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

Abstract

The application discloses a method for efficiently separating and utilizing whole components of wood fiber raw materials, and belongs to the field of wood fiber raw material utilization. The application utilizes a binary solid acid-water solvent system composed of dilute sulfuric acid and salicylic acid to pretreat wood fiber raw materials, so that hemicellulose and lignin in the wood fiber raw materials can be effectively removed at a lower pretreatment temperature, the specific surface area and porosity of the raw materials are improved, and the materials are easy to be hydrolyzed by cellulase, and the materials can be prepared into wood nanofibers after treatment; hemicellulose dissolved in the reaction solution is prepared into furfural through dehydration reaction; and the reaction solution can be recovered into lignin by simple water dilution. Through the combined use of the two groups of solid acids, the lignin is not only effectively separated from the raw materials under the mild conditions, but also selectively degraded hemicellulose, and the lignin is protected, so that the utilization rate of the three components of the wood fiber raw materials is effectively improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of clean separation, efficient conversion and utilization of whole components of lignocellulosic raw materials, and in particular to a method for efficient separation and utilization of whole components of lignocellulosic raw materials. BACKGROUND

[0002] China is facing the challenge of survival due to climate change and overuse of fossil energy. At present, in order to meet the future energy demand of China, China is increasingly attaching importance to the use of renewable resources to produce bio-based materials, chemicals and bioenergy. Lignocellulosic biomass materials, as a sustainable alternative to fossil resources, continue to attract global attention, as they can produce second-generation biofuels and other bio-based chemicals without compromising global food security, and can be adjusted and increased through appropriate forest economy and climate change policies.

[0003] Lignocellulosic raw materials are mainly composed of cellulose, hemicellulose and lignin, among which cellulose and hemicellulose are cross-linked in a physical and chemical manner, tightly wrapping cellulose to form a dense biological structure of lignocellulosic raw materials, so that the plant body can resist external physical, chemical and biological attacks. Therefore, in order to process lignocellulosic raw materials, a pretreatment step is first needed to break the dense physical and chemical structure, so as to achieve effective separation of cellulose, hemicellulose and lignin, and then efficient utilization of the three major components in lignocellulose.

[0004] At present, the technologies for separating lignocellulosic biomass mainly include physical method, biological method, physical-chemical combined method and chemical method, such as mechanical extrusion pretreatment, fungal method, supercritical CO2 method, ammonia fiber explosion method, acid method, alkali method, sulfite method, ionic liquid method, etc. Although these methods can effectively separate lignin, cellulose and hemicellulose in lignocellulosic raw materials, there are still problems to be optimized, such as high equipment requirement and large investment for physical method; long pretreatment time and large reaction space for biological method; and severe conditions for conventional acid or alkali pretreatment, which leads to serious degradation of carbohydrates, and severe polycondensation of lignin under severe pretreatment conditions, making it difficult to utilize the polycondensed lignin; although the new pretreatment method of ionic liquid has mild pretreatment conditions, the ionic liquid itself has certain toxicity, and it is difficult to recycle and expensive, which is not suitable for large-scale industrial production. Therefore, developing a mild and green solvent with simple steps for efficient separation technology is the key to realizing the industrialization of lignocellulosic biorefining.

[0005] In recent years, the use of solid acid-water solvent system separation method for lignocellulose pretreatment has become a hot spot. In this separation method, solid organic acid is used to rapidly separate the three components of lignocellulosic biomass at a lower temperature. The method has strong universality, simple separation method, mild separation conditions, and the solid acid can be recovered by evaporation concentration. The separated lignin, cellulose and hemicellulose can be further processed and utilized. At present, improving the dissolution rate of lignin, increasing the saccharification rate of hemicellulose and cellulose, reducing the toxicity of solid acid and reducing its use, and improving the minimum solubility of solid acid are still the further development methods of solid acid-water solvent system. Therefore, finding a new type of solid acid-water solvent system with low toxicity, high dissolution rate, mild reaction conditions and easy recovery is conducive to its industrial application. SUMMARY

