JPH07318036A - Waste gas purification method - Google Patents

Abstract

(57) [Summary] [Structure] A catalyst composed of a mixture of at least one selected from the group consisting of manganese, copper, nickel, cobalt, iron, tungsten, silver, platinum, gold, and palladium and an oxide carrier or titania and iron, zinc. , A photocatalyst oxide process consisting of a mixture of tungsten, cadmium sulfide, gallium and phosphorus and sodium hydroxide, potassium hydroxide, sodium carbonate,
A waste gas purification system consisting of a series of post-treatment steps consisting of a mixture of one or more selected from potassium carbonate, calcium hydroxide, potassium hydroxide and calcium carbonate. [Effect] By reliably removing the methyl bromide contained in the waste gas, it is possible to prevent the release to the outside and contribute to the environmental purification.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention is preferably discarded from a series of steps of a decomposition step for decomposing waste gas containing methyl bromide and a post-treatment step of removing the decomposition product gas by alkali. It relates to a method of purifying gas.

[0002]

Methyl bromide is used in the field of fumigation and insecticidal treatment of fruits and vegetables and grains. At that time, the generated waste gas containing methyl bromide is diluted with a large amount of air and discharged to the outside, but no special purification treatment is performed. The method for removing methyl bromide and / or its compound contained in the waste gas is, for example, as described in JP-A-5-23598, air on a catalyst in which a transition metal is supported on γ-alumina. It is proposed to remove them by contacting them at a temperature of 250 ° C. or higher in the presence.
However, there was a problem in terms of disassembly performance.

[0003]

The object of the present invention is to catalyze waste gas containing methyl bromide, hydrogen peroxide, or ozone, or waste gas containing methyl bromide, water vapor, air, or oxygen. The waste gas is purified from a series of steps including a decomposition step of contacting and decomposing on a photocatalyst at a temperature range of 100 to 600 ° C. or room temperature and a post-treatment step of absorbing or adsorbing and removing the decomposition product gas. To provide a purification system.

[0004]

[Means for Solving the Problems] In order to achieve the above object, the inventors of the present invention have conducted extensive studies, and as a result, as a result of waste gas or odor containing one or more of methyl bromide, hydrogen peroxide and ozone. Waste from a series of decomposition processes in which waste gas containing waste gas containing methyl chloride and water vapor, air and oxygen is decomposed by contacting it on a catalyst, and the post-treatment process of absorbing or adsorbing the product gas from the decomposition process. We have found a purification system for purifying gas. That is, the present invention relates to methyl bromide and hydrogen peroxide,
When a waste gas containing at least one kind of ozone is brought into contact with the catalyst in the temperature range of 100 to 600 ° C., the reaction shown by the following formula proceeds.

[0005]

CH ₃ Br + 3H ₂ O ₂ = CO ₂ + HBr + 4H ₂ O (Chemical formula 1)

[0006]

CH ₃ Br + O ₃ = CO ₂ + HBr + H ₂ O (Chemical formula 2)

[0007]

## STR3 ## _{CH 3 Br + 2H 2 O +} 3 / 2O 2 = CO 2 + HBr + 3H 2 O ... ( Formula 3) any reactions carbon dioxide in the decomposition step, hydrogen bromide, to produce water. The gas produced from the decomposition step is brought into contact with an absorbent or adsorbent made of an alkaline compound, whereby the reaction of the following formula proceeds,

[0008]

[Chemical formula 4] HBr + NaOH = NaBr + H ₂ O (Chemical formula 4)

[0009]

CO ₂ + NaOH = Na ₂ HCO ₃ (Chemical Formula 5) Sodium bromide and sodium bicarbonate are produced to obtain purified air. The products are also widely used, soda bromide is used for photography, painkillers, reagents, etc., and sodium bicarbonate is widely used for papermaking, dye industry, reagents, etc.

