Method for fractionating lignocellulose biomass by using eutectic solvent and recycling lignocellulose biomass

Abstract

The invention relates to the technical field of fractionation of lignocellulose biomass, and discloses a method for fractionating lignocellulose biomass by using a eutectic solvent, which comprises the following steps: mixing betaine and malic acid, stirring, and cooling to room temperature after the reaction is finished to obtain a clear and transparent eutectic solvent; the method comprises the following steps: mixing crushed lignocellulose biomass with a deep-eutectic solvent, and putting the mixture into a high-pressure reaction kettle; acetone and n-butyl alcohol are mixed according to the volume ratio of 3: 2-4: 1, and an anti-solvent is prepared; the method comprises the following steps: slowly adding an anti-solvent into a mixture of the lignocellulose biomass and the eutectic solvent, carrying out ultrasonic treatment, and then carrying out suction filtration. The glass electrode pH meter is used for measuring the pH value of the recovered deep-eutectic solvent, and the newly prepared deep-eutectic solvent is added according to the pH value, so that the stability of the solvent performance can be effectively maintained, the deep-eutectic solvent always keeps a good fractionation effect in multiple times of recycling, the utilization rate of the solvent is greatly improved, and the production cost is reduced.

Description

Technical Field

[0001] The present invention relates to the technical field of fractionating lignocellulosic biomass, and specifically to a method for fractionating lignocellulosic biomass with a deep eutectic solvent. Background Art

[0002] As the most abundant renewable resource on earth, lignocellulose is mainly composed of cellulose, hemicellulose and lignin, and can produce up to 10^11 tons of biomass annually through photosynthesis, covering wood, crop straws and energy crops, etc. Due to its sustainability and renewability characteristics, it is regarded as one of the most potential resources, and each component can be used as raw materials for producing biofuels, biomaterials and chemicals. Among various separation methods, deep eutectic solvents have attracted much attention, which can disrupt the hydrogen bond network in lignocellulose, selectively dissolve lignin and achieve component separation.

[0003] However, during the recycling process of traditional deep eutectic solvents, their performance is prone to change, resulting in a decline in fractionation effect, low solvent utilization rate and increased production costs. Summary of the Invention

[0004] Aiming at the deficiencies of the prior art, the present invention provides a method for fractionating lignocellulosic biomass with a deep eutectic solvent, which solves the problems that during the multiple recycling process, the performance is prone to change, resulting in a decline in fractionation effect, low solvent utilization rate and increased production costs.

[0005] To achieve the above objectives, the present invention is realized through the following technical solutions: A method for fractionating lignocellulosic biomass with a deep eutectic solvent, comprising the following steps:

[0006] Mix betaine and malic acid and then stir. After the reaction ends, cool to room temperature to obtain a clear and transparent deep eutectic solvent;

[0007] Mix the crushed lignocellulosic biomass with the deep eutectic solvent and put it into a high-pressure reactor;

[0008] Mix acetone and n-butanol in a volume ratio of 3:2 - 4:1 to prepare an anti-solvent;

[0009] Slowly add the anti-solvent to the mixture of lignocellulosic biomass and deep eutectic solvent. After stirring, perform ultrasonic treatment, then perform suction filtration, and wash the filter residue with deionized water;

[0010] Place the washed filter residue in a vacuum drying oven to obtain a cellulose-rich solid.

[0011] By adopting the above technical solution, betaine and malic acid are stirred and mixed for reaction to prepare a eutectic solvent with stable performance, which has stronger dissolution and separation ability for lignocellulosic biomass, and helps the subsequent fractionation of lignocellulosic biomass;

[0012] Crushing the biomass can increase its contact area with the eutectic solvent, and using a high-pressure environment to promote the full reaction of the eutectic solvent with lignocellulosic biomass helps to destroy the structure of the biomass and create conditions for separating cellulose components;

[0013] By using acetone and n-butanol mixed to prepare an anti-solvent, it can act on the mixture of the eutectic solvent and lignocellulosic biomass, and promote the precipitation of components such as cellulose in a suitable form, which is convenient for subsequent separation operations;

[0014] The anti-solvent is slowly added to the mixture of lignocellulosic biomass and the eutectic solvent. After stirring, ultrasonic treatment is carried out to promote the reaction and dispersion, and then suction filtration is carried out to achieve preliminary solid-liquid separation. The filter residue is washed with deionized water to remove residual impurities and solvents, the anti-solvent is added and stirred, and it is fully mixed with the mixture, and the anti-solvent is evenly dispersed;

[0015] The vacuum drying oven speeds up the drying speed and at the same time avoids the oxidation of cellulose during drying, and obtains a stable and high-purity solid product rich in cellulose;

[0016] Preferably, the betaine and malic acid are mixed in a molar ratio of 1:3 - 1:5 and loaded into a three-necked flask with stirring and temperature control functions, and stirred and reacted at 50 - 70 °C for 3 - 5 hours, the stirring speed is 300 - 500 r / min, and nitrogen is continuously introduced for protection during the reaction.

