Oxidation of Coals in Liquid Phases. VII. Oxidation of Oxygen-containing Model Compounds of Coal by Oxygen in Concentrated Sodium Hydroxide Solutions

Abstract

Abstract Oxidation of 26 model compounds of low-ranked coal was performed to study the formation mechanisms of oxalic acid from coal. A mixture of 0.02 mol of the model compound, 4–60 g of NaOH, and 50 g of water was placed in a 300 cm3 autoclave and oxidized at 523 K and PO2=5 MPa for 120 min. Acetic acid was produced from phenols within 15 min and oxidized selectively to oxalic acid. The yield ratio(yield of oxalic acid(%)/yield of CO2 (%)) from most of the model compounds was higher than 1. These phenomena agreed well with those of low-ranked coal under the same oxidation conditions. The overall reaction rates, yields of oxalic acid, and yield ratios increased rapidly with an increasing concentration of NaOH as in the oxidation of coal. This behavior can be explained resonably well by an alkali-catalyzed oxidation mechanism regarding organic substances.