Method for liquid-liquid extraction of aromatics with extract recycle streams

Abstract

The present invention relates to a method and to a device for separating aromatic compounds from a feedstock (1) comprising a mixture of aromatic and non-aromatic compounds, in which aromatics are extracted from the feedstock in a liquid-liquid extractor (T1) fed with a solvent stream (2) in order to produce at least an extract (4) concentrated in aromatic compounds, with respect to the feedstock, and a raffinate (3) concentrated in non-aromatic compounds, with respect to the composition of the feedstock; and in which an upper part (Z1) and a lower part (Z2) of the liquid-liquid extractor (T1) are fed respectively with a first fraction (51) and a second fraction (52) of extract recycle stream (5), the upper part and the lower part being defined with respect to the position of the feed point of the feedstock in the liquid-liquid extractor.

Description

[0001] Liquid-liquid extraction process for aromatics with recycling of the extract

[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 petrochemistry from a feed comprising a mixture of aromatic and non-aromatic compounds, such as a gasoline feed.

[0004] Prior art

[0005] With reference to the work "Process of Separation" by J. -P. Wauquiez (Edition Technip 1998, p. 438-444), and to the field of the invention previously described, the BTX aromatics extraction process comprises three main operations which are extraction, purification of the aromatics and regeneration of the solvent. The prior art concerns the aromatics extraction process comprising a liquid-liquid aromatics extraction column, an extractive distillation column and a solvent regeneration column. The feed comprising a mixture of aromatics and non-aromatics is sent to the middle of the extraction column, the solvent is sent to the top of the column and the extraction is carried out by contacting the feed and the solvent on the upper section of the extraction column.Within the same column, the solvent loaded with aromatics enters a so-called backwash zone where said solvent is contacted with a recycle of light aromatic / non-aromatic mixture from the top of the extractive distillation column to partially purify the aromatics to produce an extract. The extract is sent to an extractive distillation column for purification by means of a reboil rate adjusted so that the aromatics at the bottom of the column are at predetermined specifications of non-aromatic content. The purified extract is sent to a regeneration column by azeotropic distillation to separate the aromatics from the solvent.

[0006] Summary of the invention

[0007] In the context previously described, a first object of the present description is to propose a process for separating a hydrocarbon feedstock for the production of aromatics with an improved yield, in particular compatible with injection into an aromatic complex.

[0008] According to a first aspect, the aforementioned objects, as well as other advantages, are obtained by a process for separating aromatic compounds from a feedstock comprising a mixture of aromatic and non-aromatic compounds, the process comprising the following steps:

[0009] - extracting aromatics from the feed by means of a liquid-liquid extractor supplied with a solvent flow 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;

[0010] - feeding an upper part and a lower part of the liquid-liquid extractor with respectively a first fraction and a second fraction of extract recycling, the upper part and the lower part being defined relative to the position of the feed point of the load in the liquid-liquid extractor.

[0011] According to one or more embodiments, the solvent flow 2 feeds the head of the upper part Z1 of the liquid-liquid extractor T1

[0012] According to one or more embodiments, the first fraction feeds said upper part at a point arranged at a position between 0.05* L1 and 0.95x|_1, preferably between 0.2x|_1 and 0.9x|_1 and preferably between 0.3x|_1 and 0.8x|_1, L1 being the length of the head of the liquid-liquid extractor T1 at the position of the feed point of the load.

[0013] According to one or more embodiments, the first fraction feeds said upper portion below the feed point of the solvent stream.

[0014] According to one or more embodiments, the second fraction feeds said lower part at a point arranged at a position between 0x|_2 and 0.3x|_2, preferably between Ox L2 and 0.2x L2 and preferably between Ox L2 and 0.1 x [_2, L2 being the length of the position of the bottom of the liquid-liquid extractor T1 at the feed point of the load.

[0015] According to one or more embodiments, the mass ratio of the first fraction to the second fraction is between 0.01 and 0.99, preferably between 0.1 and 0.95, preferably between 0.15 and 0.85 and preferably between 0.2 and 0.8.

[0016] According to one or more embodiments, the mass ratio of the solvent to the charge is between 0.1 and 50, preferably between 0.5 and 20, preferably between 1 and 9, preferably between 3 and 8.

[0017] According to one or more embodiments, the mass ratio of extract recycling to the feedstock is between 0.05 and 10, preferably between 0.1 and 8, preferably between 0.2 and 5, preferably between 0.3 and 2. According to one or more embodiments, the feedstock contains aromatic and non-aromatic compounds comprising from 6 to 11 carbon atoms.

[0018] According to one or more embodiments, the liquid-liquid extractor is operated at 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.

[0019] According to one or more embodiments, the method comprises the following steps:

[0020] - stripping the extract using an extract stripping section to separate a gas stream comprising non-aromatic compounds and a purified extract;

[0021] - separation of aromatics from the purified extract by means of an aromatics recovery tower to separate the solvent stream and overhead vapors comprising an aromatic stream.

