Extraction column with alternating spill sections

Abstract

The invention relates to a column for the liquid-liquid extraction of a raw material by means of an extraction solvent, comprising: perforated trays (Pi) through which a dispersed phase (B) passes, the perforated trays being separated by inter-tray spaces (8); the invention relates to an extraction column (1) comprising a perforated tray (2) and comprising an overflow channel (6) which is a hole allowing a continuous phase (A) to pass through the perforated tray, the extraction column (1) alternately comprising a type I perforated tray with two peripheral overflow channels and a type II perforated tray with a single central overflow channel, in which: the central overflow channel has a cross-section S2 larger than the cross-section S1 of the peripheral overflow channels, and the cross-section S2 of the central overflow channel is larger than the cross-section S1 of the peripheral overflow channels; and the cross section S1 corresponds to the sum of the cross sections of the two peripheral overflow channels. The invention also relates to a liquid-liquid extraction method using the liquid-liquid extraction tower.

Description

Technical Field

[0001] The field of the invention is liquid-liquid extraction in sieve tray columns with riser / downcomer conduits, such as are used in many chemical processes, including processes for extracting aromatic hydrocarbons present in various petrochemical fractions or from refining processes. The liquid-liquid extraction column is particularly suitable for liquid-liquid separation of hydrocarbon compounds, such as aromatic (e.g. A6-A11) compounds originating from a wide hydrocarbon fraction (e.g. C6-C11 fraction), such as from a catalytic cracking (FCC, fluid catalytic cracking) unit. Prior art

[0002] The operating principle of a liquid-liquid extraction column is based on the solubility differences of the compounds of a homogeneous liquid feed in a suitable solvent (e.g., a polar aprotic solvent such as sulfolane or DMSO). Addition of a partially miscible solvent to the feed results in the appearance of a second phase, to which a portion of the most soluble constituent compounds (e.g., aromatic compounds) are preferentially transferred.

[0003] Reference Figure 1 , the liquid-liquid extraction tower 1 comprises the following elements:

[0004] - a first injection point 2 for injecting the first phase (liquid feed to be separated);

[0005] - a second injection point 3 for injecting the second phase (liquid separation solvent), the first and second injection points 2 and 3 being positioned in such a way as to allow the first and second phases to circulate in countercurrent;

[0006] - a first extraction point for extracting an extract 4 (in liquid phase), such as a solvent enriched in the compounds extracted from the feedstock; and

[0007] - a second extraction point for extracting a raffinate 5 (in liquid phase), such as a depleted feedstock from which compounds have been extracted, one of the first and second extraction points being located at the bottom of the extraction column 1 and the other being located at the top of the extraction column 1. Furthermore, the first injection point 2 for injecting the feedstock to be separated is usually located between the second injection point 3 for injecting the liquid separation solvent and the first extraction point for extracting the extract 4. Similarly, the second injection point 3 for injecting the liquid separation solvent is usually located between the first injection point 2 for injecting the feedstock to be separated and the second extraction point for extracting the raffinate 5. In this reference example, the first phase is a light phase, and the second phase is a heavy phase.

[0008] refer to Figure 2, a liquid-liquid extraction column 1 comprises a plurality of sieve trays P, each sieve tray P being equipped with from one to several riser / downcomer ducts 6, depending on the desired capacity, such ducts 6 being openings allowing a first phase A, referred to as "continuous", to pass through the sieve tray P. The sieve tray P comprises at least one zone perforated with holes 7, through which a second phase B, referred to as "dispersed", circulates. The dispersed second phase B circulates in each inter-tray space 8 defined by the space between two adjacent sieve trays P, in the form of droplets passing through the continuous first phase A. Figure 2 In the example of , the dispersed second phase B is the heavy phase and accumulates above the sieve plate tray P until it forms a coalescing layer 9 above the sieve plate tray. The thickness of this coalescing layer 9 can typically be measured from 1 cm to 8 cm. It must be understood that if the dispersed phase is the light phase, the dispersed phase accumulates below the sieve plate tray. The dispersed second phase B then passes through the perforated area of ​​the sieve plate tray P to supply the next sieve plate tray P (if the dispersed phase is the heavy phase, it is supplied to the tray below), and so on. Figure 2 In this example, the continuous first phase A follows a serpentine path through the inter-tray spaces 8, passing via the conduits 6 in an upward direction, since the continuous phase is the light phase.

[0009] Patents US 3632315 and US 4588563 describe examples of liquid-liquid extraction columns comprising sieve trays equipped with one and / or two riser / downcomer conduits.

[0010] Thus, the liquid-liquid extraction column allows two partially immiscible liquid phases A and B to contact each other in a countercurrent manner. Depending on the choice of dispersed phase (heavy phase or light phase), the sieve tray P is designed to collect (with the aid of weir plates 10) the coalescing layer 9 on the upper part (when the dispersed phase is the heavy phase) or on the lower part (when the dispersed phase is the light phase) of the sieve tray. In the figures of this specification, only the case where the liquid separation solvent is the dispersed phase and the heavy phase is described.

