Electrosynthesis of Chlorate in the Nineteenth Century

Vogt, Helmut

doi:10.1149/1.2127407

Cited by 20 publications

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“…In the early days large amounts of calcium(II) salts were added to the electrolyte to achieve acceptable current efficiency [6,7]. In the end of the 19th and beginning of the 20th century several research groups worked with the chlorate process and at that time it was discovered that the addition of multivalent metal ions could enhance the current efficiency [8].…”

Section: Introductionmentioning

confidence: 99%

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A review of chromium(VI) use in chlorate electrolysis: Functions, challenges and suggested alternatives

Endrődi

Simic

Wildlock

et al. 2017

Electrochimica Acta

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Sodium chlorate is industrially produced by electrolysis of an aqueous salt solution, in which chromium (VI) constitutes an important excipient component. It is added to a concentration of a few grams Na 2 Cr 2 O 7 /liter to the electrolyte and has several functions in the process, the most important being to increase the Faradaic efficiency for hydrogen evolution in the undivided electrochemical cells. A thin film of Cr(OH) 3 Â nH 2 O formed by reductive deposition on the cathodes decreases the rate of unwanted side reactions, while still enabling hydrogen evolution to occur. In addition chromium(VI) buffers the electrolyte at the optimum pH for operation and promotes the desired homogeneous reactions in the electrolyte bulk. Chromium species also affect the rates of hydrogen and oxygen evolution at the electrodes and are said to protect the steel cathodes from corrosion. Although chromium(VI) stays in a closed loop during chlorate production, chromate is a highly toxic compound and new REACH legislation therefore intends to phase out its use in Europe from 2017. A production without chromium(VI), with no other process modifications is not possible, and today there are no commercially available alternatives to its addition. Thus, there is an urgent need for European chlorate producers to find solutions to this problem. It is expected that chromium-free production will be a requirement also in other parts of the world, following the European example. As the chromium(VI) addition affects the chlorate process in many ways its replacement might require a combination of solutions targeting each function separately. The aim of this paper is to explain the role and importance of chromium(VI) in the chlorate manufacturing process. Previous achievements in its replacement are summarized and critically evaluated to expose the current state of the field, and to highlight the most promising avenues to be followed. An attempt is also made to reveal connections with other research fields (e.g. photochemical water splitting, corrosion science) facing similar problems. Allied effort of these different communities is expected to open up research avenues to the mutual benefit of these fields.

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Section: Introductionmentioning

confidence: 99%

“…The invention was described in 1899 by E. Müller as "the electrolysis with chromate present represents one of the most ideal diaphragm processes one can imagine" [12]. Compared to the previous calcium salt based electrolyte current efficiencies were improved from 40% to almost 90% [7].…”

Section: Introductionmentioning

confidence: 99%

A review of chromium(VI) use in chlorate electrolysis: Functions, challenges and suggested alternatives

Endrődi

Simic

Wildlock

et al. 2017

Electrochimica Acta

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“…Calcium hydroxide forms a diaphragm at the cathode surface, thus obstructing the reduction of hypochlorite [5]. Another suggested alternative to chromate is Mo(VI), which is claimed to have synergistic effects with Cr(VI) in increasing the current efficiency [6].…”

Section: The Chlorate Processmentioning

confidence: 99%

Rare earth metal salts as potential alternatives to Cr(VI) in the chlorate process

2010

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Chromate is today added to industrial chlorate electrolyte, where it forms a thin cathode film of chromium hydroxide that hinders unwanted reduction of hypochlorite and chlorate. The aim of this study was to investigate rare earth metal (REM) ions as an environmentally friendly alternative to the toxic chromate addition. Potential sweeps and iR-corrected polarisation curves were recorded using rotating disc electrodes of iron and gold. Addition of Y(III), La(III) or Sm(III) to 5 M NaCl at 70°C suppressed hypochlorite reduction. Activation of hydrogen evolution by REM ion addition to 0.5 M NaCl was more significant at 25°C than at 50 and 70°C. Increasing the chloride concentration to 5 M had a detrimental effect on this activation. The major problem in replacing chromate with REM salts is the poor solubility of REM ions at normal chlorate process conditions, and therefore REM salts are not a realistic alternative to chromate addition.

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“…Of particular note for the work in Chapter 3 of this thesis is that while it is known that chromium reduction produces more charge than the corresponding oxidation, and it has been proposed that an excess of reduced chromium goes into solution as Cr(OH)4 - [31], this mechanism was never demonstrated or quantified. The mechanism of reduction has been proposed as a direct 3-electron reduction of Cr(VI) to Cr(III) [12], although work on the reverse process, oxidation of Cr(III) to Cr(VI), suggests a series of 1-electron steps including formation of Cr(V) and Cr(IV) [52]. A container of sodium dichromate boasts five different hazard symbols as shown in Figure 1.6.…”

Section: Cathode Selectivitymentioning

confidence: 99%

“…In addition the reductive pathway is unclear. A direct 3-electron reduction of Cr(VI) to Cr(III) has been proposed [12], although work on the reverse process, oxidation of Cr(III) to Cr(VI), suggests a series of 1-electron steps including formation of Cr(V) and Cr(IV) [52].…”

Section: Introductionmentioning

confidence: 99%

Understanding selective thin films in the chlorate process

Smulders¹

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This chapter provides context and background information for the work in this thesis. First, chlorate is introduced and its applications are described. Then, an overview of the chlorate production process is provided, describing the reactions involved, the conditions in the industrial process, and a history of its development. 1.1.4 History of chlorate production and research Chlorate is one of the oldest electrochemical processes, with the first confirmed electrosynthesis dating back to 1802 [12]. The process was discovered by Wilhelm von Hisinger and Jöns Jakob Berzelius [12], hobbyist scientists, only two years after Alessandro Volta first invented the pile, a source of electrical current [13]. The first electrochemical plant opened in 1886 in Villers-St. Sépulcre, Switzerland, using a diaphragm setup in a reactor made of wood. It was not very successful due to cathodic losses, and production ended in 1898 [12]. Around the same year, plants opened in Buckingham and Niagara in Quebec, Canada. These had no diaphragm and used bipolar electrodes with a small cell gap (1.5 to 3 mm), already remarkably similar to today's designs [14]. At the turn of century there were also factories in Switzerland, Sweden, and France. Surprisingly, there were no factories in Germany, despite most chlorate research being performed there [12]. Research focused on developing an understanding of the formation of chlorate. Initially it was believed that the formation was a purely chemical process, but within a few years this theory was completely upended several times. The revisions were driven by thorough experiments and reportedly accompanied by "sometimes violent discussions" [12]. Several papers and discussions in rude tones were exchanged between Foerster and Wohlwill [15], [16] in particular. Foerster insisted there was no electrochemical aspect to chlorate formation, while Wohlwill, a student of Nernst, held that there was. The matter was eventually clarified in 1900 when Lorenz and Wehrlin published extensive experimental results that showed chlorate could be formed electrochemically under certain circumstances [17], although Foerster nevertheless maintained his stance [12]. Regardless of the exact mechanism, it was generally agreed that hypochlorite plays an important part in chlorate formation, and that its Finally, Chapter 7 summarizes my findings and provides a perspective on the future of this topic.

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Electrosynthesis of Chlorate in the Nineteenth Century

Cited by 20 publications

References 19 publications

A review of chromium(VI) use in chlorate electrolysis: Functions, challenges and suggested alternatives

A review of chromium(VI) use in chlorate electrolysis: Functions, challenges and suggested alternatives

Rare earth metal salts as potential alternatives to Cr(VI) in the chlorate process

Understanding selective thin films in the chlorate process

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