Hydrocracking of Octacosane and Cobalt Fischer–Tropsch Wax over Nonsulfided NiMo and Pt-Based Catalysts

The effect of activation environment (N₂, H₂ and H₂S/H₂) on the hydrocracking performance of a NiMo/Al catalyst was studied at 380 °C and 3.5 MPa using octacosane (C₂₈). The catalyst physical structure and acidity were characterized by BET, XRD, SEM-EDX and FTIR techniques. The N₂ activation generated more active nonsulfided NiMo/Al catalyst relative to the H₂ or H₂S activation (X_C28, 70–80% versus 6–10%). For a comparison, a NiMo/Si-Al catalyst was also tested after normal H₂ activation and showed higher activity at the same process conditions (X_C28, 81–99%). The high activity of the NiMo/Al (N₂ activation) and NiMo/Si-Al catalysts was mainly ascribed to a higher number of Brønsted acid sites (BAS) on the catalysts. The hydrocracking of cobalt wax using Pt/Si-Al and Pt/Al catalysts confirmed the superior activity of the Si-Al support. A double-peak product distribution occurred at C₄–C₆ and C₁₀–C₁₆ on all catalysts, which illustrates secondary hydrocracking and faster hydrocracking at the middle of the chain. The nonsulfided NiMo/Al and Pt/Al catalysts, and NiMo/Si-Al catalyst produced predominantly diesel (sel. 50–70%) and gasoline range (sel. > 50%) hydrocarbons, respectively, accompanied by some CH₄ and light hydrocarbons C₂–C₄. On the other hand, the hydrocarbon distribution of the Pt/Si-Al varied with conditions (i.e., diesel sel. 87–90% below 290 °C or gasoline sel. 60–70% above 290 °C accompanied by little CH₄) The dependence of the isomer/paraffin ratio on chain length was studied as well. The peak iso/paraffin value was observed at C₁₀–C₁₃ for the SiAl catalyst.