Showing papers in "Separation Science and Technology in 1990"
TL;DR: In this article, two zeolites were analyzed by X-ray diffraction and inductively coupled plasma analysis (ICP) to test the effectiveness of clinoptilolite for treating a multiion wastewater.
Abstract: Zeolites from abundant natural deposits were investigated by the Bureau of Mines for efficiently cleaning up mining industry wastewaters. Twenty-two zeolites were analyzed by X-ray diffraction and inductively coupled plasma analysis (ICP). These included clinoptilolite, mordenite, chabazite, erionite, and phillipsite. The zeolites were primarily in the sodium or calcium form, but potassium and magnesium counter ions were also present. Bulk densities of a sized fraction (minus 40, plus 65 mesh) varied from 0.48 to 0.93 g/cc. Heavy metal ion exchange loading values on two clinoptilolites ranged from 1.6 meq/g for lead to 0 meq/g for mercury in single ion tests. The selectivity series was determined to be Pb>Cd>Cs>Cu(II)>Co(II)>Cr(III)>Zn>Ni(II)>Hg(II). Sodium was the most effective exchangeable ion for ion exchange of heavy metals. Wastewater from an abandoned copper mine in Nevada was used to test the effectiveness of clinoptilolite for treating a multiion wastewater. Aluminum, Fe(III), Cu(II), an...
291 citations
TL;DR: The physicochemical nature of the metal-extractant aggregates formed in the organic phase of acidic organophosphorus solvent extraction systems was investigated to further understand hydrometallurgical extraction as discussed by the authors.
Abstract: The physicochemical nature of the metal-extractant aggregates formed in the organic phase of acidic organophosphorus solvent extraction systems was investigated to further understand hydrometallurgical extraction. The experimental techniques of fluorescence, FT-IR, and NMR spectroscopy, static and dynamic light-scattering, tensiometry, as well as classical physicochemical methods and extraction measurements, were employed to clarify the nature of the molecular aggregates associated with the extraction of Ca2+, Co2+, Ni2+, and Zn2+ by di(2-ethylhexyl)phosphoric acid (HDEHP) in n-alkane diluents. Significantly, there appears to be three regimes of aggregation behavior in solvent extraction systems consistent with the mechanism suggested earlier by Neuman and co-workers [Colloids Surfaces, 46, 45 (1990)]. A simplified model is proposed herein for the aggregation of metal-extractant complexes in acidic organophosphorus solvent extraction systems: as the concentration of metal-extractant complexes inc...
70 citations
TL;DR: In this paper, the effects of temperature and permeate-side pressure on membrane transport with dilute ethanol feed solutions were investigated and a poly(dimethyl siloxane) membrane exhibited ethanol selectivity during all process runs.
Abstract: The separation of ethanol/water mixtures by pervaporation with a poly (dimethyl siloxane) membrane has been studied. The membrane exhibited ethanol selectivity during all process runs. Investigations focused on the effects of temperature and permeate-side pressure on membrane transport with dilute ethanol feed solutions. An increase in temperature increased the flux exponentially but had little effect on selectivity. As the permeate-side pressure was increased, the flux decreased. Selectivity did not change appreciably over the pressure range evaluated. Studies also analyzed the effect of feed concentration on flux and selectivity. Flux increased and selectivity decreased as the ethanol feed concentration increased. The permeate concentration profile is superior to a standard vapor–liquid equilibrium curve at low ethanol feed concentrations.
52 citations
TL;DR: A recent survey of liquid pertraction as mentioned in this paper shows that there are more than 160 research teams around the world exploring this new, emerging separation operation, and that it has attracted the attention of many scientists and engineers.
Abstract: Liquid pertraction∗ or liquid membranes appeared as a prospective separation process relatively recently. Due to its obvious advantages over solid membranes and liquid-liquid extraction, liquid pertraction has attracted the attention of many scientists and engineers. At present there are more than 160 research teams around the world exploring this new, emerging separation operation.
