Effect of Feed Distribution on Hydrocracking of Fischer-Tropsch Wax

Two Fischer-Tropsch waxes having a different chain length distribution (i.e. heavy wax with C22+: 73%; light wax with C22+: 36%) have been subjected to hydrocracking. The tests were carried out in the range of temperature and pressure of 616-648 K and 3.5-6.0 MPa respectively. The catalyst used was platinum (0.6%) on amorphous silica-alumina. Hydrocracking reaction led in both cases to an increase of middle distillate yields and maximum values achieved was 80-85%. The results obtained show a strong effect of feed carbon distribution on isomer content of hydrocracking products. Particularly, it was found that C5-9 and middle distillate (C10-22) fractions from the heavy feed have a higher isomerization degree than the products from the light feed. The higher isomer content of products from heavier Fischer-Tropsch wax was explained in terms of currently known hydrocracking reaction pathways of n-paraffins and vapour-liquid equilibrium in the reacting system.