EP4267293A1

EP4267293A1 - Method for oligomerisation in a gas/liquid reactor comprising a central duct

Info

Publication number: EP4267293A1
Application number: EP21824596.7A
Authority: EP
Inventors: Ludovic Raynal; Alexandre VONNER; Pedro MAXIMIANO RAIMUNDO
Original assignee: IFP Energies Nouvelles IFPEN
Current assignee: IFP Energies Nouvelles IFPEN
Priority date: 2020-12-23
Filing date: 2021-12-14
Publication date: 2023-11-01
Also published as: CA3202284A1; TW202239467A; FR3117891A1; CN116685395A; WO2022136012A1; KR20230124954A

Abstract

The present invention relates to a gas/liquid reactor for oligomerising gaseous ethylene, comprising a central duct defining, inside the enclosure of the reactor, a downward-flow central area and an upward-flow outer area, thereby increasing the travel time of the gas bubbles injected into the liquid phase, without increasing the volume of the liquid phase and consequently the volume of the reactor.

Description

OLIGOMERIZATION METHOD IN A GAS/LIQUID REACTOR COMPRISING A CENTRAL PIPE

TECHNICAL AREA

The present invention relates to the field of gas/liquid reactors allowing the oligomerization of olefins into linear olefins by homogeneous catalysis.

The invention also relates to the use of the gas/liquid reactor in a process for the oligomerization of a gaseous olefin feedstock, preferably gaseous ethylene, into linear alpha-olefins such as but-1-ene, hex- 1-ene, or oct-1-ene or a mixture of linear alpha-olefins.

PRIOR ART

The invention relates to the field of gas/liquid reactors also called bubble column, as well as their implementation in a process for the oligomerization of an olefinic feedstock, preferably ethylene. A drawback encountered during the implementation of such reactors in ethylene oligomerization processes is the management of the gas overhead, corresponding to the upper part of the reactor in the gaseous state. Said gaseous sky includes gaseous compounds which are not very soluble in the liquid phase, compounds partially soluble in the liquid but inert, as well as gaseous ethylene not dissolved in said liquid. The passage of gaseous ethylene from the lower liquid part of the reaction chamber to the gaseous headspace 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 significant, the purging of the gaseous headspace leads to a significant loss of ethylene, which affects the productivity and the cost of the oligomerization process. In addition, a significant piercing phenomenon means that a lot of gaseous ethylene has not been dissolved in the liquid phase and therefore has not been able to react, which is detrimental to, in addition to productivity, the selectivity of the oligomerization process. .

In order to improve the efficiency of the oligomerization process in particular in terms of productivity and cost, it is therefore essential to limit the phenomenon of ethylene piercing in order to improve its conversion in said process while maintaining good selectivity. into desired linear alpha olefins. The processes of the prior art implementing a gas/liquid reactor, as illustrated in FIG. 1, do not make it possible to limit the loss of gaseous ethylene and the purging of the gaseous sky causes an outlet of gaseous ethylene from the reactor. detrimental to the yield and cost of the process.

The applicant has described processes in applications WO2019/011806 and W02019/011609 making it possible to increase the contact surface between the upper part of the liquid fraction and the gaseous headspace by means of dispersion means or vortexes 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. These processes do not make it possible to limit the phenomenon of piercing and are not sufficient when the quantity of ethylene in the gaseous headspace is significant due to a high rate of piercing.

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, which determines the dissolution time of the injected gas bubbles. By dissolution time, it is understood the time between the moment when the bubble is injected, and the moment when it disappears (total dissolution) or leaves the liquid phase (piercing). 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 rate of penetration.

The applicant has discovered that it is possible to improve the conversion of olefin(s), in particular of ethylene, while maintaining a high selectivity for the desired linear olefin(s), and in particular for alpha-olefin(s), by limiting the phenomena of piercing by means of a gas/liquid reactor for the oligomerization of gaseous ethylene comprising a central pipe delimiting inside the enclosure of the reactor a central zone allowing a flow downward and an outer zone allowing an upward flow, thus making it possible to increase the travel time of the gas bubbles injected into the liquid phase, without increasing the volume of the liquid phase and therefore the volume of the reactor.

BRIEF DESCRIPTION OF THE INVENTION

An object of the present invention relates to a gas/liquid reactor for the oligomerization of a gaseous olefin feedstock, preferably gaseous ethylene, comprising

- A reactor enclosure 1 of elongated shape along a vertical axis; - a gas injection device 3,

- a liquid injection device 11 ,

- a central pipe 12 positioned along the vertical axis inside said enclosure; said central pipe being immersed in a liquid phase and delimiting a central zone able to allow a downward flow and an outer zone able to allow an upward flow of flow, in which the gas injection device is positioned in the upper part of said central pipe and the liquid injection device is positioned in the reactor enclosure so as to be able to drive the injected gas towards the lower part of the reactor, from the descending central zone towards the ascending external zone.

