A method for separating aromatics from diesel fuel

Abstract

This invention discloses a method for separating aromatics from diesel fuel. The process is simple, short, and energy-efficient, enabling high-value utilization of diesel fractions. It separates aromatics from non-aromatics in diesel fuel while reducing the number of distillation columns and other equipment, providing high-quality feedstock for downstream high-value utilization and reducing energy consumption and investment.

Description

Technical Field

[0001] This invention relates to the field of diesel fuel processing, and more specifically to a method for separating aromatic hydrocarbons from diesel fuel. Background Technology

[0002] Diesel fractions mainly originate from atmospheric and vacuum distillation, catalytic cracking, and hydrocracking units. Diesel fractions primarily contain aromatic and non-aromatic components. Among the aromatic components, monocyclic and polycyclic aromatic hydrocarbons are unsuitable as diesel blending components, while non-aromatic hydrocarbons are suitable for diesel blending and as chemical feedstock components. With my country's refining and chemical transformation and high-quality development, the trend of diesel surplus is intensifying. Efficient, low-energy-consumption, and flexible production to fully utilize diesel blending components is an important path for the high-quality and sustainable development of petrochemical enterprises.

[0003] Currently, research on diesel separation technology in my country is in its initial stage and has not yet been truly industrialized. The patent situation is as follows:

[0004] CN104945328B proposes a method using ionic liquids and organic solvents as composite extractants to separate aromatics and non-aromatics from diesel fuel using a three-tower process. The ionic liquid is formulated according to actual needs, and the organic solvent is mainly N,N-dimethylformamide, N,N-dimethylacetamide, or sulfolane. The back-extraction agent is C4-C10 alkanes or cycloalkanes. This patent separates diesel fuel using a three-tower process, which is long and energy-intensive.

[0005] CN104073285B proposes a dual-extractant, three-tower process to separate aromatics and non-aromatics. The first extractant is one of N,N-dimethylformamide, ethylene glycol methyl ether, furfural, or morpholine. The second extractant is the first extractant with a water content of 3-15% by mass. In this patent, the first extractant, the second extractant, and diesel fuel all enter a conventional tower, resulting in a long residence time and low dispersion and mixing performance.

[0006] CN108203595A proposes a four-tower process using ionic liquids as extractants to separate aromatics and non-aromatics from diesel fuel: an extraction tower, a light aromatics removal tower, a back-extraction tower, and a solvent recovery tower. The ionic liquid cation has an alkyl-substituted imidazole or pyridine structure, and the anion is hexafluorophosphate, tetrafluoroborate, or bis(trifluoromethanesulfonate)imine. The back-extraction agent is a C4-C10 alkane or a C6-C10 cycloalkanes. This patented process is lengthy, involves reduced pressure for light aromatics removal, and uses an atmospheric pressure back-extraction tower, resulting in high operating costs and complex operation.

[0007] CN108003915A proposes using ionic liquids as extractants, with the extractant consisting of a main extractant and an auxiliary extractant. A three-tower process—extraction tower, back-extraction tower, and solvent recovery tower—is used to separate aromatics and non-aromatics from diesel fuel. The ionic liquid cation has an alkyl-substituted imidazole or pyridine structure, and the main and auxiliary extractants are the same. The anion is hexafluorophosphate, tetrafluoroborate, or bis(trifluoromethanesulfonate)imine, and the main and auxiliary extractants differ. The back-extraction agent is a C4-C10 alkane or cycloalkanes. This patented process is lengthy, costly, and complex to operate.

[0008] CN108018067A proposes using ionic liquids as extractants, with the extractant consisting of a main extractant and an auxiliary extractant. A three-tower process—extraction tower, back-extraction tower, and solvent recovery tower—is used to separate aromatics and non-aromatics from diesel fuel. The ionic liquid cation has an alkyl-substituted imidazole or pyridine structure, with the main and auxiliary extractants being different. The anion is hexafluorophosphate, tetrafluoroborate, or bis(trifluoromethanesulfonate)imine, with the main and auxiliary extractants being the same. The back-extraction agent is cyclohexane or n-heptane. This patented process is lengthy, costly, and complex to operate.

[0009] CN104945327B proposes using ionic liquids as extractants and a three-tower process (extraction tower, back-extraction tower, and solvent recovery tower) to separate aromatics and non-aromatics from diesel fuel. The ionic liquid cation has an alkyl-substituted imidazole or pyridine structure, and the anion is hexafluorophosphate or tetrafluoroborate. The back-extraction agent is a C4-C10 alkanes or cycloalkanes, preferably C6-C8 alkanes or cycloalkanes. This patented process is lengthy and costly.

