Reaction apparatus and method for alkaline oxidation continuous stage extraction of lignin

Abstract

The application discloses a reaction device and method for alkaline oxidation continuous step-by-step extraction of lignin, and relates to the technical field of high-efficiency utilization of biomass. Different lignin products in different extraction stages are collected respectively, and serious secondary degradation reaction of the lignin products is avoided. The reaction device comprises an oxidizing alkali solution preparation system, an oxidation extraction system and a product collection system. The oxidizing alkali solution preparation system comprises a high-pressure gas cylinder, a heatable pressure-resistant container, a heatable magnetic stirrer and a gas supply pressure regulating system. The oxidation extraction system comprises a rapid heating box, a heat radiation preheater arranged in the rapid heating box and a flow-through reaction tube. The product collection system comprises an equilocal pump and a sample collection bottle. In the application, the biomass lignin can be continuously extracted and collected in different alkaline oxidation solvents, different time gradients and different temperature gradients, and the secondary reaction of the extracted lignin in the reaction system is significantly weakened.

Description

Reaction apparatus and method for alkaline oxidation continuous stepwise extraction of lignin Technical Field

[0001] This invention relates to the field of biomass high-efficiency utilization technology, and more specifically to a reaction apparatus and method for continuous stepwise extraction of lignin from biomass. Background Technology

[0002] Biomass, the world's most abundant renewable organic low-carbon resource, is considered an ideal alternative to fossil fuels for the production of sustainable liquid fuels and fine chemicals. The chemical diversity of biomass components offers limitless possibilities for producing various energy, chemical, and material products. Lignin, the only renewable resource in nature that provides aromatic ring structures and possesses phenolic structures, can be used to replace petrochemicals and polymers as aromatic feedstocks. The high-quality utilization of lignin is a crucial component in improving the level and economic efficiency of biomass refining. Given the prominent role of aromatic structures in important chemical fields such as perfumes, fragrances, polymers, coatings, and resins, the high-value utilization of lignin continues to receive widespread attention.

[0003] Lignin typically constitutes 15-30 wt% of woody fiber biomass in agriculture and forestry. It is an amorphous polymer composed of three phenylpropane units: guaiacol (G), syringyl (S), and p-hydroxyphenyl (H). Its macromolecular structure allows for the production of carbon materials, adhesives, and hydrophobic agents, while its depolymerization can generate aromatic compounds. Studies have shown that the properties of the separated lignin (purity, degree of polymerization, and structure) directly affect its further conversion and utilization. The lignin structure is closely related to the type of biomass and the separation method, and the ease of monomer extraction and the stability of inter-monomer bonds vary. Research indicates that the removal of lignin from biomass generally involves three stages. Globally, over 5 × 10⁵ kilometres are produced as byproducts of plant fiber utilization annually. 7 Of the tons of lignin produced, 95% is primarily burned as low-grade fuel and as waste, with only about 5% of lignin products used in the manufacture of chemicals and materials, resulting in a severe waste of lignin resources. The main reason is that the structure of the by-product lignin is severely damaged during the separation process, with a significant reduction in ether bonds and an increase in stable C-C bonds, leading to low reactivity and severely restricting its efficient conversion and utilization. Efficient and green separation and enrichment of lignin is a crucial foundation and research direction for achieving diversified and high-value biomass refining.

[0004] Alkaline oxidation can selectively oxidize and depolymerize lignin, achieving cellulose enrichment while obtaining well-soluble lignin. Since alkaline oxidation utilizes only inexpensive and green reagents such as water, oxidants (O2, H2O2, O3, etc.), and alkaline solutions (NaOH, Na2CO3, CaO, etc.) to selectively oxidize, depolymerize, and remove lignin, it is a potential method for achieving lignin enrichment without chlorine or sulfur. During alkaline oxidation extraction, lignin undergoes a series of secondary reactions, such as deep oxidative degradation, Ar-O-alkyl bond breaking, side-chain rearrangement, CC condensation, and aromatic nucleus oxidative cleavage. The longer the residence time of lignin in the extraction system, the more severe these secondary reactions become, resulting in more severe structural damage to the obtained lignin, and higher dispersibility and structural complexity. To weaken or avoid these secondary reactions, measures need to be taken to promptly "quench" them, which can produce active lignin with lower dispersibility and structural complexity.

[0005] Typically, biomass lignin extraction commonly uses batch reactors. Because the extracted product cannot be promptly removed and collected from the reaction system, the initial extracted product undergoes severe secondary reactions, including degradation and repolymerization. Furthermore, with the accumulation of extraction and secondary degradation products, the reaction system undergoes continuous changes, severely limiting the acquisition of high-yield, highly active lignin. Moreover, obtaining accurate information about the initial lignin extracted product is difficult, if not impossible, thus significantly restricting research into the lignin extraction process and its mechanisms.