49 citations
TL;DR: In this paper, the catalytic dehydrogenation of ethylbenzene to styrene in a membrane reactor was studied at 600° to 640°C, where the pore diameter increased to 60 ∼ 90A and the microstructure of membrane remained intact.
Abstract: The catalytic dehydrogenation of ethylbenzene to styrene in a membrane reactor was studied at 600° to 640°C. The reactor selected in this study is a commercial alumina membrane tube with 40A pore diameter packed with granular catalysts. One of the reaction products, hydrogen, was separated through the membrane. Therefore, the catalytic dehydrogenation was enhanced by reducing the hydrogen partial pressure in the reactor. The conversion of ethylbenzene increased ∼15% compared to the conversion in the packed-bed reactor. The hydrothermal stability of membrane reactor after reactions was examined by nitrogen permeation test and SEM. It indicated that the pore diameter increased to 60 ∼ 90A and the microstructure of membrane remained intact.
47 citations
TL;DR: In this paper, hollow-fiber supported liquid membranes (SLM) were used to separate and concentrate U(VI) in the strip solution, and the results were obtained both with a conventional module and with a module containing a carrier solution reservoir.
Abstract: The separation of uranium from Hanford site groundwater as studied by hollow-fiber supported liquid membranes, SLM. The carrier bis(2,4,4-trimethylpentyl)phosphinic acid, H(DTMPep), contained in the commercial extractant Cyanex{trademark} 272 was used as a membrane carrier, because of its selectivity for U over calcium and magnesium. The water soluble complexing agent, 1-hydroxyethane-1,1-diphosphonic acid, HEDPA, was used as stripping agent. Polypropylene hollow-fibers and n-dodecane were used as polymeric support and diluent, respectively. Laboratory scale hollow-fiber modules were employed in a recycling mode, using as feed synthetic groundwater at pH 2, to confirm the capability of the proposed SLM system to separate and concentrate U(VI) in the strip solution. Information was obtained on the U(VI) concentration factor and on the long-term performance of the SLMs. Encouraging results were obtained both with a conventional module and with a module containing a carrier solution reservoir. Industrial scale modules were used at Hanford to test the SLM separation of U(VI) from real contaminated groundwater. The uranium concentration was reduced from approximately 3500 ppB to about 1 ppB in a few hours. 9 refs., 8 figs., 4 tabs.
47 citations
TL;DR: In this paper, the binding of hydrophillic solutes to both ionic and nonionic micelles is considered and shown to be a function of the molecular structure of the surfactants, the concentration of surfactant, and the electrolyte composition of the water.
Abstract: The selection of a surfactant is an important issue in designing separations processes based on micellar-enhanced ultrafiltration. The binding of hydrophillic solutes to both ionic and nonionic micelles is considered and shown to be a function of the molecular structure of the surfactants, the concentration of the surfactant, and the electrolyte composition of the water. It is also shown that the passage of micelles is only partly restricted by polycarbonate membranes with 100 A ports but is effectively restricted by some cellulose acetate membranes. Swelling the micelles by cosolubilizing certain nonpolar compounds was found to only marginally improve the separation efficiency. There appears to be an optimum surfactant molecular structure, but it will not be possible even under the best conditions to completely remove a hydrophilic solute such as phenol in a single stage. Thus, the process will necessarily be multistage.
43 citations
TL;DR: In this article, a technique for the chemical modification of 40A γ-alumina membranes with Tridecafluoro-1,1,2,2,-tetrahydrooctyl-1-trichlorosilane is presented.
Abstract: A technique for the chemical modification of 40A γ-alumina membranes with Tridecafluoro-1,1,2,2,-tetrahydrooctyl-1-trichlorosilane is presented. The modification is carried out in order to reduce the membrane's pore size so that selective separation of low molecular weight liquid mixtures may be possible. Pure gas permeability measurements with He, H2, Ar, and SF6 are reported for an unmodified and two modified membranes which varied in their reaction times from one day to two weeks. The permeability measurements indicate that the short-term modification produced a membrane that still had an appreciable amount of surface flow, while the membrane modified for two weeks had a hindered surface transport. Also reported are data on the separation of toluene from a high molecular weight (M∼660) lube oil. The data indicate an increase in selectivity due to the short-term modification; however, after the two-week modification, the selectivity drops to near unity.
