A process for the extraction of nitrogen-containing aromatic hydrocarbons from coal tar

Abstract

The present application belongs to the technical field of coal chemical industry, and discloses a method for extracting nitrogen-containing aromatic hydrocarbons from coal tar, which comprises the following steps: S1, mixing, stirring and layering coal tar, a non-polar solvent and a liquid eutectic solvent to obtain a polar phase rich in nitrogen-containing aromatic hydrocarbons and a non-polar phase containing denitrogenated oil; the liquid eutectic solvent comprises a hydrogen bond donor and a hydrogen bond acceptor; S2, adding a back-extraction agent to the polar phase, stirring and layering to obtain a back-extraction phase rich in nitrogen-containing aromatic hydrocarbons and a liquid eutectic solvent phase, and distilling the back-extraction phase to obtain nitrogen-containing aromatic hydrocarbons and a back-extraction agent. The present application is simple in operation, environmentally friendly and strong in recycling, enriches coal tar products and improves the added value of coal tar.

Description

Technical Field

[0001] This invention belongs to the field of coal chemical technology, specifically relating to a method for extracting nitrogen-containing aromatic hydrocarbons from coal tar. Background Technology

[0002] Coal tar is rich in various nitrogen-containing aromatic hydrocarbons, such as quinoline, carbazole, acridine, and indole, which have a wide range of applications in pesticides, pharmaceuticals, and important chemical intermediates, making it a high-value-added product. If coal tar is directly used to produce fuel oil through hydrogenation, the presence of nitrogen-containing aromatic hydrocarbons increases hydrogen consumption and wastes these high-value-added nitrogen-containing products. Therefore, a separation-then-conversion approach can be adopted to utilize coal tar, separating and utilizing different substances to maximize atom utilization and ensure complete extraction.

[0003] Currently, acid washing is used industrially to remove basic nitrogen-containing aromatic hydrocarbons, achieving a high extraction rate. However, this process uses large amounts of acid and alkali reagents, which not only corrodes equipment but also generates significant amounts of oily wastewater, resulting in excessively high environmental treatment costs. For non-basic nitrogen-containing aromatic hydrocarbons, solvent crystallization is often used to obtain high-purity hydrocarbons, but the throughput is often small and the process is complex. Patent CN117736768A utilizes three-stage extraction to obtain quinoline and indole monomers from coal tar wash oil fractions, but the overall process is complex and some extractants cannot be recycled. Patent CN113354570B uses a eutectic solvent to extract carbazole from anthracene oil, achieving an extraction rate of over 90%. However, the extraction rate for quinoline is only 44.68%, failing to simultaneously remove both basic and non-basic nitrogen-containing aromatic hydrocarbons. Patent CN116023980A utilizes polar and non-polar solvents to perform multiple reverse extractions on nitrogen-containing heavy oil to remove nitrogen-containing compounds. However, the purpose of this process is to ensure a high yield of denitrified oil, and it does not involve the extraction rate of nitrogen-containing aromatics. Summary of the Invention

[0004] The purpose of this invention is to provide a method for extracting nitrogen-containing aromatics from coal tar, so as to solve the problem that the existing technology cannot simultaneously and efficiently remove alkaline and non-alkaline nitrogen-containing aromatics from coal tar.

[0005] To achieve the above objectives, the present invention provides an extraction method for extracting nitrogen-containing aromatic hydrocarbons from coal tar, comprising the following steps:

[0006] S1, coal tar, a nonpolar solvent, and a eutectic solvent are mixed, stirred, and allowed to stand to separate into layers, resulting in a polar phase rich in nitrogen-containing aromatics and a nonpolar phase containing denitrified oil; the eutectic solvent contains hydrogen bond donors and hydrogen bond acceptors;

[0007] S2, add back-extraction agent to the polar phase, stir and let stand to obtain a back-extraction phase rich in nitrogen-containing aromatics and a eutectic solvent phase. Distill the back-extraction phase to obtain nitrogen-containing aromatics and back-extraction agent.

[0008] This invention adds a non-polar solvent and a eutectic solvent to coal tar. The addition of the non-polar solvent can effectively enhance the mass transfer between the coal tar and the eutectic solvent.

