Method for extracting phenol compound and pyridine compound from naphthalene oil stepwise by using deep eutectic solvent

Abstract

The present application provides a method for extracting a phenol compound and a pyridine compound from naphthalene oil stepwise by using a deep eutectic solvent (DES). The method comprises: step 1, mixing a naphthalene oil with an alkane and a DES and performing liquid separation on the mixture to obtain a deep eutectic extraction phase and a solvent raffinate phase; step 2, mixing the deep eutectic extraction phase with a first back-extraction agent and filtering the mixture to obtain a first back-extraction phase and a recyclable DES; step 3, distilling the first back-extraction phase to obtain a heteroatom mixture, mixing the heteroatom mixture with a hydrogen-acceptor-type deep eutectic extraction agent and an alkane, and performing liquid separation on the mixture to obtain a deep eutectic phenol compound extraction phase and a pyridine compound and alkane raffinate phase; and step 4, mixing the phenol compound extraction phase with a second back-extraction agent and filtering the mixture to obtain a phenol-containing second back-extraction solution and a hydrogen-acceptor-type extraction agent. A phenol product is recovered from a second back-extraction agent solution by distillation. The DES is tetraethylammonium chloride, tetrabutylammonium chloride, tetrabutylammonium bromide or tetrabutylphosphonium bromide, and glycolic acid, oxalic acid, citric acid, or p-toluenesulfonic acid.

Description

A method for stepwise extraction of phenolic and pyridine compounds from naphthalene oil using eutectic solvents

[0001] This disclosure claims priority to Chinese Patent Application No. 202411178093.7, filed on August 26, 2024, entitled "A Method for Stepwise Extraction of Phenolic and Pyridine Compounds from Naphthalene Oil Using a Eutectic Solvent", the entire contents of which are incorporated herein by reference. Technical Field

[0002] This application relates to the field of separation of fine chemicals in coal chemical industry, specifically to a method for stepwise extraction of phenolic and pyridine compounds from naphthalene oil using a eutectic solvent. Background Technology

[0003] Coal tar and liquefied petroleum oil are important coal-based liquid chemical products. Through vacuum distillation, a series of mixed products of phenols and aromatics can be obtained. Industrial naphthalene oil is a significant source of phenols and pyridine compounds. Because phenolic hydroxyl groups are typically acidic, and there are Brønsted-Lowry interactions between phenolic hydroxyl groups and basic pyridine derivatives, as well as widespread π-π interactions between benzene rings, phenol, pyridine, and naphthalene derivatives are always enriched in the naphthalene oil fraction. Therefore, developing efficient and simple methods for separating phenol, pyridine derivatives, and mixtures of benzene and naphthalene is a major challenge in the value-added utilization of modern coal-based liquid fine chemicals.

[0004] Several mature industrial processes exist for separating mixtures of phenols and quinolines. In industrial naphthalene oil processing, the naphthalene oil fraction is first washed with strong acids such as sulfuric acid to obtain sulfates of quinoline-based alkaline substances. These sulfates are then refolded using dilute alkali. Next, the acid-washed naphthalene oil is neutralized with a strong alkali and washed with alkali to obtain sodium phenolate. Finally, the phenols are refolded using dilute acid. This method is cumbersome, and more importantly, it involves the repeated use of strong acids and alkalis, causing severe corrosion to equipment, has a complex process, high energy consumption, and is prone to polluting surrounding water bodies.

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[0008] Based on the above analysis, some techniques for separating phenols and pyridines from industrial naphthalene oil require harsh conditions and the acid-base extraction solvents cannot be recycled. Therefore, there is an urgent need to develop a simple, efficient, and easily recyclable method for separating phenols and pyridines from industrial naphthalene oil. Technical issues

[0009] The main objective of this application is to provide a method for stepwise extraction of phenolic and pyridine compounds from naphthalene oil using a eutectic solvent, in order to overcome the shortcomings of some separation methods that require the use of strong acids and alkalis, which cause severe corrosion to equipment, environmental pollution, and high energy consumption. Solution

[0010] To achieve the above objectives, this application provides a method for stepwise extraction of phenolic and pyridine compounds from naphthalene oil using a eutectic solvent, comprising the following steps:

[0011] Step 1: Mix naphthalene oil, alkanes and eutectic solvent, separate the liquids to obtain heteroatom eutectic phase and hydrocarbon raffinate phase;

[0012] Step 2: Mix the heteroatom eutectic phase with the first back-extractant, separate the phases to obtain the first back-extractant phase and the first back-extractant residue phase;

[0013] Step 3: Separate the heteroatom mixture in the first back-extraction phase from the first back-extraction agent. The heteroatom mixture, alkanes and hydrogen bond acceptor extractant are mixed and separated to obtain a phenolic eutectic phase and a pyridine raffinate phase.

