Liquid-liquid extraction column and method with adjusted weir head loss

Abstract

The invention relates to a liquid-liquid extraction column (1) and a method using / comprising feed (2), wash (3) and optionally backwash (4) injection points, two draw-off points (5, 6), and trays (Pi) defining n zones comprising: at least one extraction zone Zi comprising zones Z1 to Zx, with x ≥ 1, and optionally at least one backwash zone comprising zones Zx+1 to Zn, with n ≥ x; in which the trays of the same zone present weirs (11) in which head-loss generating elements (13) are arranged, and when x > 1, the ratio of the head-loss coefficient of the head-loss-generating element of a zone Zi to that of a zone Zi+1 is between 0.8 and 8; and optionally when x = 1, the head-loss coefficient of the at least one backwash zone is greater than that of zone Z1.

Description

[0001] Liquid-liquid extraction process and column with pressure drop in adjusted weir

[0002] technical field

[0003] The field of the invention relates to a process and a column (extractor) for the liquid-liquid separation of hydrocarbon compounds, such as aromatic compounds (e.g. A6-A11) from extended hydrocarbon cuts (e.g. C6-C11 cut, such as from a Fluid Catalytic Cracking (FCC) unit.

[0004] Previous technique

[0005] A liquid-liquid extraction operation is a key component of processes for separating hydrocarbon fractions, such as the separation of aromatic and non-aromatic mixtures. The operating principle relies on the differences in solubility of the compounds in a homogeneous liquid feed in a suitable solvent (e.g., aprotic and polar solvents, such as sulfolane or DMSO). The addition of a partially miscible solvent to the feed causes the formation of a second phase into which some of the compounds (e.g., the aromatic compounds), the most soluble constituents, are preferentially transferred.

[0006] Typically, liquid-liquid extraction technology employs a liquid-liquid separation column comprising a plurality of perforated trays, each equipped with one or more weirs depending on the required capacity (referred to as a single-pass or two-pass tray, or a multi-pass system with more than three weirs). This is a long-established liquid-liquid extraction technology that can be used in petrochemicals and, more generally, in any other application requiring liquid-liquid separation technology.

[0007] With reference to Figure 1, a liquid-liquid extraction column 1 has the following counter-current operating principle: - a first phase 2 (or liquid to be separated), such as a feed (e.g., a mixture of aromatic and non-aromatic C6-C11 compounds), is injected towards the bottom of column 1 (in this example the feed is lighter than the solvent); a second phase 3 (or separating liquid), such as a solvent (e.g., Sulfolane), is injected towards the top of column 1; and an extract 4 (in liquid phase), such as a solvent enriched in extracted compounds (e.g., aromatic compounds), is withdrawn from the bottom of column 1; and - a raffinate 5 (in liquid phase), such as a feed depleted in extracted compounds, is withdrawn from the top of column 1.

[0008] To better understand the liquid-liquid extraction technology, a two-pass liquid-liquid extraction column 1 comprising m trays Pj perforated with holes 10 is shown in Figure 2. In this example, the second phase 3 (solvent) is the heavier phase and is dispersed through the holes 10 of the perforated trays Pj. The solvent droplets recoalescent on the next tray to form a liquid mat (or layer) preventing the first phase 2 (the lighter, continuous phase of liquid to be separated) from passing through the perforated tray. The first phase 2 flows counter-currently to the second phase 3 (from bottom to top): the first phase 2 passes through the weirs 11, then through the gap between the edge of the tray and the tray above. The first phase 2 then passes through the emulsion in the gap and exits through the next weir 11.

[0009] Liquid-liquid extraction processes have been widely deployed industrially for the separation of light fractions, such as C6-C8 fractions (e.g., catalytic reformat and pyrolysis gasoline, also known as pygas in Anglo-Saxon terminology). The aim is to implement this process on broader fraction pairs (C6-C10, such as high-severity fluidized bed catalytic cracking (HSFCC) with adapted tray technology).

[0010] The design of a liquid-liquid extraction column should preferably respect one or more constraints such as: a range between 15% and 30% of the average volume fraction of dispersed phase (e.g., solvent / heavy phase) in a compartment (e.g., area including a perforated tray and an adjacent free space); the non-entrainment of dispersed phase droplets in the weirs by the continuous phase (e.g., feed / light phase) in order to limit axial mixing of the dispersed phase;

[0011] - a height (thickness) H1 of the coalesced layer 12 of the dispersed phase on each plate sufficient to prevent the passage of the continuous phase through the perforated plate (and force the exclusive passage of the continuous phase into the weirs); a suitable transverse velocity of the continuous phase, which does not disturb the flow of the dispersed phase;

[0012] The characteristics of the perforated plates (hole diameter dN, hole velocity VN, and free space (cross-section) between the plates, plate spacing (pitch)) are defined to maximize the interfacial area and to confine the height H1 of the coalesced layer 12 within the target range (generally approximately 3–8 cm). The present invention aims to overcome the aforementioned deficiencies and, in particular, to allow improved control of the height H1 of the coalesced layer 12.

[0013] US patent 4,247,521 describes liquid-liquid extraction trays comprising differential pressure equipment allowing the height of the coalescing liquid layer to be maintained at sufficient levels.

[0014] US patent application 2005 / 0045558 A1 describes the presence of perforated plates in the tray spillways to reduce the risk of carryover of phase dispersed droplets by the continuous phase.

[0015] US patent 2012 / 0024977 describes examples of restricting the passage of the continuous phase in weirs by means of reduced cross-section pipe, perforated plates or baffles to limit axial dispersion between compartments.

[0016] Summary of the invention

[0017] In the context described above, one objective of this description is to provide a liquid-liquid extraction column that allows for a sufficient coalesced layer height of the dispersed phase on each tray to prevent the continuous phase from passing through the perforated tray (and to force the exclusive passage of the continuous phase through the weirs). To achieve this, the applicant has identified that specific characteristics of the perforated trays, such as the use of particular differential pressure elements in the weirs depending on their position in the liquid-liquid extraction column, make it possible to control the hydrodynamics along the entire length of the column by ensuring a homogeneous coalesced layer thickness and thus limiting axial mixing. This technical solution makes it possible to maintain satisfactory mass transfer efficiency on each tray.

