A refined process for the production of intermediate distilled products by oligomerization of olefin-containing feedstocks.

Abstract

DEPCT68 This invention relates to a process for preparing intermediate distillate products from... Process feed raw materials containing olefins, which include: a) The oligomerization step is fed with process feed materials containing recycled olefins. The first and second recycling processes are performed when at least one oligomerization catalyst is present, in order to... It produces the release agents of reactions that consist of dimers, timers, and oligomers; b) The steps for fractionalization of the released substances of the reaction are: - A light fraction sequence consisting of at least a portion of process feed raw materials containing olefins. Not transformed; -A middle segment sequence consisting of at least a dimer and a timer; and -A heavy metal sequence composed of oligomers; c) Recycling process, which includes: The initial recycling preparation, which includes at least: A portion of the light section sequence; and a second recycled section consisting of at least a portion of the section sequence. Intermediate; and the transfer of the first and second recycling processes to step a); d) The hydrogenation step of at least a portion of the heavy fraction;

Description

[0001] Improved process for producing middle distillates by oligomerization of an olefinic feedstock

[0002] Technical field

[0003] The present invention relates to a process for producing middle distillates, in particular kerosene and / or diesel, meeting the specifications in force, in particular those defined in the ASTM D1655 or ASTM D7566 standard for kerosene and those defined in the ASTM D975 standard or the European standard 15940 for diesel, by heterogeneous oligomerization of an olefinic feedstock, in particular a biosourced olefinic feedstock.

[0004] Prior art

[0005] Airlines have committed to carbon-neutral growth, particularly in commercial aviation, starting in 2021, and US airlines have set a target of reducing CO2 emissions by 50% by 2050 compared to 2005 levels. However, improvements in aircraft and engine efficiency are not enough to achieve carbon neutrality. Sustainable Aviation Fuel (SAF) is therefore critical to achieving this goal.

[0006] It therefore seems necessary to develop methods for manufacturing synthetic kerosene, preferably from bio-sourced feedstocks.

[0007] Patent FR 2926812 thus discloses a process for the oligomerization of olefins, allowing the production of fuel, for example the production of gasoline and / or kerosene from light olefinic feedstocks containing between 2 and 8 carbon atoms (C2-C8), and in particular from light olefinic feedstocks containing high proportions of propylene and / or butenes and / or pentenes and using an oligomerization catalyst based, preferably consisting solely, of silica-alumina with a reduced macropore content.

[0008] Patent EP 1 396 532 describes a process for upgrading a liquid hydrocarbon feedstock, comprising: a) separating from said hydrocarbon feedstock a fraction (01) essentially comprising compounds containing 5 carbon atoms (C5) including at least 2% by weight of pentenes; b) bringing said fraction (01) into contact with a hydrocarbon cut (02) comprising hydrocarbons having a number of carbon atoms between 6 and 10 (C6-C10), including at least 2% by weight of olefins, in the presence of an acid catalyst promoting the dimerization and alkylation reactions of the species; (c) a separation of the effluent obtained into at least two cuts, including a gasoline cut (a) whose upper distillation point is less than 100°C and comprising the majority of unreacted reagents, and a kerosene cut ( ) with a distillation range between 100°C and 300°C.

[0009] Patent EP 1 602 637 describes a process for simply and economically modulating the respective production of gasoline and diesel, by transforming the initial charge of hydrocarbons comprising 4 to 15 carbon atoms (C4-C15) into a gasoline fraction with an octane number improved compared to that of the charge and a diesel fraction with a high cetane number.

[0010] Patent EP 1 739 069 describes a process for preparing a diesel cut from an olefinic feedstock with 2-12 carbon atoms (C2-C12), comprising two oligomerization steps between which a separation step is interposed. The intermediate separation step makes it possible to obtain a light cut of C4-C5 olefinic hydrocarbons, an intermediate cut having a T95 of between 180°C and 240°C and a heavy cut with a T95 greater than 240°C. The intermediate cut is then mixed with at least a fraction of the light cut in a mass ratio (intermediate cut / light cut) of between 60 / 40 and 80 / 20 and then undergoes a second oligomerization.

[0011] Patent EP 2 385 092 describes a process for producing middle distillate hydrocarbon bases from ethanol, more particularly bioethanol.

[0012] Patent EP 2 707 462 discloses a process for the oligomerization of olefins comprising 4 to 6 carbon atoms (C4-C6) into a middle distillate cut having predominantly 10 to 20 carbon atoms (C10-C20). In the process of patent EP 2 707 462, the starting olefinic feedstock must contain a minimum of branched olefins (or iso-olefins), preferably at least 10% by weight and preferably 20% by weight of iso-olefins relative to all the olefins in the feedstock.

[0013] Patent FR 2 959 750 describes a process for producing middle distillate hydrocarbon bases, preferably kerosene hydrocarbon bases, from an ethanol feedstock derived from biomass, said process comprising the dehydration of ethanol into a predominantly ethylenic effluent, two successive oligomerization stages to obtain a middle distillate effluent.

[0014] Patent FR 3 053 355 describes a process for the oligomerization of light olefinic feedstocks containing between 2 and 10 carbon atoms (C2-C10) per molecule, using a catalytic system comprising a silica-alumina-based catalyst and a zeolite-based catalyst having pore openings of 10 or 12 oxygen atoms, and carried out at a temperature between 130 and 350°C, at a pressure between 0.1 and 10 MPa and at a WH (hourly volumetric flow rate) between 0.1 and 5 h' 1 The process of EP 3 053 355 makes it possible to improve the yield of middle distillates and in particular the yield of diesel, compared to an oligomerization process using only one of the catalysts of the catalytic system used, at iso-volume of catalyst.

[0015] US Patent 6,372,949 describes the transformation of oxygenates into gasoline and distillates (C4-C12 cut) in a single dehydration-oligomerization step using a composite catalyst comprising a monodimensional 10 MR zeolite selected from the group consisting of ZSM 22, ZSM 23, ZSM 35, ZSM 48, ZSM 57 and ferrierite and mixtures thereof, with a multidimensional zeolite having an average pore size, such as ZSM-5 zeolite.

[0016] However, none of the processes of the state of the art discloses a means for producing from light olefins C3 to C6, preferably C3 to C4, in particular from bio-sourced feedstocks, middle distillates, in particular kerosene and / or diesel, in a very specific manner and with improved yields of middle distillates, in particular kerosene and / or diesel, meeting the specifications in force, in particular the specifications of standard ASTM D7566 and / or European standard 15940, while maintaining a very satisfactory, even high, conversion of the olefinic feedstock.

[0017] Summary of the invention

[0018] Thus, the present invention relates to a process for preparing middle distillates from an olefinic feedstock, comprising: a) an oligomerization step supplied with at least the olefinic feedstock, a first recycle and a second recycle, and carried out in the presence of at least one oligomerization catalyst, at a temperature between 20 and 500°C, a pressure between 1.0 and 10 MPa and a WH between 0.1 and 0.5 h' 1 , to produce a reaction effluent comprising dimers, trimers and oligomers; b) a step of fractionating the reaction effluent obtained at the end of step a), into at least:

[0019] - a light fraction comprising at least part of the olefinic feedstock not converted in step a);

[0020] - an intermediate fraction comprising at least a portion of the dimers and trimers produced in step a); and

[0021] - a heavy fraction comprising the oligomers; c) a recycle step, comprising the preparation of a first recycle comprising at least a portion of the light fraction; the preparation of a second recycle comprising at least a portion of the intermediate fraction; and the transfer of the first recycle and the second recycle to step a) of oligomerization; d) a step of hydrogenation of at least a portion of the heavy fraction separated in step b) in the presence of hydrogen, to obtain a hydrogenated heavy fraction comprising middle distillates.

[0022] The advantage of the process according to the invention is to propose a process for the efficient conversion of light olefinic feedstocks, in particular comprising olefins with between 3 and 6, preferably between 3 and 4, carbon atoms, and more particularly at least partly biosourced, to selectively produce a middle distillate cut, and more particularly a kerosene cut or a diesel cut, meeting the specifications in force and in particular the specifications of standard ASTM D7566 or European standard 15940 respectively.

[0023] The process according to the invention also makes it possible to significantly improve the selectivity for middle distillates, or more particularly for kerosene or diesel, compared to the oligomerization processes of the state of the art, and therefore to maximize the yields of middle distillates, or more particularly for kerosene or diesel, while maintaining a satisfactory, or even high, overall conversion of the starting olefinic feedstock.

[0024] Another advantage of the process according to the invention lies in the fact that any type of feedstock and in particular bio-sourced olefinic feedstocks which typically comprise a high proportion of olefins and are therefore very reactive, can be converted into hydrocarbon products and in particular with high yields in middle distillates, and more particularly in kerosene or diesel.

[0025] Description of the embodiments

[0026] According to the present invention, the expressions "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.

[0027] 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 range of preferred pressure values ​​may be combined with a range of more preferred temperature values.

[0028] 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.

