JP2011092808A - Adsorbent and method for manufacturing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an adsorbent which is composed mainly of silica/alumina with the capability of efficiently adsorbing even a volatile chemical substance which is hardly water-soluble, and to provide a method for manufacturing this kind of adsorbent. <P>SOLUTION: The adsorbent is manufactured through the following three processes: that is, (1) a mixing process to prepare a raw material mixture by mixing a waste molding sand containing a carbon component with a calcium phosphate compound and a dispersion medium, (2) a molding process to make a molded form of a desired shape by molding and drying the raw material mixture, and (3) a calcining process to obtain a calcined product containing carbon by calcining the molded form in a reducing atmosphere. These series of the processes can obtain the adsorbent as a calcined product containing the carbon with an excellent adsorption activity while preventing the carbon component from being lost. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to an adsorbent that can be used for deodorizing materials and other uses, and a method for producing the same.

  Conventionally, by adsorbing malodorous components and harmful substances (referred to as "treated substances") in exhaust gas or wastewater, and biologically decomposing treated substances with organic-degradable microorganisms, Various techniques for deodorizing or detoxifying have been proposed.

  For example, in “deodorizing material, method for producing deodorizing material and deodorizing method” disclosed in Patent Document 1, a calcium phosphate compound (for example, hydroxyapatite derived from bone component) is dispersed in a porous silica / alumina carrier derived from foundry sand. It constitutes a deodorizing material. By supporting the phosphoric acid component and regulating the elution of the phosphoric acid component from the deodorizing material, the adherence and propagation of microorganisms in the deodorizing material are improved, and long-term deodorization performance is realized. According to Patent Document 1, such a deodorizing material can be obtained by molding (granulating) a raw material in which foundry sand, a calcium phosphate compound and water are mixed into granules, and firing the molded product in a normal oxidizing atmosphere.

JP 2006-116421 A

  In the deodorizing material of Patent Document 1, an increase in the number of inhabiting microorganisms is observed as compared with a material in which a porous material is simply impregnated with a phosphoric acid component (prior art of Patent Document 1). Although improvement was seen, it was difficult to say that immediate deodorization performance was always sufficient. The cause is the inadequate adsorption and retention of malodorous components and harmful substances (treated substances) that are preconditions for biological treatment, and the absolute amount of treated substances that are actually used for biological treatment, that is, microorganisms. This is because the amount of the substance to be treated incorporated into the slag is small. In particular, when the substance to be treated is a poorly water-soluble volatile organic compound (VOC) such as toluene, the deodorizing effect by the deodorizing material of Patent Document 1 may be reduced. It is considered that the opportunity for the substance to be treated to be taken up by the microorganisms is largely lost because the substance to be treated is volatile and hardly water-soluble.

  An object of the present invention is to provide a silica / alumina-based adsorbent capable of efficiently adsorbing even a poorly water-soluble volatile chemical substance, and a method for producing such an adsorbent.

  The present invention provides a mixing step of preparing a raw material mixture by mixing a dispersion medium with a casting waste sand containing a carbon component (or mixing a calcium phosphate compound and a dispersion medium with a casting waste sand containing a carbon component to prepare a raw material mixture. A mixing step to be prepared), a molding step in which the raw material mixture is molded and dried to obtain a molded body having a desired shape, and a firing step in which the molded body is fired in a reducing atmosphere to obtain a carbon-containing fired product. It is the manufacturing method of the adsorbent characterized by implementing.

  Further, the present invention prepares a raw material mixture by mixing a dispersion medium with casting waste sand containing a carbon component (or mixes a calcium phosphate compound and a dispersion medium with casting waste sand containing a carbon component to prepare a raw material mixture. The adsorbent is characterized in that the raw material mixture is molded and dried to form a molded body having a desired shape, and the molded body is fired in a reducing atmosphere to be obtained as a carbon-containing fired product.

  According to the present invention, the waste carbon sand containing the carbon component is used as a silica / alumina supply source, and the molded body using the waste sand foundry as a main raw material is fired in a reducing atmosphere, thereby It is possible to obtain an adsorbent as a carbon-containing fired product excellent in adsorption activity while preventing disappearance. Such an adsorbent can efficiently adsorb even a poorly water-soluble (hydrophobic) volatile chemical substance.