Preferably, the liquid and gas injection devices are positioned in the upper part of said central pipe so as to cause the gaseous olefin feedstock injected in the direction of the lower part of the reactor and the descending central zone towards the outer zone. ascending. Preferably, the liquid injection device 11 is positioned above the gas injection device 3.

Preferably, the central pipe 12 has a solid wall over the entire height of the central pipe or has openings over 5 to 10% of the lower part of the height of the central pipe from the opening of the lower end. .

Preferably, the lower part of the central pipe at the opening of the lower end has a flare or a narrowing.

Preferably, the central pipe comprises a deflector positioned in the reactor enclosure and facing the opening of the lower end of the central pipe. Preferably, the deflector is positioned at a distance with the lower opening of the central pipe corresponding to a distance comprised between 1 and 2 times the equivalent diameter of the central pipe. Preferably, the equivalent diameter of the deflector is at least equal to the diameter of the central equivalent pipe and preferably between 0.5 and 2.0 the diameter of the central pipe.

Preferably, the reactor comprises a recirculation loop comprising a withdrawal means located at the base of the reactor enclosure, a heat exchanger located outside the reactor enclosure and an introduction means located on or in the reactor enclosure to allow the introduction of a cooled liquid fraction into the reactor enclosure. Preferably, the liquid injection device 11 is positioned in the upper part of the central pipe and is connected to the introduction means of the recirculation loop.

Preferably, the central pipe has an equivalent diameter with a ratio of the equivalent diameter of the central pipe to the internal diameter of the reactor enclosure is between 0.2 and 0.9, preferably between 0.3 and 0, 8.

Preferably, the central pipe has a height with a ratio of the height of the central pipe to the height of the reactor enclosure of between 0.2 and 0.8 and preferably between 0.3 and 0.7.

Preferably, the gas injection device (3) comprises at least one gas injection port and the liquid injection device (11) comprises at least one liquid injection port, each injection port of gas being positioned at an orifice of the liquid injection device (11), so that the injection of the liquid can cause a shear reduction in the size of the bubbles during the injection of the charge gaseous olefinic. Preferably, the gas injection orifices and the liquid injection orifices are extended by an injection tube.

Another object of the invention relates to a process for the oligomerization of a gaseous olefin feedstock implementing a gas/liquid reactor as described above at a temperature between 30 and 200° C., a pressure between 0.1 and 10.0 MPa, in the presence of a catalytic system comprising at least a metal precursor.

Preferably, the gaseous olefin feedstock is chosen from preferably between 2 and 6 carbon atoms, preferably between 2 and 4 carbon atoms, and preferably from butenes, more particularly isobutene or butene-1, propylene and ethylene, alone or as a mixture.

DEFINITIONS & ABBREVIATIONS

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

By oligomerization of olefins is meant any reaction of addition of a first olefin to a second olefin, identical to or different from the first. The olefin thus obtained has the molecular formula C _n H2n 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.

By gaseous phase is meant 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 (or gas overhead of the reactor).

The terms "reactor enclosure" and "reaction enclosure" are used interchangeably to designate the reactor enclosure (1).

The term “lower zone of the reaction enclosure” means the part of the enclosure comprising the liquid phase, the gaseous olefin feedstock, in particular gaseous ethylene, the reaction products such as the desired linear alpha olefin (/ .e butene-1, hexene-1, octene-1 or the mixture of linear alpha-olefins), the catalytic system and optionally a solvent.

By upper zone of the reaction chamber is meant the part of the chamber located at the top of the chamber, that is to say directly above the lower zone and consisting of the gaseous phase corresponding to the sky gaseous.

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 ( for example here: ethane). The terms reactor or device denote all the means allowing the implementation of the oligomerization process according to the invention, such as in particular the reaction enclosure and the recirculation loop.

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

The upper part of the reaction enclosure means the upper quarter of the reaction enclosure containing the liquid phase.

The expression saturation rate of dissolved gaseous olefinic feedstock, in particular dissolved ethylene, designates the ratio of the quantity of dissolved gaseous olefinic feedstock, in particular of dissolved ethylene, to the maximum quantity of dissolved gaseous olefinic feedstock, in particular of ethylene, which it is possible to dissolve in the liquid under the temperature and pressure conditions considered.

Equivalent diameter is understood as being the diameter of the circle inscribed in the section (horizontal cross section) of the central pipe.

The various components of the reactor will be described with reference to all the figures, each component retaining the same reference from one figure to another.

