Commercial Ion Exchange Membranes Research Articles

Characterizing Macroporous Ion Exchange Membrane Adsorbers for Natural Organic Matter (NOM) Removal—Adsorption and Regeneration Behavior

Addressing the characterization of Natural Organic Matter (NOM) removal by functionalized membranes in water treatment, this study evaluates the effectiveness of two commercial ion-exchange membrane adsorbers: Sartobind® Q (with quaternary amines) and D (with tertiary amines). Using Suwannee River NOM (SRNOM) as a surrogate, Langmuir adsorption isotherms revealed maximum capacities (Qmax) of 2966 ± 153 mg C/m2 and 2888 ± 112 mg C/m2, respectively. Variations in flux from 50 to 500 LMH had a minimal impact on breakthrough times, proving low diffusion limitations. The macroporous (3–5 µm) functionalized cellulose-based membranes exhibited high permeabilities of 10800 L/(h m2 bar). Q maintained positive zeta potential vs. pH, while D’s zeta potential decreased above pH 7 due to amine deprotonation and turning negative above an isoelectric point of 9.1. Regeneration with 0.01 M NaOH achieved over 95% DOC regeneration for Sartobind® D, characterizing reversibility through a pH-swing. Cyclic adsorption showed that Q maintained its capacity with over 99% DOC regeneration, while D required acidic conditioning after the first regeneration cycle to mitigate capacity reduction and re-deprotonate the adsorber. These results have demonstrated the potential suitability of adsorber membranes, designed originally for biotechnological purposes, for the possible removal of disinfection byproduct precursors in drinking water treatment.

Fabrication of pore-filling cation-exchange membrane from waste polystyrene and Spunbond Meltblown Spunbond (SMS) non-woven polypropylene fabric as the substrate

Commercial ion-exchange membranes are typically thick, possessing limited mechanical strength, and have relatively high fabrication costs. In this study, we utilize a three-layer polypropylene fabric known as Spunbond Meltblown Spunbond (SMS) as the substrate. This choice ensures that the resulting membrane exhibits high strength and low thickness. SMS substrates with various area densities, including 14.5, 15, 17, 20, 25, and 30 g/m2, were coated with different concentrations of waste polystyrene solution (ranging from 5 × 104 to 9 × 104 mg/l) before undergoing sulfonation using concentrated sulfuric acid. The physicochemical and mechanical properties of the membrane were characterized and compared with those of commercial Neosepta CMX and Nafion-117 cation-exchange membranes. Remarkably, the fabricated membrane exhibited good performance compared to commercial ones. The cation-exchange capacity (2.76 meq/g) and tensile strength (37.15 MPa) were higher, and the electrical resistance (3.603Ω) and the thickness (130 μm) were lower than the commercial membranes.

Membrane‐assisted capacitive deionization: Effect of Poly(vinyl alcohol) cross‐linking on the properties of ion exchange membranes

AbstractNovel composite electrodes were developed for application in membrane capacitive deionization (MCDI). Activated carbon (AC) was dispersed in a solution of poly(vinyl alcohol) (PVA) mixed with polyacrylic acid (PAA) or poly dimethyl diallyl ammonium chloride (PDMDAAC), and cast onto the surface of an AC‐based modified graphite electrode, prepared by phase inversion, to form a composite membrane further cross‐linked with glutaraldehyde (GA). The effect of the cross‐linking on the chemical structure of the PVA‐based membranes was determined by attenuated total reflectance Fourier‐transform infrared (ATR‐FTIR) spectroscopy. Cyclic voltammetry was conducted to examine the specific capacitance of the composite electrodes. Desalination experiments were then performed with MCDI unit cells to study the effect of cross‐linking on the desalination efficiency. It was proved that after optimization, the synthesized composite electrodes exhibited one and a half times higher NaCl removal capacity and three times higher adsorption rate as compared to that of a conventional CDI cell using commercial ion exchange membranes (IEMs) with almost the same energy consumption. The enhanced desalination performance was attributed to the optimized properties of the selected polymers and the improved adhesion of IEMs to the electrodes. This research paves the way for the application of new materials in MCDI processes for improved water desalination.

