EP1965912A1

EP1965912A1 - Process for preparing a catalyst containing a modified zeolite and its use in oligomerization of light olefins

Info

Publication number: EP1965912A1
Application number: EP06831068A
Authority: EP
Inventors: Laurent Simon
Original assignee: IFP Energies Nouvelles IFPEN
Current assignee: IFP Energies Nouvelles IFPEN
Priority date: 2005-12-20
Filing date: 2006-11-03
Publication date: 2008-09-10
Also published as: US20090240008A1; JP2009519824A; WO2007080240A1; FR2894850A1; JP5577036B2; US7847037B2; FR2894850B1

Abstract

A process is described for preparing a catalyst containing at least one modified zeolite, the said zeolite prior to modification having a maximum pore opening diameter of less than or equal to 7 Å, the said process comprising at least a) a step of introducing at least one metal selected from the metals of groups VIB and VIII of the periodic classification of the elements onto a support based on a protonated zeolite, b) a step of treating the said zeolite in the presence of at least one molecular compound containing at least one silicon atom, the said compound having a diameter greater than the maximum opening diameter of the pores of the said zeolite, and c) at least one step of heat treatment.

Description

PROCESS FOR THE PREPARATION OF A CATALYST CONTAINING MODIFIED ZEOLITHE AND THE USE THEREOF IN OLIGOTING LIGHT OLEFINS

Technical area

The present invention relates to a process for the preparation of a catalyst based on a modified zeolite having small and / or pore means, that is to say having a maximum pore opening diameter of less than or equal to at 7 A, in order to obtain a catalyst advantageously used in various chemical conversion processes for hydrocarbons. More particularly, the invention also relates to the use of said catalyst containing said modified zeolite in a process for oligomerization of a light olefinic feedstock.

State of the art

The use of zeolites with a shape selectivity such as zeolite ZSM-5 for the olefin oligomerization reaction has been known for a long time. The process for oligomerization of olefins of Mobil developed in the 1980s described inter alia in US Patents 4,150,062 and US 4,227,992 uses a ZSM-5 zeolite for the conversion of butenes to oligomers. The products obtained have a very low degree of connection and make jet fuel and diesel cuts of good qualities. This process gives very low yield in diesel cut (cut obtained after distillation of Poligomerate between 200 ⁰ C - 36O ⁰ C), it is used mainly to produce jet fuel.

Several patents have already reported methods for modifying zeolites. In particular, US Pat. No. 4,402,867 describes a method for preparing a zeolite-based catalyst comprising a step of depositing in the aqueous phase at least 0.3% by weight of amorphous silica inside the pores of the zeolite. US Pat. No. 4,996,034 describes a process for substitution of aluminum atoms present in a zeolitic framework with silicon atoms, said process being carried out in one step in an aqueous medium using fluorosilicate salts. No. 4,451,572 describes the preparation of a zeolitic catalyst comprising a step of depositing organosilicic materials in the vapor or liquid phase, the targeted zeolites being large-pore zeolites, in particular zeolite Y.

US Pat. No. 5,057,640 describes a process for the oligomerization of propylene using a catalyst containing a zeolite of Si / Al ratio greater than 12 and a stress index (Cl) of between 1 and 12 and in which at least 0.1 % by weight of silica with respect to weight of the zeolite was added. The catalyst referred to in this US Pat. No. 5,056,640 has an n-hexane adsorption of 1% less than on the starting material.

summary

The present invention relates to a process for the preparation of a catalyst containing at least one modified zeolite, said zeolite having, before being modified, a maximum pore opening diameter of less than or equal to 7 Å, said process comprising at least: a) a step of introducing at least one metal chosen from the metals of groups VIB and VIII of the periodic table of elements on a support based on at least one protonated zeolite, b) a step of treating said zeolite in the presence of at least one molecular compound containing at least one silicon atom, said compound having a diameter greater than the maximum pore opening diameter of said zeolite is deposited on the outer surface of said zeolite in the gas phase, c) at least one heat treatment step.

Said zeolite is preferably chosen from zeolites of structural type MEL, MFI, ITH, NES, EUO, ERI, IRON, CHA, MFS, MWW, MTT, TON and MOR.

The present invention also relates to the use of said catalyst in a process for oligomerizing an olefinic feedstock containing hydrocarbon molecules having 2 to 12 carbon atoms per molecule.

