A method for separating aromatics in a diesel fraction by liquid-liquid separation and a system for separating aromatics

Abstract

The method provided by the application uses one of N, N-dialkyl pyrrolidone and N, N-dialkoxy pyrrolidone as an extraction solvent, the boiling point of the extraction solvent is much higher than that of diesel oil fraction, the extraction solvent is easy to be directly rectified and separated, and the extraction solvent has great polarity and strong solubility to aromatic hydrocarbons, can be applied to various diesel oil fractions, can extract almost all aromatic hydrocarbon components from the diesel oil fraction to extract oil, and improves the recovery rate of aromatic hydrocarbons; the extract oil is washed with water, so that the aromatic hydrocarbon phase and the water washing extraction phase are separated, the extract and the solvent are more easily separated, the energy consumption and solvent loss are reduced, and the efficiency of aromatic hydrocarbon separation is improved; the water washing extraction phase is subjected to vacuum rectification, and the extraction solvent is recovered and reused.

Description

Technical Field

[0001] This invention relates to the field of diesel fraction separation technology, and in particular to a method and system for liquid-liquid separation of aromatics from diesel fractions. Background Technology

[0002] As one of the most important petroleum products, diesel fuel has faced increasingly stringent requirements regarding its aromatic content and cetane number in recent years. Currently, straight-run diesel accounts for approximately 60% of the diesel fuel in Chinese refineries, catalytic cracking (FCC) diesel accounts for approximately 30%, and the remainder is coking and other types of diesel. FCC diesel is a typical low-quality diesel fraction characterized by high aromatic content and low cetane number, with aromatic content reaching as high as 80%. Naphthalene compounds are the most abundant aromatic components in catalytic cracking diesel. This high aromatic content not only lowers the CN value of FCC diesel but also causes environmental pollution. Therefore, reducing aromatic content is a necessary measure to improve the quality of catalytic cracking diesel. Furthermore, aromatics have a wide range of applications worldwide and are crucial basic raw materials for the chemical industry, representing important organic compounds.

[0003] Diesel fuel aromatics extraction technology mainly includes liquid-liquid extraction and extractive distillation. Liquid-liquid extraction utilizes the different solubilities and relative volatility of different hydrocarbon components in the extraction solvent to separate relatively pure aromatics from a hydrocarbon mixture. Also known as solvent extraction, it is a widely used industrial technology. Industrialized aromatics extractive distillation processes are mainly based on the UDEX process using glycol solvents, the IFP process based on dimethyl sulfoxide, the Sulfolane process based on sulfolane, and the SAE process. Liquid-liquid extraction technology has advantages such as simple operating conditions and large throughput, and has been widely used in industry. For example, CN1408689A discloses a method for recovering aromatic components from hydrocarbon mixtures using extraction and extractive distillation. This method mainly involves pre-fractionating diesel fuel, sending the toluene fraction obtained from the fractionation to a liquid-liquid extraction tower, and then separating the solvent and aromatics through a series of extractive distillations and vacuum distillation. This technology is mainly suitable for raw material mixtures containing 60%–99% aromatics and is not applicable to all types of diesel fuel.

[0004] The most crucial aspect of diesel fuel extraction technology is the selection of the extraction solvent. Commonly used solvents include glycols, sulfolane, N-formylmorpholine, N-methylpyrrolidone, ionic liquids, and compound solvents. For example, CN102021024A discloses a system and method for preparing high-quality diesel fuel. This method uses sulfolane, N-methylpyrrolidone, or dimethyl sulfoxide as the extraction solvent, which separates aromatics from the diesel fuel, significantly increasing the cetane number and lowering the pour point. To improve the solubility and selectivity of aromatics, existing technologies have developed composite solvents for separating aromatic components from hydrocarbon mixtures. For instance, CN103160310A discloses a composite solvent and extraction method for extracting and separating aromatics from hydrocarbon mixtures in oil refining and chemical industries. The composite solvent is prepared by uniformly mixing a main solvent, a co-solvent, and a modifier, which significantly increases the solvent's solubility and selectivity for aromatics, thereby improving the aromatics recovery rate. CN104945327A discloses an extraction solvent for separating aromatics and alkanes from diesel fractions, using an ionic liquid as the extraction solvent. The ionic liquid has an alkyl-substituted imidazole or pyridine cation and an anion of BF4. - or PF6 - .

[0005] While these common extraction solvents can separate some aromatics from diesel fractions to a certain extent, they also have their own problems. For example, organic solvents such as sulfolane and N-formylmorpholine have low boiling points, making it difficult to separate the solvent from the heavy aromatic components, which is not easy to recover and consumes too much energy. Ionic liquids are easy to separate, but they cause a lot of pollution, are difficult to recycle and reuse, and are not easy to industrialize. Summary of the Invention

[0006] In view of this, the present invention provides a method for liquid-liquid separation of aromatics in diesel fractions, which achieves efficient separation of aromatics in diesel fractions, improves the recovery rate of aromatics, and uses an extraction solvent with a high boiling point, which is easy to separate from the aromatic components. It also realizes the recycling of the extraction solvent.