[0009] The present invention discloses an extraction method for extracting nitrogen-containing aromatics from coal tar, wherein the hydrogen bond acceptor contains both a hydrogen bond acceptor group and a hydrogen bond donor group. The hydrogen bond donor forms hydrogen bonds with the hydrogen bond acceptor group through hydrogen bonds, promoting the formation of a eutectic solvent. During this formation process, the properties of the hydrogen bond donor group on the hydrogen bond acceptor are enhanced due to the shielding effect of the hydrogen bond acceptor site. The addition of a nonpolar solvent not only fully dissolves the coal tar but also reduces its density, which is beneficial for mass transfer during the extraction process. Furthermore, the enhanced hydrogen bond donor in the eutectic solvent allows for selective hydrogen bond formation with nitrogen atoms on the nitrogen-containing aromatics in the coal tar, thereby completing the extraction process.

[0010] The present invention discloses an extraction method for extracting nitrogen-containing aromatic hydrocarbons from coal tar, wherein the hydrogen bond donor comprises one or more of amide compounds, alkanolamine compounds, and thiourea compounds, and the hydrogen bond acceptor comprises one or more of alcohols, organic acids, phenols, and imidazoles; the molar ratio of the hydrogen bond donor to the hydrogen bond acceptor is 0.1:1 to 1:1.

[0011] The present invention discloses an extraction method for extracting nitrogen-containing aromatic hydrocarbons from coal tar, wherein the nonpolar solvent comprises one or more of alkanes, aromatic hydrocarbons, and cycloalkanes; and the back-extraction agent comprises one or more of alkanes, cycloalkanes, and esters.

[0012] The extraction method for extracting nitrogen-containing aromatics from coal tar according to the present invention includes an eutectic solvent added in an amount of 1 to 5 times the mass of coal tar, and a non-polar solvent added in an amount of 0.3 to 5 times the mass of coal tar.

[0013] In the extraction method for extracting nitrogen-containing aromatics from coal tar of the present invention, in step S1, a non-polar solvent is first added to the coal tar and mixed evenly, and then a eutectic solvent is added. After adding the eutectic solvent, the mixture is stirred at 20~50℃ for 30~50 min.

[0014] In the extraction method for extracting nitrogen-containing aromatics from coal tar of the present invention, the amount of back-extraction agent added in step S2 is 5 to 10 times the mass of the eutectic solvent, the stirring temperature is 15 to 40°C, and the stirring time is 20 to 60 min.

[0015] The extraction method for extracting nitrogen-containing aromatics from coal tar of the present invention, wherein in step S2, the temperature of the back-extraction phase distillation is 50~100℃, the pressure is 100~500mbar, and the time is 30~60min.

[0016] The extraction method for extracting nitrogen-containing aromatics from coal tar according to the present invention further includes: distilling a nonpolar phase containing denitrified oil to obtain a nonpolar solvent and denitrified coal tar, wherein the distillation temperature is 50~200℃, the pressure is 100~500mbar, and the time is 30~60min.

[0017] The present invention relates to an extraction method for extracting nitrogen-containing aromatic hydrocarbons from coal tar, wherein the coal tar is a full-fraction coal tar oil or a coal tar distillate oil, and the coal tar distillate oil includes one or more of phenolic oil, naphthalene oil, wash oil, and anthracene oil.

[0018] Beneficial effects of this invention:

[0019] This invention achieves the extraction of nitrogen-containing aromatic hydrocarbons from coal tar through a combination of eutectic and non-polar solvents. By adjusting the types of hydrogen bond donors and acceptors, the hydrogen bond donor properties of the eutectic solvent are enhanced, thereby directly acting on the nitrogen atoms of nitrogen-containing aromatic hydrocarbons to achieve selective extraction. A solvent recycling process is also established to reduce the cost of coal tar processing. Through the process route and eutectic solvent preparation of this invention, the high-value utilization of coal tar can be achieved, improving the comprehensive utilization efficiency of coal tar. This invention is simple to operate, environmentally friendly, and highly recyclable, enriching coal tar products and increasing the added value of coal tar. Attached Figure Description

[0020] Figure 1 This is a process flow diagram of the extraction method for extracting nitrogen-containing aromatic hydrocarbons from coal tar according to the present invention. Detailed Implementation

[0021] 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.

[0022] Example 1

[0023] Weigh 9.0g of 1-methylnaphthalene, 0.5g of quinoline, and 0.5g of carbazole and add them to a beaker to prepare a model oil with a quinoline and carbazole mass fraction of 5.0%. Weigh 10.0g of n-heptane and add it to the beaker containing the model oil, and stir for 30 minutes.