43 citations
TL;DR: In this paper, the effects of added anion and the pH in the source phase, and the plasticizer incorporated in the membrane on the lanthanide flux were examined by using hinokitiol and flavonol (HFL) as carriers.
Abstract: Fluxes of trivalent lanthanide ions across cellulose triacetate membranes were determined by using hinokitiol (HIPT) and flavonol (HFL) as carriers. The transport of the lanthanides was coupled to a flow of hydrogen ions. The effects of added anion and the pH in the source phase, and the plasticizer incorporated in the membrane on the lanthanide flux, were examined. In the case of HIPT, the fluxes for the lanthanides from samarium to lutetium were much higher than those for lanthanum to neodymium. In the transport using HFL, the flux increased with decreasing ionic radius of the lanthanide species. The addition of perchlorate or thiocyanate ions to the source phase resulted in a rise in the lanthanide flux. With decreasing pH difference between the aqueous phases, the fluxes using HIPT decreased gradually while those using HFL decreased rapidly. The flux was affected by the type of plasticizer added to the membrane.
43 citations
TL;DR: In this paper, the synthesis and properties of some novel solvent extractants that are highly selective for gold and silver in very acidic chloride solutions are described, and the study of one of these reagents; Dodecyl-thiourea (DTH), which has shown to be a very selective extractant for Au(III) and Ag(I) in the presence of Cu(II) and Fe(III).
Abstract: The synthesis and properties of some novel solvent extractants that are highly selective for gold and silver in very acidic chloride solutions are described. In this paper we also report on the study of one of these reagents; Dodecyl-thiourea (DTH), which has shown to be a very selective extractant for Au(III) and Ag(I) in the presence of Cu(II) and Fe(III). The extraction of Au and Ag was found to be fast. The Gold-DTH extraction data were explained by the formation of AuCl3.(DTH)3 species while silver forms AgCl.(DTH)2 complex. The extractant has been also tested for practical application by determining the loading and stripping isotherms.
42 citations
TL;DR: In this paper, a computer program for the interpretation of solvent extraction data in systems that can include two extractants, one acidic and one neutral, has been extended to treat the effects of: (1) variation of activity coefficients of solute species and of water activity in the aqueous phase, calculated by the Pitzer treatment; (2) variations of activity coefficient of solutes in the organic phase calculated by Hildebrand-Scott treatment; and (3) product species formed in the anion phase.
Abstract: A previously reported computer program for the interpretation of solvent extraction data in systems that can include two extractants, one acidic and one neutral, has been extended to treat the effects of: (1) variation of activity coefficients of solute species and of water activity in the aqueous phase, calculated by the Pitzer treatment; (2) variation of activity coefficients of solute species in the organic phase, calculated by the Hildebrand-Scott treatment; and (3) product species formed in the aqueous phase. The interaction parameters of the Pitzer treatment and the solubility parameters of the Hildebrand-Scott treatment can be refined along with the formation constants of various assumed product species to fit the data. Like its predecessor, the program is capable of fitting simultaneously a variety of data, including the distribution of an extractable cation, anion, or water, as well as spectra, vapor pressure, or heats of mixing for the organic phase. Use of the program is illustrated by...
TL;DR: A review of membrane pervaporation has been presented in this paper, along with discussion of the potential for removal of organics from water and its application in the removal of water-laden solvents.
Abstract: The recovery of water-laden solvents by membrane pervaporation has become an industrially-accepted practice. A review of the technology is presented, along with discussion of the potential for removal of organics from water.
TL;DR: In this article, a membrane and a membrane process for the recovery of off gases from gasoline storage and handling was developed, and a 300 m3/h vapor recovery unit for the treatment of off gas from a gasoline tank farm started operation in October 1989.
