Studies on ion transport of some rare earth elements through solvating extractants immobilised on supported liquid membrane

The studies on ion transport of terbium and dysprosium through a porous supported liquid membrane (SLM) containing TOPO (trioctyl phosphine oxide) and TBP (tributyl phosphate) as immobilised carriers have been carried out. The effect of stirring of bulk solutions on permeability coefficient has been investigated. The permeability coefficient increases with increase in pH of source phase from 0–6, and hydrogen ion concentration from 0.01 to 0.1 M of receiving solution. The dependency of permeability coefficient on the carrier concentration has been explored. The effect of ammonium thiocyanate concentration on permeability coefficient has been studied. In order to develop a method for enrichment of rare earth elements, further investigations were carried out by using a hollow fibre membrane extractor. The mechanism of ion transport of terbium and dysprosium in SLM systems has been explained.     

Electroosmotic Transport through a Cation-Exchange Membrane: Effect of the Stirring on the Dependence of the Electroosmotic Permeability on the Temperature

The electroosmotic flux through a cation-exchange membrane has been obtained in different situations. From these measurements, the apparent electroosmotic permeability, W, of a cation-exchange membrane has been determined as a function of the temperature, T, and the stirring rate, v, of the solutions. In all the experimental situations studied, W decreases when v increases, while it can increase or decrease with T depending on the temperature range considered. For this last reason, the (T,W) curves show a minimum whose value and position depend on the experimental conditions established. The influence of the concentration polarization effect in the value of W and in its dependence with v and T is studied and quantified. Copyright 1999 Academic Press.     

Development of a simple hollow fibre supported liquid membrane extraction method to extract and preconcentrate dinitrophenols in environmental samples at ng L(-1) level by liquid chromatography

An easy and rapid hollow-fibre supported liquid membrane method (HFSLM) has been developed to extract and determinate the total concentration of four dinitrophenols in environmental water at ng L(-1) level. This extraction method provides a high selectivity, short extraction time and very low cost for real samples. It is a three-phase system, aqueous-organic-aqueous, where the organic solvent is held into the fibre pores, being in contact with the two other phases. The organic phase is formed by two different organic solvents, with two different polarities, n-undecane and toluene (1:1). The optimization step was performed using a three-variable Doehler design, involving three factors, stirring speed, fibre length and sample volume. The organic phase composition, as well as the pH of the acceptor and donor phases was also optimized. The extraction equilibrium was reached after 30 min, after which essentially the total amount (90-80%) of the four dinitrophenolic compounds were extracted from the sample. Better repeatability and reproducibility at the expense of lower enrichment factors was obtained compared with other methods, employing incomplete extraction during a fixed time. The matrix effect was tested by performing extractions from leachate water and river water. This method is linear in the range 0.1-100 microgL(-1) in different matrices, with detection limit around 100 ng L(-1), after extraction of 6 mL of sample and using high performance liquid chromatography for final analysis.     

Diffusion of electrolytes of different natures through the cation-exchange membrane

Diffusion of different electrolytes through a negatively charged (cation-exchange) membrane into distilled water has been studied. It has been established theoretically (with no regard to the presence of diffusion layers) that the integral diffusion permeability coefficient of an electrolyte depends on the diffusion coefficients and the ratio between the charge numbers of a cation–anion pair, the ratio between the density of charges fixed in the membrane and electrolyte concentration, and the averaged coefficient of equilibrium distribution of cation?anion ion pairs in the membrane matrix. It has been found that, when co-ions have a higher mobility, the dependence of diffusion permeability on electrolyte concentration passes through a maximum. Derived equations have been compared with experimental dependences of the diffusion permeability of an MC-40 membrane with respect to different solutions of inorganic 1: 1 and 2: 1 electrolytes. The developed method has been shown to be applicable for describing diffusion of any electrolytes (including asymmetric ones) through arbitrary uniformly charged membranes.     