[0014] Step 4: Mix the phenolic eutectic phase with the second back-extractant, separate the phases, and obtain the phenolic compound;

[0015] The eutectic solvent is a mixture of at least one of tetraethylammonium chloride, tetrabutylammonium chloride, tetrabutylammonium bromide, and tetrabutylphosphine bromide with at least one of glycolic acid, oxalic acid, citric acid, and p-toluenesulfonic acid; the hydrogen bond acceptor extractant is at least one of tetraethylammonium chloride, tetrabutylammonium chloride, tetrabutylammonium bromide, and tetrabutylphosphine bromide.

[0016] The method for stepwise extraction of phenolic and pyridine compounds from naphthalene oil using a eutectic solvent as described in this application further includes:

[0017] The hydrocarbon raffinate from step 1 is distilled to obtain alkanes, a mixture of benzene and naphthalene, and so on; the alkanes are recycled back to step 1 for reuse.

[0018] The method for stepwise extraction of phenolic and pyridine compounds from naphthalene oil using a eutectic solvent as described in this application, wherein the first back-extraction agent is selected from at least one of acetone, ethyl acetate, carbon disulfide, and tetrachloromethane; the first back-extraction residue is a eutectic solvent, which is recycled back to step 1 for reuse.

[0019] The method for stepwise extraction of phenolic and pyridine compounds from naphthalene oil using a eutectic solvent as described in this application, wherein the heteroatom mixture in the first back-extraction phase is separated from the first back-extraction agent by distillation, and the separated first back-extraction agent is recycled back to step 2 for reuse.

[0020] The method for stepwise extraction of phenolic and pyridine compounds from naphthalene oil using a eutectic solvent as described in this application, wherein the second back-extractant is selected from at least one of acetone, ethyl acetate, carbon disulfide, and tetrachloromethane; the mixture of the phenolic eutectic phase and the second back-extractant is subjected to phase separation to obtain phenolic compounds and a hydrogen bond acceptor extractant, and the hydrogen bond acceptor extractant obtained from the phase separation is recycled back to step 3 for reuse.

[0021] The method for stepwise extraction of phenolic and pyridine compounds from naphthalene oil using a eutectic solvent as described in this application, wherein the pyridine raffinate is separated by distillation to obtain pyridine compounds and alkanes, and the alkanes are recycled.

[0022] The method for stepwise extraction of phenolic and pyridine compounds from naphthalene oil using a eutectic solvent described in this application, wherein the alkanes in step 1 and step 3 are the same or different, and are independently selected from n-hexane and cyclohexane.

[0023] The method for stepwise extraction of phenolic and pyridine compounds from naphthalene oil using a eutectic solvent as described in this application, wherein in step 1, the mass ratio of the eutectic solvent to naphthalene oil is 0.2 to 2, the mixing temperature is 30°C to 50°C, and the mixing time is 60 min to 120 min.

[0024] The method for stepwise extraction of phenolic and pyridine compounds from naphthalene oil using a eutectic solvent as described in this application includes the following steps: In step 3, the mixing temperature is 30°C to 50°C; in step 2, the mass ratio of the first back-extractant to the heteroatom eutectic phase is 0.5 to 1, and the mixing time is 10 min to 30 min; in step 4, the mass ratio of the second back-extractant to the phenolic eutectic phase is 0.5 to 1, and the mixing time is 10 min to 30 min.

[0025] The method for stepwise extraction of phenolic and pyridine compounds from naphthalene oil using a eutectic solvent as described in this application, wherein the ratio of the amount of tetraethylammonium chloride, tetrabutylammonium chloride, tetrabutylammonium bromide, or tetrabutylphosphine bromide in the eutectic solvent to the amount of glycolic acid, oxalic acid, citric acid, or p-toluenesulfonic acid is 2:1 to 1:2. Beneficial effects

[0026] This application uses a eutectic solvent and a hydrogen bond acceptor extractant as the extractant, combined with back-extraction and distillation, to achieve highly selective separation of phenolic and pyridine compounds in naphthalene oil. The operation is simple and efficient, the extraction conditions are mild, the extractant can be recycled after drying, and the back-extraction agent and alkane solvent can be recycled through atmospheric distillation. Furthermore, the reagents used are non-corrosive to the equipment. Attached Figure Description

[0027] Figure 1 is a schematic diagram of a system for separating phenolic and pyridine compounds from naphthalene oil according to an embodiment of this application. Embodiments of the present invention

[0028] The technical solution of this application is described in detail below. The following embodiments are implemented based on the technical solution of this application and a detailed implementation process is given. However, the protection scope of this application is not limited to the following embodiments. Structures or experimental methods that do not specify specific conditions in the following embodiments are generally performed under conventional conditions.

[0029] This application provides a method for stepwise extraction of phenolic and pyridine compounds from naphthalene oil using a eutectic solvent, comprising the following steps:

[0030] Step 1: Mix naphthalene oil, alkanes and eutectic solvent, separate the liquids to obtain heteroatom eutectic phase and hydrocarbon raffinate phase;

[0031] Step 2: Mix the heteroatom eutectic phase with the first back-extractant, separate the phases to obtain the first back-extractant phase and the first back-extractant residue phase;

[0032] Step 3: Separate the heteroatom mixture in the first back-extraction phase from the first back-extraction agent. The heteroatom mixture, alkanes and hydrogen bond acceptor extractant are mixed and separated to obtain a phenolic eutectic phase and a pyridine raffinate phase.

