Method for producing glucose and catalyst for same

Abstract

The present invention provides a method for producing glucose, the method comprising bringing a liquid which contains cellulose and water into contact with a solid acid catalyst. The solid acid catalyst contains elemental carbon, elemental titanium, and silica, and has a sulfo group as a surface functional group. The present invention also provides a solid acid catalyst for glucose production, the solid acid catalyst containing elemental carbon, elemental titanium, and silica, while having a sulfo group as a surface functional group.

Description

Method for producing glucose and catalyst therefor

[0001] The present invention relates to a method for producing glucose and a solid acid catalyst for producing glucose.

[0002] Toward achieving carbon neutrality, bioethanol has been widely considered as a raw material for low-carbon footprint materials. In particular, the production of bioethanol from edible biomass, followed by dehydration to olefinize and polymerize it, has been investigated. The conversion of edible biomass to bioethanol is well established and is considered a promising method for producing raw materials for plastic products. However, competition with food use for edible biomass has become an issue, and in recent years, efforts have been made to switch from edible biomass to nonedible biomass as a raw material for bioethanol production. Cellulose, a nonedible biomass, can be hydrolyzed to glucose using enzymatic or sulfuric acid methods, and the glucose can then be converted to ethanol by microbial fermentation. However, the decomposition to glucose is generally difficult due to the chemically stable structure of cellulose, resulting in low cellulose conversion rates and glucose yields.

[0003] In recent years, in the method of producing glucose by hydrolysis of cellulose, solid acid catalysts have attracted attention as hydrolysis catalysts, and various studies have been conducted. For example, Patent Document 1 describes a method of producing glucose from cellulose using a solid acid catalyst, "800m ２ / g or more 2500m ２The publication describes a method for producing a sugar-containing liquid containing glucose as a main component, which comprises hydrolyzing cellulose in the presence of at least one catalyst for cellulose or hemicellulose hydrolysis, the catalyst being a porous carbon material having a specific surface area of ​​100 mmol / kg or less and a phenolic hydroxyl group content of 100 mmol / kg or more and 700 mmol / kg or less, and water. Furthermore, Non-Patent Document 1 describes a method for producing sugars such as glucose by hydrolyzing cellulose using a sulfonated silica / carbon nanocomposite. Non-Patent Document 1 states that this sulfonated silica / carbon nanocomposite has a high glucose conversion efficiency in the hydrolysis of cellulose to glucose.

[0004] International Publication No. 2011 / 036955

[0005] Green Chem., 2010, 12, 1560-1563

[0006] The method described in Patent Document 1 and the method described in Non-Patent Document 1, which is said to have a high conversion efficiency to glucose, also do not provide sufficient glucose yields. Furthermore, as described above, it is important to research and develop methods for producing glucose from cellulose with an eye toward achieving carbon neutrality, with industrialization in mind, and further improvement in glucose yield is required in light of the feasibility of industrialization. An objective of the present invention is to provide a method for producing glucose from cellulose in high yield by utilizing a cellulose hydrolysis reaction using a solid acid catalyst, and a solid acid catalyst that can produce glucose from cellulose in high yield.

[0007] That is, the objects of the present invention have been achieved by the following means. <1> A method for producing glucose, comprising contacting a liquid containing cellulose and water with a solid acid catalyst, wherein the solid acid catalyst contains carbon, titanium, and silica and has sulfo groups as surface functional groups. <2> The production method according to <1>, wherein the silica has mesopores. <3> The production method according to <1> or <2>, wherein the carbon element is supported on the surface of the silica. <4> The production method according to any one of <1> to <3>, wherein the titanium element is contained in the silica. <5> A solid acid catalyst for producing glucose, comprising carbon, titanium, and silica and having sulfo groups as surface functional groups. <6> The solid acid catalyst for producing glucose according to <5>, wherein the silica has mesopores. <7> The production method according to <5> or <6>, wherein the carbon element is supported on the surface of the silica. <8> The production method according to any one of <5> to <7>, wherein the titanium element is contained in the silica.

[0008] The present invention provides a method and a solid acid catalyst that can produce glucose from cellulose in high yield. The above and other features and advantages of the present invention will become more apparent from the following description.

[0009] FIG. 1 shows an example of a chromatogram obtained by HPLC analysis of a cellulose decomposition solution.

[0010] In the present invention and this specification, a numerical range expressed using "to" means a range that includes the numerical values ​​written before and after "to" as the lower and upper limits.

[0011] [[Glucose Production Method]] The glucose production method of the present invention (hereinafter sometimes referred to as the "production method of the present invention") involves contacting a liquid containing cellulose and water with a solid acid catalyst. In the production method of the present invention, a solid acid catalyst containing carbon, titanium, and silica and having sulfo groups as surface functional groups (hereinafter sometimes referred to as the "solid acid catalyst of the present invention") is used as the solid acid catalyst. High-yield glucose can be produced by the simple and safe process of contacting cellulose with the solid acid catalyst of the present invention. This is believed to be due to the promotion of the hydrolysis reaction by contacting cellulose with the solid acid catalyst of the present invention, thereby increasing the efficiency of the cellulose hydrolysis reaction. Therefore, the production method and solid acid catalyst of the present invention can produce glucose, a raw material for bioethanol production that is important for achieving carbon neutrality, at high yields while effectively utilizing cellulose, a nonedible biomass that can avoid competition with food applications, and thus can be commercialized. As a result, the production method and solid acid catalyst of the present invention can be suitably applied to methods for producing bioethanol using nonedible biomass. First, the components used in the production method of the present invention will be described.

[0012] [Liquid Containing Cellulose and Water] The production method of the present invention uses a liquid containing cellulose and water (sometimes referred to as the "reaction liquid"). This reaction liquid need only contain cellulose and water, and may also contain other components. The other components may be any that do not inhibit the cellulose hydrolysis reaction, such as hemicellulose, lignocellulose, fatty acids, polymeric surfactants, and aluminum sulfate. The cellulose content in the reaction liquid is not particularly limited, but is preferably 0.01 to 1 kg per 1 L of water, and more preferably 0.05 to 0.5 kg, in terms of the cellulose hydrolysis reaction efficiency (hereinafter sometimes simply referred to as the "hydrolysis reaction efficiency") and the glucose yield (hereinafter sometimes referred to as the "glucose yield"). In the present invention, the cellulose content in the reaction liquid refers to the substantial cellulose content (cellulose equivalent) when a mixture such as waste pulp is used as the cellulose source. The reaction liquid is typically obtained as a suspension or dispersion by mixing cellulose with water.

