Ion Exchange Membranes

Wastewater and by-product treatments are substantial issues with consequences for our society, both in terms of environmental impacts and economic losses. With an overall global objective of sustainable development, it is essential to offer eco-efficient and circular solutions. Indeed, one of the major solutions to limit the use of new raw materials and the production of wastes is the transition toward a circular economy. Industries must find ways to close their production loops. Electrodialysis (ED) processes such as conventional ED, selective ED, ED with bipolar membranes, and ED with filtration membranes are processes that have demonstrated, in the past decades and recently, their potential and eco-efficiency. This review presents the most recent valorization opportunities among different industrial sectors (water, food, mining, chemistry, etc.) to manage waste or by-product resources through electrodialysis processes and to improve global industrial sustainability by moving toward circular processes. The limitations of existing studies are raised, especially concerning eco-efficiency. Indeed, electrodialysis processes can be optimized to decrease energy consumption and costs, and to increase efficiency; however, eco-efficiency scores should be determined to compare electrodialysis with conventional processes and support their advantages. The review shows the high potential of the different types of electrodialysis processes to treat wastewaters and liquid by-products in order to add value or to generate new raw materials. It also highlights the strong interest in using eco-efficient processes within a circular economy. The ideal scenario for sustainable development would be to make a transition toward an eco-circular economy.

Evaluation of treatment and recovery of leachate by bipolar membrane electrodialysis process

Bipolar membrane electrodialysis (BMED) is a promising technique for upgrading traditional manufacturing procedures and achieving a circular economy. However, the industrial applications of BMED technology have been restricted by the large consumption of expensive bipolar membranes and the unmatching behavior between water splitting and ion migration. Herein, we proposed a novel asymmetric bipolar membrane electrodialysis (ABMED) to regulate the water splitting in the bipolar membrane and orientational ion migration in the electrodialysis (ED). It was found that the ABMED exhibited comparable performances to BMED for acid/base production when the area of the bipolar membrane was reduced to 50% of the monopolar membrane. The total process cost of ABMED was 0.78 $/kg NaOH, which is 21% lower than the BMED process. The asymmetric membrane design was capable to boost the water splitting in the bipolar membrane and to eliminate the concentration polarization in the ED process.

Hybridization of electrodialysis (ED) and batch reverse osmosis (BRO) process is used to reduce the brine volume and water production cost. The ED process has the benefit of high water volume recovery in brackish water desalination, while reverse osmosis can produce pure water at a low production cost. Here, a simple hybrid process layout is preferred in which the ED process is kept in the reject stream of the BRO process and permeate from both ED and BRO is mixed. Recovery of the ED process is kept at 70% which can decide the blending ratio of ED and BRO permeates. The capital cost and operating cost of ED and BRO processes are used to calculate water production cost. The water production cost from the hybrid ED–BRO process is found to be 0.22 $ m−3 of freshwater when the feed concentration is 1,100 ppm. The cost increases from 0.20 to 0.34 $ m−3 with feed concentration from 1,000 to 2,000 ppm. In the cost, a major portion comes from the capital equipment in which the highest contributor is the membrane for both ED and BRO processes.

The purpose of this study was to accelerate pH variation in cloudy apple juice using electrodialysis (ED). The testing was conducted using two ED configurations. The bipolar and cationic membrane configuration showed that reducing the spacing from 8 to 0.75 mm had little effect on treatment time, whereas stacking eight bipolar membranes reduced acidification time by 30%, although the treatment still took too long (21 min). Furthermore, it was not possible to acidify apple juice to a pH of 2.0 to completely inhibit enzymatic browning. The bipolar and anionic membrane configuration helped to accelerate the acidification step by a factor of 3, increasing the yield from 3.3 to 10 L of juice/m(2) membrane/min. Moreover, treatment time was inversely proportional to the size of the membrane stack. The speed at which the pH of acidified juice returned to its initial value was, however, 4 times slower than the speed of acidification, giving a yield of 2.5 L of juice/m(2) membrane/min. By accelerating the acidification step, ED treatment with bipolar and anionic membranes results in more effective polyphenol oxidase activity and more rapid control of juice browning at pH 2.0. Also, the treatment has very little effect on the chemical composition and organoleptic quality of apple juice.

