A method for separating aromatics from gasoline C6+ fraction

Abstract

The present invention relates to a method for separating aromatic hydrocarbons from the C6+ fraction of gasoline. Specifically, the C6+ fraction of gasoline is contacted with a selective solvent in countercurrent in an extraction tower, the top stream enters an extraction distillation tower to recover the C9+ aromatic hydrocarbons therein, the rich solvent obtained at the bottom of the extraction tower enters a stripping tower, and then the mixed C6+ aromatic hydrocarbon product is obtained through solvent recovery. Through further distillation, superior C6-C8 aromatic hydrocarbons can be obtained, and the yield is not less than 99%; the purity of the C9+ aromatic hydrocarbon product is not less than 99wt%, and the yield is not less than 95%; and the raw materials do not need to be pre-fractionated, and the energy consumption is low. The method can be used to recover C9+ aromatic hydrocarbons while producing C6-C8 aromatic hydrocarbons, thereby reducing the content of C9+ aromatic hydrocarbons in gasoline. The method process described in the present invention can be achieved by modifying the existing BTX liquid-liquid extraction device.

Description

Technical Field

[0001] The present invention relates to a method for separating aromatic hydrocarbons from gasoline fractions, and specifically, to a method for separating all aromatic hydrocarbons (i.e., C6-C11 aromatic hydrocarbons) in gasoline fractions with a final boiling point less than 205°C with low energy consumption through a combined process of liquid-liquid extraction and extractive distillation. Background Art

[0002] With the continuous increase in environmental protection efforts, on the one hand, the product standards for automotive gasoline continue to upgrade, the aromatic content and 50% evaporation temperature of gasoline continue to decrease, and the proportion of C9+ heavy aromatics that can be adjusted into gasoline gradually decreases; on the other hand, in the chemical industry, aromatics, as an important basic organic chemical raw material for social development, are widely used in polyester, chemical fiber, rubber, medicine, fine chemicals and many other fields, and the market demand is strong.

[0003] In the traditional separation process, only benzene, toluene and xylene (BTX) in the gasoline C6-C8 fraction are separated, while C9+ aromatics directly enter the gasoline pool. However, this method obviously cannot meet the new environmental protection requirements. Therefore, it is of great significance to adopt appropriate separation means to recover C9+ aromatics in gasoline fractions with low energy consumption and high yield, which can not only meet the new gasoline standards, but also expand aromatic resources.

[0004] Patent application CN108690658A discloses a method for recovering aromatics from low aromatic content oil from wide fraction raw materials, wherein the raw oil is subjected to pre-fractionation, extraction, stripping, distillation, water washing, water fractionation and other operations to obtain a mixed aromatic product. The method has a long process and complex operation, wherein the aromatic content in the raw material is 5wt% to 25wt%, and finally C6 to C11 mixed aromatics are obtained, and the dearomatization rate of the raw material is 85wt% to 99wt%.

[0005] Patent application CN1258717A discloses an aromatic extraction process, which can realize the recovery of C9 aromatics, and the solvent can be cyclopentane or tetraethylene glycol ether. The method does not set up a heavy component removal tower, and directly extracts aromatics from a C5-C11 hydrocarbon mixture with an aromatic content of 20wt% to 90wt%, separates non-aromatics and mixed aromatics, and further distills the mixed aromatics to obtain aromatic products. The invention can only recover 30-70% of C9 aromatics.

[0006] Patent CN1408689A discloses a method for recovering aromatic hydrocarbons by extraction and extractive distillation, comprising the following steps: (1) pre-fractionating a hydrocarbon mixture to obtain a benzene fraction, a toluene fraction and a mixed xylene fraction; (2) feeding the toluene fraction obtained by the pre-fractionation into a liquid-liquid extraction tower from the middle and lower part, contacting it with a selective solvent entering from the top of the extraction tower for liquid-liquid extraction, wherein an extract phase rich in aromatic hydrocarbons is discharged from the bottom of the tower, and non-aromatic hydrocarbons are discharged from the top of the tower; (3) introducing the benzene fraction obtained by the pre-fractionation into the middle part of the extractive distillation tower, introducing the extract phase described in step (2) into the middle part of the extractive distillation tower, contacting it with a selective solvent entering from the top of the extractive distillation tower for extractive distillation, wherein a rich solvent rich in aromatic hydrocarbons is discharged from the bottom of the tower, and non-aromatic hydrocarbon components at the top of the tower are refluxed into the bottom of the liquid-liquid extraction tower; (4) introducing the rich solvent described in step (3) into a solvent recovery tower from the middle part, separating the solvent and aromatic hydrocarbons by vacuum distillation, wherein the mixed aromatic hydrocarbons are discharged from the top of the recovery tower, and the lean solvent obtained at the bottom of the tower is circulated back to the liquid-liquid extraction tower and the extractive distillation tower. This method is mainly used to recover benzene, toluene and xylene, and separates light and heavy aromatic components in the raw material by distillation (pre-fractionation), but the energy consumption is relatively high.

