A method for preparing cellulose nanofilaments using reed biomass and cellulose nanofilaments

Abstract

The invention relates to the technical field of wetland biomass industrial treatment, and discloses a preparation method of cellulose nanofilaments using reed sedge biomass and the cellulose nanofilaments. The method comprises treating reed sedge biomass with acetic acid hydrolyzate to remove hemicellulose to obtain a cellulose precursor, then treating the cellulose precursor with an alkaline low eutectic solvent to remove lignin to obtain a cellulose nanofilament precursor, and then subjecting the cellulose nanofilament precursor to high pressure homogenization to obtain cellulose nanofilaments, wherein the acetic acid hydrolyzate and the alkaline low eutectic solvent are recovered and concentrated after use to obtain the acetic acid hydrolyzate and the alkaline low eutectic solvent that can be reused. The product obtained by the invention comprises a hemicellulose yield of 56%, a lignin yield of 95%, and a cellulose nanofilament yield of 71% relative to the cellulose nanofilament precursor, thereby significantly improving the value of the reed sedge biomass raw material.

Description

Technical Field

[0001] The invention relates to the technical field of wetland biomass industrial treatment, and in particular to a method for preparing cellulose nanofilaments by utilizing reed biomass and the cellulose nanofilaments. Background Art

[0002] Miscanthus lutarioriparius belongs to the genus Miscanthus in the Poaceae family, and Phragmites australias Trin. belongs to the genus Phragmites in the Poaceae family. Both are tall perennial aquatic or wetland grasses. Nearly 1 million tons of high-quality Miscanthus lutarioriparius lignocellulosic biomass can be produced annually on the wetlands of the Dongting Lake area in my country, which is an ideal raw material for the preparation of non-food bio-based materials.

[0003] Cellulose nanofibril (CNF) is a kind of nanofiber with a diameter of 1-100 nanometers and a length of several micrometers. It is widely used in the fields of electrical components, biomedicine, biocomposite materials and food processing. Compared with cellulose nanocrystals, it has a high aspect ratio and a network entanglement structure, and the direction of industrial utilization is also different. At present, the preparation of cellulose nanofibrils mainly uses high-grade pulp as raw material, usually using physical methods, TEMPO oxidation methods, enzymatic methods, etc., but the high cost of raw materials and low yield limit its large-scale production progress (Chen Wenshuai et al., Preparation and Morphological Characteristics Analysis of Lignocellulose Nanofibrils, Acta Polymerica Sinica, pp. 1320-1326, November 2010).

[0004] A Chinese patent application with application publication number CN116752366A discloses a method for preparing cellulose nanofibers, which discloses that lignocellulosic biomass raw materials are pretreated in a low eutectic solvent, and then subjected to high-pressure homogenization to obtain cellulose nanofibrils, wherein the hydrogen bond acceptor in the low eutectic solvent is choline chloride, the hydrogen bond donor is a polyol, and the low eutectic solvent is acidified with sulfuric acid before use. In addition to being rich in cellulose, the residue obtained after pretreatment still retains a certain amount of lignin to reduce the subsequent aggregation of CNF. However, the use of an acidic low eutectic solvent in this method is likely to cause significant damage to cellulose, resulting in a reduction in the cellulose extraction rate. Summary of the invention

[0005] In view of the problem in the prior art that the fiber filaments are severely damaged during the fiber filament preparation process, resulting in a decrease in yield, the present invention provides a method for preparing cellulose nanofilaments using reed biomass, during which cellulose damage is minimal and the yield of the obtained cellulose nanofilaments is high; the present invention also provides cellulose nanofilaments prepared by the method for preparing cellulose nanofilaments using reed biomass, which has a high yield of cellulose nanofilaments.

[0006] The present invention is achieved through the following technical solutions:

[0007] A method for preparing cellulose nanofilaments using reed biomass comprises treating the reed biomass with acetic acid hydrolysate to remove hemicellulose to obtain a cellulose precursor, then treating the cellulose precursor with an alkaline low eutectic solvent to remove lignin to obtain a cellulose nanofilament precursor, and then subjecting the cellulose nanofilament precursor to high pressure homogenization to obtain cellulose nanofilaments, wherein the acetic acid hydrolysate and the alkaline low eutectic solvent are recovered and concentrated after use to obtain the acetic acid hydrolysate and the alkaline low eutectic solvent that can be reused.

[0008] The acetic acid hydrolyzate can remove most of the hemicellulose, and a small amount of residual hemicellulose can maintain the suspension stability of the subsequent cellulose nanofilament precursor and cellulose nanofilaments; the traditional method uses an acidic low eutectic solvent to separate lignin and cellulose, which is easy to destroy the crystallinity of cellulose and reduce the degree of polymerization, resulting in a decrease in the secondary extraction yield of cellulose, while the present invention uses an alkaline low eutectic solvent to well maintain the integrity of cellulose and fully separate lignin, significantly improving the lignin yield and the yield and purity of cellulose; the acetic acid hydrolyzate and the alkaline low eutectic solvent can be concentrated and recovered and put into use again, which greatly saves the reaction raw materials.

