Eutectic solvent, preparation method thereof and application of eutectic solvent in lignocellulose separation

Abstract

The invention discloses a eutectic solvent, a preparation method thereof and application of the eutectic solvent in lignocellulose separation. The invention provides a deep-eutectic solvent. A preparation method of the deep-eutectic solvent comprises the following steps: stirring and mixing a hydrogen bond acceptor and a hydrogen bond donor until the mixture is transparent and uniform; the hydrogen bond acceptor is quaternary ammonium salt containing a benzene ring; the hydrogen bond donor is salicylic acid. The eutecticevaporate solvent provided by the invention has the capability of efficiently deconstructing lignocellulose, the deconstruction of lignocellulose can be realized in a short time (more than or equal to 5 minutes), the retention rate of cellulose can reach 80% or above, the removal rate of hemicellulose can reach 73% or above, the extraction rate of lignin can reach 66% or above, and the enzymolysis efficiency can reach 65% or above; the method solves the problems of low reaction efficiency, poor separation effect and low enzymolysis efficiency of the treated product when the existing eutectic solvent is used for treating the lignocellulose, and provides a high-efficiency, green, low-cost and easy-to-industrialize solution for high-value utilization of biomass resources.

Description

Technical Field

[0001] This invention relates to the field of efficient conversion and utilization technology of biomass resources, and more specifically, to a eutectic solvent and its preparation method, and its application in the separation of lignocellulose. Background Technology

[0002] Lignocellulose, as the most abundant renewable biomass resource in nature, is mainly composed of cellulose, hemicellulose, and lignin cross-linked by complex chemical bonds. Its efficient conversion and utilization are of great significance for the development of green energy and sustainable materials. However, lignocellulose's unique resistance to degradation makes it difficult to directly convert and utilize. Therefore, effectively breaking down this stubborn structure and achieving the separation and deconstruction of its components is a key prerequisite for converting it into bioenergy, high-value-added chemicals, and sustainable materials. Pretreatment technology is an indispensable first step in overcoming this barrier and paving the way for subsequent conversion.

[0003] To overcome this barrier, various mainstream pretreatment technologies have been explored, but all face significant limitations. Hydrothermal pretreatment (such as steam explosion and liquid hot water methods) relies on a high-temperature, high-pressure aqueous environment, which can hydrolyze hemicellulose to some extent. However, its lignin removal efficiency is generally low; lignin is prone to rearrangement and condensation rather than effective dissolution, which may hinder subsequent enzymatic cellulosic hydrolysis. More importantly, maintaining high-temperature, high-pressure conditions leads to huge energy consumption and generates large amounts of wastewater, resulting in high environmental and economic costs. Organic solvent methods (such as alcohols and organic acids) are more effective in dissolving lignin. However, their main challenges lie in the high cost of solvents, their often toxic or corrosive nature, and the complex recovery and purification processes (involving distillation, extraction, etc.). These factors significantly increase operating costs, equipment requirements, and safety risks, severely restricting the feasibility of large-scale industrial applications. In contrast, eutectic solvents (DES) have emerged as a new green solution for the selective decomposition of lignocellulose due to their ease of preparation, low toxicity, biodegradability, and low cost.

[0004] Chinese patent CN117604799A discloses a method for separating lignocellulose components. Specifically, it involves adding salicylic acid as a penetrant and forming a ternary eutectic solvent with hydrogen bond donors and acceptors to promote the degradation and dissolution of lignocellulose biomass components. However, this ternary eutectic solvent suffers from long reaction times and low separation capacity when treating lignocellulose, resulting in limited component separation and low enzymatic hydrolysis efficiency of the treated product.

[0005] Therefore, it is particularly important to develop a low eutectic solvent that can achieve efficient separation of various components of lignocellulose in a short time and produce a product with high enzymatic hydrolysis efficiency. Summary of the Invention

[0006] The purpose of this invention is to overcome the shortcomings or defects of existing eutectic solvents and provide a eutectic solvent. This eutectic solvent has the ability to efficiently decompose lignocellulose, and can achieve efficient separation of various components of lignocellulose in a short time, resulting in a product with high enzymatic hydrolysis efficiency.

