A method for pretreatment and resource utilization of lignocellulose

Abstract

The application relates to a pretreatment agent for lignocellulose, which is a eutectic solvent and comprises glycerol, choline chloride and sulfuric acid, and has good lignocellulose pretreatment effect and recycling treatment performance. The application also relates to a method for lignocellulose pretreatment and resource utilization, which comprises the following schemes: recycling pretreated lignocellulose by using a eutectic solvent, recycling choline chloride after solvent fermentation, and preparing a hydrogel by concentrating the recycled choline chloride and mixing the concentrated choline chloride with a pretreatment residual liquid from which an antisolvent is removed, and a new idea for pretreating lignocellulose by using a eutectic solvent and recycling and utilizing lignocellulose resources is provided. Through experiment verification, the method can ensure efficient separation of three components of pretreated lignocellulose, solve the problems of pretreatment solvent waste, high cost and low recycling rate, and has important theoretical guiding significance and practical value for industrialized production and application of efficient treatment and utilization of pretreatment solvents on lignocellulose resources.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of biomass energy and bio-fermentation, and relates to a method for pretreatment and resource utilization of lignocellulose. BACKGROUND

[0002] At present, the overuse of mineral energy has brought about serious energy crisis and environmental pollution, and the development and utilization of renewable energy have been widely studied and concerned. As the most widely renewable resource on earth, lignocellulose has the natural advantages of large output, easy availability and low cost. However, the three main components of lignocellulose (cellulose, hemicellulose and lignin) are intertwined to form an anti-degradation barrier that is difficult to remove artificially. At present, extensive research has been conducted on the pretreatment of lignocellulose, mainly including mechanical crushing, steam explosion, strong alkali and inorganic acid pretreatment and other physical and chemical methods. However, these pretreatment methods have serious problems of high energy consumption and high pollutant emission, which do not meet the requirements of environmental protection for industrial production.

[0003] Deep eutectic solvent (DES) as a new type of green renewable solvent has shown significant advantages in the resource separation and utilization of lignocellulose, and has strong separation ability for cellulose, hemicellulose and lignin. At present, extensive research has been conducted on the utilization of all components after the separation of the three components of lignocellulose, but there is still no DES pretreatment process for lignocellulose to realize industrialization. Because the consumption of DES solvent is large when pretreating lignocellulose, the solvent has low reuse rate, resulting in high cost of the pretreatment process, which limits its large-scale application. SUMMARY

[0004] In order to solve the above problems, the present application provides a method for pretreatment and resource utilization of lignocellulose. The method not only realizes the high-value utilization of lignocellulose, but also overcomes the defects of large consumption of DES solvent when pretreating lignocellulose, low reuse rate of the solvent and high cost, and therefore has great value for large-scale industrial production and practical application.

[0005] Therefore, the first aspect of the present application provides a pretreatment agent for lignocellulose, which comprises glycerol, choline chloride and sulfuric acid.

[0006] In some embodiments of the present application, in the pretreatment agent for lignocellulose, the molar ratio of glycerol to choline chloride is 2-10:1, and the sulfuric acid is 0.5wt%-3wt% of the total amount of glycerol and choline chloride.

[0007] The second aspect of the present application provides a method for pretreatment and resource utilization of lignocellulose, which comprises:

[0008] Step A, mixing pretreatment agent with lignocellulosic raw material to perform pretreatment, and then performing vacuum filtration separation to obtain solid cellulose residue and lignin-containing pretreatment residue;

[0009] Step B, adding anti-solvent water to the lignin-containing pretreatment residue to precipitate, and then removing lignin by centrifugation to obtain delignified pretreatment residue;

[0010] Step C, removing anti-solvent water from the delignified pretreatment residue by rotary evaporation to obtain delignified pretreatment residue;

[0011] Step D, adding sulfuric acid to the delignified pretreatment residue to prepare a pretreatment agent, and then recycling the pretreatment agent to steps A-C for N times until the lignin removal rate is less than 70%, and stopping the recycling, wherein N = 0-5;

[0012] When N = 0, the pretreatment agent is the pretreatment agent for lignocellulose according to the first aspect of the present application.

[0013] When N = 1-5, the pretreatment agent is prepared from the delignified pretreatment residue and sulfuric acid.

[0014] In some embodiments of the present application, in step D, the amount of sulfuric acid added is 0.5wt% to 3wt% of the delignified pretreatment residue.

