CN116988331A - Method for efficiently separating and utilizing all components of wood fiber raw material - Google Patents

Abstract

The invention discloses a method for efficiently separating and utilizing all components of lignocellulosic raw materials, and belongs to the field of lignocellulosic raw material utilization. The present invention uses a binary solid acid-water solvent system composed of dilute sulfuric acid and salicylic acid to pretreat lignocellulosic raw materials, and can effectively remove hemicellulose and lignin in lignocellulosic raw materials at a lower pretreatment temperature. , increase the specific surface area and porosity of the raw materials, and obtain materials that are easy to be hydrolyzed by cellulase. After processing, the materials can be prepared into wood nanofibers; hemicellulose is dissolved in the reaction solution, and furfural is prepared through dehydration reaction; the reaction solution is simply added with water By dilution, lignin can be recovered. Through the combined use of two groups of solid acids, the present invention not only effectively separates lignin from raw materials under mild conditions, but also selectively degrades hemicellulose, has a protective effect on lignin, and effectively improves the quality of lignin. The utilization rate of the three major components of fiber raw materials.

Description

A method for efficient separation and utilization of all components of lignocellulosic raw materials

Technical field

The present invention relates to the field of clean separation, efficient conversion and utilization of all components of lignocellulosic raw materials, and specifically relates to a method for efficient separation and utilization of all components of lignocellulosic raw materials.

Background technique

Our country faces existential challenges brought about by climate change and overuse of fossil energy. Currently, in order to meet our country's future energy needs, our country is paying more and more attention to the use of renewable resources to produce bio-based materials, chemicals, and bioenergy. Lignocellulosic biomass materials continue to receive global attention as a sustainable alternative to fossil resources that can produce second-generation biofuels and other bio-based chemicals without compromising global food security and through appropriate Forest economics and climate change policies to adapt and increase.

Lignocellulosic raw materials are mainly composed of cellulose, hemicellulose and lignin. Cellulose and hemicellulose are physically and chemically cross-linked, tightly wrapping cellulose, forming a dense biological structure of lignocellulosic raw materials, making the plant body Able to resist external physical, chemical and biological attacks. Therefore, to process lignocellulose raw materials, a pretreatment step is first needed to break its dense physical and chemical structure, achieve effective separation of cellulose, hemicellulose and lignin, and then remove the three major elements in lignocellulose. for efficient use.

At this stage, the technologies for separating lignocellulosic biomass are mainly divided into physical methods, biological methods, physical-chemical combined methods and chemical methods, such as: mechanical extrusion pretreatment, fungal method, supercritical _CO2 method, ammonia fiber blasting method , acid method, alkali method, sulfate method, ionic liquid method, etc. Although these methods can effectively separate lignin, cellulose and hemicellulose in lignocellulosic raw materials, they still have their own problems that need to be optimized. For example, physical methods The equipment requirements are high and the investment is large; the biological method requires a long pretreatment time and requires a large reaction space; while the conventional acid method or alkali method pretreatment is carried out at high temperature. Under severe conditions, although cellulose and hemicellulose Although lignin and lignin can be effectively separated, carbohydrate degradation is serious; at the same time, severe condensation polymerization may occur in lignin under severe pretreatment conditions, and it is difficult to utilize the condensation lignin in high value; although new pretreatment methods such as ionic liquids The pretreatment conditions are mild, but the ionic liquid itself has certain toxicity, and the ionic liquid recycling is difficult and expensive, making it unsuitable for large-scale industrial production. Therefore, developing a mild, green solvent and efficient separation technology with simple steps is the key to realizing the industrialization of lignocellulosic biorefinery.

In recent years, research on the pretreatment of lignocellulose using solid acid-water solvent system separation methods has become a hot topic. In this separation method, solid organic acids are used to quickly separate the three major components of lignocellulosic biomass under lower temperature conditions. This method has strong versatility, simple separation method, and mild separation conditions. The solid acid can also be recovered through evaporation and concentration, and the separated lignin, cellulose, and hemicellulose can also be further processed and utilized. At present, improving the dissolution rate of lignin, increasing the saccharification rate of hemicellulose and cellulose, reducing the toxicity and usage of solid acids, and increasing the minimum solubility of solid acids are still further development methods for the solid acid-water solvent system. . Therefore, finding a new solid acid-water solvent system with low toxicity, high dissolution rate, mild reaction conditions, and easy recovery is beneficial to its industrial application.

