Separation of metals by liquid surfactant membranes containing crown ether carboxylic acids

A water-in-oil-in-water emulsion liquid membrane system is used to transport alkali metal and alkaline earth cations from an external alkaline aqueous source phase through an organic membrane containing a crown ether carboxylic acid and into the internal acidic aqueous phase of the emulsion droplet. The influence of varying the crown ether carboxylic acid structure upon the selectivity and efficiency of competitive metal ion transport is examined.     

Liquid membrane extraction of Cephalosporin-C from fermentation broth

The extraction of Cephalosporin-C (CPC) from dilute fermentation broth of Cephalosporium acremonium was studied in a bulk liquid membrane as well as in an emulsion liquid membrane system. Aliquat-336 was used as the extracting agent to provide facilitated transport of CPC via liquid–liquid ion exchange mechanism. By maintaining an appropriate pH gradient in the feed and receiving phases, facilitated uphill transport could be achieved in the bulk liquid membrane system. The culture broth contains CPC and deacetyl CPC (DCPC) which are structurally almost similar, but CPC is more hydrophobic in nature. Selective separation of CPC could be achieved in a suitably formulated liquid membrane system. A simple mass transfer model predicts the permeation rate in the bulk liquid membrane. The permeation process in an emulsion liquid membrane appears to be controlled by the aqueous boundary layer resistance and diffusion in the emulsion globule. This is perhaps the first demonstration of the liquid membrane as an effective technique for selective extraction of CPC from fermentation broth of Cephalosporium acremonium.     

Studies on emulsion liquid membrane extraction of cephalexin

An experimental study on batch extraction of cephalexin using an emulsion liquid membrane system has been reported. The effects of surfactant, carrier and solute concentrations, phase volume ratio, stirring speed, and counterion concentration on the extraction rate were examined. Surfactant, carrier and diluent used were Span-80, Aliquat-336 and n-heptane–kerosene (1:1), respectively. Under the optimised experimental conditions, emulsion swelling was found to be marginal. By maintaining an appropriate pH gradient in the feed and receiving aqueous phase, facilitated transport could be realised. Selective separation of cephalexin from a mixture of 7-aminodeacetoxy cephalosporanic acid (7-ADCA) could be demonstrated in the emulsion liquid membrane system. A mathematical model based on mass transfer across aqueous boundary layer, interfacial chemical reaction and diffusion in the emulsion globule provides a reasonable fit of the experimental solute concentration versus time profiles in the emulsion liquid membrane system.     

环烷酸类载体液膜体系对金属离子传输机理的研究

本文先在大块液膜体系中以环已烷甲酸为载体,通过正交设计,系统地研究了各种因素对希土离子输送作用的影响规律。比较了相同条件下RE~(3+)(希土)同Na~+,NH_4~+、Ca~(2+)和Fe~(3+)等离子的输送作用。发现在适当条件下,无皂化的羧酸载体对RE~(3+)离子具有良好的输送效果,同时证实,羧酸输送RE~(3+)离子是通过三个H~+离子与一个RE~(3+)离子的交换,而当载体皂化时,皂化的载体直接与接收相H~+离子发生交换,从而降低了羧酸对RE~(3+)离子的输送和分离效果。 在大块液膜研究的基础上,建立了一个以无皂化的环烷酸为载体的乳状液膜体系,从模拟离子矿的硫酸铵浸出液中萃取希土,通过正交试验确定了最优的液膜萃取条件,希土萃取率达96％以上,富集度30～40倍。     

Proton-ionizable crown compounds. 12. Proton-Coupled selective membrane transport of Li+ using a proton-ionizable pyridono macrocycle

The macrocycle-mediated fluxes of several alkali metal cations have been determined in a H₂O-CH₂Cl₂-H₂O liquid membrane system. Water-insoluble proton-ionizable macrocycles of the pyridono type were used. The proton-ionizable feature allows the coupling of cation transport to reverse H⁺ transport. This feature offers promise for the effective separation and/or concentration of alkali metal ions with the metal transport being driven by a pH gradient. A counter anion in the source phase is not co-transported. The desired separation of a particular metal ion involves its selective complexation with the macrocycle, subsequent extraction from the aqueous phase to the organic phase, and exchange for H⁺ at the organic phase-receiving phase interface. Factors affecting transport which were studied include ring size, source phase pH, and receiving phase pH. Lithium was transported at a rate higher than that of the other alkali metals in both single and competitive systems using a 15-crown-5 pyridono carrier.     