Interest

Surprisingly, it has been discovered that a catalyst comprising a modified zeolite, prepared according to a process comprising at least a) a step of introduction of at least one metal chosen from the metals of groups VIB and VIII of the classification periodic element on a support based on at least one protonated zeolite, b) a step of treating said zeolite in the presence of at least one molecular compound containing at least one silicon atom, said compound having a diameter greater than the diameter maximum opening pore of said zeolite, c) at least one heat treatment step, leads to improved catalytic performance, particularly in terms of yield and selectivity of the diesel cut in an oligomerization reaction of an olefinic feedstock containing hydrocarbon molecules having 2 to 12 carbon atoms per molecule, preferably 3 to 7 carbon atoms per molecule, and very preferably containing from 4 to 6 carbon atoms per molecule. In particular, such a catalyst makes it possible to significantly increase the efficiency of the diesel cut relative to that obtained by using a catalyst of the state of the art. The cetane number, which reflects the linearity of the hydrocarbon chains present in the diesel cut and which represents the quality of the diesel cut, is also advantageously improved compared with that usually presented by a diesel cut obtained by this reaction. The use of the catalyst as described above in a process for oligomerizing an olefinic feed containing hydrocarbon molecules having from 2 to 12 carbon atoms per molecule, preferably from 3 to 7 carbon atoms per molecule, and very preferably containing from 4 to 6 carbon atoms per molecule allows the production of an oligomer of very good quality which can advantageously after distillation at the appropriate cutting point, be integrated in the diesel pool of a refinery.

Description of the invention

The present invention relates to a process for the preparation of a catalyst containing at least one modified zeolite, said zeolite having, before being modified, a maximum pore opening diameter of less than or equal to 7 Å, said process comprising at least: a) a step of introducing at least one metal selected from the metals of groups VIB and VIII of the periodic table of elements on a support based on at least one protonated zeolite, b) a step of treating said zeolite in the presence of at least one molecular compound containing at least one silicon atom, said compound having a diameter greater than the maximum pore opening diameter of said zeolite is deposited on the outer surface of said zeolite in the gas phase; least one heat treatment step.

According to the invention, the initial zeolite, which has not yet been modified to be contained in the catalyst prepared according to the process of the invention, has a maximum pore opening diameter of less than or equal to 7 A and Preferred zeolite is selected from zeolites defined in the "Atlas of Zeolite Structure Types" classification, W. M Meier, DH Oison and Ch. Baerlocher, 5th revised edition, 2001, Elsevier "to which reference is made also the present application but may also be any zeolite having a maximum pore opening diameter of less than or equal to 7 A. The zeolites listed in the "Atlas of Zeolite Structure Types" are classified according to their structural type All zeolites having a maximum pore opening diameter of less than or equal to 7 A and preferably less than 6.5 A are suitable for carrying out the preparation process according to the invention and in particular for the implementation process step b) of the process according to the invention. According to the invention, the maximum pore opening diameter of a zeolite corresponds to the maximum dimension of the "ring dimensions" mentioned in the "Atlas of Zeolite Structure Types" for each of the structural types. Advantageously, the zeolite initially used, before being modified, to be contained in the catalyst prepared according to the process of the invention has either one or channels whose opening is defined by a ring with 10 oxygen atoms. (10 MR), one or more channels whose opening is defined by a ring of 12 oxygen atoms (12 MR) or at the same time one or more channels whose opening is defined by an 8 atom ring of oxygen (8 MR) and one or more channels whose opening is defined by a ring with 10 oxygen atoms (10 MR) ₁ is also at the same time one or more channels whose opening is defined by a ring at 8 oxygen atoms (8 MR) and one or more channels whose opening is defined by a ring of 12 oxygen atoms (12 MR), or at the same time one or more channels whose opening is defined by a ring with 8 oxygen atoms (8 MR) and one or more channels whose opening is defined by a ring with 10 atoms of oxygen e (10 MR) and one or more channels whose opening is defined by a ring of 12 oxygen atoms (12 MR), said channels being interconnectable. A zeolite having at least channels whose opening is defined by a ring of 12 oxygen atoms (12 MR) is particularly suitable for carrying out the process for preparing the catalyst according to the invention provided that it has a maximum pore opening diameter less than or equal to 7 A. In particular, a zeolite of structural type MOR which has both channels whose opening is defined by an 8-atom oxygen ring (8 MR) and channels whose opening is defined by a ring of 12 oxygen atoms (12 MR) is suitable for carrying out the preparation process according to the invention. MOR structural type zeolites have a maximum pore opening diameter of 7.0 Å.

The zeolite, modified according to the different steps of the process according to the invention, initially contains, that is to say, before being modified, at least silicon and aluminum in a proportion such that the Si / Si atomic ratio Ai is preferably between 2 and 200, more preferably between 5 and 100 and even more preferably between 8 and 80. It advantageously contains at least one other element W, different from silicon and aluminum, integrating tetrahedral form into the framework of the zeolite. Preferably, said element W is chosen from iron, germanium, boron and titanium and represents a weight portion of between 5 and 30% of all the constituent atoms of the zeolitic framework other than the oxygen atoms. The zeolite then has a ratio (Si + W) / Al of between 2 and 200, preferably of between 5 and and 100 and very preferably between 8 and 80, W being defined as above.

