Heterogeneous Anion-exchange Membranes Research Articles

Effect of Surface Modification with Cerium Oxide on the Transport Properties of Heterogeneous Anion Exchange Membranes MA-41

Effect of Surface Modification with Cerium Oxide on the Transport Properties of Heterogeneous Anion Exchange Membranes MA-41

Synthesis of an Imidazolium Ionic Liquid as an Additive to Enhance the Electrochemical Properties of Heterogeneous Anion Exchange Membranes

Synthesis of an Imidazolium Ionic Liquid as an Additive to Enhance the Electrochemical Properties of Heterogeneous Anion Exchange Membranes

Heterogeneous Anion-Exchange Membranes with Enhanced Ion Conductivity for Continuous Electrodeionization.

In this study, the optimal fabrication parameters of a heterogeneous anion-exchange membrane (AEM) using an ionomer binder are investigated to improve the performance of continuous electrodeionization (CEDI) for producing ultrapure water. Poly(2,6-dimethyl-1,4-phenylene oxide) (PPO) is selected as the base material for preparing the ionomer binder and quaternized to have various ion exchange capacities (IECs). The optimal content of ion-exchange resin (IER) powder according to the IEC of the ionomer binder is then determined through systematic analyses. In conclusion, it is revealed that a heterogeneous AEM with optimal performance can be fabricated when the IEC of the ionomer binder is lowered and the content of IER powder is also lower than that of conventional heterogeneous membranes. Moreover, crosslinked quaternized PPO (QPPO) nanofiber powder is used as an additive to improve ion conductivity without deteriorating the mechanical properties of the membrane. The membrane fabricated under optimal conditions exhibits significantly lower electrical resistance (4.6 Ω cm2) despite a low IER content (30 wt%) compared to the commercial membrane (IONAC MA-3475, 13.6 Ω cm2) while also demonstrating moderate tensile strength (9.7 MPa) and a high transport number (ca. 0.97). Furthermore, it is proven that the prepared membrane exhibits a superior ion removal rate (99.86%) and lower energy consumption (0.35 kWh) compared to the commercial membrane (99.76% and 0.4 kWh, respectively) in CEDI experiments.

Tyrosine Amino Acid as a Foulant for the Heterogeneous Anion Exchange Membrane.

The features of organic fouling have been revealed for highly basic anion exchange membranes during prolonged electrodialysis in solutions containing the aromatic amino acid tyrosine. With increased operation time when using MA-41 heterogeneous membranes in tyrosine solution, an increase in hydrophobicity and roughness characteristics of the material surface is detected. A reduction in tyrosine flux through the membrane occurs which is caused by its pores plugging and deposition of the amino acid at the membrane surface induced by tyrosine adsorption and local supersaturation of the solution in the membrane phase. The long-term contact of the anion exchange membrane with a solution of tyrosine leads to some structural changes in the anion exchange material. An accumulation of the studied amino acid with phenolic fragment and tyrosine oxidation products (DOPA, DOPA-quinone) is found and confirmed by IR- and UV-spectroscopy techniques. The organic fouling is accompanied by an increase in density and a decrease in moisture content of the studied membrane. A comparative analysis of the chemical and electrochemical cleaning results for fouled samples of the MA-41 membrane demonstrates a partial restoration of the material transport characteristics using electrochemical cleaning in the intensive current mode of electrodialysis. The best efficiency of regeneration is reached when carrying out chemical cleaning with a solution of hydrochloric acid, providing almost complete restoration of the membrane characteristics.

