OLIGOMERIZATION GAS / LIQUID REACTOR COMPRISING A CENTRAL PIPELINE

Abstract

The present invention relates to a gas / liquid reactor for the oligomerization of gaseous ethylene comprising a central conduit delimiting within the reactor enclosure a central zone allowing downward flow and an external zone allowing upward flow, thus making it possible to increase the travel time of the gas bubbles injected in the liquid phase, without increasing the volume of the liquid phase and therefore the volume of the reactor.

Description

Title of the invention: GAS / LIQUID OLIGOMERIZATION REACTOR COMPRISING A CENTRAL PIPE Technical field

[0001] The present invention relates to the field of gas / liquid reactors allowing the oligomerization of olefins into linear olefins by homogeneous catalysis.

[0002] The invention also relates to the use of the gas / liquid reactor in a process for oligomerizing a gaseous olefinic 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. PREVIOUS ART

[0003] The invention relates to the field of gas / liquid reactors also called bubble columns, 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 processes for the oligomerization of ethylene is the management of the gaseous headspace, corresponding to the upper part of the reactor in the gaseous state. Said gaseous headspace comprises gaseous compounds that are poorly soluble in the liquid phase, compounds that are 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 vessel to the gaseous headspace is a phenomenon called piercing. However, the gaseous headspace is purged in order to eliminate said gaseous compounds.When the amount of ethylene gas present in the gaseous headspace is large, purging the gaseous headspace results in a significant loss of ethylene, which is detrimental to the productivity and cost of the oligomerization process. In addition, a significant breakthrough phenomenon means that a lot of ethylene gas 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.

[0004] In order to improve the efficiency of the oligomerization process in terms of productivity and cost, it is therefore essential to limit the phenomenon of ethylene breakthrough in order to improve its conversion in said process while maintaining good selectivity for the desired linear alpha olefins.

[0005] The processes of the prior art using a gas / liquid reactor, as illustrated in [Fig.l], do not make it possible to limit the loss of gaseous ethylene and the purging of the gaseous overhead results in an exit of gaseous ethylene from the reactor which is detrimental to the yield and cost of the process.

[0006] The applicant has described methods in applications WO2019 / 011806 and WO2019 / 011609 for increasing the contact surface between the upper part of the liquid fraction and the gaseous sky by means of dispersion or vortex means in order to promote the passage of the ethylene contained in the gaseous sky towards the liquid phase at the liquid / gas interface. These methods do not make it possible to limit the breakthrough phenomenon and are not sufficient when the quantity of ethylene in the gaseous sky is significant due to a high breakthrough rate.

[0007] Furthermore, during this research, the applicant found that in a reactor operating at a constant flow rate of injected ethylene gas, the quantity of dissolved ethylene and therefore the breakthrough rate is dependent on the dimensions of the reactors implementing the process and in particular on 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 (breakthrough). Indeed, the lower the height, the shorter the time during which the ethylene gas travels through the liquid phase to dissolve and the higher the breakthrough rate.

[0008] The applicant has discovered that it is possible to improve the conversion of olefin(s), in particular ethylene, while maintaining a high selectivity for the desired linear olefin(s), and in particular for alpha-olefin(s), by limiting the breakthrough phenomena by means of a gas / liquid reactor for the oligomerization of gaseous ethylene comprising a central pipe delimiting inside the reactor enclosure a central zone allowing a downward flow and an external 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

[0009] An object of the present invention relates to a gas / liquid reactor for oligomerization of a gaseous olefinic feedstock, preferably gaseous ethylene, comprising

[0010] - a reactor enclosure 1 of elongated shape along a vertical axis;

[0011] - a gas injection device 3,

[0012] - a liquid injection device 11,

[0013] - a central pipe 12 positioned along the vertical axis inside said enclosure; said central conduit delimiting a central zone capable of allowing a downward flow and an external zone capable of allowing an upward flow,

[0014] wherein the gas injection device is positioned in the upper part of said central conduit 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 to the ascending external zone.

[0015] Preferably, the liquid and gas injection devices are positioned in the upper part of said central conduit so as to drive the injected gaseous olefinic feedstock towards the lower part of the reactor and from the descending central zone towards the ascending external zone. Preferably, the liquid injection device 11 is positioned above the gas injection device 3.

[0016] 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.

[0017] Preferably, the lower portion of the central conduit at the lower end opening has a flare or narrowing.