BRIEF DESCRIPTION OF FIGURES

Figure 1 illustrates a reactor according to the prior art. This reactor consists of a reactor enclosure 1 comprising a lower zone comprising a liquid phase and an upper zone comprising a gaseous phase, a means 2 for introducing an olefin feed such as gaseous ethylene through the intermediary of a gas injection device 3 in the liquid phase. The upper part of the reaction enclosure 1 comprising the gaseous phase comprises a purge means 4. In the bottom of the reaction enclosure 1 there is a pipe for withdrawing a liquid fraction 5. Said fraction 5 is divided into 2 stream, a first main stream 7 sent to a heat exchanger 8 then introduced via a pipe 9 into the liquid phase and a second stream 6 corresponding to the effluent sent to a subsequent stage. The conduit 10 in the bottom of the reaction chamber allows the introduction of the catalytic system. Figure 2 illustrates a reactor according to the invention which differs from that of Figure 1 in that the upper part of the lower zone of the enclosure 1 comprises a central pipe 12 at the top of which are positioned the injection device of gas 3 and a liquid injection device 11 so that the injection of the liquid causes a flow of the injected liquid and gas from the descending central zone towards the ascending outer flow zone with respect to the central pipe 12 The arrows represent the direction of circulation of the liquid and of the gas injected into the reactor enclosure 1 .

FIG. 3 illustrates another embodiment of the reactor according to the invention which differs from that of FIG. 2 in that the liquid injection device 11 is connected to the pipe 9. Thus, the liquid flow at the outlet of the heat exchanger 8 is injected at the top of the central pipe 12 via a liquid injection device 11 arranged with the gas injection device 3 so that the injection of the liquid causes a flow down the gas and liquid reactor vessel in the central conduit 12.

Figure 4A is a schematic view of a bottom view of a section perpendicular to the vertical axis of the reactor vessel of a preferred embodiment of the invention in which the gas injection devices 3 and liquid 11 are arranged so that the injection of the liquid can cause by shear a reduction in the size of the gas bubbles of the gaseous olefin feedstock injected by the injected liquid. The gas 3 and liquid 11 injection devices are annular in shape and arranged so that the outlet orifices 13 of the gas injection device 3 inject the gas towards the wall of the enclosure 1 and that the gas injection trajectory perpendicularly crosses the trajectory of the liquid injected through the orifices 14 so as to cause the shearing of the gas in order to reduce the size of the bubbles of injected gas.

Figure 4B is a schematic view of a vertical section along the vertical axis of the injection device of Figure 4A. The liquid injection device 11 is a ring having a diameter greater than that of the gas injection device 3. The liquid injection device 11 is positioned on a plane greater than that of the gas injection device 3 so that each of the orifices 13 for injecting gas 3 is positioned perpendicularly and on the side of one of the orifices 14 of the liquid injection device 11, so that the flow of injected gas is on the path of the flow liquid injected at the orifices 14 of the liquid injection device 11. FIG. 4C is a schematic view of a vertical section along the vertical axis of the injection devices according to FIG. 4A illustrating the shearing effect of the gas injected by the gas injection device 3 by the liquid injected by the liquid injection device 11 .

DETAILED DESCRIPTION OF THE INVENTION

It is specified that, throughout this description, the expression "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 range of preferred pressure values can be combined with a range of more preferred temperature values.

In the following description and in the claims, the positions ("bottom", "top", "above", "below", "horizontal", "vertical", "lower half", etc.) of the various elements are defined with respect to the column in the operating position.

The present invention relates to a gas/liquid reactor for the oligomerization of a gaseous olefin feedstock, preferably gaseous ethylene, comprising

- an elongated reactor enclosure 1 along a vertical axis;

- a gas injection device 3,

- a liquid injection device 11 ,

- A central pipe 12 positioned along the vertical axis within said enclosure; said central conduit delimiting a descending central zone and an ascending outer flow zone, in which the gas injection device is positioned in the upper part of the said central conduit and the liquid injection device in the reactor vessel so as to drive the gas injected in the direction of the lower part of the reactor, from the descending zone towards the ascending zone. Within the meaning of the present invention, the gas injection device is intended to inject, into an oligomerization reactor, an olefin feedstock in the gaseous state.

Advantageously, the reactor according to the invention makes it possible to increase the time during which the gaseous olefin feed travels through the liquid phase, and therefore to improve the dissolution of said feed in the liquid phase, which synergistically reduces the phenomenon of piercing . Another advantage of the reactor according to the invention is that the Archimedean thrust exerted on the gaseous olefinic charge injected makes it possible to limit the speed of descent into the central pipe, which increases the travel time of the gaseous olefinic charge in the phase. liquid

Advantageously, the saturation rate of dissolved gaseous olefinic filler, in particular of dissolved ethylene, in the liquid phase is greater than 70.0%, preferably between 70.0 and 100%, preferably between 80.0 and 100%, preferably 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 phase chromatographic analysis (commonly called GC) of a fraction of the liquid phase withdrawn from the reaction chamber. .

Another advantage of the present invention is to improve the conversion of the olefin feed, in particular ethylene, and/or the selectivity in particular for alpha-olefins, as well as the volume productivity of the oligomerization process.

Another advantage of the reactor according to the invention is to make it possible to reduce the reaction volume and therefore the dimensions of the reactor compared to a reactor according to the prior art, with identical performance.

