Method for preparing zanthoxylum bungeanum seed cellulose by ultrafine grinding assisted with low eutectic solvent

Abstract

This invention discloses a method for preparing Sichuan pepper seed cellulose using ultrafine grinding-assisted eutectic solvent. The method includes: pretreating Sichuan pepper seeds with ultrafine grinding to obtain ultrafine Sichuan pepper seed powder; treating the ultrafine Sichuan pepper seed powder with a eutectic solvent system to obtain a reaction slurry; separating the slurry, taking the precipitate, washing and drying it to obtain Sichuan pepper seed cellulose; wherein, the preferred eutectic solvent is a choline chloride-oxalic acid system, with a molar ratio of choline chloride to oxalic acid of 1:(2-3); during eutectic solvent treatment, the material-to-liquid ratio of the ultrafine Sichuan pepper seed powder to the eutectic solvent is 1:(15-30). The cellulose retention rate of the Sichuan pepper seed cellulose obtained using the method provided by this invention is as high as 89%, significantly higher than that obtained by conventional alkali dissolution methods; the Sichuan pepper seed cellulose has a cellulose type I structure, a crystallinity of 62.61%, and an average particle size D. 50 The size is 16.30 μm; at the same time, the cellulose obtained by the method of the present invention contains cellulose oxalate, which facilitates the further preparation of nanocellulose.

Description

Technical Field

[0001] This invention belongs to the field of agricultural and sideline product processing technology, specifically relating to a method for preparing pepper seed cellulose using ultrafine grinding-assisted eutectic solvent. Background Technology

[0002] Sichuan pepper is an important economic tree species in my country with a long history of cultivation and wide distribution, used as a spice, oilseed, and medicinal ingredient. Sichuan pepper seeds, a major byproduct of Sichuan pepper production, account for about 60% of the total weight of the pepper and contain up to 74.39% lignocellulose, including 35% cellulose, 18.56% hemicellulose, and 20.83% lignin. They are an excellent raw material for cellulose production, but are currently usually discarded as processing waste, causing environmental pollution and resource waste.

[0003] One of the key steps in the preparation of plant cellulose is the effective separation of cellulose from lignocellulose. Currently, methods for preparing plant cellulose include physical-mechanical methods, chemical acid-base methods, ionic liquid methods, and eutectic solvent methods. For example, invention patent application number 201910905896.0 discloses a method for extracting dietary fiber from Sichuan pepper seed cake, including acid soaking, pressure pretreatment, enzymatic hydrolysis, and centrifugation to obtain insoluble and soluble dietary fiber. Although this method achieves the separate extraction of insoluble and soluble dietary fiber, the use of acid soaking makes the degradation degree difficult to control, and the disposal of waste acid causes environmental pollution, which is inconsistent with the current concept of green development.

[0004] Compared with other methods, the preparation of cellulose using deep eutectic solvent (DES) has a better effect on separating lignocellulose and is non-toxic, harmless, and environmentally friendly. MA et al. (MA CY, XU LH, ZHANG C, et al. A synergistic hydrothermal-deep eutectic solvent (DES) pretreatment for rapid fractionation and targeted valorization of hemicelluloses and cellulose from poplar wood[J]. Bioresour Technol, 2021, 341:125828.) developed a method using superheated water and a ternary deep eutectic solvent system for stepwise treatment, which can preferentially dissociate hemicellulose in poplar wood and then remove lignin, while retaining the cellulose-rich substrate. However, this method still requires pressurization and microwave assistance, and the cellulose microstructures corresponding to different types of raw materials are different, so the deep eutectic solvent treatment parameters cannot be simply replicated.

[0005] In addition, the invention patent application with publication number CN 109468872 A, entitled "Method for Extracting and Separating Loofah Cellulose Using Choline-Based Eutectic Solvents", specifically discloses "(1) treating with a benzene-alcohol mixture to obtain benzene-alcohol-extracted loofah powder; (2) preparing a choline-based eutectic solvent using choline chloride and oxalic acid; (3) preparation of loofah cellulose: adding the benzene-alcohol-extracted loofah powder to the choline-based eutectic solvent, reacting at 50-65℃ for 30-50 min, then reacting at 80-100℃ for 2-4 h, naturally cooling to room temperature, ultrasonic treatment, then centrifugation, washing the precipitate obtained by centrifugation with deionized water, and then drying to obtain loofah cellulose". However, this method requires organic solvent pretreatment of the plant raw materials to remove resin and fat components from the raw materials.

