Preparation of ternary acidic deep-eutectic solvent and method for efficiently and circularly separating bamboo-wood fiber biomass by using ternary acidic deep-eutectic solvent

Abstract

According to the invention, a novel ternary acidic deep eutectic solvent (DES) is prepared, ethylamine hydrochloride (EH) is used as a hydrogen bond acceptor (HBD), and DL-malic acid (MA) and polyethylene glycol-400 (PEG-400) are used as hydrogen bond donors (HBA). The DES solvent has good performance on wood fiber biomass refining pretreatment, and three major components of lignocellulose can be efficiently separated. The ternary acidic DES disclosed by the invention is easy to synthesize, good in stability and simple in use method, and an ideal separation effect can be achieved when high biomass solid content is treated, that is, most cellulose is reserved in a solid form, and most hemicellulose and lignin are converted into a liquid form through dissolution or partial degradation to be separated; and separating the lignin component from the hemicellulose by anti-solvent precipitation. The prepared DES can be recycled after being filtered and subjected to rotary evaporation, still has a separation effect equivalent to that of an original solvent after being recycled for six times, and has good industrial application prospect and value.

Description

Technical Field

[0001] This invention relates to the field of eutectic solvents and their applications, specifically to a method for synthesizing ternary DES and its applications. Background Technology

[0002] With the depletion of non-renewable energy sources and their environmental pollution, the development of green energy has become a research hotspot in recent years. Biomass, widely distributed in nature, is a renewable carbon energy source. Its main chemical components include cellulose, hemicellulose, and lignin (accounting for approximately 80-95% of the total raw material mass), which form a dense structure through complex chemical bonds. The applications of these three elements involve multiple fields such as textiles, chemicals, fuels, food, medicine, biotechnology, environmental protection, and energy. To achieve high-value utilization of biomass, efficient pretreatment is essential. This pretreatment primarily aims to break down the natural dense structure of the raw material, separating the three elements and improving the utilization rate of fiber and hemicellulose.

[0003] Traditional pretreatment methods, such as mechanical crushing, acid processing, and alkaline processing, suffer from high energy consumption, high cost, harsh reaction conditions, and varying degrees of environmental pollution. While biological treatment is pollution-free, its long reaction cycle prevents large-scale industrial application. Currently developed ionic liquids (ILs) represent a novel and effective potential solvent for the pretreatment of lignocellulosic biomass and are environmentally friendly. However, traditional ILs are expensive, have complex synthesis processes, possess certain toxicity, and exhibit poor biodegradability. Eutectic solvents (ULS) share similar physicochemical properties with ILs and offer advantages such as lower preparation costs, lower or even non-toxicity, and biodegradability, making them a current research hotspot. As a novel green solvent, ULS possess advantages such as simple preparation processes, biodegradability, and good biocompatibility, making them promising for applications in electrochemistry, organic synthesis, and biocatalysis, particularly in biomass refining and lignocellulosic biomass treatment.

[0004] Low eutectic solvent (DES): This is a molten salt mainly composed of hydrogen bond acceptors (HBAs, such as quaternary ammonium salts and quaternary phosphate salts) and hydrogen bond donors (carboxylic acids, polyols, etc., such as HBDs) linked together in a specific molar ratio through hydrogen bonding, van der Waals forces, or electrostatic interactions. It exists in a fluid state at or near room temperature. DES has a strong hydrogen bond network structure. The main principle of biomass pretreatment is to utilize the difference in solubility of the three main components of the raw material in DES solution to separate lignin. Then, the thermally unstable hemicellulose is dissolved through heating and hydrolysis, thereby achieving the separation of the three main components of the biomass. This improves the efficiency of enzymatic hydrolysis and saccharification. Summary of the Invention

[0005] Based on the above research, this invention prepares a novel ternary acidic eutectic solvent (DES) using oil bath heating, wherein ethylamine hydrochloride (EH) serves as the hydrogen bond acceptor (HBD), and DL-malic acid (MA) and polyethylene glycol-400 (PEG-400) serve as hydrogen bond donors (HBA). This can be applied to the efficient separation of bamboo and wood fiber biomass. The method involves placing bamboo and wood fiber biomass and the eutectic solvent in a reactor at a specific ratio and separating the biomass components under oil bath heating. To investigate the effect of this DES on the separation of bamboo and wood fiber biomass components, this invention optimizes the conditions by studying the solid-liquid ratio, reaction temperature, and reaction time of the separation reaction to achieve the best separation effect.

