The catalyzing effect of chromate in the chlorate formation reaction

Wanngard, J.; Wildlock, Mats

doi:10.1016/j.cherd.2017.03.021

Cited by 25 publications

(70 citation statements)

References 25 publications

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“…Importantly, the decomposition rate no longer follows the third‐ order kinetic model, involving only hypochlorite species as reactants. Instead, in agreement with previous literature data, the hypochlorite decomposition rate

(r = - \frac{d C_{H}}{italicdt})

can be described by the sum of an uncatalyzed third‐order reaction

(r_{1} = k_{1} C_{H}^{3})

, and a parallel catalyzed reaction

(r_{2} = k_{2} C_{H}^{α})

(Eqn (6), further detailed in the Supporting information in File S1). Using this model, the experimental data was fitted to give a partial order of α = 2, with respect to hypochlorite species, in the second term.…”

Section: Resultssupporting

confidence: 89%

“…Recently, three papers reported on the rate enhancing effect of Na 2 Cr 2 O 7 addition on the homogeneous decomposition of hypochlorite . Regarding the kinetics of the decomposition, Spasojević found that the reaction order with respect to hypochlorite was 3, both in the absence and presence of chromium(VI).…”

Section: Introductionmentioning

confidence: 99%

“…Regarding the kinetics of the decomposition, Spasojević found that the reaction order with respect to hypochlorite was 3, both in the absence and presence of chromium(VI). Wanngård and Kalmár on the other hand found that in the presence of chromium(VI) the hypochlorite decomposition could be described by the sum of an uncatalyzed third‐order reaction, and a parallel catalyzed reaction of order ∼2 with respect to hypochlorite. In all studies, chromium(VI) species were included in the rate expressions.…”

Section: Introductionmentioning

confidence: 99%

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Suppressed oxygen evolution during chlorate formation from hypochlorite in the presence of chromium(VI)

Endrődi

Sandin

Wildlock

et al. 2019

J of Chemical Tech & Biotech

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Background Chromium(VI) is a crucial electrolyte component in industrial chlorate production. Due to its toxicity, it urgently needs to be abandoned and its functions fulfilled by new solutions. In the industrial production of sodium chlorate, homogeneous decomposition of the hypochlorite intermediate to chlorate is a key step. As a competing loss reaction, hypochlorite can decompose to oxygen. How chromium(VI) affects these reactions is not well understood. Results This work shows, for the first time, that chromium(VI) selectively accelerates the chlorate formation from hypochlorite both in dilute and concentrated, industrially relevant solutions. The effect of the ionic strength and the specific contribution of different electrolyte components were systematically studied. By simultaneously measuring the concentration decay of hypochlorite (UV–vis spectroscopy) and the oxygen formation (mass spectrometry), both the rate and the selectivity of the reactions were evaluated. Conclusion In the presence of chromium(VI) the hypochlorite decomposition is described by the sum of an uncatalyzed and a parallel catalyzed reaction, where oxygen only forms in the uncatalyzed reaction. When removing chromium(VI), the homogeneous oxygen formation increases, causing economic and safety concerns. The need for a catalyst selective for chlorate formation is emphasized. © 2018 The Authors. Journal of Chemical Technology & Biotechnology published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

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(r = - \frac{d C_{H}}{italicdt})

can be described by the sum of an uncatalyzed third‐order reaction

(r_{1} = k_{1} C_{H}^{3})

, and a parallel catalyzed reaction

(r_{2} = k_{2} C_{H}^{α})

Section: Resultssupporting

confidence: 89%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Suppressed oxygen evolution during chlorate formation from hypochlorite in the presence of chromium(VI)

Endrődi

Sandin

Wildlock

et al. 2019

J of Chemical Tech & Biotech

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“…3a. This result is in line with full-scale plant experiences and other pilot trials, as discussed in the literature [9,33]. In contrast, Hardee and Mitchel show in their experiments that the oxygen formation is constant with respect to the dichromate concentration in the range of 1-5 g dm -3 [9].…”

