Method for preparing biomass oil through catalytic degradation of lignin

Abstract

The invention discloses a method for preparing biomass oil by catalytic degradation of lignin, and belongs to the field of biomass resource utilization. The method comprises the following steps: step 1, pretreatment of lignin: primarily depolymerizing lignin macromolecules and generating part of aldehyde enzymolysis products; 2, collection of a pretreatment product: filtering the turbid liquid and solid residues by using a lignin degradation device; 3, catalysis of lignin and products thereof: catalyzing degradation of lignin through hydrogenation reaction; and 4, biomass oil extraction: extracting and drying to prepare the biomass oil. The method is novel and effective, lignin macromolecules are pretreated through biological enzyme, lignin is depolymerized, interfering alkali metal in lignin is removed through an acidic enzymolysis solution environment, then lignin is thoroughly degraded through hydrogenation reaction catalyzed by a metal catalyst, an enzymolysis product is reduced into biomass oil, the reaction conditions of the degradation reaction are reduced, and the yield of the biomass oil is increased. The production cost is reduced, and the degradation efficiency is optimized.

Description

Technical Field

[0001] The present invention belongs to the field of biomass resource utilization, and particularly relates to a method for catalytic degradation of lignin to prepare bio-oil. Background Art

[0002] Biomass is a key resource to replace fossil energy. Lignin, as the main component of plant cell walls, has been widely used in many industries. The lignin content in different plants varies. Among them, the lignin content in herbaceous plants is about 15%-25%, the lignin content in hardwoods is about 19%-28%, and generally, the lignin content in softwoods is the highest, about 24%-33%. However, due to the complex structure and difficult degradation of lignin, it has become the biggest obstacle to the utilization of biomass resources. Removing or degrading lignin is a key step in using other components in the cell wall.

[0003] Traditional lignin degradation methods mainly use metal catalysts to catalyze the intensity of hydrogenation reactions to promote lignin degradation and reduction to produce various bio-alcohols. As shown in the document with publication number: CN107557048B. During this degradation process, high-temperature and high-pressure conditions are required to ensure the normal progress of the hydrogenation reaction, which consumes a large amount of energy. Moreover, there are certain limitations on the types of metal catalysts, and the cost is relatively high. Currently, certain progress has been made in the research on enzymatic degradation of lignin. Both prokaryotes and eukaryotes have unique enzyme systems that can specifically degrade lignin. The advantages of enzymatic degradation of lignin are that the reaction conditions are suitable, the reaction rate is fast, the reaction selectivity is strong, and the by-products are few.

[0004] Therefore, it is necessary to propose a method for catalytic degradation of lignin to prepare bio-oil that can use bio-enzymes to depolymerize lignin macromolecules and remove alkali metals, and can reduce the requirements for subsequent hydrogenation reaction conditions and reduce the catalyst cost. Summary of the Invention

[0005] In order to solve the above problems, the object of the present invention is to provide a method for catalytic degradation of lignin to prepare bio-oil. Through the pretreatment of lignin macromolecules by bio-enzymes, lignin is depolymerized. The interfering alkali metals in lignin are removed through an acidic enzymatic hydrolysis solution environment. Then, a hydrogenation reaction catalyzed by a metal catalyst is used to completely degrade lignin and reduce the enzymatic hydrolysis products to bio-oil, reducing the reaction conditions of the degradation reaction, reducing production costs, and optimizing the degradation efficiency.

[0006] To achieve the above object, the technical solution of the present invention is as follows: A method for catalytic degradation of lignin to prepare bio-oil, comprising the following steps:

[0007] Step 1, Pretreatment of lignin: Add lignin into the lignin degradation device, suspend it with citrate buffer solution, add an appropriate amount of laccase and laccase mediator, adjust the pH value to 4 - 4.8 with hydrochloric acid solution, heat up and stir while continuously passing oxygen to preliminarily depolymerize the lignin macromolecules and produce some aldehyde enzymatic hydrolysis products;

[0008] Step 2, Collection of pretreatment products: Use the lignin degradation device to filter the pretreated lignin enzymatic hydrolysate into two parts, a suspension and a solid residue. The suspension is extracted with isopropanol to obtain lipophilic lignin monomer molecules and aldehyde enzymatic hydrolysis products, and the solid residue is rinsed with deionized water to restore to neutral and dried;

[0009] Step 3, Catalysis of lignin and its products: Mix the isopropanol extract and the solid residue and place them in the lignin degradation device, add a copper-based catalyst, then continuously stir and mix while purging with nitrogen to remove oxygen, and then continuously pass hydrogen and electricity under high temperature conditions to catalyze the degradation of lignin;

[0010] Step 4, Extraction of bio-oil: Use the lignin degradation device to directly filter to obtain the solution after lignin degradation, then rotate and evaporate the solution to remove isopropanol, extract the residue with ethyl acetate, and then rotate and evaporate ethyl acetate again and dry to prepare bio-oil.

