Biomass lignin micro-nano spheres based on deep eutectic solvent and preparation method and application thereof

Abstract

The application discloses biomass lignin micro-nano balls based on a eutectic solvent and a preparation method and application thereof, and relates to the technical field of biomass lignin micro-nano balls. The preparation method comprises the following steps: carrying out hydrolysis reaction on wood fiber biomass raw materials under the action of acid induction at 80-180 DEG C, and obtaining residues through solid-liquid separation after the reaction is completed; drying and crushing the residues; adding the crushed residues into a eutectic solvent, uniformly stirring, and obtaining lignin-containing eutectic solvent through solidification separation; adding deionized water into the lignin-containing eutectic solvent drop by drop, uniformly stirring, and obtaining lignin micro-nano balls through freezing solidification, wherein the volume of the deionized water is 1-30 times that of the lignin-containing eutectic solvent. The preparation method can efficiently obtain lignin micro-nano balls with adjustable sizes.

Description

Technical Field

[0001] This invention belongs to the field of biomass-based lignin nanomaterial preparation, specifically relating to a method for preparing biomass lignin micro / nanospheres based on a eutectic solvent. Background Technology

[0002] Lignin is the second largest source of woody biomass in nature after cellulose, and it is also the most abundant renewable aromatic organic compound. It possesses good biocompatibility and excellent antibacterial and antioxidant properties. Its unique chemical structure and high reactivity make it widely used in biomedicine, agricultural production, and environmental protection. However, due to the diversity of lignin sources and the complexity of its chemical structure, it exhibits heterogeneity, polydispersity, and difficulty in structural determination, which limits its applications. Improving the physical morphology and chemical structure of lignin to achieve its high-value utilization has become a current research hotspot and challenge.

[0003] Nanotechnology has effectively solved the problems of heterogeneity and dispersibility of lignin. Compared with macromolecular lignin, micro / nano-sized lignin particles have controllable size, uniform structure, and good dispersion. Lignin micro / nanospheres are generally considered to have advantages such as large specific surface area, tunable size, and numerous active sites, proving to be an excellent form for utilization. The micro / nano-sizing of lignin, especially the preparation of micro / nanospheres, has shown great application potential in fields such as natural sunscreens, drug carriers, and nanofillers.

[0004] Currently, there are various methods for the micro- and nano-scale transformation of lignin, including precipitation, ultrasonication, cross-linking, and biological methods.

[0005] Patent application CN107774204A discloses a method of dissolving lignin using organic solvents such as tetrahydrofuran, dioxane, and dimethylformamide, followed by reverse titration, dialysis to remove the organic solvent, and drying to obtain the target product. This method involves solvents with a certain degree of toxicity, requires a long dialysis time, and is cumbersome, making it unsuitable for large-scale mass production.

[0006] To avoid the use of toxic and dangerous reagents, some scholars have used imidazole ionic liquids as solvents. The invention patent application with publication number CN108940218A discloses the preparation of lignin microspheres by titrating phytic acid after dissolving lignin. This method involves ionic liquids, which has high preparation costs and complicated preparation processes, making it difficult to scale up production.

[0007] Patent application CN108940218A discloses a method for preparing lignin microspheres by dissolving lignin in a sodium hydroxide solution containing a surfactant and then titrating with hydrochloric acid. While this method is simple and avoids harmful reagents, the acid and alkali can be highly corrosive to equipment, and the process requires significant energy. Additionally, some researchers have prepared lignin microspheres through ultrasonic treatment. This process is highly dependent on the ultrasonic treatment conditions, and the resulting micro / nanoparticles exhibit uneven size distribution and irregular shapes. Nano-lignin has been extracted from coconut fiber using Aspergillus via a biological method. This process is green and mild, yielding small lignin nanospheres. However, the reaction conditions for microorganisms are quite demanding, affecting the quality and yield of the nano-lignin. Summary of the Invention

[0008] To address the problems existing in the prior art, this invention provides a method for preparing biomass lignin micro / nanospheres based on a eutectic solvent. This method can efficiently obtain lignin micro / nanospheres with tunable size.