[0010] CN1295302C separates the middle fractions of gasoline and diesel fractions from catalytic cracking products. After extractive distillation, aromatics and non-aromatics are separated. The aromatic components are further separated into gasoline and heavy aromatic components. The gasoline components can be blended into gasoline, while the heavy aromatics exit the unit. The non-aromatic components are further separated into light chemical oil and diesel fractions. The light chemical oil and diesel are used as feedstock for ethylene, while the diesel fraction can be blended into diesel. This patent achieves optimal utilization of the middle fractions through the redistribution of gasoline, diesel, and hydrocarbon middle fractions. This patented technology has been applied in five companies of China National Petroleum Corporation (CNPC), but the high energy consumption problem urgently needs to be addressed.

[0011] CN101914389B achieves high-quality diesel production through a six-tower system consisting of an extraction tower, a back-extraction tower, a residual oil washing tower, an extracted oil washing tower, an extracted oil cutting tower, a solvent recovery tower, and two hydrogenation reactors: a residual oil hydrogenation reactor and an extracted oil hydrogenation reactor.

[0012] CN104593056A describes the preparation of ionic liquids by mixing quaternary ammonium compounds with dicarboxylic acids. The ionic liquids are then mixed with diesel fuel and hydrogen peroxide is added to carry out diesel desulfurization. The mixture is then allowed to stand and separate into layers, with diesel fuel on the upper layer and ionic liquid on the lower layer. The ionic liquids are extracted by one or more back-extraction agents, such as carbon tetrachloride, chloroform, or ethyl acetate, and then recycled.

[0013] CN105327677B describes a method for preparing an adsorbent for separating bicyclic aromatic hydrocarbons from diesel fuel. This adsorbent exhibits strong adsorption capacity for bicyclic aromatic hydrocarbons in diesel fuel and can effectively separate them.

[0014] CN101265152B uses ionic liquid as the extractant and a two-tower process to separate benzene and cyclohexane, replacing the traditional extractant and improving separation accuracy. The ionic liquid is an imidazole cation and a fluorophosphate anion.

[0015] CN100489070C proposes a system consisting of two hydrogenation reaction systems, one thermal high-precision separation system, and two conventional extraction towers for processing low-quality diesel fuel. The extraction solvent is one or more of sulfolane, N-methylpyrrolidone, furfural, or dimethyl sulfoxide. This patent does not mention any back-extraction agent.

[0016] CN105289466B proposes a method for preparing tunable pore size silica gel or metal-loaded modified silica gel for adsorbing polycyclic aromatic hydrocarbons (PAHs) in diesel fuel. This adsorbent has a strong adsorption capacity for PAHs in diesel fuel. The PAH desorbent is one or more of benzene, toluene, cyclohexane, methylcyclohexane, ethanol, and methanol. It can effectively adsorb and separate PAHs in diesel fuel with high selectivity, and the adsorbent can be regenerated and reused repeatedly.

[0017] CN104073289B proposes a four-tower process (extraction tower 1, extraction tower 2, water washing tower, and solvent recovery tower) for liquid-liquid extraction to separate aromatics and non-aromatics from diesel fuel. The main extractant is dimethylformamide (DMF), ethylene glycol methyl ether, furfural, or morpholine, or one or more of these, and the co-solvent is water. This process is lengthy and energy-intensive. It can be simplified to a three-tower process using a partition tower, resulting in a shorter process and lower energy consumption.

[0018] CN104073291B employs a liquid-liquid extraction process, consisting of a three-tower liquid-liquid extraction column, a residual oil washing tower, and a solvent recovery tower, to separate aromatics and non-aromatics from diesel fuel. The main extractant is dimethylformamide (DMF), ethylene glycol methyl ether, furfural, or morpholine, or one or more of these, with water as the co-solvent. This process is based on the same principle as CN104073289B, except that the first and second liquid-liquid extraction columns are stacked into one tower; the underlying process principle remains unchanged.

[0019] CN103483394B describes the synthesis method and application of MOFs adsorbent materials centered on zinc. This material can selectively adsorb polycyclic aromatic hydrocarbons (PAHs), specifically naphthalene, 1-methylnaphthalene, 2-methylnaphthalene, acenaphthene, acenaphthene, anthracene, phenanthrene, and fluoranthene mixtures, with acenaphthene and anthracene being the most selective adsorptions. Furthermore, this material can also be coated onto capillary columns for PAH detection and can adsorb PAHs from water.

