Ion-Exchange Membranes

Experience with plate-and-frame ultrafiltration and hyperfiltration systems for desalination of water and purification of waste water

In this study, molecularly imprinted polymers (MIPs) prepared using a multifunctional and a monofunctional monomer were compared with respect to their affinities, selectivities, and imprinting efficiencies for organophosphates. This is of interest because multifunctional monomers have higher affinities than traditional monofunctional monomers for their target analytes and thus should yield MIPs with higher affinities and selectivities. However, polymers containing multifunctional monomer may also have a higher number of unselective, non-templated binding sites. This increase in background binding sites could lead to a decrease in the magnitude of the imprinting effect and in the selectivity of the MIP. Therefore, phosphate selective imprinted and non-imprinted polymers (NIPs) were prepared using a novel multifunctional triurea monomer. The binding properties of these polymers were compared with polymers prepared using a monofunctional monourea monomer. The binding affinities and selectivities of the monomers, imprinted polymers, and NIPs were characterized by NMR titration, binding uptake studies, and binding isotherms. MIPs prepared with the triurea monomer showed higher binding affinity and selectivity for the diphenylphosphate anion in organic solvents than the MIPs prepared with the monofunctional monomer. Surprisingly, the binding properties of the NIPs revealed that the polymers prepared using the multifunctional and monofunctional monomers were very similar in affinity and selectivity. Thus, the multifunctional monomers increase not only the affinity of the MIP but also enhance the imprinting effect.

Novel electrodialysis membranes with hydrophobic alkyl spacers and zwitterion structure enable high monovalent/divalent cation selectivity

Nanofibrous composite membranes (NFCMs) for mono/divalent cations separation

The world's population is growing, leading to an increasing demand for freshwater resources for drinking, sanitation, agriculture, and industry. Interfacial solar steam generation (ISSG) can solve many problems, such as mitigating the power crisis, minimizing water pollution, and improving the purification and desalination of seawater, rivers/lakes, and wastewater. Cellulosic materials are a viable and ecologically sound technique for capturing solar energy that is adaptable to a range of applications. This review paper aims to provide an overview of current advancements in the field of cellulose‐based materials ISSG devices, specifically focusing on their applications in water purification and desalination. This paper examines the cellulose‐based materials ISSG system and evaluates the effectiveness of various cellulosic materials, such as cellulose nanofibers derived from different sources, carbonized wood materials, and two‐dimensional (2D) and 3D cellulosic‐based materials from various sources, as well as advanced cellulosic materials, including bacterial cellulose and cellulose membranes obtained from agricultural and industrial cellulose wastes. The focus is on exploring the potential applications of these materials in ISSG devices for water desalination, purification, and treatment. The function, advantages, and disadvantages of cellulosic materials in the performance of ISSG devices were also deliberated throughout our discussion. In addition, the potential and suggested methods for enhancing the utilization of cellulose‐based materials in the field of ISSG systems for water desalination, purification, and treatment were also emphasized.

We investigated property of a FeCrAl type stainless steel as a porous alloy substrate of metal supported SOFCs especially on the cathode side. We confirmed not only good heat resistance but also low electrical resistance at the interface between the porous substrate and La0.6Sr0.4Co0.2Fe0.8O3 (LSCF) coating at 700oC in air. Morphology and crystal structure of the surface oxide layer of the FeCrAl alloy was analyzed by STEM-EDS and TEM in detail to clarify the cause of such a low electrical resistance. Long-term stability of the oxidation resistance of the porous FeCrAl alloy substrate was investigated by increasing operating temperature up to 900oC. Oxidation rate of the alloy at 700oC in air was estimated by the increase in weight, thickness of the surface oxide and electrical resistance.

