阅读说明：本技术 一种利用低共熔溶剂对木质纤维原料进行预处理的方法及其使用的低共熔溶剂 (Method for pretreating wood fiber raw material by using eutectic solvent and eutectic solvent used by method ) 是由 黄晨 詹云妮 程金元 邓拥军 房桂干 于 2020-12-03 设计创作，主要内容包括：本申请公开了一种利用低共熔溶剂对木质纤维原料进行预处理的方法及其使用的低共熔溶剂。该所述的低共熔溶剂由氯化胆碱、氯化铝和愈创木酚组成,氯化胆碱和愈创木酚的摩尔比为1∶0.5～5,氯化胆碱和愈创木酚的摩尔之和与氯化铝的摩尔比为50～200∶1。本申请利用该体系对木质纤维原料进行预处理,在较低预处理温度下即可有效脱除物料中半纤维素和木质素,提高原料的比表面积和孔隙率,得到易于纤维素酶水解的物料。在预处理过程中脱除的木质素主要以小分子芳香化合物形式存在于低共熔体系中,易于分离和下游利用。同时由于该体系的预处理温度较低,可避免木质素发生缩聚反应,因此获得的木质素品质较高。(The application discloses a method for pretreating wood fiber raw materials by using a eutectic solvent and the eutectic solvent used by the method. The eutectic solvent consists of choline chloride, aluminum chloride and guaiacol, the molar ratio of the choline chloride to the guaiacol is 1: 0.5-5, and the molar ratio of the sum of the moles of the choline chloride and the guaiacol to the aluminum chloride is 50-200: 1. The system is used for pretreating the wood fiber raw material, hemicellulose and lignin in the material can be effectively removed at a lower pretreatment temperature, the specific surface area and the porosity of the raw material are improved, and the material easy to hydrolyze by cellulase is obtained. The lignin removed in the pretreatment process exists in the eutectic system mainly in the form of small-molecule aromatic compounds, and is easy to separate and utilize downstream. Meanwhile, the pretreatment temperature of the system is low, so that the lignin can be prevented from undergoing a polycondensation reaction, and the quality of the obtained lignin is high.)

1. A method for pretreating wood fiber raw materials by using a eutectic solvent is characterized by comprising the following steps: the method comprises the following steps:

1) choline chloride, guaiacol and aluminum chloride are mixed according to a certain proportion and then heated to be dissolved to form a uniform and clear eutectic solvent system;

2) mixing a wood fiber raw material with a eutectic solvent system, reacting at 80-130 ℃, and performing solid-liquid separation to obtain a solid and a pretreatment solution;

3) washing the solid to obtain a pretreated solid easy to hydrolyze by enzyme; the pretreatment liquid contains micromolecular lignin which is recycled.

2. The method for pretreating wood fiber raw material by using eutectic solvent according to claim 1, wherein: in the eutectic solvent system, the molar ratio of choline chloride to guaiacol is 1: 0.5-5, and the molar ratio of the sum of the moles of choline chloride and guaiacol to aluminum chloride is 50-200: 1.

3. The method for pretreating wood fiber raw material by using eutectic solvent according to claim 1, wherein: the mass ratio of the wood fiber raw material to the eutectic solvent system is 1: 5-1: 10.

4. The method for pretreating wood fiber raw material by using eutectic solvent according to claim 1, wherein: the wood fiber raw material is mixed with the eutectic solvent system and then reacts for 60min at the temperature of 80-130 ℃.

5. The method for pretreating wood fiber raw material by using eutectic solvent according to claim 1, wherein: the wood fiber raw material agricultural waste and forest biomass.

6. A eutectic solvent for pretreating lignocellulosic feedstocks, comprising: the eutectic solvent consists of choline chloride, aluminum chloride and guaiacol.

7. The eutectic solvent for pretreating wood fiber raw materials according to claim 6, wherein the molar ratio of choline chloride to guaiacol is 1: 0.5-5, and the molar ratio of the sum of the moles of choline chloride and guaiacol to aluminum chloride is 50-200: 1.

