Method for efficiently extracting L-glucan from wood fiber biomass

Abstract

The invention relates to the technical field of high-valued utilization of biomass, in particular to a method for efficiently extracting levodextran from wood fiber biomass, which is characterized in that water is used as a reaction medium for hydrothermal pretreatment of biomass, hemicellulose and lignin are selectively removed under a subcritical condition, and the content of cellulose is increased by 1.5-2.0 times. Aiming at the pretreated cellulose-rich biomass, a'reduced-pressure thermal cracking-volatile component rapid cooling 'synergistic pyrolysis system is constructed, and secondary cracking of volatile components and generation of carbon deposit are inhibited through dual effects of accelerating escape of pyrolysis volatile components in vacuum and rapidly cooling the volatile components. By means of the synergistic mechanism, the yield of the levodextran breaks through 400 mg / g, and the selectivity is not lower than 62%. According to the method disclosed by the invention, water is taken as a reaction medium, the core bottlenecks of high biomass refining cost and poor target product selectivity are solved through a synergistic path of directional enrichment of pretreatment and precise regulation and control of a pyrolysis process, and an efficient and environment-friendly technical scheme is provided for industrial production of the L-glucan.

Description

Technical Field

[0001] This invention relates to the field of biomass high-value utilization technology, specifically to a method for efficiently extracting L-glucan from lignocellulosic biomass. Background Technology

[0002] L-glucan, or 1,6-dehydrated-β-D-glucopyranose, is an important glucose derivative with a unique rigid structure (formed by acetal rings within C1 and C6) and three modifiable hydroxyl groups. This structural characteristic makes it a highly valuable platform compound, widely used in oligosaccharide synthesis, chiral drug preparation, and functional resin development. The triol structure of L-glucan can be used to synthesize polymers such as polyurethanes, high-performance adhesives, and biodegradable plastics. Furthermore, its biodegradability makes it an ideal carbon source for bio-fermentation, used in the production of bio-based chemicals such as itaconic acid, levulinic acid, and ethanol. Currently, the chemical synthesis of L-glucan faces challenges such as high raw material costs, complex process routes, and demanding reaction conditions.

[0003] The preparation of L-glucan from renewable lignocellulosic biomass via pyrolysis has industrial potential and has attracted much attention in recent years, but the following key bottlenecks exist. Cellulose, the most abundant component of biomass, is a high-molecular-weight polymer composed of glucose monomers linked by β-1,4-glycosidic bonds. Direct pyrolysis can yield L-glucan, but the yield is significantly reduced due to the inhibitory interaction between hemicellulose and lignin components during pyrolysis. To overcome the complexity of biomass components, pretreatment with organic solvents, acids, or alkalis is often used to separate the components. However, these methods are not only uneconomical and corrode equipment, but may also introduce impurities such as alkali metals, which catalyze the decomposition of L-glucan during subsequent pyrolysis. Furthermore, in traditional pyrolysis processes, the prolonged residence time of pyrolysis products in high-temperature regions inevitably leads to violent secondary reactions. On the one hand, these reactions decompose to generate low-value small-molecule compounds such as furan, furfural, and carboxylic acids; on the other hand, they depolymerize to generate heavy coke deposits. Both of these factors severely restrict the yield and selectivity of L-glucan.

[0004] Therefore, developing an economical, efficient, and environmentally friendly biomass refining and pyrolysis process to effectively enrich cellulose, significantly improve the yield and selectivity of L-glucan, and effectively inhibit the formation of by-products (especially carbon deposits) is a key technical problem that urgently needs to be solved. Summary of the Invention

[0005] To address existing problems, this invention provides a method for the efficient pyrolysis extraction of L-glucan from lignocellulosic biomass, aiming to achieve efficient enrichment of cellulose and highly selective preparation of L-glucan. This invention employs a fixed-bed hydrothermal pretreatment device, utilizing subcritical water extraction to extract hemicellulose and lignin components from lignocellulosic biomass, significantly enriching the cellulose component and increasing its content by 1.5-2.0 times, providing high-quality raw materials for subsequent efficient pyrolysis. For the pretreated cellulose-rich biomass, this invention constructs a novel fixed-bed pyrolysis system, the core process of which is "reduced pressure pyrolysis-rapid cooling of volatiles." This system accelerates the escape of pyrolysis volatiles from biomass particles and the high-temperature reaction zone through vacuum, and simultaneously inhibits secondary pyrolysis and depolymerization reactions by rapidly cooling the volatiles. This synergistic mechanism effectively reduces the formation of byproducts such as coke deposits, thereby increasing the yield of L-glucan to greater than 400 mg / g and the selectivity to no less than 62%.