[0013] <Cellulose> The cellulose used in the production method of the present invention has the molecular formula (C ６ H １０ O ５ ) ｎThe term "cellulose" may be any carbohydrate (polysaccharide) represented by the formula (I), and includes not only cellulose but also hemicellulose and lignocellulose. The cellulose used in the production method of the present invention may be a mixture of cellulose and hemicellulose and / or lignocellulose. However, when lignocellulose is used or when lignocellulose is included, it is preferable to perform the lignin removal process described below. The cellulose may be a synthetic or commercially available product, may be derived from non-edible biomass, or may be a waste or recovered product thereof. Examples of non-edible biomass-derived cellulose include cellulose (lignocellulose) derived from plants such as trees, thinned wood, and lumber, and cellulose obtained by appropriately treating chemical pulp obtained by bleaching defatted plant flour with alkali. Considering its potential as an alternative to bioethanol derived from edible biomass, it is preferable to use cellulose derived from non-edible biomass in the production method of the present invention. Plants are typical non-edible biomass, but using their waste or recovered materials is preferable in terms of efficient resource utilization and cost reduction. Examples of non-edible biomass include wood flour and wood chips from trees, thinned wood, and lumber, various types of pulp (unused), and further, waste pulp such as board pulp and pulp sludge (paper sludge) discharged in the papermaking or pulp manufacturing process, and pulp recovered from used diapers. Among these, waste pulp such as pulp sludge and pulp recovered from used diapers is particularly preferred because it can be recovered in large quantities, allows for effective use of resources (and also enables cost reduction), and also avoids poisoning of the solid acid catalyst by lignin without the need for the lignin removal step described below.

[0014] Cellulose typically exhibits crystallinity due to the hydrogen bonding of two or more cellulose molecules. The production method of the present invention can use crystalline cellulose (sometimes referred to as "crystalline cellulose"), or cellulose whose crystallinity has been reduced by conventional methods (sometimes referred to as "low-crystalline cellulose" or "microcrystalline cellulose"). Low-crystalline cellulose may be crystalline cellulose whose crystallinity has been partially reduced or whose crystallinity has been (almost) completely eliminated. The treatment method for reducing crystallinity is not particularly limited, but a treatment that can at least partially produce single-chain cellulose molecules by cleaving the hydrogen bonds is preferred. Cellulose containing at least partially single-chain cellulose molecules exhibits significantly higher hydrolysis reaction efficiency. Specific examples of treatment methods for reducing crystallinity include the various methods described in Patent Document 1, among which physical methods such as jet mills, hammer mills, ball mills, and bead mills are preferred.

[0015] The shape of the cellulose used in the production method of the present invention is not particularly limited, but from the viewpoints of hydrolysis reaction efficiency and glucose yield, it is preferably in the form of particles, powder, small pieces, etc. The size of the cellulose is not particularly limited and can be appropriately determined taking into consideration the hydrolysis reaction efficiency and glucose yield.

[0016] <Water> The water used in the production method of the present invention is not particularly limited, but industrial water, well water, city water, ion-exchanged water, purified water, (ultra)pure water, etc. can be used, and ion-exchanged water, purified water, and (ultra)pure water are preferred.

[0017] [Solid Acid Catalyst] The solid acid catalyst used in the production method of the present invention is a solid acid catalyst containing carbon, titanium, and silica, and having sulfo groups as surface functional groups. Glucose can be produced in high yield by contacting this solid acid catalyst with cellulose in water. When used to produce glucose from the cellulose, this solid acid catalyst is particularly called a solid acid catalyst for glucose production. This solid acid catalyst is a catalyst containing carbon, titanium, and sulfo groups (-SO ) on a substrate (also called a "silica substrate") whose main component is silica (silicon dioxide). ３ H). The shape of the solid acid catalyst is not particularly limited, but is preferably particulate, powdery, or flake-shaped in terms of hydrolysis reaction efficiency and glucose yield. The size (average particle diameter) of the solid acid catalyst is not particularly limited, but is preferably 0.1 to 10,000 μm, for example. The average particle diameter is a value measured by the method described in the Examples below. The substrate is preferably a porous substrate (porous body), more preferably a porous body having mesopores (mesoporous body), and even more preferably mesoporous silica, in terms of being able to increase hydrolysis reaction efficiency and glucose yield. In the present invention, mesopores refer to pores with an average pore diameter of 2 to 50 nm.

[0018] When the substrate is a porous substrate, its characteristics or physical properties, such as the average pore diameter, specific surface area, and total pore volume, are not particularly limited and can be determined appropriately. For example, the average pore diameter is preferably 2 to 10 nm, more preferably 2 to 5 nm, from the viewpoints of hydrolysis reaction efficiency and glucose yield. The specific surface area is preferably 10 to 3,000 m, from the viewpoints of hydrolysis reaction efficiency and glucose yield. ２ / g, and 100 to 2000m ２ / g is more preferable. From the viewpoint of hydrolysis reaction efficiency and glucose yield, the total pore volume is preferably 0.1 to 2 mL / g, and more preferably 0.2 to 1 mL / g. The average pore diameter, specific surface area, and total pore volume of the porous substrate are values ​​measured by the methods described in the Examples below.

