H. Garth Spencer

Calcium alginate gels: formation and stability in the presence of an inert electrolyte

The effects of a simple salt (1:1 electrolyte, KCl) on the calcium alginate gel formation and the gel stability of alginates varying in molecular weight and mannuronate/guluronate (MG) ratio were investigated by an equilibrium dialysis technique. There was no significant dependence of the calcium binding capacity among the alginates. However, the G residues exhibited a stronger affinity for Ca2+ than M residues. The addition of a simple salt to the dialysis solution resulted in displacement of bound Ca2+ and swelling of the calcium alginate gel that increased with concentration of the simple salt. Even the Ca2+ bound with the G block was displaced by monovalent cations at high salt concentration.

Dye-salt separations by nanofiltration using weak acid polyelectrolyte membranes

Abstract Separation of a dye, Cibacron blue, from a salt, NaNO3, with a common counterion by nanofiltration of dilute salt solutions containing trace concentrations of the dye using dynamically-formed weak acid polyelectrolyte membranes, was investigated. The separation factor increased with decreasing flux and ionic strength, and with increasing pH, cross flow velocity and dye-to-salt concentration ratio. The separation behavior over broad ranges of the operating parameters was described by a model requiring filtration experiments with the two electrolytes in single-solute solutions and two experiments with mixed-solute experiments to evaluate the model parameters.

Formation and characterization of chitosan formed-in-place ultrafiltration membranes

Formed-in-place (FIP) ultrafiltration (UF) membranes were formed from dilute solutions of chitosans with different molecular weights in 1% acetic acid on a macroporous titanium dioxide substrate. The ultrafiltration properties were characterized by investigating the rejection and permeability of a 1.0 g/L bovine serum albumin (BSA) solution at various pH and ionic strength conditions. The membrane stability to the crossflow shear and to the ionic strength was investigated. There was very little dependence of the membrane-formation capability and the membrane properties on the chitosan molecular weight. In contrast, pH had a marked effect on membrane surface properties, membrane stability, and membrane morphology.

Transport of electrolytes through a weak acid nanofiltration membrane : Effects of flux and crossflow velocity interpreted using a fine-porous membrane model

Abstract A one-dimensional fine-porous membrane model has been exploited to determine the reflection coefficient, σ, and the internal solute mass transport coefficient, km, for the nanofiltration of simple salts and dyes by two weak-acid membranes, HR and LR, differing in σ for a NaNO3 solution. The rejection, r, was strongly dependent on the crossflow velocity, u, and the flux, J, in these experiments. The dependence of the external solute mass transport coefficient, ks, on u was also determined. The dominant parameter in determining the limiting, low J and high u, rejection for the systems is σ. It was influenced primarily by the charge of the coion for the simple sodium salts, NaNO3 and Na2SO4. The km remained constant within experimental error, for NaNO3 and Na2SO4 using membrane HR and for the two dyes NaR4 and Na2R1 using membrane LR even though the charge on the coions and their formula weights differed in each comparison. Transitions from regime I, i.e., decreasing r with increasing J at constant u, to regime II, i.e., increasing r with increasing J at constant u, behavior were observed at low u for a trivalent dye using membrane LR.

Thermal Decomposition and Crystallization of Aqueous Sol-Gel Derived Zirconium Acetate Gels: Effects of the Additive Anions

Zirconia powders were prepared by forming gels by desiccation of aqueous precursor solutions of zirconium acetate containing nitric or sulfuric acid at pH 2.4 and 1.4 and pyrolyzing the gels to temperatures up to 825°C. The structure development in the gels and solid pyrolysis products was investigated. The crystalline zirconia structures produced monoclinic (m), metastable cubic (c) and tetragonal (t) polymorphs. The structure transition temperatures were strongly dependent on the pH, the anions and the stoichiometry of the zirconium complex in the precursor solution. The monoclinic polymorph fraction in the zirconia formed by pyrolyzing the gel formed from the precursor solution containing sulfuric acid at pH 2.4 to 750°C approaches zero while this ratio in the zirconia formed by pyrolyzing the gel formed from the precursor solution containing nitric acid at pH 1.4 to 825°C is 0.7.