[0024] Weigh 8.1g of formamide and 1.9g of methanol (molar ratio of formamide to methanol is 3:1) and place them in a sample bottle. Stir at room temperature for 30 minutes to form a eutectic solvent.

[0025] The eutectic solvent was added to the model oil mixed with the nonpolar solvent. The mixture was stirred at room temperature for 30 minutes, allowed to stand, and allowed to separate into layers. The upper nonpolar phase (i.e., the nonpolar phase containing denitrogenated oil) and the lower eutectic solvent phase A (i.e., the polar phase rich in nitrogen-containing aromatics) were separately taken out and weighed. Their composition was determined using GC-MS. The extraction rate of quinoline (mass of quinoline in eutectic solvent phase A / mass of quinoline in the model oil) was 99.9%, the extraction rate of carbazole (mass of carbazole in eutectic solvent phase A / mass of carbazole in the model oil) was 65.9%, and the entrainment rate of 1-methylnaphthalene (mass of 1-methylnaphthalene in eutectic solvent phase A / mass of 1-methylnaphthalene in the model oil) was 3.5%.

[0026] 100.0 g of back-extraction agent (n-octane) was added to the eutectic solvent phase A, stirred at room temperature for 60 min, and allowed to stand to separate into layers, resulting in eutectic solvent phase B and back-extraction phase rich in nitrogen-containing aromatics. The back-extraction phase was then distilled under reduced pressure at 80 °C and 200 mbar for 60 min to obtain recycled back-extraction agent and nitrogen-containing aromatics.

[0027] The nonpolar phase was distilled under reduced pressure at 150℃ and 300mbar for 60 min to obtain a recycled nonpolar solvent (n-heptane) and a denitrified model oil.

[0028] Example 2

[0029] This embodiment is basically the same as Example 1, except that: the hydrogen bond acceptor of the eutectic solvent is ethanolamine, and the preparation ratio is 8.5g ethanolamine and 1.5g methanol (the molar ratio of ethanolamine to methanol is 3:1). All other aspects are the same as in Example 1.

[0030] The extraction rates of quinoline were 98.9%, carbazole was 55.0%, and 1-methylnaphthalene was 6.0%.

[0031] Example 3

[0032] This embodiment is basically the same as Example 1, except that the non-polar solvent is n-decane, and everything else is the same as in Example 1.

[0033] The extraction rate of quinoline was 100.0%, the extraction rate of carbazole was 58.7%, and the entrainment rate of 1-methylnaphthalene was 2.1%.

[0034] Example 4

[0035] This embodiment is basically the same as Example 1, except that: the hydrogen bond donor of the eutectic solvent is formic acid, and the preparation ratio is 7.5g formamide and 2.5g formic acid (the molar ratio of formamide to formic acid is 3:1). Everything else is the same as in Example 1.

[0036] The extraction rates of quinoline were 98.2%, carbazole was 40.5%, and 1-methylnaphthalene was 8.2%.

[0037] Example 5

[0038] Weigh 2.0g of full-fraction coal tar, 5.0g of decahydronaphthalene and 5.0g of n-heptane and add them to a beaker. Stir at room temperature for 30 minutes to form a homogeneous nonpolar phase mixed with coal tar.

[0039] Weigh 9.0g of formamide and 1.0g of formic acid (molar ratio of formamide to formic acid is 9:1) and place them in a sample bottle. Stir at room temperature for 30 minutes to form a eutectic solvent.

[0040] The eutectic solvent was added to the nonpolar phase mixed with coal tar, stirred at 35°C for 30 min, and allowed to stand to separate into layers. The upper nonpolar phase and the lower eutectic solvent phase A were taken out and weighed. The extraction rates of quinoline (mass of quinoline in eutectic solvent phase A / mass of quinoline in the whole coal tar fraction) were 100.0%, carbazole (mass of carbazole in eutectic solvent phase A / mass of carbazole in the whole coal tar fraction) were 50.0%, acridine (mass of acridine in eutectic solvent phase A / mass of acridine in the whole coal tar fraction) were 100.0%, indole (mass of indole in eutectic solvent phase A / mass of indole in the whole coal tar fraction) were 70%, and pyridine (mass of pyridine in eutectic solvent phase A / mass of pyridine in the whole coal tar fraction) were 100.0%.

