Abstract
AbstractBackgroundChromium(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.ResultsThis 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.ConclusionIn 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.
Highlights
About 95% of the sodium chlorate produced worldwide is used in kraft pulp bleaching.[1]
An authorization must be granted by the European Commission for continued industrial use in Europe and a search for alternatives[6] to chromium(VI) in the chlorate process is of high concern
The effect of chromium(VI) on hypochlorite decomposition in dilute solutions The rate and selectivity of hypochlorite decomposition was first studied in dilute solutions (80 mmol dm−3 hypochlorite (B)
Summary
About 95% of the sodium chlorate produced worldwide is used in kraft pulp bleaching.[1]. An authorization must be granted by the European Commission for continued industrial use in Europe and a search for alternatives[6] to chromium(VI) in the chlorate process is of high concern. In this search, it is important to gain a better understanding of the functions of chromium(VI) in the process.[5] Even though the effect of chromium(VI) on the cathode reactions has been extensively studied,[7,8,9,10,11] less is known about its role in the homogenous decomposition of hypochlorite, and most importantly, the losses due to oxygen formation has not been clarified yet. How chromium(VI) affects these reactions is not well understood
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