Method for carrying out stacking pretreatment on lignocellulose biomass under assistance of alkaline organic solution

Abstract

The invention discloses a method for stacking pretreatment of lignocellulose biomass assisted by an alkaline organic solution. The method comprises the following steps: firstly, immersing lignocellulose biomass in an alkaline organic solution, and then carrying out compression densification treatment to obtain a homogenized raw material; and finally, stacking the homogenized raw materials at the ambient temperature for a period of time to finish pretreatment. According to the method, consumption of alkaline reagents and solvents is effectively reduced, the pretreatment process is mild, washing or detoxification is not needed, residues can be directly used for bioconversion, lignin components can be recycled, and the method has the advantages of low energy consumption, low cost, high efficiency and the like and is suitable for large-scale industrial application. According to the method, under the condition that the alkali dosage is 0.02 g / g, the sugar concentration of the enzymatic hydrolysate is more than 200 g / L by feeding in batches.

Description

Technical Field:

[0001] The present invention relates to the technical field of biomass energy conversion and utilization, and particularly to a method for pretreating lignocellulosic biomass stacking assisted by an alkaline organic solution. Background Art:

[0002] Pretreatment is the basis for separating cellulose, hemicellulose, and lignin components in lignocellulosic agricultural and forestry waste, so as to convert them into fuels, materials, and chemicals through the biorefining process. Although existing pretreatment methods such as crushing and grinding, acid / alkali pretreatment, steam explosion, hydrothermal method, organic solvent method, and DES method can effectively improve the enzymatic hydrolysis or conversion and utilization efficiency of lignocellulose components, they have deficiencies such as harsh pretreatment conditions, difficult solvent recycling, large reagent consumption, and a large amount of inhibitors generated, resulting in a cumbersome pretreatment technical process and limited economic feasibility. Therefore, it is necessary to develop a new type of pretreatment technology with high efficiency and low cost. On the basis of ensuring the efficient disassembly and separation of pretreatment components, achieving low energy consumption, low consumption, and low inhibition in the pretreatment process is the key to effectively reducing costs. At the same time, lignocellulosic agricultural and forestry waste is loose in form and has problems such as seasonal acquisition and easy deterioration during storage, which are also key issues that need to be considered and solved in pretreatment.

[0003] Therefore, an ideal pretreatment technology, while paying attention to the efficient utilization of cellulose and hemicellulose components, should preferably have the following characteristics as much as possible: 1) A pretreatment method for raw materials with high density and good storability to reduce processing and storage costs; 2) Carried out at normal pressure at room temperature or ambient temperature to reduce energy consumption and equipment requirements; 3) An extremely low liquid-solid ratio to reduce solvent consumption; 4) An extremely low dosage of reagents such as acids / alkalis / salts to reduce reagent costs and equipment requirements; 5) The pretreatment residue can be directly and efficiently converted and utilized without washing or reprocessing to simplify the process and reduce consumption; 6) Considering the stabilization and value-added utilization of lignin components under solvation to improve the overall economy of the process; 7) The pretreatment liquid should reduce or avoid the recycling and regeneration process to simplify the pretreatment process and consumption.

[0004] By means of densification, the density and transportation efficiency of lignocellulose can be significantly improved. Chemical densification involves adding chemical reagents (such as acidic reagents, alkaline reagents, or inorganic salts, etc.) during the densification process to disrupt the structure of lignocellulose and improve its digestibility. For example, Patent CN111793662A discloses a method of adding an alkaline reagent during the densification of lignocellulose, achieving the pretreatment of the densification process, saving the pretreatment cost and improving the enzymatic hydrolysis efficiency. Patent CN112111540A and CN117737158A respectively disclose a method of adding an acidic reagent and a combination of calcium hydroxide and hydrogen peroxide during the densification process. These methods can improve the sugar conversion rate and fermentation performance of lignocellulose while reducing the severity of pretreatment. In addition, Patent CN117265039A also discloses a pretreatment method of densifying lignocellulose together with Fenton's reagent. By the strong oxidizing property of Fenton's reagent to disrupt the structure of lignocellulose, the enzymatic hydrolysis saccharification efficiency is significantly improved. Although the above chemical densification pretreatment technologies can effectively disrupt the structure of lignocellulose and achieve effective enzymatic hydrolysis saccharification of the raw material cellulose and hemicellulose components at room temperature, they neglect the utilization of the lignin component, and the mixing of the raw material and a small amount of solution during the pretreatment limits the liquid-solid mass transfer. Problems such as the high concentration of chemical reagents in the solution being prone to corrode equipment, high reagent consumption, and the subsequent conversion of the disassembled components being prone to generate inhibitors still need to be further improved. Summary of the Invention:

[0005] The present invention solves the problems existing in the prior art and provides a method for pretreating lignocellulosic biomass stacking assisted by an alkaline organic solution to achieve effective disassembly of lignocellulosic agricultural and forestry waste with low energy consumption, low consumption, and low inhibition.

[0006] The object of the present invention is to provide a method for pretreating lignocellulosic biomass stacking assisted by an alkaline organic solution, comprising the following steps:

[0007] (1) Pre-impregnation: Immerse the lignocellulosic biomass in the alkaline organic solution until the alkaline catalyst effectively infiltrates the interior of the raw material to obtain the raw material infiltrated with the alkaline catalyst. The alkaline organic solution is prepared by mixing an alkaline catalyst and an organic solution. The organic solution is a homogeneous solution composed of a lignin-dissolving organic solvent, a co-solvent, and water. The volume content of the lignin-dissolving organic solvent in the organic solution is not less than 1%, the volume content of the co-solvent is not more than 40%, and the volume content of water is not less than 20%;

[0008] (2) Homogenization: Perform compression densification treatment on the raw material infiltrated with the alkaline catalyst to obtain a homogenized lignocellulose raw material and a press filtrate;

[0009] (3) Stacking: After stacking the homogenized lignocellulosic raw materials at ambient temperature for a period of time, lignocellulose pretreatment residues are obtained, which can be directly used for bioconversion or used for bioconversion after separating and recovering lignin.

[0010] The method proposed by the present invention first realizes the effective penetration of the alkaline catalyst inside the lignocellulosic raw materials by pre-impregnating with an organic solution; then realizes the homogenized mixing of the lignocellulosic raw materials and the solution through methods such as pressure filtration, extrusion, granulation, briquetting or their combination, while effectively reducing the actual consumption of the solution and the alkaline catalyst; finally, the homogenized lignocellulosic raw materials are placed at ambient temperature for a period of time to complete the pretreatment process.

[0011] This pretreatment method utilizes the solvent effect of the organic solvent to promote the effective swelling of the solution on the lignocellulosic raw materials in the pre-impregnation stage, strengthen the cleavage of the raw material components during the stacking stage, couple with the good lignin-dissolving performance of the solvent, and achieve the low-energy and effective separation of lignocellulose components at ambient temperature; this pretreatment process is mild, without the generation of inhibitors, and the residues can be directly used for high-efficiency enzymatic hydrolysis without water washing or detoxification to obtain a high-concentration reducing sugar solution, and the lignin components can be recovered by collecting the precipitate in the pretreatment solution; in addition, the homogenized raw materials obtained by this method are convenient for transportation and storage, effectively reducing the raw material transportation cost, and pretreatment can be achieved during storage.

[0012] Preferably, the particle size of the lignocellulosic biomass in step (1) is not greater than 5 mm, and the lignocellulosic biomass contains cellulose or hemicellulose components.

[0013] More preferably, the lignocellulosic biomass in step (1) includes pennisetum, miscanthus, wood chips, straw, bagasse, bamboo chips, furfural residues, agricultural and forestry waste, and processing waste of the above substances.

[0014] Preferably, the lignocellulosic biomass in step (1) is impregnated in an alkaline organic solution, and the usage amount of the organic solution is limited to the minimum volume for submerging the raw materials (i.e., the lignocellulosic biomass). More preferably, the volume-mass ratio of the organic solution to the raw materials is (4 - 8) mL / g.

[0015] Preferably, the lignin-dissolving organic solvent in step (1) is an organic solvent that can swell lignocellulose and dissolve lignin, and the co-solvent is an organic solvent with a content less than that of the lignin-dissolving organic solvent in the organic solution and strengthens the solvent effect during pretreatment.