[0009] This invention provides a method for preparing biomass lignin micro / nanospheres based on a eutectic solvent, comprising:

[0010] (1) The lignocellulose biomass raw material is hydrolyzed under acid-induced reaction at 80-180℃. After the reaction is completed, the solid and liquid are separated to obtain the residue, which is then dried and pulverized.

[0011] (2) Add the pulverized residue from step (1) to a eutectic solvent, stir evenly, and solidify and separate to obtain a lignin-containing eutectic solvent;

[0012] (3) Add deionized water dropwise to the lignin-containing eutectic solvent in step (2), stir evenly, and freeze solidify to obtain lignin micro-nanospheres. The volume of the deionized water is 1-30 times that of the lignin-containing eutectic solvent.

[0013] This invention extracts the required amount of hydrophobic polymeric lignin from lignocellulosic biomass raw materials by controlling the temperature under acid induction, while avoiding lignin carbonization. The hydrophobic polymeric lignin is dissolved using a eutectic solvent, and then the hydrophobic lignin is leached out by controlling the volume content of the added deionized water to obtain micro-nano spherical lignin. The size and content of the micro-nano spherical lignin can be controlled. This invention obtains micro-nano spheres and can achieve size control of micro-nano spheres through the synergistic effect of acid induction at appropriate temperature, dissolution by a eutectic solvent, and dissolution by deionized water.

[0014] Preferably, the hydrolysis reaction temperature is 100-180℃. By controlling the hydrolysis reaction temperature, a large amount of polymeric lignin can be extracted from the lignocellulosic biomass raw material. Due to the high content of extracted lignin, biomass lignin micro-nanospheres of suitable size can be obtained in subsequent eutectic flux dissolution and deionized water control.

[0015] More preferably, the volume of the deionized water is 10-15 times that of the eutectic solvent containing lignin. By controlling the volume of the deionized water, the hydrophobic lignin is partially precipitated, which allows for further reduction of the size of larger lignin micro / nanospheres, thereby achieving further control over the size of the lignin micro / nanospheres.

[0016] Preferably, the mass ratio of the pulverized residue to the eutectic solvent is 1:10-1:30. If the content of the pulverized residue is too high, the distribution of lignin micro-nanospheres will be uneven, and the micro-nanosphere morphology may not even be formed after the subsequent addition of deionized water. Excessive use of eutectic solvent is also not conducive to the hydrophobic dissolution of the obtained lignin in the subsequent aqueous environment, resulting in poor morphology, with the lignin sticking together and failing to obtain the desired spherical morphology.

[0017] Preferably, the lignocellulosic biomass raw material is agricultural and forestry waste and its residue, wherein the agricultural and forestry waste is derived from one or more of poplar, eucalyptus, larch, spruce, wheat straw, corn cob, and corn stalk.

[0018] Preferably, the acid used for acid induction includes one or more of sulfuric acid, hydrochloric acid, phosphoric acid, oxalic acid, citric acid, maleic acid, malic acid, and p-toluenesulfonic acid.

[0019] More preferably, the acid used for acid induction includes one or more of sulfuric acid, hydrochloric acid, and phosphoric acid. Using inorganic acids allows for the extraction of more polymerized lignin from fibrous biomass raw materials.

[0020] Preferably, the concentration of the acid used for acid induction is 0.05-5M, and the reaction time of the hydrolysis reaction is 30-180 min.

[0021] Preferably, the ternary eutectic solvent is composed of a polyol and a polyacid that provide hydrogen bond donors, and choline chloride or betaine that provide hydrogen bond acceptors.

[0022] More preferably, the polyacid is one or two of alanine, lactic acid, and formic acid; and the polyol is one or more of ethylene glycol, glycerol, or ethanol.

