The degradation of twenty-one low-molecular-weight organic carboxylates has been studied at 90 and 180 °C in a synthetic Bayer liquor consisting of 6 mol kg -1 aqueous NaOH solution for periods of up to 36 days. The reactions were monitored and the major degradation products identified by HPLC and NMR spectroscopy. The carboxylates chosen for study either could be intermediates, or occur as a result of decomposition of organic matter in the Bayer process. Aliphatic carboxylates without hydroxyl substituents were stable at 90 °C but decomposed at 180 °C, except for formate, acetate, oxalate and succinate. The corresponding aromatic carboxylates were stable even at 180 °C. Both aliphatic and aromatic carboxylates with hydroxyl substituents were unstable at 90 °C, except for lactate and 4-hydroxybenzoate. The most frequently detected decomposition products for both aliphatic and aromatic carboxylates were formate, acetate, oxalate, succinate and lactate. Phenolate was also observed for some aromatic carboxylates. These products are briefly discussed with reference to possible mechanisms for the degradation reactions.

The degradation of nineteen low-molecular-weight phenolates, polyalcohols and selected aliphatic and aromatic carboxylates of relevance to the Bayer process has been studied in 6 mol kg -1 NaOH(aq) at 90 °C for up to 36 d, and (for some species) at 180 °C for up to 12 d, using HPLC and 13 C-NMR spectroscopy. Aliphatic polyalcohols degraded readily at 90 °C to lactate, oxalate, acetate, and formate. As observed previously, aliphatic carboxylates with hydroxyl groups also degraded readily at 90 °C but there is evidence that the position of the hydroxyl group may be important. The observed degradation products for most, but not all, of these species can be explained in terms of well-known organic reaction mechanisms. Phenolate adn 5-hydroxyisophthalate were stable at 180 °C but other phenolic species degraded partially at 90 °C. However, the reaction products could not be identified and no trends in reactivity were discernible. Consistent with previous studies both aliphatic and aromatic carboxylates without hydroxyl groups were generally stable in NaOH(aq) even at 180 °C.

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The formation of volatile substances such as hydrogen, methane, ketones, and aldehydes during alumina production using the Bayer process is of interest because of their process and occupational safety and health implications. To better understand how these substances are generated in the Bayer process, the decomposition of a selection of low- and high-molecular-weight organic materials has been studied at 180 °C in a synthetic Bayer liquor consisting of 6 m NaOH. The main vapor-phase products were identified using gas chromatography with thermal conductivity or mass spectrometry detection. The results showed that caustic degradation of organic compounds commonly occurring in Bayer process liquors produces a range of substances known to be present in alumina refinery emissions. The main volatile products were H2, CH4, and certain carbonyl compounds with low odor thresholds, such as 2-butanone and propanone. There was also some evidence for the production of volatile pentacyclic compounds.

The oxidative scission of methyl ethyl ketone and 2-butanol on a VO x -TiO2 and a VO x /SbO y -TiO2 catalyst was studied in the temperature range of 120 to 280°C in the presence of water vapour. The catalytic performance of the two catalysts was investigated by variation of reaction temperature and contact time, and the catalysts were characterized by BET, XRD, XPS, TPR-H2, TPD-NH3, and temperature programmed desorption of lattice oxygen (TPD-O2). The investigations indicate that the addition of Sb2O3 to VO x -TiO2 favours the selective formation of acetic acid and depresses total oxidation to CO x in the catalytic oxidation of methyl ethyl ketone and 2-butanol due to changes in the redox properties of the VO x -TiO2 system. Moreover, the higher acidity of the VO x -TiO2 catalyst favours the dehydration of 2-butanol to n-butenes.