Improved method for producing middle distillates by oligomerization of olefinic feedstocks - Patents.com

Abstract

The present invention relates to a method for preparing a middle distillate from an olefinic feedstock, comprising the steps of: a) an oligomerization step, in which at least an olefinic feedstock, a first recycle material and a second recycle material are fed, in the presence of at least one oligomerization catalyst, to produce a reaction effluent comprising dimers, trimers and oligomers; b) a fractionation step of the reaction effluent to give: a light fraction, comprising at least a portion of the unconverted olefinic feedstock; an intermediate fraction, comprising at least a portion of the dimers and trimers; and a heavy fraction, comprising oligomers; c) a recycling step, comprising preparing a first recycle material comprising at least a portion of the light fraction; preparing a second recycle material comprising at least a portion of the intermediate fraction; and transferring the first recycle material and the second recycle material to step a); d) a hydrogenation step of at least a portion of the heavy fraction.

Description

[Technical field]

[0001] The present invention relates to a process for the production of middle distillates, in particular kerosene and / or gas oil, by heterogeneous oligomerization of an olefinic feedstock, in particular a bio-based olefinic feedstock, which meets the specifications in force, in particular those laid down in ASTM D1655 or ASTM D7566 for kerosene and those laid down in standard ASTM D975 or European standard 15940 for gas oil. [Background technology]

[0002] Airlines undertake carbon-neutral growth, especially in commercial aviation, from 2021, with American airlines setting a target of reducing CO2 emissions by 50% relative to 2005 levels. However, improvements in aircraft and engine efficiency are proving not to be enough to achieve carbon neutrality. Sustainable aviation fuels (or SAF) therefore appear to be key to achieving this goal.

[0003] It therefore appears necessary to develop processes for producing synthetic kerosene, preferentially from bio-based feedstocks.

[0004] Patent document 1 therefore discloses an olefin oligomerization process for producing fuels, for example gasoline and / or kerosene, from light olefinic feedstocks containing 2 to 8 carbon atoms (C2-C8), in particular light olefinic feedstocks containing a high proportion of propylene and / or butenes and / or pentenes, and using an oligomerization catalyst based, preferably consisting exclusively of, silica-alumina with reduced macropore content.

[0005] Patent document 2 describes, in part, a method for upgrading a liquid hydrocarbon feedstock, comprising the steps of: a) separating from said hydrocarbon feedstock a fraction (O1) essentially comprising compounds containing 5 carbon atoms (C5), of which at least 2% by weight are pentenes; b) placing said fraction (O1) in contact with a hydrocarbon fraction (O2) comprising hydrocarbons having a number of carbon atoms between 6 and 10 (C6-C10), of which at least 2% by weight are olefins, in the presence of an acid catalyst promoting the reactions of dimerization and alkylation of said species; c) separating the resulting effluent into at least two fractions, including a gasoline fraction (α) and a kerosene fraction (β), the gasoline fraction (α) having an end temperature below 100° C. and containing most of the unreacted reagents, the kerosene fraction (β) having a distillation range of 100° C. to 300° C.

[0006] Patent document 3 describes a simple and economical method for adjusting the production of gasoline and gas oil fuels, respectively, by converting an initial feedstock of hydrocarbons containing 4 to 15 carbon atoms (C4-C15) into a gasoline fraction having an improved octane number compared to that of the feedstock and a gas oil fraction having a high octane number.

[0007] Patent document 4 describes a process for preparing a gas oil fraction from an olefinic feedstock containing 2 to 12 carbon atoms (C2-C12), which comprises two oligomerization steps with a separation step between them. The intermediate separation step produces a light fraction of C4-C5 olefinic hydrocarbons, a middle fraction with a T95 of 180°C to 240°C, and a heavy fraction with a T95 of more than 240°C. The middle fraction is then mixed with at least a portion of the light fraction in a mass ratio (middle fraction / light fraction) of 60 / 40 to 80 / 20, and then undergoes a second oligomerization.

[0008] US Pat. No. 5,399,633 describes a method for producing a middle distillate hydrocarbon base from ethanol, more specifically bioethanol.

[0009] US Patent No. 5,399,636 discloses a process for the oligomerization of olefins containing from 4 to 6 carbon atoms (C4-C6) to middle distillate cuts (C10-C20) containing mainly from 10 to 20 carbon atoms. In the process of US Patent No. 5,399,636, the starting olefinic feedstock must contain a minimum of branched olefins (or isoolefins), preferably at least 10 wt. %, preferably at least 20 wt. %, of isoolefins relative to the total olefins in the feedstock.

[0010] US Patent No. 5,399,633 describes a process for producing a middle distillate hydrocarbon base, preferably a kerosene hydrocarbon base, from an ethanol feedstock derived from biomass, said process comprising the dehydration of ethanol to a mainly ethylene effluent and two successive oligomerization steps to obtain a middle distillate effluent.

[0011] Patent Document 8 describes a process for the oligomerization of a light olefinic feedstock containing 2 to 10 carbon atoms (C2-C10) per molecule, using a catalyst system containing a silica-alumina catalyst and a zeolite catalyst having pore openings of 10 or 12 oxygen atoms, the process being carried out at a temperature of 130 to 350° C., a pressure of 0.1 to 10 MPa, and an HSV (hourly space velocity) of 0.1 to 5 h -1 The process of US Pat. No. 5,999,633 improves the yield of middle distillates, and in particular the yield of gas oil, compared to oligomerization processes using only one catalyst of the catalyst system used with an equivalent volume of catalyst.

[0012] US Pat. No. 5,399,633 describes the conversion of oxygen-based compounds to gasoline and distillates (C4-C12 fractions) in a single dehydration oligomerization step, using a composite catalyst comprising a unidimensional 10MR zeolite selected from the group consisting of ZSM 22, ZSM 23, ZSM 35, ZSM 48, ZSM 57 and ferrierite and mixtures thereof, together with a multidimensional zeolite having medium pore size, such as zeolite ZSM-5.

[0013] However, none of the prior art processes discloses the means to produce middle distillates, in particular kerosene and / or gas oils, from C3-C6, preferably C3-C4, light olefins, especially those obtained from bio-based feedstocks, in a very specific manner and with improved yields of middle distillates, in particular kerosene and / or gas oils, which meet current specifications, in particular those of standard ASTM D7566 and / or European standard 15940, while at the same time maintaining a very satisfactory and even high conversion of the olefinic feedstock. [Prior art documents] [Patent documents]

[0014] [Patent Document 1] French Patent Application Publication No. 2926812 (JP 2009-173935 A) [Patent Document 2] European Patent Application Publication No. 1396532 (JP Patent Publication No. 2004099891) [Patent Document 3] European Patent Application Publication No. 1602637 (JP Patent Publication No. 2005344118) [Patent Document 4] European Patent Application Publication No. 1739069 [Patent Document 5] European Patent Application Publication No. 2385092 [Patent Document 6] European Patent Application Publication No. 2707462 [Patent Document 7] French Patent Application Publication No. 2959750 [Patent Document 8] French Patent Application Publication No. 3053355 [Patent Document 9] U.S. Patent No. 6,372,949 (JP Patent Publication No. 2003-512502) Summary of the Invention [Means for solving the problem]

[0015] (Summary of the invention) The present invention therefore relates to a process for preparing a middle distillate from an olefinic feedstock comprising monoolefins containing 3 to 6 carbon atoms, the process comprising the steps of: a) an oligomerization step, which comprises feeding at least an olefinic feedstock, a first recycle and a second recycle, in the presence of at least one oligomerization catalyst, at a temperature of 20-500°C, a pressure of 1.0-10 MPa and a reaction time of 0.1-0.5 h; -1 producing a reaction effluent containing dimers, trimers and oligomers; b) fractionating the reaction effluent obtained at the end of step a) into at least the following: - a light fraction, comprising at least a portion of the olefinic feedstock not converted in step a); - an intermediate fraction, which contains at least a portion of the dimers and trimers formed in step a); and - Heavy fraction; contains oligomers; c) a recycling step, comprising: preparing a first recycle comprising at least a portion of the light fraction; preparing a second recycle comprising at least a portion of the intermediate fraction; and transferring the first recycle and the second recycle to the oligomerization step a); d) hydrogenating at least a portion of the heavy fraction separated off in step b) in the presence of hydrogen; to obtain a hydrogenated heavy fraction comprising middle distillates.

[0016] The value of the process according to the invention lies in the fact that it proposes a method for the efficient conversion of light olefinic feedstocks, in particular those containing olefins containing from 3 to 6, preferably from 3 to 4, carbon atoms, and more particularly those that are at least partially branched, selectively giving rise to middle distillate cuts, more particularly kerosene or gas oil cuts, which meet current specifications, in particular those of standard ASTM D7566 or European standard 15940, respectively.

