Loop polymerization reactor

Abstract

The present invention relates to a loop polymerization reactor (1), comprising a loop-shaped reaction section intended to circulate a reaction medium in the loop, the reaction section being provided with one or more feed inlets (11) at least for a reagent, optionally for a catalyst and / or for a solvent, and at least one draw-off outlet (12), said reactor comprising at least one means (7) for causing the reaction medium to move in the loop-shaped reaction section, the loop comprising a plurality of duct portions fluidically connected to one another, including at least one straight portion (5, 3), such that the or at least one of the duct portions, in particular the or at least one of the straight portions, houses an insert extending over at least 50% of the length of said portion and over at least 50% of the cross section of said portion.

Description

[0001] Loop polymerization reactor

[0002] Technical field

[0003] The invention relates to so-called loop reactors of the tubular type. This type of reactor is designed so that the reaction mixture can be recycled / recirculated several times in a reaction section forming a loop. The loop in question may consist of tubular pipes, in particular a series of straight and bent tubular pipes.

[0004] The invention is more particularly concerned with the use of this type of reactor for carrying out polymerization reactions, in particular catalytic ones, of olefins comprising 2 to 4 carbons, called C2-C4, in order to convert them into higher olefins, of the α-olefin type, such as butenes, hexenes, octenes, nonenes, decenes, which are olefins used as first petrochemical intermediates, the reaction medium being able to be two-phase gas / liquid or single-phase liquid.

[0005] The invention relates more particularly to the oligomerization of ethylene into linear olefins such as 1-butene, 1-hexene, 1-octene, or a mixture of linear alpha-olefins from 1-butene to 1-dodecene, using a catalyst. This may in particular involve the oligomerization of ethylene into 1-butene and / or 1-hexene.

[0006] Prior art

[0007] Loop reactors are known in principle, and one can refer in particular to patents EP1842861 for the polymerization of ethylene and EP1316566 for the polymerization of propylene to find examples.

[0008] In the case of the oligomerization of ethylene (this example of implementation will be used in the present text for illustration purposes, without the invention being limited to it), the reaction is exothermic, which requires the provision of cooling means equipping at least part of the reaction section.

[0009] Whether a reactor operating in a two-phase or single-phase reaction medium is used, there is a problem common to this type of reaction, which is that this oligomerization reaction generates a fouling solid by-product, of a polymeric nature, as explained in the publication by RF Rossouw, RLJ Coetzer and PD Pretorius "Simulation experiments for maximizing the availability of a commercial octene production facility", Volume 26(1) pp.53-77 of 2010 - publisher ORSON. This by-product, although produced in small quantities, tends to be deposited on the walls of the reaction section, particularly in the zone(s) equipped with cooling means. Its accumulation requires cleaning at regular intervals, which is restrictive.

[0010] Furthermore, we seek to homogenize as much as possible the composition of the reaction medium which circulates in the loop, and also to promote as much as possible the homogenization of its temperature within the reaction medium, in particular by promoting heat transfers within the reaction medium in the zones equipped with cooling means. These cooling means can for example be in the form of double-walled envelopes in which a cooling fluid circulates (known under the Anglo-Saxon name of "cooling jacket").

[0011] The invention then aims to improve the operation of loop reactors, in particular to facilitate heat transfers within the reaction medium circulating in the loop and / or to limit the risks of fouling of the walls of the reactor loop.

[0012] Summary of the invention

[0013] The invention firstly has a loop polymerization reactor, comprising a loop-shaped reaction section intended to circulate a reaction medium in said loop,

[0014] - said reaction section being provided with one or more feed inlets at least for a reactant, possibly for a catalyst and / or for a solvent, and at least one withdrawal outlet,

[0015] - said reactor comprising at least one means for ensuring the movement of the reaction medium in the loop-shaped reaction section,

[0016] - said loop comprising a plurality of conduit portions fluidly connected to each other, at least one of which is straight, and such that at least one of said conduit portions, „ houses an insert, fixed or mobile, extending over at least 50% of the length of said portion and over at least 50% of the section of said portion.

[0017] A "mobile" insert is understood to mean an insert which is set in motion either actively by a dedicated device causing its movement, or passively under the sole effect of the circulation movement of the reaction medium from one end of the loop to the other.

