Method for producing glucose and catalyst therefor

Abstract

To provide a method enabling production of glucose from cellulose with high yield by utilizing a hydrolysis reaction of cellulose using a solid acid catalyst, and also to provide a solid acid catalyst for glucose production.SOLUTION: A method for producing glucose is provided, comprising bringing liquid including cellulose and water into contact with a solid acid catalyst. The solid acid catalyst includes carbon element, titanium element, and silica, and has a sulfo group as a surface functional group. The present invention also provides A solid acid catalyst for glucose production is also provided, the solid acid catalyst includes carbon element, titanium element, and silica, and has a sulfo group as a surface functional group.SELECTED DRAWING: None

Description

[Technical Field]

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

[0002] Toward achieving carbon neutrality, bioethanol is being 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, is being investigated. The conversion of edible biomass to bioethanol is a well-established technology, and it is considered a promising method for producing raw materials for plastic products. However, edible biomass competes with food use, and in recent years, there has been a shift from edible biomass to non-edible biomass as a raw material for bioethanol production. Cellulose, a non-edible biomass, can be decomposed into glucose by enzymatic or sulfuric acid hydrolysis, and the glucose can then be converted into ethanol by microbial fermentation. However, the decomposition reaction into glucose is generally difficult because cellulose has a chemically stable structure, resulting in low cellulose conversion rates and low 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." Non-Patent Document 1 also 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. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] International Publication No. 2011 / 036955 [Non-patent literature]

[0005] [Non-Patent Document 1] Green Chem., 2010, 12, 1560-1563 Summary of the Invention [Problem to be solved by the invention]

[0006] The yield of glucose is insufficient even in the method described in Patent Document 1, and even in the method described in Non-Patent Document 1, which is said to have a high conversion efficiency to glucose. 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 of the glucose yield is required in light of the feasibility of industrialization. An object 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. [Means for solving the problem]

[0007] That is, the object of the present invention has 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 element, titanium element, and silica, and has a sulfo group as a surface functional group. <2> The silica has mesopores. <1> The manufacturing method described in <3> The carbon element is supported on the surface of the silica. <1> or <2> The manufacturing method described in <4> The titanium element is contained in the silica. <1> ~ <3> The manufacturing method according to any one of the above. <5> A solid acid catalyst for glucose production, comprising carbon, titanium and silica, and having a sulfo group as a surface functional group. <6> The silica has mesopores. <5> The solid acid catalyst for producing glucose according to claim 1. <7> The carbon element is supported on the surface of the silica. <5> or <6> The manufacturing method described in <8> The titanium element is contained in the silica. <5> ~ <7> The manufacturing method according to any one of the above. [Effects of the Invention]

[0008] The present invention can provide a method and a solid acid catalyst that can produce glucose from cellulose in high yield. [Brief explanation of the drawings]

[0009]

Figure 1

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

[0011] [[How glucose is produced]] 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. The production method of the present invention uses 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"). 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 industrialized. 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 a "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 hydrolysis reaction of cellulose, such as hemicellulose, lignocellulose, fatty acids, polymeric surfactants, and aluminum sulfate. The cellulose content in the reaction solution is not particularly limited, but is preferably 0.01 to 1 kg, and more preferably 0.05 to 0.5 kg, per liter of water, in terms of the cellulose hydrolysis reaction efficiency (hereinafter sometimes simply referred to as "hydrolysis reaction efficiency") and the glucose yield (hereinafter sometimes referred to as "glucose yield"). In the present invention, the cellulose content in the reaction solution refers to the substantial cellulose content (cellulose equivalent amount) when a mixture such as waste pulp is used as the cellulose source. The reaction liquid is usually 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 (CH 10 O5) n The term "cellulose" may be used in any form, including, in addition to cellulose, hemicellulose and lignocellulose. The cellulose used in the production method of the present invention may be a mixture of cellulose, hemicellulose and / or lignocellulose. However, when lignocellulose is used or when lignocellulose is contained, it is preferable to carry out the lignin removal step described below. The cellulose may be synthetic, derived from non-edible biomass, or derived from waste or recovered materials of these. Examples of cellulose derived from non-edible biomass include cellulose (lignocellulose) derived from plants such as trees, thinned wood, and wood, 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, the cellulose used in the production method of the present invention is preferably derived from non-edible biomass. Plants are typical examples of non-edible biomass, but it is preferable to use waste or recovered materials from these biomass 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 wood, as well as various types of pulp (unused), pulp sludge (paper sludge), and waste pulp such as pulp recovered from used diapers. Among these, waste pulp such as pulp sludge and pulp recovered from waste diapers is particularly preferred because it can be recovered in large quantities, allowing for effective utilization of resources (and also reducing costs), and because it can avoid poisoning of the solid acid catalyst by lignin without having to carry out the lignin removal step described below.

