Ion-exchange Membranes Research Articles

Enhanced Alkali Recovery and Desalination by Cation Exchange Membranes Utilizing Dry Wet Phase Inversion Technique: Impact of Co-ions, Osmotic, and Electro-Osmotic Phenomena

Enhanced Alkali Recovery and Desalination by Cation Exchange Membranes Utilizing Dry Wet Phase Inversion Technique: Impact of Co-ions, Osmotic, and Electro-Osmotic Phenomena

Selective phosphate removal with manganese oxide composite anion exchange membranes in membrane capacitive deionization

The discharge of excessive phosphorous into water bodies can lead to serious eutrophication threatening aquatic ecosystem. Membrane capacitive deionization (MCDI) is an effective platform for deionizing aqueous streams; however, conventional MCDI is unable to selectively remove targeted ions from a liquid mixture. In this work, we fabricated manganese oxide composite anion exchange membranes (AEMs) for MCDI to enhance phosphate removal selectivity from sodium chloride-sodium dihydrogen phosphate (10:1 M ratio) aqueous mixtures. We systematically investigated several critical factors, such as constant current or voltage operation, applied voltage amount, process stream pH, and manganese oxide (Mn2O3) content in the AEM, on phosphate removal efficiency and phosphate selectivity. A trade-off was observed between phosphate removal and selectivity when increasing the cell voltage. Under the best conditions, a MCDI unit with a 20 wt% Mn2O3 composite AEM and a bipolar membrane facilitated high phosphate removal efficiency of ≥ 31.8 % and a phosphate over chloride selectivity of 1.1 while showing stability for at least 30 cycles. To help understand how Mn2O3 composite AEM boosts phosphate selectivity, static electronic structure calculations were performed, and they revelated that hydrogen phosphate absorption on Mn2O3 composite AEM was 314 kcal/mol more exothermic than that on pristine AEM while chloride adsorption on Mn2O3 composite AEM was 2.2 kcal/mol less exothermic than that on a pristine AEM. Overall, this work presents an effective strategy for selectively removing phosphate from model wastewater solutions and the mechanistic understanding that governs ion selectivity in composite ion-exchange membranes used in MCDI.

Performance of a novel CO2 absorption and reverse electrodialysis system with different amine solutions for simultaneous energy and bicarbonate recovery

In this study, the performance of a novel integrated carbon dioxide (CO2) capture and reverse electrodialysis (RED) system was evaluated. The optimal operating conditions and carbon dioxide absorption and desorption mechanisms were identified. The proposed system utilizes a RED device to recover energy from the desorption step of the CO2 capture process, which is known to have high energy requirements in conventional processes. It has the potential as a hybrid process capable of recovering absorbent, energy, and bicarbonate through RED. To verify the performance of the system, CO2 loading, power density, and absorbent regeneration were evaluated using primary (monoethanolamine, MEA), secondary (diethanolamine, DEA), and tertiary (N-methyldiethanolamine, MDEA) amines. In the case of primary and secondary amines, carbamates, intermediate products, are formed and pass through the ion exchange membrane of RED, thereby achieving high power density. However, they are re-substituted with amines after passing through the ion exchange membrane (IEM), leading to the loss of absorbent. Conversely, in the case of tertiary amines, no intermediate products were formed, and excellent absorbent regeneration performance of more than 99.9% was demonstrated through multi-stage RED. Through this, the feasibility of future applications of this technology was confirmed.

Desalination performance in versatile capacitive/battery deionization configurations using a cation intercalating electrode

Capacitive deionization (CDI) is an alternative desalination technique for low-to-moderate salinity feeds. Despite significant advances in electrode material design, CDI's thermodynamic energy efficiency (TEE) remains low and has become important in assessing feasibility for real-world applications. Innovative cell configurations are key to improving TEE; however, their performance trends need to be contextualized, given the scattered information that can be challenging to compare. This study evaluates various desalination cells, including conventional CDI, single- and multi-channel asymmetric CDI, and multi-channel battery deionization (BDI). Using MoS2 as a representative intercalating material, the position of active sites on composite electrodes was first optimized. Hydrothermally-grown MoS2 on carbon nanofibers exhibited enhanced charge transfer compared to MoS2 embedded in nanofibers. Among the tested configurations using 20 mM NaCl in single-pass mode and 50% water recovery, BDI demonstrated over 3.7 times higher TEE than asymmetric setups and 50 times higher than typical CDI while maintaining consistent desalination performance. BDI benefited from the combined effects of electrosorption/intercalation and ion exchange membranes in symmetric conformation, effectively utilizing charge. These findings provide insights into process engineering for improved electrochemical desalination and the enhancement of ion intercalation-based desalination configurations.