(A)-(c) is a perspective view which shows the example of a shape of a molded object (or adsorbent).

The present invention relates to an adsorbent and a method for producing the same. The main points common to the inventions and method inventions of the present invention are the use of casting waste sand containing a carbon component as a main raw material, and The firing is performed in a reducing atmosphere (non-oxidizing atmosphere). That is, the present invention
A mixing step of preparing a raw material mixture by mixing a dispersion medium with waste sand containing a carbon component,
A molding step of molding and drying the raw material mixture to obtain a molded body having a desired shape, and
The molded body is fired in a reducing atmosphere to provide at least three steps of a firing step for obtaining a carbon-containing fired product.

  The “foundry waste sand” as the main raw material refers to foundry sand that has been used for sand mold making and casting at least once, and this foundry waste sand includes not only sand obtained by separating used sand molds, This includes dust collected by a dust collector installed at a foundry where sand molds are dismantled. Both the sand obtained by separating the sand mold and the dust collection dust are still “cast waste sand recovered as waste from the used casting sand mold”. Generally, about 10% to about 30% of carbon components (for example, coal powder such as coke) are contained in foundry sand generated in a foundry. The dust collecting dust has a relatively small average particle size of about 1 to 200 μm, more preferably about 3 to 50 μm, and therefore it is preferably used as foundry sand.

  As a dispersion medium when preparing the raw material mixture, for example, water can be used. The dispersion medium is not limited to water as long as the waste sand can be made into a paste or slurry and can be evaporated substantially when the formed body is dried in the forming step.

  In preparing the raw material mixture, a calcium phosphate compound can be used in combination with the dispersion medium. When a calcium phosphate compound is used in combination, the adsorbent of the present invention is extremely suitable as a deodorizing material for biological deodorization as disclosed in Patent Document 1 (Japanese Patent Laid-Open No. 2006-116421). In other words, the calcium phosphate compound has low water solubility, and the phosphorus component elutes little by little in the water in contact with the adsorbent (deodorant), so that the adsorbent surface and its surroundings provide a comfortable nutritional environment for microorganisms. This comfortable nutritional environment can be maintained over a long period of time. Moreover, since the calcium phosphate compound has high affinity with microorganisms, the supportability and adhesion of microorganisms to the surface of the adsorbent are improved. As a result, the carrying density and adhesion density of microorganisms per unit area in the adsorbent (deodorizing material) can be increased, and the deodorizing performance can be improved as a whole.

In addition, as a calcium phosphate compound, calcium phosphate [Ca ₃ (PO ₄ ) ₂ ], hydroxyapatite [Ca ₁₀ (PO ₄ ) ₆ (OH) ₂ ], calcium monohydrogen phosphate (CaHPO ₄ ), calcium dihydrogen phosphate [ Ca (H ₂ PO ₄ ) ₂ ], calcium pyrophosphate (Ca ₂ P ₂ O ₇ ), calcium metaphosphate [Ca (PO ₃ ) ₂ ], fluorapatite [Ca ₁₀ (PO ₄ ) ₆ F ₂ ], 4 calcium phosphate (Ca ₄ P ₂ O ₉ ), Ca-deficient hydroxyapatite [Ca _10-X H _2X (PO ₄ ) ₆ (OH) ₂ ] and the like can be exemplified, but are not limited thereto. Moreover, among the calcium phosphate compounds, one type may be used alone as the calcium phosphate compound, or two or more types may be used in combination. As an example, a biological bone component may be used as hydroxyapatite. In addition, all illustrated as a calcium phosphate compound mentioned above are hardly water-soluble. In this case, poorly water-soluble means that the solubility is 0.1 g / 100 g or less.

  In preparing the raw material mixture, an organic binder may be used in combination with the dispersion medium. Examples of the organic binder include methyl cellulose. Use of the organic binder is useful for improving the moldability of the molded body in the molding process.

  The blending ratio at the time of preparing the raw material mixture can be appropriately determined. For example, the dispersion medium is 5 to 50 parts by weight, the calcium phosphate compound is 5 to 30 parts by weight, and the organic binder is 0.5 to 0.5 parts by weight with respect to 100 parts by weight of the casting waste sand. It is preferable to blend 10 parts by weight. In the mixing step, a kneader can be used.