[0006] The technical solution of the present invention is as follows:

[0007] 1) Weigh a certain amount of EH and MA and PEG-400 in the corresponding molar ratio into a round-bottom flask, then heat and stir in an oil bath at 80°C until a clear and transparent homogeneous liquid is formed.

[0008] 2) Once the reaction is complete, remove the DES and store it in a sealed bottle.

[0009] The aforementioned DES can achieve efficient separation of bamboo and wood fiber biomass.

[0010] The DES mentioned is EH:MA:PEG-400;

[0011] The specific applications are as follows:

[0012] Add bamboo powder and DES to a 250ml round-bottom flask at a mass ratio of 1:3 to 1:10. The reaction temperature is 100-150℃ and the reaction time is 1-3h.

[0013] Beneficial effects: Compared with current research techniques, the advantages of this invention include: the ternary acidic DES is easy to synthesize, has good stability, and is simple to use. Even at high solid content, it achieves ideal separation results, retaining most of the cellulose while removing the vast majority of hemicellulose and lignin, thus achieving a high enzymatic hydrolysis yield. Furthermore, the DES can be recycled again through filtration and rotary evaporation, thus significantly reducing production costs from an economic perspective. Attached Figure Description

[0014] Figure 1 These are SEM images of untreated bamboo powder and bamboo powder treated in Examples 1, 3, and 6.

[0015] Figure 2 These are infrared diffraction patterns of untreated bamboo powder and pretreated bamboo from Examples 1-6.

[0016] Figure 3 This is the result of six iterations of preprocessing for Examples 1 and 12-17. Detailed Implementation

[0017] The present invention will be further described in detail below with reference to the embodiments and accompanying drawings, but the embodiments of the present invention are not limited thereto.

[0018] Example 1

[0019] 1. Preparation of EH:MA:PEG-400 eutectic solvent:

[0020] Ethylamine hydrochloride (EH), DL-malic acid (MA), and polyethylene glycol-400 (PEG-400) were weighed into a round-bottom flask in a molar ratio of 1:1:1. The mixture was heated in a water bath and stirred until a uniform and transparent liquid was obtained. After cooling to room temperature, the mixture was poured into a sealed bottle for storage.

[0021] 2. Pretreatment of bamboo and wood fiber biomass with EH:MA:PEG-400 eutectic solvent

[0022] 5g of bamboo powder and 35g of EH:MA:PEG-400 eutectic solvent were added to a round-bottom flask and stirred at 130℃ and 500rpm for 3 hours. After the reaction was completed, a certain amount of ethanol / water was added to stop the reaction, and the mixture was washed with ethanol / water solution until the filtrate was colorless and transparent. Solid crude fibers and a liquid fraction rich in lignin and fiber and hemicellulose degradation products were recovered. The crude fibers were dried overnight and sealed. Ethanol was removed from the liquid fraction by rotary evaporation, and deionized water was added to the concentrated liquid to precipitate the regenerated lignin. The solid and liquid components were separated by high-speed centrifugation. The regenerated lignin was washed to neutral, freeze-dried, and sealed for storage. The liquid fraction was evaporated to remove water, and after drying, DES could be recovered.

[0023] 3. Component analysis experiment

[0024] The chemical composition of the raw material, crude fiber, and regenerated lignin was analyzed using a two-step acid hydrolysis method. Determination was performed according to the standard method of the National Renewable Energy Laboratory (NREL). All sugars were determined by high-performance liquid chromatography (HPLC) using an Aminex HPX-87H column. The specific procedure was as follows: 0.3 g of dried crude cellulose sample was placed in a 100 mL vial, and 3 mL of 72% concentrated sulfuric acid was added to swell the sample. The vial was then placed in a 30°C constant-temperature shaker for 1 hour, vortexing every 10 minutes. After swelling, the vial was removed, and 84 mL of deionized water was added to dilute the sulfuric acid concentration in the hydrolysis solution to 4%. The vial was sealed and placed in an autoclave at 121°C for 1 hour. The mixture after autoclaving was separated into solid and liquid components using a glass frit funnel. The solid fraction, after drying, was weighed to represent the acid-insoluble lignin content in the crude cellulose sample. The liquid fraction mainly consisted of monosaccharides produced from the acid hydrolysis of cellulose and hemicellulose in the crude cellulose sample. The peak intensity of the liquid fraction at 205 nm was measured using a UV spectrophotometer at room temperature, and the content of acid-soluble lignin was calculated accordingly. The lignin removal rate was 85.30%, the hemicellulose removal rate was 75.42%, and the cellulose retention rate was 87.53%.

