A method and device for producing low-aromatic diesel and aromatic hydrocarbons

Abstract

A method and device for producing low-aromatic diesel and aromatics, characterized in that the production method is carried out in a device comprising an extraction tower (101), a raffinate water washing tower (102), a stripping tower (103), an aromatics recovery tower (104), a water distillation tower (106), and a stripping agent distillation tower (107). The method couples the stripping and washing processes, optimizes the water cycle, and fully utilizes the stripping steam energy to obtain low-aromatic diesel with a polycyclic aromatic hydrocarbon content of no more than 1% by mass and an aromatics product with a purity of more than 95% by mass and a yield of more than 85% by mass.

Description

Technical Field

[0001] The present invention relates to a method and device for producing low-aromatic diesel and aromatic hydrocarbons, and more specifically, to a method and device for producing low-aromatic diesel and aromatic hydrocarbons by separating aromatic hydrocarbons from diesel fractions using a selective solvent. Background Art

[0002] In recent years, the diesel market in my country has shown a new trend. On the one hand, the growth rate of diesel demand has slowed down, and the annual consumption has experienced negative growth many times since 2014. At the same time, the scale of domestic refining has continued to expand, and the phenomenon of diesel overcapacity has become increasingly prominent. On the other hand, the quality standards of automotive diesel have been continuously improved. In order to reduce the emission of diesel engine exhaust pollutants, the latest National VI diesel standard has reduced the volume fraction of polycyclic aromatic hydrocarbons from 11% to 7%. Therefore, reducing the aromatic content in diesel, especially the content of polycyclic aromatic hydrocarbons, and converting excess diesel into chemical raw materials has become an important topic in domestic refining process research.

[0003] Diesel in my country mainly includes three parts: straight-run diesel, catalytic diesel, and coking diesel, accounting for 59%, 30%, and 11% of the diesel pool, respectively. Diesel from different sources has different compositions, and the aromatic content of the above three types of diesel is about 25%, 70%, and 35%, respectively. These monocyclic and polycyclic aromatic hydrocarbons not only reduce the cetane number of diesel, affecting its performance, but also lead to carbon deposition and deactivation of catalysts used in subsequent deep processing processes such as refining and reforming, and loss of high cetane number components. Therefore, using an appropriate process to first separate the aromatics from diesel can not only improve the quality of diesel, but also the obtained low-aromatic diesel can be used as a raw material for ethylene steam cracking. The aromatic products separated from diesel can also be used as raw materials for aromatic production to increase the production of high-value-added chemicals such as ethylene, propylene, benzene, toluene, and xylene, providing an economically feasible method to solve the problem of excess diesel production capacity.

[0004] At present, the methods for separating aromatics from diesel mainly include hydrogenation and non-hydrogenation. Conventional diesel hydrogenation process can significantly reduce the aromatic content, but there are problems such as high equipment investment, harsh operating conditions (temperature 320-410℃, pressure 814MPa), high hydrogen consumption, and high loss of non-aromatic components; non-hydrogenation method includes extraction, adsorption and other technical routes.

[0005] CN87107146A discloses a method for extracting aromatics from diesel fractions by using two solvents, wherein the diesel fraction has a boiling range of 300-530°C, the first solvent selected is furfural, phenol, sulfoxide, dimethylpyrrolidone, preferably furfural, and the second solvent is light oil. The method can obtain heavy aromatics with a purity higher than 95% by mass, and the aromatics extraction rate is 50-95% by mass. The boiling point range of the solvent is much lower than the boiling range of the raw material, so the solvent can be recovered by flash evaporation and steam stripping. However, the method fails to realize the recycling of stripping steam, resulting in the generation of a large amount of wastewater containing solvent (furfural), high energy consumption, serious solvent loss, and environmental unfriendliness.

[0006] CN101921624A discloses a method for preparing high-quality diesel by a combined extraction and hydrogenation process, wherein the extraction solvent is selected from sulfolane, N-methylpyrrolidone, and dimethyl sulfoxide, and the solvent in the raffinate oil is separated by washing, and the separation of the solvent and aromatics in the extracted oil is achieved by back extraction, washing, and distillation. The method can ultimately obtain aromatics with a purity of 90% to 92% by mass and a yield of about 80% by mass. However, the patent does not disclose a stripping agent and a purification method for raffinate oil washing water and extracted oil washing water. For the extraction of aromatics from diesel fractions, the amount of washing water used is significantly higher than the amount of water used in the extraction process of aromatics from gasoline fractions (i.e., benzene, toluene, and xylene). If the process is not optimized and designed, and the heat of steam is not used reasonably, the energy consumption required for purifying water will cause a significant increase in the energy consumption of the entire process.

