Liquid-liquid extraction column with variable inter-plate spacing

Abstract

Liquid-liquid extraction column (1) comprising feed injection points (2), washing points (3), and backwash points (4), two withdrawal points (5, 6), and trays (Pi) arranged along the column defining 2 to 30 zones, each comprising at least two trays. The n zones comprise: at least one extraction zone Zi including zones Z1 to Zx, where x is greater than or equal to 1, and at least one backwash zone including zones Zx+1 to Zn, where n is greater than x; wherein the trays in the same zone have the same inter-tray height H (10); wherein, when x > 1, the height H of the Zi zones increases as i increases; and when x = 1, the height H of at least one backwash zone is less than the height H of zone Z1. Figure 4 to be published

Description

Title of the invention: Liquid-liquid extraction column with variable inter-plate spacing technical field

[0001] The field of the invention relates to 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. Previous technique

[0002] A liquid-liquid extraction operation is a key component of processes for separating hydrocarbon fractions, such as the separation of a mixture of aromatics and non-aromatics. The operating principle is based on the differences in solubility of the compounds in a homogeneous liquid 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 formation of a second phase into which some of the compounds (e.g., the aromatic compounds), the most soluble constituents, are preferentially transferred.

[0003] Typically, liquid-liquid extraction technology implements a liquid-liquid separation column comprising a plurality of perforated trays equipped with one or more weirs per tray depending on the capacities targeted (we speak of a 1 or 2 pass tray or multi-pass beyond 3 weirs).

[0004] The design rules for a conventional liquid-liquid extraction column consider a reference tray dimensioned based on the maximum flow rates of each phase and their physicochemical properties. This design is then implemented for the entire column by stacking a plurality of trays, the trays thus all being substantially identical.

[0005] The applicant has identified, however, that the operation of a liquid-liquid extraction column can generate a great deal of variability, depending in particular on - the flow rate of each phase along the column - this phenomenon is linked, on the one hand, to the transfer of matter from the solutes in the feed to the solvent and, on the other hand, to the possibility of modulating the backwash flow rate according to the nature of the feed and the specifications required; and - physicochemical properties, and in particular the interfacial tension between the feed and the solvent related to the progressive enrichment in compounds extracted from the feed towards the solvent.

[0006] The present invention aims to remedy the deficiencies mentioned above. Summary of the invention

[0007] In the context described above, a first objective of this description is to propose a liquid-liquid extraction column enabling: - to maintain a range of between 5% and 20% of the average volume fraction of dispersed phase (i.e., solvent / heavy phase) in a compartment (i.e., area comprising a perforated tray and an adjacent inter-tray space); - the non-entrainment of dispersed phase droplets in the weirs by the continuous phase (i.e., charge / light phase) in order to limit the axial mixing of the dispersed phase; - a coalesced layer height of the dispersed phase on each tray sufficient to prevent the continuous phase from passing through the perforated tray (and to force the exclusive passage of the continuous phase into the weirs); - a suitable continuous phase transverse velocity, which does not disturb the flow of the dispersed phase.

[0008] Surprisingly, the applicant identified that specific characteristics of perforated trays, such as the height of the inter-tray spaces, make it possible to control the hydrodynamics along the entire length of the column by limiting axial mixing. This technical solution makes it possible to maintain satisfactory mass transfer efficiency on each tray.

