A method for fractionally extracting lignin and preparing lignin nanomicrospheres with adjustable particle size

Abstract

The application discloses a method for grading extraction of lignin and preparation of lignin nanomicrospheres with adjustable particle size, and belongs to the technical field of lignin nanomaterial preparation. The application takes poplar powder as an extraction raw material, adjusts the temperature or pH value of a reaction system, adjusts the intensity of a reaction, and then realizes grading extraction of lignin and regulation of chemical structures, so that the extraction efficiency of lignin is remarkably improved, and lignin with different structures is obtained. Furthermore, lignin nanomicrospheres with large specific surface area, adjustable particle size, high proportion of surface atoms, and strong surface modifiability are prepared by using the grading-extracted lignin as a raw material, which lays an important theoretical foundation for separation and high-value utilization of lignin.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of lignin nanomaterial preparation, and more particularly relates to a method for grading lignin extraction and preparation of lignin nanomicrospheres with adjustable particle size. BACKGROUND

[0002] Wood fiber raw material is one of the most abundant green raw materials in the world, and its comprehensive utilization has far-reaching significance. Due to the complex composition structure of lignin, it is difficult to be effectively utilized. At present, lignin is mainly used as fuel for combustion and heat release, so most of it cannot be effectively utilized. Therefore, efficient utilization of lignin is particularly important for the full component utilization of wood fiber raw materials.

[0003] Lignin nanomaterials have excellent properties such as large specific surface area, high surface atom number, and surface modifiability, and can be applied in various fields. Therefore, exploring the relationship between lignin molecular structure and lignin nanoparticle construction, and preparing high-yield, size-uniform and well-dispersed high-activity lignin nanoparticles through a green, economical and simple method is a major challenge for realizing high-value utilization of lignin. SUMMARY

[0004] The purpose of the present application is to provide a method for grading lignin extraction and preparing lignin nanomicrospheres with adjustable particle size, to solve the problems existing in the prior art, to prepare high-yield, size-uniform and well-dispersed high-activity lignin nanoparticles, and to realize high-value utilization of lignin.

[0005] To achieve the above purpose, the present application provides the following solutions:

[0006] One of the technical solutions of the present application is to provide a method for adjusting reaction conditions, grading lignin extraction and preparing lignin nanomicrospheres with different particle sizes, comprising the following steps:

[0007] Step 1: mixing poplar powder and solvent for reaction to obtain solid phase and liquid phase;

[0008] Step 2: using the solid phase as raw material, repeating step 1 reaction, and gradually reducing the pH value of the reaction system or gradually increasing the temperature of the reaction system in the repeating process;

[0009] The liquid phases obtained in steps 1 and 2 are mixed with hydrochloric acid solution, washed and freeze-dried in sequence to obtain lignin;

[0010] The obtained lignin is treated by solvent displacement method using eutectic solvent as solvent and water as displacement solvent to obtain lignin nanomicrospheres with different particle sizes.

[0011] The present application takes poplar powder as the extraction raw material, adjusts the reaction intensity by changing the pH value or temperature of the reaction system, thereby realizing the fractionated extraction and chemical structure regulation of lignin, significantly improving the extraction efficiency of lignin and obtaining lignin with different structures, and when the lignin has lower molecular weight, lower content of β-O-4 linkage and higher content of H-type lignin, the lignin is more conducive to forming lignin nanoparticles with uniform particle size and smaller size through the anti-solvent titration method; and the lignin nanospheres prepared by the above regulation have large specific surface area, high proportion of surface atoms and strong surface modifiability.

