Method for simultaneously extracting alkaline and neutral nitrogen heterocyclic compounds from wash oil

Abstract

The invention discloses a method for simultaneously extracting alkaline and neutral nitrogen heterocyclic compounds from wash oil, belongs to the technical field of coal chemical industry, and can solve the problems of equipment corrosion by acid and alkali, environmental pollution, high cost, low efficiency, complex extraction agent preparation process and the like when the nitrogen heterocyclic compounds are extracted from the wash oil in the prior art. The method comprises the following steps: heating and mixing a hydrogen bond acceptor and a hydrogen bond donor according to a certain molar ratio to prepare a eutectic solvent; the method comprises the following steps: mixing model wash oil containing a nitrogen heterocyclic compound with a deep-eutectic solvent according to a certain molar ratio, and carrying out extraction operation; adding a back extraction agent into the solvent phase rich in the nitrogen heterocyclic compound for back extraction to obtain a nitrogen heterocyclic compound product; and carrying out rotary evaporation on the deep eutectic solvent, and recovering to obtain the regenerated deep eutectic solvent. According to the present invention, the extraction rate of the basic nitrogen heterocyclic compound (quinoline) in the wash oil is 90-100%, and the extraction rate of the neutral-basic nitrogen heterocyclic compound (indole) is 80-99%. The method greatly improves the extraction rate of the nitrogen heterocyclic compounds in the wash oil, has excellent extraction and separation effects, and is high in extraction efficiency, simple to operate, low in cost, safe, environment-friendly and harmless to human bodies and the environment.

Description

Technical Field

[0001] The present invention belongs to the technical field of coal chemical industry, and specifically relates to a method for simultaneously extracting and separating alkaline and neutral nitrogen heterocyclic compounds from washing oil by using a low eutectic solvent, which can obtain valuable nitrogen heterocyclic compound resources and reduce the nitrogen content in coal tar washing oil, thereby facilitating the deep processing and utilization of coal tar and being green and environmentally friendly. Background Art

[0002] Thermochemical conversion is the main method of coal processing, which can produce coal liquefied oil and coal tar. The former is the main product of direct coal liquefaction, and the latter is a by-product of coal pyrolysis / coking process. Wash oil is the product of 230-300℃ during coal tar distillation, accounting for about 4.5-10% of the mass of coal tar, and is a complex mixture. Wash oil is rich in a variety of fine chemical raw materials or products, and can directly separate and extract benzene, naphthalene, acenaphthene, fluorene, dibenzofuran, phenol, nitrogen heteroaromatic ring (especially quinoline), etc., and has very valuable deep processing value.

[0003] The nitrogen heterocyclic compounds in the wash oil are divided into basic nitrogen heterocyclic compounds (such as quinoline) and neutral nitrogen heterocyclic compounds (such as indole). On the one hand, these nitrogen heterocyclic compounds will affect the quality of the wash oil, and the NO2 produced after combustion is one of the causes of acid rain. Nitrogen oxides will damage the respiratory tract and endanger human health. On the other hand, quinoline and indole are not only raw materials for spices, metallurgy, dyes, polymers and agricultural chemicals, but also can be used to produce a variety of industrial products such as rubber vulcanization accelerators, flotation agents and pesticides. Therefore, the direct extraction and separation of nitrogen heterocyclic compounds from wash oil has important economic value and practical significance.

[0004] Methods for separating indole from washing oil include alkali melting method, acid polymerization method, azeotropic method, complexation method, pressure crystallization method, solvent extraction method, adsorption method and supercritical method, etc. The above methods for separating indole all have other problems such as high cost, high energy consumption, high equipment requirements, difficult to treat wastewater, and serious environmental pollution. Patent CN109718575A uses adsorption method to extract indole from washing oil with polyvinyl pyrrolidone as adsorbent. This method has the characteristics of non-corrosiveness, high extraction efficiency, environmental friendliness, and energy saving, but the consumption of adsorbent is large and the recyclability is poor; Patent CN106631967A uses indole to form a low eutectic solvent with quaternary ammonium salt extractant, and the low eutectic solvent is insoluble in the oil phase, thereby realizing the separation of indole from washing oil. This method has the characteristics of environmental friendliness, simple process, and high extraction efficiency. However, the phenomenon of neutral oil entrainment is obvious; Patent CN1746158A uses salt auxiliary components to add to the indole extractant, so that the composite extractant repels raw material components such as methylnaphthalene, thereby improving the extraction and separation effect of indole. This method is simple to operate and has low energy consumption. However, the use of salt extractants will increase costs, and will also increase subsequent processing processes, causing certain pollution to the environment; Patent CN101774879A mentions a method for extracting high-purity indole by efficient distillation-azeotropic distillation, which has low raw material requirements, good product quality, and is suitable for large-scale industrial production. However, azeotropic substances have certain harm to the environment.

