Method for preparing nano lignin at low cost

Abstract

The invention belongs to the technical field of lignin nano materials, and particularly discloses a low-cost method for preparing nano lignin. The method comprises the following steps: dispersing a lignin raw material through a mixed solution of ethanol, gamma-valerolactone and water, stirring a lignin solution, pumping water into the lignin solution through a peristaltic pump, self-assembling to form nano lignin, and finally centrifuging the mixed solution to precipitate nano lignin particles. The obtained nano lignin has a uniform particle size of 200-600nm, and is in the shape of a solid or hollow sphere.

Description

Technical Field

[0001] The invention belongs to the technical field of lignin nanomaterials, and particularly relates to a method for preparing nano lignin at low cost. Background Art

[0002] In recent years, with the overconsumption of fossil energy and increasingly serious environmental pollution, natural biomass materials have been widely studied by researchers due to their wide distribution, abundant resources, low pollution, and renewable nature. Lignin is the second largest biomass resource in nature after cellulose and is the most abundant renewable aromatic organic compound discovered to date. However, although the pulp and paper industry extracts over 50 million tons of lignin annually, only approximately 5% is effectively utilized. Most of this lignin is directly discharged or burned as a byproduct of the papermaking industry, polluting the environment and causing a significant waste of resources.

[0003] With the rapid development of modern nanotechnology, the production of lignin nanoparticles (LNPs) has provided a new direction for the high-value utilization of lignin. Lignin colloids and lignin nanoparticles offer advantages such as UV resistance, antibacterial properties, and non-cytotoxicity, showing great potential for applications as natural sunscreens, drug carriers, and nanofillers. Currently, methods for preparing nanolignin include antisolvent, ultrasonic, acid precipitation, crosslinking, and biological methods. Different methods produce nanolignin with varying morphologies and sizes, with the antisolvent method being the most commonly used. For example, patent CN118667183A discloses alkali-resistant lignin nanospheres, their preparation method, and applications. These alkali-resistant lignin nanospheres are prepared by crosslinking inhibited lignin with bisphenol diglycidyl ether. Under conditions of a pH of 7 to 11, an immersion time of 1 to 3 hours, and a stirring speed of 180 rpm, the majority of the alkali-resistant lignin nanospheres maintain a relatively intact morphology. The inhibited lignin contains abundant aldehyde and aliphatic hydroxyl groups. Dissolving lignin in an organic solvent and then performing reverse titration is the most common method for preparing micro- and nano-lignin. CN 116731350A discloses using 60% γ-valerolactone / water to dissolve and fractionate lignin, followed by reverse titration to obtain lignin micro- and nano-spheres.

[0004] While numerous methods exist for preparing lignin microspheres, existing technologies suffer from the following challenges: complex production procedures, high solvent prices, and persistently high production costs. Furthermore, the resulting microspheres are often large and uneven in size. For example, γ-valerolactone is an excellent lignin solvent, but its high price hinders its commercialization. Summary of the Invention

[0005] The present invention addresses the shortcomings of existing technologies and provides a low-cost method for preparing nano-lignin using ethanol, water, and a small amount of γ-valerolactone as solvents. The method involves dispersing the lignin raw material in a mixture of ethanol, γ-valerolactone, and water. The lignin solution is stirred, and water is pumped into the lignin solution via a peristaltic pump to self-assemble into nano-lignin. Finally, the mixed solution is centrifuged to precipitate nano-lignin particles.

[0006] In order to achieve the above object, the present invention adopts the following technical solutions: A method for preparing low-cost nano-lignin using a ternary system comprises the following steps: S1 adds lignin to a mixed solution of ethanol, γ-valerolactone, and water to form a lignin solution; wherein the mixed solution is mainly composed of ethanol, and the content of ethanol is 50% to 80%; S2 stirs the lignin solution and adds water dropwise to the lignin solution using a peristaltic pump; S3 was centrifuged to precipitate the nano-lignin particles.