[0017] The process according to the invention makes it possible to significantly improve the selectivity towards middle distillates, and more particularly towards kerosene or gas oil, compared to the oligomerization processes of the prior art, and therefore also to maximize the yield of middle distillates, and more particularly kerosene or gas oil, while at the same time maintaining a satisfactory and even high overall conversion of the starting olefinic feedstock.

[0018] Another advantage of the process according to the invention lies in the fact that any type of feedstock, which typically contains a high proportion of olefins and is therefore highly active, in particular bio-based olefinic feedstocks, can be converted into hydrocarbon products, with middle distillates, more particularly kerosene or gas oil, being converted in particularly high yields. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0019] (Description of the embodiment) According to the present invention, the expressions "of between A and B" and "between A and B" are synonymous and mean that both limits of the interval (A, B) are included in the stated range of values. If this is not the case and if both limits are not included in the stated range, such information is introduced by the present invention.

[0020] For the purposes of the present invention, the various ranges of parameters for a given process, such as pressure ranges and temperature ranges, may be used alone or in combination, for example, a range of preferred pressure values ​​may be combined with a range of more preferred temperature values ​​within the meaning of the present invention.

[0021] In the remainder of the text, specific embodiments of the present invention may be described, which may be implemented separately or in combination together, with no limitation on combinations where this is technically feasible.

[0022] The terms "upstream" and "downstream" should be understood according to the general flow of the stream or streams under consideration in the method.

[0023] The term "biobased" means that the material / product / compound it qualifies is an organic material / product / compound whose carbon originates from CO2 present in the atmosphere, but has been recently (at the human scale) fixed by solar energy (photosynthesis). On land, this CO2 is captured or fixed by plants (e.g. agricultural crops or forest materials). In the ocean, the CO2 is captured or fixed by photosynthetic bacteria and phytoplankton. For example, the biobased materials 14 C / 12 The C isotope ratio is greater than 0. Conversely, the C isotope ratio of materials of fossil origin is 14 C / 12 The C isotope ratio is about 0. The terms "renewable" or "derived from renewable sources" may also be used. To determine if a material / product / compound is biomass-based or derived from renewable sources, its present carbon content (or percent modern carbon (pMC)) is measured according to standard ASTM D 6866-21 ("Determination of the biobased content of natural-range materials via isotopic and radiocarbon ratio mass spectrometry analysis"). The method of this standard actually determines the amount of carbon in the sample. 14 C / 12 The C isotope ratio was measured and used as the standard biobased standard. 14C / 12 Compared with the C isotope ratio, it gives the percent biobased content of the sample; this standard gives a radiocarbon content roughly equivalent to the rate of atmospheric radiation in 1950. The pMC of a standard biobased standard material is therefore equal to 100%. The pMC of biobased materials is strictly higher than 0%, e.g., 1% or higher. The pMC of materials of fossil origin is around 0%. The pMC of current biobased materials may therefore be greater than 100%.

[0024] In this specification, the terms "T95" or "T95 temperature" are used interchangeably and indicate the temperature at which 95% by weight of the product in question has evaporated, as determined by standardized method ASTM D2887. In parallel, "T5" or "T5 temperature" is the temperature at which 5% by weight of the product in question has evaporated, as determined by the same standardized method ASTM D2887.

[0025] As used herein, the term "Cx" refers to a compound containing x carbon atoms. For example, a C3 chemical compound contains 3 carbon atoms. The term "Cx+" refers to a compound containing at least x carbon atoms. For example, a C9+ compound is a compound containing at least 9 carbon atoms (i.e., 9 or more carbon atoms). The term "Cx-" refers to a compound containing up to x carbon atoms.

[0026] Throughout this document, groups of chemical elements are described according to the new IUPAC classification. For example, groups 9 and 10 correspond to the metals in columns 9 and 10 of the IUPAC classification or the last two columns of group VIIIB of the CAS classification, respectively (CRC Handbook of Chemistry and Physics, CRC Publishing Company, Editor in Chief DR Lide, 81st Edition, 2000-2001). Similarly, group 6 corresponds to the metals in column 6 of the IUPAC classification or the metals in group VIB of the CAS classification.

[0027] According to the present invention, the terms "olefin" and "mono-olefin" are used without distinction and refer to hydrocarbons containing a double bond. Preferably, the olefins of the olefinic feedstock of the process contain 3 to 6 carbon atoms (C3-C6), preferably 3 and / or 4 carbon atoms (C3 and / or C4). The olefins obtained after oligomerization preferably contain 6 to 30 carbon atoms (C6-C30), preferably 9 to 25 carbon atoms (C9-C25), in particular 9 to 16 carbon atoms (C9-C16) or 10 to 25 carbon atoms (C10-C25).

[0028] According to the present invention, the term "oligomerization" refers to any addition reaction of one olefin onto another olefin until a compound, in particular a hydrocarbon compound, more particularly a monoolefinic hydrocarbon compound, is obtained, typically containing from 6 to 30 carbon atoms, preferably from 9 to 25 carbon atoms (C9-C25), in particular from 9 to 16 carbon atoms (C9-C16) or from 10 to 25 carbon atoms (C10-C25). The products obtained are therefore oligomers corresponding to dimers or trimers of the olefins of the olefinic feedstock, i.e. olefinic compounds resulting from the condensation of two or three olefinic molecules of the olefinic feedstock, respectively, or olefinic compounds resulting from the condensation of several olefinic molecules of the olefinic feedstock ("several" here means more than 3 but less than 10, preferably not more than 5, preferably not more than 4). Typically, oligomers are obtained from C4 olefins, the number of carbon atoms of which is not more than 30, most preferably 9-25, in particular 9-16 or 10-25. Oligomerization is distinguished from polymerization by addition of a limited number of molecules. The number of molecules added in the context of the present invention is 2-10, preferentially 3-6, even more preferably 3-6. Oligomers may, however, contain a number of molecules more than 10 and traces of oligomerized olefins. Usually, these traces represent less than 5% by weight relative to the oligomers formed.

[0029] The term "heterogeneous catalysis" in the present disclosure defines reactions, in particular oligomerization reactions, in which at least two phases coexist and the catalyst is in solid form. In particular, the oligomerization step of the process according to the invention involves the oligomerization of an olefinic feedstock by heterogeneous catalysis, i.e. in the presence of a catalyst in solid form, the feedstock and advantageously the obtained product being preferably in the liquid phase.

[0030] More specifically, the present invention relates to a process for the preparation of a middle distillate, preferably a kerosene fraction and / or a gas oil fraction, from a C3-C6 olefinic feedstock, preferably a C3-C4, in particular a C3 or C4 feedstock or a mixture thereof, comprising, preferably consisting of, the following steps: a') optionally pretreating the olefinic feedstock; preferably using at least one adsorption section, water wash section, hydrotreating section and / or selective hydrogenation section; a'') optionally separating the olefinic feedstock; at least partially separating the C5 and C6 compounds present in said olefinic feedstock; a) an oligomerization step, which is fed at least with an olefinic feedstock, optionally pretreated and / or separated, a first recycle and a second recycle; which is preferably operated in the liquid phase and in the presence of at least one, preferably solid, oligomerization catalyst, the temperature being preferably between 20 and 500° C., the pressure being preferably between 1.0 and 10 MPa and the HSV being preferably between 0.1 and 0.5 h -1 resulting in a reaction effluent containing dimers, trimers and oligomers; b) fractionating the reaction effluent obtained at the end of step a) into at least the following: - a light fraction, comprising at least a portion of the olefinic feedstock not converted in step a); - an intermediate fraction, which contains at least a portion of the dimers and trimers advantageously formed in step a); and - a heavy fraction, comprising the oligomers present in the reaction effluent obtained from step a); c) a recycling step, comprising: preparation of a first recycle comprising, preferably consisting of, at least a portion of the light fraction obtained from fractionation step b); preparation of a second recycle comprising, preferably consisting of, at least a portion of the intermediate fraction obtained from fractionation step b); and transfer of the first and second recycles to the oligomerization step a); d) hydrogenating at least a portion of the heavy fraction separated off in step b) in the presence of hydrogen; obtaining a hydrogenated heavy fraction; said heavy fraction advantageously comprising at least one middle distillate cut; e) optionally separating out the hydrogenated heavy fraction; obtaining at least one middle distillate fraction, in particular a kerosene fraction and / or a gas oil fraction.

[0031] (Olefinic Feedstocks) The feedstock to be treated by the process according to the invention is advantageously a "light olefinic feedstock", i.e. comprising hydrocarbon compounds, in particular olefins, preferably monoolefins, containing from 3 to 6 carbon atoms (i.e. C3, C4, C5 and C6), preferably from 3 to 4 carbon atoms (i.e. C3 and C4), preferably 3 or 4 carbon atoms (i.e. C3 or C4).

