Column with helical perforated plates

Abstract

The invention relates to an extraction column and method, for example for liquid-liquid or gas-liquid extraction, or distillation, in which: a first injection point (§2) for a first phase and a second injection point (§3) for a second phase are arranged so as to allow the countercurrent flow of the first phase and of the second phase, wherein one of the two phases is a continuous phase (§A) and the other is a dispersed phase (§B); a first draw-off point for an extract (§4) and a second draw-off point for a raffinate (§5) are provided, wherein one is arranged at the bottom of the extraction column (§1) and the other is arranged at the top of the extraction column (§1); and a plurality of helical perforated plates (§16) spaced apart by an inter-plate space (§8) are provided and have rims suitable for receiving a coalesced layer (§9) of the dispersed phase either above or below the helical perforated plates.

Description

[0001] Column with helical perforated plates

[0002] Technical field

[0003] The invention relates to the fields of perforated tray (or contactor) columns for applications in liquid-liquid extraction, gas-liquid extraction and distillation, as used in numerous chemical processes including processes for separating aromatics present in different petroleum fractions or resulting from refining processes. For example, liquid-liquid extraction columns are particularly suitable for the separation of hydrocarbon compounds, such as aromatic compounds (e.g. A6-A11) from an extended hydrocarbon fraction (e.g. C6-C11 fraction), such as from a fluid catalytic cracking (FCC) unit.

[0004] Prior art

[0005] The state of the art concerns columns with perforated trays with overflows whose operating principle is based on the differences in solubility of the compounds of a liquid or gas feed in a suitable solvent (e.g. aprotic and polar solvent, such as Sulfolane or DMSO). The addition of a partially miscible solvent to the feed causes the appearance of a second phase to which a part of the compounds (e.g. aromatic compounds), the most soluble constituents, is preferentially transferred.

[0006] With reference to Figure 1, an extraction column §1, for example for liquid-liquid or gas-liquid extraction, comprises the following elements:

[0007] - a first injection point §2 of a first phase (eg liquid or gas charge to be separated);

[0008] - a second injection point §3 of a second phase (e.g. liquid fluid or separation gas), said first and second injection points §2 and §3 being arranged in the extraction column §1 to allow the circulation of said first and second phases in counter-current (one with respect to the other) between said first and second injection points §2 and §3;

[0009] - a first point of withdrawal of an extract §4 (eg in liquid or gas phase), such as a solvent enriched with compounds extracted from the load; and

[0010] - a second point of withdrawal of a raffinate §5 (eg in liquid or gas phase), such as a feed depleted in extracted compounds, one of said first and second points of withdrawal being arranged at the bottom of extraction column §1 and the other at the top of extraction column §1. According to figure 1, the first injection point §2 is used to inject the feed to be separated and is typically arranged between the second injection point §3 of the separation fluid (or solvent) and the first point of withdrawal of the extract §4. In the same way, the second injection point §3 of the separation fluid is typically arranged between the first injection point §2 of the feed to be separated and the second point of withdrawal of the raffinate §5. In this reference example, the first phase is the light phase and the second phase is the heavy phase.It is understood that the first phase may be the heavy phase and the second phase may be the light phase, for example when the filler is in liquid form.

[0011] With reference to Figure 2 and Figure 3, an extraction column §1 comprises a plurality of perforated trays §15, each perforated tray §15 being equipped with one or more weirs §6 depending on the targeted capacities, a weir §6 being a recess allowing the passage of the first phase §A called "continuous" through the perforated tray §15 to a non-perforated zone §14 of the following perforated tray §15 (in the direction of flow of the continuous phase). We speak of single-pass trays (if there is 1 weir per tray) or multi-pass trays (if there is more than 1 weir per tray). A perforated tray §15 comprises at least one zone perforated with holes §7, through which the second phase §B called "dispersed" circulates. The second dispersed phase §B circulates in the form of drops (or bubbles in the case of a gas) crossing the first continuous phase §A in each inter-plate space §8 defined by the space between two adjacent perforated plates §15.In the example of Figure 2 and Figure 3, the second dispersed phase §B is the heavy phase and accumulates above the perforated tray §15 by means of rims §10, until it forms a coalesced layer §9 (see Figure 3) above the perforated area. This coalesced layer §9 can typically be from 1 cm to 8 cm thick. In the present description, it is understood that if the dispersed phase is the light phase, the dispersed phase accumulates below the perforated tray. The second dispersed phase §B then passes through the perforated area of ​​the perforated tray §15 to feed the next perforated tray §15 (upper tray if the dispersed phase is the light phase, lower tray if the dispersed phase is the heavy phase), and so on. The first continuous phase §A winds through the inter-plateau spaces §8 passing through the spillways §6, upwards in this example of figure 2 because the continuous phase is the light phase.

[0012] US Patents 3,632,315 and US Patents 4,588,563 describe examples of liquid-liquid extraction columns comprising perforated trays equipped with one and / or two weirs.

[0013] Thus, an extraction column §1 makes it possible to bring two partially immiscible phases §A and §B into contact, in counter-current. Depending on the choice of the dispersed phase §B (heavy phase or light phase), the perforated tray §15 is adapted to accommodate (by means of the rims §10) a coalesced layer §9 of the dispersed phase §B on the upper part of the perforated tray (case where dispersed phase §B is the heavy phase) or on the lower part (case where dispersed phase §B is the light phase). In the figures of the present description, only the case of the separation fluid being the dispersed phase §B and the heavy phase is described.

