Method for producing low-sulfur low-mercaptan gasoline

Abstract

The invention discloses a method for producing low-sulfur low-mercaptan gasoline. The method comprises the following steps: a gasoline raw material sequentially enters a hydrofining reaction zone and an alkali metal treatment reaction zone for reaction, and then the obtained material is separated to obtain a clean gasoline product; and the sulfur content of the reaction effluent mercaptan in the hydrofining reaction zone is controlled to be 20-60 [mu] g / g, preferably 30-50 [mu] g / g. According to the method, hydrofining and alkali metal treatment technologies are organically combined, and the low-sulfur and low-mercaptan clean gasoline can be directly produced by utilizing the high-sulfur gasoline raw material.

Description

Technical Field

[0001] The invention belongs to the technical field of petrochemical industry and relates to a method for producing low-sulfur and low-mercaptan gasoline, in particular to a method for producing low-sulfur and low-mercaptan gasoline from catalytic cracking gasoline. Background Art

[0002] As environmental protection requirements become increasingly stringent, countries around the world have put forward higher requirements for the quality of automotive fuels. Sulfur content is the most critical environmental indicator in automotive gasoline. In order to further reduce automobile pollutant emissions, my country implemented the National V automobile standard nationwide from January 1, 2018, reducing the sulfur content limit from 50ppm in the National IV stage to 10ppm, a reduction of 80%.

[0003] At present, catalytic cracking gasoline is the main blending component of domestic commercial gasoline, accounting for about 70-80wt% of the total gasoline pool. Catalytic cracking gasoline has a high sulfur content, and more than 90wt% of the sulfur in gasoline products comes from catalytic cracking gasoline. As can be seen from the above, reducing the sulfur content of catalytic cracking gasoline is the key to producing clean gasoline. An effective way to solve the above problems is to carry out hydrofining and desulfurization of catalytic cracking gasoline. In the process of hydrodesulfurization of catalytic cracking gasoline, in order to suppress olefin saturation and avoid octane number loss, mild reaction conditions such as low temperature and medium pressure are usually adopted. However, under mild reaction conditions, olefins and hydrogen sulfide are more likely to react to generate macromolecular mercaptans, especially when producing low-sulfur gasoline, the reaction of olefins and hydrogen sulfide to generate mercaptans is even close to equilibrium under selective hydrogenation process conditions. Therefore, solving the problem of excessive mercaptans after gasoline hydrofining becomes the key to producing ultra-low sulfur gasoline.

[0004] CN101619234A discloses a method for producing low-sulfur gasoline from light gasoline, which can produce high-quality clean gasoline with a sulfur content of less than 10μg / g. The process adopts a two-stage hydrogenation technology: the first stage uses a selective hydrodesulfurization catalyst to selectively hydrodesulfurize the gasoline raw material, and the reaction product enters the second stage reactor to contact with a hydrodesulfurization catalyst to obtain a clean gasoline product after the reaction. The selective hydrodesulfurization catalyst used uses aluminum oxide as a carrier, molybdenum and cobalt as active components, and contains additives potassium and phosphorus. The hydrodesulfurization catalyst used has copper and zinc as main components.

[0005] CN102757818A discloses a method for producing sulfur-free gasoline, wherein the whole fraction gasoline is first fractionated into a light gasoline fraction and a heavy gasoline fraction; the light gasoline enters an alkali extraction and desulfurization unit for desulfurization and then enters a product tank; the heavy gasoline fraction enters a first reaction zone for dediene removal and then enters a second reaction zone for selective hydrodesulfurization. The liquid phase flow obtained by cooling and separating the material at the outlet of the second reactor enters a third reactor for hydrodesulfurization, and the liquid phase flow obtained by cooling, separating and fractionating the effluent of the third reactor enters a product tank. The light gasoline fraction and the heavy gasoline fraction entering the product tank are mixed to obtain a whole fraction gasoline product.