[0014] Cellulose is typically crystalline, with two or more cellulose molecules bound together by hydrogen bonds. The production method of the present invention can use crystalline cellulose (sometimes referred to as "crystalline cellulose"), or cellulose obtained by reducing the crystallinity of crystalline cellulose using conventional methods (sometimes referred to as "low-crystalline cellulose" or "microcrystalline cellulose"). Low-crystalline cellulose may be crystalline cellulose with partially reduced crystallinity or cellulose with (almost) completely eliminated crystallinity. 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 efficiency. Specific examples of treatment methods for reducing crystallinity include the various methods described in Patent Document 1, with physical methods such as jet mills, hammer mills, ball mills, and bead mills being 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. By contacting this solid acid catalyst with cellulose in water, glucose can be produced in high yield. When used to produce glucose from the cellulose, this solid acid catalyst is particularly referred to as a solid acid catalyst for glucose production. This solid acid catalyst has carbon, titanium, and sulfo groups (-SO3H) on a substrate (also referred to as a "silica substrate") primarily composed of silica (silicon dioxide). The shape of the solid acid catalyst is not particularly limited, but is preferably in the form of particles, powder, small pieces, etc., 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, for example, 0.1 to 10,000 μm. 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 that it can increase the 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 explained in the Examples below.

[0019] In the present invention, the solid acid catalyst, typically the substrate, contains a carbon element. In the present invention, "a substrate containing a carbon element" refers to the presence (presence) of a carbon element on the surface and / or inside the substrate. Examples include a substrate in which a carbon element is supported or adsorbed on the surface of the substrate (a carbon-element-supported substrate), a substrate in which a carbon element is contained inside the substrate (a substrate formed of a composite of silica and a carbon element), and a substrate in which a carbon element is present on the surface and inside the substrate. The carbon-element-containing form (structure) of the solid acid catalyst is preferably a substrate in which a carbon element is supported or adsorbed on the surface of the substrate (a carbon-element-supported substrate), because this allows for the bonding or immobilization of a surface functional group (described below) to the surface, thereby increasing the hydrolysis reaction efficiency and glucose yield. In the present invention, the surface of a substrate generally refers to the outer surface, but when the substrate is porous, it includes the inner surfaces of the pores in addition to the outer surface. On the other hand, the inside of the substrate refers to the part not exposed on the surface. The carbon element content in the solid acid catalyst is not particularly limited, but is preferably 1 to 70 mass % and 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" means that elemental titanium is present on the surface and / or inside the substrate, and 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 present on the surface and inside the substrate. In a solid acid catalyst, when the substrate contains elemental titanium on its surface and / or inside, the hydrolysis reaction efficiency and glucose yield can be increased. The content of titanium element 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 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.

[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 improving 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 having sulfo groups as surface functional groups" means that sulfo groups are chemically bonded to the surface of the substrate and / or carbon elements. Some or all of these sulfo groups may be in the form of a salt, as long as they are capable of promoting the hydrolysis reaction of cellulose. The content of sulfo groups in the solid acid catalyst is not particularly limited, but the amount present per gram of solid acid catalyst is preferably 0.01 to 2 mmol / g, more preferably 0.05 to 1 mmol / g, in terms of increasing the hydrolysis reaction efficiency and glucose yield. The content of sulfo groups in the solid acid catalyst is a value measured by the measurement method in the examples described below.

[0023] Although a commercially available product may be used as the solid acid catalyst, it is preferable to use an appropriately synthesized product since it contains both carbon and titanium elements and a sulfo group. The method for introducing carbon elements into the substrate is not particularly limited, and various known methods can be applied. For example, a method for supporting or adsorbing carbon elements on the surface of a substrate includes a method of 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, and typically an organic compound is used; for example, sugars such as sucrose, alcohols such as furfuryl alcohol, hydrocarbon compounds, and alkylene oxides are preferably used. The method for introducing titanium element into the substrate is not particularly limited, and various known methods can be applied.For example, as a method for supporting or adsorbing titanium element on the surface of the substrate, there can be mentioned 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, as a method for incorporating titanium element into the inside or the inside and the surface of the substrate, there can be mentioned a method for forming a substrate using a mixture of a silica precursor compound described later and a titanium-containing compound described later, for example, the sol-gel method described later. 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 carbon atoms supported or adsorbed on its surface, with sulfuric acid, specifically the method described in Non-Patent Document 1.