[0006] Therefore, it is urgent to optimize and improve existing methods for extracting cellulose from Sichuan pepper seeds, in order to achieve efficient and green extraction of cellulose from Sichuan pepper seeds and promote the biomass conversion and application of Sichuan pepper seeds. Summary of the Invention

[0007] To address the problems of conventional chemical acid reduction methods and eutectic solvent treatments for preparing cellulose from Sichuan pepper seeds, which involve significant environmental impact from acid-base treatments and high consumption of organic reagents, failing to meet current green development requirements, this invention provides a method for preparing cellulose from Sichuan pepper seeds using ultrafine grinding and eutectic solvents. This method introduces ultrafine grinding technology to physically modify and pretreat Sichuan pepper seeds, increasing their specific surface area while disrupting the interactions between cellulose molecules and promoting the interaction between the eutectic solvent system and the seeds. Simultaneously, a choline chloride-oxalic acid binary eutectic solvent system is optimally selected for treating the ultrafine Sichuan pepper seed powder. Extensive experiments have been conducted to optimize the eutectic solvent system treatment parameters, resulting in cellulose with high purity and significantly higher water and oil holding capacity than cellulose prepared by conventional chemical acid-base methods.

[0008] The technical solution adopted in this invention is as follows:

[0009] A method for preparing Sichuan pepper seed cellulose using ultrafine grinding-assisted eutectic solvent, the method comprising:

[0010] Sichuan pepper seeds were pretreated by ultrafine grinding to obtain ultrafine Sichuan pepper seed powder;

[0011] The ultrafine powder of Sichuan pepper seeds was treated with a eutectic solvent system to dissolve hemicellulose and lignin, resulting in a reaction slurry.

[0012] The reaction slurry was centrifuged, the precipitate was collected, and the precipitate was washed and dried to obtain pepper seed cellulose.

[0013] Furthermore, the preferred ultrafine powder pretreatment time is 5-20 min to obtain the particle size D of the Sichuan pepper seed ultrafine powder. 50 It is 7-16 μm;

[0014] By controlling the ultrafine pulverization pretreatment conditions to a pulverization time of 5-20 min (e.g., 5 min, 10 min, 15 min, 20 min), the average particle size D of the pepper seed ultrafine powder can be controlled. 50 Distributed in the range of 7-16 μm, it increases the surface area of ​​the ultrafine powder of Sichuan pepper seeds and weakens the interaction between cellulose molecules, while ensuring that the ultrafine powder of Sichuan pepper seeds does not agglomerate.

[0015] Furthermore, in the process of treating the ultrafine powder of Sichuan pepper seeds using a eutectic solvent system, the eutectic solvent treatment conditions are optimized and screened based on the cellulose retention rate, hemicellulose and lignin removal rate. The preferred conditions are: eutectic solvent is prepared using choline chloride as hydrogen bond acceptor and oxalic acid as hydrogen bond donor, with a molar ratio of choline chloride to oxalic acid of 1:(2-3) (e.g., 1:2, 1:2.2, 1:2.5, 1:3); the two components are mixed and then directly heated until the system is homogeneous and transparent, and then cooled at room temperature to form the eutectic solvent system.

[0016] Using the aforementioned hydrogen acceptor and hydrogen donor ensures the solvent is green and non-toxic, and the introduction of oxalic acid facilitates the anhydrous formation of cellulose oxalate, which is beneficial for the further preparation of Sichuan pepper seed nanocellulose. The preparation of nanocellulose using cellulose oxalate has been disclosed in relevant literature and will not be repeated here. Furthermore, using the aforementioned molar mass ratio can reduce the viscosity of the system as much as possible while ensuring the high conductivity of the binary eutectic solvent, thereby improving the convenience of Sichuan pepper seed cellulose preparation.