[0014] The applicant identified that, although this technology is common, there are numerous drawbacks. Beyond 1 pass, the successive trays are not identical because the weirs are alternated and there is in fact a different number of passes between 2 trays (alternating 1-2 passes or 2-3 passes) which complicates the design. In addition, the weir zones are useless areas for material transfer because they are not traversed by the feedstock / separation fluid mixture. The weir zones are therefore useful areas for the circulation of phases but not for material transfer. Finally and above all to increase the useful transfer volume (therefore traversed by the emulsion), the projected surfaces of the weirs are usually reduced.This results in high continuous phase overspeeds §A near the weirs, which can cause disturbances in the flow of the dispersed phase §B, which can lead to axial mixing and therefore to a loss of efficiency. Thus, the weir surfaces cannot be minimized too much. As a result, the useful mass transfer volume represents only 40% to 75% of the total volume of the extraction column.

[0015] The present invention aims to remedy the deficiencies mentioned above and to increase the performance of extraction columns.

[0016] Summary of the invention

[0017] In the context previously described, a first object of the present description is to propose an extraction column allowing:

[0018] - to increase the volume available for contacting the two phases;

[0019] - to increase the capacity of said extraction columns (consequence of the previous point);

[0020] - to better control the training of the dispersed phase;

[0021] - to standardize the height of the coalesced layer of the dispersed phase on the perforated trays;

[0022] - to reduce the risk of congestion of the column,

[0023] - to standardize the transverse velocity of the continuous phase, making it possible to reduce disturbances in the flow of the dispersed phase;

[0024] - to simplify the manufacturing stages of perforated trays;

[0025] - to propose a technology implementing a single type of tray, which simplifies the design, manufacture and assembly of the column. According to a first aspect, the aforementioned objects, as well as other advantages, are obtained by an extraction column, for example for liquid-liquid or gas-liquid extraction or distillation, comprising the following elements:

[0026] - a first injection point of a first phase;

[0027] - a second injection point for a second phase, the first and second injection points being arranged on the extraction column to allow the circulation of the first phase and the second phase countercurrently (with respect to each other) in the extraction column, one of said first and second phases being a continuous phase and the other being a dispersed phase;

[0028] - a first point for drawing off an extract and a second point for drawing off a raffinate, one being arranged at the bottom of the extraction column and the other being arranged at the top of the extraction column; and

[0029] - a plurality of helical perforated trays arranged from the top (or bottom) of the extraction column to the bottom (or top) of the extraction column, the helical perforated trays being spaced apart by an inter-tray space allowing the passage of the continuous phase and comprising rims adapted to receive a coalesced layer of the dispersed phase (above or below the helical perforated trays).

[0030] According to one or more embodiments, the helical perforated trays are arranged around a central axis of the extraction column according to a helical isometry comprising a rotation of angle p around the central axis of the extraction column and a translation of a distance H1 along the central axis of the extraction column; the angle p is between 20° and 180°, preferably between 30° and 120°, very preferably between 40° and 90; and the distance H1 is between 0.01 m and 1 m, preferably between 0.1 m and 0.9 m or between 0.2 m and 0.8 m, very preferably between 0.3 m and 0.7 m.

[0031] According to one or more embodiments, each helical perforated tray comprises a panel perforated with holes and comprises an upstream rim and a downstream rim, in a direction opposite to the flow of the continuous phase, the upstream rim and the downstream rim forming a reservoir adapted to receive the coalesced layer.

[0032] According to one or more embodiments, the downstream edge has a height H3 of between 1 cm and 150 cm, preferably between 1 cm and 30 cm, preferably between 2 cm and 20 cm, very preferably between 5 cm and 15 cm.

[0033] According to one or more embodiments, the upstream rim has a height greater than, less than or substantially equal to the height H3 of the downstream rim. According to one or more embodiments, the upstream rim of a downstream helical perforated plate is connected to the adjacent upstream helical perforated plate, in a direction opposite to the flow of the continuous phase.

[0034] According to one or more embodiments, each helical perforated tray forms an angular perforated panel with an angle a of between 20° and 180°, preferably between 30° and 120°, very preferably between 40° and 90°.

[0035] According to one or more embodiments, the angle a is substantially equal to the angle p, or the angle a is greater than the angle p.

[0036] According to one or more embodiments, the extraction column comprises one or more open partitions adapted to establish a predetermined passage section of the continuous phase in the extraction column.

[0037] According to one or more embodiments, the extraction column comprises N helical perforated plates arranged approximately at the same height in the extraction column (e.g. as a double helix or a triple helix), N being between 1 and 4, preferably between 1 and 3, the term approximately corresponding to an approximation of ± 50%, preferably ± 20%, very preferably ± 10% of the distance H1, the distance H1 being the translation along the central axis between two adjacent helical perforated plates.

[0038] According to one or more embodiments, the extraction column comprises:

[0039] - an extraction sector, extending substantially from the first injection point of the first phase to substantially the second injection point of the second phase, and

[0040] - an optional backwash sector, adjacent to the extraction sector and extending from the first injection point of the first phase to substantially a third backwash fluid injection point.

