Liquid-liquid extraction method for aromatics without backwash

Abstract

The present invention relates to a method and device for separating aromatic compounds from a feed (1), the feed comprising a mixture of aromatic and non-aromatic compounds, wherein aromatic compounds are extracted from the feed (1) in a liquid-liquid extractor (T1) supplied with a solvent (2) in order to produce at least one extract (4) concentrated in aromatic compounds relative to the feed (1), and a raffinate (3) concentrated in non-aromatic compounds relative to the composition of the feed (1); and wherein the liquid-liquid extractor (T1) is supplied with the entirety of an extract recycle (5) at one or more positions in the liquid-liquid extractor (T1) arranged between a feed point for the feed (1) and a feed point for the solvent (2).

Description

[0001] Liquid-liquid extraction process for aromatics without backwashing

[0002] technical field

[0003] The field of the invention relates to the separation of aromatic compounds, such as benzene, toluene, xylenes (BTX), but also aromatic compounds with 9, 10 or 11 carbon atoms (A9, A10, A11), for petrochemicals from a feed comprising a mixture of aromatic and non-aromatic compounds, such as a gasoline feed.

[0004] Previous technique

[0005] The prior art relates to the aromatic extraction process comprising a liquid-liquid aromatic extraction column as described in the book "Process of Separation" by J.-P. Wauquiez (Technip Edition 1998, p. 438-444) and in patent application FR3133765. In particular with reference to figure 1, a reference process allows the charge 1 (continuous phase) to be treated with a solvent stream 2 (dispersed phase) in a reference liquid-liquid extractor T1 to produce a concentrated (i.e. enriched) stream of non-aromatic compounds (raffinate 3) and a concentrated stream of aromatic compounds (extract 4).Specifically, feed 1, comprising a mixture of aromatics and non-aromatics, is fed into the middle of the liquid-liquid extraction column T1, solvent 2 is fed into the top of the liquid-liquid extraction column T1, and liquid-liquid extraction is carried out by contact between feed 1 and solvent 2 in the upper part Z1 (the so-called extraction zone) of the liquid-liquid extraction column T1. Within the same column, the aromatic-laden solvent enters the lower part Z2 (the so-called backwash zone) where said solvent is contacted with at least a portion 52 of an extract recycle 5 comprising light non-aromatic compounds. A portion 51 of the extract recycle 5 may also be fed into the extraction zone.

[0006] Typically, in the reference T1 liquid-liquid extractor, the mass ratio between the backwash flow rate and the feed is between 0.05 and 10. For typical operation of the liquid-liquid extractor, for example with a heavy feed (e.g., C6-C8+ feed), extract recycling is implemented. Figure 2 schematically illustrates the evolution of the continuous phase flow rate Q c (fed by extract recycle 5 and load 1) from bottom to top (Z-axis) in the column. The following points are observed in particular:

[0007] - between the bottom of the column and the injection point of charge 1 (backwash zone), the continuous phase flow rate changes little (slight decrease), and corresponds approximately to the extract recycle flow rate 5 injected at the bottom of the column: the heavy non-aromatic compounds contained in the dispersed phase (fed by solvent 2) are back-extracted by the continuous phase while the aromatics are extracted by the solvent; - at the injection point of charge 1, the charge 1 flow rate and the extract recycle flow rate 5 are added together, which leads to a maximum total continuous phase flow rate which sizes the liquid-liquid extractor T1;

[0008] - above the charge injection point 1 (extraction zone), the continuous phase flow rate decreases due to the extraction of aromatics in the counter-currently circulating dispersed phase;

[0009] - in certain configurations, not all of the extract recycle flow 5 is injected at the bottom of the column, a part 51 of the extract recycle 5 is injected into the extraction zone.

[0010] Consequently, the continuous phase flow rate in the backwash zone is generally lower than in the extraction zone fed by the feed. This operation can lead to significant relative deviations in continuous phase flow rate, reaching -100% and +100% compared to the feed flow rate 1 at the inlet of the liquid-liquid extractor T1. However, gravity column technology, commonly used in aromatic (non-exclusive) extraction processes, is known for its inflexibility. Therefore, this type of operation is not optimal from an extractor design perspective and can lead to efficiency losses.

[0011] Summary of the invention

[0012] In the context described above, a primary objective of this description is to propose a process for separating a hydrocarbon feedstock for the production of aromatics, enabling:

[0013] - a very high purity of aromatics in the concentrated extract of aromatic compounds;

[0014] - an increase in the extraction yields of aromatics present in the feed;

[0015] - a reduction in flow variation of the continuous phase passing through the liquid-liquid extractor;

[0016] - a more homogeneous flow hydrodynamics;

[0017] - a reduction in the solvent / filler mass ratio at the same yield in aromatics;

[0018] - a reduction in column diameter at isocapacity;

[0019] - an increase in the efficiency of the platters (and therefore a reduction in the number of platters) at the same performance.

[0020] According to a first aspect, the aforementioned objects, as well as other advantages, are obtained by a process of separating aromatic compounds from a feed comprising a mixture of aromatic and non-aromatic compounds, the process comprising the following steps: extracting aromatics from the feed by means of a liquid-liquid extractor supplied with a solvent to produce at least one extract concentrated in aromatic compounds relative to the composition of the feed, and a raffinate concentrated in non-aromatic compounds relative to the composition of the feed;

[0021] - feed the liquid-liquid extractor with the entirety of an extract recycle at one or more positions of the liquid-liquid extractor arranged between a feed point and a solvent feed point.