Advances in Redox Flow Batteries – A Comprehensive Review on Inorganic and Organic Electrolytes and Engineering Perspectives

AbstractDevelopment and application of large‐scale energy storage systems are surging due to the increasing proportion of intermittent renewable energy sources in the global energy mix. Redox flow batteries are prime candidates for large‐scale energy storage due to their modular design and scalability, flexible operation, and ability to decouple energy and power. To date, several different redox couples are exploited in redox‐flow batteries; some are already commercialized. This battery technology is facing a lot of challenges in the science, engineering, and economic front. Issues plaguing flow batteries are low energy density, high overall cost, poor stability of electrolytes, shifting of solvent from anolyte to catholyte while using cation exchange membrane, reverse flow with anion exchange membrane, and corrosion of graphite felt in the catholyte side. Significant research efforts are ongoing to address these challenges. This comprehensive and critical review summarizes the recent progress in electrolyte technologies, including electrochemical performance and stability, strategies to enhance the energy and power densities and, in the end, the levelized and life‐cycle cost of these batteries analyzed. A comprehensive outlook on this technology with respect to practical energy storage applications is also provided.

EXPLORING FACTORS AFFECTING NITROGEN ISOLATION BY CATION EXCHANGE MEMBRANE AND THEIR IMPLICATIONS FOR MICROBIAL FUEL CELL PERFORMANCE IN WASTEWATER TREATMENT

This study explores the utilization of a cation exchange membrane (CEM) in a microbial fuel cell (MFC) system to isolate nitrogen from wastewater influents. While employing a CEM in an MFC system has drawbacks, such as increased internal resistance and reduced power output, it also provides a means for optimal energy recovery from organics while allowing isolated nitrogen to be treated in subsequent steps. This study evaluated the diffusion of ammonium through CEM in a dual-chamber MFC under different operating conditions. Results indicated that the MFC reactor with CEM as a separator isolated 88-93% of the nitrogen input, demonstrating the feasibility of this approach for nitrogen separation in wastewater treatment applications. Factors affecting nitrogen isolation, including COD input at the anode, dissolved oxygen (DO) at the cathode, and external resistance (ER), are identified. Higher COD input at the anode and the DO at the cathode were found to enhance nitrogen separation, while increased ER had an adverse effect on nitrogen isolation capacity. Additionally, changes in the surface characteristics of the CEM during operation could impact nitrogen isolation, emphasizing the need for careful monitoring and maintenance of the CEM to ensure consistent performance over time. In conclusion, this study highlighted the potential of using a CEM in MFC systems for nitrogen isolation, provided insights into the factors affecting the efficacy of nitrogen separation, and underscored the need for monitoring and maintenance of the CEM. These results could significantly impact the development of more efficient and sustainable wastewater treatment using the MFC system.

Modeling Ion Transport across Thin-Film Composite Membranes During Saltwater Electrolysis.

Affordable thin-film composite (TFC) membranes are a potential alternative to more expensive ion exchange membranes in saltwater electrolyzers used for hydrogen gas production. We used a solution-friction transport model to study how the induced potential gradient controls ion transport across the polyamide (PA) active layer and support layers of TFC membranes during electrolysis. The set of parameters was simplified by assigning the same size-related partition and friction coefficients for all salt ions through the membrane active layer. The model was fit to experimental ion transport data from saltwater electrolysis with 600 mM electrolytes at a current density of 10 mA cm-2. When the electrolyte concentration and current density were increased, the transport of major charge carriers was successfully predicted by the model. Ion transport calculated using the model only minimally changed when the negative active layer charge density was varied from 0 to 600 mM, indicating active layer charge was not largely responsible for controlling ion crossover during electrolysis. Based on model simulations, a sharp pH gradient was predicted to occur within the supporting layer of the membrane. These results can help guide membrane design and operation conditions in water electrolyzers using TFC membranes.

