Conduction and Mass Transfer in Reinforced Cation Exchange Membranes

Abstract

The transport of sodium chloride and calcium chloride through two types of reinforced perfluorinated cation exchange membranes under an electrical field gradient was studied to determine the effect of calcium ion interferences to sodium ion migration. Electromigration-electroosmosis experiments were performed in a diaphragm cell. The concentration of all ions in each half cell was maintained constant by a feedback mechanism. For single salt experiments, the salt flux of calcium ions was half the salt flux for sodium ions. The water flux was higher for the membrane with the greater reinforcement. The effect of two cations competing for migration to the membrane matrix was studied by experiments utilizing a feedback mechanism for each cation. The flux ratio of sodium ions to calcium ions decreased as the concentration of calcium chloride was increased for experiments where the solutions contained mixtures of sodium chloride and calcium chloride.

The electrical conductivity of the membranes was measured using in a diaphragm cell having one movable electrode, allowing for resistance measurements at different path lengths. The resistivity for the membranes in solutions having only one cation was greater for calcium chloride solutions than for sodium chloride solutions. The resistivity of the more reinforced membrane was greater. For a mixture of sodium and calcium ions, as the calcium ion content decreased and the sodium ion concentration was held constant, an increase in resistivity was observed.     

Fortschritte auf dem Gebiet der Alkalichlorid-Elektrolyse

Progress in the field of alkali chloride electrolysis . In the field of alkali chloride electrolysis, new developments are restricted almost solely to the membrane cell process, and no longer concern the conventional mercury and diaphragm processes. At present, the membrane process has a roughly 10% share of the world's caustic soda production capacity of about 48 million t NaOH/a. This share includes membrane cells and retrofit diaphragm cells. After dealing with electrolytes and electrolysis products, this review then turns to a discussion of the optimum current density, of cell voltages, current efficiency, and energy consumption. Subsequently, economic aspects are considered in relation to energy and capital expenditure costs as well as to plant construction. Finally, the most recent developments are discussed, especially in the field of oxygen consuming cathodes in membrane cells.     

Aktuelle Entwicklungslinien der elektrochemischen Prozeßtechnik

Development trends in electrochemical process engineering . Important electrochemical production processes have recently been crucially modified or newly developed and this opened new horizons for the future of industrial electrochemistry. The thrust of this development is discussed in three selected areas: alkali chloride electrolysis, water electrolysis, and organic electrosynthesis. Important past steps are the invention of the dimensionally stable anodes, the development of the cation exchange membrane and membrane electrolysis, the successful testing of zero gap cells, SPE electrolysis and the economic use of two phase electrolytes. These successes have arisen mainly from an improved knowledge and understanding of the fundamental principles of electrochemical engineering.     

碱性膜电解水制氢技术现状与展望

开发清洁高效的可再生能源是未来能源转型的必然趋势。氢能作为一种绿色无污染的能源载体,可通过电解水技术实现氢能与电能的高效转化,有望作为风力、光伏发电的重要调节手段。碱性膜电解水制氢能够提高电流密度,增加能量转化效率,优于碱性水溶液电解水制氢;与此同时,可采用铁、镍等非贵金属制备催化剂,克服质子交换膜电解水制氢使用贵金属催化剂带来的设备昂贵、资源受限问题。本文综述了碱性膜电解制氢技术发展现状,重点围绕自支撑催化电极、耐碱腐蚀离子膜、有序结构膜电极开展讨论,包括催化剂制备策略,耐碱离子膜发展现状,以及有序化膜电极的应用优势,阐释电化学工程中的传质与反应耦合原理。本文为进一步研究开发高性能电化学关键材料提供了指导思路,推动电解水制氢技术的发展。     

20 Jahre Entwicklung einer bipolaren Membranzelle für die Alkalichlorid-Elektrolyse vom Labor bis zur weltweiten Anwendung

First samples of perfluorinated cation exchange membranes were obtained in 1971. They were tested for use in the diaphragm process as a replacement for asbestos diaphragms. However, the special features of these membranes led to the decision to develop special new membrane electrolysis cells. A patent was sought for the first new cell design in 1975. After extensive material testing and many improvements, the HOECHST bipolar membrane cell was produced, consisting of an electrolyzer made up of individual elements, i.e. individual sealed electrolysis cells. Starting in 1982, this cell type was developed further in cooperation with UHDE GmbH. In 1983 it was installed for the first time in an industrial electrolysis plant. Despite strong competition, the bipolar HOECHST -UHDE membrane cell has now gained an important market share. In 1998 it will be installed worldwide in 43 electrolysis plants, with a total NaOH capacity then amounting to 2.5 million mtpa.     

