Halogen-free dication liquid as well as preparation method and application thereof

Abstract

Belonging to the technical field of organic chemistry, the invention discloses a halogen-free dication liquid, the molecular formula of the dication liquid is [MIMCnN111] [SCN] 2, where n = 2, 3 or 5; the structural formula of the [MIMCnN111] [SCN] 2 is as follows: # imgabs0 #. Imidazolyl and quaternary ammonium are connected through a methylene chain to obtain cations in dication liquid, thiocyanate is selected as anions in the dication liquid, and the dication liquid with high thermal stability, low solubility in oil and excellent phenol separation performance is obtained; and the dication liquid used in the invention does not contain water-soluble halogen, does not corrode steel production equipment, and is more environment-friendly.

Description

Technical Field

[0001] The invention belongs to the technical field of organic chemistry, and in particular relates to a halogen-free dicationic liquid and a preparation method and application thereof. Background Art

[0002] Phenolic compounds are important chemical raw materials. There is a large gap in the supply of phenols in the market every year, and they have considerable market demand and application value. Extracting phenolic compounds from coal tar is one of the main sources of phenolic compounds. The content of phenolic compounds in medium and low temperature coal tar is usually 15-30wt%. Extracting phenolic compounds can increase the stability of coal tar, which is beneficial to the storage and transportation of oil products; in addition, it will significantly reduce the hydrogen consumption in the subsequent process, and obtain market-scarce chemicals with high added value.

[0003] The main methods for extracting phenolic compounds from coal tar include alkali washing, solvent extraction, ionic liquid and deep eutectic solvent. The most mature and widely used method in industry is alkali washing, which has high extraction efficiency, but uses a large amount of strong acid and alkali, which seriously corrodes the equipment, and produces a large amount of phenol-containing wastewater in the process, which is difficult to handle and pollutes the environment. In recent years, the ionic liquid method has been widely studied and applied in component separation or removal due to its high selectivity and designability, but some current ionic liquids have problems such as thermal instability, easy decomposition, high selectivity but high viscosity, etc.

[0004] Therefore, it is an urgent problem for those skilled in the art to provide a stable ionic liquid with high separation efficiency and short separation time, which can extract phenolic compounds from coal tar in a more environmentally friendly and efficient manner. Summary of the invention

[0005] In order to solve the above problems, the present invention provides a halogen-free dicationic liquid and a preparation method and application thereof.

[0006] In order to achieve the above object, the present invention adopts the following technical solution:

[0007] A halogen-free dicationic liquid, the molecular formula of which is [MIMC n N 111 ][SCN]2, where n=2, 3 or 5;

[0008] The [MIMC n N 111 The structural formulas of ][SCN]2 are as follows:

[0009]

[0010] The ionic liquid method can avoid the use of strong acid and strong base, and the dicationic liquid (DIL) therein has the characteristics of the traditional monocationic liquid. In addition, it has a larger molecular structure, so that it has higher thermal stability and its solubility in oil can be greatly reduced, thereby reducing the pollution to the oil phase. At the same time, since the ionic liquid is designable, the present invention connects the imidazole group and the quaternary ammonium group through a methylene chain to obtain the cation in the dicationic liquid. Since the phenolic hydroxyl group in the phenolic compound contains active hydrogen, the thiocyanate group contains a nitrogen atom with strong electronegativity, which can form a hydrogen bond with the phenolic hydroxyl group to separate the phenolic compound from the coal tar, so the thiocyanate group is selected as the anion in the dicationic liquid, aiming to obtain a dicationic liquid with high thermal stability, low solubility in oil and excellent phenol separation performance. In addition, the dicationic liquid used in the present invention does not contain water-soluble halogens, will not corrode steel production equipment, and is more environmentally friendly.

[0011] The method for preparing a halogen-free dicationic liquid as described above comprises the following specific steps:

[0012] (1) reflux N-methylimidazole and compound I under nitrogen protection to obtain a precipitate, which is an intermediate;

[0013] (2) The intermediate is reacted with potassium thiocyanate to obtain a halogen-free dicationic liquid.

[0014] Preferably, the molar ratio of the N-methylimidazole to the compound I in step (1) is 1-3:1, in order to ensure that the compound I reacts as completely as possible.

[0015] Preferably, the compound I in step (1) is any one of 2-bromoethyltrimethylammonium bromide, 3-bromopropyltrimethylammonium bromide and 5-bromo-N,N,N-trimethylpentane-1-ammonium bromide.

