Catalytic composition comprising chromium and a supported methylaluminoxane

Abstract

The present invention relates to a catalytic composition for the selective oligomerization of ethylene, in particular for the tetramerization of ethylene to octene-1, comprising: - a chromium-based metallic precursor; - a heteroatomic ligand; - methylaluminoxane supported on an inorganic support; - an additive in the form of an aluminum-based compound; the composition having a molar ratio of aluminum in the inorganic-supported methylaluminoxane to chromium in the metallic precursor greater than 250, and a molar ratio of aluminum in the additive to chromium in the metallic precursor greater than 200. Figure 3 to be published.

Description

Title of the invention: Catalytic composition comprising chromium and a supported methylaluminoxane Technical field

[0001] The present invention relates to a catalytic composition based on chromium and supported methylaluminoxane (MAO), and its use for the selective oligomerization of ethylene, in particular for the tetramerization of ethylene to octene-1. Prior art

[0002] Linear alpha olefins (or LAOs for linear alpha olefins according to Anlo-Saxon terminology) with 4 to more than 20 carbon atoms are important raw materials for the manufacture of petrochemical intermediates. Despite the wide range of applications, the global demand for LAOs is mainly dominated by short-chain α-olefins such as 1-butene, 1-hexene and 1-octene which can be used as co-monomers for the polymer industry. The global supply of LAOs is mainly covered by two types of ethylene oligomerization processes using homogeneous catalysts: processes that produce a broad distribution of olefins (generally from C4 to C30), and selective processes that will produce only one α-olefin as the main product (1-butene, 1-hexene or 1-octene).However, as the demand for short-chain LAOs from C4 to C10 is growing faster than that of the C10+ range, significant progress has recently been made to control the product distribution towards shorter α-olefin distributions or even to selectively produce a single α-olefin. In this field, the tetramerization of ethylene to octene-1 by a homogeneous chromium-based catalyst has led to many developments in recent years (PWNM van Leeuwen et al., Coordination Chemistry Reviews 255 (2011) 1499-1517). Examples of systems known to lead to the selective production of octene-1 include those described in WO2004056477, WO2004056478 or WO2004056479. These catalysts use a Cr(III)-based metal precursor associated with a PNP ligand (such as Ph2PN(iPr)PPh2) activated in situ by an aluminoxane (MAO: Me-thylAluminOxane; MMAO: Modified MethylAluminOxane; etc.).They lead to the "selective" production of octene-1 (more than 60% selectivity). Other Cr-based catalytic systems have subsequently been developed, examples include documents WO2010034102, WO2011156892 or WO2011108772.

[0003] The main disadvantage of chromium-based catalytic systems for ethylene oligomerization is the formation of a significant amount of polymers, in parallel with that of the targeted olefin (octene-1). This formation of polymers, with a sticky morphology, can be the cause of rapid deactivation of the catalyst and increased difficulty in process operability. In this area, a first approach, inherited from polymerists (used to managing large quantities of polymer in their process), consists of supporting the homogeneous catalyst on an inorganic support, in particular to control the morphology of the polymer formed. The transposition of this strategy to the oligomerization of ethylene was notably described by R. Duchateau with the use of a MAO supported on silica for the selective trimerization of ethylene to hexene-1 by titanium complexes (ACS Catalysis, 2015, 5, 5068-5076). The polymer produced during this transformation is in the form of a non-sticky solid, significantly reducing reactor fouling.A supported MAO is an MAO that has been immobilized on an inorganic support. It is generally insoluble in traditional organic solvents and can be directly used for catalyst formation. Such supported MAOs are described, for example, in US2015353658, US20180354870 or US6211311.

[0004] The aim of the present invention is to provide a new catalytic composition for the tetramerization of ethylene which overcomes the problems of the conventional catalytic compositions of the prior art and in particular those comprising an MAO cocatalyst in homogeneous phase.

[0005] The applicant has surprisingly demonstrated that a composition comprising a chromium-based metal precursor, a heteroatomic ligand, an MAO supported on an inorganic support, and an additive in the form of an aluminum-based compound, makes it possible to obtain an active and selective catalytic composition in the oligomerization of ethylene (tetramerization of ethylene into octene-1), while allowing control of the morphology of the polymer-type by-products, thus solving the problem of reactor fouling. Summary of the invention

[0006] The present invention relates to a catalytic composition for the selective oligomerization of ethylene, in particular for the tetramerization of ethylene to octene-1, comprising:

[0007] - a chromium-based metallic precursor;

[0008] - a heteroatomic ligand;

[0009] - methylaluminoxane supported on an inorganic support;

[0010] - an additive in the form of an aluminum-based compound;

[0011] the composition having a molar ratio of aluminum of the methylaluminoxane supported on an inorganic support to the chromium of the metal precursor greater than 250, and a molar ratio of aluminum in the additive to chromium in the metal precursor greater than 200.

[0012] An advantage of the catalytic composition according to the present invention is in particular to control the morphology of the polymeric by-products formed, thus allowing their easy removal from the reactor, while maintaining a high level of selectivity for octene-1. DETAILED DESCRIPTION OF THE INVENTION

[0013] According to the present invention, the expression "between ... and ..." and "between .... and ..." are equivalent and mean that the limit values ​​of the interval are included in the range of values ​​described. If this is not the case and the limit values ​​are not included in the range described, such precision will be provided by the present invention.

[0014] In the sense of the present invention, the different parameter ranges for a given step such as pressure ranges and temperature ranges may be used alone or in combination. For example, in the sense of the present invention, a preferred pressure value range may be combined with a more preferred temperature value range.

