Electrochemistry, Past and Present - American Chemical Society

Chapter 34

Industrial Diaphragms and Membranes

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P. R. Roberge Department of Chemistry and Chemical Engineering, Royal Military College, Kingston, Ontario K 7 K 5L0, Canada In any electrolytic process, where it is necessary to control the diffusion of the products of decomposition, the most vital point to life and efficiency of the cell is the diaphragm or more recently the membrane. This tough reality, which was met with crude short lived diaphragms at the turn of the century, has forced inventors to eventually produce more stabilized materia and ion specific membranes with parallel progress in cell efficiency and quality of the electrolysis products. This paper will review the various electrochemical processes using separators in 1900 and attempt to describe the improvements achieved during the following decades. In his 1915 description of an improved diaphragm material, C.J. Thatcher (1) summarized very well the problems associated with such development: "The lack of a satisfactory diaphragm material has probably hindered or prevented the commercial success of many promising electrolytic processes. At first thought it might seem that there should be no difficulty in obtaining cheap, porous or semi-permeable materials, suitable for prolonged commercial use as a diaphragm in any given electrolyte. Experience, or at least that of the writer, has not warranted any such optimistic view of the matter. A diaphragm should be moistened by, but not be permeable to liquids except by diffusion, so that the anolyte and catholyte, or suspended solid constituents therein, will not commingle during considerable periods. For this reason a diaphragm material should either not be porous, or should have such exceedingly fine pores as to offer a high resistance to the passage of liquids therethrough." "But, on the other hand, a diaphragm material should offer little resistance to diffusion or migration of ions, so that the electrical resistance will not be so great as to be prohibitory. This requires that the diaphragm material should be somewhat porous." "These two fundamental considerations limit the range of materials suitable for diaphragms to those which are somewhat, but not very porous. But this is not all that a diaphragm should be. For commercial use it should be strong, of course, so as to stand 0097-6156/89/0390-0510$06.00/0 © 1989 American Chemical Society

In Electrochemistry, Past and Present; Stock, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1989.

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the wear and tear of factory operations; and it should be permanent, that is, not disintegrated by the electrolytes or products of the electrolysis. If the material is not strong or permanent it should be very cheap, easily replaced and readily obtainable in all shapes and sizes."


Early days - 1900 The first industrial electrolytic process to be operated with a diaphragm started to produce chlorine at Griesheim, Germany, in 1888 (2). The electrical transmission of power was worldwide extremely limited in 1890 (3) but this mode of carrying energy was expanding very rapidly (4). When the first issue of Electrochemical Industry (now Chemical Engineering) came out in September 1902, the American Electrochemical Society (now the Electrochemical Society) was only six months old but the electrochemical industry was booming. The feeling of optimism, then expressed by some people for the future of electrochemical processes is best described by the following quotation from J.W. Richards' article (5) on the electrochemical industries of Niagara Falls, published in this first issue of Electrochemical Industry: "No field in the whole range of the applied sciences is succeeding more signally, promising more attractively, or so pregnant with suggestions of future applications, than electrochemistry. In the hands of the masterful chemist, acquainted with the facts of chemistry and the needs of civilization, the uniting and decomposing powers of the electric current, its almost infinite control of chemical analysis and synthesis, the generation of inconceivable temperatures on a commercial scale and the methods it furnishes of torturing poor Mother Nature into new shapes and wringing from her new secrets, has brought to realization fancies which were undreamed of by the alchemists." In fact, the developing electrochemical industry gave incentive for, and was practically the mainspring of the development of power at Niagara Falls where, by the end of year 1902, the Niagara Falls Power Co. would be developing 60,000 horse-power; of which 45000 (75%) was to be used electrochemically. Only a fraction of that electricity was to be run through a diaphragm since the Roberts Chemical Co. was the only industry to produce the chemicals that necessitated a separator. This company was all contained in a one-story frame building 60-by 200 feet and its electrical usage estimated at 500 horse power for the production of caustic potash and hydrochloric acid from potassium chloride. Alkali-Chlorine. For the first part of the 20th century the electrolytic production of chlorine and alkali seems to have been the main process that successfully made use of diaphragms. The first commercial production of chlorine (6) in 1898 by the Griesheim Company was achieved with cells equiped with porous cement diaphragms, invented earlier (1886) by Brauer. These diaphragms were prepared by mixing Portland cement with an acidified brine. The porosity was created by soaking the set cement in water to remove soluble salts. Twelve anode compartments constructed of this



