Fremgangsmåte for fremstilling av mellomdestillater ved hydroisomerisering og hydrokrakking av fødestrømmer fra Fischer Tropsch prosessen

The process uses a hydrocracking/isomerization catalyst comprising a hydro-dehydrogenating element from group VIII supported on a non-zeolitic support based on silica/alumina .The catalyst has closely defined characteristics particularly with regard to porosity and surface area. The catalyst support contains more than 5% and less than or equal to 95% of silica. The mean porous diameter and total porous vol (by mercury and nitrogen porosimetry) are 20-140 Angstrom and 0.1-0.6 ml/g respectively. The porous volumes (mercury porosimetry) in the pores of diameters greater than 140 Angstrom, 160 Angstrom, 200 Angstrom and 500 Angstrom are less than 0.1 ml/g. The surface area, BET, is 100-550 m2/g. The X-ray diffraction diagram comprises main peaks characteristic of at least one transition alumina from the group alpha, rho, chi, eta, gamma, kappa, theta or delta.