[0009] According to a first aspect, the aforementioned objects, as well as other advantages, are obtained by a liquid-liquid extraction column, comprising the following elements: - a first injection point of a first phase located at an intermediate position between the top and bottom of the column; - a second injection point for a second phase and a third injection point for a backwash liquid, one (of the second and third injection points) being located at the top of the column and the other being located at the bottom of the column; - a first extraction point for an extract and a second extraction point for a refinement, one (of the first and second extraction points) being located at the bottom of the column and the other being located at the top of the column; - a plurality of trays arranged from the top of the column to the bottom of the column and defining n zones, each zone comprising at least two trays, n being between 2 and 30, preferably between 3 and 30; in which the n zones comprise: - at least one extraction zone Zj situated between a zone (e.g., column head) Z i comprising the second injection point of the second phase, and a feed zone Zx comprising the first injection point of the first phase, x being greater than or equal to 1 (preferably x is greater than 1); and - at least one backwash zone included between a Zx+i zone and a zone (e.g. bottom of column) Zn including the third injection point of the backwash liquid, n being greater than x; in which the plateaus of the same zone have approximately the same height H of inter-plateau space; and in which: - when x is greater than 1, the height H of the inter-plateau spaces of the Z zones increases as the value i increases; and - when x equals 1, the height H of the inter-plate spaces of at least one backwash zone is less than the height H of the inter-plate spaces of zone Zb

[0010] . According to one or more embodiments, n is between 3 and 30, and x is greater than 1.

[0011] According to one or more embodiments, the liquid-liquid extraction column comprises the following elements: - a first injection point of a first phase located at an intermediate position between the top and bottom of the column; - a second injection point for a second phase located at the top of the column; - a third injection point for a backwash liquid located at the bottom of the column; - a first point of extraction of an extract placed at the bottom of the column; - a second point for drawing off a refinery arranged at the top of the column; - a plurality of trays arranged from the top of the column to the bottom of the column and defining n zones, each zone comprising at least two trays, n being between 3 and 30; in which the n zones comprise: - a plurality of extraction zones Z comprising between a column head zone Zi including the second injection point of the second phase, and a feed zone Zx including the first injection point of the first phase, x being greater than 1; and - at least one backwash zone included between a Zx+[ zone and a column bottom zone Zn including the third injection point of the backwash liquid, n being greater than x; in which the plateaus of the same area exhibit essentially the same height H of the inter-platform space; and in which the height H of the inter-plateau spaces of the Zj zones increases when the value i increases.

[0012] According to one or more embodiments, in the extraction zones Zj or i varies from 1 to x (i.e., x greater than 1), the ratio between the height H of an inter-plateau space of a zone Zj and the height H of an inter-plateau space of a zone Zi+b is between 0.20 and 0.95.

[0013] According to one or more embodiments, in the extraction zones Zj or i varies from 1 to x (i.e., x greater than 1), the ratio between the height H of an inter-plateau space of a zone Zj and the height H of an inter-plateau space of a zone Zi+b is between 0.40 and 0.90.

[0014] According to one or more embodiments, in the extraction zones Zj or i varies from 1 to x (i.e., x greater than 1), the ratio between the height H of an inter-plateau space of a zone Zi and the height H of an inter-plateau space of a zone Zi+b is between 0.75 and 0.85.

[0015] According to one or more embodiments, when x is equal to 1, the ratio between the height H of an inter-plate space of at least one backwash zone and the height H of the inter-plate space of zone Zb is between 0.20 and 0.95.

[0016] According to one or more embodiments, the at least one backwash zone is a plurality of zones, from a zone Zx+[ to the zone (e.g. bottom of column) Zn, and in which the height H of the inter-plate spaces increases, is constant, or decreases from the zone Zx+[ to the zone Zn.

[0017] According to one or more embodiments, the at least one backwash zone is a plurality of zones subdivided into: - a plurality of zones Zj contained between the zone Zx+[ and a zone Zy, y being greater than x+1; and - a plurality of Zk zones located between the Zy+ zone and the (e.g., column bottom) Zn zone, and in which: - in zones Zj where j varies from x+1 to y, the height H of the inter-plateau spaces increases, is constant, or decreases when the value j increases; and / or - in the zones Zk or k varies from y+1 to n, the height H of the inter-plateau spaces increases, is constant, or decreases when the value k increases.

[0018] According to one or more embodiments, in the zones Zj or j varies from x+1 to y, the ratio between the height H of the inter-platform spaces of a zone Zj and the height H of the inter-platform spaces of a zone Zj+b is between 0.20 and 0.95.