[0006] The above invention method has the following problems: first, hydrogenation technology undertakes all the desulfurization functions, but the deep hydrogenation desulfurization process needs to further increase the reaction severity, which will cause the olefin saturation rate to increase and the octane number loss to increase; second, the large molecular mercaptan generated by the reaction of olefins and hydrogen sulfide is removed by hydrogenation. The removal of the above large molecular mercaptan is difficult. If hydrogenation is used, on the one hand, it will cause increased energy consumption and cost, and on the other hand, the cyclic addition of ammonia will further increase the olefin saturation, which will cause octane number loss. Summary of the invention

[0007] In view of the shortcomings of the prior art, the present invention provides a method for producing low-sulfur and low-mercaptan gasoline. The method organically combines hydrofining and alkali metal treatment technology, and can directly produce low-sulfur and low-mercaptan clean gasoline using high-sulfur gasoline raw materials.

[0008] A method for producing low-sulfur and low-mercaptan gasoline, the method comprising the following contents: gasoline raw materials sequentially enter a hydrofining reaction zone and an alkali metal treatment reaction zone for reaction, and the obtained materials are separated to obtain a clean gasoline product; and the mercaptan sulfur content of the reaction effluent of the hydrofining reaction zone is controlled to be 20-60 μg / g, preferably 30-50 μg / g.

[0009] In the above method for producing low-sulfur and low-mercaptan gasoline, the total sulfur content of the reaction effluent from the hydrotreating reaction zone is controlled to be 30-120 μg / g, preferably 40-80 μg / g.

[0010] A specific method for producing low-sulfur and low-mercaptan gasoline, the method comprising the following steps: (1) The gasoline raw material is fractionated to obtain light gasoline fraction and heavy gasoline fraction; (2) the heavy gasoline fraction obtained in step (1) enters a hydrotreating reaction zone, and contacts with a hydrotreating catalyst in the presence of hydrogen to react to obtain a reaction effluent; (3) the reaction effluent obtained in step (2) and the light gasoline fraction obtained in step (1) are mixed with an alkali metal and introduced into an alkali metal treatment reaction zone for reaction; (4) The reaction effluent obtained in step (3) enters the separation and purification zone to obtain a clean gasoline product.

[0011] In the above method for producing low-sulfur and low-mercaptan gasoline, the gasoline feedstock in step (1) is catalytic cracking gasoline; the total sulfur content of the gasoline feedstock is 50-1500 μg / g, the mercaptan sulfur content is 20-200 μg / g, and the olefin volume fraction is 5-60%.

[0012] In the above method for producing low-sulfur and low-mercaptan gasoline, the cut point between the light gasoline fraction and the heavy gasoline fraction in step (1) is 60-120°C, preferably 80-100°C.

[0013] In the above method for producing low-sulfur and low-mercaptan gasoline, the mercaptan sulfur content of the light gasoline fraction in step (1) is controlled to be 100-250 μg / g; the mercaptan sulfur content of less than C4 is controlled to be 80-200 μg / g.

[0014] In the above method for producing low-sulfur and low-mercaptan gasoline, the hydrotreating reaction zone in step (2) is provided with 1 to 3 hydrotreating reactors, and the hydrotreating reactors can be one or more of a fixed bed reactor, a moving bed reactor and a fluidized bed reactor, preferably a fixed bed reactor.

[0015] In the above method for producing low-sulfur and low-mercaptan gasoline, the hydrotreating reaction zone in step (2) generally includes 1 to 4, preferably 2 to 3, hydrotreating catalyst beds along the liquid phase flow direction.

[0016] In the above method for producing low-sulfur and low-mercaptan gasoline, the hydrorefining catalyst in step (2) includes a carrier and an active metal; the carrier is alumina and / or amorphous silicon-alumina; the active metal includes a main active metal and an auxiliary metal, the main active metal is a metal of Group VIB of the periodic table, such as W and / or Mo; the auxiliary metal is a metal of Group VIII of the periodic table, such as Co and / or Ni. The hydrorefining catalyst can be prepared according to common sense in the art, or a commercial catalyst can be selected, such as the RGO-3 and RSDS series hydrorefining catalysts produced by the Changling Branch of Sinopec Catalyst Co., Ltd.

