Process and apparatus for aromatic extraction

Abstract

The present application relates to the technical field of aromatic hydrocarbon extraction, and discloses a method and device for aromatic hydrocarbon extraction. The method comprises the following steps: (1) contacting reforming gasoline with an extraction solvent to perform extraction, to obtain first rich agent and raffinate; (2) separating the first rich agent to obtain second rich agent and reflux aromatic hydrocarbon; (3) returning the reflux aromatic hydrocarbon to step (1); (4) contacting the second rich agent with stripping water vapor to perform stripping, to obtain lean solvent and aromatic hydrocarbon; (5) dividing the lean solvent into at least A part and B part, returning the A part to step (1) as extraction solvent, and returning the B part to step (2). The method for aromatic hydrocarbon extraction provided by the present application introduces lean solvent into the top of the stripping column, reduces the content of aromatic hydrocarbon, especially toluene, in the gas phase at the top of the stripping column, moves most of the toluene to the stripping column to be distilled out, thereby reducing the extraction amount of the reflux aromatic hydrocarbon, and further reducing the aromatic hydrocarbon reflux ratio and improving the extraction capacity of the extraction column.

Description

Technical Field

[0001] This invention relates to the field of aromatic hydrocarbon extraction technology, and more specifically to an aromatic hydrocarbon extraction method and apparatus. Background Technology

[0002] Benzene and aromatic compounds are potent carcinogens. Excessive levels of these compounds in gasoline, and the residual residues from incomplete combustion of gasoline in vehicle exhaust, can seriously harm human health with prolonged exposure. Due to increasing environmental pressure and growing environmental awareness, my country has imposed higher requirements on gasoline.

[0003] my country's new gasoline standards pose new challenges to the production of clean fuels and my country's oil refining technology. The changes in the new standards for automotive gasoline show a significant reduction in the content of benzene and aromatics. Benzene, toluene, and xylene (BTX) are the most basic raw materials in petrochemicals, collectively known as the "three benzenes." Their production volume and scale are second only to ethylene and propylene among the "three olefins," and they hold an extremely important position in chemical industrial production. BTX is an important chemical raw material for synthetic fibers, rubber, plastics, detergents, dyes, pharmaceuticals, and fragrances. As the foundation of aromatic petrochemicals, BTX production indicates the degree of industrialization. With the implementation of the stricter National VI standard for automotive gasoline, a large amount of aromatic resources will be squeezed out of the gasoline pool; this material can provide chemical raw materials for the production of high value-added products.

[0004] One of the main sources of aromatics is extraction and separation from catalytic reformed gasoline. Aromatics extraction processes are mainly divided into liquid-liquid extraction and extractive distillation. Liquid-liquid extraction is the primary method, while extractive distillation mainly targets C6 and C6-C7 components. Typical liquid-liquid extraction processes include UOP's Sulfolane and Udex processes, and Union Carbide's Tetra process. The Sulfolane process, using sulfolane as a solvent, is the most widely used among similar processes. The Udex extraction process, using diethylene glycol and triethylene glycol as solvents, is rarely used anymore, but the Tetra process, using tetraethylene glycol as a solvent, is still applied in the extraction of aromatics from reformed oils. Extractive distillation processes include Lurgi's Distapex process, Uhde's Morphylane process, GTC's GT-BTX process, the Petrochemical Research Institute's SED process, and Jinweihui Engineering's SUPER-SAE-Ⅱ, among others. Although aromatic hydrocarbon extraction and separation technology has been developed relatively maturely both domestically and internationally, it still faces problems such as low selectivity of extractants, high solvent-to-oil ratio, high energy consumption, and enrichment of heavy hydrocarbons in the solvent leading to poor extractant performance.

[0005] In liquid-liquid extraction processes, the separated mixture of non-aromatic and aromatic hydrocarbons is generally returned to the extraction tower as reflux aromatic hydrocarbons. The reflux ratio of reflux aromatic hydrocarbons varies depending on the extractant used in the liquid-liquid extraction process, and is generally quite high.

[0006] A high aromatic reflux ratio means that the amount of non-aromatic and aromatic hydrocarbons separated from the extraction tower is too high. On the one hand, this will lead to an excessively high gas phase load in the extraction distillation tower, or even tower overflow. On the other hand, it will cause a large amount of aromatic hydrocarbons to circulate between the extraction tower and the extraction distillation tower, which will reduce the actual solvent-to-oil ratio of the extraction tower and affect the extraction capacity of the aromatic extraction unit.

