PROCESS FOR PRODUCING AVIATION FUEL FROM A FEED COMPRISING OLEFINS COMPRISING AN OLIGOMERIZATION STAGE AND A HETEROGENEOUS OLIGOMERIZATION STAGE

Abstract

The present invention relates to a process for producing aviation fuel from an olefinic feedstock, said process comprising the following steps: a) a step of fractionating said feedstock and obtaining at least: - a first fraction rich in ethylene; - a second fraction rich in compounds having at least 3 carbon atoms; b) a first step of oligomerizing at least a portion of the first fraction from step a) and obtaining at least a first effluent; c) a second step of heterogeneous oligomerizing at least: - a portion of the first effluent from step b), - a portion of the second fraction from step a), and obtaining a second effluent; d) a step of hydrogenating the second effluent from step c) and obtaining a third effluent; e) a step of fractionating the third effluent from step d). Figure 1 to be published

Description

Title of the invention: PROCESS FOR PRODUCING AVIATION FUEL FROM A FEED COMPRISING OLEFINS COMPRISING AN OLIGOMERIZATION STAGE AND A HETEROGENEOUS OLIGOMERIZATION STAGE Technical field

[0001] The present invention relates to a process for manufacturing aviation fuel comprising the conversion of light olefins into heavier olefins by oligomerization technologies. Prior art

[0002] The demand for Sustainable Aviation Fuels (SAF) is very important to meet the commitments to decarbonize aviation. To achieve the objective set by the International Civil Aviation Organization (ICAO) of carbon-neutral growth in aviation from 2020, it is necessary to replace fossil-based kerosene with liquid fuels made from bio-sourced carbon. The need for CAD production by 2050 is estimated at around 500 million tonnes of CAD per year worldwide.

[0003] In order to achieve this objective, it is necessary to mobilize different types of loads and therefore to develop different technological transformation solutions.

[0004] One of the known transformation routes involves, for example, methanol; today there are several technologies for generating light olefins from methanol (MTO route: Methanol To Olefins according to English terminology).

[0005] More generally, there are many ways of producing light olefins. The controlled oligomerization of these light olefins makes it possible to produce longer carbon chains which can then be used in the composition of naphtha, gasoline, kerosene or diesel.

[0006] Document FR2620724 describes a process for producing olefin oligomers for the production of premium fuel, jet fuel and automotive diesel, from C2 to C8 light olefins using a heterogeneous phase oligomerization step. The starting olefins can come from any suitable source. They can also be produced by catalytic decomposition of methanol.

[0007] However, state-of-the-art aviation fuel manufacturing processes face the difficulty of oligomerizing ethylene with heavier olefins, and often propose to recycle ethylene in the upstream stage at the cost of carbon losses and additional operating costs.

[0008] The applicant has surprisingly demonstrated that separating the ethylene fraction from the feedstock and sending it specifically to an oligomerization step, preferably in a homogeneous phase, makes it possible to convert it into a stream of higher olefins having 4 or more carbon atoms (C4+) which is then sent to a heterogeneous oligomerization step together with the fraction comprising the compounds having 3 or more carbon atoms (C3+), makes it possible to obtain a very high selectivity towards the kerosene cut meeting the specifications in force and in particular the specifications of standard ASTM D7566 or European standard 15940 respectively, while maintaining a satisfactory, or even high, overall conversion of the starting olefinic feedstock.

[0009] This addition of an oligomerization unit, preferably in homogeneous phase, of ethylene to an aviation fuel manufacturing process comprising only a heterogeneous oligomerization section thus makes it possible to recover the ethylene included in the olefinic feedstocks, in particular originating from methanol decomposition units MTO, by oligomerizing it independently of the other olefins so that it is converted into more reactive olefins for the heterogeneous oligomerization step. Summary of the invention

[0010] The present invention relates to a process for producing aviation fuel from a feedstock comprising olefins and comprising:

[0011] - a content greater than or equal to 50% by weight, preferably greater than or equal to 65% by weight, preferably greater than or equal to 80% by weight of olefins.

[0012] - less than 80% by weight, preferably less than 65% by weight, preferably less than 50% by weight of ethylene relative to the total weight of olefins contained in the feedstock,

[0013] said method comprising the following steps:

[0014] a) a step of fractionating said charge and obtaining at least:

[0015] - a first fraction comprising at least 85%, preferably at least 90%, of preferably at least 95% of the ethylene present in the feed entering step a);

[0016] - a second fraction having a content of compounds having at least 3 atoms of carbon of at least 90% by weight, preferably at least 95% by weight, more preferably at least 98% by weight;

[0017] b) a first step of oligomerization of at least a part of the first fraction resulting from step a) and obtaining at least a first effluent comprising at least 60% by weight of olefins having a number of carbon atoms greater than or equal to 4, relative to the total weight of the olefins contained in said first effluent, said first oligomerization step being carried out in the presence of an oligomerization catalyst;

[0018] c) a second oligomerization step of at least:

[0019] - a part of the first effluent from step b),

[0020] - a part of the second fraction from step a), and obtaining a second effluent comprising at least 85% by weight, preferably at least 90% by weight, more preferably at least 95% by weight of olefins having 7 carbon atoms or more relative to the total weight of the olefins contained in said second effluent, said second oligomerization step being carried out in the presence of a heterogeneous amorphous or zeolitic catalyst;

[0021] d) a step of hydrogenation of the second effluent from step c) and obtaining a third effluent comprising a content of at least 90% by weight, preferably at least 95% by weight, preferably at least 98% by weight of paraffins;

[0022] e) a step of fractionating the third effluent from step d) and obtaining at least one aviation fuel type cut. DETAILED DESCRIPTION OF THE INVENTION

[0023] 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.

[0024] 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.

[0025] In the present description, the term "Cx" designates hydrocarbon compounds containing x carbon atoms. The term "Cx+" designates hydrocarbon compounds containing at least x carbon atoms. The term "Cx-" designates hydrocarbon compounds containing at most x carbon atoms. The term "Cx to Cy" designates hydrocarbon compounds having between x and y carbon atoms.

[0026] Throughout this text, the groups of chemical elements are given according to the CAS classification (CRC Handbook of Chemistry and Physics, publisher CRC press, editor-in-chief DR Lide, 81st edition, 2000-2001). For example, group VIIIB according to the CAS classification corresponds to the metals of columns 8, 9 and 10 according to the new IUP AC classification, and group IB according to the CAS classification corresponds to column 11 metals according to the new IUP AC classification.

[0027] 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.

