Method for producing glucose and catalyst for the same

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 glucose production.

Background Art

[0002] Towards achieving carbon neutrality, bioethanol has been widely studied as a raw material for materials with a low carbon footprint. In particular, the production of bioethanol from edible biomass, its olefination by dehydration reaction, and its polymerization have been studied. Here, the conversion method from edible biomass to bioethanol has been technically established and is regarded as promising as a raw material production method for plastic products. However, there is a problem that edible biomass competes with food uses, and in recent years, the raw material conversion from edible biomass to inedible biomass as a production raw material for bioethanol has been progressing. Cellulose, which is inedible biomass, can be decomposed into glucose by a hydrolysis reaction using an enzymatic method or a sulfuric acid method, and can be further led to ethanol by a fermentation method using microorganisms from glucose. However, the decomposition reaction into glucose generally involves difficulties because cellulose has a chemically stable structure, and the conversion rate of cellulose and the yield of glucose are low.

[0003] In recent years, in a method for producing glucose by subjecting cellulose to a hydrolysis reaction, solid acid catalysts have attracted attention and have been variously studied as hydrolysis catalysts. For example, as a method for producing glucose from cellulose using a solid acid catalyst, Patent Document 1 discloses that " 2 / g or more and 2500 m 2A cellulose or hemicellulose hydrolysis catalyst comprising a porous carbon material having a specific surface area of 1 / g or less and a phenolic hydroxyl group content of 100 mmol / kg or more and 700 mmol / kg or less is described. A method for producing a sugar-containing liquid mainly composed of glucose is also described, which includes hydrolyzing cellulose in the presence of at least one kind and water to produce at least oligosaccharides and glucose. Non-Patent Document 1 describes a method for producing saccharides such as glucose by subjecting cellulose to a hydrolysis reaction using a sulfonated silica / carbon nanocomposite. In Non-Patent Document 1, this sulfonated silica / carbon nanocomposite is said to have a high conversion efficiency to glucose in the hydrolysis reaction of cellulose to glucose.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Non-Patent Documents

[0005]

Non-Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0006] In the method described in Patent Document 1 and also in the method described in Non-Patent Document 1, which is said to have a high conversion efficiency to glucose, the yield of glucose is not sufficient. Also, as described above, for a method of producing glucose from cellulose towards achieving carbon neutrality, it is important to conduct research and development with industrialization in mind, and it is required to further improve the yield of glucose in view of the feasibility of industrialization. An object of the present invention is to provide a method for producing glucose from cellulose in a high yield by utilizing a hydrolysis reaction of cellulose using a solid acid catalyst, and a solid acid catalyst capable of producing glucose from cellulose in a high yield.

Means for Solving the Problems

[0007] That is, the problems 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 a carbon element, a titanium element, and silica, and has a sulfo group as a surface functional group. <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 glucose production, containing a carbon element, a titanium element, and silica, and having a sulfo group as a surface functional group. <6>The solid acid catalyst for glucose production 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.

Effects of the Invention

[0008] The present invention can provide a method and a solid acid catalyst for producing glucose from cellulose in a high yield.

Brief Description of the Drawings

[0009]

Figure 1

Mode for Carrying Out the Invention

[0010] In the present invention and this specification, a numerical range represented by "~" means a range including the numerical values described before and after "~" as the lower limit value and the upper limit value.

[0011] [Method for Producing Glucose] The method for producing glucose of the present invention (hereinafter sometimes referred to as "the production method of the present invention") is a method for producing glucose including contacting a liquid containing cellulose and water with a solid acid catalyst. In the production method of the present invention, as the solid acid catalyst, a solid acid catalyst containing a carbon element, a titanium element, and silica and having a sulfo group as a surface functional group (hereinafter sometimes referred to as "the solid acid catalyst of the present invention") is used. Glucose can be produced in a high yield by a simple and safe process of contacting the solid acid catalyst of the present invention with cellulose. It is considered that the hydrolysis reaction is promoted by the contact of cellulose with the solid acid catalyst of the present invention, and the hydrolysis reaction efficiency of cellulose is increased. Therefore, the production method of the present invention and the solid acid catalyst of the present invention can produce glucose, which is an important raw material for producing bioethanol for achieving carbon neutrality, in a high yield while effectively utilizing cellulose, a non-edible biomass that can avoid competition with food applications, and can also be considered in view of the realization of industrialization. As a result, the production method of the present invention and the solid acid catalyst of the present invention can be suitably applied to a method for producing bioethanol using non-edible 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 "reaction liquid"). This reaction liquid only needs to contain cellulose and water, and may also contain other components. As other components, those that do not inhibit the hydrolysis reaction of cellulose may be used, and examples thereof include hemicellulose, lignocellulose, fatty acids, polymer surfactants, and sulfate bands. The content of cellulose in the reaction solution is not particularly limited, but in terms of the hydrolysis reaction efficiency of cellulose (hereinafter sometimes simply referred to as "hydrolysis reaction efficiency") and the yield of glucose (hereinafter sometimes referred to as "glucose yield"), it is preferably 0.01 to 1 kg, more preferably 0.05 to 0.5 kg, per 1 L of water. In the present invention, when a mixture such as waste pulp is used as the cellulose source, the content of cellulose in the reaction solution refers to the substantial cellulose content (cellulose equivalent amount). The reaction solution is usually obtained as a suspension or dispersion by mixing cellulose and water.