[0018] Preferably, the central conduit comprises a deflector positioned in the reactor enclosure and facing the opening of the lower end of the central conduit. Preferably, the deflector is positioned at a distance from the lower opening of the central conduit corresponding to a distance between 1 and 2 times the equivalent diameter of the central conduit. Preferably, the equivalent diameter of the deflector is at least equal to the diameter of the central equivalent conduit and preferably between 0.5 and 2.0 the diameter of the central conduit.

[0019] 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 conduit and is connected to the introduction means of the recirculation loop.

[0020] 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 of between 0.2 and 0.9, preferably between 0.3 and 0.8.

[0021] 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.

[0022] Preferably, 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 gas injection orifice being positioned at an orifice of the liquid injection device (11), 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 olefinic feedstock. Preferably, the orifices gas injection and liquid injection ports are extended by an injection tube.

[0023] Another subject of the invention relates to a process for oligomerization of a gaseous olefinic feedstock using 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 one metal precursor.

[0024] Preferably, the gaseous olefinic 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

[0025] Throughout the description, the following terms or abbreviations have the following meaning.

[0026] Oligomerization of olefins is understood to mean any addition reaction of a first olefin to a second olefin, identical or different from the first. The olefin thus obtained has the empirical formula CnH2n where n is equal to or greater than 4.

[0027] Linear alpha-olefin means an olefin on which the double bond is located in the terminal position of the linear alkyl chain.

[0028] A catalytic system is understood to mean a chemical species which allows the implementation of the catalyst. The catalytic system may 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 comprises at least one metal precursor. The mixture of compounds may further comprise an activating agent. The mixture of compounds may comprise an additive. The compound or mixture of compounds may optionally be in the presence of a solvent.

[0029] 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.

[0030] The term gaseous phase 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 (or gaseous ceiling of the reactor).

[0031] The terms “reactor enclosure” and “reaction enclosure” are used interchangeably to designate the reactor enclosure (1).

[0032] The lower zone of the reaction chamber is understood to mean the part of the chamber comprising the liquid phase, the gaseous olefinic feedstock, in particular gaseous ethylene, the reaction products such as the desired linear alpha olefin (i.e. butene-1, hexene-1, octene-1 or the mixture of linear alpha-olefins), the catalytic system and optionally a solvent.

[0033] The upper zone of the reaction enclosure is understood to mean the part of the enclosure located at the top of the enclosure, i.e. directly above the lower zone and consisting of the gaseous phase corresponding to the gaseous ceiling.

[0034] By non-condensable gas is meant a species in physical gas form which only partially dissolves in the liquid at the temperature and pressure conditions of the reaction vessel, and which can, under certain conditions, accumulate in the reactor ceiling (for example here: ethane).

[0035] The terms reactor or device designate all of the means allowing the implementation of the oligomerization process according to the invention, such as in particular the reaction chamber and the recirculation loop.

[0036] The lower part of the reaction enclosure is understood to mean the lower quarter of the reaction enclosure containing the liquid phase.

[0037] The upper part of the reaction chamber is understood to mean the upper quarter of the reaction chamber containing the liquid phase.

[0038] The expression saturation rate in dissolved gaseous olefinic feedstock, in particular in 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.

[0039] Equivalent diameter is understood to be the diameter of the circle inscribed in the section (horizontal cross section) of the central pipe.

[0040] The various components of the reactor will be described with reference to all of the figures, each component retaining the same reference from one figure to another.

[0041] BRIEF DESCRIPTION OF THE FIGURES

[0042] [Fig. 1] [Fig. 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 olefinic feedstock such as gaseous ethylene via a gas injection device 3 into 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 is located a pipe for withdrawing a liquid fraction 5. Said fraction 5 is divided into 2 flows, a first main flow 7 sent to a heat exchanger 8 then introduced via a pipe 9 into the liquid phase and a second flow 6 corresponding to the effluent sent to a subsequent stage. The pipe 10 in the bottom of the reaction enclosure allows the introduction of the catalytic system.

[0043] [Fig.2] [Fig.2] illustrates a reactor according to the invention which differs from that of [Fig.l] 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 gas injection device 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 to the ascending external flow zone relative to the central pipe 12. The arrows represent the direction of circulation of the liquid and gas injected into the reactor enclosure 1.

[0044] [Fig.3] [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 by means of a liquid injection device 11 arranged with the gas injection device 3 so that the injection of the liquid causes a flow towards the bottom of the reactor enclosure of the gas and the liquid in the central pipe 12.