Adsorption of amylase enzyme on ultrafiltration membranes

A method to measure the static adsorption on membrane surfaces has been developed and described. The static adsorption of amylase-F has been measured on two different ultrafiltration membranes, both with a cutoff value of 10 kDa (a PES membrane and the ETNA10PP membrane, which is a surface-modified PVDF membrane). The adsorption follows the Langmuir adsorption theory. Thus, the static adsorption consists of monolayer coverage and is expressed both as a permeability drop and an adsorption resistance. From the adsorption isotherms, the maximum static permeability drops and the maximum static adsorption resistances are determined. The maximum static permeability drop for the hydrophobic PES membrane is 75%, and the maximum static adsorption resistance is 0.014 m2.h.bar/L. The maximum static permeability drop for the hydrophilic surface-modified PVDF membrane (ETNA10PP) is 23%, and the maximum static adsorption resistance is 0.0046 m2.h.bar/L. The difference in maximum static adsorption, by a factor of around 3, affects the performance during the filtration of a 5 g/L amylase-F solution at 2 bar. The two membranes behave very similarly during filtration with almost equal fluxes and retentions even though the initial water permeability of the PES membrane is around 3 times larger than the initial water permeability of the ETNA10PP membrane. This is mainly attributed to the larger maximum static adsorption of the PES membrane. The permeability drop during filtration exceeds the maximum static permeability drop, indicating that the buildup layer on the membranes during filtration exceeds monolayer coverage, which is also seen by the increase in fouling resistance during filtration. The accumulated layer on the membrane surface can be described as a continually increasing cake-layer thickness, which is independent of the membrane type. At higher concentrations of enzyme, concentration polarization effects cannot be neglected. Therefore, stagnant film theory and the osmotic pressure model can describe the relationship between flux and bulk concentration.     

Steady-state and transient electrical properties of ion-exchange membrane systems in asymmetric arrangements

The steady-state and transient electrical properties of ion-exchange membranes placed between two solutions with different values of the electrolyte concentration, have been simulated using the network simulation method. The ionic transport processes are theoretically described on the basis of the Nernst-Planck and Poisson equations. The system under study is constituted by a cation-exchange membrane in which the fixed-charge is homogeneously distributed in space and two diffusion boundary layers on both sides of the membrane, the electric double layers at the interfaces being included. The steady-state voltage-current characteristic and the profiles of the ionic concentrations and the electric potential, are analysed. Also, the choronopotentiometric response of the system has been discussed and the time evolution of the electric energy consumption evaluated. In particular, the influence of the ratio of the bathing concentrations on the permselectivity and the chronopotentiometric response of the ion-exchange membrane systems, has been established.     

Membrane distillation: theory and experiments

A theoretical approach is presented that describes membrane distillation processes due to the simultaneous action (in a proactive or in a counteractive way) of temperature and concentration differences through porous hydrophobic membranes. The model developed emphasizes the importance of the boundary layers, shows the existence of a coupling term between the two thermodynamic forces acting on the system, and permits the definition and characterization of the so-called steady states. In order to check the model, two membranes have been studied in different experimental conditions. The influence of some relevant parameters, such as solution concentration, stirring rate, mean temperature and temperature difference has been considered and the theoretical predictions of the model have been applied to the obtained results. The accordance may be considered good.     

Hydraulic and osmotic permeabilities of water and water/sucrose solutions through cellophane membranes

Measurements were made of different transport phenomena in cellophane membranes, using a specially designed device. The aqueous, hydraulic permeability was studied over a range of temperatures between 30 and 50°C. The hydraulic permeability/temperature relationship was found to be linear. The use of sucrose solutions of equal concentration in the two phases on either side of the membrane produced a considerable variation in the hydraulic permeability when the solution concentrations were greater than 0.1 M. Osmotic flow experiments were carried out for sucrose/water solutions, and the coefficient of osmotic permeability was found to be independent of the solution concentrations separated by the membrane within the range of concentrations studied (up to 0.2 M). The equivalent pore radius was calculated for the membranes used; these values are higher than that of the molecular diameter of water. The reflection coefficient was calculated for one of the membranes used and a value of 0.077 was obtained.     

