WO2022210558A1 - Pellets and method for producing pellets - Google Patents

Abstract

The present invention provides: plant-based pellets that generate little dust, that reduce the amount of air pollutants from a boiler and improve the operational safety of a biomass boiler when used as a fuel, and that can be used to advantageously reduce management costs during transportation; and a method for producing the pellets. More specifically, the present invention provides pellets and a method for producing the pellets in which lignocellulosic biomass is used as a starting material and the average surface roughness of a side surface section of the pellets is 50-250 nm.

Description

Pellets and methods for producing pellets Reference to Related Applications

This patent application claims priority based on Japanese Patent Application No. 2021-56162 filed on March 29, 2021, and the entire disclosure content in such earlier patent application is incorporated by reference. incorporated herein.

The present invention relates to pellets made from lignocellulosic biomass and a method for producing pellets.

　Biomass energy, which uses plant-based biomass as a raw material, is attracting a great deal of attention as a means of curbing global warming. Biomass energy is thought to be neutral during its lifecycle in emissions of carbon dioxide, which is one of the causes of global warming (emission and absorption are equal). expected.

When plant-based biomass is used as fuel, it is often pelletized due to its low weight per volume (high bulk density). A pellet is a cylindrical fuel having a diameter of about 6 to 10 mm and a length of about 10 to 70 mm. Pelleting plant biomass increases bulk density and energy density (calorific value per unit volume), facilitating storage and transportation. Also, by adjusting the moisture content of the pellets, it is possible to control the ignitability and combustibility. Pellets are used as various heat sources by burning them in a boiler.

Prior art related to plant-based biomass fuels include a method of burning saccharified biomass to generate energy (Patent Document 1), and residues discharged in the process of producing sugars and/or ethanol using lignocellulosic biomass as a raw material. (Patent Document 2), pellets with good moldability made from lignocellulosic biomass materials (Patent Document 3), and the like are known.

Japanese translation of PCT publication No. 2016-517268 JP 2014-132052 A JP 2017-100382 A

When pelletizing plant biomass and burning it in a boiler, if there is too much dust from the pellets, it will flow outside and cause air pollution. There are several issues, such as the safety of operation being compromised due to air pollution, and the management burden on transportation companies due to dust leaks during transportation. Accordingly, it is an object of the present invention to provide pellets made from plant-based biomass and producing less dust.

The present inventors focused on lignocellulose-based biomass as a raw material for pellets, and as a result of intensive studies, the amount of dust derived from pellets was significantly reduced by setting the average surface roughness of the side surface of the pellet to 50 nm or more and 250 nm or less. It has been found that the quality of pellets can be improved.
That is, according to one embodiment of the present invention, the following [1] to [13] are provided.
[1] A pellet made from lignocellulose-based biomass and having an average surface roughness of 50 nm or more and 250 nm or less on the side surface of the pellet.
[2] The pellet according to [1], which is used for fuel.
[3] The pellets according to [1] or [2], wherein the lignocellulosic biomass is bagasse.
[4] The pellet according to any one of [1] to [3], wherein the raw material is saccharification residue of lignocellulosic biomass.
[5] The pellet according to [4], wherein the lignocellulosic biomass saccharification residue is a saccharification residue of an alkali pretreated lignocellulosic biomass.
[6] The pellet according to any one of [1] to [5], having a lignin content of 16% by weight or more and 40% by weight or less.
[7] The pellet according to any one of [1] to [6], which has a dust rate of 0.5% by weight or less.
[8] A method for producing the pellets according to any one of [1] to [7],
Step (1) of hydrolyzing a pretreated product obtained by pretreating lignocellulosic biomass with an alkali, using a saccharifying enzyme;
Step (2) of solid-liquid separation of the hydrolyzate of lignocellulosic biomass obtained in step (1) to obtain a saccharification residue of lignocellulosic biomass as a solid content;
Step (3) of pulverizing the saccharified residue of lignocellulosic biomass obtained in step (2), and Step (4) of compressing and pelletizing the saccharified residue of lignocellulosic biomass obtained in step (3). ), methods.
[9] The method according to [8], wherein in the step (1), the alkali pretreatment temperature is 80 to 100°C.
[10] The method according to [8] or [9], wherein in the step (1), the alkali pretreatment is an alkali pretreatment under normal pressure.
[11] The method according to any one of [8] to [10], wherein in the step (3), the saccharification residue of the lignocellulosic biomass obtained in the step (2) is pulverized to a diameter of 10 mm or less.
[12] The method according to any one of [8] to [11], wherein the moisture content of the saccharification residue of the lignocellulosic biomass subjected to compression molding in the step (4) is 10% or more and less than 30%.
[13] The method according to any one of [8] to [12], wherein the lignocellulosic biomass is bagasse.

With the present invention, it is possible to reduce the dust rate of pellets, which was a problem with pellets made from plant-based biomass. Therefore, the present invention can be advantageously used to reduce the amount of air pollutants from boilers, improve the operational safety of biomass boilers, and reduce management costs during transportation.

FIG. 1 is a side view of bagasse saccharification residue pellets of Example 1 observed with an atomic force microscope. FIG. 2 is a side view of bagasse pellets of Comparative Example 4 observed with an atomic force microscope.