[0007] Optionally, step S3 further comprises pouring off the supernatant after centrifugation, adding deionized water again and centrifuging again to precipitate the nano-lignin particles.

[0008] Optionally, the method further comprises pouring out the supernatant in S4, and freeze-drying the remaining precipitated nano-lignin particles to obtain dry nano-lignin particles.

[0009] The volume ratio of ethanol, γ-valerolactone and water in the mixed solution is 4-23:2-4:1, preferably 4-16:2-4:1, and more preferably 8-12:3:1.

[0010] The mass volume ratio of the lignin to the mixed solution is 2 mg / ml to 10 mg / ml; Preferably, the lignin is industrial lignin produced by pulping or biorefining enterprises; Preferably, the industrial lignin includes but is not limited to alkali lignin and / or sulfate lignin; Preferably, the stirring time of the lignin solution in S2 is 0.5 h to 1.5 h; the stirring rate is 400 rpm to 600 rpm; the specific stirring time is 50-70 minutes, more specifically 60 minutes.

[0011] The present invention utilizes an antisolvent method to prepare nano-lignin. The antisolvent is added dropwise to a lignin solution, where water acts as the antisolvent, causing self-assembly to form a colloidal lignin solution, thereby regenerating the dissolved lignin. In step S2, water is added dropwise to the lignin solution using a peristaltic pump. The ratio of water (i.e., antisolvent) to lignin solution is 5.7:1 to 10:1. Preferably, the dripping rate of the peristaltic pump in S2 is 5 ml / min to 8 ml / min; Preferably, the centrifugal speed in S3 is 8000 rpm / min to 10000 rpm / min; the centrifugal time is 10 min to 15 min; The nano-lignin prepared according to the above method has a uniform particle size of about 200 to 600 nm and a solid or hollow spherical shape.

[0012] γ-Valerolactone was selected as the solvent for dissolving lignin because of its excellent solubility for lignin and high applicability to various types of lignin.

[0013] The beneficial effects brought about by the technical solution of the present invention are: (1) The present invention uses ethanol-water as the main solvent (ethanol accounts for no more than 90%), and adds a small amount of γ-valerolactone to dissolve lignin to prepare nano-lignin particles. This method effectively reduces costs and is simple to operate, which helps to achieve large-scale production of nano-lignin.

[0014] (2) The main solvent used in the present invention, ethanol, is mixed with other organic solvents to adjust the polarity and optimize the dissolution and dispersion of lignin. The hydroxyl groups (-OH) in the ethanol molecules can form hydrogen bonds with the phenolic hydroxyl groups, ether bonds and other groups in the lignin molecules, weakening the hydrophobic interactions (such as π-π stacking) between lignin molecules and preventing their agglomeration, thereby promoting the uniform dispersion of lignin in the solvent and forming a stable precursor solution.

[0015] (3) Ethanol, the main solvent used in the present invention, can reduce the surface energy of nano-lignin particles. Ethanol molecules are adsorbed on the surface of lignin through hydrogen bonds or van der Waals forces, forming a molecular layer barrier, reducing direct contact and attraction between particles, thereby forming more uniform nanoparticles.

[0016] (4) The ethanol, γ-valerolactone and water used in the present invention are all green organic solvents that are environmentally friendly, non-toxic, easy to handle, recyclable and widely available. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 This is a morphology image of the nano-lignin particles obtained in Example 1 observed by scanning electron microscopy.

[0018] Figure 2 This is a morphology image of the nano-lignin particles obtained in Example 2 observed by scanning electron microscopy.

[0019] Figure 3 This is a morphology image of the nano-lignin particles obtained in Example 3 observed by scanning electron microscopy.

[0020] Figure 4This is a morphology image of the nano-lignin particles obtained in Example 4 observed by scanning electron microscopy.

[0021] Figure 5 This is a morphology image of the nano-lignin particles obtained in Example 5 observed by scanning electron microscopy. DETAILED DESCRIPTION

[0022] In order to better understand the technical content of the present invention, specific examples are provided below to further illustrate the present invention.