[0015] In the following, particular embodiments of the invention may be described. They may be implemented separately or combined with each other, without limitation of combinations when this is technically feasible. Metallic precursor

[0016] The term “metal precursor” means: a compound comprising a metal center and at least one stabilizing ligand of the precursor which may be charged or neutral, organic or inorganic.

[0017] In the present application, the terms “metal precursor” or “chromium-based metal precursor” will be used equivalently.

[0018] The composition according to the present invention comprises a chromium-based metal precursor, preferably chosen from a chromium (II) or chromium (III) salt. Preferably, the chromium-based metal precursor comprises one or more identical or different anions chosen from the group formed by halides, carboxylates, acetylacetonates, alkoxy and aryloxy anions.

[0019] Preferably, the halide anions are chosen from chloride, bromide, fluoride or iodide.

[0020] Preferably, the carboxylate anions are chosen from carboxylates having a linear or branched C3-C20, preferably C3-C15, preferably C4-C12, preferably C5-C10 alkyl chain, preferably said alkyl chain is substituted or not by one or more fluorine, chlorine or bromine atoms.

[0021] Preferably, the alkoxy anions are chosen from alkoxy having a linear, branched, cyclic or non-cyclic C1-C20 alkyl chain, preferably C2-C15, preferably C3-C12, preferably C4-C10, preferably said alkyl chain is substituted or not by one or more fluorine, chlorine or bromine atoms.

[0022] Preferably, the aryloxy anions are chosen from aryloxy having a C5-C30, preferably C5-C20, preferably C6-C15, preferably C6-C12 aryl group, preferably said aryl group is substituted or not by one or more fluorine, chlorine or bromine atoms.

[0023] In one embodiment, the chromium-based metal precursor used in the invention is a chromium (III) compound, but a chromium (I) or chromium (II) compound may also be suitable. Non-limiting examples include Cr (III) acetylacetonate, Cr (III) trifluoroacetylacetonate, Cr (III) hexafluoroacetylacetonate, Cr (III) acetate, Cr (III) 2-ethylhexanoate, Cr (III) heptanoate, Cr (III) naphthenate, Cr (III) chloride, Cr (III) bromide, taken alone or as a mixture, pure or diluted. Preferred Cr precursor derivatives are Cr (III) acetylacetonate, Cr (III) 2-ethylhexanoate and Cr (III) heptanoate taken alone or as a mixture, pure or diluted. Most preferably, the chromium-based metal precursor is Cr(III) acetylacetonate. Heteroatomic ligand

[0024] The composition according to the present invention comprises a heteroatomic ligand.

[0025] The term "heteroatom ligand" means an ion or molecule carrying functional groups (heteroatoms) allowing it to bind to one or more atoms of the metal precursor to give it the electronic and structural properties required for the chemical transformation of interest.

[0026] Advantageously, the heteroatomic ligand corresponds to the following general formula:

[0027] [Chem.l] R*

[0028] in which

[0029] R1, R2, R3, R4 and R5 are identical or different from each other, linked or not to each other, are chosen from a cyclic or non-cyclic alkyl group having from 1 to 15 carbon atoms (C1-C15), containing or not one or more heteroelements and a substituted or unsubstituted aryl group having between 4 and 15 carbon atoms (C4-C15) containing or not one or more heteroelements.

[0030] Preferably, said heteroelements are chosen from iodine, bromine, chlorine, fluorine, nitrogen, sulfur and / or oxygen.

[0031] Preferably, R1, R2, R3, R4 and R5 are identical or different, chosen from a C1-C10 alkyl group, a C3-C10 cycloalkyl group, a C5-C15 aryl group.

[0032] Preferably, R1, R2, R3, R4 and R5 are identical or different, chosen from a C1-C6 alkyl group, a C3-C6 cycloalkyl group, a C5-C12 aryl group.

[0033] Preferably, the groups R1, R2, R3, R4 and R5 are identical or different from each other, linked or not to each other, chosen from the methyl, ethyl, n-propyl, i-propyl, n-butyl, i-butyl, tert-butyl, pentyl, cyclopentyl, hexyl, cyclohexyl, adamantyl groups, substituted or not; and / or the phenyl, o-tolyl, m-tolyl, p-tolyl, mesityl, 3,5-dimethylphenyl, 4-n-butylphenyl, 2-methoxyphenyl, 3-methoxyphenyl, 4-methoxyphenyl, 2-isopropylphenyl, 4-methoxy-3,5-dimethylphenyl, 3,5-ditert-butyl-4-methoxyphenyl, 2-chlorophenyl, 3-chlorophenyl, 4-chlorophenyl, 2-fluorophenyl, 3-fluorophenyl, 4-fluorophenyl, 4-trifluoromethylphenyl, 3,5-di(trifluoromethyl)phenyl, benzyl, naphthyl, bis-naphthyl, pyridyl, furanyl, thiophenyl groups.

[0034] De manière préférée, les ligands hétéroatomiques sont choisis parmi : (phenyl)2 PN(methyl)P(phenyl)2, (phenyl)2PN(i-propyl)P(phenyl)2,(phenyl)2 PN(phényl)P(phenyl)2,(2-methoxyphenyl)2PN(i-propyl)P(phenyl)2, (2-methoxyphenyl) 2PN(i-propyl)P(2-methoxyphenyl)2, (4-methoxyphenyl)2 PN(i-propyl)P(4-methoxyphenyl)2, (2-fluorophenyl)2PN(i-propyl)P(2-fluorophenyl)2, (2-fluorophenyl)(phenyl)PN(i-propyl)P(2-fluorophenyl)2, (2-fluorophenyl)(phenyl)PN(i-propyl)P(2-fluorophenyl)(phenyl), (2-fluorophenyl)(phenyl)PN(i-propyl)P(phenyl)2.