  The raw material mixture prepared in the mixing step is molded and dried to form a molded body having a desired shape (molding step). The shape of the molded body can be arbitrarily determined according to the purpose of use of the adsorbent. For example, a honeycomb body as shown in FIG. 1 (a), a quadrangular prism shape with four through holes as shown in FIG. 1 (b), and the like. 1, a cylindrical Raschig ring with one through-hole as shown in FIG. 1C, a granular material, a string-like or short columnar pellet, and the like.

  In the firing step, the compact is fired in a reducing atmosphere. The “reducing atmosphere” means a non-oxidizing atmosphere, that is, an atmosphere in which oxygen is not present, or even if oxygen is present, its oxidizing action is inhibited or suppressed. As a specific example or a specific brewing method of such a reducing atmosphere, the whole atmosphere is filled with an inert gas such as nitrogen, helium or argon, and an oxygen scavenger such as activated carbon is disposed around the molded body. It is possible to prevent the surface of this material from being exposed to oxygen directly.

  The heating temperature at the time of firing can be appropriately changed according to the combination of the raw material mixture, the blending composition, the size of the molded body, the strength required as an adsorbent, and the like. In general, examples of the lower limit value of the heating temperature include 600 ° C, 650 ° C, 700 ° C, and 750 ° C, and examples of the upper limit value of the heating temperature include 950 ° C, 900 ° C, and 850 ° C. Accordingly, the heating temperature may be 600 to 950 ° C., 650 to 900 ° C., or 700 to 850 ° C., but is not particularly limited to these heating temperatures. The heating time is selected according to the heating temperature, the size of the molded body, the hardness required for the adsorbent, etc., and is set to, for example, 10 minutes to 10 hours, 20 minutes to 5 hours, or 1-2 hours. can do. However, the heating time is not particularly limited.

  Through the series of steps (mixing step, molding step, firing step), an adsorbent that is a carbon-containing fired product is obtained. In addition, since this adsorbent uses casting foundry sand as a main raw material, it is formed mainly with silica and alumina. Moreover, as components other than silica and alumina, at least one component such as iron oxide, magnesium oxide, manganese oxide, sodium oxide, and potassium oxide may be included.

  As described above, according to the present invention, casting waste sand containing a carbon component is used as a silica / alumina supply source, and a molded body using such casting waste sand as a main raw material is fired in a reducing atmosphere. Thus, the disappearance of the carbon component from the fired product can be prevented. Therefore, the adsorbent of the present invention is obtained as a carbon-containing fired product having excellent adsorption activity, and as a result, even a poorly water-soluble (hydrophobic) volatile chemical substance can be adsorbed efficiently. There is an excellent effect of being able to.

  In addition, in the production of adsorbents, when a calcium phosphate compound is used in combination with waste casting sand, not only the adsorptivity of treated substances (bad odor components and harmful substances) is improved, but also the adhesion and reproduction of microorganisms are improved. Therefore, long-term deodorization performance (biological decomposition treatment) can be achieved. In other words, even when the activity of microorganisms temporarily decreases due to the period of acclimatization of microorganisms, environmental changes, etc., the deodorant with high adsorptivity (adsorbent) itself remains treated until the microbial activity is restored. Therefore, long-term deodorizing performance can be achieved.

Examples 1 and 2 of the present invention and Comparative Examples 1 and 2 will be described. In addition, the raw material used in the following Examples and Comparative Examples is as follows.
(1) Foundry waste sand Foundry waste sand as a raw material is foundry waste sand (dust collection dust) as dust waste collected by a dust collector of a foundry. This foundry waste sand contains silica and alumina as main components, and also contains metal oxides such as iron oxide, and also contains organic substances such as carbonaceous powder particles. More specifically, silica (SiO ₂₎ of 52.9 wt%, alumina _(Al 2 _{O 3)} 15.5 wt%, iron oxide _(Fe 2 _{O 3)} 5.17 wt%, magnesium oxide ( MgO) 2.77% by mass, calcium oxide (CaO) 2.05% by mass, manganese oxide (MnO) 0.076% by mass, sodium oxide (Na ₂ O) 1.70% by mass, potassium oxide ( K ₂ O) 0.478% by mass, sulfur (S) 0.228% by mass, phosphorus (P) 0.029% by mass, IL (Ignition Loss) derived from carbon components, etc. 18.5% by mass Foundry sand was used.
(2) Calcium Bone Phosphate Bone calcium phosphate as a raw material is a powdered calcium phosphate component obtained from a pulverized bovine bone, and is mainly composed of hydroxyapatite.

