JP5463627B2 - Method for separating saccharification of plant fiber material - Google Patents

Description

  The present invention relates to a saccharification / separation method for plant fiber materials, in which sugars mainly composed of glucose are produced by saccharification of plant fiber materials, and the resulting sugars are separated.

Decompose plant fibers that are biomass, such as sugar cane (bagasse) and wood fragments, to produce sugars, mainly glucose and xylose, from cellulose and hemirose, and use the resulting sugars as food or fuel It has been proposed and put into practical use. In particular, a technique for fermenting monosaccharides obtained by decomposing plant fibers to produce alcohols such as ethanol as fuel has attracted attention.
Conventionally, various methods for decomposing cellulose and hemicellulose to produce sugars such as glucose have been proposed (for example, Patent Documents 1 to 4). As a general method, sulfuric acid such as dilute sulfuric acid or concentrated sulfuric acid is proposed. And a method of hydrolyzing cellulose using hydrochloric acid (Patent Document 1, etc.). There are also a method using a cellulase enzyme (Patent Document 2, etc.), a method using a solid catalyst such as activated carbon or zeolite (Patent Document 3, etc.), and a method using pressurized hot water (Patent Document 4, etc.).

JP-A-8-299000 JP 2006-149343 A JP 2006-129735 A JP 2002-59118 A

  However, the method of hydrolyzing cellulose using an acid such as sulfuric acid has a problem that it is difficult to separate the acid as a catalyst and the produced sugar from the hydrolysis reaction mixture obtained by hydrolysis. This is because glucose, which is a main component of the hydrolysis product of cellulose, and an acid, which is a catalyst for hydrolysis, are both water-soluble. Acid removal from the hydrolysis reaction mixture by neutralization or ion exchange is not only labor and costly, but it is difficult to completely remove the acid, and the acid often remains in the ethanol fermentation process. . As a result, even in the ethanol fermentation process, even when the pH is adjusted to the optimum pH for the yeast activity, the yeast activity decreases due to the increase in the salt concentration, resulting in a decrease in fermentation efficiency.

In particular, when concentrated sulfuric acid is used, it is very difficult to remove the sulfuric acid to the extent that the yeast is not inactivated in the ethanol fermentation process, and a great deal of energy is required. In contrast, when dilute sulfuric acid is used, sulfuric acid can be removed relatively easily, but cellulose must be decomposed under high temperature conditions, and energy is required.
Furthermore, acids such as sulfuric acid and hydrochloric acid are very difficult to separate, recover and reuse. Therefore, using these acids as a catalyst for producing glucose is one of the causes for raising the cost of bioethanol.

  Moreover, in the method using pressurized hot water, it is difficult to adjust the conditions, and it is difficult to produce glucose with a stable yield. There is also concern that not only glucose will be degraded and the yield of glucose will be reduced, but also the action of yeast will be reduced by the degradation components, and fermentation will be suppressed. In addition, since the reaction apparatus (supercritical apparatus) is expensive and has low durability, there is a problem in terms of cost.

As a result of intensive studies on the saccharification of cellulose, the present inventors have found that the cluster acid in a pseudo-molten state has excellent catalytic activity for hydrolysis of cellulose and can be easily separated from the produced sugar. The patent application has already been filed (Japanese Patent Application Nos. 2007-115407 and 2007-230711). According to this method, unlike the conventional concentrated sulfuric acid method and dilute sulfuric acid method, it is possible to recover and reuse the hydrolysis catalyst, and from the hydrolysis of cellulose to the recovery of aqueous sugar solution and the recovery of hydrolysis catalyst. Can improve the energy efficiency of all processes.
Further, the present inventors have found that an organic solvent in which the cluster acid catalyst is soluble can be used as a hydrolysis reaction solvent for plant fiber materials, and has filed a patent application.

When the plant fiber material is hydrolyzed to generate sugar, the reaction rate is improved by reducing the particle diameter of the plant fiber material as a raw material. Plant fiber materials contain lignin in addition to cellulose and hemicellulose, and these are intricately mixed. Therefore, the plant fiber material having a large particle size is unlikely to hydrolyze cellulose and hemicellulose present therein, and the reaction rate tends to decrease. For example, the plant fiber material having a particle size of 50 μm or less has a reaction rate of about 85%, while the plant fiber material having a particle size of 150 μm or less has a reaction rate of about 40%. .
However, energy is required to pulverize the plant fiber material and reduce its particle size. For example, the energy for pulverizing wood to about 150 μm or less is about 5% of the high calorific value, but the energy for crushing wood to 20 μm or less jumps to about 200% of the high calorific value. That is, depending on the raw material of the plant fiber material, the energy balance may be deteriorated by the energy required for the pulverization.

  The present invention has been accomplished in view of the above circumstances, and provides a saccharification and separation method having a high contact opportunity between the cluster acid catalyst and cellulose or hemicellulose contained in the plant fiber material and having a high reaction rate of the plant fiber material. The purpose is to do.

The saccharification / separation method of a plant fiber material of the present invention is a saccharification / separation method of a plant fiber material that hydrolyzes a plant fiber material to produce and separate sugars mainly composed of glucose, and is in a pseudo-molten state. using cluster acid catalyst, the cellulose contained in the plant fiber material is hydrolyzed, it comprises a hydrolysis step to produce glucose, before the hydrolysis step, in advance, to the plant fiber material, water , ethanol, methanol, n- propanol, octanol, diethyl ether and at least one of the cluster acid catalyst selected from diisopropyl ether aft by filling a soluble liquid, in the hydrolysis step, the pseudo-molten state The cluster acid catalyst and the plant fiber material have a weight ratio of the cluster acid catalyst: the plant fiber material = 1: 1 to 4: 1. They were mixed in ratio as an inner, characterized in that to function the cluster acid catalyst in a pseudo-molten state as the reaction solvent.

