Properties Of Ion-exchange Membranes Research Articles

Investigations on the interfacial capacitance and the diffusion boundary layer thickness of ion exchange membrane using electrochemical impedance spectroscopy

Electrochemical impedance spectroscopy (EIS) is a powerful tool to investigate the electrochemical processes. This work investigated the interfacial properties of ion exchange membranes using EIS. Scanning electron microscope (SEM), X-ray photoelectron spectroscopy (XPS) and zeta potential were also used to characterize the membranes. With the comparison of two equivalent circuits and the consideration of the physical and electrochemical understanding of the ion exchange membrane systems (IEMs), a better equivalent circuit was selected for quantitatively analyzing each component of the systems. The diffusion boundary layer thickness was estimated with the derived equation (δ=3RdCdD). The effects of solution concentration, flow rate and temperature on the IEMs were investigated in a systematic way. The results clearly showed that the effective capacitance and the electrical double layer resistance were consistent with the concentration dependence of the Debye equation; the diffusion boundary layer thickness decreased with the increase of solution concentration, flow rate and temperature. The effective capacitance and the thickness of the membranes interface obtained by EIS were important for understanding the relationship with membrane surface microstructure, ion transport and electrical properties. It is confirmed that the EIS can be used as an alternative method to characterize the ion exchange membrane systems.

Relationships between transport and physical–mechanical properties of ion exchange membranes

This review focuses on the characterization of properties of ion exchange membranes, on the compromises between ion exchange capacity, relative water content and electrochemical properties of ion exchange membranes. Properties of heterogeneous ion exchange membranes prepared from polyethylene as matrix, ion exchange resin powder and polyester fabric were studied. Ion exchange membranes were prepared with using different ion exchange resins. These ion exchange membranes can be used in many electro separation processes like electro dialysis, electrode ionization, membrane electrolysis or electrophoresis. Desalination of brackish and surface water, purification of waste water or mine water, water desalination after tertiary biological treatment, purification of organic substances, stabilization of wine or demineralization of whey are the most frequent applications where these prepared ion exchange membranes can be utilized. All prepared ion exchange membranes were characterized with same methods and monitored the parameters of ion exchange membranes were ion exchange capacity using Mohr method, electric resistance measured in a special experimental cell using a compensation method, permselectivity measured in the same measuring cell as electric resistance and relative water content. The relationships between the transport and physical–mechanical properties were found. An ion exchange membrane with specific required properties can be prepared on the basis of resultant values of monitored properties.

Effect of chromium compounds on the properties of ion-exchange membranes

The transport properties of ion-exchange membranes MK-40 and MF-4SK, MA-40, and MA-41 in solutions of sodium chloride, chromium(III) chloride, and chromium(VI) oxide have been studied. It has been found that the MA-40 and MA-41 membranes retain their transport properties in chromium chloride(III) solutions, whereas the anion-exchange membranes in chromium(VI) oxide solutions undergo partial or complete degradation. The oxidative impact of chromate ions on both the hydrocarbon matrix of the MK-40 membranes and the chemically resistant perfluorocarbon matrix of the MF-4SK membrane has been revealed.

The Performance Analysis Study of Vanadium Redox Flow Battery Influenced By Critical Properties of Ion Exchange Membrane

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Steady-state and transient electrical properties of ion-exchange membrane systems in asymmetric arrangements

The steady-state and transient electrical properties of ion-exchange membranes placed between two solutions with different values of the electrolyte concentration, have been simulated using the network simulation method. The ionic transport processes are theoretically described on the basis of the Nernst-Planck and Poisson equations. The system under study is constituted by a cation-exchange membrane in which the fixed-charge is homogeneously distributed in space and two diffusion boundary layers on both sides of the membrane, the electric double layers at the interfaces being included. The steady-state voltage-current characteristic and the profiles of the ionic concentrations and the electric potential, are analysed. Also, the choronopotentiometric response of the system has been discussed and the time evolution of the electric energy consumption evaluated. In particular, the influence of the ratio of the bathing concentrations on the permselectivity and the chronopotentiometric response of the ion-exchange membrane systems, has been established.

