Mobilization of the hydroxyls in a brown coal with solvent-induced swelling evaluated by pulsed H-1 NMR

The amount of hydroxylic hydrogen mobilized with the solvent-induced swelli ng of a brown coal was measured using a pulsed H-1 NMR technique. Yallourn brown coal (YL), and deuterated YL (YL-d), prepared by selectively deuterat ing all the hydroxyls in YL, were swollen in binary solvents, including dif ferent pyridine-d(5)/benzene-d(6) and dimethyl sulfoxide(DMSO)-d(6)/benzene -d(6) mixtures, at 303 K. The volumetric swelling ratio (Q) and the amount of mobile hydrogen were measured as a function of the composition of the so lvent. The amount of hydroxylic hydrogen remaining immobile, f(IM(OH)), was also determined experimentally by comparing the amounts of mobile hydrogen in YL and YL-d. The f(IM(OH)) of YL in DMSO-benzene mixtures was found to be smaller than that in pyridine-benzene mixtures over the entire range of Q from 1 to 3.5, demonstrating that DMSO reduces the hydrogen bonding assoc iations between coal macromolecules more extensively than pyridine does for the swelling with equivalent Q. The effects of these polar solvents on the relationship between f(IM(OH)) and Q can be attributed to the differences in their hydrogen bonding abilities.