Structural evaluation of Xiaolongtan lignite by direct characterization and pyrolytic analysis

Organic matter in Xiaolongtan lignite (XL) from Southwest China was analyzed by direct characterization instruments (including solid-state ¹³C nuclear magnetic resonance spectrometer, X-ray photoelectron spectrometer, and Fourier transform infrared spectrometer) and pyrolytic tools (including thermogravimetric analyzer and Curie-point pyrolyzer-gas chromatograph/mass spectrometer). Organic carbons in XL mainly consist of aliphatic and aromatic carbons. Specifically, methylene dominates in the aliphatic carbons and average carbon number in the methylene chains is ca. 5. Each aromatic cluster contains 2 rings and each aromatic ring has 4 substituents on average. XL is rich in oxygen-functional moieties (OFMs), including C_al-O, C_ar-O, > C=O, and -COOH, among which C_al-O and C_ar-O are predominant and thereby cleaving C_al-O and C_ar-O bonds facilitates the devolatilization of organic matter in XL. Phenols are the richest components in the volatiles from flash pyrolysis of XL, which may result from the cleavage of C_ar-O in the organic matter. The pyrolytic analyses imply that selectively cracking these bonds would greatly facilitate converting XL into liquid fuels or fine chemicals.