[0024] Methods for producing porous silica as a substrate for a solid acid catalyst include the sol-gel method (also called the "molecular template method" or "template method"), which uses a silica source (silica precursor compound) and an amphiphilic compound as a template. Hereinafter, a method for producing a carbon-supported mesoporous silica-titanium composite material having sulfo groups as surface functional groups, which is suitable as a solid acid catalyst, by a sol-gel method will be described as an example. A typical sol-gel method involves, for example, forming a cationic surfactant and subjecting a silica precursor compound to a sol-gel reaction (hydrolysis reaction and condensation reaction) around self-assembled micelle particles to form an inorganic-organic nanocomposite, which is then calcined or acid-treated (to remove the cationic surfactant). The above-described suitable solid acid catalyst is first prepared by using the above-described sol-gel method to produce a mesoporous silica-titanium composite material containing titanium element on the surface and / or inside of a substrate. This process can be carried out in the same manner as a general sol-gel method, except that a titanium precursor compound (described later) 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 mesoporous silica-titanium composite material, as well as the operation and reaction conditions for each step, can be appropriately determined by referring to general sol-gel methods. For example, the method described in Non-Patent Document 1 and the series of steps in the synthesis method in the examples described later, as well as the operation and reaction conditions for each step, are useful references. In the sol-gel method, as in the general sol-gel method, the characteristics or physical properties of the porous body, such as the size (average pore diameter) and shape of the mesopores, as well as the skeletal shape of the porous body, 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 and block copolymers 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 more preferred. Ammonium salts containing a long-chain (6 or more carbon atoms) linear alkyl group are more preferred, and monolong-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. Examples of mesoporous silica prepared by the sol-gel method using cationic surfactants include MCM-41, and examples of porous silica prepared by the sol-gel method using block copolymers include SBA-15.

[0026] The silica precursor compound can be any compound commonly used in a general sol-gel method without any particular limitation, and examples thereof 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 method, a titanium-containing compound is used together with a silica precursor compound. Examples of titanium-containing compounds include titanium precursor compounds that are converted into elemental titanium together with the silica precursor compound by the sol-gel method. Preferred titanium precursor compounds 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 or adsorbed on 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 into the carbon-supported silica-titanium composite mesoporous material obtained in this manner. The method for introducing sulfo groups is not particularly limited and is as described above. The silica-titanium mesoporous composite material, the carbon-element-supported silica-titanium mesoporous composite material and / or the sulfo group-introduced element-supported silica-titanium mesoporous composite material 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 includes contacting a liquid (reaction liquid) containing cellulose and water with the solid acid catalyst of the present invention, and by this contact, cellulose can be hydrolyzed in the presence of the solid acid catalyst to convert it into glucose. The components used in this contacting step may be one kind or two or more kinds.

[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 glucose-containing sugar-containing liquid (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 tetrameric 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, so glucose can 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 can be 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, with its improved composition and properties, can be used as a feedstock for glucose ethanol fermentation, suppressing the occurrence or promotion of side reactions and allowing glucose ethanol fermentation to proceed preferentially as the main reaction. Furthermore, even in the presence of acetic acid bacteria, their growth and acetic acid fermentation can be significantly 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, glucose, and other reactants, 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"). 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, and other factors, but typically include components with lower molecular weights than glucose among the partial hydrolysis reaction product of cellulose, glucose, and other reactants. Examples include levoglucosan, HMF, furfural, and even unidentifiable components, with levoglucosan, HMF, and furfural being preferred.

[0032] Although the content of glucose 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 mass ratio of glucose to all components contained in the cellulolytic composition, the content of glucose 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 production of ethanol.

