A high-yield lignin nanoparticle prepared from Miscanthus sacchariflorus cellulose precursor and its preparation method

Abstract

The present invention relates to the technical field of reed processing, and discloses a lignin nanoparticle prepared based on reed cellulose precursor with a high yield and a preparation method thereof. The preparation raw material uses reed cellulose precursor, and the lignin nanoparticle is obtained by separating lignin from the raw material with an alkaline deep eutectic solvent; the deep eutectic solvent is filtered to remove the lignin nanoparticle and then concentrated for recycling; the particle size of the lignin nanoparticle is less than 100 nm, and the yield is as high as 90% - 95%. Traditional acidic deep eutectic solvents separate lignin and cellulose by destroying the cellulose structure, and often the separation is not sufficient. However, the present invention uses an alkaline deep eutectic solvent that neither destroys cellulose nor can fully separate lignin, so the yield is as high as 90% - 95%.

Description

Technical Field

[0001] The present invention relates to the technical field of Miscanthus sacchariflorus processing, and particularly relates to a high-yield lignin nanoparticle prepared from Miscanthus sacchariflorus cellulose precursor and a preparation method thereof. Background Art

[0002] In the industrial production of xylo-oligosaccharide and xylose by the acid method, a large amount of extraction residue rich in cellulose and lignin, also known as "cellulose precursor", is generated. It is an ideal raw material for preparing cellulose and lignin products, but currently it is only used for low-end products such as boiler fuel and seedling trays. Therefore, finding a way to utilize cellulose precursor with high value has become an important issue for the transformation and upgrading of the sugar industry. According to incomplete statistics, the global paper industry produces more than 70 million tons of lignin every year, most of which is used as fuel, and the rest is discharged with pulping black liquor, and only 5% is used for the manufacture of deep-processed products such as additives, dispersants, adhesives and surfactants (Xiong Fuquan et al., Research status of the preparation and application of nano-lignin, Polymer Materials Science and Engineering, pp. 156-161, December 2016). At the same time, due to the complex amorphous structure of lignin, which limits its high-value utilization, the high-value utilization and development of lignin have become a research hotspot in current lignin research (Zhang Wenxin et al., Research progress of lignin-based nanomaterials, Polymer Bulletin, pp. 32-37, September 2009).

[0003] Lignin nanoparticles (LNPs) are lignin colloids with a physical size in the nanometer range (1-100 nm). Due to the decrease in particle size, the increase in specific surface area and active surface functional sites, they have excellent antioxidant, antibacterial and ultraviolet absorption properties compared with the original lignin (Wang Huan et al., Research progress on the preparation and application of lignin-based functional materials, Chemical Industry and Engineering Progress, pp. 434-448, July 2018). Currently, in the laboratory, mainly alkali lignin (or lignin sulfonate) produced by the paper industry or enzymatic lignin produced by the cellulose ethanol industry is used as raw materials, and usually prepared by acid precipitation self-assembly, mechanical method, organic solvent method, and modification method. Since the existing methods are all in the laboratory stage, and the preparation process is too complex, with high cost, large pollution and low yield, there is no commercial production report (Liu Xue et al., Research progress on the preparation and functional application of lignin nanoparticles, Biomass Chemical Engineering, pp. 53-65, September 2020).

[0004] Deep Eutectic Solvents (DESs) are emerging green functional solvents in recent years. They have the advantages of being prepared from renewable raw materials, low cost, easy to recycle, biodegradable, etc. They can directly separate lignin from lignocellulose and are a type of new green solvent with great application prospects (Xue Zhimin et al., Research progress on choline chloride-based deep eutectic solvents for lignocellulose pretreatment, Journal of Forestry Engineering, pp. 32 - 44, August 2023). Different from traditional inorganic solvents for pulping and papermaking such as sodium hydroxide, sodium sulfide, sulfite, hydrogen peroxide, and organic solvents such as formaldehyde, acetone, γ-valerolactone, deep eutectic solvents are generally formed by a hydrogen bond acceptor (HBA) and a hydrogen bond donor (HBD) in a certain proportion. They have physicochemical properties similar to ionic liquids, but lower toxicity, easier biodegradability, and cheaper price, and have the potential for commercial promotion (Wei Lu et al., Research progress on deep eutectic solvents and their applications, Chemical Bulletin, pp. 333 - 339, October 2010).

