Comparative studies on the structural features of soluble portions from thermal dissolution/methanolysis and catalytic hydroconversion of an extraction residue from Heishan lignite

Heishan lignite (HL) was extracted with isometric acetone/carbon disulfide mixed solvent under ultrasonic irradiation. The extraction residue (ER) was subjected to thermal dissolution/methanolysis (TD/M) in methanol and catalytic hydroconversion (CHC) in cyclohexane (CH) at 300 °C under 1 MPa of N2 over a supported acid (SA). The methanol-soluble portion (MSP) from the TD/M and CH-soluble portion (CHSP) from the CHC were analyzed with a gas chromatograph/mass spectrometer (GC/MS) and Fourier transform infrared (FTIR) spectrometer, while ER and the residues from the TD/M (RTD/M) and CHC (RCHC) were characterized with the FTIR spectrometer and an X-ray photoelectron spectrometer (XRPES). The results show that the yields of MSP and CHSP are ca. 22.6% and 16.1%, respectively. According to the analysis with GC/MS, CHSP is rich in tetramethylbenzenes and dimethylnaphthalenes, while most of the GC/MS-detectable compounds in MSP are xylenols, trimethylphenols, and methyl normal alkanoates. During the TD/M, the cleavage of some CO bonds could be the main reaction, whereas the SA effectively catalyzed the cleavage of CarCalk bonds connecting some aromatic rings (ARs) and side chains on the ARs in ER. No significant difference in the distribution of functional groups was observed in FTIR spectra between HL and ER, while the distribution of functional groups in MSP is extraordinarily different from that in CHSP. According to the analysis with XRPES, RTD/M has higher carbon content but lower oxygen content.