[0018] With the addition of this or these inserts, it turned out that the loop-type reactor had improved operation in at least two ways: if we start again from the example of ethylene oligomerization, the oligomerization reaction produces polyethylene as a by-product, and, even in small quantities, it tends to be deposited on the internal walls of the loop, more particularly in the areas of the loop that are cooled (exothermic reaction), which are generally straight portions of the loop conduit, which creates wall fouling.However, this fouling has two unfavorable consequences: on the one hand, it gradually hinders the circulation of the reaction medium, requiring regular cleaning between production campaigns, and on the other hand, it gradually hinders the evacuation of the heat released by the walls of the loop: it disrupts the thermal homogenization of the reaction medium, particularly in the cooling zones by external cooling means (double wall surrounding certain portions of the loop with circulation of a cooling fluid therein): the fouling reduces the heat transfer capacity from these cooling means to the reaction medium, and reduces the heat evacuation capacities through the walls of the loop.

[0019] The inserts according to the invention will therefore both combat fouling of the walls and promote heat exchanges within the reaction medium, by creating turbulence in the flow of the reaction medium, and by creating shear near the walls. Preferably, the insert extends over at least 70 to 100%, in particular 80 to 95% of the length of the portion of conduit which houses it, and over at least 70%, in particular at least 80% and preferably at most 95% or 98% of its section.

[0020] Thus, if the loop of the reaction section comprises x portions of straight conduit connected to each other by y portions of curved conduit, the inserts can advantageously be arranged in at least one of the straight portions, in particular all the straight portions or at least all those which are equipped with cooling means, i.e. those where the risk of fouling is the highest. And the insert can then occupy a large part of the portion of conduit in its length and in its cross-section, so as to maximize its efficiency (in particular its shearing effect near the walls).

[0021] According to one embodiment, the insert according to the invention is fixed at at least one of its ends, or at each of its ends, in the portion of conduit which houses it.

[0022] According to another embodiment, its ends are free.

[0023] Preferably, the mobility of the insert is “passive”, in the sense that the insert will move / rotate on itself / move in the portion of conduit that houses it under the action of the sole circulation of the reaction medium in the loop.

[0024] Advantageously, the insert is fixed at at least one of its ends by a mechanical device allowing free rotation of the insert, in particular around the longitudinal axis of said portion when said portion is a straight portion. Here, the insert is rotated around the axis of the conduit portion, it turns on itself.

[0025] The mechanical device in question may for example comprise a member forming a bearing which is fixed to the internal wall of the portion of conduit and on which is mounted a journal in free rotation relative to said bearing, said insert being fixed at one of its ends to said journal.

[0026] The geometric shape of the insert can be very varied: we want the insert to be able to create as much turbulence / shear as possible within the reaction medium, while limiting the pressure loss created by its presence in the flow of the reaction medium.

[0027] According to one variant, the insert according to the invention is in the form of a twisted strip, of helical shape for example, in particular of constant or variable width.

[0028] According to another variant, the insert according to the invention is in the form of a rod provided with fins, in particular a rod oriented along the longitudinal axis of the pipe portion when it is straight, the fins preferably being distributed regularly along the length of the rod, facing each other or offset, with a flat or curved geometric shape, or in the form of blades with several curvatures. The rod can remain stationary, with only the fins being mobile, or the rod can rotate, with the fins fixed - or not - relative to the rod.

[0029] According to another variant, the insert according to the invention is in the form of a spiral wire, in particular a helical one, of the spring type.

[0030] In this variant, the spiral wire may have a pitch (distance from one turn to the next) of between 10 and 100 mm, particularly between 10 and 40 mm. The pitch may be constant or variable along the length of the spiral. The cross-section of the wire may be circular or square.

[0031] Preferably, the insert is made of a material of a lower hardness than that of the material constituting the internal walls of the portion of conduit in which it is housed: this guarantees that the internal walls of the conduit where the insert is located are not damaged in the event of insert / wall contact.

[0032] Preferably, the insert material is selected from a metal or metal alloy such as carbon steel, stainless steel or an Inconel alloy.

[0033] Advantageously, the reactor according to the invention is intended to contain a two-phase gas / liquid or single-phase all-liquid reaction medium. Advantageously, the conduit portions of the loop are in the form of tubular conduits, of cylindrical or substantially cylindrical section.

