Properties Of Ion-exchange Membranes Research Articles

Selective adsorption in ion exchange membranes: The effect of solution ion composition on ion partitioning

Electrodialysis is a water desalination technology that enables selective separation of ions, making it a promising solution for sustainable water reuse. The selectivity of the process is mainly determined by the properties of ion exchange membranes that can vary depending on the composition of ions in water, such as water uptake and charge density. In this work, we studied selective adsorption of Na+ and K+ ions in various ion exchange membranes considering the effect of solution ion composition on membrane water volume fraction. For that purpose, we conducted membrane adsorption experiments using solutions with Na+ and K+ ions with different ion compositions including Li+, Ca2+ or Mg2+ ions at different concentrations (0.001 – 0.25 M). The experiments showed that with the total ion concentration and the amount of divalent ions in solution, the membrane water volume fraction decreases while the selective adsorption of the smaller (hydrated) K+ ions over the Na+ ions in the membrane increases. We developed a theoretical framework based on Boublik-Mansoori-Carnahan-Starling-Leland (BMCSL) theory to describe the effect of membrane water volume fraction on selective adsorption of the ions by including volumetric effects, such as size exclusion. The developed framework was used to describe ion partitioning results of the membrane adsorption experiments. In addition, the effect of solution ion composition on selective ion removal during electrodialysis operation was evaluated using experimental data and theoretical calculations. The results of this study show that considering volumetric effects can improve the ion partitioning description in ion exchange membranes for solutions with various ion compositions.

Effects of cation exchange membrane properties on the separation of salt from high-salt organic wastewater by electrodialysis

High-salt organic wastewaters have attracted an increasing attention in recent decades. The separation of salt from high-salt organic wastewater is helpful to improve the efficiency of biological treatment. One possible separation method is through electrodialysis (ED), given the high selectivity and anti-fouling properties of ion exchange membrane. In this paper several cation exchange membranes (CEMs) with different properties were fabricated and applied in ED stack to desalt landfill leachate. The effects of CEMs properties on the ED separation performances were studied by the correlation analysis and linear regression. The results demonstrated that ion exchange capacity and surface hydrophilicity of CEMs were strongly correlated with the salt flux of ED, the correlation coefficient were 0.71 and −0.69, respectively. While the zeta-potential and crosslinking degree of CEMs significantly affected the rejection of organic matters by ED with the correlation coefficient of 0.72 and −0.71, respectively. Reducing the zeta-potential of CEMs and increasing the cross-linking degree of CEMs could improve the salt-organic separation ability of ED, and the separation factor reached 40.16, which was more than 2 times higher than that of commercial ED. The results provided reference for the preparation or modification of CEMs for salt-organic separation, and demonstrate the possibility of desalting high-salt organic wastewater by ED technology.

Effect of Lactose on the Transport Properties of Ion-Exchange Membranes

Effect of Lactose on the Transport Properties of Ion-Exchange Membranes

The Effect of Lactose on the Transport Properties of Ion-Exchange Membranes

The influence of lactose on the basic transport characteristics of ion exchange membranes, including cation-exchange membranes modified by polyaniline, has been studied. A positive effect on biofouling by Bacillus sp. or Shewanella oneidensis MR-1 cell cultures of modified MK-40 and Ralex CMHPES membranes has been found. That is mainly due to the different area of the conductive surface of these membranes. It has been revealed that the presence of lactose in a solution leads to a decrease in the conductivity of all studied membranes. However, the most significant effect is manifested for MK-40 membrane modified by polyaniline: its electrical conductivity is reduced by 15–25%. The diffusion permeability of the anion-exchange and initial cation-exchange membranes is poorly dependent on the presence of lactose in the solution. However, its decrease is observed by 2–2.5 times in the case of cation-exchange membranes modified by polyaniline. A significant effect of lactose on the current-voltage characteristics of the anion-exchange membranes has been found. This fact indicates significant adsorption of lactose on membrane surface in an external electric field. It is shown that ion-exchange membranes remain quite effective for electrodialysis of hydrochloric serum solutions, but their use is more effective at under limiting current modes.

Composite Anion Exchange Membranes Based on Quaternary Ammonium-Functionalized Polystyrene and Cerium(IV) Phosphate with Improved Monovalent-Ion Selectivity and Antifouling Properties.