[0018] According to a first aspect, the aforementioned objects, as well as other advantages, are obtained by a liquid-liquid extraction process, comprising the following steps: injecting a first phase (2), a second phase (3) and optionally a backwash liquid (6) into a liquid-liquid extraction column (1); and withdrawing an extract (4) and a raffinate (5) from the liquid-liquid extraction column (1), the liquid-liquid extraction column (1) comprising the following elements: a first injection point of the first phase (2) disposed at a position (e.g. intermediate) between the top and the bottom of the liquid-liquid extraction column (1);a second injection point of the second phase (3) and optionally a third injection point of the backwash liquid (6), one (of the second and third injection points) being disposed at the top of the liquid-liquid extraction column (1) and the other of said injection points being disposed at the bottom of the liquid-liquid extraction column (1); a first withdrawal point of the extract (4) and a second withdrawal point of the raffinate (5), one (of the first and second withdrawal points) being disposed at the bottom of the liquid-liquid extraction column (1) and the other of said withdrawal points being disposed at the top of the liquid-liquid extraction column (1); a plurality of trays (Pi) arranged from the top of the liquid-liquid extraction column (1) to the bottom of the liquid-liquid extraction column (1) and defining n zones, each zone comprising at least two trays (Pi), n being between 2 and 30;in which the n zones comprise: at least one extraction zone Zj included between a zone (e.g. column head) Zi comprising the second injection point of the second phase (3), and a feed zone Z; x including the first injection point of the first phase (2), x being greater than or equal to 1 (preferably x is greater than 1); and optionally at least one backwash zone included between a Z zone x +i and a zone (e.g., column background) Z nincluding the third backwash fluid injection point (6), n being greater than or equal to x; wherein: the trays Pi of the same zone have weirs (11) in which are arranged differential pressure elements (13) (a device inserted in each weir to create a head loss or pressure drop, for example by limiting the cross-sectional area of ​​the continuous phase passing through the differential pressure element); when x is greater than 1, the ratio between the head loss coefficient (of the cross-sectional area of ​​the continuous phase) of the differential pressure element (13) of a zone Zj and the head loss coefficient of the differential pressure element (13) of a zone Z i+i, is between 0.8 and 8, preferably between 0.9 and 4, most preferably between 1.05 and 2.5, more preferably between 1.1 and 1.8 (for example, the transition cross-section of the continuous phase of the deprimogenic element 13 of the Zj zone is more limited than the transition cross-section of the continuous phase of the deprimogenic element 13 of the Z zone i+ i) ; and optionally when x is equal to 1 , the pressure loss coefficient of the deprimogen element (13) of the zone Zi is less than the pressure loss coefficient of the deprimogen element (13) of at least one backwash zone.

[0019] According to one or more embodiments, the ratio between the pressure loss coefficient of the deprimogenituring element 13 of a zone Zj and the pressure loss coefficient of the deprimogenituring element 13 of a zone Zj+i varies.

[0020] According to one or more embodiments, when x is greater than 1, the ratio between the pressure loss coefficient of the deprimogen element (13) of a zone Zj and the pressure loss coefficient of the deprimogen element (13) of a zone Zj+i is between 1.05 and 8, preferably between 1.05 and 5, very preferably between 1.05 and 4.0, more preferably between 1.1 and 4.0.

[0021] According to one or more embodiments, when x is greater than 1, the ratio between the pressure loss coefficient of the differential element (13) of a zone Zj and the pressure loss coefficient of the differential element (13) of a zone Z i+i , is between 0.8 and 0.95, preferably between 0.8 and 0.9.

[0022] According to one or more embodiments, when x is equal to 1, the ratio between the pressure loss coefficient of the deprimogen element (13) of the zone Z1 and the pressure loss coefficient of the deprimogen element (13) of at least one backwash zone, is between 0.01 and 0.9, preferably between 0.1 and 0.5, very preferably between 0.12 and 0.25.

[0023] According to one or more embodiments, in the zones Zj or j varies from x+1 to n, the deprimogen element (13) is adapted so that the pressure loss coefficient decreases when the value j increases.

[0024] According to one or more embodiments, the ratio between the pressure loss coefficient of the differential element (13) of a zone Zi and the pressure loss coefficient Ç i+i The differential pressure of the element (13) of a zone Zj+i is a function of the flow rate variation of the continuous phase as described by the following formula:

[0025] Math. 1 in which Q c is the flow rate of the continuous phase and A is a constant between 0.8 and 3.0, preferably between 0.9 and 2.0.

[0026] According to one or more embodiments, the ratio between the pressure loss coefficient of the differential element (13) of zone Z x on the pressure loss coefficient of the differential element (13) of a zone Zj is a function of the flow rate variation of the continuous phase as described by the following formula:

[0027] Math. 2 in which Q c is the flow rate of the continuous phase and A is a constant between 0.8 and 3.0, preferably between 0.9 and 2.0. According to one or more embodiments, the ratio between the pressure loss coefficient of the differential pressure element (13) of a zone Zj and the pressure loss coefficient Ç j+iThe differential pressure of the element (13) of a zone Zj+i is a function of the flow rate variation of the continuous phase as described by the following formula:

[0028] Math. 3 in which Q c is the flow rate of the continuous phase and A is a constant between 0.8 and 3.0, preferably between 0.9 and 2.0.

[0029] According to one or more embodiments, the pressure loss coefficient varies from one zone to another by modifying the passage section of the deprimogen element (13).

[0030] According to a second aspect, the aforementioned objects, as well as other advantages, are obtained by a liquid-liquid extraction column (1) comprising the following elements: a first injection point of a first phase (2) disposed at a position (e.g. intermediate) between the top and bottom of the liquid-liquid extraction column (1); a second injection point of a second phase (3) and optionally a third injection point of a backwash liquid (6), one of said injection points being disposed at the top of the liquid-liquid extraction column (1) and the other of said injection points being disposed at the bottom of the liquid-liquid extraction column (1); a first extraction point (4) and a second extraction point (5), one of said extraction points being disposed at the bottom of a liquid-liquid extraction column (1) and the other of said extraction points being disposed at the top of a liquid-liquid extraction column (1);a plurality of trays (Pi) arranged from the top of the liquid-liquid extraction column (1) to the bottom of the liquid-liquid extraction column (1) and defining n zones, each zone comprising at least two trays (Pi), n being between 2 and 30; in which the n zones comprise: at least one extraction zone Zj included between a zone Zi comprising the second injection point of the second phase (3), and a feed zone Z; x including the first injection point of the first phase (2), x being greater than or equal to 1; and optionally at least one backwash zone included between a Z zone x +i and a Z zone nincluding the third injection point of the backwash liquid (6), n being greater than or equal to x; in which: the trays Pi of the same zone have weirs (11) in which are arranged deprimogen elements (13); when x is greater than 1, the ratio between the passage cross-section of the deprimogen element (13) of a zone Zj to the passage cross-section of the deprimogen element (13) of a zone Zj+i, is between 0.12 and 3.0, preferably between 0.25 and 1.25, very preferably between 0.40 and 0.95, more preferably between 0.55 and 0.90; and optionally when x is equal to 1, the passage section of the deprimogen element (13) of the at least one backwash zone is less than the passage section of the passage section (of the continuous phase) of the deprimogen element (13) of the Zi zone.

[0031] According to one or more embodiments, the ratio between the passage section of the deprimogen element (13) of a zone Zj and the passage section of the deprimogen element (13) of a zone Zj+i varies.

[0032] According to one or more embodiments, when x is greater than 1, the ratio between the passage section of the deprimogen element (13) of a zone Zj and the passage section of the deprimogen element (13) of a zone Zj+i is between 0.12 and 0.98, preferably between 0.25 and 0.95, very preferably between 0.40 and 0.95, more preferably between 0.55 and 0.90 or between 0.70 and 0.90.

[0033] According to one or more embodiments, when x is greater than 1, the ratio between the passage section of the deprimogen element 13 of a zone Zj and the passage section of the deprimogen element 13 of a zone Zj+i is between 1.05 and 1.25, preferably between 1.05 and 1.11.

[0034] According to one or more embodiments, when x is equal to 1, the ratio between the passage section of the deprimogen element 13 of the zone Zi and the passage section of the deprimogen element 13 of at least one backwash zone (e.g. the zone Z2) is between 1.1 and 11, preferably between 1.5 and 5, very preferably between 1.8 and 3.0.

