The present invention relates to an integrated fluid bed catalytic cracking process (FCC) which allows hydrocarbon mixtures to be obtained having a high quality as fuel. According to a particular aspect, the invention relates to an integrated process comprising a fluid bed catalytic cracking stage in which hydrocarbon cuts of a petroliferous origin are converted, in the presence of a catalyst, with at least two components containing ERS-10, into mixtures with a high content of light cycle oil (LCO) having a high quality in terms of density and nature of the aromatic compounds contained therein, which, after a separation stage and a hydrotreatment stage, are subjected to an upgrading stage by treatment with hydrogen and with a catalyst comprising one or more metals selected from Pt, Pd, Ir, Ru, Rh and Re and a silico-aluminate of an acid nature.

WO 2006/124175 describes a process for the conversion of hydrocarbon cuts for producing olefins, aromatic compounds and diesel with a low sulfur content, which comprises a fluid bed catalytic cracking stage to produce olefins and in a smaller quantity LCO, a transformation stage of the high-boiling part of the olefins to ethylene and propylene and a hydrocracking stage in which the LCO cut is mainly transformed into aromatic compounds and a smaller percentage of diesel with a low sulfur content.

WO2007/006473 describes a process for improving the quality as fuel of hydrotreated hydrocarbon mixtures which comprises putting said mixtures in contact with hydrogen in the presence of a catalytic system comprising one or more metals selected from Pt, Pd, Ir, Ru, Rh and Re and a silico-aluminate of an acid nature.

MI2007A001610 describes an integrated process comprising a fluid bed catalytic cracking stage in which hydrocarbon cuts of a petroliferous origin are converted to mixtures with a high content of LCO which, after a separation stage and a hydrotreatment stage, is subjected to an upgrading stage by treatment with hydrogen and with a catalyst comprising one or more metals selected from Pt, Pd, Ir, Ru, Rh and Re and a silico-aluminate of an acid nature.

MI2008A001036 describes a process in which ERS-10 zeolite is used as additive in cracking processes of hydrocarbon mixtures . An integrated process for the production of hydrocarbon mixtures with a high quality as fuel has now been found, which comprises a fluid bed catalytic cracking stage (FCC) carried out in the presence of a catalyst with at least two components containing ERS-10 zeolite to give a fraction of LCO, a hydrotreatment stage of said LCO fraction and an upgrading stage of the resulting hydrotreated LCO by reaction with hydrogen in the presence of a catalytic system comprising one or more metals selected from Pt, Pd, Ir, Ru, Rh and Re and a silico-aluminate of an acid nature.

The fluid bed catalytic cracking stage according to the process of the present invention not only allows a higher conversion to be obtained with respect to the results that can be reached with the traditional catalytic systems, but also optimum performances also in the conversion of the heavier fraction (bottom cracking) expressed as a ratio between LCO and HCO, with a reduced production of HCO even up to 50% with respect to the known processes. u _^

The upgrading stage according to the process of the present invention comprises enrichment of the resulting mixture in alkyl-benzene compounds at least partly deriving from the conversion of the naphtha-aromatic structures contained in the LCO cut, generated during the FCC stage and also during the hydrotreatment stage. The integrated process of the present invention leads to hydrocarbon mixtures with a further improved cetane index and a reduced density, the latter being comparable to that obtained through total dearomatization, but obtained with a much lower hydrogen consumption. A particularly preferred aspect of the present invention is to effect the fluid bed catalytic cracking stage (FCC) under such conditions as to obtain a higher-quality LCO fraction with a high yield, in terms of density and nature of the aromatic compounds contained therein. In particular, in this case, the LCO fraction is characterized not only by a high quality in terms of density, but also by an extremely favourable composition in terms of aromatic compounds which makes it particularly suitable for being treated in the subsequent stages of the integrated process of the invention. The content of polyaromatics is in fact lower with respect to the LCO cuts obtained under normal FCC conditions, whereas the content of benzonaphthene compounds is higher. This preliminary enrichment in benzonaphthene compounds simplifies the subsequent hydrotreatment and upgrading stages, allowing mixtures with optimum characteristics to be obtained as fuels using lower overall hydrogen quantities with respect to what is described in the known art.

The mixture resulting from the FCC stage contains HCO as major by-product, which can be at least partly recycled to the FCC stage thus allowing a higher overall yield to LCO to be obtained.