[0045] [Fig.4A] [Fig.4A] is a schematic view of a view from below of a section perpendicular to the vertical axis of the reactor enclosure of a preferred embodiment of the invention in which the gas 3 and liquid 11 injection devices are arranged in such a way that the injection of the liquid can cause, by shearing, a reduction in the size of the gas bubbles of the gaseous olefinic feedstock injected by the injected liquid. The gas 3 and liquid 11 injection devices are annular in shape and arranged in such a way 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 path crosses perpendicularly the path of the liquid injected by the orifices 14 so as to cause the gas to shear in order to reduce the size of the injected gas bubbles.

[0046] [Fig.4B] [Fig.4B] is a schematic view of a vertical section along the vertical axis of the injection device of [Fig.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 gas injection orifices 13 is positioned perpendicularly and on the side of one of the orifices 14 of the liquid injection device 11, so that the injected gas flow is on the path of the injected liquid flow at the orifices 14 of the liquid injection device 11.

[0047] [Fig.4C] [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 device liquid injection 11. DETAILED DESCRIPTION OF THE INVENTION

[0048] It is specified that, throughout this description, the expression “between ... and ...” must be understood as including the limits cited.

[0049] 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.

[0050] In the sense of the present invention, the different parameter ranges for a given step such as pressure ranges and temperature ranges can be used alone or in combination. For example, in the sense of the present invention, a range of preferred pressure values ​​can be combined with a range of more preferred temperature values.

[0051] In the remainder of the description and in the claims, the positions (“bottom”, “top”, “above”, “below”, “horizontal”, “vertical”, “lower half”, etc.) of the different elements are defined relative to the column in the operating position.

[0052] The present invention relates to a gas / liquid reactor for oligomerization of a gaseous olefinic feedstock, preferably gaseous ethylene, comprising

[0053] - a reactor enclosure 1 of elongated shape along a vertical axis;

[0054] - a gas injection device 3,

[0055] - a liquid injection device 11,

[0056] - a central pipe 12 positioned along the vertical axis within said enclosure; said central pipe delimiting a central descending zone and an external ascending flow zone,

[0057] wherein the gas injection device is positioned in the upper part of said central conduit and the liquid injection device in the reactor enclosure so as to drive the injected gas towards the lower part of the reactor, from the descending zone towards the ascending zone.

[0058] In the sense of the present invention, the gas injection device is intended to inject, into an oligomerization reactor, an olefinic feedstock in the gaseous state.

[0059] Advantageously, the reactor according to the invention makes it possible to increase the time during which the gaseous olefinic feedstock travels through the liquid phase, and therefore to improve the dissolution of said feedstock in the liquid phase, which synergistically reduces the piercing phenomenon. Another advantage of the reactor according to the invention is that the Archimedes thrust exerted on the injected gaseous olefinic feedstock makes it possible to limit the speed of descent in the central pipe, which increases the travel time of the gaseous olefinic feedstock in the liquid phase.

[0060] Advantageously, the saturation rate of dissolved gaseous olefinic feedstock, in particular 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%.

[0061] 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.

[0062] Another advantage of the present invention is to improve the conversion of the olefinic feedstock, in particular ethylene, and / or the selectivity, in particular towards alpha-olefins, as well as the volume productivity of the oligomerization process.

[0063] Another advantage of the reactor according to the invention is that it makes 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

[0064] The present invention relates to a gas / liquid reactor for oligomerization of a gaseous olefinic feedstock, preferably gaseous ethylene, comprising

[0065] - a reactor enclosure (1) of elongated shape along a vertical axis;

[0066] - a gas injection device (3),

[0067] - a liquid injection device (11),

[0068] - a central pipe (12) positioned along the vertical axis inside said enclosure; said central conduit delimiting a central zone capable of allowing a downward flow and an external zone capable of allowing an upward flow of flow,

[0069] wherein the gas injection device is positioned in the upper part of said central conduit 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.

[0070] In a preferred embodiment, the liquid and gas injection devices are positioned in the upper part of said central conduit and preferably close to each other, so as to advantageously drive the injected gaseous olefinic feedstock towards the lower part of the reactor and from the central zone towards the external 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 feedstock by the liquid in the direction of a downward flow in the central conduit.

[0071] In another embodiment, the liquid injection device is positioned in the rising zone between the reactor enclosure and the central conduit so as to drive the injected gaseous olefinic feedstock towards the lower part of the reactor from the descending zone towards the rising zone.

[0072] Preferably, the central pipe 12 is positioned substantially in the center of the reactor enclosure along the vertical axis within said enclosure.

[0073] Preferably, the oligomerization reactor is a dimerization, trimerization or tetramerization reactor, for example of ethylene.