Abstract: Many industrial processes which handle volatile hydrocarbons produce organic vapors. These vapors which are generated during storage, trans- portation and the handling of hydrocarbons cause environmental problems. The contaminants dispersed in the air are contributing factors to the development of photochemical smog. In addition they represent valuable resources which should be recovered, GKSS has developed a membrane and a membrane process for the recovery of off gases from gasoline storage and handling [1, 2]. A 300 m3/h vapor recovery unit for the treatment of off gases from a gasoline tank farm started operation in October 1989.
TL;DR: In this article, five different estimation procedures for micelle-water partition constants for organic solutes are discussed and potential advantages and drawbacks of each of these methods are explored, including their advantages and disadvantages.
Abstract: Five different estimation procedures for micelle-water partition constants for organic solutes are discussed. The procedures are based on 1) knowledge of octanol-water partition constants for the solutes, 2) aqueous solubilities of the solutes, 3) normal boiling points of the solutes, 4) a bond contribution scheme, and 5) a group contribution scheme. Available data in the literature including our own are used in obtaining these correlations. Potential advantages and drawbacks of each of the methods are explored.
TL;DR: In this paper, a modified channel structure was proposed to reduce the relaxation effect, reduce sample adhesion to the wall, and where possible eliminate the stop-flow procedure and thus greatly increase the speed and stability of operation.
Abstract: A continuous flow FFF process for the separation of samples of particles which uses a modified channel structure to reduce the relaxation effect, reduce sample adhesion to the wall, and where possible eliminate the stop-flow procedure and thus greatly increase the speed and stability of operation, said modified channel comprises a thin channel whose thickness is reduced at the inlet end for a substantial distance beyond the inlet, such as the conventional triangular or near triangular piece, and then broadened out at the outlet end of the channel.
TL;DR: In this paper, a mathematical model is developed to evaluate the performance of a tubular membrane module under oscillatory flow conditions, and the model considers the convective-diffusive mass transport without decoupling the momentum equation from the solute continuity equation.
Abstract: Various methods have been proposed to control or minimize concentration polarization and membrane fouling. A brief review of these alternatives is presented in this paper. Flow pulsation as a means of improving transmembrane flux has been studied experimentally by a few investigators. A mathematical model is developed to evaluate the performance of a tubular membrane module under oscillatory flow conditions. Besides the effect of osmotic pressure and axial pressure variation, the model considers the convective-diffusive mass transport without decoupling the momentum equation from the solute continuity equation. Model equations are solved by a finite difference method as part of an iterative solution. Model predictions of transmembrane flux with experimental data are found to be in good agreement. By flow pulsing, it is possible to improve the transmembrane flux by more than 68% at pulsing frequency of 60 cycles · min−1. An analysis of extra power requirement for flow oscillation shows that the ga...
TL;DR: In this paper, a solvent extraction system with a continuous sample feeding process called continuous countercurrent fractional extraction (CFE) was used to resolve the DL-Valine problem.
Abstract: DL-Valine was resolved completely by a solvent extraction system with a continuous sample feeding process called continuous countercurrent fractional extraction (CFE). The two-phase system contained n-butanol and water with a copper(II) complex of N-n-dodecyl-L-hydroxproline as a resolving reagent. The upper (alcohol-rich) phase and the lower (water-rich) phase proceeded in the segmented extraction columns countercurrently; the D-isomer was recovered in the upper phase, while the L-isomer was recovered in the lower phase. The optical purity of the enantiomers obtained was consistently 99.5% or higher. The D-isomer extracted in the upper phase was recovered completely by using a backextraction column in series after the extraction column, allowing the upper phase to be used repeatedly for the resolution. The efficiency of the CFE system was estimated at more than 24 theoretical stages.
TL;DR: The U.S. Department of Energy is researching high-temperature ceramic gas separation membranes to remove the sulfur and nitrogen contaminants found in gas streams of advanced coal-based power generation systems as discussed by the authors.
