A method for pretreating lignocellulosic biomass and application thereof

Abstract

The application discloses a pretreatment method of lignocellulose biomass and application thereof, and belongs to the technical field of biomass energy conversion. The pretreatment method of the lignocellulose biomass comprises the following steps: mixing the lignocellulose biomass with an organic amine aqueous solution and then reacting to obtain pretreated lignocellulose biomass. The pretreatment method of the lignocellulose biomass selectively breaks the ester bond and ether bond in a lignin-carbohydrate complex (LCC) by controlling the amine concentration, pretreatment temperature and time, promotes lignin dissolution and removal, and almost completely retains cellulose and hemicellulose, so that the subsequent enzymatic hydrolysis sugar production efficiency is significantly improved.

Description

Technical Field

[0001] This invention belongs to the field of biomass energy conversion technology, specifically relating to a pretreatment method for lignocellulosic biomass and its application. Background Technology

[0002] Lignocellulosic biomass, as the most abundant renewable resource in nature, has an annual total output exceeding 200 billion tons, of which agricultural waste (corn cobs, corn stalks, wheat straw, etc.) accounts for a large proportion. Corn cobs are a typical lignocellulosic agricultural waste, whose main components are cellulose (39-45%), hemicellulose (25-35%), and lignin (17-21%). A large portion of it is often used as low-value fuel, leading to serious air pollution and resource waste, including land degradation, resource depletion, and air pollution.

[0003] Currently, while acid pretreatment can effectively hydrolyze hemicellulose, its ability to remove lignin is limited, typically below 30%, and it produces fermentation inhibitors such as furfural and 5-hydroxymethylfurfural. Although the acid treatment in the invention patent with publication number CN122012649A uses low-concentration organic acids to reduce environmental pollution and fermentation inhibition, it still generates inhibitory byproducts such as dissolved lignin and humin after acid treatment. It also requires precise control of reaction conditions (acid concentration, temperature, time) and presents potential cost and process complexity issues in large-scale industrial applications. Alkali pretreatment (such as NaOH) can remove more lignin, but the cost of treating alkaline wastewater is high, and it easily leads to carbohydrate degradation losses. The invention patent with publication number CN104561183A discloses a method for pretreating corn stalks using ethylenediamine vapor in a closed reactor. However, this method has a low glucose yield after ethylenediamine treatment, and its enzymatic hydrolysis efficiency still has room for improvement, and its lignin removal effect is unsatisfactory. The invention patent with publication number CN120330274A proposes a technology for efficiently obtaining glucose by enzymatically hydrolyzing corn cobs using a stepwise acid-base pretreatment method. It has the advantages of low cost, environmental protection and high efficiency, but the disadvantage is that it has high requirements for acid-base concentration and reaction conditions, which limits its industrial implementation.

[0004] Therefore, there is an urgent need to develop a pretreatment method that can efficiently and selectively remove lignin, retain cellulose and hemicellulose to the greatest extent, and has recyclable and environmentally friendly solvents. Summary of the Invention

[0005] The first objective of this invention is to provide a pretreatment method for lignocellulosic biomass that solves the technical problems of easy generation of fermentation inhibitors and low lignin removal rate in traditional pretreatment methods.

[0006] The second objective of this invention is to provide a pretreatment method for lignocellulosic biomass and its application in biomass enzymatic hydrolysis and saccharification.

[0007] The third objective of this invention is to provide a method for the enzymatic hydrolysis and saccharification of lignocellulose biomass.

[0008] To achieve the above objectives, the technical solution of the present invention is as follows: In a first aspect, the present invention provides a pretreatment method for lignocellulosic biomass, comprising the following steps: mixing lignocellulosic biomass with an aqueous solution of organic amine and reacting the mixture to obtain pretreated lignocellulosic biomass.

[0009] Furthermore, the reaction process further includes: cooling, filtering to obtain a solid, washing the obtained solid, and drying to obtain the pretreated lignocellulosic biomass.

[0010] Furthermore, the drying temperature is 70–100 °C, and the drying time is 10–14 h.

[0011] Furthermore, the lignocellulosic biomass is corn cob.