[0013] <Cellulose> The cellulose used in the production method of the present invention may be a carbohydrate (polysaccharide) represented by the molecular formula (C6H 10 O5) n and includes hemicellulose and lignocellulose in addition to cellulose. 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 it contains lignocellulose, it is preferable to carry out the lignin removal step described later. The cellulose may be a synthetic product, may be derived from inedible biomass, or may be these wastes or recyclables. Examples of those derived from inedible biomass include cellulose (lignocellulose) derived from plants such as trees, thinned wood, and lumber, and cellulose obtained by appropriately subjecting chemical pulp obtained by bleaching defatted powder of plants and the like to alkali treatment. Considering the substitutability of bioethanol derived from edible biomass, it is preferable to use cellulose derived from inedible biomass in the production method of the present invention. Plants are typical of inedible biomass, but in terms of effective utilization of resources and cost reduction, it is preferable to use their wastes or recyclables. Examples of inedible biomass include wood powder and wood chips such as trees, thinned wood, and lumber, various pulps (unused products), and further, waste pulps such as pulp sludge (paper sludge) and pulp recovered from waste diapers. Among them, waste pulps such as pulp sludge and pulp recovered from waste diapers are particularly preferable because they have a large recovery amount and can effectively utilize resources (cost reduction is also possible), and can avoid poisoning of the solid acid catalyst by lignin without performing the lignin removal step described later.

[0014] Cellulose usually shows crystallinity when two or more cellulose molecules are bonded by hydrogen bonds. The production method of the present invention can also use cellulose showing crystallinity (sometimes referred to as "crystalline cellulose"), and can also use cellulose with reduced crystallinity of crystalline cellulose by a conventional method (sometimes referred to as "low-crystalline cellulose" or "microcrystalline cellulose"). The low-crystalline cellulose may be one with partially reduced crystallinity of the crystalline cellulose, or one with (substantially) completely disappeared crystallinity. The treatment method for reducing crystallinity is not particularly limited, and it is preferably a treatment that can cleave the above hydrogen bond to at least partially generate single-stranded cellulose molecules. Cellulose containing at least partially single-stranded cellulose molecules has a significantly higher hydrolysis reaction efficiency. Specific examples of the treatment method for reducing crystallinity include various methods described in Patent Document 1. Among them, physical methods such as jet mills, hammer mills, ball mills, and bead mill methods are preferred.

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

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

[0017] [Solid acid catalyst] The solid acid catalyst used in the production method of the present invention contains a carbon element, a titanium element, and silica, and is a solid acid catalyst having a sulfo group as a surface functional group. By bringing this solid acid catalyst into contact with cellulose in water, glucose can be produced in a high yield. When this solid acid catalyst is used for the production of glucose from the above cellulose, it is particularly referred to as a solid acid catalyst for glucose production. This solid acid catalyst has a carbon element, a titanium element, and a sulfo group (-SO3H) in a substrate mainly composed of silica (also referred to as a "silica substrate"). The shape of the solid acid catalyst is not particularly limited, but in terms of hydrolysis reaction efficiency and glucose yield, it is preferably in the form of particles, powder, small flakes, etc. The size (average particle diameter) of the solid acid catalyst is not particularly limited, but for example, it is preferably 0.1 to 10000 μm. The average particle diameter is the value measured by the method described in the examples below. The substrate is preferably a porous substrate (porous body) in terms of enhancing the hydrolysis reaction efficiency and glucose yield, more preferably a porous body having mesopores (mesoporous body), and even more preferably mesoporous silica. In the present invention, the mesopore refers to a pore having an average pore diameter of 2 to 50 nm.

[0018] When the substrate is a porous substrate, its properties or physical properties, such as average pore diameter, specific surface area, total pore volume, etc., are not particularly limited and can be appropriately determined. For example, as the average pore diameter, in terms of hydrolysis reaction efficiency and glucose yield, it is preferably 2 to 10 nm, and more preferably 2 to 5 nm. As the specific surface area, in terms of hydrolysis reaction efficiency and glucose yield, it is preferably 10 to 3000 m 2 / g, and more preferably 100 to 2000 m 2 / g. As the total pore volume, in terms of hydrolysis reaction efficiency and glucose yield, it 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 the values measured by the method described in the examples below.