[0074] 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 feedstock remains in the liquid phase, before possibly joining the gaseous overhead, which improves the dissolution of the gaseous olefinic feedstock, in particular gaseous ethylene, in said liquid phase.

[0075] Thus, according to the invention, the lower end and the upper end of the central pipe 12 are open so as to allow the liquid to circulate freely and to 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 so as to direct the flow of gas and liquid according to a downward flow inside the central pipe, and an upward flow outside the central pipe.

[0076] The central pipe may advantageously have a circular, oval, triangular, square or any other geometric shape suitable for implementing 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.

[0077] It is understood that the central pipe is immersed in the liquid phase when the reactor according to the invention is used in a process for oligomerization of a gaseous olefinic feedstock.

[0078] 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.

[0079] Preferably, the lower portion of the central conduit at the lower end opening has a flare or narrowing.

[0080] In a preferred embodiment, the central conduit further comprises a deflector positioned opposite the opening of the lower end. Preferably, said deflector is positioned at a distance from the lower opening of the conduit central pipe corresponding to a distance 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.

[0081] Advantageously, whatever the embodiment, the central pipe and / or the optional deflector are secured in the reactor enclosure 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 lugs 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 central pipe and the wall of the reactor enclosure are secured in such a way as to free up a passage section corresponding to the ascending external zone.

[0082] 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 cool said withdrawn liquid fraction which is then introduced into the reactor by the introduction means.

[0083] 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 be advantageously injected into said central pipe. An advantage of this embodiment is that the injected cooled liquid flow participates in the entrainment of the olefinic feedstock, preferably ethylene, towards the bottom of the central pipe from the descending central zone to the ascending external zone.

[0084] 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.

[0085] Another advantage is that the liquid 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.

[0086] Advantageously, the descending central zone inside the central pipe may comprise a structured packing, such as a static mixer or any other equivalent equipment generating good agitation of the gas-liquid flow, over part or all of its height, thus allowing better dissolution of the gas in the liquid via the turbulence generated by the structured packing.

[0087] 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.

[0088] 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 of 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 cross section) of the central pipe.

[0089] 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 enclosure is equal to 0.2, 0.3, 0.4, 0.5 or 0.6.

[0090] Preferably, the reactor enclosure 1 is elongated along the vertical axis and may contain 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 (or gaseous headspace) located in an upper zone above the lower zone, comprising a fraction of the gaseous olefinic feedstock, preferably gaseous ethylene, as well as incondensable gases (notably ethane).

[0091] In particular, the gas / liquid reactor further comprises:

[0092] - 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,

[0093] - a means for withdrawing the liquid phase to recover a reaction effluent including the alpha-olefins produced;

[0094] - possibly a system for purging the gaseous sky;

[0095] - and possibly a gas phase recycle loop, to recycle to at least a fraction of the gaseous phase to the lower zone of the liquid phase, comprising a withdrawal means located in the upper zone of the reactor enclosure for withdrawing a gaseous fraction at the level of the gaseous phase and an introduction means in the lower zone of the reactor enclosure for allowing said withdrawn gaseous fraction to be introduced into the liquid phase.

[0096] 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 reactor enclosure suitable for allowing the circulation of liquid and gaseous flows.

[0097] Preferably, the gas injection device 3 is chosen from a pipe, a network of pipes, a multi-tubular distributor, a perforated plate, concentric tubes or any other means known to those skilled in the art.

[0098] Preferably, the liquid injection device 11 is chosen from a pipe, a network of pipes, a multi-tubular distributor, a perforated plate, concentric tubes or any other means known to those skilled in the art.

[0099] 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 gas injection orifice 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 shearing of the size of the bubbles during the injection of the gaseous olefinic 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 injected gas to shear and cause 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 the gas and the liquid.

[0100] 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 shearing of the size of the bubbles during the injection of the gaseous olefinic feedstock.

[0101] Advantageously, the arrangement according to this preferred embodiment makes it possible to reduce the size of the injected gas bubbles by at least 20% compared to the size of the gas bubbles injected without shearing. Preferably, the percentage reduction in the size of the bubbles by this shearing is at least 25% compared to the size of the gas bubbles injected without shearing, preferably at least 30%, preferably at least 35% and preferably at least 40%.

[0102] Advantageously, breaking 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%, breaking a gas bubble into 4 smaller bubbles of the same size generates an increase of 59%, breaking a gas bubble into 6 smaller bubbles of the same size generates an increase of 82%. Thus, a reactor according to the invention facilitates and therefore significantly improves the absorption of gas in the liquid phase, which makes it possible to increase the saturation of gaseous olefinic feedstock in the liquid phase and to limit the piercing phenomenon.