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ELECTROCHEMISTRY, PAST AND PRESENT

diaphragm material supported by angle-irons were hung into the tank illustrated in figure 1. Porous pots were provided in each anode compartment for addition of solid KCl. The cell was operated batchwise at a temperature of 90°C. The KCl solution was introduced initially and electrolysis was continued for about three days until a concentration of approximately 7% KOH was obtained. The current efficiency was low (70% to 80%) but the cell was simple, inexpensive and relatively large in capacity (2.5 kA). The first use of a percolating diaphragm is credited to Le Sueur who put it to practice for the first time in 1890. By permitting brine to flow into the anolyte and through the diaphragm much higher current efficiency could be obtained and the process was continuous. The first cell employed at the Rumford Falls plant, U.S.A., was of an improved design (figure 2) of the original Le Sueur cell (figure 3 ) . The possibility of eliminating convection effects and mechanical disturbance enabled anode and cathode to be placed near to one another, and for higher current densities to be used than would otherwise have been possible without great losses through interaction between the alkali and the chlorine. This gain in current density was obtained in parallel with a gain in the alkali concentration of the catholyte. These diaphragms could also be vertical. The respective advantages and disadvantages of the two arrangements have been reviewed by Billiter (7) in 1911. Vertical diaphragms permitted a more accessible cell construction, could be easily changed and for the same power consumption would give a far more compact cell. Further, impurities would settle on the bottom of the cell instead of on the diaphragm. On the other hand the horizontal diaphragm was completely soaked with the alkaline liquor. If the plant was to make money from its alkali production this was a double advantage. First the catholyte was free of the unavoidable losses due to the dissolved chlorine and acid coming from the anode. The second point was that is was easier to prepare diaphragms chemically resistant against alkali than against acid. Allmand, in his first edition of Applied Electrochemistry published in 1912 (8), described the general features and merits of the various cells that were then in operation. The Hargreaves-Bird cell (figure 4) is an example of a cell with a vertical diaphragm. The Hooker Electrochemical Co. used a modified version of this design, the Townsend cell illustrated in figure 5, at the Niagara plant around the turn of the century. Another very popular design, during that period, was the one called the Billiter Diaphragm cell (figure 6 ) . Its diaphragm was closing each anode compartment and consisted of woven asbestos cloth, resting on an iron-wire network (the cathode) and carefully cemented all around its edges to the belljar. The upper surface of the diaphragm was uniformly covered with a buffering mixture consisting of asbestos wool and BaSO4. This fine insoluble powder was used to reduce convection and diffusion through the diaphragm and to give it very uniform properties at all points. Table I illustrates the electrochemical data obtained during the normal operation of some of these cells. As a comparison the data for a mercury cathode cell is included, the Castner rocking cell (9).



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Figure 1. Griesheim non-percolating diaphragm cell with diaphragm indicated by an arrow (Reproduced with permission from Ref. 6. Copyright 1972 Robert E. Krieger).

Figure 2. Le Sueur cell (Reproduced with permission from Ref. 6. Copyright 1972 Robert E. Krieger).


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514


Figure 3. Original Le Sueur cell (Reproduced with permission from Ref. 6. Copyright 1972 Robert E. Krieger).

Figure 4. Hargreaves-Bird cell (Reproduced with permission from Ref. 8. Copyright 1912 Edward Arnold).



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Figure 5. Townsend cell (Reproduced with permission from Ref. 8. Copyright 1912 Edward Arnold).

Figure 6. Billiter cell, flat cathode (Reproduced with permission from Ref. 8. Copyright 1912 Edward Arnold).


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516


Table I. Parameters of normal operation of alkali-chlorine cells used at theturn of the century


Cell

KWh/ Voltage Energy Alkali Cathodic efficiency (kgNaOH) (N) Current (V) efficiency (%) (%)

Griesheim - carbon anode 1-2 - magnetite anodes 1-2 Billiter 3-4 Hargreaves-Bird 3 Townsend 4 Castner 5