[0017] The ratio of the ultrafine Sichuan pepper seed powder to the eutectic solvent is controlled to be 1:(15-30) (e.g., 1:15, 1:17, 1:20, 1:30), in g / mL, and treated at 70℃ or above or in a boiling water bath for 5-6 hours (e.g., 5 hours, 5.3 hours, 5.5 hours, 6 hours). The ultrafine Sichuan pepper seed powder is directly mixed with the binary eutectic solvent system. The treatment of the ultrafine Sichuan pepper seed powder with the aforementioned eutectic solvent is examined to determine whether it can maximize the removal of lignin and hemicellulose while retaining cellulose.

[0018] Further, the reaction slurry is centrifuged at 6000-1000 r / min for 10-15 min; after centrifugation, the precipitate is collected, repeatedly washed with deionized water until neutral, and then dried or freeze-dried to obtain pepper seed cellulose.

[0019] Furthermore, the cellulose in the Sichuan pepper seeds has a type I structure, with a cellulose retention rate as high as 89%, a crystallinity of 62.61%, and an average particle size D. 50It is 16.3 μm.

[0020] Beneficial technical effects of the present invention:

[0021] The method provided by this invention introduces a physical modification pretreatment technique for ultrafine grinding. The modified Sichuan pepper seed ultrafine powder is directly treated with a eutectic solvent, making the process simple. The Sichuan pepper seed cellulose obtained by the method provided by this invention has significantly higher purity than that obtained by conventional acid subtraction methods and exhibits good water and oil holding capacity. Furthermore, the entire Sichuan pepper seed cellulose preparation process requires no additional organic solvents or acid / alkali treatments, making it environmentally friendly. The presence of cellulose oxalate structures in the cellulose prepared by this invention will facilitate the further preparation of Sichuan pepper seed nanocellulose. Attached Figure Description

[0022] Figure 1 This illustrates the effect of ultrafine grinding on the crystallinity of Sichuan pepper seeds in this embodiment of the invention.

[0023] Figure 2 This is a graph showing the effect of ultrafine grinding treatment on the water / oil holding capacity of Sichuan pepper seed ultrafine powder in an embodiment of the present invention;

[0024] Figure 3 The effects of different DES systems on the treatment of Sichuan pepper seed ultrafine powder in the embodiments of the present invention;

[0025] Figure 4 This invention illustrates the effect of DES on ultrafine powder of Sichuan pepper seeds with different particle sizes in this embodiment.

[0026] Figure 5 The effects of different DES ratios on the treatment of Sichuan pepper seed ultrafine powder in the embodiments of the present invention;

[0027] Figure 6 This invention illustrates the effect of the material-to-liquid ratio on the DES-treated ultrafine powder of Sichuan pepper seeds in this embodiment.

[0028] Figure 7 XRD results of Sichuan pepper seed cellulose corresponding to different processing methods of the present invention;

[0029] Figure 8 Infrared results of Sichuan pepper seed cellulose under different processing methods according to the present invention. Detailed Implementation

[0030] The embodiments of the present invention are described in detail below. The embodiments described below are exemplary and are only used to explain the present invention, and should not be construed as limiting the present invention. To further illustrate the technical means and effects adopted by the present invention to achieve the intended inventive objective, the specific implementation methods, structures, features, and effects according to the present invention are described in detail below with reference to the accompanying drawings and preferred embodiments.

[0031] The ultrafine pulverizer used in this invention is the BFM-6B ultrafine pulverizing vibration mill from Jinan Beili Powder Engineering Technology Co., Ltd.

[0032] This invention provides a method for preparing Sichuan pepper seed cellulose using ultrafine grinding and a eutectic solvent, comprising the following steps: pre-treating Sichuan pepper seeds with ultrafine grinding to obtain Sichuan pepper seed ultrafine powder; preparing a eutectic solvent system, mixing the Sichuan pepper seed ultrafine powder with the eutectic solvent system, centrifuging the mixture, and collecting the precipitate; washing and drying the precipitate to obtain Sichuan pepper seed cellulose. The above preparation method is simple to operate, does not involve acids, alkalis, or organic solvents, and is environmentally friendly.