[0019] Solid acid catalysts usually have a substrate containing a carbon element. In the present invention, the substrate containing a carbon element means that the carbon element is present on the surface and / or inside of the substrate. For example, there are modes in which the carbon element is supported or adsorbed on the surface of the substrate (carbon element-supported substrate), modes in which the carbon element is contained inside the substrate (modes in which the substrate is formed of a composite of silica and a carbon element), and modes in which the carbon element is present on the surface and inside of the substrate. The form (structure) in which the carbon element is contained in the solid acid catalyst is preferably a mode in which the carbon element is supported or adsorbed on the surface of the substrate (carbon element-supported substrate) in that it can enhance the hydrolysis reaction efficiency and glucose yield by bonding or fixing the surface functional groups described below to the surface. In the present invention, the surface of the substrate usually refers to the outer surface, but when the substrate is a porous body, it includes the inner surface of the pores in addition to the outer surface. On the other hand, the inside of the substrate refers to the portion not exposed on the surface. The content of the carbon element contained in the solid acid catalyst is not particularly limited, but in terms of enhancing the hydrolysis reaction efficiency and glucose yield, it is preferably 1 to 70% by mass, more preferably 5 to 50% by mass, in the mass of the solid acid catalyst (excluding the mass of the sulfo group). The content of the carbon element in the solid acid catalyst is the value measured by the measurement method in the examples described below.

[0020] The substrate of the solid acid catalyst used in the production method of the present invention usually contains a titanium element. In the present invention, the substrate containing a titanium element means that the titanium element is present on the surface and / or inside of the substrate. For example, there are modes in which the titanium element is supported or adsorbed on the surface of the substrate (titanium element-supported substrate), modes in which the titanium element is contained inside the substrate (modes in which the substrate is formed of a composite of silica and a titanium element), and modes in which the titanium element is present on the surface and inside of the substrate. When the substrate of the solid acid catalyst has the titanium element on its surface and / or inside, the hydrolysis reaction efficiency and glucose yield can be enhanced. The content of titanium element contained in the solid acid catalyst is not particularly limited, but in terms of enhancing the hydrolysis reaction efficiency and glucose yield, it is preferably 0.1 to 10% by mass, more preferably 0.5 to 5% by mass, based on the mass of the solid acid catalyst (excluding the mass of carbon atoms and sulfonic groups). The content of carbon element in the solid acid catalyst shall be the value measured by the measurement method in the examples described later.

[0021] In the aspect where the solid acid catalyst contains carbon element and titanium element, the above-described aspect containing carbon element and the aspect containing titanium element can be appropriately combined. However, in terms of enhancing the hydrolysis reaction efficiency and glucose yield, a form in which a titanium element is contained on the surface and / or inside of the substrate and a carbon element is supported or adsorbed on the surface of the substrate is combined (this form of solid acid catalyst is also referred to as a carbon element-supported silica-titanium composite mesoporous body).) is preferred.

[0022] The solid acid catalyst used in the production method of the present invention has a sulfonic group as a surface functional group. In the present invention, that the solid acid catalyst has a sulfonic group as a surface functional group means that a sulfonic group is chemically bonded to the surface of the substrate and / or the carbon element. As long as this sulfonic group can promote the hydrolysis reaction of cellulose, a part or all of it may be in the form of a salt. The content of the sulfonic group contained in the solid acid catalyst is not particularly limited, but in terms of enhancing the hydrolysis reaction efficiency and glucose yield, the amount present per 1 g of the solid acid catalyst is preferably 0.01 to 2 mmol / g, more preferably 0.05 to 1 mmol / g. The content of the sulfonic group in the solid acid catalyst shall be the value measured by the measurement method in the examples described later.

[0023] Commercially available products may be used as the solid acid catalyst, but since it has both carbon and titanium elements and a sulfonic group, it is preferably a synthetic product appropriately. The method for introducing a carbon element into the substrate is not particularly limited, and various known methods can be applied. For example, as a method for supporting or adsorbing a carbon element on the surface of the substrate, there is a method of carbonizing the carbon source after mixing the substrate and 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 usually an organic compound is used. For example, saccharides such as sucrose, alcohols such as furfuryl alcohol, hydrocarbon compounds, and alkylene oxides are preferably used. The method for introducing a 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 a titanium element on the surface of the substrate, the same method as the method for supporting or adsorbing the above carbon element can be used except that a titanium-containing compound is used. On the other hand, as a method for incorporating a titanium element into the interior or the interior and surface of the substrate, there is a method of 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 the substrate is not particularly limited, and various known methods can be applied. For example, there is a method of treating the substrate, preferably a substrate having a carbon element supported or adsorbed on the surface, with sulfuric acid, specifically, the method described in Non-Patent Document 1.

[0024] As a method for producing a silica porous body as a substrate of a solid acid catalyst, there is a sol-gel method (also referred to as a "molecular templating method" or a "template method") using a silica source (silica precursor compound) and an amphiphilic compound as a template. Hereinafter, a method for producing a carbon element-supported silica-titanium composite mesoporous body having a sulfo group as a surface functional group, which is suitable as a solid acid catalyst, will be described by taking the sol-gel method as an example. A general sol-gel method is, for example, a method in which a silica precursor compound is subjected to a sol-gel reaction (hydrolysis reaction and condensation reaction) around self-assembled micelle particles formed by a cationic surfactant to form an inorganic-organic nanocomposite, and then this is calcined or acid-treated (to remove the cationic surfactant). The above-mentioned suitable solid acid catalyst first uses the sol-gel method to produce a silica-titanium composite mesoporous body in which titanium elements are contained on the surface and / or inside of the substrate. At this time, it can be carried out in the same manner as a general sol-gel method except for using a titanium precursor compound described later together with a silica precursor compound (coexisting the silica precursor compound and the titanium precursor compound). Therefore, the types of each step, the operations and reaction conditions in each step in the sol-gel method applied when producing the silica-titanium composite mesoporous body can be appropriately determined with reference to the general sol-gel method. For example, the method described in Non-Patent Document 1 and a series of steps, the operations and reaction conditions in each step in the synthesis method in the examples described later are helpful for reference. In the above sol-gel method, by changing the type of the silica precursor compound, particularly the type of the amphiphilic compound, or the preparation conditions such as the solvent composition, temperature, and time, the characteristics or physical properties of the porous body such as the size of the mesopores (average pore diameter) and the shape of the mesopores, and the skeleton shape of the porous body can be adjusted or changed, which is the same as the general sol-gel method.

