New Insights into the Conversion of Acetic Acid in Sodium Aluminate Solutions by AOPs

Acetic acid is an abundant and relatively stable organic compound in Bayer liquors. Oxalic acid can be formed by the conversion of acetic acid in sodium hydroxide solutions. However, some conditions under which conversion occurs and the conversion mechanism remain unclear. In this work, the conversion behavior of acetic acid in sodium aluminate solutions was investigated using advanced oxidation techniques. Several factors, such as SPS dosage, initial organic concentration, caustic soda concentration, reaction temperature, reaction time, activator type (CuO, Fe2O3, MnO2, Ni2O3) and dosage, on the conversion behavior of acetic acid were also investigated. In addition, the intermediates were measured under different conditions, and the conversion mechanism was also discussed. The results showed that the type of conversion products was not changed by changing the SPS dosage, initial organic concentration, reaction temperature, reaction time, and type and concentration of activator. However, it was changed by the caustic soda concentration. In solutions with low caustic soda concentrations (< 110 g/L), oxalic acid was produced by the conversion of acetic acid, and succinic acid synthesis was also observed for the first time; formic acid was generated at high caustic soda concentrations (>= 110 g/L). Total organic carbon (TOC) removal was directly proportional to SPS dosage, initial organic concentration, reaction temperature, and reaction time and inversely proportional to caustic soda concentration. The TOC removal and conversion of acetic acid to oxalic acid were enhanced by the addition of an activator. The EPR results showed that SO4-center dot\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${\text{SO}}_{{4}}<^>{ - \cdot }$$\end{document}, HO center dot\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${\text{HO}}<^>{ \cdot }$$\end{document}, and O2 center dot-\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${\text{O}}_{{{2}<^>{ \cdot - } }}$$\end{document} were the main reactive groups leading to the conversion of acetic acid.