A method for selectively separating pyridine bases in coal-based crude phenol

Abstract

The application discloses a method for selectively separating pyridine bases in coal-based crude phenol, and belongs to the technical field of coal chemical industry. The method uses binary or ternary acidic deep eutectic solvents (DES) and non-polar solvents to construct a two-phase solvent extraction system. Pyridine bases are selectively extracted into the DES phase through the acid-base and hydrogen bond interactions between the binary or ternary acidic DES and the pyridine bases. Meanwhile, the non-polar solvents and phenolic compounds are used to enrich the phenols in the non-polar phase through the van der Waals interaction. The DES can be regenerated through back extraction, and the non-polar solvent can be regenerated through vacuum distillation. Based on the acid-base and polarity differences between the two-phase solvents, the application realizes the efficient separation of phenols and pyridine bases, and has the characteristics of simple operation, high separation efficiency, recyclable solvents and the like, and significantly improves the added value and resource utilization efficiency of the coal-based crude phenol.

Description

Technical Field

[0001] This invention belongs to the field of coal chemical technology, specifically relating to a method for selectively separating pyridine bases from crude phenols in coal. Background Technology

[0002] Coal-based oil products can be initially separated to obtain crude phenol products, whose main components include phenolic compounds such as phenol, cresol, and xylenol, and usually contain small amounts of basic pyridine compounds. The presence of pyridine bases not only reduces the content of phenolic compounds in the crude phenol product but also adversely affects subsequent refining processes. Therefore, a separation-then-refining approach can be adopted, separating the basic pyridine compounds first before subsequent refining. Currently, the industrial separation of pyridine bases mainly uses acid washing. Although this method has a high pyridine removal efficiency, it requires the use of large amounts of strong acid during operation, which not only causes severe corrosion to the separation equipment but also generates a large amount of acidic wastewater. Therefore, there is an urgent need to develop an efficient and environmentally friendly separation method. Summary of the Invention

[0003] To address the problems of severe equipment corrosion and large amounts of wastewater generated in the separation of pyridine bases in existing technologies, this invention provides a method for selectively separating pyridine bases from coal-based crude phenols. By using biphasic solvent extraction (binary or ternary acidic eutectic solvent, non-polar solvent), the method can selectively separate pyridine bases from coal-based crude phenols, achieving efficient separation, eliminating its impact on subsequent processing, and significantly improving the quality of crude phenol products.

[0004] To achieve the above objectives, the present invention adopts the following technical solution: This invention provides a method for selectively separating pyridine bases from coal-based crude phenols, comprising the following steps: (1) Add a biphase solvent (acidic eutectic solvent and nonpolar solvent) to coal-based crude phenol, stir, let stand and separate into two phases, separate the two phases to obtain a polar phase rich in pyridine compounds and a nonpolar phase rich in phenol compounds; The specific addition method is as follows: First, a non-polar solvent is added to coal-based crude phenol to obtain a premixed non-polar phase, and then an acidic eutectic solvent is added to the premixed non-polar phase and stirred. (2) Add back-extraction agent to the polar phase rich in pyridine compounds, stir, let stand and separate into two phases, separate the two phases to obtain the back-extraction phase rich in pyridine compounds and the eutectic solvent phase; distill the back-extraction phase rich in pyridine compounds to obtain pyridine compounds (containing phenolic compounds, because some phenolic compounds were also carried along during the extraction of pyridine) and back-extraction agent; (3) Distill the nonpolar phase rich in phenolic compounds to obtain phenolic compounds and nonpolar solvents.

[0005] The above method will be explained in further detail: The coal-based crude phenol includes phenolic compounds such as phenol, cresol, and xylenol, as well as basic pyridine compounds, with a mass concentration of 1-30%.

[0006] This invention involves simultaneously adding an acidic eutectic solvent and a non-polar solvent to crude phenol, and through two-phase solvent extraction, achieving selective separation of pyridine compounds and phenolic compounds to obtain a high-quality crude phenol product.

