Change in the associated molecular structure of coals in pyridine/CS2 mixed solvents

In order to evaluate noncovalent interactions in coal, change in the associated molecular structure of coals in pyridine/CS₂ mixed solvents have been investigated. For bituminous coal, variation in L-band EPR spectra with mixing ratio of the solvents is in a close correspondence to that in equilibrium swelling ratio and in molecular mobility obtained from ¹H-NMR. The EPR spectra for lignite show similar variation to that for bituminous coal, however, does not correlate with equilibrium swelling ratio and molecular mobility. Since the L-band EPR characteristics appear to reflect the situation of aromatic π-π and charge transfer interactions in coal, these results indicate that swelling in the mixed solvents proceed with the declining of non-covalent interaction, such as aromatic π-π and charge transfer interaction, in coal.