[0025] As the amphiphilic compound used as a template, a compound commonly used in a general sol-gel method can be used without particular limitation. Usually, an amphiphilic surfactant is used, and a cationic surfactant, a block copolymer, etc. are preferably used. In the present invention, it is preferable to use a cationic surfactant as a template in that the average pore diameter of the mesopores can be set relatively small, and the hydrolysis reaction efficiency and the glucose yield can be further increased. As the cationic surfactant, a surfactant commonly used as a template in the sol-gel method can be used without particular limitation, and examples thereof include ammonium-based cationic surfactants. As the ammonium-based cationic surfactant, an alkylammonium salt is preferable, a tetraalkylammonium salt is preferable, an ammonium salt containing a long-chain (6 or more carbon atoms) linear alkyl group is more preferable, and a mono-long-chain linear alkyltri-short-chain (4 or less carbon atoms) alkylammonium salt is particularly preferable. The anion forming the quaternary ammonium salt is not particularly limited, and examples thereof include inorganic anions such as hydroxide ions, halide ions, and perhalate ions. In addition, MCM-41 etc. are cited as representatives of silica mesoporous bodies prepared by the sol-gel method using a cationic surfactant, and SBA-15 etc. are cited as representatives of silica porous bodies prepared by the sol-gel method using a block copolymer.

[0026] As the silica precursor compound, a compound commonly used in a general sol-gel method can be used without particular limitation. For example, halides, hydroxides, alkoxides, etc. of silicon can be cited, and alkoxides and / or alkyl alkoxides of silicon are preferable. The number of carbon atoms of the alkyl group forming the alkyl alkoxide is not particularly limited, but 1 to 6 is preferable, and 1 to 3 is more preferable. In the sol-gel method described above, a titanium-containing compound is used together with a silica precursor compound. Examples of the titanium-containing compound include titanium precursor compounds that are converted into titanium elements together with the silica precursor compound by the sol-gel method. Preferred examples of the titanium precursor compound include titanium halides, hydroxides, alkoxides, etc., and titanium alkoxides and / or alkyl alkoxides of titanium (alkoxytitanium) are more preferred. The number of carbon atoms of 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, a carbon element is supported or adsorbed on the surface of the obtained silica-titanium composite mesoporous body. The method for supporting or adsorbing the carbon element is not particularly limited and is as described above. A sulfo group is introduced as a surface functional group into the carbon element-supported silica-titanium composite mesoporous body thus obtained. The method for introducing the sulfo group is not particularly limited and is as described above. The silica-titanium composite mesoporous body, the carbon element-supported silica-titanium composite mesoporous body, and / or the carbon element-supported silica-titanium composite mesoporous body with a sulfo group introduced can be appropriately pulverized or crushed.

[0028] [Step of bringing a liquid containing cellulose and water into contact with a solid acid catalyst] The production method of the present invention includes bringing a liquid (reaction liquid) containing cellulose and water into contact with the solid acid catalyst of the present invention. By this contact, cellulose can be hydrolyzed in the presence of the solid acid catalyst to be converted into glucose. Each component used in this contacting step may be one kind or two or more kinds.

[0029] In the step of bringing into contact, the hydrolysis reaction of cellulose that occurs is generally considered to involve the hydrolysis reaction of cellulose to oligosaccharides and the hydrolysis reaction of oligosaccharides to glucose. Therefore, in the step of bringing into contact, as the hydrolysis treatment (saccharification treatment) of cellulose, a sugar-containing solution containing glucose (also referred to as "saccharified solution" or "cellulose degradation product") is obtained. This sugar-containing solution usually contains glucose as the main component in addition to water and the solid acid catalyst, and also contains other components. Other components that the sugar-containing solution may contain include partial hydrolysis reactants of cellulose, reactants of glucose, etc. For example, sugars such as oligosaccharides of tetramer or higher, cellotriose, cellobiose, mannose, fructose, levoglucosan, and further, 5-hydroxymethylfurfural, furfural, etc. are included. In the present invention, the main component refers to the component with the largest contained mass among the contained components. In the step of bringing into contact using the solid acid catalyst of the present invention, the hydrolysis reaction efficiency of cellulose is high, and moreover, the occurrence and promotion of each side reaction with respect to the hydrolysis reaction to glucose can be suppressed. Therefore, glucose can be obtained with a high selectivity and a high yield. Therefore, the sugar-containing solution obtained in the step of bringing into contact contains glucose as the main component and contains other components in a low content. For example, as an example of the sugar-containing solution, a sugar-containing solution containing glucose as the main component and containing cellobiose, fructose, levoglucosan, 5-hydroxymethylfurfural (HMF) and furfural in a low total content can be mentioned.

