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© 2008 Elsevier B.V. The authors of this study gratefully acknowledge Prof. C. Larchet and Prof. V. Nikonenko for donating MK40 membrane samples. Financial support from Comunidad de Madrid and Universidad Complutense de Madrid under Project CCG06-UCM/MAT-1037 is also gratefully acknowledged., Liquid permeation and uptake measurements of pure water and methanol were carried out using three commercial cation-exchange membranes: Nafion-117 (perfluorinated polyethylene with pendant ether-linked side chains terminated with sulfonated groups), MK-40 (microparticles of polystyrene-divinylbenzene with sulfonic groups randomly dispersed in a polyethylene matrix) and CR61-CZL-412 (crosslinked sulfonated copolymer of styrene-divinylbenzene). Methanol uptake by the Nafion-117 membrane was higher than that of water, in contrast, for MK-40 and CR61-CZL-412 membranes the opposite behavior is observed. Differences in the water and methanol liquid uptakes by the membranes were discussed in terms of the chemical interaction between the liquids and the polymers, and also on the size of the liquid molecules. On the other hand, the methanol permeation flow values through the membranes were higher than those of water for all the studied membranes., Comunidad de Madrid, Universidad Complutense de Madrid, Depto. de Estructura de la Materia, Física Térmica y Electrónica, Fac. de Ciencias Físicas, TRUE, pub

© 2003 Elsevier Inc. This work was supported by the Ministry of Science and Technology of Spain, Project BFM2000-0625., 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., Ministry of Science and Technology of Spain, Depto. de Estructura de la Materia, Física Térmica y Electrónica, Fac. de Ciencias Físicas, TRUE, pub

© 2009 Elsevier B.V. The authors of this study gratefully acknowledge financial support from Comunidad de Madrid and Universidad Complutense de Madrid under Project CCG06-UCM/MAT-1037., This study investigates the influence of different operating parameters in the transport of water and methanol through a Nafion membrane when it is used to separatewater fromamethanol–water solution. For this purpose, measurements of mass flux and concentration change have been performed at different values of circulation velocity, concentration of themethanol–water solutions and temperature conditions. From the experimental data, thewater and methanol partial fluxes have been estimated, and itwas found that the water flux is always lower than the methanol flux, but it cannot be neglected. Whereas total and methanol fluxes seem to have predictable and similar behaviors, the water flux seems to be less predictable and it exhibits a very distinct behavior. Methanol and water permeabilities have been calculated, and from these values the activation energy of methanol and water fluxes in the membrane has been estimated. The results have been discussed in terms of the methanol and water solubilities in the membrane., Comunidad de Madrid, Universidad Complutense de Madrid, Depto. de Estructura de la Materia, Física Térmica y Electrónica, Fac. de Ciencias Físicas, TRUE, pub

© 2003 American Chemical Society., The pervaporation characteristics of toluene/methanol, toluene/ethanol, and toluene/propanol mixtures through a linear low-density polyethylene membrane were investigated at different feed compositions. These characteristics were obtained from quantities such as the swelling ratio, permeation rate, and selectivity. In all cases toluene permeates preferentially through the membrane, with a separation factor up to 66 and fluxes varying between 0.1 and 1.4 kg/ m2.h. Predictions based on the Flory-Huggins theory have shown that toluene is preferentially sorbed by the membrane. The pervaporation flux increases and the selectivity decreases with the toluene content in the feed. The experimental results show that pure-alcohol fluxes decrease with the molecular size., Depto. de Estructura de la Materia, Física Térmica y Electrónica, Fac. de Ciencias Físicas, TRUE, pub

© 2001 John Wiley & Sons, Inc., In recent years, we have investigated gas-transport phenomena in coextruded linear low-density polyethylene (LLDPE) membranes. For the most part, coextruded LLDPE membranes were investigated because of their excellent mechanical properties, which explain their extensive use in the packaging industry. Because of the small thickness of coextruded LLDPE membranes, significant errors can be involved in the determination of the diffusion coefficient of gases in the membranes by the time-lag method. To obtain more precise transport parameters for LLDPE membranes, we determined the permeability and diffusion coefficients for O-2, CO2, He, and N-2 from 298 to 348 K by employing an alternative method recently developed. The results indicate that the procedure used in this study for determining the diffusivity of gases in membranes was precise and more efficient than a method based on the evaluation of the time-lag parameter. With respect to permeability, the coefficients obtained in this work agree satisfactorily with those obtained by the time-lag method. In general, the permeability and diffusivity results are in satisfactory agreement with the literature values reported for semicrystalline polyethylene membranes., Depto. de Estructura de la Materia, Física Térmica y Electrónica, Fac. de Ciencias Físicas, TRUE, pub

© 2003 Elsevier Science (USA). Financial support from Ministerio de Ciencia y Tecnología of Spain under Project BFM2000-0625 is gratefully acknowledged., In this paper, an experimental study was carried out in order to investigate the osmotic transport of methanol-water electrolyte solutions through a Nation 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., Ministerio de Ciencia y Tecnología, Depto. de Estructura de la Materia, Física Térmica y Electrónica, Fac. de Ciencias Físicas, TRUE, pub

© 2010 Elsevier B.V. The authors of this study gratefully acknowledge Prof. C. Larchet and Prof. V. Nikonenko for donating MK-40 membrane samples. Financial support from Universidad Complutense de Madrid under Project PR1/08-15918-A is also gratefully acknowledged., The aim of this work was to study the sorption and transport of different water–alcohol solutions (methanol, ethanol, 1-propanol and 2-propanol solutions) when a Nafion 117 membrane is separating them. It was observed that methanol permeability remains constant when varying the composition of the mixture. However, the permeability for the other alcohol solutions decreases from alcohol concentrations that are different for each alcohol. In addition, it was aimed to compare the behavior of membraneswith different morphologies when they were separating water and water–alcohol solutions. Nafion 117membrane and two sulfonated cation-exchange membranes (CR65-AZL-412 and MK-40) were used. Measurements of sorption and liquid transport were made using methanol and ethanol solutions. The uptake values for Nafion 117 membrane were higher than those obtained for CR65-AZL-412 and MK-40 membranes. The results reveal that, in contrast to Nafion membrane, a non-negligible water flux through CR65-AZL-412 and MK-40 membranes was observed along with the alcohol diffusion through them. For these two latter membranes the permeability could not be calculated since the alcohol diffusion is not the only physical process that should be considered. In spite of it, the alcohol and water fluxes through CR65-AZL-412 and MK-40 were estimated; turning out that the water flux was higher than alcohol flux., Universidad Complutense de Madrid, Depto. de Estructura de la Materia, Física Térmica y Electrónica, Fac. de Ciencias Físicas, TRUE, pub

