CN113999269B

CN113999269B - Method for promoting extraction of lignin in straws and catalytic preparation of levulinic acid and ethyl ester thereof by using ammonium-based Bronsted acidic ionic liquid

Info

Publication number: CN113999269B
Application number: CN202111502391.3A
Authority: CN
Inventors: 赵炜; 王仃凯; 刘序堂; 蒋志杰; 崔明昱; 梁冲; 董林阳; 王飞
Original assignee: China University of Mining and Technology CUMT
Current assignee: China University of Mining and Technology CUMT
Priority date: 2021-12-09
Filing date: 2021-12-09
Publication date: 2022-06-17
Anticipated expiration: 2041-12-09
Also published as: CN113999269A

Abstract

The invention discloses a method for promoting extraction of lignin in straws and catalytic preparation of levulinic acid and ethyl ester thereof by using ammonium Bronsted acidic ionic liquid, which comprises the following steps: 1) taking pretreated straw powder as a raw material, adopting an organic solvent method, and taking an ammonium group type

Acidic ionic liquid is used as an accelerant, and lignin is extracted from the straws under a proper reaction condition; 2) in the ammonium group form

The acidic ionic liquid is used as a catalyst to catalyze residue CRR and waste liquid CRL which are rich in cellulose and generated after the straws are used for extracting lignin to prepare the levulinic acid and the ethyl levulinate. The preparation method is simple and effective, low in cost, low in reaction temperature and low in toxicity, overcomes the defects of complex process, high cost, high toxicity, high energy consumption, low product yield and the like in the prior art, and has a good effect on lignin extraction and catalytic degradation of carbohydrate to prepare levulinic acid and ethyl levulinate.

Description

Method for promoting extraction of lignin in straw and catalyzing preparation of levulinic acid and ethyl ester thereof by ammonium-based Bronsted acidic ionic liquid

Technical Field

The invention relates to the technical field of crop straw waste conversion and recycling, in particular to a method for promoting extraction of lignin in straws and catalytic preparation of levulinic acid and ethyl ester thereof by using an ammonium-based Bronsted acidic ionic liquid.

Background

Chinese straw resources are very rich, but are in a single component resource utilization state or low-value utilization for a long time, so that other components are damaged and discarded in the processing process, and huge waste of straw resources is caused. With the gradual decrease of fossil resources, as an important approach for solving the shortage of energy, materials and chemicals in the future, the full-component high-valued utilization technology of straws is greatly concerned and valued by researchers at home and abroad.

From the perspective of raw materials, the straw contains fiber components with shorter fiber and poor strength, and is not suitable for the field of cellulose materials with higher mechanical property requirements; if the target product is a small molecule compound, such as a liquid fuel, a platform compound, etc., the sugar platform should be actively constructed while achieving separation of components as much as possible. Compared with fiber components, lignin has a complex natural structure, and the network structure is collapsed and the reaction activity is reduced due to the common occurrence of aryl ether bond breakage and C-C condensation structure generation in the separation process, so that effective separation and high-value conversion can not be realized under the existing industrial separation condition. However, lignin as the only renewable aromatic compound in nature can be used for producing fuel, aromatic small molecular compounds and the like, and has great application potential and wide prospect.

At present, the method for separating lignin from plant resources mainly comprises a physical method, an acid method, an alkali method, an organic solvent method, a biological method and the like, wherein the organic solvent method is to select a proper organic solvent and hydrolyze or dissolve the lignin under certain conditions, so that the cellulose and the lignin are fully separated, and the effect is good. The organic solvent method adopts organic solvents such as methanol, ethanol, acetic acid, acetone and the like, is an efficient delignification technology, and can recover quite pure lignin fractions; while acid hydrolysis is particularly useful for hydrolysis and solubilization of hemicellulose, e.g. H₂SO₄Or HCl, therefore, a system for organic solvent extraction of ligninThe proper amount of acid is added to facilitate the reaction. In general, conventional

And Lewis acids and bases are powerful promoters for this process. The homogeneous promoter is difficult to separate and purify, and the heterogeneous promoter is limited in contact with the straw, so that the reaction activity is relatively low and cannot be ignored. It is necessary to find an acidic promoter suitable for pretreatment and dissolution of straw. In recent years, the ionic liquid is widely applied to straw dissolution and depolymerization as a novel green solvent and accelerator.