The waste gas produced by the method of the present invention is not particularly limited, such as the waste gas emitted from the vegetable and vegetable fumigation equipment and the waste gas emitted from the wood fumigation equipment.

Hydrogen peroxide used in the present invention is a concentrated liquid,
Any of the diluents may be used. Ozone is generated by the ozonizer
It is generated and used. Methyl bromide undergoes a decomposition reaction with oxygen and air, but it is preferable to add water vapor, but it is not particularly limited. By adding steam,
Hydrogen bromide is easily generated and is easily absorbed or adsorbed by alkali.

The second feature of the present invention is the catalyst or photocatalyst used in the decomposition process. Reaction temperature 100-600
Manganese, copper, nickel,
A catalyst comprising a mixture of at least one oxide selected from the group consisting of cobalt, iron, tungsten, silver, platinum, gold, palladium, zinc, cadmium sulfide, gallium and phosphorus and an oxide carrier is used. The catalyst preferably has a catalytically active component content of 0.5% by weight or more based on the oxide carrier.

The oxide carrier of the present invention comprises titania, silica,
It is characterized by comprising a mixture of at least one selected from the group consisting of zirconia, magnesia and zeolite.

The shape of the catalyst used in the decomposition step of the present invention is not particularly limited, such as granular, honeycomb, plate, and three-dimensional mesh.

The active ingredient of the catalyst or photocatalyst used in the present invention can be used by producing an oxide by thermal decomposition of nitrate, chloride, sulfate, alcohol compound, oxide, or neutralization of aqueous solution.

The titania used in the present invention can be used by thermal decomposition of a sulfate, chloride or alcohol compound or by producing an oxide.

For the preparation of the catalyst according to the present invention, any of the commonly used impregnation method, kneading method, precipitation method and the like can be used.

For the preparation of the photocatalyst according to the present invention, any of the commonly used impregnation method, kneading method and coating method can be used.

As the oxidizing agent added in the decomposition step, any one or more of water vapor, hydrogen peroxide, ozone, air, oxygen and the like can be used.

The supply rate of the exhaust gas to the decomposition process of methyl bromide is 100 to 100,000 / h per unit volume of the catalyst.
Is preferred.

In the present invention, excess water at the outlet of the decomposition process can be recycled and used before the decomposition process.
It is also possible to recycle a part of the generated gas at the outlet of the post-treatment process to the stage before the decomposition process. Hydrogen bromide, carbon dioxide, and water produced from the decomposition process are introduced into the post-treatment process.
In the post-treatment step, a mixture of one or more selected from the group consisting of sodium hydroxide, potassium hydroxide, sodium carbonate, potassium carbonate, calcium hydroxide, calcium carbonate, calcium oxide, aqueous ammonia and activated carbon under a reaction temperature of 100 ° C or less. Is absorbed by the absorbent or adsorbent. The concentration of the absorbing liquid is preferably in the range of 1-50%. The absorption method in the post-treatment process includes a spray method and / or a sparger method,
The grid is legal.

The post-treatment step of the present invention may be either a solid absorbent or a liquid absorbent.

[0023]

According to the present invention, methyl bromide can be reliably removed by a series of combinations of the decomposition step and the post-treatment step, and high removal performance can be obtained for a long time. The system of the present invention is effective for environmental purification.

[0024]

EXAMPLES Hereinafter, the contents of the present invention will be described more specifically with reference to examples.

(Embodiment 1) FIG. 1 is a block diagram showing an embodiment of the present invention. Waste gas 1 containing methyl bromide and / or its compound is mixed with hydrogen peroxide, ozone, water vapor, air and oxygen 2 and introduced into decomposition step 3 at a reaction temperature of 300 ° C. In the decomposition step 3, the MnO ₂ —TiO ₂ catalyst is filled, and the hydrolysis reaction of methyl bromide in the waste gas proceeds on the catalyst to generate hydrogen bromide, carbon dioxide gas, and water. Next, the produced gas is introduced into the alkaline post-treatment step 4. In the alkaline post-treatment step 4, hydrogen bromide, carbon dioxide, and water in the produced gas are absorbed, and hydrogen bromide becomes sodium bromide and carbon dioxide becomes sodium bicarbonate and is recovered. The purified gas 5 is released to the atmosphere.