[0011] The applicant company has found that the operation of the liquid-liquid extraction column can cause significant variations in performance, depending in particular on:

[0012] - the interfacial surface area between the phases in the space between the trays, which depends on the size of the dispersed phase droplets and their volume fraction; and

[0013] - Flow of each phase in the inter-tray spaces, riser / downcomer conduits and perforated zones.

[0014] It is known to those skilled in the art and is well described in the literature on liquid-liquid extraction (see Lo, Baird and Hanson, Handbook of Solvent Extraction, Krieger Publishing Company, 1991) that plug flow of each phase is beneficial to the transfer performance in a countercurrent extraction column. Plug flow is a conventional concept, which assumes that, over a given cross-section of the column, each phase (heavy or light) circulates at a consistent speed and in only one direction. It is also known that the presence of any recirculation, eddy currents or any other liquid movement that causes a spatial velocity distribution will lead to a degradation of the plug flow. Flow degradation or deviations from pure plug flow are grouped under the general heading of "axial mixing". It may also be called axial dispersion. The effect of axial mixing tends to homogenize the concentration gradients present in one or the other phase along the column and tends to minimize the efficiency of the liquid-liquid extraction.

[0015] In particular, recirculation of the continuous phase in the riser / downcomer conduits is very detrimental. As for the flow of the dispersed phase, it is important that the flow remains substantially downward (or upward) through the perforated zone. Any entrainment of the dispersed phase by the continuous phase in the riser / downcomer conduits will be detrimental because it tends to reduce the concentration difference of the continuous phase in the spaces between successive trays. For this reason, those skilled in the art use riser / downcomer conduits that are large enough to minimize the entrainment of the dispersed phase in these conduits. In order to avoid using too much surface area, it is also preferred that the cross-section of the riser / downcomer conduits is not too large; for a given diameter, making the conduit surface area too large may result in:

[0016] - a reduction in the tower capacity (and therefore, an increase in its cost for the same performance),

[0017] - Reduced extraction efficiency: the quality of contact between the phases deteriorates by reducing the remaining surface area available for heavy phase dispersion,

[0018] - Producing a recirculation of the continuous phase in the riser / downcomer conduit itself, the plug flow nature of the flow of the continuous phase is reduced and, therefore, the extraction efficiency is reduced.

[0019] For example, the cross-sections of the riser / downcomer conduits may be selected so that the velocity of the continuous phase in these conduits does not exceed the terminal velocity of droplets falling with a diameter smaller than the average droplet diameter. For example, the maximum velocity of the light phase in the riser / downcomer conduits may be calculated taking into account fine droplets with a diameter of 30 μm to 150 μm.

[0020] Another aspect that requires careful consideration is the effect of the flow of the continuous phase in each tray space. The flow of the continuous phase is controlled by the circulating continuous phase flow rate and the geometry of the tray space, particularly including the height of the tray space.

[0021] If the continuous phase circulates through the column too quickly, various undesirable behaviors may occur, such as:

[0022] - disturbances in the flow of the dispersed phase, which may be entrained by the continuous phase towards the riser / downcomer conduits;

[0023] - Deformation of the layer that has coalesced on the trays downstream in the direction of dispersed phase flow, which deformation also tends to cause the dispersed phase to accumulate below the outlet ducts in the space between the trays.

[0024] These two behaviors may promote the presence of dispersed phase in the riser / downcomer conduit and potentially lead to the entrainment of the dispersed phase by the continuous phase toward the inter-tray space downstream in the direction of continuous phase flow. Specifically, the presence of dispersed phase in the riser / downcomer conduit of tray P is detrimental to the extraction performance because it may cause backmixing of the dispersed phase and significantly reduce the height of the coalescing layer on tray P+1 (the tray downstream in the direction of dispersed phase flow). In addition, the reduction in the height of the coalescing layer may lead to partial drying of the sieve plate tray, resulting in uneven distribution of the dispersed phase in the inter-tray space downstream in the direction of dispersed phase flow, or even cause some of the continuous phase to pass through the tray, which phenomenon increases axial dispersion and reduces tower efficiency.

[0025] In order to keep the flow of the dispersed phase at a non-problematic velocity level, there are many solutions that can be implemented, such as:

[0026] -Increase the height of the space between trays;

[0027] -Increase the number of riser / downcomer ducts on each tray.

[0028] Increasing the height of the compartments makes it possible to effectively reduce the entrainment of the heavy phase towards the outlet riser / downcomer conduit, but naturally increases the height of the extraction column, which has associated costs and cannot be pushed too high.

[0029] Increasing the number of riser / downcomer ducts is highly effective, since this allows for local lateral splitting of the circulating flow of the dispersed phase. Trays with 1 riser / downcomer duct are usually reserved for small-sized (diameter < 2 m) towers. Trays with 2 riser / downcomer ducts are very conventional and effective in reducing the velocity of the light phase. Trays with a greater number of riser / downcomer ducts are also possible.

[0030] Increasing the number of riser / downcomer ducts increases the non-perforated cross-section of the column and thus results in a loss of volume available for contacting the phases. For this reason, it is not economically justifiable to increase the number of riser / downcomer ducts beyond the minimum required to prevent entrainment of the heavy phase into these ducts.