[0011] The beneficial effects of the basic scheme are as follows: 1. Through the pretreatment of lignin macromolecules by bio-enzymes, the present invention can effectively promote the depolymerization of lignin. The use of laccase and laccase mediator, combined with appropriate pH value and oxygen supply conditions, not only accelerates the initial destruction of the lignin structure but also removes interfering alkali metals in lignin, providing a more favorable reaction basis for subsequent steps.

[0012] 2. By using a copper-based catalyst for the hydrogenation reaction, the present invention can completely degrade lignin and reduce the enzymatic hydrolysis products to bio-oil. Compared with traditional methods, this method reduces the reaction conditions (such as temperature and pressure) of the degradation reaction, thereby reducing production costs. At the same time, the operations of purging with nitrogen to remove oxygen and continuously passing hydrogen and electricity ensure the smooth progress of the catalytic reaction.

[0013] 3. The bio-enzymes, laccase mediator, and solvents used throughout the process are all environmentally friendly materials, and the efficient utilization of lignin, as an abundant renewable resource, helps to promote the sustainable development of biomass energy.

[0014] Furthermore, the lignin degradation device in the above steps includes a reaction kettle. A support is fixedly connected to the bottom of the reaction kettle. A stirring motor with a vertically downward output shaft is fixedly connected to the center of the top wall of the reaction kettle. The output shaft of the stirring motor is coaxially fixedly connected with a stirring shaft. The stirring shaft vertically passes through the top wall of the reaction kettle and extends into the reaction kettle. A gas delivery pipe is fixedly connected to the center of the inner top wall of the reaction kettle. The gas delivery pipe extends downward and sleeves the stirring shaft. A turbine fan is fixedly connected to the bottom end of the stirring shaft. The turbine fan includes a shaft ring and a plurality of turbine fan blades fixedly connected to the outside of the shaft ring. The shaft ring is fixedly sleeved with the stirring shaft. A ring groove is formed on the radial surface at the bottom end of the gas delivery pipe. A convex ring is fixedly connected to the top wall of the shaft ring. The ring groove is in sliding fit with the top wall of the shaft ring. A plurality of air pipes corresponding to the turbine fan blades are communicated with the top wall of the shaft ring. The air pipes all extend outward to the middle of the bottom wall of the turbine fan blades and are communicated with the outside. A temperature control device is fixedly connected to the inside of the side wall of the reaction kettle. A filter screen is laid at the bottom inside the reaction kettle below the turbine fan. A collection valve is communicated with the center of the bottom wall of the reaction kettle. The bottom end of the collection valve is communicated with a collection pipe.

[0015] The beneficial effects of the basic solution are as follows: 1. By driving the stirring shaft to rotate through the stirring motor, sufficient stirring of the materials in the reaction kettle is achieved. This design ensures the uniform mixing of reactants such as lignin, solvent, and catalyst during the reaction, which is beneficial to improving the reaction rate and product uniformity. The design of the turbine fan further enhances the stirring effect. The turbine fan blades rotate at high speed driven by the stirring shaft, generating a strong liquid flow, which helps to turn up the materials at the bottom of the reaction kettle and mix them fully with the upper materials. At the same time, the design of the air pipes enables the gas to be evenly distributed to the bottom of the turbine fan blades, further enhancing the stirring and mixing effects.

[0016] 2. The gas delivery pipe introduces gas (such as nitrogen, hydrogen, etc.) into the reaction kettle, and through the sliding fit with the turbine fan and the distribution of the air pipes, uniform transmission and distribution of the gas are achieved. This design ensures the full participation and effective utilization of the gas during the reaction, which is beneficial to improving the efficiency of the catalytic reaction and the product quality. The gas is introduced into the bottom of the turbine fan blades through the air pipes, and the rotating action of the turbine fan is used to evenly distribute the gas to all corners of the reaction kettle. This design not only improves the utilization rate of the gas but also helps to reduce gas waste and environmental pollution.

