Solid-State 13C NMR in Oil Shale Research: An Introduction with Selected Applications

Abstract

An introduction to solid-state 13C NMR techniques and their applications to oil shale research are discussed. Techniques include cross polarization and magic-angle spinning with high-power decoupling, single pulse excitation, dipolar dephasing, and sideband suppression at high magnetic fields. The quantitative reliability of solid-state 13C NMR measurements is discussed also. Results from recent studies on coals show that single pulse methods give more reliable carbon aromaticities than those obtained using cross polarization. This is because a greater percentage of the total carbons are observed in the single pulse experiment than in the cross polarization experiment. Similar comparisons for oil shales have not been made. However, because oil shales generally are more aliphatic than coals, differences in measured carbon aromaticities and percentages of carbons observed may not be as serious a problem for oil shales. Selected applications of solid-state 13C NMR techniques to oil shale resource evaluation, oil shale conversion, and structure are presented.