Fremgangsmåte for fremstilling av hydrokarbonfraksjoner fra blandinger av en biologisk opprinnelse

A process is described for producing hydrocarbon fractions which can be used as diesel fuel or as components of diesel fuel, starting from a mixture of a biological origin containing esters of fatty acids possibly with amounts of free fatty acids, which comprises the following steps: 1) hydrodeoxygenation of the mixture of a biological origin; 2) hydroisomerization of the mixture resulting from step (1), after possible 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 greater than 500 m2/g, a pore volume ranging from 0.3 to 1.3 ml/g, an average pore diameter lower than 40 Å, b) a metallic component containing one or more metals of group VIII, possibly mixed with one or more metals of group VIB.