[0022] According to one or more embodiments, the solvent substantially feeds the head of the liquid-liquid extractor.

[0023] According to one or more embodiments, the charge substantially feeds the bottom of the liquid-liquid extractor.

[0024] According to one or more embodiments, the extract recycle feeds the liquid-liquid extractor between the feed point and the solvent feed point at a single injection point.

[0025] According to one or more embodiments, the extract recycle feeds the liquid-liquid extractor between the feed point and the solvent feed point at several injection points.

[0026] According to one or more embodiments, the process comprises the following steps:

[0027] - supply the liquid-liquid extractor with the charge at a charge supply point located at the bottom of the liquid-liquid extractor;

[0028] - supply the liquid-liquid extractor with the solvent at a solvent supply point located at the head of the liquid-liquid extractor.

[0029] According to one or more embodiments, the mass ratio of solvent to charge is between 0.1 and 50, preferably between 0.5 and 20, preferably between 1 and 9, preferably between 3 and 8.

[0030] According to one or more embodiments, the mass ratio of the extract recycle to the load is between 0.05 and 10, preferably between 0.1 and 8, preferably between 0.2 and 5, preferably between 0.3 and 2.

[0031] According to one or more embodiments, the charge contains aromatic and non-aromatic hydrocarbon compounds comprising 5 to 11 carbon atoms.

[0032] According to one or more embodiments, the liquid-liquid extractor is operated under at least one of the following operating conditions: a pressure between 0.05 MPa and 3 MPa, preferably between 0.1 MPa and 2 MPa, preferably between 0.2 MPa and 1.5 MPa, preferably between 0.3 MPa and 1 MPa; a temperature between 10°C and 150°C, preferably between 15°C and 130°C, preferably between 30°C and 120°C, preferably between 40°C and 110°C.

[0033] According to one or more embodiments, the process comprises the following steps:

[0034] - stripping of the extract using an extract stripping section to separate a gas stream comprising non-aromatic compounds and a purified extract;

[0035] - separation of aromatics from the purified extract by means of an aromatics recovery tower to separate the solvent and overhead vapors comprising an aromatic stream.

[0036] According to one or more embodiments, the process comprises the following steps:

[0037] - feeding the liquid-liquid extractor with the solvent comprising a solvent selected from the list 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, pyrrolidine-2-one, furfural, 1,1,3,3-tetramethylurea and a mixture of these;

[0038] - phase separation of the gas stream in a decanting condenser to separate the extract recycle and an aqueous phase;

[0039] - washing of the raffinate with water using a water-fed washing tower supplied with water to produce a non-aromatic stream and wash water;

[0040] - regeneration of at least a portion of the solvent by means of a solvent regeneration section by vacuum steam entrainment;

[0041] - condensation of overhead vapors in a decanting condenser to produce the aromatic stream.

[0042] According to one or more embodiments, the process comprises the following steps:

[0043] - feeding the liquid-liquid extractor with a solvent 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 of these;

[0044] - stripping of hydrocarbon compounds present in the wash water and / or in the aqueous phase by means of a water stripping section to produce water; feeding of the aromatics recovery tower with steam to produce overhead vapors including steam, and condensation of the overhead vapors in the decanting condenser to produce the aromatic stream and decanted water.

[0045] According to one or more embodiments, the process comprises the following steps:

[0046] - feeding the liquid-liquid extractor with a solvent comprising sulfolane and water;

[0047] - recycling of water produced by the water stripping section to the aromatics recovery tower.

[0048] According to a second aspect, the aforementioned objects, as well as other advantages, are obtained by a device for separating aromatic compounds from a feed comprising a mixture of aromatic and non-aromatic compounds, the device comprising a liquid-liquid extractor adapted to extract aromatics from the feed with a solvent to produce at least one extract concentrated in aromatic compounds relative to the composition of the feed, and a raffinate concentrated in non-aromatic compounds relative to the composition of the feed, the liquid-liquid extractor comprising:

[0049] - a feed point for the charge, for example located at the bottom of the liquid-liquid extractor;

[0050] - a solvent supply point, for example located at the head of the liquid-liquid extractor;

[0051] - one or more feed points for extract recycle suitable to feed the entirety of an extract recycle, the feed point or feed points for extract recycle being arranged between the feed point for charge and the feed point for solvent.

[0052] Embedding methods 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.

[0053] List of figures

[0054] Figure 1 schematically shows the operating principle of a reference liquid-liquid extractor.

[0055] Figure 2 schematically illustrates the evolution of the continuous phase flow rate from bottom to top in a reference liquid-liquid extractor. Figure 3 schematically illustrates the operating principle of the liquid-liquid extractor according to the invention.

[0056] Figure 4 schematically shows the evolution of the continuous phase flow rate from bottom to top in a liquid-liquid extractor according to the invention.

[0057] Figure 5 schematically shows a separation process according to the invention.

[0058] Description of the implementation methods

[0059] 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.

[0060] 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." The term "based on" is synonymous with "comprises at least 50% by weight of." Furthermore, in this description, the terms "essentially" or "substantially" correspond to an approximation of ±10%, preferably ±5%, most preferably ±1%, or ±0.5%. For example, an effluent consisting essentially of or made up of compound A corresponds to an effluent comprising at least 90% by weight of compound A. In this description, the term "one-compound concentrated flow" corresponds, for example, to a flow comprising at least 80% by weight, preferably at least 90% by weight, most preferably at least 95% by weight of said compound.