[0019] The solid acid catalyst, typically the substrate, contains carbon. In the present invention, "a substrate containing carbon" refers to the presence (presence) of carbon on the surface and / or inside of the substrate. Examples include a substrate in which carbon is supported or adsorbed on the surface (carbon-supported substrate), a substrate in which carbon is contained inside (a substrate formed of a composite of silica and carbon), and a substrate in which carbon is present on both the surface and inside. The carbon-containing form (structure) of the solid acid catalyst is preferably a substrate in which carbon is supported or adsorbed on the surface (carbon-supported substrate), since this allows for the bonding or immobilization of surface functional groups (described below) to the surface, thereby improving the hydrolysis reaction efficiency and glucose yield. In the present invention, the "surface" of the substrate typically refers to the outer surface, but if the substrate is porous, it also includes the inner surfaces of the pores in addition to the outer surface. Meanwhile, the "interior" of the substrate refers to the portion not exposed to the surface. The carbon element content in the solid acid catalyst is not particularly limited, but is preferably 1 to 70 mass %, more preferably 5 to 50 mass %, of the mass of the solid acid catalyst (excluding the mass of sulfo groups), in order to increase the hydrolysis reaction efficiency and glucose yield. The carbon element content in the solid acid catalyst is a value measured by the measurement method in the examples described below.

[0020] The solid acid catalyst used in the production method of the present invention, typically the substrate, contains elemental titanium. In the present invention, "the substrate contains elemental titanium" refers to the presence (presence) of elemental titanium on the surface and / or inside the substrate. Examples include an embodiment in which elemental titanium is supported or adsorbed on the surface of the substrate (elemental titanium-supported substrate), an embodiment in which elemental titanium is contained inside the substrate (an embodiment in which the substrate is formed of a composite of silica and elemental titanium), and an embodiment in which elemental titanium is contained on the surface and inside the substrate. In a solid acid catalyst, when elemental titanium is contained on the surface and / or inside the substrate, the hydrolysis reaction efficiency and glucose yield can be improved. The content of elemental titanium contained in the solid acid catalyst is not particularly limited, but is preferably 0.1 to 10 mass% and more preferably 0.5 to 5 mass% of the mass of the solid acid catalyst (excluding the mass of carbon atoms and sulfo groups) in order to improve the hydrolysis reaction efficiency and glucose yield. The content of elemental titanium in the solid acid catalyst is a value measured using the measurement method described in the Examples below.

[0021] The solid acid catalyst containing elemental carbon and elemental titanium can be an appropriate combination of the above-mentioned embodiments containing elemental carbon and the embodiment containing elemental titanium. However, in terms of being able to increase the hydrolysis reaction efficiency and glucose yield, a combination of an embodiment in which elemental titanium is contained on the surface and / or inside of a substrate and an embodiment in which elemental carbon is supported or adsorbed on the surface of a substrate is preferred (a solid acid catalyst of this type is also referred to as a carbon-element-supported silica-titanium composite mesoporous material).

[0022] The solid acid catalyst used in the production method of the present invention has sulfo groups as surface functional groups. In the present invention, the term "solid acid catalyst has sulfo groups as surface functional groups" means that sulfo groups are chemically bonded to the surface of the substrate and / or carbon elements. These sulfo groups may be partially or entirely in the form of salts, as long as they are capable of promoting the hydrolysis reaction of cellulose. The content of sulfo groups contained in the solid acid catalyst is not particularly limited, but in terms of being able to increase the hydrolysis reaction efficiency and glucose yield, the amount present per gram of solid acid catalyst is preferably 0.01 to 2 mmol / g, and more preferably 0.05 to 1 mmol / g. The content of sulfo groups in the solid acid catalyst is a value measured by the measurement method in the Examples described below.

[0023] Commercially available solid acid catalysts may be used, but because they contain both carbon and titanium elements and sulfo groups, it is preferable to use a properly synthesized catalyst. The method for introducing carbon element into the substrate is not particularly limited, and various known methods can be applied. For example, a method for supporting or adsorbing carbon element onto the surface of a substrate includes mixing the substrate with a carbon source and then carbonizing the carbon source, specifically the method described in Non-Patent Document 1. The carbon source is not particularly limited as long as it is a compound containing carbon atoms. Typically, organic compounds are used, and preferred examples include sugars such as sucrose, alcohols such as furfuryl alcohol, hydrocarbon compounds, and alkylene oxides. The method for introducing titanium element into the substrate is not particularly limited, and various known methods can be applied. For example, a method for supporting or adsorbing titanium element onto the surface of a substrate includes the same method as the above-mentioned method for supporting or adsorbing carbon element, except that a titanium-containing compound is used. On the other hand, a method for incorporating titanium element into the interior or interior and surface of a substrate includes a method for forming a substrate using a mixture of a silica precursor compound described below and a titanium-containing compound described below, such as the sol-gel method described below. The method for introducing a sulfo group into a substrate is not particularly limited, and various known methods can be applied, such as a method of treating a substrate, preferably a substrate having a carbon element supported or adsorbed on its surface, with sulfuric acid, specifically the method described in Non-Patent Document 1.

[0024] One method for producing porous silica as a substrate for a solid acid catalyst is the sol-gel method (also known as the "molecular templating method" or "template method"), which uses a silica source (silica precursor compound) and an amphiphilic compound as a template. Hereinafter, we will explain a method for producing a carbon-supported silica-titanium composite mesoporous material having sulfo groups as surface functional groups, which is suitable as a solid acid catalyst, by the sol-gel method. A typical sol-gel method involves, for example, subjecting a silica precursor compound to a sol-gel reaction (hydrolysis and condensation reaction) around self-assembled micellar particles formed with a cationic surfactant to form an inorganic-organic nanocomposite, which is then calcined or acid-treated (to remove the cationic surfactant). The suitable solid acid catalyst is first produced using the sol-gel method to produce a silica-titanium composite mesoporous material containing titanium element on the surface and / or inside the substrate. This can be carried out in the same manner as the typical sol-gel method, except that a titanium precursor compound (described below) is used together with the silica precursor compound (i.e., the silica precursor compound and the titanium precursor compound are allowed to coexist). Therefore, the type of each step in the sol-gel method used to produce a silica-titanium composite mesoporous material, as well as the operations and reaction conditions for each step, can be appropriately determined with reference to general sol-gel methods. For example, the method described in Non-Patent Document 1 and the series of steps in the synthesis method, as well as the operations and reaction conditions for each step, in the Examples described below are useful references. In the above sol-gel method, just like general sol-gel methods, the characteristics or physical properties of the porous material, such as the size (average pore diameter) and shape of the mesopores, and the skeletal shape of the porous material can be adjusted or changed by changing the type of silica precursor compound, particularly the type of amphiphilic compound, or preparation conditions such as the solvent composition, temperature, and time.