[0033] The following are specific examples:

[0034] Example 1: A method for preparing Sichuan pepper seed cellulose using ultrafine grinding-assisted eutectic solvent:

[0035] (1) Commercially available green Sichuan pepper seeds were directly processed using an ultrafine pulverizer for 10 minutes. The average particle size D of the resulting ultrafine Sichuan pepper seed powder was... 50 It is 10.6 μm;

[0036] (2) Mix choline chloride and oxalic acid at a molar mass ratio of 1:2.2, heat directly until transparent, and cool to room temperature to obtain a binary eutectic solvent system;

[0037] (3) Mix the ultrafine powder of Sichuan pepper seeds with the above eutectic solvent system at a ratio of 1:17 (g / mL) and react for 5 hours under boiling water bath conditions to obtain Sichuan pepper seed reaction slurry.

[0038] (4) Cool the above reaction slurry to room temperature, centrifuge at 8000 r / min for 12 min, and collect the precipitate for later use;

[0039] (5) The above precipitate was repeatedly washed with deionized water until neutral, and dried at low temperature to obtain pepper seed cellulose A.

[0040] Example 2: A method for preparing Sichuan pepper seed cellulose using ultrafine grinding-assisted eutectic solvent:

[0041] (1) Commercially available green Sichuan pepper seeds were directly processed using an ultrafine pulverizer for 5 minutes. The average particle size D of the resulting ultrafine Sichuan pepper seed powder was... 50 It is 15.8 μm;

[0042] (2) Mix choline chloride and oxalic acid in a molar mass ratio of 1:2, heat directly until transparent, and cool to room temperature to obtain a binary eutectic solvent system.

[0043] (3) Mix the ultrafine powder of Sichuan pepper seeds with the above eutectic solvent system at a ratio of 1:20 (g / mL) and react at 90℃ for 5.8h to obtain Sichuan pepper seed reaction slurry.

[0044] (4) Cool the above reaction slurry to room temperature, centrifuge at 7000 r / min for 13 min, and collect the precipitate for later use;

[0045] (5) The above precipitate was repeatedly washed with deionized water until neutral, and dried at low temperature to obtain pepper seed cellulose.

[0046] Example 3: A method for preparing Sichuan pepper seed cellulose using ultrafine grinding-assisted eutectic solvent:

[0047] (1) Commercially available green Sichuan pepper seeds were directly processed using an ultrafine pulverizer for 20 minutes. The average particle size D of the resulting ultrafine Sichuan pepper seed powder was... 50 It is 7.7 μm;

[0048] (2) Mix choline chloride and oxalic acid in a molar mass ratio of 1:3, heat directly until transparent, and cool to room temperature to obtain a binary eutectic solvent system.

[0049] (3) Mix the ultrafine powder of Sichuan pepper seeds with the above eutectic solvent system at a ratio of 1:15 (g / mL) and react at 70°C for 6 hours to obtain Sichuan pepper seed reaction slurry.

[0050] (4) Cool the above reaction slurry to room temperature, centrifuge at 10000 r / min for 10 min, and collect the precipitate for later use;

[0051] (5) The above precipitate was repeatedly washed with deionized water until neutral, and dried at low temperature to obtain pepper seed cellulose.

[0052] Example 4: A method for preparing Sichuan pepper seed cellulose using ultrafine grinding-assisted eutectic solvent:

[0053] (1) Commercially available green Sichuan pepper seeds were directly processed using an ultrafine pulverizer for 10 minutes. The average particle size D of the resulting ultrafine Sichuan pepper seed powder was... 50 It is 10.6 μm;

[0054] (2) Mix choline chloride and oxalic acid at a molar mass ratio of 1:2.5, heat directly until transparent, and cool to room temperature to obtain a binary eutectic solvent system;

[0055] (3) Mix the ultrafine powder of Sichuan pepper seeds with the above eutectic solvent system at a ratio of 1:30 (g / mL) and react for 5 hours under boiling water bath conditions to obtain Sichuan pepper seed reaction slurry.

[0056] (4) Cool the above reaction slurry to room temperature, centrifuge at 6000 r / min for 15 min, and collect the precipitate for later use;

[0057] (5) The above precipitate was repeatedly washed with deionized water until neutral, and dried at low temperature to obtain pepper seed cellulose.

