Hydrodynamic Effects in Scaled-Down Hydrocracking of Iron-Based Fischer−Tropsch Wax

Abstract

Iron-based low-temperature Fischer−Tropsch (LTFT) wax was hydrocracked in upflow and downflow mode of operation using fixed-bed bench-scale and pilot-scale reactors. Heavy paraffin conversion was higher in the upflow mode whereby lower diesel selectivities were observed. It was also shown that the diesel properties are a function of the mode of operation. The results indicate the presence of macrokinetic (hydrodynamic) limitations on the overall hydrocracking rate that is present due to the comparatively low liquid superficial velocity. The higher hydrocracking efficiency in the upflow mode is likely due to complete particle wetting (compared to the partial wetting in the downflow mode) that enhances both external and internal mass transfer of the liquid phase reagent. The results highlight the danger of scaled-down reactors that might not be representative of industrial operation.