Modification of transport properties of ion-exchange membranes VIII. Changes in properties of anion exchange membranes on introduction of hydrophobic groups

A copolymer membrane composed of 4-vinylpyridine-styrene-divinylbenezene was reacted with long chain alkyl bromides (octyl bromide, dodecyl bromide, and hexadecyl bromide) in order to introduce hydrophobic groups into the anion exchange membrane by the quaternization reaction. The resulting membranes show a marked increased in fixed ion concentration as a result of lowered water content. Although the electrical resistance of the membranes increased slightly, the apparent diffusion coefficient of hydrochloric acid through the membranes decreased markedly. Complete quaternization of the membranes by methyl iodide after reaction with the long-chain alkyl bromides caused an increase in the water content and in the apparent diffusion coefficient of the acid and a decrease in the current efficiency in electrodialysis of the acid. This is explained by the high water content of the anion exchange membranes quaternized by methyl iodide.     

Modification of properties of ion exchange membranes. VI. Electrodialytic transport properties of cation exchange membranes with a electrodeposition layer of cationic polyelectrolytes

When a cation exchange membrane is immersed in a cationic polyelectrolyte solution to form a thin layer on the membrane surface, the membrane properties are changed: permselectivity between cations with different electric charges (a relative transport number of the calcium ions to sodium ions, P), current efficiency, and electric resistance of the membrane. Here the more compact the cationic polyelectrolyte layer, the more outstanding the change in permselectivity. To make a more compact layer, an electrodeposition method was adopted and a change in the permselectivity of the resultant cation exchange membrane was investigated. By using the electrodeposition method a strongly basic polyelectrolyte with a larger molecular weight effectively changed the permselectivity of the cation exchange membrane: the P value dropped to about 0.3 from about 2.5 of the P of the untreated membrane during electrodialysis of the sodium chloride—calcium chloride system, and an increase in the electric resistance of the membrane (i.e., organic fouling) due to a cationic surface-active agent could be prevented. It is noteworthy that by using the strongly basic polyelectrolyte with a larger molecular weight the electrodeposition method was effective, whereas the immersion method was ineffective. Furthermore, even with the electrodeposition method the cationic polyelectrolyte which had a relatively smaller molecular weight resulted in a more remarkable change in the P value than did that with a larger molecular weight. In the electrodeposition method the amount of polyelectrolyte cohered onto the membrane surface in creased with an increase in the concentration of the polyelectrolyte, and weakly basic polyelectrolyte, and weakly basic polyelectroyte (polyethyleneimine) was also available independent of its molecular weight.     

Comparison of chromatographic ion-exchange resins IV. Strong and weak cation-exchange resins and heparin resins

A comparative study was performed on heparin resins and strong and weak cation exchangers to investigate the pH dependence, efficiency, binding strength, particle size distribution, static and dynamic capacity, and scanning electron microscopy pictures of chromatographic resins. The resins tested include: Heparin Sepharose FF, SP Sepharose FF, CM Sepharose FF, Heparin Toyopearl 650 m, SP Toyopearl 650 m, CM Toyopearl 650 m, Ceramic Heparin HyperD M, Ceramic S HyperD 20, and Ceramic CM HyperD F. Testing was performed with four different proteins: anti-FVII Mab (IgG), aprotinin, lysozyme, and myoglobin. Dependence of pH on retention was generally very low for proteins with high isoelectric point (pI), though some decrease of retention with increasing pH was observed for CM Ceramic HyperD F and S Ceramic HyperD 20. Binding of anti-FVII Mab with pI < 7.5 was observed on several resins at pH 7.5. Efficiency results show the expected trend of increasing dependence of the plate height with increasing flow rate of Ceramic HyperD resins followed by Toyopearl 650 m resins and the highest flow dependence of the Sepharose FF resins corresponding to their pressure resistance. Determination of particle size distribution by two independent methods, coulter counting and SEM, was in good agreement. Binding strength of cation-exchange resins as a function of ionic strength varies depending on the protein. Binding and elution at high salt concentration may be performed with Ceramic HyperD resins, while binding and elution at low salt concentration may be performed with model proteins on heparin resins. Employing proteins with specific affinity for heparin, a much stronger binding is observed, however, some cation exchangers may still be good substitutions for heparin resins. Dynamic capacity at 10% breakthrough compared to static capacity measurements and dynamic capacity displays that approximately 40-80% of the total available capacity is utilized during chromatographic operation depending on flow rate. A general good agreement was obtained between results of this study and data obtained by others. Results of this study may be used in the selection of resins for testing during protein purification process development.     

