Production of benzenepolycarboxylic acids by oxidation of pre-pyrolyzed Shengli lignite

Abstract

ABSTRACTLignite oxidation would produce benzene polycarboxylic acids (BPCAs), however, the coexisting aliphatic acids in the resulting oxidation products seriously affect the separation of BPCAs. In the study, Shengli lignite was pre-pyrolyzed at different temperatures from 250°C to 550°C, and then the obtained pyrolyzed residues were subjected to oxidation under the same condition. Oxidation reactivity of pyrolyzed residues decreased with increasing pyrolysis temperature. However, compared with Shengli lignite, its pyrolyzed residues at proper temperatures (250°C and 350°C) generated more BPCAs, especially mellitic acid with more yield and relative content. By XRD analyses of the pyrolyzed residues, more condensed aromatic structures would result in decreasing oxidation reaction activity of the pyrolyzed residues, while more amounts of aromatic species and larger aromatic unit would contribute to the increase of BPCAs and mellitic acid, respectively.