[0007] CN105542835A discloses a method for separating polycyclic aromatic hydrocarbons from diesel fractions by adsorption using a simulated moving bed. The method uses molecular sieves, oxides or metal modified materials as adsorbents. The diesel fraction is first pretreated with an adsorbent to remove impurities such as colloids, sulfur and nitrogen, and then passed into a simulated moving bed for adsorption separation. The separated product is distilled to recover the desorbent, and finally a clean diesel component and a polycyclic aromatic hydrocarbon component are obtained. The polycyclic aromatic hydrocarbon content in the clean diesel component obtained by this method is higher than 1% by mass, and the aromatic content of the polycyclic aromatic hydrocarbon component is 83.42-92.18% by mass. Compared with the solvent extraction method, the adsorption separation method has a high investment cost. Summary of the invention

[0008] When the solvent extraction method is used to separate the aromatics in the diesel fraction and produce low-aromatic diesel and aromatics, the solvent and the diesel fraction are contacted to obtain an extracted oil containing solvent and aromatics. The solvent and aromatics in the extracted oil need to be separated to obtain an aromatic product and a recycled solvent that can be recycled. The lower the aromatic content in the recycled solvent, the better. Since the diesel fraction has a wide boiling range and overlaps with the boiling point of the aromatic extraction solvent (such as cyclopentane, N-formylmorpholine, and N-methylpyrrolidone), the solvent and aromatics in the extracted oil cannot be separated by simple distillation. The existing technology uses a variety of methods such as water washing, stripping, and steam stripping to separate the solvent and aromatics in the extracted oil to ensure the purity of the recycled solvent and avoid solvent loss, but the number of equipment required is large, the process is complicated, and the water purification process has high energy consumption.

[0009] The inventors have found that when separating the solvent and aromatics in the extracted oil, the stripping and water washing processes are coupled, that is, a stripping agent and water are added to the extracted oil at the same time so that stripping and water washing are carried out simultaneously. This can enhance the separation effect of stripping, and the aromatic content in the recovered solvent is lower than that in the series process of stripping first and then washing, and the separation effect is better.

[0010] The inventors also found that by introducing the top water of the aromatics recovery tower into the raffinate water washing tower, the stripping tower, and the water distillation tower respectively, and introducing the steam obtained from the top of the water distillation tower into the aromatics recovery tower as stripping gas, the solvent recovery and water purification processes can be combined, the water circulation can be optimized, the stripping steam energy can be fully utilized, and the energy consumption of the entire process can be further reduced.

[0011] One of the purposes of the present invention is to provide a method for producing low-aromatic diesel and aromatics. Specifically, a method for producing low-aromatic diesel and aromatics by separating aromatics from diesel fractions using a selective solvent is provided. The method couples the stripping process with the water washing process, optimizes the water circulation, and fully utilizes the stripping steam energy to obtain low-aromatic diesel with a polycyclic aromatic hydrocarbon content of no more than 1% by mass and an aromatic hydrocarbon product with a purity of more than 95% by mass and a yield of more than 85% by mass.

[0012] The method is characterized in that it is carried out in a device including an extraction tower 101, a raffinate oil washing tower 102, a stripping tower 103, an aromatic recovery tower 104, a water distillation tower 106, and a stripping agent distillation tower 107;

[0013] The raw material 1 and the solvent 2 are countercurrently contacted in the extraction tower 101 to obtain an extracted oil 6 and a raffinate oil 3;

[0014] The raffinate oil 3 and water 4 are introduced into the raffinate oil water washing tower 102 for water washing to obtain low-aromatic diesel and washed water 7;

[0015] The extracted oil 6 is mixed with the washed water 7 and introduced into the stripping tower 103, the stripping agent 9 is introduced into the stripping tower 103, and the water 8 is introduced into the stripping tower 103. After stripping, the stream obtained at the top of the tower is introduced into the aromatic recovery tower 104, and the stream obtained at the bottom of the tower is introduced into the stripping agent distillation tower 107;

[0016] Aromatic hydrocarbons are obtained at the bottom of the aromatic hydrocarbon recovery tower 104, and stripping agent 9 and water 13 are obtained at the top of the tower;

[0017] The stripping agent 19 obtained at the top of the stripping agent distillation tower 107 and the bottom stream enter the water distillation tower 106;

[0018] The water vapor 14 obtained at the top of the water distillation tower 106 enters all or part of it into the bottom of the aromatics recovery tower 104 as stripping gas, and the purified solvent obtained at the bottom of the tower is returned to the extraction tower 101 for recycling.