[0061] The present invention relates to the separation of aromatic compounds, and in particular BTX, but also aromatic compounds with 9, 10, or even 11 carbon atoms (A9, A10, A11), for the petrochemical industry, originating, for example, from a gasoline feedstock, such as catalytic cracking gasoline. It relates in particular to an improved process and device for separating so-called C6-C11 compounds, i.e., aromatic hydrocarbon compounds with 6 to 11 carbon atoms, from a feedstock comprising a mixture of aromatic and non-aromatic compounds, such as gasoline.

[0062] Specifically with reference to Figure 3, the process according to the invention allows the feed 1 to be treated with a solvent stream 2 in a liquid-liquid extractor T1 (gravity column) to produce a concentrated (i.e. enriched) stream of non-aromatic compounds, i.e., a raffinate 3, and a concentrated stream of aromatic compounds, i.e., an extract 4. According to the invention, the feed point of the feed 1 is advantageously located at the bottom of the liquid-liquid extractor T1, the feed point of the solvent 2 is advantageously located at the top of the liquid-liquid extractor T1, the outlet point of the raffinate 3 is advantageously located at the top of the liquid-liquid extractor T1, and the outlet point of the extract 4 is advantageously located at the bottom of the liquid-liquid extractor T1. The feed point for charge 1 is, for example, located between a settling zone for extract 4 and a (first) separation element (e.g.tray or packing) adjacent to said settling zone. According to one or more embodiments, the liquid-liquid extractor T1 is a gravity column, for example, with perforated trays and / or packing. Preferably, the liquid-liquid extractor T1 is a gravity column with perforated trays.

[0063] According to the invention, the liquid-liquid extractor T1 is fed with the entirety of a recycle of extract 5 (recycle of light compounds, in particular C5-C7 hydrocarbons rich in non-aromatic compounds compared to extract 4, from the head of the stripping section of extract T3) at a position of the liquid-liquid extractor T1 located between the feed point 1 and the solvent feed point 2. In this description, the term "entire recycle" is used to express that the recycle feeds the liquid-liquid extractor T1 only between the feed point 1 and the solvent feed point 2, and more particularly above the feed point 1. It follows that the liquid-liquid extractor T1 according to the invention does not include a backwash zone.

[0064] Advantageously, the liquid-liquid extractor T1 according to the invention allows for reduced variations in continuous phase flow rate compared to a reference liquid-liquid extractor T1 with a backwash zone. For example, Figure 4 schematically shows the evolution of the continuous phase flow rate Q c (fed by extract recycle 5 and feed 1) from bottom to top (Z-axis) in a liquid-liquid extractor T1 according to the invention. The following points are particularly noteworthy:

[0065] - an increase in aromatic yield of at least 5% at iso mass ratio of solvent to feed (S / F), knowing that the last percentages of aromatics to be extracted are the most difficult (note: yields are calculated downstream of the stripping section of extract T3 and / or recovery tower T6);

[0066] - a very high purity of the extract, in particular in benzene (>99.95% by weight), in toluene (>99.0% by weight), in aromatics with 8 carbon atoms (A8) (>98.0% by weight) and aromatics with at least 9 carbon atoms (A9+) (>97.0% by weight), values ​​observed after passing through the extract stripping section T3 and / or the aromatics recovery tower T6;

[0067] - a reduction in flow variation of the continuous phase passing through the liquid-liquid extractor: the injection of the entire extract recycle 5 above the feed point 1 compensates for the losses of the continuous phase as it progresses through the extractor (due to mass transfer by affinity with the solvent), which smooths the flow variations (flow differences for the continuous phase up to -55% and +0% compared to the incoming feed);

[0068] - a more homogeneous flow hydrodynamics which improves the operation of the equipment (better efficiency);

[0069] - a reduction (up to 40%) in the solvent / filler mass ratio at the same aromatic yield;

[0070] - a reduction in column diameter at isocapacity: by reducing the flow rate differences within the extractor, the volume (e.g. the diameter) of the extractor is reduced - the decrease in the solvent / load ratio combined with the reduction of flow rate differences makes it possible to reduce (up to 30%) the diameter of the column;

[0071] - an increase (up to 30%) in the efficiency of the trays (and therefore a reduction in the number of trays) at the same performance.

[0072] The charge

[0073] The separation process according to the invention allows for the treatment of a feed 1 comprising a mixture of aromatic and non-aromatic compounds. Preferably, the feed 1 is hydrotreated and / or hydrogenated. According to one or more embodiments, the feed 1 is a gasoline feed that is optionally hydrotreated and / or hydrogenated.

[0074] In one or more embodiments, charge 1 is a C5+ hydrocarbon fraction, i.e., containing compounds with 5 or more carbon atoms. In one or more embodiments, charge 1 is a C5-C10 or C5-C11 fraction, i.e., containing hydrocarbon compounds with 5 to 10 or 5 to 11 carbon atoms. In one or more embodiments, charge 1 is a C6-C10 or C6-C11 fraction, i.e., containing hydrocarbon compounds with 6 to 10 or 6 to 11 carbon atoms.

[0075] According to one or more embodiments, the charge 1 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.

[0076] According to one or more embodiments, the aromatic compounds of charge 1 are mono-aromatic compounds of at least 95% by weight, preferably at least 98% by weight, most preferably at least 99% by weight.

[0077] According to one embodiment of the invention, charge 1 comprises less than 50 ppm by weight of sulfur, preferably less than 10 ppm by weight of sulfur, and most preferably less than 1 ppm by weight of sulfur. According to another embodiment of the invention, charge 1 comprises less than 100 ppm by weight of nitrogen, preferably less than 10 ppm by weight of nitrogen, and most preferably less than 1 ppm by weight of nitrogen.

