Production method for porous body and porous body

Abstract

To provide a production method for a further improved porous body and the porous body.SOLUTION: A production method for a porous body comprises a first step of crushing a sea urchin shell, and a second step of firing the crushed sea urchin shell crushed in the first step at a temperature of 650°C or higher and 720°C or lower, in an atmosphere with a carbon dioxide concentration of 40% or higher and an oxygen concentration of 20% or higher.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] The present invention relates to a method for producing a porous body and a porous body.

Background Art

[0002] Conventionally, a method has been proposed in which sea urchin shells are fired to obtain a pure white and fine powder mainly composed of calcium carbonate (see, for example, Patent Document 1).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] Here, it is known that calcium carbonate has an adsorption effect and a deodorizing effect on volatile organic compounds (VOCs: Volatile Organic Compounds). In particular, coral skeletons, sea urchin shells, etc. are used as raw materials for calcium carbonate derived from natural products, and it is known that even when pulverized into a powder, a fine porous structure is maintained. These have a larger specific surface area compared to powders of calcium carbonate that do not have a porous structure, and a higher VOC adsorption effect and deodorizing effect can be expected.

[0005] However, the method for producing calcium carbonate described in Patent Document 1 includes a step of generating calcium oxide by secondary firing, and there is room for improvement in the production method. Calcium carbonate is considered to undergo thermal decomposition when heated to a temperature exceeding 550 degrees in air. Therefore, in the method for producing calcium carbonate described in Patent Document 1, due to the progress of thermal decomposition, a large amount of calcium oxide may be contained as an impurity in the final product.

[0006] The present invention has been made to solve such conventional problems, and an object thereof is to provide an improved method for producing a porous body of calcium carbonate and a porous body.

Means for Solving the Problems

[0007] In order to solve such problems, a method for producing a porous body according to the present disclosure includes a first step of pulverizing a porous body having calcium carbonate as a main component and having an organic substance in pores, and pulverizing the pulverized product in the first step at a temperature of 650 degrees or more and 720 degrees or less in an atmosphere having a carbon dioxide concentration of 40% or more and an oxygen concentration of 20% or more.

[0008] The porous body according to the present disclosure is a porous body in which pores surrounded by walls having a thickness of 3 μm or more and 7 μm or less in an observation image at 200 times are present 50 or more and 90 or less in a 100 μm square, and the average pore diameter of these pores is 2.0 μm or more and 31.3 μm or less. There are two or more cracks having a length of 30 nm or more and 170 nm or less in a 5 μm square in an observation image at 5000 times, and the porous body has 90% by mass or more of calcium carbonate.

Effects of the Invention

[0009] According to the present invention, it is possible to provide an improved method for producing a porous body of calcium carbonate and a porous body.

Brief Description of the Drawings

[0010]

Figure 1

Figure 2

Figure 3

Figure 4

Best Mode for Carrying Out the Invention

[0011] Hereinafter, the present invention will be described in accordance with preferred embodiments. Note that the present invention is not limited to the embodiments shown below, and can be appropriately changed without departing from the gist of the present invention. Also, in the embodiments shown below, there are some parts where the illustration and description of some configurations are omitted. However, it goes without saying that well-known or well-understood technologies are appropriately applied within the range that does not conflict with the content described below regarding the details of the omitted technologies.

[0012] FIG. 1 is a scanning electron microscope (SEM) photograph of a porous body manufactured by the method for manufacturing a porous body according to the present embodiment. Note that in FIG. 1, since there are a large number of reference numerals 2 and CR, only a part of them will be indicated by reference numerals. As the electron microscope, JSM-6010 manufactured by JEOL Ltd. was used.

[0013] As shown in FIG. 1, the porous body 1 has a skeleton 10 that forms a large number of pores 2. The skeleton 10 contains calcium carbonate as a main component.

[0014] As a result of image analysis of an arbitrary portion of the porous body 1 from an SEM photograph (microscope magnification: 200 times, 100 μm square), 50 or more and 90 or less pores 2 surrounded by a wall (the wall constituting the skeleton 10) having a thickness of about 5 μm (specifically, 3 μm or more and 7 μm or less) were measured. Note that the average pore diameter of the pores 2 was calculated to be 2.0 μm or more and 31.3 μm or less from the measurement value by the mercury intrusion method.