A model for methanol transport through Nafion membrane in diffusion cell

The transport of methanol through Nafion^® membrane in diffusion cell is investigated using the open circuit potential method at different initial methanol concentration solutions. A simple mathematical model based on quasi-steady-state diffusion for the transport of methanol across the membrane in a diffusion cell is developed to simulate the experimental data in order to measure the methanol permeability. The influence of the diffusion cell parameters and thickness of the membrane on the methanol permeability measurement has been evaluated and analyzed. By means of Maclaurin expansion technique, this model can be used to predict the deviation of methanol permeability determined by steady-state diffusion model.     

Comparison of several image analysis methods for fiber dispersion uniformity in water

In order to evaluate fiber dispersion in water, a comparative study of different image analysis methods has been carried out. Furthermore, a vision system has been established to observe and capture the distribution of polyester fiber dispersed in water. This paper focuses on the difference of image analysis methods and investigates the effect of dispersant and stirring parameters. Besides, our results indicate that the effect of dispersant concentration, fiber length, and the stirring rate on uniform distribution can be revealed by employing the quadrat analysis method. In addition, the influence of stirring parameters on dispersion quality can be well represented by the histogram analysis method, such as the stirring rate and dispersion time.     

Permeation and thermal osmosis of water through cellulose acetate membranes

Isothermal permeation and thermal osmosis of pure water through cellulose acetate membranes have been studied. In all cases the results have been analyzed and compared with those of the literature. Two kinds of isothermal permeation experiments have been carried out, in order to find the influence of temperature and stirring rate on the phenomenon. The activation energy for permeation has been calculated.In the case of thermal osmosis two different kinds of experiments have been developed. In the first, thermoosmotic flows have been measured. In the second, evolution towards steady states has been obtained. In both cases the experiments have been performed by varying separately the temperature difference, the mean temperature and the stirring rate. The activation energy for thermal osmosis has been calculated. The influence of stirring rate on thermal osmosis has shown that “temperature polarization” cannot be avoided with the experimental setup, but its influence may be evaluated. A method is proposed to evaluate the differential thermoosmotic permeability. It is suggested that the results obtained from steady states are more reliable than those obtained from thermoosmotic flows.     

Carrier‐Mediated Transport of Hg(II) through Bulk and Supported Liquid Membranes

The transport of Hg (II) ions from an aqueous solution into an aqueous receiving solution through bulk and supported liquid membranes containing a calix[4]arene derivative 1 as a carrier was examined. The kinetic parameters of bulk liquid membrane studies were analyzed assuming two consecutive, irreversible first‐order reactions. The influence of temperature, stirring rate, carrier concentration and solvent on the kinetic parameters (k₁, k₂, R_m ^max, t_max, J_d ^max, J_a ^max) has also been investigated. The membrane entrance rate, k₁, and the membrane exit rate, k₂, increased with increasing temperature and stirring rate. The activation energy values are calculated as 4.87 and 48.63 kj mol^?1 for extraction and reextraction, respectively. The values of calculated activation energy indicate that the process is diffusionally controlled by species. Also, the transport behavior of Hg²⁺ from aqueous solution through a flat‐sheet supported liquid membrane has been investigated by the use of calix[4]arene derivative 1 as carrier and Celgard 2500 as the solid support. A Danesi mass transfer model was used to calculate the permeability coefficients for each parameter studied. The highest values of permeability were obtained with 2‐nitrophenyloctyl‐ether (NPOE) solvent and the influence was found to be in the order of NPOE>chloroform>xylene.     