[0023] More preferably, the molar ratio of choline chloride or betaine, polyacid, and polyol is 1:(2-6):1-3, preferably 1:4:1.

[0024] Preferably, the stirring time in step (3) is 1-3 hours and the temperature is 50-80℃.

[0025] On the other hand, the present invention also provides a biomass lignin micro / nanosphere, which is prepared by the aforementioned method for preparing biomass lignin micro / nanospheres based on a eutectic solvent.

[0026] Preferably, the size of the biomass lignin micro-nanospheres is 30-200 nm.

[0027] On the other hand, this invention also provides an application of biomass lignin micro / nanospheres in superhydrophobic films. A polyvinyl alcohol-lignin nanosphere composite film is prepared using a solution casting method.

[0028] The biomass lignin micro / nanospheres and polyvinyl alcohol solution are mixed and stirred to obtain a mixed solution. The mixed solution is then heated and cured in a polyethylene mold to obtain a composite membrane material. The junction angle of the prepared membrane material can reach over 120°.

[0029] Preferably, lignin nanospheres and 3 wt% polyvinyl alcohol are mixed in a certain proportion and stirred for 2 hours. After stirring, the mixture is transferred to a polytetrafluoroethylene mold and dried at 60°C for 12 hours. The resulting dried material is a hydrophobic film material with good hydrophobic properties, a contact angle of over 120°, and is also green and biodegradable.

[0030] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0031] This invention hydrolyzes hydrophobic lignin from wood-based biomass fibers, dissolves the hydrophobic lignin in a eutectic solvent, and then controls the size of the hydrophobic lignin using deionized water. Through the synergistic effect of acid induction at a suitable temperature, dissolution in a eutectic solvent, and control by deionized water, lignin micro-nanospheres are obtained, and the size of the lignin micro-nanospheres is controlled. The preparation method provided by this invention does not use organic solvents for size control, making it environmentally friendly. Attached Figure Description

[0032] Figure 1 The image shows the morphology of the lignin micro-nanospheres obtained in Example 1 of this invention.

[0033] Figure 2 These are morphology images of the lignin micro / nanospheres obtained in Examples 2-5 of this invention;

[0034] Figure 3 This is a morphology diagram of the lignin micro-nanospheres obtained in Example 6 of the present invention;

[0035] Figure 4The image shows the morphology of the lignin micro-nanospheres obtained in Example 7 of this invention.

[0036] Figure 5 This is a morphology diagram of the lignin micro-nanospheres prepared in Comparative Example 1 of the present invention.

[0037] Figure 6 This is a morphology diagram of the lignin micro-nanospheres prepared in Comparative Example 2 of the present invention.

[0038] Figure 7 This is a morphology diagram of the lignin micro-nanospheres prepared in Comparative Example 3 of the present invention.

[0039] Figure 8 The bar chart shows the contact angle of the composite membrane material prepared in Application Example 1 of this invention under different contents of lignin micro-nanospheres. Detailed Implementation

[0040] The present invention will now be described in detail with reference to specific embodiments. These embodiments are merely examples illustrating the implementation of the present invention and do not constitute a limitation thereof. Any modifications and optimizations based on the essence and concept of the present invention fall within the protection scope of the present invention.

[0041] Example 1

[0042] (1) Hydrolyzed lignocellulosic biomass: Take 10g of corn cob powder, add 100mL of 3M sulfuric acid solution, react at 180℃ for 120min, after the reaction is completed, separate the solid and liquid, dry the residue, crush it and set it aside.

[0043] (2) Preparation of eutectic solvent: Betaine, which acts as a hydrogen bond acceptor, and lactic acid and ethylene glycol, which act as hydrogen bond donors, are stirred at 80°C and 500 rpm for 30 minutes in a molar ratio of 1:4:1 to form a clear and transparent solution, which is the eutectic solvent.

[0044] (3) The hydrolyzed lignocellulosic biomass residue was added to the prepared eutectic solvent at a solid-liquid ratio of 1:10 g / mL, and then stirred at 120°C and 500 rpm for 3 hours.

