Ethylene oligomerisation plant for producing alpha-olefins

Abstract

The present invention relates to an ethylene oligomerisation plant for producing oligomerised alpha-olefins, with the production of a fouling by-product in the form of a deposit, said plant comprising a reaction section comprising: - a reactor (c) for two-phase gas / liquid or single-phase all-liquid oligomerisation from a possible solvent, an oligomerisation catalyst and ethylene, and - cooling means associated with said reactor in the form of at least one cooling circuit external to the reactor and / or in the form of a double shell of the reactor walls. Packings are arranged in the reaction section to increase the contact area per unit of volume available for depositing the by-product.

Description

[0001] ETHYLENE DOLIGOMERIZATION PLANT FOR THE PRODUCTION OF ALPHA-OLEFINS

[0002] technical field

[0003] The invention relates to the field of C2-C4 olefin oligomerization. This oligomerization aims to produce higher olefins such as butenes, hexenes, octenes, nonenes, and decenes, which are olefins used as first petrochemical intermediates. More particularly, the invention relates to the oligomerization of ethylene into linear alpha-olefins such as 1-butene, 1-hexene, 1-octene, or a mixture of linear alpha-olefins from 1-butene to 1-dodecene.

[0004] The oligomerization reaction is most often carried out in a homogeneous catalysis process, particularly in the liquid phase. It is also highly exothermic, generally requiring external cooling via heat exchangers.

[0005] Previous technique

[0006] The invention relates first to the field of oligomerization processes using two-phase gas / liquid reactors, generally implemented in the form of bubble columns. Due to the exothermic nature of oligomerization reactions, bubble columns generally also include one or more recirculation loops. These loops consist of drawing off a liquid fraction, cooling it with one or more heat exchangers, and reintroducing it into the reaction vessel. This recirculation loop ensures good homogeneity of concentrations and controls the temperature throughout the entire reaction volume. The installation also generally includes, downstream of the oligomerization reactor, one or more separation columns, allowing the desired reaction products to be isolated and, optionally, the unreacted solvent and / or ethylene to be recycled.Installations of this type are described, for example, in patents EP-2 703373 and EP-3338884.

[0007] The invention also relates to the field of oligomerization processes using single-phase liquid reactors which are used in particular to carry out more specifically a tetramerization of ethylene towards a mixture of alpha-olefins of the 1-hexene and 1-octene type, with the same type of recirculation loop equipped with heat exchanger(s), and the same type of separation columns downstream of the reactor: This oligomerization reaction is also exothermic and also requires means of cooling.

[0008] Whether using a two-phase or single-phase reactor, a common problem arises with this type of reaction: the oligomerization reaction generates a solid, fouling, polymeric byproduct, as explained in the publication by RF Rossouw, RLJ Coetzer, and PD Pretorius, "Simulation experiments for maximising the availability of a commercial octene production facility," Volume 26(1), pp. 53-77, 2010, published by ORION. This byproduct tends to deposit on the reactor walls and all associated equipment in the reaction section, particularly on heat exchange surfaces, notably the heat exchanger tubes of the recirculation loops mentioned above.However, fouling of these heat exchange surfaces, even more so than on the other walls of the reaction section, is problematic because it progressively reduces the efficiency of the exchangers as the reaction proceeds and the fouling deposits thicken. This is why regular, targeted cleaning of the heat exchangers is necessary: ​​production must be stopped and the exchangers cleaned, generally by passing a hot fluid over their surface to dissolve and remove the deposits. These production stoppages are detrimental to the profitability of the process.

[0009] Patent EP-3338884 proposes an improved method for cleaning heat exchangers by duplicating the cooling system for a single reactor. This involves two solvent recirculation loops, each equipped with heat exchangers, operating alternately: one loop is operational while the other, inoperative, is being cleaned, for example, using a hot fluid circulating in the cooling loop being cleaned, which dissolves and removes deposits from the exchangers. This technical solution offers the significant advantage of not requiring production to be stopped during exchanger cleaning, a task that must be performed more frequently than cleaning the rest of the reaction section. However, the need for regular switching between the two cooling loops poses a challenge for operating the process on an industrial scale.

[0010] And whatever the method of cleaning the exchangers, it remains that it must be carried out at fairly high frequencies, for example on the order of a few hours on an industrial scale, which is a strong constraint for the conduct of the industrial process, and, ultimately, for its profitability.

[0011] The invention aims to improve the oligomerization installation / process using a gas / liquid reactor or an all-liquid reactor. In particular, it seeks to improve the productivity / profitability of the process, notably by acting more effectively on fouling deposits produced during the oligomerization reaction.

[0012] In the context of this text, the term "reaction section" refers to the gas / liquid type reactor(s), with a single reactor or several reactors in series and / or in parallel, as well as their possible associated equipment, and, in particular, in the case of the oligomerization processes relevant to the invention: - the cooling loop(s) comprising one or more heat exchangers and associated with each of the reactors to control the exotherm of the reaction, - the means of introducing the catalyst into the reactor(s), for example in the form of an introduction loop - separate or not - from the cooling loop, - the means external to the reactor for separating / neutralizing the catalyst.

[0013] In the context of this text, the term "fractionation section" refers to the separation device(s), in particular by distillation, located downstream of the reaction section, with a single device or a plurality of devices arranged in series and / or in parallel, devices which may be identical or different in their dimensions or their design / operation.

[0014] In the context of this text, the terms "upstream" and "downstream" are understood in terms of the general direction of flow of the reaction fluid in the production unit.

[0015] In the context of this text, when specifically mentioning the oligomerization of ethylene, for the sake of brevity, we are also referring to the oligomerization of all C2 to C4 olefins, therefore also propylene and 2-butenes or isobutenes.

[0016] Summary of the invention

[0017] The invention relates firstly to a C2-C4 olefin oligomerization plant, particularly for ethylene, to produce alpha-olefins, with the production of a fouling by-product in the form of deposits. The plant comprises a reaction section having: - a two-phase gas / liquid or single-phase liquid oligomerization reactor (c) using an optional solvent, a homogeneous oligomerization catalyst, and ethylene; and - cooling means associated with said reactor in the form of at least one external cooling circuit and / or a double jacket for the reactor walls. According to the invention, packings are arranged in the reaction section to increase the contact surface area per unit volume accessible for the deposition of the by-product.

[0018] These packings help to slow down the fouling of the cooling systems, and therefore their cleaning frequency.

[0019] Note that the invention applies mutatis mutandis not only to the oligomerization of ethylene, but also to C2 to C4 olefins, either starting from only one of these olefins (for example, only ethylene) or a mixture of at least two of these olefins (for example, an ethylene + propylene mixture).

[0020] It should also be noted that the homogeneous oligomerization catalyst can comprise several components, as detailed later, and is also referred to interchangeably as the catalytic (oligomerization) system in this text. A homogeneous catalyst is defined as one in which the catalyst or catalytic system is in the same phase as the reactants and products of the oligomerization reaction.

[0021] The invention demonstrated that the usual purpose of packings, typically used to increase the contact surface between two different phases, for example, between a liquid and a gas, could be repurposed. Here, the aim was not to promote contact between reactants or between a reactant and its catalyst, but rather to increase the surface area within the reactor where the fouling by-product can be deposited, thereby reducing the quantity, and thus the thickness, of these by-product deposits on the heat exchangers. In fact, the invention made it possible to significantly reduce the frequency of cleaning the cooling systems, since the rate of fouling of the exchangers was greatly slowed. This effectively shifts the fouling from the cooling systems to the reactor, which is, to say the least, an unconventional approach.Furthermore, the presence of these packings did not complicate or disrupt reactor operation; the production yield between cleanings remained the same, even though one might have feared that this would cause problems, particularly in all-liquid reactors that never use such packings. Preferably, the increase in the contact area per unit volume of the reaction section (which therefore includes the internal volume of the reactor and the associated recirculation loops) due to the presence of the packings in the reactor is chosen to be at least 5 m². 2 / m 3 , in particular of at least 10 m 2 / m 3 preferably between 10 and 500 m 2 / m 3 . Therefore, a significant increase in surface area is targeted in order to achieve a sufficient slowing of the fouling of the exchangers and thus a sufficiently long interval between their cleaning.

