Aldehyde-stabilized lignin and preparation method and particle size prediction method of monodisperse lignin microspheres thereof
By reacting aldehyde compounds with lignin to form a stable acetal product, combined with specific solvent systems and solubility parameter control, the problems of uneven size and low yield in the preparation of lignin microspheres are solved, and efficient and stable preparation of monodispersed lignin microspheres are achieved.
Patent Information
- Application Number
- CN202510280150.0
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-03-11
- Publication Date
- 2025-08-01
AI Technical Summary
The prior art is difficult to efficiently prepare lignin microspheres with uniform size, stable properties and high yields, making it difficult to apply on a large scale.
Monodisperse lignin microspheres are prepared by reacting aldehyde compounds with lignin to form acetal stable product, and combined with specific solvent systems and solubility parameter control.
The efficient stability and particle size uniformity of lignin microspheres are achieved, the preparation process is simplified, the yield is improved, and the demand for high-value utilization is met.
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Abstract
Description
Technical Field
[0001] The present invention relates to the field of derivatives of natural macromolecular compounds, and more specifically, to a method for preparing aldehyde-stabilized lignin and monodisperse lignin microspheres and a method for predicting the particle size thereof. Background Art
[0002] Lignin is a three-dimensional amorphous macromolecular polymer composed of sinapyl alcohol (S), coniferyl alcohol (G), and p-coumaric alcohol (H), and is disorderly connected by C-O bonds and C-C bonds. It contains various functional groups such as aliphatic and aromatic hydroxyl groups, carboxyl groups, carbonyl groups, and methoxy groups. It is the second largest renewable resource after cellulose and is also the only biomass resource with renewable aromatic compounds in nature. It mainly exists in the plant cell wall and plays an important role in plants as an "adhesive" connecting cellulose and hemicellulose, including transporting water and minerals, supporting, and protecting plants from chemical or microbial attacks. The paper industry generates approximately 5.0×107t of lignin by-products every year. However, the heterogeneity of lignin makes it difficult to be efficiently utilized, and more than 95% of lignin is still mainly directly discharged into rivers as industrial pulping waste or burned as cheap fuel, with a very low utilization rate of lignin.
[0003] Lignin nanospheres have excellent properties such as amphiphilicity, biocompatibility, antibacterial property, and antioxidant property, and have great application potential in sunscreen, antibacterial, drug delivery, surfactants, etc., which brings new opportunities for the high-value utilization of lignin. However, in the vast majority of reports, the particle size distribution of LNPs is relatively wide, which is caused by the highly heterogeneous structure of lignin. The size distribution of nanoparticles is usually measured by the polydispersity index (PDI). Monodisperse lignin microspheres with a PDI below 0.1 are considered to have uniform size and stable properties. Since most physicochemical properties of LNPs highly depend on the size, LNPs with different sizes usually have completely different performances, which limits the high-value application of LNPs.
[0004] So far, many methods for preparing LNPs with extremely narrow size distribution and stable performance have been reported. For example, Jingyu Wang et al. fractionated enzymatically hydrolyzed lignin with absolute ethanol and acetone to obtain lignin components with moderate polarity, and then prepared monodisperse lignin colloidal spheres (PDI is 0.04 - 0.13) by self-assembly with the addition of water. Moreover, structural color materials were successfully prepared (Wang J Y, Chen W H, Yang D J, et al. Monodispersed Lignin Colloidal Spheres with Tailorable Sizes for Bio-Photonic Materials. [J]. Small, 2022, 18(19): e2200671 - e2200671.). However, the yield after fractionation by this method is low (less than 10%), and the structural stability of the colloidal spheres is poor. Another method is to prepare by the solvent / antisolvent method. Therefore, it is of great significance to study efficient preparation strategies for LNPs with uniform size and stable properties.
[0005] Jingqian Chen et al. first prepared lignin colloidal spheres by self-assembly by adding a lignin solution to water, and then controlled the centrifugal force during centrifugation to obtain monodisperse lignin colloidal spheres of various sizes (PDI is 0.02 - 0.09) by gradient centrifugation. Similarly, structural color materials were prepared with lignin colloidal spheres (Chen J Q, Tian J, Feng N J, et al. Monodispersed Renewable Particles by Cascade and Density Gradient Size Fractionation to Advance Lignin Nanotechnologies. [J]. Small, 2024, 20(34)), but the centrifugation process of this method is relatively cumbersome.
