Thermal dissolution of Shengli and Xiaolongtan lignites in methanol and analysis of the soluble portions

Thermal dissolution behaviors of Shengli (SL) and Xiaolongtan (XLT) lignite in methanol were investigated. The composition and structural characteristics of soluble portions (SPs) obtained at 320 ℃ were characterized with Fourier transform infrared spectroscopy, gas chromatograph /mass spectrometer (GC/MS) and atmospheric solid analysis probe/time of flight mass spectrometer (ASAP/TOF-MS). For the two lignites, the yield of SPs increase with temperature increasing, while the yield of SPs from XLT (SP_XLT) is obvious higher than that from SL (SP_SL) above 240 ℃. GC/MS analysis results show that compounds in the SPs are dominated in oxygen-containing organic species, especially the relative content of phenols is higher than 49%. The relative contents of alkenes, arenes, ethers, carboxylic acids, esters, organosulfur compounds (OSCs) in SP_SL are higher, while the relative contents of alkanes, phenols, ketones and organonitrogen compounds in SP_SL are lower than those in SP_XLT. Additionally, the OSCs in SP_SL and SP_XLT are mainly composed of thiophenes and mercaptan, respectively. Many compounds with high polarity and low volatility which could not be identified by GC/MS were identified using ASAP/TOF-MS. The relative contents of CHO and CHS class species in SP_SL are higher, but the relative contents of CHN, CHNO, CHOS, CHNS and CHNOS in SP_SL are lower than those in SP_XLT. The carbon number and double bond equivalent (DBE) of the compounds in SP_SL and SP_XLT mainly distribute in 0-10 and 3-15, respectively, while the distribution of carbon number and DBE of the compound in SP_XLT are more concentrated than those in SP_SL.