[0103] The term injection orifice means 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, i.e. round holes.

[0104] 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 ethylene bubbles in the liquid of millimeter dimension. Preferably, the liquid injection orifices have a diameter of 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 near said gas injection orifice is between 0.1 and 1.0, preferably between 0.4 and 0.8.

[0105] 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 coaxially inside the liquid injection tube. The outlet orifice of the gas injection tube is directed towards the outlet orifice of the liquid injection tube.

[0106] Preferably, the liquid injection tube 15 comprises a deflector as a means of partially closing the tube, preferably a circular, round or square plate, perforated or not. Advantageously, the deflector makes it possible to improve the shearing effect of the gas bubbles by the liquid.

[0107] Preferably, the end of the liquid injection tube has a narrowing of the outlet diameter. Said narrowing causes the gas-liquid mixture to accelerate, which makes it possible to increase the shear forces and further improves the breaking of the gas bubbles into smaller gas bubbles.

[0108] In a highly preferred embodiment, the tube has a narrowing of the outlet diameter and a baffle.

[0109] Advantageously, a gas injection orifice and a liquid injection orifice are positioned opposite 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 liquid are injected through said respective orifices on the same trajectory axis 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°.

[0110] In a particular embodiment, the gas injection device is a cylindrical tube having a circular ring shape, for example round or oval, and having injection orifices. Advantageously, the liquid injection device is also a cylindrical tube having a circular ring shape, for example round or oval, and having injection orifices. Preferably, said liquid injection device is positioned in the upper part of said central conduit, 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 trajectory is in the same plane as the gas injection trajectory in order to cause shearing of said gas.

[0111] 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 less than that of the liquid injection device, the gas injection device is positioned inside the liquid injection device, as illustrated in [Fig.4A], on a different plane, i.e. 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, i.e. higher or lower.

[0112] In a particular embodiment, a sequence of several circular liquid and gas injection devices of decreasing diameters are alternated from the periphery towards the center represented by the central axis of the injection device having the largest diameter. Said devices are positioned so that a gas injection orifice of a gas injection device is positioned close to and opposite an orifice of the adjacent liquid injection device, such that the liquid injection trajectory is in the same plane as the gas injection trajectory in order to cause shearing of said gas.

[0113] OLIGOMERIZATION PROCESS

[0114] Another subject of the invention relates to the process for oligomerization of a gaseous olefinic feedstock, preferably gaseous ethylene, using a gas / liquid reactor according to the invention as defined above.

[0115] 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 conduit located in the reactor enclosure, so as to drive the injected gas towards the lower part of the reactor, then from the descending zone towards the ascending zone.

[0116] Preferably, the injection rate of the liquid is greater than the injection rate of the gaseous olefinic feedstock so as to promote the shearing of the bubbles of the injected gaseous olefinic feedstock into smaller gaseous bubbles.

[0117] The gaseous olefinic feedstock is preferably chosen from hydrocarbon molecules having between 2 and 6 carbon atoms, preferably between 2 and 4 carbon atoms. Preferably, the olefinic feedstock is chosen from butene, more particularly isobutene or butene-1, propylene, and ethylene, alone or as a mixture.

[0118] Preferably, the oligomerization process is a dimerization, trimerization or tetramerization process, for example of ethylene.

[0119] The process for oligomerization of a gaseous olefinic feedstock using the reactor according to the invention makes it possible to produce linear alpha olefins by bringing said olefinic feedstock into contact with a catalytic system, optionally in the presence of a solvent.

[0120] All 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 the invention. Said catalytic systems as well as their implementations are described in particular in applications FR2984311, FR2552079, FR3019064, FR3023183, FR3042989 or in application FR3045414.

[0121] Preferably, the catalytic systems comprise, preferably consist of:

[0122] - a metallic precursor preferably based on nickel, titanium or chromium,

[0123] - optionally an activating agent,

[0124] - optionally an additive, and

[0125] - optionally a solvent. The metallic precursor

[0126] The metal precursor used in the catalytic system is chosen from compounds based on nickel, titanium or chromium.