[0025] Example 2

[0026] The DES synthesis is exactly the same as in Example 1, except that:

[0027] In the reaction step, the reaction temperature was 100℃, the lignin removal rate was 21.08%, the hemicellulose removal rate was 15.70%, and the cellulose retention rate was 88.51%.

[0028] Example 3

[0029] The DES synthesis is exactly the same as in Example 1, except that:

[0030] In the reaction step, the reaction temperature was 110℃, the lignin removal rate was 34.36%, the hemicellulose removal rate was 30.84%, and the cellulose retention rate was 89.52%.

[0031] Example 4

[0032] The DES synthesis is exactly the same as in Example 1, except that:

[0033] In the reaction step, the reaction temperature was 120℃, the lignin removal rate was 54.82%, the hemicellulose removal rate was 51.82%, and the cellulose retention rate was 90.35%.

[0034] Example 5

[0035] The DES synthesis is exactly the same as in Example 1, except that:

[0036] In the reaction step, the reaction temperature was 140℃, the lignin removal rate was 78.93%, the hemicellulose removal rate was 82.81%, and the cellulose retention rate was 84.81%.

[0037] Example 6

[0038] The DES synthesis is exactly the same as in Example 1, except that:

[0039] In the reaction step, the reaction temperature was 150℃, the lignin removal rate was 67.31%, the hemicellulose removal rate was 88.57%, and the cellulose retention rate was 79.56%.

[0040] Example 7

[0041] The DES synthesis is exactly the same as in Example 1, except that:

[0042] In the reaction step, the solid-liquid ratio was 1:3, the lignin removal rate was 59.25%, the hemicellulose removal rate was 57.00%, and the cellulose retention rate was 88.06%.

[0043] Example 8

[0044] The DES synthesis is exactly the same as in Example 1, except that:

[0045] In the reaction step, the solid-liquid ratio was 1:5, the lignin removal rate was 78.62%, the hemicellulose removal rate was 72.10%, and the cellulose retention rate was 86.95%.

[0046] Example 9

[0047] The DES synthesis is exactly the same as in Example 1, except that:

[0048] In the reaction step, the solid-liquid ratio was 1:10, the lignin removal rate was 90.10%, the hemicellulose removal rate was 79.50%, and the cellulose retention rate was 86.99%.

[0049] Example 10

[0050] The DES synthesis is exactly the same as in Example 1, except that:

[0051] In the reaction step, the reaction time was 1 hour, the lignin removal rate was 36.32%, the hemicellulose removal rate was 41.23%, and the cellulose retention rate was 92.97%.

[0052] Example 11

[0053] The DES synthesis is exactly the same as in Example 1, except that:

[0054] In the reaction step, the reaction time was 2 hours, the lignin removal rate was 70.08%, the hemicellulose removal rate was 63.67%, and the cellulose retention rate was 85.33%.

[0055] Example 12

[0056] The reaction steps are exactly the same as in Example 1, except that:

[0057] In the pretreatment step, the DES used was the DES recovered from the initial pretreatment. The lignin removal rate was 73.82%.

[0058] Example 13

[0059] The reaction steps are exactly the same as in Example 1, except that:

[0060] In the pretreatment step, the DES used was the DES recovered from the second pretreatment. The lignin removal rate was 80.83%.

[0061] Example 14

[0062] The reaction steps are exactly the same as in Example 1, except that:

[0063] In the pretreatment step, the DES used was the DES recovered from the third pretreatment. The lignin removal rate was 82.47%.

[0064] Example 15

[0065] The reaction steps are exactly the same as in Example 1, except that:

[0066] In the pretreatment step, the DES used was the DES recovered from the fourth pretreatment. The lignin removal rate was 84.05%.

[0067] Example 16

[0068] The reaction steps are exactly the same as in Example 1, except that:

[0069] In the pretreatment step, the DES used was the DES recovered from the fifth pretreatment. The lignin removal rate was 79.88%.