[0022] The invention can be implemented in various embodiments. The packings can thus be located solely within the reactor, or also, or alternatively, in other areas of the reaction section. Where the cooling means consist of at least one cooling circuit external to the reactor, the packings can be located only within the reactor, or within the reactor and the cooling circuit(s), or only within the cooling circuit(s).

[0023] Preferably, the packings are placed in the liquid-filled volume VI of the reactor, in particular in at least 5% of said volume VI, in particular at most 100% of said volume VI, preferably between 30 or 50 and 90% or between 70 and 90% of said volume VI. In the case of an all-liquid reactor, it is therefore possible to fill the entire available volume of the reactor; in the case of a gas / liquid reactor, the packings are confined to the submerged part of the inside of the reactor, since that is where fouling deposits occur, and it is unnecessary to provide them in the "head" of the reactor.

[0024] The invention proposes the use of any type of packing. Specifically, packings can be chosen from at least one of the following: structured packing, loose packing, internal packing defining fins, or other developed geometric shapes. Their geometry can vary considerably, particularly depending on the shape and size of the reactor.

[0025] According to one embodiment, the external cooling circuit includes at least one recirculation loop for the liquid phase of the reactor, said loop incorporating one or more heat exchangers.

[0026] In this case, the external cooling circuit may include at least two separate recirculation loops, each incorporating one or more heat exchangers, and which are alternately operational.The installation according to the invention may include a section for separating the reaction effluents from the reaction section, downstream of the oligomerization reactor. This separation section includes at least one first fractionation column for the effluents, so as to obtain a fraction (header) containing the starting olefin(s) and at least one other fraction (bottomer). The reaction mixture resulting from the oligomerization carried out in the reactor is thus separated. This mixture comprises the C2-C4 olefin(s) (ethylene), solvent, an oligomerization catalyst, and oligomerization products, so as to obtain a head fraction containing the starting olefin(s) (ethylene in this case) and at least one bottomer fraction. Any known means of separation, such as a distillation column, downstream of the reactor, may be used for this purpose.The aim of this separation is to recover the starting C2-C4 olefin(s) (ethylene) that have not reacted, in particular for reuse.

[0027] In this case, the separation section may also include, downstream of the first fractionation column, at least a second fractionation column to obtain at least one fraction enriched in alpha-olefins (oligomerization products) and one fraction enriched in solvent. Any known separation method can be used for this purpose, such as another distillation column downstream of the first. The objective of this separation is to recover any solvent for reuse: at least a portion of the bottom fraction resulting from the separation of the mixture is thus separated into at least one upper fraction enriched in oligomerization products and one lower fraction enriched in solvent, or into at least one upper fraction enriched in solvent and one lower fraction enriched in oligomerization products (the latter case, in particular, when the aim is to separate any solvent from the heavier products).

[0028] Advantageously, at least part of the fraction enriched in potential solvent, known as recycled potential solvent, from the second separation can thus be recycled to form part of the liquid phase entering the oligomerization reactor, particularly after optional compression (especially in cases where the oligomerization reactor operates at high pressure). This liquid fraction is essentially composed of solvent but may also include traces of alpha-olefin(s) (ethylene), reaction products or by-products, and / or the liquid-soluble catalyst.

[0029] It should be noted that, depending on the type of fractionation scheme chosen in the fractionation section, which must be adapted according to the products sought, the solvent separation can be carried out in the second separation or in a n. emeseparation, carried out downstream of the reaction section, at the top of the column or at the bottom of the column, the terms "first" and "second" separations are therefore not to be understood literally and are just indicated to signify that one takes place downstream of the other, but not necessarily consecutively.

[0030] Advantageously, the installation according to the invention includes a recycling loop for the starting olefin(s) from the separation section to the reaction section. This allows for the recycling of at least a portion of the overhead fraction from the first fractionation column mentioned above, this overhead fraction containing the starting C2-C4 olefin(s). This gaseous fraction is composed essentially of the C2-C4 olefin(s) in question (ethylene), but may also include traces of heavier products (the desired alpha-olefin, or other alkenes and / or alkanes produced by the reaction) and / or traces of solvent and / or traces of other compounds present in the ethylene feedstock (traces of methane, ethane, etc.).

[0031] The installation according to the invention can therefore also include a recycling loop of the starting olefin(s) from the separation section to the reaction section.

[0032] The invention also relates to a process for the oligomerization of ethylene, for producing alpha-olefins from an optional solvent and a catalyst in a reaction section comprising: - a two-phase gas / liquid or single-phase all-liquid oligomerization reactor (c) using a solvent, a homogeneous oligomerization catalyst, and ethylene; and - cooling means associated with said reactor in the form of at least one cooling circuit external to the reactor and / or in the form of a double jacket for the reactor walls, such that the contact surface area per unit volume of the reactor available for the deposition of the fouling by-product is increased by placing packings in the reaction section. It thus advantageously implements the installation described above.

[0033] According to one embodiment, the reactor's external cooling circuit comprises, according to the invention, at least two separate recirculation loops, each incorporating one or more heat exchangers, which are operated alternately: at least one of the loops is operational while the heat exchangers of the other loop(s) that are not operational are being cleaned, notably using a fluid whose temperature is higher than the dissolution temperature of the fouling by-product. Preferably, oligomerization in the reactor is carried out at a pressure between 0.1 and 10.0 MPa and at a temperature between 30 and 200°C.

[0034] The invention will be described by means of non-limiting examples of the oligomerization process in question, illustrated by the figures listed below. List of figures

[0035] Figure 1 represents a diagram of an ethylene oligomerization (tetramerization) installation suitable for implementing the invention.

[0036] Figure 2 shows an example of packing for a reactor in an oligomerization plant according to the invention. Figure 3 shows another example of packing for a reactor in an oligomerization plant according to the invention.

[0037] Figure 4 represents another example of packing for a reactor in an oligomerization plant according to the invention.

[0038] Figure 5 represents another example of packing for a reactor in an oligomerization plant according to the invention.

[0039] Figure 6 is a variant of the oligomerization installation scheme of Figure 1 adapted for the dimerization of ethylene suitable for implementing the invention.

[0040] Figures 1 and 6 are highly schematic and represent the various components of the installation without necessarily respecting the scale or relative spatial configuration of the components in question, limiting themselves to representing the most important components with regard to the invention, in order to facilitate their interpretation. Thus, in particular, the external cooling loop for the oligomerization reactor, necessary for controlling the exothermicity of the reaction in the reactor, the catalyst injection system, and the means for introducing the fluids are not shown, as these are known in oligomerization installations. The same reference numerals from one figure to the other correspond to the same flows / devices.

[0041] Furthermore, it should be noted that the fractionation scheme can be more complex and include more than two columns; it can also incorporate additional separation methods other than columns, particularly for separating the spent catalyst from the reaction products and by-products, such as flashes, thin-film evaporators, or any other technology known to those skilled in the art. See, for example, patent EP-3,338,884 for further details.

[0042] Definitions, abbreviations and conventions within the scope of the present invention

[0043] - The terms "upstream" and "downstream" are to be understood in terms of the general flow of the fluid in question in the installation, from the introduction of the reactants, such as ethylene here, to the recovery of the product of interest, namely the alpha-olefin or alpha-olefins considered in the process.