[0035] According to one or more embodiments, in the zones Zj or j varies from x+1 to n, the passage section of the deprimogen element (13) increases when the value j increases.

[0036] In this application, the specific capacity C of the column is defined as follows: C = Qtot / S, where Q tot = Q c + Qd; we define the total surface area S of the column such that S = Pi*Dc below A 2 / 4, where De is the column diameter; the specific DC phase capacitance Q is defined c , s such as below Q c ,s = Qc / S; and we define the specific discontinuous phase capacitance Q, s such as below Q, s =Qd / S. According to one or more embodiments, C is between 1 m 3 / h / m 2 and 80 m 3 / h / m 2 preferably between 5 m 3 / h / m 2 and 70 m 3 / h / m 2 , preferably between 10 m 3 / h / m 2 and 60 m 3 / h / m 2 ; De is between 0.2 and 10 m; S is between 0.03 and 80 m 2 Q c , s is between 0.1 m 3 / h / m 2 and 70 m 3 / h / m 2 , preferably between 0.5 m 3 / h / m 2 and 65 m 3 / h / m 2 and very preferably between 1 m 3 / h / m 2 and 55 m 3 / h / m 2 and Qd, s is between 0.1 m 3 / h / m 2 and 70 m 3 / h / m 2 , preferably between 0.5 m3 / h / m 2 and 65 m 3 / h / m 2 and very preferably between 1 m 3 / h / m 2 and 55 m 3 / h / m 2 .

[0037] Embodiments of the process and liquid-liquid extraction column according to the aforementioned aspects, as well as other characteristics and advantages, will become apparent from the following description, given for illustrative purposes only and not as a limitation, and with reference to the following drawings.

[0038] List of figures

[0039] Figure 1 schematically shows a cross-sectional view of a reference liquid-liquid extraction column.

[0040] Figure 2 schematically shows a cross-sectional view of the flow of the dispersed phase and the continuous phase in a reference liquid-liquid extraction column.

[0041] Figure 3 schematically shows a cross-sectional view of a liquid-liquid extraction column according to the present invention.

[0042] Figure 4 schematically shows a cross-sectional view of the flow of the dispersed phase and the continuous phase in a liquid-liquid extraction column according to the present invention.

[0043] Figure 5 schematically shows a cross-sectional view of a liquid-liquid extraction column according to the present invention, defined by a plurality of zones Zj comprising the column head zone 1 and the feed zone Z x , and a plurality of zones Zj included between zone Z x +i and the Z zone n from the bottom of the column.

[0044] Figure 6 schematically shows a cross-sectional view of a liquid-liquid extraction column used in the reference examples and according to the invention.

[0045] Figure 7 shows the variations in coalesced layer thickness and continuous phase flow rate in the liquid-liquid extraction column of reference example 1.

[0046] Figure 8 shows the variations in coalesced layer thickness and continuous phase flow rate in the liquid-liquid extraction column of reference example 2 with minimum flow rate.

[0047] Figure 9 shows the variations in coalesced layer thickness and continuous phase flow rate in the liquid-liquid extraction column of Example 3 according to the invention, divided into 3 pressure loss coefficient zones. Figure 10 shows the variations in coalesced layer thickness and continuous phase flow rate in the liquid-liquid extraction column of Example 3 according to the invention, divided into 4 pressure loss coefficient zones.

[0048] Description of the implementation methods

[0049] Embodiments of the invention will now be described in detail. In the following detailed description, numerous specific details are presented to provide a more thorough understanding of the invention. However, it will be apparent to those skilled in the art that the invention can be implemented without these specific details. In other cases, well-known features have not been described in detail to avoid unnecessarily complicating the description.

[0050] In this description, the term "include" is synonymous with (means the same as) "include" and "contain," and is inclusive or open-ended and does not exclude other unstated elements. It is understood that the term "include" includes the exclusive and closed term "consist." Furthermore, in this description, the term "approximately" corresponds to an approximation of ±10%, preferably ±5%, most preferably ±2%, of a reference value such as a distance, speed, flow rate, compound content, temperature, pressure, etc. In this description, the term "CX," in which X is a number, is synonymous with a hydrocarbon compound with X carbon atoms; similarly, the term "AX," in which X is a number, is synonymous with an aromatic compound with X carbon atoms.

[0051] With reference to Figure 3, a liquid-liquid extraction column 1 according to the invention comprises the following elements: a first injection point for a first phase 2 (or liquid to be separated), such as a feedstock (e.g., a mixture of aromatic and non-aromatic C6-C11 compounds), located at an intermediate position between the top and bottom of column 1; a second injection point for a second phase 3 (or separating liquid), such as a solvent (e.g., Sulfolane), located at the top of column 1; optionally, a third injection point for a backwash liquid 6, such as a recycle (e.g., a mixture comprising at least 50% by weight of light compounds, i.e., C5-C8 compounds, preferably C5-C6), located at the bottom of column 1; a first withdrawal point for an extract 4 (in liquid phase), such as a solvent enriched in extracted compounds (e.g.,aromatic compounds), arranged at the bottom of column 1; and a second withdrawal point of a raffinate 5 (in liquid phase), such as a feed depleted in extracted compounds, arranged at the top of column 1. According to one or more embodiments, when the optional third injection point of backwash liquid 6 is not present, the first injection point of the first phase 2 is preferably arranged at the top or bottom of column 1. According to these embodiments, the column does not include a so-called backwash zone.

[0052] According to one or more embodiments, the liquid-liquid extraction column 1 is substantially cylindrical with a diameter between 0.2 m and 10 m and / or the liquid-liquid extraction column 1 has a height H2 between 1 m and 80 m. The height H2 corresponds to the height of the column shell.

[0053] In addition, in order to increase yield and purity, two distinct operating zones are defined opposite the injection point of the liquid to be separated 2: an extraction sector 8, extending substantially from the first injection point of the first phase 2 to substantially the second injection point of the second phase 3, allows in particular the extraction of compounds (e.g. aromatics) from the liquid to be separated 2 by contacting it with the separation liquid 3 in counter-current flow (the so-called yield zone), and optionally a backwash sector 9, adjacent to the extraction sector 8 and extending to substantially the third injection point of the backwash liquid 6, allows in particular the counter-extraction of undesired compounds (e.g. heavy non-aromatics) contained in the extract 4 by the backwash liquid in order to guarantee a high level of purity.

[0054] Specifically, with reference to Figure 3, the separation liquid exits column 1, carrying with it compounds of interest to be separated (e.g., aromatics) to form extract 4. The extract may also contain unwanted compounds (e.g., light non-aromatics, such as C6-C7s) which can be separated downstream (e.g., by distillation and / or stripping). Advantageously, extract 4 contains little or no (e.g., less than 1 wt%) unwanted compounds that are difficult to separate (e.g., heavier non-aromatics, such as C8+s), which are separated from the extract in the backwash section 9. With reference to Figure 3, the separation liquid 3 is heavier than the liquid to be separated 2 and is injected at the top of column 1, while the backwash liquid 6 is injected at the bottom of column 1.It is understood that the present invention also relates to liquid-liquid extraction columns, in which the separation liquid 3 is lighter than the liquid to be separated 2, and it follows that: the second injection point of the separation liquid 3 is at the bottom of column 1; the third injection point of the backwash liquid 6 is at the top of column 1; the first withdrawal point of an extract 4 is located at the top of column 1; and the second withdrawal point of a raffinate 5 is located at the bottom of column 1. With reference to Figure 4, a two-pass liquid-liquid extraction column 1 comprises m perforated trays Pj, i being between 1 and m. Each perforated tray Pj is arranged so that the dispersed phase (i.e., the separation liquid 3, which is heavier than the liquid to be separated) is located at the bottom of column 1.