[0005] Methods for separating quinoline from washing oil include acid washing, solvent extraction, supercritical extraction, etc. However, the traditional method requires the use of a large amount of solvent, and the operation is complicated and has serious environmental pollution. Patent CN103641780A uses the alkaline characteristics of quinoline to obtain crude isoquinoline from coal tar by simple acid washing and alkali washing, and then enriches and distills to obtain an enriched fraction containing isoquinoline with higher purity. This patent uses low energy consumption, less waste liquid and is environmentally friendly, but there are three waste problems and leads to the loss of indole. Patent CN102746221A uses ethanol as a supercritical solvent to extract quinoline from washing oil. The present invention uses an acidic salt solution instead of sulfuric acid to enrich quinoline, avoids the generation of industrial waste acid to pollute the environment, greatly reduces the production cost, and the entire process is simple and controllable, but the energy consumption is large and the impurity content of the produced quinoline is large. Patent CN105670671A uses a high-speed centrifugal combined filtration method to remove quinoline from coal tar, which has a good separation effect and is environmentally friendly, but the method uses a high cost of equipment.

[0006] Among the many separation methods, liquid-liquid extraction separation and adsorption separation are easy to operate and can be reused, which are suitable for separating a variety of targets. In addition, as people's awareness of green environmental protection gradually increases, ionic liquids (ILs), deep eutectic solvents (DES) and other extractants have gradually replaced traditional organic solvents with their green and environmentally friendly characteristics. Compared with ionic liquids, the preparation method of deep eutectic solvents is simple, cheap, and biodegradable. Therefore, deep eutectic solvents are widely used in absorption and dissolution, extraction and separation, organic synthesis, biocatalysis, electrocatalysis and other fields. There are hydrogen bonds, π-π and other interactions between aromatic nitrogen compounds (such as quinoline and indole) and deep eutectic solvents. Due to the strong electronegativity of N, the H atom in indole NH is an active H, and the deep eutectic solvent can share electrons with the active H atom of indole to form a hydrogen bond to achieve the extraction effect; the nitrogen atom with lone pair of electrons in the quinoline molecule is easy to combine with the H atom in DES, so the extraction of quinoline is affected by acid-base interaction. Moreover, the extraction and separation of nitrogen heterocyclic compounds from the wash oil by using a low eutectic solvent does not require the use of a large amount of solvent, has little environmental pollution, and can be recycled. In addition, the method is simple to operate, low in cost, and easy to industrialize, laying the foundation for the efficient and clean separation of nitrogen-containing compounds. Summary of the invention

[0007] In view of this, the low eutectic solvent used in the present invention is non-toxic, biodegradable, simple to synthesize, low in energy consumption, low in cost, green and environmentally friendly, and can be recycled and reused, and can efficiently extract and separate the alkaline and neutral nitrogen heterocyclic compounds in the wash oil, and has good economic benefits.

[0008] In order to achieve the above object, the present invention adopts the following technical solution:

[0009] A method for simultaneously extracting basic and neutral nitrogen heterocyclic compounds from wash oil comprises the following steps:

[0010] (1) Mix the typical components of washing oil in a certain proportion in a container, stir for 30-60 minutes at 20-30°C to obtain simulated washing oil.

[0011] (2) Mix the hydrogen bond acceptor and hydrogen bond donor reagents in a molar ratio of 1:1-1:10 in a container, stir at 60-100°C for 30-90 minutes to form a low eutectic solvent.

[0012] (3) The simulated wash oil obtained in step (1) is added to the low eutectic solvent obtained in step (2) at a molar ratio of 1:1-1:5, stirred at 25-50° C. for 20-90 min, and allowed to stand for 1-2 h to separate the layers, thereby obtaining an extract phase and an oil phase of the nitrogen-containing heterocyclic compound.