[0012] The specific analysis is as follows:

[0013] The 2D-nuclear magnetic quantitative results of the poplar lignin obtained by adjusting the temperature of the fractionated extraction show that in the poplar raw material lignin, the content of H-type lignin is low, and the H-type lignin is preferentially extracted at 120℃, so the H-type lignin is not detected in the lignin extracted subsequently. When the temperature increases from 120℃ to 140℃, S / G increases, mainly because as the temperature increases, S-type lignin is more easily removed. When the fractionated extraction temperature continues to rise, S / G decreases, which is mainly because under severe conditions, more G-type lignin is removed, so as the temperature increases, S / G first increases and then decreases. The content of β-O-4, β-β and β-5 linkages in lignin increases continuously as the lignin extraction temperature increases, indicating that the lignin linkages in the solid residue are less depolymerized and the structure is more complete. Lignin rich in these linkages is better extracted, and these linkages are more stable. The content of β-β and β-5 is very low at 180℃, indicating that lignin containing these two linkages has been extracted in the previous extraction. The weight average molecular weight (M w ) of the fractionated lignin gradually increases as the extraction temperature increases, and reaches a maximum at 180℃, and the number average molecular weight (M n ) also increases as the temperature increases, indicating that as the reaction temperature increases, G-type lignin with rich linkages is extracted, increasing the molecular weight of lignin.

[0014] The 2D-nuclear magnetic quantitative result of the poplar lignin obtained by adjusting the pH value of the fractional extraction shows that the S / G of the lignin decreases with the decrease of the pH value, mainly at pH=7, because the S-type lignin is easier to be removed, and the remaining G-type lignin is more, and with the decrease of the pH value, the G-type lignin is further removed under the severe conditions. The content of β-O-4, β-β and β-5 increases with the decrease of the pH value, which shows that the lignin with the connection bonds is better extracted from the solid residue, and the connection bonds are more stable. The weight average molecular weight (Mw) of the lignin extracted by the fractional extraction first increases with the decrease of the extraction pH value, and when the pH value is 3, the weight average molecular weight is the largest (2797 g / mol), and with the increase of the acidity, the molecular weight of the extracted lignin decreases, and the change trend of the number average molecular weight (Mn) is the same, which shows that when the acid concentration of the reaction solution is higher, the lignin is depolymerized to a certain extent, so that the molecular weight of the lignin decreases.

[0015] The present application gradually reduces the pH value of the reaction system or gradually increases the temperature of the reaction system, thereby increasing the severity of the reaction, the extraction efficiency of the lignin first increases and then decreases with the decrease of the pH value, and when the pH value is 5, the lignin extraction rate reaches the maximum value of 3.57%, and with the continuous decrease of the pH value, the lignin extraction rate decreases. With the increase of the temperature, the extraction efficiency of the lignin gradually decreases.

[0016] Preferably, the step of gradually reducing the pH value of the reaction system comprises: taking the solid phase as the raw material, repeating step 1, and gradually reducing the pH value of the reaction system with the pH value of 7, 6, 5, 4, 3, 2 or 1, and the temperature of the reaction is 120-180 ℃.

[0017] Preferably, the step of gradually increasing the temperature of the reaction system comprises: taking the solid phase as the raw material, repeating step 1, and gradually increasing the temperature of the reaction system with the temperature of 120 ℃, 130 ℃, 140 ℃, 150 ℃, 160 ℃, 170 ℃ or 180 ℃, and the pH value of the reaction is 1-7.

[0018] Preferably, the reaction time is 0.5-1 h.

[0019] Preferably, the solvent is an ethanol aqueous solution, the volume ratio of ethanol to water in the ethanol aqueous solution is 1:1-5, and the solid-liquid ratio of the poplar powder to the solvent is 1g:5-10 mL.

[0020] Preferably, the pH value of the hydrochloric acid solution is 2, and the volume ratio of the liquid phase to the hydrochloric acid solution is 1:5-10.

[0021] Preferably, the temperature of the freeze-drying is-50 ℃, and the freeze-drying time is 24-72 h.

[0022] Preferably, the eutectic solvent is prepared from lactic acid and choline chloride, and the mass ratio of the lactic acid and the choline chloride is 5-2:1.

