阅读说明：本技术 一种利用路易斯碱辅助中性低共熔溶剂预处理木质纤维素的方法 (Method for pretreating lignocellulose by using Lewis base to assist neutral eutectic solvent ) 是由 徐峻 谢俊贤 李军 王斌 陈克复 于 2021-07-12 设计创作，主要内容包括：本发明属于生物质资源综合利用范畴,具体涉及一种利用路易斯碱辅助中性低共熔溶剂预处理木质纤维素的方法。所述方法包括：将风干粉碎后的植物纤维原料置于配制的丙三醇/氯化胆碱低共熔溶剂中,然后加入路易斯碱。将固液混合物进行加热预处理,混合液经真空过滤,洗涤液洗涤得到固体残渣和液体馏分。通过酸沉淀法收集液体馏分的再生木质素。本发明以路易斯碱作为催化剂辅助中性低共熔溶剂预处理木质纤维素,具有良好的脱除木素和半纤维素而保留纤维素的效果,显著提高了酶解糖化效率,而且低共熔溶剂水溶液经浓缩脱水后可循环。利用本发明提供的预处理方法在生物质预处理以及制浆造纸领域具有良好的应用前景。(The invention belongs to the field of comprehensive utilization of biomass resources, and particularly relates to a method for pretreating lignocellulose by using a Lewis base-assisted neutral eutectic solvent. The method comprises the following steps: and (3) placing the air-dried and crushed plant fiber raw material into a prepared glycerin/choline chloride eutectic solvent, and then adding Lewis base. And (3) heating the solid-liquid mixture for pretreatment, carrying out vacuum filtration on the mixed solution, and washing the washing solution to obtain solid residues and liquid fractions. The regenerated lignin of the liquid fraction was collected by acid precipitation. The method takes Lewis base as a catalyst to assist the neutral eutectic solvent to pretreat the lignocellulose, has good effects of removing lignin and hemicellulose and retaining the cellulose, obviously improves the enzymolysis saccharification efficiency, and can recycle the eutectic solvent aqueous solution after concentration and dehydration. The pretreatment method provided by the invention has good application prospect in the fields of biomass pretreatment and pulping and papermaking.)

1. A method for pretreating lignocellulose by using a Lewis base to assist a neutral eutectic solvent is characterized by comprising the following steps of:

(1) placing the air-dried and crushed lignocellulose raw material into a prepared eutectic solvent, and then adding Lewis base;

(2) heating the solid-liquid mixture to obtain a mixed solution;

(3) vacuum filtering the mixed solution, and washing residues with washing solution to obtain solid fraction and liquid fraction rich in cellulose;

(4) and (4) carrying out an acid precipitation method on the liquid fraction to obtain regenerated lignin.

2. The method for pretreating lignocellulose by using the Lewis base assisted neutral eutectic solvent as claimed in claim 1, wherein the step (1) is a mixture of ethylene glycol and choline chloride.

3. The method for pretreating lignocellulose by using the Lewis base-assisted neutral eutectic solvent as claimed in claim 2, wherein the molar ratio of the ethylene glycol to the choline chloride is (2-3): 1.

4. The method for pretreating lignocellulose by using the Lewis base assisted neutral eutectic solvent as claimed in claim 1, wherein the solid-to-liquid ratio of the lignocellulose raw material to the eutectic solvent in the step (1) is 1: 10-1: 20.

5. The method for pretreating lignocellulose by using the lewis base auxiliary neutral eutectic solvent according to claim 1, characterized in that the lewis base in step (1) comprises at least one of sodium carbonate, sodium acetate and sodium sulfite.

6. The method for pretreating lignocellulose by using the Lewis base assisted neutral eutectic solvent as recited in claim 1, wherein the Lewis base added in the step (1) accounts for 15% -25% of the lignocellulose raw material.

7. The method for pretreating lignocellulose by using the Lewis base assisted neutral eutectic solvent as claimed in claim 1, wherein the lignocellulose raw material in the step (1) is needle wood, broad leaf wood, bamboo wood or grass raw material.