[0031] refer to Figure 2 A conventional implementation of a liquid-liquid extraction column comprising a tray with two riser / downcomer ducts is to use two different trays alternately so that the flow of the continuous phase circulates along a serpentine path in the tower, passing through the zones in which the dispersed phase droplets are present. This makes it possible to increase the mass transfer between the phases. The first type of tray (Type I) uses two peripheral or lateral riser / downcomer ducts (orthogonal to the central / vertical axis Z of the tower), which are essentially incorporated into the outer shell of the tower and are arranged in diametrically opposed positions. The second type of tray (Type II) uses only one central riser / downcomer duct, which is in the form of a strip (perpendicular to the central / vertical axis Z of the tower) that essentially covers the entire diameter of the tower. As Figure 2 The liquid-liquid extraction column depicted is a type of column known as a two-pass column, i.e. a column in which the continuous phase follows a Figure 2 The two different routes indicated by the dashed arrows follow the winding path loop of the tower.

[0032] In this specification, when the dispersed phase is the heavy phase, the inter-tray space of the type I tray is the inter-tray space located directly above the type I tray; the inter-tray space of the type II tray is the inter-tray space located directly above the type II tray. i The space on one side of the weir plate 10 and the coalescing layer 9, i.e., the tray P i The inter-tray space corresponds to the space between trays P in the direction of continuous phase flow. i Downstream space.

[0033] The prior art consists in using alternating type I and type II trays having a common intertray space height and identical riser / downcomer duct cross-sections, the cross-section of the central riser / downcomer duct of a type II tray then being equal to the sum of the cross-sections of the two riser / downcomer ducts of a type I tray.

[0034] The object of the present invention is to overcome the above-mentioned performance drawbacks and to improve the performance of a liquid-liquid extraction column. Summary of the invention

[0035] In the above context, a first object of the present description is to provide a liquid-liquid extraction column which makes it possible to:

[0036] - maintaining an average volume fraction of the dispersed phase (e.g., solvent / heavy phase) in the compartment (i.e., the zone including the sieve trays and the spaces between adjacent trays) in a range between 5% and 20%;

[0037] - the continuous phase (e.g. feed / light phase) does not entrain droplets of the dispersed phase into the riser / downcomer conduits so as to limit axial mixing of the dispersed phase;

[0038] - the height of the coalesced layer of dispersed phase on each tray is sufficient (e.g. at least 2 cm, such as from 2 cm to 4 cm) to prevent the continuous phase from passing through the sieve trays (and to force the continuous phase to pass exclusively into the riser / downcomer conduits);

[0039] - A suitable lateral velocity of the continuous phase which does not disturb the flow of the dispersed phase.

[0040] Surprisingly, the Applicant Company has found that the specific characteristics of the sieve trays, such as the cross-section of the riser / downcomer ducts and optionally the height of the inter-tray spaces, make it possible to control the fluid dynamics along the entire column while limiting axial mixing. This technical solution makes it possible to maintain a satisfactory material transfer efficiency on each tray.

[0041] According to a first aspect, the above objects and other advantages are achieved by a liquid-liquid extraction column comprising the following elements:

[0042] - a first injection point for injecting a first phase;

[0043] a second injection point for injecting the second phase, the first and second injection points being positioned on the extraction column in such a way as to allow the first and second phases to circulate in the extraction column in a countercurrent manner, one of the first and second phases being the continuous phase and the other being the dispersed phase;

[0044] - a first extraction point for extracting the extract and a second extraction point for extracting the raffinate, one located at the bottom of the extraction column and the other located at the top of the extraction column; and

[0045] - a plurality of sieve trays positioned from the top of the extraction column to the bottom of the extraction column, the sieve trays being separated by inter-tray spaces and comprising weirs designed to retain layers of dispersed phase that have coalesced above or below the sieve trays;

[0046] - a plurality of riser / downcomer conduits which are openings adjacent to the weir and allow the continuous phase to pass through the sieve trays,

[0047] The extraction column alternatively comprises:

[0048] - a sieve tray known as type I, which comprises two peripheral riser / downcomer ducts; and

[0049] - sieve trays known as Type II, which comprise a single central riser / downcomer duct,

[0050] Among them, the extraction tower:

[0051] the cross-section S2 of the central riser / downcomer duct is greater than the cross-section S1 of the peripheral riser / downcomer ducts, the cross-section S1 corresponding to the sum of the cross-sections of the two peripheral riser / downcomer ducts; and

[0052] Optionally, in the flow direction of the continuous phase, the height H1 of the inter-tray spaces located directly downstream of the type I trays is greater than the height H2 of the inter-tray spaces located directly downstream of the type II trays.

[0053] According to one or more embodiments, a ratio S2 / S1 of the cross section S2 to the cross section S1 is comprised between 1.1 and 2.

[0054] According to one or more embodiments, the ratio S2 / S1 of the cross section S2 to the cross section S1 is comprised between 1.1 and 1.5.

[0055] According to one or more embodiments, the cross-sections S1 and S2 of the riser / downcomer conduits are included within 0.3 m 2 and 15m 2 between.