[0041] According to one or more embodiments, the extraction column is suitable for liquid-liquid or gas-liquid extraction, preferably for liquid-liquid extraction.

[0042] According to a second aspect, the aforementioned objects, as well as other advantages, are obtained by an extraction method comprising the following steps:

[0043] - injecting a first phase and a second phase into an extraction column according to the first aspect; and

[0044] - withdrawing an extract and a raffinate from the extraction column. According to one or more embodiments, the extraction column is operated at a pressure of between 0.05 MPaa and 3 MPaa, preferably between 0.1 MPaa and 2 MPaa, preferably between 0.2 MPaa and 1.5 MPaa, preferably between 0.3 MPaa and 1 MPaa; and at a temperature of between 10°C and 150°C, preferably between 15°C and 130°C, preferably between 30°C and 120°C, preferably between 40°C and 110°C.

[0045] According to one or more embodiments, the first phase comprises a mixture of aromatic and non-aromatic compounds.

[0046] According to one or more embodiments, the second phase comprises a compound selected from ethylene glycol, diethylene glycol, triethylene glycol, hexamethylphosphoramide, propylene carbonate, ethylene carbonate, sulfolane, 3-methylsulfolane, N-methylacetamide, N,N-dimethylacetamide, butyrolactone, 1-methylpyrrolidone, dimethylsulfoxide, caprolactam, N-methylformamide, pyrrolidin-2-one, furfural, 1,1,3,3-tetramethylurea and a mixture thereof.

[0047] Embodiments of the column and the extraction method according to the aforementioned aspects as well as other characteristics and advantages will appear on reading the description which follows, given for illustrative and non-limiting purposes only, and with reference to the following drawings.

[0048] List of figures

[0049] Figure 1 schematically shows a sectional view of an extraction column.

[0050] Figure 2 schematically shows a top view and a 3D view of a reference extraction column comprising perforated trays with overflows.

[0051] Figure 3 schematically shows a cross-sectional view of the flow of the dispersed phase and the continuous phase in the reference extraction column.

[0052] Figure 4 schematically shows a top view and a 3D view of an extraction column according to the present invention comprising helical perforated trays.

[0053] Figure 5 schematically shows a cross-sectional view of the flow of the dispersed phase and the continuous phase in the extraction column as shown in Figure 4.

[0054] Figure 6 schematically shows a cross-sectional view of the flow of the dispersed phase and the continuous phase in an extraction column according to the present invention. Figure 7 schematically shows a 3D view of an extraction column according to the present invention comprising helical perforated trays arranged in a double helix.

[0055] Description of the embodiments

[0056] Embodiments of the invention will now be described in detail. In the following detailed description, numerous specific details are set forth in order to provide a more thorough understanding of the invention. However, it will be apparent to those skilled in the art that the invention may be practiced without these specific details. In other instances, well-known features have not been described in detail to avoid unnecessarily complicating the description.

[0057] In this specification, the term "comprise" is synonymous with (means the same as) "include" and "contain", and is inclusive or open and does not exclude other elements not recited. It is understood that the term "comprise" includes the exclusive and closed term "consist". Furthermore, in this specification, the term "substantially" corresponds to an approximation of ± 10%, preferably ± 5%, very preferably ± 2%, of a reference value such as a distance, an angle, a speed, a flow rate, a compound content, a temperature, a pressure, etc.

[0058] Extraction column

[0059] An extraction column according to the present invention comprises all the elements as defined above with reference to Figure 1. An extraction column according to the present invention comprises one or more distinct operating zones.

[0060] According to one or more embodiments, the extraction column §1 according to the present invention comprises or consists of an extraction sector §11, extending substantially from the first injection point §2 of the first phase to substantially the second injection point §3 of the second phase (separation fluid (liquid or gas). The extraction sector §11 makes it possible in particular to extract compounds from the feedstock to be separated (e.g. aromatic compounds) by contact with the separation fluid (so-called yield zone).

[0061] According to one or more embodiments, the extraction column §1 according to the present invention comprises several distinct operating zones, such as for example:

[0062] - an extraction sector §11, extending substantially from the first injection point §2 of the first phase to substantially the second injection point §3 of the second phase; and

[0063] - an optional backwash sector §12 (or "backwash" according to English terminology), adjacent to the extraction sector §11 and extending from the first injection point §2 of the first phase to substantially a third injection point §13 of backwash fluid (e.g. liquid) (optional), such as an extract recycle. The backwash sector §12 makes it possible in particular to back-extract unwanted compounds (e.g. heavy non-aromatic compounds) contained in the extract §4 by the backwash fluid in order to guarantee a high level of purity. According to one or more embodiments, the third injection point §13 of backwash fluid is arranged between the first injection point §2 and the first extraction point of the extract §4.

[0064] Concretely, with reference to Figure 1, the separation fluid leaves the extraction column §1, carrying with it compounds of interest to be separated (e.g. aromatic compounds) to form the extract §4. The extract §4 may also contain undesired compounds (e.g. light non-aromatic compounds, such as C6-C7) which can be separated downstream (e.g. by distillation and / or stripping). Advantageously, the extract §4 contains substantially no (or very few) undesired compounds that are difficult to separate (e.g. heavier non-aromatic compounds, such as C8+), which are separated from the extract in the backwash sector §12. With reference to Figure 1, the separation fluid is heavier than the feedstock to be separated and is injected at the top of the extraction column §1, while the optional backwash fluid is injected at the bottom of the extraction column §1.It is understood that the present invention also relates to extraction columns, in which the separation fluid is lighter than the load to be separated, the injection point §3 of the separation fluid then being at the bottom of the extraction column §1 and the injection point §13 of the backwash fluid being at the top of the extraction column §1.