Proton ionizable crown compounds. 18. Comparison of alkali metal transport in a H2O-CH2Cl2-H2O liquid membrane system by four proton-ionizable macrocycles containing the dialkylhydrogenphosphate moiety

The macrocycle-mediated fluxes of alkali, alkaline earth, and several transition metal cations have been determined and compared in a H₂O-CH₂Cl₂-H₂O liquid membrane system using four water-insoluble macrocycles containing a dialkylhydrogenphosphate moiety. Transport of alkali metal cations by these ligands was greatest from a source phase pH = 12 or above into an acid receiving phase (pH = 1.5). Very low fluxes were observed for the transport of the alkaline earth cations and all transition metal ions studied except Ag⁺ and Pb²⁺ which were transported reasonably well by these new macrocycles.Deceased: September 5, 1987.     

Role of Ion exchange in permeation processes

The single ion transport of transition metal ions like Cu²⁺, Co²⁺, Ni²⁺ and Zn²⁺ were carried out through the H⁺ and alkali metal ion forms of Nafion membrane. These studies showed that the ion exchange selectivity coefficient of the permeating ion had an effect on its transport process. It was found that the diffusion coefficient values (D) were directly proportional to the selectivity coefficient (K). This shows that the initial stage of permeation is governed by ion exchange process (effect of K on D).     

Proton-ionizable crown compounds. 11. Synthesis of macrocyclic ligands containing two sulfonamide groups and chloro substituents or pyridine subcyclic units and a preliminary study of cation transport by three of these ligands

Five new macrocyclic ligands each containing two sulfonamide groups have been prepared. Three of these compounds contain one or two chloro substituents and the other two have one or two pyridine subcyclic units. A seventeen-membered ring ligand (4) was found to be an excellent transport agent for all alkali metal cations in a water-methylene chloride-water bulk liquid membrane system when the pH of the source phase was 13 or higher. The chlorine-substituted analog (5) was a poor transport agent for the alkali metal cations possibly because the chlorine atom blocked entry to the macrocycle cavity. An open-chain analog containing two sulfonamide groups was particularly effective in transporting cesium ions.     

Emulsion liquid membrane extraction of Ni(II) and Co(II) from acidic chloride solutions using bis-(2-ethylhexyl) phosphoric acid as extractant

An emulsion liquid membrane process using bis-(2-ethylhexyl) phosphoric acid (D2EHPA) to extract and separate Ni(II) and Co(II) from acidic chloride solutions is described. Liquid membrane consists of a diluent, a surfactant (Span 80), and an extractant (D2EHPA). Hydrochloric acid was used as the stripping solution. The important parameters governing the permeation of nickel and their effect on the separation process have been studied. These parameters are stirring speed, feed phase pH, surfactant concentration, extractant concentration, stripping phase concentration, phase ratio, initial concentration of metal, and treatment ratio. The optimum conditions have been determined. The separation factors of Ni(II) with respect to Co(II), based on initial feed concentration, have been experimentally determined. Furthermore, the extraction selectivity for Co(II) over Ni(II) has been improved by using D2EHPA during the initial minutes.     

Mathematical modeling of penicillin G extraction in an emulsion liquid membrane system containing only a surfactant in the membrane phase

An extraction experiment of penicillin G was performed in an emulsion liquid membrane system in which only ECA 4360J exists in the organic membrane phase without a predominant carrier, Amberlite LA-2, used in our previous works and it functions as a carrier as well as a surfactant. A permeation model for the present system has been developed as a primary study to examine the transport mechanism of penicillin G in the previous batch and continuous systems with two carriers of Amberlite LA-2 and ECA 4360J. The model takes into account the mass transfer in the external aqueous film, the extraction reaction between penicillin G and ECA 4360J at the external interface, the diffusion of penicillin G in the emulsion phase, the stripping reaction at the internal interface and the pH change of internal aqueous solution containing Na₂CO₃ with penicillin G transported into the internal phase. The experimental data were well fitted with the present model. Also, an expression for the reaction of penicillin G with ECA 4360J was obtained through a series of equilibrium measurements in liquid–liquid extraction system.     

Redox-driven transport of copper ions in an emulsion liquid membrane system

A new redox-driven type of emulsion liquid membrane separation is described. Milligram amounts of copper(II) in 0.2 M hydrochloric acid were reduced to copper(I) in the presence of ascorbic acid (1 M≡1 mol l⁻¹). The copper solution was emulsified with a (1+4) mixture of toluene and n-heptane using Span-80 (sorbitan monooleate) as an emusifier. The resulting water-in-oil emulsion was dispersed in 0.2 M hydrochloric acid containing hydrogen peroxide and neocuproine (2,9-dimethyl-1,10-phenanthroline) by stirring for 10 min. The copper in the internal aqueous phase was selectively transported to the external one, leaving other heavy metals (e.g., Mn, Co, Ni, Cd and Pb) in the internal aqueous phase. After collecting the dispersed emulsion globules, they were demulsified by heating and the metals in the segregated aqueous phase were determined by graphite-furnace atomic absorption spectrometry (GFAAS). The selective transport of copper offered the multielement separation of trace heavy metals from a copper matrix, allowing the GFAAS determination of impurities at the 0.01% level in copper metal.     