REACTOR

The present invention relates to a process for the oligomerization of a gaseous olefin feedstock, at a temperature between 30 and 200° C., a pressure between 0.1 and 10.0 MPa, in the presence of a catalytic system comprising at least metallic precursor , said process implementing a gas/liquid reactor for the oligomerization of a gaseous olefin feedstock, preferably gaseous ethylene, comprising - a reactor enclosure (1) of elongated shape along a vertical axis;

- a gas injection device (3),

- a liquid injection device (11),

- a central pipe (12) positioned along the vertical axis inside said enclosure in a lower zone of said enclosure; said central pipe delimiting a central zone able to allow a downward flow and an outer zone able to allow an upward flow of flow, in which the gas injection device is positioned in the upper part of the said central pipe and the The injection of liquid is positioned in the lower zone of the reactor enclosure so as to be able to entrain the injected gas in the direction of the lower part of the reactor, from the descending central zone towards the ascending external zone.

In a preferred embodiment, the liquid and gas injection devices are positioned in the upper part of said central pipe and preferably close to each other, so as to advantageously drive the gaseous olefin feedstock injected into direction from the lower part of the reactor and from the central zone towards the outer zone. In this embodiment, the liquid injection device 11 is positioned above the gas injection device 3 so as to improve the entrainment of the gas corresponding to the gaseous olefinic charge by the liquid in the direction of downward flow in the central pipe.

In another embodiment, the liquid injection device is positioned in the rising zone between the reactor containment and the central pipe so as to drive the gaseous olefin feedstock injected in the direction of the lower part of the reactor from the zone descending to the ascending zone.

Preferably, the central pipe 12 positioned substantially in the center of the reactor enclosure along the vertical axis within said enclosure.

Preferably, the oligomerization reactor is a reactor for the dimerization, trimerization or tetramerization, for example of ethylene.

The combination of the liquid 11 and gas 3 injection devices and the central pipe 12, when the reactor is implemented in an oligomerization process, makes it possible to increase the residence time during which the gaseous olefinic charge remains phase liquid, before optionally joining the gas overhead, which improves the dissolution of the gaseous olefin feedstock, in particular gaseous ethylene, in said liquid phase.

Thus, according to the invention, the lower end and the upper end of the central pipe 12 are open so as to allow free circulation and direct the circulation of the liquid in the reactor enclosure 1, as illustrated in FIG. 2. The injection of liquid, preferably in the upper part of the central pipe, is carried out in such a way as to direct the flow of gas and liquid according to a downward flow inside the central pipe, and upward at the exterior of the central pipe.

The central pipe can advantageously have a circular, oval, triangular, square section or any other geometric shape suitable for the implementation of the reactor according to the invention. Preferably, the central pipe has a circular section. Advantageously, the section is identical over the entire height of the pipe.

It is understood that the central pipe, as well as the gas and liquid injection devices are positioned in a lower zone so as to be immersed in the liquid phase when the reactor according to the invention is implemented in a process of oligomerization of a gaseous olefin feedstock.

In a particular embodiment, the central pipe 12 has a solid wall over the entire height of the central pipe or has openings over 5 to 10% of the lower part of the height of the central pipe from the opening of the lower end.

In a preferred embodiment, the central duct further comprises a baffle positioned opposite the lower end opening. Preferably, said deflector is positioned at a distance with the lower opening of the central pipe corresponding to a distance comprised between 1 and 2 times the equivalent diameter of the central pipe. Preferably, the deflector can be of any shape, for example a circular or oval disc, and can advantageously be solid or include holes. Advantageously, said holes can be round, oval or even rectangular slots. Preferably, the central pipe is cylindrical in shape, the deflector is cylindrical in shape and the diameter of said deflector is at least equal to the diameter of the central pipe, preferably between 0.5 and 2.0 and preferably between 1.0 and 1.5 times the diameter of the central pipe. Advantageously, whatever the embodiment, the securing of the central pipe and/or of the optional deflector in the reactor containment is carried out for example by means of lugs, beams or any other rigid structure, connecting the different elements to be assembled, such as the central pipe wall and the reactor enclosure, said tabs being able to be fixed by welding, by gluing, by screwing, by bolting alone or in combination, or any other similar means. In particular, the joining of the central pipe and the wall of the reactor containment is carried out in such a way as to release a passage section corresponding to the upward external zone.

Preferably, the reactor also comprises a recirculation loop comprising a withdrawal means located at the base (preferably at the bottom) of the reactor enclosure, a heat exchanger, advantageously located outside the reactor enclosure, and an introduction means, advantageously located on or in the reactor enclosure, to allow the introduction of a cooled liquid fraction into the reactor enclosure. Thus, when the reactor is implemented in an oligomerization process and the recirculation loop is in operation, a liquid fraction is withdrawn from the reactor enclosure and sent to the heat exchanger to achieve cooling of said fraction withdrawn liquid which is then introduced into the reactor by the introduction means.