[0044] Oligomerization corresponds to any reaction involving the addition of one olefin to a second olefin, whether identical or different from the first. The olefin thus obtained has the molecular formula C n H 2n where n is equal to or greater than 4. In the examples, this refers to the main reaction of ethylene with itself to produce 1-butene and / or 1-hexene and / or higher oligomers. It includes the case of tetramerization.

[0045] - An alpha-olefin (here the product obtained after oligomerization) is a linear olefin whose double bond is located at the terminal position of the alkyl chain.

[0046] - The homogeneous oligomerization catalyst is in the examples a mixture (also called catalytic system) of at least one metallic precursor and at least one activating agent, optionally in the presence of at least one additive and possibly a solvent.

[0047] - The liquid phase corresponds to the mixture of all the compounds which are in a liquid physical state under the temperature and pressure conditions of the reaction section, including the incoming fluid flows and the outgoing flows to the fractionation section.

[0048] - The gaseous phase can correspond to a mixture of all the compounds that exist in a gaseous physical state under the temperature and pressure conditions of the reaction vessel (oligomerization reactor). This gaseous phase is present as bubbles in the liquid phase, particularly in the aforementioned inlet streams, and also in a single-phase state in the inlet / outlet streams of the reactor and possibly in the upper part of the reactor (called the "gaseous head" of the reactor). - As already mentioned, the oligomerization reaction section comprises the oligomerization reactor and its equipment, including at least one cooling loop, and the means for introducing / discharging the various fluids and the catalyst, in its simplest form. The invention also includes a reaction section composed of several oligomerization reactors, in series and / or in parallel.For the sake of brevity, we can refer to the reaction section as a “reactor”.

[0049] - A "fresh" component (ethylene, solvent) is a component that is not recycled from a downstream step of the oligomerization process to a more upstream step or during the same step

[0050] Conversely, a "recycled" component is a component produced in a downstream step of the process, separated, and recycled to an upstream step. Recycled ethylene or solvent should be understood as consisting primarily of ethylene and solvent, respectively, but potentially containing traces of other components.

[0051] For the sake of brevity, we will not describe in detail below the entire oligomerization installation and the operating conditions of its implementation, which are not closely related to the invention. For more details on oligomerization as a whole, and non-limiting examples of installations and oligomerization processes relevant to the invention, reference may be made in particular to the aforementioned patents EP-2 703373 and EP-3338884. However, examples of reagents, solvents, and catalysts, as well as the main methods of conducting the oligomerization, are given below: The oligomerization process according to the invention allows the production of linear alpha-olefins by contacting ethylene with a catalytic system and optionally a solvent.

[0052] All catalytic systems known to those skilled in the art and suitable for use in dimerization, trimerization, tetramerization processes, and more generally in oligomerization processes according to the invention, fall within the scope of the invention. These catalytic systems and their implementations are described in particular in patents FR2984311, FR2552079, FR3019064, FR3023183, FR3042989, and FR3045414. It should be noted that:

[0053] - The dimerization of ethylene mainly yields butenes, notably butene-1, (generally without solvent)

[0054] - The trimerization of ethylene mainly yields hexenes, notably hexene-1,

[0055] - Tetramerization of ethylene primarily yields octenes, notably octene-1. (generally with a solvent)

[0056] Preferably, catalytic systems comprise, preferably are made up of:

[0057] - a metallic precursor, preferably nickel-, titanium-, or chromium-based, - an activating agent or a mixture of activating agents,

[0058] - optionally an additive, and

[0059] - optionally a solvent.

[0060] The metallic precursor

[0061] The metallic precursor used in the catalytic system is chosen from compounds based on nickel, titanium or chromium.

[0062] In one embodiment, the metallic precursor is nickel-based and preferably comprises nickel of oxidation state (+11). Preferably, the nickel precursor is chosen from nickel(II) carboxylates such as, for example, nickel(II) 2-ethylhexanoate, nickel(II) phenates, nickel(II) naphthenates, nickel(II) acetate, nickel(II) trifluoroacetate, nickel(II) triflate, nickel(II) acetylacetonate, nickel(II) hexafluoroacetylacetonate, TT-allylnickel(II) chloride, TT-allylnickel(II) bromide, methallylnickel(II) chloride dimer, h3-allylnickel(II) hexafluorophosphate, r|3-methallylnickel(II) hexafluorophosphate and nickel(II) 1,5-cyclooctadienyl, in their hydrated or non-hydrated form, taken alone or in mixtures. In a second embodiment, the metallic precursor is titanium-based and preferably comprises an aryloxy or alkoxy compound of titanium.

[0063] The alkoxy compound of titanium advantageously conforms to the general formula [Ti(OR)4] in which R is a linear or branched alkyl radical. Preferred alkoxy radicals include, but are not limited to, tetraethoxy, tetraisopropoxy, tetra-n-butoxy, and tetra-2-ethylhexyloxy.

[0064] The aryloxy compound of titanium advantageously conforms to the general formula [Ti(OR')4] in which R' is an aryl radical, substituted or not with alkyl or aryl groups. The radical R' may contain heteroatom-based substituents. Preferred aryloxy radicals are chosen from phenoxy, 2-methylphenoxy, 2,6-dimethylphenoxy, and...

[0065] 2,4,6-trimethylphenoxy, 4-methylphenoxy, 2-phenylphenoxy, 2,6-diphenylphenoxy, the

[0066] 2,4,6-triphenylphenoxy, 4-phenylphenoxy, 2-tert-butyl-6-phenylphenoxy, 2,4-ditertbutyl-6-phenylphenoxy, 2,6-diisopropylphenoxy, 2,6-ditert-butylphenoxy, 4-methyl-2,6-ditert-butylphenoxy, 2,6-dichloro-4-tert-butylphenoxy and 2,6-dibromo-4-tert-butylphenoxy, the biphenoxy radical, binaphtoxy, 1,8-naphthalene-dioxy.

[0067] According to a third embodiment, the metallic precursor is chromium-based and preferably comprises a chromium(II) salt, a chromium(III) salt, or a salt of a different oxidation state that may contain one or more identical or different anions, such as, for example, halides, carboxylates, acetylacetonates, alkoxy or aryloxy anions. Preferably, the chromium-based precursor is selected from CrCl3, CrCl3(tetrahydrofuran)3, Cr(acetylacetonate)3, Cr(naphthenate)3, Cr(2-ethylhexanoate)3, Cr(acetate)3.

[0068] The concentration of nickel, titanium or chromium is between 0.01 and 300.0 ppm by mass of atomic metal relative to the reaction mass, preferably between 0.02 and 100.0 ppm, preferably between 0.03 and 50.0 ppm, more preferably between 0.5 and 20.0 ppm and even more preferably between 2.0 and 50.0 ppm by mass of atomic metal relative to the reaction mass.

[0069] The activating agent

[0070] Regardless of the metallic precursor, the catalytic system further comprises one or more activating agents selected from aluminium-based compounds such as methyl aluminium dichloride (MeAICI2), dichloroethyl aluminium (EtAICI2), ethyl aluminium sesquichloride (Et3Al2Cl3), chlorodiethyl aluminium (Et2AICI), chlorodiisobutyl aluminium (i-Bu2AICI), triethyl aluminium (AIEt3), tripropyl aluminium (Al(n-Pr)3), triisobutyl aluminium (Al(i-Bu)3), diethyl ethoxy aluminium (Et2AIOEt), methylaluminoxane (MAO), ethylaluminoxane (EAO), and modified methylaluminoxanes (MMAO).

[0071] The additive

[0072] Optionally, the catalytic system includes one or more additives.