[0013] (4) Add the stripping agent to the extraction phase in a ratio of 10:1 to 20:1 by mass, stir for 60-120 min at 20-50 °C, let stand for 1-2 h to separate the layers, and repeat the operation 3-5 times to obtain a denitrogenated low eutectic solvent and a stripping phase rich in nitrogen heterocyclic compounds.

[0014] (5) The low eutectic solvent is rotary evaporated to recover the regenerated low eutectic solvent, and the extraction operation is repeated.

[0015] The model wash oil in step (1) is aromatic hydrocarbons, basic nitrogen heterocyclic compounds and neutral nitrogen heterocyclic compounds. The aromatic hydrocarbons are methylnaphthalene, acenaphthene and xylene, the basic nitrogen heterocyclic compound is quinoline, and the neutral nitrogen heterocyclic compound is indole.

[0016] Preferably, the main components of the model wash oil in step (1) are 70 wt.% xylene, 12 wt.% methylnaphthalene, 6 wt.% quinoline, 4 wt.% indole and 8 wt.% acenaphthene.

[0017] Preferably, the hydrogen bond acceptor in step (2) is one or more of choline chloride, tetraethylammonium chloride, tetrabutylammonium bromide, anhydrous magnesium chloride, 1-butyl-3-methylimidazole chloride, and PEG-400, and the hydrogen bond donor is one or more of malonic acid, methanesulfonic acid, acetic acid, p-toluenesulfonic acid (monohydrate), oxalic acid (dihydrate), and formic acid.

[0018] Preferably, the preparation of the low eutectic solvent in step (2) requires heating and stirring until all the solids are melted and the solvent becomes transparent.

[0019] Preferably, the stripping agent in step (4) is a mixture of one or more of cyclohexane, n-hexane, n-heptane, n-octane and petroleum ether.

[0020] Preferably, the rotary evaporation temperature in step (5) is 40-70° C., and the rotary evaporation time is 5-60 min.

[0021] Through the above technical scheme, the present invention provides a method for simultaneously extracting alkaline and neutral nitrogen heterocyclic compounds from washing oil through extraction, back extraction, rotary evaporation and other processes, aiming at the problems that the existing separation method of nitrogen heterocyclic compounds and oil products uses acid-base corrosion equipment, serious pollution, harsh equipment, high extraction cost, low extraction rate, and complicated extraction agent preparation process. It is low-cost, green and environmentally friendly, simple in method and process, and achieves good economic and practical benefits. Specific implementation plan The technical solutions in the embodiments of the present invention are described clearly and completely below. The described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments made by other persons without creative development are within the scope of protection of the present invention.

[0023] Example 1 The present invention provides a method for simultaneously extracting basic and neutral nitrogen heterocyclic compounds from wash oil, comprising the following steps: (1) Weigh 7 g of xylene, 1.2 g of methylnaphthalene, 0.8 g of acenaphthene, 0.6 g of quinoline and 0.4 g of indole into a conical flask with a lid, stir for 30-60 min at 20-30 °C to obtain a model wash oil with a mass fraction of quinoline and indole of 6% and 4% respectively; (2) Tetraethylammonium chloride and malonic acid were mixed in a molar ratio of 1:2 in a 50 ml conical flask with a lid, placed in a magnetic stirring constant temperature oil bath, and stirred continuously at 90°C for 30-90 min until a colorless, transparent and uniform liquid was formed to prepare a low eutectic solvent; (3) The simulated wash oil obtained in step (1) was added to the prepared low eutectic solvent (the molar ratio of the wash oil to the low eutectic solvent was 1:3), stirred at 30° C. for 60 min, and allowed to stand for 60 min to separate layers, thereby obtaining an extract phase and an oil phase of the nitrogen-containing heterocyclic compound. The upper oil phase was removed, and the mass of 1 ml of the oil phase was weighed. The mass concentrations of quinoline and indole in the upper oil phase were determined by GC, and the quinoline extraction rate was calculated to be 97.97%, and the indole extraction rate was 92.62%.