[0019] Another object of the present invention is to provide a device for producing low-aromatic diesel and aromatics, characterized in that the device comprises an extraction tower 101, a raffinate water washing tower 102, a stripping tower 103, an aromatics recovery tower 104, an aromatics recovery tower reflux tank 105, a water distillation tower 106, a stripping agent distillation tower 107, and a stripping agent extraction tower reflux tank 108;

[0020] The extraction tower 101 is connected to the raffinate oil washing tower 102 through a pipeline at the top, and the bottom pipeline is connected to the lower part of the stripping tower 103 through a pipeline after merging with the bottom pipeline of the raffinate oil washing tower 102;

[0021] The stripping tower 103 is connected to the aromatic recovery tower 104 through a pipeline at the top, and is connected to the stripping agent distillation tower 107 through a pipeline at the bottom;

[0022] The top of the aromatics recovery tower 104 is connected to the aromatics recovery tower reflux tank 105 through a pipeline, and the water bag of the aromatics recovery tower reflux tank 105 is respectively connected to the raffinate oil washing tower 102, the water distillation tower 106 and the stripping tower 103 through pipelines, and the bottom pipeline of the aromatics recovery tower reflux tank 105 is connected to the upper part of the stripping tower 103 through a pipeline after merging with the bottom pipeline of the stripping agent extraction tower reflux tank 108;

[0023] The stripping agent distillation tower 107 is connected to the stripping agent extraction tower reflux tank 108 through a pipeline at the top, and is connected to the water distillation tower 106 through a pipeline at the bottom;

[0024] The water distillation tower 106 is connected at its top to the lower part of the aromatics recovery tower 104 through a pipeline, and at its bottom to the upper part of the extraction tower 101 through a pipeline.

[0025] The method for producing low-aromatic diesel and aromatics provided by the present invention has the following characteristics:

[0026] (1) The purity of the aromatic hydrocarbon product is greater than 95% by mass, and the yield is higher than 85% by mass; the content of polycyclic aromatic hydrocarbons in the low-aromatic diesel oil does not exceed 1% by mass.

[0027] (2) Adopt optimized stripping and water purification process, low energy consumption and no wastewater discharge.

[0028] (3) The process operating conditions are mild, there is no hydrogen consumption, and the investment cost is low. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 The present invention provides a schematic flow diagram of a method for separating aromatics from a diesel fraction.

[0030] Figure 1 In the figure, extraction tower 101, raffinate oil washing tower 102, stripping tower 103, aromatics recovery tower 104, aromatics recovery tower reflux tank 105, water distillation tower 106, stripping agent distillation tower 107, stripping agent extraction tower reflux tank 108, raw material 1, solvent 2, raffinate oil 3, extracted oil 6, washing water 7, water 4, 8, 13, 15, stripping agent 9, 19, water vapor 14, mixture of stripping agent and water 16, 18, pipelines 5, 10, 11, 12, 17, 18, 20. DETAILED DESCRIPTION

[0031] The present invention provides a method for producing low-aromatic diesel and aromatics, characterized in that the production method is carried out in a device including an extraction tower 101, a raffinate water washing tower 102, a stripping tower 103, an aromatics recovery tower 104, a water distillation tower 106, and a stripping agent distillation tower 107;

[0032] The raw material 1 and the solvent 2 are countercurrently contacted in the extraction tower 101 to obtain an extracted oil 6 and a raffinate oil 3;

[0033] The raffinate oil 3 and water 4 are introduced into the raffinate oil water washing tower 102 for water washing to obtain low-aromatic diesel and washed water 7;

[0034] The extracted oil 6 is mixed with the washed water 7 and introduced into the stripping tower 103, the stripping agent 9 is introduced into the stripping tower 103, and the water 8 is introduced into the stripping tower 103. After stripping, the stream obtained at the top of the tower is introduced into the aromatic recovery tower 104, and the stream obtained at the bottom of the tower is introduced into the stripping agent distillation tower 107;

[0035] Aromatics are obtained at the bottom of the aromatic recovery tower 104, and stripping agent 9 and water 13 are obtained at the top of the tower. The stripping agent 9 is returned to the stripping tower 103 for recycling, and the water 13 is divided into three parts. The first part of water 4 is introduced into the upper part of the raffinate water washing tower 102, the second part of water 8 is introduced into the upper part of the stripping tower, and the third part of water 15 is introduced into the upper part of the water distillation tower 106;