The pellets of the present invention are made from lignocellulosic biomass. Lignocellulosic biomass refers to biomass containing cellulose, hemicellulose, and lignin as constituents. Preferred examples of lignocellulosic biomass include herbaceous biomass such as bagasse, switchgrass, napiergrass, erianthus, corn stover, and straw; woody biomass such as trees, wood chips, and waste building materials; Environmental biomass, grain biomass such as corn husks, wheat husks, soybean husks, rice husks, cassava pulp, and beet pulp. Among these, bagasse is particularly preferably used as lignocellulose biomass. Bagasse is the pomace of sugar cane.

The method for producing the pellet of the present invention is not particularly limited as long as it is a method that allows the average surface roughness of the side surface of the pellet, which is the final product, to be in the desired range of 250 nm or less. Any method can be used as long as it can be produced by appropriately arranging it within the scope of ordinary creation, but a method of pelletizing saccharification residue of lignocellulosic biomass is preferable. The method for producing the pellets of the present invention by pelletizing the saccharification residue of lignocellulosic biomass will be described in detail below.

The saccharification residue of lignocellulosic biomass is a solid residue obtained when producing sugar by hydrolyzing lignocellulosic biomass as a raw material (also referred to as “raw material biomass” in this specification), and is preferably is the solid residue obtained during hydrolysis to produce sugar after pretreatment of raw biomass.

The pretreatment of the raw material biomass is a pre-process for hydrolyzing the raw material biomass, and may be a process known to those skilled in the art. However, in the present invention, the pretreatment of the raw material biomass is preferably alkali pretreatment in order to make the average surface roughness of the pellet side surface as the final product a desired range of 250 nm or less.

The alkaline solution used for alkali pretreatment is not particularly limited, but sodium hydroxide aqueous solution, potassium hydroxide aqueous solution, calcium hydroxide aqueous solution, ammonia water, or the like can be used. Among these, an aqueous sodium hydroxide solution is preferable from the viewpoint of being inexpensive and easy to handle. As for the alkaline pretreatment conditions, it is preferable to set the raw material biomass solid content concentration in the range of 5 to 10% by weight in a state of being mixed with the alkaline aqueous solution.

As the amount of alkali added in the alkali pretreatment, for example, when using an aqueous sodium hydroxide solution, the amount of sodium hydroxide added is in the range of 5 to 15% by weight relative to the solid content of lignocellulosic biomass. It is suitable for making the average surface roughness of the side surface of the pellet as a product a desired range of 250 nm or less.

The temperature for alkali pretreatment is preferably 80 to 100°C, more preferably 85 to 100°C, in order to make the average surface roughness of the pellet side surface of the final product 250 nm or less.

The time for alkali pretreatment can be set appropriately according to the amount of alkali, etc., and is usually about 0.5 to 6 hours.

Alkaline pretreatment may be performed under normal pressure or under pressure, but preferably under normal pressure.

As the alkali pretreatment method, it is preferable to adopt a pretreatment method in which an alkaline solution is repeatedly passed through the raw biomass in order to make the average surface roughness of the side surface of the pellet, which is the final product, a desired range of 250 nm or less. is. Such a method includes at least a storage unit that stores raw biomass, a filtration unit that passes an alkaline solution through the raw biomass, and a filtrate circulation unit that collects and circulates the alkaline solution obtained from the filtration unit. It is preferable to use the filtering equipment provided, and it is also possible to use known filtering equipment. Preferable examples of known filtration devices include belt-type filters (DeSmet LM), basket-type filters, rotary-type filters (Carousel, Rotocell, REFLEX), Bonnot-type filters, screen-type filters, and the like. be done. Among these, in order to make the average surface roughness of the pellet side surface of the final product a desired range of 250 nm or less, it is more preferable to use an in-tank screen filtration type device (Izumi Food Machinery Co., Ltd.), a conveyor type screen filtration type device (Crown Iron Works, Model 2, Model 3).

A pretreated product obtained by alkali pretreatment of lignocellulosic biomass (also referred to herein as an “alkali pretreated product”) may be directly subjected to a hydrolysis reaction. It is preferable to subject the solid content obtained by liquid separation to hydrolysis as an alkali pretreated product. As a solid-liquid separation method, a known method such as a centrifugal separation method such as a screw decanter, a filtration method such as pressure/suction filtration, or a membrane filtration method such as microfiltration can be used. Also, the solid content of the alkali pretreated product may be washed with pure water before and after the solid-liquid separation. By washing the solid content, enzyme reaction inhibitors such as lignin degradation products can be further reduced, and the amount of acid required for pH adjustment during the hydrolysis reaction can also be reduced, which is preferable.

Although the saccharification enzyme used for the hydrolysis reaction of the pretreated raw biomass as described above is not particularly limited, it is preferable to use a cellulase composition. A cellulase composition is a mixture of different hydrolases that hydrolyze the glycosidic bonds of β-1,4-glucans. Hydrolytic enzymes contained in the cellulase composition include, for example, cellobiohydrolase, xylanase, endoglucanase, β-glucosidase, β-xylosidase, arabinofuranosidase, xylan esterase, ferulic acid esterase, α-glucuronidase, chitosanase, chitinase, mannanase, mannosidase, α-galactosidase, β-galactosidase and the like. Among these, the cellulase composition used in the hydrolysis reaction has at least the activities of xylanase, theobirohydrolase and β-glucosidase when hydrolyzing lignocellulosic biomass, and also exhibits the activity of β-xylosidase. A cellulase composition that is substantially free is preferably used from the viewpoint of xylo-oligosaccharide production. Moreover, the origin of these enzymatic activities is not particularly limited. Examples of preparation of such cellulase compositions are described in WO2017/170919 or WO2017/170917. In addition, a culture solution obtained by culturing microorganisms may be used as it is as a cellulase composition, or an enzyme purified from the culture solution and other commercially available enzyme products may be mixed and used.