Reducing Ohmic Resistances in Membrane Capacitive Deionization Using Micropatterned Ion‐Exchange Membranes, Ionomer Infiltrated Electrodes, and Ionomer‐Coated Nylon Meshes

Membrane capacitive deionization (MCDI) is an emerging water desalination platform that is compact, electrified, and does not require high‐pressure piping. Herein, highly conductive poly(phenylene alkylene) ion‐exchange membranes (IEMs) are micropatterned with different surface geometries for MCDI. The micropatterned membranes increase the interfacial area with the liquid stream leading to a 700 mV reduction in cell voltage when operating at constant current (2 mA cm−2; 2000 ppm NaCl feed) while improving the energy normalized adsorbed salt (ENAS) value by 1.4 times. Combining the micropatterned poly(phenylene alkylene) IEMs with poly(phenylene alkylene) ionomer‐filled electrodes reduces the cell voltage by 1000 mV and improves the ENAS values by 2.3 times relative to the base case. This reduction in cell voltage allows for higher current density operation (i.e., 3–4 mA cm−2) . The reduction in cell voltage is ascribed to the ameliorating ohmic resistances related to ion transport at the membrane‐process stream interface and in the carbon cloth electrode. Finally, porous ionic conductors are implemented into the spacer channel with flat and micropatterned IEM configurations and ionomer infiltrated electrodes. For the configuration with flat IEMs, the porous ionic conductor improves ENAS values across the current density regime (2–4 mA cm−2), while for micropatterned IEMs it gets improved only at 4 mA cm−2.

Generating sustainable cement material from seawater with low-cost ultrafiltration (UF) membrane electrolysis

Membrane electrolysis offers a promising avenue for in-situ generation of hydroxide ions (OH−), facilitating the recovery of magnesium (Mg2+) and calcium (Ca2+) ions from seawater as alkaline earth hydroxide precipitates. This process paves the way for an alternative greener method in the production of raw materials for cement manufacturing compared to limestone mining. Despite its potential, the application of conventional ion migration membranes, such as anion exchange membrane (AEM) and cation exchange membrane (CEM), is hampered by their high cost and low mechanical quality, posing significant barriers to industrial scalability. In this work, we introduce the utilization of commercially available high mechanical strength ultrafiltration (UF) membrane within a two-chamber electrochemical system, repurposing it as an ion migration membrane due to its distinct advantages in terms of simplicity and relative cost-efficiency than conventional AEM. This research demonstrates that the UF membrane exhibited a comparable performance to AEM in terms of OH− production. Both membranes achieved 97–99 % removal of Mg2+ and Ca2+ within 3 h at a current density of 8 mA/cm2 and maintained comparable migration rate of SO42− ion. Compared to AEM, a notable distinction of the UF membrane is its reduced migration rate of Cl− ions, resulting in lower membrane discoloration/oxidation. Furthermore, the investigation reveals that utilizing a Na2SO4 solution as an alternative anolyte, despite being slower for OH− production, offers economic advantages and facilitates higher selective recovery of Mg2+ over Ca2+. The end products of this process, MgO and CaO, are viable raw materials for cement production, underscoring a sustainable and low carbon approach compared to conventional limestone mining of cement production.

Detection of available heavy metals in soil using gold nanoparticles-modified ion exchange membrane with laser-induced breakdown spectroscopy

The available heavy metals in soil can directly threaten food security and human health. However, traditional detection methods are often complicated and time-consuming. In this study, a novel method with nanoparticles-modified ion exchange membrane with laser-induced breakdown spectroscopy (NMIEM-LIBS) was proposed for the sensitive detection of available heavy metals in soil samples. Gold nanoparticles modified-ion exchange membrane was used to high-efficiency enrich lead (Pb) and cadmium (Cd) ions in soil solution and detected after separation. This method can realize the highly sensitive quantitative analysis of available Pb and Cd in soil, with the detection limits (LoDs) of 2.62 mg/kg and 0.24 mg/kg, respectively. Furthermore, the method was successfully applied to detect available Pb and Cd concentrations in three spiked soil samples, with recoveries of 87.02–115.79 % and 82.45–114.81 %, respectively. The developed method can provide a simple, rapid, and sensitive strategy for monitoring available heavy metals in environmental samples.

