Method for producing cellulose

Abstract

To provide a safe and low-cost method for producing cellulose using lignocellulosic biomass as a raw material.SOLUTION: There is provided a method for producing cellulose using lignocellulosic biomass as a raw material, which comprises a step of irradiating water to which biomass has been added with ultrasonic waves under conditions in which the pressure applied to the water is higher than atmospheric pressure.SELECTED DRAWING: None

Description

[Background technology]

[0001] Bioethanol is a type of biofuel produced by fermenting biomass such as wood, sugarcane, and corn. The consumption of fossil fuels increases the concentration of carbon dioxide (CO2) in the atmosphere, causing global warming to become a major problem. In this regard, bioethanol emits less CO2 over its life cycle than fossil fuels, and is therefore expected to be an eco-friendly fuel for transportation.

[0002] Here, the process of producing bioethanol from biomass, particularly lignocellulosic biomass, mainly consists of a step of extracting cellulose from lignocellulosic biomass (a step of separating lignin, which forms a strong wall surrounding the cellulose, from semicellulose), a step of treating the cellulose with enzymes such as cellulase to produce glucose, and a step of treating the glucose with ethanol-fermenting yeast. Of these, methods using sulfuric acid and enzymes have been proposed for the step of extracting cellulose from lignocellulosic biomass (e.g., Patent Documents 1 to 3). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Special Publication No. 2011-529091 [Patent Document 2] Patent No. 6026026 [Patent Document 3] Re-tabled publication 2015 / 033948 Summary of the Invention [Problem to be solved by the invention]

[0004] An object of the present invention is to provide a safe and low-cost method for producing cellulose using lignocellulosic biomass as a raw material. [Means for solving the problem]

[0005] The present invention provides a method for producing cellulose using lignocellulosic biomass as a raw material, comprising a step of irradiating water containing added biomass with ultrasonic waves under conditions where the pressure applied to the water is higher than atmospheric pressure, wherein the pressure may be applied to the water in a liquid-tight state during the step. [Effects of the Invention]

[0006] According to the present invention, it is possible to provide a safe and low-cost method for producing cellulose using lignocellulosic biomass as a raw material. [Brief explanation of the drawings]

[0007] [Figure 1] 1 is a block diagram of an ultrasonic irradiation device according to an embodiment of the present invention. [Figure 2] FIG. 2 is an image of the product according to Example 1 taken by a SEM (scanning electron microscope). [Figure 3] FIG. 3 is an image of the product according to Example 2 taken by a SEM (scanning electron microscope). [Figure 4] FIG. 4 is an image of the product according to Example 3 taken by a SEM (scanning electron microscope). [Figure 5] Figure 5 shows an image of commercially available cellulose taken with a SEM (scanning electron microscope). DETAILED DESCRIPTION OF THE INVENTION

[0008] Specific embodiments of the present invention will be described below. However, the present invention is not limited to the following specific embodiments. In the following, "A to B" means A or more and B or less.

[0009] This embodiment is a method for producing cellulose using lignocellulosic biomass as a raw material, characterized by including a step of irradiating water containing added biomass with ultrasound under conditions where the pressure applied to the water is higher than atmospheric pressure. The following describes the raw material, the process, and the final product in that order.

[0010] ≪Raw materials≫ (lignocellulosic biomass) Lignocellulosic biomass refers to carbohydrate materials derived from biological resources that contain so-called lignocellulose (mainly composed of three types of components: cellulose, hemicellulose, and lignin). Examples of lignocellulosic biomass include agricultural and forestry resources such as conifers (e.g., cedar), broad-leaved trees, construction waste, forest residues, pruning waste, rice straw, rice husks, wheat straw, wood chips, wood fiber, chemical pulp, waste paper, and plywood; agricultural and forestry waste products such as sugarcane bagasse, sugarcane stover, and corn stover; processed agricultural and forestry products; and plant tissues such as macroalgae and microalgae.

[0011] (water) The water to which lignocellulosic biomass is added is not particularly limited as long as it is a liquid medium containing water as the main component. Here, "main component" means that water accounts for 50% by mass or more (e.g., 55% by mass or more, 60% by mass or more, 65% by mass or more, 70% by mass or more, 75% by mass or more, 80% by mass or more, 85% by mass or more, 90% by mass or more, 92.5% by mass or more, 95% by mass or more, 97.5% by mass or more, 98% by mass or more, 99% by mass or more, 99.5% by mass or more, 99.9% by mass or more) based on the total mass of the liquid medium.