The possibility of targeted change of the properties of ion exchange membranes by incorporation of various nanoparticles into the membranes is attracting the attention of many research groups. Here we studied for the first time the influence of cerium phosphate nanoparticles on the physicochemical and transport properties of commercial anion exchange membranes based on quaternary ammonium-functionalized polystyrenes, such as heterogeneous Ralex® AM and pseudo-homogeneous Neosepta® AMX. The incorporation of cerium phosphate on one side of the membrane was performed by precipitation from absorbed cerium ammonium nitrate (CAN) anionic complex with ammonium dihydrogen phosphate or phosphoric acid. The structures of the obtained hybrid membranes and separately synthesized cerium phosphate were investigated using FTIR, P31 MAS NMR, EDX mapping, and scanning electron microscopy. The modification increased the membrane selectivity to monovalent ions in the ED desalination of an equimolar mixture of NaCl and Na2SO4. The highest selectivities of Ralex® AM and Neosepta® AMX-based hybrid membranes were 4.9 and 7.7, respectively. In addition, the modification of Neosepta® membranes also increased the resistance to a typical anionic surfactant, sodium dodecylbenzenesulfonate.

Monoethanolamine (MEA) Degradation: Influence on the Electrodialysis Treatment of MEA-Absorbent.

The thermal-oxidative degradation of aqueous solutions of carbonized monoethanolamine (MEA, 30% wt., 0.25 mol MEA/mol CO2) was studied for 336 h at 120 °C. Based on the change in the color of the solution and the formation of a precipitate, the occurrence of thermal-oxidative degradation of the MEA solution with the formation of destruction products, including insoluble ones, was confirmed. The electrokinetic activity of the resulting degradation products, including insoluble ones, was studied during the electrodialysis purification of an aged MEA solution. To understand the influence of degradation products on the ion-exchange membrane properties, a package of samples of MK-40 and MA-41 ion-exchange membranes was exposed to a degraded MEA solution for 6 months. A comparison of the efficiency of the electrodialysis treatment of a model absorption solution of MEA before and after long-time contact with degraded MEA showed that the depth of desalination was reduced by 34%, while the magnitude of the current in the ED apparatus was reduced by 25%. For the first time, the regeneration of ion-exchange membranes from MEA degradation products was carried out, which made it possible to restore the depth of desalting in the ED process by 90%.

Improved ionic and mechanical properties of ion-exchange membrane with an ionic silica network for high-performance ionic polymer-metal composites

Ion-exchange membranes considerably affect the actuation of ionic polymer–metal composites (IPMCs) through ion movement under an applied voltage. To enhance the performances of IPMCs, previous studies have increased the ionic content of the ion-exchange membrane, thereby improving its ionic conductivity and water uptake. Although this increased ionic content enhances IPMC displacement, the increased water uptake diminishes IPMC stiffness, resulting in decreased IPMC blocking force. Therefore, a new approach is needed to resolve the trade-off between displacement and force. Here, we reinforced the Nafion membrane by forming a sulfonated polysilsesquioxane structure inside. The incorporation of this ionic silica network increased the total ion content of the membrane and included silica as a mechanically reinforcing filler. The force of the IPMC can be enhanced despite increased water uptake by the membrane. Therefore, IPMCs were obtained with improvements in displacement and blocking force. Comparison of the IPMCs with commercial Nafion films revealed similar displacement and superior force, demonstrating their applicability. These findings represent a breakthrough in enhancing the actuation of IPMCs while resolving the trade-off between displacement and force.

Modeling the Conductivity and Diffusion Permeability of a Track-Etched Membrane Taking into Account a Loose Layer.

The microheterogeneous model makes it possible to describe the main transport properties of ion-exchange membranes using a single set of input parameters. This paper describes an adaptation of the microheterogeneous model for describing the electrical conductivity and diffusion permeability of a track-etched membrane (TEM). Usually, the transport parameters of TEMs are evaluated assuming that ion transfer occurs through the solution filling the membrane pores, which are cylindrical and oriented normally to the membrane surface. The version of the microheterogeneous model developed in this paper takes into account the presence of a loose layer, which forms as an intermediate layer between the pore solution and the membrane bulk material during track etching. It is assumed that this layer can be considered as a "gel phase" in the framework of the microheterogeneous model due to the fixed hydroxyl and carboxyl groups, which imparts ion exchange properties to the loose layer. The qualitative and quantitative agreement between the calculated and experimental concentration dependencies of the conductivity and diffusion permeability is discussed. The role of the model input parameters is described in relation to the structural features of the membrane. In particular, the inclination of the pores relative to the surface and their narrowing in the middle part of the membrane can be important for their properties.