[0034] Preferably, the diameter of the section, when it is cylindrical, of the loop conduit portions is between 5 cm and 100 cm, in particular between 20 and 80 or between 30 and 60 cm. This diameter can be constant or variable. Thus, the loop reactor can comprise straight conduit portions connected to each other by bent portions, with straight conduit portions oriented vertically, with an alternation of so-called "descending" straight portions (in which the reaction medium circulates from bottom to top) and so-called "ascending" straight portions (in which the reaction medium circulates from top to bottom). And in this case, it can be advantageous for the section (the diameter) of the "ascending" straight portions to be larger than that of the "descending" straight portions.

[0035] Preferably, the length of the straight conduit portions of the reaction section is at least 5 m, it is in particular between 10 and 100 m, for example between 20 and 90 or between 30 and 60 m.

[0036] In total, the loop length may be at least 100 meters or several hundred meters, including having a length of at least 800 to 900 m, for example between 1000 and 1500 m.

[0037] Preferably, at least one of the conduit portions of the loop, and in particular the or one of the straight portions, is equipped with cooling means, in particular in the form of a cooling jacket.

[0038] Preferably, the loop-shaped reaction section comprises at least two straight conduit portions, in particular parallel or perpendicular to each other, and connected to each other by a curved conduit portion, in particular in the form of an elbow or semi-circular shape.

[0039] The invention also relates to a process for the polymerization, or oligomerization or trimerization, of starting C2-C4 olefins into linear olefins. This may in particular be a process for the oligomerization of ethylene into 1-butene and / or 1-hexene, such that said process uses the reactor described above. Advantageously, according to the process of the invention, the reactor is operated

[0040] - under a pressure of at least 5.10 5 Pa, in particular between 1.10 6 and 7.10 6 Pa,

[0041] - at a temperature between 20 and 150°C, and,

[0042] - preferably with a speed of reaction medium circulating in the loop reaction section of between 1 and 30 m / s.

[0043] Preferably, the superficial velocity of the liquid phase flowing in the reactor is between 1 and 30 m.s' 1 , preferably between 1 and 15 m.s' 1 .

[0044] Preferably, when the reactor is intended for reactions between reactants including at least one reactant in gas form, the superficial velocity of the gas phase before dissolution is between 0.1 and 2 m.s' 1 .

[0045] We recall that the superficial velocity is the ratio between the volume flow rate of the fluid considered by the section through which the fluid passes.

[0046] Note that in the most upstream part of the loop, in the area near the gas phase injection point, when one of the reactants is injected in the form of a gas into the reactor, we have a gas / liquid mixture, and, progressively downstream, we move to an entirely liquid phase, because the injected gas gradually reacts / gradually dissolves in the liquid phase.

[0047] The terms "upstream" and "downstream" are understood by referring to the direction of progression of the reaction medium in the loop from the injection points of the reactants and catalyst.

[0048] The invention will be described below in more detail using exemplary embodiments and figures.

[0049] List of figures

[0050] Figure 1 represents a first example of a loop reactor.

[0051] Figure 1 shows a second example of a loop reactor.

[0052] Figure 1 represents the second example of a loop reactor according to Figure 2, modified according to the invention.

[0053] Figure 4 is an enlargement of a portion of Figure 3. Figure 5 is a representation of an insert according to the invention.

[0054] All these figures are extremely schematic, represent components that are not necessarily to scale, and focus on the components most useful for illustrating the invention. The components are represented in space according to a possible mode of operation.

[0055] The same references correspond to the same components, the same flows or others from one figure to another.

[0056] Description of the embodiments

[0057] To describe the invention in detail, Figures 1 and 2 show two different types of loop reactor to which the invention can be applied.

[0058] The invention applies in a similar manner to any other type of loop reactor.

[0059] The example of use of the loop reactor of the invention concerns the oligomerization of ethylene in the presence of solvent and catalyst(s):

[0060] Oligomerization corresponds to any reaction of addition of a first olefin to a second olefin, identical or different from the first. The olefin thus obtained has the empirical formula Cnhten where n is equal to or greater than 4, and is notably linear (called alpha).

[0061] For example, this is the main reaction of ethylene on itself to produce 1-butene and / or 1-hexene and / or higher oligomers. It includes the case of tetramerization.