[0017] 3. The filter screen laid at the bottom inside the reaction kettle can effectively filter out the solid residues during the reaction. At the same time, the design of the filter screen is also convenient for subsequent cleaning and maintenance. Through the cooperation of the collection valve and the collection pipe, the biomass oil mixture after the reaction can be conveniently collected. This design not only improves the convenience of product collection but also helps to reduce product loss and waste.

[0018] Furthermore, parallel cables are symmetrically fixedly connected to the outside of the gas pipe, the cables extend to the bottom end of the gas pipe, and a number of wires corresponding to the turbine blades are fixedly connected to the top wall of the shaft ring. Electrodes are laid on the bottom wall of the middle part of the turbine blades, and the wires are fixedly connected to the corresponding electrodes respectively. The top wall of the wires is located on the movement trajectory of the bottom wall of the cable.

[0019] The beneficial effects of the basic scheme are: 1. When the cable is powered, static electricity will be generated between the electrode and the wire, and then a strong eddy current effect will be generated under the stirring of the turbine blades. This eddy current effect can further promote the stirring and mixing of the materials in the reactor, so that the reactants such as lignin, solvent, catalyst, etc. are more evenly distributed in the reactor.

[0020] 2. After the cable is powered on, the electrostatic field generated can also ionize the hydrogen gas to a certain extent through the electrodes. The ionized gas molecules are more active and more likely to react with the reactants, thereby improving the utilization rate of the gas and the efficiency of the catalytic hydrogenation reaction.

[0021] Furthermore, the pH value of the citrate buffer in step 1 is 6.5 and the concentration is 0.4M.

[0022] The beneficial effects of the basic scheme are: 1. The pH value of the citrate buffer is 6.5, which can provide a stable dissolution environment for laccase before the start of lignin hydrolysis. And the citrate buffer can protect the enzyme from the influence of pH changes, thereby maintaining its catalytic activity. During the enzymatic hydrolysis of lignin, the citrate buffer plays a role in stabilizing the enzyme.

[0023] Furthermore, the laccase mediator in step 1 includes monocyclic phenol-derived aldehydes, ketones and acid compounds.

[0024] The beneficial effects of the basic scheme are: 1. Aldehydes, ketones and acid compounds derived from monocyclic phenols as laccase mediators can significantly enhance the catalytic oxidation ability of laccase on lignin, promote the enzymatic reaction between laccase and lignin, and improve the reaction rate and efficiency. Under suitable conditions, the laccase mediator system can efficiently catalyze the degradation of lignin and provide sufficient substrate for subsequent hydrogenation reactions.

[0025] 2. Using aldehydes, ketones and acids derived from monocyclic phenols as laccase mediators can reduce the generation of by-products during the degradation process. These mediators can guide the degradation of lignin molecules along a specific path, thereby generating more valuable lignin enzymatic components.

[0026] 3. As natural laccase mediators, aldehydes, ketones and acid compounds derived from monocyclic phenols often do not need to be synthesized using chemical technology, but are extracted from natural materials, thus avoiding the pollution and environmental hazards of the early mediator synthesis process.

[0027] Further, the lignin degradation device in Step 1 is heated to 40°C - 50°C and stirred at a constant temperature for 1 - 4 hours.

[0028] The beneficial effects of the basic solution are as follows: 1. Laccase used in the lignin degradation process has high activity in the temperature range of 40°C - 60°C. Constant temperature stirring can ensure that enzymes fully act at this optimal temperature, thereby improving the degradation efficiency of lignin. Constant temperature stirring helps to promote the full contact and mixing between the lignin substrate and enzyme molecules, enabling the enzyme to more effectively catalyze the depolymerization reaction of lignin.

[0029] 2. Under suitable temperature and stirring conditions, the chemical bonds on the lignin molecular chain are more likely to break, thereby reducing the molecular weight of lignin. This helps the subsequent catalyst to more effectively degrade lignin and improve the yield of bio - oil.

[0030] 3. By optimizing the lignin degradation conditions, the generation of by - products during the degradation process can be reduced. These by - products may affect the quality and stability of bio - oil. Constant temperature stirring and suitable temperature conditions help to guide the lignin molecules to degrade along a specific path, thereby generating more valuable components.

[0031] Further, some aldehyde enzymatic hydrolysis products generated in Step 1 include monomeric aromatic aldehydes and furfural compounds oxidized and degraded by laccase.

[0032] The beneficial effects of the basic solution are as follows: The generation of monomeric aromatic aldehydes and furfural compounds means that lignin has been effectively enzymatically hydrolyzed, and in the subsequent hydrogenation reaction, some aldehyde enzymatic hydrolysis products will also be reduced to alcohol substances by the hydrogenation reaction, becoming an important part of bio - oil.