[0032] Preferably, the C3-C6 olefinic feedstock comprises at least 20% by weight, preferably at least 50% by weight, preferably at least 90% by weight, preferentially at least 95% by weight, in particular at least 98% by weight or at least 99% by weight of olefins, relative to the total weight of the olefinic feedstock, the olefins containing 3, 4, 5 and 6 carbon atoms, preferably 3 and / or 4 carbon atoms, said olefins being preferably mono-olefins.

[0033] The olefinic feedstock may optionally contain paraffins, in particular different fractions of paraffins at the limits of the initial and final distillation points of the feedstock under consideration, more particularly C3-C6 paraffins, i.e. fully hydrogenated hydrocarbon compounds, which are preferably aliphatic and preferably contain 3 to 6 carbon atoms. Preferably, the olefinic feedstock may optionally contain up to 80% by weight, preferably up to 50% by weight, more preferably up to 10% by weight, preferentially up to 5% by weight, in particular up to 2% by weight, even up to 1% by weight of paraffins relative to the total weight of the olefinic feedstock, in particular up to 2% by weight, even more preferably up to 1% by weight of paraffins relative to the total weight of the olefinic feedstock. Highly preferably, the olefinic feedstock is free from paraffins, i.e. it contains less than 0.5% by weight of paraffins, preferably less than 0.1% by weight of paraffins relative to the total weight of the olefinic feedstock. Processing an olefinic feedstock having a low paraffin content, in particular a paraffin content of 10 wt. % or less, preferably 5 wt. % or less, preferably 2 wt. % or less, and even a paraffin-free olefinic feedstock, allows the oligomerization step to be carried out at low pressures, in particular at pressures lower than those conventionally used for conventional (or fossil) feedstocks which generally contain paraffin contents of more than 10 wt. %, often between 40 wt. % and 80 wt. %.

[0034] In particular, suitable olefinic feedstocks contain mainly propylene and / or butenes (isobutene and / or n-butenes) and / or pentenes, preferably propylene and / or butenes. The term "mainly" is understood to mean at least 80% by weight, preferentially at least 90% by weight, relative to the total weight of the olefinic feedstock.

[0035] Olefinic feedstocks particularly suitable for the process according to the invention are essentially C3 and C4, preferably C3 or C4, olefinic feedstocks, i.e. at least 90% by weight, preferentially at least 95% by weight and 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. The olefinic feedstock therefore 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, preferentially at least 95% by weight and 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 selected from "polymer grade" propylene feedstocks, feedstocks containing essentially propylene (i.e., at least 90 wt. % propylene) and small amounts of butenes (i.e., less than 10 wt. % butenes), feedstocks consisting essentially of isobutene (i.e., at least 90 wt. % isobutene), feedstocks consisting essentially of n-butenes (but-1-ene and but-2-ene) (i.e., at least 90 wt. % but-1-ene and but-2-ene), and mixtures thereof.

[0036] In a preferred embodiment of the present invention, where the olefinic feedstock is a C3 and / or C4 olefinic feedstock, said olefinic feedstock may contain C5 and / or C6 compounds. In this case, the content of C5 and / or C6 compounds in the olefinic feedstock is preferably 5% by weight or less, preferably 2% by weight or less, or more preferably 1% by weight or less, 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 contain paraffins, in particular propane and / or butane. Preferably, the C3 and / or C4 olefinic feedstock is free from propane and / or butane (i.e. it contains less than 0.5 wt. % paraffins, preferably less than 0.1 wt. % paraffins relative to the total weight of the olefinic feedstock), thus allowing the oligomerization step to be carried out at lower pressures relative to the oligomerization of paraffin-containing feedstocks. Preferably, the olefinic feedstock is free from C5 and / or C6 paraffins, i.e. it contains less than 0.5 wt. %, preferably less than 0.1 wt. %, C5 and / or C6 paraffins, limiting the amount of inert compounds introduced inter alia in step a).

[0037] A suitable olefinic feedstock is an olefinic C4 cut, which contains a minimum of 98% by weight of n-butenes, 1-butene and 2-butene, preferably less than 2% by weight of n-butane, preferably less than 0.5% by weight of n-butane, the percentages being given relative to the total weight of the olefinic feedstock.

[0038] Another suitable olefinic feedstock is an olefinic C4 cut, which in particular comprises at least 90% by weight of isobutene, furthermore at least 92% by weight of isobutene and in particular at most 97% by weight of isobutene, optionally butane and / or isobutane and / or n-butenes, in particular 3% to 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.

[0039] The olefinic feedstock may be an olefinic C3-C4 cut (i.e. containing propylene and butenes), for example containing a minimum of 90 wt.% propylene and a maximum of 10 wt.% butenes, said feedstock being preferably free of paraffins (i.e. containing less than 0.5 wt.% paraffins, preferably less than 0.1 wt.% paraffins), the percentages being given relative to the total weight of the olefinic feedstock.

[0040] Another suitable olefinic feedstock is an olefinic C3 cut, preferably containing at least 90% by weight of propylene, preferably at least 98% by weight of propylene. It may contain propane, preferentially at most 2% by weight of propane.

[0041] Preferably, the olefinic feedstock is at least partly, and very advantageously entirely, bio-based, resulting in a bio-based upgradeable product. The C3-C6 olefinic feedstock, preferably a C3 and / or C4 olefinic feedstock, may in particular originate from a Fischer-Tropsch unit, a unit for the production of olefins from methanol and / or a unit for the dehydration of alcohols, such as isobutanol, and may in particular originate from biomass, for example from the fermentation of sugars.

[0042] The olefinic feedstock may be supplied from a conventional unit. In this case, it is preferably used as a mixture with a feedstock of bio-based origin, preferably in a weight ratio between the conventional olefinic feedstock and the bio-based olefinic feedstock of 90 / 10 to 10 / 90, preferably 80 / 20 to 20 / 80. Preferably, the conventional olefinic feedstock is supplied in high purity or as a mixture from a steam cracking unit, an FCC catalytic cracking unit, a selective diolefin hydrogenation unit (known as SHU) or a paraffin dehydrogenation unit and / or any other unit leading to the production of light olefins.

[0043] The olefinic feedstock treated in the process according to the invention can advantageously undergo a pretreatment step before being sent to the oligomerization step a), such pretreatment making it possible to remove any compounds which may cause poisoning of the oligomerization catalyst, in particular basic nitrogen compounds, water, sulfur derivatives and basic nitrogen derivatives.

[0044] Preferably, the olefinic feedstock is free of sulphur or sulphur compounds, i.e. it contains sulphur in a content of less than or equal to 20 ppm by weight, preferably less than or equal to 12 ppm by weight and preferentially less than or equal to 10 ppm by weight, 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 sulphur (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 comprising 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).

[0045] Preferably, the feedstock of the process according to the invention is free of nitrogen or nitrogen compounds, i.e. it contains elemental nitrogen in a content of less than or equal to 0.1 ppm by weight relative to the total weight of the olefinic feedstock, thus avoiding or at least limiting the poisoning of the oligomerization catalyst of step a). If the olefinic feedstock contains nitrogen, the process advantageously comprises a pretreatment step of the olefinic feedstock, located upstream of the oligomerization step a), preferably comprising an adsorption and / or water washing and / or hydrotreatment section, thus making it possible to protect the oligomerization catalyst of step a).

[0046] Preferably, the olefinic feedstock treated by the process according to the invention is free of butadiene, in particular 1,3-butadiene, i.e. it contains a content of butadiene, in particular 1,3-butadiene, of less than or equal to 0.1% by weight, preferably less than or equal to 500 ppm by weight, relative to the total weight of the olefinic feedstock, thus protecting the oligomerization catalyst. If the olefinic feedstock contains butadiene, in particular 1,3-butadiene, the process advantageously comprises a step of pretreatment of the olefinic feedstock, which is located upstream of the oligomerization step a) and which preferably comprises a selective hydrogenation section.

[0047] According to a particular embodiment of the invention, the process may include an optional olefinic feedstock separation step, advantageously located upstream of the oligomerization step a), which at least partially separates the C5 and C6 compounds present in said olefinic feedstock. This optional separation step therefore makes it possible to produce a fraction comprising the C5 and C6 compounds that may be present in the feedstock and at least one fraction comprising C3 and C4 compounds. The skilled person can regulate the separation so as to more or less promote the fractionation and separate the fraction comprising C3 and C4 compounds into a C3 fraction (in particular rich in C3, more particularly rich in propylene) and a C4 fraction (in particular rich in C4, more particularly rich in isobutene and / or n-butene). This optional separation step therefore makes it possible to enrich the feedstock in particular in C3 and / or C4 olefinic compounds. The fraction containing C3 and C4 compounds, the C3 fraction or the C4 fraction, is then advantageously sent to the oligomerization step a), preferably directly. The fraction containing C5 and C6 compounds can be purged and upgraded for a part, for example by being integrated into the gasoline pool. According to the most specific embodiment of the invention, the process may include an optional olefinic feedstock separation step, located upstream of the oligomerization step a), separating at least the C3 and C4 fractions, the two fractions C3 and C4 fractions undergoing steps a), b) and c) and optionally d), respectively, in parallel, the heavy fraction being recombined at the end of step c) or optionally at the end of the hydrogenation step d).

