Classifications

• • C—CHEMISTRY; METALLURGY
  • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
  • C25B—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES FOR THE PRODUCTION OF COMPOUNDS OR NON-METALS; APPARATUS THEREFOR
  • C25B11/00—Electrodes; Manufacture thereof not otherwise provided for
  • C25B11/04—Electrodes; Manufacture thereof not otherwise provided for characterised by the material
  • C25B11/051—Electrodes formed of electrocatalysts on a substrate or carrier
  • C25B11/073—Electrodes formed of electrocatalysts on a substrate or carrier characterised by the electrocatalyst material
  • C25B11/091—Electrodes formed of electrocatalysts on a substrate or carrier characterised by the electrocatalyst material consisting of at least one catalytic element and at least one catalytic compound; consisting of two or more catalytic elements or catalytic compounds
  • C25B11/093—Electrodes formed of electrocatalysts on a substrate or carrier characterised by the electrocatalyst material consisting of at least one catalytic element and at least one catalytic compound; consisting of two or more catalytic elements or catalytic compounds at least one noble metal or noble metal oxide and at least one non-noble metal oxide

Definitions

• ABSTRACT Described is a method of electrolyzing brine in a mercury cell, at applied current densities of at least 6 amperes per square inch, employing as the anode a titanium substrate bearing on at least a portion of the surface thereof a mixed oxide coating of from 30 to 90 percent stannic oxide, from 1.0 to 10 percent antimony oxide, from 1.0 to 50 percent of at least one platinum group metal oxide, and from 0.5 to 30 percent of a valve metal oxide selected from the group consisting of titanium and tantalum oxides.
• the apparatus employed for this purpose is quite expensive and a primary concern in commercial operation is to obtain the maximum amount of production per unit of floor space.
• One method of so doing is to increase the anode current density at which the cell operates.
• the maximum current density that could be employed without drastically reducing the useful life of the anode was on the order of 5.0 asi.
• the apparent cause of this passivation was brine depletion across the cell, oxygen evolution increasing with decreasing brine concentration.
• an improvement consists essentially of employing as the anode a titanium substrate bearing on at least a portion of the surface thereof a mixed oxide coating of from 30 to 90 percent by weight stannic oxide, from 1.0 to percent antimony oxide, calculated as Sb O from 1.0 to 50 percent of at least one platinum group metal oxide, and from 0.5 to 30 percent of a valve metal oxide selected from the group consisting of titanium and tantalum oxides, with the proviso that the mole ratio of tin to antimony oxides be between 85:15 and 95:5, and applying current to said anode at a rate of at least 6 amperes per square inch.
• valve metal oxide is TiO
• platinum group metal oxide is a combination of RuO,and IrO,.
• the mercury cells to which the practice of the present invention may be applied may be of the horizontal, vertical, or inclined plane type, all of which are well known to those skilled in the art. Such cells and their operation are described, for example, at Kirk-Othmer,
• Such cells operate on aqueous sodium chloride solutions having concentrations at or approaching saturation (brine), e.g., 325 grams per liter, although sea water has been successfully electrolyzed in some instances.
• concentrations at or approaching saturation e.g., 325 grams per liter
• the distance between the parallel anodes and mercury cathode of the cell is kept quite low, often on the order of 0.1 to 0.3 inch.
• Such cells are operated at temperatures up to the boiling point of brine and at sodium-mercury amalgam concentrations on the order of from 0.1 to 0.15 percent, the latter factor being controllable to some extent by regulating the mercury flow rate.
• Conventional operation is at anode current densities on the order of 3 to 4 asi and up to 6 asi.
• the amount of current supplied to the cell is at least 6 amperes per square inch of anode surface, preferably 6 to 10 asi.
• the brine becomes severely depleted during its passage from inlet to outlet thereby increasing the amount of oxygen evolved at the anode surface and normally contributing to the rapid passivation of same.
• the anode comprises a titanium substrate bearing on at least a portion of the surface thereof a mixed coating of the oxides of tin, antimony, at least one platinum group metal, and a valve metal selected from the group titanium and tantalum.
• Such anodes also exhibit a long life, i.e., a low platinum group metal wear-rate per ton of chlorine.
• the conductive substrate is generally titanium, although a more conductive material, such as copper or aluminum, bearing a surface of titanium may be employed. Additionally, layers on the substrate intermediate the titanium and the coating, such as those described in US Pat. No. 3,711,397, are contemplated.
• the configuration of the substrate may vary considerably but it is generally in the form of a sheet, particularly a foraminous sheet, such as expanded mesh.
• stannic oxide preferably present in the form of crystalline SnO and employed within the range of from 30 to 90, especially 30 to 50, percent by weight of the total coating composition.
