EVIDENCE FOR THE FORMATION OF STABLE COAL-N-METHYLPYRROLIDINONE AND COAL-PYRIDINE GELS

Differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) have been used to investigate the physical state of N-methylpyrrolidinone (NMP) and pyridine in swollen coals. NMP and Illinois No. 6 coal form a metastable gel of composition about 65 wt % NMP and 33 wt % coal which contains no free NMP. All of the normally liquid NMP is incorporated into the solid gel. Breakdown of this gel is an activated process. At higher and lower concentrations of NMP, free solvent is present. Pyridine also displays ''nonfreezing'' behavior, but it is unclear whether this is due to the formation of a similar gel. At all solvent:coal ratios, a significant amount of both solvents is associated with the coal and not present in a free ''freezable'' form.