Amphoteric Ion Exchange Membrane Research Articles

Synthesis and characterization of new ion‐exchange membranes

AbstractThe synthesis of grafted polymers of polyethylene (PE) with acrylic acid and N,N‐dimethylamino‐2 ethyl acrylate is performed in two steps. The first one needed the ozonization of powder of PE in well‐defined conditions to obtain an expected activation. The second one consisted in bulk grafting the two monomers by thermal decomposition of the above hydroperoxides and peroxides of the activated PE. After elimination of homoacrylated by selective solubilization, we obtained films by pressing the copolymers either alone or the mixture of the two copolymers to prepare the anion (or cation) exchange membrane and the amphoteric ion‐exchange membrane. The second part of the study deals with the physicochemical characterization of these membranes: thickness, exchange capacity, electrical resistance, transport number, and water content. These characteristics are given for various concentrations of equilibrating solutions and for various pH. The results show that we have perfectly corrected membranes that are competitive with the commercial ones.

Synthesis and characterization of an amphoteric ion-exchange membrane

An amphoteric ion-exchange membrane was prepared by chemical grafting of acrylic acid and dimethyl amino-2-ethyl methacrylate on ozonized polyethylene. The effects of the variation of external pH on the physicochemical properties of this membrane were studied (exchange capacity, electrical resistance, water and electrolyte content, and membrane potential). The determination of the mean activity coefficient of the NaCl in the membrane phase using the Donnan equilibrium equation reveals that this coefficient increases with the NaCl concentration in the external solution. Fundamental electrochemical properties of the amphoteric membrane are discussed on the basis of the variation of the membrane selectivity with the external electrolyte concentrations and the pH. The properties at neutral pH are accounted for by a mutual neutralization of some acidic and basic groups in the membrane phase.

NaCl diffusion across an amphoteric ion exchange membrane

The diffusion of NaCl across an amphoteric ion exchange membrane has been studied by measuring the diffusion flux of NaCl and the self-diffusion fluxes of Na + and Cl − ions through this membrane. The NaCl fluxes through the amphoteric membrane are analysed on the basis of the Nernst-Planck equation and the TMS theory. The self-diffusion measurements make possible calculations of the individual difusion coefficients. The effects of the external pH on the physicochemical properties of the membrane are discussed. The measurement of the NaCl content in the membrane combined with the result of the membrane potential and with the result of the self diffusion measurements make it possible to obtain the theoretical values of the NaCl flux. These values are in satisfactory agreement with the experimental values.

Membrane phenomena of an amphoteric membrane in mixed electrolyte solution

To obtain a better understanding of the ion selectivity in an amphoteric ion-exchange membrane—mixed electrolyte solution system, three independent experiments were carried out. The transport numbers of ions across the amphoteric membrane were evaluated through electrodialysis experiments. The membrane conductances were obtained from the measurements of membrane resistances. The ionic concentrations within the membrane were given as the total amount of Donnan salt and ion-exchange capacity. The conventional selectivity coefficient and ionic mobility within the membrane were calculated by means of three kinds of data, and given as a function of calcium ion concentration in the solution. The order of Ca 2+ > Na + > Cl − in selectivity turned out to be determined by the product of ionic mobility and ionic concentration within the membrane. In particular, it was pointed out that the partition coefficients ( C M/ a M) played an important role in ion selectivity in this mixed system. A new physical quantity for estimating selectivity, i.e. the permeability coefficient, P, was proposed.

Study of Ion Transport across Amphoteric Ion-Exchange Membrane. V. Nonequilibrium Thermodynamic Analyses of Ion Selectivity

Abstract Ion-transport processes across an amphoteric ion-exchange membrane were investigated by means of estimating the membrane permeability matrix, a set of modified linear phenomenological coefficients, from the electrochemical and the ion flux data. Systematic comparisons of phenomenological analyses on an amphoteric ion-exchange membrane system with those on an ordinary cation-exchange membrane system were carried out to investigate the correlations of singly- and binary-charged membrane structures to characteristic transport properties. The modes of ion permselectivity of an amphoteric ion-exchange membrane in the metal chloride concentration-cell systems are characterized by the potentiometric selective response due to the ion-sieve effect, the low membrane conductance, and the large ion flux, while those of an ordinary cation-exchange membrane are characterized by the totally charge-dependent potential response, the high conductance, and the extremely small ion flux. The cross elements of the membrane permeability matrix, which represent the partial contributions of cation-anion interactions to the membrane permselectivity, are positive for an amphoteric membrane and negative for a cation-exchange membrane. The positive cross matrix elements act deceleratively on the membrane permeability, whereas the negative elements do acceleratively. It was pointed out based on the nonequilibrium thermodynamic theory that the preferable and efficient permeation mechanism is the simple diffusion process in an amphoteric ion-exchange membrane, whereas the electroconductive process in a cation-exchange membrane.