[0015] In some embodiments of the present application, in step A, the mass-to-volume ratio of lignocellulosic raw material to pretreatment agent is 1:10; and / or, the pretreatment temperature is 140°C, and the pretreatment time is 3h.

[0016] In some embodiments of the present application, in step B, the amount of anti-solvent water used is 5 times the volume of the lignin-containing pretreatment residue.

[0017] According to the present application, the method further comprises, after step B:

[0018] Step E, preparing the delignified pretreatment residue into a culture medium to perform microbial fermentation, centrifuging the obtained fermentation liquor to remove the bacterial bodies, removing water by rotary evaporation to obtain a choline chloride concentrate, and measuring the types and total phenol content of phenolic compounds;

[0019] Step F, adding sulfuric acid to the choline chloride concentrate to prepare a pretreatment agent, and then recycling the pretreatment agent to steps A-D for M times until the lignin removal rate is less than 70%, and stopping the recycling, wherein M = 0-2.

[0020] When M = 0, the delignified pretreatment residue is the delignified pretreatment residue obtained by recycling N times in step D.

[0021] In some embodiments of the present application, in step F, the amount of sulfuric acid added is 0.5wt% to 3wt% of the choline chloride concentrate.

[0022] It is detected that the choline chloride concentrate contains phenolic compounds, which are generated in the pretreatment process and exist in the pretreatment agent residual liquid, and exist in the fermentation liquid after fermentation of the pretreatment agent residual liquid.

[0023] The present inventors have found that phenolic compounds can form a solvent with choline chloride, which can be used for pretreatment of lignocellulosic raw materials.

[0024] According to the present application, the method further comprises step G after step F: mixing the choline chloride concentrate with acrylic acid, polyvinyl alcohol aqueous solution, crosslinking agent and initiator to form a choline chloride-based polymerization reaction liquid, and performing polymerization reaction to prepare a choline chloride-based hydrogel.

[0025] In some embodiments of the present application, in the choline chloride-based polymerization reaction liquid, the mass ratio of the choline chloride concentrate to acrylic acid (AA) is 5:3.3.

[0026] In some embodiments of the present application, in the choline chloride-based polymerization reaction liquid, the concentration of the polyvinyl alcohol (PVA) aqueous solution is 10wt%; preferably, the mass ratio of the choline chloride concentrate to the polyvinyl alcohol (PVA) aqueous solution is 1:1.

[0027] In some embodiments of the present application, in the choline chloride-based polymerization reaction liquid, the crosslinking agent is N,N-methylenebisacrylamide (MBA), and the mass ratio of the choline chloride concentrate to N,N-methylenebisacrylamide (MBA) is 100:1.

[0028] In some embodiments of the present application, in the choline chloride-based polymerization reaction liquid, the initiator is ammonium persulfate (APS), and the mass ratio of the choline chloride concentrate to ammonium persulfate (APS) is 250:1.

[0029] According to the present application, the choline chloride-based polymerization reaction liquid further comprises a desolvated pretreatment residual liquid.

[0030] In some embodiments of the present application, in step G, the mass ratio of the choline chloride concentrate to the desolvated pretreatment residual liquid is 1:1.

[0031] The present application has the following beneficial effects:

[0032] The method for pretreating and recycling lignocellulose provided by the application selects glycerol, choline chloride and sulfuric acid to prepare a eutectic solvent, repeatedly circulates and recycles the eutectic solvent to pretreat lignocellulose at high temperature, uses the recycled eutectic solvent to ferment microorganisms to consume glycerol, removes water to form choline chloride concentrate, recycles the choline chloride concentrate for new pretreatment reaction, and finally, the choline chloride concentrate after multiple cycles is used alone or mixed with the pretreatment residue after desolvation to prepare a hydrogel by adding acrylic acid, polyvinyl alcohol as raw materials and crosslinking agent acrylamide, initiator ammonium persulfate, etc., and the hydrogel is applied to antibacterial and moisturizing.

[0033] The eutectic solvent selected by the application has good pretreatment effect on lignocellulose and good recycling performance. The multiple recycling and pretreatment of the eutectic solvent and the recycling of the choline chloride concentrate after fermentation realize efficient separation and utilization of lignocellulose, greatly reduce the use cost of the eutectic solvent, and improve the recycling rate of the solvent. Fermentation of the recycled eutectic solvent and preparation of the hydrogel by mixing the choline chloride concentrate after multiple cycles alone or with the pretreatment residue after desolvation promote the recycling utilization of the components of the eutectic solvent, reduce the waste of the solvent, and do not produce waste. These have important theoretical guiding significance and practical value for industrialized production and application of the eutectic solvent for efficient treatment and utilization of lignocellulose resources. BRIEF DESCRIPTION OF DRAWINGS

[0034] In order to make the application easy to understand, the application will be described in detail below in combination with the drawings.