Abstract: The U.S. Department of Energy is researching high-temperature ceramic gas separation membranes. DOE will demonstrate the feasibility of using these membranes to remove the sulfur and nitrogen contaminants found in gas streams of advanced coal-based power generation systems. These contaminants must be removed to protect not only the turbine system components but also the environment. This paper discusses the integration of passive, faciltated, and catalytic membranes, and the expected benefits of applying this membrane technology.
TL;DR: In this paper, the authors studied the permeate characteristics of membrane distillation considering heat and mass transfers and concentration polarization, theoretical and experimental studies were performed to understand the effect of concentration polarization.
Abstract: To study the permeate characteristics of membrane distillation considering heat and mass transfers and concentration polarization, theoretical and experimental studies were performed. To understand the effect of concentration polarization, concentrated solutions of LiBr and H2SO4 were used as feed. The permeate flux was found to be proportional to the vapor pressure difference between the feed and cooled surface and decreased with increasing concentration because of the concentration and temperature polarization. Furthermore, when considering the heat and mass transfers and concentration polarization, the permeate flux could be estimated accurately.
TL;DR: In this article, the Fourier transform infrared (FTIR)/internal reflection spectroscopy (IRS) was used for in-situ measurements of surface reactions in the four major flotation systems.
Abstract: Infrared spectroscopy has been one of the most useful experimental techniques for the analysis of surface reactions. In particular, Fourier transform infrared (FTIR)/internal reflection spectroscopy (IRS) is most often used for in-situ studies. To date, three FTIR/IRS methods have been used for in-situ measurements. These techniques are evaluated for use in the characterization of surface reactions common to flotation systems. The method which uses mineral crystals as reactive internal reflection elements (IREs) is of particular interest because it allows surfactant adsorption densities to be calculated directly from in-situ spectral data in real time, and is the focus of this paper. Application of in-situ FTIR/IRS with reactive IREs is demonstrated for collector adsorption reactions in each of the four major flotation systems. Also, the use of reactive IREs in the near-IR spectral region and in spectroelec-trochemical research is discussed.
TL;DR: In this paper, a liquid membrane transport study of Co(II) using di(2-ethylhexyl) phosphoric acid (D2EPHA) as carrier and CCl4, as diluent supported on polypropylene microporous film has been carried out.
Abstract: A liquid membrane transport study of Co(II) using di(2-ethylhexyl) phosphoric acid (D2EPHA) as carrier and CCl4, as diluent supported on polypropylene microporous film has been carried out. The carrier concentration in the membrane and HCl concentration in the stripping phase have been varied to see the effect on transport of Co(II) ions across the membrane. Maximum flux and permeability values of 1.23 × 10−5 mol · m−2 · s−1 and 7.66 × 10−11 m2/s, respectively, at a 0.87 mol/dm3 carrier concentration in the membrane have been found. At 1 mol/dm3 HCl concentration in the stripping phase the flux and permeability have maximum values of 1.4 mol · m−2 · s−1 and 5.27 × 10−11 m2/s, respectively. The distribution coefficient of Co(II) ions into organic phase has been found to increase with increasing carrier concentration. The diffusion coefficient determined varies from 13.73 × 10−11 to 0.83 × 10−11 m2/s, which is the reverse order of the values of the distribution coefficient and explains the permeabi...
TL;DR: In this paper, composite sorbents were prepared by depositing molybdenum dioxide on Super A activated carbon and the adsorption isotherms of CH4 and N2 were measured.
Abstract: Composite sorbents were prepared by depositing molybdenum dioxide on Super A activated carbon. The adsorption isotherms of CH4 and N2 were measured. The adsorption capacities and BET surface areas of these adsorbents decreased with an increase in the amount of MoO2; however, the equilibrium selectivity ratio (CH4/N2) increased significantly. Therefore, an optimum quantity of MoO2 should be used to produce a sorbent with high adsorption capacity and selectivity ratio (CH4/N2). An adsorbent containing 18.2 wt% MoO2 was found to be optimum which showed a CH4/N2 selectivity ratio of 4.25. The selectivity ratio decreased with pressure, and leveled off to about 3 at 12 atm. The separation of a CH4/N2 (50/50) mixture by pressure swing adsorption (PSA) was studied by using an equilibrium model. A new PSA cycle is described by which pipeline quality methane (>90% CH4 purity) could be produced using the composite sorbent at a recovery of 73% and a throughput of 200 L STP/h/kg.
