Transport of strontium cation through a hollow fiber supported dichlorobenzene membrane using 18-C-6 crown ether,nitrate and anion of dinonylnaphtalen sulfonic acid

The transport of strontium cation through a hollow fiber supported dichlorobenzene membrane using 18-C-6 crown ether, nitrate and anion of dinonylnaphtalen sulfonic acid has been studied. A permeation device-single hollow fiber module with on-line radiometric detection of strontium using⁸⁵Sr tracer was used.     

Transport of99mTc across TBP-kerosene oil supported liquid membranes

Transport of^99mTc across tri-n-butylphosphate (TBP) kerosene oil supported liquid membranes (SLM) has been studied under various conditions. Presence of dichromate ions helps avoid activity scavenging effects. Concentration increase of TBP, the complexing carrier used in the present study has a positive effect on flux (J) and permeability (P) of these ions, as up to 2.87M there is an increase in J and P values. HCl concentration in the feed solution increases J and P with their maximum values at 2.5–3.0M HCl in the feed. Above this concentration there is a decrease in flux and permeability of^99mTc(VII) ions. The given ions are stripped with LiCl or NaCl solutions but more with NaOH. The optimum conditions of transport of the given ions are 2.5M HCl concentration in the feed, 2.87M TBP concentration in the membrane and 1M NaOH concentration in the strip solution. Equations have been developed to indicate the relation between flux, J, viscosity, of TBP in organic membrane phase, temperature, T, [H⁺], in the aqueous feed solutions and Tc ion concentration in the feed solution. Based on P, the values determined from liquid membrane experiments, the quantitative flux values of Tc(VII) ions were also determined as a function of TBP concentration in the membranes, and HCl and Tc concentration in the feed solution using the given equations. This experimental technique provides quantitative results from trace level activity transfer experiments.     

Transport of Ca2+, Sr2+, Ba2+, Na+, K+ and Cs+ through hollow fiber supported liquid membrane

The transport of metal ions (Ca²⁺, Sr²⁺, Ba²⁺, Na⁺, K⁺, Cs⁺) through hollow fiber supported dichlorobenzene liquid membrane has been studied. The transport of cations using 8-crown-6 ether as a carrier and picrate as co-counter ion as well as a pertraction device and capillary isotachophoresis (ITP) measurement of the cation concentration is described.     

Uranyi ion transport through tri-n-octylamine-xylene based supported liquid membranes

Tri-n-octylamine (TOA) dissolved in xylene has been used as carrier, constituting liquid membrane supported in Celgard 2400 polypropylene microporous film for the transport of uranyl ions against their concentration gradient from aqueous acid solutions to an alkaline aqueous phase. Effect of sttrring rate, nitric acid concentration and TOA concentration in the organic membrane phase, on the flux of uranyl ions through the membrane has been studied. Viscosity and density data have been obtained to estimate diffusion coefficients and hence the permeability coefficients to compare the same with experimental values, using distribution coefficient data, measured from solvent extraction experiments and available in the literature. Analysis of the flux data has been performed to study the stoichiometry of the chemical reaction involved in complex formation reaction. The results have been compared with simple liquid-liquid extraction data.     

Conductive diamond hollow fiber membranes

Boron-doped diamond hollow fiber membrane (BDD–HFM) was fabricated as a novel type of porous conductive diamond. BDD–HFM was obtained by deposition of BDD polycrystalline film onto a quartz filter substrate consisting of quartz fibers, followed by etching of the substrate in HF/HNO₃ aqueous solution. Cross-sectional scanning electron microscope (SEM) observation showed the inner diameter and wall thickness of the BDD hollow fibers were in the range of 0.4–2 and 0.2–2 μm, respectively. The BDD–HFM electrode exhibited a relatively large double-layer capacitance (ca. 13 F g⁻¹) in 0.1 M H₂SO₄. Electrochemical AC impedance properties were simulated using an equivalent circuit model containing a transmission line model, which indicated characteristics of a porous electrode material.     

Induction time in metal permeation processes through supported liquid membranes

The origin of the induction time observed in the permeation process of cadmium species through trilaurylammonium chloride in triethylbenzene supported liquid membranes is discussed. A model for the non-steady state transference process, where aqueous film diffusion coupled to an interfacial chemical reaction are the main rate determining processes, was developed. By comparison with experimental transference data, the rate constant of the interfacial reaction between cadmium chloride aqueous complexes and the membrane carrier, trilaurylammonium chloride, was evaluated. The time evolution of the concentration profiles through the aqueous diffusion film is also described.     