[0012] Furthermore, the organic amine aqueous solution is a triethylamine aqueous solution, and the mass fraction of the triethylamine aqueous solution is 20-40%.

[0013] Furthermore, the mass fraction of the triethylamine aqueous solution is preferably 30%.

[0014] Furthermore, the mass ratio of the lignocellulosic biomass to the organic amine aqueous solution is 1:(3-6).

[0015] Furthermore, the reaction temperature is 120–160 °C, and the reaction time is 1–3 h.

[0016] Secondly, the present invention provides an application of the pretreatment method for lignocellulosic biomass as described above in the enzymatic hydrolysis and saccharification of biomass.

[0017] Thirdly, the present invention provides a method for enzymatic hydrolysis and saccharification of lignocellulosic biomass, comprising the following steps: pretreating the lignocellulosic biomass using the pretreatment method for lignocellulosic biomass as described above, and then adding cellulase for enzymatic hydrolysis to obtain the final product.

[0018] Furthermore, the amount of cellulase used is 5–15 FPU / g.

[0019] Furthermore, the enzymatic hydrolysis temperature is 40–60 °C, and the enzymatic hydrolysis time is 24–72 h.

[0020] Furthermore, the enzymatic hydrolysis also includes enzymatic hydrolysis under stirring conditions, wherein the stirring speed is 200-300 rpm.

[0021] The beneficial effects of this invention are: The pretreatment method for lignocellulosic biomass of the present invention effectively avoids the generation of fermentation inhibitors, solves the problem of carbohydrate degradation, and can also efficiently remove lignin, improve the sugar production efficiency of enzymatic hydrolysis of pretreated materials, and the solvent is easy to recover, eliminating the need for complex treatment of waste liquid, thus further improving environmental protection and economy.

[0022] The pretreatment method for lignocellulose biomass of the present invention selectively breaks ester and ether bonds in the lignin-carbohydrate complex (LCC) by controlling the amine concentration, pretreatment temperature and time, thereby promoting the dissolution and removal of lignin. The lignin removal rate can reach 74%, while cellulose and hemicellulose are almost completely retained, thus significantly improving the efficiency of subsequent enzymatic hydrolysis for sugar production.

[0023] The pretreatment method for lignocellulosic biomass of the present invention can achieve efficient lignin removal under mild conditions, creating ideal conditions for the subsequent high-value utilization of lignin. Simultaneously, carbohydrate components such as cellulose and hemicellulose are fully protected, and a large amount of fermentable sugar precursors are retained in the solid phase, resulting in extremely high enzymatic saccharification efficiency. Both glucose content and total sugar release rate reach high levels. After pretreatment, cellulose and hemicellulose in the lignocellulosic biomass are almost undegraded, and a large amount of fermentable sugar precursors are retained in the solid phase. After enzymatic hydrolysis, the glucose yield of the pretreated lignocellulosic biomass can reach 99.4%, and the total sugar yield can reach 93.7%, fully ensuring the utilization value of the carbon source.

[0024] In the pretreatment method for lignocellulosic biomass of this invention, the selected triethylamine has the outstanding characteristic of a low boiling point, which can be efficiently recovered and recycled through simple evaporation or distillation, significantly reducing process costs and environmental impact. The entire pretreatment process is mild, and based on the overall performance and conversion efficiency evaluation of the enzymatic hydrolysis products, no significant inhibitory effect was observed. Typical fermentation inhibitors such as furfural and 5-hydroxymethylfurfural are hardly generated, and the inhibitory effect of sugar-derived compounds is not significant, giving the hydrolysate excellent fermentation adaptability and clearing obstacles for subsequent biomass conversion processes.

