Processed chaff ash and process for its production

Abstract

To provide a chaff ash more suitable than a conventional chaff ash for the production of aqueous alkaline silicate solutions and a process for its production.SOLUTION: A chaff ash as a raw material is processed into a chaff ash having a bulk density of 400-800 g / l in a dried state and a moisture content of 30% by mass or less.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to processed rice husk ash and a method for producing the same. [Background technology]

[0002] In recent years, there has been a growing demand to realize a sustainable and regenerative society in order to protect the global environment. As one of the concrete measures to achieve this, biomass technologies that do not use fossil fuels, such as biomass boilers and biomass power generation, are becoming more widespread in various regions. In facilities that use such technologies, rice husk ash is often used as fuel. However, rice husks contain a lot of components that cannot be burned (especially silica components), and in these facilities, the disposal of combustion ash (rice husk ash) that contains a lot of unburned components is an issue.

[0003] As one method for solving this problem, attempts have been made in the past to dissolve rice husk ash, which contains a large amount of silica components, in an alkaline aqueous solution (an aqueous solution containing an alkali metal salt, such as an aqueous solution of sodium hydroxide), produce an aqueous solution of silicic acid containing an alkali metal component (hereinafter referred to as an alkaline aqueous solution of silicate), and reuse this as a raw material for wet-process silica (for example, Patent Documents 1 and 2).

[0004] In addition to being used as a raw material for wet-process silica, aqueous solutions of alkali silicate are also widely used in the fields of raw material for synthetic zeolite, ground hardening agents for civil engineering, detergents, and fibers and pulp. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Special Publication No. 2007-510613 [Patent Document 2] Special Publication No. 2007-522069 Summary of the Invention [Problem to be solved by the invention]

[0006] However, when rice husk ash discharged from a biomass boiler or the like is used to produce an alkali silicate aqueous solution for industrial use based on the conventional technology, the present inventors have found that there are new problems, for example, as follows.

[0007] (1) If rice husk ash is directly added to an alkaline aqueous solution, the rice husk ash absorbs the solvent during dissolution, increasing the viscosity and making it difficult to make a slurry. On the other hand, if rice husk ash is added to an alkaline aqueous solution together with water to make a slurry, only a low-concentration aqueous solution of alkaline silicate can be produced.

[0008] (2) When rice husk ash is added to an alkaline aqueous solution, the rice husk ash floats on the top of the solution, and the dissolution efficiency, especially the initial sinking ability into the alkaline aqueous solution, is poor.

[0009] (3) Rice husk ash has a low apparent density and is bulky relative to its weight. Therefore, only a small amount of rice husk ash can be transported at one time, meaning that transportation efficiency is poor. In particular, the longer the distance from the boiler facility to the melting facility, the higher the transportation costs. Furthermore, because rice husk ash is bulky, storage efficiency is poor and storage costs also rise.

[0010] The present invention has been made in view of the above problems, and has an object to provide rice husk ash which is more suitable for producing an alkali silicate aqueous solution than conventional rice husk ashes, and a method for producing the same. [Means for solving the problem]

[0011] In order to solve the above problems, the present inventors have conducted extensive research. As a result, the present inventors have found that the above problems can be solved by increasing the apparent density of rice husk ash through compaction or pulverization. <1> and preferably <2> This is shown below. <1> Rice husk ash having an apparent density in a dry state of 400 to 800 g / L and a moisture content of 30 mass% or less. <2> The carbon content is 0.1 to 8.0 mass% and the silica content is 85 to 95 mass%. <1> Rice husk ash described in. <3> The volume average particle diameter D50 measured by a laser diffraction method is 5.0 to 200 μm. <1> or <2> Rice husk ash described in. <4> Consolidating or crushing raw rice husk ash having an apparent density of 350 g / L or less in a dry state so that the apparent density in a dry state is 400 to 800 g / L; and A method for producing rice husk ash, which optionally includes adjusting the moisture content of the raw rice husk ash to a range of 30 mass% or less. <5> The compaction or pulverization is carried out so that the volume average particle diameter D50 is 5.0 to 200 μm. <4> The manufacturing method described in <6> The compaction or crushing was carried out using a roller compactor at a rate of 1.2 x 10 3 Carry out with a linear pressure of N / cm or more. <4> or <5> The manufacturing method described in Effect of the Invention

[0012] According to the present invention, it is possible to provide rice husk ash and a method for producing the same that are more suitable for producing an aqueous alkali silicate solution than conventional rice husk ash. The aqueous alkali silicate solution produced from the rice husk ash of the present invention can be used as a raw material for wet-process silica, as well as for the same applications as conventional aqueous sodium silicate solutions derived from silica sand. [Brief description of the drawings]

[0013] [Figure 1] FIG. 1 is a photograph of the raw rice husk ash used in the examples and a photograph of the processed rice husk ash in one embodiment of the present invention. [Diagram 2] Figure 2 is a photograph showing the state of the liquid surface after unprocessed rice husk ash was dropped into an aqueous sodium hydroxide solution and a short time had passed since the solution had finished sinking. [Diagram 3] FIG. 3 is a graph showing the relationship between time and SiO2 concentration after rice husk ash is added to an aqueous sodium hydroxide solution. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0014] <Rice husk ash> The rice husk ash of the present invention has an apparent density in a dry state of 400 to 800 g / L and a moisture content of 30 mass % or less.

[0015] Usually, the apparent density of unprocessed rice husk ash after combustion is 350 g / L or less, and often 300 g / L or less, and the rice husk ash of the present invention has a higher apparent density than unprocessed rice husk ash. The rice husk ash of the present invention has a moderately high apparent density and a moderate weight, so that it has improved sinking properties in an alkaline aqueous solution and absorbs less solvent. Compared to unprocessed rice husk ash, a larger amount of rice husk ash can be put into a container, so that the SiO2 concentration can be increased. In addition, since the moisture content is 30 mass% or less, the rice husk ash of the present invention maintains a weight within a range suitable for transportation and a moderate solid state. In addition, since the rice husk ash of the present invention has a moderately high apparent density, it is not bulky, and transportation efficiency and storage efficiency are improved. As a result, the rice husk ash of the present invention improves transportation efficiency, storage efficiency, and sinking properties in an alkaline aqueous solution, and a higher concentration slurry can be obtained. Thus, the rice husk ash of the present invention is more suitable for producing an aqueous alkali silicate solution than unprocessed rice husk ash after combustion.

