Isothermal decomposition of Colorado oil shale

Isothermal decomposition studies have been conducted in the temperature range of 368 to 500/sup 0/C using a 52-gallon-per-ton Colorado oil shale. A tubular and a heated sand-bath reactor system were used, both yielding material balances of at least 99.7 +- 0.2%. Kerogen conversion to bitumen, oil, gas, and solid product was measured for different residence times at isothermal conditions. Elemental analyses were obtained on the bitumen, oil, and solid reaction products. Product gas composition was measured using an on-line gas chromatograph. Liquid and solid state /sup 13/C NMR measurements were made to determine the aliphatic and aromatic carbon fractions in the liquid and solid products. Molecular weights of the bitumens and oils were measured also. The hydrogen to carbon ratios, carbon aromaticities, and molecular weights of the produced oils were remarkably constant at all temperatures and residence times. The bitumen showed compositional changes indicative of progressive aromatization during decomposition. The aliphatic carbon in the residue decreased, having a time dependence similar to the total organic carbon, whereas the aromatic carbon exhibited almost no time dependence. The total aromatic carbon in the products increased by about 30% over the original aromatic carbon in the raw shale. One set of experiments showedmore » a 94% conversion of kerogen to total soluble products. Rate constants for the kerogen decomposition and product evolution were obtained by simple first-order, distributed activation energy, and initial slope methods of analyses. Attempts were not successful in modeling the kerogen decomposition using a bitumen intermediate. While good fits were obtained for the oil and gas data, the model did not provide satisfactory fits to the bitumen or residue data. The lack of fit to the bitumen data is attributed to the changing composition of the bitumen. 27 refs., 21 figs., 3 tabs.« less