A kind of π conjugated eutectic solvent and its method for deconstructing lignocellulose to extract lignin

Abstract

The application discloses a kind of π conjugated eutectic solvent and method for extracting lignin by destructing lignocellulose thereof.The π conjugated eutectic solvent includes p-toluenesulfonic acid monohydrate and other benzene ring structure-containing substances.The p-toluenesulfonic acid monohydrate and other benzene ring structure-containing substances are combined by π-π bond and hydrogen bond, so that the melting point of the solvent is reduced;In the process of destructing lignocellulose, a large number of hydrogen ions can be ionized due to the strong acidity of p-toluenesulfonic acid, effectively destroying the close action between lignin and other components, so that lignin can be extracted at a lower temperature and in a shorter time.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of biological refining, and particularly relates to a kind of π conjugated eutectic solvent and a method for extracting lignin from lignocellulose by deconstructing lignin. BACKGROUND

[0002] Biomass is mainly composed of cellulose, hemicellulose and lignin. With the in-depth research of researchers, the method of converting cellulose and hemicellulose into high value-added products has gradually matured, but the high value utilization of lignin is still in the development stage. At present, the main method of removing lignin is based on the commercial technology of wood pulping, which usually uses alkaline or sulfite process to produce cellulose fibers. Although this method can effectively remove lignin and increase the yield of sugar after enzymatic hydrolysis, high temperature is used in the separation process, which leads to the obtained lignin being highly condensed, thus reducing the reactivity and losing the value for use.

[0003] There are many main separation methods for lignocellulose, including acid method, alkali method, organic solvent treatment method, ionic liquid pretreatment method, and low eutectic solvent pretreatment method. Acid method such as sulfuric acid, p-toluenesulfonic acid and other strong acid systems can break the C-O bond between lignin and cellulose. The advantages of acid method are fast rate and high yield, but the lignin treated by acid method is highly condensed and loses its value for use; the organic solvent system such as γ-valerolactone and tetrahydrofuran has the advantages of mild separation conditions, and the extracted lignin has the advantages of high activity and small molecular weight, but the disadvantages are high energy consumption, difficult recovery of organic reagents, slow separation rate, low efficiency, etc.; the ionic liquid treatment method has the advantage of selective extraction of lignin, but the disadvantage is high energy consumption and most of the ionic liquids have toxicity; the low eutectic solvent pretreatment method has the advantages of preserving the original structure of lignin and high separation efficiency, but the disadvantages are high energy consumption and difficult recovery of reagents. In addition, compared with traditional alkali and inorganic acid, γ-valerolactone, tetrahydrofuran and ionic liquid not only have high cost but also require large amount of solvent, so very high chemical waste liquid treatment is required, which is difficult to achieve for economic biological refining operation.

[0004] Although there are various methods for separating lignocellulose, the actual production application of lignocellulose still faces many challenges, especially in large-scale use and environmental impact. Therefore, it is essential to develop an efficient and green separation method. In the traditional separation method of plant cellulose, there are problems such as low separation efficiency, lack of environmental protection concept, and highly condensed lignin after separation, which has no use value. Therefore, when using traditional eutectic solvent to separate plant fiber, the conditions required for separation, such as time and reaction temperature, are very harsh, although the lignin retention rate is high, but the strict conditions are obstacles; although the eutectic solvent is a green solvent, but after the separation of lignocellulose, the solvent cannot be effectively recycled, and the efficiency of repeated use is low.

[0005] In summary, any extraction method has advantages and disadvantages for lignin extraction, so it is necessary to consider both lower reaction energy consumption and high lignin extraction rate. SUMMARY

[0006] To solve the shortcomings and deficiencies of the prior art, the primary purpose of the present application is to provide a kind of π conjugated eutectic solvent.

[0007] Another purpose of the present application is to provide a method for extracting lignin by deconstructing lignocellulose using the above π conjugated eutectic solvent.