Thermal membrane potential across cation-exchange membranes for various halide solutions

Thermal membrane potential across cation-exchange membranes was measured for various halide solutions. Linear relationships between thermal membrane potential () and temperature difference (T) were observed, and the temperature coefficient of thermal membrane potential (/T) decreases with increase in the molality of the external solution as predicted by a theory reported. When counterions of membranes are hydrogen ions, the sign of the coefficients turns into minus near 0.01 mol/kg of the external solution for all membranes, although the coefficients are always positive for all the other forms. The dependence of the coefficients on the molality of the external solutions sometimes deviated slightly from the theory. This deviation is attributed to some change in water content of the membranes. A reproducible method of measuring water content of membranes was applied to discuss the change in the state of the membranes.     

Comparison of chromatographic ion-exchange resins. III. Strong cation-exchange resins

A comparative study was performed on strong cation-exchangers to investigate the pH dependence, efficiency, binding strength, particle size distribution, static and dynamic capacity, and SEM pictures of chromatographic resins. The resins tested included: SP Sepharose XL, Poros 50 HS, Toyopearl SP 550c, SP Sepharose BB, Source 30S, TSKGel SP-5PW-HR20, and Toyopearl SP 650c. Testing was performed with four different proteins: anti-FVII Mab (IgG), aprotinin, lysozyme, and myoglobin. Dependence of pH on retention was generally very low for proteins with high pI. An unexpected binding at pH 7.5 of anti-FVII Mab with pI < 7.5 was observed on several resins. Efficiency results show the expected trend of higher dependence of the plate height with increasing flow rate of soft resins compared to resins for medium and high-pressure operation. Determination of particle size distribution by two independent methods, Coulter counting and SEM, was in very good agreement. The mono-dispersed nature of Source 30S was confirmed. Binding to cation-exchange resins as a function of ionic strength varies depending on the specific protein. Generally, binding and elution at high salt concentration may be performed with Toyopearl SP 550c and Poros 50 HS, while binding and elution at low salt concentration may be performed with Toyopearl SP 650c. A very high binding capacity was obtained with SP Sepharose XL. Comparison of static capacity and dynamic capacity at 10% break-through shows in general approximately 50-80% utilisation of the total available capacity during chromatographic operation. A general good agreement was obtained between this study and data obtained by others. The results of this study may be used for selection of resins for testing in process development. The validity of experiments and results with model proteins were tested using human insulin precursor in pure state and in real feed-stock on Toyopearl SP 550c, SP Sepharose BB, and Toyopearl SP 650c. Results showed good agreement with experiments with model proteins.     

Transport properties of highly ordered heterogeneous ion-exchange membranes

Model "ordered" heterogeneous ion exchange membranes are made with ion exchange particles heaving ion exchange capacity in the range 3 to 2.5 meq/gr (dry basis) and diameters ranging from 37 to 7 microm and 2 component room-temperature vulcanizing silicon rubber as a polymeric matrix, by applying an electric field normal to the membrane surface during preparation. These membranes were shown to have an improved ionic conductivity compared with "nonordered" membranes based on the same ion exchange content (for instance, at 10% resin content "nonordered" membranes show <10(-5) mS/cm while "ordered" membranes have conductivity of 1 mS/cm). The transport properties of ordered membranes were compared with those of nonordered membranes, through the current-voltage characteristics. Limiting currents measured for the ordered membranes were significantly higher than those of the nonordered membranes with the same resin concentration. In addition, higher limiting currents were observed in ordered membranes as the resin particles became smaller. Energy dispersion spectrometry analyses revealed that the concentration of cation exchange groups on the membrane surface was higher for ordered membrane as compared to that of nonordered membranes. This implies that the local current density for the conducting domains at the surface of the nonordered membranes is higher, leading to higher concentration polarization and, eventually, to lower average limiting current densities. The effect of ordering the particles on the membrane conductivity and transport properties was studied, and the advantages of the ordered membranes are discussed.     