When using a cellulase composition derived from a microorganism, a fungus can be preferably used as the microorganism. Specific examples of fungi include Trichoderma fungi, Aspergillus fungi, Cellulomonas fungi, Clostridium fungi, Streptomyces fungi, and Humicola fungi. , Acremonium fungi, Irpex fungi, Mucor fungi, Talaromyces fungi, and the like. Among these fungi, fungi of the genus Trichoderma and fungi of the genus Aspergillus are preferred.

Specific examples of the fungi of the genus Trichoderma include Trichoderma reesei QM9414, Trichoderma reesei QM9123, Trichoderma reesei RutC-30, Trichoderma reesei RutC-30, Trichoderma reesei RutC-30, and Trichoderma reesei RutC-30. Ｔｒｉｃｈｏｄｅｒｍａ　ｒｅｅｓｅｉ　ＰＣ３－７）、トリコデルマ・リーセイＣＬ－８４７（Ｔｒｉｃｈｏｄｅｒｍａ　ｒｅｅｓｅｉ　ＣＬ－８４７）、トリコデルマ・リーセイＭＣＧ７７（Ｔｒｉｃｈｏｄｅｒｍａ　ｒｅｅｓｅｉ　ＭＣＧ７７）、トリコデルマ・リーセイＭＣＧ８０（Ｔｒｉｃｈｏｄｅｒｍａ　ｒｅｅｓｅｉ　ＭＣＧ８０）、トリコデルマ・ビリデＱＭ９１２３（Ｔｒｉｃｈｏｄｅｒｍａ　ｖｉｒｉｄｅ　ＱＭ９１２３） can be exemplified. Among these fungi of the genus Trichoderma, Trichoderma reesei is preferred. Mutant strains in which the productivity of the cellulase composition is improved or mutant strains in which the activity of β-xylosidase is reduced by subjecting the fungi constituting the cellulase composition to mutation treatment with a mutating agent or ultraviolet irradiation are also preferred. can be used.

Specific examples of Aspergillus fungi include Aspergillus niger, Aspergillus fumigatus, Aspergillus aculeatus, and Aspergillus terreus.

As the cellulase composition, a cellulase composition derived from one of the above fungi may be used, or a mixture of cellulase compositions derived from a plurality of fungi may be used. When cellulase compositions derived from a plurality of fungi are mixed and used, the combination is not particularly limited. For example, a cellulase composition derived from a fungus of the genus Trichoderma and a cellulase composition derived from a fungus of the genus Aspergillus may be mixed and used. Specific examples of β-glucosidases derived from fungi of the genus Aspergillus include "Novozyme 188" (Novozymes), "β-Glucosidase from Aspergillus niger" (Megazyme), and "Sumizyme BGA" (Shinnihon Chemical Industry Co., Ltd.). can be exemplified. The β-glucosidase active ingredient preferably contains the β-glucosidase active ingredient of the fungus belonging to the genus Aspergillus.

The conditions for hydrolysis by saccharifying enzymes (also referred to as "saccharifying reaction" in this specification) are not particularly limited, but hydrolysis conditions that allow production of xylooligosaccharides, glucose, and xylose are preferable.

The lignocellulosic biomass saccharification residue is obtained by solid-liquid separation of the hydrolyzate by saccharifying enzymes of the pretreated lignocellulosic biomass. The solid-liquid separation method includes, but is not limited to, centrifugal separation, membrane separation, pressurized solid-liquid separation, and the like. Also, a plurality of such solid-liquid separation methods may be combined. Examples of solid-liquid separators include continuous centrifuges, screw decanters, disc centrifuges, screw presses, filter presses, roll presses, wash presses, belt filters, and drum filters.

The lignocellulosic biomass saccharification residue obtained from the solid-liquid separation step (also referred to herein as "solid residue") is preferably pulverized with a pulverizer. The pulverization method is not particularly limited, and includes hammer mill, cutter mill, ball mill, jet mill and the like, preferably cutter mill or hammer mill. Pulverization is carried out so that the diameter of the solid residue (also referred to herein as "grinding degree") is 20 mm or less, preferably 10 mm or less. This is to prevent clogging before the die when the solid residue is passed through a hole called a die during pelletization. Also, pulverizing the solid residue improves the efficiency of drying in the post-process.

By appropriately drying the solid residue, the moisture content of the solid residue can be adjusted. The method for drying the solid residue is not particularly limited, and includes drying by air drying, hot air, and contact with a heating jacket. The temperature during drying is not particularly limited, but when drying by a method other than air drying, the environmental load used in the process can be reduced by effectively utilizing the waste heat generated from the biomass boiler.

The water content of the solid residue at the time of pulverization is preferably 10-55%, more preferably 30-50%. If the water content at the time of pulverization is too higher than the above-mentioned water content, the pulverizer is likely to clog. If the water content at the time of pulverization is lower than the above-mentioned water content, the rate of dust generation increases, and there is a concern that dust fires may occur during transportation to the cutter mill and subsequent processes.

