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Electrode reactions in the chlorate process
KTH, Superseded Departments, Chemical Engineering and Technology.ORCID iD: 0000-0001-5816-2924
2002 (English)Doctoral thesis, comprehensive summary (Other scientific)
Place, publisher, year, edition, pages
Stockholm: KTH , 2002. , 47 p.
Series
Trita-KET, ISSN 1104-3466 ; 163
National Category
Chemical Engineering
Identifiers
URN: urn:nbn:se:kth:diva-3442OAI: oai:DiVA.org:kth-3442DiVA: diva2:9242
Public defence
2002-12-06, 00:00 (English)
Note
QC 20100525Available from: 2002-12-03 Created: 2002-12-03 Last updated: 2010-05-25Bibliographically approved
List of papers
1. Ruthenium-based dimensionally stable anode in chlorate electrolysis - Effects of electrolyte composition on the anode potential
Open this publication in new window or tab >>Ruthenium-based dimensionally stable anode in chlorate electrolysis - Effects of electrolyte composition on the anode potential
2003 (English)In: Journal of the Electrochemical Society, ISSN 0013-4651, Vol. 150, no 1, D6-D12 p.Article in journal (Refereed) Published
Abstract [en]

In this work the anodic reactions taking place on a dimensionally stable anode (DSA) in chlorate electrolyte have been investigated. Rotating disk electrodes were made from commercial RuO2-catalyzed DSAs and studied in steady-state polarization measurements, mainly IR-corrected polarization curves. Effects of varying pH and electrolyte concentrations of chloride, chlorate, chromium(VI), hypochlorite (ClO- + ClOH) as well as mass transport were studied. The kinetics for the chlorine evolution reaction, with a Tafel slope of 40 mV/decade of current, was not dependent on pH in the region 2-8, at potentials lower than 1.2 V vs. Ag/AgCl. The slope of the polarization curves increased at about 1.2 V vs. Ag/AgCl, a pH-dependent bend not due to mass-transport limitations in the electrolyte. At a pH of 6.5, typical for the chlorate process, oxygen evolution is an important side reaction favored by the dichromate buffer and by increased mass transport, both keeping down the pH at the anode. In the chlorine evolution region the potentials increased when adding Cr(VI) to the electrolyte, whereas no major effect was seen from additions of NaClO. (C) 2002 The Electrochemical Society.

Keyword
CHLORINE EVOLUTION, HYPOCHLORITE, REDUCTION, HYDROXIDE, CHROMATE, OXYGEN, CELL
Identifiers
urn:nbn:se:kth:diva-13050 (URN)10.1149/1.1522386 (DOI)000180069000036 ()
Note
QC 20100525Available from: 2010-05-25 Created: 2010-05-25 Last updated: 2010-05-25Bibliographically approved
2. Ruthenium based DSA in chlorate electrolysis–critical anode potential and reaction kinetics
Open this publication in new window or tab >>Ruthenium based DSA in chlorate electrolysis–critical anode potential and reaction kinetics
2003 (English)In: Electrochimica Acta, ISSN 0013-4686, E-ISSN 1873-3859, Vol. 48, no 5, 473-481 p.Article in journal (Refereed) Published
Abstract [en]

Ruthenium based DSA®s have been investigated in chlorate electrolyte using rotating discs made from commercial electrodes. Measurements of the voltammetric charge, q*, and of iR-corrected polarisation curves up to current densities of 40 kA/m2 were recorded on new anodes and on aged anodes from 3 years of production in a chlorate plant. Anodic polarisation curves in chloride containing electrolytes bend towards a higher slope at approximately 1.2 V versus Ag/AgCl, likely due to oxidation of ruthenium. The potential and current density at which the curves bend have been defined as the critical potential, Ecr, and the critical current density, icr. New anodes that operate at a relatively high potential, >Ecr, obtain an increase in real surface area and thereby a decrease in anode potential and in the selectivity for oxygen formation during the first months of operation. Experiments at constant ionic strength under chlorate process conditions showed that Ecr decreased with increasing chloride concentration with a factor of −0.09 V/log Cl, whereas icr increased with increasing chloride concentration. The chlorine evolution reaction was of the first order with respect to chloride concentration. A possible reaction mechanism for chlorine formation is suggested.