[0025] The pretreatment method for lignocellulosic biomass of the present invention uses a low-cost organic amine aqueous solution, reducing material costs. Furthermore, the mild reaction conditions (<160 °C) and low equipment requirements make the method highly suitable for industrial application. In addition, the process is simple to operate, has controllable conditions, and is easy to scale up, making it very suitable for industrial promotion. Attached Figure Description

[0026] Figure 1 The lignin removal rates of Examples 1 and Comparative Examples 1-11 are shown. Figure 2 The concentrations of glucose, xylose, and arabinose in the hydrolysates of Examples 1 and Comparative Examples 4-10; Figure 3 The concentrations of glucose, xylose, and arabinose in the sugar solutions obtained under different pretreatment-enzymatic hydrolysis conditions; Figure 4 The images are SEM images of lignocellulosic biomass before and after amine treatment and the pretreatment of Example 1. (a) is an SEM image of the untreated lignocellulosic biomass, and (b) is an SEM image of the pretreated lignocellulosic biomass of Example 1. Figure 5 Laser particle size analysis diagram of untreated lignocellulosic biomass; Figure 6 This is a laser particle size analysis diagram of the pretreated lignocellulosic biomass of Example 1; Figure 7 This is a process flow diagram of the pretreatment-enzymatic hydrolysis and saccharification method for lignocellulose biomass. Detailed Implementation

[0027] The following will provide further details with reference to embodiments of the present invention.

[0028] In the following examples, the cellulase used was Cellic CTec3 HS, purchased from Beijing Gaoruisen Technology Co., Ltd.

[0029] Example 1 The pretreatment method for lignocellulosic biomass in Example 1 includes the following steps: Weigh 3 g of corn cob powder (100-200 mesh) and add it to 30 mL of a reactor lined with polytetrafluoroethylene. Add 17 g of 30% (w / w) triethylamine aqueous solution. After sealing, react in an oil bath at 140 °C for 3 h. After the reaction is complete, cool to 25 °C and filter to separate the solid and liquid phases to obtain hydrolysate and solid residue. Wash the solid residue with deionized water until neutral and dry at 80 °C for 12 h to obtain pretreated lignocellulosic biomass.

[0030] The liquid obtained from solid-liquid separation was concentrated by rotary evaporation to recover organic amines. The remaining material after rotary evaporation was dried to constant weight at 60-90℃ to obtain brown-black lignin-enriched material.

[0031] The pretreated lignocellulosic biomass was weighed, and the lignin content was determined. The lignin removal rate was calculated to be 74.4%.

[0032] Example 2 The pretreatment method for lignocellulosic biomass in Example 2 includes the following steps: Weigh 3 g of corn cob powder (100-200 mesh) and add it to 30 mL of a reactor lined with polytetrafluoroethylene. Add 17 g of 20% (w / w) triethylamine aqueous solution. After sealing, react in an oil bath at 160 °C for 1 h. After the reaction is complete, cool to 25 °C and filter to separate the solid and liquid components, obtaining hydrolysate and solid residue. Wash the solid residue with deionized water until neutral and dry at 70 °C for 14 h to obtain pretreated lignocellulosic biomass.

[0033] The liquid obtained from solid-liquid separation was concentrated by rotary evaporation to recover organic amines. The remaining material after rotary evaporation was dried to constant weight at 60-90℃ to obtain brown-black lignin-enriched material.

[0034] Example 3 The pretreatment method for lignocellulosic biomass in Example 3 includes the following steps: Weigh 3 g of corn cob powder (100-200 mesh) and add it to 30 mL of a reactor lined with polytetrafluoroethylene. Add 17 g of 40% (w / w) triethylamine aqueous solution. After sealing, react in an oil bath at 120 °C for 2 h. After the reaction is complete, cool to 25 °C and filter to separate the solid and liquid phases to obtain hydrolysate and solid residue. Wash the solid residue with deionized water until neutral and dry at 100 °C for 10 h to obtain pretreated lignocellulosic biomass.

[0035] The liquid obtained from solid-liquid separation was concentrated by rotary evaporation to recover organic amines. The remaining material after rotary evaporation was dried to constant weight at 60-90℃ to obtain brown-black lignin-enriched material.

[0036] Example 4 The enzymatic hydrolysis and saccharification method for lignocellulose biomass in Example 4 includes the following steps: Take 1 g of the pretreated lignocellulosic biomass from Example 1 as a substrate and add it to an Erlenmeyer flask. Then add cellulase to make the amount of cellulase in the entire hydrolysis system 15 FPU / g (substrate). Finally, seal the mouth of the flask with plastic wrap and place it on a shaker. Under 50 °C, continuously stir at a stirring speed of 200 rpm for enzymatic hydrolysis for 72 h. Samples were taken at 0 h, 24 h, 48 h and 72 h. After the enzymatic hydrolysis was completed, the enzymatic hydrolysate was obtained, which included glucose, xylose and arabinose.