70-80 70-80

95 85 94 92

3.6 4.0 3.7 3.7 4.8 4.2

41-51 40-46

59 45 50

3.0-3.4 3.3-3.8

2.6 as Na 2 CO 3

3.4 3.1

The basic material used then to fabricate diaphragms was asbestos. This remained so until the development of sturdy ion specific membrane materials started to make a difference, in the early 1980's. J.R. Crocker (±0) made a very good review of the many attempts which have been made, before 1908, to meet the various requirements of diaphragms. This author suggested the use of the following method to construct a diaphragm with an asbestos fiber material: "When the asbestos fiber has been formed as desired, it is subjected to an acid bath, sulphuric or nitric acid, for a short time, and, afterwards baked under an intense heat. The heat changes the fiber into the crystallized state, and the acid bath serves to eliminate any metallic oxide which may be in the asbestos and strengthens the same". The first era of industrial electrolytic activities was very prolific in inventions and trials. "Claims were made for special features such as submerged diaphragms, unsubmerged diaphragms, special compounds to incorporate in the diaphragm, use of petroleum oil in the cathode compartment etc. Although considered quite important at the time, in retrospect these differences are not of great importance." (6) Table II. 1949 Survey of U.S. patents issued on chlor-alkali diaphragm cells Period 1883-1889 1890-1899 1900-1909 1910-1919 1920-1929 1930-1939 1940-1949

No of Patents 5 105 129 90 69 54 43

A great deal of cell development was done in the United States between 1890 and 1910 as the survey (11) of U.S. patents presented in Table II indicates.


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Water Electrolysis. The production of hydrogen and oxygen by the electrolysis of water has been practiced on the industrial scale since the beginning of the century. Some important dates in the development of the technology are shown in Table III (.12). Table III. Year


1800 1888 1890 1892 1899 1902 1910 1912 1925 1926

Important dates in the development of water electrolysis Development

Electrolytic Decomposition of Water Experiments with Pressure Cells Monopolar Tubular Cell Load Levelling Electrolyser Design of Filter-Press Cell Production of Filter-Press Electrolyser Design of Knowles Cell Operation of Knowles Cell Design of Pressure Cell Design of Filter-Press Electrolyser

Inventors or Company Nicholson, Carlisle Latchinoff Renaud Garutti Schmidt Oerlikon International Electrolytic International Electrolytic Noegerath, Lavaczek Zdansky

This apparently slow industrial start was due in part to the success of the chlorine-alkali processes which also produced hydrogen. "Where one only of these gases (hydrogen and oxygen) is needed, its preparation by electrolysis is usually uneconomical. Hydrogen is produced in large quantities in electrolytic alkali works, and can be manufactured very cheaply from water-gas, whilst oxygen is best obtained by fractional distillation of liquid air. But where both gases are required, and particularly for the oxyhydrogen flame, used extensively in platinum working and in some kinds of lead burning, electrolysis is the most convenient method of preparation" (8). The first major installation of water electrolysers was constructed in 1912 in Port Sunlight, England. It contained 200 Knowles cells that could consume 1.5 MW of power at 3.5 kA. Some of these Knowles cells have been in operation for sixty years. They were simple in design and maintenance. These tank electrolysers used paper or woven asbestos as semi-diaphragms. The separators were immersed in a concentrated alkaline solution and open at their lower edges. From 1910 to 1940 In diaphragm cells both the cell efficiency depend upon: - cell construction - electrode materials

voltage and the current


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- electrolysis conditions - diaphragm properties

