13C-NMR OF SOLID ORGANIC DEPOSITS ON SPENT HYDROPROCESSING CATALYSTS

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Abstract
Carbonaceous deposits on four spent hydroprocessing catalysts were studied using carbon-13 NMR spectroscopy with cross polarization/magic angle spinning (CP/MAS) and dipolar-dephasing technique. The spent catalysts were extracted with methylene chloride and methanol before analysis of insoluble organic material. These deposits, which are generally referred to as “coke”, were found to contain a significant proportion of aliphatic and hydroaromatic structures in addition to aromatic compounds. Different feedstocks and operating conditions formed carbonaceous deposits with different aliphatic carbon contents, ranging from a gas oil catalyst with 62% aliphatic carbon to a bitumen catalyst with only 9% aliphatic carbon. Qualitative dipolar-dephasing experiments showed that the amount of methyl carbon on gas oil catalysts was much greater than on catalysts used to treat naphtha or bitumen. This study shows that solid-state NMR spectroscopy can be used to quantitatively investigate the nature of catalyst residues formed under different conditions.