[0016] Preferably, the reflux reaction conditions in step (1) are: reflux reaction at 70-90° C. for 30-48 h.

[0017] Preferably, the molar ratio of the intermediate to the potassium thiocyanate in step (1) is 1:2-3, in order to ensure that the intermediate reacts as completely as possible.

[0018] Preferably, the precipitate in step (1) further comprises washing with ethyl acetate, and then drying in a vacuum oven at 60-80° C. for at least 24 hours until its weight no longer changes.

[0019] Preferably, the reaction conditions in step (2) are: reacting at room temperature for 36-48 hours.

[0020] Preferably, in step (2), the intermediate is dissolved in methanol or anhydrous ethanol as a solvent to prepare an intermediate solution, and the solvent is continuously added until the intermediate is completely dissolved;

[0021] The potassium thiocyanate is dissolved in anhydrous ethanol to prepare a potassium thiocyanate solution, and the anhydrous ethanol is continuously added until the potassium thiocyanate is completely dissolved.

[0022] Preferably, step (2) further comprises obtaining a filtrate after the reaction is completed, subjecting the filtrate to rotary evaporation to obtain a crude product, and purifying and drying the crude product to obtain a halogen-free dicationic liquid.

[0023] Application of the halogen-free dicationic liquid described above or the halogen-free dicationic liquid prepared by the preparation method described above in extracting and separating phenolic compounds in an oil-phenol mixture.

[0024] Preferably, the phenolic compound is phenol.

[0025] Compared with the prior art, the present invention has the following beneficial effects:

[0026] (1) The dicationic liquid prepared by the present invention has high thermal stability and a wider temperature application range;

[0027] (2) The dicationic liquid provided by the present invention has high separation efficiency and short separation time;

[0028] (3) The dicationic liquid provided by the present invention does not contain halogen, will not corrode steel equipment during the extraction process, and is environmentally friendly;

[0029] (4) The dicationic liquid extractant provided by the present invention can be recycled and reused. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the provided drawings without paying creative work.

[0031] Figure 1 The dicationic liquid synthesized in Examples 1-3 of the present invention 1 H NMR spectrum;

[0032] Figure 2 This is a graph showing the extraction performance of the dicationic liquids synthesized in Examples 1-3 of the present invention;

[0033] Figure 3This is a graph showing the effect of the molar ratio of the dicationic liquid synthesized in Example 2 of the present invention to phenol on the performance of extracting phenol;

[0034] Figure 4 is the recycling capacity of the dicationic liquid synthesized in Example 2, wherein a is the regeneration extraction efficiency, b is the extraction agent recovery rate, c is the regeneration FT-IR spectrum, d is the regeneration 1 H NMR spectrum. DETAILED DESCRIPTION

[0035] The technical solutions in the embodiments of the present invention are described clearly and completely below. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0036] Example 1

[0037] The present invention provides a halogen-free dicationic liquid ([MIMC2N 111 ][SCN]2) preparation method, comprising the following specific steps:

[0038] (1) 0.02 mol of 2-bromoethyltrimethylammonium bromide was added to a round-bottom flask, followed by 50 mL of anhydrous ethanol and 0.06 mol of N-methylimidazole under magnetic stirring. The round-bottom flask was placed in a constant temperature oil bath at 80° C. and refluxed for 40 h under nitrogen protection. After the reaction was completed, the precipitate was filtered and washed three times with ethyl acetate. The precipitate was placed in a vacuum oven at 80° C. and dried for at least 24 h until its weight no longer changed. This was the intermediate.

[0039] (2) Methanol was continuously added to a beaker containing 0.015 mol of the intermediate until the intermediate was completely dissolved to obtain an intermediate solution; then anhydrous ethanol was continuously added to a beaker containing 0.03 mol of potassium thiocyanate until the potassium thiocyanate was completely dissolved to obtain a potassium thiocyanate solution; finally, the potassium thiocyanate solution was added dropwise to the intermediate solution and reacted at room temperature for 48 h, the precipitate was filtered out, and the filtrate was subjected to rotary evaporation to obtain a crude product; the crude product was dissolved in acetonitrile, the precipitate at the bottom was removed by centrifugation, the acetonitrile was removed by rotary evaporation, and the target product [MIMC2N] was obtained after drying in a vacuum drying oven at 60°C for at least 12 h. The operation was repeated three times. 111 ][SCN]2, its synthetic route is as follows:

[0040]

[0041] Example 2

[0042] The present invention provides a halogen-free dicationic liquid ([MIMC3N 111 ][SCN]2) preparation method, comprising the following specific steps:

[0043] (1) 0.02 mol of 3-bromopropyltrimethylammonium bromide was added to a round-bottom flask, followed by 50 mL of isopropanol and 0.06 mol of N-methylimidazole under magnetic stirring. The round-bottom flask was placed in a constant temperature oil bath at 80° C. and refluxed for 40 h under nitrogen protection. After the reaction was completed, the precipitate was filtered and washed three times with ethyl acetate. The precipitate was placed in a vacuum oven at 80° C. and dried for at least 24 h until its weight no longer changed. This was the intermediate.