[0017] In the above method for producing low-sulfur and low-mercaptan gasoline, the operating conditions of the hydrofining reaction zone in step (2) are: reaction temperature 160-360°C, reaction pressure 1.0-5.0 MPa, volume space velocity 2.0-10.0 h -1 , hydrogen oil volume ratio 200-1000Nm 3 / m 3 .

[0018] In the above method for producing low-sulfur and low-mercaptan gasoline, the alkali metal in step (3) is one or more of lithium, sodium and potassium, preferably sodium; the molar ratio of the alkali metal to the total sulfur content of the feed is (2.0-3.5):1, and the total sulfur content of the feed is the total sulfur content of the mixed material obtained by mixing the reaction effluent obtained in step (2) and the light gasoline fraction obtained in step (1).

[0019] In the above method for producing low-sulfur and low-mercaptan gasoline, the alkali metal treatment reaction zone in step (3) is provided with 1 to 3 alkali metal treatment reactors; the alkali metal treatment reactors may be any of the reactors in the prior art that can achieve liquid-liquid two-phase mixing, such as a tubular reactor and / or a kettle reactor.

[0020] In the above method for producing low-sulfur and low-mercaptan gasoline, the operating conditions of the alkali metal treatment reaction zone in step (3) are as follows: reaction temperature 250-380°C, reaction pressure 1.0-18.0 MPa, reaction time / residence time 0.1-1.0 h, hydrogen-to-oil volume ratio 300-1800 Nm 3 / m 3 .

[0021] In the above method for producing low-sulfur and low-mercaptan gasoline, the separation and purification zone in step (4) includes a desolidification separation zone and an extraction separation zone.

[0022] In the above method for producing low-sulfur and low-mercaptan gasoline, the specific process flow of the separation and purification zone in step (4) is as follows: (a) the reaction effluent obtained in step (3) enters a desolidification separation zone to obtain a desolidified flow; (b) The desolidified stream obtained in step (a) enters the extraction separation zone, is mixed with the extractant and then separated to obtain a clean gasoline product.

[0023] In the above step (a), the desolidification separation zone is solid-liquid separation, and there is no limitation on the means of solid-liquid separation. Any means capable of achieving solid-liquid separation in the prior art may be used, such as one or more of sedimentation, filtration, membrane filtration, filter press and centrifugation.

[0024] In the above step (b), the extractant is selected from one or more of ethanol, furfural, diethylene glycol, dimethyl sulfoxide (DMSO) and N,N-dimethylformamide (DMF); the extractant to oil volume ratio of the extractant to the desolidified stream is 0.5-1.0.

[0025] In the above step (b), the extraction separation zone adopts liquid-liquid extraction, which is a unit operation that utilizes the different solubility of components in the desolidification stream in the extractant to remove impurities such as alkali metal mercaptides. The liquid-liquid extraction means include one or more of single-stage extraction, multi-stage cross-current extraction, multi-stage countercurrent extraction and continuous countercurrent extraction.

[0026] Compared with the prior art, the present invention has the following advantages: 1. The method of the present invention organically combines hydrofining and alkali metal treatment technology, and can directly produce clean gasoline with low sulfur and low mercaptan using high sulfur gasoline as raw material.

[0027] 2. The method of the present invention controls the mercaptan sulfur content and total sulfur content of the reaction effluent of the hydrofining reaction zone, and transfers the difficult-to-remove sulfur-containing compounds such as dibenzothiophene sulfides, secondary mercaptans generated by the reaction of heavy olefins and hydrogen sulfide to the alkali metal treatment reaction zone for processing. Furthermore, the method of the present invention reduces the requirements for the reaction effluent of the hydrofining reaction zone, thereby further reducing the reaction severity of the hydrofining reaction zone and reducing the loss of olefin saturation and octane number.