[0078] According to one embodiment of the invention, charge 1 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.

[0079] According to one embodiment of the invention, the charge 1 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.

[0080] According to one embodiment of the invention, the charge 1 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.

[0081] According to one embodiment of the invention, the feed 1 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 1 is carried out in a fractionation column.

[0082] According to one embodiment, said feed 1 is at least partly a gasoline fraction from a fluidized bed catalytic cracking unit (FCC unit for "Fluid Catalytic Cracking" according to Anglo-Saxon terminology), 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 feed 1 is obtained from the hydrogenation of pyrolysis gasoline (PyGas according to Anglo-Saxon terminology) mixed with a gasoline fraction from an FCC unit.

[0083] Extraction

[0084] The extraction of aromatics in the present invention makes it possible to treat the feed 1 in order to recover, on the one hand, a concentrated stream of non-aromatic compounds called raffinate 3 and on the other hand, a concentrated stream of aromatics called extract 4, with respect to the composition of the feed 1.

[0085] According to the invention, the extraction of aromatics is a liquid-liquid extraction of aromatics.

[0086] With reference to Figure 5, according to one or more embodiments, the liquid-liquid extraction of aromatics comprises the following steps: - liquid-liquid extraction using a liquid-liquid extractor T1 supplied with a solvent stream 2 to separate the raffinate 3 and the extract 4,

[0087] - washing of raffinate 3 with a T2 water washing tower (optional step),

[0088] - stripping of the water used in the T2 scrubbing tower with a water stripping section (optional step),

[0089] - stripping (e.g., with water) of extract 4 with a stripping section of extract T3,

[0090] - separation of aromatics with a T6 recovery tower to separate an aromatic stream 13 and the solvent stream 2, and

[0091] - solvent regeneration with a solvent regeneration section (optional step).

[0092] For the sake of simplicity, the optional water stripping and solvent regeneration sections are not shown in Figure 5.

[0093] Liquid-liquid extractor T 1

[0094] Liquid-liquid extraction allows the separation of aromatics from non-aromatic compounds, such as paraffins and naphthenes, from charge 1.

[0095] In one or more embodiments, the liquid-liquid extractor T1 is adapted to contact a continuous phase and a dispersed phase (within the continuous phase). In one or more embodiments, solvent 2 feeds the continuous phase of the liquid-liquid extractor T1, and feed 1 feeds the dispersed phase of the liquid-liquid extractor T1. Preferably, feed 1 feeds the continuous phase of the liquid-liquid extractor T1, and solvent 2 feeds the dispersed phase of the liquid-liquid extractor T1.

[0096] According to the invention, the extract recycle stream 5, for example from the stripping section of extract T3, feeds the extraction zone Z1 of the liquid-liquid extractor T1, i.e. above the feed point of the charge 1 and below the feed point of the solvent stream 2. According to one or more embodiments, the extract recycle 5 feeds the extraction zone Z1 at at least one point located at a position between 0.05* L1 and 0.95* L1, and preferably between 0.2xL1 and 0.9xL1 and preferably between 0.3xL1 and 0.8xL1, L1 being the length (from) the feed point of the charge 1 (to) the feed point of the solvent 2, L1 thus corresponding to the length of the upper part Z1. In this description, 0xL1 corresponds to the position of the supply point of load 1.

[0097] In one or more embodiments, the extract recycle 5 feeds the liquid-liquid extractor T1 at a single injection point. In one or more embodiments, the extract recycle 5 feeds the liquid-liquid extractor T1 at several injection points. In one or more embodiments, the positions of the various injection points of the extract recycle 5 are determined so as to smooth out the flow rate variations of the continuous phase in the liquid-liquid extractor T1. In one or more embodiments, an injection point of the extract recycle 5 is located at a given tray i of the extraction zone of the liquid-liquid extractor T1, when the flow rate variation of said tray i relative to the maximum flow rate of the continuous phase in the liquid-liquid extractor T1 (Qc,i - Qc,max) / Qc,max) is greater than 20%, preferably greater than 40%, and most preferably greater than 60%.

[0098] The liquid-liquid extractor T1 separates a raffinate 3, which is depleted in aromatic compounds compared to feed 1, from an extract 4, which is concentrated in aromatic compounds compared to feed 1. The raffinate 3 exits at the top of the liquid-liquid extractor T1 and is optionally sent to the water scrubber T2. The extract 4 exits at the bottom of the liquid-liquid extractor T1 and is sent to the extract stripping section T3, preferably with heat exchange with the solvent stream 2 (not shown in Figure 5 for simplicity).

[0099] According to one or more embodiments, the T1 liquid-liquid extractor operates adiabatically.

[0100] According to one or more embodiments, the mass ratio of solvent 2 to feed 1 is between 0.1 and 50, preferably between 0.5 and 20, preferably between 1 and 10, preferably between 3 and 8. According to one or more embodiments, the mass ratio of extract recycle 5 to feed 1 is between 0.05 and 10, preferably between 0.1 and 8, preferably between 0.2 and 5, preferably between 0.5 and 2.

[0101] In 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. In one or more embodiments, the solvent comprises or consists of sulfolane. In 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. 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 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. According to one or more embodiments, the liquid-liquid extractor T1 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), for example when the solvent includes sulfolane.According to one or more embodiments, the extractor is operated at a temperature between 10°C and 150°C, preferably between 30°C and 130°C, preferably between 40°C and 120°C, for example when the solvent includes sulfolane.

