Method for producing lignin decomposition product, and method for producing methanol

Abstract

This method for producing a lignin decomposition product has a step for bringing a substrate including at least one selected from the group consisting of lignin and lignin derivatives into contact with a catalyst containing at least one selected from the group consisting of divalent and trivalent metal ions to obtain a lignin decomposition product containing methanol, wherein in said step, the light intensity of visible light with which a mixture containing the substrate and the catalyst is irradiated is less than 10 mW / cm3.

Description

Method for producing lignin decomposition product and method for producing methanol

[0001] The present disclosure relates to a method for producing a lignin decomposition product and a method for producing methanol.

[0002] Toward the realization of a carbon-neutral society, methods for obtaining useful chemical substances by decomposing lignin, a renewable biomass resource, are being investigated. Patent Document 1 discloses a lignin decomposition method in which lignin is reacted with a transition metal complex catalyst and hydrogen peroxide to obtain various decomposition products. Patent Document 2 describes that an iron ion extract of lignin functions as a cell growth inhibitor. Patent Document 3 discloses a lignin decomposition catalyst in which a copper compound is immobilized on a metal substrate.

[0003] International Publication No. 2019 / 203051 Japanese Patent Application Laid-Open No. 2020-023583 International Publication No. 2022 / 149532

[0004] Cellulose and hemicellulose, which account for two-thirds of wood components, are used as raw materials for pulp. On the other hand, lignin, which accounts for the remaining one-third of wood components, is a rigid and stable substance with a complex chemical structure and is therefore used as a heat resource. Therefore, decomposing lignin and converting it into other active components leads to the effective use of biomass resources. The present disclosure provides a method for producing a lignin decomposition product that can decompose lignin in a simple process to obtain a lignin decomposition product containing methanol, and a method for producing methanol.

[0005] One aspect of the present disclosure provides a method for producing a lignin decomposition product containing methanol by contacting a substrate containing at least one selected from the group consisting of lignin and lignin derivatives with a catalyst containing at least one selected from the group consisting of divalent and trivalent metal ions, wherein the light intensity of visible light irradiated onto a mixture containing the substrate and the catalyst in the step is 10 mW / cm ３ The present invention provides a method for producing a lignin decomposition product, wherein the amount of the decomposition product is less than 1000 kJ / kg.

[0006] The method for producing a lignin decomposition product described above can obtain a lignin decomposition product containing methanol by contacting a substrate containing at least one selected from the group consisting of lignin and lignin derivatives with a metal ion catalyst. This method for producing a lignin decomposition product can decompose lignin to obtain a lignin decomposition product containing methanol in a simple process without irradiating the substrate with high-intensity visible light.

[0007] One aspect of the present disclosure relates to a method for producing methanol by contacting a substrate containing at least one selected from the group consisting of lignin and lignin derivatives with a catalyst containing at least one selected from the group consisting of divalent and trivalent metal ions, wherein the light intensity of visible light irradiated onto a mixture containing the substrate and the catalyst in the step is 10 mW / cm ３ The present invention provides a method for producing methanol in which the reaction temperature is less than 100°C.

[0008] The above-described method for producing methanol can obtain methanol by contacting a substrate containing at least one selected from the group consisting of lignin and lignin derivatives with a metal ion catalyst. This method for producing methanol can decompose lignin to obtain methanol in a simple process without irradiating the substrate with high-intensity visible light. Furthermore, the production of other low-molecular-weight compounds can be reduced, allowing for selective production of methanol.

[0009] The present disclosure can provide a method for producing a lignin decomposition product, which can decompose lignin in a simple process to obtain a lignin decomposition product, and a method for producing methanol.

[0010] (a) is a diagram showing an example of the results of gas chromatography of a recovered product obtained by vacuum distillation of a lignin decomposition product. (b) is a diagram showing an example of the results of mass spectrometry of (a). (a) is a diagram showing the change in absorption spectrum at wavelengths of 250 to 1000 nm when 0 to 6 equivalents of guaiacol are added to iron ions. (b) is a diagram plotting the relationship between absorbance at a wavelength of 470 nm and guaiacol equivalent.

[0011] Embodiments of the present disclosure will be described below. However, the following embodiments are merely examples for explaining the present disclosure and are not intended to limit the present disclosure to the following content. In the description, the same reference numerals will be used for identical elements or elements having the same functions, and redundant explanations will be omitted where appropriate. Furthermore, unless otherwise specified, positional relationships such as up, down, left, and right will be based on the positional relationships based on the orientation of the reference numerals shown in the drawings. The dimensional ratios of each element are not limited to those shown. The numerical ranges exemplified as "a to b" are numerical ranges inclusive of a and b, with a lower limit being a and an upper limit being b. The present disclosure also includes cases where the upper or lower limit of each numerical range is replaced with the numerical value of any of the examples. When multiple materials are exemplified, one of the materials may be used alone, or multiple materials may be used in combination.

[0012] A method for producing a lignin degradation product according to one embodiment includes a step of contacting a substrate containing at least one selected from lignin and lignin derivatives with a catalyst containing at least one selected from the group consisting of divalent and trivalent metal ions to obtain a lignin degradation product containing methanol. By including such a step, lignin can be decomposed to obtain a lignin degradation product in a simple process.

[0013] The above step may be performed with or without irradiation of visible light. The light intensity of the visible light irradiated onto the mixture containing the substrate and the catalyst contained in the reaction vessel is 10 mW / cm. ３ Less than 5 mW / cm ３ Below, 2mW / cm ３ Below, 1mW / cm ３ Below, 0.5mW / cm ３ Below, 0.1mW / cm ３ or less, or 0 mW / cm ３ Such light intensity per volume may be calculated by dividing the light intensity [W] irradiated onto a mixture containing a substrate and a catalyst by the volume [cm ３] can be obtained by dividing by the lignin decomposition product (methanol). When the light intensity of the visible light is within the above range, it is not necessary to irradiate the mixture with high-intensity visible light, and lignin can be decomposed in a simple process to obtain a lignin decomposition product containing methanol. Furthermore, the above process may be performed while blocking the light irradiated onto the mixture. Since a catalytic reaction proceeds in the mixture, the mixture is also referred to as a reaction liquid. The mixture may be a mixed liquid or a dispersion in which a solid component is dispersed in a liquid phase.

