The Removal of Zn(II) Through Calix[4]Recorcinarene Derivative Based Polymer Inclusion Membrane From Aqueous Solution

In the present work, the transport of Zn(II) metal ion from an aqueous nitrate solution of different metal ions through a polymer inclusion membrane (PIM) containing calix[4]resorcinarene derivative used as a carrier were investigated. Zn(II)metal ion showing high permeability were transported through PIMs prepared from cellulose triacetate (CTA) as a polymeric support material and 2-NPOE as a plasticizer. Total Zn(II) concentration was determined with an Atomic Absorption Spectrometer (AAS) in the acceptor phase. The prepared PIM and supported liquid membrane (SLM) were characterized by using Scanning Electron Microscopy(SEM) and Atomic Force Microscopy (AFM) techniques. The effects of membrane composition, effects of type of plasticizer in the membrane, effects of carrier concentration, and the thickness of the membranes were examined in the facilitated transport experiments of Zn(II) ion through PIM. We compared the performance of SLM experiments under the optimum conditions identified by the PIM studies. Higher permeability coefficient values for Zn(II) was found for SLM, while lower values were ascertained for PIM. The kinetic parameters which have been calculated as the constant rate (k), permeability coefficient (P), flux (J) and diffusion coefficient (D).     

Some observations on the stability of supported liquid membranes

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.     

Performance and stability of supported liquid membranes using LIX 984N for copper transport

The transport of copper through supported liquid membranes (SLM) using Celgard and Accurel membranes as supports and a novel commercial extractant LIX 984N as a carrier was investigated. LIX 984N provides good overall transport performance for copper from the acidic and dilute solution to the concentrated copper sulfuric acid. The instability of the supported liquid membranes using Celgard 2500 as the membrane support has been studied. It has been demonstrated that initially the surface shear forces due to stirring are a main cause for membrane liquid loss leading to SLM instability. However, during long term permeation no single instability mechanism dominants. The instability of long term operation involves a complex interaction of a number of factors, including surface shear forces, Marangoni effects, changes to membrane morphology, Bernard instabilities and membrane preparation protocal.     

Effect of membrane preparation on the lifetime of supported liquid membranes

A new observation on the stability of supported liquid membranes (SLMs) is reported. Membranes prepared with ‘dry’ outer surfaces, free from organic wetting, were found to be more stable than the conventional SLM prepared with external surfaces wetted with a film of the organic membrane liquid phase. For copper transport the ‘dry’ surface SLM had a similar initial flux to the ‘wet’ surface SLM, and 2 to 4 times the flux after 100 h. Over a 50 h period the ‘dry’ SLM lost about 10% of its membrane liquid, whereas the ‘wet’ SLM lost about 50%. The difference is ascribed to the loss of membrane by emulsion formation at one of the aqueous-organic interfaces which would be greater for the ‘wet’ SLM with a continuous liquid film over the surface of the support.     

Supported liquid membranes modification with sulphonated poly(ether ether ketone): Permeability,selectivity and stability

The development of a new type of composite membrane consisting of a microfiltration support membrane, an immobilised liquid membrane phase and a hydrophilic, charged polymer layer and its function as a supported liquid membrane (SLM) for copper selective transport are described. The ion-exchange layers function as stabilisation layers to improve the membrane lifetime and consist of sulphonated poly(ether ether ketone) (SPEEK). This polymer shows a high permeability for copper ions due to the presence of fixed negative charges and to its swelling capacity in an aqueous phase.A method was developed to prepare composite membranes composed of the support membranes Celgard with one stabilisation layer on either the feed or strip side of the membrane or on both sides. Good adhesion of homogeneous, negatively charged, hydrophilic SPEEK layers to the hydrophobic macroporous support membranes could only be established when the support membranes were first hydrophilised with a concentrated sulphuric acid solution containing 5 wt% free SO₃.The lifetime of the SLMs is significantly improved when one stabilisation layer is applied at the strip side or two layers at both sides of the SLM. A second advantage of this composite SLM is the increase in copper flux caused by a decrease in thickness of liquid membrane phase. However, when SPEEK penetrates entirely through some pores of the support membrane, ions diffuse non-specifically through the SPEEK matrix resulting in an undesired selectivity loss. This phenomenon occurs only when thin Celgard membranes are used as support membranes.     

