Method for extracting and separating phenolic pollutants in semi-coke wastewater by using hydrophobic deep-eutectic solvent based on menthol

Abstract

The invention discloses a method for extracting and separating phenolic pollutants in semi-coke wastewater by using a hydrophobic deep-eutectic solvent based on menthol, and belongs to the technical field of wastewater treatment. According to the method, a hydrogen bond acceptor (such as DL-menthol) and a hydrogen bond donor (such as n-hexanoic acid, octanoic acid, capric acid, nonanoic acid or thymol) are utilized to form hydrogen bonds, and a hydrophobic deep-eutectic solvent with good fluidity is formed. By controlling the molar ratio of the hydrogen bond acceptor to the hydrogen bond donor, the hydrophilicity of the solvent can be adjusted, and the extraction requirements of different phenolic substances can be met. The hydrophobic deep-eutectic solvent prepared by the method has good thermal stability and can be kept stable at lower and higher temperatures. In addition, the eutectic solvent can be used for extracting and separating phenolic pollutants such as p-cresol in semi-coke wastewater. The whole operation process is simple, convenient and rapid, the extraction efficiency is high, and secondary pollution is avoided.

Description

Technical Field

[0001] The present invention belongs to the technical field of wastewater treatment, and particularly relates to a method for extracting and separating phenolic pollutants in semi-coke wastewater based on menthol-based hydrophobic deep eutectic solvents. Background Art

[0002] Semi-coke wastewater mainly comes from the wastewater generated during the medium and low temperature dry distillation of low-rank coal, including raw gas circulating condensate and gas purification wastewater, etc. Its composition is complex and contains a large number of pollutants such as coal tar, phenols, ammonia nitrogen, sulfides, and cyanides. If directly discharged without treatment, it will cause serious pollution to water bodies, soil, and ecosystems, and disrupt the ecological balance. Among them, phenolic compounds have high concentrations, various types, and high toxicity. After entering the water body, they will have extremely high toxicity to aquatic organisms, and even cause water pollution and disrupt the ecological balance even at very low concentrations. They can accumulate through the food chain and affect the growth and reproduction of fish and other aquatic organisms. Phenols can also cause harm to the human body through skin contact, inhalation, or ingestion, triggering various health problems such as dermatitis, respiratory irritation, and liver and kidney damage. Long-term exposure to a phenolic environment may also increase the risk of cancer. Therefore, it is necessary to systematically treat semi-coke wastewater and reduce the pollutant concentration through multi-stage processes to reduce its harm to the environment.

[0003] Phenolic substances in semi-coke wastewater are both a type of new pollutant and play a versatile role in industry. They are not only the key raw materials for manufacturing products such as phenolic resins, plastics, explosives, drugs, antioxidants, dark dyes, and wood preservatives, but also play an important role as intermediates and disinfectants in the pharmaceutical field. In addition, phenolic compounds are widely used in industries such as synthetic fibers, rubber, spices, and coatings, and are used as fuel additives in the energy field to improve combustion efficiency, and as water treatment agents in the environmental protection field to reduce pollution. Phenolic substances have an indispensable position in many industrial fields such as chemical engineering, medicine, energy, and environmental protection.