[0055] 2) flows through the holes 10 of the perforated plate Pj, the droplets of the dispersed phase recoaling on the perforated plate P i+i next to form a liquid volume preventing the passage of the continuous phase (i.e., the liquid to be separated² being lighter than the separating liquid)

[0056] 3) through the perforated tray P i+ i. The liquid to be separated 2 flows counter-currently to the separation liquid 3, i.e., from bottom to top through weirs 11 (central and peripheral) and transversely between two adjacent trays. With reference to Figure 4, the heavy phase is the dispersed phase and the light phase is the continuous phase. It is understood that a liquid-liquid extraction column 1 may include perforated trays adapted so that the dispersed phase is the light phase and the continuous phase is the heavy phase.

[0057] According to one or more embodiments, the total number m of trays is between 2 and 150, preferably between 10 and 120, very preferably between 40 and 110.

[0058] According to one or more embodiments, the perforated plates Pj are 1-pass plates (e.g. one type of weir) or 2-pass plates (e.g. two types of weirs) or multi-pass plates (e.g. having more than two weirs).

[0059] The applicant identified that the operation of a liquid-liquid extraction column can generate significant variations in flow rate and physicochemical properties of the phases circulating in the column, and that the implementation of different trays depending on their position in the column can lead to ensuring homogeneous column efficiency contrary to the prior art.

[0060] According to the invention, with reference to Figure 5, a liquid-liquid extraction column 1 is further defined by: at least one extraction zone Zj, and preferably a plurality of extraction zones Zj defining the extraction sector 8, i.e., the extraction zone or zones Zj are located between the column head zone Zi comprising the second injection point of the second phase 3, and the feed zone Z x including the first injection point of the first phase 2, x being greater than or equal to 1, preferably x being greater than 1; and optionally at least one backwash zone defining the backwash sector 9, i.e., the backwash zone(s) is / are located between zone Z x +i and the Z column background area nincluding the third injection point of the backwash liquid 6, n being greater than or equal to x (depending on the presence or absence of the backwash zone Zj). According to the invention, each extraction and optionally backwash zone comprises at least two trays, each extraction and backwash zone defining the structural characteristics of the perforated trays Pj present in said extraction and backwash zones. Thus, according to the invention, the perforated trays Pj of the same extraction and optionally backwash zone have substantially the same number of holes 10 per perforated tray Pj.

[0061] According to one or more embodiments, with reference to Figure 5, the at least one backwash zone is a plurality of zones subdivided into a plurality of zones Zj comprising zone Z x +i and the Z column background area n .

[0062] Advantageously, the number of zones Zj and Zj can be defined with regard to the variability of flow of the continuous phase and the physico-chemical properties of the phases passing through said zones Zj and Zj.

[0063] According to one or more embodiments, the total number n of zones is between 2 and 30, preferably between 3 and 30, most preferably between 4 and 24, such as between 4 and 18, in particular between 4 and 8.

[0064] In this description, i, j, x, m and n are natural integers.

[0065] Depending on one or more embodiments, the number of zones Zj (number of zones Zi to Z) x ) is between 1 and 10, preferably between 2 and 10, most preferably between 2 and 6, such that between 2 and 4.

[0066] Depending on one or more embodiments, the number of backwash zones (number of Z zones) x+i to Z n) is between 1 and 10, preferably between 1 and 6, most preferably between 1 and 4. According to one or more embodiments, the number of backwash zones (number of Z zones) x+i to Z n ) is greater than or equal to 2. According to one or more embodiments, the number of backwash zones is equal to 1.

[0067] According to one or more embodiments, the number of floors per zone Zj and Zj can be determined by the number of actual floors required for separation divided by the number of zones Zj and Zj.

[0068] Control of the coalesced layer height

[0069] An object of the present invention is to provide a liquid-liquid extraction column 1 having (in operation) a coalesced layer height H1 12 of the dispersed phase on each perforated tray Pj sufficient to prevent the passage of the continuous phase through the perforated tray Pj (and force the exclusive passage of the continuous phase into the weirs 11). The applicant has identified, for example, systems with low interfacial tension (e.g., < 20 mN / m or < 10 mN / m or even < 5 mN / m) and / or exhibiting high density differences (Ap = |pd-pc|) (e.g., > 100 kg / m³). 3It is difficult to guarantee a sufficient height H1 of the coalesced layer 12 for the proper functioning of the column (pd: density of the dispersed phase; pc: density of the continuous phase). Indeed, the height H1 of the coalesced layer 12 is the result of the pressure balance exerted on either side of the plate Pj for each of the phases 2 and 3. The main positive contributions are: the pressure drop generated by the passage of the dispersed phase through the holes 10 of the plate Pj (a function of the design velocity at the hole V). N preferably between 0.1 ms' 1 and 1 ms' 1 ); the pressure loss due to capillary forces in hole 10, a generally small contribution in the case of low interfacial tension; and the pressure loss due to the continuous phase flow.

[0070] These contributions are balanced by the weight of the emulsion acting on the coalesced layer 12. In the case where the height H1 of the coalesced layer 12 on the plates is too low, negative pressure equipment can be positioned in the weirs so as to increase it.

[0071] Typically, liquid-liquid extraction columns 1 are designed with a perforated tray (equipped with one or more reference weirs) cut to the maximum flow rates of each phase. This perforated tray design is then implemented for the entire column. However, column operation can generate significant variability: in the flow rate of each phase along the column: this phenomenon is linked, on the one hand, to the transfer of mass from the feed solutes to the solvent and, on the other hand, to the possibility, within the process flow diagram, of modulating the flow rate in the backwash section 9 according to the nature of the feed and the desired specifications; in the physicochemical properties, and in particular the density difference and interfacial tension between the feed 2 and the solvent 3 (e.g., Sulfolane / hydrocarbons) related to the progressive enrichment in the product of interest (e.g.,aromatics) in the solvent phase; and the variability of the "holdup" in the column linked to variations in physicochemical properties. The "holdup" is the average volume fraction of phase dispersed in the column.

[0072] Table 1 below shows the large variability of the (volumetric) flow rate ranges Qd of the dispersed phase and Q c of the continuous phase (relative to the column inlet flow rates) and interfacial tension (IFT) encountered along the column for different reference examples. Table 1

[0073] Adjustments to certain characteristics of the trays, such as the height between trays (see FR3130630), the number of perforations per tray (see FR3130631), and the weir width (see FR3130632), have already been proposed based on the zoning. The present invention proposes to extend this methodology to the control of head loss by means of differential pressure elements arranged in the weirs so as to improve the hydraulic operation of the column and, in particular, to maintain a predefined range of height H1 of the coalesced layer 12 over the entire liquid-liquid extraction column 1.