Inclusion extraction of alkali metals by emulsion liquid membranes bearing nano-baskets

Nano-assisted inclusion separation of alkali metals from basic solutions was reported by inclusion-facilitated emulsion liquid membrane process. The novelty and significance of this study is application of nano-baskets of calixarene in the selective and efficient separation of alkali metals, as both carrier and surfactant. For this aim, four derivatives of p-tert-calix[4]arene bearing different sulfonamide moieties were synthesized and their inclusion-extraction parameters were optimized. Maximum extraction was achieved using calixarene scaffold 03 (3.45 × 10^?2 M) as carrier/demulsifier, commercial kerosene as diluent in membrane, sulphonic acid (0.2 M) and ammonium carbonate (0.4 M) as the strip and the feed phases, the phase and the treat ratios of 0.8 and 0.3, mixing speed (300 rpm), and initial solute concentration (100 mg/L). The selectivity of membrane over more than ten interfering cations was examined and the results reveled that under the optimized operating conditions, the extraction percent of alkali metals was 98–99 %.     

Diffusion potential is induced by coupled transport of ions through liquid membrane: nonlinear response to pH change in a reverse permeation system

In a cation exchange liquid membrane-aqueous alkali metal chloride system, diffusional flux of alkali metal ion driven by proton was observed. A supported liquid membrane formed on a Teflon filter by impregnating it with stearic acid-doped 1-octanol was used. The internal aqueous phase contained KCl and HCl, and the external aqueous phase also contained KCl. The initial concentrations of K⁺ ions of both phases were 1×10⁻¹ mol dm⁻³ for all the measurements. The concentration of HCl in the internal solution was kept at 1×10⁻² mol dm⁻³. The pH of the external solution was changed successively with HCl, appropriate buffer solution, or KOH. The pH dependence of membrane potential showed hysteresis loop in the range from neutral to alkaline pH, where reverse ion permeation was observed after the flux had been measured in the system with the external solution of an alkaline pH (pH 13). In the acidic range below neutral pH, the hysteresis of the membrane potential as well as reverse ion permeation was not observed. To elucidate the correlation between the appearance of hysteresis loop and the reverse ion permeation driven by proton across the membrane, the time course of the membrane potential in response to pH change was investigated. In the pH range where reverse permeation phenomena appeared, the time dependence of the membrane potential in nonsteady-state showed biphasic behavior. From the time course curve of the membrane potential, the total membrane potential was divided into the Donnan potential and the diffusion potential. From these findings, it was demonstrated that the diffusion potential was generated within the membrane only in the alkaline range where reverse ion permeation occurred. Analyzing the diffusional flux, the diffusion coefficient of potassium ion in the membrane was obtained taking the Donnan potential into account to be much greater than that in the membrane solvent. As a result of comparison of the diffusional fluxes measured by atomic absorption spectrometry and solution conductometry, the flux of the potassium ion was found to be significantly greater than that of the hydrogen ion in the opposite direction, especially at extremely high pH region. This implies the flows of hydroxide ions and neutralization reaction within the membrane facilitate the reverse ion permeation process of potassium ions.     

Structures of sym-(R)dibenzo-16-crown-5-oxyacetic acids and their alkali metal cation binding

To provide insight into the influence of geminal group (R) variation in sym-(R)dibenzo-16-crown-6-oxyacetic acids upon their selectivity in alkali metal cation separations by solvent extraction and liquid membrane transport, studies have been conducted for R=hydrogen and decyl in homogeneous solutions by ¹H NMR spectroscopy and titration calorimetry and in the solid state.     

Extraction of free phenols from blood by a liquid membrane enzyme reactor

The development of a liquid membrane enzyme reactor for the extraction of phenols from blood and plasma is described. Phenol permeation across the liquid membrane is studied, the transport of the toxins is linked with an enzymatic reaction. The encapsulation of the enzyme is described in detail. The stability of the multi-emulsion as well as the loss of enzyme activity during encapsulation and treatment axe examined thoroughly. The resulting liquid surfactant membrane emulsion is applied in in-vitro experiments to remove phenols from blood and plasma.     