[0048] (Oligomerization step a) The process according to the invention comprises an oligomerization step, more specifically a heterogeneous oligomerization reaction (or called heterogeneous catalysis), carried out in the presence of at least one oligomerization catalyst and giving rise to a reaction effluent containing dimers, trimers and oligomers. In particular, this oligomerization step a) makes it possible to obtain a hydrocarbon mixture containing mono-olefins with a large number of carbon atoms, mainly 6 or more, preferably 8 or more, preferably 9 or more carbon atoms, the term "mainly" meaning here a minimum of 90% by weight of C6+, preferably C8+, preferably C9+ hydrocarbons, relative to the weight of the obtained hydrocarbon mixture. The obtained hydrocarbon mixture may also contain unreacted C3-C6 feedstock olefins.

[0049] According to the invention, the oligomerization step a) is fed with at least an olefinic feedstock, optionally pretreated and / or optionally separated. Preferably, the oligomerization step a) is also fed with a first recycle, which comprises, and preferably consists of, at least a portion of the light fraction from step b); said first recycle is advantageously prepared in step c) and then transferred to step a). Preferably, the oligomerization step a) is also fed with a second recycle, which comprises, and preferably consists of, at least a portion of the intermediate fraction obtained from step b); said first recycle is advantageously prepared in step c) and then transferred to step a).

[0050] Advantageously, the oligomerization step a) is preferably carried out 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, which is preferably solid. Preferably, the 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 an associated HSV of preferably between 0.1 and 0.5 h -1 , preferably 0.2 to 0.3 h -1HSV (or hourly space velocity) is defined according to the invention by the ratio between the volumetric flow rate of the fresh olefinic feedstock, in particular the olefinic feedstock at 15° C. and 1 atm, and the volume of the oligomerization catalyst, in particular the oligomerization catalyst in operation (also called in use). The temperature at which the oligomerization step a) is carried out is between 20 and 500° C. and 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 space velocity may be adjusted by the person skilled in the art, in particular depending on the composition of the olefinic feedstock and the nature of the oligomerization catalyst used, in order to maximize the yield of middle distillates, in particular the yield of kerosene or gas oil.

[0051] Advantageously, step a) uses at least one oligomerization catalyst, preferably 1 to 3 different oligomerization catalysts, preferably one oligomerization catalyst. Any type of oligomerization catalyst known to the skilled person may be used in step a) as oligomerization catalyst. More specifically, the oligomerization catalyst or catalysts of step a) may be any type of acid catalyst, in particular selected from silica-impregnated phosphoric acid-based catalysts (supported phosphoric acid of the "SPA" type), ion exchange resins, silica-alumina and high-purity zeolites or zeolites supported on an alumina support. Preferably, the oligomerization catalyst or catalysts of step a) are selected from ion exchange resins, preferably cation exchange resins, silica-alumina (i.e. comprising silica and alumina) and high-purity alumina or zeolites supported on an alumina support.

[0052] When the oligomerization catalyst is selected from SPA type catalysts, step a) is preferably carried out at a temperature, advantageously an inlet temperature, of 100-300° C., preferentially 160-250° C., and at a pressure, preferably 1.5-6.5 MPa, preferentially 1.5-4.0 MPa.

[0053] Zeolite-based catalysts are particularly suitable for producing linear or slightly branched heavy olefins, which in particular allow the production of high quality gas oils, i.e. gas oils having a cetane number of more than 45 after hydrogenation. When the oligomerization catalyst is selected from zeolite-based catalysts, the temperature at which step a) is preferably carried out, advantageously the inlet temperature, is between 150 and 500° C., preferentially between 200 and 350° C., and the pressure is preferably between 2.0 and 10.0 MPa, preferentially between 3.0 and 6.5 MPa. Preferably, the zeolite-based oligomerization catalyst comprises at least one zeolite selected from the group consisting of zeolites of the aluminosilicate type with an overall Si / Al atomic ratio of more than 10 and a pore structure of 8, 10 or 12 MR. The zeolite is more preferably selected from the group consisting of zeolites having the structure 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 and SAPO, and mixtures thereof. Highly preferably, the zeolite is selected from the group consisting of ferrierite, ZSM-5, mordenite and ZSM-22 zeolites, and mixtures thereof. Even more preferably, the zeolite used is ZSM-5.

[0054] Catalysts of the ion exchange resin type are chosen for their good mechanical strength in the range of temperatures and pressures used in step a). When the oligomerization catalyst is chosen from ion exchange resins, the temperature at which step a) is preferably carried out, advantageously the inlet temperature, is between 20° C. and 250° C., preferentially between 70° C. and 180° C., and the pressure is preferably between 2.0 and 10.0 MPa, preferentially between 3.0 and 6.5 MPa. Ion exchange resin catalysts have the advantage of being cheap and non-renewable and having acceptable cycle times in fixed bed operation, since they are less sensitive to pollutants than zeolites and silica-alumina. Highly preferably, the ion exchange resin catalyst used in step a) is a copolymer of a monovinyl aromatic compound and a polyvinyl aromatic compound, preferably a copolymer of divinylbenzene and styrene, which is preferably sulfonated and has, in particular, a degree of crosslinking between 20% and 45%, preferably between 30% and 40%, preferably equal to 35%, and an acid strength, respectively, between 1 and 10 mmol H + equivalents / gram, preferably 3.5-6 mmol H + The acid strength represents the number of active sites in the resin, and the Na + H released by acidic resin after exchange with ions + It is determined by ionic assay, preferably conductimetric method (see standard ASTM D4266). For example, the acidic oligomerization catalyst of ion exchange resin type used in step a) is a commercial acidic resin sold under the reference TA801 by the company Axens.

[0055] Silica-alumina type catalysts have the advantage of being regenerative, so that, despite their higher cost than that of resins, considerable savings are made in terms of catalyst consumption. When the oligomerization catalyst is chosen from silica-alumina, the temperature at which step a) is preferably carried out is between 20 and 300° C., preferentially between 30 and 220° C., preferably between 40 and 200° C., and the pressure is preferably between 1.5 and 6.5 MPa, preferentially between 2.0 and 4.0 MPa. The temperature at which the oligomerization step a) is carried out in the presence of silica-alumina: 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 used in step a). The silica-alumina based oligomerization catalyst(s) are / are amorphous catalyst(s), preferably consisting of amorphous mineral materials selected from silica-alumina and silica-treated alumina, preferably silica-alumina. In the silica-alumina based oligomerization catalyst used in step a), the SiO2 / Al2O3 mass ratio is between 0.1 and 10. Preferentially, the silica-alumina present in the oligomerization catalyst used in the oligomerization step a) has the following characteristics: the mass content of silica (SiO2) is between 5% and 95% by weight, preferably between 10% and 80% by weight, more preferably between 20% and 80% by weight, even more preferably between 25% and 75% by weight, relative to the weight of silica-alumina present in the oligomerization catalyst; the content of cationic impurities is 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 alkali, and in particular sodium.

[0056] Catalysts prepared as described in patent FR 2 926 812 may be suitable as oligomerization catalysts for step a).

[0057] According to a particular embodiment of the invention, the oligomerization catalyst used in step a) consists entirely of silica-alumina, i.e. it is free of any other elements (i.e. it contains less than 0.5% by weight, preferably less than 0.1% by weight, of any elements other than silica and alumina).

[0058] According to another particular embodiment of the invention, the oligomerization catalyst used in step a) may contain at least one metallic element selected from 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 row of the group VIII metals, 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 contain silicon as a doping element, deposited on silica-alumina.

[0059] Highly advantageously, the oligomerization step a) is carried out in the presence of a silica-alumina based catalyst, advantageously at a temperature of 20° C. to 300° C., preferentially 25 to 220° C., preferably 30° C. to 200° C. at the inlet of step a), and at a pressure of 1.5 to 6.5 MPa, preferentially 2.0 to 4.0 MPa. According to a particular embodiment, in case the olefinic feedstock is a C3 and / or C4 olefinic feedstock, the oligomerization step a) is preferably carried out in the presence of a silica-alumina catalyst, advantageously at a temperature of 25 to 200° C., preferentially 30 to 190° C., preferably at a pressure of 1.5 to 6.5 MPa, preferably 2.0 to 4.0 MPa at the inlet of step a), and preferentially giving kerosene. According to another particular embodiment, when the olefinic feedstock is a C3 and / or C4 olefinic feedstock, the oligomerization step a) is preferably carried out in the presence of a silica-alumina catalyst, advantageously at a temperature advantageously between 35 and 200° C., preferentially between 40 and 190° C., at the inlet of step a), and at a pressure advantageously between 1.5 and 6.5 MPa, preferentially between 2.0 and 4.0 MPa, giving preferentially a gas oil.

