Composite Cation Exchange Membranes Research Articles

Development and analysis of the physical and electrochemical characteristics of a nano titanium (IV) tungstomolybdate supported on polyethersulfone composite cation exchange membrane

In this study, a series of novel composite membranes were synthesized utilizing polyethersulfone (PES), sulfonated polyethersulfone (SPES) as base polymer and titanium tungstomolybdate (TWM) as an inorganic ion exchange resin. The membranes were fabricated through the solution casting technique. The composite membranes exhibited enhanced thermal and chemical stability, as well as improved oxidative stability. All the composite membranes demonstrated higher hydrophilicity, with the SPES-TWM composite membranes displaying the lowest contact angle of 65°. The composite membranes also displayed favorable water uptake (up to 26% for SPES-TWM) and lower methanol uptake (maximum 12% for SPES-TWM) and better mechanical stability (maximum of 40 MPa for SPES-TWM). The SPES-TWM composite membranes exhibited the maximum ion exchange capacity of 1.32 meq.g−1. The transport number of 0.95 was obtained for SPES-TWM, which is comparable to the Nafion-117 membrane. The proton conductivity of both membranes increased as the temperature increased. The maximum proton conductivity of 6.3 mScm−1 was observed for SPES-TWM at 60 °C.

Functionalized graphene oxide-modified sulfonated poly (2,6-dimethyl-1,4-phenylene oxide) based thermal-resistance anti-fouling bi-functional cation exchange membrane for electrodialytic desalination

We report a sustainable strategy for fabricating thermal-resistance anti-fouling cation exchange membrane (CEM), using sulfonated poly (2,6-dimethyl-1,4-phenylene oxide) (SPPO), and phosphorylated graphene oxide (FGO). The GO was phosphorylated, and different CEMs (3.0–7.0 % weight ratio of FGO) were prepared to investigate their electrodialysis (ED) performance. Structural features of SPPO-FGO composite CEMs such as ̴ 21.51 % degree of sulphonation (SPPO), bi-functional (-SO3H, and -PO3H2) nature, and balanced hydrophobic-hydrophilic segments, etc., were attributed for thermal-resistance and anti-fouling membrane nature of the membrane. The presence of FGO in the SPPO polymer matrix significantly improved mechanical, thermal, oxidative stabilities, ionic conductivity (κm), and counter-ion transport number (tm+). Suitable optimized SPPO-FGO/7 % (7.0 % of FGO) showed excellent physicochemical properties (14.1 % water uptake, 3.2 % swelling ratio, and 1.76 m eq./g ion exchange capacity), along with 10.92 × 10−2 S cm−1 conductivity, and 0.95 counter-ion transport number at 30 °C. Improved i-V curves and ED performance at 60 °C, showed relatively low energy consumption (0.72 k W hr/kg of NaCl removed), and high current efficiency (99.0 %) for SPPO-FGO/7 % CEM revealed, its potential candidature for electrodialytic water desalination. Further, CEM also avoids any significant deterioration in ED performance due to the presence of cationic, anionic and zwitterionic foulants.

Synthesis of potassium-zinc hexacyanoferrate and their SPEEK composite cation exchange membranes for selective recovery of cesium from aqueous system

Potassium-Zinc hexacyanoferrate adsorbent was prepared by precipitation method and further its composite membrane has been fabricated using sulphonated poly (ether ether ketone) (SPEEK) to investigate cesium (Cs+) recovery from aqueous media. The formation of desired adsorbent material was confirmed by Powder X-ray diffraction (PXRD) while chemical structure was assessed by Fourier-transform infrared spectroscopy (FT-IR). The BET surface area, pore volume and pore diameter found as 298.6 m2/g, 0.1034 cm3/g and 3.04 nm respectively calculated by Brunauer and Emmett and Teller (BET) surface area analyzer. The adsorbent synthesized was observed to work efficiently with maximum adsorption capacity of 54.64 mg Cs/g of adsorbent for Langmuir isotherm model. There was no effect of competing ion (Na+, K+, Mg2+, Ca2+) on adsorption performance during Cs+ removal. Cs+ recovery from the aqueous system in presence of 1000 ppm NaCl was performed using SPEEK composite membrane by electrodialysis. Observing the electrodialysis performance, composite membrane exhibited a high removal/recovery for Cs+ ions than Na+, K+, Mg2+ and Ca2+. The composite membrane exhibited a remarkable removal efficiency for Cs+ ion, which is 33.85 times larger than pristine SPEEK membrane. These results confirm composite membrane as promising candidate for the selective recovery/removal of cesium ions from aqueous solution in existence of intrusive ions and can effectively be applicable for industrial applications.

