DIFFUSION OF PYRIDINE IN ILLINOIS NO-6 COAL - MEASURING THE SWELLING AND DESWELLING CHARACTERISTICS BY COMBINED METHODS OF NUCLEAR-MAGNETIC-RESONANCE (NMR) AND NUCLEAR-MAGNETIC-RESONANCE IMAGING (NMRI)

The time-dependent swelling and deswelling of Illinois No. 6 coal by p yridine were measured by combined NMR and NMRI techniques. The results indicate that pyridine transport in this coal proceeds via Case II di ffusion for swelling and via Fickian diffusion for deswelling. Once th e relative pyridine concentrations reach values between 0.65 and 0.45, the coal's physical state changes from a glassy to a rubbery state. T ransitions are well recorded by an inflection observed in the trend of spin-lattice relaxation or spin-spin relaxation of pyridine, as the c oal swells and deswells. NMRI data indicate that the coal swelling is anisotropic, with swelling in a plane perpendicular to the coal beddin g plane being 13% greater than that parallel to the coal bedding plane ; however, the process of deswelling is almost isotropic. The differen ces between the swelling and deswelling characteristics are discussed from the viewpoint of coal's intrinsic structural properties and store d geologic pressure effects.