[0033] Step 4: Mix the phenolic eutectic phase with the second back-extractant, separate the phases, and obtain the phenolic compound;

[0034] The eutectic solvent is a mixture of at least one of tetraethylammonium chloride, tetrabutylammonium chloride, tetrabutylammonium bromide, and tetrabutylphosphine bromide with at least one of glycolic acid, oxalic acid, citric acid, and p-toluenesulfonic acid; the hydrogen bond acceptor extractant is at least one of tetraethylammonium chloride, tetrabutylammonium chloride, tetrabutylammonium bromide, and tetrabutylphosphine bromide.

[0035] This application uses a eutectic solvent and a hydrogen bond acceptor extractant as the extractant, combined with back-extraction and distillation, to achieve highly selective separation of phenolic and pyridine compounds in naphthalene oil. The operation is simple and efficient, the extraction conditions are mild, the extractant can be recycled after drying, and the back-extraction agent and alkane solvent can be recycled through atmospheric distillation. Furthermore, the reagents used are non-corrosive to the equipment.

[0036] This application refers to naphthalene oil, specifically the naphthalene oil fraction of coal tar at atmospheric pressure and 210-230℃. Naphthalene oil is rich in phenols, pyridine compounds, and naphthalene derivatives. Its typical composition ratio is: phenols to pyridines by mass ratio of 2 or more, and naphthalene derivatives by mass exceeding 50%. In one embodiment, this application prepares model oil according to a phenol:pyridine:aromatic hydrocarbon mass ratio of 2:1:3. The composition of real naphthalene oil varies considerably; phenols are quantified after normalization by gas chromatography. Extraction and separation are then performed according to the ratios specified in this application. In this application, pyridine compounds refer to pyridine, quinoline, etc., and phenolic compounds refer to phenol, ethylphenol, etc.

[0037] In one embodiment, naphthalene oil is first mixed with alkanes to prepare a solution, and then the solution is mixed with a eutectic solvent for extraction. This application does not specifically limit the alkanes; they can be low-boiling-point alkanes, such as n-hexane or cyclohexane. In another embodiment, the concentration of naphthalene oil in the solution formed by naphthalene oil and alkanes is 180 g / kg to 360 g / kg. In yet another embodiment, the mass ratio of the eutectic solvent to naphthalene oil is 0.2 to 2. Stirring can be performed during the extraction process. The extraction temperature for mixing the above solution with the eutectic solvent can be 30°C to 50°C, and the extraction time can be 60 min to 120 min. After extraction, the mixture is allowed to stand for separation. This application does not specifically limit the separation method; separation can be performed by pouring or using a dropper to obtain a heteroatom eutectic phase and a hydrocarbon raffinate phase. The heteroatom eutectic phase mainly includes the eutectic solvent and heteroatom compounds, while the hydrocarbon raffinate phase mainly includes benzene, naphthalene compounds, and alkane solvents.

[0038] The hydrocarbon extract phase can be distilled to recover the alkane solvent, yielding a benzene and naphthalene mixture. The distillation method can be, for example, atmospheric distillation, but this application does not specify a particular method. The recovered alkane solvent can be recycled, and the benzene and naphthalene mixture can be exported as a product for use as feedstock in other processes.

[0039] The heteroatom eutectic phase is mixed with the first back-extractant and separated to obtain the first back-extractant phase and the first back-extractant residue phase.

[0040] In one embodiment, the first back-extractant is selected from acetone, ethyl acetate, carbon disulfide, tetrachloromethane, etc. In another embodiment, the mass ratio of the first back-extractant to the heteroatom eutectic phase is 0.5–1. The heteroatom eutectic phase is mixed with the first back-extractant for back-extraction. Stirring can be performed during mixing, the mixing temperature can be room temperature (20–30°C), and the mixing time can be 10–30 minutes. Then, phase separation is performed to obtain the first back-extracted phase and the first back-extract residue phase.

[0041] The first back-extraction residue mainly consists of a eutectic solvent, which can be recycled after drying. The first back-extraction phase mainly consists of a first extractant and a heteroatom compound. The first back-extraction phase can be distilled, for example, by atmospheric distillation, to separate the heteroatom mixture and the first back-extractant in the first back-extraction phase, respectively, to obtain heteroatom compounds and the first back-extractant in yields greater than 98%. The first back-extractant obtained by distillation can be recycled.

[0042] The heteroatom mixture, alkanes and hydrogen bond acceptor extractant were mixed and separated to obtain a phenolic eutectic phase and a pyridine raffinate phase.