[0044] (2) Add anhydrous ethanol continuously to a beaker containing 0.015 mol of the intermediate until the intermediate is completely dissolved to obtain an intermediate solution; then add anhydrous ethanol continuously to a beaker containing 0.03 mol of potassium thiocyanate until the potassium thiocyanate is completely dissolved to obtain a potassium thiocyanate solution; finally, add the potassium thiocyanate solution dropwise to the intermediate solution and react at room temperature for 48 hours, filter out the precipitate, and perform rotary evaporation on the filtrate to obtain a crude product; dissolve the crude product in acetonitrile, remove the precipitate at the bottom by centrifugation, remove the acetonitrile by rotary evaporation, and dry in a vacuum drying oven at 60° C. for at least 12 hours. Repeat the operation three times to obtain the target product [MIMC3N 111 ][SCN]2, its synthetic route is as follows:

[0045]

[0046] Example 3

[0047] The present invention provides a halogen-free dicationic liquid ([MIMC5N 111 ][SCN]2) preparation method, comprising the following specific steps:

[0048] (1) 0.02 mol of 5-bromo-N,N,N-trimethylpentane-1-ammonium bromide was added to a round-bottom flask, followed by 60 mL of acetonitrile and 0.06 mol of N-methylimidazole under magnetic stirring. The round-bottom flask was placed in a thermostatic oil bath at 80° C. and refluxed for 40 h under nitrogen protection. After the reaction was completed, the acetonitrile was removed by rotary evaporation to obtain a crude product. Deionized water was added to dissolve the crude product. Ethyl acetate was added to dissolve the unreacted N-methylimidazole, and then the water was removed by rotary evaporation to obtain a precipitate, which was washed three times with ethyl acetate. The precipitate was dried in a vacuum oven at 80° C. for at least 24 h until its weight no longer changed, which was the intermediate.

[0049] (2) Add anhydrous ethanol continuously to a beaker containing 0.015 mol of the intermediate until the intermediate is completely dissolved to obtain an intermediate solution; then add anhydrous ethanol continuously to a beaker containing 0.03 mol of potassium thiocyanate until the potassium thiocyanate is completely dissolved to obtain a potassium thiocyanate solution; finally, add the potassium thiocyanate solution dropwise to the intermediate solution and react at room temperature for 48 hours, filter out the precipitate, and perform rotary evaporation on the filtrate to obtain a crude product; dissolve the crude product in acetonitrile, remove the precipitate at the bottom by centrifugation, remove the acetonitrile by rotary evaporation, and dry in a vacuum drying oven at 60° C. for at least 12 hours. Repeat the operation three times to obtain the target product [MIMC3N 111 ][SCN]2, its synthetic route is as follows:

[0050]

[0051] Example 4

[0052] The present invention provides a halogen-free dicationic liquid ([MIMC2N 111 The other preparation conditions are the same as those in Example 1, except that the reaction temperature in step (1) of Example 1 is 70° C. and the reaction time is 48 h.

[0053] Example 5

[0054] The present invention provides a halogen-free dicationic liquid ([MIMC3N 111 The other preparation conditions are the same as those in Example 2, except that the reaction temperature in step (1) of Example 2 is 70° C. and the reaction time is 48 h.

[0055] Example 6

[0056] The present invention provides a halogen-free dicationic liquid ([MIMC5N 111 The other preparation conditions are the same as those in Example 3, except that the reaction temperature in step (1) of Example 3 is 70° C. and the reaction time is 48 h.

