Investigation on structural features of Shengli lignite through oxidation under mild conditions

► The structural features of SL were investigated through mild oxidations. ► -CH2CH2- is a dominant bridged linkage connecting aromatic rings in SL. ► Most of organic matter in SL became soluble fractions by mild oxidations. ► SL is rich in hydroxyl-, methoxy-, and/or methyl-substituted benzene rings.