Transport and conductivity properties of an advanced cation exchange membrane in concentrated sodium hydroxide

An electrochemical concentrator for application to the chlorine-caustic industry is currently under development. In it 30 to 35 wt % NaOH enters the anolyte and catholyte chambers and exits at 20 and 50 wt %, respectively. Consequently, in support of the electrochemical concentrator development, the conductance and transport properties of advanced cation exchange membranes in concentrated sodium hydroxide, are being investigated. The membrane voltage drop, sodium ion transport and water flux of these membranes in 20 to 35 wt % sodium hydroxide anolyte and 30 to 50 wt % sodium hydroxide catholyte at 75°C are presented. To better understand the behaviour of these membranes, electrolyte sorption measurements were conducted in the anolyte/catholyte environment appropriate for the electrochemical concentrator. The water uptake data appear to correlate well with the conductance data and the combined NaOH and water sorption data are consistent with the sodium ion transport data.     

Active transport and selective transport of alkali metal ions through polyelectrolyte complex membranes consisting of the three materials [2-(diethylamino)ethyl]dextran hydrochloride,sodium carboxymethyldextran,and sulfate of poly(vinyl alcohol)

Active and selective transport of alkali metal ions through the polyelectrolyte complex membranes consisting of [2-(diethylamino)ethyl]dextran hydrochloride, sodium carboxymethyldextran, and sulfate of poly(vinyl alcohol) have been investigated for the first time. The transport behavior was much affected by the hydrogen ion concentration. The driving force for the active transport of alkali metal ions was considered to be the hydrogen ion concentration. It was suggested that both the appropriate changes of chemical and physical properties of polyelectrolyte complex membrane and the affinity of the carrier fixed to the membrane for alkali metal ions controlled the active transport and selectivity through the membranes.     

Effect of ultraviolet irradiation on the selective transport of alkali metal ions through 2,3-epithiopropyl methacrylate–methacrylic acid copolymer membrane

Cationic exchange membranes were prepared with 2,3-epithiopropyl methacrylate (ETMA)–methacrylic acid (MAc) copolymer. Transport of alkali metal ions against their concentration gradient through the membranes was investigated by using the system which contains HCl (left side) and alkali metal solution including two kinds of alkali hydroxides (right side). The effect of ultraviolet (UV) irradiation on the selective transport of alkali metal ions through the ETMA–MAc copolymer membranes was investigated. The membranes were irradiated with a 6-W low pressure mercury lamp at a distance of 10 cm at room temperature in air. The transport selectivity could be increased by using UV-irradiated membranes and the selectivity increased with increasing irradiation time up to 2–3 h, although the transport rate of alkali metal ions decreased with increasing time of UV irradiation. The maximum selectivity of K⁺/Na⁺, Na⁺/Li⁺, and K⁺/Li⁺ were 1.7, 2.0, and 4.2, respectively. In order to explain this phenomena, the effect of UV irradiation on the properties of the membranes was studied. It was concluded that the increase of the selectivity is attributed to the formation of the dense membrane by photocrosslinking of the membrane by UV irradiation.     

Reverse Osmosis Transport of Alkali Halides and Nickel Salts through Cellulose Triacetate Membranes. Performance Prediction from NaCl Experiments

Abstract

The separation of alkali metal halides, nickel chloride, and nickel sulfate was determined for cellulose triacetate reverse osmosis (CTA RO) membranes. From transport analysis, the relative free energy parameters for transport of these salts through CTA membranes were determined. From these relative free energy parameters of salts, the solute separation by CTA membranes could be predicted from RO experiment with NaCl solution. The transport analysis and an illustration of how the concept is useful are presented in this paper.     

Preparation of Branch Polyethyleneimine (BPEI) Crosslinked Anion Exchange Membrane Based on Poly(styrene-b-(ethylene-co-butylene)-b-styrene) (SEBS)

Anion exchange membranes with chemical stability, high conductivity, and high mechanical properties play an important role in alkaline fuel cells. Here, a series of CPX anion exchange membranes based on poly(styrene-b-(ethylene-co-butylene)-b-styrene) (SEBS) and branch polyethyleneimine (BPEI) are achieved by casting, in which BPEI acts as both a crosslinking agent and an OH⁻ conducting functional group. The introduction of BPEI facilitates the formation of good hydrophilic/hydrophobic microphase separation structure, thus improving the ion transport channel of CPX membrane. The physicochemical and electrochemical properties of the CPX membrane are significantly improved when the mass ratio of SEBS to BPEI is within an appropriate range. The OH⁻ conductivity of the CP2 membrane (the mass ratio of SEBS to BPEI is 2) can reach 66.63 mS cm⁻¹ at 80 °C, and more than 80% initial OH⁻ conductivity is maintained in 1.0 m NaOH solution for 20 d at 60 °C. The strategy of using a polymer with excellent alkali resistance and oxidation resistance as the main body and introducing a conductive group that can construct microphase separation can simultaneously improve the conductivity and membrane stability. This viable strategy is a promising construction method for anion exchange membranes that can be applied to fuel cells.     