Effect of particulate matter on mass transfer through microporous hollow fiber membranes

Inner walls of microporous hollow fibers were exposed to a particle-laden gas stream for 80 h. The gas stream contained 0.25-μm diameter particles, typical of fly ash particles found in flue gas streams, that were generated by a wet-particle technique. During the deposition period, the pressure drop across the length of the fibers increased slowly at the start of the experiment and then more rapidly later, reaching 100 in. of water in 30 h. Particle interception by fibers at the feed inlet may be the chief reason for the rise in the pressure drop. The mass transfer coefficient (MTC) for SO₂ absorption into water dropped by 20% during this time. Particles coating the inside fiber walls may be the chief reason for the reduction in MTC. While the pressure drop could be reversed to its original value by the backflow of a pressurized air-jet, the MTC could not.     

Oxygen selective ceramic hollow fiber membranes

Oxygen ion conducting Ba_0.5Sr_0.5Co_0.8Fe_0.2O_3−δ hollow fiber membranes with o.d. 1.15 mm and i.d. 0.71 mm were fabricated using a sequence of extrusion, gelation, coating and sintering steps. The starting ceramic powder was synthesized by combined EDTA–citrate complexing followed by thermal treatment at 900 °C. The powder was then dispersed in a polymer solution, and extruded through a spinerette. After gelation, an additional thin coating of the ceramic powder was applied on the fiber, and sintering was carried out at 1190 °C to obtain the final ceramic membrane. The fibers were characterized by SEM, and tested for air separation at ambient pressure and at temperatures between 700 and 950 °C. The maximum oxygen flux measured was 5.1 mL/min/cm² at 950 °C.     

Studies on phenol permeation through supported liquid membranes containing functionalized polyorganosiloxanes

In this study, the functionalized, linear, hydrophobic fluid organosiloxane polymers, namely, methylhydrosiloxane–dimethylsiloxane copolymers supported on a polypropylene microporous flat sheet membrane (Celgard 2502 and 2402) have been tested as supported liquid membranes (SLMs) for phenol recovery from aqueous phases into a 0.1 M NaOH phase. The functionalized polymers include, Me₃SiO[MeSi(OR)O]_x[Me₂SiO]_ySiMe₃ (containing x = 15–18, 25–35 and 50–55 mol% of R, where R is –(CH₂)_nNMe₂ (n = 3 or 4 or 6) or –(CH₂)₂OEt pendent organofunctional groups. The functionalities, R, tested were derived from the commercially available 3-dimethylamino-1-propanol and 2-ethoxyethanol as well as newly synthesized 4-dimethylamino-1-butanol and 6-dimethylamino-1-hexanol which have been made for the purpose of this study.

The study showed that phenol permeation expressed as permeate flux through the membranes increases with the larger number of carbon spacers in the alkyl chain of the aminoalcohol pendent, larger porosity of the polypropylene support films, higher mol% of the methylhydrosiloxane portion functionalized and faster flow rates of both the feed and the receiving phases. Phenol permeation was enhanced significantly when the mol% of the methylhydrosiloxane portion was 50–55 or 25–35 with 6-dimethylamino-1-hexanol functionality supported on Celgard 2502.     

支撑液膜研究及应用进展

支撑液膜技术是高选择性膜分离技术,本文对支撑液膜分离技术的研究进展进行了回顾,详述了用于金属离子分离的支撑液膜所采用的载体、影响支撑液膜稳定性的原因以及改善途径,并对支撑液膜的发展前景进行了展望。     

Extraction and stripping study of strontium ions across D2EHPA-TBP-kerosene oil based supported liquid membranes

A Sr ion transport study across D2EHPA-TBP kerosene oil based liquid membranes supported on microporous polypropylene film has been performed. The parameters studied were the effect of di(2-ethylhexyl)phosphoric acid (D2EHPA) and TBP concentration variation in the membrane liquid, HNO₃ concentration variation in the stripping phase and citric acid concentration variation in the feed solution. The optimum conditions of transport are 0.3 mol/dm³ D2EHPA, 0.1 mol/dm³ TBP, 0.01 mol/dm³ citric acid in feed and 2 mol/dm³ HNO₃ in the stripping phase. The mechanism of transport observed is counter-ion coupled transport. The coupling ions are protons. The maximum flux for Sr ion transport observed is 5.33·10^–5 mol·m^–2·s^–1 and maximum permeability under optimum conditions observed is 8.08·10^–11 m^–2·s^–1.     

Bromine recovery with hollow fiber gas membranes

Gas membranes supported by microporous hollow fibers have been used to concentrate bromine from a variety of brines similar to seawater. The bromine transport is governed by diffusion in the brine, and hence is almost independent of membrane properties except the surface area per volume. In some cases, this type of membrane can be an alternative to packed towers, simultaneously carrying out both absorption and stripping.     