[0006] In order to solve the problems of increasing the dissolution rate of lignin, increasing the saccharification rate and reducing the toxicity of solid acid, the technical problem to be solved by the present application is to provide a method for efficient separation and utilization of whole components of lignocellulosic raw materials. The lignocellulosic raw materials are treated by using a new and efficient binary solid acid-water solvent system, which can effectively separate hemicellulose, cellulose and lignin under weak reaction conditions, improve the dissolution rate of lignin, and promote the saccharification efficiency of pretreated materials. The three components can be further processed and utilized.

[0007] In order to solve the above problems, the technical scheme adopted by the present application is as follows:

[0008] A method for efficient separation and utilization of whole components of lignocellulosic raw materials, which uses a binary solid acid-water solvent system to pretreat lignocellulosic raw materials, effectively removes hemicellulose and lignin in the lignocellulosic raw materials at a lower temperature, and obtains a material that is easy to hydrolyze by cellulase. After the material is treated by mechanical method, it is easier to prepare lignocellulose nanofiber; the reaction solution is diluted by adding water, and the lignin is recovered, while the hemicellulose dissolved in the reaction solution is prepared into furfural by dehydration reaction.

[0009] 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.

[0010] Further, the lower pretreatment temperature is 70-120 ℃.

[0011] Further, the method for efficient separation and utilization of whole components of lignocellulosic raw materials comprises the following specific steps:

[0012] 1) Dilute sulfuric acid, salicylic acid and water are mixed according to the mass ratio of 0.1-1:1, and then heated and dissolved to form a uniform and clear binary solid acid-water solvent system;

[0013] 2) mixing the wood fiber raw material with the binary solid acid-water solvent system obtained in step 1), reacting the mixture at 70-120° C., and performing solid-liquid separation after the reaction to obtain a water-insoluble solid and a pretreatment reaction liquid;

[0014] 3) The water-insoluble solids are washed with ultrapure water and then dried to serve as raw materials for enzymatic hydrolysis and sugar production and LCNF preparation. The pretreatment reaction solution is diluted until the acid content in the reaction solution drops below 10 wt.% to precipitate the dissolved lignin. The pretreatment solution contains small molecular weight lignin, which is then frozen and precipitated after dilution and centrifuged. After washing with ultrapure water, the lignin is freeze-dried when the washing solution reaches a pH of 7 and recycled.

[0015] 4) The diluted pretreatment reaction liquid is concentrated, and the concentrate is distilled to produce furfural;

[0016] 5) After the concentrate is distilled to prepare furfural, it is further concentrated and evaporated to recover the solid acid in the reaction liquid.

[0017] Furthermore, in the binary solid acid-water solvent system, the concentration of dilute sulfuric acid is 1-10 wt.%.

[0018] Furthermore, in the preparation method of the binary solid acid-water solvent system, the dilute sulfuric acid, salicylic acid and water are mixed in proportion and heated to dissolve at a temperature of 50°C.

[0019] Furthermore, the solid-liquid mass ratio of the wood fiber raw material to the binary solid acid-water solvent system is 1:5-1:15.

[0020] Furthermore, the water-insoluble solids after washing are used as raw materials for enzymatic hydrolysis to produce sugar and raw materials for preparing LCNF. The concentrated pretreatment reaction liquid is used to prepare furfural through a dehydration reaction in a distillation process, and the dissolved low-condensation lignin is used to prepare lignin-based materials.

[0021] Furthermore, the main sources of the wood fiber raw materials include: one or more of agricultural and forestry production waste and residues, woody plants and forestry processing waste, and grass plants.

[0022] Furthermore, the mass fraction of the total acid in the pretreatment reaction liquid is 30-50 wt.%.

[0023] Beneficial effects: Compared with the existing technology, the advantages of the present invention include:

[0024] 1. This application uses salicylic acid with a relatively low acidity of 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.