[0007] Therefore, there is an urgent need to provide an aromatic extraction method and apparatus that can reduce the aromatic reflux ratio. Summary of the Invention

[0008] The purpose of this invention is to overcome the technical problem of high aromatic reflux in the existing aromatic extraction process, and to provide an aromatic extraction method and apparatus.

[0009] To achieve the above objectives, a first aspect of the present invention provides a method for aromatic hydrocarbon extraction, the method comprising the following steps:

[0010] (1) Extraction is performed by contacting reformed gasoline with an extraction solvent to obtain a first enrichment agent and raffinate;

[0011] (2) Separate the first enriching agent to obtain the second enriching agent and reflux aromatics;

[0012] (3) Return the refluxed aromatics to step (1);

[0013] (4) The second enriching agent is contacted with stripping steam to strip the solvent and aromatics.

[0014] (5) Divide the lean solvent into at least part A and part B, with part A being returned to step (1) as the extraction solvent and part B being returned to step (2).

[0015] A second aspect of the present invention provides an aromatic hydrocarbon extraction apparatus, the apparatus comprising an extraction column 1, a stripping column 2, and a stripping column 3; wherein the bottom of the extraction column 1 is connected to the stripping column 2, the top of the stripping column 2 is connected to the extraction column 1, the bottom of the stripping column 2 is connected to the stripping column 3, and the bottom of the stripping column 3 is connected to the top of the extraction column 1 and the top of the stripping column 2, respectively.

[0016] The beneficial technical effects achieved by the present invention through the above technical solution are as follows:

[0017] 1) The aromatic extraction method provided by the present invention introduces a lean solvent into the top of the stripping column, which reduces the content of aromatics, especially toluene, in the gas phase at the top of the stripping column. Most of the toluene is moved to the stripping column for distillation, thereby reducing the amount of refluxed aromatics produced, which in turn reduces the aromatics reflux ratio and improves the extraction capacity of the extraction column.

[0018] 2) The aromatic hydrocarbon extraction device provided by the present invention is simple to operate, has low energy consumption, and has good aromatic hydrocarbon extraction effect, making it suitable for industrial promotion. Attached Figure Description

[0019] Figure 1 This is a diagram of an aromatic hydrocarbon extraction apparatus according to a preferred embodiment of the present invention;

[0020] Figure 2 This is a graph showing the pressure change at the top of the distillation column in Embodiment 1 and Comparative Example 1 provided by the present invention;

[0021] Figure 3 This is a distribution diagram of toluene concentration in the distilled liquid from Test Example 1 and Test Example 2 provided by the present invention.

[0022] Explanation of reference numerals in the attached figures

[0023] 1. Extraction tower 2. Stripping tower 3. Steam stripping tower

[0024] 4. Water washing tower; 5. Process water storage tank; 6. Stripping tower heat exchanger

[0025] 7. Stripping tower condenser; 8. Aromatics storage tank; 9. Distillation tower condenser.

[0026] 10. Reflux aromatics storage tank 11. Residual oil cooler

[0027] S1, reformed gasoline; S2, extraction solvent; S3, first enrichment agent.

[0028] S4, raffinate oil; S5, second enriching agent; S6, reflux aromatics.

[0029] S61, anhydrous reflux aromatics; S71, water; S8, stripping steam.

[0030] S9, lean solvent S91, Part A S92, Part B

[0031] S10, Aromatic hydrocarbons; S101, Anhydrous aromatic hydrocarbons; S72, Water

[0032] S11, Wash water; S12, Non-aromatic hydrocarbons; S13, Residual oil wash water Detailed Implementation

[0033] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0034] A first aspect of the present invention provides a method for extracting aromatic hydrocarbons, the method comprising the following steps:

[0035] (1) Extraction is performed by contacting reformed gasoline with an extraction solvent to obtain a first enrichment agent and raffinate;

[0036] (2) Separate the first enriching agent to obtain the second enriching agent and reflux aromatics;

[0037] (3) Return the refluxed aromatics to step (1);

[0038] (4) The second enriching agent is contacted with stripping steam to strip the solvent and aromatics.

[0039] (5) Divide the lean solvent into at least part A and part B, with part A being returned to step (1) as the extraction solvent and part B being returned to step (2).

[0040] In step (1):

[0041] In a preferred embodiment, the reformed gasoline refers to gasoline produced during the reforming reaction, primarily composed of C42O4. 6-8 The present invention contains aromatic hydrocarbons and alkanes, including possible alkanes such as n-hexane, isohexane, n-heptane, isoheptane, n-octane, and isooctane, and aromatic hydrocarbons mainly including benzene, toluene, and xylene. This invention does not impose any special limitations on reformed gasoline; its general understanding in the art is sufficient.