[0007] The acidic eutectic solvent is a ternary or binary mixture, formed by mixing and thoroughly stirring a hydrogen bond donor, a hydrogen bond acceptor, and a ternary additive. The hydrogen bond acceptor is one or more of alcohols, alkanolamines, and amides. Alcohols include ethylene glycol, glycerol, diethylene glycol, and triethylene glycol; alkanolamines include ethanolamine, isopropanolamine, and diethanolamine; and amides include formamide. The hydrogen bond donor is selected from monobasic organic acids, dibasic organic acids, polybasic organic acids, or organic sulfonic acids, specifically including glycolic acid, lactic acid, malonic acid, oxalic acid, citric acid, p-toluenesulfonic acid, xylenesulfonic acid, and dodecylbenzenesulfonic acid. The ternary additive is a hydroxy acid, including tartaric acid, malic acid, mandelic acid, and gluconic acid.

[0008] In the acidic eutectic solvent, the mass ratio of hydrogen bond donor, hydrogen bond acceptor and tertiary additive is in the range of 1:(0.1~10):(0~10).

[0009] The nonpolar solvent is an alkane compound, such as one or more of n-hexane, cyclohexane, n-decane, and decahydronaphthalene.

[0010] Preferably, the amount of acidic eutectic solvent added is 0.5 to 50 times the mass of crude phenol, and the amount of non-polar solvent added is 0.5 to 10 times the mass of crude phenol. The ratio of acidic eutectic solvent to non-polar solvent is in the range of 1:(0.05 to 20).

[0011] Preferably, the present invention further includes a technique for adding water to the acidic eutectic solvent. The water serves as an auxiliary regulator in the extraction system and is not an additive constituting the binary or ternary acidic eutectic solvent. First, a hydrogen bond donor, a hydrogen bond acceptor, and a ternary additive are mixed and thoroughly stirred to obtain an acidic eutectic solvent. After the obtained acidic eutectic solvent is cooled, water is added and stirred until the system is homogeneous to obtain a water-modified acidic eutectic solvent. Subsequently, the water-modified acidic eutectic solvent and a non-polar solvent are simultaneously added to crude phenol for extraction. The amount of water added is 0 to 2 times the mass of the acidic eutectic solvent.

[0012] Preferably, an acidic eutectic solvent and a non-polar solvent are simultaneously added to the crude phenol, and the mixture is stirred for 30 to 60 minutes at 25 to 50 °C.

[0013] After two-phase solvent extraction and separation, a polar phase rich in pyridine compounds and a nonpolar phase rich in phenolic compounds were obtained.

[0014] For polar phases rich in pyridine compounds: Back-extraction is performed using a back-extraction agent to obtain a back-extraction phase rich in pyridine compounds and an acidic eutectic solvent phase. After 3 to 10 back-extractions, the acidic eutectic solvent can be recycled.

[0015] The back-extraction agent is selected from one or more of ether compounds, ester compounds, and sulfides; such as one or more of diethyl ether, ethyl acetate, and carbon disulfide.

[0016] Preferably, the amount of back-extractant added is 0.5 to 10 times the mass of the polar phase rich in pyridine compounds.

[0017] Preferably, the stirring temperature when adding the back-extraction agent is 25-50°C and the stirring time is 30-60 min.

[0018] The pyridine-rich back-extraction phase is distilled under reduced pressure to obtain the pyridine compounds and the back-extraction agent. The back-extraction agent can be recycled. The reduced pressure distillation temperature is 25-50℃, the pressure is 300-500 mbar, and the time is 30-60 min.

[0019] Preferably, for the nonpolar phase rich in phenolic compounds: The nonpolar phase rich in phenolic compounds is distilled to obtain phenolic compounds and a nonpolar solvent. The nonpolar solvent can be recycled. The distillation temperature of the nonpolar phase is 30–60 °C, the pressure is 300–500 mbar, and the time is 30–60 min.

[0020] The principle of this invention is as follows: The acidic interaction sites of the acidic DES can interact with pyridine compounds through acid-base and hydrogen bonding, driving the pyridine compounds to break their interaction with the original system and migrate from the oil phase to the acidic DES phase, thereby achieving the separation of pyridine compounds. The introduction of the ternary additive hydroxy acid can reduce the number of available alcohol hydroxyl hydrogen bonding sites for phenolic compounds, thereby reducing phenolic compound entrainment. Due to the similarity between phenolic and pyridine compounds, phenolic compounds are easily entrained during the extraction of pyridine. Currently, binary extractants have a high extraction rate for pyridine, but also entrain a large amount of phenols. The purpose of adding the tertiary additive hydroxy acid is to reduce phenolic entrainment. The nonpolar solvent and phenolic compounds are combined through van der Waals interactions, thereby achieving the separation of phenols. The addition of water can reduce the viscosity of the acidic eutectic solvent and adjust its polarity, improving the mass transfer performance of the system and increasing the selectivity of extraction separation. Based on the differences in acidity, basicity, and polarity between the two solvents, efficient separation of pyridine and phenolic compounds from crude phenol is achieved.

