Extraction column with alternating compartment heights
Patent Information
- Authority / Receiving Office
- ES · ES
- Patent Type
- Patents
- Current Assignee / Owner
- IFP ENERGIES NOUVELLES
- Filing Date
- 2023-04-26
- Publication Date
- 2026-07-09
Smart Images
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Abstract
Description
technical field
[0001] The field of the invention relates to liquid-liquid extraction in perforated tray columns with weirs, such as those used in numerous chemical processes, including the extraction of aromatics present in various petroleum fractions or from refining processes. Liquid-liquid extraction columns are particularly suitable for the liquid-liquid separation of hydrocarbon compounds, such as aromatic compounds (e.g., A6-A11) from extended hydrocarbon fractions (e.g., C6-C11 fraction), such as those from a Fluid Catalytic Cracking (FCC) unit. Previous technique
[0002] The operating principle of liquid-liquid extraction columns is based on the differences in solubility of 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 to which some of the compounds (e.g., aromatic compounds), the most soluble constituents, are preferentially transferred.
[0003] With reference to the figure 1 A liquid-liquid extraction column 1 comprises the following elements: a first injection point 2 of a first phase (liquid feed to be separated); a second injection point 3 of a second phase (liquid separation solvent), the first and second injection points 2 and 3 being arranged to allow the first and second phases to flow counter-currently; a first withdrawal point of an extract 4 (in liquid phase), such as a solvent enriched in compounds extracted from the feed; and a second withdrawal point of a raffinate 5 (in liquid phase), such as a feed depleted in extracted compounds, one of the first and second withdrawal points being arranged at the bottom of the extraction column 1 and the other at the top of the extraction column 1. In addition, the first injection point 2 of the feed to be separated is typically arranged between the second injection point 3 of the liquid separation solvent and the first withdrawal point of the extract 4.Similarly, the second injection point 3 of the liquid separating solvent is typically arranged between the first injection point 2 of the feed to be separated and the second withdrawal point of the raffinate 5. In this reference example, the first phase is the light phase and the second phase is the heavy phase.
[0004] With reference to the figure 2 , a liquid-liquid extraction column 1 comprises a plurality of perforated trays P, each perforated tray P being equipped with one or more weirs 6 depending on the capacities targeted, a weir 6 being a recess allowing the passage of the first phase A called "continue" through the perforated plate P. A perforated plate P includes at least one area perforated with holes 7, through which the second phase B, called "dispersed".The second dispersed phase B circulates as droplets passing through the first continuous phase A in each inter-plate space 8 defined by the space between two adjacent perforated plates P. In the example of the figure 2 The second dispersed phase B is the heavy phase and accumulates above the perforated tray P, forming a coalesced layer 9 above the perforated area. This coalesced layer 9 is typically 1 cm to 8 cm thick. It is understood that if the dispersed phase is the light phase, it accumulates below the perforated tray. The second dispersed phase B then flows through the perforated area of the perforated tray P to feed the next perforated tray P (the lower tray if the dispersed phase is the heavy phase), and so on. The first continuous phase A meanders through the inter-tray spaces 8 via the weirs 6, upwards in this example of the figure 2because the continuous phase is the light phase.
[0005] US patents 3,632,315 and 4,588,563 describe examples of liquid-liquid extraction columns comprising perforated trays equipped with one and / or two weirs.
[0006] Thus, a liquid-liquid extraction column allows two partially immiscible liquid phases, A and B, to be brought into contact in a counter-current flow. Depending on the choice of the dispersed phase (heavy or light), the perforated tray P is adapted to accommodate (by means of rims 10) the coalesced layer 9 on the upper part of the perforated tray (dispersed phase being the heavy phase) or on the lower part (dispersed phase being the light phase). In the figures in this description, only the case of the separating liquid solvent being the dispersed phase and the heavy phase is shown.
[0007] The applicant identified that the operation of a liquid-liquid extraction column can generate significant variability in performance, depending in particular on: the interfacial area between the phases in the inter-plate spaces, which depends on the size of the drops of the dispersed phase and their volume fraction; and the flow of each phase in the inter-plate spaces, weirs and perforated areas.
[0008] It is well known to those skilled in the art, and thoroughly described in liquid-liquid extraction textbooks (see Handbook of Solvent Extraction, by Lo, Baird, and Hanson, Krieger Publishing Company, 1991), that plug flow of each phase is favorable to transfer performance in countercurrent extraction columns. Plug flow is a classic concept that considers that, over a given column cross-section, each phase (heavy or light) flows at a uniform velocity and in a single direction. It is also known that any recirculation, vortex, or other liquid movement that generates a spatial velocity distribution can induce a degradation of plug flow. Flow degradations, or deviations from pure plug flow, are grouped under the generic term "axial mixing." Axial dispersion can also be used.The effect of axial mixing tends to homogenize the concentration gradients present in one phase or the other along the column, and tends to minimize the efficiency of liquid-liquid extraction.
