Comb-shaped anion exchange membrane to enhance phosphoric acid purification by electro-electrodialysis

Anion Exchange Membranes Based on Bis-Imidazolium and Imidazolium-Functionalized Poly(phenylene oxide) for Vanadium Redox Flow Battery Applications

Although the Nafion membrane has a high energy efficiency, long service life, and operational flexibility when applied for vanadium redox flow battery (VRFB) applications, its applications are limited due to its high vanadium permeability. In this study, anion exchange membranes (AEMs) based on poly(phenylene oxide) (PPO) with imidazolium and bis-imidazolium cations were prepared and used in VRFBs. PPO with long-pendant alkyl-side-chain bis-imidazolium cations (BImPPO) exhibits higher conductivity than the imidazolium-functionalized PPO with short chains (ImPPO). ImPPO and BImPPO have a lower vanadium permeability (3.2 × 10^-9 and 2.9 × 10^-9 cm² s^-1) than Nafion 212 (8.8 × 10^-9 cm² s^-1) because the imidazolium cations are susceptible to the Donnan effect. Furthermore, under the current density of 140 mA cm^-2, the VRFBs assembled with ImPPO- and BImPPO-based AEMs exhibited a Coulombic efficiency of 98.5% and 99.8%, respectively, both of which were higher than that of the Nafion212 membrane (95.8%). Bis-imidazolium cations with long-pendant alkyl side chains contribute to hydrophilic/hydrophobic phase separation in the membranes, thus improving the conductivity of membranes and the performance of VRFBs. The VRFB assembled with BImPPO exhibited a higher voltage efficiency (83.5%) at 140 mA cm^-2 than that of ImPPO (77.2%). These results of the present study suggest that the BImPPO membranes are suitable for VRFB applications.

Removal of Metal Ions in Phosphoric Acid by Electro-Electrodialysis with Cross-Linked Anion-Exchange Membranes

There are numerous metallic impurities in wet phosphoric acid, which causes striking negative effects on industrial phosphoric acid production. In this study, the purification behavior of metallic impurities (Fe, Mg, Ca) from a wet phosphoric acid solution employing the electro-electrodialysis (EED) technology was investigated. The cross-linked polysulfone anion-exchange membranes (AEMs) for EED were prepared using N,N,N',N'-tetramethyl-1,6-hexanediamine (TMHDA) to achieve simultaneous cross-linking and quaternization without any cross-linkers or catalysts. The performance of the resulting membranes can be determined using quaternization reagents. When the molar ratio of trimethylamine/TMHDA/chloromethylated polysulfone is 3:1:1, the cross-linked membrane CQAPSU-3-1 exhibits lower water swelling and membrane area resistance than the non-cross-linked membrane. The low membrane area resistance of CQAPSU-3-1 with long alkyl chains is obtained due to the hydrophilic-hydrophobic microphase separation structure formed by TMHDA. EED experiments with different initial phosphoric acid concentrations of 0.52 and 1.07 M were conducted to evaluate the phosphoric acid purification of different AEMs. The results show that the EED experiments were more suitable for the purification of wet phosphoric acid solution at low concentrations. It was found that the phosphoric acid concentration in the anode compartment could be increased from 0.52 to 1.04 M. Through optimization, with an initial acid concentration of 0.52 M, CQAPSU-3-1 exhibits an enhanced metallic impurity removal ratio of higher than 72.0%, the current efficiency of more than 90%, and energy consumption of 0.48 kWh/kg. Therefore, CQAPSU-3-1 exhibits much higher purification efficiency than other membranes at a low initial phosphoric acid concentration, suggesting its potential in phosphoric acid purification application.

Electrodialytic Processes: Market Overview, Membrane Phenomena, Recent Developments and Sustainable Strategies

In the context of preserving and improving human health, electrodialytic processes are very promising perspectives. Indeed, they allow the treatment of water, preservation of food products, production of bioactive compounds, extraction of organic acids, and recovery of energy from natural and wastewaters without major environmental impact. Hence, the aim of the present review is to give a global portrait of the most recent developments in electrodialytic membrane phenomena and their uses in sustainable strategies. It has appeared that new knowledge on pulsed electric fields, electroconvective vortices, overlimiting conditions and reversal modes as well as recent demonstrations of their applications are currently boosting the interest for electrodialytic processes. However, the hurdles are still high when dealing with scale-ups and real-life conditions. Furthermore, looking at the recent research trends, potable water and wastewater treatment as well as the production of value-added bioactive products in a circular economy will probably be the main applications to be developed and improved. All these processes, taking into account their principles and specificities, can be used for specific eco-efficient applications. However, to prove the sustainability of such process strategies, more life cycle assessments will be necessary to convince people of the merits of coupling these technologies.

Reuse of manganese sulfate as raw material by recovery from pesticide's wastewater using nanofiltration and electro-electrodialysis: process simulation and analysis from actual data

Reuse of wastewater, as well as recovery of valuable, toxic or harmful products in industrial discharges, still represents an important issue, not only because it reduces the effect on receiving water bodies, but also because of the economic resources it represents for industry itself. In this research, in situ regeneration of Mn₂SO₄ is evaluated, for its reuse as the main raw material in the original process of a fungicide plant. The regeneration is evaluated by selective recovery of Mn²⁺, Zn²⁺ and SO₄ ⁼ present in the wastewater produced by the industrial plant, and utilizing nanofiltration, electro-electrodialysis and chemical precipitation as separation alternatives. Each alternative was designed and evaluated technically and economically through simulations in Aspen Plus^®, with data and information of the real process supplied by the company. Because zinc concentration is relatively low, its selective recovery was not attractive. The resulting Mn₂SO₄ solution and treated water quality in conventional alternatives were significantly poor with high costs. In contrast, nanofiltration and electro-electrodialysis alternatives generate water and by-products of higher quality and reuse potential with significantly lower costs. However, their viability depends on the membrane performance. The results were satisfactory, but future experimental studies are required to optimize the alternatives and define the correct pretreatment process.

Partially fluorinated copolymers containing pendant piperidinium head groups as anion exchange membranes for alkaline fuel cells

A new series of partially fluorinated copolymers with varying alkyl side chain length (C3, C6 and C9) and piperidinium head groups have been synthesized and characterized in detail in an effort to improve membrane properties for alkaline fuel cell applications. The copolymers (QPAF4-Cx-pip) provided thin and bendable membranes by solution casting, and achieved high hydroxide ion conductivity up to 97 mS cm⁻¹ in water at 80 °C. Membrane properties such as water absorbability, conductivity, and mechanical properties were tunable with the side chain length. The copolymer main chain and the piperidinium groups were both alkaline stable and the membranes retained high conductivity in 4 M KOH at 80 °C for as long as 1000 h, however, conductivity was lost in 8 M KOH due to Hofmann degradation of the side chain. QPAF4-C3-pip copolymer with the best-balanced properties as anion exchange membrane functioned well in a hydrogen/oxygen alkaline fuel cell to achieve 226 mW cm⁻² peak power density at 502 mA cm⁻² current density under fully humidified conditions with no back pressure.

Piperidinium functionalized partially fluorinated copolymers with varying alkyl spacer length were synthesized and evaluated as anion exchange membranes to achieve improved performance in alkaline fuel cells.