[0020] CN109022020A proposes a method for separating alkanes, monocyclic aromatics, polycyclic aromatics, and cycloalkanes from diesel fuel using two simulated moving beds. The first simulated moving bed utilizes one or more of the type-selective molecular sieves SAPO-11, Na-ZSM-11, Na-ZSM-22, and Na-ZSM-23 to adsorb alkanes, with one or more of n-heptane, n-octane, or cyclohexane as the desorbent. The remaining monocyclic aromatics, polycyclic aromatics, and cycloalkanes enter the second simulated moving bed, where a modified MCM-41 molecular sieve adsorbs monocyclic aromatics and polycyclic aromatics. Cycloalkanes exit the unit directly. Monocyclic aromatics are replaced by cyclohexane, methylcyclohexane, and methylcyclopentane, while polycyclic aromatics are replaced by toluene, ethylbenzene, or p-diethylbenzene.

[0021] CN105194895B proposes a method for coupling the reaction and separation processes in biodiesel production using a partitioned column. The feedstock oil and methanol enter the reaction zone from the same side of the partitioned column, with the feedstock oil entering from the top and the methanol from the bottom. The reaction product, water, is distilled off from the top of the column on the feed side, while the methanol is distilled off from the top of the column on the other side. Biodiesel is distilled off from the bottom of the column after exchanging heat with the two feedstocks. This is a short-process, energy-saving and consumption-reducing method for producing biodiesel.

[0022] CN200910092958.7 describes a method for producing high-quality diesel fuel by separating aromatics from non-aromatics in diesel fuel using seven towers: an extraction tower, a backwashing tower, a residual oil washing tower, an extracted oil washing tower, a residual oil cutting tower, an extracted oil cutting tower, and a solvent recovery tower, along with hydrogenation of the residual oil. The extractants are sulfolane, N-methylpyrrolidone (NMP), and dimethyl sulfoxide. The backwashing agent is not explicitly specified. This patent describes a complex and lengthy production process.

[0023] CN1274382C details the concept of ionic liquids, proposing suitable cations and anions. Given the extremely low vapor pressure at the top of the column, ionic liquids do not require secondary separation in the raffinate phase, thus saving energy. Separation of ionic liquids in the extract phase can be achieved through distillation, extraction, etc. It proposes that changing the cation can alter the solubility of the ionic liquid and the extracted system, therefore, the separation performance can be modified by adjusting the cation type. Examples of separation using ionic liquids include: butene-butane; cyclohexanol-cyclohexanone; propanol-methanol; ethanol-water; tetrahydrofuran-water; propanol-water; and isopropanol-water. It also proposes that headspace chromatography can be used to analyze the separation performance.

[0024] Currently, diesel fraction separation generally employs traditional 3-4 tower separation or simulated moving bed adsorption separation to obtain the corresponding products, which suffers from large equipment investment, high energy consumption, low product yield, and high production costs. Summary of the Invention

[0025] The purpose of this invention is to provide a method for separating aromatics from diesel fuel. This method can efficiently, with low energy consumption and a short process, recover the aromatic and non-aromatic components from diesel fuel fractions, thereby realizing their high-value utilization.

[0026] To achieve the above objectives, the present invention provides a method for separating aromatics from diesel fuel, using a partition wall column and a solvent recovery column for separation. The partition wall column is radially divided into a first chamber and a second chamber by a partition plate. The top of the partition plate is connected to the top of the partition wall column, preventing communication between the first and second chambers at the top. A gap is left between the bottom of the partition plate and the bottom of the partition wall column, allowing communication between the first and second chambers at the bottom. Diesel fuel enters the partition wall column from the middle of the first chamber, and a composite extractant exits from the first chamber. The upper part of the mixture enters the partition tower. The composite extractant mixes with diesel in the first chamber and extracts the aromatic components from the diesel, which then flow to the bottom of the partition tower. The first raffinate oil, which is rich in non-aromatics, flows out from the top of the first chamber. The back-extraction solvent enters the partition tower from the lower part of the second chamber and mixes with the composite extractant used to extract aromatics in the lower part of the partition tower to back-extract the aromatics. The back-extraction solvent, which is rich in aromatics, flows out from the top of the second chamber and enters the solvent recovery tower to separate the back-extraction solvent and aromatics. The composite extractant is discharged from the bottom of the partition tower.