[0042] In a preferred embodiment, the extraction solvent is selected from one or more of triethylene glycol, tetraethylene glycol, sulfolane, dimethyl sulfoxide, 2-pyrrolidone, N-methylpyrrolidone, N-ethylpyrrolidone, N-methylformamide, N-methylbenzylmethylamide, N-formylmorpholine, N,N-dimethylformamide, hydrazine hydrate, furfural, ethylene glycol, glyceryl methyl acetal, polyethylene glycol, and polycarbonate.

[0043] More preferably, the extraction solvent is selected from one of tetraethylene glycol, dimethyl sulfoxide, N-methylformamide, N-formylmorpholine, hydrazine hydrate, and polyethylene glycol.

[0044] In a preferred embodiment, the feed temperature of the reformed gasoline is 110-150°C, preferably 125-135°C; the feed temperature of the extraction solvent is 110-150°C, preferably 120-130°C.

[0045] In a preferred embodiment, the mass ratio (oil-solvent ratio) of the reformed gasoline and the extraction solvent is 1:2-8, preferably 1:3-5.

[0046] In this invention, unless otherwise specified, the description of the aromatic hydrocarbon extraction method refers to the state under stable operation. The mass ratio of reformed gasoline to extraction solvent defined in this invention is the mass ratio of the two under stable operation conditions. During startup, the mass ratio of reformed gasoline to extraction solvent can be greater than that under stable operation conditions.

[0047] In a preferred embodiment, the extraction is carried out in an extraction tower, the operating conditions of which include: a bottom temperature of 100-130°C, preferably 110-120°C; and a top pressure of 0.5-1 MPa, preferably 0.6-0.8 MPa.

[0048] In step (2):

[0049] In a preferred embodiment, the feed temperature of the first enrichment agent is 115-130°C, preferably 120-130°C.

[0050] In a preferred embodiment, the separation is carried out in a stripping column, the operating conditions of which include: a bottom temperature of 105-130°C, preferably 110-125°C; a top pressure of 10-20 kPa, preferably 10-15 kPa; and a bottom pressure of 0.1-0.3 MPa, preferably 0.15-0.25 MPa.

[0051] In step (3):

[0052] In a preferred embodiment, the feed temperature of the reflux aromatics is 60-90°C, preferably 60-70°C.

[0053] In a preferred embodiment, the mass ratio of the refluxed aromatics to the reformed gasoline (aromatics reflux ratio) is 0.9-1.05:1, preferably 0.9-0.95:1.

[0054] In a preferred embodiment, the reflux aromatics are dehydrated to obtain anhydrous reflux aromatics, and all of the anhydrous reflux aromatics are returned to step (1). In this invention, the water content in the reflux aromatics is ≤1 wt%, therefore, the mass ratio of the anhydrous reflux aromatics to the reformed gasoline can be considered unchanged before and after dehydration. In this invention, the feed temperature of the anhydrous reflux aromatics is also the same as that of the reflux aromatics.

[0055] In this invention, the method of removing water from refluxed aromatics is not specifically limited. Preferably, the refluxed aromatics are subjected to sedimentation for water removal: the refluxed aromatics are first cooled, then allowed to stand and separate into layers, and water is separated out. The water separated from the refluxed aromatics can be used as washing water for residual oil.

[0056] In step (4):

[0057] In a preferred embodiment, the mass ratio of the second enriching agent to stripping steam is 15-35:1; preferably 20-30:1.

[0058] In a preferred embodiment, the stripping is carried out in a stripping tower, the operating conditions of which include: a top temperature of 100-125°C, preferably 105-115°C; a bottom temperature of 130-160°C, preferably 140-150°C; and a top pressure of 4.5-6 kPa, preferably 5-5.5 kPa.

[0059] In a preferred embodiment, the second enriching agent is stripped by contacting stripping steam to obtain lean solvent and aromatics, wherein the lean solvent is the regenerated extraction solvent. The aromatics are condensed to separate the water entrained in the aromatics, yielding anhydrous aromatics. A portion of the obtained anhydrous aromatics can be collected as product, and a portion can be returned to the stripping operation as reflux liquid. Alternatively, it can be used for further processing as needed. The separated water can be used as washing water for residual oil.

[0060] In step (5):

[0061] In a preferred embodiment, portion A is 65-80% of the mass of the lean solvent, preferably 70-75%.

[0062] In a preferred embodiment, the feed temperature of section A is 135-155°C, preferably 140-150°C.