[0004] Therefore, separating phenolic substances from semi-coke wastewater can not only be recycled to reduce energy consumption, but also reduce the concentration of phenolic pollutants in semi-coke wastewater to the standard that can be degraded by advanced oxidation and biological treatment, thereby reducing the biochemical treatment load. There are many methods for the adsorption and degradation treatment of phenolic substances, mainly including adsorption method, solvent extraction method and steam stripping method, etc. The adsorption method mainly uses porous solid substances as adsorbents, such as activated carbon, diatomite and ion exchange resin, etc., to adsorb phenolic pollutants in the wastewater through the surface of the adsorbent. After adsorption, desorption can be carried out with lye or organic solvents. This method has simple equipment, small floor area and stable treatment, but the adsorption efficiency is not high, and secondary pollution is likely to occur during subsequent treatment; the steam stripping method mainly recovers and treats volatile phenolic substances in the wastewater, and separates the volatile phenolic substances in the wastewater through steam or other gases for recycling. The phenol removal efficiency of the steam stripping method is not high, and non-volatile phenolic substances cannot be recovered, and the phenol removal effect is unstable, so it is necessary to further improve the technology to improve its phenol removal efficiency. The solvent extraction method is the most commonly used wastewater treatment method in industry. For wastewater with different water qualities and concentrations, factors such as the solubility of the extractant in phenolic substances, the recovery of the extractant, the physical and chemical properties of the extractant, and the cost of the extractant need to be comprehensively considered to select a suitable extractant. The complexation extraction and phenol removal method is a solvent extraction method for phenolic substances with a wide range of applications, high separation efficiency and convenient operation, but its single nature limits its extensive application. The existing methods for recovering phenolic substances have the defects of low efficiency and poor effect. Therefore, it is necessary to find a method for recovering and utilizing phenolic pollutants that is efficient, green and recyclable. Summary of the Invention

[0005] In view of the above technical problems, the present invention proposes a method for extracting and separating phenolic pollutants from semi-coke wastewater based on a hydrophobic deep eutectic solvent (HDES) of menthol.

[0006] To achieve the above object, the present invention provides the following technical solutions:

[0007] One of the objects of the present invention is to provide a hydrophobic deep eutectic solvent based on menthol, which includes a hydrogen bond acceptor and a hydrogen bond donor. The hydrogen bond acceptor (HBA) is DL-menthol, and the hydrogen bond donor (HBD) is one of n-hexanoic acid, octanoic acid, decanoic acid, nonanoic acid and thymol.

[0008] In the present invention, DL-menthol is used as a hydrogen bond acceptor, and one of n-hexanoic acid, octanoic acid, decanoic acid, nonanoic acid, and thymol is used as a hydrogen bond donor. The hydrogen bond acceptor and the hydrogen bond donor interact with each other by forming hydrogen bonds, reducing the melting point of the system and forming a deep eutectic solvent. DL-menthol is a mixture of L-menthol and D-menthol, and its chemical structure is relatively more stable. This stability enables DL-menthol to better combine with other hydrogen bond donors (HBDs) when acting as a hydrogen bond acceptor, forming a stable eutectic mixture. Using DL-menthol as a hydrogen bond acceptor and one of n-hexanoic acid, octanoic acid, decanoic acid, nonanoic acid, and thymol as a hydrogen bond donor, the formed deep eutectic solvent has good hydrophobicity. The specific reasons are as follows: On the one hand, the molecular structure of DL-menthol contains a non-polar hydrophobic alkyl part, which occupies a considerable proportion in the molecule, making DL-menthol itself have a certain degree of hydrophobicity. When DL-menthol acts as a hydrogen bond acceptor and combines with other compounds, its hydrophobic alkyl part often faces the outside of the solvent, thus enhancing the hydrophobicity of the entire solvent system. On the other hand, fatty acids such as n-hexanoic acid, octanoic acid, decanoic acid, and nonanoic acid are used as hydrogen bond donors, and their molecular structures contain long carbon-hydrogen chains. These carbon-hydrogen chains are non-polar and thus hydrophobic. When these fatty acids combine with DL-menthol to form DES, their carbon-hydrogen chains will intertwine with each other, further enhancing the hydrophobicity of the solvent system. In addition, although the carboxyl part of the fatty acid molecule has a certain degree of hydrophilicity, during the formation of DES, this hydrophilic group often forms hydrogen bonds with the hydrophilic groups such as the hydroxyl group of DL-menthol, and thus is "fixed" inside the solvent system, reducing the interaction with external water molecules. Thymol, as a compound with a special fragrance, also contains a non-polar hydrophobic part in its molecular structure. When thymol acts as a hydrogen bond donor and combines with DL-menthol, its hydrophobic part also faces the outside of the solvent, further enhancing the hydrophobicity of the solvent system. In addition, thymol also has certain antibacterial and antioxidant properties, and these properties may be retained and enhanced in DES, thus endowing DES with more application advantages. All in all, during the formation of DES, DL-menthol and hydrogen bond donors such as fatty acids and thymol are tightly combined with each other through hydrogen bond and other interactions. This combination makes the non-polar parts in the solvent system (such as the hydrophobic alkyl group of DL-menthol, the carbon-hydrogen chain of fatty acids, and the hydrophobic part of thymol) aggregate with each other and face the outside of the solvent, while the hydrophilic parts are "fixed" inside the solvent system. This special structure makes DES as a whole exhibit good hydrophobicity.