[0035] De manière très préférée, le ligand hétéroatomique est choisi parmi le (phenyl)2 PN(i-propyl)P(phenyl)2 et le (2-fluorophenyl)2PN(i-propyl)P(2-fluorophenyl)2.

[0036] Preferably, the molar ratio of the heteroatomic ligand to the chromium-based metal precursor, denoted LH / Cr, is between 0.5 and 10, preferably between 0.8 and 6, preferably between 1.0 and 4.0, very preferably between 1.2 and 2.0. Co-catalyst in the form of supported MAO

[0037] The supported MAO is composed of a methylaluminoxane (MAO) which has been immobilized on a solid support. The supported MAO allows, when using the catalytic composition, the formation of the catalyst via ionic interactions between the metal complex and the supported MAO, such a catalyst structure can be called a floating cation. The catalysis reaction is carried out on the surface or in the pores of the formed supported catalyst.

[0038] The catalytic composition according to the present invention comprises methylalu- minoxane supported on an inorganic support (noted SMAO).

[0039] The description of a supported MAO usable in the catalytic composition according to the invention as well as its manufacturing process can be found in the work Tailor-Made Polymers Via Immobilisation of Alpha-Olefin Polymerisation Catalysts, document US2015353658 in the name of KING FAHD PET & MINERALS UNIVERSITY, document US20180354870 in the name of SAUDI ARABIAN OIL COMPANY or document US6211311 in the name of the company EQUISTAR CHEM LP.

[0040] In the present application, the terms “supported MAO” or “MAO supported on an inorganic support” or “SMAO” will be used equivalently.

[0041] MAO is advantageously obtained by controlled hydrolysis of trimethylaluminum (TMA) in an organic solvent such as toluene. The nature and composition of the MAO usable in this invention can be found in the document Methylalumoxane - History, Production, Properties, and Applications. Eur. J. Inorg. Chem 2015, 19-43.

[0042] The MAO used in the present invention advantageously comprises polymer chains (PMAO) formed by Al, O atoms and methyl groups (-Me or -CH3) defined by the formula below:

[0043] [Chem.2]

[0044] of which n can advantageously take a value between 1 and 60, preferably between 10 and 50. Advantageously, the MAO also comprises in its structure trimethylaluminium associated, free or in interaction with the PMAO chains. The PMAO can have a linear, cyclic or branched structure, as long as the polymer chains satisfy the above formula.

[0045] In one embodiment, the MAO used in the present invention contains PMAO of linear and / or branched structure, but also cyclic fragments and residual molecules of the solvent interacting with the TMA, free or interacting with the PMAO.

[0046] SMAO is advantageously obtained by direct reaction of a MAO solution with an inorganic support in an organic solvent.

[0047] Advantageously, the inorganic support is chosen from silica, alumina, silica-alumina, zeolites, TiO2.

[0048] Preferably the support is silica-based, preferably the support is SiO2. Advantageously, the silica contains Si-OH or Si-O-Si groups.

[0049] In one embodiment, the SiO2 is selected from high purity silicas which do not contain traces of metals. Preferably the SiO2 contains less than 10 ppm of Fe, Na, Al and / or Ti.

[0050] In one embodiment, the SiO2 may have a crystalline, amorphous, or partially crystalline structure. Preferably, the SiO2 has an amorphous structure.

[0051] Advantageously, the inorganic support is in the form of particles defined by an average diameter less than or equal to 200 qm, preferably less than or equal to 150 qm, preferably less than or equal to 100 qm, and very preferably less than or equal to 50 qm.

[0052] In a preferred embodiment, the inorganic support has a granular or spherical morphology. Most preferably, the inorganic support has a spherical morphology.

[0053] In a preferred embodiment, the inorganic support is in the form of particles defined by an average diameter of between 1 and 100 qm, preferably between 10 and 50 qm, preferably between 20 and 40 qm, preferably between 30 and 35 qm.

[0054] In one embodiment, the inorganic support is mesoporous in nature. Preferably, it has an average pore diameter of between 2 and 50 nm, preferably between 10 and 40 nm, more preferably between 15 and 30 nm, and very preferably between 20 and 25 nm.

[0055] In one embodiment, the inorganic support has a pore volume of between 0.5 and 2.5 mL / g, preferably between 1 and 2 mL / g, more preferably between 1.25 and 1.75 mL / g, and very preferably between 1.4 and 1.6 mL / g. Pore volume is understood to mean the volume measured by intrusion with a mercury porosimeter according to standard ASTM D4284-83 at a maximum pressure of 4000 bar (400 MPa), using a surface tension of 484 dyne / cm and a contact angle of 140°. The wetting angle was taken to be equal to 140° following the recommendations of the work “Techniques de l'ingénieur, traité analyse et caractérisation”, P 1050-5, written by Jean Charpin and Bernard Rasneur.

[0056] In one embodiment, the inorganic support has a specific surface area of ​​between 1 and 600 m2 / g, preferably between 100 and 500 m2 / g, more preferably between 200 and 400 m2 / g, and very preferably between 300 and 350 m2 / g. The specific surface area is calculated by the Brunauer-Emmett-Teller (BET) method, and measured by nitrogen adsorption analysis.

[0057] Advantageously, the aluminum content of the SMAO is between 1 and 25% by mass, preferably between 5 and 15% by mass, more preferably between 8 and 12% by mass, very preferably between 9 and 11% by mass, relative to the total mass of the SMAO. This ensures that the SMAO will have good properties such as the ability to prevent leaching of the catalyst into the solution.