[0006] Researchers have conducted extensive trials and studies on the efficient separation of biomass components in recent years. Patent (CN116283846A) reports a method for extracting lignin from biomass using a ternary deep eutectic solvent system. After collecting the reaction phase and the extraction phase, acetone and water are added to the liquid phase for washing. After evaporating the acetone, lignin is obtained, and hemicellulose and cellulose are used to prepare furfural. Patent (CN115894961A) reports a method for preparing L-cysteine ​​lignin by treating lignocellulosic biomass with L-cysteine ​​hydrochloride and an aqueous solution of organic acid. The separated lignin has promising applications in areas such as UV protection. Patent (CN112029115A) reports an in-situ synthesis method for separating and extracting lignin using a deep eutectic solvent. Treatment at 120℃ for 2 hours resulted in a lignin removal rate of 81% and a purity of 87%. Invention (CN110527111A) reports a mild and rapid method for separating lignin, using a zinc chloride / lactic acid (ZnCl-2 / Lac) solvent system. At 110°C for 3 hours, the lignin yield is 73.3%. Patent (CN106079000A) reports a method for separating lignin from lignocellulosic biomass using an ionic liquid-alcohol-water mixed solution. At 200°C for 30 minutes, the lignin removal rate reaches 98%. Patent (CN114805843A) mentions a method for extracting lignin from bamboo powder by pretreating it with active oxygen and solid alkali, and performs fractional separation of the extracted lignin. The lignin extraction process is essentially an alkaline oxidation treatment, in which the lignin undergoes an oxidative depolymerization reaction. Patent (CN110628844A) reports a method for separating lignin, hemicellulose, and cellulose from rice straw using H2O2 and NaOH solution. After alkaline oxidation treatment, lignin is obtained through acid precipitation.

[0007] Although these methods all yield lignin products by extracting lignin from biomass, they all utilize a batch reactor for one-pot extraction, failing to achieve continuous, stepwise extraction of lignin. The products extracted at different stages are mixed together and inevitably undergo varying degrees of secondary degradation reactions, thus hindering process and mechanism analysis of lignin extraction. Summary of the Invention

[0008] To address the above problems, this invention proposes a reaction apparatus and method for continuous stepwise extraction of lignin using alkaline oxidation. This method effectively prevents back-mixing of lignin products at different extraction stages, enables separate collection of lignin products at different extraction stages, avoids severe secondary degradation reactions of the extracted lignin products, preserves the active structure of lignin, reduces lignin dispersion, and can be extended to the research and analysis of lignin extraction processes and mechanisms.

[0009] The technical solution of the present invention is as follows: the reaction device includes an oxidizing alkaline solution preparation system, an oxidative extraction system, and a product collection system;

[0010] The oxidizing alkaline solution preparation system includes a high-pressure gas cylinder 1, a heatable pressure-resistant container 3, a heatable magnetic stirrer 4, and a gas supply pressure regulating system. The heatable pressure-resistant container 3 is installed on the heatable magnetic stirrer 4, and a thermometer 7 is installed in the heatable pressure-resistant container 3. The high-pressure gas cylinder 1 is connected to the heatable pressure-resistant container 3 through a pipeline, and the internal pressure of the heatable pressure-resistant container 3 is controlled by the gas supply pressure regulating system.

[0011] The oxidation extraction system includes a rapid heating chamber 9 and a thermal radiation preheater 10 and a flow-through reaction tube 11 arranged in the rapid heating chamber 9. The inlet of the flow-through reaction tube 11 is connected to a heatable pressure-resistant container 3 via the thermal radiation preheater 10, and a first shut-off valve 8 is provided in the pipeline between the thermal radiation preheater 10 and the heatable pressure-resistant container 3. A temperature and pressure detection device 14 and an extractant distribution filter device 13 are provided in the flow-through reaction tube 11.

[0012] The product collection system includes a horizontal flow pump 18 and a sample collection bottle 20, with the outlet of the flow-through reaction tube 11 connected to the sample collection bottle 20 via the horizontal flow pump 18.

[0013] The gas supply pressure regulating system includes a two-stage pressure reducing valve 2, a back pressure valve 5, and a pressure gauge 6. The two-stage pressure reducing valve 2 is connected in the pipeline between the high-pressure gas cylinder 1 and the heatable pressure-resistant container 3. One end of the pressure gauge 6 and the back pressure valve 5 are both connected to the heatable pressure-resistant container 3 through pipelines. The other end of the back pressure valve 5 is the exhaust pressure relief end.

[0014] Biomass particles are fixedly packed in the flow-through reaction tube 11 to form a biomass bed, and extractant distribution filter elements 13 are respectively arranged above and below the biomass bed.

[0015] The product collection system also includes a metal mesh filter 15, a cooling tank 16, a second shut-off valve 17, and a back pressure regulator 19. The metal mesh filter 15, the cooling tank 16, the second shut-off valve 17, the horizontal flow pump 18, the back pressure regulator 19 and the sample collection bottle 20 are connected in series. The metal mesh filter 15 is connected to the outlet of the flow-through reaction tube 11.

[0016] Preferably, the thermal radiation extractant preheater is a coil-type preheater, and the coil is a corrosion-resistant pipe with a diameter of φ4 or smaller, and the length of the coil is such that the extractant passage time is 2 minutes or longer.