[0043] In one embodiment, the heteroatom mixture is mixed with an alkane solvent to prepare a solution, which is then mixed with a hydrogen bond acceptor extractant for extraction. This application does not specifically limit the alkane solvent; it can be a low-boiling-point alkane, such as n-hexane or cyclohexane. In another embodiment, the mass ratio of the added alkane solvent to the heteroatom mixture is 1 to 5. In yet another embodiment, the molar ratio of the added hydrogen bond acceptor extractant to the phenol in the naphthalene oil is 0.5 to 1. Stirring can be performed during the mixing and extraction process, and the mixing and extraction temperature can be 30°C to 50°C, for example, 40°C or 50°C. After extraction, the mixture can be separated by pouring or dropper aspiration to obtain a phenolic eutectic phase and a pyridine raffinate phase. The phenolic eutectic phase mainly includes the hydrogen bond acceptor extractant and the target phenol, while the pyridine raffinate phase mainly includes pyridine compounds and an alkane solvent.

[0044] The pyridine raffinate can be distilled, for example, by atmospheric distillation, to obtain pyridine compounds with a purity greater than 99%. The alkane solvent obtained from distillation can be recycled.

[0045] The eutectic phase of phenols is mixed with a second back-extractant, and the phases are separated to obtain phenolic compounds.

[0046] In one embodiment, the second back-extractant may be the same as or different from the first back-extractant, and may be selected from acetone, ethyl acetate, carbon disulfide, tetrachloromethane, etc. In another embodiment, the mass ratio of the second back-extractant to the phenolic eutectic phase is 0.5–1. The phenolic eutectic phase is mixed with the second back-extractant for back-extraction. Stirring may be performed during mixing, the mixing temperature may be room temperature (20–30°C), and the mixing time may be 10–30 minutes. Then, phase separation is performed to obtain a second back-extractant phase containing phenolic compounds and a second stripping residue phase. The second back-extractant phase mainly comprises phenolic compounds and the second back-extractant, while the second stripping residue phase mainly comprises a hydrogen bond acceptor extractant.

[0047] The second back-extraction phase, after drying, yields a hydrogen bond acceptor extractant, which can be recycled. The second back-extraction phase, after distillation (e.g., atmospheric distillation), yields phenolic compounds with a purity greater than 90%, and the resulting second back-extraction agent can also be recycled.

[0048] Therefore, this application provides a method for extracting and separating phenolic and pyridine compounds from naphthalene oil, a typical coal-based liquid mixture. This method targets naphthalene oil fractions (210-230°C) rich in phenols, pyridines, and naphthalene derivatives. The extraction and separation process includes: dissolving naphthalene oil in an alkane solvent; using an acidic eutectic solvent as the extractant; completing liquid-liquid extraction by forming a two-phase mixture with the alkane solvent; and capturing heteroatom compounds in the naphthalene oil fraction by the acidic eutectic solvent. Then, heteroatom compounds (including phenols and basic nitrogen heterocyclic compounds) are obtained through back-extraction. Furthermore, the high selectivity of separating phenols and pyridine compounds is achieved by utilizing the characteristic of hydrogen bond acceptor extractants readily associating with phenols to form a eutectic phase. Finally, phenolic and pyridine compounds are obtained separately through back-extraction and distillation. This method is simple and efficient, with mild extraction conditions. The extractant can be recycled after drying, and the back-extraction agent and alkane solvent are recycled through atmospheric distillation.

[0049] In this application, the acidic eutectic solvent extractant and heteroatom compounds are separated through hydrogen bonding and acid-base synergy. The selective separation of phenols and pyridine compounds relies on the structural difference that the pyridine group lacks hydrogen bond donor sites. The extraction principle is analyzed using the charge shielding surface density model of COSMO-RS software: (1) The interaction energy between the extractant and heteroatom compounds is greater than the interaction energy between heteroatom compounds and aromatics in alkane solvents, thereby breaking the original associated structure of the extractant; (2) The hydrogen bond acceptor extractant has a significant hydrogen bond interaction with phenols, and the high selectivity of phenols is achieved by utilizing the structural difference that the pyridine group lacks hydrogen bond donor sites. Based on the calculation of interaction energy, the preliminary screening is completed. The preferred acidic eutectic solvent in this application is selected from at least one of tetraethylammonium chloride, tetrabutylammonium chloride, tetrabutylammonium bromide, and tetrabutylphosphine bromide, and a binary composition of at least one of glycolic acid, oxalic acid, citric acid, and p-toluenesulfonic acid; the preferred hydrogen bond acceptor extractant is selected from at least one of tetraethylammonium chloride, tetrabutylammonium chloride, tetrabutylammonium bromide, and tetrabutylphosphine bromide.

[0050] Compared with traditional acid-base extraction separation methods, the extraction and separation method for phenols and pyridines provided in this application has the following advantages: (1) The process is simple, the extractant and solvent are added and reacted at one time, and liquid-liquid extraction can be completed by simple separation; (2) The separation conditions are mild, the separation process temperature is between 30℃ and 50℃, and the process energy consumption is low; (3) Organic solvent is used for back-extraction and DES (eutectic solvent) is used for extraction, both of which can be reused and there is no water pollution; (4) The overall process operation has a high degree of continuity and has strong industrial scale-up potential.