Electrodialytic 2-compartment cells for emerging organic contaminants removal from effluent

Water shortage in the world has stimulated the rapid development of water treatment technology. As one of the most promising technologies, membrane separation has tremendous hopes in producing fresh water and dealing with wastewater. The blend of inorganic component into polymer membrane has become an efficient way to increase the antifouling property and realize the multifunction of polymer membrane. In this paper, we summarize recent results published in patent and literatures for the preparation and applications of organic-inorganic hybrid membranes (OIHM) used in water treatment. Special attentions are paid on the selection of new nanoparticles, improvement of fabrication process, and discussion about the new function and application of OIHM in water treatment. The emphasis is providing some efficient methods of preparing OIHM with high antifouling property and multifunction, and extending their application ranges in future water treatment. Keywords: Organic-inorganic hybrid membrane (OIHM), water treatment, nanoparticles, membrane separation.

In this study, the removal of MB from saline solutions was evaluated by two methods by adsorption and electrodialysis; the adsorption of the mixture dye/salt on dried orange peel waste (OPW) was studied in batch method. In this study the biosorption of cationic dye by OPW was investigated as a function of initial solution pH, and initial salt (sodium chloride) concentration. The maximal dye uptake at pH >= 3.6 in the absence and in the presence of salt and the dye uptake diminished considerably in the presence of increasing concentrations of salt up to 8 g/L. The Redlich Peterson and Langmuir were the most suitable adsorption models for describing the biosorption equilibrium data of the dye both individually and in salt containing medium. As well, this work deals with the electrodialysis application to remove the dye. Synthetic solutions were used for the investigation of the main operational factors affecting the treatment performance; such as applied voltage, pH, initial dye concentration and ionic strength. The experimental results for adsorption and electrodialysis confirmed the importance of electrostatic interactions on the dye. The electrodialysis process with standard ion exchange membranes enabled efficient desalination of cationic dye solutions; there are two main factors in fouling: electrostatic interaction between cations of dyes and the fixed charged groups of the CEM, and affinity interactions.

Preparation of polyvinylidene fluoride blend anion exchange membranes via non-solvent induced phase inversion for desalination and fluoride removal

The demand for clean water is vast, whether it is used for human consumption, agricultural activities or industrial applications. To find a solution for this important issue, a small attempt has been made in the present work towards developing reinforced monopolar and bipolar membranes based on functionalized polysulfone and evaluated for electrodialysis of salt water. Polyvinyl pyrrollidone was used as the intermediate layer for the preparation of the bipolar membrane. The concentration of salt water taken for the bipolar membrane electrodialysis (BPMED) process ranged from 5 to 25 g/L. A commercially procured monopolar and bipolar membranes made of polystyrene divinyl benzene was also evaluated for the purpose of comparison. The BPMED performance reached a highest current efficiency of 75.8 and 53.6 % with the energy consumption of 0.36 and 1.39 Wh for the synthesized and commercial membranes respectively. Also the performance of the fabricated unit was assessed in terms of electrical conductivity, salinity and ion (sodium and chloride) concentrations in the feed solution after 8 h duration. The reproducibility performance of the membranes was also analyzed for various concentrations of the synthetic salt solution.