[0035] Figure 1 Process flow chart for pretreating lignocellulose by eutectic solvent and recycling utilization thereof. DETAILED DESCRIPTION

[0036] In order to make the application easy to understand, the application will be described in detail below in combination with the drawings and specific embodiments. However, before the detailed description of the application, it should be understood that the application is not limited to the specific embodiments described. It should also be understood that the terms used herein are only for describing specific embodiments and do not represent limitations.

[0037] Where numerical ranges are provided, it is understood that every number within that range is also specifically contemplated. The upper and lower limits of these smaller ranges are also independently combinable with each other to encompass the specification within this application. The upper and lower limits of these smaller ranges can be independently included in the smaller ranges and are also encompassed within the application, subject to any explicitly excluded limit in the defined range. In cases where the defined range contains one or both of the limits, ranges excluding either or both of those included limits are also intended to be encompassed within the application.

[0038] Unless otherwise defined, all terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. Although any methods and materials similar or equivalent to those described herein can be used in the practice or testing of the present application, the preferred methods and materials are now described.

[0039] I. Terms

[0040] The "lignocellulosic raw material" described in the present application includes, but is not limited to, grasses (e.g., giant reed), forest trees (e.g., poplar), and straw (e.g., corn straw), etc.

[0041] The term "anti-solvent water" described in the present application refers to water that can precipitate lignin from the pretreatment agent system.

[0042] The term "DES" described in the present application refers to a deep eutectic solvent.

[0043] The term "water" described in the present application refers to deionized water or distilled water without specific limitation or description.

[0044] II. Embodiments

[0045] As described previously, due to the large consumption of DES solvent in pretreating lignocellulose and the low solvent reuse rate, the pretreatment process is too costly, which limits its large-scale application. In view of this, the present inventors have conducted a large amount of research on the pretreatment of lignocellulose using DES solvent.

[0046] The present inventors have found that a deep eutectic pretreatment agent for lignocellulose can be prepared using glycerol, choline chloride, and sulfuric acid as components, which has good lignocellulose pretreatment effect and recycling performance.

[0047] Preferably, in the pretreatment agent for lignocellulose, the molar ratio of glycerol to choline chloride is 2-10:1, and the sulfuric acid is 0.5wt% to 3wt% of the total amount of glycerol and choline chloride, preferably 2wt% to 3wt%.

[0048] In some specific preferred embodiments of the present application, the preparation method of the pretreatment agent for lignocellulose in the present application is as follows: glycerol and choline chloride are weighed according to a molar ratio of 10:1 and placed in a round-bottom flask, stirred uniformly at 80-100°C, and after cooling to room temperature, 2wt% of concentrated sulfuric acid of the total amount of glycerol and choline chloride is added, and stirred to form a homogeneous phase liquid.

[0049] The present inventors have further researched and designed a new method (process) for pretreating and resource utilization of lignocellulose, as shown in Figure 1As shown, the process includes recycling the above eutectic pretreatment agent to pretreat lignocellulose and a recycling scheme of choline chloride after solvent fermentation, and also includes recycling the concentrated choline chloride solution after multiple cycles to prepare hydrogel alone or mixed with the anti-solvent pretreatment residue for resource utilization, and proposes a new idea for eutectic solvent pretreatment of lignocellulose and resource recycling.

[0050] According to some embodiments of the present application, the lignocellulose pretreatment and resource utilization method includes a scheme for recycling the above eutectic pretreatment agent to pretreat lignocellulose, which includes:

[0051] Step A: The pretreatment agent is mixed with the lignocellulose raw material at a mass ratio of 1:10, and the mixture is pretreated at 140°C for 3h, and then vacuum filtration is performed to separate the solid cellulose residue and the lignin-containing pretreatment residue;

[0052] Step B: Anti-solvent water is added to the lignin-containing pretreatment residue at a volume of 5 times the volume of the lignin-containing pretreatment residue, and after precipitation and centrifugation to remove lignin, a delignified pretreatment residue is obtained;

[0053] Step C: The delignified pretreatment residue is subjected to rotary evaporation to remove the anti-solvent water, and a desolventized pretreatment residue is obtained;

[0054] Step D: Sulfuric acid is added to the desolventized pretreatment residue at an addition amount of 0.5wt% to 3wt% of the desolventized pretreatment residue to prepare a pretreatment agent for recycling in steps A-C, and the recycling is performed N times until the lignin removal rate is <70%, and the recycling is stopped, wherein N=0-5.