[0033] Further, the copper - based catalyst in Step 3 includes Cu / ZnO / Al2O3, where the content of Cu is 30 - 60 wt%, and the weight ratio of the copper - based catalyst to the solid residue is 1:60 - 1:80.

[0034] The beneficial effects of the basic solution are as follows: 1. Cu, as the active component of the catalyst, plays a key role in the Cu / ZnO / Al2O3 system. Controlling the content of Cu within the range of 30 - 60 wt% can ensure that the catalyst has sufficient active sites, thereby improving the catalytic efficiency. At the same time, an appropriate content of Cu also helps to maintain the stability and uniform distribution of the catalyst.

[0035] 2. The Cu / ZnO / Al2O3 catalyst has good anti-coking performance and can maintain high catalytic activity during long-term reactions. This helps to extend the service life of the catalyst and reduce the replacement frequency. This catalyst system has high thermal stability and can maintain stable catalytic performance at high reaction temperatures. This helps to broaden the reaction condition range and increase the yield of bio-oil.

[0036] 3. The production technology of the Cu / ZnO / Al2O3 catalyst is relatively mature, and the production cost is low. Compared with noble metal-based catalysts, it has the advantage of being put into large-scale production.

[0037] Furthermore, the high temperature condition for catalyzing lignin degradation in step three is 300 °C, with continuous stirring for 5 - 10 hours.

[0038] The beneficial effects of the basic scheme are: 1. High temperature conditions can accelerate the breakage of chemical bonds inside lignin molecules, especially those carbon-carbon bonds and carbon-oxygen bonds connecting aromatic rings. The breakage of these chemical bonds is a key step in the degradation of lignin into low-molecular-weight compounds, which helps to improve the degradation efficiency of lignin.

[0039] 2. At high temperatures, the active sites of the Cu / ZnO / Al2O3 catalyst are more active and can more effectively catalyze the degradation reaction of lignin. In addition, continuous stirring helps the catalyst particles to be evenly distributed in the reaction system, further improving the utilization efficiency of the catalyst.

[0040] 3. Under high temperature conditions, the degradation path of lignin is clearer, which helps to generate specific types of bio-oil components and reduce the generation of by-products. By controlling the reaction time and temperature, the selectivity of the product can be optimized, making the content of valuable components in the bio-oil higher.

[0041] Furthermore, the applied voltage in step three is 1.2 V.

[0042] The beneficial effects of the basic scheme are: 1. The electric field generated by the applied voltage can affect the charge distribution on the catalyst surface, thereby promoting the interaction between lignin molecules and the active sites of the catalyst. This interaction helps to accelerate the adsorption and degradation processes of lignin molecules, thus improving the catalytic efficiency.

[0043] 2. By ionizing nearby hydrogen molecules into hydrogen ions through electrification, the reaction rate of the hydrogenation reaction can be promoted, the degradation efficiency of lignin and the selectivity of the product can be improved, thereby reducing the waste of raw materials and increasing the utilization rate. This helps to reduce production costs and improve economic benefits. Description of the Drawings

[0044] Figure 1Schematic diagram of the method for catalytic degradation of lignin to prepare bio-oil in the embodiments of the present invention.

[0045] Figure 2 Axonometric view of the lignin degradation device in the embodiments of the present invention.

[0046] Figure 3 Lateral sectional view of the lignin degradation device in the embodiments of the present invention.

[0047] Figure 4 Lateral sectional view of the turbine fan of the lignin degradation device in the embodiments of the present invention.

[0048] Reference numerals in the accompanying drawings of the specification include: 1, reaction kettle; 2, bracket; 3, collection pipe; 4, stirring motor; 5, gas transmission pipe; 6, collection valve; 7, filter screen; 8, turbine fan blade; 9, shaft collar; 10, stirring shaft; 11, ring groove; 12, convex ring; 13, ventilation pipe; 14, electrode; 15, cable; 16, wire. Detailed implementation manners

[0049] The following is further detailed through specific implementation manners:

[0050] Example 1

[0051] Basically as shown in the attached Figure 1 shown: A method for catalytic degradation of lignin to prepare bio-oil, including the following steps:

[0052] Step 1, pretreatment of lignin: Add lignin to the lignin degradation device, and add a citrate buffer solution with a pH value of 6.5 and a concentration of 0.4 M for suspension. Add an appropriate amount of laccase and laccase mediator. The laccase mediator includes aldehydes, ketones, and acid compounds derived from monocyclic phenols. Use hydrochloric acid solution to adjust the pH value to 4 - 4.8, heat to 40°C - 50°C and continuously stir and aerate for 1 - 4 hours to preliminarily depolymerize the lignin macromolecules and produce some aldehyde enzymatic hydrolysis products. Some aldehyde enzymatic hydrolysis products include monomeric aromatic aldehydes and furfural compounds oxidized and degraded by laccase;

[0053] Step 2, collection of pretreatment products: Use the lignin degradation device to filter the pretreated lignin enzymatic hydrolysis solution into two parts, a suspension and solid residues. The suspension is extracted with isopropanol to obtain lipophilic lignin monomer molecules and aldehyde enzymatic hydrolysis products. The solid residues are rinsed with deionized water to restore to neutral and dried;

[0054] Step 3, Catalysis of Lignin and Its Products: Mix the isopropanol extract and the solid residue and place them in a lignin degradation device. After adding a copper-based catalyst, continuously stir and mix and purge with nitrogen to remove oxygen. The copper-based catalyst includes Cu / ZnO / Al2O3, where the content of Cu is 30-60 wt%, and the weight ratio of the copper-based catalyst to the solid residue is 1:60-1:80. Then, under the condition of a high temperature of 300 °C, continuously purge with hydrogen and stir while applying an electric current for 5-10 hours to catalyze the degradation of lignin, and the applied voltage is 1.2 V;

[0055] Step 4, Extraction of Bio-oil: Use the lignin degradation device to directly filter to obtain the solution after lignin degradation, then rotary evaporate the solution to remove isopropanol, extract the residue with ethyl acetate, and rotary evaporate ethyl acetate again after extraction, and dry to prepare bio-oil.

[0056] The specific implementation process is as follows: Conduct an experiment on the degradation of lignin to prepare bio-oil using a lignin degradation device.

[0057] 1. Prepare a citrate buffer solution with a pH value of 6.5 and a concentration of 0.4 M. Weigh 6.047 g of citric acid and 95.104 g of trisodium citrate and dissolve them in 1 L of deionized water.

[0058] 2. Select pulverized corn straw lignin for lignin, pass through a 40-mesh sieve, select laccase from the white rot fungus laccase / mediator system, namely Trametes versicolor laccase / syringaldehyde, and select Cu / ZnO / Al2O3 prepared by the co-precipitation method for the copper-based catalyst.

[0059] 3. Take three portions of 200 g of lignin, divided into Group 1, Group 2, and Group 3. Group 1 is not pretreated, Group 2 is not enzymatically hydrolyzed during the pretreatment process, and Group 3 is treated according to this lignin degradation method. In each group of treatments, add 200 g of lignin to 1 L of citric acid solution, add the Trametes versicolor laccase / syringaldehyde system, the dosage of Trametes versicolor laccase is 0.1 IU / mL, and make the concentration of syringaldehyde reach 0.3 mmol / L, adjust the pH to 4.8, and put the whole into the lignin degradation device, and carry out enzymatic hydrolysis by purging with oxygen and stirring at 40 °C for 2 hours, the oxygen purging rate is 0.3 L / min, and the stirring rate is 180 rpm.

[0060] 4. During the collection process, use 200 mL of isopropanol to extract the suspension of each group, and add all the dried solid residues to the isopropanol solution after extraction, add the Cu / ZnO / Al2O3 catalyst according to the proportion and mix well, and add it to the lignin degradation device and seal it.

[0061] 5. First, introduce nitrogen gas to expel the air in the device, then introduce hydrogen gas to expel the nitrogen gas in the device, and finally introduce hydrogen gas at a hydrogen flow rate of 0.5 L / min. Group 1 and Group 2 maintain the pressure at 1.5 Mpa, and Group 3 also reacts with stirring at 200 rpm for 8 hours at a temperature of 300 °C. After cooling, filter to obtain a liquid. The liquid is subjected to rotary evaporation and extraction with ethyl acetate, and then rotary evaporation again to obtain bio-oil, and weigh it. The results are shown in the following table.

[0062] Table 1. Yield of bio-oil prepared by lignin degradation

[0063]

[0064] Combined with the results in the above table, it can be seen that the bio-oil yield of Group 3 after enzymatic hydrolysis pretreatment is much higher than that of Group 1 and Group 2, and there is no need for pressure-maintaining degradation treatment, reducing the energy required in the production process. This is because enzymatic hydrolysis preliminarily depolymerizes the lignin macromolecules, improving the efficiency of subsequent hydrogenation reaction degradation. And the acidic enzymatic hydrolysis environment is conducive to the precipitation of alkaline metals contained in lignin into the solution, avoiding affecting the catalytic effect of the catalyst in the subsequent hydrogenation reaction, indicating that the pretreatment enzymatic hydrolysis step in the present invention plays a key role in increasing the lignin degradation efficiency.