In a preferred embodiment, the liquid injection device 11 is positioned in the upper part of the central pipe and is connected to the introduction means of the recirculation loop. Thus, the cooled liquid can advantageously be injected into said central pipe. An advantage of this embodiment is that the flow of cooled liquid injected participates in the entrainment of the olefinic load, preferably ethylene, towards the bottom of the central pipe from the descending central zone towards the ascending outer zone.

Another advantage of this embodiment is to limit the material investment by maximizing the use of the recirculation loop and thus to limit the overall cost of the oligomerization reactor.

Another advantage is that the liquid coming from the recirculation loop and introduced by the liquid injection device is colder and contains less ethylene than the liquid phase contained in the reactor. Thus, these two characteristics make it possible to improve the dissolution of gaseous ethylene in the cooled liquid fraction. Advantageously, the descending central zone inside the central pipe may comprise structured packing, of the static mixer type or any other equivalent equipment generating good agitation of the gas-liquid flow, over part or all of its height, thus allowing a better dissolution of the gas in the liquid via the turbulence generated by the structured packing.

Preferably, the reactor enclosure 1 is cylindrical. In the case of a cylindrical enclosure, the diameter D is the diameter of the cylinder. Such a geometry makes it possible in particular to limit the presence of “dead” volumes in the column.

Preferably, the central pipe has an equivalent diameter with a ratio of the equivalent diameter of the central pipe to the internal diameter of the reactor enclosure is between 0.2 and 0.9, preferably between 0.3 and 0, 8. In the case where the central pipe is cylindrical in shape, the equivalent diameter of the pipe corresponds to the diameter of the section (horizontal straight section) of the central pipe.

Preferably, the central pipe has a height with a ratio of the height of the central pipe to the height of the reactor enclosure of between 0.2 and 0.8 and preferably between 0.3 and 0.7. In particular, the ratio of the height of the central pipe to the height of the reactor containment is equal to 0.2, 0.3, 0.4, 0.5 or 0.6.

Preferably, the reactor enclosure 1 is elongated in shape along the vertical axis and can contain a liquid phase located in a lower zone comprising, and preferably consisting of, reaction products, dissolved ethylene and gas, a catalytic system and an optional solvent, and a gas phase (or gas overhead) located in an upper zone above the lower zone, comprising a fraction of the gaseous olefin feedstock, preferably ethylene gas, as well as incondensable gases (ethane in particular).

In particular, the gas/liquid reactor further comprises:

- a means for introducing the catalytic system, said catalytic system comprising a metal catalyst, at least one activator and at least one additive, optionally said means being located in the lower part of the reactor enclosure,

- means for drawing off the liquid phase to recover a reaction effluent comprising the alpha-olefins produced, - possibly a purge system of the gaseous sky,

- and optionally a loop for recycling the gas phase, for recycling at least a fraction of the gas phase towards the lower zone of the liquid phase, comprising a withdrawal means located in the upper zone of the reactor enclosure making it possible to withdraw a gaseous fraction at the level of the gaseous phase and an introduction means in the lower zone of the reactor enclosure to make it possible to introduce said gaseous fraction withdrawn into the liquid phase.

Advantageously, the central pipe is positioned in the reactor enclosure in the upper part of the lower zone, that is to say the zone intended to contain the liquid phase, and preferably at a distance from the bottom of the enclosure. reactor adapted to allow the circulation of liquid and gas flows.

Preferably, the gas injection device 3 is chosen from a pipe, a network of pipes, a multitubular distributor, a perforated plate, concentric tubes or any other means known to those skilled in the art.

Preferably, the liquid injection device 11 is chosen from a pipe, a network of pipes, a multitubular distributor, a perforated plate, concentric tubes or any other means known to those skilled in the art.

In a preferred embodiment, the gas injection device 3 comprises at least one gas injection orifice and the liquid injection device (11) comprises at least one liquid injection orifice, each orifice injection of gas being positioned relative to at least one orifice of the liquid injection device 11, in particular in the upper part of the central pipe, so that the injection of the liquid can cause a reduction by shear of the size of the bubbles during the injection of the gaseous olefin feedstock. Thus the gas injection trajectory is advantageously in the plane of the liquid injection trajectory. In this configuration, the injection of the liquid can then cause the shearing of the injected gas and lead to a reduction in the size of the gas bubbles, making it possible to improve the dissolution of the gas in the liquid phase via an increase in the interface. between gas and liquid.

It is understood that the gas and liquid injection devices may comprise a plurality of injection orifices depending on the dimensions of the reactor insofar as said injection devices are arranged in such a way that the injection of the liquid can cause a reduction by shear in the size of the bubbles during the injection of the gaseous olefinic feedstock

Advantageously, the arrangement according to this preferred embodiment makes it possible to reduce the size of the gas bubbles injected by at least 20% compared to the size of the gas bubbles injected without shear. Preferably, the percentage reduction in the size of the bubbles by this shear is at least 25% compared to the size of the gas bubbles injected without shear, preferably at least 30%, preferably at least 35 % and preferably at least 40%.