[0025] 2、The toxicity of both the dilute sulfuric acid and the salicylic acid used in the application is low, the salicylic acid is a medicine, the binary solid acid-water solvent system composed of the two can reduce the toxicity of the reaction system, greatly improve the safety factor of the reaction, and the salicylic acid has a high minimum solubility, is easy to recover, and greatly reduces the cost.

[0026] 3、The pretreatment reaction condition of the application is relatively mild, the lignin fiber can be rapidly separated (≤30 min) at a lower temperature (≤100 ℃), the lignin dissolution rate is more than 90%, and the final saccharification rate is also more than 90%.

[0027] 4、The pretreatment condition of the system is relatively low and contains salicylic acid and water, so that the condensation reaction of lignin can be avoided, and the obtained lignin has high quality and is easy to separate and utilize downstream. BRIEF DESCRIPTION OF DRAWINGS

[0028] Figure 1 is a graph of the yield of water-insoluble solids under various conditions;

[0029] Figure 2 is a graph of the chemical component analysis of water-insoluble solids;

[0030] Figure 3 is a graph of the retention rate and dissolution rate of each component of lignocellulosic raw materials in the pretreatment process;

[0031] Figure 4 is a graph of the enzymatic saccharification yield of water-insoluble solids obtained under different reaction conditions;

[0032] Figure 5 is a graph of the furfural preparation yield of the pretreatment reaction liquid obtained under different reaction conditions;

[0033] Figure 6 is a graph of the diameter distribution of LCNF;

[0034] Figure 7 is a graph of the morphology of LCNF (AFM). DETAILED DESCRIPTION

[0035] In order to make the above-mentioned purposes, features and advantages of the application more obvious and easy to understand, the specific embodiments of the application will be described in detail below.

[0036] Example 1

[0037] 1) First, mix salicylic acid with dilute sulfuric acid with a concentration of 0.1 mol / L, then add water to mix, heat to dissolve at 60℃, until a uniform and clear solution is obtained, which is a binary solid acid-water solvent system. The mass ratio of sulfuric acid in the dilute sulfuric acid to the mass of salicylic acid is 1:1, and the total acid content in the system reaches 50 wt.%.

[0038] 2) Cotton stalks were mixed with a binary solid acid-water solvent system at a mass ratio of 1:10 and reacted at 80-120 ℃ for 40 min. After the pretreatment (MxxTyytzz: M is the total acid concentration of dilute sulfuric acid and salicylic acid, wt.%, T is the reaction temperature, ℃, and t is the reaction time, min; the following reaction conditions were reached: M50T80t40, M50T90t40, M50T100t40, M50T110t40, and M50T120t40, respectively), the insoluble solid and the pretreatment liquid containing lignin were obtained by solid-liquid separation using a Buchner funnel. The insoluble solid was washed with ultrapure water, and the pretreatment liquid containing lignin was diluted to reduce the acid concentration to 10 wt.%, and the dissolved lignin in the pretreatment reaction liquid was precipitated.