[0016] The organic solvents for dissolving lignin are not easily volatile and usually have a boiling point greater than 100 °C. The enhanced solvent effect refers to the beneficial effects on pretreatment after adding the organic solvents for dissolving lignin and co-solvents in the solution, including but not limited to enhancing the liquid-solid mass transfer between the solution and the raw material by reducing the solution viscosity and forming a homogeneous solution; occurring a solvent grafting reaction between the solvent and the raw material components to generate solvated components; modulating the solubility parameter of the solution to improve the lignin dissolution performance of the solution; enhancing the alkalinity of the catalyst to promote the bond breaking and decomposition of components, etc.

[0017] Further preferably, the organic solvents for dissolving lignin in step (1) are selected from one or more of triethylene glycol, phenoxyethanol, glycerol formal, dihydrolevoglucosenone, tetrahydrofurfuryl alcohol, and dimethyl isosorbide, and the co-solvents are selected from one or more of ethanol, acetone, isobutanol, ethylene glycol, glycerol, triethylene glycol, phenoxyethanol, glycerol formal, dihydrolevoglucosenone, tetrahydrofurfuryl alcohol, and dimethyl isosorbide.

[0018] Preferably, the basic catalyst in step (1) is an inorganic base, an organic base, or a strongly basic weak acid salt dissolved in the organic solution, and the mass-volume ratio of the basic catalyst to the organic solution is less than 0.05 g / mL. The basic catalysts include calcium hydroxide, sodium hydroxide, potassium hydroxide, ethylenediamine, triethylamine, ammonia water, sodium acetate, disodium hydrogen phosphate, etc.

[0019] Further preferably, the mass-volume ratio of the basic catalyst to the organic solution is 0.01 - 0.03 g / mL; the volume ratio of the organic solvents for dissolving lignin, co-solvents, and water in the organic solution is (10 - 50):(0 - 25):(25 - 90).

[0020] The purpose of the pre-impregnation process is to effectively infiltrate the reagents into the interior of the raw material. The usage amount of the organic solution is limited to the minimum volume for submerging the raw material. Usually, the volume-mass ratio of the organic solution to the raw material is (4 - 8) mL / g; the impregnation time is not less than 30 min, and methods such as stirring, ultrasonic treatment, and heating can be adopted to enhance the mass transfer to shorten the impregnation time.

[0021] The compression densification treatment refers to extruding the solution contained in the infiltrated raw material by means of pressure filtration, extrusion, granulation, briquetting, or a combination thereof to increase the density and uniformity of the pretreated raw material, and obtaining a homogenized lignocellulosic raw material and a filtrate; in the homogenized lignocellulosic raw material, the volume-mass ratio of the organic solution to the raw material is (0.5 - 3.5) mL / g; the filtrate is the organic solution containing the basic catalyst extruded after the compression densification treatment, and it can be directly reused in the pre-impregnation process to effectively reduce the actual consumption of the organic solution.

[0022] In the alkaline organic solution-assisted stacking pretreatment method for lignocellulosic biomass proposed by the present invention, the concentration of the alkaline catalyst in the alkaline organic solution is less than 0.05 g / mL, and the amount of the alkaline catalyst consumed per unit mass of the raw material (dry weight) in the pretreatment is less than 0.10 g / g.

[0023] Preferably, the stacking conditions in step (3) are as follows: the stacking time is not less than 3 days, and the average daily stacking temperature is not lower than -20°C. Ambient temperature stacking refers to the storage or placement without artificial heating or cooling intervention in temperature, and preferably the average daily stacking temperature is not lower than 20°C.

[0024] Preferably, the specific steps for directly performing biological conversion and utilization in step (3) are as follows: subjecting the lignocellulose pretreatment residue to enzymatic hydrolysis to obtain reducing sugars. Direct biological conversion and utilization means that the lignocellulose pretreatment residue can be directly used as a raw material without reprocessing steps such as washing, detoxification, and heating, and chemicals and fuels are prepared through biochemical conversion pathways, including but not limited to reducing sugars, glucose, ethanol, butanol, acetone, acetic acid, lactic acid, oils and fats, proteins, biogas, amino acids, etc.

