Evaluation of Macromolecular Structure of a Brown Coal by Means of Oxidative Degradation in Aqueous Phase

Abstract

Acid-washed Morwell brown coal was oxidized at 85 °C in a 0.5 N Na2CO3 aqueous solution in a closed system, through which oxygen gas was bubbled. The oxidation took 1−12 h and consumed 1.8−5.8 mmol of O2 per gram of the coal. Analyses of the products revealed that aromatic carbon was selectively oxidized into carboxyls in the residual solid (oxidized coal), water-soluble nonaromatic acids, and carbon dioxide, while aliphatic carbon was minimally involved in the reaction. Considering that the coal consists of two major structural elements, aromatic clusters (mono- or fused aromatic rings with peripheral groups) and intercluster bridges (alkyl groups and ethers connecting clusters), it was concluded that the oxidation converted aromatic carbons bonded to bridges into peripheral carboxyl groups on the neighboring clusters and also converted the other aromatic carbons into nonaromatic acids or carbon dioxide. According to the mechanism of the oxidation, which decomposed the macromolecular network of the coal-...