Anion-Exchange Membrane “Polikon A” Based on Polyester Fiber Fabric (Functionalized by Low-Temperature High-Frequency Plasma) with Oxidized Metal Nanoparticles

An experimental laboratory set of samples of composite heterogeneous anion-exchange membranes was obtained by us for the development of our original method of polycondensation filling. Anion-exchange membranes were prepared on plasma-treated and non-plasma-treated polyester fiber fabrics. The fabric was treated with low-temperature argon plasma at a power of 400 W for 10 min at a pressure of 5 × 10−5 mbar. On the surface and bulk of the polyester fiber, a polyfunctional anionite of mixed basicity was synthesized and formed. The anion-exchange membrane contained secondary and tertiary amino groups and quaternary ammonium groups, which were obtained from polyethylene polyamines and epichlorohydrins. At the stage of the chemical synthesis of the anion matrix, oxidized nanoparticles (~1.5 wt.%) of silicon, nickel, and iron were added to the monomerization composition. The use of ion-plasma processing of fibers in combination with the introduction of oxidized nanoparticles at the synthesis stage makes it possible to influence the speed and depth of the synthesis and curing processes; this changes the formation of the surface morphology and the internal structure of the ion-exchange polymer matrix, as well as the hydrophobic/hydrophilic balance and—as a result—the different operational characteristics of anion-exchange membranes.

Short term fouling tests on homogeneous and heterogeneous anion-exchange membranes from food and bio-based industrial streams: Foulant identification and characterization

Electrodialysis is used in food and bio-based industries for selective separation and recovery of target ions and neutral molecules. Anion exchange membranes (AEM) are prone to fouling due to their complex interactions with organics. Currently, research has focussed mainly on fouling tests using model organic foulants. In this study, three different complex industrial feed streams: corn steep liquor (CSL), citric acid by-product (CA), and cheese whey (CW), were used to foul two commercial AEM types: Fujifilm type-10 (homogeneous) and RALEX (heterogeneous). A 1.5 – 2.3 fold higher membrane resistance after fouling was a result of a difference in membrane structure, ion exchange capacity, water uptake, and thickness (depending on the feed used). Liquid Chromatography – Organic Carbon Detection (LC-OCD) analysis of feed revealed highly hydrophilic (CDOC) fractions in CSL (85%), CA (87%), and CW (100%). This analysis was extended to foulant desorption solutions (NaCl (35 g/L) and EtOH-water-H2SO4 mixtures), which revealed that > 90 % of humic substances (HS) and building blocks (BB) desorbed when using NaCl (35 g/L), following a (concentration wise) desorption order: HS > BB > LMWN > BP > LMWA. For the EtOH-water-H2SO4 solution, low molecular weight neutrals and acids (LMW(A + N)) were desorbed majorly (>60%) and followed a desorption order: LMWN > LMWA > BB > BP > HS. Desorption due to the ion-exchange mechanism was dominant for NaCl (35 g/L) solution, while foulant-desorbant polar interactions were prevalent for the EtOH-water-H2SO4 solution. Upon foulant desorption using NaCl (35 g/L) solution, RALEX AEM owing to the presence of nanovoids in them, showed a 1.5 – 4 fold higher concentration difference vs. FF10 AEM, while this difference was not dominantly observed when EtOH-water-H2SO4 mixture was used. This study revealed that LMW fractions could possibly enter into the membrane matrix whereas HS and BB fractions owing to their high molecular weight, majorly adsorbed on surfaces.

Comparative Study of Different Ion-Exchange Membrane Types in Diffusion Dialysis for the Separation of Sulfuric Acid and Nickel Sulfate

The possibility of using various types of ion-exchange membranes in diffusion dialysis for the separation of sulfuric acid and nickel sulfate has been evaluated. The process of the dialysis separation of a real waste solution from an electroplating facility containing 252.3 g/L of sulfuric acid, 20.9 g/L of nickel ions and small amounts of zinc, iron, copper ions, etc. has been studied. Heterogeneous cation-exchange membrane containing sulfonic groups and heterogeneous anion-exchange membranes with different thicknesses (from 145 μm to 550 μm) and types of fixed groups (four samples with quaternary ammonium base and one sample with secondary and tertiary amines) have been used. The diffusion fluxes of sulfuric acid, nickel sulfate, and the total and osmotic fluxes of the solvent have been determined. The use of a cation-exchange membrane does not allow the separation of the components, since the fluxes of both components are low and comparable in magnitude. The use of anion-exchange membranes makes it possible to efficiently separate sulfuric acid and nickel sulfate. Anion-exchange membranes with quaternary ammonium groups are more effective in the diffusion dialysis process, while the thin membrane turns out to be the most effective.