[0016] The apparent density of the rice husk ash of the present invention is 400 to 800 g / L. By having an apparent density of 400 g / L or more, the bulkiness relative to the weight is appropriately reduced, the transportation efficiency, storage efficiency, and sinking property in an alkaline aqueous solution are improved, and a high-concentration slurry is obtained. From the viewpoint of further improving the transportation efficiency, storage efficiency, and sinking property in an alkaline aqueous solution and making it easier to obtain a high-concentration slurry, the lower limit of the apparent density range is preferably 450 g / L or more, more preferably 500 g / L or more, and even more preferably 550 g / L or more. By having an apparent density of 800 g / L or less, an appropriate space is formed between the rice husk ash particles, and the sinking property in an alkaline aqueous solution is improved. From the viewpoint of further improving the sinking property in an alkaline aqueous solution, the upper limit of the apparent density range is preferably 750 g / L or less, more preferably 730 g / L or less, and even more preferably 720 g / L or less.

[0017] The apparent density is measured in a dry state (approximately less than 1.5% by mass of moisture). Unprocessed rice husk ash after combustion is usually in a dry state, and the apparent density can be measured as is. The apparent density of rice husk ash that is not in a dry state can be measured after sufficient drying treatment (e.g., 125°C, 6 hours).

[0018] The moisture content of the rice husk ash of the present invention is 30% by mass or less. By having a moisture content of 30% by mass or less, the rice husk ash of the present invention maintains a weight in a range suitable for transportation and a moderate solid state. The moisture content may be 25% by mass or less, 20% by mass or less, 15% by mass or less, or 10% by mass or less. When the rice husk ash of the present invention contains a certain amount of moisture, the scattering of dust can be suppressed, and the handling properties during packaging, transportation, and unpacking, as well as the handling properties when the rice husk ash is put into an aqueous solution, are improved. In addition, when the rice husk ash of the present invention contains a certain amount of moisture, the sinking property of the rice husk ash in an alkaline aqueous solution is improved due to a moderate increase in weight. The moisture content may be 0.1% by mass or more, 0.5% by mass or more, 0.7% by mass or more, or 1.0% by mass or more. The moisture content can be adjusted by any treatment such as adding water to the rice husk ash and drying treatment. The moisture content of the rice husk ash of the present invention may not be adjusted at all, that is, no water may be added at all.

[0019] The silica content and carbon content in the rice husk ash of the present invention are not particularly limited, but since rice husk ash is used as a silica source, it is preferable that the silica content is high and the content of carbon as an impurity is low. The silica content in rice husk ash may be 85% by mass or more, and is preferably 90% by mass or more. The upper limit of the silica content varies depending on the type of rice, the growing region, and the combustion method of rice husk ash (boiler type, combustion conditions, etc.), but is typically about 95% by mass or less. The silica content in rice husk ash can be measured, for example, by a fluorescent X-ray analyzer or an ICP emission analyzer. On the other hand, the carbon content in the rice husk ash of the present invention is preferably 0.1 to 8.0% by mass. The carbon content in rice husk ash discharged from a general combustion facility is about 0.1% by mass or more. The carbon content in rice husk ash may be 0.3% by mass or more, 0.5% by mass or more, or 1.0% by mass or more. By making the carbon content in the rice husk ash 8.0% by mass or less, the incomplete combustion components of the rice husk are reduced, and the quality of the rice husk ash (e.g., the content of silica components) is improved. The carbon content in the rice husk ash is preferably 6.0% by mass or less, 5.0% by mass or less, or 4.0% by mass or less. The carbon content in the rice husk ash can be measured, for example, with a carbon analyzer.

[0020] The rice husk ash of the present invention preferably has a volume average particle diameter D50 in the range of 5.0 to 200 μm by laser diffraction method. When the volume average particle diameter D50 is 5.0 to 200 μm, the apparent density is easily maintained in the range of 400 to 800 g / L. Furthermore, when the volume average particle diameter D50 is 5.0 μm or more, the generation of excessive dust is suppressed and the handling property is further improved. When the volume average particle diameter D50 is 5.0 to 200 μm, the amount of void between particles is in an appropriate range, and when the rice husk ash is put into an alkaline aqueous solution, the rice husk ash absorbs the alkaline aqueous solution appropriately. As a result, combined with the appropriate weight, the time required for the rice husk ash to sink into the alkaline aqueous solution is shortened, and the sinking property is further improved. Since it is preferable that the proportion of fine particles of 1.0 μm or less in the particle size distribution is as small as possible, the volume average particle size D50 is preferably 10 to 150 μm, more preferably 15 to 100 μm, and particularly preferably 20 to 80 μm.

[0021] The particle size distribution can be measured by a commercially available laser diffraction particle size distribution measuring device. Specifically, the particle size distribution is measured by dispersing a sample in water to a predetermined concentration, feeding the dispersion into a circulation system in the measuring device, and adopting the value when the value of D50 becomes stable as the measured value. When the rice husk ash is processed into a compacted compact as described later, it is preferable to adjust the compaction conditions so that the volume average particle diameter D50 measured by the above method is in the range of 5.0 to 200 μm.

[0022] The form of the rice husk ash of the present invention may be either a powder or a molded body, and the shape of the molded body is not particularly limited. As described later, the rice husk ash of the present invention is processed by compaction or pulverization, and it is easily possible to distinguish it from the unprocessed rice husk ash after combustion based on the appearance, apparent density, particle shape and particle size distribution of the rice husk ash observed visually or under a microscope. For example, in terms of appearance, the particles of the rice husk ash of the present invention have a relatively uniform particle size compared to the unprocessed rice husk ash, and there are almost no particles exceeding 1.0 mm. The apparent density of the rice husk ash of the present invention is 400 g / L or more, while that of the unprocessed rice husk ash is 350 g / L or less.