[0022] According to one or more embodiments, the method comprises at least one of the following steps:

[0023] - feeding the liquid-liquid extractor with a solvent stream 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, dimethylsulfoxide, caprolactam, N-methylformamide, pyrrolidin-2-one, furfural, 1,1,3,3-tetramethylurea and a mixture thereof;

[0024] - phase separation of the gas stream in a decanter condenser to separate the extract recycle and an aqueous phase;

[0025] - water washing of the raffinate using a water washing tower supplied with water to produce a non-aromatic stream and wash water;

[0026] - regeneration of at least a portion of the solvent stream by means of a solvent regeneration section by vacuum steam entrainment;

[0027] - condensation of the overhead vapors in a decanter condenser to produce the aromatic stream.

[0028] According to one or more embodiments, the method comprises at least one of the following steps:

[0029] - feeding the liquid-liquid extractor with a solvent stream selected from ethylene glycol, diethylene glycol, triethylene glycol, hexamethylphosphoramide, propylene carbonate, ethylene carbonate, sulfolane, 3-methylsulfolane, N-methylacetamide, N,N-dimethylacetamide, butyrolactone, 1-methylpyrrolidone, dimethylsulfoxide, caprolactam, N-methylformamide, pyrrolidin-2-one, furfural, 1,1,3,3-tetramethylurea and a mixture thereof;

[0030] - 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;

[0031] - supplying the aromatic recovery tower with water vapor to produce overhead vapors further comprising water vapor, and condensing the overhead vapors in the decanter condenser to produce the aromatic stream and decanted water.

[0032] According to one or more embodiments, the method comprises at least one of the following steps:

[0033] - feeding the liquid-liquid extractor with a solvent stream comprising sulfolane and water;

[0034] - recycling of water produced by the water stripping section to the aromatics recovery tower.

[0035] 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 flow and produce at least one extract concentrated in aromatic compounds relative to the feed, and a raffinate concentrated in non-aromatic compounds relative to the composition of the feed, the liquid-liquid extractor comprising:

[0036] - a load supply point;

[0037] - a solvent flow feed point;

[0038] - a feed point for a first recycling fraction of extract arranged in an upper part of the liquid-liquid extractor;

[0039] - a feed point for a second extract recycling fraction arranged in a lower part of the liquid-liquid extractor, the upper part and the lower part being defined relative to the position of the feed point of the load in the liquid-liquid extractor.

[0040] Embodiments according to the aforementioned aspects as well as other characteristics and advantages will appear on reading the following description, given for illustrative and non-limiting purposes only, and with reference to the following drawings.

[0041] List of figures

[0042] Figure 1 schematically shows a separation process according to the invention. Figure 2 schematically shows the operating principle of the liquid-liquid extractor according to the invention.

[0043] Figure 3 schematically shows a separation method according to the prior art.

[0044] Description of the embodiments

[0045] Embodiments of the invention will now be described in detail. In the following detailed description, numerous specific details are set forth in order to provide a more thorough understanding of the invention. However, it will be apparent to those skilled in the art that the invention may be practiced without these specific details. In other instances, well-known features have not been described in detail to avoid unnecessarily complicating the description.

[0046] In the present application, the term "comprise" is synonymous with (means the same as) "include" and "contain", and is inclusive or open and does not exclude other elements not recited. It is understood that the term "comprise" includes the exclusive and closed term "consist". The term "based on" is synonymous with "comprises at least 50% by weight of". Furthermore, in the present description, the terms "essentially" or "substantially" correspond to an approximation of ± 5%, preferably ± 1%, very preferably ± 0.5%. For example, an effluent essentially comprising or consisting of compounds A corresponds to an effluent comprising at least 95% by weight of compounds A. In the present description, the term "stream concentrated in a compound" corresponds for example to a stream comprising at least 80% by weight, preferably at least 90% by weight, very preferably at least 95% by weight of said compound.

[0047] The present invention relates to the separation of aromatic compounds, and in particular BTX, but also aromatic compounds with 9 or 10 or even 11 carbon atoms (A9, A10, A11), for petrochemicals, originating for example from a gasoline feedstock, such as a catalytic cracking gasoline. It relates in particular to an improved method and device for separating aromatic compounds with 6 to 11 carbon atoms from a feedstock comprising a mixture of aromatic and non-aromatic compounds, such as a gasoline feedstock.

[0048] Specifically with reference to Figure 1, the method according to the invention makes it possible to treat the feed 1 with a solvent stream 2 in a liquid-liquid extractor T1 to produce a stream concentrated (i.e. enriched) in non-aromatic compounds (raffinate 3) and a stream concentrated in aromatic compounds (extract 4), a process in which an extract recycling 5 is fed to both an upper part Z1 and a lower part Z2 of the liquid-liquid extractor T1. Advantageously, the method / device for separating aromatics according to the invention makes it possible to obtain an improved recovery yield of aromatics while guaranteeing high purity, in particular in BTX. In addition, the raffinate 3 (optionally washed) can be sent to a thermal cracking step / unit or to a catalytic reforming step / unit for example in order to increase the production of aromatics.