[0065] After the bio-oil is prepared, perform property analysis. Use gas chromatography-mass spectrometry (GC-MS) to analyze the mass fraction of oxygen (ω O ) of the bio-oil prepared by the three treatments, and test the viscosity, acidity and alkalinity, and calorific value (bomb calorimetry) of the bio-oil at different temperatures. The results are shown in the following table.

[0066] Table 2. Properties of bio-oil prepared by lignin degradation

[0067]

[0068] Since the hydrogenation reaction does not use high pressure triggering, the oxygen content in the three groups is not much different from that in the first and second groups. When bio-oil contains more polar groups (generally oxygen-containing groups) and larger molecules, the intermolecular force is large and the viscosity is relatively high. The difference in oxygen content in the bio-oil products under the three groups of treatments is small, so the viscosity difference is not significant either. However, the viscosity of the bio-oil products under the three groups of normal degradation is also the smallest, probably because after the lignin macromolecules are depolymerized, the degradation is more complete, resulting in a lower content of macromolecular products in the bio-oil products. The calorific values of the bio-oil products under the three groups of treatments are relatively high because the water content is low after extraction, and a higher water content leads to a lower calorific value. Finally, the bio-oil products are generally acidic because they contain more small molecule organic acids. It can be seen from this that in the method for catalytic degradation of lignin to prepare bio-oil of the present invention, although it is difficult to reduce the oxygen content of the bio-oil products, because the enzymatic hydrolysis step is added to pretreat the depolymerization of lignin macromolecules, the subsequent catalytic hydrogenation process reacts more fully, which can effectively reduce the macromolecular products in bio-oil, reduce the viscosity of bio-oil, and increase the calorific value of bio-oil.

[0069] Example 2

[0070] The difference from the above embodiment is that as shown in the attached Figure 2 、 Figure 3 and Figure 4 : The lignin degradation device in the above steps includes a reaction kettle 1. A bracket 2 is welded to the bottom of the reaction kettle 1. A stirring motor 4 with a vertically downward output shaft is welded to the center of the top wall of the reaction kettle 1. The output shaft of the stirring motor 4 is coaxially welded with a stirring shaft 10. The stirring shaft 10 vertically passes through the top wall of the reaction kettle 1 and extends into the reaction kettle 1. A gas delivery pipe 5 is welded to the center of the inner top wall of the reaction kettle 1. The gas delivery pipe 5 extends downward and sleeves the stirring shaft 10. A turbine fan is welded to the bottom end of the stirring shaft 10. The turbine fan includes a shaft ring 9 and a plurality of turbine fan blades 8 welded to the outside of the shaft ring 9. The shaft ring 9 is welded to the stirring shaft 10. A ring groove 11 is formed in the radial surface at the bottom end of the gas delivery pipe 5. A convex ring 12 is welded to the top wall of the shaft ring 9. The ring groove 11 is in sliding fit with the convex ring 12. A plurality of air pipes 13 corresponding to the turbine fan blades 8 are communicated with the top wall of the shaft ring 9. The air pipes 13 all extend outward to the middle of the bottom wall of the turbine fan blades 8 and are communicated with the outside. A temperature control device is installed inside the side wall of the reaction kettle 1. The temperature control device is a spiral eddy current heating wire. A filter screen 7 located below the turbine fan is laid at the bottom of the reaction kettle 1. A collection valve 6 is communicated with the center of the bottom wall of the reaction kettle 1. The bottom end of the collection valve 6 is communicated with a collection pipe 3.

[0071] Parallel cables 15 are symmetrically welded to the outside of the gas delivery pipe 5. The cables 15 extend to the bottom end of the gas delivery pipe 5. A plurality of wires 16 corresponding to the turbine fan blades 8 are welded to the top wall of the shaft ring 9. Electrodes 14 are laid on the middle bottom wall of each of the turbine fan blades 8. The wires 16 are respectively welded to the corresponding electrodes 14. The top walls of the wires 16 are located on the movement track of the bottom wall of the cables 15.

[0072] The specific implementation process is as follows: During the pretreatment process and the degradation process of lignin, it is necessary to continuously introduce gas while stirring. Although the ordinary reactor 1 is also ventilated from the bottom, the fusion of gas and reaction liquid is ordinary, and it is difficult to fully utilize the introduced gas to participate in the reaction.