[0041] 100.0 g of back-extraction (n-decane) was added to the eutectic solvent phase A, stirred at room temperature for 60 min, and allowed to stand to separate into layers, yielding the eutectic solvent phase B and the back-extraction phase rich in nitrogen-containing aromatics. The back-extraction phase was then distilled under reduced pressure at 80 °C and 200 mbar for 60 min to obtain the recycled back-extraction agent and nitrogen-containing aromatics.

[0042] The nonpolar phase was distilled under reduced pressure at 150 °C and 300 mbar for 60 min to obtain a recycled nonpolar solvent (decahydronaphthalene and n-heptane) and denitrified coal tar.

[0043] Example 6

[0044] The difference between this embodiment and Example 5 is that the ratio of the eutectic solvent is 8.0g of formamide and 2.0g of formic acid (the ratio of formamide to formic acid is 4:1), while the rest is the same as in Example 5.

[0045] The extraction rates of quinoline were 100.0%, carbazole was 62.3%, acridine was 100.0%, indole was 76.1%, and pyridine was 100.0%.

[0046] Example 7

[0047] This embodiment is basically the same as embodiment 5, except that: the eutectic solvent donor is methanol, and the preparation ratio is 9.0g formamide and 0.7g methanol (the molar ratio of formamide to methanol is 9:1). All other aspects are the same as in embodiment 5.

[0048] The extraction rates were 93.2% for quinoline, 56.3% for carbazole, 98.2% for acridine, 71.1% for indole, and 89.5% for pyridine.

[0049] Example 8

[0050] Weigh 2.0g of anthracene oil, 5.0g of decahydronaphthalene and 5.0g of n-octane and add them to a beaker. Stir at room temperature for 30 minutes to form a homogeneous nonpolar phase mixed with anthracene oil.

[0051] Weigh 5.0g of formamide and 5.0g of formic acid (molar ratio of formamide to formic acid is 1:1) and place them in a sample bottle. Stir at room temperature for 30 minutes to form a eutectic solvent.

[0052] The eutectic solvent was added to the nonpolar phase mixed with anthracene oil, stirred at 35°C for 30 min, and allowed to stand to separate into layers. The upper nonpolar phase and the lower eutectic solvent phase A were then removed and weighed. The extraction rate of quinoline (mass of quinoline in eutectic solvent phase A / mass of quinoline in anthracene oil) was 100.0%, and the extraction rate of carbazole (mass of carbazole in eutectic solvent phase A / mass of carbazole in anthracene oil) was 74.2%.

[0053] 100.0 g of back-extraction (n-nonane) was added to the eutectic solvent phase A, stirred at room temperature for 60 min, and allowed to stand to separate into layers, yielding the eutectic solvent phase B and the back-extraction phase rich in nitrogen-containing aromatics. The back-extraction phase was then distilled under reduced pressure at 80 °C and 200 mbar for 60 min to obtain the recycled back-extraction agent and nitrogen-containing aromatics.

[0054] The nonpolar phase was distilled under reduced pressure at 150 °C and 300 mbar for 60 min to obtain a recycled nonpolar solvent (decahydronaphthalene and n-octane) and denitrogenated anthracene oil.

[0055] Example 9

[0056] Weigh 2.0g of naphthalene oil, 5.0g of decahydronaphthalene and 5.0g of n-octane and add them to a beaker. Stir at room temperature for 30 minutes to form a homogeneous nonpolar phase mixed with naphthalene oil.

[0057] Weigh 5.0g of formamide and 5.0g of formic acid (molar ratio of formamide to formic acid is 1:1) and place them in a sample bottle. Stir at room temperature for 30 minutes to form a eutectic solvent.

[0058] The eutectic solvent was added to the nonpolar phase mixed with naphthalene oil, stirred at 35°C for 30 min, and allowed to stand to separate into layers. The upper nonpolar phase and the lower eutectic solvent phase A were then taken out and weighed. The extraction rate of quinoline (mass of quinoline in eutectic solvent phase A / mass of quinoline in naphthalene oil) was 100.0%, and the extraction rate of indole (mass of indole in eutectic solvent phase A / mass of indole in naphthalene oil) was 89.9%.

[0059] 100.0 g of back-extraction (n-decane) was added to the eutectic solvent phase A, stirred at room temperature for 60 min, and allowed to stand to separate into layers, yielding the eutectic solvent phase B and the back-extraction phase rich in nitrogen-containing aromatics. The back-extraction phase was then distilled under reduced pressure at 80 °C and 200 mbar for 60 min to obtain the recycled back-extraction agent and nitrogen-containing aromatics.

