A method for separating heavy aromatics from kerosene fractions

Abstract

A method for separating heavy aromatics from kerosene fractions comprises contacting a raw material with a selective main solvent and a co-solvent in an extraction tower for liquid-liquid extraction. The overhead stream is distilled and washed with water to obtain a raffinate product. The rich solvent at the bottom of the tower is stripped and the solvent is recovered to obtain a heavy aromatics product. The selective main solvent has high selectivity for heavy aromatics and strong dissolving power. This method can produce a heavy aromatics product with a purity exceeding 99% by weight and a yield exceeding 95% by weight. It also achieves internal recycling of multiple streams without wastewater discharge.

Description

Technical Field

[0001] The present invention relates to a method for separating heavy aromatic hydrocarbons from kerosene fractions, specifically, a method for separating heavy aromatic hydrocarbons from kerosene by liquid-liquid extraction using a selective solvent and a co-solvent. Background Art

[0002] Jet kerosene is typically derived from the kerosene fraction obtained from the atmospheric and vacuum distillation of crude oil. This fraction contains a high concentration of paraffins, making it an effective heavy cracking feedstock. However, this fraction also contains approximately 30 wt% aromatics, although this content can be reduced to 5-10 wt% through further hydrorefining. The steam cracking process for ethylene production yields distinct cracking products from different hydrocarbons. Aromatic cracking involves only dehydrogenation, not the formation of paraffins, significantly impacting the operating cycle. Therefore, separating the aromatics from the kerosene fraction for the production of high-value-added carbon materials, while using the remaining fraction for steam cracking, is an effective solution for jet kerosene disposal and improving refinery profitability.

[0003] Solvent extraction is a common method for removing aromatics from petroleum distillates. When the raw material is a C6-C8 fraction, sulfolane is generally used as the solvent, and the corresponding separation process involves liquid-liquid extraction or extractive distillation, ultimately yielding triphenyl products (i.e., benzene, toluene, and xylene). However, as the raw material's boiling range increases, sulfolane's solubility for heavy aromatics decreases significantly, making it difficult to meet separation requirements. CN87107146A discloses a dual-solvent method for extracting aromatics from a diesel fraction with a boiling range of 300-530°C. The first solvent is furfural, phenol, sulfoxide, or dimethylpyrrolidone, preferably furfural, and the second solvent is a light oil. Since the boiling point of the solvent is well below the raw material's boiling range, solvent recovery can be achieved through flash evaporation or steam stripping. However, this method fails to recycle the stripping steam, resulting in the generation of large amounts of solvent-containing (furfural) wastewater, high energy consumption, significant solvent loss, and environmentally unfriendly properties. This method can obtain heavy aromatics with a purity higher than 95 wt%, and the aromatics extraction rate is 50~95 wt%.

[0004] US4333824 uses N-methylpyrrolidone as a solvent to extract aromatics from lubricating oil to produce lubricating base oil. Because the boiling point range of the solvent and the aromatics differs slightly, the method involves recovering the solvent from the extracted oil through a process involving low-pressure distillation, high-pressure distillation, vacuum flash evaporation, and steam stripping. The solvent is then recovered from the raffinate using a vacuum flash evaporation and steam stripping process. Furthermore, a solvent purification system (not described in detail) is also included to further purify the solvent, resulting in a complex process. The resulting extracted oil volume yield is 10-70%, and the purity of heavy aromatics in the extracted oil is 80 wt%.

[0005] CN101921624A discloses a method for preparing high-quality diesel using a combined extraction and hydrogenation process. The raw oil has a boiling range of 160 to 389°C, and the extraction solvent is selected from one of sulfolane, N-methylpyrrolidone, and dimethyl sulfoxide. The method separates the solvent from the raffinate by washing with water, and then separates the solvent from heavy aromatics using a process of stripping, washing, and distillation. However, the stripping agent is not disclosed. The resulting heavy aromatics have a purity of 90 to 92 wt% and a yield of approximately 80 wt%.