[0045] (4) After solid-liquid separation of the lignin-containing eutectic solvent from step (3), deionized water (10 times the volume of the lignin-containing eutectic solvent) is added dropwise to the resulting lignin-containing eutectic solvent while stirring. The mixture is then stirred at 1500 rpm for 2 hours, followed by freeze-drying to obtain micro / nano lignin nanospheres. Electron microscopy analysis shows that the diameter of these lignin nanospheres is approximately 201 nm. Figure 1 As shown.

[0046] Examples 2-5

[0047] Unlike Example 1, the hydrolysis temperatures in Examples 2-5 were 100℃, 120℃, 160℃, and 180℃, respectively. The specific steps are as follows:

[0048] (1) Hydrolyzed lignocellulosic biomass: Take 10g of corn cob powder, add 100mL of 3M sulfuric acid solution, and react at 100℃, 120℃, 160℃ and 180℃ for 120min. After the reaction is completed, the solid and liquid are separated, the residue is dried and crushed for later use.

[0049] (2) Preparation of eutectic solvent: Betaine, which acts as a hydrogen bond acceptor, and lactic acid and ethylene glycol, which act as hydrogen bond donors, are stirred at 80°C and 500 rpm for 30 minutes in a molar ratio of 1:4:1 to form a clear and transparent solution, which is the eutectic solvent.

[0050] (3) The hydrolyzed lignocellulosic biomass residue was added to the prepared eutectic solvent at a solid-liquid ratio of 1:10 g / mL, and then stirred at 120°C and 500 rpm for 3 hours.

[0051] (4) After solid-liquid separation of the lignin-containing eutectic solvent in step (3), add water with a volume 10 times that of the lignin-containing eutectic solvent dropwise to the obtained lignin-containing eutectic solvent while stirring. Then stir at 1500 rpm for 2 hours and dry to obtain micro-nano lignin nanospheres.

[0052] Electron microscopy revealed a correlation between the diameter of the lignin nanospheres and the hydrolysis temperature. The lignin nanospheres corresponding to the residues obtained at 100℃, 120℃, 160℃, and 180℃ were 30, 100, 150, and 200 nm, respectively. Figure 2 As shown.

[0053] Example 6

[0054] (1) Hydrolyzed lignocellulosic biomass: Take 10g of corn cob powder, add 100mL of 3M sulfuric acid solution, react at 180℃ for 120min, after the reaction is completed, separate the solid and liquid, dry the residue, pulverize it and set it aside for later use;

[0055] (2) Preparation of eutectic solvent: Betaine, which acts as a hydrogen bond acceptor, and lactic acid and ethylene glycol, which act as hydrogen bond donors, are stirred at 80°C and 500 rpm for 30 minutes in a molar ratio of 1:4:1 to form a clear and transparent solution, which is the eutectic solvent.

[0056] (3) The hydrolyzed lignocellulosic biomass residue was added to the prepared eutectic solvent at a solid-liquid ratio of 1:10 g / mL, and then stirred at 120°C and 500 rpm for 3 hours.

[0057] (4) After solid-liquid separation of the lignin-containing eutectic solvent from step (3), water, 15 times the volume of the lignin-containing eutectic solvent, is added dropwise to the resulting lignin-containing eutectic solvent while stirring. The mixture is then stirred at 1500 rpm for 2 hours. After drying, micro / nano lignin nanospheres are obtained. Electron microscopy analysis shows that the diameter of these lignin nanospheres is 150 nm. Figure 3 As shown.

[0058] Example 7

[0059] Unlike Example 1, the hydrolyzed lignocellulosic biomass residue was added to a prepared eutectic solvent at a solid-liquid ratio of 1:20 g / mL, resulting in lignin nanospheres with a diameter of 180 nm. Figure 4 As shown.