Precise Cation Separations with Composite Cation-Exchange Membranes: Role of Base Layer Properties.

Separation of specific ions from water could enable recovery and reuse of essential metals and nutrients, but established membrane technologies lack the high-precision selectivity needed to facilitate a circular resource economy. In this work, we investigate whether the cation/cation selectivity of a composite cation-exchange membrane (CEM), or a thin polymer selective layer on top of a CEM, may be limited by the mass transfer resistance of the underlying CEM. In our analysis, we utilize a layer-by-layer technique to modify CEMs with a thin polymer selective layer (∼50 nm) that has previously shown high selectivity toward copper over similarly sized metals. While these composite membranes have a CuCl2/MgCl2 selectivity up to 33 times larger than unmodified CEMs in diffusion dialysis, our estimates suggest that eliminating resistance from the underlying CEM could further increase selectivity twofold. In contrast, the CEM base layer has a smaller effect on the selectivity of these composite membranes in electrodialysis, although these effects could become more pronounced for ultrathin or highly conductive selective layers. Our results highlight that base layer resistance prevents selectivity factors from being comparable across diffusion dialysis and electrodialysis, and CEMs with low resistance are necessary for providing highly precise separations with composite CEMs.

Surface smoothening and formation of nano-channels improved mono-selectivity and antifouling property in TiO2 incorporated cation exchange membrane

Green liquor solution (GLS) is waste pollutant from pulp and paper mills. Causticization process is a common treatment method for GLS, which is energy intensive and environmentally unsafe, because of high operating cost, and solid waste generation. We reported synergetic effect of titanium dioxide nanoparticle (TiO2) incorporated sulfonated PEEK, on the performance cation exchange membrane (CEM), for producing NaOH from industrial GLS by electro-electroldiaysis (EED). Reported composite CEM was studied for morphology, physicochemical, electrochemical properties. The counter-ion transport number, stability and antifouling properties of CEM were significantly improved after the addition of TiO2 nanoparticles in the sulfonated PEEK membrane matrix. Two compartment EED cell (active membrane area: 66 cm2) was used to perform the experiments for producing NaOH using industrial GLS at 60 mA·cm−2 constant current density. The reported results shed light on production of NaOH along with prevention of sulfur scaling in treatment of wood based pulp and paper mills GLS stream. The modified membrane named SPK-T-5 (5 wt% of TiO2) by utilizing containing sulfonated polymer matrix outperforms an increasing trend of NaOH production along with notable sulfur antifouling. The obtained research outcomes are expected to be a valuable source for NaOH production with the aim of zero solid discharge practice for pulp and paper mills.

Concrete-structured Nafion@MXene/Cellulose acetate cation exchange membrane for reverse electrodialysis

In a situation facing the limitations of previous renewable energy systems, salinity gradient power (SGP), which is not affected by climate and time, can be a new alternative. SGP can generate electricity by salt concentration difference between two feeds without pollutant emission. One of the representative SGP systems is reverse electrodialysis (RED). An essential part of the RED system is the ion exchange membrane (IEM). However, the research on IEMs for RED, with low areal resistance and high permselectivity, is still lacking. This study proposes a cation exchange membrane (CEM) with engineering nanostructure and introducing new material. Nafion@MXene/Cellulose acetate (CA) composite CEM is fabricated by inspiration from the concrete structure of the building. The electrospun MXene/CA nanofiber is a framework, and the Nafion ionomer is a filler in structure. As a result, the Nafion@MXene/CA CEM shows better physical/electrochemical properties than the casted Nafion and layered membrane. In addition, the Nafion@MXene/CA CEM exhibits a higher power density (2.30 W m −2 ) in the RED system than the commercial membrane, casted Nafion, and layered membrane. High power generation through structural/material engineering. • The MXene/CA nanofiber acts as a framework, and the Nafion ionomer is a filler of the concrete-structured NMC CEM. • The MXene nanosheets improve the physical/electrochemical properties of the cellulose acetate nanofiber-based CEM. • The concrete-structured NMC is strong even if the thickness is reduced due to its unique structure. • High power density (2.30 W m −2 ) was obtained due to the thin membrane and the high permselectivity affected by MXene.