[0055] As understood by those skilled in the art, when N=0, i.e. the first time the pretreatment agent is mixed with the lignocellulose raw material for pretreatment, the pretreatment agent is the above pretreatment agent for lignocellulose provided by the present application.

[0056] When N=1-5, i.e. in subsequent cycles, the pretreatment agent is prepared from the desolventized pretreatment residue and sulfuric acid, wherein the addition amount of sulfuric acid is 0.5wt% to 3wt% of the desolventized pretreatment residue.

[0057] In the present application, the lignocellulose raw material includes but is not limited to grass (e.g. giant reed), forest trees (e.g. poplar) and straw (e.g. corn straw) and the like.

[0058] The detection found that the royal bamboo grass contains cellulose 31.65%, hemicellulose 16.38%, lignin 27.31%; poplar contains cellulose 45.10%, hemicellulose 18.30%, lignin 22.00%; corn straw contains cellulose 38.52%, hemicellulose 20.51%, lignin 21.32%.

[0059] According to some embodiments of the application, the lignocellulose pretreatment and resource utilization method further comprises a recycling scheme of choline chloride after solvent fermentation, which comprises the following steps after step B:

[0060] Step E, the delignified pretreatment residue is prepared into a culture medium for microbial fermentation, the obtained fermentation liquor is centrifuged to remove the bacteria, and then rotary evaporation is performed to remove water to obtain a choline chloride concentrate, and the types and total phenol content of phenolic compounds are measured;

[0061] Step F, a pretreatment agent is prepared by adding sulfuric acid in an amount of 0.5wt%-3wt% of the choline chloride concentrate into the choline chloride concentrate, and the pretreatment agent is recycled to steps A-D, and the recycling is stopped until the lignin removal rate is less than 70%, and the recycling M times, wherein M=0-2;

[0062] When M=0, the delignified pretreatment residue is the delignified pretreatment residue obtained by recycling N times in step D.

[0063] The low eutectic solvent fermentation method used in the application is the oil fermentation of Rhodotorula glutinis, and the preservation number of the Rhodotorula glutinis strain is CGMCC No.2258.

[0064] The culture medium is an oil fermentation culture medium: the delignified pretreatment residue after lignin extraction is diluted with water to adjust the composition: glycerol 75g / L, choline chloride (Chcl) 25g / L, yeast powder 1.0g / L, urea 5.0g / L, dipotassium hydrogen phosphate 1.0g / L, potassium dihydrogen phosphate 2.0g / L, ammonium sulfate 2.0g / L, and pH is adjusted to 5-6.

[0065] According to some embodiments of the application, the lignocellulose pretreatment and resource utilization method further comprises a scheme for resource utilization of the choline chloride concentrate obtained by multiple cycles to prepare a hydrogel, which comprises the following step G after step F: the choline chloride concentrate is used as a medium, acrylic acid (PAA), polyvinyl alcohol (PVA) aqueous solution, crosslinking agent N,N-methylene bisacrylamide (MBA), and initiator ammonium persulfate (APS) are added, mixed to form a choline chloride-based polymerization reaction liquid, and then polymerization reaction is performed to prepare a choline chloride-based PAA / PVA double-crosslinked hydrogel.

[0066] In the present application, the polyvinyl alcohol (PVA) aqueous solution is prepared by dissolving polyvinyl alcohol (PVA) in water, and preferably, the concentration of the polyvinyl alcohol (PVA) aqueous solution is 10 wt%.

[0067] In the choline chloride-based polymerization reaction solution, the mass ratio of the choline chloride concentrate to the polyvinyl alcohol (PVA) aqueous solution is 1:1; the mass ratio of the choline chloride concentrate to acrylic acid (AA) is 5:3.3; the mass ratio of the choline chloride concentrate to the crosslinking agent N,N-methylenebisacrylamide (MBA) is 100:1; and the mass ratio of the choline chloride concentrate to the initiator ammonium persulfate (APS) is 250:1.