[0037] According to the test, in the enzymatic hydrolysis and saccharification method of lignocellulose biomass in Example 4, the total sugar yield of the hydrolysate of Example 1 and the enzymatic hydrolysate of Example 4 was 93.7%, of which the yield of glucose was 99.4%, the yield of xylose was 89.1%, and the yield of arabinose was 79.5%.

[0038] Example 5 The enzymatic hydrolysis and saccharification method for lignocellulose biomass in Example 5 includes the following steps: Take 1 g of the pretreated lignocellulosic biomass from Example 2 as a substrate and add it to an Erlenmeyer flask. Then add cellulase to make the amount of cellulase in the entire hydrolysis system 10 FPU / g (substrate). Finally, seal the flask with plastic wrap and place it on a shaker. Under 40 °C, continuously stir at a stirring speed of 300 rpm for enzymatic hydrolysis for 48 h. Samples were taken at 0 h, 24 h and 48 h. After the enzymatic hydrolysis was completed, the enzymatic hydrolysate was obtained, which included glucose, xylose and arabinose.

[0039] Example 6 The enzymatic hydrolysis and saccharification method for lignocellulose biomass in Example 6 includes the following steps: Take 1 g of the pretreated lignocellulosic biomass from Example 3 as a substrate and add it to an Erlenmeyer flask. Then add cellulase to make the amount of cellulase in the entire hydrolysis system 5 FPU / g (substrate). Finally, seal the mouth of the flask with plastic wrap and place it on a shaker. Under the condition of 60 ℃, continuously stir at a stirring speed of 250 rpm for enzymatic hydrolysis for 24 h. Samples were taken at 0 h, 12 h and 24 h respectively. After the enzymatic hydrolysis was completed, the enzymatic hydrolysate was obtained, which included glucose, xylose and arabinose.

[0040] Comparative Examples 1-11 The pretreatment methods for the lignocellulosic biomass of Comparative Examples 1-11 are basically the same as those of Example 1. The difference between the pretreatment methods for the lignocellulosic biomass of Comparative Examples 1-11 and those of Example 1 is as follows: In Comparative Example 1, the organic amine aqueous solution was a 10% (w / w) butylamine aqueous solution; In Comparative Example 2, the organic amine aqueous solution was a 30% (w / w) butylamine aqueous solution; In Comparative Example 3, the organic amine aqueous solution was a 50% (w / w) butylamine aqueous solution; In Comparative Example 4, the organic amine aqueous solution was a 10% (w / w) triethylamine aqueous solution; The organic amine aqueous solution in Comparative Example 5 was a 50% (w / w) triethylamine aqueous solution; In Comparative Example 6, the organic amine aqueous solution was a mixed amine aqueous solution with a mass fraction of 50% (w / w), wherein the mixed amine was triethylamine and butylamine, and the mass ratio of triethylamine to butylamine was 9:1; In Comparative Example 7, the organic amine aqueous solution was a mixed amine aqueous solution with a mass fraction of 50% (w / w), wherein the mixed amine was triethylamine and butylamine, and the mass ratio of triethylamine to butylamine was 7:3; In Comparative Example 8, the organic amine aqueous solution was a mixed amine aqueous solution with a mass fraction of 50% (w / w), wherein the mixed amine was triethylamine and butylamine, and the mass ratio of triethylamine to butylamine was 1:1; In Comparative Example 9, an organic amine mixture was used instead of an aqueous organic amine solution. The organic amine mixture was obtained by mixing triethylamine and butylamine, wherein the mass ratio of triethylamine to butylamine was 1:1. In Comparative Example 10, an organic amine mixture was used instead of an aqueous organic amine solution. The organic amine mixture was obtained by mixing triethylamine and butylamine, wherein the mass ratio of triethylamine to butylamine was 7:3.

[0041] In Comparative Example 11, an organic amine mixture was used instead of an aqueous organic amine solution. The organic amine mixture was obtained by mixing triethylamine and butylamine, wherein the mass ratio of triethylamine to butylamine was 1:9.