[0062] An alpha-olefin (here the product obtained after oligomerization) is a linear olefin whose double bond is located in the terminal position of the alkyl chain.

[0063] The homogeneous oligomerization catalyst is, for example, a mixture (also called a catalytic system) of at least one metal precursor and at least one activating agent, optionally in the presence of at least one additive and possibly a solvent.

[0064] The reaction medium circulating in the loop reactor is, for example, a gas / liquid mixture, the solvent dissolving the ethylene and the catalyst(s). The invention applies in a similar manner to any other oligomerization or polymerization reaction, catalytic or not.

[0065] Figure 1 represents a first example of a loop reactor 1, in the simplest configuration: the loop comprises four 2, 3, 4, 5 straight conduit portions of cylindrical section, arranged for example in a vertical plane, perpendicular to each other, and connected to each other by four bent portions 6, 7, 8, 9 of the same cylindrical section, to form a loop of approximately rectangular shape with rounded edges (in front view), with two opposite straight conduit portions 3, 5 longer than the other two straight conduit portions 2, 4.

[0066] The diameter of the conduit sections can be constant or variable over the entire length of the loop and for example between 20 and 60 cm

[0067] These conduits are preferably made of metal or metal alloy.

[0068] The loop is provided in the bent conduit portion 9 with an inlet 10 for the solvent and the catalyst(s), and in the opposite bent portion 8 with an inlet 11 for the reactant (here for example ethylene), and an outlet 12 for the reaction product.

[0069] A turbine 13 ensures the circulation of the reaction medium in the loop thus formed.

[0070] Heat exchangers, in the form of double cooling jackets 14 in which a cooling fluid circulates, equip the straight conduit portions 3 and 5 (the longest), so as to control the exothermicity of the reaction.

[0071] Once loop 1 has been supplied with solvent, catalyst and ethylene (to take the non-limiting example of the polymerization of ethylene), the reaction medium rotates in the loop thanks to turbine 13, with a progressive production of the desired product, which is withdrawn via outlet 12. The supply and / or withdrawal can be continuous or discontinuous. The turbine is an example, and can be replaced by any type of suitable pump, such as a so-called "slurry" flow pump, also known as a Lawrence pump.

[0072] Figure 2 represents a second example of a loop reactor 1', in a slightly different configuration, with this loop comprising five straight portions 21, 22, 23, 24, 25 here as an example arranged along a vertical plane, parallel to each other and connected by semi-circular conduit portions or defining a double curvature to allow the fluidic connection between two straight portions. This configuration allows both a significant loop length and a great compactness thereof. As seen above, it is preferred, for the "ascending" vertical straight portions, a larger section than for the "descending" vertical straight portions. The length of the vertical straight portions is at least 10 meters, up to 100 meters, and the total length of the loop is for example 1200 meters.

[0073] We find, as in figure 1, at least one entry 11 for the reagent, one entry

[0074] 10 for the solvent and the catalyst(s) and an outlet 12 for the reaction product, and all the straight portions are equipped with heat exchangers 14.

[0075] These figures 1 and 2 are only examples of loop reactors, the invention being able to be implemented in any type of loop reactor, having in particular a different overall configuration, a different number of straight pipe sections, different lengths of pipe sections, etc. Likewise, the inlet and withdrawal points can vary in their arrangements, as well as the number, arrangement and type of cooling means.

[0076] The invention therefore proposes adding inserts to loop reactors, to improve the homogenization of the reaction medium, promote heat exchanges and avoid, or at least reduce, fouling of the walls, particularly in the areas most at risk, i.e. generally the portions of the loop equipped with cooling means.

[0077] This is what is shown in Figure 3, which represents the loop reactor of Figure 2 equipped according to the invention: all other things being equal with respect to the reactor of Figure 2, an insert 40 is therefore placed in each of the straight portions of the loop.

[0078] 11 is here of helical shape, its diameter of turns corresponds to at least 80% of the circular section of the portion of pipe in which it is arranged, and preferably at least 90% and at most 95 or 98%. It extends over the entire length of each straight portion of pipe, or at least 50 or 80 or 90% of this length. The wire is of circular (or square) section, of diameter (or diagonal) between 1 and 3 mm. The pitch between turns is between 10 and 50 mm, for example in the vicinity of 20-40 mm. It is metallic. The longitudinal axis of the insert is coincident with the longitudinal axis of the portion of pipe where it is arranged. The insert is fixed at its upper end so as to allow its free rotation under the effect of the circulation of the reaction medium in the loop, its lower end is free.

