SUSPENSION

Description

CROSS REFERENCE TO RELATED APPLICATIONS

This application is based on and claims priority under 35 U.S.C. § 119 to Japanese Patent Application 2024-131099, filed on Aug. 7, 2024, the entire content of which is incorporated herein by reference.

TECHNICAL FIELD

This disclosure relates to a suspension.

BACKGROUND DISCUSSION

In recent years, a technique for producing a biomass fuel from non-food biomass (cellulosic biomass) such as wood, grass, and rice straw has attracted attention instead of food biomass such as sugar cane and corn.

JP 2013-111034A (Reference 1) discloses a method for solubilizing a biomass raw material in which a biomass raw material containing cellulose is pulverized under heating at 100° C. or higher and lower than 300° C., and a water-soluble component is extracted with water. The biomass raw material undergoes a mechanochemical effect when subjected to a heat pulverizing treatment, and is decomposed into components such as cellulose, and further crystallinity and a molecular weight of each component are reduced, resulting in production of a water-soluble component.

The method for solubilizing a biomass raw material described in Reference 1 includes a step of extracting, with water, a water-soluble component contained in a pulverized material obtained by subjecting a biomass raw material to a heat pulverizing treatment. Therefore, when utilizing the pulverized material, a step of extracting the water-soluble component is required, and the utilization efficiency of the pulverized material is not high.

A need thus exists for a suspension which is not susceptible to the drawback mentioned above.

SUMMARY

According to an aspect of this disclosure, a suspension contains: a pulverized material obtained from a biomass raw material containing cellulose; and water, in which the pulverized material has an average particle diameter of 1 μm or more and 300 μm or less, and the suspension has a viscosity at 20° C. of 2 mPa·s or more and 100 mPa·s or less.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing and additional features and characteristics of this disclosure will become more apparent from the following detailed description considered with the reference to the accompanying drawings, wherein:

FIG. 1 is a graph illustrating average particle diameters of pulverized materials according to Example and Comparative Example; and

FIG. 2 is a diagram illustrating a viscosity of a suspension according to Example.

DETAILED DESCRIPTION

Hereinafter, an embodiment of a suspension disclosed here will be described with reference to the drawings. The embodiment described below is an example for explaining this disclosure, and this disclosure is not limited to the embodiment. Therefore, this disclosure can be implemented in various forms without departing from the gist thereof.

A suspension disclosed here contains water and a pulverized material obtained by subjecting a biomass raw material containing cellulose to a mechanochemical treatment.

The biomass raw material disclosed here may contain, in addition to cellulose, oligosaccharides and polysaccharides such as lignin, starch, hemicellulose, and pectin. Examples of the biomass raw material include grass or plant biomass such as rice straw, wheat straw, and bagasse, thinned wood such as bamboo and bamboo grass, wood waste from wood processing such as sawdust, chips, and offcuts, roadside tree pruning, wooden building waste, a wood biomass such as bark and driftwood, and a cellulose product such as waste paper. Sludge, livestock excrement, agricultural waste, urban waste, and the like can also be used so long as cellulose, lignin, oligosaccharides, or the like are contained to an extent that they can be used as the biomass raw material. These biomass raw materials may be used alone or in combination of a plurality of different types.

The mechanochemical treatment refers to a treatment in which a substance is physically and chemically changed by applying a mechanical stress such as pulverization to the substance. The mechanochemical treatment is performed by applying a mechanical stress to the biomass raw material using, for example, a ball mill such as a planetary ball mill, a grinder having a grinding medium such as a rod mill or a vibrating mill, or a disperser. By the mechanochemical treatment, the biomass raw material is decomposed into components such as cellulose and lignin, and crystallinity and a molecular weight of these components are reduced, resulting in production of a pulverized material containing a water-soluble component. A solubilization treatment of the biomass raw material by such a mechanochemical treatment is safe in a production process and has a low environmental load as compared with a solubilization treatment of the biomass raw material using chemicals such as sulfuric acid.

The mechanochemical treatment disclosed here may be performed under any conditions, and for example, the biomass raw material may be subjected to a pulverization treatment in a range of room temperature to 300° C. A heating method in the case of subjecting the biomass raw material to a heat pulverizing treatment is not particularly limited, and a container can be heated using an electric heater, a high frequency, a microwave, steam, or the like. The pulverization treatment is preferably performed for 10 minutes or more. Since a depolymerization reaction proceeds as a time increases, it is desirable to perform a long-time treatment. However, in order to efficiently obtain the water-soluble component, the treatment is preferably performed for about 10 minutes to 2 hours.

A rotation speed of the ball mill in the mechanochemical treatment is preferably in a range of 200 rpm or more and 2000 rpm or less. The higher the rotation speed is, the easier the carbonization proceeds, and the rotation speed is preferably more than 300 rpm and less than 1500 rpm in consideration of a balance between the production energy and the load of the apparatus. A ball diameter and a ball weight can be set to any values, and when a vessel capacity of the ball mill is 2 L, the ball diameter and the ball weight are preferably 1 mmφ to 30 mmφ and 1 kg to 8 kg, respectively, from the viewpoint of pulverizing the biomass raw material to 10 mm or less.