The role of ionic concentration polarization on the behavior of nanofluidic membranes

Water, the elixir of life, faces a pressing challenge—salinity. As humanity's demand for freshwater intensifies, the significance of efficient desalination processes becomes paramount. The promising prospects of nanofluidic membranes and unique electrokinetic phenomena like ion concentration polarization (ICP) signal optimistic strides in enhancing salt removal processes. This study is dedicated to elucidating the transport mechanism of buffer ions at interfaces between micro and nanochannels. To achieve this, we introduce a multiphysics coupling model that incorporates a boundary condition for the fixed surface voltage, offering a comprehensive description of the impact of nanochannel arrays. In this context, it is important to note that the nanochannel array is characterized by a positive charge density, akin to a cation exchange membrane (CEM), seamlessly integrated into the microchannel wall to serve as a cationic half-cell. The analysis involved solving governing equations, including the Poisson-Nernst-Planck, continuity, and Navier-Stokes equations, numerically using the finite element method in an unsteady state. Employing cylindrical nanochannel array configurations—single, dual, and triple—we scrutinized their impact on salt species concentration and removal efficiency under specified conditions (c0=1mM, ρv=2C/m3, LN=10μm, VT=26mV, Vsurr=4VT, VL/VR=8,t≥0.5 and ζ=−60mV). The single nanochannel array configuration demonstrated a relatively uniform salt distribution, achieving a removal efficiency of approximately 58%. The introduction of two nanochannel arrays at distinct locations resulted in a notable increase in removal efficiency, reaching 72%, particularly in the "down first" configuration, emphasizing a synergistic effect. The presence of three nanochannel arrays, each with varying lengths, produced intricate patterns, with the highest removal efficiency observed at 91% in the "different length" condition. This study emphasizes the superior desalination capabilities achievable through multiple nanochannel arrays, advancing our understanding of nanofluidic membrane applications for efficient water desalination. In conclusion, emulating electrodialysis membrane procedures, particularly by integrating an anionic half-cell, holds promise for further advancing desalination processes, offering a potential avenue to enhance efficiency.

Multi-component ion equilibria and transport in ion-exchange membranes

At the interface between an ion-exchange membrane and a multi-electrolyte solution, charged species redistribute themselves to minimize the free energy of the system. In this paper, we explore the Donnan equilibrium of membranes with quaternary electrolyte (Na+/Mg2+/K+/Ca2+/Cl−) solutions, experimentally. The data was used to calculate the ion activity coefficients for six commercial cation-exchange membranes (CEMs). After setting one of the activity coefficients to an arbitrary value, we used the remaining (N-1) activity coefficients as fitting parameters to describe the equilibrium concentrations of (N) ionic species with a mean relative error of 3 %. At increasing solution ionic strengths, the equivalent ion fractions of monovalent counter-ions inside the membrane increased at the expense of the multivalent ones in alignment with the Donnan equilibrium theory. The fitted activity coefficients were employed in a transport model that simulated a Donnan dialysis experiment involving all four cations simultaneously. The arbitrary value assigned to one activity coefficient affects the calculated Donnan potential at the membrane interface. Nevertheless, this arbitrary value does not affect the prediction of the ion concentrations inside the membrane and consequently does not affect the modeled ion fluxes.

Heavy Metal Detection and Removal by Composite Carbon Quantum Dots/Ionomer Membranes.

The combination of ion exchange membranes with carbon quantum dots (CQDs) is a promising field that could lead to significant advances in water treatment. Composite membranes formed by sulfonated poly(ether ether ketone) (SPEEK) with embedded CQDs were used for the detection and removal of heavy metal ions, such as lead and cadmium, from water. SPEEK is responsible for the capture of heavy metals based on the cation exchange mechanism, while CQDs detect their contamination by exhibiting changes in fluorescence. Water-insoluble "red" carbon quantum dots (rCQDs) were synthesized from p-phenylenediamine so that their photoluminescence was shifted from that of the polymer matrix. CQDs and the composites were characterized by several techniques: FTIR, Raman, UV/VIS, photoluminescence, XPS spectroscopies, and AFM microscopy. The heavy metal ion concentration was analyzed by inductively coupled plasma-optical emission spectroscopy (ICP-OES). The concentration ranges were 10.8-0.1 mM for Pb2+ and 10.0-0.27 mM for Cd2+. SPEEK/rCQDs showed a more pronounced turn-off effect for lead. The composite achieved 100% removal efficiency for lead and cadmium when the concentration was below a half of the ion exchange capacity of SPEEK. The regeneration of membranes in 1 M NaCl was also studied. A second order law was effective to describe the kinetics of the process.

Electrokinetic Desalting and Salting of Water-in-Oil Droplets.

Droplet-based microfluidic platforms demand modifications to the droplet composition to facilitate reactions and analyses. However, limited techniques exist to modify the droplet contents post their generation. Here, ion transport across two ion-exchange membranes possessing distinct selectivity is employed to introduce ions into (salt) or extract ions from (desalt) water-in-oil droplets. The ion concentration distribution and transport mechanisms are visualized using a precipitation reaction and a charged fluorescent tracer. Furthermore, current measurements reveal characteristic regimes in desalting and salting modes and demonstrate that the rates of ion transport linearly correlate with applied voltage and the ionic strength of the droplets. Importantly, up to 98% desalting efficiency is achieved. This technique advances droplet-based sample preparation through the straightforward manipulation of droplet contents.