[0007] This invention provides a method for liquid-liquid separation of aromatics from diesel fractions, comprising the following steps:

[0008] Diesel fractions are mixed with extraction solvents, and after standing, raffinate oil and extracted oil are obtained respectively. The extraction solvent is one of N,N-dialkyl(oxy)pyrrolidone, and the boiling point of the extraction solvent is higher than that of the diesel fraction, with a boiling point greater than 380°C.

[0009] The extracted oil is subjected to multi-stage water washing to obtain aromatic oil and water-washed extract phase, wherein the number of multi-stage water washing is at least 3 stages;

[0010] The water-washed extract phase was subjected to vacuum distillation to recover the extraction solvent;

[0011] The structure of the N,N-dialkyl(oxy)pyrrolidone is shown in Formula I:

[0012]

[0013] R is an alkylene group, and n ≥ 0.

[0014] Preferably, the alkyl group in the N,N-dialkylpyrrolidone is a C5-C10 alkyl group, and the number of carbon atoms of the alkoxy group in the N,N-dialkoxypyrrolidone is 1-10.

[0015] Preferably, the extraction solvent is N,N-di-n-hexylpyrrolidone and / or N,N-di-3,6-dioxooctylpyrrolidone.

[0016] Preferably, the volume ratio of the extraction solvent to the diesel fraction is 0.5-10:1; the mixing temperature is 30-70℃, the mixing time is 1-5h, and the settling time is 1-8h.

[0017] Preferably, during the multi-stage water washing, the volume ratio of water to extracted oil is 0.3-1.5:1, and the washing temperature is 30-70℃.

[0018] Preferably, the number of stages in the multi-stage washing is 4 or 5.

[0019] Preferably, the operating temperature of the vacuum distillation is 45-80℃; the pressure of the vacuum distillation is 10-20 kPa.

[0020] Preferably, the aromatics in the diesel fraction include straight-run diesel, catalytic diesel, or hydrotreated diesel, and the volume content of aromatics in the diesel fraction is 10-90%.

[0021] The present invention provides a system for liquid-liquid separation of aromatics, including a solvent extraction tower 10, wherein the solvent extraction tower 10 has an extraction solvent inlet and a non-aromatic oil outlet on the upper side wall, and a diesel fraction inlet and an extracted oil outlet on the bottom side wall.

[0022] A multi-stage water washing tower 11 is connected to the extracted oil outlet of the solvent extraction tower 10. The first water washing tower 11 has a water inlet above the side wall and an extracted oil inlet at the bottom of the side wall. The last water washing tower has an aromatic oil outlet above the side wall and a water washing extract phase outlet at the bottom of the side wall.

[0023] A vacuum distillation column 12 is connected to the water wash extract phase outlet of the multi-stage water washing column 11. The vacuum distillation column 12 has a water wash extract phase inlet in the middle of its side wall, a water outlet above its side wall, and a recovery extraction solvent outlet at the bottom of its side wall. The recovery extraction solvent outlet is connected to the extraction solvent inlet on the solvent extraction column.

[0024] The method provided by this invention uses one of N,N-dialkylpyrrolidone and N,N-dialkoxypyrrolidone as the extraction solvent. The boiling point of the extraction solvent is much higher than that of diesel fractions, making it easy to directly distill and separate. It also has high polarity and strong solubility for aromatics, making it applicable to various diesel fractions. It can extract almost all aromatic components from diesel fractions into the extract oil, improving the recovery rate of aromatics. The extract oil is then washed with water. Based on the polarity order of water ≥ extraction solvent > aromatics, the aromatic phase and the water-washed extract phase can be separated. The extract and solvent are more easily separated, reducing energy consumption and solvent loss, and improving the efficiency of aromatic separation. The water-washed extract phase is then subjected to vacuum distillation to recover the extraction solvent, which can be reused. Attached Figure Description

[0025] To more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0026] Figure 1 This is a schematic diagram of the system structure for liquid-liquid separation of diesel fractions according to an embodiment of the present invention;

[0027] Figure 1 In the diagram: 1 is the extraction solvent, 2 is the diesel fraction, 3 is the non-aromatic oil, 4 is the extracted oil, 5 is water, 6 is the high-aromatic oil, 7 is the water-washed extract phase, 8 is water, 9 is the recovered extraction solvent, 10 is the solvent extraction tower, 11 is the water washing tower, and 12 is the vacuum distillation tower.

[0028] Figure 2 The effect of the number of washing stages obtained in Example 8 of the present invention on the washing process;

[0029] Figure 3 The compound with the structure shown in Formula III prepared in the embodiments of the present invention 1 H NMR spectrum.

[0030] Figure 4 The compound with the structure shown in Formula II prepared in the embodiments of the present invention 1 H NMR spectrum. Detailed Implementation

[0031] This invention provides a method for liquid-liquid separation of aromatics from diesel fractions, comprising the following steps:

[0032] Diesel fractions are mixed with an extraction solvent, and after standing, non-aromatic oil and extracted oil are obtained respectively. The extraction solvent is one of N,N-dialkyl(oxy)pyrrolidone, and the boiling point of the extraction solvent is higher than that of the diesel fraction, with a boiling point greater than 380°C.

[0033] The extracted oil is subjected to multi-stage water washing to obtain aromatic oil and water-washed extract phase, wherein the number of multi-stage water washing is at least 3 stages;

[0034] The water-washed extract phase was subjected to vacuum distillation to recover the extraction solvent;

[0035] The structure of the N,N-dialkyl(oxy)pyrrolidone is shown in Formula I:

[0036]

[0037] R is an alkylene group, and n ≥ 0.