[0068] The present inventors have found that the choline chloride concentrate contains choline chloride, phenolic compounds, and small molecule lignin, and the use of the choline chloride concentrate as a medium for preparing the hydrogel can increase the moisturizing capacity of the hydrogel, and the presence of small molecule lignin and phenolic compounds in the choline chloride concentrate has antibacterial and antifungal capacity.

[0069] The present inventors have further found that the glycerol contained in the desolvation pretreatment residue can increase the viscosity and low-temperature frost resistance of the hydrogel; after the desolvation pretreatment residue is mixed with the choline chloride concentrate, acrylic acid, polyvinyl alcohol aqueous solution, crosslinking agent N,N-methylenebisacrylamide (MBA), and initiator ammonium persulfate (APS) are added to form a choline chloride-based polymerization reaction solution, and polymerization reaction is performed, the prepared choline chloride-based PAA / PVA double-crosslinked hydrogel has antibacterial and moisturizing capacity, high viscosity, increased mechanical strength, and can resist frost at low temperatures; preferably, in the choline chloride-based polymerization reaction solution, the mass ratio of the choline chloride concentrate to the desolvation pretreatment residue is 1:1.

[0070] Through experimental verification, the method for pretreating lignocellulose with a eutectic solvent and recycling lignocellulose resources can ensure efficient separation of three components of pretreated lignocellulose, solve the problems of waste of pretreatment solvent, high cost, and low recycling rate, and has important theoretical guiding significance and practical value for industrial production and application of efficient treatment and utilization of lignocellulose resources with pretreatment solvent.

[0071] III. Detection method

[0072] The determination method involved in the present application is as follows:

[0073] The components of the cellulose solid residue (including cellulose, hemicellulose, and lignin) are determined according to the agricultural industry standard of the People's Republic of China NY / T 3494-2019, which includes two-step acid hydrolysis combined with high-performance liquid chromatography for determining the contents of cellulose and hemicellulose, and ultraviolet spectrophotometry and gravimetric method for determining the content of lignin.

[0074] 1. Determination of cellulose and hemicellulose content by two-step acid hydrolysis method combined with high performance liquid chromatography method

[0075] (1) Take 0.25 g of sample into a pressure-resistant tube, and make more than two parallel experiments for each sample. Immediately after adding 3 mL of 72% sulfuric acid solution into the pressure-resistant bottle, mix it evenly, and place the pressure-resistant bottle into a 30°C water bath, stirring once every 10 min. After constant temperature for 60 min, take it out, add 84 mL of water into the pressure-resistant bottle, tighten the bottle cap, and mix it evenly;

[0076] (2) Place the pressure-resistant bottle containing the sample into an autoclave, and hydrolyze at 121°C for 1 h. After the hydrolysis product is cooled to room temperature, vacuum filter it through a glass filter crucible (G4) to obtain solid acid-insoluble lignin and filtrate. Take 2 mL of liquid through a 0.22-micron filter membrane to obtain the filtrate, determine the cellulose and hemicellulose components by a high performance liquid chromatography instrument, and calculate them according to formula (1) and formula (2), respectively.

[0077]

[0078]

[0079] 2. Determination of lignin content by ultraviolet spectrophotometry and gravimetric method

[0080] Determination of acid-soluble lignin by ultraviolet spectrophotometry: use a UV-5100 ultraviolet-visible spectrophotometer (Shanghai Yuanzhi Instrument Co., Ltd.) to measure the absorbance value of the two-step acid hydrolysis filtrate at a wavelength of 320 nm, and use water as a blank control.

[0081] Determination of acid-insoluble lignin by gravimetric method: dry the solid acid-insoluble lignin obtained after vacuum filtration through a glass filter crucible (G4) after two-step acid hydrolysis at 60-80°C to constant weight, weigh it, and calculate the lignin content and lignin removal rate according to formula (3) and formula (4), respectively.

[0082]

[0083]

[0084] In formula (4), M1 is the mass of the raw material, M2 is the mass of the cellulose residue, C1 is the percentage content of lignin in the raw material, and C2 is the percentage content of lignin in the cellulose residue.

[0085] 3. Determination of monosaccharide components, types of phenolic compounds, and total phenol content in DES solution by high performance liquid chromatography method (Thermo Ultimate 3000 high performance liquid chromatography instrument, Thermo Fisher Scientific Co., Ltd.).

