Types Of Anion Exchange Membranes Research Articles

The removal of fluoride from water based on applied current and membrane types in electrodialyis

In many places over the world, the fluoride concentration in ground water as raw water is higher than the threshold standard for healthy drinking water. This paper discusses a fluoride ion removal from sodium fluoride solution by using batch-system electrodialysis (ED) process. The effect of type of anion exchange membranes on the deionization rate of fluoride ion is investigated. The removal of fluoride ion from water by electrodialysis using CMX/AMX and CMX/ACS cation/anion exchange membranes combinations has been investigated on various applied currents, such as 3.64, 5.45, 9.09, 12.7, and 18.2 (A/m2). It was found that the increase of current densities made an operational time of ED shorter to achieve maximal ion removal. The effect of other coexistent ions such as chloride ion in water on the profile of ion removal and the ED cell resistance was discussed. It was also found that chloride ion passed more easily through anion exchange membranes than through fluoride ion.

Alkaline-Stable Anion Exchange Blend Membranes (AEBMs) with a Novel Sterically Hindered Cationic Head Group

In this study, synthesis and characterization of Anion Exchange Blend Membranes (AEBMs) are introduced. AEBMs were prepared by mixing polymer solutions of a halomethylated polymer (Br-PPO, brominated poly(2,6-dimethyl-1,4-phenylene oxide)), polybenzimidazole (PBI, F6PBI or PBI-OO) and a sulfonated polymer (S-polymer, SAC 098 (a sulfonated poly(phenylethersulfone), nonfluorinated) or SFS 001 (a sulfonated aromatic polyether, partially fluorinated)). A halomethylated polymer was used as the anion exchange ionomer precursor. Polybenzimidazole was used as a matrix polymer in order to enhance the mechanical strength of the AEBN. A minor amount of sulfonated polymer was added, forming ionic cross-links, and covalent bonds were formed in the blend membrane by reaction of a small amount of the CH2Br groups of Br-PPO with imidazole N-H groups of the PBI, respectively, leading to an increase of the chemical and dimensional stability of the novel AEBMs [1]. Membranes were fabricated by following procedure 1) mixing of the polymer solutions to homogeneity, 2) solvent evaporation in oven, 3) quaternization of the blend membrane by soaking the membrane in amine solution, 4) Ion exchange into chloride form in sodium chloride solution. It is well known that many types of anion exchange membranes are chemically unstable under alkaline condition. S. Holdcroft published a novel polybenzimidazolium AEM with a mesitylene building block shielding the dimethylimidazolium moiety of the polybenzimidazolium from OH- attack, leading to excellent hydroxide stability of this AEM: after immersion of this AEM in 2M KOH for 10 days at 60°C, no significant change of the NMR spectrum was observed [2]. Therefore it can be concluded that introduction of bulky steric hindrance groups in the vicinity of the cationic groups of AEMs can prevent the quaternized amine in the polymer structure from nucleophilic attack of hydroxide ions. Consequently in this study several types of sterically hindered tertiary amines were introduced in the polymer blend system for quaternization with Br-PPO, among them 1,2,2,6,6-pentamethylpiperidine (pempidine), quinuclidine, and 1,2,4,5-tetramethyl-1H-imidazole (abbreviated TMIm). Among these AEBMs, the TMIm-based membranes showed the best properties in terms of conductivity and stability. We investigated different combinations of polymers for AEBMs. The membrane containing PBI-OO and SAC098 showed good weight maintenance than other material combinations in DMAc extraction test at 90oC. This membrane was prepared and post-treated with TMIm as mentioned above. The membrane exhibited a chloride conductivity of 6.5 mS/cm at 30oC and 90% RH which is higher than that of commercial membrane (Tokuyama A202) under the same condition. The change of ion exchange capacities (IECs) was also investigated in order to examine the hydroxide stability. The membrane was exposed to 1M KOH solution at 90oC for 10days, and ion-exchange capacities (IECs) were compared to each other before and after KOH treatment. The IECs before and after KOH treatment were 2.63 and 2.59 mmol/g respectively, indicating excellent hydroxide stability. Apart from Br-PPO, other halomethylated polymers such as polyvinylbenzylchloride and polyepichlorohydrine were also investigated as precursors for AEBMs in this study, yielding good Cl- conductivities (in excess of 30 mScm-1) and alkaline stabilities with the novel 1,2,4,5-tetramethyl-1H-imidazolium head group. Addition of a hydrophilic polymer phase to the novel AEBMs resulted in even higher Cl- conductivities (e. g. 131 mScm-1@90°C@90% r.h.) after 10 d of KOH treatment (1M, 90°C).