[0023] The rice husk ash of the present invention can contribute to improving transportation efficiency, whether in bulk or packaged transportation. Since the processed rice husk ash of the present invention has a high apparent density, it is possible to load a larger amount of rice husk ash per transportation, for example, compared to conventional rice husk ash. In addition, when the rice husk ash of the present invention is stored in a packaging bag (paper bag, polyethylene bag, FIBC bag, etc.), the storage space per storage amount can be reduced. In addition, the rice husk ash of the present invention has the advantage of being able to suppress the generation of dust when packaging in a packaging bag or when unpacking it.

[0024] The rice husk ash of the present invention can be used as a silica source. For example, the rice husk ash of the present invention can be used alone or mixed with silica sand as a raw material for an aqueous alkali silicate solution. The aqueous alkali silicate solution can be produced by a known method, for example, by putting rice husk ash into an aqueous sodium hydroxide solution and dissolving it. The dissolution conditions are not particularly limited, and known dissolution methods can be used. Under normal pressure, dissolution can be carried out at 70°C or higher, and in a pressurized container such as an autoclave, dissolution can be carried out at 100°C or higher. Generally, the silica component in rice husk ash that dissolves in an aqueous alkali solution is about 70 to 90% by mass, so the rice husk ash to be put into the aqueous alkali solution needs to be charged in an amount greater than the amount of silica that achieves the target concentration. Since the rice husk ash of the present invention has a high apparent density, a larger amount of rice husk ash can be charged into a container than conventional rice husk ash. In addition, since the rice husk ash of the present invention has a moderately high apparent density, it absorbs less solvent and does not need to add water to form a slurry. Therefore, there is an advantage that a large amount of alkali silicate aqueous solution can be produced at one time, or a high-concentration alkali silicate aqueous solution can be produced. For example, once a pressurized container such as an autoclave is sealed, it is difficult to add additional raw materials. Thus, when a large amount of silica source needs to be added at one time, the rice husk ash of the present invention, which can be charged in a larger amount than conventional rice husk ash, is more effective.

[0025] In addition, the rice husk ash of the present invention has a higher apparent density and a suitable weight than conventional rice husk ashes, and therefore has improved sinking properties in an alkaline aqueous solution. By using the rice husk ash of the present invention, it is possible to shorten the industrial process time, reduce energy consumption, and improve production efficiency.

[0026] The aqueous alkali silicate solution produced from the rice husk ash of the present invention can be used as a raw material for wet-process silica, either alone or mixed with a conventional aqueous alkali silicate solution (e.g., one produced from silica sand).Wet-process silica has a high BET specific surface area and micropores to mesopores, and is therefore widely used in a wide variety of applications, such as reinforcing fillers for industrial rubber, tires, and silicone rubber, paper fillers, matting agents for paints, abrasives for toothpaste, and antiblocking agents for films.

[0027] <Manufacturing method of rice husk ash> The method for producing rice husk ash of the present invention includes compressing or crushing raw rice husk ash, which has an apparent density in a dry state of 350 g / L or less, so that the apparent density in a dry state is 400 to 800 g / L, and optionally adjusting the moisture content of the raw rice husk ash to a range of 30 mass% or less.

[0028] The raw rice husk ash is not particularly limited as long as it is ash discharged by burning rice husks. However, from the viewpoint of suppressing the burden on the environment such as CO2 emissions, the raw rice husk ash is preferably combustion ash of rice husks discharged from a combustion facility using biomass fuel, such as a biomass boiler for heat recovery and power generation or a biomass power generation. The apparent density of the raw rice husk ash in a dry state is 350 g / L or less. In the manufacturing method of the present invention, the raw rice husk ash is subjected to processing by compaction or pulverization to adjust the apparent density to an appropriate range. The lower limit of the apparent density of the raw rice husk ash is not particularly limited, but from the viewpoint of processing efficiency, it is preferably 150 g / L or more, 200 g / L or more, 250 g / L or more, or 300 g / L or more. The facility for burning rice husks is not particularly limited, and may be, for example, a boiler or a combustion furnace that is normally used.

[0029] The silica content and carbon content in the raw rice husk ash are not particularly limited, but since these contents are reflected in the silica content and carbon content in the rice husk ash of the present invention, it is preferable that the silica content is high and the carbon content is low. A low carbon content also contributes to improving the energy utilization efficiency of biofuel in combustion equipment. The silica content in the raw rice husk ash may be 85% by mass or more, and is preferably 90% by mass or more. The upper limit of the silica content varies depending on the type of rice, the growing region, and the combustion method of the rice husk ash (boiler type, combustion conditions, etc.), but is typically about 95% by mass or less. On the other hand, the carbon content in the raw rice husk ash is preferably 0.1 to 8.0% by mass. The carbon content in rice husk ash discharged from a general combustion equipment is about 0.1% by mass or more. It is possible to reduce the carbon content in the rice husk ash to less than 0.1% by mass by high-temperature combustion, but in such a case, crystalline silica components such as cristobalite are likely to be by-produced in the rice husk ash, which may be undesirable when using the rice husk ash as a silica source. For example, when using rice husk ash as a silica source to produce an alkali silicate aqueous solution, the crystalline silica components may not dissolve in the solvent and remain as foreign matter. The carbon content in the raw rice husk ash may be 0.3% by mass or more, 0.5% by mass or more, or 1.0% by mass or more. By making the carbon content in the raw rice husk ash 8.0% by mass or less, the incomplete combustion components of the raw rice husk are reduced, and the quality of the raw rice husk ash (for example, the content of silica components) is improved. The carbon content in the raw rice husk ash is preferably 6.0% by mass or less, 5.0% by mass or less, or 4.0% by mass or less.

[0030] In the manufacturing method of the present invention, the raw rice husk ash is subjected to a processing treatment of compaction or pulverization to increase its apparent density in a dry state to a desired range. Compaction refers to a process of compressing the raw rice husk ash, and pulverization refers to a process of crushing the raw rice husk ash. The processing treatment may be either compaction or pulverization, or both may be performed simultaneously or in sequence. Depending on the type and conditions of the processing treatment, it may be difficult to distinguish between compaction and pulverization, and it is not necessary to distinguish between them.

