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Ultrafiltration membranes were prepared from homopolymer [polyacrylonitrile (PAN), polyethersulfone (PES), and polyvivylidenefluoride (PVDF)] and acrylonitrile copolymers with increasing acrylamide content. The membranes containing acrylamide were more hydrophilic and had a smaller dispersive surface energy than those prepared from the acrylonitrile homopolymer. A new nonfouling index (NFI) test was devised and appears to distinguish well between ultrafiltration membranes of different hydrophilicity–hydrophobicity balance. The NFI indices of acrylamide containing copolymer membranes were much higher than those of membranes cast with commercial membrane materials such as PAN, PES, and PVDF. The NFI of ultrafiltration membranes increased as acrylamide substitution in the copolymer increased. The use of acrylamide containing copolymers substantially eliminated intrinsic fouling. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 77: 1600–1606, 2000

Solvent extraction of acetic acid at low concentrations from aqueous solutions was studied. Decalin was found to be the optimal solvent and trioctyl phosphine oxide an effective carrier species. Phase equilibrium constants were measured and the results agree with the theoretical equation in the low carrier concentration range. The polymer supported solvent membranes carrying the same solvent and carrier, under various physical and chemical conditions, were prepared and the apparent diffusion coefficients of acetic acid through these membranes were measured and the results were discussed. The apparent diffusion coefficient of acetic acid in these tests was not interfered with by the existence of hydrochloric acid in the feed stream.

Porous interpolymer anion exchange membranes were prepared from poly-(vinylidene fluoride) and poly(l-vinyl-3-methylimidazolium iodide). Depending on the membrane composition, the hydraulic permeability and the membrane conductance were varied over four orders of magnitude. The rejection of potassium chloride, calcium chloride, and methylene blue solutions was determined during ultrafiltration. A model was developed to account for the observed salt rejection. The membrane porosity and tortuosity parameters for this interpolymer membrane system were compared with an analogous system of cation-exchange membranes derived from poly(styrenesulfonic acid) and poly(vinylidene fluoride).

Donnees sur l'utilisation de l'electrodialyse en vue de la production de solutions relativement concentrees de bases et d'acides faibles a partir des solutions salines correspondantes

This communication describes how ethanol, other liquid fuels, and organic chemicals can be produced from cellulosic biomass at prices that can compete with those of petroleum derived materials by employing presently available or soon to be developed membrane technologies. Contemporary membrance technologies can already effect major savings in process costs for the conventional fermentation of grains or molasses to produce ethanol; developing membrance technologies could employ cheap cellulosic substrates for ethanol production.

The selective uptake of potassium ions versus tetramethylethyl‐, ethyl‐,and propylammonium ions by fully neutralized, crosslinked polymethacrylate gels was measured in aqueous, mixed aqueous, and nonaqueous solvents. Swelling pressures in water were calculated from isopiestic data, so the Coulombic contribution to the total free energy of the exchange process could be calculated and compared with theory. A good fit between experiment and theory was possible only by assigning values for the dielectric constant of water in these gels of about 30 in the K–TMA state and 15 in the K–TEA state.

Implicit equations were derived for interactions between a charged rod polyelectrolyte model and counterions of different size. The selectivity of the polymer for the smaller of two counterions as a function of its charge density, distances of approach and annular volume was calculated. Ion binding (site binding) was calculated by assigning a finite thickness to the Stern layer so as to include a finite number of closely held counterions. Further refinements included the consideration of counterion polarizability as a function of the electric field.

Highly porous interpolymer ion-exchange membranes of poly(styrene sulfonic acid) and poly(vinylidene fluoride) have been investigated under pressure filtration with KCI, Na2SO4, erythrosin, and bovine serum albumin as solutes in the feed solution. The rejection of the ionic solutes is governed by a Donnan exclusion of electrolyte from the membrane phase. A model for the transport behavior is proposed that includes both diffusive and convective salt transport. The calculated rejections agree adequately with the observed data.

The mercuration of soluble polystyrene was investigated, and it was found that an addition of perchoric acid to the reaction mixture significantly accelerated the polymer transformation. The mercuration proceeds as a polymer analogous reaction, i.e., without any change in the degree of the polymerization. The mercurated product could be converted back to the original polystyrene by hydrolysis or to the corresponding bromopolystyrene by bromination. Ultracentrifuge measurements show that even at low conversion rates all macromolecules were mercurated and unreacted polystyrene could not be identified in the product. Calorimetry indicated the presence of styrene–mercuric acetate blocks in copolymers with high mercury contents.

The rate of sorption of toluene by dry oleophilic anion exchange resins in the hydroxide state was measured both by direct weight measurements and also by the visual observation of the rate of movement of a refractive index gradient between unreacted and reacted zones. The rate of sorption of carboxylic acids from solution in toluene was also measured by beads swollen in toluene, both by direct chemical analysis of the solution and by the visual method. Diffusion coefficients of acids in the resins were calculated using three different theories for diffusion in gels coupled with chemical reactions, and reasonable agreement between theory and experiment was found.

