Method for decomposing lignin contained in lignocellulose raw materials and method for producing lignin decomposition products

Abstract

This invention provides a method that uses an inexpensive catalyst to directly and selectively decompose lignin contained in lignocellulosic raw materials without extraction, and that also contributes to the miniaturization of lignocellulosic raw materials. [Solution] The method for decomposing lignin contained in a lignocellulosic raw material according to the present disclosure comprises a mixing step of mixing a lignocellulosic raw material mainly comprising cellulose, hemicellulose, and lignin, at least one organic catalyst selected from diaryl ketones, and an organic solvent to obtain a mixture, and a step of irradiating the mixture with light to decompose the lignin while removing it from the lignocellulosic raw material.

Description

[Technical Field]

[0001] This disclosure relates to a method for decomposing lignin contained in lignocellulosic raw materials and a method for producing lignin decomposition products. [Background technology]

[0002] Lignocellulose is a plant material composed of cellulose, hemicellulose, and lignin, possessing a complex, intertwined higher-order structure. These components form the structural framework of plant cell walls. Specifically, cellulose, a linear polymer, forms a crystalline structure through intramolecular and intermolecular hydrogen bonding, constituting strong microfibrils (cellulose microfibrils). Hemicellulose such as xylan and glucomannan intertwines with these microfibrils, and lignin, an irregular aromatic polymer, fills the voids in this polysaccharide matrix. In this way, lignin is strongly bonded to cellulose and hemicellulose.

[0003] To decompose cellulose contained in lignocellulosic biomass and ultimately obtain bioethanol, pretreatment to remove hemicellulose and lignin is necessary. Furthermore, technologies are being developed to decompose lignin separated from lignocellulose to obtain useful organic compounds.

[0004] Non-patent document 1 describes how lignin extracted from lignocellulosic biomass was decomposed by photoirradiation in the presence of a catalyst called [Ir(dF(CF3)ppy)2(5,5'-d(CF3)-bpy)]PF6, and the production of aldehydes such as vanillin was confirmed. Non-patent document 2 describes how a lignin model molecule was decomposed by photoirradiation in the presence of a specific organic catalyst, which is benzophenone or a derivative thereof, and the production of aldehydes and phenols was confirmed. [Prior art documents] [Non-patent literature]

[0005] [Non-Patent Document 1] Suong T. Nguyen et al., Light-Driven Depolymerization of Native Lignin Enabled by Proton-Coupled Electron Transfer, ACS Catal., 2020, 10, 800-805 [Non-Patent Document 2] Tomotoki Matsuo et al., Organic photoredox-catalyzed unimolecular PCET of benzylic alcohols, Chem. Sci., 2025, Advance Article [Overview of the project] [Problems that the invention aims to solve]

[0006] However, Non-Patent Document 1 has the drawback that catalysts containing Ir are expensive and costly. Furthermore, Non-Patent Document 1 only demonstrates the decomposition of lignin extracted from lignocellulosic biomass, and does not attempt to directly decompose lignin contained in lignocellulosic biomass without extraction. In fact, because the Ir-containing catalyst used in Non-Patent Document 1 has a large molecular size, it is not easy to access the lignin in lignocellulosic biomass, and direct decomposition is considered difficult.

[0007] Furthermore, Non-Patent Document 2 only describes the decomposition of a lignin model molecule, and does not attempt to directly decompose lignin contained in lignocellulosic biomass without extracting it.

[0008] Until now, no technology had been proposed that could directly and selectively degrade lignin from lignocellulose raw materials, which are complex plant materials containing three main components: cellulose, hemicellulose, and lignin (i.e., without the need to extract lignin from the lignocellulose raw material, and while leaving cellulose in the cell wall). If lignin contained in lignocellulose raw materials can be directly degraded, the cellulose microfibrils that were fixed by lignin will be released, and it is expected that this will contribute to the miniaturization of lignocellulose raw materials. In this case, it may be possible to utilize direct degradation as a pretreatment for lignocellulose raw materials, but no such technology had been proposed.

[0009] In view of the above issues, this disclosure aims to provide a method for decomposing lignin contained in lignocellulosic raw materials that can directly and selectively decompose lignin contained in lignocellulosic raw materials without extraction using an inexpensive catalyst, and that can also contribute to the miniaturization of lignocellulosic raw materials. Furthermore, this disclosure aims to provide a method for producing lignin decomposition products using the said lignin decomposition method. [Means for solving the problem]

[0010] In order to solve the above problems, the inventors diligently investigated and found that lignin contained in lignocellulose raw materials can be directly and selectively decomposed without extraction by light irradiation in the presence of a specific organic catalyst, which is a diaryl ketone. Furthermore, it was confirmed that the lignocellulose raw materials become finer during this process.

[0011] Based on the above findings, the gist of the present invention is as follows. [1] A mixing step of mixing a lignocellulose-based raw material mainly composed of cellulose, hemicellulose, and lignin, at least one organic catalyst selected from diaryl ketones, and an organic solvent to obtain a mixture, A step of irradiating the mixture with light to decompose the lignocellulosic raw material while detaching the lignin therefrom; A method for decomposing lignin contained in a lignocellulosic raw material, which has .