[0056] According to one or more embodiments, the cross section of the riser / downcomer conduit is predetermined such that the velocity of the continuous phase passing through said riser / downcomer conduit is comprised between 0.005 m / s and 0.050 m / s.

[0057] According to one or more embodiments, a ratio H1 / H2 of the height H1 to the height H2 is comprised between 1.1 and 2.

[0058] According to one or more embodiments, a ratio H1 / H2 of the height H1 to the height H2 is comprised between 1.1 and 1.5.

[0059] According to one or more embodiments, the height H1 of the intertray spaces of the I-type 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 0.82 m.

[0060] According to one or more embodiments, the height H2 of the intertray spaces 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.

[0061] According to one or more embodiments, the liquid-liquid extraction column comprises:

[0062] an extraction zone extending substantially from a first injection point for injection of the first phase substantially as far as a second injection point for injection of the second phase, and

[0063] - A backwash zone adjacent to the extraction zone and extending from the first injection point for injection of the first phase substantially as far as a third injection point for injection of the backwash liquid.

[0064] According to a second aspect, the above objects and other advantages are obtained by a liquid-liquid extraction method comprising the steps of:

[0065] - injecting the first phase and the second phase into a liquid-liquid extraction column according to the first aspect; and

[0066] - Extracting an extract and a raffinate from the liquid-liquid extraction column.

[0067] According to one or more embodiments, the extraction column 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.

[0068] According to one or more embodiments, the first phase includes a mixture of aromatic and non-aromatic compounds.

[0069] According to one or more embodiments, the second phase includes a compound selected from the group consisting of 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 mixtures thereof.

[0070] According to one or more embodiments, the second phase comprises sulfolane and water.

[0071] Embodiments of the liquid-liquid extraction column and the method according to the aforementioned aspects, as well as other features and advantages, will become apparent from a reading of the following description, given purely by way of non-limiting illustration, and from reference to the following drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0072] Figure 1 A cross-sectional view of a liquid-liquid extraction column is schematically shown.

[0073] Figure 2 A cross-sectional view schematically illustrates the flow of dispersed and continuous phases in a reference liquid-liquid extraction column.

[0074] Figure 3 A cross-sectional view schematically shows the flow of dispersed phase and continuous phase in a liquid-liquid extraction column according to the present invention.

[0075] Figure 4 The top view of a Type I sieve tray and a Type II sieve tray according to the present invention is schematically shown. DETAILED DESCRIPTION

[0076] Embodiments of the present invention will now be described in detail. In the following detailed description, in order to provide a deeper understanding of the present invention, many specific details are presented. However, it will be apparent to those skilled in the art that the present invention can be implemented without these specific details. In other cases, in order to avoid unnecessarily complicating the description, well-known characteristics are not described in detail.

[0077] In this specification, the term "comprising" is synonymous with "including" and "containing", and is inclusive or open-ended, and does not exclude other elements not stated. It should be understood that the term "comprising" contains the exclusive and closed term "consisting of ..." In addition, in this specification, the term "substantially" corresponds to an approximation of ±10%, preferably ±5%, very preferably ±2% of a reference value, such as distance, speed, flow rate, compound content, temperature, pressure, etc.

[0078] Liquid-Liquid Extraction Column

[0079] The liquid-liquid extraction column according to the present invention comprises Figure 1 In addition, in order to improve the yield and purity, in the liquid-liquid extraction column according to the present invention, opposite to the first injection point 2 for injecting the liquid to be separated, two different operating zones can be defined:

[0080] an extraction zone 11 which extends substantially from a first injection point 2 for the injection of the first phase substantially as far as a second injection point 3 for the injection of the second phase, making it possible to extract compounds (for example aromatics) from the liquid to be separated, in particular by contacting in countercurrent with a liquid separation solvent (“yield” zone), and

[0081] an optional backwashing zone 12, which is adjacent to the extraction zone 11 and extends from the first injection point 2 for the injection of the first phase substantially up to a third injection point 13 for the injection of a backwashing liquid (optional), such as for the recycling of the extract, making it possible in particular to back-extract undesirable compounds (for example heavy non-aromatic compounds) contained in the extract 4 by means of the backwashing liquid, in order to ensure a high level of purity. According to one or more embodiments, the third injection point 13 for the injection of the backwashing liquid is arranged between the first injection point 2 and the first extraction point for extracting the extract 4.

[0082] Specific reference Figure 1, the separation liquid exits the liquid-liquid extraction column 1, while entraining the compounds of interest to be separated (e.g., aromatic compounds) to form an extract 4. The extract may also contain undesirable compounds (e.g., light non-aromatic compounds, such as C6-C7 compounds), which can be separated downstream (e.g., by distillation and / or stripping). Advantageously, the extract 4 contains substantially no (or very little) undesirable compounds (e.g., heavier non-aromatic compounds, such as C8+ compounds), which are difficult to separate and are separated from the extract in the backwash zone 12. Reference Figure 1 , the 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 to be understood that the present invention also relates to a liquid-liquid extraction column in which the separation liquid is lighter than the liquid to be separated, the injection point 3 for injecting the separation liquid is at the bottom of the liquid-liquid extraction column 1, and the injection point 13 for injecting the backwash liquid is at the top of the liquid-liquid extraction column 1.

