A method of extracting plant fibers at low temperature using an electrically driven deep eutectic solvent system

Abstract

The application discloses a kind of plant fiber raw material pretreatment methods of electrically driven deep eutectic solvent, work electrode, auxiliary electrode, reference electrode are placed into electrolytic cell to form three-electrode electrolysis device, and deep eutectic solvent (DES) is added into electrolytic cell as pretreatment liquid;Plant fiber raw material is added to pretreatment liquid and electrolysis is carried out;After electrolysis is completed, the prepared fiber is washed and dried;After plant fiber extraction is completed, DES in pretreatment liquid is recovered and then used for plant fiber extraction again.Compared with the process of traditional plant fiber extraction using only deep eutectic solvent, the temperature required in the reaction process of the method is lower, the reaction time is relatively shorter, in the extracted plant fiber, not only the content of lignin is lower (the removal rate of lignin is high), but also the damage of DES to fiber polymerization degree and strength is smaller, the selectivity of system can be regulated by controlling voltage and other electrolysis parameters, and then the chemical composition of the prepared fiber can be regulated.

Description

Technical Field

[0001] This invention relates to a method for extracting plant fibers at low temperatures using an electrically driven eutectic solvent system, belonging to the field of natural fiber extraction and utilization. Background Technology

[0002] Plant fiber raw materials (PFMs, such as hemp, cotton stalk bark, sugarcane bagasse, bamboo, etc.) are the world's largest renewable resource, mainly composed of cellulose and its byproducts (hemicellulose, lignin, pectin, etc.). After processing (physical, chemical, biological, etc.), most of the cellulose byproducts are removed, allowing cellulose to be separated into fibers of various lengths and finenesses. These fibers, replacing petrochemical resources, are used in textiles, papermaking, nanomaterials / composite materials, cellulose enzymatic hydrolysis, fermentation, and other fields, playing a significant role in achieving peak carbon emissions and carbon neutrality.

[0003] In recent years, the method of pretreating plant fiber raw materials using low eutectic solvents (DES) has received increasing attention due to its advantages such as extremely low water consumption, environmental friendliness, and ease of separation and recovery of dissolved components. DES is a deep eutectic mixture composed of hydrogen bond acceptors (HBA) and hydrogen bond donors (HBD). Adjusting the types of HBA and HBD can regulate the deconstruction ability of DES on various chemical components in PFMs. Existing DES pretreatment systems can successfully separate PFM components, but they have low selectivity for removing cellulose byproducts; that is, the lignin removal rate is low after treatment, or the treatment process easily causes a large amount of cellulose degradation and damage. For example, alkaline DES systems such as choline chloride / urea can remove most of the hemicellulose under the condition that only 5% of the cellulose is degraded, but the lignin removal rate is low (<30%). Therefore, it is very effective for the pretreatment of ramie (lignin content <2%), but the treatment effect is poor for systems with high lignin content such as flax, hemp, bagasse, and straw, which often require auxiliary processes such as ultrasonic / microwave treatment and sodium hydroxide boiling to complete the process. Furthermore, alkaline DES systems such as choline chloride / urea require very high reaction temperatures (generally above 110℃) to extract plant fibers. Although acidic DES systems such as choline chloride / lactic acid and choline chloride / glycerol require lower temperatures (50-130℃) and achieve lignin removal rates exceeding 75%, they result in high cellulose degradation (>40%) and fiber fragmentation. Therefore, simply adjusting the composition, pH, and reaction temperature of the DES is insufficient for achieving efficient extraction of plant fiber raw materials. Consequently, it is necessary to develop a method for efficient plant fiber extraction at low temperatures. Summary of the Invention

[0004] The present invention aims to provide a method for extracting plant fibers at low temperature using an electrically driven eutectic solvent system, in order to solve the problems of excessively high temperatures, low lignin removal rates, or excessive cellulose degradation and damage in existing DES pretreatment systems.

[0005] To address the aforementioned technical problems, this invention provides a method for extracting plant fibers at low temperatures using an electrically driven eutectic solvent (DES) system, comprising the following steps:

[0006] Step (1): Place the working electrode, auxiliary electrode, and reference electrode into the electrolytic cell to form a three-electrode electrolysis device; add DES into the electrolytic cell as a pretreatment solution;

[0007] Step (2): Add the plant fiber raw material to the pretreatment solution for electrolysis;

[0008] Step (3): After electrolysis, wash and dry the resulting fibers.

