B. Seoane

Permeation of electrolyte water-methanol solutions through a Nafion membrane

The volume flux through a cation-exchange membrane (Nafion 117) separating two equal electrolyte water-methanol solutions as a function of the pressure difference was determined under different experimental conditions. The results show that permeation rates through the membrane are strongly dependent on the methanol content of the solutions, thus the value of the flux increases when the methanol percentage increases. The effect of the electrolyte concentration of the solution on the membrane permeability is less important, although its influence becomes significant at low electrolyte concentration and high methanol content on solvent. This behavior is explained in terms of the amount of solvent sorbed by the membrane. Typical flux behaviors observed with pressure difference are linear at low pressures, exhibiting a positive deviation at higher pressure difference values.

Experimental estimation of equilibrium and transport properties of sulfonated cation-exchange membranes with different morphologies

Solvent uptake, hydraulic and electroosmotic permeabilities, true cation transport number, effective fixed charge concentration, and limiting current values have been determined in aqueous LiCl solutions for three commercial cation-exchange membranes with different morphologies and similar electric properties. The differences found in the equilibrium and transport properties of the membranes have been analyzed on the basis of their different structures. The experimental results show that the membrane morphology has an influence on the effect that the presence of an electrolyte has in the solvent uptake and in the liquid permeation. Differences have also been found in the polarization concentration effects, and on the loss of the membrane selectivity with the increase of the electrolyte concentration.

Osmotic behavior of a Nafion membrane in methanol–water electrolyte solutions

In this paper, an experimental study was carried out in order to investigate the osmotic transport of methanol-water electrolyte solutions through a Nafion membrane. The experimental data indicated that the Nafion membrane showed the typical anomalous osmotic behavior of charged membranes. The influence of some relevant parameters, such as electrolyte concentration difference, weight fraction of methanol on solution, and nature of cation was considered. The results showed that the osmotic volume flow was decreased with the presence of methanol on solvent, but did not alter the anomalous osmotic behavior of the membrane.

Permeation of carbon dioxide through multiple linear low-density polyethylene films

Abstract We have investigated the effect of stacking on the permeation of carbon dioxide through multilayer LLDPE films. The measurements were carried out using samples made up of one, two, four, eight and 12 films, respectively, over the temperature interval of 25–85°C. The results indicate that the permeability coefficient P of carbon dioxide does not show any variation on the number of films stacked. In contrast, the time lag values increase in a non-linear way with increasing the number of films in the samples. The analysis of these results, according to gas permeation models through multilayer systems, shows that boundary effects at the interface between films are not found, on the one hand, and the experimental values determined for the time lags are in good agreement with the theoretical predictions, on the other hand.

Methanol-Water Solution Transport in Nafion Membranes with Different Cationic Forms

Measurements of liquid transport were made with a Nafion membrane at different cationic forms. The experimental data are used to estimate the alcohol permeability when the membrane is separating water and water-methanol solutions. The obtained permeability coefficient values were useful for analyzing the influence of the substituted cations on the transport process in the membranes. In the present article, the permeability coefficient of methanol in Nafion substituted by Na+, K+, Cs+, Mg2+, Ca2+, Ba2+, Fe2+, Fe3+, and Al3+ were reported at different methanol concentration values. The analysis of the results revealed that, in general, for ions with the same period in the periodic table, the alcohol permeability decreases with increasing the valence. In contrast, when ions with the same valence are compared, the alcohol permeability decreases when the atomic mass increases, with the exception of the Mg2+. As a general trend, similar alcohol permeability variation with the concentration is observed for all the cationic forms of the membrane. There is an initial increase in the permeability, and, when the methanol concentration in the solutions is about 60%, the permeability decreases with the alcohol concentration. However, in the case of trivalent ions, the methanol permeability decreases with the methanol concentration.