[0005] Chinese Patent with publication number CN112851977B discloses a lignin nanoparticle and its preparation method and application. The lignocellulose raw material is mixed with a deep eutectic solvent, then heat-treated, cooled and washed, and solid-liquid separated to obtain a solid-phase pretreated cellulose residue and a liquid-phase component. The solid-phase pretreated cellulose residue is dried and collected; the liquid component is evaporated and concentrated, added to an antisolvent to precipitate lignin nanoparticles, centrifuged, dried and collected, and then the deep eutectic solvent in the centrifugate is recovered and recycled. The deep eutectic solvent used in this patent is acidic, and the raw material is Dendrocalamus giganteus, and the yield of lignin nanoparticles only reaches 47.5% - 59.9%. There is still room for further improvement in the yield of lignin nanoparticles. Summary of the Invention

[0006] According to the prior art, there is still room for further improvement in the yield of preparing lignin nanoparticles from natural products. The present invention provides a high-yield lignin nanoparticle prepared based on Miscanthus sacchariflorus cellulose precursor, with a preparation yield as high as 90% - 95%; the present invention also provides a preparation method of a high-yield lignin nanoparticle prepared based on Miscanthus sacchariflorus cellulose precursor, with a preparation yield as high as 90% - 95%.

[0007] The present invention is achieved through the following technical solutions:

[0008] A high-yield lignin nanoparticle prepared based on Miscanthus sacchariflorus cellulose precursor, the preparation raw material uses Miscanthus sacchariflorus cellulose precursor, and an alkaline deep eutectic solvent is used to separate lignin from the raw material to obtain the lignin nanoparticle; the deep eutectic solvent is filtered to remove the lignin nanoparticle and then concentrated for recovery; the particle size of the lignin nanoparticle is less than 100 nm, and the yield is as high as 90% - 95%.

[0009] Traditional methods use acidic deep eutectic solvents to separate lignin and cellulose, which are prone to damaging the crystallinity of cellulose and reducing the degree of polymerization, resulting in a decrease in the secondary extraction yield of cellulose. In contrast, the present invention uses alkaline deep eutectic solvents, which can well maintain the integrity of cellulose and can fully separate lignin, significantly improving the lignin yield and the cellulose yield.

[0010] Preferably, the alkaline deep eutectic solvent is a mixture of choline chloride and ethanolamine.

[0011] Preferably, the nano-particle size of lignin is 70 - 90 nm.

[0012] A preparation method of lignin nanoparticles prepared from a high-yield reed cellulose precursor as described above specifically includes the following steps:

[0013] 1) After the reed cellulose precursor and the alkaline deep eutectic solvent are mixed evenly, they are transferred into a reactor for reaction. The reaction temperature is 80 - 120 °C, and ethanol with a volume concentration of 60% - 85% is added to terminate the reaction. Solid-liquid separation is carried out to obtain a lignin nanoparticle suspension;

[0014] 2) The lignin nanoparticle suspension prepared in step 1) is diluted with water and allowed to stand to precipitate lignin nanoparticles, and then filtered and concentrated. The retentate is the lignin nanoparticles, and the filtrate is the recovered solution of the alkaline deep eutectic solvent.

[0015] Preferably, it further includes step 3) evaporating and concentrating the recovered solution of the alkaline deep eutectic solvent at 50 - 60 °C and then refluxing for the next round of reaction.

[0016] Preferably, in step 1), the alkaline deep eutectic solvent is obtained by mixing choline chloride and ethanolamine in a molar ratio of 1:1 - 15 and stirring at 75 - 85 °C; the solid-liquid ratio of the reed cellulose precursor and the alkaline deep eutectic solvent is 1:5 - 30, and the reaction time is 1 - 8 h.

[0017] Preferably, in step 2), a reverse osmosis filtration device is used for filtration and concentration.

[0018] The beneficial effects of the present invention:

[0019] (1) The present invention uses a reed cellulose precursor as the preparation raw material. Although the lignin content is high by itself, the lignin and cellulose are mixed together and need to be fully separated to obtain a higher yield. Traditional acidic deep eutectic solvents separate lignin by destroying the cellulose structure and often do not separate it sufficiently. However, the present invention uses an alkaline deep eutectic solvent that neither destroys cellulose nor can fully separate lignin. Therefore, the yield is as high as 90% - 95%.

