Preparation method of ionic liquid and application of ionic liquid in efficient extraction of iodine

Abstract

The invention relates to the field of ionic liquids, in particular to a preparation method of an ionic liquid and application of the ionic liquid in efficient iodine extraction. The ionic liquid is 1-amyl-3-methylimidazolium bromide [C5Mimm] [Br], the structural formula is shown in the formula (I), the ionic liquid is prepared from N-methylimidazole and bromopentane, and the ionic liquid is low in melting point and wide in liquid state range. The 1-pentyl-3-methylimidazolium bromide ionic liquid is synthesized by a one-step method, the preparation process is simple, and the 1-pentyl-3-methylimidazolium bromide ionic liquid has a remarkable advantage in the aspect of extracting elemental iodine. The optimal extraction condition is that extraction is performed for 15 minutes at 25 DEG C, and the extraction effect reaches 99.07%. # imgabs0 #

Description

Technical Field

[0001] The invention relates to the field of ionic liquids, and in particular to a method for preparing an ionic liquid and application of the ionic liquid in efficient extraction of iodine. Background Art

[0002] my country's iodine resources are in short supply and the pressure of import is huge. At the same time, the production process of nuclear energy will produce radioactive nuclear waste iodine ( 129 I and 131 I), has a long half-life and is directly harmful to the human immune system.

[0003] Ionic liquids can replace traditional organic solvents as new solvents and play an important role in clean treatment. However, there is a lack of targeted design for the extraction and separation of iodine, resulting in problems such as large dosage of ionic liquids and low efficiency. Therefore, it is very important to study efficient and stable adsorbents for iodine extraction.

[0004] Due to the difference and adjustability of the combination of positive and negative ions, ionic liquids can be designed and synthesized with specific functional groups and special functions according to actual conditions. They have been widely used in electrochemistry, organic synthesis, separation and purification, and can be further used as efficient extraction solvents to extract iodine. Summary of the invention

[0005] In view of the above technical problems, the ionic liquid provided by the present invention can extract iodine in an organic solvent, and the method is simple to operate, efficient and has a high extraction rate.

[0006] To achieve the above object, the technical solution of the present invention is as follows: an ionic liquid, wherein the ionic liquid is 1-pentyl-3-methylimidazolium bromide [C5Mim][Br], and the structural formula is shown in formula (I),

[0007]

[0008] The preparation method of the above-mentioned ionic liquid comprises the following steps:

[0009] 1) Synthesis of 1-pentyl-3-methylimidazolium bromide [C5Mim][Br]: Under the protection of nitrogen, bromopentane was slowly added dropwise to N-methylimidazole that had been distilled in the dark for multiple times to react. After the reaction was completed, cooling and crystallization were performed to obtain a solid crude product of 1-pentyl-3-methylimidazolium bromide.

[0010] -3-Methylimidazolium bromide;

[0011] 2) Purification of the crude product 1-pentyl-3-methylimidazolium bromide [C5Mim][Br]: dissolve the solid crude product in a mixed solution of ethyl acetate and acetonitrile, and perform recrystallization, suction filtration, and drying in sequence to obtain 1-pentyl-3-methylimidazolium bromide ionic liquid.

[0012] In the above preparation method, in step 1), the molar ratio of N-methylimidazole to bromopentane is 1:1.1.

[0013] In the above preparation method, in step 1), the temperature range of collecting fractions by distillation in the dark is 198-199°C.

[0014] In the above preparation method, in step 1), the reaction temperature is 65° C. and the reaction time is 48 h.

[0015] In the above preparation method, in step 2), the volume ratio of ethyl acetate to acetonitrile is 2:1.

[0016] The reaction formula of the ionic liquid of the present invention is as follows:

[0017]

[0018] The above-mentioned ionic liquid is used for the efficient extraction of iodine.

[0019] The above application method is as follows: the ionic liquid is placed in a container, heated and stirred to form a thin film of the ionic liquid at the bottom of the container, an iodine cyclohexane solution is poured into the container, and the iodine is extracted under magnetic stirring conditions.

[0020] In the above application, the temperature during magnetic stirring was 25°C.

[0021] In the above application, the iodine concentration in the cyclohexane solution of iodine is 0.01 mol / L.

[0022] The ionic liquid of the present invention is mainly composed of molecules. The electron-rich large π-bond ring and the nitrogen atom containing a lone electron pair contained in the aromatic nitrogen heterocyclic compound can interact with the empty orbit of iodine, providing a basis for its use in extraction.