[0006] The objective of this invention can be achieved through the following technical solutions:

[0007] A method for efficiently extracting L-glucan from lignocellulosic biomass includes the following steps:

[0008] Biomass is loaded into the stainless steel reaction tube of the fixed-bed hydrothermal pretreatment device, and deionized water is continuously pumped in using a liquid injection pump. After the entire flow path is filled with liquid, the system pressure is adjusted by the back pressure valve.

[0009] The stainless steel reaction tube is heated to the target temperature, so that the flowing water is in a subcritical fluid state, and the biomass is pretreated by hydrothermal treatment at the target temperature for a certain period of time.

[0010] After the pretreatment is completed, the reaction system is cooled and depressurized, and the resulting mixture is subjected to solid-liquid separation and drying to obtain hydrothermally pretreated biomass.

[0011] The hydrothermally pretreated biomass is placed in a specially designed quartz tube reactor. The reactor outlet is designed with a jacket structure, and circulating cooling water is introduced into the outer jacket layer to ensure that the pyrolysis volatiles can be rapidly cooled to room temperature after leaving the high temperature zone.

[0012] Heat the quartz reaction tube to the required pyrolysis temperature, start the vacuum pump, reduce the pressure of the pyrolysis system, and quickly push the biomass to the high-temperature zone for pyrolysis reaction, and maintain it at the pyrolysis temperature for 20 minutes.

[0013] After the reaction is completed, the pyrolysis volatiles are rapidly condensed through the outlet jacket. The liquid product rich in L-glucan obtained from the condensation, as well as the solid semi-coke in the reactor and the carbon deposits on the inner wall of the reaction tube, are collected and weighed to calculate the yield of each product.

[0014] As a further technical solution of the present invention: the biomass is one of rice husks and poplar wood chips.

[0015] As a further technical solution of the present invention: the flow rate of the deionized water pumped in is 5.0 mL / min.

[0016] As a further technical solution of the present invention: the system pressure is adjusted to 50 bar by means of a back pressure valve.

[0017] As a further technical solution of the present invention: the stainless steel reaction tube is heated to 200°C.

[0018] As a further technical solution of the present invention: the hydrothermal pretreatment time of biomass is 150 min.

[0019] As a further technical solution of the present invention: the drying temperature is 105°C until completely dry.

[0020] As a further technical solution of the present invention: the distance between the jacket structure at the outlet end of the pyrolysis reactor and the high-temperature pyrolysis zone is designed to be 5mm.

[0021] As a further technical solution of the present invention: the temperature of the circulating cooling water introduced into the interlayer is set to 20°C.

[0022] As a further technical solution of the present invention: the pyrolysis temperature is 450°C, and the pressure of the pyrolysis system is reduced to 5 kPa by a vacuum pump.

[0023] The beneficial effects of this invention are:

[0024] The biomass pretreatment system of this invention uses water as the sole reaction medium, eliminating the use of organic solvents, acids, or alkalis in traditional methods. This not only significantly reduces costs but also avoids equipment corrosion problems and prevents the introduction of impurities such as metal ions that could affect subsequent pyrolysis reactions. Utilizing the unique physicochemical properties of water under subcritical conditions (high temperature and high pressure), such as low viscosity, high diffusion coefficient, and low dielectric constant, this system can effectively break the glycosidic bonds between cellulose and hemicellulose, efficiently degrade hemicellulose, and dissolve a large amount of lignin, while retaining cellulose components to the maximum extent.

