Pore-filled Membranes Research Articles

Modelling of the pore structure variation with pH for pore-filled pH-sensitive poly(vinylidene fluoride)–poly(acrylic acid) membranes

Pore structure variation as a function of pH was investigated for the pore-filled pH-sensitive poly(acrylic acid)-poly(vinylidene fluoride) membranes. The pore radius reduced drastically as the poly(acrylic acid) gel incorporated inside the nascent substrate, which is from 113 nm of nascent substrate to as low as 7.0 nm of pore-filled membranes at pH acidic. For the membranes, the pore radii at pH neutral estimated by the extend Nernst–Planck equation (2.76–4.20 nm) and by the Spiegler–Kedem model with the steric-hindrance pore model (3.4–4.1 nm) are close to each other and comparable with that calculated from the poly(acrylic acid) gel correlation length (1.79–2.93 nm). The calculated pore density at pH neutral (49–258 × 10 14 m −2) is much higher than that at pH acidic (2.8–39.8 × 10 14 m −2). The results are interpreted in terms of the gel structure in the pore-filled membranes.

Temperature responsive pore‐filled membranes based on a BSA/poly(N‐isopropylacrylamide) hydrogel

AbstractA temperature‐sensitive hydrogel based on a copolymer of BSA and poly(N‐isopropylacrylamide) (PNIPAAm) has been synthesized using carbodiimide chemistry. Fourier transform infrared spectroscopy confirmed primary complex formation between carbodiimide‐activated carboxylic acids on the protein with protein amino groups. As a result of temperature‐induced conformational changes in PNIPAAm grafted onto the protein backbone, these protein hydrogels show significant morphological changes in response to temperature. The structural changes of the gels in response to temperature were assessed using scanning electron microscopy, and the effect of temperature on their balance of hydrophobicity was found using turbidity measurements. Composite pore‐filled membranes formed by impregnating glass fiber filters with the polymer mixture prior to gelation were used to determine permeability changes in response to temperature using both low (riboflavin) and intermediate (lysozyme) molecular weight diffusates. Clear correlation was found between changes in morphology, turbidity, and gel permeability as the gel temperature was increased from 24–37°C. In the case of permeability studies, significant transport of lysozyme only occurred at temperatures above the lower transition temperature of the hydrogel, suggesting the gel was acting as a mechanical “valve'' to control flux. © 2008 Wiley Periodicals, Inc. Adv Polym Techn 27:27–34, 2008; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/adv.20113

Preparation of radiochemically pore-filled polymer electrolyte membranes for direct methanol fuel cells

Polymer electrolyte pore-filled membranes, for possible use in direct methanol fuel cells (DMFCs), have been prepared by radiochemical grafting of styrene into porous poly(vinylidene fluoride) (PVDF) films using simultaneous irradiation with an electron beam (EB) followed by a sulfonation reaction. The physico-chemical properties of the obtained polystyrene sulfonic acid pore-filled membranes are evaluated using Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), ac impedance, and a methanol diffusion cell. The effects of variation of the grafting yield ( Y%) on the ionic conductivity and the methanol permeability of the membranes are investigated. The ionic conductivity of the membranes increases with increase in Y% and exceeds that of the perfluorinated ionomer membrane, Nafion 117, at a grafting yield of 46%. The methanol permeability of 40 and 46% pore-filled membranes is lower than that of Nafion 117 by 53 and 71%, respectively. The performance characteristic factor suggests that these membranes are potential candidates for DMFC applications.

DMFC performances using a pore-filling polymer electrolyte membrane for portable usages

To develop portable direct methanol fuel cells (DMFCs) with high power density, a high concentration of methanol in aqueous solution must be used as the fuel. We have developed a new type of membrane, namely the pore-filling membrane, and its membrane–electrode assembly (MEA) gives high DMFC performance with high concentration methanol fuel (around 10 M). The results were compared with a commercial Nafion membrane MEA.