In the present invention, at least one liquid selected from water, ethanol, methanol, n-propanol, octanol, diethyl ether, and diisopropyl ether in which the cluster acid catalyst is soluble in the plant fiber material (hereinafter referred to as filling liquid). Therefore, the cluster acid catalyst can diffuse in the filling liquid filled in the plant fiber material and penetrate into the plant fiber material. Therefore, according to the present invention, when the filling liquid is not filled, even the cellulose existing inside the plant fiber material that cannot be contacted with the cluster acid catalyst is filled with the filling liquid. Since it is contacted with the cluster acid catalyst and hydrolyzed, the reactivity can be improved. Moreover, according to this invention, it is possible to reduce the energy required to reduce the diameter of the plant fiber material. In addition, since the cluster acid catalyst in the pseudo-melted state also functions as a reaction solvent, the form (size, fiber state, etc.) of the plant fiber material, water or an organic solvent as the reaction solvent in the hydrolysis step, etc. It may not be used.

  Examples of the method of filling the plant fiber material with the liquid include a method of immersing the plant fiber material in a liquid in which the cluster acid catalyst is soluble and applying ultrasonic vibration to the liquid. .

  According to the present invention, in the saccharification and separation of plant fiber materials using a cluster acid catalyst, the chance of contact between the cluster acid catalyst and cellulose or hemicellulose contained in the plant fiber material is increased, and the reaction rate of the plant fiber material is increased. can do. Therefore, in the present invention, it is possible to reduce the energy required for pulverizing the plant fiber material, and the energy efficiency in the saccharification and separation of the plant fiber material can be improved.

  The saccharification / separation method for a plant fiber material according to the present invention is a saccharification / separation method for a plant fiber material that hydrolyzes the plant fiber material to produce and separate sugars mainly composed of glucose, and comprises a cluster acid catalyst And a hydrolysis step of hydrolyzing cellulose contained in the plant fiber material to produce glucose. Before the hydrolysis step, the cluster fiber catalyst is previously added to the plant fiber material. It is characterized by being filled with a soluble liquid.

A heteropolyacid that is a typical cluster acid catalyst has a diameter of about 1 to 2 nm, typically just over 1 nm, and has a molecular size capable of diffusing in the plant fiber material. Cellulose, hemicellulose, and lignin are mixed in a complicated manner, which prevents the diffusion of the cluster acid catalyst.
The present invention improves the diffusibility of the cluster acid catalyst in the plant fiber material by filling the plant fiber material with a liquid that can dissolve the cluster acid catalyst (filling liquid) in advance. . When the plant fiber material is filled with a liquid capable of dissolving the cluster acid catalyst, the cluster acid catalyst is mixed with the plant fiber material in the hydrolysis step. It can be dissolved in the filling liquid and diffused in the filling liquid to reach the inside of the plant fiber material. That is, the contact property between the cluster acid catalyst and cellulose or hemicellulose contained in the plant fiber material is improved, and the hydrolysis reaction of cellulose or the like is promoted.
Therefore, according to the present invention, the reaction rate of the plant fiber material can be increased. In addition, since there is a high chance of contact between cellulose and hemicellulose present in the plant fiber material and the cluster acid catalyst, a high reaction rate can be achieved even when plant fiber materials having a larger diameter than before are used. Can be maintained. That is, it is possible to reduce the energy required for the pulverization of the plant fiber material, and the energy efficiency in the saccharification and separation of the plant fiber material can also be achieved.

Hereinafter, the saccharification separation method of the plant fiber material of the present invention will be described in detail.
First, the process (henceforth a filling process) of filling a plant-based fiber material with a soluble liquid of a cluster acid catalyst will be described.

The plant-based fiber material is not particularly limited as long as it contains cellulose or hemicellulose. A cellulosic biomass is mentioned. Further, cellulose or hemicellulose separated from the biomass, or artificially synthesized cellulose or hemicellulose itself may be used.
These fiber materials are usually used in a powder form from the viewpoint of dispersibility in the reaction system. As a method for forming a powder, a general method may be used. In the present invention, since the reaction opportunity between the cluster acid catalyst and the plant fiber material in the hydrolysis process is improved by the filling liquid, even a plant fiber material having a diameter of 50 μm or more has a high reaction rate. Can be secured. From the viewpoint of the filling efficiency of the filling liquid, the miscibility with the cluster acid catalyst, and the improvement of the reaction opportunity, it is particularly preferably in the form of a powder having a diameter of several μm to 200 μm.

Moreover, the fiber material may dissolve the lignin contained by performing a cooking process beforehand as needed. By dissolving and removing lignin, it is possible to improve the chance of contact between the cluster acid catalyst and cellulose in the hydrolysis process, and at the same time, the amount of residue contained in the hydrolysis reaction mixture can be reduced, It is possible to suppress a decrease in sugar yield and a decrease in cluster acid recovery rate by mixing the generated sugar and cluster acid. When cooking is performed, the degree of pulverization of the plant fiber material can be made relatively small (the pulverization is rough), so that the labor, cost and energy for making the fiber material into powder can be reduced. is there.
Examples of the cooking treatment include alkalis and salts such as NaOH, KOH, Ca (OH) ₂ , Na ₂ SO ₃ , NaHCO ₃ , NaHSO ₃ , Mg (HSO ₃ ) ₂ , Ca (HSO ₃ ) _2, and aqueous solutions thereof. A method in which a mixture of an SO ₂ solution, a gas such as NH ₃ , and a plant fiber material (for example, several centimeters to several millimeters) is brought into contact with water under steam. Specific conditions include a reaction temperature of 120 to 160 ° C. and a reaction time of several tens of minutes to about 1 hour.

The liquid that fills the plant fiber material and is soluble in the cluster acid catalyst (filled liquid) is not particularly limited as long as it can dissolve the cluster acid catalyst. Specifically, it is preferable that the solubility of the cluster acid in the filling liquid is 50 g / 100 ml or more, particularly 100 g / ml or more, and further 500 g / 100 ml or more.
Specific examples of the liquid include alcohols such as water, ethanol, methanol, n-propanol and octanol, and ethers such as diethyl ether and diisopropyl ether. Of these, octanol is preferred from the viewpoints of handleability and safety.