[0007] To solve the above-mentioned technical problems, the present invention is achieved through the following technical solution: A eutectic solvent, wherein the method for preparing the eutectic solvent is to stir and mix a hydrogen bond acceptor and a hydrogen bond donor until the mixture is transparent and homogeneous; The hydrogen bond acceptor is a quaternary ammonium salt containing a benzene ring; the hydrogen bond donor is salicylic acid.

[0008] This invention selects salicylic acid as a hydrogen bond donor and a quaternary ammonium salt containing a benzene ring as a hydrogen bond acceptor, and prepares a eutectic solvent by uniformly mixing them together. The inventors discovered that a synergistic effect occurs between salicylic acid and the quaternary ammonium salt containing a benzene ring, giving the prepared eutectic solvent a unique selective dissolution ability for lignocellulose components.

[0009] To solve the above-mentioned technical problems, the present invention is achieved through another technical solution: A eutectic solvent, wherein the method for preparing the eutectic solvent is to stir and mix a hydrogen bond acceptor, a hydrogen bond donor, and a co-solvent until the mixture is transparent and homogeneous; The hydrogen bond acceptor is a quaternary ammonium salt containing a benzene ring; the hydrogen bond donor is salicylic acid; and the co-solvent is a C2-C6 diol.

[0010] The inventors discovered that adding a co-solvent can reduce the viscosity of the eutectic solvent system, promote the penetration of the solvent into the biomass and the diffusion of dissolved components, and further improve the separation efficiency of the eutectic solvent.

[0011] Preferably, the molar ratio of the hydrogen bond acceptor to the hydrogen bond donor to the co-solvent is 1:1:0.1~1.

[0012] More preferably, the molar ratio of the hydrogen bond acceptor to the hydrogen bond donor to the cosolvent is 1:1:0.3~0.7.

[0013] Preferably, the stirring temperature is 60~100℃.

[0014] Preferably, the stirring speed is 100~500 rpm.

[0015] The application of the aforementioned eutectic solvents in the separation of lignocellulose is also within the scope of protection of this invention.

[0016] The present invention provides a method for pretreating lignocellulose using a eutectic solvent, comprising the following steps: stirring and mixing the above-mentioned eutectic solvent with lignocellulose raw material to obtain a lignocellulose pretreated product.

[0017] Preferably, the lignocellulose raw material is one or more of sugarcane bagasse, wood, bamboo, corn cob, or straw.

[0018] More preferably, the lignocellulose raw material is sugarcane bagasse.

[0019] Those skilled in the art will know that lignocellulose raw materials need to be pulverized before reacting with eutectic solvents. The pulverization requirements for lignocellulose can refer to existing technologies; for example, the pulverized lignocellulose raw material can pass through a sieve of 80 mesh or less.

[0020] Preferably, the mass ratio of the lignocellulose raw material to the eutectic solvent is 1:10~20.

[0021] More preferably, the mass ratio of the lignocellulose raw material to the eutectic solvent is 1:15.

[0022] The inventors discovered that when too little eutectic solvent is added, the lignocellulose raw material cannot be completely dissolved, affecting its separation effect. When too much eutectic solvent is added, the solvent reaches saturation in dissolving the lignocellulose raw material, resulting in waste of the solvent.

[0023] Preferably, the reaction temperature is 130~180℃.

[0024] More preferably, the reaction temperature is 160~180°C.

[0025] As is known to those skilled in the art, when treating lignocellulose with eutectic solvents, while an excessively long reaction time may facilitate the dissolution of lignin and hemicellulose, it often results in excessive degradation or structural damage of the cellulose itself, leading to a significant decrease in cellulose retention. If the cellulose retention is too low, the overall application value of the treatment process will be greatly reduced.

[0026] Preferably, the reaction time is 5 to 360 minutes.

