Modeling of Amine-Facilitated Liquid Membrane Transport of Binary Organic Acids

ABSTRACT

The transport rates of lactic and citric acids from binary solutions across supported liquid membranes containing tri-n-ocytylamine are measured. A mass transfer model is proposed which considers aqueous film diffusion, interfacial chemical reaction, and membrane diffusion. It is shown that the difference between the measured and modeled rates was more significant at high total acid and amine concentrations. This could be partly due to the ignorance of mutual interactions between the acids in the aqueous phase and the complexes in the membrane phase in this model (chemical effect), and to limited validity of “fixed” transport properties over a rather wide concentration range (mechanical effect).     

Selective Transport of Bismuth Ions through Supported Liquid Membrane

A new supported liquid membrane (SLM) system was prepared for the selective transport of bismuth ions from the aqueous feed into the aqueous permeate phase. The support of the SLM was a thin porous polypropylene or polyvinylidene fluoride membrane impregnated with diisooctyldithiophosphinic acid (Cyanex 301) as mobile carrier in 4‐chloroacetophenon as organic solvent. Cyanex 301 acts as a highly selective carrier for the uphill transport of bismuth ions through the SLM. In the presence of HNO₃ as a metal ion acceptor in the strip solution, the transport of bismuth ions into the strip side reached 70 % of the initial feed concentration after 3.5 hours. The selectivity and efficiency of bismuth transport from aqueous solutions containing different mixtures of cations were investigated. In the presence of P₂O₇^2– ions as suitable masking agent in the feed solution, the interfering effects of other cations were completely eliminated. The selective transport of bismuth through SLM is superior to liquid‐liquid extraction or through bulk liquid membranes. This is due to the high efficiency. The SLM reduces the solvent requirements, combines extraction and stripping operations in a single process and allows the use of highly selective extractants. The system may be applied to samples containing very low bismuth concentrations.     

Effect of Macrocycle Type on Pb2+ Transport through an Emulsion Liquid Membrane

Abstract

The relative effectiveness of 14 different macro-cycles in transporting Pb(NO₃)₂ has been determined at 25 °C using a water-toluene-water emulsion membrane system. The largest amount of Pb²⁺ transport was found with dideeyl-1,1O-diaza-18-crown-6 (91%), followed by dicyclohexano-18-crown-6 (81%), di-tert-butyl-dicyclohexano-l8-crown-6 (77%), 1,10-diaza-18-crown-6 (27%), and cryptand 2.2.1 (4,7,13,16,21,24-pentoxa-1,10-diazabicyclo(8, 8, 5)-tricosane) (16%). The use of the other macrocycles produced little Pb²⁺ transport. Analysis of the transport results shows that, for most effective transport, the macrocycle should distribute preferentially to the organic phase and the log K value for the binding of the macrocycle with Pb²⁺ must be large enough for quantitative extraction of the Pb2 + into the membrane. However, this log K value must be sufficiently smaller than that for interaction of Pb²⁺ with P₂O₇ ^4?, the receiving phase complexing agent, to allow a large Pb²⁺ concentration gradient to be established. These features provide information which should be useful in designing systems for cation separations using emulsion membranes.     

Transport of Palladium(II) through Trioctylamine Liquid Membrane

Abstract

The permeation behavior of palladium(II) through a supported liquid membrane (SLM) impregnated with trioctylamine (TOA) in kerosene has been investigated. By selecting perchloric or nitric acid as a stripping agent, Pd(II) was transported through the SLM containing 0.5 M TOA and 20% 1-octanol without remaining in the liquid membrane. The permeation rate (k _{f. obs}) of Pd(II) for HNO₃ was faster than that for HClO₄. Palladium(II) was concentrated across the SLM from the 0.5 M CHI solution into the HClO₄ or HNO₃ solution.     

Optical Resolution of Racemic Mixtures of Amino Acids through Nanofiltration Membrane Process