[0073] like Figure 3 As shown, in the lignin degradation device, the gas pipe 5 is sleeved on the outside of the stirring shaft 10, and the sliding fit between the annular groove 11 at the bottom end of the gas pipe 5 and the convex ring 12 on the top wall of the shaft ring 9 ensures the air tightness of the gas pipe 5. The gas introduced into the gas pipe 5 is introduced into the reaction liquid from the middle of the bottom wall of the turbine blade 8 through the ventilation pipe 13 connected to the shaft ring 9. Since the liquid flow direction generated by the rotation of the turbine fan is downward, the gas can be pushed downward and then gradually leave the liquid surface from the outer periphery of the turbine blade 8 upward, ensuring that the bubbles formed by the gas fully pass through the reaction liquid in the radial and axial directions of the turbine fan and fully participate in the pretreatment enzymatic reaction and the hydrogenation reaction of lignin degradation, thereby improving the reaction efficiency and reducing the generation of by-products.

[0074] In addition, the bottom end of the cable 15 on the outside of the gas pipe 5 is slidably matched with the top end of the conductor 16. During the rotation of the turbine fan of the lignin degradation and hydrogenation reaction, the negative cable 15 is continuously connected with the conductor 16 of each corresponding turbine fan, and the hydrogen introduced is enriched at the electrode 14 connected to the negative cable 15 on the periphery of the ventilation pipe 13 in the middle of the bottom wall of each turbine fan blade 8, thereby promoting the ionization trend of hydrogen in the reaction liquid, generating hydrogen ions to participate in the hydrogenation reaction, reducing other physical conditions required for the hydrogenation reaction, reducing the energy consumption for preparing other physical conditions (such as high pressure), making the catalyst selection range for the hydrogenation reaction wider, reducing the cost of materials and equipment required in the lignin degradation process, and making the lignin degradation to prepare biomass oil more gentle and smooth.

[0075] The temperature control unit of the spiral eddy current heating wire can control the temperature in the reactor 1 more sensitively. Maintaining a constant temperature reaction is conducive to the smooth and thorough progress of the reaction. The filter screen 7 laid under the turbine fan in the reactor 1 can separate the lignin from the reaction solution, help to terminate and separate the reactions in each step of the lignin degradation, and allow the entire process to be carried out in the same reactor 1, thereby reducing the equipment cost of production and the complexity of the production process operation.

[0076] It should be noted that in this text, relational terms such as first and second are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any actual relationship or order between these entities or operations. Moreover, the term "comprising", "including" or any other variant thereof is intended to cover non-exclusive inclusion, such that a process, method, article or device comprising a series of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, method, article or device.

[0077] The above are only embodiments of the present invention. Common knowledge such as specific structures and characteristics in the prior art are not described in detail herein. Those of ordinary skill in the art know all the common general technical knowledge in the technical field to which the invention pertains before the filing date or the priority date, are able to know all the prior art in this field, and have the ability to apply conventional experimental means before this date. Those of ordinary skill in the art can, under the inspiration given in this application and in combination with their own abilities, perfect and implement this solution. Some typical well-known structures or well-known methods should not be an obstacle for those of ordinary skill in the art to implement this application. It should be pointed out that for those skilled in the art, without departing from the structure of the present invention, several deformations and improvements can be made, and these should also be regarded as the protection scope of the present invention, and these will not affect the implementation effect of the present invention and the practicality of the patent. The protection scope claimed in this application should be based on the content of its claims, and the specific implementation manners and the like described in the specification can be used to interpret the content of the claims.

Claims

1. A method for preparing biomass oil by catalytic degradation of lignin, characterized in that: The following steps are involved: Step 1, pretreatment of lignin: adding lignin to a lignin degradation device, suspending it in a citrate buffer, adding an appropriate amount of laccase and laccase mediator, adjusting the pH value to 4-4.8 with a hydrochloric acid solution, heating and stirring, and continuously passing oxygen to preliminarily depolymerize the lignin macromolecules and produce some aldehyde enzymatic hydrolysis products; Step 2: Collecting pretreatment products: Using a lignin degradation device, the pretreated lignin enzymatic hydrolyzate is filtered and divided into two parts: a suspension and a solid residue. The suspension is extracted with isopropanol to extract fat-soluble lignin monomer molecules and aldehyde enzymatic hydrolyzate. The solid residue is washed with deionized water to restore to neutrality and dried. Step 3, catalysis of lignin and its products: the isopropanol extract and the solid residue are mixed and placed in a lignin degradation device, a copper-based catalyst is added, the mixture is continuously stirred and mixed, nitrogen is passed through to remove oxygen, and then hydrogen and electricity are continuously passed through at high temperature to catalyze the degradation of lignin; Step 4, biomass oil extraction: use a lignin degradation device to directly filter to obtain a solution after lignin degradation, then rotary evaporate the solution to remove isopropanol, use ethyl acetate to extract the residue, rotary evaporate the ethyl acetate again after extraction, and dry to prepare biomass oil.