Furthermore, by effecting the fluid bed catalytic cracking stage in the presence of a catalyst containing ERS-IO, the conversion of the heavier fraction is increased, further increasing the overall yield to LCO. An object of the present invention therefore relates to an integrated process for the conversion of hydrocarbon cuts of petroliferous origin in hydrocarbon mixtures with high quality as fuel that comprises the following stages : - subjecting the hydrocarbon cut to fluid bed catalytic cracking (FCC) in the presence of a catalyst containing zeolite ERS-10, said catalyst having at least two components, for producing Light cycle oil (LCO) ; - subjecting the Light cycle oil to hydrotreatment; - reacting the hydrotreated Light cycle oil deriving from the previous hydrotreatment stage with hydrogen in the presence of a catalytic system comprising: al) one or more metals selected from Pt, Pd, Ir, Ru, Rh and Re bl) an acidic silico-aluminate selected from a zeolite belonging to the MTW family and a completely amorphous micro-mesoporous silico-alumina having an SiO ₂ /Al ₂ O ₃ molar ratio of between 30 and 500, a surface area of over 500 m ² /g, a volume of the pores of between 0.3 and 1.3 ml/g and an average diameter of the pores of less than 40 A.

According to a particularly preferred aspect, the process of the present invention is effected by means of the following stages: (1) subjecting a hydrocarbon cut of petroliferous origin to fluid bed catalytic cracking (FCC) in the presence of a catalyst containing zeolite ERS-10, said catalyst having at least two components, for producing a mixture containing LCO,

(2) subjecting the mixture resulting from the previous fluid catalytic cracking stage to separation so as to separate at least an LCO fraction and an HCO fraction,

(3) possibly re-feeding the fluid bed catalytic cracking stage (FCC) with at least part of the HCO fraction obtained in stage (2) ,

(4) subjecting the LCO fraction obtained in stage (2) to hydrotreatment ,

(5) reacting the product resulting from the previous step with hydrogen in the presence of a catalytic system comprising: al) one or more metals selected from Pt, Pd, Ir, Ru, Rh and Re bl) an acidic silico-aluminate selected from a zeolite belonging to the MTW family and a completely amorphous micro-mesoporous silico-alumina having an SiO ₂ Ml ₂ O ₃ molar ratio of between 30 and 500, a surface area of over 500 m ² /g, a volume of the pores of between 0.3 and

1.3 ml/g and an average diameter of the pores of less than 40 A.

The catalyst used in the first step contains at least two different components: (a) a component containing one or more cracking catalysts, preferably fluid bed catalytic cracking catalysts, and (b) a component containing ERS-IO zeolite. In accordance with this, in the first stage of the integrated process object of the present invention, a catalytic composition can be used comprising: a) a first component containing one or more catalysts selected from zeolites, amorphous cracking catalysts based on inorganic oxides and non-zeolitic crystalline cracking catalysts based on inorganic oxides b) a second component containing a ERS-IO zeolite. In this catalyst, component (a) , containing one or more catalysts for catalytic cracking, preferably for fluid bed catalytic cracking, is combined with component (b) , having the function of additive. ^•

Examples of amorphous materials which can be conveniently used in component (a) , as described in EP 1011291, are for example clay, silico-alumina, silico- magnesia, silico-zirconia, silico-titania, silico- alumina-magnesia, silico-alumina-zirconia, silico- magnesia-zirconia.

A crystalline silico-alumina, as described for example in US 4,309,279, can be used as non-zeolitic crystalline material in component (a) .

A preferred aspect of the present invention is to use a zeolite as component (a) , even more preferably a large-pore zeolite. Zeolites which can be used for this purpose are zeolite Y (US 3,130,007), zeolite L (US 3,216,789), Omega zeolite (Cryst. Struct. Comm. , 3, 339-344 (1974)), Beta zeolite (US 3,308,069) and Mordenite (Z.

Kristallogr. , 115, 439-450 (1961)). Zeolite Y is preferably used. The same zeolite ERS-10 can be used in component (a) as cracking catalyst, in a mixture with at least another cracking catalyst.

Y zeolites which can be used are those exchanged with hydrogen and/or with rare earth or those which have been subjected to thermal treatment by means of techniques well-known to experts in the field. Examples of zeolites which can be typically used as catalyst components are described in:

• "Paul B. Venuto, E. Thomas Habib, Jr "Fluid Catalytic Cracking with Zeolite Catalysts" vol.l, M. Dekker, Inc . ; • Julius Scherzer, "Octane-Enhancing Zeolitic FCC Catalysts", M. Dekker Inc.

