INTEGRATED FLUID CATALYTIC CRACKING PROCESS FOR OBTAINING HYDROCARBON BLENDS HAVING A HIGH QUALITY AS FUEL

The present invention relates to an integrated fluid catalytic cracking process (FCC) which allows hydrocarbon blends having a high quality as fuel, to be obtained.

According to a particular aspect, it relates to an integrated process comprising a fluid catalytic cracking step wherein hydrocarbon cuts of an oil origin are converted into blends having a high content of light cycle oil (LCO) with high quality in terms of density and nature of the aromatic products contained, which, after a separation and a hydrotreatment step, is subjected to an upgrading step by means of treatment with hydrogen and a catalyst comprising one or more metals selected from Pt, Pd, Ir, Ru, Rh and Re and a silicoaluminate of an acidic nature.

Said upgrading step comprises enrichment of the resulting blend to alkyl benzene compounds, at least partially deriving from the conversion of naphtho-aromatic structures contained in the LCO cut, generated during the FCC step and

also the hydrotreatment step.

The integrated process of the present invention leads to hydrocarbon blends having a high cetane index and a reduced density, the latter being of a degree comparable to that which would be obtained by means of total de- aromatization, but effected with a much lower hydrogen consumption.

WO2006/124175 describes a process for the conversion of hydrocarbon cuts for producing olefins, aromatic and diesel compounds having a low sulphur content, comprising a fluid catalytic cracking step for producing olefins and, to a lesser extent, LCO, a transformation step of the high- boiling portion of olefins to ethylene and propylene and a hydrocracking step wherein the LCO cut is mainly trans- formed into aromatic compounds and, to a lesser extent, to diesel having a low sulphur content.

WO2007/006473 describes a process for improving the quality as fuel of hydrotreated hydrocarbon blends which includes putting said blends in contact with hydrogen in the presence of a catalytic system comprising one or more metals selected from Pt, Pd, Ir, Ru ₇ Rh and Re and a sili- coaluminate of an acidic nature.

We have now found an integrated process for the production of hydrocarbon blends having a high quality as fuel, which comprises a fluid catalytic cracking (FCC) step to

give an LCO fraction, a hydrotreating step of said LCO fraction and an upgrading step of the resulting hy- drotreated LCO by means of reaction with hydrogen in the presence of a catalytic system comprising one or more met- als selected from Pt, Pd, Ir. Ru. Rh and Rε and a sili- coaluminate of an acidic nature.

A particularly preferred aspect of the present invention is to effect the fluid catalytic cracking (FCC) step under such conditions as to obtain, with a high yield, a better-quality LCO fraction in terms of density and nature of the aromatic compounds contained. In particular, in this case, the LCO fraction is characterized not only by a high quality in terms of density, but also by a favourable composition in terms of aromatic compounds, which makes it particularly suitable for being treated in the subsequent steps of the integrated process of the invention. The content of polyaromatic compounds is in fact lower with respect to the LCO cuts obtained under normal FCC conditions, whereas the content of benzo-naphthene compounds is higher. This preliminary enrichment in terms of benzo-naphthene compounds makes the subsequent hydrotreatment and upgrading steps easier, allowing the production of blends having optimum characteristics as fuel, using overall amounts of hydrogen lower than what is described in the known art. Furthermore, the blend resulting from the FCC step con-

tains HCO as major by-product, which can be at least partially recycled to the FCC step thus allowing an overall higher yield to LCO.