[0009] In particular, continuous phase recirculation in weirs is very detrimental. Regarding dispersed phase flow, it is essential that the flow remains essentially downward (or upward) through the perforated areas. Any entrainment of dispersed phase by the continuous phase in the weirs would be detrimental because it would tend to reduce the concentration differential of the continuous phase in the successive inter-plate spaces. For this reason, those skilled in the art use weirs large enough to minimize dispersed phase entrainment. It is also preferable that the weir cross-section not be excessively large, as this would result in overuse of surface area; for a given diameter, oversizing the weir area can lead to: a decrease in the capacity of the column (and therefore an increase in its cost at iso performance), a decrease in the efficiency of the extraction: by reducing the remaining surface available for the dispersion of the heavy phase, the quality of the contact between phases is degraded, a generation of continuous phase recirculations in the weirs themselves, a reduction in the piston character of the continuous phase and thus a reduction in the efficiency of the extraction.
[0010] The cross-section of the weirs can, for example, be chosen so that the velocity of the continuous phase within the weirs does not exceed the terminal settling velocity of droplets with a diameter smaller than the average droplet diameter. For example, a fine droplet diameter of 30 µm to 150 µm can be considered when calculating the maximum velocity of the light phase within the weirs.
[0011] Another important aspect to consider is the impact of continuous phase flow in each inter-plate space. Continuous phase flow is determined by the circulating continuous phase flow rate and by the geometry of the inter-plate spaces, particularly their height.
[0012] If the continuous phase flows too quickly through the column, various adverse behaviors can occur, such as: disturbances in the flow of the dispersed phase, which can be carried by the continuous phase towards the spillway; a deformation of the coalesced layer on the downstream plateau in the direction of the flow of the dispersed phase, this deformation also tends to accumulate dispersed phase under the outlet spillway of the inter-plateau space.
[0013] These two behaviors can promote the presence of dispersed phase in the weirs and its potential entrainment by the continuous phase towards the downstream inter-plate space in the direction of continuous phase flow. Indeed, the presence of dispersed phase in the weir of a plate P is detrimental to extraction performance because it can generate backmixing of the dispersed phase and significantly reduce the coalescing layer height on plate P+1 (the downstream plate in the direction of dispersed phase flow). Furthermore, the reduction in coalescing layer height can cause partial drying of the perforated plates, generating heterogeneities in the distribution of dispersed phase in the downstream inter-plate space in the direction of dispersed phase flow, or even a passage of the continuous phase through the plates, a phenomenon that increases axial dispersion and reduces column efficiency.
[0014] To maintain the flow of the dispersed phase at a non-problematic velocity level, several solutions can be implemented, such as: increase the height of the inter-plateau space; increase the number of weirs on each platform.
[0015] Increasing the height of the compartments effectively reduces the heavy phase entrainment towards the outlet weir, but naturally increases the height of the extraction columns, which has a cost and cannot be pushed to excessively high values.
[0016] Increasing the number of weirs is very effective, as it allows for the local lateral flow of dispersed phase to be divided. Single-weir plates are generally reserved for small columns (diameter < 2 m). Two-weir plates are very common and effectively reduce the velocity of the light phase. Plates with a greater number of weirs are also possible.
[0017] Increasing the number of weirs increases the cross-sectional area of the unperforated column, thus reducing the usable volume at the contact point between the phases. For this reason, it is not economically viable to increase the number of weirs beyond the minimum required to prevent the entrainment of heavy phases into the weirs.
[0018] With reference to the figure 2A classic implementation of liquid-liquid extraction columns with two-weep trays involves alternating two separate trays, allowing the continuous phase to meander through the column and pass through areas containing dispersed phase droplets. This increases mass transfer between the phases. The first type of tray (Type I) uses two peripheral or lateral weep holes (orthogonal to the column's central / vertical Z-axis), closely attached to the column shell and positioned diametrically opposite each other. The second type of tray (Type II) uses a single central weep hole in the form of a band (perpendicular to the column's central / vertical Z-axis) covering approximately the entire column diameter. A liquid-liquid extraction column such as the one shown in the diagram... figure 2 is a so-called 2-pass column, i.e.,a column in which the continuous phase flows along two different paths, as represented by the dotted arrows of the figure 2 .