The zeolite modified according to the different steps of the process according to the invention is preferably chosen from zeolites of structural type MEL, MFI, ITH, NES, EUO, ERI, IRON, CHA, MFS, MWW, MTT, TON and MOR and of very preferably chosen from zeolites of structural type MFI, MOR and FER. Among zeolites of structural MEL type, zeolite ZSM-11 is preferred. Among zeolites of structural type MFI, zeolite ZSM-5 is preferred. Among zeolites of ITH structural type, zeolite ITQ-13 is preferred (US 6,471,941). Among zeolites of structural NES type, zeolite NU-87 is preferred. Of zeolites of EUO structural type, zeolite EU-1 is preferred. Among the zeolites of structural type ERI, zeolite erionite is preferred. Of the zeolites of FER structural type, ferrierite zeolites and ZSM-35 are preferred. Among zeolites of structural type CHA, zeolite chabazite is preferred. Among the zeolites of structural MFS type, zeolite ZSM-57 is preferred. Of the MWW structural type zeolites, the MCM-22 zeolite is preferred. Among zeolites of MTT structural type, zeolite ZSM-23 is preferred. Of zeolites of structural type TON, zeolite ZSM-22 is preferred. Among zeolites of structure type MOR, mordenite zeolite is preferred. These zeolites and their method of preparation are well known to those skilled in the art.

According to the invention, the first step of the catalyst preparation process according to the invention is either step a) or step b). Step b), whether before or after step a), is preferably followed immediately by step c).

The zeolite used for carrying out the first step of the process for preparing the catalyst according to the invention, that is to say employed for the implementation of step a) carried out in the presence of at least one metal of groups VIB and / or VIII of the periodic table of elements or for the implementation of step b) carried out in the presence of at least one molecular compound containing at least one silicon atom having a well-defined diameter, present in calcined form and contains at least one proton such that it is in its protonated form (hydrogen form H ⁺ ) in which the cation content other than H ⁺ is less than 30% of the total number of cations, preferably less than 20% and very preferably less than 15% based on the total number of cation on the zeolite. In the case where, prior to the implementation of the first step of the process for preparing the catalyst according to the invention (step a) or step b), the zeolite to be modified is in its raw form of synthesis, still containing the structuring agent. organic material used to prepare it, calcination may be carried out said zeolite at a temperature between 300 and 700 ⁰ C, preferably between 400 and 600 ⁰ C and if the zeolite contains one or more metal (s) alkali / alkaline earth, proceed to one or more ion exchange (s) (s) by a solution containing at least one ammonium salt, for example ammonium nitrate NH ₄ NO ₃ , so as to remove at least partly, preferably almost completely, an alkaline cation present in the zeolite. A step of calcination under dry air flow, at a temperature generally between approximately 400 and 500 ⁰ C, is then intended to generate the formation of protons in the zeolite by desorption of ammonia thus leading to the hydrogen form of the zeolite, ready for the implementation of the first step of the preparation process according to the invention.

The zeolite used for carrying out the first step of the process for preparing the catalyst according to the invention is an acidic zeolite containing between 70 and 100%, preferably between 80 and 100% and very preferably between 85 and 100% proton form H ⁺ compensation cations, the rest of the cations being preferably chosen from the metals of groups IA and NA of the periodic table of elements, and more particularly said cation is chosen from Na ⁺ , Li ⁺ cations, K ⁺ , Rb ⁺ , Cs ⁺ , Ba ²⁺ and Ca ²⁺ .

Step a) of the process for preparing the catalyst according to the invention is a step of introducing at least one metal chosen from the metals of groups VIB and VIII of the periodic table of the elements on a carrier based on minus a protonated zeolite. Preferably, said metal chosen from metals of groups VIB and VIII of the periodic table of elements is chosen from nickel, iron, palladium, ruthenium and chromium, very preferably from nickel and chromium. Very advantageously, the Group VIII metal is nickel. Of the Group VIB metals, chromium is preferred. For the preparation of the catalyst according to the invention, the deposition of at least one metal chosen from Group VIB and VIII metals is generally carried out by dry impregnation, by excess impregnation or by ion exchange (s) according to methods well known to those skilled in the art, preferably by ion exchange (s). With regard to the ion exchange introduction of nickel, it is preferred to use an aqueous solution containing nickel under the oxidation state + 2, for example nickel sulphate. The weight content of the metal chosen in groups VIB and VIII, introduced on the zeolite support, is advantageously between 0.01 and 10% by weight, and preferably between 0.1 and 5% by weight relative to the weight of the catalyst prepared according to method of the invention. According to a first embodiment of step a) of the method of the invention, the support based on at least one protonated zeolite consists entirely of said protonated zeolite, which has in terms of maximum pore opening diameter, structure and chemical composition, the characteristics described above. . According to a second embodiment of step a) of the process of the invention, the support based on at least one protonated zeolite consists of said protonated zeolite shaped with a matrix and optionally a binder.

The method for preparing the catalyst according to the invention comprises a step b) of selectivation of the zeolite, in its protonated form, said selectivation step can be carried out either before the step of introducing at least one metal of the groups VIB and / or VIII according to said step a) after said step a). By "selectivation" is meant in the sense of the present invention, the neutralization of the acidity of the outer surface of each of the crystals of the zeolite. The neutralization of the acidity can be done by any method known to those skilled in the art. Conventional methods generally employ, for specific selectivation of acidic sites on the outer surface of zeolites, molecules whose kinetic diameter is greater than the pore opening diameter of the zeolite. More precisely, step b) of selectivation consists in treating the zeolite, in its protonated form, possibly previously subjected to said step a), in the presence of at least one molecular compound containing at least one silicon atom whose diameter is greater than the maximum pore opening diameter of the zeolite to be treated according to step b). Preferably, the process for preparing the catalyst according to the invention comprises only one step b).