[0025] The amphiphilic compound used as the template can be any compound commonly used in a typical sol-gel process, without any particular limitations. Typically, an amphiphilic surfactant is used, with cationic surfactants, block copolymers, and the like being preferred. In the present invention, the use of a cationic surfactant as the template is preferred because it allows the average pore diameter of the mesopores to be set relatively small, further increasing the hydrolysis reaction efficiency and glucose yield. The cationic surfactant can be any surfactant commonly used as a template in the sol-gel process, without any particular limitations, and includes ammonium-based cationic surfactants. As the ammonium-based cationic surfactant, alkylammonium salts are preferred, with tetraalkylammonium salts being preferred. Ammonium salts containing long-chain (6 or more carbon atoms) linear alkyl groups are more preferred, and mono-long-chain linear alkyltrishort-chain (4 or less carbon atoms) alkylammonium salts are particularly preferred. The anion forming the quaternary ammonium salt is not particularly limited, but examples include inorganic anions such as hydroxide ions, halide ions, and perhalogen acid ions. A representative example of a mesoporous silica material prepared by the sol-gel method using a cationic surfactant is MCM-41, and a representative example of a porous silica material prepared by the sol-gel method using a block copolymer is SBA-15.

[0026] The silica precursor compound can be any compound commonly used in a general sol-gel process, without any particular limitations. Examples include silicon halides, hydroxides, and alkoxides, with silicon alkoxides and / or alkyl alkoxides being preferred. The number of carbon atoms in the alkyl group forming the alkyl alkoxide is not particularly limited, but is preferably 1 to 6, and more preferably 1 to 3. In the sol-gel process, a titanium-containing compound is used together with the silica precursor compound. Examples of the titanium-containing compound include titanium precursor compounds that are converted to elemental titanium together with the silica precursor compound by the sol-gel process. Examples of the titanium precursor compound include titanium halides, hydroxides, and alkoxides, with titanium alkoxides and / or titanium alkyl alkoxides (alkoxytitanium) being more preferred. The number of carbon atoms in the alkyl group forming the alkyl alkoxide is not particularly limited, but is preferably 1 to 6, and more preferably 1 to 3.

[0027] Next, carbon element is supported on or adsorbed onto the surface of the obtained silica-titanium composite mesoporous material. The method for supporting or adsorbing carbon element is not particularly limited and is as described above. Sulfo groups are introduced as surface functional groups onto the carbon element-supported silica-titanium composite mesoporous material thus obtained. The method for introducing sulfo groups is not particularly limited and is as described above. The silica-titanium composite mesoporous material, the carbon element-supported silica-titanium composite mesoporous material, and / or the element-supported silica-titanium composite mesoporous material into which sulfo groups have been introduced can also be crushed or disintegrated as appropriate.

[0028] [Step of Contacting a Liquid Containing Cellulose and Water with a Solid Acid Catalyst] The production method of the present invention comprises contacting a liquid containing cellulose and water (reaction liquid) with the solid acid catalyst of the present invention, and this contacting allows cellulose to undergo a hydrolysis reaction in the presence of the solid acid catalyst and convert it to glucose. Each component used in this contacting step may be one type, or two or more types.

[0029] The cellulose hydrolysis reaction occurring in the contacting step is generally thought to involve hydrolysis of cellulose to oligosaccharides and hydrolysis of oligosaccharides to glucose. Therefore, the contacting step results in the hydrolysis of cellulose (saccharification treatment), resulting in a sugar-containing liquid containing glucose (also referred to as a "saccharified liquid" or "cellulose degradation product"). In addition to water and a solid acid catalyst, this sugar-containing liquid typically contains glucose as the main component, as well as other components. Examples of other components that may be contained in the sugar-containing liquid include partial hydrolysis products of cellulose and glucose reaction products, such as tetramer or higher oligosaccharides, sugars such as cellotriose, cellobiose, mannose, fructose, and levoglucosan, as well as 5-hydroxymethylfurfural and furfural. In the present invention, the term "main component" refers to the component with the largest mass content among the components contained. In the contacting step using the solid acid catalyst of the present invention, the cellulose hydrolysis reaction efficiency is high, and the occurrence and promotion of various side reactions in the hydrolysis reaction to glucose can be suppressed, thereby enabling glucose to be obtained with high selectivity and high yield. Therefore, the sugar-containing liquid obtained in the contacting step contains glucose as the main component and contains other components in low amounts. For example, an example of a sugar-containing liquid is a sugar-containing liquid containing glucose as the main component and containing cellobiose, fructose, levoglucosan, 5-hydroxymethylfurfural (HMF), and furfural in low total amounts.

[0030] A suitable sugar-containing solution obtained by the contacting step is one having a composition in which, when subjected to LC analysis using a differential refractive index detector, the total area value of peaks derived from components with molecular weights lower than glucose is 0.01 to 0.2 times the area value of the glucose-derived peak. When the area ratio of this total area value to the area value of the glucose-derived peak (hereinafter sometimes referred to as the "component area ratio") is 0.01 to 0.2, it can be seen that cellulose can be converted to glucose with high selectivity in the contacting step. Such a suitable sugar-containing solution has improved composition and properties, and when used as a raw material solution for ethanol fermentation of glucose, it can suppress the occurrence or promotion of side reactions and preferentially proceed with ethanol fermentation of glucose as the main reaction. Moreover, even in the presence of acetic acid bacteria, their growth and acetic acid fermentation can be highly inhibited, further increasing the yield and selectivity (content) of ethanol produced by ethanol fermentation. In order to further increase the efficiency of ethanol fermentation and further suppress the growth of acetic acid bacteria and acetic acid fermentation, thereby producing ethanol in high yields and with high selectivity, the component area ratio is preferably 0.05 to 0.2 times, and more preferably 0.1 to 0.2 times. Here, the component area ratio is a value measured by the method described in the Examples below.

