Insight into structural feature of the extraction residue from Shenmu coal char powder

•Highly condensed aromatic moieties are predominant in the extraction residue from SCCP.•PMBPCs were identified with both GC/MS and DART/TOF-MS.•[M-OCH3]+ and [M + NH4]+ are the main ions from PMBPCs during analysis with DART/TOF-MS.•A series of dimers and trimers of PMBPCs were identified with DART/TOF-MS.

Ruthenium ion-catalyzed oxidation of the extraction residue from Shenmu coal char powder (ERSCCP) was conducted. The resulting soluble portions (SPs) were analyzed with a gas chromatograph/mass spectrometer (GC/MS) and direct analysis in real time/time-of-flight mass spectrometer (DART/TOF-MS) to obtain carboxylic acids and to understand the structural feature of ERSCCP. The results show that benzenepolycarboxylic acids with 3–6 carboxy groups are predominant in the SPs, suggesting that ERSCCP is rich in highly condensed aromatic moieties. In addition, small amounts of long-chain alkanoic acids were detected with GC/MS. According to analysis with positive-ion DART/TOF-MS, [M - OCH3]+ and [M + NH4]+ are dominant ions generated from polymethylbenzenepolycarboxylates (PMBPCs) in the methyl esterified SPs. A series of dimers and trimers of PMBPCs were also identified with positive-ion DART/TOF-MS.