[0008] By composing a π conjugated eutectic solvent with p-toluenesulfonic acid monohydrate and other substances containing benzene ring structure, lignin is extracted by deconstructing lignocellulose. First, p-toluenesulfonic acid monohydrate and other substances containing benzene ring structure are combined by π-π bond and hydrogen bond, which reduces the melting point of the solvent; second, in the process of deconstructing lignocellulose, p-toluenesulfonic acid has strong acidity and can ionize a large number of hydrogen ions, effectively destroying the close interaction between lignin and other components, so lignin can be extracted at lower temperature and shorter time.

[0009] The purpose of the present application is achieved by the following technical solutions:

[0010] A kind of π conjugated eutectic solvent, comprising p-toluenesulfonic acid monohydrate and other substances containing benzene ring structure.

[0011] Preferably, the molar ratio of p-toluenesulfonic acid monohydrate and other substances containing benzene ring structure is 1:2 to 1:8.

[0012] More preferably, the molar ratio of p-toluenesulfonic acid monohydrate and other substances containing benzene ring structure is 1:2.

[0013] Preferably, the other substance containing benzene ring structure is at least one of benzaldehyde, benzaldehyde derivative, phenol and phenol derivative.

[0014] More preferably, the benzaldehyde derivative is p-methylbenzaldehyde; and the phenol derivative is at least one of thymol and p-methylphenol.

[0015] Further more preferably, the other substance containing benzene ring structure is at least one of benzaldehyde, p-methylbenzaldehyde, phenol, thymol and p-methylphenol.

[0016] Most preferably, the other substance containing benzene ring structure is at least one of benzaldehyde, p-methylbenzaldehyde and p-methylphenol.

[0017] Further more preferably, the other substance containing benzene ring structure is p-methylbenzaldehyde.

[0018] The preparation method of the above-mentioned π-conjugated co-melting solvent is as follows: mixing p-toluenesulfonic acid monohydrate and other substances containing benzene ring structure, and then heating and dissolving at 70-120°C to obtain a transparent and clear solution.

[0019] More preferably, the heating and dissolving temperature is 70-100°C, and the time is 20-40 min.

[0020] The method for deconstructing lignocellulose to extract lignin by using the above-mentioned π-conjugated co-melting solvent comprises the following steps:

[0021] Mixing the π-conjugated co-melting solvent and lignocellulose raw materials uniformly, heating and reacting, filtering, purifying the filtrate to obtain lignin; and the filter residue is used as paper pulp raw material.

[0022] Preferably, the ratio of the π-conjugated co-melting solvent and lignocellulose raw materials is (10-20) ml:1 g.

[0023] More preferably, the ratio of the π-conjugated co-melting solvent and lignocellulose raw materials is 15 ml:1 g.

[0024] Preferably, the lignocellulose raw materials are at least one of poplar, pine and eucalyptus.

[0025] Preferably, the heating and reacting temperature is 70-120°C, and the time is 5-120 min.

[0026] More preferably, the heating and reacting temperature is 70°C, and the time is 60-120 min.

[0027] Preferably, the method for purifying the filtrate is as follows: first washing the filtrate with small molecule alcohol solvent until the filtrate is colorless, then extracting lignin with petroleum ether and water and centrifuging, washing with water, and freeze-drying to obtain lignin.

[0028] The present application mixes p-toluenesulfonic acid and other substances containing benzene ring structure in a certain amount ratio, and then uniformly mixes at a certain temperature to become a solution. The p-toluenesulfonic acid, as a hydrogen bond donor with strong ionization ability, and the other substances containing benzene ring structure, as a hydrogen bond acceptor, form a π-conjugated eutectic solvent. Meanwhile, the p-toluenesulfonic acid, as an organic strong acid, can cut the C-O bond in lignocellulose, and the p-toluenesulfonic acid and the other substances containing benzene ring structure can dissolve lignin through hydrogen bond network, so as to realize effective extraction of lignin from lignocellulose, reduce condensation of lignin, and improve the reaction activity of the lignin. +

[0029] Compared with the prior art, the present application has the following advantages and beneficial effects:

[0030] The present application proposes a new concept of π-conjugated eutectic solvent. The p-toluenesulfonic acid, benzaldehyde, benzaldehyde derivatives, phenol and phenol derivatives are all hydrogen bond donors in the traditional sense, but because of the strong ionization ability of the p-toluenesulfonic acid, the benzaldehyde, benzaldehyde derivatives, phenol and phenol derivatives become hydrogen bond acceptors, thus forming a special solvent similar to a eutectic solvent. Since there are a large number of oxygen-containing functional groups and benzene ring structures in lignin, and the π-conjugated eutectic solvent has strong acidity, hydrogen bonds and π-π bonds, under the combined action of these bonds, the lignin in poplar is rapidly removed and dissolved in large quantities in the π-conjugated eutectic solvent. Compared with the traditional eutectic solvent treatment of poplar, the treatment time is relatively shorter, the lignin yield is more, and the reaction activity of the obtained lignin is higher. BRIEF DESCRIPTION OF DRAWINGS

[0031] Figure 1 It is a solution state diagram of examples 1-3.

[0032] Figure 2 It is a differential scanning calorimetry diagram of the eutectic solvent of p-toluenesulfonic acid-p-methyl benzaldehyde in example 1.

[0033] Figure 3 It is an infrared spectrum diagram of the poplar lignin prepared in example 7 and comparative examples 3-4.

[0034] Figure 4 It is a two-dimensional nuclear magnetic resonance diagram of the poplar lignin prepared in example 7. DETAILED DESCRIPTION

[0035] The present application will be further described in detail below in combination with examples and drawings, but the embodiments of the present application are not limited thereto.

[0036] In the embodiments of the present application, the specific conditions not specified are carried out according to the conventional conditions or the conditions recommended by the manufacturers. The raw materials, reagents and the like not specified by the manufacturers are all conventional products that can be purchased on the market. ​

[0037] Example 1

[0038] Prepare p-toluenesulfonic acid-p-methylbenzaldehyde π-conjugated eutectic solvent, take 5.76 g of p-toluenesulfonic acid monohydrate in a beaker, add 7.2 g of p-methylbenzaldehyde, mix evenly, heat to 70°C, and rotate stir for 30 min until the solid gradually dissolves, forming a yellow transparent clear solution.

[0039] Example 2

[0040] Prepare p-toluenesulfonic acid-p-methylbenzaldehyde π-conjugated eutectic solvent, take 5.76 g of p-toluenesulfonic acid monohydrate in a beaker, add 7.2 g of p-methylbenzaldehyde, mix evenly, heat to 70°C, and rotate stir for 30 min until the solid gradually dissolves, forming a yellow transparent clear solution.

[0041] Example 3

[0042] Prepare p-toluenesulfonic acid-p-methylbenzaldehyde π-conjugated eutectic solvent, take 5.76 g of p-toluenesulfonic acid monohydrate in a beaker, add 7.2 g of p-methylbenzaldehyde, mix evenly, heat to 70°C, and rotate stir for 30 min until the solid gradually dissolves, forming a yellow transparent clear solution.

[0043] Example 4

[0044] Prepare p-toluenesulfonic acid-p-methylbenzaldehyde π-conjugated eutectic solvent, take 5.76 g of p-toluenesulfonic acid monohydrate in a beaker, add 7.2 g of p-methylbenzaldehyde, mix evenly, heat to 70°C, and rotate stir for 30 min until the solid gradually dissolves, forming a yellow transparent clear solution.

[0045] Take 1.0 g of poplar powder and 15 ml of freshly prepared π-conjugated eutectic solvent, mix in a water bath at 70°C, magnetic stirring reaction for 5 min, filter the reaction liquid, and wash with ethanol for 2 times until the filtrate is colorless, the insoluble part can be used as the raw material of paper pulp, the filtrate part is extracted with petroleum ether and water to extract lignin and centrifuged, washed with water for 3 times and freeze-dried. Record as PP-1. The yield of lignin is 10.75%.

