PROCESS FOR THE PRODUCTION OF HYDROCARBONS, USEFUL FOR MOTOR VEHICLES, FROM MIXTURES OF A BIOLOGICAL ORIGIN

The present invention describes a process for producing, in a single step, hydrocarbon fractions useful as diesel fuel or as a component of diesel fuel, from a mixture of a biological origin containing esters of fatty acids, and possibly also containing aliquots of free fatty acids. The process comprises the contemporaneous hydrodeoxygenation and hydroisomerization of the mixture of a biological origin, with the formation of linear and branched paraffins. The process is carried out in the presence of a catalytic composition comprising:A) an amorphous carrier of an acidic nature, selected from:(1) an amorphous silica-alumina having a SiO/AlOmolar ratio higher than or equal to 5,(2) a porous solid comprising silicon, aluminium, phosphorus and oxygen bonded together so as to form an amorphous mixed oxide forming a single phase, characterized by a Si/Al atomic ratio ranging from 15 to 250, a P/Al ratio of at least 0.1, but lower than 5, preferably ranging from 0.3 to 3.5, a total pore volume of between 0.5 and 2.0 ml/g, an average pore diameter of between 3 nm and 40 nm and a specific surface area ranging from 200 to 1,000 m/g, preferably from 300 to 900;B) a metallic component containing one or more metals of group VIII, possibly in a mixture with one or more metals of group VIB. If a catalytic composition consisting of a silica-alumina of type (1) and Pt, is used, the composition is pretreated by means of a hydrocarbon containing 7 to 16 carbon atoms, when the silica-alumina is a completely amorphous, micro-mesoporous silica-allumina (1a) having a SiO/AlOmolar ratio comprised between 30 and 500, a surface area greater than 500 m/g, a pore volume comprised between 0.3 and 1.3 ml/g, an average pore diameter smaller than 40 Å.