Structural Characterization of HyperCoal Extracts from the Depolymerization of Shengli Lignite Using NaOH/Methanol

To develop efficient utilization technologies for lignite, HyperCoal was prepared from the depolymerization of Shengli lignite by reacting it with NaOH and methanol. A series of HyperCoal extracts were obtained using different solvents and characterized using elemental analysis, Fourier-transform infrared spectroscopy, gel permeation chromatography, and synchronous fluorescence spectroscopy. The results indicate that solvent polarity is the primary factor influencing both the extraction yield and the structure of the extracts as polar solvents can disrupt or break hydrogen bonds within the extracts. The extraction yield increases with the polarity of the extraction solvent. HyperCoal is a complex mixture of aromatic derivatives containing alkyl substituents and oxygen-containing functional groups. The O/C ratio and molecular size of the extracts, the amount of oxygen-containing functional groups, the proportion of aromatic structures, and the size of aromatic nuclei in the extracts increase with increasing solvent polarity, while the H/C ratio and proportion of aliphatic structures decrease. These findings aid developing methods for producing high-value-added chemicals from HyperCoal through staged conversion.