[0009] Furthermore, the molar ratio of the hydrogen bond acceptor to the hydrogen bond donor is (3:1)-(1:3). Within this ratio range, the hydrogen bond donor and the acceptor can form a stable hydrogen bond network, making the solvent have good hydrophobicity and fluidity.

[0010] The second object of the present invention is to provide a preparation method of a hydrophobic eutectic solvent based on menthol, comprising the following steps: mixing a hydrogen bond acceptor and a hydrogen bond donor, followed by heating in a water bath to obtain a transparent and homogeneous liquid sample, and standing to obtain the hydrophobic eutectic solvent based on menthol.

[0011] Further, the conditions of the water bath heating are: temperature 60 °C, stirring rate 500 - 800 rpm, and heat preservation time 20 - 40 min. Water bath heating can enable heat to be evenly transferred to the mixture, avoiding decomposition or side reactions caused by local overheating. A temperature of 60 °C is conducive to the dynamic balance of the formation and destruction of hydrogen bonds, promoting the interaction between the hydrogen bond donor and acceptor, and enabling the mixture to form a homogeneous eutectic solvent. A stirring rate of 500 - 800 rpm can ensure sufficient mixing of the mixture, enabling the hydrogen bond donor and acceptor to fully contact and accelerating the formation of the eutectic solvent. The heat preservation time of 20 - 40 min is to allow sufficient time for the hydrogen bond donor and acceptor to interact and form a stable eutectic solvent.

[0012] Further, the standing time is 2 h. This further stabilizes the hydrogen bond network in the eutectic solvent system to form a homogeneous and transparent liquid. During the standing process, the tiny bubbles and impurities in the system can gradually float or precipitate, making the properties of the solvent more stable.

[0013] The third object of the present invention is to provide a method for extracting and separating phenolic pollutants from semi-coke wastewater, using the hydrophobic eutectic solvent based on menthol to extract and separate the phenolic pollutants from semi-coke wastewater.

[0014] The present invention utilizes the characteristics of hydrogen bonds in the prepared hydrophobic eutectic solvent, enabling compounds that are unstable at room temperature to form stable complexes. This eutectic solvent has good hydrophobicity and can form an obvious layer separation with water. Phenolic compounds (such as p-cresol, etc.) usually have a certain degree of hydrophobicity and are more likely to dissolve in hydrophobic solvents. The hydrogen bond donor and acceptor in the eutectic solvent can form hydrogen bonds with phenolic compounds, further enhancing its dissolution ability for phenols.

[0015] Further, it comprises the following steps: mixing the hydrophobic eutectic solvent based on menthol with phenolic wastewater, stirring, standing for layer separation, and performing liquid chromatography analysis on the lower aqueous phase.

[0016] Further, the volume ratio of the hydrophobic eutectic solvent based on menthol to the phenolic wastewater is 1∶1.

[0017] Further, the stirring time is 5 - 10 min. Mix the menthol-based hydrophobic deep eutectic solvent with the phenol-containing wastewater and stir for 5 - 10 min. Stirring can enable the deep eutectic solvent to fully contact the phenol-containing wastewater, increase the mass transfer area between the solvent and the wastewater, and improve the mass transfer rate, thereby accelerating the transfer of phenolic pollutants from the wastewater to the deep eutectic solvent.

