A method for selective photocatalytic depolymerization of lignin β-O-4 bonds in a supramolecular structure solvent

Abstract

A method for photocatalytic selective depolymerization of β-O-4 bonds of lignin in a supramolecular structure solvent, which relates to a method for depolymerizing β-O-4 bonds of lignin. The present invention is to solve the problem that the existing method for depolymerizing lignin will cause environmental pollution and is not convenient for industrial-scale production and application. The present invention can achieve selective cleavage of different chemical bonds by selecting different solvents, and can achieve green, environmentally friendly and non-toxic solvents while ensuring yield. The present invention achieves selective cleavage of β-O-4 chemical bonds in lignin under the excitation of visible light sources. The present invention belongs to the technical field of photocatalytic depolymerization of lignin.

Description

Technical Field

[0001] The invention relates to a method for depolymerizing lignin beta-O-4 bonds, and belongs to the technical field of photocatalytic depolymerization of lignin. Background Art

[0002] Lignin is a polyhydroxyl supramolecular compound existing in nature with a wide molecular weight distribution (100-30000). It contains rich aromatic compounds, so it is an indispensable raw material in the production of phenolic organic chemicals. Depolymerizing it into small molecules can greatly increase its value. At the same time, lignin can also be depolymerized into hydrocarbons, which can replace the increasingly depleted disposable energy.

[0003] Lignin has a large structure and many types of chemical bonds. During the depolymerization process, the bond breaking conditions are harsh and non-selective. Usually, a high-temperature and high-pressure hydrothermal method or hydrogenation reduction is used, which has a long reaction time and harsh conditions. Among them, photocatalytic oxidation depolymerization is the most gentle, and the photocatalyst is used. Under the action of the photocatalyst, light is used to form electrons and holes on the catalyst surface to promote the photocatalytic reaction. However, the band gap of traditional photocatalysts is wide, which limits the absorption of visible light and shackles the efficiency of photocatalysis. Therefore, the selection of photocatalysts with narrower band gaps has become a research hotspot in recent years.

[0004] In many physical and chemical reactions, the role of solvents is an existence that cannot be ignored. Common water and organic solvents have been used in various fields. With the improvement of people's requirements for living environment, the application of new green solvents has become the goal of large-scale production. Therefore, environmentally friendly supramolecular solvents have begun to attract people's attention. It has been proved to be a material that can be completely degraded by biomass, and has very good biocompatibility. It has excellent thermal stability, can be miscible with water and most solvents in any ratio, has adjustable viscosity, has a low melting point, and is cheap to produce and non-toxic. In addition, the preparation process of supramolecular solvents is also relatively simple. After the raw materials are put into the system, they only need to be stirred under heating conditions to synthesize a clear and transparent solution. It is usually a two-component or multi-component supramolecular low-melting-point mixture composed of solid halide salts (as hydrogen bond acceptors, such as quaternary ammonium salts) and alcohols (as hydrogen bond donors, such as compounds such as amides, carboxylic acids and polyols). By selecting different hydrogen bond acceptors and hydrogen bond donors, according to different ratio combinations, some basic properties of supramolecular solvents can be adjusted in a large range, thereby changing its physicochemical properties. Considering that lignin is also a type of supramolecular compound, it dissolves more fully in supramolecular low eutectic solvents, and effective dissolution can improve the depolymerization efficiency; moreover, the depolymerized small molecular phenolic compounds can also be effectively dissolved in supramolecular solvents, and the hydrogen bond donor components in the solvent can be used as a hydrogen source during the depolymerization of lignin. The selectivity of bond breaking can be achieved by regulating the chemical composition and proportion of supramolecular solvents, so it is advantageous to choose supramolecular solvents as the solvent system for the reaction.

[0005] Patent CN108014782B introduces a method for obtaining liquid fuel components by depolymerizing lignin using a recyclable layered solid acid catalyst. The catalyst is composed of a layered solid acid catalyst and a carbon-supported metal catalyst. The solvent used is a mixed solvent of dioxane and water. Lignin is depolymerized under a hydrogen pressure of 2Mpa to obtain an aromatic compound product. The solvent used in this method produces an organic solvent as waste liquid after the reaction, which has poor selectivity and pollutes the environment. The hydrogen environment is used in the reaction process, which is highly dangerous and difficult to achieve reaction conditions.