[0019] According to one or more embodiments, in zones Zj or j, the ratio between the height H of the inter-platform spaces of a zone Zj and the height H of the inter-plateau spaces of a zone Zj+b is between 1.10 and 2.0.

[0020] According to one or more embodiments, in the zones Zk or k varies from y+1 to n, the ratio between the height H of the inter-platform spaces of a zone Zk and the height H of the inter-platform spaces of a zone Zk+b is between 0.20 and 0.95.

[0021] According to one or more embodiments, in the zones Zk or k varies from y+1 to n, the ratio between the height H of the inter-platform spaces of a zone Zk and the height H of the inter-platform spaces of a zone Zk+b is between 1.10 and 2.0.

[0022] According to one or more embodiments, the number of Z zones is between 2 and 10 and / or the number of backwash zones is between 1 and 10.

[0023] According to one or more embodiments, the number of zones Zj is between 2 and 10 and / or the number of zones Zk is between 2 and 10.

[0024] According to one or more embodiments, the height H of the inter-plate spaces of the backwashing zone Zx+i is less than, equal to or greater than the height H of the inter-plate spaces of the extraction zone Zx.

[0025] According to one or more embodiments, the height H of the inter-plate spaces of the backwashing zone Zx+[ is less than the height H of the inter-plate spaces of the extraction zone Zx.

[0026] According to one or more embodiments, the height H of each inter-platform space is between 0.2 m and 1.2 m.

[0027] Embodiments of the liquid-liquid extraction column according to the first aspect, as well as other features and advantages, will become apparent from the following description, given by way of illustration only and not limitation, and with reference to the following drawings. List of figures

[0028] Fig. 1 schematically shows a cross-sectional view of a liquid-liquid extraction column according to the present invention.

[0029] Fig. 2 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.

[0030] Fig. 3 schematically shows a cross-sectional view of a liquid-liquid extraction column according to the present invention defined by a plurality of Z zones between the column head zone 1 and the feed zone Zx, a plurality of Zj zones between the Zx+i zone and a Zy zone, and a plurality of Zk zones between the Zy+i zone and the column bottom zone Zn.

[0031] Fig. 4 is a graph showing the evolution of the transverse interplate velocity of the continuous phase along a liquid-liquid extraction column according to the present invention, in which the height H of the interplate spaces is variable.

[0032] Fig. 5 and Fig. 6 are graphs showing the evolution of the transverse inter-plate velocity of the continuous phase along reference liquid-liquid extraction columns in which the height H of the inter-plate spaces is constant. Description of the implementation methods

[0033] Embodiments of the invention will now be described in detail. In the following detailed description, many specific details are set forth 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.

[0034] 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.

[0035] With reference to [Fig. 1], a liquid-liquid extraction column 1 comprises the following elements: - a first injection point of 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), arranged at an intermediate position between the top and bottom of column 1; - a second injection point of a second phase 3 (or separation liquid), such as a solvent (e.g. Sulfolane), arranged at the top of column 1; - a third injection point of a backwash liquid 4, 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), disposed at the bottom of column 1; - a first withdrawal point of an extract 5 (in liquid phase), such as a solvent enriched in extracted compounds (e.g., aromatic compounds), located at the bottom of column 1; and - a second withdrawal point of a raffinate 6 (in liquid phase), such as a feed depleted in extracted compounds, arranged at the top of column 1.

[0036] Furthermore, in order to increase efficiency and purity, two distinct operating zones are defined opposite the injection point of the liquid to be separated 2: - an extraction sector 7, extending substantially from the first injection point of the The first phase 2, up to approximately 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 contact with the separation liquid 3 in a counter-current flow (the so-called yield zone), and - a backwash sector 8 (or backwash according to English terminology), adjacent to the extraction sector 7 and extending to substantially the third injection point of the backwash liquid 4, allows in particular to back-extract undesired compounds (e.g. heavy non-aromatics) contained in the extract 5 by the backwash liquid 4 in order to guarantee a high level of purity.