[0007] Patent CN110628459A discloses an aromatics extraction combined device and process. The method first divides the raw material into two streams of light and heavy streams through pre-fractionation. For the light fraction, an extraction distillation method is adopted. After the light aromatics are extracted, they are sent to the downstream distillation system to distill out high-purity light aromatic products; for the heavy fraction, a liquid-liquid extraction method is adopted. The extracted heavy aromatics are directly sent to the heavy aromatics distillation system to distill out high-purity heavy aromatic products. The gasoline fraction raw material described in the method does not contain C8+ non-aromatics, and the mass fraction of C9-C10 aromatics does not exceed 5%. It is not a conventional full-fraction gasoline raw material; and the energy consumption of separating light and heavy aromatics by distillation is relatively high. Summary of the invention

[0008] In view of the shortcomings of the prior art, the present invention aims to provide a method for recovering all aromatics separated from the C6+ fraction of gasoline with low energy consumption and high yield. Specifically, by utilizing the solubility and selectivity of the extraction solvent for aromatics of different carbon numbers in the whole fraction gasoline, a method for obtaining high-grade C6-C8 aromatic products and C9+ aromatics with a yield of more than 95% and a purity of more than 99wt% is obtained through a combined process of liquid-liquid extraction and extractive distillation.

[0009] To achieve the purpose of the present invention, the present invention provides a method for separating aromatics from a gasoline C6+ fraction, characterized in that it comprises the following steps:

[0010] (a) the gasoline C6+ fraction enters the lower middle part of the liquid-liquid extraction tower, the solvent enters the upper part of the liquid-liquid extraction tower and contacts with the gasoline C6+ fraction in countercurrent, and the first rich solvent obtained at the bottom of the liquid-liquid extraction tower enters the stripping tower;

[0011] (b) the overhead stream of the liquid-liquid extraction tower enters the middle part of the C9+ extractive distillation tower, the solvent enters the upper part of the C9+ extractive distillation tower, and the second rich solvent obtained at the bottom of the C9+ extractive distillation tower enters the solvent recovery tower;

[0012] (c) The third rich solvent obtained at the bottom of the stripping tower enters the solvent recovery tower together with the second rich solvent, and a C6+ mixed aromatics product is obtained at the top of the solvent recovery tower.

[0013] The aromatics separation method provided by the present invention has the following advantages compared with the prior art:

[0014] (1) The C6+ fraction of the raw gasoline does not require pre-fractionation, and the energy consumption is low;

[0015] (2) Aromatic products are of high purity and diversity. C6+ mixed aromatic products include all C6-C11 aromatics, which can be further distilled to obtain C6-C8 aromatics and C9+ aromatics. C9+ aromatics can be used as solvent oil, or used for disproportionation and light-weighting to produce C6-C8 aromatics, or further separated to obtain a single aromatic product (such as mesitylene, durene, etc.) as a fine chemical raw material.

[0016] (3) Only four main towers are needed, and the process is simple. This can be achieved by modifying the existing C6-C8 aromatic liquid-liquid extraction device. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 A schematic diagram of the process flow for separating aromatics from the gasoline C6+ fraction provided by the present invention. DETAILED DESCRIPTION

[0018] The present invention will be further described in detail below through the accompanying drawings and embodiments. Through these descriptions, the characteristics and advantages of the present invention will become more clear and distinct.

[0019] The word "exemplary" is used exclusively herein to mean "serving as an example, embodiment, or illustration." Any embodiment described herein as "exemplary" is not necessarily to be construed as preferred or advantageous over other embodiments. Although various aspects of the embodiments are shown in the drawings, the drawings are not necessarily drawn to scale unless otherwise noted.

[0020] In addition, the technical features involved in different embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0021] In the present invention, the term "C6+" refers to aromatic hydrocarbons containing 6 or more carbons, and the term "C6+ aromatic hydrocarbons" refers to aromatic hydrocarbons containing 6 or more carbons.

