FR3112342A1 - OLIGOMERIZATION PROCESS USING A GAS/LIQUID EXCHANGER - Google Patents

Abstract

The present invention relates to an oligomerization process implemented in a gas/liquid reactor comprising a gas-liquid separation step. In particular, the process 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.

Description

OLIGOMERIZATION PROCESS USING A GAS/LIQUID EXCHANGER

The present invention relates to an oligomerization process implemented in a gas/liquid reactor comprising a recycling loop of the gas overhead. In particular, the process 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.

PRIOR ART

The invention relates to the field of oligomerization processes implementing gas/liquid reactors also called bubble column . Due to the exothermic nature of the oligomerization reactions, the bubble columns also include a recirculation loop consisting of withdrawing a liquid fraction, cooling it and reintroducing it into the reaction chamber. Said recirculation loop makes it possible to obtain good homogeneity of the concentrations and to control the temperature in the whole of the reaction volume, due to the good heat transfer capacity associated with the recirculation loop.

A drawback encountered in oligomerization processes during the implementation of this type of column is the management of the gas phase also called gas overhead. Indeed, said gaseous headspace comprises gaseous compounds that are not very soluble in the liquid phase, compounds that are partially soluble in the liquid but inert, oligomerization reaction products, as well as gaseous ethylene not dissolved in said liquid. The passage of ethylene gas from the liquid phase to the gas phase (or sky) is a phenomenon called piercing. However, the gaseous headspace is purged in order to eliminate said gaseous compounds. When the quantity of gaseous ethylene present in the gaseous headspace is large, the purging of the gaseous headspace leads in particular to a significant loss of ethylene, which is detrimental to the productivity, the saving of resources and the cost of the oligomerization process.

In order to improve the efficiency of the oligomerization process in terms of productivity, saving of resources and cost, it is therefore essential to limit in particular the loss of unreacted ethylene contained in the gaseous headspace in order to improve its conversion in said process while maintaining good selectivity for the desired linear alpha olefins.

The methods of the prior art implementing a recirculation loop, as illustrated in , do not make it possible to limit the loss of gaseous ethylene and the purging of the gaseous headspace leads to an outlet of gaseous ethylene from the reactor which is detrimental to the yield and the cost of the process.

The applicant has described processes in applications WO2019/011806 and WO2019/011609 making it possible to increase the contact surface between the upper part of the liquid fraction and the gaseous headspace by means of dispersion or vortex means in order to promote the passage of the ethylene contained in the gaseous headspace towards the liquid phase at the level of the liquid/gas interface. However, these processes are not sufficient when the quantity of ethylene in the gaseous headspace is high due to a high penetration rate.

In addition, during this research, the applicant has found that in a reactor operating at a constant flow rate of injected ethylene gas, the quantity of dissolved ethylene and therefore the rate of penetration is dependent on the dimensions of the reactors implementing the process and in particular the height of the liquid phase. Indeed, the lower the height, the lower the time during which the gaseous ethylene travels through the liquid phase to dissolve and the higher the penetration rate.

The object of the present invention aims to overcome the drawbacks of the prior art so as to improve the performance of an oligomerization process.

Surprisingly, the applicant has discovered a new oligomerization process implementing a step of gas-liquid separation of a fraction withdrawn from the lower part of the liquid phase and which makes it possible to optimize the dissolution of ethylene gas. involved in the process and the productivity of alpha-olefins, regardless of the size of the reactor used. In particular, the process allows the selective production of linear alpha-olefins such as 1-butene, 1-hexene, 1-octene or a mixture of linear alpha-olefins.

An advantage of the process according to the invention is to make it possible to reduce in a simple and economical way the phenomenon of gaseous ethylene piercing in the gaseous headspace in an oligomerization process, by increasing the rise time of the ethylene bubbles in the liquid phase whatever the dimensions of the reactor.

Another advantage of the process according to the invention is to make it possible to increase the height of the reactor and therefore the height of the liquid phase without modifying the volume of the reactor or of the liquid phase used in an oligomerization reaction, which makes it possible to improve the dissolution of gaseous ethylene and therefore to limit the phenomenon of piercing for a given volume of liquid phase.

BRIEF DESCRIPTION OF THE INVENTION

An object of the present invention relates to a process for the oligomerization of gaseous ethylene implemented in a gas/liquid reactor at a pressure comprised between 0.1 and 10.0 MPa, at a temperature comprised between 30 and 200° C. comprising the following steps:

a) a step of introducing a catalytic oligomerization system into the reactor comprising a reaction chamber comprising a liquid phase in a lower zone and a gaseous phase in an upper zone,

b) a step of introducing gaseous ethylene into the lower zone of the reaction enclosure,

c) a step of withdrawing at least one fraction comprising part of the liquid phase and gaseous ethylene,

d) a step of separating the fraction withdrawn in step c) into a liquid fraction and a gaseous fraction comprising ethylene,

e) a step of cooling at least part of the liquid fraction separated in step d),

f) a step of introducing the fraction cooled in step e) into the upper part of the liquid phase of the reaction chamber.

Preferably, the method further comprises a step g) of introducing the gaseous fraction comprising ethylene separated in step d) into the liquid phase contained in the reaction enclosure.

Preferably, the gaseous fraction comprising ethylene separated in step d) is introduced into the liquid phase in the lower part of the reaction enclosure.

Preferably, the gaseous fraction separated in stage d) is mixed with the gaseous ethylene introduced in stage b).

Preferably, the method further comprises a step h) of recycling a gaseous fraction withdrawn from the gaseous phase of the reaction enclosure and introduced at the level of the lower part of the reaction enclosure into the liquid phase.

Preferably, the gaseous phase withdrawn in step h) is introduced into the reaction chamber mixed with the gaseous ethylene introduced in step b) and/or in optional step g).

Preferably, step d) is implemented using a gas-liquid separation drum, a decanter and/or a flash.

Preferably, the withdrawal implemented in step c) is carried out in the lower part of the reaction enclosure, preferably below the level of the introduction of gaseous ethylene, and preferably in the bottom of the enclosure.

Preferably, the liquid fraction separated in step d) is divided into two streams, a first so-called main stream is sent to cooling step f), and a second stream is sent to a downstream section.

Preferably, the liquid phase in the lower zone of the reaction enclosure has a dissolved ethylene saturation rate greater than 70.0%.

Preferably, in step b) a flow of hydrogen gas is introduced into the reaction chamber, with a flow representing 0.2 to 5.0% by mass of the incoming ethylene flow.

Another object of the present invention relates to a gas/liquid reactor also called a reaction device for implementing the method described above, comprising:

- a reaction chamber i), of elongated shape along the vertical axis containing a liquid phase located in a lower zone comprising reaction products, dissolved and gaseous ethylene, a catalytic system and a optional solvent, and a gaseous phase located in an upper zone above the lower zone and comprising gaseous ethylene,

- a means for introducing ethylene gas ii), into said reaction chamber and optionally implementing a means for distributing ethylene gas within said liquid phase of the reaction chamber,

- a means for introducing the catalytic system iii), into the reaction device, a withdrawal means iv) in the lower part of the reaction chamber capable of withdrawing a fraction comprising part of the liquid phase and ethylene gas ,

- a means for separating v) the fraction comprising part of the liquid phase and gaseous ethylene so as to obtain a liquid fraction and a gaseous fraction comprising ethylene,

- a recirculation loop vi) of the liquid fraction towards a heat exchanger allowing the cooling of said liquid, and a means of introducing said cooled liquid, said introduction being carried out in the liquid phase in the upper part of the lower zone of the reaction chamber.