[0006] Currently, there is a lack of a method for effectively separating heavy aromatics from kerosene fractions in a low-energy and environmentally friendly manner. Summary of the Invention

[0007] In view of the shortcomings of the existing technology, the present invention aims to provide a method for effectively separating heavy aromatics from kerosene fractions, which not only increases the added value of kerosene fractions, but also provides a more economical way out for aviation kerosene and improves economic benefits.

[0008] To achieve the purpose of the present invention, the present invention provides a method for separating heavy aromatic hydrocarbons from kerosene fractions, characterized in that the method comprises contacting the kerosene fraction raw material with a selective main solvent and a co-solvent in an extraction tower to perform liquid-liquid extraction, distilling and washing the first raffinate oil obtained at the top of the extraction tower to obtain a raffinate oil product, and stripping and solvent recovery of the rich solvent obtained at the bottom of the extraction tower to obtain a heavy aromatic hydrocarbon product.

[0009] This invention utilizes a selective main solvent and a cosolvent to separate heavy aromatics from kerosene fractions. The selective main solvent has high selectivity and high solubility for heavy aromatics, while the cosolvent improves the purity of the heavy aromatics and reduces the difficulty of solvent recovery. Through a combined extraction-stripping-distillation process, a heavy aromatics product with a purity exceeding 99 wt% and a yield exceeding 95 wt% is obtained. The raffinate oil obtained from the kerosene fraction after extraction, distillation, and water washing can be used as industrial white oil (II) or steam cracking feedstock, with the aromatics content reduced to no more than 0.2 wt%.

[0010] The separation method of the present invention has the following characteristics compared with the prior art:

[0011] (1) The selective main solvent has high selectivity for heavy aromatics and strong dissolving power, and the purity of the obtained heavy aromatics product is higher than 99wt% and the yield is higher than 95wt%;

[0012] (2) Using high-boiling-point solvents and matching separation processes, the solvent content in the raffinate oil and heavy aromatics does not exceed 10 ppm, and there is no wastewater discharge.

[0013] (3) The process operating conditions are mild and can be used to remove aromatics from kerosene fractions. It has no hydrogen consumption, low energy consumption, and can significantly reduce the aromatics content in kerosene fractions. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 The present invention provides a schematic diagram of a process for separating heavy aromatics from kerosene fractions using a selective solvent and a co-solvent. DETAILED DESCRIPTION

[0015] The present invention will be further described in detail below through the accompanying drawings and examples. Through these descriptions, the characteristics and advantages of the present invention will become more clear and distinct. It should be understood that the specific embodiments described herein are only for illustration and explanation of the present invention and are not intended to limit the present invention.

[0016] The word "exemplary" is used exclusively herein to mean "serving as an example, example, 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 indicated.

[0017] 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.

[0018] There are two key challenges in separating heavy aromatics from kerosene fractions. First, it's difficult to balance solvent selectivity and solubility. Conventionally used aromatic extraction solvents (such as sulfolane and tetraethylene glycol) have poor solubility for C8-C12 heavy aromatics, resulting in low heavy aromatic yields and the presence of a significant amount of heavy aromatics in the raffinate oil, making the raffinate oil a poor choice for cracking feedstock. Solvents such as N-methylpyrrolidone and N-formylmorpholine, on the other hand, have good solubility for heavy aromatics but poor selectivity, resulting in low raffinate oil yields and low purity of the heavy aromatics in the extracted oil. Second, the high boiling points of heavy aromatics, which are close to or even completely overlap those of conventional aromatic extraction solvents (such as N-formylmorpholine and N-methylpyrrolidone), make separation of the solvent and aromatics by distillation difficult. To ensure the purity of the circulating solvent, multiple methods such as water washing, stripping, and steam stripping are required, which result in high energy consumption and complex processes. If low-boiling-point solvents (such as acetonitrile and methanol) are used, on the one hand, the solvent selectivity is poor, and on the other hand, all the solvent must be evaporated, which also results in high energy consumption. The present invention uses alkyl sulfolane as the selective main solvent. While ensuring high selectivity for heavy aromatics, it significantly improves the solubility of the selective main solvent for heavy aromatics, thereby ensuring the yield of heavy aromatics. By adding a co-solvent (C5-C7 saturated hydrocarbons), the purity of heavy aromatics is further improved, and the difficulty of the solvent recovery process is reduced. The combined extraction-stripping-distillation process achieves the circulation of the selective main solvent, co-solvent, and water, reducing solvent loss, thereby reducing energy consumption and avoiding environmental pollution.

