JP2002355558A - Method for oxidation removal of formaldehyde - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method which is capable of completely removing formaldehyde at a low temperature without using hazardous materials, such as ozone. SOLUTION: The method of removing the formaldehyde in the presence of oxygen by using a catalyst containing metallic particulates and metal oxide.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for removing formaldehyde (HCHO) by air oxidation.

[0002]

2. Description of the Related Art In recent years, sick house syndrome caused by a trace amount of a chemical substance present in a living space such as a house, a building, a car, etc. has been attracting attention, and there is an eager desire to develop a method for removing HCHO, which is a causative substance. Have been.

[0003] As a method for removing HCHO, an adsorption method and an oxidation method are known. The adsorption method is a method in which HCHO is adsorbed and removed by an adsorbent such as activated carbon, and has a disadvantage that the adsorbent needs to be exchanged and regenerated.

[0004] The oxidative decomposition method is a method of oxidizing HCHO to convert it into carbon dioxide and water, thereby rendering it harmless. This method has the advantage that HCHO can be completely removed. However, conventionally known platinum-based catalysts require a temperature of at least 120 ° C., and HCHO cannot be completely removed at a relatively low temperature from room temperature to about 100 ° C.

Heretofore, as a method for removing HCHO at a relatively low temperature, a photolysis method has been known in which a catalyst such as titanium oxide is irradiated with ultraviolet rays to promote oxidative decomposition by light. However, this method requires a light source for generating ultraviolet light and has low processing efficiency.

There is also known an ozone oxidation method in which ozone is generated by high-voltage discharge, and HCHO is oxidatively decomposed using the strong oxidizing power of ozone. In this method, high-voltage discharge is required to improve the removal performance, and it is necessary to increase the ozone concentration. Furthermore, there is a drawback that ozone is harmful to the human body even in a very small amount.

[0007]

SUMMARY OF THE INVENTION In view of the above-mentioned problems of the prior art, the present inventors have developed a method capable of completely removing HCHO at a relatively low temperature without using harmful substances such as ozone. I have been conducting diligent research to find out. as a result,
When a mixture comprising a metal oxide and gold is used as a catalyst for removing HCHO, it has been found that HCHO can be decomposed and removed at a relatively low temperature in the presence of oxygen, and the present invention has been completed.

[0008]

Means for Solving the Problems Item 1. Formaldehyde
Oxidizing and removing in the presence of a catalyst,
Is at least one of the following: (I) gold particles having a particle size of 10 nm or less, (II) cobalt oxide,
Nickel oxide, manganese oxide, iron oxide, titanium oxide, AB
_TwoO _Four(A represents Mg, Fe, Co, Ni, Cu, Mn and Zn, and B
Represents Al, Fe, Co and Ti; provided that A and B are the same
Compound of spinel type crystal structure represented by
Oxide and CDO_Three(C represents La, Sr and Ce, D is Fe,
Perovskiy represented by Co, Ni, Cu, Mn and Al)
Metal selected from the group consisting of composite oxides with
A catalyst comprising at least one oxide. Item 2. Catalyst immobilizes gold on metal oxide
Item 2. The method according to Item 1, which is a catalyst comprising a metal oxide. Item 3. The catalyst is a catalyst in which a gold-immobilized metal oxide is supported on a carrier.
Item 3. The method according to Item 2, which is a medium. Item 4. The carrier is alumina, silica, alumina-silica,
Selected from cordierite, zeolite and titanium oxide
Metal oxide carrier, stainless steel, iron, copper and
At least one metal support selected from aluminum
Item 3. The method according to Item 3, wherein

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION The gold catalyst for removing HCHO used in the present invention comprises a metal oxide and gold. Gold needs to be fine particles having a particle size of about 10 nm or less. The shape of the metal oxide is not particularly limited. The metal oxide can be used not only in powder form but also in a state of being molded in advance or in a state of being fixed to various supports.

In the present invention, as the metal oxide,
Cobalt oxide, nickel oxide, manganese oxide, iron oxide,
Oxides such as titanium oxide, AB having a spinel crystal structure
₂ O ₄ (A is Mg, Fe, Co, Ni, Cu, Mn, Zn, etc., B is Al, F
e, Co, Ti, etc. are exemplified, and A and B are not the same. ), CDO ₃ having a perovskite crystal structure (C is La, Sr, Ce, etc., D is Fe, Co, Ni, C
u, Mn, Al, etc.) are preferred.