TL;DR: In this paper, the effects of the electric field strength, field polarity, temperature, phase composition, and buffer concentration on demixing rates of a polyethylene glycol-maltodextrin (PEG-MDX) system were quantitatively measured.
Abstract: Aqueous two-phase extraction techniques have been successfully applied to the purification of enzymes and cells. However, due to their similar physical properties, immiscible aqueous phases do not separate rapidly. A method for enhanced demixing of aqueous two-phase systems in a thermostated vertical electrophoresis column was therefore studied. The effects of the electric field strength, field polarity, temperature, phase composition, and buffer concentration on demixing rates of a polyethylene glycol-maltodextrin (PEG-MDX) system were quantitatively measured. At normal electrical polarity (anode at the top of the column), using a maximum practicable field strength of 26.4 V/cm, the demixing rate was twice that in zero electric field at 25 ± 2°C. With poiarity reversed (anode at the bottom, electric field opposing gravitational settling) at a field of 26.4 V/cm, demixing was 5.5 times as fast as in zero field. Reduction of the temperature from 25 to 14°C caused an increase in demixing rate in th...
TL;DR: In this article, a simple thermodynamic model was developed to predict separation factors for the selective adsorption of solutes from solute mixtures, based on their hydrogen bonding abilities.
Abstract: Current evidence suggests that adsorption of solutes from a nonpolar solvent onto a polycarboxylic ester sorbent involves the formation of a hydrogen bond. This bond appears to be formed between a hydrogen atom of the solute and the carbonyl group of the sorbent. From studies involving single solutes it was observed that the primary amine aniline adsorbed nearly twice as much as the secondary amine N-methylaniline. The tertiary amine N,N-dimethylaniline, which does not contain a nitrogen-bonded hydrogen atom, was unable to bind to the sorbent. In studies involving mixtures, solutes were observed to be selectively adsorbed based on their hydrogen bonding abilities. A simple thermodynamic model which was developed to explain this adsorption was capable of accurately predicting separation factors for the selective adsorption of solutes from solute mixtures.
TL;DR: In this article, the authors presented an NH3-selective membrane, poly(vinylammonium thiocyanate), which exhibits a high NH3 permeance, 5−20 × 10−5 cm3/cm2·s·cmHg with selectivity, α(CO2/H2), ranging from 360-30.
Abstract: Experimental results are presented on membranes of novel composition which selectively permeate ammonia and carbon dioxide from mixtures containing hydrogen. The CO2-selective membrane, which consists of a thin liquid film of the salt hydrate tetramethylammonium fluoride tetrahydrate, exhibits a CO2 permeance of 4-1 × 10−5 cm3/cm2·s·cmHg with selectivity, α(CO2/H2), ranging from 360-30. The NH3-selective membrane, poly(vinylammonium thiocyanate), displays a high NH3 permeance, 5−20 × 10−5 cm3/cm2·s·cmHg, with α(NH3/N2) as high as 3600 and α(NH3/H2) as high as 6000. Such membranes, which retain H2 at pressure in the feed stream, may offer new opportunities in the design of separation processes.
TL;DR: In this paper, an ion exclusion process to perform acid/sugar separation has been designed using standard resins, and economic analysis based on a process computer model indicates that ion exclusion is 40 % less costly than a lime precipitation process.
Abstract: The economic feasibility of using acid hydrolysis to convert agricultural waste products, such as corn stovers, to alcohol is very dependent upon developing a cost effective sulfuric acidglucose sugar separation process. Presently, an acid/sugar stream from sulfuric acid hydrolysis of cellulose is treated with lime to precipitate the acid as gypsum. This technique not only consumes acid and lime, but also generates waste gypsum that is sent to a landfill. An ion exclusion process to perform acid/sugar separation has been designed using standard resins. Economic analysis based on a process computer model indicates that ion exclusion is 40 % less costly than a lime precipitation process.
