Katsuroku Takahashi

Some observations on the stability of supported liquid membranes

Abstract Stabilities of two types of supported liquid membrane (SLM), hollow fiber and flat sheet, have been studied in terms of the leakage of water across the membrane by using various kinds of polymeric solid supports and organic solvents. From lifetime data as a relative measure of SLM stability, it was found that the pore size of the support has the most significant effect on the stability. More stable membranes can be attained by use of membrane solvents with higher interfacial tension, and therefore of aliphatic hydrocarbons of higher boiling point; aromatics show a trend to be simply washed or forced sout of the SLM. In practical SLM separations, a membrane solution containing a surface-active carrier reduces the stability of the SLM by lowering the solvent-water interfacial tension. Membrane liquids held within the pores of a polymeric solid with lower surface energy may be more sensitive to variation of the interfacial tension.

Separation of Co(II)/Ni(II) via micellar-enhanced ultrafiltration using organophosphorus acid extractant solubilized by nonionic surfactant

Ultrafiltration (UF) of cobalt(II) and nickel(II) in the presence of a micelle-solubilized hydrophobic ligand has been investigated, using polyoxyethylene nonyl phenyl ether with 10 ethylene oxide units (PONPE10) and 2-ethylhexyl phosphonic acid mono-2-ethylhexyl ester (EHPNA) as a nonionic surfactant and an extractant, respectively. In aqueous media, the metals are entrapped within the surfactant micelles containing the extractant, and are effectively rejected by UF membranes with their consequent concentration in the retentate solution. The selective rejection of Co(II) over Ni(II) can be attained; the separation is enhanced with increasing solution pH and the extractant concentration. On the other hand, it was found that sodium dodecyl sulfate (SDS) as a surfactant and di-2-ethylhexyl phosphoric acid (D2EHPA) as an extractant give no selectivity between these heavy metals in the same operation. The effects of the surfactant concentration, applied pressure, salt addition and the membrane geometry on the rejection were also examined in the EHPNA/PONPE10 system.

Separation of La and Ce with PC-88A by counter-current mixer-settler extraction column

Abstract The separation of La and Ce with 2-ethylhexyl phosphonic acid mono-2-ethylhexyl ester (commercially known as PC-88A) from nitrate media was studied with a multistage counter-current mixer-settler extraction column of seven stages developed by the authors. The effect of flow rate ratio of the aqueous phase ( Q w ) to the organic phase ( Q o ) on the separation was studied. The maximum separation was obtained at Q w / Q o =3.2 and the separation degree was 63. Scrubbing of the organic phase was also studied in order to enhance the separation. La was scrubbed from the organic phase with nitric acid at pH 2.7 and the separation degree during scrubbing was 45. Simulations of the extraction and scrubbing processes were carried out and compared with the obtained experimental results. Stripping of Ce was achieved by using 100 mol/m 3 nitric acid. The organic phase was successfully recycled during the experiments without any effect on the extraction efficiency.

Study of drop coalescence behavior for liquid-liquid extraction operation

Abstract Using a video camera, a time course of coalescence was observed for toluene droplets formed at the top of adjacent nozzles in water. Several parameters which may control the coalescence have been investigated, such as concentration of acetone added to toluene, direction of mass transfer, time for attaining contact of the droplets, and flow rate of the continuous phase. The average coalescence times decrease with acetone concentration when acetone is transferred from the dispersed phase towards the continuous phase, and they increase with the time required for attaining contact. At high acetone concentration, oscillation of droplets appears, which restrains the coalescence. The average coalescence time increases when the acetone is transferred from the continuous phase towards the dispersed phase. An attempt has been made to predict coalescence times at low solute concentration (no oscillation) by assuming that the difference of interfacial tension causes the film drainage and leads to the drop coalescence. The agreement between the calculated and experimental values is not sufficiently quantitative but reasonable. For lower solute concentration, calculated coalescence times depend strongly on the time for attaining contact, which is in agreement with our experimental observation.

Extraction of rare earth metals with a multistage mixer-settler extraction column

Abstract Extraction behavior of rare earth metals within a mixer–settler extraction column has been analyzed with the stage efficiency calculated from mass transfer coefficients and interfacial area. The mass transfer coefficient within the dispersed drops is determined from a rigid sphere model by taking into account the residence time distribution of drops, and the coefficient around the drops is calculated by Ranz–Marshalls correlation with the terminal settling velocity of a rigid sphere. The interfacial area of dispersed drops is calculated by the use of correlations for the drop diameter and the holdup of dispersed phase in the mixer–settler extraction column. The calculated results for the separation of samarium and gadolinium with a five-stage mixer–settler extraction column are compared with the experimental results at various agitation speeds and flow ratios between two phases. The extraction behavior in the multistage column is explained by a model based on the hydrodynamics and the mass transfer within the mixer. Effects of the pH value in aqueous phase, the extractant concentration in organic phase and the number of stages on the extraction behavior in the mixer–settler column are also shown.