[0028] In the present application, the term "comprise" is synonymous with (means the same as) "include" and "contain", and is inclusive or open and does not exclude other elements not recited. It is understood that the term "comprise" includes the exclusive and closed term "consist". Charge

[0029] According to the invention, the feedstock comprises olefins and comprises:

[0030] - a content greater than or equal to 50% by weight, preferably greater than or equal to 65% by weight, preferably greater than or equal to 80% by weight of olefins.

[0031] - less than 80% by weight, preferably less than 65% by weight, preferably less than 50% by weight of ethylene relative to the total weight of olefins contained in the feedstock.

[0032] Advantageously, the feed comprises between 2% and 30% by weight, preferably between 5 and 25%, more preferably between 7 and 15% of ethylene relative to the total weight of the olefins contained in the feed.

[0033] Advantageously, the feed comprises more than 40% by weight, preferably more than 45%, more preferably more than 50% by weight of propylene, relative to the total weight of the olefins contained in the feed.

[0034] Advantageously, the filler comprises at least 50% by weight, preferably at least 65% by weight, more preferably at least 80% by weight of olefins having between 2 and 6 carbon atoms relative to the total weight of the filler.

[0035] Advantageously, the filler comprises at least 80% by weight of compounds having between 3 and 6 carbon atoms relative to the total weight of the filler.

[0036] Advantageously, the feed comprises at least 95% by weight, preferably at least 97% by weight, more preferably at least 98% by weight of olefins having between 2 and 6 carbon atoms relative to the total weight of the olefins contained in the feed.

[0037] Advantageously, the feed comprises at least 80% by weight of olefins having between 3 and 6 carbon atoms relative to the total weight of the olefins contained in the feed.

[0038] Advantageously, the feedstock comes from a catalytic alcohol decomposition unit, preferably from a catalytic methanol or ethanol decomposition unit.

[0039] In one embodiment, the filler further comprises Dimethyl Ether (DME).

[0040] In one embodiment, the feedstock may be from cracking units and / or dehydration of heavier alcohols such as propanol or butanol, or an FCC (Fluid Catalytic Cracking) type unit, or steam cracking.

[0041] The feed does not come from an ethanol dehydration unit (ETE route: Ethanol To Ethylene according to English terminology).

[0042] In one embodiment, the filler may further comprise compounds having more than 6 carbon atoms, preferably compounds having between 7 and 8 carbon atoms. Operating conditions and catalysts

[0043] Step a) of fractionation

[0044] The method according to the invention comprises a step a) of fractionating said charge and obtaining at least:

[0045] - a first fraction comprising at least 85%, preferably at least 90%, of preferably at least 95% of the ethylene present in the feed entering step a)

[0046] - a second fraction having a content of compounds having at least 3 atoms of carbon of at least 90% by weight, preferably at least 95% by weight, more preferably at least 98% by weight;

[0047] Fractionation step a) can be carried out by any means known to those skilled in the art, for example with successive continuous distillation or continuous or batch multi-cut distillation, using a lateral draw-off to extract the intermediate boiling cut. Internal wall columns can also be used to carry out this separation while reducing energy consumption. The use in addition to or as a replacement for solutions using molecular sieves or separating membranes is also a possibility for separating our cuts of interest.

[0048] In one embodiment, a heavy fraction is further obtained in step a), comprising a content of at least 90% by weight, preferably at least 95% by weight, more preferably at least 98% by weight of benzene and compounds heavier than this.

[0049] In one embodiment, all or part of the heavy fraction is sent to hydrogenation step d). Optionally, a fractionation of the heavy fraction is carried out in order to recover a fraction comprising compounds heavier than benzene, which will be sent at least in part to hydrogenation step d).

[0050] In one embodiment, a fraction comprising at least 90%, preferably at least 95%, more preferably at least 98% of the Dimethyl ether (DME) contained in the feedstock entering step a) is further obtained in step a).

[0051] This fractionation step a) is advantageously designed so as to be able to isolate any compounds that may have a negative impact on oligomerization reactions and catalysts, and in particular aims to eliminate DME when the feedstock comes from an MTO unit.

[0052] In one embodiment, this fraction containing DME will be recycled in a catalytic alcohol decomposition unit upstream of step a).

[0053] Step b) of first oligomerization

[0054] The process according to the invention comprises a first step of oligomerization of at least a portion of the first fraction resulting from step a) and obtaining at least one first effluent comprising at least 60% by weight of olefins having a number of carbon atoms greater than or equal to 4, relative to the total weight of the olefins contained in said first effluent, said first oligomerization step being carried out in the presence of an oligomerization catalyst.

[0055] Advantageously, the first effluent from the first oligomerization step b) comprises less than 20% by weight, preferably less than 10% by weight, more preferably less than 5% by weight of ethylene not having reacted during the first oligomerization step b), relative to the total weight of the olefins contained in said first effluent.

[0056] Advantageously, at least a portion, i.e. at least 50% by weight, preferably at least 70% by weight, preferably 90% by weight of the first fraction from step a) and preferably all of said fraction is subjected to said first oligomerization step.

[0057] Advantageously, the first oligomerization step b) leads to the production of a first effluent comprising at least 80% by weight relative to the total weight of the olefins contained in said olefinic effluent, of olefins having a number of carbon atoms greater than or equal to 4. In particular, said effluent is rich in olefinic hydrocarbons having a number of carbon atoms between 4 and 8 and also comprises olefinic hydrocarbons having 9 carbon atoms or more (C9+).More particularly, said first effluent produced during the first oligomerization step b), advantageously comprises at least 80% by weight, preferably at least 90% by weight, of olefinic compounds having a number of carbon atoms between 4 and 8 and less than 20% by weight and preferably less than 10% by weight, of olefinic compounds having a number of carbon atoms greater than or equal to 9, the weight percentages being expressed relative to the total mass of olefins contained in said first effluent.

[0058] The oligomerization catalyst used in step b) may be any oligomerization catalyst known to those skilled in the art; it may be in homogeneous form, i.e. the catalyst is soluble in the liquid phase composed of dissolved ethylene and its oligomerization products, or in non-soluble heterogeneous form.

[0059] In a particular embodiment, the catalyst used in the first oligomerization step b) is a heterogeneous catalyst. The heterogeneous catalyst comprises at least one element from group VIII and at least one porous oxide refractory support preferably chosen from alumina, silica, silica-aluminas, zirconias, titanium oxide, magnesia, clays taken alone or as a mixture. The element from group VIII is preferably chosen from nickel, cobalt, iron, platinum and palladium and preferably, said element from group VIII is nickel. The heterogeneous catalyst may also comprise one or more additional elements chosen from the elements from groups VI, IA and IIA. For example, the element from group VI is chosen from chromium, molybdenum and tungsten. The group IA element is selected from lithium, sodium or potassium and the group IIA element includes magnesium, calcium and strontium.Preferably, the support is an alumina or a silica-alumina. The support may in particular be an amorphous silica-alumina which comprises between 70 and 99.5% by weight of SiO2 and the remainder to 100% being alumina.