[0024] Example 2 The present invention provides a method for simultaneously extracting basic and neutral nitrogen heterocyclic compounds from wash oil, comprising the following steps: (1) Weigh 7 g of xylene, 1.2 g of methylnaphthalene, 0.8 g of acenaphthene, 0.6 g of quinoline and 0.4 g of indole into a conical flask with a lid, stir for 30-60 min at 20-30 °C to obtain a model wash oil with a mass fraction of quinoline and indole of 6% and 4% respectively; (2) Mix choline chloride and methanesulfonic acid in a molar ratio of 1:1 in a 50 ml conical flask with a lid, place in a magnetic stirring constant temperature oil bath, and continue stirring at 90°C for 30-90 minutes until a colorless, transparent and uniform liquid is formed to prepare a low eutectic solvent; (3) The simulated wash oil obtained in step (1) was added to the prepared low eutectic solvent (the molar ratio of the wash oil to the low eutectic solvent was 1:3), stirred at 30° C. for 60 min, and allowed to stand for 60 min to separate layers, thereby obtaining an extract phase and an oil phase of nitrogen-containing heterocyclic compounds. The upper oil phase was removed, and the mass of 1 ml of the oil phase was weighed. The mass concentrations of quinoline and indole in the upper oil phase were determined by GC, and the quinoline extraction rate was calculated to be 99.73%, and the indole extraction rate was 97.14%.

[0025] Example 3 The present invention provides a method for simultaneously extracting basic and neutral nitrogen heterocyclic compounds from wash oil, comprising the following steps: (1) Weigh 7 g of xylene, 1.2 g of methylnaphthalene, 0.8 g of acenaphthene, 0.6 g of quinoline and 0.4 g of indole into a conical flask with a lid, stir for 30-60 min at 20-30 °C to obtain a model wash oil with a mass fraction of quinoline and indole of 6% and 4% respectively; (2) Tetrabutylammonium bromide and methanesulfonic acid were mixed in a molar ratio of 1:3 in a 50 ml conical flask with a lid, placed in a magnetic stirring constant temperature oil bath, and stirred continuously at 90°C for 30-90 min until a colorless, transparent and uniform liquid was formed, thereby preparing a low eutectic solvent; (3) The simulated wash oil obtained in step (1) was added to the prepared low eutectic solvent (the molar ratio of the wash oil to the low eutectic solvent was 1:3), stirred at 30° C. for 60 min, and allowed to stand for 60 min to separate layers, thereby obtaining an extract phase and an oil phase of nitrogen-containing heterocyclic compounds. The upper oil phase was removed, and the mass of 1 ml of the oil phase was weighed. The mass concentrations of quinoline and indole in the upper oil phase were determined by GC, and the quinoline extraction rate was calculated to be 99.51%, and the indole extraction rate was 97.16%.

[0026] Example 4 The present invention provides a method for simultaneously extracting basic and neutral nitrogen heterocyclic compounds from wash oil, comprising the following steps: (1) Weigh 7 g of xylene, 1.2 g of methylnaphthalene, 0.8 g of acenaphthene, 0.6 g of quinoline and 0.4 g of indole into a conical flask with a lid, stir for 30-60 min at 20-30 °C to obtain a model wash oil with a mass fraction of quinoline and indole of 6% and 4% respectively; (2) Mix anhydrous magnesium chloride and acetic acid in a molar ratio of 1:10 in a 50 ml conical flask with a lid, place in a magnetic stirring constant temperature oil bath, and continue stirring at 90°C for 30-90 minutes until a colorless, transparent and uniform liquid is formed to prepare a low eutectic solvent; (3) The simulated wash oil obtained in step (1) was added to the prepared low eutectic solvent (the molar ratio of the wash oil to the low eutectic solvent was 1:1), stirred at 30° C. for 60 min, and allowed to stand for 60 min to separate layers, thereby obtaining an extract phase and an oil phase of nitrogen-containing heterocyclic compounds. The upper oil phase was removed, and the mass of 1 ml of the oil phase was weighed. The mass concentrations of quinoline and indole in the upper oil phase were determined by GC, and the quinoline extraction rate was calculated to be 97.88%, and the indole extraction rate was 87.57%.