[0009] After the plant fiber extraction is complete, the DES in the pretreatment solution can be recovered and reused for plant fiber extraction.

[0010] In one embodiment of the present invention, after the plant fiber extraction is completed, the DES in the pretreatment solution is electrolyzed to degrade the dissolved substances, and then it is used to continue the extraction of plant fibers.

[0011] In one embodiment of the present invention, in step (1), the eutectic solvent (DES) is prepared by mixing hydrogen bond donors and hydrogen bond acceptors in a certain proportion and then heating and stirring. The hydrogen bond donors include urea, thiourea, carboxylic acids (phenylacetic acid, malic acid, citric acid, succinic acid, etc.), polyols (ethylene glycol, glycerol, butanediol, xylitol, etc.), amino acids, sulfamic acid, sugars (glucose, fructose), trifluoroacetamide, etc. The hydrogen bond acceptors include, but are not limited to, quaternary ammonium salts (such as choline chloride) and zwitterions (such as betaine).

[0012] In one embodiment of the present invention, in step (1), the mass ratio of hydrogen bond acceptor and hydrogen bond donor mixed when configuring DES is 1:2 to 2:1; the heating and stirring temperature is 70 to 90°C.

[0013] In one embodiment of the present invention, in step (1), the eutectic solvent includes at least one of the following: choline chloride / benzoic acid mixture, choline chloride / benzoic acid / ethylene glycol mixture, choline chloride / urea mixture, choline chloride / glycerol mixture, choline chloride / oxalic acid mixture, choline chloride / lactic acid mixture, choline chloride / ethylene glycol mixture, betaine / oxalic acid / ethylene glycol mixture, choline chloride / 1,4-butanediol mixture, choline chloride / 1,2-propanediol mixture, and choline chloride / ethylene glycol / aluminum chloride mixture, but does not include choline chloride / citric acid mixture or choline chloride / betaine mixture.

[0014] From the perspective of hydrogen bond donor and acceptor combinations, the preferred eutectic solvents of this invention include at least one of the following: choline chloride / benzoic acid mixture, choline chloride / benzoic acid / ethylene glycol mixture, choline chloride / urea mixture, choline chloride / glycerol mixture, choline chloride / oxalic acid mixture, choline chloride / lactic acid mixture, choline chloride / ethylene glycol mixture, betaine / oxalic acid / ethylene glycol mixture, choline chloride / 1,4-butanediol mixture, choline chloride / 1,2-propanediol mixture, and choline chloride / ethylene glycol / aluminum chloride mixture. Among these, the choline chloride / benzoic acid mixture and the choline chloride / benzoic acid / ethylene glycol mixture gradually become solid or gel-like during electrolysis, but still maintain good extraction efficiency for plant fibers. The remaining solvents remain liquid throughout the electrolysis process and exhibit good plant fiber extraction efficiency. However, the solvents choline chloride / citric acid mixture and choline chloride / betaine mixture exhibit excessive viscosity during electrolytic treatment, making them unsuitable for extracting plant fibers.

[0015] In one embodiment of the present invention, step (1) further includes adding water to DES to reduce its viscosity and increase its conductivity, wherein the mass percentage of DES after adding water is less than 50%.

[0016] In one embodiment of the present invention, in step (2), the bath ratio of the plant fiber raw material to DES is 1:(10-80).

[0017] In one embodiment of the present invention, in step (1), the working electrode includes one of the following: an inorganic non-metallic electrode (e.g., an electrode made of glassy carbon, graphite, diamond, etc.), a metallic electrode (e.g., an electrode made of ruthenium titanium, lead dioxide, etc.), and a polymer electrode (e.g., a polypyrrole electrode).

[0018] In one embodiment of the present invention, in step (1), the working electrode includes one of a sheet electrode, a mesh electrode, a disc electrode, a foam electrode, and a gas diffusion electrode.

