A deep eutectic solvent and its preparation and application

Abstract

The present invention provides a deep eutectic solvent and its preparation and application. The deep eutectic solvent comprises choline chloride, p-toluenesulfonic acid, 1,4-butanediol, and water; wherein the molar ratio of choline chloride, p-toluenesulfonic acid, and 1,4-butanediol is 1-2:3-6:2-8, and the ratio of the total mass of choline chloride and p-toluenesulfonic acid to the mass of water is 20:9-11. When used for the pretreatment of Miscanthus sinensis, the deep eutectic solvent of the present invention can effectively remove hemicellulose and lignin from the cell walls of Miscanthus sinensis, thereby significantly improving the efficiency of its enzymatic hydrolysis of cellulose.

Description

Technical Field

[0001] The present invention belongs to the technical field of biomass conversion and utilization, and more specifically relates to a deep eutectic solvent and its preparation and application. Background Art

[0002] With my country's increasing focus on environmental pollution, resource shortages, and ecological damage, the use of clean, renewable lignocellulose as a substitute for petroleum-based chemical feedstocks has become a consensus. Due to its rapid growth, high yield, adaptability, and high cellulose content, Pennisetum serratum is a high-quality lignocellulose suitable for enzymatic hydrolysis to produce glucose. However, the cell walls of Pennisetum serratum contain large amounts of hemicellulose and lignin, which can severely hinder enzymatic hydrolysis of cellulose. Therefore, pretreatment of Pennisetum serratum is often required before enzymatic hydrolysis.

[0003] Deep eutectic solvents (DESs) are currently widely used for the pretreatment of lignocellulose due to their advantages, such as being green, renewable, and recyclable raw materials, mild reaction, high efficiency, and easy operation. For example, existing technologies provide deep eutectic solvents made from choline chloride, p-toluenesulfonic acid, and ethanol. However, these solvents have limited effectiveness in removing hemicellulose and lignin from the cell walls of Miscanthus sinensis, resulting in poor pretreatment efficiency and low enzymatic hydrolysis efficiency of the cellulose. Summary of the Invention

[0004] In response to the deficiencies of the prior art, the present invention aims to provide a low eutectic solvent comprising choline chloride, p-toluenesulfonic acid, 1,4-butanediol, water and other ingredients. When used for the pretreatment of Miscanthus sinensis, it can effectively remove hemicellulose and lignin on the cell walls of Miscanthus sinensis, thereby significantly improving the enzymatic hydrolysis efficiency of its cellulose.

[0005] A second object of the present invention is to provide a method for preparing the above-mentioned deep eutectic solvent.

[0006] The third object of the present invention is to provide the use of the above-mentioned deep eutectic solvent in the pretreatment of Miscanthus sinensis.

[0007] The fourth object of the present invention is to provide a pretreatment method for Pennisetum chinense.

[0008] The above-mentioned purpose of the present invention is achieved through the following technical solutions:

[0009] The present invention provides a deep eutectic solvent comprising choline chloride, p-toluenesulfonic acid (p-CH3C6H4SO3H, also known as TsOH), 1,4-butanediol, and water; wherein the molar ratio of choline chloride, p-toluenesulfonic acid, and 1,4-butanediol is 1-2:3-6:2-8, and the ratio of the total mass of choline chloride and p-toluenesulfonic acid to the mass of water is 20:9-11.

[0010] The present invention compounds choline chloride, p-toluenesulfonic acid, 1,4-butanediol, water, and other ingredients to produce a deep eutectic solvent that effectively removes hemicellulose and lignin from the cell walls of Miscanthus sinensis, thereby significantly improving the efficiency of its enzymatic hydrolysis of cellulose. Compared with deep eutectic solvents that do not contain 1,4-butanediol or replace it with other solvents, the deep eutectic solvent of the present invention has a significantly better pretreatment effect on Miscanthus sinensis, can better remove hemicellulose and lignin from the cell walls of Miscanthus sinensis, and further significantly improve the efficiency of its enzymatic hydrolysis of cellulose.