[0086] III. Examples

[0087] In order to make the present application more easily understood, the present application will be further described in detail below in conjunction with the accompanying drawings and examples, which are only illustrative and not limited to the scope of the present application. The raw materials or components used in the present application can be obtained by commercial channels or conventional methods if not otherwise specified.

[0088] The strain used in the present application for producing microbial oil is Rhodotorula mucilaginosa (CGMCC No. 2258).

[0089] The main lignocellulosic raw materials used in the following examples are royal bamboo grass, poplar and corn straw.

[0090] Example 1

[0091] A eutectic solvent 100 g was prepared with glycerol and choline chloride in a molar ratio of 10:1, wherein glycerol was 87 g, choline chloride was 13 g, and 2% by mass of concentrated sulfuric acid was additionally added to prepare a eutectic pretreatment agent.

[0092] (1) 10 g of royal bamboo grass was mixed with the eutectic pretreatment agent in a solid-liquid ratio of 1:10 at 140°C for 3 h, and vacuum filtration was performed while hot. The solid part was washed with water and dried to obtain 4.7 g of solid cellulose residue, and the liquid part was a lignin-containing pretreatment residue;

[0093] (2) Water (anti-solvent water) was added to the lignin-containing pretreatment residue to make up to 500 mL, and lignin was precipitated. After standing, centrifugation and drying, 0.7 g of lignin was obtained;

[0094] (3) The delignified pretreatment residue after lignin extraction in step (2) was subjected to anti-solvent water removal using a rotary evaporator to obtain 100 g of anti-solvent pretreatment residue;

[0095] (4) 2% by mass of sulfuric acid was added to the anti-solvent pretreatment residue 100 g as a pretreatment agent, and was recycled for pretreating royal bamboo grass in steps (1) to (3) until the lignin removal rate was <70%, and the recycling was stopped.

[0096] The final recycling number was 5 times, and the components of the royal bamboo grass cellulose residue and the lignin removal rate obtained by different recycling numbers are shown in Table 1:

[0097] Table 1 Components of royal bamboo grass cellulose residue obtained by different recycling numbers

[0098] Cycles Cellulose (%) Hemicellulose (%) Lignin (%) Lignin removal (%) 1 69.91 6.33 13.00 78.36 2 68.39 6.40 14.16 76.90 3 67.74 6.43 15.08 74.89 4 66.44 6.45 15.13 72.55 5 65.26 6.57 16.17 69.55

[0099] Example 2:

[0100] (1) Take 500 mL of delignified pretreatment residual liquid after lignin extraction in the fifth repeated reaction in Example 1, supplement with 3 g of glycerol, prepare an oil fermentation medium, add water to 1.2 L, and culture Rhodotorula glutinis in a fermentation tank. The culture conditions are pH 5-6, temperature 30°C, and stirring speed 500 rpm. The initial glycerol concentration is 75 g / L, and the ChCl concentration is 10.8 g / L. The fermentation is ended after 300 h, and the fermentation liquor is obtained. The total biomass is 38 g / L, and the oil content is 3.7 g / L.

[0101] (2) After removing most of the water from the fermentation liquor obtained in step (1) by a rotary evaporator, 17.3 g of ChCl concentrate is obtained, which contains 13 g of ChCl. The types and total phenol content of the phenolic compounds in the ChCl concentrate are shown in Table 2:

[0102] Table 2 Types and total phenol content of phenolic compounds in ChCl concentrate

[0103]

[0104] (3) The ChCl concentrate is directly recycled for pretreatment of Yushancao in steps (1) to (4) of Example 1 under the conditions of solid-liquid ratio 1:10, temperature 140°C, and time 3 h. The amount of added sulfuric acid is 2% of the mass of the ChCl concentrate. The pretreatment effect is good, and the lignin removal rates are 70.6% and 69.1% for 2 cycles, respectively.

[0105] Example 3:

[0106] Take 5 g of the ChCl concentrate recycled for the second time in Example 2 (containing ChCl, phenolic compounds, and small molecular lignin) as the medium, and prepare a ChCl-based PAA / PVA double-crosslinked hydrogel by adding 3.3 g of acrylic acid (AA) with a mass ratio of 5:3.3, 5 g of 10 wt% polyvinyl alcohol (PVA) aqueous solution with a mass ratio of 1:1 as raw materials, 0.05 g of ammonium persulfate (APS) with a mass ratio of 250:1 as an initiator, and 0.02 g of N,N-methylenebisacrylamide (MBA) with a mass ratio of 250:1 as a crosslinking agent. The hydrogel has good antibacterial performance, moisturizing and water absorption capacity, and good mechanical properties when dried, and can withstand a tensile stress of 150 KPa.