© 2007 Elsevier B.V. Financial support from University Complutense of Madrid under project PR1/06-14460-B is gratefully acknowledged., Heterogeneous carbon molecular sieves and hypercrosslinked polystyrene microparticles adsorbent-based membranes with a (ODPA-BIS P) polyimide binder were prepared. The effect of adsorbent particles on the gas transport properties of heterogeneous membranes was studied. Permeability, diffusion and solubility coefficients of He, CO2, O-2 and N-2 were estimated for homogeneous and heterogeneous membranes at a feed pressure of 1 atm for different temperatures between 25 and 60 degrees C. It was observed that adsorbent-filled (ODPA-BIS P) polyimide membranes exhibit higher gas permeability in comparison with adsorbent-free membrane, while permselectivity is maintained. The results also showed that the adsorbents enhance significantly gas diffusivity in (ODPA-BIS P) polyimide membrane, whereas the gas solubility is clearly reduced. In both type of heterogeneous membranes, gas permeation and diffusion are thermal activated processes described by the Arrhenius equation, whereas the Sorption process is exothermic. The addition of both type of adsorbents to the (ODPA-BIS P) polyimide membrane increases the activation energy of permeability, this is mainly due to a significant increase of the heat of sorption, because the activation energy for diffusion is slightly decreased., University Complutense of Madrid, Depto. de Estructura de la Materia, Física Térmica y Electrónica, Fac. de Ciencias Físicas, TRUE, pub

© 2004 American Chemical Society. Financial support from the University Complutense of Madrid under Project PR78/02-10993 is gratefully acknowledged., Pervaporation separation and swelling experiments of methanol/methyl tert-butyl ether mixtures were performed by using a flat-sheet, dense poly(2,6-dimethyl-1,4-phenylene oxide) membrane prepared from a chloroform casting solvent. The effect of the feed composition on the membrane performance was described by the permeability of the components, the separation factor, and the sorption selectivity. The effect of the feed temperature on the separation was also studied, and the Arrhenius activation energy for permeability was determined over the whole range of feed composition. Pervaporation operations offered a maximum methanol selectivity of 5.4 and an overall normalized flux of 110 kg(.)mum/m(2)-h. Pervaporation and sorption experiments were also conducted using ethanol, propanol, butanol, and octanol to study the effect of the size of the alcohol molecule on the transport across the membrane., University Complutense of Madrid, Depto. de Estructura de la Materia, Física Térmica y Electrónica, Fac. de Ciencias Físicas, TRUE, pub

© 1998 Elsevier Science Ltd, Micrographs obtained using scanning electron microscopy reveal that the drawing of co-extruded linear low-density polyethylene (LLDPE) films produces numerous changes in their surface. It is necessary to analyse the effect of these changes on gas transport in LLDPE films in order to test their efficiency in the packaging industry. Permeability of He, O-2, N-2 and CO2 has been measured in a temperature range from 25 to 85 degrees C using the variable-pressure technique with the time-lag method. Results show that the drawing process does not have a significant effect on the gas transport mechanism. The influence of drawing on the permeability of LLDPE films to gases is discussed in the light of previous studies of diffusion and mechanical relaxation in the same material and compared with results obtained in the present work., Depto. de Estructura de la Materia, Física Térmica y Electrónica, Fac. de Ciencias Físicas, TRUE, pub

© 2008 Elsevier B.V, The authors gratefully acknowledge Prof. C. Larchet and Prof. V. Nikonenko for donating MK40 membrane samples. Financial support from Comunidad de Madrid and Universidad Complutense de Madrid under project CCG06(UCM/MAT(1037 is also gratefully acknowledged., Electro-osmosis experiments through three cation-exchange membranes with different morphology and similar electric properties have been performed using methanol-water solutions under different experimental conditions. The influence on the electro-osmotic transport of the percentage of methanol on solvent with two different electrolytes, NaCl and LiCl, has been studied. The experimental results show that the presence of methanol in the solutions affects strongly the electro-osmotic flow, and this influence is different depending on the membrane morphology. Correlations among electro-osmotic permeability, swelling behavior, and cell resistance are studied for these membrane systems at different percentages of methanol in solvent., Comunidad de Madrid, Universidad Complutense de Madrid, Depto. de Estructura de la Materia, Física Térmica y Electrónica, Fac. de Ciencias Físicas, TRUE, pub

© 2003 Elsevier B.V. Financial support from Ministerio de Ciencia y Tecnología of Spain under Project BFM2000-0625 is gratefully acknowledged., The mass flow originated when two methanol–water solutions of different methanol concentrations are separated by a membrane has been studied for two Nafion membranes. From the experimental results, the methanol and water permeabilities have been estimated. The experiments were carried out in absence and in presence of an electrolyte in the solutions. The obtained results show that, in the absence of the electrolyte, the methanol diffusion flow is higher than the osmotic water flow at all the methanol concentration gradient established, observing that the total mass flow takes place always from the concentrated toward the dilute solution. In contrast, in the presence of the electrolyte, an inversion of the total mass flow is observed at percentages of methanol higher than 40 wt.%. These experimental results could be important in relation to the problem of the methanol crossover in direct methanol fuel cells., Ministerio de Ciencia y Tecnología of Spain, Depto. de Estructura de la Materia, Física Térmica y Electrónica, Fac. de Ciencias Físicas, TRUE, pub