[0022] In the present invention, the term "C9+" refers to aromatic hydrocarbons containing 9 or more carbons, and the term "C9+ aromatic hydrocarbons" refers to aromatic hydrocarbons containing 9 or more carbons.

[0023] The present invention provides a method for separating aromatics from a gasoline C6+ fraction, characterized in that it comprises the following steps:

[0024] (a) the gasoline C6+ fraction enters the lower middle part of the liquid-liquid extraction tower, the solvent enters the upper part of the liquid-liquid extraction tower and contacts with the gasoline C6+ fraction in countercurrent, and the first rich solvent obtained at the bottom of the liquid-liquid extraction tower enters the stripping tower;

[0025] (b) the liquid-liquid extraction tower overhead stream enters the middle of the C9+ extractive distillation tower, the solvent enters the upper part of the C9+ extractive distillation tower, the raffinate oil product obtained at the top of the C9+ extractive distillation tower enters the gasoline pool, and the second rich solvent obtained at the bottom of the C9+ extractive distillation tower enters the solvent recovery tower;

[0026] (c) The stripping tower top stream is returned to the lower part of the liquid-liquid extraction tower as backwash liquid, and the third rich solvent obtained at the bottom of the stripping tower enters the solvent recovery tower together with the second rich solvent, and a C6+ mixed aromatic hydrocarbon product is obtained at the top of the solvent recovery tower. The lean solvent obtained at the bottom of the solvent recovery tower is divided into two streams, which are respectively returned to the upper part of the liquid-liquid extraction tower and the upper part of the C9+ extraction distillation tower for recycling.

[0027] Conventional aromatic extraction solvents have high solubility for C6-C8 aromatics, but significantly reduce solubility for C9+ aromatics (i.e., C9-C11 aromatics). Therefore, liquid-liquid extraction can be used to separate C6-C8 aromatics, thereby effectively avoiding the high energy consumption caused by the separation of light and heavy components by distillation (i.e., pre-fractionation). For the separation of C9+ aromatics and non-aromatics, extractive distillation can be used. In the C9+ extractive distillation tower, since C6-C8 non-aromatics have a low boiling point, they are easily evaporated to the top of the extractive distillation tower, and C9+ non-aromatics can also be evaporated to the top of the extractive distillation tower under high vacuum, high temperature and large solvent ratio conditions, thereby achieving the separation of C9+ aromatics and non-aromatics. In addition, a small amount of solvent entrained by the liquid-liquid extraction tower top logistics can also be recovered in the C9+ extractive distillation tower, thereby completely eliminating the complex processes such as raffinate oil water washing-water stripping in the conventional liquid-liquid extraction process.

[0028] According to one embodiment of the present invention, the solvent entering the liquid-liquid extraction tower and the C9+ extraction distillation tower is the same, which is a polar compound or a mixture thereof having a boiling point higher than 230°C, preferably sulfolane, sulfolane-tetraethylene glycol monomethyl ether composite solvent, sulfolane-3-methyl sulfolane composite solvent, and when the solvent is a composite solvent, the sulfolane content is greater than 80wt%. Optionally, the solvent may contain 0.5wt% to 2.0wt% of water and / or 0.01wt% to 1.0wt% of hydrocarbon compounds.

[0029] According to one embodiment of the present invention, the solvent ratio of the liquid-liquid extraction tower is 2:1 to 4:1, and the solvent ratio is the mass ratio of the solvent entering the liquid-liquid extraction tower to the gasoline C6+ fraction. The solvent inlet temperature is 40°C to 90°C, and the raw material inlet temperature is 30°C to 50°C, preferably 50°C to 80°C; the absolute pressure at the top of the liquid-liquid extraction tower is 0.2MPa to 0.7MPa, and the number of theoretical plates is 8 to 20.

[0030] According to one embodiment of the present invention, the solvent ratio of the C9+ extractive distillation tower is 5:1 to 10:1, and the solvent ratio is the mass ratio of the solvent entering the C9+ extractive distillation tower to the liquid-liquid extraction tower top logistics, preferably 6:1 to 9:1; the solvent inlet temperature is 70°C to 100°C, the absolute pressure at the top of the C9+ extractive distillation tower is 0.02MPa to 0.06MPa, the bottom temperature is 140°C to 180°C, preferably 150°C to 170°C, the reflux ratio is 0 to 0.5, and the number of theoretical plates is 20 to 50.