The molecules generally used to passivate or selectivize the outer surface of the zeolite are compounds containing atoms that can interact with the outer surface sites of each of the zeolite crystals. The molecules used according to the invention are organic or inorganic molecules containing one or more silicon atom (s). Also, in accordance with step b) of treatment of the process according to the invention, the protonated zeolite, possibly previously subjected to said step a), is subjected to a treatment step in the presence of at least one molecular compound containing at least a silicon atom. Said step b) allows the deposition of a layer of said molecular compound containing at least one silicon atom on the outer surface of the zeolite which will be transformed after step c) into an amorphous silica layer on the outer surface of each of the crystals of the zeolite. Preferably, the molecular compound containing at least one silicon atom is chosen from compounds of formula Si-R ₄ and Si ₂ -Re where R may be either hydrogen, an alkyl, aryl or acyl group, an alkoxy group (O-R ¹ ), a hydroxyl group (-OH) or a halogen, preferably an alkoxy group (OR ¹ ) . Within the same molecule Si-R ₄ or Si ₂ -Re, the group R may be either identical or different. For example, it will be possible, according to the formulas described above, to choose molecular compounds of formula Si ₂ H ₆ or Si (C ₂ H ₅ ) ₃ (CH 3). Thus, the molecular compound containing at least one silicon atom used in step b) of the process according to the invention may be a compound of silane, disilane, alkylsilane, alkoxysilane or siloxane type. Very preferably, said molecular compound has a composition of general formula Si- (OR ') ₄ where R' is an alkyl, aryl or acyl group, preferably an alkyl group and very preferably an ethyl group. Said molecular compound used for the implementation of step b) of the process according to the invention has a diameter greater than the maximum pore opening diameter of the zeolite and preferably comprises at most two silicon atoms per molecule. The tetraethylorthosilicate (TEOS) molecular compound of formula Si (OCH ₂ CH ₃ ) ₄ , which has a diameter equal to 9.6 Å, is very advantageous for carrying out step b) of the process according to the invention. In particular, TEOS is advantageous when it is a question of treating a structural type zeolite MOR having a maximum pore opening diameter of 7 Å, a zeolite of structural type MFI having a maximum pore opening diameter of 5.6 Å or a zeolite of structural type FER having a maximum pore opening diameter of 5.4 Å.

Said step b) of the process according to the invention which consists in treating the protonated zeolite, possibly previously subjected to step a), in the presence of at least one molecular compound containing at least one silicon atom is carried out by depositing said compound on the outer surface of the zeolite. According to the invention, said step b) is carried out by depositing said molecular compound containing at least one silicon atom in the gas phase.

Step b) according to the process of the invention is carried out in a fixed bed reactor. Prior to the gas phase deposition (CVD) reaction in said fixed bed reactor, the zeolite is preferably activated. Activation of the zeolite in the fixed bed reactor is carried out under oxygen, in air or under an inert gas, or in a mixture of air and inert gas or oxygen and inert gas. The activation temperature of the zeolite is advantageously between 100 and 600 ^° C., and very advantageously between 300 and 55 ^° C. The molecular compound containing at least one silicon atom to be deposited on the outer surface of each of the crystals of the zeolite is sent into the vapor phase reactor, said molecular compound being diluted in a carrier gas which can be either hydrogen (H ₂ ), or air, or Argon (Ar), either helium (He) or again nitrogen (N ₂ ), preferably the carrier gas is an inert gas selected from Ar, He, and N ₂ . Said molecular compound containing at least one silicon atom is deposited on the outer surface of said zeolite in the vapor phase, in the absence of any hydrocarbon compound. To obtain an amorphous silica layer of optimal quality on the outer surface of the zeolite, it is necessary to choose the operating conditions for the deposition of the molecular compound containing at least one silicon atom. In particular, the temperature of the zeolite bed during the deposition is preferably between 10 and 300 ^° C., and very preferably between 50 and 200 ^° C., the partial pressure, in the gas phase, of the molecular compound to be deposited on the surface. external of the zeolite is preferably between 0.001 and 0.5 bar, and very preferably between 0.01 and 0.2 bar, the duration of the deposit is preferably between 10 minutes and 10 hours and very preferably between 30 minutes and 5 hours and even more preferably between 1 and 3 hours.

According to step c) of the process according to the invention, the molecular compound containing at least one silicon atom is decomposed by a heat treatment which is carried out at a temperature preferably between 200 and 700 ° C, more preferably between 300 and 500 ^° C. Said heat treatment step is carried out under air, under oxygen, under hydrogen, under nitrogen or under argon or under a mixture of nitrogen and argon. The duration of this treatment is advantageously between 1 and 5 hours. At the end of said heat treatment, an amorphous silica layer is deposited on the outer surface of each of the crystals of the zeolite. According to the invention, the inner surface of each of the crystals of the zeolite is preferably free of a deposit of an amorphous silica layer. The maximum pore opening diameter of the modified zeolite, present in the catalyst prepared according to the process of the invention, is preferably unchanged compared with that of the initial zeolite still unmodified. Consequently, the modified zeolite contained in the catalyst prepared according to the process of the invention preferably has a maximum pore opening diameter of less than or equal to 7 Å and preferably less than 6.5 Å.

