Anna Narebska

Diffusion Dialysis. Effect of Membrane Composition on Acid/Salt Separation

Diffusion dialysis is an energy-saving separation technique. In order to highlight the relationship between membrane composition and ability to separate acid/salt mixtures by diffusion dialysis, a few anion-exchange membranes were examined. Experiments on solubility/diffusivity phenomena were carried out in contact with hydrochloric acid and sodium chloride solutions (single- and two-solute experiments). Computations using Glueckauf and Tye models have indicated high nonuniformity in the distribution of fixed charged within the membranes and different accessibilities of the internal membrane volumes for the acid and salt. The Neosepta AFN-7 membrane (Tokuymam Soda Co.) has proved effective in differentiating the permeants by sorption (k{sub HCl}/k{sub NaCl} {approx} 2) and diffusivity ({bar D}{sub HCl}/{bar D}{sub NaCl} up to 10). This membrane is also the only one which, when in contact with two-solutes solutions, absorbs the acid preferentially to the salt. For this membrane the preferential sorption and transport of the acid depends not only on the physical structure of the membrane but also on the chemical nature of the polymer which contains pyridine moieties.

A Fully Automated System for the Determination of Pore Size Distribution in Microfiltration and Ultrafiltration Membranes

Abstract An automated system controlled by a Amstrad CPC 6128 microcomputer was designed. The apparatus can be used for a fast characterization of MF and UF membranes by the bubble point method. The theory for a modified bubble-point method is reviewed. The system determines pore size, pore size distribution, and surface porosity for the membranes of pore radii not less than 45 nm. The whole experiment takes 3–5 h to complete. The apparatus was tested on various MF and UF membranes (Nuclepore, Synpor, PVC UF, PAN UF, CA UF).

Separation of Carboxylic Acids from Carboxylates by Diffusion Dialysis

Abstract Acetic acid/sodium acetate and propionic acid/sodium propionate were separated by the diffusion dialysis technique using Neosepta AFN‐7 and Selemion DSV membranes. Accounting for molarities of carboxylic acids and salts in broths produced by the pH controlled bacterial fermentation (pH 4–6), the experiments were carried out with carboxylates in excess of acids. The sorption equilibria established for acetic acid, propionic acid, and the sodium salts of both acids (single solute experiments) revealed a high sorption of acids in both membranes and the rejection of carboxylates. The partition coefficients were found to be from unity up to 2 for the acids and 0.04–0.05 for the salts. Reflecting a high sorption, the fluxes for the acids amounted from 1.5 to 2.0 mol · m−2 · h−1 and only 0.07–0.08 mol · m−2 · h−1 for the salts (one molar solutions). The separation factors computed upon the experiments performed with the ternary solutions were found between 20 to 37 for the Neosepta AFN‐7 membrane and about 29 for the Selemion DSV membrane. Accounting additionally, for the results of the separation of lactic acid from sodium lactate reported in our earlier paper the results prove the diffusion dialysis to be applicable to the separation of mean strength and weak carboxylic acids from their salts.

Two-Component Emulsion Liquid Membranes with Macromolecular Carriers of Divalent lons

Abstract Experimental investigations are presented on the application of poly-[poly(ethylene glycol) phosphate] (PEGP) as a macromolecular, multisite, carrier of ions in an emulsion liquid membrane system. This polymer acts as a mobile carrier and surfactant-stabilizing W/O/W emulsion. The transport properties of PEGP have been checked for systems composed of (a) a feed phase containing Ni(II), Co(II) or Cu(II) ions; (b) an organic phase, i.e., PEGP dissolved in 1,2- dichloroethane; and (c) 1 M sulfuric acici as a receiving solution. Fast and effective membrane extraction of Ni(II) has been found for membranes with PEGP of molecular weight 22,000. It has been proved that the affinity of PEGP toward the studied ions is reversed in comparison with that for poly(ethylene glycol). The affinity order of PEGP toward the tested ions is Ni(II) > Co(II) > Cu(II).

Separation of Fermentation Products by Membrane Techniques. II. Conversion of Lactate to Lactic Acid by Electrodialysis

ABSTRACT The yield of an electrodialysis unit operating for the conversion of lactate to lactic acid (LA) is depressed by low conductivity of the lactic acid solution. Experiments performed with a laboratory electrodialysis unit (ED) designed to establish the limiting current density ilim for the whole unit and for each of the membrane/solution elements revealed high voltage drops for membranes in contact with the lactic acid solution. By filling the LA compartment with a cation-exchange resin as the conducting turbulence promoter, it was possible to increase ilim from 2.7 ± 0.3 to 18.3 ± 2.0 mA/cm2. With a resin suspension the rate of lactic acid formation was 6.0 molâ2 â1, the current efficiency amounted to 92%, and the energy consumption was 3.3 kWgâ1. A hypothesis for the 7-fold increase of ilim by filling the LA compartment with a grained conducting resin is presented.

Current Efficiency and Transport Phenomena in Systems with Charged Membranes

Abstract The interaction between the current efficiency of electrodialytic separation with ion-exchange membranes and all the fluxes depressing selectivity, i.e., electric transport of coions, electroosmotic flow of water, diffusion, and osmosis, are described and experimentally examined. A simple method for the determination of current efficiency for any concentration difference across the membrane and current density is presented. A simple relationship between the current efficiency and the efficiency of energy conversion in the desalination process is shown.

Separation of Fermentation Products by Membrane Techniques. Part III. Continuous Isolation of Lactic Acid by Facilitated Membrane Extraction

ABSTRACT Facilitated membrane extraction (FME) has been examined for the continuous isolation of lactic acid from its dilute solutions. The technique is intended for continuous fermentation technology, with the pH of a broth regulated by extraction of the acid. Standard dialysis membranes and a conventional diffusion dialyzer were the equipment used for carrying out the separation. By FME, slow diffusional transport across a membrane is accelerated by the neutralization of an acid in the receiving side of a dialyzer. By using this technique the fluxes of lactic acid were found to be 0.7−1.3 mol·m∼2·h∼1 (pH 11.7−12.8) against 0.013−0.015 mol·m2h−1 reported for conventional diffusion dialysis (the same feed, caCid = 0.01 mol·dmminus;3). The accumulation of lactate in a permeate established experimentally was 0.5−0.6 mol·dm∼3. The concentration of lactic acid left in a feed after extraction was 10∼3−10∼4 mol·dm∼3. FME integrated with electrodialysis seems to offer an effective separation system for continuou...