Oxidation of Shengli lignite with aqueous sodium hypochlorite promoted by pretreatment with aqueous hydrogen peroxide

Shengli lignite (SL) was pretreated in H2O2 aqueous solution at 40 °C for 4 h to obtain pretreated SL (PTSL). Both the SL and PTSL were oxidized in NaOCl aqueous solution at 30 oC for 5 h to investigate the effect of pretreatment (PT) on SL oxidation with NaOCl. Gas chromatography/mass spectrometry analysis shows that the PT with H2O2 significantly increased the yields of alkanoic acids, alkanedioic acids, and benzene carboxylic acids (BCAs), but substantially suppressed the formation of chloro-substituted alkanoic acids (CSAAs). The total yield (daf) of BCAs was 7.4% from SL and increased to 10.1% from PTSL, while that of CSAAs decreased from 5.4% for SL to 0.8% for PTSL. Direct analysis in real time ionization source coupled to mass spectrometry analysis exhibits that the PT with H2O2 enhanced the formation of compounds with molecular from m/z 300 to 500. The possible mechanisms for the PT and subsequent oxidation are discussed according to the experimental results. The cleavage of covalent bonds and introduction of oxygen functional groups such as −COOH and −OH by the PT could be responsible for the increase in the yields of soluble species.