In the case where the support based on at least one protonated zeolite used for the implementation of step a) of the process according to the invention consists of said protonated zeolite shaped with a matrix and optionally with a binder (second mode of bet of step a)), the metal chosen from the metals of groups VIB and VIII may be introduced either substantially completely onto the matrix, partly on the zeolite and partly on the matrix, or, preferably, almost completely on the zeolite, this being done, in the manner known to those skilled in the art, by the appropriate choice of parameters used during said deposition, such as for example the nature of the precursor of said metal. In the case where the support based on at least one protonated zeolite used for the implementation of step a) of the process according to the invention consists solely of said protonated zeolite (first embodiment of the invention). step a)) whose characteristics in terms of maximum pore opening diameter, structure, chemical composition are in accordance with what has been said above in the present description, the metal chosen from metals of groups VIB and VIII is introduced directly onto the protonated zeolite which is preferably in the form of a powder. The shaping of the protonated zeolite with a matrix and optionally a binder is carried out during a step d). Said step d) of shaping can take place either directly after step a) of introduction of the metal on the protonated zeolite and prior to the implementation of steps b) and c) of the process of the invention or after the steps a), b) and c) of the process according to the invention is again after the implementation of said steps b) and c) and before the implementation of said step a) when said steps b) and c) of the according to the invention are carried out before step a).

The matrix used for the shaping of the protonated zeolite, said shaping being carried out either before step a) of the process of the invention when the support based on said zeolite consists of said zeolite shaped with a matrix either during step d) of the process according to the invention when the support based on said protonated zeolite consists solely of said zeolite, is an amorphous or poorly crystallized porous mineral matrix of oxide type. It is chosen from alumina, silica, silica-alumina, clays, in particular natural clays such as kaolin or bentonite, magnesia, titanium oxide, boron oxide, zirconia, aluminum phosphates, titanium phosphates, zirconium phosphates and coal. One can also choose a matrix among the aluminates. Preferably, the matrix is an alumina in all its forms known to those skilled in the art, and preferably gamma alumina. The shaping of said zeolite with at least one matrix is generally such that the catalyst is in the form of cylindrical or multi-lobed extrusions such as bilobed, trilobed, straight-lobed or twisted, but may possibly be such that the catalyst is in the form of crushed powders, tablets, rings, balls, wheels. The conditions for shaping the zeolite, the choice of the matrix, optionally the preliminary grinding of the zeolite, the peptization process, the addition of pore-forming agents, the mixing time, the extrusion pressure if the catalyst is extruded, the speed and the drying time are determined for each matrix according to the well-known rules of the skilled person. The shaping of the zeolite with at least one matrix as described above can be carried out at different stages of the process according to the invention. More particularly, when the support based on said zeolite used during step a) consists of said zeolite shaped with a matrix, the shaping is carried out prior to the implementation of step a) of the process of the invention. When the support based on said zeolite used during step a) consists solely of said zeolite, the shaping is carried out either directly after said step a) and before the implementation of steps b ) and c), or after the implementation of said steps b) and c) and before the implementation of said step a) when said steps b) and c) precede said step a), or even after the implementation steps a), b) and c).

For example, one of the preferred methods for preparing the catalyst according to the invention consists in exchanging a protonated zeolite with at least one metal chosen from Group VIB and VIII metals, preferably with nickel under its +2 oxidation state. Said ion exchange step is followed by a step of activating the zeolite at a temperature of between 300 and 55O ⁰ C and then the zeolite is treated at a temperature of between 50 and 200 ^° C. in the presence of tetraethylorthosilicate (TEOS) vapor deposited on the outer surface of said zeolite. The TEOS is decomposed by a heat treatment generally carried out at a temperature between 300 and 500 ° C in air. A zeolite modified in protonated form and having an amorphous silica layer on its external surface is thus obtained. Said modified zeolite is then shaped by extrusion by mixing it in a wet matrix gel (generally obtained by mixing at least one acid and a matrix powder), for example alumina, for a period of time necessary to obtaining a good homogeneity of the dough thus obtained, for example for about ten minutes, and then passing said dough through a die to form extrudates, for example having a diameter of between 0.4 and 4 mm inclusive preferably between 0.4 and 2.5 mm inclusive and more preferably between 0.8 and 2.0 mm inclusive. The extrudates thus shaped then undergo drying for a few hours at about 120 ^° C. in an oven and a final calcination step, for example for about 2 hours at about 400 ^° C. They generally consist of 10 to 90% by weight, preferably from 30 to 80% by weight of said modified zeolite, the remainder being formed of a matrix. Another subject of the invention is the use of the catalyst prepared according to the process of the invention and comprising a modified zeolite in hydrocarbon chemical conversion processes and in particular in a process for oligomerization of an olefinic feed containing hydrocarbon molecules having 2 to 12 carbon atoms per molecule. Preferably, the feedstock used for carrying out said oligomerization process contains hydrocarbon molecules containing from 3 to 7 carbon atoms per molecule, and very preferably containing from 4 to 6 carbon atoms per molecule. The catalyst prepared according to the process of the invention is treated according to said steps a), b) and c) ex-situ: it is introduced into the reactor to carry out the oligomerization of hydrocarbon molecules containing from 3 to 7 carbon atoms per molecule once said steps a), b) and c) of the process for preparing the catalyst according to the invention have been carried out. The feed used in the oligomerization process according to the invention contains from 20 to 100% by weight, and preferably from 25 to 80% by weight of olefins.