[0070] Example 17

[0071] The reaction steps are exactly the same as in Example 1, except that:

[0072] In the pretreatment step, the DES used was the DES recovered from the sixth pretreatment. The lignin removal rate was 79.78%.

[0073] Figure 1These are SEM images of untreated lignocellulosic biomass and pretreated crude fiber recycled solids. The morphology of raw bamboo powder (a), bamboo powder treated with DES at 110℃ (b), bamboo powder treated with DES at 130℃ (c), and bamboo powder treated with DES at 150℃ (d) were analyzed by SEM. Figure 1 The results showed that untreated bamboo exhibited a dense, smooth, and flat surface. After pretreatment, the surface of the solid coarse fibers showed more broken fiber fragments, severe surface deconstruction, and observed cracks. These changes indicate that pretreatment disrupted the original stubborn structure of cellulose.

[0074] Figure 2 Infrared spectroscopy was used to detect the recovered solid crude fibers after pretreatment at different temperatures in Examples 1-6. Fourier transform infrared spectroscopy was used to analyze the changes in functional groups of biomass after pretreatment at different temperatures. After DES pretreatment, the correlation peaks related to cellulose were enhanced, while the correlation peaks related to hemicellulose and lignin were weakened or disappeared.

[0075] Figure 3 Examples 1 and 12-17 were run six times, and the lignin removal rate was recorded for each cycle. Even after multiple cycles, good recyclability and a high lignin removal rate were still observed.

[0076] Table 1 shows the separation effect of each component of the recovered solid crude fiber after pretreatment at different temperatures in Examples 1-6.

[0077] Table 2 shows the separation effect of each component of the recovered solid crude fiber after pretreatment with different solid-liquid ratios in Examples 7-9.

[0078] Table 3 shows the separation effect of each component of the recovered solid crude fiber after pretreatment at different times in Examples 10-11.

[0079] Table 1 shows the separation effect of each component of the recovered solid crude fiber after pretreatment at different temperatures in Examples 1-6.

[0080]

[0081] Table 2 shows the separation effect of each component of the recovered solid crude fiber after pretreatment with different solid-liquid ratios in Examples 7-9.

[0082]

[0083] Table 3 shows the separation effect of each component of the recovered solid crude fiber after pretreatment at different times in Examples 10-11.

[0084]

[0085] The above embodiments are implementation methods adopted by the present invention, but the implementation methods of the present invention are not limited to the above embodiments. Any changes, modifications, substitutions, combinations, or simplifications made without departing from the spirit and principle of the present invention shall be considered equivalent substitutions and shall be included within the protection scope of the present invention.

Claims

1. A ternary acidic DES synthesized using ethylamine hydrochloride (EH) as the hydrogen bond acceptor (HBD) and DL-malic acid (MA) and polyethylene glycol-400 (PEG-400) as hydrogen bond donors (HBA). Its characteristics are: The ternary DES was synthesized using an oil bath heating method with EH, MA, and PEG-400 in a specific ratio, and remained stable at room temperature. The preparation method is as follows: 1) Weigh a certain amount of EH and MA and PEG-400 in the corresponding molar ratio into a round-bottom flask, then heat and stir in an oil bath at 80°C until a clear and transparent homogeneous liquid is formed. 2) Once the reaction is complete, remove the DES and store it in a sealed bottle.

2. The method for preparing ternary DES according to claim 1, characterized in that, The molar ratio of EH, MA, and PEG-400 in the ternary DES is 1:1:

1.

3. The preparation method according to claim 1, characterized in that, The heating method uses a temperature of 80℃.

4. The preparation method according to claim 1, characterized in that, The stirring speed for the heating method is 500 rpm.

5. A method for efficient separation of bamboo and wood fiber biomass. The method involves placing bamboo and wood fiber biomass and a eutectic solvent in a reactor at a certain ratio and separating the components of the biomass under oil bath heating.

6. The method according to claim 5, characterized in that, The oil bath heating reaction temperature is 100℃-150℃.

7. The method according to claim 5, characterized in that, The heating reaction time is 1-3 hours.

8. The method according to claim 5, characterized in that, A certain amount of ethanol / water was added to the DES-treated sample to stop the reaction. The sample was then vacuum filtered and washed until the filtrate was colorless. The cellulose-rich solid sample was then dried in an oven at 60°C for at least 12 hours.

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