[0038] This invention does not impose any special restrictions on the type and source of the diesel fraction, and is applicable to all types of diesel fractions, such as straight-run diesel, catalytic diesel, or hydrotreated diesel.

[0039] In embodiments of the present invention, the aromatic hydrocarbons in the diesel fraction may include monocyclic aromatic hydrocarbons, bicyclic aromatic hydrocarbons, and tricyclic aromatic hydrocarbons; the volume content of aromatic hydrocarbons in the diesel fraction is preferably 10-90%. The boiling point of the diesel fraction is 180-380°C.

[0040] This invention involves mixing an extraction solvent with a diesel fraction, allowing the mixture to stand, and then obtaining extracted oil and non-aromatic oil, respectively. The main components of the extracted oil are aromatics and the extraction solvent.

[0041] In this invention, the extraction solvent is one of N,N-dialkylpyrrolidone and N,N-dialkoxypyrrolidone. In this invention, the alkyl group in the N,N-dialkylpyrrolidone is preferably a C5-C10 alkyl group, more preferably a C5-C8 alkyl group, and may specifically be n-pentyl, n-hexyl, n-heptyl, or n-octyl. In an embodiment of this invention, the extraction solvent may be N,N-di-n-hexylpyrrolidone, with the structure shown in Formula II:

[0042]

[0043] The boiling point of the N,N-di-n-hexylpyrrolidone is 430℃.

[0044] In this invention, the number of carbon atoms of the alkoxy group in the N,N-dialkoxypyrrolidone is preferably 1-10, more preferably N,N-di-dioxoethoxypyrrolidone, N,N-di-dioxobutoxypyrrolidone, N,N-di-dioxohexylpyrrolidone or N,N-di-3,6-dioxooctylpyrrolidone (abbreviated as NN in the examples, with the structure shown in Formula III);

[0045]

[0046] In this invention, the boiling point of N,N-di-3,6-dioxooctylpyrrolidone is 450°C.

[0047] In this invention, the preparation method of the N,N-dialkyl(oxy)pyrrolidone is carried out under normal pressure and includes the following steps:

[0048] γ-Butyrolactone was preheated and then mixed with an alkyl(oxy)diamine for the first stage reaction to obtain an intermediate product, wherein the alkyl(oxy)diamine was NH2-(RO). n -R-NH2;

[0049] The intermediate product is heated to carry out a second-stage reaction to obtain N,N-dialkyl(oxy)pyrrolidone. During the second-stage reaction, water, a byproduct, is discharged.

[0050] The structure of the N,N-dialkyl(oxy)pyrrolidone is shown in Formula I:

[0051]

[0052] R is an alkylene group, and n ≥ 0.

[0053] The preparation method provided by this invention is carried out under normal pressure, does not require the use of a high-pressure reactor, has low equipment requirements, and can reduce production energy consumption and reduce costs.

[0054] This invention involves mixing γ-butyrolactone and alkyl(oxy)diamine for a first-stage reaction to obtain an intermediate product, wherein the alkyl(oxy)diamine is NH2-(RO). n -R-NH2. In this invention, the first stage reaction between the γ-butyrolactone and the alkyl(oxy)diamine is amination ring-opening to obtain an intermediate product; in this invention, the γ-butyrolactone is first preheated to a set temperature, and when the alkyl(oxy)diamine is added to the γ-butyrolactone that has reached the reaction temperature, the raw materials react rapidly to generate the intermediate product. In this invention, the structure of the intermediate product is shown in Formula IV:

[0055]

[0056] The route for the amination ring-opening reaction is as follows:

[0057]

[0058] In this invention, γ-butyrolactone is first preheated to the reaction temperature of the first stage reaction. The temperature of the first stage reaction is preferably 50-180℃, more preferably 80-180℃, and in the embodiments of this invention, it can be specifically 50, 60, 70, 80, 90, 100, 110, 120, 130, 140, 150, 160, 170 or 180℃.

[0059] After preheating the γ-butyrolactone to the reaction temperature of the first stage reaction, the present invention adds alkyl(oxy)diamine to the γ-butyrolactone preheated to the set temperature. The addition method is preferably dropwise addition. In the present invention, the dropwise addition rate is preferably 120 drops / min.

[0060] In this invention, the alkyl(oxy)diamine has the structure NH2-(RO). n -R-NH2, where R is an alkylene group, preferably a C1-C10 alkylene group, and in the embodiments of the present invention, it may specifically be methylene, ethylene, propylene, or butylene, etc. In the present invention, n≥0, preferably 0, 1, 2, 3, or 4.

[0061] In this invention, the molar ratio of γ-butyrolactone to alkyl(oxy)diamine is preferably (1-4):1, more preferably (2-3):1; in the embodiments of this invention, it can be specifically 1:1, 1.5:1, 2:1, 2.5:1, 3:1, 3.5:1 or 4:1.

[0062] In this invention, the time for the first stage of reaction begins when the alkyl(oxy)diamine is added, and the time for the first stage of reaction is preferably 2-30 min, more preferably 2-20 min; in the embodiments of this invention, it can be specifically 2, 5, 6, 10, 14, 15, 16, 20, 25 or 30 min.