The ionic liquid can selectively break the connecting bonds among cellulose, hemicellulose and lignin, and realize effective separation. The extraction of lignin from biomass by using imidazole-based ionic liquid has been studied by many researchers, but the extraction has high cost and strong toxicity, and is difficult to decompose, so that the extraction causes certain harm to the environment. In recent years, ammonium-based ionic liquids have been attracting much attention because of their low cost, low toxicity to imidazole, and environmental friendliness. Recently, triethylammonium hydrogen sulfate ([ Et ]₃NH][HSO₄]) Have been used to treat biomass (i.e., the breakdown of lignocellulosic feedstocks). The cheap ionic liquid has low vapor pressure and good thermal stability and can be recycled. In addition to olive pomace, [ Et ]₃NH][HSO₄]The effectiveness of (b) has been demonstrated in other biomasses. Depending on the treatment conditions and the type of substrate, the lignin recovery is between 30 and 100%. However, the previous researches on extracting lignin basically adopt the ionic liquid as a solvent directly, the ionic liquid is not beneficial to full contact of biomass and the solvent due to higher viscosity, and the prepared ionic liquid is used as the solvent directly for extracting the lignin, so that the cost is increased.

The separation of components is the basis of the high-value utilization of the waste straws, the high-value utilization of the components is the key of the extension and development of the industrial chain of the straws, and the continuous and rapid development of the whole industry can be promoted only if downstream products have certain market prospects and vitality.

The production of levulinic acid and esters thereof is generally requiredInorganic acid aqueous solution catalyst, use of inorganic acid catalyst (H)₂SO₄) The carbohydrate was processed to give a yield of 55%. Although such catalysts have a high yield of ethyl levulinate under optimal conditions, they are not recyclable, corrosive and difficult to separate from the product. The solid acid catalyst shows good catalytic performance in the production of ethyl levulinate, but has the advantages of high inactivation speed, difficult regeneration, complex distribution of reaction products and unsuitability for large-scale application. Ion exchange resins have also been used to make ethyl levulinate, but are hindered by low thermal stability.

The ionic liquid can be used as a solvent and a catalyst, and has wide application prospects in the aspects of biomass degradation and high value-added product formation.

Disclosure of Invention

The invention aims to provide a method for promoting extraction of lignin in straws and catalytic preparation of levulinic acid and ethyl levulinate thereof by using an ammonium-based Bronsted acidic ionic liquid, and solves the problems of low yield, high cost, complex operation process, resource waste and environmental pollution caused by waste generated in the reaction process in the conventional method for extracting lignin.

In order to achieve the purpose, the technical scheme adopted by the invention is as follows: a method for promoting extraction of lignin in straws and catalytic preparation of levulinic acid and ethyl ester thereof by using ammonium-based Bronsted acidic ionic liquid comprises the following steps:

1) a certain amount of pre-treated straw powder and ammonium base form

Placing the acidic ionic liquid and the ethanol water solution in a reaction kettle, and uniformly stirring; sealing the reaction kettle, and heating and stirring the reaction kettle for reaction under the protection of inert gas;

2) after the reaction is finished, rapidly cooling to room temperature, filtering, washing, adding a certain amount of deionized water into the obtained liquid product, and standing for 12-36 hours;

3) standing, filtering, washing, drying and grinding the obtained mixture to obtain brown solid powder, namely lignin, sealing, drying and storing;

4) a certain amount of CRR and ammonium radical type residues after the filtration of the step 2)

Placing the acidic ionic liquid and absolute ethyl alcohol in a reaction kettle, and uniformly stirring; sealing the reaction kettle, and heating and stirring the reaction kettle for reaction under the protection of inert gas;

5) after the reaction is finished, quickly cooling to room temperature, filtering, washing, distilling the obtained liquid product under reduced pressure to remove ethanol, finally drying until no alcohol smell exists, sealing, drying and storing;

6) carrying out reduced pressure rotary evaporation and vacuum drying dehydration on the waste liquid filtered in the step 3) to obtain liquid CRL, adding the liquid CRL and absolute ethyl alcohol into a reaction kettle, and uniformly stirring; sealing the reaction kettle, heating and stirring for reaction,

7) after the reaction is finished, the reaction product is quickly cooled to room temperature, quickly filtered and washed, the obtained liquid product is subjected to reduced pressure distillation to remove ethanol, and finally dried until no alcohol smell exists, sealed, dried and stored.

Preferably, in the step 1), the pretreated straw powder is obtained by washing, drying, crushing, sieving, degreasing and drying agricultural waste straws.

Preferably, in the step 1), the volume ratio of ethanol to water in the ethanol aqueous solution is 4: 1.