[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 (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 brought into contact with a solid acid catalyst under appropriate reaction conditions, usually under heating. The contacting method may be any method that can bring the three components, cellulose, water, and solid acid catalyst, into contact, and examples thereof include a method of contacting a pre-prepared reaction solution with a solid acid catalyst, a method of contacting cellulose, water, and a solid acid catalyst without pre-preparing a reaction solution (a method of contacting cellulose with a solid acid catalyst in the presence of water), etc. In the contacting step of the present invention, when the reaction solution is contacted with or introduced into a solid acid catalyst, this also includes an embodiment in which cellulose and water are contacted with or introduced into a solid acid catalyst separately instead of the reaction solution. In the contacting step, for example, the reaction solution and the solid acid catalyst are placed in a sealed container and then heated. The heating temperature (reaction temperature) of 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 and suppress the by-production of other components, thereby increasing the glucose yield. The heating time (reaction time) is appropriately determined 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 is usually pressurized, with the 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, but can be, for example, more than 0.1 MPa and 20 MPa or less, preferably 0.1 to 10 MPa. The reaction environment (atmosphere) is not particularly limited and may be an inert gas atmosphere, an air atmosphere, or a water vapor atmosphere. In consideration of 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 1000 times, and more preferably 1 to 100 times by mass, the amount of cellulose present, in terms of the mixability (stirability) and handleability 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, and 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 the solid acid catalyst used can be appropriately determined taking into consideration the reaction conditions, hydrolysis reaction efficiency, glucose yield, etc., and is, for example, preferably 0.01 to 10 times by mass, and 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-processing process] 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 subjecting the reaction mixture to solid-liquid separation. The reaction mixture can be subjected to solid-liquid separation without cooling; however, cooling is preferred to suppress further reaction of glucose or to take into consideration workability and safety. 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 100°C or lower. From the viewpoint of suppressing further reaction of glucose and maintaining a high glucose yield, 80°C or lower is preferred. From the viewpoint of workability and safety, a temperature near room temperature (e.g., 15 to 40°C) is preferred. The lower limit of the cooling temperature can be, for example, 0°C or higher, and preferably 15°C or higher, from the viewpoint of workability. The cooling rate can be determined appropriately, and a decrease of 0.1 to 10°C per minute is preferred. The cooling time can be determined appropriately depending on the heating temperature, cooling rate, etc. 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 processes] In the production method of the present invention, steps other than the contacting step and post-treatment step can also be performed, such as 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, a step of removing impurities and contaminants from the waste when the waste is used as a cellulose source, and a step of removing lignin from the cellulose. As a method for isolating and purifying glucose, various known isolation and purification methods can be applied without any particular limitation. Furthermore, the solid acid catalyst used in the present invention can be reused in a separated and recovered state (for example, as a mixture with unreacted cellulose), and there is no need to perform the steps of isolating, washing, and regenerating the solid acid catalyst. However, since the catalytic activity of a solid acid catalyst usually gradually decreases with increasing use, the solid acid catalyst can also be washed and / or regenerated in consideration of decreases 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, since the occurrence and promotion of various side reactions during the cellulose hydrolysis reaction can be suppressed, glucose can be produced 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 methods. [Example]

[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% by 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 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 (36% by mass content) 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, the solid was refluxed with 200 mL of methanol for 1 hour, and then finally filtered and 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 powdery porous silica material (i) with an average particle size of 10 μm. The average particle size was measured using a laser diffraction / scattering particle size distribution measuring device (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 with a specific surface area of ​​1160 m 2 / g, total pore volume 0.60 mL / g, and 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 (Microtrac-Bell) after vacuum degassing the porous silica material (i) for 2 hours at 120°C, and then using the BET method and the nitrogen adsorption amount at a relative pressure of approximately P / P = 0.96. The average pore diameter was calculated from the total pore volume and specific surface area using the following formula (1): (Formula 1): Average pore diameter (nm) = 4 × total pore volume (mL / g) / specific surface area (m 2 / g) x 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), which serves as a carbon source. After impregnation, the FA on the outer surface of the porous silica was washed with mesitylene and then heated at 150°C for 24 hours to polymerize the FA within the pores. After polymerization, the solid was filtered and dried under reduced pressure at 120°C for 12 hours. The resulting solid was heat-treated at 550°C for 3 hours in a nitrogen atmosphere to carbonize the polymerized FA within the pores, producing porous silica-carbon composite (i) as a carbon-loaded 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 treatment, the mixture was washed with water at 50°C until the pH of the washings reached the same value as 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 mesoporous silica-titanium composite having sulfo groups as surface functional groups.