8. The method for preparing a eutectic solvent for pretreating lignocellulosic raw materials as claimed in claim 6, wherein choline chloride, guaiacol and aluminum chloride are mixed in proportion and then dissolved by heating at 80 ℃ until a stable and uniform eutectic solvent is formed.

9. Use of the eutectic solvent of claim 6 in the pretreatment of lignocellulosic feedstocks.

Technical Field

The invention relates to the field of clean separation and efficient utilization of wood fiber raw materials, in particular to a pretreatment method of a wood fiber raw material.

Background

The gradual decrease of fossil energy reserves such as petroleum and the environmental pollution caused by burning fossil fuels become serious, and people are forced to seek a clean and renewable energy source. Among the various renewable energy sources, biomass ethanol is regarded as important due to the advantages of wide raw material source, renewability, complete combustion, no pollution and the like. The method for producing the fuel ethanol by the wood fiber raw material mainly comprises three steps of pretreatment, enzyme hydrolysis and fermentation, wherein an efficient pretreatment technology is the key for improving the saccharification efficiency of the cellulose. The wood fiber raw material mainly comprises cellulose, hemicellulose and lignin, wherein the cellulose and the hemicellulose are crosslinked in a physical and chemical mode and tightly wrap the cellulose to form a compact biological structure of the wood fiber raw material, so that a plant body can resist the invasion of external physics, chemistry and biology. Therefore, when the wood fiber raw material is processed, a step of pretreatment is firstly needed to break the compact physical and chemical structures of the wood fiber raw material, so that the effective separation of cellulose, hemicellulose and lignin is realized, and the saccharification efficiency of the cellulose is further improved.

Common methods for pre-treating lignocellulosic feedstocks include acid, alkaline, sulfate, ionic liquid, and the like, which, while effective in improving saccharification efficiency of the pre-treated material, have their own drawbacks. Conventional acid or alkaline pretreatment is carried out at high temperature, and under severe conditions, although cellulose, hemicellulose and lignin can be effectively separated, carbohydrate is seriously degraded; meanwhile, the polycondensation reaction of the lignin is serious under the condition of severe pretreatment, and the high-value utilization of the condensed lignin is difficult; although the pretreatment conditions of the novel pretreatment methods such as ionic liquid are mild, the ionic liquid has certain toxicity, and the ionic liquid is difficult to recycle and expensive, so that the method is not suitable for large-scale industrial production. Therefore, the development of a cheap, mild and green solvent to realize the efficient separation of the wood fiber raw material is the key to realize the industrialization of the wood fiber biorefinery.

In recent years, studies on pretreatment of lignocellulose with a eutectic solvent have been focused. The eutectic solvent consists of a hydrogen bond acceptor and a hydrogen bond donor in a certain proportion, a hydrogen bond is formed between the hydrogen bond donor and the hydrogen bond acceptor, and simultaneously, electric charges are delocalized, so that the melting point of a eutectic system is greatly reduced. The eutectic system has the advantages of nonvolatility, low melting point, low toxicity, reproducibility, biodegradation, low cost, easy preparation and the like, and is widely applied to the fields of chemical synthesis, biomass refining and the like. Currently, the main hydrogen bond acceptor is choline chloride, while hydrogen bond donors are numerous, mainly including carboxylic acids and polyols (e.g. lactic acid, acetic acid, glycerol, etc.). A large amount of literature investigation shows that most of common hydrogen bond donors are synthetic chemicals and often need complicated chemical routes to obtain the hydrogen bond donors. Thus, finding a lignocellulosic-derived hydrogen bond donor would be beneficial in reducing the cost of eutectic systems.

Disclosure of Invention

Aiming at the problem that the synthesis path of the hydrogen bond donor of the existing eutectic system is complex, the invention aims to provide a novel and efficient eutectic system, wherein the hydrogen bond donor of the system is derived from wood fiber biomass, and meanwhile, the effective separation of hemicellulose and lignin can be obviously realized, and the saccharification efficiency of pretreated materials is promoted.

