Method for the oligomerisation of ethylene using a catalytic composition comprising chromium, supported methylaluminoxane, and an additive

Abstract

The present invention relates to a method for the oligomerisation, preferably tetramerisation, of ethylene to octene-1, the method comprising a step of injecting into an oligomerisation reactor at least the following four compounds: - a chromium-based metal precursor; - a heteroatomic ligand; - methylaluminoxane supported on an inorganic support; - an additive in the form of an aluminium-based compound; wherein the chromium-based metal precursor and the heteroatomic ligand are never brought into contact with the methylaluminoxane supported on an inorganic support in the absence of the additive in the form of an aluminium-based compound.

Description

[0001] Process for the oligomerization of ethylene using a catalytic composition comprising chromium, a supported methylaluminoxane and an additive

[0002] TECHNICAL FIELD

[0003] The invention relates to a process for the oligomerization of ethylene, preferably the tetramerization of ethylene to octene-1, using a chromium-based catalytic composition, a supported methylaluminoxane (MAO) and an additive.

[0004] PRIOR TECHNIQUE

[0005] Linear alpha olefins (LAOs) 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 alpha olefins such as 1-butene, 1-hexene and 1-octene, which can be used as comonomers 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 (usually from C4 to C30), and selective processes that will produce only one alpha 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). Among the systems known to lead to the selective production of octene-1, we can cite for example the systems described in documents W02004056477, W02004056478 or W02004056479. These catalysts use a Cr(III)-based metal precursor associated with a PNP ligand (such as PhaPN(iPr)PPh2) activated in situ by an aluminoxane (MAO: MethylAluminOxane; 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, WO201 1156892 or WO2011 108772.

[0006] The main drawback 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 field, 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 ethylene oligomerization has been described in particular 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 US621131 1.

[0007] The aim of the present invention is to provide a new process for the oligomerization of ethylene, in particular for the tetramerization of ethylene, using a catalytic composition which overcomes the problems of conventional catalytic compositions of the prior art and in particular those comprising an MAO co-catalyst in homogeneous phase.

[0008] The applicant has surprisingly demonstrated that the use of 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 a selective process (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. The applicant has also surprisingly demonstrated that the order of addition of the components in the catalytic reactor has an impact on the productivity of the catalyst.

[0009] SUMMARY OF THE INVENTION

[0010] The present invention relates to a process for the oligomerization, preferably the tetramerization of ethylene to octene-1, carried out at a total pressure of between 0.1 and 20.0 MPa, preferably between 0.1 and 15.0 MPa, and 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 80°C, the process comprising the following steps: a) injection into an oligomerization reactor of at least the following 4 compounds:

[0011] - a chromium-based metal precursor, - a heteroatomic ligand,

[0012] - methylaluminoxane supported on an inorganic support,

[0013] - an additive in the form of an aluminum-based compound, the chromium-based metal precursor and the heteroatomic ligand never being brought into contact with the methylaluminoxane supported on an inorganic support in the absence of the additive in the form of an aluminum-based compound; b) injection of a feedstock comprising ethylene into the oligomerization reactor.

[0014] An advantage of the process 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 in octene-1 and high productivity.

[0015] DETAILED DESCRIPTION OF THE INVENTION

[0016] 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.

[0017] For the purposes 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, for the purposes of the present invention, a preferred pressure value range may be combined with a more preferred temperature value range.

[0018] 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 technically feasible.

[0019] Operating conditions and implementation

[0020] The oligomerization process according to the invention is carried out 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 80°C.

[0021] Preferably, ethylene is injected into the reactor in gaseous form.

[0022] 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 feedstock comprising ethylene is between 0% and 10%, preferably between 0.1% and 5%, very preferably between 1% and 3%.

[0023] Advantageously, the heat generated by the reaction can be eliminated by any means known to those skilled in the art.

[0024] Advantageously, the oligomerization process according to the invention can be implemented in discontinuous mode (also called “batch” according to English terminology) or in continuous mode.

[0025] In one embodiment, the at least 4 compounds 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.

[0026] In a preferred embodiment, the reactor is stirred at room temperature before introduction of the feed comprising ethylene and after introduction of the methylaluminoxane supported on an inorganic support (denoted SMAO) to allow immobilization of the catalytically active species on the support. The stirring time is a few minutes, for example 5 minutes.