Advantageously, the breaking of a gas bubble into two smaller ones of the same size generates an increase in the exchange surface between the gas and the liquid of 26%, a breaking of a gas bubble into 4 smaller bubbles of the same size generates a 59% increase, breaking a gas bubble into 6 smaller bubbles of the same size generates an 82% increase. Thus, a reactor according to the invention therefore facilitates and significantly improves the absorption of gas in the liquid phase, which makes it possible to increase the saturation of gaseous olefinic charge in the liquid phase and to limit the phenomenon of piercing.

By injection orifice is meant a round hole, an oval hole, a slot or any other shape allowing the injection of liquid or gas into the reactor. Preferably, the gas injection and liquid injection orifices are circular, that is to say round holes.

Preferably, the gas injection orifices have a diameter of between 1.0 and 15.0 mm, preferably between 3.0 and 20.0 mm, to form bubbles of ethylene in the liquid of millimetric size. Preferably, the liquid injection orifices have a diameter between 1.0 and 15.0 mm, preferably between 3.0 and 20.0 mm. Preferably, the liquid injection orifices have a diameter greater than or equal to the diameter of the gas injection orifices. Preferably, the ratio between the diameter of a gas injection orifice and the diameter of the liquid injection orifice arranged close to said gas injection orifice is between 0.1 and 1.0, preferably between 0.4 and 0.8.

In a preferred embodiment, the orifices of the gas and liquid injection devices are extended by a tube. Preferably, the tube of the gas injection device 13 has a smaller diameter than that of the liquid injection tube 15 and is positioned inside the liquid injection tube coaxially. The outlet port of the gas injection tube is directed towards the outlet port of the liquid injection tube. Preferably, the liquid injection tube 15 comprises a deflector as a means of partially closing off the tube, preferably a circular, round or square plate, perforated or not. Advantageously, the deflector makes it possible to improve the effect of shearing of the gas bubbles by the liquid.

Preferably, the end of the liquid injection tube has a narrowing of the outlet diameter. Said shrinkage leads to the acceleration of the gas-liquid mixture, which increases the shear forces and further improves the breaking of the gas bubbles into smaller gas bubbles.

In a highly preferred mode, the tube has an outlet diameter constriction and a baffle.

Advantageously, a gas injection orifice and a liquid injection orifice are positioned facing each other at an angle of between 0° and 180°. When the orifices of the gas and liquid injection devices are extended by a tube, the gas and liquid injection orifices correspond to the outlet orifices of the gas and liquid injection tube(s). An angle of 0° means that the gas and the liquid are injected through said respective orifices on the same axis of trajectory and in the same direction. Preferably, the angle formed by the trajectories is between 0° and 120°, preferably between 30° and 120°, preferably between 45° and 90°. Very preferably, the angle formed by the trajectories is between 0° and 90°. Preferably, the angle formed by the trajectories is equal to 0°, 30°, 45°, 90°, 120° or 180°.

In a particular embodiment, the gas injection device is a cylindrical tube having the shape of a circular ring, for example round or oval, and having injection orifices. Advantageously, the liquid injection device is also a cylindrical tube having the shape of a circular ring, for example round or oval, and having injection orifices. Preferably, said liquid injection device is positioned in the upper part of said central pipe, close to said gas injection device and so that one (preferably each) gas injection orifice is positioned close to an orifice of the liquid injection device 11 so that the liquid injection path is in the same plane as the gas injection path in order to cause the shearing of said gas. Advantageously, the gas injection device is in the form of a ring and has a diameter greater or less than that of the liquid injection device in the form of a ring. When the diameter of the gas injection device is smaller than that of the liquid injection device, the gas injection device is positioned inside the liquid injection device, as shown in Figure 4A , on a different plane, that is to say higher or lower, preferably lower (the liquid injection device then being above the gas injection device). Conversely, when the diameter of the gas injection device is greater than that of the liquid injection device, the gas injection device is positioned outside the liquid injection device on a different plane, c ie higher or lower.

In a particular embodiment, a sequence of several liquid and gas injection devices of circular shape of decreasing diameters are alternated from the periphery towards the center represented by the central axis of the injection device having the largest diameter big. Said devices are positioned so that a gas injection orifice of a gas injection device is positioned close to and facing an orifice of the adjacent liquid injection device, so that the liquid injection trajectory is in the same plane of the gas injection trajectory in order to cause the shearing of said gas.

OLIGOMERIZATION PROCESS

Another object of the invention relates to the process for the oligomerization of a gaseous olefin feedstock, preferably gaseous ethylene, using a gas/liquid reactor according to the invention as defined above.