[0060] When the first oligomerization step is carried out with a heterogeneous catalyst, it is advantageously carried out at a temperature of between 30 and 400°C, preferably between 50 and 300°C, at an absolute pressure of between 0.5 and 10 MPa, preferably between 1 and 10 MPa and more preferably between 1 and 8 MPa, and at a weight hourly space velocity (WHSV) defined as being the ratio between the total mass flow rate of the incoming feedstock and the total mass of catalyst of between 0.1 and 10 h 1 and preferably between 0.4 and 5 h 1 .

[0061] In a preferred embodiment, the catalyst used in the first oligomerization step b) is a homogeneous oligomerization catalyst.

[0062] Advantageously, the homogeneous catalyst used in step b) of oligomerization of the process according to the invention comprises:

[0063] - at least one nickel precursor with oxidation state (+11),

[0064] - and at least one activating agent chosen from the group formed by the compounds chlorinated and brominated hydrocarbylaluminium compounds, taken alone or in mixture.

[0065] Optionally, the homogeneous catalyst used in step b) of oligomerization of the process according to the invention further comprises at least one organic Brônsted acid, or at least one carboxylic acid anhydride, or at least one phosphine ligand of formula PR1R2R3 in which the groups RI, R2 and R3, identical or different from each other, linked or not to each other.

[0066] The nickel compounds of oxidation degree (+11) are preferably compounds soluble at more than one gram per liter in hydrocarbon medium, and more particularly in the reagents and the reaction medium and preferably, carboxylates of nickel of general formula (RCOO)2Ni where R is a hydrocarbyl radical, for example alkyl, cycloalkyl, alkenyl, aryl, aralkyl or alkaryl containing up to 20 carbon atoms, preferably a hydrocarbyl radical of 5 to 20 carbon atoms. The radical R may be substituted by one or more halogen atoms, by one or more hydroxy, ketone, nitro, cyano groups or other groups which do not hinder the reaction. The two radicals R may also constitute an alkylene radical of 6 to 18 carbon atoms. The divalent nickel compounds are advantageously chosen from the following divalent nickel salts: octoate, ethyl-2-hexanoate, decanoate, stearate, oleate, salicylate and hydroxydecanoate, taken alone or in a mixture and preferably, the divalent nickel compound is nickel ethyl-2-hexanoate.

[0067] The activating agent is chosen from the group formed by chlorinated and brominated hydrocarbylaluminium compounds corresponding to the formula A1RX2, in which R is a hydrocarbyl radical and X is a halogen chosen from chlorine and bromine taken alone or as a mixture. The hydrocarbylaluminium halides are advantageously chosen from dichloroethylaluminium, dichloroisobutylaluminium and dibromoethylaluminium. These hydrocarbylaluminium dihalides can be advantageously enriched with aluminium trihalides (A1X3) such as aluminium trichloride.

[0068] The organic Brônsted acid compounds preferably correspond to the formula HY, where Y is an organic anion, for example carboxylic, sulfonic or phenolic. Said compounds preferably have a pKa at 20°C at most equal to 3 and are preferably chosen from the group formed by halogenocarboxylic acids of formula RCOOH in which R is a halogenated alkyl radical and preferably a halogenated alkyl radical containing at least one halogen atom alpha to the -COOH group with a total of 2 to 10 carbon atoms. Preferably, a haloacetic acid of formula CXpH(3-p)-COOH is used in which X is fluorine, chloro, bromine or iodine, with p being an integer from 1 to 3. Examples that may be mentioned are trifluoroacetic, difluoroacetic, fluoroacetic, trichloroacetic, dichloroacetic and chloroacetic acids.These examples are not limiting, and it is also possible to use arylsulfonic, alkylsulfonic, fluoroalkylsulfonic acids, picric acid, nitroacetic acid.

[0069] The catalyst used in the first oligomerization step b) may also contain at least one carboxylic acid anhydride of formula (RCO)2O in which R is a hydrocarbyl radical which may advantageously contain one or more halogen atoms. The carboxylic acid anhydrides are advantageously chosen from octoic, ethyl-2-hexanoic, decanoic, stearic, oleic, trifluoroacetic, monofluoroacetic, trichloroacetic, monochloroacetic, pentafluoropropionic or heptafluorobutyric anhydrides, taken alone or as a mixture. Preferably, the carboxylic acid anhydride is trifluoroacetic acid anhydride.

[0070] Finally, the catalyst used in the first oligomerization step b) may also contain a phosphine ligand of formula PR1R2R3 in which the groups RI, R2 and R3, identical or different from each other, linked or not to each other. The hydrocarbyl groups RI, R2 and R3 of the phosphine ligand PR1R2R3 advantageously comprise 1 to 20 carbon atoms, preferably 2 to 15 carbon atoms, preferably between 3 and 10 carbon atoms. Preferably, the hydrocarbyl groups RI, R2 and R3 of the phosphine ligand PR1R2R3 are chosen from the group formed by the methyl, ethyl, propyl, isopropyl, n-butyl, tert-butyl, cyclopentyl, cyclohexyl, benzyl, adamantyl groups.

[0071] Preconditioning of the catalyst may be carried out before bringing the catalyst into contact with ethylene. Preconditioning of the catalytic composition consists of mixing the three components in a hydrocarbon solvent, for example an alkane or an aromatic hydrocarbon, or a halogenated hydrocarbon, or preferably the olefins produced in the oligomerization reaction, with stirring and under an inert atmosphere, for example under nitrogen or argon, at a controlled temperature of between 0 and 80°C, preferably between 10 and 60°C, for a period of 1 minute to 5 hours, preferably 5 minutes to 1 hour. The solution thus obtained is then transferred under an inert atmosphere into the oligomerization reactor.

[0072] This preconditioning of the catalyst makes it possible to increase the activity of the catalyst in the oligomerization of ethylene.

[0073] The catalyst present in said unit carrying out the oligomerization step b) is in liquid form. Depending on the chemical composition of said catalyst, the weight proportions of each of the components of the catalyst must be controlled during the synthesis of the catalyst. The molar ratio of the hydrocarbylaluminium halide to the nickel compound, expressed by the Al / Ni ratio, is from 2 / 1 to 50 / 1, and preferably from 2 / 1 to 20 / 1.