Preferably, the device further comprises a loop for recycling the gaseous phase in the lower part of the reaction enclosure.

Preferably, the introduction of the gaseous fraction drawn off is carried out by the means for introducing ethylene gas ii).

Preferably, the means of introduction ii) is chosen from among a pipe, a network of pipes, a multitubular distributor and a perforated plate.

DEFINITIONS & ABBREVIATIONS

Throughout the description, the terms or abbreviations below have the following meaning.

By oligomerization is meant any addition reaction of a first olefin to a second olefin, which is identical to 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.

By linear alpha-olefin is meant an olefin on which the double bond is located in the terminal position of the linear alkyl chain.

By catalytic system is meant a chemical species which allows the implementation of the catalyst. The catalytic system can be a metal precursor comprising one or more metal atoms or a mixture of compounds making it possible to catalyze a chemical reaction, and more specifically an olefin oligomerization reaction. The mixture of compounds includes at least one metal precursor. The mixture of compounds may further comprise an activating agent. The mixture of compounds may include an additive. The compound or the mixture of compounds can optionally be in the presence of a solvent.

The term “liquid phase” means the mixture of all the compounds which are in a liquid physical state under the temperature and pressure conditions of the reaction chamber.

Gas phase, also called gas overhead, means the mixture of all the compounds which are in the physical gas state under the temperature and pressure conditions of the reaction chamber: in the form of bubbles present in the liquid , and also in the upper part of the reactor (head of the reactor).

By lower zone of the reaction chamber is meant the part of the chamber comprising the liquid phase, gaseous ethylene, the reaction products such as the desired linear alpha olefin ( ie butene-1, hexene-1 , octene-1 or the mixture of linear alpha-olefins) the catalytic system and optionally a solvent.

The upper zone of the reaction chamber means the part of the chamber located at the top of the chamber, i.e. directly above the lower zone and consisting of the gaseous headspace.

By lower lateral part of the reaction chamber is meant a part of the reactor envelope located in the lower part and on the side.

By incondensable gas is meant a species in physical gas form which dissolves only partially in the liquid under the temperature and pressure conditions of the reaction enclosure, and which can, under certain conditions, accumulate in the top of the reactor ( example here: ethane).

We understand by t/h, the value of a flow expressed in tons per hour and by kg/s, the value of a flow in kilograms per second.

The terms reactor or device designate all the means allowing the implementation of the oligomerization process according to the invention, such as in particular the reaction chamber and the recirculation loop.

The term “lower part” means the lower quarter of the reaction chamber containing the liquid phase.

By upper part is meant the upper quarter of the reaction chamber containing the liquid phase.

By fresh gaseous ethylene is meant the ethylene external to the process introduced in step b) by means ii) of the process according to the invention.

Flash means a gas/liquid separation effected by a change in pressure and/or temperature.

DETAILED DESCRIPTION OF THE INVENTION

It is specified that, throughout this description, the expression “included between … and …” must be understood as including the limits mentioned.

Within the meaning of the present invention, the various embodiments presented can be used alone or in combination with each other, without limitation of combination.

Within the meaning of the present invention, the various ranges of parameters for a given stage such as the pressure ranges and the temperature ranges can be used alone or in combination. For example, within the meaning of the present invention, a preferred pressure value range can be combined with a more preferred temperature value range.

The present invention relates to a process for the oligomerization of ethylene implemented in a gas/liquid reactor at a pressure comprised between 0.1 and 10.0 MPa, at a temperature comprised between 30 and 200°C comprising the following steps :

a) a step of introducing a catalytic oligomerization system into the reactor comprising a reaction chamber comprising a liquid phase in a lower zone and a gaseous phase in an upper zone,

b) a step of introducing gaseous ethylene into the lower zone of the reaction enclosure,

c) a step of withdrawing at least one fraction comprising part of the liquid phase and gaseous ethylene,

d) a step of separating the fraction withdrawn in step c) into a liquid fraction and a gaseous fraction comprising ethylene

e) a step of cooling at least part of the liquid fraction separated in step d),

f) a step of introducing the fraction cooled in step e) into the upper part of the liquid phase of the reaction chamber,

g) an optional step of introducing the gaseous fraction comprising ethylene separated in step d) into the liquid phase contained in the reaction chamber,

h) an optional step of recycling a gaseous fraction withdrawn from the gaseous phase of the reaction enclosure and introduced at the level of the lower part of the reaction enclosure into the liquid phase.

Advantageously, the process according to the invention has a saturation rate of dissolved ethylene in the liquid phase greater than 70.0%, preferably between 70.0 and 100%, preferably between 80.0 and 100%, preferably comprised between 80.0 and 99.0%, preferably between 85.0 and 99.0% and even more preferably between 90.0 and 98.0%.

The dissolved ethylene saturation rate can be measured by any method known to those skilled in the art and for example by gas chromatographic analysis (commonly called GC) of a fraction of the liquid phase withdrawn from the reaction chamber. .

Another advantage of the process according to the invention is to make it possible to have a withdrawal rate in step c) adapted so as to obtain a fraction comprising a mixture of liquid and gaseous ethylene. Thus said withdrawal makes it possible to slow down the rise of the gaseous ethylene introduced into the reaction chamber, which makes it possible to improve the saturation of ethylene in the liquid phase and therefore the productivity of the process.

Another advantage of the process according to the invention is to allow an increase in the height to diameter ratio of the reactor, while maintaining the same residence time, which makes it possible to improve the dissolution of ethylene in the reactor, and therefore the performance. of the process.

OLIGOMERIZATION PROCESS

The ethylene oligomerization process according to the invention makes it possible to produce linear alpha olefins by bringing ethylene into contact with a catalytic system and optionally in the presence of a solvent.

All the catalytic systems known to those skilled in the art and capable of being implemented in the dimerization, trimerization, tetramerization processes and more generally in the oligomerization processes according to the invention, are part of the field of invention. Said catalytic systems as well as their implementations are described in particular in applications FR2984311, FR2552079, FR3019064, FR3023183, FR3042989 or even in application FR3045414.

Preferably, the catalytic systems comprise, preferably consist of:

- a metallic precursor preferably based on nickel, titanium or chromium,

- optionally an activating agent,

- optionally an additive, and

- optionally a solvent.

The metallic precursor

The metal precursor used in the catalytic system is chosen from compounds based on nickel, titanium or chromium.

In one embodiment, the metal precursor is nickel-based and preferably comprises nickel of oxidation state (+II). Preferably, the nickel precursor is chosen from nickel(II) carboxylates such as, for example, nickel 2-ethylhexanoate, nickel(II) phenates, nickel(II) naphthenates, nickel(II) acetate, II), nickel(II) trifluoroacetate, nickel(II) triflate, nickel(II) acetylacetonate, nickel(II) hexafluoroacetylacetonate, π-allylnickel(II) chloride, nickel(II) bromide, π-allylnickel(II), methallylnickel(II) chloride dimer, η ³ -allylnickel(II) hexafluorophosphate, η ³ -methallylnickel(II) hexafluorophosphate and nickel 1,5-cyclooctadienyl( II), in their hydrated or non-hydrated form, taken alone or as a mixture.

In a second embodiment, the metal precursor is titanium-based and preferably comprises an aryloxy or alkoxy compound of titanium.

The titanium alkoxy compound advantageously corresponds to the general formula [Ti(OR) ₄ ] in which R is a linear or branched alkyl radical. Among the preferred alkoxy radicals, mention may be made by way of non-limiting example of: tetraethoxy, tetraisopropoxy, tetra-n-butoxy and tetra-2-ethyl-hexyloxy.