[Example 1]
20 g of calcium calcium phosphate was added to and mixed with 100 g of casting waste sand dried by heating at 105 ° C. for 2 hours, and 50 ml of water was added stepwise thereto and kneaded until the water was uniformly dispersed. This kneaded product was filled in a ceramic-type injection molder (so-called ceramic clay gun) and extruded from this molder to form a large number of short columnar pellets having a thickness of 4 mm and a length of about 15 mm. These pellets were naturally dried and then fired in a reducing atmosphere.
At the time of reduction firing, about half of the volume of the pellet was put into a heat-resistant container having a volume of 50 ml, and activated carbon was added from above to fill the remaining half of the heat-resistant container with activated carbon, and the pellet was buried in the activated carbon. . The heat resistant container was covered with a lid, and the lid was put into a closed state, which was transferred to an electric furnace and heated at 800 ° C. for 2 hours. Residual oxygen in the heat-resistant container is captured by activated carbon and carbonized (carbon oxide) by heat, so that the pellets in the heat-resistant container are subjected to firing (reduction firing) in a non-oxidizing atmosphere. After such firing, a large number of pellets were obtained. The appearance of these fired products was black. The fact that the appearance is black is a proof of the fact that the pellet-like fired product of Example 1 did not undergo oxidation during firing in comparison with Comparative Example 1 described later. Table 1 shows the weight ratio of the pellet-like fired product of Example 1 when the weight of the short columnar pellets after natural drying and before reduction firing is 1. Table 2 shows the result of fluorescent X-ray analysis of the pellet-like fired product of Example 1.

[Comparative Example 1]
Comparative Example 1 corresponds to the reduction firing in Example 1 replaced with ordinary oxidation firing. That is, in Comparative Example 1, short columnar pellets were molded and naturally dried in exactly the same procedure as in Example 1. The dried pellets were fired in an oxidizing atmosphere.
At the time of oxidation firing, about half of the volume of the pellets was put in a heat-resistant container having a volume of 50 ml and opened without being covered. The heat-resistant container was transferred to an electric furnace and heated at 800 ° C. for 2 hours in the same manner as in Example 1 to obtain a large number of pellets. The appearances of these fired products were brick-colored. That the appearance is a brick color is a proof of the fact that the pellet-like fired product of Comparative Example 1 was oxidized during firing in comparison with Example 1. In addition, Table 1 shows the weight ratio of the pellet-like fired product of Comparative Example 1 when the weight of the short columnar pellets after natural drying and before reduction firing is 1. Table 2 shows the result of fluorescent X-ray analysis of the pellet-like fired product of Comparative Example 1.

[Toluene adsorption test]
In order to measure the adsorption performance of toluene as VOC, the pellets of Example 1 and Comparative Example 1 were subjected to the following tests. Specifically, 5 g of a sample (pellet-like fired product) is put into a sampling bag for gas analysis in a deflated state (so-called Tedlar bag) (maximum volume of 3 liters when expanded), followed by 3 parts of 5000 ppm toluene / air mixed gas. Filled with liter and left in a sealed state for 75 minutes. Thereafter, the residual gas in the sampling bag was sampled with a syringe, and the toluene concentration was measured with a gas chromatograph. In addition, as a blank test, it measured also when filling only 3 liters of 5000 ppm toluene-air mixed gas without putting a sample in a sampling bag, and leaving it to stand for 75 minutes. Based on the difference between the toluene concentration after 75 minutes in the blank test and the toluene concentration after 75 minutes in the sample bag, the toluene adsorption amount (mg of toluene adsorbed per 1 g of sample) was calculated. Table 3 shows the measurement results of Example 1 and Comparative Example 1 in this adsorption test.