[0023] Preferably, the solvent displacement method comprises: mixing the lignin and the eutectic solvent to obtain a mixed solution, and adding water dropwise into the mixed solution; the water dropwise adding speed is 0.1-0.4 mL / s.

[0024] The second technical scheme of the present application provides a method for regulating the particle size of lignin nanospheres, which uses poplar powder as raw material and an ethanol aqueous solution as solvent, and then the lignin is extracted by adjusting the pH value of the reaction system or the temperature of the reaction system, and then the solvent displacement method is used to treat the obtained lignin to obtain lignin nanospheres with different particle sizes.

[0025] Preferably, the lignin nanospheres with gradually increased particle sizes are obtained by gradually reducing the pH value of the reaction system; or the lignin nanospheres with gradually increased particle sizes are obtained by gradually increasing the temperature of the reaction system.

[0026] The present application discloses the following technical effects:

[0027] 1. The solvent (ethanol / water) used for extracting lignin in the present application is low in price and green in environment protection, and by adjusting the extraction conditions (temperature or pH value) and the extraction intensity, the extraction efficiency of lignin is improved and the structure of lignin is successfully regulated, which lays a foundation for obtaining lignin nanospheres with large specific surface area, high surface atom ratio and strong surface modifiability.

[0028] 2. The present application uses the eutectic solvent system of choline chloride / lactic acid to dissolve lignin, and uses a simple solvent displacement method to obtain lignin nanospheres, which lays an important theoretical foundation for the separation and high-value utilization of lignin. DETAILED DESCRIPTION

[0029] Figure 1 The particle size distribution diagram of the lignin nanospheres prepared from the lignin L-7 in Example 1 is shown in the figure;

[0030] Figure 2 The particle size distribution diagram of the lignin nanospheres prepared from the lignin L-5 in Example 1 is shown in the figure;

[0031] Figure 3 The particle size distribution diagram of the lignin nanospheres prepared from the lignin L-120 in Example 2 is shown in the figure;

[0032] Figure 4 The SEM diagram of the lignin nanospheres prepared from the lignin L-120 in Example 2 is shown in the figure;

[0033] Figure 5 Figure 2 is a graph showing the particle size distribution of the lignin nanospheres prepared from lignin L-140 in Example 2. DETAILED DESCRIPTION

[0034] The following detailed description of various example embodiments of the application is not to be considered limiting in any way. Rather, the following description is presented to describe certain aspects, features, and embodiments of the application.

[0035] It should be understood that the terms used herein are merely descriptive, but that the application should not be limited thereto. In addition, for numerical ranges recited in the application, it is contemplated that each and every value and sub-range within the range is specifically included and disclosed. Every

[0036] Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. Although preferred methods and materials are described herein, any methods and materials similar or equivalent to those described herein can be used in the practice or testing of the present application. All documents mentioned herein are incorporated by reference to disclose and describe in further detail the methods and / or materials associated with the documents. In the case of conflict between the present specification and any document incorporated by reference, the present specification will control.

[0037] Many modifications and variations of this application can be made in the light of the above teachings without departing from the spirit and scope thereof. Other implementations of the application will be apparent to those skilled in the art from consideration of the specification and practice of the application disclosed herein. The examples in the specification including the examples given in the experimental section are to be considered as illustrative and not restrictive.

[0038] As used herein, the terms "comprises", "comprising", "includes", "including", "has", "having", and the like are open-ended terms that are intended to mean including, but not limited to.

[0039] The eutectic solvent used in the following examples was prepared as follows: lactic acid and choline chloride were mixed in a mass ratio of 2:1, heated in a water bath at 60°C for 2h, and a transparent eutectic solvent was obtained;

[0040] The poplar powder used had a particle size of 50 mesh;

[0041] The other raw materials used were commercially available products, unless otherwise specified.

