AMV Membrane Research Articles

Solvent-free green synthesis of anion exchange membranes via photo-polymerization for efficient desalination by electrodialysis

A green anion exchange membrane for electrodialysis desalination was synthesized using a solvent-free photo-polymerization approach. Vinylbenzyl chloride (monomer), tripropylene glycol diacrylate (crosslinker), and photoinitiator were mixed and subjected to UV polymerization for 20 min to create the base membrane, followed by positive charge modification with 1-methylimidazole. This method avoids organic solvents, offering economic and environmental benefits. By adjusting the degrees of crosslinking and positive charge, precise control over the membrane's microstructure and properties was achieved. The optimized membrane showed an area resistance of 1.67 Ω cm2 and a transport number of 0.956, demonstrating exceptional electrochemical performance. Under comparable conditions, the optimized membrane improved the NaCl removal rate by 11.47 %, increased current efficiency by 10.61 %, and reduced energy consumption by 16.75 % compared to commercial AMV membrane, highlighting its potential for scalable seawater desalination through electrodialysis.

Rational Design of Ion Exchange Membrane Material Properties Limits the Crossover of CO2 Reduction Products in Artificial Photosynthesis Devices.

Efficient operation is crucial for the deployment of photoelectrochemical CO2 reduction devices for large-scale artificial photosynthesis. In these devices, undesired transport of CO2 reduction products from the reduction electrode to the oxidation electrode may occur through a liquid electrolyte and an ion exchange membrane, reducing device productivity and increasing the energy required for product purification. Our work investigated the CO2 reduction product crossover through ion exchange membranes separating the cathode and anode compartments in CO2 reduction cells. The concentrations of liquid products produced by CO2 reduction on copper foil were measured. A systematic approach for the investigation of product crossover was developed. The crossover of products was analyzed over a range of working electrode potentials (-1.08 V vs RHE to -0.88 V vs RHE) in cells employing a commercial Selemion AMV membrane and a new poly(vinylimidazolium) family of ion exchange membranes with variable chemical and structural properties. We found that product loss due to electromigration of charged species in the device was more significant than product loss due to diffusion of uncharged species. To reduce the crossover of CO2 reduction products, the influence of membrane properties such as the ionic conductivity and water volume fraction was investigated for the Selemion AMV membrane and poly(vinylimidazolium) membranes with variable material properties. We show that the water volume fraction and, by extension, ionic conductivity of the membrane may be controlled to reduce product crossover in CO2 reduction artificial photosynthesis devices.

Removal of nitrate from groundwater by Donnan dialysis

Nitrate removal from groundwater by Donnan dialysis involves the dynamics of a multi-component solution. Transport kinetics of nitrate, and the accompanying anions sulfate and bicarbonate were investigated with three synthetic groundwater solutions. The effects of the water quality and of the anion exchange membrane type (Selemion AMV, Neosepta AMX, and Fumasep FAB) were examined using a Donnan dialyzer. It was found that water quality had only negligible effect on nitrate and sulfate transport through the AMV membrane. This was indicated by similar concentration decays of these anions with time as well as by comparable mass transfer coefficients obtained in the three water qualities tested. Additionally, very close nitrate and sulfate removal rates were obtained with the AMV and AMX membranes. Bicarbonate transport was the least efficient compared to the nitrate and sulfate. It was strongly impacted by both the water quality and the membrane type. The bicarbonate transport increased with augmentation of its molar fraction relative to the total anions in the solution. Overall, the results points to the high potential of Donnan dialysis for treating contaminated nitrate groundwaters.