[0017] Preferably, the detachable sealing head is a compression fitting type fixed seal, with a necking to φ4 or smaller for connection with the pipeline;

[0018] Preferably, the middle end of the reaction tube is inserted into the interior by a sleeve of 1 cm or less to house the temperature and pressure detection device.

[0019] Preferably, the extractant distribution filter is a sintered metal mesh sheet, wherein the metal mesh aperture is <5μm or smaller, and the water pressure drop is <0.05MPa or smaller.

[0020] Preferably, the reactor assembly consisting of a flow-through reaction tube and a removable sealing head is detachable at both ends and can withstand a pressure of at least 10 MPa or higher.

[0021] Preferably, the pore size of the metal mesh filter element is <2μm or smaller.

[0022] Preferably, the back pressure regulator is continuously adjustable.

[0023] Preferably, the pressure of the extractant supplied by the horizontal flow pump is equivalent to the pressure inside the flow-through reaction tube.

[0024] Preferably, the temperature at the middle end of the flow-through reaction tube is equivalent to the reaction temperature inside the reactor.

[0025] Regarding the various components of this case:

[0026] High-pressure gas cylinder 1 is suitable for controlling the supply pressure and flow rate of oxidizing gas. The high-pressure gas cylinder is located at the upstream end of the extraction reaction system and further provides system pressure.

[0027] The heatable pressure-resistant container 3 is suitable for controlling the dissolution of oxidizing gas into an alkaline solution at a certain temperature. The gas inlet end is connected to the high-pressure gas cylinder 1 via a two-stage pressure reducing valve 2, and the liquid outlet end is connected to the thermal radiation extractant preheater 10 via a shut-off valve 8.

[0028] The heatable magnetic stirrer 4 is suitable for controlling the mixing and heat preservation of oxidizing alkaline solutions.

[0029] The gas supply pressure regulating system is suitable for controlling the pressure when oxidizing gases dissolve in alkaline solutions. It mainly consists of a two-stage pressure reducing valve 2, a back pressure valve 5, and a pressure gauge 6.

[0030] The secondary pressure reducing valve 2 is suitable for controlling the pressure of the oxidizing gas entering the heatable pressure-resistant container 3. The upstream of the secondary pressure reducing valve is connected to the high-pressure gas cylinder 1, and the downstream is connected to the heatable pressure-resistant container 3 through a pipeline.

[0031] Back pressure valve 5 is adapted to control the gas pressure in the heatable pressure vessel 3 and to continuously regulate the pressure.

[0032] Pressure gauge 6 is adapted to display the gas pressure in the heatable pressure vessel 3 in real time.

[0033] Thermometer 7 is adapted to display the temperature of the solution in the heatable pressure-resistant container 3 in real time.

[0034] The first shut-off valve 8 is adapted to control whether or not the oxidizing alkaline solution is supplied to the extraction reaction system.

[0035] An oxidative extraction system suitable for liquid-solid extraction reactions.

[0036] The rapid heating chamber 9 is continuously adjustable, and the conditions for preparing oxidizing alkaline solutions are continuously adjustable within the range of 0-10MPa and 30-300℃.

[0037] The thermal radiation extractant preheater 10 is suitable for preheating the oxidizing alkaline solution to the extraction temperature. The preheater is located upstream of the flow-through reaction tube 11 and downstream of the shut-off valve 8.

[0038] The flow-through reaction tube 11 is a tubular reactor, suitable for placing a biomass solid bed, and the bed thickness is controllable.

[0039] The flow-through reaction tube is equipped with quick-release sealing heads 12 at both ends, and the temperature and pressure detection device 14 is embedded through the middle. The solution distribution filter device 13 is installed inside the front and rear ends.

[0040] The detachable sealing head 12 is a detachable sealing device for the flow-through reaction tube 11, which is corrosion-resistant and resistant to high temperature and high pressure.

[0041] The extractant distribution filter element 13 is disposed inside the inlet and outlet ends of the flow-through reaction tube 11. The inlet end is suitable for distributing the extractant, and the outlet end is suitable for filtering solid particles.

[0042] The temperature and pressure detection device 14, which is suitable for detecting the internal temperature and pressure of the flow-through reaction tube 11, is embedded in the middle of the flow-through reaction tube 11.

[0043] The rapid heating chamber 9 is suitable for heating the extractant preheater 10 and the flow-through reaction tube 11, using a forced-air heating method with a heating rate ≥100℃ / min.

[0044] A product collection system adapted to filter, cool and collect lignin extraction products, and stabilize the reaction pressure within the flow-through reaction tube 11.

[0045] The product collection system mainly consists of a metal mesh filter 15, a cooling tank 16, a second shut-off valve 17, a horizontal flow pump 18, a back pressure regulator 19, and a sample collection bottle 20.

[0046] A metal mesh filter 15, suitable for filtering solid particles carried in the extraction product, is placed downstream of the flow-through reaction tube 11 and upstream of the cooling tank.

[0047] Cooling tank 16, which is suitable for cooling the extracted product, is located downstream of the metal mesh filter 15 and connected to shut-off valve 17.