Comparison of chromatographic ion-exchange resins V. Strong and weak cation-exchange resins

Strong and weak cation-exchangers were compared for a number of chromatographic parameters, i.e. pH dependence, efficiency, binding strength, particle size distribution, static and dynamic capacity, and scanning electron microscopy (SEM) pictures. Chromatographic resins investigated were Fractogel EMD SO3- (M), Fractogel EMD SE Hicap (M), Fractogel EMD COO- (M), MacroPrep 25S, MacroPrep High S, MacroPrep CM, CM HyperZ, and Matrex Cellufine C-500. Testing was done with three proteins: Anti-FVII Mab (IgG), aprotinin, and lysozyme. For lysozyme and aprotinin with pI above experimental pH, dependence of pH on retention was generally low, though some pronounced decrease of retention with increasing pH was observed for CM HyperZ. For Anti-FVII Mab with pI<7.5, binding was observed on several resins at pH 7.5. Efficiency results present the expected trend of increasing dependence of plate height as a function of increasing flow rate, and the highest flow dependence was observed for Fractogel EMD COO-. Particle size distribution was determined by two independent methods, coulter counting and SEM pictures, with fair agreement. Binding strength data of cation-exchange resins as a function of ionic strength depends on the protein, but binding and elution at high salt concentration may in general be performed with MacroPrep resins. Comparison of dynamic capacity data at 10% break-through and static capacity measurements shows that a very diverse utilization of approximately 25-90% of the total available capacity is employed during chromatographic operation. The effect of competitive binding from yeast fermentation components on dynamic binding capacity of aprotinin was studied showing a significant decrease in binding capacity. Sepharose FF, Toyopearl 650 M, and Ceramic HyperD F strong and weak cation-exchange resins were included in this study. Resins with good pure aprotinin capacity also performed well for aprotinin in fermentation broth, but the highest relative capacity was obtained with MacroPrep High S having a fairly low pure component dynamic capacity. Results of this paper may be used in the selection of resins for further testing in biopharmaceutical protein purification process development.     

Evaluation of the Zn2+ transport properties through a cation-exchange membrane by chronopotentiometry

In this work the effect of zinc concentration, pH, and boric acid concentration on the zinc transport properties through an IONICS 67-HMR-412 cation-exchange membrane was evaluated. The limiting current density and the transport numbers were determined by means of chronopotentiometry. A model between the limiting current density and the bulk zinc concentration was established, assuming a potential relationship between the zinc transport number through the membrane and the bulk zinc concentration together with the Levich equation for the DBL thickness. A decrease in the initial pH value of the solutions causes considerable modifications both in the plateau region and in the overlimiting current density region of the current–membrane potential curves. The results show that the presence of boric acid produces the precipitation of zinc metaborate on the anodic layer of the cation-exchange membrane.     

Modification of properties of polymer membranes by low-temperature plasma treatment

The results of investigations into the use of low-temperature plasma for modification of porous polymer membranes are summarized. The basic lines of research in this area are considered. It is shown that plasma treatment is a quite effective tool for both improving the properties of existing polymer membranes and manufacturing new composite membranes with unique characteristics.     

Synthesis and ion-exchange properties of cerium(IV) molybdate

Cerium(IV) molybdate, prepared under the optimum conditions of concentration, acidity etc., shows exchange capacity of 0.96 meq per g of exchanger. The sorption of a large number of metal ions has been investigated and the compound shows promising behaviour as cation exchanger. Numerous separations of analytical and radiochemical interest have been performed on the columns of this exchanger with great efficiency.     