Quaternized graphene oxide modified PVA-QPEI membranes with excellent selectivity for alkali recovery through electrodialysis

Composite anion exchanges membranes are prepared by incorporating quaternized graphene oxide (QGO) within poly(vinyl alcohol) (PVA) or the mixture of PVA and quaternized polyethyleneimine (QPEI), followed by cross-linking with formaldehyde. The PVA-QGO series of membranes have low ion exchange capacities (IECs) of 0.10–0.37mmol/g and low water uptakes (WR) of 16.1%–22.0%, leading to high area resistances (>60Ωcm2). The PVA-QPEI-QGO series of membranes show much lower area resistances of 2.47–6.04Ωcm2, which is ascribed to the improved IECs (0.86–1.37mmol/g) and WR (46.8%–71.4%). Both series of membranes show higher alkali resistance than commercial membrane AMV. Their weight losses are in the range of 0.5%–8.9% after immersion in 60°C 2mol/L NaOH alkaline solution for 32 days, while the value of AMV membrane is 19.2%. When utilized for electrodialysis (ED) application to recover NaOH from NaOH/Na2WO4 mixture, the prepared membranes exhibit high selectivity, as evidenced by the low leakage ratio of Na2WO4. The leakage ratio of the optimized composite membrane to WO42− is only 5.1%, while the leakage ratio of AMV membrane is up to 61.4%. To explore this reason, the composite membranes are selected for the ED separation of monovalent ions. The separation efficiency (S) of the optimized membrane is 83.9%, which is similar to the value of commercial anion selective membrane NEOSEPTA® ACS (88.7%), confirming further the selectivity of the composite membranes.

Gypsum scaling of anion exchange membranes in electrodialysis

Scaling of homogeneous AMV and heterogeneous MA-40 anion exchange membranes (AEM) by gypsum (CaSO4·2H2O) was investigated during electrodialysis (ED) at constant current conditions. The effects of scale development on counter-ion flux, electrical potential difference across the scaled-membrane, the overall electrical stack resistance and the extent of water splitting, were studied as a function of the current density and flow velocity of the solution in the relevant compartments.It was found that scale grows mainly in the interior of MA-40 while for the homogeneous AMV membrane scale grows mainly on the membrane surface facing the concentrate compartment. This implies that the homogeneous membrane could be more easily cleaned and its properties almost fully retained, compared with the case of the heterogeneous membrane where the internal scale was strongly attached to the internal matrix domains. These findings have important implications for the use of ED in the treatment of highly concentrated solutions and as part of a chain of treatment towards zero liquid discharge (ZLD).

Bipolar membrane electrodialysis for treatment of sodium acetate waste residue

Abstract Large amounts of solid waste residue containing high salinity and a series of organic impurities are produced during the manufacturing process of dithianon in insecticide factories, posing a severe environmental pollution problem. Here sodium acetate (CH 3 COONa) waste residue is firstly tested by diffusion dialysis (DD) to investigate the permeability of different commercial ion exchange membranes. Selemion CMV and AMV membranes show low permeability to the organic impurities of the waste residue, and hence are chosen for the following bipolar membrane electrodialysis (BMED) experiments to regenerate acid and base. The BMED firstly uses a BP-A-C-BP configuration to select an optimized current density of ∼50 mA/cm 2 . Afterwards, four membrane stack configurations are compared including BP-A-C-BP, C-BP-A-C, BP-C-BP and BP-A-BP. In consideration of the high current efficiency, low energy consumption, and high concentrations of the produced acid/base, C-BP-A-C is a favorable configuration. Finally, the addition of a strong acid 001 ∗ 7 type of cation-exchange resin into acid compartment can substantially decrease the voltage drop across the stack and reduce the energy consumption. The C-BP-A-C configuration at 50 mA/cm 2 can have a high output (0.491 mol/L CH 3 COOH and 0.556 mol/L NaOH), high current efficiency (87.7% for CH 3 COOH and 99.0% for NaOH), and a relatively low energy consumption (22.3 kW h/kg CH 3 COOH and 29.7 kW h/kg NaOH). Overall, this study illustrates the practical significance of BMED process for treating sodium acetate waste residue, including reducing soil and water pollution and producing valuable products in insecticide industries.