[0037] Specifically, with reference to [Fig. 1], the separation liquid exits column 1, carrying with it compounds of interest to be separated (e.g., aromatics) to form extract 5. The extract may also contain undesired compounds (e.g., light non-aromatics, such as C6-C7s) which can be separated downstream (e.g., by distillation and / or stripping). Advantageously, extract 5 contains no (or very few) undesired 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 8. With reference to [Fig. 1], 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 4 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 is lighter than the liquid to be separated 2, the injection point of the separation liquid 3 is at the bottom of column 1 and the injection point of the backwash liquid 4 is at the top of column 1.

[0038] With reference to [Fig. 2], a two-pass liquid-liquid extraction column 1 comprises n perforated trays P, i being between 1 and n. Each perforated tray P is arranged so that the dispersed phase (i.e., the separation liquid 3, which is heavier than the liquid to be separated 2) flows through the holes 9 of the perforated tray P, the droplets of the dispersed phase recoaling on the next perforated tray P1+i to form a liquid volume preventing the passage of the continuous phase (i.e., the liquid to be separated 2, which is lighter than the separation liquid 3) through the perforated tray P1+i. The liquid to be separated 2 flows counter-currently to the separation liquid 3, i.e., from bottom to top through the central weirs 11 and peripheral weirs 12 of cross-sectional area Sc and SP, respectively, and transversely in an inter-tray space 10 of height H. With reference to [Fig.2], 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.

[0039] According to one or more embodiments, the perforated plates P; are single-pass plates (e.g., one type of weir) or two-pass plates (e.g., two types of weirs) or multi-pass.

[0040] The applicant has identified that the operation of a liquid-liquid extraction column can generate significant variations in flow rate and physico-chemical 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.

[0041] According to the invention, with reference to [Fig. 3], a liquid-liquid extraction column 1 is further defined by: - at least one extraction zone Zi5 and preferably a plurality of extraction zones Zi5 defining the extraction sector 7, 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 Zx comprising the first injection point of the first phase 2, x being greater than or equal to 1, preferably x being greater than 1; and - at least one backwash zone defining the backwash sector 8, i.e., the backwash zone(s) is or are located between the Zx+[ zone and the column bottom zone Zn including the third backwash liquid injection point 4, n being greater than x.

[0042] According to the invention, each extraction and backwash zone comprises at least two trays, each extraction and backwash zone defining the structural characteristics of the inter-tray spaces present in said extraction and backwash zones. Thus, according to the invention, the trays P of the same extraction or backwash zone have substantially the same inter-tray space height H 10.

[0043] According to one or more embodiments, with reference to [Fig.3], the at least one backwash zone is a plurality of zones, said plurality of zones starting from the Zx+i zone to the column bottom zone Zn.

[0044] According to one or more embodiments, with reference to [Fig. 3], the at least one backwash zone is a plurality of zones subdivided into: - a plurality of zones Zj contained between the zone Zx+i and a zone Zy, y being greater than x+1; and - a plurality of Zk zones located between the Zy+i zone and the Zn column bottom zone.

[0045] Advantageously, the number of zones Z, Zj and Zk can be defined with regard to the variability of flow and the physico-chemical properties of the phase passing through said zones Z, Zj and Zk.

[0046] 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 that between 4 and 18, in particular between 4 and 8.

[0047] In the present description, i, j, k, x, y and n are natural integers.

[0048] The number of extraction zones Z can be defined with respect to the phase which presents the greatest variability of flow rate in the column. According to one or more embodiments, the number of Z zones (number of zones Zi to Zx) is between 1 and 10, preferably between 2 and 10, most preferably between 2 and 6, such as between 2 and 4.