In his second edition of Principles of Applied Electrochemistry (13), Allmand describes the virtues of a good diaphragm material before citing materials used effectively in some industrial processes: Alkali-resisting Diaphragms - asbestos - Portland cement Acid-resisting Diaphragms - mixture of alumina/silica, LeBlanc - mixture of kaolin/corundum, Buchner - fused silica-electrofilters, Thatcher The main advantage offered then by the alkali-resisting asbestos was its flexibility. The rigidity of the other materials made them more difficult to seal properly and, because of the forces involved, more easy to crack. Chlorine-Alkali. With the exception of the Griesheim cell, the diaphragm cells have had a variety of shapes, sizes and materials of construction, but the diaphragms have always been based on asbestos used as paper, cloth or fiber. The LeSueur cell, for example, used a horizontal paper diaphragm over the horizontal cathode screen. Glass rods placed on the diaphragm served to support the anode graphite blades and maintain the proper spacing as the graphite wore away. Where intermediate supports were required, bricks were stacked on the diaphragm (14). Another early diaphragm cell, the Townsend cell, which was developed for commercial use in 1905 with financing by the Elon H. Hooker's Development and Funding Company (later Hooker Electrochemical Co.) was of a vertical type with a long, high central row of graphite anodes. Opposing these anodes on either side of the cell was a paper diaphragm backed up with a wire screen cathode. The original paper diaphragm of Townsend's was soon replaced with an impregnated (a colloidal mixture of iron oxide and loose asbestos fibers) asbestos cloth diaphragm developed by Leo Baekeland. In 1913 Marsh designed a cell with finger cathodes and side-entering anodes and cathodes. Asbestos paper was wrapped over this surface and sealed top and bottom with cement and putty. These putty joints provided a poor seal and thus a low cell efficiency. In order to improve the construction of a Marsh cell, K. Stuart, of the Hooker Electrochemical Company developed in 1928 a method of depositing asbestos fibre directly on the cathode by immersing it and applying a vacuum. The flexibility of design permitted by this new type of diaphragm was incorporated in the Hooker Type S series of cells. These modifications have improved the amperage capacity from 5 kA to 30 kA over the next decades. A sign of importance of the Stuart invention is the fact that more than 90 percent of the chlorine produced in diaphragm cells in the 1970's came from cells using deposited asbestos diaphragms. The filter-press concept, which became very popular for the electrolysis of water and of hydrochloric acid, had many attractive features for chlor-alkali producers. It required a minimum of conductor material between cells, a minimum of floor space and



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essentially low capital costs. The only commercial use of filter-press cells for chlor-alkali has been by the Dow Chemical Company. Early workers of this design were Kellner, Guthrie and Finally but the original patents for the bipolar cells themselves were granted to Thomas Griswold in 1911 (15) and 1913 (16). Water Electrolysis. The demand for electrolytic hydrogen, during the same period, was still variable and mostly linked to the production of ammonia for fertilizers. In the early 1920's a few installations, made with Casale and Fauser's cells, were running in Italy for a total production of approximately 90 MW (17). After twenty years of commercial success the old Schmidt electrolyser, built by Oerlikon in Switzerland, was superseded by a much more powerful competitor, the Pechkrang electrolyser which was built by the Hydrogène Co. in Geneva. While the biggest Schmidt electrolyser ever built could hardly produce 32 kW of hydrogen, the new unit contained up to 140 cells that could sink a current of 2.5 λA for a total power of 0.88 MW. During the first two years of its existence (1926-1927) the new electrolyser was to be installed in six European countries for a total production potential of 176 MW. The biggest electrolyser for a long while was built during the same period (1924-1928) by E.A. Zdansky, an engineer working for the German company, the Bamag-Meguin. The largest model of this filter-press electrolyser was the Model C. It had electrodes with 2 an individual surface area of 3 m and could produce up to 2.6 MW of electrolytic hydrogen. Various attempts were made to develop pressure water electrolysers between 1920 and the second world war, but all came short of industrial recognition: Noeggerath in 1927 (150 bar), Neiderreither in 1929 (bipolar electrodes, 5 kW), Lawaczek in 1928 (300 bar), Siemens and Halske in the late 30's (5 to 10 bar). 1940-1975, The Material Revolution An 1. 2. 3.

ideal diaphragm should be (18): permeable to ions but not to molecules of high void fraction to minimize electrical resistance of small mean pore size to prevent the passage of gas bubbles and minimise diffusion 4. homogeneous to ensure good current efficiency and even current distribution 5. non-conducting to prevent action as an electrode 6. chemically resistant to the reactants and products 7. resistant to cell operating conditions of temperature, pH, etc. 8. of some mechanical strength and rigidity 9. cheap or long lasting. Several of these properties were in conflict and generally a compromise had to be made. The most widely used materials up to then were asbestos, either in the form of fibre cloth or paper, and ceramics. Neither material was ideal, asbestos being slowly attacked in acid or in very alkaline conditions and ceramics having a high electrical resistance whilst at the same time being brittle and thus unstable to temperature change and mechanical shock. Since the production of large ceramic diaphragms was still not possible