Contents of the invention

In view of the problems of increasing the dissolution rate of lignin, increasing the saccharification rate and reducing the toxicity of solid acids, the technical problem to be solved by the present invention is to provide a method for efficient separation and utilization of all components of lignocellulosic raw materials, using new and efficient Binary solid acid-water solvent system treats lignocellulosic raw materials, which can significantly achieve effective separation of hemicellulose, cellulose and lignin under weaker reaction conditions, improve the dissolution rate of lignin, and promote the saccharification efficiency of pretreated materials. , all three major components can be further processed and utilized.

In order to solve the above problems, the technical solutions adopted by the present invention are as follows:

A method for efficient separation and utilization of all components of lignocellulosic raw materials, which uses a binary solid acid-water solvent system to pretreat lignocellulosic raw materials and effectively remove hemicellulose and hemicellulose in lignocellulosic raw materials at a lower temperature. Lignin is a material that is easy to be hydrolyzed by cellulase. After the material is mechanically treated, it is easier to prepare lignin nanocellulose; the reaction solution is diluted with water to recover lignin, and the hemicellulose dissolved in the reaction solution is Furfural is produced by dehydration reaction.

Further, the binary solid acid-water solvent system is composed of dilute sulfuric acid and salicylic acid, and the mass ratio of dilute sulfuric acid to salicylic acid is 0.1-1:1.

Further, the lower pretreatment temperature is 70-120°C.

Further, the specific steps of the method for efficiently separating and utilizing all components of lignocellulosic raw materials include:

1) Mix dilute sulfuric acid, salicylic acid and water at a mass ratio of 0.1-1:1, then heat and dissolve to form a uniform and clear binary solid acid-water solvent system;

2) Mix the lignocellulosic raw material with the binary solid acid-water solvent system obtained in step 1) and react at 70-120°C. After the reaction is completed, solid-liquid separation is performed to obtain water-insoluble solids and pretreatment reaction liquid. ;

3) Water-insoluble solids are washed with ultrapure water and then dried and used as raw materials for enzymatic hydrolysis of sugar and preparation of LCNF. The pretreatment reaction solution is diluted until the acid content in the reaction solution drops to 10wt.%. In the following, dissolved lignin is precipitated. The pretreatment liquid contains small molecule lignin, which is diluted, frozen and precipitated, and then centrifuged. After washing with ultrapure water, when the pH of the washing liquid is 7, the lignin is freeze-dried and recovered. use;

4) The diluted pretreatment reaction solution is concentrated, and the concentrated solution is distilled to prepare furfural;

5) After the concentrated liquid is distilled to prepare furfural, it is further concentrated and evaporated to recover the solid acid in the reaction liquid.

Further, in the binary solid acid-water solvent system, the concentration of dilute sulfuric acid is 1-10 wt.%.

Further, in the preparation method of the binary solid acid-water solvent system, after mixing dilute sulfuric acid, salicylic acid and water in proportion, the temperature for heating and dissolving is 50°C.

Further, the solid-liquid mass ratio of the lignocellulosic raw material and the binary solid acid-water solvent system is 1:5-1:15.

Further, the water-insoluble solids after washing are used as raw materials for enzymatic hydrolysis of sugar and preparation of LCNF. The concentrated pretreatment reaction liquid is used to prepare furfural through the distillation process through dehydration reaction, and the dissolved low-condensation lignin is used to prepare lignin. base material.

Further, the main sources of the lignocellulosic raw materials include: one or more of agricultural and forestry production wastes and residues, woody plants and forestry processing wastes, and grass plants.

Further, the mass fraction of total acid in the pretreatment reaction solution is 30-50 wt.%.

Beneficial effects: Compared with existing technology, the advantages of the present invention include:

1. This application uses salicylic acid with lower acidity pKa = 2.97, dilute sulfuric acid and water to form a uniform and stable system, which can effectively reduce the reaction intensity in the reaction system and enable the reaction to proceed peacefully and stably.

2. The dilute sulfuric acid and salicylic acid used in this application have low toxicity. Salicylic acid is an available drug. The binary solid acid-water solvent system composed of the two can reduce the toxicity of the reaction system and make the present invention more efficient. The safety factor of the reaction is greatly improved, and salicylic acid has a high minimum solubility and is easy to recycle, greatly reducing the cost.