[0065] According to one or more embodiments, the extraction column §1 according to the present invention is a column for liquid-liquid or gas-liquid extraction or distillation, preferably for liquid-liquid or gas-liquid extraction, very preferably for liquid-liquid extraction. According to one or more embodiments, the extraction column §1 according to the present invention is of circular section.

[0066] With reference to Figures 4, 5 and 6, an extraction column §1 according to the present invention comprises a plurality of helical perforated trays §16. Advantageously, the helical perforated trays §16 are arranged around a central axis Z of the extraction column §1 according to a helical isometry comprising a rotation of angle p around the central axis Z and a translation H1 along the central axis Z, i.e., said trays are in a helical arrangement. The plurality of helical perforated trays §16 thus arranged in the column forms a right or left helix (in the form of a staircase), each helical perforated tray §16 being arranged at a distance H1 (in a direction parallel to the central axis Z; eg according to the direction of flow of the dispersed phase §B) from an adjacent helical perforated tray §16. The distance H1 thus corresponds to the step height between two adjacent helical perforated trays §16.Similarly, each helical perforated tray §16 is arranged according to a rotation of angle p around the central axis Z (eg substantially according to the direction of flow of the continuous phase §A) relative to an adjacent helical perforated tray §16. Advantageously, the helical perforated trays §16 each extend from the internal wall of the extraction column (§1) to substantially the central axis Z.

[0067] According to one or more embodiments, the angle p is between 20° and 180°, preferably between 30° and 120°, very preferably between 40° and 90°, such as for example substantially 45° or 60°. The angle p also expresses the number of helical perforated trays §16 per revolution (360°) of the helix in the column. According to one or more embodiments, a helix of helical perforated trays §16 comprises between 2 and 18 perforated trays, preferably between 3 and 12 perforated trays, very preferably between 4 and 9 perforated trays.

[0068] According to one or more embodiments, the distance H1 is between 0.01 m and 1 m, preferably between 0.1 m and 0.9 m or between 0.2 m and 0.8 m, very preferably between 0.3 m and 0.7 m.

[0069] Advantageously, the helical perforated trays §16 are in the form of a radial cut or a pie-cut, i.e. a section corresponding to an angular section of the extraction column §1. With reference to figures 4, 5 and 6, each helical perforated tray §16 comprises a perforated panel (substantially perpendicular to the direction of flow of the dispersed phase §B) of angular shape of angle a. Preferably, the helical perforated trays §16 have the same angle a. According to one or more embodiments, the angle a is between 20° and 180°, preferably between 30° and 120°, very preferably between 40° and 90°, such as for example substantially 45° or 60°.

[0070] Referring to Figures 4 and 5, according to one or more embodiments, the angle a is substantially equal to the angle p. According to one or more embodiments, the helical perforated trays §16 are fully perforated. According to this embodiment, the helical perforated trays §16 do not include a spillway and do not include a non-perforated area. Advantageously, the separation is improved because the areas unnecessary for the transfer of material are limited.

[0071] With reference to Figure 6, according to one or more embodiments, the angle a is greater than the angle p. Advantageously, the support of the helical perforated plates §16 can be improved. According to this embodiment, the helical perforated plate is not perforated (i.e., formed from a solid plate) in the area located directly above the downstream helical perforated plate §16 (see overlap area R of Figure 6), in particular so as not to generate preferential passage of dispersed phase from one plate to the other.

[0072] According to one or more embodiments, the helical perforated trays §16 are arranged around a central mast (not described in the figures) arranged in the extraction column §1 along the central axis Z of the column. Advantageously, the central mast provides part of the mechanical resistance necessary to maintain the structure.

[0073] With reference to Figure 5, each helical perforated tray §16 is arranged so that the dispersed phase §B flows through the holes §7 of a helical perforated tray §16, the drops or bubbles of the dispersed phase §B recoalescing on the next helical perforated tray §16 (in the direction of flow of the dispersed phase §B) to form a volume of the coalesced layer §9 preventing the passage of the continuous phase §A through the holes §7 of said next helical perforated tray §16. The feedstock to be separated flows countercurrently to the separation fluid in a substantially transverse manner in an inter-tray space §8. With reference to Figure 5, the heavy phase is the dispersed phase §B and the light phase is the continuous phase §A. It is understood that an extraction column §1 may comprise helical perforated trays adapted so that the dispersed phase is the light phase and the continuous phase is the heavy phase.It is also understood that the feedstock can be the dispersed phase or the continuous phase. Similarly, depending on the choice of separation fluid, the feedstock can be the light phase or the heavy phase.

[0074] According to one or more embodiments, the holes §7 of the helical perforated plates §16 have a diameter between 2 mm and 12 mm. According to one or more embodiments, the diameter of the holes is predetermined so that the speed of the dispersed phase (at the hole) is between 0.2 m / s and 0.8 m / s, such as between 0.2 m / s and 0.5 m / s. It is understood that the perforation of the holes §7 can be carried out according to a very variable perforation plan (in type of hole, pitch, hole diameter).