[0006] In summary, due to the complex lignin components, wide molecular weight distribution and inhomogeneous structural properties, the lignin microspheres prepared by existing technologies or processes still have key problems such as wide size distribution, poor surface property homogeneity and low yield, which makes it difficult to scale up production and application. Summary of the Invention
[0007] The present invention aims to overcome the defects of the above-mentioned existing technologies, such as poor lignin stability, wide size distribution of lignin microspheres, poor surface property homogeneity, low yield and cumbersome preparation process, and provides an aldehyde-stabilized lignin;
[0008] Another object of the present invention is to provide a preparation method of the aldehyde-stabilized lignin;
[0009] Another object of the present invention is to provide a method for preparing monodisperse lignin microspheres;
[0010] Another object of the present invention is to provide a method for predicting the particle size of lignin microspheres.
[0011] To solve the above technical problems, the technical solution of the present invention is as follows:
[0012] A method for preparing aldehyde-stabilized lignin, comprising the following steps: mixing an aldehyde compound with organic solvent A, adding an acidic reagent; adding a biomass product, heating and stirring to react to obtain an acetal-stabilized product; after solid-liquid separation, concentrating the liquid phase; precipitating the obtained concentrated liquid, performing solid-liquid separation, and the obtained solid is aldehyde-stabilized lignin.
[0013] Preferably, the organic solvent A includes dioxane, ethanol, and acetone.
[0014] Preferably, the organic solvent A is dioxane.
[0015] Preferably, the concentrated liquid is precipitated in a solution, and the solution includes at least one of ether, n-hexane, and water.
[0016] Preferably, the reaction temperature in the heating and stirring reaction is 80-90 °C, and the reaction time is 2-4 h.
[0017] Furthermore, the aldehyde compound includes aromatic aldehyde.
[0018] Preferably, the aromatic aldehyde includes at least one of p-carboxybenzaldehyde, benzaldehyde, and p-chlorobenzaldehyde.
[0019] Preferably, the aldehyde further includes aliphatic aldehyde.
[0020] Preferably, the aliphatic aldehyde includes formaldehyde, propionaldehyde, octanal, and glyoxylic acid.
[0021] Furthermore, the biomass product is the product obtained by extracting a biomass raw material with a polar solvent and a non-polar solvent.
[0022] Preferably, the extraction method includes the following steps: passing the biomass raw material through a 40-60 mesh sieve, performing one-time extraction with an ethanol solution and dichloromethane, and obtaining a biomass product.
[0023] Preferably, the biomass raw material passes through a 40-60 mesh sieve, is extracted with an 80% ethanol solution at 80 °C for 3-5 times, and dichloromethane is extracted once.
[0024] Preferably, the biomass raw material includes softwood and hardwood.
[0025] Preferably, the biomass raw material is hardwood.
[0026] An aldehyde-stabilized lignin, which is prepared by the preparation method of the aldehyde-stabilized lignin.
[0027] A preparation method of monodisperse lignin microspheres, comprising aldehyde-stabilized lignin.
[0028] Further, the preparation method comprises the following steps: dissolving the aldehyde-stabilized lignin in organic solvent B; dropping water; and obtaining monodisperse lignin microspheres after removing organic solvent B.
[0029] Preferably, the particle size of the obtained lignin microspheres is in the range of 170 - 560 nm.
[0030] Preferably, the organic solvent B comprises one or two of acetone, tetrahydrofuran, dioxane, dimethyl sulfoxide, N,N-dimethylformamide, and N,N-dimethylacetamide.
[0031] Preferably, when the organic solvent B contains two components, the volume ratio of the two components is 1:9 - 9:1.
[0032] Further, after the aldehyde-stabilized lignin is dissolved in organic solvent B, the concentration is 0.5 - 7.0 g / L.
[0033] Further, the rate of dropping water is 1.0 - 4.0 mL / min.
[0034] A monodisperse lignin microsphere, which is prepared by the preparation method.