[0031] The types of compaction and pulverization are not particularly limited. The pulverization process may be dry or wet. In the case of dry processing, dust is likely to be generated, but a pretreatment process is not required, and processing can be performed efficiently. In the case of wet processing, pretreatment such as a slurrying process is required, but dust generation can be suppressed. The dry pulverization process can be performed using a commercially available dry pulverizer such as a roller mill, a high-speed rotary mill (pin mill), a jet mill, a ball mill, or a bead mill. The wet pulverization process can be performed using a commercially available wet pulverizer such as an in-line mixer, a jet mill, a ball mill, or a bead mill. By pulverization, the plant-derived structures in the rice husk ash can be destroyed and the voids between the particles can be reduced, thereby increasing the apparent density of the rice husk ash. The compaction process can be performed using a commercially available granulator such as a roller compactor using a compression roller or a briquetting roller, and a tablet press. Compaction can compress the rice husk ash and reduce the voids between the particles, thereby increasing the apparent density of the rice husk ash while suppressing dust generation. When both compaction and crushing are performed, the rice husk ash can be compressed while destroying the plant-derived structures in the rice husk ash, making it easier to obtain a higher apparent density while suppressing dust generation.

[0032] The compaction treatment is preferably carried out using a roller compactor, and the compaction rate is 1.2×10 3 It is more preferable to carry out the process at a linear pressure of 1.2×10 N / cm or more. The linear pressure is the total pressure (N) applied to the rolls of the roller compactor divided by the width (cm) of the roll in the direction of the rotation axis. 3 N / cm or more, it is easy to obtain a suitable apparent density. The linear pressure during consolidation is 2.9×10 3 N / cm or 4.7×10 3 The linear pressure during consolidation is preferably 12.8×10 3 N / cm or less is preferable, and 11.7×10 3 It is more preferable that the hardness is less than N / cm.

[0033] In the manufacturing method of the present invention, the moisture content of the raw rice husk ash may be adjusted to a range of 30% by mass or less, if necessary. By adjusting the moisture content within this range, the rice husk ash of the present invention, which is the final product, maintains a weight within a range suitable for transportation and a suitable solid state. Usually, the moisture content of unprocessed rice husk ash after combustion is about 1.0% by mass. The moisture content may be 5.0% by mass or more, 10% by mass or more, and 25% by mass or less, or 20% by mass or less. The moisture content can be adjusted by drying or adding moisture. The timing of the moisture adjustment may be before or after compaction or pulverization. When moisture is added before compaction or pulverization, it also contributes to suppressing dust generation during these processing steps. When moisture is added before compaction or pulverization, it is preferable to adjust the moisture content within a range in which the raw rice husk ash does not solidify in the device due to the influence of moisture. When moisture is added after compaction or pulverization, it also contributes to suppressing dust generation during transportation and packaging of the processed rice husk ash. When the water is added after compaction or pulverization, it is preferable to mix the water and rice husk ash uniformly. In addition, if the water content of the rice husk ash of the present invention, which is the final product, is 30 mass% or less, the water adjustment may be performed multiple times. EXAMPLES

[0034] The present invention will be described in more detail below with reference to examples. The materials, amounts, ratios, processing contents, processing procedures, etc. shown in the examples can be appropriately changed without departing from the spirit of the present invention. Therefore, the scope of the present invention is not limited to the specific examples shown below.

[0035] <Rice husk ash raw material> In the examples, the following raw rice husk ashes A to C were used. Table 1 shows the basic physical properties of the rice husk ash. Raw rice husk ash A: Ash discharged from a fluidized bed type biomass boiler. Raw rice husk ash B: Ash discharged from a fixed-bed type biomass boiler. Raw rice husk ash C: Ash produced by burning rice husks in a small muffle furnace (model: KDF S100G, manufactured by Denken Co., Ltd.). Specifically, 500g of rice husks were placed in each of two stainless steel saggers (300 x 300 x 115mm) with lids and air holes, stacked in two layers, and fired at 500℃ for two hours and then at 700℃ for two hours.

[0036] [Table 1]

[0037] <Analysis method for rice husk ash> ●Moisture content (heat loss) (mass%) The water content was determined from the mass loss of the sample after drying at 105° C. for 2 hours in accordance with JIS K 5101-15-1 (pigment test method - heat loss).

[0038] Apparent density (g / L) Based on JIS K 5101-12-1:2004 (Pigment test method - apparent density or apparent specific volume - static method), a dedicated measuring device (0.5 mm mesh sieve, funnel, 30 mL cylindrical receiver, receiver stand and funnel stand) was used. The sample (rice husk ash) was dropped from the sieve into the funnel with a brush, and the heaped part of the sample that had accumulated in the receiver was scraped off with a spatula, after which the mass of the sample was measured. The apparent density of the rice husk ash in g / L was calculated based on its mass using the following formula.

[0039]

number

[0040] Bulk density (g / mL) Based on the section "7.8 Bulk density" of JIS K 6220-1:2015 (Rubber compounding agents - Organic chemicals - Test methods - Part 1: General), a dedicated measuring device (a cylinder with an inner diameter of 22.00 ± 0.05 mm and an internal depth of 100 mm made of general steel, and a piston with an outer diameter of 21.80 ± 0.05 mm, a length of 115 mm, a mass of 190 g, and a cavity inside) was used. The piston was allowed to fall naturally into the cylinder before the sample (rice husk ash) was placed, and the height of the piston protruding from the top of the cylinder was measured. Next, a weighed sample of about 1 g was placed in the cylinder, the piston was slowly dropped over 5 seconds, the side wall of the cylinder was lightly tapped with a piece of wood to make the piston well blended, and the height of the piston protruding from the top of the cylinder was measured. The bulk density in g / mL was calculated using the change in the height of the piston protruding from the top of the cylinder and the bottom area of ​​the cylinder using the following formula.

[0041]

number

[0042] ●Volume average particle size (D50) The particle size distribution was measured using a laser diffraction particle size distribution analyzer (model: SYNC30, manufactured by Microtrack Bell), and the particle size value at which the volume-integrated cumulative value in the particle size distribution was 50% was calculated as D50.

