Eutectic solvent as well as preparation and application thereof

Abstract

The invention provides a deep eutectic solvent as well as preparation and application thereof. The deep eutectic solvent is prepared from choline chloride, p-toluenesulfonic acid, 1, 4-butanediol and water, wherein the molar ratio of choline chloride to p-toluenesulfonic acid to 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 the eutectic solvent is used for pretreating the pennisetum hydridum, hemicellulose and lignin on cell walls of the pennisetum hydridum can be effectively removed, and then the enzymolysis efficiency of cellulose of the pennisetum hydridum is remarkably improved.

Description

Technical Field

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

[0002] As my country pays more and more attention to environmental pollution, resource shortages and ecological damage, the use of clean and renewable lignocellulose to replace petroleum-based chemical raw materials has become a consensus. Due to its fast growth, high yield, strong adaptability and large amount of cellulose, King bamboo grass can be used as high-quality lignocellulose for enzymatic hydrolysis to produce glucose. However, the cell wall of King bamboo grass contains a large amount of hemicellulose and lignin, which will seriously affect the enzymatic hydrolysis of cellulose. Therefore, it is usually necessary to pretreat King bamboo grass before enzymatic hydrolysis.

[0003] At present, deep eutectic solvents (DESs) have been widely used in the pretreatment of lignocellulose due to the advantages of green, renewable and recyclable raw materials, mild reaction, high efficiency and easy operation. For example, the prior art provides a deep eutectic solvent made from choline chloride, p-toluenesulfonic acid and ethanol as raw materials, but it has limited effect on the removal of hemicellulose and lignin in the cell wall of King bamboo grass, and the pretreatment effect is poor, resulting in low enzymatic hydrolysis efficiency of cellulose. Summary of the invention

[0004] In view of the deficiencies in 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 the low eutectic solvent is used for the pretreatment of king bamboo grass, hemicellulose and lignin on the cell wall of king bamboo grass can be effectively removed, thereby significantly improving the enzymatic hydrolysis efficiency of cellulose.

[0005] The 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 deep eutectic solvent in pre-treating King Grass.

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

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

[0009] The present invention provides a low 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 obtain a low eutectic solvent that can effectively remove hemicellulose and lignin on the cell wall of the royal bamboo grass, thereby significantly improving the enzymatic hydrolysis efficiency of cellulose. Compared with a low eutectic solvent that does not add 1,4-butanediol or replaces it with other solvents, the low eutectic solvent of the present invention has a significantly better pretreatment effect on royal bamboo grass, can better remove hemicellulose and lignin on the cell wall of the royal bamboo grass, thereby more significantly improving the enzymatic hydrolysis efficiency 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 system of the low eutectic solvent is homogeneous and transparent.

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

[0017] When the above-mentioned low eutectic solvent is used for the pretreatment of King bamboo grass, it can effectively remove the hemicellulose and lignin on the cell wall of King bamboo grass, thereby significantly improving the enzymatic hydrolysis efficiency of cellulose. Therefore, the use of the above-mentioned low eutectic solvent in the pretreatment of King bamboo grass should be within the protection scope 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 low 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 meshes before mixing, and most preferably to 20 meshes.

[0020] Preferably, the ratio of the dry weight of King Grass 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 that the pH of the residue is neutral.

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

[0025] 1. When the low eutectic solvent of the present invention is used for the pretreatment of King Bamboo Grass, it can effectively remove the hemicellulose and lignin on the cell wall of King Bamboo Grass, thereby significantly improving the enzymatic hydrolysis efficiency of cellulose.

[0026] 2. After the pretreatment of the grass, the recovery rate of the low eutectic solvent of the present invention can reach more than 85%, and can still maintain a good pretreatment effect after multiple cycles. DETAILED DESCRIPTION

[0027] The present invention is further described below with reference to specific examples, but the examples do not limit the present invention in any form. 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 are commercially available.

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

[0030] (1) Preparation of deep eutectic solvent

[0031] Choline chloride, p-toluenesulfonic acid, and 1,4-butanediol were weighed 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), and then the reagent bottle was placed in a constant temperature oil bath at 80° C. and stirred and heated for 2 h (stirring speed was 300 rpm) to obtain the low eutectic solvent.