The water content of the solid residue to be subjected to the subsequent pelletizing step is preferably 10% or more and less than 30%. If the moisture content is less than 10%, it may become impossible to control the temperature of the biomass in the die at the die part of the pelletizer during pelletization. Therefore, some components of the biomass undergo glass transition and become adhesive-like, causing clogging and making continuous pelletization difficult. On the other hand, if the water content is 30% or more, the raw material will bridge inside the pelletizer, making it impossible to feed the material up to the die, making it difficult to stably produce the material. The moisture content of the solid residue can be calculated by heating the object to be measured to 105° C. and calculating the weight change before and after heating.

The order of the pulverization step and the drying step is not particularly limited, and the pulverization and drying steps may be performed multiple times. Although the number of times is not limited, it is preferable to perform the drying process after the pulverization process. This enables high-quality pelletization and stable and safe operation.

The solid residue is compression-molded and pelletized. The device for pelletization (pelletizer) is not particularly limited, but may be a briquetteer (manufactured by Kitagawa Ironworks Co., Ltd., etc.), a ring die type pelletizer (manufactured by CPM Co., Ltd., Thai Sumi, Triumph, etc.), flat A die-type pelletizer (manufactured by Dalton Co., Ltd., etc.) is preferred. A part with multiple holes for compression molding is called a die. As described above, by adjusting the degree of pulverization and the water content of the saccharification residue, it is possible to suppress the occurrence of clogging in the loading section inside the pelletizer before the die and the occurrence of clogging in the die itself. By adjusting the conditions of the pulverization step and the drying step, it becomes possible to stably produce high-quality biomass pellets with a low dust content for a long period of time.

In the pellet of the present invention, the average surface roughness of the side surface of the pellet is 250 nm or less, preferably 200 nm or less, more preferably 180 nm or less. In addition, in the pellet of the present invention, the average surface roughness of the side surface of the pellet is preferably 50 nm or more, more preferably 80 nm or more, still more preferably 100 nm or more, still more preferably 110 nm or more. Further, according to one embodiment of the present invention, the range of average surface roughness of the side surface of the pellet is 50 nm or more and 250 nm or less, preferably 80 nm or more and 200 nm or less, more preferably 100 nm or more and 180 nm or less. More preferably, it is 110 nm or more and 180 nm or less. Pellets obtained by a pelletizer usually have a substantially cylindrical shape, and the side surface of the substantially cylindrical pellet is a side surface sandwiched between two substantially circular bottom surfaces (cut surfaces). Surface roughness is the state of the surface (unevenness). Using an atomic force microscope, it is quantified from the atomic force acting between the sample and the stylus. The arithmetic mean roughness of the measurement area is calculated by averaging the absolute values of the displacement from . The average surface roughness of the side surface of the pellet is the average value of arithmetic mean roughnesses in three atomic force microscope measurement areas on the side surface of one pellet.

The pellet of the present invention has an average surface roughness of 250 nm or less on the side surface of the pellet, so that the generation of dust derived from the pellet can be suppressed. The degree of dust generated from pellets is evaluated by the dust rate, and the dust rate of the pellets of the present invention is preferably 0.5% by weight or less, more preferably 0.35% by weight or less, and still more preferably 0.2% by weight. It is below. The dust ratio can be calculated from the ratio of the weight of dust that passes through the sieve when a certain amount of pellets is placed in the sieve and vibrated for a certain period of time.

Although the diameter and length of the substantially circular bottom surface (cut surface) of the pellet are not particularly limited, the diameter is preferably 6 to 10 mm, and the length is preferably 10 to 70 mm. Smaller diameters tend to clog inside the die of the pelletizer. If the pellet length is too short, strong breaking forces may occur during pellet production, resulting in increased dust content in the product. If the length of the pellet is too long, the bulk density of the product will be low, resulting in increased transport costs and costs during use. The diameter and length of the substantially circular bottom surface (cut surface) of the pellet can be adjusted with a pelletizer.

The lignin content of the pellets of the present invention is preferably 16% by weight or more and 40% by weight or less, more preferably 17% by weight or more and 40% by weight or less, still more preferably 18% by weight or more and 40% by weight or less, still more preferably 18% by weight or more. % by weight or more and 30% by weight or less, more preferably 18% by weight or more and 25% by weight or less. In the saccharification residue of the raw biomass, particularly in the saccharification residue of the alkali pretreated raw biomass, other components such as cellulose and hemicellulose are decomposed by the saccharification reaction, and the lignin content relatively increases. It is presumed that when the lignin content is 16% by weight or more, sufficient lignin is present on the surface of the pellets, resulting in excellent moldability and surface smoothness. The upper limit of the lignin content of the pellets of the present invention is usually about 40% by weight.

The lignin content of the pellets of the present invention is the lignin content (% by weight) relative to the dry weight of the raw material biomass (preferable specific example, saccharification residue or pulverized product thereof) processed immediately before pelletization, and is expressed by the following formula: can be found at
Lignin content (%) = lignin amount (g) in raw material biomass immediately before pelletization/dry weight (g) of raw material biomass processed until just before pelletization × 100. The amount of lignin in the raw material biomass processed until just before pelletization is the sum of the acid-insoluble lignin content and the acid-soluble lignin content.
According to a particularly preferred embodiment of the present invention, the raw biomass that has been treated immediately before pelletization is obtained by hydrolyzing a pretreated raw biomass (preferably pretreated with alkali) with a saccharifying enzyme. It is a saccharification residue or pulverized product.