[0021] The beneficial effects of this invention are: (1) This invention constructs a two-phase solvent system composed of a ternary acidic eutectic solvent and a nonpolar solvent, and utilizes acid-base and hydrogen bonding to achieve selective separation of pyridine compounds. By introducing a nonpolar solvent, the amount of phenolic compounds entrained is effectively suppressed.

[0022] (2) The present invention can separate pyridine compounds in crude phenol, thereby significantly reducing their content, eliminating their adverse effects on subsequent processing, and significantly improving the quality and added value of crude phenol products.

[0023] (3) The present invention is simple to operate and environmentally friendly. The ternary acidic eutectic solvent, non-polar solvent and back-extraction agent used can all be recycled, which greatly reduces the process operating cost and significantly improves the comprehensive utilization value of coal-based crude phenol. Attached Figure Description

[0024] Figure 1 This is a process flow diagram of the present invention. Detailed Implementation

[0025] The present invention will be further described below with reference to the embodiments. It should be noted that the following embodiments are provided for illustrative purposes only and do not constitute a limitation on the scope of protection of the present invention.

[0026] The specific process of this invention is as follows: Figure 1 As shown.

[0027] Unless otherwise specified, the raw materials, reagents, and methods used in the embodiments are all conventional raw materials, reagents, and methods in the art. Example 1

[0028] The experiment was conducted using model oil.

[0029] Weigh 9 g of m-cresol and 1 g of pyridine into a glass bottle to prepare a model oil with a pyridine mass fraction of 10.0%. Add 90.0 g of cyclohexane as a nonpolar solvent to the model oil and mix well to obtain 100.0 g of premixed nonpolar phase.

[0030] Weigh out 70.8 g of glycerol and 29.2 g of glycolic acid, making the molar ratio of glycerol to glycolic acid 2:1. Place both in a glass bottle and stir for 60 min in an oil bath at 100 ℃ to form 100.0 g of a homogeneous and transparent acidic eutectic solvent.

[0031] An acidic eutectic solvent was added to the premixed nonpolar phase, stirred at 25 °C for 30 min, and allowed to stand to separate into layers. The upper nonpolar phase and the lower polar phase were then removed and weighed separately, and their compositions were determined using GC-MS. The extraction rate of pyridine (mass of pyridine in the polar phase / mass of pyridine in the model oil) was 29.6%, and the entrainment rate of m-cresol (mass of m-cresol in the polar phase / mass of m-cresol in the model oil) was 78.7%.

[0032] Five back-extraction processes were performed. Each time, an equal mass of back-extractant (carbon disulfide) was added to the polar phase. The mixture was stirred at 25 °C for 30 min, allowed to stand, and allowed to separate into layers. This yielded a eutectic solvent phase and a back-extraction phase containing pyridine compounds. The back-extraction phase was then subjected to vacuum distillation (500 mbar, 30 °C) to obtain a regenerated back-extractant. The non-polar phase was then subjected to vacuum distillation (300 mbar, 50 °C) to obtain phenolic compounds and a regenerated non-polar solvent. Example 2

[0033] The difference between this embodiment and Example 1 is that the hydrogen bond donor of the acidic eutectic solvent is oxalic acid, and the preparation ratio is 67.2 g glycerol and 32.8 g oxalic acid, with a molar ratio of glycerol to oxalic acid of 2:1. All other aspects are the same as in Example 1.

[0034] The extraction rate of pyridine was 99.9%, and the entrainment rate of m-cresol was 83.8%. Example 3

[0035] The difference between this embodiment and Example 1 is that the hydrogen bond donor of the acidic eutectic solvent is citric acid, and the preparation ratio is 48.9 g glycerol and 51.1 g citric acid, with a molar ratio of glycerol to citric acid of 2:1. All other aspects are the same as in Example 1.