[0029] The terms "upstream" and "downstream" should be understood in terms of the general flow of the stream(s) in question in the process. The term "bio-based" means that the material / product / compound it describes is an organic material / product / compound whose carbon comes from atmospheric CO2 recently fixed (on a human scale) using solar energy (photosynthesis). On land, this CO2 is captured or fixed by plant life (e.g., agricultural crops or forestry materials). In the oceans, CO2 is captured or fixed by photosynthesizing bacteria or phytoplankton. For example, a bio-based material has an isotopic ratio 14 C / 12 C greater than 0. Conversely, a material of fossil origin has an isotopic ratio 14 C / 12C of approximately 0. The terms "renewable" or "renewably derived" can also be used. To determine whether a material / product / compound is bio-based or renewable, its percent modern carbon (pMC) content is measured according to ASTM D 6866-21 ("Determination of Bio-Based Content of Natural Range Materials Using Radiocarbon and Isotope Ratio Mass Spectrometry Analysis"). The method in this standard measures the isotope ratio 14 C / 12 C in a sample and compares it to the isotopic ratio 14 C / 12C of a standard bio-based reference to obtain the percentage of bio-based content of the sample, the reference giving a radiocarbon content approximately equivalent to the atmospheric radiocarbon fraction in 1950. The pMC of the standard bio-based reference material is therefore equal to 100%. The pMC of a bio-based material is strictly greater than 0%, for example greater than or equal to 1%. The pMC of a material of fossil origin is approximately 0%. A current bio-based material may therefore also possibly have a pMC greater than 100%.

[0030] In this description, the terms "T95" or "T95 temperature" are interchangeable and designate the temperature at which 95% by weight of the product under consideration is evaporated. It is determined according to the standard method ASTM D2887. Similarly, "T5" or "T5 temperature" is the temperature at which 5% by weight of the product under consideration is evaporated, determined according to the same standard method ASTM D2887.

[0031] In this description, the term "Cx" denotes compounds having x carbon atoms. For example, a chemical compound C3 contains 3 carbon atoms. The term "Cx+" denotes compounds having at least x carbon atoms. For example, C9+ compounds are compounds containing at least 9 carbon atoms (i.e., 9 or more carbon atoms). The term "Cx-" denotes compounds having at most x carbon atoms.

[0032] Throughout this text, groups of chemical elements are described according to the new IUPAC classification. For example, groups 9 or 10 correspond to the metals in columns 9 and 10, respectively, according to the IUPAC classification or to the last two columns of group VIIIB according to the CAS classification (CRC Handbook of Chemistry and Physics, CRC editor press, editor-in-chief DR Lide, 81st edition, 2000-2001). Similarly, group 6 corresponds to the metals in column 6 according to the IUPAC classification or to the metals in columns VI B according to the CAS classification.

[0033] According to the present invention, the terms "olefin" and "mono-olefin" are used interchangeably and refer to hydrocarbons comprising a double bond. Preferably, the olefins of the olefinic feedstock of the process comprise between 3 and 6 carbon atoms (C3-C6), preferably 3 and / or 4 carbon atoms (C3 and / or C4). The olefins obtained after oligomerization preferably comprise between 6 and 30 carbon atoms (C6-C30), preferably between 9 and 25 carbon atoms (C9-C25), in particular between 9 and 16 carbon atoms (C9-C16) or between 10 and 25 carbon atoms (C10-C25).

[0034] According to the present invention, the term "oligomerization" designates any reaction of addition of an olefin to another olefin, until compounds are obtained, in particular hydrocarbon compounds, in particular mono-olefinic compounds, typically containing between 6 and 30 carbon atoms, preferably between 9 and 25 carbon atoms (C9-C25), in particular 9 and 16 carbon atoms (C9-C16) or between 10 and 25 carbon atoms (C10-C25). Thus, the products obtained are dimers or trimers of the olefins of the olefinic feedstock, that is to say olefinic compounds resulting from the condensation of respectively two or three olefin molecules of the olefinic feedstock, or oligomers which correspond to olefinic compounds resulting from the condensation of several olefin molecules of the olefinic feedstock (several meaning here more than 3 but less than 10, preferably less than or equal to 5, more preferably less than or equal to 4).Typically, from C4 olefins, oligomers are obtained whose number of carbon atoms is largely less than or equal to 30, and for the most part preferably between 9 and 25, in particular between 9 and 16 or between 10 and 25. Oligomerization is distinguished from polymerization by an addition of molecules in limited number. The number of molecules added is in the context of the invention between 2 and 10, limits included, preferably between 3 and 6, and more preferably between 3 and 6. The oligomers may however comprise traces of olefins having been oligomerized with a number of molecules greater than 10. Most often, these traces represent less than 5% by weight relative to the oligomers formed.

[0035] The term "heterogeneous catalysis" defines, in this disclosure, a reaction, in particular oligomerization reactions, where at least two phases coexist, the catalyst being in solid form. In particular, the oligomerization step of the process according to the invention implements the oligomerization of the olefinic feedstock by heterogeneous catalysis, that is to say in the presence of a catalyst in solid form, the feedstock and advantageously the products obtained preferably being in liquid phase. More particularly, the present invention relates to a process for preparing middle distillates, preferably a kerosene cut and / or a diesel cut, from a C3 to C6 olefinic feedstock, preferably C3 to C4 and in particular C3, C4 or their mixtures, comprising, preferably consisting of: a') optionally a step of pretreatment of the olefinic feedstock preferably implementing at least one adsorption section, a water washing section,a hydrotreatment section and / or a selective hydrogenation section; a”) optionally a step of separation of the olefinic feedstock to at least partially separate the C5 and C6 compounds present in said olefinic feedstock; a) an oligomerization step fed at least by the olefinic feedstock, optionally pretreated and / or separated, a first recycle and a second recycle, and operated, preferably in the liquid phase, in the presence of at least one oligomerization catalyst, preferably solid, at a temperature preferably between 20 and 500°C, at a pressure preferably between 1.0 and 10 MPa, and a WH preferably between 0.1 and 0.5 h, -1 , to produce a reaction effluent comprising dimers, trimers and oligomers; b) a step of fractionating the reaction effluent obtained at the end of step a), into at least:

[0036] - a light fraction comprising at least part of the olefinic feedstock not converted in step a);

[0037] - an intermediate fraction comprising at least a portion of the dimers and trimers advantageously produced in step a); and

[0038] - a heavy fraction, comprising the oligomers present in the reaction effluent from step a); c) a recycle step, comprising: the preparation of a first recycle comprising, preferably consisting of, at least a portion of the light fraction from fractionation step b); the preparation of a second recycle comprising, preferably consisting of, at least a portion of the intermediate fraction from fractionation step b); and the transfer of the first recycle and the second recycle to oligomerization step a); d) a step of hydrogenation of at least a portion of the heavy fraction separated in step b) in the presence of hydrogen, to obtain a hydrogenated heavy fraction advantageously comprising at least one middle distillate cut; e) optionally a step of separation of the hydrogenated heavy fraction, to obtain at least one middle distillate cut, in particular a kerosene cut and / or a diesel cut. The olefinic feedstock

[0039] The feedstock treated by the process according to the invention is advantageously a so-called light olefinic feedstock, that is to say comprising hydrocarbon compounds and in particular olefins, preferably mono-olefins, containing between 3 and 6 carbon atoms (that is to say C3, C4, C5 and C6), preferably between 3 and 4 carbon atoms (that is to say C3 and C4), preferably 3 or 4 carbon atoms (that is to say C3 or C4).

[0040] Preferably, the C3 to C6 olefinic feedstock comprises at least 20% by weight, preferably at least 50% by weight, more preferably at least 90% by weight of olefins, preferably at least 95% by weight of olefins, in particular at least 98% of olefins or at least 99% by weight of olefins, relative to the total weight of the olefinic feedstock relative to the total weight of the C3 to C6 olefinic feedstock, the olefins containing between 3, 4, 5 and 6 carbon atoms, preferably 3 and / or 4 carbon atoms, said olefins preferably being mono-olefins.

[0041] The olefinic feedstock may optionally comprise paraffins, in particular paraffins of the various cuts at the terminals of the initial and final distillation points of the feedstock in question, in particular in C3 to C6, i.e. fully hydrogenated hydrocarbon compounds, preferably aliphatic, preferably containing between 3 and 6 carbon atoms. Preferably, the olefinic feedstock may optionally comprise up to 80% by weight, preferably up to 50% by weight, preferably up to 10% by weight, preferentially up to 5% by weight, in particular up to 2% or even up to 1% by weight of paraffins, relative to the total weight of the olefinic feedstock relative to the total weight of the olefinic feedstock in C3 to C6, preferably in C3 and / or in C4.Very preferably, the olefinic feedstock is free of paraffins, i.e. comprises less than 0.5% by weight of paraffins, and preferably less than 0.1% by weight of paraffins, relative to the total weight of the olefinic feedstock. Treating an olefinic feedstock containing a low paraffin content, in particular containing paraffins at a content of less than or equal to 10% by weight, preferably less than or equal to 5% by weight, preferably less than or equal to 2% by weight, or even an olefinic feedstock free of paraffins, makes it possible to carry out the oligomerization step at low pressure, in particular lower than that conventionally used for conventional (or fossil) feedstocks which generally comprise paraffin contents greater than 10% by weight and often between 40 and 80% by weight of paraffins.

[0042] In particular, the preferred olefinic feedstocks contain predominantly propylene and / or butenes and / or pentenes, preferably propylene and / or butenes (iso-butene and / or n-butenes). By predominantly, it is meant at least 80% by weight, preferably at least 90% by weight, relative to the total weight of the olefinic feedstock.