Effect of Co-Existing Ions on Salinity Gradient Power Generation by Reverse Electrodialysis Using Different Ion Exchange Membrane Pairs.

This study investigates the influence of co-existing ions on the salinity gradient power generation performance of the reverse electrodialysis (RED) using three different commercial ion exchange membrane pairs. The feed solutions, including the mixture of two different salts, were prepared with 90 wt.% of NaCl and 10 wt.% of LiCl, KCl, CaCl2, MgCl2 or Na2SO4 by keeping the salt ratio between high concentrate solution and low concentrate solution constant as 1:30 (g/g) at various flow velocities (50, 125 and 200 mL/min). It was observed that the divalent ions exhibited a negative impact on the performance of the RED system due to their high valence and low ionic mobility depending on their high hydrated radius and low diffusion coefficients compared to those of the monovalent ions. On the other hand, the effect of the monovalent ions differed according to the properties of ion exchange membranes used in the RED stack. When the power generation performances of ion exchange membrane pairs employed in the RED stack were compared, it was considered that Neosepta AMX and CMX membranes provided the highest power density due to their low membrane thicknesses, low electrical resistances, and relatively high ion exchange capacities compared to other two commercial ion exchange membrane pairs.

Microstructural description of ion exchange membranes: The effect of PPy-based modification

Properties of ion exchange membranes (IEMs) both cationic and anionic were widely analysed before and after chemical. The modification aims to reduce the crossover phenomena typically observed in RFBs by incorporating polypyrrole (PPy) at the inner of commercial IEMs. In this work, we have explored the insight of membranes by structural and generalized conductivity considerations and its implications in terms of physicochemical characteristics. Transport Structural Parameters (TSP) have been obtained from the electrolyte concentration dependencies (NaCl, in this work). AEMs successfully increased their specific conductivity (between 2.5 and 3.9 times) whereas CEMs slightly decreased (between 1.3 and 2 times). This approach was useful for the description of membrane electro-transport by using the so-called two-phase model which considers an IEM as an heterophase system (particularly, gel and interstitial phase) and their arrangement. AEMs almost doubled increased whereas CEMs doubled decreased their internal microphase arrangement in terms of structural parameter (α). A modification of the established model was applied to the CEMs to better understand their specific behaviour after polymerization. Up to 3.5 times the diffusion coefficient was obtained in AEMs after PPy modification. Finally, based on TSP obtained we propose a microstructural description for the IEMs studied in this work.

Semi-Continuous Desalination and Concentration of Small-Volume Samples.

Electrodialysis is an electric-field-mediated process separating ions exploiting selective properties of ion-exchange membranes. The ion-exchange membranes create an ion-depleted zone in an electrolyte solution adjacent to the membrane under DC polarization. We constructed a microfluidic system that uses the ion-depleted zone to separate ions from the processed water solution. We tested the separation performance by desalting a model KCl solution spiked with fluorescein for direct observation. We showed both visually and by measuring the conductivity of the output solutions that the system can work in three modes of operation referred to as continuous desalination, desalination by accumulation, and unsuccessful desalination. The mode of operation can easily be set by changing the control parameters. The desalination factors for the model KCl solution reached values from 80 to 100%, depending on the mode of operation. The concentration factor, given as a ratio of concentrate-to-feed concentrations, reached zero for desalination by accumulation when only diluate was produced. The water recovery, therefore, was infinite at these conditions. Independent control of the diluate and concentrate flow rates and the DC voltage turned our system into a versatile platform, enabling us to set proper conditions to process various samples.

Synthesis and Properties of Ion-Exchange Membranes Based on Porous Polytetrafluoroethylene and Sulphonated Polystyrene

Synthesis and Properties of Ion-Exchange Membranes Based on Porous Polytetrafluoroethylene and Sulphonated Polystyrene

Excellent ion selectivity of Nafion membrane modified by PBI via acid-base pair effect for vanadium flow battery

As the key material of Vanadium flow battery (VFB), the properties of ion exchange membrane limit the battery performance and cost of VFB to some extent. Nafion membrane of Dupont, one of the most employed membranes in VFB, is also exposed to some issues such as high cost and low ion selectivity. To improve ion selectivity of Nafion membrane, polybenzimidazole (PBI), functional groups of which can be ionized to a positive charge and prevent vanadium ions from crossing the membrane, is introduced to prepare reinforced Nafion membrane (Nafion/PBI membrane). By this way, excellent conductivity and vanadium ion selectivity of Nafion membrane are optimized via the “acid-base pair” effect. Furthermore, a series of PBI contents have been optimized and the battery with Nafion/PBI membrane of 1 wt% PBI exhibits excellent performance (coulombic efficiency: 97.72%, energy efficiency: 81.31% at 200 mA cm−2). In the long-term cycles, higher capacity retention and superior stability of the battery with Nafion/PBI membrane (1 wt% PBI) are delivered than Nafion 212 membrane. Thus, Nafion/PBI membrane is indeed a promising candidate to promote the whole properties of VFB by surmounting the trade-off between proton conductivity and vanadium ion permeability.