[0046] Example 5

[0047] Prepare p-toluenesulfonic acid-p-methylbenzaldehyde π-conjugated eutectic solvent, take 5.76 g of p-toluenesulfonic acid monohydrate in a beaker, add 7.2 g of p-methylbenzaldehyde, mix evenly, heat to 70°C, and rotate stir for 30 min until the solid gradually dissolves, forming a yellow transparent clear solution.

[0048] Take 1.0 g of poplar powder and 15 ml of the newly prepared π conjugated co-melting solvent, stir at 70°C in water bath for 30 min, filter the reaction liquid, and wash twice with ethanol until the filtrate is colorless. The insoluble part can be used as the raw material of paper pulp. Add petroleum ether and water to extract lignin and centrifuge. Wash with water for 3 times and freeze dry. Record as PP-2. The yield of lignin is 39.7%.

[0049] Example 6

[0050] Prepare the π conjugated co-melting solvent of p-toluenesulfonic acid-p-methyl benzaldehyde, take 5.76 g of p-toluenesulfonic acid monohydrate in a beaker, add 7.2 g of p-methyl benzaldehyde, mix evenly, heat to 70°C, and rotate stir for 30 min until the solid gradually dissolves, forming a yellow transparent clear solution.

[0051] Take 1.0 g of poplar powder and 15 ml of the newly prepared π conjugated co-melting solvent, stir at 70°C in water bath for 60 min, filter the reaction liquid, and wash twice with ethanol until the filtrate is colorless. The insoluble part can be used as the raw material of paper pulp. Add petroleum ether and water to extract lignin and centrifuge. Wash with water for 3 times and freeze dry. Record as PP-3. The yield of lignin is 88.67%.

[0052] Example 7

[0053] Prepare the π conjugated co-melting solvent of p-toluenesulfonic acid-p-methyl benzaldehyde, take 5.76 g of p-toluenesulfonic acid monohydrate in a beaker, add 7.2 g of p-methyl benzaldehyde, mix evenly, heat to 70°C, and rotate stir for 30 min until the solid gradually dissolves, forming a yellow transparent clear solution.

[0054] Take 1.0 g of poplar powder and 15 ml of the newly prepared π conjugated co-melting solvent, stir at 70°C in water bath for 120 min, filter the reaction liquid, and wash twice with ethanol until the filtrate is colorless. The insoluble part can be used as the raw material of paper pulp. Add petroleum ether and water to extract lignin and centrifuge. Wash with water for 3 times and freeze dry. Record as PP-4. The yield of lignin is 85%.

[0055] Example 8

[0056] Prepare the π conjugated co-melting solvent of p-toluenesulfonic acid-p-methyl benzaldehyde, take 5.76 g of p-toluenesulfonic acid monohydrate in a beaker, add 7.2 g of p-methyl benzaldehyde, mix evenly, heat to 70°C, and rotate stir for 30 min until the solid gradually dissolves, forming a yellow transparent clear solution.

[0057] Take 1.0 g of poplar powder mixed with 15 ml of the newly prepared π conjugated co-melting solvent, stirring in water bath 70 ℃ for 120 min, filter the reaction liquid, and wash twice with ethanol until the filtrate is colorless, the insoluble part can be used as the raw material of paper pulp, the filtrate part is extracted with petroleum ether and water to extract lignin and centrifuged, washed with water 3 times and freeze-dried. Record PP-5. The yield of lignin is 76.5%.

[0058] Example 9

[0059] Prepare p-toluenesulfonic acid-p-cresol π conjugated co-melting solvent, take 5.76 g of p-toluenesulfonic acid monohydrate in a beaker, add 6.55 g of p-methyl phenol, mix evenly, heat to 70 ℃, and rotate stirring for 30 min until the solid gradually dissolves, forming a yellow transparent clear solution.

[0060] Take 1.0 g of poplar powder mixed with 15 ml of the newly prepared π conjugated co-melting solvent, stirring in water bath 70 ℃ for 120 min, filter the reaction liquid, and wash twice with ethanol until the filtrate is colorless, the insoluble part can be used as the raw material of paper pulp, the filtrate part is extracted with petroleum ether and water to extract lignin and centrifuged, washed with water 3 times and freeze-dried. Record PP-6. The yield of lignin is 71.5%.

