Method for producing porous body, and porous body

Abstract

Provided are a method for producing a porous body and a porous body, which are further improved.　This method for producing a porous body (1) comprises: a first step for pulverizing a sea urchin shell; and a second step for firing a pulverized product, which has been produced by the pulverization in the first step, at a temperature of 650°-720° in an atmosphere having a carbon dioxide concentration of 40% or more and an oxygen concentration of 20% or more.

Description

Method for producing porous body and porous body

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

[0002] Conventionally, a method has been proposed in which sea urchin shells are calcined to obtain a pure white, fine powder containing calcium carbonate as a main component (see, for example, Patent Document 1).

[0003] JP 2009-126777 A

[0004] Here, calcium carbonate is known to have an adsorption effect on volatile organic compounds (VOCs) and a deodorizing effect. In particular, coral skeletons, sea urchin shells, etc. are used as raw materials for calcium carbonate derived from natural sources, and are known to maintain a fine porous structure even when crushed into powder. These have a larger specific surface area than calcium carbonate powder that does not have a porous structure, and are expected to have a higher VOC adsorption effect and deodorizing effect.

[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. It is believed that calcium carbonate undergoes thermal decomposition when heated to a temperature exceeding 550°C in air. Therefore, in the method for producing calcium carbonate described in Patent Document 1, there is a possibility that the thermal decomposition will cause a large amount of calcium oxide to be contained as an impurity in the final product.

[0006] The present invention has been made to solve the above-mentioned problems in the prior art, and an object of the present invention is to provide an improved method for producing a porous calcium carbonate body and the porous body.

[0007] In order to solve this problem, the method for producing a porous body according to the present disclosure includes a first step of pulverizing a porous body containing calcium carbonate as a main component and having organic matter present in the pores, and 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 with a carbon dioxide concentration of 40% or higher and an oxygen concentration of 20% or higher.

[0008] Furthermore, the porous body according to the present disclosure is a porous body in which, in an image observed at 200x, there are 50 to 90 pores surrounded by walls having a thickness of 3 to 7 μm per 100 μm square, and the average pore size of these pores is 2.0 to 31.3 μm. In an image observed at 5000x, there are two or more cracks having a length of 30 to 170 nm per 5 μm square, and the porous body contains 90% by mass or more of calcium carbonate.

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

[0010] Fig. 1 is a scanning electron microscope (SEM) photograph of a porous body manufactured by the porous body manufacturing method according to this embodiment. Fig. 2 is a process diagram showing the porous body manufacturing method according to this embodiment. Fig. 3 is a table showing examples and comparative examples showing the porous body manufacturing method. Fig. 4 is a graph showing details of XRD analysis.

[0011] The present invention will be described below in accordance with preferred embodiments. Note that the present invention is not limited to the embodiments shown below and can be modified as appropriate without departing from the spirit of the present invention. In addition, in the embodiments shown below, some components are omitted from illustration and description, but it goes without saying that publicly known or well-known technologies are applied as appropriate to the details of the omitted technologies within the scope of the content described below.

[0012] Figure 1 is a scanning electron microscope (SEM) photograph of a porous body manufactured by the porous body manufacturing method according to this embodiment. Since there are many elements designated by the reference numerals 2 and CR in Figure 1, only some of them are indicated by the reference numerals. The electron microscope used was a JSM-6010 manufactured by JEOL Ltd.

[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] Image analysis of an arbitrary location of the porous body 1 from an SEM photograph (microscope magnification: 200x, 100 μm square) revealed that 50 to 90 pores 2 surrounded by walls (walls constituting the skeleton 10) with a thickness of about 5 μm (specifically, 3 μm to 7 μm) were counted. The average pore diameter of the pores 2 was calculated from the values ​​measured by mercury intrusion porosimetry to be 2.0 μm to 31.3 μm.

[0015] In this embodiment, the porous body 1 is made from sea urchin shells. The type of sea urchin used as the raw material is not particularly limited, but for example, purple sea urchin (Heliocidaris crassispina) or the like may be used.

[0016] The sea urchin shell contains various organic substances inside the numerous pores 2. Here, an example of the organic substances is protein. The manufacturing method of the porous body 1 according to this embodiment includes a firing step (an example of the second step) for removing the organic substances from the numerous pores 2.