[0035] A method for predicting the particle size of lignin microspheres, wherein the lignin microspheres are prepared by the preparation method of monodisperse lignin microspheres, and the particle size of the lignin microspheres is calculated by drawing a linear fitting graph of the Hansen solubility parameter of organic solvent B.
[0036] Preferably, when the organic solvent B is a single component, the particle size calculation formula is y = 1085.6 - 34.3x;
[0037] Preferably, when the organic solvent B is THF / DMF, the particle size calculation formula is y = 614.9 - 16.3x;
[0038] Preferably, when the organic solvent B is DMSO / Dioxane, the particle size calculation formula is y = 869.2 - 23.4x,
[0039] In the above formula, y is the particle size of the microspheres, and x is the Hansen solubility parameter of organic solvent B.
[0040] The mechanism of stabilizing lignin through acetalization in the present invention innovatively solves the polymerization problem that may occur during the treatment of lignin. The lignin molecule itself has a highly cross-linked structure and high reactivity, making it prone to polymerization reactions, resulting in its instability during high-temperature or long-term storage. By introducing aldehyde compounds and reacting with the phenolic hydroxyl groups in lignin, covalent bonds between the aldehyde groups and lignin molecules are formed, reducing the interaction between lignin molecules, thereby stabilizing the structure of lignin. Through acetal cross-linking, the active sites of lignin molecules can be blocked, and the macromolecular chains of lignin are strengthened, thus inhibiting its self-polymerization reaction. The present invention further uses acetal to stabilize lignin and directly prepares monodisperse lignin microspheres, simplifying multiple complex steps in the traditional process. By selecting a suitable solvent system, after lignin is dissolved, microspheres can be formed by self-assembly during the process of adding water dropwise, effectively controlling the formation and particle size distribution of the microspheres.
[0041] The invention also innovatively realizes precise control of the particle size by adjusting the Hansen solubility parameter of the solvent. Through the linear relationship between the particle size of the microspheres and the δ T of the solvent, by reasonably selecting the solvent and controlling the δ T value, the particle size of the microspheres can be controlled within a wide range, thereby realizing precise control of the size, distribution, and morphology of the microspheres. This innovative mechanism for particle size control makes the preparation of lignin microspheres more efficient and controllable.
[0042] Compared with the prior art, the beneficial effects of the technical solution of the present invention are as follows:
[0043] 1. Improve the stability of lignin. The present invention only requires one-step treatment of stabilizing lignin through acetal, which not only prevents lignin from polymerizing during subsequent treatment but also ensures the structural stability of lignin. The obtained acetal-stabilized lignin can be directly used to prepare monodisperse lignin microspheres, avoiding the cumbersome process of multiple treatments or optimization steps required in traditional methods.
[0044] 2. Efficient particle size control. Through a specific preparation method, monodisperse lignin microspheres with uniform particle size and good dispersibility (PDI value less than 0.1) are obtained. Such lignin microspheres have higher stability and uniformity, meeting the requirements for high-value utilization. By adjusting the Hansen solubility parameter of the solvent, the particle size of lignin microspheres can be precisely controlled, providing an efficient and adjustable particle size control method with high application potential. Description of the Drawings
[0045] Figure 1 HSQC nuclear magnetic resonance spectrum of aldehyde-stabilized lignin obtained in Example 1;
[0046] Figure 2 SEM image of monodisperse lignin microspheres obtained in Example 1;
[0047] Figure 3 SEM image of the monodisperse lignin microspheres obtained in Example 2;
[0048] Figure 4 SEM image of the monodisperse lignin microspheres obtained in Example 3;
[0049] Figure 5 SEM image of the monodisperse lignin microspheres obtained in Comparative Example 1;
[0050] Figure 6 SEM image of the monodisperse lignin microspheres obtained in Comparative Example 2;
[0051] Figure 7 SEM image of the monodisperse lignin microspheres obtained in Comparative Example 4;
[0052] Figure 8 SEM image of the monodisperse lignin microspheres obtained in Comparative Example 5;
[0053] Figure 9 Fitting graph of the solubility parameter of the solvent and the particle size of the lignin microspheres for Examples 6 - 10 (pure solvent);
[0054] Figure 10 Fitting graph of the solubility parameter of the solvent and the particle size of the lignin microspheres for Examples 11 - 15 (THF / DMF);
[0055] Figure 11 Fitting graph of the solubility parameter of the solvent and the particle size of the lignin microspheres for Examples 16 - 20 (DMSO / Dioxane). Detailed implementation manners
[0056] The present invention will be further described below in conjunction with the accompanying drawings of the specification and specific embodiments, but the embodiments do not limit the present invention in any form. Unless otherwise specified, the reagents, methods, and equipment used in the present invention are conventional reagents, methods, and equipment in the technical field.
