Method for extracting low-concentration phenol from aqueous solution by using hydrophobic deep-eutectic solvent

Abstract

The invention relates to a process for extracting low-concentration phenol from an aqueous solution by using a hydrophobic eutectic solvent. The extraction agent used in the process is mainly synthesized from tributyl phosphate and n-caprylic alcohol in a molar ratio of 0.5: 1: 2 under the condition of 353.15 K. A phenol aqueous solution is used as an extraction water phase, the influence of various experimental parameters such as pH, temperature and phase ratio on the phenol extraction efficiency is researched by changing the content of phenol in the extraction water phase, and the extraction organic phase and the water phase are fully mixed according to the volume ratio of 1: 0.2-1: 5 and then separated until a clear phase interface appears, so that the two phases are completely separated. After phase separation is finished, an organic phase rich in phenol and a water phase containing a very small amount of phenol are obtained, and the highest extraction efficiency reaches 99% or above. Through three times of back extraction experiments, the back extraction efficiency of the phenol reaches 98% or above, and cyclic utilization of the phenol is achieved in the economic aspect. The method for extracting phenol has the advantages of low energy consumption, simple process, high separation efficiency of phenol and water and the like, the adopted hydrophobic eutectic solvent is low in price, and the preparation method is simple, non-toxic and environment-friendly.

Description

[Technical field]

[0001] The invention belongs to the field of extraction chemistry, chemical purification and separation processes, and particularly relates to a method for extracting low-concentration phenol from an aqueous solution using a hydrophobic low eutectic solvent. [Background technology]

[0002] Phenol is widely used in industries such as chemical raw materials, alkylphenols, synthetic fibers, plastics, synthetic rubber, medicine, coatings and oil refining. However, the widespread production and use of phenol in the industry inevitably produces a large amount of phenolic wastewater. Phenolic wastewater that is not treated or does not meet the discharge standards will cause serious health risks to humans, animals and aquatic systems. Phenol is a highly toxic substance. If a certain amount of human body is ingested, acute poisoning symptoms will occur. Long-term drinking of water contaminated by phenol can cause dizziness, itching, anemia and nervous system disorders. Due to its toxicity and harmfulness, phenol has adverse effects on the environment and the human body. Therefore, it is very beneficial to separate phenol from wastewater.

[0003] Chinese patent CN115433061B discloses a method for separating high-concentration phenol wastewater. The method combines a high-pressure stripping tower and a low-pressure distillation tower for separation operations, and is suitable for treating wastewater with a phenol content ranging from 1% to 80%. Depending on the phenol concentration, the feed position and operating conditions of the wastewater will be adjusted to ensure that energy consumption is reduced while recovering high-purity phenol. This method is particularly suitable for a large amount of phenol-containing wastewater generated in industry, such as wastewater generated in bisphenol A or phenol acetone devices. However, during multiple evaporation and condensation processes, the overall energy consumption is still high. In some processes, the method of extractive distillation is mentioned, which may introduce additional organic solvents, posing potential risks to the environment.

[0004] Chinese patent CN111635296B discloses a method for separating and recovering phenol by coupling extraction-evaporation-phase separation. The method uses an acetone-water mixed solvent as an extractant, and obtains high-purity phenol through extraction, evaporation, liquid-liquid separation and other steps, and recycles sodium hydroxide, acetone and water. This process is not only simple in separation operation and low in cost, but also effectively recovers the valuable components in the material, which meets the development requirements of green chemical industry. However, the complexity of the process may increase the cost and maintenance difficulty of industrial operation.

[0005] Using green solvents to replace traditional organic solvents can reduce environmental pollution. Ionic liquids and deep eutectic solvents have become the preferred green solvents in many processes in recent years. It is worth mentioning that the advantages of low volatility, non-toxicity, and environmental protection of deep eutectic solvents make them more in line with the high standards of environmental governance and waste liquid treatment applications than traditional solvents and ionic liquids. Due to the limitations of using hydrophilic deep eutectic solvents in polar systems, Van Osch et al. (Green Chem. 2015, 17, 4518-4521.) proposed the first batch of hydrophobic deep eutectic solvents for extraction processes. Although hydrophobic deep eutectic solvents have developed rapidly and have good industrial application value, they have become a new hotspot and new direction for deep eutectic solvents, but the research on phenol extraction is still in its preliminary stage. Liquid-liquid extraction has high efficiency, especially when dealing with complex mixtures, it can simplify the process and improve purity, high selectivity and mild operating conditions. Therefore, liquid-liquid extraction was selected for the separation of phenol and water. [Summary of the invention]

[0006] [Technical issues to be solved]

[0007] The purpose of the present invention is to solve the above-mentioned problems and provide a method for separating a low-concentration phenol aqueous solution by liquid-liquid extraction using a hydrophobic deep eutectic solvent. The method uses a hydrophobic deep eutectic solvent as an extractant, which not only solves the difficulty of phase separation after extraction and the environmental pollution caused by the dissolution of organic solvents in water, but also solves the economic recycling of phenol.