[0027] More preferably, the reaction time is 5 to 240 minutes.

[0028] More preferably, the reaction time is 5 to 120 minutes.

[0029] Most preferably, the reaction time is 30-120 min.

[0030] Those skilled in the art will know that stirring is necessary to improve reaction efficiency during the reaction of lignocellulose raw materials with a eutectic solvent. Preferably, the stirring speed is 100-150 rpm.

[0031] Those skilled in the art will know that after treating lignocellulose with a eutectic solvent, the lignocellulose pretreated product needs to be subjected to post-treatment such as stirring, filtration and washing with anhydrous ethanol to achieve solid-liquid separation and obtain eutectic solvent filtrate and eutectic solvent residue.

[0032] Preferably, the amount of anhydrous ethanol added is 2 to 6 times the volume of the lignocellulose pretreatment product.

[0033] More preferably, the amount of anhydrous ethanol added is three times the volume of the lignocellulose pretreatment product.

[0034] Preferably, the stirring temperature is 50~60℃.

[0035] Preferably, the stirring time is 1 to 2 hours.

[0036] Preferably, the stirring speed is 100~150 rpm.

[0037] The method for extracting regenerated lignin from eutectic solvent filtrate can refer to existing technologies, such as rotary evaporation to concentrate the eutectic solvent filtrate, allowing it to stand, filtering under reduced pressure, washing, and drying to obtain regenerated lignin.

[0038] Methods for obtaining cellulose from eutectic solvent filter residue can refer to existing technologies, such as centrifuging, washing, drying and pulverizing the eutectic solvent filter residue to obtain cellulose-rich residue.

[0039] Compared with the prior art, the beneficial effects of the present invention include: This invention provides a eutectic solvent, prepared by stirring and mixing a hydrogen bond acceptor and a hydrogen bond donor until transparent and homogeneous. The hydrogen bond acceptor is a quaternary ammonium salt containing a benzene ring, and the hydrogen bond donor is salicylic acid. The inventors discovered a synergistic effect between salicylic acid and the benzene ring-containing quaternary ammonium salt, resulting in a eutectic solvent with unique selective dissolution capabilities for lignocellulose components, enabling efficient decomposition of lignocellulose. The inventors also found that selecting C2-C6 diols as co-solvents, and stirring them together with the hydrogen bond acceptor and hydrogen bond donor until transparent and homogeneous, further enhances the eutectic solvent's ability to efficiently decompose lignocellulose. This is attributed to the fact that the addition of the co-solvent reduces the viscosity of the eutectic solvent system, promoting solvent penetration into the biomass and diffusion of dissolved components, thereby further improving its separation efficiency. The eutectic solvent provided by this invention can decompose lignocellulose in a short time (≥5 min), with a cellulose retention rate of over 80%, a hemicellulose removal rate of over 73%, a lignin extraction rate of over 66%, and an enzymatic hydrolysis efficiency of over 65%. This solves the problems of low reaction efficiency, poor separation effect, and low enzymatic hydrolysis efficiency of existing eutectic solvents for lignocellulose treatment. The eutectic solvent provided by this invention achieves a significant breakthrough in reaction efficiency and selectivity in lignocellulose separation processes, effectively reducing energy consumption and time costs, and providing an efficient, green, low-cost, and easily industrialized solution for the high-value utilization of biomass resources. Detailed Implementation

[0040] The present invention will be further described below with reference to embodiments and comparative examples. These embodiments are merely typical descriptions of the present invention, but the present invention is not limited thereto. Unless otherwise specified, the test methods used in the following embodiments and comparative examples are conventional methods, and the raw materials and reagents used are commercially available from conventional commercial sources.

[0041] The bagasse used in this embodiment and comparative example comes from Guangxi Guitang Group Co., Ltd., and is the residue left over from the sugar production process.