[0036] The stripping agent 19 obtained at the top of the stripping agent distillation tower 107 enters the water distillation tower 106 as a bottom stream; the water vapor 14 obtained at the top of the water distillation tower 106 all enters the bottom of the aromatic recovery tower 104 as stripping gas, or part of it enters the bottom of the aromatic recovery tower 104 as stripping gas, and the rest of it is condensed and enters one or more of the raffinate washing tower (102), the stripping tower (103) and the water distillation tower (106); the purified solvent obtained at the bottom of the tower is returned to the extraction tower 101 for recycling.

[0037] The stripping agent 9 and the stripping agent 19 can be mixed and returned to the lower part of the stripping tower.

[0038] The extraction tower 101 is used to contact the raw material with the solvent and perform multi-stage extraction, so that the aromatic hydrocarbons in the diesel are dissolved in the solvent, and the raffinate oil is obtained at the top of the tower and the extracted oil is obtained at the bottom of the tower. The solvent is selected from sulfolane, alkyl sulfolane and mixtures thereof, and the alkyl sulfolane is preferably 3-methyl sulfolane and 2,4-dimethyl sulfolane; the solvent may contain 0.5-5.0% by mass of water and 0.01-1.0% by mass of hydrocarbon compounds. The theoretical plate number of the extraction tower is 8-15, the mass ratio of the solvent to the raw material is 1-5, the top pressure is 0.2-0.7MPa (absolute), the solvent inlet temperature is 60-180°C, preferably 80-160°C, the raw material inlet temperature is 20-60°C, and the bottom temperature is 80-130°C.

[0039] The raffinate oil washing tower 102 is used to remove the solvent in the raffinate oil to obtain low-aromatic diesel. The raffinate oil washing tower has a theoretical plate number of 2 to 10, a tower top pressure of 0.4 to 0.7 MPa (absolute), a mass ratio of washing water to raffinate oil of 0.05 to 0.5, preferably 0.1 to 0.3, and a washing water inlet temperature of 30 to 80°C.

[0040] The stripping tower 103 is used to separate aromatic hydrocarbons and solvents in the extracted oil. The stripping agent is selected from non-aromatic hydrocarbons with a boiling point of 40 to 150° C., preferably one or more of petroleum ether, cyclopentane, cyclohexane, C6 non-aromatic hydrocarbons or a mixture of C6 and C7 non-aromatic hydrocarbons. The C6 non-aromatic hydrocarbons are derived from the raffinate oil obtained from the benzene extraction process, and the mixture of C6 and C7 non-aromatic hydrocarbons are derived from the raffinate oil obtained from the benzene and toluene extraction process. The stripping tower has 4 to 12 theoretical plates, a tower top pressure of 0.2 to 0.8 MPa (absolute), a stripping agent inlet temperature of 30 to 80°C, preferably 35 to 75°C, a water inlet temperature of 30 to 78°C, preferably 35 to 60°C, a tower bottom temperature of 40 to 80°C, preferably 35 to 60°C, a stripping agent to extracted oil mass ratio of 0.05 to 0.8, preferably 0.1 to 0.6, and a water to extracted oil mass ratio of 0.01 to 0.2, preferably 0.05 to 0.15.

[0041] The aromatics recovery tower 104 obtains aromatics products at the bottom and recyclable stripping agent and water at the top. The theoretical plate number is 15 to 40, the top pressure is 0.03 to 0.2 MPa (absolute), the bottom temperature is 120 to 200°C, preferably 130 to 190°C, and the reflux ratio (mass) is 0.2 to 2.

[0042] The purified solvent obtained at the bottom of the water distillation tower (106) can be recycled, and its theoretical plate number is 5 to 30, the top pressure (absolute) is 0.03 to 0.15 MPa, the bottom temperature is 90 to 200°C, and the reflux ratio is 0 to 1.0.

[0043] The stripping agent distillation tower 107 is preferably fed from the first tower plate, and the stripping agent is obtained from the top of the tower and can be recycled. The theoretical number of plates is 2 to 10, and the top pressure is 0.1 to 0.2 MPa (absolute); the bottom temperature is 110 to 160°C, and the residual stripping agent content in the bottom flow is 0 to 0.5% by mass, preferably 0 to 0.1% by mass.