[0019] In the present invention, the term "normal first line" refers to the fraction on the side line of the atmospheric distillation unit in the petroleum industry.

[0020] Specifically, the method for separating heavy aromatics from kerosene fractions provided by the present invention comprises the following steps:

[0021] (1) The kerosene fraction feedstock enters the solvent extraction tower from the middle and lower part, the selective main solvent enters the extraction tower from the top, and the co-solvent C5~C7 saturated hydrocarbons are injected from the bottom of the extraction tower; the first raffinate oil is obtained from the top of the extraction tower, and the rich solvent is obtained from the bottom of the tower;

[0022] (2) The first raffinate oil obtained from the top of the extraction tower enters the raffinate oil distillation tower, and the C5~C7 saturated hydrocarbon stream is separated from the top of the raffinate oil distillation tower, and the second raffinate oil is obtained from the bottom of the tower; the second raffinate oil enters the water washing tower, and after the solvent is removed, it is discharged from the top of the water washing tower as the raffinate oil product, and the washing water of the water washing tower enters the water stripping tower;

[0023] (3) The rich solvent obtained at the bottom of the extraction tower enters the top of the stripping tower, and the C5~C7 saturated hydrocarbon stream enters the lower part of the stripping tower; the stream rich in heavy aromatics and C5~C7 saturated hydrocarbons obtained at the top of the stripping tower enters the middle of the aromatics recovery tower, and the solvent is recovered through distillation; the C5~C7 saturated hydrocarbon stream is obtained at the top of the aromatics recovery tower, and the heavy aromatics product is obtained in the bottom of the tower;

[0024] (4) The main solvent containing C5~C7 saturated hydrocarbons obtained at the bottom of the stripping tower enters the solvent recovery tower, and the C5~C7 saturated hydrocarbon stream is obtained at the top of the tower. The lean solvent obtained at the bottom of the tower is circulated to the extraction tower as the selective main solvent;

[0025] (5) The C5~C7 saturated hydrocarbon streams obtained from the top of the raffinate distillation tower, aromatics recovery tower, and solvent recovery tower are divided into two streams, one of which enters the bottom of the extraction tower as a co-solvent, and the other enters the lower part of the stripping tower; the top stream of the water stripping tower enters the condenser at the top of the raffinate distillation tower, and the solvent-containing water produced in the bottom of the tower enters the bottom of the solvent recovery tower; the water in the reflux tank water bag at the top of the solvent recovery tower is returned to the water washing tower as washing water.

[0026] In an embodiment of the present invention, the selective main solvent is selected from alkyl sulfolane, preferably 3-methyl sulfolane and / or 2,4-dimethyl sulfolane. The selective main solvent may contain 0.5 wt% to 3.0 wt% of water and / or 0 to 1.0 wt% of a hydrocarbon compound. In an embodiment of the present invention, the cosolvent is a C5 to C7 saturated hydrocarbon, preferably selected from one or more of C6 raffinate oil, n-hexane, and n-heptane.

[0027] In an embodiment of the present invention, in step (1) of the method, the mass ratio of the selective main solvent to the kerosene fraction raw material is 3:1 to 7:1, and the mass ratio of the co-solvent C5 to C7 saturated hydrocarbons to the kerosene fraction raw material is 0.2 to 0.6; the selective main solvent inlet tower temperature is 80°C to 180°C, preferably 90°C to 140°C, the extraction tower top pressure is 0.2 MPa to 0.7 MPa absolute pressure, and the number of theoretical plates is 8 to 15.

[0028] In an embodiment of the present invention, in step (2) of the method, the theoretical plate number of the raffinate distillation tower is 10 to 30, the reflux ratio is 0.2 to 2, the tower top pressure is 0.1 MPa to 0.5 MPa absolute pressure, and the tower bottom temperature is 150°C to 250°C.