[0012] (Other ingredients) Water to which lignocellulosic biomass has been added (hereinafter referred to as "biomass water") may contain other components. However, from the viewpoint of ensuring safety and low cost, it is preferable that it is substantially free of sulfuric acid and / or enzymes, as in conventional technology. In this specification, "substantially free" means that these are not intentionally added, and for example, the content of these ingredients relative to the total mass of the biomass water is 0.1% by mass or less (e.g., 0.05% by mass or less, typically 0.01% by mass or less).

[0013] <Process> The production method according to the present embodiment includes a step of irradiating biomass water with ultrasonic waves using an ultrasonic irradiation device, which will be described in detail below.

[0014] (Device) 1, the ultrasonic irradiation device 10 includes a storage tank 1, which is a container for irradiating biomass water with ultrasonic waves, and is capable of circulating degassed and pressurized biomass water in the storage tank 1. In detail, the ultrasonic irradiation device 10 further includes a degassing tank 31 for degassing the biomass water, a circulation pump 34 for circulating the biomass water, a cooler 35 which is a heat exchanger for controlling the biomass water to a predetermined temperature, a pressurizing device 36 for pressurizing the biomass water, and a tank 37 for holding the biomass water.

[0015] The degassing tank 31 can be of any type as long as it can degas the biomass water. For example, a common type using hollow fibers is acceptable, but a high degassing capacity is preferable. For example, the degassing tank 31 can be a type that performs both vacuuming and ultrasonic irradiation. In this case, a roughly cylindrical container is provided, and a liquid phase using a liquid medium and a gas phase for vacuuming are formed in the closed space inside. A vacuum pump 33 is attached to the upper side of the cylindrical container to communicate with the gas phase, and an ultrasonic vibrator 32 is attached to the lower side to irradiate the liquid phase with ultrasonic waves. This allows the biomass water to be irradiated with ultrasonic waves while being vacuumed in the degassing tank 31. Furthermore, by generating cavitation in the biomass water, the discharge of gases dissolved in the biomass water into the gas phase can be promoted. With this configuration, the degassing tank 31 has high degassing capacity. The conduit for discharging the biomass water from the degassing tank 31 is provided with an outlet 39 for discharging the biomass water to the outside of the ultrasonic irradiation device 10.

[0016] The circulation pump 34 circulates the biomass water degassed in the degassing tank 31 through the ultrasonic irradiation device 10 by sending it to the cooler 35. As will be described later, the circulation pump 34 may also circulate the biomass water discharged from the storage tank 1 through the cooler 35.

[0017] The cooler 35 can control the temperature of the biomass water supplied to the storage tank 1 to a predetermined value. By keeping the temperature of the biomass water low and stable, it is possible to keep the energy of the cavities generated by the ultrasonic waves high and stable in the storage tank 1. It is also preferable to perform heat exchange between the inlet and outlet paths of the biomass water to the cooler 35 to improve the heat exchange rate.

[0018] The pressurizing device 36 is connected to the pipeline between the cooler 35 and the storage tank 1 and can apply a predetermined pressure to the biomass water circulating in a liquid-tight state. The pressurizing device 36 can be, for example, a pneumatic-hydraulic converter equipped with an air-hydraulic pressure converter cylinder with gas and liquid phases that converts air pressure to hydraulic pressure. The air-hydraulic pressure converter cylinder is a vertically placed cylinder approximately 50-100 mm in diameter and 200-300 mm long. It can use compressed air, which is relatively easily available in factories, and allows for easy pressure adjustment. In this case, it is preferable to make the connecting path from the pressurizing device 36 to the pipeline thin and long, so that biomass water with dissolved air in the air-hydraulic pressure converter cylinder does not flow into the storage tank 1. A pump can also be used as the pressurizing device, but a pressure regulator such as a pressure reducing valve is required.

[0019] The tank 37 stores biomass water under atmospheric pressure to be circulated within the ultrasonic irradiation device 10. The tank 37 is piped so that it can receive biomass water from the storage tank 1 or the cooler 35 and supply the biomass water to the degassing tank 31, and is also connected to a liquid supply port 38 that receives a supply of biomass water from outside the ultrasonic irradiation device 10.

[0020] (ultrasound) The frequency of the ultrasonic waves applied in this step is not particularly limited and may be, for example, 19.0 KHz or more, 40 KHz or less, or 25 KHz or less. The ultrasonic power density of the ultrasonic waves applied in this step is not particularly limited and may be, for example, 100 W / L or more. The duration of ultrasonic wave application is not particularly limited and may be, for example, 1 to 10 hours.

