A ternary deep eutectic solvent and preparation and application thereof

Abstract

The application belongs to the technical field of deep eutectic solvents, and particularly relates to a ternary deep eutectic solvent and preparation and application thereof. The ternary deep eutectic solvent is composed of choline chloride, 5-sulfosalicylic acid and gamma valerolactone according to a molar ratio of 1:4:(3-25). The strong hydrogen bond network structure between the green solvent system first destroys the ester bond between lignin and hemicellulose, then cuts off the beta-O-4 bond between lignin molecules, so as to separate lignin. Meanwhile, the deep eutectic solvent can improve the stability of carbon cations due to the conjugation effect between the lone pair electrons on the heteroatom oxygen and the central carbon in the molecular structure of gamma valerolactone, so as to inhibit the condensation reaction of lignin.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of deep eutectic solvents, and particularly relates to a ternary deep eutectic solvent and preparation and application thereof. BACKGROUND

[0002] Lignin is a three-dimensional network natural polymer of polyphenol with phenylpropane as a structural unit. Its monomer has an aromatic compound structure, can be used as a substitute for gasoline, and can replace phenol to produce chemical products. Due to its special structure and functional characteristics, lignin has become a most promising renewable resource. Therefore, lignin fractionation with high quality and high value has become the mainstream of recent research and development work.

[0003] At present, traditional lignin fractionation methods mainly include alkali method, acid method, organic solvent method and ionic liquid method. The chemical cracking of the above methods lacks selectivity and the severe treatment conditions can irreversibly produce a large amount of condensed lignin. In addition, with the deposition of condensed lignin on the surface of lignocellulose, a new blocking effect is formed, which has a significant impact on the application of cellulose components. In recent years, it has been found that deep eutectic solvents (DES) have unique lignin fractionation capacity. They have low volatility, thermal stability and recyclability, and have more excellent catalytic effect than traditional fractionation systems. Through the interaction between hydrogen donor (HBD) and hydrogen acceptor (HBA), DES can selectively cut unstable ether bonds, so as to depolymerize and separate lignin. For example, the patent with publication number CN113637295A discloses a deep eutectic solvent for separating lignin, which is composed of choline chloride and lactic acid; the patent with publication number CN115591530A discloses a eutectic solvent made of choline chloride and organic acid; and the patent with publication number CN113331369A discloses a natural deep eutectic solvent for softening betel nuts, which comprises betaine or choline chloride, lactic acid and water.

[0004] However, the condensation reaction of lignin in the acidic environment of DES cannot be ignored, and the condensation will cause the change of lignin structure, thereby limiting the good application of lignin. Therefore, it is of great significance to construct a DES system with the dual functions of efficient lignin fractionation and condensation inhibition. SUMMARY

[0005] The present application is directed to the deficiencies of the prior art, and proposes a ternary deep eutectic solvent and preparation and application thereof.

[0006] Specifically, the following technical solutions are used:

[0007] One of the purposes of the present application is: a ternary deep eutectic solvent, which is composed of choline chloride, 5-sulfosalicylic acid and gamma valerolactone.

[0008] Further, the ternary deep eutectic solvent is composed of choline chloride, 5-sulfosalicylic acid and gamma valerolactone in a molar ratio of 1:4:(3-25).

[0009] The second object of the present application is a preparation method of a ternary deep eutectic solvent, comprising the following steps:

[0010] (1) choline chloride and 5-sulfosalicylic acid are added to a conical flask, and magnetic stirring is carried out under the condition of an oil bath at a reaction temperature of 82-87℃ for 50-90 min, until the mixture becomes a transparent homogeneous liquid, and then it is taken out and stored in a desiccator for cooling, which is a deep eutectic solvent precursor;

[0011] (2) gamma valerolactone is taken, and deionized water is added to mix thoroughly, so as to prepare a gamma valerolactone solution with a mass concentration of 10-90%;

[0012] (3) the deep eutectic solvent precursor of step (1) is mixed with the gamma valerolactone solution of step (2), and magnetic stirring is carried out under the condition of an oil bath at a reaction temperature of 82-87℃ for 20-30 min, until the mixed solution is uniform, and then it is taken out and stored in a desiccator for cooling, which is a ternary deep eutectic solvent.