[0074] The molar ratio of Bronsted acid to nickel compound is from 0.25 / 1 to 10 / 1, and preferably from 0.25 / 1 to 5 / 1. If the catalyst comprises carboxylic acid anhydride, the molar ratio of carboxylic acid anhydride to nickel compound is advantageously between 0.001 / 1 and 1 / 1, very advantageously between 0.01 / 1 and 0.5 / 1. If the catalyst comprises a phosphine ligand, the molar ratio of phosphine ligand to nickel compound is advantageously between 2 and 25, preferably between 5 and 20, more preferably between 5 and 15.

[0075] In one embodiment, said homogeneous catalyst is the catalyst described in document WO2017017087.

[0076] The first step b) of oligomerization implemented by homogeneous catalysis is advantageously carried out continuously: the catalytic solution is injected into the unit carrying out the oligomerization step and the ethylene is injected therein continuously. The unit carrying out said step of oligomerization of ethylene by homogeneous catalysis comprises one or more reactors of the perfectly stirred type, in series, with recycle of at least part of the effluent from the reactor into the reactor, this recycle having been advantageously cooled.

[0077] The first oligomerization step b) can advantageously be implemented in a reactor with one or more reaction stages in series, the predominantly ethylenic feedstock and / or the previously preconditioned catalytic composition being introduced continuously, either into the first stage or into the first and any other of the stages.

[0078] The operating conditions in the reactor(s) carrying out the oligomerization step by homogeneous catalysis are such that the temperature is between -20°C and +80°C and the pressure is sufficient to allow the existence of a liquid phase in the reactor(s). Preferably, the absolute total pressure in the reactor(s) is between 0.5 and 8 MPa.

[0079] At the outlet of the first oligomerization step b), the homogeneous catalytic system is mixed with the effluent produced during step b) and the ethylene which has not reacted.

[0080] Advantageously, said olefinic effluent produced during the first oligomerization step b) undergoes at least one step of treatment / separation of the homogeneous catalytic system of said effluent before being sent to the second oligomerization step c).

[0081] The term “step of treatment / separation of the homogeneous catalytic system” means a step in which said catalytic system is deactivated and separated from the homogeneous reaction medium and in particular from the olefinic effluent resulting from the first oligomerization step b).

[0082] In one embodiment, the first effluent from the first oligomerization step b) undergoes a fractionation step to obtain at least one fraction comprising a content of at least 90% by weight, preferably at least 95% by weight, preferably at least 98% by weight of compounds having between 4 and 8 carbon atoms which is sent to the second oligomerization step c), and a fraction comprising a content of at least 90% by weight, preferably at least 95% by weight, preferably at least 98% by weight of compounds having 9 or more carbon atoms (C9+) which is sent to the hydrogenation step d).

[0083] In one embodiment, the first effluent from the first oligomerization step b) undergoes a fractionation step to obtain a fraction comprising a content of at least 90% by weight, preferably at least 95% by weight, more preferably at least 98% by weight of compounds having 2 carbon atoms or less which is advantageously purged.

[0084] An example of the first oligomerization step b) is the DimEne-B® process marketed by the company Axens.

[0085] Another example of a first oligomerization step b) is the Dhnersol-E® process marketed by the company Axens.

[0086] Step c) of second oligomerization

[0087] The process according to the invention comprises a second step c) of oligomerization of at least:

[0088] - a part of the first effluent from step b),

[0089] - a part of the second fraction from step a), and obtaining a second effluent comprising at least 85% by weight, preferably at least 90% by weight, more preferably at least 95% by weight of olefins having 7 carbon atoms or more relative to the total weight of the olefins contained in said second effluent, said second oligomerization step being carried out in the presence of an amorphous or zeolitic heterogeneous catalyst.

[0090] According to one embodiment, the catalyst used in the second oligomerization step c) is an amorphous catalyst comprising and preferably consisting of an amorphous mineral material chosen from silica-aluminas and siliceous aluminas.

[0091] According to one embodiment, the catalyst used in the second oligomerization step c) is a zeolitic catalyst comprising and preferably consisting of a zeolite, preferably having at least pore openings containing 10 or 12 oxygen atoms (10MR or 12MR), and preferably chosen from aluminosilicate type zeolites having an overall Si / Al ratio greater than 10.

[0092] According to one embodiment, the zeolite catalyst comprises a zeolite chosen from zeolites of structural type MFI, MTW, MOR, TON, MEL, MFS, MTT, taken alone or as a mixture.

[0093] According to another embodiment, the zeolite catalyst used in the second oligomerization step c) comprises a zeolite chosen from the zeolites ZSM-5, ZSM-12, NU-86, Mordenite, ZSM-22, NU-10, ZBM-30, ZSM-48, ZSM-11, ZSM-57, IZM-2, ITQ-6 and IM-5, taken alone or in a mixture, preferably from the zeolites ZSM-5, NU-10 and ZBM-30, taken alone or in a mixture, very preferably the zeolite is ZBM-30 and even more preferably, the zeolite is ZBM-30 synthesized in the presence of the structuring agent triethylenetetramine.

[0094] The zeolite used in the catalyst used in step c) of the process according to the invention can advantageously undergo several post-treatments known to man of the art such as for example being modified by dealumination or desilication according to any method of dealumination, external surface passivation or desilication known to those skilled in the art, with the aim of improving its activity and / or its stability.

[0095] Said catalyst used in step c) of the process according to the invention also advantageously comprises at least one oxide type matrix also called binder. By matrix according to the invention is meant an amorphous or poorly crystallized matrix.

[0096] Said matrix is advantageously chosen from the elements of the group formed by clays (such as for example among natural clays such as kaolin or bentonite), magnesia, aluminas, silicas, silica-aluminas, aluminates, titanium oxide, boron oxide, zirconia, aluminum phosphates, titanium phosphates, zirconium phosphates, and coal. Preferably said matrix is chosen from the elements of the group formed by aluminas, clays and silicas, more preferably said matrix is chosen from aluminas, and even more preferably said matrix is gamma alumina.

[0097] The catalysts used in step c) of the process according to the invention are advantageously shaped in the form of grains of different shapes and sizes. They are advantageously used in the form of cylindrical or polylobed extrudates such as bilobed, trilobed, polylobed of straight or twisted shape, but can optionally be manufactured and used in the form of crushed powder, tablets, rings, balls, wheels, spheres. Preferably, said catalysts are in the form of extrudates of size between 1 and 10 mm.

[0098] The second oligomerization step c) is advantageously implemented in at least one fixed-bed reactor.

