Imidazolyl ionic liquid, preparation method and method for extracting p-methylphenol from coal tar

Abstract

The invention discloses imidazolyl ionic liquid, a preparation method and a method for extracting p-methylphenol from coal tar, the ionic liquid is 1-ethyl-3-methylimidazole-arginine ionic liquid, and the ionic liquid is environmentally friendly, free of halogen pollution, green and environmentally friendly, and does not cause corrosion to steel equipment; the preparation method comprises the following steps: removing chloride ions from 1-ethyl-3-methylimidazolium chloride through anion exchange resin to obtain an intermediate 1-ethyl-3-methylimidazolium hydroxide, and reacting the intermediate 1-ethyl-3-methylimidazolium hydroxide with an arginine aqueous solution to prepare the target ionic liquid. In extraction application, the ionic liquid and model oil containing p-methylphenol are mixed and stirred, a two-phase system is formed after standing and phase splitting, and p-methylphenol can be efficiently extracted and separated. After separation, collecting a lower-layer ionic liquid phase, carrying out ethyl acetate back extraction and standing layering, and carrying out rectification treatment on an upper-layer oil phase, so as to realize recovery and recycling of the ionic liquid. The extraction separation efficiency of the ionic liquid on methylphenol can reach 99% or above.

Description

Technical Field

[0001] This invention belongs to the field of coal tar separation and purification technology, specifically relating to an imidazole ionic liquid, its preparation method, and a method for extracting p-methylphenol from coal tar. Background Technology

[0002] Coal tar, a byproduct of coal dry distillation and pyrolysis, is rich in phenolic compounds and is one of the main sources of p-cresol. p-Cresol, as an important chemical raw material, can be used to synthesize antioxidants and is the mainstream raw material for the synthesis of 2,6-di-tert-butyl-p-cresol; it can be used to synthesize flavorings with notes of anise, vanilla, and cherry; and it can be used as a coupling component in the synthesis of certain azo dyes and pigments, having wide applications in industry and daily life. Furthermore, the presence of p-cresol exacerbates hydrogen loss during the subsequent hydrorefining of coal tar, and separating p-cresol can increase the economic efficiency of subsequent coal tar processing. Therefore, the separation and purification of p-cresol from coal tar is of great significance.

[0003] Coal tar has a complex composition and is difficult to process. Currently used separation methods include alkaline washing and ionic liquid extraction. However, alkaline washing consumes large amounts of acids and alkalis, resulting in cumbersome subsequent processing and severe environmental pollution. Ionic liquids, due to their good stability, excellent solubility, and environmental friendliness, are widely used in the extraction of p-methylphenol. However, most currently used ionic liquids contain halogens, which can severely corrode steel equipment, limiting their industrial-scale application.

[0004] Therefore, there is an urgent need to develop an ionic liquid system with high raw material utilization, excellent extraction efficiency and environmental friendliness, and to construct a corresponding simple and efficient preparation process to achieve efficient and selective separation of p-methylphenol from coal tar. Summary of the Invention

[0005] To address the problems existing in the prior art, the present invention aims to provide an imidazole-based ionic liquid, its preparation method, and a method for extracting p-cresol from coal tar. The present invention uses a 1-ethyl-3-methylimidazolium-arginine ionic liquid as the extractant, achieving the separation of p-cresol from coal tar through hydrogen bonding formed by the interaction between the ionic liquid and p-cresol. To achieve a green and efficient synthesis, the present invention preferably uses an anion exchange resin method to prepare the key intermediate. Specifically, a D201 type OH- ion exchange resin is used. - The use of strongly basic anion exchange resins eliminates the need for highly toxic silver salts or the generation of saline wastewater, making the process more environmentally friendly.

[0006] The objective of this invention is achieved through the following technical solutions.