[0043] An olefinic feedstock particularly suitable for the process according to the invention is an olefinic feedstock essentially C3 and C4, preferably C3 or C4, i.e. at least 90% by weight, preferably at least 95% by weight, preferably at least 98% by weight of C3 and / or C4 olefins relative to the total weight of the olefins contained in the olefinic feedstock. Thus, the olefinic feedstock advantageously comprises at least 85% by weight of propylene and / or butenes (in particular isobutene and / or n-butenes), preferably at least 90% by weight, preferably at least 95% by weight, preferably at least 98% by weight of propylene and / or butenes relative to the total weight of the olefinic feedstock.The olefinic feedstock may in particular be chosen from a “polymer grade” propylene feedstock, a feedstock comprising essentially propylene (i.e. at least 90% by weight of propylene) and a small amount of butenes (i.e. less than 10% by weight of butenes), a feedstock consisting essentially of isobutene (i.e. at least 90% by weight of isobutene), a feedstock consisting essentially of n-butenes (but-1-ene and but-2-ene) (i.e. at least 90% by weight of but-1-ene and but-2-ene), and mixtures thereof.

[0044] In the preferred embodiment of the invention in which the olefinic feedstock is a C3 and / or C4 olefinic feedstock, said olefinic feedstock may also contain C5 and / or C6 compounds. In this case, the content of C5 and / or C6 compounds is preferably less than or equal to 5% by weight in the olefinic feedstock, preferably less than or equal to 2% by weight, or even preferably less than or equal to 1% by weight relative to the weight of the olefinic feedstock. In this case, the content of C5 and / or C6 olefins in the olefinic feedstock is preferably less than 0.8% by weight, preferably less than 0.6% by weight. Optionally, the olefinic feedstock of this preferred embodiment may also comprise paraffins, in particular propane and / or butane.Preferably, the C3 and / or C4 olefinic feedstock is free of propane and / or butane (i.e. comprises less than 0.5% by weight of paraffins, and preferably less than 0.1% by weight of paraffins, relative to the total weight of the olefinic feedstock), which makes it possible to carry out the oligomerization step at a lower pressure compared to the oligomerization of a feedstock comprising paraffins. Preferably, the olefinic feedstock is free of C5 and / or C6 paraffins, i.e. comprises less than 0.5% by weight, preferably less than 0.1% by weight of C5 and / or C6 paraffins, in order to limit the quantity of inert compounds introduced in particular in step a).

[0045] A preferred olefinic feedstock is a C4 olefinic cut, which comprises at least 98% by weight of n-butenes 1-butene and 2-butene, preferably less than 2% of n-butane, and preferably less than 0.5% of n-butane, the percentages being given relative to the total weight of the olefinic feedstock.

[0046] Another preferred olefinic feedstock is a C4 olefinic cut, which comprises in particular at least 90% by weight of isobutene, or even at least 92% by weight of isobutene, and in particular at most 97% by weight of isobutene, and optionally butane and / or isobutane and / or n-butenes, in particular between 3 and 10% by weight of butane and / or isobutane and / or n-butenes, the percentages being given relative to the total weight of the olefinic feedstock.

[0047] The olefinic feedstock may also be a C3-C4 olefinic cut (i.e. comprising propylene and butenes), for example comprising at least 90% by weight of propylene and up to 10% by weight of butenes, said feedstock preferably being free of paraffins (i.e. comprising less than 0.5% by weight of paraffins, preferably less than 0.1% by weight of paraffins), the percentages being given relative to the total weight of the olefinic feedstock.

[0048] Another preferred olefinic feedstock is a C3 olefinic cut, preferably comprising at least 90% by weight of propylene, preferably at least 98% by weight of propylene. It may comprise propane, preferably up to 2% by weight of propane.

[0049] Preferably, the olefinic feedstock is at least partly, very advantageously entirely, bio-sourced, in order to produce bio-sourced recoverable products. The C3 to C6 olefinic feedstock, preferably C3 and / or C4, may in particular come from a Fischer Tropsch unit, from a unit for producing olefins from methanol and / or from a unit for dehydrating alcohols, for example isobutanol, in particular from biomass, for example from the fermentation of sugars.

[0050] The olefinic feedstock may also come from a conventional unit. In this case, it is preferably used in a mixture with feedstocks of bio-sourced origin, preferably in weight proportions between a conventional olefinic feedstock and a bio-sourced olefinic feedstock of between 90:10 and 10:90, preferably between 80:20 and 20:80. Preferably, a conventional olefinic feedstock comes from a steam cracking unit, a fluid catalytic cracking unit (FCC), a selective hydrogenation unit for diolefins (called a SHU unit), or a paraffin dehydrogenation unit, pure or in a mixture and / or any other unit leading to the production of light olefins.

[0051] The olefinic feedstock treated in the process according to the invention can advantageously undergo a pretreatment step before being sent to step a) of oligomerization. Such a pretreatment step makes it possible to eliminate any compound which could cause poisoning of the oligomerization catalysts, in particular basic nitrogen compounds, water, sulfur derivatives, basic nitrogen derivatives.

[0052] Preferably, the olefinic feedstock is free of sulfur or sulfur compounds, i.e. it comprises a content of less than or equal to 20 ppm by weight, preferably less than or equal to 12 ppm by weight, preferably less than or equal to 10 ppm by weight of sulfur relative to the weight of the olefinic feedstock, making it possible to avoid or at least limit the poisoning of the oligomerization catalyst of step a). If the olefinic feedstock contains sulfur (i.e. more than 20 ppm by weight), the process advantageously comprises a step of pretreatment of the olefinic feedstock, located upstream of the oligomerization step a), preferably using an adsorption section and / or a water washing section and / or a dedicated hydrotreatment section, thus making it possible to protect the oligomerization catalyst of step a).

[0053] Preferably, the feedstock of the process according to the invention is free of nitrogen or nitrogen compounds, i.e. it comprises a content of less than or equal to 0.1 ppm by weight of nitrogen element relative to the total weight of the olefinic feedstock, making it possible to avoid or at least limit the poisoning of the oligomerization catalyst of step a). If the olefinic feedstock contains nitrogen, the process advantageously comprises a step of pretreatment of the olefinic feedstock, located upstream of step a) of oligomerization, preferably implementing an adsorption and / or water washing and / or hydrotreatment section, thus making it possible to protect the oligomerization catalyst of step a).

[0054] Preferably, the olefinic feedstock treated by the process according to the invention is free of butadiene, in particular 1,3-butadiene, i.e. comprises a content of less than or equal to 0.1% by weight, preferably less than or equal to 500 ppm by weight of butadiene, in particular 1,3-butadiene, relative to the total weight of the olefinic feedstock, which makes it possible to protect the oligomerization catalyst. If the olefinic feedstock contains butadiene, in particular 1,3-butadiene 1,3-butadiene, the process advantageously comprises a step of pretreatment of the olefinic feedstock, located upstream of step a) of oligomerization, preferably implementing a selective hydrogenation section.

[0055] According to a particular embodiment of the invention, the process may comprise an optional step of separation of the olefinic feedstock, advantageously located upstream of step a) of oligomerization, in order to at least partially separate the C5 and C6 compounds present in said olefinic feedstock. This optional separation step thus makes it possible to produce a fraction comprising the C5 and C6 compounds possibly present in the feedstock and at least one fraction comprising the C3 and C4 compounds. A person skilled in the art can adjust the separation so as to push the fractionation more or less and separate the fraction comprising the C3 and C4 compounds into a C3 fraction (in particular enriched in C3, in particular in propylene) and a C4 fraction (in particular enriched in C4, in particular in isobutene and / or in n-butenes). Thus, this optional separation step makes it possible to concentrate the feedstock in compounds, in particular olefinic compounds, in C3 and / or C4.The fraction comprising the C3 and C4 compounds, the C3 fraction or the C4 fraction is then advantageously sent to oligomerization step a), preferably directly. The fraction comprising the C5 and C6 compounds can be purged and recovered, for example by being integrated into a gasoline pool. According to a very particular embodiment of the invention, the process can comprise an optional step of separation of the olefinic feedstock, located upstream of oligomerization step a), to separate at least one C3 fraction and one C4 fraction, the two fractions, the C3 fraction and the C4 fraction, each undergoing steps a), b) and c) and optionally d) in parallel, and the heavy fractions can be remixed at the end of step c) or optionally at the end of hydrogenation step d).

[0056] Step a) of oligomerization

[0057] The process according to the invention comprises an oligomerization step, more particularly implementing a heterogeneous oligomerization reaction (or so-called heterogeneous catalysis), carried out in the presence of at least one oligomerization catalyst, to produce a reaction effluent comprising dimers, trimers and oligomers. Indeed, this oligomerization step a) makes it possible to obtain a mixture of hydrocarbons containing mono-olefins with a number of carbon atoms predominantly greater than or equal to 6, preferably greater than or equal to 8, preferably greater than or equal to 9, the term "predominantly" meaning here at least 90% by weight of C6+ hydrocarbons, preferably C8+, preferably C9+, relative to the weight of the mixture of hydrocarbons obtained. The mixture of hydrocarbons obtained may also comprise unreacted C3 to C6 olefins from the feedstock.