Coupled-diffusion transport of Cr(VI) across anion-exchange membranes prepared by physical and chemical immobilization methods

Anion-exchange membranes with different configurations were examined for the removal of Cr(VI) from aqueous medium. The polymer inclusion membranes (PIM) were formed by physical immobilization of an organic anion-exchanger Aliquat-336 into the matrix of plasticized cellulose triacetate (CTA). The supported liquid membrane (SLM) was prepared by impregnating microporous poly(propylene) host membrane with an organic phase containing Aliquat-336. The pore-filled membrane (PFM) was prepared by anchoring poly(vinyl benzyl chloride) (PVBCl) within the pores of a poly(propylene) microporous host membrane by in situ crosslinking of PVBCl with a diamine 1,4-diazabicyclo[2.2.2.]octane (DABCO). The resulting PVBCl-filled precursor membrane was converted to anion-exchange membrane by reacting it with excess of DABCO followed by alkylation with α,α′-dibromo- p-xylene. The permeability of Cr(VI) across these membranes from aqueous feed having pH 2 or 8 was studied. The choice of these two pH was based on the fact that Cr(VI) exists in aqueous medium as HCrO 4 −/Cr 2O 7 2− at pH 2 and CrO 4 2− at pH 8. In the concentration range of Cr(VI) used in the permeation experiment (≈10 −6 mol/L), HCrO 4 − is expected to be the predominant Cr(VI) species in the aqueous solution at pH 2. However, the IR spectra of membrane samples loaded with different amounts of Cr(VI) from aqueous solution containing 10 −6 mol/L of Cr(VI) at pH 2 indicated that HCrO 4 − dimerizes to Cr 2O 7 2− in the membrane phase. The permeability coefficients ( P) of Cr(VI) across PIM, SLM and PFM were measured using 1 mol/L NaNO 3 as a receiver phase. The permeability coefficient ( P) values of Cr(VI) were found to be P(PFM) ≈ P(SLM) > P(PIM) at pH 2 and, P(PFM) > P(SLM) ≈ P(PIM) at pH 8. It was also observed that the P-values for Cr(VI) across PFM were similar from aqueous feed at pH 2 and 8. However, the P-value of Cr(VI) across PIM and SLM from aqueous feed at pH 2 was found to be significantly higher than that at pH 8. In order to understand the variations in P-values of Cr(VI) in these membranes, the self-diffusion coefficients of Cr(VI) were measured in these membranes by radiotracer isotopic-exchange method. In order to optimize PIM, the permeability of Cr(VI) across PIMs made up of different plasticizers were studied. An attempt was made to explain the permeability of Cr(VI) in different PIMs in terms of dielectric constant of the plasticizer which plays an important role in Cr(VI) transport across the PIM. The PIM and PFM were found to be effective for recovery of Cr(VI) from municipal water. However, only PIM could quantitatively recover Cr(VI) from seawater.

溶媒分離膜および燃料電池用電解質膜としての細孔フィリング膜の開発・設計

A new membrane, called the pore-filling membrane, was proposed. The membrane is composed of two kinds of polymer materials. One is a porous substrate film or hollow fiber which is inert to organic liquids, and the other is a polymer, soluble with only specific solvents, filling the substrate pores. The solubility difference of the filling polymer exhibits permselectivity, and the substrate matrix restrains the swelling of the filling polymer. The membrane showed high separation performances based on the concept, and moreover the membrane performances can be predicted by model simulation. Thus, membrane design can be realized with high performances. Also, the pore-filling membrane can be used for membranes of polymer electrolyte fuel cells. Proton conductivity was achieved through the filling electrolyte polymer inside the porous matrix. Fuel crossover was restricted by suppression of the swelling of the electrolyte polymer, and the mechanical strength at high temperature was maintained by the substrate. The membrane showed high fuel cell performances for both PEMFC and DMFC.

燃料電池用高分子膜の最前線 高分子電解質膜設計のためのシステム的アプローチ

A new type of fuel cell materials, especially polymer electrolyte membrane (PEM), has been developed based on the systematic approach. In this approach, some functions needed for fuel cell applications are separated to some different materials. Pore-filling membrane has been developed, which is composed of substrate matrix and filling polymer and they have some different functions. This method leads to an excellent membrane. On the other hand, it is found that the suppression of methanol permeation and the proton conductivity have a trade-off relationship, with the same filling polymer. Therefore, based on this relationship, the performance of membrane has been able to control with the concept of pore-filling membrane. In addition to this, a mathematical model, which can couple the performance of PEM with its fuel cell performance, has been developed and subsequently used for selecting appropriate membrane for applications. The fuel cell performance has been estimated with the model based on some parameters, divided into physicochemical and structural properties. Some guideline and information have been obtained to design or select the materials, i.e., higher proton conductive membrane should be selected when higher current density is needed, whereas lower methanol permeable membrane should be selected when higher voltage is needed. Fuel cell system has complicated hierarchical structures. Therefore, it becomes virtually impossible to solve some problems for fuel cell application with partially specialized knowledge. Structural design of whole fuel cell system should be considered as for optimization of its performance and development of PEM, which can be used in actual applications. The systematic approach, reported here, will be one of the key methods.

