Sequential Extraction and Thermal Dissolution of Baiyinhua Lignite in Isometric CS2/Acetone and Toluene/Methanol Binary Solvents

Baiyinhua lignite (BL) was sequentially extracted and thermally dissolved in isometric CS2/acetone and toluene/methanol binary solvents to obtain an extract in isometric CS2/acetone (E-ICA) and a soluble portion (SP) in isometric toluene/methanol (SPITM). The yields of E-ICA and SPITM are notably higher than the total extract yield from sequential extraction with CS2 and acetone (or acetone and CS2) and the total SP yield from sequential thermal dissolution in toluene and methanol (or methanol and toluene), indicating that there exists an obvious synergic effect between CS2 and acetone during the extraction and between toluene and methanol during the thermal dissolution. E-ICA and SPITM mainly consist of hydrocarbons and oxygen-containing organic species, respectively. Little difference in Fourier transform infrared spectroscopy spectra of BL and its extraction residue was observed, while the intensities of absorbances assigned to the phenolic OH, C-O, and CO/COC groups of the thermal dissolution residue are obviously lower than those of BL and its extraction residue. X-ray photoelectron spectroscopy analysis shows that CO/COC groups in BL remarkably decreased after thermal dissolution, corresponding to the abundant phenols dissolved in SPITM. The difference in weight loss between BL and its extraction residue is close to the yield of E-ICA, while the difference in weight loss between extraction and thermal dissolution residues is significantly lower than the yield of SPITM.