[0049] The charge

[0050] The separation process according to the invention makes it possible to treat a feedstock 1 comprising a mixture of aromatic and non-aromatic compounds. Preferably, feedstock 1 is hydrotreated and / or hydrogenated. According to one or more embodiments, feedstock 1 is a gasoline feedstock that is optionally hydrotreated and / or hydrogenated.

[0051] According to one or more embodiments, charge 1 is a C5+ cut, i.e. containing compounds with 5 carbon atoms or more. According to one or more embodiments, charge 1 is a C5-C10 or C5-C11 cut, i.e. containing compounds comprising from 5 to 10 or from 5 to 11 carbon atoms. According to one or more embodiments, charge 1 is a C6-C10 or C6-C11 cut, i.e. containing compounds comprising from 6 to 10 or from 6 to 11 carbon atoms.

[0052] According to one or more embodiments, the filler 1 comprises at least 20% by weight, preferably at least 30% by weight, very preferably at least 40% by weight, (eg at least 50% by weight) of aromatic compounds of 6 to 11 carbon atoms, relative to the total weight of the filler.

[0053] According to one or more embodiments, the filler 1 comprises at least 20% by weight, preferably at least 30% by weight, very preferably at least 40% by weight, (eg at least 50% by weight) of mono-aromatic compounds of 6 to 11 carbon atoms, relative to the total weight of the filler.

[0054] According to one or more embodiments, the aromatic compounds of charge 1 are mono-aromatic compounds at least 95% by weight, preferably at least 98% by weight, very preferably at least 99% by weight.

[0055] According to one embodiment of the invention, feed 1 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.

[0056] According to one embodiment of the invention, feedstock 1 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. According to one embodiment of the invention, feedstock 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.

[0057] According to one embodiment of the invention, feedstock 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.

[0058] According to one embodiment of the invention, the feedstock 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, in compounds having a boiling point greater than 217°C, such as naphthalene.

[0059] According to one embodiment of the invention, feed 1 is free of the following compounds: H2, H2S, light gas such as ethane, propane and butane. According to one embodiment of the invention, the removal of these compounds in feed 1 is carried out in a fractionation column.

[0060] According to one embodiment, said feed 1 is at least partly a gasoline cut from a fluidized bed catalytic cracking unit (FCC unit for "Fluid Catalytic Cracking" according to English terminology), the gasoline cut having preferably been selectively hydrogenated to transform diolefins into olefins, then fractionated to obtain a C5-C10, C5-C11, C6-C10 or C6-C11 cut, then hydrogenated to saturate the olefinic compounds. According to one embodiment of the invention, feed 1 is obtained from the hydrogenation of a pyrolysis gasoline (PyGas according to English terminology) mixed with a gasoline cut from an FCC unit.

[0061] Extraction

[0062] The extraction of aromatics in the present invention makes it possible to treat feed 1 in order to recover, on the one hand, a stream concentrated in non-aromatic compounds called raffinate 3 and on the other hand a stream concentrated in aromatics called extract 4, relative to the composition of feed 1.

[0063] According to one or more embodiments, with reference to FIG. 1, the extraction of the aromatics is a liquid-liquid extraction of the aromatics.

[0064] According to one or more embodiments, the liquid-liquid extraction of aromatics comprises the following steps:

[0065] - liquid-liquid extraction using a liquid-liquid extractor T1 fed with a solvent stream 2 to separate raffinate 3 and extract 4, - water washing of raffinate 3 with a water washing tower T2 (optional step),

[0066] - stripping of the water used in the T2 washing tower with a water stripping section (optional step),

[0067] - stripping of extract 4 with a stripping section of extract T3,

[0068] - separation of aromatics with a T6 recovery tower to separate an aromatic stream 13 and the solvent stream 2, and

[0069] - solvent regeneration with a solvent regeneration section (optional step).

[0070] For simplification, the optional water stripping and solvent regeneration sections are not shown in Figure 1.

[0071] Liquid-liquid extractor T 1

[0072] Liquid-liquid extraction allows the separation of aromatics from non-aromatic compounds, such as paraffins and naphthenes, from feed 1.

[0073] Referring to Figure 2, the feed 1 is substantially at an intermediate point in the liquid-liquid extractor T1 (eg in the middle of the extractor).

[0074] According to one or more embodiments, the intermediate point is a point located between the head and the bottom of the liquid-liquid extractor T1. According to one or more embodiments, the intermediate point corresponds to a point arranged at a position between 0.1 *L and 0.9xL, more preferably between 0.2xL and 0.8xL, such as between 0.3xL and 0.7xL or between 0.4xL and 0.6xL, L being the length (from) the head (to) the bottom of the liquid-liquid extractor T1.