[0039] After plant fiber raw material component analysis (NEAL analysis method, 0.3 g of lignocellulosic raw material was subjected to two-step acid hydrolysis (72% and 4% sulfuric acid hydrolysis), the solid residue was washed to neutral with water, and the acid-insoluble lignin content was determined by constant weight determination, the acid hydrolysis liquid was analyzed by HPLC to determine the mass of glucan, xylan, and arabinan, and the acid-soluble lignin content was determined at 205 nm under ultraviolet light, and finally the proportion of lignin, cellulose, and hemicellulose in the lignocellulosic raw material was obtained), the results of the influence of the binary solid acid-water solvent system on the separation of the three main components of cotton stalks with changes in the reaction temperature showed that, as the temperature increased, the yield of the insoluble solid in the pretreatment decreased from 73.2% to 49.7%, indicating that a large amount of components were dissolved in the pretreatment reaction liquid; as shown in Figure 1 Figure 3 From the component analysis of the insoluble solid, the retention rate of glucan in the solid decreased from 87.2% (M50T80t40) to 77.5% (M50T120t40) (glucan retention rate = (residual solid yield Residual solid glucan component proportion Reaction before lignocellulosic mass) / Reaction before lignocellulosic mass Reaction before lignocellulosic glucan component proportion 100%); as shown in Figure 3 It can be seen that, as the temperature increased, the hemicellulose dissolution rate increased (from 48.8% to 99.5%), and when the temperature increased to 120 ℃, the recovery rate was only 0.5%. In this pretreatment system, a large amount of lignin also degraded, as shown in Figure 3 It can be seen that, as the temperature increased, the lignin removal rate gradually increased and reached a maximum value of about 88% at 120 ℃. The above results show that the binary solid acid-water solvent system can effectively promote the degradation of lignin and hemicellulose, while retaining a large amount of glucan.

[0040] ​Example 2

[0041] Weigh 1g of pretreated material (absolute dry weight) and place it in a hydrolysis flask. Add 50mM acetate buffer and a cellulase concentration of 10 FPU / g of glucan. Finally, add distilled water to a solids concentration of 1%. The flask is then placed in a shaker at 50°C and 200 rpm for 96 hours. After the enzymatic hydrolysis is complete, centrifuge the solution, analyze the glucose yield in the enzymatic supernatant, and calculate the enzymatic hydrolysis yield. The results are as follows: Figure 4 shown.

[0042] The results showed that the enzymatic hydrolysis yield of glucan in water-insoluble solids after pretreatment with binary solid acid-water solvent system changed with the change of pretreatment intensity (determined by Figure 4 The reaction conditions shown in the figure are from M50T80t40 to M50T100t40 and finally to M50T120t40). Figure 4 It can be found that within 10 h, the enzymatic hydrolysis rate increased the fastest, but the enzymatic hydrolysis yields under the three reaction conditions were close. However, after more than 10 h, as the reaction intensity increased (such as M50T100t40 Vs. M50T80t40), the enzymatic hydrolysis yield began to increase. When the reaction conditions reached M50T120t40, the hydrolysis efficiency of the water-insoluble solids obtained reached the highest, and the corresponding residual lignin content inside was the lowest (less than 10%, such as Figure 2 As pretreatment conditions gradually increased, the enzymatic hydrolysis yield of glucan increased significantly, with the highest yield increasing from 49.0% (M50T80t40) to 75.1% (M50T100t40) and then to 83.2% (M50T120t40). These results demonstrate that the binary solid acid-water solvent system employed in this example significantly improves the enzymatic hydrolysis of water-insoluble solids even at a relatively low enzyme dosage (10 FPU / g). The enzymatic glucose yield significantly increased with increasing reaction intensity.

[0043] Example 3

[0044] The pretreatment reaction liquid was diluted to 10% to precipitate lignin, and the supernatant was collected by centrifugation. The pretreatment reaction liquid was re-concentrated and evaporated until the acid concentration reached 40%. 50 mL of the concentrated pretreatment reaction liquid was added to a 100 mL stainless steel container and reacted at 180 °C for 30 min to perform dehydration reaction to prepare furfural. The results are as follows: Figure 5 shown.

[0045] The results show that after the treatment in the binary solid acid-water solvent system, the xylan in the pretreatment reaction liquid is basically hydrolyzed into xylose, and the yield of furfural is gradually increased with the change of reaction intensity, in which the yield of furfural is increased from 34.3% (80 ℃) to 48.6% (100 ℃), and finally reaches 70.2% (120 ℃). The results show that after the treatment of the binary solid acid-water solvent system in the present embodiment, the hemicellulose in the lignocellulosic raw material is largely dissolved and hydrolyzed into xylose. The xylose dissolved in the pretreatment reaction liquid is directly prepared into furfural through dehydration reaction at high temperature without using catalyst. With the increase of pretreatment reaction intensity, the more xylose in the pretreatment reaction liquid, the yield of furfural is increased.