Influence of Donnan and dielectric exclusion on ion sorption in sulfonated polysulfones

The Donnan – Manning model accurately describes the thermodynamic properties (e.g., ion sorption) of many charged polymers equilibrated with aqueous electrolytes, such as the commercial ion exchange membranes CR61 and Nafion. It less accurately describes the ion sorption properties of sulfonated polysulfone, which is a promising desalination membrane polymer. One possible explanation is that other ionic interactions that are not included in the Donnan – Manning model, e.g., dielectric exclusion (or ion solvation effects) that can be described via the Born model, may have a significant influence on ion sorption in sulfonated polysulfones. We developed a model to account for the influence of both Donnan – Manning and dielectric exclusion factors on ion sorption properties and applied it to sulfonated polysulfones and Nafion. This Donnan – Manning – Born model described the ion sorption properties of sulfonated polysulfones more accurately than the Donnan – Manning model alone. The Donnan – Manning – Born model also predicted ion sorption properties in Nafion with improved accuracy relative to Donnan – Manning predictions, but the improvement was less significant than in the sulfonated polysulfone case. These results provide an approach for quantifying the influence of dielectric exclusion on ion sorption in charged polymers and could be particularly important for materials where dielectric exclusion is relevant.

Electroconvective instability at the surface of one-dimensionally patterned ion exchange membranes

The development of an electroconvective vortex explains the induction of overlimiting current in high voltage applications. However, an in-depth understanding of the dynamics remains challenging because the electrohydrodynamic behavior is unstable. Here, we show how the vortex develops and actively control this using a one-dimensional (1D) grid-patterned ion exchange membrane (IEM). We employed ultraviolet nanosecond laser ablation to fabricate micro-scale (100 μm) non-conductive 1D grid patterns on a commercial IEM. Vortex growth and the electrical responses were simultaneously monitored to derive correlations between the vortex dynamics and ion transport. The rate of electric potential fall increased rapidly during vortex development but decreased more gradually on transverse merging of the vortices. When shear flow was present, the modified scaling law was redefined via dimensionless number analysis of the electroconvective flow by the length of the impermeable 1D grid pattern and the applied voltage. The overlimiting currents and the desalination performances of 1D grid-patterned IEMs were successfully demonstrated. Based on these insights into the electroconvective vortex, we show that the electrical heterogeneity of the IEM actively controls the vortex and enhances desalination performance.

Counter-ion Conductivity and Selectivity Trade-Off for Commercial Ion-Exchange Membranes at High Salinities

Counter-ion Conductivity and Selectivity Trade-Off for Commercial Ion-Exchange Membranes at High Salinities

(Invited) New Membranes for Preventing Crossover in Non-Aqueous Redox Flow Batteries

Non-aqueous redox flow batteries have been considered as an alternative battery technology for grid storage due to the ability to operate at higher potentials with organic solvents. However, there are no commercial ion exchange membranes capable to handling these non-aqueous redox flow batteries, because they swell or degrade over time. This paper will discuss strategies for synthesizing stable anion exchange membrane separators for non-aqueous redox flow batteries to prevent crossover and improve long term stability.

Valorization of Seawater Reverse Osmosis Brine by Monovalent Ion-Selective Membranes through Electrodialysis.

This paper proposes the use of monovalent selective electrodialysis technology to concentrate the valuable sodium chloride (NaCl) component present in seawater reverse osmosis (SWRO) brine for direct utilization in the chlor-alkali industry. To enhance monovalent selectivity, a polyamide selective layer was fabricated on commercial ion exchange membranes (IEMs) through interfacial polymerization (IP) of piperazine (PIP) and 1,3,5-Benzenetricarbonyl chloride (TMC). The IP-modified IEMs were characterized using various techniques to investigate changes in chemical structure, morphology, and surface charge. Ion chromatography (IC) analysis showed that the divalent rejection rate was more than 90% for IP-modified IEMs, compared to less than 65% for commercial IEMs. Electrodialysis results demonstrated that the SWRO brine was successfully concentrated to 14.9 g/L NaCl at a power consumption rate of 3.041 kWh/kg, indicating the advantageous performance of the IP-modified IEMs. Overall, the proposed monovalent selective electrodialysis technology using IP-modified IEMs has the potential to provide a sustainable solution for the direct utilization of NaCl in the chlor-alkali industry.