[0058] According to the invention, oligomerization step a) is fed at least with the olefinic feedstock, optionally pretreated and / or optionally separated. Preferably, oligomerization step a) is also fed by a first recycle comprising, preferably consisting of, at least a portion of the light fraction from step b), said first recycle is advantageously prepared and then transferred to step a) in step c). Preferably, oligomerization step a) is also fed by a second recycle comprising, preferably consisting of, at least a portion of the intermediate fraction from step b), said first recycle is advantageously prepared and then transferred to step a) in step c).Advantageously, oligomerization step a) is carried out, preferably in the liquid phase (i.e. the olefinic feedstock and the products formed are in liquid form under the temperature and pressure conditions used), in the presence of an oligomerization catalyst, preferably solid. Preferably, oligomerization step a) is carried out at a temperature between 20 and 500°C, at a pressure between 1.0 and 10 MPa, and with a WH preferably between 0.1 and 0.5 h'. 1 , preferably between 0.2 and 0.3 h' 1. The WH (or hourly volumetric flow rate) 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 atm, and the volume of oligomerization catalyst, in particular in operation (also called in operation). The temperature at which oligomerization step a) is carried out, between 20 and 500°C, advantageously corresponds to the temperature at the inlet of step a), preferably at the inlet of the reactor used in step a). The operating conditions of temperature, pressure and hourly volumetric flow rate can be adjusted by a person skilled in the art, in particular depending on the composition of the olefinic feedstock and the nature of the oligomerization catalyst used, to maximize the yields of middle distillates, in particular the yields of kerosene or diesel.

[0059] Advantageously, step a) uses at least one oligomerization catalyst, preferably between one and three different oligomerization catalysts, preferably one oligomerization catalyst. Any type of oligomerization catalyst known to those skilled in the art may be used as oligomerization catalyst in step a). More particularly, the oligomerization catalyst(s) of step a) may be any type of acid catalyst, in particular chosen from catalysts based on phosphoric acid impregnated on silica (supported phosphoric acid, known as SPA type), ion exchange resins, silica-aluminas and pure zeolites or zeolites supported on an alumina support.Preferably, the oligomerization catalyst(s) of step a) is (are) chosen from ion exchange resins, preferably cation exchange resins, silica-aluminas (i.e. comprising silica and alumina) and pure zeolites or zeolites supported on an alumina support.

[0060] When the oligomerization catalyst is chosen from SPA type catalysts, step a) is preferably carried out at a temperature, advantageously an inlet temperature, of between 100 and 300°C, preferably between 160 and 250°C, and at a pressure preferably of between 1.5 and 6.5 MPa, preferably between 1.5 and 4.0 MPa.

[0061] Zeolite-based catalysts are particularly suitable for producing linear or low-branched heavy olefins, which in particular allow the production of high-quality diesel, i.e., after hydrogenation, having a cetane number greater than 45. When the oligomerization catalyst is chosen from zeolite-based catalysts, step a) is preferably carried out at a temperature, advantageously an inlet temperature, between 150 and 500°C, preferably between 200 and 350°C, at a pressure preferably between 2.0 and 10.0 MPa, preferably between 3.0 and 6.5 MPa. Preferably, the zeolite-based oligomerization catalyst comprises at least one zeolite selected from the group consisting of aluminosilicate zeolites having an overall Si / Al atomic ratio greater than 10 and an 8, 10 or 12MR pore structure.Said zeolite is more preferably selected from the group consisting of zeolites of the structural type ferrierite, chabazite, Y and US-Y, ZSM-5, ZSM-12, NU-86, mordenite, ZSM-22, NU-10, ZBM-30, ZSM-11, ZSM-57, ZSM-35, IZM-2, ITQ-6 and IM-5, SAPO, and mixtures thereof. Very preferably, said zeolite is selected from the group consisting of zeolites ferrierite, ZSM-5, Mordenite, ZSM-22, and mixtures thereof. Even more preferably, the zeolite used is ZSM-5.

[0062] The ion exchange resin type catalysts are chosen for their good mechanical strength in the temperature and pressure ranges used in step a). When the oligomerization catalyst is chosen from ion exchange resins, step a) is preferably carried out at a temperature, advantageously an inlet temperature, between 20°C and 250°C, preferably between 70°C and 180°C, and at a pressure preferably between 2.0 and 10.0 MPa, preferably between 3.0 and 6.5 MPa. The ion exchange resin type catalysts, which are inexpensive and non-regenerable, have the advantage of having acceptable cycle times in a fixed bed operation because they are less sensitive to contaminants than zeolites and silica-aluminas.Very preferably, the ion exchange resin catalyst used in step a) is a copolymer of monovinyl aromatics and polyvinyl aromatics, preferably a copolymer of divinyl benzene and styrene, preferably sulfonated, in particular having a crosslinking rate of between 20 and 45%, preferably between 30 and 40%, and preferably equal to 35%, and an acid strength, representing the number of active sites of said resin, determined by assay, preferably by conductimetry, of the H+ ions released by the acid resin after exchange with Na+ ions (see ASTM D4266), of between 1 and 10 mmol H+ equivalent per gram and preferably of between 3.5 and 6 mmol H+ equivalent per gram. For example, the acid oligomerization catalyst, of the ion exchange resin type, used in step a), is a commercial acid resin sold under the reference TA801 by the company Axens.

[0063] Silica-alumina catalysts have the advantage of being regenerable so that, despite their higher cost than resins, substantial savings are made in terms of catalyst consumption. When the oligomerization catalyst is chosen from silica-aluminas, step a) is preferably carried out at a temperature between 20 and 300°C, preferably between 30 and 220°C, more preferably between 40 and 200°C, and at a pressure preferably between 1.5 and 6.5 MPa, preferably between 2.0 and 4.0 MPa. The temperature at which step a) of oligomerization in the presence of silica-alumina is carried out, preferably between 20 and 300°C, preferentially between 30 and 220°C, preferably between 40 and 200°C, advantageously corresponds to the temperature at the inlet of step a), preferably at the inlet of the reactor carried out in step a).The silica-alumina-based oligomerization catalyst(s) is (are) an amorphous catalyst(s) preferably consisting of an amorphous mineral material chosen from silica-aluminas and siliceous aluminas, and preferably from silica-aluminas. In the silica-alumina-based oligomerization catalyst used in step a), the SiCWAhOa mass ratio is between 0.1 and 10. Preferably, the silica-alumina present in the oligomerization catalyst used in oligomerization step a) has the following characteristics:.

[0064] - a mass content of silica (SiO2) of between 5% and 95% by weight, preferably between 10 and 80% by weight, more preferably between 20% and 80% by weight and even more preferably between 25% and 75% by weight, relative to the weight of the silica-alumina present in the oligomerization catalyst;

[0065] - a content of cationic impurities advantageously less than 0.1% by weight, preferably less than 0.05% by weight and even more preferably less than 0.025% by weight, relative to the weight of the silica-alumina present in the oligomerization catalyst, the content of cationic impurities being the total content of alkalis, in particular sodium.

[0066] The catalysts as prepared as described in patent FR2926812 may be suitable as oligomerization catalyst for step a).

[0067] According to a particular embodiment of the invention, the oligomerization catalyst used in step a) consists entirely of silica-alumina, that is to say it is free of any other element (that is to say it comprises less than 0.5% by weight, preferably less than 0.1% by weight of any element other than silica and alumina).

[0068] According to another particular embodiment of the invention, the oligomerization catalyst used in step a) may contain at least one metallic element chosen from the metals of groups IVB, VB, VIB and VIII. Among the metals of group IVB, titanium, zirconium and / or hafnium may be present in the oligomerization catalyst. Among the metals of group VB, vanadium, niobium and / or tantalum may be present in the oligomerization catalyst. Among the metals of group VIB, chromium, molybdenum and / or tungsten may be present in the oligomerization catalyst. Among the metals of group VIII, the metals belonging to the first line of metals of group VIII, namely iron, cobalt and nickel, are preferred. The content of these metals may be up to 10% by weight relative to the weight of the oligomerization catalyst.The oligomerization catalyst may optionally also contain silicon as a doping element deposited on the silica-alumina.

[0069] Very advantageously, oligomerization step a) is carried out in the presence of a silica-alumina-based catalyst at a temperature, advantageously at the inlet of step a), of between 20°C and 300°C, preferably between 25 and 220°C, preferably between 30°C and 200°C, and at a pressure of between 1.5 and 6.5 MPa, preferably from 2.0 to 4.0 MPa. According to a particular embodiment, when the olefinic feedstock is a C3 and / or C4 olefinic feedstock, oligomerization step a) is preferably carried out in the presence of a silica-alumina catalyst, at a temperature, advantageously at the inlet of step a), preferably between 25 and 200°C, preferably between 30 and 190°C, and a pressure between 1.5 and 6.5 MPa, preferably between 2.0 and 4.0 MPa, to preferentially produce kerosene.According to another particular embodiment, when the olefinic feedstock is a C3 and / or C4 olefinic feedstock, oligomerization step a) is preferably carried out in the presence of a silica-alumina catalyst, at a temperature, advantageously at the inlet of step a), preferably between 35 and 200°C, preferably between 40 and 190°C, and a pressure between 1.5 and 6.5 MPa, preferably between 2.0 and 4.0 MPa, to preferentially produce diesel.