[0021] (pressure) The pressure applied to the biomass water is not particularly limited as long as it is higher than atmospheric pressure (e.g., standard atmospheric pressure = 101,325 Pascals), and the lower limit is, for example, 0.01 MPa or more, 0.05 MPa or more, 0.075 MPa or more, 0.1 MPa or more, 0.125 MPa or more, or 0.15 MPa or more, and the upper limit is, for example, 10 MPa or less, 5 MPa or less, 1 MPa or less, 0.75 MPa or less, or 0.5 MPa or less, higher than atmospheric pressure. Applying ultrasound under a pressure higher than atmospheric pressure can generate powerful shock waves that enable cellulose to be extracted from lignocellulosic biomass in high yield.

[0022] (dissolved oxygen content) The amount of dissolved oxygen in biomass water is preferably 1.5 mg / L or less. When the amount of dissolved oxygen is within the preferred range, the shape of the cavities generated by negative pressure in the cavitation phenomenon caused by ultrasonic vibration becomes closer to a sphere. Therefore, when the cavities are compressed and disappear, a stronger shock wave can be generated. As a result, cellulose can be extracted efficiently.

[0023] (temperature) The temperature of the biomass water (water temperature) is preferably 4° C. to 15° C. Within this range, stronger shock waves can be generated when cavities generated by the cavitation phenomenon are compressed and disappear, resulting in efficient extraction of cellulose.

[0024] Final product The final product (product) obtained by the production method of this embodiment contains easily degradable cellulose. Preferably, the product obtained by the production method of this embodiment contains easily degradable cellulose in an amount of 1% by mass or more, 1.5% by mass or more, 2% by mass or more, or 2.5% by mass or more, based on the dry mass of the product. The content of easily degradable cellulose is defined as the amount of easily degradable cellulose calculated by back-calculation from the amount of glucose produced relative to the dry mass of the product when the product is treated with cellulase (Cellulase 9012-54-8, manufactured by Tokyo Chemical Industry Co., Ltd.; temperature: 35°C; no pH treatment; fermentation period: 12 hours) under specified conditions. Furthermore, the easily degradable cellulose includes not only general cellulose but also nanocellulose and nanocellulose fiber. [Example]

[0025] The present invention will be described in more detail below with reference to examples, although the present invention is not limited to the following examples.

[0026] Example 1 Using the apparatus shown in Figure 1, cedar wood was placed in water as lignocellulosic biomass and ultrasonic treatment was carried out under the following conditions. Ultrasonic frequency: 20KHz Ultrasonic bath diameter: 100φ Ultrasonic power output: 160W Ultrasonic power density: 128W / L Temperature: 6℃ Dissolved oxygen content: 0.8 mg / L Ultrasonic irradiation time: 6 hours Pressure: atmospheric pressure + 0.2 MPa Example 2 The ultrasonic treatment was carried out under the same conditions as in Example 1, except that the lignocellulosic biomass was corn and the applied pressure was atmospheric pressure + 0.15 MPa. Example 3 The ultrasonic treatment was carried out under the same conditions as in Example 1, except that the lignocellulosic biomass was bagasse and the applied pressure was atmospheric pressure + 0.15 MPa.

[0027] 2 to 4 are SEM (scanning electron microscope) images of the product. Also, FIG. 5 is a SEM (scanning electron microscope) image of commercially available cellulose. From this, it can be seen that the product obtained by the method according to this example is a bare cellulose fiber with lignin and semicellulose removed. Furthermore, when the products according to Examples 1 to 3 were treated with cellulase (Cellulase 9012-54-8, manufactured by Tokyo Chemical Industry Co., Ltd.; temperature: 35°C; no pH treatment; fermentation period: 12 hours) under specified conditions, the amount of easily degradable cellulose calculated by back-calculation from the amount of glucose produced relative to the dry mass of the product is shown in the table below. As can be seen, the products according to all of the examples contain 2% or more by mass of easily degradable cellulose.

[0028] [Table 1] [Industrial Applicability]

[0029] The present invention is useful in the fields of cosmetics, quasi-drugs, pharmaceuticals, supplements, food, etc., which utilize cellulose or materials obtained from cellulose as a raw material (for example, bioethanol).

Claims

1. A method for producing cellulose using lignocellulosic biomass as a raw material, The method includes a step of irradiating water containing lignocellulosic biomass with ultrasonic waves under conditions where the pressure applied to the water is higher than atmospheric pressure. A manufacturing method characterized by:

2. The manufacturing method according to claim 1 , wherein in the step, the pressure is applied to the water in a liquid-tight state.

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