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 (RE). Then RE was subjected to sequential thermal dissolution (TD) in ethanol at 200, 240, 280, and 320°C and TD at each temperature was conducted for 2h. The sequential TD provided soluble portions (SPs) 1–4 (SP1–SP4) and residue 4 (R4). EP and the SPs were analyzed with a gas chromatograph/mass spectrometer and Fourier transform infrared (FTIR) spectrometer, while PSBC, RE, and R4 were characterized with a solid-state 13C nuclear magnetic resonance (SS 13C NMR), FTIR, and X-ray photoelectron spectrometer (XPS). In total, ca. 36wt% 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 SP1 and esters are the main compounds in SP2–SP4. No significant difference in the distribution of functional groups was observed in FTIR spectra of PSBC and RE, while the distribution of functional groups in R4 is significantly different from that in either PSBC or RE. According to analysis with XPS, the content of oxygen-containing species in R4 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 R4 is significantly lower than that (4.4%) in PSBC based on analysis with SS 13C NMR.