[0036] The extraction rate of pyridine was 83.3%, and the entrainment rate of m-cresol was 45.3%. Example 4

[0037] The difference between this embodiment and Example 1 is that the hydrogen bond donor of the acidic eutectic solvent is p-toluenesulfonic acid, and the preparation ratio is 51.7 g glycerol and 48.3 g p-toluenesulfonic acid, with a molar ratio of glycerol to p-toluenesulfonic acid of 2:1. All other aspects are the same as in Example 1.

[0038] The extraction rate of pyridine was 99.9%, and the entrainment rate of m-cresol was 88.4%. Example 5

[0039] The difference between this embodiment and Example 1 is that the hydrogen bond acceptor of the acidic eutectic solvent is ethylene glycol, the hydrogen bond donor is glycolic acid, the preparation ratio is 62.0 g ethylene glycol and 38.0 g glycolic acid, and the molar ratio of ethylene glycol to glycolic acid is 2:1. All other aspects are the same as in Example 1.

[0040] The extraction rate of pyridine was 21.5%, and the entrainment rate of m-cresol was 88.1%. Example 6

[0041] The difference between this embodiment and Example 1 is that the hydrogen bond acceptor of the acidic eutectic solvent is ethylene glycol, the hydrogen bond donor is oxalic acid, the preparation ratio is 58.0 g ethylene glycol and 42.0 g oxalic acid, and the molar ratio of ethylene glycol to oxalic acid is 2:1. All other aspects are the same as in Example 1.

[0042] The extraction rate of pyridine was 99.9%, and the entrainment rate of m-cresol was 84.8%. Example 7

[0043] The difference between this embodiment and Example 1 is that the hydrogen bond acceptor of the acidic eutectic solvent is ethylene glycol, the hydrogen bond donor is citric acid, the preparation ratio is 39.3 g ethylene glycol and 60.7 g citric acid, and the molar ratio of ethylene glycol to citric acid is 2:1. All other aspects are the same as in Example 1.

[0044] The extraction rate of pyridine was 82.0%, and the entrainment rate of m-cresol was 59.6%. Example 8

[0045] The difference between this embodiment and Example 1 is that the hydrogen bond acceptor of the acidic eutectic solvent is ethylene glycol, the hydrogen bond donor is p-toluenesulfonic acid, the preparation ratio is 41.9 g ethylene glycol and 58.1 g p-toluenesulfonic acid, and the molar ratio of ethylene glycol to p-toluenesulfonic acid is 2:1. All other aspects are the same as in Example 1.

[0046] The extraction rate of pyridine was 99.9%, and the entrainment rate of m-cresol was 86.2%. Example 9

[0047] This embodiment investigates the effect of the mass ratio of a binary acidic eutectic solvent to a premixed nonpolar phase on the extraction efficiency.

[0048] 100.0 g of a premixed nonpolar phase, comprising 9.0 g m-cresol, 1.0 g pyridine and 90.0 g cyclohexane, was prepared according to the method of Example 1.

[0049] Using glycerol as the hydrogen bond acceptor and citric acid as the hydrogen bond donor, a dibasic acid eutectic solvent was prepared at a molar ratio of glycerol to citric acid of 2:1. Different masses of glycerol and citric acid were weighed and stirred in an oil bath at 100 °C for 60 min to prepare 50.0 g, 100.0 g, 200.0 g, 300.0 g, and 400.0 g of dibasic acid eutectic solvent, respectively, with mass ratios of the dibasic acid eutectic solvent to the premixed nonpolar phase of 0.5:1, 1:1, 2:1, 3:1, and 4:1.

[0050] Different masses of binary acidic eutectic solvents were added to 100.0 g of the premixed nonpolar phase, stirred at 25 °C for 30 min, and then allowed to stand to separate into layers. The upper nonpolar phase and the lower polar phase were taken out separately, weighed, and their compositions were determined by GC-MS. The subsequent back-extraction and solvent regeneration processes were the same as in Example 1.

[0051] Table 1 Effect of the amount of binary acidic eutectic solvent added on the extraction effect . Example 10

[0052] This embodiment investigates the effect of the molar ratio of glycerol to citric acid in a dibasic acidic eutectic solvent on the extraction efficiency.