Elektromembranverfahren Teil 1: Grundlagen und Modellbildung

Electromembrane Process – Part 1: Fundamentals and Mathematical Modelling . In electromembrane processes the cation or anion selectivity of polymeric ion exchange membranes can be used for various applications. Industrially important examples are membrane electrolysis and its reversal, the fuel cell or several electrodialytic processes with mono- and bipolar membranes. The electrochemical equilibrium which is responsible for membrane selectivity is discussed together with the relevant transport mechanisms within and outside the membrane. The present status and open questions of modelling electromembrane processes are considered and the efficient combination of the different phenomena into an overall model of an electrodialytic process will be addressed. Applications and a comparison of model simulations and experiments will follow as Part 2 of this survey.     

反渗透-电去离子脱盐系统

介绍了反渗透－电去离子（RO－EDI）脱盐系统的特点和应用，RO－EDI脱盐系统具有出水质量高，连续生产，使用方便，无人值守，不用酸碱，不污染环境，占地面积小，运行经济等一系列优点，重点说明制备国产EDI设备中所用的材料（离子交换膜和离子交换剂）及寺充物填充方式等有关问题。指出推广RO－EDI脱盐系统的当务之急是制备国产设备，等空隙填充法为制备EDI设备提供了一种良好的填充方式。     

A study of reverse osmosis separation and permeation rate for sulfonated poly(2,6-dimethyl-1,4-phenylene oxide) membranes in different cationic forms

Thin film composite membranes were prepared by coating a thin layer of sulfonated poly(1,4-dimethyl-2,6-phenylene oxide) polymer on the surface of a polysulfone ultrafiltration membrane. The membrane performance was studied when the sulfonate was either in the hydrogen form or loaded fully with an alkali metal cation. It was found that the permeation rate was greater than the pure water permeation rate, when the sulfonate was in the hydrogen form and the feed solution contained an alkali metal chloride solute. The permeation rate increased with an increase in the ionic radius of the alkali metal cation. With respect to membranes in which the sulfonate was loaded with an alkali metal cation, the pure water permeation rate was found to increase with a decrease in the ionic radius of the alkali metal cation. The permeation rate was the same as the pure water permeation rate when the membranes of the latter form were tested for reverse osmosis of aqueous solutions involving either sodium chloride or an organic solute. © 1994 John Wiley & Sons, Inc.     

Detection of damaged membranes in alkali chloride electrolysers

Holes in cation exchange membranes of alkali chloride cells can have a number of different causes. They do not represent a source of great danger during operation of a membrane electrolyser as long as their number is limited or their combined diameter does not exceed a certain size. Of the different methods for detection of holes in membranes, two procedures are described in detail: the cell voltage test and the leak test with measurement of the gas flow through the holes. The cell voltage test is performed with low time consumption during start-up of an electrolyser. It mainly shows the large membrane holes in a cell. In contrast to this, with the leak test all holes in a membrane are detected. However, the procedure is time consuming and is possible only with a totally drained electrolyser. It is recommended to perform these tests immediately after installing new membranes and then from time to time in order to avoid damage to the cells or to the plant chlorine system.     

Comparison of Bulk,Emulsion, Thin Sheet Supported,and Hollo Fiber Supported Liquid Membranes in Macrocycle-Mediated Cation Separations

Abstract

The advantages, disadvantages, and possible applications of macrocycle-mediated bulk, emulsion, supported and hollow fiber liquid membranes have been investi-gated. The relative transport rates of the alkali metal cations and of Zn(II), Cd(II) and Hg(II) in sin-gle and competitive cation experiments are studied and compared in the different membrane types. The four membrane types demonstrate similar selectivities but significantly different cation fluxes under comparable conditions using analogous macrocyclic carriers. The degree of distribution of the macrocycle to the organic membrane which is necessary for significant transport varies dramatically among the membrane types, each of which requires unique solvent characteristics. In the experiments, either l8-crown-6, dicyclohexano-l8-crown-6, or 4,1′(5)bis(1-hydroxyheptylcyclohexano)-l8-crown-6 were incorporated into bulk (chloroform, raethylene chloride), emulsion (toluene), supported (phenylhexane) and hollow fiber (phenylhexane or 1-octanol) liquid membranes with the membrane solvents shown in parentheses.     

Elektrochemische Umwelttechnik

Electrochemical processes in environmental protection. Electrochemical processes can contribute considerably to environmental protection by means of waste purification processes and production integrated waste minimization. In the field of waste purification, electrochemical gas purification, purification of metal containing waste waters, and the electrolytic decomposition of neutral salt solutions will be illustrated by examples. As examples of production-integrated environmental protection, this article considers fluidized bed electrolysis, membrane process for alkali chloride electrolysis, and electroreduction of dichloroacetic acid.     