[0019] In this description, when the dispersed phase is the heavy phase, the inter-plateau space of a type I plateau is the inter-plateau space located directly above the type I plateau; the inter-plateau space of a type II plateau is the inter-plateau space located directly above the type II plateau. Thus, the inter-plateau space corresponds to the space arranged on the side of the rim 10 and the coalesced layer 9 of the plateau Pi. i.e., The inter-plateau space of a plateau P i corresponds to the space located downstream of the plateau P i, in the direction of the continuous phase flow.
[0020] The state of the art consists of using alternating type I and II platforms, with a common inter-plateau space height and identical weir sections, the central weir of type II platforms then having a section equal to the sum of the 2 weirs of type I platforms.
[0021] The present invention aims to remedy the performance deficiencies mentioned above and to increase the performance of liquid-liquid extraction columns. Summary of the invention
[0022] In the context described above, a primary objective of this description is to propose a liquid-liquid extraction column that allows: to maintain a range of between 5% and 20% of the average volume fraction of dispersed phase (e.g., solvent / heavy phase) in a compartment ( i.e.,area including a perforated tray and an adjacent inter-tray space); the non-entrainment of dispersed phase droplets into the weirs by the continuous phase (e.g., load / light phase) in order to limit axial mixing of the dispersed phase; a coalesced layer height of the dispersed phase on each tray sufficient (e.g., at least 2 cm, such as 2 cm to 4 cm) to prevent the passage of the continuous phase through the perforated tray (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.
[0023] Surprisingly, the applicant identified that specific characteristics of perforated trays, such as the height of the inter-tray spaces and optionally the weir cross-section, allow for hydrodynamic control along the entire length of the column by limiting axial mixing. This technical solution maintains satisfactory mass transfer efficiency on each tray.
[0024] According to one 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; a second injection point of a second phase, the first and second injection points being arranged on the extraction column to allow the counter-current circulation of the first and second phases in the extraction column, one of the first and second phases being a continuous phase and the other being a dispersed phase; a first withdrawal point of an extract and a second withdrawal point of a raffinate, one being arranged at the bottom of the extraction column and the other being arranged at the top of the extraction column; and a plurality of perforated trays arranged from the top of the extraction column to the bottom of the extraction column, the perforated trays being spaced by an inter-tray space and comprising rims adapted to receive a coalesced layer of the dispersed phase above or below the perforated trays;a plurality of weirs, a weir being a recess adjacent to a rim and allowing the continuous phase to pass through the perforated plate; the extraction column comprising alternatively: perforated plates called type I comprising two peripheral weirs; and perforated plates called type II comprising a single central weir, extraction column in which: the height H1 of the inter-plate spaces arranged directly downstream of the type I plates, in the direction of the continuous phase flow, is greater than the height H2 of the inter-plate spaces arranged directly downstream of the type II plates.
[0025] According to one or more embodiments, the ratio H1 / H2 between the height H1 and the height H2 is between 1.1 and 2.
[0026] According to one or more embodiments, the ratio H1 / H2 between the height H1 and the height H2 is between 1.1 and 1.5.
[0027] According to one or more embodiments, the height H1 of the inter-platform spaces of type I perforated platforms is between 0.22 m and 1.50 m, preferably between 0.27 m and 0.90 m, very preferably between 0.33 m and 0.82 m.
[0028] According to one or more embodiments, the height H2 of the inter-platform spaces of the perforated platforms of type II is between 0.20 m and 1.00 m, preferably between 0.25 m and 0.60 m, very preferably between 0.30 m and 0.55 m.
[0029] According to one or more embodiments, the liquid-liquid extraction column comprises: an extraction sector, extending substantially from the first injection point of the first phase to substantially the second injection point of the second phase, and a backwash sector, adjacent to the extraction sector and extending from the first injection point of the first phase to substantially a third backwash liquid injection point.
[0030] According to one or more embodiments, the section S2 of the central weirs is greater than the section S1 of the peripheral weirs, the section S1 corresponding to the sum of the sections of the two peripheral weirs.
[0031] According to one or more embodiments, the S2 / S1 ratio between section S2 and section S1 is between 1.1 and 2.
[0032] According to one or more embodiments, the S2 / S1 ratio between section S2 and section S1 is between 1.1 and 1.5.
[0033] According to a second aspect, the aforementioned objects, as well as other advantages, are obtained by a liquid-liquid extraction process comprising the following steps: inject a first phase and a second phase into a liquid-liquid extraction column according to the first aspect; and withdraw an extract and a raffinate from the liquid-liquid extraction column.
[0034] According to one or more embodiments, the extraction column is operated at 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; and at 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.
[0035] According to one or more embodiments, the first phase comprises a mixture of aromatic and non-aromatic compounds.