[0063] In this invention, when part A is returned to step (1) as the extraction solvent, the feeding of the extraction solvent can be stopped. That is, when the method is running stably, all the extraction solvent in step (1) is supplied by the lean solvent obtained in step (4).

[0064] In a preferred embodiment, the feed temperature of section B is 135-155°C, preferably 140-150°C.

[0065] In this invention, returning a portion of the lean solvent to step (2) to contact with the first enriching agent can reduce the content of aromatics in the reflux aromatics, reduce the yield of reflux aromatics, and thus reduce the aromatics reflux ratio and improve the extraction capacity of the extraction tower.

[0066] In a preferred embodiment, the mass ratio of the first enrichment agent to the B portion is 2-10:1, preferably 3-7:1.

[0067] In a preferred embodiment, the present invention does not specifically limit the way the B part enters the stripping tower in the return step (2). It can be mixed with the first enrichment agent and then enter the stripping tower together, or it can be introduced separately from the top of the stripping tower, preferably sprayed from the top of the stripping tower in the form of a spray.

[0068] In a preferred embodiment, the method further includes step (6), which involves contacting the raffinate oil with washing water to wash it, thereby obtaining non-aromatic hydrocarbons and raffinate oil washing water.

[0069] In this invention, the water washing operation is not specifically limited and can be carried out in accordance with conventional operations in the field. The present invention will not elaborate further.

[0070] In a preferred embodiment, the residual oil wash water is returned to step (6) for recycling as wash water.

[0071] A second aspect of the present invention provides an aromatic hydrocarbon extraction apparatus, the apparatus comprising an extraction column 1, a stripping column 2, and a stripping column 3; wherein the bottom of the extraction column 1 is connected to the stripping column 2, the top of the stripping column 2 is connected to the extraction column 1, the bottom of the stripping column 2 is connected to the stripping column 3, and the bottom of the stripping column 3 is connected to the top of the extraction column 1 and the top of the stripping column 2, respectively.

[0072] In this invention, the extraction tower 1 is used to extract reformed gasoline and extraction solvent to obtain a first enrichment S3 and raffinate; the first enrichment and extraction solvent are refined in the stripping tower 2 to reduce the yield of reflux aromatics, reduce the aromatics reflux ratio, and improve the extraction capacity of the extraction tower to obtain a second enrichment and reflux aromatics; the stripping tower 3 is used to separate the second enrichment to obtain lean solvent and aromatics.

[0073] In a preferred embodiment, the apparatus further includes a water washing tower 4 and a process water storage tank 5; wherein the bottom of the water washing tower 4 is connected to the top of the extraction tower 1, and the process water storage tank 5 is connected to both the top and bottom of the water washing tower 5.

[0074] In this invention, the water washing tower 4 is used to purify the residual oil to obtain non-aromatic hydrocarbons. The process water storage tank 5 is used to store water. The water in the process water storage tank 5 can first enter the water washing tower 4 from the top of the water washing tower 4, and then leave the water washing tower 4 from the bottom of the water washing tower 4 and return to the process water storage tank 5.

[0075] In a preferred embodiment, the apparatus further includes a stripping tower heat exchanger 6, wherein the process water storage tank 5, the stripping tower heat exchanger 6, and the bottom of the stripping tower 3 are connected in sequence.

[0076] In this invention, the stripping tower heat exchanger 6 is used to exchange heat between water from the process water storage tank 5 and the second enrichment sample taken from the bottom of the stripping tower 3. The water in the process water storage tank 5, after being heated by the stripping tower heat exchanger 6, can be used as stripping gas from the stripping tower 3.

[0077] In a preferred embodiment, the apparatus further includes a stripping tower condenser 7 and an aromatics storage tank 8; wherein the aromatics storage tank 8 is connected to the top of the stripping tower 3 via the stripping tower condenser 7, and the aromatics storage tank 8 is also directly connected to the top of the stripping tower 3 and the process water storage tank 5.

[0078] In this invention, the aromatics collected from the top of stripping tower 3 are condensed in stripping tower condenser 7 and then enter aromatics storage tank 8. After settling in aromatics storage tank 8, they can separate into oil phase and water phase, thereby separating the water to obtain anhydrous aromatics. A portion of the obtained anhydrous aromatics is returned to stripping tower 3, and the remainder is collected as product. The water separated from aromatics storage tank 8 is sent to process water storage tank 5 and used as wash water for water washing tower 4 or stripping steam for stripping tower 3.