[0030] A suitable sugar-containing solution obtained in the contacting step has a composition in which the total area value of peaks derived from components having a lower molecular weight than glucose is 0.01 to 0.2 times the area value of the peak derived from glucose when subjected to LC analysis using a refractive index detector. When the area ratio of the total area value to the area value of the peak derived from glucose (hereinafter sometimes referred to as "component area ratio") is 0.01 to 0.2 times, it can be seen that cellulose can be converted to glucose with a high selectivity in the above 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 the ethanol fermentation of glucose as the main reaction. Moreover, even if acetic acid bacteria are present, their growth and acetic acid fermentation can be highly suppressed, and the yield and selectivity (content rate) of ethanol by ethanol fermentation can be further increased. In terms of further increasing the efficiency of ethanol fermentation and further suppressing the growth and acetic acid fermentation of acetic acid bacteria to produce ethanol with a high yield and high selectivity, the above component area ratio is preferably 0.05 to 0.2 times, and more preferably 0.1 to 0.2 times. Here, the above component area ratio is a value measured by the method described in the examples described later.

[0031] The suitable sugar-containing solution may contain the above-mentioned partial hydrolysis reactant of cellulose, reactants such as glucose, etc., but satisfies the above-mentioned component area ratio for components having a lower molecular weight than glucose (sometimes referred to as "low molecular weight components") identified by LC analysis. The low molecular weight components cannot be uniquely determined by variations such as the origin and composition of the cellulose used in the hydrolysis reaction and the contacting conditions between glucose and the solid acid catalyst. Usually, low molecular weight components among the partial hydrolysis reactants of cellulose, reactants such as glucose, etc. are mentioned. For example, levoglucosan, HMF, furfural, etc., and further unidentified components are mentioned, and levoglucosan, HMF, and furfural are preferred.

[0032] Although the glucose content in the suitable sugar-containing liquid cannot be uniquely determined as described above, it is at least the content at which the above component area ratio is 0.01 to 0.2 times, and is the content within the above preferable range or the more preferable range. The glucose content in the suitable sugar-containing liquid, in terms of the mass ratio in all components contained in the cellulose decomposition composition, is preferably, for example, 50 to 99% by mass and more preferably 83 to 99% by mass in terms of efficiently producing ethanol.

[0033] In the production method of the present invention, cellulose can be efficiently hydrolyzed to obtain glucose as the main component. At this time, the conversion rate of cellulose, the selectivity of glucose (mass ratio of the glucose content to the content of other components), etc. vary depending on the type of cellulose, the type and amount of the solid acid catalyst, and further hydrolysis reaction conditions, etc., and thus cannot be uniquely determined. However, at least the yield of glucose can reach 45% or more.

[0034] In the production method of the present invention, a liquid (reaction liquid) containing cellulose and water and a solid acid catalyst are brought into contact under appropriate reaction conditions, usually under heating. The contacting method may be any method capable of bringing the three components of cellulose, water, and the solid acid catalyst into contact. Examples include a method of bringing a previously prepared reaction liquid into contact with the solid acid catalyst, and a method of bringing cellulose, water, and the solid acid catalyst into contact without previously preparing the reaction liquid (a method of bringing cellulose and the solid acid catalyst into contact in the presence of water). In the contacting step in the present invention, when the reaction liquid and the solid acid catalyst are brought into contact or introduced, etc., it includes a mode in which cellulose and water are separately brought into contact or introduced with the solid acid catalyst instead of the reaction liquid. As the step of bringing them into contact, for example, after charging a reaction solution and a solid acid catalyst into a sealed container, heating is carried out. The heating temperature (reaction temperature) of the hydrolysis reaction is not particularly limited, but can be, for example, 110 to 200 °C. In terms of enhancing the hydrolysis reaction efficiency of cellulose and suppressing the by-production of other components to increase the yield of glucose, the heating temperature is preferably 120 to 180 °C, and more preferably 120 to 150 °C. The heating time (reaction time) is appropriately determined according to the heating temperature, the hydrolysis reaction efficiency (conversion rate) of cellulose, the glucose yield, etc., and can be, for example, 1 to 48 hours. The inside of the sealed container under heating may be at normal pressure, but usually, it is in a pressurized state where the water vapor partial pressure exceeds, for example, 0.1 MPa. In the present invention, the hydrolysis reaction can also be carried out under a positively pressurized environment. The pressure at this time is not particularly limited and can be, for example, more than 0.1 MPa and 20 MPa or less, and preferably 0.1 to 10 MPa. The reaction environment (atmosphere) is not particularly limited and can be an inert gas atmosphere or the like, 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 usage amounts of the reaction solution and the solid acid catalyst are not particularly limited, but at least the amount of water in the reaction system (the amount of water present) should be not less than the amount required for the hydrolysis reaction of cellulose. The amount of water in the reaction system is preferably, for example, 0.1 to 1000 mass times, and more preferably 1 to 100 mass times, based on the amount of cellulose present, in terms of the miscibility (stirrability) and handleability of the reaction system, as well as the hydrolysis reaction efficiency and glucose yield. In addition, in the step of bringing them into contact, water can be added separately from the reaction solution, and the amount of water in the above reaction system refers to the amount of water derived from the reaction solution. When water is added, it is the total amount of the water derived from the reaction solution and the added water. The usage amount of the solid acid catalyst can be appropriately determined in consideration of reaction conditions, hydrolysis reaction efficiency, glucose yield, etc., and is preferably, for example, 0.01 to 10 mass times, and more preferably 0.1 to 5 mass times, based on the amount of cellulose present.