Section: Process Performancesupporting

confidence: 48%

“…Together with their claimed uncertainty in the measurements, it would not be possible to observe the same effect that is shown in the present work. The reason for the decrease in oxygen formation with increasing chromate concentration is due both to the buffering effect of the chromate system, keeping the electrolyte pH in the optimal region for chlorate formation, and to the catalytic activity of chromium (VI) towards the disproportionation reaction of chlorate formation [7,[33][34][35]. Both of these phenomena keep the reactant (hypochlorite and hypochlorous acid) concentrations in the electrolyte low, which in turn lowers the possibility for oxygen formation, both in the bulk electrolyte (reaction 11) and at the anode (reaction 8).…”

Section: Process Performancementioning

confidence: 99%

Current efficiency of individual electrodes in the sodium chlorate process: a pilot plant study

et al. 2017

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Current efficiency in the sodium chlorate process is a key issue in the evaluation of the power consumption. A pilot cell unit for executing the sodium chlorate process was constructed to study the current efficiency of the anode and cathode separately. The effects of sodium dichromate and sodium sulphate concentrations and the electrolyte temperature on the anode and cathode current efficiencies were studied. Corrosion products formed on the mild steel cathodes after their removal from the cell were characterised using X-ray diffraction and infrared spectroscopy. The results show that the cathodic current efficiency increases with increasing dichromate concentrations in the electrolyte until approximately 5 g dm -3 is reached. At this optimum concentration of dichromate, the presence of sulphate ions decreases the cathodic current efficiency. For moderate increases in temperature, the cathodic current efficiency increases, but oxygen evolution is promoted, and the power consumption also increases. Surface characterisation of the electrodes after their exposure to air shows two primary types of behaviour, depending on the process parameters. At low dichromate concentrations, amorphous corrosion layers are formed, while at higher concentrations, reduced forms of iron hydroxides, i.e., ''green rust'', are identified. Although the electrodes were positioned at the open circuit potential for 40 min before their removal from the cell, chromium remains on the cathode surface. This result might explain the corrosion-inhibiting effect of the addition of chromate to the electrolyte. The results from this study can be used to optimise operating procedures in real plants, decrease the energy consumption and minimise the environmental impact of these processes.Electronic supplementary material The online version of this article

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Exploring the Mechanism of Cr(VI) Catalyzed Hypochlorous Acid Decomposition**

Busch

Simic²,

Ahlberg

2022

ChemCatChem

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Chlorate is produced through electrolysis of a chloride containing electrolyte in an undivided cell. Cr(VI) is added to the electrolyte in order to minimize the amount of oxygen formed through the homogeneous decomposition of hypochlorite. Despite the importance of Cr(VI) for the chlorate process we posses only very limited knowledge regarding the active Cr(VI) species and mechanisms through which it aids chlorate formation and inhibits O 2 evolution. Using density functional theory (DFT) modeling we present for the first time a detailed reaction mechanism for the chromate catalyzed chlorate formation. Our calculations indicate, that the reaction is initialized by the formation of a Cr(VI)-OÀ ClOCl species which forms Cr(VI)-OClO intermediate. This step is found to be rate determining with a rate constant which is comparable to the disproportionation reaction without catalyst. Chlorate is then obtained either through an uncatalyzed oxidation of chlorite to chlorate or the nucleophilic attack of OCl À followed by a second Cl À elimination step. The comparison of the activity of the different Cr(VI) species reveals that only CrO 4 2À is active whereas HCrO 4À and Cr 2 O 7 2À display sluggish kinetics.[a] M.

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The catalyzing effect of chromate in the chlorate formation reaction

Cited by 25 publications

References 25 publications

Suppressed oxygen evolution during chlorate formation from hypochlorite in the presence of chromium(VI)

Suppressed oxygen evolution during chlorate formation from hypochlorite in the presence of chromium(VI)

Current efficiency of individual electrodes in the sodium chlorate process: a pilot plant study

Exploring the Mechanism of Cr(VI) Catalyzed Hypochlorous Acid Decomposition**

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