[0058] Comparative Example: A conventional acid reduction method for preparing cellulose from Sichuan pepper seeds:

[0059] A certain amount of Sichuan pepper seed ultrafine powder (same as in Example 1) was taken and mixed with 5% NaOH solution at a material-to-liquid ratio of 1:20 (g / mL). The mixture was stirred and reacted at 70℃ for 2 hours, then cooled to room temperature. The precipitate was collected by centrifugation at 8000 r / min for 12 minutes and washed repeatedly with distilled water until neutral. The collected precipitate was bleached with 5% sodium chlorite. During the bleaching process, the pH of the solution was adjusted to 4 with glacial acetic acid. The mixture was reacted at 70℃ for 2 hours, centrifuged at 8000 r / min for 12 minutes, and washed repeatedly with distilled water until neutral. The precipitate was then dried at low temperature to obtain Sichuan pepper seed cellulose B.

[0060] This invention involved extensive experiments to optimize the preparation method of Sichuan pepper seed cellulose, and evaluated the Sichuan pepper seed cellulose obtained by this invention using Sichuan pepper seed fiber obtained by conventional chemical acid subtraction method as a control. The Sichuan pepper seed powder raw material used in this invention contains 35% cellulose, 18.56% hemicellulose, and 20.83% lignin. The specific research process is as follows:

[0061] 1. Experimental Methods

[0062] This invention optimizes and screens the preparation conditions of Sichuan pepper seed ultrafine powder, the selection of eutectic solvent system, and the process conditions for treating Sichuan pepper seed ultrafine powder with eutectic solvent system.

[0063] Cellulose content determination method: Weigh 0.05g of raw material, add 5mL of a 2:1 mixture of acetic acid and nitric acid, shake well, and boil in a water bath for 25min. After cooling, centrifuge and discard the supernatant. Wash three times with distilled water. Add 10mL of 10% sulfuric acid and 10mL of 0.1mol / L potassium dichromate solution to the precipitate, shake well, and boil in a water bath for 10min. After cooling, add 5mL of 20% potassium iodide solution and 1mL of 0.5% starch solution, and titrate with 0.2mol / L sodium thiosulfate solution until the solution turns dark green. Use 10mL of 10% sulfuric acid and 10mL of 0.1mol / L potassium dichromate solution as blank controls.

[0064] Method for determining hemicellulose content: Weigh 0.05g of raw material, add 15mL of 80% calcium nitrate solution, heat to boiling for 5min, centrifuge to collect the precipitate, wash the precipitate three times with hot distilled water, add 10mL of 2mol / L hydrochloric acid, boil in a water bath for 45min, centrifuge to collect the supernatant, transfer the supernatant to a 100mL volumetric flask, wash the precipitate three times with 10mL of distilled water, combine the washings in the volumetric flask, add phenolphthalein, and neutralize with 2mol / L sodium hydroxide solution until orange-red. Take 1mL of the filtrate and 2mL of DNS reagent, boil in water for 5min, measure the absorbance at 540nm, and substitute the absorbance into the glucose standard curve to obtain the hemicellulose content.

[0065] Lignin content determination: Weigh 0.05g of raw material, add 10mL of 1% glacial acetic acid, shake well, centrifuge to collect the precipitate, wash the precipitate once with 5mL of 1% glacial acetic acid, soak the precipitate in 4mL of acetone for 3min, filter, and repeat the soaking and washing 3 times; after the acetone has completely evaporated, add 3mL of 75% sulfuric acid, let it stand at room temperature for 12h, add 10mL of distilled water, boil in a water bath for 5min, cool, add 0.5mL of 10% barium chloride solution, shake well, centrifuge, wash twice with distilled water, then add 10mL of 0.1mol / L potassium dichromate solution and 10mL of 10% sulfuric acid to the precipitate, boil in a water bath for 15min, cool, add 5mL of 20% potassium iodide and 0.5% starch solution, and titrate with sodium thiosulfate solution.

[0066] Particle size distribution of Sichuan pepper seed ultrafine powder and fiber: The particle size was determined using a Mastersizer 2000 laser particle size analyzer and a wet particle size testing system. The samples were ultrasonically dispersed before measurement.