8. The method for pretreating lignocellulose by using the lewis base auxiliary neutral eutectic solvent as claimed in claim 1, wherein the pretreatment conditions in step (2) are as follows: the temperature is 100-120 ℃, and the time is 2-3 h.

9. The method for pretreating lignocellulose by using the lewis base-assisted neutral eutectic solvent as claimed in claim 1, wherein in the step (3), the washing solution is acetone, ethanol or water.

10. The method for pretreating lignocellulose by using the Lewis base assisted neutral eutectic solvent as claimed in claim 1, wherein the aqueous eutectic solvent solution in the step (4) is recycled after dehydration through rotary evaporation.

Technical Field

The invention belongs to the field of comprehensive utilization of biomass, and particularly relates to a method for pretreating lignocellulose by using a neutral eutectic solvent assisted by Lewis base.

Background

Lignocellulosic biomass such as agricultural and forestry crops and energy crops has the characteristics of being renewable, large in production amount, rich in carbohydrate and the like, and the new energy is fully utilized to be converted into biochemical and biofuel, so that the use of fossil energy can be reduced, and economic value and ecological benefit are brought. The cellulose, hemicellulose and lignin are closely interwoven through hydrogen bonds, covalent bonds and non-covalent bonds to form a complex three-dimensional structure. From the standpoint of conversion utilization of the wood-based feedstock, the structural resistance of the wood-based feedstock can affect the liquid permeability or enzyme accessibility during processing, thereby affecting the conversion cost thereof. Different pretreatment methods are usually required to improve the utilization efficiency, such as physical treatment, thermochemical treatment, biological method, etc. However, the conventional methods have respective disadvantages, which limit the application thereof, such as high cost, long period and low enzymatic saccharification efficiency.

The eutectic solvent (DES) consists of a hydrogen bond donor and a hydrogen bond acceptor, and is a new generation green solvent with no toxicity, good biocompatibility and low cost. More importantly, the DESs can significantly disrupt lignin-carbohydrate complexes (LCCs) and selectively extract hemicellulose and lignin. Among them, neutral DESs using glycerol, ethylene glycol, or the like as a hydrogen bond donor have advantages of low viscosity, high thermal stability, and the like, compared with other DESs, and can be applied on a large scale.

Kim et al (Kim, K.H., Dutta, T., et al. Biomass pretreatment using deep electrically soluble sugars from lignin derived phenols, 2018,20(4),809-815.) studies showed that pretreatment of lignocellulose with choline chloride/4-hydroxybenzyl alcohol resulted in only 0.4% lignin removal, with an enzymatic saccharification efficiency of only 32.0%. Procences (Procences, A., Johnson, E., et al. deep electrically active solvent pretreatment and sub-sequence saccharification of corn seed. Bioresource technology, 2015,192,31-6.) et al used choline chloride/glycerol to destructure corn cores, and found that saccharification efficiencies were only 1.79% at 15h pretreatment conditions and 2.79% lignin removal at 115 ℃. It is therefore an object of the present invention to provide a method for promoting the deconstruction of lignocellulose by a neutral eutectic solvent.

Disclosure of Invention

In order to overcome the defects in the prior art, the invention aims to provide a method for pretreating lignocellulose by using a Lewis base-assisted neutral eutectic solvent.

The purpose of the invention is realized by at least one of the following technical schemes:

a method of pre-treating lignocellulose with a lewis base-assisted neutral eutectic solvent, comprising the steps of:

(1) placing the air-dried and crushed lignocellulose raw material into a prepared eutectic solvent, and then adding Lewis base;

(2) heating the solid-liquid mixture to obtain a mixed solution;

(3) vacuum filtering the mixed solution, and washing residues with washing solution to obtain solid fraction and liquid fraction rich in cellulose;

(4) and (4) carrying out an acid precipitation method on the liquid fraction to obtain regenerated lignin.