[0031] According to one embodiment of the present invention, the absolute pressure at the top of the stripping tower is 0.2MPa-0.7MPa, the bottom temperature is 140°C-180°C, the number of theoretical plates is 8-30, and the backwash ratio of the stripping tower is 0.2-2.0, which is the mass ratio of the backwash liquid discharged from the top of the stripping tower to the first rich solvent entering the stripping tower.

[0032] According to one embodiment of the present invention, the absolute pressure at the top of the solvent recovery tower is 0.02MPa-0.06MPa, the bottom temperature is 180°C-200°C, the reflux ratio is 0.2-1.0, preferably 0.3-1.0, and the number of theoretical plates is 15-40.

[0033] According to one embodiment of the present invention, the gasoline C6+ fraction of the present invention has a boiling range not exceeding 205°C, wherein the mass fraction of aromatic hydrocarbons is 30% to 80%. The gasoline may be catalytic cracking gasoline, catalytic pyrolysis gasoline, hydrocracking gasoline, gasoline obtained by a catalytic cracking-hydrocracking combined process capable of producing more aromatic hydrocarbons (LTA gasoline), etc.; the C6+ fraction includes all fraction sections having a boiling range not exceeding 205°C, such as C6-C8 fraction, C6-C9 fraction, C6-C10 fraction, etc.; when processing the C6-C8 fraction, the C9+ extractive distillation tower can be used to recover the C8 aromatic hydrocarbons that have not completely entered the rich solvent at the bottom of the liquid-liquid extraction tower, thereby improving its yield.

[0034] According to one embodiment of the present invention, the second rich solvent and the third rich solvent share a solvent recovery tower to achieve separation of solvent and aromatics. During specific implementation, two solvent recovery towers may also be set up, which are respectively used to recover C9+ aromatics and mixed aromatics mainly composed of C6-C8 aromatics. In the subsequent distillation unit, in addition to the benzene tower and the toluene tower, a xylene tower is also required to be set up. A small amount of C9+ aromatics obtained at the bottom of the xylene tower can be mixed with the product obtained at the top of the C9+ aromatics recovery tower and then sent out of the device. The benzene tower, the toluene tower and the xylene tower are operated under conventional operating conditions in this field.

[0035] The present invention is further described below in conjunction with the accompanying drawings.

[0036] Figure 1 In the process, the gasoline C6+ fraction enters the middle and lower part of the liquid-liquid extraction tower 101 through pipeline 1, and the lean solvent enters the upper part of the tower 101 from pipeline 2. After the two are in countercurrent contact, the top flow enters the middle part of the C9+ extraction distillation tower 102 through pipeline 3, and the first rich solvent is obtained at the bottom of the tower and enters the stripping tower 106 through pipeline 13. The lean solvent enters the upper part of tower 102 through pipeline 4, and the non-aromatic hydrocarbons obtained at the top of tower 102 are cooled through pipeline 5 and enter the reflux tank 103, a part of which is refluxed through pipeline 6, and the other part is produced as a raffinate oil product through pipeline 7; the second rich solvent obtained at the bottom of tower 102 enters the solvent recovery tower 104 through pipeline 8. The vapor phase evaporated from the top of tower 106 enters the bottom of tower 101 after condensation through pipeline 14, and the third rich solvent obtained at the bottom of tower 106 enters the solvent recovery tower 104 after merging with pipeline 8 through pipeline 15. The steam at the top of tower 104 enters the reflux tank 105 after condensation through pipeline 9, a part of which returns to the top of tower 104 through pipeline 10, and the rest is produced as a C6+ mixed aromatic hydrocarbon product through pipeline 11; the lean solvent obtained at the bottom of tower 104 is produced through pipeline 12 and divided into two streams, which are returned to tower 101 and tower 102 through pipelines 2 and 4 respectively for recycling.

[0037] The present invention is further described in detail below by examples, but the present invention is not limited thereto.

[0038] Example 1

[0039] according to Figure 1 The process of separating aromatics from the C6+ fraction of gasoline, the raw material hydrocarbon composition is shown in Table 1, the total aromatic content is 48.51wt%, the solvent is sulfolane, and the main operating conditions of each tower are shown in Table 2. The aromatic content in the separated raffinate oil is shown in Table 3, the C6+ mixed aromatic composition is shown in Table 4, the yield of C6-C8 aromatics is 99%, and the yield of C9+ aromatics is 95%; further distillation can obtain high-quality benzene, toluene, xylene products and C9+ aromatics with a purity of 99.2wt%.