[0007] An imidazole-based ionic liquid, wherein the ionic liquid is a 1-ethyl-3-methylimidazolium-arginine ionic liquid, synthesized using a two-step ion exchange method with anion exchange resin, is halogen-free, environmentally friendly, has a low vapor pressure, and is liquid at room temperature; its structure is as follows: .

[0008] The method for preparing an imidazole-based ionic liquid includes the following steps: Step 1: Preparation of 1-ethyl-3-methylimidazolium hydroxide: Dissolve 1-ethyl-3-methylimidazolium chloride in deionized water to prepare a 1 mol / L aqueous solution of 1-ethyl-3-methylimidazolium chloride. Pass the aqueous solution of 1-ethyl-3-methylimidazolium chloride through a fixed-bed exchange column loaded with anion exchange resin at a flow rate of 1 ml / min. During this process, the anions on the anion exchange resin exchange with the anions in 1-ethyl-3-methylimidazolium chloride, and the effluent is the aqueous solution of 1-ethyl-3-methylimidazolium hydroxide. The reaction formula is as follows: Step 2: Synthesis of 1-ethyl-3-methylimidazolium-arginine ionic liquid: An aqueous solution of 1-ethyl-3-methylimidazolium hydroxide was added to an aqueous solution of arginine, with a molar ratio of 1:1 to 1:5. The mixture was stirred at room temperature, and then excess water was removed by rotary evaporation to obtain the target product, 1-ethyl-3-methylimidazolium-arginine ionic liquid. The reaction formula is as follows: .

[0009] Preferably, in step 1, the anion exchange resin used is type D201 OH - Strongly basic anion exchange resins only exchange with anions in the solution and hardly adsorb cations, thus ensuring the integrity of the cation structure. The reaction itself only produces water and the chloride form of the resin, without generating inorganic salt waste liquid, which conforms to the principles of green chemistry. The used chloride form resin can be regenerated into the OH form with NaOH solution and can be reused, greatly reducing long-term operating costs.

[0010] Preferably, in step 2, stirring at room temperature for 8-12 hours allows for sufficient diffusion and arrangement of molecules, which is beneficial for forming a more thermodynamically stable ionic liquid.

[0011] The method for using an imidazole ionic liquid to extract p-methylphenol from coal tar includes the following steps: Step 1: Using 1-ethyl-3-methylimidazolium-arginine ionic liquid as the extractant, the mixture is mixed with model oil containing p-cresol and simulated coal tar. After extraction, the mixture is allowed to stand and separate into layers to obtain the lower layer of ionic liquid phase enriched with p-cresol and the upper layer of oil phase free of p-cresol. Step 2: Add ethyl acetate to the lower layer of ionic liquid phase enriched with p-methylphenol for back-extraction. After stirring, allow the mixture to stand and separate into layers to obtain an upper layer of ethyl acetate phase containing p-methylphenol and a lower layer of regenerated imidazole ionic liquid phase. At this point, the upper layer is an ethyl acetate phase rich in p-methylphenol, which facilitates subsequent product separation and purification.

[0012] In step 1, the mass ratio of 1-ethyl-3-methylimidazolium-arginine ionic liquid to model oil is 1:1 to 1:5, which can achieve a very high single-stage extraction rate with less ionic liquid.

[0013] In step 1, the extraction reaction time is 1-50 min, which allows the extraction equilibrium to be reached in a short time, reducing the waste of time.

[0014] In step 1, the extraction reaction temperature is 10-50 ℃, which eliminates the need for high-temperature heating and reduces energy consumption.

[0015] In step 1, the extraction efficiency of p-methylphenol is 89.61%-99.94%, which is high and the extraction performance is stable.

[0016] The extraction efficiency E% of p-methylphenol is calculated according to the following formula: E%=(C0V0 C t V t ) / C0V0×100%, where C0 represents the initial concentration of p-methylphenol in the model oil, in g / L. V0 represents the initial volume of the model oil, in mL. C t This represents the concentration of p-methylphenol remaining in the toluene phase after extraction, in g / L. V t This represents the volume of p-methylphenol remaining in the toluene phase after extraction, in mL.

