Effect of demineralization on Yimin lignite by experiments and molecular simulation techniques

Abstract

The structural changes of Yimin lignite after demineralization treatment were characterized by ultimate analysis, X–ray diffraction (XRD), 13C nuclear magnetic resonance (13C NMR) and X–ray photoelectron spectroscopy (XPS) in this study. The results showed that the number of carboxylic acid, phenolic hydroxyl and ether oxygen increased after demineralization treatment, while the number of aliphatic rings decreased and the length of aliphatic chain shortened. Based on the structural parameters, the single molecular models of raw coal and demineralized coal were constructed. In order to further analyze the changes in the three–dimensional configuration and potential energy of the large–scale molecular models before and after demineralization treatment, the periodic unit cells containing five single molecular models for raw and demineralized coal were constructed and evaluated by molecular simulation techniques. The results showed that the demineralization treatment affected the stability of the cross–linked structure of Yimin lignite molecules. The demineralization treatment has a greater impact on the electrostatic energy (EE) and the bond inversion energy (EI). For single molecules, Mulliken population analysis and frontier molecular orbital analysis results showed that the chemical reactivity of Yimin lignite molecules in nucleophilic and electrophilic reactions was weakened after demineralization treatment.