A study on the structure of Naomaohu coal and its suitability for direct coal liquefaction

Abstract

Direct coal liquefaction (DCL) is not only for fuel but also for chemicals, which shows high efficiencies in atom utilization and energy. The study on coal structure is important to select coal for direct liquefaction. Naomaohu coal is a kind of subbituminous coal and a typical coal for direct liquefaction. In this work, the structure of Naomaohu coal was investigated via alkali‑oxygen oxidation, ruthenium ion catalyzed oxidation and physical analyses and a representative structural model with a model size of 128,755 amu was constructed. The structural characteristics show that the ratio of single-, double-, triple-, and quadruple-aromatic rings is 149:164:102:63. The triple- and quadruple-rings aromatic structures are mainly connected by CC bonds of 2–4 carbon atoms. The single- or double-ring is connected on the triple- and quadruple-rings aromatic structures through ether or ester bonds, which can be broken easily under mild conditions. Long alkyl side chains with carbon atoms from 13 to 25 accounting for 0.91 wt%. The high H/C, high oxygen content (mainly weak bonds such as ether and ester bonds between aromatic clusters), abundant single-, double-, triple, and quadruple-aromatic rings, and alkyl bridge bonds of 2–4 carbon atoms are beneficial to the mild liquefaction of Naomaohu coal