JP3256660B2 - Purification method of ammonia-containing exhaust gas - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for detoxifying harmful ammonia contained in various kinds of exhaust gas by oxidizing and decomposing it into nitrogen gas and water. High-concentration ammonia-containing gases include exhaust gas from various chemical plants, urban cleaning facilities,
Ammonia stripping exhaust gas from an exhaust gas absorbing liquid of a sludge treatment facility or a reaction waste liquid of various chemical factories is exemplified.

[0002]

2. Description of the Related Art As a method of treating an ammonia-containing exhaust gas, a method of forming ammonium sulfate using a dilute aqueous sulfuric acid solution has been known for a long time. However, this method cannot be discharged as it is and requires further processing. In addition, profitability has recently become unsuitable even in places where it has been collected so far, and the ammonia stripping process is being switched.

[0003] Ammonia stripping is a useful method for reducing the total nitrogen concentration in various wastewaters, and has recently been particularly studied as a technique for preventing eutrophication of lakes and marshes and enclosed sea areas. When the method is used, it is necessary to detoxify the ammonia-containing gas emitted from the wastewater. As a method for treating ammonia gas, there are a burner combustion method and a catalytic method. As a treatment method using a catalyst,
A processing apparatus as shown in FIG. 5 is often used. This is a method in which a raw gas is diluted with air, heated to a predetermined temperature by a heater or the like, and then ammonia is decomposed by a single-stage oxidation catalyst.

[0004]

In the method for detoxifying ammonia using the one-stage catalyst, it is possible to use a relatively low concentration of ammonia at the catalyst inlet of 1% by volume or less. Must be diluted with a large amount of air to reduce the size of the device,
Accordingly, construction costs were also high.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a high-concentration exhaust gas whose ammonia content in a gas to be treated exceeds 1% by volume. However, another object of the present invention is to provide a purification method capable of decomposing this efficiently and rendering it harmless.

[0006]

A purification method according to the present invention, which can solve the above-mentioned problems, is a method of treating a high-concentration ammonia-containing exhaust gas containing oxygen having a theoretical oxygen amount or less in a reactor filled with a catalyst. After dividing into two stages and reducing the amount of ammonia corresponding to the supplied oxygen amount by reacting under the condition of the theoretical oxygen amount or less in the previous stage, air is blown at least over the theoretical oxygen amount to the remaining ammonia amount, and the temperature is reduced. Is reduced to a predetermined temperature, and is introduced into a subsequent reactor.

Further, a part of the ammonia-containing gas discharged by reacting under the condition of less than the theoretical oxygen amount in the pre-stage reactor is recycled through the heat exchanger, and the remainder is blown with air having at least the theoretical oxygen amount, and the temperature is set to a predetermined value. It is also possible to lower the temperature and introduce it into the downstream reactor. For convenience, the gas introduced into the first reactor may be referred to as "first gas", and the gas introduced into the second reactor may be referred to as "second gas".

In carrying out the above purification method,
It is desirable that the ammonia concentration in the ammonia-containing exhaust gas be 1% by volume or more in order to sufficiently exhibit its features.

[0009] The catalyst to be filled in the pre-reactor may be an oxide of at least one element selected from the group consisting of aluminum, titanium, silicon, zirconium, cerium and iron, and / or platinum. , A catalyst containing a metal and / or oxide of at least one element selected from the group consisting of palladium, rhodium, ruthenium, iridium, manganese and copper, and preferably as component A, aluminum, titanium, silicon, zirconium, An oxide of at least one element selected from cerium and iron, and a metal and / or oxide of at least one element selected from platinum, palladium, rhodium, ruthenium, iridium, manganese and copper as a B component Is preferred, , A component: 80 to 99.99% by weight, B component: 0.01 to 20% by weight, or the catalyst is selected from cordierite, mullite, alumina, titania, and silica. It is effective to use 1 to 30% by weight of an oxide on a heat-resistant substrate.