[0060] The nonpolar phase was distilled under reduced pressure at 150 °C and 300 mbar for 60 min to obtain a recycled nonpolar solvent (decahydronaphthalene and n-octane) and denitrogenated naphthalene oil.

[0061] Example 10

[0062] This embodiment is basically the same as Example 8, except that the eutectic solvent donor is methanol, and the preparation ratio is 9.0g formamide and 0.7g methanol (the molar ratio of formamide to methanol is 9:1). All other aspects are the same as in Example 8.

[0063] The extraction rate of quinoline was 99.5%, and the extraction rate of carbazole was 73.8%.

[0064] Example 11

[0065] This comparative example is basically the same as Example 8, except that thiourea is used instead of formamide, the amount of thiourea is 9.3g, and the amount of formic acid is 0.6g (the molar ratio of thiourea to formic acid is 9:1).

[0066] The extraction rate of quinoline was 99.8%, and the extraction rate of carbazole was 71.2%.

[0067] Example 12

[0068] This comparative example is basically the same as Example 8, except that m-cresol is used instead of formic acid. The amount of m-cresol is 2.1g and the amount of formamide is 7.9g (the molar ratio of formamide to m-cresol is 9:1).

[0069] The extraction rate of quinoline was 99.1%, and the extraction rate of carbazole was 70.0%.

[0070] Example 13

[0071] This comparative example is basically the same as Example 8, except that imidazole is used instead of formic acid. The amount of imidazole is 1.4g and the amount of formamide is 8.5g (the molar ratio of formamide to imidazole is 9:1).

[0072] The extraction rate of quinoline was 99.7%, and the extraction rate of carbazole was 78.1%.

[0073] Example 14

[0074] This embodiment is basically the same as Example 9, except that the non-polar solvent is tetrahydronaphthalene, and everything else is the same as in Example 9.

[0075] Extraction process: The extraction rate of quinoline was 100.0%, and the extraction rate of indole was 92.1%.

[0076] Example 15

[0077] The difference between this embodiment and Example 9 is that the hydrogen bond donor of the eutectic solvent is ethanol, and the preparation ratio is 5.0g formamide and 5.1g ethanol (the molar ratio of formamide to ethanol is 1:1). All other aspects are the same as in Example 9.

[0078] Extraction process: The extraction rate of quinoline was 80.5%, and the extraction rate of indole was 73.1%.

[0079] Comparative Example 1

[0080] This comparative example is basically the same as Example 8, except that choline chloride is used instead of formamide, the amount of choline chloride is 9.6g, and the amount of formic acid is 0.35g (the molar ratio of choline chloride to formic acid is 9:1).

[0081] The extraction rate of quinoline was 75.4%, and the extraction rate of carbazole was 38.7%.

[0082] Comparative Example 2

[0083] This comparative example is basically the same as Example 8, except that decahydronaphthalene and n-octane are not added to the anthracene oil.

[0084] The extraction rate of quinoline was 85.7%, and the extraction rate of carbazole was 33.6%.

[0085] Example 16

[0086] This embodiment examines the effects of the amount of eutectic solvent added, the amount of non-polar solvent added, and the extraction temperature on the extraction effect.

[0087] Weigh 27.0g of 1-methylnaphthalene, 1.5g of quinoline, and 1.5g of carbazole and add them to a beaker to prepare a model oil with a mass fraction of 5% quinoline and carbazole.

[0088] Formamide and formic acid (molar ratio of formamide to formic acid 1:1) were placed in an Erlenmeyer flask and stirred at room temperature for 30 minutes to form a eutectic solvent.

[0089] Weigh out a certain amount of n-heptane, which is the non-polar extractant.

[0090] (1) The effect of the amount of eutectic solvent added on the extraction effect was investigated. The range of eutectic solvent was 10.0 ~ 30.0 g.

[0091] Different amounts of polar eutectic solvent and 10.0 g of nonpolar extractant were added to 10.0 g of model oil. The mixture was stirred at 25 °C for 50 min, allowed to stand and separate into layers, and the upper nonpolar phase and lower polar phase were taken out separately. The masses of the polar and nonpolar phases were weighed, and their compositions were determined by GC-MS. The results are shown in Table 1.

[0092] Table 1. Effect of the amount of eutectic solvent of different polarities on the extraction effect.

[0093] (2) The effect of the amount of non-polar solvent added on the extraction effect was investigated. The range of non-polar extractant was 10.0 ~ 30.0 g.