[0057] Unless otherwise specified, the reagents and materials used in the following examples are all commercially available.
[0058] Example 1
[0059] 1. Preparation of aldehyde - stabilized lignin
[0060] First, extract the eucalyptus wood powder with a mesh size of 40 - 60. The extraction method is as follows: extract the eucalyptus wood powder 3 - 5 times with 500 mL of 80% ethanol at 80 °C, then extract it once with 100 mL of dichloromethane at 37 °C, and air-dry it for later use. Then, mix 6.8 mL (67 mmol) of benzaldehyde and 25 mL of 1,4-dioxane, heat and stir at 85 °C until they are fully mixed, add 0.85 mL of hydrochloric acid, and then add 5 g of the extracted eucalyptus wood powder. Heat and stir at 85 °C for 3 h to complete the inhibition reaction and obtain the inhibition product. After the product cools to room temperature, perform solid-liquid separation to obtain the liquid phase, which contains lignin. Rinse the liquid phase with 1,4-dioxane and then concentrate it by rotary evaporation to obtain the rotary evaporation concentrate. Then, add the rotary evaporation concentrate to 250 mL of stirred ether to precipitate aldehyde-stabilized lignin, continuously stir for 30 min, and then perform solid-liquid separation to obtain the precipitate. Extract and purify the impurities from the precipitate with a Soxhlet extractor using ether as the solvent to obtain the purified solid, and air-dry it to obtain the purified aldehyde-stabilized lignin.
[0061] 2. Preparation of Microspheres
[0062] Dissolve the obtained 5 mg of aldehyde-stabilized lignin in 5 mL of an acetone-water mixed solution (the volume of acetone is 4.5 mL), and add 20 mL of water dropwise to the lignin solution at a rate of 2 mL / min. After removing acetone by rotary evaporation, obtain a monodisperse lignin microsphere suspension.
[0063] Examples 2 - 3
[0064] The preparation schemes of Examples 2 - 3 are similar to those of Example 1, except that in the preparation of aldehyde-stabilized lignin, benzaldehyde is replaced with p-carboxybenzaldehyde and p-chlorobenzaldehyde respectively.
[0065] Example 4
[0066] The preparation scheme of Example 4 is similar to that of Example 1, except that in the preparation of microspheres, dissolve the obtained 30 mg of aldehyde-stabilized lignin in 5 mL of N,N-dimethylacetamide, and add 20 mL of water dropwise to the lignin solution at a rate of 4 mL / min. Remove the solvent by dialysis to obtain a monodisperse lignin microsphere suspension.
[0067] Example 5
[0068] The preparation scheme of Example 5 is similar to that of Example 4, except that in the preparation of aldehyde-stabilized lignin, benzaldehyde is replaced with p-carboxybenzaldehyde; in the preparation of microspheres, dissolve the obtained 35 mg of aldehyde-stabilized lignin in 5 mL of N,N-dimethylacetamide.
[0069] Example 6
[0070] The preparation scheme of Example 6 is similar to that of Example 5, except that in the preparation of microspheres, the acetone-water mixed solution is replaced by acetone, and water droplets are added to the lignin solution, and the solvent is removed by dialysis to obtain a monodisperse lignin microsphere suspension.
[0071] Examples 7 to 10
[0072] The preparation schemes of Examples 7 to 10 are similar to that of Example 5, except that in the preparation of microspheres, N,N-dimethylacetamide is replaced by tetrahydrofuran (THF), dioxane, N,N-dimethylformamide (DMF), and dimethyl sulfoxide (DMSO) respectively.
[0073] Example 11
[0074] The technical scheme of Example 11 is similar to that of Example 5, except that in the preparation of microspheres, N,N-dimethylacetamide is replaced with a mixed solvent of THF and DMF with a volume ratio of 1:1.