Effect of ammonium groups of sulfonated polysulfone membrane on its pervaporation performance

Ammonium-exchanged membranes were prepared and utilized for the dehydration of ethanol/water mixtures by pervaporation. This paper presents an original investigation on the influence of the ammonium content on the hydrophilic and swelling properties of ion-exchange membranes. The identification of ammonium was carried out by infrared ray (IR) spectroscopy. It was found that the content of ammonium did not significantly change the membrane surface morphology but considerably decreased the water contact angle for the membranes. The optimum ammonium substitution in the membrane resulted in a high pervaporation performance for the dehydration of ethanol solution. More than 99% of permeate water was obtained in the pervaporation process. Based on the sorption and diffusion mechanism discussion, the high selectivity of water to ethanol was mainly contributed by the diffusion rate difference of permeants in the membrane rather than the sorption. The hydrophilicity improvement and decrease in swelling of modified membranes contributed to the high selectivity of ion-exchanged membranes for pervaporation. An excellent dehydration performance of ion-exchanged membranes was observed. All the PSI values of the ion-exchanged membrane were higher than 10 5, which could be attributed to the suitable conditions applied for preparing ion-exchanged polysulfone membranes.

Removal of Nickel Ions from Dilute Heavy Metal Solutions by Electrodeionization Process

The aim of the present work was to study the effect of properties of ion exchange membrane on separation performance of electrodeionization (EDI) process for removal of nickel ions from dilute heavy metal solutions. It was shown that the properties of ion exchange membrane had a significant effect on removal of nickel ions. With feed water containing nickel ions at the concentration of 55mg•L-1, the nickel ions concentration of dilute stream was lower than 0.5mg•L-1and the nickel rejection was greater than 99% when using EDI membranes, while that was in the range of 2.48-3.55mg•L-1with conventional heterogeneous ion exchange membranes. With optimum ion exchange material and operating conditions, EDI would be a very interesting and innovative technology for the treatment of dilute heavy metal solutions.

Synthesis and electrochemical properties of ion exchange membrane based on crosslinked styrene-(2-hydroxyethyl acrylate)-lauryl methacrylate copolymer

The copolymer, Sty-HEA-LMA, was synthesized by solution polymerization based on styrene (Sty), 2-hydroxyethyl acrylate (HEA), and lauryl methacrylate (LMA). The synthesized copolymer was crosslinked with sulfosuccinic acid (SSA) and glutar aldehyde (GA) via esterification. The sulfonation reaction was performed to introduce sulfonic groups into the membrane with sulfuric acid as the sulfonating agent. The chemical structures of the membranes were characterized by Fourier transform infrared spectroscopy (FTIR) and proton nuclear magnetic resonance spectroscopy (1H NMR), respectively. The basic membrane properties, such as the water uptake, ion exchange capacity (IEC), ion transport number and electrical properties, were measured for the prepared ion exchange membranes. The IEC value and electrical conductivity increased with increasing sulfonation time due to the ionic group (−SO3H), and were in the range of 0.31–1.15 meq/g and 0.5×10−4–0.1 S/cm, respectively.

Transient electrical response of ion-exchange membranes with fixed-charge due to ion adsorption. A network simulation approach

The transient electrical properties of ion-exchange membranes with inhomogeneous fixed-charge distributions due to ion adsorption processes, have been investigated using the network simulation method. A network model is proposed for the Nernst–Planck and Poisson equations describing the transport of a binary electrolyte through an ion-exchange membrane and the two diffusion boundary layers on both sides of the membrane. An electric circuit simulation program is used to solve the network model in order to obtain the transient electrical properties of a system where the fixed-charge concentration of the membrane is due to an anion adsorption process. The chronoamperometric and chronopotentiometric responses of the whole membrane system have been simulated for the case of a membrane with surface charge described by a Langmuir kinetics.

Influence of aqueous–organic solutions containing aprotic solvent on equilibrium and transport properties of ion–exchange membranes

Equilibrium and transport properties of ion-exchange electrodialytic membranes before and after their processing in model solution containing dimethylacetamide were investigated in LiCl solutions. Values of the membranes transport structural parameters reflecting structural and kinetic characteristics of the two-phase system were derived on the basis of electroconductivity and diffusion permeability concentration dependences of investigated membranes. Aprotic solvent influence on the properties of heterogeneous membranes and their transport structural parameters ware discovered.