[0060] Comparative Example 1

[0061] Unlike Example 1, lignocellulosic biomass residue was added to a prepared eutectic solvent at a solid-liquid ratio of 1:50 g / mL, resulting in lignin as follows: Figure 5 As shown, there are many irregular shapes, making it impossible to obtain the desired spherical shape.

[0062] Comparative Example 2

[0063] Unlike Example 1, no deionized water was added after solid-liquid separation using a lignin-containing eutectic solvent. Figure 6 As shown, lignin cannot form micro-nanosphere shapes.

[0064] Comparative Example 3

[0065] Unlike Example 1, 50 times the volume of deionized water containing lignin in a eutectic solvent was added dropwise to the resulting lignin-containing eutectic solvent while stirring, forming micro / nano lignin nanospheres. Figure 7 As shown, the amount of lignin nanospheres is relatively small.

[0066] Application Example 1

[0067] Polyvinyl alcohol-lignin nanoparticle composite film materials were prepared using a simple solution casting method. The lignin nanoparticles obtained in Example 1 were mixed with a 3 wt.% polyvinyl alcohol solution at different ratios. After stirring for two hours, the mixture was transferred to a polyethylene mold. The contents of the lignin nanospheres were 1%, 3%, 5%, and 10%, respectively. The mixture was then slowly dried at 60°C for 12 hours to obtain the composite film material, whose contact angle was as follows: Figure 8 As shown, the angles are 58.9°, 88°, 95°, 113°, and 128°, respectively.

Claims

1. A method for preparing biomass lignin micro / nanospheres based on a eutectic solvent, characterized in that, include: (1) The lignocellulosic biomass raw material is hydrolyzed under acid induction at 80-180℃. After the reaction is completed, the solid and liquid are separated to obtain the residue. The residue is then dried and pulverized. (2) Add the pulverized residue from step (1) to a eutectic solvent, stir evenly, and separate the solid and liquid to obtain a eutectic solvent containing lignin. (3) Add deionized water dropwise to the lignin-containing eutectic solvent in step (2), stir evenly, and freeze solidify to obtain lignin micro-nanospheres. The volume of the deionized water is 1-30 times that of the lignin-containing eutectic solvent. The mass ratio of the pulverized residue to the eutectic solvent is 1:10-1:30; The eutectic solvent is composed of polyols and polyacids that provide hydrogen bond donors, and choline chloride or betaine that provide hydrogen bond acceptors. The size of the biomass lignin micro-nanospheres is 30-200 nm.

2. The method for preparing biomass lignin micro / nanospheres based on a eutectic solvent according to claim 1, characterized in that, The hydrolysis reaction is carried out at a temperature of 100-180℃.

3. The method for preparing biomass lignin micro / nanospheres based on a eutectic solvent according to claim 2, characterized in that, The volume of the deionized water is 10-15 times that of the lignin-containing eutectic solvent.

4. The method for preparing biomass lignin micro / nanospheres based on a eutectic solvent according to claim 1, characterized in that, The lignocellulosic biomass raw material is agricultural and forestry waste and its residue, and the agricultural and forestry waste is derived from one or more of poplar, eucalyptus, larch, spruce, wheat straw, corn cob, and corn stalk.

5. The method for preparing biomass lignin micro / nanospheres based on a eutectic solvent according to claim 1, characterized in that, The acids used for acid induction include one or more of sulfuric acid, hydrochloric acid, phosphoric acid, oxalic acid, citric acid, maleic acid, malic acid, and p-toluenesulfonic acid.

6. A biomass lignin micro / nanosphere, characterized in that, The biomass lignin micro-nanospheres are prepared by the biomass lignin micro-nanosphere preparation method based on eutectic solvent as described in any one of claims 1-5.

7. The application of biomass lignin micro / nanospheres as described in claim 6 in superhydrophobic film materials, characterized in that, The biomass lignin micro-nanospheres and polyvinyl alcohol solution are mixed and stirred to obtain a mixed solution. The mixed solution is then heated and cured in a polyethylene mold to obtain a composite membrane material.

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