[0063] After the first stage reaction yields an intermediate product, the present invention proceeds to a second stage reaction by heating the intermediate product to obtain N,N-dialkyl(oxy)pyrrolidone. In the second stage reaction, the intermediate product undergoes condensation and ring closure, generating a water byproduct. The present invention separates this water byproduct from the reaction system, promoting the forward reaction and increasing the yield of the target product. The route of the second stage reaction in the present invention is as follows:

[0064]

[0065] The heating temperature of the present invention (i.e., the reaction temperature of the second stage reaction) is preferably 200-300℃, more preferably 220-280℃; in the embodiments of the present invention, it can specifically be 200, 210, 220, 230, 240, 250, 260, 270 or 280℃. The reaction time of the second stage reaction is preferably 1-8h, more preferably 1-3h; in the embodiments of the present invention, it can specifically be 1, 1.5, 2, 2.5, 3, 3.5, 4, 4.5, 5, 5.5, 6, 6.5, 7, 7.5 or 8h.

[0066] After the second stage reaction, the present invention performs vacuum distillation on the obtained reaction mixture, collecting pure N,N-dialkyl(oxy)pyrrolidone at the bottom of the column and collecting γ-butyrolactone at the top for recycling. The present invention uses vacuum distillation on the completely reacted mixture to achieve high-purity collection of the target product, and γ-butyrolactone is separated at the top of the column for recycling. In the present invention, the temperature of the vacuum distillation is preferably 110-290℃, more preferably 120-250℃, and can also be 150-200℃; the pressure of the vacuum distillation is preferably 2-15 kPa, more preferably 6-10 kPa. In the present invention, the vacuum distillation is carried out in a distillation column, the number of trays of the distillation column is preferably 15-30, more preferably 20; the reflux ratio of the distillation column is 1:5-1:20, more preferably 1:15.

[0067] In this invention, the volume ratio of the extraction solvent to the diesel fraction is preferably 0.5-10:1, and in specific examples, it can be 0.5:1, 1:1, 2:1, 3:1, 4:1, 5:1, 6:1, 7:1, or 8:1; the extraction temperature is preferably 30-70℃, and in specific examples, it can be 30, 35, 40, 45, 50, 55, 60, 65, or 70℃; the mixing time is preferably 1-5 hours, and in specific examples, it can be 1, 1.5, 2, 2.5, 3, 3.5, 4, 4.5, or 5 hours. In this invention, the settling time is preferably 1-8 hours, and in specific examples, it can be 1, 1.5, 2, 2.5, 3, 3.5, 4, 4.5, 5, 5.5, 6, 6.5, 7, 7.5, or 8 hours.

[0068] After obtaining the extracted oil, the present invention performs multi-stage water washing on the extracted oil to obtain a high-aromatic phase and a water-washed extract phase, wherein the water-washed extract phase is the extraction solvent phase. In the present invention, the high-aromatic phase is a phase with an aromatic hydrocarbon volume content greater than 90%. The present invention separates the extraction solvent from the aromatic phase through multi-stage water washing. The number of stages of multi-stage water washing is at least 3, and in the embodiments, it can be specifically 3, 4, or 5 stages. In the embodiments of the present invention, when the number of water washing stages is 4, the content of the extraction solvent in the water-washed raffinate phase is almost 0%.

[0069] In this invention, during the multi-stage water washing, the water-to-oil volume ratio (the volume ratio of water to extracted oil) is preferably 0.5-5:1, and in the embodiments, it can be specifically 0.5:1, 1:1, 1.5:1, 2:1, 2.5:1, 3:1, or 3.5:1; the temperature of each stage of the multi-stage water washing is preferably 30-100℃, and in the embodiments, it can be specifically 30, 40, 50, 60, 70, 80, 90, or 100℃.

[0070] After obtaining the water-washed extract phase, the present invention performs vacuum distillation on the water-washed extract phase to recover the extraction solvent. In the present invention, the operating temperature of the vacuum distillation is preferably 45-80℃, more preferably 60-80℃, and in the embodiments it can be specifically 45, 50, 55, 60, 65, 70, 75 or 80℃; the pressure of the vacuum distillation is preferably 10-20 kP, more preferably 15-20 kP, and in the embodiments it can be specifically 10, 11, 12, 13, 14, 15, 16, 17, 18, 19 or 20 kP.

[0071] The present invention also provides a system for liquid-liquid separation of aromatics in diesel fractions, including a solvent extraction tower 10, wherein the solvent extraction tower 10 has an extraction solvent inlet and a non-aromatic oil outlet on the upper side wall, and a diesel fraction inlet and an extracted oil outlet on the lower side wall.

[0072] A multi-stage water washing tower 11 is connected to the extracted oil outlet of the solvent extraction tower 10. The first water washing tower 11 has a water inlet above the side wall and an extracted oil inlet at the bottom of the side wall. The last water washing tower has an aromatic oil outlet above the side wall and a water washing extract phase outlet at the bottom of the side wall.

[0073] A vacuum distillation column 12 is connected to the water wash extract phase outlet of the multi-stage water washing column 11. The vacuum distillation column 12 has a water wash extract phase inlet in the middle of its side wall, a water outlet above its side wall, and a recovery extraction solvent outlet at the bottom of its side wall. The recovery extraction solvent outlet is connected to the extraction solvent inlet on the solvent extraction column.