[0013] The reaction temperature is 85℃.

[0014] The rotating speed of the magnetic stirring is 150 rmp.

[0015] The third object of the present application is the application of a ternary deep eutectic solvent in the extraction of lignin or the preparation of lignin particles.

[0016] The method for extracting lignin comprises the following steps:

[0017] (1) a twelve-year-old poplar is cut into wood strips with a size of 1×1×5 cm, and then it is balanced in water for standby;

[0018] (2) 5 g of the poplar of step (1) is placed in a polytetrafluoroethylene inner liner of a reaction kettle, 50 mL of the ternary deep eutectic solvent is added, and then it is fully soaked, and then it is reacted in an oven at 100-140℃ for 1-5 h;

[0019] (3) the hydrolysis liquid after the reaction of step (2) is collected, deionized water is added to the collected hydrolysis liquid in a volume ratio of hydrolysis liquid: deionized water = 1:20, and then it is left to stand for 10 min, and then the precipitate at the bottom of the beaker is crude lignin;

[0020] (4) the crude lignin of step (3) is collected, and then it is washed with deionized water until it is neutral, and then the precipitate is freeze-dried, and then high-activity high-purity lignin is obtained after purification.

[0021] The method for preparing lignin particles comprises the following steps:

[0022] (1) The high-activity high-purity lignin obtained by the above method of extracting lignin is dissolved in tetrahydrofuran to prepare a lignin mother liquor with a concentration of 2.0 mg / mL;

[0023] (2) The lignin mother liquor is added to deionized water according to a volume ratio of 1:10, and stirred at 500 rpm for 10 min, and after freeze-drying for 24 h, high-activity lignin nanoparticles are obtained.

[0024] Advantages:

[0025] (1) The present application designs a ternary deep eutectic solvent for separating lignin in lignocellulose. The strong hydrogen bond network structure of the green solvent system first breaks the ester bond between lignin and hemicellulose, and then cuts the β-O-4 bond between lignin molecules, thereby separating lignin.

[0026] (2) The present application realizes efficient separation of uncondensed lignin and high retention of cellulose. Because the conjugation effect exists between the lone pair of electrons on the oxygen heteroatom and the central carbon in the molecular structure of gamma valerolactone, the deep eutectic solvent can improve the stability of carbon cations, thereby inhibiting the condensation reaction of lignin.

[0027] (3) The lignin extracted by the present application has the advantages of low molecular weight (Mn=2305 g·mol -1 ), high yield (71.35%) and high purity (98.77%), and the total phenolic hydroxyl content is as high as 6.92 mmol·g -1 , which is conducive to the development and utilization of lignin-based materials.

[0028] (4) The present application obtains high-stability (zeta potential of -21 mV), high-uniformity (average particle size of 23 nm) high-activity lignin nanoparticles, and the lignin nanoparticles exhibit excellent UV shielding performance, which is Figure 2 It can be seen that under the same ultraviolet wavelength irradiation, the light transmittance of Example 3 is significantly lower than that of Comparative Example 1. BRIEF DESCRIPTION OF DRAWINGS

[0029] Figure 1 : Comparison diagram of lignin separation in poplar in Example 3 and Comparative Example 1;

[0030] Figure 2 : Comparison diagram of lignin UV shielding performance in poplar in Example 3 and Comparative Example 1;

[0031] Figure 3 : Transmission electron microscope image of high-activity lignin nanoparticles prepared in Example 3;

[0032] Figure 4 TEM image of high activity lignin nanoparticles prepared in Comparative Example 1;

[0033] Figure 5 TEM image of high activity lignin nanoparticles prepared in Comparative Example 2. DETAILED DESCRIPTION

[0034] The specific embodiments of the present application are further described in detail below, but the present application is not limited to these embodiments, any improvement or replacement in the basic spirit of the present embodiments still belongs to the scope of protection claimed in the present application.

