Oxygen dissolution and transport in cobaltporphyrin-bound organophosphazene membranes

Rubbery poly(organophosphazene)s were synthesized, and were combined with cobaltporphyrin (CoP) which binds molecular oxygen rapidly and reversibly. The apparent oxygen-binding equilibrium constant (K_app) is in proportion to the physical solubility coefficient of oxygen in the polymer, although the reduced equilibrium and thermodynamic parameters are not dependent on the polymer matrix species. Diffusivity of oxygen via the fixed CoP(D_C) is enhanced for poly(organophosphazene) membranes with a larger oxygen diffusion constant. Poly(organophosphazene) membranes with both a large K_app and D_C yield high oxygen permeability.     

Ion transport across a bilayer lipid membrane facilitated by valinomycin

The facilitated ion transport from one aqueous phase, W1, to another, W2, across a bilayer lipid membrane, BLM, containing valinomycin, Val, as an ionophore was investigated by voltammetry. Cyclic voltammograms for the ion transfer were symmetrical about the origin (0 V, 0 A) and the magnitude of the ion transfer current increased with an increase in the absolute value of the applied potential. The magnitude of the ion transfer current at a definite potential in the voltammograms depended on the cation species added to W1 and W2 and was proportional to the concentration of Val in the BLM. The magnitude of the ion transfer current at a definite potential also varied in proportion to the hydrophobicity of the counter anion in W1 and W2. Taking into account the conjugated ion transfers at the W1|BLM and BLM|W2 interfaces, the positive current that flowed from W1 to W2 across the BLM was attributable to both the transfer of the complex-forming cation from W1 to the BLM and the transfer of the anion, which was distributed in the BLM as the counter ion from W2 to W1. The transfer from the BLM to W1 occurred at the W1|BLM interface and both the transfer of the cation from the BLM to W2 and the transfer of the anion from W2 to the BLM at the BLM|W2 interface. The negative current was then attributed to the opposite reaction. The voltammograms were asymmetrical with the origin when the ion components in W1 and W2 were different.     

Investigation of the carrier saturation in facilitated transport of unsaturated hydrocarbons

Single-component facilitated transports of ethylbenzene, styrene, cyclohexene and 1-hexene were carried out using the feed concentrations ranging from 0.5 M to pure. Equilibrium constants of the Ag⁺-solute complex formation, determined by distribution method, were 0.7, 2.2, 32.0, 129.1 M⁻¹, respectively. Carrier saturation was not found with the membrane incorporated with 2.67 M Ag⁺-ion. As the carrier concentration was reduced to 0.51 M, increase in the feed concentration beyond 4.5 M had very little effect on ethylbenzene flux, suggesting the onset of carrier saturation. Styrene and cyclohexene underwent the carrier saturation when the carrier loading was 0.25 M, while a complete saturation was not observed with 1-hexene. Extraction of solute from the membranes revealed that less than 50% of Ag⁺-ions were occupied when the carrier saturation occurred. It was also found that the ability of solute to use available Ag⁺-ions in the membrane was dependent on the equilibrium constant.     

Improvement of the performance of facilitated transport membrane process through nonuniformity

Facilitated transport process has attracted much attention because high selectivity and high permeability may be achieved. However, most research on facilitated transport process is concerned only with uniform membranes. In this paper, a model predicting the gas separation performance of a hollow-fiber module with facilitated transport membrane is developed. The influence of feed rate, operation pressure, and permeant-feed flow pattern on the module performance are analyzed and the effect of the nonuniform distribution of reaction equilibrium constant is examined. The calculated results show that the nonuniform active distribution may cause an improved module performance. Because of the passive transport characteristics of the facilitated transport process, the mass transfer driving force across the membrane has a great influence on the improvement of the module performance through a facilitated transport effect.     