[0099] The second oligomerization step c) of the process according to the invention advantageously operates at a temperature of between 20 and 500°C, preferably between 100 and 350°C and preferably between 100 and 300°C, at a pressure of between 1.0 and 10 MPa, preferably between 2 and 8 MPa and preferably between 3 and 7 MPa and with a WH of preferably between 0.1 and 0.5 h-1, preferably between 0.2 and 0.3 h-1.

[0100] The WH (or hourly volumetric velocity) is, according to the invention, defined by the ratio between the volumetric flow rate of fresh olefinic feedstock, in particular at 15°C and 1 atmosphere, and the volume of oligomerization catalyst, in particular in operation (also called in operation).

[0101] Advantageously, the second effluent produced during the second oligomerization step c) is an effluent comprising less than 20% by weight, preferably less than 10% by weight of unreacted C4 olefins, the weight percentages being expressed relative to the total mass of olefins contained in said second effluent.

[0102] Advantageously, the second effluent produced during the second stage oligomerization c) comprises less than 20% by weight and preferably less than 10% by weight of C4-C8 olefinic compounds, the weight percentages being expressed relative to the total mass of olefins contained in said second effluent.

[0103] An example of a second oligomerization step c) is the Polynaphtha® process marketed by the company Axens.

[0104] The second effluent from the heterogeneous oligomerization step c) is then sent to the hydrogenation step d). Advantageously, this can be fractionated into at least one fraction comprising a content of at least 90% by weight, preferably at least 95% by weight, preferably at least 98% by weight of compounds having between 3 and 4 carbon atoms which is advantageously purged, and a fraction comprising a content of at least 90% by weight, preferably at least 95% by weight, preferably at least 98% by weight of compounds having 5 or more carbon atoms (C5+) which is sent to the hydrogenation step d).

[0105] In one embodiment, the second effluent from step c) undergoes a fractionation step to obtain at least:

[0106] - a fraction comprising a content of at least 90% by weight, preferably at least less than 95% by weight, preferably at least 98% by weight of olefins having between 3 and 8 carbon atoms,

[0107] - a fraction comprising a content of at least 90% by weight, preferably at least less than 95% by weight, preferably at least 98% by weight of olefins having 9 or more carbon atoms (C9+).

[0108] Advantageously, the fraction comprising a content of at least 90% by weight, preferably at least 95% by weight, more preferably at least 98% by weight of olefins having 9 carbon atoms or more (C9+) is sent to the hydrogenation step d).

[0109] Advantageously, at least a portion of the fraction comprising a content of at least 90% by weight, preferably at least 95% by weight, more preferably at least 98% by weight of olefins having between 3 and 8 carbon atoms is recycled to the inlet of the second oligomerization step c).

[0110] Advantageously, a first part of the fraction comprising a content of at least 90% by weight, preferably at least 95% by weight, more preferably at least 98% by weight of olefins having between 3 and 8 carbon atoms is recycled to the inlet of the second oligomerization step c) (called in this embodiment c1)), the second part being sent to another heterogeneous oligomerization step c2) and obtaining an effluent from the other heterogeneous oligomerization step.

[0111] The other heterogeneous oligomerization step c2) advantageously operates with the same catalyst as step c1), at a temperature between 50 and 500°C, preferably between 100 and 350°C and more preferably between 130 and 300°C at a pressure between 2.0 and 12 MPa, preferably between 2 and 10 MPa and more preferably between 4 and 7 MPa and with a WH preferably between 0.1 and 1.0 h-1, preferably between 0.3 and 0.6 h-1.

[0112] In one embodiment, a first part of the effluent from the other heterogeneous oligomerization step from c2) is recycled to the inlet of the latter, the second part being sent to the hydrogenation step d).

[0113] Step d) of hydrogenation

[0114] The process according to the invention comprises a step d) of hydrogenation of the second effluent from step c) and obtaining a third effluent comprising a content of at least 90% by weight, preferably at least 95% by weight, preferably at least 98% by weight of paraffins.

[0115] In one embodiment, hydrogenation step d) is also fed with a C9+ cut resulting from a fractionation downstream of first oligomerization step b).

[0116] Advantageously, hydrogenation step d) is carried out by contacting with a hydrogen-rich gas in the presence of a catalyst comprising at least one metal from group VIII, preferably chosen from palladium and nickel taken alone or as a mixture, and a support preferably chosen from alumina, silica or silica-alumina.

[0117] The catalyst used in the hydrogenation step comprises a palladium content advantageously between 0.1 and 10% by weight and / or a nickel content, advantageously between 1 and 60% by weight relative to the total mass of the catalyst.

[0118] The hydrogenation step is advantageously carried out at a temperature of between 100 and 250°C at the reactor inlet, at a pressure of between 2 and 5 MPa and at an hourly weight rate of between 0.05 and 8 h-1.

[0119] The performance of the hydrogenation is validated by a measurement of the bromine number which is advantageously at most 5 g Br / 100g, in the case where it is desired to saturate all of the unsaturated compounds present in the cut to be hydrogenated.

[0120] Step e) of fractionation

[0121] The process according to the present invention comprises a step e) of fractionating the third effluent from step d) and obtaining at least one aviation fuel type cut.

[0122] Fractionation step e) is advantageously carried out in at least one distillation column so as to separate said effluent into at least 3 cuts:

[0123] - A naphtha type cut,

[0124] - An aviation fuel type cut,

[0125] - A diesel type cut.

[0126] In one embodiment, a gas cut is further obtained which is advantageously purged.

[0127] The term “naphtha” cut means the cut comprising hydrocarbon compounds whose boiling point is between room temperature and 220°C.

[0128] The term “aviation fuel” cut means the cut comprising hydrocarbon compounds whose boiling point is between 130°C and 300°C. This cut may also be called the “kerosene” cut.

[0129] The term “diesel” cut means the cut comprising hydrocarbon compounds whose boiling point is between 220 and 360°C. LIST OF FIGURES

[0130] [Fig.l]

[0131] The feedstock 10 is sent to a fractionation step a) to produce a first fraction 11 comprising at least 85% of the ethylene included in feedstock 10, a second fraction 12 having a content of compounds having at least 3 carbon atoms of at least 90% by weight, a heavy fraction 13 comprising a content of at least 90% by weight of benzene and compounds heavier than this, and a fraction 18 comprising at least 90% by weight of the DME present in the feedstock 10.Fraction 11 is sent to step b) of first oligomerization to produce an effluent comprising at least 60% by weight of olefins having a number of carbon atoms greater than or equal to 4, relative to the total weight of the olefins contained in this effluent, which is then fractionated to obtain a fraction 14 comprising a content of at least 90% by weight of compounds having between 4 and 8 carbon atoms, a fraction 15 comprising a content of at least 90% by weight of compounds having 2 carbon atoms or less, and a fraction 16 comprising a content of at least 90% by weight of compounds having 9 carbon atoms or more. Fractions 14 and 12 are mixed into a stream 20 which is sent to a step c) of second heterogeneous oligomerization to produce an effluent 21 comprising at least 85% by weight of olefins having 7 carbon atoms or more relative to the total weight of the olefins contained in this effluent.The effluent 21 and the fraction 16 are mixed into a stream 22 which is sent to a step d) of hydrogenation of the olefins to produce effluent 24 comprising a content of at least 90% by weight of paraffins and a purge 23 comprising the unreacted hydrogen and the lightest gases. The effluent 24 is sent to a fractionation step e) to produce a gas purge 25, a naphtha type cut 26, an aviation fuel type cut 27 and a diesel type cut 28.