Bifunctional side-chains decorating a distorted poly(aryl ether sulfone) backbone to endow an anion exchange membrane with high perm-selectivity for chloride ions

Mono-valent selective ion-exchange membrane, as the core component of selective electrodialysis (SED), has received extensive attention. In this work, we report a mono-valent selective anion-exchange membrane (AEM), which was fabricated with distorted poly(aryl ether sulfone) and decorated with bifunctional side-chains providing anion exchange groups and hydrophobic segments. By tuning the length of the hydrophobic side-chains, the nanophase separation within AEMs was finely tuned, evidenced by an ionic cluster size of about 0.47 nm from SAXS analysis. The optimized AEM (PAES-TA-7 AEM) shows a very low water swelling ratio of 6.4 %, signaling good dimensional stability. The perm-selectivity (PSO42–Cl–) of PAES-TA-7 AEM during ED reached 107 at 2.5 mA∙cm−2 (ion flux: 2.69 × 10−8 mol cm−2 s−1 at 90 min) significantly exceeding that of the commercial Neosepta ACS (11; 2.08 × 10−8 mol cm−2 s−1). It is inferred that the ion channels, resulting from nanophase separation between the side-chains and the backbone, as well as the free volume cavity created by the distorted backbone, significantly contribute to the smooth transport of the Cl− ions through the AEM with less resistance. As a result, it is believed that this work offers a useful strategy to advance the monovalent anion-selective membranes.

High-performance aqueous organic redox flow battery enabled by sulfonated anthrone-containing poly(aryl ether ketone) membranes

Aqueous organic redox flow batteries (AORFBs) have become a promising electrochemical energy storage technology due to their low cost, high safety, and sustainability. As key components of emerging AORFBs, membranes face challenges such as scarcity of available membranes and high prices. Moreover, currently available membranes have low battery performance because these membranes are not optimized for specific AORFBs. In this work, a new cation exchange membrane sulfonated anthrone-containing poly(aryl ether ketone) (SAnPEK) membrane was prepared for the first time and achieved significantly improved performance in (SPr)2V/K4[Fe(CN)6] AORFBs. SAnPEK membrane has excellent selectivity and high mechanical strength (>50 MPa). SAnPEK membranes exhibit high conductivity in 1 M NH4Cl solution. For example, SAnPEK-4 membranes exhibit low surface resistance (0.176 Ωcm2) in 1 M NH4Cl solution, which is significantly better than Nafion117 (1.02 Ωcm2) and Nafion212 membranes (0.276 Ωcm2). SAnPEK membrane exhibtis impressive performance in (SPr)2V/K4[Fe(CN)6] AORFB. The SAnPEK-4 membrane exhibits high coulombic efficiency (CE) and excellent energy efficiency (EE) (CE = 99.1 %, EE = 83.4 % at 100 mAcm−2), and the EE for SAnPEK-4 membrane is significantly better than that for the Nafion117 membrane (CE = 99.3 %, EE = 62.4 %) and Nafion212 membrane (CE = 99.1 %, EE = 80.8 %, 100 mAcm−2). In addition, the SAnPEK-4 membrane exhibits excellent cycle stability over 3000 cycles in AORFB. As a high-performance, easy-to-prepare, low-cost cation exchange membrane, SAnPEK membranes have good application potential in AORFBs.

Electrochemical Synthesis of Ferrate (VI): Factors Influencing Synthesis and Current Research Trends

Ferrate(VI) emerges as a multifaceted substance endowed with a substantial redox potential, showcasing considerable potential for utilization in realms such as battery materials and advancements in water treatment technologies. There are primarily three methods for preparing Ferrate(VI), including peroxide heating method, hypochlorite oxidation method and electrochemical synthesis method. This review centrally delves into the electrochemical synthesis of ferrate(VI), given its mild reaction conditions, emerges as a highly potent means to synthesize Ferrate(VI) with substantial potential for industrial applications.The intricacies of influencing factors, including anode materials, electrolyte composition, electrolyte additives, reaction temperature, current density, membranes (ion-exchange membranes), and reactor types, are meticulously detailed, all of which exert a discernible influence on the synthesis process. A comprehensive exposition of the current research landscape and prevailing trends in the electrochemical synthesis of ferrate(VI) is presented. However, the current discourse on the electrochemical synthesis of Ferrate(VI) remains insufficient. Addressing these issues not only demands the optimization of reaction conditions but also necessitates the exploration of novel methodologies. For instance, incorporating the contextual application of Ferrate(VI) and achieving in-situ synthesis for immediate utilization are pivotal directions for future research and development.