[0008] [Technical solution]

[0009] The present invention proposes a method for extracting low-concentration phenol from an aqueous solution using a hydrophobic deep eutectic solvent, studies the influence of different experimental parameters on the phenol extraction efficiency, and determines the optimal experimental parameters. The technical scheme adopted is: synthesized hydrophobic deep eutectic solvents of different molar ratios are mixed with low-concentration phenol aqueous solutions of different contents in a certain volume ratio, and a liquid-liquid extraction experiment is performed at a suitable temperature and normal pressure. After sufficient mixing, the mixture reaches equilibrium, and the two phases are completely separated until a clear phase interface appears. The extraction efficiency is analyzed by liquid chromatography.

[0010] A method for extracting low-concentration phenol from an aqueous solution using a hydrophobic deep eutectic solvent comprises the following steps:

[0011] (1) Synthesizing an organic phase for extraction; the organic phase for extraction is mainly composed of three different hydrophobic low eutectic solvents; wherein the hydrophobic low eutectic solvent is prepared by mixing tributyl phosphate and n-octanol at a molar ratio of 0.5, 1, and 2 at 353.15K; (2) Preparing an aqueous phase for extraction; the phenol content in the aqueous phase is 5 g / L, 20 g / L, and 60 g / L; (3) Changing extraction conditions; wherein the specific conditions include: the molar ratio of tributyl phosphate and n-octanol, the volume ratio of the organic phase and the aqueous phase, the pH of the aqueous phase, and the extraction temperature; (4) Fully mixing the organic phase for extraction with the aqueous phase at a volume ratio of 1:0.2 to 1:5, allowing the mixture to stand, and performing phase separation to obtain an organic phase rich in phenol and an aqueous phase containing a very small amount of phenol; (5) Performing a back extraction experiment, mixing the extracted organic phase with NaOH (1.0 mol / L), repeating the experiment three times, and obtaining high-purity phenol.

[0012] As a further optimization of the method for treating low-concentration phenol in an aqueous solution with a hydrophobic deep eutectic solvent of the present invention: considering the effect of the molar ratio of tributyl phosphate and n-octanol on the extraction efficiency, the molar ratio of tributyl phosphate and n-octanol is determined to be 1:1.

[0013] As a further optimization of the method of treating low-concentration phenol in an aqueous solution with a hydrophobic deep eutectic solvent of the present invention: considering the influence of the phenol content in the aqueous phase on the extraction efficiency, the phenol content in the wastewater before treatment is determined to be 60 g / L.

[0014] As a further optimization of the method of treating low-concentration phenol in an aqueous solution with a hydrophobic deep eutectic solvent according to the present invention: considering the effect of the extraction temperature on the extraction efficiency, the extraction temperature is determined to be 298.15K.

[0015] As a further optimization of the method of treating low-concentration phenol in an aqueous solution with a hydrophobic deep eutectic solvent of the present invention: considering the effect of the pH of the aqueous phase on the extraction efficiency, it is determined that there is no need to control the pH of the solution when treating phenol in the aqueous solution.

[0016] As a further optimization of the method for treating low-concentration phenol in an aqueous solution with a hydrophobic deep eutectic solvent of the present invention: considering the effect of the ratio (O / A) on the extraction efficiency, the O / A is determined to be 1:1.

[0017] Beneficial Effects

[0018] The present invention adds a hydrophobic deep eutectic solvent to a low-concentration phenol aqueous solution to achieve separation of phenol and water, and the highest extraction efficiency reaches more than 98%. After three back extraction experiments, the back extraction efficiency of phenol reaches more than 98%. Not only does it achieve the reuse of phenol, but it also makes the phenol content in wastewater meet the national standard.

Brief Description of the Drawings

[0019] Figure 1 The present invention is a process flow chart for extracting low-concentration phenol from an aqueous solution using a hydrophobic low eutectic solvent. [Specific implementation method]

[0020] The following is further described in conjunction with the accompanying drawings, which does not limit the scope of the present invention.