[0075] Advantageously, the liquid-liquid extractor T1 can therefore be divided into two parts. The upper part Z1 (relative to the intermediate feed point of the feedstock 1) makes it possible to control the yield of aromatics by liquid-liquid extraction (in particular with solvent). The lower part Z2 of the liquid-liquid extractor T1 allows an initial purification of the aromatics, in particular by means of an extract recycling flow 5.

[0076] According to one or more embodiments, the solvent flow 2 feeds the upper part Z1 of the liquid-liquid extractor T1. According to one or more embodiments, the solvent flow 2 feeds the head of the upper part Z1 of the liquid-liquid extractor T1.

[0077] According to one or more embodiments, the solvent comprises a compound selected from ethylene glycol, diethylene glycol, triethylene glycol, hexamethylphosphoramide, propylene carbonate, ethylene carbonate, sulfolane, 3-methylsulfolane, N-methylacetamide, N,N-dimethylacetamide, butyrolactone, 1-methylpyrrolidone, dimethylsulfoxide, caprolactam, N-methylformamide, pyrrolidin-2-one, furfural, 1,1,3,3-tetramethylurea and a mixture thereof. According to one or more embodiments, the solvent comprises or consists of sulfolane. According to one or more embodiments, the solvent consists of at least 80% by weight (e.g. at least 90% by weight), preferably at least 95% by weight (e.g. at least 99% by weight), sulfolane, relative to the total weight of the solvent. According to one or more embodiments, the solvent further comprises an antisolvent, such as water.According to one or more embodiments, the anti-solvent comprises or consists of water. According to 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 (eg between 0.5% by weight and 2% by weight) of anti-solvent, such as water, relative to the total weight of the solvent. According to one or more embodiments, the solvent comprises, or consists of, sulfolane and water.

[0078] According to the invention, a first fraction 51 of recycling extract 5, for example from the extract stripping section T3, feeds the upper part Z1 of the liquid-liquid extractor, i.e. above the feed point of the feed 1. According to one or more embodiments, the first fraction 51 feeds said upper part Z1 preferably below the feed point of the solvent flow 2 in the upper part Z1 of the liquid-liquid extractor T1.

[0079] According to one or more embodiments, the first fraction 51 feeds said upper part Z1 at a point arranged at a position between 0.05x|_1 and 0.95x|_1, and preferably between 0.2x|_1 and 0.9x|_1 and preferably between 0.3x|_1 and 0.8x|_1, L1 being the length (from) the head of the liquid-liquid extractor T1 (up to) the position of the feed point of the load 1 corresponding to the length of the upper part Z1. In the present description, 0x|_1 corresponds to the position of the head of the liquid-liquid extractor T 1 . According to one or more embodiments, the first fraction 51 feeds said upper part Z1 at a point arranged at a position between 0.05x|_1 and 0.8x|_1, preferably between 0.05x|_1 and 0.7x|_1, preferably between 0.05x|_1 and 0.5x|_1 and preferably between 0.05x|_1 and 0.6x|_1, such as for example between 0.1 x|_1 and 0.6x|_1.Advantageously, the high position of the first fraction in the liquid-liquid extractor allows a gain in the extraction yields of aromatics.

[0080] According to the invention, a second fraction 52 of recycling of extract 5 feeds the lower part Z2 of the liquid-liquid extractor T 1 , i.e. below the feed point of the load 1 .

[0081] According to one or more embodiments, the second fraction 52 feeds said lower part Z2 at a point arranged at a position between 0x|_2 and 0.3x|_2, preferably between 0x|_2 and 0.2x|_2 and preferably between 0x|_2 and 0.1 x|_2, L2 being the length (from) the bottom of the liquid-liquid extractor T1 (up to) the feed point of the load 1 corresponding to the length of the lower part Z2. According to one or more embodiments, the second fraction 52 feeds the bottom of the lower part Z2 of the liquid-liquid extractor T1. In the present description, 0*L2 corresponds to the position of the bottom of the liquid-liquid extractor T1.

[0082] According to one or more embodiments, the mass ratio of the first fraction 51 of the extract recycling 5 supplying the upper part Z1 to the second fraction 52 of the extract recycling 5 supplying the lower part Z2 is between 0.01 and 0.99, preferably between 0.1 and 0.95 and preferably between 0.15 and 0.85 and preferably between 0.2 and 0.8.

[0083] The liquid-liquid extractor T1 makes it possible to separate a raffinate 3 depleted in aromatic compounds compared to the feed 1 and an extract 4 concentrated in aromatic compounds compared to the feed 1. The raffinate 3 leaves at the top of the liquid-liquid extractor T1 and is optionally sent to the water washing tower T2. The extract 4 leaves 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 FIG. 2 for the sake of simplification). According to one or more embodiments, the liquid-liquid extractor T1 operates adiabatically.