Preconcentration of Fluorescent Dyes in Electromembrane Systems via Electrophoretic Migration

Microfluidic preconcentration enables the collection or extraction of low-abundance analytes at specific locations. It has attracted considerable attention as an essential technology in bioengineering, particularly for detection and diagnosis. Herein, we investigated the key parameters in the preconcentration of fluorescent dyes based on electrophoresis in a microfluidic electromembrane system. Commercial ion-exchange membrane (IEM)-integrated polydimethylsiloxane microfluidic devices were fabricated, and Alexa Fluor 488 and Rhodamine 6G were used as fluorescent dyes for sample preconcentration. Through experimental studies, the effect of the channel concentration ratio (CCR, concentration ratio of the main and buffer channels) on the performance of the sample preconcentration was studied. The results show that the preconcentration of the target sample occurs more effectively for a high CCR or high salt concentration of the main channel when the CCR is constant. We also demonstrate a phenomenon that the salt concentration in the electrolyte solution increases as the preconcentration progresses. Our results provide consolidated conditions for electrophoresis-based sample preconcentration in electromembrane systems.

Is It Possible to Prepare a "Super" Anion-Exchange Membrane by a Polypyrrole-Based Modification?

In spite of wide variety of commercial ion-exchange membranes, their characteristics, in particular, electrical conductivity and counterion permselectivity, are unsatisfactory for some applications, such as electrolyte solution concentration. This study is aimed at obtaining an anion-exchange membrane (AEM) of high performance in concentrated solutions. An AEM is prepared with a polypyrrole (PPy)-based modification of a heterogeneous AEM with quaternary ammonium functional groups. Concentration dependences of the conductivity, diffusion permeability and Cl− transport number in NaCl solutions are measured and simulated using a new version of the microheterogeneous model. The model describes changes in membrane swelling with increasing concentration and the effect of these changes on the transport characteristics. It is assumed that PPy occupies macro- and mesopores of the host membrane where it replaces non-selective electroneutral solution. Increasing conductivity and selectivity are explained by the presence of positively charged PPy groups. It is found that the conductivity of a freshly prepared membrane reaches 20 mS/cm and the chloride transport number > 0.99 in 4 M NaCl. A choice of input parameters allows quantitative agreement between the experimental and simulation results. However, PPy has shown itself to be an unstable material. This article discusses what parameters a membrane can have to show such exceptional characteristics.

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.

Active material crossover suppression with bi-ionic transportability by an amphoteric membrane for Zinc–Bromine redox flow battery

Zinc-bromine redox flow batteries (Zn/Br2 RFBs) are gaining attention as a next-generation energy storage system with the advantages of a cost-effective redox couple material price, high output, and high energy density. However, bromine (Br2) crossover through a commercial porous membrane causes self-discharge to lower the capacity retention. Nafion, a commercial ion exchange membrane, can lower the crossover but has low voltage efficiency due to high membrane resistance. To address this trade-off, the amphoteric functionalized silica (Am-SiO2) is introduced into the Nafion membrane (Nafion/Am-SiO2). It suppresses the crossover of active materials such as Br2 and polybromide (Brn−) and possesses high ionic conductivity due to the quaternary ammonium and sulfonic groups on the Am-SiO2 surface. In addition, increasing the water content in the membrane prevents the expansion of the water cluster size, which could help balance bi-ionic transport. As a result, the composite membrane showed 83.3 and 19.0 times higher ion selectivity than the commercial porous membrane (SF600) and ion-exchange membrane (NRE-212). Compared to SF600 and NRE-212, the energy efficiency of Nafion/Am-SiO2 was improved by 4.2 and 6.4%, respectively. Balancing anion and cation transport can be successfully applied in Zn/Br2 RFBs by introducing an amphoteric group into an ion-exchange membrane.