[0017] Preferably, the lignocellulosic biomass is crushed and passed through a 60 - 80 mesh sieve, the lignocellulosic biomass and the eutectic solvent are mixed in a mass ratio of 1:15 - 1:25, the temperature of the high-pressure reaction kettle is set at 120 - 150 °C, the internal pressure is set at 0.5 - 1.5 MPa, and the reaction is carried out for 4 - 8 hours and stirred at a speed of 50 - 100 r / min during the reaction.

[0018] Preferably, the volume ratio of the anti-solvent to the mixture of lignocellulosic biomass and the eutectic solvent is 1:8 - 1:12, the ultrasonic frequency during ultrasonic treatment is 20 - 40 kHz, ultrasonic treatment is carried out for 15 - 30 minutes, and the filter residue is washed with deionized water until the conductivity of the washing liquid is lower than 50 μS / cm.

[0019] Preferably, before the cellulose-rich solid is dried in a vacuum drying oven, it is first soaked in a sodium bicarbonate solution with a mass fraction of 5-10% for 1-2 hours, and the vacuum drying oven dries the filter residue at a temperature of 40-60°C and a vacuum degree of -0.08 to -0.1 MPa for 24-48 hours.

[0020] Preferably, for the method of recycling lignocellulosic biomass by eutectic solvent fractionation, the method comprises the following steps:

[0021] Combine the washing liquids in the fractionation process, add a sodium chloride solution, stir evenly and then let stand, and then perform centrifugation to collect the precipitated solid. Wash the precipitate with deionized water until no chloride ions are detected in the washing liquid, separate the supernatant from the precipitate, and then place the precipitate in a freeze dryer to obtain lignin;

[0022] Transfer the supernatant after centrifugation to a rotary evaporator to obtain the recycled eutectic solvent;

[0023] Add the recycled eutectic solvent to the new lignocellulosic biomass and repeat the above steps of pretreatment, anti-solvent addition, component fractionation, and recovery of each component. After recycling 3 times, use a glass electrode pH meter to measure the pH value of the solvent, add the newly prepared eutectic solvent to the recycled eutectic solvent, and continue to recycle.

[0024] Preferably, the mass fraction of the sodium chloride is 10-20%, so that the concentration of sodium chloride in the washing liquid reaches 0.5-1.5 mol / L, the standing time is 3-6 h, the centrifugation speed during centrifugation is 8000-10000 r / min, the centrifugation time is 10-20 min, and the precipitate is placed in a freeze dryer and dried at -40 to -50°C and a vacuum degree of 1-10 Pa for 12-24 hours.

[0025] Preferably, the supernatant is rotary evaporated in a rotary evaporator at a temperature of 50-70°C and a vacuum degree of -0.06 to -0.08 MPa to remove acetone, n-butanol, and moisture therein.

[0026] Preferably, when adding the newly prepared eutectic solvent until the pH value is the same as that of the original eutectic solvent, first add it according to 5-10% of the mass of the recycled eutectic solvent, and then detect the pH value. If the original pH value of the eutectic solvent is not reached, continue to add the newly prepared eutectic solvent in small amounts multiple times until the pH values are the same.

[0027] Preferably, before the rotary evaporator rotary evaporates the supernatant, the supernatant needs to be filtered first, and the filtration medium is a filter membrane with a pore size of 0.22-0.45 μm.

[0028] The present invention provides a method for fractionating lignocellulosic biomass with a eutectic solvent, having the following beneficial effects:

[0029] 1. In the present invention, by using a glass electrode pH meter to measure the pH value of the recycled eutectic solvent and adding newly prepared eutectic solvent according to the pH value, the stability of the solvent performance can be effectively maintained, enabling the eutectic solvent to always maintain a good fractionation effect during multiple cycles of use, greatly improving the utilization rate of the solvent and reducing the production cost.

[0030] 2. In the present invention, by using betaine and malic acid to prepare the eutectic solvent, compared with traditional eutectic solvents, it has a stronger ability to dissolve and separate lignocellulosic biomass, which helps to improve the fractionation efficiency and obtain purer cellulose-rich solids and lignin.

[0031] 3. In the present invention, by using betaine and malic acid to prepare the eutectic solvent, these two substances are natural and biodegradable, greatly reducing the risk of environmental pollution, being more environmentally friendly than oxalic acid, and conforming to the development trend of green chemistry.

[0032] 4. In the present invention, through the combined operation of filtering and rotary evaporation of the recycled eutectic solvent, first, solid particle impurities in the recycled eutectic solvent are removed, and then acetone, n-butanol, and water are removed, reducing the impact on the environment. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 is a schematic flow chart of the method for fractionating lignocellulosic biomass with the eutectic solvent of the present invention;

[0034] Figure 2 is a schematic flow chart of the method for recycling the fractionation of lignocellulosic biomass with the eutectic solvent of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0035] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the specification. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of them. All other embodiments obtained by those of ordinary skill in the art without creative efforts based on the embodiments of the present invention belong to the scope of protection of the present invention.