[0051] This application also provides a schematic diagram of a system for separating phenols and pyridines from naphthalene oil. A naphthalene oil mixture F1, an alkane solvent Sol, and a eutectic solvent E1 are mixed and extracted in a de-impurification reactor DH to obtain a heteroatom eutectic phase (DES extract phase) and a hydrocarbon raffinate phase. The hydrocarbon extract phase enters the solvent tower ST, and the solvent obtained from distillation is recycled. The benzene-naphthalene mixture enters the storage tank P3. The DES extract phase is back-extracted with a back-extractant in the back-extraction tower BE to obtain a heteroatom mixture F2, and the back-extractant is recycled. The heteroatom mixture F2 is extracted with hydrogen bond acceptor extractant E2 and an alkane solvent Sol in a phenol extraction reactor PH to obtain a phenol eutectic phase (DES extract phase) and a pyridine raffinate phase. The phenol eutectic phase (DES extract phase) is mixed and extracted with a back-extractant in the back-extraction tower BE to obtain a mixed phenol product P1, and the back-extractant is recycled. The pyridine raffinate phase enters the solvent tower ST, and the solvent obtained from distillation is recycled. The pyridine compounds enter the storage tank P2.

[0052] The technical solution of this application is further described below through specific embodiments, but the scope of protection of this application is not limited to the following embodiments. Unless otherwise specified, the raw materials, reagents, and methods used in the embodiments are all conventional raw materials, reagents, and methods in the art. Some of the following embodiments use ethylphenol, quinoline, and methylnaphthalene in a mass ratio of 2:1:3 to prepare a model naphthalene oil as a raw material for determination. Example 1

[0053] Using model naphthalene oil as raw material, it was dissolved in cyclohexane to prepare a solution of 180 g / kg. 100 g of this solution was placed in an Erlenmeyer flask with a magnetic stirrer. A eutectic extractant of tetraethylammonium chloride and oxalic acid was prepared at a molar ratio of 1:2. 18 g of the eutectic extractant (with a mass ratio of 1 to naphthalene oil) was added, and the mixture was stirred at 30°C for 60 min. The solution was then separated to obtain the DES phase. 9 g of ethyl acetate was added as a back-extraction agent, and back-extraction was performed for 30 min to obtain a back-extraction solution containing dissolved ethylphenol and quinoline. Distillation yielded a mixture of 8.82 g of ethylphenol and quinoline, with a yield of 98.1%. Then add 4.06 g of tetraethylammonium chloride (molar ratio to phenol 0.5) and 45 g of cyclohexane. Stir at 50 °C for 60 min, and separate the liquid to obtain the DES phase. Add 9 g of ethyl acetate to the DES phase and stir at room temperature for 10 min. Distill and back-extract the phase to obtain 6.19 g of ethylphenol with a purity of 95%; and obtain 2.63 g of quinoline with a purity of 99% by alkane solvent phase. Example 2

[0054] Using model naphthalene oil as raw material, it was dissolved in cyclohexane to prepare a solution of 180 g / kg. 100 g of this solution was placed in an Erlenmeyer flask with a magnetic stirrer. A eutectic extractant of tetraethylammonium chloride and glycolic acid was prepared at a molar ratio of 1:2. 36 g of the eutectic extractant (with a mass ratio of 2 to naphthalene oil) was added, and the mixture was stirred at 50 °C for 120 min. The solution was then separated to obtain the DES phase. 18 g of acetone was added as a back-extraction agent, and back-extraction was performed for 30 min to obtain a back-extraction solution containing dissolved ethylphenol and quinoline. Distillation yielded a mixture of 8.28 g of ethylphenol and quinoline, with a yield of 92%. Then add 4.06 g of tetraethylammonium chloride (molar ratio to phenol 0.5) and 45 g of cyclohexane. Stir at 50 °C for 60 min, and then separate the liquid to obtain the DES phase. Add 9 g of ethyl acetate to the DES phase and stir at room temperature for 10 min. Distill and back-extract the phase to obtain 5.75 g of ethylphenol with a purity of 96%; and obtain 2.53 g of quinoline with a purity of 99% by alkane solvent phase. Example 3

[0055] Using model naphthalene oil as raw material, it was dissolved in hexane to prepare a solution of 360 g / kg. 100 g of this solution was placed in an Erlenmeyer flask with a magnetic stirrer. Tetrabutylammonium chloride and citric acid were prepared as a eutectic extractant at a molar ratio of 1:2. 36 g of the eutectic extractant (with a mass ratio of 1 to naphthalene oil) was added, and the mixture was stirred at 40 °C for 60 min. The solution was then separated to obtain the DES phase. 36 g of ethyl acetate was added as a back-extraction agent, and back-extraction was performed for 30 min to obtain a back-extraction solution containing dissolved ethylphenol and quinoline. Distillation yielded a mixture of 17.4 g of ethylphenol and quinoline, with a yield of 96.66%. Then add 8.12 g of tetraethylammonium chloride (molar ratio to phenol 0.5) and 36 g of hexane. Stir at 50 °C for 60 min and separate to obtain DES phase. Add 18 g of carbon disulfide to DES phase and stir at room temperature for 10 min. Distill and back-extract the phase to obtain 12.61 g of ethylphenol with a purity of 92%; the alkane solvent phase to obtain 4.79 g of quinoline with a purity of 99%. Example 4