[0011] Preferably, the molar ratio of choline chloride, p-toluenesulfonic acid and 1,4-butanediol is 1:3:3.

[0012] Preferably, the mass ratio of the total mass of choline chloride and p-toluenesulfonic acid to the mass of water is 20:10.

[0013] Based on this, the present invention also provides a method for preparing the above-mentioned low eutectic solvent, namely, heating the components in the formula to obtain the low eutectic solvent.

[0014] Preferably, the heating temperature is 70-90°C, most preferably 80°C.

[0015] Preferably, the heating time is 1.8 to 2.2 hours, and most preferably 2 hours. At this time, the deep eutectic solvent system is homogeneous and transparent.

[0016] Preferably, the heating is accompanied by stirring, such as stirring at 250-350 rpm.

[0017] When used for the pretreatment of Miscanthus sinensis, the above-mentioned deep eutectic solvent can effectively remove hemicellulose and lignin on the cell wall of Miscanthus sinensis, thereby significantly improving the enzymatic hydrolysis efficiency of its cellulose. Therefore, the use of the above-mentioned deep eutectic solvent in the pretreatment of Miscanthus sinensis should be within the scope of protection of the present invention.

[0018] In addition, the present invention also provides a pretreatment method for Miscanthus sinensis, namely, mixing Miscanthus sinensis with the above-mentioned deep eutectic solvent, heating at 90-100° C. for 18-22 minutes, and then separating the solid and the liquid.

[0019] Preferably, the royal bamboo grass is crushed to 15-25 mesh before mixing, and most preferably to 20 mesh.

[0020] Preferably, the ratio of the dry weight of Miscanthus sinensis to the volume of the deep eutectic solvent is 13-17 g:170-190 mL, and most preferably 15 g:180 mL.

[0021] Preferably, after the solid-liquid separation, the residue obtained by the solid-liquid separation is washed.

[0022] More preferably, the washing is performed with ethanol and water.

[0023] More preferably, the end point of the washing is when the pH of the residue is neutral.

[0024] The present invention has the following beneficial effects:

[0025] 1. When used for the pretreatment of Miscanthus sinensis, the deep eutectic solvent of the present invention can effectively remove hemicellulose and lignin on the cell wall of Miscanthus sinensis, thereby significantly improving the enzymatic hydrolysis efficiency of cellulose.

[0026] 2. After the pretreatment of Miscanthus sinensis by the deep eutectic solvent of the present invention is completed, the recovery rate can reach more than 85%, and the good pretreatment effect can still be maintained after multiple cycles. DETAILED DESCRIPTION

[0027] The present invention is further described below with reference to specific examples, which, however, are not intended to limit the present invention in any way. Unless otherwise specified, the reagents, methods, and equipment used in the present invention are conventional reagents, methods, and equipment in the art.

[0028] Unless otherwise specified, the reagents and materials used in the following examples were commercially available.

[0029] Example 1 A pretreatment method for king bamboo grass

[0030] (1) Preparation of deep eutectic solvent

[0031] Choline chloride, p-toluenesulfonic acid, and 1,4-butanediol were weighed separately in a molar ratio of 1:3:3 and added to a blue-capped reagent bottle containing deionized water (so that the total mass ratio of choline chloride and p-toluenesulfonic acid to the mass of deionized water is 20:10). The reagent bottle was then placed in a constant temperature oil bath at 80°C and stirred and heated for 2 hours (stirring speed was 300 rpm) to obtain the deep eutectic solvent.

[0032] (2) Pretreatment of King Grass

[0033] Grind the grass to a 20-mesh size, accurately weigh 15 g of dry weight of the powder into a round-bottom flask, add 180 mL of a deep eutectic solvent, and mix thoroughly. Place the round-bottom flask in a 95°C oil bath, stirring, and heating for 20 minutes. Remove the round-bottom flask and perform solid-liquid separation using a G2 sand-core funnel. Wash the residue with 60% (v / v) ethanol and deionized water until the pH is neutral, completing the pretreatment of the grass.