[0027] Example 5 The present invention provides a method for simultaneously extracting basic and neutral nitrogen heterocyclic compounds from wash oil, comprising the following steps: (1) Weigh 7 g of xylene, 1.2 g of methylnaphthalene, 0.8 g of acenaphthene, 0.6 g of quinoline and 0.4 g of indole into a conical flask with a lid, stir for 30-60 min at 20-30 °C to obtain a model wash oil with a mass fraction of quinoline and indole of 6% and 4% respectively; (2) Choline chloride and p-toluenesulfonic acid (monohydrate) were mixed in a 50 ml conical flask with a lid at a molar ratio of 1:1, placed in a magnetic stirring constant temperature oil bath, and stirred continuously at 90°C for 30-90 min until a colorless, transparent and uniform liquid was formed, and 3% by mass of water was added to prepare a low eutectic solvent; (3) The simulated wash oil obtained in step (1) was added to the prepared low eutectic solvent (the molar ratio of the wash oil to the low eutectic solvent was 1:3), stirred at 30° C. for 60 min, and allowed to stand for 60 min to separate layers, thereby obtaining an extract phase and an oil phase of nitrogen-containing heterocyclic compounds. The upper oil phase was removed, and the mass of 1 ml of the oil phase was weighed. The mass concentrations of quinoline and indole in the upper oil phase were determined by GC, and the quinoline extraction rate was calculated to be 99.66%, and the indole extraction rate was 96.68%.

[0028] Example 6 The present invention provides a method for simultaneously extracting basic and neutral nitrogen heterocyclic compounds from wash oil, comprising the following steps: (1) Weigh 7 g of xylene, 1.2 g of methylnaphthalene, 0.8 g of acenaphthene, 0.6 g of quinoline and 0.4 g of indole into a conical flask with a lid, stir for 30-60 min at 20-30 °C to obtain a model wash oil with a mass fraction of quinoline and indole of 6% and 4% respectively; (2) 1-Butyl-3-methylimidazole chloride and oxalic acid (dihydrate) were mixed in a 50 ml conical flask with a lid at a molar ratio of 1:1, placed in a magnetic stirring constant temperature oil bath, and stirred continuously at 90°C for 30-90 min until a colorless, transparent and uniform liquid was formed, thereby preparing a low eutectic solvent; (3) The simulated wash oil obtained in step (1) was added to the prepared low eutectic solvent (the molar ratio of the wash oil to the low eutectic solvent was 1:3), stirred at 30° C. for 60 min, and allowed to stand for 60 min to separate layers, thereby obtaining an extract phase and an oil phase of nitrogen-containing heterocyclic compounds. The upper oil phase was removed, and the mass of 1 ml of the oil phase was weighed. The mass concentrations of quinoline and indole in the upper oil phase were determined by GC, and the quinoline extraction rate was calculated to be 99.67%, and the indole extraction rate was 86.03%.

[0029] Example 7 The present invention provides a method for simultaneously extracting basic and neutral nitrogen heterocyclic compounds from wash oil, comprising the following steps: (1) Weigh 7 g of xylene, 1.2 g of methylnaphthalene, 0.8 g of acenaphthene, 0.6 g of quinoline and 0.4 g of indole into a conical flask with a lid, stir for 30-60 min at 20-30 °C to obtain a model wash oil with a mass fraction of quinoline and indole of 6% and 4% respectively; (2) PEG-400 and p-toluenesulfonic acid (monohydrate) were mixed in a 50 ml conical flask with a lid at a molar ratio of 1:1, placed in a magnetic stirring constant temperature oil bath, and stirred continuously at 90°C for 30-90 min until a colorless, transparent and uniform liquid was formed, and 5% by mass of water was added to prepare a low eutectic solvent; (3) The simulated wash oil obtained in step (1) was added to the prepared low eutectic solvent (the molar ratio of the wash oil to the low eutectic solvent was 1:3), stirred at 30° C. for 60 min, and allowed to stand for 60 min to separate layers, thereby obtaining an extract phase and an oil phase of nitrogen-containing heterocyclic compounds. The upper oil phase was removed, and the mass of 1 ml of the oil phase was weighed. The mass concentrations of quinoline and indole in the upper oil phase were determined by GC, and the quinoline extraction rate was calculated to be 83.17%, and the indole extraction rate was 84.44%.

