Catalytic hydroconversion of extraction residue from Shengli lignite over Fe–S/ZSM-5

•Fe–S/ZSM-5 shows high activity for CHC of Shenli lignite extraction residue (ER).•Some CH2 and O in the ER could be connected to condensed aromatic rings (CARs).•Much higher yield of soluble portion was obtained from CHC than from NCHC of the ER.•Radical hydrogen transfer to the CARs could be a crucial step for CHC of the ER.

A highly dispersive Fe/ZSM-5 as the precursor of Fe–S/ZSM-5 was prepared by decomposing Fe(CO)5 onto ZSM-5 zeolite at 250 °C. Shengli lignite (SL) was isolated to extractable portion (EP) and extraction residue (ER) by exhaustive extraction with isometric carbon disulfide/acetone mixed solvent (IMCDSAMS) under ultrasonic irradiation. The EP and ER were analyzed with a direct analysis in real time ionization source coupled to ion trap mass spectrometer. Both of them and SL were analyzed with a Fourier transform infrared spectrometer. The ER was subjected to non-catalytic hydroconversion (NCHC) and catalytic hydroconversion (CHC) over Fe–S/ZSM-5, which was formed by in situ reaction of Fe/ZSM-5 with sulfur added, in cyclohexane under pressurized hydrogen at 300 °C. The reaction mixtures were sequentially extracted with petroleum ether, carbon disulfide, methanol, acetone, and IMCDSAMS to afford extracts 1–5 (E1–E5), which were analyzed with a gas chromatography/mass spectrometer (GC/MS). As model reactions, the CHCs of di(1-naphthyl)methane (DNM) and diphenylmethane (DPM) over Fe–S/ZSM-5 were also conducted in cyclohexane at 300 °C. The results show that more than 50% of organic matter in the ER was converted to a soluble portion by the CHC, whereas the yield of soluble portion from the NCHC is only 10.52%. GC/MS-detectable species only appear in the E1, which mainly consists of alkanes, arenes, and arenols either from the NCHC or from the CHC. DNM was selectively hydrocracked to naphthalene and 1-methylnaphthalene over Fe–S/ZSM-5, while DPM hydrocracking did not proceed, indicating that Fe–S/ZSM-5 catalyzed the formation of radical hydrogen from molecular hydrogen and subsequent radical hydrogen transfer (RHT) to the ipso-position of naphthalene ring in DNM. Some CH2 and O in the ER could be connected to condensed aromatic rings (CARs). Analogously, RHT to the ipso-position of CARs in the ER resulted in the release of arenes and phenols from the ER.