[0018] Further, the standing time is 30 - 60 min. Due to the density difference between the deep eutectic solvent and water and its hydrophobicity, it will naturally layer with the water phase. Phenolic pollutants (such as p-cresol) are more inclined to dissolve in the deep eutectic solvent, thus achieving separation from the water phase.

[0019] Liquid chromatography separates samples by the distribution and adsorption of sample molecules between the stationary phase and the mobile phase, thereby achieving qualitative and quantitative analysis of the samples. Through liquid chromatography analysis, the residual amount of phenolic pollutants in the water phase can be detected, and then the effect of extraction and separation can be evaluated.

[0020] Further, the phenolic pollutants are p-cresol, 2-chlorophenol, o-cresol, phenol or resorcinol.

[0021] Compared with the prior art, the present invention has the following advantages and technical effects:

[0022] Lancarbon wastewater is a highly polluted and toxic industrial wastewater, and its main characteristics include complex chemical composition, high ammonia nitrogen content, high pH value, high concentration of oil substances, high concentration of phenolic and cyanide pollutants, poor biodegradability, high ammonia nitrogen concentration, high chroma, and a large amount of coal tar and low molecular organics. The commonly used extractant in conventional pretreatment methods is methyl isobutyl ketone (MIBK), whose extraction efficiency for phenolic substances is about 85%, significantly reducing the burden of subsequent biochemical treatment. However, it is prone to cause secondary pollution during the subsequent treatment process, and its boiling point is 116.54 °C, while the boiling point of volatile phenols is below 230 °C, so it cannot distill and separate volatile phenolic substances with a boiling point above 117 °C. Compared with conventional organic extractants, the hydrophobic deep eutectic solvent prepared in the present invention is composed of two substances, HBA and HBD, in different molar ratios. Most of the existing deep eutectic solvents seem to be hydrophilic, and only a small part is hydrophobic. Hydrophilic deep eutectic solvents cannot be applied to phenolic extraction and will cause secondary pollution. Compared with traditional extractants, the HDES prepared in the present invention has higher thermal stability and can remain stable at both low and high temperatures. During the process of recovering phenols, high temperature will not affect its state of existence. The hydrophobic deep eutectic solvent can be recycled. After each extraction is completed, the supernatant can be separated and reused to extract high-concentration phenolic wastewater again. The extraction efficiency of phenolic substances each time is above 90%. The phenolic hydrophobic deep eutectic solvent can also be back-extracted for phenolic substances by activated carbon adsorption to regenerate the extractant for subsequent reuse.

[0023] During the process of extracting phenolic substances with the hydrophobic deep eutectic solvent prepared in the present invention, the operation process is simple, time-consuming, efficient. After extraction, an obvious HDES-water separation interface will be formed, which is easy to separate and not prone to cause secondary pollution. The separated HDES part can be reused to extract phenolic substances again and can still maintain a high extraction effect. Compared with MIBK, the components of the synthesized hydrophobic deep eutectic solvent have low toxicity, are easy to store, and can stably exist under normal temperature and pressure. The pressure on the human body and the environment is small, which is convenient for transportation and storage. Specific Embodiments

[0024] The various exemplary embodiments of the present invention will be described in detail below. This detailed description should not be considered as a limitation of the present invention, but should be understood as a more detailed description of certain aspects, characteristics, and implementation embodiments of the present invention.

[0025] It should be understood that the terms used in the present invention are only for describing specific embodiments and are not intended to limit the present invention. Additionally, for the numerical ranges in the present invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Each intermediate value within any stated value or stated range, as well as each smaller range between any other stated value or intermediate value within the stated range, is also included in the present invention. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.