[0029] In an embodiment of the present invention, in step (2) of the method, the mass ratio of the washing water of the water washing tower to the second raffinate oil is 0.1 to 0.5, preferably 0.1 to 0.3, the pressure at the top of the water washing tower is 0.4 MPa to 0.7 MPa absolute pressure, and the water washing temperature is 30°C to 50°C.

[0030] In an embodiment of the present invention, in step (3) of the method, the number of theoretical plates of the stripping tower is 8 to 12, the pressure at the top of the tower is 0.2 MPa to 0.8 MPa absolute pressure, the temperature of the C5 to C7 saturated hydrocarbon flow into the tower is 40°C to 100°C, and the mass ratio of the C5 to C7 saturated hydrocarbon flow to the rich solvent is 0.05 to 0.5, preferably 0.07 to 0.15.

[0031] In an embodiment of the present invention, in step (3) of the method, the number of theoretical plates of the aromatics recovery tower is 15 to 40, the reflux ratio is 0.2 to 2, the top pressure is 0.1 MPa to 0.5 MPa absolute pressure, and the bottom temperature is 150°C to 300°C.

[0032] In an embodiment of the present invention, in step (4) of the method, the number of theoretical plates of the solvent recovery tower is 5 to 30, the reflux ratio is 0.3 to 1.0, the top pressure is 0.05 MPa to 0.15 MPa absolute pressure, and the bottom temperature is 150°C to 200°C, preferably 160°C to 180°C.

[0033] In an embodiment of the present invention, the kerosene fraction raw material of the present invention is preferably derived from conventional first-line fuel after hydrofining, wherein the sulfur and nitrogen contents are each no more than 1 ppm, the boiling range is 140°C to 250°C, and the mass fraction of heavy aromatics is 3 wt% to 30 wt%.

[0034] The method of the present invention can obtain heavy aromatic hydrocarbon products with a purity higher than 99 wt% and a yield higher than 95 wt%, and realize the internal recycling of multiple logistics without sewage discharge.

[0035] The following is combined with Figure 1 The present invention will be further described.

[0036] exist Figure 1 In the process, the kerosene fraction feedstock enters the lower part of the extraction tower 101 via pipeline 1, the fresh selective main solvent and / or the recycled lean solvent enter the upper part of the tower 101 via pipeline 2, the fresh and / or recycled co-solvent C5~C7 saturated hydrocarbons enter from the bottom of the tower 101 via pipeline 25, and the first raffinate oil obtained at the top of the tower 101 enters the raffinate oil distillation tower 102 via pipeline 3. The C5~C7 saturated hydrocarbon flow obtained at the top of the tower 102 enters the condenser and reflux tank via pipeline 4, part of the C5~C7 saturated hydrocarbons returns to the tower 102 via pipeline 5, and the rest is collected into pipeline 25 via pipeline 6 and returned to the bottom of the tower 101. The second raffinate oil obtained at the bottom of tower 102 enters the lower part of water washing tower 103 through pipeline 7, and the washing water enters the upper part of tower 103 through pipeline 8. The raffinate oil product obtained after water washing is discharged from the top of tower 103 through pipeline 9, and the washed water enters the water stripping tower 104 through pipeline 10. The logistics evaporated from the top of tower 104 enters the condenser at the top of tower 102 through pipeline 11 and merges with pipeline 4. The solvent-containing water obtained at the bottom of tower 104 enters the bottom of solvent recovery tower 107 through pipeline 12.

[0037] The rich solvent obtained at the bottom of the extraction tower 101 enters the upper part of the stripping tower 105 through pipeline 13, the C5~C7 saturated hydrocarbons enter the lower part of the tower 105 through pipeline 14, and the heavy aromatics-rich logistics obtained at the top of the tower 105 enters the aromatics recovery tower 106 through pipeline 15. The C5~C7 saturated hydrocarbon logistics obtained at the top of the tower 106 enters the condenser and reflux tank through pipeline 16, part of which returns to the tower 106 through pipeline 17, and the rest enters pipeline 18. The heavy aromatics product obtained at the bottom of the tower is discharged through pipeline 19.