[0058] In an ethylene tetramerization reaction, the molar ratio of aluminum from methylaluminoxane supported on an inorganic support (SMAO) to chromium from metallic precursor, denoted AlSMAo / Cr, can exert a significant influence on the productivity of the catalyst and on the sticky nature of the generated polymer.

[0059] Preferably, the AlSMAo / Cr molar ratio is greater than 250 and less than 750. The AlSMAo / Cr molar ratio is calculated as the ratio between the number of moles of aluminum contained in the SMAO and the number of moles of chromium in the precursor.

[0060] Surprisingly, the applicant has demonstrated that AlSMAo / Cr ratios greater than or equal to 750 cause poisoning of the active species by reducing the productivity of the catalyst. Productivity is defined as the mass of products formed divided by the mass of Cr per hour. On the other hand, AlSMAo / Cr ratios less than or equal to 250 cause leaching of the active species and loss of morphological control over the polymer.

[0061] Additive in the form of an aluminum-based compound

[0062] The composition according to the present invention comprises an additive in the form of an aluminum-based compound.

[0063] In the present application, the terms "additive" or "additive in the form of an aluminum-based compound" will be used equivalently.

[0064] In one embodiment, the additive in the form of an aluminum-based compound is a compound of formula AI(R6)3, wherein R6 is independently selected from C1-C12 alkyl, C1-C12 alkoxy and halogen. Preferably, R6 is independently selected from C1-C10 alkyl, C1-C10 alkoxy, preferably C1-C6 alkyl, C1-C6 alkoxy and chlorine or bromine. Preferably, R6 is an alkyl and / or alkoxy group selected from methyl, ethyl, n-propyl, i-propyl, n-butyl, tert-butyl, pentyl, hexyl, heptyl, octyl and the corresponding alkyloxy groups. Preferably, R6 is an alkyl and / or alkoxy group chosen from ethyl, propyl, i-propyl, isopropyl, n-butyl, and tert-butyl and from the corresponding alkyloxy groups.

[0065] Preferably, the additive in the form of an aluminum-based compound is chosen from aluminoxanes such as methylaluminoxane (MAO), modified methylaluminoxanes (MMAO), or ethylaluminoxane (EAO), alone or as a mixture, or alkylaluminums such as trimethylaluminum (TMA), triethylaluminum (TEA), triisopropylaluminum, tri-n-butylaluminum, triisobutylaluminum, tri-tert-butylaluminum, trihexylaluminum, trioctylaluminum, diethylethoxyaluminum and dimethylethoxyaluminum, methylaluminum dichloride, ethylaluminum dichloride, dimethylaluminum chloride, diethylaluminum chloride, or ethylaluminum sesquichloride.

[0066] Preferably, the additive in the form of an aluminum-based compound is chosen from methylaluminoxane (MAO) or modified methylaluminoxanes (MMAO), alone or in a mixture.

[0067] In one embodiment, the composition of the MAO usable as an additive is equivalent to the composition of the MAO as described above before being supported on an inorganic support.

[0068] Very preferably, the additive in the form of an aluminum-based compound is chosen from modified methylaluminoxanes (MMAO). By way of non-limiting example, the MMAOs may be chosen from MMA0-3A, MMAO-7 or MMAO-21.

[0069] In a preferred embodiment, the additive is MMA0-3A. Similarly to MAO, MMA0-3A is advantageously obtained by controlled hydrolysis of TMA in the presence of triisobutylaluminium (TIBA), which gives this compound increased stability in a paraffinic solvent such as heptane or cyclohexane. MMAO-3A advantageously comprises poly-alkylaluminoxane (PAAO) polymer chains formed by Al, O atoms and methyl (-Me or -CH3) and / or isobutyl (-z'Bu) groups defined by the formula below:

[0070] [Chem.3] ■■ î(^te)A[0]n ■■ K / Bu)AiO]m -

[0071] of which n and m can advantageously take a value between 1 and 60, preferably between 10 and 50. Advantageously, the MMA0-3A also comprises in its structure trimethylaluminium associated, free or in interaction with the PAAO chains and / or isobutylaluminium associated, free or in interaction with the PAAO chains. The PAAO can have a linear, cyclic or branched structure, as long as the polymer chains satisfy the above formula.

[0072] The MMA0-3A used as an additive is composed of PAAO of linear and / or branched structure, but also cyclic fragments and residual molecules of the solvent interacting with the TMA or TIBA, free or interacting with the PAAO, as described above for an MAO.

[0073] Advantageously, the molar ratio of the aluminum of the additive to the chromium of the metal precursor, noted AlAdditif / Cr, is greater than 200 and less than or equal to 10000, preferably between 275 and 5000, preferably between 300 and 3000, very preferably between 325 and 2000.

[0074] The AlAdditive / Cr molar ratio is calculated as the ratio between the number of moles of aluminum contained in the additive and the number of moles of chromium contained in the precursor.

[0075] Without wishing to be bound by any theory, the presence of the additive in the form of an aluminum-based compound is essential to achieve the activation of the metal precursor and generate the active species involved in the catalytic reaction. Supported MAO has a significantly lower amount of associated TMA than MAO or MMAO in solution. In this context, the presence of the additive serves to achieve alkylation of the metal complex and trigger the catalytic reaction. Also, the additive helps protect the catalytically active species to prevent the formation of large amounts of polyethylene (PE). A minimum amount of additive is required to ensure activation of the metal precursor to produce octene-1 as the main product of the reaction. Optional solvent

[0076] The catalytic composition according to the invention may further comprise a solvent. A solvent chosen from organic solvents and in particular from saturated, unsaturated, cyclic or non-cyclic hydrocarbons may be used.