[0043] Pore ​​volume by mercury intrusion method (cm 3 / g) (hereinafter referred to as "mercury pore volume") Using a mercury porosimeter (model: PASCAL440, manufactured by Thermoquest), the pressure was increased from 100 kPa to 200 MPa to measure the mercury pore volume in the pore radius range of 3.6 to 6,400 nm.

[0044] Carbon content in rice husk ash (mass%) As a pretreatment, the rice husk ash was dried at 105°C for 2 hours, and then the carbon content was quantified using the following method. The carbon content was measured using a carbon analyzer (model: CS744, manufactured by LECO Japan LLC) that uses combustion in an oxygen stream and non-dispersive infrared absorption method. The samples were heated at a temperature of 1,350°C, with an oxygen inflow pressure of 0.24 MPa and a measurement time of 50 seconds, and the amount of CO gas and CO2 gas was measured using an infrared detector (NDIR) built into the device.

[0045] Composition of inorganic components other than carbon in rice husk ash (mass%) Using a wavelength dispersive X-ray fluorescence analyzer (model: ZSX PrimusII, manufactured by Rigaku Corporation), a qualitative analysis was first performed on elements other than carbon to confirm the type of inorganic impurities detected, and then a quantitative analysis of the inorganic impurities detected was performed. The measurement sample was made by placing rice husk ash in a ring-shaped mold and pressurizing it to form it. The quantitatively determined inorganic component composition (excluding carbon) was converted to oxides using the analysis software provided with the device to determine the concentration (mass%).

[0046] <Comparative Example 1 (unprocessed)> The raw material rice husk ash A was not subjected to any compaction or crushing processes, but instead subjected to the dissolution test (1) described below to evaluate the suppression of dust when the rice husk ash was added to the alkaline aqueous solution, the sinking of the rice husk ash, and the viscosity after addition. The physical properties of the product, the alkaline silicate aqueous solution, were determined, including the SiO2 concentration and the SiO2 / (Na2O+K2O) molar ratio.

[0047] <Example 1 (Consolidation)> A roller compactor (model: FR125×40, Freund Turbo) was used, with a roller rotation speed of 9 rpm and linear pressure of 5.8×10 3 Raw rice husk ash A was compressed under conditions of 90 N / cm and a screw rotation speed of 90 rpm to obtain processed rice husk ash.

[0048] After the processing, the physical properties of the rice husk ash were measured and the dissolution test (1) was carried out in the same manner as in Comparative Example 1.

[0049] <Example 2 (Dry Grinding)> The raw rice husk ash A was pulverized using a pin-type high-speed pulverizer (model: Jiyuu pulverizer M-2, manufactured by Nara Machinery Manufacturing Co., Ltd.) at a feed rate of 30 kg / h and a rotation speed of 7,600 rpm to obtain processed rice husk ash. After the processing, the physical properties of the rice husk ash were measured and the dissolution test (1) was carried out in the same manner as in Comparative Example 1.

[0050] <Example 3 (wet grinding)> 500 g of raw rice husk ash A and 1,500 g of water were mixed to prepare a rice husk ash slurry with a concentration of 25 mass%. The total amount of this slurry was poured into 4,200 g of alumina balls (diameter 10 mm, media specific gravity 4.09 g / cm3). 3 The rice husk ash slurry was wet-pulverized by rotating the ceramic pot at 700 rpm for 3 hours using a pot mill rotating table (model: ANZ-100S, manufactured by Nitto Kagaku Co., Ltd.).

[0051] After wet grinding, the alumina balls and the slurry were separated using a sieve with 1 mm openings. A 150 mm diameter magnetic Buchner funnel (Nuchner) was attached to a 3 L suction filter bottle, and a polyester plain weave filter cloth (approximately 50 μm × 400 μm openings) was placed in the funnel to create a suction filter, which was then used to further separate the slurry into solid and liquid forms. The solid fraction after solid-liquid separation was left to stand and dried at 125°C for 6 hours using a constant temperature dryer (model: NDO-420, Tokyo Rikakikai Co., Ltd.) to obtain processed rice husk ash. After the processing, the physical properties of the rice husk ash were measured and the dissolution test (1) was carried out in the same manner as in Comparative Example 1.

[0052] <Comparative Example 2 (Excessive Grinding)> Raw rice husk ash A was pulverized using a supersonic jet mill (model: PJM-100NP, manufactured by Japan Pneumatic Mfg. Co., Ltd.) under conditions of a feed rate of 2.7 kg / h, a pulverization pressure of 0.55 MPa, a number of nozzles of 4, and a nozzle diameter of 3 mm, to obtain processed rice husk ash. After the processing, the physical properties of the rice husk ash were measured and the dissolution test (1) was carried out in the same manner as in Comparative Example 1.

[0053] Example 4 (Crushing and Compaction) A roller compactor (model: FR125×40, Freund Turbo) was used, with a roller rotation speed of 9 rpm and linear pressure of 5.8×10 3 The rice husk ash pulverized in the same manner as in Comparative Example 2 was compressed under conditions of a pressure of 90 N / cm and a screw rotation speed of 90 rpm to obtain processed rice husk ash. After the processing, the physical properties of the rice husk ash were measured and the dissolution test (1) was carried out in the same manner as in Comparative Example 1.

[0054] <Comparative Example 3 (unprocessed)> The raw material rice husk ash B was not subjected to compaction or pulverization processing, and the physical properties of the rice husk ash were measured as is in the same manner as in Comparative Example 1, and a dissolution test (1) was conducted.

[0055] <Comparative Example 4 (unprocessed)> The raw material rice husk ash C was not subjected to compaction or pulverization processing, and the physical properties of the rice husk ash were measured as is in the same manner as in Comparative Example 1, and a dissolution test (1) was conducted.

[0056] <Comparative Example 5 (wet grinding)> The raw rice husk ash B was subjected to the same processing treatment (wet grinding and solid-liquid separation) as in Example 3 to obtain processed rice husk ash. After the processing, the physical properties of the rice husk ash were measured and the dissolution test (1) was carried out in the same manner as in Comparative Example 1.

[0057] <Comparative Example 6 (wet grinding)> The raw rice husk ash C was subjected to the same processing treatment (wet grinding and solid-liquid separation) as in Example 3 to obtain processed rice husk ash. After the processing, the physical properties of the rice husk ash were measured and the dissolution test (1) was carried out in the same manner as in Comparative Example 1.