[0127] In one embodiment, the metal precursor is nickel-based and preferably comprises nickel with an oxidation state (+11). 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, nickel(II) trifluoroacetate, nickel(II) triflate, nickel(II) acetylacetonate, nickel(II) hexafluoroacetylacetonate, ir-allylnickel(II) chloride, ir-allylnickel(II) bromide, methal-lylnickel(II) chloride dimer, q'-allylnickel(II) hexafluorophosphate, q3-methallylnickel(II) hexafluorophosphate and nickel(II) 1,5-cyclooctadienyl, in their hydrated or non-hydrated form, taken alone or as a mixture.

[0128] In a second embodiment, the metal precursor is titanium-based and preferably comprises an aryloxy or alkoxy compound of titanium.

[0129] 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: tetraethoxy, tetraisopropoxy, tetra-n-butoxy and tetra-2-ethylhexyloxy.

[0130] The aryloxy compound of titanium 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' may contain heteroatom-based substituents. Preferred aryloxy radicals are selected 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-naphthalenedioxy.

[0131] According to a third embodiment, the metal precursor is based on chromium and preferably comprises a chromium (II) salt, a chromium (III) salt, or a salt with a different oxidation state which may comprise one or more identical or different anions, such as, for example, halides, carboxylates, acetyla-ketonates, alkoxy or aryloxy anions. Preferably, the chromium-based precursor is chosen from CrCl3, CrCl3(tetrahydrofuran)3, Cr(acetylacetonate)3, Cr(naphthenate)3, Cr(2-ethylhexanoate)3, Cr(acetate)3.

[0132] The concentration of nickel, titanium or chromium is between 0.001 and 300.0 ppm in mass of atomic metal relative to the reaction mass, preferably between 0.002 and 100.0 ppm, preferably 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

[0133] Optionally, regardless of the metal precursor, the catalytic system comprises one or more activating agents chosen from aluminum-based compounds such as methylaluminum dichloride (MeAlCl2), dichloroethylaluminum (EtAlCl2), ethylaluminum sesquichloride (Et3Al2Cl3), chlorodiethylaluminum (Et2AlCl), chlorodiisobutylaluminum (i-Bu2AlCl), triethylaluminum (AlEt3), tripropylaluminum (Al(n-Pr)3), triisobutylaluminum (Al(i-Bu)3), diethylethoxyaluminum (Et2AlOEt), methylaluminoxane (MAO), ethylaluminoxane and modified methylaluminoxanes (MMAO). The additive

[0134] Optionally, the catalytic system comprises one or more additives.

[0135] 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

[0136] When the catalytic system is nickel-based, the additive is preferably chosen from,

[0137] - 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-diimine, or

[0138] - phosphine type compounds chosen independently from tributyl- phosphine, triisopropylphosphine, tricyclopentylphosphine, tricyclohexylphosphine, triphenylphosphine, tris(o-tolyl)phosphine, bis(diphenylphosphino)ethane, trioctylphosphine oxide, triphenylphosphine oxide, triphenylphosphite, or

[0139] - compounds corresponding to the general formula (I) or one of the tautomers of said compound : in which

[0140] - A and A', identical or different, are independently an oxygen or a bond simple between the phosphorus atom and a carbon atom,

[0141] - the groups Rla and Rlb are independently chosen from the groups methyl, trifluoromethyl, ethyl, n-propyl, i-propyl, n-butyl, i-butyl, t-butyl, pentyl, cyclohexyl, adamantyl, substituted or not, containing or not hetero-elements; phenyl, o-tolyl, m-tolyl, p-tolyl, mesityl, 3,5-dimethylphenyl, 4-n-butylphenyl, 2-methylphenyl, 4-methoxyphenyl, 2-methoxyphenyl, 3-methoxyphenyl, 4-methoxyphenyl, 2-isopropoxyphenyl, 4-methoxy-3,5-dimethylphenyl, 3,5-ditert-butyl-4-methoxyphenyl, 4-chlorophenyl, 3,5-di(trifluoromethyl)phenyl, benzyl, naphthyl, bisnaphthyl, pyridyl, bisphenyl, furanyl, thiophenyl,

[0142] - the R2 group is independently chosen from methyl, tri fluoromethyl, ethyl, n-propyl, i-propyl, n-butyl, i-butyl, t-butyl, pentyl, cyclohexyl, adamantyl, substituted or not, containing heteroelements or not; the phenyl, o-tolyl, m-tolyl, p-tolyl, mesityl, 3,5-dimethylphenyl, 4-n-butylphenyl, 4-methoxyphenyl, 2-methoxyphenyl, 3-methoxyphenyl, 4-methoxyphenyl, 2-isopropoxyphenyl, 4-methoxy-3,5-dimethylphenyl, 3,5-ditert-butyl-4-methoxyphenyl, 4-chlorophenyl, 3,5-bis(trifluoromethyl)phenyl, benzyl, naphthyl, bisnaphthyl, pyridyl, bisphenyl, furanyl, thiophenyl groups.

