Transport of iron halides through polyurethane ether-type membranes

The transport of iron(III) using polyether-based polyurethane membranes was studied. The rate at which iron passes through the membrane depends on the formation of the HFeX(4) species, which is related to the initial acid and salt concentration of the metal solution. Iron is quantitatively transported from a cell of high acid-halide concentration to one with low concentration.     

The separation and isolation of gold by selective extraction and transport through a polyurethane ether-type membrane

The separation and isolation of gold(III) by selective extraction and transport through a ether-type polyurethane membrane was studied. Gold was found to be extracted into the membrane in strongly acidic solutions of HCl and HBr as the HAuBr(4) and HAuCl(4) complexes. Once extracted, the HAuCl(4) and HAuBr(4) complexes diffuse through the membrane and are recovered quantitatively in a receiving cell solution. This phenomenon was studied for the separation of a variety of binary metal solutions as well as for the separation of gold from a solution of gold ore. The preconcentration of gold was also achieved by adjusting the starting and receiving cell solution volumes.     

Sorption of organic dyes by polyurethane foam

The sorption of fifty-nine organic dyes, indicators and stains by polyester and polyether-type polyurethane foams was investigated by use of aqueous solutions and powdered foam material. Comparisons were made with sorption from 50% methanol solutions for some dyes and also with solvent extractions done with diethyl ether or ethyl acetate for several dyes. The R(f) values for the dyes run on cellulose TLC plates in water or a mixed solvent mobile phase were compared to the distribution coefficients with polyurethane foam. The relationship between the structure of the test substances and their sorption is discussed.     

Transport of alkali halides through a liquid organic membrane containing a ditopic salt-binding receptor

A ditopic receptor is shown to have an impressive ability to recognize and extract the ion pairs of various alkali halides into organic solution. X-ray diffraction analysis indicates that the salts are bound in the solid state as contact ion pairs. Transport experiments, using a supported liquid membrane and high salt concentration in the source phase, show that the ditopic receptor can transport alkali halide salts up to 10-fold faster than a monotopic cation or anion receptor and 2-fold faster than a binary mixture of cation and anion receptors. All transport systems exhibit the same qualitative order of ion selectivity; that is, for a constant anion, the cation selectivity order is K+ > Na+ > Li+, and for a constant cation, the anion transport selectivity order is I- > Br- > Cl-. The data suggest that with a ditopic receptor, the polarity of the receptor-salt complex can be lowered if the salt is bound as an associated ion pair, which leads to a faster diffusion through the membrane and a higher maximal flux.     

Transport of heavy organic vapors through silicone rubber

Permeability, solubility, and diffusion coefficients have been determined for halothane (CF₃CHClBr) and methoxyflurane (CHCl₂CF₂OCH₃) in silicone rubber at temperatures from 17 to 60°C and at relative pressures from 0.05 to 0.96. The solubility of both penetrants in silicone rubber is a strong function of penetrant concentration (or relative pressure), and can be represented satisfactorily by the Flory-Huggins relation with single values of the interaction parameter χ. The solubility coefficients decrease with increasing temperature at constant pressure. Mutual diffusion coefficients exhibit maxima when plotted against penetrant concentration; these maxima are attributed to the mass flow of polymer together with dissolved penetrant. Intrinsic diffusion coefficients increase linearly with increasing concentration. The energies of activation for diffusion are low, probably because of the ease of segmental motion about the Si? O linkage. The diffusivity data are examined in terms of Fujita's “free volume” model and of transition-state theory. Permeability coefficients for the two penetrants are large, of the order of 10^?6–10^?5 cm³(STP)-cm/(sec-cm²-cm Hg), and increase markedly with increasing concentration or decreasing temperature. This behavior is regarded as a consequence of the low energies of activation for diffusion.     

Transport of organic acids through perfluorosulfonate polymeric membranes

Carboxylic acids in aqueous solutions permeate through perfluorosulfonate merebranes. The permeation is significantly enhanced when the sulfonic acid groups are convetted to their sodium salt form. Transport fluxes at atmospheric pressure have been found to vary in the 10^-9—10^-6 mol/cm²-sec range, depending on the nature of the acids. Interesting separation possibilities of carboxylic acids from one another or from nonpolar compounds are discussed.     

Transport of sulfuric acid through anion-exchange membrane NEOSEPTA-AFN

This paper deals with the determination of the membrane mass transfer coefficient for sulfuric acid in an anion-exchange membrane NEOSEPTA-AFN. This quantity has been determined on the basis of experiments carried out in a batch dialysis cell using the method of numerical integration of the basic differential equation describing the time dependence of sulfuric acid concentration and subsequent optimization procedure. The experiments carried out made it possible to calculate the membrane mass transfer coefficient for sulfuric acid over the concentration range from 0.1 to 1.9 kmol m⁻³ in the external solution.     