[0084] According to one or more embodiments, the mass ratio of solvent 2 to feedstock 1 is between 0.1 and 50, preferably between 0.5 and 20, preferably between 1 and 9, preferably between 3 and 8, such as 5 ± 1 or 6 ± 1. According to one or more embodiments, the mass ratio of extract recycling 5 to feedstock 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, such as 0.9 ± 0.2.

[0085] According to one or more embodiments, the liquid-liquid extractor T1 is operated at a pressure of 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), such as at 0.65 ± 0.2 MPa (6.5 + / - 2 bara), for example when the solvent comprises sulfolane. According to one or more embodiments, the extractor is operated at a temperature between 10°C and 150°C, preferably between 15°C and 130°C, preferably between 30°C and 120°C, preferably between 40°C and 110°C, such as 70 ±2°C, for example when the solvent comprises sulfolane.

[0086] Optional T2 water wash tower

[0087] Washing raffinate 3 with water allows the removal of the solvent potentially present in raffinate 3. Preferably, raffinate 3 is cooled before entering tower T2. Preferably, raffinate 3 enters the bottom of said tower T2, water 6 is introduced at the top of said tower, non-aromatic stream 7 (raffinate 3 washed and thus depleted in solvent) exits at the top of said tower, and wash water 8 (concentrated / enriched in solvent) exits at the bottom of said tower. According to one or more embodiments, non-aromatic stream 7 comprises less than 100 ppm by weight, preferably less than 10 ppm by weight, very preferably less than 1 ppm by weight of solvent. According to one or more embodiments, wash water 8 is sent to the water stripping section (not shown).

[0088] 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.

[0089] 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.

[0090] T3 Extract Stripping Section

[0091] The stripping of extract 4 allows the elimination of non-aromatic compounds still present in extract 4. Extract 4 loaded with aromatic compounds and solvent is preferably introduced at the top of the extract stripping section T3. In the extract stripping section T3, the purity of extract 4 is improved because the residual non-aromatic compounds entrained with the aromatic compounds (less soluble in the solvent) are extracted in the form of gas stream 9 at the top of the extract stripping section T3. According to one or more embodiments, gas stream 9 is combined with water, such as water recovered at the top of the water stripping section (not shown).The phase separation in the decanter condenser CD3 allows the hydrocarbon phase to be recycled to the liquid-liquid extractor T1 as extract recycle stream 5 and the aqueous phase 10 is optionally combined with the 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 (notably sulfolane) which can be recycled to the liquid-liquid extractor T1.

[0092] According to one or more embodiments, the extract recycling comprises between 50 and 95% by weight, preferably between 60 and 90% by weight (eg 70-90% by weight), of non-aromatic compounds (compounds entrained by the aromatic compounds of the extract). According to one or more embodiments, the extract recycling comprises at least 70% by weight, preferably at least 80% by weight, very preferably at least 90% by weight of compounds with 7 carbon atoms or less. The stripping of the extract 4 is preferably carried out at low pressure or even under vacuum in order to improve the removal of non-aromatics from the solvent (in particular sulfolane).According to one or more embodiments, the stripping section of the T3 extract is operated at a head pressure of 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), such as 0.1 ± 0.05 MPa, for example when the solvent comprises sulfolane. According to one or more embodiments, the stripping section of the extract T3 is operated at a bottom temperature of 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, such as 180 ±5°C, for example when the solvent comprises sulfolane.

[0093] Water stripping section (optional - not shown)

[0094] Stripping of the wash water 8 and optionally of the aqueous phase 10 makes it possible to eliminate dissolved hydrocarbons (mainly non-aromatic) from the water coming from the head of the extract stripping section T3 and optionally from the water washing tower T2.

[0095] According to one or more embodiments, at least a portion of the water obtained at the outlet of the water stripping section is sent to the aromatics recovery tower T6, in order to increase the quantity of stripping vapor sent to the bottom of the aromatics recovery tower T6.

[0096] T6 Aromatic Recovery Tower

[0097] The aromatics recovery tower T6 separates the purified extract 12 from the bottom of the extract stripping section T3 into an aromatic stream 13 and the solvent stream 2. Preferably, the aromatics recovery tower T6 operates under vacuum, in particular when the solvent comprises sulfolane. Advantageously, the vacuum operation makes it possible to avoid an excessive bottom temperature, which can lead to decomposition of the solvent. According to one or more embodiments, water vapor 11, optionally associated with (regenerated) solvent, is injected into the bottom of the aromatics recovery tower T6, to improve the extraction of aromatics from the solvent (in particular sulfolane). The overhead vapors from the tower (comprising essentially aromatic compounds and optionally water) can be condensed and optionally decanted in a decanter condenser CD6.According to one or more embodiments, a portion of the condensed overhead aromatic vapors is used for the reflux of the aromatic recovery tower T6, the remainder, constituting the aromatic stream 13, is removed from the process and preferably sent to an aromatic complex (unit for separation and production of aromatic compounds, and in particular BTX). A portion of the decanted water 14 in the decanter condenser CD6 can optionally be sent to the water washing tower T2 and the remainder is recycled to the water stripping section. The stream from the bottom of the aromatic recovery tower T6 is composed 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).