[0048] A horizontal flow pump 18, adapted to control the flow rate of the solution in the reaction system, is positioned downstream of the second shut-off valve 17 and upstream of the back pressure regulator 19.

[0049] A back pressure regulator 19, which is adapted to regulate the reaction pressure in the reaction system, is located downstream of the horizontal flow pump 18 and upstream of the sample collection bottle 20. In conjunction with the horizontal flow pump 18 and the gas supply pressure regulating system, it further provides a reaction system pressure control system.

[0050] Sample collection bottle 20 is suitable for collecting and storing extract samples and can be easily placed and removed.

[0051] A reaction method based on a reaction apparatus for continuous stepwise extraction of lignin by alkaline oxidation includes the following steps:

[0052] Step 1: Fix biomass pellets in a flow-through reaction tube 11 to form a biomass bed, and install extractant distribution filter devices 13 above and below the biomass bed;

[0053] Step 2: Fill the heatable pressure-resistant container 3 with an alkaline solution, and then fill the heatable pressure-resistant container 3 with an oxidizing gas at a predetermined pressure through the high-pressure gas cylinder 1, so that the gas dissolves in the alkaline solution at a predetermined temperature and pressure until saturation.

[0054] Step 3: Open the first shut-off valve 8 and the horizontal flow pump 18 to supply alkaline solution into the flow-through reaction tube 11 until the flow-through reaction tube 11 is full of alkaline solution.

[0055] Step 4: Heat the heatable pressure-resistant container 3 and the flow-through reaction tube 11 to the required extraction temperature. During heating, the temperature can be rapidly increased to a constant temperature mode, or the temperature can be continuously adjusted within the temperature range for stepwise heating, generally 50-200℃.

[0056] Step 5: Open the first shut-off valve 8 and the horizontal flow pump 18, and with the internal pressure in the heatable pressure-resistant container, continuously and stably fill the flow-through reaction tube 11, and finally collect it into the sample collection bottle 20.

[0057] Step 5: While turning on the horizontal flow pump 18, adjust the back pressure regulator 19 to stabilize the temperature, flow rate and pressure inside the flow-through reaction tube. Depending on the specific experimental requirements, the pressure is 1-5 MPa, and the pressure adjustment range can be 0-10 MPa.

[0058] In this case, the extractant and biomass particles are separated into liquid and solid states in a flow-through reaction tube by the filter device. After cooling, the extractant is depressurized to atmospheric pressure by a back pressure regulator and collected in a sample collection bottle as needed. The final sample pressure can be continuously adjusted by the advection pump and the back pressure regulator.

[0059] in:

[0060] The residence time of the extracted product in the reaction system can be continuously adjusted by the advection pump and the bed thickness in the flow-through reaction tube.

[0061] By using the rapid heating chamber program to raise the temperature, the continuous acquisition of lignin stepwise extraction products under different temperature conditions can be achieved.

[0062] By replacing the collection bottles in a timely manner, the products extracted at different time stages can be collected continuously and separately.

[0063] By adjusting the horizontal flow pump and the back pressure regulator, the extraction products can be continuously obtained under different pressure conditions.

[0064] By adjusting the horizontal flow pump and the bed thickness, continuous extraction of the product can be achieved under different residence time conditions.

[0065] The extracted product is discharged from the flow-through reaction tube in a timely and continuous manner along with the extractant, avoiding backmixing of the extracted products at different stages. The timely discharge of the product from the reaction system avoids secondary degradation reactions caused by prolonged residence of the extracted product in the reaction system.

[0066] The reaction apparatus of this invention can realize the stepwise continuous extraction and collection of biomass lignin under different alkaline oxidation solvents, different time gradients, and different temperature gradients. It significantly reduces the secondary reactions of extracted lignin in the reaction system, preserves the original macromolecular structure of lignin, and can be used to study the lignin extraction process and mechanism. It can be extended to the continuous stepwise extraction of lignin with any other solvent, and can also be extended to the extraction of lignin using other organic or inorganic solvents.

[0067] The advantages of this invention compared to existing technologies are:

[0068] First, it effectively avoids backmixing of the extraction products, allowing lignin products to be promptly discharged from the reaction system, inhibiting secondary reactions and preserving their original macromolecular structure.

[0069] Second, it can continuously extract lignin from biomass in stages, enabling the separate collection of lignin products extracted at different stages.

[0070] Third, it allows for flexible adjustment of extraction conditions and enables the extraction reaction to maintain stable operation under certain conditions for an extended period of time.

[0071] Fourth, the metal mesh filter avoids the possibility of blockage in the constant flow pump and back pressure valve;

[0072] 5. The residence time of the extracted product in the reaction system can be flexibly adjusted;

[0073] VI. This reaction apparatus can be extended to liquid-solid reactions using other organic or inorganic solvents. Attached Figure Description

[0074] Figure 1 is a structural diagram of this case.