[0036] According to one or more embodiments, the second phase comprises a compound selected from ethylene glycol, diethylene glycol, triethylene glycol, hexamethylphosphoramide, propylene carbonate, ethylene carbonate, sulfolane, 3-methylsulfolane, N-methylacetamide, N,N-dimethylacetamide, butyrolactone, 1-methylpyrrolidone, dimethyl sulfoxide, caprolactam, N-methylformamide, pyrrolidine-2-one, furfural, 1,1,3,3-tetramethylurea and a mixture thereof.
[0037] According to one or more embodiments, the second phase comprises sulfolane and water.
[0038] Embedding methods of the column and the liquid-liquid extraction process 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. List of figures
[0039] There figure 1 schematically shows a cross-sectional view of a liquid-liquid extraction column. figure 2 schematically shows a cross-sectional view of the flow of the dispersed phase and the continuous phase in the reference liquid-liquid extraction column. figure 3 The diagram 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. figure 4 schematically shows a top view of a type I perforated plate and a type II perforated plate according to the present invention. Description of the implementation methods
[0040] 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.
[0041] 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. Liquid-liquid extraction column
[0042] A liquid-liquid extraction column according to the present invention comprises all the elements as defined in the figure 1Furthermore, in order to increase yield and purity, two distinct operating zones can be defined in a liquid-liquid extraction column according to the present invention opposite the first injection point 2 of the liquid to be separated: an extraction sector 11, extending substantially from the first injection point 2 of the first phase to substantially the second injection point 3 of the second phase, allows in particular the extraction of compounds from the liquid to be separated (e.g. aromatics) by contact with the liquid separation solvent in counter-current flow (so-called yield zone), and an optional backwash sector 12, adjacent to the extraction sector 11 and extending from the first injection point 2 of the first phase to substantially a third injection point 13 of backwash liquid (optional), such as an extract recycle, allows in particular the back-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.According to one or more embodiments, the third injection point 13 of backwash liquid is disposed between the first injection point 2 and the first withdrawal point of the extract 4.
[0043] Specifically, in reference to the figure 1 The separating liquid exits the liquid-liquid extraction column 1, carrying with it compounds of interest to be separated (e.g., aromatics) to form extract 4. 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 4 contains substantially 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 12. With reference to the figure 1The separation liquid is heavier than the liquid to be separated and is injected at the top of the liquid-liquid extraction column 1, while the optional backwash liquid is injected at the bottom of the liquid-liquid extraction 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, the injection point 3 of the separation liquid then being at the bottom of the liquid-liquid extraction column 1 and the injection point 13 of the backwash liquid being at the top of the liquid-liquid extraction column 1.
[0044] With reference to figures 3 And 4 , a liquid-liquid extraction column 1 according to the present invention comprises n perforated trays P i , i being between 1 and n. Each perforated tray P i is arranged such that the dispersed phase B ( i.e.,the separation liquid (heavier than the liquid to be separated) flows through the holes 7 of the perforated plate P i , the droplets of the dispersed phase B recoaling on the next perforated plate P i+1 to form a liquid volume preventing the passage of the continuous phase A ( i.e., The liquid to be separated (lighter than the separation liquid) flows through the holes of the perforated tray P i+1. The liquid to be separated flows in the opposite direction to the separation liquid. i.e., from bottom to top via the central and peripheral weirs 6, and transversely in an inter-plateau space 8. With reference to the figure 3 , the heavy phase is the dispersed phase B and the light phase is the continuous phase A. 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.
[0045] According to one or more embodiments, the number n of perforated trays Pi is between 10 and 200, preferably between 50 and 150.
[0046] According to the invention, the liquid-liquid extraction column 1 comprises alternatively perforated trays P i of type II, i.e., comprising a single central weir, and perforated plates P i of type I, i.e., including two peripheral weirs.
[0047] Specifically, type II perforated trays have a perforated area of holes 7 divided into 2 parts, on either side of the central weir 6, as shown on tray P i of the figure 4 Furthermore, type I perforated trays have a perforated area of holes 7 which can be single or divided into 2 parts, as shown on tray P i+1 of the figure 4 , to remain similar to the parts of the perforated area of holes 7 of the type II perforated trays.
[0048] Thus, it is understood that the present invention relates to two-pass liquid-liquid extraction columns. Specifically, with reference to figures 3 And 4 The liquid-liquid extraction column 1 comprises trays Pi and Pi+2 with two peripheral weirs 6 (type I trays) arranged alternately with trays Pi-1 and Pi+1 with one central weir 6 (type II trays). Preferably, the peripheral weirs 6 are substantially adjacent to the column shell, or even substantially touching it. Preferably, the peripheral weirs 6 are arranged in substantially diametrically opposite positions. Preferably, the central weirs 6 are arranged in a band covering substantially the entire diameter of the column.