Transport of ions through an elliptic ion-selective membrane

The rate of transport of ions through an annular ion-selective membrane having an elliptic cross section is analyzed. This is a generalization to a hollow-fiber type of device, and represents a wide class of membranes which are capable of providing a large (surface area/volume) ratio for ion transport. The Nernst–Plank equation governing the transport of ions is solved numerically. The results obtained reveal that, if the concentration of fixed charge is high, its current efficiency is insensitive to fixed charge distribution, and the local electroneutrality can be assumed. On the other hand, if the concentration of fixed charge is low, the distribution of fixed charge becomes significant, and assuming local electroneutrality can be inappropriate. In general, the higher the average concentration (or the greater the total amount) of fixed charge of a membrane, the higher its current efficiency. We show that the results for planar and cylindrical membranes can be recovered from the present model.     

Transport of organic solutes through amorphous teflon AF films

Fluorous media have great potential for selective extraction (e.g., as applied to organic synthesis). Fluorous polymer films would have significant advantages in fluorous separations. Stable films of Teflon AF 2400 were cast from solution. Films appear defect-free (SEM; AFM). Rigid aromatic solutes are transported (from chloroform solution to chloroform receiving phase) in a size-dependent manner (log permeability is proportional to -0.0067 times critical volume). Benzene's permeability is about 2 orders of magnitude higher than in comparable gas-phase experiments. The films show selectivity for fluorinated solutes in comparison to the hydrogen-containing control. Transport rates are dependent on the solvent making up the source and receiving phases. The effect of solvent is, interestingly, not due to changes in partition ratio, but rather it is due to changes in the solute diffusion coefficient in the film. Solvents plasticize the films. A less volatile compound, -COOH-terminated poly(hexafluoropropylene oxide) (4), plasticizes the films (T(g) = -40 degrees C). Permeabilities are decreased in comparison to 4-free films apparently because of decreased diffusivity of solutes. The slope of dependence of log permeability on critical volume is not changed, however.     

Transport phenomena of sulfonated dyes into cellulose membrane: Effects of urea on parallel diffusion of mono azo dyes

 Effects of urea on transport phenomena of sulfonated azo dyes with different aggregation constants into water-swollen cellulose membrane have been studied at 25–55 °C. The results were analyzed on the basis of a parallel transport theory of surface and pore diffusion. Addition of urea decreased equilibrium adsorption of the dyes onto cellulose and increased the surface and pore diffusivities for the parallel diffusion model of the dye with high aggreg-ation constant. Temperature dependence of the effects was also discussed. Received: 30 November 1996 Accepted: 7 April 1997     

Transport of silver ion through bulk liquid membrane using macrocyclic and acyclic ligands as carriers in organic solvents

The bulk liquid membrane transport of silver (I) ion was studied by dibenzopyridino-18-crown-6(DBPY18C6), 4-nitrobenzo-15-crown-5(NB15C5), 2-aminothiaphenol and a new synthesized ligand, 1,4-dioxa-7,10-dithiacyclododecane-2,3-dione as carriers in nitrobenzene (NB). The effects of pH on the source phase and receiving phase, the nature and concentration of stripping agents in the receiving phase and the picrate concentration as counter ion in source phase were investigated. The results show that the efficiency of transport of the Ag⁺ ion through membranes, changes with the nature of the ligand. The efficiency transport increases for the ligands with donating nitrogen and sulfur atoms with respect to oxygen donor atoms. Maximum transport efficiency was observed for silver (I) ion in the presence of thiosulfate ion ( ) as a suitable stripping agent. The results show that the sequence of transport efficiency for Ag⁺ ion using DBPY18C6, NB15C5, 2-aminothiaphenol and 1,4-dioxa-7,10-dithiacyclododecane-2,3-dione as carriers in organic solvents is: nitrobenzene > dichloromethane > 1,2- dichloroethane > chloroform.     

Extraction of azo dyes by polyurethane foam

The extraction of 12 closely related mono-azo dyes by polyester and polyether-type polyurethane foams was studied to gain more information regarding the mechanism of the extraction of organic compounds. The effects on extraction of solution pH, dye concentration and salt concentration were investigated. It was found that the extraction of the dyes involved a neutral zwitterionic species and is highly dependent on the parameters studied. The dependency of the extraction on these parameters can be explained in a manner consistent with solvent extraction; however, the dual-mode sorption mechanism seems a more likely model. This mechanism involves both absorption related to solvent extraction, and an added component for surface adsorption. While the dual-mode sorption model explains the observed extraction behaviour, the data suggest that surface adsorption plays a much larger role than previously considered.     

