Thermal dissolution of Huozhou and Xinghe lignites and the occurrence forms of organic oxygen in them

Huozhou (HZ)and Xinghe (XH) lignites were extracted in turn with petroleum ether, carbon disulfide, methanol, acetone and isometric acetone/carbon disulfide mixed solvent to obtain the extracts (E₁-E₅) and the extraction residues (ER₁-ER₅), then ER₅ was thermally dissolved at 320℃ using methanol, toluene, isometric methanol/toluene mixed solvent and acetone to gain the soluble portions (SPs). The total yields of extraction for HZ and XH are 7.03% and 7.86%, respectively, in which the yield of E₃ is the highest. The SPs yield of extraction residue with isometric methanol/toluene mixed solvent is the highest, and the SPs of ER_{5, HZ} and ER_{5, XH} with isometric methanol/toluene mixed solvent reaches 45.76% and 40.14%, respectively. There exist strong adsorption peaks ascribed to aliphatic C-H in the Fourier transform infrared (FT-IR) spectra of E₁-E₅, while the intensity of adsorption peaks ascribed to C=C, C=O and O-H in the FT-IR spectra of SPs is obviously higher than that of extracts. The gas chromatography/mass spectrometer (GC/MS) analyses show that the oxygen containing organic compounds (OCOCs) in E₁-E₅ are dominated with alcohols, ethers and ketones, while it is mainly composed of alcohols, phenols and ketones in the SPs, and the strong polar solvents contribute to dissolving the OCOCs in lignites. The adsorption peaks ascribed to associated O-H, C=O and C-O-C in the FT-IR spectra of extraction residues and thermal dissolution residues are weaker than those of raw coals. The X-ray photoelectron spectroscopy (XPS) analyses indicate that the relative content of oxygen forms in XH and HZ is C-O > C=O > COO-, and the relative content of C-O and COO-in HZ is higher than that in XH.