The zeolites adopted as component (a) can be used in bound form with a binder, selected for example from silica, alumina, silico-alumina, clay, silica-zirconia, silico-magnesia, aluminum phosphate or mixtures thereof. The preparation of the bound form of the zeolite is effected according to techniques known to experts in the field.

Component (b) of the catalytic composition of the present invention contains the zeolite ERS-10, wherein said zeolite acts as additive.

This zeolite was described for the first time in EP 796,821, and is also well described in:

- S. Zanardi, G. Cruciani, L. C. Carluccio, G. Bellussi, C. Perego, R. Millini, "Framework topology of ERS-10 zeolite", Angew. Chem. Int. Ed., 41(21) (2002) 4109- 4112.

- C. Perego, M. Margotti, L. C. Carluccio, L. Zanibelli, G. Bellussi, "The catalytic performances of zeolite ERS-10", Stud. Surf. Sci. Catal . , 135 (2001) 29 O 01.

- S. Zanardi, G. Cruciani, L. C. Carluccio, G. Bellussi, C. Perego, R. Millini, "Synthesis and framework topology of the new disordered ERS-10 zeolite" , J. Porous Mater., 14 (2007) 315-323.

The preparation of the zeolite ERS-10 is well described in EP 796,821. The synthesis is preferably effected by heating a reaction mixture containing 6- azonia-spiro- [5, 5] -undecane hydroxide (Q) as organic additive, tetraethylorthosilicate (TEOS) and aluminum iso-propoxide (AiP) as silica and aluminum sources respectively, sodium hydroxide (NaOH) and water, preferably in the following molar ratios: SiO ₂ Ml ₂ O ₃ from 50/1 to ∞ Na ⁺ /SiO ₂ from 0.05/1 a 0.15/1 Q/SiO ₂ from 0.2/1 a 0.3/1 H ₂ O/SiO ₂ from 40/1 a 50/1 OH ^" /SiO ₂ from 0.25/1 a 0.45/1 to a temperature ranging from 150 to 180 ⁰ C, preferably from 155 to 17O ⁰ C, for 7-28 days, preferably for 7-14 days, under autogenous pressure in a stainless steel autoclave .

The resulting crystalline material is dried, at a maximum temperature of 170 ⁰ C, preferably between 90 and 120 ⁰ C, and calcined at a temperature ranging from 500 to 700 ⁰ C, preferably from 550 to 650 ⁰ C, for a period ranging from 4 to 20 hours, preferably from 6 to 15 hours .

From a structural point of view, it has been experimentally demonstrated that the alumino-silicate lattice of ERS-10 is disordered and can be described as an intergrowth of three structurally correlated zeolites: Nonasil (NON, zeolite of the clathrasil type) characterized by the presence of only cages not connected with the outside of the crystals) , EU-I (EUO, medium-pore zeolite characterized by a one-dimensional channel system with openings having 10 tetrahedra (10MR) with large side pockets) and NU-87 (NES, medium- pore zeolite characterized by a one-dimensional channel system with openings having 10 tetrahedra (10MR) . More specifically, the structure of ERS-10 can be constructed using two periodic units (known as Periodic Building Units, PerBU) . The random combination of these periodic units leads to the formation, inside the same zeolite crystal, of domains having the characteristics of the three zeolites indicated above (NON, EUO and NES) in addition to the presence of a further structural situation characterized by the presence of pores with openings having 14 tetrahedra (14MR) . Consequently characteristics typical of medium-pore zeolites (10MR) and extra-large-pore zeolites (14MR) co-exist in the same structure.

The ERS-10 zeolite crystallizes, in pure form, from reagent mixtures with an SiO ₂ /Al ₂ O ₃ (SAR) molar ratio within the range of 80-160, which is therefore preferred. The crystalline products undergo an enrichment in Al for SAR values within the range of 60-80: by operating with reaction mixtures having SAR values < 80 the co-crystallization of Mordenite (MOR) can be obtained. With SAR values > 160, there can be the formation of ZSM- 12 zeolite (MTW) .

As ERS-10 zeolite is the result of an intergrowth of various zeolitic phases, this implies a variability in their relative ratio or, technically speaking, the probability of stacking of the periodic units. This leads to the possibility of the products obtained having different characteristics in terms of relative abundance of the domains corresponding to the three structures NON, EUO and NES and channels with 14MR openings.