Ion transport in MF-4SK cation-exchange membranes modified with acid zirconium phosphate

An MF-4SK cation-exchange membrane has been modified to obtain composite materials containing acid zirconium phosphate particles. It is demonstrated by electron microscopy and X-ray diffraction that acid zirconium phosphate in the resulting membrane is in the crystalline state. As compared to the initial MF-4SK membrane, the modified membrane shows a somewhat lower diffusion permeability and a higher ion selectivity.     

Electrochemical properties and structure of ion-exchange membranes upon thermochemical treatment

The effect of temperature-induced morphological changes on the electrochemical and physicochemical properties of the heterogeneous sulfo cation-exchange membrane MK-40 in aqueous, alkaline, and acidic media is subjected to comparative analysis. The deviation between the surface and volume microstructure of swollen membrane samples after their chemical conditioning and thermochemical treatment are visualized by a scanning electron microscope. The porosity and the fraction of the ion-exchange component in membranes subjected to heating in water and aggressive media are observed to increase more noticeably in their surface layer as compared with their volume. The maximum effect thus modified structural characteristics on the transport (conductivity, diffusion permeability, selectivity) and physicochemical (exchange capacity, water content, density, linear sizes) properties is observed for MK-40 membrane samples when heated in a sulfuric acid solution. The effect of thermal destruction of inert polymers (divinylbenzene, caprone) involved in the membrane composition on the transport characteristics is revealed.     

Electrodialytic properties of cation-exchange membranes in the presence of N-dodecyl pyridyl compounds

Electrodialytic transport properties of cation-exchange membranes were observed in the presence of dodecyl pyridyl compounds. The transport properties measured were the relative transport number of calcium ions to sodium ions (P_Na^Ca), the current efficiency of cations and the electric resistance of the membrane during the electrodialysis. Dodecyl pyridyl compounds used were dodecyt pyridinium bromide, dodecyl dipyridyl bromide and dodecyl tripyridyl bromide. When the electrodialysis was carried out in the presence of dodecyl pyridyl compounds, P_Na^Ca decreased and the electric resistance of the membrane increased extremely during the electrodialysis. However, the current efficiency did not change except with dodecyl pyridinium bromide. These phenomena are based on the accumulation of dodecyl pyridyl ions in the definite surface part on the desalting side of the membrane and their permeation through the membrane. The results showed that the hydrophobic strength of the compounds, rather than their molecular weight, is effective in decreasing P_Na^Ca. However, the increase in the electric resistance of the membrane is mainly dependent on the molecular weight of the compounds.     

Modification of properties of ion exchange membranes

Summary Interaction between ion exchange membranes and surface active agents was observed by electrodialyzing the salt solution containing the surface active agent. The behavior of the electric resistance of the membrane during the electrodialysis, the current efficiency and the adsorbed or ion-exchanged amount and the permeated amount of the surface active agent were observed. Generally, the electric resistance of the membrane during the electrodialysis increased remarkably when the ionic surface active agent having the opposite charge to ion-exchange groups of the membrane was contained in the solution. And the correlation of the behavior of the electric resistance of the membrane to the electrodialysis condition, species of surface active agents and species of membranes was mainly observed. Results were as follows. 1) The adsorption' or ion-exchange of ionic surface active agent on the membrane was remarkably emphasized by the electric field. 2) The degree of the increase in the electric resistance of the membrane was remarkable when the surface active agent had the high molecular weight and the bulky molecular structure. 3) The degree of the increase in the electric resistance was remarkably various according to species of the membranes.From these results, a protecting method for the change of these membrane properties was examined. When the ion exchange membrane was treated with the polyelectrolyte solution having the opposite charge to ion exchange groups of the membrane, the increase in the electric resistance by ionic surface active agent was depressed. Generally, though the change of electrodialysic properties of the membrane by the ionic surface active agent was remarkable in the membrane having the tight structure, the change of the properties of the membrane having the tight structure was easy to be protected by the polyelectrolyte treatment. Though the ionic surface active agent having the bulky molecular structure made the properties of the membrane change remarkably, the change of the properties of the membrane by the bulky surface active agent could be easily protected by the polyelectrolyte treatment.