Sandwich liquid membrane in the separation and concentration of Cu++

Some tests of mass transport on a sandwich liquid membrane (SwLM) for separation and concentration of Cu++ ion are reported and the results compared with the traditional supported liquid membrane (SLM) system both in terms of stability and flux. Moreover a chemical-physical model was developed evidencing the differences in the mass transport between the two systems studied. The obtained results showed an higher Cu++ flux in the SwLM (110.4 vs. 52.4 mmol/h.m2 referred to the effective pore surface) while lifetime was lower (6 vs. 15 h). The model evidenced a lower overall resistance to Cu++ ions transport through the SwLM than the SLM because the transport in the free solution did not suffer of the pores presence. Use of permanent hydrophilic membranes can improve the SwLM lifetime in view of industrial applications.     

Origin and significance of the deviations from a pseudo first order rate law in the coupled transport of metal species through supported liquid membran

A new equation describing the permeation rate of metal species in the coupled transport through supported liquid membranes (SLM) was derived. The equation assumes that the concentration profile within the membrane never goes to zero and contains the independently measurable distribution ratios of the permeating metal species between the organic liquid membrane and the aqueous feed and strip solutions. The equation was experimentally verified by measuring the distribution ratios and the permeation rates of Eu³⁺ through SLMs consisting of a 0.1 F solution of bis(2-ethylhexyl)phosphoric acid (carrier) in n-dodecane absorbed on a thin microporous polypropylene film. The conclusion was reached that the deviations from a pseudo first order rate law, often observed when measuring the coupled transport of metal species at low concentration through SLMs, originate in the non-negligible value of the distribution ratio at the SLM—strip solution interface. Nevertheless, these deviations can easily be taken into account in a quantitative way and, by an appropriate linearization of the permeation data, information can be obtained on two, newly defined, permeability coefficients of the SLM.     

Studies of polyamines transport through liquid membranes with D2EHPA as a carrier

The transport of polyamines through the liquid membranes with di-2-ethylhexyl phosphoric acid (D2EHPA) was investigated. The study was performed in three main steps: liquid-liquid extraction (LLE), bulk liquid membrane (BLM) extraction, and supported liquid membrane (SLM) extraction. Equilibrium distribution experiments allowed determining the extraction constants and stoichiometric coefficients for each polyamine. It turned out that one amino group binds two molecules of carrier (one D2EHPA dimer) and the extractability of polyamine rises with the increase in number of function groups in the molecule. The BLM and SLM experiments showed that despite considerable differences in distribution ratio between various polyamines the extraction efficiencies for all of them are very approximate. The smaller diamines compensate the lowest affinity to membrane phase with faster interface reaction kinetics and higher diffusivity. Finally, the SLM extraction conditions were optimized. The main parameters that influence the transport are the pH of the donor and acceptor phases. The extraction efficiencies obtained for polyamines are high (80-90%) and give hope for an application in bioanalytical chemistry.     

Elaboration and characterisation of a plasticized cellulose triacetate membrane containing trioctylphosphine oxyde (TOPO): Application to the transport of uranium and molybdenum ions

A cellulose triacetate (CTA) membrane containing trioctylphosphine oxyde (TOPO) as carrier and 2-nitrophenyloctyl ether (NPOE) as a plasticizer was prepared. The membrane CTA + NPOE + TOPO was characterised using chemical techniques as well as Fourier Transform InfraRed (FTIR) spectroscopy, X-ray diffraction and Scanning Electron Microscopy (SEM). The CTA membrane is characterised by well-defined pores; these pores are completely filled with the NPOE and carrier. Surfaces of membranes with TOPO are smooth. The systems constituted by the mixture of CTA + NPOE, CTA + NPOE + TOPO do not give any diffraction. This can be due to the absence of crystallization within the membrane. On the other hand, this result should be attributable to the amorphous state of the structure, which permits us to eliminate the mechanism of transfer of the ions by electron jump. A comparative study of transport across a polymer inclusion membrane (PIM) and a supported liquid membrane (SLM) containing the same carrier in chloroform has shown that uranium or molybdenum transport efficiency was increased using PIM instead of SLM. PIM showed higher stability than SLM, the flux of transport remain constant in the former case after 2 weeks.     