[0023] The present invention provides an ionic liquid for extracting iodine. 15 minutes is selected as the optimal extraction time. The optimal extraction temperature is further determined to be 25° C. Under the above preferred extraction conditions, the ionic liquid is particularly suitable for extracting iodine, and the extraction effect reaches 99.07%. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 This is a graph showing the variation trend of the extraction rate of 1-pentyl-3-methylimidazolium bromide [C5Mim][Br] over time (ILs:I2=1:3, T=25°C).

[0025] Figure 2 This is a graph showing the variation trend of the extraction rate of 1-pentyl-3-methylimidazolium bromide [C5Mim][Br] with temperature (ILs:I2=1:3, t=15min).

[0026] Specific implementation method

[0027] The present invention is further described below by way of specific examples. The present invention is not limited to the embodiments, and slight variations are possible without departing from the scope described.

[0028] Example 1 An imidazole ionic liquid for extracting iodine

[0029] The preparation method is as follows:

[0030] 1) Preparation of ionic liquid bromide salt:

[0031] First, N-methylimidazole is distilled in the dark, and the distillation is repeated for multiple times to collect a colorless, clear, transparent liquid with a distillation temperature in the range of 198-199°C.

[0032] Use a measuring cylinder to measure the distilled N-methylimidazole (1.0 mol, 82 mL) and add it to a three-necked round-bottom flask equipped with a stirrer. Place the flask in an ice-salt bath, connect a condenser to the middle of the flask (a nitrogen balloon is connected above the condenser), and under nitrogen protection, use a constant pressure dropping funnel to slowly drop bromopentane (1.1 mol, 100 mL) into the three-necked round-bottom flask. After the dropwise addition is completed, stir and heat it at 65°C in an oil bath, and reflux for 48 hours.

[0033] After the reaction is completed, the three-necked round-bottom flask is sealed and placed in a refrigerator for cooling and crystallization. After the crystallization is complete, the unsolidified light yellow liquid on the upper layer of the flask is poured out to obtain a solid product as a crude product 1-pentyl-3-methylimidazolium bromide [C5Mim][Br].

[0034] 2) Purification of the intermediate 1-pentyl-3-methylimidazolium bromide [C5Mim][Br]:

[0035] Measure 10mL of a mixture of ethyl acetate and acetonitrile (volume ratio 2:1) and add it to the above solid product. Heat under reflux in an oil bath to dissolve the solid. After cooling to room temperature, seal again and place in a refrigerator for recrystallization. The recrystallization operation is preferably performed three times. If a light yellow liquid precipitates, pour it out and repeatedly add the acetonitrile ethyl acetate mixture until no light yellow liquid precipitates. After the recrystallization is completed, grind the crystals and filter them.

[0036] 3) Finally, 1-pentyl-3-methylimidazolium bromide ionic liquid was obtained with a purity of 99.8%.

[0037] Example 2 Application of 1-pentyl-3-methylimidazolium bromide to extract iodine

[0038] (I) Extraction and separation experiment

[0039] Use a 100mL volumetric flask to prepare a cyclohexane solution with an iodine concentration of 0.01 mol / L, weigh 0.0843g of 1-pentyl-3-methylimidazolium bromide ionic liquid in a 250mL conical flask, heat and stir to form a thin film of ionic liquid at the bottom of the conical flask. Pour the prepared iodine cyclohexane solution into the conical flask, and perform iodine extraction and separation experiments at 25°C with magnetic stirring.

[0040] During the extraction and separation experiment, the ionic liquid adheres to the bottom of the conical flask, and the supernatant is clear. The iodine content in the ionic liquid can be determined by detecting the iodine concentration in the supernatant. At intervals of 2.5 minutes, use a pipette to measure 200 μL of the cyclohexane phase solution and dilute it to a 5 mL volumetric flask with cyclohexane solution. Prepare a series of iodine cyclohexane solutions of different concentrations, and scan the spectrum to determine that the maximum absorption wavelength of iodine is at 523 nm. Perform photometric measurements at this wavelength, and draw a standard curve based on the change in absorbance with concentration.

[0041] (II) Extraction rate of iodine by 1-pentyl-3-methylimidazolium bromide ionic liquid

[0042] Table 1 Extraction rate of ionic liquid extraction at different times at 25℃

[0043] Time t / min 2.5 5 7.5 10 12.5 15 20 Extraction rate 84.55％ 91.86％ 95.82％ 97.45％ 98.66％ 99.07％ 99.07％

[0044] The extraction rate is shown in Table 1. From the beginning of extraction to 15 minutes, the extraction rate has been slowly increasing, and the extraction rate remains unchanged from 15 minutes to 20 minutes. Figure 1 From the perspective of saving time, we chose 15 minutes as the optimal extraction time.