氟涂层对聚合物-钴卟啉膜氧气输送性能及其寿命的影响

采用在聚合物-钴卟啉(CoP)膜表面旋转涂覆氟涂料法,制备了氧/氮分离膜.研究表明,与未涂层膜相比,氟涂层膜中的CoP与氧表观结合平衡常数、膜的氧渗透系数和氧/氮选择性没有发生明显变化.随氟涂层厚度增加,氧渗透系数稍有降低,但水蒸汽渗透系数显著降低.由于氟涂层的憎水性,使涂层膜的水蒸汽渗透系数显著降低,氧载体CoP与氧结合寿命延长了4倍.     

The effect of the counter anion on the transport of thiourea in a PVC-based polymer inclusion membrane using Capriquat as carrier

This paper describes the effect of four counter anions (CH₃COO⁻, Cl⁻, NO₃⁻, ClO₄⁻) of the trioctylmethylammonium (TOMA) cation on the rate of solvent extraction of thiourea and its transport across poly(vinyl chloride) (PVC)-based polymer inclusion membranes (PIMs). The membranes also contained 2-nitrophenyl octyl ether (NPOE) as the plasticizer while chloroform was used as diluent in the solvent extraction studies. It is demonstrated that the counter anion affects substantially the rate of membrane transport and the degree of extraction follows the order: CH₃COO⁻ > Cl⁻ > NO₃⁻ ? ClO₄⁻. The transport rate is negligible for the perchlorate anion. This order is consistent with thiourea interacting with the counter anion through hydrogen bonding to form a heteroconjugate anion.     

Facilitated transport of Am(III) through a flat-sheet supported liquid membrane (FSSLM) containing tetra(2-ethyl hexyl) diglycolamide (TEHDGA) as carrier

Facilitated transport of Am(III) in nitric acid medium using tetra(2-ethyl hexyl) diglycolamide (TEHDGA) in n-dodecane as carrier was studied. It was aimed at finding out the physico-chemical model for the transport of Am(III) using TEHDGA/n-dodecane as carrier under various experimental parameters like feed acidity, carrier concentration, varying strippant, varying membrane pore size, etc. The feed acidity and carrier concentrations were varied from 1 M to 6 M HNO₃ and 0.1 M to 0.3 M TEHDGA/n-dodecane, respectively. The transport of Am(III) increased with increase in feed acidity and carrier concentration reaching maximum at 3 M HNO₃ and 0.2 M TEHDGA/n-dodecane, respectively. Several stripping agents were tested and 0.1 M HNO₃ was found to be the most suitable stripping agent for this system. Almost quantitative transport of Am(III) was observed at about 180 min with feed acidity of 3 M HNO₃, 0.1 M HNO₃ as strippant and 0.2 M TEHDGA/n-dodecane as carrier. The pore size of the membrane support was varied from 0.20 μm to 5 μm and the permeation coefficient increased with increase in pore size up to 0.45 μm (2.43 × 10⁻³ cm/s), and then decreased with further increase in pore size. The plot between permeation coefficient vs. (membrane thickness)⁻¹ was linear which showed that the Am(III) transport was membrane diffusion limited. The membrane diffusion coefficient calculated from the graph was found to be 1.27 × 10⁻⁶ cm²/s and its theoretical value was 1.22 × 10⁻⁶ cm²/s. The stability of the carrier against leaching out of the membrane support as well as the integrity of membrane support was studied over a period of 30 days and was found to be satisfactory within the studied time period.     

Quantitative analysis of transport process of cerium(III) ion through polymer inclusion membrane containing N,N,N′,N′-tetraoctyl-3-oxapentanediamide (TODGA) as carrier

The facilitated transport mechanism of cerium(III) ions through polymer inclusion membrane (PIM) consisting of cellulose triacetate (CTA) as a polymer matrix, 2-nitrophenyl n-octyl ether (NPOE) as a solvent and N,N,N′,N′-tetraoctyl-3-oxapentanediamide (TODGA) as a carrier was studied. In order to evaluate the mass transport phenomena in the PIM, a mathematical model was derived from the Fick's first law and the equations for the extraction and the material balance. Methods to determine the values of the transport parameters such as the diffusion coefficient are described, and the dependency of the flux on the experimental condition was calculated. The model is very useful as a design tool to analyze and optimize the concentration process of low level radioactive wastewater using the PIM.     