[0012] [2] The method according to [1] above, wherein the organic catalyst contains at least one selected from the group consisting of benzophenone and its analogs as the diaryl ketones.

[0013] [3] The method according to [2] above, wherein the organic catalyst contains at least one selected from the group consisting of the following PC1 to PC9. [Chemical formula]

[0014] [4] The method according to [3] above, wherein the organic catalyst contains at least one selected from the group consisting of PC1, PC3, and PC4.

[0015] [5] The method according to any one of [1] to [4] above, wherein the organic solvent contains at least one selected from the group consisting of dichloromethane, fluorobenzene, benzene, N,N-dimethylformamide, acetone, hexafluoro-2-propanol, and dichloroethane.

[0016] [6] The method according to [5] above, wherein the organic solvent contains at least one selected from the group consisting of dichloromethane, N,N-dimethylformamide, and hexafluoro-2-propanol.

[0017] [7] The method according to any one of [1] to [6] above, wherein the content of the lignocellulosic raw material in the mixture is 0.1% by mass or more and 50% by mass or less.

[0018] [8] The method according to any one of [1] to [7] above, wherein the light includes ultraviolet light and visible light having a wavelength of 350 nm or more and 450 nm or less.

[0019] [9] A method according to any one of [1] to [8] above, comprising a step of pulverizing or crushing a lignocellulosic material containing cellulose, hemicellulose, and lignin as main components to obtain the lignocellulosic raw material.

[0020]

[10] The method according to [9] above, wherein the lignocellulosic material contains at least one selected from the group consisting of woody biomass, herbaceous biomass, agricultural crops, leaf materials, fruit peels, cotton, and hemp.

[0021]

[11] A method according to any one of [1] to

[10] above, comprising a hydrochloric acid treatment step of contacting hydrochloric acid with the lignocellulosic raw material and then drying it prior to the mixing step.

[0022]

[12] The method according to any one of [1] to

[11] above, and Thereafter, separating the mixture into a solid and a dissolution liquid, and obtaining a lignin decomposition product from the dissolution liquid. A method for producing a lignin decomposition product, comprising the above steps.

Effect of the Invention

[0023] The method for decomposing lignin contained in a lignocellulosic raw material and the method for producing a lignin decomposition product according to the present disclosure can directly and selectively decompose the lignin contained in the lignocellulosic raw material without extraction using an inexpensive catalyst, and can also contribute to the refinement of the lignocellulosic raw material.

Brief Description of the Drawings

[0024] [Figure 1] An optical microscope image (left figure) and a scanning electron microscope image (right figure) of the reference example (Chinese fir powder). [Figure 2] An optical microscope image (left figure) and a scanning electron microscope image (right figure) of Example 1. [Figure 3] An optical microscope image (left figure) and a scanning electron microscope image (right figure) of Example 2. [Figure 4]These are stereomicroscope images (left) and scanning electron microscope images (right) of Example 3. [Figure 5] These are stereomicroscope images (left) and scanning electron microscope images (right) of Example 4. [Figure 6] These are stereomicroscope images (left) and scanning electron microscope images (right) of Example 5. [Figure 7] These are stereomicroscope images (left) and scanning electron microscope images (right) of Example 6. [Figure 8] These are stereomicroscope images (left) and scanning electron microscope images (right) of Example 7. [Figure 9] These are stereomicroscope images (left) and scanning electron microscope images (right) of Example 8. [Figure 10] These are stereomicroscope images (left) and scanning electron microscope images (right) of Example 9. [Figure 11] These are stereomicroscope images (left) and scanning electron microscope images (right) of Example 10. [Figure 12] These are stereomicroscope images (left) and scanning electron microscope images (right) of Example 11. [Figure 13] These are stereomicroscope images (left) and scanning electron microscope images (right) of Example 12. [Figure 14] These are stereomicroscope images (left) and scanning electron microscope images (right) of Example 13. [Modes for carrying out the invention]

[0025] The embodiments of this disclosure are described below. The configurations and combinations thereof in each embodiment of this disclosure are examples, and additions, omissions, substitutions, and other modifications can be made as appropriate without departing from the spirit of this disclosure. This disclosure is not limited to the embodiments.

[0026] Each aspect disclosed herein can be combined with any other features disclosed herein.

[0027] [Method for breaking down lignin contained in lignocellulose-based raw materials] A method according to one embodiment of the present disclosure is a method for decomposing lignin contained in a lignocellulosic raw material, comprising a mixing step of mixing a lignocellulosic raw material with a specific organic catalyst and an organic solvent to obtain a mixture, and a step of irradiating the mixture with light.

[0028] (Lignocellulose-based materials and lignocellulose-based raw materials) Lignocellulose is a plant material composed of cellulose, hemicellulose, and lignin, and has a complex, intertwined higher-order structure. In this specification, "lignocellulose-based material" and "lignocellulose-based raw material" refer to materials that mainly contain lignocellulose. Furthermore, in this specification, "lignocellulose-based raw material" refers to a raw material subjected to the processing specified in this disclosure, and is preferably obtained by crushing or pulverizing a lignocellulose-based material. However, in this embodiment, crushing or pulverization is not essential, and any lignocellulose-based material having dimensions suitable for the processing specified in this disclosure can be used as a lignocellulose-based raw material as is.