[0038] The logistics rich in C5~C7 saturated hydrocarbons and main solvents obtained at the bottom of tower 105 enters the solvent recovery tower 107 via pipeline 20, and the C5~C7 saturated hydrocarbon logistics obtained at the top of tower 107 enters the condenser and reflux tank via pipeline 21. Part of it returns to tower 107 via pipeline 22, and the rest merges with pipeline 18 via pipeline 23. Then, a part is separated and enters the bottom of tower 105 via pipeline 14, and the rest merges with pipeline 6 via pipeline 24, and finally returns to the bottom of tower 101 via pipeline 25.

[0039] The water in the reflux tank water bags at the top of towers 102, 106, and 107 is respectively merged into pipeline 8 through pipelines 26, 27, and 28, and returned to the top of the water washing tower 103 as washing water.

[0040] The present invention is further described in detail below by way of examples, but the present invention is not limited thereto.

[0041] Example 1

[0042] This embodiment follows Figure 1 The process used to separate heavy aromatics from the hydrorefined kerosene fraction was shown in Table 1. The feedstock had a boiling range of 144°C to 230°C. The composition was shown in Table 1. The selective main solvent was 3-methylsulfolane, and the cosolvent was C6 raffinate. The main operating conditions for each column were shown in Table 2. The purity and yield of the heavy aromatics product are shown in Table 4.

[0043] Example 2

[0044] This embodiment follows Figure 1 The process for separating heavy aromatics from the hydrorefined kerosene fraction is as follows: the raw material composition is the same as in Example 1; the selective main solvent is 2,4-dimethylsulfolane; the cosolvent is n-hexane; the main operating conditions of each column are shown in Table 2; the purity and yield of the heavy aromatics product are shown in Table 4.

[0045] Example 3

[0046] This embodiment follows Figure 1 The process for separating heavy aromatics from the hydrorefined kerosene fraction is as follows: the raw material composition is the same as in Example 1, the selective main solvent is 3-methyl sulfolane, the cosolvent is n-heptane, the main operating conditions of each column are shown in Table 2, and the purity and yield of the heavy aromatics product are shown in Table 4.

[0047] Comparative Example 1

[0048] This comparative example is based on Figure 1 The process for separating heavy aromatics from the hydrorefined kerosene fraction is as follows: the raw material composition is the same as in Example 1; the selective main solvent is N-methylpyrrolidone; the cosolvent is C6 raffinate oil; the main operating conditions of each column are shown in Table 2; the purity and yield of the heavy aromatics product are shown in Table 4.

[0049] As can be seen from Table 4, compared with Comparative Example 1, the heavy aromatics product obtained by the method of the present invention not only has a higher yield and significantly improved purity, but also the aromatics content in the raffinate oil product is greatly reduced, which is beneficial to subsequent steam cracking. This shows the advanced nature of the present invention.

[0050] Comparative Example 2

[0051] This comparative example separated heavy aromatics from the hydrorefined kerosene fraction using a conventional aromatics liquid-liquid extraction process. The raw material passed through an extraction tower and a raffinate oil water scrubber to obtain a raffinate product free of aromatics. The rich solvent at the bottom of the extraction tower was fed to a stripping tower. The light fraction obtained at the top of the stripping tower was returned to the extraction tower as a backwash liquid. The stripping tower bottom stream was fed to a solvent recovery tower to separate the solvent and aromatics. The raw material composition was the same as in Example 1, except that the solvent was sulfolane. The main operating conditions of each tower are shown in Table 3. The purity and yield of the heavy aromatics product are shown in Table 4.

[0052] As can be seen from Table 4, compared with Comparative Example 2, the heavy aromatics product obtained by the method of the present invention not only has higher purity and significantly improved yield, but also the aromatics content in the raffinate oil product is greatly reduced, which is beneficial to subsequent steam cracking. This shows the advanced nature of the present invention.