[0143] When the catalytic system is based on titanium, the additive is preferably chosen from diethyl ether, diisopropyl ether, dibutyl ether, diphenyl ether, 2-methoxy-2-methylpropane, 2-methoxy-2-methylbutane, dimethoxy-2,2-propane, di(2-ethylhexyloxy)-2,2-propane, 2,5-dihydrofuran, tetrahydrofuran, 2-methoxytetrahydrofuran, 2-methyltetrahydrofuran, 3-methyltetrahydrofuran, 2,3-dihydropyran, tetrahydropyran, 1,3-dioxolane, 1,3-dioxane, 1,4-dioxane, dimethoxyethane, di(2-methoxyethyl)ether, benzofuran, glyme and diglyme taken alone or in mixture.

[0144] When the catalytic system is based on chromium, the additive is preferably chosen from,

[0145] - 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-diimine, or

[0146] - aryloxy compounds of general formula [M(R3O)2nXn]y in which

[0147] * M is chosen from magnesium, calcium, strontium and barium, preferably magnesium,

[0148] * R3 is an aryl radical containing from 6 to 30 carbon atoms, X is a halogen or an alkyl radical containing from 1 to 20 carbon atoms,

[0149] * n is an integer that can take the values ​​of 0 or 1, and

[0150] * y is an integer between 1 and 10, preferably y is equal to 1, 2, 3 or 4.

[0151] Preferably, the aryloxy radical R3O 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-naphthalenedioxy. Preferably, the aryloxy radical R3O is 2,6-diphenylphenoxy, 2-tert-butyl-6-phenylphenoxy or 2,4-ditert-butyl-6-phenylphenoxy. The solvent

[0152] In another embodiment according to the invention, the catalytic system optionally comprises one or more solvents.

[0153] In one embodiment, a solvent or mixture of solvents may be used during the oligomerization reaction.

[0154] 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, preferentially between 4 and 12 carbon atoms and even more preferentially between 4 and 8 carbon atoms.

[0155] Preferably, the solvent is chosen from pentane, hexane, cyclohexane, methylcyclohexane, heptane, butane or isobutane, cycloocta-1,5-diene, benzene, toluene, ortho-xylene, mesitylene, ethylbenzene, diethyl ether, tetrahydrofuran, 1,4-dioxane, dichloromethane, dichloroethane, tetrachloroethane, hexachloroethane, chlorobenzene, dichlorobenzene, butene, hexene and octene, pure or in mixture.

[0156] Preferably, the solvent may advantageously be chosen from the products of the oligomerization reaction. Preferably, the solvent used is cyclohexane.

[0157] Preferably, when a solvent is used in the oligomerization process, the mass ratio 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 more preferably between 1.0 and 4.0. The solvent ratio is the mass ratio of the total flow rate of solvent injected to the total flow rate of ethylene gas injected into the process.

[0158] 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.

[0159] Advantageously, the oligomerization process is carried out 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 of between 30 and 200°C, preferably between 35 and 150°C and preferably between 45 and 140°C.

[0160] 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 preferentially between 0.05 and 20.0 ppm and even more preferentially between 0.1 and 10.0 ppm by mass of atomic metal relative to the reaction mass.

[0161] According to one embodiment, the oligomerization process is carried out batchwise. The catalytic system, constituted as described above, is introduced into a reactor according to the invention, advantageously equipped with heating and cooling, then pressurized with ethylene to the desired pressure, and the temperature is adjusted to the desired value. The pressure is kept constant in the reactor by introducing the gaseous olefinic feedstock 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 withdrawn and separated.

[0162] According to another embodiment, the oligomerization process is carried out continuously. The catalytic system, constituted as described above, is injected at the same time as the gaseous olefinic feedstock, preferably ethylene, into a reactor according to the invention, and maintained at the desired temperature. The components of the catalytic system can also be injected separately into the reaction medium. The gaseous olefinic feedstock, preferably gaseous ethylene, is introduced through an inlet valve controlled by the pressure, which maintains the latter constant in the reactor. The reaction mixture is withdrawn by means of a valve controlled by the liquid level so as to maintain 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. The ethylene which has not been transformed can be recycled into the reactor.Catalyst residues included in a heavy fraction can be incinerated. EXAMPLES

[0163] The examples below illustrate the invention without limiting its scope.

