Hydrodeoxygenation and Hydrodenitrogenation of n-Hexadecanamide with Supported NiMo Sulfide Catalysts

Amides, which contain both oxygen and nitrogen, are present in many potential feedstocks for renewable fuels. There is a consequent need to study the hydrodenitrogenation (HDN) and hydrodeoxygenation (HDO) of amides. This work studies the HDN and HDO of hexadecanamide with sulfided NiMo/γ-Al₂O₃ and NiMo/TiO₂ catalysts. The experiments are conducted in a batch reactor, with decalin as a solvent. Hexadecanamide is found to easily undergo either dehydration into hexadecanenitrile or deammonization into palmitic acid. Hydrotreating of hexadecanamide consequently occurs either through an initial HDO step (dehydration) into hexadecanonitrile, followed by reduction and HDN of the resulting hexadecylamine, or through an initial HDN step (deammonization) followed by HDO of the resulting palmitic acid. On both NiMo/γ-Al₂O₃ and NiMo/TiO₂, HDN of the amide is slower than HDO. The secondary amine, dihexadecylamine, is a major intermediate, formed through condensation reactions between hexadecylamine and palmitic acid or by the self-condensation of hexadecylamine. Thus, after the initial dehydration or deammonization step, hydrotreating of the primary amide follows the pathways associated with the HDN of primary amines and the HDO of primary carboxylic acids. NiMo/TiO₂ is a more active amide hydrotreating catalyst than NiMo/γ-Al₂O₃. This is attributed to catalyzing the initial dehydration (HDO) step, as well as to more complete sulfidation of Mo and the better incorporation of the Ni promoter in the MoS₂ phase on TiO₂.