[0083] Reference Figure 3 and 4 The liquid-liquid extraction tower 1 according to the present invention comprises n sieve trays P i , i is included between 1 and n. Each sieve tray P i Positioned so that the dispersed phase (i.e. the separation liquid which is heavier than the liquid to be separated) flows through the sieve trays P i The droplets of dispersed phase B are deposited on the next sieve tray P. i+1 The continuous phase A (i.e. the liquid to be separated which is lighter than the separated liquid) is re-aggregated on the sieve plate tray P to form a barrier layer. i+1 The liquid to be separated circulates in countercurrent to the separating liquid, i.e. from bottom to top, through the central and peripheral riser / downcomer conduits 6 and laterally in the inter-tray spaces 8. Figure 3 , the heavy phase is the dispersed phase B, and the light phase is the continuous phase A. It is to be understood that the liquid-liquid extraction column 1 may include sieve trays designed for the dispersed phase to be the light phase and the continuous phase to be the heavy phase.

[0084] According to one or more embodiments, the sieve tray P i The number n is comprised between 10 and 200, preferably between 50 and 150.

[0085] According to the present invention, the liquid-liquid extraction column 1 comprises type II sieve trays P alternately. i (i.e. comprising only one central riser / downcomer conduit) and Type I sieve tray P i (i.e. comprising two peripheral riser-downcomer conduits).

[0086] Specifically, Figure 4Tray P i As shown above, the II-type sieve tray has a zone of perforated holes 7 divided into two parts on both sides of the central riser / downcomer conduit 6. In addition, the I-type sieve tray has a zone of perforated holes 7, which can be unique or divided into two parts, such as Figure 4 Plate P i+1 , in order to maintain similarity to the portion of the zone perforated with holes 7 of a Type II sieve tray.

[0087] Therefore, it is to be understood that the present invention relates to a double-pass liquid-liquid extraction column. Specifically, reference is made to Figure 3 and 4 The liquid-liquid extraction tower 1 comprises a tray P having two peripheral riser / downcomer conduits 6. i and P i+2 (Type I tray), which has a central riser / downcomer conduit 6 i-1 and P i+1 Preferably, the peripheral riser / downcomer conduits 6 are arranged substantially adjacent to the outer shell of the tower, or even substantially joined to said outer shell. Preferably, the peripheral riser / downcomer conduits 6 are arranged substantially in diametrically opposed positions. Preferably, the central riser / downcomer conduits 6 are arranged in a strip that covers substantially the entire diameter of the tower.

[0088] In particular, during the numerical investigation of the flow in the alternating inter-tray spaces of type I and type II sieve trays Pi, the applicant company has found that entrainment of the dispersed phase into the riser / downcomer ducts is possible and can minimize the extraction performance. This entrainment was observed to occur first in the riser / downcomer ducts of the type II trays (central riser / downcomer duct).

[0089] According to the present invention, the sieve trays are modified in different ways depending on their type. Although the prior art would suggest increasing the height of the inter-tray spaces and the cross-sectional area (surface area) of the riser / downcomer ducts for all trays, the Applicant Company has found that the entrainment of the dispersed phase in the continuous phase can be reduced by:

[0090] - Type II sieve tray P i The cross-sectional area S2 of the central riser / downcomer conduit 6 is increased to be larger than the I-type sieve tray P i The cross-section S1 of the peripheral riser / downcomer conduit 6 is at the level of Figure 4 as shown; and

[0091] - Optionally, type I sieve tray P i The height H1 of the inter-tray space 8 is increased to be greater than that of the type II sieve tray P i The height H2 of the inter-tray space 8 is as Figure 3 shown.

[0092] In the present description it is understood that the cross-section S1 of a peripheral riser / downcomer duct 6 of a sieve tray corresponds to the sum of the cross-sections of the two peripheral riser / downcomer ducts of said sieve tray.

[0093] It is to be understood in this specification that the sieve tray P i The height of the inter-tray space 8 corresponds to the sieve tray P i The distance between the sieve tray and the sieve tray arranged directly downstream in the continuous phase flow direction, i.e. Figure 3 The sieve tray P in the example i-1 .

[0094] Advantageously, an increase in the cross-section of the riser / downcomer conduits of a Type II sieve tray may be accompanied by a decrease in the perforated surface area and the transfer quality of the inter-tray spaces of a Type I sieve tray, but this decrease is independent of the inter-tray spaces of a Type II sieve tray. Thus, increasing the cross-section of the riser / downcomer conduits of a Type II sieve tray degrades the transfer performance less than a change in the cross-section of all riser / downcomer conduits according to the prior art.

[0095] Similarly, the invention makes it possible to avoid entrainment of the dispersed phase in the riser / downcomer ducts (central riser / downcomer ducts) of the type II plates, while still minimizing the disadvantages of the applied modification, by alternating type I and type II sieve plate trays in the extraction column 1. As a result, the increase in the column height is reduced by a factor of two relative to the prior art, in which the height of all the inter-tray spaces is increased.