In the use of ERS-10 zeolite as component of the new catalytic composition for the cracking of hydrocarbon mixtures, in particular FCC, the fact that it is the result of an intergrowth of various phases, in a variable ratio, does not influence its catalytic performances, as it does not even influence the presence of modest quantities of Mordenite or ZSM-12 zeolite possibly formed during the synthesis of the ERS-10 zeolite, preferably in a quantity not higher than 30% by weight with respect to the weight of the ERS-10 zeolite. Neither does the possible formation of accessory phases of NON, EUO and NES zeolites, in small quantities, preferably not higher than 30% by weight with respect to the weight of the ERS-10 zeolite, significantly influence the performances of the catalyst . For application as additive for FCC, according to the integrated process of the present invention, the ERS-10 can be used in different bound forms, prepared in accordance with techniques known to experts in the field, such as for example, granulates, or preferably microspheres. The microspheres can be prepared via spray-drying, using the known techniques, and contain the zeolite in bound form. Silica, amorphous silica- alumina, alumina or mixtures thereof, can be preferably used as binders. In component (b) , the zeolite, when in bound form with a binder, is preferably in a quantity ranging from 5 to 90% with respect to the overall weight of said component .

In the composition of the present invention, the ERS-10 zeolite is preferably present in a quantity ranging from 1 to 10% with respect to the weight of the catalyst contained in component (a) .

The catalytic composition used in the fluid catalytic cracking stage can be prepared:

- by the mechanical mixing of components (a) and (b) , according to techniques known to experts in the field, in which case the ERS-10 zeolite is a component of catalytic particles physically different from those containing the catalyst of component (a) ;

- by contemporaneously binding, according to the known techniques, the ERS-10 zeolite and the catalyst contained in component (a) , in which case the ERS-10 zeolite and the catalyst are contained in the same particle of the catalytic composition;

- in situ, by adding component (b) to component (a) already present in the cracking process, at any point of the same process.

The use of ERS-10 zeolite as cracking additive, preferably for fluid bed catalytic cracking, allows a higher conversion of the FCC feed to be obtained and in particular a high bottom cracking with the prevalent formation of the LCO fraction, diesel, with respect to the formation of the HCO fraction.

Hydrocarbon mixtures suitable for being treated according to the process of the present invention are for example gas oils, oil fractions consisting of VGO (Vacuum Gas oils) having a boiling range of 350 to 550 ⁰ C, atmospheric residues, deasphalted oils, thermal cracking products and hydrocracking residues. The products obtained from the integrated fluid bed catalytic cracking process of the present invention are listed below: Fuel Gas (H2, C1-C2) ; LPG (C3-C4); Gasoline (C5-221) ; LCO (221-350) ; HCO (350+) . The FCC step can be carried out according to the conditions known to experts in the field, described for example in Fluid Catalytic Cracking Handbook 2 ^nd edition, Reza Sadeghbeigi, ed. Gulf Professional Publishing, 2000. The fluid catalytic cracking process is generally divided into two stages, cracking effected in the riser and regeneration of the catalyst carried out in the regenerator, both stages being effected with the catalyst in fluid phase. The cracking reaction is substantially endothermic, it is sustained by the sensitive heat possessed by the flow of regenerated catalyst and takes place by putting the hydrocarbon feed in contact with the hot regenerated catalyst. The fluid catalytic cracking reaction conditions comprise a temperature ranging from 400 to 650 ⁰ C, preferably from 450 to 650 ⁰ C. The pressure in the reaction area ranges from 1 to 5 bars, preferably from 1.3 to 4.5 bars. The catalyst/oil ratio ranges from 1 to 10 kg/kg, the residence time of the vapours in the reaction area ranges from 0.5 to 10 seconds, preferably from 1 to 5 seconds .

The regeneration of the exhausted cracking catalyst takes place by combustion with oxygen of the coke deposited on the catalyst at a temperature ranging from 600 to 815°C and a pressure of the regenerator ranging from 1.3 to 4.5 kg/cm ² and preferably between 2.4 and 4.0 bars .

The fluid catalytic cracking step can operate in continuous or batchwise, with a fixed bed, moving bed or fluid bed. The flow of the hydrocarbon mixture can be fed either with the current or in countercurrent with respect to the flow of the catalyst.

