Composition and structural characteristics of soluble organic species in Baiyinhua lignite

Baiyinhua lignite was sequentially extracted with petroleum ether, cyclohexane, carbon disulfide, acetone, methanol and isometric acetone/carbon disulfide mixed solvent affording extracts, i.e. E₁-E₆, then extraction residue was sequentially thermal dissolved using methanol, toluene and isomeric methanol/toluene mixed solvent affording soluble portions (SPs), i.e.SP₁-SP₃. The composition and structural characteristics of extracts and SPs were characterized with Fourier transform infrared (FT-IR) spectroscopy, gas chromatography/mass spectrometer (GC/MS), direct analyze in real time mass spectrometer (DART-MS). The total extracts yield and SPs yield of BL are 9.37% and 21.84%, respectively. There exist strong adsorption peaks ascribed to hydroxyl in the FT-IR spectra of E₁ and E₆, while the intensity of adsorption peaks ascribed to aliphatic C-H in the FT-IR spectrum of E₁ is obviously higher than that of other extracts. There are similar FT-IR spectra among those 3 SPs, whereas the intensity of adsorption peak originated from hydroxyl in the FT-IR spectra of SP₁ and SP₃ is higher than those of SP₂. The compounds GC/MS detected in E₁ and E₅ are dominated with alkanes and arenes, respectively, and the content of oxygen-containing compounds (OCCs) in E₅ are more than that in E₁. The compounds in the 3 SPs are composed of alkanes and arenes, while the contents of OCCs, such as phenols, ketones and esters, in SP₃ are higher than those in SP₁ and SP₂. Many compounds with high polarity and low volatility which could not identified by GC/MS were detected using DART-MS. The carbon number and double bond equivalent (DBE) of the compounds with high content in SPs mainly distribute in 10-25 and 2-16, respectively, and the DBE increases with carbon number increasing.