[0019] In one embodiment of the present invention, in step (1), the auxiliary electrode material includes platinum, nickel, graphite felt, etc.; the auxiliary electrode form includes sheet, foam, etc.; the working area of ​​the auxiliary electrode needs to be larger than the working area of ​​the working electrode.

[0020] In one embodiment of the present invention, in step (1), the reference electrode includes a calomel electrode, a standard hydrogen electrode, a silver / silver chloride electrode, etc.

[0021] In one embodiment of the present invention, in step (2), the electrolysis method includes cyclic voltammetry, linear scanning voltammetry, constant current electrolysis, etc.

[0022] In one embodiment of the present invention, in step (2), the minimum scanning range of the cyclic voltammetry is -2.0 to 2.0V (the maximum voltage must be higher than 2.0V), and the scanning voltage range of the linear scanning voltammetry is 2.0 to 8.0V.

[0023] In one embodiment of the present invention, in step (2), the electrolysis temperature is 25-80°C and the electrolysis time is 0.5-3.5h. The fiber extraction effect is best when the electrolysis temperature is 25-65°C.

[0024] In one embodiment of the present invention, after the plant fiber extraction is completed, the electrolysis conditions of DES in the pretreatment solution are the same as those during the plant fiber extraction.

[0025] In one embodiment of the present invention, the pretreatment solution can be recycled 5-7 times, and the quality indicators of the resulting fiber, such as strength, chemical composition, and enzymatic hydrolysis performance, decrease by no more than 5.0%.

[0026] The present invention also discloses a plant fiber extracted according to the above method.

[0027] This invention also discloses the use of the above-mentioned plant fibers in the fields of textiles, papermaking, nano / composite materials, cellulose enzymatic hydrolysis, and fermentation.

[0028] Beneficial effects:

[0029] 1. This invention uses an electrically driven eutectic solvent system to extract plant fibers at low temperatures. The process is pollution-free, has zero emissions, and consumes little or no water. The pretreatment solution can be recycled multiple times.

[0030] 2. The method of this invention requires a lower temperature and a shorter reaction time, which can significantly reduce energy consumption. At the same time, the plant fibers extracted by this invention not only contain a lower content of cellulose byproducts, such as lignin, hemicellulose, and pectin, but also have a high lignin removal rate, up to 83.5%, and a pectin removal rate, up to 92.6% or even 94.7%. The DES also causes less damage to the degree of polymerization and strength of the fibers (the bundle fiber strength of the obtained plant fibers can reach up to 73.8 cN / dtex). The selectivity of the system can be controlled by adjusting the electrolysis parameters such as voltage, thereby controlling the chemical composition of the obtained fibers. Attached Figure Description

[0031] Figure 1 This is a schematic diagram of the experimental apparatus for pretreating PFMs using an electrically driven eutectic solvent (DES) system according to the present invention, wherein 1 is the working electrode, 2 is the auxiliary electrode, 3 is the reference electrode, 4 is the pretreatment solution, and 5 is the plant fiber raw material. Detailed Implementation

[0032] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below in conjunction with the embodiments of this invention. Obviously, the described embodiments are only some, not all, of the embodiments of this invention. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0033] The flax used in this embodiment of the invention is Xinjiang flax, which contains 69% cellulose, 13.8% hemicellulose, and 7.5% lignin; the sugarcane used in bagasse is produced in Guangdong, China, and contains 40.5% cellulose, 27.8% hemicellulose, and 21.5% lignin.

[0034] In the embodiments and comparative examples of this invention, the conductivity, resistance, pH value and other parameters of DES were tested using a multi-parameter tester.

[0035] Chemical composition test of plant fiber: The chemical composition of the fibers was tested using the method of the National Renewable Energy Laboratory (NREL) in the United States, as follows:

[0036] (1) Weigh (0.3±0.005)g of the dried sample to be tested and record the mass m; accurately measure 3mL of 72% sulfuric acid and mix it with the sample to be tested, and stir and react in a water bath at 30℃ for 1h.

[0037] (2) After the reaction is complete, the liquid obtained in the previous step is transferred to a 150mL Erlenmeyer flask and 84mL of deionized water is added. The mixture is then reacted at 121℃ for 1h in an autoclave.