Caustic production from industrial green liquor using alkali resistant composite cation exchange membrane

Kraft paper industries perform causticization (NaOH production) by fresh lime (CaO) addition in green liquor (rich in sodium carbonate) resulting calcium carbonate (CaCO3) as precipitate, which is washed, dried and calcined at ~900 °C to regain CaO, making the process energy intensive and environmentally polluting. Current investigation reports electro-electrodialysis (EED) based conversion of green liquor to NaOH using alkali resistant composite membrane made from graphene oxide (GO) and SPK [sulfonated poly (ether ether ketone)]. Using optimized process parameters: current density (60 mA·cm−2), flow rate (2.0 L·h−1), 25 °C, and batch recirculation of 0.5 L of green liquor through EED set up (66 cm2), resulted 0.5 L (2.35 mol·L−1). Corresponding current efficiency and energy consumption estimates were ~67.9% and ~0.126 kW·h·mol−1 respectively. After thirty batches of experiment, the performance of NaOH production and its energy consumption remains unaltered. Performance in house membrane was compared with commercial (FKB-PK-130). Cost estimation based on lab-scale data for treatment of 50,000 L/day of green liquor through conventional and EED technique showed ~$2050 per day without solid waste generation and environmental pollution.

Porphyrin thin-film composite cation exchange membranes enable high retention of amino acids in electrodialysis

In order to improve the retention of amino acids in desalinating a saline stream using electrodialysis, a novel porphyrin-containing thin-film composite (TFC) cation exchange membrane was prepared by interfacial polymerization (IP) using tetraphenylporphinesulfonate (TPPS), m-phenylene diamine (MPD), and trimesoyl chloride. The separation of a single amino acid [Arginine (Arg), Lysine (Lys), Histidine (His), and Proline (Pro)] and the mixture of four from a NaCl solution was investigated. Results showed that sodium ions transported much faster than the amino acid ions due to its small molar mass and high mobility. Arg migrated much faster than Lys may attribute to its guanidine that increased the polarity of the ion, thus resulting in a higher loss degree of Arg (60%) than that of Lys (32%) in the single amino acid test. In the mixed amino acid test, a competition behavior between Arg and Lys limited their transport over membrane. The loss degree of Arg and Lys was reduced to 32.7% and 9.31% with porphyrin TFC membrane, which could be attributed to combination of the TFC dense layer and the strong electrical interaction between the charge-elevated membrane surface and the amino acids. The porphyrin TFC achieved a loss degree of total amino acids of 13.8%, which was much lower than that of pristine TFC membrane (20.2%) and based membrane (27.25%), respectively. These findings indicated that using porphyrin TFC membrane can efficiently separate salts and amino acids, and may also be beneficial for other membrane separation techniques.

Sulfonated poly (ether ether ketone) composite cation exchange membrane for NaOH production by electro-electrodialysis using agro-based paper mill green liquor

Causticizing process of pulp and paper mills, is highly energy intensive and environmentally unsafe. We report environmental friendly electro-electrodialysis (EED) process using in-house prepared cation exchange membranes (CEMs) for NaOH production from green liquor solution (GLS) of agro-based paper mills. Different composite CEMs with varied composition of sulfonated graphene oxide (SGO) incorporated sulfonated poly (ether ether ketone) (SPK) were synthesized. Best optimized CEM (SPK-3 with 3.0 wt% SGO loading) exhibited 1.75 mmol·g−1 cation exchange capacity, 32.01% water uptake, 11.41% swelling ratio, conductivity 0.037 S·cm−1, and 0.97 counter-ion transport number with high alkaline and thermo-mechanical stabilities. Industrial GLS was used for NaOH production by EED at 60 mA·cm−2current density. Optimized SPK-3 membrane produced 1.17 mol·L−1 of NaOH with 61.4% current efficiency (η), and 2.58 kW·h·kg−1 energy consumption (EC) during 4 h of EED process. Under similar operating conditions, pristine (SPK), and commercial CEM (FKB-PK-130), showed inferior performance. Longevity of SPK-3 CEM was assessed with industrial GLS for fifty cycles of EED experiments 4 h duration each. Reported results are promising for sustainable NaOH production from industrial GLS of pulp and paper mills, and provide a resourceful alternate for industrial waste.