[0096] According to one or more embodiments, the ratio S2 / S1 of the cross section S2 to the cross section S1 is comprised between 1.1 and 2, preferably between 1.1 and 1.5. According to one or more embodiments, the ratio S2 / S1 of the cross section S2 to the cross section S1 is comprised between 1.2 and 1.4.

[0097] According to one or more embodiments, the cross-section of the riser / downcomer conduit 6 is predetermined so that the velocity of the continuous phase passing through said riser / downcomer conduit is comprised between 0.005 m / s and 0.050 m / s. According to one or more embodiments, the flow velocity of the continuous phase is comprised between 70 m / s and 100 m / s. 3 / hr and 400m 3 / hr, preferably 80m 3 / hr and 350m 3 / hr.

[0098] According to one or more embodiments, the cross-sections S1 and S2 of the riser / downcomer conduit 6 are included within 0.3 m2 and 15m 2 Between, preferably 2m 2 and 10m 2 According to one or more embodiments, the cross-section S1 of the central riser / downcomer conduit 6 is included in 0.33 m 2 and 15m 2 Between, preferably between 2.2m 2 and 10m 2 According to one or more embodiments, the cross-section S2 of the peripheral riser / downcomer conduit 6 is included in 0.3 m 2 and 13.5m 2 Between, preferably 2m 2 and 9m 2 between.

[0099] According to one or more embodiments, the ratio H1 / H2 of the height H1 to the height H2 is comprised between 1.1 and 2, preferably between 1.1 and 1.5. According to one or more embodiments, the ratio H1 / H2 of the height H1 to the height H2 is comprised between 1.2 and 1.9, preferably between 1.3 and 1.7.

[0100] According to one or more embodiments, the height H1 of the inter-tray spaces 8 of the I-type 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.

[0101] According to one or more embodiments, 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.

[0102] The diameter of the extraction column 1 is generally determined by a 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 included within 140 m 3 / hr and 2300m 3 / hr, preferably 200m 3 / hr and 2000m 3 / hr.

[0103] The height of the extraction column 1 generally depends on its diameter. According to one or more embodiments, the height of the extraction column is comprised between 15 m and 90 m.

[0104] According to one or more embodiments, the sieve tray P iThere is a hole 7 with a diameter comprised between 2 mm and 10 mm. According to one or more embodiments, the diameter of the hole is predetermined such that the velocity at the hole is comprised between 0.05 m / s and 0.60 m / s.

[0105] Liquid-Liquid Extraction Method

[0106] According to one or more embodiments, the extraction column 1 is operated at a pressure comprised between 0.05 MPa and 3 MPa (0.5 and 30 bar), preferably between 0.1 MPa and 2 MPa (1 and 20 bar), preferably between 0.2 MPa and 1.5 MPa (2 and 15 bar), preferably between 0.3 MPa and 1 MPa (3 and 10 bar). According to one or more embodiments, the extractor is operated at a temperature comprised 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.

[0107] Liquid raw materials to be separated

[0108] The liquid-liquid extraction method according to the present invention makes it possible to process a liquid feedstock to be separated comprising a mixture of aromatic and non-aromatic compounds. Preferably, the feedstock is hydrotreated and / or hydrogenated. According to one or more embodiments, the feedstock is a gasoline feedstock that is optionally hydrotreated and / or hydrogenated.

[0109] According to one or more embodiments, the feedstock is a C5+ fraction, i.e. a fraction containing compounds having 5 or more carbon atoms. According to one or more embodiments, the feedstock is a C5-C10 or C5-C11 fraction, i.e. a fraction containing compounds having from 5 to 10 or from 5 to 11 carbon atoms. According to one or more embodiments, the feedstock is a C6-C10 or C6-C11 fraction, i.e. a fraction containing compounds having from 6 to 10 or from 6 to 11 carbon atoms.

[0110] According to one or more embodiments, the feedstock comprises at least 20 wt. %, preferably at least 30 wt. %, very preferably at least 40 wt. %, for example at least 50 wt. %, of aromatic compounds having 6 to 11 carbon atoms, relative to the total weight of the feedstock.

[0111] According to one or more embodiments, the feedstock comprises at least 20 wt. %, preferably at least 30 wt. %, very preferably at least 40 wt. %, for example at least 50 wt. %, of monoaromatic compounds having 6 to 11 carbon atoms, relative to the total weight of the feedstock.

[0112] According to one or more embodiments, the aromatics of the feedstock are at least 95 wt%, preferably at least 98 wt%, and very preferably at least 99 wt% monoaromatics.

[0113] According to one embodiment of the invention, the feedstock 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.

[0114] According to one embodiment of the invention, the feedstock 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.

[0115] According to one embodiment of the invention, the feedstock comprises less than 0.1 wt% of dienes, preferably less than 0.05 wt% of dienes, and very preferably less than 0.01 wt% of dienes.

[0116] According to one embodiment of the present invention, the feedstock comprises less than 0.1 wt% olefins, preferably less than 0.05 wt% olefins, and very preferably less than 0.01 wt% olefins.