[0038] (3) After the reaction is complete, allow the sample to cool and separate into precipitate and supernatant. Take 10 mL of supernatant into a plastic centrifuge tube, add approximately 10 g of calcium carbonate solid to adjust the pH to neutral, centrifuge, and collect the supernatant. Filter the supernatant through a 0.22 μm organic filter membrane and place it in a liquid chromatography bottle for HPLC analysis of glucose, xylose, and arabinose content. Then calculate the cellulose and hemicellulose content using the formula. Filter the remaining reaction solution using a G4# sand core funnel, dry it to oven dryness at 105℃, cool and weigh it (m0). Then place it in a muffle furnace and ignite it at 550℃ for approximately 30 hours. Take it out and weigh it (m1). Determine the lignin content using the weight difference method. The calculation formula is as follows: Cellulose content = Glucose concentration × 87 × 10 -3 ×0.9 / 0.3×100; Hemicellulose content = (xylose concentration + arabinose concentration) ×87×10 -3 ×0.88 / 0.3×100; Lignin content = (m0-m1) / 0.3×100. Where, 0.9 is the conversion coefficient of cellulose to glucose; 0.88 is the conversion coefficient of cellulose to xylose and arabinose; 0.087 is the total volume (L) of acid hydrolysate during component determination; sugar concentration is in g / L; mass is in g.

[0039] The pectin test method was as follows: the pectin content was analyzed according to the method described in the national standard GB 5889-86 "Quantitative Analysis Method of Chemical Composition of Ramie".

[0040] Physical and mechanical performance testing:

[0041] (1) Fiber bundle strength: Referring to GB / T13783 "Determination of breaking strength of cotton fibers - flat bundle method", the fiber strength was tested using a YG011N fiber bundle strength tester (Strols tester). The fiber bundle strength was then calculated using the following formula:

[0042]

[0043] In the formula, P0 is the fiber bundle strength, cN / tex; P is the fiber bundle breaking strength, cN; L is the length of the cut fiber, mm; and G is the mass of the cut fiber, mg.

[0044] (2) Degree of aggregation:

[0045] The degree of polymerization of the fiber was tested according to FZ / T 50010.3-2011 "Determination of viscosity of pulp for viscose fiber". Each group of samples was tested 3 times and the average value was taken.

[0046] First, based on the outflow time (t) of the sample solution in the viscometer s Calculate the relative viscosity of the solution (ηrelative):

[0047] η 相对 =h×t s

[0048] In the formula: η is the relative viscosity; h is the viscometer constant; s -1 ;t s denoted as efflux time of the sample solution, in seconds.

[0049] Then, find the corresponding [η]·ρ value in the appendix table using the relative value of η. Calculate the solution viscosity ρ based on the sample mass and solution volume, and then determine the intrinsic viscosity [η] (expressed in mL / g). Finally, calculate the degree of polymerization of the fiber using the following formula:

[0050] DP 0.905 =0.75[η].

[0051] Cellulose enzymatic hydrolysis rate test: Weigh 0.5g of the sugarcane bagasse matrix to be tested (untreated sugarcane bagasse or sugarcane bagasse fiber from Examples 3-4) and place it in a 100mL shake flask. Add 25mL of citrate buffer (pH 4.8), and place it in a shaker (50℃, 180r / min) at a cellulase loading of 5FPU / g dry basis (enzyme type) for 72h of enzymatic hydrolysis. Take samples and detect the glucose concentration in the resulting enzymatic hydrolysate.

[0052] Example 1: Fiber extraction from flaxseed (diurnal grade)

[0053] Choline chloride and urea were mixed at a molar ratio of 1:2 and prepared as DES at 80°C. This DES was then used as the electrolyte for electro-driven DES extraction of plant fibers. 3g of coarse flax was added to an electrolytic cell; the electrolyte was prepared at a depth of 3×3cm. 2 The graphite plate is used as the working electrode, 4×4cm 2 A platinum sheet electrode was used as the auxiliary electrode, and a calomel electrode as the reference electrode. Electrolytic pretreatment was performed for 1.5 h at room temperature (55℃) using linear sweep voltammetry at a voltage of 2.2–2.3 V. After electrolysis, the pretreatment solution was recovered for reuse. The resulting fibers were washed and dried, and their chemical composition and physical and mechanical properties were tested. The results are shown in Table 1.