[0060] Preferably, the oligomerization catalyst or catalysts of the oligomerization step a) are in the form of spheres, pellets or extrudates, preferentially in the form of extrudates. Highly advantageously, the oligomerization catalyst or catalysts are in the form of extrudates, with a diameter between 0.5 and 5 mm, more particularly between 0.7 and 2.5 mm. The extrudates are in the form of cylinders (which may or may not be hollow), twisted cylinders, multilobes (for example with 2, 3, 4 or 5 lobes) or rings. Cylindrical and multilobes are preferably used, although any other form may be used. In a very specific embodiment of the invention, the oligomerization step is carried out in the presence of a silica-alumina-based oligomerization catalyst, which preferably consists of silica-alumina, in the form of trilobe extrudates.

[0061] Advantageously, the oligomerization step may use one or more, preferably at least two, preferably at least three and up to ten, preferably up to six reactors, arranged in parallel or in series, preferably in series, containing one or more different oligomerization catalysts, preferably the same type of oligomerization catalyst. The above operating conditions and also the oligomerization catalysts may be applied to any of the reactors. Very specifically, the oligomerization step includes at least two or even 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) in the reaction stage and the other reactor (or one of the reactor trains) in the regeneration stage if the level of impurities in the feedstock leads to rapid deactivation of the catalyst. Optionally, the oligomerization step may include heat exchange upstream of one or more reactors to heat the olefinic feedstock.

[0062] The oligomerization reaction is exothermic. At least part of the temperature rise associated with the exothermicity of the oligomerization reaction can be controlled and introduced into the oligomerization step a) by a first and a second recycle (containing at least part of the light fraction, corresponding at least partly to the unconverted feedstock and at least partly to the intermediate fraction, respectively). The exothermicity can be controlled at least partly by diluting the olefinic feedstock by adding paraffins from a source external to the process and / or by introducing a part of the hydrogenated heavy fraction obtained at the end of step a) and in particular an inerts stream corresponding to a part of the kerosene and / or gas oil fraction or a mixture of kerosene and / or gas oil fractions that may be separated off in optional step e) and the residue of optional step e), said paraffins being of the same molecular weight and / or higher than the olefinic feedstock, said paraffins being aliphatic or cyclic. In the latter case, the inerts stream is preferably 0 to 6 times by weight, preferably 0.5 to 4 times by weight, of the fresh olefinic feedstock.

[0063] The reaction effluent resulting from the oligomerization step a) therefore contains dimers, trimers and oligomers and is sent in whole or in part to a fractionation step b).

[0064] (Fractionation step b) The process according to the invention comprises the step of fractionating the reaction effluent obtained at the end of step a) into at least the following: - a light fraction, comprising at least a portion of the olefinic feedstock not converted in step a); - an intermediate fraction, which comprises at least a part, preferably all, of the dimers and trimers advantageously produced in step a); and a heavy fraction, comprising the oligomers present in the reaction effluent from step a), in particular olefinic compounds containing from 6 to 30, preferably from 9 to 25, carbon atoms, more particularly from 9 to 16 carbon atoms in the case of kerosene or from 10 to 25 carbon atoms in the case of gas oils.

[0065] The light fraction comprises, preferably consists of, at least a part, preferably the whole, of the olefinic feedstock not converted in step a). It therefore advantageously comprises C3-C6 olefins, preferably C3 and / or C4 olefins, which were not converted in step a). The light fraction may optionally comprise unreacted, i.e. non-olefinic compounds, in particular paraffins, which are notably already present in the fresh olefinic feedstock. The amount of this light fraction depends in particular on the conversion of the olefinic feedstock per pass through the oligomerization step a). This fraction is advantageously recycled in whole or in part to step a); in fact, it constitutes at least a part of the first recycle prepared in step c). Optionally, a part of this light fraction may be purged, continuously or discontinuously, in particular when the olefinic feedstock contains compounds that do not oligomerize, such as paraffins. In the case of purging, the purged stream may be upgraded, for example, to LPG (liquefied petroleum gas). In some cases, the light fraction may contain C1-C2 compounds possibly arising during step a) and resulting from cracking and recombination reactions.

[0066] Optionally, at the end of the fractionation step, a gaseous fraction may be separated off, the gaseous fraction comprising C1-C2 compounds, which optionally occur during step a) and result from the decomposition and recombination reactions. The gaseous fraction possibly separated off in step b) is preferably purged (i.e. removed from the process) in a continuous or discontinuous manner, for example to be upgraded.

[0067] The intermediate fraction comprises at least a part, preferably all, of the dimers and trimers advantageously produced in step a), preferably consisting of them. The products contained therein, in particular the dimers and trimers, are too light to be upgraded to middle distillates, in particular kerosene or gas oil. The intermediate fraction may optionally contain unconverted C5-C6 olefins, if the olefinic feedstock contains C5-C6 olefins. The intermediate fraction may contain paraffins from the olefinic feedstock boiling in the same range as the intermediate fraction. Preferably, the intermediate fraction is free from paraffins, i.e. it contains 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 contains C5+ olefin oligomers, preferably with a T95 of less than 170°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 gas oil production. It can therefore also be referred to as C5-140°C or C5-165°C (preferably C5-170°C). Optionally, at least a part of the intermediate fraction can be recovered and removed (i.e. purged) from the process and processed or directly upgraded, in particular as gasoline. This optionally purged part of the intermediate fraction can be subjected to a hydrogenation step, in particular to step d) of the process or to a hydrogenation step different from the process according to the invention, for example operated under conditions similar to those described for step d), and then integrated into the gasoline pool.

[0068] The heavy fraction advantageously comprises oligomers present in the reaction effluent from step a). Advantageously, the olefinic compounds it especially comprises contain from 6 to 30, preferably from 9 to 25 carbon atoms. Preferably, the T5 of the heavy fraction is greater than or equal to 140° C., in particular in the case of kerosene production greater than or equal to 140° C., or in the case of gas oil production greater than or equal to 165° C., preferably greater than or equal to 170° C. Preferably, the heavy fraction is composed of C9+ olefinic oligomers and highly preferably boils between 140 and 300° C. (also called 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 having a cut point making it possible to achieve 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 gas oil fraction having a cut point making it possible to achieve a flash point greater than or equal to 55° C.

[0069] Advantageously, the fractionation step b) uses one or more distillation columns, preferably from 1 to 3 distillation columns.

[0070] (Recycling process c) The recycling step c) of the process according to the invention comprises the following steps: - preparing a first recycle, the first recycle comprising, and preferably consisting of, at least a portion of the light fraction, - preparing a second recycle, which comprises, and preferably consists of, at least a portion of the intermediate fraction from fractionation step b), - transferring the first recycle to an oligomerization step a), and - transferring the second recycle to the oligomerization step a).

[0071] Advantageously, all or part of the light fraction from separation step b) constitutes a first recycle, which is then recycled to the oligomerization step a), preferably directly to the inlet of step a) and preferably upstream of any exchanger used in step a) upstream of the reactor 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 corresponds to a part of the light fraction recycled to a), which represents an amount such that the weight ratio between the first recycle and the olefinic feedstock feeding the oligomerization step a) is between 0.3 and 1.5, preferably between 0.5 and 1.2.

[0072] Advantageously, all or part of the intermediate fraction from separation step b) constitutes a second recycle, which is then recycled to step a), preferably directly, in particular upstream of any exchanger used upstream of the reactor in step a). Preferably, the intermediate fraction is not cooled, in whole or in part, before being transferred to the oligomerization step a) as the second recycle, which contributes, in particular by simple mixing, towards the preheating of the olefinic feedstock at the inlet of step a). Preferably, the second recycle corresponds to a part of the intermediate fraction recycled to a), which represents an amount such that the weight ratio between the second recycle and the olefinic feedstock feeding the oligomerization step a) is between 0.5 and 10.0, preferentially between 1.0 and 5.0, preferably between 1.0 and 4.0.

[0073] Recycling at least a portion of these two fractions, the light fraction and the middle fraction, and in particular recycling at least a portion of the middle fraction, makes it possible to increase the overall conversion and to maximize the yield of the target products, in particular the middle distillates, more particularly kerosene or gas oil, by strongly favoring the selectivity towards the target products, in particular kerosene or gas oil.