Model verification of limiting concentration by electrodialysis of an electrolyte solution

The concentration of LiCl in brine and brine volume are obtained as functions of current density by the method of limiting concentration by electrodialysis. These relationships are used for model calculations of current efficiency, the diffusion, osmotic, and electroosmotic permeability of an MK-40/MA-40 membrane pair, and also salt hydration numbers. These theoretical values of water transport numbers and LiCl hydration numbers are compared with corresponding experimental and literature data. It is shown that the model adequately describes the phenomena of the mass electrotransport occurring in electrodialyzers with noncirculating concentration compartments, and it can be successfully applied in calculating the technological parameters of the process, finding the transport properties of ion-exchange membranes, and determining salt hydration numbers in aqueous electrolyte solutions.

Preparation and properties of ion-exchange membranes prepared by the radiation-induced grafting of a styrene/acrylic acid comonomer onto low-density polyethylene

The preparation of ion-exchange membranes by the direct radiation grafting of acrylic acid and styrene onto low-density polyethylene was studied. The effects of the grafting conditions, such as the comonomer composition and concentration and the irradiation dose, on the grafting yield were also investigated. The swelling behavior, ion-exchange capacity, structural changes, and thermal properties of unsulfonated and sulfonated membranes were studied. The crystallinity decreased with grafting and sulfonation, but the chemical and thermal stability was improved by sulfonation. The removal of some toxic heavy-metal ions—Cd2+, Pb2+, and Zn2+—was studied. Some factors that influenced the metal-ion uptake were studied. The metal-ion-uptake results showed that the membranes could be used for the adsorption of the investigated metal ions and had an affinity toward Pd2+ ions in a mixture. The regeneration of the membranes was carried out by a treatment with 1M HNO3, and the membranes were used several times with high efficiency. Thus, the membranes may be suitable for pervaporation or vapor permeation to separate wastewater because of their hydrophilicity. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007

Effects of transport properties of ion-exchange membranes on desalination of 1,3-propanediol fermentation broth by electrodialysis

The electrodialysis (ED) method has been employed successfully to remove organic salts from fermentation broth. The efficiency of ED is strongly affected by the transport properties of ions and solutes through ion-exchange membranes (IEMs), that is, the conductivity of the IEM and the diffusion coefficient of neutral solutes through the IEM. Therefore, it is very important to select IEMs being suitable for ED desalination of fermentation broth based on the transport properties of IEMs. The conductivities of eight kinds of commercial IEMs and the diffusion coefficients of neutral solutes through the IEMs were measured, and ED experiments for the desalination of simulated 1,3-propanediol fermentation broth were carried out by using a combination of the eight IEMs. By comparing the efficiency of the ED process, the optimum IEMs were determined and the influences of transport properties of IEMs were discussed.

Micellar-enhanced electrodialysis: Influence of surfactants on the transport properties of ion-exchange membranes

Thin layers of ionic surfactants were formed on the surfaces of ion-exchange membranes by adsorption with electrostatic interactions and were conformed by FTIR spectra. The effect of the adsorption on the transmission characteristics were investigated by membrane resistance and permselectivity studies, and it was found that adsorption of cationic surfactant onto the cation-exchange membrane and anionic surfactant onto the anion-exchange membrane associated with the increase in membrane resistance while decrease in membrane permselectivity, which became limiting beyond the critical micelle concentration of respective surfactant. Based on the studies schematic model for the orientations of surfactant molecules on the membranes surfaces under the electrodialytic conditions was presented. Improvement in the electrodialysis (ED) process efficiencies was observed due to the adsorption of the ion-exchange membranes surfaces because of the reduction in the concentration gradient between dilute and concentrated compartments of the ED unit, and thus back diffusion. This phenomenon is also schematically presented by the concentration profiles across the ion-exchange membranes under the electrical gradient in the polarized conditions. Based on the experimental results so called micellar-enhanced electrodialysis has been proposed for the efficient electrolyte separation up to very low concentration (with high purity) with reduced energy consumption, concentration polarization and improved limiting current density.

Modeling of Mass Electrotransfer in Terms of the Transport and Structural Properties of Ion-Exchange Membranes

Mass electrotransfer in membrane systems is modeled in terms of the transport and structural properties of the membranes. Experimental concentration-dependent conductivity and diffusion flux data are used to calculate and compare the transport and structural parameters of cation- and anion-exchange membranes employed in electrodialyzers.