[0117] According to one embodiment of the invention, the feedstock exhibits a content of compounds having a boiling point greater than 217° C., such as naphthalene, 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.

[0118] According to one embodiment of the present invention, the feedstock does not contain the following compounds: H2, H2S, light gases (such as ethane), propane and butane. According to one embodiment of the present invention, the removal of these compounds from the feedstock is carried out in a fractionation column.

[0119] According to one embodiment, the feedstock is at least partly a gasoline fraction from a fluidized catalytic cracking unit (FCC (for fluid catalytic cracking) unit), which gasoline fraction has preferably been selectively hydrogenated to convert diolefins into 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 one embodiment of the invention, the feedstock comes from the hydrogenation of pyrolysis gasoline (pyrolysis gas), which is in the form of a mixture with a gasoline fraction from an FCC unit.

[0120] Liquid separation solvent

[0121] According to one or more embodiments, the solvent includes a compound selected from the group consisting of 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 mixtures thereof.

[0122] According to one or more embodiments, the solvent comprises sulfolane or is composed of sulfolane. According to one or more embodiments, relative to the gross weight of the solvent, the solvent is composed of at least 80 wt % (e.g. at least 90 wt %), preferably at least 95 wt % (e.g. at least 99 wt %) sulfolane.

[0123] According to one or more embodiments, the solvent further comprises an anti-solvent, such as water. According to one or more embodiments, the anti-solvent comprises water or consists of water. According to one or more embodiments, relative to the total weight of the solvent, the solvent comprises an anti-solvent, such as water, between 0.01 wt % and 5 wt %, preferably between 0.1 wt % and 3 wt % (e.g., between 0.5 wt % and 2 wt %). According to one or more embodiments, the solvent comprises sulfolane and water or consists of sulfolane and water.

[0124] Example

[0125] The example of a liquid-liquid extraction column described below has all of the following features: The liquid-liquid extraction column has a diameter of 4.8 m. Each tray includes 17,192 holes. The feedstock (continuous phase and light phase) is injected at the lower tray at a flow rate of 1.02E+05 kg / hr. The feedstock contains 40 wt% isooctane, 30 wt% benzene and 30 wt% p-xylene (density 724 kg / m 3 The liquid separation solvent (dispersed phase and heavy phase) was injected at the upper tray at a flow rate of 8.25E+05 kg / hr. The liquid separation solvent contained 99.5 wt% sulfolane and 0.5 wt% water (density 1136 kg / m 3 ).

[0126] Example 1 (reference): Constant inter-tray height and constant riser / downcomer duct cross section

[0127] The liquid-liquid extraction column had a height of 36.0 m and consisted of a series of 120 sieve trays.

[0128] No adjustment:

[0129] -Height of the space between trays: H1 = H2 = 0.30m,

[0130] - Cross-section of riser / downcomer duct: S1 = S2 = 1.70 m 2 .

[0131] In Reference Example 1, disturbances in the dispersed phase flow were observed, some of the dispersed phase entrained some of the continuous phase toward the riser / downcomer conduit, and deformation of the coalesced layer was observed on the tray downstream in the dispersed phase flow direction. In order to quantitatively express the performance, the height equivalent to the theoretical plate (HETP) was calculated, which is a conventional concept in separations (distillation, extraction). The lower the HETP, the more efficient the extractor.

[0132] For Reference Example 1, the HETP is 4.76 m.

[0133] Example 2 (reference): Increased height of the space between trays

[0134] Compared to Example 1, the heights H1 and H2 of the spaces between the trays are increased:

[0135] -Height of the space between trays: H1 = H2 = 0.45m,

[0136] - Cross-section of riser / downcomer duct: S1 = S2 = 1.70 m 2 .

[0137] For Reference Example 2, the HETP is 5.83 m.

[0138] The liquid-liquid extraction column had a height of 44.0 m and consisted of a series of 98 sieve trays.

[0139] Example 3 (reference): Increased cross-section of riser / downcomer conduit

[0140] Relative to Example 1, the cross-sections S1 and S2 of the riser / downcomer ducts are increased by:

[0141] -Height of the space between trays: H1 = H2 = 0.30m,

[0142] - Cross-section of riser / downcomer duct: S1 = S2 = 2.10 m 2 .

[0143] For Reference Example 3, the HETP is 4.81 m.

[0144] The liquid-liquid extraction column had a height of 36.3 m and consisted of a series of 121 sieve trays.

[0145] Example 4 (invention): Alternating cross-sections of riser / downcomer conduits

[0146] Compared to example 1, only the cross section S2 increases:

[0147] -Height of the space between trays: H1 = H2 = 0.30m,

[0148] - Cross-section of riser / downcomer duct: S1 = 1.70 m2 ; S2=2.10m 2 .

[0149] For Example 4 according to the present invention, the HETP is 4.17 m.

[0150] The liquid-liquid extraction column had a height of 31.5 m and consisted of a series of 105 sieve trays.

[0151] Example 5 (invention): Alternation of height of the inter-tray spaces and cross-section of the riser / downcomer ducts

[0152] Relative to Example 1, only the height H1 and the cross section S2 increase:

[0153] -Height of the space between trays: H1 = 0.45m; H2 = 0.30m,

[0154] - Cross-section of riser / downcomer duct: S1 = 1.70 m 2 ; S2=2.10m 2 .