[0075] In the diagram, 1 is a high-pressure gas cylinder, 2 is a secondary pressure reducing valve, 3 is a heatable pressure-resistant container, 4 is a heatable magnetic stirrer, 5 is a back pressure valve, 6 is a pressure gauge, 7 is a thermometer, 8 is a first shut-off valve, 9 is a rapid heating box, 10 is a thermal radiation preheater, 11 is a flow-through reaction tube, 12 is a removable sealing head, 13 is an extractant distribution filter, 14 is a temperature and pressure detection device, 15 is a metal mesh filter, 16 is a cooling tank, 17 is a second shut-off valve, 18 is a horizontal flow pump, 19 is a back pressure regulator, and 20 is a sample collection bottle.

[0076] Figure 2 is a graph showing the change of lignin yield over time under the same conditions in Example 1 of this case.

[0077] Figure 3 is a molecular weight distribution diagram of lignin extracted by step-by-step extraction under constant temperature mode in Example 1 of this case; the vertical axis in the figure is the signal intensity au, and the horizontal axis is the molecular weight Da.

[0078] Figure 4 is a graph showing the change in lignin extraction yield with temperature under the heating mode in Example 2 of this case.

[0079] Figure 5 is a molecular weight distribution diagram of lignin extracted in the stepwise extraction mode under the second embodiment of this case; the vertical axis in the figure is the signal intensity au, and the horizontal axis is the molecular weight Da. Detailed Implementation

[0080] To clearly illustrate the technical features of this patent, the following detailed description is provided through specific embodiments and in conjunction with the accompanying drawings.

[0081] The core of this invention is to utilize a flow-through reaction device for the liquid-solid extraction reaction of lignin in biomass. By continuously controlling the extraction reaction conditions and separately collecting the extraction products, continuous stepwise extraction of lignin from biomass is achieved. As shown in Figure 1, the reaction device includes an oxidizing alkaline solution preparation system, an oxidative extraction system, and a product collection system. The oxidizing alkaline solution preparation system mainly includes a high-pressure gas cylinder 1, a heatable pressure-resistant container 3, a heatable magnetic stirrer 4, and a gas supply and pressure regulation system. The oxidative extraction system includes a rapid heating box 9, a thermal radiation preheater 10, a flow-through reaction tube 11, a temperature and pressure detection device 14, and an extractant distribution filter 13. The product collection system includes a metal mesh filter 15, a cooling tank 16, a horizontal flow pump 18, a back pressure regulator 19, and a sample collection bottle 20.

[0082] The reaction apparatus can achieve stepwise continuous extraction and collection of biomass lignin under different extractants, time gradients, and temperature gradients, and significantly reduces secondary reactions of extracted lignin in the reaction system, retains the original macromolecular structure of lignin, and can be used to study the lignin extraction process and mechanism.

[0083] The following is an embodiment of the continuous stepwise extraction of lignin from biomass using the aforementioned reaction apparatus:

[0084] Step 1: Fix biomass pellets in a flow-through reaction tube 11. Extractant distribution filter elements 13 are set above and below the biomass bed. The flow-through reaction tube 11 is sealed by a detachable sealing head 12. The biomass pellets are generally ≤2mm. The bed thickness is related to the size of the reaction tube, the flow rate of the extractant, and the required residence time.

[0085] Step 2: Fill the heatable and pressure-resistant container 3 with an alkaline solution, the volume of which shall not exceed 2 / 3 of the capacity. After sealing the container, pressurize it with oxidizing gas at a certain pressure through the high-pressure gas cylinder 1.

[0086] Step 3: Open the first shut-off valve 8 and the horizontal flow pump 18 in the flow path to supply alkaline solution to the flow-through reaction tube 11 until the flow-through reaction tube 11 is full of alkaline solution and the air in the flow-through reaction tube 11 is completely discharged.

[0087] Step 4: Close the first shut-off valve 8 and the horizontal flow pump 18, turn on the heating function of the heatable pressure container 3 and the heatable magnetic stirrer 4, and turn on the rapid heating box 9 to heat the flow-through reaction tube 11 to the required extraction temperature. Depending on the specific experimental requirements, the temperature is generally 90-150℃. Determine whether the required reaction temperature has been reached based on the temperature and pressure detection device, i.e., the internal temperature of the flow-through reaction tube 11.

[0088] The temperature can be continuously adjusted, and a programmed heating mode or a constant temperature mode can be set to obtain lignin products at different temperatures or at different time periods under a certain temperature.

[0089] Step 5: After reaching the required reaction temperature, open the first shut-off valve 8 and the horizontal flow pump 18 in the flow path, and continuously and stably supply the oxidizing alkaline solution to the flow-through reaction tube 11 as needed. Fresh extractant continuously carries out the extracted lignin product.

[0090] According to specific experimental requirements, the flow rate is set based on the required residence time of the extract in the flow-through reaction tube 11. The residence time of the lignin extract in the system is 1s-10min. The extractant flow rate can be continuously adjusted to achieve continuous adjustment of the residence time, so as to obtain the lignin extract at different residence times.

[0091] Step 6: While turning on the horizontal flow pump 18, adjust the back pressure regulator 19 to finally bring the temperature, flow rate and pressure in the flow-through reaction tube to a stable state. Depending on the specific experimental requirements, the pressure is generally 1-5 MPa.