[0054] Example 2: Fiber extraction from flaxseed (with different DES compositions)

[0055] Choline chloride and ethylene glycol were mixed at a molar ratio of 1:2 and prepared as DES at 80°C. This DES was then used as the electrolyte for electro-driven DES extraction of plant fibers. 3g of coarse flax was added to an electrolytic cell; the electrolyte was prepared at a depth of 3×3cm. 2 The graphite plate is used as the working electrode, 4×4cm 2A platinum sheet electrode was used as the auxiliary electrode, and a calomel electrode as the reference electrode. Electrolytic pretreatment was performed for 1.5 h at room temperature (25℃) using linear sweep voltammetry at a voltage of 2.2–2.3 V. After electrolysis, the pretreatment solution was recovered for reuse. The resulting fibers were washed and dried, and their chemical composition and physical and mechanical properties were tested. The results are shown in Table 1.

[0056] Example 3: Fiber extraction from flaxseed (with different DES compositions)

[0057] Choline chloride and benzoic acid were mixed in a 1:1 molar ratio and prepared as DES at 80°C. This DES was then used as the electrolyte for electro-driven DES extraction of plant fibers. 3g of coarse flax was added to an electrolytic cell; the electrolyte was prepared at a depth of 3×3cm. 2 The graphite plate is used as the working electrode, 4×4cm 2 A platinum sheet electrode was used as the auxiliary electrode, and a calomel electrode as the reference electrode. Electrolytic pretreatment was performed for 1.5 h at room temperature (25℃) using linear sweep voltammetry at a voltage of 2.2–2.3 V. After electrolysis, the pretreatment solution was recovered for reuse. The resulting fibers were washed and dried, and their chemical composition and physical and mechanical properties were tested. The results are shown in Table 1.

[0058] Example 4: Fiber extraction from flaxseed (at different electrolysis temperatures)

[0059] Choline chloride and urea were mixed at a molar ratio of 1:2 and prepared as DES at 80°C. This DES was then used as the electrolyte for electro-driven DES extraction of plant fibers. 3g of coarse flax was added to an electrolytic cell; the electrolyte was prepared at a depth of 3×3cm. 2 The graphite plate is used as the working electrode, 4×4cm 2 A platinum sheet electrode was used as the auxiliary electrode, and a calomel electrode as the reference electrode. Electrolytic pretreatment was performed for 1.5 h at room temperature (25℃) using linear sweep voltammetry at a voltage of 2.2–2.3 V. After electrolysis, the pretreatment solution was recovered for reuse. The resulting fibers were washed and dried, and their chemical composition and physical and mechanical properties were tested. The results are shown in Table 1.

[0060] Example 5: Fiber extraction from flax (different voltages)

[0061] Choline chloride and urea were mixed at a molar ratio of 1:2 and prepared as DES at 80°C. This DES was then used as the electrolyte for electro-driven DES extraction of plant fibers. 3g of coarse flax was added to an electrolytic cell; the electrolyte was prepared at a depth of 3×3cm. 2 The graphite plate is used as the working electrode, 4×4cm 2A platinum sheet electrode was used as the auxiliary electrode, and a calomel electrode as the reference electrode. Electrolytic pretreatment was performed for 1.5 h at room temperature (55℃) using linear sweep voltammetry at a voltage of 4.1–4.2 V. After electrolysis, the pretreatment solution was recovered for reuse. The resulting fibers were washed and dried, and their chemical composition and physical and mechanical properties were tested. The results are shown in Table 1.

[0062] Example 6: Fiber extraction from flax mortis (using recycled DES)

[0063] The DES (without electrolysis) treated in Example 1 was recovered and used as the electrolyte for electro-driven DES plant fiber extraction, and continued to be used for plant fiber extraction. 3g of coarse flax was added to the electrolytic cell; at a depth of 3×3cm... 2 The graphite plate is used as the working electrode, 4×4cm 2 A platinum sheet electrode was used as the auxiliary electrode, and a calomel electrode as the reference electrode. Electrolytic pretreatment was performed for 1.5 h at room temperature (55℃) using linear sweep voltammetry at a voltage of 2.2–2.3 V. After electrolysis, the pretreatment solution was recovered for reuse. The resulting fibers were washed and dried, and their chemical composition and physical and mechanical properties were tested. The results are shown in Table 1.