[0009] Preferably, the method specifically comprises the following steps:

[0010] S1, removing hemicellulose from acetic acid hydrolyzate: removing impurities from the reed biomass raw material and crushing it to obtain reed biomass particles, mixing the reed biomass particles with the acetic acid hydrolyzate and transferring them into reactor 1, and after the reaction is completed, solid-liquid separation is performed to obtain acetic acid recovery liquid and the cellulose precursor;

[0011] S2, preliminarily concentrating the acetic acid recovery liquid prepared in S1 to obtain an acetic acid hydrolyzate and a retentate that can be reused;

[0012] S3, removing lignin with an alkaline low eutectic solvent: the cellulose precursor prepared in S1 is mixed with an alkaline low eutectic solvent and transferred into a second reactor. After the reaction is completed, ethanol is added to terminate the reaction, and then solid-liquid separation is performed to obtain an alkaline low eutectic solvent waste liquid and a cellulose nanofilament precursor;

[0013] In S4 and S3, the alkaline low eutectic solvent is a mixture of choline chloride and ethanolamine, the alkaline low eutectic solvent waste liquid is diluted with water and subjected to the primary concentration to obtain an alkaline low eutectic solvent recovery liquid and a second retentate, and the alkaline low eutectic solvent recovery liquid is concentrated again to obtain an alkaline low eutectic solvent that can be used again;

[0014] S5. Preparation of cellulose nanofilaments by high-pressure homogenization: The cellulose nanofilament precursor prepared in S3 is mixed with water and transferred into a high-pressure homogenizer for several cycles to obtain a cellulose nanofilament pulp, and then the cellulose nanofilament pulp is centrifuged or filtered to remove large cellulose particles to obtain the cellulose nanofilaments.

[0015] Preferably, the particle size of the reed biomass particles in S1 is 1 to 60 meshes, the mass fraction of the acetic acid hydrolyzate is 5 to 40%, the mass volume mixing ratio of the reed biomass particles and the acetic acid hydrolyzate is 1g:6 to 20mL, the reaction temperature is 100 to 150°C, and the reaction is stirred at 60 to 200 rpm, and the reaction time is 30 to 150 min.

[0016] Preferably, the initial concentration in S2 is reverse osmosis concentration, and the retentate contains hemicellulose.

[0017] Preferably, the ethanol concentration in S3 is 75%, the solid-liquid mixing 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 1-8 h.

[0018] Preferably, the molar mixing ratio of choline chloride and ethanolamine in the alkaline low eutectic solvent in S4 is 1:1-15, the mixing temperature is 70-90°C, the mixing time is 60-180min, the re-concentration is evaporation concentration, the evaporation temperature is 50-60°C, the evaporation time is 1-4h, and the retentate contains lignin.

[0019] Preferably, the solid-liquid mixing ratio of the cellulose nanofilament precursor and water in S5 is 1:20-100, the pressure condition during high-pressure homogenization is 500-1500 bar, and the number of cycles is 1-20 times.

[0020] A cellulose nanofilament is prepared by the above-mentioned method for preparing cellulose nanofilaments using reed biomass.

[0021] Preferably, the cellulose nanowires are distributed in a network shape, with a cross-sectional diameter of 1 to 100 nm and a length of several microns.

[0022] Beneficial effects of the present invention:

[0023] (1) The present invention uses an alkaline low eutectic solvent to remove lignin, which can effectively maintain the integrity of cellulose crystals and is not easily destroyed. Lignin is completely removed, and the cellulose yield and purity are significantly improved.

[0024] (2) The present invention uses acetic acid circulation to remove hemicellulose, thereby retaining a small portion of hemicellulose, so that the subsequent nano-product has good suspension stability.

[0025] (3) The boiling point of the alkaline low eutectic solvent of the present invention is higher than that of water and ethanol by a certain margin. During evaporation and concentration, water and ethanol are evaporated, while choline chloride and ethanolamine are retained in the remaining solvent, and the concentration process is simple and easy to use.

[0026] (4) The present invention obtains a plurality of products, including hemicellulose, lignin and cellulose nanofilaments, wherein the hemicellulose yield is 56%, the lignin yield is 95%, and the cellulose nanofilament yield relative to the cellulose precursor is 71%, thereby significantly improving the value of the reed biomass raw material.

[0027] (5) The preparation process of the present invention is simple, and the cost of recycling the reaction raw materials is low, which is conducive to large-scale industrial promotion. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 The invention discloses a process for preparing cellulose nanofilaments using reed biomass.