[Consideration on Example 1]
While the toluene adsorption amount of Example 1 was 5.1 mg / g, the toluene adsorption amount of Comparative Example 1 was only 1.7 mg / g. From a comparison between the two, it can be seen that the reduction calcination is superior to the ordinary oxidation calcination in terms of toluene adsorption. The reason why the reduced calcination has better toluene adsorptivity is thought to be because the carbon content does not burn out during the calcination because of the reduction calcination, and the carbon content remaining in the fired product exhibits the adsorptivity. The results in Table 1 indicate that Example 1 by reduction firing has less weight loss due to firing than Comparative Example 1 by oxidation firing, and this result shows that carbon content is not lost much in reduction firing. It suggests. Moreover, the result of Table 2 has shown that the baked material of Example 1 has more carbon content than the baked material of the comparative example 1. FIG. The results in Tables 1 and 2 can be said to support the above-mentioned assumption that “carbon is not lost much in the reduction firing, and the carbon remaining in the fired product increases the adsorptivity”.

[Example 2]
20 g of calcium calcium phosphate was added to and mixed with 100 g of casting waste sand dried by heating at 105 ° C. for 2 hours. In order to improve moldability, this mixture was pulverized, and 3 g of methylcellulose as an organic binder and 50 ml of water were added to 120 g of the mixture and kneaded. This kneaded product was formed into a cubic honeycomb body having a length of 50 mm, a width of 50 mm and a height of 50 mm as shown in FIG. Each cell of the honeycomb formed body has a square cross section of 2 mm in length × 2 mm in width, and the honeycomb formed body has 18 cells in the vertical direction × 18 in the horizontal direction = total 324 cells. The honeycomb formed body was naturally dried and then fired in a reducing atmosphere.
At the time of reduction firing, the honeycomb formed body is buried in activated carbon in a heat-resistant container for firing, and the heat-resistant container is covered with a lid, and is moved to an electric furnace at 800 ° C. for 2 hours. Heated for hours. As in Example 1, since the remaining oxygen in the heat-resistant container is captured by activated carbon and carbonized (carbon oxide) by heat, the honeycomb formed body is subjected to firing in a non-oxidizing atmosphere (reduction firing). Become. Thus, a honeycomb-shaped fired product was obtained.

[Comparative Example 2]
Comparative Example 2 corresponds to the reduction firing in Example 2 replaced with ordinary oxidation firing. That is, in Comparative Example 2, the honeycomb body was molded and naturally dried in exactly the same procedure as in Example 2. The dried honeycomb formed body was fired in an oxidizing atmosphere.
At the time of oxidation firing, the honeycomb formed body was put in the same heat-resistant container for firing as used in Example 2 and was opened without a lid. The heat-resistant container was transferred to an electric furnace and heated at 800 ° C. for 2 hours in the same manner as in Example 2 to obtain a honeycomb-shaped fired product.

[Adhesive VOC adsorption test]
With respect to the honeycomb-like fired products of Example 2 and Comparative Example 2, the adsorption performance of methyl ethyl ketone (MEK) and isopropyl alcohol (IPA) which are VOC components from a commercially available adhesive was measured. Specifically, in a first gas analysis sampling bag (so-called Tedlar bag), 3 liters of air and 10 g of an adhesive for PVC pipe (Mitsubishi Resin Co., Ltd. product: Hishibond) are left at room temperature for 1 hour. The VOC component was volatilized and filled in the bag. Next, 1 g of a piece cut from the honeycomb fired product is put as a sample in a second sampling bag (maximum volume of 3 liters when expanded) in a deflated state, and then 3 liters of gas from the first sampling bag is added. Filled and left to seal for 3 hours. Thereafter, the residual gas in the second sampling bag was sampled with a syringe, and the concentration of each VOC component was measured with a gas chromatograph. In addition, as a blank test, it measured even when 3 liters of gas from the 1st sampling bag was filled and it was left for 3 hours, without putting a sample in a 2nd sampling bag. Based on the difference between the VOC concentration after 3 hours in the blank test and the VOC concentration after 3 hours in the sample bag, the VOC adsorption amount (mg VOC adsorption per 1 g sample) was calculated. Table 4 shows the measurement results of Example 2 and Comparative Example 2 in the adhesive VOC adsorption test.