[0077] The solvent(s) is (are) advantageously chosen from halogenated solvents and hydrocarbons, saturated or unsaturated, cyclic or not, comprising between 1 and 20 carbon atoms, preferably between 1 and 15 carbon atoms and preferably between 4 and 15 carbon atoms.

[0078] Preferably, the solvent is chosen from butane, isobutane, pentane, hexane, heptane, cyclohexane, methylcyclohexane, 2,2,4-trimethylpentane, dichloromethane, toluene, xylene, dichloroethane, chlorobenzene, dichlorobenzene, pure or as a mixture. Preferably, the solvent is chosen from hexane, heptane, cyclohexane, methylcyclohexane, 2,2,4-trimethylpentane and isobutane.

[0079] In one embodiment, the solvent is chosen from supercritical solvents. Preferably, the supercritical solvent is chosen from supercritical propane.

[0080] In one embodiment, the solvent is chosen from the products of the oligomerization reaction. Oligomerization process

[0081] The present invention also relates to a process for the oligomerization of ethylene, preferably for the tetramerization of ethylene into octene-1, comprising bringing into contact in an oligomerization reactor a feedstock comprising ethylene with the catalytic composition according to the invention.

[0082] Advantageously, the concentration of metal precursor used in the oligomerization process according to the invention is between 0.01 and 10000 pmol / L, preferably between 0.1 and 1000 pmol / L, very preferably between 1 and 100 pmol / L.

[0083] The method can advantageously be carried out in the presence of a solvent as described previously.

[0084] Advantageously, the oligomerization process according to the invention is implemented at a total pressure of between 0.1 and 20.0 MPa, preferably between 0.1 and 15.0 MPa, and more preferably between 0.5 and 8.0 MPa, and at a temperature of between 15 and 200°C, preferably between 20°C and 100°C and very preferably between 25°C and 60°C.

[0085] The feedstock used in the process is ethylene, preferably ethylene in gaseous form.

[0086] Advantageously, the ethylene is injected into the reactor after the catalytic composition according to the invention.

[0087] Advantageously, the feedstock comprising ethylene may further contain gaseous hydrogen to reduce the selectivity to polyethylene (PE). Preferably, the volume percentage of hydrogen in the ethylene feedstock is between 0% and 10%, preferably between 0.1% and 5%, very preferably between 1% and 3%.

[0088] The heat generated by the reaction can be eliminated by any means known to those skilled in the art.

[0089] Advantageously, the oligomerization process according to the invention can be implemented continuously.

[0090] In one embodiment, the at least 4 compounds of the catalytic composition according to the invention are injected into the reactor which is advantageously stirred by conventional mechanical means or by external recirculation, in which the ethylene reacts, preferably with temperature control.

[0091] In one embodiment, a first solution comprising a mixture of the chromium-based metal precursor and the heteroatomic ligand, and a second solution comprising the additive in the form of an aluminum-based compound, are injected separately into the advantageously stirred reactor by conventional mechanical means or by external recirculation, in which the ethylene reacts, preferably with temperature control, and the SMAO being introduced last.

[0092] In a preferred embodiment, the reactor is stirred at room temperature after the introduction of the SMAO and before introduction of the feedstock to allow the immobilization of the catalytically active species on the support. The stirring time is a few minutes, for example 5 minutes.

[0093] The catalytic composition present in the oligomerization effluent downstream of the reactor can be neutralized by any means known to those skilled in the art.

[0094] The following examples illustrate the invention without limiting its scope. LIST OF FIGURES

[0095] [Fig.l]

[0096] [Fig.l] represents a photograph of the stirring blades of a reactor at the end of a ethylene tetramerization process according to Examples 2, 8 and 9 (comparative). “Sticky” polymeric by-products are observed on the stirrer which are difficult to remove and which cause fouling of the reactor.

[0097] [Fig.2]

[0098] [Fig.2] represents a scanning electron microscope image of the morphology of the polymer by-product of [Fig.l]. A “filamentous” structure characteristic of a polymer with an uncontrolled or so-called sticky morphology is observed.

[0099] [Fig.3]

[0100] [Fig. 3] represents a photograph of the stirring blades of a reactor at the end of an ethylene tetramerization process according to examples 5, 6, 7, 10, 11, 12 and 13 (according to the invention). Polymeric by-products in the form of particles are observed on the stirrer which are easy to remove and do not cause fouling of the reactor.

[0101] [Fig.4]

[0102] [Fig.4] represents a scanning electron microscope image of the morphology of the polymer by-product of [Fig.3]. A “particulate” structure characteristic of a polymer with controlled morphology is observed. EXAMPLES

[0103] Example 1: Process for the preparation of a SMAO at 10.1% wt. Al.

[0104] In a Schlenk, in a glove box, 3 g of polymerization silica (Average diameter = 33 pm; Average pore diameter DP = 21 nm; Pore volume VP = 1.56 mL / g; Specific surface SBet = 315 m2 / g) are weighed, previously dried at 80°C under vacuum for 2 hours.

[0105] Under argon flow, the silica is impregnated with 4.7 mL (corresponding to the total pore volume) of dry toluene. 13 mL of MAO is then added in toluene (4.65% wt. Al, d = 0.895 g / mL, 0.54 g theoretical Al). The mixture becomes a translucent liquid gel.

[0106] The mixture is heated at 80°C for 4 hours with manual stirring every 15 minutes. After 4 hours, the toluene is evaporated and the resulting white powder is dried under vacuum at 80°C for 1 hour.