[0073] When the catalytic system is nickel-based, the additive is chosen from: nitrogen-type compounds, such as trimethylamine, triethylamine, pyrrole, 2,5-dimethylpyrrole, pyridine, 2-methylpyridine, 3-methylpyridine, 4-methylpyridine, 2-methoxypyridine, 3-methoxypyridine, 4-methoxypyridine, 2-fluoropyridine, 3-fluoropyridine, 3-trifluoromethylpyridine, 2-phenylpyridine, 3-phenylpyridine, 2-benzylpyridine, 3,5-dimethylpyridine, 2,6-dimethylpyridine and 2,6-diphenylpyridine, quinoline, 1,10-phenanthroline, N-methylpyrrole, N-butylpyrrole, N-methylimidazole, the N-butylimidazole, 2,2'-bipyridine, N,N'-dimethylethane-1,2-diimine, N,N'-di-t-butylethane-1,2-diimine, N,N'-di-t-butylbutane-2,3-diimine, N,N'-diphenylethane-1,2-diimine, N,N'-bis-(dimethyl-2,6-phenyl)ethane-1,2-diimine, N,N'-bis-(diisopropyl-2,6-phenyl)ethane-1,2-diimine, N,N'-diphenylbutane-2,3-diimine, N,N'-bis-(dimethyl-2,6-phenyl)-butane-2,3-diimine, N,N'-bis-(diisopropyl-2,6-phenyl)-butane-2,3-diimine, or phosphine-type compounds are independently selected from tributylphosphine, triisopropylphosphine, tricyclopentylphosphine, tricyclohexylphosphine, triphenylphosphine, tris(o-tolyl)phosphine, bis(diphenylphosphino)ethane, trioctylphosphine oxide, triphenylphosphine oxide, triphenylphosphite, or compounds corresponding to the general formula (I) or one of the tautomers of said compound:, in which

[0074] - A and A', whether identical or different, are independently an oxygen or a single bond between the phosphorus atom and a carbon atom, - the R groups 1a and R 1bare independently chosen from among the methyl, trifluoromethyl, ethyl, n-propyl, i-propyl, n-butyl, i-butyl, t-butyl, pentyl, cyclohexyl, adamantyl groups, substituted or unsubstituted, containing or not containing heteroelements; the phenyl, o-tolyl, m-tolyl, p-tolyl, mesityl, 3,5-dimethylphenyl, 4-n-butylphenyl, 2-methylphenyl, 4-methoxyphenyl, 2-methoxyphenyl, 3-methoxyphenyl, 4-methoxyphenyl, 2-isopropoxyphenyl, 4-methoxy-3,5-dimethylphenyl, 3,5-dimethyl-4-methoxyphenyl, 4-chlorophenyl, 3,5-di(trifluoromethyl)phenyl, benzyl, naphthyl, bisnaphthyl, pyridyl, bisphenyl, furanyl, and thiophenyl groups

[0075] - the R group 2is chosen independently from among the methyl, trifluoromethyl, ethyl, n-propyl, i-propyl, n-butyl, i-butyl, t-butyl, pentyl, cyclohexyl, adamantyl groups, substituted or unsubstituted, containing heteroelements or not; the phenyl, o-tolyl, m-tolyl, p-tolyl, mesityl, 3,5-dimethylphenyl, 4-n-butylphenyl, 4-methoxyphenyl, 2-methoxyphenyl, 3-methoxyphenyl, 4-methoxyphenyl, 2-isopropoxyphenyl, 4-methoxy-3,5-dimethylphenyl, 3,5-dimethyl-4-methoxyphenyl, 4-chlorophenyl, 3,5-bis(trifluoromethyl)phenyl, benzyl, naphthyl, bisnaphthyl, pyridyl, bisphenyl, furanyl, thiophenyl groups.

[0076] When the catalytic system is titanium-based, the additive is chosen from diethyl ether, diisopropyl ether, dibutyl ether, diphenyl ether, 2-methoxy-2-methylpropane, 2-methoxy-2-methylbutane, dimethoxy-2,2 propane, di(2-ethylhexyloxy)-2,2 propane, 2,5-dihydrofuran, tetrahydrofuran, 2-methoxytetrahydrofuran, 2-methyltetrahydrofuran, 3-methyltetrahydrofuran, 2,3-dihydropyran, tetrahydropyran, 1,3-dioxolane, 1,3-dioxane, 1,4-dioxane, dimethoxyethane, di(2-methoxyethyl) ether, benzofuran, glyme and diglyme taken alone or in mixture.

[0077] When the catalytic system is chromium-based, the additive is chosen from:

[0078] - Nitrogen-type compounds, such as trimethylamine, triethylamine, pyrrole, 2,5-dimethylpyrrole, pyridine, 2-methylpyridine, 3-methylpyridine, 4-methylpyridine, 2-methoxypyridine, 3-methoxypyridine, 4-methoxypyridine, 2-fluoropyridine, 3-fluoropyridine, 3-trifluoromethylpyridine, 2-phenylpyridine, 3-phenylpyridine, 2-benzylpyridine, 3,5-dimethylpyridine, 2,6-dimethylpyridine and 2,6-diphenylpyridine, quinoline, 1,10-phenanthroline, N-methylpyrrole, N-butylpyrrole, N-methylimidazole, N-butylimidazole, 2,2'-bipyridine, N,N'-dimethylethane-1,2-diimine, N,N'-di-t-butylethane-1,2-diimine, N,N'-di-t-butylbutane-2,3-diimine, N,N'-diphenylethane-1,2-diimine, N,N'-bis-(dimethyl-2,6-phenyl)ethane-1,2-diimine, N,N'-bis-(diisopropyl-2,6-phenyl)ethane-1,2-diimine, N,N'-diphenylbutane-2,3-diimine, N,N'-bis-(dimethyl-2,6-phenyl)butane-2,3-diimine, N,N'-bis-(diisopropyl-2,6-phenyl)-butane-2,3-diimine,

[0079] - or among the aryloxy compounds with the general formula [M(R 3 0) 2-n X n ] y in which

[0080] • M is chosen from magnesium, calcium, strontium and barium, preferably magnesium,

[0081] • R 3 is an aryl radical containing 6 to 30 carbon atoms, X is a halogen or alkyl radical containing 1 to 20 carbon atoms,

[0082] • n is an integer that can take the values ​​of 0 or 1, and

[0083] • y is an integer between 1 and 10, preferably y is equal to 1, 2, 3 or 4.

[0084] Preferably, the aryloxy radical R sO is chosen from 4-phenylphenoxy, 2-phenylphenoxy, 2,6-diphenylphenoxy, 2,4,6-triphenylphenoxy, 2,3,5,6-tetraphenylphenoxy, 2-tert-butyl-6-phenylphenoxy, 2,4-ditertbutyl-6-phenylphenoxy, 2,6-diisopropylphenoxy, 2,6-dimethylphenoxy, 2,6-ditert-butylphenoxy, 4-methyl-2,6-ditert-butylphenoxy, 2,6-dichloro-4-tert-butylphenoxy and 2,6-dibromo-4-tert-butylphenoxy. The two aryloxy radicals can be carried by the same molecule, such as the biphenoxy radical, binaphtoxy, or 1,8-naphthalene dioxygen. Preferably, the aryloxy radical R s O is 2,6-diphenylphenoxy, 2-tert-butyl-6-phenylphenoxy or 2,4-di-tert-butyl-6-phenylphenoxy.

[0085] - or among the compounds having the general formula (R 1 ) (R 2 )XYZ(R 3 ) (R 4 ) where X and Z are independently a phosphorus, an arsenic, an antimony, a nitrogen or a bismuth and Y is a group linking X and Z.

[0086] X and Z can be independently in the oxidized state bound to an O, an N, or an S.