[0075] With reference to figures 4, 5 and 6, each helical perforated tray §16 comprises a panel (or plate) perforated (eg entirely or partially) with holes §7 and comprises an upstream (solid) rim §18 as well as a downstream (solid) rim §10 (in the opposite direction to the flow of the continuous phase §A), the upstream rim §18 and the downstream rim §10 being adapted to form a reservoir adapted to receive the coalesced layer §9 of the dispersed phase §B. According to one or more embodiments, the upstream rim §18 has a height greater than, less than or substantially equal to the height H3 of the downstream rim §10. With reference to figures 4 and 5, each helical perforated tray §16 is entirely perforated in that it comprises a panel entirely perforated with holes §7 (no non-perforated zone or spillway).It is understood that, according to the invention, a panel may comprise a non-perforated area having less than 75% (see figure 6 for example), preferably less than 85%, very preferably less than 95%, of the surface of the panel.

[0076] According to one or more embodiments, the height H3 is between 1 cm and 150 cm, preferably between 1 cm and 30 cm, preferably between 2 cm and 20 cm, very preferably between 5 cm and 15 cm, such as for example between 8 cm and 12 cm, eg substantially 10 cm.

[0077] According to one or more embodiments, the upstream rim §18 of a downstream helical perforated plate §16 is connected to the adjacent upstream helical perforated plate §16. Advantageously, said upstream helical perforated plate §16 may be supported by said downstream helical perforated plate §16. Preferably, the height of the upstream rim §18 is substantially equal to the distance H1. Advantageously, the upstream rim §18 of a downstream helical perforated plate §16 may be extended to the adjacent upstream helical perforated plate §16. Advantageously, the continuous phase may be prevented from circulating between the upstream rim §18 of a downstream helical perforated plate §16 and an adjacent upstream helical perforated plate §16. Advantageously, the dispersed phase §B is evacuated by overflow above the downstream rim §10 (and not above the upstream rim §18) towards the downstream helical perforated plate §16 (and not in the opposite direction to the flow of the continuous phase §A).

[0078] With reference to Figure 4, according to one or more embodiments, each helical perforated tray §16 comprises a reinforcing piece §17 adjacent (e.g. juxtaposed) to the internal wall of the extraction column §1. Advantageously, the reinforcing piece §17 makes it possible to reinforce the structure of the helical perforated tray §16 and in particular of the perforated panel, the reinforcing piece §17 makes it possible to physically connect the structure of the helical perforated tray §16 to the wall of the shell to provide rigidity and prevent it from bending.

[0079] According to one or more embodiments, the height H2 of the inter-tray spaces §8 of the helical perforated trays §16 is between 0.1 m and 2 m, preferably between 0.2 m and 1 m or between 0.3 m and 1 m, very preferably between 0.3 m and 0.6 m or 0.3 m and 0.5 m. It is understood in the present description that the height H2 of an inter-tray space §8 of a first helical perforated tray §16 corresponds to the distance between said first helical perforated tray §16 and the following helical perforated tray §16 in the direction of flow of the dispersed phase §B or along the central axis Z, i.e. the helical perforated tray §16 arranged below or above said first helical perforated tray §16.

[0080] Depending on the values ​​chosen for the distance H1 and the angle p, the propeller can be more or less flattened, which modifies the height H2 of the inter-plate spaces §8 and which can change the nature of the flow of the continuous phase §A. Indeed, the greater the height H2 of the inter-plate spaces §8, the greater the height of the extraction column §1 will tend to be for a targeted efficiency. This point is all the more true as the continuous phase §A circulates more vertically and may be likely to generate axial dispersion detrimental to the extraction efficiency. Conversely, the lower the height H2 of the inter-plate spaces §8, the more the flow tends towards the piston, and the more extraction is favored. But the cost of the column is higher because the number and mass of the helical perforated plates §16 are larger and the passage section of the continuous phase §A is reduced, which can limit the column capacity.

[0081] The cross-section, and in particular the diameter of the extraction column §1, is typically a function of the predetermined value of the volume flow rate of the phases passing through it. According to one or more embodiments, the sum of the volume flow rates of the continuous phase §A and the dispersed phase §B is between 10 m 3 / h / m 2 and 70 m 3 / h / m 2 .

[0082] The height of the extraction column §1 is typically a function of its diameter. According to one or more embodiments, the height of the extraction column is between 1 m and 50 m.

[0083] The transverse velocity V of the continuous phase §A is defined by the ratio between the volume flow rate Q of the continuous phase §A on the passage section S of the continuous phase §A (eg radius of a perforated panel multiplied by H2-H1-H3): V = Q / S. If the transverse velocity V of the continuous phase §A is too low, significant axial dispersion is possible because the flow of the continuous phase §A is not sufficiently compartmentalized and recirculation loops may appear. If the transverse velocity V of the continuous phase §A is too high, this can disturb the flow of the dispersed phase §B which is no longer vertical enough and which is partially entrained by the continuous phase §A. Preferably, the transverse velocity V of the continuous phase §A is between 0.01 m / s and 0.6 m / s, preferably between 0.01 m / s and 0.3 m / s.

