Permselectivity and ion-conductivity of grafted cation-exchange membranes based on UV-oxidized polymethylpenten and sulfonated polystyrene

International audienceIn the present study the properties of novel cation-exchange membranes based on UV-oxidized polymethylpentene (PMP) with grafted sulfonated polystyrene are described. A correlation between the composition of the grafted copolymer (grafting degree, cross-linking degree) and transport properties (Na+-conductivity, permselectivity, diffusion permeability) of resulted membranes are discussed. It is shown that with increasing of grafting degree (GD) and lowering of cross-linking degree (CD) the concentration of functional groups in the inner solution and permselectivity decrease, while ionic conductivity increases. The obtained membranes have the GD ranging from 29 to 120% and CD from 0 to 5%. The best membranes have ionic surface resistance of 0.3–0.6 Ω cm2 in 0.5 M NaCl, apparent cation transport numbers of 0.870–0.998 and NaCl diffusion permeability of 3.3 · 10−8–5.5 · 10−7 cm2 s−1, as well as satisfactory mechanical performance. A comparison of transport properties (conductivity and cation transport number) of the obtained membranes with a properties of number of available samples was made. It is noted that some of the obtained samples are at the level of the best perfluorinated homogeneous membranes in terms of the ratio of conductivity and cation transport numbers. High ionic conductivity and permselectivity make the prepared membranes promising candidates for possible applications in electrodialysis, dialysis, reverse electrodialysis, Red-Ox flow batteries and other membrane processes

Influence of the nature of cation on water splitting at the interface of a cation exchange membrane during electrodialysis

The phenomenon of water splitting occuring at the interface of a Selemion CMV cation exchange membrane in contact with solutions containing successively monovalent, divalent and trivalent cations was investigated. Under identical hydrodynamic conditions, this investigation is based on recording j-V curves, measurement of transport numbers and pH variations. Water splitting is not a direct consequence of concentration polarization phenomenon. The cation nature and especially its acidic character is an important parameter which explains the difference in the behavior of the Selemion CMV membrane in contact with solutions of different cations

Sulfonated polyimides as proton conductor exchange membranes. Physicochemical properties and separation H+/Mz+ by electrodialysis comparison with a perfluorosulfonic membrane

International audienceThe properties of new sulphonated polyimide membranes (SP) - ion exchange isotherms, electrical conductivity, selectivity and proton-cation electrotransport - are compared with that of perfluorinated Nafion® membrane. Both membranes when in contact with H+/Mz+ aqueous solutions (MzM+=Na+, Cu2+, Cr3+) present an affinity to cations which increases with their valencies; however the affinity of one of the SP membranes for protons is approximately 10% higher than that of Nafion The proton transport number is also 10% higher for this SP membrane than for Nafion Using SP membranes for electrodialysis of H+/Cu2+ solutions produces solutions about 10% more concentrated in H+ and about 40% less concentrated in Cu2+ ions than with Nafion® membranes in the same conditions. The difference in conductivity may be explained by differences in ionic clustering because of differences in the polymer structure of the two membranes, block copolymer for SP and statistic copolymer for Nafion The difference in properties for the two SP membranes is explained in terms of the chemical structure of the non-sulfonated diamine groups used in the polymer synthesis. These SP membranes seem to be interesting materials for electromembrane processes in acid medi

Chromic acid recovery by electro-electrodialysis. I. Evaluation of anion-exchange membrane

Electro-electrodialysis (EED) is a promising technology for economic recovery of chromic acid in plating shops. It could potentially achieve chromic acid recovery, removal of metallic impurities and purification of static rinses in one step. There are however, process limitations. These are mainly, the poor stability of the applied anion-exchange membrane (AEM) against the oxidative chromic acid solution and the increase of the AEM resistance, especially at the starting phase of the process, due to the formation of polychromates in the membrane.\ud \ud In this work, various AEM are investigated for chromic acid recovery. The membrane fumasep® FAP (FuMA-Tech GmbH) seems to be the most efficient. Its current efficiency is much higher than those previously reported in the literature. Furthermore, the fumasep® FAP is used for process optimisation experiments. The process performance depends on the concentration gradient between product (anolyte) and central compartment (exhausted rinse water) and the temperature. Our results show that batch processing is recommended and the chromate transfer rates through the AEM could be significantly increased when increasing the temperature up to 50 °C. Finally, low initial current density (10¿20 mA cm¿2), feed flow rate higher than 7 cm s¿1 could help overcoming the process limitations attributed to high AEM resistance

Chromic acid recovery by electro-electrodialysis. II. Pilot scal process, development, and optimization

Electro-electrodialysis is a promising technology for chromic acid recovery and static rinse water purification. It combines the recovery of the plating chemicals from rinse water, the elimination of metallic impurities from the process and rinse water treatment in one step. Previous industrial use was restricted due to non-resistant anion-exchange membranes and process ineffectiveness. In this work, a stable and economical process is developed and high-quality chromic acid is recovered using a new oxidative stable anion exchange membrane (AEM Fumasep® FAP, FuMA-Tech GmbH). The membrane stability and performance is evaluated by a long-term experiment for 400 h. Recovery rates were determined for batch and continuous operation and at different operation temperatures. The highest chromic acid production was reached by batch processing at 40 °C. Both measures increase significantly the chromate transfer and result in lower equipment size and operational cost

An approach to increase the permselectivity and mono-valent ion selectivity of cation-exchange membranes by introduction of amorphous zirconium phosphate nanoparticles

International audienceThis paper addresses hybrid ion exchange membranes fabricated by the synthesis of amorphous zirconiumphosphate (dopant contents from 0.5 to 24 wt%) directly in the pore and channel system of heterogeneouscation-exchange membrane RALEX® CM (by in situ technique). The incorporation of zirconium phosphate nanoparticlesinto the membrane system of pores and channels leads to the displacement of the pore water. As aresult, the cation transport numbers increase. The hybrid materials thus obtained are characterized by increasedionic resistance and enhanced monovalent ion selectivity. The former effect was eliminated by fabrication of asurface-modified membrane. The relative simplicity of modification, together with the benefits of the hybridmaterials make them promising for some membrane processes. Using 31P MAS NMR and elemental analysis,considerable difference between the zirconium phosphate composition inside and outside the membrane wasfound

"Ion exchange membraes and associated processes. A state of the art and new trends"

International audienc