[0074] In this invention, diesel fraction is fed into solvent extraction tower 10 through diesel fraction inlet, and extraction solvent is fed into solvent extraction tower 10 through extraction solvent inlet to mix with diesel fraction. After standing, non-aromatic oil is taken out above solvent extraction tower 10 and extracted oil is taken out below solvent extraction tower 10.

[0075] The extracted oil is fed into a multi-stage water washing tower 11 through the extracted oil inlet. Water is introduced through the water inlet to perform multi-stage water washing on the extracted oil. Aromatic oil is collected above the final water washing tower and water-washed extract phase is obtained below.

[0076] The water-washed extract phase is fed into a vacuum distillation column 12 for vacuum distillation. Water is discharged above the vacuum distillation column 12 and the recovered extraction solvent is obtained below, which is then refluxed to the solvent extraction column 10.

[0077] The extraction is carried out in a solvent extraction tower 10. Diesel fraction 2 is fed into the solvent extraction tower 10 through the diesel fraction inlet, and then extraction solvent 1 is fed into the solvent extraction tower 10 through the extraction solvent inlet to mix with the diesel fraction. After settling, non-aromatic oil 3 is taken out from the top of the solvent extraction tower 10, and extracted oil 4 is taken out from the bottom of the solvent extraction tower 10. In this invention, the solvent extraction tower 10 is equipped with a stirring device for stirring the mixture of extraction solvent and diesel fraction to ensure uniform mixing.

[0078] The multi-stage water washing is carried out in the multi-stage water washing tower 12. The extracted oil 4 is sent into the first water washing tower through the extracted oil inlet located at the bottom. Water is introduced into the first water washing tower through the water inlet at the top. The multi-stage water washing is carried out in the multi-stage water washing tower in sequence. The water washing extract phase 7 is discharged from the bottom of the last water washing tower and the high aromatic oil 6 is discharged from the top.

[0079] The vacuum distillation is carried out in the vacuum distillation column 12. The water-washed extract phase 7 enters the vacuum distillation column 12 through the water-washed extract phase inlet located in the middle for vacuum distillation. Water is discharged above the vacuum distillation column 12 and the extraction solvent 9 is recovered and refluxed to the extraction solvent inlet of the solvent extraction column 10 below.

[0080] The embodiments of the present invention will now be described in detail with reference to the accompanying drawings.

[0081] It should be noted that, in the absence of conflict, the following embodiments and features can be combined with each other; and, based on the embodiments of this disclosure, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this disclosure.

[0082] It should be noted that various aspects of embodiments within the scope of the appended claims are described below. It will be apparent that the aspects described herein can be embodied in a wide variety of forms, and any particular structure and / or function described herein is merely illustrative. Based on this disclosure, those skilled in the art will understand that one aspect described herein can be implemented independently of any other aspect, and two or more of these aspects can be combined in various ways. For example, any number of aspects set forth herein can be used to implement the device and / or practice the method. Additionally, this device and / or method can be implemented using structures and / or functionalities other than one or more of the aspects set forth herein.

[0083] Example 1

[0084] 1,8-Diamino-3,6-dioxaoctane was added dropwise to preheated γ-butyrolactone, and the first stage of reaction was carried out at the first temperature. The molar ratio of γ-butyrolactone to 1,8-diamino-3,6-dioxaoctane was 2.5:1, the first temperature was 180℃, and the first stage of reaction time was 15 min, to obtain the intermediate product.

[0085] The intermediate product was heated to 280℃ and reacted for 6 hours to obtain the product liquid. During the reaction, the by-product water was cooled and discharged.

[0086] The product was subjected to vacuum distillation at a temperature of 150℃ and a pressure of 6kPa to obtain the target product.

[0087] The present invention performs structural identification on the obtained target product, and the results are as follows: Figure 3 As shown, by Figure 3 It can be seen that the target product has the structure shown in Formula III:

[0088]

[0089] In this embodiment, the yield of the target product is 86%, the purity is 99%, and the boiling point is 450°C.

[0090] Example 2

[0091] 1,6-hexanediamine was added dropwise to preheated γ-butyrolactone, and the first stage reaction was carried out at the first temperature. The molar ratio of γ-butyrolactone to 1,6-hexanediamine was 3:1, the first temperature was 180℃, and the first stage reaction time was 20 min, to obtain the intermediate product.

[0092] The intermediate product was heated to 260℃ and reacted for 8 hours to obtain the product liquid. During the reaction, the by-product water was cooled and discharged.

[0093] The product was subjected to vacuum distillation at a temperature of 140℃ and a pressure of 6kPa to obtain the target product.

[0094] The present invention performs structural identification on the obtained target product, and the results are as follows: Figure 4 As shown, by Figure 4 It can be seen that the target product has the structure shown in Formula II:

[0095]

[0096] In Examples 3-9, the extraction solvent NN was N,N-di-3,6-dioxooctylpyrrolidone, and the simulated oil was 1-methylnaphthalene (1-MN) and n-hexadecane in a volume ratio of 5:5.