[0035] Example 1

[0036] S1. Construction of ternary deep eutectic solvent:

[0037] Choline chloride and 5-sulfosalicylic acid were added to a conical flask in a molar ratio of 1:4, and then placed in a magnetic stirrer, and reacted at a reaction temperature of 85°C and a rotation speed of 150rmp under oil bath conditions for 90min, until the mixture became a transparent homogeneous liquid, and then taken out and cooled and stored in a desiccator, which was the deep eutectic solvent precursor; deionized water was used as a solvent to prepare a γ-valerolactone solution with a mass concentration of 70%; the deep eutectic solvent precursor was mixed with the 70% γ-valerolactone solution and placed in a magnetic stirrer, and reacted at a reaction temperature of 85°C and a rotation speed of 150rmp under oil bath conditions for 20min, until the mixed solution was uniform, and then taken out and cooled and stored in a desiccator, which was the ternary deep eutectic solvent; the ternary deep eutectic solvent was in a molar ratio of choline chloride: 5-sulfosalicylic acid: γ-valerolactone = 1:4:15;

[0038] S2. Extraction of high activity lignin:

[0039] Five grams of poplar wood strips were cut into 1x1x5cm wood strips, and the water content was balanced before use; 5g of poplar wood strips were placed in a polytetrafluoroethylene reaction kettle liner, 50mL of ternary deep eutectic solvent prepared in step S1 was added, and after sufficient soaking, the reaction was carried out in a high-temperature oven at a reaction temperature of 110°C for 3h; after the reaction, deionized water was added to the collected hydrolyzate according to a volume ratio of hydrolyzate: deionized water = 1:20, and after standing for 10min, the obtained precipitate was crude lignin; the crude lignin was washed to neutral with deionized water, and the washed crude lignin was freeze-dried and purified to obtain high activity high purity lignin;

[0040] S3. Preparation of high activity lignin particles:

[0041] The high activity lignin prepared in step S2 was dissolved in tetrahydrofuran to prepare a solution with a concentration of 2.0mg·mL -1lignin mother liquor; 10 mL lignin mother liquor was added to 100 mL deionized water, stirred at 500 rpm for 10 min, and high-activity lignin nanoparticles were obtained after freeze-drying for 24 h.

[0042] Example 2

[0043] S1. Construction of a ternary deep eutectic solvent system:

[0044] Choline chloride and 5-sulfosalicylic acid were added to a conical flask in a molar ratio of 1:4, and then placed in a magnetic stirrer. The reaction was carried out at a reaction temperature of 85°C, a rotation speed of 150 rpm, and an oil bath condition for 90 min, until the mixture became a transparent homogeneous liquid. Then, the mixture was taken out and cooled and stored in a desiccator, which was the deep eutectic solvent precursor. A γ-valerolactone solution with a mass concentration of 80% was prepared using deionized water as the solvent. The deep eutectic solvent precursor was mixed with the 80% γ-valerolactone solution and placed in a magnetic stirrer. The reaction was carried out at a reaction temperature of 85°C, a rotation speed of 150 rpm, and an oil bath condition for 20 min, until the mixed solution was uniform. Then, the mixed solution was taken out and cooled and stored in a desiccator, which was the ternary deep eutectic solvent. The molar ratio of the ternary deep eutectic solvent was choline chloride: 5-sulfosalicylic acid: γ-valerolactone = 1:4:20;

[0045] S2. Extraction of high-activity lignin:

[0046] Poplar wood of 12 years old was cut into 1×1×5 cm wood strips and balanced in water before use. 5 g of the poplar wood strips were weighed and placed in a polytetrafluoroethylene reaction kettle liner. 50 mL of the ternary deep eutectic solvent prepared in step S1 was added, and after sufficient soaking, the reaction was carried out in a high-temperature oven at a reaction temperature of 110°C for 3 h. After the reaction, deionized water was added to the collected hydrolyzate at a volume ratio of hydrolyzate: deionized water = 1:20, and after standing for 10 min, the obtained precipitate was crude lignin. The crude lignin was washed to neutral with deionized water, and after freeze-drying, high-activity high-purity lignin was obtained after purification.