The titanium aryloxy compound advantageously corresponds to the general formula [Ti(OR') ₄ ] in which R' is an aryl radical substituted or not by alkyl or aryl groups. The R' radical may contain substituents based on heteroatoms. The preferred aryloxy radicals are chosen from phenoxy, 2-methylphenoxy, 2,6-dimethylphenoxy, 2,4,6-trimethylphenoxy, 4-methylphenoxy, 2-phenylphenoxy, 2,6-diphenylphenoxy, 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, binaphthoxy, 1,8 -naphthalene-dioxy.

According to a third embodiment, the metal precursor is chromium-based and preferably comprises a chromium (II) salt, a chromium (III) salt, or a salt with a different degree of oxidation which may comprise one or more identical anions. or different, such as for example halides, carboxylates, acetylacetonates, alkoxy or aryloxy anions. Preferably, the chromium-based precursor is chosen from CrCl ₃ , CrCl ₃ (tetrahydrofuran) ₃ , Cr(acetylacetonate) ₃ , Cr(naphthenate) ₃ , Cr(2-ethylhexanoate) ₃ , Cr(acetate) ₃ .

The nickel, titanium or chromium concentration is between 0.001 and 300.0 ppm by mass of atomic metal relative to the reaction mass, preferably between 0.002 and 100.0 ppm, preferentially between 0.003 and 50.0 ppm , more preferably between 0.05 and 20.0 ppm and even more preferably between 0.1 and 10.0 ppm by mass of atomic metal relative to the reaction mass.

The activating agent

Optionally, whatever the metal precursor, the catalytic system comprises one or more activating agents chosen from aluminum-based compounds such as methylaluminum dichloride (MeAlCl ₂ ), dichloroethylaluminum (EtAlCl ₂ ), ethylaluminum sesquichloride (Et ₃ Al ₂ Cl ₃ ), chlorodiethylaluminum (Et ₂ AlCl), chlorodiisobutylaluminum (i-Bu ₂ AlCl), triethylaluminum (AlEt ₃ ), tripropylaluminum (Al(n-Pr) ₃ ), triisobutylaluminum (Al (i-Bu) ₃ ), diethyl-ethoxyaluminum (Et ₂ AlOEt), methylaluminoxane (MAO), ethylaluminoxane and modified methylaluminoxanes (MMAO).

The additive

Optionally, the catalytic system comprises one or more additives.

The additive is chosen from monodentate phosphorus compounds, bidentate phosphorus compounds, tridentate phosphorus compounds, olefinic compounds, aromatic compounds, nitrogen compounds, bipyridines, diimines, monodentate ethers, bidentate ethers, monodentate thioethers , bidentate thioethers, monodentate or bidentate carbenes, mixed ligands such as phosphinopyridines, iminopyridines, bis(imino)pyridines

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-trifluromethylpyridine, 2-phenylpyridine, 3-phenylpyridine, 2-benzylpyridine, 3,5-dimethylpyridine, 2,6- diterbutylpyridine and 2,6-diphenylpyridine, quinoline, 1,10-phenanthroline, N-methylpyrrole, N-butylpyrrole N-methylimidazole, N-butylimidazole, 2,2'-bipyridine, N,N'-dimethyl -ethane-1,2-diimine, N,N'-di-t-butyl-ethane-1,2-diimine, N,N'-di-t-butyl-butane-2,3-diimine, N,N'-diphenyl-ethane-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'-diphenyl-butane-2,3-diimine, N,N'-bis-(dimethyl-2,6-phenyl) -butane-2,3-diimine, N,N'-bis-(diisopropyl-2,6-phenyl)-butane-2,3-d imine, or

- phosphine-type compounds chosen independently from tributylphosphine, triisopropylphosphine, tricyclopentylphosphine, tricyclohexylphosphine, triphenylphosphine, tris(o-tolyl)phosphine, bis(diphenylphosphino)ethane, trioctylphosphine oxide, triphenylphosphine, triphenylphosphite, or

- the compounds corresponding to the general formula (I) or one of the tautomers of said compound:

in which

- A and A', identical or different, are independently an oxygen or a single bond between the phosphorus atom and a carbon atom,

- the R ^1a and R ^1b groups are independently chosen from methyl, trifluoromethyl, ethyl, n-propyl, i-propyl, n-butyl, i-butyl, t-butyl, pentyl, cyclohexyl, adamantyl groups, substituted or not, whether or not containing heteroelements; phenyl, o-tolyl, m-tolyl, p-tolyl, mesityl, 3,5-dimethylphenyl, 4-n-butylphenyl, 2-methylephenyl, 4-methoxyphenyl, 2-methoxyphenyl, 3-methoxyphenyl, 4-methoxyphenyl, 2-isopropoxyphenyl, 4-methoxy-3,5-dimethylphenyl, 3,5-ditert-butyl-4-methoxyphenyl, 4-chlorophenyl, 3,5-di(trifluoromethyl)phenyl, benzyl, naphthyl, bisnaphthyl, pyridyl, bisphenyl, furanyl, thiophenyl,

- the R ² group is chosen independently from methyl, trifluoromethyl, ethyl, n-propyl, i-propyl, n-butyl, i-butyl, t-butyl, pentyl, cyclohexyl, adamantyl groups, substituted or not, containing heteroelements or not ; 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-ditert-butyl-4-methoxyphenyl, 4-chlorophenyl, 3,5-bis(trifluoromethyl)phenyl, benzyl, naphthyl, bisnaphthyl, pyridyl, bisphenyl, furanyl, thiophenyl.

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 as a mixture.

When the catalytic system is chromium-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-trifluromethylpyridine, 2-phenylpyridine, 3-phenylpyridine, 2-benzylpyridine, 3,5-dimethylpyridine, 2,6- diterbutylpyridine and 2,6-diphenylpyridine, quinoline, 1,10-phenanthroline, N-methylpyrrole, N-butylpyrrole N-methylimidazole, N-butylimidazole, 2,2'-bipyridine, N,N'-dimethyl -ethane-1,2-diimine, N,N'-di-t-butyl-ethane-1,2-diimine, N,N'-di-t-butyl-butane-2,3-diimine, N,N'-diphenyl-ethane-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'-diphenyl-butane-2,3-diimine, N,N'-bis-(dimethyl-2,6-phenyl) -butane-2,3-diimine, N,N'-bis-(diisopropyl-2,6-phenyl)-butane-2,3-d imine, or

- aryloxy compounds of general formula [M(R ³ O) _2-n X _n ] _y in which

* M is chosen from magnesium, calcium, strontium and barium, preferably magnesium,

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

* n is an integer which can take the values of 0 or 1, and

* y is an integer between 1 and 10, preferably y is equal to 1, 2, 3 or 4.

Preferably, the aryloxy radical R ³ O 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 for example the biphenoxy radical, binaphthoxy or 1,8-naphthalene-dioxy, Preferably, the aryloxy radical R ³ O is 2,6-diphenylphenoxy, 2 -tert-butyl-6-phenylphenoxy or 2,4-ditert-butyl-6-phenylphenoxy.

The solvent

In another embodiment according to the invention, the catalytic system optionally comprises one or more solvents.

In one embodiment, a solvent or a mixture of solvents can be used during the oligomerization reaction.

The solvent(s) are advantageously chosen from ethers, alcohols, halogenated solvents and hydrocarbons, saturated or unsaturated, cyclic or not, aromatic or not, comprising between 1 and 20 carbon atoms, preferably between 4 and 15 carbon atoms. carbon, preferably between 4 and 12 carbon atoms and even more preferably between 4 and 8 carbon atoms.