Kinetic modeling and selectivity of anion exchange in Donnan dialysis

The objective of this work was to compare selective sorption and transport behavior of a Selemion AMV membrane for different anions with a theoretically derived kinetic model describing the Donnan dialysis (DD) process. This analysis resulted in a suggested relation for the diffusivity of small ions through “nanochannels” of ion exchange membranes. Mass transfer through boundary layers and membrane diffusion were modeled on the basis of the Nernst–Planck equation by introducing constant diffusivity ratios between the exchanging counter ions. To indentify the kinetic and selectivity coefficients, DD batch experiments with sodium nitrate, sulfate or dihydrogen phosphate as feed electrolytes and sodium chloride as receiver electrolyte were conducted. The derived kinetic model simulated the measured concentration changes very precisely after fitting three concentration-independent parameters and the concentration-dependent permeability coefficient. The selectivity sequence was found to be nitrate>sulfate>dihydrogen phosphate>chloride, while this sequence is strongly connected to activity in solution and in the membrane. This influence was very significant for sulfate, which resulted in higher removal efficiency than expected. Regarding diffusivity the identified sequence was nitrate>sulfate>chloride>dihydrogen phosphate. These results led to a correlation that describes diffusivity of counter ions through nanochannels as a function of hydrated cross section area and valence.

Extended dynamic model for ion diffusion in all-vanadium redox flow battery including the effects of temperature and bulk electrolyte transfer

As with all redox flow batteries, the Vanadium Redox flow Battery (VRB) can suffer from capacity loss as the vanadium ions diffuse at different rates leading to a build-up on one half-cell and dilution on the other. In this paper an extended dynamic model of the vanadium ion transfer is developed including the effect of temperature and bulk electrolyte transfer. The model is used to simulate capacity decay for a range of different ion exchange membranes that are being used in the VRB. The simulations show that Selemion CMV and Nafion 115 membranes have similar behavior where the impact of temperature on capacity loss is highest within the first 100 cycles. The results for Selemion AMV membrane however are seen to be very different where the capacity loss at different temperatures observed to increase linearly with increasing charging/discharging cycles. The model is made more comprehensive by including the effect of bulk electrolyte transfer. A volume change of 19% is observed in each half-cell for Nafion 115 membrane based on the simulation parameters. The effect of this change in volume directly affects concentration, and the characteristics are analyzed for each vanadium species as well as the overall concentration in the half-cells.

Ion-exchange membrane processes for Br− and BrO3− ion removal from water and for recovery of salt from waste solution

The applicability of Donnan dialysis with an anion-exchange membrane for bromide and bromate ion removal was studied. The rate of bromide, bromates and associated ion (HCO3−, SO42−) removal with the use of Selemion AMV and Neosepta ACS membranes at different salt concentrations in the receiver was analyzed. The process of anion exchange through the Neosepta ACS membrane allows effective bromides removal (90%), at a relatively low salt concentration in the receiving solution (100mM NaCl). In order to achieve a similar effect of bromide removal by using the Selemion AMV membrane (91%) three times higher salt concentration in the receiver is required.Moreover, the potential of electrodialysis to recover NaCl from waste receiving solution after the Donnan dialysis and the usefulness of recovered solution to remove bromides and bromates was examinated. The best results of the process, i.e. required salt concentration in the concentrate (100mM NaCl), and possible minimum contamination of the ballast ions (Br− or BrO3− and HCO3− and SO42−) were obtained at a current density of 50A/m2. Depending on a modification method of the recovered salt solution, it was obtained from 61 to 78% removal of bromides and from 79 to 86% removal of bromates.

Contribution to the study of properties of Selemion AMV anion exchange membranes in acidic media