Effect of ionic charge on the electrical properties of an amphoteric ion exchange membrane

In order to clarify the mechanism of ion transport across an amphoteric membrane with sulfonate and N-methylpyridinium groups as exchange sites, membrane potential and membrane conductance measurements were carried out with varying valences of cations and anions of the electrolyte solution. It was shown that the membrane studied behaves as a cation exchange membrane in 1-1 valent and 2-2 valent electrolyte solutions. On the other hand, the membrane function was strongly influenced by the valence of the cation; the membrane in the LaCl 3 system in particular was preferentially anion selective. The permeability coefficients were evaluated according to the theory of nonequilibrium thermodynamics, and ion transport was discussed.

Conductance Matrix of Amphoteric Ion-Exchange Membrane in Three Ion System

Abstract A conductance matrix describing the ion-transport phenomena in the membrane-three ion system has been determined. It was indicated there that six independent experiments were required in order to determine six independent elements of the conductance matrix. The NaCl–CaCl2–amphoteric membrane system was chosen as the three ion system, and three kinds of fluxes, two kinds of transport numbers, and the membrane conductance were measured. Nine elements were experimentally determined on the assumption of Onsager’s reciprocal relation. The results showed that the order of elements in conductance matrix was gCaCa>gClCl>gNaNa>gCaCl>gNaCl>gCaNa. In addition, it was pointed out that the interactions among ions can never be ignored when the ion-transport phenomena across membrane are studied.

Study of ion transport across an amphoteric ion exchange membrane — general transport properties of a simple electrolyte

Basic electrochemical properties of an amphoteric ion-exchange membrane (1.0—PA—29), in which almost equal numbers of cationic and anionic sites are distributed homogeneously over the functionalized polymer networks, were studied for a variety of concentration-cell systems. Unlike the usual uniform ion-exchange membrane, potentiometric permselectivities were demonstrated even for ions of the same charge, as shown by the result that distinctive potential responses were observed for a series of alkali metal chloride, sodium salt, and tetra-alkylammonium chloride systems. The sequence of membrane permeabilities to cations and anions calculated from the electrochemical data could well be correlated to the sequence of the hydrated radii of the respective ions. So the potentiometric responses to any electrolyte system can be predicted from the permeability data or hydrated radius values of individual cations and anions. The present results suggest that the homogeneous amphoteric ion-exchange membrane functions effectively as an ion sieve, sifting out the sizes of permeating hydrated cations and anions.

Nonequilibrium Thermodynamics of the Ion and Solvent Transports through Ion-exchange Membrane

Abstract A theory for the ion and solvent transports through membrane has been developed on the basis of nonequilibrium thermodynamics. The fluxes were represented as linear functions of the effective driving potentials. The theory is reduced to that of Katchalsky when the concentration ratio of two aqueous solutions is near unity and the solutions are dilute. The effect of solvent flow on the interionic correlations was discussed. It was pointed out that Despic and Hills’ theory of the electroosmotic effect on the membrane conductance is not valid with respect to both theoretical and experimental aspects. The comparison of the present theory with the previous one was also made. The six independent phenomenological coefficients (elements of the conductance matrix) were experimentally determined as a function of concentration with the concentration cell consisting of the amphoteric ion-exchange membrane and aqueous calcium chloride solutions. The membrane properties were discussed in terms of the conductance matrix. The diffusional ion conductance was much greater than the electrical ion conductance, as an indication of the failure of the Nernst-Einstein relation. The cation-anion coupling coefficient was close to unity whereas the ion-water coupling coefficients were less than 0.1. The solvent effects on the interionic conductance elements were found to be small in spite of the fact that the water permeability was extremely high. The distinction between the cationic and amphoteric ion-exchange membranes was explored in terms of the elements of the conductance matrix.

