Simulation of Interaction of Coal Associates with Solvents Using the Molecular Dynamics Calculation

The extract obtained from a carbon disulfide−N-methyl-2-pyrrolidinone mixed-solvent extraction at room temperature for Upper Freeport coal (APCS1) was fractionated with acetone and pyridine into three fractions, i.e., acetone-soluble (AS), acetone-insoluble−pyridine-soluble (PS), and pyridine-insoluble (PI) fractions. For the three extract fractions, the model structures based on the structural parameters were constructed, and the energy-minimum conformation was calculated by the molecular mechanics and molecular dynamics methods. As the fractions got heavier, more stable associates formed among the model structures by several cooperative interactions through aromatic−aromatic interactions, hydrogen bonds, and electrostatic interactions. Furthermore, the molecular dynamics calculation in the presence of pyridine showed that a part of the coal associates was broken by their interactions with pyridine molecules. When benzene or methanol was used as the solvent, the breaking of coal associates did not take place, although the solvent molecules also interacted with the coal associates. This result can be explained as the cooperative interactions through hydrogen bonds and aromatic−aromatic interactions can form a strong associated structure, i.e., even if one interaction site is dissociated, other interactions can still hold the association structure.