[0053] 100.0 g of a premixed nonpolar phase, comprising 9.0 g m-cresol, 1.0 g pyridine and 90.0 g cyclohexane, was prepared according to the method of Example 1.

[0054] Glycerol and citric acid were weighed out at molar ratios of 1.5:1, 2:1, 2.5:1, 3:1, and 3.5:1, respectively. The total mass of the binary acidic eutectic solvent in each group was 200.0 g, and the mass ratio of the binary acidic eutectic solvent to the premixed nonpolar phase was 2:1. Glycerol and citric acid were placed in a glass bottle and stirred in an oil bath at 100 °C for 60 min to form a homogeneous and transparent binary acidic eutectic solvent.

[0055] The prepared binary acidic eutectic solvent was added to 100.0 g of the premixed nonpolar phase, and stirred at 25 °C for 30 min, followed by standing to separate the layers. The upper nonpolar phase and the lower polar phase were taken out separately, weighed, and their compositions were determined by GC-MS. The subsequent back-extraction and solvent regeneration process was the same as in Example 1.

[0056] Table 2 Effect of the molar ratio of glycerol to citric acid on extraction efficiency . Example 11

[0057] This embodiment investigates the effect of the amount of water added on the extraction effect.

[0058] 100.0 g of a premixed nonpolar phase, comprising 9.0 g m-cresol, 1.0 g pyridine and 90.0 g cyclohexane, was prepared according to the method of Example 1.

[0059] Weigh out 97.9 g of glycerol and 102.1 g of citric acid, making the molar ratio of glycerol to citric acid 2:1. Place both in a glass bottle and stir in an oil bath at 100 ℃ for 60 min to form 200.0 g of a homogeneous and transparent dibasic acidic eutectic solvent. The mass ratio of the dibasic acidic eutectic solvent to the premixed nonpolar phase is 2:1.

[0060] In this embodiment, water is added to the acidic eutectic solvent. The water serves as an auxiliary regulator in the extraction system and is not an additive constituting the binary or ternary acidic eutectic solvent. First, the hydrogen bond donor and hydrogen bond acceptor are mixed and stirred thoroughly to obtain a binary acidic eutectic solvent. After the obtained acidic eutectic solvent is cooled, water is added and stirred until the system is homogeneous to obtain a water-modified acidic eutectic solvent. Subsequently, the water-modified acidic eutectic solvent and a non-polar solvent are simultaneously added to crude phenol for extraction. The amount of water added is 0 to 2 times the mass of the acidic eutectic solvent. Specifically, 0.0 g, 50.0 g, 100.0 g, 150.0 g, and 200.0 g of water are added to different groups of binary acidic eutectic solvents, respectively.

[0061] Different masses of water were added to 100.0 g of the premixed nonpolar phase, and the mixture was stirred at 25 °C for 30 min, followed by standing to separate the phases. The upper nonpolar phase and the lower polar phase were taken out separately, weighed, and their compositions were determined by GC-MS. The subsequent back-extraction and solvent regeneration processes were the same as in Example 1.

[0062] Table 3 Effect of water addition on extraction efficiency . Example 12

[0063] This embodiment investigates the extraction effect of a ternary acidic eutectic solvent with tartaric acid as the third additive.

[0064] 100.0 g of a premixed nonpolar phase, comprising 9.0 g m-cresol, 1.0 g pyridine and 90.0 g cyclohexane, was prepared according to the method of Example 1.

[0065] Weigh out 97.9 g of glycerol, 102.1 g of citric acid, and 20.0 g of tartaric acid, wherein the molar ratio of glycerol to citric acid is 2:1. Place the above substances in a glass bottle and stir for 60 min in an oil bath at 100 °C to form a homogeneous and transparent ternary acidic eutectic solvent. The mass ratio of the ternary acidic eutectic solvent to the premixed nonpolar phase is 2.2:1. Then add 100.0 g of water and mix thoroughly.

[0066] A ternary acidic eutectic solvent containing water was added to the premixed nonpolar phase, and the mixture was stirred at 25 °C for 30 min, followed by standing to separate the phases. The upper nonpolar phase and the lower polar phase were taken out separately, weighed, and their compositions were determined by GC-MS. The subsequent back-extraction and solvent regeneration processes were the same as in Example 1.