[0029] The lignocellulosic material used in this embodiment is not particularly limited, but may include one or more selected from the group consisting of woody biomass, plant biomass, crops, foliage, fruit peels, cotton, and hemp.

[0030] The woody biomass may be coniferous trees such as Japanese cedar, cypress, and Japanese red pine, or broad-leaved trees such as eucalyptus and beech, and one or more of these may be used. From the viewpoint of effective utilization of dwindling forest resources, woody biomass that was previously discarded can be suitably used. For example, wood powder generated during lumbering, or small pieces (chips) that cannot be used as scraps may be used in this embodiment. The woody biomass may be natural wood or sawn lumber cut from natural wood. There are no particular limitations on the shape of the woody biomass, and it can be used in appropriate forms such as plates, chips, or powder.

[0031] However, kraft pulp, which is produced by chemically processing wood chips to break down lignin and hemicellulose and free up cellulose fibers, contains a small amount of lignin but is not a lignocellulose material. Also, pulp contains lignin, but because the strong bonds between hemicellulose, cellulose, and lignin are largely broken down, it is not a lignocellulose material.

[0032] Examples of herbaceous biomass include sugarcane bagasse, rice straw, wheat, wheat bran, tomato, onion, and moso bamboo, and one or more of these may be used.

[0033] It should be noted that some edible grains derived from plants do not contain any lignin at all. For example, wheat flour is one such example. This is not a lignocellulosic material. On the other hand, threshed husks (for example, rice or wheat husks) contain lignocellulose and correspond to the lignocellulosic material in this disclosure.

[0034] The lignocellulose content (i.e., the total content of cellulose, hemicellulose, and lignin) in a lignocellulose-based material is not particularly limited. The lignin content in a lignocellulose-based material is preferably 10% by mass or more, more preferably 20% by mass or more, and even more preferably 25% by mass or more. From the viewpoint of eliminating the need for a lignocellulose extraction step from the lignocellulose-based material, the lignin content in a lignocellulose-based material is preferably 50% by mass or less.

[0035] The size of the lignocellulosic raw material used in the processing specified in this disclosure is not particularly limited, but from the viewpoint of promoting the progress of the reaction, the maximum diameter in plan view may be 50 mm or less, 40 mm or less, or 30 mm or less. On the other hand, from the viewpoint of dust prevention and the reduction of energy required for fine grinding, the size of the lignocellulosic raw material is preferably 0.1 mm or more in maximum diameter in plan view. Furthermore, from the viewpoint of promoting the progress of the reaction, it is preferable to use the lignocellulosic raw material that has passed through a sieve with a nominal mesh size of 3 mm, as specified in JIS Z 8801:2019, and more preferably the lignocellulosic raw material that has passed through a sieve with a nominal mesh size of 1 mm. Furthermore, from the viewpoint of dust prevention and the reduction of energy required for fine grinding, it is preferable to use the lignocellulosic raw material that has not passed through a sieve with a nominal mesh size of 0.1 mm.

[0036] (Mixing process) In this embodiment, first, a lignocellulose-based raw material mainly consisting of cellulose, hemicellulose, and lignin is mixed with at least one organic catalyst selected from diaryl ketones and an organic solvent to obtain a mixture.

[0037] <Organic catalyst> At least one organocatalyst selected from diaryl ketones exhibits favorable catalytic activity during lignin decomposition by light irradiation by promoting proton-bonded electron transfer (PCET) without the use of a base, thereby enabling β-cleavage of the substrate, through the formation of a hydrogen bond network between the excited triplet state of the organocatalyst and the hydroxyl group of the substrate. Therefore, lignin can be decomposed while being removed from lignocellulosic raw materials.

[0038] Examples of diaryl ketones include not only common diaryl ketones, but also fluorenone derivatives, quinones, bisaryl ketones, benzophenones, acridone derivatives, xanthone derivatives, thioxanthone derivatives, and silaxanthone derivatives.

[0039] Examples of aryl groups in diarylketones include naphthyl, anthryl, thienyl, pyridyl, furyl, quinolyl, phenanthryl, benzofuranyl, and benzthiazolyl groups. These aryl groups may also have substituents such as methyl (-CH3), ethyl (-C2H5), propyl (-C3H7), butyl (-C4H9), methoxy (-OCH3), ethoxy (-OC2H5), hydroxyl (-OH), amino (-NH2), nitro (-NO2), carbonyl (-C=O), carboxyl (-COOH), cyano (-CN), and halogen (-X, where X includes fluorine, chlorine, bromine, and iodine). Specific examples of compounds include 1-naphthyl-2-thienyl ketone, 2-naphthyl-3-anthryl ketone, 3-phenanthryl-4-furyl ketone, and 9-phenanthryl-4-quinolyl ketone.