New homogeneous and bilayer anion-exchange membranes based on N,N-diallyl-N,N-dimethylammonium chloride and ethyl methacrylate copolymer

The paper presents the electrochemical characteristics of a bilayer membrane and a homogeneous anion-exchange membrane based on the new N,N-diallyl-N,N-dimethylammonium chloride and ethyl methacrylate copolymer. The electrochemical behavior and stability under high-intensity electrodialysis conditions were studied using the rotating membrane disk. It has been shown that the casting of a thin layer of an anion-exchange copolymer on the surface of a heterogeneous anion-exchange membrane MA-41 leads to a significant increase in the limiting current (from 4.0 to 8.2 mA/cm2 in 0.01 M NaCl at 100 rpm) and a decrease in the rate of water-splitting reaction at the membrane/solution interface. A decrease in water-splitting rate leads to an increase in the contribution of the electroconvective component to the overlimiting mass transfer, significantly increasing the useful transfer of ions. For membranes formed using the new copolymer, resource tests were carried out for 50 and 400 h at i = 2ilim. Heterocyclic quaternary ammonium bases formed because of N,N-diallyl-N,N-dimethylammonium chloride copolymerization are stable under conditions, while ester fragment of the copolymer undergo hydrolysis. Despite the decrease in the contribution of nonequilibrium electroconvection to the total mass transfer after resource tests, the limiting current on the bilayer and homogeneous membranes does not undergo significant changes.

Short-Term Fouling Tests on Homogeneous and Heterogeneous Anion-Exchange Membranes from Food and Bio-Based Industrial Streams: Foulant Identification and Characterization

Short-Term Fouling Tests on Homogeneous and Heterogeneous Anion-Exchange Membranes from Food and Bio-Based Industrial Streams: Foulant Identification and Characterization

Evaluation by Means of Electrochemical Impedance Spectroscopy of the Transport of Phosphate Ions through a Heterogeneous Anion-Exchange Membrane at Different pH and Electrolyte Concentration

Electrodialysis is an innovative technique to reclaim phosphates from municipal wastewater. However, chemical reactions accompany the transport of these ions through ion-exchange membranes. The present study investigates the dependence of these phenomena on the initial pH and concentration of the phosphate-containing solution using a heterogeneous anion-exchange membrane. Linear sweep voltammetry, electrochemical impedance spectroscopy, and chronopotentiometry experiments were conducted for different phosphate-containing systems. For the most diluted solution, two limiting current densities (ilim) have been observed for pH 5 and 7.2, while only one ilim for pH 10, and correlated with the appearance of Gerischer arcs in EIS spectra. For pH 7.2, sub-arcs of Gerischer impedance were separated by a loop, indicating the involvement of the membrane functional groups. Increasing the phosphate concentration changed the system’s characteristics, reporting a single ilim. In the EIS spectra, the absence of Gerischer elements determined the attenuation of chemical reactions, followed by the development of a diffusion boundary layer, as indicated by the finite-length Warburg arcs. Chronopotentiometry clarified the mass transport mechanism responsible for distorting the diffusion boundary layer thickness at lower concentrations. The obtained results are expected to contribute to the phosphates recovery using electrodialysis in the most varied conditions of pH and concentration available in the environment.

Effect of Pulsed Electric Field on the Electrodialysis Performance of Phosphate-Containing Solutions.