[0040] Example 2

[0041] according to Figure 1The process of separating aromatics from the C6+ fraction of gasoline is shown in Table 1. The composition of the raw material hydrocarbons is shown in Table 1. The total aromatic content is 56.73wt%. The solvent is a composite solvent of sulfolane-tetraethylene glycol monomethyl ether, and the mass fraction of sulfolane is 97%. The main operating conditions of each tower are shown in Table 2. The aromatic content in the separated raffinate oil is shown in Table 3, and the composition of C6+ mixed aromatics is shown in Table 4. The yield of C6-C8 aromatics is 99%, and the yield of C9+ aromatics is 96%. Further distillation can obtain high-quality benzene, toluene, xylene products and C9+ aromatics with a purity of 99.0wt%.

[0042] Example 3

[0043] according to Figure 1 The process of separating aromatics from the C6+ fraction of gasoline is shown in Table 1. The raw material hydrocarbon composition is shown in Table 1. The total aromatic content is 78.60wt%. The solvent is a sulfolane-3-methylsulfolane composite solvent, in which the mass fraction of sulfolane is 90%. The main operating conditions of each tower are shown in Table 2. The aromatic content in the separated raffinate oil is shown in Table 3, the composition of C6+ mixed aromatics is shown in Table 4, the yield of C6-C8 aromatics is 99%, and the yield of C9+ aromatics is 96%. Further distillation can obtain high-quality benzene, toluene, xylene products and C9+ aromatics with a purity of 99.3wt%.

[0044] Comparative Example 1

[0045] The BTX liquid-liquid extraction process is used to separate aromatics from the C6+ fraction of gasoline. The raw material is passed through an extraction tower and a raffinate oil washing tower to obtain a raffinate oil product after the aromatics are removed. The rich solvent at the bottom of the extraction tower enters a stripping tower, and the light component obtained at the top of the stripping tower returns to the extraction tower as a backwash liquid. The bottom stream of the stripping tower enters a solvent recovery tower for separation to obtain solvent and mixed aromatics. The raw material is the same as in Example 1, the solvent is cyclopentane, and the main operating conditions of each tower are shown in Table 5. The aromatic content in the separated raffinate oil is shown in Table 3, and the composition of mixed aromatics is shown in Table 4. The yield of C6-C8 aromatics obtained is 99%, and the purity is 99.9wt%. After further distillation, superior benzene, toluene, and xylene products can be obtained. However, the raffinate oil contains 12.82% of C9+ heavy aromatics by mass that cannot be recovered.

[0046] Comparative Example 2

[0047] A method similar to that of patent CN110628459A is used to separate aromatic hydrocarbons from gasoline C6+ fractions. The raw materials are the same as those in Example 1, and the solvent used is sulfolane. C6-C8 fractions (light fractions) and C9+ fractions (heavy fractions) are obtained by pre-fractionation, wherein the mass fraction of C8 aromatic hydrocarbons in the heavy fraction does not exceed 0.5%, and the mass fraction of C9 aromatic hydrocarbons in the light fraction does not exceed 0.1%. The light fraction is separated from BTX by a C6-C8 fraction extractive distillation tower and a C6-C8 fraction recovery tower, and the solvent ratio is 7.5; the heavy fraction is separated from C9+ aromatic hydrocarbons by conventional liquid-liquid extraction, and the solvent ratio is 3.5. The operating parameters of each tower are shown in Table 6. The purity of the separated C6-C8 aromatic hydrocarbons product is 99.0wt%, and the yield is 97.0%; the purity of the C9+ aromatic hydrocarbons product is 99.0wt%, and the yield is 92.0%, and the product composition is shown in Table 5.

[0048] Table 1 Raw material composition

[0049]

[0050] Table 2 Main operating conditions

[0051]

[0052]

[0053] Table 3 Raffinate oil composition

[0054]

[0055] Table 4 Composition of C6+ mixed aromatics

[0056]

[0057] Table 5 Comparative Example 2 Product Composition

[0058]

[0059]

[0060] Table 6 Main operating conditions

[0061]

[0062]

[0063] From the comparison of the data in Table 3, Table 4 and Table 5, it can be seen that the method of the present invention can separate aromatics from non-aromatics in the gasoline C6+ fraction with high purity and high yield. Compared with the conventional liquid-liquid extraction method described in Comparative Example 1, not only is the yield of aromatics higher, but the step of washing the raffinate oil is omitted; compared with the patented method in Comparative Example 2, the yield of aromatics is higher. This fully reflects the technical advancement of the present invention.