[0053] Table 1

[0054]

[0055] Table 2

[0056]

[0057] Table 3

[0058]

[0059] Table 4

[0060]

[0061] In the description of the present invention, it should be noted that the terms "upper", "lower", "inside", "outside", "front", "back", "left", "right", etc. indicate directions or positional relationships based on the directions or positional relationships in the working state of the present invention. They are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific direction, be constructed and operated in a specific direction. Therefore, they should not be understood as limiting the present invention.

[0062] The present invention has been described above with reference to preferred embodiments, but these embodiments are merely exemplary and serve only as illustrations. On this basis, various replacements and improvements can be made to the present invention, all of which fall within the scope of protection of the present invention.

Claims

1. A method for separating heavy aromatics from kerosene fractions, characterized in that: The method comprises contacting a kerosene fraction raw material with a selective main solvent and a co-solvent in an extraction tower for liquid-liquid extraction, distilling and washing a first raffinate oil obtained at the top of the extraction tower to obtain a raffinate oil product, and stripping and solvent recovery of a rich solvent obtained at the bottom of the extraction tower to obtain a heavy aromatic hydrocarbon product; the selective main solvent is an alkyl sulfolane, and the co-solvent is a C5-C7 saturated hydrocarbon; The first raffinate oil enters the raffinate oil distillation tower for distillation, and the co-solvent stream is obtained at the tower top. The second raffinate oil obtained in the tower bottom enters the water washing tower, and after the solvent is removed, the raffinate oil product is discharged from the top of the water washing tower. The washed water from the water washing tower enters the water stripping tower; The rich solvent obtained at the bottom of the extraction tower enters the top of the stripping tower, the co-solvent stream enters the lower part of the stripping tower, the stream rich in heavy aromatics and co-solvent is obtained at the top of the tower and enters the aromatics recovery tower from the middle for distillation to recover the solvent, the co-solvent stream is obtained at the top of the aromatics recovery tower, and the heavy aromatics product is obtained in the bottom of the aromatics recovery tower; The selective main solvent containing co-solvent obtained at the bottom of the stripping tower enters the solvent recovery tower, the co-solvent stream is obtained at the top of the tower, and the lean solvent obtained at the bottom of the tower is circulated to the extraction tower as the selective main solvent; The co-solvent flow obtained from the top of the raffinate distillation tower, aromatics recovery tower and solvent recovery tower is divided into two streams, one stream enters the bottom of the extraction tower as a co-solvent, and the other stream enters the lower part of the stripping tower as a co-solvent flow; the top flow of the water stripping tower enters the condenser at the top of the raffinate distillation tower, and the solvent-containing water produced in the bottom of the tower enters the bottom of the solvent recovery tower; the water in the water bag of the reflux tank at the top of the solvent recovery tower is returned to the water washing tower as washing water.

2. The method according to claim 1, wherein The selective main solvent is 3-methylsulfolane and / or 2,4-dimethylsulfolane.

3. The method according to claim 1, wherein The co-solvent is one or more of n-hexane and n-heptane.

4. A method for separating heavy aromatics from kerosene fractions, characterized in that: The method comprises contacting a kerosene fraction raw material with a selective main solvent and a co-solvent in an extraction tower to perform liquid-liquid extraction, distilling and washing a first raffinate oil obtained at the top of the extraction tower to obtain a raffinate oil product, and stripping and solvent recovery of a rich solvent obtained at the bottom of the extraction tower to obtain a heavy aromatic hydrocarbon product; the selective main solvent is an alkyl sulfolane, the selective main solvent further contains 0.5 wt% to 3.0 wt% of water and / or 0 to 1.0 wt% of hydrocarbons, and the co-solvent is a C5 to C7 saturated hydrocarbon; The first raffinate oil enters the raffinate oil distillation tower for distillation, and the co-solvent stream is obtained at the tower top. The second raffinate oil obtained in the tower bottom enters the water washing tower, and after the solvent is removed, the raffinate oil product is discharged from the top of the water washing tower. The washed water from the water washing tower enters the water stripping tower; The rich solvent obtained at the bottom of the extraction tower enters the top of the stripping tower, the co-solvent stream enters the lower part of the stripping tower, the stream rich in heavy aromatics and co-solvent is obtained at the top of the tower and enters the aromatics recovery tower from the middle for distillation to recover the solvent, the co-solvent stream is obtained at the top of the aromatics recovery tower, and the heavy aromatics product is obtained in the bottom of the aromatics recovery tower; The selective main solvent containing co-solvent obtained at the bottom of the stripping tower enters the solvent recovery tower, the co-solvent stream is obtained at the top of the tower, and the lean solvent obtained at the bottom of the tower is circulated to the extraction tower as the selective main solvent; The co-solvent flow obtained from the top of the raffinate distillation tower, aromatics recovery tower and solvent recovery tower is divided into two streams, one stream enters the bottom of the extraction tower as a co-solvent, and the other stream enters the lower part of the stripping tower as a co-solvent flow; the top flow of the water stripping tower enters the condenser at the top of the raffinate distillation tower, and the solvent-containing water produced in the bottom of the tower enters the bottom of the solvent recovery tower; the water in the water bag of the reflux tank at the top of the solvent recovery tower is returned to the water washing tower as washing water.