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

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

[0038] [Post-treatment step] In the production method of the present invention, the reaction mixture can be post-treated after the above-described contacting step to obtain glucose. Examples of the post-treatment of the reaction mixture include a step of cooling the reaction mixture and a step of solid-liquid separating the reaction mixture. The reaction mixture can be solid-liquid separated without cooling, but it is preferable to cool it in consideration of suppressing further reaction of glucose or workability, safety, etc. The cooling of the reaction mixture may be natural cooling or may be cooled using various refrigerants. The cooling temperature of the reaction mixture is not particularly limited and can usually be 100°C or lower, and is preferably 80°C or lower in terms of suppressing further reaction of glucose and maintaining a high yield of glucose, and is preferably near room temperature (for example, 15 to 40°C) in consideration of workability, safety, etc. The lower limit temperature of the cooling temperature can be, for example, 0°C or higher and is preferably 15°C or higher in terms of workability. The cooling rate at this time can be appropriately determined and is preferably decreased by 0.1 to 10°C per minute. The cooling time can be appropriately determined according to the heating temperature, cooling rate, etc. The appropriately cooled reaction mixture is subjected to solid-liquid separation to separate a sugar-containing liquid (cellulose decomposition liquid) mainly composed of glucose as a liquid phase and at least a solid acid catalyst and unreacted cellulose as a solid phase. The method for solid-liquid separation is not particularly limited, and examples thereof include a filtration method, a centrifugation method, and a precipitation method.

[0039] [Other steps] In the production method of the present invention, steps other than the above-mentioned contacting step and post-treatment step can also be carried out. For example, 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, when using the above-mentioned waste as a cellulose source, a step of removing impurities and contaminants in the waste, a step of removing lignin in cellulose, and the like can be mentioned. The method for isolating and purifying glucose can be applied without particular limitation to various known isolation methods and various purification methods. In addition, the solid acid catalyst used in the present invention can be reused in the separated and recovered state (for example, as a mixture with unreacted cellulose), and there is no need to perform the isolation step, washing step, and regeneration step of the solid acid catalyst. However, as the number of uses increases, the catalytic activity of the solid acid catalyst usually gradually decreases. Therefore, in consideration of a decrease in catalytic activity, hydrolysis reaction efficiency, or glucose yield, the solid acid catalyst can also be washed and / or regenerated. The washing and regeneration methods are not particularly limited.

[0040] The production method of the present invention can obtain glucose from cellulose in a relatively short time with a high yield through a simple and safe process of bringing the reaction solution into contact with the solid acid catalyst of the present invention. In addition, the post-treatment process of the contacting process is also simple and safe, and the separated and recovered solid acid catalyst can be reused. Furthermore, since the occurrence and promotion of each side reaction can be suppressed during the hydrolysis reaction of cellulose, glucose can also be produced with high selectivity (high purity). As a result, the production method of the present invention and the solid acid catalyst of the present invention are suitable as a method for obtaining a raw material for producing bioethanol using non-edible biomass as a raw material. Moreover, when using waste pulp as a cellulose source, the hydrolysis reaction efficiency of cellulose and the yield of glucose can be further increased, and the effective utilization of non-edible biomass resources becomes possible. Therefore, the production method of the present invention and the solid acid catalyst of the present invention can efficiently produce glucose from cellulose at low cost, and are also suitable for industrialization of the hydrolysis reaction of cellulose (glucose production method) and the production method of bioethanol.

Examples

[0041] Hereinafter, the present invention will be described in more detail 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 Solid Acid Catalyst (i) for Producing Glucose Containing Ti Element> (1) Preparation of Silica Porous Body (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 titanium tetraisopropoxide and 50.0 g of 2-propanol was added dropwise thereto at room temperature (25°C). After stirring for 30 minutes, 190.5 g of tetramethoxysilicate was added dropwise. After adding 5.0 g of 2-propanol, stirring was continued for 3 hours, and as a result, a precipitate was formed.

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

[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 the reflux temperature for 1 hour while stirring, and after allowing to cool, the liquid phase was removed by filtration. The same operation 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 finally filtered solid 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 under a flowing air atmosphere.

[0046] (Fifth step) The calcined solid obtained in the fourth step was pulverized 8 times with a hammer mill to obtain a powdery silica porous body (i) having an average particle diameter of 10 μm. The average particle diameter was measured using a laser diffraction / scattering particle size distribution analyzer (LA-950 manufactured by Horiba, Ltd.) with ion-exchanged water as the dispersion medium and calculated on a volume basis.