[0132] [Fig.2]

[0133] The feed 10 is sent to a fractionation step a) to produce a first fraction 11 comprising at least 85% of the ethylene included in feed 10, a second fraction 12 having a content of compounds having at least 3 atoms of carbon of at least 90% by weight, a heavy fraction 13 comprising a content of at least 90% by weight of benzene and compounds heavier than it, and a fraction 18 comprising at least 90% by weight of the DME present in the feed 10. Fraction 11 is sent to step b) of first oligomerization to produce an effluent comprising at least 60% by weight of olefins having a number of carbon atoms greater than or equal to 4, relative to the total weight of the olefins contained in this effluent, which is then fractionated to obtain a fraction 14 comprising a content of at least 90% by weight of compounds having between 4 and 8 carbon atoms, a fraction 15 comprising a content of at least 90% by weight of compounds having 2 carbon atoms or less, and a fraction 16 comprising a content of at least 90% by weight of compounds having 9 carbon atoms or more.Fractions 14 and 12 are mixed into a stream 20 which is sent to a first step cl) of heterogeneous oligomerization to produce an effluent comprising at least 90% by weight of olefins having 7 carbon atoms or more relative to the total weight of the olefins contained in this effluent, which will then be fractionated to obtain a fraction 30 comprising a content of at least 90% by weight of olefins having between 3 and 8 carbon atoms and a fraction 31 comprising a content of at least 90% by weight of olefins having 9 carbon atoms or more.A first part of fraction 30 is recycled to the inlet of step c1) and the second part 32 is sent to another heterogeneous oligomerization step c2) to produce an effluent of which a first part is recycled to the inlet of step c2) and the other part 33 is mixed with fraction 31 in a stream 21 comprising at least 85% by weight of olefins having 7 carbon atoms or more relative to the total weight of the olefins contained in this stream which is then mixed with fraction 16 in a stream 22 which is sent together with fraction 13 to a step d) of hydrogenation of the olefins to produce effluent 24 comprising a content of at least 90% by weight of paraffins and a purge 23 comprising the unreacted hydrogen and the lightest gases. The effluent 24 is sent to a fractionation step e) to produce a gas purge 25, a naphtha type cut 26, an aviation fuel type cut 27 and a diesel type cut 28. EXAMPLES

[0134] Example 1: Process for producing aviation fuel according to an embodiment of the invention:

[0135] Because there is an overlap in the boiling temperatures of the compounds present in the kerosene and diesel cuts, and for the sake of simplification, a cut point between kerosene and diesel at 290°C was chosen in the example.

[0136] In the example, “Cut 130-290” means all of the compounds hydrocarbons with a boiling point between 130°C and 290°C, this cut is of the kerosene type. The term "290-360 Cut" refers to all hydrocarbon compounds with a boiling point between 290°C and 360°C, this cut is of the diesel type.

[0137] The flow numbers are those shown in Figures 1 and 2.

[0138] The charge 10 considered is an olefinic cut resulting from the decomposition of methanol having the following composition (values in weight percentage):

[0139] [Tables 1] % weight Flux 10 Methane 0.53 Ethane 0.34 C2= 10.20 C3-C5 Paraffins 3.69 C3= 57.36 C4= 20.29 C5= 5.38 C6-C8 Paraffins 0.00 C6= 2.07 C7=C8= 0.00 Cut 130-290 0.00 Cut 290-360 0.00 DME 0.16

[0140] The sign = corresponds to olefins, for example C2= is ethylene, C3= is propylene, C4= are butenes, etc.

[0141] Step a) of fractionation

[0142] It consists of a succession of distillation columns:

[0143] A first column operated at 2.0 MPa makes it possible to recover the majority of compounds with 3 carbon atoms or less at the top and the majority of compounds with 4 carbon atoms or more as well as dimethyl ether at the bottom.

[0144] A second column operated at 3.0 MPa fractionates the top product of the first column, and makes it possible to recover the majority of compounds with 2 carbon atoms or less at the top and the majority of compounds with 3 carbon atoms or more at the bottom.

[0145] A third column operated at 1.2 MPa, fractionates the bottom product of the first column and allows the majority of the dimethyl ether to be recovered at the top, and the majority of the compounds with 4 carbon atoms or more at the bottom.

[0146] The top product 11 of the second column is directed towards step b) of first oligomerization.

[0147] The bottom product of the second column is mixed with the bottom product of the third column (stream 12) and is directed to step c) of second heterogeneous oligomerization.

[0148] [Tables2] % weight Flux 11 Flux 12 Methane 4.8 0.0 Ethane 3.0 0.0 C2= 92.2 0.0 C3-C5 Paraffins 0.0 4.1 C3= 0.1 64.6 C4= 0.0 22.9 C5= 0.0 6.1 C6-C8 Paraffins 0.0 0.0 C6= 0.0 2.3 C7=C8= 0.0 0.0 Cut 130-290 0.0 0.0 Cut 290-360 0.0 0.0 DME 0.0 0.0

[0149] Step b) first oligomerization step

[0150] The reactor of step b) is operated at 4.5 MPa and 50°C. The catalyst is the homogeneous nickel-based catalyst marketed by Axens under the name LC1251. The co-catalyst is dichloroethylaluminium (EADC). It is used in solution in n-hexane. The molar ratio between the catalyst and the co-catalyst is fixed so as to have an Al / Ni molar ratio of 15.

[0151] The catalyst concentration is adjusted so as to obtain an ethylene conversion of 97.5% in the reactor.

[0152] The effluent from the oligomerization reactor is fractionated via the succession of 2 distillation columns:

[0153] - A first column operated at 2.8 MPa allows the majority of the compounds with 2 or fewer carbon atoms at the top and the majority of compounds with 3 or more carbon atoms at the bottom

[0154] - The second column operated at 0.8 MPa fractionates the bottom product of the first column and allows the recovery of the majority of compounds having between 3 and 8 carbon atoms at the top, and the majority of compounds with 9 carbon atoms or more at the bottom.