[0070] Preferably, the oligomerization catalyst(s) of oligomerization step a) are in the form of spheres, pellets or extrudates, preferably extrudates. Very advantageously, the oligomerization catalyst(s) are in the form of extrudates with a diameter of between 0.5 and 5 mm and more particularly between 0.7 and 2.5 mm. The shapes of the extrudates are cylindrical (which may or may not be hollow), twisted cylindrical, multilobed (2, 3, 4 or 5 lobes for example) or in the form of rings. Cylindrical and multilobed shapes are preferably used, but any other shape may be used. In a very particular embodiment of the invention, the oligomerization step is carried out in the presence of a silica-alumina-based oligomerization catalyst, preferably consisting of silica-alumina, which is in the form of trilobed extrudates.

[0071] Advantageously, the oligomerization step may use one or more reactors, preferably at least two, preferably at least three reactors, and up to ten, preferably six reactors, arranged in parallel or in series, preferably in series, comprising one or more different oligomerization catalysts, preferably comprising the same oligomerization catalyst. The operating conditions as well as the oligomerization catalysts described above may be applied to any one of the reactors. In a very particular manner, the oligomerization step uses at least two or even at least three reactors in series.To ensure continuous operation of the oligomerization step, it is possible to have at least two reactors or reactor trains, one of the reactors (or one of the reactor trains) being in the reaction phase, the other reactor (or one of the reactor trains) being in the regeneration phase, if the level of impurities in the feed causes rapid deactivation of the catalyst. Optionally, the oligomerization step can also use heat exchangers upstream of the reactor(s) to heat the olefinic feed.

[0072] The oligomerization reaction is exothermic. At least part of the temperature increase linked to the exothermicity of the oligomerization reaction can be controlled by the first and second recycles (respectively comprising at least part of the light fraction corresponding at least in part to the unconverted feedstock and at least in part to the intermediate fraction), introduced in step a) of oligomerization.The exothermicity can also be controlled at least in part by diluting the olefinic feedstock by adding paraffins from a source external to the process, said paraffins being of the same molecular weight and / or heavier than the olefinic feedstock, said paraffins being aliphatic or cyclic, and / or by introducing an inert stream corresponding to a portion of the hydrogenated heavy fraction obtained at the end of step d), and in particular to a portion of the kerosene and / or diesel cut possibly separated in optional step e) or a mixture of the kerosene and / or diesel cuts and residue from optional step e). In the latter case, the inert stream preferably represents between 0 and 6 times the fresh olefinic feedstock by weight, preferably between 0.5 and 4 by weight.

[0073] The oligomerization step a) thus produces a reaction effluent which comprises dimers, trimers and oligomers. This reaction effluent is sent in whole or in part to a fractionation step b).

[0074] Step b) of splitting

[0075] The process according to the invention comprises a step of fractionating the reaction effluent obtained at the end of step a), into at least:

[0076] - a light fraction comprising at least part of the olefinic feedstock not converted in step a);

[0077] - an intermediate fraction comprising at least a portion, preferably all, of the dimers and trimers advantageously produced in step a); and

[0078] - a heavy fraction, comprising the oligomers present in the reaction effluent from step a), in particular olefinic compounds containing between 6 and 30, preferably between 9 and 25 carbon atoms, and more particularly between 9 and 16 carbon atoms in the case of kerosene or between 10 and 25 carbon atoms in the case of diesel.

[0079] The light fraction preferably comprises at least a portion, preferably all, of the olefinic feedstock not converted in step a). It therefore advantageously comprises C3 to C6 olefins, preferably C3 and / or C4 olefins, which have not been converted in step a). The light fraction may optionally also comprise compounds which do not react, i.e. which are not olefins, in particular paraffins already present in the fresh olefinic feedstock. The quantity of this light fraction depends in particular on the conversion of the olefinic feedstock per pass, from oligomerization step a). This fraction is advantageously recycled in whole or in part to step a); it in fact constitutes at least a portion of the first recycle prepared in step c).Optionally, part of this light fraction can be purged, continuously or discontinuously, in particular when the olefinic feedstock contains compounds that do not oligomerize, such as paraffins for example. In the case of purging, the purged stream can be upgraded to liquefied petroleum gas or LPG (Liquefied Petroleum Gas) for example. Optionally, the light fraction can include O1 to O2 compounds, possibly generated during step a) and resulting from cracking and recombination reactions.

[0080] Optionally, at the end of the fractionation step, a gaseous fraction may also be separated which comprises compounds from O1 to C2, possibly generated during step a) and resulting from cracking and recombination reactions. The gaseous fraction possibly separated in step b) is preferably purged (i.e. removed from the process) continuously or discontinuously, for example to be recovered.

[0081] The intermediate fraction preferably comprises at least a portion, preferably all, of the dimers and trimers advantageously produced in step a). The products it contains, in particular the dimers and trimers, are too light to be recovered as middle distillates, in particular kerosene or diesel. The intermediate fraction may also optionally contain unconverted olefins C5 to C6 if the olefinic feedstock contains C5 to C6 olefins. The intermediate fraction may also contain paraffins originating from the olefinic feedstock and boiling in the same ranges as the intermediate fraction. Preferably, the intermediate fraction is free of paraffins, i.e. comprises less than 0.5% by weight, preferably less than 0.1% by weight of paraffins relative to the total weight of the intermediate fraction.Preferably, the intermediate fraction comprises oligomers of olefins in O5+ and preferably has a T95 of less than 140°C, in particular less than 140°C in the case of kerosene production or less than 165°C, preferably less than 170°C in the case of diesel production. It can therefore also be called C5-140°C or C5-165°C (preferably C5-170°C). Optionally, at least a portion of the intermediate fraction can be recovered and removed from the process (i.e. purged) to be treated or directly recovered, in particular into gasoline. This possible purged portion of the intermediate fraction can undergo a hydrogenation step, in particular can be sent to step d) of the process or to a hydrogenation step distinct from the process according to the invention and operated, for example, under conditions similar to those described for step d), before being integrated into a gasoline pool.

[0082] The heavy fraction advantageously comprises the oligomers present in the reaction effluent from step a). Advantageously, it comprises, in particular, olefinic compounds containing between 6 and 30, preferably between 9 and 25 carbon atoms. Preferably, the heavy fraction has a T5 greater than or equal to 140°C, in particular greater than or equal to 140°C in the case of kerosene production or greater than or equal to 165°C, preferably greater than or equal to 170°C, in the case of diesel production. Preferably, the heavy fraction is composed of C9+ olefinic oligomers and very preferably boils between 140 and 300°C (also called the 140-300°C fraction) or at a temperature greater than or equal to 165°C, preferably greater than or equal to 170°C. According to a preferred embodiment of the invention, the heavy fraction may correspond to a kerosene fraction with a cutting point making it possible to reach a flash point greater than or equal to 38°C.According to another preferred embodiment of the invention, the heavy fraction may correspond to a diesel fraction with a cutting point making it possible to reach a flash point greater than or equal to 55°C.

[0083] Advantageously, fractionation step b) uses one or more distillation columns, preferably between one and three distillation columns.

[0084] Step c) of recycling

[0085] Step c) of recycling of the process according to the invention comprises:

[0086] - the preparation of a first recycle which comprises, preferably consists of, at least part of the light fraction,

[0087] - the preparation of a second recycle which comprises, preferably consists of, at least part of the intermediate fraction, resulting from fractionation step b),

[0088] - the transfer of the first recycle to step a) of oligomerization, and

[0089] - the transfer of the second recycle to step a).

[0090] Advantageously, all or part of the light fraction from separation step b) constitutes the first recycle which is then recycled to oligomerization step a), preferably directly at the inlet of step a) and preferably upstream of the exchangers possibly implemented in step a) upstream of the reactors to heat the olefinic feedstock. The first recycle advantageously makes it possible to maximize the overall conversion and also to manage at least part of the exothermicity of the oligomerization reaction in step a). Preferably, the first recycle, which corresponds to the part of the light fraction recycled to a), represents a quantity such that the weight ratio between the first recycle and the olefinic feedstock, which feeds the oligomerization step a), is between 0.3 and 1.5, preferably between 0.5 and 1.2.

[0091] Advantageously, all or part of the intermediate fraction from separation step b) constitutes the second recycle which is then recycled to step a), preferably directly and in particular upstream of the exchangers possibly implemented upstream of the reactors in step a). Preferably, the intermediate fraction is not cooled before being transferred in whole or in part, as a second recycle, to oligomerization step a), which contributes in particular to the preheating of the olefinic feedstock at the inlet of step a) by simple mixing. Preferably, the second recycle, which corresponds to the part of the intermediate fraction recycled to a), represents a quantity such that the weight ratio between the second recycle and the olefinic feedstock, which feeds the oligomerization step a), is between 0.5 and 10.0, preferably between 1.0 and 5.0, preferably between 1.0 and 4.0.

[0092] The recycling of at least part of these two fractions, the light fraction and the intermediate fraction, in particular the recycling of at least part of the intermediate fraction, makes it possible to increase the overall conversion and to maximize the yield of targeted products, in particular middle distillates, more particularly kerosene or diesel, by strongly favoring selectivity towards the targeted products, in particular kerosene or diesel.

