Effect of Pressure on the Hydrocracking of Light Cycle Oil with a Pt–Pd/HY Catalyst

Abstract

The effect of pressure (35–75 bar) has been studied on the hydrocracking of light cycle oil (LCO) on a Pt–Pd/HY catalyst. The remaining operating conditions are as follows: 400 °C; H2/LCO molar ratio (nH2), 10 molH2 (molLCO)−1; space velocity (WHSV), 2 h–1; time on stream, 0–24 h. The reaction indices studied are the conversions of hydrocracking and hydrodesulphurisation, the selectivity of naphtha and medium distillates, and the concentrations of these fractions. It has been proven that once an initial deactivation period has elapsed, the Pt–Pd/HY catalyst is very stable and has a high capacity for producing naphtha and medium distillates at 400 °C. Furthermore, the catalyst is fully regenerated by coke combustion with air at 550 °C. An increase in pressure allows reaching a pseudostable state with higher activity for hydrodesulphurisation (conversion 0.96 under 75 bar) and hydrocracking (conversion 0.87). Naphtha selectivity increases as pressure is increased and is 68% under 75 bar for a conversion of 98%, with overcracking being insignificant. The concentration of aromatics in the naphtha is 30 wt %, and it is therefore suitable for the gasoline pool. Lower values of space velocity are to be used in the hydrocracking to reduce aromatic concentration further.