[0098] According to one or more embodiments, the aromatics recovery tower T6 is operated at a head pressure of 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), such as 0.06 ± 0.04 MPa, for example when the solvent comprises sulfolane. According to one or more embodiments, the aromatics recovery tower T6 is operated at a bottom temperature of 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, such as 170 ±25°C, for example when the solvent comprises sulfolane.

[0099] Advantageously, the aromatic flow 13 comprises at least 95% by weight, preferably at least 99% by weight, very preferably at least 99.5% by weight, (eg at least 99.5% by weight) of aromatic compounds, relative to the total weight of the aromatic flow 13.

[0100] Examples

[0101] Example 1: Comparative (not in accordance with the invention)

[0102] A comparative example of a process for the separation of aromatics from a gasoline cut using catalytic cracking technologies is as follows.

[0103] The characteristics of charge 1 treated in the separation process are shown in Table 1.

[0104] Table 1 Feed 1 feeds the liquid-liquid extractor T1 of the aromatics extraction unit. A solvent stream 2 comprising 99.1% by weight of sulfolane is added at the top and an extract recycle stream 5 is added at the bottom of the liquid-liquid extractor T1, as shown in Figure 3. A mass ratio [solvent stream 2] / [feed 1] of 8, and a mass ratio [extract recycle stream 5] / [feed 1] of 0.5 are used at the liquid-liquid extractor T1 which is operated at a pressure between 0.4 MPa and 0.8 MPa and at a temperature of 70°C.

[0105] The raffinate 3 is extracted at the top of the liquid-liquid extractor T1 and then sent to the optional water washing tower T2 to remove the little sulfolane solvent which is carried over into the raffinate 3. The washing water 8 is composed essentially of water and sulfolane, the non-aromatic stream 7 is composed of the solvent-free raffinate.

[0106] For the sake of simplification, the optional water stripping and solvent regeneration sections are not shown in Figure 3. Said optional water stripping and solvent regeneration sections allow to treat the water streams used in the separation process and to purify the sulfolane.

[0107] Extract 4 from liquid-liquid extractor T1 feeds extract stripping section T3 which removes non-aromatics carried along with the solvent and aromatics and creates extract recycling flow 5 sufficient to return to liquid-liquid extractor T1. First, gas flow 9 at the top of extract stripping section T3 is sent to decanter condenser CD3 to remove aqueous phase 10.

[0108] The T3 extract stripping section comprises a stripping column operated at a bottom temperature of 180°C.

[0109] The purified extract 12 at the bottom of the extract stripping section T3 containing essentially the solvent and aromatics is sent to the aromatics recovery tower T6, which makes it possible to recover at the bottom the solvent recycled to the liquid-liquid extractor T1 as solvent stream 2, and to recover a head stream which is sent to the decanter condenser CD6 which makes it possible to withdraw decanted water 14 and aromatic stream 13. The aromatics recovery tower T6 operates by sending water vapor 11 to the bottom of the column.

[0110] The T6 aromatics recovery tower is operated at a bottom temperature of 180°C.

[0111] Table 2 shows the mass compositions of the outgoing streams from the reference separation process. Table 2

[0112] Table 3 shows the mass distribution of the reference separation process flows at the inlet and outlet of the aromatics extraction unit.

[0113] Table 3 Table 4 shows the extraction yields of aromatic compounds in aromatic stream 13 compared to feed 1.

[0114] Table 4

[0115] Example 2 according to the invention:

[0116] An example of a separation method according to the invention for the separation of aromatics from a gasoline cut resulting from catalytic cracking technologies is as follows. This example describes the technical effect of introducing two fractions of the extract recycle stream 5 corresponding to the first fraction 51 and the second fraction 52 according to Figure 1, into the upper part Z1 and the lower part Z2 of the liquid-liquid extractor T1, respectively.

[0117] Feed 1 (identical to the feed of Example 1) feeds the liquid-liquid extractor T1 of the aromatics extraction unit. A solvent stream 2 comprising 99.1% by weight of sulfolane is added at the top. Stream 52 corresponding to 50% by weight of the extract recycling stream 5 is added to the bottom of the liquid-liquid extractor T1 in the lower part Z2, as shown in Figures 1 and 2. Stream 51 corresponding to 50% by weight of the extract recycling stream 5 is added to the upper part Z1 of the liquid-liquid extractor T1 in position 0.66xL1, 0xL1 corresponding to the top of the upper part Z1.