[0049] The number of backwash zones can be defined with respect to the phase exhibiting the greatest flow variability in the column. According to one or more embodiments, the number of backwash zones (number of zones Zx+i to Zn) 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 zones Zx+[ to Zn) is greater than or equal to 2.

[0050] The number of zones Zj can be defined with respect to the phase that exhibits the greatest flow variability in the column. According to one or more embodiments, the number of zones Zj (number of zones Zx+[ to Zy]) is between 2 and 10, preferably between 2 and 6, most preferably between 2 and 4.

[0051] The number of Zk zones can be defined with respect to the phase that exhibits the greatest flow variability in the column. According to one or more embodiments, the number of Zk zones (number of Zy+i to Zn zones) is between 2 and 10, preferably between 2 and 6, and most preferably between 2 and 4.

[0052] According to one or more embodiments, the number of trays per zone Z, Zj and Zk can be determined by the number of actual floors required for separation divided by the number of zones Z, Zj and Zk.

[0053] Control of the continuous phase flow rate variation by optimized inter-plate space design

[0054] Advantageously, the liquid-liquid extraction column 1 according to the invention comprises inter-plate spaces 10 with variable height H such that the transverse velocity (orthogonal to the central axis Z of the column) of the continuous phase remains substantially constant within the column. Indeed, due to the fluctuation of the continuous phase flow rate as it passes through the column, varying the height H of the inter-plate spaces 10 allows for a more homogeneous distribution of the continuous phase within the inter-plate space 10, thereby avoiding recirculations and dead volumes, while limiting the deformation of the dispersed phase flow. This solution also reduces axial mixing of the continuous and dispersed phases.

[0055] Specifically, in order to maintain a substantially constant transverse velocity of the continuous phase, the liquid-liquid extraction column 1 according to the invention is divided into: - x extraction zones Z, and - nx backwash zones.

[0056] According to one or more embodiments, the backwashing zones are divided into: - Y zones Zj arranged from the zone Zx+i adjacent to the supply zone Zx, up to a zone Zy, for example where the height ratio between two consecutive zones Hj / Hj+i remains less than l, and - N zones Zkdont les zone Zy+i à Zn.

[0057] According to the invention, when x is equal to 1, the height H of the inter-plate spaces 10 of at least one backwash zone (e.g. zone Z2) is less than the height H of the inter-plate spaces 10 of zone Zb. According to one or more embodiments, when x is equal to 1, the ratio between the height H of an inter-plate space 10 of at least one backwash zone (e.g. zone Z2) and the height H of the inter-plate space 10 of zone Zb is between 0.20 and 0.95, preferably between 0.40 and 0.90, most preferably between 0.75 and 0.85.

[0058] According to the invention, when x is greater than 1, in extraction zones Z or i varies from 1 to x (in the extraction sector 7), the height H of the inter-plateau spaces 10 increases as the value i increases. According to one or more embodiments, in zones Z or i varies from 1 to x, the ratio between the height H of an inter-plateau space 10 of a zone Z and the height H of an inter-plateau space 10 of a zone Z i+i is between 0.20 and 0.95, preferably between 0.40 and 0.90, most preferably between 0.75 and 0.85.

[0059] According to one or more embodiments, the at least one backwash zone comprises a plurality of zones, i.e., from the Zx+[ zone to the bottom of column zone Zn, and the height H of an inter-plate space 10 increases from the Zx+[ zone to the bottom of column zone Zn.

[0060] According to one or more embodiments, the at least one backwash zone comprises a plurality of zones, i.e., from the Zx+[ zone to the bottom of column zone Zn, and the height H of an inter-plate space 10 is constant from the Zx+[ zone to the bottom of column zone Zn.

[0061] According to one or more embodiments, the at least one backwash zone comprises a plurality of zones, i.e., from the Zx+[ zone to the bottom of column zone Zn, and the height H of an inter-plate space 10 decreases from the Zx+[ zone to the bottom of column zone Zn.