An NMR study of methanol diffusion in polymer electrolyte fuel cell membranes

Methanol diffusion in two polymer electrolyte membranes, Nafion 117 and BPSH 40 (a 40% disulfonated wholly aromatic polyarylene ether sulfone), was measured using a modified pulsed field gradient NMR method. This method allowed for the diffusion coefficient of methanol within the membrane to be determined while immersed in a methanol solution of known concentration. A second set of gradient pulses suppressed the signal from the solvent in solution, thus allowing the methanol within the membrane to be monitored unambiguously. Over a methanol concentration range of 0.5–8 M, methanol diffusion coefficients in Nafion 117 were found to increase from 2.9 × 10⁻⁶ to 4.0 × 10⁻⁶ cm² s⁻¹. For BPSH 40, the diffusion coefficient dropped significantly over the same concentration range, from 7.7 × 10⁻⁶ to 2.5 × 10⁻⁶cm² s⁻¹. The difference in diffusion behavior is largely related to the amount of solvent sorbed by the membranes. Increasing the methanol concentration results in an increase in solvent uptake for Nafion 117, while BPSH 40 actually excludes the solvent at higher concentrations. In contrast, diffusion of methanol measured via permeability measurements (assuming a partition coefficient of 1) was lower (1.3 × 10⁻⁶ and 6.4 × 10⁻⁷ cm² s⁻¹ for Nafion 117 and BPSH 40 respectively) and showed no concentration dependence. The differences observed between the two techniques are related to the length scale over which diffusion is monitored and the partition coefficient, or solubility, of methanol in the membranes as a function of concentration. For the permeability measurements, this length is equal to the thickness of the membrane (178 and 132 μm for Nafion 117 and BPSH 40 respectively) whereas the NMR method observes diffusion over a length of approximately 4–8 μm. Regardless of the measurement technique, BPSH 40 is a greater barrier to methanol permeability at high methanol concentrations.     

以数字处理对魔芋葡甘聚糖膜面特征的初步研究

以天然生物材料为原料的绿色环保型膜材料取代塑料薄膜将是今后膜材料的发展趋势[1 4 ] 。从魔芋 (ＡｍｏｒｐｈｏｐａｌｌｕｓＫｏｎｊａｃＫ .ＫｏＣｈ)中提取出的魔芋精粉 ,其主要成分为葡甘聚糖 ,其优良的成膜性已引起人们的重视[4 5] 。分形维数在材料研究中得到了广泛的应用[6 ] ,本文以魔芋葡甘聚糖为主要原料制成膜 ,对膜的扫描电镜图象进行数字化处理 ,探讨膜面的微观形貌特征及制膜条件对膜面的影响。1　实验部分1 1　膜的制备以魔芋精粉 (四川安县魔芋精粉厂 )为主要原料 ,并添加明胶增强剂、甘油 (食品级 )增塑剂 (质量比为 1…     

Characterization of the mechanical properties of cross-linked serum albumin microcapsules: effect of size and protein concentration

A microfluidic technique is used to characterize the mechanical behavior of capsules that are produced in a two-step process: first, an emulsification step to form droplets, followed by a cross-linking step to encapsulate the droplets within a thin membrane composed of cross-linked proteins. The objective is to study the influence of the capsule size and protein concentration on the membrane mechanical properties. The microcapsules are fabricated by cross-linking of human serum albumin (HSA) with concentrations from 15 to 35 % (w/v). A wide range of capsule radii (～40–450 μm) is obtained by varying the stirring speed in the emulsification step. For each stirring speed, a low threshold value in protein concentration is found, below which no coherent capsules could be produced. The smaller the stirring speed, the lower the concentration can be. Increasing the concentration from the threshold value and considering capsules of a given size, we show that the surface shear modulus of the membrane increases with the concentration following a sigmoidal curve. The increase in mechanical resistance reveals a higher degree of cross-linking in the membrane. Varying the stirring speed, we find that the surface shear modulus strongly increases with the capsule radius: its increase is two orders of magnitude larger than the increase in size for the capsules under consideration. It demonstrates that the cross-linking reaction is a function of the emulsion size distribution and that capsules produced in batch through emulsification processes inherently have a distribution in mechanical resistance.     

