Process Intensification Study On Hydrocracking Of F-T Wax Over Microfibrous Structured Catalysts

Hydrocracking of F-T wax is an important process for improving diesel yield and quality of the products from low-temperature Fischer-Tropsch (LTFT) synthesis process. The industry fixed bed reactors packed with conventional catalysts are easily affected by heat transfer, inner diffusion and other transfer effects. In this paper, the hydrocracking process intensification of F-T wax was investigated over microfibrous structured catalysts.The influences of temperature and WHSV on hydrocracking of semi-refined56#wax with Pt/SAB catalysts were investigated at a pressure of3.5MPa, a temperature range of290-320℃, a WHSV range of0.7-2h-1and a hydrogen to wax ratio of1000(V/V). The four-lumped kinetic model was built based on experimental results. The simulation and optimization results from four-lumped kinetic model show that large WHSV and high reaction temperature can increase the diesel yield. When temperature is330℃and WHSV is5h-1, the conversion ratio of C20+is84.61%, diesel (C10-C20) yield is46.68%and the liquid hydrocarbon (C5-C20) yield is74.02%.The experimental results of Pt/SAB catalysts with different particle size show that inner diffusion has a disadvantageous effect on C20+conversion and makes diesel selectivity decrease when the catalysts particle size is larger than0.18mm. In the heat transfer study with constant wall temperature, the temperature rise of bed packed with microfibrous entrapped catalysts was much faster than conventional Pt/SAB catalysts. Meanwhile, the temperature difference of microfibrous entrapped catalysts was lower than the conventional Pt/SAB catalysts. These results confirmed that the microfibrous entrapped catalysts can enhance the heat transfer of fixed bed reactor. Pt/SAB2catalysts were prepared with carrier SAB calcined at850℃for1h. The results of Pt/SAB2catalysts demonstrate that the high sintering temperature in microfibrous entrapped Pt/SAB catalysts preparation damages the microstructure of SAB carrier, and makes catalysts specific surface area and acidity decrease which causes the deactivation of the microfibrous entrapped Pt/SAB catalysts.Structured microfibrous zeolite catalysts Pt/ZSM-5/SSMF were synthesized by zeolite coatings depositing technique and secondary growth process. The structured microfibrous zeolite catalysts of Pt/ZSM-5/SSMF have good hydrocracking activity. At temperature of270℃, the conversion ratio of semi-refined56#wax was80.06%, the petrol (C5-C9) yield was 53.21%and the liquid hydrocarbon (C5-C20) yield was67.23%.