[0015] In the present embodiment, the porous body 1 is manufactured from a sea urchin shell. The type of sea urchin used as a raw material is not particularly limited. For example, Heliocidaris crassispina may be used.

[0016] The sea urchin shell contains various organic substances inside a large number of pores 2. Here, as an example of the organic substance, proteins and the like can be mentioned. The method for manufacturing the porous body 1 according to the present embodiment includes a firing step (an example of the second step) for removing the organic substance from the large number of pores 2.

[0017] Furthermore, as shown in FIG. 1, the skeleton 10 has a large number of cracks CR (including micropores smaller than the pores 2). The porous body 1 according to the present embodiment has had the organic substance removed from the pores 2 to increase the surface area, and the surface area has also been increased due to the presence of the cracks CR. As a result of image analysis from an SEM photograph (microscope magnification 5000 times, 5 μm square), about 20 cracks CR were measured. The length of the cracks CR was 30 nm or more and 170 nm or less.

[0018] Note that although the porous body 1 according to the present embodiment is assumed to be manufactured from a sea urchin shell, it may be manufactured from a material including a porous structure skeleton and an organic substance existing inside the skeleton, similar to the sea urchin shell.

[0019] Hereinafter, the exemplary embodiments of the present invention will be further described with examples, but the present invention is not limited to the following examples.

[0020] FIG. 2 is a process diagram showing the method for manufacturing the porous body 1 according to the present embodiment. The following manufacturing method will explain a method for manufacturing the porous body 1 using a sea urchin shell. The porous body 1 according to the present embodiment is manufactured through a first step and a second step.

[0021] The first step is a step of pulverizing the sea urchin shell. As the raw material sea urchin shell, purple sea urchins produced in Yamaguchi Prefecture were used. First, after coarsely pulverizing with a hammer mill (screen diameter 5 mm), it was finely pulverized with a pin mill, and the particle size of the powder obtained through the two pulverization steps was generally 20 μm or more and 100 μm or less.

[0022] The first step is carried out to enhance the efficiency of removing organic substances in the subsequent second step, and it is only necessary that the sea urchin shell is moderately pulverized. Preferably, it is 100 μm or less, more preferably 50 μm or more and 100 μm or less.

[0023] The second step is a step of firing the pulverized sea urchin shell at a temperature of 650 degrees or more and 720 degrees or less in an atmosphere where the carbon dioxide concentration is 40% or more and the oxygen concentration is 20% or more. A batch-type rotary kiln was used to fire 2800 g of the pulverized sea urchin shell. A sample with a firing time of 4 hours and 20 minutes was prepared. The weight of the sample after firing was 2386 g. Figure 1 is a SEM image of the porous body 1 with a firing time of 4 hours and 20 minutes.

[0024] Generally, in order to suppress the generation of calcium oxide by the thermal decomposition reaction, it is assumed that primary combustion is carried out at a temperature of less than 550 degrees. However, since there are organic substances inside the original porous structure of the sea urchin shell, even if it is burned at a temperature of 550 degrees or less, the organic substances may not be removed, or the organic substances may not be removed promptly, requiring a large amount of manufacturing time.

[0025] Here, the inventors of the present invention have found that in the second step, at a temperature of 650 degrees or more and with an oxygen concentration of 20% or more, it is possible to prevent the removal time of the organic substances from becoming extremely long and the manufacturing from becoming extremely difficult. Furthermore, the inventors of the present invention have found that at a temperature of 720 degrees or less and with a carbon dioxide concentration of 40% or more, the generation of calcium oxide by the thermal decomposition of calcium carbonate is suppressed. In addition, the inventors of the present invention have also found that at a temperature of 720 degrees or less, the crack CR of the skeleton 10 can be made difficult to be filled by sintering or the like.

