THE FUNCTION OF PHOSPHORUS , NICKEL AND H₂S IN THE HDN OF PIPERIDINE AND PYRIDINE OVER NiMoP/Al₂O₃ CATALYSTS

Abstract

The effect of phosphorus in the hydrodenitrogenation (HDN) of piperidine and pyridine over NiMo/A1203 catalysts was studied. In the absence of H2S no effect of P was found, but in the presence of H2S the HDN activiiy of NiMo/Al203 catalysts decreased as the P content In the catalysts increased. It is concluded that phosphorus has a negative effect on the C-N bond cleavage in piperidlne, as well as on the subsequent hydrogenation of the Cs alkene intermediates. Also the influence of Ni was found to depend on the reaction conditions. A substantial promotion effect of NI could only be observed In the presence of H2S, both in the C-N bond cleavage of piperidine and in the pyrMine hydrogenation. The activity for the HDJ of piperidlne of NiMo(P)/Al203 catalysts increased with increasing H2S concentration up to H2S/H2 = 12.5~10 mdlmol.

On the Formation of Pentylpiperidine in the Hydrodenitrogenation of Pyridine

“…Not even a trace of either molecule was observed. Neither was N-(5-aminopentyl)piperidine observed in the reaction of piperidine [8].…”

“…The strong acidity of the support was probably responsible for the formation of 2-pentylpiperidine and decahydroquinoline. In a study over sulfided MoP/Al 2 O 3 and NiMoP/Al 2 O 3 catalysts at 320°C, 3 MPa, and 9 kPa H 2 S, pentylamine as well as N-pentylpiperidine were observed, and a third possibility for the formation of N-pentylpiperidine was suggested, the addition of piperidine to pentene (Scheme 6) [8]. Over sulfided Mo, CoMo, and NiMo Ledoux and Djellouli did not observe products heavier than C5 in the HDN of pyridine.…”

“…Indeed, several studies of the HDN of pyridine have been published [1][2][3][4][5][6][7][8][9][10][11][12]. In several of these studies substantial amounts of N-pentylpiperidine were observed [2,4,[6][7][8][10][11][12]. The formation of this molecule has been ascribed to the reaction of piperidine, the first intermediate in the HDN of pyridine, with another molecule of piperidine, to the reaction of piperidine with a pentylamine molecule, a secondary intermediate of the HDN of pyridine, and to the reaction of piperidine with pentene, one of the two final, denitrogenated products of the HDN of pyridine (Scheme 1).…”

“…As a consequence, pyridine has not been popular as a model molecule in HDN studies. Some studies have looked for conditions to minimalize the formation of N-pentylpiperidine and thus avoid the massbalance problem [8], while others have instead used 2-methylpyridine as model compound, which hardly shows the formation of N-hexyl-2-methylpiperidine [13,14]. In the HDN of bicyclic nitrogen-containing molecules, the formation of N-alkylated compounds has not been observed and quinoline has often been used as a model molecule for HDN studies [15][16][17].…”