Extraction and thermal dissolution of Piliqing subbituminous coal

Abstract Piliqing subbituminous coal (PSBC) was exhaustively extracted with isometric acetone/carbon disulfide mixed solvent under ultrasonic irradiation to afford extractable portion (EP) and extraction residue (R E ). Then R E was subjected to sequential thermal dissolution (TD) in ethanol at 200, 240, 280, and 320 °C and TD at each temperature was conducted for 2 h. The sequential TD provided soluble portions (SPs) 1–4 (SP 1 –SP 4 ) and residue 4 (R 4 ). EP and the SPs were analyzed with a gas chromatograph/mass spectrometer and Fourier transform infrared (FTIR) spectrometer, while PSBC, R E , and R 4 were characterized with a solid-state 13 C nuclear magnetic resonance (SS 13 C NMR), FTIR, and X-ray photoelectron spectrometer (XPS). In total, ca. 36 wt% of organic matter was released from PSBC by the ultrasonic extraction and sequential TD. EP is rich in normal alkanes and arenes, while dialkoxyalkanes are predominant in SP 1 and esters are the main compounds in SP 2 –SP 4 . No significant difference in the distribution of functional groups was observed in FTIR spectra of PSBC and R E , while the distribution of functional groups in R 4 is significantly different from that in either PSBC or R E . According to analysis with XPS, the content of oxygen-containing species in R 4 is relatively low. PSBC consists of 32.6% aliphatic carbon atoms, 63.0% aromatic carbon atoms, and 4.4% carbonyl carbon atoms, while the content (2.0%) of carbonyl carbon atoms in R 4 is significantly lower than that (4.4%) in PSBC based on analysis with SS 13 C NMR.