[0087] Y can be selected from organic hydrocarbon and heterohydrocarbon bonding groups or inorganic bonding groups, or ionic bonding groups such as 1,2-ethane, 1,2-propane, 1,2-phenylene, -N(R 5 )- , -P(R 5 )- , -B(R 5 )- , -Si(R 5 )2- where R 5 can be a hydrogen, a hydrocarbon group substituted or not by a heteroatom, or a halogen. Preferably, Y is a -(NR) type group 5 )' such as those described in patents W02004056477 and WO 2008119153. An example of a type of catalytic system usable in the invention includes: at least one chromium-based metallic precursor, at least one heteroatomic ligand of general formula (I) in which

[0088] R. 1 , R 2 , R 3 , R 4 and R 5are identical or different from each other, linked or not to each other, are chosen from a cyclic or non-cyclic alkyl group, aromatic or not, having from 1 to 15 carbon atoms, containing or not heteroelements.

[0089] Preferably, the R groups 1 , R 2 , R 3 , R 4 and R 5identical or different from each other, linked or not linked to each other, are chosen from among the methyl, ethyl, n-propyl, i-propyl, n-butyl, i-butyl, ter-butyl, pentyl, cyclopentyl, hexyl, cyclohexyl, adamantyl groups, substituted or not, containing or not heteroelements; the phenyl, o-tolyl, m-tolyl, p-tolyl, mesityl, 3,5-dimethylphenyl, 4-n-butylphenyl, 2-methoxyphenyl, 3-methoxyphenyl, 4-methoxyphenyl, 2-isopropylphenyl, 4-methoxy-3,5-dimethylphenyl, 3,5-dimethyl-4-methoxyphenyl, 2-chlorophenyl, 3-chlorophenyl, 4-chlorophenyl, 2-fluorophenyl, 3-fluorophenyl, 4-fluorophenyl, 4-trifluoromethylphenyl, 3,5-di(trifluoromethyl)phenyl, benzyl, naphthyl, bisnaphthyl, pyridyl, furanyl, thiophenyl groups, substituted or unsubstituted.

[0090] By way of non-limiting example, the following heteroatomic ligands can be cited: (phenyl)2PN(methyl)P(phenyl)2, (phenyl)2PN(i-propyl)P(phenyl)2,

[0091] (phenyl)2PN(phényl)P(phenyl)2, (2-methoxyphenyl)2PN(i-propyl)P(phenyl)2, (2- methoxyphenyl)2PN(i-propyl)P(2-methoxyphenyl)2, (4-methoxyphenyl)2PN(i-propyl)P(4- methoxyphenyl)2, (2-fluorophenyl)2PN(i-propyl)P(2-fluorophenyl)2, (2- fluorophenyl)(phenyl)PN(i-propyl)P(2-fluorophenyl)2, (2-fluorophenyl)(phenyl)PN(i- propyl)P(2-fluorophenyl)(phenyl), (2-fluorophenyl)(phenyl)PN(i-propyl)P(phenyl)2

[0092] - at least one activator chosen from aluminum-based compounds such as methylaluminum dichloride (MeAIC2), dichloroethylaluminum (EtAIC2), ethylaluminum sesquichloride (Et3Al2Cl3), chlorodiethylaluminum (Et2AIC3), chlorodiisobutylaluminum (i-Bu2AIC3), triethylaluminum (AIEt3), trimethylaluminum (AIMe3), tri-,-octylaluminum (AIOct3), tripropylaluminum (Al(n-Pr)3), triisobutylaluminum (Al(i-Bu)3), diethylethoxyaluminum (Et2AlOEt), methylaluminoxane (MAO), ethylaluminoxane (EAO), and modified methylaluminoxanes (MMAO). The solvent

[0093] In another embodiment of the invention, the catalytic system itself optionally comprises one or more solvents. This solvent or these solvents can help to introduce the catalyst into the reaction section.

[0094] The solvent or solvents are advantageously chosen from among ethers, alcohols, halogenated solvents (fluorinated, chlorinated, brominated, iodinated) and aliphatic and cycloaliphatic hydrocarbons, comprising between 1 and 20 atoms, preferably between 2 and 10 carbon atoms, preferably between 4 and 8, aromatic hydrocarbons comprising from 4 to 20 carbon atoms, and preferably between 5 and 15 carbon atoms.

[0095] Preferably, the solvent is chosen from pentane, hexane, cyclohexane, methylcyclohexane, heptane, butane or isobutane, cycloocta-1,5-diene, cyclopentadiene, benzene, toluene, ortho-xylene, mesitylene, ethylbenzene, diethyl ether, tetrahydrofuran, 1,4-dioxane, dichloromethane, chlorobenzene, methanol, ethanol, pure or in mixtures, and ionic liquids.

[0096] The solvent is chosen from the group formed by aliphatic and cycloaliphatic hydrocarbons such as hexane, cyclohexane, heptane, butane or isobutane.

[0097] Preferably, the solvent used is cyclohexane.

[0098] In one embodiment, a solvent or a mixture of solvents may be used during the oligomerization reaction. Said solvent is advantageously chosen independently from the group formed by aliphatic and cycloaliphatic hydrocarbons such as hexane, cyclohexane, heptane, butane or isobutane.

[0099] Preferably, the linear alpha-olefins obtained comprise from 4 to 20 carbon atoms, preferably from 4 to 18 carbon atoms, preferably from 4 to 10 carbon atoms, and preferably from 4 to 8 carbon atoms. Preferably, the olefins are linear alpha-olefins selected from but-1-ene, hex-1-ene, or oct-1-ene. Advantageously, the oligomerization process is carried out at a pressure between 0.1 and 10.0 MPa, preferably between 0.2 and 9.0 MPa, and preferably between 0.3 and 8.0 MPa, at a temperature between 30 and 200°C, preferably between 35 and 150°C, and preferably between 45 and 140°C.

[0100] Preferably, in the case of oligomerization, the catalyst concentration in the catalytic system is between 0.001 and 300.0 ppm by mass of atomic metal relative to the reaction mass, preferably 0.02 and 100.0 ppm, preferably between 0.1 and 50.0 ppm, preferably between 0.03 and 50.0 ppm, and even more preferably between 2.0 and 50.0 ppm, more preferably between 0.5 and 20.0 ppm, or between 0.4 and 30.0 ppm, or between 0.6 and 20.0 ppm, for example between 0.8 and 10.0 ppm or between 1.0 and 6.0 ppm by mass of atomic metal relative to the reaction mass.

[0101] In the specific case of ethylene tetramerization, the concentration in question is between 0.001 and 1 ppm, specifically between 0.01 and 0.1 ppm.

[0102] In one embodiment, the oligomerization process is carried out batchwise. The catalytic system, configured as described above, is introduced into the solvent within a reactor equipped with standard stirring, heating, and cooling devices. The system is then pressurized with ethylene to the desired pressure, and the temperature is adjusted to the desired value. The oligomerization apparatus is maintained at a constant pressure by the introduction of ethylene gas until the total volume of liquid produced fills the desired fraction of the reaction volume. The catalyst is then neutralized by any conventional means known to those skilled in the art, and the reaction products and solvent are withdrawn and separated.

[0103] In another embodiment, the oligomerization process is carried out continuously. The catalytic system, configured as described above, is injected into a stirred reactor using conventional mechanical means known to those skilled in the art or by external recirculation, and maintained at the desired temperature. Ethylene is also injected into the reactor using its own injection system. Alternatively, the components of the catalytic system can be injected separately into the reaction medium and / or the solvent. Gaseous ethylene is generally introduced through a pressure-controlled inlet valve, which maintains a constant pressure in the reactor, or through a flow-controlled inlet valve. The reaction mixture is withdrawn using a liquid-level controlled valve to maintain a constant liquid level.The catalyst present in the withdrawn reaction mixture is continuously neutralized by any conventional means known to those skilled in the art, and then the reaction products and the solvent are separated, for example, by distillation. Unreacted ethylene can be recycled back into the reactor. Catalyst residues included in a heavy fraction can be incinerated. Description of embodiments.

