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CO-OXIDATION OF REFRACTORY BAYER ORGANICS USING SODIUM MALONATE DERIVATIVES AND WET AIR OXIDATION

Tardio J, Dong J, Loh J, Power G, Vernon C, Bhargava S

Organic impurities in the liquor have a negative impact on both productivity and product quality in Bayer process refineries. Of the many organics removal processes that have been investigated, Wet Air Oxidation (WAO) is one of the few that has been successfully applied in practice. One of the limitations to wider application of WAO is that high temperatures (>275°C) are required to achieve a high level of removal of Bayer organics. Previous investigations have shown that oxidation reactions can be accelerated by the presence of free radicals produced by reaction of malonate with oxygen. This effect, in which the oxidation of a reactive compound facilitates the oxidation of less reactive compounds, has been termed “co-oxidation”.

This work extends the study of co-oxidizers to include a series of malonate derivatives, and examines some of the reaction products. It was found that reactivity of the co-oxidizer compounds themselves decreases with increasing molecular weight, in the order: malonate ≈ methyl malonate > ethyl malonate > phenyl malonate for WAO at 200oC in a synthetic Bayer liquor. The effectiveness of these compounds as co-oxidizers for succinate followed a similar order, suggesting a common mechanism. Sodium oxalate is a product of reaction in all cases, and some acetate is produced in the oxidation of methyl, ethyl and phenyl malonate.