Characterization of Macromolecular Structure Elements from a Green River Oil Shale, II. Characterization of Pyrolysis Products by 13C NMR, GC/MS, and FTIR

This paper is Part II of a study of the chemical structural components of the organic matter of oil shale in the Green River formation. Three sections of a well-characterized oil shale core from the Utah Green River formation were demineralized, and the resulting kerogen was pyrolyzed at 10 degrees C/min in nitrogen at atmospheric pressure at temperatures up to 525 degrees C. The pyrolysis products (light gas, tar, and char) were analyzed using C-13 NMR, GC/MS, and (FTIR). Pyrolysis yields of 80% (daf basis) were achieved at these conditions, with 60% daf tar yield at the highest temperature. The solid-state NMR results indicate that the aromaticity of the kerogen char increased from 20% (at RT) to 80% during pyrolysis, with a corresponding decrease in the average aliphatic carbon chain length from 12 to less than 1. The average number of aromatic carbons per cluster increased from 12 to 20 in a narrow temperature window between 425 and 525 degrees C, with an increase in the number of attachments per cluster from 6 to 8 in that same temperature window. Liquid-state NMR results of the condensed tars showed predominance of n-alkyl chains, with similar carbon aromaticities at each temperature. The alkyl chains were also observed in the GC/MS data. The light gases determined by FTIR were primarily CH4, CO, and CO2. The combination of gas, tar, and char yields and chemical structure analyses are valuable for modeling of oil shale processes based on chemical structure rather than based on empiricism.