[0046] Example 4

[0047] The water-insoluble solids (obtained under the reaction conditions of 80 ℃ and 120 ℃) are uniformly dispersed in deionized water to have a concentration of 0.5 wt%, mechanically stirred for 1 hour, and then defibrated using a laboratory fiber defibrator at a speed of 15,000 revolutions per minute for 10 min. Subsequently, the defibrated fiber suspension is mechanically fibrillated using a high-pressure homogenizer, and a wood nanofiber (LCNF) suspension having a certain concentration is obtained after 30 cycles of treatment at a working pressure of 60 MPa.

[0048] The results show that, as shown in Figure 6 , after the treatment in the binary solid acid-water solvent system, the water-insoluble solids are more easily prepared into LCNF through mechanical treatment, and with the increase of reaction conditions, the diameter of the prepared LCNF is decreased from 22 nm (80 ℃) to 14 nm (120 ℃); as shown in Figure 7 , the morphology of LCNF, it can be found that the white spherical objects are lignin in residual fibers, and the white long fibers are nanoscale LCNF.

[0049] Example 5

[0050] In the above pretreatment liquid, a proper amount of ultrapure water is added, the dissolved lignin is precipitated and centrifuged, and the lignin is washed to neutral. The lignin is freeze-dried to obtain a lignin sample. The obtained lignin sample is analyzed by GPC and 2D NMR to analyze the molecular weight and distribution, and the β-O-4' content, and the results are shown in Table 1.

[0051] Table 1 Molecular weight, molecular weight distribution and β-O-4' content of pretreated lignin (g / mol, / 100 Ar)

[0052]

[0053] As shown in Table 1, after the pretreatment by the binary solid acid-water solvent system, the molecular weight of the dissolved lignin is greatly reduced from 13594 g / mol to 5241 g / mol (120 ℃), indicating that the degraded lignin mainly exists in the form of small molecules. Moreover, the PDI value is reduced from 2.8 to 1.6, indicating that the molecular weight distribution of the dissolved lignin decreases with the increase of the reaction intensity, and the uniformity of the lignin is also improved after the binary solid acid-water solvent system.

[0054] The preferred embodiments of the present application have been described above with the aid of drawing figures, and are not intended to limit the present application, and for those skilled in the art, the present application can have various modifications and changes. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A method for efficiently separating and utilizing all components of wood fiber raw materials, characterized in that: The specific steps include: 1) Salicylic acid is mixed with 0.1 mol / L dilute sulfuric acid, and then water is added to the mixture. The mixture is heated at 60°C to dissolve until a uniform, clear solution is obtained. This is the binary solid acid-water solvent system, wherein the mass ratio of sulfuric acid to salicylic acid in the dilute sulfuric acid is 1:1, and the total acid content in the system reaches 50 wt%; 2) Cotton stalks were mixed with a binary solid acid-water solvent system in a mass ratio of 1:10 and reacted at 80-120°C for 40 min. After pretreatment, solid-liquid separation was performed using a Büchner funnel to obtain a water-insoluble solid and a pretreatment solution containing lignin. The water-insoluble solid was washed with ultrapure water, and the pretreatment solution containing lignin was diluted to reduce the acid concentration of the system to 10 wt% to precipitate the lignin dissolved in the pretreatment reaction solution.

2. The method for efficiently separating and utilizing all components of wood fiber raw materials according to claim 1, characterized in that: The water-insoluble solids after washing are used as raw materials for enzymatic hydrolysis to produce sugar and raw materials for preparing LCNF. The concentrated pretreatment reaction liquid is used to prepare furfural through a dehydration reaction in a distillation process, and the dissolved low-condensation lignin is used to prepare lignin-based materials.

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