Diffusive transport across unconfined hollow fiber membranes

The mass transfer characteristics of gas permeable, hollow fiber membranes in a liquid jet mixed reactor are studied. A membrane module, operated in the sealed-end mode, was pressurized with oxygen at the base of the fibers and centered within a submerged jet discharge. Unlike conventional membrane module designs, this configuration did not have the hollow fibers enclosed within a tubular shell. The membranes were unconfined and free to move within the generated flow field. This design is especially well suited for use in waters containing high solid concentrations. The membranes have a greater degree of freedom for movement and are therefore less likely to become fouled due to solids being lodged within the fiber bundle. Mass transfer rates were measured over a practical range of physical and process parameters. A mass transfer correlation for the unconfined configuration is presented and the transfer performance of this configuration is compared with conventional membrane contactor designs.     

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.     

Tripodal lipophilic ionophores: synthesis, cation binding and transport through liquid membranes

New C₃-symmetric lipophilic tripodal ionophores, Et(CH₂OCH₂COR)₃; R=NMePh (1), R=NEtPh (2), R=piperidyl (3), have been prepared and their binding abilities for alkali and alkaline earth metal cations evaluated by extraction equilibrium and cation transport through bulk liquid membranes. Experiments show that these ionophores have considerable potential for transporting lithium, sodium and calcium ions relative to potassium and magnesium ions. The cation transport rates by ionophores 1 and 2 decrease in the order Li⁺>Na⁺>Ca²⁺>Ba²⁺>K⁺>Mg²⁺, and the selectivities of Li⁺/K⁺, Na⁺/K⁺ and Ca²⁺/Mg²⁺ are 6.47–7.24, 6.05–6.19 and 9.39–16.13, respectively. The extraction selectivity sequences of the ionophores 1 and 2 are in agreement with the descending order of the cation transport rate, and the complexation constants in chloroform phase were estimated.     

Transport and separation of carboxylic acids through bulk liquid membranes containing tributylamine

In this study, transport and separation of carboxylic acids (formic, acetic, propionic, and butyric acids) from their aqueous solutions through bulk liquid membrane (BLM) containing tributylamine (TBA) and the parameters affecting the transport were investigated. The influence of the parameters on the separation process such as the stirring of membrane phase, the stripping phase type and concentration, the feed phase type, and the feed:membrane:stripping phase ratio (F/M/S phase ratio) were examined. In the experiments, 10% (w/w) acid solutions (formic, acetic, propionic, and butyric acids) were used as the feed phase, different concentrations of NaOH solutions within the range of 0–2?N were used as the stripping phase, and 0.5?mol/lt TBA, dissolved in oleyl alcohol, was used as the membrane phase. It was determined that the stirring of the membrane phase increases the transport of acids. In the case of 2 N NaOH solution in the stripping phase and F/M/S phase ratio 1:2:1 gave the best recovery (96.75%) for butyric acid. It was observed that BLM was an effective technique for the separation of carboxylic acids from aqueous solutions.     

Application of hollow fiber supported liquid membrane for the separation of americium from the analytical waste

Americium from analytical solid waste containing U and metallic impurities was separated using hollow fiber supported liquid membrane (HFSLM) technique impregnated with DHOA–TODGA from nitric acid medium. An aliquot of 5 g of the solid waste containing Am (19.95 mg) as minor actinide and of U (2,588 mg), Fe (1,360 mg), Ca (1,810 mg) and Na (3,130 mg) as major impurities was processed. The feed solution obtained after the dissolution of the residue in ~4 M HNO₃ was passed through HFSLM module. In the first stage using 1 M DHOA–dodecane U was recovered while Am and other impurities were left in the raffinate. In the second stage, 0.5 M DHOA + 0.1 M TODGA/dodecane was used for the separation of Am from other impurities. Though, majority of the elements were separated in this cycle, Ca was co extracted along with the americium. CMPO extraction chromatographic technique was used for further separation of americium from Ca. Significant decontamination factors were achieved in this three step separation process with respect to U, Fe, Na and Ca with ~77 % recovery of americium.     

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.     

Gas permeation properties of asymmetric carbon hollow fiber membranes prepared from asymmetric polyimide hollow fiber

Asymmetric carbon hollow fiber membranes were prepared by pyrolysis of an asymmetric polyimide hollow fiber membrane, and their mechanical and permeation properties were investigated. The carbon membrane had higher elastic modulus and lower breaking elongation than the polyimide membrane. Permeation experiments were performed for single gases such as H₂, CO₂, and CH₄, and for mixed gases such as H₂/CH₄ at high feed pressure ranging from 1 to 5 MPa with or without toluene vapor. The permeation properties of the carbon membranes and the polyimide membrane were compared. There was little change in the properties of the carbon membranes with a passage of time. The properties were hardly affected by the feed pressure, whether the feed was accompanied with the toluene vapor or not, because the carbon membranes were not affected by compaction and plasticization.