In order to solve the technical problems, the technical scheme adopted by the invention is as follows:

a method for pretreating wood fiber raw materials by using a eutectic solvent comprises the following steps:

1) choline chloride, guaiacol and aluminum chloride are mixed according to a certain proportion and then heated to be dissolved to form a uniform and clear eutectic solvent system;

2) mixing a wood fiber raw material with a eutectic solvent system, reacting at 80-130 ℃, and performing solid-liquid separation to obtain a solid and a pretreatment solution;

3) washing the solid to obtain a pretreated solid easy to hydrolyze by enzyme; the pretreatment liquid contains micromolecular lignin which is recycled.

In the eutectic solvent system, the molar ratio of choline chloride to guaiacol is 1: 0.5-5, and the molar ratio of the sum of the moles of choline chloride and guaiacol to aluminum chloride is 50-200: 1.

The mass ratio of the wood fiber raw material to the eutectic solvent system is 1: 5-1: 10.

The wood fiber raw material is mixed with the eutectic solvent system and then reacts for 60min at the temperature of 80-130 ℃.

The wood fiber raw materials comprise straws such as wheat straw and corn straw and forest biomass such as bamboo, poplar, eucalyptus and the like.

A eutectic solvent for pretreating wood fiber raw material is prepared from choline chloride, aluminium chloride and guaiacol.

The eutectic solvent for pretreating the wood fiber raw material is characterized in that the molar ratio of choline chloride to guaiacol is 1: 0.5-5, and the molar ratio of the sum of the moles of choline chloride and guaiacol to aluminum chloride is 50-200: 1.

According to the preparation method of the eutectic solvent for pretreating the wood fiber raw material, choline chloride, guaiacol and aluminum chloride are mixed according to a proportion and then heated and dissolved at 80 ℃ until a stable and uniform eutectic solvent is formed.

The eutectic solvent is applied to pretreatment of wood fiber raw materials.

Has the advantages that: compared with the prior art, guaiacol in the eutectic solvent is derived from guaiacyl in the plant lignin component, is a natural product and is easy to prepare. The system is utilized to pretreat the wood fiber raw material, hemicellulose and lignin in the material can be effectively removed at a lower pretreatment temperature, the specific surface area and the porosity of the raw material are improved, and the material which is easy to hydrolyze by cellulase is obtained. The lignin removed in the pretreatment process exists in the eutectic system mainly in the form of small-molecule aromatic compounds, and is easy to separate and utilize downstream. Meanwhile, the pretreatment temperature of the system is low, so that the lignin can be prevented from undergoing a polycondensation reaction, and the quality of the obtained lignin is high.

Drawings

FIG. 1 is a graph showing the effect of eutectic systems with and without aluminum chloride on recovery of wheat straw constituents (solids);

FIG. 2 is a graph showing the effect of eutectic systems with and without aluminum chloride on recovery of wheat straw constituents (specific constituents);

FIG. 3 is a graph showing the results of the enzymatic hydrolysis yield of wheat straw pre-treated without eutectic aluminum chloride addition;

FIG. 4 is a graph showing the results of the enzyme hydrolysis yield of wheat straw pre-treated with eutectic mixture of aluminum chloride

Detailed Description

The invention is further illustrated by the following examples. The examples are intended to illustrate, but not to limit, the invention. Those of ordinary skill in the art will understand that these embodiments do not limit the invention in any way, and that appropriate modifications can be made without departing from the spirit and scope of the invention.

Example 1

1) The molar ratio of choline chloride to guaiacol was 1: 2, and the molar ratio of choline chloride, guaiacol and aluminum chloride in the experimental group to which aluminum chloride was added was 62: 124: 1. The system is first heated at 80 ℃ until a homogeneous, clear solvent is obtained.

2) Mixing wheat straw and a eutectic solvent according to the mass ratio of 1: 10, reacting for 60min at 80-130 ℃, performing solid-liquid separation after pretreatment to obtain a pretreatment material and a pretreatment liquid containing lignin, washing the pretreatment material with ethanol, and then washing with distilled water until the washing liquid is clear.