[0010] The catalyst to be charged into the latter reactor may be an oxide of at least one element selected from the group consisting of aluminum, titanium, silicon and zirconium, and / or a group consisting of vanadium, tungsten, cesium and iron. Catalyst containing an oxide of at least one element selected and / or a metal and / or oxide of at least one element selected from the group consisting of platinum, palladium, rhodium, ruthenium, iridium, manganese, chromium, and copper Preferably, as the component A, an oxide of at least one element selected from aluminum, titanium, silica, and zirconium, and as the component B, at least one element selected from vanadium, tungsten, cesium, and iron Oxide and C As a minute, platinum, palladium,
It is preferably composed of a metal and / or oxide of at least one element selected from rhodium, ruthenium, iridium, manganese, chromium, and copper. Particularly, A component: 70 to 99% by weight, B component: 0.5 ~ 3
Those containing 0% by weight and C component: 0.001 to 20% by weight are effective.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described more specifically.

FIG. 1 shows a diagram of an apparatus that can be used in the purification method according to the present invention. First, the gas containing ammonia is adjusted to be less than the theoretical oxygen amount shown below. If necessary, it is adjusted by adding an oxygen-containing gas such as air. The adjusted gas (pre-stage gas) is introduced into the reactor 1, and ammonia is decomposed into nitrogen and water with less than the theoretical oxygen amount. Next, oxygen is added to the gas discharged from the reactor 1 (the former reactor) so as to have the theoretical oxygen amount or more, and this gas (the latter gas) is supplied to the reactor 2 (the latter reactor). Introduce the remaining ammonia into nitrogen and water.

When the ammonia-containing gas contains water vapor, the water vapor may be condensed. In order to prevent this, when introducing the gas into the reactor, the gas is heated in advance or the introduced oxygen is removed. The contained gas may need to be dried. For example, a heater is used to heat the ammonia-containing gas and then introduce the gas into the reactor. FIG. 2 shows a case where such a heater is used. The heater does not need to be used in one step, and a plurality of heaters can be used. In FIG. 2, two heaters are used. First, a gas containing oxygen is heated to about 100 ° C. by a heater in the former stage, and a gas containing ammonia is further introduced, and then the temperature is raised to a temperature suitable for the reaction. It is introduced into the reactor.

The ammonia-containing gas can be heated by utilizing the heat of the gas generated from the reactor. FIG. 3 shows this. In this method, the former gas is heated by exchanging heat with the higher gas generated from the latter reactor and the former gas.

The ammonia-containing gas suitable for the present invention may be any gas containing ammonia and oxygen less than the stoichiometric amount. For example, an industrial exhaust gas or a gas obtained by stripping ammonia water, for example, a wastewater, may be used. The obtained gas may be used. The ammonia concentration is 1 to 10% by volume, preferably 2 to 8% by volume. If it is less than 1% by volume, it is possible to cope with a single-stage reaction, and there is no need to use the present invention. If it exceeds 10% by volume, the calorific value becomes so large that the catalyst is exposed to a high temperature, which tends to cause thermal deterioration, which is not preferable.

Incidentally, in the ammonia water vapor stripping, the ammonia gas concentration may reach about 30% by volume.
In some cases, the temperature reaches as high as ° C., which may exceed the heat resistance limit of the catalyst. Therefore, the ammonia-containing gas is diluted and used for the reaction. For example, the ammonia-containing gas can be diluted and used as a pre-gas by diluting with an inert gas such as nitrogen, air, industrial exhaust gas or the like, or by recycling the gas discharged from the pre-reactor. In FIG. 4, a part of the high-temperature gas generated from the first-stage reactor is mixed with an oxygen-containing gas, and further, an ammonia-containing gas is introduced and used as the first-stage gas. When the temperature of the gas to be recycled is high, the gas may be recycled at a low temperature using a heat exchanger.

In the case of treating a gas containing high-concentration ammonia as described above, the gas from the pre-reactor cannot be sufficiently cooled with an oxygen-containing gas, so that NOx is easily generated. It is preferable to cool the gas temperature and use it as a subsequent gas.

The ammonia concentration in the preceding gas is 1% by volume.
Above, preferably 1 to 10% by volume, more preferably,
2 to 8% by volume. When the content is less than 1% by volume, the treatment can be performed without using a plurality of reactors.
If it exceeds 0% by volume, the reaction itself is possible, but the calorific value is large and the catalyst is thermally degraded, which is not preferable. The concentration of ammonia in the latter gas is sufficient if ammonia is treated to some extent in the former reaction, but is preferably less than 1% by volume. When the ammonia concentration is high, in the second-stage reaction, the ammonia is excessively supplied and the ammonia becomes NOx in combination with the high temperature.
This is because it is easily oxidized.