A Pore-Filling Electrolyte Membrane-Electrode Integrated System for a Direct Methanol Fuel Cell Application

To develop a high performance direct methanol fuel cell, a novel electrolyte membrane is needed. This electrolyte membrane should be durable up to 130°C to improve the catalytic reaction, and the methanol crossover should be reduced. Our approach was to design a pore-filling-type polyelectrolyte membrane, where the polyelectrolyte is filled into the pores of a porous substrate. This makes an integrated system with a membrane and a catalyst layer. The porous substrate was completely inert to aqueous methanol solution and was durable at high temperature. The substrate matrix could suppress membrane swelling to reduce methanol crossover, and showed mechanical strength at high temperatures. A radical polymerization technique was employed to fabricate the pore-filling membrane. A porous silica sol-gel thin base membrane on a carbon electrode was used as a membrane-electrode integrated system. The substrate pores were filled with a poly(acrylic acid-co-vinyl sulfonic acid) network. The membranes showed high proton conductivity, thermal stability, and low methanol permeation. © 2002 The Electrochemical Society. All rights reserved.

燃料電池用プロトン伝導膜 直接メタノール燃料電池用電解質膜の現状と新展開

To develop a high performance direct methanol fuel cell (DMFC), a novel electrolyte membrane is needed. This electrolyte membrane should be durable up to 130t to improve the catalytic reaction, and the methanol crossover should be reduced. Reported membranes are reviewed in this article, and our own approach is shown. Our approach is to design a pore-filling type polyelectrolyte membrane, where the polyelectrolyte is filled into the pores of a porous substrate, and the membrane swelling is suppressed by the substrate matrix. Proton conductivity was achieved through the filling electrolyte polymer. Methanol permeation was controlled by the swelling of the electrolyte polymer, and the mechanical strength at high temperature was maintained by the substrate. From this concept, a high proton conductivity was shown to exist with reduced membrane methanol permeability, and in addition, a heat-resistance was also achieved.

Ultra-low-pressure water softening with pore-filled membranes

The design parameters for high-performance, ultra-low-pressure water softening membranes based on a construct involving pore-filling microporous substrates with polyelectrolyte gels are presented. The design parameters were then used to make a series of gel-filled membranes by in situ crosslinking of poly(vinylbenzyl chloride) with diamines (piperazine and 1,4-diazabicyclo[2.2.2]octane) or poly(4-vinylpyridine) with dihalides such as α,α'-dichloro- p-xylene in DMF solutions in the pores of either a TIPS poly(propylene) or non-woven ultra-high molecular weight poly(ethylene) support. The separation properties of these membranes were tested under ultra-low pressure (100 kPa) using untreated municipal tap water. These membranes exhibit excellent separation properties, comparable to those of a commercial thin-film nanofiltration membrane (Desal-51, Osmonics), and productivity (flux) markedly higher than that of the thin-film membrane. The results of this study clearly show the importance of the mechanical strength (rigidity) of the microporous supports in designing high-performance pore-filled membranes.

Hollow-fiber-type pore-filling membranes made by plasma-graft polymerization for the removal of chlorinated organics from water

Hollow-fiber-type pore-filling membranes were prepared to reduce the emission of toxic chlorinated organics into the environment. These membranes can remove 1,1,2-trichloroethane (TCE) or dichloromethane (DM) from water, and concentrate them in the permeate. The pore-filling membrane can efficiently remove organics from water because of the suppression of the membrane swelling by the porous substrate matrix, and the fact that it can maintain a high solute diffusivity, because of the linear graft chains that fill the substrate pores. Laurylacrylate (LA) or n-butylacrylate (BA) grafted layers were formed inside the porous hollow-fiber substrate, and the pores were filled with the grafted chains formed from plasma-initiated graft polymerization. The hollow-fiber-type LA-grafted membranes showed extremely high separation properties: a 0.09 wt.% TCE aqueous solution was condensed to 99 wt.% TCE in the permeate. The membrane can remove TCE from a water stream, and at the same time, the membrane can purify the TCE for re-use. The membrane also showed high separation performance for an aqueous DM solution. The mass transfer resistance outside the membrane was estimated by using a concentration polarization model. When the mass transfer coefficient at the membrane and feed stream boundary layer was below 10 −4 m/s, the boundary layer resistance affected the membrane performance. This needs to be taken into account when designing the membrane module and operating conditions.