The effect of the eutectic system with and without aluminum chloride on the recovery of the wheat straw component shows that the recovery rate of the pretreated materials is about 95 percent along with the rise of the temperature in the pretreatment system without aluminum chloride; in the experimental group with the addition of aluminum chloride, the material recovery gradually decreased from 93.50% to 57.63% as the temperature increased from 80 ℃ to 130 ℃ (fig. 1). From the recovery rate of the specific components (fig. 2), the recovery rate of the glucan is relatively stable in the system added with the aluminum chloride and is reduced from 95.31% to 81.15%; with the increase of the temperature, the degradation of hemicellulose is serious, and when the temperature is increased to 120 ℃, the recovery rate is only 2.46 percent; when the temperature was further raised to 130 c, no hemicellulose could be detected in the pretreated material. In this pretreatment system, too, considerable degradation of the lignin takes place, as can be seen from fig. 2, the lignin removal rate increases gradually with increasing temperature and reaches a steady value of about 43% after 110 ℃. The result shows that the choline chloride/guaiacol/aluminum chloride eutectic system can effectively promote the degradation of lignin and hemicellulose, and simultaneously reserve a large amount of glucan.

Example 2

Weighing 1g of pretreatment material (dry matter weight), placing in a hydrolysis bottle, adding 1mL of 1M acetic acid-sodium acetate buffer solution, adding enzyme preparation according to 25FPU/g of cellulase and 150U/g of xylanase, and finally supplementing distilled water to make the solid concentration of the system be 5%. Then the hydrolysis flask was placed in a shaker at 50 ℃ and 150rpm for 72 h. After the enzymolysis, the supernatant was centrifuged, and the glucose and xylose concentrations in the supernatant were analyzed, and the enzymatic hydrolysis yield was calculated, and the results are shown in fig. 3 and 4.

The results show that the hydrolysis yield of glucan and xylanase in a pretreatment system without adding aluminum chloride is kept stable with the change of temperature, and is respectively about 50% and 20%. In the pretreatment system added with aluminum chloride, the enzymolysis yield of glucan and xylan is greatly increased along with the increase of the pretreatment temperature, wherein the enzymolysis yield of glucan is increased from 42.99% (80 ℃) to 43.26% (90 ℃), 68.37 ℃ (100 ℃), 81.96% (110 ℃) and 100% (120 ℃ and 130 ℃); the xylan enzymolysis yields also increased from 21.35% (80 ℃) to 22.44% (90 ℃), 28.13% (100 ℃) and 65.93% (110 ℃), and almost all xylan was removed from the pretreated material when the temperature was increased to 120 ℃ and 130 ℃, so this example did not calculate the xylan enzymolysis yields of the pretreated material under both conditions. The result shows that the eutectic system adopted in the embodiment can obviously improve the enzymolysis performance of the pretreated material.

Example 3

Adding a proper amount of distilled water into the pretreatment liquid collected by the pretreatment, precipitating and centrifuging the dissolved lignin, and freeze-drying the lignin to obtain lignin powder. The molecular weight of the obtained lignin powder was measured by gel permeation chromatography, and the results are shown in table 1.

TABLE 1 molecular weight of dissolved lignin during eutectic pretreatment

	CEL	80℃	90℃	100℃	110℃	120℃	130℃
								Mw(Da)	14654	2630	2432	2231	1866	1542	1632
Mn(Da)	8692	2363	2350	1956	1762	1436	1563
								PDI	1.69	1.11	1.03	1.14	1.06	1.07	1.04

As shown in Table 1, the molecular weight of lignin in wheat straw was 14654 Da. After the pretreatment of the eutectic solvent, the molecular weight of the dissolved lignin is greatly reduced, and is reduced from 14654Da to 2630Da (80 ℃), 2432Da (90 ℃), 2231Da (100 ℃), 1866Da (110 ℃) and 1542Da (120 ℃), which indicates that the degraded lignin exists in a small molecular form. When the pretreatment temperature was further increased to 130 ℃, the lignin molecular weight increased to 1632Da, probably due to the polycondensation of small lignin molecules. Meanwhile, as can be seen from the polydispersity of lignin, the pretreated lignin becomes more uniform than that of the raw material wheat straw.