Besides the strongly basic quaternary amines as well-known in the literature, the presence of pyridine groups at the interface of Selemion AMV membrane was evidenced by X-ray Photoelectron Spectroscopy and Infrared techniques for the first time. Quantity of the weak base functionalities was determined via the exceptional sorption properties of sulfuric acid in the membrane. This work also offered a simple way for quantitative analysis of both the sorbed acid content and the weak amine amount together. Increase in ion exchange capacity of the membrane in acidic solution due to the protonation reaction of these weakly basic groups altered the conformation and hydrophilicity of the functionalized polyelectrolyte phase which, in turn, affected the content of sorbed non-exchange acid as well as the volume fraction of the interstitial solution within the membrane. On the basis of the obtained results in this work and those recently published by the other research groups, our suggestion is the dominant role of the gel phase toward the overall membrane properties. Full membrane characterization also led to evaluate the chronopotentiometric curves of the AMV in H2SO4 and HCl solutions which show a typical behavior of homogeneous ion exchange membranes. Only sulfate anions are responsible for the electric transport inside the membrane in contact with 0.1M sulfuric acid notwithstanding the fact that the bulk solution is mainly occupied by bisulfate counter-ions (about 90%) and the membrane contains both quaternary amines and pyridinium cations as fixed ionic groups.

Interplay between the Structure and Relaxations in Selemion AMV Hydroxide Conducting Membranes for AEMFC Applications

Selemion AMV was studied to examine the relationship between the membrane chemical structure and its properties. The structure of AMV consists of two components: a functionalized polystyrene copolymer containing the ion-exchange moieties and PVC which is likely blended with copolymer. The PVC is primarily responsible for the mechanical properties of the membrane but seems to undergo degradation during the anion-exchange process that leads to a reduction of the storage modulus. The functionalized polystyrene copolymer with the ion-exchange groups is primarily responsible for the electrical properties of the membrane. The AMV and AMVOH membranes exhibited conductivities of 2 and 7 mS cm–1 at 25 °C, respectively. The membrane exhibited Arrhenius behavior in all conditions that suggests the dynamics of the membrane are not significantly involved in the mechanism of long-range conduction. The AMVOH membrane has two predominant pathways of charge exchange through the membrane: one through the bulk of the hydrop...

Donnan dialysis and electrodialysis as viable options for removing bromates from natural water

Donnan dialysis with an anion-exchange membrane and electrodialysis were used for removing bromate ions from natural water. Donnan dialysis with the Selemion AMV membrane provided total bromate removal from water containing 50μg BrO3−/L, at a salt concentration in the receiver of 100mM NaCl. The exchange of bromates for chloride ions was concomitant with the exchange of associated anions: sulfates (93% efficiency) and bicarbonates (73% efficiency). Donnan dialysis with the Neosepta ACS membrane (which is characterized by a compact surface structure) also provided total removal of bromates, but the efficiency with which SO42− and HCO3− were exchanged for chloride ions was far below that achieved with Selemion AMV (3% and 47%, respectively). Electrodialysis with standard ion-exchange membranes, Neosepta AMX/CMX, was less efficient at removing bromates (83%), but was able to reduce their concentrations in the treated water (8.8μg/L) to a level lower than the maximum admissible value for potable water (10μg/L). The efficiency of bromate removal by electrodialysis can be enhanced using the mono-anion-selective membrane Neosepta ACS, which augments the extent of removal to 94%, the concentrations of bromates in the treated water being as low as 3.3μg/L.

Bromate removal in the ion-exchange process

To remove bromates from water, use was made of anion exchange in the process of Donnan dialysis conducted with an anion-exchange membrane. Under such conditions, the removal of bromates from a one-component solution was found to be very high (more than 90%). It was observed that the presence of accompanying anions (NO 3 − and HCO 3 −), whose concentrations were by several orders of magnitude higher than the concentrations of bromates, brought about a decrease in the rate and efficiency of bromate removal from the feed. In the process with the Selemion AMV membrane the removal of bromates amounted to approximately 84% at a salt concentration of 300 mM NaCl in the receiver. Anion exchange in Donnan dialysis with Neosepta AFN (a membrane characterized by a high ion-exchange capacity and a high water content) proceeded at a faster rate and was found to be more efficient only with respect to the ions that dominated in the feed, i.e. nitrates and bicarbonates. In this process the removal of BrO 3 − ions was less efficient than in the process conducted with the Selemion AMV membrane, and failed to exceed 70%.