An object of the present invention therefore relates to an integrated process for the conversion of hydrocarbon cuts of an oil origin, into hydrocarbon blends having a high quality as fuel, which includes the following steps: subjecting the hydrocarbon cut to fluid catalytic cracking (FCC) to produce Light Cycle Oil (LCO) , - subjecting the Light Cycle Oil to hydrotreatment , reacting the hydrotreated Light Cycle Oil obtained in the previous hydrotreatment step, with hydrogen in the presence of a catalytic system comprising: a) one or more metals selected from Pt, Pd, Ir, Ru, Rh and Re b) a silicoaluminate of an acidic nature, selected from a zeolite belonging to the MTW family and a completely amorphous micro-mesoporous silico- alumina, having a molar ratio SiO ₂ /AL ₂ O ₃ ranging from 30 to 500, a surface area greater than 500 m ² /g, a pore volume ranging from 0.3 to 1.3 ml/g, an average diameter of the pores smaller than 40 A. According to a particularly preferred aspect, the process of the present invention is carried out by means of the following steps:

1) a hydrocarbon cut of an oil origin is subjected to fluid catalytic cracking (FCC) to produce a blend containing LCO,

2) the blend resulting from the previous FCC step is sub- jected to separation, in order to separate at least one LCO fraction and an HCO fraction,

3) at least a part of the HCO fraction is possibly fed again to the FCC step;

4) the LCO fraction is subjected to hydrotreatment; 5) the product resulting from step (4) is reacted with hydrogen in the presence of a catalytic system comprising: a) one or more metals selected from Pt, Pd, Ir, Ru, Rh and Re b) a silicoaluminate of an acidic nature selected from a zeolite belonging to the MTW family and a completely amorphous micro-mesoporous silicoalumina having a molar ratio SiO ₂ /Al ₂ O ₃ ranging from 30 to 500, a surface area greater than 500 m ² /g, a pore volume ranging from 0.3 to 1.3 ml/g, an average pore diameter smaller then 40 A. Hydrocarbon cuts suitable for being treated in the first step of the integrated process of the present invention are, for example, gas oil, vacuum gas oil, atmospheric residues, products from thermal cracking and hydrocracking residues . The FCC step can be carried out according to the con-

ditions known to experts in the field, described, for example in Fluid Catalytic Cracking Handbook 2 ^nd edition, Reza Sadeghbeigi, ed. Gulf Professional Publishing, 2000.

In general, the fluid catalytic cracking process is di- vided into two steps, cracking effected in the riser and regeneration of catalyst carried out in the regenerator, both steps being effected by means of a catalyst in fluid phase. The catalyst is generally a compound of silica and alumina in the form of a porous powder having an average particle-size of 65-85 micron. The cracking reaction is substantially endothermic, is sustained by the sensitive heat coming from the regenerated catalyst flow and takes place by putting the hydrocarbon feedstock in contact with the warm regenerated catalyst. The reaction conditions in- elude a temperature ranging from 450 to 65O ⁰ C, a pressure in the reaction area ranging from 1.3 to 4.5 kg/cm ² and a catalyst/oil ratio ranging from 1 to 10 kg/kg, a residence time of the vapours in the reaction area ranging from 0.5 to 10 seconds, preferably from 1 to 5 seconds. The regeneration of the exhausted cracking catalyst is effected 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 and 4.5 kg/cm ² and preferably between 2.4 and 4.0 kg/cm ² . According to a particularly preferred aspect of the

present invention, the FCC step is carried out under such conditions as to maximize the formation of LCO and allow an LCO cut to be obtained, having a high quality from the point of view of density and characterized by a composition particularly favourable in terms of aromatic compounds. The content of polyaromatic compounds is in fact reduced with respect to LCO cuts obtained under normal FCC conditions, in favour of a higher content of benzo-naphthene compounds. This composition characteristic facilitates the subsequent hydrotreatment and upgrading steps, allowing blends having optimum characteristics as fuel to be obtained, using overall lower amounts of hydrogen with respect to what is described in the known art. According to this preferred aspect of the present patent application, the high LCO yields obtained in the FCC step are reached by choosing particular and selected temperature conditions and/or by selecting particular pre-heating temperatures of the feedstock. The selection of these particular conditions for effecting the FCC step, also allows the cracking reaction to be directed towards a higher formation of HCO as reaction by-product, which, as it can be recycled to the FCC step, allows a higher overall LCO yield to be obtained.