[0029] Figure 2 This is the SEM image of cellulose nanofilaments.

[0030] Figure 3 This is the dynamic light scattering particle size diagram of cellulose nanofilaments.

[0031] Figure 4 A picture of cellulose nanofilaments suspended in aqueous solution. DETAILED DESCRIPTION

[0032] In order to make the purpose, technical scheme and advantages of the present invention more clearly understood, the present invention is further described in detail in conjunction with the embodiments below; 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 conventional means in the art; the terms "comprising", "including" or any other variations thereof used herein are intended to cover non-exclusive inclusions; for example, a composition, step, method, product or device comprising the listed elements is not necessarily limited to those elements, but may include other elements not explicitly listed or elements inherent to such a composition, step, method, product or device; in addition, the technical features involved in each embodiment of the present invention described below may be combined with each other as long as they do not conflict with each other; the experimental raw materials used in the embodiments of the present invention and the comparative examples are all commercially available products.

[0033] Example 1

[0034] A method for preparing cellulose nanofilaments using reed biomass comprises the following steps:

[0035] 6 g of reed biomass was weighed and placed in a reactor, and an acetic acid hydrolyzate with a mass concentration of 25% was added, with a mixing ratio of 1 g:10 mL, and the mixture was heated to 120° C. and reacted in a boiling state for 1 h while stirring at 100 rpm. After the reaction was completed, the mixture was cooled to room temperature to obtain an acid hydrolysis mixture, and the acid hydrolysis mixture was filtered with a plate-and-frame filter to separate the solid and the liquid, and the solid was washed to neutrality to obtain a cellulose precursor, and the liquid was filtered and concentrated to the concentration of the acetic acid hydrolyzate, and recovered for the next acetic acid hydrolysis of reed biomass;

[0036] 3 g of the reed cellulose precursor and the alkaline low eutectic solvent were mixed evenly and then moved into a reactor and stirred at 150 rpm for 3 hours. The reaction temperature was 110°C, and ethanol with a volume concentration of 75% was added to terminate the reaction. The solid-liquid separation obtained 100 mL of the alkaline low eutectic solvent suspension; the alkaline low eutectic solvent was obtained by mixing choline chloride and ethanolamine in a molar ratio of 1:8 and stirring at 80°C; the solid-liquid ratio of the reed cellulose precursor and the alkaline low eutectic solvent was 1 g: 10 mL; the alkaline low eutectic solvent suspension was subjected to solid-liquid separation to obtain an alkaline low eutectic solvent waste liquid and a reed cellulose nanofilament precursor, water was added to the alkaline low eutectic solvent waste liquid to 200 mL for dilution and standing to precipitate lignin, and then filtered and concentrated by reverse osmosis filtration equipment to obtain a permeate as an alkaline low eutectic solvent recovery liquid, which was further evaporated and concentrated at 55°C and refluxed for the next round of reaction.

[0037] The precursor of reed cellulose nanofilaments and pure water were mixed evenly at a certain solid-liquid ratio and then transferred into a high-pressure homogenizer, and reacted for several cycles under certain pressure conditions to obtain cellulose nanofilament rough pulp. The solid-liquid ratio was 1:100, the pressure condition was 900 bar, and the cycle was 10 times to obtain cellulose nanofilaments.

[0038] The preparation process of cellulose nanofilaments described in Example 1 is as follows Figure 1 As shown, the prepared cellulose nanofilaments were then subjected to scanning electron microscope (SEM) analysis and nanoparticle size analysis. Figure 2 As shown, the SEM scanning results show that the diameter of the cellulose nanofilaments prepared in Example 1 is less than 100 nm. Figure 3 As shown, the average particle size of the cellulose nanofilaments prepared in Example 1 measured by a nanoparticle size analyzer has two peaks, the first peak is 83.4 nm, the second peak is 379.7 nm, and the Zeta potential is -34 mV, indicating that the cellulose nanofilaments can maintain good suspension stability in the solvent. Figure 4The figure shows a cellulose nanofilament suspension aqueous solution with a mass concentration of 1%, and the aqueous solution has good homogeneity and stability. The detection of cellulose content in cellulose nanofilaments shows that the yield of the final product of cellulose nanofilaments measured in Example 1 is 40% relative to the mass of the reed biomass raw material, and the yield relative to the mass of the cellulose precursor is 71%. The cellulose precursor uses an alkaline low eutectic solvent to remove lignin, and the removal rate of lignin is 95%, so the lignin yield is also 95%. The alkaline low eutectic solvent removes lignin more thoroughly, but it will not destroy the cellulose crystals too much. Therefore, the yield of cellulose nanofilaments is higher than that of acidic low eutectic solvents, and the yield of lignin is also higher. In addition, the hemicellulose yield obtained by acetic acid circulation is 56%, which significantly improves the industrial utilization value of reed biomass raw materials.