[0067] Water-holding capacity test method: Weigh 1.00g of sample into a centrifuge tube, add 20mL of deionized water, shake to mix, and incubate in a constant temperature water bath at 60℃ for 40min. After cooling to room temperature, centrifuge at 4000r / min for 20min, discard the supernatant, and blot the residual liquid with filter paper. Record its mass.

[0068]

[0069] Oil holding capacity test method: Weigh 0.5g of pepper seed powder and place it in a centrifuge tube. Add 4mL of peanut oil, shake to mix, and then incubate in a constant temperature water bath at 37℃ for 1h. After cooling to room temperature, centrifuge at 4000r / min for 20min. Discard the upper layer of peanut oil and blot dry the residual oil with filter paper. Record its mass.

[0070]

[0071] The crystallinity and morphology of cellulose from Sichuan pepper seeds were analyzed using X-ray powder diffraction and a SU8020 field emission scanning electron microscope. The X-ray powder diffraction equipment parameters were set as follows: current 40 mA, tube voltage 40 kV, scanning speed 3° / min, and scanning range 3–50°.

[0072] Changes in the chemical groups of cellulose were analyzed using a Nicolet IS10 Fourier transform infrared (FTIR) spectrometer (USA). Small amounts of cellulose samples were weighed, mixed with a measured amount of KBr, ground evenly in an agate mortar, pressed into pellets, and then analyzed using a Fourier transform infrared spectrometer. The instrument scanning range was 400–4000 cm⁻¹. -1 Spatial resolution is 4cm -1 .

[0073] 2. Experimental Results

[0074] (1) As shown in Table 1, the average particle size D of Sichuan pepper seed powder is 50 From largest to smallest, the particle size was coarse powder > ZBSM-SG3 > ZBSM-SG5 > ZBSM-SG10 > ZBSM-SG25 > ZBSM-SG20. With increasing ultrafine grinding time, the particle size of the Sichuan pepper seed powder decreased significantly. However, with prolonged grinding time, ZBSM-SG25 exhibited powder agglomeration, accompanied by a decrease in specific surface area. Specifically, ZBSM-SG3, ZBSM-SG5, ZBSM-SG10, ZBSM-SG20, and ZBSM-SG25 were obtained after grinding for 3, 5, 10, 20, and 25 minutes, respectively, resulting in ultrafine Sichuan pepper seed powder; CK represents conventionally ground Sichuan pepper seed powder.

[0075] Table 1. Effect of different grinding times on the particle size of Sichuan pepper seed ultrafine powder

[0076]

[0077] Therefore, in this invention, ultrafine grinding is used to pre-treat the raw material of Sichuan pepper seeds to obtain ultrafine Sichuan pepper seed powder; the conditions for controlling the ultrafine grinding pre-treatment are a grinding time of 5-20 min (e.g., 5 min, 10 min, 15 min, 20 min). Using the above-mentioned ultrafine grinding time can control the average particle size D of the ultrafine Sichuan pepper seed powder. 50 Distributed in the range of 7-16 μm, it increases the surface area of ​​the ultrafine powder of Sichuan pepper seeds and weakens the interaction between cellulose molecules, while ensuring that the ultrafine powder of Sichuan pepper seeds does not agglomerate.

[0078] (2) By Figure 1It can be seen that the crystallinity of coarse Sichuan pepper seed powder (CK) is 6.33%. The crystallinity slightly increases after ultrafine grinding, but decreases slightly with prolonged grinding time, reaching 8.08% at ZBAM-SG25. Overall, the crystallinity of Sichuan pepper seed powder is relatively low. Ultrafine grinding mainly acts on the surface of the amorphous and crystalline regions of cellulose, having a relatively small impact on the overall crystal structure of Sichuan pepper seed fibers. Figure 2 It can be seen that, compared with ordinary grinding, ultrafine grinding can significantly improve the water and oil holding capacity of pepper seed powder (P<0.05). The improvement in water and oil holding capacity is related to the larger specific surface area and relatively loose structure of pepper seed powder obtained by ultrafine grinding, which makes it easier to contact water / oil molecules.