[0017] The method for preparing the p-cresol model oil in the extraction of p-cresol from coal tar is as follows: p-cresol is added to toluene solvent and stirred until a homogeneous and transparent solution is obtained. The concentration of p-cresol in the p-cresol model oil is 50-150 g / L. The model oil can eliminate interference from other complex components and focus on studying the selective separation performance of the extractant for p-cresol. This concentration range allows the model oil to be accurately detected on common analytical instruments without easily exceeding the linear range or causing instrument contamination.

[0018] Compared with existing ionic liquid extraction methods, the present invention has the following main advantages: The imidazole-based ionic liquid used in this invention is environmentally friendly, halogen-free, and will not corrode steel equipment. The raw materials are 1-ethyl-3-methylimidazolium chloride and arginine. The synthesized imidazole-based ionic liquid utilizes a halogen-free ionic liquid extraction technology, providing a cleaner and more sustainable separation path compared to traditional alkaline washing and acid precipitation methods (which generate large amounts of phenol-containing wastewater) or solvent extraction methods (which use volatile toxic solvents), aligning with the trend of green chemical development. The synthesis method employed in this invention selects, for example, D201 type OH... - Strongly basic anion exchange resins can achieve quantitative and efficient anion exchange, avoiding the introduction of metal impurities or byproducts that may be introduced in traditional methods, thereby ensuring the high purity and green environmental protection characteristics of the final ionic liquid product.

[0019] This invention focuses on the efficient and environmentally friendly separation of p-methylphenol from coal tar, which directly improves the economics and environmental friendliness of its downstream applications: precisely separating the specific high-value component (p-methylphenol) from coal tar (a complex mixture traditionally of low value) transforms "coarse material" into "refined material," greatly enhancing the resource value. The efficient separation method can provide higher-purity p-methylphenol raw materials for downstream high-end applications (such as pharmaceuticals and food-grade antioxidants), which is crucial for the quality of downstream products. Attached Figure Description

[0020] Figure 1 This is the FT-IR spectrum of an imidazole-based ionic liquid. Detailed Implementation

[0021] The present invention will be further described below with reference to specific embodiments and accompanying drawings, including an imidazole-based ionic liquid, a preparation method, and a method for extracting p-methylphenol from coal tar, but is not limited to the embodiments described below.

[0022] This ionic liquid is liquid at room temperature and belongs to the organic molten salt class of compounds. It features a wide liquid temperature range, low vapor pressure, and good chemical stability. It contains no halogens, is non-corrosive to equipment, and offers advantages in both environmental friendliness and economy. The preparation process utilizes a strongly basic anion exchange resin column for separation and purification, avoiding complex reaction steps and allowing for preparation under standard laboratory conditions.

[0023] Coal tar mainly consists of neutral hydrocarbons (including aromatics and aliphatic hydrocarbons), acidic phenols, and a small amount of free water. To simplify the analysis process, this invention uses p-methylphenol and toluene to prepare a simulated p-methylphenol model oil, where p-methylphenol represents acidic phenols and toluene represents neutral hydrocarbons.