[0025] Preferably, the specific steps for separating and recovering lignin and then performing biological conversion and utilization in step (3) are as follows: washing the lignocellulose pretreatment residue with an NaOH solution, performing solid-liquid separation, collecting the lignin extract and the washing residue, adjusting the pH of the lignin extract to 2 with acid, performing centrifugal separation to obtain the lignin residue, and subjecting the lignin residue to enzymatic hydrolysis to obtain reducing sugars.

[0026] More preferably, the conditions for the enzymatic hydrolysis are as follows: adding to a citric acid-sodium citrate buffer solution with a pH of 4.8 at a substrate concentration of 3% - 20%, adding CTec3 enzyme at 8 - 12 FPU / g of cellulose, and performing enzymatic hydrolysis on a shaker at 45°C - 55°C for 65 - 75 h.

[0027] Even more preferably, the conditions for the enzymatic hydrolysis are as follows: adding to a citric acid-sodium citrate buffer solution with a pH of 4.8 at a substrate concentration of 3% - 20%, adding CTec3 enzyme at 10 FPU / g of cellulose, and performing enzymatic hydrolysis on a shaker at 50°C for 72 h.

[0028] Compared with the prior art, the present invention has the following advantages:

[0029] 1. In the pretreatment of the present invention, the method of pre-impregnating with an organic solution first and then homogenously stacking is adopted. In the pre-impregnation stage, liquid-solid mass transfer is strengthened to achieve effective mixing and immersion of the reagent and the raw material, effectively reducing the concentration of the alkaline catalyst in the solution; in the homogenously stacking stage, the solvent effect is strengthened to achieve a mild pretreatment process for the high-density homogenized raw material, effectively reducing the consumption of the alkaline catalyst.

[0030] 2. By adding an organic solution, the present invention effectively modulates the solvent effect of the pretreatment solution system, not only improving the impregnation efficiency of pre-impregnation, but also effectively strengthening the bond breaking and disassembling of the catalyst and the performance of solvation components during the stacking process, obtaining a solvent-stable lignin product and a holocellulose residue that is easy to be biochemically utilized.

[0031] 3. The present invention realizes the pretreatment process with a low liquid-solid ratio at ambient temperature, with small reagent consumption, low energy consumption, few inhibitors generated during the pretreatment process, and the residue can be directly used for biochemical conversion and utilization without further treatment.

[0032] 4. The homogenized pretreatment raw materials of the present invention using organic solvents have a high density, strong antibacterial property, convenient transportation and storage, can effectively reduce the transportation and storage costs of raw materials, and can achieve pretreatment during storage, effectively alleviating the contradiction between seasonal collection of raw materials and stable supply in production.

[0033] 5. The present invention discloses a method for stacking and pretreating lignocellulosic biomass assisted by an alkaline organic solution. The method first impregnates the lignocellulosic biomass in an organic solution containing an alkaline catalyst, and then performs compression densification treatment such as pressure filtration, extrusion, granulation, briquetting or a combination thereof to obtain homogenized raw materials; finally, the homogenized raw materials are stacked at ambient temperature for a period of time to complete the pretreatment. The present invention effectively reduces the consumption of reagents and solvents, the pretreatment process is mild, no washing or detoxification is required, the residue can be directly used for biological conversion, and the lignin component can be recovered, having the advantages of low energy consumption, low cost, high efficiency, etc., and is suitable for large-scale industrial application. The present invention realizes a batch-fed enzymatic hydrolysis sugar concentration exceeding 200 g / L at an alkali dosage of 0.02 g / g of raw materials. Specific embodiments:

[0034] The following examples are further illustrations of the present invention rather than limitations thereof.

[0035] Unless otherwise defined, all professional terms used hereinafter have the same meaning as commonly understood by those skilled in the art. The professional terms used herein are only for the purpose of describing specific embodiments and are not intended to limit the protection scope of the present invention. Unless otherwise specified, the experimental materials and reagents herein are all conventional commercially available products in the technical field.