Optimizing pore structure of nanoporous membranes for high-performance salinity gradient power conversion

Nanofluidic salinity gradient power (SGP) harvesting has attracted more attention due to its abundant source and easy-to-implement nature, but its applicability is hampered by the high resistance and undesirable ion selectivity of the commercial ion-exchange membranes. The rational design and optimization of advanced membrane architectures are therefore urgently needed, which require a deep understanding of the relationship between ion transport and porous structure. Herein, a regular network model is defined to mimic the nanoporous membrane, allowing us to study the influence of porous structure on the SGP conversion using the Poisson-Nernst-Planck equations. We find that the slight change of inner porous structure can substantially affect the concentration polarization at the membrane-solution interface, which is dominated by the nanopores along the direct transport direction. The SGP conversion can be effectively improved by matching the local pore structure to electric double layer (EDL) structure. The SGP generation is more sensitive to the surface charge density at high salinity gradients. Our results highlight the significance of the precision regulation of porous structure in the SGP conversion, providing theoretical guidance to the design of nanoporous membranes for highly effective SGP harvesting.

Ion exchange membranes based on radiation-induced grafted functionalized polystyrene for high-performance reverse electrodialysis

Radiation-induced grafted ion exchange membranes based on functionalized polystyrene were tested for the first time in reverse electrodialysis (RED). Сation and anion exchange membranes based on sulfonated and quaternized/chloromethylated poly(styrene-co-divinylbenzene) grafted on UV-oxidized polymethylpentene films with different conductivity and selectivity relationships were compared with each other and with different commercial ion-exchange membranes (IEMs), FujiFim® Type 1 and Type 2 and RALEX®. The synthesized grafted membranes provided the highest power density of lab-scale stacks with a total active membrane area of 72 cm2 with the use of 0.1 М/1 М NaCl (0.67 W m−2) and 0.1 М/5 М NaCl (2.1 W m−2) solutions. The use of grafted membranes with a low resistance ~0.5 Ω cm2 (0.5 М NaCl, 25 °C) did not benefit the stack resistance; the low selectivity of such membranes resulted in a lower voltage and a high non-selective diffusion current of the RED stack. Higher power densities and current efficiencies in some model systems are observed for stacks with grafted membranes with lower conductivity and higher selectivity.

Composite Anion-Exchange Membrane Fabricated by UV Cross-Linking Vinyl Imidazolium Poly(Phenylene Oxide) with Polyacrylamides and Their Testing for Use in Redox Flow Batteries.

Composite anion-exchange membranes (AEMs) consisting of a porous substrate and a vinyl imidazolium poly(phenylene oxide) (VIMPPO)/acrylamide copolymer layer were fabricated in a straightforward process, for use in redox flow batteries. The porous substrate was coated with a mixture of VIMPPO and acrylamide monomers, then subsequently exposed to UV irradiation, in order to obtain a radically cured ion-exchange coating. Combining VIMPPO with low-value reagents allowed to significantly reduce the amount of synthesized ionomer used to fabricate the mem- brane down to 15%. Varying the VIMPPO content also allowed tuning the ionic transport properties of the resulting AEM. A series of membranes with different VIMPPO/acrylamides ratios were prepared to assess the optimal composition by studying the changes of membranes properties—water uptake, area resistivity, permeability, and chemical stability. Characterization of the membranes was followed by cycling experiments in a vanadium RFB (VRFB) cell. Among three composite membranes, the one with VIMPPO 15% w/w—reached the highest energy efficiency (75.1%) matching the performance of commercial ion-exchange membranes (IEMs) used in VRFBs (Nafion® N 115: 75.0% and Fumasep® FAP 450: 73.0%). These results showed that the proposed composite AEM, fabricated in an industrially oriented process, could be considered to be a lower-cost alternative to the benchmarked IEMs.

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.

Transport of Amino Acids in Soy Sauce Desalination Process by Electrodialysis.