[0155] The top product 14 of this second column constitutes the effluent of step b) and is sent to step c) of the second heterogeneous oligomerization. The bottom product of the second column 16 is directed to the hydrogenation step d).

[0156] [Tables3] % weight Flux 14 Flux 16 Methane 0.0 0.0 Ethane 0.0 0.0 C2= 0.0 0.0 C3-C5 Paraffins 0.2 0.0 C3= 0.0 0.0 C4= 65.5 0.0 C5= 0.0 0.0 C6-C8 Paraffins 0.0 0.0 C6= 28.7 0.0 C7=C8= 5.7 0.0 Cut 130-290 0.0 100.0 Cut 290-360 0.0 0.0 DME 0.0 0.0

[0157] Step c) of second heterogeneous oligomerization

[0158] The feed 20 to the heterogeneous oligomerization unit is the mixture of the effluent 12 from the fractionation step a) and the effluent 14 from the first oligomerization step b).

[0159] [Tables4] % weight Flux 20 Methane 0.0 Ethane 0.0 C2= 0.0 C3-C5 Paraffins 3.7 C3= 58.4 C4= 27.0 C5= 5.5 C6-C8 Paraffins 0.0 C6= 4.9 C7=C8= 0.5 Cut 130-290 0.0 Cut 290-360 0.0 DME 0.0

[0160] The heterogeneous oligomerization is carried out in two steps cl) and c2).

[0161] Step cl)

[0162] The first stage of heterogeneous oligomerization is implemented in 3 reactors in series, with an intermediate exchanger between each reactor, allowing the effluent to be cooled before entering the next reactor.

[0163] The first step of the heterogeneous oligomerization is carried out in the presence of the silica alumina catalyst IP811 marketed by Axens. The operating conditions of step cl) are a temperature of 110°C, a pressure of 4.5 MPa at the inlet of the reactors and a total hourly volumetric flow rate in the reactors of 0.2 h-1 (excluding recycle).

[0164] The reaction effluent obtained at the end of this first heterogeneous oligomerization step is separated by distillation into two cuts:

[0165] - a cut 30 essentially comprising olefins having between 3 and 8 atoms of carbon, 95% recycled to the first heterogeneous oligomerization stage cl) (which corresponds to a weight ratio of the cut comprising less than 8 carbon atoms or less (C8-) compared to the olefinic hydrocarbon feedstock entering stage cl) of 2.4);

[0166] - a C9+ 31 cut which is directed towards the hydrogenation step d).

[0167] The 5% by weight of the cut 30 essentially comprising olefins having between 3 and 8 carbon atoms which are not recycled to the first heterogeneous oligomerization step cl) 32 are directed to a second heterogeneous oligomerization step c2).

[0168] [Tables5] % weight Flux 30 Flux 31 Methane 0.0 0.0 Ethane 0.1 0.0 C2= 0.1 0.0 C3-C5 Paraffins 29.5 0.0 C3= 18.1 0.0 C4= 10.8 0.0 C5= 4.1 0.0 C6-C8 Paraffins 0.0 0.0 C6= 17.2 0.0 C7=C8= 20.1 0.1 Cut 130-290 0.0 98.6 Cut 290-360 0.0 1.3

[0169] Step c2)

[0170] The second stage of heterogeneous oligomerization is implemented in 2 reactors in series, with an intermediate exchanger between each reactor, allowing cooling before entering the next reactor.

[0171] The second step of heterogeneous oligomerization is carried out in the presence of the silica alumina catalyst IP811 marketed by Axens. The operating conditions of step c2 are a temperature of 150°C, a pressure of 7.0 MPa at the reactor inlets and a total hourly volumetric flow rate in the reactors of 0.5 h-1 (excluding recycle).

[0172] 50% of the reaction effluent obtained at the end of the second oligomerization stage heterogeneous is recycled to the inlet thereof. The remaining 50% 33 is mixed with the C9+ cut 31 from the distillation of the effluent from the first stage cl) of heterogeneous oligomerization. The mixture 21 obtained is directed to stage d) of olefin hydrogenation.

[0173] [Tableauxô] % weight Flux 32 Flux 33 Methane 0.0 0.0 Ethane 0.1 0.1 C2= 0.1 0.1 C3-C5 Paraffins 29.5 29.9 C3= 18.1 0.9 C4= 10.8 1.4 C5= 4.1 0.5 C6-C8 Paraffins 0.0 0.1 C6= 17.2 5.5 C7=C8= 20.1 13.9 Cut 130-290 0.0 39.6 Cut 290-360 0.0 8.2

[0174] Step d) of hydrogenation of olefins

[0175] Charge 22 entering the olefin hydrogenation stage consists of:

[0176] - From the bottom product 16 of the second column downstream of the first oligo- merization b),

[0177] - From the C9+ cut 31 obtained by distillation downstream of the first step cl) heterogeneous oligomerization,

[0178] - From the non-recycled part 33 of the effluent from the second stage c2) heterogeneous oligomerization.

[0179] [Tables?] % weight Flux 22 Methane 0.0 Ethane 0.0 C2= 0.0 C3-C5 Paraffins 4.0 C3= 0.1 C4= 0.2 C5= 0.1 C6-C8 Paraffins 0.0 C6= 0.7 C7=C8= 2.0 Cut 130-290 90.8 Cut 290-360 2.2 DME 0.0

[0180] Step d) of hydrogenation of the olefins operates with a nickel-based catalyst LD746 marketed by Axens and in which the majority of the olefins will be hydrogenated to produce paraffins while minimizing the production of light hydrocarbon molecules. This step operates at a temperature of 160°C and a pressure of 2.5 MPa at the reactor inlet. The hourly volumetric flow rate in the reaction section is 3 h-1 and the H2 / HC (hydrocarbons) ratio is equal to 100.

[0181] The olefin content of the effluent at the outlet of hydrogenation 24 is 1% by weight.

[0182] Step e) of fractionation

[0183] The effluent 24 at the outlet of hydrogenation step d) is sent to fractionation step e) which is carried out in a succession of 3 fractionation columns:

[0184] - A first column operated 0.7 MPa of which the head product 25 is mainly consisting of compounds with 5 carbon atoms or less

[0185] - A second column, fed from the bottom of the first operated 0.15 MPa of which the top product 26 is mainly made up of compounds between 5 and 8 carbon atoms

[0186] - A third column, fed from the bottom of the second operated at 0.05MPa whose head product 27 is the 130-290 cut and the bottom product 28 is the cut 290-360.