[0006] Patent CN109701645A introduces a method for selective depolymerization of lignin using non-precious metal catalysts. This method uses a non-precious metal bipyridine complex to catalyze the selective hydrogenolysis of lignin to produce aromatic compounds such as guaiacol and styrene. The reaction temperature of this method is 80-200°C and the reaction pressure is 1Mpa nitrogen. The reaction conditions are not mild enough and cannot be carried out under mild conditions.

[0007] Patent CN105080527A introduces a composite catalyst and a preparation method thereof, wherein the composite catalyst is composed of a titanium-containing compound and a modifier loaded on the titanium-containing compound, wherein the modifier is fullerene / fullerene derivative, and the method first mixes lignin with an alkaline solution and then contacts the solution, the catalyst and air, and then performs photocatalysis to obtain a depolymerization product. This method uses an alkaline solution, and faces the problem of difficult treatment of waste liquid after the reaction.

[0008] Patent CN104177228A introduces a method for depolymerizing lignin using a molybdenum nitride catalyst, in which lignin, a catalyst and a reaction solvent are mixed and added to a closed reactor, gas is introduced to replace the air in the reactor, the temperature is raised to the reaction temperature and maintained for a certain period of time, and after the reaction is completed, the reactor temperature is lowered to room temperature, the air is evacuated, the solid catalyst is filtered out, and the liquid product is obtained by rotary evaporation. This method requires a specific gas environment, and has strict equipment and production requirements; the gas volatilized during the rotary evaporation contains organic solvents, which requires additional protective measures.

[0009] Patent CN105037103A introduces a method for efficiently depolymerizing lignin using metal chloride and precious metal as composite catalysts. The method uses metal chloride and precious metal as catalysts and small molecule organic solvents as medium to catalyze the depolymerization of lignin under mild conditions to obtain high value-added phenolic substances and high calorific value bio-oil. Since precious metals such as Ru are used in this method, the cost is relatively high; small molecule organic solvents are used in the reaction environment, which causes great environmental pollution. Summary of the invention

[0010] The present invention aims to solve the problems that the existing method for depolymerizing lignin will cause environmental pollution and is not convenient for industrial-scale production and application, and further proposes a method for photocatalytic selective depolymerization of lignin β-O-4 bonds in a supramolecular structure solvent.

[0011] The technical solution adopted by the present invention to solve the above-mentioned problem is: the steps of the present invention include:

[0012] Step 1, put Bi(NO3)3·5H2O in a crucible, and place the crucible in a muffle furnace;

[0013] Step 2, measure HNO3 and add it to water, then add Bi(NO3)3·5H2O to obtain a dispersion, then add Bi2O3 and stir, then add NaWO4·2H2O solution and stir;

[0014] Step 3, then put it into a high-pressure reactor for reaction, dry it after the reaction, and finally wash and dry it to obtain the Bi2O3 / Bi2WO6 photocatalyst;

[0015] Step 4, mixing the reagents having hydrogen bond acceptors and hydrogen bond donors respectively, heating to 80° C. under stirring until a uniform, clear, transparent solution is obtained, and then the mixture is taken out and mixed with distilled water to prepare solutions of different volume ratios;

[0016] Step 5: Put lignin dimer or real lignin and supramolecular solvents with different water contents into a quartz bottle, remove bubbles by ultrasound, add a photocatalyst, and then place in a photoreaction dark box for reaction.

[0017] Furthermore, in step 1, the crucible is placed in a muffle furnace, the calcination temperature is 200-600° C., and the calcination time is 2-4 h to obtain light yellow Bi2O3.

[0018] Furthermore, in step 3, the catalyst is placed in a high-pressure reactor for reaction and dried after the reaction. At this time, the drying temperature of the catalyst is 100-200°C, the drying time is 12-36h, and the drying temperature after washing is 40-80°C, and the drying time is 2-4h.

[0019] Furthermore, in step 3, the ratio of Bi2O3:Bi2WO6 is 0.1 to 2:1.