聚合物-卟啉钴复合膜的氧气促进输送性能

综述了聚合物－卟啉钴复合膜的氧气促进输送性能。讨论了卟啉钴的结构及与氧的结合性能，聚合物－卟啉钴复合膜的氧气促进输送特性，影响聚合物－卟啉钴复合膜氧气透过性能的因素及卟啉钴的不可逆氧化反应机理。     

Facilitated Cd(II) transport across CTA polymer inclusion membrane using anion (Aliquat 336) and cation (D2EHPA) metal carriers

PIMs have been involved as affinity membranes for recovery of metals (Cd, Pb, Zn) by facilitated transport from aqueous solutions under different speciation forms, either anionic or cationic. The motivation of this work is to compare the efficiency of the recovery process in the case of Cd(II) using extractants such as D2EHPA and Aliquat 336 that can form complexes with the cation Cd²⁺ or the anions CdCl₃⁻ and CdCl₄²⁻, respectively. The maximal Cd(II) recovery factors obtained in 8 h are 97.5% and 91.8% with D2EHPA and Aliquat 336, respectively. Although the transport fluxes with both carriers are not strongly different (ca. 2 μmol m⁻² s⁻¹), the recovery process in case of mixture of metals is better achieved with Aliquat 336. PIMs have shown a very good stability and a constancy of the transmembrane transport flux over 12 replicate measurements, each one lasting for 8 h repeated every 24 h.     

含氟共聚物与钴卟啉复合膜的制备及促进氧输送性能

研究了甲基丙烯酸八氟戊酯-乙烯基咪唑共聚物与钴卟啉复合膜的制备及钴卟啉与氧络合、促进输送性能.共聚物中的咪唑基与钴卟啉的第五配位点在溶液中络合,制得的复合膜具有快速和可逆的氧结合特性.温度降低,钴卟啉与氧络合的平衡常数增加;膜中的钴卟啉与氧络合平衡常数大于N,N-二甲基甲酰胺(DMF)溶液中的平衡常数.钴卟啉与氧络合和选择性地促进氧的输送使共聚物/钴卟啉复合膜的氧渗透系数和氧/氮选择系数提高.     

Liquid membrane transport of cytochrome c using a calix[6]arene carboxylic acid derivative as a carrier

The present study examined the liquid membrane transport of the cationic protein cytochrome c, using the macrocyclic compound calix[6]arene, which is a carboxylic acid derivative, as a carrier. The transport rate was governed by carrier concentration and the pH gradient between the feed and the receiving phases, as well as the salt concentration in the aqueous phases. Transport of cytochrome c was examined using a series of calix[n]arene carboxylic acid derivatives (n = 4, 6 and 8). Cytochrome c successfully permeated membranes in the presence of the calix[6]arene derivative. Liquid membrane separation of cytochrome c from a mixture of cationic proteins was demonstrated under optimal conditions. Cytochrome c was selectively extracted by the calix[6]arene carboxylic acid derivative and 77% of the extracted cytochrome c was recovered into the receiving phase. In this liquid membrane system, which discriminates between the number of lysine residues on the surface of proteins, cationic proteins with similar molecular weights and pIs were separated with macrocyclic compounds.     

Selective metal ion transport through polymer inclusion membrane containing surfactin as carrier reagents

Metal ion selective polymer inclusion membrane (PIM) was prepared by using cellulose triacetate as matrix, surfactin (SF) as ion carrier, and 2-nitrophenyl n-octyl ether as plasticizer. The structure and morphology of the prepared PIM were characterized by means of thermogravimetric analysis, scanning electron microscopy, and Fourier transform infrared spectroscopy. The effects of plasticizer and the amount of SF to ionic membrane flux were investigated, and the optimized component was obtained thereof. The selectivity of the membrane toward metal cation was studied and the order of Ni(II) > Ca(II) > Co(II) > Pb(II) > Cu(II) > Mg(II) was followed. In addition, the durability of the PIM was studied by successive reuse of the membrane, and the ionic flux slightly decreased after five cycles of reuse, indicating the excellent durability of the PIM.     

