Two-step depolymerization of Zhaotong lignite in ethanol

- The total yield of soluble portions from two-step depolymerization of ZL is 88.8%.
- Oxygen-containing organic compounds are predominant in the soluble portions.
- Phenolic compounds in SP1 and PPsZL were generated through different pathways.
- Carbazole and methylcarbazoles are the main components in PPsR1.

Zhaotong lignite (ZL) was subjected to ethanolysis at 305 °C to afford soluble portion 1 (SP1) and residue 1 (R1). R1 was ethanolyzed with NaOH at 305 °C to obtain soluble portion 2 (SP2) and residue 2 (R2). SP2 was separated to extracts 1-3 (E1-E3) by sequential extraction with petroleum ether, carbon disulfide, and dichloromethane. SP1 and E1-E3 were analyzed with a gas chromatograph/mass spectrometer, while ZL, R1, and R2 were characterized with a Curie-point pyrolyzer-gas chromatograph/mass spectrometer. The total yield of SP1 and E1-E3 is 88.8%, indicating that most of organic matter in ZL was converted to soluble species by the two-step depolymerization. Ethyl alkanoates are the most abundant species detected in SP1. The distribution of group components in SP1 is quite different from that in the pyrolysis products from ZL, e.g., the relative content of alkoxyphenols is much lower than that of phenol and alkylphenols in SP1, but much higher in the pyrolysis products from ZL, indicating that the mechanism for ZL ethanolysis is quite different from that for ZL pyrolysis. Carbazole is the predominant nitrogen-containing compound in the products from R1 pyrolysis. Sulfur-containing organic compounds were only released from R2 pyrolysis. The mechanisms for the formation of typical group components from the ethanolysis of ZL, NaOH-involved ethanolysis of R1, and pyrolysis of ZL, R1, and R2 were discussed.