The biomass raw material may be coarsely pulverized before being subjected to the mechanochemical treatment. In the coarse pulverization, the biomass raw material may be pulverized into a shape that is easy to handle, for example, about 0.5 mm to 100 mm. In the coarse pulverization, a pulverizing method can be selected according to a form of the biomass raw material. For example, a general-purpose pulverizer such as a hammer mill, a cutter mill, a vibration mill, a ball mill, a rod mill, a roller mill, a colloid mill, a disk mill, or a jet mill can be used. For a pulverization treatment in the coarse pulverizing step, either a dry or wet method can be selected, and dry pulverization is preferred from a viewpoint of reducing crystallinity of cellulose.

Before being subjected to the mechanochemical treatment, the biomass raw material or the coarsely pulverized biomass raw material may be dried. This is because crystallinity of cellulose and lignin can be efficiently reduced by subjecting a biomass raw material having a low water content to dry pulverization. Drying of the biomass raw material may be performed by measuring water contained in the biomass raw material and determining whether the drying is performed according to the water content. The water content of the biomass raw material subjected to the mechanochemical treatment is preferably 20 mass % or less, and more preferably 10 mass % or less. The water content of the biomass raw material may be 0 mass %, and is preferably 3 mass % or more since drying for a long period of time is uneconomical. The drying may be performed by natural drying, or may be performed by heating the biomass raw material by hot air drying, an electric heater, or the like.

An average particle diameter of the pulverized material obtained by the mechanochemical treatment is preferably 1 μm or more and 300 μm or less. The average particle diameter is a particle diameter (D50) at which a cumulative weight part is 50% in a particle size distribution obtained by a laser diffraction and scattering method. When the average particle diameter of the pulverized material is 300 μm or less, the pulverized material is easily suspended in water, and thus the water-soluble component contained in the pulverized material is easily dissolved in water. When the average particle diameter of the pulverized material is 1 μm or more, energy required for the mechanochemical treatment can be reduced, which is economical.

A proportion of an amount of carbon contained in the water-soluble component to an amount of carbon contained in sugars such as cellulose, hemicellulose, and oligosaccharides contained in the biomass raw material (amount of water-soluble organic carbon/amount of carbon contained in saccharide contained in raw material; also referred to as a solubilization ratio) can be any value, and is preferably 10% or more from the viewpoint of efficiently producing and using the suspension. When the solubilization ratio is 10% or more, a concentration of the water-soluble component in the suspension can be increased, and thus the utilization efficiency of the suspension can be improved.

The suspension is obtained by suspending, in water, the pulverized material obtained by the mechanochemical treatment. A content of the pulverized material in the suspension on a mass basis can be any value, and is preferably 0.3% or more and 30% or less. When the content is 0.3% or more, the water-soluble component contained in the pulverized material can be dissolved in the suspension, and thus the suspension can be easily utilized in the next step. When the content is 30% or less, the viscosity of the suspension can be reduced, and thus the handleability of the suspension can be improved. By suspending the pulverized material in water and eluting the water-soluble component into the suspension, the step of extracting the water-soluble component with water can be omitted, and thus the utilization efficiency of the pulverized material can be improved. The content of the pulverized material in the suspension may be changed according to the solubilization ratio of the pulverized material, or may be changed according to various conditions of the mechanochemical treatment.

The viscosity of the suspension disclosed here is preferably 2 mPa·s or more and 100 mPa·s or less when measured using an E-type viscometer under conditions of a temperature of 20° C. and a rotation speed of 250 rpm. When the viscosity of the suspension is within the above range, the transportability of the suspension is good, and the handleability can be improved. The viscosity of the suspension is more preferably 2 mPa·s or more and 50 mPa·s or less, and still more preferably 3 mPa·s or more and 10 mPa·s or less. The viscosity may be measured using a supernatant obtained by centrifuging the suspension.

Method for Producing Suspension

Subsequently, a method for producing a suspension disclosed here will be described. The method for producing a suspension includes a treatment step of subjecting a biomass raw material to a mechanochemical treatment, and a suspension step of suspending, in water, a pulverized material obtained by the treatment step.

First, in the treatment step, a mechanical stress is applied to a biomass raw material using a pulverizer having a pulverizing medium such as a ball mill, thereby performing the mechanochemical treatment. In order to improve the treatment efficiency of the biomass raw material, the biomass raw material may be coarsely pulverized, or may be dried to adjust a water content to a predetermined value before being subjected to the treatment step. The treatment step may be performed at room temperature or may be performed under heating. A pulverized material having a desired solubilization ratio can be obtained by applying any mechanical stress to the biomass raw material by changing various conditions of the mechanochemical treatment, such as a pulverization time and a rotation speed of the pulverizer.