[0104] The following examples and figures relate, in a non-limiting way, to the oligomerization of ethylene.

[0105] In a first embodiment relating to examples 1 to 4, the tetramerization of ethylene is carried out to obtain a mixture of 1-hexene and 1-octene, in a single-phase liquid reactor, with the installation of figure 1.

[0106] In a second embodiment, ethylene is oligomerized to obtain 1-butene, 1-hexene, or a series of linear terminal olefins from 1-butene to 1-dodecene, in a two-phase liquid / gas reactor. This corresponds to Examples 5 to 8 relating to the dimerization of ethylene, with the setup shown in Figure 6. Examples 1 to 4 described below therefore correspond to the tetramerization of ethylene in a reactor with two external cooling loops operating alternately, as described in particular in the aforementioned patent EP-3338884.

[0107] As mentioned above, the invention applies mutatis mutandis to the oligomerization of other olefins of the propylene or butene type, or mixtures of at least two of them: the invention applies to C2 to C4 olefins, selected from ethylene, propylene, butene 1 or butene 2, isobutene, and preferably ethylene.

[0108] Figure 1 is a schematic diagram of an installation implementing an oligomerization process, of the tetramerization type, of ethylene to which the invention can be applied. The main components of the installation impacted by the invention are shown in a simplified manner, namely a liquid / gas oligomerization reactor, a first separation (distillation) column d, and a second separation section comprising series distillation units (columns) e, a pump g, and a compressor f. It does not represent the neutralization and catalyst separation section, which is well known in itself, nor the recirculation loop(s) associated with the reactor c, which incorporate one or more heat exchangers. The reactor c, which may be a series of reactors, and the distillation column d, and those included in section e, define enclosures, for example, substantially oriented along a vertical axis.

[0109] According to this diagram, and purely for illustrative purposes, the oligomerization reaction takes place in reactor c at high pressure, between 20 and 90 bar absolute.

[0110] The flows that are circulating are as follows:

[0111] - Stream 1 is a stream of fresh ethylene

[0112] - Stream 6 is a stream corresponding to the head fraction exiting the first column d, consisting essentially of ethylene (and traces of compounds initially present in the fresh ethylene, and / or solvent and products and by-products of the reaction), which will be recycled

[0113] - Stream 2 is a mixture of stream 1 (fresh ethylene) and stream 6 (recycled ethylene).

[0114] - flow 3 is flow 2 once compressed to the required pressure by compressor f, and which enters reactor c as a gaseous phase

[0115] - Stream 5 is the stream withdrawn from reactor c after catalyst neutralization (neutralization not shown, performed on the stream exiting the reactor); this stream is therefore a mixture of solvent, neutralized catalyst, unreacted ethylene, and reaction products

[0116] - Stream 7 is the bottom fraction from the separation carried out in the first column d; it includes the solvent, the neutralized catalyst, and the reaction products.

[0117] - Flow 8 is the flow of reaction products separated in section e that are lighter than the solvent; therefore, it is represented as exiting from the top of section e.

[0118] - Flow 9 is the flow of reaction products separated in section e that are heavier than the solvent; it is represented as exiting through the middle of section e

[0119] - Stream 4 is the solvent stream (which may also contain traces of other compounds, particularly reaction products), which is separated in section e containing the separation devices. This stream passes through a pump g and is then injected into an inlet of reactor c as recycled liquid phase. It is the heaviest stream, therefore represented as exiting at the bottom of section e. It should be noted that, regarding the streams exiting separation section e, "top," "bottom," and "middle" are used for convenience, as if section e were simply a distillation column where the heaviest products exit at the bottom.It should also be noted that in the case where the solvent was heavier than the "heavy" reaction products and lighter than the "light" reaction products, the solvent stream 4 to be recycled would exit section e through the middle, the exit position out of section e of streams 4 and 9 would thus be reversed.

[0120] The operation of such an installation, particularly in the case of an ethylene tetramerization reaction, is as follows: The oligomerization reactor c, here entirely liquid, is fed, on the one hand, by a gaseous phase 3 composed essentially of recycled ethylene 6 and fresh ethylene 1, a phase which has been compressed by the compressor f before injection at the operating pressure of the reactor c, namely here 81 bar absolute. The fresh ethylene in stream 1 before compression by the compressor f is at a pressure of a few tens of bar, and the ethylene 6 is at a pressure of 11 bar absolute.

[0121] Reactor c is fed, separately, with a liquid phase, independent of the gaseous phase. This liquid phase consists of stream 4 of solvent recycled through pump g, which has a discharge pressure of 85 bar absolute. The operating temperature in reactor c is, for example, 45°C. Column d and section e are schematic representations of a potentially complex fractionation scheme, as mentioned above. Specifically, this diagram does not depict the device used to separate the neutralized catalyst from the reaction products and the solvent. Column d and section e, as shown, allow for the isolation of reaction products 8 and 9, and the recycling of unconverted ethylene (stream 6) and the solvent (stream 4).

[0122] The principle of the reaction is that gaseous ethylene is absorbed into the liquid phase and, when brought into contact with the catalyst, is converted into reaction products before reaching the gaseous sky.

[0123] It turns out that, gradually, deposits of a fouling polymeric solid accumulate on the surface of the reaction section, on the reactor walls, and also in the recirculation loop containing the heat exchangers. As the reaction proceeds, the deposits thicken, and when a maximum thickness is reached in the heat exchangers, production must be stopped and they cleaned. This involves draining the recirculation loop and circulating a fluid hot enough to dissolve the deposits. In the case of two interchangeable recirculation loops, for example, production can be avoided, but the two loops must be switched and cleaned. This is a real challenge because, on an industrial scale, this cleaning of the heat exchangers must be carried out very regularly, often at intervals of several hours.

[0124] The invention consists of adding packings to the reaction section, here in reactor c, not to facilitate the exchange between the gas and liquid phases—especially in a single-phase reactor—but to better distribute fouling deposits by promoting these deposits within the reactor on these additional contact surfaces. The thickening of deposits on the heat exchangers is thus slowed, and it is then possible either to extend the intervals between production shutdowns when the reactor has only one recirculation loop with heat exchangers or when cooling is achieved by a double-jacketed reactor, or to extend the intervals between the two recirculation loops when there is a split of the loops as described in the aforementioned patent.

[0125] The following are non-limiting descriptions of the different types of packing suitable for the invention: in fact, any internal material that increases the surface area inside a vessel or conduit can be considered in cases where packing is to be added to the recirculation loop(s) associated with reactor c. In this text, the terms packing and internal material are used interchangeably to refer to any component introduced into the reaction section, the reactor, and / or the conduits in question, to increase its surface area in contact with the reaction medium, which is inert with respect to the intended reaction. The material of these packings can, for example, be a mineral material such as glass, ceramic, metal, or a polymer adapted to withstand the temperature and compounds of the reaction medium, or any other material inert with respect to the intended reaction.

[0126] As shown in Figure 2, it can be a structured type packing, with a packing having two or three-dimensional networks, which can be stacked on top of / next to each other in a relatively compact way.