[0034] Example 2 A pretreatment method for King Grass

[0035] (1) Preparation of deep eutectic solvent

[0036] Choline chloride, p-toluenesulfonic acid, and 1,4-butanediol were weighed separately in a molar ratio of 2:6:8 and added to a blue-capped reagent bottle containing deionized water (so that the total mass ratio of choline chloride and p-toluenesulfonic acid to the mass of deionized water is 20:9). The reagent bottle was then placed in a constant temperature oil bath at 70°C and stirred and heated for 2.2 hours (stirring speed was 250 rpm) to obtain the deep eutectic solvent.

[0037] (2) Pretreatment of King Grass

[0038] Same as Example 1.

[0039] Example 3 A pretreatment method for royal bamboo grass

[0040] (1) Preparation of deep eutectic solvent

[0041] Choline chloride, p-toluenesulfonic acid, and 1,4-butanediol were weighed separately in a molar ratio of 1:3:2 and added to a blue-capped reagent bottle containing deionized water (so that the total mass ratio of choline chloride and p-toluenesulfonic acid to the mass of deionized water is 20:11). The reagent bottle was then placed in a constant temperature oil bath at 90°C and stirred and heated for 1.8 hours (stirring speed was 350 rpm) to obtain the deep eutectic solvent.

[0042] (2) Pretreatment of King Grass

[0043] Same as Example 1.

[0044] Example 4: A pretreatment method for King Grass

[0045] (1) Preparation of deep eutectic solvent

[0046] Same as Example 1.

[0047] (2) Pretreatment of King Grass

[0048] Grind the grass into a 15-mesh size. Accurately weigh 17 g of dry weight of the powder into a round-bottom flask. Add 190 mL of a deep eutectic solvent and mix thoroughly. Place the round-bottom flask in a 100°C oil bath, stirring, and heat for 18 minutes. Remove the round-bottom flask and perform solid-liquid separation using a G2 sand-core funnel. Wash the residue with 60% (v / v) ethanol and deionized water until the pH is neutral. This completes the pretreatment of the grass.

[0049] Example 5 A pretreatment method for King Grass

[0050] (1) Preparation of deep eutectic solvent

[0051] Same as Example 1.

[0052] (2) Pretreatment of King Grass

[0053] Grind the grass to a 25-mesh size, accurately weigh 13 g of dry weight of the powder into a round-bottom flask, add 170 mL of a deep eutectic solvent, and mix thoroughly. Place the round-bottom flask in a 90°C oil bath, stirring, and heating for 22 minutes. Remove the round-bottom flask and perform solid-liquid separation using a G2 sand-core funnel. Wash the residue with 60% (v / v) ethanol and deionized water until the pH is neutral, completing the pretreatment of the grass.

[0054] Comparative Example 1: A pretreatment method for King Grass

[0055] (1) Preparation of deep eutectic solvent

[0056] Same as Example 1, except that 1,4-butanediol was not added, and the product was prepared according to the following method:

[0057] Choline chloride and p-toluenesulfonic acid were weighed separately in a molar ratio of 1:3 and added to a blue-capped reagent bottle containing deionized water (so that the total mass ratio of choline chloride and p-toluenesulfonic acid to the mass of deionized water was 20:10). The reagent bottle was then placed in a constant temperature oil bath at 80°C and stirred and heated for 2 hours (stirring speed was 300 rpm) to obtain the deep eutectic solvent.

[0058] (2) Pretreatment of King Grass

[0059] Same as Example 1.