[0057] like Figure 1 This is a nuclear magnetic hydrogen spectrum characterization diagram of the dicationic liquid synthesized in Example 1-3. It can be seen from the figure that the chemical shift and the number of resonance peaks and the integrated area on the spectrum are consistent with the chemical shift and the number of resonance peaks and the integrated area of ​​the target dicationic liquid, proving that the synthesis of the dicationic liquid is successful;

[0058] Application example: extraction and separation experiment

[0059] Considering the complexity of coal tar components, toluene-phenol was selected as the simulated oil for the phenol extraction experiment. A certain amount of phenol was dissolved in toluene to prepare a phenol concentration of 200 g / dm -310 mL of simulated oil was placed in a 20 mL sample bottle, and then 0.4 times the molar amount of phenol dicationic liquid was added. The mixture was stirred magnetically at 25 °C for 20 min. After standing for a period of time, the extract phase and the raffinate phase were separated. The concentration of phenol in the raffinate phase was analyzed by gas chromatography. The extraction efficiency EE of phenol was 1. phenol (%) is calculated according to the following formula:

[0060] Where C0 represents the initial phenol concentration, V0 represents the initial simulated oil volume, C f represents the phenol concentration in the raffinate phase, V f represents the volume of the raffinate phase;

[0061] The extraction efficiency corresponding to the preparation of dicationic liquids in Example 1-3 is as follows Figure 2 As shown, they are 92.26%, 96.02% and 96.69% respectively;

[0062] Select [MIMC3N prepared in Example 2 111 ][SCN]2 The effect of the molar ratio of extractant to phenol on the performance of phenol extraction was investigated. Figure 3 , the separation equilibrium is reached when the molar ratio of the extractant to phenol is 0.6, [MIMC3N 111 The extraction efficiency of ][SCN]2 for phenol is as high as 97.90%;

[0063] Ether was used for stripping experiments, and the recovered [MIMC3N 111 ][SCN]2 was extracted 5 times in a cycle. The results are as follows Figure 4 As shown, it was found that [MIMC3N 111 ][SCN]2 can be recycled while keeping its structure unchanged and has good recycling ability.

[0064] The various embodiments are described in a progressive manner, and each embodiment focuses on the differences from other embodiments. The same or similar parts between the various embodiments can be referred to in detail.

[0065] The above description of the disclosed embodiments enables one skilled in the art to implement or use the present invention. Various modifications to these embodiments will be apparent to one skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention will not be limited to the embodiments shown herein, but rather to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A halogen-free dicationic liquid, characterized in that: The molecular formula of the dicationic liquid is [MIMC n N 111 ][SCN]2, where n=2, 3 or 5; The [MIMC n N 111 The structural formulas of ][SCN]2 are as follows:

2. The method for preparing a halogen-free dicationic liquid according to claim 1, characterized in that: The specific steps include: (1) reflux N-methylimidazole and compound I under nitrogen protection to obtain a precipitate, which is an intermediate; (2) The intermediate is reacted with potassium thiocyanate to obtain a halogen-free dicationic liquid.

3. The method for preparing a halogen-free dicationic liquid according to claim 2, characterized in that: The molar ratio of the N-methylimidazole to the compound I in step (1) is 1-3:

1.

4. The method for preparing a halogen-free dicationic liquid according to claim 2, characterized in that: The compound I in step (1) is any one of 2-bromoethyltrimethylammonium bromide, 3-bromopropyltrimethylammonium bromide and 5-bromo-N,N,N-trimethylpentane-1-ammonium bromide.

5. The method for preparing a halogen-free dicationic liquid according to claim 2, characterized in that: The conditions of the reflux reaction in step (1) are: reflux reaction at 70-90° C. for 30-48 hours.

6. The method for preparing a halogen-free dicationic liquid according to claim 2, characterized in that: The molar ratio of the intermediate to the potassium thiocyanate in step (1) is 1:2-3.

7. The method for preparing a halogen-free dicationic liquid according to claim 2, characterized in that: The reaction conditions in step (2) are: reaction at room temperature for 36-48 hours.

8. The method for preparing a halogen-free dicationic liquid according to claim 2, characterized in that: In step (2), the intermediate is dissolved in methanol or anhydrous ethanol as a solvent to prepare an intermediate solution, and the solvent is continuously added until the intermediate is completely dissolved; The potassium thiocyanate is dissolved in anhydrous ethanol to prepare a potassium thiocyanate solution, and the anhydrous ethanol is continuously added until the potassium thiocyanate is completely dissolved.

9. The method for preparing a halogen-free dicationic liquid according to claim 7, characterized in that: Step (2) also includes obtaining a filtrate after the reaction is completed, subjecting the filtrate to rotary evaporation to obtain a crude product, and purifying and drying the crude product to obtain a halogen-free dicationic liquid.

10. Use of the halogen-free dicationic liquid according to claim 1 or the halogen-free dicationic liquid prepared by the preparation method according to any one of claims 2 to 9 in extracting and separating phenolic compounds in an oil-phenol mixture.

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