[0058] <Dissolution test (1)> Rice husk ash was dissolved in an alkaline aqueous solution according to the procedure of dissolution method (1) below to obtain an alkaline silicate aqueous solution. This alkaline silicate aqueous solution was evaluated for dust suppression when rice husk ash was added to the alkaline aqueous solution, sinking of rice husk ash, and viscosity after addition, and the SiO2 concentration and SiO2 / (Na2O+K2O) molar ratio were obtained as physical properties of the product alkaline silicate aqueous solution.

[0059] ●Dissolution method (1) The dissolution method (1) aims to prepare an alkali silicate aqueous solution in which the SiO2 concentration in the alkali silicate aqueous solution is 17-19 mass% and the molar ratio is 3.00-3.40. These values ​​are standard values ​​for commercially available alkali silicate aqueous solutions. 1,310 g of sodium hydroxide aqueous solution adjusted to 8.9 mass% was added to a 3 L stainless steel container equipped with a stirrer and heated to 90 ° C. Then, 410 g of rice husk ash was added to the container while continuing stirring, the container was covered, and mixing was continued for 6 hours while maintaining 90 ° C. After that, the aqueous solution was cooled to room temperature. A magnetic Buchner funnel (Nuchsche) with a diameter of 150 mm was attached to a 3 L suction filtration bottle, and a filter paper (1 μm mesh, standard 5C, Advantec Co., Ltd.) was placed in the funnel to prepare a suction filter, and the undissolved residue in the aqueous solution was removed using the suction filter to obtain an alkali silicate aqueous solution.

[0060] ● Suppression of dust when feeding In the above dissolution method (1), the amount of dust generated when rice husk ash was put into the alkaline aqueous solution was visually evaluated. The less dust generated, the more the deterioration of the working environment can be suppressed. The evaluation was performed on a 5-point scale, with Example 1, in which almost no dust was generated, being rated as 5, and Comparative Example 3, in which the most dust was generated, being rated as 1. If the evaluation was 4 or higher, the amount of dust generated was within the acceptable range, and the result was displayed as "GOOD", and if it was 3 or lower, it was displayed as "BAD".

[0061] ●Sinking speed In the above dissolution method (1), the time (seconds) from immediately after the rice husk ash was added until all of the rice husk ash on the liquid surface (excluding rice husk ash that was scattered as dust) became wet and sank was measured. The shorter the sinking time, the shorter the manufacturing process time, including the rice husk ash dissolution step, which contributes to improving productivity. In the results, sinking times of 60 seconds or less were displayed as "GOOD" and times of more than 60 seconds were displayed as "BAD".

[0062] ●Viscosity In the above dissolution method (1), a portion of the aqueous solution (200 mL) was taken out into a beaker immediately after the rice husk ash on the liquid surface (excluding the rice husk ash scattered as dust) had completely wetted and sunk. Using a commercially available B-type viscometer (model: TVB-10M, manufactured by Toki Sangyo Co., Ltd.), the viscosity of the sample was measured after rotating it for 1 minute at 60 rpm using a No. 20 rotor if the viscosity of the sample was 50 mPa·s or less, and the viscosity of the sample was measured after rotating it for 1 minute at 3 rpm using a No. 21 rotor if the viscosity of the sample was other than 50 mPa·s. In the results, a viscosity of 50 mPa·s or less was displayed as "GOOD", and a viscosity of more than 50 mPa·s was displayed as "BAD".

[0063] ●SiO2 concentration and molar ratio in alkaline silicate solution Using a syringe with a membrane filter with a mesh size of 1 μm, the aqueous alkali silicate solution obtained by dissolution method (1) was collected (approximately 0.2 mL) and diluted with pure water 10,000 times (standard solution for calibration curve: 20 mass ppm). Quantitative analysis of SiO2, Na2O, and K2O was performed on the diluted sample using a high-resolution ICP emission spectrometer (model: PS3520DDII, Hitachi High-Tech Science). The measured SiO2, Na2O, and K2O mass concentrations were converted to molar amounts, and the molar ratio of silicon dioxide to the total of sodium oxide and potassium oxide was calculated. Specifically, the molar masses of each component were 60.08 (SiO2), 61.98 (Na2O), and 94.19 (K2O), and the molar ratio was calculated using the following formula.

[0064]

number

[0065] Table 2 shows the characteristics of the rice husk ashes of Examples 1 to 4 and Comparative Examples 1 and 2 and the results of the dissolution test (1).

[0066] [Table 2]

[0067] <Explanation of Results: Examples 1 to 4, Comparative Examples 1 to 6> Characteristics of rice husk ash Figure 1 shows photographs of raw rice husk ash A, raw rice husk ash C, and the rice husk ash obtained in Example 1. As can be seen from Figure 1, it is easy to determine whether the rice husk ash has been processed or not based on information such as the presence or absence of particles with a plant-derived structure, the size of the maximum particle, and the uniformity of the particle size.

[0068] The apparent density of the rice husk ash in Comparative Example 1 was 300g / L, whereas the apparent density of the rice husk ash in Examples 1 to 4, which were subjected to compaction or crushing, increased significantly. Therefore, by increasing the amount of rice husk ash filled in the packaging bag, it is expected that the transportation efficiency and storage efficiency will be greatly improved. It was found that the apparent density does not increase significantly even if the rice husk ash is crushed excessively (Comparative Example 2). In other words, even if the raw rice husk ash is the same, the characteristics of the resulting rice husk ash differ depending on the processing conditions of the rice husk ash, so it was found that the processing of the rice husk ash needs to be carried out under appropriate conditions. In particular, it was found that the apparent density increased significantly by crushing the rice husk ash and then compacting it (Example 4). In addition, it was found that the evaluation differs depending on the apparent density even if the particle diameter is about the same (comparison of Example 4 and Comparative Example 2). This is thought to be because the apparent density is a parameter that also reflects the state of the voids between the particles. From the viewpoint of providing rice husk ash suitable for producing an aqueous alkali silicate solution, the state of its voids is an important feature, and therefore it can be said that the solution to the problem of the present invention cannot be determined solely by the particle size.