[0093] Preferably, the heavy fraction comprising the oligomers and which results from fractionation step b) is not recycled, and in particular is not recycled to oligomerization step a). Indeed, the heavy fraction comprises heavy olefinic compounds, in particular containing between 6 and 30, preferably between 9 and 25 carbon atoms. However, these compounds are known to have a non-negligible reactivity with respect to oligomerization. Thus, if such olefinic compounds were recycled to oligomerization step a), unwanted very heavy compounds could be generated, lowering the selectivity and therefore reducing the yields of middle distillates. The process for preparing middle distillates according to the invention is therefore preferably devoid of recycling of the heavy fraction obtained in step b).In particular, in the case of kerosene production, the process is advantageously devoid of recycling of the heavy fraction whose T5 is greater than or equal to 140°C. In the case of diesel production, the process is advantageously devoid of recycling of the heavy fraction whose T5 is greater than or equal to 165°C, preferably greater than or equal to 170°C.According to a first particular embodiment of the invention, the olefinic feedstock is composed essentially of isobutene, preferably at least 90% by weight of isobutene and very advantageously less than 0.5% by weight, or even less than 0.1% by weight of paraffins such as butane, relative to the total weight of the olefinic feedstock, and the oligomerization step a) is advantageously carried out in the presence of silica-alumina, preferably at a temperature between 20 and 100°C, preferably between 30 and 90°C and very preferably between 35°C and 85°C, at a pressure preferably between 1.5 and 6.5 MPa, preferably between 2.0 and 4.0 MPa, and a VVH preferably between 0.20 and 0.30 h'. 1 , preferably between 0.20 and 0.25 h -1. In this embodiment, a stream of inerts (i.e. a stream of compounds inert to the oligomerization reaction, i.e. which do not react under the operating conditions of step a)), preferably composed of at least in part of a portion of the hydrogenated heavy fraction obtained at the end of hydrogenation step d), is preferably used to feed step a) so as to control the exothermicity of the oligomerization reaction and therefore the reactivity. According to this first particular embodiment, the intermediate fraction separated in step b) advantageously has a T95 of less than 140°C; the heavy fraction has a T5 greater than or equal to 140°C and preferably boils between 140 and 300°C.According to this first particular embodiment, the second recycle prepared in step c) and which preferably consists of at least a part, preferably all, of the intermediate fraction separated in b), represents a weight quantity such that the weight ratio between the second recycle and the olefinic feed at the inlet of step a) is between 1.0 and 5.0, preferably between 1.5 and 2.5, the second recycle being sent to the oligomerization step a).

[0094] According to a second particular embodiment of the invention, the olefinic feedstock is composed essentially of propylene, preferably at least 90% by weight of propylene, optionally up to 10% by weight of butenes and very advantageously less than 0.5% by weight, or even less than 0.1% by weight of paraffins, relative to the total weight of the olefinic feedstock, and the oligomerization step a) is advantageously carried out in the presence of silica-alumina, preferably at a temperature between 100 and 180°C, preferably between 110 and 170°C, preferably between 115 and 165°C, at a pressure preferably between 1.5 and 6.5 MPa, preferably between 2.0 and 4.0 MPa, and a VVH preferably between 0.20 and 0.30 h' 1 , preferably between 0.20 and 0.25 h' 1. In this particular embodiment, a flow of inerts (i.e. a flow of compounds inert to the oligomerization reaction, i.e. which do not react under the operating conditions of step a)), preferably composed of at least in part of a portion of the hydrogenated heavy fraction obtained at the end of hydrogenation step d), is preferably used to feed step a) so as to control the exothermicity of the oligomerization reaction and therefore the reactivity. According to this second particular embodiment, the intermediate fraction separated in step b) advantageously has a T95 of less than 140°C; the heavy fraction has a T5 greater than or equal to 140°C and preferably boils between 140 and 300°C.According to this second particular embodiment, the second recycle prepared in step c) and which preferably consists of at least a part, preferably all, of the intermediate fraction separated in b), represents a weight quantity such that the weight ratio between the second recycle and the olefinic feed at the inlet of step a) is between 1.0 and 5.0, preferably between 1.5 and 2.0, the second recycle being sent to the oligomerization step a).

[0095] According to a third particular embodiment of the invention, the olefinic feedstock is composed essentially of n-butenes (but-1-enes and but-2-enes), preferably of at least 98% by weight of butenes and very advantageously less than 0.5% by weight of paraffins such as butane, relative to the total weight of the olefinic feedstock, and the oligomerization step a) is advantageously carried out in the presence of silica-alumina, preferably at a temperature between 130 and 200°C, preferably between 140 and 190°C, preferably between 145 and 185°C, at a pressure preferably between 1.5 and 6.5 MPa, preferably between 2.0 and 4.0 MPa, and a WH preferably between 0.20 and 0.30 h' 1 , preferably between 0.20 and 0.25 h -1. Optionally, a stream of inerts (i.e. a stream of compounds inert to the oligomerization reaction, i.e. which do not react under the operating conditions of step a)), preferably composed at least in part of a portion of the hydrogenated heavy fraction obtained at the end of hydrogenation step d), may be used to feed step a) so as to control the exothermicity of the oligomerization reaction and therefore the reactivity. According to this third particular embodiment, the intermediate fraction separated in step b) advantageously has a T95 of less than 140°C; the heavy fraction has a T5 greater than or equal to 140°C and preferably boils between 140 and 300°C.According to this third particular embodiment, the second recycle prepared in step c) and which preferably consists of at least a part, preferably all, of the intermediate fraction separated in b), represents a weight quantity such that the weight ratio between the second recycle and the olefinic feed at the inlet of step a) is between 1.0 and 5.0, preferably between 3.5 and 4.0, the second recycle being sent to the oligomerization step a).

[0096] According to a fourth particular embodiment of the invention, the olefinic feedstock is composed essentially of isobutene, preferably at least 90% by weight of isobutene and very advantageously less than 0.5% by weight, or even less than 0.1% by weight of paraffins such as butane, relative to the total weight of the olefinic feedstock, and the oligomerization step a) is advantageously carried out in the presence of silica-alumina, preferably at a temperature between 30 and 100°C, preferably between 40 and 90°C, at a pressure preferably between 1.5 and 6.5 MPa, preferably between 2.0 and 4.0 MPa, and a WH preferably between 0.20 and 0.30 h -1 , preferably between 0.25 and 0.30 h' 1. In this embodiment, a stream of inert materials, preferably composed of at least in part of a portion of the hydrogenated heavy fraction obtained at the end of hydrogenation step d), is preferably used to feed step a) so as to control the exothermicity of the oligomerization reaction. According to this fourth particular embodiment, the intermediate fraction separated in step b) advantageously has a T95 of less than 165°C; the heavy fraction has a T5 of greater than or equal to 165°C. According to this fourth particular embodiment, the second recycle which preferably consists of at least a part, preferably all, of the intermediate fraction separated in b), represents a weight quantity such that the weight ratio between the second recycle and the olefinic feed at the inlet of step a) is between 1.0 and 4.0, preferably between 1.0 and 2.0, the second recycle being sent to the oligomerization step a).

[0097] According to a fifth particular embodiment of the invention, the olefinic feedstock is composed essentially of propylene, preferably at least 90% by weight of propylene, optionally up to 10% by weight of butenes and very advantageously less than 0.5% by weight, or even less than 0.1% by weight of paraffins, relative to the total weight of the olefinic feedstock, and the oligomerization step a) is advantageously carried out in the presence of silica-alumina, preferably at a temperature between 110 and 180°C, preferably between 120 and 170°C, at a pressure preferably between 1.5 and 6.5 MPa, preferably between 2.0 and 4.0 MPa, and a WH preferably between 0.20 and 0.30 h' 1 , preferably between 0.25 and 0.30 h" 1. In this embodiment, a stream of inert materials, preferably composed of at least in part of a portion of the hydrogenated heavy fraction obtained at the end of hydrogenation step d), is preferably used to feed step a) so as to control the exothermicity of the oligomerization reaction. According to this fifth particular embodiment, the intermediate fraction separated in step b) advantageously has a T95 of less than 165°C; the heavy fraction has a T5 of greater than or equal to 165°C. According to this fifth particular embodiment, the second recycle which preferably consists of at least a part, preferably all, of the intermediate fraction separated in b), represents a weight quantity such that the weight ratio between the second recycle and the olefinic feed at the inlet of step a) is between 1.0 and 4.0, preferably between 1.0 and 1.5, the second recycle being sent to the oligomerization step a).

[0098] According to another particular embodiment of the invention, the olefinic feedstock is composed essentially of n-butenes (but-1-enes and but-2-enes), preferably of at least 98% by weight of butenes and very advantageously less than 0.5% by weight of paraffins such as butane, relative to the total weight of the olefinic feedstock, and the oligomerization step a) is advantageously carried out in the presence of silica-alumina, preferably at a temperature between 140 and 200°C, preferably between 145 and 190°C, at a pressure preferably between 1.5 and 6.5 MPa, preferably between 2.0 and 4.0 MPa, and a VVH preferably between 0.20 and 0.30 h' 1 , preferably between 0.25 and 0.30 h' 1. In this embodiment, a stream of inert materials, preferably composed of at least in part of a portion of the hydrogenated heavy fraction obtained at the end of hydrogenation step d), is preferably used to feed step a) so as to control the exothermicity of the oligomerization reaction. According to this particular embodiment, the intermediate fraction separated in step b) advantageously has a T95 of less than 165°C; the heavy fraction has a T5 of greater than or equal to 165°C. According to this particular embodiment, the second recycle which preferably consists of at least a part, preferably all, of the intermediate fraction separated in b), represents a weight quantity such that the weight ratio between the second recycle and the olefinic feed at the inlet of step a) is between 1.0 and 4.0, preferably between 3.0 and 3.5, the second recycle being sent to the oligomerization step a).