The particular and selected temperature conditions which allow the LCO formation to be maximized, are those ranging from 490 to 53O ⁰ C.

The particular pre-heating temperatures of the feedstock which allow the LCO yield to be maximized, are within the range of 240 to 350 ⁰ C.

In both cases, a pressure ranging from 2.0 to 3.5 kg/cm ² is preferably used.

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

An LCO yield at least 20% higher, preferably at least 40% higher, is obtained by carrying out the FCC step so as to satisfy at least one of the previous temperature and pre-heating temperature conditions, the remaining complement to 100 consisting of: fuel gas (H ₂ , Cl, C2) - LPG (C3-C4) gasolines (C5-210°C) HCO (370+ ⁰ C) coke

The FCC conditions mentioned above for the temperature and pre-heating temperature of the feedstock, which allow the formation of LCO to be maximized and obtaining a high- quality LCO cut from the point of view of density, characterized by a particularly favourable composition in terms of aromatic compounds, are new and represent a further as- pect of the present invention.

The blend resulting from the first integrated process step of the present invention is separated by distillation. The HCO fraction obtained by the separation is preferably recycled to the FCC step, in a blend with the feed- stock, for example.

The LCO fraction obtained from the separation, characterized by a composition, in terms of aromatic compounds, rich in benzo-naphthene compounds, is subjected to hy- drotreatment with the aim of reducing the nitrogen and sul- phur content and varying the cut composition, further enriching it with benzo-naphthene compounds.

The hydrotreatment of the LCO cut is effected in one or more fixed-bed reactors and the catalytic beds can contain the same or different catalysts. Catalysts based on metal compounds of Group VI and/or Group VIII are normally used, on a carrier, preferably an amorphous carrier, such as, for example, alumina or silico-alumina. Metals which can be used are, for example, Nickel, Cobalt, Molybdenum and Tungsten. Examples of catalysts which can be used and the preparation of the same are described in Hydrocracking Science and Technology, J. Scherzer and A. J. Gruia, Marcel Dekker, 1996. The hydrotreatment is described, for example, in Catalyst Science and Technology, Edited by R. Anderson and Boudart, Volume 11, Sprinter-Verlag of 1996. The hy- drotreating catalysts are used in the form of sulphidation

products.

The sulphidation can be obtained, for example, by sending a suitable feedstock onto the catalyst with the addition of a sulphidated compound such as dimethyl-disulphide (DMDS) , dimethyl -sulphoxide (DMSO) or other compounds which decompose with the formation of H ₂ S.

The hydrotreatment is preferably effected at a temperature ranging from 200 to 400 ⁰ C, even more preferably at a temperature ranging from 330 to 380 ⁰ C. The pressure nor- mally varies from 20 to 100 bar, preferably between 40 and 80 bar. The space velocity (LHSV) preferably ranges from 0.3 to 3 hr ^"1 . The H ₂ /feedtosck ratio is preferably between 200 and 2,000 Nl/1. During the hydrotreatment, the LCO feedstock undergoes saturation reactions of the aromatic rings with a consequent reduction in the aromatic carbon content and enrichment in naphtho-aromatic compounds.

The subsequent upgrading step is effected, according to WO 2007/006473, 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 acidic 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 the cetane index (number) , density and distillation curve, which is a result equivalent to that which can be obtained through the simple hydrogenation of the aromatic structures. In this step there is a negligible forma- tion of low-molecular-weight products and lower hydrogen consumptions are necessary with respect to the processes of the known art .

This step is carried out in the presence of hydrogen, with a catalytic system including: a) one or more metals selected from Pt, Pd, Ir, Ru, Rh and Re b) a silicoaluminate of an acidic nature selected from a zeolite belonging to the MTW family and a completely amorphous micro-porous silico-alumina having a SiO ₂ /Al ₂ O ₃ molar ratio ranging from 30 to 500, a surface area greater than 500 m ² /g, a pore volume ranging from 0.3 to 1.3 ml/g, an average pore diameter lower than 40 A.