[0027] In one embodiment, the oligomerization process according to the invention further comprises a step c) of neutralization of the catalytic composition present in the oligomerization effluent downstream of the reactor. This step can be carried out by any means known to those skilled in the art.

[0028] Injection of at least 4 compounds into the reactor

[0029] The method according to the invention comprises a step of injecting at least the following 4 compounds into an oligomerization reactor:

[0030] - a metallic precursor based on chromium;

[0031] - a heteroatomic ligand;

[0032] - methylaluminoxane supported on an inorganic support (SMAO);

[0033] - an additive in the form of an aluminum-based compound;

[0034] Advantageously, the injection of these at least 4 compounds allows the formation of a catalytic composition making it possible to activate the oligomerization reaction.

[0035] Metallic precursor

[0036] The term “metal precursor” means: a compound comprising a metal center and at least one precursor stabilizing ligand which may be charged or neutral, organic or inorganic. In the present application, the terms “metal precursor” or “chromium-based metal precursor” will be used equivalently.

[0037] 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.

[0038] Preferably, the halide anions are selected from chloride, bromide, fluoride or iodide.

[0039] Preferably, the carboxylate anions are chosen from carboxylates having a linear or branched alkyl chain in C3-C20, preferably in C3-C15, preferably in C4-C12, preferably C5-C10, preferably said alkyl chain is substituted or not by one or more fluorine, chlorine or bromine atoms.

[0040] 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.

[0041] 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.

[0042] 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.

[0043] Advantageously, the concentration of chromium-based metal precursor used in the oligomerization process is between 0.01 and 10,000 pmol / L, preferably between 0.1 and 1,000 pmol / L, very preferably between 1 and 100 pmol / L.

[0044] Heteroatom ligand A "heteroatom ligand" is 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.

[0045] Advantageously, the heteroatomic ligand corresponds to the general formula: in which

[0046] R 1 , R 2 , R 3 , R 4 and R 5are 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 (in C1-C15), containing or not containing one or more heteroelements and a substituted or unsubstituted aryl group having between 4 and 15 carbon atoms (in C4-C15) containing or not containing one or more heteroelements.

[0047] Preferably, said heteroelements are chosen from iodine, bromine, chlorine, fluorine, nitrogen, sulfur and / or oxygen.

[0048] Preferably, R 1 , R 2 , R 3 , R 4 and R 5 are identical or different, chosen from a C1-C10 alkyl group, a C3-C10 cycloalkyl group, a C5-C15 aryl group.

[0049] Preferably, R 1 , R 2 , R 3 , R 4 and R 5are identical or different, chosen from a C1-C6 alkyl group, a C3-C6 cycloalkyl group, a C5-C12 aryl group.

[0050] Preferably, the R groups 1 , R 2 , R 3 , R 4 and R 5 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, bisnaphthyl, pyridyl, furanyl, thiophenyl groups.

[0051] De manière préférée, les ligands hétéroatomiques sont choisis parmi : (phenyl)2PN(methyl)P(phenyl)2, (phenyl)2PN(i-propyl)P(phenyl)2,

[0052] (phenyl)2PN(phényl)P(phenyl)2, (2-methoxyphenyl)2PN(i-propyl)P(phenyl)2, (2- methoxyphenyl)2PN(i-propyl)P(2-methoxyphenyl)2, (4-methoxyphenyl)2PN(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.

[0053] De manière très préférée, le ligand hétéroatomique est choisi parmi le (phenyl)2PN(i- propyl)P(phenyl)2et le (2-fluorophenyl)2PN(i-propyl)P(2-fluorophenyl)2.

[0054] Preferably, the molar ratio of the heteroatomic ligand to the chromium-based metal precursor injected into the reactor, 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.

[0055] MAO supported on an inorganic support (SMAO)

[0056] SMAO is composed of a methylaluminoxane (MAO) that has been immobilized on a solid support. The supported MAO enables 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.

[0057] The description of a supported MAO usable in the process according to the invention as well as its manufacturing process can be found in the work Tailor-Made Polymers Via Immobilization of Alpha-Olefin Polymerization Catalysts, document LJS2015353658 in the name of KING FAHD PET & MINERALS UNIVERSITY, document US20180354870 in the name of SAUDI ARABIAN OIL COMPANY or document US621 1311 in the name of EQUISTAR CHEM LP.

[0058] In this application, the terms “supported MAO” or “MAO supported on an inorganic support” or “SMAO” will be used equivalently.