[0049] The applicant identified, particularly during a numerical study of the flow in the alternating inter-plate spaces of the type I and II perforated plates Pi, that dispersed phase entrainment in the weirs was possible and could minimize extraction performance. It was observed that this entrainment first appeared in the weirs of the type II plates (central weirs).
[0050] According to the invention, the perforated plates are modified differently depending on their type. While the prior art would suggest increasing the height of the inter-plate spaces and the cross-section (surface area) of the weirs on all plates, the applicant has identified that the entrainment of dispersed phase in the continuous phase can be reduced by: increasing the height H1 of the inter-platen spaces 8 of the type I perforated Pi platens to a level higher than the height H2 of the inter-platen spaces 8 of the type II perforated Pi platens, as shown in the figure 3 ; and optionally increasing the S2 section of the central weirs 6 of the type II perforated plates Pi to a level higher than the S1 section of the peripheral weirs 6 of the type I perforated plates Pi, as shown in the figure 4 .
[0051] It is understood in this description that the height of an inter-plate space 8 of a perforated plate P i corresponds to the distance between said perforated plate P i and the perforated plate arranged directly downstream in the direction of the continuous phase flow, i.e., the perforated plate P i+1 in the example of the figure 3 .
[0052] It is understood in this description that section S1 of the peripheral weirs 6 of a perforated plate corresponds to the sum of the sections of the two peripheral weirs of said perforated plate.
[0053] Advantageously, by alternating perforated plates of type I and II in the extraction column 1, the present invention prevents the entrainment of dispersed phase into the weirs of the type II plates (central weirs), while minimizing the drawbacks of the modifications applied. Thus, the increase in column height is reduced by a factor of 2 compared to the prior art, where the heights of all inter-plate spaces are increased.
[0054] Similarly, increasing the cross-section of the weirs on Type II perforated plates can be accompanied by a decrease in the perforated surface area and the quality of transfer in the inter-plate space of Type I perforated plates, but this decrease does not affect the inter-plate spaces of Type II perforated plates. Therefore, the impact of increasing the cross-section of the weirs on Type II perforated plates degrades transfer performance less than a change in cross-section affecting all the weirs, according to current best practices.
[0055] According to one or more embodiments, the ratio H1 / H2 between the height H1 and the height H2 is between 1.1 and 2, preferably between 1.1 and 1.5. According to one or more embodiments, the ratio H1 / H2 between the height H1 and the height H2 is between 1.2 and 1.9, preferably between 1.3 and 1.7.
[0056] According to one or more embodiments, the height H1 of the inter-platform spaces 8 of the perforated type I platforms is between 0.22 m and 1.50 m, preferably between 0.27 m and 0.90 m, very preferably between 0.33 m and 0.83 m.
[0057] According to one or more embodiments, the height H2 of the inter-platform spaces 8 of the perforated platforms of type II is between 0.20 m and 1.00 m, preferably between 0.25 m and 0.60 m, very preferably between 0.30 m and 0.55 m.
[0058] According to one or more embodiments, the S2 / S1 ratio between section S2 and section S1 is between 1.1 and 2, preferably between 1.1 and 1.5. According to one or more embodiments, the S2 / S1 ratio between section S2 and section S1 is between 1.2 and 1.4.
[0059] According to one or more embodiments, the cross-section of the weirs 6 is predetermined so that the velocity of the continuous phase passing through said weirs is between 0.005 m / s and 0.050 m / s. According to one or more embodiments, the continuous phase flow rate is between 70 m³ / hr and 400 m³ / hr, preferably between 80 m³ / hr and 350 m³ / hr.
[0060] According to one or more embodiments, the cross-sections S1 and S2 of the weirs 6 are between 0.3 m² and 15 m², preferably between 2 m² and 10 m². According to one or more embodiments, the cross-section S1 of the central weir 6 is between 0.33 m² and 15 m², preferably between 2.2 m² and 10 m². According to one or more embodiments, the cross-section S2 of the peripheral weirs 6 is between 0.3 m² and 13.5 m², preferably between 2 m² and 9 m².
[0061] The diameter of the extraction column 1 is typically a function of the predetermined value of the flow rate of the dispersed phase passing through it. According to one or more embodiments, the flow rate of the dispersed phase is between 140 m³ / hr and 2300 m³ / hr, preferably between 200 m³ / hr and 2000 m³ / hr.
[0062] The height of the extraction column 1 is typically a function of its diameter. Depending on one or more embodiments, the height of the extraction column is between 15 m and 90 m.