According to a particularly preferred aspect of the present invention, the fluid bed catalytic cracking step is carried out under such conditions as to allow the production of an LCO cut having a further enhanced quality from the point of view of density and characterized by a particularly favourable composition in terms of aromatic compounds. In substance, the content of polyaromatics is reduced with respect to the LCO cuts obtained under normal FCC conditions, in favour of a higher content of benzonaphthene compounds .

This composition characteristic simplifies the subsequent hydrotreatment and upgrading stages, allowing mixtures to be obtained with optimum characteristics as fuels using overall lower quantities of hydrogen with respect to what is described in the known art. According to this preferred aspect of the present patent application, the high yields to LCO obtained in the FCC step are reached by selecting particular and specific temperature conditions and/or by selecting particular preheating temperatures of the feed. The selection of these particular conditions for effecting the fluid bed catalytic cracking step also allows the cracking reaction to be directed towards a greater formation of HCO as reaction by-product, which, as this can be recycled to the FCC step, allow a higher overall LCO yield to be reached.

The particular and selected temperature conditions which allow the formation of LCO to be maximized are those within the range of 490 to 530 ⁰ C.

The particular preheating temperatures of the feed which allow the yield to LCO to be maximized are within the range of 240 to 35O ⁰ C.

In both cases, it is preferable to operate at a pressure ranging from 2.0 to 3.5 bar.

As far as the remaining process parameters are concerned, the conditions normally used by experts in the field can be adopted.

By effecting the FCC step so that at least one of the previous temperature and preheating temperature conditions is satisfied, an increase of the yield to LCO of at least 50% is obtained, the complement to 100 consisting of: - fuel gas ( H ₂ , Cl, C2 )

- GPL (C3-C4)

- gasolines (C5-210°C)

- HCO ( 370+ ⁰ C)

- coke With respect to stage (a) effected in the presence of a catalyst containing ERS-10 zeolite, the process conditions indicated above, relating to temperature and/or preheating temperature of the feed, which allow the formation of LCO to be maximized and obtaining a high-quality LCO cut with respect to the density and content of aromatic compounds, are new and are a further aspect of the present invention.

The mixture resulting from the first step of the integrated process of the present invention is separated, preferably by means of distillation.

The HCO fraction obtained from the separation is preferably recycled to the FCC step, for example in a mixture with the feed.

The LCO fraction obtained from the separation, characterized by a composition in terms of aromatic content rich in benzonaphthene compounds, is subjected to hydrotreatment , in order to reduce the nitrogen and sulfur content and vary the composition of the cut, further enriching it in benzonaphthene compounds.

The hydrotreatment of the LCO cut is carried out in one or more fixed bed reactors, and the catalytic beds can contain the same or different catalysts . Catalysts based on metallic compounds of Group VI and/or Group VIII are normally adopted, on a carrier, preferably an amorphous carrier, such as for example alumina or silica-alumina. Metals which can be conveniently used are for example nickel, cobalt, molybdenum and tungsten. Examples of catalysts which can be well adopted, and their preparation, are described in Hydrocracking Science and Technology, J.Scherzer and A.J. Gruia, Marcel Dekker, 1996. The hydrotreatment is described for example in Catalysis-Science and Technology, Edited by R. Anderson and M.Boudart, Volume 11, Sprinter-Verlag, del 1996. The hydrotreatment catalysts are used in sulfided form. The sulfidation can be obtained for example by sending onto the catalyst a suitable feed containing sulfurated compounds such as Dimethyldisulfide (DMDS) , Dimethylsulfoxide (DMSO) or other compounds which, on decomposing, give rise to the formation of H ₂ S.

The hydrotreatment is preferably carried out at a temperature ranging from 200 ⁰ C to 400 ⁰ C, even more preferably at a temperature ranging from 330 to 380 ⁰ C. The pressures normally vary from 20 to 100 bar, preferably from 40 to 80 bar. The LHSV space velocity preferably ranges from 0.3 to 3 hours ^"1 . The H ₂ /feed ratio preferably ranges from 200 to 2,000 Nl/1. During the hydrotreatment , the LCO feed undergoes saturation reactions of the aromatic rings with a reduction in the aromatic carbon content and enrichment in naphtho- aromatic compounds.