Optical resolution of racemic mixtures of arginine and alanine was performed by chiral selective nanofiltration membrane. The chiral selective layer of the membrane was prepared by interfacial polymerization of metaphenylenediamine, trimesoyl chloride, and S (-)-2-acetoxypropionyl chloride (S-2-actoxpcl) in situ on the top of polysulfone ultrafiltration membrane. S-2-actoxpcl consists of a chiral carbon atom that has an induced chiral environment in the membrane. The membranes were characterized by FTIR, scanning electron microscopy, and atomic force microscopy to establish a structure-performance relationship. The optical resolution was performed on the membrane testing module and the effect of process parameters was determined. The results indicated that the incorporation of S-2-actoxpcl made membrane chiral selective hence membranes performed optical resolution. The resolution capacity increased by increasing S-2-actoxpcl in polymerizing solution up to 0.03% but any increase beyond 0.03% reduces the resolution capacity. More than 92% enantiomeric excess of D enantiomer was observed in the permeate of the membrane which was prepared from 0.07% trimesoyl chloride and 0.03% S-2-actoxpcl. The membrane prepared without the chain terminator exhibited less volumetric flux but more solute rejection compared to those prepared with the chain terminator. The flux of the membrane increases as the amount of the chain terminator in the reaction increases.     

Bathocuproine-Mediated Copper Transport through Liquid Membrane Driven by Redox Potential

Abstract

A new type of carrier-mediated copper transport system driven by redox potential was studied. The two aqueous solutions of different redox potentials were separated by a polymer-supported organic liquid membrane in which Bathocuproine (L) was dissolved as a “carrier”. Copper(II) was reduced in the reducing phase to form [Cu¹L₂]⁺·X^? type complex at the membrane interface and extracted. The copper complex diffused to the other side of the membrane and decomposed to form the copper(II) species in the oxidizing phase, leaving the carrier in the membrane phase. The nature of the system under various operational conditions (pH, redox agents, pairing anions X^?, coexisting metals, etc.) was studied and compared with the metal transport system which can take place without the intervention of redox reaction. An extension of these transport reactions to water-in-oil-in-water type emulsion system was studied.     

Analysis of Transport Rate of Zinc Extraction through Liquid Surfactant Membrane

Abstract

Analysis of the transport rate of a metal ion through a liquid surfactant membrane is important for understanding an extraction system. A facilitated transport model for zinc extraction through a liquid surfactant membrane is proposed for the analysis of the transport rate. Based on the model, the transport rates, including the interfacial reaction rates and the diffusion rate of the zinc ion, are analyzed. From an analysis of the model, it is shown that the reactions at both interfaces are not in equilibrium before extraction is complete. It is also shown that the transport rates are not equal value in the early stage of a run. Parametric effects on the transport rates are also illustrated.     

Transport of Europium through Supported Liquid Membrane Containing Dihexyl-N,N-diethylcarbamoylmethylphosphonate

Abstract

The transport of europium has been studied through a supported liquid membrane (SLM) impregnated with dihexy-N,N-diethylcarbamoylmethylphosphonate (CMP). Europium was effectively extracted from the perchlorate solution into SLM, but was insufficiently stripped to a dilute acid solution. The addition of 1-decanol improved the stripping process, and quantitative transport of europium was achieved. By the combination of two SLM systems consisting of diiso-decylphosphoric acid and CMP, europium was transported from the feed solution (0.1 M HNO₃) through the intermediate solution (1 M HclO₄ + 4 M NaClO₄) to the product solution (0.1 M HNO₃) and effectively concentrated by a factor of about 20.     

Selective Transport of a Peptide from Its Mixture with an Amino Acid Using a Supported Liquid Membrane Process

Abstract

Some experimental results on the separation of a peptide from a mixture of peptide and amino acid through a continuous supported liquid membrane process are described. As a model system a mixture of tryptophan (Trp, an amino acid) and tryptophan-leucine (Trp-Leu, a dipeptide) was chosen. The liquid membrane contained an anionic surfactant, sodium di-2-ethylhexyl sulfosuccinate (Aerosol OT/AOT), as a carrier dissolved in oleyl alcohol, as an organic solvent, supported on a commercial grade support (Celgard 2500). The liquid-liquid extraction experiments were carried out to study the influence of feed pH, feed and strip flow rates, and feed and carrier concentrations on the selective transport of Trp-Leu from its mixture with Trp. At pH 4–5 the transport rate of Trp-Leu was significantly higher than that of Trp. The increase in flow rate up to a value of 40 mL/h did not effect the selective removal of Trp-Leu. The flux rate increased with an increase of the carrier concentration up to 20% AOT, but the selectivity for Trp-Leu was highest at 10% AOT. An increase of Trp concentration up to 10-fold had little effect on the flux rate of Trp-Leu. The stability of SLM system in continuous removal of Trp-Leu from a single component system and from a binary mixture with Trp was studied. The effect of a competitive component did not alter significantly the flux rate and long-time performance in continuous operation. A procedure for regenerating SLM was examined, and the regenerated SLM performed as good as the freshly prepared one.     

