Determination of aromatic hydrocarbon fraction in oil shale by 13C n.m.r. with magic-angle spinning

A method for estimation of aromatic content in oil shales is demonstrated. Magic-angle spinning at 2 kHz is shown to remove chemical shift anisotropy to a sufficient degree to resolve aromatic and aliphatic ¹³C n.m.r. spectral regions for a lithic oil shale specimen. The proton and carbon n.m.r. relaxation parameters are such as to allow room-temperature use of this proton-enhanced ¹³C n.m.r. technique as a quantitative analytical tool. Cross polarization times of a millisecond or less and experiment repetition periods of 0.5 s or less are optimum. The specimen examined is represented by an aromatic carbon fraction 0.264 ± 0.007; this determination is quite insensitive to the proton-carbon cross polarization time. Spectra for kerogen, shale oil, and dawsonite are also presented. Dawsonite may interfere in the determination of the aromatic fraction.