[0036] Example 1

[0037] Using bagasse with a particle size of 5 mm (containing 41.5% cellulose, 23.2% hemicellulose, and 20.1% lignin) as the raw material, an alkaline organic solution is prepared according to a NaOH concentration of 0.02 g / mL and a volume ratio of 50:25:25 of phenoxyethanol, acetone and water, and the following steps are carried out:

[0038] (1) Pre - impregnation: The raw materials are infiltrated in an alkaline organic solution at a ratio of 8 mL / g of the alkaline organic solution to the raw materials, and left standing at room temperature for 30 min to enable the effective infiltration of the reagent into the interior of the raw materials.

[0039] (2) Homogenization: The raw materials effectively infiltrated with the reagent are subjected to pressure filtration to obtain homogenized lignocellulose raw materials and filtrate.

[0040] (3) Stacking: The homogenized lignocellulose raw materials are stacked at ambient temperature (during stacking, the room temperature is 20 °C - 27 °C) for 1 day, 3 days, 7 days, 14 days, 28 days, and 56 days respectively to obtain lignocellulose pretreatment residues.

[0041] (4) Enzymatic hydrolysis and utilization: The lignocellulose pretreatment residues are directly subjected to enzymatic hydrolysis. At a substrate concentration of 5%, they are added to a citric acid - sodium citrate buffer solution with a pH of 4.8, and CTec3 enzyme at 10 FPU / g of cellulose is added, and enzymatic hydrolysis is carried out on a shaker at 50 °C for 72 h.

[0042] In this example, the volume - mass ratio of the solution to the raw materials in the obtained homogenized lignocellulose raw materials is 3.0 mL / g, and the dosage of the alkaline catalyst is 0.06 g / g of the raw materials. After stacking for 1 day, 3 days, 7 days, 14 days, 28 days, and 56 days, no traces of microbial growth were observed on the surface of the obtained lignocellulose pretreatment residues, and the direct enzymatic hydrolysis efficiencies were 20.6%, 45.2%, 83.1%, 94.5%, 90.3%, and 92.5% respectively.

[0043] Comparative Example 1

[0044] This comparative example is to compare the pretreatment effects of an alkaline aqueous solution and an alkaline organic solution (Example 1) under the same conditions. The specific process is the same as that of Example 1, except that no organic solvent is added to the alkaline aqueous solution, that is, the composition of the alkaline aqueous solution is 0.02 g / mL of NaOH concentration and 100% water.

[0045] In this comparative example, the volume - mass ratio of the solution to the raw materials in the obtained homogenized lignocellulose raw materials is 3.0 mL / g, and the dosage of the alkaline catalyst is 0.06 g / g of the raw materials. After stacking for 1 day and 3 days, no traces of microbial growth were observed on the surface of the obtained lignocellulose pretreatment residues, but after 7 days, 14 days, 28 days, and 56 days, obvious microbial growth was observed on the surface of the obtained lignocellulose pretreatment residues, and the direct enzymatic hydrolysis efficiencies were 18.9%, 32.1%, 47.2%, 54.7%, 55.2%, and 38.4% respectively.

[0046] In Comparative Example 1, there were obvious traces of microbial growth on the surface of the pretreated residue stacked for more than 3 days, while in Example 1, there was no obvious microbial growth on all the stacked pretreated residues, indicating that the addition of organic solvents had an obvious effect of inhibiting microbial growth and was beneficial to the storage of raw materials.

[0047] The enzymatic hydrolysis efficiencies in Comparative Example 1 were 18.9%, 32.1%, 47.2%, 54.7%, 55.2% and 38.4% respectively, while the enzymatic hydrolysis efficiencies in Example 1 were 20.6%, 45.2%, 83.1%, 94.5%, 90.3% and 92.5% respectively. It can be seen that the addition of organic solvents strengthened the pretreatment and significantly increased the enzymatic hydrolysis efficiency.

[0048] Comparative Example 2

[0049] Same as Example 1, except that: the raw materials of the effective infiltration reagent were not homogenized and were directly stacked.