Preferably, the solvent is chosen from pentane, hexane, cyclohexane, methylcyclohexane, heptane, butane or isobutane, cycloocta-1,5-diene, benzene, toluene, ortho -xylene, mesitylene, ethylbenzene, diethylether, tetrahydrofuran, 1,4-dioxane, dichloromethane, dichloroethane, tetrachloroethane, hexachloroethane, chlorobenzene, dichlorobenzene, butene, hexene and l pure or mixed octene.

Preferably, the solvent can advantageously be chosen from the products of the oligomerization reaction. Preferably, the solvent used is cyclohexane.

Preferably, the mass content of solvent introduced into the reactor used in the process according to the invention is between 0.5 and 10.0, preferably between 1.0 and 5.0, and more preferably between 2, 0 and 4.0. The solvent content is the mass ratio of the total flow of solvent injected to the total flow of ethylene gas injected into the process.

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, chosen from but-1-ene, hex-1-ene or oct-1-ene.

Advantageously, the oligomerization process is implemented at a pressure of between 0.1 and 10.0 MPa, preferably between 0.2 and 9.0 MPa and preferentially between 0.3 and 8.0 MPa, at a temperature between 30 and 200°C, preferably between 35 and 150°C and more preferably between 45 and 140°C.

Preferably, 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 between 0.002 and 100.0 ppm, preferentially between 0.003 and 50.0 ppm , more preferably between 0.05 and 20.0 ppm and even more preferably between 0.1 and 10.0 ppm by mass of atomic metal relative to the reaction mass.

According to one embodiment, the oligomerization process is implemented discontinuously. The catalytic system, constituted as described above, is introduced into a reactor equipped with the usual stirring, heating and cooling devices, then pressurized with ethylene to the desired pressure, and the temperature is adjusted to the desired value. The oligomerization device is maintained at a constant pressure by introducing gaseous ethylene until the total volume of liquid produced represents, for example, from 1 to 1000 times the volume of the catalytic solution previously introduced. The catalyst is then destroyed by any usual means known to those skilled in the art, then the reaction products and the solvent are drawn off and separated.

According to another embodiment, the oligomerization process is implemented continuously. The catalytic system, formed as described above, is injected at the same time as the ethylene into a reactor stirred by conventional mechanical means known to those skilled in the art or by external recirculation, and maintained at the desired temperature. It is also possible to inject the components of the catalytic system separately into the reaction medium. Ethylene gas is introduced through a pressure-controlled inlet valve, which keeps the pressure constant in the reactor. The reaction mixture is withdrawn by means of a valve controlled by the liquid level so as to keep the latter constant. The catalyst is destroyed continuously by any usual means known to those skilled in the art, then the products resulting from the reaction as well as the solvent are separated, for example by distillation. Unconverted ethylene can be recycled to the reactor. Catalyst residues included in a heavy fraction can be incinerated.

Stage a) of introduction of the catalytic system

The process according to the invention comprises a step a) of introducing a catalytic system into a reactor comprising a reaction enclosure comprising a liquid phase in a lower zone and a gaseous phase in an upper zone.

Advantageously, the introduction of the catalytic system is carried out in the liquid phase contained in the reactor.

Preferably, the introduction of the catalytic system can be carried out with the liquid phase contained in the reaction chamber, in a part of the liquid phase prior to the introduction of said part into the reaction chamber, preferably introducing step f ).

Preferably, the pressure of introduction into the reaction enclosure is between 0.1 and 10.0 MPa, preferably between 0.2 and 9.0 MPa and preferably between 0.3 and 8.0 MPa.

Preferably the temperature of introduction into the reaction chamber is between 30 and 200°C, preferably between 35 and 150°C and more preferably between 45 and 140°C.

In a preferred embodiment, the reaction enclosure has a Height to Diameter ratio, denoted H/D, greater than 1.5, preferably between 1.5 and 50, preferably between 2 and 40, preferably between 2 .5 and 10 and very preferably between 3 and 8.

Another advantage of this embodiment is that the higher the H/D ratio, the better the performance of the reactor. Indeed, the higher the height of the reaction chamber and therefore the height of the liquid phase, for the same volume of the reactor and of the liquid phase used in an oligomerization reaction, the more the dissolution of ethylene gas is improved and therefore the more the piercing phenomenon for a given volume of liquid phase is limited, and therefore the more the selectivity for the desired olefins increases.

Stage b) of introducing gaseous ethylene

The process according to the invention comprises a step b) of introducing gaseous ethylene into the lower zone of the reaction enclosure. . Said gaseous ethylene is introduced into the liquid phase at the level of the lower part of the reaction chamber, preferably on the lower side part of the reaction chamber. The ethylene gas introduced comprises fresh ethylene gas, and preferably said fresh ethylene gas is combined with ethylene gas recycled from a separation step subsequent to the oligomerization process.

During the implementation of the process according to the invention, following the step of introducing ethylene gas, the liquid phase comprises undissolved ethylene gas, thus depending on the zones of the reaction enclosure, the liquid phase corresponds to a gas-liquid mixture between in particular the liquid phase and gaseous ethylene.

Preferably, the gaseous ethylene is distributed by dispersion during its introduction into the lower liquid phase of the reaction enclosure by a means capable of carrying out said dispersion in a uniform manner over the entire section of the reactor. Preferably, the dispersion means is chosen from a distributor network with a homogeneous distribution of the injection of ethylene over the entire section of the reactor.

Preferably, the velocity of the ethylene gas leaving the orifices is between 1.0 and 30.0 m/s. Its superficial velocity (volumic velocity of gas divided by the section of the reaction chamber) is between 0.5 and 10.0 cm/s and preferably between 1.0 and 8.0 cm/s.

Preferably, the gaseous ethylene is introduced at a rate of between 0.2 and 250 t/h, preferably between 0.5 and 200 t/h, preferably between 1 and 150 t/h and preferably between 2 and 100 t/h.

Preferably, the flow of ethylene gas introduced in step b) is controlled by the pressure in the reaction chamber.

According to a particular mode of implementation of the invention, a flow of gaseous hydrogen can also be introduced into the reaction chamber, with a flow representing 0.2 to 5.0% by mass of the incoming ethylene flow, preferably representing between 0.2 and 4.0%, more preferably between 0.3 and 3.0% and very preferably between 0.4 and 2.0%. Preferably, the flow of hydrogen gas is introduced through the pipe implemented for the introduction of ethylene gas.

Step c) of withdrawing a fraction comprising part of the liquid phase and gaseous ethylene

The process according to the invention comprises a step c) of withdrawing a fraction comprising part of the liquid phase and gaseous ethylene, preferably in the lower part of the reaction enclosure.

Advantageously, the withdrawal of a fraction comprising part of the liquid phase mixed with gaseous ethylene makes it possible to operate under conditions of descending speed of the liquid phase such that it makes it possible to limit the speed of ascent of the gaseous ethylene within the liquid phase contained in the reaction chamber by creating a current generated by the withdrawal rate of said liquid-gas fraction.

The withdrawal implemented in step c) is preferably carried out in the lower part of the reaction enclosure, preferably below the level of the introduction of gaseous ethylene, and preferably in the bottom of the pregnant. Withdrawal is carried out by any means capable of carrying out the withdrawal and preferably by means of a pipe, possibly in combination with a pump.

In a preferred embodiment, the withdrawal can be carried out with one or more pipes located at the bottom of the reactor or on the side surface in the lower part of the reaction enclosure, so as to withdraw several fractions comprising part of the liquid phase mixed with ethylene gas.

Preferably, the withdrawal rate is between 100 and 10,000 t/h, and preferably between 300 and 7,000 t/h.