© 2005 Elsevier B.V. l support from Ministerio de Ciencia y Tecnología of Spain under Project BFM2000-0625 is gratefully acknowledged., Mass transport of mixtures of water and methanol through a Nation membrane as a function of the temperature difference between the two sides of the membrane was measured under different experimental conditions. The results show that the composition of the solutions, the temperature difference across the membrane, and the mean temperature in the membrane cell are governing factors in the thermo-osmotic transport process. In all cases studied, the thermo-osmotic flux through the membrane goes from the low temperature side to the high temperature side, and it increases linearly with the temperature difference. Moreover, the flux also increases with the mean temperature in the membrane cell. The thermo-osmotic coefficient of methanol in the membrane is higher than that of water. For water/methanol mixtures, the total flux through Nation membrane can be larger than the fluxes of pure solvents, and it increases with the methanol content for water/methanol mixtures., Ministerio de Ciencia y Tecnología of Spain, Depto. de Estructura de la Materia, Física Térmica y Electrónica, Fac. de Ciencias Físicas, TRUE, pub

© 2005 Elsevier. Financial support from Ministerio de Ciencia y Tecnología of Spain under Project BFM2000-0625 is gratefully acknowledged, The volume flow of methanol-water potassium chloride solutions through a Nation membrane originated by the simultaneous action of electric potential and pressure gradients has been measured at different percentage, of methanol. Measurement were conducted when both gradients act in the same and in the opposite directions under different experimental conditions. The result, indicate that the simultaneous action of the pressure and potential differences originates a total flow different from the sum of the individual electroosmotic and permeation flows due to each force acting separately. The application of the irreversible thermodynamics theory, which includes second-order terms, allowed the study of the influence of the composition of the solutions on the determination of the different phenomenological coefficients., Ministerio de Ciencia y Tecnología of Spain, Depto. de Estructura de la Materia, Física Térmica y Electrónica, Fac. de Ciencias Físicas, TRUE, pub

© 2005 Elsevier Ltd. The authors of this study gratefully acknowledge the financial support of the Ministry of Science and Technology (MCYT, Spain) through its project No PPQ2003-03299. Dr. López Manchado also acknowledges the concession of a Ramón and Cajal contract from the MCYT., The effects of silica and silane modified silica fillers on the pervaporation properties of poly (2,6-dimethyl-1,4-phenylene oxide) (PPO) dense membranes have been studied. Crystallinity, thermal and mechanical properties of unfilled and filled PPO membranes with silica and silane modified silica nanoparticles were investigated. The surface energy together with the solubility parameters of the membranes and the nanoparticles were determined. Pervaporation separation of methanol/methyl tert butyl ether (MTBE) mixtures over the entire range of concentration were carried out using both filled and unfilled membranes. The results are discussed in terms of the solubility and the diffusivity of each liquid component in the membranes. Flory-Huggins theory was used to predict the sorption methanol selectivity. Compared to the unfilled PPO membrane, the filled PPO membranes exhibit higher methanol selectivity and lower permeability. For methanol concentration in liquid feed mixture lower than 50 wt%, methanol selectivity of the filled PPO membranes with silane modified silica is better than that of the silica filled and unfilled PPO membranes., Ministry of Science and Technology (MCYT, Spain), Depto. de Estructura de la Materia, Física Térmica y Electrónica, Fac. de Ciencias Físicas, TRUE, pub

© 1998 John Wiley & Sons, Inc. Contract grant sponsors: DGICYT and Fundación Caixa-Castelló; contract grant numbers: PB95-0134-C02 and P1B95-04, respectively., The permeability and diffusivity of oxygen, carbon dioxide, nitrogen, and helium have been obtained for a range of linear low density polyethylene (LLDPE) films prepared from the same raw materials but with different processing conditions. The measurements were carried out by means of a permeation technique over the temperature interval where the alpha-relaxation processes were observed in earlier studies. The temperature dependence of the permeability and diffusion coefficients of gases shows 2 well-differentiated regions in all films. The break temperature of these regions is approximately located at the same temperature as the alpha-relaxation takes place. Both the permeability and their temperature dependence do not show a noticeable influence on the processing conditions. The effect of processing conditions on the diffusivity seems to be more complex. Differences are observed for different films in the diffusion coefficients, in the case of oxygen, and in their change with the temperature, which is particularly marked in the case of carbon dioxide. Fujita's free volume model has been applied to diffusivity data in order to study the influence of films microstructure in gas permeation properties through them., DGICYT, Fundación Caixa- Castelló, Depto. de Estructura de la Materia, Física Térmica y Electrónica, Fac. de Ciencias Físicas, TRUE, pub

© 2007 Elsevier Ltd. The authors of this study gratefully acknowledge the financial support of the Ministry of Science and Technology (MCYT, Spain) through its project No. PPQ2003-03299 and MAT 2004-00825. Dr. López Manchado also acknowledges the concession of a Ramón & Cajal contract from the MCYT., Polypropylene membranes modified with natural and organically modified montmorillonite clays were prepared. The permeability, diffusivity and solubility of helium, oxygen and nitrogen were determined for the unfilled and filled membranes over the temperature range 25-65 degrees C. Physical properties of polypropylene membranes were investigated using X-ray diffraction, thermogravimetric analyser, tensile testing and differential scanning calorimetry. The results showed that the filled membranes exhibit lower gas permeability compared to the unfilled polypropylene membrane. For helium, a reduced diffusivity is mainly responsible for the reduction in the permeability, in contrast, for nitrogen and oxygen, both diffusivity and solubility were reduced by the presence of fillers. The X-ray diffraction spectra showed that the incorporation of the unmodified and modified clay did not affect the crystallographic nature of polypropylene., Ministry of Science and Technology (MCYT, Spain), Depto. de Estructura de la Materia, Física Térmica y Electrónica, Fac. de Ciencias Físicas, TRUE, pub