[0062] According to one or more embodiments, in zones Zj where j varies from x+1 to y (in the backwash zone 8), the height H of the inter-plate spaces 10 increases as the value j increases. According to one or more embodiments, in zones Zj where j varies from x+1 to y, the ratio between the height H of an inter-plate space plateaus 10 of a zone Zj on the height H of an inter-plateau space 10 of a zone Z j+1, is between 0.20 and 0.95, preferably between 0.40 and 0.90, very preferably between 0.75 and 0.85.

[0063] According to one or more embodiments, in the zones Zj or j varies from x+1 to y (in the backwash zone 8), the height H of the inter-plate spaces 10 is constant.

[0064] According to one or more embodiments, in zones Zj where j varies from x+1 to y (in the backwash zone 8), the height H of the inter-plate spaces 10 decreases as the value j increases. According to one or more embodiments, in zones Zj where j varies from x+1 to y, the ratio between the height H of an inter-plate space 10 of a zone Zj and the height H of an inter-plate space 10 of a zone Zj+b is between 1.10 and 2.0, preferably between 1.20 and 1.60, most preferably between 1.25 and 1.50.

[0065] According to one or more embodiments, in zones Zk where k varies from y+1 to n (in the backwash sector 8), the height H of the inter-plate spaces 10 increases as the value k increases. According to one or more embodiments, in zones Zk where k varies from y+1 to n, the ratio between the height H of an inter-plate space 10 of a zone Zk and the height H of an inter-plate space 10 of a zone Zk+i is between 0.20 and 0.95, preferably between 0.40 and 0.90, and most preferably between 0.75 and 0.85.

[0066] According to one or more embodiments, in the zones Zk or k varies from y+1 to n (in the backwash zone 8), the height H of the inter-plate spaces 10 is constant.

[0067] According to one or more embodiments, in zones Zk where k varies from y+1 to n (in the backwash sector 8), the height H of the inter-plate spaces 10 decreases as the value k increases. According to one or more embodiments, in zones Zk where k varies from y+1 to n, the ratio between the height H of an inter-plate space 10 of a zone Zk and the height H of an inter-plate space 10 of a zone Zk+i is between 1.10 and 2.0, preferably between 1.20 and 1.60, and most preferably between 1.25 and 1.50.

[0068] According to one or more embodiments, in the zones Zj where j varies from x+1 to y, the height H of the inter-platform spaces 10 decreases when the value j increases; and in the zones Zk where k varies from y+1 to n, the height H of the inter-platform spaces 10 increases when the value k increases.

[0069] According to one or more embodiments, in the zones Zj where j varies from x+1 to y, the height H of the inter-platform spaces 10 increases when the value j increases; and in the zones Zk where k varies from y+1 to n, the height H of the inter-platform spaces 10 decreases when the value k increases.

[0070] According to one or more embodiments, the height H of the inter-plate spaces 10 of the backwash zone Zx+i is greater than, equal to, or less than the height H of the inter-plate spaces 10 of the extraction zone Zx. According to one or more embodiments, the height H of the inter-plate spaces 10 of the backwash zone Zx+i is less than the height H of the inter-plate spaces 10 of the extraction zone Zx. According to one or more embodiments, the ratio between the height H of the inter-plate space 10 of the zone Zx+i and the height H of the inter-plate space 10 of the zone Zx is between 0.20 and 0.95, preferably between 0.40 and 0.90, and most preferably between 0.75 and 0.85.

[0071] According to one or more embodiments, the height H of each inter-platform space 10 is between 0.2 m and 1.2 m, preferably between 0.3 m and 0.7 m, very preferably between 0.3 m and 0.5 m. Examples

[0072] Example 1: Liquid-liquid extraction column with variable inter-plate spacing

[0073] This example aims to describe the effect of adjusting the inter-plateau space on the homogeneity of the velocities of the continuous phase at this level.