[0102] Optional T2 water wash tower

[0103] Water washing of raffinate 3 allows for the removal of any solvent potentially present in the raffinate 3. Preferably, the raffinate 3 is cooled before entering tower T2. Preferably, the raffinate 3 enters at the bottom of said tower T2, water 6 is introduced at the top of said tower, the non-aromatic stream 7 (washed and thus solvent-depleted raffinate 3) exits at the top of said tower, and the wash water 8 (concentrated / enriched with solvent) exits at the bottom of said tower. In one or more embodiments, the non-aromatic stream 7 comprises less than 100 ppm by weight, preferably less than 10 ppm by weight, and most preferably less than 1 ppm by weight of solvent. In one or more embodiments, the wash water 8 is sent to the water stripping section (not shown).

[0104] Advantageously, the non-aromatic stream 7 comprises less than 25% by weight, preferably at least 20% by weight, very preferably less than 17% by weight of aromatic compounds, relative to the total weight of the non-aromatic stream 7.

[0105] Advantageously, the non-aromatic stream 7 can be sent to a thermal cracking stage / unit or to a catalytic reforming stage / unit for example in order to increase the production of aromatics.

[0106] T3 Extract Stripping Section

[0107] Stripping extract 4 allows the removal of non-aromatic compounds still present in extract 4. Extract 4, loaded with aromatic compounds and solvent, is preferably introduced at the top (head) of the stripping section of extract T3, possibly with the addition of further solvent (not shown). In the stripping section of extract T3, the purity of extract 4 is improved because the residual non-aromatic compounds carried along with the aromatic compounds (less soluble in the solvent) are extracted (e.g., by steam) as a gas stream 9 at the head of the stripping section of extract T3. According to one or more embodiments, the gas stream 9 comprises at least 50 wt%, such as between 70 wt% and 95 wt%, of light hydrocarbons, i.e., C5-C7 compounds. The gas stream 9 may comprise up to 40 wt% of aromatic compounds.According to one or more embodiments, the gas stream 9 is combined with water, such as water recovered at the top of the water stripping section (not shown). The gas stream 9 is sent to the decanter condenser CD3 for phase separation, which allows the hydrocarbon phase to be recycled to the liquid-liquid extractor T1 as an extract recycle stream 5. The aqueous phase 10 is optionally combined with wash water 8 and sent to the water stripping section (not shown). The purified extract 12 from the extract stripping section T3 can be sent to the aromatics recovery tower T6 to separate the aromatics from the solvent (in particular, sulfolane), which can then be recycled to the liquid-liquid extractor T1.

[0108] It is understood that the stripping section of the T3 extract can be replaced by a distillation section, such as a column equipped with an external reboiler.

[0109] Extract recycle 5 is a concentrated stream of C5-C7 hydrocarbons, i.e., compounds containing 5 to 7 carbon atoms, relative to the composition of extract 4. In one or more embodiments, extract recycle 5 comprises at least 40% by weight and preferably at least 50% by weight, e.g., between 60% by weight and 95% by weight, preferably between 60% by weight and 75% by weight, of non-aromatic compounds (compounds carried over by the aromatic compounds of the extract). In one or more embodiments, extract recycle comprises at least 70% by weight, preferably at least 80% by weight, and most preferably at least 90% by weight, of compounds with 7 carbon atoms or fewer. According to one or more embodiments, the extract recycle 5 comprises aromatics, for example benzene and / or toluene with a content of between 0.1% and 60% by weight, preferably between 1% and 50% by weight, very preferably between 5% and 40% by weight.

[0110] Stripping of extract 4 is preferably carried out at low pressure or even under vacuum to improve the removal of non-aromatics from the solvent (particularly sulfolane). According to one or more embodiments, the stripping section of extract T3 is operated at a head pressure between 0.001 MPa and 2 MPa (0.01 and 20 bara), preferably between 0.005 MPa and 1 MPa (0.05 and 10 bara), preferably between 0.01 MPa and 0.8 MPa (0.1 and 8 bara), preferably between 0.03 MPa and 0.5 MPa (0.3 and 5 bara), for example when the solvent contains sulfolane. According to one or more embodiments, the stripping section of the T3 extract is operated at a background temperature between 50°C and 300°C, preferably between 100°C and 250°C, preferably between 130°C and 200°C, preferably between 145°C and 195°C, for example when the solvent includes sulfolane.

[0111] Water stripping section (optional - not shown)

[0112] Stripping the wash water 8 and optionally the aqueous phase 10 removes dissolved hydrocarbons (mainly non-aromatic) from the water exiting the extract stripping section head T3 and optionally the water scrubber T2. In one or more embodiments, at least a portion of the water exiting the water stripping section is sent to the aromatics recovery tower T6 to increase the amount of stripping steam sent to the bottom of the aromatics recovery tower T6. In one or more embodiments, a portion of the water exiting the water stripping section is sent to the solvent regeneration section (not shown).