[0050] In this comparative example, the volume-mass ratio of the solution to the raw material in the non-homogenized lignocellulose raw material was 8.0 mL / g, and the dosage of the alkaline catalyst was 0.16 g / g of the raw material. After stacking for 1 day, 3 days, 7 days and 14 days, no traces of microbial growth were observed on the surface of the obtained lignocellulose pretreated residue, and the direct enzymatic hydrolysis efficiencies were 15.3%, 20.0%, 17.8% and 18.8% respectively.

[0051] The enzymatic hydrolysis efficiency of the pretreated residue in Comparative Example 2 was significantly lower. It was speculated that too much organic solvent inhibited the enzymatic hydrolysis process. It can be seen that homogenization can not only effectively reduce the actual solution consumption, but also improve the direct enzymatic hydrolysis efficiency of the residue. The combined action of the alkaline organic solution impregnation and homogenization treatment proposed in the present invention reduces the solution alkali concentration and alkali consumption, and simultaneously separates lignin.

[0052] Example 2

[0053] Using corn stover with a particle size of 2 mm (containing 32.3% cellulose, 21.0% hemicellulose, 15.6% lignin) as the raw material, a basic organic solution was prepared according to the NaOH concentration of 0.02 g / mL and the volume ratio of 20:80 of triethylene glycol and water, and the following steps were carried out:

[0054] (1) Pre-impregnation: According to the ratio of the basic organic solution to the raw material of 6 mL / g, the raw material was infiltrated in the basic organic solution and stirred at room temperature for 30 min to enable the reagent to effectively infiltrate the inside of the raw material;

[0055] (2) Homogenization: The raw material with the effective infiltration reagent was subjected to pressure filtration and granulation treatment to obtain homogenized lignocellulose raw material and filtrate;

[0056] (3) Stacking: The homogenized lignocellulosic raw materials are stacked at ambient temperature (during stacking, the room temperature is 20°C - 27°C) for 14 days to obtain lignocellulosic pretreatment residues;

[0057] (4) Enzymatic hydrolysis and utilization: The lignocellulosic pretreatment residues are subjected to high-solid enzymatic hydrolysis in a fed-batch manner. The substrate concentration is 20%, using a citric acid-sodium citrate buffer solution with pH 4.8, and CTec3 enzyme at 10 FPU / g of cellulose, and enzymatic hydrolysis is carried out on a shaker at 50°C. At 12 h, 24 h, and 36 h of enzymatic hydrolysis, an equal amount of residues and CTec3 enzyme at 10 FPU / g of cellulose are added respectively to make the substrate concentration reach 38%, until enzymatic hydrolysis for 72 h.

[0058] In this example, the volume-mass ratio of the solution to the raw material in the obtained homogenized lignocellulosic raw materials is 1.1 mL / g, and the dosage of the alkaline catalyst is 0.022 g / g of the raw material. After fed-batch high-solid enzymatic hydrolysis, the glucose concentration is 137.5 g / L, and the xylose concentration is 73.8 g / L.

[0059] Example 3

[0060] Using bamboo chips with a particle size of 5 mm (containing 42.8% cellulose, 19.2% hemicellulose, and 20.8% lignin) as raw materials, an alkaline organic solution is prepared according to a NaOH concentration of 0.01 g / mL and a volume ratio of 40:60 of tetrahydrofurfuryl alcohol and water, and the following steps are carried out:

[0061] (1) Pre-impregnation: According to the ratio of the alkaline organic solution to the raw material of 4 mL / g, the raw materials are immersed in the alkaline organic solution and stirred at room temperature for 30 min to effectively infiltrate the reagents into the interior of the raw materials;

[0062] (2) Homogenization: The raw materials effectively infiltrated with reagents are subjected to pressure filtration to obtain homogenized lignocellulosic raw materials and filtrates;

[0063] (3) Stacking: The homogenized lignocellulosic raw materials are stacked at ambient temperature (during stacking, the room temperature is 20°C - 27°C) for 28 days to obtain lignocellulosic pretreatment residues;

[0064] (4) Lignin extraction: At room temperature, the lignocellulosic pretreatment residues are washed multiple times with a NaOH solution of 0.02 g / mL, and solid-liquid separation is carried out to collect the lignin extraction solution and the washed residues. The lignin extraction solution is acidified to pH = 2 and centrifuged to obtain lignin residues;

[0065] (5) Enzymatic hydrolysis and utilization: The lignin residues are enzymatically hydrolyzed. According to a substrate concentration of 5%, they are added to a citric acid-sodium citrate buffer solution with pH 4.8, and CTec3 enzyme at 10 FPU / g of cellulose is added, and enzymatic hydrolysis is carried out on a shaker at 50°C for 72 h.