[0042] Example 1

[0043] The poplar powder was used as raw material, and the reaction liquid was an ethanol aqueous solution without adding acid (ethanol: water = 1:1, v / v, pH = 7) at 180°C for 1 h, the solid-liquid ratio was 1:10 (1 g of poplar powder: 10 mL of reaction liquid), after the reaction was completed, the product was centrifuged to obtain a solid phase and a liquid phase; the solid phase was washed with water until neutral, and was dried in a 60°C oven as raw material R-7 for subsequent reaction; 5 times the volume of hydrochloric acid aqueous solution (pH = 2) was added dropwise in the liquid phase, and stirred while adding, after the dropwise addition was completed, it was placed, and then centrifuged, and washed twice with hydrochloric acid aqueous solution (pH = 2), and then freeze-dried at -50°C for 24 h to obtain lignin L-7; 0.1 g of the obtained lignin L-7 was dissolved in 10 mL of deep eutectic solvent, 40 mL of deionized water was added at a drop rate of 0.2 mL / s under ultrasonic and stirring conditions, after the titration was completed, the solid phase was obtained by centrifugation, and then washed with deionized water until the supernatant was colorless, and then the solid phase was freeze-dried at -50°C for 48 h to obtain lignin nanomicrospheres-7;

[0044] The above obtained raw material R-7 was used as the reaction raw material at pH = 5, and the solid-liquid ratio was 1:10 (1 g of raw material R-7: 10 mL of reaction liquid), the reaction liquid was a solution at pH = 5 (ethanol: water = 1:1, v / v, the pH value was adjusted to 5 by hydrochloric acid), and the reaction was carried out at 180°C for 1 h, after the reaction was completed, the product was cooled and centrifuged to obtain a solid phase and a liquid phase; the solid phase was washed with water until neutral, and was dried in a 60°C oven as raw material R-5 for subsequent reaction; 5 times the volume of hydrochloric acid aqueous solution (pH = 2) was added dropwise in the liquid phase, and stirred while adding, after the dropwise addition was completed, it was placed, and then centrifuged, and washed twice with hydrochloric acid aqueous solution (pH = 2), and then freeze-dried at -50°C for 24 h to obtain lignin L-5; 0.1 g of the obtained lignin L-5 was dissolved in 10 mL of deep eutectic solvent, 40 mL of deionized water was added at a drop rate of 0.2 mL / s under ultrasonic and stirring conditions, after the titration was completed, the solid phase was obtained by centrifugation, and then washed with deionized water until the supernatant was colorless, and then the solid phase was freeze-dried at -50°C for 72 h to obtain lignin nanomicrospheres-5;

[0045] The above obtained raw material R-5 was used as the reaction raw material with pH = 3, the solid-liquid ratio was 1:10 (1 g of raw material R-5: 10 mL of reaction solution), the reaction solution was a solution with pH = 3 (ethanol: water = 1:1, v / v, the pH value was adjusted to 3 by hydrochloric acid), and the reaction was carried out at 180℃ for 1 h. After the reaction was completed, the product was separated by centrifugation to obtain a solid phase and a liquid phase; the solid phase was washed with water until neutral, and was dried in an oven at 60℃ to obtain raw material R-3 for the subsequent reaction; 5 times the volume of hydrochloric acid aqueous solution with pH = 2 was added dropwise into the liquid phase under stirring, and after the dropwise addition was completed, the solution was allowed to stand and then was centrifuged. The obtained solid phase was washed twice with hydrochloric acid aqueous solution (pH = 2) and was freeze-dried at -50℃ for 24 h to obtain lignin L-3; 0.1 g of the obtained lignin L-3 was dissolved in 10 mL of deep eutectic solvent, and 40 mL of deionized water was added dropwise into the solution at a rate of 0.2 mL / s under ultrasonic and stirring conditions. After the titration was completed, the solution was centrifuged, the obtained solid phase was washed with deionized water until the supernatant was colorless, and the solid phase was freeze-dried at -50℃ for 72 h to obtain lignin nanomicrospheres-3.