(Embodiment 2) FIG. 2 is an apparatus block diagram showing an embodiment of the present invention, in which a part of the gas produced in the alkali post-treatment step 4 is recycled through the recycle line 6 to the preceding stage of the decomposition step 3. Except for this, the procedure is the same as in Example 1.

(Example 3) In Example 1, the following catalyst was obtained as a catalyst used in the decomposition step.

[0028] The catalyst of Example _{A1 MnO 2 -TiO 2 A2 MnO 2} -SiO 2 A3 MnO 2 -ZrO 2 A4 MnO 2 -MgO A5 MnO 2 -Zeolite A6 CuO-TiO 2 A7 CuO-SiO 2 A8 CuO-ZrO 2 A9 CuO-MgO A10 CuO-Zeolite A11 NiO-TiO 2 A12 NiO-SiO 2 A13 NiO-ZrO 3 A14 NiO-MgO A15 NiO-Zeolite A16 CoO-TiO 2 A17 CoO-SiO 2 A18 CoO-ZrO 2 A19 CoO-MgO A20 _{CoO-Zeolite A21 Fe 2 O 3} -TiO 2 A22 Fe 2 O 3 -SiO 2 A23 Fe 2 O 3 -ZrO 2 A24 Fe 2 O 3 -MgO A25 Fe 2 O 3 -Zeolite A26 WO 3 -TiO 2 A27 WO 3 _{-SiO 2 A28 WO 3 -ZrO 2 A29} WO 3 -M _{O A30 WO 3 -Zeolite A31 Ag 2} O-TiO 2 A32 Ag 2 O-SiO 2 A33 Ag 2 O-ZrO 2 A34 Ag 2 O-MgO A35 Ag 2 O-Zeolite in these catalysts, Mn, Cu, Ni, Co, F
The weight of e, W and Ag is 10% by weight in terms of oxide with respect to the oxide carrier.

Example 4 In Example 1, the following catalyst was obtained as a catalyst used in the decomposition step.

Example Catalyst B1 MnO ₂ —Pt—TiO ₂ B2 MnO ₂ —Au—TiO ₂ B3 MnO ₂ —Pd—TiO ₂ B4 CuO—Pt—TiO ₂ B5 CuO—Au—TiO ₂ B6 CuO—Pd—TiO _{2 B7 NiO-Pt-TiO 2} B8 NiO-Au-TiO 2 B9 NiO-Pd-TiO 2 B10 CoO-Pt-TiO 2 B11 CoO-Au-TiO 2 B12 CoO-Pd-TiO 2 B13 Fe 2 O 3 -Pt _{-TiO 2 B14 Fe 2 O 3 -Au} -TiO 2 B15 Fe 2 O 3 -Pd-TiO 2 B16 WO 3 -Pt-TiO 2 B17 WO 3 -Au-TiO 2 B18 WO 3 -Pd-TiO 2 B19 Ag 2 _{O-Pt-TiO 2 B20 Ag} 2 O-Au-TiO 2 B21 Ag 2 O-Pd-TiO 2 in these catalysts, Mn, Cu, N , Co, F
The weight of e, W, Ag is 10% by weight in terms of oxide, and the weight of Pt, Au, Pd is 1% by weight in terms of metal, based on the oxide carrier.

Example 5 The following catalyst was obtained as a catalyst used in the decomposition step in Example 1.

