Material for decomposing and purifying volatile organic compounds

Abstract

An object of the present disclosure is to provide a volatile organic compound decomposing / purifying material capable of efficiently decomposing VOCs.SOLUTION: A volatile organic compound decomposing / purifying material according to one aspect of the present disclosure is a pre-alloyed iron powder containing, as metal elements, Ni: 0.2 mass% or more and 3.0 mass% or less and Mo: 0.2 mass% or more and 2.0 mass% or less.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates to a volatile organic compound decomposition and purification material. [Background technology]

[0002] Volatile organic compounds (VOCs) have a higher density than water and therefore easily penetrate into groundwater. In addition, VOCs are difficult to decompose naturally in soil, so they may be dispersed over a wide area by groundwater flow. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2004-82106 Summary of the Invention [Problem to be solved by the invention]

[0004] Patent Document 1 describes a compound containing Fe and Ni, where Fe + 2H2O → Fe 2+ +2OH - Patent Document 1 describes an iron powder that can reduce and decompose organic halides using H2 generated by the reaction of HCl with H2. Patent Document 1 also describes using Ni as a catalyst to reduce organic halides.

[0005] As mentioned above, Patent Document 1 describes that organic halides are reductively decomposed by using Ni as a catalyst.

[0006] Meanwhile, the present inventors have discovered that VOCs can be decomposed more efficiently by adding Ni and Mo to iron powder, and have completed the present invention.

[0007] The present disclosure has been made in view of the above circumstances, and aims to provide a volatile organic compound decomposition and purification material that can efficiently decompose VOCs.

[0008] Generally, methods for decomposing and purifying volatile organic compounds include chemical oxidation, which has an extremely fast purification rate but is expensive, and bioprocessing, which has a slow purification rate but is inexpensive. The present disclosure aims to provide a relatively inexpensive and highly efficient decomposition and purification material that is intermediate between the chemical oxidation and bioprocessing. [Means for solving the problem]

[0009] A volatile organic compound decomposition and purification material according to one embodiment of the present disclosure is a pre-alloyed iron powder containing, as metal elements, Ni: 0.2% by mass to 3.0% by mass and Mo: 0.2% by mass to 2.0% by mass. [Effects of the Invention]

[0010] A volatile organic compound decomposition and purification material according to one embodiment of the present disclosure can efficiently decompose VOCs. [Brief explanation of the drawings]

[0011] [Figure 1] FIG. 1 is a graph showing the purification rates of trichloroethylene for iron powders No. 1 to No. 11. DETAILED DESCRIPTION OF THE INVENTION

[0012] [Description of the embodiments of the present disclosure] First, embodiments of the present disclosure will be listed and described.

[0013] (1) A volatile organic compound decomposition and purification material according to one embodiment of the present disclosure is a pre-alloyed iron powder containing, as metal elements, Ni: 0.2% by mass to 3.0% by mass and Mo: 0.2% by mass to 2.0% by mass.

[0014] This volatile organic compound decomposition and purification material contains, as metal elements, Ni: 0.2 mass % to 3.0 mass % and Mo: 0.2 mass % to 2.0 mass %, and is therefore capable of efficiently decomposing VOCs. The reason why this volatile organic compound decomposition and purification material is able to efficiently decompose VOCs is not clear, but it is speculated, for example, as follows: Ni is known to trap hydrogen atoms on its surface. Therefore, when Ni receives electrons from Fe and becomes anionic, the hydride ions released from the Ni substrate hydrogenate VOCs in a hydride reduction manner. At this time, Mo, being more electronegative than Ni, attracts electrons from Fe and converts them into divalent iron ions (Fe 2+ ) is thought to promote the dissolution of Fe. 2+ Since Fe acts as a strong reducing agent, it is thought to accelerate the decomposition of VOCs by assisting the hydride reduction reaction by Ni. Furthermore, because this volatile organic compound decomposition and purification material is a pre-alloyed iron powder, the contact area between the metallic iron and the alloying elements is extremely large, which is thought to enhance the charge transfer effect that occurs between Fe and Ni and Mo. As a result, it is thought that the supply of more electrons from the iron to the active points on the iron powder surface can significantly accelerate the VOC decomposition reaction rate.

[0015] (2) In the above (1), when the total content of Ni and Mo is T [mass %] and the content of oxygen is Oc [mass %], it is preferable that the following formula (1) is satisfied. T≧2.5×Oc+0.3 (1)

[0016] According to this embodiment, the reaction area of ​​Ni and Mo on the surface of the iron powder can be increased, and the decomposition efficiency of VOCs can be improved.