[0164] Example 1 (comparative):

[0165] Example 1 illustrates the reference case corresponding to [Fig.l], in which the oligomerization process uses a gas-liquid reactor, according to the prior art.

[0166] A gas / liquid oligomerization reactor according to the prior art, comprising a cylindrical reaction chamber having a diameter of 1.8 m and a liquid height of 6 m, is operated at a pressure of 7.0 MPa and at a temperature of 120°C.

[0167] The catalytic system introduced into the reaction chamber is a chromium-based catalytic system, as described in patent FR3019064, in the presence of cyclohexane as solvent.

[0168] Said catalytic system is brought into contact with gaseous ethylene by introducing said gaseous ethylene into the lower part of said enclosure. The effluent is then recovered at the bottom of the reactor.

[0169] The volumetric productivity of this reactor is 17 kg of alpha-olefins produced by hour and per m3 of reaction volume.

[0170] The performance of this reactor makes it possible to convert 77.4% of the injected ethylene, for a saturation rate of ethylene dissolved in the liquid phase of 61.0% and to achieve a selectivity of 83.1% in hexene-1, for a solvent mass rate of 1.6. Said solvent mass rate is calculated as the mass ratio of the injected solvent flow rate to the injected gaseous ethylene flow rate.

[0171] Example 2 (according to the invention):

[0172] A reactor according to the invention as shown in [Fig.3] having a cylindrical central 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. In the upper part of this said central pipe are positioned the means for introducing gas (2) and liquid (9) ethylene, corresponding to the gas (3) and liquid (11) injection devices respectively.

[0173] The volume productivity of this reactor is 35.7 kg of alpha-olefin produced per hour and per m3 of reaction volume.

[0174] The performance of this reactor makes it possible to convert 59.7% of the injected ethylene, for a saturation rate of ethylene dissolved in the liquid phase of 87.2% and to achieve a selectivity of 87.1% in the desired alpha-olefin, for a solvent mass rate of 1.6. Said solvent rate is calculated as the mass ratio of the injected solvent flow rate to the injected gaseous ethylene flow rate.

[0175] 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 in 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

Claims

1. Process for oligomerization of a gaseous olefinic 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 one metal precursor chosen from nickel-, titanium- or chromium-based compounds, said process using a gas / liquid reactor for oligomerization of a gaseous olefinic 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 zone;said central conduit being immersed in a liquid phase and delimiting a central zone capable of allowing a downward flow and an external zone capable of allowing an upward flow, in which the liquid and gas injection devices are positioned in the upper part of said central conduit so as to drive the injected gaseous olefinic feedstock towards the lower part of the reactor and from the descending central zone towards the ascending external zone.;

2. A method according to claim 1 wherein the liquid injection device (11) is positioned above the gas injection device (3).

3. A method according to any preceding claim wherein the central conduit (12) has a solid wall over the entire height of the central conduit or has openings over 5 to 10% of the lower part of the height of the central conduit from the opening of the lower end.

4. A method according to any preceding claim wherein the lower portion of the central conduit at the lower end opening has a flare or narrowing.

5. A method according to any preceding claim wherein the central conduit comprises a deflector positioned in the reactor enclosure and facing the opening of the lower end of the central conduit.

6. A method according to claim 5 wherein the deflector is positioned at a distance from the lower opening of the central conduit corresponding to a distance between 1 and 2 times the equivalent diameter of the central conduit.

7. A method according to any one of claims 5 or 6, wherein the equivalent diameter of the deflector is at least equal to the diameter of the central equivalent conduit and preferably between 0.5 and 2.0 the diameter of the central conduit.

8. A method according to any preceding claim comprising a recirculation loop comprising a draw-off 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.

9. A method according to claim 8 wherein the liquid injection device (11) is positioned in the upper part of the central conduit and is connected to the introduction means of the recirculation loop.

10. Method 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 enclosure being between 0.2 and 0.9, preferably between 0.3 and 0.

8.

11. Method according to any one of the preceding claims in which the central conduit has a height with a ratio of the height of the central conduit to the height of the reactor enclosure of between 0.2 and 0.8 and preferably between 0.3 and 0.

7.

12. A method according to any one of the preceding claims wherein 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 gas injection orifice being positioned at an orifice of the liquid injection device (11), 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 olefinic feedstock.

13. A method according to claim 12 wherein the gas injection ports and the liquid injection ports are extended by a tube injection.

14. Process according to any one of the preceding claims in which the gaseous olefinic 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.

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