[0027] The composite extraction solvent comprises an organic solvent and an ionic liquid, with the ionic liquid accounting for 5% to 95% of the weight of the composite extraction solvent. The organic solvent is one or more of morpholine, N-methylmorpholine, dimethylformamide, and furfural. The ionic liquid cation is one or more of imidazole cations and pyridine cations. The ionic liquid anion is one or more of tetrafluoroborate anion, hexafluorophosphate anion, and bis(trifluoromethanesulfonate)imine anion. The back-extraction solvent is one or more of C4-C10 alkanes and cycloalkanes.

[0028] The method for separating aromatics from diesel fuel according to the present invention uses an organic solvent that is one or more of morpholine, N-methylmorpholine, and furfural.

[0029] In the method for separating aromatics from diesel fuel described in this invention, all or part of the composite extraction solvent discharged from the bottom of the partition column is returned to the partition column for recycling.

[0030] In the method for separating aromatics from diesel fuel described in this invention, all or part of the back-extraction solvent separated by the solvent recovery tower is returned to the adjacent tower for recycling.

[0031] In the method for separating aromatics from diesel fuel according to the present invention, the area ratio of the first chamber side to the second chamber side of the partition tower is 3:7 to 7:3.

[0032] The method for separating aromatics from diesel fuel according to the present invention includes one or more condensers and reboilers in the partition wall tower and / or solvent recovery tower.

[0033] The method for separating aromatics from diesel fuel according to the present invention includes a condenser at the top of the partition column and / or solvent recovery column, and a reboiler at the bottom of the column.

[0034] The method for separating aromatics from diesel fuel according to the present invention includes one or more condensers installed between the partition wall tower and / or the solvent recovery tower; and a reboiler installed between the partition wall tower and / or the solvent recovery tower.

[0035] The method for separating aromatics from diesel fuel according to the present invention uses a composite extractant to diesel fuel mass ratio of 0.5-6 and a composite extractant to back-extractant mass ratio of 0.01-2.

[0036] The method for separating aromatics from diesel fuel according to the present invention has the following characteristics: the partition wall column has a theoretical plate number of 20-150, an operating pressure of 0.05-2 MPa, a top temperature of 20-120°C, and a bottom temperature of 45-200°C; the solvent recovery column has a theoretical plate number of 5-40, an operating pressure of 10 kPa-0.1 MPa, a top temperature of 20-120°C, and a bottom temperature of 40-150°C. Preferred ranges are: the partition wall column has a theoretical plate number of 70-150, an operating pressure of 0.1-1 MPa, a top temperature of 40-90°C, and a bottom temperature of 80-180°C; the solvent recovery column has a theoretical plate number of 20-40, an operating pressure of 10 kPa-0.08 MPa, a top temperature of 40-100°C, and a bottom temperature of 60-150°C.

[0037] The method for separating aromatics from diesel fuel according to the present invention is one or more of atmospheric and vacuum diesel fuel, catalytic cracked diesel fuel, hydrocracking diesel fuel, and coking diesel fuel.

[0038] The beneficial effects of this invention are:

[0039] This invention features a simple, short, and energy-efficient process, enabling the high-value utilization of diesel fractions. It separates aromatics and non-aromatics from diesel fuel while reducing the number of distillation columns and other equipment required, providing high-quality feedstock for downstream high-value utilization and reducing energy consumption and investment. Attached Figure Description

[0040] Figure 1 This is a schematic diagram of the process flow for separating aromatics from diesel fuel according to the present invention.

[0041] In the attached figures, the following labels are used:

[0042] 1 Diesel fuel; 2 Fresh compound extraction solvent; 3 Recovered compound extraction solvent; 4 First raffinate; 5 Separator; 6 Divider tower; 7 Second raffinate; 8 Solvent recovery tower; 9 Recovered back-extraction solvent; 10 Aromatics; 11 Fresh back-extraction solvent. Detailed Implementation

[0043] The present invention will now be described in detail through embodiments. It should be noted that the following embodiments are only for further illustration of the present invention and should not be construed as limiting the scope of protection of the present invention. Those skilled in the art can make some non-essential improvements and adjustments to the present invention based on the above description.

[0044] The process of this invention is simple, and the specific process flow is as follows: Figure 1 The invention mainly comprises a partition tower 6 and a solvent recovery tower 8. The partition tower 6 of this invention achieves the separation of aromatic hydrocarbon fractions, non-aromatic hydrocarbon fractions, and composite extraction solvents in diesel fuel; the solvent recovery tower 8 achieves the separation of the back-extraction solvent from aromatic hydrocarbons. Ultimately, this achieves efficient utilization of aromatic hydrocarbon and non-aromatic hydrocarbon fractions in diesel fuel. See again. Figure 1 The partition tower 6 is equipped with a partition plate 5, which radially divides the partition tower 6 into a first chamber and a second chamber. The top of the partition plate 5 is connected to the top of the partition tower 6, so that the first chamber and the second chamber are not connected at the top of the partition tower 6. A gap is left between the bottom of the partition plate 5 and the bottom of the partition tower 6, so that the first chamber and the second chamber are connected at the bottom of the partition tower 6. The device of the present invention also includes corresponding auxiliary equipment such as pumps and heat exchangers. Since the auxiliary equipment such as pumps and heat exchangers do not have a substantial impact on the invention, they are not mentioned in the present invention.