[0017] (3) In the above (1) or (2), the oxygen content Oc is preferably 0.5 mass% or less. According to this embodiment, the reaction area of ​​Ni and Mo on the iron powder surface can be increased, and the decomposition efficiency of VOCs can be further improved.

[0018] In the present disclosure, the term "content" generally refers to a value measured using an ICP optical emission spectrometer.

[0019] [Details of the embodiments of the present disclosure] Hereinafter, embodiments of the present disclosure will be described in detail. It should be noted that the numerical values ​​described in this specification can be arbitrarily combined with the upper and lower limit values. In this specification, all numerical ranges from the upper limit value to the lower limit value that can be combined are described as suitable ranges.

[0020] [Volatile organic compound decomposition and purification material] The volatile organic compound decomposition and purification material (hereinafter also referred to as "the VOC decomposition and purification material") is a pre-alloyed iron powder and contains, as metal elements, Ni: 0.2% by mass or more and 3.0% by mass or less, and Mo: 0.2% by mass or more and 2.0% by mass or less.

[0021] This VOC decomposition and purification material contains, as metal elements, Ni: 0.2% by mass to 3.0% by mass, and Mo: 0.2% by mass to 2.0% by mass, and is therefore capable of efficiently decomposing VOCs. The reason why this VOC decomposition and purification material is able to efficiently decompose VOCs is not clear, but it is speculated, for example, as follows: Ni is known to trap hydrogen atoms on its surface. Therefore, when Ni receives electrons from Fe and becomes anionic, the hydride ions released from the Ni substrate hydrogenate VOCs in a hydride reduction manner. At this time, Mo, being more electronegative than Ni, attracts electrons from Fe and converts them into divalent iron ions (Fe 2+ ) is thought to promote the dissolution of Fe. 2+ It is believed that because Fe acts as a strong reducing agent, it accelerates the hydride reduction reaction by Ni, thereby accelerating the decomposition of VOCs. Furthermore, because this VOC decomposition and purification material is a pre-alloyed iron powder, the contact area between the metallic iron and the alloying elements is extremely large, which is thought to enhance the charge transfer effect that occurs between Fe and Ni and Mo. As a result, it is believed that the supply of more electrons from the iron to the active points on the iron powder surface can significantly speed up the VOC decomposition reaction rate.

[0022] Examples of VOCs that can be purified by the VOC decomposition and purification material include halogenated hydrocarbons such as trichloroethylene, dichloroethylene, tetrachloroethylene, vinyl chloride, trichloroethane, dichloropropene, carbon tetrachloride, and dichloromethane.

[0023] As described above, the VOC decomposition and purification material is a pre-alloyed iron powder. That is, the VOC decomposition and purification material is manufactured by adding alloying elements (Ni and Mo) in a melting process. Because the VOC decomposition and purification material is a pre-alloyed iron powder, the contact area between the metallic iron and the alloying elements is significantly larger than that of a diffusion-type alloy obtained by, for example, diffusion-bonding fine powders of alloying elements to pure iron powder.

[0024] The lower limit of the iron content in the VOC decomposition and purification material may be 60 mass%, 75 mass%, 85 mass%, or 95 mass%, from the viewpoint of increasing the contact area between the metallic iron and alloy elements and thereby accelerating the VOC decomposition and purification reaction rate, while the upper limit of the iron content in the VOC decomposition and purification material may be 99.6 mass%.

[0025] In this VOC decomposition and purification material, Ni becomes anionized by receiving electrons from Fe. As a result, hydride ions are released from the Ni substrate, and these hydride ions are substituted for the chloro groups of VOCs, thereby decomposing the VOCs. In addition, chloride ions (Cl) released from VOCs - ) substitutes for hydrogen on the Ni substrate, and H + After reacting with the iron to produce hydrochloric acid, the ferrous ions Fe 2+It is believed that Ni reacts with the VOC decomposition and purification material to produce iron chloride. From the viewpoint of promoting the VOC decomposition reaction, the lower limit of the Ni content in the VOC decomposition and purification material is 0.2 mass%, preferably 0.5 mass%, and may be 1.0 mass% or 1.5 mass%. On the other hand, from the viewpoint of effectively obtaining the effect of improving the VOC decomposition efficiency and reducing the manufacturing cost of the VOC decomposition and purification material, the upper limit of the Ni content in the VOC decomposition and purification material is 3.0 mass%, may be 2.8 mass%, or may be 2.6 mass%.