Sulfur autotrophic electrodialysis ion exchange membrane bioreactor (SEDIMB) for nitrate removal in water: Synergism and adaptability of electrodialysis and sulfur autotrophy

In this study, the novel sulfur autotrophic electrodialysis ion-exchange membrane bioreactor (SEDIMB) with high denitrification performance was developed without the addition of carbon source. Sulfur autotrophic denitrification occurs at the same time of nitrate enrichment by electric field to achieve harmless nitrate transformation in water. The final nitrate concentration in water chamber was 2.16 mg-N/L (removal efficiency of 94.49 %) at an initial nitrate concentration of 40 mg-N/L, with the maximum nitrate concentration in biological chamber of 4.09 mg-N/L. Nitrate removal in water chamber of the SEDIMB conformed to the first-order kinetic model (R2 = 0.98) and reaction rate constant K1 = 0.0030 (1/min). The effect of environmental variables (i.e., voltage, initial nitrate concentration and water body) on the SEDIMB denitrification performance was investigated. Increasing voltage could promote nitrate migration in water chamber, and when the voltage was 7 V, initial nitrate concentrations of 20 ∼ 60 mg-N/L was effectively removed (all > 93.54 %). Moreover, the change of water body (i.e., tap water, lake water and deionized water) did not affect denitrification performance of SEDIMB. Microbial community structure analysis indicated that Betaproteobacteria were dominant in the SEDIMB. Membrane characterizations (ATR-IR, SEM and CLSM) confirmed that the bacteria in biological chamber tended to accumulate and grow on one side of the anion exchange membrane (AEM), while could not affect the selective permeability of AEM.

Electrochemical analysis of ion-exchange membranes fouling during electrodialysis treatment of real shale gas flowback water

Electrodialysis (ED) is considered an effective technology for desalinating shale gas flowback fluid toward environmental risk control and resource recovery. However, membrane fouling remains a significant challenge and the particular fouling behavior of ion-exchange membranes (IEMs) in real scenario remains unclear. In this study, we employed interface characterization techniques including electrochemical impedance spectroscopy (EIS) to investigate the fouling behavior of both anion-exchange membranes (AEMs) and cation-exchange membranes (CEMs) during the desalination process. Notably, a positive correlation was observed between the transmembrane electric potential (TMEP) of the target membrane and the extent of membrane fouling during ED processing. EIS data revealed the membrane bulk exhibited the most pronounced increase in modeled electrical resistance, suggesting that internal fouling more significantly inhibited mass transfer compared to external fouling. Under varying current densities, the resistance of the AEM and CEM membrane bulk increased from an initial value of 3.93–16.53 Ω cm2 and from 3.90 to 9.87 Ω cm2, respectively, corresponding to their maximum TMEP increase by factors of 6.0 and 2.0 during the ED treatment. Our results demonstrate that AEM undergone a more severe organic fouling than CEM (scaling) during desalination of real shale gas flowback fluid. Effective strategies to mitigate the fouling issue in IEMs were finally proposed. These findings provide valuable guidance on future process optimizing and fouling mitigation in the ED treatment of real shale gas flowback fluid.

Mathematical modeling of the transport characteristics of a PVDF-based cation-exchange membrane with low water content

New effective ion-exchange membranes are needed for a variety of applications, with a particularly pressing need for membranes used in fuel cells and membrane water electrolysis. PVDF-based membranes are promising for these and other applications. Two samples of such membranes with a low water content are studied. The interest in the behavior of these samples is that with an increase in the bathing NaCl solution concentration, the diffusion permeability decreases, whereas usually it increases along with increasing membrane conductivity. The hypothesis is that with increasing concentration, the water content decreases even more, which leads to a narrowing of the intercluster ion-conducting channels and a reduction in the effective mobility of coions, since the latter have to go around narrowed sections of channels. To simulate the concentration dependence of conductivity, diffusion permeability and transport numbers for the two above samples, the microheterogeneous model is extended to describe the loss of water with increasing external concentration and take into account the decrease of coion percolation through the membrane. The results of simulation are compared with the experimental data.