Transport and separation of small organic molecules through nanotubules.

An electroless plating method was applied to deposit Au onto the surfaces and the walls of pores of polycarbonate membranes to prepare gold nanotubules. The nanotubules were modified with cysteine (Cys) or with carbamidine thiocyante (Gua). The effects of modifiers and of the fine structure of organic molecules on the transport properties of those molecules through the gold nanotubules were investigated. Studies show that the hydrophilicity of modifiers and the planar structure of permeating molecules clearly affect the transport of small organic molecules in gold nanotubules. Tryptophan (Try) and vitamin B(2) (VB(2)) was cleanly separated at pH 6.8.     

Transport of organic and inorganic solutes through charged mosaic composite membranes

A template pattern with alternating poly(4-vinylpyridine) (P4VP)/poly(vinyl alcohol) (PVA) lamellae was fabricated upon a microporous poly(vinyl chloride) (PVC) membrane by casting of poly[4-vinylpyridine(4VP)-g-vinyl alcohol (VA)] graft copolymer. After a treatment of both binding of microporous membrane with graft copolymer and domain fixing of the PVA matrix, a dilute solution of poly[acrylic acid (AA)-benzyl N,N-dimethyldithiocarbamate (DMTC)]/P4VP or poly[sodium p-styrenesulfonate (SSS)-DMTC]/P4VP binary blend was cast on this template surface. Two types of weak acid/strong base or strong acid/strong base microdomains formed by phase growth were oriented perpendicularly to the membrane surface. After the chemical treatments: introduction of the charge and domain fixing of ion exchange regions, two types of such mosaic microdomains could be constructed on a microporous membrane. We studied the transport behaviors of organic and inorganic solutes through charged mosaic composite membranes. The permeability of inorganic electrolyte, such as KCl was about 20-fold compared to those of organic nonelectrolytes, such as glucose and sucrose. l-Phenylalanine exhibits a low value of permeability at the pH of its isoelectric point.     

Transport of organic vapors through poly(1-trimethylsilyl-1-propyne)

Poly(1-trimethylsilyl-1-propyne) [PTMSP], a high-free-volume glassy polymer, has the highest gas permeability of any known synthetic polymer. In contrast to conventional, low-free-volume, glassy polymers, PTMSP is more permeable to large, condensable organic vapors than to permanent gases. The organic-vapor/permanent-gas selectivity of PTMSP based on pure gas measurements is low. In organic-vapor/permanent-gas mixtures, however, the selectivity of PTMSP is much higher because the permeability of the permanent gas is reduced dramatically by the presence of the organic vapor. For example, in n-butane/methane mixtures, as little as 2 mol% n-butane (relative n-butane pressure 0.16) lowers the methane permeability 10-fold from the pure methane permeability. The result is that PTMSP shows a mixed-gas n-butane/methane selectivity of 30. This selectivity is the highest ever observed for this mixture and is completely unexpected for a glassy polymer. In addition, the gas mixture n-butane permeability of PTMSP is considerably higher than that of any known polymer, including polydimethylsiloxane, the most vapor-permeable rubber known. PTMSP also shows high mixed-gas selectivities and vapor permeabilities for the separation of chlorofluorocarbons from nitrogen. The unusual vapor permeation properties of PTMSP result from its very high free volume - more than 20% of the total volume of the material. The free volume elements appear to be connected, forming the equivalent of a finely microporous material. The large amount of condensable organic vapor sorbed into this finely porous structure causes partial blocking of the small free-volume elements, reducing the permeabilities of the noncondensable permanent gases from their pure gas values.     

Transport processes through track-etch membrane filters in a reagent delivery cell

A reagent delivery cell with a track-etch membrane filter for on-line dilution of concentrated salt solutions is described. The influence of several system parameters such as concentration of the stock solution, temperature. transmembrane pressure and the dependence on the diffusion coefficients of several salt components on the dilution was evaluated. As an application example, the use of the reagent delivery cell for on-line calibration of an atomic absorption spectrometer was studied. Fluxes through the membrane filter of 10 to 50 nL mm(-2) min(-1) with relative standard deviations of 0.8% within a day and 1.9% from day to day were achieved. The permeation experiments with the track-etch membrane filter for the dilution of aqueous solutions of several chlorides and sodium salts confirm a diffusion process. Flux rates can be estimated mathematically using Fick's first law with an agreement between measured and calculated dilution factors within 86 to 113%.