Progress in Applications of Polymer-Based Membranes in Gas Separation Technology

Separation of gases through polymeric membrane by selective transport has immense advantages such as light weight, economical, high process flexibility, and space requirements. Fabrication methods of polymeric membrane (polysulfone, polyimide, polyamide, polycarbonate) and their properties along with fundamental principles for gas separation mechanism are discussed in this review. Polysulfone membranes are fabricated by dry/wet phase inversion process to investigate membrane properties. Polyimide membranes show great potential for gas separation and reveal good selectivity for CO₂/N₂ and CO₂/CH₄ gas pairs. Transport characteristics of polycarbonate membrane are improved by functionalization. Superior properties allow potential use of polymeric membranes in large-scale industrial applications.     

Studies on syntheses and permeabilities of special polymer membranes

Summary An active transport of alkali metal ion through cation exchange membranes was studied under various conditions. This active transport was facilitated by using a greater anion species on an acidic side in a diaphragm cell, in which one side of the solution was adjusted to be acidic and the other side alkaline across the membrane. An active transport fraction of alkali metal ion was in order poly(styrenesulfonate)>benzenesulfonate>Cl^– >I^–>Br^– of anion species on the acidic side. A rate, fraction and period of the active transport of metal ion were significantly influenced by an electric potential gradient in the membrane.     

Analysis of transport phenomena in cellulose diacetate membranes

Summary Osmosis-dialysis transport properties and hydration characteristics were determined for various Manjikian type membranes. Some analogies were established between the behaviour of these membranes and the membranes of Loeb type. Particular attention was paid to show the generality of the correlations between the specific transport coefficients and the state of water (free or bound) in unilayer membranes.     

Gas transport and structural features of sulfonated poly(phenylene oxide)

The effect of ionomer structure on gas transport properties of membranes was investigated. For this purpose physical and transport properties of poly(phenylene oxide) (PPO) and its sulfonated derivative (SPPO) were compared. SPPO has a more rigid structure and a lower free volume, which determines low gas permeability and high permselectivity. Gas transport properties of two types of SPPO—PPO composite membranes with top layers prepared from solutions in methanol or N,N-dimethylacet-amide (DMA) were investigated. The use of SPPO solution in DMA leads to the formation of membranes with higher gas permeability. It was shown that DMA is a morphologically active solvent for SPPO. Strong complexes of SPPO with DMA are formed in solution and retained upon transition into the condensed state. The plasticizing effect of DMA on SPPO determines the high gas permeability of the membranes and is in agreement with their mechanical properties. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 66: 1439–1443, 1997     

New performance of a modified poly(amide-12-b-ethyleneoxide)

The purpose of this work was the investigation of the water vapour transport through thermoplastic dense films of a poly(amide-12-b-ethylenoxide) such as Pebax^®2533. Similar polymers have gained a unique position in many technologies for different reasons, such as their good physical properties, high processability, notable strength and transport properties to gases and vapours. Moreover, a rising demand of materials with specific characteristics in terms of water vapour transport comes from various market niches (i.e. textiles, building trade, packaging). For these reasons in this work particular attention has been paid to an elastomeric polymer such as the Pebax^®2533, an easily processable material with good transport properties. Previous studies have pointed out that Pebax^® copolymers can be used as precursors of membranes for separation processes of condensable vapours and gases. In this work a further investigation of the water transport properties through Pebax^®2533 and derivative films allowed an understanding of their potential applications. The efficiency of these films has been tested by means of vapour permeability, solubility, diffusivity, and hydrophobicity/hydrophilicity measurements.     