[0045] Diesel fuel 1 from outside the boundary enters from the middle of the first chamber of the adjacent tower 6. Fresh composite extraction solvent 2 from outside the boundary enters from the upper part of the first chamber. The composite extractant mixes with the diesel fuel in the first chamber and extracts the aromatic components from the diesel fuel, flowing to the bottom of the adjacent tower 6. The first raffinate oil 4, rich in non-aromatic hydrocarbons, flows out from the top of the tower on the side of the first chamber. Fresh back-extraction solvent 11 enters from the bottom of the second chamber on the side of the adjacent tower 6. It mixes with the composite extractant used to extract aromatic hydrocarbons in the lower part of the adjacent tower 6 to back-extract the aromatic hydrocarbons. The back-extraction solvent rich in aromatic hydrocarbons, as the second raffinate oil 7, flows out from the top of the second chamber and enters the solvent recovery tower 8. The back-extraction solvent 9 is separated from the top of the tower, and aromatic hydrocarbons 10 are separated from the bottom of the tower. The composite extraction solvent 3 flows out from the bottom of the adjacent tower 6. The recovered composite extraction solvent 3 is divided into two parts. One part is mixed with the fresh composite extraction solvent 2 and returned to the adjacent tower 6 for recycling, and the other part exits the unit. The recovered back-extraction solvent 9 is divided into two parts. One part is mixed with the fresh back-extraction solvent 11 and returned to the adjacent tower 6 for recycling, and the other part exits the unit.

[0046] Condensers and reboilers may also be installed in the partition tower 6 and solvent recovery tower 8. Depending on actual needs, one or more condensers may be installed, and they may be installed at the top or middle of the partition tower 6 and solvent recovery tower 8; reboilers may be installed at the bottom or middle of the partition tower 6 and solvent recovery tower 8.

[0047] Diesel fractions mainly consist of aromatic hydrocarbons containing monocyclic, bicyclic, and polycyclic aromatic hydrocarbons, as well as non-aromatic hydrocarbons containing alkanes and cycloalkanes. They primarily originate from atmospheric and vacuum distillation diesel, catalytic cracking diesel, hydrocracking diesel, and coking diesel, but are not limited to these sources. Typical compositions of atmospheric and vacuum distillation diesel and catalytic cracking diesel are shown in Tables 1 and 2.

[0048] Table 1. Typical composition of straight-run diesel fuel

[0049]

[0050] Table 2 Typical Composition of Catalytic Cracking Diesel

[0051]

[0052] The table above is intended to illustrate the components contained in diesel fuel. The content of these components is highly dependent on their source, but this does not affect the applicability of the invention.

[0053] Example 1

[0054] The raw materials used are those listed in Table 1. The feed pressure is 0.3 MPa, and the feed temperature is 35°C. The operating conditions for the partition wall tower are: 20 theoretical plates, 0.1 MPa top pressure, 20°C top temperature, 45°C bottom temperature, and a 4:6 ratio of the first to second chamber area. The operating conditions for the solvent recovery tower are: 5 theoretical plates, 10 kPa top pressure, 82°C top temperature, and 105°C bottom temperature. In this embodiment, the composite extractant is dimethylformamide (DMF) containing 5% ionic liquid, wherein the ionic liquid cation is 1-methyl-3-ethylimidazolium (MEIM+), and the anion is tetrafluoroborate (BF4-1). The back-extraction solvent is cyclohexane. The mass ratio of the composite extractant to diesel oil is 0.5, and the mass ratio of the composite extractant to the back-extraction agent is 0.5. The aromatic hydrocarbon mass fraction in the second raffinate is 88%, and the non-aromatic hydrocarbon mass fraction in the first raffinate is 85%.