[0079] In a preferred embodiment, the apparatus further includes a stripping column condenser 9 and a reflux aromatics storage tank 10. The stripping column condenser 9 connects the top of the stripping column 2 and the reflux aromatics storage tank 10, and the reflux aromatics storage tank 10 is also connected to the extraction column 1 and the process water storage tank 5.

[0080] In this invention, the reflux aromatics collected from the top of the stripping column 2 are condensed by the stripping column condenser 9 and then enter the reflux aromatics storage tank 10. After settling in the reflux aromatics storage tank 10, they can be separated into an oil phase and an aqueous phase, thereby separating the water from the reflux aromatics to obtain anhydrous reflux aromatics. The separated anhydrous reflux aromatics are returned to the extraction column 1 for further extraction, while the separated water is sent to the process water storage tank 5.

[0081] In a preferred embodiment, the apparatus further includes a raffinate oil cooler 11, which is disposed between the extraction tower 1 and the water washing tower 4 for cooling the raffinate oil.

[0082] The present invention will be described in detail below through examples. The extraction solvent in the examples and comparative examples is tetraethylene glycol.

[0083] Example 1

[0084] The aromatic hydrocarbon extraction method provided in this invention is used in Figure 1 The aromatics extraction apparatus shown extracts reformed gasoline, including the following steps:

[0085] (1) Reformed gasoline S1 from the reforming unit is introduced into the extraction tower from the middle of the extraction tower, and extraction solvent S2 is introduced into the extraction tower from the top of the extraction tower. Reformed gasoline S1 and extraction solvent S2 are extracted in contact in the extraction tower. First enrichment S3 is collected from the bottom of the extraction tower and raffinate S4 is collected from the top of the extraction tower.

[0086] (2) The first enrichment agent S3 is introduced from the top of the stripping column to the stripping column for contact and separation in the stripping column, the second enrichment agent S5 is taken out from the bottom of the stripping column, and the reflux aromatic hydrocarbon S6 is taken out from the top of the stripping column.

[0087] (3) First, the above-mentioned reflux aromatics S6 is cooled by the condenser of the distillation tower and introduced into the reflux aromatics storage tank. Water is separated from the reflux aromatics storage tank to obtain anhydrous reflux aromatics S61. Then, all the anhydrous reflux aromatics S61 is returned to the extraction tower in step (1), and the water S71 separated from the reflux aromatics storage tank is sent to the process water storage tank.

[0088] (4) The second enriching agent S5 is introduced into the stripping tower from the middle of the stripping tower, and the stripping steam S8 is introduced into the stripping tower from the bottom of the stripping tower. The second enriching agent S5 and the stripping steam S8 are contacted in the stripping tower for stripping. The lean solvent S9 is taken out from the bottom of the stripping tower and the aromatics S10 is taken out from the top of the stripping tower.

[0089] The collected aromatic hydrocarbon S10 is condensed in the stripping tower condenser and then introduced into the aromatic hydrocarbon storage tank. Water is separated from the aromatic hydrocarbon storage tank to obtain anhydrous aromatic hydrocarbon S101. Part of the obtained anhydrous aromatic hydrocarbon S101 is collected as product and part is returned to the stripping tower as reflux liquid. The water S72 separated from the aromatic hydrocarbon storage tank is sent to the process water storage tank.

[0090] (5) The extracted lean solvent S9 is divided into part A and part B. Part A S91 is returned to the extraction tower in step (1) as extraction solvent S2, and part B S92 is returned to the distillation tower in step (2).

[0091] (6) After cooling the raffinate oil S4 obtained in step (1) in the raffinate oil cooler, it is introduced into the water washing tower from the bottom. The water washing water S11 from the process water storage tank is introduced into the water washing tower from the top. The raffinate oil S4 and the water washing water S11 come into contact in the water washing tower for water washing. Non-aromatic hydrocarbon S12 is collected from the top of the water washing tower, and raffinate oil water washing water S13 is collected from the bottom of the water washing tower. The obtained non-aromatic hydrocarbon S12 is collected as a product, and the obtained raffinate oil water washing water S13 is returned to the process water storage tank for recycling.

[0092] The specific operating conditions during the aromatic hydrocarbon extraction process are shown in Table 1. After 24 hours of stable operation, samples were taken for analysis, and the material information is shown in Table 2. The composition of anhydrous reflux aromatic hydrocarbon S61 is shown in Table 3, and the pressure changes inside the extraction tower are shown in Table 4. Figure 2 As shown.

[0093] Comparative Example 1

[0094] Similar to Example 1, the difference is that in step (5), all the lean solvent is returned to the extraction tower, that is, no lean solvent is introduced into the distillation tower.