[0097] Example 3

[0098] Simulated oil was first fed into the extraction tower at a solvent-to-oil volume ratio of 1:1, followed by the addition of solvent (NN) from the top of the tower. The mixing times for the solvent and oil were 1 h, 2 h, 3 h, 4 h, and 5 h, respectively, while maintaining the extraction temperature at 30 °C. After thorough mixing, the mixture was allowed to stand for 4 h. The lower extract phase (extracted oil) and the upper raffinate phase (non-aromatic oil) were then collected for qualitative and quantitative analysis of diesel fuel components. The results are shown in Table 1.

[0099] Table 1. Effect of mixing time on extraction efficiency of the oil-prepared agent obtained in Example 3.

[0100]

[0101] As can be seen from Table 1, the component distribution in the extract phase hardly changes with the increase of stirring time, so the stirring time has little effect on the extraction.

[0102] Example 4

[0103] Simulated oil was first fed into the extraction tower at a solvent-to-oil volume ratio of 1:1, followed by the introduction of solvent (NN) from the top of the tower. The extraction temperature was maintained at 30°C, and the mixture was stirred for 1 hour. The settling times were 1 hour, 2 hours, 3 hours, 4 hours, 5 hours, 6 hours, and 8 hours, respectively. The lower extract phase (extracted oil) and the upper raffinate phase (non-aromatic oil) were collected for qualitative and quantitative analysis of diesel components. The results are shown in Table 2.

[0104] Table 2 shows the effect of the settling time of the mixed oil and extractant obtained in Example 4 on the extraction effect.

[0105]

[0106] As can be seen from Table 2, after standing for 1 hour, the component distribution in the extract phase hardly changes with the increase of standing time. Therefore, the optimal standing time is 1 hour.

[0107] Example 5

[0108] Simulated oil was first fed into the extraction tower at solvent-to-oil volume ratios of 0.5:1, 1:1, 3:1, 4:1, and 5:1, respectively. Then, solvent (NN) was introduced from the top of the tower. The extraction temperature was maintained at 30°C, and the mixture was stirred for 1 hour and allowed to stand for 1 hour. The lower extract phase (extracted oil) and the upper raffinate phase (non-aromatic oil) were taken separately for qualitative and quantitative analysis of diesel components. The results are shown in Table 3.

[0109] Table 3. Effect of the agent-to-oil volume ratio obtained in Example 5 on the extraction effect.

[0110]

[0111]

[0112] Taking into account selectivity and distribution coefficient, Table 3 shows that as the agent-to-oil ratio increases, D... 1-MN The content of D and S shows an increasing trend. When the solvent-to-oil ratio is 4:1, further increasing the content of extraction solvent does not change the content of D and S, nor does it change the content of aromatics. Therefore, the optimal solvent-to-oil ratio is 4:1.

[0113] Example 6

[0114] Simulated oil was first fed into the extraction tower at a solvent-to-oil volume ratio of 4:1, and then solvent (NN) was introduced from the top of the tower. The extraction temperatures were 30℃, 50℃, and 70℃, respectively, and the mixture was stirred for 1 hour and then allowed to stand for 1 hour. The lower extract phase (extracted oil) and the upper raffinate phase (non-aromatic oil) were taken separately for qualitative and quantitative analysis of diesel components. The results are shown in Table 4.

[0115] Table 4 shows the effect of extraction temperature on extraction efficiency obtained in Example 6.

[0116]

[0117] As can be seen from Table 4, the extraction effect is not significantly affected by the increase of the extraction operation temperature. Therefore, the optimal extraction temperature is 30℃.

[0118] Example 7

[0119] The extract phase (extracted oil, heavy aromatics + extraction solvent) obtained in Example 6 was further fed into a water washing tower. The extract phase contained 5.4% 1-methylnaphthalene, 2.8% hexadecane, and 61.8% extraction solvent.

[0120] The oil was poured into a water washing tower at a water-to-oil volume ratio of 1:1. The water washing temperatures were 30℃, 50℃, 70℃, 80℃, 90℃, and 100℃, respectively. The mixture was stirred thoroughly for 1 hour and then allowed to stand for 1 hour. The raffinate phases (heavy aromatics phase) from the bottom and top were taken for qualitative and quantitative analysis of diesel components. The results are shown in Table 5.

[0121] Table 5 shows the effect of washing temperature on washing effect obtained in Example 7.

[0122]

[0123] As can be seen from Table 5, the washing effect is significantly improved with the increase of water washing temperature. When the water washing temperature reaches 80℃, further increasing the temperature does not significantly improve the washing effect. Therefore, the optimal water washing temperature is 80℃.

[0124] Example 8

[0125] The oil was washed with water at water ratios of 0.5:1, 1:1, 2:1, 3:1, 4:1, and 5:1, respectively, using the same extracted oil as in Example 7. The extraction temperature was maintained at 30°C, and the mixture was stirred thoroughly and allowed to stand for 1 hour. The raffinate phases (heavy aromatics phase) were taken from both the lower and upper parts of the sample for qualitative and quantitative analysis of diesel components. The results are shown in Table 6.

[0126] Table 6 shows the effect of the water-oil volume ratio obtained in Example 8 on the water washing effect.

[0127]

[0128]

[0129] As can be seen from Table 6, when the water-to-oil ratio is 3:1, further increasing the amount of water does not significantly change the washing effect. Therefore, the optimal water-to-oil ratio is 3:1.