Interpolymer ion exchange membranes were prepared from a compatible casting solution that contained poly(styrene sodium sulfonate), poly(vinyl methyl ether–alt–maleic anhydride), and poly(vinyl alcohol). Crosslinking of the films was accomplished through the formation of ester linkages that were stable in aqueous environments. Membrane properties (water content, capacity, concentration potential, equivalent conductivity) were measured over a wide range of membrane compositions. Ultrafiltration was carried out with a feed solution that was 0.01N in KCI and 15 ppm in erythrosin. Rejection and hydraulic permeability data were reported as a function of membrane composition.

Various high molecular weight copolymers of acrylonitrile and a vinyl comonomer containing an aryl amine, a pyridine, or an aliphatic hydroxyl group were synthesized via slurry polymerization techniques so as to contain from 1 to 15 mol % functional comonomer. The comonomer content was quantitated by ultraviolet absorbance, base titration of acid polymer salts, and/or relative chemical reactivity with trichloro-s-triazine. Thin films were cast from copolymer solutions, coagulated into unsupported ultrafiltration membrances, and characterized with respect to both water permeability and pore size distribution. Analysis by size exclusion chromatography of the membrane permeate of a pool of dextran fractions yielded a continuous distribution curve for membrane pore size over the range 1.5 to 70 nm. The ultrafiltration membranes were used for protein immobilization after appropriate chemical activation. The three distinct types of functional copolymers gave comparable results for α-chymotrypsin, with protein weight loadings of 6–12% and 40–65% retention of enzymatic specific activity.

Pressure-driven conditions are used to activate and couple enzymes to ultrafiltration membranes such as a homoporous cellulosic membrane having pores of about 15-200 angstroms in diameter. The resultant enzyme-coupled ultrafiltration membranes can be used under pressure-driven conditions for enzymatic conversion of a substrate. The rate of conversion at low substrate concentrations is larger than the rate achieved with the native enzyme.

Highly porous interpolymer ion-exchange membranes have been prepared from poly(styrene sulfonic acid), PSSA and poly(vinylidene fluoride) PVdF using a casting solvent of dimethylformamide and hexamethylphosphoramide. The membranes have been characterized by their water content, concentration potential, ionic conductivity, and their hydraulic permeability. An estimation of the porosity of the membranes has been made from the relative conductance of the potassium and the tetrabutylammonium ions in the film. This porosity has been compared with that derived from a consideration of the water flux through a Poiseuille-type pore.

A dilute aqueous solution of polydisperse neutral dextrans was used to determine the sieving properties (flux and rejection) of porous polyacrylonitrile membranes. Gel ermeation chromatography was used to measure the solute mole and concentration in the permeate. From these data, rejection coefficients were calculated as a function of solute molecular size. A mathematical model was then developed to relate the flux and solute rejection to pore size distribution and the total number of pores, based upon the assumption that solute rejection was the result of purely geometric considerations. As a first approximation, a solute molecule was considered either too large to enter a membrane pore, or if it entered, its concentration in the permeate from that pore, as well as the solvent flux through the pore, were not affected. This model also considered the effects of steric hindrance and hydrodynamic lag on the convection of solute through a membrane. The shape and sharpness of pore size distributions were found to be useful in comparisons of ultrafiltration membranes.

The swelling characteristics of an oleophilic anion-exchange resin in methanol–benzene and ethanol–chloroform mixed solvent systems were compared with those of a conventional anion-exchange resin. The oleophilic resin was prepared by amination of chloromethylated polystyrene 1% DVB with N,N-dimethyldodecylamine. It showed a large shift of the swelling peak from polar to less polar solution compositions in both methanol–benzene and ethanol–chloroform systems as compared with the swelling of conventional resins. Total solvent uptake and solvent distribution between resin and solvent phases were also determined. The less polar solvent (benzene or chloroform) was sorbed preferentially by the oleophilic resin over a wide range of composition, while preference for the more polar solvent (methanol or ethanol) by the conventional resin was shown over the entire composition of the mixed solvent systems. The Newman-Krigbaum treatment of mixed solvents was applied to swelling data on the ethanol–chloroform–oleophilic resin system, where the volume of the gel network plus the solvent imbibed was relatively constant over the entire range of composition. The result suggests a strong similarity of the liquid–liquid interaction terms in this gel phase compared with those in the pure binary liquid phase.