Transport characterisation of a PIM system used for the extraction of Pb(II) using d2ehpa as carrier

The facilitated transport of lead(II) through polymeric inclusion membranes consisting of cellulose triacetate as polymeric support, bis-(2-ethylhexyl)-phosphoric acid (d2ehpa) as carrier, and tris-(2-butoxyethyl)phosphate as plasticiser (tbep), is investigated. The influence of some of the aqueous and membrane components on the permeability of Pb(II) was studied. The maximum flux obtained with these membranes is 3.5×10⁻⁶ mol m⁻² s⁻¹, which is of the same order of magnitude of those reported for supported liquid membranes and is in the upper range of those reported for polymeric inclusion membranes. Aqueous and membranes resistances were determined from a model that describes the transport mechanism across the membranes using the stoichiometric relationship and the extraction equilibrium constant value of 6.2×10⁻⁴ determined independently by solid–liquid extraction. An activation energy of 11 kJ mol⁻¹ was also determined for Pb(II) migration, which suggest that the transport of Pb(II) is controlled by a membrane diffusion mechanism. Membrane characterisation was performed using several techniques including atomic force microscopy, scanning electron microscopy coupled with energy-dispersive spectroscopy, and thermal analysis.     

离子液体支撑液膜分离CO2

支撑液膜是一种在湿法冶金、生物技术以及气体分离等多个领域都有应用的重要膜分离技术。本文回顾了支撑液膜技术分离CO2的研究进展,按照液膜相的不同,分类介绍了常规载体支撑液膜和离子液体支撑液膜,指出了常规载体支撑液膜分离CO2的局限性,重点介绍了离子液体支撑液膜分离CO2的发展,分析了气体在离子液体支撑液膜中的传质机理以及常规离子液体结构、含量和支撑膜材料等对分离效果的影响;讨论了离子液体的功能化方法以及功能化离子液体支撑液膜分离CO2的渗透率、选择性和液膜稳定性;介绍了两种新的离子液体支撑液膜改进方法:聚离子液体膜与凝胶化离子液体支撑液膜。最后指出了今后用于CO2分离的离子液体支撑液膜的发展方向。     

Permeation of metal ions through a series of two complementary supported liquid membranes

The permeation of Am³⁺ and Eu³⁺. through two composite supported liquid membranes, SLM, consisting of a series of two complementary SLMs, separated by an aqueous solution, has been studied. The first liquid membrane was a neutral membrane, i.e., a solution of a bifunctional neutral organophosphorous extractant in decalin. The second liquid membrane was an acidic membrane, i.e., a solution of bis(2-ethylhexyl)phosphoric acid in n-dodecane or of dinonylnaphthalene sulphonie acid in decalin. The solid support was a microporous polypropylene film. The composite SLM system had the sequence “Solution A — SLM(A) -Solution B — SLM(B) — Solution A”, where aqueous solution A promotes extraction of th the metal cations into SLM(A) and their stripping from SLM(B), and aqueous solution B promotes stripping of metal cations from SLM(A) and their extraction into SLM(B). SLM(A) and SLM(B) are a neutral or an acidic S/aVis or vice versa. The study has demonstrated that the single-stage character of SLM separations of metal ions in solution can be in principle overcome by repeating the composite SLM arrangement a number of times. The equations describing the concentration variations in the aqueous solutions which are adjacent to the acidic and neutral SLMs are also reported. They allow one to predict quantitatively the degree of enrichment of each aqueous solution as function of time and the degree of separation among different cations achievable with the composite SLM system. The overall permeability of the composite SLM system to a given cation is shown to be a function of the single-membrane permeability coefficients as well as of the volumes of the aqueous solutions and the SLM area.     

Stabilization of supported liquid membranes by interfacial polymerization top layers

In this paper, a new method of stabilizing supported liquid membranes is presented. The stabilization is based on the application of polymeric top layers to the surface of microfiltration membranes, preventing loss of the liquid membrane phase out of the support pores. The modified microfiltration membranes were used as supports for supported liquid membranes and tested on selective nitrate transport and stability. Screening experiments revealed that most applied top layers did not hinder the transport of nitrate ions. However, a few were able to improve the stability of the liquid membranes. Best results were obtained when piperazine (PIPA) and trimesoyl chloride (TMCl) were used as monomers. For Accurel polypropylene supports with PIPA/TMCl top layer, nitrate flux was constant at the initial 18 × 10⁻¹⁰ mol cm⁻² s⁻¹ for 350 h of simulated operation. For uncoated supported liquid membranes (SLMs), the flux decreased within one day from 18 × 10⁻¹⁰ to almost 0 mol cm⁻² s⁻¹. Scanning electron microscopy investigations revealed a particular, rippled surface texture of layers prepared with these monomers.     