[0074] The column has a diameter of 4.9 m and comprises a series of 118 perforated trays. The feedstock is injected at intermediate tray No. 71. The heavy solvent is injected at the top of the column at tray 1. The counter-solvent is injected at the bottom of the column at tray 118.

[0075] 3 zones are defined to adjust the inter-plateau space to variations in flow rate of the continuous phase along the column: - the first zone Zb is between plateau 1 to 48: the inter-platform space has a height H1 of 0.37 m, the rest of the geometry being unchanged; - the second zone Z2, is located between plateau 49 and 71: the inter-plateau space is increased to a height H2 of 0.44 m, in relation to the increased flow rate of the continuous phase, zones Zi and Z2 corresponding to extraction sector 7; and - the third zone Z3, is between platform 72 to 118: this zone corresponds to the backwash sector 8, the inter-platform space being of height H3 of 0.30 m.

[0076] In the extraction sector 7 between the head tray x =1 and the feed tray x = 71, the height H of the inter-tray space 10 of the zone Zi is less than the height H of an inter-tray space 10 of a zone Z2: the ratio between the height H of the inter-tray space 10 of the zone Zi and the height H of the inter-tray space 10 of the zone Z2 is equal to 0.84.

[0077] Figure 4 illustrates the technical effect of this adjustment: it ensures homogeneity of hydraulic operation along the column: the phase velocity The continuous inter-plateau flow rate is always within an optimal range. This solution ensures consistent performance regardless of flow rate variations in the continuous phase along the column, while also guaranteeing an optimized column height.

[0078] Counterexample 2: Liquid-liquid extraction column with constant inter-plate spacing

[0079] The column has a diameter of 4.9 m, a height of 42 m, and is composed of a series of 118 perforated trays. The feedstock is injected at intermediate tray No. 71. The heavy solvent is injected at the top of the column at tray 1. The counter-solvent is injected at the bottom of the column at tray 118.

[0080] No adjustment is implemented: the inter-platform space is constant (H = 0.3 m) and the characteristics of the platforms are identical at every point.

[0081] Fig. 5 illustrates that, without adjustment of the inter-plateau space, the transverse velocity of the continuous phase can exceed the maximum target values ​​and thus degrade the efficiency of the platters 13 to 71, maximum target values ​​beyond which the transverse velocity disturbs in particular the flow of the dispersed phase and causes droplets of dispersed phase.

[0082] In order to overcome the difficulty of transverse speed exceeding the maximum target values, the height of the inter-plateau space is increased (H of 0.44 m) at every point of the column: such a solution is illustrated in [Fig.6]; it leads to an increase in column height of 25%.

Claims

Demands

1. Liquid-liquid extraction column (1) comprising the following elements: - a first injection point for a first phase (2) disposed at an intermediate position between the top and bottom of the column (1); - a second injection point for a second phase (3) and a third injection point for a backwash liquid (4), one being disposed at the top of the column (1) and the other being disposed at the bottom of the column (1); - a first withdrawal point for an extract (5) and a second withdrawal point for a raffinate (6), one being disposed at the bottom of the column (1) and the other being disposed at the top of the column (1); - a plurality of trays (Pi) disposed from the top of the column (1) to the bottom of the column (1) and defining n zones, each zone comprising at least two trays (Pi), n being between 2 and 30; wherein the n zones comprise: - at least one extraction zone Z;comprising between a zone Zi including the second injection point of the second phase (3), and a supply zone Zx including the first injection point of the first phase (2), x being greater than or equal to 1; and - at least one backwash zone comprising between a zone Zx+i and a zone Zn including the third injection point of the backwash liquid (4), n being greater than x; in which the trays (Pi) of the same zone have the same height H of inter-tray space (10); and in which: - when x is greater than 1, the height H of the inter-tray spaces (10) of the zones Zi increases as the value i increases; and - when x is equal to 1, the height H of the inter-tray spaces (10) of the at least one backwash zone is less than the height H of the inter-tray spaces (10) of the zone Zb;

2. Liquid-liquid extraction column (1) according to claim 1, wherein n is between 3 and 30, and x is greater than 1.

3. Liquid-liquid extraction column (1) according to claim 1 or claim 2, wherein, in extraction zones Z; or i varies from 1 to x, the ratio between the height H of an inter-plate space (10) of a zone Z; to the height H of an inter-plate space (10) of a zone Zi+b is between 0.20 and 0.