Example Catalyst C 1 MnO ₂ —TiO ₂ —ZrO ₂ C 2 CuO—TiO ₂ —ZrO ₂ C 3 NiO—TiO ₂ —ZrO ₂ C 4 CoO—TiO ₂ —ZrO ₂ C 5 Fe ₂ O ₃ —TiO ₂ —ZrO ₂ in _{C6 WO 3 -TiO 2 -ZrO 2 C7} Ag 2 O-TiO 2 -ZrO 2 these catalysts, Mn, Cu, Ni, Co , F
The weight of e, W and Ag was 10% by weight in terms of oxide, based on the oxide carrier, and the mixing ratio of TiO ₂ and ZrO ₂ was 1 /
It is 1.

(Comparative Example 1) Comparative Example catalyst H was prepared by supporting 5% by weight of copper chloride on γ-alumina.

Example 6 For the catalysts A1 to A35 and B1 to B21 of Example, the concentration of methyl bromide was 100.
0 ppm (remaining air), H ₂ O: 20%, reaction temperature: 30
The oxidative decomposition reaction was carried out under the conditions of 0 ° C. and space velocity: 20000 / h to evaluate the performance of various catalysts.

The removal rate of methyl bromide was determined according to the following formula.

Methyl bromide removal rate (%) = (1-inlet methyl bromide concentration / outlet methyl bromide concentration) × 100 Table 1, Table 2 and Table 3 show.

[0037]

[Table 1]

[0038]

[Table 2]

[0039]

[Table 3]

Example catalysts A1 to A35 (Table 1), B1 to
It was confirmed that B21 (Table 2) and C1 to C7 (Table 3) had higher methyl bromide decomposition activity than Comparative Catalyst H.

Example 7 The same method as in Example 6 was carried out except that hydrogen peroxide was used instead of steam. (Example 8) Using the catalysts A1, B1 and C1 of Example, the reaction temperature was set to 250 ° C and 3 by the experimental method of Examples 6 and 7.
The removal rates at 00 ° C and 350 ° C were obtained. The result is shown in FIG. As is clear from the figure, it was confirmed that the removal performance of methyl bromide was high even when the reaction temperature was changed.

(Example 9) Example catalysts A1, B1, C1
Using the above, the removal rate of methyl bromide was determined by changing the space velocity to 20000 / h, 40000 / h, 60,000 / h by the experimental method of Examples 6 and 7. The result is shown in FIG. As is clear from the figure, it was confirmed that the removal performance of methyl bromide was high even if the conditions were changed.

Example 10 The following photocatalyst was obtained as a catalyst used in the decomposition step in Example 1. In Example photocatalyst _{L1 TiO 2 -Fe 2 O 3 L2} TiO 2 -ZnO L3 TiO 2 -WO 3 L4 TiO 2 -CdS L5 TiO 2 -GaP these catalysts, Fe, Zn, W, CdS , Ga
The weight of P is 10% by weight in terms of TiO ₂ .

Comparative Example 2 TiO ₂ was used as a comparative example photocatalyst LH
And

(Example 11) Methyl bromide concentration of the photocatalysts L1 to L5 of the examples and the photocatalyst LH of the comparative example: 100
0ppm (remaining air), H ₂ O concentration: 1%, reaction temperature: 27 ° C
The model gas was filled in a reaction vessel of 50 liters (400 mm in height, 400 mm in width, and 300 mm in depth) under the above conditions.
Irradiation with a light source having a wavelength of about 300 nm was performed to evaluate the performance of various catalysts from the reduction rate of methyl bromide. It was confirmed that the photocatalysts A1 to E1 of the example shown in FIG. 5 had higher methyl bromide decomposition activity than the comparative photocatalyst F1.

(Example 12) In Example 1, the following absorbents were prepared as the absorbent used in the post-treatment process.

Example Absorbent 1 NaOH solution 2 KOH solution 3 Na ₂ CO ₃ solution 4 K ₂ CO ₃ solution 5 Ca (OH) ₂ solution In these absorbents, the concentration of the absorbent is 10% by weight.