[0084] In order to control the transverse velocity V of the continuous phase §A independently of the diameter of the extraction column and / or the height H2 of the inter-tray spaces §8, it is possible to control the passage section S of the continuous phase §A. According to one or more embodiments, the extraction column §1 comprises one or more open partitions §19 (see figure 4), such as vertical metal plates arranged in the inter-tray space §8. The open partitions §19 make it possible in particular to reduce the passage section S of the continuous phase §A and / or to channel the continuous phase. The position of the open partitions §19 in the extraction column §1 may vary, such as on each helical perforated tray §16, one in two, one in three, or every n helical perforated trays §16, n being for example between 1 and 6, preferably between 2 and 4. The shape of the open partitions §19 may vary.According to one or more embodiments, an open partition §19 comprises one or more vertical plates disposed between two subsequent helical perforated trays §16 (in the direction of flow of the continuous phase or along the central axis Z). For example, a vertical plate may connect a helical perforated tray §16 to the next helical perforated tray §16. For example, a horizontal plate may extend an upstream edge §18 of a helical perforated tray §16 (see example of Figure 4). It is understood that the shape of the opening of the open partition §19 may be varied, such as round, rectangular, square, triangular, or any other shape, and the position of the opening may be centered or off-center to combat centrifugal force.Preferably, the opening is arranged on the external side of the open partition §19, for example close to (or even adjacent to) the wall of the extraction column §1, for example when the continuous phase is the light phase. According to one or more embodiments, the open fraction (corresponding to the passage section) of an open partition §19 can vary between 20% and 90% of the open partition §19.

[0085] With reference to Figure 7, according to one or more embodiments, the extraction column §1 comprises several helical perforated trays §16 arranged approximately at the same height in the extraction column §1 (i.e., at the same level relative to the central axis Z). Thus, the helical perforated trays §16 rotate around each other like a double helix, a triple helix, etc. In this embodiment, the term "approximately" corresponds to an approximation of ± 50%, preferably ± 20%, very preferably ± 10% of the height H1. According to one or more embodiments, the extraction column §1 comprises 2 or 3 or N helical perforated trays §16 arranged at substantially the same height in the extraction column §1, N being for example between 1 and 4, preferably between 1 and 3, such as 2.Advantageously, the helical perforated plates §16 thus arranged in the extraction column §1 in a bundle of N coaxial helices translated relative to each other, for example in the form of a double helix (triple helix, etc.), for example of the Chambord staircase type, make it possible to divide the flow of the continuous phase §A into a plurality of flows §20 and §21. These embodiments make it possible to divide the volume flow rate Q of the continuous phase §A by N, thus reducing the transverse velocity V of the continuous phase §A.

[0086] Extraction process

[0087] According to one or more embodiments, the extraction column §1 is operated at a pressure (absolute) of between 0.05 MPaa and 3 MPaa (0.5 and 30 bara), preferably between 0.1 MPaa and 2 MPaa (1 and 20 bara), preferably between 0.2 MPaa and 1.5 MPaa (2 and 15 bara), preferably between 0.3 MPaa and 1 MPaa (3 and 10 bara). According to one or more embodiments, the extractor is operated at a temperature of between 10°C and 150°C, preferably between 15°C and 130°C, preferably between 30°C and 120°C, preferably between 40°C and 110°C.

[0088] Charge to be separated

[0089] The extraction method according to the invention makes it possible to treat a feedstock to be separated comprising a mixture of aromatic and non-aromatic compounds. Preferably, the feedstock is hydrotreated and / or hydrogenated. According to one or more embodiments, the feedstock is an optionally hydrotreated and / or hydrogenated gasoline feedstock.

[0090] According to one or more embodiments, the filler is a C5+ cut, ie, containing compounds with 5 carbon atoms or more. According to one or more embodiments, the filler is a C5-C10 or C5-C11 cut, ie, containing compounds comprising from 5 to 10 or from 5 to 11 carbon atoms. According to one or more embodiments, the filler is a C6-C10 or C6-C11 cut, ie, containing compounds comprising from 6 to 10 or from 6 to 11 carbon atoms.

[0091] According to one or more embodiments, the filler comprises at least 20% by weight, preferably at least 30% by weight, very preferably at least 40% by weight, (eg at least 50% by weight) of aromatic compounds of 6 to 11 carbon atoms, relative to the total weight of the filler.

[0092] According to one or more embodiments, the filler comprises at least 20% by weight, preferably at least 30% by weight, very preferably at least 40% by weight, (eg at least 50% by weight) of mono-aromatic compounds of 6 to 11 carbon atoms, relative to the total weight of the filler.

[0093] According to one or more embodiments, the aromatic compounds of the feed are mono-aromatic compounds at least 95% by weight, preferably at least 98% by weight, very preferably at least 99% by weight.

[0094] According to one embodiment of the invention, the feed comprises less than 50 ppm by weight of sulfur, preferably less than 10 ppm by weight of sulfur, and very preferably less than 1 ppm by weight of sulfur. According to one embodiment of the invention, the feed comprises less than 100 ppm by weight of nitrogen, preferably less than 10 ppm by weight of nitrogen, and very preferably less than 1 ppm by weight of nitrogen.

[0095] According to one embodiment of the invention, the filler comprises less than 0.1% by weight of diolefins, preferably less than 0.05% by weight of diolefins, and very preferably less than 0.01% by weight of diolefins.