Acid-insoluble lignin, also called Clason lignin, is obtained by adding 72% (w/w) sulfuric acid to lignin-containing biomass to swell and partially hydrolyze the polysaccharides, adding water to dilute the sulfuric acid, and autoclaving. is obtained by removing the ash from the insoluble fraction obtained by hydrolyzing the polysaccharide to make it acid-soluble. "Determination of Structural Carbohydrates and Lignin in Biomass" (A. Sluiter et al. 7 authors, National Renewable Energy Laboratory (NREL), April 2008 (Revision August 2012)) to measure the acid-insoluble lignin content can be done.

The acid-soluble lignin content can be measured by absorbance with reference to "Wood science experiment manual" (edited by the Japan Wood Research Society, 2000, Buneidou Publishing), edited by the Japan Wood Research Society (2000). .
The pellets of the present invention may have a characteristic that they have a lower ignition temperature and are more combustible than ordinary biomass pellets, and those having such characteristics can be suitably used as fuel. The ignition temperature of pellets suitable for fuel applications is preferably 300° C. or higher and 350° C. or lower, more preferably 300° C. or higher and 340° C. or lower, and particularly preferably 310° C. or higher and 330° C. or lower. The ignition temperature is the temperature indicated by the highest peak of the DTG curve obtained as the first derivative of the TG curve with respect to temperature after performing thermogravimetry (TG).

The present invention will be specifically described below based on Reference Examples, Examples, and Comparative Examples. However, the present invention is not limited to these.

[Reference Example 1] Pretreatment of raw material biomass (bagasse) Bagasse was pulverized using a cutter mill (Baryonyx BRX-400, Nara Machinery Co., Ltd.). The pulverization conditions were set to 70 mm for the opening of the sieve of the cutter mill, and pulverization was performed while feeding at a rotational speed of 600 rpm and a feed rate of 1000 kg/hr. To the obtained pulverized bagasse (water content: 50%, dry weight: 100 g), 10 g of sodium hydroxide and an aqueous sodium hydroxide solution and water are added so that the solid content concentration is 5% by weight to prepare a mixture. and pretreated at 80° C. for 3 hours. The solid content after solid-liquid separation using a sieve was used as the raw material (pretreated bagasse) for the saccharification reaction. This operation was repeated to obtain a raw material (pretreated bagasse) for the saccharification reaction.

[Reference Example 2] Preparation of enzyme composition for producing xylooligosaccharide [Pre-culture]
Corn steep liquor 5% (w/vol), glucose 2% (w/vol), ammonium tartrate 0.37% (w/vol), ammonium sulfate 0.14% (w/vol), phosphorus 0.2% (w/vol) potassium dihydrogenate, 0.03% (w/vol) calcium chloride dihydrate, 0.03% (w/vol) magnesium sulfate heptahydrate, 0.03% (w/vol) zinc chloride. 02% (w/vol), iron (III) chloride hexahydrate 0.01% (w/vol), copper (II) sulfate pentahydrate 0.004% (w/vol), manganese chloride tetrahydrate An aqueous solution was prepared containing 0.0008% (w/vol) of hydrate, 0.0006% (w/vol) of boric acid and 0.0026% (w/vol) of hexaammonium heptamolybdate tetrahydrate. 100 mL of the prepared aqueous solution was placed in a 500 mL baffled Erlenmeyer flask and autoclave sterilized at 121° C. for 15 minutes. After cooling, 0.01% (w/vol) of PE-M and Tween 80, which had been autoclaved at 121°C for 15 minutes, were separately added to prepare a pre-culture medium. In 100 mL of this pre-culture medium, Trichoderma reesei ATCC66589 (distributed by ATCC) was inoculated to 1×10 ⁵ cells/mL, and cultured with shaking at 180 rpm at 28° C. for 72 hours to obtain pre-culture (shake culture). Apparatus: BIO-SHAKER BR-40LF manufactured by TAITEC).

[Main culture]
Corn steep liquor 5% (w/vol), glucose 2% (w/vol), cellulose (Avicel) 10% (w/vol), ammonium tartrate 0.37% (w/vol), with distilled water. 0.14% (w/vol) ammonium sulfate, 0.2% (w/vol) potassium dihydrogen phosphate, 0.03% (w/vol) calcium chloride dihydrate, 0.03% (w/vol) magnesium sulfate heptahydrate. 0.02% (w/vol) zinc chloride, 0.01% (w/vol) iron (III) chloride hexahydrate, 0.01% (w/vol) copper (II) sulfate pentahydrate. 004% (w/vol), 0.0008% (w/vol) manganese chloride tetrahydrate, 0.0006% (w/vol) boric acid and 0.0026% (w/vol) hexaammonium heptamolybdate tetrahydrate ( w/vol) was prepared. 2.5 L of the prepared aqueous solution was placed in a 5 L stirring jar DPC-2A (manufactured by ABLE) and autoclaved at 121° C. for 15 minutes. After cooling, 0.1% (w/vol) of PE-M and Tween 80, which had been autoclaved at 121° C. for 15 minutes, were separately added to prepare the main culture medium. Into 2.5 L of this main culture medium was inoculated 250 mL of Trichoderma reesei ATCC66589 pre-cultured in the pre-culture medium. Thereafter, the cells were cultured at 28° C. for 87 hours at 300 rpm and an aeration rate of 1 vvm. After centrifugation, the supernatant was subjected to membrane filtration using Stericup-GV (manufactured by Merck Millipore). To this culture solution, β-glucosidase (Novozymes 188) was added at a protein weight ratio of 1/100 to obtain an enzyme composition.