Influence of Titanium Dioxide Particles Percentage in Modifying Layer on Surface Properties and Current-Voltage Characteristics of Composite Cation-Exchange Membranes

Influence of Titanium Dioxide Particles Percentage in Modifying Layer on Surface Properties and Current-Voltage Characteristics of Composite Cation-Exchange Membranes

Sulfonated poly ether ether ketone (SPEEK) based composite cation exchange membranes for salt removal from brackish water

Availability of fresh water is a serious concern due water pollution in these days. Several efforts have been made for water desalination where membrane based technology is considered prominently. Here, we synthesised sulfonated poly ether ether ketone (SPEEK) based functionalized hexagonal boron nitride (SBN) composite cation exchange membranes for water desalination. The morphology of BN and presence of sulfonic acid group are confirmed by TEM analysis. Ionic conductivity for SPEEK membrane is found to be 2.02 × 10−2 S. cm−1, which reaches to 4.05 × 10−2 S. cm−1 for SBN-10/SPEEK composite membrane. Ion exchange capacity of the SBN-10/SPEEK composite membrane also increased by 40 % and reaches to 1.66 meq.g-1 as compared to SPEEK membrane. Incorporation of SBN in membrane matrix not only improve the ion exchange capacity and ionic conductivity as well as expand the stability of the membranes. SEM micrograph confirm the uniform distribution of SBN in SPEEK membrane matrix. The composite membranes show the better ion transport properties in term of current efficiency and power consumption during salt removal from brackish water by electrodialysis. For SBN-10/SPEEK composite membrane power consumption was 0.75 kW h.Kg-1 with 98.5 % current efficiency.

Functionalized carbon dots composite cation exchange membranes: Improved electrochemical performance and salt removal efficiency

Here, we investigated the functionalized carbon dots as a possible organic filler for the sulfonated poly (ether sulfone) (SPES) based composite cation exchange membranes to improve the membrane performance. Sulfonated carbon dots (SCDs) are synthesised by simple pyrolysis of citric acid in presence of sodium 4-styrene sulfonate. Functionalized carbon dots provide excellent hydrophilicity, and affinity towards SPES due to the intra hydrogen bonding between sulfonic group of SPES and functionalized carbon dot. Addition of filler material leads to the improvement in physicochemical and electrochemical properties of the composite membranes. 32 % increment in ionic conductivity is noted after the addition of 2% SCDs for SMQ-2 membrane while ion exchange capacity goesets double. Membranes are evaluated for salt removal from brackish water by electrodialysis and found that SMQ-2 membrane showed 30 % reduction in the power consumption than the SM membrane. Composite membranes can efficiently be used for the salt removal from brackish water.

Modified composite cation exchange membrane with enhanced stability and electrochemical performance

Herein, we elaborated on the feasibility of coupling polyvinyl chloride with tin aluminium molybdophosphate to form composite membranes that facilitate enhanced electro-transport properties. Additionally, the effect of appropriate material selection on attaining excellent stability and selectivity of a membrane was investigated, and the membrane with 25% polymer had the best results in terms of improved ion exchange capacity, water uptake, porosity, membrane potential, and chemical and thermal stabilities. The electrochemical properties of the membrane that had the most stable polymer ratio were evaluated according to the membrane potential and fixed charge density measurements using different 1:1 ratios of electrolytes with various concentrations (1 M to 0.01 M). The membrane potential, transport number, and mobility ratio of the electrolytes from the highest to lowest were NaCl > KCl > NaNO3 > KNO3.The measured membrane potentials closely agreed with the theoretical predictions from a mathematical model called the Toerell, Maeyer, and Siever (TMS) model, confirming efficiency and selectivity.

Sulfonated poly (ether ether ketone) composite cation exchange membrane for selective recovery of lithium by electrodialysis

Lithium is in demand since decades due to high applicability in batteries for electronic devices, which is expected to increase by 8 to 11% every year and Lithium ion battery market is estimated to grow to € 180 billion by 2024. Land deposits and seawater are two major sources of lithium but availability in sea water is higher than land. So an efficient technology is required to recover the lithium from sea water. Electrodialysis (ED) may be an alternate approach to recover the lithium from sea by selective ion exchange membranes. Here, Lithium selective ion exchange membranes have been synthesized by modification of sulfonated poly (ether ether ketone) (SPEEK) with lithium selective nanomaterial. Synthesized membranes were characterized for their chemical, structural and morphological structures and uniform dispersion of lithium selective nanomaterials. Composite membrane shows better lithium exchange capacity with excellent lithium conductivity as compared to SPEEK membrane. The adsorption of lithium (15.2 mg/g) found to be five times higher than that of Mg while recovery of lithium was 64% using electrodialysis process by NC-4 composite membrane. Selectivity factor for composite membrane were 4.82, 3.0 and 2.17 for Li/Mg, Li/K and Li/Na, respectively. The selective composite membranes can be suitable for Li-ion recovery from sea brine/bittern on large scale.

