Investigation on compositional and structural features of Xianfeng lignite through sequential thermal dissolution

Xianfeng lignite (XL) was subjected to sequential thermal dissolution (TD) in cyclohexane at 200–320°C. The yields of soluble portions (SPs) decreased with raising temperature from 200 to 260°C, but then increased with further raising the temperature. The SPs were analyzed with a Fourier transform infrared spectrometer, gas chromatograph/mass spectrometer, and atmospheric pressure solid analysis probe/time-of-flight mass spectrometer (ASAP/TOF-MS). The results show that cyclohexane is effective for thermally extracting inherent hydrocarbons in XL without breaking the covalent bonds. Intermolecular interactions such as hydrogen bonds, π–hydrogen bonds, and π–π interactions can be destroyed at higher temperatures and thereby release arenes and arenols trapped in the capsule structure of XL. According to ASAP/TOF-MS analysis, the molecular mass of organic species in the SPs is smaller than 550 u and SPs from different TD temperatures have different molecular mass distributions. The organic species detected with ASAP/TOF-MS have double bond equivalent values ranging from 0 to 11 and carbon numbers from 3 to 35. A series of arenes and alkylarenols were also confirmed by ASAP/TOF-MS analysis. •TDT has a great effect on the yields and compositions of the soluble portions.•TD in cyclohexane is effective for extracting hydrocarbons from Xianfeng lignite.•Intermolecular interactions and capsule structure were easily destroyed at high TDTs.