CPMAS C-13 NMR AND PYROLYSIS-GC-MS STUDIES OF STRUCTURE AND LIQUEFACTION REACTIONS OF MONTANA SUBBITUMINOUS COAL

This paper reports on the application of solid-state CPMAS C-13 NMR an d flash pyrolysis-GC-MS for characterization of the macromolecular net work of a Montana subbituminous coal and its residues from temperature -programmed and non-programmed liquefaction (TPL and N-PL) at final te mperatures ranging from 300 to 425-degrees-C in H-donor and non-donor solvents. The combined use of C-13 NMR and Py-GC-MS revealed that this coal contains significant quantities of oxygen-bearing structures, co rresponding to about 18 O-bound C per 100 C atoms and one 0-bound C pe r every five to six aromatic C's. The oxygen-bearing components in the coal include catechol-like structures, which seem to disappear from t he liquefaction residues above 300-degrees-C; carboxyl groups, which a lmost disappear after 350-degrees-C; and phenolic structures, which ar e most important in the original coal but diminish in concentration wi th increasing temperature. These results point to the progressive loss of oxygen functional groups and aliphatic-rich species from the macro molecular network of the coal during programmed heat-up under TPL cond itions. The higher conversions in TPL runs in H-donor tetralin (relati ve to the conventional N-PL runs) suggest that the removal of carboxyl ic and catechol groups from the coal and the capping of the reactive s ites by H-transfer from H-donors at low temperatures (less-than-or-equ al-to 350-degrees-C) have contributed to minimizing the retrogressive crosslinking at higher temperatures. Quantitative calculation of NMR d ata and mathematical correlation were also attempted in this work. For 24 liquefaction residues derived under significantly different condit ions, linear correlations between C-distribution and reaction temperat ure (greater-than-or-equal-to 300-degrees-C) have been found, which ca n be expressed by a simple equation, C(i) = alphaf(i) + betaT, where f (i) and C(i) represent content of aromatic, aliphatic, or oxygen-bound carbons in the original coal and residue, respectively; T stands for the reaction temperature; alpha and beta are constants.