[0024] Example 1: A method for preparing an imidazole-based ionic liquid The D201 type strong basic anion exchange resin was repeatedly rinsed with deionized water to remove impurities; then, it was successively washed with 1 mol / L NaOH solution and deionized water for alkaline washing and rinsing until the effluent was neutral, allowing the resin to be fully converted to OH-. - Type; Weigh 14.66g of 1-ethyl-3-methylimidazolium chloride and dissolve it in 100ml of deionized water. Pour the solution into a reaction column packed with D201 type strong basic anion exchange resin and pass it through the resin column at a flow rate of 1ml / min, allowing the imidazole cations to react with the OH groups on the resin. - A reaction occurs, Cl - The resin adsorbs the ions, and a 1-ethyl-3-methylimidazolium hydroxide solution is obtained in the effluent. 17.42 g of arginine was weighed and dissolved in 100 ml of deionized water. The arginine aqueous solution was added to the 1-ethyl-3-methylimidazolium hydroxide aqueous solution. The molar ratio of 1-ethyl-3-methylimidazolium hydroxide to arginine was 1:1. The mixture was stirred at room temperature for 12 h. Excess water was removed by rotary evaporation to obtain the target product 1-ethyl-3-methylimidazolium-arginine ionic liquid 1. 52.26 g of arginine was weighed and dissolved in 300 ml of deionized water. This aqueous solution was then added to a solution of 1-ethyl-3-methylimidazolium hydroxide, with a molar ratio of 1-ethyl-3-methylimidazolium hydroxide to arginine of 1:3. The mixture was stirred at room temperature for 12 h, and excess water was removed by rotary evaporation to obtain the target product, 1-ethyl-3-methylimidazolium-arginine ionic liquid 2. 87.10 g of arginine was weighed and dissolved in 500 ml of deionized water. This aqueous solution was then added to a solution of 1-ethyl-3-methylimidazolium hydroxide, with a molar ratio of 1-ethyl-3-methylimidazolium hydroxide to arginine of 1:5. The mixture was stirred at room temperature for 12 h. Excess water was removed by rotary evaporation to obtain the target product, 1-ethyl-3-methylimidazolium-arginine ionic liquid 3.

[0025] Example 2: Effect of reaction time of an imidazole ionic liquid with p-cresol model oil on p-cresol extraction efficiency The imidazole-based ionic liquid described in this invention is a 1-ethyl-3-methylimidazolium-arginine ionic liquid. Under the conditions of a 1:1 mass ratio of the ionic liquid to p-cresol model oil and a reaction temperature of 25°C, the reaction was carried out on a magnetic stirrer for 1 min, 2 min, 3 min, 4 min, 5 min, 10 min, 20 min, 30 min, 40 min, and 50 min, respectively. The concentration of p-cresol in the upper oil phase was determined by gas chromatography, and its extraction rate was calculated. The results were 99.82%, 99.83%, 99.85%, 99.83%, 99.86%, 99.88%, 99.86%, 99.92%, 99.86%, and 99.90%, respectively. Experiments show that the optimal reaction time is 30 min.

[0026] Example 3: Effect of reaction temperature of an imidazole ionic liquid on the extraction efficiency of p-cresol model oil The imidazole-based ionic liquid described in this invention is a 1-ethyl-3-methylimidazolium-arginine ionic liquid. Under the conditions of a 1:1 mass ratio of the ionic liquid to p-cresol model oil and a reaction time of 30 min, extraction reactions were carried out at 10℃, 15℃, 20℃, 25℃, 30℃, 35℃, 40℃, 45℃, and 50℃, respectively. The concentration of p-cresol in the upper oil phase was determined by gas chromatography, and the extraction rates were calculated. The results were 99.82%, 99.82%, 99.88%, 99.87%, 99.91%, 99.76%, 99.76%, 99.76%, and 99.76%, respectively. Experiments show that the optimal reaction temperature is 30℃.

[0027] Example 4: Effect of different mass ratios of an imidazole-based ionic liquid to p-cresol model oil on the extraction efficiency of p-cresol The imidazole-based ionic liquid described in this invention is a 1-ethyl-3-methylimidazolium-arginine ionic liquid. The extraction effect of the ionic liquid with p-cresol model oil at different mass ratios (1:1, 1:2, 1:3, and 1:4) was investigated under the conditions of a reaction temperature of 30°C and a stirring time of 30 min. The concentration of p-cresol in the upper oil phase was determined by gas chromatography, and the calculated extraction rates of p-cresol were 99.78%, 92.77%, 90.81%, and 89.61%, respectively. The results indicate that the optimal mass ratio is 1:1.