[0036] Please refer to the attached Figure 1 , an embodiment of the present invention provides a method for fractionating lignocellulosic biomass with a eutectic solvent, including the following steps:

[0037] Mix betaine and malic acid and stir, and after the reaction is completed, cool to room temperature to obtain a clear and transparent eutectic solvent;

[0038] Mix the pulverized lignocellulosic biomass with a deep eutectic solvent and place it in a high-pressure reactor;

[0039] Mix acetone and n-butanol in a volume ratio of 3:2 - 4:1 to prepare an anti-solvent;

[0040] Slowly add the anti-solvent to the mixture of lignocellulosic biomass and deep eutectic solvent. After stirring, perform ultrasonic treatment, then carry out suction filtration, and wash the filter residue with deionized water;

[0041] Place the washed filter residue in a vacuum drying oven to obtain a cellulose-rich solid.

[0042] Specifically, by stirring and mixing betaine and malic acid to react, a deep eutectic solvent with stable performance can be prepared, which has a stronger ability to dissolve and separate lignocellulosic biomass, helps the subsequent fractionation of lignocellulosic biomass, and provides a suitable solvent environment for the entire fractionation process. Among them, in a natural white light environment, at a distance of 30 cm from the prepared deep eutectic solvent, when viewed directly with the naked eye, there are no visible suspended substances or turbidity, that is, a clear and transparent deep eutectic solvent;

[0043] Pulverizing the biomass can increase its contact area with the deep eutectic solvent, improve the reaction efficiency. Placing it in a high-pressure reactor and using the high-pressure environment can promote the full reaction of the deep eutectic solvent and lignocellulosic biomass, help destroy the structure of the biomass, and create conditions for separating cellulose components;

[0044] Mix acetone and n-butanol in a volume ratio of 3:2 - 4:1 to prepare an anti-solvent, which can act on the mixture of the deep eutectic solvent and lignocellulosic biomass, change the phase equilibrium of the system, and promote the cellulose component to precipitate in a suitable form, facilitating subsequent separation operations;

[0045] Slowly add the anti-solvent to the mixture of lignocellulosic biomass and deep eutectic solvent. After stirring, perform ultrasonic treatment, then carry out suction filtration, and wash the filter residue with deionized water. Adding the anti-solvent and stirring can make the anti-solvent evenly dispersed and fully act with the mixture. Ultrasonic treatment can further promote the reaction and dispersion, enhance the separation effect. Suction filtration realizes the preliminary solid-liquid separation, and washing the filter residue with deionized water can remove residual impurities and solvents, improving the product purity;

[0046] The vacuum environment provided by the vacuum drying oven can reduce the boiling point of water, accelerate the drying speed, and at the same time avoid the oxidation of cellulose during drying, so as to obtain a stable and high-purity cellulose-rich solid product.

[0047] Betaine and malic acid are mixed in a molar ratio of 1:3 - 1:5 and loaded into a three-necked flask equipped with stirring and temperature control functions. The reaction is carried out with stirring for 3 - 5 hours at 50 - 70 °C, and the stirring speed is 300 - 500 r / min. Nitrogen is continuously introduced to protect during the reaction process.

[0048] Specifically, betaine and malic acid are mixed in a molar ratio of 1:3 - 1:5 in a three-necked flask equipped with stirring and temperature control functions. The three-necked flask is convenient for installing stirring, temperature control, and nitrogen introduction devices to meet the reaction conditions. Stirring the reaction at 50 - 70 °C at a speed of 300 - 500 r / min for 3 - 5 hours can ensure the full reaction of betaine and malic acid to form a eutectic solvent with stable properties. Continuously introducing nitrogen can exclude air, prevent the reactants from being oxidized, and ensure the preparation quality of the eutectic solvent and the stability of the reaction process.

[0049] The lignocellulosic biomass is crushed and sieved through a 60 - 80 mesh sieve. The lignocellulosic biomass and the eutectic solvent are mixed in a mass ratio of 1:15 - 1:25. The temperature of the high-pressure reactor is set at 120 - 150 °C, and the internal pressure is set at 0.5 - 1.5 MPa. The reaction is carried out for 4 - 8 hours, and stirring is carried out at a speed of 50 - 100 r / min during the reaction process.

[0050] Specifically, crushing the lignocellulosic biomass and sieving it through a 60 - 80 mesh sieve can increase its specific surface area and make it contact with the eutectic solvent more fully. Mixing in a mass ratio of 1:15 - 1:25 is beneficial to the reaction. In the high-pressure reactor, a temperature of 120 - 150 °C, a pressure of 0.5 - 1.5 MPa, and a stirring speed of 50 - 100 r / min can accelerate the penetration and reaction of the eutectic solvent to the lignocellulosic biomass, destroy the complex structure of the biomass, weaken the connections between lignin, hemicellulose, and cellulose, thereby efficiently realizing the separation of each component of the biomass, improving the fractionation efficiency and effect, and the betaine and malic acid in the eutectic solvent do not decompose or undergo significant side reactions.