[0092] The back pressure regulator can continuously adjust the reaction pressure in the flow-through reaction tube 11 to obtain lignin products under different reaction pressures;

[0093] Step 7: The lignin extraction product is carried by the unidirectionally flowing extraction agent, filtered through the filter device, and discharged from the reaction system in a timely manner; during this period, the lignin solution and biomass particles achieve liquid-solid separation in the flow-through reaction tube 11 through the extraction agent distribution filter device 13.

[0094] Step 8: After the lignin solution is discharged from the reaction system, it is cooled by the cooling tank 16, and then the pressure is reduced to atmospheric pressure by the back pressure regulator 19 before being collected in the sample collection bottle 20.

[0095] Example 1: Step-by-step extraction under constant temperature mode.

[0096] Specifically, the following operations are included:

[0097] Raw material pretreatment: The wood fiber plant raw materials are crushed and screened, washed with water to remove dust and impurities, and air-dried; the raw materials are agricultural and forestry wastes such as wheat straw, corn stalks, bagasse, rice straw or sawdust, and their solids after hemicellulose has been removed.

[0098] Raw material loading: The pretreated raw materials are loaded into the flow-through reaction tube 11 as described above, and appropriately compacted to make the porosity of the biomass bed 60-80%.

[0099] Preparation of oxidizing alkaline solution: Fill the heatable pressure-resistant container 3 with alkaline solution, the volume of which shall not exceed 2 / 3 of the capacity. After sealing the container, fill it with oxidizing gas at a certain pressure through a high-pressure gas cylinder.

[0100] Alkali pre-filling: Open the first shut-off valve 8 of the flow path and the horizontal flow pump 18 to slowly inject alkali into the flow-through reaction tube 11 until the flow-through reaction tube 11 is full of alkali, the gas in the flow-through reaction tube 11 is completely discharged, and the biomass pellets are completely immersed in the alkali.

[0101] Preparation of oxidizing alkaline solution: Close the first shut-off valve 8 and the horizontal flow pump 18, turn on the heating function of the heatable pressure-resistant container 3 and the heatable magnetic stirrer 4 to heat to the required extraction temperature, so that the oxidizing gas is saturated in the alkaline solution at a certain temperature and pressure. Depending on the specific experimental requirements, the temperature is generally 90-150℃ and the pressure is generally 1-5 MPa.

[0102] Reactor heating: Turn on the rapid heating box 9 to heat the flow-through reaction tube 11 and the thermal radiation preheater 10 until the required extraction temperature is reached. The preferred extraction temperature is generally around 120°C.

[0103] Continuous delivery of oxidizing alkaline solution: After the flow-through reaction tube 11 and the thermal radiation preheater 10 reach the temperature, the first shut-off valve 8 of the flow path and the horizontal flow pump 18 are opened to continuously and stably deliver oxidizing alkaline solution to the reaction system. The fresh oxidizing alkaline solution is preheated to the extraction temperature by the preheater and then continuously and stably injected into the flow-through reaction tube. When the oxidizing alkaline solution flows through the biomass bed in the flow-through reaction tube 11, lignin is continuously extracted. The lignin extract is continuously carried out of the flow-through reaction tube 11 by the extractant.

[0104] The delivery rate of the oxidizing alkaline solution is set according to the residence time of the extracted product in the reactor. To effectively avoid severe secondary degradation of the lignin extracted product, the residence time of the extracted product in the reactor should be less than 5 minutes.

[0105] With the continuous delivery of fresh oxidizing alkaline solution, the bonds between lignin and other components are gradually hydrolyzed and broken, and lignin is gradually extracted and carried out, realizing stepwise extraction of lignin under isothermal mode.

[0106] Stepwise collection of extraction products: During the continuous extraction of lignin with oxidizing alkaline solution, lignin products were collected at intervals of 5-20 min at different time points.

[0107] Lignin was extracted using 0.1 mol / L sodium hydroxide solution at 130 °C and 2 MPa oxygen for 140 min. The results of lignin extraction in a flow-through reaction tube and a batch reactor under constant temperature conditions are shown in Figures 2 and 3 and Table 1.

[0108] Table 1 shows the molecular weights of lignin obtained under the same conditions as those obtained in this apparatus and in a batch reactor:

[0109]

[0110] In the above results, the lignin yield is the ratio of the total amount of lignin dissolved during the extraction time to the total amount of raw material; the extraction effect of the batch reactor refers to the overall effect under the same conditions as the flow-through reactor, such as temperature, time, and liquid-solid ratio; the lignin product is obtained by adjusting the acidity of the extraction solvent (pH<2) for precipitation.