Possible sources for the olefinic feedstock used in the oligomerization process of the invention are the light cut of the fluid catalytic cracking (FCC), the steam cracker and the etherification unit effluents.

Said oligomerization process is preferably carried out under the following operating conditions: the total pressure is between 0.1 and 10 MPa and preferably between 0.3 and 7 MPa, the temperature is between 40 and 600 ^° C. and preferentially between 100 and 400 ^° C., the hourly space velocity (WH) is between 0.01 and 100 h ^-1 and preferably between 0.4 and 20 h ^-1 .

It is specified that, according to the invention, the oligomerization process corresponds to an addition limited to essentially 2 to 6 monomers or base molecules, said monomers being olefins.

The following examples illustrate the present invention without limiting its scope.

EXAMPLES

Example 1 (Invention): Preparation of a catalyst based on a modified zeolite ZSM-5.

40 g of zeolite H-ZSM-5 (Si / Al = 45) are impregnated by ion exchange with a 500 ml solution containing 4.3 g / l of nickel sulphate. The ion exchange is carried out for 24 hours at 80 ^° C. After filtration and washing, the zeolite thus exchanged with the nickel is dried overnight. at 120 ° C. It is then introduced into a fixed-bed reactor where it is first subjected to activation under nitrogen flow at 45 ^° C. The reactor temperature is then reduced to 150 ° C. and then a partial pressure of 0.15 ° C. TEOS bar [Si (OCH ₂ CH ₃ ) ₄ ] is added to the nitrogen stream. After 2 hours of reaction, the zeolite is stripped for 2 h at 150 ^° C. to evacuate the unreacted TEOS. The decomposition of TEOS is under air at 45O ⁰ C for 3 hours. A modified zeolite Z1, in protonated form, of structural type MFI and having an amorphous silica layer on its external surface is thus obtained.

Zeolite Z1 is then shaped by extrusion with an alumina gel so as to obtain, after drying at 120 ^° C. and calcination at 450 ° C. under dry air, a catalyst which contains 60% by weight of zeolite modified with Z1 and 40% by weight. alumina.

Example 2 (Invention): Preparation of a catalyst based on a modified MOR zeolite.

40 g of zeolite H-MOR (Si / Al = 55) are impregnated by ion exchange with a 500 ml solution containing 4.3 g / l of nickel sulphate. The ion exchange is carried out for 24 hours at 80 ^° C. After filtration and washing, the zeolite thus exchanged with the nickel is dried overnight at 120 ^° C. It is then introduced into a fixed-bed reactor where it is used. first subjected to activation under nitrogen flow at 450 ° C. The temperature of the reactor is then reduced to 150 ^° C., and then a partial pressure of 0.15 bar of TEOS [Si (OCH ₂ CH ₃ ) ₄ ] is added to the nitrogen stream. After 2 hours of reaction, the zeolite is stripped for 2 hours at 150 ° C. to evacuate the unreacted TEOS. The decomposition of TEOS is under air at 450 ° C for 3 hours. A zeolite modified Z2, in protonated form, of structural type MOR and having an amorphous silica layer on its external surface is thus obtained. Zeolite Z2 is then shaped by extrusion with an alumina gel so as to obtain, after drying at 120 ^° C. and calcination at 450 ^° C. in dry air, a catalyst which contains 60% by weight of modified zeolite Z2 and 40% by weight. alumina.

Example 3 (Invention): Preparation of a catalyst based on a modified FER zeolite.

40 g of H-FER zeolite (Si / Al = 26) are impregnated by ion exchange with a 500 ml solution containing 4.3 g / l of nickel sulphate. The ion exchange is carried out for 24 hours at 80 ° C. After filtration and washing, the zeolite thus exchanged with the nickel is dried overnight at 120 ^° C. It is then introduced into a fixed-bed reactor where it is first subjected to activation under nitrogen flow at 450 ^° C. The temperature of the reactor is then reduced to 150 ^° C., and then a partial pressure of 0.15 bar of TEOS [Si (OCH ₂ CH ₃ ) ₄ ] is added to the nitrogen stream. After 2 hours of reaction, the zeolite is stripped for 2 hours at 150 ^° C. to evacuate the unreacted TEOS. The decomposition of TEOS is under air at 450 ° C for 3 hours. A zeolite modified Z3, in protonated form, of structural type FER and having an amorphous silica layer on its external surface is thus obtained. Zeolite Z3 is then shaped by extrusion with an alumina gel so as to obtain, after drying at 120 ^° C. and calcination at 450 ^° C. under dry air, a catalyst which contains 60% by weight of zeolite modified with Z3 and 40% by weight. alumina.