A comparative analysis of mass transfer characteristics and energy consumption was carried out for the electrodialysis recovery of PV from of NaH2PO4 solutions and multicomponent (0.045 M NaxH(3-x)PO4, 0.02 M KCl, 0.045 M KOH, 0.028 M CaCl2, and 0.012 M MgCl2, pH 6.0 ± 0.1) solution in conventional continuous current (CC) and pulsed electric field (PEF) modes. The advantages of using PEF in comparison with CC mode are shown to increase the current efficiency and reduce energy consumption, as well as reduce scaling on heterogeneous anion-exchange membranes. It has been shown that PEF contributes to the suppression of the "acid dissociation" phenomenon, which is specific for anion-exchange membranes in phosphate-containing solutions. Pulse and pause lapse 0.1 s-0.1 s and duty cycle 1/2 were found to be optimal among the studied PEF parameters.

A Study on Biofouling and Cleaning of Anion Exchange Membranes for Reverse Electrodialysis.

This study covers the modification, (bio)fouling characterization, use, and cleaning of commercial heterogeneous anion exchange membranes (AEMs) to evaluate their feasibility for reverse electrodialysis (RED) applications. A surface modification with poly (acrylic) acid resulted in an improved monovalent perm-selectivity (decreased sulfate membrane transport rate). Moreover, we evaluated the (bio)fouling potential of the membrane using sodium dodecyl sulfate (SDS), sodium dodecyl benzenesulfonate (SDBS), and Aeromonas hydrophila as model organic foulants and a biofoulant, respectively. A detailed characterization of the AEMs (water contact angle, ion exchange capacity (IEC), scanning electron microscopy (SEM), cyclic voltammetry (CV), and Fourier Transform Infrared (FTIR) spectra) was carried out, verifying that the presence of such foulants reduces IEC and the maximum current obtained by CV. However, only SDS and SDBS affected the contact angle values. Cleaning of the biofouled membranes using a sodium hypochlorite aqueous solution allows for (partially) recovering their initial properties. Furthermore, this work includes a fouling characterization using real surface and sea water matrixes, confirming the presence of several types of fouling microorganisms in natural streams. A lower adhesion of microorganisms (measured in terms of total bacteria counts) was observed for the modified membranes compared to the unmodified ones. Finally, we propose a cleaning strategy to mitigate biofouling in AEMs that could be easily applied in RED systems for an enhanced long-term process performance.

Hybrid surface modification of an anion exchange membrane for selective separation of monovalent anions in the electrodialysis process

Electrodialysis is an electrochemical separation process which is used for the removal of ionic species from aqueous solutions. In this study selectivity of an anion exchange membrane was tuned towards formate (CHOO-) anions compared to oxalates (C2O42- ) based on the characteristics of formate anions which show lower hydration energy. In order to enhance the removal efficiency of monovalent anions in electrodialysis, a hybrid surface modification on a heterogeneous anion exchange membrane was carried out. Surface modification consisted of three steps: plasma treatment (activation of the membrane surface), functionalization (acidification) and coupling with Polyethylenimine and Glutaraldehyde. Treatment of the membrane was verified using FTIR, Scanning Electron Microscopy, and Atomic Force Microscopy. The electrochemical properties of the membrane were measured before and after the modification. The results showed that due to the presence of the amide groups on the surface of the membrane upon modification, the water content of the membrane decreased by 8% while no other significant changes were observed in the membrane properties. Finally, the membrane selectivity towards CHOO-/ C2O42- in electrodialysis process increased from 0.88 to 4.29 upon surface modification.

Improved anti-organic fouling of polyvinyl chloride-based heterogeneous anion-exchange membrane modified by hydrophilic additives

