Type Of Cation-exchange Membrane Research Articles

A novel porous asymmetric cation exchange membrane with thin selective layer for efficient electrodialysis desalination

Ion exchange membranes (IEMs) are widely used in various electrochemical fields. Generally, identifying a solution for the trade-off between ion conductivity and dimensional stability is crucial for the further development of IEMs in the electrodialysis (ED) process. This study aimed to prepare a novel type of cation exchange membrane for electrodialysis desalination. Different from the previous cation exchange membranes with the thick and dense cross-section structure, the as-prepared asymmetric composite membranes in the present work composed of a thin and dense skin layer and a porous support layer via the pore-filling process of the skin layer of the porous poly (ether sulfone) (PES) membrane. Benefiting from such structural features, effective ion transport and dimensional stability were simultaneously achieved in the case of low ion exchange capacity. Ultimately, the optimal sulfonated poly (ether sulfone)-poly (ether sulfone) (SPES-PES) composite membrane simultaneously achieved ion transport enhancement, low swelling rate at 80 °C, and better mechanical stability compared to pure sulfonated poly (ether sulfone) (SPES) membranes. When applied to ED, the prepared 40 %SPES-PES membrane exhibited more excellent desalination performance (91.9%), higher current efficiency (127.5%), and lower energy loss (5.55 Kw·h·kg−1) compared to commercial membrane.

Transport and co‐transport of carboxylate ions and alcohols in cation exchange membranes

AbstractUnderstanding multi‐component transport behavior through hydrated dense membranes is of interest for numerous applications. For the particular case of photoelectrochemical CO2 reduction cells (PEC‐CRC), it is important to understand the multi‐component transport behavior of CO2 electrochemical reduction products including mobile carboxylates (formate and acetate) and alcohols (methanol and ethanol) in the ion exchange membranes as one role of the membrane in these devices is to minimize the permeation of these CO2 reduction products to the anolyte as they often oxidize back to CO2. Cation exchange membranes (CEM) are promising candidates for such devices as they act to minimize the permeation of mobile anions, such as carboxylates. However, the design of new CEMs is necessary as the permeation of carboxylates often increases in co‐permeation with alcohols. Here, we investigate the transport behavior of carboxylates and alcohols in two types of CEMs (1) a crosslinked CEM was prepared by free‐radical copolymerization of a sulfonated monomer (AMPS) with a crosslinker (PEGDA), and (2) Nafion® 117. We observe an increase in both PEGDA‐AMPS and Nafion® 117 diffusivities to carboxylates in co‐diffusion with alcohols. We attribute this behavior to charge screening by co‐diffusing alcohol that reduces the electrostatic repulsion between bound sulfonates and mobile carboxylates.

Combining Manning's theory and the ionic conductivity experimental approach to characterize selectivity of cation exchange membranes

The transport selectivity of different cations through cation exchange membranes (CEMs) could be estimated with the partitioning selectivity factor (Kji) and the cation mobility ratio in the membrane (uim/ujm), which in turn can be related to corresponding membrane conductivity and dimensional swelling ratio data [Journal of Membrane Science, 2020, 597, 117645]. This method has been validated in two hydrocarbon polymer-based CEMs, and the obtained K+/Na+ selectivity equals to the one obtained with conventional electrodialysis (ED) method. However, the K+/Na+ selectivity of perfluorosulfonic acid (PFSA) membranes, and the bi-/monovalent cation (Mg2+/Na+) selectivity of all three types of CEMs estimated with this ionic conductivity experimental approach deviate noticeably from corresponding values obtained with ED. In this work, it is proved that this deviation is partly due to the simplification of cation activity coefficients in the membrane. Here, the cation activity coefficients in three types of CEMs are calculated according to Manning's counter-ion condensation model. In this model, the Manning parameter (ξ) characterizing the dimensionless linear charge density is determined by the average distance between two adjacent fixed sulfonate groups (b) and the permittivity of hydrated membranes (ε). In hydrocarbon polymer-based CEMs, the average distance between fixed sulfonate groups can be estimated by assuming homogeneous distribution of the fixed groups, while in PFSA membranes three representative structure models are employed to estimate this average distance. After accounting for the cation activity coefficients in the membrane, the Mg2+/Na+ cation transport selectivity obtained with the ionic conductivity experimental approach gets closer to, but is still smaller than the selectivity obtained with the ED method. This work shows the importance of cation activity coefficients in the membrane phase in interpreting the membrane transport properties, and complements the proposed conductivity approach to characterize the counter-ion selectivity of ion exchange membranes.