[0051] The volume ratio of the anti-solvent to the mixture of lignocellulosic biomass and the eutectic solvent is 1:8 - 1:12. The ultrasonic frequency during ultrasonic treatment is 20 - 40 kHz, and ultrasonic treatment is carried out for 15 - 30 minutes. The filter residue is washed with deionized water until the value of the conductivity of the washing liquid detected by the conductivity meter is lower than 50 μS / cm.

[0052] Specifically, the anti-solvent is added to the lignocellulosic biomass and deep eutectic solvent mixture at a volume ratio of 1:8 - 1:12, which can change the dissolution equilibrium of the system and promote the precipitation of the target components from the mixture. Treatment at an ultrasonic frequency of 20 - 40 kHz for 15 - 30 minutes can utilize the cavitation effect of ultrasonic waves to enhance the mixing effect of the anti-solvent and the mixture, promote mass transfer between substances, and accelerate the aggregation and precipitation of the target components. The filter residue is washed with deionized water until the conductivity of the washing liquid is lower than 50 μS / cm. The residual deep eutectic solvent, anti-solvent, and other impurity ions on the surface of the filter residue can be ensured to be completely removed by monitoring the conductivity, thereby obtaining a cellulose-rich solid product with relatively high purity.

[0053] Before the cellulose-rich solid is dried in a vacuum drying oven, it is first soaked in a sodium bicarbonate solution with a mass fraction of 5 - 10% for 1 - 2 hours. The vacuum drying oven dries the filter residue under the conditions of a temperature of 40 - 60°C and a vacuum degree of -0.08 - -0.1 MPa for 24 - 48 hours.

[0054] Specifically, before vacuum drying, the cellulose-rich solid is soaked in a sodium bicarbonate solution with a mass fraction of 5 - 10% for 1 - 2 hours. Using the alkaline environment of the sodium bicarbonate solution, the acidic substances or impurities remaining on the surface of the cellulose can be neutralized, and at the same time, some soluble organic or inorganic pollutants can be removed. After soaking, the filter residue needs to be washed and rinsed with deionized water multiple times until the pH value of the washing liquid is close to neutral. Subsequently, it is dried in a vacuum drying oven at a vacuum degree of -0.08 - -0.1 MPa and a temperature of 40 - 60°C for 24 - 48 hours. The vacuum environment reduces the boiling point of water, accelerates the drying rate, and avoids structural damage of cellulose caused by high-temperature oxidation, decomposition, etc. Moreover, the relatively long drying time ensures the complete removal of moisture, thereby obtaining a dry, stable, and relatively high-purity cellulose solid product.

[0055] Refer to Figure 2 , a method for recycling deep eutectic solvent fractionated lignocellulosic biomass, the method comprising the following steps:

[0056] The washing liquids in the fractionation process are combined, sodium chloride solution is added, stirred evenly and then left to stand, followed by centrifugation. The precipitated solid is collected, washed with deionized water until no chloride ions can be detected in the washing liquid, the supernatant is separated from the precipitate, and then the precipitate is placed in a freeze dryer to obtain lignin;

[0057] The supernatant after centrifugation is transferred to a rotary evaporator to obtain the recycled deep eutectic solvent;

[0058] The recycled deep eutectic solvent is added to fresh lignocellulosic biomass, and the above steps of pretreatment, anti-solvent addition, component fractionation, and component recovery are repeated. After 3 cycles of use, the pH value of the solvent is measured using a glass electrode pH meter. Freshly prepared deep eutectic solvent is added to the recycled deep eutectic solvent, and the recycling is continued.

[0059] Specifically, by combining the washing liquid and adding sodium chloride solution, salting-out is used to precipitate lignin. Stirring, standing, and centrifugation can achieve solid-liquid separation. Residual chloride ions are removed by washing with deionized water to avoid impurity mixing. Freeze-drying dries the precipitate in a low-temperature vacuum environment to prevent lignin from being oxidized or structurally damaged at high temperatures, thereby obtaining a lignin product with high purity and stable structure.

[0060] Under vacuum conditions, a rotary evaporator evaporates low-boiling substances such as acetone, n-butanol, and water in the supernatant by heating, thereby separating the deep eutectic solvent from other components, efficiently recovering the deep eutectic solvent, reducing resource waste, lowering production costs, and at the same time avoiding environmental pollution caused by these volatile substances.