[0030] Example 8 The present invention provides a method for simultaneously extracting basic and neutral nitrogen heterocyclic compounds from wash oil, comprising the following steps: (1) Weigh 7 g of xylene, 1.2 g of methylnaphthalene, 0.8 g of acenaphthene, 0.6 g of quinoline and 0.4 g of indole into a conical flask with a lid, stir for 30-60 min at 20-30 °C to obtain a model wash oil with a mass fraction of quinoline and indole of 6% and 4% respectively; (2) Tetraethylammonium chloride and oxalic acid (dihydrate) were mixed in a 50 ml conical flask with a lid at a molar ratio of 1:1, placed in a magnetic stirring constant temperature oil bath, and stirred continuously at 90°C for 30-90 min until a colorless, transparent and uniform liquid was formed to prepare a low eutectic solvent; (3) Add the simulated wash oil obtained in step (1) to the prepared low eutectic solvent (the molar ratio of wash oil to low eutectic solvent is 1:3), stir at 30°C for 60 minutes, let stand for 60 minutes to separate the layers, and obtain the nitrogen-containing heterocyclic compound extraction phase and oil phase. Remove the upper oil phase, weigh 1 ml of the oil phase, and use GC to determine the mass concentration of quinoline and indole in the upper oil phase. The quinoline extraction rate is calculated to be 99.58%, and the indole extraction rate is 90.89%; (4) adding petroleum ether as the stripping agent to the extraction phase in a ratio of 10:1 by mass, stirring for 60-120 min at 20-50 °C, standing for 1-2 h to separate layers, repeating the operation three times to obtain a denitrogenated low eutectic solvent and a stripping phase rich in nitrogen heterocyclic compounds; (5) The low eutectic solvent was rotary evaporated to recover the regenerated low eutectic solvent, and the above extraction process was repeated three times, and the extraction rates of quinoline were 97.79%, 84.34%, and 64.86%, respectively; the extraction rates of indole were 82.76%, 80.54%, and 79.55%, respectively.

[0031] Example 9 The present invention provides a method for simultaneously extracting basic and neutral nitrogen heterocyclic compounds from wash oil, comprising the following steps: (1) Weigh 7 g of xylene, 1.2 g of methylnaphthalene, 0.8 g of acenaphthene, 0.6 g of quinoline and 0.4 g of indole into a conical flask with a lid, stir for 30-60 min at 20-30 °C to obtain a model wash oil with a mass fraction of quinoline and indole of 6% and 4% respectively; (2) Mix anhydrous magnesium chloride and formic acid in a molar ratio of 1:6 in a 50 ml conical flask with a lid, place in a magnetic stirring constant temperature oil bath, and continue stirring at 70°C for 30-90 minutes until a colorless, transparent and uniform liquid is formed to prepare a low eutectic solvent; (3) Add the simulated wash oil obtained in step (1) to the prepared low eutectic solvent (the molar ratio of wash oil to low eutectic solvent is 1:3), stir at 30°C for 60 minutes, let stand for 60 minutes to separate the layers, and obtain the nitrogen-containing heterocyclic compound extraction phase and oil phase. Remove the upper oil phase, weigh 1 ml of the oil phase, and use GC to determine the mass concentration of quinoline and indole in the upper oil phase. The quinoline extraction rate is calculated to be 99.42%, and the indole extraction rate is 97.11%; (4) adding petroleum ether as the stripping agent to the extraction phase in a ratio of 10:1 by mass, stirring for 60-120 min at 20-50 °C, standing for 1-2 h to separate layers, repeating the operation three times to obtain a denitrogenated low eutectic solvent and a stripping phase rich in nitrogen heterocyclic compounds; (5) The low eutectic solvent was rotary evaporated to obtain a regenerated low eutectic solvent, and the above extraction process was repeated three times, and the extraction rates of quinoline were 99.63%, 99.48%, and 99.21%, respectively; the extraction rates of indole were 97.17%, 96.85%, and 96.76%, respectively.

[0032] Hydrogen bonds, π-π and other interactions are formed between nitrogen-containing compounds and low eutectic solvents, but this interaction cannot fully realize the efficient extraction of nitrogen-containing compounds. The denitrogenation of quinoline is based on the Lewis acid-base theory, and the mechanism lies in the acid-base neutralization effect. Therefore, the stronger the acidity of the extractant, the higher the extraction rate of the basic nitrogen compound; indole is a non-basic nitrogen compound, and its extraction mainly relies on the hydrogen bond between the extractant and indole. This hydrogen bond effect is weaker than the acid-base neutralization effect. Therefore, the research on the simultaneous extraction of basic nitrogen and non-basic nitrogen from coal tar is of far-reaching significance.