[0066] In this example, the volume-mass ratio of the solution to the raw material in the obtained homogenized lignocellulosic raw material is 3.1 mL / g, the dosage of the alkaline catalyst is 0.031 g / g of the raw material, 86.3 mg / g of the raw material of lignin residue is obtained by extraction, and the enzymatic hydrolysis rate of the washed pretreatment residue is 92.7%.

[0067] Example 4

[0068] Using bamboo chips with a particle size of 5 mm (containing 42.8% cellulose, 19.2% hemicellulose, and 20.8% lignin) as the raw material, and using the pressure filtrate recovered in Example 3 as the alkaline organic solution, the following steps are carried out:

[0069] (1) Pre-impregnation: According to the ratio of the alkaline organic solution to the raw material of 6 mL / g, immerse the raw material in the alkaline organic solution, stir at room temperature for 30 min to effectively infiltrate the reagent into the interior of the raw material;

[0070] (2) Homogenization: Carry out pressure filtration on the raw material effectively infiltrated with the reagent to obtain homogenized lignocellulosic raw material and pressure filtrate;

[0071] (3) Stacking: Stack the homogenized lignocellulosic raw material at ambient temperature (during stacking, the room temperature is 20°C to 27°C) for 28 days to obtain lignocellulose pretreatment residue;

[0072] (4) Lignin extraction: At room temperature, wash the lignocellulose pretreatment residue with 0.02 g / mL NaOH solution multiple times, perform solid-liquid separation, collect the lignin extract and the washed residue, adjust the pH of the lignin extract to 2 with acid, and perform centrifugal separation to obtain lignin residue;

[0073] (5) Enzymatic hydrolysis utilization: Enzymatically hydrolyze the washed lignocellulose pretreatment residue, add it to a citric acid-sodium citrate buffer solution with a pH of 4.8 at a substrate concentration of 5%, add CTec3 enzyme at 10 FPU / g of cellulose, and perform enzymatic hydrolysis on a shaker at 50°C for 72 h.

[0074] In this example, 91.7 mg / g of the raw material of lignin residue is obtained by extraction, and the enzymatic hydrolysis rate of the washed pretreatment residue is 90.3%.

[0075] Example 5

[0076] Using corn straw with a particle size of 2 mm (containing 32.3% cellulose, 21.0% hemicellulose, and 15.6% lignin) as the raw material, preparing an alkaline organic solution according to an ethylenediamine concentration of 0.03 g / mL and a volume ratio of 10:90 of tetrahydrofurfuryl alcohol and water, and performing the following steps:

[0077] (1) Pre-impregnation: According to the ratio of the alkaline organic solution to the raw material of 8 mL / g, immerse the raw material in the alkaline organic solution, and let it stand at room temperature for 1 h to effectively infiltrate the reagent into the interior of the raw material;

[0078] (2) Homogenization: The raw materials of the effective wetting reagent are subjected to pressure filtration and granulation to obtain homogenized lignocellulose raw materials and filtrate under pressure.

[0079] (3) Stacking: The homogenized lignocellulose raw materials are placed in a refrigerator at -20 °C for 28 days to obtain pretreated lignocellulose residues.

[0080] (4) Enzymatic hydrolysis utilization: The pretreated lignocellulose residues are directly enzymatically hydrolyzed. According to a substrate concentration of 3%, they are added to a citric acid-sodium citrate buffer solution with a pH of 4.8, and CTec3 enzyme at 10 FPU / g of cellulose is added, and enzymatic hydrolysis is carried out on a shaker at 50 °C for 72 h.

[0081] In this example, the volume-mass ratio of the solution to the raw materials in the obtained homogenized lignocellulose raw materials is 1.7 mL / g, and the dosage of the alkaline catalyst is 0.051 g / g of the raw materials. The efficiency of the direct enzymatic hydrolysis of the pretreated lignocellulose residues is 82.3%.