[0099] In these six particular embodiments of the invention, the temperature at which step a) of oligomerization in the presence of silica-alumina is carried out advantageously corresponds to the temperature at the inlet of step a), preferably at the inlet of the reactor carried out in step a).

[0100] Step d) hydrogenation

[0101] The process according to the invention comprises a step of hydrogenation of at least a part, preferably all, of the heavy fraction separated in step b) in the presence of hydrogen, to obtain a hydrogenated heavy fraction.

[0102] The hydrogenation step makes it possible to saturate the olefinic bonds of at least a portion, preferably all, of the heavy fraction from step c), in order to produce paraffins which can be incorporated directly into fuel pools, in particular the kerosene pool (or jet pool) and in a very particular manner into the SPK jet pool (SPK for the English acronym for “Synthetic Paraffinic Kerosene”) which meets the specifications of standard ASTM D7566, Annex 5, or the diesel pool and in a very particular manner into the diesel pool which meets the specifications of European standard 15940. Step d) of hydrogenation of the unsaturated compounds makes it possible in particular to significantly improve the smoke point of the heavy fraction, and in particular of the middle distillates produced, and / or the elimination of any sulfur and / or nitrogen impurities.Preferably, hydrogenation step d) is carried out in the presence of a catalyst preferably comprising at least one metal from group VIII, in particular nickel, palladium or platinum, deposited on an inert support, such as for example silica or alumina. Preferably, the hydrogenation step is carried out in the presence of a catalyst based on palladium or nickel on an alumina support. However, any other catalyst making it possible to hydrogenate the product of the oligomerization step, and in particular the heavy fraction with in particular C9+ olefins, can be used. For example, a catalyst chosen from catalysts of the NiMo, CoMo, NiCoMo on alumina type, and mixtures thereof, can be used.

[0103] Hydrogenation step d) is carried out, preferably in the liquid phase, advantageously at a pressure of between 0.5 and 5.0 MPa, preferably between 1.0 and 5.0 MPa, and preferably at a temperature of between 50 and 300°C, preferably between 60 and 200°C, in the presence of hydrogen preferably at a content of between 0.5 and 3% by weight relative to the weight of the part of the heavy fraction feeding step d).

[0104] Preferably, during step d), a hydrogenation rate of at least 90%, preferably greater than or equal to 95%, preferably greater than or equal to 99%, is achieved.

[0105] Advantageously, the hydrogenated heavy fraction comprises, preferably consists of, and thus at least partly in middle distillates, and more particularly in a kerosene cut meeting very advantageously the kerosene specifications of the standards in force, in particular the kerosene specifications of the ASTM D7566 standard, in particular of the ASTM D7566 Annex 5 standard, and / or a diesel cut meeting very advantageously the diesel specifications of the standards in force, in particular the diesel specifications of the European standard 15940. The hydrogenated heavy fraction obtained at the end of step d) may optionally in whole or in part be sent to an optional separation step e).

[0106] Optionally, a portion of the hydrogenated heavy fraction obtained at the end of step d) is separated to constitute an inert stream which can then be recycled to step a) to help control the exothermicity of the oligomerization reaction in step a), in parallel with the first recycle. Preferably, the weight quantity of the inert stream recycled to step a) represents from 0 to 6 times, preferably from 0.5 to 4 times by weight of the weight of the fresh olefinic feedstock.

[0107] Optional separation step e)

[0108] The process according to the invention comprises a step of separating the hydrogenated heavy fraction, to obtain at least one middle distillate cut, in particular at least one kerosene cut and / or one diesel fraction and optionally one gasoline fraction. In a very particular manner, a kerosene base is separated in step e) and this kerosene base preferably has a final evaporation temperature between 140 and 300°C and advantageously a flash point greater than or equal to 38°C; the separated diesel cut preferably has an evaporation temperature greater than or equal to 165°C, preferably greater than or equal to 170°C, and advantageously a flash point of at least 55°C.

[0109] According to a particular embodiment, the optional separation step e) advantageously makes it possible to obtain:

[0110] - a kerosene cut whose lower (initial) distillation point is preferably at least 140°C and very preferably at least 150°C;

[0111] - a gasoline cut whose upper (final) distillation point is preferably less than 140°C.

[0112] In this embodiment, the production of kerosene and gasoline is maximized.

[0113] According to another particular embodiment, the optional separation step e) advantageously makes it possible to obtain:

[0114] - a top cut which corresponds to a gasoline advantageously comprising hydrocarbons having a number of carbon atoms between 5 and 10;

[0115] - an intermediate cut advantageously comprising hydrocarbons having a number of carbon atoms between 9 and 24, preferably between 9 and 16, and which constitutes a kerosene cut meeting commercial specifications,

[0116] - a so-called residue cut, with an initial boiling point above 300°C, the final cut sought being kerosene, and which advantageously joins the diesel or fuel pool.

[0117] According to another particular embodiment, the optional separation step e) advantageously makes it possible to obtain:

[0118] - a kerosene cut whose lower (initial) distillation point is preferably at least 140°C and very preferably at least 150°C, and whose final distillation point is less than or equal to 300°C, which constitutes a kerosene base meeting commercial specifications

[0119] - optionally, a so-called residue cut, with an initial boiling point above 300°C which advantageously joins the diesel or fuel pool.

[0120] In this embodiment, kerosene production is maximized.

[0121] According to yet another particular embodiment, the optional separation step e) advantageously makes it possible to obtain:

[0122] - a top cut which corresponds to a gasoline advantageously comprising hydrocarbons having a number of carbon atoms between 5 and 10; - an intermediate cut advantageously comprising hydrocarbons having a number of carbon atoms between 10 and 24, and which constitutes a diesel cut meeting commercial specifications.

[0123] In this embodiment, diesel production is maximized.

[0124] Thus, the process according to the invention makes it possible to improve the selectivity of a process for the oligomerization of light olefins towards middle distillates, in particular kerosene and / or diesel, and therefore to maximize the yields of middle distillates, while having an optimal overall conversion of the olefinic feedstock. The process according to the invention is a particularly flexible process since the person skilled in the art can adapt the selectivity of the oligomerization and the separation of the effluents in order to maximize the production of kerosene and / or diesel, possibly even to the point of producing only diesel or only kerosene.

[0125] The following examples and figures illustrate the invention, in particular particular embodiments of the invention, without limiting its scope.

[0126] List of figures

[0127] Figure 1 schematically represents an implementation of the method according to the invention.

[0128] A feed (1) rich in C3 and C4 olefins is treated in an oligomerization section (a). The reaction effluent 5 is sent to a separation stage (b) and separated in a series of columns to produce:

[0129] - a stream 4 rich in C3 to C4 compounds comprising the olefins of the feed which have not been converted as well as any constituents of the feed which do not react (for example paraffins) in this boiling range;

[0130] - a stream 3 which includes the dimers and trimers, produced during oligomerization but which are too light to be recovered as middle distillates;

[0131] - a flow 9 recovered at the bottom of the last column and corresponding to the heavy fraction.

[0132] Stream 4 is at least partly recycled to the oligomerization inlet (a). Part of stream (4) can be purged or recovered in another unit (stream 6), either continuously or from time to time, depending on the nature of the feedstock.

[0133] Stream 3 is sent to the oligomerization step, at least in part, preferably in full, as oligomerization inlet (a). Part of stream 3 can also be sent for recovery in a gasoline pool (stream 8). Stream 8 can optionally be sent to hydrogenation c) to then be recovered with stream 11.

[0134] Stream 9 is sent to a hydrogenation section (c). The hydrogenated effluent 10 is then separated in a section (d), into:

[0135] - a flow 11 which is sent to the gasoline pool; - a flow 13 which is recovered as kerosene;

[0136] - a stream 14 made up of the heaviest compounds produced during the process and which can be recovered as diesel.

[0137] An optional stream 2 consisting for example of a kerosene + diesel mixture (stream 12) is sent to oligomerization step a). It corresponds to a stream of inerts used to control the exothermicity of the reaction in the reactors of oligomerization section a).

[0138] Examples

[0139] Example 1 (in accordance with the invention)

[0140] A C4 olefinic hydrocarbon feedstock, comprising 24.8% by weight of 1-butene, 75% by weight of 2-butenes and 0.2% by weight of n-butane, is oligomerized according to the method described in Figure 1, in the presence of a silica-alumina catalyst (commercial catalyst IP 811 from Axens), at a temperature between 140 and 190°C, a pressure of 3.5 MPa and at a WH of 0.3 h' 1The oligomerization reaction is carried out in 3 reactors in series, with an intermediate exchanger between each reactor, allowing cooling before entering the next reactor.