95.

4. Liquid-liquid extraction column (1) according to any one of the preceding claims, wherein, in extraction zones Zj or i varies from 1 to x, the ratio between the height H of an inter-plate space (10) of a zone Z and the height H of an inter-plate space (10) of a zone Zi+b is between 0.40 and 0.

90.

5. Liquid-liquid extraction column (1) according to any one of the preceding claims, wherein, when x is equal to 1, the ratio between the height H of an inter-plate space 10 of at least one backwash zone and the height H of the inter-plate space 10 of zone Zb is between 0.20 and 0.

95.

6. Liquid-liquid extraction column (1) according to any one of the preceding claims, wherein the at least one backwash zone is a plurality of zones, from a zone Zx+[ to the zone Zn, and wherein the height H of the inter-plate spaces (10) increases, is constant, or decreases from the zone Zx+[ to the zone Zn.

7. Liquid-liquid extraction column (1) according to any one of the preceding claims, wherein at least one backwash zone is a plurality of zones subdivided into: - a plurality of zones Zj comprising between zone Zx+1 and a zone Zy, y being greater than x+1; and - a plurality of zones Zk comprising between zone Zy+1 and zone Zn, and wherein: - in zones Zj where j varies from x+1 to y, the height H of the interplate spaces (10) increases, is constant, or decreases when the value j increases; and / or - in zones Zk where k varies from y+1 to n, the height H of the interplate spaces (10) increases, is constant, or decreases when the value k increases.

8. Liquid-liquid extraction column (1) according to claim 7, wherein, in the zones Zj or j varies from x+1 to y, the ratio between the height H of the inter-plate spaces (10) of a zone Zj and the height H of the inter-plate spaces (10) of a zone Zj+i is between 0.20 and 0.

95.

9. Liquid-liquid extraction column (1) according to claim 7, wherein, in zones Zj or j varies from x+1 to y, the ratio between the height H of the inter-plate spaces (10) of a zone Zj and the height H of the inter-plate spaces (10) of a zone Zj+i is between 1.10 and 2.

0.

10. Liquid-liquid extraction column (1) according to any one of claims 7 to 9, wherein, in the zones Zk or k varies from y+1 to n, the ratio between the height H of the inter-plate spaces (10) of a zone Zk and the height H of the inter-plate spaces (10) of a zone Zk+i is between 0.20 and 0.

95.

11. Liquid-liquid extraction column (1) according to any one of claims 7 to 9, wherein, in the zones Zk or k varies from y+1 to n, the ratio between the height H of the inter-plate spaces (10) of a zone Zk and the height H of the inter-plate spaces (10) of a zone Zk+i is between 1.10 and 2.

0.

12. Liquid-liquid extraction column (1) according to any one of the preceding claims, wherein the number of Z zones is between 2 and 10 and / or the number of backwash zones is between 1 and 10.

13. Liquid-liquid extraction column (1) according to any one of claims 7 to 12, wherein the number of zones Zj is between 2 and 10 and / or the number of zones Zk is between 2 and 10.

14. Liquid-liquid extraction column (1) according to any one of the preceding claims, wherein the height H of the interplate spaces (10) of the backwash zone Zx+i is less than, equal to or greater than the height H of the interplate spaces (10) of the extraction zone Zx.

15. Liquid-liquid extraction column (1) according to any one of the preceding claims, wherein the height H of each inter-plate space (10) is between 0.2 m and 1.2 m.

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