[0074] Preferably, the heavy fraction containing oligomers and supplied from fractionation step b) is not recycled, in particular not recycled to oligomerization step a). Indeed, the heavy fraction comprises heavy olefinic compounds, in particular containing 6 to 30, preferably 9 to 25, carbon atoms. These compounds are known to have a non-negligible reactivity towards oligomerization. Therefore, if such olefinic compounds were recycled to oligomerization step a), undesired highly heavy compounds would be formed. This reduces the selectivity and therefore the yield of the middle distillate. Advantageously, the process for preparing a middle distillate according to the invention therefore lacks a recycle of the heavy fraction obtained from step b). In particular, in the case of kerosene production, the process advantageously lacks a recycle of the heavy fraction having a T5 of 140° C. or more. In the case of gas oil production, the process advantageously lacks a recycle of the heavy fraction having a T5 of 165° C. or more, preferably 170° C. or more.

[0075] According to a first particular embodiment of the invention, the olefinic feedstock essentially consists of isobutene, preferably at least 90% by weight of isobutene, and highly advantageously less than 0.5% by weight, even less than 0.1% by weight, of paraffins, such as butanes, relative to the total weight of the olefinic feedstock, and the oligomerization step a) is advantageously carried out in the presence of silica-alumina, at a temperature preferably between 20 and 100° C., preferentially between 30 and 90° C., highly preferentially between 35° C. and 85° C., and at a pressure preferentially between 1.5 and 6.5 MPa, preferably between 2.0 and 4.0 MPa, and the HSV is preferably between 0.20 and 0.30 h -1 , preferentially 0.20~0.25h -1In this embodiment, the inerts stream (i.e. the stream of compounds inert to the oligomerization reaction, i.e. unreactive under the operating conditions of step a)) is preferably at least partially composed of a portion of the hydrogenated heavy fraction obtained at the end of hydrogenation step d) and is preferably used to feed step a) in order to control the exothermicity and therefore the reactivity of the oligomerization reaction. According to this first particular embodiment, the T95 of the intermediate fraction separated off in step b) is advantageously below 140° C.; the T5 of the heavy fraction is 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 preferably consisting of at least a part, preferably the whole, of the intermediate fraction separated off in b), represents a quantity by weight such that the weight ratio between the second recycle and the olefinic feedstock at the inlet of step a) is between 1.0 and 5.0, preferably between 1.5 and 2.5, and is sent to the oligomerization step a).

[0076] According to a second particular embodiment of the invention, the olefinic feedstock essentially consists of propylene, preferably at least 90% by weight of propylene, possibly at most 10% by weight of butenes, highly advantageously less than 0.5% by weight and 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, at a temperature preferably between 100 and 180° C., preferentially between 110 and 170° C., preferably between 115 and 165° C., at a pressure preferentially between 1.5 and 6.5 MPa, preferably between 2.0 and 4.0 MPa, and with an HSV preferably between 0.20 and 0.30 h -1 , preferentially 0.20~0.25h -1In this particular embodiment, an inerts stream (i.e. a stream of compounds which are inert to the oligomerization reaction, i.e. which do not react under the operating conditions of step a), preferably consisting 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) in order to control the exothermicity and therefore the reactivity of the oligomerization reaction. According to this second particular embodiment, the T95 of the intermediate fraction separated off in step b) is advantageously below 140° C.; the T5 of the heavy fraction is 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 preferably consisting of at least a part, preferably the whole, of the intermediate fraction separated off in b), represents a quantity by weight such that the weight ratio between the second recycle and the olefinic feedstock at the inlet of step a) is between 1.0 and 5.0, preferably between 1.5 and 2.0, and is sent to the oligomerization step a).

[0077] According to a third particular embodiment of the invention, the olefinic feedstock consists essentially of n-butenes (but-1-ene and but-2-ene), preferably at least 98% by weight of butenes, and highly advantageously less than 0.5% by weight of paraffins, such as butanes, relative to the total weight of the olefinic feedstock, and the oligomerization step a) is advantageously carried out in the presence of silica-alumina, at a temperature preferably between 130 and 200° C., preferentially between 140 and 190° C., preferably between 145 and 185° C., at a pressure preferentially between 1.5 and 6.5 MPa, preferably between 2.0 and 4.0 MPa, and with an HSV preferably between 0.20 and 0.30 h -1 , preferentially 0.20~0.25h -1Optionally, an inerts stream (i.e. a stream of compounds that are inert to the oligomerization reaction, i.e. that do not react under the operating conditions of step a), preferably consisting 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), in order to control the exothermicity and therefore the reactivity of the oligomerization reaction. According to this third particular embodiment, the T95 of the intermediate fraction separated off in step b) is advantageously below 140° C.; the T5 of the heavy fraction is 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 preferably consisting of at least a part, preferably the whole, of the intermediate fraction separated off in b), represents a quantity by weight such that the weight ratio between the second recycle and the olefinic feedstock at the inlet of step a) is between 1.0 and 5.0, preferably between 3.5 and 4.0, and is sent to the oligomerization step a).

[0078] According to a fourth particular embodiment of the invention, the olefinic feedstock essentially consists of isobutene, preferably at least 90% by weight of isobutene, and highly advantageously less than 0.5% by weight, even less than 0.1% by weight, of paraffins, such as butanes, relative to the total weight of the olefinic feedstock, and the oligomerization step a) is advantageously carried out in the presence of silica-alumina, the temperature being preferably between 30 and 100° C., preferentially between 40 and 90° C., the pressure being preferentially between 1.5 and 6.5 MPa, preferably between 2.0 and 4.0 MPa, and the HSV being preferably between 0.20 and 0.30 h -1 , preferentially 0.25~0.30h -1In this embodiment, an inert stream, preferably consisting at least in part of a portion of the hydrogenated heavy fraction obtained at the end of the hydrogenation step d), is preferably used to feed step a) in order to control the exothermicity of the oligomerization reaction. According to this fourth particular embodiment, the T95 of the intermediate fraction separated in step b) is advantageously below 165° C.; the T5 of the heavy fraction is equal to or higher than 165° C. According to this fourth particular embodiment, the second recycle preferably consists of at least a part, preferably the whole, of the intermediate fraction separated off in b), representing a quantity by weight such that the weight ratio between the second recycle and the olefinic feedstock at the inlet of step a) is between 1.0 and 4.0, preferably between 1.0 and 2.0, which second recycle is sent to the oligomerization step a).

[0079] According to a fifth particular embodiment of the invention, the olefinic feedstock essentially consists of propylene, preferably at least 90% by weight of propylene, optionally at most 10% by weight of butenes and highly advantageously less than 0.5% by weight, 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, the temperature being preferably between 110 and 180° C., preferentially between 120 and 170° C., the pressure being preferentially between 1.5 and 6.5 MPa, preferably between 2.0 and 4.0 MPa, and the HSV being preferably between 0.20 and 0.30 h -1 , preferentially 0.25~0.30h -1In this embodiment, an inerts stream, preferably consisting at least in part of a portion of the hydrogenated heavy fraction obtained at the end of the hydrogenation step d), is preferably used to feed step a) in order to control the exothermicity of the oligomerization reaction. According to this fifth particular embodiment, the T95 of the intermediate fraction separated in step b) is advantageously below 165° C.; the T5 of the heavy fraction is equal to or higher than 165° C. According to this fifth particular embodiment, the second recycle preferably consists of at least a part, preferably the whole, of the intermediate fraction separated off in b), representing a quantity by weight such that the weight ratio between the second recycle and the olefinic feedstock at the inlet of step a) is between 1.0 and 4.0, preferably between 1.0 and 1.5, which second recycle is sent to the oligomerization step a).

[0080] According to another particular embodiment of the invention, the olefinic feedstock consists essentially of n-butenes (but-1-ene and but-2-ene), preferably at least 98% by weight of butenes and highly advantageously less than 0.5% by weight of paraffins, such as butanes, relative to the total weight of the olefinic feedstock, and the oligomerization step a) is advantageously carried out in the presence of silica-alumina, the temperature being preferably between 140 and 200° C., preferentially between 145 and 190° C., the pressure being preferentially between 1.5 and 6.5 MPa, preferably between 2.0 and 4.0 MPa, and the HSV being preferably between 0.20 and 0.30 h -1 , preferentially 0.25~0.30h -1In this embodiment, an inert stream, preferably consisting at least in part of a portion of the hydrogenated heavy fraction obtained at the end of the hydrogenation step d), is preferably used to feed step a) in order to control the exothermicity of the oligomerization reaction. According to this particular embodiment, the T95 of the intermediate fraction separated in step b) is advantageously below 165° C.; the T5 of the heavy fraction is equal to or higher than 165° C. According to this particular embodiment, the second recycle preferably consists of at least a part, preferably the whole, of the intermediate fraction separated off in b), representing a quantity by weight such that the weight ratio between the second recycle and the olefinic feedstock at the inlet of step a) is between 1.0 and 4.0, preferably between 3.0 and 3.5, which second recycle is sent to the oligomerization step a).