Properties of cation-exchange membranes prepared by radiation grafting of acrylic acid onto tetrafluoroethylene–ethylene copolymers

Some properties of the ion-exchange membranes prepared by simultaneous and preirradiation techniques of grafting of acrylic acid onto tetrafluoroethylene–ethylene copolymer films, including porous microfilters, have been studied. The water content, electric resistance, transport number, distribution of grafting, thermal and chemical stability, and mechanical characteristics of the membranes were determined as a function of the grafting degree. Graft polymerization proceeds from both surfaces of the polymer film into the polymeric matrix depth. Cation-exchange membranes prepared possess good electrochemical and mechanical properties, high thermal and chemical stability at grafting degrees from 30 to 50%, and can be successfully used in electrodialysis processes. © 1993 John Wiley & Sons, Inc.     

Pervaporation membranes based on imide‐containing poly(amic acid) and poly(phenylene oxide)

Three imide‐containing poly(amic acids) were synthesized and used for homogeneous and composite membrane preparation. The transport properties of composite membranes consisting of an imide‐containing poly(amic acid) top layer on an asymmetric porous poly(phenylene oxide) support were studied in the pervaporation of aqueous solutions of organic liquids (ethanol, isopropanol, acetone, and ethylacetate) and organic/organic mixtures (ethylacetate/ethanol, methanol/cyclohexane). For most of the aqueous/organic mixtures, the composite membranes exhibited dehydration properties. Dilute aqueous solutions of ethylacetate were an exception. In these solutions, the composite membranes exhibited organophilic properties, high permeability, and selectivity with respect to ethylacetate. In the pervaporation of methanol/cyclohexane mixtures, methanol was removed with very high selectivity. To account for specific features of pervaporation on the composite membranes, the sorption and transport properties of homogeneous membranes prepared from polymers comprising the composite membrane [imide‐containing poly(amic acids) and poly(phenylene oxide)] were studied. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 2361–2368, 2003     

Preparation of amphiphilic membranes using photosensitive polymers and their applications on the enzyme electrode

To decrease the mass transfer resistance of oxygen permeation and to improve the response of the enzyme electrode, a series of hydrophilic–hydrophobic polyvinylcinnamate (PVCin) membranes were developed. The PVCins were synthesized from polyvinyl alcohol using various amounts of cinnamoyl chlorides in the presence of alkali. The amphiphilic membranes were prepared by using photosensitive PVCin and/or sensitizers that were used instead of the traditional Teflon–hydrophilic two-layer membranes. The properties of photocrosslinking, water and oxygen permeability of the amphiphilic membranes, the calibration curves, and the characteristics of the enzyme electrode prepared by the amphiphilic membranes were investigated. © 1995 John Wiley & Sons, Inc.     

Supercritical fluid processing of Nafion® membranes: Methanol permeability and proton conductivity

Nafion® membranes commonly used in direct methanol fuel cells (DMFC) are typically limited by high methanol permeability. These membranes have phase‐segregated sulfonated ionic domains in a perfluorinated backbone, which make processing difficult and limited by phase equilibria considerations. This study used supercritical fluids (SCFs) as a processing alternative, since the gas‐like mass transport properties of SCFs allow for better penetration into the membranes and the use of polar cosolvents could also influence their morphology, thus fine‐tuning their physical and transport properties. The SCF processing was performed at 40°C and 200 bars using pure CO₂ and CO₂ with several polar cosolvents of different size and chemical functionalities like: acetic acid, acetone, acetonitrile, cyclohexanone, dichloromethane, ethanol, isopropanol, methanol, and tetrahydrofuran. Methanol permeability measurements revealed that the SCF processed membranes reduced the permeation of methanol by several orders of magnitude, especially with the use of some small polar cosolvents. Proton conductivity measurements, using AC electrochemical impedance spectroscopy, were on the order of 0.03–0.09 S/cm, which indicates that processing with SCF CO₂ plus some cosolvents maintained the high proton conductivity while reducing the methanol permeability. The results are explained using XRD and SAXS. XRD analysis of the SCF processed samples revealed an increasing pattern in the crystallinity, which influenced the transport properties of the membrane. SAXS measurements confirmed the morphological differences that led to the changes in transport properties of the SCF processed membranes. Finally, processing flow direction (parallel versus perpendicular flow) played a major role in the morphological changes of this anisotropic membrane. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Alkaline blend polymer electrolytes based on polyvinyl alcohol (PVA)/tetraethyl ammonium chloride (TEAC)