[0047] S3. Preparation of high-activity lignin particles:

[0048] The high-activity lignin prepared in step S2 was dissolved in tetrahydrofuran to prepare a lignin mother liquor with a concentration of 2.0 mg·mL -1 After 10 mL of the lignin mother liquor was added to 100 mL of deionized water and stirred at 500 rpm for 10 min, high-activity lignin nanoparticles were obtained after freeze-drying for 24 h.

[0049] Example 3

[0050] S1. Construction of a ternary deep eutectic solvent system:

[0051] Choline chloride and 5-sulfosalicylic acid were added into a conical flask in a molar ratio of 1:4, and then placed in a magnetic stirrer, and reacted at a reaction temperature of 85°C and a rotation speed of 150rmp under oil bath conditions for 90 min until the mixture became a transparent homogeneous liquid, and then taken out and cooled and stored in a desiccator, thereby obtaining a deep eutectic solvent precursor; deionized water was used as a solvent to prepare a gamma valerolactone solution with a mass concentration of 70%; the deep eutectic solvent precursor was mixed with the 70% gamma valerolactone solution, and then placed in a magnetic stirrer, and reacted at a reaction temperature of 85°C and a rotation speed of 150rmp under oil bath conditions for 20 min until the mixed solution was uniform, and then taken out and cooled and stored in a desiccator, thereby obtaining a ternary deep eutectic solvent; the ternary deep eutectic solvent was in a molar ratio of choline chloride: 5-sulfosalicylic acid: gamma valerolactone = 1:4:15;

[0052] S2. Extraction of high-activity lignin:

[0053] Poplar wood of 12 years old was cut into 1x1x5cm wood strips, and then balanced in water and used; 5g of the poplar wood strips were weighed and placed in a polytetrafluoroethylene reaction kettle inner liner, 50mL of the ternary deep eutectic solvent prepared in step S1 was added, and then fully soaked, and then reacted in a high-temperature oven at a reaction temperature of 120°C for 3h; after the reaction, deionized water was added to the collected hydrolyzate in a volume ratio of hydrolyzate: deionized water = 1:20, and then stood for 10min, and then the obtained precipitate was crude lignin; the crude lignin was washed to neutral with deionized water, and then freeze-dried, and then purified to obtain high-activity high-purity lignin;

[0054] S3. Preparation of high-activity lignin particles:

[0055] The high-activity lignin prepared in step S2 was dissolved in tetrahydrofuran to prepare a lignin mother liquor with a concentration of 2.0mg·mL -1 ; 10mL of the lignin mother liquor was added to 100mL of deionized water and stirred at 500rpm for 10min, and then freeze-dried for 24h to obtain high-activity lignin nanoparticles.

[0056] Comparative Example 1

[0057] S1. Preparation of a choline chloride / lactic acid deep eutectic solvent:

[0058] Choline chloride and lactic acid were added into a conical flask in a molar ratio of 1:2, and then placed in a magnetic stirrer, and reacted at a reaction temperature of 65°C and a rotation speed of 150rmp under oil bath conditions for 60min until the mixture became a transparent homogeneous liquid, and then taken out, thereby obtaining a choline chloride / lactic acid deep eutectic solvent (ChCl-Lac);

[0059] S2. Extraction of lignin:

[0060] Twelve-year-old poplar was cut into 1x1x5cm wood strips, and the balance moisture was used. 5g poplar wood strips were weighed and placed in a polytetrafluoroethylene reactor inner lining, 50mL of ternary deep eutectic solvent prepared in step S1 was added, after sufficient soaking, the reaction was carried out in a high temperature oven with a reaction temperature of 145℃ for 6h, after the reaction, deionized water was added to the collected hydrolysate according to the volume ratio of hydrolysate:deionized water=1:20, after standing for 10min, the obtained precipitate was crude lignin. The crude lignin was washed to neutral with deionized water. The washed crude lignin was freeze-dried, and high activity and high purity lignin was obtained after purification;

[0061] S3. Preparation of high-activity lignin particles:

[0062] The high-activity lignin prepared in step S2 was dissolved in tetrahydrofuran to prepare a lignin mother liquor with a concentration of 2.0mg·mL -1 ; 10mL of lignin mother liquor was added to 100mL of deionized water and stirred at 500rpm for 10min, and high-activity lignin nanoparticles were obtained after freeze-drying for 24h.

[0063] Comparative example 2

[0064] S1. Extraction of enzymatic milled wood lignin:

[0065] After twelve-year-old poplar was ball milled for 48h, a pH=4.5 acetic acid and sodium acetate buffer solution was added, the wood powder concentration was adjusted to 5%, 255FPU·mL -1 of cellulase was added, and the reaction was carried out at 120rmp and 50℃ for 72h on a shaking bed; the wood powder after reaction was collected and extracted in 1,4 dioxane solution; the collected liquid after extraction was added dropwise into pH=2 HCl, and the collected precipitate was crude lignin. The washed crude lignin was freeze-dried, and high-activity and high-purity lignin was obtained after purification;

[0066] S3. Preparation of high-activity lignin particles:

[0067] The high-activity lignin prepared in step S2 was dissolved in tetrahydrofuran to prepare a lignin mother liquor with a concentration of 2.0mg·mL -1 ; 10mL of lignin mother liquor was added to 100mL of deionized water and stirred at 500rpm for 10min, and high-activity lignin nanoparticles were obtained after freeze-drying for 24h.

[0068] Experimental test:

[0069] Note: The samples were prepared with extracted crude lignin, and the purified lignin was only used for 31 P NMR detection of phenolic hydroxyl content.

[0070] 1. The lignin isolation in poplar in Example 3 and Comparative Example 1 is compared as follows Figure 1

[0071] 2. The lignin properties of Examples 1-3 and Comparative Examples 1-2 are as follows:

[0072] 2.1 Test method:

[0073] The molecular weight of lignin was determined by gel permeation chromatography (GPC 50, Agilent, Santa Clara, CA, USA) with dimethyl sulfoxide as mobile phase at a flow rate of 0.5 mL·min -1 , column temperature of 25 °C and injection volume of 20.0 μL.

[0074] The lignin content is the sum of acid-soluble lignin and precipitated lignin. The acid-soluble lignin content was determined by UV spectrophotometry (CARY 3500 UV-VIS, Agilent, Santa Clara, CA, USA). The precipitated lignin content was determined gravimetrically.

[0075] 2.2 The lignin properties of Examples 1-3 and Comparative Examples 1-2 are shown in Table 1 below:

[0076] Table 1

[0077]

[0078] 3. Phenolic hydroxyl content of lignin extracted in Examples 1-3 and Comparative Examples 1-2

[0079] 3.1 Test method:

[0080] First, the lignin sample was reacted with phosphorizing reagent (TMDP), the unstable hydrogen in the lignin was replaced by phosphorus to form phosphorus-containing lignin-TMDP derivative, and then the lignin structure unit ratio and hydroxyl content were analyzed by nuclear magnetic resonance spectrometer (AVANCE III HD 500M, Bruker, Karlsruhe, Germany) 31 , using cyclohexanol as internal standard.