[0118] A mass ratio [solvent flow 2] / [charge 1] of 8, and a mass ratio [extract recycle flow 5] / [charge 1] of 0.28 are used at the liquid-liquid extractor T 1 which is operated at a pressure between 0.4 MPa and 0.8 MPa and at a temperature of 70°C.

[0119] The raffinate 3 is extracted at the top of the liquid-liquid extractor T1 and then sent to the optional water washing tower T2 to remove the little sulfolane solvent which is carried over into the raffinate 3. The washing water 8 is composed essentially of water and sulfolane, the non-aromatic stream 7 is composed of the solvent-free raffinate.

[0120] For the sake of simplification, the optional water stripping and solvent regeneration sections are not shown in Figure 1. Said optional water stripping and solvent regeneration sections make it possible to treat the water streams used in the separation process according to the invention and to purify the sulfolane.

[0121] Extract 4 from liquid-liquid extractor T1 feeds extract stripping section T3 which removes non-aromatics carried along with the solvent and aromatics and creates extract recycling flow 5 sufficient to return to liquid-liquid extractor T1. First, gas flow 9 at the top of extract stripping section T3 is sent to decanter condenser CD3 to remove aqueous phase 10.

[0122] The T3 extract stripping section comprises a stripping column operated at a bottom temperature of 180°C.

[0123] The purified extract 12 at the bottom of the extract stripping section T3 containing essentially the solvent and aromatics is sent to the aromatics recovery tower T6, which makes it possible to recover at the bottom the solvent recycled to the liquid-liquid extractor T1 as solvent stream 2, and to recover a head stream which is sent to the decanter condenser CD6 which makes it possible to withdraw decanted water 14 and aromatic stream 13. The aromatics recovery tower T6 operates by sending water vapor 11 to the bottom of the column.

[0124] The T6 aromatics recovery tower is operated at a bottom temperature of 180°C.

[0125] Table 5 shows the mass compositions of the outgoing flows from the separation process according to the invention.

[0126] Table 5

[0127] Table 6 shows the mass distribution of the separation process flows at the inlet and outlet of the aromatics extraction unit.

[0128] Table 6

[0129] Table 7 shows the extraction yields of aromatic compounds in aromatic stream 13 compared to feed 1.

[0130] Table 7

[0131] Example 2 according to the invention demonstrates an improvement in the extraction yield of aromatics compared to reference example 1.

[0132] Example 3 according to the invention:

[0133] An example of a separation process according to the invention for the separation of aromatics from a gasoline cut produced by catalytic cracking technologies is as follows.

[0134] Feed 1 (identical to the feed of Example 1) feeds the liquid-liquid extractor T1 of the aromatics extraction unit. A solvent stream 2 comprising 99.1% by weight of sulfolane is added at the top. Stream 52 corresponding to 50% by weight of the extract recycling stream 5 is added to the bottom of the liquid-liquid extractor T1 in the lower part Z2, as shown in Figures 1 and 2. Stream 51 corresponding to 50% by weight of the extract recycling stream 5 is added to the upper part Z1 of the liquid-liquid extractor T1 in position 0.33xL1, 0xL1 corresponding to the top of the upper part Z1.

[0135] A mass ratio [solvent flow 2] / [charge 1] of 8, and a mass ratio [extract recycle flow 5] / [charge 1] of 0.27 are used at the liquid-liquid extractor T1 which is operated at a pressure between 0.4 MPa and 0.8 MPa and at a temperature of 70°C.

[0136] The raffinate 3 is extracted at the top of the liquid-liquid extractor T1 and then sent to the optional water washing tower T2 to remove the little sulfolane solvent which is carried over into the raffinate 3. The washing water 8 is composed essentially of water and sulfolane, the non-aromatic stream 7 is composed of the solvent-free raffinate.

[0137] For the sake of simplification, the optional water stripping and solvent regeneration sections are not shown in Figure 1. Said optional water stripping and solvent regeneration sections make it possible to treat the water streams used in the separation process according to the invention and to purify the sulfolane.

[0138] Extract 4 from liquid-liquid extractor T1 feeds extract stripping section T3 which removes non-aromatics carried along with the solvent and aromatics and creates extract recycling flow 5 sufficient to return to liquid-liquid extractor T1. First, gas flow 9 at the top of extract stripping section T3 is sent to decanter condenser CD3 to remove aqueous phase 10.

[0139] The T3 extract stripping section comprises a stripping column operated at a bottom temperature of 180°C.

[0140] The purified extract 12 at the bottom of the extract stripping section T3 containing essentially the solvent and aromatics is sent to the aromatics recovery tower T6, which makes it possible to recover at the bottom the solvent recycled to the liquid-liquid extractor T1 as solvent stream 2, and to recover a head stream which is sent to the decanter condenser CD6 which makes it possible to withdraw decanted water 14 and aromatic stream 13. The aromatics recovery tower T6 operates by sending water vapor 11 to the bottom of the column.