[0081] In these particular embodiments of the invention, the temperature at which the oligomerization step a) is carried out in the presence of silica-alumina advantageously corresponds to the temperature at the inlet of step a), preferably the temperature at the inlet of the reactor used in step a).

[0082] (Hydrogenation step d) The process according to the invention comprises a step of hydrogenation of at least a part, preferably the entirety, of the heavy fraction separated off in step b) in the presence of hydrogen to obtain a hydrogenated heavy fraction.

[0083] The hydrogenation step makes it possible to saturate at least some, preferably all, of the olefinic bonds of the heavy fraction from step c), resulting in paraffins which can be directly incorporated into fuel pools, in particular kerosene pools (or jet pools), very particularly SPK ("Synthetic Paraffinic Kerosene") jet pools meeting the specifications of standard ASTM D7566, Appendix 5, or into gas oil pools, very particularly gas oil pools meeting the specifications of European standard 15940. Step d) of hydrogenating the unsaturated compounds makes it possible in particular to significantly improve the smoke point of the heavy fraction, in particular of the resulting middle distillate, and / or to remove any sulfur and / or nitrogen impurities.

[0084] Preferably, the hydrogenation step d) is carried out in the presence of a catalyst, which preferentially comprises at least one group VIII metal, in particular nickel, palladium or platinum, deposited on an inert support, for example silica or alumina. Preferably, the hydrogenation step is carried out in the presence of a palladium-based or nickel-based catalyst on an alumina support. Nevertheless, any other catalyst may be used that allows the products of the oligomerization step, in particular the heavy fractions, in particular those having C9+ olefins, to be hydrogenated. For example, a catalyst selected from catalysts such as NiMo, CoMo, NiCoMo on alumina, and mixtures thereof may be used.

[0085] The hydrogenation step d) is preferably carried out in the liquid phase, advantageously at a pressure between 0.5 and 5.0 MPa, preferably between 1.0 and 5.0 MPa, at a temperature preferably between 50 and 300° C., preferentially between 60 and 200° C., in the presence of hydrogen, preferably at a content between 0.5% and 3% by weight relative to the weight of the portion of the heavy fraction fed to step d).

[0086] Preferably, in step d) a degree of hydrogenation of at least 90%, preferentially 95% or more, preferably 99% or more is achieved.

[0087] Advantageously, the hydrogenated heavy fraction thus comprises, and preferably consists at least in part of, middle distillates, more particularly a kerosene fraction, and / or a gas oil fraction, the latter of which highly advantageously meets the kerosene specifications of current standards, in particular the kerosene specifications of standard ASTM D7566, in particular the kerosene specifications of standard ASTM D7566 Appendix 5, and the gas oil fraction of which highly advantageously meets the gas oil specifications of current standards, in particular the gas oil specifications of European standard 15940. The hydrogenated heavy fraction obtained at the end of step d) may, as the case may be, in whole or in part, sent to an optional separation step e).

[0088] Optionally, a part of the hydrogenated heavy fraction obtained at the end of step d) is split off to form an inert stream which can then be recycled to step a) and, in parallel with the first recycle, helps to control the exothermicity of the oligomerization reaction in step a). Preferably, the weight of the inert stream recycled to step a) is 0 to 6 times, preferably 0.5 to 4 times, the weight of the fresh olefinic feedstock.

[0089] (Optional separation step e)) The process according to the invention comprises a step of fractionating the hydrogenated heavy fraction to obtain at least one middle distillate fraction, in particular at least one kerosene fraction and / or a gas oil fraction and optionally a gasoline fraction.

[0090] In particular, a kerosene base is separated off in step e), the final evaporation temperature of which is preferably between 140 and 300°C and advantageously has a flash point of at least 38°C; the evaporation temperature of the separated gas oil fraction is preferably at least 165°C, preferably at least 170°C and advantageously has a flash point of at least 55°C.

[0091] According to a particular embodiment, the optional separation step e) advantageously makes it possible to obtain: a kerosene fraction, the lower (initial) distillation point of which is preferably at least 140° C., highly preferentially at least 150° C.; a gasoline fraction; its upper (final) distillation point is preferably less than 140°C.

[0092] In this embodiment, the production of kerosene and gasoline is maximized.

[0093] According to another particular embodiment, the optional separation step e) advantageously makes it possible to obtain: - a top fraction, which corresponds to gasoline and contains preferably hydrocarbons containing from 5 to 10 carbon atoms; - middle distillates, advantageously comprising hydrocarbons containing from 9 to 24, preferably from 9 to 16, carbon atoms, constituting a kerosene fraction meeting commercial specifications; - A "residue" fraction; having an initial boiling point above 300°C, the desired final fraction is kerosene, which advantageously joins the diesel or fuel oil pool.

[0094] According to another particular embodiment, the optional separation step e) advantageously makes it possible to obtain: a kerosene fraction, the lower (initial) distillation point of which is preferably at least 140° C., highly preferentially at least 150° C., and the final distillation point of which is not more than 300° C., constituting a kerosene base meeting commercial specifications; an optional "residue" fraction; having an initial boiling point above 300° C., which advantageously joins the diesel or fuel oil pool.

[0095] In this embodiment, the production of kerosene is maximized.

[0096] According to yet another particular embodiment, the optional separation step e) advantageously makes it possible to obtain: - a top fraction, which corresponds to gasoline and contains preferably hydrocarbons containing from 5 to 10 carbon atoms; - middle distillates; advantageously comprising hydrocarbons containing from 10 to 24 carbon atoms, constituting gas oil fractions meeting commercial specifications.

[0097] In this embodiment, gas oil production is maximized.

[0098] The process according to the invention therefore thus makes it possible to improve the selectivity of the light olefin oligomerization process towards middle distillates, in particular kerosene and / or gas oil, and therefore to maximize the yield of middle distillates, while at the same time optimizing the overall conversion of the olefinic feedstock. The process according to the invention is a particularly flexible process, since it allows the skilled person to adapt the oligomerization selectivity and the separation of the effluents to maximize the production of kerosene and / or gas oil, up to the point where only gas oil or only kerosene can be produced.

[0099] The examples and figures which follow illustrate the invention and in particular certain embodiments of the invention but do not limit the scope of the invention.

[0100] (List of Drawings) FIG. 1 diagrammatically represents the implementation of the method according to the invention.

[0101] A feedstock (1) rich in C3 and C4 olefins is treated in an oligomerization section (a). The reaction effluent (5) is sent to a separation step (b) and separated in a series of columns to give: - stream (4); rich in C3-C4 compounds and containing unconverted feed olefins and any feed components (e.g. paraffins) which do not react in this boiling range; - stream (3), which contains dimers and trimers formed during oligomerization but is too light to be upgraded as middle distillate; - stream (9); it is recovered at the bottom of the last column and corresponds to the heavy fraction.

[0102] Stream (4) is at least partially recycled to the oligomerization inlet (a). A portion of stream (4) can be purged or upgraded in a separate unit (stream (6)), either continuously or ad libitum, depending on the nature of the feedstock.

[0103] Stream (3) is sent at least in part, preferably entirely, to the oligomerization step via the oligomerization inlet (a). A part of stream (3) may be sent to the gasoline pool for upgrading (stream (8)). Stream (8) may optionally be sent to hydrogenation c) and subsequently upgraded with stream (11).

[0104] Stream (9) is sent to the hydrogenation section (c). The hydrogenated effluent (10) is then separated in section (d) into: - Stream (11); sent to the gasoline pool; - Flow(13); upgraded to Kerosene; - Stream (14); consisting of the heaviest compounds generated during processing, which can be upgraded to gas oil.

[0105] Optionally, stream (2) consists, for example, of a mixture of kerosene and gas oil (stream (12)) and is sent to the oligomerization step a). It corresponds to the inerts stream used to control the exothermicity of the reaction in the reactors of oligomerization section a).

[0106] (Example) (Example 1 (according to the present invention)) The C4 olefinic hydrocarbon feedstock contained 24.8 wt. % 1-butene, 75 wt. % 2-butene and 0.2 wt. % n-butane, which was purified by catalysis in the presence of a silica-alumina catalyst (Axens commercial catalyst IP 811) at a temperature of 140-190°C, a pressure of 3.5 MPa and an HSV of 0.3 h, according to the process embodiment described in FIG. -1The oligomerization reaction is carried out in three reactors in series, with an intermediate heat exchanger between each reactor, which allows cooling before entering the next reactor.