Organic fouling – which generally gives a more severe effect on anion-exchange membranes (AEMs) – leads to performance degradation of electro-membrane processes. In this work, polyvinyl chloride (PVC)-based AEM was prepared by a solution casting method. Three AEMs were modified by different hydrophilic additives, namely polyethylene glycol 400 (PEG400), polyethylene glycol 1000 (PEG1000), and ZnO nanoparticles (M2-M4 membranes). Then, the properties of these modified membranes were compared to the pristine membrane (M1 membrane). The effect of hydrophilic additives on the anti-organic fouling properties of modified membranes was investigated during a simple electrodialysis test of feed water containing humic substances. The results of chemical structure analysis show that the additives are successfully incorporated in the membrane matrix. The presence of the hydrophilic additive in the membrane matrix increases membrane conductivity. The highest increase in conductivity is obtained by the addition of PEG400 (up to 50 %). Meanwhile, water uptake, ion-exchange capacity, and water contact angle of the modified membranes are insignificantly changed. In addition, the additives can improve membrane resistance toward organic fouling. The introduction of additive can suppress the increasing rate of membrane areal resistance by ∼60 %.

A comparative study on Donnan dialysis separation using homogeneous and heterogeneous anion-exchange membranes

A comparative study on Donnan dialysis separation using homogeneous and heterogeneous anion-exchange membranes

Overlimiting behavior of surface-modified heterogeneous anion-exchange membranes

Electrochemical and electrokinetic behavior of ion-exchange systems as a result of electrostatic interactions between the fixed charge and the ionic species present in the electrolyte can significantly vary with the type of electrolyte and the membrane composition. In this paper, we studied experimentally the effect of surface modification of a heterogeneous anion-exchange membrane on its properties and overlimiting behavior. The surface modification of the anion-exchange membrane included carboxylation of its surface through benzophenone-based photochemistry followed by covalent linkage of single stranded DNA molecules. Such surface chemistry produced molecular layers of negative charge on the positively charged membrane surface. We investigated the membrane samples with different two levels of surface modification after their exposure either to KCl solutions or solutions containing a biopolymer serving as a model membrane foulant. The surface modification resulted in larger system resistances that were especially pronounced in the limiting and overlimiting region. Water splitting reaction on both the pristine and the modified membranes occurred approximately to the same extent. Unlike water splitting, electroconvection, as another mechanism driving overlimiting current, tracked by the PIV method was largely suppressed upon surface modification especially with DNA molecules. The membranes with the chemically modified surfaces showed smaller susceptibility towards fouling.

Heterogeneous anion exchange membranes with nitrate selectivity and low electrical resistance

Selective transport of specific ions across ion-exchange membranes can be enhanced by controlling membrane properties such as hydrophobicity. Previous studies have shown that hydrophobic membranes enhance transport of ions with low hydration energy, although such membranes often have increased electrical resistance. In the present work, we study the separation of monovalent ions, specifically nitrate and chloride, using newly-designed heterogeneous anion-exchange membranes. These membranes show high selectivity for nitrate over chloride and have low electrical resistance. We use a functionalized polymeric binder (ionomer) and three ion-exchange resins with different hydrophobic groups, i.e., resins with quaternary ammonium groups and methyl, ethyl, and propyl substituents, respectively. We find that in electrolyte solutions with nitrate and chloride, nitrate over chloride selectivity in our membranes increases with increasing length of the alkyl groups. The membrane with propyl groups, i.e., which has the highest selectivity for nitrate, was further tested in electrolyte solutions containing nitrate, chloride, sulfate, and nitrate, chloride, iodate. The transport of sulfate and iodate ions across the membrane with propyl groups was 6% and 2% of the total counterions transport, respectively. For monovalent ions with similar hydrated size it is possible to report selectivity trends based on the ion hydration energy. We find that the chemical structure of the membrane can either promote or hinder the transport of ionic species.

Concentration Dependencies of Diffusion Permeability of Anion-Exchange Membranes in Sodium Hydrogen Carbonate, Monosodium Phosphate, and Potassium Hydrogen Tartrate Solutions.