[0017] Furthermore, as shown in FIG. 1 , the skeleton 10 has numerous cracks CR (including micropores smaller than the pores 2). The porous body 1 according to this embodiment has a large surface area due to the removal of organic matter from the pores 2, and the presence of the cracks CR also increases the surface area. Image analysis of an SEM photograph (microscope magnification 5000x, 5 μm square) resulted in the measurement of approximately 20 cracks CR. The length of the cracks CR was 30 nm or more and 170 nm or less.

[0018] The porous body 1 according to this embodiment is assumed to be manufactured from sea urchin shells, but may also be manufactured from a material that contains a porous skeleton and organic matter present inside the skeleton, similar to sea urchin shells.

[0019] The following examples further illustrate exemplary embodiments of the present invention, but the present invention is not limited to these examples.

[0020] 2 is a process diagram showing a method for producing the porous body 1 according to this embodiment. In the following production method, a method for producing the porous body 1 using sea urchin shells will be described. The porous body 1 according to this embodiment is produced through a first step and a second step.

[0021] The first step is to crush sea urchin shells. The raw material, sea urchin shells, were purple sea urchins from Yamaguchi Prefecture. First, the shells were coarsely crushed using a hammer mill (screen diameter 5 mm) and then finely crushed using a pin mill. The particle size of the powder obtained through these two crushing steps was generally between 20 μm and 100 μm.

[0022] The first step is performed to increase the efficiency of organic matter removal in the subsequent second step, and it is sufficient that the sea urchin shells are crushed to an appropriate size, preferably 100 μm or less, and more preferably 50 μm or more and 100 μm or less.

[0023] The second step is to fire the crushed sea urchin shells at a temperature of 650°C to 720°C in an atmosphere with a carbon dioxide concentration of 40% or more and an oxygen concentration of 20% or more. 2800 g of crushed sea urchin shells were fired using a batch rotary kiln. A sample was produced with a firing time of 4 hours and 20 minutes. The weight of the sample after firing was 2386 g. Figure 1 is an SEM image of porous body 1 fired for 4 hours and 20 minutes.

[0024] Generally, to suppress the generation of calcium oxide through pyrolysis, primary combustion is expected to be carried out at a temperature below 550°C. However, because sea urchin shells have organic matter present inside their inherent porous structure, there is a possibility that the organic matter may not be removed even if they are burned at a temperature below 550°C, or that the organic matter may not be removed quickly enough, resulting in a significant manufacturing time.

[0025] Here, the present inventors have found that in the second step, if the temperature is 650°C or higher and the oxygen concentration is 20% or higher, the organic matter removal time is not extremely long, preventing significant difficulties in manufacturing. Furthermore, the present inventors have found that if the temperature is 720°C or lower and the carbon dioxide concentration is 40% or higher, the generation of calcium oxide due to the thermal decomposition of calcium carbonate is suppressed. In addition, the present inventors have found that if the temperature is 720°C or lower, the cracks CR in the skeleton 10 are less likely to be filled by sintering or the like.

[0026] The method for producing the porous body 1 as described above suppresses the generation of calcium oxide due to the thermal decomposition of calcium carbonate, and also removes organic matter, leaving many cracks CR in the skeleton 10. Therefore, it is possible to obtain a porous body 1 containing calcium carbonate as its main component, which is more effective at adsorbing VOCs and deodorizing.

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

[0028] Fig. 3 is a table showing examples and comparative examples illustrating the manufacturing method of the porous body 1. As shown in Fig. 3, in the examples and comparative examples, nine types of gas conditions (A to I) were used, and eight types of temperature conditions (a to h) were used. Note that for temperature condition (a), experiments were actually conducted at two temperatures, 200°C and 550°C, but the results were the same, so they are listed together in the table.

[0029] As shown in Figure 3, gas type condition A stipulates that firing is performed in an atmosphere with a carbon dioxide concentration of 0%, an oxygen concentration of 20%, and an other gas concentration of 80%. Gas type condition B stipulates that firing is performed in an atmosphere with a carbon dioxide concentration of 0% and an oxygen concentration of 100%. Gas type condition C stipulates that firing is performed in an atmosphere with a carbon dioxide concentration of 20% and an oxygen concentration of 80%. Gas type condition D stipulates that firing is performed in an atmosphere with a carbon dioxide concentration of 40% and an oxygen concentration of 60%. Gas type condition E stipulates that firing is performed in an atmosphere with a carbon dioxide concentration of 50% and an oxygen concentration of 50%. The other gas is not particularly limited as long as it is an inert gas, and nitrogen, for example, is used.

