Sequential thermal dissolution and alkanolyses of extraction residue from Xinghe lignite

- Most of organic matter in ER was converted into SPs via sequential TD/alkanolyses.
- Anthracene was added to the sequential TD/alkanolyses to monitor hydrogen transfer.
- Hydrogen transfer significantly proceeded during the ER alkanolyses.

Extraction residue (ER) from ultrasonic extraction of Xinghe lignite (XL) was subjected to sequential thermal dissolution (TD) in cyclohexane from 200 °C to 320 °C and subsequently in benzene, methanol, ethanol, and isopropanol at 320 °C. The yields of soluble portions (SPs) in methanol and ethanol are much higher than those in cyclohexane and benzene, and the total SP yield is ca. 48.3%. According to gas chromatography/mass spectrometric analysis, the most abundant group components are arenols in cyclohexane-soluble portion obtained at 290 °C and methanol-soluble portion obtained at 320 °C, arenes in both cyclohexane- and benzene-soluble portions obtained at 320 °C, alkanoates in ethanol-soluble portion obtained at 320 °C, and alkenones in isopropanol-soluble portion obtained at 320 °C. Anthracene was used as hydrogen acceptor to probe hydrogen transfer (HT) from ER in terms of the formation of 9,10-dihydroanthracene (DHA) and 1,2,3,4-tetrahydroanthracene (THA) during TD. As a result, both DHA and THA were detected in all the SPs except benzene-soluble portion obtained at 320 °C and the yields of both DHA and THA increased with raising temperature in cyclohexane, indicating that raising temperature enhances HT from ER to anthracene. Compared to TD in cyclohexane, alkanols, especially isopropanol, enhance the HT more significantly at 320 °C.