Clean two-step oxidative degradation of Yima long flame coal for benzenecarboxylic acid production

Low rank coals are promising raw materials to afford oxygenated organic chemicals due to the high oxygen contents. This study reported a clean two-step coal oxidative degradation approach for low-carbon and high value-added chemical production. Oxidative degradation of Yima long flame coal (YLFC) was performed in aqueous hydrogen peroxide solution (AHPS) to activate the aromatic ring structures in YLFC, followed by the further oxidation with aqueous sodium hypochlorite solution (ASHS) to degrade the macromolecular networks in YLFC into soluble portions. Meanwhile, oxidation of YLFC with ASHS was also performed to investigate the role of pretreatment with AHPS in the oxidative degradation of YLFC in ASHS. The results show that 95.5% of the macromolecular structure in YLFC was converted by the two-step oxidation, while the conversion rate of YLFC in ASHS is only 59.3%. Noteworthily, the pretreatment with AHPS is more effective to increase the yields of more valuable pentacarboxy benzene and mellitic acid compared with benzenecarboxylic acids with fewer carboxylic groups. The sharp increase in the yield of oxidation products by pretreatment with AHPS could be related to.OH produced from H2O2 decomposition, which can break the weak oxygenated linkages and generate oxygenated functional groups. Thus, the activated aromatic ring structures and improved hydrophilicity of YLFC contribute to the deep decomposition of condensed aromatic rings caused by aggression of the reactive intermediate O2-. generated from ionization equilibriums in ASHC. The synergistic effect of the two-step oxidation leads to the complete degradation of macromolecular networks in YLFC.