Selective Cation Exchange Membrane Research Articles

Surface modification of composite ion exchange membranes by polyaniline

The aim of this work is to develop new selective cation exchange membranes (CEMs) from bivalent to monovalent selectivity by surface functional groups. So, a novel hybrid cation exchange membrane was prepared by polymerization of polyaniline on a composite membrane, made of polyvinylidene fluoride (PVDF) and sulfonated PVDF (S-PVDF). Polyaniline was doped with different doping agents and their effect on total salt extraction and selectivity of bivalent to monovalent cations was evaluated. The chemical and morphological properties of hybrid membranes were characterized by Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD) and scanning electron microscopy (SEM). Ion exchange capacity (IEC), transport number, ion conductivity and water uptake decreased after surface polymerization. Composite membrane has a good selectivity (∼2) for bivalent and excellent removal of both cations. The hybrid membrane, doped with pTSA has a very high selectivity for monovalent ions (∼7.1) and a high removal of monovalent ions.

Preparation and evaluation of chiral selective cation-exchange PMMA–PNIPAm thermal-sensitive membranes

Selective cation-exchange membranes are placing a key role in separation processes. The application of selective cation-exchange membranes is wide since there are many kinds of mixtures needed to be separated for reuse. In this study, a facile and efficient one-pot approach was used to obtain monodispersed methyl methacrylate–N-isopropyl acrylamide (MMA–NIPAm) polymer by atom transfer radical precipitation polymerization (ATRPP) and then MMA–NIPAm chiral selective separation membranes were prepared for separating racemic equol. Firstly, using dodecylbenzenesulfonyl chloride (DBSC) as the initiator, bipyridine (bipy)/CuCl as the catalyst system, acetonitrile as the solvent, and S-equol as template molecule by which a MMA–NIPAm copolymer was synthesized and it was characterized by TEM, FTIR, TGA, UV–vis absorption spectrum, and dynamic layer scattering analysis. Lastly, MMA–NIPAm chiral separation membranes were prepared by casting 3 wt% of MMA–NIPAm copolymer dimethyl formamide (DMF) solution on a rimmed glass plate and evaporated the solvent completely at 100 °C under vacuum. Then, the PMMA–PNIPAm chiral selective cation-exchange membranes were prepared by immersing in methanol/acetic acid (95:5, v/v) to remove the template molecules. Most worthy of mention was that the prepared chiral selective separation membranes could separate S-equol and R-equol from the mixture of racemic equol. In application of a thermo-responsive monomer, the separation ability of the prepared PMMA–PNIPAm chiral separation membranes could be tunable according to environment temperature changes.

The reclamation of brine generated from desalination process by bipolar membrane electrodialysis

Some techno-economical analyses and environmental impact evaluation have proved that bipolar membrane electrodialysis (BMED) is feasible for the reclamation of industrial saline water. However, to date, the technology cannot be put into practice due to some unsolved application-oriented problems, such as the requirements of BMED for feed solution, the availability of the produced acid and base, relatively high salt concentration of the effluent, and relatively low desalinating efficiency and capacity. In this work, a novel hybrid process, which coupled conventional electrodialysis installed with monovalent selective cation-exchange membranes with BMED running in a constant-voltage mode, was designed to reclaim brine generated from surface water desalination by the ion-exchange process. Subsequently, the response surface methodology was employed to establish the empirical models for understanding the influences of some initial operating conditions on BMED performance. Finally, the BMED-based reclamation scheme was confirmed again by a continuous BMED experiment on real solution. Specially, the effects of product concentration on current efficiency and energy consumption were investigated. In this case, an acceptable current efficiency and energy consumption were obtained on the basis of the conventional membranes and spacers when the product concentration was set as 0.9M, which is adequate for the regeneration of ion-exchange resins.

Preparation of Mono-Valent Cation Selective Cation-Exchange Membranes for Electrodialysis of Seawater by Electron-Beam-Induced Graft Polymerization

Preparation of Mono-Valent Cation Selective Cation-Exchange Membranes for Electrodialysis of Seawater by Electron-Beam-Induced Graft Polymerization

Controlling the oxidation of organic brightener during electroplating using an ion-exchange membrane

The effect of an ion-exchange membrane combined with a dimensionally stable anode on the oxidation rate of organic brightener and electroplating performance was investigated. The oxidation rate of the brightener was measured by analyzing the total organic carbon content in the plating solution. The oxidation rate increased rapidly as the current density increased when there was no ion-exchange membrane. However, when an ion-exchange membrane was present, the oxidation rate of the brightener was significantly reduced by Neosepta CMX and CMS cation-exchange membranes. The CMS monovalent selective cation-exchange membrane in particular was the most effective in reducing organic brightener oxidation, regardless of the current density. Through-hole printed circuit board electroplating was more precise with an ion-exchange membrane than with no membrane. These results confirmed that the electroplating performance was improved by the presence of an ion-exchange membrane on the anode, effectively inhibiting the oxidation of organic brightener.