Transport behavior of protein in bulk liquid membrane using reversed micelles

Abstract Transport of lysozyme through a liquid membrane of reversed micelles of aerosol-OT (AOT) was studied. The feed phase was aqueous KCl or NaCl solution of lysozyme, and the recovery phase was aqueous KCl or BaCl 2 solution, while the membrane is the solutions of AOT with or without contacting the feed solution. The cations in feed phase are transferred through the liquid membrane and this cation transfer affects that of lysozyme and the size of reversed micelles of the membrane phase. Following transfer mechanisms have been proposed for the three systems investigated: the system NaCl–KCl, for which formation of large aggregates in the membrane phase was observed, has a so flexible interface that the micelles could become unstabilized in the membrane phase. For KCl–BaCl 2 system, the divalent ion Ba 2+ is selectively and excessively adsorbed on the interface and the negatively charged lysozyme molecules may be re-extracted at the interface of the recovery side by the electrostatic interaction with the adsorbed Ba 2+ ions. Both sides of the interfaces of the system KCl–KCl have an adequate flexibility that extraction and back-extraction of lysozyme through the membrane are attainable, although the transfer rate is rather low.

Fractionation of IgG Fragments Using Reversed Micellar Extraction

Abstract Reversed micellar extraction was applied for the fractionation of IgG fragments. With isooctane solution containing 50 mM AOT, Fab, Fe and IgG were extracted to the micellar phase. Each protein had an optimum pH range in the extraction. Fab and Fc were separated from the mixture at pH 7.0, with Fab being extracted to the micellar phase and Fe remaining in the aqueous phase. Extracted Fab fragments were recovered by bringing them into contact with 6M guanidine/HCl followed by dilution with PBS. Fab and Fc fragments were separated and recovered by reversed micellar extraction from IgG lysate digested with papain. Since the procedure is simple and rapid compared with column chromatography, mass preparation of the fragments can be expected by this method.

SOLVENT EXTRACTION OF TITANIUM(IV) FROM NITRIC ACID SOLUTION BY DI(2-ETHYLHEXYL)PHOSPHORIC ACID

ABSTRACT The extraction equilibrium of Ti(IV) was studied between aqueous nitric acid solutions (0.1-6M) and n-heptane solutions of di(2-ethylhexyl(phosphoric acid. The kinetics of the extraction and stripping reaction was also examined in a dispersion system using a stirred vessel. With increasing the acid concentration, the distribution ratio of Ti(IV) decreases and goes through a minimum. It was shown that the extraction of Ti(IV) from low acidic media in the concentration range 0.1-2M is a cation exchange reaction. For the higher acid solutions, the equilibrium distribution increases with the concentration of nitrate as well as nitric acid. This suggests that the extraction takes place by solvation reaction at high acidities. Furthermore, rate equations of the Ti(IV) extraction were obtained for the forward and backward reactions of the cation exchange. It was shown that a good agreement exists between the extraction constants from the equilibrium data and the two rate equations.

The film condensation of mixed vapour in a vertical column

Abstract In the film condensation of mixed vapour, the heat-transfer coefficient for the liquid film is given by the same equation as previously presented for the condensation of pure vapour. The dependence of the mass-transfer coefficient in vapour phase upon the rate of condensation is explained by the film theory, but for the mass transfer in liquid film, the agreement of the experimental values of the masstransfer coefficients with the values calculated on the basis of the penetration theory is excellent.

Process Development for Recovery of Vanadium and Nickel from Heavy Oil Fly Ash by Leaching and Ion Exchange

A process for recovering V and Ni from oil fly ash and for making the ash harmless has been developed. More than 80% of V and Ni are recovered. This process involves two-step leaching and ion exchange. The first step is leaching with water to dissolve Ni, Mg, Al, and Zn, and acid solution is used in the second step to recover V. The metals Ni and V are separated from other metals in each leached liquor. After neutralization and oxidation of the first liquor, Fe and Al are precipitated and removed from solution. Both Ni and Zn are then loaded on CR20 resin. Nickel can be selectively desorbed from the resin due to a remarkable difference in ion exchange isotherm between Ni and Zn. By using the resin C467, V is selectively separated from the second leached liquor containing V and Fe. The advantage of this separation process is that acidic leachant can be reused, saving separation energy.