5. The method according to claim 1, wherein The kerosene fraction raw material enters the extraction tower from the middle and lower part of the extraction tower, the selective main solvent enters the extraction tower from the top of the extraction tower, and the co-solvent is injected into the bottom of the extraction tower. The first raffinate oil is obtained at the top of the extraction tower, and the rich solvent is obtained at the bottom of the extraction tower.

6. The method according to claim 1, wherein The mass ratio of the selective main solvent to the kerosene fraction raw material entering the extraction tower is 3:1 to 7:1, the mass ratio of the co-solvent to the kerosene fraction raw material is 0.2 to 0.6, the temperature of the selective main solvent entering the extraction tower is 80° C. to 180° C., the pressure at the top of the extraction tower is 0.2 MPa to 0.7 MPa absolute pressure, and the number of theoretical plates is 8 to 15.

7. The method according to claim 6, wherein The temperature of the selective main solvent entering the extraction tower is 90°C to 140°C.

8. The method according to claim 1, wherein The theoretical plate number of the raffinate distillation tower is 10 to 30, the reflux ratio is 0.2 to 2, the tower top pressure is 0.1 MPa to 0.5 MPa absolute pressure, and the tower bottom temperature is 150° C. to 250° C.

9. The method according to claim 1, wherein The mass ratio of the washing water of the water washing tower to the second raffinate oil is 0.1-0.5, the top pressure of the water washing tower is 0.4MPa-0.7MPa absolute pressure, and the water washing temperature is 30℃-50℃.

10. The method according to claim 9, wherein The mass ratio of the washing water of the water washing tower to the second raffinate oil is 0.1 to 0.

3.

11. The method according to claim 1, wherein The number of theoretical plates of the stripping tower is 8 to 12, the tower top pressure is 0.2 MPa to 0.8 MPa absolute pressure, the co-solvent flow inlet temperature is 40° C. to 100° C., and the mass ratio of the co-solvent flow to the rich solvent is 0.05 to 0.

5.

12. The method according to claim 11, wherein The mass ratio of the co-solvent stream to the rich solvent is 0.07 to 0.

15.

13. The method according to claim 1, wherein The number of theoretical plates of the aromatics recovery tower is 15 to 40, the reflux ratio is 0.2 to 2, the top pressure is 0.1 MPa to 0.5 MPa absolute pressure, and the bottom temperature is 150° C. to 300° C.

14. The method according to claim 1, wherein The number of theoretical plates of the solvent recovery tower is 5 to 30, the reflux ratio is 0.3 to 1.0, the top pressure is 0.05 MPa to 0.15 MPa absolute pressure, and the bottom temperature is 150° C. to 200° C.

15. The method according to claim 1, wherein The kerosene fraction raw material comes from the conventional first-line after hydrofining, wherein the sulfur and nitrogen contents are not more than 1 ppm respectively, the boiling range is 140° C. to 250° C., and the mass fraction of heavy aromatics is 3wt% to 30wt%.

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