[0026] In the manufacturing method of the porous body 1 as described above, the generation of calcium oxide by the thermal decomposition of calcium carbonate can be suppressed, the organic substances can be removed, and many cracks CR of the skeleton 10 can also be left. Therefore, it is possible to obtain a porous body 1 mainly composed of calcium carbonate that can more effectively exhibit the VOC adsorption effect and the deodorizing effect.

[0027] In the second step, the firing time is determined from the relationship between the size of the furnace used, the amount of sea urchin shells to be fired, and the firing temperature.

[0028] Figure 3 is a chart showing examples and comparative examples of the method for manufacturing the porous body 1. As shown in Figure 3, in the examples and comparative examples, nine types of gas species conditions were set as A to I, and eight types of temperature conditions were set as a to h. Regarding the temperature condition a, actually, experiments were conducted at two temperatures of 200 degrees and 550 degrees, but since the results were the same, they are collectively described in the chart.

[0029] As shown in Figure 3, for the gas species condition A, it is conditioned to be fired in an atmosphere where the carbon dioxide concentration is 0%, the oxygen concentration is 20%, and the concentration of other gases is 80%. For the gas species condition B, it is conditioned to be fired in an atmosphere where the carbon dioxide concentration is 0% and the oxygen concentration is 100%. For the gas species condition C, it is conditioned to be fired in an atmosphere where the carbon dioxide concentration is 20% and the oxygen concentration is 80%. For the gas species condition D, it is conditioned to be fired in an atmosphere where the carbon dioxide concentration is 40% and the oxygen concentration is 60%. For the gas species condition E, it is conditioned to be fired in an atmosphere where the carbon dioxide concentration is 50% and the oxygen concentration is 50%. The other gas is not particularly limited as long as it is an inert gas, and for example, nitrogen is adopted.

[0030] For the gas species condition F, it is conditioned to be fired in an atmosphere where the carbon dioxide concentration is 50%, the oxygen concentration is 20%, and the concentration of other gases is 30%. For the gas species condition G, it is conditioned to be fired in an atmosphere where the carbon dioxide concentration is 60% and the oxygen concentration is 40%. For the gas species condition H, it is conditioned to be fired in an atmosphere where the carbon dioxide concentration is 80% and the oxygen concentration is 20%. For the gas species condition I, it is conditioned to be fired in an atmosphere where the carbon dioxide concentration is 100% and the oxygen concentration is 0%.

[0031] In addition, temperature condition a is conditioned that the firing temperature is 200 degrees or more and 550 degrees or less. Temperature condition b is conditioned that the firing temperature is 640 degrees. Temperature condition c is conditioned that the firing temperature is 650 degrees. Temperature condition d is conditioned that the firing temperature is 660 degrees. Temperature condition e is conditioned that the firing temperature is 680 degrees. Temperature condition f is conditioned that the firing temperature is 700 degrees. Temperature condition g is conditioned that the firing temperature is 720 degrees. Temperature condition h is conditioned that the firing temperature is 740 degrees.

[0032] First, for Comparative Examples 1 to 3 (gas species conditions A to C) which are temperature condition c, Comparative Examples 4 to 6 (gas species conditions A to C) which are temperature condition d, and Comparative Examples 7 to 9 (gas species conditions A to C) which are temperature condition e, all the results were "×" 1 ". Also, for Comparative Examples 10 to 12 (gas species conditions A to C) which are temperature condition f, and Comparative Examples 13 to 15 (gas species conditions A to C) which are temperature condition g, all the results were also "×" 1 ". "×" 1 indicates that during firing for removing organic substances, a phase transition occurred to calcium oxide due to thermal decomposition of calcium carbonate.

[0033] Here, when 10% or more (10 mass% or more) of calcium carbonate (100 mass%) has undergone a phase transition to calcium oxide, it is evaluated as "×" 1 ". Regarding the evaluation of whether a phase transition to calcium oxide occurred, it was performed based on the peak intensity during XRD (X-Ray Diffraction) analysis.