[0060] Comparative Example 2: A pretreatment method for King Grass

[0061] (1) Preparation of deep eutectic solvent

[0062] Same as Example 1, except that 1,4-butanediol is replaced by glycerol, that is, it is prepared according to the following method:

[0063] Choline chloride, p-toluenesulfonic acid, and glycerol were weighed separately in a molar ratio of 1:3:3 and added to a blue-capped reagent bottle containing deionized water (so that the total mass ratio of choline chloride and p-toluenesulfonic acid to the mass of deionized water is 20:10). The reagent bottle was then placed in a constant temperature oil bath at 80°C and stirred and heated for 2 hours (stirring speed was 300 rpm) to obtain the deep eutectic solvent.

[0064] (2) Pretreatment of King Grass

[0065] Same as Example 1.

[0066] Comparative Example 3: A pretreatment method for King Grass

[0067] (1) Preparation of deep eutectic solvent

[0068] Same as Example 1, except that 1,4-butanediol is replaced by ethanol, that is, it is prepared according to the following method:

[0069] Choline chloride, p-toluenesulfonic acid, and ethanol were weighed separately in a molar ratio of 1:3:3 and added to a blue-capped reagent bottle containing deionized water (so that the total mass ratio of choline chloride and p-toluenesulfonic acid to the mass of deionized water is 20:10). The reagent bottle was then placed in a constant temperature oil bath at 80°C and stirred and heated for 2 hours (stirring speed was 300 rpm) to obtain the deep eutectic solvent.

[0070] (2) Pretreatment of King Grass

[0071] Same as Example 1.

[0072] Comparative Example 4: A pretreatment method for King Grass

[0073] (1) Preparation of deep eutectic solvent

[0074] The same as Example 1, except that 1,4-butanediol is replaced by ethanol, and the ratio of choline chloride, p-toluenesulfonic acid, and ethanol is 2:6:8, that is, it is prepared according to the following method:

[0075] Choline chloride, p-toluenesulfonic acid, and ethanol were weighed separately in a molar ratio of 2:6:8 and added to a blue-capped reagent bottle containing deionized water (so that the total mass ratio of choline chloride and p-toluenesulfonic acid to the mass of deionized water is 20:10). The reagent bottle was then placed in a constant temperature oil bath at 80°C and stirred and heated for 2 hours (stirring speed was 300 rpm) to obtain the deep eutectic solvent.

[0076] (2) Pretreatment of King Grass

[0077] Same as Example 1.

[0078] Comparative Example 5: A pretreatment method for King Grass

[0079] (1) Preparation of deep eutectic solvent

[0080] Same as Example 1.

[0081] (2) Pretreatment of King Grass

[0082] Same as Example 1, except that the heating temperature is 75°C, that is, the pretreatment is performed according to the following method:

[0083] Grind the grass to a 20-mesh size, accurately weigh 15 g of dry weight of the powder into a round-bottom flask, add 180 mL of a deep eutectic solvent, and mix thoroughly. Place the round-bottom flask in a 75°C oil bath, stirring, and heating for 20 minutes. Remove the round-bottom flask and perform solid-liquid separation using a G2 sand-core funnel. Wash the residue with 60% (v / v) ethanol and deionized water until the pH is neutral, completing the pretreatment of the grass.

[0084] Test Example 1 Pretreatment Effect of Deep Eutectic Solvent on Miscanthus sinensis

[0085] 1. Test Method

[0086] (1) Test of hemicellulose and lignin removal effect

[0087] The pretreated products obtained in Examples 1 to 5 and Comparative Examples 1 to 5 were placed in a vacuum drying oven and dried. 0.15 g of the pretreated product with a dry weight and 0.15 g of unpretreated Miscanthus sinensis powder with a dry weight were weighed and added to 1.5 mL of 72% (v / v) sulfuric acid solution, respectively. The mixture was then placed in a water bath at 30±3°C to react for 60 min. The reaction product was then rinsed into a pressure-resistant bottle with 42 mL of deionized water and then placed in a high-pressure sterilizer at 121°C to react for 60 min. The mixture was cooled and subjected to solid-liquid separation to obtain a residue and a supernatant.