Carrier facilitated transport of thorium from HCl medium using Cyanex 923 in n-dodecane containing supported liquid membrane

Present studies deal with supported liquid membrane (SLM) technique for the separation of thorium from hydrochloric acid (HCl) medium using Cyanex 923 as a carrier. Effects of feed acidity, strippant, and membrane pore size and membrane thickness on the transport of thorium have been studied in detail. The optimized parameters were applied for separation of thorium from a radioanalytical waste. Stability of the membrane and membrane support was investigated. Transport of thorium increased from 78.3 to about 93.7 % with increase in acidity from 0.5 to 2 M using 0.3 M Cyanex 923 in n-dodecane as carrier and 2 M ammonium carbonate as stripping phase. The transport of thorium decreased above 2 M HCl. An attempt was made to model the physicochemical transport of thorium in SLM and understand the mechanism of thorium transport.     

Separation of lignosulfonate from its aqueous solution using supported liquid membrane

This paper presents an experimental and theoretical study on facilitated transport of lignosulfonate (LS) through a flat sheet supported liquid membrane using trioctylamine (TOA) as carrier and dichloroethane as diluent. The studies were carried out with various support materials and operating conditions (viz. carrier concentration, strip phase concentration, salt concentration, etc.) and their effects on the transport of LS. The results were analyzed to identify a suitable combination of support and operating condition that would yield best performance of the supported liquid membrane (SLM) in terms of fast and efficient transport of LS. The stability of the SLM was assessed in terms of loss of liquid from the pores of membrane support. The SLM is found to be stable till 10 h. Co-transport mechanism has been adopted in this work by using NaOH as the strip phase. It was observed that extraction of LS is increased with increase in concentration of NaOH up to a limiting value of 0.5 M NaOH. Difference of salt concentration between feed and strip phase considerably affect the separation process. The diffusional resistances of organic membrane (Δorg) and aqueous solution (Δaq) calculated from the permeation model, which is again a combination of three unique mechanisms viz., diffusion through a feed aqueous layer, a fast interfacial chemical reaction, and diffusion of carrier–complex through the organic membrane, are found to be 609.9 and 176.6 s cm⁻¹, respectively. The values of the diffusion coefficient in the membrane (D_org) and in the bulk organic phase (D_complex) are 1.67×10⁻⁹ and 6.68 × 10⁻⁸ m²s⁻¹, respectively. The extraction of LS is about 90%. Nearly 43% of LS can be recovered at optimum condition.     

Flux enhancement of stagnant sandwich compared to supported liquid membrane systems in the removal of Gemfibrozil from waters

Removal of the drug Gemfibrozil (GEM), as a target molecule, from aqueous media by using a carrier mediated transport in supported liquid membrane (SLM) and Stagnant Sandwich LM (SSwLM) systems has been investigated. Optimal chemical conditions to use in the transport tests were determined by means of solubility and liquid–liquid extraction tests. The results showed that the best LM phase to realize stable LM systems was tributylphosphate (TBP) 30% (v/v) in n-decane. Transport tests by using the “traditional” SLM system showed an average flux J_AV(0–CTT) of 0.421 mmol h⁻¹ m⁻² and a system stability of 1410 min. Three different microfiltration membranes, GH-Polypro, FP-Vericel and Supor 200, made of polypropylene, polyvinylidene fluoride and polyethersulphone polymers, respectively, were used to assemble the SSwLM. Contact angle and adsorption measurements evidenced hydrophilic/lypophilic character of the supports. The best results in terms of average flux (0.873 mmol h⁻¹ m⁻²), permeability coefficient (21.88 L h⁻¹ m⁻²) and stability (7170 min ≈120 h) were obtained by using the SSwLM made with the Supor 200 support. The overall results showed that the SSwLM made with this type of support achieves both high flux and high stability compared to the SLM. Thus SSwLMs seems very interesting to employ transport in LM for removing molecular species (e.g. drugs) from aqueous solutions.     