[0064] In the description of the present invention, it should be noted that the directions or positional relationships indicated by the terms "upper", "lower", "inside", "outside", "front", "back", "left", "right", etc. are directions or positional relationships based on the working state of the present invention, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific direction, be constructed and operated in a specific direction, and therefore cannot be understood as a limitation on the present invention.

[0065] The present invention has been described above in conjunction with preferred embodiments, but these embodiments are only exemplary and serve only as an illustration. On this basis, the present invention may be subjected to a variety of substitutions and improvements, all of which fall within the scope of protection of the present invention.

Claims

1. A method for separating aromatics from a gasoline C6+ fraction, characterized in that: The steps include: (a) The gasoline C6+ fraction enters the lower middle part of the liquid-liquid extraction tower, the solvent enters the upper part of the liquid-liquid extraction tower and contacts with the gasoline C6+ fraction in countercurrent, and the first rich solvent obtained at the bottom of the liquid-liquid extraction tower enters the stripping tower; (b) the overhead stream of the liquid-liquid extraction tower enters the middle part of the C9+ extraction distillation tower, the solvent enters the upper part of the C9+ extraction distillation tower, and the second rich solvent obtained at the bottom of the C9+ extraction distillation tower enters the solvent recovery tower; (c) the third rich solvent obtained at the bottom of the stripping tower enters the solvent recovery tower together with the second rich solvent, and a C6+ mixed aromatics product is obtained at the top of the solvent recovery tower; Wherein, the solvent ratio of the C9+ extractive distillation tower is 5:1 to 10:1, the solvent inlet temperature is 70°C to 100°C, the absolute pressure at the top of the C9+ extractive distillation tower is 0.02 MPa to 0.06 MPa, the bottom temperature is 140°C to 180°C, the reflux ratio by mass is 0 to 0.5, and the number of theoretical plates is 20 to 50; the solvent ratio is the mass ratio of the solvent entering the C9+ extractive distillation tower to the liquid-liquid extraction tower top flow; The solvent entering the liquid-liquid extraction tower and the C9+ extraction distillation tower is the same.

2. The method according to claim 1, characterized in that The solvent entering the liquid-liquid extraction tower and the C9+ extraction distillation tower is a polar compound or a mixture thereof having a boiling point higher than 230°C.

3. The method according to claim 1, characterized in that The solvent is sulfolane, sulfolane-tetraethylene glycol monomethyl ether composite solvent, and sulfolane-3-methylsulfolane composite solvent.

4. The method according to any one of claims 1 to 3, characterized in that The solvent contains 0.5 wt% to 2.0 wt% of water and / or 0.01 wt% to 1.0 wt% of a hydrocarbon compound.

5. The method according to any one of claims 1 to 3, characterized in that: The raffinate oil product obtained from the top of the C9+ extractive distillation tower enters the gasoline pool.

6. The method according to any one of claims 1 to 3, characterized in that: The top stream of the stripping tower is returned to the lower part of the liquid-liquid extraction tower as backwash liquid, and the lean solvent obtained at the bottom of the solvent recovery tower is divided into two streams, which are respectively returned to the upper part of the liquid-liquid extraction tower and the upper part of the C9+ extraction distillation tower for recycling.

7. The method according to any one of claims 1 to 3, characterized in that The solvent ratio of the liquid-liquid extraction tower is 2:1 ~ 4:1, the solvent inlet temperature is 40 ℃ ~ 90 ℃, the absolute pressure at the top of the liquid-liquid extraction tower is 0.2 MPa ~ 0.7 MPa, and the number of theoretical plates is 8 ~ 20; the solvent ratio is the mass ratio of the solvent entering the liquid-liquid extraction tower to the gasoline C6+ fraction.

8. The method according to claim 6, characterized in that The absolute pressure at the top of the stripping tower is 0.2 MPa ~ 0.7 MPa, the bottom temperature is 140 ℃ ~ 180 ℃, the number of theoretical plates is 8 ~ 30, and the backwash ratio is 0.2 ~ 2.0, and the backwash ratio is the mass ratio of the backwash liquid discharged from the top of the stripping tower to the first rich solvent entering the stripping tower.

9. The method according to any one of claims 1 to 3, characterized in that The absolute pressure at the top of the solvent recovery tower is 0.02MPa ~ 0.06MPa, the bottom temperature is 180℃ ~ 200℃, the reflux ratio by mass is 0.2 ~ 1.0, and the number of theoretical plates is 15 ~ 40.

10. The method according to any one of claims 1 to 3, characterized in that The boiling range of gasoline C6+ fraction does not exceed 205℃, and the mass fraction of aromatics is 30% ~ 80%.

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