Characterization of fluid catalytic cracking catalyst coke by C-13 NMR and mass spectrometry

Coke has been concentrated from deactivated FCC catalysts via demineralisation to facilitate characterisation by solid state C-13 NMR and mass spectrometry. The catalysts were obtained from refinery operations with a residue feed and a hydrotreated vacuum gas oil and from microreactivity runs with n-hexadecane and various additives. As for solid fuels, the use of a low-field spectrometer in conjunction with the single pulse excitation (or Bloch decay) technique has enabled quantitative carbon skeletal parameters to be obtained from C-13 NMR for the cokes. Internal standard measurements demonstrated that most of the carbon is detectable by SPE and, therefore, NMR-invisible graphitic layers are not thought to be major structural features of the cokes. Differences in feedstock composition were reflected in the structure of the cokes with the aromatic nuclei being most highly condensed in the residue-derived coke and corresponding to 15-20 peri-condensed aromatic rings.