[0130] Example 9

[0131] The same extracted oil as in Example 7 was used for water washing at a water-to-oil ratio of 3:1. The washing temperature was maintained at 30°C, and the mixture was stirred thoroughly for 1 hour, then allowed to stand for 1 hour. Water washing was performed using different back-extraction techniques (stage 1, stage 2, stage 3, stage 4, and stage 5). The upper and lower raffinate phases (heavy aromatics phase) were collected for qualitative and quantitative analysis of diesel components. After one water wash, the NN content of the extraction solvent was approximately 3 wt%. With further increases in the number of water washes, the NN content decreased; after two stages of water washing, the NN content was approximately 1.5 wt%, and after three stages, the NN content was approximately 0.5 wt%. Specific results are as follows: Figure 2 As shown.

[0132] Depend on Figure 2 It can be seen that as the number of extraction stages increases, the content of NN in the raffinate after water washing decreases. When the number of water washing stages reaches 4, the content of NN in the raffinate after water washing is almost 0%. Therefore, the optimal number of water washing stages is 4.

[0133] Example 10

[0134] Using N,N-di-3,6-dioxooctylpyrrolidone as the aromatic extraction solvent, actual diesel oil (crude oil A) was separated. Diesel oil mass spectrometry analysis showed that crude oil A contained 18.6% saturated hydrocarbons and 81.4% aromatic hydrocarbons.

[0135] At a volume ratio of 4:1, raw material oil A is first added to the extraction tower, and then the extraction solvent is added from the top of the tower. Under the condition of operating temperature of 30℃, the mixture is stirred for 1 hour and allowed to stand for 1 hour, and then extracted once.

[0136] The extracted oil from the bottom and the non-aromatic oil from the top were collected for qualitative and quantitative analysis of diesel components. The component analysis of the extracted oil and non-aromatic oil is shown in Table 7. The extracted oil contained 7.3% non-aromatics and 92.7% aromatics.

[0137] The extracted oil was washed with water at a volume ratio of 3:1 and a washing temperature of 70°C. After the number of water washing stages reached 4, the content of the extraction solvent in the water-washed raffinate was almost 0%.

[0138] The extract phase in the water washing tower is subjected to vacuum distillation at a distillation temperature of 80℃ and a distillation pressure of 15kP. The water and other impurities obtained from the top of the tower are separated out, and the recovered extraction solvent obtained from the bottom of the tower is recycled back into the extraction tower.

[0139] Table 7. Component analysis results of the extracted oil and raffinate obtained by solvent extraction in Example 10.

[0140]

[0141]

[0142] As shown in Table 7, using N,N-di-3,6-dioxooctylpyrrolidone as the extraction solvent can extract approximately 90% of the aromatic components from crude oil A, with total bicyclic aromatics accounting for about 64%. The saturated hydrocarbon content in the raffinate can reach as high as 80%, making it an excellent extraction solvent. After water washing, the aromatic content in the raffinate phase...

[0143] Example 11

[0144] Using N,N-di-3,6-dioxooctylpyrrolidone as the aromatic extraction solvent, actual diesel oil (crude oil B) was separated. Diesel oil mass spectrometry analysis showed that crude oil B contained 32% saturated hydrocarbons and 68% aromatic hydrocarbons.

[0145] At a volume ratio of 4:1, raw material oil B is first added to the extraction tower, and then the extraction solvent is added from the top of the tower. Under the condition of operating temperature of 30℃, the mixture is stirred for 1 hour and allowed to stand for 1 hour, and then extracted once.

[0146] The extracted oil from the bottom and the non-aromatic oil from the top were collected for qualitative and quantitative analysis of diesel components. The component analysis of the extracted oil and non-aromatic oil is shown in Table 8. The proportion of non-aromatics in the extract phase was 5.4%, and the proportion of aromatics was 94.6%.

[0147] The extracted oil was washed with water at a volume ratio of 3:1 and a washing temperature of 70°C. After the number of water washing stages reached 4, the content of the extraction solvent in the water-washed raffinate was almost 0%.

[0148] The extract phase in the water washing tower is subjected to vacuum distillation at a distillation temperature of 85℃ and a distillation pressure of 14kP. The water and other impurities obtained from the top of the tower are separated out, and the recovered extraction solvent obtained from the bottom of the tower is recycled back into the extraction tower.

[0149] Table 8. Component analysis results of the extracted oil and raffinate obtained by solvent extraction in Example 11.

[0150]

[0151]

[0152] Example 12

[0153] Using N,N-di-3,6-dioxooctylpyrrolidone as the aromatic extraction solvent, actual diesel oil (crude oil C) was separated. Diesel oil mass spectrometry analysis showed that crude oil B contained 57% saturated hydrocarbons and 43% aromatic hydrocarbons.

[0154] At a volume ratio of 4:1, raw material oil B is first added to the extraction tower, and then the extraction solvent is added from the top of the tower. Under the condition of operating temperature of 30℃, the mixture is stirred for 1 hour and allowed to stand for 1 hour, and then extracted once.