[0088] Take 3 mL of supernatant, add 0.1 g of CaCO3, react until no bubbles are generated, let it stand until complete precipitation, then take the supernatant into a 4 mL centrifuge tube, dilute the volume 5 times with deionized water, shake well and take 1.5 mL with a syringe for filtration. The glucose concentration C1 and xylose concentration C2 in the filtrate were determined by liquid chromatography (chromatographic column SUGAR KS-801, matrix styrene-divinylbenzene copolymer, eluent H2O), and the mass fractions of cellulose and hemicellulose were calculated according to the formula "cellulose mass fraction (%) = (C1×0.9×0.0435) / (a×sample dry weight)×100%", "hemicellulose mass fraction (%) = (C2×0.88×0.0435) / (a×sample dry weight)×100%", respectively (where a represents the correction factor for glucose or xylose, respectively) are 0.97 and 0.88; the dry weight of the sample is the aforementioned 0.15 g), and finally the hemicellulose removal rate is calculated according to the formula "hemicellulose removal rate (%) = [1-(mass fraction of hemicellulose in pretreated product × dry weight of pretreated product) / mass fraction of hemicellulose in mesenteriae powder × dry weight of mesenteriae powder)] × 100%" (wherein the dry weight of the pretreated product is the dry weight of the pretreated products obtained in Examples 1 to 5 and Comparative Examples 1 to 5, and the dry weight of mesenteriae powder is the dry weight of the mesenteriae powder raw material used in Examples 1 to 5 and Comparative Examples 1 to 5).

[0089] Take the residue, place it in a sand core funnel for filtration, then transfer it to an oven and dry it until it is absolutely dry, record the mass M1 at this time, and then transfer it to a muffle furnace at 575°C for calcination for 4 hours, record the mass M2 after calcination, and calculate the mass fraction of lignin according to the formula "lignin mass fraction (%) = (M2-M1) / sample dry weight × 100%". Finally, calculate the lignin removal rate according to the formula "lignin removal rate (%) = [1-(lignin mass fraction in pretreatment product × pretreatment product dry weight) / lignin mass fraction in royal bamboo grass powder × royal bamboo grass powder dry weight)] × 100%".

[0090] (2) Enzymatic hydrolysis efficiency test

[0091] 2 g of the pretreated products obtained in Examples 1 to 5 and Comparative Examples 1 to 5 were weighed and placed in a conical flask. 100 mL of acetic acid-sodium acetate buffer (pH 4.8) was added and the mixture was allowed to react on a shaker at 50° C. and 150 rpm for 72 h. The reaction solution was then centrifuged and the supernatant obtained by centrifugation was diluted 20 times with deionized water. The glucose concentration in the dilution solution was determined by liquid chromatography, and the enzymatic hydrolysis efficiency of cellulose in the pretreated product was calculated according to the formula “enzymatic hydrolysis efficiency (%) = (glucose concentration in the dilution solution × 20 × 0.1) / (cellulose mass fraction in the pretreated product × 1.11 × 2) × 100%”. The cellulose mass fraction in the pretreated product was measured by the cellulose mass fraction determination method described in “(1) Hemicellulose and Lignin Removal Effect Test”.

[0092] 2. Test Results

[0093] The results are shown in Table 1.

[0094] Table 1

[0095]

[0096]

[0097] visible:

[0098] (1) The hemicellulose removal rate, lignin removal rate, and enzymatic hydrolysis efficiency of Examples 1 to 5 were significantly higher than those of Comparative Examples 1 to 4. This indicates that the deep eutectic solvent of the present invention can effectively remove hemicellulose and lignin from the cell walls of Miscanthus sinensis, thereby significantly improving the enzymatic hydrolysis efficiency of cellulose.