The oxygen-containing gas used in the present invention is oxygen,
Air and gas containing oxygen discharged in various processes can also be used.

The theoretical oxygen content in the present invention is shown. Unless otherwise specified, the theoretical oxygen amount indicates the amount when introduced into the pre-stage reactor, and is the amount specified by the following formula.

4NH ₃ + 3O ₂ → 2N ₂ + 6H ₂ O The amount of oxygen in the pre-stage gas is less than the stoichiometric oxygen amount, preferably more than 0 times and 0.9 when the stoichiometric oxygen amount is 1.
9 times, more preferably 0.4 to 0.98 times, and 0.5 to 0.97 times, 0.6 to 0.96 times, and 0.
It is 7 to 0.95 times, most preferably 0.75 to 0.93 times. This is because if the amount of oxygen is small, the decomposition rate of ammonia is low and the effect of using the method of the present invention is low, and if oxygen is introduced in excess of the theoretical amount of oxygen, NOx is likely to be generated.

The amount of oxygen in the latter gas is introduced at a level higher than the theoretical amount of oxygen. If the amount is less than the theoretical oxygen amount, ammonia remains, which is not preferable. Therefore, it is preferable that the theoretical oxygen amount is introduced at 1 or more, more preferably at least 2 times. Usually, the temperature is set in consideration of economic efficiency based on the outlet gas temperature from the first reactor and the inlet temperature of the second reactor.

The reactor inlet temperature during exhaust gas treatment according to the present invention is 100 to 500 ° C., preferably 200 to 400 ° C. in the first stage reactor. If the temperature is lower than 100 ° C., the treatment efficiency is not sufficient. If the temperature exceeds 500 ° C., the reaction is not economical because the temperature rises. In addition, the latter reactor is 250
To 450 ° C, preferably 300 to 400 ° C. If the temperature is lower than 250 ° C., the treatment efficiency of ammonia is not sufficient, and if it is higher than 450 ° C., it is difficult to remove NOx to a high degree.

The space velocity (SV) of the catalyst according to the present invention is:
The pre-catalyst is 5000~500000Hr ^-1, preferably 10000~300000Hr ^-1. 50
If it is less than 00 Hr ⁻¹ , the processing apparatus becomes too large and inefficient, and if it exceeds 500 000 Hr ⁻¹ , the decomposition efficiency is reduced and the pressure loss is undesirably increased. In stage catalyst is 500~100000Hr ^-1, preferably 1000~50000Hr ^-1. If it is less than 500 Hr ⁻¹ , the processing device becomes too large and inefficient,
If it exceeds 000Hr ⁻¹ , the decomposition efficiency will decrease.

A plurality of reactors can be used, and when catalysts having different types and composition ratios are used, each catalyst can be charged into the reactor to precisely control the reaction.

In consideration of economy and the like, it is preferable to use one for each of the first and second reactors.

In the pre-catalyst according to the present invention, the pre-catalyst is an oxide of at least one element selected from the group consisting of aluminum, titanium, silicon, zirconium, cerium and iron, and / or platinum, palladium, rhodium, ruthenium. Containing at least one metal and / or oxide of at least one element selected from the group consisting of iridium, manganese, and copper,
A component, that is, a compound and / or oxide of at least one element selected from aluminum, titanium, silica, zirconium, cerium and iron, and B component,
That is, platinum, palladium, rhodium, ruthenium,
A metal and / or oxide of at least one element selected from iridium, manganese and copper may be simultaneously supported on a heat-resistant substrate of a crystalline oxide selected from cordierite, mullite, alumina, titania and silica. And may be carried separately.

The pre-catalyst according to the present invention contains the A component, that is, an oxide of at least one element selected from aluminum, titanium, silicon, zirconium, cerium and iron in a total amount of 80 to 99.99% by weight. What is effective is. If it is less than 80% by weight, the activity and durability of the catalyst may be insufficient, and 99.99
When the content exceeds% by weight, the activity is often insufficient.
Component B, that is, one containing a metal and / or oxide of at least one element selected from platinum, palladium, rhodium, ruthenium, iridium, manganese and copper in total of 0.01 to 20% by weight,
When the amount is less than 0.01% by weight, the activity is insufficient. When the amount exceeds 20% by weight, the effect corresponding to the high cost cannot be expected. Further, when the above catalyst is supported on a heat-resistant substrate of a crystalline oxide selected from cordierite, mullite, alumina, titania, and silica, 1 to
It is effective to carry 30% by weight, preferably 5 to 20% by weight. If it is less than 1% by weight, the activity and durability of the catalyst may be insufficient, and if it exceeds 30% by weight, the supporting strength is often insufficient.