[0021] Embodiment 1:

[0022] A method for treating low-concentration phenol in an aqueous solution with a hydrophobic deep eutectic solvent comprises the following steps:

[0023] A hydrophobic low eutectic solvent synthesized from tributyl phosphate and n-octanol was added to a low-concentration phenol aqueous solution. The volume ratio of the hydrophobic low eutectic solvent to the low-concentration phenol aqueous solution was 1:1 under the conditions of 298.15K and 301.15KPa. The mixture was fully mixed at 200r / min on a magnetic stirrer for 30 minutes. A liquid-liquid extraction experiment was performed. After being fully mixed, the mixture was allowed to reach equilibrium, and the mixture was transferred to a centrifuge tube and centrifuged at 10000r / min for 5 minutes. A clear phase interface appeared and the two phases were completely separated. Sampling was performed and the extraction efficiency of phenol was 96.5% by liquid chromatography analysis.

[0024] Embodiment 2:

[0025] A method for treating low-concentration phenol in wastewater with a hydrophobic deep eutectic solvent comprises the following steps:

[0026] Adjust the pH of the low-concentration phenol aqueous solution to 7 with sodium hydroxide or hydrochloric acid, add a low eutectic solvent, and at 298.15K and 301.15KPa, the volume ratio of the hydrophobic low eutectic solvent to the phenol aqueous solution is 1:1, and mix thoroughly at 200r / min on a magnetic stirrer for 30 minutes. Perform a liquid-liquid extraction experiment. After thorough mixing, allow the mixture to reach equilibrium, transfer the mixture to a centrifuge tube, and centrifuge it at 10000r / min for 5 minutes. A clear phase interface appears, and the two phases are completely separated. Sampling is performed and detected by liquid chromatography. The extraction efficiency of phenol is 95.7%.

[0027] Embodiment 3:

[0028] A hydrophobic low eutectic solvent was added to a low concentration phenol aqueous solution. The volume ratio of the hydrophobic low eutectic solvent to the low concentration phenol aqueous solution was 2:1 under the conditions of 298.15K and 301.15KPa. The mixture was fully mixed at 200r / min for 30 minutes on a magnetic stirrer. A liquid-liquid extraction experiment was performed. After being fully mixed, the mixture was allowed to reach equilibrium, and the mixture was transferred to a centrifuge tube and centrifuged at 10000r / min for 5 minutes. A clear phase interface appeared and the two phases were completely separated. Sampling was performed and the extraction efficiency of phenol was 98.1% by liquid chromatography.

Claims

1. A method for extracting low-concentration phenol from an aqueous solution using a hydrophobic deep eutectic solvent, characterized in that: Includes steps: (1) synthesizing an organic extraction phase, wherein the organic extraction phase is mainly composed of three different hydrophobic low eutectic solvents; wherein the hydrophobic low eutectic solvent is a mixture of tributyl phosphate and n-octanol in a molar ratio of 0.5, 1, and 2; (2) preparing an aqueous phase for extraction, wherein the phenol content in the aqueous phase for extraction is 5 g / L, 20 g / L, and 60 g / L; (3) changing the extraction conditions, wherein the specific conditions include: the molar ratio of tributyl phosphate to n-octanol, the volume ratio of the organic phase to the aqueous phase, the pH of the aqueous phase, and the extraction temperature; (4) the extracted organic phase and the aqueous phase are fully mixed in a volume ratio of 1:0.2 to 1:5, and then allowed to stand for phase separation to obtain an organic phase rich in phenol and an aqueous phase containing a very small amount of phenol; (5) A back extraction experiment was conducted by mixing the extracted organic phase with NaOH (1.0 mol / L). The experiment was repeated three times to obtain high-purity phenol.

2. The method for extracting low-concentration phenol from an aqueous solution according to claim 1, characterized in that: The extractant is synthesized from tributyl phosphate and n-octanol at 353.15K.

3. The method for extracting low-concentration phenol from an aqueous solution according to claim 1, characterized in that: The molar ratio of tributyl phosphate to n-octanol is 0.5, 1, and 2.

4. The method for extracting low-concentration phenol from an aqueous solution according to claim 1, characterized in that: The extraction temperature was 298.15K during the extraction process.

5. The method for extracting low-concentration phenol from an aqueous solution according to claim 1, characterized in that: The phenol content in the extraction water phase is 5 g / L, 20 g / L, and 60 g / L.

6. The method for extracting low-concentration phenol from an aqueous solution according to claim 1, characterized in that: The extraction time in the extraction process is 1 min to 30 min.

7. The method for extracting low-concentration phenol from an aqueous solution according to claim 1, characterized in that: The volume ratio of the extraction organic phase to the aqueous phase is 1:0.2 to 1:5.

Images