[0042] Example 1 This embodiment provides a method for preparing a eutectic solvent and a method for pretreating lignocellulose using a eutectic solvent, specifically including the following steps: S1. Weigh 1 mol of triethylbenzylammonium chloride and 1 mol of salicylic acid into a beaker, and stir at 80°C until homogeneous and transparent to obtain the eutectic solvent; S2. Weigh 8g of bagasse powder and 120g of eutectic solvent and place them in a reaction vessel. React at 140℃ and 100rpm for 60min to obtain the lignocellulose pretreated product.

[0043] Example 2 This embodiment provides a method for preparing a eutectic solvent and a method for pretreating lignocellulose using a eutectic solvent, specifically including the following steps: S1. Weigh 1 mol of triethylbenzylammonium chloride, 1 mol of salicylic acid and 0.5 mol of ethylene glycol into a beaker, and stir at 80°C until homogeneous and transparent to obtain the eutectic solvent; S2. Weigh 8g of bagasse powder and 120g of eutectic solvent and place them in a reaction vessel. React at 140℃ and 100rpm for 60min to obtain the lignocellulose pretreated product.

[0044] Examples 3-14 Examples 3-14 provide different methods for preparing eutectic solvents and methods for pretreating lignocellulose using eutectic solvents. The only difference from Example 2 is the reaction parameters in step S2. The specific differences are shown in Table 1 below.

[0045] Table 1. Reaction parameters for step S2 in Examples 2-14

[0046] Comparative Example 1 This comparative example provides a method for preparing a eutectic solvent and a method for pretreating lignocellulose using a eutectic solvent. The only difference from Example 2 is the type of hydrogen bond donor in step S1, specifically, salicylic acid is replaced with an equimolar amount of benzoic acid.

[0047] Comparative Example 2 This comparative example provides a method for preparing a eutectic solvent and a method for pretreating lignocellulose using a eutectic solvent. The only difference from Example 2 is the type of hydrogen bond donor in step S1, specifically, salicylic acid is replaced with an equimolar amount of phenylpropionic acid.

[0048] Comparative Example 3 This comparative example provides a method for preparing a eutectic solvent and a method for pretreating lignocellulose using a eutectic solvent. The only difference from Example 2 is the type of hydrogen bond donor in step S1, specifically, salicylic acid is replaced with an equimolar amount of p-hydroxybenzoic acid.

[0049] Comparative Example 4 This comparative example provides a method for preparing a eutectic solvent and a method for pretreating lignocellulose using a eutectic solvent. The only difference from Example 2 is the type of hydrogen bond donor in step S1, specifically, salicylic acid is replaced with an equimolar amount of m-hydroxybenzoic acid.

[0050] Comparative Example 5 This comparative example provides a method for preparing a ternary eutectic solvent and a method for pretreating lignocellulose using a ternary eutectic solvent. The only difference from Example 12 is the type of hydrogen bond donor in step S1, specifically, salicylic acid is replaced with an equimolar amount of lactic acid.

[0051] Comparative Example 6 This comparative example provides a method for preparing a ternary eutectic solvent and a method for pretreating lignocellulose using a ternary eutectic solvent. The only difference from Example 12 is the type of hydrogen bond donor in step S1, specifically, salicylic acid is replaced with an equimolar amount of oxalic acid.

[0052] Comparative Example 7 This comparative example provides a method for preparing a ternary eutectic solvent and a method for pretreating lignocellulose using a ternary eutectic solvent. The only difference from Example 12 is the type of hydrogen bond donor in step S1, specifically, salicylic acid is replaced with an equimolar amount of formic acid.

[0053] Comparative Example 8 This comparative example provides a method for preparing a eutectic solvent and a method for pretreating lignocellulose using a eutectic solvent. The only difference from Example 2 is the step S1, which is as follows: 1 mol of triethylbenzylammonium chloride and 0.5 mol of ethylene glycol are weighed and placed in a beaker, stirred at 80°C until homogeneous and transparent, and then 1 mol of salicylic acid is added and stirred until homogeneous to obtain the eutectic solvent.