[0061] Reusing the recycled deep eutectic solvent reduces production costs and improves resource utilization rate. Measuring the pH value and supplementing freshly prepared deep eutectic solvent after 3 cycles of use can maintain the chemical stability of the solvent system, ensure that the fractionation effect of the deep eutectic solvent on lignocellulosic biomass does not decrease due to multiple uses, and ensure the sustainability and stability of the entire fractionation process.

[0062] The mass fraction of sodium chloride is 10 - 20%, so that the concentration of sodium chloride in the washing liquid reaches 0.5 - 1.5 mol / L. The standing time is 3 - 6 h. The centrifugation speed during centrifugation is 8000 - 10000 r / min, and the centrifugation time is 10 - 20 min. The precipitate is placed in a freeze-dryer and dried for 12 - 24 hours under the conditions of -40 - -50 °C and a vacuum degree of 1 - 10 Pa.

[0063] Specifically, using a sodium chloride solution with a mass fraction of 10 - 20% to make the sodium chloride concentration in the washing liquid reach 0.5 - 1.5 mol / L can effectively promote the precipitation of lignin and improve the recovery rate of lignin. Standing for 3 - 6 hours allows lignin to precipitate sufficiently. A centrifugation speed of 8000 - 10000 r / min and a centrifugation time of 10 - 20 min achieve solid-liquid separation and ensure complete collection of the precipitate. In the freeze-dryer, the low temperature of -40 - -50 °C, the vacuum degree of 1 - 10 Pa, and the drying duration of 12 - 24 hours can both prevent lignin from undergoing oxidation and degradation reactions at high temperatures during drying and ensure complete removal of moisture, thereby obtaining a lignin product with high purity and complete structure.

[0064] The supernatant was rotary evaporated in a rotary evaporator under the conditions of a temperature of 50 - 70°C and a vacuum degree of -0.06 to -0.08 MPa to remove acetone, n-butanol, and moisture therein.

[0065] Specifically, under the conditions of a temperature of 50 - 70°C and a vacuum degree of -0.06 to -0.08 MPa, the supernatant was rotary evaporated using a rotary evaporator, which could not only rapidly evaporate and separate low-boiling-point substances such as acetone, n-butanol, and moisture, but also avoid the decomposition and deterioration reactions of the deep eutectic solvent caused by too high a temperature. The rotary evaporation process expanded the liquid evaporation area by continuous rotation, accelerating the evaporation efficiency, thereby removing acetone, n-butanol, and moisture from the supernatant and realizing the effective recovery and purification of the deep eutectic solvent.

[0066] Freshly prepared deep eutectic solvent was added until the pH value was the same as that of the original deep eutectic solvent. First, it was added according to 5 - 10% of the mass of the recovered deep eutectic solvent, and then the pH value was detected. If the original pH value of the deep eutectic solvent was not reached, fresh freshly prepared deep eutectic solvent was continuously added in small amounts multiple times until the pH values were the same.

[0067] Specifically, adding freshly prepared deep eutectic solvent until the pH value was the same as that of the original deep eutectic solvent and controlling the freshly prepared deep eutectic solvent to account for 5 - 10% of the mass of the recovered deep eutectic solvent could effectively maintain the stability of the acidity and alkalinity of the recovered deep eutectic solvent system, ensure the consistency of the chemical properties of the solvent, supplement the components lost or deteriorated during multiple recycling processes, and avoid wasting resources caused by adding too much fresh solvent, ensuring that the deep eutectic solvent maintained good reaction activity and fractionation effect during the subsequent fractionation of lignocellulosic biomass.

[0068] Before the rotary evaporator rotary evaporates the supernatant, the supernatant needs to be filtered first, and the filtration medium is a filter membrane with a pore size of 0.22 - 0.45 μm.

[0069] Specifically, filtering the supernatant with a filter membrane with a pore size of 0.22 - 0.45 μm before rotary evaporation could effectively intercept suspended solid particles, impurities, or incompletely precipitated substances in the supernatant, prevent these substances from entering the rotary evaporator and blocking the instrument pipeline, avoid impurities adhering to the surface of the recovered deep eutectic solvent during the evaporation process and affecting the purity, ensure the smooth progress of the rotary evaporation process, and ensure the stable and reliable quality of the recovered deep eutectic solvent.

[0070] Example 1

[0071] Mix betaine and malic acid in a molar ratio of 1:3, load them into a three-necked flask equipped with stirring and temperature control functions, stir and react at a speed of 300 r / min under the condition of 50 °C for 3 hours, continuously introduce nitrogen for protection during the reaction, and cool to room temperature after the reaction to obtain a clear and transparent eutectic solvent without visible suspended matter and turbidity when viewed directly with the naked eye at a distance of 30 cm from the sample under natural white light environment;