[0055] Example 2

[0056] The raw materials used are those listed in Table 2. The feed pressure is 0.3 MPa, and the feed temperature is 40°C. The operating conditions for the partition wall tower are: 150 theoretical plates, 0.1 MPa top pressure, 40°C top temperature, 150°C bottom temperature, and an area ratio of 4:6 between the first and second chambers. The operating conditions for the solvent recovery tower are: 40 theoretical plates, 10 kPa top pressure, 82°C top temperature, and 110°C bottom temperature. In this embodiment, the composite extractant is dimethylformamide (DMF) containing 10% ionic liquid, where the ionic liquid cation is 1-heptyl-3-methylimidazolium (C7MIM+) and the anion is hexafluorophosphate (PF6-). The back-extraction solvent is n-heptane. The mass ratio of the composite extractant to diesel oil is 2, and the mass ratio of the composite extractant to the back-extraction agent is 1.5. The aromatic hydrocarbon mass fraction in the second raffinate is 90%, and the non-aromatic hydrocarbon mass fraction in the first raffinate is 92%.

[0057] Example 3

[0058] The raw materials used are those listed in Table 1. The feed pressure is 0.5 MPa, and the feed temperature is 60°C. The operating conditions for the partition wall tower are: 100 theoretical plates, 0.05 MPa top pressure, 50°C top temperature, 80°C bottom temperature, and a 5:5 area ratio between the first and second chambers. The operating conditions for the solvent recovery tower are: 20 theoretical plates, 20 kPa top pressure, 100°C top temperature, and 140°C bottom temperature. In this embodiment, the composite extractant is dimethylformamide (DMF) containing 50% ionic liquid, where the ionic liquid cation is 1-methyl-3-ethylimidazolium (MEIM+) and the anion is tetrafluoroborate (BF4-1). The back-extractant is n-hexane. The mass ratio of the composite extractant to diesel oil is 4, and the mass ratio of the composite extractant to back-extractant is 2. The aromatic hydrocarbon content in the second raffinate is above 90%, and the non-aromatic hydrocarbon content in the first raffinate is 90%.

[0059] Example 4

[0060] The raw materials used are those listed in Table 2. The feed pressure is 0.5 MPa, and the feed temperature is 60°C. The operating conditions for the partition wall tower are: 40 theoretical plates, 0.2 MPa top pressure, 50°C top temperature, 80°C bottom temperature, and a 5:5 area ratio between the first and second chambers. The operating conditions for the solvent recovery tower are: 30 theoretical plates, 20 kPa top pressure, 100°C top temperature, and 150°C bottom temperature. In this embodiment, the composite extractant is an N-methylmorpholine solution containing 70% ionic liquid, wherein the ionic liquid cation is 1,3-dimethylpyridine (MMPY+), and the anion is tetrafluoroborate (BF4-1). The back-extractant is cyclohexane. The mass ratio of the composite extractant to diesel oil is 6, and the mass ratio of the composite extractant to the back-extractant is 1. The aromatic hydrocarbon mass fraction in the second raffinate is 86%, and the non-aromatic hydrocarbon mass fraction in the first raffinate is 87%.

[0061] Example 5

[0062] The raw materials used are those listed in Table 1. The feed pressure is 0.5 MPa, and the feed temperature is 60°C. The operating conditions for the partition wall tower are: 100 theoretical plates, 1 MPa top pressure, 50°C top temperature, 100°C bottom temperature, and a 5:5 area ratio between the first and second chambers. The operating conditions for the solvent recovery tower are: 25 theoretical plates, 80 kPa top pressure, 82°C top temperature, and 110°C bottom temperature. In this embodiment, the composite extractant is a morpholine solution containing 90% ionic liquid, wherein the ionic liquid cation is 1-heptyl-3-methylpyridine (C7MPY+), and the anion is bis(trifluoromethanesulfonate)imine. The back-extractant is cyclohexane. The mass ratio of the composite extractant to diesel oil is 4, and the mass ratio of the composite extractant to back-extractant is 2. The aromatic hydrocarbon mass fraction in the second raffinate is 90%, and the non-aromatic hydrocarbon mass fraction in the first raffinate is 92%.

[0063] Example 6

[0064] The raw materials used are those listed in Table 1. The feed pressure is 1 MPa, and the feed temperature is 50°C. The operating conditions for the partition wall tower are: 120 theoretical plates, 0.2 MPa top pressure, 20°C top temperature, 70°C bottom temperature, and an area ratio of 3:7 between the first and second chambers. The operating conditions for the solvent recovery tower are: 10 theoretical plates, 10 kPa top pressure, 93°C top temperature, and 140°C bottom temperature. In this embodiment, the composite extractant is a furfural solution containing 10% ionic liquid, wherein the ionic liquid cation is 1-methyl-3-ethylimidazolium (MEIM+), and the anion is tetrafluoroborate (BF4-1). The back-extraction solvent is cyclohexane. The mass ratio of the composite extractant to diesel oil is 3, and the mass ratio of the composite extractant to the back-extraction agent is 2. The aromatic hydrocarbon mass fraction in the second raffinate is 90%, and the non-aromatic hydrocarbon mass fraction in the first raffinate is 91%.