[0067] The extraction rate of pyridine was determined to be 99.9%, and the entrainment rate of m-cresol was 18.7%. Example 13

[0068] The difference between this embodiment and Example 12 is that the third additive in the ternary acidic eutectic solvent is malic acid, and the preparation ratio is 97.9 g glycerol, 102.1 g citric acid and 20.0 g malic acid, wherein the molar ratio of glycerol to citric acid is 2:1, and the rest are the same as in Example 12.

[0069] The extraction rate of pyridine was determined to be 99.9%, and the entrainment rate of m-cresol was 19.4%. Example 14

[0070] The difference between this embodiment and Example 12 is that the third additive in the ternary acidic eutectic solvent is mandelic acid, and the preparation ratio is 97.9 g glycerol, 102.1 g citric acid and 20.0 g mandelic acid, wherein the molar ratio of glycerol to citric acid is 2:1, and the rest are the same as in Example 12.

[0071] The results showed that the pyridine extraction rate was 99.9% and the m-cresol entrainment rate was 23.5%. Example 15

[0072] This embodiment investigates the extraction effect of a binary acidic eutectic solvent on actual coal-based crude phenols.

[0073] Weigh 10.0 g of actual coal-based crude phenol, add 90.0 g of cyclohexane as a non-polar solvent, mix well to obtain 100.0 g of premixed non-polar phase.

[0074] Weigh out 97.9 g of glycerol and 102.1 g of citric acid, making the molar ratio of glycerol to citric acid 2:1. Place both in a glass bottle and stir for 60 min in an oil bath at 100 ℃ to form 200.0 g of a homogeneous and transparent dibasic acidic eutectic solvent. The mass ratio of the dibasic acidic eutectic solvent to the premixed nonpolar phase is 2:1. Then add 100.0 g of water and mix thoroughly.

[0075] An aqueous binary acidic eutectic solvent was added to the premixed nonpolar phase, and the mixture was stirred at 25 °C for 30 min, followed by standing to separate the phases. The upper nonpolar phase and the lower polar phase were taken out separately, weighed, and their compositions were determined by GC-MS.

[0076] The extraction rate of pyridine compounds was determined to be 99.9%, while the entrainment rate of phenolic compounds was 27.4%. The subsequent back-extraction and solvent regeneration processes were the same as in Example 1. Example 16

[0077] This embodiment investigates the extraction effect of a ternary acidic eutectic solvent with tartaric acid as the third additive on actual coal-based crude phenols.

[0078] The difference between this embodiment and Example 15 is that 20.0 g of tartaric acid was added as a tertiary additive to the acidic eutectic solvent. The ratio of the tertiary acidic eutectic solvent was 97.9 g glycerol, 102.1 g citric acid, and 20.0 g tartaric acid, with a molar ratio of glycerol to citric acid of 2:1. The amounts of raw materials, extraction conditions, back-extraction process, and solvent regeneration conditions were the same as in Example 15.

[0079] The extraction rate of pyridine compounds was determined to be 99.9%, while the entrainment rate of phenolic compounds was 19.6%.

[0080] The above embodiments are merely illustrative of the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein, without departing from the spirit and substance defined by the claims of the present invention; and such modifications or substitutions are still within the scope defined by the claims of the present invention.

Claims

1. A method for selectively separating pyridine bases from coal-based crude phenols, characterized in that... Includes the following steps: (1) Add the biphase solvent to the coal-based crude phenol, stir, let stand and separate into two phases, separate the two phases to obtain a polar phase rich in pyridine compounds and a nonpolar phase rich in phenol compounds; the biphase solvent is composed of an acidic eutectic solvent and a nonpolar solvent, and the specific addition method is as follows: first, add the nonpolar solvent to the coal-based crude phenol to obtain a premixed nonpolar phase, and then add the acidic eutectic solvent to the premixed nonpolar phase and stir. (2) Add back-extraction agent to the polar phase rich in pyridine compounds, stir, let stand and separate into two phases, separate the two phases to obtain the back-extraction phase rich in pyridine compounds and the eutectic solvent phase; The back-extraction phase rich in pyridine compounds is distilled to obtain pyridine compounds and back-extraction agent; (3) Distill the nonpolar phase rich in phenolic compounds to obtain phenolic compounds and nonpolar solvents.