Alkaline blend polymer electrolytes based on PVA/TEAC were obtained by a solution casting technique. Tetraethyl ammonium chloride (TEAC) was added to PVA polymer matrix to form an alkaline blend polymer electrolyte exhibiting excellent ionic transport and mechanical properties. The ionic conductivity of the alkaline PVA/TEAC blend polymer electrolyte was found to be of the order of 10⁻² S cm⁻¹ at ambient temperature when the blend ratio of PVA:TEAC varied from 1:0.2 to 1:2. The characteristic properties of alkaline PVA/TEAC blend polymer electrolytes were examined using DSC, TGA, XRD, SEM, EA, stress–strain tests and AC impedance spectroscopy. The ionic transport properties for the blend polymer electrolytes were measured using Hittorf’s method. It was found that the anionic transport numbers (t ⁻) were between 0.82 and 0.99; the membranes are highly dependent on the types of alkali metal salts and the chemical composition of the polymer blend. The ionic transport and mechanical properties were greatly improved at the expense of the ionic conductivity. In this work we demonstrate that alkaline blend polymer electrolyte can be tailored with a blend technique to achieve specific characteristic properties for battery applications.     

Incorporating functionalized silica nanoparticles in polyethersulfone‐based anion exchange nanocomposite membranes

In order to investigate for anion exchange membranes (AEMs) with improved properties, four series of polyethersulfone‐based composite AEMs are fabricated by incorporating pristine and three functionalized silica nanoparticles containing propylamine, trimethylpropylamine, and melamine‐based dendrimer amine groups. The results show that by choosing appropriate functional agent, anion exchange membranes with improved parameters can be achieved. The polymeric matrix of the membranes is synthesized by chloromethylation of polyethersulfone using thionyl chloride followed by amination with trimethylamine (TMA). The effectiveness of chloromethylation process is confirmed by ¹H NMR analysis. The effects of functional groups on characteristic and transport properties of the prepared composite membranes i.e., SEM, IEC, water uptake, porosity transport properties, and conductivity are investigated. The scanning electron microscope images illustrates that the synthesized membranes possess dense structures. Ion exchange capacity (IEC), water uptake, transport properties, and conductivity of the composite membranes are measured. In addition, the morphology and thermal stability are characterized. IECs and ion conductivities of up to 1.45 meq g^?1 and 45.46 mS cm^?1 and moderate transport characteristics are obtained from the modified membranes which confirm that these membranes are appropriate for applying in electro‐membrane processes. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134 , 44596.     

Zum bildungsmechanismus asymmetrischer membranen

The key to a successful application of the ‘membrane filtration technique&’ is the development of synthetic polymer membranes with the particular transport properties suited to a specific separation problem, i.e. a membrane which rejects molecules of a certain size or chemical nature while being permeable to others. Recent progress in polymer chemistry has led to development of tailor made membranes with high filtration rates and high specific separation characteristics and which also show good chemical, mechanical and thermal stability. These membranes generally are of asymmetric structure and are prepared by a phase inversion process. This membrane preparation technique is described and the main process parameters with their effect on the membrane separation characteristics are discussed in detail.     

Development and evaluation of a Pt-Ru bimetallic catalyst based alkali concentrator in NaOH solutions

An alkaline H₂-O₂ fuel cell based electrochemical alkali concentrator using Nafion® 961 cation exchange membrane has been constructed. It is found that the concentrator can operate at a cell voltage around 0.6 V and the catholyte can be simultaneously concentrated to a level of 40 wt %, provided the outlet anolyte concentration is maintained at a level not below 23 wt %. Some possible directions for further improvement are indicated.

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基于电荷模型的荷电膜传递现象的研究进展

根据电荷模型（空间电荷和固定电荷模型）,将荷电膜传递现象分为膜的分离性能、电性质及传递参数3类.其中膜的分离性能用截留率和通量来表征;膜的电性质包括膜的电化学性质和膜的动电性质,膜的电化学性质用膜电位来表征,膜的动电性质用流动电位、Zeta电位和电滞效应等参数来表征;膜的传递参数则用反射系数、溶质透过系数、纯水透过系数、电导率、离子的迁移数及电渗系数6个系数来表征.概述了空间电荷和固定电荷模型描述电解质溶液在荷电膜中的传递现象的研究进展,介绍了两种模型在荷电膜中应用时的各自优势,展望了电荷模型在荷电膜体系中应用的发展方向.     

Selective permeability of PVA membranes. I. Radiation-crosslinked membranes

The water and salt transport properties of ionizing radiation crosslinked poly(vinyl alcohol) (PVA) membranes were investigated. The studied membranes showed high permeabilities and low selectivities for both water and salt. The results were found to be in accord with a modified solution–diffusion model for transport across the membranes, in which pressure-dependent permeability coefficients are employed.