[0056] Using model naphthalene oil as raw material, it was dissolved in cyclohexane to prepare a solution with a concentration of 360 g / kg. 100 g of this solution was placed in an Erlenmeyer flask with a magnetic stirrer. Tetrabutylammonium bromide and p-toluenesulfonic acid eutectic extractant were prepared at a molar ratio of 1:2. 7.2 g of the eutectic extractant (0.2 mass ratio to naphthalene oil) was added, and the mixture was stirred at 50 °C for 60 min. The solution was then separated to obtain the DES phase. 36 g of acetone was added as a back-extraction agent, and back-extraction was performed for 30 min to obtain a back-extraction solution containing dissolved ethylphenol and quinoline. Distillation yielded a mixture of 17.71 g of ethylphenol and quinoline, with a yield of 98.41%. Then add 16.24 g of tetraethylammonium chloride (molar ratio to phenol 1) and 18 g of cyclohexane. Stir at 50 °C for 60 min and separate the liquid to obtain the DES phase. Add 18 g of carbon disulfide to the DES phase and stir at room temperature for 10 min. Distill and back-extract the phase to obtain 13.12 g of ethylphenol with a purity of 90%; the alkane solvent phase to obtain 4.59 g of quinoline with a purity of 99%. Example 5

[0057] Using model naphthalene oil as raw material, it was dissolved in cyclohexane to prepare a solution of 360 g / kg. 100 g of this solution was placed in an Erlenmeyer flask with a magnetic stirrer. A eutectic extractant of tetraethylammonium chloride and oxalic acid was prepared at a molar ratio of 1:2. 36 g of the eutectic extractant (with a mass ratio of 1 to naphthalene oil) was added, and the mixture was stirred at 50 °C for 60 min. The solution was then separated to obtain the DES phase. 18 g of ethyl acetate was added as a back-extraction agent, and back-extraction was performed for 30 min to obtain a back-extraction solution containing dissolved ethylphenol and quinoline. Distillation yielded a mixture of 17.69 g of ethylphenol and quinoline, with a yield of 98.29%. Then add 16.24 g of tetraethylammonium chloride (molar ratio of 1 to ethylphenol) and 90 g of cyclohexane. Stir at 50 °C for 60 min and separate the liquid to obtain the DES phase. Add 18 g of ethyl acetate to the DES phase and stir at room temperature for 10 min. Distill and back-extract the phase to obtain 12.29 g of ethylphenol with a purity of 96%; the alkane solvent phase to obtain 5.41 g of quinoline with a purity of 99%. Example 6

[0058] Using model naphthalene oil as raw material, it was dissolved in cyclohexane to prepare a solution of 360 g / kg. 100 g of this solution was placed in an Erlenmeyer flask with a magnetic stirrer. Tetraethylammonium chloride and oxalic acid were prepared as a eutectic extractant at a molar ratio of 1:2. 36 g of the eutectic extractant (with a mass ratio of 1 to naphthalene oil) was added, and the mixture was stirred at 50 °C for 60 min. The solution was then separated to obtain the DES phase. 18 g of ethyl acetate was added as a back-extraction agent, and back-extraction was performed for 30 min to obtain a back-extraction solution containing dissolved ethylphenol and quinoline. Distillation yielded a mixture of 17.48 g of ethylphenol and quinoline, with a yield of 97.11%. Then add 27.36 g of tetrabutylammonium chloride (molar ratio of 1 to ethylphenol) and 90 g of cyclohexane. Stir at 50 °C for 60 min and separate the liquid to obtain the DES phase. Add 18 g of ethyl acetate to the DES phase and stir at room temperature for 10 min. Distill and back-extract the phase to obtain 12.40 g of ethylphenol with a purity of 94%; and obtain 5.08 g of quinoline with a purity of 99% by alkane solvent phase. Example 7

[0059] Using model naphthalene oil as raw material, it was dissolved in hexane to prepare a solution of 360 g / kg. 100 g of this solution was placed in an Erlenmeyer flask with a magnetic stirrer. A eutectic extractant of tetraethylammonium chloride and oxalic acid was prepared at a molar ratio of 2:1. 36 g of the eutectic extractant (with a mass ratio of 1 to naphthalene oil) was added, and the mixture was stirred at 50 °C for 60 min. The solution was then separated to obtain the DES phase. 18 g of carbon tetrachloride was added as a back-extraction agent, and back-extraction was performed for 30 min to obtain a back-extraction solution containing dissolved ethylphenol and quinoline. Distillation yielded a mixture of 17.66 g of ethylphenol and quinoline, with a yield of 98.11%. Then add 31.68 g of tetrabutylammonium bromide (molar ratio of 1 to ethylphenol) and 90 g of cyclohexane. Stir at 50 °C for 60 min and separate the liquid to obtain the DES phase. Add 36 g of carbon tetrachloride to the DES phase and stir at room temperature for 10 min. Distill and back-extract the phase to obtain 13.08 g of ethylphenol with a purity of 90%; the alkane solvent phase to obtain 4.58 g of quinoline with a purity of 99%. Example 8