[0072] Mix the pulverized lignocellulosic biomass that has passed through a 60-mesh sieve with the eutectic solvent in a mass ratio of 1:15, put it into a high-pressure reactor, set the temperature at 120 °C, the internal pressure at 0.5 MPa, stir and react at a speed of 50 r / min for 4 hours, mix acetone and n-butanol in a volume ratio of 3:2 to prepare an anti-solvent, slowly add it according to the volume ratio of the anti-solvent to the mixture of 1:8, stir, ultrasonically treat it at an ultrasonic frequency of 20 kHz for 15 minutes, then carry out suction filtration, and wash the filter residue with deionized water until the conductivity of the washing liquid is lower than 50 μS / cm;

[0073] Soak the washed filter residue in a 5% sodium bicarbonate solution for 1 hour, rinse it with deionized water multiple times until the pH value of the washing liquid is close to neutral, and then place it in a vacuum drying oven at a vacuum of -0.08 MPa and a temperature of 40 °C for 24 hours to obtain a cellulose-rich solid;

[0074] Combine the washing liquids during the fractionation process, add a 10% sodium chloride solution to make the sodium chloride concentration in the washing liquid reach 0.5 mol / L, stir evenly and let it stand for 3 h, centrifuge at a speed of 8000 r / min for 10 min, collect the precipitated solid, wash the precipitate with deionized water until no chloride ions can be detected, and dry the precipitate in a freeze dryer at -40 °C and a vacuum of 1 Pa for 12 hours to obtain lignin; after filtering the supernatant after centrifugation through a 0.22-μm filter membrane, rotate and evaporate it in a rotary evaporator at a temperature of 50 °C and a vacuum of -0.06 MPa to obtain the recycled eutectic solvent. Add the recycled eutectic solvent to the new lignocellulosic biomass and repeat the above operations. After recycling 3 times, first add the newly prepared eutectic solvent accounting for 5% of the mass of the recycled solvent, and measure the pH value. If it does not reach the pH value of the original eutectic solvent, continue to add the newly prepared eutectic solvent in small amounts and multiple times until the pH values are the same, and continue to recycle.

[0075] Example 2

[0076] The difference between this example and Example 1 is that: betaine and malic acid are mixed in a molar ratio of 1:4, stirred and reacted in a three-necked flask at 60 °C and 400 r / min for 4 hours under nitrogen protection, and a eutectic solvent is obtained after cooling;

[0077] The lignocellulosic biomass is crushed and sieved through a 70-mesh sieve, and then mixed with the deep eutectic solvent at a mass ratio of 1:20. The high-pressure reactor is maintained at a temperature of 135 °C, a pressure of 1 MPa, and a stirring speed of 75 r / min for 6 hours. The antisolvent acetone and n-butanol are added at a volume ratio of 7:2 and a volume ratio of 1:10 to the mixture, and ultrasonic treatment is carried out at 30 kHz for 20 minutes. Then, filtration and washing are performed until the conductivity meets the standard:

[0078] The filter residue is soaked in an 8% sodium bicarbonate solution for 1.5 hours, washed until neutral, and dried in a vacuum drying oven at -0.09 MPa and 50 °C for 36 hours:

[0079] 15% sodium chloride solution is added to the washing liquid until the concentration reaches 1 mol / L, and it is left standing for 4.5 h. Then, centrifugation is carried out at 9000 r / min for 15 min. The precipitate is freeze-dried at -45 °C and 5 Pa for 18 hours to obtain lignin. After the supernatant is filtered, the solvent is recovered by rotary evaporation at 60 °C and -0.07 MPa, and the cycle is repeated 3 times. First, 7% of the newly prepared deep eutectic solvent is replenished.

[0080] Example 3

[0081] The difference between this example and Example 1 is that betaine and malic acid are mixed at a molar ratio of 1:5, and the reaction is carried out with stirring at 70 °C and 500 r / min in a three-necked flask for 5 hours under nitrogen protection. After cooling, the deep eutectic solvent is obtained:

[0082] The lignocellulosic biomass is sieved through an 80-mesh sieve and mixed with the deep eutectic solvent at a ratio of 1:25. The high-pressure reactor is maintained at 150 °C, 1.5 MPa, and a stirring speed of 100 r / min for 8 hours. The antisolvent has a volume ratio of 4:1 and is added at a volume ratio of 1:12 to the mixture, and ultrasonic treatment is carried out at 40 kHz for 30 minutes. Then, filtration and washing are performed until the conductivity meets the standard:

[0083] The filter residue is soaked in a 10% sodium bicarbonate solution for 2 hours, washed until neutral, and dried in a vacuum drying oven at -0.1 MPa and 60 °C for 48 hours:

[0084] 20% sodium chloride solution is added to the washing liquid until the concentration reaches 1.5 mol / L, and it is left standing for 6 h. Then, centrifugation is carried out at 10000 r / min for 20 min. The precipitate is freeze-dried at -50 °C and 10 Pa for 24 hours to obtain lignin. After the supernatant is filtered, the solvent is recovered by rotary evaporation at 70 °C and -0.08 MPa, and the cycle is repeated 3 times. First, 10% of the newly prepared deep eutectic solvent is replenished.