[0047] The powdery silica porous body (i) prepared as described above is a silica-titanium composite mesoporous body, with a specific surface area of 1160 m 2 / g, a total pore volume of 0.60 mL / g, and an average pore diameter of 2.1 nm. The specific surface area and the total pore volume were measured by measuring the nitrogen adsorption isotherm at liquid nitrogen temperature with BELSORP MINI X (manufactured by MicrotracBEL) after vacuum degassing the silica porous body (i) at 120 °C for 2 hours, and were determined from the BET method and the value of the nitrogen adsorption amount near the relative pressure (P / P0 = 0.96), respectively. The average pore diameter was calculated from the value of the total pore volume and the value of the specific surface area by the following (Equation 1). (Formula 1): Average pore diameter (nm) = 4 × total pore volume (mL / g) / specific surface area (m 2 / g) × 1000

[0048] When the Ti concentration in the powdered silica porous body (i) prepared as described above was analyzed by XRF, it was 1.5% by mass.

[0049] (2) Preparation of silica porous body-carbon composite (i) To 2.5 g of the silica porous body (i), furfuryl alcohol (FA) serving as a carbon source was vacuum-impregnated into the pores of the silica porous body at room temperature. After impregnation, the FA on the outer surface of the silica porous body was washed with mesitylene, and then heated at 150 °C for 24 hours to polymerize the FA in the pores. The solid obtained after 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 in the pores, and the silica porous body-carbon composite (i) was prepared as a carbon element-supported silica-titanium composite mesoporous body.

[0050] (3) Preparation of solid acid catalyst (i) 1 g of the silica porous body-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, it was washed with water at 50 °C until the pH of the washing liquid showed the same value as that of purified water. After washing with water, the solid obtained by filtration was dried under reduced pressure at 120 °C for 12 hours to obtain 1 g of the solid acid catalyst (i) as a carbon element-supported silica-titanium composite mesoporous body having a sulfo group as a surface functional group.

[0051] <Experimental Example 1-2. Preparation of Ti element-free solid acid catalyst (ii)> (1) Preparation of silica porous body-carbon composite (ii) The solid acid catalyst (ii) was prepared by the same method as 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 Pluronic F127 (a reagent manufactured by Fujifilm Wako Pure Chemical Corporation), which is a surfactant serving as a mold, was added to a solution obtained by mixing 32 g of ethanol and 0.3 g of concentrated hydrochloric acid, and ultrasonic treatment was performed for 1 hour. Next, 8.32 g of tetraethoxysilane (TEOS) serving as a silica source and 10 g of an aqueous sucrose solution serving as a carbon source were added, and ultrasonic treatment was performed again for 1 hour. The mass ratio of the Si element contained in TEOS to the C element contained in sucrose was Si:C = 33:66. Thereafter, heating was performed at 40°C for 20 hours to evaporate ethanol, and then heating was performed at 160°C for 24 hours for thermal polymerization. The solid obtained after thermal polymerization was heat-treated in an electric furnace at 550°C for 3 hours in a nitrogen atmosphere for carbonization to prepare a silica porous body-carbon composite (ii).

[0052] (2) Preparation of solid acid catalyst (ii) 1 g of the silica porous body-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, washing with water was performed at 50°C until the pH of the washing liquid showed the same value as that of purified water. After washing with water, the filtered solid was dried under reduced pressure at 120°C for 12 hours to obtain a solid acid catalyst (ii).

[0053] [Experimental Example 1-3. Preparation of Ti element-free solid acid catalyst (iii)] (1) Preparation of silica porous body-carbon composite (iii) As the silica porous body, commercially available MCM-41 (a reagent manufactured by Sigma-Aldrich, Ti element-free, average pore diameter 2.1 to 2.7 nm (catalog value)) was used. 2.5 g of MCM-41 was vacuum-impregnated with furfuryl alcohol (FA) serving as a carbon source into the pores at room temperature. After impregnation, the FA on the outer surface of MCM-41 was washed with mesitylene, and then heated at 150°C for 24 hours to polymerize the FA in the pores. The solid obtained after 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 in the pores, thereby preparing a silica porous body-carbon composite (iii).

[0054] (2) Preparation of solid acid catalyst (iii) 1 g of the silica porous body-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, washing with water was carried out at 50 °C until the pH of the washing liquid showed the same value as that of purified water. After washing with water, the filtered solid was dried under reduced pressure at 120 °C for 12 hours to obtain a solid acid catalyst (iii).

[0055] <Experimental Example 2. Measurement of Carbon Content of Silica Porous Body-Carbon Composite> The carbon contents of the silica porous body-carbon composites (i) to (iii) were determined from the weight loss rate by thermogravimetric analysis. The thermogravimetric analysis was carried out in an air atmosphere with the furnace temperature increased 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 Sulfonic Group Content of Solid Acid Catalyst> The sulfonic group contents of the solid acid catalysts (i) and (ii) were measured by titration using an automatic potentiometric titrator (manufactured by Kyoto Electronics). 50 mg of each solid acid catalyst was weighed into a screw tube vial, 30 mL of an NaCl aqueous solution prepared to 0.05 N was added using a whole pipette, and the mixture was stirred with a stirrer for 15 hours. After stirring, the solution in the screw tube vial was filtered, 10 mL was collected from the filtrate using a whole pipette and transferred to a 50 mL beaker. 2 drops of phenolphthalein solution were added to the 50 mL beaker using a Pasteur pipette, and 0.005 N NaOH aqueous solution was added dropwise by 0.1 mL each for titration. The Na + exchange amount was calculated to determine the sulfonic group content. The results are shown in Table 2.

