Hydroisomerization and hydrocracking over platinum loaded ZSM-23 catalysts in the presence of sulfur and nitrogen compounds for the dewaxing of diesel fuel

Abstract

Hydroisomerization and hydrocracking of n-hexadecane in the presence of sulfur and nitrogen compound were investigated over four different platinum loaded ZSM-23 catalysts (Pt/ZSM-23, Pt–Pd/ZSM-23, Pt–Mg/ZSM-23 and Pt–Pd–Mg/ZSM-23). Sulfur and nitrogen compounds could poison metal and acid sites of bifunctional catalysts, respectively. In this study, effort has been made to improve the sulfur and nitrogen tolerance in the conversion of n-hexadecane by introducing palladium and magnesium as additives. Pt–Pd bimetallic catalysts increased the electron-deficiency of metal sites, leading to the improvement of sulfur tolerance. The addition of magnesium on platinum loaded ZSM-23 increased the concentration of Lewis acid sites and thereby the poisoning of nitrogen compound was discouraged. The applicability of Pt–Pd–Mg/ZSM-23 catalyst for dewaxing process was further examined using diesel feeds with sulfur compound such as dimethyl disulfide in a high pressure pilot plant. Pt–Pd–Mg/ZSM-23 catalyst showed good catalytic performance for dewaxing process in terms of diesel product yield and long-term stability.