Microhole‐voltammograms Controlled by Solution Reservoir at Cationic and Anionic Ion Exchange Membranes

AbstractMicrohole‐voltammetry in which ions pass through a hole by electric migration exhibits rectified current‐voltage curves. The rectification ratio, being of the high conductance to the low one, seems to depend on properties of ion exchange membranes. Our experiments at a cationic and an anionic membrane showed that the ratios for both the membranes were similar in spite of large difference in ionic capacities. The ratio was controlled by geometry of the reservoir of the solution rather than hole geometry and properties of membranes. Our model was composed of resistances of the hole, the membranes and the reservoir in series.

Estimation of the through-plane thermal conductivity of polymeric ion-exchange membranes using finite element technique

The aim of this study is to calculate the through-plane thermal conductivity of commercial polymeric ion-exchange membranes. Different membranes were considered to study the influence of membrane properties on the thermal conductivity values. In particular we focused on reinforcement, ion exchange capacity and membrane density and thickness. For this purpose, we use a simple experimental setup and a numerical simulation to estimate the thermal conductivity from the experimental temperature profiles. Once the system is calibrated, the model includes as the only unknown parameter the membrane thermal conductivity. To validate the method, the thermal conductivity of the well-known Nafion membranes has been determined, a very good agreement was achieved in context from reliable literature values. The study also provides the thermal conductivity of other polymeric ion-exchange membranes with great potential in diverse applications under non-isothermal conditions. The calculated thermal conductivity for the different ion-exchange membranes is in the range from 0.04 Wm−1K−1 to 0.42 Wm−1K−1. The results show that the reinforcement leads to lower values of thermal conductivity whereas a higher density or heterogenous structure leads to higher thermal conductivity values. The approach presented here, combining experimental and simulation techniques, may provide a basis for confirming the effect of the polymeric ion-exchange membrane properties on the thermal conductivity and may shed light on the best choice for the electrolyte of membrane-based applications performance under non-isothermal conditions.

Using a microheterogeneous model to assess the applicability of ion-exchange membranes in the process of reverse electrodialysis

This paper shows the possibility of using a microheterogeneous model to describe the properties of ion-exchange membranes and calculate the characteristics of a reverse electrodialyzer from the data obtained. We studied the properties of eight samples of heterogeneous cation exchange membranes (two samples of each type of membrane). The samples differed in the year of issue and storage conditions. It is shown that for heterogeneous ion-exchange membranes MK-40 and MA-41, the samples' properties can differ significantly. The counterions transport numbers calculated within the framework of the microheterogeneous model for Ralex membranes differ insignificantly. The counterion transport number in 1 mol/L sodium chloride solution is 0.96 for Ralex CM and 0.98 ± 0.01 for Ralex AMH. For the MK-40 membrane, the transport number in the same solution is 0.94 ± 0.04, and for the MA-41 membrane, it is 0.85 ± 0.1. The possibility of calculating the transport numbers and predicting the open-circuit voltage based on simple physicochemical measurements allows selecting the best membrane pairs for the reverse electrodialysis process. Comparison of the open-circuit potential value calculated using the obtained transfer numbers with experimental data showed that in the case of using Ralex membranes, the difference between the experimental and calculated values is 2%. The calculated value of the open circuit potential was 0.19 V/membrane pair or 1.69 V for the investigated reverse electrodialyzer with nine pair chambers.

