A STUDY OF CATALYTIC HYDRODENITRIFICATION BY THE USE OF AMMONIA CHEMICAL IONIZATION GC MS AND GC MS MS

Ammonia chemical ionization gas chromatography-tandem mass spectrometry (NH3/CI GC/MS/MS was used to differentiate the structure of partially hydrogenated nitrogen-containing intermediates produced during the catalytic hydrodenitrification (HDN) of model compounds, 2,6-dimethylquioline and acridine. The structural data indicate that the HDN mechanism proceeds by two competing pathways involving the initial hydrogenation of either the heterocyclic ring or the adjacent aromatic ring. Additional HDN experiments using alkylpyridine model compounds were performed and the samples were analyzed by NH3/CI GC/MS. The results revealed that the HDN was strongly retarded when the nitrogen atom was sterically hindered by alkyl groups substituted at the carbons adjacent to nitrogen (positions 2 and 5). A similar steric effect was observed when a methyl group was substituted at the carbon adjacent to nitrogen (position 1) of carbazole. The relative concentration of 1-methylcarbazole was higher in the HDN product than in the catalytic cracker feed, indicating that the removal of 1-methylcarbazole relative to the 2-, 3- and 4-methylcarbazoles was retarded due to the steric hindrance.