[0032] (2) Pretreatment of King Grass

[0033] The grass was crushed into 20 meshes, and 15 g of grass powder with a dry weight was accurately weighed into a round-bottom flask, and 180 mL of a low eutectic solvent was added and mixed evenly. The round-bottom flask was placed in a constant temperature oil bath at 95° C. and stirred and heated for 20 minutes, and then the round-bottom flask was taken out and solid-liquid separation was performed using a G2 sand core funnel. The residue obtained by solid-liquid separation was then washed with 60% (v / v) ethanol solution and deionized water until the pH was neutral, and the pretreatment of the grass was completed.

[0034] Example 2 A pretreatment method for King Bamboo Grass

[0035] (1) Preparation of deep eutectic solvent

[0036] Choline chloride, p-toluenesulfonic acid, and 1,4-butanediol were weighed 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), and then the reagent bottle was placed in a constant temperature oil bath at 70°C and stirred and heated for 2.2h (stirring speed was 250rpm) to obtain the low eutectic solvent.

[0037] (2) Pretreatment of King Grass

[0038] Same as Example 1.

[0039] Example 3 A pretreatment method for King Grass

[0040] (1) Preparation of deep eutectic solvent

[0041] Choline chloride, p-toluenesulfonic acid, and 1,4-butanediol were weighed 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), and then the reagent bottle was placed in a constant temperature oil bath at 90° C. and stirred and heated for 1.8 h (stirring speed was 350 rpm) to obtain the low 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] The grass was crushed into 15 meshes, and the dry weight of 17g of grass powder was accurately weighed into a round-bottom flask, and 190mL of a low eutectic solvent was added and mixed evenly. The round-bottom flask was placed in a constant temperature oil bath at 100°C and stirred and heated for 18 minutes, and then the round-bottom flask was taken out and solid-liquid separation was performed using a G2 sand core funnel. The residue obtained by solid-liquid separation was then washed with 60% (v / v) ethanol solution and deionized water until the pH was neutral, and the pretreatment of the grass was completed.

[0049] Example 5 A pretreatment method for royal grass

[0050] (1) Preparation of deep eutectic solvent

[0051] Same as Example 1.

[0052] (2) Pretreatment of King Grass

[0053] The grass was crushed into 25 meshes, and 13 g of grass powder with a dry weight was accurately weighed into a round-bottom flask, and 170 mL of a low eutectic solvent was added and mixed evenly. The round-bottom flask was placed in a constant temperature oil bath at 90° C. and stirred and heated for 22 minutes, and then the round-bottom flask was taken out and solid-liquid separation was performed using a G2 sand core funnel. The residue obtained by solid-liquid separation was then washed with 60% (v / v) ethanol solution and deionized water until the pH was neutral, and the pretreatment of the grass was completed.

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

[0055] (1) Preparation of deep eutectic solvent

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

[0057] Choline chloride and p-toluenesulfonic acid were weighed at 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), and then the reagent bottle was placed in a constant temperature oil bath at 80° C. and stirred and heated for 2 h (stirring speed was 300 rpm) to obtain the low 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 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), and then the reagent bottle was placed in a constant temperature oil bath at 80° C. and stirred and heated for 2 h (stirring speed was 300 rpm) to obtain the low 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, prepared according to the following method:

[0069] Choline chloride, p-toluenesulfonic acid, and ethanol were weighed 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), and then the reagent bottle was placed in a constant temperature oil bath at 80° C. and stirred and heated for 2 h (stirring speed was 300 rpm) to obtain the low 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 usage 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 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), and then the reagent bottle was placed in a constant temperature oil bath at 80° C. and stirred and heated for 2 h (stirring speed was 300 rpm) to obtain the low 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] The grass was crushed into 20 meshes, and 15 g of grass powder with a dry weight was accurately weighed into a round-bottom flask, and 180 mL of a low eutectic solvent was added and mixed evenly. The round-bottom flask was placed in a constant temperature oil bath at 75° C. and stirred and heated for 20 minutes, and then the round-bottom flask was taken out and solid-liquid separation was performed using a G2 sand core funnel. The residue obtained by solid-liquid separation was then washed with 60% (v / v) ethanol solution and deionized water until the pH was neutral, and the pretreatment of the grass was completed.