[0107] Example 4:

[0108] Prepare a eutectic solvent by mixing glycerol and ChCl in a molar ratio of 2:1, wherein the glycerol is 57 g, the ChCl is 43 g, and 3 g of concentrated sulfuric acid is additionally added as a mass fraction of 3%. The eutectic pretreatment agent is prepared.

[0109] The corn stalk 10 g was mixed with the eutectic pretreatment agent in a solid-liquid ratio of 1:10 and reacted at 140°C for 3 h. Then, the pretreated corn stalk was recycled according to the procedures of (1) to (4) in Example 1, wherein the amount of sulfuric acid added was 3 wt%, until the lignin removal rate was <70%, and the recycling was stopped. The final recycling number was 5, and 100 g of the delignified pretreated residue was obtained, which contained 57 g of glycerol and 43 g of choline chloride.

[0110] The components of the cellulose residue and the lignin removal rate of the corn stalk obtained in different recycling numbers are shown in Table 3:

[0111] Table 3 Components of the cellulose residue of the corn stalk obtained in different recycling numbers

[0112] Repetitions Cellulose (%) Hemicellulose (%) Lignin (%) Lignin removal (%) 0 38.52 20.51 21.32 0.00 1 69.47 3.85 12.68 75.36 2 68.39 4.60 13.36 73.90 3 66.74 5.53 14.08 72.89 4 65.44 5.78 15.13 70.55 5 63.26 6.92 16.17 65.45

[0113] Example 5:

[0114] The eutectic pretreatment agent was prepared by mixing glycerol and choline chloride in a molar ratio of 2:1, wherein the glycerol was 57 g and the choline chloride was 43 g, and 3 g of concentrated sulfuric acid with a mass fraction of 3% was additionally added.

[0115] (1) The poplar 10 g was mixed with the eutectic pretreatment agent in a solid-liquid ratio of 1:10 and reacted at 140°C for 3 h. Then, the pretreated poplar was recycled according to the procedures of (1) to (4) in Example 1, wherein the amount of sulfuric acid added was 3 wt%, until the lignin removal rate was <70%, and the recycling was stopped. The final recycling number was 5, and the components of the cellulose residue and the lignin removal rate of the poplar obtained in different recycling numbers are shown in Table 4:

[0116] Table 4 Components of the cellulose residue of the poplar obtained in different recycling numbers

[0117] Repetitions Cellulose (%) Hemicellulose (%) Lignin (%) Lignin removal (%) 0 45.10 18.30 22.00 0.00 1 80.85 1.02 8.60 80.23 2 78.69 2.10 12.90 73.21 3 74.58 3.73 14.30 71.88 4 71.23 2.73 15.01 70.89 5 69.36 3.40 16.50 68.15

[0118] (2) The delignified pretreated residue 500 mL after the fifth repeated reaction and lignin extraction was taken, 33.1 g of glycerol was added to prepare a lipid fermentation medium, and the Rhodotorula mucilaginosa culture and fermentation were carried out according to the operation mode of Example 2. The fermentation was ended after 300 h, and the total biomass was measured to be 45 g / L, and the lipid content was 4.8 g / L.

[0119] (3) After the fermentation broth obtained in step (2) was removed by a rotary evaporator to remove most of the water, a choline chloride concentrate 50.3 g was obtained, which contained ChCl 43 g.

[0120] Example 6:

[0121] The delignified pretreatment residue 25 g obtained in Example 4 and the choline chloride concentrated solution 25 g in step (3) of Example 5 were weighed according to a mass ratio of 1:1, and mixed to obtain 50 g of a mixed solution. The mixed solution was used as a raw material, and 33 g of acrylic acid (AA) and 50 g of 10 wt% polyvinyl alcohol (PVA) aqueous solution were added according to a mass ratio of 5:3.3 and a mass ratio of 1:1, respectively. 0.5 g of ammonium persulfate (APS) was added as an initiator according to a mass ratio of 100:1, and 0.2 g of N,N-methylene bisacrylamide (MBA) was added as a crosslinking agent according to a mass ratio of 250:1, to prepare a choline chloride-based PAA / PVA double-crosslinked hydrogel. It was determined that the hydrogel had good anti-freezing performance, could inhibit bacteria and keep moisture, and had good mechanical properties when dried, and could withstand a tensile stress of 250 KPa of tensile strength.