© 2005 Published by Elsevier B.V. The authors acknowledge the financial support from the Spanish Ministry of Science and Technology (MCYT) through its project PPQ2003-03299. Thanks are due to Prof. T. Matsuura from the Industrial Membrane Research Institute (IMRI) for supplying PPO polymer., The effect of the membrane thickness on the pervaporation separation of methanol and methyl tertiary butyl ether mixtures through membranes was studied. Membranes of a wide range of thicknesses were prepared from two different polymers: cellulose acetate and poly(2,6-dimethyl-1,4-phenylene oxide). For each membrane, the experiments were performed at the same feed pressure, feed temperature and permeate pressure. The results showed that the permeate flux through both membrane types decreased markedly with increasing the membrane thickness, while the separation factor remained nearly constant. This behavior was discussed in terms of a resistance-in-series model., Spanish Ministry of Science and Technology (MCYT), Depto. de Estructura de la Materia, Física Térmica y Electrónica, Fac. de Ciencias Físicas, TRUE, pub

© 2006 Elsevier Ltd., The sorption of water-methanol mixtures containing a dissolved chloride salt in a Nafion 117 membrane, and their transport through the membrane under the driving force of a pressure gradient, have been studied. Both type of experiments was performed by using five different salts: lithium chloride, sodium chloride, cesium chloride, magnesium chloride and calcium chloride. It was observed that both the permeation flow through the membrane and the membrane swelling increase significantly with the methanol content of the solutions. These facts are attributed to the increase in wet membrane porosity, which brings about the increase of the mobility of solvents in the membrane, besides the increase of the mobility of the polymer pendant chains. In contrast, the influence of the type of electrolyte on the membrane porosity and permeability is not very important, with the exception of the CsCl solutions, which is probably due to the small hydration ability of the Cs+ ion., Depto. de Estructura de la Materia, Física Térmica y Electrónica, Fac. de Ciencias Físicas, TRUE, pub

© 2008 Elsevier B.V. The authors of this study gratefully acknowledge Prof. C. Larchet and Prof. V. Nikonenko for donating MK40 membrane samples. Financial support from Comunidad de Madrid and Universidad Complutense de Madrid under Project CCG06-UCM/MAT-1037 is also gratefully acknowledged., The salt flow through several commercial cation-exchange membranes separating two NaCl alcohol-water solutions with the same alcohol concentration, but different NaCl concentration was investigated. Homogeneous (Nafion-115) and heterogeneous (MK-40 and CR65-AZL-412) membranes were used in this work. The integral permeability coefficient was determined from the temporal evolution of the concentration in the dilute solution. The results showed that the integral permeability coefficient depends on both the solution alcohol concentration and the type of alcohol. It is observed that this dependence is function of the membrane structure. In general, for the heterogeneous membranes, the integral permeability coefficient is less sensible to alcohol concentration than for the homogeneous membrane at low and intermediate values of the alcohol percentage in the solutions., Comunidad de Madrid, Universidad Complutense de Madrid, Depto. de Estructura de la Materia, Física Térmica y Electrónica, Fac. de Ciencias Físicas, TRUE, pub

© 2004 Elsevier Inc., Dense flat-sheet membranes were prepared from poly(2,6-dimethyl-1,4-phenylene oxide) (PPO) using the casting solvents chloroform and 1,1,2-trichloroethylene. X-ray diffraction, tapping mode atomic force microscopy (TM-AFM), and contact angle studies were used to characterize the membranes. The surface energy and the solubility parameters of the PPO membranes were determined from the measured contact angles and compared with the predicted ones from the group contribution method. Swelling experiments and pervaporation separation of methanol from its mixture with ethylene glycol over the entire range of concentration, 0-100%, were conducted using these membranes. Flory-Huggins theory was used to predict the sorption selectivity. The results are discussed in terms of the solubility parameter approach and as function of the morphological characteristics of the membranes. It was found that PPO membranes prepared with chloroform exhibited better pervaporation performance than PPO membranes prepared with 1, 1,2-trichloroethylene., University Complutense of Madrid, MCYT (Spain), Depto. de Estructura de la Materia, Física Térmica y Electrónica, Fac. de Ciencias Físicas, TRUE, pub

© 2004 Elsevier B.V. Financial support from Ministerio de Ciencia y Tecnología of Spain under Project BFM2000-0625 is gratefully acknowledged., Electroosmosis experiments through a Nafion membrane have been performed using methanol–water KCl solutions in different experimental situations. The influence on the electroosmotic transport of the percentage of methanol on solvent at different electrolyte concentrations has been studied. The experimental results show that the presence of methanol on the solutions affects strongly to the electroosmotic flow. From the current–voltage curves determined for this membrane system, the limiting currents were obtained at different volume percentages of methanol. The values obtained decrease with increasing the percentage of methanol and a minimum value seems to be reached at certain percentage of alcohol., Ministerio de Ciencia y Tecnología of Spain, Depto. de Estructura de la Materia, Física Térmica y Electrónica, Fac. de Ciencias Físicas, TRUE, pub

© 2009 Wiley Periodicals, Inc. Sponsor: Comunidad de Madrid and Universidad Complutense de Madrid; contract grant number: CCG06–UCM/MAT–1037., Liquid permeation measurements of water, methanol, and 2-propanol were carried out using a commercial cation-exchange membrane Nafion-117 (perfluorinated polyethylene with pendant ether-linked side chains terminated with sulfonated groups). The experimental permeation data are treated and analyzed using the capillary model, leading to the determination of equivalent pore radius of the membrane structure., Comunidad de Madrid, Universidad Complutense de Madrid, Depto. de Estructura de la Materia, Física Térmica y Electrónica, Fac. de Ciencias Físicas, TRUE, pub

© 2006 Elsevier B. V. Conference of the European-Membrane-Society (2006. Giardini Naxos, Italy), Depto. de Estructura de la Materia, Física Térmica y Electrónica, Fac. de Ciencias Físicas, TRUE, pub