[0028] 3. The method of the present invention cuts the gasoline raw material into light gasoline fraction and heavy gasoline fraction, and the light gasoline fraction is doped in the feed of the alkali metal treatment reaction zone. The light gasoline fraction is rich in small molecular mercaptans, which are highly active and can be used as initiators, thereby accelerating the reaction rate and promoting the reaction. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 The present invention is a process flow diagram of a method for producing low-sulfur and low-mercaptan gasoline.

[0030] Among them, 1 is gasoline feedstock, 2 is a hydrotreating reactor, 3 is a reaction effluent from a hydrotreating reactor, 4 is an alkali metal, 5 is an alkali metal treatment reactor, 6 is a reaction effluent from an alkali metal treatment reactor, 7 is a gas-liquid separator, 8 is a solid-liquid two-phase flow, 9 is a hydrogen-containing gas, 10 is a hydrogen compressor, 11 is high-pressure hydrogen, 12 is a solid-liquid separator, 13 is a solid phase flow, 14 is a liquid phase flow, 15 is an extractant, 16 is an extraction reactor, 17 is a raffinate phase, 18 is a clean gasoline product, and 19 is new hydrogen.

[0031] Figure 2 The present invention is another process flow diagram of a method for producing low-sulfur and low-mercaptan gasoline.

[0032] Among them, 1 is gasoline feedstock, 2 is a hydrotreating reactor, 3 is a reaction effluent from a hydrotreating reactor, 4 is an alkali metal, 5 is an alkali metal treatment reactor, 6 is a reaction effluent from an alkali metal treatment reactor, 7 is a gas-liquid separator, 8 is a solid-liquid two-phase flow, 9 is a hydrogen-containing gas, 10 is a hydrogen compressor, 11 is high-pressure hydrogen, 12 is a solid-liquid separator, 13 is a solid phase flow, 14 is a liquid phase flow, 15 is an extractant, 16 is an extraction reactor, 17 is a raffinate phase, 18 is a clean gasoline product, 19 is new hydrogen, 20 is a fractionation tower, 21 is a light gasoline fraction, and 22 is a heavy gasoline fraction. Implementation

[0033] The method provided by the present invention is described below in conjunction with the accompanying drawings.

[0034] like Figure 1 As shown, the gasoline feedstock 1 is mixed with high-pressure hydrogen 11 and enters the hydrofining reactor 2 to contact with the hydrofining catalyst for reaction to obtain a reaction effluent 3; the reaction effluent 3 is mixed with the alkali metal 4 and enters the alkali metal treatment reactor 5 for reaction, and the reaction effluent 6 enters the gas-liquid separator 7 for separation to obtain a solid-liquid two-phase flow 8 and a hydrogen-containing gas 9, wherein the hydrogen-containing gas 9 is mixed with new hydrogen 19 and enters the hydrogen compressor 10 to obtain high-pressure hydrogen 11, and the solid-liquid two-phase flow 8 enters the solid-liquid separator 12 for separation to obtain a solid phase flow 13 and a liquid phase flow 14. The liquid phase flow 14 enters the extraction reactor 16, and is countercurrently contacted with the extractant 15 for extraction to obtain a raffinate phase 17 and a clean gasoline product 18.

[0035] like Figure 2 As shown, the gasoline feedstock 1 enters the fractionation tower 20 and is cut to obtain a light gasoline fraction 21 and a heavy gasoline fraction 22. The heavy gasoline fraction 22 is mixed with high-pressure hydrogen 11 and then enters the hydrofining reactor 2 to contact with the hydrofining catalyst for reaction to obtain a reaction effluent 3; the reaction effluent 3 and the light gasoline fraction 21 are mixed with alkali metal 4 and enter the alkali metal treatment reactor 5 for reaction, and the reaction effluent 6 enters the gas-liquid separator 7 and is separated to obtain a solid-liquid two-phase flow 8 and a hydrogen-containing gas 9, wherein the hydrogen-containing gas 9 is mixed with new hydrogen 19 and enters the hydrogen compressor 10 to obtain high-pressure hydrogen 11, and the solid-liquid two-phase flow 8 enters the solid-liquid separator 12 and is separated to obtain a solid phase flow 13 and a liquid phase flow 14. The liquid phase flow 14 enters the extraction reactor 16 and is countercurrently contacted with the extractant 15 for extraction to obtain a raffinate phase 17 and a clean gasoline product 18.