[0061] Comparative Example 1

[0062] Prepare maleic acid-p-methyl benzaldehyde solution, take 3.4 g of maleic acid in a beaker, add 7.2 g of p-methyl benzaldehyde, mix evenly, heat to 100 ℃, rotate stirring for 120 min, the solid cannot be dissolved, stand for a period of time, the solid and liquid are completely separated.

[0063] Comparative Example 2

[0064] Prepare p-toluenesulfonic acid-cyclohexyl methyl aldehyde solution, take 5.76 g of p-toluenesulfonic acid monohydrate in a beaker, add 6.73 g of cyclohexyl methyl aldehyde, mix evenly, just drop cyclohexyl methyl aldehyde, the inner wall of the beaker releases a lot of heat, and the mixture gradually changes from white to brown.

[0065] Comparative Example 3

[0066] Prepare p-toluenesulfonic acid aqueous solution, take 5.76 g of p-toluenesulfonic acid monohydrate in a beaker, add 7.2 g of water, mix evenly, heat to 70 ℃, rotate stirring for 30 min, the solid gradually dissolves, forming a colorless transparent clear solution.

[0067] Mix 1.0 g of poplar wood powder with 15 ml of freshly prepared p-toluenesulfonic acid aqueous solution, stir and react in a water bath at 70 °C for 2 hours. Filter the reaction solution; the insoluble portion can be used as raw material for pulp. Add water to the filtrate to extract lignin, centrifuge, wash three times with water, and freeze-dry. This is denoted as D-1. The lignin yield was 13.66%.

[0068] Comparative Example 4

[0069] To prepare a p-toluenesulfonic acid-ethanol solution, take 5.76 g of p-toluenesulfonic acid monohydrate in a beaker, add 7.2 g of ethanol solution and mix well. Heat to 70°C and stir for 30 min. The solid gradually dissolves, forming a colorless, transparent and clear solution.

[0070] Mix 1.0 g of poplar powder with 15 ml of freshly prepared p-toluenesulfonic acid-ethanol solution, and stir the mixture in a water bath at 70 °C for 2 hours. Filter the reaction solution; the insoluble portion can be used as raw material for pulp. Add water to the filtrate to extract lignin, centrifuge, wash three times with water, and freeze-dry. This is denoted as D-2. The lignin yield was 18.96%.

[0071] Result detection

[0072] (1) Analysis of the formation of eutectic solvent:

[0073] Experiments were conducted on Examples 1-3, and the results are as follows: Figure 3 As shown, p-toluenesulfonic acid-p-methylbenzaldehyde, p-toluenesulfonic acid-benzaldehyde, and p-toluenesulfonic acid-p-methylphenol can all form solutions with lower melting points than p-toluenesulfonic acid, with melting points of 45℃, 45℃, and 60℃, respectively. It can be seen that the stacking of hydrogen bonds and π-π bonds allows substances possessing these two properties to form stable and transparent solutions. However, without the stacking of π-π bonds, the system will not form a stable and transparent solution, similar to Comparative Examples 1 and 2.

[0074] (2) Differential Scanning Calorimetry (DSC):

[0075] p-Toluenesulfonic acid monohydrate and p-methylbenzaldehyde were mixed in a water bath at 70°C for 30 minutes to obtain a clear, yellow solution. The solution was allowed to gradually cool and solidify before differential scanning calorimetry (DSC) was performed. The results are as follows: Figure 2 As shown in the figure, the endothermic peak is at 100℃ during the first scan calorimetry because p-toluenesulfonic acid monohydrate is used to remove the bound water inside. In the subsequent second scan, the endothermic peak reaches about 45℃, indicating that there is a significant phase transition in the solution system at a stable temperature of about 45℃, that is, the melting point of the p-toluenesulfonic acid-p-methylbenzaldehyde eutectic solvent is about 45℃.