[0051] <Experimental Example 1-2. Preparation of Ti-element-free solid acid catalyst (ii)> (1) Preparation of porous silica-carbon composite (ii) A solid acid catalyst (ii) was prepared by the same method as that described in Non-Patent Document 1 (average pore diameter 6 to 8 nm (literature value)). The preparation method is shown below. 6.4 g of the template surfactant Pluronic F127 (a reagent manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) was added to a solution of 32 g of ethanol and 0.3 g of concentrated hydrochloric acid and sonicated for 1 hour. Next, 8.32 g of the silica source tetraethoxysilane (TEOS) and 10 g of the carbon source sucrose solution were added, and sonicated again for 1 hour. The mass ratio of silicon in TEOS to carbon in sucrose was Si:C = 33:66. The mixture was then heated at 40 °C for 20 hours to evaporate the ethanol, and then heated at 160 °C for 24 hours for thermal polymerization. The solid obtained after thermal polymerization was carbonized by heat treatment in an electric furnace at 550 °C for 3 hours under a nitrogen atmosphere to prepare 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 treatment, the mixture 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) The porous silica material used was commercially available MCM-41 (Sigma-Aldrich reagent, Ti-free, average pore diameter 2.1–2.7 nm (catalog value)). 2.5 g of MCM-41 was vacuum-impregnated into the pores of the MCM-41 at room temperature with furfuryl alcohol (FA), which serves 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 was filtered and dried under reduced pressure at 120°C for 12 hours. The resulting solid was heat-treated at 550°C for 3 hours under a nitrogen atmosphere to carbonize the polymerized FA within the pores, producing a porous silica-carbon composite (iii).

[0054] (2) Preparation of solid acid catalyst (iii) 1 g of the 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 treatment, the mixture was washed with water at 50°C until the pH of the washings reached the same value 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 composite> 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 performed 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] [Table 1]

[0057] <Experimental Example 3: Measurement of sulfo group content of solid acid catalyst> 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. The mixture was stirred for 15 hours with a stirrer. After stirring, the solution in the screw cap bottle was filtered, and 10 mL of the filtrate was taken 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 NaOH 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] [Table 2]

[0059] Example 1 (1) Hydrolysis of cellulose The cellulose used as the reaction substrate was treated as follows. 1 kg of zirconia balls with a diameter of 1 cm and 5 g of microcrystalline cellulose (Avicel PH-101, a reagent manufactured by Sigma-Aldrich) were placed in a ceramic pot mill, which was then set on a tabletop pot mill turntable and subjected to ball mill treatment at 200 rpm for 120 hours. 50 mg of 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 the cellulose hydrolysis reaction was carried out at 150°C for 24 hours (internal pressure 0.5 MPa). After the reaction was completed, the autoclave was cooled to room temperature. The reaction solution was then filtered and separated into liquid and solid, yielding cellulose decomposition solution (i) and solid residue (i).

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

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

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

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

[0064] Next, the peak area values ​​of the obtained chromatogram, which are derived from glucose and components with lower 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 / height of 1000 counts, and the area values ​​are calculated under these conditions. Using the area values ​​of each component thus obtained, the peak area value derived from glucose is divided by the total peak area value derived from the low molecular weight components to calculate the component area ratio. The component area ratio of the cellulose decomposition liquid (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 cellulose hydrolysis reaction was carried out using the solid acid catalyst (ii) 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 cellulose hydrolysis reaction was carried out using the solid acid catalyst (iii) 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. [Table 3]

[0069] It was found that Comparative Example 1, which did not use a solid acid catalyst, and Comparative Examples 2 and 3, which used solid acid catalyst (ii) or (iii) not containing Ti element, had low glucose yields and were not sufficient for industrial use. In contrast, Example 1, which used a solid acid catalyst (i) containing Ti element, achieved a high glucose yield of 70%. In Example 1, the hydrolysis reaction was carried out using commercially available cellulose, but the results show 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 assumed 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-carbon composite (i) with a structure suitable for the cellulose hydrolysis reaction. Thus, the production method and solid acid catalyst of the present invention can produce glucose from cellulose through a simple and safe process at low cost, in a high yield sufficient for industrial production, and preferably with high selectivity (high purity). Therefore, it can be seen that the production method and solid acid catalyst of the present invention are suitable as a method and solid acid catalyst for obtaining a raw material for bioethanol production using nonedible biomass as a raw material, and are suitable for cellulose hydrolysis reactions and industrial production of bioethanol.

Claims

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

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

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

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

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

6. A solid acid catalyst for glucose production, comprising carbon, titanium 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. 8. The solid acid catalyst for glucose production according to claim 6, 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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