[Paint VOC adsorption test]
About the honeycomb-like fired products of Example 2 and Comparative Example 2, xylene, toluene, methyl ethyl ketone (MEK), methyl isobutyl ketone (MIBK), butyl acetate (BuAc) and isopropyl alcohol (IPA) which are VOC components from commercially available paints The adsorption performance of was measured. Specifically, 3 liters of air and 10 g of an organic solvent-based paint (trade name: Plycoat 1300-1) are placed in a first gas analysis sampling bag (so-called Tedlar bag) and left at room temperature for 1 hour. The VOC component was volatilized and filled in the bag. Next, 1 g of a piece cut from the honeycomb fired product is put as a sample in a second sampling bag (maximum volume of 3 liters when expanded) in a deflated state, and then 3 liters of gas from the first sampling bag is added. Filled and left to seal for 3 hours. Thereafter, the residual gas in the second sampling bag was sampled with a syringe, and the concentration of each VOC component was measured with a gas chromatograph. In addition, as a blank test, it measured even when 3 liters of gas from the 1st sampling bag was filled and it was left for 3 hours, without putting a sample in a 2nd sampling bag. Based on the difference between the VOC concentration after 3 hours in the blank test and the VOC concentration after 3 hours in the sample bag, the VOC adsorption amount (mg VOC adsorption per 1 g sample) was calculated. Table 5 shows the measurement results of Example 2 and Comparative Example 2 in the paint VOC adsorption test.

[Consideration on Example 2]
As shown in Tables 4 and 5, compared with the fired product of Comparative Example 2 made by normal oxidation firing, the fired product of Example 2 made by reduction firing has a higher adsorption performance for various VOCs. ing. This result is consistent with the result of Example 1. In addition, about the adsorption amount of IPA in the paint VOC adsorption test, a remarkable difference is not seen by Example 2 and the comparative example 2 (refer Table 5). As the cause, it is considered that the adsorption active point derived from the residual carbon contained in the casting waste sand is superior in hydrophobicity to hydrophilicity. That is, in the presence of hydrophobic (poorly water-soluble) VOCs such as xylene and toluene, when hydrophilic (easy-water-soluble) VOCs such as IPA coexist, adsorption of hydrophobic (poorly water-soluble) VOCs takes precedence. On the other hand, it is presumed that adsorption of hydrophilic (easy water-soluble) VOC is postponed, and as a result, the number of adsorption active sites for hydrophilic (easy-water-soluble) VOC is relatively reduced.

  The adsorbent of the present invention can be used in various applications to adsorb malodorous components and harmful substances in the gas phase or liquid phase, and in particular, a carrier for holding microorganisms used for biological deodorization (biology). It is useful as a deodorizing material).

Claims (4)

A mixing step of preparing a raw material mixture by mixing a dispersion medium with casting waste sand containing a carbon component;
A molding step of molding and drying the raw material mixture to form a molded body having a desired shape;
A method for producing an adsorbent, comprising sequentially performing a firing step of firing the molded body in a reducing atmosphere to obtain a carbon-containing fired product. A mixing step of preparing a raw material mixture by mixing a calcium phosphate compound and a dispersion medium with waste waste sand containing a carbon component;
A molding step of molding and drying the raw material mixture to form a molded body having a desired shape;
A method for producing an adsorbent, comprising sequentially performing a firing step of firing the molded body in a reducing atmosphere to obtain a carbon-containing fired product.   A raw material mixture is prepared by mixing a dispersion medium with casting waste sand containing a carbon component, and this raw material mixture is molded and dried to form a molded body having a desired shape, and this molded body is fired in a reducing atmosphere. An adsorbent characterized by being obtained as a carbon-containing fired product.   A calcium phosphate compound and a dispersion medium are mixed with waste sand containing a carbon component to prepare a raw material mixture. The raw material mixture is molded and dried to form a molded body having a desired shape, and the molded body is fired in a reducing atmosphere. Thus, an adsorbent obtained as a carbon-containing fired product.

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