2. The method for selectively separating pyridine bases from coal-based crude phenols according to claim 1, characterized in that, The coal-based crude phenol includes phenol, cresol, and xylenol, as well as basic pyridine compounds, with a mass concentration of 1-30%.

3. The method for selectively separating pyridine bases from coal-based crude phenols according to claim 1, characterized in that, The acidic eutectic solvent is a ternary or binary mixture, formed by mixing and thoroughly stirring a hydrogen bond donor, a hydrogen bond acceptor, and a ternary additive; the hydrogen bond acceptor is one or more of alcohols, alkanolamines, and amides; the hydrogen bond donor is selected from monobasic organic acids, dibasic organic acids, polybasic organic acids, or organic sulfonic acids; and the ternary additive is a hydroxy acid; the mass ratio of the hydrogen bond donor, hydrogen bond acceptor, and ternary additive is in the range of 1:(0.1~10):(0~10).

4. The method for selectively separating pyridine bases from coal-based crude phenols according to claim 3, characterized in that, The alcohols are one of ethylene glycol, glycerol, diethylene glycol, and triethylene glycol; the amines include one of ethanolamine, isopropanolamine, and diethanolamine; the amides include formamide; the hydrogen bond donors include one or more of glycolic acid, lactic acid, malonic acid, oxalic acid, citric acid, p-toluenesulfonic acid, xylenesulfonic acid, and dodecylbenzenesulfonic acid; and the hydroxy acids include one or more of tartaric acid, malic acid, mandelic acid, and gluconic acid.

5. The method for selectively separating pyridine bases from coal-based crude phenols according to claim 3, characterized in that, The acidic eutectic solvent also includes water. First, the hydrogen bond donor, hydrogen bond acceptor, and ternary additive are mixed and stirred thoroughly to obtain the acidic eutectic solvent. After the obtained acidic eutectic solvent is cooled, water is added and stirred until the system is homogeneous to obtain a water-adjusted acidic eutectic solvent. The amount of water added is 0 to 2 times the mass of the acidic eutectic solvent.

6. The method for selectively separating pyridine bases from coal-based crude phenols according to claim 1, characterized in that, The nonpolar solvent is an alkane compound, including one or more of n-hexane, cyclohexane, n-decane, and decahydronaphthalene.

7. The method for selectively separating pyridine bases from coal-based crude phenols according to claim 1, characterized in that, The amount of acidic eutectic solvent added is 0.5 to 50 times the mass of crude phenol, and the amount of non-polar solvent added is 0.5 to 10 times the mass of crude phenol.

8. The method for selectively separating pyridine bases from coal-based crude phenols according to claim 1, characterized in that, An acidic eutectic solvent and a non-polar solvent were simultaneously added to the crude phenol, and the mixture was stirred at 25-50 °C for 30-60 min. After two-phase solvent extraction and separation, a polar phase rich in pyridine compounds and a non-polar phase rich in phenolic compounds were obtained.

9. The method for selectively separating pyridine bases from coal-based crude phenols according to claim 8, characterized in that, For the polar phase rich in pyridine compounds, back-extraction is performed using a back-extraction agent to obtain a back-extraction phase rich in pyridine compounds and an acidic eutectic solvent phase. After 3 to 10 back-extractions, the acidic eutectic solvent can be recycled. The back-extraction agent is selected from one or more of ether compounds, ester compounds, and sulfides; including one or more of diethyl ether, ethyl acetate, and carbon disulfide; the amount of back-extraction agent added is 0.5 to 10 times the mass of the polar phase rich in pyridine compounds; the stirring temperature when adding the back-extraction agent is 25 to 50 ℃, and the stirring time is 30 to 60 min; The back-extraction phase rich in pyridine compounds is distilled under reduced pressure to obtain pyridine compounds and back-extraction agent; The back-extraction agent can be recycled; the temperature for vacuum distillation is 25 ~ 50℃, the pressure is 300 ~ 500 mbar, and the time is 30 ~ 60 min.

10. The method for selectively separating pyridine bases from coal-based crude phenols according to claim 8, characterized in that, The nonpolar phase rich in phenolic compounds is distilled to obtain phenolic compounds and a nonpolar solvent. The distillation temperature of the nonpolar phase is 30-60 °C, the pressure is 300-500 mbar, and the time is 30-60 min. The obtained nonpolar solvent can be recycled.

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