[0085] Comparative Example

[0086] Betaine and oxalic acid are mixed in a molar ratio of 1:2. Betaine and oxalic acid are placed in a common beaker and stirred at 40 °C at a speed of 200 r / min for 2 hours under the action of a magnetic stirrer. Gas protection is not carried out during the reaction. After the reaction, it is cooled to room temperature to obtain the deep eutectic solvent;

[0087] The lignocellulosic biomass that has been pulverized and passed through a 60-mesh sieve is mixed with a deep eutectic solvent at a mass ratio of 1:10, placed in a common reaction kettle, the temperature is set at 100 °C, and under the normal pressure condition of an internal pressure of 0.1 MPa, it is stirred and reacted at a speed of 50 r / min for 3 hours. Acetone and n-butanol are mixed in a volume ratio of 2:1 to prepare an anti-solvent, which is added at an anti-solvent to mixture volume ratio of 1:5. After stirring, the filter residue is washed with deionized water until the conductivity of the washing liquid is lower than 50 μS / cm;

[0088] The washed filter residue is first soaked in a 3% sodium bicarbonate solution for 0.5 hours, rinsed with deionized water, and then dried in a vacuum drying oven at a vacuum degree of -0.05 MPa and a temperature of 35 °C for 12 hours to obtain a cellulose-rich solid;

[0089] In the first round, betaine and oxalic acid are reacted in a molar ratio of 1:2 in a common beaker at 40 °C and 200 r / min for 2 hours to prepare a deep eutectic solvent, which is reacted with the lignocellulosic biomass that has been pulverized and passed through a 60-mesh sieve in a common reaction kettle at 100 °C, 0.1 MPa, and 50 r / min for 3 hours. Then, an anti-solvent of acetone and n-butanol mixed in a volume ratio of 2:1 is added to the reacted mixed system and stirred evenly. The filter residue is separated by suction filtration, and the filter residue is washed with deionized water until the conductivity of the washing liquid is lower than 50 μS / cm. The filtrate containing the deep eutectic solvent, unreacted oxalic acid and betaine, lignocellulose degradation products, and anti-solvent is collected;

[0090] The collected filtrate is transferred to a distillation device. Since the boiling point of acetone is about 56 °C and the boiling point of n-butanol is about 117.7 °C, the distillation temperature is set slightly higher than the boiling point of acetone, and distillation is carried out under normal pressure to separate and recover acetone. Subsequently, the distillation temperature is raised to close to the boiling point of n-butanol to distill and recover n-butanol. After the distillation is completed, the remaining concentrated liquid is the preliminarily recovered deep eutectic solvent;

[0091] The preliminarily recovered deep eutectic solvent is filtered using a 0.22 μm filter membrane to remove the residual lignocellulose solid particles and other insoluble impurities therein;

[0092] An appropriate amount of activated carbon is added to the filtered deep eutectic solvent, stirred for 30 minutes, and the residual organic small molecule impurities and pigments are removed by the adsorption of activated carbon. Then, the activated carbon is separated by suction filtration to obtain a further purified deep eutectic solvent;

[0093] Since the components of the deep eutectic solvent will be somewhat depleted during the reaction and recovery process, an appropriate amount of betaine and oxalic acid raw materials are supplemented to the purified deep eutectic solvent according to the original molar ratio, and the supplement amount is estimated according to the mass and loss situation of the recovered solvent;

[0094] The eutectic solvent after adding supplementary raw materials is mixed with the newly pulverized lignocellulosic biomass that has passed through a 60-mesh sieve at a mass ratio of 1:10, and then placed in a common reaction kettle. The second-round reaction is carried out under the conditions of 100 °C, 0.1 MPa, and 50 r / min. After the reaction, repeat the above steps of "treatment of the mixed solution after the first-round reaction" and "purification treatment of the eutectic solvent" for the third round and subsequent recycling.

[0095] Experimental Table 1

[0096]

[0097] According to the above experimental table, the method of fractionating lignocellulosic biomass with the eutectic solvent improves the dissolution rate of lignocellulose, the purity of cellulose-rich solids, and the purity of lignin.

[0098] Experimental Table 2

[0099]

[0100]

[0101] Through the above experimental table, the method of recycling the fractionation of lignocellulosic biomass with the eutectic solvent improves the fractionation efficiency of the eutectic solvent after recycling, increases the recovery rate of the eutectic solvent, and reduces the impurity content in the product.

[0102] Although the embodiments of the present invention have been shown and described, for those of ordinary skill in the art, it can be understood that various changes, modifications, substitutions, and variations can be made to these embodiments without departing from the principles and spirit of the present invention. The scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. Method for fractionating lignocellulosic biomass by deep eutectic solvent, characterized in that, It includes the following steps: Mix betaine and malic acid and then stir. After the reaction ends, cool it to room temperature to obtain a clear and transparent deep eutectic solvent; Mix the crushed lignocellulosic biomass with the deep eutectic solvent and put it into a high-pressure reactor; Mix acetone and n-butanol in a volume ratio of 3:2 - 4:1 to prepare an anti-solvent; Slowly add the anti-solvent to the mixture of lignocellulosic biomass and deep eutectic solvent. After stirring, perform ultrasonic treatment, then perform suction filtration, and wash the filter residue with deionized water; Place the washed filter residue in a vacuum drying oven to obtain a cellulose-rich solid.