3. The pretreatment reaction conditions of this application are relatively mild, and the reaction can quickly separate lignin fibers (≤30min) at lower temperatures (≤100°C). The lignin dissolution rate exceeds 90%, and the final saccharification rate also exceeds 90%.

4. In this application, since the pretreatment conditions of the system are low and it contains ethanol, it can avoid the polycondensation reaction of lignin, so the lignin obtained is of higher quality and is easy to separate and utilize downstream.

Description of the drawings

Figure 1 is a graph showing the yield of water-insoluble solids under various conditions;

Figure 2 is an analysis diagram of the chemical components of water-insoluble solids;

Figure 3 is a diagram of the retention rate and dissolution rate of each component of the lignocellulosic raw material during the pretreatment process;

Figure 4 is a graph showing the enzymatic sugar yield of water-insoluble solids obtained under different reaction conditions;

Figure 5 is a graph showing the furfural yield obtained from the pretreated reaction solution under different reaction conditions;

Figure 6 is the diameter distribution diagram of LCNF;

Figure 7 is the topography image (AFM) of LCNF.

Detailed ways

In order to make the above objects, features and advantages of the present invention more obvious and understandable, specific implementation modes of the present invention will be described in detail below with reference to specific embodiments.

Example 1

1) First mix salicylic acid with dilute sulfuric acid with a concentration of 0.1mol/L, then add water to mix, and heat and dissolve at 60°C until a uniform and clear solution is obtained, which is a binary solid acid-water solvent system. Among them, the mass ratio of sulfuric acid to salicylic acid in dilute sulfuric acid is 1:1, and the total acid content in the system reaches 50wt.%.

2) Mix the cotton stalk with the binary solid acid-water solvent system at a mass ratio of 1:10, and react at 80-120°C for 40 minutes. After the pretreatment is completed (MxxTyytzz: M is the total acid concentration of dilute sulfuric acid and salicylic acid , wt.%, T is the reaction temperature, ℃, t is the reaction time, min; the following reaction conditions are reached respectively (M50T80t40, M50T90t40, M50T100t40, M50T110t40 and M50T120t40), and the Buchner funnel solid-liquid separation is used to obtain water-insoluble solids and water-containing solids. In the lignin pretreatment solution, water-insoluble solids are washed with ultrapure water, the pretreatment solution containing lignin is diluted, the acid concentration of the system is reduced to 10wt.%, and the dissolved lignin in the pretreatment reaction solution is precipitated.

After plant fiber raw material component analysis (NEAL analysis method), 0.3g of lignocellulosic raw material underwent two-step acid hydrolysis (72% and 4% sulfuric acid hydrolysis) to obtain a solid residue that was washed with water until neutral, and then the acid-insoluble lignin content was measured at a constant weight. , the acidolysis solution is analyzed by HPLC to determine the quality of glucan, xylan and arabinan. At the same time, the acidolysis solution is measured at 205nm ultraviolet light to determine the content of acid-soluble lignin, and finally the content of lignin, cellulose and hemicellulose in the wood fiber is obtained. proportion in the raw material), as the reaction conditions and temperature change, the effect of the binary solid acid-water solvent system on the separation of the three major components of cotton stalks shows that, as shown in Figure 1, as the temperature increases, the pretreatment does not dissolve The yield of water solids dropped from 73.2% to 49.7%, indicating that a large number of components were dissolved in the pretreatment reaction solution; from the component analysis of water-insoluble solids in Figure 3, it can be seen that the retention rate of glucan in the solids From 87.2% (M50T80t40) to 77.5% (M50T80t120) (glucan retention rate = (residual solid yield * proportion of glucan component in residual solid * mass of wood fiber before reaction) / wood fiber before reaction Mass * Proportion of glucan component in wood fiber before reaction * 100%); from Figure 3, it can be seen that as the temperature increases, the dissolution rate of hemicellulose increases (from 48.8% to 99.5%) , when the temperature rises to 120°C, its recovery rate is only 0.5%. In this pretreatment system, lignin also undergoes a large amount of degradation. As shown in Figure 3, as the temperature increases, the lignin removal rate gradually increases, and reaches the highest value after 120°C, which is about 88%. The above results indicate that the binary solid acid-water solvent system can effectively promote the degradation of lignin and hemicellulose while retaining a large amount of glucan.