[0020] Furthermore, the hydrogen bond acceptor is preferably choline chloride or betaine, and the hydrogen bond donor is preferably urea, glycerol, ethylene glycol, malic acid, citric acid, 1,2-propylene glycol or oxalic acid.

[0021] Furthermore, the molar ratio of the hydrogen bond donor to the hydrogen bond acceptor in step 4 is preferably 0.4 to 2.0:1.

[0022] Furthermore, the water content of the supramolecular solvent in step 5 is preferably 20% to 80%.

[0023] Furthermore, the illumination time during the depolymerization process is preferably 0 to 10 h; and the illumination intensity is preferably 190W to 270W.

[0024] Furthermore, in step 5, the mass ratio of the raw material lignin to the catalyst is 1:2-10.

[0025] The beneficial effects of the present invention are:

[0026] 1. Under the conditions of the present invention, the β-O-4 bond is selectively depolymerized, wherein the solution after the alkali lignin reaction contains p-hydroxymethylbenzaldehyde (0.26%) and isoferulic acid (0.17%), the solution after the klason lignin depolymerization contains guaiacol (0.11%), and the solution after the dioxane lignin depolymerization contains p-hydroxybenzaldehyde (0.09%) and p-coumaric acid (0.12%);

[0027] 2. The present invention provides a method for photocatalytic selective depolymerization of β-O-4 bonds of lignin in a supramolecular solvent, which includes the synthesis of Bi2O3 / Bi2WO6 photocatalyst, the preparation of supramolecular solvent, and the depolymerization of lignin. The method provided by the present invention is applicable to a variety of supramolecular solvents, and depolymerization of lignin dimer model compounds and real lignin is carried out under the conditions of visible light as a light source and Bi2O3 / Bi2WO6 as a photocatalyst. By using supramolecular solvents of different compositions as the reaction environment, efficient depolymerization of lignin is achieved while avoiding the problem of environmental pollution caused by traditional organic solvents and most ionic liquids after the reaction is completed, providing a way to selectively depolymerize lignin to obtain small molecule products and utilize visible light, which is convenient for industrial-scale production and application.

[0028] 3. The bismuth tungstate (Bi2WO6) used in the present invention is a photocatalyst with advantages such as high stability of nanostructure and high catalytic performance, but the band gap of Bi2WO6 is relatively large and can only absorb light below 450nm. The light absorption range can be expanded by composite modification of Bi2WO6, and the recombination of hole-electron pairs can be reduced, thereby improving the photocatalytic activity of the material. Studies have shown that after adding Bi2O3, a heterojunction will be formed on the surface of the catalyst, which increases the transmission rate of the photogenerated electron-hole of the catalyst and reduces the recombination rate; the addition of Bi2O3 can make the band gap of Bi2WO6 smaller to expand the response range to visible light, thereby improving the catalytic activity; Bi2WO6 has the advantages of simple preparation and low price, and is suitable for large-scale industrial production; the research and development of Bi2WO6 photocatalytic materials can improve the utilization rate of solar energy and save energy, and is a new type of photocatalyst in line with the development of the times. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 are infrared spectra of Bi2O3, Bi2WO6 and different ratios of Bi2O3 / Bi2WO6 prepared in Example 1;

[0030] Figure 2 is the fluorescence spectra of Bi2O3 / Bi2WO6 with different ratios prepared in Example 1;

[0031] Figure 3 The UV-visible diffuse reflectance spectra of Bi2O3, Bi2WO6 and different ratios of Bi2O3 / Bi2WO6 prepared in Example 1 are shown;

[0032] Figure 4 It is the bandgap width diagram of Bi2O3, Bi2WO6 and different ratios of Bi2O3 / Bi2WO6 prepared in Example 1;

[0033] Figure 5 is the transient light response curve of Bi2O3 / Bi2WO6 with different ratios prepared in Example 2;

[0034] Figure 6 The impedance curves of Bi2O3 / Bi2WO6 with different ratios prepared in Example 2;

[0035] Figure 7 It is the adsorption-desorption isotherms of Bi2O3 / Bi2WO6 with different ratios prepared in Example 2;