[0107] The Al content in SMAO is determined by ICP-AES: %wt Al = 10.1 ± 0.5%.

[0108] Example 2 (comparative): Process for the tetramerization of ethylene, using a solution of MMA0-3A in homogeneous phase in cyclohexane as co-catalyst (1100 equivalents of Al relative to Cr)

[0109] In a Schlenk, in a glove box, 14.0 mg of Cr(acac)2 and 28.0 mg of N,N-bis[di(2-fluorophenyl)]phosphino isopropylamine (PNP heteroatomic ligand) are weighed. Under argon flow, 20.0 mL of toluene are added (Cr concentration = 2 mmol / L; PNP concentration = 2.8 mmol / L; PNP / Cr ratio = 1.4).

[0110] 93 mL of cyclohexane are introduced into a 250 mL reactor whose internal temperature has been previously set at 25°C and the ethylene pressure at 0.5 bar (0.05 MPa). The solvent is then saturated with ethylene after introducing 5 bar (0.5 MPa) of ethylene gas with stirring at 1500 rpm for one minute. Again, the reactor pressure is lowered to 0.5 bar (0.05 MPa) and stirring is stopped. 5 mL of nonane dried on molecular sieve (3.6 g, internal standard), 1.2 mL of MMAO 3A in solution in cyclohexane (7% wt. Al; d = 0.803 g / mL, approximately 2.2 mmol Al) and 1.0 mL of Cr / PNP solution (2 pmol Cr, 2.8 pmol PNP) are then introduced. The ethylene inlet valve is then opened (30 bars (3 MPa) pressure), stirring is started and the reactor heating setpoint is raised to 45°C.

[0111] At the end of the test, the ethylene supply is cut off, the medium is cooled to 20°C, then the gas phase is removed through the vent. The reactor is then opened. The liquid is transferred into a flask containing 1.00 ml of 10% H2SO4 solution. A sample of the organic phase is taken and filtered for analysis. The results are described in Table 1.

[0112] Example 3 (comparative): Process for the tetramerization of ethylene, using SMAO suspended in cyclohexane as co-catalyst (100 equivalents of Al relative to Cr)

[0113] In a Schlenk, in a glove box, 588 mg of SMAO at 10.1% Al prepared according to example 1, i.e. 59.4 mg Al (2.2 mmol Al), are weighed. Then 5.0 mL of cyclohexane are introduced to form a suspension.

[0114] 89 mL of cyclohexane is introduced into a 250 mL reactor whose internal temperature has been previously set at 25°C and the ethylene pressure at 0.5 bar (0.05 MPa). The solvent is then saturated with ethylene after introducing 5 bar (0.5 MPa) of ethylene gas with stirring at 1500 rpm for one minute. Again, the reactor pressure is lowered to 0.5 bar (0.05 MPa) and stirring is stopped. 5.0 mL of nonane dried on molecular sieve (3.6 g, internal standard), the suspension of SMAO in the 5.0 mL of cyclohexane and 1.0 mL of a Cr / PNP solution at 2 mmol / L Cr and a PNP / Cr ratio of 1.4 (2 pmol Cr, 2.8 pmol PNP) are then introduced. The reactor is then stirred at 250 rpm for 5 min at 25°C under 2 bar (0.2 MPa) ethylene pressure. The ethylene inlet valve is then opened (30 bar (3 MPa) pressure), stirring is started and the reactor heating setpoint is increased to 45°C.

[0115] At the end of the test, the ethylene supply is cut off, the medium cools to 20°C, then the gas phase is removed through the vent. The reactor is then opened. The liquid is transferred into a flask containing 1.00 ml of 10% H2SO4 solution. A sample of the organic phase is collected and filtered for analysis. The results are described in Table 1.

[0116] Example 4 (comparative): Process for the tetramerization of ethylene, using SMAO suspended in cyclohexane as co-catalyst (250 equivalents of Al relative to Cr) and MMA0-3A as additive (300 equivalents of Al relative to Cr)

[0117] In a Schlenk, in a glove box, 134 mg of SMAO at 10.1% Al prepared according to example 1, i.e. 13.5 mg Al (0.5 mmol Al), are weighed. Then, 5 mL of cyclohexane are introduced to form a suspension.

[0118] In another Schlenk, under Ar, 1.0 mL of MMA0-3A in cyclohexane (7% wt. Al, d = 0.803 g / mL, approximately 2.1 mmol Al) and 20 mL of dry cyclohexane are added to form a 0.10 mol / L solution.

[0119] In a 250 mL reactor whose internal temperature has been previously set at 25°C and the ethylene pressure at 0.5 bar (0.05 MPa), 83 ml of cyclohexane is introduced. Then, the solvent is saturated with ethylene after introducing 5 bar (0.5 MPa) of ethylene gas with stirring at 1500 rpm for one minute. Again, the reactor pressure is lowered to 0.5 bar (0.05 MPa) and stirring is stopped. Then 5.0 mL of nonane dried on molecular sieve (3.6 g, internal standard), 6.0 mL of a 0.1 mol / L MMA0-3A solution (i.e. 0.6 mmol) and 1.0 mL of a Cr / PNP solution at 2 mmol / L Cr and a PNP / Cr ratio of 1.4 (2 pmol Cr, 2.8 pmol PNP) are introduced. The mixture is stirred at 250 rpm for 5 min at 25 °C. The SMAO suspension is injected into the 5.0 mL of cyclohexane. The reactor is then stirred at 250 rpm for 5 min at 25 °C under a pressure of 2 bar (0.2 MPa) of ethylene.The ethylene inlet valve is then opened (30 bars (3 MPa) pressure), stirring is started and the reactor heating setpoint is raised to 45°C.