[0059] 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.

[0060] The MAO used in the present invention advantageously comprises polymer chains (PMAO) formed by AI, O atoms and methyl groups (-Me or -CH3) defined by formula (ii) below:

[0061] - [(Me)AIO] n 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.

[0062] 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 TMA, free or interacting with PMAO.

[0063] SMAO is advantageously obtained by direct reaction of a MAO solution with an inorganic support in an organic solvent.

[0064] Advantageously, the inorganic support is chosen from silica, alumina, silica-alumina, zeolites, TiOa. Preferably, the support is silica-based, more preferably the support is SiOa. Advantageously, the silica contains Si-OH or Si-O-Si groups.

[0065] In one embodiment, the SiOa is selected from high purity silicas that do not contain trace metals. Preferably the SiOa contains less than 10 ppm of Fe, Na, Al and / or Ti.

[0066] In one embodiment, the SiOs may have a crystalline, amorphous, or partially crystalline structure. Preferably, the SiOs has an amorphous structure.

[0067] Advantageously, the inorganic support is in the form of particles defined by an average diameter less than or equal to 200 pm, preferably less than or equal to 150 pm, preferably less than or equal to 100 pm, and very preferably less than or equal to 50 pm.

[0068] In a preferred embodiment, the inorganic support has a granular or spherical morphology. Most preferably, the inorganic support has a spherical morphology.

[0069] In a preferred embodiment, the inorganic support is in the form of particles defined by an average diameter of between 1 and 100 pm, preferably between 10 and 50 pm, preferably between 20 and 40 pm, preferably between 30 and 35 pm.

[0070] 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. 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 defined as the volume measured by intrusion with a mercury porosimeter according to 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 as 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.

[0071] In one embodiment, the inorganic support has a specific surface area of ​​between 1 and 600 m 2 / g, preferably between 100 and 500 m 2 / g, more preferably between 200 and 400 m 2 / g, and very preferably between 300 and 350 m 2 / g. The specific surface area is calculated by the Brunauer-Emmett-Teller (BET) method, and measured by nitrogen adsorption analysis.

[0072] 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 solution.

[0073] Advantageously, the molar ratio of the aluminum of the methylaluminoxane supported on an inorganic support to the chromium of the chromium-based metallic precursor injected into the reactor, noted AlsMAo / Cr, is greater than 250.

[0074] 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 contained in the precursor.

[0075] Additive in the form of an aluminum-based compound

[0076] In this application, the terms "additive" or "additive in the form of an aluminum-based compound" will be used interchangeably.

[0077] In one embodiment, the additive in the form of an aluminum-based compound is a compound of formula AI(R 6 )3, in which R 6is independently selected from C1-C12 alkyl, C1-C12 alkoxy and halogen. Preferably, R 6 is independently selected from C1-C10 alkyl, C1-C10 alkoxy, preferably C1-C10 alkyl, C1-C10 alkoxy and chlorine or bromine. Preferably, R 6 is an alkyl and / or alkoxy group chosen from methyl, ethyl, n-propyl, i-propyl, n-butyl, tert-butyl, pentyl, hexyl, heptyl, octyl and from the corresponding alkyloxy groups. Preferably, R 6 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.

[0078] 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.

[0079] Preferably, the additive in the form of an aluminum-based compound is chosen from methylaluminoxane (MAO) or modified methylaluminoxanes (MMAO), alone or as a mixture.

[0080] 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.

[0081] 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 MMAO-3A, ​​MMAO-7 or MMAO-21.

[0082] In a preferred embodiment, the additive is MMAO-3A. ​​Similar to MAO, MMAO-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 (- / Bu) groups defined by the formula below:

[0083] - [(Me)AIO] n - K©u)AiO] m- of which n and m can advantageously take a value between 1 and 60, preferably between 10 and 50. Advantageously, the MMAO-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. 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 in interaction with the TMA or TIBA, free or in interaction with the PAAO, as described above for an MAO.

[0084] Advantageously, the molar ratio of the aluminum of the additive in the form of an aluminum-based compound to the chromium of the chromium-based metal precursor injected into the reactor, noted Atadditive / Cr, is greater than 200.

[0085] Advantageously, the Atadditive / Cr molar ratio is greater than 200 and less than or equal to 10,000, preferably between 275 and 5,000, preferably between 300 and 3,000, very preferably between 325 and 2,000.