[0084] Test Example 1 Pretreatment Effect of Deep Eutectic Solvent on King Grass

[0085] 1. Test Method

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

[0087] The pretreated products obtained in Examples 1 to 5 and Comparative Examples 1 to 5 were placed in a vacuum drying oven for drying, and then 0.15 g of the pretreated product with a dry weight and 0.15 g of unpretreated grass powder with a dry weight were weighed and added to 1.5 mL of 72% (v / v) sulfuric acid solution, respectively. The mixture was placed in a water bath at 30±3° C. for reaction for 60 min, and then the reaction product was rinsed into a pressure bottle with 42 mL of deionized water. The mixture was then placed in an autoclave at 121° C. for reaction for 60 min, 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 stand until complete precipitation, take the supernatant in 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 are determined by liquid chromatography (chromatographic column SUGAR KS-801, matrix styrene-divinylbenzene copolymer, eluent H2O), and the mass fractions of cellulose and hemicellulose are 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%" (where a represents the correction factor for glucose or xylose, respectively is 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 grass powder × dry weight of grass powder)] × 100%” (wherein the dry weight of the pretreated product is the dry weight of the pretreated product obtained in Examples 1 to 5 and Comparative Examples 1 to 5, and the grass powder dry weight is the dry weight of the grass 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 efficiency test

[0091] Weigh 2 g of the pretreated products obtained in Examples 1 to 5 and Comparative Examples 1 to 5 in a conical flask, add 100 mL of acetic acid-sodium acetate buffer (pH 4.8), place on a shaker at 50° C. and 150 rpm for 72 hours, centrifuge the reaction solution, and dilute the supernatant obtained by centrifugation by 20 times the volume with deionized water. Determine the concentration of glucose in the dilution by liquid chromatography, and then calculate the enzymatic hydrolysis efficiency of cellulose in the pretreated product according to the formula "enzymatic hydrolysis efficiency (%) = (glucose concentration in the dilution × 20 × 0.1) / (cellulose mass fraction in the pretreated product × 1.11 × 2) × 100%". Wherein, the cellulose mass fraction in the pretreated product is measured by the cellulose mass fraction determination method in the aforementioned "(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 are 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 on the cell wall of King bamboo grass, 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 are significantly higher than those of Comparative Example 5, indicating that when the pretreatment temperature is 90-100°C, it is more conducive to exerting the pretreatment effect of the low eutectic solvent of the present invention on King bamboo grass. Test Example 2 Recycling of the low eutectic solvent

[0100] Take the pretreatment liquid obtained by "solid-liquid separation" in the process of "(2) Pretreatment of King Grass" in Example 1, add ultrapure water (so that the volume ratio of the pretreatment liquid to the ultrapure water is 1:10), stir at 300 rpm for 24 hours and then filter, then place the filtrate obtained by filtration in a rotary evaporator at 70°C for rotary evaporation separation for 1.5 hours (to remove moisture), then add deionized water in an amount equal to that in the process of "(1) Preparation of Low Eutectic Solvent" in Example 1, and then place it in a constant temperature oil bath at 80°C and stir and heat for 2 hours (stirring speed is 300 rpm) to obtain the recovered low eutectic solvent. The recovered low eutectic solvent is again used to pretreat new King Grass according to the steps of "(2) Pretreatment of King Grass" 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 efficiency (test method is the same as test example 1) were used to evaluate the pretreatment effect of the low eutectic solvent, and the recovery rate of the low eutectic solvent was combined to characterize its recycling performance. Among them, the recovery rate is calculated according to the formula "recovery rate (%) = volume of low eutectic solvent after recovery / volume of low eutectic solvent after last recovery × 100%".

[0102] Table 2

[0103]

[0104]

[0105] It can be seen that after the pretreatment of King Grass with the low 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.

[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 equivalent replacement methods and are included in the protection scope of the present invention.

Claims

1. A deep eutectic solvent, characterized in that The invention 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 deep eutectic solvent 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 deep eutectic solvent according to claim 1, characterized in that The mass ratio of the total mass of choline chloride and p-toluenesulfonic acid to the mass of water is 20:

10.

4. The method for preparing the deep eutectic solvent according to any one of claims 1 to 3, characterized in that: The product is obtained by heating each component of the formula.

5. The preparation method according to claim 4, characterized in that: The heating temperature is 70-90°C.

6. The preparation method according to claim 4, characterized in that: The heating time is 1.8 to 2.2 hours.

7. Use of the deep eutectic solvent according to any one of claims 1 to 3 in pre-treating King Grass.

8. A method for pretreating King bamboo grass, characterized in that: The method comprises mixing the king bamboo grass with the low eutectic solvent according to any one of claims 1 to 3, heating at 90 to 100° C. for 18 to 22 minutes, and then separating the solid from the liquid.

9. The method according to claim 8, characterized in that: The ratio of the dry weight of King Grass to the volume of the low eutectic solvent is 13-17 g: 170-190 mL.

10. The method according to claim 8, characterized in that: The royal bamboo grass is also crushed into 15-25 meshes before mixing.

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