[0026] In this VOC decomposition and purification material, Mo acts as an electron-withdrawing substance, and Fe 2+ The lower limit of the Mo content in the VOC decomposition and purification material is Fe. 2+ From the viewpoint of sufficiently eluting the VOCs, the content of Mo is preferably 0.2% by mass, more preferably 0.4% by mass, and may be 0.5% by mass or 0.6% by mass. On the other hand, the upper limit of the content of Mo in the VOC decomposition and purification material is 0.2% by mass, more preferably 0.4% by mass, and may be 0.5% by mass or 0.6% by mass. 2+ From the viewpoint of effectively obtaining the effect of improving the amount of elution of the VOC and from the viewpoint of reducing the manufacturing cost of the VOC decomposition and purification material, the content is 2.0 mass %, or may be 1.5 mass %, 1.3 mass %, or 1.2 mass %.

[0027] The VOC decomposition and purification material contains Fe as the main component and Ni and Mo as active components. The content of elements other than Fe, Ni, and Mo in the VOC decomposition and purification material is not particularly limited. The term "main component" refers to the component with the largest content by mass.

[0028] When the total content of Ni and Mo is T [mass %] and the content of oxygen is Oc [mass %], it is preferable that the following formula (1) is satisfied. T≧2.5×Oc+0.3 (1)

[0029] Moreover, it is also preferable that the VOC decomposition and purification material satisfies the following formula (2) or (3) instead of the above formula (1). T≧2.5×Oc+0.6 (2) T≧2.5×Oc+0.8 (3)

[0030] By satisfying the above formula, the VOC decomposition and purification material can increase the Ni and Mo content relative to the iron oxide film that may be present on the surface of the iron powder, thereby increasing the reaction area of ​​Ni and Mo on the iron powder surface and improving the VOC decomposition efficiency.

[0031] In the VOC decomposition and purification material, the upper limit of the oxygen content Oc is preferably 1.0% by mass, more preferably 0.7% by mass, and even more preferably 0.5% by mass, and may be 0.2% by mass or 0.1% by mass. When the VOC decomposition and purification material contains oxygen, this oxygen may form an iron oxide film on the surface layer of the iron powder. By setting the oxygen content Oc to the above upper limit or less, the reaction area of ​​Ni and Mo on the iron powder surface can be increased, thereby further improving the VOC decomposition efficiency. In other words, it is preferable that the VOC decomposition and purification material does not have an iron oxide film formed on its surface, in terms of improving the VOC decomposition efficiency. The lower limit of the oxygen content Oc in the VOC decomposition and purification material may be, for example, 0% by mass, or 0.05% by mass from the viewpoint of ease of production.

[0032] The VOC decomposition and purification material may contain elements other than Fe, Ni, Mo, and O, as long as the desired effect is achieved. Examples of elements other than Fe, Ni, Mo, and O include copper (Cu), manganese (Mn), cobalt (Co), and sulfur (S).

[0033] By reducing the contents of elements other than Fe, Ni, Mo, and O, the VOC decomposition and purification material can significantly exhibit the VOC decomposition effect achieved by setting the Ni and Mo contents to a predetermined value. From this perspective, for example, the upper limit of the content of at least one element selected from the group consisting of Cu, Mn, Co, and S may be 1.0 mass%, 0.7 mass%, 0.5 mass%, 0.3 mass%, 0.1 mass%, or 0.05 mass%. Furthermore, the upper limit of the content of elements other than Fe, Ni, Mo, and O in the VOC decomposition and purification material may be 1.0 mass%, 0.7 mass%, 0.5 mass%, 0.3 mass%, 0.1 mass%, or 0.05 mass%, respectively.

[0034] In the VOC decomposition and purification material, elements other than Fe, Ni, Mo, and O may be unavoidable impurities. That is, the VOC decomposition and purification material may be a pre-alloyed iron powder produced by dissolving pure iron and adding NiMo as an alloy element.

[0035] The VOC decomposition and purification material may be, for example, an aggregate of a large number of pre-alloyed iron powders. The VOC decomposition and purification material may be used, for example, as a material for a permeable reaction wall, or may be buried underground.

[0036] [Other embodiments] The above-described embodiments do not limit the configuration of the present invention. Therefore, the above-described embodiments may include omissions, substitutions, or additions of components based on the description in this specification and common general technical knowledge, and all of these should be construed as falling within the scope of the present invention. [Example]

[0037] The present invention will be described in detail below based on examples, but the present invention should not be construed as being limited by the descriptions in these examples.