Example 4 (comparative): Preparation of a catalyst based on a ZSM-5 zeolite not exchanged with a metal.

40 g of zeolite H-ZSM-5 (Si / Al = 45) are introduced into a fixed-bed reactor where they are first subjected to activation under nitrogen flow at 450 ^° C. The temperature of the reactor is then reduced to 150 ⁰ C, then a partial pressure of 0.15 bar of TEOS [Si (OCH ₂ CH ₃ ) ₄ ] is added to the nitrogen stream. After 2 hours of reaction, the zeolite is stripped for 2 hours at 150 ^° C. to evacuate the unreacted TEOS. The decomposition of TEOS is under air at 450 ^° C. for 3 hours. A zeolite Z4, in protonated form, of structural type MFI and having an amorphous silica layer on its external surface is thus obtained. Zeolite Z4 is then shaped by extrusion with an alumina gel so as to obtain, after drying at 120 ^° C. and calcination at 45 ^° C. in dry air, a catalyst which contains 60% by weight of zeolite Z4 and 40% by weight of water. alumina.

Example 5 (Comparative): Preparation of a catalyst based on a non-metal exchanged zeolite MOR.

40 g of zeolite H-MOR (Si / Al = 55) are introduced into a fixed-bed reactor where they are first subjected to activation under nitrogen flow at 450 ^° C. The temperature of the reactor is then reduced to 150 ⁰ C, then a partial pressure of 0.15 bar TEOS [Si (OCH ₂ CHa) ₄ ] is added to the nitrogen stream. After 2 hours of reaction, the zeolite is stripped for 2 hours at 150 ^° C. to evacuate the unreacted TEOS. The decomposition of TEOS is under air at 450 ^° C. for 3 hours. A zeolite Z5, in protonated form, of structural type MOR and having an amorphous silica layer on its external surface is thus obtained. Zeolite Z5 is then shaped by extrusion with an alumina gel so as to obtain, after drying at 120 ^° C. and calcination at 450 ^° C. in dry air, a catalyst which contains 60% by weight of zeolite Z5 and 40% by weight of alumina.

Example 6 (comparative): Preparation of a catalyst based on an iron zeolite not exchanged with a metal.

40 g of H-FER zeolite (Si / Al = 26) are introduced into a fixed bed reactor where they are first subjected to activation under nitrogen flow at 450 ^° C. The temperature of the reactor is then reduced to 15O ⁰ C, then a partial pressure of 0.15 bar of TEOS [Si (OCH ₂ CH ₃ ) ₄ ] is added to the nitrogen stream. After 2 hours of reaction, the zeolite is stripped for 2 hours at 150 ^° C. to evacuate the unreacted TEOS. The decomposition of TEOS is under air at 45O ⁰ C for 3 hours. A zeolite Z6, in protonated form, of structural type FER and having an amorphous silica layer on its external surface is thus obtained. Zeolite Z6 is then shaped by extrusion with an alumina gel so as to obtain, after drying at 120 ^° C. and calcination at 450 ^° C. under dry air, a catalyst which contains 60% by weight of zeolite Z6 and 40% by weight of water. alumina.

Example 7 (Invention): Preparation of a catalyst based on a modified MFI zeolite. 40 g of zeolite H-ZSM-5 (Si / Al = 45) are impregnated by ion exchange with a 500 ml solution containing 20 g / l of chromium acetate. The ion exchange is carried out for 24 hours at 70 ^° C. After filtration and washing, the zeolite thus exchanged with chromium is dried overnight at 120 ^° C. and then calcined for 2 hours in air at 550 ^° C. It is then introduced. in a fixed-bed reactor where it is first subjected to activation under a stream of nitrogen at 450 ^° C. The temperature of the reactor is then reduced to 15O ⁰ C, then a partial pressure of 0.15 bar of TEOS [ If (OCH ₂ CH ₃ ) ₄ ] is added to the nitrogen stream. After 2 hours of reaction, the zeolite is stripped for 2 hours at 150 ° C. to evacuate the unreacted TEOS. The decomposition of TEOS is under air at 450 ^° C. for 3 hours. A modified zeolite Z7, in protonated form, of structural type MFI and having an amorphous silica layer on its external surface is thus obtained.

Zeolite Z7 is then shaped by extrusion with an alumina gel so as to obtain, after drying at 120 ^° C. and calcination at 450 ^° C. under dry air, a catalyst which contains 60% by weight of Z7 modified zeolite and 40% by weight. alumina.

Example 8 Catalytic Evaluation of Catalysts Based on Z1, Z2 Modified Zeolites Z3 and Z7 and based zeolites Z4, Z5 and Z6 in oligomerization of light olefins.