[Preparation of enzyme composition for producing xylooligosaccharide]
The pH of the enzyme composition was adjusted to 7.5 with an aqueous sodium hydroxide solution, diluted with water to a protein concentration of 4 g/L, and then kept at 40° C. for 2 hours.

[Reference Example 3] Measurement of xylan degradation activity A substrate solution was prepared by suspending xylan (Xylam from Birch wood, manufactured by Fluca) in 50 mM sodium acetate buffer (pH 5.0) to a concentration of 1% by weight. . To 500 μL of the dispensed substrate solution, 5 μL of the resulting enzyme composition solution was added and reacted at 50° C. while rotating and mixing. The reaction time was 30 minutes. After the reaction, the tube was centrifuged, and the reducing sugar concentration of the supernatant was measured by the DNS method. In this reaction system, the amount of enzyme that produces 1 μmol of reducing sugar per minute was defined as 1 U, and the activity value (U/mL) was calculated according to the following formula.
Xylan degradation activity (U/mL) = reducing sugar concentration (g/L) x 1000 x 505 (µL)/(150.13 x reaction time (min) x 5 (µL)).

[Reference Example 4] Xylooligosaccharide analysis Xylooligosaccharides, glucose and xylose were quantitatively analyzed under the following conditions using a Hitachi high-performance liquid chromatograph LaChrom Eite (HITACHI).
Xylooligosaccharides, glucose and xylose were quantitatively analyzed based on a calibration curve prepared from standards of xylooligosaccharides (xylobiose, xylotriose, xylotetraose, xylopentaose and xylohexose), glucose and xylose. The xylo-oligosaccharide described in this reference example refers to an oligosaccharide in which 2 to 6 xyloses are linked via β-glycosidic bonds.
Column: KS802, KS803 (SHODEX)
Mobile phase: Water Detection method: RI
Flow rate: 0.5mL/min
Temperature: 75°C.

[Reference Example 5] Preparation of Bagasse Saccharification Residue in Production of Xylooligosaccharide Water was added to the pretreated bagasse prepared in Reference Example 1 so that the solid content concentration was 5%, and hydrochloric acid was further added to adjust the pH to 7.0. To 200 L of this slurry liquid, the enzyme composition for producing xylo-oligosaccharides prepared in Reference Example 2 was added so that the xylan-degrading activity was 250 U per 1 g of solid content, and the mixture was heated at 40° C. for 8 hours with stirring. The obtained solid content was subjected to solid-liquid separation using a screw press (manufactured by Fukoku Industry Co., Ltd.), and the bagasse saccharification residue was recovered as the solid content. The liquid was further centrifuged at 8000 G for 20 minutes to recover the supernatant, which was then subjected to microfiltration using Sartopore 2 (manufactured by Sautorius Japan Co., Ltd.). Xylooligosaccharides, glucose and xylose contained in the liquid after microfiltration were quantified by the method of Reference Example 4. Table 1 shows the concentrations of the components contained in the liquid after microfiltration.

[Measurement of average surface roughness]
The surface roughness of the pellet was measured using an atomic force microscope (Nanowizard 3 manufactured by JPK). As the operation mode of the atomic force microscope, an "APPNANO ACST" type needle (needle diameter: 10 nm or less) was set at a frequency of 150 kHz, a k value of 7.8 N/m, a scan speed of 0.8 Hz, and a measurement area of 10 μm ² . One randomly selected measurement area on the side surface of the pellet was divided into 256×256 areas, the displacement of each point was measured, and the arithmetic mean roughness was calculated therefrom. Further, two locations were selected at random from one pellet, their arithmetic average roughness was calculated, and the arithmetic average roughness of a total of three locations was averaged to calculate the average surface roughness.

[Measurement of dust rate]
Dust rate was measured using a low tap. Using a low-tap sieve shaker (R-1, manufactured by Tanaka Tech Co., Ltd.), Tokyo Screen's stainless steel sieve #16 (JIS standard, opening 1000 μm) is installed, and 1.0 kg of pellets discharged from the pelletizer for a certain period of time was passed through a sieving machine at 30 rpm and 15 tpm for 10 minutes, and the weight of the dust that passed through #16 was measured. The value obtained by dividing the measured weight by the parameter of 1.0 kg was measured five times in total, and the average value was taken as the dust rate.

[Example 1] Preparation, drying and pelletization of bagasse saccharification residue The saccharification residue collected in Reference Example 5 was pulverized with a cutter mill (Baryonics, manufactured by Nara Machinery Co., Ltd.) so that the pulverization degree was 10 mm or less. After that, it was dried in the sun and stirred once every 3 hours, and adjusted so that the moisture content was 10% or more and less than 30% (average moisture content: 20%). The reason for drying after pulverization is that if pulverization is performed after drying, the generation of dust in the cutter mill increases sharply, increasing the risk of dust explosion in the work area. After the drying in the sun, the moisture content was measured while stirring by hand, and if it was too dry, water was added to adjust the moisture content. The bagasse saccharification residue after adjusting the moisture content was charged into a pelletizer (“Pellet mill” manufactured by Triumph) to produce pellets, and the average surface roughness and dust rate of the obtained pellets were measured (Table 2). FIG. 1 shows the result of atomic force microscope observation when the average surface roughness of the pellet side surface was measured.