[0044] The boiling range of the raw material is 180-380° C., and one or more of straight-run diesel, catalytic diesel or coker diesel is preferred. The aromatic content in the raw material is 15-80% by mass.

[0045] The polycyclic aromatic hydrocarbons described in the present invention refer to aromatic hydrocarbons containing two or more benzene rings.

[0046] The device for producing low-aromatic diesel and aromatics of the present invention is characterized in that the device comprises an extraction tower 101, a raffinate water washing tower 102, a stripping tower 103, an aromatics recovery tower 104, an aromatics recovery tower reflux tank 105, a water distillation tower 106, a stripping agent distillation tower 107, and a stripping agent extraction tower reflux tank 108;

[0047] The extraction tower 101 is connected to the raffinate oil washing tower 102 through a pipeline at the top, and the bottom pipeline is connected to the lower part of the stripping tower 103 through a pipeline after merging with the bottom pipeline of the raffinate oil washing tower 102;

[0048] The stripping tower 103 is connected to the aromatic recovery tower 104 through a pipeline at the top, and is connected to the stripping agent distillation tower 107 through a pipeline at the bottom;

[0049] The top of the aromatics recovery tower 104 is connected to the aromatics recovery tower reflux tank 105 through a pipeline, and the water bag of the aromatics recovery tower reflux tank 105 is respectively connected to the raffinate oil washing tower 102, the water distillation tower 106 and the stripping tower 103 through pipelines, and the bottom pipeline of the aromatics recovery tower reflux tank 105 is connected to the upper part of the stripping tower 103 through a pipeline after merging with the bottom pipeline of the stripping agent extraction tower reflux tank 108;

[0050] The stripping agent distillation tower 107 is connected to the stripping agent extraction tower reflux tank 108 through a pipeline at the top, and is connected to the water distillation tower 106 through a pipeline at the bottom;

[0051] The water distillation tower 106 is connected at its top to the lower part of the aromatics recovery tower 104 through a pipeline, and at its bottom to the upper part of the extraction tower 101 through a pipeline.

[0052] The present invention is further described below in conjunction with the accompanying drawings.

[0053] Figure 1 In the process, the raw material 1 enters the lower part of the extraction tower 101, and the solvent 2 enters the upper part of the tower 101, and the two are in countercurrent contact, and the extracted oil 6 is obtained at the bottom of the tower, and the raffinate oil 3 obtained at the top of the tower is introduced into the lower part of the raffinate oil water washing tower 102, and the water 4 is introduced into the upper part of the water washing tower 102. After washing, the low-aromatic diesel oil is obtained at the top of the water washing tower 102 and discharged through the pipeline 5. The washed water 7 obtained at the bottom of the tower is mixed with the extracted oil 6 discharged from the bottom of the extraction tower 101 and introduced into the middle and lower part of the stripping tower 103, and the water 8 is introduced into the upper part of the stripping tower 103. The stripping agent is introduced into the lower part of the stripping tower 103. After stripping, the logistics obtained at the bottom of the stripping tower 103 is introduced into the upper part of the stripping agent distillation tower 107 through the pipeline 12, and the logistics obtained at the top of the stripping tower 103 is introduced into the upper part of the stripping agent distillation tower 107 through the pipeline 10 The aromatic hydrocarbons are separated by distillation and separation. The aromatic hydrocarbons obtained at the bottom of the aromatic hydrocarbon recovery tower 104 are discharged through a pipeline 17. The mixture 16 of stripping agent and water obtained at the top of the aromatic hydrocarbon recovery tower 104 is condensed and enters the reflux tank 105 of the aromatic hydrocarbon recovery tower to separate the oil phase and water. A part of the oil phase is returned to the upper part of the 104 tower through a pipeline 11, and the remaining oil phase is introduced into the lower part of the stripping tower 103 as the stripping agent 9. The water 13 separated from the water bag of the reflux tank 105 of the aromatic hydrocarbon recovery tower is divided into three parts. The first part of the water 4 is introduced into the upper part of the raffinate water washing tower 102, the second part of the water 8 is introduced into the upper part of the stripping tower 103, and the third part of the water 15 is introduced into the upper part of the water distillation tower 106. The mixture 18 of stripping agent and water obtained at the top of stripping agent distillation tower 107 is condensed and enters stripping agent extraction reflux tank 108, and then stripping agent 19 is discharged and mixed with stripping agent 9 and sent to the lower part of stripping tower 103. The logistics discharged from the bottom of stripping agent distillation tower 107 enters water distillation tower 106 through pipeline 20. After rectification, water vapor 14 obtained at the top of the tower is introduced into the lower part of 104, and the solvent 2 discharged from the bottom of the tower is introduced into the upper part of extraction tower 101 for recycling. The present invention is further illustrated by examples below, but the present invention is not limited thereto.