[0141] The reaction effluent obtained at the end of the oligomerization step is separated by distillation into three cuts:

[0142] 1) a C4- cut, comprising the unreacted feedstock and corresponding to approximately 17% by weight of the reaction effluent, said C4 cut being entirely returned to the oligomerization stage (and which corresponds to a weight ratio of the C4- cut relative to the fresh C4 olefinic hydrocarbon feedstock of between 0.8 and 1.0);

[0143] 2) a C5-140°C cut, constituting the intermediate fraction and corresponding to approximately 64% by weight of the reaction effluent, said C5-140°C cut being entirely recycled at the inlet of the oligomerization stage so that the weight ratio of the C5-140°C cut relative to the fresh C4 olefinic hydrocarbon feedstock is equal to 3.6;

[0144] 3) a 140-300°C cut, corresponding to 19% by weight of the reaction effluent, which is sent to hydrogenation.

[0145] The conversion of the olefinic feedstock is greater than or equal to 90% by weight.

[0146] Hydrogenation is carried out in the presence of a nickel catalyst on an alumina support, at 180°C under 3.0 MPa of hydrogen with a WH of 0.5 h -1 and a hydrogen flow rate of 50 NL / h.

[0147] The olefin content observed after hydrogenation is very low (bromine number < 0.8 g / 100 g), i.e. a high hydrogenation rate (greater than 99%). The hydrogenation effluent is then sent to a distillation section where it is separated into three cuts:

[0148] - a light gasoline cut whose upper distillation point is less than 140°C with a yield of 7% by weight relative to the weight of the olefins in the initial C4 olefinic hydrocarbon feedstock and;

[0149] - a kerosene cut, with a distillation range of 140°C-300°C, with a yield of 86% by weight relative to the weight of the olefins in the C4 olefinic hydrocarbon feedstock;

[0150] - a 300+ residue corresponding to 7% by weight relative to the weight of the olefins in the C4 olefinic hydrocarbon feedstock.

[0151] Example 2 (in accordance with the invention)

[0152] A bio-sourced C4 olefinic hydrocarbon feedstock (from the dehydration of isobutanol obtained by fermentation of sugars), comprising 94.5% by weight of isobutene and

[0153] 5.5% by weight of isobutane is oligomerized in the presence of a silica-alumina catalyst (commercial catalyst IP 811 from Axens), at a temperature between 30 and 90°C, a pressure of 3.5 MPa and a WH of 0.3 h' 1 The oligomerization reaction is carried out in 3 reactors in series, with an intermediate exchanger between each reactor, allowing cooling before entering the next reactor. Part of the hydrogenated finished product is recycled to step a) of oligomerization, in order to control the exotherm in the reactors. This recycle represents

[0154] 3.5 times by weight the weight quantity of fresh olefinic feedstock.

[0155] The reaction effluent obtained at the end of the oligomerization step is separated by distillation into four cuts:

[0156] 1) a C4- cut, comprising the unreacted feedstock and corresponding to approximately 7.1% by weight of the reaction effluent, said C4- cut being entirely returned to the oligomerization stage (corresponding to a weight ratio of the C4 cut relative to the fresh C4 olefinic hydrocarbon feedstock of between 0.4 and 0.6);

[0157] 2) a C5-140°C cut, constituting the intermediate fraction and corresponding to approximately 31.4% by weight of the reaction effluent, said C5-140°C cut being entirely recycled at the inlet of the oligomerization stage so that the weight ratio of the C5-140°C cut relative to the fresh C4 olefinic hydrocarbon feedstock is equal to 2.0;

[0158] 3) a 140-300°C cut, corresponding to approximately 61.5% by weight of the reaction effluent and which is sent to hydrogenation.

[0159] The conversion of the olefinic feedstock is greater than or equal to 90% by weight. The hydrogenation of the 140-300°C cut is carried out in the presence of a nickel catalyst on an alumina support, at 180°C under 3.0 MPa of hydrogen with a WH of 0.5 h -1 and a hydrogen flow rate of 50 NL / h.

[0160] The olefin rate observed after hydrogenation is very low (bromine number < 0.8 g / 100g), i.e. a high hydrogenation rate (greater than 99%).

[0161] The hydrogenation effluent is then sent to a distillation section where it is separated into three cuts:

[0162] - a light gasoline cut whose upper distillation point is less than 140°C with a yield of 6% by weight relative to the weight of the olefins in the initial C4 olefinic hydrocarbon feedstock and;

[0163] - a kerosene cut, with a distillation range of 140°C-300°C, with a yield of 89% by weight relative to the weight of the olefins in the C4 olefinic hydrocarbon feedstock;

[0164] - a 300+ residue corresponding to 5% by weight relative to the weight of the olefins in the C4 olefinic hydrocarbon feedstock.

[0165] Example 3 (not in accordance with the invention)

[0166] A C4 olefinic hydrocarbon feedstock similar to that treated by the process described in Example 1 is treated in Example 3: it comprises 24.8% by weight of 1-butene, 75% by weight of 2-butenes and 0.2% by weight of n-butane.

[0167] The C4 olefinic hydrocarbon feedstock is oligomerized under operating conditions similar to those of the process described in Example 1. However, the C5-140°C cut of the reaction effluent is not recycled to the inlet of the oligomerization stage.

[0168] The reaction effluent obtained at the end of the oligomerization step is separated by distillation into three cuts:

[0169] 1) a C4- cut, comprising the unreacted feedstock and corresponding to approximately 60.1% by weight of the reaction effluent, said C4 cut being partly returned to the oligomerization stage such that the recycle rate corresponds to a weight ratio of the C4- cut relative to the fresh C4 olefinic hydrocarbon feedstock equal to 0.5);

[0170] 2) a C5-140°C cut, constituting the intermediate fraction and corresponding to approximately 20.1% by weight of the reaction effluent;

[0171] 3) a 140+ cut, corresponding to 19.8% by weight of the reaction effluent, which is sent to hydrogenation. The conversion of the olefinic C4s of the feedstock is approximately 85% by weight. The conversion of the olefinic feedstock to C4 (85% by weight) is lower than that obtained with the process described in Example 1 (at least 90% by weight).

[0172] Hydrogenation is carried out under the same conditions as example 1. The hydrogenation effluent is then sent to a distillation section where it is separated into three cuts:

[0173] - a light gasoline cut with an upper distillation point below 40°C with a yield of 40% by weight relative to the olefins of the initial C4 olefinic hydrocarbon feedstock and; - a kerosene cut, with a distillation range of 140°C-300°C, with a yield of 40% by weight relative to the olefins of the initial C4 olefinic hydrocarbon feedstock.

[0174] The kerosene yield (40%) is lower than that obtained with the process described in example 1 (86%).

Claims

DEPCT681. Process for the preparation of intermediate distillate products from process feeds containing olefins, including monoolefins with between 3 and 6 carbon atoms, in which the process consists of: a) an oligomerization step which is fed with at least olefin-containing process feeds, first and second recycling, and which is operated in the presence of at least one oligomerization catalyst, at temperatures between 20 and 500 °C, pressures between 1.0 and 10 MPa and HSV between 0.1 and 0.5 hours to produce the reaction release product consisting of dimers, timers, and oligomers; b) the fractional separation step of the reaction release product obtained at the end of step a), to at least: - a light fraction consisting of at least a fraction of the process feed containing olefins not converted in step a); - a medium fraction consisting of at least a fraction of the dimers and timers produced in step a); and - a heavy fraction consisting of oligomers; c) the recycling step, consisting of: the first recycling preparation consisting of at least a fraction of the light fraction; the second recycling preparation consisting of at least a fraction of the medium fraction; and the transfer of the first and second recycling to the oligomerization step a); d) the step for hydrogenating at least a fraction of the heavy fraction separated in step b) when hydrogen is present, so that the hydrogenated heavy fraction consists of the medium fraction product.

2. The process according to claim 1, in which the process feed contains olefins consisting of monoolefins with 3 and / or 4 carbon atoms. 3.

4. A process pursuant to one of the preceding claims, in which the first recycled feed in step a) is in a weight ratio between 0.3 and 1.5, preferably between 0.5 and 1.2, relative to the olefin-based process feed.

5. A process pursuant to one of the preceding claims, in which the second recycled feed in step a) is in a weight ratio between 0.5 and 10.0, preferably between 1.0 and 5.0, and preferably between 1.0 and 4.0, relative to the olefin-based process feed.

6. A process pursuant to one of the preceding claims, in which the oligomerization catalyst in step a) is selected from a phosphoric acid-based catalyst impregnated with silica, ion-exchange resin, silica-alumina and pure zeolite, or zeolite supported on alumina. 7.A process pursuant to one of the preceding claims, in which the oligomerization step a) is performed in the presence of a silica-alumina-based catalyst and at a temperature between 20°C and 300°C, preferably between 25 and 220°C, and ideally between 30°C and 200°C.

8. A process pursuant to one of the preceding claims, in which the oligomerization step a) is performed at a pressure between 1.5 and 6.5 MPa, preferably between 2.0 and 4.0 MPa.

9. A process pursuant to one of the preceding claims, in which the oligomerization step a) is operated at an HSV between 0.2 and 0.3 per hour.

10. A process pursuant to one of the preceding claims, which also includes step e) of hydrogenated heavy fraction separation obtained from step d), to separate at least one fraction into intermediate distillate products, particularly the kerosene fraction and / or the gas fraction;

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