Computer simulation of solvent swelling of coal molecules: Effect of different solvents

We used a molecular mechanics/molecular dynamics computational method to si mulate solvent swelling of the pyridine-insoluble (PI) fraction obtained fr om extraction of Upper Freeport bituminous coal, an Argonne premium coal sa mple. The effects of benzene and cyclohexane on swelling were examined and compared with previous results for methanol. A model structure for the PI f raction was placed in a periodic boundary cell. As solvent molecules were i ntroduced into the cell, the potential energy of the PI-solvent system decr eased and the volume of the cell increased up to the limiting number of sol vent molecules-9 for benzene and 2 for cyclohexane-that could be added to p roduce stable structures. The contribution of the electrostatic interaction to the decrease in the total energy of the PI-solvent system was larger th an those of the hydrogen bond and van der Waals interactions, regardless of the solvent used. Swelling ratios estimated from the ratio of the weight i ncrease with the number of the solvent molecules introduced were in good ag reement with the ratio determined experimentally from sorption data, and we re much lower than ratios obtained from volumetric swelling measurements.