(Example 13) In the absorbent of Example, the absorption rate of hydrogen bromide was determined by the sparger method with the absorbing solution temperature set at 25 ° C by the experimental method of Example 4. The results are shown in Table 4.

[0049]

[Table 4]

As is clear from the results in the table, it was confirmed that the absorption rate was high in all cases.

[0051]

According to the present invention, waste gas is purified by removing methyl bromide at a high decomposition rate.

[Brief description of drawings]

FIG. 1 is a block diagram of an apparatus showing the present invention.

FIG. 2 is a block diagram of an apparatus showing the present invention.

FIG. 3 is a characteristic diagram showing reaction temperature and methyl bromide removal performance by various catalysts.

FIG. 4 is a characteristic diagram showing space velocity and methyl bromide removal performance by various catalysts.

FIG. 5 is a characteristic diagram showing methyl bromide removal performance by various photocatalysts.

[Explanation of symbols]

1 ... Waste gas, 2 ... Steam, hydrogen peroxide, ozone, air,
Oxygen, 3 ... Decomposition step, 4 ... Post-treatment step, 5 ... Purified gas.

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁶ Identification number Internal reference number FI Technical display location F23G 7/06 J B01D 53/86 ZAB C10L 3/10 (72) Inventor Akira Kato Hitachi City, Ibaraki Prefecture 7-1-1 Omika-cho Hitachi Ltd. Hitachi Research Laboratory (72) Inventor Akio Tanaka 1-1-14 Kanda, Chiyoda-ku, Tokyo

Claims (8)

[Claims] 1. A decomposition step of adding at least one of hydrogen peroxide and ozone to a methyl bromide-containing gas to decompose it on a catalyst, and a post-treatment step of absorbing or adsorbing a gas component produced from the decomposition step. A method for purifying waste gas, which comprises: 2. A gas containing methyl bromide, air and oxygen,
One or more selected from the group of titania, silica, zirconia, magnesia, zeolite as the first component and manganese, copper, nickel, cobalt, iron, tungsten, silver, platinum, gold, palladium, zinc, cadmium sulfide as the second component, A waste gas purification method comprising: a decomposition step of decomposing on a catalyst containing at least one selected from the group consisting of gallium and phosphorus, and a post-treatment step of absorbing or adsorbing a product gas from the decomposition step. 3. The waste gas purification method according to claim 1, wherein the addition molar ratio of hydrogen peroxide and ozone to methyl bromide is 1 or more. 4. The catalyst according to claim 1, wherein the catalyst used in the decomposition step is titania, silica,
One or more selected from the group of zirconia, magnesia, and zeolite, and the second component selected from the group of manganese, copper, nickel, cobalt, iron, tungsten, silver, platinum, gold, palladium, zinc, cadmium sulfide, gallium, and phosphorus. A method for purifying waste gas containing one or more oxides. 5. The waste gas purification system according to claim 1 or 2, wherein light is irradiated in the decomposition step. 6. The method according to claim 1, 2, 3, 4 or 5.
The content of manganese, copper, nickel, cobalt, iron, tungsten, silver, platinum, gold, palladium, zinc, cadmium sulfide, gallium, and phosphorus as the second components with respect to the titania, silica, zirconia, magnesia, and zeolite is 0.5. A method for purifying waste gas, which is at least wt%. 7. The adsorbent or adsorbent used in the post-treatment step according to claim 1, 2, 3, 4, 5 or 6, wherein sodium hydroxide, potassium hydroxide, sodium carbonate, potassium carbonate, water is used. Waste gas purification method using one or more selected from calcium oxide, calcium carbonate, calcium oxide, aqueous ammonia, and activated carbon. 8. The method of purifying waste gas according to claim 1, 2, 3, 4, 5, 6 or 7, wherein a part of the gas produced at the outlet of the post-treatment process is recycled to the preceding stage of the decomposition process.