[0045] After 15 minutes of extraction with 1-pentyl-3-methylimidazolium bromide ionic liquid, the iodine concentration of the supernatant was detected to be 0.000009378 mol / L, and the extraction rate of iodine by 1-pentyl-3-methylimidazolium bromide ionic liquid reached 99.07%.

[0046] Example 3 Study on the Extraction Performance of 1-pentyl-3-methylimidazolium Bromide

[0047] In order to study the effect of temperature on the performance of 1-pentyl-3-methylimidazolium bromide ionic liquid in extracting iodine, the iodine extraction capacity of 1-pentyl-3-methylimidazolium bromide ionic liquid was measured at 15°C, 25°C, 35°C and 45°C. To ensure that the extraction equilibrium can be achieved at different temperatures, the optimal extraction time of 15 min was used.

[0048] like Figure 2As shown in the figure, as the temperature increases, the extraction rate of [C5Mim][Br] for iodine decreases, and the increase in temperature is not conducive to extraction. Although the extraction rate at 15°C is 99.31% and the extraction rate at 25°C is 99.07%, the extraction rates of the two are similar, and 25°C is easier to achieve without additional energy consumption, so the optimal extraction condition is determined to be 25°C for 15 minutes.

[0049] Comparison of extraction performance of comparative ionic liquids

[0050] The mass ratio of [C5Mim][Br] ionic liquid to iodine was adjusted, and the extraction was performed for 15 min at the optimal extraction condition of 25°C. The extraction results were compared with those of 1-propyl-3-methylimidazolium threonine ionic liquid and 1-pentyl-3-methylimidazolium threonine ionic liquid.

[0051] Table 2 Extraction performance of iodine by different ionic liquids at different ratios

[0052] Ionic Liquids Mass ratio of ionic liquid to iodine Extraction equilibrium time Extraction rate of iodine <![CDATA[[C3Mim][Thr] [1] ]]> 1：1 60min 94.33％ <![CDATA[[C5Mim][Thr] [2] ]]> 1：1 60min 82.64％ <![CDATA[[C5Mim][Br]]]> 1：1 15min 99.26％ <![CDATA[[C5Mim][Br]]]> 1：3 15min 99.07％

[0053] Note [1]: The extraction rate of [C3Mim][Thr] is from the patent "Application of an amino acid functional ionic liquid in iodine extraction" CN 116477576A

[0054] Note [2]: The extraction rate of [C5Mim][Thr] is from the patent "An amino acid functional ionic liquid, its preparation method and application in iodine extraction" CN 116655539 A

[0055] As shown in Table 2, in comparison, the [C5Mim][Br] ionic liquid of the present invention has a more excellent extraction effect on elemental iodine when used in a small amount, and has a significant advantage.

[0056] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modification, equivalent substitution or improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. An ionic liquid, characterized in that The ionic liquid is 1-pentyl-3-methylimidazolium bromide [C5Mim][Br], and its structural formula is shown in formula (I).

2. The method for preparing the ionic liquid according to claim 1, characterized in that: The steps include: 1) Synthesis of 1-pentyl-3-methylimidazolium bromide [C5Mim][Br]: Under the protection of nitrogen, pentane bromide is slowly added dropwise to N-methylimidazole that has been distilled in the dark for multiple times to react. After the reaction is completed, cooling and crystallization are performed to obtain a solid crude product of 1-pentyl-3-methylimidazolium bromide; 2) Purification of the crude product 1-pentyl-3-methylimidazolium bromide [C5Mim][Br]: dissolve the solid crude product in a mixed solution of ethyl acetate and acetonitrile, and perform recrystallization, suction filtration, and drying in sequence to obtain 1-pentyl-3-methylimidazolium bromide ionic liquid.

3. The preparation method according to claim 2, characterized in that: In step 1), the molar ratio of N-methylimidazole to bromopentane is 1:1.

1.

4. The preparation method according to claim 2, characterized in that: In step 1), the temperature range of collecting fractions by distillation in the dark is 198-199°C.

5. The preparation method according to claim 2, characterized in that: In step 1), the reaction temperature is 65° C. and the reaction time is 48 h.

6. The preparation method according to claim 2, characterized in that: In step 2), the volume ratio of ethyl acetate to acetonitrile is 2:

1.

7. Use of the ionic liquid according to claim 1 in the efficient extraction of iodine.

8. The use according to claim 7, characterized in that: The method is as follows: placing the ionic liquid in a container, heating and stirring, so that the ionic liquid forms a thin film at the bottom of the container, pouring the iodine cyclohexane solution into the container, and extracting the iodine under magnetic stirring conditions.

9. The use according to claim 8, characterized in that: The temperature during magnetic stirring was 25°C.

10. The use according to claim 8, characterized in that: The iodine concentration in the cyclohexane solution is 0.01 mol / L.

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