[0075] Examples 12 to 15
[0076] The technical schemes of Examples 12 to 15 are similar to that of Example 11, except that in the preparation of microspheres, the volume ratios of THF to DMF are 1:4, 4:1, 1:9, and 9:1 respectively.
[0077] Example 16
[0078] The technical scheme of Example 16 is similar to that of Example 5, except that in the preparation of microspheres, N,N-dimethylacetamide is replaced with a mixed solvent of DMSO and dioxane with a volume ratio of 1:1.
[0079] Examples 17 to 20
[0080] The technical schemes of Examples 17 to 20 are similar to that of Example 16, except that in the preparation of microspheres, the volume ratios of DMSO to dioxane are 1:4, 4:1, 1:9, and 9:1 respectively.
[0081] Example 21
[0082] The technical scheme of Example 21 is similar to that of Example 5, except that in the preparation of microspheres, 2.5 mg of aldehyde-stabilized lignin obtained is dissolved in 5 mL of N,N-dimethylacetamide.
[0083] Comparative Example 1
[0084] The technical scheme of Comparative Example 1 is similar to that of Example 1, except that in the preparation of aldehyde-stabilized lignin, benzaldehyde is replaced by formaldehyde with a volume fraction of 37%, and diethyl ether is replaced by deionized water.
[0085] Comparative Example 2
[0086] The technical solution of Comparative Example 2 is similar to that of Example 1, except that in the preparation of aldehyde-stabilized lignin, benzaldehyde is replaced by propionaldehyde.
[0087] Comparative Example 3
[0088] The technical solution of Comparative Example 3 is similar to that of Example 1, except that in the preparation of microspheres, the dropping rate of water is 1.0 mL / min.
[0089] Comparative Example 4
[0090] The technical solution of Comparative Example 2 is similar to that of Example 1, except that in the preparation of aldehyde-stabilized lignin, benzaldehyde is replaced by octanal, diethyl ether is replaced by n-hexane, and the precipitate is placed in 50 mL of n-butyl ether and sonicated to purify lignin.
[0091] Comparative Example 5
[0092] The technical solution of Comparative Example 5 is similar to that of Example 1, except that in the preparation of aldehyde-stabilized lignin, benzaldehyde is replaced by glyoxylic acid.
[0093] Testing method
[0094] Explanation of Hansen solubility parameter calculation:
[0095] δ D is the dispersion force parameter part, δ P is the polar force parameter part, δ H is the hydrogen bond adhesion force parameter part, δ T is the total force of the three, and the calculation formula is as follows:
[0096] δ T =(δ D 2 +δ P 2 +δ H 2 ) 1 / 2
[0097] δ of the mixed solvent Tm The calculation formula is as follows:
[0098] δ Tm ={[nδ Da +(1 - n)δ Db 2 +[nδ Pa +(1 - n)δ Pb 2 +[nδ Ha +(1 - n)δ Hb 2 )} 1 / 2
[0099] Among them, a and b represent two solvents; n is the volume ratio of solvent a in the mixed solvent.
[0100] The results are shown in Table 1.
[0101] Table 1 Hansen solubility parameters of solvents
[0102]
[0103] Analysis and explanation
[0104] Figure 1 It can be seen that through the acetal protection of benzaldehyde in Example 1, the side chain of lignin was chemically modified to form a six-membered ring structure. This structure has an inhibitory effect on polymerization, that is, it prevents lignin from forming unstable polymers due to self-polymerization during the reaction.