Studies of Ion Transport through a Liquid Membrane by Using Crown Ethers

Abstract

Studies on ion transport through a liquid membrane system composed of two extraction processes have been carried out. Kinetic models based on extraction processes with consideration of the controlled parameters were developed for mediated ion transport through liquid membranes, especially those using crown ethers as the ion carrier. A study of the concentration change in the receiving or source phase envisages the determination of the equilibrium constant by a kinetic method corresponding to the chemical reaction at the interface as well as the maximum initial flux through the membrane. The equilibrium constant values determined by the kinetic process were checked by the solvent extraction method.     

The Transport of Copper(II) through Hollow Fiber Renewal Liquid Membrane and Hollow Fiber Supported Liquid Membrane

Abstract

In this paper, hollow fiber renewal liquid membrane (HFRLM) and hollow fiber supported liquid membrane (HFSLM) were used to simultaneously remove and recover copper(II) from aqueous solutions, and the transport performance of these two techniques were compared under the similar conditions for the system of CuSO₄ +D2EHPA in kerosene +HCl. The results showed that the HFRLM process was more stable than the HFSLM process. The HFRLM process had a higher overall mass transfer coefficient than that of HFSLM process in single-pass experiments. These were because the renewal effect of the liquid membrane layer could reduce the mass transfer resistance of the lumen side and replenish the loss of the membrane liquid in the HFRLM process. The transport results were better in the HFRLM process than that in the HFSLM process with recycling experiments. Therefore, HFRLM technique is a promising method for simultaneous removal and recovery of heavy metal from aqueous solutions.     

Selective Transport of Cu2+ Ions through Bulk Liquid Membrane System Mediated by Erythromycin Ethyl Succinate

The carrier mediated transport of Cu²⁺ ions from an aqueous medium has been examined. The ability of Erythromycin Ethyl Succinate (EES) as a carrier to form a complex with Cu²⁺ ions and transport them to the receiving phase is reported. The fundamental parameters influencing the transport of Cu²⁺ ions such as the pH in the source and receiving phases and concentration of the stripping agent in the receiving phase have been optimized and accordingly, the amount of Cu²⁺ transported across the liquid membrane after 5 h was 94.3 ± 1.8% in the presence of L-histidine as a suitable stripping agent. Moreover, the selectivity and efficiency of Cu²⁺ ions transport from aqueous solution over other cations in ternary and quaternary mixtures have been investigated. The results indicate that our fabricated membrane is very sensitive toward Cu⁺² ions in the presence of heavy metal ions.     

Transport of Europium(III) through Supported Liquid Membrane Containing Diisodecylphosphoric Acid

Abstract

Carrier mediated transport of europium has been investigated by the use of a flat-sheet membrane impregnated with diisodecylphosphoric acid (DIDPA). The addition of 1-octanol to the membrane improves the stripping process, and hence europium can be quantitatively transported from the feed solution of 0.1 M HNO₃ into the product solution of 5 M HNO₃. Its concentration in the feed solution decreases as [Eu] _f,t = [Eu] _f,0 exp (-k _obs t). The apparent rate constant (k _obs) increases with increasing carrier concentration and becomes nearly constant above 0.05 M DIDPA The europium flux is proportional to initial europium concentrations less than 10^?3 M, and becomes constant at high concentrations.     

Facilitated Transport of Zinc Chloride through Hollow Fiber Supported Liquid Membrane. Part 1. Transport Mechanism

Abstract

The facilitated transport of zinc chloride through a liquid membrane of tri-n-octylamine dissolved in n-dodecane with 2-ethylhexyl alcohol, supported on a microporous polyethylene hollow fiber, has been studied in a series of three papers. This first paper deals with the transport mechanism. The distribution of zinc chloride between the liquid membrane phase and the aqueous hydrochloric acid solution was clarified. The characteristics of the support membrane and of the flow system were examined through phenol transport experiments. The initial permeation rate of zinc chloride was explained by the sum of film resistances in the two aqueous phases and a membrane phase resistance     

Facilitated Transport of Zinc Chloride through Hollow Fiber Supported Liquid Membrane. Part 2. Membrane Stability