[0096] According to one embodiment of the invention, the feedstock comprises less than 0.1% by weight of olefins, preferably less than 0.05% by weight of olefins, and very preferably less than 0.01% by weight of olefins.

[0097] According to one embodiment of the invention, the feedstock has a content of less than or equal to 5000 ppm by weight, preferably less than or equal to 4500 ppm by weight, and very preferably less than or equal to 3000 ppm by weight, in compounds having a boiling point greater than 217°C, such as naphthalene.

[0098] According to one embodiment of the invention, the feedstock is free of the following compounds: H2, H2S, light gas such as ethane, propane and butane. According to one embodiment of the invention, the removal of these compounds in the feedstock is carried out in a fractionation column.

[0099] According to one embodiment, said feedstock is at least partly a gasoline cut from a fluidized bed catalytic cracking unit (e.g. FCC unit), the gasoline cut preferably having been selectively hydrogenated to transform diolefins into olefins, then fractionated to obtain a C5-C10, C5-C11, C6-C10 or C6-C11 cut, then hydrogenated to saturate the olefinic compounds. According to one embodiment of the invention, the feedstock is derived from the hydrogenation of a pyrolysis gasoline ("PyGas" according to English terminology) mixed with a gasoline cut from an FCC unit.

[0100] Separation fluid

[0101] According to one or more embodiments, the separation fluid (or solvent) comprises a compound selected from ethylene glycol, diethylene glycol, triethylene glycol, hexamethylphosphoramide, propylene carbonate, ethylene carbonate, sulfolane, 3-methylsulfolane, N-methylacetamide, N,N-dimethylacetamide, butyrolactone, 1-methylpyrrolidone, dimethylsulfoxide, caprolactam, N-methylformamide, pyrrolidin-2-one, furfural, 1,1,3,3-tetramethylurea and a mixture thereof. According to one or more embodiments, the separation fluid comprises or consists of sulfolane. According to one or more embodiments, the separation fluid consists of at least 80% by weight (e.g. at least 90% by weight), preferably at least 95% by weight (e.g. at least 99% by weight), sulfolane, relative to the total weight of the separation fluid.

[0102] According to one or more embodiments, the separation fluid further comprises an antisolvent, such as water. According to one or more embodiments, the antisolvent comprises or consists of water. According to one or more embodiments, the separation fluid comprises between 0.01% by weight and 5% by weight, preferably between 0.1% by weight and 3% by weight (eg between 0.5% by weight and 2% by weight) of antisolvent, such as water, relative to the total weight of the separation fluid. According to one or more embodiments, the separation fluid comprises, or consists of, sulfolane and water.

[0103] Example

[0104] A first comparative example 1 is shown in table 1. It is a comparison between:

[0105] - a reference example 1A represented by an extraction column comprising perforated trays with overflow (of the one-pass type as represented in FIG. 2) of the prior art;

[0106] - an example according to the invention 1 B represented by an extraction column comprising helical perforated plates (perforation diameter of 7 mm).

[0107] Table 1

[0108] Definitions: Total area is the area of ​​a cross-section of the column (Total area = pi * R 2 ); the term “Hold-up” represents the percentage by volume of the dispersed phase in the continuous phase: holdup = (dispersed volume) I (total volume) = (dispersed volume) I (dispersed volume + continuous phase volume).

[0109] Advantageously, for similar "hold-ups" and flow rates, the helical perforated trays allow the column diameter to be reduced by 10% and the column capacity to be increased by 20%.

[0110] A second comparative example 2 and a third comparative example 3 are shown in Table 2 and Table 3. This is a comparison between:

[0111] - a reference example A represented by an extraction column comprising perforated trays with overflow (of the single pass type as represented in figure 2) of the prior art;

[0112] - an example according to the invention B represented by an extraction column comprising helical perforated trays;

[0113] - an example according to the invention C represented by an extraction column comprising helical perforated trays and a central mast.

[0114] For the second comparative example 2, a calculation is carried out for a column of 1 meter diameter for a standard water / acetone / butyl acetate system (medium interfacial tension) at 20°C according to a first volume flow rate ratio, water and acetone forming the continuous phase (heavy phase): volume flow rate ratio of the continuous phase to volume flow rate of the dispersed phase Qc / Qd = 0.4.

[0115] For the third comparative example 3, a calculation is carried out for a column of 1 meter diameter for the standard water / acetone / butyl acetate system (medium interfacial tension) at 20°C according to a second volume flow rate ratio, water and acetone forming the continuous phase (heavy phase): volume flow rate ratio of the continuous phase to volume flow rate of the dispersed phase Qc / Qd = 0.67.

[0116] The maximum permissible traffic in the column is adjusted so as to respect a maximum holdup of 17%, a value defined to avoid congestion.

[0117] Table 2 Table 3

[0118] The capacity is significantly increased for a low Qc / Qd ratio: between 40% and 53% gain, i.e. a reduction in the total diameter of the column between 15 - 20%.

[0119] The capacity is even more significantly increased for a high Qc / Qd ratio: between 88% and 107% gain, i.e. a reduction in the total diameter of the column between 25 - 30%.