Preferably, in step 1), said ammonium group is of the type

The acidic ionic liquid is prepared by sulfonating and acidifying triethylamine. Cheap triethylamine is used as raw material, 1, 4-butyl sultone is sulfonated to form zwitterion, and then sulfuric acid is used for acidification to form

Acidic ionic liquids, abbreviated as [ BSTEA]HSO₄。

Preferably, in step 1), said ammonium group is of the type

Acidic ionic liquid: the ratio of the pre-treated straw powder to the ethanol aqueous solution is 2 mmol: 3 g: 50 mL.

Preferably, in the step 1), the initial pressure is 0-2 MPa, the set temperature is 180-220 ℃, the set time is 10-60 min, and the rotating speed is 100-500 r/min.

Preferably, in the step 2), the ratio of the amount of the deionized water to the volume of the ethanol aqueous solution in the step 1) is 3: 8 to 1: 4.

Preferably, in step 4), the ammonium group is in the form of

The dosage of the acidic ionic liquid is 20-40 wt.% of the dosage of the CRR, and the ratio of the dosage of the absolute ethyl alcohol to the dosage of the CRR is 10-30 mL: 0.3-0.7 g.

Preferably, in the step 4), the set temperature is 180-220 ℃, the set time is 30-120 min, and the rotating speed is 400-800 r/min.

Preferably, in the step 6), the set temperature is 180-220 ℃, the set time is 30-120 min, and the rotating speed is 400-800 r/min.

The invention starts with the accelerant and the catalyst to prepare the ammonium base type with high efficiency, low price and low toxicity

Acidic ionic liquid ([ BSTEA)]HSO₄) As an accelerant and a catalyst, the ionic liquid well solves the problems of poor catalytic performance, high cost, high toxicity and serious environmental pollution of the original ionic liquid. At the same time, [ BSTEA ]]HSO₄The sulfonic acid functionalized ionic liquid can well break hydrogen bonds in straw raw materials, promote the degradation of cellulose, improve the extraction rate of lignin, reasonably utilize residual residues and waste liquid after the extraction of the lignin, reduce the resource waste and reduce the pollution of the emission of industrial wastes to the environment; on the other hand, [ BSTEA]HSO₄Directly acts on the carbohydrate after lignin removal, and reduces wood qualityThe influence of the steric structure of the element on the catalytic reaction, thereby improving the yield of the levulinic acid and the ethyl levulinate. [ BSTEA]HSO₄Due to the unique property, the catalyst has better recycling performance, realizes the use and circulation of the accelerator and the catalyst, and reduces the cost. In conclusion, the invention is cheap and efficient [ BSTEA]HSO₄The method for promoting the extraction of lignin in the waste straws and the catalytic preparation of levulinic acid and ethyl levulinate accords with the green chemical development direction, and provides a reliable path for the full utilization of agricultural waste straws.

Compared with the prior art, the invention has the following beneficial effects:

1) compared with the existing ionic liquid which is used as a solvent for extracting the organic solvent lignin from the biomass, the ionic liquid is used as an accelerant and has the advantages of small dosage, low cost, low toxicity and better performance;

2) compared with the existing method for extracting lignin from biomass, the method considers the treatment of the residual carbohydrate-rich waste liquid and waste residue after the lignin is extracted, reduces the waste of resources, reduces the pollution to the environment caused by the discharge of industrial wastes, and accords with the concept of sustainable development;

3) the levulinic acid and ethyl levulinate are prepared by depolymerizing the carbohydrate after the lignin is catalytically removed, so that the obstruction of the lignin to the catalytic process in the catalytic process is reduced, and the yield of the levulinic acid and ethyl levulinate is effectively improved;

4) the ionic liquid used for extracting the lignin in the straws does not need to be separated, and can directly carry out the catalytic reaction of the waste liquid along with the waste liquid, thereby simplifying the process flow and reducing the cost.

Drawings

FIG. 1 shows the preparation of ionic liquid [ BSTEA]HSO₄Is/are as follows¹H NMR (a) and¹³c NMR spectrum (b);

FIG. 2 is [ BSTEA]HSO₄A flow chart for promoting the straw to extract lignin and catalyzing the residual components to prepare levulinic acid and ethyl levulinate;

FIG. 3 shows the treated straw without ionic liquid and with BSTEA]HSO₄Extracted woodFourier transform infrared spectrogram of texel (teall);

FIG. 4 shows the addition of [ BSTEA ]]HSO₄TGA and DTG curves of extracted lignin (teall);

FIG. 5 is [ BSTEA]HSO₄A total ion current chromatogram of a liquid product obtained by catalyzing CRL;

FIG. 6 shows the ionic liquid [ BSTEA ]]HSO₄The recycling performance of (2).