[0081] 3.2. The phenolic hydroxyl content of lignin extracted in Examples 1-3 and Comparative Examples 1-2 is shown in Table 2 below:

[0082] Table 2

[0083] ​

Claims

1. A ternary deep eutectic solvent, characterized in that, The ternary deep eutectic solvent is composed of choline chloride, 5-sulfosalicylic acid and γ-valerol in a molar ratio of 1:4:(3-25); The method for preparing a ternary deep eutectic solvent includes the following steps: (1) Add choline chloride and 5-sulfosalicylic acid to an Erlenmeyer flask and stir magnetically for 50-90 minutes at a reaction temperature of 82-87℃ and an oil bath until the mixture becomes a transparent and uniform liquid. Then take it out and cool it in a desiccator for storage. This is the deep eutectic solvent precursor. (2) Take γ-valerol, add deionized water and stir thoroughly to prepare a γ-valerol solution with a mass concentration of 10-90%. (3) Mix the deep eutectic solvent precursor from step (1) with the γ-valerol solution from step (2), and stir magnetically for 20-30 minutes at a reaction temperature of 82-87℃ and in an oil bath until the mixture is homogeneous. Then take it out and cool it in a desiccator for storage. This is the ternary deep eutectic solvent.

2. The ternary deep eutectic solvent as described in claim 1, characterized in that, The reaction temperature is 85°C.

3. The ternary deep eutectic solvent as described in claim 1, characterized in that, The magnetic stirrer rotates at a speed of 150 rpm.

4. The application of the ternary deep eutectic solvent as described in claim 1 in the extraction of lignin.

5. The application of a ternary deep eutectic solvent as described in claim 4 in the extraction of lignin, characterized in that, The method for extracting lignin includes the following steps: (1) Cut twelve-year-old poplar into strips of 1×1×5 cm, and set aside after balancing the moisture content; (2) Take 5 g of poplar wood from step (1) and place it in the PTFE reaction vessel liner. Add 50 mL of ternary deep eutectic solvent and fully impregnate the wood. Then, react in an oven at 100-140℃ for 1-5 hours. (3) Collect the hydrolysate after the reaction in step (2), add deionized water to the collected hydrolysate according to the volume ratio of hydrolysate: deionized water = 1:20, let it stand for 10 minutes, and the precipitate at the bottom of the beaker is crude lignin. (4) Collect the crude lignin from step (3), wash it with deionized water until neutral, freeze-dry the precipitate, and purify it to obtain high-activity, high-purity lignin.

6. The application of the ternary deep eutectic solvent as described in claim 1 in the preparation of lignin particles.

7. The application of the ternary deep eutectic solvent as described in claim 6 in the preparation of lignin particles, characterized in that, The method for preparing lignin particles includes the following steps: (1) Cut twelve-year-old poplar into strips of 1×1×5 cm, and set aside after balancing the moisture content; (2) Take 5 g of poplar wood from step (1) and place it in the PTFE reaction vessel liner. Add 50 mL of ternary deep eutectic solvent and fully impregnate the wood. Then, react in an oven at 100-140℃ for 1-5 hours. (3) Collect the hydrolysate after the reaction in step (2), add deionized water to the collected hydrolysate according to the volume ratio of hydrolysate: deionized water = 1:20, let it stand for 10 minutes, and the precipitate at the bottom of the beaker is crude lignin. (4) Collect the crude lignin from step (3), wash it with deionized water until neutral, freeze-dry the precipitate, and purify it to obtain high-activity, high-purity lignin. (5) Dissolve the highly active and pure lignin obtained by the above method of lignin extraction in tetrahydrofuran to prepare a lignin mother liquor with a concentration of 2.0 mg / mL. (6) Add the lignin mother liquor to the deionized water at a volume ratio of 1:10 and stir at 500 rpm for 10 min. After freeze drying for 24 h, highly active lignin nanoparticles are obtained.

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