[0028] Example 5: 1-Ethyl-3-methylimidazolium-arginine ionic liquid 1 and model oil with a p-cresol concentration of 225.27 g / L were added to a container at a mass ratio of 1:1. The mixture was stirred at 30°C for 30 min, and then allowed to stand to separate into an upper organic phase and a lower aqueous phase. The upper organic phase was taken for gas chromatography to test the m-cresol extraction rate, which was 99.76%. 1-Ethyl-3-methylimidazolium-arginine ionic liquid 2 and model oil with a p-methylphenol concentration of 225.27 g / L were added to a container at a mass ratio of 1:1. The mixture was stirred at 30°C for 30 min, and then allowed to stand to separate into an upper organic phase and a lower aqueous phase. The upper organic phase was taken for gas chromatography to test the m-methylphenol extraction rate, which was 98.95%. 1-Ethyl-3-methylimidazolium-arginine ionic liquid 3 and model oil with a p-methylphenol concentration of 225.27 g / L were added to a container at a mass ratio of 1:1. The mixture was stirred at 30°C for 30 min and then allowed to stand to separate into an upper organic phase and a lower aqueous phase. The upper organic phase was taken for gas chromatography to test the m-methylphenol extraction rate, which was 98.13%.

[0029] The results of Example 5 show that the optimal molar ratio of 1-ethyl-3-methylimidazolium hydroxide to arginine is 1:1.

[0030] Example 6: Back-extraction of p-methylphenol from 1-ethyl-3-methylimidazolium-arginine ionic liquid phase using water and ethyl acetate After extracting p-cresol from the model oil using 1-ethyl-3-methylimidazolium-arginine ionic liquid, the ionic liquid phase was separated. 3 mL of ethyl acetate was added, and stirring was continued for 20 min, followed by standing to separate the layers. The concentration of p-cresol in the upper ethyl acetate phase was analyzed by gas chromatography, and the back-extraction efficiency was calculated to be 99.19%.

[0031] From the above examples, the optimal reaction conditions are: a molar ratio of 1-ethyl-3-methylimidazolium-arginine ionic liquid to arginine of 1:1; a reaction time of 30 min; a reaction temperature of 30℃; and a mass ratio of 1:1 with the p-cresol model oil. The concentration of p-cresol in the upper oil phase was determined by gas chromatography, and the p-cresol extraction rate was 99.94%. The extraction efficiency (E%) of p-cresol was calculated using the following formula: E%=(C0V0 C t V t ) / C0V0×100%, where C0 represents the initial concentration of p-methylphenol in the model oil, in g / L. V0 represents the initial volume of the model oil, in mL. C tThis represents the concentration of p-methylphenol remaining in the toluene phase after extraction, in g / L. V t This represents the volume of p-methylphenol remaining in the toluene phase after extraction, in mL.

[0032] Figure 1 The FT-IR spectrum of the 1-ethyl-3-methylimidazolium-arginine ionic liquid is shown. Its characteristic absorption peaks are attributed to 3697–2953 cm⁻¹. - The broad peak at ¹ (OH and NH stretching vibrations) confirms the presence of the arginine anion; 3300 cm⁻¹ - The absorption peak at ¹ (CH stretching vibration) indicates the presence of imidazole cations; and the 1170 cm⁻¹... - The absorption peak at ¹ (imidazolium ring skeletal vibration). These characteristic peaks collectively confirm the successful synthesis of the target compound in the liquid.