[0120] By way of illustration, the design of examples 2 and 3 according to the invention is explained below:

[0121] - the inter-tray space H2 is set at 0.3 m;

[0122] - the height of the edge, H3 is set at 0.1 m;

[0123] - the number of steps is set at 4, i.e. a height H1 = 7.5 cm.

Claims

CLAIMS 1. Extraction column comprising the following elements: a first injection point (§2) of a first phase; a second injection point (§3) of a second phase, the first and second injection points (§2, §3) being arranged on the extraction column (§1) to allow the circulation of the first phase and the second phase countercurrently in the extraction column (§1), one of said first and second phases being a continuous phase (§A) and the other being a dispersed phase (§B); a first withdrawal point for an extract (§4) and a second withdrawal point for a raffinate (§5), one being arranged at the bottom of the extraction column (§1) and the other being arranged at the top of the extraction column (§1);and a plurality of so-called helical perforated trays (§16) arranged helically, from the top of the extraction column (§1) to the bottom of the extraction column (1), the helical perforated trays (§16) being spaced apart by an inter-tray space (§8) allowing the passage of the continuous phase and comprising rims (§10, §18) adapted to receive a coalesced layer (§9) of the dispersed phase (§B).; 2. Extraction column according to claim 1, wherein: the helical perforated plates (§16) are arranged around a central axis (Z) of the extraction column (§1) according to a helical isometry comprising a rotation of angle p around the central axis (Z) of the extraction column (§1) and a translation of a distance H1 along the central axis (Z) of the extraction column (§1); the angle p is between 10° and 120°, preferably between 20° and 90°, very preferably between 30° and 75°; and the distance H1 is between 0.01 m and 1 m, preferably between 0.1 m and 0.9 m or between 0.2 m and 0.8 m, very preferably between 0.3 m and 0.7 m.

3. Extraction column according to claim 1 or claim 2, in which each helical perforated tray (§16) comprises a panel perforated with holes (§7) and comprises an upstream rim (§18) and a downstream rim (§10), in a direction opposite to the flow of the continuous phase (§A), the upstream rim (§18) and the downstream rim (§10) forming a reservoir adapted to receive the coalesced layer (§9).

4. Extraction column according to claim 3, in which the downstream rim (§10) has a height H3 of between 1 cm and 150 cm, preferably between 1 cm and 30 cm, preferably between 2 cm and 20 cm, very preferably between 5 cm and 15 cm.

5. Extraction column according to claim 3 or claim 4, in which the upstream rim (§18) has a height greater than, less than or substantially equal to the height H3 of the downstream rim (§10).

6. Extraction column according to any one of claims 3 to 5, in which the upstream rim (§18) of a downstream helical perforated tray (§16) is connected to the adjacent upstream helical perforated tray (§16), in a direction opposite to the flow of the continuous phase (§A).

7. Extraction column according to any one of the preceding claims, in which each helical perforated tray (§16) forms an angular perforated panel with an angle a of between 10° and 120°, preferably between 20° and 90°, very preferably between 30° and 75°.

8. An extraction column according to any preceding claim, wherein angle a is substantially equal to angle p, or angle a is greater than angle p.

9. Extraction column according to any one of the preceding claims, comprising one or more open partitions (§19) adapted to establish a predetermined passage section of the continuous phase (§A) in the extraction column (§1).

10. Extraction column according to any one of the preceding claims, comprising N helical perforated plates (§16) arranged approximately at the same height in the extraction column, N being between 1 and 4, preferably between 1 and 3, the term approximately corresponding to an approximation of ± 50%, preferably ± 20%, very preferably ± 10% of the distance H1, the distance H1 being the translation along the central axis (Z) between two adjacent helical perforated plates (§16).

11. Extraction column according to any one of the preceding claims, comprising: an extraction sector (§11), extending substantially from the first injection point (§2) of the first phase to substantially the second injection point (§3) of the second phase, and a backwash sector (§12), adjacent to the extraction sector (§11) and extending from the first injection point (§2) of the first phase to substantially a third injection point (§13) of backwash fluid.

12. Extraction method comprising the following steps: injecting a first phase and a second phase into the extraction column according to any one of claims 1 to 11; and withdrawing an extract (§4) and a raffinate (§5) from the extraction column.

13. Extraction method according to claim 12, wherein the extraction column (§1) is operated at a pressure of between 0.05 MPaa and 3 MPaa, preferably between 0.1 MPaa and 2 MPaa, preferably between 0.2 MPaa and 1.5 MPaa, preferably between 0.3 MPaa and 1 MPaa; and at a temperature of between 10°C and 150°C, preferably between 15°C and 130°C, preferably between 30°C and 120°C, preferably between 40°C and 110°C.

14. An extraction method according to claim 12 or claim 13, wherein the first phase comprises a mixture of aromatic and non-aromatic compounds.

15. An extraction method according to any one of claims 12 to 14, wherein the second phase comprises a compound selected from ethylene glycol, diethylene glycol, triethylene glycol, hexamethylphosphoramide, propylene carbonate, ethylene carbonate, sulfolane, 3-methylsulfolane, N-methylacetamide, N,N-dimethylacetamide, butyrolactone, 1-methylpyrrolidone, dimethylsulfoxide, caprolactam, N-methylformamide, pyrrolidin-2-one, furfural, 1,1,3,3-tetramethylurea and a mixture thereof.

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