Keyword
Chlorate electrolysis, DSA, RuO2, Critical potential, Reaction kinetics
Identifiers
urn:nbn:se:kth:diva-13051 (URN)10.1016/S0013-4686(02)00679-5 (DOI)000180654800003 ()2-s2.0-0037438760 (Scopus ID)
Note

QC 20100525

Available from: 2010-05-25 Created: 2010-05-25 Last updated: 2016-05-31Bibliographically approved
3. The effect of addition of chromate on the hydrogen evolution reaction and on iron oxidation in hydroxide and chlorate solutions
Open this publication in new window or tab >>The effect of addition of chromate on the hydrogen evolution reaction and on iron oxidation in hydroxide and chlorate solutions
1992 (English)In: Electrochimica Acta, ISSN 0013-4686, E-ISSN 1873-3859, Vol. 37, no 10, 1873-1881 p.Article in journal (Refereed) Published
Abstract [en]

The addition of chromate to the electrolyte has been shown in previous papers to hinder almost completely the electroreduction of hypochlorite, while the hydrogen evolution reaction can still proceed on the cathode surface. The effect of chromate on the latter reaction has been studied with cyclic voltammetry and by measuring polarization curves for iron electrodes in both chlorate and hydroxide electrolyte. For the sake of comparison, the investigations have also included the effects on the gold electrode in hydroxide solution. The results showed that the kinetics is changed in a way that decreases the differences in electrocatalytic activity between different electrode materials. Also, the innermost layer of the chromium hydroxide film seems to be the most active part in the HER. The chromate also affects the oxidation of the iron surface. A practical result of this is that the activity for the HER on corroded iron in chlorate electrolyte depends on whether the electrolyte contained chromate during the period of corrosion. The activation becomes much smaller if chromate is present.

Keyword
chlorate manufacture, chromate, chromium hydroxide, hydrogen evolution reaction, iron oxidation
National Category
Chemical Engineering
Identifiers
urn:nbn:se:kth:diva-13052 (URN)10.1016/0013-4686(92)85093-Z (DOI)
Note

QC 20100525

Available from: 2010-05-25 Created: 2010-05-25 Last updated: 2016-05-31Bibliographically approved
4. Ruthenium Dioxide as Cathode Material for Hydrogen Evolution in Hydroxide and Chlorate Solutions
Open this publication in new window or tab >>Ruthenium Dioxide as Cathode Material for Hydrogen Evolution in Hydroxide and Chlorate Solutions
1993 (English)In: Journal of The Electrochemical Society, Vol. 140, no 11, 3123-3129 p.Article in journal (Refereed) Published
Abstract [en]

Ruthenium dioxide as electrocatalyst on an activated cathode for chlorate production was investigated with respect toits activity towards hydrogen evolution, hypochlorite reduction, and chlorate reduction, respectively. Investigations weremade in the presence, as well as in the absence, of a chromium hydroxide film in 1M NaOH and in typical chlorateelectrolyte. Low overvoltages for hydrogen evolution were found and, at technical current densities, an effect of catalystcoating thickness. Commercial DSA® electrodes with RuO2 as the active compound were tested as cathodes and were lessactive but more stable than the coatings produced by us. Hypochlorite and chlorate were reduced in the absence ofchromate, chlorate reduction being fast on ruthenium dioxide compared to the other electrode materials and by far thedominating cathodic reaction in chlorate electrolyte without chromate and hypochlorite at 70°C, 3 kA/m2

Keyword
catalysts; catalysis; ruthenium compounds; oxygen compounds; electrochemistry; electrochemical electrodes; reduction (chemical); reaction kinetics
National Category
Chemical Engineering
Identifiers
urn:nbn:se:kth:diva-13053 (URN)10.1149/1.2220996 (DOI)
Note
QC 20100525Available from: 2010-05-25 Created: 2010-05-25 Last updated: 2013-02-08Bibliographically approved

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