[0034] In addition, for Comparative Examples 16 to 24 (gas species conditions A to I) which are temperature condition a, Comparative Examples 25 to 30 (gas species conditions D to I) which are temperature condition b, and Comparative Examples 31 to 35 (gas species condition I) which are temperature conditions c to g, all the results were "×" 2 ". "×" 2" indicates that the organic substances could not be removed. That is, it indicates that the organic substances could not be removed even if it took several days or more. The presence or absence of residual organic substances was evaluated by colorimetric analysis using the COD method. When it was 5 ppm or less, it was evaluated that the organic substances were removed, and when it exceeded 5 ppm, it was evaluated that the organic substances could not be removed.

[0035] Also, for Comparative Examples 36 to 40 (gas species conditions D to H) under temperature condition h, all the results were "×" 3 ". "×" 3 " indicates that the nanostructure was lost, such as sintering occurring and the crack CR in the skeleton 10 being filled.

[0036] Regarding the evaluation of whether the crack CR was filled or not, the number of cracks CR before firing that could be confirmed within a range of 5 μm square by a scanning electron microscope (SEM) was observed, and as a result of observing the number of cracks CR again after firing, when the number of cracks CR with a length of 30 nm or more and 170 nm or less was less than 2, it was evaluated that the crack CR was filled, and when it was 2 or more, it was evaluated that the crack CR was not filled.

[0037] Also, for Comparative Examples 41 to 43 (gas species conditions A to C) under temperature condition b, all the results were "×" 12 ". "×" 12 " means that it is the result of both "×" 1 " and "×" 2 ". That is, it indicates that calcium carbonate underwent a phase transition to calcium oxide and the organic substances could not be removed.

[0038] Also, for Comparative Examples 44 to 46 (gas species conditions A to C) under temperature condition h, all the results were "×" 13 ". "×" 13 " means that it is the result of both "×" 1 " and "×" 3 ". That is, it indicates that calcium carbonate underwent a phase transition to calcium oxide and the nanostructure was lost.

[0039] Comparative Example 47 (gas species condition I) under temperature condition h resulted in "×" 23 ". "×" 23 " means that the results were both "×" 2 " and "×" 3 ". That is, it indicates that the organic matter could not be removed and the nanostructure was lost.

[0040] In contrast, for Examples 1 to 5 (gas species conditions D to H) under temperature condition c, Examples 6 to 10 (gas species conditions D to H) under temperature condition d, and Examples 11 to 15 (gas species conditions D to H) under temperature condition e, all evaluations were "〇". That is, the events indicated by "×" 1 ", "×" 2 ", and "×" 3 " did not occur. Similarly, for Examples 16 to 20 (gas species conditions D to H) under temperature condition f and Examples 21 to 25 (gas species conditions D to H) under temperature condition g, all evaluations were "〇".

[0041] From the above examples and comparative examples, it was found that even when firing was carried out at a temperature of 640 degrees or lower, the organic matter could not be removed and the production became difficult. Furthermore, it was found that even when firing was carried out in an atmosphere with an oxygen concentration of 0%, the combustibility assisted by oxygen could not be obtained and the organic matter could not be removed.

[0042] Also, when the firing temperature was 740 degrees, it was considered that the nanostructure was lost, such as the cracks CR being filled by sintering, which led to a decrease in the specific surface area of the porous body 1. In addition, it was found that when the carbon dioxide concentration was 20% or less, calcium carbonate underwent a phase transition to calcium oxide.

[0043] On the other hand, it was found that when the firing temperature was 650 degrees or higher and 720 degrees or lower, and the firing was carried out with a carbon dioxide concentration of 40% or higher and an oxygen concentration of 20% or higher, the organic matter could be removed. Also, it was found that the generation of calcium oxide could be extremely suppressed and calcium carbonate with a large specific surface area could be produced.

[0044] Figure 4 is a graph showing the details of the XRD analysis. The data indicated by reference numeral 4a are the standard data of calcium oxide, and the data indicated by reference numeral 4b are the standard data of calcium carbonate. The data indicated by reference numeral 4c show the XRD analysis results of Example 2 (temperature condition c and gas species condition E).