Stage d) of separation into a liquid fraction and an ethylene gas fraction

The process according to the invention comprises a step d) of separating the fraction withdrawn in step c) into a liquid fraction and a gaseous fraction comprising ethylene.

Preferably, step d) of separation of the fraction withdrawn in step c) can be implemented by any means making it possible to obtain a liquid fraction and a gaseous fraction. Preferably, step d) is implemented by means of a gas-liquid separation drum, a decanter, a flash.

According to a preferred embodiment, one or more liquid fractions separated in step d) can be divided into two streams. The first so-called main stream is sent to stage f) of cooling, and the second stream corresponds to the effluent and is sent to a preferably downstream separation section.

According to a preferred embodiment, when several fractions are withdrawn in step c) by means of several pipes, each of said fractions can be subjected to a step d) of separation into a liquid fraction and a gaseous fraction comprising ethylene by means of one or more separating means.

Advantageously, the flow rate of said second stream is regulated to maintain a constant liquid level in the reactor. Preferably, the flow rate of said second flow is 5 to 200 times lower than the liquid flow sent to the cooling stage. Preferably, the flow rate of said effluent is 5 to 150 times lower, preferably 10 to 120 times lower and more preferably 20 to 100 times lower.

Advantageously, the combination of steps c) and d) makes it possible to slow down the rise of the gaseous ethylene in the liquid phase and therefore to limit the phenomenon of piercing, which makes it possible to improve the saturation of the ethylene dissolved in the liquid phase. contained in the reaction enclosure and therefore the productivity of the process.

Step e) of cooling the liquid fraction

The method according to the invention comprises a step e) of cooling at least part of the liquid fraction separated in step d), preferably by passing said fraction through a heat exchanger.

When several fractions are withdrawn in step c) and separated in step d), the separated liquid fractions can each be subjected to a step e) of cooling, or be combined to subject the mixture to a single step e) of cooling.

Preferably, the cooling step is implemented by the circulation of the main liquid stream(s) withdrawn in step d), through one or more heat exchangers located inside or outside the enclosure reaction and preferably outside.

When the liquid fraction(s) separated in step d) are not divided, the whole of the fraction(s) separated is sent to step e).

In a particular embodiment, when several fractions are withdrawn in step c) and separated in step d), one of the fractions, preferably consisting of liquid phase, corresponds to the effluent and is sent to a downstream section preferably separation.

The heat exchanger makes it possible to reduce the temperature of the liquid fraction from 1.0 to 30.0°C, preferably between 2.0 and 20°C, preferably between 2.0 and 15.0°C, preferably between 2.5 and 10.0°C, preferably 3.0 to 9.0°C, preferably 4.0 to 8.0°C. Advantageously, the cooling of the liquid fraction makes it possible to maintain the temperature of the reaction medium within the desired temperature ranges.

Step f) introducing a cooled liquid fraction

The process according to the invention comprises a step f) of introducing one or more cooled liquid fractions in step e).

The introduction of the cooled liquid fraction or fractions from step e) is preferably carried out in the liquid phase of the reaction enclosure, preferably in the upper part of said enclosure, by any means known to the Man of the trade.

Preferably, the overall rate of introduction of the cooled liquid fraction(s) is between 100 and 10,000 t/h, and preferably between 300 and 7,000 t/h.

Steps c) to f) constitute a recirculation loop. If several fractions comprising part of the liquid phase and ethylene gas are subjected to steps c) to f), the reactor then comprises several recirculation loops. Advantageously, the recirculation loop(s) make it possible to stir the reaction medium, and thus to homogenize the concentrations of the reactive species throughout the liquid volume of the reaction chamber.

Step g) optional introduction of the gaseous fraction comprising ethylene

The process according to the invention comprises a step g) of introducing the gaseous fraction or fractions comprising ethylene separated in step d) into the liquid phase contained in the reaction chamber.

Preferably, said gaseous fraction or fractions comprising ethylene are introduced into the liquid phase at the level of the lower part of the reaction enclosure, preferably on the lower lateral part of the reaction enclosure.

Preferably, the introduction of the gaseous fraction or fractions comprising ethylene separated in step d) is carried out at the same level as the introduction of step b) by a means capable of carrying out its dispersion in a uniform manner. over the entire section of the reactor. Preferably, the dispersion means is chosen from a distributor network with a homogeneous distribution of the injection points of the gaseous phase over the entire section of the reactor.

In a particular embodiment, said gaseous fraction or fractions separated in stage d) are mixed with the gaseous ethylene introduced in stage b). The gas mixture thus obtained is then introduced into the reaction chamber.

Advantageously, the optional step g) of recycling the gaseous fraction or fractions comprising ethylene resulting from the separation step d) makes it possible to optimize the consumption of ethylene in the oligomerization process.

Step h) optional recycling of a gaseous fraction withdrawn from the gaseous phase

Advantageously, the method can comprise a step h) of recycling a gaseous fraction withdrawn from the gaseous phase of the reaction enclosure and introduced at the level of the lower part of the reaction enclosure into the liquid phase, preferably on the part lower side of the reaction chamber, preferably at the bottom of the reaction chamber. The lower part designates the lower quarter of the reaction chamber.

Step h) of recycling the gaseous fraction is also called a recycle loop. The withdrawal of the gaseous fraction implemented in step h) is carried out by any means suitable for carrying out the withdrawal and preferably by a pipe possibly in combination with a compressor.

Advantageously, the optional step h) of recycling also makes it possible to compensate for the phenomenon of piercing of the ethylene in the gaseous headspace. The piercing phenomenon corresponds to gaseous ethylene which crosses the liquid phase without dissolving and which passes into the gaseous sky. When the flow rate of injected ethylene gas and the volume of sky are fixed at a given value, the drilling then leads to an increase in pressure in the reaction chamber. In a gas/liquid reactor implemented according to a preferred method, the rate of introduction of ethylene in step b) is controlled by the pressure in the reaction enclosure. Thus, in the event of an increase in the pressure in the reactor due to a high penetration rate of ethylene in the gas phase, the flow rate of gaseous ethylene introduced in stage b) decreases, which leads to a reduction of the quantity of ethylene dissolved in the liquid phase and therefore of the saturation. The decrease in saturation is detrimental for the conversion of ethylene and is accompanied by a decrease in the productivity of the reactor. The step of recycling a gaseous fraction also makes it possible to optimize the saturation of the dissolved ethylene and therefore to improve the volume productivity of the process.

The gaseous phase drawn off in step h) can be introduced into the reaction chamber alone or mixed with the gaseous ethylene introduced in step b) and/or in optional step g). Preferably, the gaseous phase is introduced mixed with the gaseous ethylene introduced in stage b) and/or in optional stage g).

In a particular embodiment, the gaseous phase withdrawn in step h) is introduced into the reaction chamber by dispersion in the lower liquid phase of the reaction chamber by a means capable of carrying out said dispersion in a uniform manner over the entire section of the reactor. Preferably, the dispersion means is chosen from among a distributor network with a homogeneous distribution of the injection points of the gaseous phase withdrawn in step h) over the entire section of the reactor.

Preferably, the speed of the gaseous fraction drawn off at the outlet of the orifices is between 1.0 and 30.0 m/s. Its superficial velocity (volumic velocity of gas divided by the section of the reaction chamber) is between 0.5 and 10.0 cm/s and preferably between 1.0 and 8.0 cm/s.

Preferably, the rate of withdrawal of the fraction is between 0.1 and 100% of the rate of gaseous ethylene introduced in step b), preferably 0.5 and 90.0%, preferably 1.0 and 80.0%, preferably between 2.0 and 70.0%, preferably between 4.0 and 60.0%, preferably between 5.0 and 50.0%, preferably between 10.0 and 40, 0% and preferably between 15.0 and 30.0%.