Selective permeation of CO 2 through pore-filled polyacrylonitrile membrane with poly(ethylene glycol)

Pore-filling concept was applied to prepare high permselective composite membranes for CO 2 separation. The membrane is composed of two polymeric materials: a porous substrate and filling polymers that fills the pore of the substrate. In this study, asymmetric polyacrylonitrile (PAN) membrane was used for a substrate and methoxy poly(ethylene glycol) acrylate (MePEGA, M w=454) was used for a photoinitiated graft polymer. The analysis of graft membrane by Fourier transform infrared and attenuated total reflection (FT-IR, FT-IR/ATR), electron spectroscopy for chemical analysis (ESCA) and field emission scanning electron microphotography (FE-SEM) revealed that the graft polymer filled the pores of the substrate. High CO 2/N 2 permselectivity was shown by this pore-filling membrane: carbon dioxide permeation flux, J CO 2 =5.65 GPU (10 −6 cm 3(STP)/cm 2 s cmHg) and selectivity of CO 2 over N 2, J CO 2 / J N 2 =32.4 at 30°C, measured by the time-lag method. The high permselectivity of the present pore-filling membrane is attributed to the high solubility selectivity due to the affinity of CO 2 to PEO segment.

Nanofiltration using pore-filled membranes: effect of polyelectrolyte composition on performance

Several series of membranes composed of microporous poly(propylene) substrates filled with polyelectrolyte gels of different chemical structure, polymer concentration and charge densities have been prepared in order to examine the effect of polyelelctrolyte composition on the performance of these membranes in nanofiltration. The membranes were made by two different routes involving either in situ chemical cross-linking of poly(4-vinylpyridine) or poly(vinylbenzyl chloride), or by in situ polymerization of acrylic acid with tetra(ethylene glycol) diacrylate or N,N-methylenebisacrylamide as cross-linking agents in the pores of the substrates. The resulting pore-filled membranes were characterized by the concentration (volume fraction) of the polyelectrolyte in the pores, ion exchange capacity (charge density), water content, and thickness. The different series of membranes were tested under pressure to determine their hydrodynamic permeabilities and salt separation properties (NaCl). It was found that there was a good correlation between hydrodynamic (Darcy) permeability and gel polymer concentration that holds irrespective of the gel polymer chemistry in the pore-filling gels. Membranes with different pore-filling gels, whether positively or negatively charged, followed the same relationship. The separation properties of the membranes are very good and the salt rejection was found to be practically constant over a wide range of permeabilities (gel concentrations). It was also found that the increase in the nominal charge density above approximately 0.2 mmol/cm3 of the swollen gel had a negligible effect on the separation properties of the gel-filled membranes. The results of this study provide a basis for the further design and optimization of polyelectrolyte filled membranes for nanofiltration applications.

Ultra-low pressure water softening: a new approach to membrane construction

The ultra-low pressure water softening properties of a series of novel membranes containing cross-linked poly(4-vinylpyridinium) salts incorporated into the pores of polyethylene or polypropylene microfiltration membranes have been examined. It has been shown that these membranes exhibit excellent separation properties with high permeabilities at low trans-membrane pressures. The separation mechanism in these pore-filled membranes is primarily due to Donnan exclusion, and as such bivalent cations are more strongly rejected than monovalent ions. Moreover, it has been shown that relatively large molecules such as sucrose are only rejected to a limited extent. The membranes have been shown to withstand free chlorine at ambient temperatures. The performance of the pore-filled membranes has been shown to compare favorably with existing state of the art thin-film composite (TFC) nanofiltration membranes (Osmonics Desal-51 and BQO1 and Hydranautics TFV-7450). In contrast to the TFC membranes, the separating layer in these pore-filled membranes has been shown to be thick, ranging from 80 to 160μm. These polyelectrolyte opre-filled membranes offer a new paradigm in the construction of high performance water softening membranes.

Polyacrylic acid pore-filled microporous membranes and their use in membrane-mediated synthesis of nanocrystalline ferrihydrite

Polyacrylic acid pore-filled microporous membranes and their use in membrane-mediated synthesis of nanocrystalline ferrihydrite