[0054] Comparative Example 9 This comparative example provides a method for preparing a eutectic solvent and a method for pretreating lignocellulose using a eutectic solvent. The only difference from Example 2 is the molar ratio of hydrogen bond acceptor, hydrogen bond donor and cosolvent. Specifically, the molar ratio of hydrogen bond acceptor, hydrogen bond donor and cosolvent is 1:1:2, that is, the amount of ethylene glycol added is 2 mol.

[0055] Performance testing The separation effect of the lignocellulose pretreated products prepared in Examples 1-14 and Comparative Examples 1-9 was tested, and the specific methods are as follows: S1. Add 360 mL of ethanol to the lignocellulose pretreatment product, stir for 60 min at a temperature of 60 °C and a stirring speed of 150 rpm, cool the reaction product to room temperature, remove the reaction product and filter under reduced pressure, and wash the filter residue with anhydrous ethanol to obtain eutectic solvent residue and eutectic solvent filtrate. S2. The eutectic solvent filtrate was rotary evaporated at 50°C to recover ethanol. Then, 300g of deionized water was added to the concentrated liquid after rotary evaporation and allowed to stand for 4 hours. The liquid was then filtered under reduced pressure and washed with deionized water to obtain a precipitate. Finally, the precipitate was placed in a vacuum drying oven at 50°C and dried for 24 hours to obtain regenerated lignin. S3. Centrifuge the eutectic solvent filter residue at 10,000 rpm for 5 min, transfer the lower precipitate after centrifugation to a vacuum drying oven, and vacuum dry at 50°C for 24 h to obtain a cellulose-rich solid residue. S4. Referring to the two-step acid hydrolysis method of the National Renewable Energy Laboratory (NREL) in the United States, the cellulose retention rate, hemicellulose removal rate, lignin extraction rate, and enzymatic hydrolysis efficiency were calculated. The test results are shown in Table 2, where:

[0056]

[0057]

[0058]

[0059] Table 2 Test results of Examples 1-14 and Comparative Examples 1-9

[0060] As can be seen from the data in Examples 1 to 14 in Table 2, the eutectic solvent provided by the present invention has the ability to efficiently decompose lignocellulose. It can decompose lignocellulose in a short time (≥5 min), with a cellulose retention rate of over 80%, a hemicellulose removal rate of over 73%, a lignin extraction rate of over 66%, and an enzymatic hydrolysis efficiency of over 65%, achieving a breakthrough in reaction efficiency and selectivity.

[0061] Data from Examples 1 and 2 show that adding ethylene glycol as a co-solvent can reduce the viscosity of the eutectic solvent system, promote the penetration and diffusion of the eutectic solvent into the biomass, improve the ability of the eutectic solvent to decompose lignocellulose, and achieve improvements in fiber retention rate, hemicellulose removal rate, lignin extraction rate, and enzymatic hydrolysis efficiency.

[0062] Data from Examples 2-7 show that as the reaction temperature between the eutectic solvent and the lignocellulose raw material increases, the cellulose retention rate gradually decreases, while the hemicellulose removal rate and lignin extraction rate gradually increase. The enzymatic hydrolysis efficiency, however, shows a trend of first increasing and then decreasing. This is because excessively high reaction temperatures cause cellulose to become keratinized, leading to a decrease in enzymatic hydrolysis efficiency.

[0063] As can be seen from the data in Examples 5, 8-14, as the reaction time between the eutectic solvent and the lignocellulose raw material increases, the cellulose retention rate gradually decreases, while the hemicellulose removal rate, lignin extraction rate, and enzymatic hydrolysis efficiency gradually increase.

[0064] Data from Examples 2 and Comparative Examples 1-4 show that, under the same reaction conditions, the choice of hydrogen bond donor is a key factor affecting the ability of the eutectic solvent to decompose lignocellulose. When salicylic acid is chosen as the hydrogen bond donor, it synergistically interacts with quaternary ammonium salts containing benzene rings, giving the prepared eutectic solvent the ability to specifically target and dissolve lignocellulose. However, when benzoic acid, phenylpropionic acid, p-hydroxybenzoic acid, or m-hydroxybenzoic acid are chosen as hydrogen bond donors, they cannot synergistically interact with quaternary ammonium salts containing benzene rings, resulting in the prepared eutectic solvent failing to effectively remove hemicellulose and extract lignin, and the enzymatic hydrolysis efficiency of the treated product remains below 65%.