[0025] This invention innovatively constructs a synergistic pyrolysis system of "reduced pressure pyrolysis-rapid cooling of volatiles" through a unique reactor design. This system utilizes vacuum to accelerate the escape of pyrolysis volatiles from biomass particles and the high-temperature reaction zone, and effectively suppresses secondary pyrolysis and depolymerization reactions of volatiles through rapid cooling of volatiles, significantly reducing the formation of by-products such as coke deposits, thereby achieving efficient and highly selective preparation of the high-value-added product L-glucan. Attached Figure Description

[0026] To more clearly illustrate the technical solutions in the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0027] Figure 1 This is a schematic diagram of a hydrothermal pretreatment reaction device;

[0028] Figure 2 This is a schematic diagram of a pyrolysis reaction apparatus;

[0029] Figure 3 This is a diagram showing the effect of hydrothermal pretreatment on the distribution of pyrolysis products;

[0030] Figure 4 This is a graph showing the effect of hydrothermal pretreatment on the yield and selectivity of L-glucan. Detailed Implementation

[0031] To enable those skilled in the art to better understand the present invention, the technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of the present invention.

[0032] Example 1

[0033] like Figure 1-4 As shown in the figure, the method for efficient extraction of L-glucan from lignocellulosic biomass provided by this invention specifically includes the following steps:

[0034] S1. Biomass hydrothermal pretreatment for cellulose enrichment

[0035] Biomass hydrothermal pretreatment in Figure 1 The experiment was conducted in the apparatus shown. 5g of rice husks were placed in a stainless steel reaction tube, and deionized water was continuously pumped in at a flow rate of 5.0mL / min using a liquid injection pump. After the system flow path was filled with liquid, the system pressure was adjusted to 50bar using a back pressure valve, and hydrothermal pretreatment was performed at 200℃ for 150min. After pretreatment, the pretreated solid product was collected and dried to absolute dryness at 105℃. Using agricultural industry standard NY / T3494-2019, the hemicellulose content of the pretreated rice husks was found to be 3.3%, the lignin content to be 21.3%, and the cellulose content to be 63.5%, which is 2.0 times the cellulose content of the original rice husks (see Table 1 for details).

[0036] S2. Preparation of L-glucan from pretreated biomass pyrolysis

[0037] Pretreatment of biomass pyrolysis reaction in Figure 3 The reaction was carried out in the apparatus shown. 1g of pretreated rice husks was placed in a quartz tube reactor. Circulating water at 20°C was introduced into the jacket at the reactor outlet. The pyrolysis temperature was 450°C, and the pressure of the pyrolysis system was 5kPa (absolute pressure). Biomass was rapidly pushed into the high-temperature zone of the reactor for pyrolysis and maintained at 450°C for 20 minutes. After the reaction, solid semi-coke, condensed liquid products, and carbon deposits on the inner wall of the reaction tube were collected. The yields of the pyrolysis byproducts semi-coke and carbon deposits were calculated to be 9.7% and 0.5%, respectively. High-performance liquid chromatography (HPLC) determined the yield of L-glucan to be 406 mg / g using the external standard method, with a selectivity of 62.5% in bio-oil.

[0038] Example 2

[0039] like Figure 1-4 As shown in the figure, the method for efficient extraction of L-glucan from lignocellulosic biomass provided by this invention specifically includes the following steps:

[0040] S1. Biomass hydrothermal pretreatment for cellulose enrichment

[0041] Biomass hydrothermal pretreatment in Figure 1 The experiment was conducted in the apparatus shown. 5g of poplar sawdust was placed in a stainless steel reaction tube, and deionized water was continuously pumped in at a flow rate of 5.0mL / min using a liquid injection pump. After the system flow path was filled with liquid, the system pressure was adjusted to 50bar using a back pressure valve, and hydrothermal pretreatment was performed at 200℃ for 150min. After pretreatment, the pretreated solid product was collected and dried to absolute dryness at 105℃. Using agricultural industry standard NY / T3494-2019, the pretreated poplar sawdust was found to contain 7.9% hemicellulose, 19.4% lignin, and 71.6% cellulose, which is 1.5 times the cellulose content of the original poplar sawdust (see Table 1 for details).