Further, the lignocellulose raw material in the step (1) is needle-leaved wood, broad-leaved wood, bamboo wood or grass raw material,

more preferably, the lignocellulose raw material is agricultural and forestry waste corn stalks.

Further, the wood fiber raw material in the step (1) is crushed and then screened by a 40-60-mesh sieve.

Further, the eutectic solvent in the step (1) is a mixture of ethylene glycol and choline chloride; preferably, the molar ratio of the ethylene glycol to the choline chloride is (2-3): 1,

further, the solid-to-liquid ratio of the lignocellulose raw material and the eutectic solvent in the step (1) is 1: 10-1: 20.

Further, the lewis base in step (1) includes at least one of sodium carbonate, sodium acetate and sodium sulfite;

further, the addition amount of the lewis base in the step (1) accounts for 15 to 25 percent of the lignocellulose raw material.

Further, the pretreatment conditions in the step (2) are as follows: the temperature is 100-120 ℃, and the time is 2-3 h

Further, the washing solution in the step (3) is acetone, ethanol or water. More preferably, the washing solution is a mixture of ethanol/water (v/v ═ 1: 1).

Further, the liquid part of the lignin removed in the step (4) is recycled after concentration and dehydration.

Furthermore, the eutectic solvent aqueous solution is recycled after rotary evaporation and dehydration.

The lignocellulose pretreatment method provided by the invention can be applied to the technical field of biofuel preparation or pulping and papermaking.

Compared with the prior art, the invention has the following advantages and effects:

(1) the pretreatment method provided by the invention has the advantages of low cost, no toxicity, easy synthesis, recycling and effective deconstruction of lignocellulose;

(2) the pretreatment method provided by the invention can effectively remove hemicellulose and lignin and obviously improve the accessibility of the cellulose. And the provided alkaline environment can protect the end group of the cellulose, and compared with other acidic pretreatments, the method can retain most of the cellulose, and is favorable for saccharification and enzymolysis in the later period.

(3) The pretreatment method provided by the invention has good application prospect in the fields of biofuel preparation or pulping and papermaking.

Detailed Description

The present invention is described below by way of examples, but the embodiments of the present invention are not limited by the examples, and any other changes, modifications, substitutions, combinations, and simplifications which do not depart from the spirit and principle of the present invention should be construed as equivalents thereof, and they are included in the scope of the present invention. The reagents or apparatus used are not indicated to the manufacturer, and are considered to be conventional products available by commercial purchase.

Example 1

A method of pre-treating lignocellulose with a lewis base-assisted neutral eutectic solvent, comprising the steps of:

mixing ethylene glycol and choline chloride according to a molar ratio of 2:1 to obtain a liquid eutectic solvent. And (3) placing the oven-dried corn straws which are sieved by a 40-mesh sieve into a eutectic solvent, wherein the mass ratio of the corn straws to the eutectic solvent is 1: 10. Then adding sodium acetate (15% of oven dried corn stalk) and mixing them uniformly. And (3) adding the solid-liquid mixture into a normal pressure reaction kettle for heating pretreatment, wherein the treatment time is 2 hours, the treatment temperature is 100 ℃, and the mixed solution after eutectic solvent treatment is obtained. After pretreatment, the mixture was vacuum filtered and washed with ethanol/water (v/v ═ 1:1) to give a solid residue (cellulose rich fraction) and a liquid fraction. The regenerated lignin in the liquid fraction was collected by acid precipitation.

Example 2

A method of pre-treating lignocellulose with a lewis base-assisted neutral eutectic solvent, comprising the steps of:

mixing ethylene glycol and choline chloride according to a molar ratio of 3:1 to obtain a liquid eutectic solvent. And (3) placing the oven-dried corn straws which are sieved by a 40-mesh sieve into a eutectic solvent, wherein the mass ratio of the corn straws to the eutectic solvent is 1: 15. Sodium sulfite (20% of oven dried corn stover) was then added and mixed well. And (3) adding the solid-liquid mixture into a normal pressure reaction kettle for heating pretreatment, wherein the treatment time is 2 hours, the treatment temperature is 110 ℃, and a mixed solution after eutectic solvent treatment is obtained. After pretreatment, the mixture was vacuum filtered and washed with ethanol/water (v/v ═ 1:1) to give a solid residue (cellulose rich fraction) and a liquid fraction. The regenerated lignin in the liquid fraction was collected by acid precipitation.