Effect of the polarity of silver nanoparticles induced by ionic liquids on facilitated transport for the separation of propylene/propane mixtures

The effect of ionic liquids on the formation of a partial positive charge on the surface of silver nanoparticle and its subsequent effect on facilitated olefin transport were investigated. Three different ionic liquids of 1-butyl-3-methylimidazolium tetrafluoroborate (BMIM⁺BF₄⁻), 1-butyl-3-methylimidazolium triflate (BMIM⁺Tf⁻), and 1-butyl-3-methylimidazolium nitrate (BMIM⁺NO₃⁻) were employed to control the positive charge density of the surface of silver nanoparticles. The positive charge density of the silver nanoparticles, as characterized by the binding energy of the silver atom, was in the following order: BMIM⁺BF₄⁻/Ag ? BMIM⁺Tf⁻/Ag > BMIM⁺NO₃⁻/Ag. This order was consistent with the tendency of ionic liquids to form free ions. The best separation performance for the propylene/propane mixtures was a mixed gas selectivity of 17 and a permeance of 7 GPU through a composite membrane consisting of BMIM⁺BF₄⁻/Ag. A better separation performance for olefin/paraffin mixtures was observed with a higher positive charge density of the silver nanoparticles. It was therefore concluded that facilitated olefin transport was a direct consequence of the surface positive charge of the silver nanoparticles induced by ionic liquids.     

Facilitated transport of copper(II) across supported liquid membrane and polymeric plasticized membrane containing 3-phenyl-4-benzoylisoxazol-5-one as carrier

The potential of 3-phenyl-4-benzoylisoxazol-5-one (HPBI) as metal extractant has been evaluated for the first time for Cu(II) transport from aqueous nitrate solutions by supported liquid membrane (SLM) in the solvents chloroform, 2-nitro phenyl octyl ether (NPOE) and dodecyl nitro phenyl ether (DNPE). The efficiency of the membrane transport was optimized as a function of pH, temperature, aqueous phases and membrane composition. It follows the sequence CHCl₃ > DNPE > NPOE. The results suggested that the transport mechanism was mainly controlled by the diffusion of the Cu(PBI)₂ complex in the membrane core. A comparative investigation of Cu(II) transport ions has been made between SLM and polymeric plasticized membrane (PPM), containing HPBI with NPOE and DNPE as organic solvents or plasticizers in order to evaluate the feasibility of PPM with HPBI.     

Facilitated transport of CO2 across a liquid membrane: Comparing enzyme, amine, and alkaline

In this work we compare the efficiency of facilitated transport of CO₂ across a liquid membrane by different facilitators as tested in either a supported liquid membrane (SLM) or a hollow fiber contained liquid membrane (HFCLM) configuration. Permeance and selectivity were evaluated by both experimental test and numerical simulation. These comparisons were used to define the best liquid membrane composition to maximize separation performance. We also consider other factors that affect the choice of the facilitator, e.g. operation temperature and cost. Under ambient operating conditions, carbonic anhydrase (CA) combined with an alkaline carbonate gives better performance than does diethanolamine (DEA).     

Facilitated transport of CO2 in novel PVAm/PVA blend membrane

A defect-free ultra thin PVAm/PVA blend facilitated transport membrane cast on a porous polysulfone (PSf) support was developed and evaluated in this study. The target membrane was prepared from commercial polyvinyl amine (PVAm) and polyvinyl alcohol (PVA). Effects of experimental conditions were investigated for a CO₂–N₂ mixed gas. A CO₂/N₂ separation factor of up to 174 and a CO₂ permeance up to 0.58 m³(STP)/(m² h bar) were documented. Experimental results suggest that CO₂ is being transported according to the facilitated transport mechanism through this membrane. The fixed amino groups in the PVAm matrix function as CO₂ carriers to facilitate the transport whereas the PVA adds mechanical strength to the blend by entanglement of the polymeric chains hence creating a supporting network. The good mechanical properties obtained from the blend of PVA with PVAm, enabled an ultra thin selective layer (down to 0.3 μm) to be formed on PSf support (with MWCO of 50,000), resulted in both high selectivity and permeance. The PVAm/PVA blend membrane also exhibited a good stability during a 400 h test.     