[0014] The above process is carried out under conditions where the irradiance of visible light is 10 mW / cm ２ Less than 5 mW / cm ２ Below, 2mW / cm ２ Below, 1mW / cm ２ Below, 0.5mW / cm ２ Below, 0.1mW / cm ２ or less, or 0 mW / cm ２ The process may be carried out in an environment where the irradiance is within the above range. The irradiance refers to the light intensity irradiated per unit area of ​​the object. When the irradiance is within the above range, it is not necessary to irradiate visible light with a high light intensity, and it is possible to decompose lignin in a simple process to obtain a lignin decomposition product containing methanol. Furthermore, the process may be carried out in a light-blocking environment.

[0015] In a modified example of this embodiment, for the purpose of inspecting the inside of the reaction vessel, visible light may be irradiated at an intensity and for a duration that does not contribute to the decomposition of lignin. The light source of visible light in this disclosure is not particularly limited, and examples include sunlight, fluorescent lamps, LED lamps, and lighting. Visible light in this disclosure is light in the wavelength range of 385 to 740 nm.

[0016] The substrate containing at least one selected from lignin and lignin derivatives may be at least one selected from the group consisting of a solid containing lignin, a solid containing a lignin derivative, a liquid containing lignin (water-soluble lignin), and black liquor. The lignin derivative may be lignin that has been subjected to some chemical treatment, such as introduction of a functional group or substitution of atoms.

[0017] Black liquor is a waste liquor generated during the production of pulp from wood and contains woody components such as lignin. Black liquor can be obtained, for example, by a cooking method. The raw material used to produce black liquor may be any hardwood or softwood, and is not particularly limited. The cooking method may be any chemical pulping method, such as KP cooking, modified KP cooking, AP cooking, and SP cooking. Other cooking conditions, such as cooking temperature, pressure, cooking liquor composition, liquor ratio, and cooking chemical addition rate, for each cooking method can be within known ranges. KP cooking is widely used industrially, and the black liquor produced during KP cooking and the kraft lignin produced using it are cost-effective.

[0018] In the KP cooking method, the sulfidity of the cooking liquor may be 5 to 75%, the effective alkali addition rate may be 5 to 30% by weight based on the bone-dry wood weight, and the cooking temperature may be 130 to 170°C. KP cooking or modified KP cooking methods that use an auxiliary include polysulfide cooking, kraft anthraquinone cooking, and polysulfide anthraquinone cooking. The cooking liquor composition and the cooking reaction conditions such as the cooking temperature, pressure, cooking liquor composition, liquor ratio, and cooking chemical addition rate may be within known ranges. The cooking method may be either continuous cooking or batch cooking.

[0019] The conditions for AP cooking may be within known ranges, as with the KP cooking and modified KP cooking methods described above. There are various SP cooking methods depending on the combination of the type of base that absorbs sulfurous acid and the pH of the cooking liquor. There are four types of bases: calcium-based, magnesium-based, ammonia-based, and sodium-based. Classification based on the pH of the cooking liquor includes four types: acid sulfite, bisulfite, slightly acid sulfite (ASCP), and neutral sulfite (SCP). Multi-stage cooking may also be used.

[0020] Examples of wood materials that can be used as raw materials for black liquor include plants of the genus Cedar, Chamaecyparis obtusa, Pinus serrata, Larch, Acacia, Abies serrata, and Eucalyptus. One of these may be used alone, or two or more may be used in combination.

[0021] The lignin may include lignin purified from black liquor, or may include at least one selected from the group consisting of kraft lignin, sulfite lignin, and soda lignin. The kraft lignin may be obtained by drying black liquor removed during the production of pulp from wood. The sulfite lignin may be lignin obtained by treating wood with, for example, a sulfite during the production of pulp from wood. Examples of sulfite lignin include sodium lignosulfonate and modified sodium lignosulfonate. The soda lignin may be lignin obtained by treating wood with, for example, sodium hydroxide during the production of pulp from wood. From the viewpoint of promoting the reaction, the lignin may include kraft lignin.

[0022] The substrate may be a biomass resource containing at least one selected from lignin and lignin derivatives. The type of biomass resource is not particularly limited. Examples of biomass resources containing lignin include plants of the genus Cedar, Chamaecyparis obtusa, Pinus, Larch, Acacia, Abies, and Eucalyptus. One of these may be used alone, or two or more may be used in combination. The substrate may be in the form of a solid, such as a powder or chips, or in liquid form. The average particle size of the powder may be 1 to 3,000 μm, 10 to 2,000 μm, or 100 to 1,000 μm. Having the average particle size of the powder within the above range can promote the reaction. The average particle size can be measured using a particle size distribution analyzer using a laser diffraction scattering method. An example of a particle size distribution analyzer using a laser diffraction scattering method is the "LS-13 320" (device name) manufactured by Beckman Coulter.

[0023] The catalyst contains at least one selected from the group consisting of divalent and trivalent metal ions. Such metal ions can be obtained by dissolving a metal compound in water. The catalyst may be in the form of a complex ion in the aqueous solution. The catalyst may contain an iron ion as the metal ion. That is, the catalyst may be an ionic metal compound having iron as a constituent element. Examples of the ionic metal compound having iron (iron compound) include FeＩＩＩ (NO ３ ) ３ , Fe ＩＩＩ Cl ３ , Fe ＩＩＩ ２ (SO ４ ) ３ , Fe ＩＩＩ ２ O ３ , Fe ＩＩ (NO ３ ) ２ , Fe ＩＩ Cl ２ , and Fe ＩＩ (SO ４ ) and the like. Catalysts containing such metal ions can be easily prepared because they use water as a solvent. Furthermore, they can be reused without deterioration after the reaction, making lignin decomposition even easier and reducing the burden on the environment.

