PHASE-BEHAVIOR AND MACROMOLECULAR STRUCTURE OF SWOLLEN COALS - A LOW-TEMPERATURE H-1 AND H-2 NMR-STUDY

H-1 and H-2 NMR line-shape studies have been used to investigate the l ow-temperature phase behavior of pyridine-d(5) and N-methylpyrrolidino ne-d(9) (NMP) swollen-Pittsburgh No. 8 coal, Illinois No. 6 coal, and Zap lignite. Good solvents like pyridine and NMP greatly reduce second ary interactions within coals, transforming them from the glassy to th e rubbery state at room temperature when the solvent-to-coal mass rati o (W-s/W-c) is over about 1. Using deuterated swelling solvents permit s complementary studies of the coal structure (with H-1 NMR) and dynam ics of the deuterated solvent molecules (with H-2 NMR). For solvent sw ollen coals with W-s/W-c similar to 2, the H-1 NMR line width is reduc ed by more than an order of magnitude, indicating the onset of a high level of molecular motion which averages the dipolar interactions amon g protons. The increase of line width with decreasing temperature is r eversible, independent of solvent employed, and similar for all three coals examined (lignites to high-volatile type A bituminous coals). Th e line-width increase extending from similar to 280 to 170 K and cente red at 210 K is attributed to a glass-to-rubber transition. The H-2 NM R studies of the deuterated solvent molecules suggests that they becom e immobile at significantly lower temperatures than that observed for the transition of the coals. Analyses of the NMR data suggest isolatio n of the individual components of the coal as a consequence of the swe lling process.