The second-stage catalyst according to the present invention is characterized in that the second-stage catalyst is an oxide of at least one element selected from the group consisting of aluminum, titanium, silicon and zirconium, and / or a group consisting of vanadium, tungsten, cesium and iron. And / or a metal and / or oxide of at least one element selected from the group consisting of oxides of at least one element selected from the group consisting of platinum, palladium, rhodium, ruthenium, iridium, manganese, chromium, and copper. Preferably, a component A, that is, a molded body made of an oxide of at least one element selected from aluminum, titanium, silica, and zirconium, a component B shown below,
At least one compound and / or oxide selected from the component C may be supported simultaneously or separately. Further, at least one compound and / or oxide selected from the A component, the B component, and the C component may be simultaneously mixed and molded. The component A of the catalyst according to the present invention forms an oxide and / or a composite oxide. The amounts of components A, B and C shown below are 100% in total.

The second-stage catalyst according to the present invention is effective when the component A, that is, the oxide containing at least one element selected from aluminum, titanium, silica and zirconium in a total amount of 70 to 99% by weight is effective. It is a target. If it is less than 70% by weight, the activity and durability of the catalyst may be insufficient, and if it exceeds 99% by weight, the activity is often insufficient. The component A is preferably contained in the catalyst as an oxide and / or a composite oxide. In this case, a catalyst having particularly excellent activity and durability can be obtained.

The component B is preferably an oxide of at least one element selected from the group consisting of vanadium, tungsten, cesium, and iron.
Those containing 30 to 30% by weight are preferable, and those containing 2 to 15% by weight are more preferable. If it is less than 0.5% by weight, the selectivity of the catalyst is insufficient, and if it exceeds 30% by weight, the activity is often insufficient.

When the component C is platinum, palladium, rhodium,
Among ruthenium, iridium, manganese, chromium, and copper, a metal and / or oxide of at least one element selected from the group consisting of platinum, palladium, rhodium, ruthenium, and iridium, or manganese, chromium, and copper It is preferably at least one oxide of at least one element selected from the group. The catalyst contains 0.001 to 20% by weight of the C component.

Further, the C component is preferably composed of C1 and / or C2, and the C1 component is platinum, palladium, rhodium, ruthenium, iridium, manganese,
Among chromium and copper, it is a metal and / or oxide of at least one element selected from the group consisting of platinum, palladium, rhodium, ruthenium, and iridium, and the group consisting of manganese, chromium, and copper as the C2 component Oxides of at least one element selected from the group consisting of: In this case, it is preferable to contain 0.001 to 10% by weight of the C1 component and / or 1 to 20% by weight of the C2 component (the total of C1 and C2 is 0.001 to 10% by weight of the C component. 20% by weight). C as C component
When one component is contained, the activity is particularly high. However, when the content is less than 0.001% by weight, the activity is insufficient. When the content exceeds 10% by weight, an effect corresponding to high cost cannot be expected. . When a C2 component is contained as the C component, the content is preferably set to 1 to 20% by weight in order to obtain sufficient catalytic activity.

[0034] BET specific surface area of the catalyst according to the present invention, since too low a low activity, in the case of the rear catalyst, 30 m ² /
g or more, more preferably 40 m ² / g or more. In the case of a pre-catalyst which is a supported catalyst, it is usually preferably 5 m ² / g or more, although it depends on the supporting rate.

The shape of the catalyst according to the present invention is plate-like,
It may be used by shaping it into a corrugated plate, a net, a sphere, a column, a cylinder, or a honeycomb. Further, plate-like, corrugated, net-like, spherical, etc. made of cordierite, mullite, alumina, titania, silica, silica aminal, stainless steel wire mesh, etc.
It can also be used by supporting it on a columnar, cylindrical, or honeycomb heat-resistant substrate.