[0024] The catalyst may contain, as metal ions, divalent or trivalent manganese ions, calcium ions, cobalt ions, zinc ions, ruthenium ions, osmium ions, etc. Examples of ionic metal compounds (manganese compounds) having manganese as a constituent element include Mn ＩＩ (NO ３ ) ２ , and Mn ＩＩ Cl ２ Examples of ionic metal compounds (calcium compounds) having calcium as a constituent element include Ca ＩＩ Cl ２ Examples of ionic metal compounds having cobalt as a constituent element (cobalt compounds) include Co ＩＩ Cl ２ Examples of ionic metal compounds (zinc compounds) having zinc as a constituent element include Zn ＩＩ Cl ２ etc.

[0025] In the above process, a substrate containing lignin is contacted with a catalyst containing at least one selected from the group consisting of divalent and trivalent metal ions. The substrate and catalyst may be contacted in a liquid phase containing water. Water may be added to the substrate as a solvent for dissolving the catalyst, or may be contained in the substrate, such as black liquor, beforehand. When the substrate and catalyst are contacted in a liquid phase containing water, water can be used as the reaction solvent, thereby reducing the amounts of reagents that impose a burden on the environment, such as organic solvents, oxidizing agents, and reducing agents.

[0026] The contact of the substrate with the catalyst may be carried out by mixing the substrate and the catalyst to prepare a mixture. When the substrate is a solid such as kraft lignin, the mixture may contain 0.01 to 0.10 mmol, 0.02 to 0.08 mmol, or 0.03 to 0.06 mmol of catalyst per 10 mg of substrate. The catalyst content within the above range can further promote the reaction. The amount of substrate used per batch is not limited to 10 mg, and may be more than 10 mg or less than 10 mg. The amount of catalyst can be adjusted to fall within the above-mentioned ratio range depending on the amount of substrate.

[0027] When the substrate is a dispersion liquid such as black liquor, the mixture may contain 0.01 to 15 mmol, 0.02 to 12 mmol, 0.03 to 10 mmol, 0.05 to 5 mmol, or 0.1 to 2 mmol of catalyst per 1 mL of substrate. Having the catalyst content within the above range can further promote the reaction. The amount of substrate used per batch is not limited to 1 mL, and may be more than 1 mL or less than 1 mL. The amount of catalyst can be adjusted to fall within the above-mentioned ratio range depending on the amount of substrate.

[0028] An acid may be further added to the mixture when the substrate and catalyst are contacted. This promotes the hydrolysis reaction of lignin through contact between the substrate and the acid, allowing for more efficient production of lignin decomposition products. The type of acid is not particularly limited, and examples include concentrated hydrochloric acid, dilute hydrochloric acid, nitric acid, and sulfuric acid. The amount of acid added may be, for example, 50 to 300 μL, 70 to 250 μL, or 80 to 150 μL per 1 mL of substrate.

[0029] In the above step, from the viewpoint of further promoting the reaction, the substrate and the catalyst may be contacted at a temperature of 45°C or higher, 85°C or higher, or 120°C or higher. This can further improve the production amount of lignin decomposition products containing methanol. From the viewpoint of further simplifying the process, the temperature at which the substrate and the catalyst are contacted may be 250°C or lower, 200°C or lower, or 170°C or lower. The temperature at which the substrate and the catalyst are contacted may be, for example, 45 to 250°C, 45 to 200°C, 45 to 170°C, 85 to 250°C, 85 to 200°C, 85 to 170°C, 120 to 250°C, 120 to 200°C, or 120 to 170°C.

[0030] In the above process, the substrate and catalyst may be contacted under pressure exceeding atmospheric pressure. Contact under pressure exceeding atmospheric pressure increases the boiling point of the liquid phase, allowing the substrate and catalyst to be contacted in a liquid phase at a higher temperature. This further promotes the reaction and further improves the production amount of lignin decomposition products containing methanol. The pressure at which the substrate and catalyst are contacted may be 105 to 1700 kPa, 120 to 1200 kPa, 150 to 1000 kPa, or 200 to 800 kPa. In the present disclosure, pressure refers to absolute pressure.

[0031] In the above step, the mixture containing the substrate and catalyst may be stirred. The mixture may also contain water. Stirring can be performed using a device with a stirring function, such as a stirrer, a stirring blade, or an in-line mixer. Stirring increases the frequency of contact between the substrate and the catalyst, further accelerating the reaction. The reaction time may be, for example, 5 minutes to 10 hours, 7 minutes to 7 hours, 7 minutes to 4 hours, or 10 minutes to 2 hours.

[0032] The lignin decomposition product contains methanol. By the above production method, a lignin decomposition product containing methanol can be obtained from lignin in a simple process. Methanol can be obtained by isolating it from the lignin decomposition product obtained after the above process.

[0033] The lignin degradation product may contain a catechol structure represented by the following formula (1): Formula (1) contains a catechol structure having two hydroxy groups at the ortho-position of the benzene ring. By using the above production method, the number of catechol structures in the structure of the lignin degradation product can be increased, and a lignin degradation product containing a catechol structure with improved reactivity can be easily obtained. Such a lignin degradation product with improved reactivity can be used for various applications, and can be used, for example, as a raw material derived from biomass resources.

[0034]

[0035] The reaction by which lignin and metal ions produce lignin decomposition products containing methanol is described below with reference to reaction formula (2). Reaction formula (2) shows the reaction mechanism when lignin is brought into contact with trivalent iron ions, which are an example of a catalyst. As shown in reaction formula (2), lignin is coordinated to the trivalent iron ions. This causes the methoxy groups of the lignin to react with the hydroxy groups of the iron ions, resulting in elimination as methanol. The resulting lignin decomposition product can be distilled under reduced pressure to obtain methanol.

[0036]

[0037] Furthermore, the iron ions coordinated to the lignin after the reaction are released by the addition of hydrogen ions to the coordinate bonds, as shown in reaction formula (3). This allows for the production of a lignin decomposition product containing a catechol structure. The hydrogen ions may be derived from the water used as the solvent, from the water contained in the substrate, or from an additionally added acid. Because the iron ions can be released easily in this way, they can be reused as a catalyst. Furthermore, the residue containing the catechol structure after the reaction can be recovered by filtration or the like. In this way, the catalyst can be reused through a simple process, thereby reducing the burden on the environment.