[0069] Even in the case of rice husk ashes (Comparative Examples 3 and 4) in which the rice husks were burned by a different method, the apparent density was small, and therefore similar results to those of Comparative Example 1 were obtained. In addition, even if the same processing was performed, the characteristics of the resulting rice husk ash differ depending on the raw rice husk ash, and therefore it was found that the processing of rice husk ash must be performed under appropriate conditions according to the raw rice husk ash (comparison of Example 3 and Comparative Examples 5 to 6).

[0070] -Evaluation of dissolution test In both the Examples and Comparative Examples, aqueous alkali silicate solutions having the targeted SiO2 concentration (17 to 19 mass%) and molar ratio (3.00 to 3.40) could be prepared.

[0071] Fig. 2 is a photograph showing the state of the liquid surface of the aqueous solution after the raw rice husk ash A had completely sunk into the aqueous sodium hydroxide solution and was then thoroughly stirred for several tens of seconds in the dissolution test (1) of Comparative Example 1. The rice husk ash of Comparative Example 1 took a long time to sink and was in a highly viscous state. In Comparative Example 1, the highly viscous state continued for a while, and the solubility was insufficient.

[0072] In contrast, the rice husk ash of Examples 1 to 4 all generated little dust, had a short sinking time, had low viscosity, and had excellent solubility. In the case of Comparative Example 2, in which excessive grinding was performed, dust was generated and the sinking time was long, but it was found that by further consolidating the rice husk ash, it was possible to obtain suitable rice husk ash that suppresses dust generation and has a short sinking time.

[0073] As described above, it was found that rice husk ash suitable for producing an alkaline silicate aqueous solution can be provided by appropriately processing rice husk ash so that the apparent density becomes 400 to 800 g / L.

[0074] <Example 5> Using the rice husk ash (apparent density: 590 g / L) obtained in Example 1, an attempt was made to produce a high-concentration aqueous alkali silicate solution according to the dissolution method (2) described below. If a high-concentration aqueous alkali silicate solution could be produced, the production efficiency of aqueous alkali silicate solutions of standard concentrations could be improved, and the use of rice husk ash as a silica source could be expanded.

[0075] ●Dissolution method (2) The dissolution method (2) aims to prepare an alkali silicate aqueous solution in which the SiO2 concentration in the alkali silicate aqueous solution is 28-29% by mass and the molar ratio is 3.00-3.40. 1,080 g of sodium hydroxide aqueous solution adjusted to 17.0% by mass was added to a 3 L stainless steel container equipped with a stirrer and heated to 90 ° C. Then, 649 g of rice husk ash was added to the container while continuing stirring, the container was covered, and mixing was continued for 6 hours while maintaining 90 ° C. After that, the aqueous solution was cooled to room temperature. A magnetic Buchner funnel (Nuchsche) with a diameter of 150 mm was attached to a 3 L suction filtration bottle, and a filter paper (1 μm mesh, standard 5C, Advantec Co., Ltd.) was placed in the funnel to prepare a suction filter, and the undissolved residue in the aqueous solution was removed using the suction filter to obtain an alkali silicate aqueous solution.

[0076] <Comparative Example 7> As a comparison with Example 5, an attempt was made to produce a high-concentration aqueous alkali silicate solution using the rice husk ash of Comparative Example 1 (apparent density: 300 g / L) according to dissolution method (2) in the same manner as in Example 5. However, the entire amount of the rice husk ash did not sink into the aqueous sodium hydroxide solution, and the load on the stirrer increased, so the dissolution operation was interrupted. As a result, dissolution according to dissolution method (2) could not be achieved with the rice husk ash of Comparative Example 1.

[0077] <Explanation and Discussion of Results I> Table 3 and Figure 3(a) show the relationship between the time from when the rice husk ash obtained in Example 1 was added and the SiO2 concentration when it was dissolved in an aqueous sodium hydroxide solution using dissolution method (1) and dissolution method (2). By using the rice husk ash (apparent density: 590 g / L) of Example 1, it was possible to produce an aqueous alkali silicate solution with a high concentration of SiO2 of 28 to 29 mass%. Since the thermal energy and time required to dissolve rice husk ash are almost the same for dissolution methods (1) and (2), this result shows that by using the rice husk ash of the present invention, more rice husk ash can be dissolved in an aqueous alkali solution with the same thermal energy.

[0078] [Table 3]

[0079] <Example 6> Using the rice husk ash (apparent density: 590 g / L) obtained in Example 1, an attempt was made to produce a high-concentration aqueous alkali silicate solution by pressurized dissolution according to the dissolution method (3) below. If pressurized dissolution can be applied, the production time for a high-concentration aqueous alkali silicate solution can be further shortened compared to Example 5. Note that, because the apparent density of unprocessed rice husk ash (raw rice husk ash A to C) is low, it was not even possible to charge the required amount of rice husk ash into the pressure vessel.

[0080] ●Dissolution method (3) Dissolution method (3) is a method for obtaining an alkali silicate aqueous solution of the same quality as that of dissolution method (2) in a shorter time than dissolution method (2). 450 g of sodium hydroxide aqueous solution adjusted to 17.0 mass% and 270 g of rice husk ash were put into a 1 L pressure vessel (autoclave) equipped with a stirring device while stirring, the vessel was covered, and dissolution was performed under a pressurized condition of 150 °C and 0.47 MPa. In the case of dissolution under pressurized conditions, since the vessel was sealed and sampling was not possible during the process, multiple experiments were performed with pressurized times set to 0.5, 1, 2, and 3 hours. After completion of dissolution, the pressure was released and the aqueous solution was cooled to room temperature. After cooling, a magnetic Buchner funnel (Nuchner) with a diameter of 150 mm was attached to a 3 L suction filtration bottle, and a filter paper (1 μm mesh, standard 5C, Advantec) was placed in the funnel to prepare a suction filter, and the undissolved residue in the aqueous solution was removed using the suction filter to obtain an alkali silicate aqueous solution.