This step of the process allows a substantial increase in the cetane index (number) to be obtained, and a decrease in the density and T95 of the hydrotreated LCO blend. The LCO blend thus obtained also proves to be further enriched in alkyl-benzene compounds which at least partially derive from the partially hydrogenated polycyclic aromatic compounds of the benzo-naphthene type, both already present in the LCO cut coming from the particular FCC step of the pre-

sent integrated process and also generated during the hy- drotreatment .

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

The catalysts used are those described in patent application WO2007/006473. The component of an acidic nature (b) 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 can be effectively used in the present invention, is a silico-alumina 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 (b) is a silico- alumina, a preferred aspect is for the SiO ₂ /Al ₂ O ₃ molar ra- tio 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, useful for the present invention, called MSA, and their preparation are described in US 5,049,536, EP 659,478, EP 812,804. Their X-ray spectrum from powders does not show a crystalline structure or peak. Catalytic compositions useful for the present invention, wherein the acid component is a silico-alumina of the MSA type, are described in EP 582,347.

The silico-aluminas useful for the process of the present invention can be prepared, in accordance with EP 659,478, starting from tetra-alkyl ammonium hydroxide, a compound of aluminium which can be hydrolyzed to Al ₂ O ₃ , and a silicon compound which can be hydrolyzed to SiO ₂ , wherein said tetra-alkyl ammonium hydroxide is a tetra (C ₂ C ₅ ) alkyl ammonium hydroxide, said compound of aluminium which can be hydrolyzed is an aluminium tri (C ₂ C ₄ ) -alkoxide and said silicon compound which can be hydrolyzed is a tetra CiC ₅ ) alkyl ortho-silicate: 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 formed as a by-product of said hydrolysis reaction, with no elimination, or with no substantial elimination, of said alcohols from the reaction environment. The gel produced is dried and calcined, preferably under an oxidizing atmosphere, at a temperature ranging from 500 to 700 ⁰ C for a period of 6-10 hrs .

An aqueous solution of tetra-alkylammonium hydroxide and aluminium tri-alkoxide is prepared and tetra-alkylortho silicate is added to the aqueous solution, operating at a temperature lower than the hydrolysis temperature, with a quantity of the reagents which is such as to respect the molar ratios of SiO ₂ /AL ₂ O ₃ from 30/1 to 500/1, tetra-alkyl ammonium hydroxide/Si0 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 gelation are induced by heating to a temperature higher than about 65 ⁰ C up to 110 ⁰ C, operating in an autoclave, at autogenous pressure of the system, or at atmospheric pressure in a reactor equipped with a condenser.

As far as the metal 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 and Re and mixtures thereof. According to a particularly pre- ferred aspect of the present invention, the metal is

platinum, iridium of mixtures thereof.

The quantity of metal or mixture of metals preferably ranges from 0.1 to 5% by weight with respect to the total weight of the catalytic composition, and preferably from 0.3 to 1.5%.

The weight percentage of the metal, or metals, refers to the content of metal (s) expressed as metallic element; in the final catalyst, after calcination, said metal is in the form of an oxide . Before being used, the catalyst is activated by means of known techniques, for example by means of a reduction treatment, preferably by means of drying and subsequent reduction. Drying is effected under an inert atmosphere at temperatures ranging from 25 to 100 ⁰ C, whereas the reduc- tion is obtained by thermal treatment of the catalyst under a reducing atmosphere (H ₂ ) at temperatures ranging from 300 and 450 ⁰ C at a pressure preferably ranging from 1 to 50 atm.