Chapter nine - Electrodialysis membrane technology for industrial wastewater treatment: recent advances

Electrodialysis with bipolar membrane (EDBM) combined with a subsequent 4–6 fold dilution was demonstrated to allow high phospholipid (PL) recovery and defatting rate. However, the economic and environmental drawbacks of such dilution limit the process application in the food industry. To overcome them, original combinations of treatment with EDBM, applicable in the food industry (demineralization by conventional electrodialysis (ED) and diafiltration), were tested for the first time and compared with the EDBM + dilution process. The most promising combination was the EDBM + ED process. Indeed, demineralization by ED after EDBM allowed to reach the highest divalent cation removal (70.2 % versus 2.3 and 39.7 % respectively for dilution and diafiltration) and defatting rate (76.6 % versus 54.2 and 23.0 % respectively for dilution and diafiltration). Furthermore, this combination allowed to concentrate phosphatidylethanolamine by 15 X compared to its content in initial sweet whey and to reach the highest PL yield (25.9 g/100 L of sweet whey versus 13.3 and 8.99 g/100 L respectively for dilution and diafiltration). These high performances were associated with different phenomena occurring during the treatments performed after EDBM and leading to specific impacts on ionic strength, mineral content and composition. From those phenomena, it was possible to understand the key role of the removal of divalent cations in the formation of lipoprotein complexes, highlighting that it was not only due to the reduction in pH and ionic strength. Consequently, EDBM combined with ED appears to be an attractive industrial process, as it combined the ecofriendly advantages of electrodialytic technics, while limiting water consumption, avoiding the production of large volumes of effluents and the use of chemical agents.

Recycling lithium-ion battery materials is a crucial step to achieving a circular economy. Among a few methods for recycling spent battery materials, a novel hydrometallurgical recycling process with leaching by acids and precipitation by bases was proposed [1]. Lithium sulfate (Li2SO4) leachate solution is generated at the end of the closed-loop recycling process. Such Li2SO4 solution can be separated by electrodialysis (ED) to form H2SO4 and LiOH solutions, which are reused for leaching and precipitation of the recycling process. The present study attempts to model this ED process and validate the model with experimental data.An ED stack based on bipolar membranes (EDBM); see Fig. 1a, was built with repetitive unit cells, each consisting of a bipolar membrane, anion exchange membrane (AEM), and cation exchange membrane (CEM). Li2SO4 enters the dilute channel and splits into SO4 2- and Li+, which travel through the AEM and CEM, respectively. Water electrolysis occurs within the bipolar membrane to produce H+ and OH-, which react with SO4 2- and Li+ to form H2SO4 and LiOH, respectively; see Fig. 1b. A two-dimensional (2D) multiphysics model is developed to elucidate the coupled transport processes within the unit cell. Conservation equations for mass, momentum, and species are solved. The transport of ions is described by the Nernst-Planck equation. Electroneutrality equations are satisfied in these membranes and channels. Electro-osmotic water transport across the membranes is considered.The effective cross-sectional area of the stack was 121.8 cm2 (70mm×174mm). The flow channel between consecutive membranes was 0.8 mm, with a mesh inserted to facilitate mixing. Experiments were carried out with the EDBM stack over different conditions such as current density, number of cell pairs, and flow rates. All experiments were operated at constant current mode [2]. The feed, acid, and base solutions were recirculated through their tanks at initial concentrations of 1.1, 0.1, and 0.1 mol/L. The ion concentrations of the solutions were measured periodically with inductively coupled plasma (ICP) mass spectrometry. The weight and the pH value of the solution tanks were also recorded.The concentration of H2SO4 is found to increase with time linearly, whereas that of LiOH levels off due to a significant electro-osmosis that drags water through the CEM into the concentrate channel. This drag reduces the performance of EDBM due to the dilution of water into the concentrate compartment. However, electro-osmotic water transport also leads to a velocity increase in the concentrate channel, which is consistent with the simulation results in our previous ED model [3]. It is found that the voltage loss across the bipolar membrane ca. 1V accounts for a significant part of the unit cell of about 1.27V.The migration of ions in electrodialysis mainly relies on diffusion and electric drive. The streamlines and the concentration distribution of Li+ under different voltages indicate that increasing voltage accelerates ion migration, see Fig. 1(c). Furthermore, the effect of the potential and concentration variations on EDBM performance is also investigated. The effects of applied current density and inlet velocity are studied on species concentrations and fluxes. Increasing the stack current density accelerates the separation process, see Fig. 1(d). It is found that increasing the solution flow rate can increase LiOH solution concentration, ion recovery rate, and current efficiency. However, the impact of the flow rate is low.This work demonstrates that EDBM can be a simple and energy-saving alternative to the current chemical precipitation method to produce LiOH from Li2SO4. The present study provides new insights into optimal operation and design for Li2SO4 EDBM. The findings are helpful in determining how the stack can be scaled up for practical application.[1] A review of recycling spent lithium-ion battery cathode materials using hydrometallurgical treatments, JCY Jung, PC Sui, J Zhang, J. Energy Storage 35, 102217, 2021.[2] Electrodialysis of a Lithium Sulphate Solution: An Experimental Investigation. B Kang, D Kang, JCY Jung, A Asadi, PC Sui, J. Electrochem. Soc. 169 (6), 063515, 2022.[3] A Comprehensive Computational Fluid Dynamics Modeling of Lithium Sulphate Electrodialysis, A Asadi, HB Harandi, JCY Jung, PC Sui, J. Electrochem. Soc. 170(9), 093502, 2023. Figure 1