[0065] The cellulose retention rate directly reflects the theoretical yield of sugar source conversion, while the enzymatic hydrolysis efficiency directly reflects the speed of sugar source conversion. Both are core indicators for evaluating the effectiveness of lignocellulose pretreatment. Data from Comparative Example 6 shows that although the enzymatic hydrolysis efficiency reached 78.74%, the cellulose retention rate decreased significantly to only 72.83%. This indicates substantial cellulose loss during pretreatment, leading to a reduction in the total amount of convertible sugar source.

[0066] Data from Example 2 and Comparative Example 8 show that the order of addition of salicylic acid has a crucial impact on the ability of the eutectic solvent to decompose lignocellulose. Only when the preparation method involves mixing salicylic acid, a benzene-ring-containing quaternary ammonium salt, and a co-solvent until transparent and homogeneous can the prepared eutectic solvent possess an efficient ability to decompose lignocellulose. Adding salicylic acid only after the triethylbenzylammonium chloride and ethylene glycol have been thoroughly mixed prevents the salicylic acid from synergistically interacting with the benzene-ring-containing quaternary ammonium salt, resulting in a decrease in the ability of the prepared eutectic solvent to remove hemicellulose and extract lignin.

[0067] The data from Comparative Example 9 show that when the molar ratio of hydrogen bond acceptor to hydrogen bond donor to cosolvent is not 1:1:0~1, ethylene glycol will disrupt the synergistic effect between salicylic acid and quaternary ammonium salt containing benzene ring, resulting in a decrease in cellulose retention rate, hemicellulose removal rate, lignin extraction rate and enzymatic hydrolysis efficiency.

[0068] The specific embodiments of the present invention have been described above. It should be understood that the present invention is not limited to the specific embodiments described above, and those skilled in the art can make various modifications or variations within the scope of the claims, which do not affect the essence of the present invention.

Claims

1. A eutectic solvent, characterized in that, The method for preparing the eutectic solvent is to stir and mix the hydrogen bond acceptor and the hydrogen bond donor until the mixture is transparent and homogeneous; The hydrogen bond acceptor is a quaternary ammonium salt containing a benzene ring; the hydrogen bond donor is salicylic acid.

2. A eutectic solvent, characterized in that, The method for preparing the eutectic solvent is to stir and mix the hydrogen bond acceptor, hydrogen bond donor and co-solvent until transparent and homogeneous; The hydrogen bond acceptor is a quaternary ammonium salt containing a benzene ring; the hydrogen bond donor is salicylic acid; and the co-solvent is a C2-C6 diol.

3. The eutectic solvent according to claim 2, characterized in that, The molar ratio of the hydrogen bond acceptor to the hydrogen bond donor to the cosolvent is 1:1:0.1~1.

4. The eutectic solvent according to any one of claims 1 to 3, characterized in that, The stirring temperature is 60~100℃.

5. The use of the eutectic solvent according to any one of claims 1 to 4 in the separation of lignocellulose.

6. A method for pretreating lignocellulose using a eutectic solvent, characterized in that, Includes the following steps: The eutectic solvent described in any one of claims 1 to 4 is stirred and mixed with the lignocellulose raw material to obtain the lignocellulose pretreated product.

7. The method according to claim 6, characterized in that, The lignocellulose raw material is one or more of sugarcane bagasse, wood, bamboo, corn cob, or straw.

8. The method according to claim 6, characterized in that, The mass ratio of the lignocellulose raw material to the eutectic solvent is 1:10~20.

9. The method according to claim 6, characterized in that, The reaction time is 5 to 360 minutes.

10. The method according to claim 6, characterized in that, The reaction temperature is 130~180℃.

Images