[0036] Figure 8 is the pore size distribution diagram corresponding to the adsorption-desorption of Bi2O3 / Bi2WO6 with different ratios prepared in Example 2;

[0037] Fig. 9 is a liquid chromatogram of the reaction solution after depolymerization of 2-(2-methoxyphenoxy)-1-(4-methoxyphenyl)ethanone prepared in Example 2 and a mass spectrum of the product 4-methoxyacetophenone;

[0038] Fig.10 It is the liquid chromatogram of the solution after the reaction of the alkali lignin prepared in Example 2 and the standard product. DETAILED DESCRIPTION

[0039] Specific implementation method 1: The method for photocatalytic selective depolymerization of lignin β-O-4 bonds in a supramolecular structure solvent described in this implementation method is achieved by the following steps:

[0040] Step 1, put Bi(NO3)3·5H2O in a crucible, and place the crucible in a muffle furnace;

[0041] Step 2, measure HNO3 and add it to water, then add Bi(NO3)3·5H2O to obtain a dispersion, then add Bi2O3 and stir, then add NaWO4·2H2O solution and stir;

[0042] Step 3, then put it into a high-pressure reactor for reaction, dry it after the reaction, and finally wash and dry it to obtain the Bi2O3 / Bi2WO6 photocatalyst;

[0043] Step 4, mixing the reagents having hydrogen bond acceptors and hydrogen bond donors respectively, heating to 80° C. under stirring until a uniform, clear, transparent solution is obtained, and then the mixture is taken out and mixed with distilled water to prepare solutions of different volume ratios;

[0044] Step 5: Put lignin dimer or real lignin and supramolecular solvents with different water contents into a quartz bottle, remove bubbles by ultrasound, add a photocatalyst, and then place in a photoreaction dark box for reaction.

[0045] Specific implementation method 2: In step 1 of the method for photocatalytic selective depolymerization of lignin β-O-4 bonds in a supramolecular structure solvent described in this implementation method, a crucible is placed in a muffle furnace, the calcination temperature is 200-600°C, and the calcination time is 2-4h to obtain light yellow Bi2O3.

[0046] Specific implementation method three: In step 3 of the method for photocatalytic selective depolymerization of lignin β-O-4 bonds in a supramolecular structure solvent described in this implementation method, a high-pressure reactor is placed for reaction, and dried after the reaction. At this time, the drying temperature of the catalyst is 100-200°C, and the drying time is 12-36h. The drying temperature after washing is 40-80°C, and the drying time is 2-4h.

[0047] Specific implementation method 4: In step 3 of the method for photocatalytic selective depolymerization of lignin β-O-4 bonds in a supramolecular structure solvent described in this implementation method, the ratio of Bi2O3:Bi2WO6 is 0.1 to 2:1.

[0048] Specific embodiment 5: The hydrogen bond acceptor in the method for photocatalytic selective depolymerization of lignin β-O-4 bonds in a supramolecular structure solvent described in this embodiment is preferably choline chloride and betaine, and the hydrogen bond donor used is preferably urea, glycerol, ethylene glycol, malic acid, citric acid, 1,2-propylene glycol, and oxalic acid.

[0049] Specific embodiment 6: The molar ratio of the hydrogen bond donor to the hydrogen bond acceptor in step 4 of the method for photocatalytic selective depolymerization of lignin β-O-4 bonds in a supramolecular structure solvent described in this embodiment is preferably 0.4 to 2.0:1.

[0050] Specific implementation method 7: The water content of the supramolecular solvent described in step 5 of the method for photocatalytic selective depolymerization of lignin β-O-4 bonds in a supramolecular structure solvent described in this implementation method is preferably 20% to 80%.

[0051] Specific embodiment eight: In the method for photocatalytic selective depolymerization of lignin β-O-4 bonds in a supramolecular structure solvent described in this embodiment, the illumination time during the depolymerization process is preferably 0 to 10 hours; the illumination intensity is preferably 190W to 270W.

[0052] Specific implementation method 9: In step 5 of the method for photocatalytic selective depolymerization of lignin β-O-4 bonds in a supramolecular structure solvent described in this implementation method, the mass ratio of raw material lignin to catalyst added is 1:2-10.