[0036] The following examples will further illustrate the method provided by the present invention, but are not intended to limit the present invention.

[0037] Unless explicitly stated otherwise, throughout the specification and claims, the term “comprise” or variations such as “include” or “comprising”, etc., will be understood to include the stated elements or components but not to exclude other elements or components.

[0038] In this document, for the convenience of description, spatial relative terms such as "below", "below", "down", "above", "above", "upper", etc. may be used to describe the relationship between one element or feature and another element or feature in the accompanying drawings. It should be understood that the spatial relative terms are intended to include different directions of objects in use or operation in addition to the directions drawn in the drawings. For example, if the object in the figure is turned over, the elements described as being "below" or "below" other elements or features will be oriented "above" the elements or features. Therefore, the exemplary term "below" can include both below and above directions. Objects may also have other orientations (rotated 90 degrees or other orientations) and the spatial relative terms used in this document should be interpreted accordingly.

[0039] In this document, the terms "first", "second", etc. are used to distinguish two different elements or parts, and are not used to limit a specific position or relative relationship. In other words, in some embodiments, the terms "first", "second", etc. can also be interchangeable.

[0040]

[0043] All numerical values ​​for parameters (eg, amounts or conditions) herein are to be understood as being modified in all instances by the term "about", whether or not "about" actually appears before the numerical value.

[0041] The properties of the gasoline raw materials used in the examples and comparative examples are shown in Table 1.

[0042] Table 1 Gasoline raw material properties

[0043] Example 1 use Figure 1 The process flow shown is as follows: (1) The gasoline feedstock enters the hydrotreating reaction zone. A fixed-bed hydrotreating reactor is set in the hydrotreating reaction zone. The reactor is filled with RGO-3, RSDS-21 and RSDS-22 hydrotreating catalysts produced by Changling Branch of Sinopec Catalyst Co., Ltd., with a filling volume ratio of 30:30:40. The mercaptan sulfur content of the reaction effluent of the hydrotreating reaction zone is 26μg / g, and the total sulfur content is 48μg / g.

[0044] (2) The reaction effluent from the hydrotreating reaction zone is mixed with sodium and enters the alkali metal treatment reaction zone for reaction. The alkali metal treatment reaction zone is provided with a high-pressure autoclave reactor with a stirring speed of 800 r / min.

[0045] (3) The reaction effluent from the alkali metal treatment reaction zone is subjected to solid-liquid separation in a high-speed centrifuge at a speed of 8000 r / min. The liquid phase obtained by solid-liquid separation then enters the extraction reactor and contacts with ethanol for three-stage countercurrent extraction. The catalyst-to-oil volume ratio is 0.8, the extraction temperature is 35°C, and the extraction time is 15 min, thereby finally obtaining a clean gasoline product.

[0046] Example 2 Compared with Example 1, the difference is: (1) The mercaptan sulfur content of the reaction effluent from the hydrotreating reaction zone is 25 μg / g, and the total sulfur content is 41 μg / g.

[0047] Example 3 use Figure 2 The process flow shown is as follows: (1) The gasoline feedstock enters the distillation tower and is fractionated to obtain a light gasoline fraction and a heavy gasoline fraction; the cut point is 80°C, the mercaptan sulfur content of the light gasoline fraction is 162 μg / g, and the mercaptan sulfur content of less than C4 is 147 μg / g.