高稳定碱性离子膜分子设计研究进展

以阴离子交换膜（碱性离子膜）为基础的能量转化与储能过程十分重要,包括碱性膜燃料电池、碱性膜电解水制氢等,该类电膜过程对未来能源结构会产生深远影响。现有阴离子交换膜存在耐碱性差、性能衰减显著的问题,严重制约高效能源储存及转化技术发展。为了获得高稳定的碱性离子膜,近年来,围绕耐碱高分子材料的分子设计开展大量工作。本综述从碱性膜材料的高分子骨架和阳离子基团两个角度出发,针对膜材料耐碱性,重点阐述聚烯烃和聚芳基的主链结构,以及非金属中心、金属中心,两类阳离子的分子结构设计策略,展望高稳定碱性膜的结构设计规律及主要挑战,为设计与合成高性能碱性离子膜,满足清洁能源转化与储能膜过程提供新思路。     

Electrochemically switchable polypyrrole coated membranes

A method for coating membranes with polypyrrole (PPy) has been developed. Different membranes, such as microfiltration as well as ion exchanger membranes have been coated with PPy to yield electrical conductivity of the membranes.The coated membranes have been investigated by cyclic voltammetry and scanning electron microscopy and their permeability and permselectivity have been tested. The results show that PPy can be tailored as cation or anion exchanger and its porosity can be controlled to avoid any impairment of the membrane by the polymer layer. These PPy coated membranes can be applied as electrochemically switchable, functionalised membranes with controllabel and variable separation properties.     

Ion exchange membranes and separation processes with chemical reactions

Recent research trends in the development of ion exchange membranes and their use in separation processes with chemical reactions are reviewed. Emphasis in research on the ion exchange membrane is trending toward analysis of micro-structure of the membranes and to development of new functionalized ion exchange membranes in response to industrial requirements. Separation processes with chemical reactions are discussed according to the following classifications: (1) double decomposition of electrolytes; (2) production of acid and base by bipolar ion exchange membrane processes; (3) separators for electrolysis; (4) separators for batteries; (5) use as solid polyelectrolytes; (6) active transport through ion exchange membranes; (7) acceleration of chemical reactions by ion exchange membranes; (8) carrier transport in ion exchange membranes; (9) transducers for electrical signals from chemical reactions; and (10) modified electrodes.     

Material properties of cation exchange membranes for chloralkali electrolysis,water electrolysis and fuel cells

Owing to the development of perfluorinated ion-exchange membranes, the application of the membranes in electrochemical cells has advanced greatly, especially in chloralkali electrolysis. Material properties of perfluorinated carboxylate membranes used for chloralkali electrolysis are described in relation to the conditions of their use. Some new membranes for water electrolysis and fuel cells are briefly described.Paper presented at the meeting on Materials Problems and Material Sciences in Electrochemical Engineering Practice organised by the Working Party on Electrochemical Engineering of the European Federation of Chemical Engineers held at Maastricht, The Netherlands. September 17th and 18th 1987.     

Effect Of Grain Boundaries on Diffusion-Controlled Processes in Aluminum Oxide

Oxygen ion diffusion coefficients in single-crystal Al₂O₃ are several orders of magnitude less than alminum ion diffusion coefficients in polycrystalline Al₂O₃. In polycrystalline Al₂O₃, oxygen ion diffusion is enhanced by the presence of grain boundaries as in the chloride ion diffusion in the alkali halides. Creep and sintering of polycrystalline Al₂O₃ occur at a faster rate than is possible through control by lattice diffusion of oxygen; the rates are in fair quantitative agreement with cation diffusion. It is tentatively concluded that enhanced oxygen diffusion in regions adjacent to boundaries allows aluminum ion bulk diffusion to be rate controlling for these processes. The electrical conductivity in Al₂O₃ is too high to be related to either anion or cation diffusion and is predominantly electronic.     

四甲基氢氧化铵的提纯实验研究

通过单因素实验考察了四甲基氢氧化铵的电解工艺。以钛基镀铱板为阳极,不锈钢为阴极,在电解槽中恒电流密度电解提纯四甲基氢氧化铵,主要考察了电解工艺中离子交换膜种类、原料浓度、电解温度和电流密度对电流效率的影响。当采用上海上化水处理厂3361为阳离子交换膜,在原料室四甲基氢氧化铵浓度25%、电解液温度50℃、电流密度8 ASD(A/dm2)时,电流效率可达66.74%,产品中金属离子杂质总含量从25×10-6降至0.8×10-6,氯离子浓度从0.65×10-6降至0.01×10-6。采用等离子体发射光谱仪(ICP-AES)、分光光度计对产品四甲基氢氧化铵进行表征。