[0105] Table 2 Average particle size, PDI and Hansen solubility parameters
[0106]
[0107]
[0108] The PDI of lignin microspheres stabilized by aromatic aldehydes (benzaldehyde, p-carboxybenzaldehyde, p-chlorobenzaldehyde) used in the examples are all less than 0.1. For example, the PDIs of Examples 1-3 are 0.023, 0.019, and 0.038 respectively, all showing monodispersity. The molecular structure of aromatic aldehydes contains a benzene ring, which can produce π-π interactions with the aromatic structure in lignin molecules, enhancing the non-covalent force between lignin chains. This stabilizing effect makes the lignin chains more evenly distributed in the solvent and can form microspheres with uniform size during the self-assembly process. From Figures 2 to 4 It can also be seen that the morphology of lignin microspheres stabilized by aromatic aldehydes is regular and the particle size is uniform. While for the lignin obtained by stabilizing with aliphatic aldehydes (formaldehyde, propionaldehyde, octanaldehyde) in the comparative examples, the PDI are all greater than 0.15, and the PDI of Comparative Example 5 is as high as 0.470, with the microspheres being severely polydisperse. From Figures 5 to 8 It can also be seen that there are obvious size differences and aggregation phenomena among the lignin microspheres stabilized by aliphatic aldehydes. In addition, in Comparative Example 3, a slower dropping rate was adopted, resulting in uneven diffusion of lignin chains in the solution, and the aggregation of microspheres became uneven, and finally the PDI increased to 0.260.
[0109] Figure 9 shows the relationship between the particle size of lignin microspheres stabilized by benzaldehyde and the Hansen solubility parameter δT of a single solvent (Examples 6-10), and the fitting curve shows a high linear correlation (R 2 = 0.976).Figures 10 to 11 The relationships between the particle size of benzaldehyde-stabilized lignin microspheres and the solubility parameters δT of the mixed solvents THF / DMF (Examples 11-15) and DMSO / Dioxane (Examples 16-20) are respectively shown. The fitting curves also exhibit a very high linear correlation, with R 2 = 0.992 and R 2 = 0.988, respectively. Figures 9 to 11 Among them, as the solubility parameter of the solvent increases, the particle size of the lignin microspheres becomes smaller, and the use of the mixed solvent shows a more significant particle size control effect than that of the pure solvent. This indicates that the particle size of the microspheres can be effectively regulated by adjusting the solubility parameter of the solvent.
[0110] Obviously, the above-mentioned embodiments of the present invention are merely examples for clearly illustrating the present invention, rather than limitations on the implementation manners of the present invention. For those of ordinary skill in the art, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to enumerate all implementation manners here. Any modifications, equivalent replacements, and improvements made within the spirit and principle of the present invention shall be included within the protection scope of the claims of the present invention.
Claims
1. A preparation method of aldehyde-stabilized lignin, characterized in that, Comprising the following steps: After mixing an aldehyde compound with organic solvent A, an acidic reagent is added; A biomass product is added, and the mixture is heated and stirred for reaction to obtain an acetal-stabilized product; After solid-liquid separation, the liquid phase is concentrated; precipitation is carried out on the obtained concentrated liquid, followed by solid-liquid separation, and the obtained solid is aldehyde-stabilized lignin.
2. The preparation method of aldehyde-stabilized lignin according to claim 1, characterized in that, The aldehyde compound includes aromatic aldehyde.
3. The preparation method of the aldehyde-stabilized lignin according to claim 1, wherein, The biomass product is a product obtained by extracting a biomass raw material with a polar solvent and a non-polar solvent.
4. An aldehyde-stabilized lignin, characterized in that, Prepared by the preparation method of aldehyde-stabilized lignin according to any one of claims 1 to 3.
5. A preparation method of monodisperse lignin microspheres, characterized in that, Comprising the aldehyde-stabilized lignin according to claim 4.
6. The preparation method of the monodisperse lignin microspheres according to claim 5, characterized in that, Comprising the following steps:
7. The preparation method of the monodisperse lignin microspheres according to claim 6, characterized in that, The aldehyde-stabilized lignin is dissolved in organic solvent B; water is added dropwise; after removing organic solvent B, monodisperse lignin microspheres are obtained.
8. The preparation method of the monodisperse lignin microspheres according to claim 6, wherein After the aldehyde-stabilized lignin is dissolved in organic solvent B, the concentration is 0.5 - 7.0 g / L.
9. A monodisperse lignin microsphere, characterized in that, The rate of adding water dropwise is 1.0 - 4.0 mL / min.
10. A method for predicting the particle size of lignin microspheres, characterized in that, Prepared by the preparation method according to any one of claims 5 to 8. The lignin microspheres are prepared by the preparation method of monodisperse lignin microspheres according to any one of claims 5 to 9, and the particle size of the lignin microspheres is calculated by plotting a linear fitting graph of the Hansen solubility parameters of the solvent.