[0113] T6 Aromatic Recovery Tower

[0114] The aromatics recovery tower T6 separates the purified extract 12 from the bottom of the stripping section of extract T3 into an aromatic stream 13 and a solvent stream 2. Preferably, the aromatics recovery tower T6 operates under vacuum, particularly when the solvent contains sulfolane. Advantageously, vacuum operation prevents excessive bottom temperatures, which can lead to solvent decomposition. In one or more embodiments, steam 11, optionally mixed with (regenerated) solvent, is injected into the bottom of the aromatics recovery tower T6 to enhance the extraction of aromatics from the solvent (especially sulfolane). The vapors at the top of the tower (comprising mainly aromatic compounds and optionally water) can be condensed and optionally decanted in a decanting condenser CD6.According to one or more embodiments, a portion of the condensed overhead aromatic vapors is used for reflux in the aromatics recovery tower T6. The remainder, constituting the aromatic stream 13, is exited from the process and preferably sent to an aromatics complex (a unit for separating and producing aromatic compounds, particularly BTX). A portion of the decanted water 14 in the decanting condenser CD6 can optionally be sent to the water scrubber tower T2, and the remainder is recycled to the water stripping section. The stream from the bottom of the aromatics recovery tower T6 consists of regenerated solvent, which can be sent to the liquid-liquid extractor T1 and, optionally, to the extract stripping section T3 and / or to the solvent regeneration section (not shown).

[0115] According to one or more embodiments, the T6 aromatics recovery tower is operated at a head pressure between 0.001 MPa and 2 MPa (0.01 and 20 bara), preferably between 0.005 MPa and 1 MPa (0.05 and 10 bara), preferably between 0.01 MPa and 0.5 MPa (0.1 and 5 bara), preferably between 0.015 MPa and 0.2 MPa (0.15 and 2 bara), for example when the solvent includes sulfolane. According to one or more embodiments, the T6 aromatics recovery tower is operated at a bottom temperature between 50°C and 300°C, preferably between 100°C and 250°C, preferably between 120°C and 200°C, preferably between 130°C and 195°C, for example when the solvent includes sulfolane.

[0116] Solvent regeneration section (optional - not shown) According to one or more embodiments, at least a portion of the regenerated solvent from the T6 aromatics recovery tower is sent to the solvent regeneration section. According to one or more embodiments, 0.1% to 10%, preferably 0.5% to 5%, most preferably 1% to 2% of the regenerated solvent is sent to the solvent regeneration section. The solvent regeneration section is adapted to subject the regenerated solvent to steam entrainment, preferably under vacuum, to remove any potentially heavy polymers present in the regenerated solvent. The overhead vapors from the solvent regeneration section, consisting of vapors from the regenerated solvent and said vapor, are sent to the bottom of the T6 aromatics recovery tower. The heavy bottoms of the solvent regeneration section can be removed continuously or intermittently for disposal.

[0117] Advantageously, the aromatic stream 13 exiting the process / device according to the invention comprises at least 97% by weight, preferably at least 99% by weight, most preferably at least 99.5% by weight (e.g., at least 99.7% by weight) of aromatic compounds, relative to the total weight of the aromatic stream 13, making it possible to obtain a purity in:

[0118] - benzene of at least 99.95%, preferably of at least 99.98%;

[0119] - toluene of at least 99.0%, preferably of at least 99.5%;

[0120] - aromatic compounds with 8 carbon atoms (A8) of at least 97.0%, preferably of at least 98.0%; and

[0121] - aromatic compounds with at least 9 carbon atoms (A9+) of at least 97.0%, preferably of at least 98.0%.

[0122] Advantageously, the flow deviations of the continuous phase passing through the liquid-liquid extractor T1 are between -80% and +30%, preferably between -60% and +20%, very preferably between -55% and +5%, such as between -55% and +0% with respect to the flow of the incoming charge 1.

[0123] Advantageously, the diameter of the liquid-liquid extractor T1 according to the invention can be reduced by up to 10%, preferably by up to 20%, very preferably by up to 30% compared to a reference liquid-liquid extractor T1 being used at iso-capacity.

[0124] Advantageously, the number of separation elements (e.g. tray or packing) of the liquid-liquid extractor T1 according to the invention can be reduced by up to 10%, preferably by up to 20%, very preferably by up to 30% compared to a reference liquid-liquid extractor T1 being used at iso-performance.

[0125] All of these improvements result in savings of up to 25%, preferably up to 30% or even more, on utility needs. Examples

[0126] The reference example and the examples of liquid-liquid extraction separation processes according to the invention described below have the following characteristics.

[0127] Charge 1 in these examples is the continuous phase and the light phase, and is injected at a flow rate of 220 t / h and has a density of 724 kg / m³ 3 Table 1 below describes the constituent contents of charge 1.

[0128] Table 1

[0129] The separation solvent 2 comprises 99 wt% sulfolane, 0.7 wt% water, and traces of hydrocarbons. Solvent 2 is the dispersed and heavy phase and has a density of 1225 kg / m³ 3 .

[0130] The liquid-liquid extractor T1 used in these examples is a column comprising a plurality of complementary injection points for injecting a light fluid containing a mixture of C7- hydrocarbons, referred to as extract recycle 5. The injection position of extract recycle 5 is modified in the following examples. Table 2 below describes the constituent contents of extract recycle 5 for each example. Table 3 describes the flow rate of extract recycle 5 for each example. It is understood that, depending on the injection position of extract recycle 5, the constituents of extract recycle 5, as well as the flow rate of extract recycle 5, will vary. It is understood that the combination of the liquid-liquid extractor T1 and the extract stripping section T3 allows the specifications for aromatic yield and purity to be met.The flow rate and composition of the extract recycle stream vary depending on the operating conditions of the stripper and the extractor, as well as the position of the extract recycle injection 5.