[0064] Example 7: Fiber extraction from flax mortis (using recycled DES)

[0065] The DES recovered after treatment in Example 1, after electrolysis (using the same electrolysis parameters as for fiber extraction), was used as the electrolyte for electro-driven DES plant fiber extraction and continued to be used for plant fiber extraction. 3g of coarse flax was added to the electrolytic cell; at a depth of 3×3cm... 2 The graphite plate is used as the working electrode, 4×4cm 2 A platinum sheet electrode was used as the auxiliary electrode, and a calomel electrode as the reference electrode. Electrolytic pretreatment was performed for 1.5 h at room temperature (55℃) using linear sweep voltammetry at a voltage of 2.2–2.3 V. After electrolysis, the pretreatment solution was recovered for reuse. The resulting fibers were washed and dried, and their chemical composition and physical and mechanical properties were tested. The results are shown in Table 1.

[0066] Comparative Example 1: Non-electrochemically driven DES extraction of flax dicellulose

[0067] Choline chloride and urea were mixed at a molar ratio of 1:2 and prepared as DES at 80°C. This DES was then used for the extraction of plant fibers. 3g of coarse flax was added to the DES solution and heated to 150°C for 2.5h. The resulting fibers were then removed, washed, and dried. The chemical composition and physical and mechanical properties of the fibers were tested. The results are shown in Table 1.

[0068] Comparative Example 2: Non-electrochemically driven DES secondary extraction of flax

[0069] Choline chloride and oxalic acid were mixed at a molar ratio of 1:2 and prepared as DES at 80°C. This DES was then used for the extraction of plant fibers. 3g of coarse flax was added to the DES solution, heated to 60°C for 1.5h, and then the fibers were removed, washed, and dried. The chemical composition and physical and mechanical properties of the fibers were tested. The results are shown in Table 1.

[0070] Comparative Example 3: Electrochemical extraction of flax coarse fiber at voltages below 2V

[0071] Choline chloride and urea were mixed at a molar ratio of 1:2 and prepared as DES at 80°C. This DES was then used as the electrolyte for electro-driven DES extraction of plant fibers. 3g of coarse flax was added to an electrolytic cell; the electrolyte was prepared at a depth of 3×3cm. 2 The graphite plate is used as the working electrode, 4×4cm 2 A platinum sheet electrode was used as the auxiliary electrode, and a calomel electrode as the reference electrode. Electrolytic pretreatment was performed for 2.5 h at room temperature (55℃) using linear sweep voltammetry at a voltage of 0.5–0.7 V. After electrolysis, the pretreatment solution was recovered for reuse. The resulting fibers were washed and dried, and their chemical composition and physical and mechanical properties were tested. The results are shown in Table 1.

[0072] Table 1 Properties of flax dicerol extracted by electrochemically driven DES

[0073]

[0074] Example 8: Electrochemically driven DES extraction of sugarcane bagasse fiber and its enzymatic hydrolysis properties

[0075] Add DES (choline chloride / glycerol, molar ratio 1:1) and 5g of sugarcane bagasse to the electrolytic cell; dilute at a depth of 4×4cm. 2 The titanium mesh electrode is the working electrode, 4×4cm 2 A platinum sheet electrode was used as the auxiliary electrode, and a calomel electrode as the reference electrode. Electrolytic pretreatment was performed at 80℃ and 6.0V for 1.0h using linear sweep voltammetry. After electrolysis, the resulting fibers were washed and dried; the pretreatment solution was recovered. The chemical composition and enzymatic hydrolysis rate of the fibers were tested, and the results are shown in Table 2.

[0076] Example 9: Electrochemically driven DES extraction of sugarcane bagasse fiber and its enzymatic hydrolysis properties

[0077] Add DES composed of choline chloride / benzoic acid (molar ratio 2:1) and 5g of sugarcane bagasse to the electrolytic cell; dilute the electrolyte at a depth of 5×5cm. 2 The titanium mesh electrode is the working electrode, 5×5cm 2A platinum sheet electrode was used as the auxiliary electrode, and a calomel electrode as the reference electrode. Electrolytic pretreatment was performed at 80℃ using cyclic voltammetry at a voltage of -6.0 to 6.0 V for 1.0 h. After electrolysis, the resulting fibers were washed and dried; the pretreatment solution was recovered. The chemical composition and enzymatic hydrolysis rate of the fibers were tested. The results are shown in Table 2.