© 2000 Elsevier Science Ltd., 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 degrees 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., Depto. de Estructura de la Materia, Física Térmica y Electrónica, Fac. de Ciencias Físicas, TRUE, pub

© 2009 Elsevier Inc. The authors of this study gratefully acknowledge Prof. C. Larchet and Prof. V. Nikonenko for donating MK40 membrane samples. Financial support from Universidad Complutense de Madrid under Project PR1/08-15918-A is also gratefully acknowledged., 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., Universiclad Complutense de Madrid, Depto. de Estructura de la Materia, Física Térmica y Electrónica, Fac. de Ciencias Físicas, TRUE, pub

© 2004 Elsevier. Financial support from the Ministerio de Ciencia y Tecnología of Spain under Project BFM2000-0625 is gratefully acknowledged., The volume flow through a Nafion membrane originated by the simultaneous action of an electric potential difference and a pressure difference has been measured using aqueous KCl solutions under different experimental conditions. The behavior has been analyzed when both gradients act in the same and in the opposite sense. The results indicate that the simultaneous action of the pressure and potential differences originates a total flow different from the sum of the electroosmotic and permeation flows due to each force acting separately. The application of irreversible thermodynamics, which includes second-order terms, allowed the determination of the phenomenological coefficients. Moreover, from these values, the equivalent pore radius was estimated on the assumption that the membrane is a porous medium filled with an internal solution., Ministerio de Ciencia y Tecnología, Depto. de Estructura de la Materia, Física Térmica y Electrónica, Fac. de Ciencias Físicas, TRUE, pub

© 2006 Elsevier B.V. Financial support from the University Complutense of Madrid under Project 052PR13273 is gratefully acknowledged., The mass flux originated when two methanol-water solutions of different methanol concentration are separated by a Nation 117 membrane in acid (H+) and different alkali metal forms (Li+, Na+, K+, Rb+, Cs+) have been measured, as a function of the methanol concentration difference. From the experimental results, the methanol and water permeabilities have been estimated for the different forms of the membrane. The results show that the cationic form of the membrane strongly influences on the methanol and water permeabilities with respect to the values corresponding to its acid form. Moreover, this influence is different for water and methanol depending on the substituted cation. This strong influence of the cationic form of the membrane on the methanol and water permeabilities could be important in relation to the development of new membranes to decrease the methanol crossover in direct methanol fuel cells., University Complutense of Madrid, Depto. de Estructura de la Materia, Física Térmica y Electrónica, Fac. de Ciencias Físicas, TRUE, pub

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., Depto. de Estructura de la Materia, Física Térmica y Electrónica, Fac. de Ciencias Físicas, TRUE, pub

© 2010 Elsevier B.V. The authors of this study gratefully acknowledge Prof. C. Larchet and Prof. V. Nikonenko for donating MK-40 membrane samples. Financial support from Universidad Complutense de Madrid under Project PR1/08-15918-A is also gratefully acknowledged., The aim of this work was to study the sorption and transport of different water–alcohol solutions (methanol, ethanol, 1-propanol and 2-propanol solutions) when a Nafion 117 membrane is separating them. It was observed that methanol permeability remains constant when varying the composition of the mixture. However, the permeability for the other alcohol solutions decreases from alcohol concentrations that are different for each alcohol. In addition, it was aimed to compare the behavior of membraneswith different morphologies when they were separating water and water–alcohol solutions. Nafion 117membrane and two sulfonated cation-exchange membranes (CR65-AZL-412 and MK-40) were used. Measurements of sorption and liquid transport were made using methanol and ethanol solutions. The uptake values for Nafion 117 membrane were higher than those obtained for CR65-AZL-412 and MK-40 membranes. The results reveal that, in contrast to Nafion membrane, a non-negligible water flux through CR65-AZL-412 and MK-40 membranes was observed along with the alcohol diffusion through them. For these two latter membranes the permeability could not be calculated since the alcohol diffusion is not the only physical process that should be considered. In spite of it, the alcohol and water fluxes through CR65-AZL-412 and MK-40 were estimated; turning out that the water flux was higher than alcohol flux., Universidad Complutense de Madrid, Depto. de Estructura de la Materia, Física Térmica y Electrónica, Fac. de Ciencias Físicas, TRUE, pub

© 2009 Elsevier B.V. The authors of this study gratefully acknowledge financial support from Comunidad de Madrid and Universidad Complutense de Madrid under Project CCG06-UCM/MAT-1037., This study investigates the influence of different operating parameters in the transport of water and methanol through a Nafion membrane when it is used to separatewater fromamethanol–water solution. For this purpose, measurements of mass flux and concentration change have been performed at different values of circulation velocity, concentration of themethanol–water solutions and temperature conditions. From the experimental data, thewater and methanol partial fluxes have been estimated, and itwas found that the water flux is always lower than the methanol flux, but it cannot be neglected. Whereas total and methanol fluxes seem to have predictable and similar behaviors, the water flux seems to be less predictable and it exhibits a very distinct behavior. Methanol and water permeabilities have been calculated, and from these values the activation energy of methanol and water fluxes in the membrane has been estimated. The results have been discussed in terms of the methanol and water solubilities in the membrane., Comunidad de Madrid, Universidad Complutense de Madrid, Depto. de Estructura de la Materia, Física Térmica y Electrónica, Fac. de Ciencias Físicas, TRUE, pub

© 2008 Elsevier B.V. The authors of this study gratefully acknowledge Prof. C. Larchet and Prof. V. Nikonenko for donating MK40 membrane samples. Financial support from Comunidad de Madrid and Universidad Complutense de Madrid under Project CCG06-UCM/MAT-1037 is also gratefully acknowledged., The salt flow through several commercial cation-exchange membranes separating two NaCl alcohol-water solutions with the same alcohol concentration, but different NaCl concentration was investigated. Homogeneous (Nafion-115) and heterogeneous (MK-40 and CR65-AZL-412) membranes were used in this work. The integral permeability coefficient was determined from the temporal evolution of the concentration in the dilute solution. The results showed that the integral permeability coefficient depends on both the solution alcohol concentration and the type of alcohol. It is observed that this dependence is function of the membrane structure. In general, for the heterogeneous membranes, the integral permeability coefficient is less sensible to alcohol concentration than for the homogeneous membrane at low and intermediate values of the alcohol percentage in the solutions., Comunidad de Madrid, Universidad Complutense de Madrid, Depto. de Estructura de la Materia, Física Térmica y Electrónica, Fac. de Ciencias Físicas, TRUE, pub