Detailed Description

The following embodiments are intended to illustrate the present invention, but should not be construed as limiting the invention thereto. The reagents and equipment used in the following examples are commercially available.

The straw powder used in the embodiment of the invention is prepared by washing, drying, crushing, sieving, degreasing and drying agricultural waste straws.

Ammonium radical type for use in the examples of the invention

Acidic ionic liquids, abbreviated as [ BSTEA]HSO₄The preparation method comprises the following steps: putting 0.2mol of triethylamine, 0.2mol of 1, 4-butanesultone and 20mL of ethyl acetate into a reaction kettle, uniformly stirring, sealing the reactor, setting the rated power of 500W, the rotating speed of 150r/min, the reaction temperature of 60 ℃, the reaction time of 60min, filtering, washing and drying after the reaction is finished, thereby obtaining the zwitterion. And (2) slowly and uniformly stirring 0.1mol of zwitterion, 0.1mol of sulfuric acid and 20mL of deionized water in a reactor, sealing the reactor, setting the rated power at 500W, the rotating speed at 150r/min, the reaction temperature at 60 ℃, reacting for 60min, washing with ethyl acetate after the reaction is finished, and then carrying out reduced pressure rotary evaporation and vacuum drying to remove water to obtain the finished product. The yield of the ionic liquid is 86.01%, [ BSTEA%]HSO₄Is/are as follows¹H NMR and¹³the C NMR spectrum is shown in FIG. 1. Characteristic peaks of other byproducts are not shown in FIG. 1, which shows that the prepared ionic liquid has high purity; the characteristic peaks of all proton hydrogen and carbon atoms in the ionic liquid structure appear in the figure, which indicates that the prepared product is the target ionic liquid [ BSTEA]HSO₄。

Example 1

As shown in figure 2, 9g of the pretreated straw powder and 6mmol of ammonium group

Acidic ionic liquid and 150mL of ethanol aqueous solution (V)_C2H5OH/V_H2O(ii) a 4: 1) is placed in a reaction kettle, nitrogen is introduced for protection, the initial pressure is 1MPa, the set rotating speed is 300r/min, the reaction temperature is 200 ℃, the reaction time is 30min, the reaction product is taken out after the reaction is finished, the reaction product is rapidly cooled to the room temperature, filtered and washed (deionized water, 3 multiplied by 30mL), and then 500mL of deionized water is added for standing for 24 h. Finally, the mixture was filtered, washed, dried and ground to give a brown solid powder, i.e. lignin, which was stored dry in a sealed environment with a lignin yield of 23.73%.

FIG. 3 shows pretreated stalks, no ionic liquid added and BSTEA added]HSO₄Fourier transform infrared spectrogram of extracted lignin (TEAILL). 3450 and 3300cm in FIG. 3^-1、2935cm^-1And 2841cm^-1The peak at (A) is due to-OH, -OCH₃and-CH₂The vibration of (2). 1606cm^-1、1512cm^-1、1462cm^-1And 838cm^-1The absorption peak is attributed to the characteristic peak of benzene ring in lignin. 1738cm^-1It is considered as a stretching vibration absorption peak of C ═ O in hemicellulose. 1426cm^-1、1373cm^-1(C-H deformation vibration) 1249cm^-1、1056cm^-1(C-O stretching and O-H deforming vibration) and 897cm^-1The absorption peak at (. beta. -dextran anhydride linkage) is a characteristic peak of cellulose. As can be seen from FIG. 3, the FTIR spectra of straw, no added ionic liquid (blank) and TEAILL are significantly different. Hemicellulose (1164 cm)^-1The absorption peak at (A) is due to the stretching vibration of C-O-C in furan ring skeleton, indicating the existence of arabino side chain) and the characteristic peak of cellulose substantially disappeared in the spectrum of extracting lignin, while the characteristic peak of aromatic skeleton (1606 cm)^-1、1512cm^-1And 1426cm^-1) And C-H stretching vibration in lignin (838 cm)^-1) The signal was enhanced, indicating that the process of extracting lignin was efficient. At 1326cm^-1And 1116cm^-1The absorption peaks at (A) are respectively attributed to C-O stretching vibration in the syringyl ring and C-H plane deformation vibration in the syringyl type aromatic compound. 1269cm^-1、1116cm^-1And 838cm^-1The peak at (a) is the characteristic absorption peak of the guaiacol-based structure. 1212cm^-1The absorption peak is related to the stretching vibration of C-O on the benzene ring in the syringyl and guaiacol group structures.