[0111] As shown in Figure 2, the lignin yields extracted by this device within 40 and 90 minutes were 10% and 23%, respectively, while the lignin yields extracted by a batch reactor under the same conditions were 5% and 14%, respectively. This demonstrates that the lignin extraction efficiency of this device is higher than that of a traditional batch reactor. The lignin extraction yield varied within different time periods; the lignin extraction rate gradually increased from 0 to 30 minutes, increased significantly from 30 to 100 minutes, and gradually leveled off after 100 minutes. As shown in Figure 3 and Table 1, the molecular weight distribution of lignin varies across different extraction time periods using this device. The molecular weight of lignin extracted from 0-10 min is Mw=3125 Da, from 10-20 min it is Mw=6100 Da, from 20-40 min it is Mw=4864 Da, from 40-60 min it is Mw=3415 Da, and from 60-80 min it is Mw=2218 Da. This indicates that the device and method of this invention can achieve stepwise extraction of lignin under isothermal conditions to obtain lignin products with different properties. Compared with the extraction effect of a batch reactor under the same conditions, the lignin extraction rate is significantly improved, and the molecular weight of the obtained lignin is generally larger, indicating that the device and method of this invention significantly inhibits the secondary degradation reaction of the lignin extraction product.

[0112] Example 2: Stepwise extraction under programmed heating mode.

[0113] Specifically, the following operations are included:

[0114] Raw material pretreatment: The wood fiber plant raw materials are crushed and screened, washed with water to remove dust and impurities, and air-dried; the raw materials are agricultural and forestry wastes such as wheat straw, corn stalks, bagasse, rice straw or sawdust.

[0115] Raw material loading: The pretreated raw materials are loaded into the flow-through reaction tube as described above, and properly compacted to make the porosity of the biomass bed 60-80%.

[0116] Preparation of oxidizing alkaline solution: Fill the heatable pressure-resistant container 3 with alkaline solution, the volume of which shall not exceed 2 / 3 of the capacity. After sealing the container, fill it with oxidizing gas at a certain pressure through a high-pressure gas cylinder.

[0117] Alkali pre-filling: Open the first shut-off valve 8 of the flow path and the horizontal flow pump 18 to slowly inject alkali into the flow-through reaction tube 11 until the flow-through reaction tube 11 is full of alkali, the gas in the flow-through reaction tube 11 is completely discharged, and the biomass pellets are completely immersed in the alkali.

[0118] Heated pressure vessel and rapid heating box program heating: Turn on the heating function of heated pressure vessel 3 and rapid heating box 9 to program the heating of oxidizing alkaline solution, flow-through reaction tube 11 and thermal radiation preheater 10. The temperature range of 50-150℃ is increased in stages at certain intervals. The preferred extraction temperature is maintained for 30-60 minutes.

[0119] Continuous delivery of oxidizing alkaline solution: After the flow-through reaction tube 11 and the thermal radiation preheater 10 reach the initial extraction temperature, the horizontal flow pump 18 is turned on to continuously and stably deliver oxidizing alkaline solution to the flow-through reaction tube 11. The fresh oxidizing alkaline solution is preheated to the extraction temperature by the thermal radiation preheater 10 and then continuously and stably injected into the flow-through reaction tube 11. When the oxidizing alkaline solution flows through the biomass bed in the flow-through reaction tube 11, lignin is continuously extracted. The lignin extract is continuously carried out of the flow-through reaction tube 11 by the oxidizing alkaline solution.

[0120] The delivery rate of the oxidizing alkaline solution is set according to the residence time of the extracted lignin product in the reactor. To effectively avoid severe secondary degradation of the lignin extracted product, the residence time of the lignin extracted product in the reactor should be less than 5 minutes.

[0121] As fresh oxidizing alkaline solution is continuously supplied, the extraction temperature gradually increases, the bonds between lignin and other components are gradually oxidized and broken, and lignin is gradually extracted and carried out, realizing stepwise extraction of lignin under programmed temperature rise mode.

[0122] Stepwise collection of extraction products: During the continuous extraction of lignin from oxidizing alkaline solution, lignin products at different temperature ranges are collected separately.

[0123] Using 0.1 mol / L sodium hydroxide solution, the extraction results of lignin by this device under the conditions of 2 MPa oxygen, oxidizing alkaline solution flow rate of 5 mL / min and extraction at different temperature ranges for 30 min are shown in Figures 4 and 5 and Table 2.

[0124] Table 2 shows the molecular weight of lignin extracted in the stepwise temperature rise mode of this device:

[0125]

[0126] In the above results, the lignin yield is the ratio of the total amount of lignin dissolved at different temperature stages to the total amount of raw material; the lignin product is obtained by adjusting the acidity of the extraction solvent (pH<2) for precipitation.

[0127] As shown in Figure 4, this device can obtain lignin extraction yields at different temperature ranges, generally showing a trend of first decreasing (<70℃), then increasing (90-140℃), and then decreasing again (>140℃). The lignin extraction efficiency only significantly improves when the temperature exceeds 120℃, reaching its maximum at 140℃. Figure 5 and Table 2 show that the molecular weight distribution of lignin varies across different extraction temperature ranges: lignin extracted at room temperature - 50℃ has a molecular weight of Mw = 1509 Da; extracted at 50-90℃ has a molecular weight of Mw = 2447 Da; extracted at 90-120 min has a molecular weight of Mw = 3849 Da; extracted at 120-140 min has a molecular weight of Mw = 3655 Da; and extracted at 140-150 min has a molecular weight of Mw = 2267 Da. This indicates that the device and method of this invention can achieve stepwise extraction of lignin under programmed temperature rise mode to obtain lignin products with different properties. However, batch reactors cannot achieve continuous stepwise extraction of lignin under programmed temperature rise mode, nor can they separately obtain lignin products in different extraction temperature ranges.