[0026] Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. Although the present invention only describes preferred methods and materials, any methods and materials similar or equivalent to those described herein may also be used in the practice or testing of the present invention. All documents mentioned in this specification are incorporated by reference to disclose and describe the methods and / or materials related to the documents. In case of conflict with any incorporated document, the content of this specification shall prevail.

[0027] Without departing from the scope or spirit of the present invention, various improvements and changes can be made to the specific embodiments of the present invention specification, which are obvious to those skilled in the art. Other embodiments obtained from the specification of the present invention are obvious to those skilled in the art. The specification and examples of the present invention are merely exemplary.

[0028] Regarding the use of "comprising", "including", "having", "containing", etc. herein, they are all open-ended terms, meaning including but not limited to.

[0029] An embodiment of the present invention provides a method for extracting and separating phenolic pollutants in semi-coke wastewater based on menthol-based hydrophobic deep eutectic solvents, comprising the following steps:

[0030] (1) Mix a hydrogen bond acceptor and a hydrogen bond donor in a required molar ratio, and keep them warm in a 60 °C water bath under vigorous magnetic stirring at 500 - 800 rpm (such as 500 rpm or 800 rpm). After stirring for 20 - 40 min (such as 20 min, 30 min or 40 min), a transparent and homogeneous liquid sample is obtained, and then it is allowed to stand for 2 h to ensure that no precipitation forms during cooling. The successfully prepared HDES is used for phenol extraction;

[0031] (2) Mix the successfully prepared HDES with the phenol-containing wastewater and stir. After stirring for 5 - 10 min (such as 10 min), let it stand for 30 - 60 min (such as 30 mim) for layering treatment.

[0032] The molar ratio of the hydrogen bond acceptor to the hydrogen bond donor is (3:1)-(1:3), and their viscosities are measured respectively to ensure hydrophobicity and stability. The hydrogen bond acceptor is DL-menthol, and the hydrogen bond donor is one of n-caproic acid, octanoic acid, decanoic acid, nonanoic acid and thymol. Exemplarily, in the following examples of the present invention, the molar ratio of the hydrogen bond acceptor to the hydrogen bond donor can be selected as 2:1, 1:2 or 1:1.

[0033] The phenolic pollutants are p-cresol, 2-chlorophenol, o-cresol, phenol or resorcinol.

[0034] In the following examples of the present invention, the hydrophobic deep eutectic solvent and the phenolic wastewater are mixed in an equal volume ratio, and the effect is verified with the concentration of phenolic substances being 5000 mg / L.

[0035] In the present invention, "room temperature" refers to 30 °C unless otherwise specified.

[0036] All raw materials used in the present invention are obtained by purchasing on the market.

[0037] The technical solution of the present invention is further described below through examples.

[0038] Example 1

[0039] A method for extracting and separating p-cresol pollutants from semi-coke wastewater, comprising the following steps:

[0040] Mix DL-menthol and decanoic acid in a molar ratio of 2:1, and keep them warm in a 60 °C water bath under vigorous magnetic stirring at 800 rpm. After 20 min, a transparent and homogeneous liquid sample is obtained, and then it is allowed to stand for 2 h to ensure that no precipitation forms during cooling, obtaining HDES;

[0041] Under room temperature conditions, a certain concentration of aqueous phase (the concentration of phenol in semi-coke wastewater is 5000 mg / L) and HDES with equal volume (50 mL, A / O = 1) are mixed in a beaker and magnetically stirred at a stirring speed of 500 rpm for 10 min. After the two phases reach extraction equilibrium, the stirred solution is allowed to stand for 30 min to separate layers, and the lower aqueous phase is analyzed by liquid chromatography. The extraction rate of phenol is 93.64%.