[0079] Figure 4 is an enlargement of Figure 3, in the area of ​​attachment of the upper end of the insert 40: the insert comprises a bearing 41 fixed to the walls of the pipe portion by mechanical means 42 (any known mechanical means, such as screwing, clipping, riveting, etc.) and a journal 43, the bearing and the journal being integral but the journal is free to rotate relative to the bearing. The insert comprises a helical wire 44, the upper part of which is inserted into the journal and held integral with the latter, the wire terminating in an end 44a wider than the orifice made in the journal to pass the wire therein, to lock in position, longitudinally, the part of the wire inserted in the journal.

[0080] It is therefore understood (circular arrow in Figure 4) that, when the reaction medium circulates, the wire 44 rotates around the longitudinal axis of the pipe, and creates additional mixing / turbulence in the reaction medium. It rotates close to the walls of the pipe, "scraping" the walls (preferably without touching them), which has the effect of limiting the fouling of the walls, therefore reducing the frequency of cleaning the walls, and promoting heat exchanges between the reaction mixture and the cooling means.

[0081] This type of insert can be arranged, in a similar manner, in the vertical straight portions 3 and 5 of the reactor shown in Figure 1.

[0082] The configuration of a spring-shaped insert is particularly advantageous, because it ensures good mixing while limiting the pressure losses induced by its presence.

[0083] Naturally, the insert according to the invention can take other forms: a spring of different pitch, a twisted band, a rod with fins of all shapes (in the form of rosettes, blades, arranged along the rod opposite each other or offset, etc.). A variant of the twisted band type insert 40' is thus shown in Figure 5. It can also be fixed at none or both of its ends, as long as it is capable of being mobile under the effect of the circulation of the reaction medium. It can also be configured so as to remain fixed, for example by being rigidly fixed at each of its ends.

[0084] Particularly when it equips straight and substantially vertically oriented sections of conduit, we tend to favor a fixing on its upper edge for the “descending” sections and a fixing on each of its edges for the “ascending” sections.

[0085] As seen above, the portions of conduit to be equipped with inserts can be very long, from several meters to several tens of meters. In this case, it is possible to provide for the insert to be in several parts, which are assembled together to obtain the insert of the desired length, the assembly being able to be done before inserting them into the conduit, or once each of the insert parts is inserted into the conduit. It is thus possible to design portions of inserts of standard length, which are assembled in x portions to achieve the desired insert length.

[0086] The insert can also be fixed differently, for example not by mechanical fasteners on the internal walls of the ducts, but on the external walls of the ducts or others.

[0087] The insert can also only equip certain sections of the duct, and not only those equipped with cooling means.

[0088] The insert can also have a configuration that makes it operational in curved / elbowed sections of conduit.

[0089] Examples

[0090] To illustrate the advantages of the present invention, the estimates obtained with the invention for a process for trimerizing ethylene to 1-hexene with a capacity of 90 KTA (kilo-ton-year) of 1-hexene are presented below. The operating conditions are summarized below:

[0091] - Number of passes: 9 - Length per pass: 100 m

[0092] - Operating temperature: 135°C

[0093] - Operating pressure: 60 bars (6.10 6 Pa)

[0094] - Catalyst: Chrome-based, concentration 1.11 ppm by weight

[0095] - Ethylene flow rate: 5.2 kg / s

[0096] - Solvent Flow Rate: 7.75 kg / s

[0097] - Ethylene conversion: 63.2%

[0098] - Selectivity to 1-hexene: 95.1%

[0099] - Helical spiral insert: wire diameter 2mm, pitch 45mm, stainless steel material, rotating effect

[0100] The tube-side heat transfer coefficients obtained in the straight sections with and without inserts are:

[0101] - Heat transfer coefficient on the tube side with insert installation: 879 W / m 2 / K

[0102] - Heat transfer coefficient on the tube side without insert: 481 W / m 2 / K

[0103] The invention thus makes it possible to improve convective heat transfer by +30% (at least) and to reduce the rate of fouling by polyethylene deposition on the wall by a factor of 2 (at least). The combined gains thus make it possible to increase the transfer coefficient by 82% (at least) when the insert is in place.