[0074] With reference to Figure 5, the present invention relates to the control of the weir head loss by zones. The number of zones, n, is defined primarily with regard to the variability of the continuous phase flow rate and the physicochemical properties (e.g., p c, Pd and IFT). The number of trays per zone is determined by the number of actual stages required for separation divided by the number of zones n. The head loss of the weir is sized so as to achieve a predetermined coalesced layer thickness on each perforated tray.

[0075] Since the reference embodiments are conservative and propose to size (all) the perforated plates and in particular (all) the weirs, at maximum flow of the phases passing through them, the variations in phase flow, and in particular of the continuous phase, lead to oversizing the differential element whose operation is reduced or even ineffective in areas of lower flow.

[0076] To overcome these problems, it is proposed to adjust the pressure loss coefficient of the differential pressure element to the maximum continuous phase flow rate of zone n in order to increase the coalesced layer thicknesses and ensure the most homogeneous operation possible. Zoning allows the pressure loss coefficient of the differential pressure element to be adapted for areas of lower flow rate. This technological solution can be implemented for single-pass, double-pass, or multi-pass trays.

[0077] Specifically according to the invention: the plurality of trays Pj arranged from the top of the liquid-liquid extraction column 1 to the bottom of the liquid-liquid extraction column 1 define n zones, each zone comprising at least two trays (Pi); the n zones comprise: at least one extraction zone Zj located between the zone Zi comprising the second injection point of the second phase 3, and a feed zone Z xincluding the first injection point of the first phase 2, x being greater than or equal to 1; and optionally at least one backwash zone Zj included between zone Z x +i and the Z zone nincluding the third injection point of the backwash liquid 6, n being greater than or equal to x (n being equal to x without backwash zone Zj; n being greater than x with backwash zone Zj); the trays Pi of the same zone have weirs 11 in which are arranged differential pressure elements 13 (device inserted in each weir to create a pressure loss or a pressure drop, for example by limiting the cross-section of the continuous phase passing through the differential pressure element);when x is greater than 1, the ratio between the pressure loss coefficient of the negative pressure element 13 of a zone Zj and the pressure loss coefficient of the negative pressure element 13 of a zone Zj+i is between 0.8 and 8, preferably between 0.9 and 4, very preferably between 1.05 and 2.5, more preferably between 1.1 and 1.8 (for example, the continuous phase passage cross-section of the negative pressure element 13 of zone Zj is more limited than the continuous phase passage cross-section of the negative pressure element 13 of zone Zj+i); and optionally when x is equal to 1, the pressure loss coefficient of the passage cross-section of the negative pressure element 13 of zone Zi is less than the pressure loss coefficient of the negative pressure element 13 of at least one backwash zone.

[0078] Advantageously, due to the fluctuation of the continuous phase flow rate and the physicochemical properties of the phases as they pass through the column, the zone-by-zone variation of the pressure drop coefficient of the continuous phase passing through the differential pressure element 13 in the weirs 11 of the perforated plates Pj makes it possible to guarantee a coalesced layer height H1 12 within a predetermined range along the entire column. In particular, the liquid-liquid extraction column 1 according to the invention makes it possible to maintain, during operation, a coalesced layer height H1 12 of the perforated plates Pi between 2 cm and 8 cm from zone 1 to zone n.

[0079] It is known that the pressure loss is directly proportional to the kinetic energy of the fluid (e.g., the continuous phase) passing through a medium (e.g., the differential pressure element 13), and the pressure loss is generally characterized by a pressure loss coefficient, a dimensionless value denoted " " in the following formula, where:

[0080] AP is the pressure loss (of singular type), expressed in Pa or kg.m' 1 .s' 2 ; p is the density of the continuous phase, expressed in kg / m³ 3 ; and v is the characteristic velocity of the continuous phase through the weir, expressed in ms' 1 and defined as the ratio of the continuous phase flow rate passing through this weir to the surface area of ​​said weir. Math. 4

[0081] It is understood that, when the medium considered is a multi-pass platform, an average head loss can be defined as a function of the average velocity of the continuous phase passing through the weirs of said multi-pass platform. Preferably, the dimensions of the weirs 11 and / or the differential pressure elements 13 of a multi-pass platform are defined such that the cross-sectional area of ​​the weirs of the multi-pass platform and / or the velocities of the continuous phase passing through the weirs of the multi-pass platform are substantially identical.

[0082] Preferably, all the trays Pj have a substantially constant total cross-sectional area (passage area) of the weir 11. Advantageously, the weirs 11 of the liquid-liquid extraction column can all be substantially identical (e.g., weirs of single-pass trays) or dimensioned according to only two or three models (e.g., peripheral and central weirs of two-, three-, or four-pass trays). For example, in Figure 4 showing two-pass trays, each tray Pj comprises either peripheral weirs with cross-sectional area S1 or a central weir with cross-sectional area S2, S2 being substantially equal to 2*S1).Advantageously, the present invention allows the construction of liquid-liquid extraction columns using substantially identical trays along the entire length of the shell and the division of the column into zones by selecting suitable differential pressure elements 13 and arranging these elements in the weirs 11, which greatly simplifies the construction or modification of the column. The present invention also allows the modification of existing columns.

[0083] According to one or more embodiments, the ratio between the pressure loss coefficient of the differential pressure element 13 of a zone Zj and the pressure loss coefficient of the differential pressure element 13 of a zone Zj+i varies (ratio 1, 0). According to one or more embodiments, when x is greater than 1, the ratio between the pressure loss coefficient of the differential pressure element 13 of a zone Zj and the pressure loss coefficient of the differential pressure element 13 of a zone Zj+i varies (ratio 1, 0). i+i, is between 1.05 and 8, preferably between 1.05 and 5, most preferably between 1.05 and 4.0, more preferably between 1.1 and 4.0, in order to separate, for example, aromatic compounds (e.g., A6-A11). According to one or more embodiments, when x is greater than 1, the ratio between the pressure drop coefficient of the deprimogenizing element 13 of a Zj zone and the pressure drop coefficient of the deprimogenizing element 13 of a Zj+i zone is between 0.8 and 0.95, preferably between 0.8 and 0.9, in order to separate, for example, 5-(hydroxymethyl)furfural or a mercaptan. According to one or more embodiments, when x is equal to 1, the ratio between the pressure loss coefficient of the deprimogenituring element 13 of the zone Zi and the pressure loss coefficient of the deprimogenituring element 13 of at least one backwash zone (e.g., zone Z2) is between 0.01 and 0.9, preferably between 0.1 and 0.5, most preferably between 0.12 and 0.25.

[0084] According to one or more embodiments, in zones Zj where j varies from x+1 to n (in the backwash sector 9), the pressure-reducing element 13 is adapted so that the pressure loss coefficient is substantially constant, or increases when the value j increases, or decreases when the value j increases. Preferably, the pressure loss coefficient decreases when the value j increases.

[0085] According to one or more embodiments, the ratio between the pressure loss coefficient of the differential element 13 of a zone Zj and the pressure loss coefficient Ç i+i of the deprimogen element 13 of a zone Zj+1 is a function of the flow variation of the continuous phase as described by the following formula, in which A is a constant between 0.8 and 3.0, preferably between 0.9 and 2.0.