[0060] Using model naphthalene oil as raw material, it was dissolved in hexane to prepare a solution of 360 g / kg. 100 g of this solution was placed in an Erlenmeyer flask with a magnetic stirrer. A eutectic extractant of tetraethylammonium chloride and oxalic acid was prepared at a molar ratio of 2:1. 36 g of the eutectic extractant (with a mass ratio of 1 to naphthalene oil) was added, and the mixture was stirred at 50 °C for 60 min. The solution was then separated to obtain the DES phase. 18 g of carbon tetrachloride was added as a back-extraction agent, and back-extraction was performed for 30 min to obtain a back-extraction solution containing dissolved ethylphenol and quinoline. Distillation yielded a mixture of 17.72 g of ethylphenol and quinoline, with a yield of 98.45%. Then add 31.68 g of tetrabutylphosphine bromide (molar ratio of 1 to ethylphenol) and 90 g of cyclohexane. Stir at 50 °C for 60 min and separate to obtain the DES phase. Add 36 g of carbon tetrachloride to the DES phase and stir at room temperature for 10 min. Distill and back-extract the phase to obtain 13.27 g of ethylphenol with a purity of 89%; the alkane solvent phase to obtain 4.45 g of quinoline with a purity of 99%. Example 9

[0061] Using model naphthalene oil as raw material, it was dissolved in cyclohexane to prepare a solution of 360 g / kg. 100 g of this solution was placed in an Erlenmeyer flask with a magnetic stirrer. Tetrabutylammonium chloride and p-toluenesulfonic acid were prepared as a eutectic extractant at a molar ratio of 1:2. 36 g of the eutectic extractant (with a mass ratio of 1 to naphthalene oil) was added, and the mixture was stirred at 50 °C for 60 min. The solution was then separated to obtain the DES phase. 18 g of ethyl acetate was added as a back-extraction agent, and back-extraction was performed for 10 min to obtain a back-extraction solution containing dissolved alkylphenols and quinolines. Distillation yielded a mixture of 18.96 g of ethylphenol and quinolines, with a yield of 98.7%. Then add 16.24 g of tetraethylammonium chloride (molar ratio of 1 to ethylphenol) and 90 g of cyclohexane. Stir at 50 °C for 60 min and separate the liquid to obtain the DES phase. Add 36 g of ethyl acetate to the DES phase and stir at room temperature for 30 min. Distill and back-extract the phase to obtain 13.04 g of ethylphenol with a purity of 89%; the alkane solvent phase to obtain 5.92 g of quinoline with a purity of 94%. Example 10

[0062] Experiments were conducted using tetraethylammonium chloride and DES oxalate (circulated five times) as a eutectic solvent, tetraethylammonium chloride as a hydrogen bond acceptor extractant, cyclohexane as a solvent, and ethyl acetate as a back-extraction agent. The model mixture was dissolved in cyclohexane to prepare a solution of 360 g / kg. 100 g of this solution was placed in an Erlenmeyer flask with a magnetic stirrer, and 36 g of DES extractant (mass ratio of 1 to naphthalene oil) was added. After stirring at 50 °C for 60 min, the mixture was separated to obtain the DES phase. Then, 18 g of ethyl acetate was added as a back-extraction agent, and back-extraction was performed for 30 min to obtain a back-extraction solution containing dissolved alkylphenols and quinolines. Distillation yielded a mixture of 18.7 g of ethylphenol and quinolines, with a yield of 96.3%. Then add 16.24 g of tetraethylammonium chloride (molar ratio of 1 to ethylphenol) and 90 g of cyclohexane. Stir at 50 °C for 60 min and separate to obtain the DES phase. Add 36 g of carbon disulfide to the DES phase and stir at room temperature for 10 min. Distill and back-extract the phase to obtain 12.77 g of ethylphenol with a purity of 95%; the alkane solvent phase to obtain 5.93 g of quinoline with a purity of 97%. Example 11

[0063] Using industrial naphthalene oil samples (coal tar fraction at 210-230℃) as raw material, it was dissolved in cyclohexane to prepare a solution of 180 g / kg. 100 g of this solution was placed in an Erlenmeyer flask with a magnetic stirrer. Tetraethylammonium chloride and oxalic acid eutectic extractant were prepared at a molar ratio of 1:2. 18 g of the eutectic extractant (at a mass ratio of 1 to naphthalene oil) was added, and the mixture was stirred at 30℃ for 60 min. The solution was then separated to obtain the DES phase. 9 g of ethyl acetate was added as a back-extraction agent, and back-extraction was performed for 30 min to obtain a back-extraction solution containing dissolved phenol and pyridine compounds. Distillation yielded 8.21 g of a heteroatom mixture, with a yield of 104% (naphthalene oil was quantified by GC-MS, and the total content of phenol and pyridine compounds was determined to be 43.86 wt.%) using the area normalization method. Then add 4.06 g of tetraethylammonium chloride (molar ratio to phenol 0.5) and 45 g of cyclohexane. Stir at 50 °C for 60 min and separate the liquid to obtain the DES phase. Add 9 g of ethyl acetate to the DES phase and stir at room temperature for 10 min. Distill and back-extract the phase to obtain 6.19 g of mixed phenol with a purity of 90%; and obtain 1.52 g of pyridine derivative with a purity of 99% from the alkane solvent phase.