[0063] According to one or more embodiments, the perforated plates P i have holes 7 with diameters ranging from 2 mm to 10 mm. According to one or more embodiments, the diameter of the holes is predetermined so that the velocity at the hole is between 0.05 m / s and 0.60 m / s. Liquid-liquid extraction process
[0064] According to one or more embodiments, the extraction column 1 is operated at a pressure between 0.05 MPa and 3 MPa (0.5 and 30 bara), preferably between 0.1 MPa and 2 MPa (1 and 20 bara), preferably between 0.2 MPa and 1.5 MPa (2 and 15 bara), preferably between 0.3 MPa and 1 MPa (3 and 10 bara). According to one or more embodiments, the extractor is operated at 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. Liquid charge to be separated
[0065] The liquid-liquid extraction process according to the invention allows for the treatment of a liquid feed to be separated, comprising a mixture of aromatic and non-aromatic compounds. Preferably, the feed is hydrotreated and / or hydrogenated. In one or more embodiments, the feed is a gasoline feed that is optionally hydrotreated and / or hydrogenated.
[0066] According to one or more embodiments, the load is a C5+ cut, i.e., containing compounds with 5 or more carbon atoms. According to one or more embodiments, the filler is a C5-C10 or C5-C11 cut, i.e., containing compounds comprising 5 to 10 or 5 to 11 carbon atoms. According to one or more embodiments, the filler is a C6-C10 or C6-C11 cut, i.e., containing compounds comprising 6 to 10 or 6 to 11 carbon atoms.
[0067] According to one or more embodiments, the charge comprises at least 20% by weight, preferably at least 30% by weight, most preferably at least 40% by weight, (e.g. at least 50% by weight) of aromatic compounds of 6 to 11 carbon atoms, relative to the total weight of the charge.
[0068] According to one or more embodiments, the charge comprises at least 20% by weight, preferably at least 30% by weight, very preferably at least 40% by weight, (e.g. at least 50% by weight) of mono-aromatic compounds of 6 to 11 carbon atoms, relative to the total weight of the charge.
[0069] According to one or more embodiments, the aromatic compounds of the filler are mono-aromatic compounds of at least 95% by weight, preferably at least 98% by weight, very preferably at least 99% by weight.
[0070] According to one embodiment of the invention, the charge comprises less than 50 ppm by weight of sulfur, preferably less than 10 ppm by weight of sulfur, and very preferably less than 1 ppm by weight of sulfur.
[0071] According to one embodiment of the invention, the charge comprises less than 100 ppm by weight of nitrogen, preferably less than 10 ppm by weight of nitrogen, and very preferably less than 1 ppm by weight of nitrogen.
[0072] According to one embodiment of the invention, the charge comprises less than 0.1% by weight of diolefins, preferably less than 0.05% by weight of diolefins, and very preferably less than 0.01% by weight of diolefins.
[0073] According to one embodiment of the invention, the charge comprises less than 0.1% by weight of olefins, preferably less than 0.05% by weight of olefins, and very preferably less than 0.01% by weight of olefins.
[0074] According to one embodiment of the invention, the charge has a content of less than or equal to 5000 ppm by weight, preferably less than or equal to 4500 ppm by weight, and very preferably less than or equal to 3000 ppm by weight, of compounds having a boiling point greater than 217°C, such as naphthalene.
[0075] According to one embodiment of the invention, the feed is free of the following compounds: H₂, H₂S, and light gases such as ethane, propane, and butane. According to another embodiment of the invention, the removal of these compounds from the feed is carried out in a fractionation column.
[0076] According to one embodiment, the feedstock is at least partly a gasoline fraction from a fluidized bed catalytic cracking unit (FCC unit), the gasoline fraction having preferably been selectively hydrogenated to convert diolefins to olefins, then fractionated to obtain a C5-C10, C5-C11, C6-C10, or C6-C11 fraction, and then hydrogenated to saturate the olefinic compounds. According to another embodiment of the invention, the feedstock is obtained by hydrogenating pyrolysis gasoline (PyGas in English) mixed with a gasoline fraction from an FCC unit. Separating liquid solvent
[0077] According to one or more embodiments, the solvent comprises a compound selected from ethylene glycol, diethylene glycol, triethylene glycol, hexamethylphosphoramide, propylene carbonate, ethylene carbonate, sulfolane, 3-methylsulfolane, N-methylacetamide, N,N-dimethylacetamide, butyrolactone, 1-methylpyrrolidone, dimethyl sulfoxide, caprolactam, N-methylformamide, pyrrolidine-2-one, furfural, 1,1,3,3-tetramethylurea and a mixture thereof.