[0095] The specific operating conditions during the aromatic hydrocarbon extraction process are shown in Table 1. After 24 hours of stable operation, samples were taken for analysis, and the material information is shown in Table 2. The composition of anhydrous reflux aromatic hydrocarbon S61 is shown in Table 3. The pressure changes inside the extraction tower are shown in Table 4. Figure 2 As shown.

[0096] Table 1

[0097]

[0098]

[0099] Table 2

[0100]

[0101] Note: Extraction solvent S2 in Table 1 is the flow path at start-up. After the method stabilizes, part A S92 is returned to replace extraction solvent S2.

[0102] Table 3

[0103]

[0104] Table 2-3 shows that introducing regenerated extraction solvent into the stripping column results in the following process optimizations: 1) The flow rate of reflux aromatics from the top of the stripping column decreases, and the content of benzene and toluene in the anhydrous reflux aromatics decreases; 2) The pressure at the top of the stripping column decreases, and the bottom temperature is 5°C higher than when no lean solvent is introduced; 3) The aromatics reflux ratio of the extraction column decreases, and the feed rate of reformed gasoline increases. Therefore, the aromatics extraction method provided by this invention can reduce the aromatics reflux ratio, improve the extraction capacity and separation accuracy of the extraction column, and reduce the energy consumption of the entire unit.

[0105] Figure 2 The diagram shows the pressure changes within the distillation columns in Example 1 and Comparative Example 1. Figure 2 It can be seen that the pressure at the top of the stripping column in Comparative Example 1 fluctuates within the range of 18-20 kPa, which is a relatively large fluctuation range. In Example 1, the pressure at the top of the stripping column is basically stable at around 14 kPa. The introduction of lean solvent can reduce the pressure of the stripping column, that is, reduce the gas phase load, prevent column overflow, and facilitate the stable operation of the process.

[0106] Example 2

[0107] Similar to Example 1, except that the operating conditions are kept unchanged, but the feed rate of reformed gasoline S1 in the extraction tower and the amount of lean solvent B returned to the stripping tower are changed.

[0108] In Example 2, the mass flow rate of reformed gasoline S1 is 32.5 kg / h, the mass flow rate of lean solvent B portion S92 is 20 kg / h, the mass flow rate of anhydrous reflux aromatics S61 is 30.8 kg / h, and the aromatics reflux ratio is 0.95.

[0109] Example 3

[0110] Similar to Example 1, except that the operating conditions are kept unchanged, but the feed rate of reformed gasoline S1 in the extraction tower and the amount of lean solvent B portion S92 returned to the stripping tower are changed.

[0111] In Example 3, the mass flow rate of reformed gasoline S1 is 33 kg / h, the mass flow rate of lean solvent B portion S92 is 40 kg / h, the mass flow rate of anhydrous reflux aromatics S61 is 30.5 kg / h, and the aromatics reflux ratio is 0.92.

[0112] By comparing Examples 2 and 3, it can be seen that as the amount of lean solvent used in the distillation tower increases, the amount of refluxed aromatics decreases from 30.8 kg / h to 30.5 kg / h, the aromatics reflux ratio decreases from 0.95 to 0.92, and the extraction tower throughput increases from 32.5 kg / h to 33 kg / h.

[0113] Test Example 1

[0114] 150g of the first enrichment agent S3 from Comparative Example 1 was placed in a flask for distillation. The solution was heated from room temperature at a rate of 2.5℃ / min until it deteriorated and changed color, and no more distillate flowed out. During the heating process, the distillate was collected in test tubes, and a new test tube was used every 2mL of liquid collected. Each test tube was numbered sequentially, and the distillation temperature at the beginning of collection was recorded.

[0115] The distilled liquid collected from each test tube was weighed and its components were analyzed. The results are shown in Tables 4 and 5. Figure 3 As shown.

[0116] Test Example 2

[0117] Similar to Test Example 1, except that a distillation tube packed with Raschig rings was connected to the flask, and a straight tube was connected to a condenser. During distillation, 15 g of lean solvent was added from the top of the distillation tube at a mass flow rate of 0.5 g / min. The test results are shown in Tables 4 and 5. Figure 3 As shown.

[0118] Table 4

[0119]

[0120]

[0121] As can be seen from the data in Table 4, in Test Example 1, liquid began to evaporate at 101℃, and when the temperature reached 174℃, almost no more liquid evaporated, with a cumulative evaporated weight of 20.27g. In Test Example 2, liquid began to evaporate at 120℃, and when the temperature reached 187℃, almost no more liquid evaporated, with a cumulative evaporated weight of 17.38g. Therefore, it can be concluded that in the solution with added lean solvent, the initial temperature for liquid evaporation is higher, and the final weight of the evaporated liquid is significantly reduced.