[0086] The molar ratio Ataddm / Cr 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.

[0087] Optional solvent

[0088] In one embodiment, a solvent is also injected into the reactor. A solvent chosen from organic solvents and in particular from saturated, unsaturated, cyclic or non-cyclic hydrocarbons may be used.

[0089] 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.

[0090] 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.

[0091] In one embodiment, the solvent is selected from supercritical solvents. Preferably, the supercritical solvent is selected from supercritical propane.

[0092] In a preferred embodiment, the solvent may be chosen from the products of the oligomerization reaction. Implementation of the at least 4 compounds in the reactor

[0093] In the process according to the invention, the chromium-based metal precursor and the heteroatomic ligand are never brought into contact with the methylaluminoxane supported on an inorganic support in the absence of the additive in the form of an aluminum-based compound.

[0094] In one embodiment, the method is carried out in a batch reactor, in which the at least 4 compounds are injected into the reactor in a particular order to avoid contacting the metal precursor and the heteroatomic ligand with the SMAO in the absence of the additive, the injection being carried out in the following order: i) metal precursor and heteroatomic ligand, ii) additive, iii) SMAO; or i) additive, ii) metal precursor and heteroatomic ligand, iii) SMAO; or i) additive, ii) SMAO, iii) metal precursor and heteroatomic ligand; or i) SMAO, ii) additive, iii) metal precursor and heteroatomic ligand.

[0095] This embodiment is illustrated for example in Figures 5 and 6.

[0096] In another embodiment, in which the method is carried out in a batch reactor, 2 or 3 of the at least 4 compounds are co-injected into the reactor in a particular order to avoid contacting the metal precursor and the heteroatomic ligand with the SMAO in the absence of the additive, the injection being carried out in the following order: i) metal precursor, heteroatomic ligand and additive, ii) SMAO; or i) SMAO, ii) metal precursor, heteroatomic ligand and additive; or i) additive and SMAO, ii) metal precursor and heteroatomic ligand; or i) metal precursor and heteroatomic ligand, ii) additive and SMAO.

[0097] In one embodiment, the method is carried out in a reactor in continuous mode, in which the at least 4 compounds are mixed upstream of the injection into the reactor, following a particular order by any technique known to those skilled in the art, so as to avoid bringing the metal precursor and the heteroatomic ligand into contact with the SMAO in the absence of the additive. By way of non-limiting example, the injection comprises the following steps: i) metal precursor, heteroatomic ligand and additive are mixed in a mixer 1, ii) the solution leaving the mixer 1 and the SMAO are mixed in a mixer 2, iii) the solution leaving the mixer 2 is injected into the reactor; or i) SMAO and additive are mixed in the mixer 1, ii) the solution leaving the mixer 1, metal precursor and heteroatomic ligand are mixed in a mixer 2, iii) the solution leaving the mixer 2 is injected into the reactor.

[0098] These embodiments are illustrated for example in Figures 8 and 9.

[0099] In another embodiment, in which the method is carried out in a reactor in continuous mode, one or more of the at least 4 compounds are injected directly into the reactor by any technique known to those skilled in the art so as to avoid bringing the metal precursor and the heteroatomic ligand into contact with the SMAO in the absence of the additive. By way of non-limiting example, the injection comprises the following steps: i) metal precursor, heteroatomic ligand and additive are mixed in a mixer 1, ii) the solution leaving the mixer 1 is injected into the reactor, iii) direct injection of the SMAO into the reactor; or i) SMAO and additive are mixed in a mixer 1, ii) the solution leaving the mixer 1 is injected into the reactor, iii) direct injection of the metal precursor and the ligand into the reactor.

[0100] These embodiments are illustrated for example in Figures 10 and 11.

[0101] The applicant has surprisingly demonstrated that the presence of the additive at the time of contact between the SMAO and the metal precursor / heteroatomic ligand pair makes it possible to obtain high productivity, expressed in mass of products per mass of chromium and per hour.

[0102] LIST OF FIGURES

[0103] Figure 1 shows a snapshot of the stirring blades of a reactor following an ethylene tetramerization process according to Example 2. "Stick" polymeric by-products are observed on the stirrer which are difficult to remove and which cause fouling of the reactor.

[0104] Figure 2 represents a scanning electron microscope image of the morphology of the polymer by-product of Figure 1. A "filamentous" structure characteristic of a polymer with uncontrolled morphology is observed.