Soy sauce is a common condiment that has a unique flavor, one that is derived from its rich amino acids and salts. It is known that excessive intake of high-sodium food will affect human health, causing a series of diseases such as hypertension and kidney disease. Therefore, removing sodium from the soy sauce and retaining the amino acids is desirable. In this study, electrodialysis (ED) was employed for the desalination of soy sauce using commercial ion exchange membranes (IEMs). The influence of the current density and initial pH on the desalination degree of the soy sauce was explored. Results showed that the optimal desalination condition for ED was reached at a current density of 5 mA/cm2 and pH of 5, with the desalination degree of 64% and the amino acid loss rate of 29.8%. Moreover, it was found that the loss rate of amino acids was related to the initial concentration and molecular structure. In addition, the amino acid adsorption by IEMs was explored. Results implied that the molecular weight and structure affect amino acid adsorption. This study illustrated that the ED process can successfully reduce the salt content of the soy sauce and retain most of the amino acids without compromising the original flavor.

Continuous separation of submicron-scale oil droplets in aqueous electrolyte by electrophoretic migration

Separation of tiny oil droplets, which is not readily achieved by conventional oily wastewater treatment, is becoming important in the petrochemical industries with regard to public health and the global environment. Herein, we report a continuous and filterless separation of submicron-scale oil droplets based on electrophoretic migration in a three-dimensional (3D) printed microfluidic free-flow electrophoresis (μFFE) device which is miniaturized system of conventional electrodialysis (ED). Microscale electrodialysis system with commercial ion exchange membrane (IEM) is proposed to control the dynamics of negatively (or positively) charged tiny oil droplets. We examined separation performance for various parameters, such as applied voltage, recovery ratio, flow velocity, solution concentration, and flow-channel dimension, with visualization of fluorescent oil droplets. Separation of several non-fluorescent submicron-scale oil droplets (e.g. gasoline engine, diesel engine, gear, and palm oils) were also investigated, including measurement of droplet diameters and surface charge (zeta potential). Future scale-up of the proposed microfluidic ED system will be a promising method for the treatment and relevant applications of industrial oily wastewater.

Nanofluidics for osmotic energy conversion

The osmotic pressure difference between river water and seawater is a promising source of renewable energy. However, current osmotic energy conversion processes show limited power output, mainly owing to the low performance of commercial ion-exchange membranes. Nanofluidic channels with tailored ion transport dynamics enable high-performance reverse electrodialysis to efficiently harvest renewable osmotic energy. In this Review, we discuss ion diffusion through nanofluidic channels and investigate the rational design and optimization of advanced membrane architectures. We highlight how the structure and charge distribution can be tailored to minimize resistance and promote energy conversion, and examine the possibility of integrating nanofluidic osmotic energy conversion with other technologies, such as desalination and water splitting. Finally, we give an outlook to future applications and discuss challenges that need to be overcome to enable large-scale, real-world applications. Osmotic energy conversion is a promising renewable energy source. This Review discusses nanofluidics-based osmotic energy conversion systems, investigating the principles of ion diffusion in nanofluidic systems, optimization of membrane architectures to increase energy conversion and possible integration with other technologies, such as water splitting.

Performance of Reverse Electrodialysis System for Salinity Gradient Energy Generation by Using a Commercial Ion Exchange Membrane Pair with Homogeneous Bulk Structure

Salinity gradient energy is a prominent alternative and maintainable energy source, which has considerable potential. Reverse electrodialysis (RED) is one of the most widely studied methods to extract this energy. Despite the considerable progress in research, optimization of RED process is still ongoing. In this study, effects of the number of membrane pairs, ratio of salinity gradient and feed velocity on power generation via the reverse electrodialysis (RED) system were investigated by using Fujifilm cation exchange membrane (CEM Type 2) and FujiFilm anion exchange membrane (AEM Type 2) ion exchange membranes. In the literature, there is no previous study based on a RED system equipped with Fujifilm AEM Type II and CEM Type II membranes that have homogeneous bulk structure. Using 400 µm of intermembrane distance, maximum obtainable power density by 5 pairs of Fujifilm membranes at 1:45 salinity ratio and with a linear flow rate of 0.833 cm/s was 0.426 W/m2.