[0038]

[0039] The coordination of lignin with iron ions as shown in the above reaction formula (2) can be inferred from the following reaction formula (4). Reaction formula (4) represents the coordination of guaiacol with iron ions when trivalent iron ions and guaiacol are mixed. When two equivalents of guaiacol are added to iron ions, the absorbance of the solution increases at a wavelength of around 470 nm. From this, as shown in reaction formula (4), it is believed that up to two molecules of guaiacol coordinate with iron ions. Therefore, it is believed that lignin having a structure similar to guaiacol also coordinates with iron ions as shown in the above reaction formula (2). Reaction formulas (2) to (4) are merely examples, and the reaction between the substrate and the catalyst may differ from the above reaction formulas (2) to (4).

[0040]

[0041] The conversion rate to methanol based on the methoxy groups contained in lignin may be 6.0% or more. The conversion rate to methanol of methoxy groups may be 10% or more, 15% or more, or 25% or more, from the viewpoint of further improving the amount of methanol produced. The conversion rate may be 100% or less, 80% or less, or 60% or less. The conversion rate can be calculated by [(number of moles of methanol produced) / (number of moles of methoxy groups in the substrate) × 100]. For example, if the substrate contains 15% by mass of methoxy groups and the molar mass of the methoxy groups is 31.03 (g / mol), the conversion rate can be calculated by the following formula (5). The content of methoxy groups in lignin can be determined, for example, by infrared spectroscopy, nuclear magnetic resonance spectroscopy, mass spectrometry, gas chromatography, liquid chromatography, etc. Conversion rate (%) = [amount of methanol produced (mM) × volume of reaction solution (L) × 31.03 (g / mol)] / [mass of substrate (mg) × 0.15] × 100 (5)

[0042] A method for producing methanol according to one embodiment includes a step of producing methanol by contacting a substrate containing at least one selected from the group consisting of lignin and lignin derivatives with a catalyst containing at least one selected from the group consisting of divalent and trivalent metal ions. The method for producing methanol can produce methanol by obtaining a lignin decomposition product using a procedure similar to that of the method for producing a lignin decomposition product described above. Therefore, the description of the method for producing a lignin decomposition product described above also applies to the method for producing methanol. After the above step, a purification step may be performed to reduce components other than methanol from the lignin decomposition product. In the purification step, methanol may be isolated.

[0043] Methanol can be isolated by recovering low-boiling compounds by vacuum distillation. Methanol isolation can also be performed by methods other than vacuum distillation, such as ion exchange resin and extraction with an organic solvent. GC-MS or the like can be used for identification and quantification after isolation. Figure 1(a) shows an example of GC measurement results after isolation. Figure 1(b) shows an example of MS measurement results after isolation. The recovered product after vacuum distillation may contain components other than methanol, or may contain only methanol. When the recovered product contains only methanol, no additional separation operation is required, and methanol can be obtained using a simplified process. Therefore, methanol can be produced using a simple process.

[0044] Although several embodiments of the present disclosure have been described above, the present disclosure is not limited to the above-described embodiments. As described above, the present disclosure includes the following embodiments [1] to

[13] .

[0045] [1] A method for producing a lignin decomposition product containing methanol by contacting a substrate containing at least one selected from the group consisting of lignin and lignin derivatives with a catalyst containing at least one selected from the group consisting of divalent and trivalent metal ions, wherein the light intensity of visible light irradiated onto a mixture containing the substrate and the catalyst in the method is 10 mW / cm ３[2] A method for producing a lignin decomposition product, comprising a step of contacting a substrate containing at least one selected from the group consisting of lignin and lignin derivatives with a catalyst containing at least one selected from the group consisting of divalent and trivalent metal ions to obtain a lignin decomposition product containing methanol, wherein the step is carried out under conditions where the irradiance of visible light is less than 10 mW / cm ２ [3] A method for producing a lignin decomposition product according to [1] or [2], wherein the substrate containing lignin comprises at least one selected from the group consisting of a solid containing lignin, a solid containing a lignin derivative, and black liquor. [4] A method for producing a lignin decomposition product according to any one of [1] to [3], wherein the lignin comprises lignin purified from black liquor. [5] A method for producing a lignin decomposition product according to any one of [1] to [4], wherein the lignin comprises at least one selected from the group consisting of kraft lignin, sulfite lignin, and soda lignin. [6] A method for producing a lignin decomposition product according to any one of [1] to [5], wherein the catalyst comprises an iron ion as the metal ion. [7] A method for producing a lignin decomposition product according to any one of [1] to [6], wherein the substrate and the catalyst are contacted at a temperature of 45°C or higher in the step. [8] The method for producing a lignin decomposition product according to any one of [1] to [7], wherein the substrate and the catalyst are contacted at a temperature of 85°C or higher in the step. [9] The method for producing a lignin decomposition product according to any one of [1] to [8], wherein the substrate and the catalyst are contacted in a liquid phase containing water in the step.

[10] The method for producing a lignin decomposition product according to any one of [1] to [9], wherein the substrate and the catalyst are contacted under a pressure exceeding atmospheric pressure in the step.

[11] The method for producing a lignin decomposition product according to any one of [1] to

[10] , wherein the lignin decomposition product contains a catechol structure represented by the following formula (1):

[0046]

[12] The method for producing a lignin degradation product according to any one of [1] to

[11] , wherein the conversion rate to methanol based on the methoxy groups contained in the lignin is 6.0% or more.

[13] The method for producing methanol comprises a step of contacting a substrate containing at least one selected from the group consisting of lignin and lignin derivatives with a catalyst containing at least one selected from the group consisting of divalent and trivalent metal ions, wherein the light intensity of visible light irradiated onto a mixture containing the substrate and the catalyst in the step is 10 mW / cm. ３

[14] A method for producing methanol, comprising a step of contacting a substrate containing at least one selected from the group consisting of lignin and lignin derivatives with a catalyst containing at least one selected from the group consisting of divalent and trivalent metal ions, wherein the step is carried out under conditions where the irradiance of visible light is less than 10 mW / cm ２ A method for producing methanol carried out in an environment below 500°C.