[0078] Comparative Example 4: Non-electrochemically driven DES extraction of sugarcane bagasse fiber and its enzymatic hydrolysis properties

[0079] A DES mixture composed of betaine and lactic acid (molar ratio 2:1) was used. 5 g of sugarcane bagasse was added to the DES mixture and treated at 130℃ for 2.5 h. The fiber chemical composition and enzymatic hydrolysis rate were then tested. The results are shown in Table 2.

[0080] Table 2 Properties of sugarcane bagasse fiber extracted by electrochemically driven DES

[0081] Lignin removal rate (%) Hemicellulose removal rate (%) Enzymatic hydrolysis rate (%) Room temperature conductivity (μs / cm) Example 8 82％ 33.3 92.3 957.2 Example 9 78％ 26.8 89.6 5045 Comparative Example 4 67.3％ 21.3 73.2 ——

[0082] Comparing Examples 1-7 with Comparative Examples 1-3, it can be seen that, compared with extracting plant fibers in a DES system, electrochemically driven DES can achieve the extraction of flax sub-coarse fibers at a lower temperature. At the same time, DES causes less damage to the degree of fiber polymerization and strength.

[0083] Comparative Examples 8-9 and Comparative Example 4 show that electrochemically driven DES can extract sugarcane bagasse fiber at a lower temperature, and its lignin removal rate and the enzymatic hydrolysis performance of the obtained fiber are better than those of conventional DES method (which only relies on adjusting the DES composition and reaction temperature).

Claims

1. A method of extracting plant fibers, characterized by, This method is a way to extract plant fibers at low temperatures using an electrically driven eutectic solvent system, and includes the following steps: (1) The working electrode, auxiliary electrode and reference electrode are placed in the electrolytic cell to form a three-electrode electrolysis device. The eutectic solvent DES is added to the electrolytic cell as a pretreatment solution. The eutectic solvent is composed of a hydrogen bond donor and a hydrogen bond acceptor. The hydrogen bond donor is selected from at least one of urea, thiourea, benzoic acid, ethylene glycol, glycerol, oxalic acid and lactic acid. The hydrogen bond acceptor is selected from at least one of choline chloride and betaine. (2) The plant fiber raw material is added to the pretreatment solution for electrolysis. The electrolysis temperature is 25~65℃ and the electrolysis time is 1.0~1.5h. The electrolysis method includes one of cyclic voltammetry, linear scanning voltammetry, and constant current electrolysis. The minimum value of the scanning voltage of the cyclic voltammetry is -2.0~2.0V, and the scanning voltage of the linear scanning voltammetry is 2.0~8.0V. (3) After electrolysis, the obtained fiber is washed and dried, and the bundle fiber strength of the plant fiber is not less than 65 cN / dtex. After the plant fiber extraction is complete, the DES in the pretreatment solution is recovered and reused for plant fiber extraction.

2. The method of claim 1, wherein, When preparing DES, the mass ratio of the hydrogen bond acceptor to the hydrogen bond donor is 1:2 to 2:1, and the heating and stirring temperature is 70 to 90°C.

3. The method according to claim 1 or 2, characterized in that, The working electrode includes one of inorganic non-metallic electrodes, metallic electrodes, and polymer electrodes. The shape of the working electrode includes one of sheet-like, mesh-like, disc-like, foam-like, and gas diffusion electrodes. The auxiliary electrode material includes one of platinum, nickel, and graphite felt. The reference electrode includes one of calomel electrode, standard hydrogen electrode, and silver / silver chloride electrode.

4. The method of claim 1, wherein, In step (2), the ratio of the plant fiber raw material to DES is 1:(10-80).

5. Plant fibers extracted by the method according to any one of claims 1 to 4.

6. The use of the plant fiber according to claim 5 in the fields of textiles, papermaking, nano / composite materials, cellulose enzymatic hydrolysis, and fermentation.

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