Preferably, said method comprises bringing a liquid and the gaseous olefinic feedstock, preferably gaseous ethylene, into contact by means of a gas injection device and a liquid injection device, said gas and liquid injection devices being positioned in the upper part of a central pipe located in the reactor containment, so as to drive the injected gas in the direction of the lower part of the reactor, then of the descending zone towards the ascending zone.

Preferably, the injection speed of the liquid is greater than the injection speed of the gaseous olefinic feedstock so as to promote the shearing of the bubbles of the gaseous olefinic feedstock injected into gaseous bubbles of smaller size. The gaseous olefin feed is preferably chosen from hydrocarbon molecules having between 2 and 6 carbon atoms, preferably between 2 and 4 carbon atoms. Preferably, the olefin feedstock is chosen from butene, more particularly isobutene or butene-1, propylene, and ethylene, alone or as a mixture.

Preferably, the oligomerization process is a dimerization, trimerization or tetramerization process, for example of ethylene.

The process for the oligomerization of a gaseous olefin feedstock implementing the reactor according to the invention makes it possible to produce linear alpha olefins by bringing said olefin feedstock into contact with a catalytic system, 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(ll) carboxylates such as, for example, nickel 2-ethylhexanoate, nickel(ll) phenates, nickel(ll) naphthenates, nickel(ll) acetate, ll), nickel(ll) trifluoroacetate, nickel(ll) triflate, nickel(ll) acetylacetonate, nickel(ll) hexafluoroacetylacetonate, TT-allylnickel(ll) chloride, TT-allylnickel(ll) bromide, methallylnickel(ll) chloride dimer, q ³ - allylnickel(ll) hexafluorophosphate , q ³ -methallylnickel(II) hexafluorophosphate and nickel(II) 1,5-cyclooctadienyl, 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 radical R' can 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 CrCh, CrCh(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 (MeAICh), dichloroethylaluminum (EtAICh), ethylaluminum sesquichloride (EtsAhC ), chlorodiethylaluminum (Et2AICI), chlorodiisobutylaluminum (i-Bu2AICI), triethylaluminum (AIEt ₃ ), tripropylaluminum (Al(n-Pr)s), triisobutylaluminum (Al(i-Bu)s), diethyl- ethoxyaluminum (Et2Al0Et), 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 preferably 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 l)-butane-2,3-diimine, or

- compounds of the phosphine type chosen independently from tributylphosphine, triisopropylphosphine, tricyclopentylphosphine, tricyclohexylphosphine, triphenylphosphine, tris(o-tolyl)phosphine, bis(diphenylphosphino)ethane, trioctylphosphine oxide, triphenylphosphine oxide, 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, substituted or unsubstituted groups , 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 preferably chosen from diethyl ether, diisopropyl ether, dibutyl ether, diphenyl ether, 2-methoxy-2-methylpropane, 2-methoxy-2-methylbutane, 2,2-dimethoxy-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 preferably chosen from

- aryloxy compounds of general formula [M(R ³ O)2-nX _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 radical aryloxy 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 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, when a solvent is used in the oligomerization process, the mass content of solvent introduced into the reactor used in the process according to the invention is between 0.2 and 10.0, preferably between 0.5 and 5.0, and preferably between 1.0 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 according to the invention, advantageously provided with heating and cooling, then it is pressurized with ethylene to the desired pressure, and the temperature is adjusted to the value desired. The pressure is kept constant in the reactor by introducing the gaseous olefin feed 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 gaseous olefin feedstock, preferably ethylene, into a reactor according to the invention, and maintained at the desired temperature. It is also possible to inject the components of the catalytic system separately into the reaction medium. The gaseous olefin feedstock, preferably ethylene gas, is introduced through a pressure-controlled inlet valve, which keeps the latter 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. EXAMPLES

The examples below illustrate the invention without limiting its scope. (comparative):

Example 1 illustrates the reference case corresponding to Figure 1, in which the oligomerization process implements a gas-liquid reactor, according to the prior art.

A gas/liquid oligomerization reactor according to the prior art, comprising a reaction vessel of cylindrical shape having a diameter of 1.8 m and a liquid height of

6 m, is implemented at a pressure of 7.0 MPa and at a temperature of 120°C.

The catalytic system introduced into the reaction enclosure is a catalytic system based on chromium, as described in patent FR3019064, in the presence of cyclohexane as solvent.

Said catalytic system is brought into contact with ethylene gas by introducing said ethylene gas into the lower part of said enclosure. The effluent is then recovered at the bottom of the reactor.

The volume productivity of this reactor is 17 kg of alpha-olefins produced per hour and per m ³ of reaction volume.