The acidic component (b) of the catalyst which is used in the upgrading step of the process of the present invention, can be in the form of an extruded product with traditional binders, such as, for example, aluminium oxide, bo- hemite, or pseudo-bohemite. The extruded product can be prepared according to techniques well-known to experts in the field. The acidic component (b) and the binder can be

pre-mixed in weight ratios of between 30:70 and 90:10, preferably between 50:50 and 70:30. At the end of the mixing, the product obtained is consolidated in the desired final form, for example, in the form of extruded cylinders or tablets. Alternatively, when component (b) is a silico- alumina, the catalyst in an extruded form, prepared as described in EP 665055, can be used as component (b) .

As far as the metal phase (a) of the catalyst is concerned, this can be introduced by impregnation or ion ex- change. According to the first technique, the component of an acidic nature (b) , also in extruded form, is wetted by means of an aqueous solution of a metal compound, operating, for example, at room temperature and with a pH ranging from 1 to 4. The resulting product is dried, preferably in air, at room temperature, and is calcined under an oxidizing atmosphere at a temperature ranging from 200 to 600 ⁰ C.

In the case of alcohol impregnation, the acidic component (b) is suspended in an alcohol solution containing the metal. After impregnation, the solid product is dried and calcined.

According to the ion exchange technique, the component

(b) 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 product is separated, washed with water, dried and finally

thermally treated under an inert or oxidizing atmosphere. Useful temperatures for the purpose are those within the range of 200 to 600 ⁰ C.

Metal compounds which can be used in the above- mentioned preparations are: H ₂ PtCl ₆ , Ft (NH ₃ ) ₄ (OH) _2/ Pt(NH ₃ J ₄ Cl ₂ , Pd(NHa) ₄ (OH) ₂ , PdCl ₂ , H ₂ IrCl ₆ , RuCl ₃ , RhCl ₃ . The upgrading step of the process of the present invention is preferably effected 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 hrs ^"1 and a ratio between hydrogen and feedstock (H ₂ /HC) ranging from 400 to 2,000 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 is preferably between 250 and 330 ⁰ C if the acidic component (b) is a zeolite of the MTW type, whereas it preferably ranges from 300 to 380 ⁰ C if the acidic component (b) is a silico-alumina .

The following experimental examples are provided for a better illustration of the present invention, they are purely illustrative of particular aspects of the invention and cannot be considered as limiting its overall scope. Example 1

A feedstock having the characteristics shown in table 1 is fed to an FCC pilot plant of the DCR (Davison Circulat- ing Riser) type, using as catalyst NEKTOR 766 produced by

Grace Davison.

The operational conditions and results of the conversion and yield are indicated in Table 2, first column (Case D •

The same feedstock, with the addition of the recycled product, was subsequently treated under the conditions indicated in the second column of Table 2 (Case 2) . The relative results are shown in the same second column. The third column indicates the results of case 2, expressed as a conversion variation and yield, wherein said variations were obtained considering the results obtained for Case 1 as 100%:

Table 1

Table 2

From Table 2 it can be seen that, by operating under the preferred conditions of the present invention, in terms of both temperature and pre-heating temperature, an increase of 52% is obtained in the yield. The LCO separated by distillation is then fed to the subsequent hydrotreatment and upgrading steps. Example 2

A feedstock having the characteristics indicated in Table 3 is fed to an FCC pilot plant of the DCR (Davison Circulating Riser) type, using NOMUS 215P produced by Grace Davison, as catalyst. The operational conditions and results

relating to the conversion and yield are shown in table 4, first column (Case 3) .

The same feedstock, with the addition of the recycled product, was subsequently treated under the conditions indicated in the second column of Table 4 (Ca.se 4) . The results obtained are shown in the same second column.

The third column also indicates the results for Case 4 expressed as variations of conversion and yield, wherein said variations were obtained considering the results obtained for Case 3, as 100%.

Table 3

Table 4

From Table 4 it can be seen that, by operating under the same preferred conditions of the present invention, in terms of both temperature and pre-heating temperature, an increase of 44% of the yield to LCO is obtained. The LCO separated by distillation can be fed to the subsequent hy- drotreatment and upgrading steps.