Anion‐Exchange Membranes for Fuel Cells: Synthesis Strategies, Properties and Perspectives

AbstractThis review focuses on various synthesis strategies of anion‐exchange membranes (AEMs) for fuel cells, diverse methodologies of AEM‐forming, together with relationship between structures and properties. AEMs are discussed from seven categories, including (1) AEMs derived from Nafion precursors with sulfonyl fluoride groups, which display excellent stability and well‐developed morphologies that similar to Nafion, but has potentially high costs. (2) AEMs prepared by grafting technologies, such as chemical grafting technique, ATRP technique, plasma grafting technique and radiation grafting technique. (3) AEMs based on functionalized commercial polymers, including PVA, SEBS, CPP, PEEK, PES, PEI, PPO, and so on. (4) AEMs prepared by newly‐synthesized polymers, in which the most interesting approach is to synthesize alkaline multi‐block copolymers with enough long hydrophilic/hydrophobic blocks. (5) AEMs containing heterogeneous composition, which mainly prepared by blending and sol‐gel methods, reinforced or pore‐filling AEMs and IPN or s‐IPN. (6) AEMs with functional groups different from quaternary ammonium, which includes the studies of new type of AEMs with highly chemical stability in alkaline solution. (7) Hybrid membranes combining AEM with PEM, in which new configuration results in different performances. At last, conclusions and perspectives for the future researches of AEMs are presented.

“Hybrid” Anion-Exchange-Membranes for Direct Ethanol Fuel Cells

In the past few years, we have developed novel anion-exchange-membranes (AEMs) based on block copolymers for H2/O2 fuel cell applications [1-2] and discovered that dimensional stability of an AEM is very critical for achieving optimal performance in the fuel cells. Since ethanol is a non-toxic bio-fuel with a rather high energy density, it has attracted great attentions to be fed directly into polymeric electrolyte fuel cells. Ethanol oxidation reaction (EOR) in an alkaline media is much faster than that in an acid media and can be catalyzed on non-Pt catalysts. In this work, we aim to develop AEMs suitable for direct ethanol fuel cell (DEFC) applications.Four types of AEMs were prepared by varying "hybrid" SEBS-based copolymers. The swelling, water uptake, ionic conductivity, thermal stability and ion exchange capacity of the membranes were measured using the methods described in our previous work [1]. The impacts of ionic exchange capacity in the membranes on the performance of DEFCs were studied and compared with the commercial membrane (Tokuyama’s A201).DEFCs performances of various "hybrid" types of QSEBS membranes (Type I, II, III and IV) and commercial membrane (A201) will be presented. The correlations of the swelling, water uptake, ionic conductivity, thermal stability and ion exchange capacity of the membranes with the performance of DEFCs will be established and discussed. The key factors for developing AEMs for DEFC applications will be identified.

