Proposed Model Structures for Upper Freeport and Lewiston-Stockton Vitrinites

Molecular models of vitrinites (obtained from obvious tree remains) from the Upper Freeport and Lewiston-Stockton coal seams are presented. Utilizing pure telocollinite reduced the complexity of the model and resulted in more realistic molecular structures than from whole coal analyses. The structures presented are in agreement with experimentally determined bulk chemical parameters. These were easily achieved with current software and computational expense. However, it was more difficult to produce model structure's which have calculated physical parameters (of the global minimum structure determined from molecular mechanics and dynamics) in agreement with experimentally determined parameters. For these bituminous vitrinites, the addition of physical parameters severely constrained the type of model structures that could be produced. The molecular structures presented are covalently linked aromatic and hydroaromatic structures with a distribution of cross-link densities. Despite being very close in maturation (as determined from vitrinite reflectance) the structural differences have a significant impact on behavior. The current models are not yet consistent with some behavioral aspects such as solvent swelling. It is suggested that a greater molecular scale is needed before multiple facets of coals behavior can be explained.