[0127] As shown in Figure 3, the packing can also consist of bulk materials, such as individual elements, in this case small cylinders, which are stacked loosely in the reactor. As shown in Figures 4 and 5, the packing can also consist of fins, grids, spirals, tubes, or any other geometric shape that develops a certain surface area per unit volume. In Figure 4, these are solid cylindrical tubular elements with spiral fins on their outer surface. In Figure 5, they are flat fins placed on a cylinder with a diameter smaller than, but close to, that of the reactor vessel, and a length close to, but shorter than, the cylindrical portion of the reactor. Advantageously, these elements are arranged / oriented in the reactor (when they are arranged in the reactor) in such a way as to minimize any obstruction they may cause to the flow of fluids from the reactor inlets 3 and 4 to its outlet 5.The surface area developed by packing can be from 10 to 200 m². 2 / m 3 For bulk packing, structured packing can reach up to 200m 2 / m 3 and more.

[0128] The packing can be deposited loose inside the reactor vessel (with grids above and below to prevent it from being drawn into the rest of the installation), or in the form of "slabs" sized to the reactor diameter and stacked one on top of the other. In this case, grids and / or mechanical reinforcement beams can also be provided if necessary.

[0129] Finally, it is conceivable to have other custom-made internals added, which would allow for the creation of surface area while meeting certain constraints specific to the process, such as, in particular, a given spacing between two packing surfaces, a preferred direction of passage, the need to avoid areas without fluid circulation...

[0130] Examples 1 to 4: Tetramerization of ethylene

[0131] Example 1 (comparative)

[0132] This example implements the process as shown in Figure 1, with the operating conditions described above for the tetramerization of ethylene, to obtain mainly octene-1 and possibly also hexene-1.

[0133] The selectivity of the ethylene conversion reaction is such that 3000 ppm of fouling solid is produced for each kilogram of reactant converted. Production of the recovered product requires the conversion of 4600 kg / h of reactant, diluted in solvent. The fouling solid is produced at the same rate as the reactant conversion, therefore 13.8 kg / h is produced. The density of the solid is 900 kg / m³. 3 0.0.153m³ is produced 3 / h, which is distributed uniformly over all surfaces of the reaction section of the process.

[0134] Since this reaction is exothermic, the heat from the reaction is removed via heat exchangers located on a recirculation loop external to the reactor, with a diameter of 1400 m 2 of total surface area. The total reaction volume is 72 m³ 3 is distributed between the volume occupied by the heat exchangers and their recirculation loop, and a reaction vessel, i.e., the reactor. The total reaction volume is broken down as follows: 17 m 3 for the heat exchange loop, and 55 m 3 for the reactor. The deposit of fouling solids inhibits heat removal from the heat exchanger, and the efficiency of the heat exchangers is no longer satisfactory when the solid layer reaches 3 mm in thickness. The unit must then be cleaned.

[0135] The total surface area of ​​the exchange loops is 1600 m² 2 that of the reactor is 130 m 2 The solid deposit therefore increases by 8.86 x 10⁻¹⁰ 6m / h and reaches the maximum acceptable thickness of 3 mm in 338 hours, or in approximately 14.1 days.

[0136] Example 2 (according to the invention)

[0137] Example 1 is reproduced, except that loose packing (here, for example, metal rings as shown in Figure 3, with an external diameter of 50 mm, a height of 50 mm, and a thickness of 0.5 mm) is added to the reactor. This packing provides an additional surface area of ​​100 m². 2 / m 3 which is added to 80% of the reactor's liquid volume. The surface area of ​​the heat exchange loop remains at 1600 m². 2 , while the surface area of ​​the reactor, including the internal surface area, is now 4530 m 2 The solid deposit this time increases by 2.50 x 10 6m / h and reaches the maximum acceptable thickness of 3 mm in 1200 hours, or approximately 50.0 days. With these linings, the unit's operating time before cleaning was therefore multiplied by a factor of 3.5, which is very significant.

[0138] Example 3 (comparative)

[0139] This time, we use a double-jacketed reactor, which replaces the recirculation loop(s) equipped with heat exchangers from the previous examples. An exothermic reaction occurs in this reactor, producing a fouling solid as a by-product. The reaction is so selectivity that 3000 ppm of fouling solid is produced for every kilogram of reactant converted. Production of the recovered product requires the conversion of 4600 kg / h of reactant, diluted in solvent, in a 55 m³ reaction vessel. 3 in total, which only corresponds to the internal volume defined by the reactor here.

[0140] The fouling solid is produced at the rate of reactant conversion, therefore 13.8 kg / h is produced. The density of the solid is 900 kg / m³. 3 0.0153m³ is produced 3 / h, which is distributed uniformly over all surfaces of the reaction section of the process. The heat of the reaction is dissipated through the walls of the reactor's double jacket, 130 m 2 of total surface area. The surface area on which the solid is deposited is that of the reactor, i.e., 130 m² 2 The solid deposit therefore increases by 1.18 x 10 4 m / h and reaches the maximum acceptable thickness in 25.4 hours, or 1.06 days.

[0141] Example 4 (according to the invention) Example 3 is reproduced, except that packing is added to the reactor: an additional surface area of ​​100 m² 2 / m 3 is added to 80% of the reactor's liquid volume. The reactor surface area remains at 130 m². 2, while the internal surface area is 4400 m 2 The fouling deposit increased this time by 3.38 x 10 6 m / h and reaches the maximum acceptable thickness of 3 mm in 886 hours, or approximately 36.9 days. The invention therefore made it possible, in this example, to multiply the unit's operating time before cleaning by a factor of 35.

[0142] Examples 5 to 8: Dimerization of ethylene

[0143] This second series of examples implements the process adapted from that shown in Figure 1, and implemented in the installation in Figure 6, with the operating conditions modified compared to the previous examples, to carry out this time a dimerization of ethylene to produce butene-1.

[0144] If we compare figures 1 and 6, we see that the dimerization process differs from the tetramerization process essentially by the fact that: - there is no longer the solvent recycle loop 4 equipped with pump g (no more solvent),

[0145] - and that there is no compressor f to compress the flow from flows 1 and 6.

[0146] The principle of the reaction is that gaseous ethylene is absorbed into the liquid phase and, when brought into contact with the catalyst, is converted into reaction products before reaching the gaseous sky.

[0147] The operation of such an installation, in the case of an ethylene dimerization reaction, is as follows: The oligomerization reactor c, here a gas / liquid reactor, is fed, on the one hand, by a gaseous phase 3 composed essentially of recycled ethylene 6 and fresh ethylene 1, at the operating pressure of reactor c, namely here 26 bar absolute. The fresh ethylene in stream 1 is at a pressure of a few tens of bar, and the ethylene 6 is at a pressure of 29 bar absolute.

[0148] The operating temperature in reactor c is, for example, 50°C. Column d and section e are schematic representations of a potentially complex fractionation scheme, as mentioned above. Specifically, this diagram does not depict the device used to separate the neutralized catalyst from the reaction products. Column d and section e, as shown, allow for the isolation of reaction products 8 and 9, and the recycling of unconverted ethylene (stream 6).

[0149] Example 5 (comparative) This example implements the process as modified from Figure 1, with the operating conditions described above.

[0150] The selectivity of the ethylene conversion reaction is such that 300 ppm of fouling solid is produced for each kilogram of reactant converted. Production of the recovered product requires the conversion of 4000 kg / h of reactant. The fouling solid is produced at the same rate as the reactant conversion, therefore 1.20 kg / h is produced. The density of the solid is 500 kg / m³. 3 0.0024m³ is produced 3 / h, which is distributed uniformly over all surfaces of the reaction section of the process. Since this reaction is exothermic, the heat of the reaction is removed via heat exchangers located on a 1000 m external recirculation loop outside the reactor. 2 of total surface area. The total reaction volume is 85 m³ 3is distributed between the volume occupied by the heat exchangers and their circulation loop, and a reaction vessel, i.e., the reactor. The total reaction volume is broken down as follows: 25 m 3 for the heat exchange loop, and 60 m 3 for the reactor.