Effect of phase separation and adsorbed water on power consumption and current efficiency of terpolymer conetwork-based anion exchange membrane

We report the preparation of a new type of anion exchange membrane (AEM) from a random terpolymer of poly n-butyl acrylate (PnBA), polyacrylonitrile (PAN) and poly(2-dimethyl aminoethyl)methacrylate (PDMA) through quaternization and cross-linking. Moderate amounts of hydrophobic and soft PnBA (ca. 18 wt%) in the terpolymer considerably influenced the electrochemical properties and desalination performance of the membrane. Standardization experiments revealed that a membrane (AEM-2) prepared from a terpolymer containing 18 wt% PnBA, 50 wt% PAN and 32 wt% PDMA exhibited low power consumption (W) (0.66–0.95 kW h kg−1) and high current efficiency (CE) (94–96%) at an applied potential of 1.5–2 volts per cell pair during the desalination of water (containing 2000 mg L−1 NaCl) via electrodialysis (ED). On the other hand, membranes prepared from the bi-component PAN-co-PDMA with a similar PDMA content (28–34 wt%) exhibited a relatively higher W (0.94–1.32 kW h kg−1) and lower CE (68–80%) under similar experimental conditions compared to AEM-2. The remarkable effect of hydrophobic PnBA on AEM-2 performance is attributed to the nanophase separation of quaternized PAN-co-PDMA domains, low degree of water uptake (12%) along with the absence of freezing bound water in the membrane. Rapid desalination (low W) with high CE by five pairs of alternative AEM-2 and standard cation exchange membrane in the ED unit (13 × 5 cm2) shows promise for the development of en energy efficient ED unit.

Gypsum scaling on anion exchange membranes during Donnan exchange

The formation of gypsum (CaSO4·2H2O) scale in ion-exchange membranes was investigated under a Donnan exchange regime. Two types of anion exchange membranes (AEM), homogeneous AMV and heterogeneous MA-40, were used for the study. Counter-ion flux, scaling-cation concentration in the fouled membrane and membrane potential served as indicators for membrane scaling. Locations of scaling domains were dependent on the membrane structure, and lead to different effects on the membrane performance. Scaling in the homogeneous membrane was mainly characterized by surface deposits, resulting in a moderate decrease of the counter-ion flux. On the other hand, the heterogeneous membrane showed a high degree of internal precipitation resulting in a complete clogging of the membrane, thus leading to earlier and more severe decline in counter-ion flux. Significant amounts of calcium were found within the fouled MA-40, supporting the other indications of internal scaling.The potential difference across the homogeneous AMV did not change significantly after operating under scaling conditions. However, for the MA-40, an increase of the membrane potential was observed, suggesting that CaSO4 scale blocks defects and imperfections in the heterogeneous matrix. Scaling experiments were conducted in a specially designed Donnan cell with optical apparatus for in-situ observation of scales. This allowed real-time observation of surface scaling on the ion exchange membranes. Gypsum growth centers were observed on the homogeneous AMV significantly earlier than flux decline appeared. This finding shows that it is feasible to detect onset of scaling on homogeneous anion-exchange membranes before the appearance of significant effects on membrane performance.

Anion Exchange Membranes for Vanadium Redox Flow Batteries

Cross-linked quaternary ammonium functionalized Radel membranes with a high degree of functionalization (DF) were synthesized and evaluated in a vanadium redox flow battery. The permeation of vanadium cations through this type of anion exchange membrane was reduced significantly compared to sulfonated ion exchange membranes, while the ion conductivity of the AEM was low. Increasing the DF increased the ion conduction and crosslinking endowed mechanical strength in water by restricting swelling. However, crosslinking decreased the ion conductivity of the membrane, which offset the benefit of increasing the DF and the very low vanadium permeation. The resulting cell performance was similar to that of N212.

Optimization of Chromium (Vi) Removal by Donnan Dialysis

The removal of chromium (VI) from aqueous solutions by Donnan dialysis has been investigated in this paper. In this process, two anion-exchange membranes (AEMs) were used: Selemion? AMV and Neosepta? AFN. The amount of chromium (VI) removed was determined in terms of the following parameters: initial concentration of chromium (VI), type of anion-exchange membrane, concentration of counter-ion and magnetic stirring rate. A 24 full factorial design analysis was performed to screen the parameters affecting the Cr (VI) removal efficiency. Using the experimental results, a linear mathematical model representing the influence of the different parameters as well as their interactions was obtained. Analysis of the variance (ANOVA), the F-test and the student’s test shows that the type of anion-exchange membrane is the most significant parameter affecting the chromium (VI) removal. The statistical analysis of the experimental data assumes it to be a normal distribution.