[0053] Example

[0054] Embodiment 1:

[0055] A certain amount of Bi(NO3)3·5H2O was placed in a crucible, and the crucible was placed in a muffle furnace, the temperature was set to 400℃, and then calcined at a constant temperature for 2h to obtain light yellow Bi2O3;

[0056] Accurately measure 1ml HNO3. Add to the alkane ring with 40ml distilled water, add 0.97g Bi(NO3)3·5H2O, stir to dissolve. Add appropriate amount of Bi2O3, continue stirring for 5min, then add 30ml solution containing 0.33g NaWO4·2H2O. Stir for 30min, pour into the high pressure reaction device. Put it into the electric constant temperature blast drying oven at 160℃ for 24h, take it out after cooling, take appropriate amount of anhydrous ethanol and distilled water to wash and centrifuge several times, then dry it at 60℃ for 3h. The Bi2O3 / Bi2WO6 photocatalyst is obtained.

[0057] A certain amount of reagents containing betaine and ammonium citrate were mixed in a ratio of 1.2:1, and heated to 80°C under stirring until the experimental drug became a uniform, clear and transparent solution. After taking it out, it was mixed with distilled water into solutions of different volume ratios and sealed for later use.

[0058] In this experiment, the model substance 2-(2-methoxyphenoxy)-1-(4-methoxyphenyl)ethanone was used as the raw material, and visible light was used to induce depolymerization in a supramolecular solvent. The light source used was a xenon light source under Zhongjiao Jinyuan, with an operating voltage of 14V and an operating current of 14-21A.

[0059] Accurately weigh 5 mg of 2-(2-methoxyphenoxy)-1-(4-methoxyphenyl)ethanone and 25 ml of a supramolecular solvent with a water content of 60% in a quartz vial, mix them under ultrasonic conditions for 5 minutes to remove the gas in the solution, cover the lid and place it in a photoreaction dark box, take it out after a certain reaction time, extract the reacted solution, filter it through a membrane and store it in a liquid phase vial, and test its content under liquid phase conditions.

[0060] Embodiment 2:

[0061] A certain amount of Bi(NO3)3·5H2O was placed in a crucible, and the crucible was placed in a muffle furnace, the temperature was set to 400℃, and then calcined at a constant temperature for 2h to obtain light yellow Bi2O3;

[0062] Accurately measure 1ml HNO3. Add to the alkane ring with 40ml distilled water, add 0.97g Bi(NO3)3·5H2O, stir to dissolve. Add appropriate amount of Bi2O3, continue stirring for 5min, then add 30ml solution containing 0.33g NaWO4·2H2O. Stir for 30min, pour into the high pressure reaction device. Put it into the electric constant temperature blast drying oven at 160℃ for 24h, take it out after cooling, take appropriate amount of anhydrous ethanol and distilled water to wash and centrifuge several times, then dry it at 60℃ for 3h. The Bi2O3 / Bi2WO6 photocatalyst is obtained.

[0063] A certain amount of reagents containing betaine and ammonium citrate were mixed in a ratio of 1.2:1, and heated to 80°C under stirring until the experimental drug became a uniform, clear and transparent solution. After taking it out, it was mixed with distilled water into solutions of different volume ratios and sealed for later use.

[0064] In this experiment, alkali lignin extracted from spruce was used as raw material, and visible light was used to induce depolymerization in a supramolecular solvent. The light source used was a xenon light source from Zhongjiao Jinyuan, with an operating voltage of 14V and an operating current of 14-21A.

[0065] 5 mg of alkali lignin and 25 ml of supramolecular solvents with different water contents were accurately weighed into quartz vials, mixed under ultrasonic conditions for 5 minutes to remove the gas in the solution, covered with a lid and placed in a photoreaction dark box. After a certain reaction time, the reaction solution was taken out, filtered through a membrane and stored in a liquid phase vial, and its content was tested under liquid phase conditions.