[0042] Example 2

[0043] A method for extracting and separating p-cresol pollutants from semi-coke wastewater, comprising the following steps:

[0044] Mix DL-menthol and octanoic acid in a molar ratio of 1:2, and keep them warm in a 60 °C water bath under vigorous magnetic stirring at 800 rpm. After 20 min, a transparent and homogeneous liquid sample is obtained, and then it is allowed to stand for 2 h to ensure that no precipitation forms during cooling, obtaining HDES;

[0045] At room temperature, an aqueous phase with a certain concentration (the concentration of phenol in the semi-coke wastewater is 5000 mg / L) and an equal volume of HDES (50 mL, A / O = 1) were mixed in a beaker, and magnetically stirred at a stirring speed of 500 rpm for 10 min. After the two phases reached extraction equilibrium, the stirred solution was allowed to stand for 30 min to separate into layers, and the lower aqueous phase was analyzed by liquid chromatography. The extraction rate of phenol was 92.36%.

[0046] Example 3

[0047] A method for extracting and separating p-cresol pollutants from semi-coke wastewater, comprising the following steps:

[0048] DL-menthol and n-hexanoic acid were mixed in a molar ratio of 1:1 and kept warm in a 60 °C water bath under vigorous magnetic stirring at 800 rpm. After 20 min, a transparent and homogeneous liquid sample was obtained, and then it was allowed to stand for 2 h to ensure that no precipitation formed during cooling, obtaining HDES;

[0049] At room temperature, an aqueous phase with a certain concentration (the concentration of phenol in the semi-coke wastewater is 5000 mg / L) and an equal volume of HDES (50 mL, A / O = 1) were mixed in a beaker, and magnetically stirred at a stirring speed of 500 rpm for 10 min. After the two phases reached extraction equilibrium, the stirred solution was allowed to stand for 30 min to separate into layers, and the lower aqueous phase was analyzed by liquid chromatography. The extraction rate of phenol was 94.32%.

[0050] Example 4

[0051] A method for extracting and separating p-cresol pollutants from semi-coke wastewater, comprising the following steps:

[0052] DL-menthol and thymol were mixed in a molar ratio of 1:1 and kept warm in a 60 °C water bath under vigorous magnetic stirring at 800 rpm. After 20 min, a transparent and homogeneous liquid sample was obtained, and then it was allowed to stand for 2 h to ensure that no precipitation formed during cooling, obtaining HDES;

[0053] At room temperature, an aqueous phase with a certain concentration (the concentration of phenol in the semi-coke wastewater is 5000 mg / L) and an equal volume of HDES (50 mL, A / O = 1) were mixed in a beaker, and magnetically stirred at a stirring speed of 500 rpm for 10 min. After the two phases reached extraction equilibrium, the stirred solution was allowed to stand for 30 min to separate into layers, and the lower aqueous phase was analyzed by liquid chromatography. The extraction rate of phenol was 94.41%.

[0054] Example 5

[0055] A method for extracting and separating p-cresol pollutants from semi-coke wastewater, comprising the following steps:

[0056] Mix DL-menthol and nonanoic acid in a molar ratio of 1:1, and keep them warm in a 60 °C water bath under vigorous magnetic stirring at 800 rpm. After 20 min, a transparent and homogeneous liquid sample is obtained, and then it is allowed to stand for 2 h to ensure that no precipitation forms during cooling, obtaining HDES;

[0057] Under room temperature conditions, mix an aqueous phase with a certain concentration (the concentration of p-cresol in semi-coke wastewater is 5000 mg / L) and HDES in equal volumes (50 mL, A / O = 1) in a beaker, and magnetically stir at a stirring speed of 500 rpm for 10 min. After the two phases reach extraction equilibrium, let the stirred solution stand for 30 min to separate layers, and perform liquid chromatography analysis on the lower aqueous phase. The extraction rate of phenol is 96.87%.