[0042] Comparative Examples 12-23 The enzymatic hydrolysis and saccharification methods of lignocellulose biomass in Comparative Examples 12-23 are basically the same as those in Example 4. The difference between the enzymatic hydrolysis and saccharification methods of lignocellulose biomass in Comparative Examples 12-23 and those in Example 4 is as follows: In Comparative Example 12, the pretreated lignocellulosic biomass from Comparative Example 1 was used as the substrate; In Comparative Example 13, the pretreated lignocellulosic biomass from Comparative Example 2 was used as the substrate; In Comparative Example 14, the pretreated lignocellulosic biomass from Comparative Example 3 was used as the substrate; In Comparative Example 15, the pretreated lignocellulosic biomass from Comparative Example 4 was used as the substrate; In Comparative Example 16, the pretreated lignocellulosic biomass from Comparative Example 5 was used as the substrate; In Comparative Example 17, the pretreated lignocellulosic biomass from Comparative Example 6 was used as the substrate; In Comparative Example 18, the pretreated lignocellulosic biomass from Comparative Example 7 was used as the substrate; In Comparative Example 19, the pretreated lignocellulosic biomass from Comparative Example 8 was used as the substrate; In Comparative Example 20, the pretreated lignocellulosic biomass from Comparative Example 9 was used as the substrate; In Comparative Example 21, the pretreated lignocellulosic biomass from Comparative Example 10 was used as the substrate; In Comparative Example 22, the pretreated lignocellulosic biomass of Comparative Example 11 was used as the substrate; In Comparative Example 23, lignocellulosic biomass that had not undergone organic amine pretreatment was used as the substrate.

[0043] The lignin removal rates of Examples 1 and Comparative Examples 1-11 are as follows: Figure 1 As shown, in the triethylamine-only system, the lignin removal rate first increased and then decreased with the increase of triethylamine concentration, with Example 1 showing the best performance, reaching the highest lignin removal rate. In contrast, whether using only butylamine or a combination of butylamine and triethylamine, the lignin removal rate was significantly lower than that of the pure triethylamine system, indicating that only specific amines have a good lignin removal rate from corn cob powder.

[0044] The concentrations of glucose, xylose, and arabinose in the hydrolysates of Examples 1 and Comparative Examples 4-10 are as follows: Figure 2 As shown, with the increase of triethylamine concentration, the concentrations of glucose, xylose, and arabinose in the hydrolysate showed a trend of first increasing and then decreasing. Among them, Example 1 showed the best effect, with the total sugar concentration reaching the highest value. After the introduction of butylamine, regardless of whether it was anhydrous or aqueous compounding, the overall monosaccharide release and hydrolysis efficiency were generally lower than those of the triethylamine aqueous solution system. This indicates that the triethylamine aqueous solution system has high enzymatic hydrolysis efficiency and high monosaccharide yield in degrading lignocellulosic biomass.

[0045] The concentrations of glucose, xylose, and arabinose in the sugar solutions obtained under different pretreatment-enzymatic hydrolysis conditions are as follows: Figure 3 As shown in the figure, the total sugar concentration of the enzymatic hydrolysate obtained by directly enzymatically hydrolyzing lignocellulosic biomass without pretreatment with organic amine aqueous solution in Comparative Example 23 is relatively low. The total sugar concentration of the mixed sugar solution obtained by hydrolysate obtained by Comparative Example 9 and enzymatic hydrolysate obtained by Comparative Example 20 using anhydrous pure amine compound system is even lower, showing a certain inhibitory effect. The total sugar concentration of the mixed sugar solution obtained by hydrolysate obtained by Comparative Example 8 and enzymatic hydrolysate obtained by Comparative Example 19 using aqueous compound system is significantly increased, but still significantly lower than the total sugar concentration of the mixed sugar solution obtained by hydrolysate obtained by Example 1 and enzymatic hydrolysate obtained by Example 4 using "30% triethylamine aqueous solution" pretreatment and enzymatic hydrolysis. Among them, the glucose, xylose and total sugar concentrations of the mixed sugar solution obtained by hydrolysate obtained by Example 1 and enzymatic hydrolysate obtained by Example 4 all reach the highest levels. This proves that the triethylamine aqueous solution pretreatment of lignocellulosic biomass of the present invention can greatly break down the physical barrier of biomass and effectively synergize with the subsequent enzymatic hydrolysis and saccharification process, significantly improving the total sugar release yield.