[0105] Figure 3 shows a snapshot of the stirring blades of a reactor following an ethylene tetramerization process according to Examples 3, 4, 5, 6 and 7. 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. Figure 4 shows a scanning electron microscope snapshot of the morphology of the polymeric by-product of Figure 3. A "particulate" structure characteristic of a polymer with controlled morphology is observed.

[0106] Figure 5 describes a process according to one embodiment of the invention, in batch mode in which the at least 4 compounds are injected into a reactor R1 in the following order: i) metal precursor and heteroatomic ligand, ii) additive, iii) SMAO.

[0107] Figure 6 describes a process according to one embodiment of the invention, in batch mode in which the at least 4 compounds are injected into a reactor R1 in the following order: i) additive, ii) SMAO, iii) metal precursor and heteroatomic ligand.

[0108] Figure 7 describes a process according to an embodiment which does not correspond to the invention, in batch mode in which the at least 4 compounds are injected into a reactor R1 in the following order: i) metal precursor and heteroatomic ligand, ii) SMAO, iii) additive.

[0109] Figure 8 describes a process according to an embodiment of the invention, in continuous mode comprising the following steps: i) metal precursor, heteroatomic ligand and additive are mixed in a mixer M1, ii) the solution leaving the mixer M1 and the SMAO are mixed in a mixer M2, iii) the solution leaving the mixer M2 is injected into the reactor R1.

[0110] Figure 9 describes a method according to an embodiment of the invention, in continuous mode comprising the following steps: i) SMAO and additive are mixed in mixer 1, ii) the solution leaving mixer M1, metal precursor and heteroatomic ligand are mixed in a mixer M2, iii) the solution leaving mixer M2 is injected into reactor R1.

[0111] Figure 10 describes a process according to one embodiment of the invention, in continuous mode comprising the following steps: i) metal precursor, heteroatomic ligand and additive are mixed in a mixer M1, ii) the solution leaving the mixer M1 is injected into the reactor R1, iii) direct injection of the SMAO into the reactor.

[0112] Figure 11 describes a process according to one embodiment of the invention, in continuous mode comprising the following steps: i) SMAO and additive are mixed in a mixer M1, ii) the solution leaving the mixer M1 is injected into the reactor, iii) direct injection of the metal precursor and the ligand into the reactor.

[0113] Figure 12 describes a method according to an embodiment not corresponding to the invention, in continuous mode comprising the following steps: i) the additive and the SMAO are mixed in a mixer M1, ii) the solution leaving the mixer M1, metal precursor and heteroatomic ligand are mixed in a mixer M2, iii) the solution leaving the mixer M2 is injected into the reactor R1.

[0114] Figure legend: R = reactor; M = mixer; P = Chromium-based metal precursor; L = heterotaomic ligand; A = Additive in the form of an aluminum-based compound.

[0115] EXAMPLES

[0116] Example 1: Process for the preparation of a SMAO at 10.1 wt% Al.

[0117] In a Schlenk, in a glove box, we weigh 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 m 2 / g) previously dried at 80°C under vacuum for 2 hours.

[0118] Under argon flow, the silica is impregnated with 4.7 mL (corresponding to the total pore volume) of dry toluene. 13 mL of MAO in toluene (4.65 wt% Al, d = 0.895 g / mL, 0.54 g Al theoretical) is then added. The mixture becomes a translucent liquid gel.

[0119] 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.

[0120] The AI ​​content in SMAO is determined by ICP-AES: %wt Al = 10.1 ± 0.5%.

[0121] Example 2 (comparative): Process for the tetramerization of ethylene, using a solution of MMAO-3A in homogeneous phase in cyclohexane as co-catalyst (1100 equivalents of AI relative to Cr)

[0122] In a Schlenk flask, 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 is added (Cr concentration = 2 mmol / L; PNP concentration = 2.8 mmol / L; PNP / Cr ratio = 1.4).

[0123] 93 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 while stirring at 1500 rpm for one minute. The reactor pressure is again lowered to 0.5 bar (0.05 MPa) and stirring is stopped. 5 mL of nonane dried over molecular sieve (3.6 g, internal standard), 1.2 mL of MMAO 3A dissolved 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 bar (3 MPa) pressure), stirring is started and the reactor heating setpoint is raised to 45°C. 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 taken and filtered for analysis. The results are described in Table 1.