  The method of filling the plant fiber material with the filling liquid is not particularly limited as long as the gas or liquid in the plant fiber material can be replaced with the filling liquid. For example, as a suitable method, a method of immersing the plant fiber material in the filling liquid and applying ultrasonic vibration to the filling liquid, the plant fiber material is evacuated, and the internal air is removed, A method of contacting the filling liquid, and a method of condensing the filling liquid in the plant fiber material by heating the filling liquid in a state where the plant fiber material is immersed in the filling liquid to increase the saturated vapor pressure of the filling liquid. , Etc. Among these, from the viewpoint of cost and ease, a method of immersing the plant fiber material in the filling liquid and applying ultrasonic vibration to the filling liquid is preferable.

Next, a hydrolysis process for hydrolyzing cellulose contained in the plant fiber material to generate sugars mainly composed of glucose will be described.
Although the description here mainly focuses on the process of producing glucose from cellulose, the plant fiber material contains hemicellulose in addition to cellulose, and the product is not limited to glucose but other simple substances such as xylose. There are sugars, and these cases are also included in the scope of the present invention.

  In the present invention, the cluster acid used as a catalyst for hydrolysis of plant fiber materials is a condensed product of a plurality of oxo acids, that is, a so-called polyacid. Many polyacids are often oxidized to the maximum oxidation number due to the combination of multiple oxygen atoms in the central element, exhibiting excellent properties as oxidation catalysts, and known to be strong acids. It has been. For example, the acid strength (pKa = −13.16) of phosphotungstic acid that is a heteropolyacid is stronger than the acid strength (pKa = −11.93) of sulfuric acid. That is, for example, even under mild conditions such as 50 ° C., cellulose and hemicellulose can be decomposed into monosaccharides such as glucose and xylose.

  The cluster acid used in the present invention may be a homopolyacid or a heteropolyacid, but a heteropolyacid is preferred because of its strong oxidizing power and acid strength. The heteropolyacid is not particularly limited, and HwAxByOz (A: heteroatom, B: polyatom that forms the skeleton of polyacid, w: composition ratio of hydrogen atom, x: composition ratio of heteroatom, y: composition ratio of polyatom , Z: composition ratio of oxygen atom). Examples of the poly atom B include atoms such as W, Mo, V, and Nb that can form a polyacid. Examples of the hetero atom A include atoms such as P, Si, Ge, As, and B that can form a heteropolyacid. One or more polyatoms and heteroatoms may be contained in one heteropolyacid molecule.

From the balance between the strength of the acid strength and the oxidizing power, phosphotungstic acid H ₃ [PW ₁₂ O ₄₀ ] and silicotungstic acid H ₄ [SiW ₁₂ O ₄₀ ], which are tungstates, are preferable. Next, phosphomolybdic acid H ₃ [PMo ₁₂ O ₄₀ ], which is a molybdate, can be suitably used.

Here, FIG. 1 shows the structure of a heteropolyacid (phosphotungstic acid) of Keggin type [X ^{n +} M ₁₂ O ₄₀ : X = P, Si, Ge, As, M = Mo, W, etc.]. A tetrahedron XO ₄ exists at the center of a polyhedron composed of octahedral MO ₆ units, and has a lot of crystal water around the structure. The structure of the cluster acid is not particularly limited, and may be, for example, a Dawson type other than the Keggin type.
Here, water that is hydrated or coordinated with a clustered cluster acid catalyst composed of a crystalline cluster acid catalyst and a clustered acid catalyst of several molecules is referred to as “crystal water” that is generally used. Use terms instead. This crystal water contains anion water hydrogen-bonded to the anion constituting the cluster acid catalyst, coordinated water coordinated to the cation, lattice water not coordinated to the cation and anion, and OH group. Is also included.
A clustered cluster acid catalyst is an aggregate composed of about 1 to several molecules of cluster acid and is different from a crystal. A cluster state can be obtained even in a solid state, a pseudo-molten state, or a state dissolved (colloidal) in a solvent.

The cluster acid catalyst as described above is in a solid state at room temperature, but when heated and heated, it becomes a pseudo-melted state, acts as a catalyst that exhibits catalytic activity for the hydrolysis reaction of cellulose and hemicellulose, and is a reaction solvent. Also works. Here, the pseudo-molten state is apparently melted, but is not a completely melted liquid state, but a state close to a colloid (sol) in which cluster acids are dispersed in the liquid, This is a state showing fluidity. Whether or not the cluster acid is in a pseudo-molten state can be confirmed by visual observation, or in the case of a homogeneous system, can also be confirmed by a DTG (differential scanning calorimeter) or the like.
The pseudo-molten state of the cluster acid varies depending on the temperature and the amount of crystallization water contained in the cluster acid catalyst (see FIG. 2). Specifically, phosphotungstic acid, which is a cluster acid, lowers the temperature at which a pseudo-molten state is developed as the amount of crystal water contained increases. That is, the cluster acid catalyst containing a large amount of crystal water exhibits a catalytic action for the hydrolysis reaction of cellulose at a lower temperature than the cluster acid catalyst having a relatively small amount of crystal water. That is, by controlling the amount of crystallization water contained in the cluster acid catalyst in the reaction system of the hydrolysis step, the cluster acid catalyst can be put in a pseudo-molten state at the target hydrolysis reaction temperature. For example, when phosphotastenic acid is used as the cluster acid catalyst, the hydrolysis reaction temperature can be controlled within the range of 110 ° C. to 40 ° C. by the amount of water of crystallization of the cluster acid (see FIG. 2).

  FIG. 2 shows the relationship between the water ratio of crystallization of a heteropolyacid (phosphotungstic acid), which is a typical cluster acid catalyst, and the temperature at which a pseudo-molten state begins to appear (apparent melting temperature). The cluster acid catalyst is in a solidified state in the region below the curve and in a pseudo-melted state in the region above the curve. In FIG. 2, the water ratio of crystallization (%) is a value where the standard amount of crystallization water n (n = 30) of cluster acid (phosphotungstic acid) is 100%. The amount of water of crystallization can be specified by a thermal decomposition method (TG measurement) because there is no component that thermally decomposes and volatilizes even when the cluster acid catalyst is at a high temperature such as 800 ° C.