[0054] Comparative Example 1 and Example 1 investigate the effects of different stripping processes on the results of separating the solvent and aromatics in the extracted oil.

[0055] Comparative Example 1

[0056] Comparative Example 1-1 Stripping

[0057] 3-Methylcyclopentane was used as solvent to simulate the extracted oil to be stripped, and its composition is shown in Table 1. The stripping agent was cyclopentane. At 40°C, the stripping agent and the extracted oil were fully mixed, wherein the mass ratio of the stripping agent to the extracted oil was 0.5. Then, the mixture was placed in a constant temperature oven at 40°C for 2 hours to form a liquid-liquid two-phase with a clear phase interface, wherein the upper layer was the stripping agent and aromatics, and the lower layer was the recovery solvent. The aromatic content in the recovery solvent was analyzed, and the results are shown in Table 2.

[0058] Comparative Example 1-2 Water washing

[0059] 3-Methylcyclobutane sulfone was used as solvent to simulate the extracted oil to be stripped, and its composition is shown in Table 1. At 40°C, water and extracted oil were fully mixed, wherein the mass ratio of water to extracted oil was 0.1, and then placed in a constant temperature oven at 40°C for 2 hours to form a liquid-liquid two-phase with a clear phase interface, wherein the upper layer was aromatic hydrocarbons and the lower layer was a recovered solvent containing water. The aromatic hydrocarbon content in the recovered solvent was analyzed, and the results are shown in Table 2.

[0060] Comparative Example 1-3: Stripping followed by water washing

[0061] The recovered solvent obtained in Comparative Example 1-1 was washed with water using the method described in Comparative Example 1-2 to obtain a recovered solvent after stripping and then washing with water. The aromatic content of the recovered solvent was analyzed. The results are shown in Table 2.

[0062] Example 1

[0063] Example 1: Stripping-Water Washing Coupling

[0064] 3-Methyl sulfolane was used as solvent to simulate the extracted oil to be stripped, and its composition is shown in Table 1. The stripping agent was cyclopentane. At 40°C, the stripping agent, water and extracted oil were fully mixed, wherein the mass ratio of the stripping agent, water and extracted oil was 0.5:0.1:1. Then, it was placed in a constant temperature oven at 40°C for 2 hours to form a liquid-liquid two-phase with a clear phase interface, wherein the upper layer was the stripping agent and aromatics, and the lower layer was the recovered solvent containing water. The aromatic content in the recovered solvent was analyzed, and the results are shown in Table 2.

[0065] Table 1

[0066] Extracted oil components Mass fraction % Aromatics n-Hexylbenzene 1.05 Tetralin 0.89 1-Methylnaphthalene 1.06 Dodecylbenzene 1.41 Solvents 3-Methylsulfolane 95.59 total 100

[0067] Table 2

[0068] serial number Treatment process Aromatic content in recovered solvent, mass % Comparative Example 1-1 Stripping 1.51 Comparative Example 1-2 Washing 0.92 Comparative Examples 1-3 Stripping followed by water washing 0.54 Example 1 Stripping-water washing coupling 0.38

[0069] It can be seen from Table 2 that the aromatic content in the recovered solvent obtained by the water washing-stripping coupling process is the lowest, indicating that the water washing-stripping coupling process is the best for separating the solvent and aromatics in the extracted oil.

[0070] Example 2 investigates the effect of temperature on the results of the stripping-water washing coupled process for separating the solvent and aromatics in the extracted oil.

[0071] Example 2

[0072] The stripping agent was cyclohexane, and the simulated oil extraction and test steps were the same as those in Example 1. The temperature of the constant temperature oven was changed, and the lower solvent phase was taken to analyze its composition, and the aromatic content in the recovered solvent after stripping was obtained as shown in Table 5.

[0073] Table 3

[0074]

[0075] It can be seen from Table 3 that at a lower temperature, the stripping-water washing coupling process has the lowest aromatic content in the recovered solvent and the best effect. As the temperature increases, the aromatic content in the recovered solvent increases significantly and the separation effect becomes worse.

[0076] Examples 3 to 5 and Comparative Examples 2 to 3 investigate the effects of different stripping agents and stripping processes on low aromatic diesel and aromatic products.