Example 2

Weigh 1g of pretreatment material (absolute dry amount), place it in a hydrolysis bottle, add 50mM acetate buffer, cellulase 10FPU/g dextran, and finally add distilled water to make the system solid concentration 1%. Then the hydrolysis bottle was placed in a shaker at 50°C and 200 rpm for enzymatic hydrolysis for 96 hours. After the enzymatic hydrolysis, centrifuge, analyze the glucose yield in the enzymatic hydrolysis supernatant, and calculate the enzymatic hydrolysis yield. The results are shown in Figure 4.

The results show that after pretreatment with a binary solid acid-water solvent system, the enzymatic hydrolysis yield of glucan in water-insoluble solids changes with the change of pretreatment intensity (reaction conditions shown in the legend of Figure 4, by M40T80t40 rises to M40T100t40, and finally reaches M40T120t40). It can be found from Figure 4 that within 10h, the enzymatic hydrolysis rate increases the fastest, but the enzymatic hydrolysis yield under the three reaction conditions is close. However, after more than 10h, as the reaction intensity increases (such as M40T100t40Vs.M40T80t40), the enzyme hydrolysis yield begins to increase, and when the reaction conditions reach M40T120t40, the hydrolysis efficiency of the water-insoluble solid obtained reaches the highest, and the corresponding internal residual lignin content is the lowest (less than 10%, as shown in the figure shown in 2). As the pretreatment conditions gradually increased, the enzymatic hydrolysis yield of glucan increased significantly, with the highest enzymatic hydrolysis yield of glucan ranging from 49.0% (M40T80t40) to 75.1% (M40T100t40) and then to 83.2% (M40T120t40). . The results show that the binary solid acid-water solvent system used in this example can still significantly improve the enzymatic hydrolysis performance of water-insoluble solids at a lower enzyme dosage (10FPU/g). As the reaction intensity increases, the enzymatic glucose yield increases significantly.

Example 3

Dilute the pretreatment reaction solution to 10%, precipitate lignin, centrifuge and take the supernatant, re-concentrate and evaporate the pretreatment reaction solution until the acid concentration reaches 40%, take 50mL of the concentrated pretreatment reaction solution and add it to a 100mL stainless steel container. At 180°C, react for 30 minutes to perform dehydration reaction to prepare furfural. The results are shown in Figure 5.

The results show that after treatment in the binary solid acid-water solvent system, the xylan in the pretreatment reaction solution is basically hydrolyzed into xylose, and the yield of furfural is gradually increased as the reaction intensity changes. Large, the furfural yield increased from 34.3% (80°C) to 48.6% (100°C), and finally reached 70.2% (120°C). The results show that the binary solid acid-water solvent system used in this example, after treating the lignocellulosic raw materials, dissolves a large amount of hemicellulose and hydrolyzes it into xylose. The xylose dissolved in the pretreatment reaction solution undergoes a simple distillation process, and the xylose is dehydrated at high temperature to directly produce furfural without using a catalyst. As the intensity of the pretreatment reaction increases, the more xylose there is in the pretreatment reaction solution, and the yield of furfural is increased.

Example 4

Evenly disperse the water-insoluble solids (obtained from the reaction conditions of 80°C and 120°C) in deionized water to a concentration of 0.5wt%, stir mechanically for 1 hour, and use a laboratory fiber deflasing machine to defuse at a speed of 15,000 rpm. 10 minutes. Then, a high-pressure homogenizer was used to mechanically fibrillate the defibrated fiber suspension. The working pressure was 60MPa. After 30 cycles, a certain concentration of wood nanofiber (LCNF) suspension was obtained.

The results show that, as shown in Figure 6, after treatment in a binary solid acid-water solvent system, water-insoluble solids are easier to prepare LCNF through mechanical treatment. As the reaction conditions intensify, the diameter of the prepared LCNF increases. decreases from 22nm (80°C) to 14nm (120°C); as shown in Figure 7, in the morphology of LCNF, white spherical objects can be found, which are the lignin in the residual fibers, and the long white fibers are nanoscale LCNF.

Example 5

Add an appropriate amount of ultrapure water to the above pretreatment solution, precipitate the dissolved lignin in it and centrifuge, wash the lignin until neutral, and freeze-dry the lignin to obtain a lignin sample. The obtained lignin samples were analyzed by GPC and 2D NMR for molecular weight, distribution, and β-O-4’ content. The results are shown in Table 1.