[0094] 20.0 g of eutectic solvent and different amounts of nonpolar extractant were added to 10.0 g of model oil. The mixture was stirred at 25 °C for 50 min, allowed to stand and separate into layers, and the upper nonpolar phase and lower polar phase were taken out separately. The masses of the polar and nonpolar phases were weighed, and their compositions were determined by GC-MS. The results are shown in Table 2.

[0095] Table 2. Effect of different amounts of nonpolar solvent added on extraction efficiency.

[0096] (3) Investigate the effect of extraction temperature on the two-phase solvent extraction process. The temperature range is 25 ~ 50℃.

[0097] 20.0 g of eutectic solvent and 25.0 g of nonpolar extractant were added to the model oil. The mixture was stirred for 50 min at different temperatures, allowed to stand and separate into layers, and the upper nonpolar phase and lower polar phase were taken out separately. The masses of the nonpolar phase and polar phase were weighed separately, and their compositions were determined by GC-MS. The results are shown in Table 3.

[0098] Table 3. Effect of different extraction temperatures on the two-phase solvent extraction process

[0099] 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 extracting nitrogen-containing aromatic hydrocarbons from coal tar, characterized in that, Includes the following steps: S1, coal tar, a nonpolar solvent, and a eutectic solvent are mixed, stirred, and allowed to stand to separate into layers, resulting in a polar phase rich in nitrogen-containing aromatics and a nonpolar phase containing denitrified oil; the eutectic solvent contains hydrogen bond donors and hydrogen bond acceptors; S2, add back-extraction agent to polar phase, stir and let stand to obtain back-extraction phase rich in nitrogen-containing aromatic hydrocarbons and eutectic solvent phase. Distill back-extraction phase to obtain nitrogen-containing aromatic hydrocarbons and back-extraction agent. The hydrogen bond acceptor comprises one or more of amide compounds, alkanolamine compounds, and thiourea compounds, and the hydrogen bond donor comprises one or more of alcohols, organic acids, phenols, and imidazoles; The nonpolar solvent comprises one or more of alkanes, aromatics, and cycloalkanes.

2. The method for extracting nitrogen-containing aromatics from coal tar according to claim 1, characterized in that, The hydrogen bond acceptor contains both a hydrogen bond acceptor group and a hydrogen bond donor group.

3. The method for extracting nitrogen-containing aromatics from coal tar according to claim 1, characterized in that, The molar ratio of the hydrogen bond donor to the hydrogen bond acceptor is 0.1:1 to 1:

1.

4. The method for extracting nitrogen-containing aromatics from coal tar according to claim 1, characterized in that, The back-extraction agent comprises one or more of alkanes, cycloalkanes, and esters.

5. The method for extracting nitrogen-containing aromatics from coal tar according to claim 1, characterized in that, The amount of the eutectic solvent added is 1 to 5 times the mass of the coal tar, and the amount of the non-polar solvent added is 0.3 to 5 times the mass of the coal tar.

6. The method for extracting nitrogen-containing aromatics from coal tar according to claim 1, characterized in that, In step S1, a non-polar solvent is first added to the coal tar and mixed evenly. Then, a eutectic solvent is added. After adding the eutectic solvent, the mixture is stirred at 20-50°C for 30-50 minutes.

7. The method for extracting nitrogen-containing aromatics from coal tar according to claim 1, characterized in that, In step S2, the amount of back-extraction agent added is 5 to 10 times the mass of the eutectic solvent, the stirring temperature is 15 to 40°C, and the stirring time is 20 to 60 minutes.

8. The method for extracting nitrogen-containing aromatics from coal tar according to claim 1, characterized in that, In step S2, the temperature during back-extraction phase distillation is 50~100℃, the pressure is 100~500mbar, and the time is 30~60min.

9. The method for extracting nitrogen-containing aromatics from coal tar according to claim 1, characterized in that, Also includes: The nonpolar phase containing denitrified oil is distilled to obtain a nonpolar solvent and denitrified coal tar. The distillation temperature is 50~200℃, the pressure is 100~500mbar, and the time is 30~60min.

10. The method for extracting nitrogen-containing aromatics from coal tar according to claim 1, characterized in that, The coal tar is a full-fraction coal tar oil or a coal tar distillate oil, and the coal tar distillate oil includes one or more of phenol oil, naphthalene oil, wash oil and anthracene oil.

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