[0033] Through the testing of the above specific implementation scheme, the hydrogen bond acceptor and hydrogen bond donor reagents used in the technical solution of the present invention are relatively common, low-cost, non-toxic and pollution-free, and have a good denitrification effect.

[0034] The embodiments in this specification mainly focus on the selection and mixing ratio of hydrogen bond acceptors and hydrogen bond donors in the low eutectic solvent. Due to the different structures and compositions of hydrogen bond donors and hydrogen bond acceptors, the low eutectic solvents formed have greatly different denitrification effects on simulated wash oils. Therefore, the same and similar parts between the embodiments can be referenced to each other.

[0035] It should be understood that the above-disclosed embodiments are merely exemplary. For professionals in the field, the above-disclosed embodiments can be modified, replaced, improved, etc. in various ways, and the general principles defined herein can be applied to other embodiments without departing from the spirit and scope of the present technical solution. Therefore, the above-disclosed embodiments do not limit the present invention, and the scope of limitation should be the widest scope consistent with the principles and innovations disclosed in the present technical solution.

Claims

1. A method for simultaneously extracting basic and neutral nitrogen heterocyclic compounds from wash oil, characterized in that: The steps include: (1) Mix typical components of washing oil in a certain proportion in a container, stir for 30-60 minutes at 20-30°C to obtain simulated washing oil; (2) Mix the hydrogen bond acceptor and hydrogen bond donor reagent in a molar ratio of 1:1-1:10 in a container, stir for 30-90 minutes at 60-100°C to form a low eutectic solvent; (3) adding the simulated wash oil obtained in step (1) to the low eutectic solvent obtained in step (2) at a molar ratio of 1:1-1:3, stirring for 20-90 min at 25-50° C., standing for 1-2 h to separate the layers, and obtaining an extract phase and an oil phase of the nitrogen-containing heterocyclic compound; (4) adding the stripping agent to the extraction phase in a ratio of 10:1 to 20:1 by mass, stirring for 60-120 min at 20-50° C., standing for 1-2 h to separate layers, and repeating the operation 3-5 times to obtain a denitrogenated low eutectic solvent and a stripping phase rich in nitrogen heterocyclic compounds; (5) The low eutectic solvent is rotary evaporated to recover the regenerated low eutectic solvent, and the extraction operation is repeated.

2. A method for simultaneously extracting basic and neutral nitrogen heterocyclic compounds from wash oil according to claim 1, wherein the model wash oil in step (1) is aromatic hydrocarbons, basic nitrogen heterocyclic compounds and neutral nitrogen heterocyclic compounds. The aromatic hydrocarbons are methylnaphthalene, acenaphthene and xylene, the basic nitrogen heterocyclic compound is quinoline, and the neutral nitrogen heterocyclic compound is indole.

3. A method for simultaneously extracting basic and neutral nitrogen heterocyclic compounds from wash oil according to claim 1, wherein the main components of the model wash oil in step (1) are 70 wt.% xylene, 12 wt.% methylnaphthalene, 6 wt.% quinoline, 4 wt.% indole and 8 wt.% acenaphthene.

4. A method for simultaneously extracting alkaline and neutral nitrogen heterocyclic compounds from wash oil according to claim 1, wherein the hydrogen bond acceptor in step (2) is one or more of choline chloride, tetraethylammonium chloride, tetrabutylammonium bromide, anhydrous magnesium chloride, 1-butyl-3-methylimidazole chloride, and PEG-400, and the hydrogen bond donor is one or more of malonic acid, methanesulfonic acid, acetic acid, p-toluenesulfonic acid (monohydrate), oxalic acid (dihydrate), and formic acid.

5. According to the method for simultaneously extracting alkaline and neutral nitrogen heterocyclic compounds from wash oil according to claim 1, the preparation of the low eutectic solvent in step (2) requires heating and stirring until all the solids are melted and the solvent is transparent.

6. A method for simultaneously extracting basic and neutral nitrogen heterocyclic compounds from wash oil according to claim 1, wherein the stripping agent in step (4) is a mixture of one or more of cyclohexane, n-hexane, n-heptane, n-octane and petroleum ether.

7. A method for simultaneously extracting basic and neutral nitrogen heterocyclic compounds from wash oil according to claim 1, wherein the rotary evaporation temperature in step (5) is 40-70°C and the rotary evaporation time is 5-60 min.