[0141] The T6 aromatics recovery tower is operated at a bottom temperature of 180°C.

[0142] Table 8 shows the mass compositions of the streams leaving the separation process according to the invention.

[0143] Table 8

[0144] Table 9 shows the mass distribution of the separation process flows between the inlet and outlet of the aromatics extraction unit. Table 9

[0145] Table 10 shows the extraction yields of aromatic compounds in aromatic stream 13 compared to feed 1.

[0146] Table 10 Example 3 according to the invention demonstrates an improvement in the extraction yield of total aromatics compared to reference Example 1. In addition, Example 3 according to the invention also demonstrates an improvement for the recovery of the heavier aromatics compared to Example 2 according to the invention (see Table 7 vs Table 10).

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: - extract aromatics from the feed (1) using a liquid-liquid extractor (T1) fed with a solvent stream (2) to produce at least one extract (4) concentrated in aromatic compounds relative to the composition of the feed (1), and one raffinate (3) concentrated in non-aromatic compounds relative to the composition of the feed (1); - to feed an upper part (Z1) and a lower part (Z2) of the liquid-liquid extractor (T1) with respectively a first fraction (51) and a second fraction (52) of extract recycling (5), the upper part (Z1) and the lower part (Z2) being defined with respect to the position of the feed point of the charge (1) in the liquid-liquid extractor (T1).

2. A method according to claim 1, wherein the solvent stream 2 feeds the head of the upper part Z1 of the liquid-liquid extractor T1 3. Method according to claim 1 or claim 2, wherein the first fraction (51) feeds said upper part (Z1) at a point disposed at a position between 0.05x|_1 and 0.95x|_1, preferably between 0.2x|_1 and 0.9x|_1 and preferably between 0.3x|_1 and 0.8x|_1, L1 being the length of the head of the liquid-liquid extractor T1 at the position of the feed point (1).

4. A method according to any one of the preceding claims, wherein the first fraction (51) feeds said upper part (Z1) below the point of supply of the solvent flow (2).

5. A method according to any one of the preceding claims, wherein the second fraction (52) feeds said lower part (Z2) at a point disposed at a position between 0x|_2 and 0.3x|_2, preferably between 0x|_2 and 0.2x|_2 and preferably between Ox L2 and 0.1x[_2, L2 being the length of the position of the bottom of the liquid-liquid extractor T1 at the feed point (1).

6. A method according to any one of the preceding claims, wherein the mass ratio of the first fraction (51) to the second fraction (52) is between 0.01 and 0.99, preferably between 0.1 and 0.95, preferably between 0.15 and 0.85 and preferably between 0.2 and 0.

8.

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 recycling of extract (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 method according to any one of the preceding claims, wherein the feed (1) contains aromatic and non-aromatic compounds comprising from 6 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 method according to any one of the preceding claims, comprising the following steps: - stripping of 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); - separation of aromatics from the purified extract (12) by means of an aromatics recovery tower (T6) to separate the solvent stream (2) and overhead vapors comprising an aromatic stream (13).

12. A method according to claim 11, comprising at least one of the following steps: feeding the liquid-liquid extractor (T1) with a solvent stream (2) comprising a solvent selected from the list consisting of ethylene glycol, diethylene glycol, triethylene glycol, hexamethylphosphoramide, propylene carbonate, the 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 recycled extract (5) and an aqueous phase (10); - washing with water of the raffinate (3) by means of a water washing tower (T2) supplied with water (6) to produce a non-aromatic stream (7) and washing water (8); - regeneration of at least a portion of the solvent flow (2) by means of a solvent regeneration section by vacuum steam entrainment; - condensation of the overhead vapors in a settling condenser (CD6) to produce the aromatic stream (13). A process according to claim 12, comprising at least one of the following steps: - feeding the liquid-liquid extractor (T1) with a solvent stream 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; - 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 steam (11) to produce overhead vapors further comprising steam, and condensing the overhead vapors in the settling condenser (CD6) to produce the aromatic stream (13) and settled water (14). A process according to claim 13, comprising at least one of the following steps: - feeding the liquid-liquid extractor (T1) with a solvent stream (2) comprising sulfolane and water; - recycling of the water produced by the water stripping section to the aromatics recovery tower (T6). 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 stream (2) and produce at least one extract (4) concentrated in aromatic compounds relative to the feed (1), and one raffinate (3) concentrated in non-aromatic compounds relative to the composition of the feed (1), the liquid-liquid extractor (T1) comprising: - a load supply point (1); - a solvent flow feed point (2); - a feed point for a first fraction (51) of extract recycling (5) disposed in an upper part (Z1) of the liquid-liquid extractor (T1); - a feed point for a second fraction (52) of extract recycling (5) disposed in a lower part (Z2) of the liquid-liquid extractor (T1), the upper part (Z1) and the lower part (Z2) being defined with respect to the position of the feed point of the charge (1) in the liquid-liquid extractor (T1).

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