[0099] (2) The hemicellulose removal rate, lignin removal rate, and enzymatic hydrolysis efficiency of Example 1 were significantly higher than those of Comparative Example 5, indicating that when the pretreatment temperature was 90-100°C, it was more conducive to the pretreatment effect of the deep eutectic solvent of the present invention on Miscanthus sinensis.

[0100] The pretreated liquid obtained by "solid-liquid separation" in the process of "(2) Pretreatment of Miscanthus sinensis" in Example 1 was taken, and ultrapure water was added (so that the volume ratio of the pretreated liquid to the ultrapure water was 1:10). After stirring at 300 rpm for 24 hours, the mixture was filtered. The filtrate obtained by filtration was then placed in a rotary evaporator at 70°C for rotary evaporation separation for 1.5 hours (to remove moisture). Then, an equal amount of deionized water as that in the process of "(1) Preparation of Low Eutectic Solvent" in Example 1 was added, and the mixture was placed in a constant temperature oil bath at 80°C and stirred and heated for 2 hours (stirring speed was 300 rpm) to obtain the recovered low eutectic solvent. The recovered low eutectic solvent was again used to pretreat new Miscanthus sinensis according to the steps of "(2) Pretreatment of Miscanthus sinensis" in Example 1.

[0101] The above recovery and pretreatment processes were repeated three times, and each time the three indicators of hemicellulose removal rate, lignin removal rate, and enzymatic hydrolysis efficiency (testing methods are the same as those in Test Example 1) were used to evaluate the pretreatment effect of the deep eutectic solvent. The recovery rate was combined with the recovery rate of the deep eutectic solvent to characterize its recycling performance. The recovery rate was calculated according to the formula "recovery rate (%) = volume of deep eutectic solvent after current recovery / volume of deep eutectic solvent after previous recovery × 100%".

[0102] Table 2

[0103]

[0104]

[0105] It can be seen that after the deep eutectic solvent of the present invention completes the pretreatment of Miscanthus sinensis, its recovery rate can reach more than 85%, and the good pretreatment effect can still be maintained after multiple cycles.

[0106] The above embodiments are preferred implementation modes of the present invention, but the implementation modes of the present invention are not limited to the above embodiments. Any other changes, modifications, substitutions, combinations, and simplifications that do not deviate from the spirit and principles of the present invention should be considered as equivalent replacement methods and are included in the scope of protection of the present invention.

Claims

1. A pretreatment method for Pennisetum scabra, characterized in that: The royal jellyfish is mixed with a low eutectic solvent, heated at 90-100° C. for 18-22 minutes, and then the solid-liquid separation is performed; wherein the low eutectic solvent comprises choline chloride, p-toluenesulfonic acid, 1,4-butanediol, and water; wherein the molar ratio of choline chloride, p-toluenesulfonic acid, and 1,4-butanediol is 1-2:3-6:2-8, and the ratio of the total mass of choline chloride and p-toluenesulfonic acid to the mass of water is 20:9-11.

2. The pretreatment method according to claim 1, characterized in that The molar ratio of choline chloride, p-toluenesulfonic acid and 1,4-butanediol is 1:3:

3.

3. The pretreatment method according to claim 1, wherein: The mass ratio of the total mass of choline chloride and p-toluenesulfonic acid to the mass of water is 20:

10.

4. The pretreatment method according to claim 1, characterized in that: The preparation method of the deep eutectic solvent is as follows: heating the components in the formula.

5. The pretreatment method according to claim 4, wherein In the preparation method of the deep eutectic solvent, the heating temperature is 70-90°C.

6. The pretreatment method according to claim 4, wherein In the preparation method of the deep eutectic solvent, the heating time is 1.8 to 2.2 hours.

7. The pretreatment method according to claim 4, wherein The ratio of the dry weight of Pennisetum oxyphylla to the volume of the deep eutectic solvent is 13-17 g: 170-190 mL.

8. The pretreatment method according to claim 4, characterized in that: The royal bamboo grass is further crushed into 15-25 meshes before being mixed.

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