[0079] (3) By Figure 3 It is known that using choline chloride (ChCl) as the hydrogen bond acceptor in a eutectic solvent system, six eutectic solvent systems were prepared: glycerol (an alcoholic hydrogen bond donor), phenol (a phenolic hydrogen bond donor), urea (an amine hydrogen bond donor), formic acid (a monocarboxylic acid hydrogen bond donor), oxalic acid (a dicarboxylic acid hydrogen bond donor), and citric acid (a tricarboxylic acid hydrogen bond donor). These systems were categorized as choline-glycerol (ChCl-G), choline-phenol (ChCl-P), choline-urea (ChCl-U), choline-formic acid (ChCl-FA), choline-oxalic acid (ChCl-OA), and choline-citric acid (ChCl-CA). The ChCl-OA system had the highest cellulose content at 69.58%. In terms of hemicellulose removal efficiency, the ChCl-OA system exhibited the highest removal efficiency, reaching 68.69%. The ChCl-FA system can also be tried in actual production.

[0080] (4) By Figure 4It can be seen that the ChCl-OA eutectic solvent system can remove hemicellulose and lignin from various Sichuan pepper seed ultrafine powder samples to varying degrees, and the removal rates of both are correlated with the particle size of the Sichuan pepper seed ultrafine powder. The removal rate of hemicellulose gradually increases with the increase of powder particle size, from 34.92% for coarse powder to 0.56% for ZBAM-SG 10. The hemicellulose removal rate of ZBAM-SG 20 increases slightly, and then the hemicellulose removal rate of ZBAM-SG 25 decreases significantly; the lignin removal rate also shows a similar trend. The reason for this phenomenon is that ultrafine grinding reduces the particle size of the Sichuan pepper seed powder, increases its specific surface area, and correspondingly increases the contact area with the eutectic solvent. This improves the reaction efficiency and more significantly disrupts the binding layer between lignin and hemicellulose and cellulose, causing hemicellulose and lignin to disintegrate from the fiber polymer. Therefore, the content of hemicellulose and lignin decreases. However, with further reduction in particle size, agglomeration occurs between the powder particles, which to some extent hinders the dissolution of lignin. Preferably, in this invention, the ultrafine grinding time of the Sichuan pepper seed powder is controlled within 5-20 minutes.

[0081] (5) By Figure 5 It was found that different ratios of eutectic solvent systems significantly affected the removal efficiency of hemicellulose and lignin in ultrafine Sichuan pepper seed powder. Specifically, as the proportion of oxalic acid increased, the cellulose content in the sample treated with the eutectic solvent gradually increased from 66.66% to 75.42%, while the contents of hemicellulose and lignin gradually decreased, from 5.82% to 4.32% and 11.25% to 8.38%, respectively. Subsequently, when the proportion of oxalic acid was further increased (1:4), the removal efficiency of hemicellulose and lignin decreased, which may be related to the acidity and conductivity of the system. Preferably, the molar ratio of choline chloride to oxalic acid was controlled at 1:(2-3).

[0082] (6) By Figure 6 It is known that the ratio of the DES low eutectic solvent system to the ultrafine powder of Sichuan pepper seeds significantly affects the preparation of cellulose from Sichuan pepper seeds. With increasing ratio, the cellulose content gradually increases from 65% to 75.25%, while the hemicellulose content significantly decreases from 10% to 4.80%, and the lignin content slightly decreases from 11.67% to 9%. From the perspective of cellulose content, there is no significant difference between samples treated with ratios of 1:15, 1:20, 1:30, and 1:40 g / mL. Considering the actual production situation, the preferred ratio of ultrafine powder of Sichuan pepper seeds to the low eutectic solvent system is 1:(15-30) g / mL.

[0083] The cellulose retention rate of Sichuan pepper seed cellulose A obtained by the method of this invention is 89.24%, and the average particle size is approximately 16.30 μm, which is higher than the 66.58% cellulose retention rate of Sichuan pepper seed cellulose B obtained by the conventional chemical acid-base method, and close to its average particle size of 6.10 μm. Analysis of the crystal structure of Sichuan pepper seed cellulose is as follows... Figure 7 It can be seen that the ultrafine powder CK of Sichuan pepper seeds shows two obvious diffraction peaks near 2θ = 12 and 22.3°, corresponding to the