Fabrication of cation exchange membrane with excellent stabilities for electrodialysis: A study of effective sulfonation degree in ion transport mechanism

Composite cation exchange membranes (CEMs) based on sulfonated polyether sulfone (SPES) with low sulfonation degree (DS) have been prepared in our previous studies. The results provided an approach for the preparation of CEM with low cost, environment-friendly technology, and ideal properties. On the basis of the previous research, the first purpose of this study was aimed to explore more suitable hydrophilic additives to further improve CEM properties. Hydrophilic polyethylene glycol (PEG) and polyvinylpyrrolidone (PVP) with different molecular weight (Mw) were used as hydrophilic additives, while SPES was still used as the matrix material. The results showed that PEG was not a suitable additive for CEMs due to the low MW, while stability was clearly improved with increased PVP MW. Hence, for researchers, there is no need to waste time on PEG as a hydrophilic agent of CEM prepared with this method in the future. The second purpose of this study, which was the further optimization of the CEM performance, was achieved in the research of suitable hydrophilic additives. The results of stability and electrodialysis showed that SPES blended with PVP K90 was the best prepared CEM. The third purpose was the investigation of mechanism of synergistic effects between sulfonated groups and hydrophilicity on membrane properties. In this part, an innovative concept of effective DS was put forward. This innovative concept will directly impact on ion transport mechanism, and have a very important influence on the preparation idea of CEM. In conclusion, this study is of great significance for selection of CEM materials, improvement of membrane stability and further study of ion transport mechanism.

Sulfonated Poly(ether sulfone) based sulfonated molybdenum sulfide composite membranes and their applications in salt removal and alkali recovery

The adequate and potable water to meet present and future demand is much lower than the fresh water available. To fulfil the surplus demand of fresh drinking water, the management and treatment of waste water to be taken forward. In this view, electrodialysis (ED) has attracted immense attention nowadays to satisfy current water demands for drinking and industrial purpose. Ion exchange membranes are the cores of electrodialysis. Herein, composite cation exchange membranes are prepared for salt removal and water treatment using sulfonated poly(ether sulfone) (SPES) and sulfonated molybdenum sulfide (S–MoS2). Effect of S–MoS2 in membranes, water-related properties, ion transport, thermal and mechanical properties of synthesized composite membranes are evaluated. Incorporation of S–MoS2 in SPES enhance the performance of the membranes, and 5 wt % S–MoS2 composite membrane (DES-5) shows the 67% higher water sorption and 25% higher IEC compared to pristine SPES membrane. Their suitability is accessed in terms of salt removal via electrodialysis and alkali recovery via diffusion dialysis. The 5 wt % S–MoS2/SPES composite membrane exhibits 0.98 kWh/kg power consumption during salt removal that is 22% lower than 1.26 kWh/kg obtained for pristine SPES. Current efficiency towards salt removal and separation factor for alkali recovery for DES-5 membrane are 69.47% and 60.32, respectively, which are much higher than virgin SPES membrane.

Investigation of the effects of SPEEK and its clay composite membranes on the performance of Direct Borohydride Fuel Cell

In this study, composite cation exchange membranes (CEM) were developed. With the experience from widely studied proton exchange membrane fuel cells (PEMFC), sulfonated polyether ether ketone (SPEEK) was prepared to be a more effective and cheaper ionomer alternative to the industry standard Nafion ®. SPEEK polymer membrane can reach sufficient ionic conductivities but have some mechanical and chemical stability problems (at a high degree of sulfonations (DS)). Therefore, in order to optimize the membrane, composite mixing with a well-known organic/inorganic clays called Cloisite® 15A, Cloisite ® 30B and MMT were used. Test cells for both single-cell and conductivity were designed and constructed. The ionic conductivity cell was different than the ones used in most studies, measuring conductivity in-plane with 4 probes using EIS. The membranes were characterized for their proton conductivity with electrochemical impedance spectroscopy (EIS), for DS with H NMR, water uptake, and fuel cell performance tests. First results showed that the acidic sulfonic groups of SPEEK interacted with organic/inorganic clays and as a result of partial barrier the ionic conductivity was decreased but power densities were increased. SPEEK-Cloisite® 30B composite membrane has given 40 mW/cm2 power density value which is higher than pure SPEEK membrane (35 mW/cm2). The proton conductivities of the final composite membranes were close to bare SPEEK membranes which are 0,065 and 0,075 S/cm for SPEEK-Cloisite ® 30B and pristine SPEEK, respectively.

