Observing the structural variation of Dahuangshan lignite and four derived residues by non-destructive techniques and flash pyrolysis

Abstract

Structural features of Dahuangshan lignite (DL) and 4 derived residues (DRs) were analyzed to understand the internal correlation between the associative fragments and organic macromolecular structures in DL. The structural changes before and after DL extraction and degradation can be effectively understood through the combination of multiple tools. The results show that >C-OH and >C-O- moieties are dominated on all the sample surfaces, while pyrrolics and SSSs (i.e., SO42−, SO42−, and -SO3H) are the most abundant nitrogen- and sulfur-containing species, respectively, from X-ray photoelectron spectrometric analysis. According to thermogravimetric and Fourier transform infrared semi-quantitative analyses, the cleavage of weak and medium strength covalent bonds, i.e., >Cal-X bonds (X denotes H, Cal<, O-, N<, and S-), should be the main reaction during the DL degradation. With increasing the destructive degree, the aromaticity of organic matter from the DRs gradually increases, which is consistent with X-ray photoelectron spectrometric analysis. In addition, combined with the Curie-point pyrolyzer-gas chromatograph/mass spectrometric analysis, a considerable portion of arenes and arenols, especially alkyl-substituted naphthalenes and phenols are also present in nested forms. The possible macromolecular frameworks and nested groups of DL were further speculated. Insight into the structural difference among DL and DRs facilitates the rational and targeted utilization of such DRs.