Piperidine hydrogenolysis on a commercial hydrocracking catalyst: II. The Effects of Initial Piperidine Concentration, Temperature, Catalyst Presulfidation, and Hydrogen Partial Pressure on Catalyst Activity, Deactivation, and Coke Formation

Abstract

The formation of coke in the piperidine hydrogenolysis reaction over a fresh sulfided hydrocracking catalyst was examined at temperatures ranging from 281 to 321°C, hydrogen partial pressures of 11.2 to 15.9 atm (1.1 to 1.6 MPa), and initial concentrations of piperidine of 3.94 × 10 −3 to 11.84 × 10 −3 g mol/liter using elemental analysis, 13C NMR spectroscopy, and ESCA. The results indicated that most of the coke present on the catalyst after 17 h on stream was deposited in the initial 90 min of the reaction. Coke formation and hence catalyst deactivation were found to increase with both reaction temperature and initial concentration of piperidine. Reducing the catalyst instead of sulfiding it had no effect on the final coke content. Nitrogen was found to be present on the catalyst surface after reaction indicating that nitrogen-containing compounds were participating in the formation of coke. The H/C ratio of the coke decreased very slowly with reaction time and was invariant to changes in temperature, initial concentration of piperidine, or catalyst pretreatment method. Comparing the activity of reduced versus sulfided fresh catalysts in the hydrogenolysis of piperidine, it was found that under the present conditions, catalyst presulfidation increased the activity of the metallic catalyst function and decreased the rate of catalyst deactivation. Furthermore, decreasing the partial pressure of hydrogen resulted in an activity decrease of the metallic catalyst function and had a negative effect on the overall catalyst activity maintenance. The intrinsic activity of the acidic catalyst function was not affected by the change in hydrogen partial pressure.