Here, the standard amount of crystallization water is the amount of crystallization water (number of molecules) contained in one molecule of cluster acid in a solid state at room temperature, and varies depending on the type of cluster acid. For example, phosphotungstic acid is about 30 [H ₃ [PW ₁₂ O ₄₀ ] · nH ₂ O (n≈30)], and silicotungstic acid is about 24 [H ₄ [SiW ₁₂ O ₄₀ ] · nH ₂ O (n≈ 24)] and phosphomolybdic acid is about 30 [H ₃ [PMo ₁₂ O ₄₀ ] · nH ₂ O (n≈30)].

  The amount of water of crystallization contained in the cluster acid catalyst can be adjusted by controlling the amount of water present in the hydrolysis reaction system. Specifically, when it is desired to increase the amount of water of crystallization of the cluster acid catalyst, that is, to lower the reaction temperature, for example, water is added to the mixture containing the plant fiber material and the cluster acid catalyst, or the atmosphere of the reaction system Water may be added to the hydrolysis reaction system, for example, by increasing the relative humidity. As a result, the cluster acid takes in the added water as crystal water, and the apparent melting temperature of the cluster acid catalyst decreases.

On the other hand, when it is desired to reduce the amount of water of crystallization of the cluster acid catalyst, that is, to increase the reaction temperature, water is removed from the hydrolysis reaction system, for example, the reaction system is heated to evaporate the water, By adding a desiccant to the mixture containing the plant fiber material and the cluster acid catalyst, the crystallization water of the cluster acid catalyst can be reduced. As a result, the apparent melting temperature of the cluster acid catalyst is increased.
As described above, the amount of crystallization water of the cluster acid can be easily controlled, and the hydrolysis reaction temperature of cellulose can be easily adjusted by controlling the amount of crystallization water.

When the cluster acid catalyst is used in a pseudo-molten state, the ratio of the plant fiber material to the cluster acid catalyst is the property (for example, size) and type of the plant fiber material used, the stirring method and the mixing method in the hydrolysis step. Depends on etc. Therefore, it may be determined as appropriate according to the conditions of the hydrolysis step, but is preferably in the range of cluster acid catalyst: plant fiber material (weight ratio) = 1: 1 to 4: 1, usually About 1: 1 to 2: 1. However, this ratio varies depending on the mixing method, but considering the energy cost, it is better to have as few cluster acid catalysts as possible.
Since the cluster acid catalyst in the pseudo-melted state also functions as a reaction solvent, it can be used for the form (size, fiber state, etc.) of the plant fiber material, the mixing ratio and volume ratio of the cluster acid catalyst and the plant fiber material, etc. However, it is not necessary to use water or an organic solvent as a reaction solvent in the hydrolysis step.

  In the hydrolysis step, the cluster acid catalyst is not limited to a pseudo-molten state, and an organic solvent capable of dissolving the cluster acid catalyst can be used as a reaction solvent and dissolved in the organic solvent. When using an organic solvent as the hydrolysis reaction solvent, the mixing and contact properties of the cluster acid catalyst and the plant fiber material are high, so that the saccharification reactivity of cellulose contained in the plant fiber material is maintained and the pseudo-melt state As compared with the case of using the cluster acid catalyst, the amount of the cluster acid catalyst used can be reduced. That is, the amount of cluster acid catalyst used per unit sugar weight to be produced can be reduced, and the sugar production cost can be reduced.

As an organic solvent soluble in the cluster acid catalyst that can be used as a hydrolysis reaction solvent (hereinafter sometimes referred to as a reaction organic solvent), it is sufficient that the cluster acid catalyst is soluble at least at the hydrolysis reaction temperature. However, usually, a cluster acid catalyst that is soluble at a temperature lower than the hydrolysis reaction temperature, typically at room temperature, is used. Specifically, it is preferable that the solubility of the cluster acid catalyst is 50 g / 100 ml or more, particularly 250 g / 100 ml or more, and further 500 g / 100 ml or more.
From the viewpoint of suppressing evaporation of the reaction organic solvent in the hydrolysis step, the reaction organic solvent preferably has a boiling point higher than the reaction temperature in the hydrolysis step. Specifically, the boiling point of the reaction organic solvent is preferably 90 ° C. or higher, particularly 125 ° C. or higher, and more preferably 150 ° C. or higher.

In addition, in the sugar separation step, which is a subsequent step of the hydrolysis step, in order to increase the sugar separation efficiency, it is preferable that the reaction organic solvent is hardly soluble in sugar such as glucose. When the sugar is hardly soluble in the reaction organic solvent, the produced sugar precipitates in the reaction organic solvent in the hydrolysis step, so the hydrolysis reaction mixture obtained after the hydrolysis step (generated sugar, cluster acid catalyst) And a reaction organic solvent (including a residue in some cases) may be separated into a liquid component containing a cluster acid catalyst and a reaction organic solvent and a solid component containing a sugar by solid-liquid separation by filtration or the like. it can.
Here, the organic solvent in which sugar is hardly soluble refers to an organic solvent having a sugar solubility in an organic solvent of 1 g / 100 ml or less, preferably 0.2 g / 100 ml or less, more preferably 0.1 g / 100 ml. It is as follows. Most preferably, the sugar is insoluble in the reaction organic solvent (solubility is 0 g / 100 ml).

Examples of the organic solvent having cluster acid catalyst solubility and poor sugar solubility as described above include, for example, a polar organic solvent, specifically, a polar organic solvent having a relative dielectric constant of 8 or more, and more specifically, a relative dielectric constant. 8-18 polar organic solvents are mentioned.
From the above viewpoint, the first organic solvent is preferably a high-boiling polar organic solvent having a boiling point higher than the reaction temperature in the hydrolysis step and hardly soluble in sugar. Specifically, a high boiling polar organic solvent having a boiling point of 90 ° C. or higher and a relative dielectric constant of 8 to 18 is preferable.