[0128] There are many specific ways to implement this invention. The above description is only a preferred embodiment of this invention. It should be noted that for those skilled in the art, several improvements can be made without departing from the principle of this invention, and these improvements should also be considered within the scope of protection of this invention.

Claims

1. A reaction apparatus for continuous stepwise extraction of lignin via alkaline oxidation, characterized in that, The reaction apparatus includes an oxidizing alkaline solution preparation system, an oxidative extraction system, and a product collection system. The oxidizing alkaline solution preparation system includes a high-pressure gas cylinder (1), a heatable pressure-resistant container (3), a heatable magnetic stirrer (4), and a gas supply and pressure regulation system. The heatable pressure-resistant container (3) is mounted on the heatable magnetic stirrer (4), and a thermometer (7) is installed inside the heatable pressure-resistant container (3). The high-pressure gas cylinder (1) is connected to the heatable pressure-resistant container (3) through a pipeline, and the internal pressure of the heatable pressure-resistant container (3) is controlled by the gas supply and pressure regulation system. The oxidative extraction system includes a rapid heating chamber (9) and a product collection system. The rapid heating chamber (9) contains a thermal radiation preheater (10) and a flow-through reaction tube (11). The inlet of the flow-through reaction tube (11) is connected to a heatable pressure-resistant container (3) via the thermal radiation preheater (10), and a first shut-off valve (8) is provided in the pipeline between the thermal radiation preheater (10) and the heatable pressure-resistant container (3). The flow-through reaction tube (11) is equipped with a temperature and pressure detection device (14) and an extractant distribution filter device (13). The product collection system includes a horizontal flow pump (18) and a sample collection bottle (20). The outlet of the flow-through reaction tube (11) is connected to the sample collection bottle (20) via the horizontal flow pump (18).

2. The reaction apparatus for continuous stepwise extraction of lignin via alkaline oxidation according to claim 1, characterized in that, The gas supply pressure regulating system includes a two-stage pressure reducing valve (2), a back pressure valve (5), and a pressure gauge (6). The two-stage pressure reducing valve (2) is connected in the pipeline between the high-pressure gas cylinder (1) and the heatable pressure-resistant container (3). One end of the pressure gauge (6) and the back pressure valve (5) are connected to the heatable pressure-resistant container (3) through pipelines. The other end of the back pressure valve (5) is the exhaust pressure relief end.

3. The reaction apparatus for continuous stepwise extraction of lignin via alkaline oxidation according to claim 1, characterized in that, Biomass particles are fixedly packed in the flow-through reaction tube (11) to form a biomass bed, and extractant distribution filter elements (13) are respectively set above and below the biomass bed.

4. The reaction apparatus for continuous stepwise extraction of lignin via alkaline oxidation according to claim 1, characterized in that, The product collection system also includes a metal mesh filter (15), a cooling tank (16), a second shut-off valve (17), and a back pressure regulator (19). The metal mesh filter (15), cooling tank (16), second shut-off valve (17), horizontal flow pump (18), back pressure regulator (19) and sample collection bottle (20) are connected in series. The metal mesh filter (15) is connected to the outlet of the flow-through reaction tube (11).

5. A reaction method for alkaline oxidation and continuous stepwise extraction of lignin based on the reaction apparatus of claim 1, characterized in that, Includes the following steps: Step 1: Fix biomass pellets in a flow-through reaction tube (11) to form a biomass bed, and install extractant distribution filter elements (13) above and below the biomass bed; Step 2: Fill an alkaline solution into a heatable pressure-resistant container (3), and inject oxidizing gas at a predetermined pressure into the heatable pressure-resistant container (3) through a high-pressure gas cylinder (1) to dissolve it into the alkaline solution at a predetermined temperature and pressure until saturation; Step 3: Open the first shut-off valve (8) and the horizontal flow pump (18) to inject extractant into the flow-through reaction tube (11). Alkali solution is supplied into the flow-through reaction tube (11) until it is full; Step 4: The heatable pressure-resistant container (3) and the flow-through reaction tube (11) are heated to the required extraction temperature. During heating, the temperature can be rapidly increased to a constant temperature mode, or the temperature can be continuously adjusted within the temperature range for stepwise heating; Step 5: The first shut-off valve (8) and the horizontal flow pump (18) are opened. With the help of the internal pressure in the heatable pressure-resistant container, the solution is continuously and stably filled into the flow-through reaction tube (11) and finally collected into the sample collection bottle (20).

6. The reaction method for continuous stepwise extraction of lignin via alkaline oxidation according to claim 5, characterized in that, Step 5: While turning on the horizontal flow pump (18), adjust the back pressure regulator (19) to stabilize the temperature, flow rate and pressure inside the flow-through reaction tube. The pressure is 1-5 MPa depending on the specific experimental requirements.

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