In the present invention, the catalyst is particularly preferably a gold-immobilized metal oxide in which gold is immobilized on a metal oxide. As described above, the catalyst in which gold is immobilized on the metal oxide has a large contact area between the gold and the metal oxide, and can exhibit excellent catalytic activity. Even when gold is immobilized on metal oxide, gold is preferably in the form of fine particles having a particle size of about 10 nm or less, preferably about 2 to 5 nm.In this case, the shape of the metal oxide is particularly limited. Instead, it can be used in a powdered state, in a pre-formed state, or in a state of being fixed to various supports.

Methods for immobilizing gold on metal oxides are known, for example, 1) coprecipitation method (Japanese Patent Application Laid-Open No. 60-238148), and 2) drop neutralization precipitation method (Japanese Patent Application Laid-Open No. 63-238148). 252908), 3) a method of adding a reducing agent (JP-A-63-252908),
4) pH-controlled neutralization precipitation method (JP-A-63-252908),
5) Addition method of carboxylic acid metal salt (JP-A-2-252610), 6) Precipitation precipitation method (JP-A-3-97623), 7)
It can be carried out by a method such as an organic gold complex adsorption method (JP-A-9-122478).

In the method for producing the catalyst of the present invention, as a starting material, for example, a water-soluble gold compound such as chloroauric acid can be used as a gold compound as in a known method. Metal nitrates, sulfates, acetates,
Chloride can be used. Further, after depositing a precipitate by the above-described coprecipitation method or the like, drying and baking may be performed in the same manner as in the known method, and the baking temperature may be appropriately selected from the range of known baking conditions. Usually about 200-600 ° C, preferably about 250-550 ° C, more preferably 300-4
About 00 ° C. is appropriate.

In the catalyst of the present invention, the content of gold is about 0.1 to 30% by weight, preferably about 0.1 to 10%, more preferably about 0.1 to 3%, based on the total amount of the metal oxide and gold. And it is sufficient.

In the present invention, practicability is improved by supporting a metal oxide-based carrier having various shapes or a catalyst comprising the above-mentioned gold and metal oxide on a metal-based carrier. Examples of the metal oxide-based carrier include alumina, silica, alumina-silica, cordierite, zeolite, and titanium oxide. Examples of the metal-based carrier include stainless steel, iron,
Examples include copper and aluminum. The shape of the carrier is not particularly limited, for example, powder, spherical, granular, honeycomb,
All shapes generally used as a catalyst carrier at present, such as foam, fiber, cloth, plate, and ring, can be used. Various methods can be used for carrying, for example, the method described in JP-A-1-94945 may be used.

To remove HCHO using the catalyst of the present invention,
Depending on the conditions such as HCHO concentration, gold content, and coexisting components in the gas, the catalyst of the present invention and HCHO are allowed to stand at room temperature (10
The temperature may be about 400 ° C. to about 400 ° C. The oxygen concentration is not particularly limited, as long as it is at least the amount required for completely oxidatively decomposing HCHO, and the treatment may usually be performed in air. Also, other gas components, for example, hydrogen,
Even when a combustible gas such as carbon monoxide or hydrocarbon is present, it can be oxidized and removed at the same time.

[0017]

The following examples are provided to further clarify the features of the present invention.

[0018] Example 1 chloroauric acid _{[HAuCl 4 · 4H 2 O]} 0.250g (0.000606 mol), iron nitrate _{[Fe (NO 3) · 9H} 2 O] 16.2g (0.040 mol) and nickel nitrate [Ni (NO _{3) 2 · 6H 2 O]} 5.82g of (0.020 mol) was dissolved in distilled water 600ml was obtained a solution. On the other hand, sodium carbonate [Na ₂ C
O ₃ ] 10.3 g (0.0972 mol) dissolved in 400 ml of distilled water
Liquid B was obtained.

Solution A was dropped into solution B and stirred for 1 hour.
After that, the obtained coprecipitate is thoroughly washed with water, dried, and
By baking at 400 ° C for 5 hours, the particle size is about 2 to 5 nm.
Gold-immobilized nickel-iron oxide with fine-particle gold immobilized
(Catalyst No. 1 of the present invention) [Au / NiFe _TwoO_Four, Atomic ratio Au / (Fe + Ni) = 1 /
99].