  Although a thing suitable as a reaction organic solvent is not specifically limited, Specifically, C6-C10 alcohol (it may be linear or may have a branched structure) is mentioned, Especially, it is flammability. From the viewpoint, the alcohol having 8 to 10 carbon atoms is preferable. Specific examples include 1-hexanol, 1-heptanol, 2-heptanol, 1-octanol, 2-octanol, 1-decanol, 1-nonanol and the like, among which 1-octanol, 2-octanol, 1-decanol 1-nonanol is preferable, and 1-octanol and 2-octanol are particularly preferable.

  In the hydrolysis step, when the cluster acid catalyst is dissolved in a reaction organic solvent and used, the preferred ratio of the plant fiber material to the cluster acid catalyst is the property of the plant fiber material to be used (for example, size, type of fiber material). Etc.), depending on the stirring method in the hydrolysis step, the amount of reaction organic solvent used, and the like. Therefore, what is necessary is just to determine suitably according to the implementation conditions of a hydrolysis process. For example, specifically, it is preferably within the range of cluster acid catalyst: plant-based fiber material (weight ratio) = 1: 4 to 1: 1, and particularly 1: 4 to 1: 2. . However, this ratio varies depending on the mixing method, but considering the energy cost, it is better to have as few cluster acid catalysts as possible.

As described above, the cluster acid exhibits high catalytic activity for the hydrolysis reaction of cellulose even at low temperatures because of its strong acid strength. In addition, since the cluster acid molecule has a diameter of about 1 to 2 nm, it is excellent in mixing with the plant fiber material as a raw material, and can efficiently promote hydrolysis of cellulose. Accordingly, cellulose can be hydrolyzed under mild conditions, energy efficiency is high, and environmental load is small.
Furthermore, unlike the conventional cellulose hydrolysis method using an acid such as sulfuric acid, the method of the present invention using a cluster acid as a catalyst has a high separation efficiency of sugar and catalyst and can be easily separated. Since the cluster acid becomes a solid state depending on the temperature, it can be separated from the product saccharide. Therefore, the separated cluster acid can be recovered and reused. That is, the present invention using cluster acid as a hydrolysis catalyst for cellulose can reduce the cost for saccharification and separation of plant fiber materials and has a small environmental burden.

In the hydrolysis step, the order of adding the cluster acid catalyst and the plant fiber material is not particularly limited. For example, when the cluster acid catalyst is used in a pseudo-molten state, the cluster acid catalyst is first charged and heated. After making the quasi-melted state, the plant fiber material may be added, or after adding both the cluster acid catalyst and the plant fiber material, heating them to bring the cluster acid catalyst into the quasi-melted state. Good. When the cluster acid catalyst and the plant fiber material are added and then heated, it is preferable that the cluster acid catalyst and the plant fiber material are mixed and stirred in advance before heating. By mixing the cluster acid catalyst to some extent before it becomes a pseudo-molten state, the contact property between the cluster acid and the plant fiber material can be enhanced.
On the other hand, when the cluster acid catalyst is used after being dissolved in the reaction organic solvent, it is preferable to previously prepare the cluster acid catalyst organic solvent solution by dissolving the cluster acid catalyst in the reaction organic solvent. Furthermore, it is preferable that the cluster acid catalyst organic solvent solution is heated in advance to the hydrolysis reaction temperature, the plant fiber material is put into the heated cluster acid catalyst organic solvent solution, and the hydrolysis step is performed. .

In the hydrolysis step, water for hydrolyzing cellulose is necessary. Specifically, (n-1) water molecules are required to decompose cellulose in which n glucoses are polymerized into n glucoses. Therefore, at least water necessary for hydrolyzing the total amount of cellulose contained in the plant fiber material into glucose is added to the reaction system. Preferably, a minimum amount of water necessary for hydrolyzing the total amount of cellulose charged as a plant fiber material into glucose is added. This is because when excessive water is added, the generated sugar and cluster acid are dissolved in excess water, and the sugar separation step becomes complicated.
On the other hand, when the cluster acid catalyst is used in a pseudo-molten state, the amount of water of crystallization water necessary for the cluster acid catalyst to be in a pseudo-melt state at the reaction temperature and the total amount of cellulose charged are contained in the reaction system. In the absence of the total amount of water required to be hydrolyzed to glucose, the cluster acid catalyst water of crystallization is used for cellulose hydrolysis, the cluster acid catalyst water of crystallization is reduced, and the cluster acid is in a solidified state. turn into. That is, not only does the contact between the cluster acid catalyst and the plant fiber material decrease, but the viscosity of the mixture of the plant fiber material and the cluster acid catalyst increases, and it takes time to sufficiently mix the mixture. .

  There is no particular limitation on the timing of water addition. In the hydrolysis step, it is preferable that water necessary for hydrolysis of glucose can be secured even if the relative humidity of the reaction system is reduced by heating. Specifically, for example, a saturated vapor pressure state is created at the hydrolysis reaction temperature in a pre-sealed reaction vessel so that the reaction system atmosphere becomes a saturated vapor pressure at a predetermined reaction temperature, and the sealed state is maintained. A method of condensing the vapor by lowering the temperature while keeping the temperature is mentioned.

Lowering the reaction temperature in the hydrolysis step has the advantage that energy efficiency can be improved. Moreover, the selectivity of glucose production for hydrolysis of cellulose contained in the plant fiber material varies depending on the temperature of the hydrolysis step. It is common that the reaction rate increases as the reaction temperature increases. For example, as reported in Japanese Patent Application No. 2007-115407, the hydrolysis reaction of cellulose using phosphotungstic acid with a crystal water ratio of 160% The reaction rate R at 50 ° C. to 90 ° C. increases as the temperature increases, and almost all cellulose reacts at about 80 ° C. On the other hand, the yield of glucose shows an increasing tendency similar to the cellulose reaction rate from 50 ° C. to 60 ° C., but decreases at a peak at 70 ° C. That is, while glucose is produced with high selectivity at 50 to 60 ° C., reactions other than glucose production, for example, other sugar production such as xylose, degradation product production, and the like proceed at 70 to 90 ° C.
Therefore, the reaction temperature of hydrolysis is an important factor affecting the reaction rate of cellulose and the selectivity of glucose production, and it has been stated that the hydrolysis reaction temperature is preferably low from the viewpoint of energy efficiency. It is preferable to determine the temperature of the hydrolysis reaction in consideration of the reaction rate and the selectivity of glucose production.