[0038] [No.1 to No.11] Prealloyed iron powders with the compositions shown in Table 1 were produced for No. 1 to No. 10. A diffusion-type alloy with the composition shown in Table 1 was produced for No. 11. The compositions of Nos. 1 to 4, 7, 8, and 11 were measured using an inductively coupled plasma (ICP) optical emission spectrometer (Shimadzu Corporation, "ICPV-8000"). The compositions of Nos. 5, 6, 9, and 10 were measured using a solid-state optical emission spectrometer (Shimadzu Corporation, "PDA-7000"). In Table 1, "white powder" refers to iron powder in which metallic iron is present up to the surface by performing a reduction treatment after crushing molten steel using water atomization. "black powder" refers to iron powder in which the surface is covered with iron oxide after crushing molten steel using water atomization. In Table 1, elements other than O, Cu, Ni, and Mo represent Fe and unavoidable impurities.

[0039] [Table 1]

[0040] (VOC purification test) For No. 1 to No. 11, a trichloroethylene purification test was conducted using the following test procedure. [Test Procedure] For each of the iron powder samples (No. 1 to No. 11), a test container was prepared by placing 100 mL of a 1 mg / L trichloroethylene aqueous solution in a 125 mL vial. Ten grams of each iron powder sample (No. 1 to No. 11) was added to the test container, which was then maintained at 25°C and shaken at 140 rpm. After 50, 100, and 240 hours, the shaking was stopped and the aqueous solution in the vial was sampled and analyzed for residual trichloroethylene concentration. The trichloroethylene concentration was analyzed using a GL Sciences AquaPT 5000J plus purge and trap concentration introduction system and an Agilent Technologies 7890B / MSD5977B GC system. The results are shown in Figure 1.

[0041] (reaction rate constant) Based on the results of the VOC purification test, the reaction rate constants for No. 1 to No. 11 were calculated 100 hours and 240 hours after the start of the test using the following procedure. The results are shown in Table 2. [procedure] The decrease in concentration due to trichloroethylene decomposition was considered to be a pseudo-first-order reaction, and the natural logarithm of the trichloroethylene concentration was taken 100 hours and 240 hours after the start of the test. An approximate line was obtained based on the natural logarithm of the trichloroethylene concentration at the start of the test and after each time elapsed. The absolute value of the slope of this approximate line was then calculated as the reaction rate constant.

[0042] [Table 2]

[0043] [Evaluation results] As shown in Table 2, iron powders No. 1 to No. 6 are prealloyed iron powders with appropriately controlled Ni and Mo contents. Therefore, they exhibit excellent reaction rate constants after 100 and 240 hours, and trichloroethylene is decomposed satisfactorily after 240 hours. Iron powder No. 11 decomposes trichloroethylene to the same extent as Nos. 1 to 6, but contains a higher Ni content than Nos. 1 to 6. This is presumably because iron powder No. 11 is a diffusion-type alloy, which does not allow for a sufficiently large contact area between the metallic iron and the alloying elements. Conversely, iron powders No. 1 to No. 6 are prealloyed iron powders, and therefore can effectively decompose trichloroethylene despite their relatively low Ni content.

[0044] Furthermore, comparing No. 1 to No. 6, No. 1 to No. 4 have a lower oxygen content, which allows them to have a larger reaction rate constant 100 hours after the start of the test. This indicates that iron powder without an iron oxide film on its surface is more effective at immediately decomposing. On the other hand, No. 1 to No. 6 all have similar reaction rate constants 240 hours after the start of the test. This indicates that iron powder with an iron oxide film on its surface is less effective at immediately decomposing trichloroethylene at a constant rate over a long period of time.

[0045] Furthermore, comparing No. 3 and No. 4, No. 3 has a higher Ni content, but the reaction rate constants are about the same. This suggests that in this VOC decomposition and purification material, the Ni content and trichloroethylene purification efficiency are not simply proportional, and that there is an appropriate content in relation to Mo, etc. [Industrial Applicability]

[0046] A VOC decomposition and purification material according to one embodiment of the present disclosure is suitable for efficiently decomposing VOCs.

Claims

1. It is a pre-alloyed iron powder, As a metallic element, Ni: 0.2% by mass or more and 3.0% by mass or less, Mo: 0.2 mass% or more and 2.0 mass% or less Volatile organic compound decomposition and purification material.

2. 2. The volatile organic compound decomposition and purification material according to claim 1, which satisfies the following formula (1), where T [mass %] is the total content of Ni and Mo, and Oc [mass %] is the oxygen content. T≧2.5×Oc+0.3 (1)

3. 3. The volatile organic compound decomposition and purification material according to claim 1, wherein the oxygen content Oc is 0.5 mass % or less.

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