[0048] (2) The heavy gasoline fraction obtained in step (1) enters the hydrotreating reaction zone, and a fixed-bed hydrotreating reactor is set in the hydrotreating reaction zone. The reactor is filled with RGO-3, RSDS-21 and RSDS-22 hydrotreating catalysts produced by Changling Branch of Sinopec Catalyst Co., Ltd., with a filling volume ratio of 30:30:40. The mercaptan sulfur content of the reaction effluent of the hydrotreating reaction zone is 53 μg / g, and the total sulfur content is 112 μg / g.

[0049] (3) The reaction effluent obtained in step (2) and the light gasoline fraction obtained in step (1) are mixed with sodium and enter an alkali metal treatment reaction zone for reaction. The alkali metal treatment reaction zone is provided with a high-pressure autoclave reactor with a stirring speed of 800 r / min.

[0050] (4) The reaction effluent obtained in step (3) is subjected to solid-liquid separation in a high-speed centrifuge at a speed of 8000 r / min. The liquid phase obtained by the solid-liquid separation enters the extraction reactor and contacts with dimethyl sulfoxide for four-stage countercurrent extraction. The solvent-oil volume ratio is 0.9, the extraction temperature is 40°C, and the extraction time is 15 min, thereby finally obtaining a clean gasoline product.

[0051] Example 4 Compared with Example 3, the difference is: (1) The cut point is 100°C, the mercaptan sulfur content of the light gasoline fraction is 136 μg / g, and the mercaptan sulfur content of less than C4 is 115 μg / g.

[0052] (2) The mercaptan sulfur content of the reaction effluent from the hydrotreating reaction zone is 34 μg / g, and the total sulfur content is 67 μg / g.

[0053] Example 5 Compared with Example 3, the difference is: (1) The cut point is 100°C, the mercaptan sulfur content of the light gasoline fraction is 136 μg / g, and the mercaptan sulfur content of less than C4 is 115 μg / g.

[0054] (2) The mercaptan sulfur content of the reaction effluent from the hydrotreating reaction zone is 34 μg / g, and the total sulfur content is 67 μg / g.

[0055] The reaction conditions and product properties of Examples 1-5 are shown in Table 2 and Table 3.

[0056] Table 2 Reaction conditions of Examples 1-5

[0057] Table 3 Product properties of Examples 1-5

[0058] Comparative Example 1 The gasoline feedstock enters the hydrofining reaction zone, and the hydrofining reaction zone is equipped with two fixed-bed hydrofining reactors, the first reactor and the second reactor. The first reactor is filled with RGO-3, RSDS-21 and RSDS-22 hydrofining catalysts produced by the Changling Branch of Sinopec Catalyst Co., Ltd., with a filling volume ratio of 30:30:40; the second reactor is filled with RSDS-22 hydrofining catalyst produced by the Changling Branch of Sinopec Catalyst Co., Ltd. The reaction conditions and product properties are shown in Table 4.

[0059] Table 4 Reaction conditions and product properties of Comparative Example 1

Claims

1. A method for producing low-sulfur, low-mercaptan gasoline, characterized in that: The method comprises the following contents: the gasoline raw material enters the hydrofining reaction zone and the alkali metal treatment reaction zone in sequence for reaction, and the obtained materials are separated to obtain a clean gasoline product; and the mercaptan sulfur content of the reaction effluent of the hydrofining reaction zone is controlled to be 20-60 μg / g, preferably 30-50 μg / g.

2. The method according to claim 1, characterized in that: The total sulfur content of the reaction effluent from the hydrofining reaction zone is controlled to be 30-120 μg / g, preferably 40-80 μg / g.

3. The method according to claim 1, characterized in that: The method comprises the following steps: (1) The gasoline raw material is fractionated to obtain light gasoline fraction and heavy gasoline fraction; (2) the heavy gasoline fraction obtained in step (1) enters a hydrotreating reaction zone, and contacts with a hydrotreating catalyst in the presence of hydrogen to react to obtain a reaction effluent; (3) the reaction effluent obtained in step (2) and the light gasoline fraction obtained in step (1) are mixed with an alkali metal and introduced into an alkali metal treatment reaction zone for reaction; (4) The reaction effluent obtained in step (3) enters the separation and purification zone to obtain a clean gasoline product.