[0040] Examples of fluorenone derivatives include those having a naphthyl, thienyl, pyridyl, or phenanthryl group attached to the aryl group. Furthermore, these aryl groups may have substituents such as methyl, ethyl, propyl, butyl, methoxy, ethoxy, hydroxyl, amino, nitro, carbonyl, carboxyl, cyano, or halogen groups. Specific examples of compounds include 2-naphthyl-3-fluorenone, 3-pyridyl-9-fluorenone, 4-phenanthryl-9-fluorenone, and 9-fluorenone-2-carboxylic acid.

[0041] Examples of quinones include anthraquinone, phenanthrenequinone, naphthaquinone, pyrenequinone, and benzoanthraquinone. Furthermore, these aryl groups may have substituents such as methyl, ethyl, propyl, butyl, methoxy, ethoxy, hydroxyl, amino, nitro, carbonyl, carboxyl, cyano, and halogen groups. Specific examples of compounds include 1,4-anthraquinone-2-sulfonic acid, 2-phenanthryl-anthraquinone, 3-naphthyl-phenanthrenequinone, and 9,10-phenanthrenequinone.

[0042] Examples of bisaryl ketones include those having naphthyl, anthryl, phenanthryl, pyrene, and pyridyl groups. These aryl groups may also have substituents such as methyl, ethyl, propyl, butyl, methoxy, ethoxy, hydroxyl, amino, nitro, carbonyl, carboxyl, cyano, and halogen groups. Specific examples of compounds include 1,1'-naphthyl ketone, 2,2'-bis(phenanthryl) ketone, 3,3'-bis(pyridyl) ketone, and 4,4'-bis(anthryl) ketone.

[0043] Examples of benzophenones and their derivatives include substituents bonded to the phenyl group such as methyl (-CH3), ethyl (-C2H5), methoxy (-OCH3), amino (-NH2), hydroxyl (-OH), halogen (-X, where X includes fluorine, chlorine, bromine, and iodine), trifluoromethyl (-CF3), nitro (-NO2), carboxyl (-COOH), sulfone (-SO3H), and phosphonyl (-PO3H2). Specific examples of these compounds include 1-naphthylbenzophenone, 2-pyridylbenzophenone, 4-hydroxybenzophenone, and 9-anthrylbenzophenone.

[0044] Examples of acridones and their derivatives include those having a methyl group (-CH3), ethyl group (-C2H5), methoxy group (-OCH3), amino group (-NH2), hydroxyl group (-OH), halogen group (-X, where X includes fluorine, chlorine, bromine, and iodine), trifluoromethyl group (-CF3), nitro group (-NO2), and carboxyl group (-COOH). Specific examples of compounds include 2-methylacridone, 4-phenylacridone, 2,4-difluoroacridone, and 2,4-dinitroacridone.

[0045] Examples of xanthones and their derivatives include those having a methyl group (-CH3), ethyl group (-C2H5), methoxy group (-OCH3), amino group (-NH2), hydroxyl group (-OH), halogen group (-X, where X includes fluorine, chlorine, bromine, and iodine), trifluoromethyl group (-CF3), nitro group (-NO2), and carboxyl group (-COOH). Specific examples of compounds include 2,4-dimethylxanthone, 4-phenylxanthone, 2,4-dibromoxanthone, and 2,4-dinitroxanthone.

[0046] Thioxanthones and their derivatives include those having a methyl group (-CH3), ethyl group (-C2H5), methoxy group (-OCH3), amino group (-NH2), hydroxyl group (-OH), halogen group (-X, where X includes fluorine, chlorine, bromine, and iodine), trifluoromethyl group (-CF3), nitro group (-NO2), and carboxyl group (-COOH). Specific examples of compounds include 2-methylthioxanthone, 4-hydroxythioxanthone, 2,4-difluorothioxanthone, and 2,4-dinitrothioxanthone.

[0047] Silaxanthones and their derivatives include those having a methyl group (-CH3), ethyl group (-C2H5), methoxy group (-OCH3), amino group (-NH2), hydroxyl group (-OH), halogen group (-X, where X includes fluorine, chlorine, bromine, and iodine), trifluoromethyl group (-CF3), nitro group (-NO2), and carboxyl group (-COOH). Specific examples of compounds include 9H-silaxanthen-9-one, 2-phenyl-9H-silaxanthen-9-one, 2,4-dibromo-9H-silaxanthen-9-one, and 2,4-dinitro-9H-silaxanthen-9-one.

[0048] From the viewpoint of suitably obtaining the effects of this disclosure, the organic catalyst used in this embodiment preferably includes at least one selected from the group consisting of benzophenone and its analogs as diaryl ketones, and more preferably includes at least one selected from the group consisting of PC1 to PC9 as follows. PC7 is benzophenone (diphenyl ketone), and the other organic catalysts are analogs of benzophenone. Among these, the effects of this disclosure can be obtained particularly well when the organic catalyst includes at least one selected from the group consisting of PC1, PC3, and PC4. [ka]

[0049] The organic catalyst used in this embodiment preferably has an absorption maximum at 300 nm or higher, and more preferably at 350 nm or higher. Furthermore, the organic catalyst used in this embodiment preferably has an absorption maximum at 700 nm or lower, and more preferably at 500 nm or lower. As long as the absorption maximum is within this range, the organic catalyst can efficiently absorb ultraviolet and visible light, as described above, and can fully exert its effect as a photocatalyst that promotes the reaction, thereby particularly fully obtaining the effects of this disclosure. Of the above PC1 to PC9, all except PC7 have an absorption maximum at 350 nm or higher.