[0131] Table 2

[0132] Table 3 The specifications referred to in the examples are:

[0133] - a minimum total aromatic yield of 94% by weight;

[0134] - a minimum benzene purity of 99.95% by weight;

[0135] - a minimum toluene purity of 99.00% by weight;

[0136] - a minimum purity of A8 Aromatics of 98.00% by weight; and - a minimum purity of A9+ Aromatics of 97.00% by weight.

[0137] The following formulas [Math 1], [Math 2], [Math 3], and [Math 4] describe the methods for calculating the purities obtained in the examples. The purity values ​​in formulas [Math 1], [Math 2], [Math 3], and [Math 4] are evaluated in aromatic flow 13. Math 1

[0138] Benzene in aromatic stream 13 (by weight)

[0139] Benzene purity = - ; - - - - - - - - - —

[0140] Benzene + non-aromatic C5-C7 compounds in aromatic flux 13 (by weight)

[0141] Math 2

[0142] Toluene in aromatic stream 13 (by weight)

[0143] Toluene purity =

[0144] Toluene + non-aromatic C8 compounds in aromatic flux 13 (by weight)

[0145] Math 3

[0146] A8 in aromatic flux 13 (weight)

[0147] Purity A8 =

[0148] A8 + non-aromatics in C9 in aromatic flux 13 (by weight)

[0149] Math 4

[0150] A9 +in aromatic flux 13 (weight)

[0151] Purity A9 —

[0152] A9 + + non-aromatic C10 + in aromatic flux 13 (weight)

[0153] Finally, the solvent temperature in the examples is set at 110°C, with extractor T1 operating at 110°C.

[0154] Example 1 (reference)

[0155] Example 1 concerns an extraction process with a backwash zone: injection of extract recycle 5 between the feed point of charge 1 and the outlet point of extract 4. In particular, all of the extract recycle 5 is injected at the bottom of the column at a flow rate of 140 t / h (corresponding to 64% by weight of the flow rate of charge 1).

[0156] The liquid-liquid extractor is a column with a diameter of 8.60 m, a height of 32.1 m, and consisting of 108 physical trays. The liquid-liquid extractor is fed with load 1 at a low feed point, specifically at the 27th ème tray from the bottom. The mass ratio of solvent to charge (S / F) is defined with regard to the expected performance in terms of yields and purities of aromatics: the value of the mass ratio S / F is 5.75.

[0157] With this configuration, the total aromatic yield is 94.0% by weight.

[0158] It should be noted that, in this reference example 1, significant variations in flow rate relative to the feed flow rate exist within the column. This is particularly pronounced for the continuous phase, with a total amplitude representing more than 100% of the incoming flow rate: the positive amplitude (AQc+ = 61.1%) is linked to the presence of the backwash zone, leading to a local overflow at the feed injection point; the negative amplitude (AQc- = -44%) is explained, on the one hand, by the transfer of matter occurring from one phase to the other, particularly in the extraction zone, and on the other hand, by the flow rate difference in the backwash zone.

[0159] However, the extraction columns typically used for aromatics extraction are known to be inflexible. Such variations in flow rates disrupt the hydrodynamics within the column and can lead to inhomogeneous operation, thus reducing performance.

[0160] Note that the energy consumption of the process in example 1, including: the liquid-liquid extractor T1, the water washing tower T2, the extract stripping section T3, the aromatics recovery tower T6, the water stripping section and the solvent regeneration section, is 3.1 MW / t (aromatics) / h.

[0161] Example 2 (invention)

[0162] Example 2 concerns an extraction process without a backwash zone: injection of extract recycle 5 between the feed point 1 and the solvent feed point 2. All of the extract recycle 5 is injected halfway up the column, specifically at 54 ème platform from the bottom, at a flow rate of 101 t / h (corresponding to 46% weight of the flow rate of load 1.

[0163] The liquid-liquid extractor is a column with a diameter of 8.10 m, a height of 31 m, and consisting of 103 physical trays. The liquid-liquid extractor is fed with load 1 at a low feed point, specifically below the 1st tray. er plateau from the bottom. The solvent mass ratio (S / F) is defined with regard to the expected performance in terms of yields and purities of aromatics: the value of the S / F mass ratio is 5.75. In example 2, we keep an S / F mass ratio identical to the reference example 1 to identify the effect on the yield, keeping the same specificities on the minimum purities to be respected.

[0164] With this configuration, the total aromatic yield is 98.7% by weight.

[0165] Advantageously, the amplitude of the continuous phase flow rate variations relative to the inlet feed rate is reduced by 50% compared to Example 1, notably with an absence of positive variations and a 53% reduction in the negative amplitude AQc-. This result is a direct consequence of the new arrangement of the extract recycle injection point.

[0166] Consequently, the column diameter is reduced by approximately 8%, and the tray efficiencies and total aromatic yield are increased by approximately 5% due to more homogeneous flow. Finally, the energy consumption of the process in Example 2 is 2.7 MW / t (aromatics) / h, representing a relative energy saving of approximately 13% compared to Example 1.

[0167] Example 3 (invention)

[0168] In Example 2, improved performance was identified, notably through a reduction in column diameter and higher yields compared to the reference Example 1. Advantageously, these higher-than-specification yield values ​​provide a margin on the S / F ratio. This allows for a lower S / F ratio, thereby reducing the overall energy consumption of the aromatics extraction unit while still meeting product specifications.

[0169] In example 3, the configuration is identical to example 2, only the S / F ratio is reduced to a value of 4.5 instead of 5.75.