Electrochemical removal of sulfide ions and recovery of sulfur from sulfide ions containing wastes

In this work a two-compartment galvanic cell with two graphite rod electrodes and two types of cation exchange membranes: namely the Nafion membrane and synthetic fabric membrane is tested in treating sulfide containing wastes and recovery of elemental sulfur. The cell reactions are sulfide oxidation at the anode and chromium (VI) reduction at the cathode. The effect of different parameters such as external resistance, initial concentration of K2Cr2O7 solution, H2SO4 concentration, and initial concentration of Na2S, the pH of the solution, NaCl concentration, and temperature of the solution is investigated. The cell performance as a reactor and as an energy converter is expressed in terms of % sulfide removal and current-voltage plots, respectively. Depending on the effects of the aforementioned factors, the optimal conditions that give the highest performance were determined, and then the cell was tested on real wastes from refinery processing at those conditions. The cell showed high selectivity in sulfide removal and sulfur recovery with almost no interference with other contaminants.

Ion mobility and partition determine the counter-ion selectivity of ion exchange membranes

Ion (perm)selectivity and conductivity are the two essential properties of an ion exchange membrane, yet no quantitative relation between them has been suggested. Here, the selectivity between two different counter-ions is correlated to the membrane conductivity. We show that the counter-ion selectivity measured by conventional electrodialysis (ED) can be expressed by the product of: (a) the mobility ratio between two different counter-ions in the membrane and (b) their partition coefficient between the solution and the membrane. This is reminiscent of the classical solution-diffusion model. Via the counter-ion mobility in the membrane, the selectivity could be simply expressed with the membrane conductivity and dimensional swelling degree. This correlation is validated experimentally for the ion selectivity of K+/Na+ in two commercial hydrocarbon-based cation exchange membranes (CEMs). For K+/Na+ in a perfluorosulfonic CEM, and for Mg2+/Na+ in all the three types of CEMs, the correlation could predict the counter-ion partition very well; but there is an underestimation of the K+/Na+ and Mg2+/Na+ mobility ratios. This work offers a convenient method to decouple experimentally the effect of partition and mobility in controlling the membrane selectivity, and also proposes a new perspective to study the selectivity as well as conductivity of ion exchange membranes.

Removal profile of sulfate ion from mix ion solution with different type and configuration of anion exchange membrane in elctrodialysis

Electrodialysis (ED) is a potential option that can be used for treatment of groundwater or surface water containing ions or mineral salts in excess of the limits for health. In this reseach, electrodialysis was used to study the elimination of sulfate and its concurrent ions (nitrate, fluoride) from groundwater by using of cation exchange membrane and anion exchange membrane whose ion exchange capacity was different. The effect of the two different membrane types, the type of electrode solution, and the form of configuration of the cation exchange membrane and anion exchange membranes on the rate and removal efficiency of the ions were investigated. The performance of the ED process included the reduction profile of the ion concentrations in the diluted tank and the removal efficiency. The results showed that the type of cation exchange membrane and anion exchange membrane, and the membrane configuration are influenced how quickly ion removal occured by ED. Generally, the ion removal efficiency was greater than 90% for all investigated variables.

Carbon dioxide recovery from carbonate solutions using bipolar membrane electrodialysis

Process design and cost estimation were conducted for CO2 recovery by liquid absorption with alkaline solution, coupled with bipolar membrane electrodialysis for CO2 gas separation and alkaline solution regeneration. The electrodialysis performances and power consumption for CO2 recovery and alkaline solution regeneration were examined using laboratory-scale electrodialysis equipment under various conditions; degree of CO2 absorption, CO2 recovery ratio, alkaline concentration, and type of cation exchange membrane. The total cost of CO2 recovery was estimated for the treatment of CO2 emitted from a 400MW coal-fired thermal power plant. The minimum cost for the optimum condition was about US$180 per ton-CO2 removed, which is higher than that for the conventional process using amine absorption and thermal desorption. However, a sensitivity analysis indicates that the overall cost could be significantly reduced if the cost of membranes was reduced.

Estimation of effect of amino acid’s sorption on surface state of ion-exchange membranes using atomic-force microscopy data

Atomic-force microscopy is used to study the surface morphology of different types of cationexchange membranes (MF-4SK homogeneous and MK-40 heterogeneous) in hydrogen and lysine forms. Irregularities of various scales are visualized on the membrane surface. The differences in the surface structure of heterogeneous and homogeneous membranes are found and the features of the effect of sorption of a lysine amino acid on the supramolecular structure of the ion-exchange membranes under study are revealed. The absorption of amino acids by a heterogeneous membrane leads to a decrease in the amount and size of both large defects and nanopores; the surface becomes more homogeneous. In the case of a homogeneous perfluorinated membrane, on the contrary, the sorption of the amino acid makes the surface more heterogeneous due to the formation of supramolecular aggregates.

