Harry P. Gregor

Modelling of the pore size distribution of ultrafiltration membranes

Abstract 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.

Acetic Acid Extraction by Solvent Membrane

Abstract 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.

Fixed-Charge Ultrafiltration Membranes

The properties of a series of sulfonic acid fixed-charge membranes of graded porosity were described in terms of their fixed-charge molality, hydraulic permeability, concentration potential and rejection to a number of charged and uncharged solutes of differing molecular weight. Their use in ultrafiltration processes employing a number of test solutions and also solutions from the sewage-treatment, pulp and paper, and cheese industries was also described. The salient property of these membranes was their non-fouling character as exemplified by their ability to maintain their hydraulic flux and solute rejection properties with solutions known to foul conventional ultrafiltration membranes.

Coulombic reactions of polyelectrolytes with counterions of different sizes

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.

ETHANOLIC FUELS FROM RENEWABLE RESOURCES IN THE SOLAR AGE

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.

Acrylonitrile copolymers: Synthesis, characterization, and formation of ultrafiltration membranes

A variety of poly(acrylonitrile-co-acrylamide) polymers of different compositions were synthesized by free radical copolymerization. Thin films were cast from polymer solutions, and coagulated into ultrafiltration membranes. The effect of preparative parameters on membrane gel structure was investigated. For nonsupported membranes, concentrated polymer solutions produce fine pore membranes with a lower flux; extending the drying time causes a diminution in membrane thickness, swelling index, and fluxes; the membrane thickness, swelling index, and permeate flux all increased with increasing coagulation bath temperature. For supported membranes, dilute polymer casting solutions, small casting gate opening, and added polyvinylpyrrolidone to the casting solution all increased the permeate flux. The membranes containing acrylamide were more hydrophilic, and had a smaller dispersion force component of the surface free energy than those prepared from the polyacrylonitrile homopolymer.

MEMBRANE SEPARATIONS IN ALCOHOL PRODUCTION

Substantial process improvements can be made in the conversion of sugar-starch feedstocks into ethanol by the use of one or more of the three membrane processesultrafiltration (UF), electrodialysis (ED), and reverse osmosis (R0)-all of which are available on a commercial scale. These have been evaluated in detail a t the laboratory level with several different feedstocks and for different steps in the process. This is a report of those laboratory studies, including an estimation of the costs of such processes a t full scale production and the status of pilot plant programs. FIGURE 1 outlines the conventional and membrane-controlled processes that could be employed. The dilute feedstocks of cane, beet, and sorghum juice (about 12% sugar content) are now used directly as feedstocks; substantial process savings could be achieved by concentrating these to 22% using UF and R O prior to fermentation. The beer which is produced at an alcohol content of about 11% is conventionally distilled after some solids separation, depending on the feedstock, and the thin stillages produced are dewatered either by multiple effect evaporators or by vapor compression stills to approximately 50% total solids and sold as distillers dried grain (DDG). Ultrafiltration can be employed either directly upon the beer to produce a DDG concentrate of high molecular weight fractions and a clear permeate for efficient distillation or upon the stillage to produce the high molecular weight DDG concentrate. Subsequent treatment of the UF permeates by ED can remove the excess salts present; this deionate is capable of being treated by R O to produce pure water for recycling and a low molecular weight concentrate to supplement the DDG produced. The ultrafiltration of fermenter contents can allow for a higher yeast cell level and the removal of product alcohol, both of which accelerate the rate of alcohol production. The savings in process and energy costs have been estimated and appear to be considerable.

Selective uptake of counterions of different size by ion‐exchange gels: Effect of swelling pressure and Coulombic interactions

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.

The Modes of Specific Binding of Ions to Polyelectrolytes

The contributions to this Advanced Study Institute on Charged and Reactive Polymers represented three different points of view of the same scientific subject. Some authors were concerned with solutions of polymers as whole entities, as for example the density of these solutions as reflecting the electrostriction of solvent by the polymer. A second group of authors was concerned with polymers per se, as with their general thermodynamic and dynamic properties as influenced by general considerations of ionic strength, etc., as with the configurational entropy entity of polymers. The third group of authors was not concerned with polymer systems as a whole but rather with a highly localized phenomenon, their binding to ions in solution, with a primary concern on the nature and extent of these bindings reactions.

Interpolymer ultrafiltration membranes prepared from poly(vinylidene fluoride) and poly(1-vinyl-3-methylimidazolium iodide)

Abstract 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).