  The temperature conditions in the hydrolysis step may be appropriately determined in consideration of several factors (for example, reaction selectivity, energy efficiency, cellulose reaction rate, etc.) as described above. From the balance of the rate and the glucose yield, it is usually preferably 140 ° C. or lower, particularly preferably 120 ° C. or lower. Depending on the form of the plant fiber material, a low temperature such as 100 ° C. or less is also possible, and in that case, glucose can be produced with particularly high energy efficiency.

  Further, the pressure in the hydrolysis step is not particularly limited, but since the catalytic activity of the cluster acid catalyst for the hydrolysis reaction of cellulose is high, it is efficient even under mild pressure conditions such as normal pressure (atmospheric pressure) to 1 MPa. Cellulose hydrolysis can proceed.

  Since the mixture containing the cluster acid catalyst and the plant fiber material in the hydrolysis step has high viscosity, for example, a heating ball mill is advantageous as the stirring method, but a general stirrer may be used.

  The time of the hydrolysis step is not particularly limited, and may be set as appropriate depending on the shape of the plant fiber material to be used, the ratio of the plant fiber material and the cluster acid catalyst, the catalytic ability of the cluster acid catalyst, the reaction temperature, the reaction pressure, and the like. .

When the temperature of the reaction system is lowered after completion of hydrolysis, the saccharide produced in the hydrolysis step is an aqueous saccharide solution when there is water to dissolve the sugar in the hydrolysis reaction mixture, and there is no water to dissolve. Is precipitated and contained in a solid state. Some of the produced saccharides may be contained in the hydrolysis reaction mixture in the form of a sugar aqueous solution and the rest in the solid state. On the other hand, the cluster acid catalyst is also in a solid state (when used in a pseudo-molten state) due to a decrease in temperature, or is dissolved in a reaction organic solvent (when used after being dissolved in a reaction organic solvent).
Since the cluster acid catalyst is also water-soluble, the cluster acid catalyst is also dissolved in water depending on the water content of the mixture after the hydrolysis step. In addition, depending on the conditions of the hydrolysis step and the plant fiber material used, the hydrolysis reaction mixture also contains residues (unreacted cellulose, lignin, etc.) as solids.

  Next, the saccharide separation step of separating the saccharide (mainly glucose) produced in the hydrolysis step and the cluster acid catalyst from the hydrolysis reaction mixture will be described. Here, in the hydrolysis step, the sugar separation step will be described for the case where the cluster acid catalyst is used in a pseudo-molten state and the case where it is used after being dissolved in the reaction organic solvent. In the saccharification / separation method of the present invention, the method for separating sugar and cluster acid is not limited to the following method.

  First, the case where it is used in a pseudo-molten state will be described. The cluster acid catalyst is soluble in an organic solvent in which a sugar mainly composed of glucose is hardly soluble or insoluble. Therefore, after adding an organic solvent, which is a poor solvent for sugar and a good solvent for a cluster acid catalyst, to the hydrolysis reaction mixture and stirring, the cluster acid catalyst is selectively dissolved in the organic solvent. By solid-liquid separation, it can be separated into an organic solvent solution (liquid component) containing the cluster acid catalyst dissolved and a solid component containing sugar. Depending on the plant fiber material used, the solid content including sugar may include residues. The method for separating the organic solvent solution and the solid component is not particularly limited, and general solid-liquid separation methods such as decantation and filtration can be employed.

  The organic solvent is not particularly limited as long as it has a solubility characteristic that it is a good solvent for a cluster acid catalyst, but is a poor solvent for sugar, but in order to suppress the dissolution of sugar in an organic solvent. The solubility of the saccharide in the organic solvent is preferably 0.6 g / 100 ml or less, and particularly preferably 0.06 g / 100 ml or less. At this time, in order to increase the recovery rate of the cluster acid catalyst, the solubility of the cluster acid in the organic solvent is preferably 20 g / 100 ml or more, particularly preferably 40 g / 100 ml or more.

  Specific examples of the organic solvent include alcohols such as ethanol, methanol, n-propanol and octanol, and ethers such as diethyl ether and diisopropyl ether. Alcohols and ethers can be preferably used, and among them, ethanol and diethyl ether are preferable from the viewpoints of solubility and boiling point. Diethyl ether is one of the most suitable solvents for separating the saccharide and the cluster acid catalyst because saccharides such as glucose are insoluble and the solubility of the cluster acid is high. On the other hand, ethanol is one of the most suitable solvents because sugars such as glucose are hardly soluble and the solubility of the cluster acid catalyst is high. Diethyl ether is advantageous in distillation compared to ethanol, and ethanol has the advantage of being easier to obtain than diethyl ether.

The amount of the organic solvent used varies depending on the solubility characteristics of the organic solvent with respect to the sugar and cluster acid catalyst, the amount of water contained in the hydrolysis reaction mixture, and the like.
The stirring of the hydrolysis reaction mixture and the organic solvent is usually preferably performed in the range of room temperature to 60 ° C., although it depends on the boiling point of the organic solvent. Moreover, the stirring method etc. with a hydrolysis reaction mixture and an organic solvent are not specifically limited, A general method may be sufficient. From the viewpoint of cluster acid recovery efficiency, the stirring method is preferably stirring and pulverization using a ball mill or the like.

  The solid content obtained by solid-liquid separation is obtained by adding water such as distilled water and stirring to dissolve the sugar in water. And can be separated. In order to improve the recovery rate of sugar and cluster acid and to increase the purity of the obtained sugar, the organic solvent (poor solvent for sugar and good solvent for cluster acid catalyst) is further added to the solid content. It is preferable to perform washing with an organic solvent (see FIG. 4). This is because the cluster acid catalyst mixed in the solid component can be removed and recovered. A mixture obtained by adding an organic solvent to a solid component can be separated into a solid component and a cluster acid organic solvent solution by solid-liquid separation, like the hydrolysis reaction mixture. The solid content can be washed with an organic solvent a plurality of times as required (see FIG. 4).