A simplified procedure for ion-exchange membrane characterisation

A new procedure for the characterisation of the transport properties of ion-exchange membranes (IEM) is proposed. Only three characteristics have to be measured: the electrical conductivity, the diffusion permeability coefficient and the apparent transport number. To complete the set of parameters, two complementary characteristics, the true counter-ion transport number and the water transport number, are calculated from the Scatchard equation and from a novel equation deduced earlier. The possibilities to reduce the number of initial measurements are discussed in three cases.

Conductivity and selectivity of ion exchange membranes: structure-correlations

Apart from their stability in various operating conditions, the two main properties of ion-exchange membranes (IEMs) are the conductivity and selectivity, but both are difficult to obtain simultaneously at high values. This presentation deals with different ways of measurements, including specific characterization such as electrochemical impedance spectroscopy, Raman vibrational spectroscopy and radiotracers. Different transport models to reach fundamental transport parameters are also presented. Two cases of structure correlations will illustrate this topic: a cation-exchange membrane in strong basic solutions and a high-proton-conducting membrane based on sulfonated polyimide polymers.

The effect of conducting spacers on transport properties of ion-exchange membranes in electrodriven separation

A conventional non-conducting spacer (interpolymer of polyethylene styrene-divinylbenzene copolymer) was transformed into an ion-conducting spacer by chemical modifications. Electrochemical characterization of cation-and anion-exchange membranes when it was alone or kept in between the non-, cation- or anion-conducting spacers was carried out by recording membrane potential and current-voltage curves in contact with NaCl solution of 220 ppm concentration at different flow rate of the solution. Transport parameters such as the counter-ion transport number, ionic permeability, membrane resistance and permselectivity were estimated for different experimental systems. Introduction of cation-conducting spacer near cation-exchange membrane and anion-conducting spacer near anion-exchange membrane led to a dramatic increase in counter-ion transport number and limiting current density along with the reduction in membrane resistance and thickness of diffusion boundary layer. On the basis of these studies, the position of conducting spacers (CS) in electrodialysis (ED) stack were optimized and packed. The performance of this ED stack has been tested with non-conducting and cation-conducting spacers in electrolytic solution of NaCl, NiCl 2 and CuCl 2 having concentration 500–1000ppm. The presence of conducting spacers not only suppress the concentration polarization but out put of the unit and its current efficiency also increases by about two times.

Modification of transport properties of ion exchange membranes: XIV. Effect of molecular weight of polyethyleneimine bonded to the surface of cation exchange membranes by acid–amide bonding on electrochemical properties of the membranes

In order to prepare a cation exchange membrane having excellent monovalent cation permselectivity, a thin polyethyleneimine (PEI) layer was formed on one surface of the membrane by sulfonyl–amide bonding. The electrochemical properties of the cation exchange membranes, which had been prepared by the reaction of an aqueous PEI solution with chlorosulfonylated membranes, were examined in accordance with the number of the successive PEI reaction batches. The monovalent cation permselectivity decreased with the increase in the number of reaction times of the reused PEI solution. The smaller molecular weight of PEI was found to be consumed during the reaction, which means that PEI with higher molecular weight has difficulty reacting with the chlorosulfonylated membrane.

Application of the Network Simulation Method To Ionic Transport in Ion-Exchange Membranes Including Diffuse Double-Layer Effects

The electrical properties of ion-exchange membranes have been investigated using the network simulation method. A network model is proposed for the Nernst−Planck and Poisson equations describing the ionic transport through an ion-exchange membrane and the two diffusion boundary layers on both sides of the membrane. An electric circuit simulation program is used to solve the network model in order to obtain the steady-state, transient, and small-amplitude ac electrical properties of a cation-exchange membrane in contact with an asymmetric electrolyte solution. The steady-state, chronopotentiometric, chronoamperometric, and small-amplitude ac responses of the whole membrane system have been simulated. The study is mainly intended to analyze the characteristics of the equilibrium and nonequilibrium diffuse double layers in ion-exchange membranes and to quantify some interesting aspects of the nonstationary polarization phenomena occurring at the charged membrane|solution interfaces.