Claims

Claims 1. Loop polymerization reactor (1), comprising a loop-shaped reaction section intended to circulate a reaction medium in said loop, said reaction section being provided with one or more feed inlets (11) at least for a reactant, optionally for a catalyst and / or for a solvent, and at least one withdrawal outlet (12), said reactor comprising at least one means (7) for ensuring the movement of the reaction medium in the loop-shaped reaction section, said loop comprising a plurality of conduit portions fluidly connected to each other, including at least one straight portion (5,320,22,23,25) characterized in that the or at least one of said conduit portions, in particular the or at least one of the straight portions, houses a fixed or movable insert (40,40') extending over at least 50% of the length of said portion and over at least 50% of the section of said portion.

2. Reactor (1) according to the preceding claim, characterized in that the insert (40,40') extends over at least 70 to 100%, in particular 80 to 95% of the length of the portion of conduit which houses it, and over at least 70%, in particular at least 80% and preferably at most 95% or 98% of its section.

3. Reactor (1) according to one of the preceding claims, characterized in that the insert (40,40') is fixed at at least one of its ends, or at each of its ends, in the portion of conduit which houses it.

4. Reactor (1) according to the preceding claim, characterized in that the insert (40,40') is fixed at at least one of its ends by a mechanical device allowing free rotation of the insert, in particular around the longitudinal axis of said portion when said portion is a straight portion.

5. Reactor (1) according to the preceding claim, characterized in that the mechanical device comprises a member forming a bearing (41) which is fixed to the internal wall of the conduit portion (23) and on which is mounted a journal (43) in free rotation relative to said bearing, said insert being fixed at one of its ends to said journal.

6. Reactor (1) according to one of the preceding claims, characterized in that the insert is in the form of a twisted strip (40'), in particular of constant or variable width.

7. Reactor (1) according to one of claims 1 to 5, characterized in that the insert (40,40') is in the form of a rod provided with fins, in particular a rod oriented along the longitudinal axis of the pipe portion when it is straight, the fins preferably being distributed regularly along the length of the rod, face to face or offset, with a flat or curved geometric shape, or in the form of blades with several curvatures.

8. Reactor (1) according to one of the preceding claims, characterized in that the insert is in the form of a spiral wire (40), in particular helical, of spring type.

9. Reactor (1) according to the preceding claim, characterized in that the insert is a spiral wire (40) whose pitch is between 10 and 100 mm, in particular between 10 and 40 mm, the pitch being constant or variable over the length of the spiral, the section of the wire being in particular circular or square.

10. Reactor (1) according to one of the preceding claims, characterized in that the insert (40, 40') is made of a material of a hardness lower than that of the material constituting the internal walls of the portion of conduit in which it is housed, preferably made of a material chosen from a metal or metal alloy such as carbon steel, stainless steel or an Inconel alloy.

11. Reactor (1) according to the preceding claim, characterized in that said reactor (1) is intended to contain a two-phase gas / liquid or single-phase all-liquid reaction medium.

12. Reactor (1) according to one of the preceding claims, characterized in that the conduit portions of the loop are in the form of conduits of cylindrical section, the diameter of the cylindrical section of the conduit portions of the loop being preferably between 5 and 100 cm, in particular between 20 and 80 or between 30 and 60 cm.

13. Reactor (1) according to one of the preceding claims, characterized in that the length of the straight conduit portions of the reaction section is at least 5 meters, in particular between 10 and 100 meters or between 20 and 80 meters.

14. Reactor (1) according to one of the preceding claims, characterized in that at least one of the conduit portions of the loop, and in particular the or one of the straight portions, is equipped with cooling means (14), in particular in the form of a cooling jacket.

15. Reactor (1) according to one of the preceding claims, characterized in that the loop-shaped reaction section comprises at least two straight conduit portions (20, 25), in particular parallel or perpendicular to each other, and connected to each other by a curved conduit portion (27) in particular in the form of an elbow or semi-circular shape.

16. Process for the polymerization or oligomerization or trimerization of starting C2-C4 olefins into linear olefins, in particular a process for the oligomerization of ethylene into 1-butene and / or 1-hexene, characterized in that said process uses the reactor (1) according to one of the preceding claims.

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