Solvent extraction of superfine pulverized Coal. Part 4. Carbon skeleton characteristics.

[Display omitted] • SS 13C NMR is introduced into the research for all coal extraction products. • Carbon skeleton characteristics are quantitatively analyzed for all extraction products. • Influence of particle size on the evolution of coal microstructure during the extraction is focused on. • The work promotes the thorough elucidation on the carbon skeleton structure for all extraction products at a molecular level. To better understand the molecular structure of superfine pulverized coal and promote its practical utilization, the NMR (nuclear magnetic resonance) technology is adopted to study the structural information of all the products from the solvent extraction process, including raw coal, residue, and extract. The whole set of NMR spectra is resolved into different individual curves with specific linewidths, shapes, and intensities. According to the chemical shift, the carbon skeleton characteristics like the aromaticity, cluster size, and other structural lattice parameters are analyzed in detail. More importantly, the influences of coal maturity, coal size, and solvent on the carbon structural evolution during the extraction process are focused on. The results show that the aromatic ring stacking and aromatic ring exposure and fragmentation occur competitively during the superfine comminution, promoting the structural evolution of the coal. In addition, aliphatic carbon transfers more from raw coal into the extract than aromatic carbon in the whole extraction process, which is accompanied by the disappearance of carbonyl groups. Furthermore, the reduction of particle size can promote the extraction effect of the extractant on the coal powder, and reduce the proportion of aliphatic carbon in the residue. The work introduces the correlations among the raw coal, residue and extract from a carbon skeleton point of view, providing a reference for elucidating the solvent extraction mechanisms. The results shed light on better understanding the coal structure and its further molecular modeling. [ABSTRACT FROM AUTHOR]