[0064] Of course, this application may have other various embodiments. Without departing from the spirit and essence of this application, those skilled in the art can make various corresponding changes and modifications based on this application, but these corresponding changes and modifications should all fall within the protection scope of the claims of this application.

Claims

1. A method for stepwise extraction of phenolic and pyridine compounds from naphthalene oil using a eutectic solvent, characterized in that, Includes the following steps: Step 1: Mix naphthalene oil, alkanes and eutectic solvent, separate the liquids to obtain heteroatom eutectic phase and hydrocarbon raffinate phase; Step 2: Mix the heteroatom eutectic phase with the first back-extractant, separate the phases to obtain the first back-extractant phase and the first back-extractant residue phase; Step 3: Separate the heteroatom mixture in the first back-extraction phase from the first back-extraction agent. The heteroatom mixture, alkanes and hydrogen bond acceptor extractant are mixed and separated to obtain a phenolic eutectic phase and a pyridine raffinate phase. Step 4: Mix the phenolic eutectic phase with the second back-extractant, separate the phases, and obtain the phenolic compound; The eutectic solvent is a mixture of at least one of tetraethylammonium chloride, tetrabutylammonium chloride, tetrabutylammonium bromide, and tetrabutylphosphine bromide with at least one of glycolic acid, oxalic acid, citric acid, and p-toluenesulfonic acid; the hydrogen bond acceptor extractant is at least one of tetraethylammonium chloride, tetrabutylammonium chloride, tetrabutylammonium bromide, and tetrabutylphosphine bromide.

2. The method for stepwise extraction of phenolic and pyridine compounds from naphthalene oil using a eutectic solvent according to claim 1, characterized in that, Also includes: The hydrocarbon raffinate from step 1 is distilled to obtain alkanes, a mixture of benzene and naphthalene, and so on; the alkanes are recycled back to step 1 for reuse.

3. The method for stepwise extraction of phenolic and pyridine compounds from naphthalene oil using a eutectic solvent according to claim 1, characterized in that, The first back-extraction agent is selected from at least one of acetone, ethyl acetate, carbon disulfide, and tetrachloromethane; the first back-extraction residue is a eutectic solvent, which is recycled back to step 1 for reuse.

4. The method for stepwise extraction of phenolic and pyridine compounds from naphthalene oil using a eutectic solvent according to claim 1, characterized in that, The heteroatom mixture in the first back-extraction phase is separated from the first back-extraction agent by distillation, and the separated first back-extraction agent is recycled back to step 2 for reuse.

5. The method for stepwise extraction of phenolic and pyridine compounds from naphthalene oil using a eutectic solvent according to claim 1, characterized in that, The second back-extraction agent is selected from at least one of acetone, ethyl acetate, carbon disulfide, and tetrachloromethane; the mixture of the phenolic eutectic phase and the second back-extraction agent is separated to obtain phenolic compounds and hydrogen bond acceptor extractants, and the hydrogen bond acceptor extractants obtained by phase separation are recycled back to step 3 for reuse.

6. The method for stepwise extraction of phenolic and pyridine compounds from naphthalene oil using a eutectic solvent according to claim 1, characterized in that, The pyridine raffinate is separated by distillation to obtain pyridine compounds and alkanes, and the alkanes are recycled.

7. The method for stepwise extraction of phenolic and pyridine compounds from naphthalene oil using a eutectic solvent according to claim 1, characterized in that, The alkanes in step 1 may be the same as or different from those in step 3, and are independently selected from n-hexane and cyclohexane.

8. The method for stepwise extraction of phenolic and pyridine compounds from naphthalene oil using a eutectic solvent according to claim 1, characterized in that, In step 1, the mass ratio of the eutectic solvent to naphthalene oil is 0.2 to 2, the mixing temperature is 30℃ to 50℃, and the mixing time is 60 min to 120 min.

9. The method for stepwise extraction of phenolic and pyridine compounds from naphthalene oil using a eutectic solvent according to claim 1, characterized in that, In step 3, the mixing temperature is 30℃~50℃; in step 2, the mass ratio of the first back-extractant to the heteroatom eutectic phase is 0.5~1, and the mixing time is 10min~30min; in step 4, the mass ratio of the second back-extractant to the phenolic eutectic phase is 0.5~1, and the mixing time is 10min~30min.

10. The method for stepwise extraction of phenolic and pyridine compounds from naphthalene oil using a eutectic solvent according to claim 1, characterized in that, In the eutectic solvent, the ratio of the amount of tetraethylammonium chloride, tetrabutylammonium chloride, tetrabutylammonium bromide or tetrabutylphosphine bromide to the amount of glycolic acid, oxalic acid, citric acid or p-toluenesulfonic acid is 2:1 to 1:2.

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