[0124] Example 3 (comparative): Process for the tetramerization of ethylene, using SMAO suspended in cyclohexane as co-catalyst (1,100 equivalents of AI relative to Cr}

[0125] 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.

[0126] 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), 89 mL of cyclohexane is introduced. Then, the solvent is saturated with ethylene after introduction of 5 bar (0.5 MPa) of ethylene gas while 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), 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 introduced. The reactor is then stirred at 250 rpm for 5 min at 25 e C under pressure of 2 bars (0.2 MPa) of ethylene. The ethylene inlet valve is then opened (30 bars (3 MPa) of pressure), stirring is started and the reactor heating setpoint is raised to 45°C.

[0127] At the end of the test, the ethylene supply is cut off, the medium is cooled to 20°C, and the gas phase is then 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.

[0128] Example 4 (according to the invention): Process for the tetramerization of ethylene, using SMAO suspended in cyclohexane as co-catalyst (400 equivalents of AI relative to Cr) and MMAO-3A as additive (1000 equivalents of AI relative to Cr). Order of addition: i) MMAO-3A, ​​ii) Cr / PNP, iii) SMAO.

[0129] In a Schlenk flask, in a glove box, 107 mg of SMAO at 10.1% Al prepared according to example 1, i.e. 10.8 mg Al (0.4 mmol Al), are weighed. Then, 5 mL of cyclohexane are introduced to form a suspension.

[0130] In another Schlenk, under Ar, 1.0 mL of MMAO-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. 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), 80 mL of cyclohexane is introduced. Then, the solvent is saturated with ethylene after introduction of 5 bar (0.5 MPa) of ethylene gas while 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), 10.0 mL of a 0.1 mol / L MMAO-3A solution (i.e. 1.0 mmol) and 1.0 mL of a Cr / PNP solution at 1 mmol / L Cr and a PNP / Cr ratio of 1.4 (1 pmol Cr, 1.4 pmol PNP) are introduced. The mixture is stirred at 250 rpm for 5 min at 25 eC. 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 e C under pressure of 2 bars (0.2 MPa) of ethylene. The ethylene inlet valve is then opened (30 bars (3 MPa) of pressure), stirring is started and the reactor heating setpoint is raised to 45°C.

[0131] At the end of the test, the ethylene supply is cut off, the medium is cooled to 20°C, and the gas phase is then 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.

[0132] Example 5 (according to the invention): Process for the tetramerization of ethylene, using SMAO suspended in cyclohexane as co-catalyst (400 equivalents of AI relative to Cr) and MMAO-3A as additive (1000 equivalents of AI relative to Cr). Order of addition: i) Cr / PNP, ii) MMAO-3A, ​​iii) SMAO.

[0133] This test is carried out under conditions similar to Example 4 but the order of addition of the components is modified: i) 1.0 ml of a Cr / PNP solution at 1 mmol / L Cr and a PNP / Cr ratio of 1.4 (1 pmol Cr, 1.4 pmol PNP) is added; ii) 10.0 mL of a 0.1 mol / L MMAO-3A solution (i.e. 1.0 mmol) is then stirred at 250 rpm at 25 e C for 5 min and iii) injecting the suspension containing the 107 mg of SMAO into 5.0 mL of cyclohexane and stirring at 250 rpm for 5 min at 25 e C under pressure of 2 bars (0.2 MPa) of ethylene.

[0134] Example 6 (according to the invention): Process for the tetramerization of ethylene, using SMAO suspended in cyclohexane as co-catalyst (400 equivalents of AI relative to Cr) and MMAO-3A as additive (1000 equivalents of AI relative to Cr). Order of addition: i) MMAO-3A, ​​ii) SMAO, iii) Cr / PNP.

[0135] This test is carried out under conditions similar to Example 4 but the order of addition of the components is modified: i) 10.0 mL of a 0.1 mol / L MMAO-3A solution (i.e. 1.0 mmol) is added; ii) the suspension containing the 107 mg of SMAO is injected into 5.0 mL of cyclohexane and stirred at 250 rpm for 5 min at 25 e C under pressure of 2 bars (0.2 MPa) of ethylene and iii) 1.0 ml of a Cr / PNP solution at 1 mmol / L Cr and a PNP / Cr ratio of 1.4 (1 pmol Cr, 1.4 pmol PNP) is added and then stirred at 250 rpm at 25 e C for 5 min.