[0031] A suitable sugar-containing liquid may contain the above-mentioned partial hydrolysis reaction product of cellulose, reactants such as glucose, etc., but satisfies the above-mentioned component area ratio for components with lower molecular weights than glucose identified by LC analysis (sometimes referred to as "low molecular weight components"). The low molecular weight components cannot be uniquely determined due to variations in the origin and composition of the cellulose used in the hydrolysis reaction, the contact conditions between glucose and the solid acid catalyst, etc., but typically include components with lower molecular weights than glucose among the partial hydrolysis reaction product of cellulose, reactants such as glucose, etc. Examples include levoglucosan, HMF, furfural, and even unidentifiable components, with levoglucosan, HMF, and furfural being preferred.

[0032] Although the glucose content in a suitable sugar-containing liquid cannot be uniquely determined as described above, it is at least a content that makes the component area ratio 0.01 to 0.2 times, and is a content that falls within the above-mentioned preferred range or a more preferred range. In terms of the mass ratio of glucose to all components contained in the cellulose-decomposing composition, the glucose content in a suitable sugar-containing liquid is, for example, preferably 50 to 99 mass%, more preferably 83 to 99 mass%, from the viewpoint of efficient ethanol production.

[0033] In the production method of the present invention, cellulose can be efficiently hydrolyzed to obtain glucose as the main component. The cellulose conversion rate and glucose selectivity (the mass ratio of glucose content to other components) cannot be determined unequivocally because they vary depending on the type of cellulose, the type and amount of solid acid catalyst used, and the hydrolysis reaction conditions, but at least a glucose yield of 45% or more can be achieved.

[0034] In the production method of the present invention, a liquid containing cellulose and water (reaction liquid) is contacted with a solid acid catalyst under appropriate reaction conditions, typically under heating. The contacting method may be any method that allows the three components of cellulose, water, and the solid acid catalyst to come into contact, including contacting a pre-prepared reaction liquid with the solid acid catalyst and contacting cellulose, water, and the solid acid catalyst without pre-preparing a reaction liquid (contacting cellulose with the solid acid catalyst in the presence of water). In the contacting step of the present invention, when the reaction liquid and the solid acid catalyst are contacted or introduced, this also includes embodiments in which cellulose and water are contacted or introduced separately with the solid acid catalyst instead of the reaction liquid. For example, the contacting step involves introducing the reaction liquid and the solid acid catalyst into a sealed container and then heating. The heating temperature (reaction temperature) for the hydrolysis reaction is not particularly limited, but can be, for example, 110 to 200°C. The heating temperature is preferably 120 to 180°C, more preferably 120 to 150°C, in order to increase the efficiency of the cellulose hydrolysis reaction while suppressing the by-production of other components and thereby increasing the glucose yield. The heating time (reaction time) is determined appropriately depending on the heating temperature, the cellulose hydrolysis reaction efficiency (conversion rate), the glucose yield, and the like, and can be, for example, 1 to 48 hours. The pressure inside the sealed container under heating may be normal pressure, but typically the pressure is increased to, for example, a water vapor partial pressure exceeding 0.1 MPa. In the present invention, the hydrolysis reaction can also be carried out in an actively pressurized environment. The pressure at this time is not particularly limited and can be, for example, greater than 0.1 MPa and 20 MPa or less, with 0.1 to 10 MPa being preferred. The reaction environment (atmosphere) is not particularly limited and can be an inert gas atmosphere, but can also be an air atmosphere or a water vapor atmosphere. Considering industrial production, the reaction environment is preferably an air atmosphere and / or a water vapor atmosphere.

[0035] The amounts of the reaction solution and solid acid catalyst used are not particularly limited, but the amount of water in the reaction system (amount of water present) should be at least the amount necessary for the cellulose hydrolysis reaction. The amount of water in the reaction system is preferably 0.1 to 1,000 times by mass, more preferably 1 to 100 times by mass, relative to the amount of cellulose present, in terms of the mixability (stirability) and ease of handling of the reaction system, as well as the hydrolysis reaction efficiency and glucose yield. In the contacting step, water can be added separately from the reaction solution. The amount of water in the reaction system refers to the amount of water derived from the reaction solution. When water is added, the amount refers to the total amount of water derived from the reaction solution and the added water. The amount of solid acid catalyst used can be determined appropriately taking into account the reaction conditions, hydrolysis reaction efficiency, glucose yield, and the like. For example, it is preferably 0.01 to 10 times by mass, more preferably 0.1 to 5 times by mass, relative to the amount of cellulose present.

[0036] The contacting step can be carried out batchwise using a sealed vessel such as an autoclave, or can be carried out continuously using a reaction tube filled with a solid acid catalyst. In the batchwise process, it is preferable to mix the reaction solution and the solid acid catalyst by appropriate means such as stirring or shaking, in terms of hydrolysis reaction efficiency and glucose yield. An example of a continuous process is a method in which the reaction solution is continuously or intermittently passed through a heated reaction tube.

[0037] As described above, cellulose can be subjected to a hydrolysis reaction in the presence of a solid acid catalyst to obtain a mixture (also referred to as a reaction mixture) of a sugar-containing liquid containing glucose as the main component and the solid acid catalyst.

[0038] [Post-treatment Step] In the production method of the present invention, glucose can be obtained by post-treating the reaction mixture after the contacting step. Post-treatment of the reaction mixture includes a step of cooling the reaction mixture and a step of solid-liquid separation of the reaction mixture. While the reaction mixture can be subjected to solid-liquid separation without cooling, cooling is preferred to suppress further reaction of glucose or to take into account workability, safety, and the like. The reaction mixture may be cooled naturally or using various refrigerants. The cooling temperature of the reaction mixture is not particularly limited and can usually be set to 100°C or below. From the viewpoint of suppressing further reaction of glucose and maintaining a high glucose yield, 80°C or below is preferred. From the viewpoint of workability, safety, and the like, a temperature near room temperature (e.g., 15 to 40°C) is preferred. The lower limit of the cooling temperature can be set to 0°C or above, and preferably 15°C or above, from the viewpoint of workability. The cooling rate can be determined as appropriate, and a decrease of 0.1 to 10°C per minute is preferred. The cooling time can be determined as appropriate depending on the heating temperature, cooling rate, and the like. The reaction mixture, which has been appropriately cooled, is subjected to solid-liquid separation to separate a sugar-containing liquid (cellulose decomposition liquid) containing glucose as a main component as a liquid phase from at least the solid acid catalyst and unreacted cellulose as a solid phase. The method for solid-liquid separation is not particularly limited, and examples thereof include filtration, centrifugation, and precipitation.