520


without increasing the thickness of the material, ceramics did not invade the electrolytic scene of that period. In order to improve the properties of asbestos diaphragms, many attempts had been made to modify the structure of the diaphragm by impregnating or combining the asbestos with various compounds. Many new materials were also starting to be fabricated into porous sheets with controlled properties for use as diaphragms for electrolytic processes. Most of these materials were to fail in chlorine electrolysis due to the high surface area exposed to the corrosive nature of the anolyte which enhances chemical degradation. Polytetrafluoroethylene would withstand the cell conditions but the porous P.T.F.E. made then failed as a diaphragm because of its non-wettability (19). The breakthrough was to be inspired by fuel cell technologists who were then using P.T.F.E. powder (20) to limit the wettability of fuel cell electrodes. Chlor-Alkali. Major changes in materials of construction were to happen to this half century-old electrochemical technology. Chlorine production in the U.S. had increased about six-fold between 1950 and 1975: 7000 tons per day in the early 1950's compared to 41000 tons per day in 1976 (21). The replacement of graphite anodes by coated titanium anodes had been a great advantage to diaphragm cells. With graphite anodes, the anode-cathode gap increased as the graphite wore away. This increase in electrode gap would increase cell voltage and heat evolution, and shorten the life of the diaphragm due to clogging of the pores by graphite particles and chlorinated products. The new anodes were not only very stable but could be moved very close to the diaphragm by an adjustable feature. The swelling and increasing porosity of asbestos diaphragms with operation were finally overcome by curing the asbestos diaphragm with special additives (chlorinated fluoro-polymers, wetting agent ec.). These additives lent dimensional stability to the diaphragm so that the anode could be moved very close to the cathode without invading the diaphragm layer. The result of incorporating the modified diaphragm and expandable anode produced a total cell voltage reduction of 400 mV at a typical current density of 2.2 kA/m2 (22). Diamond Shamrock Corporation had been experimenting with Dimensionally Stable Anodes (DSA) since 1966. Their cells had, by 1975, expandable anode, FRP cover and a modified asbestos diaphragm (23). These cells could produce 360% more chlorine at 2.5% less power per ton on half of the original floor space. The modified asbestos diaphragm retained the good qualities of asbestos and the troublesome properties were reduced. It also provided easier hydrogen evolution, prevented swelling, had a longer life, improved uniformity and flow properties, was easy to remove and could be stored up to 5 months before use. Hooker Chemicals and Plastics Corporation also modified drastically the power profile of its cells by incorporating similar improvement in their construction. Table IV shows an analysis of voltage improvement in Hooker cells for two generations of electrolysers (24). The frequency of cutout activity was reduced by a factor of from 6 to 11 times for the new bipolar PPG-De Nora Glanor cells (25)


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Table IV. Analysis of voltage improvements at 1 kA/m2 in Hooker cells


Model Date Decomposition, anode Decomposition, cathode Overvoltage, anode Overvoltage, cathode Brine gap Hardware Diaphragm Total

S-3

H-4

1960

1976

1.32 0.93 0.33 0.27 0.49 0.36 0.30 4.00 V

1.32 0.93 0.03 0.27 0.27 0.17 0.16 3.15 V

even if their diaphragm material was still of the deposited asbestos type. A life expectancy of one year was expected from the diaphragm in such cells. With additives it was claimed to become 2 to 3 times longer. Electrolysis of Hydrochloric Acid. Development of this process was conducted initially at Bitterfield in the I.G. Farben Industrie Plant (26). The German patent application covering this innovation was dated October 15, 1942. It took 14 years before this work became known and taken up by De Nora in Milan. The original HC1 electrolysis cell constructed on this concept had vertical bipolar electrodes. An extensive study made of possible diaphragm materials had resulted in a choice that gave satisfaction since the last electrolyser was operated by I.G. Farben continuously for fifteen months, but the details of manufacture of the diaphragm were never published. On the other hand the De Nora electrolysis unit is well described in the literature (26, 27). The standard assembly was composed of 40 cells of the filter-press type (De Nora was already in the water electrolyser business). The diaphragm itself consisted of PVC cloth pressed between the ribs of graphite anodes and cathodes so as to separate the electrodes by a width of 2 mm. The life expectancy of such a diaphragm, under good operating conditions, was approximately three years. Water electrolysis. In 1975 electrolytic hydrogen accounted only for 2% of the worldwide production of hydrogen (28). Large plants (>100 MW installed power) were scarce and they relied basically upon very cheap water power. Hydrogen production by electrolytic decomposition of water was restricted to small plants where the purity of the product and the flexibility of the process are prime qualities. It was felt that electrolytic hydrogen could become competitive with chemical hydrogen if the energy efficiency of water electrolysers reached 75 to 80%. Only three ways of doing that were then possible: - decreasing the electrical resistance of the diaphragm - increasing the working temperature - improving the activation of the electrodes Most installations were comparatively small in size, with a few notable exceptions. At the Aswan High Dam, for instance, 40,000