[0047] The present disclosure will be described in more detail below with reference to examples and comparative examples, but the present disclosure is not limited to the following examples.

[0048] [When the Substrate is Kraft Lignin] (Example 1) 10 mg of kraft lignin (manufactured by Nippon Paper Industries Co., Ltd.) was prepared as the substrate, and an iron compound (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) shown in Table 1 was prepared as the catalyst. In a 5 mL screw tube, 22.5 mg of catalyst was dissolved in 3 mL of water to prepare a catalyst aqueous solution. The blending amounts of the substrate and catalyst were as shown in Table 1. 10 mg of substrate was added to the prepared catalyst aqueous solution to prepare a mixed solution. A stirrer was placed in the screw tube and the lid was closed, and the surfaces of the screw tube and the lid were covered with aluminum foil to block light. This prevented the mixed solution from being exposed to visible light. The screw tube was placed in water heated to 50°C, and the mixed solution was heated with gentle stirring to cause a reaction. In other words, the reaction temperature (the temperature at which the substrate and catalyst come into contact) was 50°C. Because the mixed solution was placed inside a sealed screw tube and heated, the pressure inside the screw tube was higher than atmospheric pressure. A lignin decomposition product was obtained one hour after the start of heating.

[0049] The lignin decomposition product was distilled under reduced pressure, and low-boiling compounds were separated from the lignin decomposition product. These low-boiling compounds were measured by GC-MS, and qualitative and quantitative analysis of methanol was performed. In the quantitative analysis, the peak area of ​​the obtained methanol was converted using a previously prepared calibration curve, and the amount of methanol produced (mM) was calculated.

[0050] Assuming that kraft lignin contains 15% by mass of methoxy groups, the conversion rate from methoxy groups to methanol was calculated using the following formula (5). The molar mass of the methoxy groups was set to 31.03 (g / mol). The volume of the reaction solution was set to 3 mL, i.e., 0.003 L. The reaction conditions and results are shown in Table 1. Conversion rate (%) = [amount of methanol produced (mM) × volume of reaction solution (L) × 31.03 (g / mol)] / [mass of substrate (mg) × 0.15] × 100 (5)

[0051] (Example 2) A reaction was carried out in the same manner as in Example 1, except that the reaction temperature was 90°C, to obtain a lignin decomposition product. The amount of methanol produced and the conversion rate were calculated in the same manner as in Example 1. The reaction conditions and results are shown in Table 1.

[0052] (Example 3) A reaction was carried out in the same manner as in Example 1, except that the reaction temperature was 150°C, to obtain a lignin decomposition product. The amount of methanol produced and the conversion rate were calculated in the same manner as in Example 1. The reaction conditions and results are shown in Table 1.

[0053] Comparative Example 1 A mixed solution was prepared in the same manner as in Example 1, except that the amount of substrate used was 100 mg, and the iron compound shown in Table 1 (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) was prepared as the catalyst, and the substrate and catalyst were mixed so that the amount of catalyst was 0.04 mmol per 100 mg of substrate. Thereafter, the mixture was stirred at room temperature (approximately 20°C) for 18 hours. After stirring, the composition of low-boiling-point compounds was measured according to the procedure in Example 1. As a result, no methanol was produced in Comparative Example 1.

[0054] Comparative Example 2 An iron compound (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) shown in Table 1 was prepared as a catalyst, and a mixed solution was prepared in the same manner as in Example 1. 3 mL (3 cm) of the mixed solution contained in a screw tube not covered with aluminum foil was poured at room temperature (about 20°C). ３ ) was gently stirred using a stirrer. While stirring the mixture, visible light having a wavelength of 385 to 740 nm was irradiated so that the light intensity of the visible light irradiated onto the mixture was 200 mW, thereby initiating the reaction between the substrate and the catalyst. Therefore, the light intensity of the visible light irradiated onto the mixture per unit volume was 200 / 3 ≒ 66.7 mW / cm. ３ The mixture was irradiated with visible light using a visible light irradiation device (product name: 300W xenon light source MAX-303, manufactured by Asahi Spectroscopy Co., Ltd.). The irradiation time, i.e., the reaction time, was 1 hour. After the reaction, the amount of methanol produced and the conversion rate were calculated in the same manner as in Example 1. The reaction conditions and results are shown in Table 1.

[0055] Comparative Example 3 An iron compound (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) shown in Table 1 was prepared as a catalyst, and a mixed solution was prepared in the same manner as in Example 1, except that 10.8 mg of catalyst was used so that the amount of catalyst was 0.04 mmol per 10 mg of substrate. Visible light irradiation was carried out in the same manner as in Comparative Example 2, except that the irradiation time (reaction time) of visible light was 3 hours. After the reaction, the amount of methanol produced and the conversion rate were calculated in the same manner as in Example 1. The reaction conditions and results are shown in Table 1.

[0056]

[0057] As shown in Table 1, the light intensity of visible light is 10 mW / cm ３ Compared with Comparative Examples 2 and 3, the amount of methanol produced was improved in Examples 1, 2, and 3, in which the reaction was carried out without irradiation with visible light. Therefore, it was confirmed that methanol can be produced by a simple process. Furthermore, when Comparative Example 1 is compared with Comparative Examples 2 and 3, the amount of methanol produced was increased by irradiation with visible light. Therefore, it is believed that in Examples 1 to 3, the amount of methanol produced would be further increased if the substrate and catalyst were brought into contact with each other while being irradiated with visible light.

[0058] [When the substrate is black liquor obtained from acacia] (Example 4) The raw material is 100% by mass of acacia, the liquor ratio is 4, the sulfidity is 28%, and the effective alkali is 18.5% (Na ２ Kraft cooking (batch cooking) was carried out for 2 hours at a cooking temperature of 160°C using cooking white liquor prepared so that the pulp had a carbon dioxide content of 1000 ppm (calculated as 0.0 ppm). Here, the liquor ratio is the ratio of the total weight of water contained during cooking to the dry weight of the raw material. In other words, the liquor ratio is the ratio of the total weight of water used in cooking to the dry weight of the raw material. After kraft cooking, black liquor was obtained by separating it from the pulp. The obtained black liquor was used as the substrate.