Further, catalysts Nos. 2 to 9 of the present invention were obtained using various metal salts in the same manner as described above.

0.0 containing [0021] chloroauric acid _{0.260g [HAuCl 4 · 4H 2 O} ]
The pH was adjusted to 8 using a 0.1 molar aqueous solution of potassium hydroxide [KOH] in the 01 molar aqueous solution. To this solution, 5 g of titanium oxide (P-25, manufactured by Nippon Aerosil) having a specific surface area of 50 m ² / g was added, and the mixture was aged for 1 hour.

After washing the obtained catalyst with water, it is calcined at 400 ° C. for 5 hours to obtain a gold-fixed titanium oxide catalyst (the catalyst of the present invention No. 10).
[Au / TiO ₂ , atomic ratio Au / Ti = 1/99] was obtained.

Subsequently, each of the above catalysts (Nos. 1 to 10) was
0.15 g sieved to 0 mesh is filled in a glass tube having an inner diameter of 8 mm, and at various temperatures of 30, 50, 80, and 100 ° C, 100 ml of air gas containing 50 ppm of HCHO in the glass tube.
The HCHO concentration was measured by flowing at a flow rate of / minute, and the HCHO removal rate (%) was calculated by the following equation.

HCHO removal rate (%) = [1- ｛H at catalyst layer outlet
CHO concentration (ppm) / HCHO concentration at catalyst layer inlet (ppm)｝] × 100 The results are shown in Table 1. Table 1 shows NiFe ₂ O for comparison.
₄ The result when (Comparative product 1) is used is also described.

[0025]

[Table 1]

From the above results, it is clear that HCHO can be efficiently removed at a relatively low temperature by using a catalyst having gold immobilized on a metal oxide.

When the concentration of the produced carbon dioxide was measured by an infrared carbon dioxide meter, it almost coincided with the amount of HCHO removed. This indicates that HCHO was converted to carbon dioxide.

Example 2 To 50 g of γ-alumina beads having a specific surface area of 200 m ² / g and having a diameter of 3 mm, 5.17 g of iron nitrate [Fe (NO ₃ ) · 9H ₂ O] and nickel nitrate
[Ni (NO ₃ ) ₂・ 6H ₂ O] Impregnated with an aqueous solution in which 1.86 g was dissolved,
The resultant was baked at 00 ° C. for 4 hours to obtain alumina beads supporting NiFe ₂ O ₄ . 0.005 molar aqueous solution containing chloroauric acid _{0.523g [HAuCl 4 · 4H 2 O} ] with 1 molar aqueous solution of potassium hydroxide [KOH]
The pH was adjusted to 8. NiFe ₂ O ₄ -supported alumina beads were added to this solution, and the solution was aged for 1 hour.

The obtained catalyst is washed with water, and then calcined at 400 ° C. for 5 hours to obtain a gold-immobilized nickel iron oxide-supported alumina bead catalyst having immobilized fine-particle gold having a particle size of about 2 to 3 nm. (Au / NiFe ₂ O ₄ / alumina beads, gold content 0.5
Wt%, NiFe ₂ O ₄ content 3 wt%).

0.30 g of the above catalyst was filled in a glass tube having an inner diameter of 12 mm, and at various temperatures of 30, 50, and 80 ° C., an air gas containing 50 ppm of HCHO was passed through the glass tube at a flow rate of 200 ml / min. The removal performance of HCHO was determined by measuring the concentration. Table 2 shows the results.

[0031]

[Table 2]

From the above results, it can be seen that as a practical form, even when a metal oxide on which gold is immobilized is supported on alumina beads, the catalyst exhibits practically sufficient activity as an HCHO removal catalyst.

Example 3 Nickel naphthenate (5% naphtex nickel, Nihon Kagaku Sangyo Co., Ltd.) was used on a cordierite honeycomb (5 cells × 5 cells × 10 cm in length) having 400 cells (400 cells / in 2).
Dip coating with a mixed solution of iron naphthenate (5% naphtex iron, manufactured by Nippon Chemical Industry Co., Ltd.) (mixed so that the atomic ratio is Ni / Fe = 1/2), dried, and dried at 400 ° C. After firing for a time, a cordierite honeycomb supporting NiFe ₂ O ₄ was obtained. The amount of NiFe ₂ O ₄ carried (calculated by the change in honeycomb weight before and after carrying NiFe ₂ O ₄ ) was 2% by weight. Chloroauric acid [H
AuCl ₄ · 4H ₂ O] Potassium hydroxide 0.002 molar aqueous solution 100 ml [K
[OH] was adjusted to pH 8 using a 0.5 molar aqueous solution of [OH]. 2m of this liquid
l, add one NiFe ₂ O ₄ supporting cordierite honeycomb
Aged at ℃ for 1 hour.