[0078] According to one or more embodiments, the solvent comprises or consists of sulfolane. According to one or more embodiments, the solvent consists of at least 80% by weight (e.g., at least 90% by weight), preferably at least 95% by weight (e.g., at least 99% by weight), of sulfolane, relative to the total weight of the solvent.
[0079] In one or more embodiments, the solvent further comprises an anti-solvent, such as water. In one or more embodiments, the anti-solvent comprises or consists of water. In one or more embodiments, the solvent comprises between 0.01% by weight and 5% by weight, preferably between 0.1% by weight and 3% by weight (e.g., between 0.5% by weight and 2% by weight) of an anti-solvent, such as water, relative to the total weight of the solvent. In one or more embodiments, the solvent comprises or consists of sulfolane and water. Examples
[0080] The liquid-liquid extraction column examples described below all have the following characteristics: The liquid-liquid extraction column has a diameter of 4.8 m. Each tray contains 17,192 holes. The feed (continuous, light phase) is injected into the lower tray at a flow rate of 1.02E+05 kg / hr. The feed consists of 40 wt% isooctane, 30 wt% benzene, and 30 wt% paraxylene (density of 724 kg / m³). The liquid separation solvent (dispersed, heavy phase) is injected into the upper tray at a flow rate of 8.25E+05 kg / hr. The liquid separation solvent consists of 99.5 wt% sulfolane and 0.5 wt% water (density of 1136 kg / m³). Example 1 (reference): height of inter-plateau spaces and weir sections of constants.
[0081] The liquid-liquid extraction column has a height of 36.0 m and is composed of a succession of 120 perforated trays.
[0082] No adjustments are being made: heights of the inter-plateau spaces: H1 = H2 = 0.30 m, sections of the spillways: S1 = S2 = 1.70 m 2< .
[0083] In the reference example 1, disturbances in the flow of the dispersed phase are observed. Some of the dispersed phase is carried along with the continuous phase towards the weir, and deformation of the coalesced layer is observed on the downstream plate in the direction of the dispersed phase flow. To quantitatively express performance, the Equivalent Theoretical Plate Height (ETPH) is calculated, a classic concept in separation (distillation, extraction). The lower the ETPH, the more efficient the extractor.
[0084] For reference example 1, the HEPT is 4.76 m. Example 2 (reference): increasing the height of the spaces between the shelves
[0085] Compared to example 1, the heights H1 and H2 of the inter-platform spaces are increased: heights of the inter-plateau spaces: H1 = H2 = 0.45 m, sections of the spillways: S1 = S2 = 1.70 m 2< .
[0086] For reference example 2, the HEPT is 5.83 m.
[0087] The liquid-liquid extraction column has a height of 44.0 m and is composed of a succession of 98 perforated trays. Example 3 (reference): increasing the cross-sectional areas of the weirs
[0088] Compared to example 1, sections S1 and S2 of the weirs are increased: heights of the inter-plateau spaces: H1 = H2 = 0.30 m, sections of the spillways: S1 = S2 = 2.10 m 2< .
[0089] For reference example 3, the HEPT is 4.81 m.
[0090] The liquid-liquid extraction column has a height of 36.3 m and is composed of a succession of 121 perforated trays. Example 4 (invention): alternating heights of the inter-platform spaces
[0091] Compared to example 1, only the heights H1 are increased: heights of inter-plateau spaces: H1 = 0.45; H2 = 0.30 m, sections of spillways: S1 = S2 = 1.70 m 2< .
[0092] For example 4 according to the invention, the HEPT is 4.26 m.
[0093] The liquid-liquid extraction column has a height of 32.2 m and is composed of a succession of 86 perforated trays. Example 5 (invention): alternating heights of inter-plateau spaces and alternating sections of spillways
[0094] Compared to example 1, only the heights H1 and sections S2 are increased: heights of the inter-plateau spaces: H1 = 0.45 m; H2 = 0.30 m, sections of the spillways: S1 = 1.70 m 2< ; S2 = 2.10 m 2< .
[0095] For example 5 according to the invention, the HEPT is 4.08 m.
[0096] The liquid-liquid extraction column has a height of 30.8 m and is composed of a succession of 82 perforated trays.
[0097] Table 1 below summarizes the performance levels of reference examples 1, 2, 3 and examples 4 and 5 according to the invention. Table 1 Example 1 (réf.) 2 (réf.) 3 (réf.) 4 (inv.) 5 (inv.) H1 (m) 0,30 0,45 0,30 0,45 0,45 H2 (m) 0,30 0,45 0,30 0,30 0,30 S1 (m 2< ) 1,70 1,70 2,10 1,70 1,70 S2 (m 2< ) 1,70 1,70 2,10 1,70 2,10 HEPT (m) 4,76 5,83 4,81 4,26 4,08 Column height (m) 36,0 44,0 36,3 32,3 30,8 Number of trays 120 98 121 86 82
[0098] Advantageously, the HEPT, column height, and number of trays of examples 4 and 5 according to the invention are reduced compared to those of reference examples 1, 2 and 3.