[0151] The buildup of fouling solids inhibits heat transfer from the heat exchanger, and the efficiency of the heat exchangers becomes unsatisfactory when the solid layer reaches 1 mm in thickness. The unit must then be cleaned.

[0152] The total surface area of ​​the exchange loops is 1200 m² 2 (1000 for the heat exchangers and 200 for the lines), that of the reactor is 78 m 2 The solid deposit therefore increases by 1.88 x 10 6 m / h and reaches the maximum acceptable thickness of 1 mm in 532 hours, or in approximately 22.2 days.

[0153] Example 6 (according to the invention)

[0154] Example 5 is reproduced, except that loose packing (here, for example, metal rings as shown in Figure 3, with an external diameter of 50 mm, a height of 50 mm, and a thickness of 0.5 mm) is added to the reactor. This packing provides an additional surface area of ​​100 m². 2 / m 3 which is added to 80% of the reactor's liquid volume. The surface area of ​​the heat exchange loop remains at 1200 m². 2 , while the surface area of ​​the reactor, including the internal surface area, is now 4878 m² 2 The solid deposit this time increases by 3.95 x 10 7 m / h and reaches the maximum acceptable thickness of 1 mm in 2532 hours, or approximately 105.5 days.

[0155] With these fillings, we were able to multiply the unit's usage time before cleaning by a factor of 4.8, which is very significant.

[0156] Example 7 (comparative)

[0157] This example implements the process as shown in Figure 1, with modified operating conditions compared to the previous tetramerization examples described above, as follows, to perform a dimerization of ethylene to produce butenes or butene-1, using the dimerization operating conditions described above for Examples 5 and 6. The selectivity of the ethylene conversion reaction is such that 100 ppm of fouling solid is produced for each kilogram of reagent converted. Production of the valuable product requires the conversion of 35,000 kg / h of reagent.

[0158] The fouling solid is produced at the rate of reactant conversion, therefore 3.5 kg / h is produced. The density of the solid is 500 kg / m³. 3 0.007m³ is produced 3 / h, which is distributed uniformly over all surfaces of the reaction section of the process.

[0159] Since this reaction is exothermic, the heat from the reaction is removed via heat exchangers located on several external recirculation loops of 7500 m 2 of total surface area. The total reaction volume is 323 m³ 3 is distributed between the volume occupied by the heat exchangers and recirculation loops, and a reaction vessel, i.e., the reactor. The total reaction volume is broken down as follows: 175 m 3 for heat exchange loops and 148 m 3 for the reactor.

[0160] The buildup of fouling solids inhibits heat transfer to the heat exchangers, and their efficiency becomes unsatisfactory when the solid layer reaches 1 mm in thickness. The unit must then be cleaned.

[0161] The total surface area of ​​the exchange loops is 7500 m² 2 (7000 for the heat exchangers and 500 for the lines), that of the reactor is 141 m 2The solid deposit therefore increases by 9.16 x 10 7 m / h and reaches the maximum acceptable thickness of 1 mm in 1092 hours, or in about 45.5 days.

[0162] Example 8 (according to the invention)

[0163] Example 7 is reproduced, except that loose packing (here, for example, metal rings as shown in Figure 3, with an external diameter of 50 mm, a height of 50 mm, and a thickness of 0.5 mm) is added to the reactor. This packing provides an additional surface area of ​​100 m². 2 / m 3 which is added to 80% of the reactor's liquid volume. The surface area of ​​the heat exchange loop remains at 7500 m². 2 , while the surface area of ​​the reactor, including the internal surface area, is now 11981 m² 2 The solid deposit this time increases by 3.60 x 10 7 m / h and reaches the maximum acceptable thickness of 1 mm in 2783 hours, or approximately 116.0 days.

[0164] With these packings, the unit's operating time before cleaning was increased by a factor of 2.55, which is highly significant. It was therefore verified that adding packing at least doubles, and possibly even triples, the system's operating time before shutdown for heat exchanger cleaning. This represents a considerable productivity gain, which, moreover, does not disrupt the system's operation, nor the yield or quality of the alpha-olefins produced. This has been demonstrated regardless of whether the reaction involved is ethylene dimerization or tetramerization.

Claims

A plant for oligomerizing C2 to C4 olefins to produce oligomerized alpha-olefins, with production of a fouling by-product in the form of a deposit, said plant comprising a reaction section comprising: - a reactor (c) for two-phase gas / liquid or single-phase all-liquid oligomerization proceeding from a homogeneous oligomerization catalyst and C2 to C4 olefins, and - cooling means associated with said reactor in the form of at least one cooling circuit external to the reactor or in the form of a jacket of the walls of the reactor, characterized in that packings are disposed in the reaction section in order to increase the contact surface area per unit volume that is accessible to the deposition of the byproduct.The plant as claimed in claim 1, characterized in that the cooling means are at least one cooling circuit external to the reactor (c), and in that the packings are disposed in the reactor only, or in the reactor and in the cooling circuit(s), or in the cooling circuit(s) only.The plant as claimed in claim 1 or 2, characterized in that the packings are disposed in the liquid-filled volume Vl of the reactor in at least 5% of said volume Vl.The plant as claimed in claim 1 or 2, characterized in that the packings are selected from one at least of the following packings: structured packing, random packing, internals defining fins.The plant as claimed in claim 1 or 2, characterized in that the external cooling circuit comprises a recirculation loop for the liquid phase of the reactor, said loop incorporating one or more heat exchangers.The plant as claimed in claim 1 or 2, characterized in that the external cooling circuit comprises at least two separate recirculation loops each incorporating one or more heat exchangers, and which are operational in alternation.The plant as claimed in claim 1 , characterized in that it comprises a section for separating the reaction effluents resulting from the reaction section, downstream of the oligomerization reactor (c), said separation section comprising at least a first column (d) for fractionating said effluents so as to obtain a fraction containing the olefin(s), and at least one bottom fraction.The plant as claimed in claim 7, characterized that a solvent is used and in that the separation section comprises, downstream of the first fractionating column, a section (e) for fractionating by distillation so as to obtain at least one fraction enriched in alpha-olefin oligomerization products and one fraction enriched in solvent.The plant as claimed in claim 7 or 8, characterized in that a solvent is used and in that the plant comprises a loop (4) for recycling the solvent from the separation section to the reaction section.The plant as claimed in claim 7 or 8, characterized in that it comprises a loop (6) for recycling the starting olefin(s) from the separation section to the reaction section.A process for oligomerizing C2-C4 starting olefins to produce oligomerized alpha-olefins proceeding from an oligomerization catalyst and said starting olefins, with production of a solid fouling by-product, in a reaction section comprising:- a reactor (c) for two-phase gas / liquid or single-phase all-liquid oligomerization proceeding from an optional solvent, an oligomerization catalyst and said C2-C4 starting olefins, and - cooling means associated with said reactor in the form of at least one cooling circuit external to the reactor or in the form of a jacket of the walls of the reactor, characterized in that the contact surface area per unit volume of the reaction section which is available for the deposition of the fouling by-product is increased by disposing packings in the reactor.The process as claimed in claim 11, characterized in that the external cooling circuit of the reactor comprises at least two separate recirculation loops each incorporating one or more heat exchangers, which are operational in alternation, and in that at least one of the loops is operational while the exchangers of the other loop(s) which are not operational are being cleaned, with the aid of a fluid the temperature of which is greater than the dissolution temperature of the fouling by-product.The process as claimed in claim 11 or 12, characterized that the contact surface area per unit volume of the reaction section is increased by virtue of the presence of the packings in the reaction section by at least 5 m2 / m3.The process as claimed in claim 11 or 12, characterized in that the oligomerization relates to the dimerization, trimerization or tetramerization of ethylene.

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