[0086] Math. 5 = A n 2

[0087] Q 2 .

[0088] According to one or more embodiments, the ratio between the pressure loss coefficient of the differential element 13 of zone Z x on the pressure loss coefficient of the differential element 13 of a zone Zj (zone of the backwash sector 9) is a function of the flow variation of the continuous phase as described by the following formula, in which A is a constant between 0.8 and 3.0 preferably between 0.9 and 2.0.

[0089] Math. 6

[0090] According to one or more embodiments, the ratio between the pressure loss coefficient of the differential element 13 of a zone Zj and the pressure loss coefficient Ç j+i The differential pressure of the element 13 of a zone Zj+i is a function of the flow rate variation of the continuous phase as described by the following formula, in which A is a constant between 0.8 and 3.0, preferably between 0.9 and 2.0. Math. 7

[0091] According to one or more embodiments, the pressure loss coefficient varies from one zone to another by modifying the passage section (of the continuous phase) of the deprimogeniting element 13.

[0092] According to one or more embodiments: when x is greater than 1, the ratio between the cross-section of the deprimogenic element 13 of a zone Zj and the cross-section of the deprimogenic element 13 of a zone Z i+i , is between 0.12 and 3.0, preferably between 0.25 and 1.25, very preferably between 0.40 and 0.95, more preferably between 0.55 and 0.90; and optionally when x is equal to 1, the passage section of the deprimogen element 13 of the at least one backwash zone is less than the passage section of the passage section (of the continuous phase) of the deprimogen element 13 of the Zi zone.

[0093] According to one or more embodiments, the ratio between the cross-sectional area of ​​the deprimogenic element 13 of a zone Zj and the cross-sectional area of ​​the deprimogenic element 13 of a zone Zj+i varies (ratio 1.0). According to one or more embodiments, when x is greater than 1, the ratio between the cross-sectional area of ​​the deprimogenic element 13 of a zone Zj and the cross-sectional area of ​​the deprimogenic element 13 of a zone Zj+i is between 0.12 and 0.98, preferably between 0.25 and 0.95, most preferably between 0.40 and 0.95, more preferably between 0.55 and 0.90 or between 0.70 and 0.90, in order to separate, for example, aromatic compounds (e.g., A6-A11).According to one or more embodiments, when x is greater than 1, the ratio between the passage section of the deprimogenic element 13 of a Zj zone to the passage section of the deprimogenic element 13 of a Zj+i zone is between 1.05 and 1.25, preferably between 1.05 and 1.11, in order to separate for example 5-(hydroxymethyl)furfural or a mercaptan.

[0094] According to one or more embodiments, when x is equal to 1, the ratio between the passage section of the deprimogen element 13 of the zone Zi and the passage section of the deprimogen element 13 of at least one backwash zone (e.g. the zone Z2) is between 1.1 and 11, preferably between 1.5 and 5, very preferably between 1.8 and 3.0.

[0095] According to one or more embodiments, in zones Zj where j varies from x+1 to n (in the backwash sector 9), the cross-sectional area of ​​the differential pressure element 13 is substantially constant, or decreases as the value j increases, or increases as the value j increases. Preferably, the cross-sectional area increases as the value j increases.

[0096] The differential pressure element 13 can be, for example, a perforated plate, a grid, or any other equipment generating a limitation of the flow and / or a pressure loss in the weir 11. The differential pressure element 13 can be positioned: either horizontally in the weir 11, perpendicular to the continuous phase flow; or vertically, in the direction of the continuous phase flow, for example at the outlet of the weir 11.

[0097] In one or more embodiments, the negative pressure element 13 comprises a plate perforated with holes, said holes being preferably evenly distributed over the perforated plate, preferably in a triangular pattern. In one or more embodiments, the perforated plates have between 5 and 500 holes. In one or more embodiments, for each perforated plate, the ratio of the area of ​​the holes to the total area of ​​the perforated plate is less than 20%, preferably less than 10%, and / or is between 0.5% and 8%, preferably between 1% and 5%. In one or more embodiments, the size of the holes in the negative pressure elements 13 is substantially constant. In one or more embodiments, the diameter of the holes in the negative pressure elements 13 is between 0.5 cm and 8 cm, preferably between 1 cm and 5 cm, most preferably between 2 cm and 4 cm.

[0098] According to one or more embodiments, the depression element 13 is a perforated plate and, when x is greater than 1, in extraction zones Zj or i varies from 1 to x (in extraction sector 8), the number of holes in the depression element 13 increases as the value i increases. According to one or more embodiments, in zones Zj or i varies from 1 to x, the ratio between the number of holes in the depression element 13 of a zone Zj and the number of holes in the depression element 13 of a zone Zj i+ i, is between 0.3 and 0.98, preferably between 0.6 and 0.95, most preferably between 0.75 and 0.90.

[0099] According to one or more embodiments, when x is equal to 1, the ratio between the number of holes of the deprimogen element 13 of the zone Zi and the number of holes of the deprimogen element 13 of at least one backwash zone (e.g. the zone Z2), is between 1.1 and 11, very preferably between 1.5 and 5, very preferably between 1.8 and 3.0.

[0100] According to one or more embodiments, the pressure-reducing element 13 is a perforated plate, and the number of holes in the pressure-reducing elements 13 of at least one backwash zone Zj is less than the number of holes in the pressure-reducing elements 13 of at least one extraction zone Zj. According to one or more embodiments, in zones Zj where j varies from x+1 to n (in the backwash sector 9), the pressure-reducing element 13 is a perforated plate, and the number of holes in the pressure-reducing elements 13 is substantially constant, or decreases as the value j increases, or increases as the value j increases. Preferably, the number of holes increases as the value j increases.

[0101] According to one or more embodiments, the pressure drop AP of the differential pressure elements 13 is between 1 Pa and 200 Pa, preferably between 10 Pa and 50 Pa. According to one or more embodiments, the density ρ of the continuous phase is between 500 kg. 3 and 1500 kg. 3 preferably between 600 kg. 3 and 1000 kg. 3 According to one or more embodiments, the velocity v of the continuous phase through a weir is between 0.001 ms' 1 and 0.1 ms' 1 , preferably between 0.01 ms' 1 and 0.1 ms' 1 It is understood that the value of the flow rate Q c The continuous phase is not limiting. For example, the flow rate Qc can vary by 1 m 3 / h and 500 m 3 / h. According to one or more embodiments, the height H1 is between 0.5 cm and 15 cm, preferably between 2 cm and 10 cm. [

[0102] According to one or more embodiments, the liquid-liquid extraction column 1 is operated at least one of the following operating conditions: a pressure between 0.05 MPa and 3 MPa, preferably between 0.1 MPa and 2 MPa, preferably between 0.2 MPa and 1.5 MPa, preferably between 0.3 MPa and 1 MPa; a temperature 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.