[0065] Example 7

[0066] The raw materials used are those listed in Table 2. The feed pressure is 1 MPa, and the feed temperature is 70°C. The operating conditions for the partition wall tower are: 50 theoretical plates, 1 MPa top pressure, 40°C top temperature, 80°C bottom temperature, and an area ratio of 7:3 between the first and second chambers. The operating conditions for the solvent recovery tower are: 35 theoretical plates, 50 kPa top pressure, 64°C top temperature, and 100°C bottom temperature. In this embodiment, the composite extractant is dimethylformamide (DMF) containing 20% ​​ionic liquid, wherein the ionic liquid cation is 1-heptyl-3-methylimidazolium (C7MIM+), and the anion is hexafluorophosphate (PF6-). The back-extraction solvent is n-heptane. The mass ratio of the composite extractant to diesel oil is 1.3, and the mass ratio of the composite extractant to the back-extraction agent is 0.08. The aromatic hydrocarbon mass fraction in the second raffinate is 87%, and the non-aromatic hydrocarbon mass fraction in the first raffinate is 85%.

[0067] Example 8

[0068] The raw materials are as shown in Table 1. The feed pressure is 0.5 MPa and the feed temperature is 50°C. The operating conditions of the partition tower are: 140 theoretical plates, 0.2 MPa top pressure, 20°C top temperature, and 70°C bottom temperature. The area ratio of the first chamber side to the second chamber side of the partition tower (6) is 6:4. The operating conditions of the solvent recovery tower are: 40 theoretical plates, 0.1 MPa top pressure, 71°C top temperature, and 110°C bottom temperature. In this embodiment, the composite extractant is: dimethylformamide (DMF) containing 10% ionic liquid, wherein the ionic liquid cation is 1-heptyl-3-methylimidazolium (C7MIM+), the anion is hexafluorophosphate (PF6-), and the back-extraction solvent is n-heptane. The mass ratio of the composite extractant to diesel is 1, and the mass ratio of the composite extractant to the back-extraction agent is 0.5. The aromatic mass fraction in the second raffinate is 86%, and the non-aromatic mass fraction in the first raffinate is 85%.

[0069] Example 9

[0070] The raw materials are as shown in Table 1. The feed pressure is 0.5 MPa and the feed temperature is 50°C. The operating conditions of the partition tower are: 140 theoretical plates, 0.2 MPa top pressure, 55°C top temperature, 150°C bottom temperature, and the area ratio of the first chamber side to the second chamber side of the partition tower (6) is 6:4. The operating conditions of the solvent recovery tower are: 40 theoretical plates, 0.07 MPa top pressure, 71°C top temperature, and 110°C bottom temperature. In this embodiment, the composite extractant is a furfural solution containing 30% ionic liquid, wherein the ionic liquid cation is 1-heptyl-3-methylimidazolium (C7MIM+), the anion is hexafluorophosphate (PF6-), and the back-extraction solvent is n-heptane. The mass ratio of the composite extractant to diesel is 0.5, and the mass ratio of the composite extractant to the back-extraction agent is 0.5. The aromatic mass fraction in the second raffinate is 91%, and the non-aromatic mass fraction in the first raffinate is 93%.

[0071] Comparative Example 1

[0072] The raw materials are as shown in Table 1. The feed pressure is 0.5 MPa and the feed temperature is 50°C. The operating conditions of the partition tower are: 40 theoretical plates, 0.01 MPa top pressure, 35°C top temperature, 100°C bottom temperature, and the area ratio of the first chamber side to the second chamber side of the partition tower (6) is 6:4. The operating conditions of the solvent recovery tower are: 40 theoretical plates, 0.1 MPa top pressure, 71°C top temperature, and 110°C bottom temperature. In this embodiment, the extractant is dimethylformamide without ionic liquid, and the back-extraction solvent is n-butane. The mass ratio of extractant to diesel is 0.1, and the mass ratio of extractant to back-extraction agent is 8. The aromatic hydrocarbon mass fraction in the second raffinate is 70%, and the non-aromatic hydrocarbon mass fraction in the first raffinate is 80%.

