1H- and 13C-n.m.r. studies on naphtha and light distillate saturate hydrocarbon fractions obtained from in-situ shale oil

Abstract Shale oil, obtained from an in-situ oil shale experiment, from the Green River formation in Southwestern Wyoming was thermally fractionated into naphtha, light distillate, heavy distillate and residue fractions. The naphtha and light distillate fractions were further separated into saturates, olefins and aromatic subfractions. 1 H- and 13 C-n.m.r. spectra and mass spectral data were obtained for the saturated hydrocarbons of the naphtha and light distillate fractions. Resonances in the n.m.r. spectra were assigned to normal alkanes and to methyl- and dimethyl-branched alkanes. The composition as determined by n.m.r. of the naphtha saturates was found to be ≈82% straight-chain alkanes with an average carbon-chain-length of ≈C 11 and ≈18% branched/cyclo-alkanes. The composition of the light distillate saturates was found to be ≈ 69% straight-chain alkanes with an average carbon-chain-length of ≈C 15 and ≈31% branched/cyclo-alkanes. The dimethyl-branched alkanes in both saturate fractions were proposed to have the molecular substructure of saturated isoprenoids. In the naphtha saturates the isoprenoid substructure is evident. However, in the light distillate saturates, both isoprenoid substructures, and , are evident. 13 C spin-lattice re-laxation times also were determined for the dominant resonances observed in the spectra of the naphtha and light distillate saturates. Relaxation times for the molecular species in the naphtha saturate fraction were observed to be longer than those observed for the light distillate saturate fraction. It was found that the ratio of the overall average relaxation times for the naphtha and light distillate saturate fractions corresponded to the inverse ratio of the average molecular weights of each fraction as determined from average alkane carbon-chain-length determination. Intermolecular (segmental) motion of the carbon chain of the straight-chain alkanes in both saturate fractions is also evident from the relaxation time measurements.