1. It has been established that NChK is poorly oxidized by biochemical reactions, and negatively affects the biological purification of waste water. 2. The limiting admissible NChK concentration for the biochemical purification of ELOU waste water was determined by experiments in laboratory aerotankmixers. 3. The high NChK doses, as are used in the treatment of crude Arlan type oils of high sulfur content, complicate the methods of completely purifying the waste water emulsions, since considerable amounts of NChK (up to 15 g/liter) are accumulated in the waste water. Owing to this and the high content of mineral salts, it is necessary to dilute the waste water to bring the NChK content down to 200 mg/liter, and the content of mineral salts to 10 g/liter. The dilution of ELOU waste water must be done with domestic-fecal sewage, or with conventional pure water if the waste water is admixed with sewage from industrial plants that contains fairly oxidizing organic compounds. 4. Since NChK negatively affects the biochemical purification, it is indispensable in the very near future to search for deemulsifiers that can be used in the treatment of crude oils of high sulfur content, and be oxidized more efficiently by biochemical processes.

【Thin pore-filled cation and anion-exchange membranes (PFCEM and PFAEMs, $t_m=25-30{\mu}m$ ) were prepared using a porous polymeric substrate for efficient all-vanadium redox flow battery (VRB). The electrochemical and charge-discharge performances of the membranes have been systematically investigated and compared with those of commercially available ion-exchange membranes. The pore-filled membranes were shown to have higher permselectivity as well as lower electrical resistances than those of the commercial membranes. In addition, the VRBs employing the pore-filled membranes exhibited the respectable charge-discharge performances, showing the energy efficiencies (EE) of 82.4% and 84.9% for the PFCEM and PFAEM, respectively (cf. EE = 87.2% for Nafion 1135). The results demonstrated that the pore-filled ion-exchange membranes could be successfully used in VRBs as an efficient separator by replacing expensive Nafion membrane.】

1. Ozone is a promising reagent for purifying and repurifying waste water. Since it has the highest oxidation-reduction potential of any known oxidant, it gives practically complete purification of the waste water. 2. Ozone may be used to purify and repurify waste water of petroleum products, hydrogen sulfide, sulfur compounds, phenols, cyanides, and other substances. 3. Ozonation of waste water requires no complicated equipment, nor transportation of the reagent. The ozone is produced on the spot where the waste water is being purified from the air, using ozonators that require nothing more than electric power. 4. No precipitates are formed in the purified waste water, which makes the purification equipment considerably easier to operate.

In this work, we developed pore-filled ion-exchange membranes (PFIEMs) fabricated for the application to an all-vanadium redox flow battery (VRFB) by filling a hydrocarbon-based ionomer containing a fluorine moiety into the pores of a porous polyethylene (PE) substrate having excellent physical and chemical stabilities. The prepared PFIEMs were shown to possess superior tensile strength (i.e., 136.6 MPa for anion-exchange membrane; 129.9 MPa for cation-exchange membrane) and lower electrical resistance compared with commercial membranes by employing a thin porous PE substrate as a reinforcing material. In addition, by introducing a fluorine moiety into the filling ionomer along with the use of the porous PE substrate, the oxidation stability of the PFIEMs could be greatly improved, and the permeability of vanadium ions could also be significantly reduced. As a result of the evaluation of the charge–discharge performance in the VRFB, it was revealed that the higher the fluorine content in the PFIEMs was, the higher the current efficiency was. Moreover, the voltage efficiency of the PFIEMs was shown to be higher than those of the commercial membranes due to the lower electrical resistance. Consequently, both of the pore-filled anion- and cation-exchange membranes showed superior charge–discharge performances in the VRFB compared with those of hydrocarbon-based commercial membranes.

Multifunctional and sustainable chitosan-based interfacial materials for effective water evaporation, desalination, and wastewater purification: A review.

Electrochemical Methods for Purification of Waste Waters

Hybrid membrane system for desalination and wastewater treatment : Integrating forward osmosis and low pressure reverse osmosis