[0039] [Other Steps] In the production method of the present invention, steps other than the contacting step and post-treatment step can also be performed. Examples include a step of isolating and purifying glucose from the separated and recovered sugar-containing liquid, a step of isolating the solid acid catalyst and unreacted cellulose from the separated and recovered solid phase, a step of washing and regenerating the isolated solid acid catalyst, and, when using the above-mentioned waste as a cellulose source, a step of removing impurities and contaminants from the waste, and a step of removing lignin from the cellulose. Various known isolation and purification methods can be used for glucose isolation and purification without particular limitation. Furthermore, the solid acid catalyst used in the present invention can be reused in the separated and recovered state (e.g., as a mixture with unreacted cellulose), eliminating the need for the solid acid catalyst isolation, washing, and regeneration steps. However, since the catalytic activity of a solid acid catalyst usually gradually decreases with increased use, the solid acid catalyst can also be washed and / or regenerated taking into account the decrease in catalytic activity, hydrolysis reaction efficiency, or glucose yield. The washing and regeneration methods are not particularly limited.

[0040] The production method of the present invention enables the production of glucose from cellulose in a high yield in a relatively short time through a simple and safe process of contacting a reaction solution with the solid acid catalyst of the present invention. Furthermore, the post-treatment process of the contacting step is simple and safe, allowing the separated and recovered solid acid catalyst to be reused. Furthermore, the occurrence and promotion of various side reactions during the cellulose hydrolysis reaction can be suppressed, thereby enabling the production of glucose with high selectivity (high purity). As a result, the production method and solid acid catalyst of the present invention are suitable as a method for obtaining raw materials for the production of bioethanol from nonedible biomass. Furthermore, when waste pulp is used as a cellulose source, the efficiency of the cellulose hydrolysis reaction and the glucose yield can be further increased, enabling the effective use of nonedible biomass resources. Therefore, the production method and solid acid catalyst of the present invention not only enable the efficient production of glucose from cellulose at low cost, but are also suitable for the industrialization of cellulose hydrolysis (glucose production method) and bioethanol production.

[0041] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples.

[0042] [Preparation of Solid Acid Catalyst] <Experimental Example 1-1. Preparation of Ti-containing solid acid catalyst (i) for glucose production> (1) Preparation of porous silica (i) (First step) 625.5 g of a 16 mass % aqueous solution of hexadecyltrimethylammonium hydroxide was stirred, and a mixed solution of 9.25 g of tetraisopropyl titanate and 50.0 g of 2-propanol was added dropwise to the stirred solution at room temperature (25°C). After stirring for 30 minutes, 190.5 g of tetramethyl orthosilicate was added dropwise. After adding 5.0 g of 2-propanol, stirring was continued for 3 hours, resulting in the formation of a precipitate.

[0043] (Second Step) The resulting precipitate was filtered and washed with 5 L of ion-exchanged water, and the washed solid was dried under reduced pressure at 100° C. for 5 hours.

[0044] (Third Step) 20 g of the dried solid obtained in the second step was placed in a flask, and a mixed solution of 200 mL of methanol and 10 g of concentrated hydrochloric acid (content 36% by mass) was added (acid treatment). Heating was continued at reflux temperature for 1 hour with stirring, and after cooling, the liquid phase was removed by filtration. The same procedure was repeated once more using a mixed solution of 200 mL of methanol and 5 g of concentrated hydrochloric acid. Finally, after refluxing with 200 mL of methanol for 1 hour, the solid finally filtered out was dried under reduced pressure at 120 °C and 10 mmHg for 1.5 hours.

[0045] (Fourth Step) The solid obtained in the third step was heat-treated (calcined) at 600° C. for 3 hours in an air stream.

[0046] (Fifth Step) The fired solid obtained in the fourth step was pulverized eight times with a hammer mill to obtain a powdered porous silica material (i) having an average particle size of 10 μm. The average particle size was measured using a laser diffraction / scattering particle size distribution analyzer (LA-950 manufactured by Horiba, Ltd.) using ion-exchanged water as a dispersion medium, and calculated on a volume basis.

[0047] The powdered porous silica (i) prepared as described above is a silica-titanium composite mesoporous material having a specific surface area of ​​1160 m ２ / g, total pore volume 0.60 mL / g, average pore diameter 2.1 nm. The specific surface area and total pore volume were determined by measuring the nitrogen adsorption isotherm at liquid nitrogen temperature using a BELSORP MINI X (manufactured by Microtrac-Bell) after vacuum degassing the silica porous material (i) for 2 hours at 120°C, and then determining the nitrogen adsorption amount by the BET method and at a relative pressure of approximately (P / P0 = 0.96). The average pore diameter was calculated from the total pore volume and specific surface area values ​​using the following (Equation 1): (Equation 1): average pore diameter (nm) = 4 × total pore volume (mL / g) / specific surface area (m ２ / g) × 1000

[0048] The Ti concentration in the powdered porous silica material (i) prepared as described above was analyzed by XRF and found to be 1.5 mass %.

[0049] (2) Preparation of Porous Silica-Carbon Composite (i) 2.5 g of porous silica (i) was vacuum-impregnated into the pores of the porous silica at room temperature with furfuryl alcohol (FA) as a carbon source. After impregnation, the FA on the outer surface of the porous silica was washed with mesitylene, and then the mixture was heated at 150°C for 24 hours to polymerize the FA within the pores. After polymerization, the solid separated by filtration was dried under reduced pressure at 120°C for 12 hours. The resulting solid was heat-treated in a nitrogen atmosphere at 550°C for 3 hours to carbonize the polymerized FA within the pores, thereby preparing porous silica-carbon composite (i) as a carbon-supported silica-titanium composite mesoporous material.