Claims

1. An imidazolium-based ionic liquid, characterized in that: The ionic liquid is a 1-ethyl-3-methylimidazolium-arginine ionic liquid, synthesized using a two-step ion exchange method with anion exchange resin. It is halogen-free, environmentally friendly, has a low vapor pressure, and is liquid at room temperature. Its structure is as follows: 。 2. The method for preparing an imidazole-based ionic liquid according to claim 1, characterized in that, Includes the following steps: Step 1: Preparation of 1-ethyl-3-methylimidazolium hydroxide: Dissolve 1-ethyl-3-methylimidazolium chloride in deionized water to prepare a 1 mol / L aqueous solution of 1-ethyl-3-methylimidazolium chloride. Pass the aqueous solution of 1-ethyl-3-methylimidazolium chloride through a fixed-bed exchange column loaded with anion exchange resin at a flow rate of 1 ml / min. During this process, the anions on the anion exchange resin exchange with the anions in 1-ethyl-3-methylimidazolium chloride, and the effluent is the aqueous solution of 1-ethyl-3-methylimidazolium hydroxide. The reaction formula is as follows: Step 2: Synthesis of 1-ethyl-3-methylimidazolium-arginine ionic liquid: An aqueous solution of 1-ethyl-3-methylimidazolium hydroxide was added to an aqueous solution of arginine, with a molar ratio of 1:1 to 1:

5. The mixture was stirred at room temperature, and then excess water was removed by rotary evaporation to obtain the target product, 1-ethyl-3-methylimidazolium-arginine ionic liquid. The reaction formula is as follows: 。 3. The method for preparing an imidazole-based ionic liquid according to claim 2, characterized in that, In step 1, the anion exchange resin used is type D201 OH - Strongly basic anion exchange resin.

4. The method for preparing an imidazole-based ionic liquid according to claim 2, characterized in that, In step 2, stir at room temperature for 8-12 hours.

5. The method for extracting p-methylphenol from coal tar using an imidazole ionic liquid as described in claim 1, characterized in that, Includes the following steps: Step 1: Using 1-ethyl-3-methylimidazolium-arginine ionic liquid as the extractant, the mixture is mixed with model oil containing p-cresol and simulated coal tar. After extraction, the mixture is allowed to stand and separate into layers to obtain the lower layer of ionic liquid phase enriched with p-cresol and the upper layer of oil phase free of p-cresol. Step 2: Add ethyl acetate to the obtained lower layer of ionic liquid phase enriched with p-methylphenol for back-extraction, stir and let stand to separate the layers, and obtain the upper layer of ethyl acetate phase containing p-methylphenol and the lower layer of regenerated imidazole ionic liquid phase.

6. The method for using an imidazole-based ionic liquid according to claim 5 to extract p-methylphenol from coal tar, characterized in that, In step 1, the mass ratio of 1-ethyl-3-methylimidazolium-arginine ionic liquid to model oil is 1:1 to 1:

5.

7. A method for extracting p-methylphenol from coal tar using an imidazole ionic liquid according to claim 5, characterized in that, In step 1, the extraction reaction time is 1-50 min.

8. The method for using an imidazole-based ionic liquid according to claim 5 to extract p-methylphenol from coal tar, characterized in that, The extraction reaction temperature in step 1 is 10-50℃.

9. A method for extracting p-methylphenol from coal tar using an imidazole ionic liquid according to claim 5, characterized in that, The extraction efficiency of p-methylphenol in step 1 is 89.61%-99.94%. The extraction efficiency E% of p-methylphenol is calculated according to the following formula: E%=(C0V0 C t V t ) / C0V0×100%, where C0 represents the initial concentration of p-methylphenol in the model oil, in g / L. V0 represents the initial volume of the model oil, in mL. C t This represents the concentration of p-methylphenol remaining in the toluene phase after extraction, in g / L. V t This represents the volume of p-methylphenol remaining in the toluene phase after extraction, in mL.

10. A method for extracting p-methylphenol from coal tar using an imidazole ionic liquid according to claim 5, characterized in that, The preparation method of the model oil includes the following steps: weighing p-methylphenol solid and adding it to toluene solvent; stirring continuously at room temperature until homogeneous to obtain the model oil. The concentration of p-methylphenol in the model oil is 50-150 g / L.

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