The following upgrading step is effected, in accordance with WO2007/006473 , in the presence of a bifunctional catalytic system comprising one or more metals selected from Pt, Pd, Ir, Rh, Ru, and Re, and a silico-aluminate of an acid nature selected from a micro-mesoporous silico-alumina having a suitable composition and a zeolite belonging to the MTW family. This process step leads to a substantial improvement in the properties of the hydrotreated LCO, in particular in terms of cetane index (number) , density and distillation curve, which proves to be equivalent to that obtained by means of simple hydrogenation of the aromatic structures. In this stage, a negligible formation of low- molecular-weight products is determined and lower hydrogen consumptions are necessary with respect to the known processes.

This step is carried out in the presence of hydrogen, with a catalytic system comprising: al) one or more metals selected from Pt, Pd, Ir, Rh, Ru, and Re, bl) an acidic silico-aluminate selected from a zeolite belonging to the MTW family and a completely amorphous micro-mesoporous silico-alumina having an SiO ₂ /Al ₂ O ₃ molar ratio of between 30 and 500, a surface area of over 500 m ² /g, a volume of the pores of between 0.3 and 1.3 ml/g and an average diameter of the pores of less than 40 A.

This stage of the process allows a substantial increase in the cetane index (number) to be obtained together with a decrease in the density and T95 of the hydrotreated LCO mixture. The LCO mixture thus obtained is, among other things, further enriched in alkyl- benzene compounds which at least partly derive from the partially hydrogenated polycyclic aromatic compounds of the benzonaphthene type either already present in the LCO cut deriving from the particular FCC step of the present integrated process or generated during the hydrotreatment .

The catalysts used in this process step direct the process towards the formation of alkyl-benzene structures by means of hydrodecyclization of the naphthene ring of naphtha-benzene or dinaphtho-benzene structures, thus obtaining the best possible compromise between hydrogen consumption and improvement of the properties of the product, at the same time limiting both the complete hydrogenation reaction of the aromatic rings and also the cracking reaction to form light products.

The catalysts used are those described in patent application WO2007/006473. The component of an acid nature (bl) of the catalytic composition used in the present invention can be selected from zeolites of the

MTW type: the MTW family is described in Atlas of zeolite structure types, W.M.Meier and D.H.Olson, 1987, Butterworths . The zeolite of the MTW structural type, which is suitable for being used in the present invention is a silico-aluminate with an SiO ₂ /Al ₂ O ₃ molar ratio higher than or equal to 20. This zeolite and its preparation are described in A. Katovic and G. Giordano, Chem. Ind. (Dekker) (Synthesis of Porous

Materials ) 1997, 69 , 127-137. According to a preferred aspect, ZSM-12 zeolite is used, described in

US 3,832,449, and in Ernst et al . , Zeolites, 1987, Vol.7 , September.

In the preparation of the catalytic composition, the zeolite is used in its acid form. If the component of an acid nature (bl) is a silico-alumina, a preferred aspect is for the SiO ₂ /Al ₂ O ₃ molar ratio to range from 50 to 300. According to another preferred aspect, the silico-alumina has a porosity ranging from 0.4 to 0.5 ml/g. Completely amorphous micro-mesoporous silico- aluminas which can be used for the upgrading stage of the present invention, called MSA, and their preparation are described in US 5,049,536, EP 659,478, EP 812,804. Their XRD powder spectrum does not have a crystalline structure and does not show any peak.

Catalytic compositions which can be used in the upgrading stage of the present invention, in which the acid component is a silico-alumina of the MSA type are described in EP 582,347.

The silico-aluminas which can be used for the upgrading step of the process of the present invention can be prepared, according to EP 659,478, starting from tetra-alkylammonium hydroxide, an aluminium compound hydrolyzable to Al ₂ O ₃ , and a silicon compound hydrolyzable to SiO ₂ , wherein said tetra-alkylammonium hydroxide is a tetra (C ₂ -C ₅ ) alkylammonium hydroxide, said hydrolyzable aluminium compound is an aluminium tri (C ₂ - C ₄ ) -alkoxide and said hydrolyzable silicon compound is a tetra (Ci-C ₅ ) alkyl orthosilicate : these reagents are subjected to hydrolysis and gelification operating at a temperature equal to or higher than the boiling point, at atmospheric pressure, of any alcohol which is developed as by-product of said hydrolysis reaction, without elimination or without any substantial elimination of these alcohols from the reaction environment . The gel thus produced is dried and calcined, preferably in an oxidizing atmosphere at a temperature ranging from 500 to 700 ⁰ C, for a period of 6-10 hours. The procedure comprises preparing an aqueous solution of tetra-alkylammonium hydroxide and aluminum trialkoxide and the tetra-alkyl orthosilicate is added to this aqueous solution, operating at a temperature lower than the hydrolysis temperature, with a quantity of reagents which is such as to respect molar ratios of SiO ₂ Ml ₂ O ₃ ranging from 30/1 to 500/1, tetra- alkylammonium hydroxide/SiO ₂ from 0.05/1 to 0.2/1 and H ₂ O/SiO ₂ from 5/1 to 40/1, and the hydrolysis and gelification are triggered by heating to a temperature ranging from about 65 ⁰ C to about 110 ⁰ C, operating in an autoclave at the autogenous pressure of the system or at atmospheric pressure in a reactor equipped with a condenser. As far as the metallic component of the catalytic compositions used in the upgrading step of the present invention is concerned, this is selected from Pt, Pd, Ir, Ru, Rh , Re and mixtures thereof. According to a particularly preferred aspect of the present invention, the metal is platinum, iridium or mixtures thereof.