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Zusammenfassung Die Wechselwirkung von Ionenaustauschermembranen mit grenzflächenaktiven Stoffen wird durch Elektrodialyse untersucht. Der elektrische Widerstand der Membranen steigt während der Elektrodialyse beträchtlich an, wenn die grenzflächenaktiven Ionen entgegengesetzte Ladungen wie die Austauschergruppen der Membranen haben. Es wurde gefunden, daß 1. die Adsorption oder der Ionenaustausch der grenzflächenaktiven Ionen an der Membran beträchtlich durch das elektrische Feld verstärkt wird; 2. die Zunahme des elektrischen Widerstandes groß ist, wenn das grenzflächenaktive Ion ein hohes Molekulargewicht hat und möglichst sperrig ist; 3. die Widerstandsänderung merklich von der Art der Membran beeinflußt wird. Auf Grund dieser Versuche wurde die Möglichkeit geprüft, die Zunahme des Membranwiderstandes bei Gegenwart grenzflächenaktiver Stoffe durch Adsorption von Polyelektrolyten zu reduzieren.

     

Proton transport properties in hybrid membranes investigated by ac-electrogravimetry

In this paper, a hybrid organic/inorganic membrane, based on poly(VDF-co-HFP) polymer associated to mesostructured modified silica and made through sol–gel techniques, was characterized by using ac-electrogravimetry. In order to perform experiments, a polypyrrole–heteropolyanion doped mediator film was inserted between the working electrode of the microbalance and the hybrid membrane. This mediator film, which is characterized by mixed conducting properties, is necessary to provide proton transfer between the different interfaces and in that way, the proton transport inside the hybrid film which is only an ionic conducting material. Proton transfer and transport was characterized through ac-electrogravimetry and an original theoretical approach was developed for extracting the attractive parameters. The change of the exchanged species concentration and the diffusion coefficient of the protons in the hybrid membrane, were estimated, for the first time, according to the applied potential. These studies pointed out that the low conductivity value in this hybrid membrane is related to i) the low diffusion coefficient of proton (10^? 7 cm² s^? 1) in this membrane associated, ii) the low concentration of proton in the membrane (0.4 meq g^? 1).     

Comparative investigations of ion-exchange membranes

The equilibrium and transport properties (conductivity, transport number, diffusion) of crosslinked ionomer membranes based on sulfinated and sulfonated PSU in aqueous solutions of HCl, NaCl and KCl have been investigated and compared with a Nafion 117 membrane. It has been found that these membranes are more compact and their conducting paths are of smaller dimension than that of the Nafion 117. The influence of length of crosslinking chain, changing from –(CH₂)₄– to –(CH₂)₁₂–, is particularly indicated by the diffusion coefficients; the conductivity and transport numbers of counterions are influenced only slightly. Practically no dependence of this effect on the transport number of H⁺ has been found.     

Modification of properties of ion exchange membranes. VII. Relative transport number between various cations of cation exchange membrane having cationic polyelectrolyte layer and mechanism of selective permeation of particular cations

Electrodialytic behavior of cation exchange membrane having cationic polyelectrolyte layer on its surface (relative transport number between two cations, P, current efficiency, and electric resistance of the membrane during the electrodialysis) was measured using various cations, and the mechanism of selective permeation of lower-valent cations than the higher and of larger hydrated cations than the smaller was investigated. The following conclusions were obtained: (1) the cationic polyelectrolyte layer narrowed the pathway for ions; (2) when the pathway was made narrower by other methods, the remarkable change of the permselectivity of the membrane did not occur; (3) the effectiveness of the cationic polyelectrolyte layer was depressed by the treatment with anionic polyelectrolytes to neutralize the cationic charge on the membrane surface; and (4) the cation with larger hydrated diameter (potassium ions) more easily permeated through the membrane having the polyelectrolyte layer than that with the smaller hydrated diameter (sodium ions). It is concluded that the change of P by the cationic charge layer on the membrane surface is based on the difference in the strength of the electrostatic repulsion between two cations against the cationic charge layer.