[0122] It should be noted that the above-described examples are only the preferred embodiments of the present application, which are used to explain the present application and do not constitute any limitation on the present application. The present application is described by referring to typical examples, but it should be understood that the words used therein are descriptive and explanatory words, rather than limiting words. The present application can be modified within the scope of the claims of the present application, and the present application can be revised without departing from the scope and spirit of the present application. Although the present application described therein relates to specific methods, materials and examples, it does not mean that the present application is limited to the specific examples disclosed therein, but on the contrary, the present application can be extended to all other methods and applications having the same function.

Claims

1. A method for pretreatment and resource utilization of lignocellulose, comprising: Step A: The pretreatment agent is mixed with the lignocellulose raw material for pretreatment, and then vacuum filtration is performed to separate the solid cellulose residue and the pretreatment residue containing lignin. Step B: Add antisolvent water to the lignin-containing pretreatment residue, precipitate, and centrifuge to remove lignin to obtain a deligninized pretreatment residue. Step C: The pretreatment residue after delignification is subjected to rotary evaporation to remove the antisolvent water, resulting in a pretreatment residue after antisolvent removal. Step D: Add sulfuric acid to the pretreatment residue of the solvent removal process to prepare a pretreatment agent for recycling back to steps A-C, repeat N times until the lignin removal rate is <70%, then stop the cycle, where N=1-5; The pretreatment agent is used for lignocellulose; it is a eutectic solvent comprising glycerol, choline chloride, and sulfuric acid; in the pretreatment agent, the molar ratio of glycerol to choline chloride is 2~10:1, and the sulfuric acid accounts for 2wt%~3wt% of the total amount of glycerol and choline chloride. When N=1-5, the pretreatment agent is prepared from the pretreatment residue of the de-reacting solvent and sulfuric acid; In step D, the amount of sulfuric acid added is 0.5 wt% to 3 wt% of the pretreatment residue after solvent removal. In step B, the amount of antisolvent water used is 5 times the volume of the lignin-containing pretreatment residue; The method further includes the following after step B: Step E: Prepare a culture medium from the pretreatment residue of delignification, carry out microbial fermentation, centrifuge the obtained fermentation broth to remove the bacterial cells, remove water by rotary evaporation, obtain choline chloride concentrate, and determine the types of phenolic compounds and the total phenol content. Step F: Add sulfuric acid to the choline chloride concentrate to prepare a pretreatment agent, which is then recycled to steps A-D for M cycles until the lignin removal rate is <70%, at which point the cycle is stopped, where M=2. Wherein, the delignification pretreatment residue is the delignification pretreatment residue obtained by cycling N times in step D; In step F, the amount of sulfuric acid added is 0.5 wt% to 3 wt% of the concentrated choline chloride solution; The method further includes step G after step F, in which concentrated choline chloride solution is mixed with acrylic acid, polyvinyl alcohol aqueous solution, crosslinking agent and initiator to form choline chloride polymerization reaction solution, and a polymerization reaction is carried out to produce choline chloride hydrogel.

2. The method according to claim 1, characterized in that, In step A, the mass-to-volume ratio of lignocellulose raw material to pretreatment agent is 1:10; and / or, the pretreatment temperature is 140°C, and the pretreatment time is 3 hours.

3. The method according to claim 1, characterized in that, In the choline chloride polymerization reaction solution, the mass ratio of the choline chloride concentrate to acrylic acid (AA) is 5:3.3; And / or, the concentration of the polyvinyl alcohol (PVA) aqueous solution is 10 wt%; the mass ratio of the choline chloride concentrate to the polyvinyl alcohol (PVA) aqueous solution is 1:1; And / or, the crosslinking agent is N,N-methylenebisacrylamide (MBA), and the mass ratio of the choline chloride concentrate to N,N-methylenebisacrylamide (MBA) is 100:1; And / or, the initiator is ammonium persulfate (APS), and the mass ratio of the choline chloride concentrate to ammonium persulfate (APS) is 250:

1.

4. The method according to claim 3, characterized in that, The choline chloride polymerization reaction solution also contains pretreatment residue from the de-reaction solvent; the mass ratio of the choline chloride concentrate to the pretreatment residue from the de-reaction solvent is 1:1.

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