NMR determination of carbon aromatization during hydrous pyrolysis of coals from the Mesaverde Group, Greater Green River Basin

Solid- and liquid-state C-13 NMR measurements have been made on the residues and liquids produced during hydrous pyrolysis experiments conducted on Almond and Lance Formation coals from the Upper Cretaceous Mesaverde Group in the Greater Green River Basin. The NMR spectra of the residues showed a decrease in aliphatic carbon fraction, a partial resolution of aliphatic carbons attached to aromatic rings, a narrowing of the aromatic carbon resonance band, and a loss of carboxylate functionality with increasing temperature. These changes are indicative of aromatization reactions, cleavage of alkyl substituents on aromatic rings and evolution of CO2 occurring during hydrous pyrolysis. Only a small percentage of the total carbon (13%) was converted to volatile products for both coals during hydrous pyrolysis. An accounting of the aliphatic carbons was obtained by comparing the aliphatic carbons in the gas, oil, water, and residue products with that of the starting coals. The amount of aliphatic carbons in the products was not sufficient to account for the total amount of aliphatic carbons that disappeared. From this it was inferred that 41 and 50% of the aliphatic carbons aromatized during hydrous pyrolysis of the Almond and Lance coal, respectively. NMR spectra were obtained on Almond coal samples taken from different depths of burial. These spectra had characteristics similar to the hydrous pyrolysis residues generated at different temperatures.