Characterization of Macromolecular Structure of Pyrolysis Products from a Colorado Green River Oil Shale

Volatile products from an oil shale from the Colorado Green River formation were studied by several methods. The oil shale was demineralized, and the resulting kerogen was also chemically analyzed. Both the oil shale and the demineralized kerogen were pyrolyzed at 10 K/min, and the pyrolysis products (light gas, tar, and char) were analyzed using C-13 NMR, XPS, GC/MS, and FTIR Low temperature ashing was performed in order to compare pyrolysis yields of oil shale and demineralized kerogen on a dry ash-free basis. Volatile yields of approximately 75% were achieved in an oil shale retort and 79% in the kerogen retort on a daf basis, with over 60% of the kerogen converted to tar. A carbon aromaticity of 21% was determined for the demineralized kerogen based on the NMR analysis, with an average number of 8.4 aromatic carbons per cluster, 4.4 attachments per cluster, an average cluster molecular weight of 666 amu, and an average molecular weight per side chain of 128 amu. At elevated temperatures, carbon aromaticity in the residual char increased to 81%, with an increase in the number of aromatic carbons per cluster to 19, and a corresponding increase in the number of attachments per cluster during kerogen pyrolysis. The GC/MS analysis of tars showed significant amounts of alkane/alkene pairs of straight chain hydrocarbons ranging from 9 to 20 carbons in length. XPS data were obtained to identify the nitrogen and oxygen species present in the kerogen, showing that nitrogen mainly occurs as heteroatoms. The nitrogen and sulfur preferentially stayed in the char compared to carbon and hydrogen.