Subsequently, the suspension step is performed to obtain a suspension by dispersing the pulverized material in water. In the suspension step, the pulverized material may be suspended in water such that a content of the pulverized material contained in the suspension on a mass basis is 0.3% or more and 30% or less. At this time, the content of the pulverized material may be changed depending on the solubilization ratio of the pulverized material and various conditions of the mechanochemical treatment. The suspension step can be performed, for example, by stirring the pulverized material and water at a predetermined rotation speed. The suspension step may be performed by adding water to the pulverized material, or may be performed by adding the pulverized material to water. A temperature of water in the suspension step can be any value.

Example

Hereinafter, Example disclosed here will be described, but this disclosure is not limited to the description of this Example.

Example

A pulverized material was prepared using a biomass raw material having a sugar component of 66.8%, other components of 28.6%, and a water content of 4.6%. The sugar component of the biomass raw material was calculated by constituent sugar analysis. The biomass raw material was first coarsely pulverized using a cutting mill so as to pass through a 1 mm pore screen, and then pulverized using a ball mill equipped with a heater at a temperature of 120° C., a rotation speed of 700 rpm, and a pulverization time of 10 minutes, 47 minutes, 62 minutes, 92 minutes, or 107 minutes. Thereafter, the pulverized material was suspended in water such that a content of the pulverized material on a mass basis was 15% to obtain a suspension.

Comparative Example

A suspension was obtained in the same manner as in Example except that a coarsely pulverized material was suspended in water instead of a pulverized material.

An average particle diameter of each of the pulverized materials according to Example and Comparative Example was determined by a laser diffraction and scattering method. FIG. 1 is a graph in which the average particle diameter is plotted with respect to a pulverization time of the biomass raw material. As illustrated in FIG. 1, the coarsely pulverized material used in Comparative Example had an average particle diameter of about 500 μm, whereas the pulverized material according to Example had an average particle diameter of 20 μm to 48 μm. The suspension according to Example was in a slurry state by visual observation, whereas the suspension according to Comparative Example was in a liquid state in which the coarsely pulverized material could be visually confirmed. Therefore, it was suggested that the smaller the average particle diameter is, the easier it is to suspend the pulverized material in water, and the easier it is to handle the suspension.

FIG. 2 is a measurement result of a viscosity of the suspension according to Example in which the pulverization time is 87 minutes. The viscosity was measured using a supernatant obtained by centrifuging the suspension at 10,000×g and 15° C. for 10 minutes. The measurement was performed using an E-type viscometer under conditions of a rotation speed of 250 rpm, and a temperature of 4° C., 20° C., and 40° C. At any temperature, the viscosity was 2 mPa·s or more and 100 mPa·s or less. The suspension was in a slurry state and had good handleability.

In the embodiment described above, the following configurations are conceivable.

(1) A suspension containing: a pulverized material obtained from a biomass raw material containing cellulose; and water, in which the pulverized material has an average particle diameter of 1 μm or more and 300 μm or less, and the suspension has a viscosity at 20° C. of 2 mPa·s or more and 100 mPa·s or less.

According to the present configuration, a water-soluble component contained in the pulverized material can be dissolved in the suspension by suspending the pulverized material in water, and thus a step of extracting the water-soluble component can be omitted when the pulverized material is utilized. The suspension can be used as it is in other steps, and thus the utilization efficiency of the pulverized material can be improved. Further, when the average particle diameter of the pulverized material is 1 μm or more and 300 μm or less, the pulverized material is easily suspended in water, and thus the water-soluble component is easily dissolved in the suspension. Since the viscosity at 20° C. is 2 mPa·s or more and 100 mPa·s or less, the viscosity of the suspension is relatively low, transportability of the suspension is good, and handling is easy.

(2) In the suspension of (1), it is preferable that a content of the pulverized material on a mass basis is 0.3% or more and 30% or less.

According to the present configuration, the viscosity of the suspension can be maintained in a certain range, and thus the handleability of the suspension can be improved.

(3) In the suspension of (1) or (2), it is preferable that the pulverized material is obtained by subjecting the biomass raw material to a mechanochemical treatment.

According to the present configuration, cellulose or the like contained in the biomass raw material can be converted into a water-soluble component and dissolved in the suspension, and the biomass raw material can be utilized effectively. Since the water-soluble component can be obtained from the biomass raw material without using chemicals or the like, the production process is safe and the environmental load is low.

INDUSTRIAL APPLICABILITY

This disclosure is applicable to a suspension containing a pulverized material and water.

The principles, preferred embodiment and mode of operation of the present invention have been described in the foregoing specification. However, the invention which is intended to be protected is not to be construed as limited to the particular embodiments disclosed. Further, the embodiments described herein are to be regarded as illustrative rather than restrictive. Variations and changes may be made by others, and equivalents employed, without departing from the spirit of the present invention. Accordingly, it is expressly intended that all such variations, changes and equivalents which fall within the spirit and scope of the present invention as defined in the claims, be embraced thereby.