[0120] At the end of the test, the ethylene supply is cut off, the medium is cooled to 20°C, then the gas phase is removed through the vent. The reactor is then opened. The liquid is transferred into a flask containing 1.00 ml of 10% H2SO4 solution. A sample of the organic phase is taken and filtered for analysis. The results are described in Table 1.

[0121] Example 5 (according to the invention): Process for the tetramerization of ethylene, using SMAO suspended in cyclohexane as co-catalyst (500 equivalents of Al relative to Cr) and MMA0-3A as additive (300 equivalents of Al relative to Cr)

[0122] This test is carried out under conditions similar to Example 4 but by introducing a suspension of 268 mg of SMAO at 10.1% by weight, i.e. 1.0 mmol, in 5.0 mL of cyclohexane. The results are described in Table 1.

[0123] Example 6 (according to the invention): Process for the tetramerization of ethylene, in using SMAO suspended in cyclohexane as co-catalyst (750 equivalents of Al relative to Cr) and MMA0-3A as additive (300 equivalents of Al relative to Cr)

[0124] This test is carried out under conditions similar to Example 4 but by introducing a suspension of 402 mg of SMAO at 10.1% by weight, i.e. 1.5 mmol, in 5.0 mL of cyclohexane. The results are described in Table 1.

[0125] Example 7 (according to the invention): Process for the tetramerization of ethylene, using SMAO suspended in cyclohexane as co-catalyst (1000 equivalents of Al relative to Cr) and MMA0-3A as additive (300 equivalents of Al relative to Cr)

[0126] This test is carried out under conditions similar to Example 4 but by introducing a suspension of 536 mg of SMAO at 10.1% by weight, i.e. 2.0 mmol, in 5.0 mL of cyclohexane. The results are described in Table 1.

[0127] The results of Examples 2 to 7 are described in Table 1.

[0128] [Tableauxl] Exempt / Cf Al^ Cr Time W Productivity (■ÿga-0) CS CS t-C8* '09 CIG (¾) C12* PE iW Asped PE 2 1100 0.27 1 307 500 31.2 60.2 90.8 1.6 6.9 0.1 Cotent- 3 w 1.0 ns soo 6.5 7.0 180 0.5 1.6 34 4 Controlled 4 253 308 0.13 3 095 300 45.2 43.1 90.8 4.1 6 J 1.4 Mixed 5 503 303 0.23 1 145 008 25.5 66.8 03.7 1.4 3.9 Cosifeâé 6 750 303 0.5 71S000 24.5 60.9 90.7 1.3 7.0 SJ Cositreiè 7 1000 300 1.0 23S 000 23.0 60.7 100 V 6.6 8.4 Conttâè

[0129] * Represents the percentage of octene-1 isomers among the 8-atom molecules of carbon (C8) (selectivity)

[0130] It is observed that at a constant AlAdditive / Cr ratio, the use of an AlSMAo / Cr ratio greater than 250 makes it possible to obtain a quantity of C8 greater than 50% with a selectivity in octene-1 close to 100%, and a “controlled” polymer morphology (here polyethylene PE). An AlSMAo / Cr ratio greater than or equal to 750 lowers the productivity below 1 million. The “mixed” PE aspect means the joint presence of “controlled” and “sticky” PE.

[0131] Example 8 (comparative): Process for the tetramerization of ethylene, using SMAO suspended in cyclohexane as co-catalyst (500 equivalents of Al relative to Cr) and MMA0-3A as additive (100 equivalents of Al relative to to the Cr)

[0132] This test is carried out under conditions similar to Example 5 but by introducing 2.0 mL of a 0.1 mol / L (i.e. 0.2 mmol) MMA0-3A solution. The results are described in Table 2.

[0133] Example 9 (comparative): Process for the tetramerization of ethylene, using SMAO suspended in cyclohexane as co-catalyst (500 equivalents of Al relative to Cr) and MMA0-3A as additive (200 equivalents of Al relative to Cr)

[0134] This test is carried out under conditions similar to Example 5 but by introducing 4.0 mL of a 0.1 mol / L (i.e. 0.4 mmol) MMA0-3A solution. The results are described in Table 2.

[0135] Example 10 (according to the invention): Process for the tetramerization of ethylene, using SMAO suspended in cyclohexane as co-catalyst (500 equivalents of Al relative to Cr) and MMA0-3A as additive (400 equivalents of Al relative to Cr)

[0136] This test is carried out under conditions similar to Example 5 but by introducing 8.0 mL of a 0.1 mol / L (i.e. 0.8 mmol) MMA0-3A solution. The results are described in Table 2.

[0137] Example 11 (according to the invention): Process for the tetramerization of ethylene, using SMAO suspended in cyclohexane as co-catalyst (500 equivalents of Al relative to Cr) and MMA0-3A as additive (500 equivalents of Al relative to Cr)

[0138] This test is carried out under conditions similar to Example 5 but by introducing 10.0 mL of a 0.1 mol / L (i.e. 1.0 mmol) MMA0-3A solution. The results are described in Table 2.

[0139] Example 12 (according to the invention): Process for the tetramerization of ethylene, using SMAO suspended in cyclohexane as co-catalyst (500 equivalents of Al relative to Cr) and MMA0-3A as additive (600 equivalents of Al relative to Cr)

[0140] This test is carried out under conditions similar to Example 5 but by introducing 12.0 mL of a 0.1 mol / L (i.e. 1.2 mmol) MMA0-3A solution. The results are described in Table 2.