Example 3

A method of pre-treating lignocellulose with a lewis base-assisted neutral eutectic solvent, comprising the steps of:

mixing ethylene glycol and choline chloride according to a molar ratio of 2:1 to obtain a liquid eutectic solvent. And (3) placing the oven-dried corn straws which are sieved by a 40-mesh sieve into a eutectic solvent, wherein the mass ratio of the corn straws to the eutectic solvent is 1: 20. Then sodium carbonate (25% of oven dried corn stover) was added and mixed well. And (3) adding the solid-liquid mixture into a normal pressure reaction kettle for heating pretreatment, wherein the treatment time is 3h, the treatment temperature is 120 ℃, and a mixed solution after eutectic solvent treatment is obtained. After pretreatment, the mixture was vacuum filtered and washed with ethanol/water (v/v ═ 1:1) to give a solid residue (cellulose rich fraction) and a liquid fraction. The regenerated lignin in the liquid fraction was collected by acid precipitation.

Example 4

After the treatment of lignocellulose by the Lewis base assisted neutral eutectic solvent, the recycling of the lignocellulose comprises the following steps:

the liquid fraction from which lignin precipitated in example 3 was evaporated in a rotary evaporator at 60 c to remove ethanol/water. The recovered lewis base/eutectic solvent was then used without further purification to pretreat the corn stover as described in example 3, and was thus recycled for 4 times.

Comparative examples

To further illustrate the effect of lewis base on the efficiency of pretreatment of neutral eutectic solvents, lignocellulose was pretreated with only neutral eutectic solvents, as a comparative example, comprising the following steps:

mixing ethylene glycol and choline chloride according to a molar ratio of 2:1 to obtain a liquid eutectic solvent. And (3) placing the oven-dried corn straws which are sieved by a 40-mesh sieve into a eutectic solvent, wherein the mass ratio of the corn straws to the eutectic solvent is 1: 20. And (3) adding the solid-liquid mixture into a normal pressure reaction kettle for heating pretreatment, wherein the treatment time is 3h, the treatment temperature is 120 ℃, and a mixed solution after eutectic solvent treatment is obtained. After pretreatment, the mixture was vacuum filtered and washed with ethanol/water (v/v ═ 1:1) to give a solid residue (cellulose rich fraction) and a liquid fraction. The regenerated lignin in the liquid fraction was collected by acid precipitation.

Effect verification

The pretreated substrate was analyzed for compositional changes according to the national renewable energy laboratory standard NREL analysis method.

And (3) enzymolysis saccharification: 300mg of the cellulose residue was weighed into a centrifuge tube, and 15mL of 0.05mol/L, PH ═ 4.8 citric acid-sodium citrate buffer was added in an amount of 15FPU/g substrate cellulase. Mixing, placing in shaking table (50 deg.C, 150r/min), saccharifying for 72 hr, taking out, and measuring sugar release amount of reaction solution by ion chromatography.

TABLE 1 composition change and saccharification efficiency (%)

As can be seen from the data in Table 1, the lignocellulose pretreatment method disclosed by the embodiment of the invention has the characteristics of low cost, no toxicity and the like, is simple and feasible in preparation method, has a good deconstruction effect on lignocellulose, has the enzymolysis saccharification efficiency which is 3.8-4.9 times that of untreated lignocellulose, has the saccharification efficiency which is still 85.5% after four cycles, has a good recycling effect, and has a wide application prospect in the fields of biomass fuel and pulping and papermaking.

The above examples are only preferred embodiments of the present invention, which are intended to be illustrative and not limiting, and those skilled in the art should understand that they can make various changes, substitutions and alterations without departing from the spirit and scope of the invention.