A study of chemical structural evolution of thermally altered coal and its effect on graphitization

Abstract

Thermally altered coal has some special characteristics compared to coal subjected to normal coalification, for examples, it has more anisotropic components, which may be beneficial to the conversion of coal to graphite. The study of chemical structure of thermally altered coal can increase its benefits, even improve industrial technology. Herein, a series of thermally altered coal was selected to investigate their chemical structure, especially aromatic structure, and the effect of the chemical structure on graphitization. According to the changes of chemical structural parameters in this study, three chemical structural stages in the vitrinite reflectance (Ro) range of 2.45 to 8.32% were divided: 2.45–2.79%, 2.79–5.17%, and 5.17–8.32%. From 2.45 to 2.79%, the content of aromatic carbon decreased and the size of aromatic layers increased, suggesting the polycondensation of existing aromatic layers. From 2.79 to 5.17%, the content of aromatic carbon increased obviously and the aromatic layers size increased slightly, indicating the formation of new aromatic layers. From 5.17 to 8.32%, it is characterized by the polycondensation of aromatic structures formed in the Ro of 2.79 to 5.17% stage. Different stages have different chemical structural characteristics after graphitization. The samples in the stage of aromatic layer polycondensation have alarger extension after graphitization, and the samples in the stage of forming new aromatic layers have more layers in the graphite structure. Oxygen-containing structures in thermally altered coal may be beneficial to graphitization. The samples SL-3 and SL-5, rich in oxygen-containing structures, have a tight arrangement and fewer lattice defects after graphitization.