[Comparative Example 1] Preparation, drying and pelletization of bagasse saccharification residue The saccharification residue collected in Reference Example 5 was pulverized in the same manner as in Example 1 so that the pulverization degree was 10 mm or less. After that, it was dried in the sun for a longer period of time than in Example 1 to adjust the moisture content to less than 10%. An attempt was made to produce pellets by putting the bagasse saccharification residue after adjusting the moisture content into the same pelletizer as in Example 1, but clogging occurred in the die part of the pelletizer, and pellets could not be produced (Table 2).

[Comparative Example 2] Preparation, drying and pelletization of bagasse saccharification residue The saccharification residue collected in Reference Example 5 was pulverized in the same manner as in Example 1 so that the pulverization degree was 10 mm or less. After that, after drying in the sun for a short period of time, water was added to adjust the moisture content to 30% or more (average moisture content of 40%) when the moisture content was too much to evaporate. When the bagasse saccharified residue after moisture content adjustment was put into the pelletizer and pellet production was attempted, pellets could be produced immediately after the start, but the pelletizer inlet quickly became clogged and pellet production was not possible. is no longer possible. The obtained pellet average surface roughness and dust rate were measured (Table 2).

[Comparative Example 3] Preparation, drying, and pelletization of bagasse The bagasse used in Reference Example 1 was pulverized so that the mesh diameter after the cutter mill attached to the cutter mill of Example 1 was reduced to a pulverization degree of 1 mm or less. did. This is because, in preliminary tests, bagasse pulverized to a pulverization degree of 10 mm or less caused clogging in various devices such as the inlet of the pelletizer and before the die. The fibers of the bagasse itself were hard, and it was difficult to pelletize with the same grinding degree as in Example 1, Comparative Examples 1 and 2, and with the same equipment and conditions as in Example 1. After pulverizing to 1 mm or less, it was adjusted with a dryer so that the water content was less than 10%. When the bagasse after moisture content adjustment was put into a pelletizer and an attempt was made to produce pellets, pellets were obtained, but not all of the bagasse could be pelletized, and the die clogged with bagasse during production. The average surface roughness and dust rate of the obtained pellets were measured (Table 2).

[Comparative Example 4] Preparation, drying and pelletization of bagasse The bagasse used in Reference Example 1 was pulverized in the same manner as in Comparative Example 3 so that the degree of pulverization was 1 mm or less. After that, the mixture was dried in the sun and water was added, and the mixture was stirred by hand to adjust the moisture content to 10% or more and less than 30% (average moisture content: 20%). Bagasse with adjusted moisture content was charged into a pelletizer in the same manner as in Comparative Example 3 to produce pellets. The average surface roughness and dust rate of the obtained pellets were measured (Table 2). In addition, when the average surface roughness of the side surface of the pellet was measured, observation with an atomic force microscope revealed that, as shown in FIG. .

[Comparative Example 5]
The bagasse used in Reference Example 1 was pulverized so that the mesh diameter after the cutter mill attached to the cutter mill of Example 1 was larger than those of Comparative Examples 3 and 4, and the degree of pulverization was 2 mm or less. Then, it was adjusted with a dryer so that the water content was less than 10%. Bagasse after moisture content adjustment was put into the same pelletizer as in Example 1 and Comparative Example 3 to try to produce pellets, but the pelletizer inlet was immediately clogged, and pellets could not be produced. (Table 2).

[Example 2] Measurement of lignin Pulverize the saccharified residue pellets produced in Example 1, evaporate an appropriate amount to dryness on a water bath, and then dry at 105 ° C. Weight loss after drying (however, drying until constant weight ), the moisture content (% by weight) was calculated. Next, an appropriate amount (0.2899 g) of the dried sample was placed in a beaker, 3 mL of 72% sulfuric acid was added, and the mixture was allowed to stand at 30° C. for 1 hour with occasional stirring. This was completely transferred to a pressure bottle while being mixed with 84 mL of pure water. This was thermally decomposed in an autoclave at 120° C. for 1 hour. After thermal decomposition, the decomposition liquid and residue were separated by filtration. The residue was dried at 105°C and weighed 0.0760 g. Furthermore, when the dry sample was ignited at 600° C. and the ash content was measured, it was 35.1% in the decomposition residue. Therefore, the acid-insoluble lignin content in the dry sample was calculated as 17.0%. After the autoclave, the filtrate obtained by filtering the decomposition liquid and the residue was adjusted to 100 mL by adding the washing liquid of the residue, and the volume was measured with an absorbance meter at a wavelength of 210 nm. The acid-soluble lignin content in the dried sample was 1.12%, calculated using the absorption coefficient of acid-soluble lignin (110 L/g/cm). From the above, the lignin content in the pellet was calculated to be 18.1%.

[Reference Example 6] Measurement of lignin The bagasse pellets produced in Comparative Example 3 were measured for lignin in the same manner as in Example 2. As a result, the lignin content in the pellet was calculated to be 22.3%.