Studies on the partitioning of actinides from high level liquid waste solution employing supported liquid membrane with Cyanex-923 as carrier

The present paper deals with the studies on the partitioning of actinides from high level liquid waste solution of PUREX origin employing supported liquid membrane technique. The process uses solution of Cyanex-923 in n-dodecane as a carrier with poly tetra fluoro ethylene support and a mixture of citric acid, formic acid and hydrazine hydrate as a receiving phase. Transport studies are carried out for ²⁴¹Am under different experimental conditions to optimize the transport parameters such as feed acidity, carrier concentration, effect of uranium, trivalent metal ion and salt concentration in the feed. Studies indicated good transport of actinides across the membrane from nitric acid medium. Under the optimized conditions the transport of ²⁴¹Am is studied from a uranium depleted synthetic PHWR-HLLW and finally the technique has been used for the partitioning of alpha emitters from an actual research reactor-HLLW. High concentration of uranium in the feed is found to retard the transport of americium, suggesting the need for prior removal of uranium from the waste.     

Synthesis and transport studies of new enantiopure lipophilic crown ethers containing a diarylphosphinic acid unit

The synthesis of new enantiopure lipophilic crown ethers (S,S)-6, (R,R)-6 and (S,S)-7 containing a diarylphosphinic acid unit has been carried out. The transport ability of these ligands has been studied in an aqueous source phase/lipophilic organic bulk liquid membrane/aqueous receiving phase system controlled by the pH of the media. The transport of metal ions and amines has also been studied. These studies showed high selectivity for protonated amines.     

Thioether-mediated copper transport through liquid membranes with the aid of redox reaction

A thioether-mediated copper transport with the aid of redox reaction was studied in a polymer-supported liquid membrane and in a liquid surfactant membrane. A photochemical generation of the redox potential led to a photo-assisted copper separation and concentration system. Tetradentate thioethers 1 and 2 (L) selectively extracted copper ion into organic solution in the presence of a reducing agent, and served as a copper-selective carrier in a liquid membrane system. In the polymer-supported organic liquid membrane system, the thioether was dissolved in the membrane phase which separated the two aqueous solutions of different redox potentials. The copper ion was extracted into the membrane phase by formation of the [Cu^IL]⁺ ? X^? type complex on the reducing solution interface and permeated through the membrane toward the oxidizing solution interface, where the complex was decomposed to release the copper(II) species into the oxidizing aqueous solution. The nature of the system was studied in detail under various operational conditions (redox agents, pairing anion X^?, coexisting metals, etc.) and compared with that of the previously reported Bathocuproine-mediated system. The transport system was extended to the water-in-oil-in-water emulsion system (liquid surfactant membrane), and the selective concentration of copper ion from dilute external aqueous solutions into inner stripping solutions was achieved. Photo-induced redox reactions, triethanolamine—acriflavine—methyl viologen—hv and glucose—titanium oxide—hv, were successfully coupled to the systems, leading to a photo-assisted copper transport in the polymer-supported liquid membrane as well as in the liquid surfactant membrane. Tentative explanations were given on the nature of the membrane transport reactions.     

Selective separation of aromatic hydrocarbons through supported liquid membranes based on ionic liquids

Ionic liquids are emerging as alternative solvents for volatile organic compounds traditionally used in liquid–liquid extraction and liquid membrane separation. In this paper, we examine whether room-temperature ionic liquids as a membrane solution can be utilized for hydrocarbon separation by using a supported liquid membrane. Aromatic hydrocarbons, benzene, toluene and p-xylene were successfully transported through the membrane based on the ionic liquids. Although the permeation rates through the membrane based on the ionic liquids were less than those of water, the selectivity of aromatic hydrocarbons was greatly improved. The maximum selectivity to heptane was obtained using benzene in the aromatic permeation and 1-n-butyl-3-methylimidazolium hexafluorophosphate in the liquid membrane phase.     

Studies on transport mechanism of Cr(VI) extraction from an acidic solution using liquid surfactant membranes

A mathematical model for analysing the extraction of Cr(VI) from aqueous acidic solution by emulsion liquid membrane using Aliquat 336 as extractant and NaOH as stripping agent has been presented. The existing models developed so far do not account for the existence of different forms of Cr(VI) ions in the aqueous phase depending on pH conditions. Accordingly, in the present model, reaction equilibrium has been considered instead of distribution coefficient to represent realistically the transport mechanism for this type of system through liquid surfactant membrane. Unlike other models, liquid–liquid equilibrium of sodium hydroxide-chloride of Aliquat 336 has also been considered. The carrier thus exists in the membrane phase in hydroxide and chloride forms and extraction of hexavalent chromium from the external phase proceeds by the two carriers. The validity of the model has been checked from comparison of the simulated curves and experimental data using chemical reaction equilibrium constant and D_eff/R² as fitting parameters.