Carbon structure characteristics and evolution mechanism of different rank coals

Based on the X-ray diffraction (XRD) and 13 C nuclear magnetic resonance spectrum (13 C-NMR),the car- bon structure characteristics and the evolution mechanism of five different ranks of coals(WMC long flame coal,LL3 coking coal,LL4 coking coal,CZ anthracite and SH anthracite) have been studied. The results indicate that:The coal metamorphic degree is the most important influencing factors for coal structure. With the increase of coal rank,the ali- phatic carbon content decreases while the aromatic carbon content increases. Furthermore with the increase of coal rank,the condensation degree of aromatic nuclei increases while the arrangement of aromatic structure units tends to be ordered. The metamorphic environment can bring important influence to the evolution of coal carbon structure. At a high temperature and low pressure con-dition,the aromatic structural units of WMC have evolved in advance,which forms a series of aromatic structural systems with high vertical stacking degree and small horizontal extension degree. For the fatty substances of WMC coal,the aliphatic chains form many ring methyl groups on aromatic rings by the fast pyrolysis while the aliphatic rings break down and form the new fatty chains which leads to the huge branching degree of WMC. In the middle maturate coals there may be the aliphatic cyclization effect which leads to the decrease of the degree of branching and the increase of the content of quaternary carbons. As the increase of coal rank,the aliphatic rings will break down and form the new fatty chains which contributes to the huge degree of branching and might lay the foundation for the formation of bigger aromatic system in high rank coals.