[0076] (3) Infrared analysis:

[0077] The poplar lignin obtained in Example 7 and Comparative Examples 3 and 4 was subjected to infrared testing, and the results are shown in Figure 1. Figure 3 As can be seen from the figure, 3415 cm -1 is a hydroxyl characteristic peak, 2930 cm -1 is a methyl characteristic peak, 2868 cm -1 is a methylene characteristic peak, 1695 cm -1 is a non-conjugated carbonyl characteristic peak, 1654 cm -1 is a conjugated carbonyl characteristic peak, 1604 cm -1 , 1511 cm -1 , 1430 cm -1 is a lignin benzene ring skeleton characteristic peak, 1463 cm -1 is a C-H characteristic peak connected to the benzene ring, 1343 cm -1 is a lignin syringyl structure characteristic peak, 1268 cm -1 , 1224 cm -1 and 1142 cm -1 are lignin guaiacyl structure characteristic peaks, indicating that the extracted lignin has the typical structure of lignin compounds, containing chemical active groups such as methyl, phenolic hydroxyl and carbonyl groups.

[0078] (4) Two-dimensional nuclear magnetic testing

[0079] The poplar lignin obtained in Example 7 was subjected to two-dimensional nuclear magnetic testing, and the results are shown in Figure 2. The two-dimensional nuclear magnetic resonance spectrum of the lignin can be divided into a side chain region and an aromatic region. In the side chain region (δC / δH 50.0-90.0 / 2.50-6.00), resin alcohol (β-β, B) and methoxyl (OMe, δC / δH 55.9 / 3.73) were detected. Figure 4

[0080] In the aromatic region (δC / δH 90.0-150.0 / 6.00-8.00), PB, syringyl (S), guaiacyl (G) and p-hydroxyphenyl (H) units are located at δC / δH 130 / 7.8, δC / δH 127 / 7.5, δC / δH 127 / 7.2, δC / δH 130.0 / 7.41, δC / δH 130.0 / 7.0, δC / δH 145.0 / 7.41, corresponding to S2, S6, G 2,6 , G5, G6 and H 2,6 , respectively.

[0081] (5) Yield:

[0082] ​The calculation method is the ratio of the weight of poplar lignin obtained by freeze-drying to the total weight of lignin in poplar itself, wherein the total weight of lignin in poplar itself is determined by the component analysis method (NREL), and the specific steps are as follows: 0.3 g of dried poplar powder is weighed into a test tube, 3 ml of 72 wt% concentrated sulfuric acid is added and stirred uniformly, and then the mixture is placed in a water bath at 30°C for 60 min. Then the concentrated sulfuric acid hydrolysate is transferred to a conical flask, 84 ml of ultrapure water is added to dilute the acid concentration to 4 wt%. The conical flask is placed in a 121°C high-pressure sterilization pot for 60 min, then the dilute acid hydrolysate is filtered through a G3 sand core funnel to obtain a filtrate, and the volume is weighed. 1 ml of the filtrate is taken for high performance liquid chromatography detection, the injection volume is 20 ul, the mobile phase is 5 mmol / L sulfuric acid, the flow rate is 0.5 ml / min, and the concentrations of cellulose, lignin and hemicellulose are determined. The filter residue is dried in an oven at 105°C, weighed, and then placed in a muffle furnace for ashing at 575°C. Finally, the total content of lignin in 1 g of poplar is calculated to be 203 mg.

[0083] The lignin obtained in Examples 4-9 and Comparative Examples 3-4 is counted for yield to obtain Table 1, and it can be seen that the extraction efficiency of p-toluenesulfonic acid-p-methylbenzaldehyde is significantly improved compared with the extraction efficiency of p-toluenesulfonic acid and ordinary solvents for lignin.