2. The method for preparing biomass oil by catalytic degradation of lignin according to claim 1, characterized in that: The lignin degradation device in the above steps comprises a reactor (1), the bottom of the reactor (1) is fixedly connected to a bracket (2), the center of the top wall of the reactor (1) is fixedly connected to a stirring motor (4) with an output shaft pointing vertically downward, the output shaft of the stirring motor (4) is coaxially fixedly connected to a stirring shaft (10), the stirring shaft (10) vertically passes through the top wall of the reactor (1) and extends into the reactor (1), the center of the top wall of the reactor (1) is fixedly connected to an air supply pipe (5), the air supply pipe (5) extends downward and sleeves the stirring shaft (10), the bottom end of the stirring shaft (10) is fixedly connected to a turbine fan, the turbine fan comprises a shaft ring (9) and a plurality of turbine blades (8) fixedly connected to the outside of the shaft ring (9) The shaft collar (9) is fixedly sleeved with the stirring shaft (10), the radial surface of the bottom end of the gas delivery pipe (5) is provided with an annular groove (11), the top wall of the shaft collar (9) is fixedly connected with a convex ring (12), the annular groove (11) and the top wall of the shaft collar (9) are slidably matched, the top wall of the shaft collar (9) is connected with a plurality of ventilation pipes (13) corresponding to the turbine blades (8), the ventilation pipes (13) are all extended outward to the middle of the bottom wall of the turbine blades (8) and are connected to the outside, the side wall of the reactor (1) is fixedly connected with a temperature control unit, the bottom of the reactor (1) is provided with a filter screen (7) located below the turbine fan, the center of the bottom wall of the reactor (1) is connected with a collecting valve (6), and the bottom end of the collecting valve (6) is connected with a collecting pipe (3).

3. The method for preparing biomass oil by catalytic degradation of lignin according to claim 2, characterized in that: The outer side of the gas transmission pipe (5) is symmetrically and fixedly connected with parallel cables (15), the cables (15) extend to the bottom end of the gas transmission pipe (5), the top wall of the collar (9) is fixedly connected with a plurality of wires (16) corresponding to the turbine blades (8), the bottom wall of the middle part of the turbine blades (8) is provided with electrodes (14), the wires (16) are respectively fixedly connected with the corresponding electrodes (14), and the top wall of the wires (16) is located on the movement trajectory of the bottom wall of the cables (15).

4. The method for preparing biomass oil by catalytic degradation of lignin according to claim 1, characterized in that: The pH value of the citrate buffer in step 1 is 6.5 and the concentration is 0.4M.

5. The method for preparing biomass oil by catalytic degradation of lignin according to claim 1, characterized in that: The laccase mediators in step 1 include monocyclic phenol-derived aldehydes, ketones and acids.

6. The method for preparing biomass oil by catalytic degradation of lignin according to claim 1, characterized in that: The lignin degradation device in step 1 is heated to 40°C-50°C and stirred at a constant temperature for 1-4 hours.

7. The method for preparing biomass oil by catalytic degradation of lignin according to claim 1, characterized in that: Part of the aldehyde enzymatic hydrolysis products produced in step 1 include monomeric aromatic aldehydes and aldehyde compounds oxidatively degraded by laccase.

8. The method for preparing biomass oil by catalytic degradation of lignin according to claim 1, characterized in that: The copper-based catalyst in step three comprises Cu / ZnO / Al2O3, wherein the content of Cu is 30-60wt%, and the weight ratio of the copper-based catalyst to the solid residue is 1:60-1:

80.

9. The method for preparing biomass oil by catalytic degradation of lignin according to claim 1, characterized in that: In step 3, the high temperature condition for catalyzing the degradation of lignin is 300° C., and stirring is continued for 5-10 hours.

10. The method for preparing biomass oil by catalytic degradation of lignin according to claim 1, characterized in that: The power-on voltage in step 3 is 1.2V.

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