Yoshikazu Miyake

Modeling of the Permeation of Copper through Liquid Surfactant Membranes

Abstract A general permeation model for the extraction of copper by liquid surfactant membranes using a chelating agent as a carrier is presented in which the internal mass transfer in the W/O emulsion drop, the external mass transfer around the drop, the rates of the formation and decomposition of the complex at the aqueous-organic interface, and the leakage of the internal aqueous phase to the external phase due to the membrane breakup are taken into account. The batch extraction of copper using SME529 as a carrier was carried out under various experimental conditions. It is shown that the extraction rates can be satisfactorily simulated by the present model.

Extraction of amino acids by emulsion liquid membranes containing di(2-ethylhexyl)phosphoric acid as a carrier biotechnology ; coupled, facilitated transport ; diffusion

An experimental and analytical study on the batch extraction of amino acids such as tryptophan (Trp) and phenylalanine (Phe) was performed with emulsion liquid membranes containing di (2-ethylhexyl)phosphoric acid (D2EHPA) as a carrier. A series of preliminary experiments on the extraction equilibria for aqueous-organic two-phase systems showed that the complex formation reaction can be expressed as follows: n nA+ + 2 (HL)2 = AL (HL)3 + H+, Kex = ( [AL(HL)3] [H+]/[A+] [ (HL)2]2) n nHere, A+ is the cation of the amino acid, and (HL)2 is the dimer of D2EHPA. The distribution ratio of the amino acid is given by n nD=Kex[(HL)2]2/(Ka + [H+]) n nwhere Ka is the acid dissociation constant of the carboxylic group in the amino acid. The rate of extraction of Trp with D2EHPA, measured by using a Lewis-type stirred cell, in a two-phase system suggested that the complex formation reaction is so fast that the extraction equilibrium is established at the aqueous-organic interface. On the basis of the above results, the mechanism and the rate of extraction of the amino acids with emulsion liquid membranes are discussed, and a permeation model is proposed which takes into account the mass transfer in both the external aqueous phase and the organic membrane phase, and also the extraction equilibria. It was found that the effects of various experimental conditions on the extraction rate and the extent of recovery were satisfactorily explained by the proposed model. The results of the permeation of β-phenethylamine (β-PhA) and tryptophan methyl ester (TrpMe) are also discussed.

Kinetics and mechanism of metal extraction with acidic organophosphorus extractants (I): Extraction rate limited by diffusion process

Abstract The extraction mechanism of metal ion by acidic organophosphorus extractant was discussed by taking into account the physicochemical properties of extractant. Since the acidity of the extractant is higher than that of chelating agent, the rate of complex formation of metal ion with the extractants is rapid compared to that with the chelating agents. It is found that the rate determining step of the extraction such as Cu(II) and Co(II) by 2-ethylhexyl phosphonic acid mono-2-ethylhexyl ester is not the complex formation at the interface, but the diffusion of the metal complex in the organic stagnant film, which is instantaneously formed at the interface. This result was also confirmed by the stirring speed dependence of the initial extraction rate. Furthermore, the time course of Co(II) extraction from the initial stage to the equilibrium state was quantitatively interpreted by considering only the diffusion rates of reactants and products in both stagnant films.

Extraction of Lanthanoids by Liquid Surfactant Membranes

Abstract Separation and concentration of lanthanoids such as La3+, Nd3+, Sm3+, Eu3+, Gd3+, Dy3+, and Yb3+ were carried out using liquid surfactant membranes containing 2-ethylhexyl phosphonic acid mono-2-ethylhexyl ester as a carrier. Under the condition of sufficiently high distribution ratio, more than 98% of these metal ions was extracted within 5 min even if the volume ratio of W/O emulsion to the external aqueous phase was as low as 1/32. The ratio of the concentration of metal ions in the internal aqueous phase to that in the external feed phase reached about 50,000 within 20 min. In the conventional solvent extraction of Yb3+, the aggregates of metal-carrier complexes, which were insoluble in the organic membrane phase, were formed at high loading ratio. In the extraction of Yb3+ by liquid surfactant membranes, however, formation of such aggregates was suppressed because both extraction and stripping occurred simultaneously on both sides of the membranes. The rate of interfacial reaction between la...