[0077] Example 3

[0078] according to Figure 1 The process shown produces low aromatic diesel and aromatics, and the properties of the raw materials are shown in Table 4. The solvent is 3-methylcyclobutane sulfone, the stripping agent is C6 non-aromatic hydrocarbons, the main operating conditions of each tower are shown in Table 5, and the composition and yield of low aromatic diesel and aromatic products are shown in Table 6.

[0079] Table 4

[0080]

[0081] Example 4

[0082] according to Figure 1 The process shown produces low-aromatic diesel and aromatics. The properties of the raw materials are shown in Table 4. The solvent is a composite solvent of sulfolane and 3-methylsulfolane in a mass ratio of 1:1. The stripping agent is the raffinate oil extracted from the C6-C7 fraction aromatics. The main operating conditions of each tower are shown in Table 5. The composition and yield of the low-aromatic diesel and aromatics products are shown in Table 6.

[0083] Example 5

[0084] according to Figure 1 The process shown produces low-aromatic diesel and aromatics. The properties of the raw materials are shown in Table 4. The solvent is cyclopentane sulfone, the stripping agent is petroleum ether, the main operating conditions of each tower are shown in Table 5, and the composition and yield of the low-aromatic diesel and aromatics products are shown in Table 6.

[0085] Comparative Example 2

[0086] according to Figure 1The process shown produces low aromatic diesel and aromatics, and the raw materials are the same as those in Example 3. The solvent is N-methylpyrrolidone, and the stripping agent is the raffinate oil extracted from the C6 fraction aromatics. The main operating conditions of each tower are shown in Table 5, and the composition and yield of the obtained low aromatic diesel and aromatics products are shown in Table 6.

[0087] As can be seen from Table 6, Example 3 and Comparative Example 2 process the same raw material. Compared with Comparative Example 2, Example 3 has higher yield of aromatic products and total aromatic content; the yield of low aromatic diesel is also higher, and the total aromatic content and polycyclic aromatic hydrocarbon content in the low aromatic diesel are lower, indicating that the present invention has achieved better results.

[0088] Comparative Example 3

[0089] This comparative example adopts the process of stripping first and then washing to separate aromatics from diesel fraction, and the raw materials, solvents and stripping agents are the same as those in Example 3. The main operating conditions of each tower are shown in Table 7, and the composition and yield of the obtained low-aromatic diesel and aromatic products are shown in Table 6.

[0090] As can be seen from Table 6, Example 3 and Comparative Example 3 use different processes, the same solvent, and the same stripping agent to treat the same raw material. Compared with Comparative Example 3, Example 3 has higher aromatic product yield and total aromatic content; the total aromatic content and polycyclic aromatic hydrocarbon content in the low-aromatic diesel are lower, indicating that the present invention has achieved better results.

[0091] Table 5

[0092]

[0093]

[0094] Table 6

[0095]

[0096] Table 7

[0097]

[0098]

Claims

1. A method for producing low-aromatic diesel and aromatics, characterized in that The method is carried out in a device comprising an extraction tower (101), a raffinate water washing tower (102), a stripping tower (103), an aromatics recovery tower (104), a water distillation tower (106), and a stripping agent distillation tower (107); The raw material (1) and the solvent (2) are contacted in countercurrent in the extraction tower (101) to obtain extracted oil (6) and raffinate oil (3); The raffinate oil (3) and water (4) are introduced into a raffinate oil washing tower (102) for washing to obtain low-aromatic diesel and washed water (7); The extracted oil (6) and the washed water (7) are mixed and introduced into a stripping tower (103), a stripping agent (9) is introduced into the stripping tower (103), and water (8) is introduced into the stripping tower (103). After stripping, the stream obtained at the top of the tower is introduced into an aromatic recovery tower (104), and the stream obtained at the bottom of the tower is introduced into a stripping agent distillation tower (107); Aromatic hydrocarbons are obtained at the bottom of the aromatic hydrocarbon recovery tower (104), and stripping agent (9) and water (13) are obtained at the top of the tower; The stripping agent stripping tower (107) obtains the stripping agent (19) at the top, and the bottom stream enters the water distillation tower (106); The water vapor (14) obtained at the top of the water distillation tower (106) enters all or part of it into the bottom of the aromatics recovery tower (104) as stripping gas, and the purified solvent obtained at the bottom of the tower is returned to the extraction tower (101) for recycling.