522


m 3 /h _ 1 of hydrogen were produced by electrolysis, using Demag electroiysers (12). The commercial water electrolysis units were of the types and models shown in Table V. Of the materials available to serve as diaphragms, woven asbestos-fibre cloth was still almost invariably chosen, although fine metal-mesh was also marginally used. For diaphragms of large area, asbestos was interwoven with fine nickel wire to give increased strength.


1975-2000 Advanced Membrane Materials The availability of perfluorinated ion exchange membranes of exceptional chemical stability and electrochemical properties has opened new opportunities for the application of electrochemical technology in the chemical process industry (29). Chlor-Alkali. The energy crisis of the 1970's combined with tougher environmental regulations accelerated drastically the integration of the newly developed membrane material by this electrochemical industry. In Japan, for example, the mercury cells that had been producing most of the country's chlor-alkali production since the second world war were legislated out of existence in the early 1980's. At the same time working with asbestos became recognized as a serious hazard for the workers handling the fiber material. During the first four years (1978-1982) after commercialization of its Flemion membrane, Asahi Glass Co of Japan (30) has installed three plants (two in Japan, one in Thailand) for a total potential production of 41400 tons NaOH/year. During the following 4 years (1982-1986) Asahi Glass Co equipped electrolysers with its membranes for a total estimated production of 691,400 NaOH ton/year. The new process presents a real savings in energy and capital as well as improvement in the environmental area. All the major companies involved in the production of electrolysers for chlor-alkali have their own version of the original ion-exchange Nafion membrane (31). This search for innovation will itself generate new niches in the industrial transformation of chemicals (29, 32). Water Electrolysis. The predictions, made in 1978 (33), that water electrolysers were soon to become more energy efficient to be competitive with other sources of hydrogen seem to have recently materialised (34). While the advanced hydrogen plant at Becancour, Quebec, still has asbestos for separator material, an extensive study of other possible materials for use in alkaline water electrolysers (35) has demonstrated how some replacement materials could become advantageous for higher operating temperature or efficiency. One such alternative is the use of a solid polymer electrolyte on the basis of outstanding performance and operating characteristics which have been demonstrated in systems developed for aerospace and military applications (36). The modern alkaline water electrolysis technologies available commercially have the following common features: they operate at atmospheric pressure between 70-90°C with a current density of up to 5 kA/m2 and energy efficiency reaching 85% (37). Some pre-commercial technologies have demonstrated higher values for these four parameters.


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Table V. Operating conditions of commercial water electrolysers available in 1970 Type Model

Operating Temperature


°C Tank electrolyser • Knowles cell • Stuart cell Filter-press electrolyser • CJB electrolyser • Demag electrolyser • Oerlikon electrolyser • Pintsch Banrag • Moritz oxyhydrolyser • De Nora electrolyser Pressure electrolyser • Zdansky-Lonza • CJB electrolyser • Treadwell generator

