Process for producing hydrocarbon fractions from mixtures of a biological origin

A process for producing a hydrocarbon fraction which can be used as diesel fuel or as a component of diesel fuel, starting from a mixture of biological origin containing esters of fatty acids, and optionally containing free fatty acids, which comprises:

• 1) hydrodeoxygenation of the mixture of biological origin containing esters of fatty acids and optionally free fatty acids, wherein the hydrodeoxygenation is the first step of the process;
• and
• 2) hydroisomerization of the mixture resulting from (1), after optional purification treatment, said hydroisomerization being effected in the presence of a catalytic system which comprises:
• a) a carrier of acid nature comprising a completely amorphous micro-mesoporous silico-alumina having a SiO2/Al2O3 molar ratio ranging from 30 to 500, a surface area higher than 500 m2/g, a pore volume ranging from 0.3 to 1.3 ml/g, an average pore diameter lower than 40 Å, and
• b) a metallic component containing one or more metals of group VIII, optionally mixed with one or more metals of group VIB.