[0155] For Example 5 according to the present invention, the HETP is 4.08 m.

[0156] The liquid-liquid extraction column had a height of 30.8 m and consisted of a series of 82 sieve trays.

[0157] Table 1 below summarizes the performance levels of Reference Examples 1, 2 and 3 and Examples 4 and 5 according to the present invention.

[0158] Table 1

[0159] Example 1(reference) 2(reference) 3(reference) 4(Invention) 5(Invention) H1(m) 0.30 0.45 0.30 0.30 0.45 H2(m) 0.30 0.45 0.30 0.30 0.30 <![CDATA[S1(m 2 )]]> 1.70 1.70 2.10 1.70 1.70 <![CDATA[S2(m 2 )]]> 1.70 1.70 2.10 2.10 2.10 HETP(m) 4.76 5.83 4.81 4.17 4.08 Tower height(m) 36.0 44.0 36.3 31.5 30.8 Number of trays 120 98 121 105 82

[0160] Advantageously, the HETP, column height and number of trays of Examples 4 and 5 according to the invention are reduced relative to the HETP, column height and number of trays of Reference Examples 1, 2 and 3.

Claims

1. A liquid-liquid extraction tower comprising the following elements: - a first injection point (2) for injecting a first phase; a second injection point (3) for injecting a second phase, said first and second injection points (2, 3) being positioned on said extraction column (1) in such a way as to allow said first and second phases to circulate in said extraction column (1) in a countercurrent manner, one of said first and second phases being a continuous phase (A) and the other being a dispersed phase (B); - a first extraction point for extracting the extract (4) and a second extraction point for extracting the raffinate (5), one located at the bottom of the extraction column (1) and the other located at the top of the extraction column (1); and - a plurality of sieve trays (P) positioned from the top of the extraction column (1) to the bottom of the extraction column (1) i ), the sieve plate tray (P i ) are separated by inter-tray spaces (8) and include weir plates (10) designed to retain the sieve trays (P i ) a layer (9) of dispersed phase (B) agglomerated above or below; - a plurality of riser / downcomer conduits (6) which are openings adjacent to the weir (10) and allow the continuous phase (A) to pass through the sieve trays (P i ), The extraction column (1) alternately comprises: - Sieve trays called Type I (P i ) comprising two peripheral riser / downcomer conduits (6); and - Sieve trays called Type II (P i ), comprising a single central riser / downcomer conduit (6), Wherein, the extraction tower (1): The cross-section S2 of the central riser / downcomer duct (6) is greater than the cross-section S1 of the peripheral riser / downcomer duct (6), the cross-section S1 corresponding to the sum of the cross-sections of the two peripheral riser / downcomer ducts (6).

2. The liquid-liquid extraction tower according to claim 1, wherein: The ratio S2 / S1 of the cross section S2 to the cross section S1 is comprised between 1.1 and 2.

3. The liquid-liquid extraction tower according to claim 1 or claim 2, wherein: The ratio S2 / S1 of said cross section S2 to said cross section S1 is comprised between 1.1 and 1.

5.

4. A liquid-liquid extraction column according to any one of the preceding claims, wherein: In the flow direction of the continuous phase, the height H1 of the inter-tray space (8) located directly downstream of the type I tray is greater than the height H2 of the inter-tray space (8) located directly downstream of the type II tray.

5. The liquid-liquid extraction tower according to claim 4, wherein: The ratio H1 / H2 of the height H1 to the height H2 is comprised between 1.1 and 2.

6. The liquid-liquid extraction tower according to claim 4 or claim 5, wherein: The ratio H1 / H2 of the height H1 to the height H2 is comprised between 1.1 and 1.

5.

7. The liquid-liquid extraction tower according to any one of claims 4 to 6, wherein: The height H1 of the intertray spaces ( 8 ) of the I-type 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.

8. The liquid-liquid extraction tower according to any one of claims 4 to 7, wherein: The height H2 of the intertray 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.

9. A liquid-liquid extraction column according to any one of the preceding claims, comprising: an extraction zone (11) extending substantially from a first injection point (2) for the injection of the first phase substantially as far as a second injection point (3) for the injection of the second phase, and A backwash zone (12) adjacent to the extraction zone (11) and extending from the first injection point (2) for the injection of the first phase substantially as far as a third injection point (13) for the injection of the backwash liquid.

10. A liquid-liquid extraction method comprising the following steps: - injecting the first phase and the second phase into a liquid-liquid extraction column according to any one of claims 1 to 9; and - Extracting an extract (4) and a raffinate (5) from the liquid-liquid extraction column.

11. The liquid-liquid extraction method according to claim 10, 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.

12. The liquid-liquid extraction method according to claim 10 or 11, wherein: The first phase comprises a mixture of aromatic and non-aromatic compounds.

13. The liquid-liquid extraction method according to any one of claims 10 to 12, wherein: The second phase comprises a compound selected from the group consisting of 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 mixtures thereof.

Images