Formation and characterization of asymmetric nanofiltration membrane: Effect of shear rate and polymer concentration

In this study, we report the effects of shear rates and polymer concentrations in the formation of asymmetric nanofiltration membrane using a simple dry/wet phase inversion technique. Employing the combination of irreversible thermodynamic model, solution-diffusion model (Spiegler–Kedem equation), steric-hindrance pore (SHP) model and Teorell–Meyers (TMS) model, the transport mechanisms and membrane structural properties were determined and have been characterized for different cases of those formation parameters. The experimental and modeling showed very promising results in terms of membrane performance with interesting structural details. The optimum shear rate (critical shear rate) was found to be at about 203.20 s⁻¹ and the best polymer concentration toward the formation of high performance nanofiltration membrane is in the range of 19.60–23.10%. The modeling results suggested that the pore radius of the membranes produced lies within the range of pore radius of 29 commercial available membranes. This study also proposed that the electrolytes transport through nanofiltration membrane was dominated by a convection factor which accounted approximately 30% more than a diffusion factor. This study also indicated that shear rate and polymer concentration were found to affect the membrane performance and structural properties by providing, to a certain extent, an oriented membrane skin layer which in turn exhibiting an improvement in membrane separation ability.     

Gas transport property of polyallylamine–poly(vinyl alcohol)/polysulfone composite membranes

Polyallylamine (PAAm) was synthesized by free radical polymerization and characterized by Fourier transform infrared resonance (FT-IR) spectroscopy, hydrogen nuclear magnetic resonance (¹H NMR) spectroscopy and differential scanning calorimetry (DSC). The composite membranes were prepared by using PAAm–poly(vinyl alcohol) (PVA) blend polymer as the separation layer and polysulfone (PSF) ultrafiltration membranes as the support layer. The surface and cross-section morphology of the membrane was inspected by environmental scanning electron microscopy (ESEM). The gas transport property of the membranes, including gas permeance, flux and selectivity, were investigated by using pure CO₂, N₂, CH₄ gases and CO₂/N₂ gas mixture (20 vol% CO₂ and 80 vol% N₂) and CO₂/CH₄ gas mixture (10 vol% CO₂ and 90 vol% CH₄). The plots of gas permeance or flux versus feed gas pressure imply that CO₂ permeation through the membranes follows facilitated transport mechanism whereas N₂ and CH₄ permeation follows solution–diffusion mechanism. Effect of PAAm content in the separation layer on gas transport property was investigated by measuring the membranes with 0–50 wt% PAAm content. With increasing PAAm content, gas permeance increases initially, reaches a maximum, and then decreases gradually. For CO₂/N₂ gas mixture, the membranes with 10 wt% PAAm content show the highest CO₂ permeance of about 1.80 × 10⁻⁵ cm³ (STP) cm⁻² s⁻¹ KPa⁻¹ and CO₂/N₂ selectivity of 80 at 0.1 MPa feed gas pressure. For CO₂/CH₄ gas mixture, the membranes with 20 wt% PAAm content display the highest CO₂ permeance of about 1.95 × 10⁻⁵ cm³ (STP) cm⁻² s⁻¹ KPa⁻¹ and CO₂/CH₄ selectivity of 58 at 0.1 MPa feed gas pressure. In order to explore the possible reason of gas permeance varying with PAAm content, the crystallinity of PVA and PAAm–PVA blend polymers was measured by X-ray diffraction (XRD) spectra. The experimental results show an inverse relationship between crystallinity and gas permeance, e.g., a minimum crystallinity and a maximum CO₂ permeance are obtained at 20 wt% PAAm content, indicating that the possibility of increasing CO₂ permeance with PAAm content due to the increase of carrier concentration could be weakened by the increase of crystallinity.