[0020] (2) The present invention uses an alkaline deep eutectic solvent to treat the raw materials, in which the cellulose structure is less damaged. After solid-liquid separation, the purity of cellulose in the solid is 64% - 66%. Moreover, cellulose can be further extracted. Therefore, the raw materials are fully utilized and the value is significantly improved.

[0021] (3) The alkaline deep eutectic solvent of the present invention can be recycled, greatly reducing emissions. Moreover, the solvent itself is environmentally friendly and has green properties.

[0022] (4) The present invention has low cost and simple process, which is conducive to large-scale industrial promotion. Description of the Drawings

[0023] Figure 1 It is a process flow chart for preparing lignin nanoparticles using reed cellulose precursor.

[0024] Figure 2 It is an SEM image of lignin nanoparticles. A is the first reaction and B is the third reaction. Detailed Embodiments

[0025] In order to make the objectives, technical solutions and advantages of the present invention clearer, the following further details the present invention in conjunction with embodiments; it should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention; in the embodiments, unless otherwise specified, the means used are all conventional means in the art; the terms "comprising", "including" or any other variation thereof used herein are intended to cover non-exclusive inclusion; for example, a composition, step, method, article or device containing the listed elements does not necessarily only include those elements, but may include other elements not explicitly listed or elements inherent to such composition, step, method, article or device; in addition, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other; the experimental raw materials used in the embodiments and comparative examples of the present invention are all commercially available products.

[0026] Detection Method:

[0027] Scanning electron microscope (SEM) analysis: Use a scanning electron microscope to characterize the microstructure of lignin nanoparticles. The type of detector: INLENS, acceleration voltage 3 kV, working distance 6.4 mm, magnification 20,000 times.

[0028] The method for measuring with a nano particle size analyzer is as follows: The particle size is measured through the dynamic light scattering (DLS) process, and at the same time, the electrophoretic light scattering is used to detect the charged property of the particle surface, for 50 s at 25 °C.

[0029] The cellulose content is detected, and the detection method is the determination of chemical components of lignocellulosic biomass raw materials NB / T 34057 - 2017.

[0030] The calculation formula for the yield of lignin nanoparticles is: Yield of lignin nanoparticles = Mass of lignin nanoparticles / (Mass of cellulose precursor × Lignin content of cellulose precursor). The yield is the same as the recovery rate.

[0031] The calculation formula for the yield of cellulose is: Yield of cellulose = (Mass of cellulose × Purity of cellulose) / (Mass of cellulose precursor × Cellulose content of cellulose precursor).

[0032] Example 1

[0033] A preparation method of lignin nanoparticles prepared based on Miscanthus sacchariflorus cellulose precursor with high yield specifically includes the following steps:

[0034] 1) Mix 3 g of Miscanthus sacchariflorus cellulose precursor and the alkaline deep eutectic solvent evenly, then transfer them into a reactor, stir and react at 150 rpm for 3 h, the reaction temperature is 110 °C, add ethanol with a volume concentration of 75% to terminate the reaction, and perform solid-liquid separation to obtain 100 mL of lignin nanoparticle suspension; the alkaline deep eutectic solvent is obtained by mixing choline chloride and ethanolamine in a molar ratio of 1:8 and stirring at 80 °C; the solid-liquid ratio of Miscanthus sacchariflorus cellulose precursor and the alkaline deep eutectic solvent is 1 g:10 mL;

[0035] 2) Add water to the lignin nanoparticle suspension prepared in step 1) to 200 mL, dilute and let it stand to precipitate lignin nanoparticles, and then filter and concentrate with a reverse osmosis filtration device to obtain the retentate as lignin nanoparticles and the permeate as the recovered solution of the alkaline deep eutectic solvent.

[0036] 3) Evaporate and concentrate the recovered solution of the alkaline deep eutectic solvent at 55 °C, and then reflux for the next round of reaction.

[0037] React the recovered solution of the alkaline deep eutectic solvent two more times, take the lignin nanoparticles obtained from the first reaction and the third reaction for scanning electron microscope (SEM) analysis, and take the lignin nanoparticle products obtained from the first, second, and third reactions for nanoparticle size analyzer analysis.