Advantageously, the rate of withdrawal of the gaseous fraction in step h) is controlled by the pressure within the reaction chamber, which makes it possible to maintain the pressure at a desired value or range and therefore to compensate for the phenomenon of piercing ethylene gas in the sky.

In a particular embodiment, the gaseous fraction withdrawn in step h) is divided into two streams, a first so-called main gaseous stream is recycled directly into the reaction enclosure, and a second gaseous stream.

In a preferred embodiment, said second gas flow corresponds to a purge of the gaseous headspace, which makes it possible to eliminate part of the incondensable gases.

Preferably, the flow rate of the second gas stream is between 0.005 and 1.00% of the flow rate of ethylene introduced in step b), preferably between 0.01 and 0.50%.

Oligomerization reaction device

Many reactors implementing a liquid phase and a gas phase consist of a reaction chamber comprising a liquid phase in a lower zone comprising gaseous ethylene and a gas phase in an upper zone, one or more recirculation loops of a liquid fraction to one or more heat exchangers allowing the cooling of the liquid fraction before its reintroduction into the reaction chamber. The flow rate of the recirculation loop(s) makes it possible to obtain good homogenization of the concentrations and to control the temperature in the liquid phase within the reaction chamber.

The reaction device implemented by the process according to the invention belongs to the field of gas/liquid reactors such as bubble columns. In particular, the reaction device according to the invention comprises the following elements:

- a reaction chamber i), of elongated shape along the vertical axis containing a liquid phase located in a lower zone comprising, and preferably consisting of, reaction products, dissolved and gaseous ethylene, a catalytic system and a possible solvent, and a gaseous phase located in an upper zone above the lower zone comprising gaseous ethylene, as well as incondensable gases (ethane in particular),

- a means for introducing ethylene gas ii), into said reaction chamber and optionally implementing a means for distributing ethylene gas within said liquid phase of the reaction chamber,

- a means of introducing the catalytic system iii) into the reaction device,

- a withdrawal means iv) in the lower part, preferably at the bottom, of the reaction chamber for withdrawing a fraction comprising part of the liquid phase and ethylene gas,

- a means for separating v) the fraction comprising part of the liquid phase and ethylene gas so as to obtain a liquid fraction and a gaseous fraction comprising ethylene,

- a recirculation loop vi) of the liquid fraction towards a heat exchanger allowing the cooling of said liquid, and a means of introducing said cooled liquid, said introduction being carried out in the liquid phase in the upper part of the lower zone of the reaction chamber.

i) a reaction chamber

According to the invention, any reaction chamber known to those skilled in the art and able to implement the method according to the invention can be envisaged.

In a preferred embodiment, the reaction enclosure has a Height to Diameter ratio, denoted H/D, greater than 1.5, preferably between 1.5 and 50, preferably between 2 and 40, preferably between 2 5 and 10 and very preferably between 3 and 5.

Indeed, an H/D ratio greater than 1.5 makes it possible to increase the height of the reaction chamber and therefore the height of the liquid phase without modifying the volume of the reactor or of the liquid phase used in a reaction of oligomerization, which has the effect of improving the dissolution of gaseous ethylene and therefore of limiting the phenomenon of piercing for a given volume of liquid phase.

Preferably, the reaction chamber comprises a means for purging the incondensable gases at the level of the gas phase.

Preferably, the reaction enclosure also comprises a pressure sensor, making it possible to control the pressure within the reaction enclosure, and preferably to maintain the pressure constant. Preferably, in the event of a decrease in pressure, said pressure is kept constant by the introduction of gaseous ethylene into the reaction chamber.

According to the invention, in the event of the phenomenon of ethylene piercing in the gas phase, said pressure is kept constant by the implementation of the withdrawal means iv).

Thus, the means for withdrawing a fraction comprising a mixture of liquid and gaseous ethylene combined with a gas/liquid separation means advantageously makes it possible, in the event of the ethylene being pierced, to maintain the saturation of ethylene dissolved in it at a given value. the liquid phase of the lower zone.

Preferably, the reaction enclosure also comprises a liquid level sensor, said level is kept constant by modulating the flow rate of the effluent withdrawn in step c). Preferably, the level sensor is located at the interface between the liquid phase and the gaseous headspace.

In a particular embodiment, the reaction chamber also comprises means for withdrawing a liquid fraction corresponding to the effluent and said fraction being able to be sent to a preferably downstream section for separation.

ii) a means of introduction of ethylene

According to the invention, the reaction enclosure i) comprises a means for introducing ethylene gas, preferably located in the lower part of said enclosure, and more preferably in the lower side part.

Preferably, the means for introducing ii) the ethylene is chosen from a pipe, a network of pipes, a multitubular distributor, a perforated plate or any other means known to those skilled in the art.

In a particular embodiment, the means for introducing ethylene is located in the recirculation loop iv).

Preferably, a gas distributor, which is a device allowing the gas phase to be dispersed uniformly over the entire liquid section, is positioned at the end of the introduction means ii) within the reaction chamber i). Said device comprises a network of perforated pipes, the diameter of the orifices of which is between 1.0 and 12.0 mm, preferably between 3.0 and 10.0 mm, to form ethylene bubbles in the liquid of dimension millimeter.

iii) a means of introduction of the catalytic system

According to the invention, the reaction device comprises a means for introducing iii) the catalytic system.

Advantageously, the means for introducing the catalytic system can be any means such as a pipe capable of introducing a liquid fraction which may contain the catalytic system into the reaction chamber i).

Preferably, the introduction means iii) is located on the lower part of the reaction enclosure, and preferably at the bottom of said enclosure.

According to a variant embodiment, the introduction of the catalytic system is carried out in the recirculation loop.

The means of introduction iii) of the catalytic system is chosen from any means known to those skilled in the art and preferably is a pipe.

In the embodiment where the catalytic system is implemented in the presence of a solvent or a mixture of solvents, said solvent is introduced by means of introduction located in the lower part of the reaction enclosure, preferably at the bottom of the reaction chamber or in the recirculation loop.

iv) means for withdrawing a fraction comprising part of the liquid phase and gaseous ethylene

According to the invention, the reaction chamber i) comprises one or more means for withdrawing iv) a fraction comprising part of the liquid phase and gaseous ethylene.

Preferably the withdrawal means or means are on the lower part of the reaction enclosure, preferably at the bottom, so as to carry out the withdrawal of a fraction comprising a gas-liquid mixture.

The withdrawal means according to the present invention are chosen from any means known to those skilled in the art capable of carrying out the withdrawal of a liquid and/or gaseous fraction, without being limiting, said means may be a pipe alone or in combination with a pump.

v) a gas/liquid separation means

According to the invention, the reaction device comprises a means for gas/liquid separation v) of a fraction comprising part of the liquid phase and gaseous ethylene, into a liquid fraction and a gaseous fraction comprising ethylene.

Preferably, if the device comprises several withdrawal means iv), then said device comprises several gas/liquid separation means v). In a particular embodiment, the number of separation means v) is equal to the number of withdrawal means iv).

Said gas/liquid separation means can be any device known to those skilled in the art capable of separating a liquid/gas mixture. Thus, without being limiting, said means may for example be a gas/liquid separation drum, a decanter, a flash separator.