The performance of this reactor makes it possible to convert 77.4% of the ethylene injected, for a saturation rate of dissolved ethylene in the liquid phase of 61.0% and to achieve a selectivity of 83.1% for hexene-1 , for a solvent mass content of 1.6. Said mass ratio of solvent is calculated as the mass ratio of the flow of solvent injected to the flow of ethylene gas injected. (according to invention):

A reactor according to the invention as represented in FIG. 3 having a central cylindrical pipe with a height of 4 m and an internal diameter equal to 0.55 m is implemented under the same conditions as Example 1. upper part of this said central pipe are positioned the means for introducing ethylene gas (2) and liquid (9), corresponding to the injection devices of gas (3) and liquid (11) respectively. The productivity by volume of this reactor is 35.7 kg of alpha-olefin produced per hour and per m ³ of reaction volume.

The performance of this reactor makes it possible to convert 59.7% of the ethylene injected, for a saturation rate of dissolved ethylene in the liquid phase of 87.2% and to achieve a selectivity of 87.1% for alpha -olefin sought, for a mass content of solvent of 1.6.

Said solvent content is calculated as the mass ratio of the flow of solvent injected to the flow of ethylene gas injected.

In example 2, the reactor according to the invention makes it possible to increase the saturation of ethylene by 26.2%, to increase the selectivity for alpha-olefin by 4.0% and to multiply the productivity by 2, 1, compared to the case according to the prior art of Example 1.

Claims

tl

CLAIMS Process for the oligomerization of a gaseous olefin feedstock, at a temperature between 30 and 200°C, a pressure between 0.1 and 10.0 MPa, in the presence of a catalytic system comprising at least a metallic precursor, said process putting implements a gas/liquid reactor for the oligomerization of a gaseous olefin feedstock, preferably gaseous ethylene, comprising:

- a reactor enclosure (1) of elongated shape along a vertical axis;

- a gas injection device (3),

- a liquid injection device (11),

- a central pipe (12) positioned along the vertical axis inside said enclosure in a lower zone of said enclosure; said central pipe delimiting a central zone able to allow a downward flow and an outer zone able to allow an upward flow of flow, in which the gas injection device is positioned in the upper part of the said central pipe and the The injection of liquid is positioned in the lower zone of the reactor enclosure so as to be able to entrain the injected gas in the direction of the lower part of the reactor, from the descending central zone towards the ascending external zone. Process according to Claim 1, in which the liquid and gas injection devices are positioned in the upper part of the said central pipe so as to entrain the gaseous olefin feedstock injected in the direction of the lower part of the reactor and the zone central descending towards the external ascending zone. A method according to claim 2 wherein the liquid injection device (11) is positioned above the gas injection device (3). A method according to any preceding claim in which the central pipe (12) has a solid wall over the entire height of the central pipe or has openings over 5 to 10% of the lower part of the height of the central pipe at from the bottom end opening. 5. Method according to any one of the preceding claims, in which the lower part of the central pipe at the level of the opening of the lower end has a flare or a narrowing.

6. Method according to any one of the preceding claims, in which the central pipe comprises a deflector positioned in the reactor enclosure and facing the opening of the lower end of the central pipe.

7. Method according to claim 6 wherein the deflector is positioned at a distance with the lower opening of the central pipe corresponding to a distance between 1 and 2 times the equivalent diameter of the central pipe.

8. Method according to any one of claims 6 or 7, in which the equivalent diameter of the deflector is at least equal to the diameter of the central equivalent pipe and preferably between 0.5 and 2.0 the diameter of the central pipe.

9. Method according to any one of the preceding claims comprising a recirculation loop comprising a withdrawal means located at the base of the reactor enclosure, a heat exchanger located outside the reactor enclosure and a means of introduction located on or in the reactor enclosure to allow the introduction of a cooled liquid fraction into the reactor enclosure.

10. Method according to claim 9 in which the liquid injection device (11) is positioned in the upper part of the central pipe and is connected to the introduction means of the recirculation loop.

11 . Process according to any one of the preceding claims, in which the central conduit has an equivalent diameter, with a ratio of the equivalent diameter of the central conduit to the internal diameter of the reactor vessel being between 0.2 and 0.9, of preferably between 0.3 and 0.8.

12. Method according to any one of the preceding claims, in which the central pipe has a height with a ratio of the height of the central pipe to the height of the reactor enclosure of between 0.2 and 0.8 and preferably between 0.3 and 0.7. Method according to any one of the preceding claims, in which the gas injection device (3) comprises at least one gas injection orifice and the liquid injection device (11) comprises at least one injection orifice. of liquid, each gas injection orifice being positioned at an orifice of the liquid injection device (11), so that the injection of the liquid can cause a shear reduction in the size of the bubbles during the injection of the gaseous olefinic feedstock. Process according to Claim 13, in which the gas injection orifices and the liquid injection orifices are extended by an injection tube. Process according to any one of the preceding claims, in which the gaseous olefin feedstock is chosen from preferably between 2 and 6 carbon atoms, preferably between 2 and 4 carbon atoms, and more preferably from butenes, more particularly isobutene or butene-1, propylene and ethylene, alone or as a mixture.