[0030] Gas type condition F requires firing in an atmosphere with a carbon dioxide concentration of 50%, an oxygen concentration of 20%, and other gas concentrations of 30%. Gas type condition G requires firing in an atmosphere with a carbon dioxide concentration of 60% and an oxygen concentration of 40%. Gas type condition H requires firing in an atmosphere with a carbon dioxide concentration of 80% and an oxygen concentration of 20%. Gas type condition I requires firing in an atmosphere with a carbon dioxide concentration of 100% and an oxygen concentration of 0%.

[0031] Furthermore, temperature condition a requires that the baking temperature be between 200°C and 550°C. Temperature condition b requires that the baking temperature be 640°C. Temperature condition c requires that the baking temperature be 650°C. Temperature condition d requires that the baking temperature be 660°C. Temperature condition e requires that the baking temperature be 680°C. Temperature condition f requires that the baking temperature be 700°C. Temperature condition g requires that the baking temperature be 720°C. Temperature condition h requires that the baking temperature be 740°C.

[0032] First, for Comparative Examples 1 to 3 (gas type conditions A to C) under temperature condition c, Comparative Examples 4 to 6 (gas type conditions A to C) under temperature condition d, and Comparative Examples 7 to 9 (gas type conditions A to C) under temperature condition e, the results were all "x". １ Furthermore, the results for Comparative Examples 10 to 12 (gas type conditions A to C) under temperature condition f and Comparative Examples 13 to 15 (gas type conditions A to C) under temperature condition g were all "x". １ " " １ " indicates that the calcium carbonate was thermally decomposed and transformed into calcium oxide during firing to remove organic matter.

[0033] Here, when 10% or more (10% or more by mass) of calcium carbonate (100% by mass) has undergone a phase transition to calcium oxide, the result is "× １The evaluation of whether or not a phase transition to calcium oxide occurred was based on the peak intensity in XRD (X-ray diffraction) analysis.

[0034] Furthermore, for Comparative Examples 16 to 24 (gas type conditions A to I) under temperature condition a, Comparative Examples 25 to 30 (gas type conditions D to I) under temperature condition b, and Comparative Examples 31 to 35 (gas type condition I) under temperature conditions c to g, the results were all "x". ２ " " ２ " indicates that the organic matter could not be removed. In other words, it indicates that the organic matter could not be removed even if several days or more were required. The presence or absence of remaining organic matter was evaluated by colorimetric analysis using the COD method, and when the concentration was 5 ppm or less, it was evaluated that the organic matter had been removed, and when the concentration exceeded 5 ppm, it was evaluated that the organic matter could not be removed.

[0035] In addition, for Comparative Examples 36 to 40 (gas type conditions D to H) under temperature condition h, all the results were "x". ３ " " ３ " indicates that sintering has occurred, filling up cracks CR in the skeleton 10, and the nanostructure has been lost.

[0036] To evaluate whether the cracks CR were filled, the number of cracks CR that could be confirmed within a 5 μm square area before firing was observed using a scanning electron microscope (SEM), and the number of cracks CR was observed again after firing.If there were fewer than two cracks CR with a length of 30 nm to 170 nm, the cracks CR were evaluated as filled, and if there were two or more cracks CR, the cracks CR were evaluated as not filled.

[0037] In addition, for Comparative Examples 41 to 43 (gas type conditions A to C) under temperature condition b, all the results were "x". １２ " " １２ " is "× １ " and "× ２ This shows that both the calcium carbonate phase transitioned to calcium oxide and the organic matter could not be removed.

[0038] In addition, for Comparative Examples 44 to 46 (gas type conditions A to C) under temperature condition h, all the results were "x". １３ " " １３ " is "× １ " and "× ３ This shows that both the calcium carbonate and the nanostructure were lost as the calcium carbonate transformed into calcium oxide.