2. The method according to claim 1, characterized in that The water (13) obtained at the top of the aromatic recovery tower (104) is divided into three parts. The first part of the water (4) is introduced into the upper part of the raffinate water washing tower (102), the second part of the water (8) is introduced into the upper part of the stripping tower, and the third part of the water (15) is introduced into the upper part of the water distillation tower (106).

3. The method according to claim 1, characterized in that Part of the water vapor (14) obtained at the top of the water distillation tower (106) enters the bottom of the aromatic recovery tower (104) as stripping gas, and the remaining part is condensed and enters one or more of the raffinate washing tower (102), the stripping tower (103) and the water distillation tower (106).

4. The method according to claim 1, characterized in that The solvent in the extraction tower (101) is selected from sulfolane, alkyl sulfolane and a mixture thereof.

5. The method according to claim 1 or 4, characterized in that: The solvent contains 0.5-5.0 mass % of water and 0.01-1.0 mass % of hydrocarbon compounds.

6. The method according to claim 1, characterized in that The stripping agent is a non-aromatic hydrocarbon with a boiling point of 40-150°C.

7. The method according to claim 1 or 6, characterized in that The stripping agent is selected from one or more of petroleum ether, cyclopentane, cyclohexane, C6 non-aromatic hydrocarbons or a mixture of C6 and C7 non-aromatic hydrocarbons.

8. The method according to claim 1, wherein: In the extraction tower (101), the mass ratio of solvent to raw material is 1-5, the solvent inlet temperature is 60-180°C, and the tower top pressure is 0.2-0.7 MPa.

9. The method according to claim 1, wherein: In the raffinate oil washing tower (102), the mass ratio of washing water to raffinate oil is 0.05-0.5, the tower top pressure is 0.4-0.7 MPa, and the washing water inlet temperature is 30-80°C.

10. The method according to claim 1, wherein: In the stripping tower (103), the tower top pressure is 0.2-0.8 MPa, the stripping agent inlet temperature is 30-80°C, the stripping agent to extracted oil mass ratio is 0.05-0.8, the water (8) inlet temperature is 30-78°C, and the water to extracted oil mass ratio is 0.01-0.

2.

11. The method according to claim 1, wherein: In the aromatic recovery tower (104), the reflux ratio is 0.2-2, the tower top pressure is 0.03-0.2 MPa, and the tower bottom temperature is 120-200°C.

12. The method according to claim 1, wherein: In the water distillation tower (106), the reflux ratio is 0-1.0, the tower top pressure is 0.03-0.15 MPa, and the tower bottom temperature is 90-200°C.

13. The method according to claim 1, wherein: In the stripping agent distillation tower (107), the top pressure is 0.1-0.2 MPa and the bottom temperature is 110-160°C.

14. The method according to claim 1, characterized in that The boiling range of the raw material is 180-380°C.

15. The method according to claim 1 or 14, characterized in that The raw material is selected from one or more of straight-run diesel, catalytic diesel or coking diesel.

16. A device for producing low-aromatic diesel and aromatic hydrocarbons, characterized in that The device comprises an extraction tower (101), a raffinate water washing tower (102), a stripping tower (103), an aromatics recovery tower (104), an aromatics recovery tower reflux tank (105), a water distillation tower (106), a stripping agent distillation tower (107), and a stripping agent extraction tower reflux tank (108); The top of the extraction tower (101) is connected to the raffinate oil washing tower (102) through a pipeline, and the bottom pipeline is connected to the bottom of the stripping tower (103) through a pipeline after merging with the bottom pipeline of the raffinate oil washing tower (102); The stripping tower (103) is connected to the aromatics recovery tower (104) via a pipeline at the top, and is connected to the stripping agent distillation tower (107) via a pipeline at the bottom; The top of the aromatics recovery tower (104) is connected to the aromatics recovery tower reflux tank (105) through a pipeline, the water bag of the aromatics recovery tower reflux tank (105) is respectively connected to the raffinate water washing tower (102), the water distillation tower (106) and the stripping tower (103) through pipelines, and the bottom pipeline of the aromatics recovery tower reflux tank (105) is connected to the upper part of the stripping tower (103) through a pipeline after merging with the bottom pipeline of the stripping agent extraction tower reflux tank (108); The stripping agent distillation tower (107) is connected to the stripping agent extraction tower reflux tank (108) through a pipeline at the top, and is connected to the water distillation tower (106) through a pipeline at the bottom; The water distillation tower (106) is connected at its top to the lower part of the aromatics recovery tower (104) via a pipeline, and at its bottom to the upper part of the extraction tower (101) via a pipeline.

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