[0082] The description of the above examples is only used to help understand the technical solution and its core idea of the present invention. It should be pointed out that for those skilled in the art of this technology, without departing from the principle of the present invention, several improvements and modifications can still be made to the present invention, and these improvements and modifications also fall within the protection scope of the claims of the present invention.

Claims

1. A method for pre - treating lignocellulosic biomass stacking assisted by an alkaline organic solution, characterized in that It includes the following steps: (1) Pre-impregnation: Immerse lignocellulosic biomass in an alkaline organic solution until the alkaline catalyst effectively infiltrates the interior of the raw material to obtain the raw material infiltrated with the alkaline catalyst. The alkaline organic solution is prepared by mixing an alkaline catalyst and an organic solution. The organic solution is a homogeneous solution composed of a lignin-dissolving organic solvent, a co-solvent, and water. The volume content of the lignin-dissolving organic solvent in the organic solution is not less than 1%, the volume content of the co-solvent is not more than 40%, and the volume content of water is not less than 20%; (2) Homogenization: Perform compression densification treatment on the raw material infiltrated with the alkaline catalyst to obtain homogenized lignocellulose raw material and recyclable pressure filtrate; (3) Stacking: After stacking the homogenized lignocellulose raw material at ambient temperature for a period of time, obtain lignocellulose pretreatment residue, and directly carry out bioconversion utilization on it or carry out bioconversion utilization after separating and recovering lignin.

2. The method according to claim 1, wherein The particle size of the lignocellulosic biomass in step (1) is not more than 5 mm, and it includes pennisetum, miscanthus, wood chips, straw, bagasse, bamboo chips, furfural residue, agricultural and forestry waste, and processing waste of the above substances.

3. The method according to claim 1, characterized in that, In step (1), the lignocellulosic biomass is immersed in the alkaline organic solution, and the usage amount of the organic solution is limited to the minimum volume for submerging the raw material.

4. The method according to claim 1, wherein The lignin-dissolving organic solvent in step (1) is an organic solvent that can swell lignocellulose and dissolve lignin, and the co-solvent is an organic solvent with a content less than that of the lignin-dissolving organic solvent in the organic solution and can enhance the solvent effect in the pretreatment.

5. The method according to claim 4, characterized in that The lignin-dissolving organic solvent in step (1) is selected from one or more of triethylene glycol, phenoxyethanol, glycerol formal, dihydrolevoglucosenone, tetrahydrofurfuryl alcohol, and dimethyl isosorbide. The co-solvent is selected from one or more of ethanol, acetone, isobutanol, ethylene glycol, glycerol, triethylene glycol, phenoxyethanol, glycerol formal, dihydrolevoglucosenone, tetrahydrofurfuryl alcohol, and dimethyl isosorbide.

6. The method according to claim 1, characterized in that The alkaline catalyst in step (1) is an inorganic base, an organic base, or a strongly basic weak salt that is soluble in the organic solution, and the mass-volume ratio of the alkaline catalyst to the organic solution is less than 0.05 g / mL.

7. The method according to claim 1, characterized in that In the homogenized lignocellulose raw material in step (2), the volume-mass ratio of the organic solution to the raw material is (0.5 - 3.5) mL / g.

8. The method according to claim 1, characterized in that, The stacking conditions in step (3) are: the stacking time is not less than 3 days, and the average daily temperature during stacking is not lower than -20 °C.

9. The method according to claim 1, wherein The specific steps of directly carrying out bioconversion utilization in step (3) are: subject the lignocellulose pretreatment residue to enzymatic hydrolysis treatment to obtain reducing sugar.

10. The method according to claim 1, characterized in that, The specific steps of carrying out bioconversion utilization after separating and recovering lignin in step (3) are: wash the lignocellulose pretreatment residue with NaOH solution, perform solid-liquid separation, collect the lignin extraction solution and the washing residue, adjust the pH of the lignin extraction solution to 2 with acid, perform centrifugal separation to obtain lignin residue, and subject the lignin residue to enzymatic hydrolysis treatment to obtain reducing sugar.