FIG. 4 is a thermogravimetric analysis of the extracted lignin TEAILL of example 1. From thermogravimetric analysis (TGA), it can be seen that the degradation range of teall is mainly between 200 ℃ and 480 ℃, specifically, it is analyzed that the degradation range of teall is 30 ℃ to 105 ℃ in the initial temperature rise stage, the teall is not greatly changed (2.0%), and the free water in the lignin component is mainly evaporated in the stage. The major thermal weight loss was between 200 and 480 ℃ and a large degree of degradation (40%) of TEAILL occurred at this stage. As can be seen from the DTG curve, the initial degradation temperature of TEAILL is 204 ℃, and the weight loss strength reaches the maximum at 358 ℃; the DTG curve begins to become gentle at about 480 ℃, and the weight loss (200-480 ℃) reaches 40 percent.

TABLE 1

Note: yield of lignin (wt.%) x 100 (mass of extracted lignin ÷ mass of straw), straw being dry, anhydrous basis.

As can be seen from Table 1, the ionic liquid [ BSTEA ] was added]HSO₄The extraction of lignin in the straw is promoted, the yield of the lignin is greatly improved, the extraction of the lignin is influenced by the addition amount of the ionic liquid, and the yield of the lignin is the highest when the straw powder (g)/the ionic liquid (mmol) is 3/2.

TABLE 2

Note:^*the blank control is lignin extracted under the same condition without adding ionic liquid;

^**dulong's equation: HHV (MJ/kg) 0.3383 XC +1.422 (H-O/8).

As can be seen from table 2, the ash content in teall is slightly higher and the volatile content is lower compared to lignin extracted without ionic liquid, which may be related to incompletely removed fiber components contained in lignin extracted without ionic liquid. Further studies by elemental analysis showed a higher carbon content in teall compared to lignin extracted without ionic liquid. In addition, the higher oxygen content of the molecular formula lignin C9 without ionic liquid extraction may also be an effect of the oxygen-rich fiber component. Table 2 also shows that teall has a Higher Heating Value (HHV) than lignin extracted without addition of ionic liquid.

Example 2

As shown in FIG. 2, 0.5g of the fiber component-rich residue CRR obtained by filtration after completion of the heating reaction in example 1, 30 wt.% (based on CRR) of the ammonium form

Placing the acidic ionic liquid and 20mL of absolute ethyl alcohol into a reaction kettle, setting the rotating speed at 600r/min, the reaction temperature at 200 ℃ and the reaction time at 60min, taking out a reaction product after the reaction is finished, quickly cooling to room temperature, quickly filtering and washing, carrying out reduced pressure rotary evaporation on the obtained liquid product to remove the ethyl alcohol, and carrying out vacuum drying on the obtained liquid product, wherein the conversion rate of residues is 9.78%, the yield of ethyl levulinate is 0.18% respectively, and the process efficiency is 0.63%.

Filtering the mixture obtained in the example 1 to remove lignin, performing reduced pressure rotary evaporation and vacuum drying on the obtained waste liquid to remove water to obtain liquid CRL rich in carbohydrate, putting the liquid CRL and 50mL of absolute ethyl alcohol into a reaction kettle, setting the rotation speed at 600r/min, the reaction temperature at 200 ℃ and the reaction time at 60min, taking out a reaction product after the reaction is finished, rapidly cooling to room temperature, rapidly filtering and washing, performing reduced pressure rotary evaporation and vacuum drying on the obtained liquid product, wherein the conversion rate of the waste liquid is 79.11%, the yields of levulinic acid and ethyl levulinate are respectively 38.85% and 23.33%, and the process efficiency is 62.18%.

And analyzing the mixture after the carbohydrate in the waste liquid is further catalytically depolymerized after the lignin is extracted by adopting a gas chromatography-mass spectrometry combined technology. The total ion chromatogram for the liquid product is shown in FIG. 5. As can be seen from fig. 5, the relative amounts of levulinic acid and ethyl levulinate in the liquid product were higher, 38.85% and 23.33%, respectively.