[0066] Figure 1 The infrared spectra of Bi2O3, Bi2WO6 and different ratios of Bi2O3 / Bi2WO6 are shown in Figure 1. -1 and 1384cm -1The two consecutive peaks are Bi-O absorption peaks. Bi2WO6 at 708cm -1 589cm -1 The absorption peaks at 1456cm are the absorption peaks of WOW and WO, which are mainly caused by the stretching vibration of WOW and WO. -1 and 1330cm -1 Judging from the peak shape, the composite catalyst contains Bi-O bonds. Due to the existence of the composite structure, the peak has red-shifted, indicating that the entire structure is more active. -1 and 589cm -1 From the absorption peaks of WOW and WO, it can be seen that W was successfully introduced into the composite catalyst, indicating that Bi2O3 and Bi2WO6 were successfully composited.

[0067] Figure 2 The fluorescence detection is carried out on three composite catalysts with different proportions at an excitation wavelength of 390nm. When the photogenerated electrons and holes recombine, the material will emit fluorescence. Therefore, the fluorescence detection can reflect the photocatalytic performance of the catalyst to a certain extent. The lower the fluorescence intensity, the lower the recombination rate of photogenerated carriers, the stronger the ability of holes to capture electrons, and the better the photocatalytic performance. Conversely, the weaker the catalytic performance. Figure 2 The emission peaks of the three catalysts are all 518nm. As the ratio of Bi2O3 / Bi2WO6 increases, the fluorescence intensity decreases first and then increases. It can be seen that when the molar ratio of Bi2O3 / Bi2WO6 is 1:1, its fluorescence intensity is the lowest and the photocatalytic performance is the best.

[0068] Figure 3 It can be seen that all samples have a certain absorption in the visible light region. From the edge position of the absorption, it can be seen that compared with the single materials of Bi2O3 and Bi2WO6, the absorption sidebands of the composite catalysts have undergone a certain degree of red shift, indicating that the composite catalysts have enhanced absorption of visible light and some charges have been transferred at the Bi2O3 / Bi2WO6 interface.

[0069] Figure 4 is the bandgap width of these five samples. The tangent is extended and the bandgap width is calculated based on its intersection with the coordinate axis. It can be seen that when the molar ratio of Bi2O3 / Bi2WO6 is 0.1:1, 1:1, and 2:1, the corresponding bandgap widths are 2.69eV, 2.63eV, and 2.73eV, respectively, and the bandgap width of Bi2WO6 is 2.78eV. It can be seen that when the molar ratio of Bi2O3 / Bi2WO6 is 1:1, its optical performance is the best. It may be that after Bi2O3 and Bi2WO6 are compounded in a certain proportion, the bandgap energy of a single raw material can be reduced, thereby expanding the overall light absorption wavelength.

[0070] Figure 5 From the trapezoidal curve, we can see that the composite materials with three ratios all showed highly repeatable photocurrents when illuminated, showing good stability. Compared with the three materials, when the molar ratio of Bi2O3 / Bi2WO6 was 1:1, it showed a better light response. This shows that the composite catalyst prepared according to this ratio has improved the photoelectric properties to a certain extent.

[0071] Figure 6 From the trend of the impedance curve, it can be seen that when the molar ratio of Bi2O3 / Bi2WO6 is 1:1, the impedance is smaller, indicating that the catalyst with this ratio has better conductivity, has less effect on the transfer of interface electrons, and is conducive to the transmission of photoelectrons.

[0072] Figure 7 The adsorption-desorption isotherm was determined to be a type IV curve. The appearance of the hysteresis loop indicated the presence of a mesoporous structure in the sample, and the rise of the isotherm in the high pressure zone indicated the presence of a certain amount of macropores in the sample.

[0073] Figure 8 This is the pore size distribution curve of the composite catalyst. As can be seen from the figure, the pore size distribution is mainly concentrated between 2-10nm, indicating that mesopores are dominant. Compared with the three catalysts, when the molar ratio of Bi2O3 / Bi2WO6 is 1:1, the number of pores at 3-5nm is dominant. The rich pore structure is conducive to the rapid adsorption of the catalyst to the raw materials and the rapid transfer and diffusion of electrons, which is beneficial to improving the photoelectric effect of the material.

[0074] Fig. 9 The solution after the reaction was processed for liquid phase detection. After internal standard method and mass spectrometry analysis, it was determined that the product with the highest content was 4-methoxyacetophenone.

