-, two-, and three-solute mixed solutions were measured using a standard diffusion cell, and ATR FTIR spectra were used to obtain time-resolved concentration data that were fit to a model describing transport of ions and small molecules through hydrated polymer films. The permeability of Nafion ® 117 to methanol measured using this methodology was in agreement with literature reports. The sorption of methanol, sodium formate, and sodium acetate, and mixtures thereof, were measured using a desorption technique. From the measured permeabilities and solubilities, diffusivities of each solute were calculated. Differences in permeability among the solutes were found to be primarily due to differences in their solubility in Nafion ® 117.

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

“…The thickness of membranes equilibrated in 1 M aqueous methanol was within error of those equilibrated in DI water, further suggesting negligible membrane swelling during permeation experiments. As a control, the same methanol solubility measurement method was applied to Nafion 117, resulting in a methanol solubility of (0.50 ± 0.03), similar to the previously reported literature values 29,47,66 . Table 2 presents the measured physical and transport properties of Nafion 1100 obtained in this work using at least 3 independent samples.…”

“…Time-resolved concentration data are key to this process, and it is essential to be confident in their accuracy. As described in the Experimental Development section, we were able to identify and implement three improvements to the experimental methodology described previously 32,47 eliminating gas bubble formation, adjusting for instrument drift, and utilizing a two-point baseline during data analysis that enable a closing of the mass balance within 0.005 g methanol across the more than 3 days duration of the experiment ( Figure S4 of the SI). A closed mass balance supports confidence in the accuracy of the time-resolved downstream concentration profile as measured using infrared spectroscopy.…”

Transport of Neutral and Charged Solutes in Imidazolium-Functionalized Poly(phenylene oxide) Membranes for Artificial Photosynthesis

“…36 The details of this experimental apparatus and associated methods have been previously published and are included in the Supplemental Information. 36,54…”

Permeation of CO2 and N2 through glassy poly(dimethyl phenylene) oxide under steady‐ and presteady‐state conditions

“…Non-porous polymeric materials are commonly used as membrane separators for gas purification, reverse osmosis, and pervaporation, among other applications. [1][2][3][4][5] For gas transport through any non-porous polymer, the widely accepted model for permeability, P, is the solution-diffusion model, which gives a phenomenological description of the permeability as the product of the solubility coefficient, S, and the diffusion coefficient, D, at steady state, i.e., [6][7] P=D S (1) In the typical use of the solution-diffusion model, the diffusion coefficient is assumed to be the proportionality constant between the flux and the concentration (or chemical potential) gradient; as such, it should be constant so long as the material properties and temperature are constant (Case I diffusion). [7][8] The diffusion rate may also depend on changes in the bulk polymer morphology upon exposure to permeants (Case II diffusion) or a combination of concentration gradient and polymer morphology change (anomalous diffusion).…”

“…Results using the dual mode model for permeation (Eqn 3. and Figures 3aand 3b) are listed inTable 4and are used in the dual mode multiscale simulations.…”