Recovery of Zn (II) from its EDTA complexes by electro-membrane process

Factors affecting the efficiency of electrochemical recovery of Zn (II) from its ethylenediaminetetraacetic acid (EDTA) complexes were systematically examined using three types of cation-exchange membranes in a two compartment electrolysis cell. In these experiments, the catholyte contained an equimolar amount of Zn (II) and EDTA, and the anolyte contained 0.1 M NaNO3. The platinium and stainless steel were used as an anode and a cathode, respectively. The effect of current densities, metal concentration, the type of the cation-exchange membrane on the recovery of metals were determined. It was found that recovery of Zn (II) increased with increase of current density, concentration of catholyte solution, concentration ratio between metal—chelate and changed with the type of membrane in CMB>CMS>CMX order. The obtained numerical results showed that electrodeposition seems to be applicable method for the recovery of metals under appropriate conditions.

Salt splitting with cation-exchange membranes

The regeneration of acid and base from different salt forms of potassium by electrodialysis (ED) method was investigated in a two-compartment membrane electrolysis cell. Three types of commercial cation-exchange membranes (CEMs) were used to recover acids from solutions containing salt forms of metals. In the experiments, base solutions were used as a catholyte and different salts of potassium were used as an anolyte. The effects of flow rate, current density, initial concentrations of salt and base solutions, the type of salt solution and the type of the cation-exchange membrane on the recovery ratio of acids were investigated. The results obtained show that electrodialysis seems to be an applicable method for the recovery of acids at suitable conditions.

Donnan dialysis for hardness removal from water before electrodialytic desalination

In the paper the authors assessed usefulness of Donnan dialysis with cation-exchange membranes for the removal of troublesome calcium and magnesium cations before electrodialytic water desalination. The rate and efficiency of cation exchange were examined with the use of two types of cation-exchange membranes: Neosepta CMX and Selemion CMV. The authors analyzed the influence of some process parameters (salt concentration in the receiver and stream volume ratio) on the ion exchange. It was observed that both membranes examined assured similar effect of the Ca 2+ and Mg 2+ removal, i.e. from 80 to 88% of removal, with the NaCl concentration in the receiver 200 mmol/dm 3 and the stream volume ratio 4:1. However, ionic fluxes for the Selemion CMV membrane were higher by about 30% than those for the Neosepta CMX membrane — and that significantly reduces the time of the process. In the second part of the paper, the authors compared the results of electrodialysis of a raw two-component solution and of a solution after cation exchange. It was concluded that due to the change of ionic composition of the solution, electrodialysis can be conducted at a higher current density, and the salt removal rate is more than 20% higher (the salt fluxes from the raw solution and from the solution after Donnan dialysis are, respectively, 0.421 and 0.512 eq/m 2h, at a current density of 30 A/m 2). The authors also observed a positive effect of the changed ionic composition of the solution on the energy consumption for the ion transport: the removal of a given amount of salt requires up to three times less energy than in the case of the raw solution.

プラズマグラフト重合法を用いる新規なＣＯ２高選択的促進輸送膜の作製と透過機構の解析に関する研究

New types of cation-exchange membranes were prepared by grafting acrylic acid to substrates such as microporous polyethylene and homogeneous poly [1- (trimethylsilyl) -1-propyne] by the use of plasma graft polymerization technique. Ethylenediamine was immobilized by the electrostatic force in the ion exchange membranes as the carrier of CO2 and the facilitated transport of CO2 through the grafted membranes was studied. The obtained membrane showed remarkably high selectivity of CO2 over N2 and high CO2 permeance. The newly prepared membrane was also stable. Membrane having tertiary amine group which has an affinity for CO2, was also prepared by plasma grafting of 2- (N, N-dimethyl) aminoethyl methacrylate. It was suggested that the membrane acts as a fixed reaction site membrane under the water-containing condition. Furthermore, an approximate solution on the facilitated transport of CO2 through a liquid membrane containing primary or secondary amine has been developed. The effect of chemical equilibrium constant on CO2 permeance was quantitatively clarified by the simulation based on this approximate solution.

Transport of metal ions through cation exchange membranes containing episulfide (or thiol) groups and/or triethylenetetramine side chains

Two types of cation exchange membranes bearing sulfonic acid groups were prepared. One membrane (EA membrane), having episulfide groups beside sulfonic acid groups, was prepared with 2,3-epithiopropylmethacrylate (ETMA)-2-acrylamide-2-methylpropane sulfonic acid (AMPS) copolymers and the another one (EA-TTA membrane) having thiol groups, triethylenetetramide (TTA) side chains, and carboxyl groups beside sulfonic acid groups was prepared by treating EA membranes with TTA in a water-1,4-dioxane mixture solution. The transport of metal ions such as K +, Li +, Ag +, Ca 2+, and Cu 2+ through the membranes was investigated. The transport rate of Ag + through the EA membranes was considerably lower than those of other metal ions from solution. High selective transport of Ag + from mixed solution could be observed using the EA and EA-TTA membranes. Transport of Cu 2+ and Ca 2+ through the EA-TTA membrane was depressed by an electrostatic repulsion between ammonium groups in the membranes and metal ions when HNO 3 or sodium ethylenediamine tetraacetate was used as receiving solution.