[0042] S2. Preparation of L-glucan from pretreated biomass pyrolysis

[0043] Pretreatment of biomass pyrolysis reaction in Figure 2The reaction was carried out in the apparatus shown. 1g of pretreated rice husks was placed in a quartz tube reactor. Circulating water at 20°C was introduced into the jacket at the reactor outlet. The pyrolysis temperature was 450°C, and the pressure of the pyrolysis system was 5kPa (absolute pressure). Biomass was rapidly pushed into the high-temperature zone of the reactor for pyrolysis and maintained at 450°C for 20 minutes. After the reaction, solid semi-coke, condensed liquid products, and carbon deposits on the inner wall of the reaction tube were collected. The yields of the pyrolysis byproducts semi-coke and carbon deposits were calculated to be 6.0% and 0.1%, respectively. High-performance liquid chromatography (HPLC) determined the yield of L-glucan to be 417 mg / g using the external standard method, with a selectivity of 65.4% in bio-oil.

[0044] Comparative Example 1

[0045] like Figure 1-4 As shown, the pyrolysis conditions were the same as in Example 1, except that untreated rice husks were used for direct pyrolysis. The rice husks contained 19.3% hemicellulose, 24.2% lignin, and 31.8% cellulose. The yields of the pyrolysis byproducts, semi-coke and char, were 25.0% and 0.8%, respectively. The yield of L-glucan, determined by high-performance liquid chromatography using the external standard method, was 54 mg / g, with a selectivity of 12.1% in bio-oil.

[0046] As shown in Example 1 and Comparative Example 1, under the same pyrolysis conditions, the cellulose content of rice husks increased by 2.0 times after hydrothermal pretreatment, and the yield and selectivity of the pyrolyzed L-glucan increased by 7.5 and 5.1 times, respectively. Therefore, hydrothermal pretreatment significantly improves the efficiency of L-glucan preparation from rice husks by enriching cellulose.

[0047] Comparative Example 2

[0048] like Figure 1-4 As shown, the pyrolysis conditions were the same as in Example 2, except that poplar sawdust without hydrothermal pretreatment was used for direct pyrolysis. The poplar sawdust contained 22.3% hemicellulose, 21.5% lignin, and 46.6% cellulose. The yields of the pyrolysis byproducts, semi-coke and char, were 21.4% and 0.9%, respectively. The yield of L-glucan, determined by high-performance liquid chromatography using the external standard method, was 72 mg / g, with a selectivity of 15.6% in bio-oil.

[0049] As shown in Example 2 and Comparative Example 2, under the same pyrolysis conditions, the cellulose content of poplar sawdust increased by 1.5 times after hydrothermal pretreatment, and the yield and selectivity of the pyrolysis-produced L-glucan increased by 5.8 times and 4.2 times, respectively. Hydrothermal pretreatment significantly improved the efficiency of L-glucan preparation from poplar sawdust pyrolysis by enriching cellulose.

[0050] More specifically, based on Examples 1 and 2, and Comparative Examples 1 and 2, the present invention provides analytical results of the chemical composition of biomass, as shown in Table 1:

[0051]

[0052] Comparative Example 3

[0053] like Figure 1-4 As shown, the pretreatment conditions were the same as in Example 1, except that the pyrolysis of the pretreated rice husks was carried out under normal pressure, and the volatiles were not rapidly cooled by circulating water. The yields of the pyrolysis byproducts, semi-coke and char, were 18.8% and 14.8%, respectively. The yield of L-glucan, determined by high-performance liquid chromatography using the external standard method, was 191 mg / g, with a selectivity of 47.3% in bio-oil.

[0054] As demonstrated in Example 1 and Comparative Example 3, the pyrolysis method of "reduced pressure pyrolysis-rapid cooling of volatiles" can significantly reduce the formation of pyrolysis byproducts such as semi-coke and coke deposits, and the yield and selectivity of L-glucan produced by pyrolysis are increased by 2.1 times and 1.3 times, respectively. The pyrolysis method of "reduced pressure pyrolysis-rapid cooling of volatiles" promotes the formation of L-glucan by inhibiting secondary reactions between pyrolysis products.

[0055] Comparative Example 4

[0056] like Figure 1-4 As shown, the pretreatment conditions were the same as in Example 2, except that the pyrolysis of the pretreated poplar sawdust was carried out under normal pressure, and the volatiles were not rapidly cooled by circulating water. The yields of the pyrolysis byproducts, semi-coke and char, were 16.2% and 15.5%, respectively. The yield of L-glucan, determined by high-performance liquid chromatography using the external standard method, was 202 mg / g, with a selectivity of 46.1% in bio-oil.