[0081] Table 4 and Figure 3(b) show the relationship between the time from when the rice husk ash obtained in Example 1 was added and the SiO2 concentration when it was dissolved in an aqueous sodium hydroxide solution by dissolution method (2) and dissolution method (3). When the rice husk ash (apparent density: 590 g / L) of Example 1 was dissolved in an aqueous alkali solution under pressurized conditions, a high-concentration aqueous alkali silicate solution could be produced in a shorter time than by dissolution method (2). Specifically, the time required to produce a high-concentration aqueous alkali silicate solution with an SiO2 concentration of 28 to 29 mass% was 6 hours by dissolution method (2), whereas it was 2 hours by dissolution method (3).

[0082] [Table 4]

[0083] <Reference Example: Example of wet silica production> It was confirmed whether the aqueous alkali silicate solution produced using the rice husk ash of the present invention exhibits performance equivalent to that of a conventional aqueous sodium silicate solution derived from silica sand. Specifically, wet-process silica (hydrated silicic acid) for rubber tires was produced, and silica properties and rubber performance were evaluated. The production of wet-process silica, evaluation of silica properties, and evaluation of rubber performance were carried out in the same manner as in Example 1 of International Publication No. 2020 / 031523. When there is a difference in the evaluation equipment between the international publication and the respective descriptions in this specification, it means that the evaluation was carried out in accordance with the conditions described in the international publication using the evaluation equipment described in this specification.

[0084] The aqueous alkali silicate solution of the Reference Example was produced by preparing a high-concentration aqueous alkali silicate solution in the same manner as in Example 5, except that a 240 L stirred vessel was used and the amount of materials was increased by 60 times. This was then diluted with water to adjust the SiO2 concentration to 12.44 mass%, Na2O concentration to 3.74 mass%, K2O concentration to 0.41 mass%, and the SiO2 / (Na2O+K2O) molar ratio to 3.20.

[0085] The sodium silicate aqueous solution for comparison was produced by dissolving commercially available sodium silicate cullet produced from silica sand (medium molar grade, Na2O: 24.51 mass%, SiO2: 75.44 mass%, purity 99.5 mass% or more, manufactured by Tokuyama Corporation) in warm water and further diluting it with water to adjust the SiO2 concentration to 12.44 mass%, the Na2O concentration to 4.01 mass%, and the SiO2 / Na2O molar ratio to 3.20.

[0086] Then, each of these aqueous alkali silicate solutions was used to produce wet-process silica. The physical properties of the wet-process silica are shown in Table 5. In addition, each of these wet-process silicas was used to produce rubber compounds. The rubber performance evaluation is shown in Table 6.

[0087] [Table 5]

[0088] [Table 6]

[0089] The results in Table 5 show that the aqueous alkali silicate solution produced using the rice husk ash of the present invention can produce wet-process silica having the same physical properties as the aqueous sodium silicate solution derived from silica sand. Furthermore, the results in Table 6 show that the wet-process silica produced using the rice husk ash of the present invention as a raw material imparts to a rubber compound the same rubber physical properties as the wet-process silica produced using silica sand as a raw material.

[0090] As explained above, the rice husk ash of the present invention has a moderately high apparent density, and therefore the following effects can be expected. (1) A larger amount of rice husk ash can be put into the container compared to unprocessed rice husk ash, resulting in a highly concentrated slurry. (2) Compared with unprocessed rice husk ash, it has improved sinkability in an alkaline aqueous solution and absorbs less solvent, which reduces the time and energy required to produce a slurry and improves the productivity of the alkaline silicate aqueous solution. (3) Compared to unprocessed rice husk ash, it is less bulky, allowing a larger amount of rice husk ash to be transported in one shipment and a larger amount of rice husk ash to be stored in a limited space, thereby improving transportation and storage efficiency. (4) Compared to unprocessed rice husk ash, it generates less dust and is easier to handle when packaging and unpacking, improving the working environment when handling rice husk ash. (5) Although the rice husk ash of the present invention is a recycled waste material, the performance of an aqueous alkali silicate solution produced using the rice husk ash as a raw material is equivalent to that of an aqueous sodium silicate solution derived from silica sand. The rice husk ash of the present invention can be considered an environmentally friendly material that can be used as a substitute for silica sand. [Industrial Applicability]

[0091] In addition to producing aqueous alkali silicate solutions, the processed rice husk ash of the present invention can also be used as a silica source for other applications.

Claims

1. Rice husk ash for use in producing an alkali silicate aqueous solution has an apparent density in a dry state of 400 to 800 g / L, a volume average particle diameter D50 measured by a laser diffraction method of 5.0 to 200 μm, and a moisture content of 30 mass% or less.

2. The rice husk ash according to claim 1, wherein the carbon content is 0.1 to 8.0% by mass and the silica content is 85 to 95% by mass.

3. The rice husk ash according to claim 1 or 2, wherein the volume average particle diameter D50 measured by a laser diffraction method is 10 to 150 μm.

4. Consolidating or pulverizing raw rice husk ash having an apparent density of 350 g / L or less in a dry state so that the apparent density in a dry state is 400 to 800 g / L and the volume average particle diameter D50 measured by a laser diffraction method is 5.0 to 200 μm; A method for producing rice husk ash, optionally including adjusting the moisture content of the raw rice husk ash to a range of 30 mass% or less.

5. The method according to claim 4, wherein the compaction or pulverization is carried out so that the volume average particle diameter D50 is 10 to 150 μm.

6. The compaction or crushing was carried out using a roller compactor. 3 The method according to claim 4 or 5, wherein the method is carried out at a linear pressure of 100 N / cm or more.

7. Rice husk ash having an apparent density in a dry state of 400 to 800 g / L and a moisture content of 5.0% by mass or more and 30% by mass or less.

8. The rice husk ash according to claim 7, which is used for producing an aqueous alkali silicate solution.

9. Compressing or pulverizing raw rice husk ash having an apparent density of 350 g / L or less in a dry state to an apparent density of 400 to 800 g / L in a dry state; A method for producing rice husk ash, comprising adjusting the moisture content of raw rice husk ash to a range of 5.0 mass% or more and 30 mass% or less.

10. The method according to claim 4 or 9, wherein the rice husk ash is used for producing an aqueous alkali silicate solution.

Images