[0073] Of course, the present invention may have other various embodiments. Without departing from the spirit and essence of the present invention, those skilled in the art can make various corresponding changes and modifications according to the present invention, but these corresponding changes and modifications should all fall within the protection scope of the claims of the present invention.

Claims

1. A method for separating aromatics from diesel fuel, characterized in that, Separation is performed using a partition tower and a solvent recovery tower. The partition tower is radially divided into a first chamber and a second chamber by a partition plate. The top of the partition plate is connected to the top of the partition tower, so that the first chamber and the second chamber are not connected at the top of the partition tower. A gap is left between the bottom of the partition plate and the bottom of the partition tower, so that the first chamber and the second chamber are connected at the bottom of the partition tower. Diesel fuel enters the partition tower from the middle of the first chamber. The composite extractant enters the partition tower from the upper part of the first chamber. The composite extractant mixes with the diesel fuel in the first chamber and extracts the aromatic components from the diesel fuel, which flow into the bottom of the partition tower. The first raffinate oil, which is rich in non-aromatic hydrocarbons, flows out from the top of the tower on the side of the first chamber. The back-extractant enters the partition tower from the lower part of the second chamber and mixes with the composite extractant that extracts aromatic hydrocarbons in the lower part of the partition tower to back-extract the aromatic hydrocarbons. The back-extractant rich in aromatic hydrocarbons flows out from the top of the second chamber and enters the solvent recovery tower for separation of the back-extractant and aromatic hydrocarbons. The composite extractant is discharged from the bottom of the partition tower. The composite extractant comprises an organic solvent and an ionic liquid, with the ionic liquid accounting for 5% to 95% of the weight of the composite extractant. The organic solvent is one or more of morpholine, N-methylmorpholine, dimethylformamide, and furfural. The ionic liquid cation is an imidazole cation and / or a pyridine cation, and the ionic liquid anion is one or more of tetrafluoroborate anion, hexafluorophosphate anion, and bis(trifluoromethanesulfonate)imine anion. The back-extraction agent is one or more of C4-C10 alkanes and cycloalkanes. The theoretical plate number of the adjacent column is 20-150, the operating pressure is 0.05-2 MPa, the top temperature is 20-120℃, and the bottom temperature is 30-200℃; the theoretical plate number of the solvent recovery column is 5-40, the operating pressure is 10 kPa-0.1 MPa, the top temperature is 20-120℃, and the bottom temperature is 25-150℃.

2. The method for separating aromatics from diesel fuel according to claim 1, characterized in that, The organic solvent is one or more of morpholine, N-methylmorpholine and furfural.

3. The method for separating aromatics from diesel fuel according to claim 1, characterized in that, All or part of the compound extractant discharged from the bottom of the adjacent tower is returned to the adjacent tower for recycling.

4. The method for separating aromatics from diesel fuel according to claim 1, characterized in that, All or part of the back-extraction agent separated from the solvent recovery tower is returned to the adjacent tower for recycling.

5. The method for separating aromatics from diesel fuel according to claim 1, characterized in that, The area ratio of the first chamber side to the second chamber side of the adjacent tower is 3:7 to 7:

3.

6. The method for separating aromatics from diesel fuel according to claim 1, characterized in that, A reboiler and one or more condensers are provided in the partition column and / or solvent recovery column.

7. The method for separating aromatics from diesel fuel according to claim 6, characterized in that, The top of the adjacent column and / or solvent recovery column is equipped with one or more condensers, and the bottom of the column is equipped with a reboiler.

8. The method for separating aromatics from diesel fuel according to claim 6, characterized in that, One or more condensers are provided between the partition tower and / or the solvent recovery tower; a reboiler is provided between the partition tower and / or the solvent recovery tower.

9. The method for separating aromatics from diesel fuel according to claim 1, characterized in that, The mass ratio of the compound extractant to diesel oil is 0.5-6, and the mass ratio of the compound extractant to the back-extractant is 0.01-2.

10. The method for separating aromatics from diesel fuel according to claim 1, characterized in that, The theoretical plate number of the adjacent column is 50-150, the operating pressure is 0.1-1 MPa, the top temperature is 30-100℃, and the bottom temperature is 50-180℃; the theoretical plate number of the solvent recovery column is 20-40, the operating pressure is 10 kPa-0.08 MPa, the top temperature is 30-120℃, and the bottom temperature is 50-150℃.

11. The method for separating aromatics from diesel fuel according to claim 1, characterized in that, Diesel fuel is one or more of atmospheric and vacuum diesel fuel, catalytic cracking diesel fuel, hydrocracking diesel fuel, and coking diesel fuel.

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