Promoting the electrochemical and separation properties of heterogeneous cation exchange membrane by embedding 8-hydroxyquinoline ligand: Chromium ions removal

In this probe, an attempt was made to remove the chromium ions using heterogeneous cation exchange membrane (HCEM) incorporated with 8-hydroxyquinoline (8-HQ) ligand as the chelating agent. Composite cation exchange membranes were provided by utilizing solution casting method. Computational study of resin particle and 8-HQ molecule also has been performed in order to accomplish detailed evaluation of their reactive properties. Molecular electrostatic potential (MEP) of 8-HQ molecule and resin particle showed that both particles have appropriate reactive sites for electrophilic and nucleophilic attack. Furthermore, interaction energy between 8-HQ molecule and resin particle were calculated which confirmed the presence of strong interactions between them. Elemental mapping, scanning electron microscopy (SEM), and scanning optical microscopy (SOM) images of the resultant membranes indicated a relatively uniform surface and particles distribution. Membrane water uptake and surface hydrophilicity were enhanced in the attendance of 8-HQ. The blended membranes demonstrated better selectivity (up to 95.5%), lower electrical resistance (∼5.8 Ω.cm2) and better ionic permeability compared to the bare one whereas the selectivity and electrical resistance of unmodified sample measured 77% and 14 Ω.cm2, respectively. The ligand modified membranes showed more dialytic rate in chromium ions removal (up to 74%) compared to bare membrane which could be assigned to strong affinity of 8-HQ in heavy metal ions adsorption.

Potentiometric titration studies of poly(aniline-co-pyrrole)-Sn(IV)tungstoarsenate composite cation exchange membrane and their application as a Ni(II) selective electrode

The synthesis of poly(aniline-co-pyrrole)-Sn(IV)tungstoarsenate((PA-co-Ppy)-STA) nanocomposite cation exchange membrane was prepared through solution casting method in order to ensure the homogeneity of the obtained membrane. The synthesis of the membrane was confirmed by characterization of the nanocomposite membrane by various instrumentation techniques like Scanning Electron Microscopy (SEM), Energy Dispersive X-Ray analysis (EDX), Fourier Transform Infrared Spectroscopy (FTIR), X-Ray Diffraction (XRD) and Thermogravimetric Analysis (TGA) techniques. The selective detection of Ni(II), having detection limit 1 × 10−9–1 × 10−1 M, the range of pH 5–8 and response time 35 s. The analytical efficacy of this electrode was built up by utilizing it as an indicator in the potentiometric titration. Various experimental parameter studies proved the absorption of Ni(II) on nanocomposite. The method used is a classical method for fabrication of an ion selective electrode and hence is easier and cost effective, other than being most precise for the detection of Ni(II) ions. Along these lines, this novel effort may be a reliable and effective to detect Ni(II) in environmental and biomedical sector in a broad scale.

Evaluation of the ideal selectivity and the performance of selectrodialysis by using TFC ion exchange membranes

The current methods for determination of the membrane specific permselectivity between two competing counter-ions are dependent on various factors, which hinder the comparison of ion selectivity of ion selective membranes. In this work, a new characteristic, “ideal selectivity” is suggested to be used for the evaluation of the specific permselectivity of monovalent selective membranes. Ideal selectivity is determined in a single electrolyte solution containing only one of the competing counterions. We show that this characteristic exhibits a stable value, which is independent from the molar fraction of ions in a solution. Thus, it may be directly used to predict the purity of a salt produced in a dynamic selectrodialysis (SED) process with a monovalent selective membrane. To elaborate this, thin film composite (TFC) cation exchange membranes were prepared with piperazine and trimesoyl chloride by interfacial polymerization. These membranes were compared with a commercial monovalent selective cation exchange membrane CIMS (ASTOM, Japan) in view of their permselectivity (Na+/Mg2+) and the performance in SED. The results show that when the TFC membranes were applied in SED, the purity of Mg2+ in the product reached 75%, which was higher than in the case of CIMS. Furthermore, ideal selectivity of those TFC and CIMS membranes were calculated and fitted with the experimental Mg2+ purity. It was found that ideal selectivity linearly correlates with the product final purity. The extrapolation of the fitting line predicts that when ideal selectivity approaches to 2, SED process the purity could theoretically approach to 100% in the same experimental conditions. Therefore, ideal selectivity can be used to predict the separation efficiency and the final product purity of SED process.