4. The method according to claim 3, characterized in that: The gasoline feedstock in step (1) is catalytic cracking gasoline; the total sulfur content of the gasoline feedstock is 50-1500 μg / g, the mercaptan sulfur content is 20-200 μg / g, and the olefin volume fraction is 5-60%.

5. The method according to claim 3, characterized in that: The cutting point between the light gasoline fraction and the heavy gasoline fraction in step (1) is 60-120°C, preferably 80-100°C.

6. The method according to claim 3, characterized in that: The mercaptan sulfur content of the light gasoline fraction in step (1) is controlled to be 100-250 μg / g; the mercaptan sulfur content of less than C4 is controlled to be 80-200 μg / g.

7. The method according to claim 3, characterized in that: In step (2), the hydrotreating reaction zone is provided with 1 to 3 hydrotreating reactors, and the hydrotreating reactors may be one or more of a fixed bed reactor, a moving bed reactor and a fluidized bed reactor, preferably a fixed bed reactor.

8. The method according to claim 3, characterized in that: The hydrotreating reaction zone in step (2) generally includes 1 to 4, preferably 2 to 3 hydrotreating catalyst beds along the liquid phase flow direction.

9. The method according to claim 3, characterized in that: The operating conditions of the hydrotreating reaction zone in step (2) are: reaction temperature 160-360°C, reaction pressure 1.0-5.0 MPa, volume space velocity 2.0-10.0 h -1 , hydrogen oil volume ratio 200-1000Nm 3 / m 3 .

10. The method according to claim 3, characterized in that: The alkali metal in step (3) is one or more of lithium, sodium and potassium, preferably sodium; the molar ratio of the alkali metal to the total sulfur content of the feed is (2.0-3.5):1, and the total sulfur content of the feed is the total sulfur content of the mixed material obtained by mixing the reaction effluent obtained in step (2) and the light gasoline fraction obtained in step (1).

11. The method according to claim 3, characterized in that: In step (3), the alkali metal treatment reaction zone is provided with 1 to 3 alkali metal treatment reactors; the alkali metal treatment reactors are tubular reactors and / or kettle reactors.

12. The method according to claim 3, characterized in that: The operating conditions of the alkali metal treatment reaction zone in step (3) are as follows: reaction temperature 250-380°C, reaction pressure 1.0-18.0 MPa, reaction time / residence time 0.1-1.0 h, hydrogen to oil volume ratio 300-1800 Nm 3 / m 3 .

13. The method according to claim 3, characterized in that: The separation and purification zone in step (4) includes a solid removal separation zone and an extraction separation zone.

14. The method according to claim 13, characterized in that: The specific process flow of the separation and purification zone in step (4) is as follows: (a) the reaction effluent obtained in step (3) enters a desolidification separation zone to obtain a desolidified flow; (b) The desolidified stream obtained in step (a) enters the extraction separation zone, is mixed with the extractant and then separated to obtain a clean gasoline product.

15. The method according to claim 14, characterized in that: In step (a), the solid-liquid separation zone is solid-liquid separation, using one or more of sedimentation, filtration, membrane filtration, filter press and centrifugation.

16. The method according to claim 14, characterized in that: In step (b), the extractant is selected from one or more of ethanol, furfural, diethylene glycol, dimethyl sulfoxide (DMSO) and N,N-dimethylformamide (DMF); the extractant-to-oil volume ratio of the extractant to the desolidified stream is 0.5-1.

0.

17. The method according to claim 14, characterized in that: In step (b), the extraction and separation zone adopts liquid-liquid extraction means, and the liquid-liquid extraction means includes one or more of single-stage extraction, multi-stage cross-current extraction, multi-stage countercurrent extraction and continuous countercurrent extraction.

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