[0046] SEM images and laser particle size analysis (LPSA) results of corn cobs without organic amine pretreatment and lignocellulosic biomass pretreated in Example 1 are shown below. Figure 4 , Figure 5 As shown, from Figure 4 As shown in (a), the corn cob powder without organic amine pretreatment has a smooth and flat surface, clear longitudinal stripes, and a more complete fiber structure. Laser particle size analysis results show a narrow, single-peak distribution, with a median particle size (D50) of 12.82 μm and a peak particle size of 2.909 μm. This indicates that the natural lignin-hemicellulose-cellulose crosslinking network in the corn cob powder without organic amine pretreatment is not destroyed, and the particle size uniformity is good. This is also the structural basis of the natural anti-degradation barrier of biomass. The SEM image of the pretreated lignocellulosic biomass in Example 1 is shown below. Figure 4 As shown in (b), physical tearing and porosification of the structure can be observed. The structure is loose, the surface is rough, and it exhibits a clear "fiber bundle separation" state. Triethylamine achieves efficient delignification by breaking the ether bonds between lignin molecules, while simultaneously disrupting the hydrogen bonds between cellulose molecules, causing severe fiber swelling. The volume expansion effect outweighs the effect of structural breakage, ultimately leading to an increase in hydrodynamic particle size. SEM microstructure and laser particle size analysis indicate that the pretreatment with triethylamine aqueous solution is characterized by "delignification-fiber swelling-pore construction." By increasing porosity, it enhances the accessibility of enzyme molecules, effectively breaking down the natural anti-degradation barrier of biomass and providing a favorable structural prerequisite for subsequent enzymatic hydrolysis, saccharification, and high-value conversion.

Claims

1. A pretreatment method for lignocellulosic biomass, characterized in that, Includes the following steps: Pretreated lignocellulosic biomass is obtained by mixing and reacting it with an aqueous solution of organic amines.

2. The pretreatment method for lignocellulosic biomass according to claim 1, characterized in that, The reaction process further includes: cooling, filtering to obtain a solid, washing the obtained solid, and drying to obtain the pretreated lignocellulosic biomass.

3. The pretreatment method for lignocellulosic biomass according to claim 2, characterized in that, The drying temperature is 70–100 °C, and the drying time is 10–14 h.

4. The pretreatment method for lignocellulosic biomass according to claim 1, characterized in that, The lignocellulosic biomass is corn cob, and the organic amine aqueous solution is triethylamine aqueous solution with a mass fraction of 20-40%.

5. The pretreatment method for lignocellulosic biomass according to claim 4, characterized in that, The triethylamine aqueous solution has a mass fraction of 30%.

6. The pretreatment method for lignocellulosic biomass according to claim 1, characterized in that, The reaction temperature is 120–160 °C, the reaction time is 1–3 h, and the mass ratio of the lignocellulosic biomass to the organic amine aqueous solution is 1:(3–6).

7. The application of a pretreatment method for lignocellulosic biomass as described in any one of claims 1 to 6 in the enzymatic hydrolysis and saccharification of biomass.

8. A method for enzymatic hydrolysis and saccharification of lignocellulose biomass, characterized in that, Includes the following steps: The lignocellulosic biomass is pretreated using the pretreatment method described in any one of claims 1 to 6, and then cellulase is added for enzymatic hydrolysis to obtain the final product.

9. The method for enzymatic hydrolysis and saccharification of lignocellulosic biomass according to claim 8, characterized in that, The amount of cellulase used is 5–15 FPU / g.

10. The method for enzymatic hydrolysis and saccharification of lignocellulosic biomass according to claim 8, characterized in that, The enzymatic hydrolysis temperature is 40–60 °C, and the enzymatic hydrolysis time is 24–72 h; the enzymatic hydrolysis also includes enzymatic hydrolysis under stirring conditions, and the stirring speed is 200–300 rpm.

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