Production of Middle Distillate from Synthesis Gas in a Dual-bed Reactor Through Hydrocracking of Wax Over Mesoporous Pd-Al₂O₃ Composite Catalyst

Abstract

Production of middle distillate (C₁₀–C₂₀) from synthesis gas (CO + H₂) through hydrocracking of wax (>C₂₁₊) was carried out in a dual-bed reactor. Co/TiO₂ catalyst was used in the first-bed reactor to produce wax from synthesis gas, and a mesoporous Pd-alumina composite catalyst (Pd-Al₂O₃) was used in the second-bed reactor to produce middle distillate through hydrocracking of wax. For comparison, a Pd catalyst supported on mesoporous alumina (Pd/Al₂O₃) was also examined as a second-bed catalyst. The catalytic performance of Pd-Al₂O₃ and Pd/Al₂O₃ for hydrocracking of wax to middle distillate was tested and compared. It was revealed that selectivity for middle distillate in the dual-bed reactor was much higher than that in the first-bed reactor, indicating that both Pd-Al₂O₃ and Pd/Al₂O₃ catalysts in the second-bed reactor served as an efficient catalyst for hydrocracking of wax to middle distillate. Furthermore, Pd-Al₂O₃ catalyst showed a higher selectivity for middle distillate than Pd/Al₂O₃. The enhanced catalytic performance of Pd-Al₂O₃ for hydrocracking of wax to middle distillate was due to high Pd dispersion and high Pd surface area. Large medium acidity of Pd-Al₂O₃ catalyst was also responsible for its high catalytic performance in the hydrocracking of wax to middle distillate.