Abstract

The stability of a hollow fiber supported liquid membrane of tri-n-octylamine diluted in n-dodecane with 2-ethylhexyl alcohol was examined for the facilitated transport of zinc chloride. The liquid membrane was unstable when the feed and the strip aqueous solutions were not saturated with the organic phase used as the liquid membrane. This was found to be due to the dissolution of relatively soluble 2-ethylhexyl alcohol to the aqueous phases. When both aqueous phases were presaturated with the organic phase used, a rather constant flux could be maintained for a long time by the reimpregnation of the organic phase approximately once a day. The continuous impregnation of the organic phase to the support membrane drastically increased the stability of the liquid membrane, even without presaturation of the two aqueous phases with the organic phase     

Transport of Chromium(VI) through a Supported Liquid Membrane Containing Tri-n-octylphosphine Oxide

ABSTRACT

In this study the transport of chromium(VI) from aqueous solutions of pH 2–4 through a supported liquid membrane (SLM) with tri-n-octylphosphine oxide (TOPO) dissolved in kerosene as a mobile carrier was investigated. The transport flux of Cr(VI) increased with an increase in the concentrations of Cr(VI) in the feed phase and of TOPO in the membrane phase, but with a decrease in pH of the feed phase. Considering the equilibria of various Cr(VI) species in the aqueous phase and of the Cr(VI)—TOPO complexes formed in the membrane phase, a permeation model including the aqueous film diffusion of HCrO₄ ^? and Cr₂O₇ ^2? toward the membrane, the interfacial chemical reaction between them and TOPO, and the membrane diffusion of the Cr(VI)—TOPO complexes (H₂CrO₄(TOPO) and H₂Cr₂O₇(TOPO)₃) was proposed to describe the transport of Cr(VI) through the SLM. By best fitting the transport flux equations of Cr(VI) with the experimental data using the Rosenbrock method, the apparent mass-transfer coefficients of HCrO₄ ^? and Cr₂O_7^. across the aqueous film, and those of H₂CrO₄(TOPO) and H₂Cr₂O₇(TOPO)₃ across the membrane phase, were obtained. This work helps to clarify the transport mechanism of Cr(VI) through an SLM.     

Involvement of a Cluster of Basic Amino Acids in Phosphorylation-Dependent Functional Repression of the Ceramide Transport Protein CERT

Ceramide transport protein (CERT) mediates ceramide transfer from the endoplasmic reticulum to the Golgi for sphingomyelin (SM) biosynthesis. CERT is inactivated by multiple phosphorylation at the serine-repeat motif (SRM), and mutations that impair the SRM phosphorylation are associated with a group of inherited intellectual disorders in humans. It has been suggested that the N-terminal phosphatidylinositol 4-monophosphate [PtdIns(4)P] binding domain and the C-terminal ceramide-transfer domain of CERT physically interfere with each other in the SRM phosphorylated state, thereby repressing the function of CERT; however, it remains unclear which regions in CERT are involved in the SRM phosphorylation-dependent repression of CERT. Here, we identified a previously uncharacterized cluster of lysine/arginine residues that were predicted to be located on the outer surface of a probable coiled-coil fold in CERT. Substitutions of the basic amino acids in the cluster with alanine released the SRM-dependent repression of CERT activities, i.e., the synthesis of SM, PtdIns(4)P-binding, vesicle-associated membrane protein-associated protein (VAP) binding, ceramide-transfer activity, and localization to the Golgi, although the effect on SM synthesis activity was only partially compromised by the alanine substitutions, which moderately destabilized the trimeric status of CERT. These results suggest that the basic amino acid cluster in the coiled-coil region is involved in the regulation of CERT function.     

An Organic Liquid Membrane System for the Separation and Production of Histamine

Abstract

The recovery of histamine (Hm) produced by histidine decarboxylase (HD) from histidine (His) by using an organic liquid membrane system was investigated. The system was composed of two aqueous phases (phase I of pH 4.5 and phase II of pH 7.2) separated by a third organic chloroform phase containing di-(2-ethylhexyl) phosphoric acid (EHP) as a carrier. His could not be moved from phase I of pH 4.5, the optimum pH of HD into the organic layer. On the other hand, Hm was moved from phase I into the organic layer, and Hm was released from the organic layer into phase II. The removal of Hm from phase I into the organic layer increased at dose dependency with EHP concentration up to 50 mM and decreased at concentrations above 50 mM. According to these results, the recovery of Hm from His by HD was investigated. In this experiment phase I was pH 4.5 containing 1 mM His, 40 μg/mL pyridoxal-5-phosphate, and a suitable concentration of HD; and phase II was set at pH 7.2. 170 μM Hm (3 h later) and 760 μM (8 h later) were transported into phase II by using 120 μg/mL HD and 50 mM EHP, as confirmed by HPLC.