[0038] The detection of the cellulose content in the solid obtained by solid-liquid separation in step 1) shows that the measured cellulose purity in Example 1 is 78%; the yield of the final product lignin nanoparticles is 92%, and the yield of cellulose is 96%.

[0039] The SEM scanning results show that, as Figure 2 shown, the particle size of the lignin nanoparticles prepared in Example 1 measured by the method is 1 - 100 nm, and the product morphologies of the first and third preparations are uniform and there are no significant differences.

[0040] The particle size of the lignin nanoparticles prepared in Example 1 was measured by a nano-particle size analyzer to be 75 nm, and there was no significant difference.

[0041] Comparative Example 1

[0042] The difference from Example 1 was that the cellulose precursor of Miscanthus lutarioriparius after physical pulverization was used to replace the cellulose precursor of Triarrhena lutarioriparia as the raw material. The yield of the obtained lignin nanoparticles was detected to be 75%, the cellulose yield was 92%, and the particle size of the lignin nanoparticles was 204 nm.

[0043] Compared with the cellulose precursor of Miscanthus lutarioriparius residue after extracting xylooligosaccharides, the pore volume and looseness are both lower, and the separation of cellulose and lignin is not thorough enough.

[0044] Comparative Example 2

[0045] The difference from the example was that an acidic deep eutectic solvent (lactic acid: choline chloride = 8:1) was used to replace the basic deep eutectic solvent. The yield of the obtained lignin nanoparticles was detected to be 80%, and the cellulose yield was 91%.

[0046] The acidic deep eutectic solvent is relatively easier to destroy the crystallization of cellulose than the basic deep eutectic solvent, and the separation of lignin is not sufficient enough, so the cellulose yield is lower than that of Example 1.

[0047] The above-described embodiments only represent several implementation manners of the present invention, and the description thereof is relatively specific and detailed, but it should not be construed as a limitation on the scope of the invention patent.

[0048] For those of ordinary skill in the art, without departing from the concept of the present invention, several modifications and improvements can still be made, and these all belong to the protection scope of the present invention. Therefore, the protection scope of the present invention patent shall be subject to the appended claims.

Claims

1. A high-yield lignin nanoparticle prepared based on a cellulose precursor, characterized in that: The preparation raw material adopts a cellulose precursor of Nandi extract residue from which oligoxylose is extracted, and an alkaline low eutectic solvent is used to separate lignin from the raw material. The alkaline low eutectic solvent is obtained by mixing choline chloride and ethanolamine in a molar ratio of 1:1-15 and stirring at 75-85°C. The solid-liquid ratio of the cellulose precursor and the alkaline low eutectic solvent is 1:5-30, the reaction temperature is 80-120°C, and the reaction time is 1-8h. The low eutectic solvent is filtered to remove the lignin nanoparticles, and then concentrated to be recovered. The particle size of the lignin nanoparticles is less than 100nm, and the yield is as high as 90%-95%.

2. The high-yield lignin nanoparticles prepared based on cellulose precursor according to claim 1, characterized in that: The diameter of the lignin nanoparticles is 70 to 90 nm.

3. A method for preparing high-yield lignin nanoparticles based on cellulose precursors as claimed in claim 1, characterized in that: The specific steps include: 1) The cellulose precursor and the alkaline low eutectic solvent are mixed evenly and then transferred into a reactor for reaction at a reaction temperature of 80 to 120° C. for a reaction time of 1 to 8 hours, and ethanol with a volume concentration of 60% to 85% is added to terminate the reaction, and solid-liquid separation is performed to obtain a lignin nanoparticle suspension; 2) diluting the lignin nanoparticle suspension prepared in step 1) with water and letting it stand to precipitate the lignin nanoparticles, and then filtering and concentrating the retentate to obtain the lignin nanoparticles, and the filtrate to obtain the alkaline low eutectic solvent recovery liquid.

4. The method for preparing high-yield lignin nanoparticles based on cellulose precursors according to claim 3, characterized in that: The invention also comprises the step 3) evaporating and concentrating the recovered alkaline low eutectic solvent solution at 50-60° C., and then refluxing for the next round of reaction.

5. The method for preparing high-yield lignin nanoparticles based on cellulose precursors according to claim 3, characterized in that: In step 2), reverse osmosis filtration equipment is used for filtration and concentration.

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