The obtained catalyst is washed with water and calcined at 400 ° C. for 5 hours to obtain a gold-fixed nickel iron oxide-supported cordierite honeycomb in which particulate gold having a particle size of about 2 to 4 nm is fixed. A catalyst (Au / NiFe ₂ O ₄ / cordierite honeycomb, gold content 0.3% by weight, NiFe ₂ O ₄ content 2% by weight) was obtained.

One of the above catalysts was filled in a glass tube having an inner diameter of 12 mm, and the catalyst was added to the glass tube at various temperatures of 30, 50 and 80 ° C.
The removal performance of HCHO was determined by measuring the concentration of HCHO by flowing an air gas containing 50 ppm of HCHO at a flow rate of 140 ml / min (equivalent to a space velocity of 20,000 / hour). Table 3 shows the results.

[0036]

[Table 3]

From the above results, as a practical form,
It can be seen that even when a metal oxide having gold immobilized thereon is supported on a cordierite honeycomb, the catalyst has practically sufficient activity as an HCHO removal catalyst, and HCHO can be removed.

[0038]

According to the catalyst of the present invention, HCHO can be easily oxidized and removed at a relatively low temperature without using harmful substances such as ozone. For this reason, for example, the following applications are possible.

1) Pollution Prevention Catalyst HCHO contained in the waste gas generated in various plants can be completely burned to purify the waste gas, and the heat energy generated at that time can be recovered to improve energy efficiency. Can be enhanced.

2) General consumer use It can be used for cooking utensils, heating utensils, air purification utensils, etc. used for business and home use, and is generated from these utensils.
It can be used for removing HCHO and HCHO generated from building materials such as wall materials, plywood and carpets and existing in dwellings and buildings. It can also be used as an air purification device in a car cabin.

3) Production of high-purity gas By completely burning a small amount of HCHO contained in various high-purity gases, it is converted into water and carbon dioxide, which are easily removed substances, and further purification is achieved. it can.

 ──────────────────────────────────────────────────続 き Continuing on the front page F term (reference) 4C080 AA07 BB02 CC02 CC12 HH05 JJ04 KK08 LL03 MM02 NN01 NN03 NN04 NN06 4D048 AA19 AB01 BA01X BA03X BA07X BA16X BA28X BA34X BA35X BA36X BA37X BA38A BAAAABABA02A02A02A BA06B BA13B BB06B BC31B BC33B BC35B BC62B BC66B BC67B BC68B CA01 CA07 CA11 CA17 DA06 EA02X EA19 FB08 FB09

Claims (4)

[Claims] 1. Oxidation of formaldehyde in the presence of a catalyst
In the method of removing, the catalyst comprises at least one of the following:
A method characterized by being a seed: (I) gold particles having a particle size of 10 nm or less, (II) cobalt oxide,
Nickel oxide, manganese oxide, iron oxide, titanium oxide, AB
_TwoO _Four(A represents Mg, Fe, Co, Ni, Cu, Mn and Zn, and B
Represents Al, Fe, Co and Ti; provided that A and B are the same
Compound of spinel type crystal structure represented by
Oxide and CDO_Three(C represents La, Sr and Ce, D is Fe,
Perovskiy represented by Co, Ni, Cu, Mn and Al)
Metal selected from the group consisting of composite oxides with
A catalyst comprising at least one oxide. 2. The method according to claim 1, wherein the catalyst is a catalyst comprising a gold-immobilized metal oxide having gold immobilized on the metal oxide. 3. The method according to claim 2, wherein the catalyst is a catalyst having a gold-immobilized metal oxide supported on a carrier. 4. A carrier comprising alumina, silica, alumina
Silica, cordierite, metal oxide carrier selected from zeolite and titanium oxide, stainless steel,
4. The method according to claim 3, which is at least one metal-based support selected from iron, copper and aluminum.