Enzymatic reaction in water-in-oil microemulsions. Part 2.—Rate of hydrolysis of a hydrophobic substrate, 2-naphthyl acetate

The catalytic hydrolysis rates of a hydrophobic substrate, 2-naphthyl acetate (NA), have been measured both in aqueous solution and in water-in-oil microemulsions (ME) formed by di(2-ethylhexyl)sodium sulfosuccinate (AOT) in heptane. The catalysts used were lipase, α-chymotrypsin and imidazole.The dependence of Wo=[H2O]ov/[AOT]ov at a constant [AOT]ov and of [AOT]ov at a constant Wo on the overall rate constant were discussed in terms of a reaction model. The reaction model includes three parameters, the distribution constants of NA and the catalysts and the rate constant of the local reaction field. The distribution constant of NA was evaluated by measurements of the distribution of NA between the ME in the Winsor II region and the aqueous phase, but that of catalysts was treated as a fitting parameter.It is suggested that the reactions with these catalysts proceeds at the interfacial region of ME. For the imidazole-catalysed reaction, if the imidazole exists preferentially at the interface, the rate constant is independent of Wo, but the value was 0.2 times that in the aqueous phase.Superactivity of lipase was observed, that is the turnover number in ME was greater than that in the aqueous phase. However, as the michaelis constant was also large, the rate constant (kCAT/km) in ME was smaller than that in the aqueous phase. The rate constant increased as Wo increased. The dependence was caused by the conformation change of lipase due to the interaction of AOT molecules. The rate constants for both imidazole and lipase decreased with increase in [AOT] at constant Wo, which might be caused by the change in the structure of ME.The turnover number for α-chymotrypsin at the interface was lower than that in the aqueous phase and approached the values in the aqueous phase as Wo and [AOT] increased. However, the Michaelis constant decreased with increase in Wo and approached a constant value, which was 25 times that in the aqueous phase.

Enzymatic reaction in water-in-oil microemulsions. Part 1.—Rate of hydrolysis of a hydrophilic substrate: acetylsalicylic acid

The rates of catalytic hydrolysis of a hydrophilic substrate, acetylsalicylic acid (AA), have been measured both in aqueous solution and in water-in-oil (w/o) microemulsions formed by AOT in n-heptane. Catalysts used were lipase from Rhizopus delemar, α-chymotrypsin from Bovine pancreas and imidazole as an acid–base catalyst.Since the hydrolysis of AA proceeds in aqueous solution without catalyst (intramolecular catalysis), the rate of hydrolysis was measured in microemulsions. The rate constant for the hydrolysis of AA increased with increasing concentration ratio of water to AOT, W0=[H2O]ov/[AOT]ov, at constant [AOT]ov, and was asymptotic to the value obtained in aqueous solution. For constant W0 the rate constant was almost independent of [AOT]ov over the range 0.15–0.65 mol dm–3.The overall rate constant for the catalytic hydrolysis of AA in microemulsions was obtained by subtracting the rate constant for the intramolecular catalysis of AA from the rate constant observed. The intrinsic rate constant in the water pools of the microemulsion was then evaluated by considering the volume fraction of water determined by Karl Fischer titration.For W0 > 10 at [AOT]ov= 0.5 mol dm–3, the intrinsic rate constant for imidazole-catalysed hydrolysis of AA was equal to that obtained in the aqueous phase. As W0 decreased below 10, the intrinsic rate constant decreased and the value at W0= 6.5 was 0.6 times that in the aqueous phase. The intrinsic rate constant was independent of [AOT]ov.The addition of lipase to the aqueous phase did not enhance the rate of hydrolysis of AA. However, the reaction in microemulsions was catalysed by the lipase and was linearly dependent on lipase concentration. Lipase in microemulsions exhibits activity for the hydrolysis of AA owing to a change in the conformation of lipase. The intrinsic rate constant in the water pool is a maximum at W0= 7 and is independent of [AOT]ov.The rate of hydrolysis of AA was little affected by the presence of α-chymotrypsin either in the aqueous phase or in microemulsions.