Claims
1. Liquid-liquid extraction column comprising the following elements: - a first injection point (2) for injection of a first phase; - a second injection point (3) for injection of a second phase, the first and second injection points (2, 3) being positioned on the extraction column (1) in such a way as to allow the first and second phases to circulate in the extraction column (1) in a countercurrent manner, one of the first and second phases being a continuous phase (A) and the other being a dispersed phase (B); - a first withdrawal point for withdrawal of an extract (4) and a second withdrawal point for withdrawal of a raffinate (5), one being located at the bottom of the extraction column (1) and the other being located at the top of the extraction column (1); and - a plurality of sieve trays (Pi) located from the top of the extraction column (1) to the bottom of the extraction column (1), the sieve trays (Pi) being spaced apart by an inter-tray space (8) and comprising weir plates (10) designed to hold a layer (9) of the dispersed phase (B) that has coalesced above or below the sieve trays (Pi); - a plurality of riser / downcomer conduits (6), a riser / downcomer conduit (6) being an opening adjacent to a weir plate (10) and allowing the continuous phase (A) to pass through the sieve tray (Pi), the extraction column (1) comprising in alternation: - sieve trays (Pi) said to be of type I, comprising two peripheral riser / downcomer conduits (6); and - sieve trays (Pi) said to be of type II, comprising a single central riser / downcomer conduit (6), the extraction column (1); the extraction column (1) being characterized in that: - the height H1 of the inter-tray spaces (8) situated directly downstream of the type-I trays, in the direction of flow of the continuous phase, is greater than the height H2 of the inter-tray spaces (8) positioned directly downstream of the type-II trays.
2. Liquid-liquid extraction column according to Claim 1, wherein the ratio H1 / H2 of the height H1 to the height H2 is comprised between 1.1 and 2.
3. Liquid-liquid extraction column according to Claim 1 or Claim 2, wherein the ratio H1 / H2 of the height H1 to the height H2 is comprised between 1.1 and 1.5.
4. Liquid-liquid extraction column according to any one of the preceding claims, wherein the height H1 of the inter-tray spaces (8) of the type-I sieve trays is comprised between 0.22 m and 1.50 m, preferably between 0.27 m and 0.90 m, very preferably between 0.33 m and 0.83 m.
5. Liquid-liquid extraction column according to any one of the preceding claims, wherein the height H2 of the inter-tray spaces (8) of the type-II sieve trays is comprised between 0.20 m and 1.00 m, preferably between 0.25 m and 0.60 m, very preferably between 0.30 m and 0.55 m.
6. Liquid-liquid extraction column according to any one of the preceding claims, comprising: - an extraction sector (11), extending substantially from the first injection point (2) for injection of the first phase as far as substantially the second injection point (3) for injection of the second phase, and - a backwash sector (12), adjacent to the extraction sector (11) and extending from the first injection point (2) for injection of the first phase as far as substantially a third injection point (13) for injection of a backwash liquid.
7. Liquid-liquid extraction method comprising the following steps: - injecting a first phase and a second phase into the liquid-liquid extraction column according to any one of Claims 1 to 6; and - withdrawing an extract (4) and a raffinate (5) from the liquid-liquid extraction column.
8. Liquid-liquid extraction method according to Claim 7, wherein the extraction column (1) is operated at a pressure comprised between 0.05 MPa and 3 MPa, preferably between 0.1 MPa and 2 MPa, preferably between 0.2 MPa and 1.5 MPa, and preferably between 0.3 MPa and 1 MPa; and at a temperature comprised between 10°C and 150°C, preferably between 15°C and 130°C, preferably between 30°C and 120°C, and preferably between 40°C and 110°C.
9. Liquid-liquid extraction method according to Claim 7 or Claim 8, wherein the first phase comprises a mixture of aromatic and nonaromatic compounds.
10. Liquid-liquid extraction method according to any one of Claims 7 to 9, wherein the second phase contains a compound selected from ethylene glycol, diethylene glycol, triethylene glycol, hexamethylphosphoramide, propylene carbonate, ethylene carbonate, sulfolane, 3-methylsulfolane, N-methylacetamide, N,N-dimethylacetamide, butyrolactone, 1-methylpyrrolidone, dimethyl sulfoxide, caprolactam, N-methylformamide, pyrrolidin-2-one, furfural, 1,1,3,3-tetramethylurea and a mixture of these.