[0059] 1 mL (1.06 g) of substrate was placed in a 5 mL screw cap tube, and 2 mL of water was added. Furthermore, an iron compound shown in Table 2 was added as a catalyst to prepare a mixed solution. The amounts of substrate and catalyst were as shown in Table 2. A stirrer was placed in the screw cap tube and the lid was closed, and the surfaces of the screw cap tube and lid were covered with aluminum foil to block light. This screw cap tube was placed in water heated to 150°C, and the mixed solution was heated while gently stirring to cause a reaction. In other words, the reaction temperature was 150°C. Lignin decomposition products were obtained one hour after the start of heating. The amount of methanol produced (mM) was calculated using the same procedure as in Example 1. The reaction conditions and results are shown in Table 2.

[0060] (Example 5) A lignin decomposition product was obtained by carrying out the reaction in the same manner as in Example 4, except that the reaction time was changed to 3 hours. The amount of methanol produced (mM) was calculated in the same manner as in Example 1. The reaction conditions and results are shown in Table 2.

[0061] Example 6: 0.1 mL of substrate was placed in a 5 mL screw tube, and 2.9 mL of water was added to the mixture. 0.04 mmol of the iron compound shown in Table 2 was added as a catalyst to prepare a mixed solution. The reaction was then carried out in the same manner as in Example 4 to obtain a lignin decomposition product. The amount of methanol produced (mM) was calculated in the same manner as in Example 1. The reaction conditions and results are shown in Table 2.

[0062] Example 7 A mixed solution was prepared and a reaction was carried out in the same manner as in Example 6, except that the amount of catalyst was changed to 0.4 mmol, to obtain a lignin decomposition product. The amount of methanol produced (mM) was calculated in the same manner as in Example 1. The reaction conditions and results are shown in Table 2.

[0063] (Example 8) A lignin decomposition product was obtained by carrying out the reaction in the same manner as in Example 7, except that the reaction time was changed to 5 hours. The amount of methanol produced (mM) was calculated in the same manner as in Example 1. The reaction conditions and results are shown in Table 2.

[0064] Example 9 A mixed solution was prepared and a reaction was carried out in the same manner as in Example 4, except that the amount of catalyst was changed to 0.4 mmol, to obtain a lignin decomposition product. The amount of methanol produced (mM) was calculated in the same manner as in Example 1. The reaction conditions and results are shown in Table 2.

[0065] Comparative Example 4 A mixed solution was prepared using the same procedure as in Example 4. The reaction between the substrate and the catalyst was initiated by irradiating with visible light using the same procedure as in Comparative Example 2. The irradiation time, i.e., the reaction time, was 1 hour. After the reaction, the amount of methanol produced (mM) was calculated using the procedure in Example 1. The reaction conditions and results are shown in Table 2.

[0066]

[0067] As shown in Table 2, the light intensity of visible light is 10 mW / cm ３ Compared to Comparative Example 4, Examples 4 to 9, in which the reaction was carried out without irradiation with visible light, showed an improved amount of methanol produced per 1 mL of substrate. Therefore, it was confirmed that methanol can be produced by a simple process.

[0068] (Example 10) An iron compound (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) shown in Table 3 was prepared as a catalyst. A mixed solution was prepared in the same manner as in Example 4, except that the catalyst shown in Table 3 was added in the catalytic amount shown in Table 3. A reaction was carried out in the same manner as in Example 4 to obtain a lignin decomposition product. The amount of methanol produced (mM) was calculated in the same manner as in Example 1. The reaction conditions and results are shown in Table 3.

[0069] Example 11: 3 mL of substrate was placed in a 5 mL screw tube. 2.4 mmol of the iron compound shown in Table 3 was added as a catalyst to prepare a mixed solution. The reaction was then carried out in the same manner as in Example 4 to obtain a lignin decomposition product. The amount of methanol produced (mM) was calculated in the same manner as in Example 1. The reaction conditions and results are shown in Table 3.

[0070] Example 12: 1.5 mL of substrate was placed in a 5 mL screw tube, and 1.5 mL of water was added. 4.0 mmol of the iron compound shown in Table 3 was added as a catalyst to prepare a mixed solution. The reaction was then carried out using the same procedure as in Example 4 to obtain a lignin decomposition product. The amount of low-boiling point compounds was measured using the same procedure as in Example 1, and the amount of methanol produced (mM) was calculated. The reaction conditions and results are shown in Table 3.

[0071] Example 13: 0.1 mL of substrate was placed in a 5 mL screw tube, and 2.9 mL of water was added to the mixture. 0.8 mmol of an iron compound shown in Table 3 was added as a catalyst to prepare a mixed solution. The reaction was then carried out in the same manner as in Example 4 to obtain a lignin decomposition product. The amount of methanol produced (mM) was calculated in the same manner as in Example 1. The reaction conditions and results are shown in Table 3.

[0072] Example 14 A mixed solution was prepared and reacted in the same manner as in Example 13, except that the reaction time was 10 minutes, to obtain a lignin decomposition product. The amount of methanol produced (mM) was calculated in the same manner as in Example 1. The reaction conditions and results are shown in Table 3.

[0073] (Example 15) A mixed solution was prepared and reacted in the same manner as in Example 13, except that the reaction time was 20 minutes, to obtain a lignin decomposition product. The amount of methanol produced (mM) was calculated in the same manner as in Example 1. The reaction conditions and results are shown in Table 3.

[0074] (Example 16) A mixed solution was prepared and reacted in the same manner as in Example 13, except that the reaction time was 30 minutes, to obtain a lignin decomposition product. The amount of methanol produced (mM) was calculated in the same manner as in Example 1. The reaction conditions and results are shown in Table 3.