[0103] In this application, the specific capacity C of the column is defined as follows: C = Qtot / S, where Q tot = Q c + Qd; we define the total surface area S of the column such that S = Pi*Dc below A 2 / 4, where De is the column diameter; the specific DC phase capacitance Q is defined c , s such as below Q c , s = Qc / S; and we define the discontinuous phase specific capacitance Q d ,s such as below Q d , s =Qd / S. According to one or more embodiments, C is between 1 m 3 / h / m 2 and 80 m 3 / h / m 2 preferably between 5 m 3 / h / m 2 and 70 m 3 / h / m 2 , preferably between 10 m 3 / h / m 2 and 60 m 3 / h / m 2 ; De is between 0.2 and 10 m; S is between 0.03 and 80 m 2 Q c , s is between 0.1 m 3 / h / m 2 and 70 m 3 / h / m 2 , preferably between 0.5 m 3 / h / m 2 and 65 m 3 / h / m 2 and very preferably between 1 m 3 / h / m 2 and 55 m 3 / h / m 2 and Q, s is between 0.1 m 3 / h / m 2 and 70 m 3 / h / m 2 , preferably between 0.5 m 3 / h / m 2 and 65 m 3 / h / m 2and very preferably between 1 m 3 / h / m 2 and 55 m 3 / h / m 2 .

[0104] Examples

[0105] The liquid-liquid extraction column examples 1 described below all have the following characteristics with reference to Figure 6: The liquid-liquid extraction column 1 has a diameter of 8.5 m with 4-pass trays. The perforation diameter (holes) of the trays is 5 mm. The free space between the trays is 30 cm (space for the passage of the continuous phase). In each weir 11 is arranged a differential pressure element 13 in the form of a perforated plate positioned horizontally and provided with perforations of 3 cm in diameter.

[0106] The charge 3 (continuous phase and light phase) is injected to a height equal to 2 / 5*H2 (height of the liquid-liquid extraction column 1) from the bottom of the column, with a flow rate of 2.20*10 5kg / hr. Load 2 comprises 55% by weight of C6-C10 aromatics (6% by weight of A6, 12% by weight of A7, 15% by weight of A8 and 22% by weight of A9-A10) and 45% by weight of a mixture of C5-C10 paraffins and naphthenes (density of 743 kg / m³). 3 ).

[0107] Solvent 3 (dispersed phase and heavy phase) is injected at the top of the column with a flow rate of 1.76*10 6 kg / hr. Solvent 3 comprises 99% wt. Sulfolane, 0.7% wt. water and traces of hydrocarbons (density of 1225 kg / m³). 3 ).

[0108] The liquid-liquid extraction column 1 also includes a third backwash injection point 6 located at the column foot to back-extract C8+ molecules from the extract (backwash zone). The backwash liquid 6 is a hydrocarbon mixture (lighter than the feed) with a total flow rate of 8.6 x 10 4 kg / hr.

[0109] Reference Example 1

[0110] In this first example, the same plate Pj is sized for the entire liquid-liquid extraction column 1, the pressure loss of the differential element 13 being sized on the maximum flow rate, i.e. the first injection point of the charge 2. In particular, the perforated plates Pj are provided with 308 perforations of 3 cm in diameter.

[0111] The variation in height H1 of the coalesced layer 12 is shown in Figure 7 and directly follows the evolution of the (volumetric) flow rate Q c of the continuous phase within the liquid-liquid extraction column 1.

[0112] The average height H1 is 2.2 cm, with negative and positive variations of -0.8 cm and +1.9 cm, respectively. The active column height is therefore 10 m. The active height corresponds to the height at which the perforated trays are physically located and where the interphase transfer occurs. The total height of the column shell also includes areas such as settling zones, which are not part of the active height. The smaller the active height, the smaller the column can be for equivalent performance.

[0113] Furthermore, this operating mode leads to fluctuations in volumetric flow rate Q c of the continuous phase between +33% and -65% relative to the feed rate ((Q c ,i / Q c (input) / Qc (input) ■ Reference Example 2

[0114] To avoid excessively low heights H1 of the coalesced layer 12, this second reference example proposes to size the head loss of the weir 11 by considering the minimum continuous phase flow rate within the column. The perforated plate of the weir 11 has a limited number of 103 holes, each 3 cm in diameter.

[0115] The variation of the height H1 of the coalesced layer 12 is shown in Figure 8. Although the average height H1 of the coalesced layer 12 is 9.9 cm, this embodiment is not realistic insofar as, in areas of high continuous phase flow, the height H1 of the coalesced layer 12 exceeds the dimension of the free space between the plates, i.e. 34 cm.

[0116] In reference examples 1 and 2, only one type of tray Pj is considered, with the differential pressure element 13 being sized either based on the maximum or minimum continuous phase flow rate within the column. Such embodiments lead to suboptimal column operation with either: in the first case, thin coalesced layers with heterogeneity along the column – this is particularly true in areas near the top and bottom of the column where the continuous phase flow rate is up to 65% lower; in the second case, coalesced layers of excessive thickness, exceeding the value of the free space between the trays.

[0117] Example 3 according to the invention

[0118] This time, in accordance with the invention, the pressure-reducing elements 13 are differentiated by zones, allowing better control of the pressure loss within the liquid-liquid extraction column 1. In particular, 3 zones are defined with regard to the variations in continuous phase flow rates: a zone 1 between the top of the column and a height equal to 4 / 5*H2 from the bottom of the column (extraction zone); a zone 2 between said height equal to 4 / 5*H2 and the second first phase 2 injection point; and a zone 3 between the second first phase 2 injection point and the bottom of the column (backwash zone 9).

[0119] The perforated plates, constituting the deprimogen element 13, have a number of holes that vary according to the zone considered, equal to 270 in zone 1, 310 in zone 2 and 120 in zone 3.

[0120] The variation in the height H1 of the coalesced layer 12 is shown in Figure 9. This embodiment ensures an average height H1 of the coalesced layer 12 of 3.4 cm (gain +50%). The gain in tray efficiency is estimated at +13%. The active column height is estimated at 8.7 m.

[0121] Example 4 according to the invention

[0122] This last example considers an adjustment of the pressure loss over 4 zones as illustrated in Figure 10, the perforated plates having a number of holes varying according to the zone considered equal to 260 in zone 1, 300 in zone 2, 310 in zone 3 and 120 in zone 4.

[0123] This embodiment guarantees an average coalesced layer height H1 of 3.6 cm (Gain +60%) with positive variations up to three times smaller compared to the reference example 1. The gain in tray efficiency is estimated at +18%. The active column height is estimated at 8.4 m.

[0124] With reference to Table 2 below, the thicknesses of the coalesced layers in Examples 3 and 4 according to the invention are increased and more homogeneous compared to those of Example 1. Furthermore, Example 2 is not feasible. Advantageously, the invention improves the operation of the liquid-liquid extraction column 1, which consequently allows for higher extraction efficiencies and therefore a reduction in the active column height.