Supported liquid membrane separation of amine and amino acid derivatives with chiral esters of phosphoric acids as carriers

Studies on the possible use of phosphate and phosphonate esters bearing chiral menthol or nopol moieties as carriers for the transport of amines, amino acids, and amino acid esters through supported liquid membranes (SLM) are presented. Additionally, the enantioselectivity of the SLM transport of alkyl esters of aromatic amino acids and a non‐protein amino acid was also evaluated. It could be concluded that the extent of transport strongly depends on the hydrophobicity of the amino compound. Moreover, the carrier structure also influences the transport of those compounds through SLM: chiral phosphate and phosphonate esters appear to be poor or moderate carriers for enantioselective SLM transport of amino acids and their esters. The transport efficiency and selectivity is strongly dependent on the structure of both the transported compounds and the carrier. However, no meaningful relationship exists between these structural features and transportation or enantioselectivity.     

Membrane drotaverine-selective electrodes based on tetraphenylborate derivatives: Electrochemical, adsorption, and transport properties and analytical application

The potentiometric response of ion-selective electrodes (ISEs) based on different lipophilic derivatives of tetraphenylborate to drotaverine hydrochloride was studied. The composition of a polymeric membrane was optimized to obtain the best electroanalytical properties of ISEs. The transport properties of selective membranes, the permeability and the flow of ions through the interface, were studied. Linear correlations between the solubility of ionophoric membrane components, membrane transport, and electroanalytical properties were revealed. The kinetic studies of ion-exchange adsorption showed that two limiting stages of transfer, namely, diffusion through the boundary layer and diffusion throug the membrane phase, occurred. Procedures for the potentiometric determination of drotaverine hydrochloride in pharmaceutical forms were proposed.     

Polymer inclusion membranes: The concept of fixed sites membrane revised

The mechanism of facilitated transport of metal ions across polymer inclusion membranes (PIMs) is revised on the basis of transport flux measurements and of new data brought by techniques sensitive to local inter-molecular interactions and molecular diffusion. Cellulose triacetate (CTA) membranes built with two types of inclusion carriers: a liquid one Aliquat 336 and a crystalline one Lasalocid A, both able to carry metal ions across PIMs and supported liquid membranes (SLMs) made of the same components, have been compared. Both PIM systems show similar effects for what concern the need of a carrier threshold concentration for the occurrence of a transport flux across PIM as revealed by flux and fluorescence correlation spectroscopy (FCS) measurements, and the dependence of the chemical nature of plasticizers on the metal ion flux. These systems also present similar Raman and far IR signatures of structural evolution of PIMs with the increase of the carrier concentration within the CTA matrix.

All the presented data are interpreted as concern PIMs, according to an evolution of chemical interactions between components of the polymeric membrane able to lead to a phase transition. This phase transition type of the carrier-plasticized polymer system is induced by the increase of carrier concentration in the polymer chains. The PIM progressively organizes itself like a liquid SLM because of the enhancement of preferential solvent interactions between the carrier and the plasticizer.

The main conclusion of this study is that the classically adopted “hopping” transport mechanism between fixed carrier sites in a PIM does not apply to such carrier chemically unbound to polymer membrane systems.     

Facilitated transport of copper(II) across supported liquid membrane and polymeric plasticized membrane containing 3-phenyl-4-benzoylisoxazol-5-one as carrier

The potential of 3-phenyl-4-benzoylisoxazol-5-one (HPBI) as metal extractant has been evaluated for the first time for Cu(II) transport from aqueous nitrate solutions by supported liquid membrane (SLM) in the solvents chloroform, 2-nitro phenyl octyl ether (NPOE) and dodecyl nitro phenyl ether (DNPE). The efficiency of the membrane transport was optimized as a function of pH, temperature, aqueous phases and membrane composition. It follows the sequence CHCl₃ > DNPE > NPOE. The results suggested that the transport mechanism was mainly controlled by the diffusion of the Cu(PBI)₂ complex in the membrane core. A comparative investigation of Cu(II) transport ions has been made between SLM and polymeric plasticized membrane (PPM), containing HPBI with NPOE and DNPE as organic solvents or plasticizers in order to evaluate the feasibility of PPM with HPBI.