Effects of immobilized pectinase on the microfiltration of dilute pectin solutions by macroporous titania membranes: resistance model interpretation

Abstract The retentive microfiltration of 1 g/dm3 solutions of citrus and apple pectin was investigated at crossflow velocities up to 1.64 m/s using a tubular macroporous titania membrane 1.6 cm in diameter with an immobilized pectinase. The flux was compared to the flux obtained using the same membrane without immobilized pectinase as a control membrane. The flux was significantly higher through the membrane with immobilized pectinase than through the control membrane at the intermediate crossflow velocities, 0.80 and 1.2 m/s. Analysis of the flux results using a resistance model indicates that the resistance of the irreversible fouling layer was increased by the presence of immobilized pectinase at the intermediate crossflow velocities. However, the resistance associated with concentration polarization, or resistance reversible to a water rinse, was reduced sufficiently under these crossflow conditions to increase the flux over that obtained with the control membrane. Minor differences in the flux behavior were observed for the pectins from the two sources. The enzyme was active in reducing the molecular weight of the pectin in the permeate in all the experiments.

Effects of calcium ions on the streaming potentials of zirconium hydrous oxide-polyacrylate formed-in-place membranes

Abstract The effects of calcium ions on the electrokinetic properties of a zirconium hydrous oxide-polyacrylate membrane were investigated by measuring streaming potentials of this membrane and its precursor substrate, a zirconium hydrous oxide membrane, in potassium and calcium chloride solutions. The streaming potential per unit of transmembrane flux was calculated and used as a parameter to characterize the electrokinetic properties of the membrane-electrolyte systems. This parameter for the zirconium hydrous oxide-polyacrylate membrane was more positive in the calcium chloride solutions over the pH range investigated, 3.5 to 8.5, than in the potassium chloride solutions. However, for the zirconium hydrous oxide membrane it was the same within experimental variation in both electrolyte solutions at pH greater than and including the common zero point of charge. These results imply that the effect of the calcium ion on the electrokinetic properties of the zirconium hydrous oxide-polyacrylate membrane in this pH range is constrained to an interaction with the polyacrylate, probably through site binding with the carboxylate groups of the polymer. At pH less than the zero point of charge, the parameter was more positive for the calcium chloride solution than for the potassium chloride solution for both types of membranes, which implies alteration of the surface of the zirconium hydrous oxide by the calcium.

Thermal Decomposition and Crystallization of Aqueous Sol-Gel Derived Zirconium Acetate Gels: Effects of the Precursor Solution pH

Crystalline zirconia has previously been formed by desiccation and pyrolysis of a pH 3.4 zirconium acetate precursor solution. In this study, amorphous gels were formed by desiccation of zirconium acetate precursor solutions at pH 0.9 to 3.4 obtained by adding hydrochloric acid and at pH 8.0 by adding ammonium hydroxide to the available pH 3.4 precursor solution. The concentrations of the uncomplexed zirconium ion and the 1 : 1 and 1 : 2 zirconium acetate complexes varied with pH. Decomposition of the amorphous gel and its structure evolution to form crystalline zirconia by pyrolysis were studied. Several decomposition and structure transition temperatures occurring in the pyrolysis and the polymorph distribution in the pyrolysis products were dependent on the pH of the precursor solution. These variations of structure evolution with pH were also related to the relative concentrations of specific zirconium complexes in the precursor solutions. Removal of carbon by pyrolysis was improved by adding hydrochloric acid or ammonium hydroxide to the pH 3.4 precursor solution.

Selective protein separations using Formed-In-Place anion exchange membranes

Anion exchange membranes prepared by adsorption of polymers on Formed-In-Place microfiltration substrates were formed and ion-exchange separations of solutions containing two proteins were determined by ion exchange membrane sequential separation procedures, similar to affinity membrane separation procedures. Representative ion exchange separation processes utilizing adsorbed poly(ethylene imine) (PEI) as the ion exchange membrane for the separation of the components of solutions containing two proteins, bovine serum albumin (BSA) and lysozyme and ovalbumin and lysozyme, are described. The stability of the PEI adsorbed layer, binding characteristics of the BSA to the membrane and purification properties of the procedure were determined.

Transient diffusion through a membrane separating finite and semi-infinite volumes

The transient diffusion of penetrant through a membrane separating a finite from a semi-infinite volume is investigated. Solutions of the diffusion equation reduce for long times to relatively simple expressions from which diffusion constants, solubilities and permeabilities may be calculated. The procedures developed are applied to the diffusion of carbon dioxide and propane through a silicone rubber membrane.