The metal or mixture of metals is preferably in a quantity ranging from 0.1 to 5% by weight with respect to the total weight of the catalytic composition, and preferably ranges from 0.3 to 1.5%. The weight percentage of the metal or metals refers to the metal content expressed as metallic element; in the final catalyst, after calcination, said metal is in oxide form.

Before being used in the upgrading step, the catalyst is activated by means of the known techniques, for example by means of a reduction treatment, and preferably by means of drying and subsequent reduction. The drying is effected in an inert atmosphere at temperatures ranging from 25 to 100 ⁰ C, whereas the reduction is obtained by means of heat treatment of the catalyst in a reducing atmosphere (H ₂ ) at a temperature ranging from 300 to 45O ⁰ C, and a pressure preferably ranging form 1 to 50 atm.

The acidic component (bl) of the catalyst which is used in the upgrading step of the process of the present invention can be in extruded form with traditional binders, such as for example aluminum oxide, bohemite or pseudobohemite . The extruded product can be prepared according to techniques well-known to experts in the field. The acidic component (bl) and the binder can be pre-mixed in weight ratios ranging from 30:70 to 90:10, preferably from 50:50 to 70:30. At the end of the mixing, the product obtained is consolidated in the final form desired, for example in the form of extruded pellets or tablets. Alternatively, if the component (bl) is a silico-alumina, the catalyst in extruded form prepared as described in EP 665,055 can be used as extruded component (bl) .

As far as the metallic phase (al) of the upgrading catalyst is concerned, this can be introduced by means of impregnation or ion exchange. According to the former technique, the acidic component (bl) , also in extruded form, is wet with an aqueous solution of a compound of the metal, operating for example at room temperature, and at a pH ranging from 1 to 4. The resulting product is dried, preferably in air, at room temperature, and is calcined in an oxidizing atmosphere at a temperature ranging from 200 to 600 ⁰ C. In the case of alcohol impregnation, the acid component (bl) is suspended in an alcohol solution containing the metal. After impregnation, the solid is dried and calcined.

According to the ion exchange technique, the acid component (bl) is suspended in an aqueous solution of a complex or salt of the metal, operating at room temperature and at a pH ranging from 6 to 10. After the ion exchange, the solid is separated, washed with water, dried and finally thermally treated in an inert or oxidizing atmosphere. Temperatures which can be used for the purpose are those ranging from 200 to 600 ⁰ C.

Metal compounds which can be used in the preparations described above are: H ₂ PtCl ₆ , Pt(NH ₃ J ₄ (OH) ₂ , Pt(NH ₃ J ₄ Cl ₂ , Pd(NH ₃ ) ₄ (OH) ₂ , PdCl ₂ , H ₂ IrCl ₆ RuCl ₃ , RhCl ₃ . The upgrading stage of the process of the present invention is preferably carried out at a temperature ranging from 240 to 380 ⁰ C, at a pressure ranging from 10 to 100 atm, a WHSV ranging from 0.5 to 5 hours ^"1 and with a ratio between hydrogen and feed (H ₂ /HC) ranging from 400 to 2000 Nlt/kg. It is preferable to operate at a pressure higher than 20 atm and lower than or equal to 80 atm, whereas the temperature preferably ranges from 250 to 33O ⁰ C if the acid component (bl) is a zeolite of the MTW type, whereas it preferably ranges from 300 to 38O ⁰ C if the acid component (bl) is a silico-alumina .