[101] crystal plane of cellulose type II and the

[002] crystal plane of cellulose type I structure, respectively, which is a transitional structure of cellulose type I / II; cellulose A and cellulose B both show obvious diffraction peaks near 2θ = 14.44, 22.3 and 34.9°, with sharp peak shapes, corresponding to the

[101] ,

[002] and

[040] crystal planes of cellulose type I structure, respectively, that is, Sichuan pepper seed cellulose is a cellulose type I structure; indicating that the Sichuan pepper seed cellulose prepared by both conventional and DES methods retains the original cellulose I configuration, of which the crystallinity of cellulose A is 62.61% and the crystallinity of cellulose B is 44.4%, indicating that the DES system provided by the present invention has a better destructive effect on the amorphous region of Sichuan pepper seed cellulose and can retain most of the crystalline region in cellulose; in addition, Figure 8 Infrared results show that, compared with cellulose B obtained by conventional methods, cellulose A obtained by this invention has a lower chromaticity at 738 cm⁻¹. -1 There is a characteristic absorption peak at this point, which corresponds to the absorption peak formed by the overlap of the carbonyl group of the ester and the carbonyl group of the carboxylic acid. This is a typical characteristic peak of cellulose dicarboxylic acid half ester, indicating that an esterification reaction occurs between oxalic acid and cellulose in a eutectic solvent system to generate dicarboxylic acid half ester, forming cellulose oxalate, which is more conducive to the preparation of pepper seed nanocellulose.

[0084] Regarding water and oil holding capacity, as shown in Table 2, the water holding capacity of Sichuan pepper seed cellulose A reaches 7.63±0.68 g / g, and the oil holding capacity reaches 4.37±0.95 g / g. The water and oil holding capacity of Sichuan pepper seed cellulose A obtained according to the present invention is significantly higher than that of Sichuan pepper seed ultrafine powder, and significantly higher than that of Sichuan pepper seed cellulose B prepared by conventional acid-base method.

[0085] Table 2. Water-holding / oil-holding capacity analysis of Sichuan pepper seed cellulose.

[0086]

[0087] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make some modifications or alterations to the above-disclosed technical content to create equivalent embodiments without departing from the scope of the present invention. Any simple modifications, equivalent changes and alterations made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the scope of the present invention.

Claims

1. A method for preparing Sichuan pepper seed cellulose using ultrafine grinding-assisted eutectic solvent, characterized in that, The specific steps are as follows: Sichuan pepper seeds were pretreated by ultrafine grinding to obtain ultrafine Sichuan pepper seed powder; the ultrafine grinding time was 5-20 min; the particle size D of the ultrafine Sichuan pepper seed powder was... 50 It is 7-16 μm; The ultrafine powder of Sichuan pepper seeds was treated with a eutectic solvent system to dissolve hemicellulose and lignin, resulting in a reaction slurry. The hydrogen acceptor in the eutectic solvent system was choline chloride, and the hydrogen donor was oxalic acid. Choline chloride and oxalic acid were mixed in a specific ratio and heated and stirred until a homogeneous and transparent system was formed. The molar ratio of choline chloride to oxalic acid was 1:(2-3). The ratio of the ultrafine powder of Sichuan pepper seeds to the eutectic solvent system was 1:(15-30) g / mL. The ultrafine powder of Sichuan pepper seeds was treated with the eutectic solvent system at a temperature above 70°C to a boiling water bath for 5-6 hours. The reaction slurry was centrifuged, the precipitate was collected, and the precipitate was washed and dried to obtain pepper seed cellulose.

2. The method for preparing Sichuan pepper seed cellulose using ultrafine grinding-assisted eutectic solvent according to claim 1, characterized in that, The reaction slurry was centrifuged at 6000-10000 r / min for 10-15 min; after centrifugation, the precipitate was collected, repeatedly washed with deionized water until neutral, and dried to obtain pepper seed cellulose.

3. The method for preparing Sichuan pepper seed cellulose using ultrafine grinding-assisted eutectic solvent according to claim 1 or 2, characterized in that, The cellulose in the Sichuan pepper seeds has a type I structure, with a cellulose retention rate as high as 89%, a crystallinity of 62.61%, and an average particle size D. 50 It is 16.3 μm.

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