[0122] Figure 3 This is a graph showing the toluene concentration distribution in the distilled liquids from Test Example 1 and Test Example 2. Figure 3 It can be seen that in the first half of the distillation stage (before 147℃), the toluene concentration in Test Example 1 was generally higher than that in Test Example 2, indicating that adding lean solvent can effectively condense and extract toluene in the gas phase, hindering the evaporation of toluene and thus reducing the gas phase load. In the second half of the distillation stage (147℃-187℃), the toluene concentration in Test Example 2 gradually increased, even exceeding that in Test Example 1. The operating temperature in this stage is relatively high. In actual production, this part of toluene should belong to the aromatic hydrocarbon component distilled in the stripping tower. Therefore, Test Example 1 can reduce the gas phase load at the top of the extraction distillation tower. Its essence lies in the fact that this scheme can reduce the flash evaporation of toluene in the liquid phase at the top of the tower, moving the toluene as far as possible to the stripping tower, thereby effectively reducing the amount of aromatic hydrocarbons circulating in the reflux aromatic hydrocarbons.

[0123] The distilled liquids from test tubes numbered 1-1 to 1-21 in Example 1 and from test tubes numbered 2-1 to 2-13 in Example 2 were subjected to component analysis. The test results from Example 1 and Example 2 were then summed, and the results are shown in Table 5.

[0124] Table 5

[0125] Total distillate Benzene content after distillation Toluene distillation amount Distillation of non-aromatic amounts Test Example 1 17.81g 6.49g 9.74g 1.58g Test Example 2 11.11g 6.64g 3.12g 1.35g Comparison of differences 6.7g -0.15g 6.62g 0.23g

[0126] In Test Example 1, the cumulative distillation amount was 17.81g of liquid, of which 6.49g of benzene, 9.74g of toluene, and 1.58g of non-aromatic distillation were distilled. In Test Example 2, the cumulative distillation amount was 11.11g of liquid, of which 6.64g of benzene, 3.12g of toluene, and 1.35g of non-aromatic distillation were distilled.

[0127] At the same operating temperature, the toluene with a higher boiling point in Test Example 1 was not distilled off in large quantities, resulting in a 37.62% reduction in the weight of the mixed liquid in Test Example 2 compared to Test Example 1. This indicates that the technique of adding an extraction solvent in Test Example 2 can effectively reduce the gas phase load and decrease the amount of aromatics recycled.

[0128] The preferred embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. A process for aromatic extraction, characterized in that, The method includes the following steps: (1) The reformed gasoline is contacted with the extraction solvent for extraction to obtain the first enrichment agent and the raffinate; (2) The first enrichment agent is separated to obtain the second enrichment agent and reflux aromatic hydrocarbons; (3) Return the refluxed aromatics to step (1); (4) The second enriching agent is contacted with stripping steam to strip, thereby obtaining lean solvent and aromatics; (5) Divide the lean solvent into at least part A and part B, with part A being returned to step (1) as the extraction solvent and part B being returned to step (2). Wherein, part A is 65-80% of the mass of the lean solvent, and the mass ratio of the first enriching agent to part B is 2-10:

1.

2. The method of claim 1, wherein, The extraction solvent is selected from one or more of the following: triethylene glycol, tetraethylene glycol, sulfolane, dimethyl sulfoxide, 2-pyrrolidone, N-methylpyrrolidone, N-ethylpyrrolidone, N-methylformamide, N-methylbenzylmethylamide, N-formylmorpholine, N,N-dimethylformamide, hydrazine hydrate, furfural, ethylene glycol, glyceryl methyl acetal, polyethylene glycol, and polycarbonate.

3. The method according to claim 2, wherein, The extraction solvent is selected from one of tetraethylene glycol, dimethyl sulfoxide, N-methylformamide, N-formylmorpholine, hydrazine hydrate, and polyethylene glycol.

4. The method according to claim 1, wherein, In step (1), the feed temperature of the reformed gasoline is 110-150°C, and the feed temperature of the extraction solvent is 110-150°C.

5. The method according to claim 4, wherein, In step (1), the feed temperature of the reformed gasoline is 125-135°C, and the feed temperature of the extraction solvent is 120-130°C.