[0075]

[0076] As shown in Table 3, the amount of methanol produced tended to increase with increasing substrate amount, and the amount of methanol produced also tended to increase with increasing reaction time.

[0077] [When the substrate is black liquor obtained from larch] (Example 17) The raw material is larch 100% by mass, the liquor ratio is 4, the sulfidity is 28%, and the effective alkali is 24% (Na ２ Black liquor was obtained in the same manner as in Example 4, except that kraft cooking (batch cooking method) was carried out at a cooking temperature of 160°C for 2 hours using cooking white liquor adjusted to a carbon dioxide equivalent (CO₂ content converted to 0). The obtained black liquor was used as the substrate.

[0078] 1 mL (1.08 g) of substrate was placed in a 5 mL screw tube, and 2 mL of water was added. Furthermore, an iron compound (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) shown in Table 4 was added as a catalyst to prepare a mixed solution. The amounts of substrate and catalyst were as shown in Table 4. A stirrer was placed in the screw tube, and the cap was closed. The surfaces of the screw tube and cap were covered with aluminum foil to block light. This screw tube was placed in water heated to 150°C, and the mixed solution was heated with gentle stirring to cause a reaction. In other words, the reaction temperature was 150°C. Lignin decomposition products were obtained 1 hour after the start of heating. The amount of methanol produced (mM) was calculated using the same procedure as in Example 1. The reaction conditions and results are shown in Table 4.

[0079] Example 18 A mixed solution was prepared and a reaction was carried out in the same manner as in Example 17, except that the amount of catalyst was 0.4 mmol, to obtain a lignin decomposition product. The amount of methanol produced (mM) was calculated in the same manner as in Example 1. The reaction conditions and results are shown in Table 4.

[0080] Comparative Example 5 A mixed solution was prepared using the same procedure as in Example 17. Visible light was irradiated using the same procedure as in Comparative Example 2 to initiate the reaction between the substrate and the catalyst. The irradiation time, i.e., the reaction time, was 1 hour. After the reaction, a lignin decomposition product was obtained. The amount of methanol produced was measured using the same procedure as in Example 1. The reaction conditions and results are shown in Table 4.

[0081]

[0082] As shown in Table 4, the light intensity of visible light is 10 mW / cm ３ Compared to Comparative Example 5, Examples 17 and 18, in which the reaction was carried out at a temperature of 150°C without irradiating visible light, showed an improved amount of methanol produced per 1 mL of substrate. Therefore, it was confirmed that methanol can be produced by a simple process.

[0083] Example 19: 0.1 mL of substrate was placed in a 5 mL screw tube, and 2.9 mL of water was added to the tube. An iron compound (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) shown in Table 5 was added as a catalyst to prepare a mixed solution. The amounts of substrate and catalyst were as shown in Table 5. The reaction was then carried out in the same manner as in Example 17 to obtain a lignin decomposition product. The amount of methanol produced (mM) was calculated in the same manner as in Example 1. The reaction conditions and results are shown in Table 5.

[0084] Example 20 A mixed solution was prepared and reacted in the same manner as in Example 19, except that the reaction time was 10 minutes, to obtain a lignin decomposition product. The amount of low-boiling compounds was measured in the same manner as in Example 1, and the amount of methanol produced (mM) was calculated. The reaction conditions and results are shown in Table 5.

[0085] (Example 21) A mixed solution was prepared and reacted in the same manner as in Example 19, except that the reaction time was 30 minutes, to obtain a lignin decomposition product. The amount of methanol produced (mM) was calculated in the same manner as in Example 1. The reaction conditions and results are shown in Table 5.

[0086] (Example 22) A mixed solution was prepared and reacted in the same manner as in Example 19, except that the reaction time was 50 minutes, to obtain a lignin decomposition product. The amount of methanol produced (mM) was calculated in the same manner as in Example 1. The reaction conditions and results are shown in Table 5.

[0087]

[0088] As shown in Table 5, the amount of methanol produced tended to increase as the reaction time increased.

[0089] [When the substrate is black liquor obtained from hardwood] (Example 23) Hardwood black liquor obtained from the kraft cooking process in the production of kraft pulp at a paper mill was used as the substrate.

[0090] One mL of substrate was placed in a 5 mL screw cap tube. An iron compound (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) shown in Table 6 was added as a catalyst to prepare a mixed solution. The amounts of substrate and catalyst were as shown in Table 6. A stirrer was placed in the screw cap tube and the cap was closed, and the surfaces of the screw cap tube and cap were covered with aluminum foil to block light. The screw cap tube was placed in water heated to 150°C, and the mixed solution was heated with gentle stirring to cause a reaction. In other words, the reaction temperature was 150°C. A lignin decomposition product was obtained one hour after the start of heating. The amount of methanol produced (mM) was calculated using the same procedure as in Example 1. The reaction conditions and results are shown in Table 6.

[0091] (Example 24) A mixed solution was prepared and a reaction was carried out in the same manner as in Example 23, except that the catalyst amount was as shown in Table 6, to obtain a lignin decomposition product. The amount of methanol produced (mM) was calculated in the same manner as in Example 1. The reaction conditions and results are shown in Table 6.

[0092] Example 25 A mixed solution was prepared and a reaction was carried out in the same manner as in Example 23, except that 100 μL of concentrated hydrochloric acid was added together with the catalyst, to obtain a lignin decomposition product. The amount of methanol produced (mM) was calculated in the same manner as in Example 1. The reaction conditions and results are shown in Table 6.

[0093] Example 26 A mixed solution was prepared and reacted in the same manner as in Example 23, except that 100 μL of concentrated hydrochloric acid was added together with the catalyst and the reaction time was 3 hours, to obtain a lignin decomposition product. The amount of methanol produced (mM) was calculated in the same manner as in Example 1. The reaction conditions and results are shown in Table 6.

[0094] (Example 27) An iron compound (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) shown in Table 6 was prepared as a catalyst. A mixed solution was prepared and a reaction was carried out in the same manner as in Example 23, except that the catalyst was added in the catalytic amount shown in Table 6 and 100 μL of concentrated hydrochloric acid was added together with the catalyst, to obtain a lignin decomposition product. The amount of methanol produced (mM) was calculated in the same manner as in Example 1. The reaction conditions and results are shown in Table 6.