1. 1. The periods of time required in which final, stable electrical resistances are established with three electrolytes—potassium chloride, potassium iodate, and magnesium chloride—across three types of permselective protamine collodion membranes vary from about 15 min. to many hours, being somewhat longer, for unknown causes, than in the case of the analogous permselective collodion membranes. The influence of the ionic properties of the electrolytes with which the membranes are equilibrated on the rates of equilibration closely resembles that observed with the permselective oxidized collodion membranes. 2. 2. The final, stable resistances of three types of permselective protamine collodion membranes equilibrated with solutions of six electrolytes at six concentrations were measured and tabulated. The data are evaluated as to the differences of the various types of membranes, the influence of the concentration on membrane resistance, the influence of the nature of the electrolyte, and various concentration functions. The regularities found are strictly analogous with those observed with permselective oxidized collodion membranes. 3. 3. The experimental data on equilibrium resistance of permselective collodion and protamine collodion membranes given in this and in the preceding paper are discussed jointly from the point of view of the basic concept of the fixed charge theory of electrochemical membrane behavior. Various complications which arise with real membranes which are heteroporous and have inhomogenous pores are sketched. Certain cases of membrane behavior under limiting conditions as to concentration of the adjacent solutions, the nature of the critical ions, etc., are discussed and compared to the experimental results. 4. 4. The direction of further fruitful investigations on membrane resistance is pointed out and the increasing number of points of close contact and even of overlapping between the physical chemistry of membranes and studies on ion exchangers is indicated.

New anion-exchange membranes are described, prepared from solutions of Dynel and poly-N-vinylimidazole neutralized with an excess of acid, and dissolved in a polar orgamic solvent. These highly selective membranes could be further improved to give virtually theoretical concentration potentials in 0.1 M potassium chloride solutions by simultaneous quaternization and cross-linking of the free base form by 1.5-dibromopentane. Es werden neue Anionen-Austausch-Membranen beschrieden, dargestellt aus Losungen von Dynel und Poly-N-vinylimidazol, die mit einem Uberschus an Saure neutralisiert und in einem polaren organischen Losungsmittel gelost wurden. Diese hoch selektives Membranen konnten durch gelichzeitige Quaternierung und Vernetzung der freien Base mit 1,5-Dibrompentan so verbessert werden, das sie in 0,1 m KCl-Losungen praktisch theoretische Konzentrationspotentiale ergaben.

Selectivity coefficients of a quaternary base ammonium anion-exchange resin toward a number of univalent anions have been measured. In some systems the selectivity coefficients varied little with composition, while in others a marked dependence was observed. Examples of the former included systems made up of various pairs of ions from Group A-halide, acetate, iodate and nitrate, or of pairs of ions from Group B-thiocyanate, perchlorate, di- and trichlolroacetate, trifluoroacetate, toluenesulfonate and naphthalenesulfonate. Examples of systems where the selectivity coefficient changed markedly were made up of an anion from Group A with one from Group B. These data were interpreted in terms of two postulated types of specific interactions (ion-pair formation) of these ions with those of the resin matrix. The ion-pairs of Group A were assumed to be randomly distributed in the resin phase, while those of Group B were assumed to occur in the form of “patches,” i.e., form clusters. The effect of temperature on the distribution coefficient was small; the concentration of the solution (when dilute) had a negligible effect upon the selectivity.

Monomolecular films of stearic and behenic acid were formed on substrates 0.1 M in sodium chloride, sodium bicarbonate, or sodium phosphate. The film was removed by skimming and its composition determined by infrared analysis. On all substrates only the pure acids could be detected by pH < 6. At pH 6–10 a mixture of the acid and the sodium salt was observed. The apparent pKa of the acids in the monolayer was 3–4 units higher than the estimated value in the bulk solution. The Gouy-Chapman theory was applied to these results and the true pKa was calculated to be 5.6–6.5, reasonably close to the bulk value. It was concluded that the binding of sodium ions to the monolayer is almost entirely ionic.

The study of a complex system such as an ion-exchange membrane can be approached from two directions, which are not mutually exclusive. We can make use of the theoretical framework of irreversible thermodynamics as first applied by Staverman1 to membrane systems, and as amplified by a number of other investigators, particularly Kedem and Katchalsky2–4. Here, we measure fluxes and generalized forces (the latter all too often involving the estimation of thermodynamic activity coefficients) and compute the phenomenological coefficients. This is essentially a ‘‘black box” approach which must give us correct and exact answers, provided the requirement of linearity between flux and force is obeyed, as they seem to be under the conditions which obtain in these systems.

The effect of the ionic radius of counterions has been introduced into the dissociation theory of polyelectrolytes, using the familiar rod-like model. Increments in the average dissociation constant pKa and slope n for polyacrylic acid with increasing size of the gegenion have been calculated and compared with data using potassium and some tetraalkylammonium hydroxides. Good agreement is encountered. The effects of changes in concentration of the polyacid and of the presence of neutral salt are also considered.