[0046] Figure 1 A particle size distribution diagram of the lignin nanomicrospheres prepared from the lignin L-7 obtained in Example 1; Figure 2 A particle size distribution diagram of the lignin nanomicrospheres prepared from the lignin L-5 obtained in Example 1.

[0047] Analysis Figures 1-2 It can be found that the particle size of the prepared lignin nanomicrospheres gradually increases as the pH value of the reaction system decreases.

[0048] Example 2

[0049] An ethanol aqueous solution with pH = 5 (ethanol: water = 1:1, v / v, the pH value was adjusted to 5 by hydrochloric acid) was used as the reaction solution, and poplar powder was used as the raw material. The reaction was carried out at 120℃ for 1 h, and the solid-liquid ratio was 1:10 (1 g of poplar powder: 10 mL of reaction solution). After the reaction was completed, the product was separated by centrifugation to obtain a solid phase and a liquid phase; the solid phase was washed with water until neutral, and was dried in an oven at 60℃ to obtain raw material R-120 for the subsequent reaction; 5 times the volume of hydrochloric acid aqueous solution with pH = 2 was added dropwise into the liquid phase under stirring, and after the dropwise addition was completed, the solution was allowed to stand and then was centrifuged. The obtained solid phase was washed twice with hydrochloric acid aqueous solution (pH = 2) and was freeze-dried at -50℃ for 48 h to obtain lignin L-120; 0.1 g of the obtained lignin L-120 was dissolved in 10 mL of deep eutectic solvent, and 40 mL of deionized water was added dropwise into the solution at a rate of 0.2 mL / s under ultrasonic and stirring conditions. After the titration was completed, the solution was centrifuged, the obtained solid phase was washed with deionized water until the supernatant was colorless, and the solid phase was freeze-dried at -50℃ for 72 h to obtain lignin nanomicrospheres-120.

[0050] The obtained raw material R-120 was used as raw material, and pH=5 ethanol aqueous solution (ethanol: water = 1:1, v / v, pH value was adjusted to 5 by hydrochloric acid) was used as reaction liquid, and the reaction was carried out at 140℃ for 1h, the solid-liquid ratio was 1:10 (1g of raw material R-120: 10mL of reaction liquid), after the reaction was completed, the product was separated by centrifugation, and solid phase and liquid phase were obtained; the solid phase was washed with water until neutral, and was dried in an oven at 60℃, and was used as raw material R-140 for subsequent reaction; 5 times volume of pH=2 hydrochloric acid aqueous solution was added dropwise into the liquid phase, and stirring was carried out during the dropwise addition, after the dropwise addition was completed, standing was carried out, and then centrifugation was carried out, and the obtained solid phase was washed twice with hydrochloric acid aqueous solution (pH=2), and was freeze-dried at-50℃ for 24h, and lignin L-140 was obtained; 0.1g of the obtained lignin L-140 was dissolved in 10mL of deep eutectic solvent, and 40mL of deionized water was added dropwise into the solution at a drop rate of 0.2mL / s under ultrasonic and stirring conditions, after the titration was completed, centrifugation was carried out, the obtained solid phase was washed with deionized water until the supernatant was colorless, and the solid phase was freeze-dried at-50℃ for 72h, and lignin nanomicrospheres-140 were obtained.