Preparation of chiral selective membranes for electrodialysis separation of racemic mixture

Chiral selective cation-exchange membrane (CSCM) and chiral selective anion-exchange membrane (CSAM) were prepared by blending poly(vinyl alcohol) (PVA) as basic material, β-cyclodextrin (β-CD) as chiral selector, and ion-exchange materials. Chiral selective capacities of these membranes were evaluated by electrodialysis resolution experiment. Electrodialysis separation of dl-4-hydroxyphenylglycine (HPG) racemic mixture showed that the chiral selective membranes had resolution effect. In acid medium, d-HPG + took the precedence over l-HPG + in passing through the CSCM and the selectivity α d/ l of two kinds of CSCM were 1.21 and 1.34, respectively. In base medium, l-HPG − took the precedence over d-HPG − in passing through the CSAM and the selectivity α d/ l was 0.84.

Preparation and characterisation of monovalent ion selective cation exchange membranes based on sulphonated poly(ether ether ketone)

This paper analyses the separation properties of various commercial cation exchange membranes (CEMs) and tailor made membranes based on sulphonated poly(ether ether ketone) and poly(ether sulphone) for binary electrolyte solutions containing protons and calcium ions. All membranes are thoroughly characterised and relations between their electrochemical properties and ion selectivity are drawn. The effect of current density and calcium ion concentration in the feed stream on the membrane selectivity is investigated. Our results show that the conductivity and the charge density of the membranes determine the calcium transport through the membranes. The calcium transport increases with increasing conductivity, however, it is lower for membranes with lower charge density. Therefore, the preparation of membranes with reasonable conductivities and low calcium transport is possible. Besides, the calcium flux increases with the increase of current density and/or calcium concentration for all membranes. For CEMs having a positively charged coating, the calcium flux is low at low current density but increases strongly at high current densities.

Electrolyte diffusive flux determination through a highly selective cation exchange membrane

A new method for evaluating highly selective ion exchange membranes is devised, which is competitive with the counter-ion transport number determination method. It is based on the evaluation of a strong electrolyte leakage through a membrane. This study uses a CM2 polystyrene and divinylbenzene sulfonated cation exchange membrane, separating two solutions, one containing the electrolyte at a given concentration C0 and the other permuted water. The electrolyte diffuses under its concentration gradient and induces an increase of the conductivity in the diluted compartment, allowing the determination of its flux. This new method is shown to be reliable and sufficiently accurate over a large concentration range. The bilogarithmic variation of the flux versus the concentration, for the KCl (10-2⩽C0⩽4 mol L-1)/CM2/H2O system, shows the existence of three linear sections, each one corresponding to a diffusion state. The concentration range 10-1–2 mol L-1 seems to be the most interesting one for experimental and theoretical studies of the diffusion phenomenon of a strong electrolyte through an ion exchange membrane. In this domain the concentration is high enough that the proton contribution to the measured values of the conductivity can be neglected and sufficiently low that the osmosis flux, which would slow down the electrolyte as it diffuses, is not important. Une nouvelle me′thode simple d'e′valuation des performances des membranes e′changeuses d'ions (MEI) fortement se′lectives est propose′e. Cette me′thode est concurrentielle à celle de la de′termination du nombre de transport du contre-ion. Elle est base′e sur l'e′valuation de la fuite d'un e′lectrolyte fort à travers une membrane (dans cette e′tude, nous avons utilise′ une membrane sulfonique e′changeuse de cation, CM2) se′parant deux solutions, l'une contenant cet e′lectrolyte à la concentration C0 et l'autre initialement de l'eau permute′e. L'e′lectrolyte diffuse alors sous l'effet de son gradient de concentration et fait augmenter la conductivite′ du compartiment dilue′, laquelle nous permet de de′terminer son flux. Nous avons montre′ que cette nouvelle me′thode est sûre et suffisamment pre′cise sur une large gamme de concentrations. La variation bilogarithmique du flux en fonction de la concentration pour le système KCl (10-2⩽C0⩽4 mol L-1)/CM2/H2O montre l'existence de trois domaines line′aires dont chacun correspond à un re′gime de diffusion. La gamme de concentrations 10-1–2 mol L-1 semble être la plus inte′ressante pour les e′tudes expe′rimentales et the′oriques du phe′nomène de diffusion d'un e′lectrolyte fort à travers une MEI. Dans ce domaine la concentration est suffisamment e′leve′e pour pouvoir ne′gliger la contribution des protons aux valeurs mesure′es de la conductivite′ et suffisamment faible pour ne pas ge′ne′rer un important flux osmotique qui ralentit l'e′lectrolyte lors de sa diffusion.

