Investigation on the structural features of Hecaogou subbituminous coal and its residues by multiple technical strategies.

[Display omitted] • Extraction and subsequent E can release many SSs from HSBC and IEP. • The predominant CS in HSBC and its R s are aliphatic and aromatic carbons. • The main oxygen occurrence are >C-OH and >C-O- moieties in HSBC and its R s. • R S , especially R IEP , can be further used in pyrolysis or porous material precursors. The structural features (SFs) of Hecaogou subbituminous coal (HSBC) and its residues (R s) were investigated with non-destructive tools, including scanning electron microscope (SEM), solid-state 13C nuclear magnetic resonance (SS 13C NMR), Fourier transform infrared spectrometer (FTIRS), and X-ray photoelectron spectrometer (XRPES), combined with thermogravimetric analyzer (TGA) and flash pyrolysis (FP). SS 13C NMR analysis shows that both HSBC and its R s consist of aliphatic, aromatic, and carbonyl carbon species. The total content of aliphatic carbon species in the R s is lower than that in HSBC, but the content of carbonyl carbon species is basically unchanged. In both HSBC and its R s, aliphatic linkages connect 3–5 aromatic rings (ARs) and the number of substituents on each AR is up to 2 on average. Based on the semi-quantitative analysis with FTIRS and TGA, cleavaging weak- and medium-strength covalent bonds (>C al -X-, X denotes H, N, S, or >C al) should be the main reactions during the ethanolysis of HSBC and its inextractable portion. The analysis with XRPES indicates that the main oxygen-, nitrogen-, and sulfur-containing moieties are >C-O- groups, pyrrolic, and aromatic and sulfonic sulfurs, respectively, on the surface of HSBC and its R s. Considerable amounts of alkanes and alkenes were released and non-substituted arenes are the main arenes released from the FP of HSBC and its R s. [ABSTRACT FROM AUTHOR]