2. The method for fractionating lignocellulosic biomass with a deep eutectic solvent according to claim 1, wherein Mix the betaine and malic acid in a molar ratio of 1:3 - 1:5 and load them into a three-necked flask with stirring and temperature control functions. Stir and react at 50 - 70 °C for 3 - 5 hours. The stirring speed is 300 - 500 r / min, and nitrogen is continuously introduced for protection during the reaction.

3. The method for fractionating lignocellulosic biomass with a eutectic solvent according to claim 1, wherein The lignocellulosic biomass is crushed and passed through a 60 - 80 mesh sieve. The lignocellulosic biomass and the deep eutectic solvent are mixed in a mass ratio of 1:15 - 1:

25. The temperature of the high-pressure reactor is set at 120 - 150 °C, and the internal pressure is set at 0.5 - 1.5 MPa. React for 4 - 8 hours and stir at a speed of 50 - 100 r / min during the reaction.

4. The method for fractionating lignocellulosic biomass by eutectic solvent according to claim 1, characterized in that, The volume ratio of the anti-solvent to the mixture of lignocellulosic biomass and deep eutectic solvent is 1:8 - 1:

12. The ultrasonic frequency during ultrasonic treatment is 20 - 40 kHz. Ultrasonic treatment is carried out for 15 - 30 minutes. Wash the filter residue with deionized water until the conductivity of the washing liquid is lower than 50 μS / cm.

5. The method for fractionating lignocellulosic biomass with a eutectic solvent according to claim 1, characterized in that, Before drying the cellulose-rich solid in the vacuum drying oven, soak it in a sodium bicarbonate solution with a mass fraction of 5 - 10% for 1 - 2 hours. The vacuum drying oven dries the filter residue at a temperature of 40 - 60 °C and a vacuum degree of -0.08 - -0.1 MPa for 24 - 48 hours.

6. Method for recycling lignocellulosic biomass by eutectic solvent fractionation, characterized in that, For the method of fractionating lignocellulosic biomass with the deep eutectic solvent according to any one of claims 1 - 8, the method includes the following steps: Combine the washing liquids during the fractionation process, add sodium chloride solution, stir evenly and then let it stand, then perform centrifugation, collect the precipitated solid, wash the precipitate with deionized water until no chloride ions can be detected in the washing liquid, separate the supernatant from the precipitate, and then place the precipitate in a freeze dryer to obtain lignin; Transfer the centrifuged supernatant to a rotary evaporator to obtain the recycled deep eutectic solvent; Add the recycled deep eutectic solvent to the new lignocellulosic biomass, and repeat the above steps of pretreatment, anti-solvent addition, component fractionation, and component recovery. After recycling 3 times, use a glass electrode pH meter to measure the pH value of the solvent. Add newly prepared deep eutectic solvent to the recycled deep eutectic solvent and continue to recycle.

7. The method for recycling lignocellulosic biomass by eutectic solvent fractionation according to claim 6, characterized in that, The mass fraction of sodium chloride is 10-20%, so that the concentration of sodium chloride in the washing solution reaches 0.5-1.5 mol / L. The standing time is 3-6 h. When centrifuging, the centrifugal speed is 8000-10000 r / min, and the centrifugal time is 10-20 min. The precipitate is placed in a freeze dryer and dried for 12-24 hours under the conditions of -40--50 °C and a vacuum degree of 1-10 Pa.

8. The method for recycling lignocellulosic biomass by eutectic solvent fractionation according to claim 6, wherein The supernatant is rotary evaporated in a rotary evaporator under the conditions of a temperature of 50-70 °C and a vacuum degree of -0.06--0.08 MPa to remove acetone, n-butanol and water therein.

9. The method for recycling lignocellulosic biomass by eutectic solvent fractionation according to claim 6, characterized in that, Add the newly prepared deep eutectic solvent until the pH value is the same as that of the original deep eutectic solvent. First, add it according to 5-10% of the mass of the recovered deep eutectic solvent, and then detect the pH value. If the pH value does not reach that of the original deep eutectic solvent, continue to add the newly prepared deep eutectic solvent in small amounts and multiple times until the pH values are the same.

10. The method for recycling lignocellulosic biomass by eutectic solvent fractionation according to claim 6, characterized in that, Before rotary evaporating the supernatant in the rotary evaporator, the supernatant needs to be filtered first, and the filtering medium is a filter membrane with a pore size of 0.22-0.45 μm.

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