[0141] Example 13 (according to the invention): Process for the tetramerization of ethylene, using SMAO suspended in cyclohexane as co-catalyst (500 equivalents of Al relative to Cr) and MMA0-3A as additive (1000 equivalents of Al relative to Cr)

[0142] This test is carried out under conditions similar to Example 5 but by introducing 20.0 mL of a 0.1 mol / L (i.e. 2.0 mmol) MMA0-3A solution. The results are described in Table 2.

[0143] [Tables2] Exempt Cf Time Productivity tgjgaJ) CS w G8 { 6 ce 4 CW <% C12 + (¾) PE Asped. PE S 500 100 IJ 225 003 12-9 18.8 180 OJ 1.3 ■68.3 Sticky 9 500 200 1.0 185 000 11.7 11.1 180 0.5 1.0 75.7 Coding w 500 400 D3S 928 000 24.1 63.8 99.7 1.4 7.3 3.3 Controlled 71 500 500 0.3 1 305 000 23.8 59.7 99.7 2.0 1SJ 4.4 Controlled 12 500 600 0.3 1 4SI 008 27.1 60 2 99.7 2.,2 9.4 fl Controlled 13,500 woo 0:3 1,241,000 25.1 64.8 99.3 1.3 7.8 1.0 Controlled

[0144] * Represents the percentage of octene-1 isomers among the 8-atom molecules of carbon (C8) (selectivity)

[0145] It is observed that at a constant AlSMAo / Cr ratio, the use of an AlAdditive / Cr ratio greater than 200 makes it possible to obtain a quantity of C8 greater than 50% with a selectivity in octene-1 close to 100%, a productivity close to or greater than 1 million, and a controlled PE morphology.

[0146] These examples therefore demonstrate that the catalytic compositions according to the invention are functional due to the presence of the correct AlSMAo / Cr and AlAdditive / Cr ratio, and make it possible to obtain a high selectivity in the chosen molecule (here octene-1) close to the catalytic compositions based on MMAO in homogeneous phase of the prior art, and make it possible to obtain polymeric by-products (here PE) having a “controlled” morphology, that is to say which do not foul the oligomerization reactor and can be easily removed from the reactor, unlike the “sticky” PE filaments.

Claims

Claims ^Claim 1] A catalytic composition for the selective oligomerization of ethylene, in particular for the tetramerization of ethylene to octene-1, comprising: - a chromium-based metal precursor; - a heteroatomic ligand; - methylaluminoxane supported on an inorganic support; - an additive in the form of an aluminum-based compound; the composition having a molar ratio of the aluminum of the methylaluminoxane supported on an inorganic support to the chromium of the metal precursor greater than 250, and a molar ratio of the aluminum of the additive to the chromium of the metal precursor greater than 200. ^Claim 2] A composition according to claim 1, in which the chromium-based metal precursor is Cr (III) acetylacetonate. ^Claim 3] A composition according to claim 1 or 2, in which the heteroatomic ligand corresponds to the following general formula: [Chem.l] R* R \ . R.. , .R” to 4 in which R1, R2, R3, R4 and R5 are identical or different from each other, linked or not to each other, are chosen from a cyclic or non-cyclic alkyl group, having from 1 to 15 carbon atoms, containing or not containing one or more heteroelements and a substituted or unsubstituted aryl group having between 4 and 15 carbon atoms containing or not containing one or more heteroelements. ^Claim 4] Composition according to any one of the preceding claims in which the molar ratio of the heteroatomic ligand to the chromium-based metal precursor is between 0.5 and 10, preferably between 0.8 and 6, preferably between 1.0 and 4.0, very preferably between 1.2 and 2.

0. ^Claim 5] Composition according to any one of the preceding claims in which the inorganic support is chosen from silica, alumina, silica-alumina, zeolites, TiO2.

6. Composition according to claim 5 in which the support is silica-based, preferably the support is SiO2.

7. Composition according to any one of the preceding claims, in which the inorganic support is in the form of particles defined by an average diameter of between 1 and 100 qm, preferably between 10 and 50 pm, preferably between 20 and 40 qm, preferably between 30 and 35 qm.

8. Composition according to any one of the preceding claims, in which the aluminum content of the methylaluminoxane supported on an inorganic support is between 1 and 25% by mass, preferably between 5 and 15% by mass, more preferably between 8 and 12% by mass, very preferably between 9 and 11% by mass, relative to the total mass of the methylaluminoxane supported on an inorganic support.

9. A composition according to any preceding claim wherein the molar ratio of aluminum of the methylaluminoxane supported on an inorganic support to the chromium of the metal precursor is greater than 250 and less than 750.

10. Composition according to any one of the preceding claims in which the additive in the form of an aluminum-based compound is chosen from methylaluminoxane or modified methylaluminoxanes, alone or as a mixture.

11. Composition according to claim 10 in which the additive is MMA0-3A.

12. Composition according to any one of the preceding claims in which the molar ratio of the aluminum of the additive to the chromium of the metal precursor is greater than 200 and less than or equal to 10,000, preferably between 275 and 5,000, more preferably between 300 and 3,000, very preferably between 325 and 2,000.

13. Composition according to any one of the preceding claims, further comprising a solvent chosen from saturated, unsaturated, cyclic or non-cyclic hydrocarbons.

14. A process for the oligomerization of ethylene, preferably the tetramerization of ethylene to octene-1, comprising contacting in an oligomerization reactor a feedstock comprising ethylene with the catalytic composition according to any one of claims 1 to 13.

15. Process according to claim 14 wherein the feed comprising ethylene further contains hydrogen gas with a volume percentage of hydrogen in the feed of between 0% and 10%, preferably between 0.1% and 5%, very preferably between 1% and 3%.

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