TL;DR: In this paper, a test apparatus for continuous demulsification was constructed in which a pulsed dc high potential was applied to W/O emulsions flowing between parallel copper electrodes of a perforated plate.
Abstract: The development of an efficient, continuous demulsification apparatus is needed in the industrial separation process utilizing the liquid surfactant membrane technique. A test apparatus for continuous demulsification was constructed in which a pulsed dc high potential is applied to W/O emulsions flowing between parallel copper electrodes of a perforated plate. Efficient demulsification was achieved by an operation in which the demulsified oil phase was absent between the emulsion and the upper electrode. When the feed rate of emulsion was adjusted to be equal to the demulsification rate, the latter value was proportional to the square root of the applied potential and independent of the distance between the electrodes.
TL;DR: In this paper, experimental results were presented for a palladium reactor system designed to investigate the feasibility of using palladium (Pd) alloy as the membrane material for 1-butene dehydrogenation.
Abstract: In current industrial practice dehydrogenation reactions require high temperatures and large amounts of inert (usually steam). Membrane reactors can be used to shift the equilibrium for these reversible reactions by removing products from the reaction zone. In this paper, experimental results will be presented for a palladium reactor system designed to investigate the feasibility of using palladium (Pd) alloy as the membrane material. Experiments have been conducted for isothermal and adiabatic conditions with air on the permeation side, wherein the oxygen reacts exothermically with the permeating hydrogen to decrease its partial pressure, thereby increasing its flux, and provide heat for the endothermic dehydrogenation reaction. Both theoretical and experimental results have been presented for dehydrogenation of 1-butene.
TL;DR: In this article, a macrocycle-mediated dual-hulled fiber membrane conformer was used to separate metal cations in aqueous solution by using dicyclohexano-18-crown-6 as the carrier.
Abstract: Separation of metal cations in aqueous solution by a macrocyclemediated Dual Hollow Fiber Membrane Contactor is described. The advantages of this type of supported liquid membrane configuration include easily accessible source, receiving and membrane phases; transport rates competitive with those of other types of membranes; and the potential for continuous operation. The new system was investigated to determine the effect of aqueous solution flow rate and membrane solvent stirring rate on Na+ and K+ transport using dicyclohexano-18-crown-6 as the carrier. The results demonstrated that transport increases with increasing stirring speed, but remains constant with increased aqueous flow rate through the fibers within the range of four to twelve m1/min. The membrane solvents hexane, toluene, octane, 1-octanol, 4-methyl-2-pentanone, octanal, and 2-octanone were tested for their ability to preserve membrane integrity in the presence of aqueous solutions of low pH, and to maximize transport. Of these s...
TL;DR: In this article, the authors studied the transport of Mo(VI) ions through tri-n-octylamine (TOA)-xylene liquid membranes supported in polypropylene hydrophobic microporous film.
Abstract: The study of Mo(VI) ions transport through tri-n-octylamine (TOA)-xylene liquid membranes supported in polypropylene hydrophobic microporous film has been performed with varying concentrations of HC1, TOA, and NaOH in the feed membrane, strip solution, and temperature. Maximum flux of the order of 1.62 × 10−4 mol · m−2 · s−1 and permeability of 2.51 × 10−10 m2/s at 1.35 mol/dm3 TOA and 0.1 mol/dm3 NaOH at 35 ± 2°C have been observed. The flux of metal ions increases with an increase in temperature. Decomposition of [Mo7O24]6- ions into lower species appears to occur, and a pH decrease in the feed with the passage of time during transport of these metal ions is an indication of this effect. Mixed polymetal anions appear to be responsible for complexing with TOA molecules and the transport through the membrane. The transport mechanism of this metal ion through the membrane is based on the association of metal anions with protonated tri-n-octylamine (TOA) molecules on the feed-side interface, diffus...