[0050] The organic catalyst used in this embodiment preferably has a molecular weight of 200 to 500, and more preferably 300 or less. An organic catalyst with a molecular weight within this range has a sufficiently small molecular size, making it easy to access lignin in the lignocellulosic raw material, and thus allowing the effects of this disclosure to be obtained particularly fully. Of the above PC1 to PC9, catalysts other than PC5 and PC9 have a molecular weight of 200 to 300.

[0051] <Thiol cocatalyst> A thiol may be added to the mixture as a cocatalyst. By adding a thiol, the effects of the present disclosure can be obtained more fully. Examples of thiols that can be used in this embodiment include alkyl thiols such as methyl thiol (CH3SH), ethyl thiol (C2H5SH), propyl thiol (C3H7SH), butyl thiol (C4H9SH), isopropyl thiol (C3H7SH), hexane thiol (C6H 13 SH), and 2-methylthiophenol (C6H4(CH3)SH); aromatic thiols such as benzyl thiol (C6H5CH2SH), benzenethiol (C6H5SH), naphthalene-1-thiol (C 10 H9SH), naphthalene-2-thiol (C 10 H9SH), toluenethiol (C6H4(CH3)SH), 4-methylbenzenethiol (C6H4(CH3)SH), triphenylmethanethiol, and 2,4,6-triisopropylbenzenethiol; dithiols such as 1,2-ethanedithiol (C2H4(SH)2), 1,3-propanedithiol (C3H6(SH)2), and 1,4-butanedithiol (C4H8(SH)2); long-chain alkyl thiols such as octadecyl thiol (C 18 H 39 SH), nonadecyl thiol (C 19 H 41 SH), and dicyclohexyl thiol (C 12 H 24 S); silane thiols such as trimethylsilane thiol, triethylsilane thiol, tripropylsilane thiol, triisopropylsilane thiol, and triphenylsilane thiol; 1-adamantanethiol; biphenyl-4-thiol; 1-phenylethyl mercaptan, etc. One or more selected from the group consisting of these can be used.

[0052] <Organic solvent> The organic solvent used in this embodiment is not particularly limited, but it is preferable to include at least one selected from the group consisting of dichloromethane, fluorobenzene, benzene, N,N-dimethylformamide, acetone, hexafluoro-2-propanol, and dichloroethane. Among these, the effects of this disclosure can be obtained particularly well when the organic solvent includes at least one selected from the group consisting of dichloromethane, N,N-dimethylformamide, and hexafluoro-2-propanol.

[0053] <Mixing conditions> From the viewpoint of fully obtaining the effects of this disclosure, the amount of organic catalyst added to the mixture is preferably 0.001 mmol or more, and more preferably 0.01 mmol or more, per 1 g of lignocellulosic raw material in the mixture. On the other hand, from the viewpoint of economic efficiency for industrial use, the amount of organic catalyst added to the mixture is preferably 1.5 mmol or less, more preferably 1.2 mmol or less, even more preferably 0.5 mmol or less, and most preferably 0.3 mmol or less, per 1 g of lignocellulosic raw material in the mixture.

[0054] When thiols are added, the amount of thiol added to the mixture is preferably 0.001 mmol or more, and more preferably 0.01 mmol or more, per 1 g of lignocellulosic raw material in the mixture, from the viewpoint of obtaining the effects of this disclosure to the fullest extent. On the other hand, from the viewpoint of economic efficiency for industrial use, the amount of thiol added to the mixture is preferably 1.5 mmol or less, more preferably 1.2 mmol or less, even more preferably 0.5 mmol or less, and most preferably 0.3 mmol or less, per 1 g of lignocellulosic raw material in the mixture.

[0055] The content of lignocellulosic raw materials in the mixture is preferably 50% by mass or less, more preferably 30% by mass or less, even more preferably 20% by mass or less, even more preferably 10% by mass or less, and most preferably 5% by mass or less, from the viewpoint of ensuring a sufficient amount of organic solvent so that the organic catalyst can adequately access the lignin in the lignocellulosic raw materials and transmit light to the inside of the liquid. On the other hand, if the content of lignocellulosic raw materials is too low, the amount of lignin decomposition will not be sufficient, and from the viewpoint of reducing solvent usage, the content of lignocellulosic raw materials in the mixture is preferably 0.1% by mass or more, and more preferably 1% by mass or more.

[0056] The mixing method is not particularly limited, but for example, one method involves placing lignocellulose raw materials, an organic solvent, and an organic catalyst into a vial, optionally adding thiols, adding a magnetic stirrer bar, and mixing with a magnetic stirrer. The environment during mixing is not particularly limited and can be at room temperature. Furthermore, the mixing time is not particularly limited as long as the mixture is sufficiently mixed.