[0058] Example 6

[0059] A method for extracting and separating p-cresol pollutants from semi-coke wastewater, comprising the following steps:

[0060] Mix DL-menthol and decanoic acid in a molar ratio of 2:1, and keep them warm in a 60 °C water bath under vigorous magnetic stirring at 800 rpm. After 40 min, a transparent and homogeneous liquid sample is obtained, and then it is allowed to stand for 2 h to ensure that no precipitation forms during cooling, obtaining HDES;

[0061] Under room temperature conditions, mix an aqueous phase with a certain concentration (the concentration of p-cresol in semi-coke wastewater is 5000 mg / L) and HDES in equal volumes (50 mL, A / O = 1) in a beaker, and magnetically stir at a stirring speed of 500 rpm for 10 min. After the two phases reach extraction equilibrium, let the stirred solution stand for 30 min to separate layers, and perform liquid chromatography analysis on the lower aqueous phase. The extraction rate of phenol is 97.93%.

[0062] After the HDES prepared in Example 6 is repeatedly extracted 5 times in the same wastewater environment as in Example 6, the extraction rate of phenol is 86.5%.

[0063] After activated carbon adsorption and regeneration, the extraction rate of HDES can be restored to over 95%.

[0064] Example 7

[0065] A method for extracting and separating p-cresol pollutants from semi-coke wastewater, comprising the following steps:

[0066] Mix DL-menthol and octanoic acid in a molar ratio of 1:2, and keep them warm in a 60 °C water bath under vigorous magnetic stirring at 500 rpm. After 40 min, a transparent and homogeneous liquid sample is obtained, and then it is allowed to stand for 2 h to ensure that no precipitation forms during cooling, obtaining HDES;

[0067] At room temperature, mix an aqueous phase with a certain concentration (the concentration of p-cresol in the semi-coke wastewater is 5000 mg / L) and an equal volume (50 mL, A / O = 1) of HDES in a beaker, and magnetically stir at a stirring speed of 500 rpm for 10 min. After the two phases reach extraction equilibrium, let the stirred solution stand for 30 min to separate layers, and perform liquid chromatography analysis on the lower aqueous phase. The extraction rate of phenol is 97.32%.

[0068] Example 8

[0069] A method for extracting and separating p-cresol pollutants from semi-coke wastewater includes the following steps:

[0070] Mix DL-menthol and octanoic acid in a molar ratio of 1:2, and keep them warm in a 60 °C water bath under vigorous magnetic stirring at 500 rpm. After 30 min, a transparent and homogeneous liquid sample is obtained, and then it is allowed to stand for 2 h to ensure that no precipitation forms during cooling, obtaining HDES;

[0071] At room temperature, mix an aqueous phase with a certain concentration (the concentration of p-cresol in the semi-coke wastewater is 5000 mg / L) and an equal volume (50 mL, A / O = 1) of HDES in a beaker, and magnetically stir at a stirring speed of 500 rpm for 10 min. After the two phases reach extraction equilibrium, let the stirred solution stand for 30 min to separate layers, and perform liquid chromatography analysis on the lower aqueous phase. The extraction rate of phenol is 97.56%.

[0072] Comparative Example 1

[0073] A method for extracting and separating p-cresol pollutants from semi-coke wastewater is the same as that in Example 6, except that DL-menthol is replaced with an equimolar amount of menthol, and the extraction rate of phenol is 94.5%.

[0074] Comparative Example 2

[0075] A method for extracting and separating p-cresol pollutants from semi-coke wastewater is the same as that in Example 6, except that decanoic acid is replaced with an equimolar amount of dodecanoic acid and octadecanoic acid respectively. The prepared HDES presents a colorless and transparent solid state and a yellow transparent liquid state at room temperature respectively. The solid state is inconvenient to use at room temperature, and the colored liquid is not conducive to observing its subsequent conditions, indicating that the HDES formed by fatty acids with a chain length exceeding ten and DL-menthol is unstable. Therefore, fatty acids with a chain length exceeding ten are not considered for use.

[0076] Comparative Example 3

[0077] A method for extracting and separating p-cresol pollutants from semi-coke wastewater is the same as Example 6, except that p-cresol is replaced with 2-chlorophenol, o-cresol, and phenol in equal volumes respectively, and the extraction rates of phenols are 96.74%, 96.18%, and 85.45% in sequence.