[0155] The extracted oil from the bottom and the non-aromatic oil from the top were collected for qualitative and quantitative analysis of diesel components. The component analysis of the extracted oil and non-aromatic oil is shown in Table 9. The proportion of non-aromatics in the extract phase was 7.6%, and the proportion of aromatics was 92.4%.

[0156] The extracted oil was washed with water at a volume ratio of 3:1 and a washing temperature of 70°C. After the number of water washing stages reached 4, the content of the extraction solvent in the water-washed raffinate was almost 0%.

[0157] The extract phase in the water washing tower is subjected to vacuum distillation at a distillation temperature of 80°C and a distillation pressure of 13 kPa. The water and other impurities obtained from the top of the tower are separated out, and the recovered extraction solvent obtained from the bottom of the tower is recycled back into the extraction tower.

[0158] Table 9. Component analysis results of the extracted oil and raffinate obtained by solvent extraction in Example 12.

[0159]

[0160]

[0161] As shown in Table 7-9, N,N-dialkoxypyrrolidone is an excellent diesel oil extraction solvent. Its ability to separate aromatics from non-aromatics remains almost unchanged as the aromatic content in crude oil increases. The aromatic content in the extracted oil can reach approximately 90%, while the non-aromatic content in the raffinate can reach approximately 80%. After four stages of water washing, the high-aromatic components are efficiently separated from the extract phase, yielding high-purity high-aromatic oil. The water-washed extract phase is then subjected to vacuum distillation. Compared to direct distillation to separate the extraction solvent and high-aromatic oil from the extracted oil, this method lowers the distillation temperature and effectively reduces energy consumption.

[0162] Example 13

[0163] Using N,N-di-n-hexylpyrrolidone as the aromatic extraction solvent, actual diesel oil (crude oil A) was separated.

[0164] At a volume ratio of 7:1, raw material oil A is first added to the extraction tower, and then the extraction solvent is added from the top of the tower. Under the condition of operating temperature of 60℃, the mixture is stirred for 1 hour and allowed to stand for 1 hour, and then extracted once.

[0165] The extracted oil from the bottom and the non-aromatic oil from the top were collected for qualitative and quantitative analysis of diesel components. The component analysis of the extracted oil and non-aromatic oil is shown in Table 10. The extracted oil contained 10.3% non-aromatics and 89.7% aromatics.

[0166] The extracted oil was washed with water at a volume ratio of 3:1 and a washing temperature of 70°C. After the number of water washing stages reached 4, the content of the extraction solvent in the water-washed raffinate was almost 0%.

[0167] The extract phase in the water washing tower is subjected to vacuum distillation at a distillation temperature of 80°C and a distillation pressure of 14 kPa. The water and other impurities obtained from the top of the tower are separated out, and the recovered extraction solvent obtained from the bottom of the tower is recycled back into the extraction tower.

[0168] Table 10. Component analysis results of the extracted oil and raffinate obtained by solvent extraction in Example 13.

[0169]

[0170]

[0171] As can be seen from Table 10, N,N-dialkylpyrrolidone is also an excellent aromatic extraction solvent, and the aromatics extracted from the oil can reach up to about 90%.

[0172] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1.A method for separating aromatic hydrocarbons in a diesel fraction by liquid-liquid separation, comprising the following steps: mixing a diesel fraction with an extraction solvent to obtain raffinate and extract after standing, wherein the extraction solvent is one of N, N-dialkyl pyrrolidone and N, N-dialkoxy pyrrolidone, the boiling point of the extraction solvent is higher than the boiling point of the diesel fraction, and the boiling point is greater than 380 ℃; performing multi-stage water washing on the extract to obtain aromatic hydrocarbon oil and water washing extraction phase, wherein the number of stages of the multi-stage water washing is at least 3; performing vacuum rectification on the water washing extraction phase to recover the extraction solvent; the structure of the N, N-dialkyl pyrrolidone or N, N-dialkoxy pyrrolidone is shown in formula I: R is an alkylene group, and n is greater than or equal to 0; the number of carbon atoms of R in the N, N-dialkyl pyrrolidone is 5-10, and the number of carbon atoms of R in the N, N-dialkoxy pyrrolidone is 1-10; the extraction solvent is N, N-dinormal hexyl pyrrolidone or N, N-dialkyl-3, 6-dioxaoctyl pyrrolidone; the volume ratio of the extraction solvent to the diesel fraction is 0.5-10:1; the mixing temperature is 30-70 ℃, the mixing time is 1-5 h, and the standing time is 1-8 h; the volume ratio of water to the extract in the multi-stage water washing is 0.5-5:1, and the water washing temperature is 30-100 ℃; the number of stages of the multi-stage water washing is 4 or 5; the operation temperature of the vacuum rectification is 45-80 ℃, and the pressure of the vacuum rectification is 10-20 kPa; the diesel fraction includes straight-run diesel, catalytic diesel or hydrogenated diesel, and the volume content of aromatic hydrocarbons in the diesel fraction is 10-90%. ​ ​ ​ ​ ； ​ 2. The method of claim 1, wherein, ​ 3. The method of claim 2, wherein, ​ 4. The method according to any one of claims 1 to 3, characterized in that, ​ 5. The method of claim 1, wherein, ​ 6. The method according to claim 1 or 5, characterized in that, ​ 7. The method of claim 1, wherein, ​ 8. The method of claim 1, wherein, ​

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