The concentration dependencies of diffusion permeability of homogeneous (AMX-Sb and AX) and heterogeneous (MA-41 and FTAM-EDI) anion-exchange membranes (AEMs) is obtained in solutions of ampholytes (sodium bicarbonate, NaHCO3; monosodium phosphate, NaH2PO4; and potassium hydrogen tartrate, KHT) and a strong electrolyte (sodium chloride, NaCl). It is established that the diffusion permeability of AEMs increases with dilution of the ampholyte solutions, while it decreases in the case of the strong electrolyte solution. The factors causing the unusual form of concentration dependencies of AEMs in the ampholyte solutions are considered: (1) the enrichment of the internal AEM solution with multiply charged counterions and (2) the increase in the pore size of AEMs with dilution of the external solution. The enrichment of the internal solution of AEMs with multiply charged counterions is caused by the Donnan exclusion of protons, which are the products of protolysis reactions. The increase in the pore size is conditioned by the stretching of the elastic polymer matrix due to the penetration of strongly hydrated anions of carbonic, phosphoric, and tartaric acids into the AEMs.

Effect of Surface Modification of Heterogeneous Anion-Exchange Membranes on the Intensity of Electroconvection at Their Surfaces

Electroconvection is the principal mechanism that allows markedly increasing the rate of ion transfer through ion-exchange membranes in intensive current regimes. In this work, we investigated the possibility of intensifying electroconvection in solution near heterogeneous MA-41 anion-exchange membrane (Shchekinoazot production) by the modifying of its surface. The use of weakly crosslinked ion-exchange resin (MA-41P) in the course of the membrane manufacturing, with subsequent chemical modification of its surface (MA-41PM), is shown to make it possible to increase the limiting current density almost twice. The value of the reduced potential drop (after subtracting the ohmic contribution), at which significant generation of H+ and OH– ions begins, is shifted from 0.8 V in the case of MA-41 to 1.7 V in the case of MA-41PM. The current density related to the onset of water splitting is equal to 0.9$$i_{{{\text{lim}}}}^{{{\text{Lev}}}},$$ in the case of MA-41; 2$$i_{{{\text{lim}}}}^{{{\text{Lev}}}},$$ in the case of MA-41PM (where $$i_{{{\text{lim}}}}^{{{\text{Lev}}}}$$ is the theoretical value of the limiting current density). The special feature of the modified membrane behavior is the presence of a range of potential drop (between 50 and 80 mV in the reduced scale), in which the system with the MA-41PM has negative differential resistance: in this range, the potential drop decreases when the current density increases. This behavior occurs when measuring quasi-stationary I–V curves; correspondingly, in the chronopotentiogram there is a time interval, where the potential drop decreases with time. The electroconvection is intensified near a modified membrane due to a higher fraction of conductive areas on the surface of the modified membrane and the redistribution of these areas via formation of their agglomerates in the centers of the cells formed by the reinforcing mesh. Mathematical modeling shows the concentration polarization of the modified membrane being less than that of the pristine one. Meanwhile, the structure of electroconvective vortices is optimized: the vortices near the modified membrane are larger; they do not extinguish each other, unlike the case of MA-41.

Membrane-based electrochemical precipitation for water softening

Electrochemical precipitation has been widely employed for recirculating cooling water softening because of its environmental friendliness, convenient operation, and high treatment efficiency. However, this technique uses many expensive electrodes, and thus requires a very large investment. In this study, a novel process called membrane-based electrochemical precipitation (MEP) was proposed and tested for water softening. This new process utilises membrane polarisation, an undesirable phenomenon that occurs in conventional electrodialysis, to precipitate hardness ions on the surface of membranes. Compared with conventional electrodialysis, MEP involves only one kind of exchange membrane. Moreover, unlike traditional electrochemical precipitation, MEP only needs one pair of electrodes, and thus can reduce equipment cost significantly. Different types of membranes were examined, and heterogeneous anion exchange membranes were found to be the best. It was demonstrated that MEP could soften water effectively. The precipitation rate and energy consumption were 64.0–84.6 g/h/m2 and 8.8–12.0 kW h/kg CaCO3, respectively. The scale deposited on the membranes could be detached easily through polarity reversal of electrodes. Repeated experiments showed that MEP could run stably without any performance deterioration.