© 2009 Wiley Periodicals, Inc. Sponsor: Comunidad de Madrid and Universidad Complutense de Madrid; contract grant number: CCG06–UCM/MAT–1037., Liquid permeation measurements of water, methanol, and 2-propanol were carried out using a commercial cation-exchange membrane Nafion-117 (perfluorinated polyethylene with pendant ether-linked side chains terminated with sulfonated groups). The experimental permeation data are treated and analyzed using the capillary model, leading to the determination of equivalent pore radius of the membrane structure., Comunidad de Madrid, Universidad Complutense de Madrid, Depto. de Estructura de la Materia, Física Térmica y Electrónica, Fac. de Ciencias Físicas, TRUE, pub

© 2009 Elsevier Inc. The authors of this study gratefully acknowledge Prof. C. Larchet and Prof. V. Nikonenko for donating MK40 membrane samples. Financial support from Universidad Complutense de Madrid under Project PR1/08-15918-A is also gratefully acknowledged., 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., Universiclad Complutense de Madrid, Depto. de Estructura de la Materia, Física Térmica y Electrónica, Fac. de Ciencias Físicas, TRUE, pub

© 2008 Elsevier B.V. The authors of this study gratefully acknowledge Prof. C. Larchet and Prof. V. Nikonenko for donating MK40 membrane samples. Financial support from Comunidad de Madrid and Universidad Complutense de Madrid under Project CCG06-UCM/MAT-1037 is also gratefully acknowledged., Liquid permeation and uptake measurements of pure water and methanol were carried out using three commercial cation-exchange membranes: Nafion-117 (perfluorinated polyethylene with pendant ether-linked side chains terminated with sulfonated groups), MK-40 (microparticles of polystyrene-divinylbenzene with sulfonic groups randomly dispersed in a polyethylene matrix) and CR61-CZL-412 (crosslinked sulfonated copolymer of styrene-divinylbenzene). Methanol uptake by the Nafion-117 membrane was higher than that of water, in contrast, for MK-40 and CR61-CZL-412 membranes the opposite behavior is observed. Differences in the water and methanol liquid uptakes by the membranes were discussed in terms of the chemical interaction between the liquids and the polymers, and also on the size of the liquid molecules. On the other hand, the methanol permeation flow values through the membranes were higher than those of water for all the studied membranes., Comunidad de Madrid, Universidad Complutense de Madrid, Depto. de Estructura de la Materia, Física Térmica y Electrónica, Fac. de Ciencias Físicas, TRUE, pub

© 2008 Elsevier B.V, The authors gratefully acknowledge Prof. C. Larchet and Prof. V. Nikonenko for donating MK40 membrane samples. Financial support from Comunidad de Madrid and Universidad Complutense de Madrid under project CCG06(UCM/MAT(1037 is also gratefully acknowledged., Electro-osmosis experiments through three cation-exchange membranes with different morphology and similar electric properties have been performed using methanol-water solutions under different experimental conditions. The influence on the electro-osmotic transport of the percentage of methanol on solvent with two different electrolytes, NaCl and LiCl, has been studied. The experimental results show that the presence of methanol in the solutions affects strongly the electro-osmotic flow, and this influence is different depending on the membrane morphology. Correlations among electro-osmotic permeability, swelling behavior, and cell resistance are studied for these membrane systems at different percentages of methanol in solvent., Comunidad de Madrid, Universidad Complutense de Madrid, Depto. de Estructura de la Materia, Física Térmica y Electrónica, Fac. de Ciencias Físicas, TRUE, pub

© 2007 Elsevier B.V. Financial support from University Complutense of Madrid under project PR1/06-14460-B is gratefully acknowledged., Heterogeneous carbon molecular sieves and hypercrosslinked polystyrene microparticles adsorbent-based membranes with a (ODPA-BIS P) polyimide binder were prepared. The effect of adsorbent particles on the gas transport properties of heterogeneous membranes was studied. Permeability, diffusion and solubility coefficients of He, CO2, O-2 and N-2 were estimated for homogeneous and heterogeneous membranes at a feed pressure of 1 atm for different temperatures between 25 and 60 degrees C. It was observed that adsorbent-filled (ODPA-BIS P) polyimide membranes exhibit higher gas permeability in comparison with adsorbent-free membrane, while permselectivity is maintained. The results also showed that the adsorbents enhance significantly gas diffusivity in (ODPA-BIS P) polyimide membrane, whereas the gas solubility is clearly reduced. In both type of heterogeneous membranes, gas permeation and diffusion are thermal activated processes described by the Arrhenius equation, whereas the Sorption process is exothermic. The addition of both type of adsorbents to the (ODPA-BIS P) polyimide membrane increases the activation energy of permeability, this is mainly due to a significant increase of the heat of sorption, because the activation energy for diffusion is slightly decreased., University Complutense of Madrid, Depto. de Estructura de la Materia, Física Térmica y Electrónica, Fac. de Ciencias Físicas, TRUE, pub

