Kinetic study of pyrrole and pyridine HDN on Ni-W and Ni-Mo catalysts

Abstract

The kinetics are studied of the hydrodenitrogenation (HDN) of pyrrole and pyridine on the laboratory prepared Ni-W/Al 2O 3 and the standard industrial Ni-Mo/Al 2O 3 (HR 346 Procatalyse) catalysts at 573 K, 3 MPa of a mixture of H 2+1.1% dimethylsulfide. The kinetic scheme of pyrrole HDN at its low initial partial pressure can be simplified, owing to the higher relative reactivity of pyrrolidine and 1-butylamine, to a one-step reaction: pyrrole→NH 3+C 4 hydrocarbons, in contrast to the consecutive reaction scheme of pyridine HDN: pyridine→piperidine→n-pentylamine→NH 3+C 5-hydrocarbons. The most active Ni-W catalyst reached about the same activity for pyrrole HDN as the standard Ni-Mo one. In competitive reaction with pyridine, pyrrole HDN is inhibited to a larger extent on the Ni-W catalyst than on the standard Ni-Mo one. The low reactivity of pyrrole is due to its poor adsorptivity in comparison with the other nitrogen bases as indicated by competitive kinetic measurements as well as IR spectroscopy. A single set of HDN integral kinetic data has been successfully fitted by the first-order kinetic model for all three steps. To fit two and more coherent sets of experimental data simultaneously, a relatively simple four-parameter Langmuir-Hinshelwood kinetic model has been applied.