6. The method according to claim 1, wherein, The mass ratio of the reformed gasoline to the extraction solvent is 1:2-8.

7. The method according to claim 6, wherein, The mass ratio of the reformed gasoline to the extraction solvent is 1:3-5.

8. The method according to claim 1, wherein, The extraction is carried out in an extraction tower, and the operating conditions of the extraction tower include: a bottom temperature of 100-130℃ and a top pressure of 0.5-1MPa.

9. The method according to claim 8, wherein, The operating conditions of the extraction tower include: a bottom temperature of 110-120℃ and a top pressure of 0.6-0.8MPa.

10. The method according to claim 1, wherein, In step (2), the feed temperature of the first enrichment agent is 115-130℃.

11. The method according to claim 10, wherein, In step (2), the feed temperature of the first enrichment agent is 120-130℃.

12. The method according to claim 1, wherein, The separation is carried out in a stripping column, and the operating conditions of the stripping column include: a bottom temperature of 105-130℃ and a top pressure of 10-20kPa.

13. The method according to claim 12, wherein, The operating conditions of the distillation column include: a bottom temperature of 110-125℃ and a top pressure of 10-15 kPa.

14. The method according to claim 1, wherein, In step (3), the feed temperature of the reflux aromatics is 60-90℃.

15. The method according to claim 14, wherein, In step (3), the feed temperature of the reflux aromatics is 60-70°C.

16. The method according to claim 1, wherein, The mass ratio of the reflux aromatics to the reformed gasoline is 0.9-1.05:

1.

17. The method according to claim 16, wherein, The mass ratio of the reflux aromatics to the reformed gasoline is 0.9-0.95:

1.

18. The method according to claim 1, wherein, The reflux aromatic hydrocarbons are dehydrated to obtain anhydrous reflux aromatic hydrocarbons, which are then returned to step (1).

19. The method according to claim 1, wherein, In step (4), the stripping is carried out in a stripping tower, and the operating conditions of the stripping tower include: a top temperature of 100-125℃, a bottom temperature of 130-160℃, and a top pressure of 4.5-6kPa.

20. The method according to claim 19, characterized in that, The operating conditions of the stripping tower include: a top temperature of 105-115℃, a bottom temperature of 140-150℃, and a top pressure of 5-5.5 kPa.

21. The method according to claim 1, wherein, In step (5), the feed temperature of section A is 135-155℃.

22. The method according to claim 21, wherein, In step (5), the feed temperature of section A is 140-150℃.

23. The method according to claim 1, wherein, The feed temperature of section B is 135-155℃.

24. The method according to claim 23, wherein, The feed temperature of section B is 140-150℃.

25. The method according to claim 1, wherein, The mass ratio of the first enrichment agent to part B is 3-7:

1.

26. The method according to claim 1, wherein, Part A is 70-75% of the mass of the lean solvent.

27. An aromatic hydrocarbon extraction apparatus, characterized in that, The apparatus includes an extraction column (1), a stripping column (2), and a stripping column (3); wherein the bottom of the extraction column (1) is connected to the stripping column (2), the top of the stripping column (2) is connected to the extraction column (1), the bottom of the stripping column (2) is connected to the stripping column (3), and the bottom of the stripping column (3) is connected to the top of the extraction column (1) and the top of the stripping column (2) respectively.

28. The apparatus according to claim 27, wherein, The device also includes a water washing tower (4) and a process water storage tank (5); wherein the bottom of the water washing tower (4) is connected to the top of the extraction tower (1), and the process water storage tank (5) is connected to the top and bottom of the water washing tower (4) respectively.

29. The apparatus according to claim 27, wherein, The device also includes a stripping tower heat exchanger (6), wherein the process water storage tank (5), the stripping tower heat exchanger (6), and the bottom of the stripping tower (3) are connected in sequence.

30. The apparatus according to claim 27, wherein, The apparatus also includes a stripping tower condenser (7) and an aromatics storage tank (8); wherein the aromatics storage tank (8) is connected to the top of the stripping tower (3) via the stripping tower condenser (7), and the aromatics storage tank (8) is also directly connected to the top of the stripping tower (3) and the process water storage tank (5).

31. The apparatus according to claim 27, wherein, The apparatus further includes a stripping column condenser (9) and a reflux aromatics storage tank (10); wherein the stripping column condenser (9) is connected to the top of the stripping column (2) and the reflux aromatics storage tank (10), and the reflux aromatics storage tank (10) is also connected to the extraction column (1) and the process water storage tank (5) respectively.

32. The apparatus according to claim 27, wherein, The device also includes a raffinate oil condenser (11), which is disposed between the extraction tower (1) and the water washing tower (4) for cooling the raffinate oil.

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