© 2007 Elsevier Ltd. The authors of this study gratefully acknowledge the financial support of the Ministry of Science and Technology (MCYT, Spain) through its project No. PPQ2003-03299 and MAT 2004-00825. Dr. López Manchado also acknowledges the concession of a Ramón & Cajal contract from the MCYT., Polypropylene membranes modified with natural and organically modified montmorillonite clays were prepared. The permeability, diffusivity and solubility of helium, oxygen and nitrogen were determined for the unfilled and filled membranes over the temperature range 25-65 degrees C. Physical properties of polypropylene membranes were investigated using X-ray diffraction, thermogravimetric analyser, tensile testing and differential scanning calorimetry. The results showed that the filled membranes exhibit lower gas permeability compared to the unfilled polypropylene membrane. For helium, a reduced diffusivity is mainly responsible for the reduction in the permeability, in contrast, for nitrogen and oxygen, both diffusivity and solubility were reduced by the presence of fillers. The X-ray diffraction spectra showed that the incorporation of the unmodified and modified clay did not affect the crystallographic nature of polypropylene., Ministry of Science and Technology (MCYT, Spain), Depto. de Estructura de la Materia, Física Térmica y Electrónica, Fac. de Ciencias Físicas, TRUE, pub

© 2005 Elsevier B.V. l support from Ministerio de Ciencia y Tecnología of Spain under Project BFM2000-0625 is gratefully acknowledged., Mass transport of mixtures of water and methanol through a Nation membrane as a function of the temperature difference between the two sides of the membrane was measured under different experimental conditions. The results show that the composition of the solutions, the temperature difference across the membrane, and the mean temperature in the membrane cell are governing factors in the thermo-osmotic transport process. In all cases studied, the thermo-osmotic flux through the membrane goes from the low temperature side to the high temperature side, and it increases linearly with the temperature difference. Moreover, the flux also increases with the mean temperature in the membrane cell. The thermo-osmotic coefficient of methanol in the membrane is higher than that of water. For water/methanol mixtures, the total flux through Nation membrane can be larger than the fluxes of pure solvents, and it increases with the methanol content for water/methanol mixtures., Ministerio de Ciencia y Tecnología of Spain, Depto. de Estructura de la Materia, Física Térmica y Electrónica, Fac. de Ciencias Físicas, TRUE, pub

© 2006 Elsevier Ltd., The sorption of water-methanol mixtures containing a dissolved chloride salt in a Nafion 117 membrane, and their transport through the membrane under the driving force of a pressure gradient, have been studied. Both type of experiments was performed by using five different salts: lithium chloride, sodium chloride, cesium chloride, magnesium chloride and calcium chloride. It was observed that both the permeation flow through the membrane and the membrane swelling increase significantly with the methanol content of the solutions. These facts are attributed to the increase in wet membrane porosity, which brings about the increase of the mobility of solvents in the membrane, besides the increase of the mobility of the polymer pendant chains. In contrast, the influence of the type of electrolyte on the membrane porosity and permeability is not very important, with the exception of the CsCl solutions, which is probably due to the small hydration ability of the Cs+ ion., Depto. de Estructura de la Materia, Física Térmica y Electrónica, Fac. de Ciencias Físicas, TRUE, pub

© 2006 Elsevier B. V. Conference of the European-Membrane-Society (2006. Giardini Naxos, Italy), Depto. de Estructura de la Materia, Física Térmica y Electrónica, Fac. de Ciencias Físicas, TRUE, pub

© 2006 Elsevier B.V. Financial support from the University Complutense of Madrid under Project 052PR13273 is gratefully acknowledged., The mass flux originated when two methanol-water solutions of different methanol concentration are separated by a Nation 117 membrane in acid (H+) and different alkali metal forms (Li+, Na+, K+, Rb+, Cs+) have been measured, as a function of the methanol concentration difference. From the experimental results, the methanol and water permeabilities have been estimated for the different forms of the membrane. The results show that the cationic form of the membrane strongly influences on the methanol and water permeabilities with respect to the values corresponding to its acid form. Moreover, this influence is different for water and methanol depending on the substituted cation. This strong influence of the cationic form of the membrane on the methanol and water permeabilities could be important in relation to the development of new membranes to decrease the methanol crossover in direct methanol fuel cells., University Complutense of Madrid, Depto. de Estructura de la Materia, Física Térmica y Electrónica, Fac. de Ciencias Físicas, TRUE, pub

© 2005 Elsevier Ltd. The authors of this study gratefully acknowledge the financial support of the Ministry of Science and Technology (MCYT, Spain) through its project No PPQ2003-03299. Dr. López Manchado also acknowledges the concession of a Ramón and Cajal contract from the MCYT., The effects of silica and silane modified silica fillers on the pervaporation properties of poly (2,6-dimethyl-1,4-phenylene oxide) (PPO) dense membranes have been studied. Crystallinity, thermal and mechanical properties of unfilled and filled PPO membranes with silica and silane modified silica nanoparticles were investigated. The surface energy together with the solubility parameters of the membranes and the nanoparticles were determined. Pervaporation separation of methanol/methyl tert butyl ether (MTBE) mixtures over the entire range of concentration were carried out using both filled and unfilled membranes. The results are discussed in terms of the solubility and the diffusivity of each liquid component in the membranes. Flory-Huggins theory was used to predict the sorption methanol selectivity. Compared to the unfilled PPO membrane, the filled PPO membranes exhibit higher methanol selectivity and lower permeability. For methanol concentration in liquid feed mixture lower than 50 wt%, methanol selectivity of the filled PPO membranes with silane modified silica is better than that of the silica filled and unfilled PPO membranes., Ministry of Science and Technology (MCYT, Spain), Depto. de Estructura de la Materia, Física Térmica y Electrónica, Fac. de Ciencias Físicas, TRUE, pub

© 2005 Elsevier. Financial support from Ministerio de Ciencia y Tecnología of Spain under Project BFM2000-0625 is gratefully acknowledged, The volume flow of methanol-water potassium chloride solutions through a Nation membrane originated by the simultaneous action of electric potential and pressure gradients has been measured at different percentage, of methanol. Measurement were conducted when both gradients act in the same and in the opposite directions under different experimental conditions. The result, indicate that the simultaneous action of the pressure and potential differences originates a total flow different from the sum of the individual electroosmotic and permeation flows due to each force acting separately. The application of the irreversible thermodynamics theory, which includes second-order terms, allowed the study of the influence of the composition of the solutions on the determination of the different phenomenological coefficients., Ministerio de Ciencia y Tecnología of Spain, Depto. de Estructura de la Materia, Física Térmica y Electrónica, Fac. de Ciencias Físicas, TRUE, pub

