Quantification by in situ ¹H n.m.r. of the contributions from pyridine-extractables and metaplast to the generation of coal plasticity

High-temperature H-1 n.m.r. measurements were made on four Australian bituminous coals and their pyridine extracts and residues to quantify the contributions from the extractable material and fluid material generated by thermolytic reactions (metaplast) to the overall development of fluidity. Solid-state C-13 n.m.r. and e.s.r. indicated that the pyridine-extractables are less aromatic than the parent coals and contain lower concentrations of free radicals. Although the pyridine-insolubles did not soften appreciably up to 550 degrees C, some partly fluid material was discernible at the temperature of maximum fluidity and, for the good coking coals, this accounted for between one-third and one-half of the fluid phase generated. Although the pyridine-extractables softened at temperatures as low as 150 degrees C, giving halfwidths of only similar to 1.2 kHz, they still did not soften completely at maximum fluidity (25% rigid material). Taking the separate contributions from the pyridine-extractables and residues for the whole coals, the predicted proportions of the total hydrogen in the fluid phase at maximum fluidity were in close agreement with these observed. Further, the predicted spin-spin relaxation times from the two separate contributions were also close to those observed. Thus the pyridine-extractables do not appear to increase markedly the amount of metaplast generated; they serve mainly to increase the mobility of the fluid phase. (C) 1997 Elsevier Science Ltd.