[0050] (3) Preparation of solid acid catalyst (i) 1 g of the porous silica-carbon composite (i) and 20 mL of 95% by mass sulfuric acid were added to an autoclave and treated at 150°C for 15 hours. After the treatment, the composite was washed with water at 50°C until the pH of the washings was the same as that of purified water. After washing with water, the solid separated by filtration was dried under reduced pressure at 120°C for 12 hours to obtain 1 g of solid acid catalyst (i) as a carbon-supported silica-titanium composite mesoporous material having sulfo groups as surface functional groups.

[0051] Experimental Example 1-2. Preparation of Ti-free solid acid catalyst (ii) (1) Preparation of porous silica-carbon composite (ii) A solid acid catalyst (ii) was prepared using the same method as described in Non-Patent Document 1 (average pore diameter 6-8 nm (literature value)). The preparation method is described below. 6.4 g of Pluronic F127 (a reagent manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.), a surfactant used as a template, was added to a solution containing 32 g of ethanol and 0.3 g of concentrated hydrochloric acid, and the mixture was subjected to ultrasonic treatment for 1 hour. Next, 8.32 g of tetraethoxysilane (TEOS), a silica source, and 10 g of an aqueous sucrose solution, a carbon source, were added, and the mixture was again subjected to ultrasonic treatment for 1 hour. The mass ratio of the Si element contained in the TEOS to the C element contained in the sucrose was Si:C = 33:66. Thereafter, the mixture was heated at 40°C for 20 hours to evaporate the ethanol, and then heated at 160°C for 24 hours to carry out thermal polymerization. The solid obtained after the thermal polymerization was carbonized by heat treatment at 550°C for 3 hours in a nitrogen atmosphere in an electric furnace to prepare a porous silica-carbon composite (ii).

[0052] (2) Preparation of solid acid catalyst (ii) 1 g of the porous silica-carbon composite (ii) and 20 mL of 95% by mass sulfuric acid were added to an autoclave and treated at 150°C for 24 hours. After the treatment, the composite was washed with water at 50°C until the pH of the washings was the same as that of purified water. After washing with water, the solid separated by filtration was dried under reduced pressure at 120°C for 12 hours to obtain solid acid catalyst (ii).

[0053] Experimental Example 1-3. Preparation of Ti-free solid acid catalyst (iii) (1) Preparation of porous silica-carbon composite (iii) Commercially available MCM-41 (Sigma-Aldrich reagent, Ti-free, average pore diameter 2.1 to 2.7 nm (catalog value)) was used as the porous silica. 2.5 g of MCM-41 was vacuum-impregnated into the pores of the MCM-41 at room temperature with furfuryl alcohol (FA) as a carbon source. After impregnation, the FA on the outer surface of the MCM-41 was washed with mesitylene and then heated at 150°C for 24 hours to polymerize the FA within the pores. After polymerization, the solid separated by filtration was dried under reduced pressure at 120°C for 12 hours. The obtained solid was heat-treated at 550°C for 3 hours in a nitrogen atmosphere to carbonize the polymerized FA within the pores, thereby preparing porous silica-carbon composite (iii).

[0054] (2) Preparation of solid acid catalyst (iii) 1 g of porous silica-carbon composite and 20 mL of 95% by mass sulfuric acid were added to an autoclave and treated at 150°C for 24 hours. After the treatment, the composite was washed with water at 50°C until the pH of the washings was the same as that of purified water. After washing with water, the solid separated by filtration was dried under reduced pressure at 120°C for 12 hours to obtain solid acid catalyst (iii).

[0055] Experimental Example 2: Measurement of carbon content in porous silica-carbon composites The carbon content of each of the porous silica-carbon composites (i) to (iii) was determined from the weight loss rate by thermogravimetric analysis. The thermogravimetric analysis was carried out in an air atmosphere by increasing the furnace temperature to 1000°C at a rate of 5°C / min. The results are shown in Table 1.

[0056]

[0057] Experimental Example 3: Measurement of sulfo group content of solid acid catalysts The sulfo group content of solid acid catalysts (i) and (ii) was measured by titration using an automatic potentiometric titrator (Kyoto Electronics). 50 mg of each solid acid catalyst was weighed into a screw cap bottle, and 30 mL of a 0.05 N aqueous NaCl solution was added using a volumetric pipette, followed by stirring for 15 hours with a stirrer. After stirring, the solution in the screw cap bottle was filtered, and 10 mL of the filtrate was sampled using a volumetric pipette and transferred to a 50 mL beaker. Two drops of phenolphthalein solution were added to the 50 mL beaker using a Pasteur pipette, and titration was performed by adding 0.1 mL of 0.005 N aqueous NaOH solution dropwise. The Na content was determined from the equivalence point of the titration result. ＋ The amount of exchange was calculated to determine the sulfo group content, and the results are shown in Table 2.

[0058]

[0059] Example 1 (1) Cellulose Hydrolysis Reaction The cellulose used as the reaction substrate was treated as follows. 1 kg of 1 cm diameter zirconia balls and 5 g of microcrystalline cellulose (Avicel PH-101, a reagent manufactured by Sigma-Aldrich) were placed in a ceramic pot mill. The mixture was placed on a tabletop pot mill turntable and subjected to ball mill treatment at 200 rpm for 120 hours. 50 mg of the ball mill-treated cellulose, 50 mg of solid acid catalyst (i), and 5 mL of purified water were added to an autoclave equipped with a stirrer. While stirring at 300 rpm, the temperature was raised from room temperature to 150°C over approximately 30 minutes, and then the cellulose hydrolysis reaction was carried out at 150°C for 24 hours (internal pressure 0.5 MPa). After completion of the reaction, the autoclave was cooled to room temperature. The reaction solution was then filtered and separated into liquid and solid, yielding a cellulose decomposition solution (i) and a solid residue (i).