Electrodialysis (ED), an ion exchange membrane-based desalination method is particularly notable for its application in treating brackish water and ion separations [1]. In an ED system, anion exchange membranes (AEMs) that increase the permselectivity of anions is crucial to enhancing the separation efficiency of an ED process, requiring not only high ions selectivity, but also a low ionic resistance, low fouling, and good chemical stability. Polymers based on poly[2,2’-(2,2",4,4",6,6"-hexamethyl-p-terphenyl-3,3"-diyl)-5,5’-bibenzimidazole] (HMT-PMBI) exhibit enhanced chemical stability and modifiable properties based on the degree of methylation (dm). HMT-PMBI with 75% degree of methylation (HMT-PMBI 75dm) exhibit exceptionally large mono/divalent permselectivity but relatively lower ionic conductivity (high resistance) [2]; higher degrees of methylation, such as 89% (HMT-PMBI 89dm), increases ionic conductivity at the expense of decreased permselectivity [2]. Therefore, in this work, we examined the formation of bilayers HMT-PMBI having two different degrees of methylation, 75dm and 89 dm, and thus two different properties. When the 89dm layer of the bilayer 75dm/89dm membrane faced the cathode, an improved permselectivity (= 4.3 for 23 µm) was noted compared to single layer 89dm (= 0.9 for 23 µm). Additionally, fouling resistance to a surfactant (sodium dodecyl benzenesulfonate, SDBS) exhibited a significant improvement, with a transition time of 18.4 minutes, around thirteen times greater than the single layer 75dm membrane (transition time of 1.37 min). In conclusion, the bilayer configuration membrane effectively brought the advantage of the higher hydrophilicity of the 89dm layer to enhance conductivity and fouling resistance while preserving the permselectivity afforded by 75dm layer. This work highlights that significant advances in the field of membrane technology for ED applications may potentially be achieved through bilayer and multilayer systems of ion-containing polymers of similar types but different ion exchange capacities, balancing individual layers of differing ionic conductivity and fouling resistance, and making use of inherent permselectivity interfaces that lie between multiplayers.[1] M.A. Alkhadra, X. Su, M.E. Suss, H. Tian, E.N. Guyes, A.N. Shocron, K.M. Conforti, J.P. De Souza, N. Kim, M. Tedesco, K. Khoiruddin, I.G. Wenten, J.G. Santiago, T.A. Hatton, M.Z. Bazant, Electrochemical Methods for Water Purification, Ion Separations, and Energy Conversion, Chem Rev 122 (2022) 13547–13635. https://doi.org/10.1021/acs.chemrev.1c00396.[2] A.S. Gangrade, B. Tusi, P.C. Ghosh, S. Holdcroft, High monovalent/divalent permselectivity and low ionic resistance of ionene-based anion exchange membranes in electrodialysis, J Memb Sci 685 (2023). https://doi.org/10.1016/j.memsci.2023.121906. Figure 1

Driven by sustainable development and circular economy, wastewater treatment has shifted from the simple removal of pollutants to the simultaneous recovery of valuable resources. Among various technologies, electrodialysis (ED) and its related processes are regarded as promising perspectives for wastewater treatment and resource recovery. In this thesis work, two studies were conducted: (1) ED for ammonium concentration, and (2) bipolar membrane electrodialysis (BPED) for acid and base production from pre-treated seawater desalination brine. Firstly, to obtain a high concentration ammonium solution for subsequent more effective recovery, ED was used to concentrate ammonium from low concentration domestic wastewater. In this process, various operating parameters, including current density, the volume ratio between dilute and concentrate solution, and the ion exchange membrane (IEM) arrangement in ED stacks, were investigated. In addition, the transport number and selectivity of cations (i.e., Na+, K+, Ca2+, or Mg2+) over NH4+ into concentrate chambers were studied to elucidate the mechanism of competitive ion transport in ED. Results show that a higher applied current density (2 mA/cm2), a greater volume ratio between dilute and concentrate (20:1), and the configuration with anion exchange membranes (AEMs) adjacent to electrode chambers could achieve better ammonium concentration efficiency. In the second part of using BPED for acid and base production, the BPED performance was experimentally evaluated using different commercial anion exchange membranes (AEMs) and cation exchange membranes (CEMs). The results revealed that acid production is mainly influenced by the properties of AEMs rather than the CEMs, while base production is mainly influenced by the properties of CEMs rather than the AEMs. Specifically, both IEMs with higher permselectivity and lower electrical resistance could achieve better performance, i.e., higher acid and base production, lower energy consumption, and higher current efficiency. A long-term BPED batch-test up to 26 h was conducted, which produces 0.97 M HCl and 0.80 M NaOH with high purity for both products (around 95%) and low energy consumption. This research demonstrates the high promise of ED-based ion exchange membrane processes for resource recovery and waste valorization.