Unit Capacity Nm3H2h- 1

Energy Efficiency

%

80 85

2.1 2.4

70 60

80 80 75 80 60 75

240 150 210 100 40 18

60 65 68 65 67 64

90 65 90

145 2 0.3

65 67 40

Other Processes, Other Membrane Materials. Many other industrial processes use membranes or diaphragms. Some also operate in conditions very similar to those of the electrolysers described so far in this paper. Reverse-osmosis, batteries and fuel cells are amongst mature technologies that are forcing material developers to produce stabler, more performant and cheaper separators. The new porous materials will themselves probably inspire innovators with novel designs and applications. Literature Cited 1. Thatcher, C.J. Met. Chem. Enq. 1915, ,13, 336-8. 2. Gardiner W.C. Proc. Symposium on Selected Topics in the History of Electrochemistry, ECS 1978, pp 413-428. 3. Richards J.W. Electrochem. Ind., 1902, 1, 49-55. 4. Greene S.D. Cassier's Mag., 1895, 8, 175. 5. Richards J.W. Electrochem. Ind., 1902, 1, 11-23. 6. Kircher M.S. In Chlorine, Science J.S., Ed.; Robert & Krieger: New York, 1972; Chapter 5. 7. Billiter J. In Die Elektrochemischen Verfalnen, 1911, Vol. II, p 203. 8. Allmand A.J. In The Principles of Applied Electrochemistry; Edward Arnold: London, 1912; Chapter XXI and XXII. 9. Ornstein G. Trans. Am. Electrochem. Soc., 1916, 29, 530. 10. Crocker J.R. Electrochem. Metal. Ind., 1908, 6, 153-6. 11. Murray R.L. Ind. Eng. Chem., 1949, 41, 2155. 12. Smith D.H. In Industrial Electrochemical Processes; Kuhn A.T., Ed.; Elsevier, Amsterdam, 1971; Chapter 4. 13. Allmand A.J. In The Principles of Applied Electrochemistry; Edward Arnold: London, 1924. 14. Hubbard D.O. J. Electrochem. Soc., 1952, 99, 307C-309C. 15. Griswold T. Jr. U.S. Patent 987, 717, 1911.



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16. Griswold T. Jr. U.S. Patent 1, 070, 454, 1913. 17. Aureille R. In Hydrogen Energy Progress V: Veziroglu T.N., Taylor J.B., Ed.; Pergamon, New York, 1984; pp 21-43. 18. Jackson C , Cooke B.A., Woodhall B.J. In Industrial Electrochemical Processes; Kuhn A.T., Ed.; Elsevier: Amsterdam, 1971; Chapter 15. 19. Chapman E.A. Chem. Process Eng., 1965, Aug., 387. 20. Liebhafsky H.A., Cairns E.J. In Fuel Cells and Fuel Batteries; John Wiley, New York, 1968; Chapter 7. 21. Gardiner W.C. J. Electrochem. Soc., 1978, 125, 22C-29C. 22. Sikstrom L.E., Liederback T.A. Chem. Ing. Technik, 1975, 47, 157. 23. Thomas V.H., O'Leary K.J. In Chlorine Bicentennial Symposium; Jeffrey T.C., Danna P.A., Holden, H.S., Ed.; ECS: Princeton, 1974: p 218. 24. Grotheer M.P., Harke, C.J. In Chlorine Bicentennial Symposium; Jeffrey T.C., Danna P.A., Holden, H.S., Ed: ECS: Princeton, 1974: p 209. 25. Kienholz P.J. In Chlorine Bicentennial Symposium; Jeffrey T.C., Danna P.A., Holden, H.S., Ed.; ECS: Princeton, 1974; p 198. 26. Berkey F.M. In Chlorine; Sconce J.S., Ed.; Robert & Krieger: New York, 1972; Chapter 7. 27. Prayer S., Strewe W. In Chlorine Bicentennial Symposium; Jeffrey T.C., Danna P.A., Holden, H.S., Ed.; ECS: Princeton, 1974, p. 257. 28. Mas L., Solm J.C., Damien A. Proc. 1st World Hydrogen Energy Conference, University of Miami, Florida, 1976; 6B41-6B62. 29. Grot W.G.F. Proc. Diaphragms, Separators, and Ion-Exchange Membranes; 1986 ECS Symposium, pp 1-14. 30. Sajima Y., Sato K., Ukihashi H. Industrial Membrane Process Symposium, 1985 Spring National AIChE Meeting, Houston, Texas; pp 108-113. 31. Robinson J.S. In Chlorine Production Processes: Recent and Energy Saving Developments; Noyes Data, New Jersey, 1981. 32. Ezzell B.R., Carl W.P., Mod W.A. Industrial Membrane Process Symposium, 1985 Spring National AIChE Meeting, Houston, Texas; pp 45-50. 33. LeRoy R.L., Stuart A.K., Industrial Water Electrolysis Symposium, 153rd Meeting of the ECS, Seattle, 1978. 34. Crawford G.A., Hufnagl A.F., Int. J. Hydrogen Energy, 1987, .12, 297-303. 35. Renaud R., LeRoy R.L., Int. J. Hydrogen Energy, 1982, 7, 155-166. 36. Nuttall L.J., Russell J.H., Int. J. Hydrogen Energy, 1980, 5, 75-81. 37. Crawford G.A., Benzimra S., Int. J. Hydrogen Energy, 1986, 11., 691-701. RECEIVED August 3, 1988


Electrochemistry, Past and Present - American Chemical Society

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