Transport competition between monovalent and divalent cations through cation-exchange membranes. Exchange isotherms and kinetic concepts

Separation of Ca 2+ or Cu 2+ ions from binary solutions with Na + or protons by electrotransport through strong cation-exchange membranes (CEM) has been studied in the case where no sorbed species is present within the membrane material. The study was achieved on two conventional CEM and two CEM manufactured to be preferentially permselective to monovalent cations. Without any applied driving force, the exchange isotherms exhibit no significant increase in permselectivity for the modified CEM. Divalent cations are preferred by the membranes due to their higher electrostatic attraction with the oppositely fixed charged exchange sites. When the CEM are submitted to an electrical field, radiotracer measurements exhibit the difference of permselectivity of these two types of CEM. The apparent rate constants of the ionic interfacial transfer were calculated on the basis of unidirectional fluxes and concentration profiles of cations within the unstirred layer. The values of these kinetic constants were always greater for monovalent than for divalent cations but the difference was more important for modified membranes. Lastly, comparison between the potential profiles showed that the potential decrease within the depleted unstirred layer was more important for the solutions less concentrated in protons.

Development of a new functional cation-exchange membrane and its application to facilitated transport of CO 2

A new type of cation-exchange membrane was prepared by grafting acrylic acid onto a microporous polyethylene membrane by use of plasma-grafted polymerization technique. The facilitated transport of CO 2 through the plasma-grafted membrane containing ethjylenediamine was studied. The obtained membrane showed remarkably high CO 2 permeability and selectivity of CO 2 over N 2. When the CO 2 partial pressure in the feed gas was 0.047 atm, the CO 2 permeability and the selectivity obtained were 1.0×10 −4 cm 3 cm −2 s −1 cmHg −1 and 4700, respectively. These efficiencies were much higher than those of conventional polymer membranes, and were also superior to efficiencies of ion-exchange membranes containing a carrier, reported so far. These excellent results are probably attributable to the high ion-exchange capacity and the high water content. The newly prepared membrane was stable.

Facilitated transport of ethene across polyelectrolyte gels with silver ions as a carrier

Three types of cation exchange membranes loaded with Ag + ion are used to study the selective transport of ethene gas in ethene/methane gas mixtures across the membranes. The Ag + ions act as a carrier for selective transport of ethene. The carrier concentration is varied by two methods: (a) partial substitution of Ag + ions by H + ions. The H + ions do not act as a carrier. (b) Introduction of coions (NO − 3) and the corresponding counter-ions (Ag +) into the membrane phase by treatment of the membranes with concentrated aqueous AgNO 3 solutions. The functional relation between the rate of transport of ethene and the carrier concentration reflects structural differences between the membrane matrices.

Electrodialysis for clean-up of strongly alkaline samples in ion chromatography

An electrodialysis method is described for the off-line neutralization of strongly alkaline samples containing trace levels of common inorganic anions. This method uses an electrodialysis cell comprising three compartments separated from each other by cation-exchange membranes. These compartments comprise an anode compartment housing, a platinum wire anode and 10 ml of a suitable hydrogen ion donating medium, a sample compartment which contains 1 ml of the alkaline sample, and a cathode compartment housing a platinum wire cathode and a dilute solution of sodium hydroxide. During electrodialysis at either constant applied current or constant applied power, hydrogen ions from the anode compartment displace sodium ions from the sample, thereby effecting neutralization. Experimental parameters, such as the magnitude of the applied current or power, the type of cation-exchange membrane used and the design of the cell have been studied and optimum results were obtained using a Neosepta CM-2 membrane, of area 616 mm 2 supported between two perspex discs, with an applied current of 150 mA or applied power of 3 W. Under these conditions, a 1 ml sample of 1 M sodium hydroxide could be neutralized in 11 min. The most effective hydrogen ion donating medium consisted of a 2:1 (w/v) slurry of BioRad AG 50W-X8 (200–400 mesh, H + form) cation-exchange resin in 1 m M octanesulfonic acid. Recoveries of solute anions (3–10 μg/ml) from the dialysed solution were close to quantitative, except for fluoride and nitrite, which gave recoveries of less than 60%. It is suggested that low recoveries for these ions are due to formation of neutral, protonated species within the membrane with subsequent loss by diffusion.