NMR of petroleum cokes II: Studies by high resolution solid state NMR of 1H and 13C

Abstract

Chemical functionalities of hydrogen and carbon in a series of cokes obtained from heavy crude oils in a Mobile continuous flow laboratory coker pilot unit are probed with high-resolution solid state NMR. The fractions of aromatic hydrogen and carbon, as determined from 1H combined rotation and multiple-pulse spectroscopy (CRAMPS), and 13C magic angle spinning (MAS) experiment with and without cross polarization (CP), varied only slightly between 0.49 and 0.65 and between 0.88 and 0.92, respectively, for the samples studied. A comparison with the results of direct excitation ( 13C MAS) NMR showed that CP/MAS NMR spectra taken with a contact time of 1 ms well represented relative carbon intensities. The high-resolution spectra, in combination with previously reported wideline 1H NMR data and the results of elemental analysis, are used to derive several structural parameters, including aromatic and aliphatic hydrogen to carbon ratios and the average formula per 100 carbon atoms. Finally, the “average” structures for studied cokes are proposed and discussed. Most cokes are concluded to consist of molecules having approximately 10 aromatic rings bearing only few substitutions.