On the structure–properties relationship of the AMV anion exchange membrane

Important parameters such as ion exchange capacity, conductivity, permselectivity, quantity of sorbed electrolyte and water uptake of the Selemion AMV anion exchange membrane conditioned in KCl and NaCl solutions were determined in order to assess the applicability of the two-phase model of structure microheterogeneity to this case. In general, a good consistency between the experimental results and the theoretical approach was obtained. Electrical conductivity measurements allowed evaluating the volume fractions of two distinct internal phases inside the membrane. Aside from the chronopotentiometric behaviour of the AMV membrane, SEM and XPS techniques contributed to provide a better description of the overall membrane homogeneity. Influence of co-ions in relation with water uptakes on the conductivity and permselectivity of the studied membrane has been shown. An existence of partition equilibrium between the electrolytes sorbed in the membrane and the external solution confirmed in this work should be introduced within the microheterogeneous model.

Permselectivity and microstructure of anion exchange membranes

The water content, the ion exchange capacity, the transport number of counter-ion of the AMV and AMX anion exchange membranes were determined. The two-phase model (gel phase and interstitial phase) of structure microheterogeneity was validated by means of conductivity measurements. The chronopotentiometric results allowed us to affirm the overall surface homogeneity of the membranes. According to the two-phase model, the influence of the gel phase and the interstitial phase on the membrane permselectivity was discussed in detail. Majorities of co-ions exist in the interstitial phase, thus they have no influence on the transport of counter-ions in the gel phase. The determination of the KCl amount sorbed in the interstitial phase confirmed the existence of partition equilibrium between the interstitial phase and the external solution. Such partition equilibrium can be considered within the microheterogeneous model in order to represent the internal structure of the electromembranes.

Transport of zinc complexes through an anion exchange membrane

The transport of zinc complexes ions through an anion exchange membrane was evaluated by the treatment of solutions with and without cyanide. The ionic transport was analyzed as a function of the applied current density and of the cyanide and hydroxyl concentration. Experimental results showed that the ionic transfer in electrodialysis was mainly affected by concentration. There is an ideal molar relationship among the concentration of the cyanide ions, hydroxyl and zinc ions, in solution, in which the zinc transport is maximized. For values above or below this, the transport decreases. Zinc extraction from solution containing CN − was more effective when the current density of 29 mA.cm −2 was applied. The current–voltage curves (CVC) of the anion exchange membrane show that the electrical resistance of the AMV membrane increases with the presence of the zinc–cyanide complex in the solution.

Multicomponent absorption of anions in commercial anion-exchange membranes

The equilibrium uptake of aqueous NaCl–NaBr and NaCl–NaNO 3 mixtures into Neosepta ® AMX and Selemion ® AMV anion-exchange membranes was measured experimentally and modeled theoretically, where the total external salt concentration was fixed at 0.1 M. The model, which considered the membrane microstructure as an array of cylindrical pores of identical radius and included electrostatic interactions and ion hydration effects, accurately predicted anion uptake in the membranes. During competitive uptake, the anion with the larger hard-sphere radius was preferentially absorbed, with an observed and computed selectivity trend of NO 3 − > Br − > Cl −. By matching experimental data to the model, the average radius of pores in water-equilibrated membranes was found to be 3.3 nm (AMX) and 2.4 nm (AMV), indicating that an AMV membrane (1.98 mmol/g IEC) contains a greater number of smaller pores as compared to AMX (1.35 mmol/g IEC). The calculated pore-wall charge density in the two membranes was nearly the same. The NO 3 −/Cl − uptake selectivity was greater than that for Br −/Cl − in both membranes, but the selectivity for a given anion pair was effectively the same for the two membranes at a given external solution composition. This result was explained by model calculations which showed that anion uptake selectivity was essentially independent of pore radius (for pores in the 1.5–4.0 nm range) and a strong function of the fixed-charge site concentration on the pore wall.