The performance of the catalysts prepared according to Examples 1 to 7 above were evaluated in the oligomerization reaction of a light olefinic cut containing 58% of C4 olefins in a mixture of paraffins.

The operating conditions of tests are as follows:

Temperature: 230 ° C

Pressure: 6 MPa

WH (h ^-1 ) [catalyst volume / volume flow rate of charge]: 1 h ^-1 The catalysts are activated beforehand in situ under N ₂ at 450 ^° C. for 2 hours. The performance of catalysts based on the zeolite MFI structural type are given in Table 1.

Table 1: Performance of catalysts based on the MFI zeolite.

Catalyst Catalyst Catalyst Converter based on Z1 base Z4 base Z7

(invention) (comparative) (invention)

C4 olefinic conversion (%) 99 99 99

Yield cut gasoline (%) 55 60 52

Diesel cutting efficiency (%) 45 40 48

Cetane number 46.7 44.6 46.5

The performance of catalysts based on the zeolite of structural type FER are given in Table 2.

Table 2: Performance of catalysts based on the FER zeolite.

Catalyst catalyst based on Z3 based on Z6 (invention) (comparative)

C4 olefinic conversion (%) 85 85

Fuel cut performance (%) 60 61

Diesel cutting efficiency (%) 40 39

Cetane number 39.2 36.2

The performance of catalysts based on zeolite MOR structural type are given in Table 3. Table 3: Performance of catalysts based on the MOR zeolite.

Catalyst Catalyst based on Z2 base Z5

C4 olefinic conversion (%) 99 99

Yield cut gasoline (%) 42 44

Diesel cutting efficiency (%) 58 56

Cetane number 42.4 39.3

The catalytic performances presented in Tables 1, 2 and 3 demonstrate that the catalysts comprising a modified zeolite and prepared according to the process of the invention make it possible to significantly increase the yield in diesel cuts when they are tested in an oligomerization reaction. light olefins. The quality of this gas oil, measured by its cetane number (CI), is also improved compared to that presented by a diesel cut obtained using a catalyst comprising a zeolite which has not been modified according to the process of the invention. 'invention.

Claims

A process for the preparation of a catalyst containing at least one modified zeolite, said zeolite having, before being modified, a maximum pore opening diameter of less than or equal to 7 Å, said process comprising at least: a) a step of introduction of at least one metal chosen from metals of groups VIB and VIII of the periodic table of elements on a support based on at least one protonated zeolite, b) a step of treating said zeolite in the presence of at least one at least one molecular compound containing at least one silicon atom, said compound having a diameter greater than the maximum pore opening diameter of said zeolite is deposited on the outer surface of said zeolite in the gas phase, c) at least one treatment step thermal.

2. Preparation process according to claim 1, wherein said zeolite contains, before being modified, at least silicon and aluminum in a proportion such that the Si / Al atomic ratio is between 2 and 200.

3. Preparation process according to claim 1 or claim 2, wherein said zeolite is chosen from zeolites of structural type MEL, MFI, ITH, NES, EUO, ERI, IRON, CHA, MFS, MWW, MTT, TON and MOR. .

4. Preparation process according to claim 3, wherein said zeolite is chosen from zeolites of structural type MFI, MOR and FER.

5. Preparation process according to one of claims 1 to 4 such that said metal selected from the metals of groups VIB and VIII of the periodic table of elements is selected from nickel, iron, palladium, ruthenium and chromium. .

6. Preparation process according to claim 5 wherein said metal is selected from nickel and chromium.

7. Preparation process according to one of claims 1 to 6 such that said support based on at least one protonated zeolite used for the implementation of said step a) consists entirely of said protonated zeolite.

8. Preparation process according to claim 7 as it comprises a step of shaping said protonated zeolite with a matrix and optionally a binder.

9. Preparation process according to one of claims 1 to 6 such that said support based on at least one protonated zeolite used for the implementation of said step a) consists of said protonated zeolite shaped with a matrix and optionally a binder.

10. Preparation process according to one of claims 1 to 9 such that said molecular compound containing at least one silicon atom is selected from compounds of formula Si-R ₄ and Si ₂ -Re where R can be either of hydrogen, an alkyl, aryl or acyl group, an alkoxy group (OR ¹ ), a hydroxyl group (-OH) or a halogen, R being the same or different.

11. Preparation process according to one of claims 1 to 10 such that said molecular compound has a composition of general formula Si- (OR ') ₄ wherein R' is an alkyl, aryl or acyl.

12. Preparation process according to one of claims 1 to 11 such that said step b) is carried out by depositing said molecular compound containing at least one silicon atom in the gas phase.

13. Preparation process according to claim 12, wherein said step b) is carried out in a fixed-bed reactor.

14. Use of a catalyst prepared according to one of claims 1 to 13 in a process for oligomerization of an olefinic feed containing hydrocarbon molecules having 2 to 12 carbon atoms per molecule.

15. Use of a catalyst according to claim 14, wherein said oligomerization process is carried out at a temperature of between 40 and 600 ^° C., with a total pressure of between 0.1 and 10 MPa and an hourly space velocity. (WH) between 0.01 and 100 hr ^-1 .