[0084] Table 1

[0085]

[0086] Result discussion

[0087] Under the stacking action between π-π bonds and hydrogen bonds, p-toluenesulfonic acid as a hydrogen bond acceptor, and p-methylbenzaldehyde, benzaldehyde and p-methylphenol as hydrogen bond donors, p-toluenesulfonic acid and any one of the hydrogen bond donors can form a low eutectic solvent system. However, if cyclohexylmethanol or maleic acid is used as a hydrogen bond donor, a stable low eutectic solvent system cannot be formed due to the lack of stacking of π-π bonds; similarly, when maleic acid is used as a hydrogen bond acceptor, a stable low eutectic solvent system cannot be formed. In addition, the strong acidity of p-toluenesulfonic acid can quickly break the C-O bond between lignin and cellulose, and under the strong action of hydrogen bonds and π-π bonds, lignin is quickly dissolved into the p-toluenesulfonic acid-p-methylbenzaldehyde solvent system after being separated from cellulose, thereby obtaining pulp fibers with a higher degree of delignification and a high-concentration lignin solution. As can be seen from Example 7 and Comparative Examples 3 and 4, the low eutectic solvent system of p-toluenesulfonic acid-p-methylbenzaldehyde can effectively remove lignin from poplar, and the yield is significantly improved. At the same time, as can be seen from Example 6 and Example 5 by appropriately reducing the reaction time, high-yield poplar lignin can still be obtained in a shorter time.

[0088] The above embodiments are the preferred embodiments of the present application, but the embodiments of the present application are not limited to the above embodiments, and any changes, modifications, substitutions, combinations, simplifications, etc. made without departing from the spirit and principles of the present application should be equivalent replacement manners and should be included in the protection scope of the present application.

Claims

1. A method for deconstructing lignocellulose to extract lignin using a π- conjugated eutectic solvent, characterized in that, The method comprises the following steps: mixing the π-conjugated co-melting solvent and the lignocellulose raw material, heating and reacting, filtering, and purifying the filtrate to obtain lignin; the residue is used as a paper pulp raw material; the π-conjugated co-melting solvent comprises p-toluenesulfonic acid monohydrate and other substances containing benzene ring structure; the molar ratio of the p-toluenesulfonic acid monohydrate and the other substances containing benzene ring structure is 1:2-1:8; the other substances containing benzene ring structure are at least one of benzaldehyde, p-methylbenzaldehyde, phenol, thymol and p-methylphenol.

2. The method according to claim 1, wherein the π-conjugated eutectic solvent is used for deconstructing lignocellulose and extracting lignin. the molar ratio of the p-toluenesulfonic acid monohydrate and the other substances containing benzene ring structure is 1:

2.

3. The method for extracting lignin from lignocellulose using a π-conjugated eutectic solvent according to claim 1, characterized in that, the other substances containing benzene ring structure are at least one of benzaldehyde, p-methylbenzaldehyde and p-methylphenol.

4. The method for extracting lignin from lignocellulose using a π-conjugated eutectic solvent according to claim 1, characterized in that, the other substances containing benzene ring structure are p-methylbenzaldehyde.

5. The method for extracting lignin from lignocellulose using a π-conjugated eutectic solvent according to claim 1, characterized in that, the preparation method of the π-conjugated co-melting solvent is: mixing the p-toluenesulfonic acid monohydrate and the other substances containing benzene ring structure, and then heating and dissolving at 70-120°C to obtain a transparent and clear solution.

6. The method for extracting lignin from lignocellulose using a π-conjugated eutectic solvent according to claim 1, characterized in that, the ratio of the π-conjugated co-melting solvent to the lignocellulose raw material is (10-20) ml:1 g; the heating and reacting is performed at 70-120°C for 5-120 min.

7. The method for extracting lignin from lignocellulose using a π-conjugated eutectic solvent according to claim 1, characterized in that, the ratio of the π-conjugated co-melting solvent to the lignocellulose raw material is 15 ml:1 g; the heating and reacting is performed at 70°C for 60-120 min.

8. The method for extracting lignin from lignocellulose using a π-conjugated eutectic solvent according to claim 1, characterized in that, the lignocellulose raw material is at least one of poplar, pine and eucalyptus.

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