Said gaseous fraction comprising ethylene can advantageously be introduced into the reaction chamber via the means for introducing ethylene gas ii). Preferably, said gaseous fraction is compressed beforehand by means of a compressor or any other device known to those skilled in the art.

vi) a recirculation loop

According to the invention, the homogeneity of the liquid phase, as well as the regulation of the temperature within the reaction enclosure are achieved by the use of a recirculation loop comprising the sending of the liquid fraction separated by the gas-liquid separation means v) to one or more heat exchanger(s) allowing said liquid to be cooled, and a means for introducing said cooled liquid into the liquid phase in the upper part of the reaction chamber.

The recirculation loop(s) can advantageously be implemented by any means necessary and known to those skilled in the art, such as a pump, a means capable of regulating the flow rate of the liquid fraction withdrawn, or even a purge line of at least a part of the liquid fraction.

The heat exchanger(s) capable of cooling the liquid fraction is (are) chosen from any means known to those skilled in the art.

The recirculation loop(s) allow good homogenization of the concentrations and control of the temperature in the liquid phase within the reaction chamber.

vii) an optional overhead gas recycle loop

In a preferred embodiment, the device comprises a loop for recycling the gaseous phase in the lower part of the reaction enclosure which can contain the liquid phase. Said loop comprising means for drawing off a gaseous fraction at the level of the gaseous phase of the reaction enclosure and means for introducing said gaseous fraction withdrawn into the liquid phase in the lower part of the reaction enclosure.

Advantageously, the recycle loop also makes it possible to compensate for the phenomenon of piercing and to avoid increasing the pressure in the reaction chamber, while maintaining the saturation of ethylene dissolved in the liquid phase at a desired value.

Advantageously, the recycling loop also makes it possible to improve the volumetric productivity of the device and therefore to reduce costs. In a preferred embodiment, the recycle loop further includes a compressor.

In one embodiment, the introduction of the withdrawn gaseous fraction is carried out by the means for introducing ethylene gas ii).

In another embodiment, the introduction of the gaseous fraction drawn off is carried out by a gaseous distributor which is a device making it possible to disperse the gas phase in a uniform manner over the entire liquid section, is positioned at the end of the means of introduction into the reaction chamber i). Said device comprises a network of perforated pipes, the diameter of the orifices of which is between 1.0 and 12.0 mm, preferably between 3.0 and 10.0 mm, to form ethylene bubbles in the liquid of dimension millimeter.

Preferably, the means for introducing the withdrawn gaseous fraction is chosen from a pipe, a network of pipes, a multitubular distributor, a perforated plate or any other means known to those skilled in the art.

DESCRIPTION OF FIGURES

There illustrates a reaction device according to the prior art. This device consists of a reaction chamber (1) comprising a lower zone comprising a liquid phase A and an upper zone comprising a gaseous phase B, a means of introducing gaseous ethylene (2) via of a gaseous distributor (3) in the liquid phase A. The gaseous phase B comprises a purge means (4). In the bottom of the reaction chamber (1) there is a pipe for withdrawing a liquid fraction (5). Said fraction (5) is divided into 2 streams, a first main stream (7) sent to a heat exchanger (8) then introduced via a pipe (9) into the liquid phase A and a second stream ( 6) corresponding to the effluent sent to a later stage. The pipe (10) in the bottom of the reaction chamber allows the introduction of the catalytic system.

There illustrates a device allowing the implementation of the method according to the invention. Said device differs from the device of the in that a fraction (11) comprising part of the liquid phase and gaseous ethylene is withdrawn from the liquid phase A. Said fraction (11) is sent to a gas liquid separation means (12) allowing the obtaining a gaseous fraction (13) comprising ethylene and a liquid fraction (5). Said gaseous fraction (13) is recycled in the lower part of the reaction enclosure. Said liquid fraction (5) is divided into 2 streams, a first main stream (7) sent to a heat exchanger (8) as in the device according to .

There illustrates a variant of the device allowing the implementation of the method according to the invention. Said device differs from the device of the in that the gaseous fraction (13) is sent to a compressor (14) and the compressed gas stream (15) is recycled via an introduction means allowing mixing with the gaseous ethylene introduced by the means (2).

There illustrates a variant of the device allowing the implementation of the method according to the invention. Said device differs from the device of the in that the reaction chamber (1) has an H/D ratio greater than 10

Figures 2, 3 and 4 schematically illustrate particular embodiments of the object of the present invention without limiting its scope.

EXAMPLES

The examples below illustrate the invention without limiting its scope.

Example 1: comparison corresponding to the

The ethylene oligomerization process is carried out in a bubble column type reactor. The reactor is operated at a pressure of 7.0 MPa and at a temperature of 130°C. The reaction volume is composed, in accordance with the figure in 1, in two zones A and B, in a column 3.34 m in diameter and 9.0 m in height, containing 5.0 m in liquid height, and d a recirculation loop having a total volume of 9 m ³ .

The column is equipped with an ethylene gas injection device, located 0.7 m from the bottom of the column.

The catalytic system introduced into the reaction chamber is a chromium-based catalytic system with a chromium content of 3.9 ppm, as described in patent FR3019064, in the presence of cyclohexane as solvent.

The volume productivity of this reactor is 0.156 tonnes of hexene-1 produced per hour and per m ³ of reaction volume.

The performance of this reactor makes it possible to have a dissolved ethylene saturation of 71.3%.

The production of hexene-1 is 6.25 tonnes/hour, the selectivity for hexene-1 is 80.1% by weight, for a conversion of 78.0% of ethylene, and the residence time in the reactor is 91.6 minutes, for a mass ratio of solvent of 1.0. Said solvent content is calculated as the mass ratio of the flow of solvent injected to the flow of ethylene gas injected.

Example 2: according to the invention corresponding to the

The oligomerization process according to the invention is implemented in a device of identical dimensions to that implemented in example 1, additionally comprising and in accordance with the invention a means of gas-liquid separation of the fraction comprising part of the liquid phase and ethylene gas as described in .

The ethylene oligomerization process is implemented in a bubble column type reactor. The reactor is operated at a pressure of 7.0 MPa and at a temperature of 130°C.

The catalytic system introduced into the reaction enclosure is a chromium-based catalytic system with a 5.8 ppm chromium content, as described in patent FR3019064, in the presence of cyclohexane as solvent.

The productivity by volume of this reactor is 0.178 tonnes of hexene-1 produced per hour and per m ³ of reaction volume.

The performance of the oligomerization process according to the invention makes it possible to have a dissolved ethylene saturation of 74.8%.

The production of hexene-1 is 9.38 tonnes/hour, the selectivity for hexene-1 is 81.0% by weight, for a conversion of 76.9% of ethylene, and the residence time in the reactor is 60.9 minutes, for a solvent mass ratio of 1.0. Said solvent content is calculated as the mass ratio of the flow of solvent injected to the flow of ethylene gas injected.

Thus the process according to the invention in which the withdrawal of a fraction comprising a part of the liquid phase and gaseous ethylene combined with a means of gas-liquid separation clearly makes it possible to increase the saturation of ethylene in the liquid phase, which makes it possible to improve the productivity of the oligomerization process with a shorter residence time and better selectivity for hexene-1.

Example 3: according to the invention corresponding to the

The oligomerization process according to the invention is implemented in a device according to the invention as described in Example 2, with the difference that the reaction enclosure has a height of 13.3 m, with a height of liquid of 7.4 m and an internal diameter of the reaction chamber of 2.7. Thus in this example the H/D ratio is 4.9. The ethylene oligomerization process is implemented in a bubble column type reactor. The reactor is operated at a pressure of 7.0 MPa and at a temperature of 130°C.

The catalytic system introduced into the reaction enclosure is a chromium-based catalytic system with a chromium content of 3.8 ppm, as described in patent FR3019064, in the presence of cyclohexane as solvent.

