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Method For Improving The Performance of Nickel Electrodes

a technology of nickel electrodes and performance, applied in the direction of electrodes with substrates, electrolysis components, electrodes, etc., can solve the problems of increasing cell voltage, increasing cell voltage, and cathode coatings without long-term stability, etc., and achieve the effect of improving the performance of nickel electrodes

Inactive Publication Date: 2008-10-23
COVESTRO DEUTSCHLAND AG
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  • Summary
  • Abstract
  • Description
  • Claims
  • Application Information

AI Technical Summary

Benefits of technology

[0018]The object of the invention is, therefore, to develop a specific method for improving nickel electrodes coated with platinum metals, platinum metal oxides or mixtures thereof, for use as cathodes in the electrolysis of sodium chloride, which process can be used while electrolysis operation continues and avoids a prolonged interruption in electrode operation to restore cathode activity.
[0025]The invention provides a method for improving the performance of nickel electrodes having a coating based on platinum metals, platinum metal oxides or mixtures of platinum metals and platinum metal oxides, for sodium chloride electrolysis according to the membrane process, characterised in that, in the electrolysis of sodium chloride, a water-soluble or alkali-soluble platinum compound, in particular hexachloroplatinic acid or especially preferably an alkali platinate, particularly preferably sodium hexachloroplatinate (Na2PtCl6) and / or sodium hexahydroxyplatinate (Na2Pt(OH)6), is added to the catolyte.

Problems solved by technology

This is technically complex, because the electrolysis must be stopped and the electrodes must be removed from the electrolytic cells.
The ELTECH publication contradicts this teaching, however, because, according to the information from ELTECH, coating the cathodes with iron is said to interfere with the electrolysis and to increase the cell voltage.
The cathode coating does not have long-term stability, in particular not under conditions in which electrolysis does not occur or during interruptions in the electrolysis, during which pole reversal processes, for example, can occur.
Accordingly, more or less pronounced damage occurs to the coating over the operating time of the electrolyser.
The consequence is that the cell voltage rises, with the result that the energy consumption for the production of chlorine, hydrogen and sodium hydroxide solution increases and the economy of the process is markedly impaired.
It is likewise possible for only individual elements to exhibit damage to the cathode coating, and it is not always economical to stop the entire electrolyser therefor and remove the element with the damaged coating, because this is associated with considerable production losses and costs.

Method used

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Examples

Experimental program
Comparison scheme
Effect test

example 1

[0045]A commercial electrolyser having 144 elements whose nickel cathodes were provided with a coating based on ruthenium / ruthenium oxide from Denora was operated at a mean voltage of 3.12 V. Of these 144 elements, one exhibited a voltage increased by more than 100 mV as compared with the mean value. The following treatment cycle was begun: 65.88 litres of a hexachloroplatinate solution (1.19 g Pt / l) was metered at a rate of 10.98 l / h, during operation, into the sodium hydroxide solution (conc. 31.5%) of a membrane electrolyser at a current density of 4.18 kA / m2 over a period of 6 hours. 78.25 g of platinum thus reached the surface of 144 cathodes (surface area of a cathode: 2.71 m2). This corresponds to an amount of platinum of 0.21 g Pt / m2. The cell voltage fell on average to 3.08 V, the current consumption rose to 4.57 kA / m2. Converted to 4 kA / m2, this corresponds to a reduction in the voltage by 80 mV, accordingly from 3.09 to 3.01. Elements having a markedly higher voltage were...

example 2

[0048]A laboratory electrolytic cell was operated as described in Example 1 at a current density of 4 kA / m2 at a cell voltage of 3.05 V with a standard cathode coating from Denora on the nickel cathode. After shutting down the cell without applying a protective potential, damage to the cathode coating occurred. A protective potential is conventionally applied during a shut-down in order to protect the coating of the cathode from damage. After re-starting, the cell voltage was 3.17 V.

[0049]A solution of hexachloroplatinate having a platinum content of 1250 mg / l Pt was metered into the catolyte while the cell was operating. After metering the solution for 2 hours with a metered amount of 5 ml / h, the voltage fell to 3.04 V. A total of 12.5 mg of platinum (12.5 mg / 100 cm2) was added.

example 3

[0050]The test of Example 2 was repeated, but a solution having a platinum concentration of 250 mg / l was metered in (same metering time and same feed capacity). Addition here 2.5 mg Pt / 100 cm2. The voltage fell from 3.16 V to 3.07 V, i.e. by 90 mV.

[0051]Further additional metering did not bring about any further voltage reduction.

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Abstract

The invention relates to a method for improving the performance of nickel electrodes in alkali chloride electrolysis by adding water-soluble platinum compounds to the catolyte.

Description

RELATED APPLICATIONS[0001]This application claims benefit to German Patent Application No. 10 2007 003 554.5, filed Jan. 24, 2007 which is incorporated by reference in its entirety for all useful purposes.1. FIELD OF THE INVENTION[0002]The invention relates to a method for improving the performance of nickel electrodes in alkali chloride electrolysis.2. BACKGROUND OF THE INVENTION[0003]In sodium chloride electrolysis, hydrogen is evolved from an alkaline solution. Conventionally, the cathodes in the process are made of iron, copper, steel, or nickel. Nickel electrodes can be either solid nickel or nickel plated.[0004]As mentioned in Offenlegungsschrift EP 298 055 A1, nickel electrodes can be coated with a metal from sub-group VIII, especially the platinum metals (inter alia Pt, Ru, Rh, Os, Ir, or Pd), of the periodic system of the elements or with an oxide of such a metal or with mixtures thereof. After a calcination process, the corresponding noble metal oxides are then usually pre...

Claims

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Application Information

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IPC IPC(8): C25C7/00
CPCC25B1/46C25B15/08C25B11/0447C25B11/0405C25B11/051C25B11/075C25D5/18C25D3/50C25D3/567C25D21/14C25D21/18
Inventor BULAN, ANDREASWEBER, RAINERMALCHOW, RICHARDSPATZ, ROLFWOMELSDORF, HERMANN-JENS
Owner COVESTRO DEUTSCHLAND AG