[0051] The obtained raw material R-120 was used as raw material, and pH=5 ethanol aqueous solution (ethanol: water = 1:1, v / v, pH value was adjusted to 5 by hydrochloric acid) was used as reaction liquid, and the reaction was carried out at 140℃ for 1h, the solid-liquid ratio was 1:10 (1g of raw material R-120: 10mL of reaction liquid), after the reaction was completed, the product was separated by centrifugation, and solid phase and liquid phase were obtained; the solid phase was washed with water until neutral, and was dried in an oven at 60℃, and was used as raw material R-140 for subsequent reaction; 5 times volume of pH=2 hydrochloric acid aqueous solution was added dropwise into the liquid phase, and stirring was carried out during the dropwise addition, after the dropwise addition was completed, standing was carried out, and then centrifugation was carried out, and the obtained solid phase was washed twice with hydrochloric acid aqueous solution (pH=2), and was freeze-dried at-50℃ for 24h, and lignin L-140 was obtained; 0.1g of the obtained lignin L-140 was dissolved in 10mL of deep eutectic solvent, and 40mL of deionized water was added dropwise into the solution at a drop rate of 0.2mL / s under ultrasonic and stirring conditions, after the titration was completed, centrifugation was carried out, the obtained solid phase was washed with deionized water until the supernatant was colorless, and the solid phase was freeze-dried at-50℃ for 72h, and lignin nanomicrospheres-140 were obtained.

[0052] Figure 3 Particle size distribution diagram of the lignin nanomicrospheres prepared from lignin L-120 in Example 2; Figure 4 SEM diagram of the lignin nanomicrospheres prepared from lignin L-120 in Example 2; Figure 5 Particle size distribution diagram of the lignin nanomicrospheres prepared from lignin L-140 in Example 2.

[0053] Analysis Figures 3-5 It can be found that the particle size of the prepared lignin nanomicrospheres gradually increases with the increase of the temperature of the reaction system.

[0054] The various embodiments described in this specification are presented by way of example, and each embodiment is not necessarily composed of all features described with respect to other embodiments. Each embodiment describes a distinct aspect of the present application, and each aspect can be used in combination with one or more other aspects.

[0055] The previous description of the disclosed embodiments is provided to enable any person skilled in the art to make or use the present application. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the generic principles defined herein can be applied to other embodiments without departing from the spirit or scope of the application. Thus, the present application is not intended to be limited to the embodiments shown herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for graded extraction of lignin with different structures and preparation of lignin nanospheres with different particle sizes by adjusting reaction conditions, characterized in that, Includes the following steps: Step 1: Mix poplar wood powder and solvent to react and obtain a solid phase and a liquid phase; Step 2: Using the solid phase as raw material, repeat the reaction in Step 1, gradually decreasing the pH value of the reaction system or gradually increasing the temperature of the reaction system during the repetition process; The liquid phases obtained in steps 1 and 2 were mixed with hydrochloric acid solution, and then washed and freeze-dried sequentially to obtain lignin. Using a eutectic solvent as the solvent and water as the displacement solvent, the obtained lignin was treated by solvent displacement method to obtain lignin nanospheres of different particle sizes. The step of gradually reducing the pH value of the reaction system includes: using a solid phase as raw material, repeating step 1, and gradually reducing the pH value of the reaction system with a pH value of 7, 6, 5, 4, 3, 2 or 1, and the reaction temperature is 120~180℃. The step of gradually increasing the temperature of the reaction system includes: using a solid phase as raw material, repeating step 1, and gradually increasing the temperature of the reaction system by values ​​of 120℃, 130℃, 140℃, 150℃, 160℃, 170℃ or 180℃, with the pH value of the reaction being 1~7. The reaction time is 0.5~1h; The solvent is an aqueous ethanol solution, wherein the volume ratio of ethanol to water in the aqueous ethanol solution is 1:1~5; the solid-liquid ratio of poplar powder to solvent is 1g:5~10mL.

2. The method according to claim 1, characterized in that, The hydrochloric acid solution has a pH of 2, and the volume ratio of the liquid phase to the hydrochloric acid solution is 1:5~10.

3. The method according to claim 1, characterized in that, The freeze-drying temperature is -50℃, and the freeze-drying time is 24~72h.

4. The method according to claim 1, characterized in that, The eutectic solvent is prepared from lactic acid and choline chloride, wherein the mass ratio of lactic acid to choline chloride is 5~2:1.

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