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- Endrodi, Balázs, et al.
(författare)
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Suppressed oxygen evolution during chlorateformation from hypochlorite in the presenceof chromium(VI)
- 2019
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Ingår i: Journal of chemical technology and biotechnology (1986). - : Wiley. - 0268-2575 .- 1097-4660. ; 94:5, s. 1520-1527
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Tidskriftsartikel (refereegranskat)abstract
- BACKGROUND: Chromium(VI) is a crucial electrolyte component in industrial chlorate production. Due to its toxicity, iturgently 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 hypochloriteboth in dilute and concentrated, industrially relevant solutions. The effect of the ionic strength and the specific contributionof different electrolyte components were systematically studied. By simultaneously measuring the concentration decayof hypochlorite (UV–vis spectroscopy) and the oxygen formation (mass spectrometry), both the rate and the selectivity of thereactions were evaluated.CONCLUSION: In the presence of chromium(VI) the hypochlorite decomposition is described by the sum of an uncatalyzedand 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 selectivefor chlorate formation is emphasized.
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| 2. |
- Sandin, Staffan, 1984-, et al.
(författare)
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Deactivation and selectivity for electrochemical ozone production at Ni- and Sb-doped SnO2 / Ti electrodes
- 2020
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Ingår i: Electrochimica Acta. - : PERGAMON-ELSEVIER SCIENCE LTD. - 0013-4686 .- 1873-3859. ; 335
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Tidskriftsartikel (refereegranskat)abstract
- This work reports on a time-resolved study of the deactivation of electrochemical ozone production (EOP) active anodes using a novel approach to measure total ozone production. The reproducibility and change of the electrodes over time have been investigated using a number of electrochemical and physical techniques. The dissolution of antimony from the surface of the nickel- and antimony-doped tin oxide (NATO) electrode is the main process behind the deactivation of the EOP. When surface antimony is depleted, the continued deactivation seems to be connected to the dissolution of nickel. Despite tin (from the coating) and titanium (from the substrate) continuously dissolving during galvanostatic polarization of the NATO electrode, our experiments point to no connection between these processes and the EOP activity. In addition, the selectivity of the electrode is affected by electrolyte penetration, accessing fresh reaction sites that are active on the EOP. The results indicate that both antimony (III) and nickel present at the surface of the NATO are responsible for the EOP activity.
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| 3. |
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| 4. |
- Sandin, Staffan, 1984-
(författare)
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Oxygen formation in the chlorate process and preparation and deactivation of ozone selective anodes
- 2019
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis presents experimental studies concerning two differ-ent electrolytic processes. One part deals with the electrochemicalformation of ozone and focuses on the preparation and deactiva-tion of a highly ozone-selective metal oxide anode (NATO - nickeland antimony doped tin oxide). The preparation of this anode bythermal decomposition of metal chloride salts was investigated anddifficulties and complications of common procedures were identi-fied. The same anodes were also studied regarding the deactivationof their ozone selective properties, identifying possible underlyingmechanisms for this as well as providing indications of the ozoneformation mechanism on the anode. When preparing these anodesby thermal decomposition, the volatility of the precursor salt usedfor the different components needs to be considered. For instanceextensive evaporation of the precursors of tin and antimony canlead to an unreliable preparation process resulting in the difficultyof controlling the properties of the prepared electrodes and a poorreproducibility of the process. The deactivation of the NATOelectrodes was investigated using the ozone current efficiency as amain indicator. The electrodes and the electrolyte were examinedusing electrochemical as well as physical techniques after differentperiods of galvanostatic polarization. The main mechanism behindthe deactivation was identified as the dissolution of antimony fromthe electrode surface. Also contributing, but not as detrimental,seems to be the dissolution of nickel. Both dopants, Ni and Sb, arepresent at the surface of the oxide anode and both seem equallyimportant for enabling the electrochemical ozone formation.The second part of this thesis concerns the decomposition ofhypochlorite, an important intermediate in the industrial chlorateprocess. A connection was found between the formation of chlorateand oxygen, both occurring according to 3rd order kinetics withregard to hypochlorite and both having their highest rates atpH 6 - 7. In the presence of chromium(VI) the hypochloritedecomposition can be modelled as the sum of two parallel reactions:one catalyzed by chromium(VI) and one uncatalyzed reaction.The byproduct oxygen seems to be formed only in the latter. Thusvaddition of chromium(VI) in the electrolyte increases both therate and the selectivity of chlorate formation. These findings areimportant as chromium(VI) needs to be removed from the processdue to its toxicity and in its absence the uncatalyzed decompositionpath would lead to an increase in oxygen formation, resultingin efficiency losses as well as potentially explosive gas mixtures.There is a need for a catalyst that can replace chromium(VI) inthis function.
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