Removal of bromate and associated anions from water by Donnan dialysis with anion-exchange membrane

Ozone is considered as a strongest oxidizer and disinfectant applied in drinking water treatment. If the water to be ozonated contains bromides, this will lead to the formation of bromates, ions with potential carcinogenic implications to human organisms. We proposed Donnan dialysis process with an anion-exchange membrane to remove bromate ions from water. The rate and efficiency of anion removal (BrO3 –, SO4 2–, HCO3 –) from the natural water were examined with the use of two types of anion-exchange membranes: Selemion AMV and Neosepta ACS and with the use of varying salt concentration in the receiver: 50, 100 or 200 mM NaCl. Bromate ions were removed from natural water with 90% efficiency in the process with the Neosepta ACS (of a highly cross-linked surface layer) when salt concentration in the receiver equalled 100 mM NaCl. The application of the Selemion AMV yielded similar efficiency of bromate removal (94%) but NaCl concentration in the receiver had to be twice as high as with Neosepta ACS (200 mM). However, Neosepta ACS rejected bicarbonates ranged between 35 and 53% and almost entirely rejected sulphates (in 97%). In turn, the Selemion AMV enabled flow of sulphates (93% of removal) and bicarbonates (ranged from 60 to 87% of removal).

Modeling the electric transport of sulfuric and phosphoric acids through anion-exchange membranes

The electric transport of the H 2SO 4 and H 3PO 4 mixture through two types of anion-exchange membranes (strong base: ACM; weak base: AAV) was investigated. The H 2SO 4 removal efficiency from the mixture and the H 3PO 4 retention efficiency were calculated. It was found that the effectiveness of the separation process is diminished by the association of phosphoric anions with the fixed charges which reduces the effective charge concentration. The transport of acids was quantitatively described by the model based on the extended Nernst–Planck equation and the Donnan equilibria. It satisfactorily describes the electro-membrane process except its last stage when H 2SO 4 concentration at the cathode side of a membrane is of a low value. When the association equilibrium between H 2PO 4 − and the fixed charges of the ACM membrane is introduced into the model, the concentration changes of H 3PO 4 could be much better described. Assuming the ideal Donnan equilibrium to occur, the transport of the both acids cannot be described by the same parameter related to the membrane porosity, tortuosity and the ion diffusivities. Regarding H 3PO 4, different ionic equilibria were taken into account in order to show their effects on the values of optimal model parameters.

Separation of nutrient ions and organic compounds from salts in RO concentrates by standard and monovalent selective ion-exchange membranes used in electrodialysis

To allow water recycling and nutrient recovery from reverse osmosis (RO) concentrates from a food industry plant, separation of salts from the organic fraction and from nutrient anions is required. In this study, the use of ion-exchange membranes in electrodialysis was investigated to this purpose. Two types of anion-exchange membranes from PCA, Germany, were investigated: a nonselective membrane (SA) and a membrane selective for monovalent anions (MVA). Different approaches including lowering the initial current density and increasing the initial pH were applied. The transport properties of different anions and different small charged organic compounds through ion-exchange membranes were discussed. The separation efficiency, which represents the selectivity, was compared under different conditions. The results show that separation of non-nutrient anions from nitrate and phosphate was difficult, whereas separation of salts from the organic fraction was feasible provided that the organic solutes are similar to uncharged test solutes used in the experiments; it was shown that a higher molar mass of the organic solute has a positive effect on the separation. Lowering the current density can increase the separation efficiency of monovalent/multivalent anions with either the SA membrane (a nonselective membrane) or the MVA membrane (a monovalent selective membrane). When the initial pH was increased, the separation efficiency of monovalent/multivalent anions can be improved for the MVA membrane, however, no obvious change was found for the SA membrane. Finally, experiments on real RO concentrates proved that the separation of salts from organics by electrodialysis is similar to the separation of salts from uncharged solutes and therefore feasible.