TABLE 3

Note:^*the data is based on the amount of waste liquid used under appropriate conditions;

^**the data is based on the amount of waste residue used under appropriate conditions;

^***process efficiency (%) + yield of levulinic acid + yield of ethyl levulinate.

Example 3

The recovered ionic liquid [ BSTEA]HSO₄The dried product was dried overnight at 80 ℃ and then used directly in the next lignin extraction reaction, the results of which are shown in FIG. 6. [ BSTEA]HSO₄After 5 times of recycling, the activity is not obviously reduced, and the lignin yield is 19.90 percent, which indicates that the [ BSTEA]HSO₄Better stability.

Claims

1. A method for promoting extraction of lignin in straws and catalytic preparation of levulinic acid and ethyl ester thereof by using ammonium-based Bronsted acidic ionic liquid is characterized by comprising the following steps:

1) putting a certain amount of pretreated straw powder, ammonium Bronsted acidic ionic liquid and ethanol aqueous solution into a reaction kettle, and uniformly stirring; sealing the reaction kettle, and heating and stirring the reaction kettle for reaction under the protection of inert gas; wherein the ammonium Bronsted acidic ionic liquid is an ionic liquid obtained by sulfonating and acidifying triethylamine;

4) placing a certain amount of residue rich in fiber components obtained by filtering in the step 2), ammonium based Bronsted acidic ionic liquid and absolute ethyl alcohol in a reaction kettle, and uniformly stirring; sealing the reaction kettle, and heating and stirring the reaction kettle for reaction under the protection of inert gas;

6) carrying out reduced pressure rotary evaporation and vacuum drying dehydration on the waste liquid filtered in the step 3) to obtain liquid rich in carbohydrate, adding the liquid and absolute ethyl alcohol into a reaction kettle, and uniformly stirring; sealing the reaction kettle, and heating and stirring for reaction;

2. The method for promoting extraction of lignin in straws and catalytically preparing levulinic acid and ethyl ester thereof by using the ammonium-based Bronsted acidic ionic liquid according to claim 1, wherein in the step 1), the pretreated straw powder is obtained by washing, drying, crushing, sieving, degreasing and drying agricultural waste straws.

3. The method for promoting the extraction of lignin from straws and catalytically preparing levulinic acid and ethyl ester thereof by using the ammonium Bronsted acidic ionic liquid as claimed in claim 1, wherein in the step 1), the volume ratio of ethanol to water in the ethanol aqueous solution is 4: 1.

4. The method for promoting the extraction of lignin from straws and the catalytic preparation of levulinic acid and ethyl esters thereof according to claim 1, wherein in step 1), the ammonium bransted acidic ionic liquid: the ratio of the pre-treated straw powder to the ethanol aqueous solution is 2 mmol: 3 g: 50 mL.

5. The method for promoting extraction of lignin in straws and catalytic preparation of levulinic acid and ethyl ester thereof by using the ammonium Bronsted acidic ionic liquid as claimed in claim 1, wherein in the step 1), the initial pressure is 0-2 MPa, and the set temperature is 180-220 MPa^oC. The setting time is 10-60 min, and the rotation speed is 100-500 r/min.

6. The method for promoting extraction of lignin in straws and catalytic preparation of levulinic acid and ethyl ester thereof by using the ammonium-based Bronsted acidic ionic liquid according to claim 1, wherein in the step 2), the volume ratio of the deionized water to the ethanol aqueous solution in the step 1) is 3: 8-1: 4.

7. The method for promoting the extraction of lignin in straws and the catalytic preparation of levulinic acid and ethyl ester thereof by using the ammonium Bronsted acidic ionic liquid according to claim 1, wherein in the step 4), the amount of the ammonium Bronsted acidic ionic liquid is 10-50 wt.% of the amount of the fiber component-rich residue, and the ratio of the amount of absolute ethanol to the amount of the fiber component-rich residue is 10-30 mL: 0.3 to 0.7 g.

8. The method for promoting extraction of lignin in straws and catalytic preparation of levulinic acid and ethyl ester thereof by using ammonium-based Bronsted acidic ionic liquid according to claim 1, wherein in the step 4), the set temperature is 180-220%^oC. The setting time is 30-120 min, and the rotating speed is 400-800 r/min.

9. The ammonium Bronsted acidic ionic liquid for promoting extraction of lignin from straws and catalytic preparation of the same according to claim 1The method for preparing the levulinic acid and the ethyl ester thereof is characterized in that in the step 6), the set temperature is 180-220 DEG^oC, setting the time to be 30-120 min and the rotating speed to be 400-800 r/min.