The volume productivity of this reactor is 0.156 tonnes of hexene-1 produced per hour and per m ³ of reaction volume.

The performance of the oligomerization process according to the invention makes it possible to have a dissolved ethylene saturation of 83.9%.

The production of hexene-1 is 6.25 tonnes/hour, the selectivity for hexene-1 is 83.2% by weight, for a conversion of 74.1% of ethylene, and the residence time in the reactor is 90.4 minutes, for a solvent mass content of 1.0. Said solvent content is calculated as the mass ratio of the flow of solvent injected to the flow of ethylene gas injected.

Thus the process according to the invention in which the H/D ratio is increased clearly makes it possible to increase the saturation of ethylene in the liquid phase, which makes it possible to improve the selectivity for hexene-1, while maintaining the productivity of the oligomerization process with the same residence time.

Example 4: comparison corresponding to the

The ethylene oligomerization process is carried out in a bubble column type reactor. The reactor is operated at a pressure of 2.6 MPa and at a temperature of 45°C. The reaction volume is composed, in accordance with the figure in 1, in two zones A and B, in a column 2.6 m in diameter and 7.1 m in height, containing 5.1 m in liquid height, and d a recirculation loop having a total volume of 3 m ³ .

The column is equipped with an ethylene gas injection device, located 0.5 m from the bottom of the column.

The catalytic system introduced into the reaction enclosure comprises, as nickel catalyst, Ni(2-ethylhexanoate) ₂ at a concentration of 3 ppm by weight of nickel, tricyclohexylphosphine at a molar ratio of 10 of tricyclohexylphosphine to the nickel catalyst, and 15 molar equivalents of ethylaluminum dichloride relative to the nickel catalyst in the presence of n-heptane as solvent.

The volume productivity of this reactor is 0.136 tonnes of butene-1 produced per hour and per m ³ of reaction volume.

The performance of this reactor makes it possible to have a dissolved ethylene saturation of 37.5%.

The production of butene-1 is 4.1 tons/hour, the selectivity for butene-1 is 86.5% by weight, for a conversion of 92.5% of ethylene, and the residence time in the reactor is 164 minutes.

Example 5: according to the invention corresponding to the

The oligomerization process according to the invention is implemented in a device according to the invention as described in Example 2, with the difference that the reaction enclosure has a height of 16.2 m, with a height of liquid of 14.2 m and an internal diameter of the reaction chamber of 1.5 m. Thus in this example the H/D ratio is 9.5. The ethylene oligomerization process is implemented in a bubble column type reactor. The reactor is operated at a pressure of 2.6 MPa and at a temperature of 45°C.

The catalytic system introduced into the reaction enclosure comprises, as nickel catalyst, Ni(2-ethylhexanoate) ₂ at a concentration of 2.9 ppm by weight of nickel, tricyclohexylphosphine at a molar ratio of 10 of tricyclohexylphosphine on the catalyst of Nickel, and 15 molar equivalents of ethylaluminum dichloride with respect to the Nickel catalyst in the presence of n-heptane as solvent.

The volume productivity of this reactor is 0.136 tonnes of butene-1 produced per hour and per m ³ of reaction volume.

The performance of the oligomerization process according to the invention makes it possible to have a dissolved ethylene saturation of 80.8%.

The production of butene-1 is 4.1 tonnes/hour, the selectivity for butene-1 is 90.5% by weight, for a conversion of 83.9% of ethylene, and the residence time in the reactor is 151 minutes.

Thus the process according to the invention in which the withdrawal of a fraction comprising a part of the liquid phase and gaseous ethylene combined with a means of gas-liquid separation in combination with a high H / D ratio clearly makes it possible to increase the ethylene saturation in the liquid phase, which makes it possible to improve the butene-1 selectivity, while maintaining the productivity of the oligomerization process with the same residence time.

Claims (15)

Process for the oligomerization of gaseous ethylene implemented in a gas/liquid reactor at a pressure of between 0.1 and 10.0 MPa, at a temperature of between 30 and 200° C. comprising the following steps:
a) a step of introducing a catalytic oligomerization system into the reactor comprising a reaction chamber comprising a liquid phase in a lower zone and a gaseous phase in an upper zone,
b) a step of introducing gaseous ethylene into the lower zone of the reaction enclosure,
c) a step of withdrawing at least one fraction comprising part of the liquid phase and gaseous ethylene,
d) a step of separating the fraction withdrawn in step c) into a liquid fraction and a gaseous fraction comprising ethylene,
e) a step of cooling at least part of the liquid fraction separated in step d),
f) a step of introducing the fraction cooled in step e) into the upper part of the liquid phase of the reaction enclosure. Process according to claim 1 comprising a step g) of introducing the gaseous fraction comprising ethylene separated in step d) into the liquid phase contained in the reaction enclosure. Process according to Claim 2, in which the gaseous fraction comprising ethylene separated in step d) is introduced into the liquid phase in the lower part of the reaction enclosure. Process according to Claim 2, in which the gaseous fraction separated in stage d) is mixed with the gaseous ethylene introduced in stage b). Process according to any one of the preceding claims, comprising a step h) of recycling a gaseous fraction withdrawn from the gaseous phase of the reaction enclosure and introduced at the level of the lower part of the reaction enclosure into the liquid phase. Process according to Claim 5, in which the gaseous phase drawn off in stage h) is introduced into the reaction chamber mixed with the gaseous ethylene introduced in stage b) and/or in optional stage g). Process according to any one of the claims, in which step d) is implemented by means of a gas-liquid separation drum, a decanter and/or a flash. Process according to any one of the claims, in which the withdrawal implemented in step c) is carried out in the lower part of the reaction enclosure, preferably below the level of the introduction of gaseous ethylene, and preferably at the bottom of the enclosure Process according to any one of the claims, in which the liquid fraction separated in stage d) is divided into two streams, a first so-called main stream is sent to cooling stage f), and a second stream is sent to a downstream section. Process according to any one of the claims, in which the liquid phase in the lower zone of the reaction enclosure has a dissolved ethylene saturation rate greater than 70.0%. Process according to any one of the claims, in which in step b) a flow of hydrogen gas is introduced into the reaction enclosure, with a flow representing 0.2 to 5.0% by mass of the flow of ethylene entering . Reaction device for carrying out the process according to any one of Claims 1 to 11, comprising:
- a reaction chamber i), of elongated shape along the vertical axis containing a liquid phase located in a lower zone comprising reaction products, dissolved and gaseous ethylene, a catalytic system and a optional solvent, and a gaseous phase located in an upper zone above the lower zone and comprising gaseous ethylene,
- a means for introducing ethylene gas ii), into said reaction chamber and optionally implementing a means for distributing ethylene gas within said liquid phase of the reaction chamber,
- a means for introducing the catalytic system iii), into the reaction device, a withdrawal means iv) in the lower part of the reaction chamber capable of withdrawing a fraction comprising part of the liquid phase and ethylene gas ,
- a means for separating v) the fraction comprising part of the liquid phase and the gaseous ethylene so as to obtain a liquid fraction and a gaseous fraction comprising ethylene,
- a recirculation loop vi) of the liquid fraction towards a heat exchanger allowing the cooling of said liquid, and a means of introducing said cooled liquid, said introduction being carried out in the liquid phase in the upper part of the lower zone of the reaction chamber. Device according to claim 12 comprising a loop for recycling the gaseous phase in the lower part of the reaction chamber. Device according to Claim 13, in which the introduction of the gaseous fraction drawn off is carried out by the means for introducing ethylene gas ii). Device according to one of Claims 11 to 14, in which the introduction means ii) is chosen from among a pipe, a network of pipes, a multitubular distributor and a perforated plate.