[0057] (Light irradiation process) In this embodiment, the mixture is then irradiated with light to decompose the lignocellulosic raw material while detaching lignin. The method of light irradiation is not particularly limited, but for example, a light source can be placed around the vial containing the mixture, and the light emitted from the light source can be irradiated onto the mixture from the side of the vial. The environment during light irradiation is not particularly limited and can be at room temperature. From the viewpoint of ensuring that the reaction proceeds uniformly, it is preferable to keep the mixture constantly stirred during light irradiation.

[0058] The irradiated light preferably includes ultraviolet and visible light with wavelengths between 350 nm and 450 nm. This wavelength range includes blue and violet light from the visible spectrum, as well as ultraviolet light. This wavelength range effectively separates and decomposes lignin contained in lignocellulose raw materials. For example, an LED with a central wavelength of 390 nm can be used.

[0059] From the viewpoint of fully obtaining the effects of this disclosure, it is preferable to ensure a sufficient amount of light is irradiated onto the mixture.

[0060] From the viewpoint of fully obtaining the effects of this disclosure, the irradiation time is preferably 1 hour or more, more preferably 5 hours or more, and even more preferably 10 hours or more. On the other hand, if the irradiation time is too long, the reaction may saturate or side reactions may proceed, so the irradiation time is preferably 40 hours or less.

[0061] (Effects of this disclosure) According to the method disclosed herein, lignin present in the form of a lignocellulosic raw material can be directly and selectively decomposed without extraction by light irradiation in the presence of a specific inexpensive organic solvent. Furthermore, the separation of lignin from the lignocellulosic raw material allows for the lignocellulosic raw material to be refined. This is preferable because it can also serve as a pretreatment for the lignocellulosic raw material.

[0062] (Optional hydrochloric acid treatment step) In this embodiment, it is preferable to perform a hydrochloric acid treatment step prior to the mixing step, in which the lignocellulosic raw material is brought into contact with hydrochloric acid and then dried. By swelling the cell walls with hydrochloric acid, the detachment of lignin from the lignocellulosic raw material can be performed more effectively. The hydrochloric acid used is not particularly limited, and any commercially available hydrochloric acid as a general reagent may be used. The amount of hydrochloric acid supplied to the lignocellulosic raw material is not particularly limited as long as the lignocellulosic raw material is in sufficient contact with the hydrochloric acid. From the viewpoint of obtaining the full effect of this treatment, the treatment time with hydrochloric acid is preferably 1 minute or more, and more preferably 10 minutes or more. On the other hand, if the treatment time is too long, the effect will saturate, so it is preferable that the treatment time be 90 minutes or less.

[0063] [Method for producing lignin hydrolysates] A method for producing lignin degradation products according to one embodiment of the present disclosure comprises a method for decomposing lignin contained in a lignocellulosic raw material according to the above embodiment of the present disclosure, and a step of subsequently separating the mixture into a solid and a solution, and obtaining lignin degradation products from the solution. The separation method is not particularly limited, but for example, one method is to put the mixture after light irradiation into a Pasteur pipette packed with cotton at the tip and filter it. The lignin degradation products produced by the decomposition of lignin in the lignocellulosic raw material are contained in the solution when the mixture after light irradiation is separated into a solid and a solution. Therefore, lignin degradation products can be obtained from the solution.

[0064] Examples of lignin degradation products include phenols, aromatic aldehydes, aromatic ketones, aromatic alcohols, and aromatic carboxylic acids. Specifically, these include 3,4-dihydroxybenzaldehyde, 3,4-dihydroxybenzaldehyde, 3,4-dihydroxybenzoic acid, 4-(hydroxymethyl)benzene-1,2-diol, 1-(4-hydroxy-3-methoxyphenyl)ethanone, 4-hydroxy-3-methoxybenzaldehyde, 4-hydroxy-3-methoxybenzoic acid, 4-(hydroxymethyl)-2-methoxyphenol, 1-(4-hydroxyphenyl)ethanone, 4-hydroxybenzaldehyde hydroxybenzoic acid, 4-(hydroxymethyl)phenol, and 1-(4-hydroxy-3,5-dimethoxybenzoic acid). Examples include phenyl)ethanone, 4-hydroxy-3,5-dimethoxybenzaldehyde, 4-hydroxy-3,5-dimethoxybenzoic acid, 4-(hydroxymethyl)-2,6-dimethoxyphenol, 2-methoxyphenol, 2,6-dimethoxyphenol, phenol, 1-(3,4-dihydroxy-5-methoxyphenyl)ethanone, 3,4,5-trihydroxybenzaldehyde, 3,4,5-trihydroxybenzoic acid, 5-(hydroxymethyl)benzene-1,2,3-triol, benzene-1,2,3-triol, pyrocatechol, and analogs of these compounds. Examples of analogues include compounds having the above compound as a substructure, compounds in which the hydrogen of the phenol group in the above compound is replaced by other substituents, 2 to 50-mers of the above compound, and polymers having the above compound as a substructure with a number average molecular weight of 40,000 or less, 30,000 or less, 10,000 or less, 5,000 or less, or 3,000 or less.

[0065] The method for extracting lignin degradation products from a dissolution is not particularly limited, but examples include liquid-liquid extraction, steam distillation, column chromatography, distillation, molecular sieving, precipitation, membrane separation, and methods using membranes that allow only specific substances to pass through.