Electric transport of sulfuric acid through anion-exchange membranes in aqueous solutions

The current efficiency of membrane electrolysis of sulfuric acid solution using two types of anion-exchange membranes (ACM and AAV) has been determined. The transport phenomena in the membrane surrounded by polarization layers have been described by the model based on the extended Nernst–Planck equation and the Donnan equilibria, applied locally. It has been found that in the case of ACM two fitting parameters – the concentration of fixed charges ( c ¯ m = 1.1 M ) and the pore factor ( k DV θ = 0.006) – are needed for a relatively good fitting of model to the experimental data. However, the weak-base membrane AAV should be characterized by three parameters—the maximum concentration of fixed charges which can be formed in that membrane ( c ¯ m , max = 1.2 M ), the protonization constant ( K H = 6) and k DV θ = 0.0025. For both membranes the optimal values of c ¯ m are much lower than the experimental ones. The probable reasons of that discrepancy have been discussed. The thickness of the polarization layer, l pol, necessary in the model fitting has been calculated from the experimentally determined limiting current density using the equation derived for sulfuric acid. Comparing the values of l pol determined for ACM in the H 2SO 4 and HNO 3 solutions it was possible to find that only the sulfate anions carry the electric charge in that membrane in contact with dilute solutions of H 2SO 4.

Regeneration of a spent photographic fixer solution

AbstractAn attempt to regenerate an exhausted photographic fixer solution, removing the surplus silver and bromide ions has been made. The ions were removed by electrolysis in a cell containing separate anionic and cationic compartments using ion exchange membranes. Four types of anion exchange membranes in two‐ and three‐compartment cells were used: AMX, ACS (Neosepta, Japan), AMI‐7001 (Ultrex™, USA), and MA‐40 (PO Stchekino, Russia). Silver deposition occurred at the titanium rotating cylinder cathode and the deposits were compact and bright. The residual silver ion concentration after electrolysis was 0.012–0.014 mol dm−3. Of the four membranes tested the ACS membrane was the most selective for removal of bromide ions. The current efficiency of bromide ion migration through the ACS membrane was approximately two to five times greater than that achieved with AMX, AMI‐7001 and MA‐40 membranes. After five regeneration cycles the fixer's working quality did not noticeably deteriorate. Copyright © 2004 Society of Chemical Industry

Investigation into the rejuvenation of spent electroless nickel baths by electrodialysis.

Electroless nickel plating generates substantially more waste than other metal-finishing processes due to the inherent limited bath life and the need for regular bath disposal. Electrodialysis can be used to regenerate electroless nickel baths, but poor membrane permselectivity, leading to high losses of valuable bath components, continues to be a weakness of the technology. This research has investigated improving electrodialysis permselectivity for removing contaminants (sodium, orthophosphite, and sulfate) in a spent electroless nickel bath while minimizing the losses of valuable bath ions (nickel, hypophosphite, and organic acids). Ion permselectivity was explored with respect to electrodialysis operating conditions, membrane type, and cell configuration. Excellent permselectivity for sodium over nickel was attained irrespective of operating condition, membrane, or cell configuration. Studies on the effects of four different operating conditions (current density, pH, flow rate, and temperature) on anion permselectivity revealed bath pH and current density to be critical operating parameters. The type of anion exchange membrane used had a crucial effect on selectivity; one membrane (Ionac MA-3475) was identified as having superior selectivity for bath contaminants particularly for sulfate. The improvements in electrodialysis permselectivity established by this research will decrease waste generation within the electroless nickel process and increase resource productivity by minimizing the loss of valuable plating chemicals.

Macroreticular anion exchange membranes for electrodialysis in the presence of surface water foulants

In this work two new types of anion exchange membranes having pore sizes of macro dimensions are described. Static and dynamic fouling resistance to common large anions found in surface waters is evaluated. Improvements over conventional microporous anion membrane types are discussed with respect to electrodialysis.