Table 1 Molecular weight, molecular weight distribution and β-O-4’ content of pretreated lignin (g/mol, /100Ar)

As can be seen from Table 1, after pretreatment with the binary solid acid-water solvent system, the molecular weight of the dissolved lignin decreased significantly, from 13594g/mol to 5241g/mol (120°C), indicating that the degraded lignin was mostly in small amounts. Not only that, the PDI value dropped from 2.8 to 1.6, indicating that the molecular weight distribution of dissolved lignin decreased with the increase of reaction intensity, indicating that through the binary solid acid-water solvent system, the uniformity of lignin also decreased. promote.

The above descriptions are only preferred embodiments of the present invention and are not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and changes. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention shall be included in the protection scope of the present invention.

Claims (10)

1. A method for efficiently separating and utilizing all components of a wood fiber raw material is characterized in that a binary solid acid-water solvent system is utilized to pretreat the wood fiber raw material, hemicellulose and lignin in the wood fiber raw material are effectively removed at a lower temperature, a material easy for cellulose hydrolysis is obtained, and the material is easy to prepare into wood nanocellulose after being mechanically treated; the reaction liquid is diluted by adding water, lignin is recovered, hemicellulose dissolved in the reaction liquid is dehydrated to prepare furfural, and the full-component high-efficiency separation and utilization of the wood fiber raw material are realized.

2. The method for efficiently separating and utilizing the full components of the wood fiber raw material according to claim 1, wherein the binary solid acid-water solvent system consists of dilute sulfuric acid and salicylic acid, and the mass ratio of the dilute sulfuric acid to the salicylic acid is 0.1-1:1.

3. The method for efficient separation and utilization of the whole components of lignocellulosic feedstock according to claim 1, wherein the lower pretreatment temperature is 70-120 ℃.

4. The method for the efficient separation and utilization of the full components of lignocellulosic feedstock according to claim 1, wherein the specific steps include:

1) Mixing dilute sulfuric acid, salicylic acid and water according to the mass ratio of 0.1-1:1, and heating to dissolve to form a uniform and clear binary solid acid-water solvent system;

2) Mixing wood fiber raw materials with the binary solid acid-water solvent system obtained in the step 1), reacting at 70-120 ℃, and carrying out solid-liquid separation after the reaction is finished to obtain insoluble solid and pretreatment reaction liquid;

3) Washing insoluble solid, diluting the pretreatment reaction liquid until the acid content in the reaction liquid is reduced to below 10wt.%, and separating out dissolved lignin;

4) Concentrating the diluted pretreatment reaction liquid, and rectifying the concentrated liquid to prepare furfural;

5) And (3) rectifying the concentrated solution to prepare furfural, and then further concentrating and evaporating to recover solid acid in the reaction solution.

5. The method for efficient separation and utilization of a whole composition of lignocellulosic feedstock according to claim 4, wherein the concentration of dilute sulfuric acid in the binary solid acid-water solvent system is 1-10wt.%.

6. The method for efficiently separating and utilizing the full components of the lignocellulosic feedstock according to claim 4, wherein the binary solid acid-water solvent system is prepared by mixing dilute sulfuric acid, salicylic acid and water in a ratio, and heating to dissolve the mixture at a temperature of 50 ℃.

7. The method for the efficient separation and utilization of the full components of lignocellulosic feedstock of claim 4, wherein the solid to liquid mass ratio of lignocellulosic feedstock to the binary solid acid-water solvent system is from 1:5 to 1:15.

8. The method for efficiently separating and utilizing the full components of the lignocellulosic feedstock according to claim 4, wherein the washed water-insoluble solids are used as raw materials for preparing sugar by enzymatic hydrolysis and for preparing LCNF, the concentrated pretreatment reaction solution is used for preparing furfural by dehydration reaction in a rectification process, and the dissolved low-condensation lignin is used for preparing lignin-based materials.

9. The method for the efficient separation and utilization of the whole components of lignocellulosic feedstock of claim 4, wherein the main sources of lignocellulosic feedstock include: one or more of agricultural and forestry production waste and residues, woody plants, forestry processing waste, and gramineae plants.

10. The method for efficiently separating and utilizing the full components of the lignocellulosic feedstock according to claim 4, wherein the mass fraction of the total acids in the pretreatment reaction solution is 30-50wt.%.