Low Effluent Processing in the Pulp and Paper Industry: Electrodialysis for Continuous Selective Chloride Removal

Pollution prevention is currently a major focus of the United States pulp and paper industry. Significant process changes are inevitable to implement low effluent processing. The kraft pulping process is prevalent for the production of wood pulp. About 50 million tons of wood pulp are produced annually in the United States alone using the kraft process. Water consumption is currently roughly between 30 and 200 m3 of water per ton of air dry bleached kraft pulp. In-process recycling of water is now being implemented by many mills to reduce the use of increasingly scarce water resources and to reduce the need for waste-water treatment. Mass balance considerations and industrial experience show that nonprocess elements, which are detrimental to the kraft process, such as chloride and potassium, will quickly build up once water use is significantly reduced. High concentrations of chloride and potassium can cause corrosion and lead to more frequent mill shutdowns due to fouling of heat exchanger surfaces in the kraft recovery furnace. Electrodialysis with monovalent selective anion and cation exchange membranes was explored here to selectively remove chlorine as sodium and potassium chloride from a feed stream with very high ionic strength. Experiments with model solutions and extended tests with the actual pulp mill materials were performed. Very good selectivities and current efficiencies were observed for chloride over sulfate. The outstanding performance of the process with actual mill materials containing organic and inorganic contamination shows great promise for rapid transfer to the pilot scale. This work is an example of the usefulness of membrane separations as a kidney in low effluent industrial processing.

Multi-Ionic Potential and Membrane Permeability Matrix. III. Diffusion and Concentration of Ions within Membrane Phase as a Controlling Factor to Ion Permselectivity

Abstract Membrane concentrations of cations in the NaCl–CsCl and NaCl–CaCl2 systems with a highly selective cation-exchange membrane were measured under the extensive external electrolyte conditions. The modes of membrane/solution distribution and diffusion of cations, as a controlling factor to the membrane permselectivity, were correlated consistently with the electrochemical and cation flux data, as well as with the estimated membrane permselectivity parameters. The NaCl–CsCl uni-uni valent cation system was characterized well by the Na+/Cs+ concentration ratio of external solution, since the Na+/Cs+ concentration ratio in the membrane phase was related directly to the external ratio. Na+/Cs+ diffusion coefficient ratio varied from 0.5 to 3 with increasing external Na+/Cs+ concentration ratio from 1/100 to 100. While in the NaCl–CaCl2 uni-bi valent cation system, the high and constant membrane concentration of Ca2+ regulated the transport process. The Na+/Ca2+ diffusion coefficient ratio ranged from 0.5 to 500 with external Na+/Ca2+ ratio from 1/100 to 100. Analyses on the phenomenological coefficients, describing the inter-cationic correlations within the membrane phase, as a function of the external cation concentration ratio were also carried out.

Multi-Ionic Potential and Membrane Permeability Matrix. II. Na+–Ca2+ Bi-Ionic System with a Cation-Exchange Membrane and Effects of Cl− on Cation Transport

Abstract Transport characteristics of Na+–Ca2+ bi-ionic system with a highly selective cation-exchange membrane were investigated on the basis of nonequilibrium thermodynamic theory. As a principal transport parameter, the membrane permeability matrix or membrane conductance matrix can be estimated from the membrane potential, conductance, and ion flux data. Significances of diffusional and electroconductive processes of ion transport across membrane were systematically discussed in terms of these matrix elements. Partial contributions of inter-cationic (Na+–Na+, Na+–Ca2+, and Ca2+–Ca2+) correlations to the membrane transport process of ions were examined by means of comparing the estimated values of corresponding matrix elements. It was suggested that Ca2+ ions, of which membrane concentrations are kept at high level independently of the Na+/Ca2+ concentration ratio of external aqueous solutions, play a critical role in the membrane transport phenomena. Participations of Cl− transport in the cation-exchange processes were also discussed on the basis of membrane conductance matrix theory.

Multi-ionic Potential and Membrane Permeability Matrix. I. NaCl–CsCl Bi-ionic System with a Cation Exchange Membrane

Abstract This paper is concerned with analysis of membrane transport processes on the basis of nonequilibrium thermodynamics. Inter-ionic correlations between permeating ions are quantitatively estimated by applying the membrane permeability matrix theory to the system in which the NaCl and CsCl solution phases are divided by a highly selective cation exchange membrane. The membrane permeability matrix of the system may be expressed by four ionic correlation terms concerning with Na+ and Cs+. The electroconductive and diffusional membrane permeabilities are expressed as a function of the matrix elements having the dimension of permeating speed of ions. The conductive and diffusional permeabilities as well as the matrix elements are estimated from membrane potential, conductance, and ionic flux data. The external electrolyte concentration dependence of these permeability parameters is discussed. The conductive and diffusional permeabilities considerably differ from each other and their ratio changes with the external electrolyte concentration, whereas the permeability ratio of Na+ to Cs+ is constant. Electroconductive and diffusional characteristics of membrane transport processes are consistently analyzed in terms of the memberane permeability matrix theory.