Pore surface fractal analysis of palladium-alumina ceramic membrane using Frenkel-Halsey-Hill (FHH) model

The alumina ceramic membrane has been modified by the addition of palladium in order to improve the H(2) permeability and selectivity. Palladium-alumina ceramic membrane was prepared via a sol-gel method and subjected to thermal treatment in the temperature range 500-1100 degrees C. Fractal analysis from nitrogen adsorption isotherm is used to study the pore surface roughness of palladium-alumina ceramic membrane with different chemical composition (nitric acid, PVA and palladium) and calcinations process in terms of surface fractal dimension, D. Frenkel-Halsey-Hill (FHH) model was used to determine the D value of palladium-alumina membrane. Following FHH model, the D value of palladium-alumina membrane increased as the calcinations temperature increased from 500 to 700 degrees C but decreased after calcined at 900 and 1100 degrees C. With increasing palladium concentration from 0.5 g Pd/100 ml H(2)O to 2 g Pd/100 ml H(2)O, D value of membrane decreased, indicating to the smoother surface. Addition of higher amount of PVA and palladium reduced the surface fractal of the membrane due to the heterogeneous distribution of pores. However, the D value increased when nitric acid concentration was increased from 1 to 15 M. The effect of calcinations temperature, PVA ratio, palladium and acid concentration on membrane surface area, pore size and pore distribution also studied.     

A Study of the Permeation of Gold(III) Through Cyanex471x Solid Supported Liquid Membranes (SSLM)

Abstract

A solid supported liquid membrane for the selective removal of Au(III) from chloride solutions has been developed by using Triisobutiphosphine sulfide (Cyanex 471x) In cumene as organic carrier. The membrane system is shown to be effective between chloride solutions ([Cl^?]= 1.0 M) containing traces of Au(III) and SCN^? 0.1 M solutions. Different kinds of at membrane supports have been studied. The results, expressed in terms of membrane permeability, show significant differences between the different supports employed, the polypropylene supports, being the most efficient.     

乳状液膜法分离水中镉

本文报道了用乳状液膜法分离镉的研究。在此分离体系中,以煤油作为膜溶剂,span80为表面活性剂,磷酸三丁酯(TBP)为载体,液体石蜡为膜增强剂。详细讨论了制乳时间、混合时间、搅拌速度,span80、TBP以及液体石蜡的浓度,乳水比和油内比,内相氨水和外相HCl溶液的浓度对分离的影响,确立了最佳分离条件。     

A dynamic approach to diffusion and permeation measurements

A dynamic method for investigating the mechanism of permeation and diffusion through polymers has been explored. The permeation cell consists of two compartments separated by the membrane. The permeant (gas, vapor, or liquid) is introduced into one compartment; a carrier gas (helium) flows at constant rate through the other and sweeps the permeant which diffuses through the membrane to the thermal conductivity detector. Both compartments are at atmospheric pressure; thus no or little membrane support is required, and leakage problems are minimal. Moreover, the same membrane can be used over a wide temperature range and for diverse permeants. The detector signal is at any instant proportional to the permeation rate. A simple mathematical formalism for deriving the diffusion coefficient from the transient permeation rates has been developed. The measured diffusion and permeability coefficients of CO₂, O₂, and N₂ through low-density polyethylene closely agree with literature values. Permeation of hexane and benzene through polyethylene follows a complex diffusion law, and the rate depends on the thermal history of the system. The dynamic method is particularly suited to the study of transitions in polymers. Changes in permeation rates, usually occurring at transition points, can easily be discovered by slow temperature scanning of the system.     

A Study on the Competitive Permeability of Anions in Anion Exchange Membrane

The selective permeability of two species of critical ions coexisting in Solution 1 for a third species of ions of the same charge in Solution 2 penetrate through the anion exchange membrane has been studied. The competitive permeability of coexisting ions depends on various concentrations, compositions and reaction time with the restriction that the volume of solution in each compartment is finite. The species which is easy to exchange across the membrane in multi-ionic system has a high selective permeability at small composition and high total concentration condition. The experimental result shows that there exist overshooting and depletion effects for the fast ion when the reaction time is long enough, and the higher the permselectivity T^CL_OH is, the more appreciable the overshooting effect is. An explanation of the overshooting and depletion effects with finite volume of solution has been made specifically in discussion.