[0136] Example 7 (comparative): Process for the tetramerization of ethylene, using SMAO suspended in cyclohexane as co-catalyst (400 equivalents of AI relative to Cr) and MMAO-3A as additive (1000 equivalents of AI relative to Cr). Order of addition: i) SMAO, ii) Cr / PNP, iii) MMAO-3A.

[0137] This test is carried out under conditions similar to Example 2 but the order of addition of the components is modified: i) the suspension containing the 107 mg of SMAO is injected into 5.0 mL of cyclohexane; ii) 1.0 mL of a Cr / PNP solution at 1 mmol / L Cr and a PNP / Cr ratio of 1.4 (1 pmol Cr, 1.4 pmol PNP) is added and then stirred at 250 rpm for 5 min at 25 e C under pressure of 2 bars (0.2 MPa) of ethylene and iii) 10.0 mL of a 0.1 mol / L (i.e. 1.0 mmol) MMAO-3A solution is added and then stirred at 250 rpm at 25 e C for 5 min.

[0138] Table 1

[0139] * Represents the percentage of octene-1 isomers among 8-carbon (C8) molecules (selectivity)

[0140] It is observed that the process according to the invention makes it possible to obtain a quantity of C8 greater than 50% with a selectivity in octene-1 close to 100% like the processes of the prior art using MAO in homogeneous phase, while obtaining a controlled polymer morphology (here polyethylene PE) which does not foul the oligomerization reactor and can be easily removed from the reactor unlike the "sticky" PE filaments. It is also observed that bringing the metal precursor and the heteroatomic ligand into contact with SMAO in the absence of the additive causes a drastic drop in productivity and falls below the 1 million mark.

Claims

CLAIMS 1. Process for the oligomerization, preferably the tetramerization of ethylene to octene-1, carried out at a total pressure of between 0.1 and 20.0 MPa, preferably between 0.1 and 15.0 MPa, and 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 80°C, the process comprising the following steps: a) injection into an oligomerization reactor of at least the following 4 compounds: - a metallic precursor based on chromium, - a heteroatomic ligand, - methylaluminoxane supported on an inorganic support, - an additive in the form of an aluminum-based compound, the chromium-based metal precursor and the heteroatomic ligand never being brought into contact with the methylaluminoxane supported on an inorganic support in the absence of the additive in the form of an aluminum-based compound; b) injection of a feedstock comprising ethylene into the oligomerization reactor.

2. Method according to claim 1 in which the ethylene is injected into the reactor in gaseous form.

3. Process according to claim 1 or 2 wherein the feed comprising ethylene further contains gaseous hydrogen 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%.

4. Method according to any one of the preceding claims, in which the at least one compounds are injected into the reactor which is stirred by conventional mechanical means or by external recirculation, in which the ethylene reacts, preferably with temperature control.

5. Method according to any one of the preceding claims, further comprising a step c) of neutralization of the catalytic composition present in the oligomerization effluent downstream of the reactor.

6. A method according to any one of the preceding claims wherein the chromium-based metal precursor is Cr(III) acetylacetonate.

7. Method according to any one of the preceding claims, in which the concentration of chromium-based metal precursor used in the method oligomerization is between 0.01 and 10000 pmol / L, preferably between 0.1 and 1000 pmol / L, very preferably between 1 and 100 pmol / L.

8. Method according to any one of the preceding claims in which the heteroatomic ligand corresponds to the general formula: 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 one or more heteroelements and a substituted or unsubstituted aryl group having between 4 and 15 carbon atoms containing or not one or more heteroelements.

9. Method according to any one of the preceding claims in which the support is silica-based, preferably the support is SiOa.

10. Process 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.

11. A method according to any one of the preceding claims wherein the molar ratio of aluminum of the methylaluminoxane supported on an inorganic support to the chromium of the chromium-based metal precursor injected into the reactor is greater than 250.

12. Method 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.

13. Method according to claim 12 wherein the additive is MMAO-3A.

14. Method according to any one of the preceding claims, in which the molar ratio of the aluminum of the additive in the form of an aluminum-based compound to the chromium of the chromium-based metal precursor injected into the reactor is greater than 200.

15. Method according to any one of the preceding claims, in which a solvent chosen from saturated, unsaturated, cyclic or non-cyclic hydrocarbons is also injected into the reactor.

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