This paper addresses hybrid ion exchange membranes fabricated by the synthesis of amorphous zirconium phosphate (dopant contents from 0.5 to 24 wt%) directly in the pore and channel system of heterogeneous cation-exchange membrane RALEX® CM (by in situ technique). The incorporation of zirconium phosphate nanoparticles into the membrane system of pores and channels leads to the displacement of the pore water. As a result, the cation transport numbers increase. The hybrid materials thus obtained are characterized by increased ionic resistance and enhanced monovalent ion selectivity. The former effect was eliminated by fabrication of a surface-modified membrane. The relative simplicity of modification, together with the benefits of the hybrid materials 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 was found.
This communication describes the development of anion-exchange membrane (AEM) with a modified surface possessing monovalent ion selectivity and antifouling properties. Modified AEMs series was obtained by the formation of an oppositely-charged thin layer utilizing the surface sulfonation of the grafted AEMs. The creation of the interface layer leads to a significant increase in the Cl/SO4 selectivity and the appearance of humic acid sorption resistance. The surface-sulfonated anion-exchange membrane (s-AEM) has a high ionic conductivity of 11.2 mS cm−1 and high Cl/SO4 selectivity up to 6.4 in electrodialysis. The sulfonated layer was characterized by IR spectroscopy and electron microscopy. The relationship between the structure and thickness of the cation-exchange surface layer and the observed changes in membrane transport properties such as diffusion permeability, ionic conductivity, potentiometric transport numbers, and current-voltage characteristics are discussed. It was shown that the Cl/SO4 selectivity of s-AEM in the desalination process depends on the current density. The obtained data were successfully interpreted using a mathematical model based on the concept of the bipolar structure of the s-AEM surface layer and diffusion control of anion transport through it.
Cation-exchange membranes containing sulfo R–SO3M and sulfonylimide functional groups [R–SO2NSO2–X]M, where X¼CCl3, CF3, Ph, p-NO2Ph, p-CF3Ph and Mþ¼Li/Na/H, have been synthesized by the Hinsberg reaction from the polystyrene-block-poly(ethylene-ran-butylene)-block-polystyrene block copolymer. The obtained membranes have been characterized using ATR IR spectroscopy, CHNS elemental analysis, TGA, DSC, SEM and X-ray diffraction analysis, as well as mechanical properties were determined. Ionic conductivity of plasticized polymer electrolytes, containing mixtures of ethylene carbonate, propylene carbonate and ethylene carbonate, dimethylacetamide were investigated by impedance spectroscopy. It was demonstrated that membranes containing trifluorosulfonylimide functional groups have the highest ionic conductivity. The maximum ionic conductivity at 25C was observed for the membrane in contact with an ethylene carbonate – dimethylacetamide mixture.
The influence of geometrical parameters and fluid properties on the critical pressure of permeation of an oil micro-droplet into a slotted pore is studied numerically by solving the Navier-Stokes equations. We consider a long slotted pore, which is partially blocked by the oil droplet but allows a finite permeate flux. An analytical estimate of the critical permeation pressure is obtained from a force balance model that involves the drag force from the flow around the droplet and surface tension forces as well as the pressure variation inside the pore. It was found that numerical results for the critical pressure as a function of the oil-to-water viscosity ratio, surface tension coefficient, contact angle, and droplet radius agree well with theoretical predictions. Our results show that the critical permeation pressure depends linearly on the surface tension coefficient, while the critical pressure nearly saturates at sufficiently large values of the viscosity ratio or the droplet radius. These findings are important for an optimal design and enhanced performance of microfiltration systems with slotted pores.