Piperazine is an ideal desulfurizing agent but the heat-stable salts formed in desulfurization have caused secondary pollution and waste of resources. In the previous paper, a method was reported to regenerate piperazine by using BMED. To find the variety of that regeneration process, we performed experiments on the regeneration of piperazine by using ED. In comparison, ED has higher piperazine yield and current efficiency, and much lower voltage drop and energy consumption. However, its process cost is higher than that of BMED due to an extra expenditure for the base and its tank and pumps. The process cost is estimated to be 0.96 dollar/kg Pz for BMED and 1.14 dollar/kg Pz for ED. Notably, BMED has more environmental benefits and will be more economically attractive as the control on secondary pollution is strengthened and the bipolar membrane cost decreases.

Numerous attempts have been made to develop ion-exchange membranes with low resistance for various applications such as electrodialysis and fuel cells. In this study, the strategies of immersion precipitation and dry-casting were combined, to control the membrane porosity with the purpose of improving the physical and electrochemical properties of ion-exchange membranes. The porosity was tuned using the time of membrane exposure to an elevated-temperature environment. In addition to controlling the porosity to balance the membrane electrical resistance with the diffusion caused by the concentration gradient, it was experimentally shown that the porosity can influence the IEC and water uptake of the membrane and, thus, further affect the resistance. Furthermore, the surface hydrophilicity was characterized by water contact angle measurements; the results revealed that the porous membranes were more hydrophilic than the dense membranes. As demonstrated by experimental data for desalination by electrodialysis, it was found that a membrane dried at 60 °C for 1 h had the highest desalination efficiency. This is mainly because porous membranes facilitate the transport of ions. Compared to membranes with higher porosity, the membrane prepared with a 1-h aging time had more steric hindrance, which can decrease the diffusion of ions, so that a superior desalination efficiency can be obtained. To further investigate the impact of the density of −SO32– functional groups on the electrodialysis process, membranes with various weight ratios of poly(ether sulfone) (PES) to sulfonated poly(ether sulfone) (SPES) were prepared. With increasing content of SPES, the physical and electrochemical properties of the newly developed porous membranes were changed. A membrane with higher density of functional groups was found to have a higher desalination efficiency, because of the electrostatic effect of the membrane. These results were consistent with the current efficiency. Under optimal membrane preparation conditions, the obtained membrane had a high IEC (1.75 mmol/g) and water uptake (168%). The desalination efficiency reached 95%, and the current efficiency reached 100%. It was concluded that the performance of a porous membrane with controllable porosity can enhance the electrodialysis (ED) process with respect to energy efficiency and desalination efficiency. New methods of fabricating membranes with pores such as immersion precipitation and dry-casting are thought to be potential routes to decreasing the electrical resistance.