© 2005 Published by Elsevier B.V. The authors acknowledge the financial support from the Spanish Ministry of Science and Technology (MCYT) through its project PPQ2003-03299. Thanks are due to Prof. T. Matsuura from the Industrial Membrane Research Institute (IMRI) for supplying PPO polymer., The effect of the membrane thickness on the pervaporation separation of methanol and methyl tertiary butyl ether mixtures through membranes was studied. Membranes of a wide range of thicknesses were prepared from two different polymers: cellulose acetate and poly(2,6-dimethyl-1,4-phenylene oxide). For each membrane, the experiments were performed at the same feed pressure, feed temperature and permeate pressure. The results showed that the permeate flux through both membrane types decreased markedly with increasing the membrane thickness, while the separation factor remained nearly constant. This behavior was discussed in terms of a resistance-in-series model., Spanish Ministry of Science and Technology (MCYT), Depto. de Estructura de la Materia, Física Térmica y Electrónica, Fac. de Ciencias Físicas, TRUE, pub

© 2004 American Chemical Society. Financial support from the University Complutense of Madrid under Project PR78/02-10993 is gratefully acknowledged., Pervaporation separation and swelling experiments of methanol/methyl tert-butyl ether mixtures were performed by using a flat-sheet, dense poly(2,6-dimethyl-1,4-phenylene oxide) membrane prepared from a chloroform casting solvent. The effect of the feed composition on the membrane performance was described by the permeability of the components, the separation factor, and the sorption selectivity. The effect of the feed temperature on the separation was also studied, and the Arrhenius activation energy for permeability was determined over the whole range of feed composition. Pervaporation operations offered a maximum methanol selectivity of 5.4 and an overall normalized flux of 110 kg(.)mum/m(2)-h. Pervaporation and sorption experiments were also conducted using ethanol, propanol, butanol, and octanol to study the effect of the size of the alcohol molecule on the transport across the membrane., University Complutense of Madrid, Depto. de Estructura de la Materia, Física Térmica y Electrónica, Fac. de Ciencias Físicas, TRUE, pub

© 2003 Elsevier B.V. Financial support from Ministerio de Ciencia y Tecnología of Spain under Project BFM2000-0625 is gratefully acknowledged., The mass flow originated when two methanol–water solutions of different methanol concentrations are separated by a membrane has been studied for two Nafion membranes. From the experimental results, the methanol and water permeabilities have been estimated. The experiments were carried out in absence and in presence of an electrolyte in the solutions. The obtained results show that, in the absence of the electrolyte, the methanol diffusion flow is higher than the osmotic water flow at all the methanol concentration gradient established, observing that the total mass flow takes place always from the concentrated toward the dilute solution. In contrast, in the presence of the electrolyte, an inversion of the total mass flow is observed at percentages of methanol higher than 40 wt.%. These experimental results could be important in relation to the problem of the methanol crossover in direct methanol fuel cells., Ministerio de Ciencia y Tecnología of Spain, Depto. de Estructura de la Materia, Física Térmica y Electrónica, Fac. de Ciencias Físicas, TRUE, pub

© 2004 Elsevier Inc., Dense flat-sheet membranes were prepared from poly(2,6-dimethyl-1,4-phenylene oxide) (PPO) using the casting solvents chloroform and 1,1,2-trichloroethylene. X-ray diffraction, tapping mode atomic force microscopy (TM-AFM), and contact angle studies were used to characterize the membranes. The surface energy and the solubility parameters of the PPO membranes were determined from the measured contact angles and compared with the predicted ones from the group contribution method. Swelling experiments and pervaporation separation of methanol from its mixture with ethylene glycol over the entire range of concentration, 0-100%, were conducted using these membranes. Flory-Huggins theory was used to predict the sorption selectivity. The results are discussed in terms of the solubility parameter approach and as function of the morphological characteristics of the membranes. It was found that PPO membranes prepared with chloroform exhibited better pervaporation performance than PPO membranes prepared with 1, 1,2-trichloroethylene., University Complutense of Madrid, MCYT (Spain), Depto. de Estructura de la Materia, Física Térmica y Electrónica, Fac. de Ciencias Físicas, TRUE, pub

© 2004 Elsevier B.V. Financial support from Ministerio de Ciencia y Tecnología of Spain under Project BFM2000-0625 is gratefully acknowledged., Electroosmosis experiments through a Nafion membrane have been performed using methanol–water KCl solutions in different experimental situations. The influence on the electroosmotic transport of the percentage of methanol on solvent at different electrolyte concentrations has been studied. The experimental results show that the presence of methanol on the solutions affects strongly to the electroosmotic flow. From the current–voltage curves determined for this membrane system, the limiting currents were obtained at different volume percentages of methanol. The values obtained decrease with increasing the percentage of methanol and a minimum value seems to be reached at certain percentage of alcohol., Ministerio de Ciencia y Tecnología of Spain, Depto. de Estructura de la Materia, Física Térmica y Electrónica, Fac. de Ciencias Físicas, TRUE, pub

© 2004 Elsevier. Financial support from the Ministerio de Ciencia y Tecnología of Spain under Project BFM2000-0625 is gratefully acknowledged., The volume flow through a Nafion membrane originated by the simultaneous action of an electric potential difference and a pressure difference has been measured using aqueous KCl solutions under different experimental conditions. The behavior has been analyzed when both gradients act in the same and in the opposite sense. The results indicate that the simultaneous action of the pressure and potential differences originates a total flow different from the sum of the electroosmotic and permeation flows due to each force acting separately. The application of irreversible thermodynamics, which includes second-order terms, allowed the determination of the phenomenological coefficients. Moreover, from these values, the equivalent pore radius was estimated on the assumption that the membrane is a porous medium filled with an internal solution., Ministerio de Ciencia y Tecnología, Depto. de Estructura de la Materia, Física Térmica y Electrónica, Fac. de Ciencias Físicas, TRUE, pub