Patent ID: 7655136

Claim:
In a process for producing middle distillates, comprising contacting a paraffinic feed under sufficient catalytic hydrocracking and hydroisomerization conditions so as to produce said middle distillates, said paraffinic feed comprising a cut produced directly or indirectly by Fischer-Tropsch synthesis, the catalyst being a hydrocracking/hydroisomerization catalyst comprising: at least one hydrodehydrogenating element selected from elements from group VIB and group VIII of the periodic table; and a non-zeolitic support comprising alumina-silica; said alumina-silica having the following characteristics: a percentage of silica in the range of 5% to 95% by weight; a sodium content of less than 0.03% by weight; a total pore volume, measured by mercury porosimetry, in the range of 0.45 to 1.2 ml/g; a porosity such that: i) the volume of mesopores with a diameter in the range of 40 to 150 Å and a mean pore diameter in the range 80 to 140 Å represents 30-80% of the total pore volume measured by mercury porosimetry; ii) the volume of macropores with a diameter of more than 500 Å represents 20-70% of the total pore volume measured by mercury porosimetry; a BET specific surface area in the range of 100 to 550 m 2 /g; an X ray diffraction diagram which contains at least the characteristic principal peaks of at least one transition alumina included in the group composed of alpha, rho, khi, eta, gamma, kappa, theta and delta aluminas, the improvement wherein said catalyst comprises 0.01% by weight to 6% by weight of P 2 O 5 as a doping element, and wherein the concentration of P 2 O 5 as a doping element is sufficient to provide an increased yield of middle distillate compared to the same catalysts having a content of P 2 O 5 below 0.01% by weight and above 6% by weight.