[0095] (Example 28) An iron compound (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) shown in Table 6 was prepared as a catalyst. A mixed solution was prepared and a reaction was carried out in the same manner as in Example 23, except that the catalyst was added in the catalytic amount shown in Table 6, to obtain a lignin decomposition product. The amount of methanol produced (mM) was calculated in the same manner as in Example 1. The reaction conditions and results are shown in Table 6.

[0096] (Example 29) A calcium compound (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) shown in Table 6 was prepared as a catalyst. A mixed solution was prepared and a reaction was carried out in the same manner as in Example 23, except that the catalyst was added in the catalytic amount shown in Table 6, to obtain a lignin decomposition product. The amount of methanol produced (mM) was calculated in the same manner as in Example 1. The reaction conditions and results are shown in Table 6.

[0097] (Example 30) A manganese compound (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) shown in Table 6 was prepared as a catalyst. A mixed solution was prepared and a reaction was carried out in the same manner as in Example 23, except that the catalyst was added in the catalytic amount shown in Table 6, to obtain a lignin decomposition product. The amount of methanol produced (mM) was calculated in the same manner as in Example 1. The reaction conditions and results are shown in Table 6.

[0098] (Example 31) A cobalt compound (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) shown in Table 6 was prepared as a catalyst. A mixed solution was prepared and a reaction was carried out in the same manner as in Example 23, except that the catalyst was added in the catalytic amount shown in Table 6, to obtain a lignin decomposition product. The amount of methanol produced (mM) was calculated in the same manner as in Example 1. The reaction conditions and results are shown in Table 6.

[0099] (Example 32) A zinc compound (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) shown in Table 6 was prepared as a catalyst. A mixed solution was prepared and a reaction was carried out in the same manner as in Example 23, except that the catalyst was added in the catalytic amount shown in Table 6, to obtain a lignin decomposition product. The amount of methanol produced (mM) was calculated in the same manner as in Example 1. The reaction conditions and results are shown in Table 6.

[0100]

[0101] As shown in Examples 25 to 27 in Table 6, it was demonstrated that methanol was produced even when an acid was added to the substrate. Furthermore, as shown in Examples 29 to 32 in Table 6, it was demonstrated that methanol was produced even when a metal catalyst other than iron was used.

[0102] [Confirmation of the coordination structure between guaiacol and iron ions] Fe ＩＩＩ Cl ３ To this aqueous solution, 1 to 6 equivalents of guaiacol (manufactured by Tokyo Chemical Industry Co., Ltd.) were added, and the absorption spectra at each equivalent concentration were measured from 250 to 1000 nm. The results are shown in Figure 2(a). In Figure 2(a), A indicates 0 equivalents, B indicates 1 equivalent, and C indicates 2 equivalents; the other spectra are the results of measurements at 3 equivalents or more. As shown in Figure 2(a), when guaiacol was added to iron ions, a change in the absorption spectrum was observed around 470 nm. Focusing on the absorbance at a wavelength of 470 nm, as shown in Figure 2(b), the absorbance increased up to 2 equivalents of guaiacol added and then gradually decreased from 3 equivalents onwards. This confirmed that guaiacol can coordinate to iron ions up to 2 equivalents. This suggests that lignin, which has a structure similar to guaiacol, can also coordinate to metal ions. Therefore, it is believed that metal ions function as a catalyst, enabling the production of lignin decomposition products containing methanol.

[0103] According to the present disclosure, it is possible to provide a method for producing a lignin decomposition product by decomposing lignin in a simple process to obtain a lignin decomposition product, and a method for producing methanol.

Claims

1. A method for producing a lignin decomposition product containing methanol by contacting a substrate containing at least one selected from the group consisting of lignin and lignin derivatives with a catalyst containing at least one selected from the group consisting of divalent and trivalent metal ions, wherein the light intensity of visible light irradiated onto a mixture containing the substrate and the catalyst in the method is 10 mW / cm. ３ A method for producing a lignin decomposition product, wherein the amount of lignin decomposition product is less than 100%.

2. The method for producing lignin decomposition products according to claim 1, wherein the substrate comprises at least one selected from the group consisting of a solid material containing lignin, a solid material containing a lignin derivative, and black liquor.

3. The method for producing a lignin decomposition product according to claim 1, wherein the lignin includes lignin purified from black liquor.

4. The method for producing a lignin decomposition product according to claim 1, wherein the lignin comprises at least one selected from the group consisting of kraft lignin, sulfite lignin, and soda lignin.

5. A method for producing lignin decomposition products according to any one of claims 1 to 4, wherein the catalyst contains iron ions as the metal ions.

6. A method for producing a lignin decomposition product according to any one of claims 1 to 4, wherein in the step, the substrate and the catalyst are contacted at a temperature of 45°C or higher.

7. A method for producing a lignin decomposition product described in any one of claims 1 to 4, wherein in the step, the substrate and the catalyst are contacted at a temperature of 85°C or higher.

8. A method for producing a lignin decomposition product described in any one of claims 1 to 4, wherein in the step, the substrate and the catalyst are contacted in a liquid phase containing water.

9. A method for producing a lignin decomposition product according to any one of claims 1 to 4, wherein in the step, the substrate and the catalyst are contacted under a pressure exceeding atmospheric pressure.

10. A method for producing a lignin decomposition product described in any one of claims 1 to 4, wherein the lignin decomposition product contains a catechol structure shown in the following formula (1):

11. A method for producing a lignin decomposition product described in any one of claims 1 to 4, wherein the conversion rate to methanol based on the methoxy groups contained in the lignin is 6.0% or more.

12. A method for producing methanol by contacting a substrate containing at least one selected from the group consisting of lignin and lignin derivatives with a catalyst containing at least one selected from the group consisting of divalent and trivalent metal ions, wherein the light intensity of visible light irradiated onto a mixture containing the substrate and the catalyst in the step is 10 mW / cm ３ A method for producing methanol,

Images