Difference in molecular composition of soluble organic species from two Chinese lignites with different geologic ages

• The soluble organic species yield of XL is higher than that of SL.
• XL contains more free soluble aliphatics but less arenes than those of SL.
• There are more aryl ether bonds but less ester groups in SL than those in XL.

In this paper, two typical Chinese lignites, Shengli lignite (SL) and Xiaolongtan lignite (XL), with different geologic ages were firstly thermal dissolved in sub- and supercritical benzene and ethanol, then soluble organic species were analyzed with Fourier transform infrared spectroscopy (FTIR), gas chromatograph/mass spectrometer (GC/MS) and atmospheric solids analysis probe/time of flight mass spectrometer (ASAP/TOF-MS). The soluble organic species yield of XL in benzene is close to that of SL in the temperature investigated, whereas the soluble organic species yield of XL in ethanol is obviously higher than that of SL at high temperature region. Obvious difference exists in the molecular composition of the soluble organic species between SL and XL. The soluble organic species of XL contain more free aliphatics but less arenes than those of SL. The arenes in the soluble organic species of XL are mainly composed of the derivatives of benzene and naphthalene, while those from SL are dominated with condensed arenes and polycyclic biphenyls. Furthermore, the free oxygen-containing organic species in SL and XL are dominated with ketones and phenols, respectively. Additionally, ASAP/TOF-MS analysis indicates that the molecular weight of soluble organic species from SL is higher than that from XL.