Study of Ion Transport across Amphoteric Ion Exchange Membrane. II. Transport of Symmetric Tetraalkylammonium Chlorides

Abstract Transport characteristics of NH4Cl, (CH3)4NCl (TMA–Cl), (C2H5)4NCl (TEA–Cl), (n-C3H7)4NCl (TPA–Cl), and (n-C4H9)4NCl (TBA–Cl) across homogeneous type amphoteric ion exchange membrane (1.0-PA-29, Kanegafuchi Chem. Ind.) were studied. Membrane potentials and conductances of the concentration cell systems were measured to calculate the membrane permeabilities which represent a measure of ionic permselectivity. Membrane potential changed considerably with cationic species and the membrane tended to behave more anionic selectively with increasing bulkiness of cations. The cationic permeabilities calculated from electrochemical data were PNH4>PTMA>PTEA>PTPA>PTBA. Membrane permeabilities to chloride ions, PCl, were greater than those to cations in all the systems studied and it was interesting that PCl values and their dependencies on external electrolyte concentration were almost unchanged irrespective of the difference in cationic species. The present experiment was designed in order to examine the effects of ionic size on the transport processes across homogeneous type amphoteric ion exchange membrane. The obtained results indicated that the hydrated radius of permeant ion is an important factor to control the ionic transport processes and to reveal the potentiometric selectivity in these systems. It was suggested that the ion transport across homogeneous type amphoteric ion exchange membrane is strongly affected by hydrodynamic properties of permeant ion, but scarcely influenced by ionic charges of which effects are well known to be exclusive in the uniform cation and anion exchange membranes.

Study of Ion Transport across Amphoteric Ion Exchange Membrane. I. Electroconductive Membrane Permeability

Abstract Basic ion transport characteristics of a homogeneous amphoteric ion exchange membrane (Kanegafuchi Chem. Ind. 1.0-PA-29) were studied by measuring the membrane potentials and conductances. Concentration cell systems of NaCl, KCl, CaCl2, and SrCl2 with a concentration range of 10−1–10−3 mol dm−3 were studied and the electroconductive membrane permeabilities were estimated from the electrochemical data. Generally, Cl− is slightly more permeable than cations under the present experimental conditions, except the result that K+ is more permeable at low concentrations. Unlike the usual uniform cation exchange membrane of which transport characteristics to ions strongly depend upon the number of ionic charges, a “1.0-PA-29” amphoteric membrane exhibits different transport properties for the NaCl and KCl systems. In the NaCl system, the membrane was constantly anionic selective, while in the KCl system, biphasic ion selectivities were observed depending upon the external KCl concentration. Fundamental electrochemical properties of the membrane systems were discussed by examining the dependencies of membrane permeability on external electrolyte concentrations and on differences in ionic species. The present result suggests that the ionic size is one of the critical factors determining the transport characteristics across amphoteric ion exchange membrane.

両性膜の透過性 ＩＩ 無機塩，有機酸アミノ酸の選択透過性

The permselectivities of the amphoteric ion-exchange composite membrane to inorganic salts, organic acids and amino acids were examined in single solute aqueous solutions and mixed aqueous solutions of the organic compound and salt.The permselectivity to each solute in single solutions was resembled to that of the cellulose acetate asymmetric membrane;that is, the rejection of insrganic salts becomes large for cations with higher valencies, and organic acids and amino acids in charged state were impermeable. However, we observed districtly the piezo-dialytic behavior with the mixed solutes.These results shows the possibility that the concentration and the purification of the organic compounds could be made simultaneously and quite effectively by using the amphoteric ion-exchange membranes.

両性膜の透過性 Ｉ 両性膜の作製方法

Amphoteric ion-exchange composite membranes were prepared by forming ultra-thin layer of partially quarternized polymer of partially chloromethylated polystyrene, on a porous polyvinylchloride support membrane, and by introducing cross-linkages and sulfonic acid groups intothe ultra-thin layer through dipping the composite membrane into concentrated sulfuric acid.The membrane thus prepared exhibited a similar permselectivity to saccharose as the cellulose acetate asymmetric membrane, but very low permselectivity to sodium chloride.