Exploring the Function of Ion-Exchange Membrane in Membrane Capacitive Deionization via a Fully Coupled Two-Dimensional Process Model

In the arid west, the freshwater supply of many communities is limited, leading to increased interest in tapping brackish water resources. Although reverse osmosis is the most common technology to upgrade saline waters, there is also interest in developing and improving alternative technologies. Here we focus on membrane capacitive deionization (MCDI), which has attracted broad attention as a portable and energy-efficient desalination technology. In this study, a fully coupled two-dimensional MCDI process model capable of capturing transient ion transport and adsorption behaviors was developed to explore the function of the ion-exchange membrane (IEM) and detect MCDI influencing factors via sensitivity analysis. The IEM enhanced desalination by improving the counter-ions’ flux and increased adsorption in electrodes by encouraging retention of ions in electrode macropores. An optimized cycle time was proposed with maximal salt removal efficiency. The usage of the IEM, high applied voltage, and low flow rate were discovered to enhance this maximal salt removal efficiency. IEM properties including water uptake volume fraction, membrane thickness, and fixed charge density had a marginal impact on cycle time and salt removal efficiency within certain limits, while increasing cell length and electrode thickness and decreasing channel thickness and dispersivity significantly improved overall performance.

Selectivity of Transport Processes in Ion-Exchange Membranes: Relationship with the Structure and Methods for Its Improvement.

Nowadays, ion-exchange membranes have numerous applications in water desalination, electrolysis, chemistry, food, health, energy, environment and other fields. All of these applications require high selectivity of ion transfer, i.e., high membrane permselectivity. The transport properties of ion-exchange membranes are determined by their structure, composition and preparation method. For various applications, the selectivity of transfer processes can be characterized by different parameters, for example, by the transport number of counterions (permselectivity in electrodialysis) or by the ratio of ionic conductivity to the permeability of some gases (crossover in fuel cells). However, in most cases there is a correlation: the higher the flux density of the target component through the membrane, the lower the selectivity of the process. This correlation has two aspects: first, it follows from the membrane material properties, often expressed as the trade-off between membrane permeability and permselectivity; and, second, it is due to the concentration polarization phenomenon, which increases with an increase in the applied driving force. In this review, both aspects are considered. Recent research and progress in the membrane selectivity improvement, mainly including a number of approaches as crosslinking, nanoparticle doping, surface modification, and the use of special synthetic methods (e.g., synthesis of grafted membranes or membranes with a fairly rigid three-dimensional matrix) are summarized. These approaches are promising for the ion-exchange membranes synthesis for electrodialysis, alternative energy, and the valuable component extraction from natural or waste-water. Perspectives on future development in this research field are also discussed.

Dependence of the Transport Properties of Perfluorinated Sulfonated Cation-Exchange Membranes on Ion-Exchange Capacity

The transport properties of ion-exchange membranes depend on many factors, primarily, on ion-exchange capacity and chemical composition. Therefore, the correlation of transport properties with a single particular parameter is generally not quite strict. In this study, the dependence of transport properties of several perfluorinated sulfonated cation-exchange membranes that differ in side chain length and fraction of fragments containing ether groups on ion-exchange capacity is analyzed. It is shown that, with a decrease in the ion-exchange capacity from 1.35 to 0.66 mg-equiv/g, the proton conductivity of membranes contacting water and their diffusion permeability with respect to a 0.1 M HCl solution decrease by two orders of magnitude. A decrease in relative humidity leads to the most significant decrease in the conductivity of membranes with a low ion-exchange capacity. Thus, at a relative humidity of 32%, the conductivity of the studied membranes decreases more than 600-fold with a decrease in ion-exchange capacity. In general, the oxygen permeability of membranes is characterized by a similar dependence. However, in this set of membranes, it varies as little as threefold.

Membrane materials for energy production and storage

Abstract Ion exchange membranes are widely used in chemical power sources, including fuel cells, redox batteries, reverse electrodialysis devices and lithium-ion batteries. The general requirements for them are high ionic conductivity and selectivity of transport processes. Heterogeneous membranes are much cheaper but less selective due to the secondary porosity with large pore size. The composition of grafted membranes is almost identical to heterogeneous ones. But they are more selective due to the lack of secondary porosity. The conductivity of ion exchange membranes can be improved by their modification via nanoparticle incorporation. Hybrid membranes exhibit suppressed transport of co-ions and fuel gases. Highly selective composite membranes can be synthesized by incorporating nanoparticles with modified surface. Furthermore, the increase in the conductivity of hybrid membranes at low humidity is a significant advantage for fuel cell application. Proton-conducting membranes in the lithium form intercalated with aprotic solvents can be used in lithium-ion batteries and make them more safe. In this review, we summarize recent progress in the synthesis, and modification and transport properties of ion exchange membranes, their transport properties, methods of preparation and modification. Their application in fuel cells, reverse electrodialysis devices and lithium-ion batteries is also reviewed.