• the antimony oxide component enters into the tin oxide crystal lattice, rendering same more electrically conductive.
• the antimony is present in an indeterminate oxide form owing to its entrance into the stannic oxide crystal lattice, it is expressed for convenience sake as Sb,O
• the antimony oxide is present within the range from 1.0 to 10, preferably 4.0 to 8.0, percent by weight.
• tin and antimony oxides are further qualified by the proviso that they be present, respectively, in the range, on a mole ratio basis, of 95:5 to :15, especially :10. In this fashion, there is ob tained the desired doping effect of the antimony on the tin oxide without the presence of an excess separate phase of antimony oxide.
• the third component of the mixed coating is at least one platinum group metal oxide, by which term it is intended to include the oxides of platinum, palladium, ruthenium, iridium, rhodium, and osmium, especially those of ruthenium and iridium. These platinum group metal oxides are present for the most part in their most acid.
• the concentration of the metals in thesolution 3 4 highly oxidized state and within the range of from 1.0 sition is incomplete, small amounts of salts may remain it 7 to 50, especially 20 to 40, percent by weight.
• An espewithout detrimental effect in the coating, for example, cially preferred anode is one the coating of which consmall amounts of chloride in the primarily oxide coattains a combination of RuO and IrO ing.
• the final component is a valve metal oxide selected
• titanium is present in the form of embodiments by which it maybe carried into effect, TiO and is essentially crystalline (rutile) in nature
• rutile essentially crystalline
• the following specific example is afforded.
• tantalum is em loyed, a generally amorphous tantalum oxide result: Therefore, although it is ex- 10 a a A e pressed as Ta 0 it is understood that mixtures of tan- Four anodes were prepared from the following Sohb talum oxides may in fact be present.
• Ta O is tions. preferred.
• valve metal oxide em- Anodel 50m1n butano1 125 gSnC]4.5H2O, 0.91 ployed are generally within the range of from 0.5 to 30 g s c and 1 g c 14 0 33% Ru) Percent y weight, especially 15 to 25 percent 15 Anode 2 45 ml ethanol, 5.0 g orthobutyl titanate,
• a preferred electrode comprises an expanded 1,1 g sbc1,, 15.1 g SnCl -5H O, and 7.6 g R1101, titanium metal substrate bearing a coating containing H 0 3 Ru). about 47 Percent t Percent z a p Anode 3 s0 ml n-butanol, 12.5 g SnCL'SH O, 0.91 cent Ru0 4.5 percent lrO and percent Ta Or- 20 g SbCI, 7.0 g orthobutyl titanate, and 1.1 g
• Anode 4 .45 1 ethanol, 45 g c H g s a the preferred method of preparing the multicomponent 15 1 g S ch-511 0, and 7.6 g Rucl 'xll O coating composition on the titanium substrate is by de- (38%R position from a solution of the appropriate thermo- 25
• it is deslr' solution by brush to a clean titanium metal mesh with able to paint or brush an acidified alcoholic solution of h i i i between h t, fi t t 110 C for 3 said salts onto the substrate, followed by drying at minutes f ll ed b 7 minutes t 500C C for from 3 to especially 5, minutes and
• These are employed as anodes in a horizontal merfinally by aking in an
• electrolyte is a 310 g/l brine solution having a pH be repeated any number of times until the desired coatwithin the range of 33-6 and a. temperature of about 70 ing thickness is obtained, for example, 6 to 10 coats.
• electrolysis The preferred solvents for the thermally decomposable 35 is continued. at 6 amperes per square inch for 500 salts arethe lower alkanols such as ethanol, propanol, hours, the loss being determined by weight differential.
• Valve metal OXlde elected salts of the remaining materials, although it is generally from a group consisting of tltahlum and tantalum believed that preformed valve'metal oxides should not ides, with the Proviso that the mole ratio of tin to antibe employed nor should separately preformed tin and molly oxides is between 85115 and 9515; na pp y hg antimony oxides be used. Further, if thermal decompoa ijlii ii jfisl5WPPYB From the table, it is evident that Anode 1, without square inch.
• metal oxide is Ta O and is present within the range of 15 to 25 percent.
• the coating contains from 30 to 50 percent SnO 4 to 8 percent antimony oxide, 20 to 40 percent of at least one platinum metal oxide, and 15 to 25 percent Ta O

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• Chemical & Material Sciences (AREA)
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• Chemical Kinetics & Catalysis (AREA)
• Electrochemistry (AREA)
• Materials Engineering (AREA)
• Metallurgy (AREA)
• Organic Chemistry (AREA)
• Electrodes For Compound Or Non-Metal Manufacture (AREA)
• Chemically Coating (AREA)

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Cited By (14)

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• 1973
  • 1973-04-19 US US00352418A patent/US3793164A/en not_active Expired - Lifetime
• 1974
  • 1974-04-17 BR BR3074/74A patent/BR7403074D0/pt unknown
  • 1974-04-18 IT IT50462/74A patent/IT1005989B/it active
  • 1974-04-18 GB GB1710774A patent/GB1417950A/en not_active Expired
  • 1974-04-18 DE DE2418740A patent/DE2418740A1/de not_active Withdrawn
  • 1974-04-18 SE SE7405202A patent/SE7405202L/sv unknown
  • 1974-04-19 JP JP49043493A patent/JPS5011997A/ja active Pending

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