[0125] Table 2

Claims

1. 24 DEMANDS 1. Liquid-liquid extraction process, comprising the following steps: injecting a first phase (2), a second phase (3) and optionally a backwash liquid (6) into a liquid-liquid extraction column (1); and withdrawing an extract (4) and a raffinate (5) from the liquid-liquid extraction column (1), the liquid-liquid extraction column (1) comprising the following elements: a first injection point of the first phase (2) disposed at a position between the top and the bottom of the liquid-liquid extraction column (1); a second injection point of the second phase (3) and optionally a third injection point of the backwash liquid (6), one of said injection points being disposed at the top of the liquid-liquid extraction column (1) and the other of said injection points being disposed at the bottom of the liquid-liquid extraction column (1);a first extraction point (4) and a second extraction point (5), one of said extraction points being disposed at the bottom of the liquid-liquid extraction column (1) and the other of said extraction points being disposed at the top of the liquid-liquid extraction column (1); a plurality of trays (Pi) disposed from the top of the liquid-liquid extraction column (1) to the bottom of the liquid-liquid extraction column (1) and defining n zones, each zone comprising at least two trays (Pi), n being between 2 and 30; in which the n zones comprise: at least one extraction zone Zj included between a zone Zi comprising the second injection point of the second phase (3), and a feed zone Z; x including the first injection point of the first phase (2), x being greater than or equal to 1; and optionally at least one backwash zone included between a Z zone x +i and a Z zone nincluding the third injection point of the backwash liquid (6), n being greater than or equal to x; in which: the trays Pi of the same zone have weirs (11) in which are arranged deprimogeniting elements (13); when x is greater than 1, the ratio between the pressure loss coefficient of the deprimogen element (13) of a zone Zj and the pressure loss coefficient of the deprimogen element (13) of a zone Zj+i is between 0.8 and 8, preferably between 0.9 and 4, very preferably between 1.05 and 2.5, more preferably between 1.1 and 1.8; and optionally when x is equal to 1, the pressure loss coefficient of the deprimogen element (13) of the zone Zi is less than the pressure loss coefficient of the deprimogen element (13) of at least one backwash zone.

2. Method according to claim 1, wherein the ratio between the pressure loss coefficient of the deprimogenituring element 13 of a zone Zj and the pressure loss coefficient of the deprimogenituring element 13 of a zone Zj+i varies.

3. Method according to claim 1 or claim 2, wherein when x is greater than 1, the ratio between the pressure loss coefficient of the deprimogen element (13) of a zone Zj and the pressure loss coefficient of the deprimogen element (13) of a zone Zj+i is between 1.05 and 8, preferably between 1.05 and 5, most preferably between 1.05 and 4.0, more preferably between 1.1 and 4.

0.

4. Method according to claim 1 or claim 2, wherein when x is greater than 1, the ratio between the pressure loss coefficient of the deprimogenituring element (13) of a zone Zj and the pressure loss coefficient of the deprimogenituring element (13) of a zone Zj+i is between 0.8 and 0.95, preferably between 0.8 and 0.

9.

5. Method according to claim 1 or claim 2, where x is equal to 1, the ratio between the pressure loss coefficient of the deprimogenizing element (13) of the Zi zone and the pressure loss coefficient of the deprimogenizing element (13) of at least one backwash zone is between 0.01 and 0.9, preferably between 0.1 and 0.5, most preferably between 0.12 and 0.

25.

6. A method according to any one of the preceding claims, wherein, in the zones Zj or j varies from x+1 to n, the deprimogen element (13) is adapted so that the pressure loss coefficient decreases as the value j increases.

7. A method according to any one of the preceding claims, wherein the ratio between the pressure loss coefficient of the differential element (13) of a zone Zj and the pressure loss coefficient Ç i+i The differential pressure of the element (13) of a zone Zj+i is a function of the flow rate variation of the continuous phase as described by the following formula: Math. 8 in which Q c is the flow rate of the continuous phase and A is a constant between 0.8 and 3.0, preferably between 0.9 and 2.

0.

8. A method according to any one of the preceding claims, wherein the ratio between the pressure loss coefficient Çx of the differential element (13) of the Z zone x on the pressure loss coefficient § of the differential element (13) of a zone Zj is a function of the flow rate variation of the continuous phase as described by the following formula: Math. 9 in which Qc is the flow rate of the continuous phase and A is a constant between 0.8 and 3.0, preferably between 0.9 and 2.

0.

9. A method according to any one of the preceding claims, wherein the ratio between the pressure loss coefficient of the differential element (13) of a zone Zj and the pressure loss coefficient Ç j+i The differential pressure of the element (13) of a zone Zj+i is a function of the flow rate variation of the continuous phase as described by the following formula: Math. 10 in which Q c is the flow rate of the continuous phase and A is a constant between 0.8 and 3.0, preferably between 0.9 and 2.

0.

10. A method according to any one of the preceding claims, wherein the pressure loss coefficient varies from one zone to another by modifying the passage section of the differential element (13).

11. Liquid-liquid extraction column (1) comprising the following elements: - a first injection point of a first phase (2) disposed at a position between the top and the bottom of the liquid-liquid extraction column (1); 27 a second injection point of a second phase (3) and optionally a third injection point of a backwash liquid (6), one of said injection points being disposed at the top of the liquid-liquid extraction column (1) and the other of said injection points being disposed at the bottom of the liquid-liquid extraction column (1); a first withdrawal point of an extract (4) and a second withdrawal point of a raffinate (5), one of said withdrawal points being disposed at the bottom of the liquid-liquid extraction column (1) and the other of said withdrawal points being disposed at the top of the liquid-liquid extraction column (1); a plurality of trays (Pi) disposed from the top of the liquid-liquid extraction column (1) to the bottom of the liquid-liquid extraction column (1) and defining n zones, each zone comprising at least two trays (Pi), n being between 2 and 30;in which the n zones comprise: at least one extraction zone Zj included between a zone Zi comprising the second injection point of the second phase (3), and a supply zone Z; x including the first injection point of the first phase (2), x being greater than or equal to 1; and optionally at least one backwash zone included between a Z zone x +i and a Z zone n including the third backwash injection point (6), n being greater than or equal to x; wherein: the trays Pi of the same zone have weirs (11) in which are arranged pressure-reducing elements (13); when x is greater than 1, the ratio between the cross-sectional area of ​​the pressure-reducing element (13) of a zone Zj and the cross-sectional area of ​​the pressure-reducing element (13) of a zone Z i+i, is between 0.12 and 3.0, preferably between 0.25 and 1.25, very preferably between 0.40 and 0.95, more preferably between 0.55 and 0.90; and optionally when x is equal to 1, the passage section of the deprimogen element (13) of the at least one backwash zone is less than the passage section of the passage section (of the continuous phase) of the deprimogen element (13) of the Zi zone.

12. Column according to claim 11, in which the ratio between the passage section of the deprimogen element (13) of a zone Zj and the passage section of the deprimogen element (13) of a zone Zj+i varies.

13. Column according to claim 11 or claim 12, wherein, when x is greater than 1, the ratio between the cross-sectional area of ​​the deprimogenic element (13) of a zone Zj and the cross-sectional area of ​​the deprimogenic element (13) of a zone Z i+i, is between 0.12 and 0.98, preferably between 0.25 and 0.95, very preferably between 0.40 and 0.95, more preferably between 0.55 and 0.90 or between 0.70 and 0.

90.

14. Column according to claim 11 or claim 12, wherein when x is greater than 1, the ratio between the cross-section of the deprimogenizing element 13 of a zone Zj and the cross-section of the deprimogenizing element 13 of a zone Zj+i is between 1.05 and 1.25, preferably between 1.05 and 1.

11.

15. Column according to claim 11 or claim 12, wherein when x is equal to 1, the ratio between the cross-section of the deprimogen element 13 of the Zi zone and the cross-section of the deprimogen element 13 of at least one backwash zone is between 1.1 and 11, preferably between 1.5 and 5, most preferably between 1.8 and 3.0.

Images