[0045] As shown by reference numeral 4a, in the standard data of calcium oxide, there is a maximum peak around 37 deg, and there are also peaks around 32 deg and 54 deg. In contrast, as shown by reference numeral 4b, in the standard data of calcium carbonate, there is a maximum peak around 29.5 deg, and there are also small peaks around 36 deg, 39.5 deg, 43 deg, 47.5 deg, and 48.5 deg.

[0046] On the other hand, the XRD analysis results of Example 2 indicated by reference numeral 4c are substantially in agreement with the data indicated by reference numeral 4b. That is, the XRD analysis results of Example 2 have a maximum peak around 29.5 deg, and also have small peaks around 36 deg, 39.5 deg, 43 deg, 47.5 deg, and 48.5 deg. Therefore, it can be said that in Example 2, the generation of calcium oxide due to the thermal decomposition of calcium carbonate could be suppressed, and the compound obtained in Example 2 is 90% by mass or more calcium carbonate.

[0047] It should be noted that in Example 2 shown in Figure 4, the carbon dioxide concentration is 50%, but it goes without saying that when the carbon dioxide concentration exceeds 50%, the generation of calcium oxide due to thermal decomposition can be more suppressed.

[0048] Thus, according to the method for manufacturing the porous body 1 according to this embodiment, the sea urchin shell is crushed and fired at a temperature of 650°C or higher and 720°C or lower in an atmosphere where the carbon dioxide concentration is 40% or higher and the oxygen concentration is 20% or higher. Here, generally, when firing at a temperature of about 650°C or higher, the organic matter in the pores 2 can be removed earlier, but carbon dioxide is released from calcium carbonate to become calcium oxide. However, in an environment where the carbon dioxide concentration is 40% or higher, it becomes difficult for carbon dioxide to be released from calcium oxide due to the surrounding carbon dioxide, and the retention rate of calcium carbonate is increased. In addition, since the oxygen concentration is 20% or higher, the possibility that the oxygen is too little and the organic matter is difficult to burn and cannot be removed can also be reduced. Furthermore, when firing at a temperature exceeding 720°C (for example, 740°C), it is considered that the specific surface area is reduced due to the sintering of the skeleton 10. However, by firing at a temperature of 720°C or lower, the occurrence of such problems can also be suppressed. Therefore, it is possible to manufacture a more improved porous body 1 of calcium carbonate.

[0049] Moreover, according to the porous body 1 according to this embodiment, it is possible to provide a porous body 1 in which the organic matter is removed while maintaining 90% by mass or more of calcium carbonate, and while maintaining the nano-structure with cracks CR remaining, the surface area is expanded.

[0050] As described above, the present invention has been described based on the embodiments. However, the present invention is not limited to the above embodiments, and modifications may be made without departing from the spirit of the present invention, and known or well-known techniques may be combined if possible.

[0051] For example, in the above embodiment, a method for manufacturing the porous body 1 from a sea urchin shell has been described. However, it is not particularly limited to a sea urchin shell, and it may be applied to the case of manufacturing a porous body of calcium carbonate from other natural substances having a porous structure containing calcium carbonate and containing organic matter in the porous structure (for example, coral skeletons, etc.) similar to the sea urchin shell.

Explanation of Reference Numerals

[0052] 1: Porous body 2: Hole 10: Framework CR: Crack

Claims

1. A first step of pulverizing a porous body containing calcium carbonate as a main component and having organic matter present in the pores; A second step of firing the pulverized material obtained in the first step at a temperature of 650° C. or higher and 720° C. or lower in an atmosphere having a carbon dioxide concentration of 40% or higher and an oxygen concentration of 20% or higher; A method for producing a porous body comprising the steps of:

2. The manufacturing method according to claim 1, wherein the porous body contains 90% by mass or more of calcium carbonate. A method for producing a porous body.

3. A porous body having 50 to 90 pores surrounded by walls having a thickness of 3 μm to 7 μm in an image observed at 200 times magnification per 100 μm square, and an average pore size of these pores being 2.0 μm to 31.3 μm, In an image observed at 5,000 times, two or more cracks having a length of 30 nm to 170 nm are present in an area of ​​5 μm square, and the material contains 90 mass % or more of calcium carbonate. Porous body.

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