[0058]

Table 2

[0059] <Example 1> (1) Hydrolysis reaction of cellulose As the cellulose of the reaction substrate, that processed as follows was used. Into a ceramic pot mill, 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. It was set on a tabletop pot mill turntable and ball milled at 200 rpm for 120 hours. Into an autoclave equipped with a stirrer, 50 mg of the ball-milled cellulose, 50 mg of the solid acid catalyst (i), and 5 mL of purified water were added. While stirring at 300 rpm, the temperature was raised from room temperature to 150 °C in about 30 minutes, and then the hydrolysis reaction of cellulose 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. Then, the reaction solution was filtered to separate it into a liquid and a solid, obtaining 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. The HPLC analysis was performed using LC-20A (manufactured by Shimadzu Corporation), with Shоdex SP0810 (manufactured by Resonac Corporation, inner diameter 8 mm, length 300 mm) for the column, purified water (0.5 mL / min) for the mobile phase, and a differential refractive index detector (RID-20A) for the detector, 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 value obtained by subtracting the mass of the added solid acid catalyst from the mass measured after drying the solid residue (i) at 100 °C for 12 hours was determined as the mass of unreacted cellulose.

[0062] (4) Calculation of glucose yield The glucose yield was determined by the following (Equation 3) from the amount of glucose obtained calculated from the following (Equation 2) and the charged amount of cellulose. (Equation 2): Glucose yield (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 the above (2). (Equation 3): Glucose yield (%) = (glucose yield) / (charge amount of cellulose) × 100

[0063] The component area ratio of the cellulose decomposition solution is calculated as follows using the chromatogram obtained by HPLC analysis of the cellulose decomposition solution. An example of the 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 used to identify the types of each component in the cellulose decomposition product using the chromatogram. Specifically, each component detected in the chromatogram is identified by comparing it with the retention time of each compound reagent in the above column: Shоdex SP0810, for example.

[0064] Next, the peak area values derived from components with a lower molecular weight than glucose and glucose that elute after the retention time of glucose in the obtained chromatogram are obtained by the following waveform processing parameter processing. The waveform processing parameters used for peak detection calculate the area value under the conditions where the slope is 200 μV / min, the width is 5 sec, and the minimum area is 1000 counts as the minimum area / height. Using the area values of each component thus obtained, the peak area value derived from glucose is divided by the total value of the peak area values derived from components with a lower molecular weight to calculate the component area ratio. The component area ratio of the cellulose decomposition 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 hydrolysis reaction of cellulose 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 instead of the solid acid catalyst (i) in the hydrolysis reaction of cellulose.

[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 instead of the solid acid catalyst (i) in the hydrolysis reaction of cellulose.

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

Table 3

[0069] It was found that Comparative Example 1 without using a solid acid catalyst, and Comparative Examples 2 and 3 using the solid acid catalyst (ii) or (iii) not containing Ti element had low glucose yields and were not sufficient for industrial use. On the other hand, in Example 1 using the solid acid catalyst (i) containing Ti element, a high glucose yield of 70% was obtained. Although the hydrolysis reaction was carried out using commercially available cellulose in Example 1, it can be seen from this result that the same result can be obtained even when using cellulose derived from waste pulp. In the present invention, the details of the reason for obtaining a high glucose yield are not yet clear, but it is assumed that due to the catalytic action of the Ti element contained in the silica porous body (i), the carbon coating layer formed during the preparation of the silica porous body-carbon composite (i) has a structure suitable for the hydrolysis reaction of cellulose. Thus, the production method of the present invention and the solid acid catalyst of the present invention can produce glucose from cellulose by a simple and safe process at low cost and with a high yield sufficient for industrial production, preferably with a high selectivity (high purity). Therefore, the production method of the present invention and the solid acid catalyst of the present invention are suitable as a method for obtaining a raw material for producing bioethanol using non-edible biomass as a raw material and as a solid acid catalyst, and it can be seen that they are suitable for industrial production of the hydrolysis reaction of cellulose and the production method of bioethanol.

Claims

**Claim 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. **Claim 2** The production method according to claim 1, wherein the silica has mesopores. **Claim 3** The production method according to claim 1 or 2, wherein the carbon element is supported on the surface of the silica. **Claim 4** The production method according to claim 1 or 2, wherein the titanium element is contained in the silica. **Claim 5** The production method according to claim 3, wherein the titanium element is contained in the silica. **Claim 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. **Claim 7** The solid acid catalyst for glucose production according to claim 6, wherein the silica has mesopores. **Claim 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. **Claim 9** The solid acid catalyst for glucose production according to claim 6 or 7, wherein the titanium element is contained in the silica. **Claim 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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