  On the other hand, the liquid component obtained by the above solid-liquid separation (cluster acid organic solvent solution containing the dissolved cluster acid catalyst) separates the cluster acid catalyst from the organic solvent by removing the organic solvent, and collects the cluster acid catalyst. can do. The method for removing the organic solvent is not particularly limited, and examples thereof include vacuum distillation and lyophilization, and vacuum distillation is preferred among these. The recovered cluster acid catalyst can be used again as a hydrolysis catalyst for plant fiber materials. The recovered cluster acid organic solvent solution after washing the solid can be used again for washing the solid.

Depending on the amount of water in the hydrolysis step, an aqueous solution containing dissolved sugars and cluster acids may be contained in the hydrolysis reaction mixture. In this case, for example, after the dissolved sugar and cluster acid are precipitated by removing water from the hydrolysis reaction mixture, the organic solvent is added, stirred, and solid-liquid separated by solid-liquid separation. And an organic solvent in which the cluster acid catalyst is dissolved.
It is particularly preferable to adjust the water content of the hydrolysis reaction mixture so that the crystallization water ratio of all cluster acid catalysts contained in the hydrolysis reaction mixture is less than 100%. When the cluster acid catalyst has a lot of water of crystallization, typically more than the standard amount of water of crystallization, the product sugar is dissolved in excess water, and the sugar is mixed into the cluster acid organic solvent solution side. This reduces the sugar recovery rate. By setting the crystallization water ratio of the cluster acid catalyst to less than 100%, it is possible to prevent the sugar from being mixed into the cluster acid catalyst in this way.

  The method for reducing the water content of the cluster acid catalyst contained in the hydrolysis reaction mixture may be any method that can reduce the water content of the hydrolysis reaction mixture. For example, the sealed state of the reaction system is released. Then, by heating, a method of evaporating moisture in the hydrolysis mixture, a method of adding a desiccant or the like to the hydrolysis mixture, and removing moisture in the hydrolysis mixture, and the like can be mentioned.

Next, the case where the cluster acid catalyst is used after being dissolved in the reaction organic solvent will be described.
By using an organic solvent that is sparingly soluble in sugar as the reaction organic solvent, the produced sugar is precipitated in the hydrolysis reaction mixture. On the other hand, since the cluster acid catalyst is dissolved in the reaction organic solvent, the hydrolyzed reaction mixture is subjected to solid-liquid separation to obtain a solid component containing the generated sugar and a liquid component containing the cluster acid catalyst and the reaction organic solvent. And can be separated. Depending on the plant fiber material to be used, the solid content including the generated sugar may contain residues. The method for separating the hydrolysis reaction mixture into a solid component and a liquid component is not particularly limited, and a general solid-liquid separation method such as decantation or filtration can be employed.

The solid content obtained by solid-liquid separation is obtained by adding water such as distilled water and stirring to dissolve the sugar in water. And can be separated.
On the other hand, the liquid obtained by solid-liquid separation can be used again as a catalyst for the hydrolysis of the plant fiber material and a reaction solvent as a cluster acid organic solvent solution in which the cluster acid catalyst is dissolved in the reaction organic solvent.

In the sugar separation step, the hydrolysis reaction mixture is compatible with the reaction organic solvent and has a higher solubility of the cluster acid catalyst and a lower boiling point than the reaction organic solvent (hereinafter referred to as washing). By adding, stirring, and filtering, etc., into a liquid component containing a cluster acid catalyst, a reaction organic solvent and an organic solvent for washing, and a solid component containing a saccharide, While improving the recovery rate of a cluster acid catalyst, the purity of the sugar obtained can be raised.
First, the addition of a washing organic solvent that is compatible with the reaction organic solvent and has a higher solubility of the cluster acid catalyst than the reaction organic solvent allows more cluster acid catalyst to be washed with the reaction organic solvent. It can be dissolved in an organic phase (liquid phase) containing an organic solvent. As a result, the recovery rate of the cluster acid catalyst and the purity of the sugar can be improved.
In addition, since the boiling point of the washing organic solvent is lower than that of the reaction organic solvent, the liquid component containing the cluster acid catalyst and the organic solvent (reaction organic solvent and washing organic solvent) separated and recovered from the hydrolysis reaction mixture is removed. By distillation, the organic solvent for washing and the cluster acid organic solvent solution in which the cluster acid catalyst is dissolved in the reaction organic solvent can be separated. At this time, as the distillation method, a general method such as vacuum distillation or freeze-drying can be adopted, and vacuum distillation is particularly preferable.

  The organic solvent for washing is not particularly limited as long as it has the above characteristics, and ethanol is particularly preferably used. Ethanol has a very high solubility of the heteropolyacid, which is a typical cluster acid catalyst, and is highly effective in improving the recovery rate of the heteropolyacid and the purity of the sugar. As an organic solvent for washing, in addition to ethanol, alcohols such as methanol and n-propanol, ethers such as diethyl ether and diisopropyl ether, and the like can be used.

The solid content obtained by solid-liquid separation of the hydrolysis reaction mixture to which the organic solvent for washing has been added is again added to the organic solvent for washing, mixed and washed, and then separated by solid-liquid separation. It is preferable to separate into a washing organic solvent containing the dissolved cluster acid catalyst contained in the solid component and a solid containing sugar. In addition, the washing | cleaning of the solid content by the organic solvent for washing | cleaning can be performed in multiple times as needed. The organic solvent for washing | cleaning collect | recovered after washing | cleaning of a solid part can also be used for the washing | cleaning of a solid part again.
Even when the cluster acid catalyst is dissolved in the reaction organic solvent, the water content of the hydrolysis reaction mixture is such that the water ratio of crystallization of all the cluster acid catalysts contained in the hydrolysis reaction mixture is less than 100%. Is preferably adjusted. The specific method is the same as that used in the pseudo-molten state.

