Hydrogen peroxide oxidation degradation of a low-rank Naomaohu coal

A mild controllable oxidation method was developed to depolymerize the macromolecular aromatic clusters of NMH coal into water-soluble products (WSPs) without ring-open reaction. Hydrogen peroxide (H2O2) was employed to oxidize coal sample at 60 degrees C, and the effect of reaction time on coal conversion and oxidation products was studied. The results showed that H2O2 is able to break bridge bonds and side chains connected to aromatic clusters, while Car-Car bonds of arene keep unchanged at same conditions. After 10 h oxidation, the coal conversion is 83.4 wt% and the aromaticity of oxidation residue is 7.43%, indicating most of aromatics have transferred to WSPs. The aromatic ring distribution in WSP can reflect that of NMH coal to some extent, where 1ring, 2-ring and 3-ring compounds account for 58.4 mol%, 19.9 mol% and 21.7 mol%, respectively. Moreover, the pyrolysis of NMH coal and oxidation residue was conducted on an online pyrolysis-vacuum ultraviolet photoionization mass spectrometry, and the oxidation of several typical model compounds was also carried out to understand the oxidation mechanism. The results showed that the PhO-RPh bonds between aromatic clusters are most easily destroyed by H2O2. H2O2 oxidation degradation of coal are accompanied by generation of alkenes and decarboxylic reaction.