[0075] Fig.10 This is the liquid phase spectrum of the depolymerization product. The retention time of the peak in the solution after the alkali lignin reaction can completely correspond to the peak retention time of p-hydroxybenzaldehyde and isoferulic acid in the standard product.

[0076] The above is only a preferred embodiment of the present invention and does not limit the present invention in any form. Although the present invention has been disclosed as a preferred embodiment as above, it is not used to limit the present invention. Any technician familiar with this profession can make some changes or modify the technical contents disclosed above into equivalent embodiments without departing from the scope of the technical solution of the present invention. However, any simple modification, equivalent replacement and improvement made to the above embodiments without departing from the content of the technical solution of the present invention, based on the technical essence of the present invention, within the spirit and principles of the present invention, still fall within the protection scope of the technical solution of the present invention.

Claims

1. A method for selectively depolymerizing lignin β-O-4 bonds by photocatalysis in a supramolecular structure solvent, characterized in that: The method for photocatalytic selective depolymerization of lignin β-O-4 bonds in a supramolecular structure solvent is achieved by the following steps: Step 1, taking Bi(NO3)3·5H2O and placing it in a crucible, and placing the crucible in a muffle furnace; placing the crucible in the muffle furnace, calcining at a temperature of 200-600°C, and calcining for 2-4 hours to obtain light yellow Bi2O3; Step 2, measure HNO3 and add it to water, then add Bi(NO3)3·5H2O to obtain a dispersion, then add Bi2O3 and stir, then add NaWO4·2H2O solution and stir; Step 3, then put it into a high-pressure reactor for reaction, dry it after the reaction, and finally wash and dry it to obtain the Bi2O3 / Bi2WO6 photocatalyst; Step 4, mixing the reagents having a hydrogen bond acceptor and a hydrogen bond donor, respectively, and heating to 80° C. under stirring until a uniform clear transparent solution is obtained, and then the mixture is taken out and mixed with distilled water to prepare solutions of different volume ratios; Step 5: Put lignin dimer or real lignin and supramolecular solvents with different water contents into a quartz bottle, remove bubbles by ultrasound, add a photocatalyst, and then place in a photoreaction dark box for reaction.

2. The method for photocatalytic selective depolymerization of lignin β-O-4 bonds in a supramolecular structure solvent according to claim 1, characterized in that: In step 3, the catalyst is placed in a high-pressure reactor for reaction and dried after the reaction. At this time, the drying temperature of the catalyst is 100-200° C. and the drying time is 12-36 hours. The drying temperature after washing is 40-80° C. and the drying time is 2-4 hours.

3. The method for photocatalytic selective depolymerization of lignin β-O-4 bonds in a supramolecular structure solvent according to claim 1, characterized in that: In step 3, the molar ratio of Bi2O3:Bi2WO6 is 0.1-2:

1.

4. The method for photocatalytic selective depolymerization of lignin β-O-4 bonds in a supramolecular structure solvent according to claim 1, characterized in that: The hydrogen bond acceptors are choline chloride and betaine, and the hydrogen bond donors used are urea, glycerol, ethylene glycol, malic acid, citric acid, 1,2-propylene glycol, and oxalic acid.

5. The method for photocatalytic selective depolymerization of lignin β-O-4 bonds in a supramolecular structure solvent according to claim 1, characterized in that: The molar ratio of the hydrogen bond donor to the hydrogen bond acceptor in step 4 is 0.4-2.0:

1.

6. The method for photocatalytic selective depolymerization of lignin β-O-4 bonds in a supramolecular structure solvent according to claim 1, characterized in that: The water content of the supramolecular solvent in step 5 is 20% to 80%.

7. The method for photocatalytic selective depolymerization of lignin β-O-4 bonds in a supramolecular structure solvent according to claim 1, characterized in that: The illumination intensity in step 5 is 190W to 270W.

8. The method for photocatalytic selective depolymerization of lignin β-O-4 bonds in a supramolecular structure solvent according to claim 1, characterized in that: In step 5, the mass ratio of the raw material lignin to the catalyst is 1:2-10.

Images