[0060] (2) High-Performance Liquid Chromatography (HPLC) Analysis The cellulose decomposition solution (i) was subjected to HPLC analysis, and the glucose concentration (mass%) in the cellulose decomposition solution (i) was quantified by the absolute calibration curve method using a glucose reagent. HPLC analysis was performed using an LC-20A (Shimadzu Corporation) column with a Shodex SP0810 (Resonac, inner diameter 8 mm, length 300 mm), purified water as the mobile phase (0.5 mL / min), and a differential refractive index detector (RID-20A) at a column temperature of 70 ° C., a sample injection volume of 20 μL, an analysis time of 70 minutes, and a sampling rate of 100 ms.

[0061] (3) Measurement of the amount of solid residue The solid residue (i) was dried at 100°C for 12 hours, and then the mass thereof was measured, and the value obtained by subtracting the mass of the added solid acid catalyst from the mass thereof was determined as the mass of unreacted cellulose.

[0062] (4) Calculation of glucose yield The glucose yield was calculated from the glucose yield calculated from the following (Equation 2) and the amount of cellulose charged, using the following (Equation 3): (Equation 2): Amount of glucose obtained (mg) = (mass of glucose decomposition solution (i)) x (glucose concentration) / 100 Here, the glucose concentration used in (Equation 2) is the glucose concentration (mass %) measured in (2) above. (Equation 3): Glucose yield (%) = (amount of glucose obtained) / (amount of cellulose charged) x 100

[0063] The component area ratio of the cellulose decomposition solution is calculated as follows using a chromatogram obtained by HPLC analysis of the cellulose decomposition solution. An example of a chromatogram obtained by HPLC analysis of the cellulose decomposition solution is shown in Figure 1. The component area ratio of the cellulose decomposition solution is determined by identifying the type of each component in the cellulose decomposition product using the chromatogram. Specifically, each component detected in the chromatogram was identified by comparing it with the retention time of each compound reagent on, for example, the above-mentioned Shodex SP0810 column.

[0064] Next, the peak area values ​​of the obtained chromatogram derived from glucose and components lower in molecular weight than glucose that elute after the retention time of glucose are obtained by the following waveform processing parameter processing. The waveform processing parameters used for peak detection are a slope of 200 μV / min, a width of 5 sec, and a minimum area of ​​1000 counts as the minimum area / height, and the area value is calculated under these conditions. Using the area values ​​of each component obtained in this way, the peak area value derived from glucose is divided by the sum of the peak area values ​​derived from the low molecular weight components to calculate the component area ratio. The component area ratio of the cellulose degradation solution (i) calculated by the above method was in the range of 0.01 to 0.2 times.

[0065] Comparative Example 1 The glucose yield was determined in the same manner as in Example 1, except that the cellulose hydrolysis reaction was carried out without adding a solid acid catalyst.

[0066] Comparative Example 2 The glucose yield was determined in the same manner as in Example 1, except that the solid acid catalyst (ii) was used in the cellulose hydrolysis reaction instead of the solid acid catalyst (i).

[0067] Comparative Example 3 The glucose yield was determined in the same manner as in Example 1, except that the solid acid catalyst (iii) was used in the cellulose hydrolysis reaction instead of the solid acid catalyst (i).

[0068] The results of the cellulose hydrolysis reaction in Example 1 and Comparative Examples 1 to 3 are shown in Table 3.

[0069] Comparative Example 1, which did not use a solid acid catalyst, and Comparative Examples 2 and 3, which used solid acid catalysts (ii) or (iii) that did not contain Ti element, showed low glucose yields that were insufficient for industrial use. In contrast, Example 1, which used solid acid catalyst (i) containing Ti element, showed a high glucose yield of 70%. While Example 1 performed the hydrolysis reaction using commercially available cellulose, the results indicate that similar results can be obtained using cellulose derived from waste pulp. While the details of why a high glucose yield is achieved in the present invention are not yet clear, it is believed that the catalytic action of Ti element contained in the porous silica material (i) results in a carbon coating layer formed during the preparation of the porous silica material-carbon composite (i) with a structure suitable for the cellulose hydrolysis reaction. As such, the production method and solid acid catalyst of the present invention enable glucose to be produced from cellulose at low cost using a simple and safe process, with a high yield sufficient for industrial production, and preferably with high selectivity (high purity). Therefore, it can be seen that the production method of the present invention and the solid acid catalyst of the present invention are suitable as a method for obtaining raw materials for producing bioethanol using non-edible biomass as a raw material and as a solid acid catalyst, and are suitable for industrial production in the cellulose hydrolysis reaction and bioethanol production method.

[0070] While the present invention has been described in connection with embodiments thereof, we do not intend to limit our invention to any of the details of the description unless otherwise specified, and believe that the claims should be construed broadly without departing from the spirit and scope of the invention as set forth in the appended claims.

[0071] This application claims priority based on Japanese Patent Application No. 2024-000266, filed in Japan on January 4, 2024, the contents of which are incorporated herein by reference.

Claims

1. A method for producing glucose, comprising contacting a liquid containing cellulose and water with a solid acid catalyst, wherein the solid acid catalyst contains a carbon element, a titanium element, and silica and has a sulfo group as a surface functional group.

2. The production method according to claim 1, wherein the silica has mesopores.

3. The production method according to claim 1 or 2, wherein the carbon element is supported on the surface of the silica.

4. The production method according to claim 1 or 2, wherein the titanium element is contained in the silica.

5. The production method according to claim 3, wherein the titanium element is contained in the silica.

6. A solid acid catalyst for glucose production, containing a carbon element, a titanium element, and silica and having a sulfo group as a surface functional group.

7. The solid acid catalyst for glucose production according to claim 6, wherein the silica has mesopores.

8. The solid acid catalyst for glucose production according to claim 6 or 7, wherein the carbon element is supported on the surface of the silica.

9. The solid acid catalyst for glucose production according to claim 6 or 7, wherein the titanium element is contained in the silica.

10. The solid acid catalyst for glucose production according to claim 8, wherein the titanium element is contained in the silica.

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