Kinetics and Mechanism of Metal Extraction with Acidic Organophosphorus Extractants (II) : Extraction Mechanism of Fe (III) with di (2-Ethylhexyl) Phosphoric Acid

Abstract Experiments on the reaction between Fe(III) and di(2-ethylhexyl) phosphoric acid (D2EHPA) were carried out in homogeneous systems, i.e., 70 wt% ethanol solution in order to elucidate the kinetics and mechanism of the reaction. It was found that reactions of FeOH2+ with both dissociated and undissociated D2EHPA are predominant and also that both reactions obey Eigens mechanism. Further, extraction and stripping rates of Fe(III) were measured in heterogeneous systems using benzene as a diluent. Extraction and stripping rates were found to be limited by the formation and the dissociation of 1:1 complex at the interface, respectively, and could be quantitatively simulated by a proposed model using kinetic parameters obtained in the experiments of homogeneous reaction.

Modeling of the Permeation of Copper through Liquid Surfactant Membranes by Continuous Operations

Abstract A model for copper permeation through liquid surfactant membranes in a continuously stirred vessel is presented in which mass transfer resistances both in and around W/O emulsion drops, interfacial reactions at aqueous-organic interfaces, and the residence time distribution of the W/O emulsion drops in the extraction vessel are taken into account. Extraction of copper using SME529 as a carrier was carried out with a continuously stirred vessel. It is shown that the experimental data can be satisfactorily interpreted by the proposed model.

Separation of gallium and indium by supported liquid membranes containing 2-bromodecanoic acid as carrier: design of supported liquid membrane module based on batch permeation experiments

Abstract The recovery of gallium and indium from sulfate media by supported liquid membranes containing 2-bromodecanoic acid (2-BDA) as a carrier was performed by using both a batch type stirred permeation cell and a continuous-type supported liquid membrane module with flat geometry. The effect of various experimental conditions on the permeation rates of gallium and indium were studied. A simple method is proposed for designing continuous supported liquid membrane modules from the data obtained with the batch type permeation cell on the basis of the correspondence of the parameters in batch operation to those of continuous operation. By this method, the membrane area required for given feed flow rate and the percentage recovery can be easily determined even for the case of multi-component separation.

Metal–ligand complex formation in the presence of ionic micelles. Equilibrium and kinetics of the reaction between copper(II) and benzoylacetone in the presence of ionic micelles of SDS or DTACl

The equilibrium and kinetics of the metal–ligand complexation reaction between CuII and the chelating agent, 1-phenylbutane-1,3-dione (benzoylacetone), have been studied in micellar solutions of sodium dodecylsulphate (SDS) and dodecyltrimethylammonium chloride (DTACl). The apparent stability constant of the 1:1 complex passed through a maximum with the increase in the micellar concentrations for SDS solutions, while it decreased monotonically for DTACl solutions. The micellar effect on the apparent stability constant is related to the partitioning of reactants between the micellar phase and the aqueous solution. The observed rate of 1:1 complex formation was considerably enhanced by the presence of SDS micelles. The effect can be quantitatively interpreted by considering the reaction in the electric double-layer around the micelles, where CuII ions are concentrated by the electrostatic interactions. The rate constant for the reaction in this layer was found to be greater than that in aqueous solutions by a factor of ca. 18. This effect was deduced to be caused by the instability of the keto form of benzoylacetone.