[0066] Furthermore, the solid material separated from the mixture after light irradiation contains residual cellulose and lignin that were not decomposed in the lignocellulosic raw material. By measuring the lignin content in the solid material and confirming that it is lower than the lignin content in the lignocellulosic raw material before treatment, it is possible to determine that lignin has been removed from the lignocellulosic raw material. In addition, by observing the solid material under a microscope, it is possible to determine that the lignocellulosic raw material has been micronized. [Examples]

[0067] The present disclosure will be described in more detail below with reference to examples. However, the present disclosure is not limited to the following examples.

[0068] [Example 1] A 5 ml vial (Mighty Vial No. 1) was prepared. At room temperature (25°C) and under an Ar atmosphere (in a glove box), 83.3 mg of air-dried cedar wood powder (1000 μm pass pulverized material) as a lignocellulose raw material, 2.7 g of dichloromethane as an organic solvent, 0.02 mmol of organocatalyst PC3, and 0.05 mmol of 2,4,6-triisopropylbenzenethiol were added to the vial. A magnetic stirrer bar was added, and the cedar wood powder, organic solvent, organocatalyst, and thiol were mixed using a magnetic stirrer to obtain a mixture.

[0069] The mixture was irradiated with a blue LED (Kessil PR-160, center wavelength: 390nm) at a maximum output of 52W for 20 hours. The blue LED was placed 0.5cm away from the side of the vial, and the light was directed towards the mixture inside the vial. The mixture was also continuously stirred using a magnetic stirrer.

[0070] The mixture after light irradiation was placed into a Pasteur pipette fitted with cotton at the tip and separated into solid and soluble matter. The solid matter was washed with dichloromethane and vacuum-dried to obtain dried solid matter. The soluble matter was vacuum-dried to obtain the soluble matter.

[0071] [Examples 2-7] Dried solids and dissolved products were obtained in the same manner as in Example 1, except that the organic solvent was changed to the type shown in Table 1.

[0072] [Examples 8-12] Dried solids and dissolved products were obtained in the same manner as in Example 1, except that the type of organic catalyst was changed to the type shown in Table 1. Table 1 also includes the absorption maxima for each type of organic catalyst.

[0073] [Example 13] A 5 ml vial (Mighty Vial No. 1) was prepared. At room temperature (25°C), 83.3 mg of air-dried cedar wood powder (1000 μm pass pulverized material) was added to the vial as a lignocellulose raw material. Ten drops of hydrochloric acid (37%) were added to the cedar wood powder in the vial, and it was left at room temperature for 1 hour, after which it was vacuum-dried. Subsequently, at room temperature (25°C) and under an Ar atmosphere (in a glove box), 4.0 g of dichloroethane as an organic solvent, 0.02 mmol of organic catalyst PC1, and 0.05 mmol of the same thiol as in Example 1 were added to the vial containing the hydrochloric acid-treated cedar wood powder. A magnetic stirrer bar was added, and the cedar wood powder, organic solvent, organic catalyst, and thiol were mixed using a magnetic stirrer to obtain a mixture.

[0074] Two blue LEDs (Kessil PR-160, center wavelength: 390nm) were used to irradiate the mixture with light at a maximum output of 52W for 20 hours. The two blue LEDs were positioned 0.5 cm away from both sides of the vial, and the light was directed towards the mixture inside the vial. The mixture was also continuously stirred using a magnetic stirrer.

[0075] The mixture after light irradiation was placed into a Pasteur pipette fitted with cotton at the tip and separated into solid and soluble matter. The solid matter was washed with dichloromethane and vacuum-dried to obtain dried solid matter. The soluble matter was vacuum-dried to obtain the soluble matter.

[0076] (Measurement of the lignin content remaining in the dried solid material) The lignin content of the dried solid obtained in each example was measured according to the following procedure, and the results are shown in Table 1. For reference, the lignin content of cedar wood flour that had not undergone the treatment described in each example was also measured and is shown in Table 1. <Instructions> 1. 20 mg of the dried solid was mixed with 0.3 mL of 72% by mass sulfuric acid and stirred at 30°C for 1 hour. 2. 8.4 mL of water was added, and the mixture was heated and decomposed in an autoclave at 120°C for 1 hour. 3. The reaction product after thermal decomposition was centrifuged at 3500 rpm for 10 minutes to separate the supernatant from the precipitate. The precipitate is thought to be lignin remaining in the dried solid. The precipitate was washed with water until neutral, then freeze-dried for 12 hours or more to completely dry it, and its mass was measured. The lignin content (mass %) was determined by dividing the obtained mass by the pre-treatment mass of 20 mg.

[0077] As is clear from Table 1, in Examples 1 to 12, the lignin content in the dried solid was lower than the 34% lignin content in the reference example. This indicates that lignin was detached from the cedar wood powder by light irradiation and moved into the dissolution solution.