[0057] As demonstrated in Example 2 and Comparative Example 4, the pyrolysis method of "reduced pressure pyrolysis-rapid cooling of volatiles" can significantly reduce the formation of pyrolysis byproducts such as semi-coke and coke deposits, and the yield and selectivity of L-glucan produced by pyrolysis are increased by 2.1 times and 1.4 times, respectively. The pyrolysis method of "reduced pressure pyrolysis-rapid cooling of volatiles" promotes the formation of L-glucan by inhibiting secondary reactions between pyrolysis products.

[0058] The foregoing has provided a detailed description of one embodiment of the present invention, but this description is merely a preferred embodiment and should not be construed as limiting the scope of the invention. All equivalent variations and modifications made within the scope of the claims of this invention should still fall within the patent coverage of this invention.

Claims

1. A method for efficiently extracting L-glucan from lignocellulosic biomass, characterized in that, Includes the following steps: Biomass is loaded into the stainless steel reaction tube of the fixed-bed hydrothermal pretreatment device, and deionized water is continuously pumped in using a liquid injection pump. After the entire flow path is filled with liquid, the system pressure is adjusted by the back pressure valve. The stainless steel reaction tube is heated to the target temperature, so that the flowing water is in a subcritical fluid state, and the biomass is pretreated by hydrothermal treatment at the target temperature for a certain period of time. After the pretreatment is completed, the reaction system is cooled and depressurized, and the resulting mixture is subjected to solid-liquid separation and drying to obtain hydrothermally pretreated biomass. The hydrothermally pretreated biomass is placed in a specially designed quartz tube reactor. The reactor outlet is designed with a jacket structure, and circulating cooling water is introduced into the outer jacket layer to ensure that the pyrolysis volatiles can be rapidly cooled to room temperature after leaving the high temperature zone. Heat the quartz reaction tube to the required pyrolysis temperature, start the vacuum pump, reduce the pressure of the pyrolysis system, and quickly push the biomass to the high-temperature zone for pyrolysis reaction, and maintain it at the pyrolysis temperature for 20 minutes. After the reaction is completed, the pyrolysis volatiles are rapidly condensed through the outlet jacket. The liquid product rich in L-glucan obtained from the condensation, as well as the solid semi-coke in the reactor and the carbon deposits on the inner wall of the reaction tube, are collected and weighed to calculate the yield of each product.

2. The method for efficient extraction of L-glucan from lignocellulosic biomass according to claim 1, characterized in that, The biomass is one of rice husks or poplar wood chips.

3. The method for efficient extraction of L-glucan from lignocellulosic biomass according to claim 1, characterized in that, The flow rate of deionized water pumped in is 5.0 mL / min.

4. The method for efficient extraction of L-glucan from lignocellulosic biomass according to claim 1, characterized in that, The system pressure is adjusted to 50 bar using a back pressure valve.

5. The method for efficient extraction of L-glucan from lignocellulosic biomass according to claim 1, characterized in that, Heat the stainless steel reaction tube to 200°C.

6. The method for efficient extraction of L-glucan from lignocellulosic biomass according to claim 1, characterized in that, The hydrothermal pretreatment time for biomass is 150 min.

7. The method for efficient extraction of L-glucan from lignocellulosic biomass according to claim 1, characterized in that, The drying process is carried out at 105℃ until completely dry.

8. The method for efficient extraction of L-glucan from lignocellulosic biomass according to claim 1, characterized in that, The jacket structure at the outlet of the pyrolysis reactor is designed to be 5mm away from the high-temperature pyrolysis zone.

9. The method for efficient extraction of L-glucan from lignocellulosic biomass according to claim 1, characterized in that, The temperature of the circulating cooling water introduced into the jacket is set to 20℃.

10. The method for efficient extraction of L-glucan from lignocellulosic biomass according to claim 1, characterized in that, The pyrolysis temperature is 450℃, and the pressure of the pyrolysis system is reduced to 5kPa by a vacuum pump.

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