[0023] Example 1

[0024] (1) Weigh 15 mg of industrial alkali lignin and add it to 8 ml of a mixed solution of ethanol, γ-valerolactone, and water (volume ratio 4:3:1) to form a lignin solution.

[0025] (2) Stir the lignin solution at 400 rpm for 1 h.

[0026] (3) Use a peristaltic pump to add water to the lignin solution at a rate of 5 ml / min, and the total amount of water added is 40 ml.

[0027] (4) The mixed solution was centrifuged at 10,000 rpm / min for 15 min to precipitate the nano-lignin particles.

[0028] (5) Pour off the supernatant, add deionized water again and centrifuge again at 10,000 rpm / min for 15 minutes to wash.

[0029] (6) The supernatant is poured off, and the remaining precipitated nano-lignin particles are freeze-dried to obtain dry nano-lignin particles.

[0030] For the remaining examples and comparative examples, only the ratio of the solvents was changed, and the other operating steps were not changed, so they are presented in the form of a list.

[0031] Table 1

[0032] The nano-lignin particles obtained in Examples 1 to 5 were observed by scanning electron microscope, and the morphologies were shown as follows: Figures 1 to 5 However, Comparative Examples 1 and 2 failed to successfully prepare nano-lignin particles.

[0033] The size distribution and zeta potential of lignin micro-nanospheres were measured using a nanoparticle size and potential analyzer.

[0034]

[0035] As shown in the table above, the average particle size of the lignin micro- and nanospheres obtained in this embodiment of the present invention is approximately 410 nm, and the zeta potential of the formed lignin micro- and nanospheres remains between -20 mV and -40 mV, indicating that the nanoparticles have good stability in water. Furthermore, if the ethanol content in the mixed solution exceeds 80%, no nano-lignin dispersion will form during regeneration. If γ-valerolactone is not added to the mixed solution, no lignin solution will form.

[0036] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for preparing nano-lignin at low cost, characterized in that: The steps include: S1 adds lignin to a mixed solution of ethanol, γ-valerolactone, and water to form a lignin solution; wherein the mixed solution is mainly composed of ethanol, and the content of ethanol is 50% to 80%; S2 stirs the lignin solution and adds water dropwise to the lignin solution using a peristaltic pump; S3 was centrifuged to precipitate the nano-lignin particles.

2. The method according to claim 1, wherein Step S3 also includes pouring off the supernatant after centrifugation, adding deionized water again and centrifuging again to precipitate the nano-lignin particles.

3. The method according to claim 1, wherein The method further includes pouring out the supernatant in step S4, and freeze-drying the remaining precipitated nano-lignin particles to obtain dry nano-lignin particles.

4. The method according to claim 1, wherein The volume ratio of ethanol, γ-valerolactone and water in the mixed solution is 4-23:2-4:1, preferably 4-16:2-4:1, and more preferably 8-12:3:

1.

5. The method according to claim 1, wherein The mass volume ratio of the lignin to the mixed solution is 2 mg / ml to 10 mg / ml.

6. The method according to claim 1, wherein The lignin is industrial lignin produced by pulping or biorefining enterprises; preferably, the industrial lignin includes but is not limited to alkali lignin and / or sulfate lignin.

7. The method according to claim 1, wherein The stirring time of the lignin solution in S2 is 0.5 h to 1.5 h; the stirring rate is 400 rpm to 600 rpm; the specific stirring time is 50-70 minutes, more specifically 60 minutes.

8. The method according to claim 1, wherein The peristaltic pump is used to add water droplets to the lignin solution in a ratio of 5.7 to 10:1 between water and lignin solution; The drop acceleration rate of the peristaltic pump in S2 is 5ml / min to 8ml / min.

9. The method according to claim 1, wherein In S3, the centrifugal speed is 8000 rpm / min to 10000 rpm / min; the centrifugal time is 10 min to 15 min.

10. The nano-lignin obtained by the method according to any one of claims 1 to 9, wherein the nano-lignin has a particle size of 200 to 600 nm and a solid or hollow spherical shape.

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