[0039] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those generally understood by those skilled in the art to which the present invention belongs. The terms used herein in the specification of the present invention are only for the purpose of describing specific embodiments and are not intended to limit the present invention. The various technical features of the above-described embodiments can be combined arbitrarily. In order to make the description concise, all possible combinations of the various technical features in the above-described embodiments are not described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

Claims

1. A method for preparing cellulose nanofilaments using reed biomass, characterized in that: The method comprises treating reed biomass with acetic acid hydrolysate once to remove hemicellulose to obtain a cellulose precursor, and retaining part of the hemicellulose, and then treating the cellulose precursor with an alkaline low eutectic solvent to remove lignin to obtain a cellulose nanofilament precursor, and retaining the crystalline integrity of cellulose, and then subjecting the cellulose nanofilament precursor to high pressure homogenization to obtain cellulose nanofilaments, wherein the acetic acid hydrolysate and the alkaline low eutectic solvent are recovered and concentrated after use to obtain the acetic acid hydrolysate and the alkaline low eutectic solvent that can be used again; The cellulose nanofilaments are distributed in a network shape, with a cross-sectional diameter of 1 to 100 nm and a length of several microns; The particle size of the reed biomass particles is 1-60 meshes, the mass fraction of the acetic acid hydrolyzate is 5-40%, the mass volume mixing ratio of the reed biomass particles and the acetic acid hydrolyzate is 1g:6-20mL, the reaction temperature is 100-150°C, and the reaction is stirred at 60-200rpm, and the reaction time is 30-150min; The alkaline deep eutectic solvent is a mixed solution of choline chloride and ethanolamine.

2. The method for preparing cellulose nanofilaments using reed biomass according to claim 1, characterized in that: The specific steps include: S1, removing hemicellulose from acetic acid hydrolyzate: removing impurities from the reed biomass raw material and crushing it to obtain reed biomass particles, mixing the reed biomass particles with the acetic acid hydrolyzate and transferring them into reactor 1, and after the reaction is completed, solid-liquid separation is performed to obtain acetic acid recovery liquid and the cellulose precursor; S2, preliminarily concentrating the acetic acid recovery liquid prepared in S1 to obtain an acetic acid hydrolyzate and a retentate that can be reused; S3, removing lignin with an alkaline low eutectic solvent: the cellulose precursor prepared in S1 is mixed with an alkaline low eutectic solvent and transferred into a second reactor. After the reaction is completed, ethanol is added to terminate the reaction, and then solid-liquid separation is performed to obtain an alkaline low eutectic solvent waste liquid and a cellulose nanofilament precursor; In S4 and S3, the alkaline low eutectic solvent waste liquid is diluted with water and initially concentrated to obtain an alkaline low eutectic solvent recovery liquid and a second retentate, and the alkaline low eutectic solvent recovery liquid is re-concentrated to obtain an alkaline low eutectic solvent that can be used again; S5. Preparation of cellulose nanofilaments by high-pressure homogenization: The cellulose nanofilament precursor prepared in S3 is mixed with water and transferred into a high-pressure homogenizer for several cycles to obtain a cellulose nanofilament pulp, and then the cellulose nanofilament pulp is centrifuged or filtered to remove large cellulose particles to obtain the cellulose nanofilaments.

3. The method for preparing cellulose nanofilaments using reed biomass according to claim 2, characterized in that: The primary concentration in S2 is reverse osmosis concentration, and the retentate 1 contains hemicellulose.

4. The method for preparing cellulose nanofilaments using reed biomass according to claim 2, characterized in that: The ethanol concentration in S3 is 75%, the solid-liquid mixing ratio of the cellulose precursor and the alkaline low eutectic solvent is 1 g:5-30 mL, the reaction temperature is 80-120° C., and the reaction time is 1-8 h.

5. The method for preparing cellulose nanofilaments using reed biomass according to claim 2, characterized in that: The molar mixing ratio of choline chloride and ethanolamine in the alkaline low eutectic solvent in S4 is 1 mol:1-15 mol, the mixing temperature is 70-90° C., the mixing time is 60-180 min, the re-concentration is evaporation concentration, the evaporation temperature is 50-60° C., the evaporation time is 1-4 h, and the retentate contains lignin.

6. The method for preparing cellulose nanofilaments using reed biomass according to claim 2, characterized in that: The solid-liquid mixing ratio of the cellulose nanofilament precursor and water in S5 is 1:20-100, the pressure condition during high-pressure homogenization is 500-1500 bar, and the number of cycles is 1-20 times.

7. A cellulose nanofilament, characterized in that: The cellulose nanofilaments are prepared by the method for preparing cellulose nanofilaments using reed biomass as described in any one of claims 1 to 6.

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