[0039] In Comparative Example 47 (gas type condition I) under temperature condition h, the result was "x". ２３ " " ２３ " is "× ２ " and "× ３ This shows that both the organic matter and the nanostructure were lost.

[0040] In contrast, Examples 1 to 5 (gas type conditions D to H) under temperature condition c, Examples 6 to 10 (gas type conditions D to H) under temperature condition d, and Examples 11 to 15 (gas type conditions D to H) under temperature condition e were all evaluated as "Good." １ " " × ２ " " × ３ " did not occur. Similarly, Examples 16 to 20 (gas type conditions D to H) under temperature condition f and Examples 21 to 25 (gas type conditions D to H) under temperature condition g were all evaluated as "Good."

[0041] From the above examples and comparative examples, it was found that even if firing was performed at a temperature of 640° C. or less, organic matter could not be removed, making production difficult. Furthermore, it was found that even if firing was performed in an atmosphere with an oxygen concentration of 0%, oxygen could not be used to promote combustion, and organic matter could not be removed.

[0042] Furthermore, it was found that when the firing temperature was 740°C, the cracks CR were filled by sintering, and the nanostructure was lost, 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 organic matter can be removed by firing at a temperature of 650°C or higher and 720°C or lower, with a carbon dioxide concentration of 40% or higher and an oxygen concentration of 20% or higher. It was also found that calcium oxide production can be extremely suppressed and calcium carbonate with a large specific surface area can be produced.

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

[0045] As shown by reference symbol 4a, the standard data for calcium oxide has a maximum peak at around 37 degrees, with peaks also at around 32 degrees and 54 degrees. In contrast, as shown by reference symbol 4b, the standard data for calcium carbonate has a maximum peak at around 29.5 degrees, with smaller peaks also at around 36 degrees, 39.5 degrees, 43 degrees, 47.5 degrees, and 48.5 degrees.

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

[0047] In Example 2 shown in FIG. 4, the carbon dioxide concentration is 50%, but it goes without saying that if the carbon dioxide concentration exceeds 50%, the generation of calcium oxide due to thermal decomposition can be further suppressed.

[0048] According to the method for producing the porous body 1 of this embodiment, sea urchin shells are crushed and fired at a temperature of 650°C to 720°C in an atmosphere with a carbon dioxide concentration of 40% or more and an oxygen concentration of 20% or more. While firing at temperatures above 650°C generally removes organic matter from the pores 2 more quickly, carbon dioxide desorbs from the calcium carbonate, resulting in calcium oxide. However, in an environment with a carbon dioxide concentration of 40% or more, the ambient carbon dioxide hinders carbon dioxide desorption from the calcium oxide, thereby increasing the calcium carbonate retention rate. Furthermore, since the oxygen concentration is 20% or more, the presence of too little oxygen reduces the likelihood of the organic matter becoming difficult to burn and becoming unremovable. Furthermore, firing at temperatures above 720°C (e.g., 740°C) is thought to reduce the specific surface area due to sintering of the skeleton 10. However, firing at temperatures below 720°C reduces this problem. Therefore, a more improved calcium carbonate porous body 1 can be produced.

[0049] Furthermore, according to the porous body 1 of this embodiment, it is possible to provide a porous body 1 in which the organic matter has been removed while maintaining 90 mass% or more of calcium carbonate, and in which the surface area has been expanded while maintaining the nanostructure by leaving cracks CR.

[0050] The present invention has been described above based on the embodiments, but the present invention is not limited to the above embodiments, and modifications may be made within the scope of the spirit of the present invention, and if possible, publicly known or well-known technologies may be combined.

[0051] For example, in the above embodiment, a method for producing the porous body 1 from sea urchin shells has been described. However, the present invention is not limited to sea urchin shells, and may be applied to the production of a porous body of calcium carbonate from other natural materials (e.g., coral skeletons) that have a porous structure containing calcium carbonate and contain organic matter in the porous structure, similar to sea urchin shells.

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

Claims

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

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

3. A porous body in which, in an image observed at 200x, there are 50 to 90 pores surrounded by walls with a thickness of 3 to 7 μm per 100 μm square, and the average pore size of these pores is 2.0 to 31.3 μm, and in an image observed at 5,000x, there are two or more cracks with a length of 30 to 170 nm per 5 μm square, and the porous body contains 90 mass% or more calcium carbonate.

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