[Reference Example 7] Preparation of bagasse saccharification residue during xylose production Water was added to the pretreated bagasse obtained in Reference Example 1 so that the solid content concentration was 5% by weight, and hydrochloric acid was added to adjust the pH to 5.0. . To 200 L of this slurry liquid, 200 mL of saccharifying enzyme "Accelerase Duet" manufactured by Danisco Japan was added, and the mixture was kept at 48° C. for 8 hours with stirring. The 200L book was then centrifuged and the solid content was further squeezed with a screw press. The solid content after final squeezing had a moisture content of 50 to 55%. The liquid component obtained by centrifugation was subjected to microfiltration using "Sartopore 2" (manufactured by Sautorius Japan Co., Ltd.). Xylooligosaccharides, glucose and xylose contained in the liquid after microfiltration were quantified by the method of Reference Example 4. Table 3 shows the concentrations of components contained in the liquid after microfiltration.

[Example 3] Preparation, drying and pelletization of bagasse saccharification residue 2 The saccharification residue collected in Reference Example 7 was pulverized in the same manner as in Example 1 with a cutter mill so that the pulverization degree was 10 mm or less. After that, it was dried in the sun and adjusted to have a moisture content of 10% or more and less than 30% (average moisture content of 20%). Bagasse saccharified residue with adjusted moisture content was put into a pelletizer in the same manner as in Example 1, pellet production was started, and the average surface roughness and dust rate of the obtained pellets were measured (Table 4).

[Comparative Example 6] Preparation, drying and pelletization of bagasse saccharification residue 2 The saccharification residue collected in Reference Example 7 was pulverized in the same manner as in Example 1 so that the degree of pulverization was 10 mm or less. After that, it was dried in the sun so that the water content was less than 10%. When the obtained bagasse saccharification residue was put into a pelletizer and an attempt was made to produce pellets, clogging occurred in the die part of the pelletizer, and pellets could not be produced (Table 4).

[Comparative Example 7] Preparation, drying and pelletization of bagasse saccharification residue 2 The saccharification residue collected in Reference Example 7 was pulverized in the same manner as in Example 1 with a cutter mill so that the pulverization degree was 10 mm or less. After that, dry it in the sun so that the moisture content becomes 30% or more, and if it is too dry, add water and stir it by hand to check the moisture content, so that the average moisture content is 40%. adjusted to be Bagasse saccharified residue with adjusted moisture content was put into a pelletizer and pellet production was started. As a result, although pellets could be produced immediately after the start, clogging occurred in the inlet of the pelletizer quickly, making it impossible to produce pellets. The average surface roughness and dust rate of the obtained pellets were measured (Table 4).

[Comparative Example 8] Ignition temperature measurement of bagasse As an analyzer, a simultaneous differential thermogravimetric analyzer was used. The measurement was performed in an atmosphere of 40 ml/min of air, from room temperature to 800° C., with a temperature increase scan of 30° C./min. The sample weight was 4.15 g. After the TG analysis, the ignition temperature was 363°C as a result of obtaining the DTG curve.

[Example 4] Ignition temperature measurement of pellets produced from bagasse saccharification residue The ignition temperature of the pellets produced in Example 1 was measured in the same manner as in Comparative Example 8. The sample weight was 15.5 g. As a result, the ignition temperature was 322°C.

Claims (13)

1. A pellet made from lignocellulosic biomass and having an average surface roughness of 50 nm or more and 250 nm or less on the side surface of the pellet.
2. The pellet according to claim 1, which is used for fuel.
3. The pellets according to claim 1 or 2, wherein the lignocellulosic biomass is bagasse.
4. The pellet according to any one of claims 1 to 3, wherein the raw material is a saccharification residue of lignocellulosic biomass.
5. The pellets according to claim 4, wherein the saccharification residue of lignocellulosic biomass is a saccharification residue of alkali pretreated lignocellulosic biomass.
6. The pellet according to any one of claims 1 to 5, wherein the lignin content is 16% by weight or more and 40% by weight or less.
7. The pellet according to any one of claims 1 to 6, which has a dust rate of 0.5% by weight or less.
8. A method for producing the pellets according to any one of claims 1 to 7,
   Step (1) of hydrolyzing an alkali-pretreated lignocellulosic biomass obtained by alkali pretreatment of lignocellulosic biomass with a saccharifying enzyme;
   Step (2) of solid-liquid separation of the hydrolyzate of lignocellulosic biomass obtained in step (1) to obtain a saccharification residue of lignocellulosic biomass as a solid content;
   Step (3) of pulverizing the saccharified residue of lignocellulosic biomass obtained in step (2), and Step (4) of compressing and pelletizing the saccharified residue of lignocellulosic biomass obtained in step (3). ), methods.
9. The method according to claim 8, wherein in the step (1), the temperature of the alkali pretreatment is 80 to 100°C.
10. The method according to claim 8 or 9, wherein in the step (1), the alkali pretreatment is an alkali pretreatment under normal pressure.
11. The method according to any one of claims 8 to 10, wherein in the step (3), the saccharification residue of the lignocellulosic biomass obtained in the step (2) is pulverized to a diameter of 10 mm or less.
12. The method according to any one of claims 8 to 11, wherein in the step (4), the moisture content of the saccharification residue of the lignocellulosic biomass subjected to compression molding is 10% or more and less than 30%.
13. The method according to any one of claims 8 to 12, wherein the lignocellulosic biomass is bagasse.

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