Catalytic hydrodenitrogenation of pyridine and quinoline.

Abstract

The reaction networks and the kinetics of the vapor phase catalytic hydro-denitrogenation (HDN) of two model nitrogen-containing heterocyclic compounds, pyridine, quinoline and their mixture, were studied in a bench scale continuous flow, fixed-bed catalytic reactor. The catalyst used in this study was presulfided commercial Ni-Mo/$\rm Al\sb2O\sb3$ (Shell Catalyst 424). The results indicate that the impact of the process variables on the conversion, yield, and selectivity of the HDN reactions is in the following decreasing order: $T>W/F>\bar R.$ The initial aromatic ring saturation reactions of pyridine and quinoline were all reversible at the conditions studied. The removal of nitrogen in pyridine HDN occurred primarily through the pentylamine intermediate, and pentane was the major hydrocarbon produced. The removal of nitrogen in quinoline HDN occurred through the decahydroquinoline intermediate, and propylcyclohexane was the major hydrocarbon produced. The Ni-Mo/$\rm Al\sb2O\sb3$ catalyst exhibited higher selectivity for the reaction pathway of pyridine HDN than that of quinoline HDN. Cracking and hydrocracking took place at temperatures above 648 K. The presence of pyridine in the HDN of a pyridine-quinoline mixture resulted in an increase in the rate of conversion of quinoline and a decrease in that of pyridine. On the other hand, the rate of formation of propylcyclohexane (PCH) had increased while the amount of decahydroquinoline (DHQ) produced had decreased, which indicates that the presence of pyridine had enhanced the transformation of DHQ to PCH. Mixing the two heterocycles had enhanced the conversion and the selectivity of the quinoline HDN at high and low temperature, while the conversion of pyridine had been retarded by the presence of quinoline. The selectivity of the mixture was more than that for either of the components. Several rate equations were considered to fit the kinetic data. A Langmuir-Hinshelwood reaction mechanism fitted the data best. Arrhenius plots of the pseudo rate constants for the HDN reactions of pyridine, quinoline, and their mixture gave activation energies (E) of 19.84, 26.52 and 13.17 kcal/g-mol, respectively.