[0078] Comparative Example 4

[0079] A method for extracting and separating p-cresol pollutants from semi-coke wastewater comprises the following steps:

[0080] Under room temperature conditions, an aqueous phase with a certain concentration (the concentration of p-cresol in semi-coke wastewater is 5000 mg / L) and methyl isobutyl ketone (MIBK) with equal volumes (50 mL, A / O = 1) are mixed in a beaker, and magnetically stirred at a stirring speed of 500 rpm for 10 min. After the two phases reach extraction equilibrium, the stirred solution is left to stand for 30 min for layering, and the lower aqueous phase is analyzed by liquid chromatography. The extraction rate of phenol is 85%. And as the temperature rises (60 °C), the distribution coefficient of MIBK for p-cresol continuously decreases. Compared with MIBK, the HDES prepared in Example 6 is less affected by temperature and the extraction rate will not decrease. During the subsequent reuse process of the extractant, in addition to the activated carbon regeneration method, the steam stripping method can also be used, but MBIK has a low boiling point and the boiling point of volatile phenols is higher than that of MBIK, which is not conducive to the removal of phenols.

[0081] The above is only the preferred specific implementation mode of the present application, but the protection scope of the present application is not limited thereto. Any changes or substitutions that can be easily thought of by those skilled in the art within the technical scope disclosed in the present application should be covered within the protection scope of the present application. Therefore, the protection scope of the present application should be subject to the protection scope of the claims.

Claims

1. A menthol-based hydrophobic deep eutectic solvent, characterized in that: The invention comprises a hydrogen bond acceptor and a hydrogen bond donor, wherein the hydrogen bond acceptor is DL-menthol, and the hydrogen bond donor is one of n-hexanoic acid, octanoic acid, decanoic acid, nonanoic acid and thymol.

2. The menthol-based hydrophobic deep eutectic solvent according to claim 1, characterized in that The molar ratio of the hydrogen bond acceptor to the hydrogen bond donor is (3:1)-(1:3).

3. A method for preparing a menthol-based hydrophobic deep eutectic solvent according to any one of claims 1 to 2, characterized in that: The method comprises the following steps: mixing a hydrogen bond acceptor and a hydrogen bond donor, heating the mixture in a water bath to obtain a transparent and uniform liquid sample, and allowing the mixture to stand to obtain the menthol-based hydrophobic low eutectic solvent.

4. The method for preparing a menthol-based hydrophobic deep eutectic solvent according to claim 3, characterized in that: The conditions for water bath heating are: temperature 60° C., stirring speed 500-800 rpm, and insulation time 20-40 min.

5. The method for preparing a menthol-based hydrophobic deep eutectic solvent according to claim 3, characterized in that: The standing time is 2h.

6. A method for extracting and separating phenolic pollutants in blue carbon wastewater, characterized in that: Phenolic pollutants in semi-coke wastewater are extracted and separated using the menthol-based hydrophobic low eutectic solvent described in any one of claims 1-2.

7. The method for extracting and separating phenolic pollutants in blue carbon wastewater according to claim 6, characterized in that: The following steps are involved: The menthol-based hydrophobic low eutectic solvent is mixed with the phenol-containing wastewater, stirred, allowed to stand for stratification, and the lower aqueous phase is subjected to liquid chromatography analysis.

8. The method for extracting and separating phenolic pollutants in blue carbon wastewater according to claim 7, characterized in that: The stirring time is 5-10 min.

9. The method for extracting and separating phenolic pollutants in blue carbon wastewater according to claim 7, characterized in that: The standing time is 30-60 min.

10. The method for extracting and separating phenolic pollutants in blue carbon wastewater according to claim 6, characterized in that: The phenolic pollutants are p-cresol, 2-chlorophenol, o-cresol, phenol or m-diphenol.