Separation of monovalent, divalent and trivalent ions from wastewater at various operating conditions using electrodialysis

The effect of influential factors on separation of monovalent (Na +), divalent (Cu 2+, Zn 2+, Pb 2+) and trivalent (Cr 3+) ions from wastewater was investigated using AMV and CMV ion-exchange membranes. Taguchi experimental design was used to plan a minimum number of experiments. A L 9 orthogonal array (four factors in three levels) was employed to evaluate effect of concentration (100, 500, 1000 ppm), temperature (25, 40, 60°C), flow rate (0.07, 0.7, 1.2 mL/s) and voltage (10, 20, 30 V) on separation percent of the individual ions in the solution. The results show that increasing concentration, voltage and temperature improves cell performance; however, the separation percent decreases with increasing flow rate. At concentrations of more than 500 ppm, dependence of separation percent on concentration diminishes. The optimum levels of influential factors, determined for all ions are: concentration 1000 ppm, temperature 60°C, flow rate 0.07 mL/s and voltage 30 V. It was found that performance of an electrodialysis cell is almost independent of the type of ions but strongly depends on the operating conditions and cell structure. It was also found that separation percent of monovalent ions is larger than divalent and trivalent ions (S Cr<S Cu, S Zn, S Pb<S Na). For ions of similar valence, separation percent was indicated to be restricted by molecular weight and electrochemical activation energy of the ions (S Pb<S Cu<S Zn).

Cost effective electrodialytic seawater desalination

The share of electrodialysis in seawater desalination is very small in contrast to reverse osmosis. It is stated that ED may compete with RO in the range of feed water salinity up to 8–10 g/L only because ED desalination cost is proportional to the amount of salt, which must be carried through the membrane. It is assumed in the papers comparing RO and ED that exergy loss in RO is equal to 0.983 while in ED to 12.87 kWh/m 3 in the process of seawater desalination. The cited results were however achieved assuming 35 atm excess pressure in RO and 0.8 V excess voltage in an electrodialysis stack. Diminishing the aforementioned ΔP value would indeed result in a decrease in RO flux and, as a consequence, an increase in desalination costs. The voltage drop in ED may be however diminished by applying low-resistance membranes and decreasing an intermembrane distance in an ED stack. Electrodialytic desalination of seawater was investigated in a laboratory using ED stack (developed by the author) equipped with 0.19 mm spacer. The pressure drop vs. linear velocity in the ED channel is small because of a special shape of a spacer net. Asahi Glass CMV and AMV membranes were applied. Seawater was desalinated in a cascade of two electrodialyzers at current density 300–600 A/m 2 in the first stage and 300 A/m 2 in the second. The total energy consumption estimated for industrial plant was equal to 6.6–8.7 kWh/m 3 of desalinated water (TDS 0.45 g/L) depending on the first stage current density. The desalinated water cost was equal to 1.05 $/m 3 assuming 0.06 $/kWh.

Water transport study across commercial ion exchange membranes in the vanadium redox flow battery

The water transfer behaviour of Selemion CMV, AMV and DMV membranes (Asahi Glass, Japan) has been studied in the vanadium redox cell, as was the water transfer across Nafion 117 membrane (E.I. Du Pont, USA). The earlier water transport studies of a variety of commercial ion exchange membranes and non-ionic separators in the vanadium redox cell have shown that the net water transport through anion exchange membranes and non-ionic separators in the vanadium redox cell is from the positive half cell (+ve) to the negative half cell (−ve), while for cation exchange membranes the net water transport is in the opposite direction. In the present study, it was found that a significant amount of water is transferred across cation exchange membranes from the −ve vanadium half cell electrolyte to the +ve vanadium half cell electrolyte by the hydration shells of V 2+ and V 3+ ions which carry a large amount of water and can easily permeate through cation exchange membranes due to their relatively high charge numbers. The net amount of water of hydration which is transferred across anion exchange membranes from the −ve half cell electrolyte, however, is almost equal to the net amount of water of hydration which is transferred from the +ve half cell electrolyte. Thus, the net amount of water which is transferred across anion exchange membranes is in the same direction as the osmotic water transfer.