Wet oxidation of selected organic carboxylates in highly alkaline solution

Dong, S 2013, Wet oxidation of selected organic carboxylates in highly alkaline solution, Doctor of Philosophy (PhD), Applied Sciences, RMIT University.

Document type: Thesis
Collection: Theses

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Title Wet oxidation of selected organic carboxylates in highly alkaline solution
Author(s) Dong, S
Year 2013
Abstract Organic impurities in Bayer liquor have a number of adverse effects on the production of alumina (the precursor material used to produce aluminium metal). Development of improved processes for removing these impurities from Bayer liquor is therefore of great interest to the alumina industry. Removal processes based on oxidation that do not involve the introduction of foreign species have received the most interest for achieving this goal. Of the aforementioned type of processes the wet oxidation process in particular has received significant attention. A better understanding of the underlying reaction mechanisms involved in the wet oxidation of organic impurities is a key aspect in the development of this technology. Sodium malonate, an organic impurity which presents in most worldwide Bayer liquors, has been shown to be unusually reactive under typical wet oxidation conditions. It can also accelerate the degradation of other low-molecular-weight Bayer organics, which are stable in isolation under typical wet oxidation conditions. The chemistry involved in the wet oxidation of sodium malonate, and the related co-oxidation of Bayer organics by malonate, is however poorly understood. A greater understanding of this chemistry could potentially lead to significant improvements in wet oxidation technology.

In this PhD project the chemistry of the wet oxidation of sodium malonate and a range of substituted malonates under typical wet oxidation conditions were studied in detail. The influence of the key structural feature of the malonates on the reactivities of these compounds was examined by comparing their reactivities with those of their isomers that do not have the same structural feature. The main reaction steps in the oxidation mechanisms of malonate and the substituted malonates were investigated by obtaining direct and indirect experimental evidences using multiple techniques including 13C NMR, HPLC, GC/MS, EPR and detailed analysis of the reaction kinetics.

The research conducted led to a greater understanding of the chemistry involved in the wet oxidation of malonate and similar compounds in highly alkaline solution. A key finding was the discovery that the co-oxidation of other compounds by malonate most likely involves a catalytic process. Optimisation of this catalytic process could lead to a highly efficient method for removing organic impurities from Bayer liquor.

Degree Doctor of Philosophy (PhD)
Institution RMIT University
School, Department or Centre Applied Sciences
Keyword(s) Wet oxidation
Low-molecular-weight Bayer organics
Bayer liquor
Reaction mechanism
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Created: Tue, 03 Dec 2013, 15:43:29 EST by Leona Campitelli
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