Characterization Of The Soluble And Insoluble Fractions Of Upper Freeport Coal In Nmp/Cs2 And Pyridine Using Small Angle Neutron Scattering

Small angle neutron scattering (SANS) was used to characterize the solution structure of coal extract/solvent systems as well as swelling-induced structural changes in the nonextractable residues derived from the Upper Freeport (UF), medium-volatile bituminous, coal. Studies were performed on the pyridine soluble (PyS) fraction dispersed in perdeuterated pyridine (dPy); the PyS fraction dispersed in the mixed solvent [dm, perdeuterated N-methylpyrrolidinone (NMP) and carbon disulfide, CS2], and the mixed solvent soluble fraction (MS) in dM. No coherent scattering was observed for the UF-MS/dM sample in the accessible Q range, indicating that the solution contains no large particles or aggregates. Strong coherent scattering was observed for the UF-PyS/dPy and UF-PyS/dM solutions, indicating the presence of large particles, presumably molecular aggregates. Comparison of the SANS behavior of the three samples suggests that there exist molecular components intrinsic to the pyridine insoluble NMP/CS2 soluble fraction that may play a significant role in the enhanced solvation of the mixed soluble fraction of the Upper Freeport coal in NMP/CS2 solvent. SANS analysis of the dry and pyridine (d(5))-swollen UF-PyI and UF-MI residues revealed significant structure evident by power-law scattering behavior in the low Q region of both sets of samples. In the case of the UF-MI samples, significant scattering intensity was also observed in the intermediate Q region. Significant structural changes were observed in the UF-MI fractions upon swelling in pyridine, whereas minimal structural changes were observed in the case of UF-PyI sample during solvent swelling. These results reveal that the physical consequences of mixed solvent extraction are significantly different from those due to pyridine extraction.