[0078] (Microscopic observation of dried solid material) Morphological observations were carried out on Chinese fir powder without undergoing the treatment according to each embodiment and the dried solids obtained in Examples 1 to 13 using a stereomicroscope and a scanning electron microscope. Images obtained by observing under the condition of a magnification of 2 times using a stereomicroscope (SMZ1500 manufactured by Nikon Corporation) are shown in the left figures of FIGS. 1 to 14. Further, images obtained by observing at a magnification of 100 times under the conditions of a low vacuum mode and an acceleration voltage of 15.0 kV using a tabletop scanning electron microscope (JCM-7000 manufactured by JEOL Ltd.) are shown in the right figures of FIGS. 1 to 14.

[0079] In the untreated Chinese fir powder, fiber cells called false ducts are in close contact with each other, and there are masses with a width of 500 μm or more. In contrast, in the dried solids of Examples 1 to 13, many pit holes existing on the cell wall surface are exposed. This is because the binding between fiber cells is weakened by the desorption of lignin, the fiber cells are peeled off, and more pit holes are exposed due to the desorption of lignin around the pit holes. Among them, particularly in Examples 1, 8, 11, and 13, the refinement in the direction perpendicular to the fiber also progresses, indicating that further pulverization is progressing. Further, from the results of the microscopic observations of Examples 1 to 13, since the cell wall structure is not collapsed, it is suggested that cellulose mainly constituting the cell wall is not decomposed and remains.

[0080] (Analysis of the lysate: Molecular weight measurement) The lysates obtained in Examples 1, 11, and 13 were dissolved in an eluent, and molecular weight measurement was carried out under the following conditions. The number average molecular weight (polystyrene conversion value) was determined by the GPC method. <GPC measurement conditions> Apparatus: LC-4000 HPLC (manufactured by JASCO Corporation) Column: GPC KD-806M (300 × 8.0 mm) (manufactured by Shodex) Guard column: GPC KD-G 4A (10 × 4.6 mm) (manufactured by Shodex) Detector: UV detector (250 nm) Eluent: 1% (w / v) LiCl / DMAc Calibration curve: Primary approximation using standard polystyrene

[0081] The number-average molecular weight for Example 1 was 1.0 × 10⁶. 3 Example 11 is 1.0 × 10 3 Example 13 is 2.7 × 10 3 This indicates that a low molecular weight compound with absorption at 250 nm is present in the solution. Since sugars do not have absorption at 250 nm, the detected compound is derived from a component other than cellulose or hemicellulose. Among the components other than cellulose and hemicellulose, lignin and extracted components are considered to be compounds with absorption at 250 nm. Since the extracted component has a low molecular weight, the number-average molecular weight above 1000 was calculated to determine the molecular weight of the lignin-derived component. Example 1 was 4.2 × 10⁻⁶. 3 Example 11 is 4.1 × 10 3 Example 13 is 6.3 × 10 3 Therefore, it is suggested that lignin is broken down to a molecular weight (number-average molecular weight) of at least 10,000 or less and eluted as a dissolved substance.

[0082] [Table 1] [Industrial applicability]

[0083] This disclosure can be applied to the extraction of useful molecules by decomposing lignin contained in lignocellulosic raw materials, or to the pretreatment of lignocellulosic raw materials.

Claims

1. A mixing step of mixing a lignocellulose-based raw material mainly composed of cellulose, hemicellulose, and lignin, at least one organic catalyst selected from diaryl ketones, and an organic solvent to obtain a mixture, A step of irradiating the mixture with light to decompose the lignocellulose raw material while removing the lignin, A method for decomposing lignin contained in lignocellulose raw materials, comprising the following characteristics.

2. The method according to claim 1, wherein the organic catalyst comprises at least one selected from the group consisting of benzophenone and its analogs as the diaryl ketones.

3. The method according to claim 2, wherein the organic catalyst comprises at least one selected from the group consisting of the following PC1 to PC9. 【Chemistry 1】

4. The method according to claim 3, wherein the organic catalyst comprises at least one selected from the group consisting of PC1, PC3, and PC4.

5. The method according to claim 1, wherein the organic solvent comprises at least one selected from the group consisting of dichloromethane, fluorobenzene, benzene, N,N-dimethylformamide, acetone, hexafluoro-2-propanol, and dichloroethane.

6. The method according to claim 5, wherein the organic solvent comprises at least one selected from the group consisting of dichloromethane, N,N-dimethylformamide, and hexafluoro-2-propanol.

7. The method according to claim 1, wherein the content of the lignocellulosic raw material in the mixture is 0.1% by mass or more and 50% by mass or less.

8. The method according to claim 1, wherein the light includes ultraviolet light and visible light having wavelengths of 350 nm to 450 nm.

9. The method according to claim 1, further comprising the step of crushing or pulverizing a lignocellulose-based material mainly composed of cellulose, hemicellulose, and lignin to obtain the lignocellulose-based raw material.

10. The method according to claim 9, wherein the lignocellulose material comprises at least one selected from the group consisting of woody biomass, plant biomass, crops, foliage, fruit peels, cotton, and hemp.

11. The method according to claim 1, further comprising a hydrochloric acid treatment step in which the lignocellulose raw material is brought into contact with hydrochloric acid and then dried prior to the mixing step.

12. A method according to any one of claims 1 to 11, Subsequently, the mixture is separated into a solid and a solution, and a lignin decomposition product is obtained from the solution. A method for producing lignin degradation products having the following characteristics.

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