[0107] The reaction effluent obtained at the end of the oligomerization step is separated by distillation into three fractions: 1) a C4-fraction, which contains unreacted feedstock and corresponds to about 17% by weight of the reaction effluent, said C4-fraction being recycled in total to the oligomerization step (corresponding to a weight ratio of C4-fraction relative to the fresh C4 olefinic hydrocarbon feedstock of 0.8 to 1.0); 2) a C5-140° C. cut, constituting an intermediate fraction and corresponding to about 64% by weight of the reaction effluent, said C5-140° C. cut being entirely recycled to the inlet of the oligomerization step so that the weight ratio of the C5-140° C. cut relative to the fresh C4 olefinic hydrocarbon feedstock is 3.6; 3) 140-300° C. fraction; corresponding to 19% by weight of the reaction effluent, sent for hydrogenation.

[0108] The conversion of the olefinic feedstock is greater than 90% by weight.

[0109] The hydrogenation carried out in the presence of a nickel catalyst on an alumina support was carried out at 180°C under 3.0 MPa hydrogen and HSV of 0.5 h. -1 , and a hydrogen flow rate of 50NL / h.

[0110] The olefin contents observed after hydrogenation are very low (bromine number <0.8 g / 100 g), meaning that the degree of hydrogenation is high (>99%).

[0111] The hydrogenation effluent is then sent to a distillation section where it is separated into three fractions: a light gasoline fraction; having an end point below 140° C. and a yield of 7% by weight relative to the weight of olefins in the initial C4 olefinic hydrocarbon feedstock; - a kerosene fraction having a distillation range of 140°C-300°C and a yield of 86% by weight relative to the weight of olefins of the C4 olefinic hydrocarbon feedstock; and - 300+ residue; corresponding to 7% by weight relative to the weight of olefins of the C4 olefinic hydrocarbon feedstock.

[0112] ((Example 2 (according to the present invention)) A biobased C4 olefinic hydrocarbon feedstock (obtained from the dehydration of isobutanol obtained by fermentation of sugars), containing 94.5 wt. % isobutene and 5.5 wt. % isobutane, is oligomerized in the presence of a silica-alumina catalyst (Axens commercial catalyst IP 811) at temperatures between 30 and 90 °C, pressures of 3.5 MPa, and HSV of 0.3 h. -1 The oligomerization reaction is carried out in three reactors in series, with an intermediate heat exchanger between each reactor, allowing cooling before entering the next reactor. A part of the hydrogenated end product is recycled to the oligomerization step a) to control the exothermicity in the reactors. This recycle represents 3.5 times the amount of fresh olefinic feedstock by weight.

[0113] The reaction effluent obtained at the end of the oligomerization step is separated by distillation into four fractions: 1) a C4-fraction, which contains unreacted feedstock and corresponds to about 7.1% by weight of the reaction effluent, said C4-fraction being recycled in total to the oligomerization step (corresponding to a weight ratio of C4-fraction to fresh C4 olefinic hydrocarbon feedstock of 0.4 to 0.6); 2) a C5-140°C cut, constituting an intermediate fraction and corresponding to about 31.4% by weight of the reaction effluent, said C5-140°C cut being recycled in total to the inlet of the oligomerization step, the weight ratio of the C5-140°C cut to the fresh C4 olefinic hydrocarbon feedstock being equal to 2.0; 3) The 140-300° C. fraction, which corresponds to about 61.5% by weight of the reaction effluent, is sent for hydrogenation.

[0114] The conversion of the olefinic feedstock is greater than 90% by weight.

[0115] Hydrogenation of the 140-300°C fraction was carried out in the presence of an alumina-supported nickel catalyst at 180°C under 3.0 MPa hydrogen for 0.5 h at HSV. -1 and a hydrogen flow rate of 50NL / h.

[0116] The olefin content observed after hydrogenation is very low (bromine number <0.8 g / 100 g), which means that the degree of hydrogenation is high (>99%).

[0117] The hydrogenation effluent is then sent to a distillation section where it is separated into three fractions: - a light gasoline fraction; having an end point below 140°C and a yield of 6% by weight in the initial C4 olefinic hydrocarbon feedstock relative to the weight of olefins; - a kerosene fraction, having a distillation range of 140°C-300°C and a yield within 89% by weight relative to the weight of olefins of the C4 olefinic hydrocarbon feedstock; and - 300+ residue; equivalent to 5% by weight relative to the weight of olefins of the C4 olefinic hydrocarbon feedstock.

[0118] (Example 3 (not in accordance with the present invention)) A C4 olefinic hydrocarbon feedstock similar to that processed by the method described in Example 1 is processed in Example 3: it contains 24.8 wt. % 1-butene, 75 wt. % 2-butene and 0.2 wt. % n-butane.

[0119] A C4 olefinic hydrocarbon feedstock is oligomerized under operating conditions similar to those of the process described in Example 1. However, the C5-140°C fraction of the reaction effluent is not recycled to the inlet of the oligomerization step.

[0120] The reaction effluent obtained at the end of the oligomerization step is separated by distillation into three fractions: 1) a C4-fraction, comprising unreacted feedstock and representing about 60.1% by weight of the reaction effluent, said C4-fraction being partially returned to the oligomerization step with a recycle ratio of C4-fraction to fresh C4 olefinic hydrocarbon feedstock of 0.5 by weight; 2) C5-140°C fraction, which constitutes the middle fraction and represents about 20.1% by weight of the reaction effluent; 3) A 140+ fraction, which corresponds to 19.8% by weight of the reaction effluent, is sent for hydrogenation.

[0121] The conversion of olefinic C4 compounds in the feedstock is about 85 wt%. The conversion of olefinic feedstock to C4 (85 wt%) is lower than that obtained by the process described in Example 1 (minimum 90 wt%).

[0122] The hydrogenation is carried out under the same conditions as in Example 1.

[0123] The hydrogenation effluent is then sent to a distillation section where it is separated into three fractions: - a light gasoline fraction; having an end point below 40° C. and a yield within 40% by weight relative to the olefins of the initial C4 olefinic hydrocarbon feedstock; and - a kerosene fraction; having a distillation range of 140°C-300°C, the yield being 40% by weight relative to the olefins of the initial C4 olefinic hydrocarbon feedstock.

[0124] The yield of kerosene (40%) is lower than that obtained by the method described in Example 1 (86%). [Brief description of the drawings]

[0125] [Figure 1] 1 diagrammatically represents the implementation of the method according to the invention;

Claims

1. A method for preparing an intermediate distillate from an olefinic feedstock containing a monoolefin having 3 to 6 carbon atoms, comprising the following steps: a) Oligomerization process: At least an olefinic feedstock, a first recycle, and a second recycle are fed and operated in the presence of at least one oligomerization catalyst, at a temperature of 20 to 500°C, a pressure of 1.0 to 10 MPa, and an HSV of 0.1 to 0.5 h. －１ It is; it produces reaction effluent containing dimers, trimers, and oligomers; b) A step of fractionating the reaction effluent obtained at the end of step a) into at least the following: - Light fraction; comprising at least a portion of the olefinic feedstock that has not been converted in step a); - Intermediate fraction; comprising at least a portion of the dimer and trimmer produced in step a); and - Heavy fraction; contains oligomers; c) Recycling process; including preparing a first recycle containing at least a portion of the light fraction; preparing a second recycle containing at least a portion of the intermediate fraction; and transferring the first and second recycles to the oligomerization process a); d) A step to hydrogenate at least a portion of the heavy fraction separated in step b) in the presence of hydrogen; giving a hydrogenated heavy fraction containing an intermediate distillate.

2. The method according to claim 1, wherein the olefinic feedstock comprises a monoolefin containing three and / or four carbon atoms.

3. The method according to claim 1 or 2, wherein the olefinic feedstock is at least partially bio-based.

4. The method according to claim 1, wherein the first recycling is supplied to step a) in a weight ratio of 0.3 to 1.5, preferably 0.5 to 1.2, relative to the olefinic supply material.

5. The method according to claim 1, wherein the second recycling is supplied to step a) in a weight ratio of 0.5 to 10.0, preferably 1.0 to 5.0, and more preferably 1.0 to 4.0 relative to the olefinic supply material.

6. The method according to claim 1, wherein the oligomerization catalyst in step a) is selected from a silica-impregnated phosphate-based catalyst, an ion exchange resin, silica-alumina, and a high-purity zeolite or alumina-supported zeolite.

7. The method according to claim 1, wherein the oligomerization step a) is performed in the presence of a silica-alumina-based catalyst, and the temperature during the execution is 20°C to 300°C, preferably 25°C to 220°C, and more preferably 30°C to 200°C.

8. The method according to claim 1, wherein the pressure when performing the oligomerization step a) is 1.5 to 6.5 MPa, preferably 2.0 to 4.0 MPa.

9. The HSV during the oligomerization process (a) is 0.2 to 0.3h. －１ The method according to claim 1.

10. The method according to claim 1, further comprising step e) separating the hydrogenated heavy fraction obtained from step d), thereby separating at least one intermediate distillate fraction, in particular a kerosene fraction and / or a gas oil fraction.

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