[0170] The flow rate variations are virtually identical between example 2 and example 3; however, the reduction in the S / F ratio leads to a gain in column diameter of approximately 13% compared to example 1. Indeed, for example 3, the column diameter is reduced to 7.5 m, the column height is 30 m (100 plates) with a total aromatic yield of 97.5% by weight (+3.5 points compared to example 1), exceeding the yield specifications, and a purity in accordance with the specifications.

[0171] Furthermore, the energy consumption of the process in example 3 is advantageously 2.5 MW / t (aromatics) / h, which corresponds to a relative energy gain of more than 19% compared to example 1.

Claims

DEMANDS 1. A process for separating aromatic compounds from a feed (1) comprising a mixture of aromatic and non-aromatic compounds, the process comprising the following steps: extracting aromatics from the feed (1) by means of a liquid-liquid extractor (T1) fed with a solvent (2) to produce at least one extract (4) concentrated in aromatic compounds relative to the composition of the feed (1), and a raffinate (3) concentrated in non-aromatic compounds relative to the composition of the feed (1); feeding the liquid-liquid extractor (T1) with all of a recycle of extract (5) at a position or positions of the liquid-liquid extractor (T1) disposed between a feed point (1) and a solvent feed point (2).

2. Method according to claim 1, wherein the solvent (2) substantially feeds the head of the liquid-liquid extractor (T1).

3. Method according to claim 1 or claim 2, wherein the charge (1) substantially feeds the bottom of the liquid-liquid extractor (T1).

4. A method according to any one of the preceding claims, wherein the extract recycle (5) feeds the liquid-liquid extractor (T1) between the feed point (1) and the solvent feed point (2) at a single injection point.

5. A method according to any one of claims 1 to 3, wherein the extract recycle (5) feeds the liquid-liquid extractor (T1) between the feed point (1) and the solvent feed point (2) at several injection points.

6. A method according to any one of the preceding claims, the method comprises the following steps: feeding the liquid-liquid extractor with the feed at a feed point located at the bottom of the liquid-liquid extractor; feeding the liquid-liquid extractor with the solvent at a solvent feed point located at the top of the liquid-liquid extractor.

7. A method according to any one of the preceding claims, wherein the mass ratio of solvent (2) to charge (1) is between 0.1 and 50, preferably between 0.5 and 20, preferably between 1 and 9, preferably between 3 and 8.

8. A method according to any one of the preceding claims, wherein the mass ratio of the extract recycle (5) to the feed (1) is between 0.05 and 10, preferably between 0.1 and 8, preferably between 0.2 and 5, preferably between 0.3 and 2.

9. A process according to any one of the preceding claims, wherein the feed (1) contains aromatic and non-aromatic hydrocarbon compounds comprising from 5 to 11 carbon atoms.

10. A method according to any one of the preceding claims, wherein the liquid-liquid extractor (T1) is operated at least one of the following operating conditions: a pressure between 0.05 MPa and 3 MPa, preferably between 0.1 MPa and 2 MPa, preferably between 0.2 MPa and 1.5 MPa, preferably between 0.3 MPa and 1 MPa; a temperature between 10°C and 150°C, preferably between 15°C and 130°C, preferably between 30°C and 120°C, preferably between 40°C and 110°C.

11. A process according to any one of the preceding claims, comprising the following steps: stripping the extract (4) by means of an extract stripping section (T3) to separate a gas stream (9) comprising non-aromatic compounds and a purified extract (12); separating the aromatics from the purified extract (12) by means of an aromatics recovery tower (T6) to separate the solvent (2) and overhead vapors comprising an aromatic stream (13).

12. A process according to claim 11, comprising at least one of the following steps: feeding the liquid-liquid extractor (T1) with the solvent (2) comprising a solvent selected from the list 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, pyrrolidine-2-one, furfural, 1,1,3,3-tetramethylurea and a mixture thereof; phase separation of the gas stream (9) in a decanting condenser (CD3) to separate the extract recycle (5) and an aqueous phase (10); water washing of the raffinate (3) by means of a water washing tower (T2) supplied with water (6) to produce a non-aromatic stream (7) and wash water (8);regeneration of at least a portion of the solvent (2) by means of a solvent regeneration section by vacuum steam entrainment; condensation of the overhead vapors in a decanter condenser (CD6) to produce the aromatic stream (13).

13. A process according to claim 12, comprising at least one of the following steps: feeding the liquid-liquid extractor (T1) with a solvent (2) 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; stripping of hydrocarbon compounds present in the wash water (8) and / or in the aqueous phase (10) by means of a water stripping section to produce water;supplying the aromatics recovery tower (T6) with water vapor (11) to produce overhead vapors comprising further water vapor, and condensation of the overhead vapors in the decanting condenser (CD6) to produce the aromatic stream (13) and decanted water (14).

14. A process according to claim 13, comprising at least one of the following steps: feeding the liquid-liquid extractor (T1) with a solvent (2) comprising sulfolane and water; recycling the water produced by the water stripping section to the aromatics recovery tower (T6).

15. Device for separating aromatic compounds from a feed (1) comprising a mixture of aromatic and non-aromatic compounds, the device comprising a liquid-liquid extractor (T1) adapted to extract aromatics from the feed (1) with a solvent (2) and produce at least one extract (4) concentrated in aromatic compounds relative to the composition of the feed (1), and a raffinate (3) concentrated in non-aromatic compounds relative to the composition of the feed (1), the liquid-liquid extractor (T1) comprising: a feed point (1); a solvent feed point (2); one or more extract recycle feed points (5) adapted to feed all of one extract recycle (5), the extract recycle feed point(s) (5) being disposed between the feed point (1) and the solvent feed point (2).

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