[0187] [Tables8] % weight Flux 24 Flux 25 Flux 26 Flux 27 Flux 28 Methane 0.1 3.4 0.0 0.0 0.0 Ethane 0.0 0.2 0.0 0.0 0.0 C2= 0.0 0.0 0.0 0.0 0.0 C3-C5 Paraffins 3.2 89.2 0.7 0.0 0.0 C3= 0.0 0.0 0.0 0.0 0.0 C4= 0.0 0.1 0.0 0.0 0.0 C5= 0.0 0.0 0.0 0.0 0.0 C6-C8 Paraffins 2.6 6.1 82.1 0.4 0.0 C6= 0.0 0.1 0.2 0.0 0.0 C7=C8= 0.0 0.0 0.6 0.0 0.0 Cut 130-290 91.8 0.0 16.3 99.3 10.2 Cut 290-360 2.2 0.0 0.0 0.2 89.8 DME 0.0 0.0 0.0 0.0 0.0

[0188] According to the example, the production of the 130-290 cut (kerosene type) for 1 ton / hr of feed is 900kg / h. The combined production of the 130-290 cut and the 290-360 cut (kerosene type + diesel type) is 925kg / h. The invention makes it possible to maximize the production of the kerosene type cut compared to a process where ethylene would not be converted or would be little converted. Indeed, such a production of the kerosene type cut would not be achievable without the conversion of ethylene which alone represents more than 10% of the feed.

Claims

1. Claims A process for producing aviation fuel from a feedstock comprising olefins and comprising: - a content greater than or equal to 50% by weight, preferably greater than or equal to 65% by weight, preferably greater than or equal to 80% by weight of olefins. - less than 80% by weight, preferably less than 65% by weight, more preferably less than 50% by weight of ethylene relative to the total weight of the olefins contained in the feedstock, said process comprising the following steps: a) a step of fractionating said charge and obtaining at least - a first fraction comprising at least 85%, preferably at least 90%, more preferably at least 95% of the ethylene present in the feed entering step a); - a second fraction having a content of compounds having at least 3 carbon atoms of at least 90% by weight, preferably at least 95% by weight, more preferably at least 98% by weight; b) a first step of oligomerization of at least a portion of the first fraction from step a) and obtaining at least one first effluent comprising at least 60% by weight of olefins having a number of carbon atoms greater than or equal to 4, relative to the total weight of the olefins contained in said first effluent, said first oligomerization step being carried out in the presence of an oligomerization catalyst; c) a second stage of oligomerization of at least: - a portion of the first effluent from stage b), - a portion of the second fraction from stage a), and obtaining a second effluent comprising at least 85% by weight, preferably at least 90% by weight, more preferably at least 95% by weight of olefins having 7 carbon atoms or more relative to the total weight of the olefins contained in said second effluent, said second oligomerization stage being carried out in the presence of an amorphous or zeolitic heterogeneous catalyst; d) a step of hydrogenation of the second effluent from step c) and obtaining a third effluent comprising a content of at least 90% by weight, preferably at least 95% by weight, so as to preferred at least 98% by weight of paraffins; e) a step of fractionating the third effluent from step d) and obtaining at least one aviation fuel type cut.

2. A method according to claim 1, wherein the feed comprises at least 50% by weight, preferably at least 65% by weight, more preferably at least 80% by weight of olefins having between 2 and 6 carbon atoms relative to the total weight of the feed.

3. A method according to any preceding claim, wherein the feedstock is from a catalytic alcohol decomposition unit.

4. A process according to any one of the preceding claims, wherein there is further obtained in step a), a heavy fraction comprising a content of at least 90% by weight, preferably at least 95% by weight, more preferably at least 98% by weight of benzene and compounds heavier than it.

5. Process according to claim 4, in which all or part of the heavy fraction is sent to step d) of hydrogenation.

6. A process according to any preceding claim, wherein the oligomerization catalyst used in the first oligomerization step b) is a homogeneous catalyst.

7. Process according to claim 6, in which the homogeneous catalyst comprises: - at least one nickel precursor with an oxidation state (+11), - and at least one activating agent chosen from the group formed by chlorinated and brominated hydrocarbylaluminium compounds, taken alone or as a mixture.

8. Process according to any one of the preceding claims, in which the first effluent from the first oligomerization step b) comprises less than 20% by weight, preferably less than 10% by weight, more preferably less than 5% by weight of ethylene not having reacted during the first oligomerization step b), relative to the total weight of the olefins contained in said first effluent.

9. Process according to any one of the preceding claims, in which the first effluent from the first oligomerization step b) undergoes a fractionation step to obtain at least one fraction comprising a content of at least 90% by weight, preferably at least 95% by weight, more preferably at least 98% by weight of compounds having between 4 and 8 carbon atoms which is sent to step c) second oligomerization, and a fraction comprising a content of at least 90% by weight, preferably at least 95% by weight, more preferably at least 98% by weight of compounds having 9 or more carbon atoms which is sent to step d) of hydrogenation.

10. Process according to any one of the preceding claims, in which the second oligomerization step c) operates in the presence of an amorphous heterogeneous catalyst or one comprising at least one zeolite, having at least pore openings containing 10 or 12 oxygen atoms.

11. Process according to any one of the preceding claims, in which the second effluent from step c) undergoes a fractionation step to obtain at least: - a fraction comprising a content of at least 90% by weight, preferably at least 95% by weight, preferably at least 98% by weight of olefins having between 3 and 8 carbon atoms, - a fraction comprising a content of at least 90% by weight, preferably at least 95% by weight, preferably at least 98% by weight of olefins having 9 carbon atoms or more.

12. A process according to claim 11, wherein the fraction comprising a content of at least 90% by weight, preferably at least 95% by weight, more preferably at least 98% by weight of olefins having 9 or more carbon atoms is sent to the hydrogenation step d).

13. A process according to any one of claims 11 to 12, wherein at least a portion of the fraction comprising a content of at least 90% by weight, preferably at least 95% by weight, more preferably at least 98% by weight of olefins having between 3 and 8 carbon atoms is recycled to the inlet of the second oligomerization step c).

14. Process according to any one of claims 11 to 12, in which a first part of the fraction comprising a content of at least 90% by weight, preferably at least 95% by weight, more preferably at least 98% by weight of olefins having between 3 and 8 carbon atoms is recycled to the inlet of the second oligomerization step c), the second part being sent to another heterogeneous oligomerization step c2) and obtaining an effluent from the other heterogeneous oligomerization step.

15. A method according to claim 14, wherein a first portion of the effluent from the other heterogeneous oligomerization step from c2) is recycled to the inlet of the latter, the second part being sent to stage d) of hydrogenation.

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