  Hereinafter, quantification of D-(+)-glucose and D-(+)-xylose was performed by a high-performance liquid chromatograph (HPCL) post-label fluorescence detection method. The cluster acid was identified and quantified by ICP (Inductively Coupled Plasma).

[Example 1]
0.5 kg of dried cedar (150 μm or more, water content of about 4 wt%) was immersed in distilled water, subjected to ultrasonic treatment (room temperature, 10 minutes), and the cedar was filled with distilled water.
On the other hand, distilled water was put in a sealed container in advance, the temperature was raised to a predetermined reaction temperature (70 ° C.), the inside of the container was brought into a saturated vapor pressure state, and water vapor was adhered to the inner surface of the container. Next, 1 kg of heteropolyacid (phosphotungstic acid, the amount of water of crystallization has been measured in advance), the water necessary for hydrolyzing the water of crystallization of the heteropolyacid to 100% and the water required for hydrolysis of cellulose to glucose ( 55.6 g) of distilled water (35 g) in a shortage from the total amount (excluding the moisture corresponding to the saturated vapor pressure at 70 ° C.) is put into a container, heated and stirred, and the temperature in the container reaches 70 ° C. After that, stirring was continued for another 5 minutes (see FIG. 3).
Subsequently, 0.5 kg of cedar wood into which distilled water was introduced as described above (in terms of dry weight with a water content of 4 wt%) was added, and stirring was continued at 70 ° C. for 3 hours. Thereafter, the heating was stopped, and the container was cooled to room temperature while opening the container and discharging excess water vapor.

Next, as shown in FIG. 4, 500 ml of ethanol was added to the hydrolysis reaction mixture in the container and stirred for 30 minutes, followed by filtration to obtain a filtrate 1 and a filtrate 1. Filtrate 1 (heteropolyacid ethanol solution) was recovered. On the other hand, 500 ml of ethanol was further added to the filtrate 1 and stirred for 30 minutes, followed by filtration to obtain a filtrate 2 and a filtrate 2. 500 ml of ethanol was added to the filtrate 2 and stirred for 30 minutes, followed by filtration to obtain a filtrate 3 and a filtrate 3. Distilled water was added to the obtained filtrate 3 and stirred for 10 minutes. The obtained aqueous solution was filtered to obtain an aqueous sugar solution and a residue.
The residue was completely oxidized by electromagnetic induction heating and oxygen introduction, and the generated CO ₂ was quantified using an NDIR (NonDispersive InfraRed) analyzer to determine the amount of carbon in the residue. When the reaction rate was calculated from the carbon content of the residue, it was 91%.

Here, the reaction rate was calculated as follows.
First, assuming that the carbon content in holocellulose (cellulose + hemicellulose) is 44.5 wt%, the carbon content of lignin and other is 71.0 wt%, and from the carbon content in the plant fiber material (raw material) Then, the ratio of holocellulose, lignin and other components in the plant fiber material was determined, and the weight of holocellulose, lignin and other components contained in the plant fiber material (raw material) was calculated. In addition, the carbon content rate in a raw material was computed using NDIR like the said residue. Next, the amount of holocellulose remaining in the residue is calculated from the weight of the residue after the reaction and the carbon amount obtained above, (the amount of holocellulose in the residue) / (the amount of holocellulose in the raw material) × 100% (reaction rate) was determined.

[Example 2]
In Example 1, 0.5 kg of dried cedar (150 μm or more, water content of about 4 wt%) was immersed in ethanol, subjected to ultrasonic treatment (room temperature, 10 minutes), and ethanol was added to the cedar. Cedar wood was saccharified and separated in the same manner except that it was filled. The reaction rate was 92%.

[Example 3]
In Example 1, 0.5 kg of dried cedar (150 μm or more, water content of about 4 wt%) was immersed in octanol, subjected to ultrasonic treatment (room temperature, 10 minutes), and octanol was added inside the cedar. Cedar wood was saccharified and separated in the same manner except that it was filled. The reaction rate was 95%.

[Comparative Example 1]
In Example 1, cedar wood was saccharified and separated in the same manner except that (150 μm or more, water content about 4 wt%) was used as it was. The reaction rate was 45%.

[result]
Table 1 shows the reaction rates for Examples 1 to 3 and Comparative Example 1.

  As shown in Table 1, the reaction rates of Examples 1 to 3 were significantly improved as compared with Comparative Example 1. This is because, when the heteropolyacid and the plant fiber material are mixed in advance by impregnating the plant fiber material with a liquid in which the heteropolyacid is soluble, the heteropolyacid is mixed into the plant fiber material. It is considered that the diffusibility was improved and the hydrolysis of cellulose inside the plant fiber material proceeded efficiently.

It is a figure which shows the Keggin structure of heteropoly acid. It is a graph which shows the relationship between the crystal water rate of a cluster acid catalyst, and an apparent melting temperature. It is an example of the flowchart of the hydrolysis process in the saccharification separation method of this invention. It is an example of the flowchart of the saccharide | sugar separation process in the saccharification separation method of this invention.

Claims (2)

A plant fiber material saccharification and separation method for hydrolyzing plant fiber material to produce and separate sugars mainly composed of glucose,
Using a cluster acid catalyst in a pseudo-molten state, hydrolyzing cellulose contained in the plant fiber material, and having a hydrolysis step of generating glucose;
Before the hydrolysis step, a liquid in which at least one kind of the cluster acid catalyst selected from water, ethanol, methanol, n-propanol, octanol, diethyl ether, and diisopropyl ether is soluble in the plant fiber material in advance. can it allowed to fill the,
In the hydrolysis step, the cluster acid catalyst in the pseudo-molten state and the plant fiber material have a weight ratio in the range of the cluster acid catalyst: the plant fiber material = 1: 1 to 4: 1. The saccharification / separation method for plant fiber material, wherein the cluster acid catalyst in a pseudo-molten state is mixed as a reaction solvent .   The plant fiber material is filled with the liquid by immersing the plant fiber material in a liquid in which the cluster acid catalyst is soluble and applying ultrasonic vibration to the liquid. Saccharification separation method.

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