[0036]

The present invention will be described in more detail with reference to catalyst preparation examples, examples and comparative examples, but the present invention is not limited to these examples.

(Catalyst Preparation Example 1) 150 m ^{2 of} oxalic acid aqueous solution
/ G of γ-alumina powder having a specific surface area of / g was formed into a slurry. This was coated on a honeycomb-shaped cordierite carrier (80 mm square, 2.0 mm mesh, 0.5 mm wall thickness, 200 mm length), dried and calcined to prepare a catalyst support. The catalyst support had an Al2O3 content of 1
It was 5% by weight. This is impregnated with an aqueous solution containing platinum nitrate and palladium nitrate, dried at 100 ° C, and then dried at 450 ° C.
For 3 hours in an air atmosphere. The supported amounts of Pt and Pd of the catalyst were 0.15 and 0.15% by weight, respectively.

(Catalyst Preparation Example 2) A composite oxide composed of titania and silica was prepared by the following method. 10
After adding 35.5 kg of 20 wt% silica sol to 700 liter of wt% ammonia water and mixing with stirring, titanyl sulfate aqueous solution of sulfuric acid (125 g · TiO 2 / l, 0.5
300 liters (5 g H2SO4 / liter) was gradually added dropwise with stirring. After aging the obtained gel, washing with filtered water,
It was dried at 150 ° C. for 10 hours, and then fired at 500 ° C. for 3 hours. The resulting powder composition is TiO2: SiO2 =
4: 1 (molar ratio), and the BET specific surface area was 200 m ^2.
/ G. To 20 kg of this powder was added 12 kg of a 15% aqueous solution of monoethanolamine containing 2.00 kg of ammonium metavanadate and 0.77 kg of ammonium paratungstate. Starch was added as a molding aid and kneaded with a kneader. Outside size 80m
m square, aperture 2.8mm, wall thickness 0.5mm, length 450
mm was formed into a honeycomb shape. After drying this at 80 ° C, 4
Air calcination was performed at 50 ° C. for 6 hours. The composition of this honeycomb molded body was as follows: Ti—Si composite oxide: V 2 O 5: WO 3 = 9
0: 7: 3 (weight ratio). This molded body is impregnated with an aqueous solution of palladium nitrate, dried at 150 ° C. for 3 hours, and dried at 450 ° C. for 450 hours.
Calcination was performed in an air atmosphere at 3 ° C. for 3 hours. The composition of the catalyst thus obtained was as follows: Ti-Si composite oxide: V2 O5: WO
3: Pd = 89.5: 7: 3: 0.5 (weight ratio), BET specific surface area is 120 m ² / g, and pore volume is 0.
It was 45 cc / g.

(Catalyst Preparation Example 3) Catalyst preparation example 2 except that an aqueous solution of zirconium chloride was used instead of silica sol.
According to the formula, Ti-Zr composite oxide: V2 O5: WO3 = 9
A honeycomb molded body having a weight ratio of 0: 5: 5 was obtained. The molded body is impregnated with an aqueous solution of copper nitrate and platinum nitrate, and Ti-Zr
Complex oxide: V2O5: WO3: Cu: Pt = 85.1:
A catalyst having a composition of 4.7: 4.7: 5: 0.5 (weight ratio) was obtained. The BET specific surface area of this catalyst is 95 m ² / g.
Met. This catalyst can be used as a subsequent catalyst.

Example 1 The following experiment was conducted using the apparatus schematically shown in FIG. That is, the high-concentration ammonia-containing gas 63Nm ³ / Hr (NH 3 8
vol., H2O 92vol%) and 14.3Nm3 / Hr (0.8% of theoretical oxygen demand) air previously heated to ゛ 100 ° C. with a heater 1
And the temperature was raised to 250 ° C. by the heater 2. This mixed gas was used as the catalyst 1. obtained in Catalyst Preparation Example 1.
It was introduced into the first reactor 3 filled with 5 liters. The gas discharged from the reactor 3 was mixed with air of 76 Nm ³ / Hr (large excess of oxygen) to lower the gas temperature to 360 ° C., and then 31 liters of the catalyst obtained in Catalyst Preparation Example 2 was charged. It was introduced into the second reactor 4. At this time, ammonia in the exhaust gas was not detected, and NOx was 2 ppm.

(Comparative Example 1) The air introduced into the first reactor 3 in Example 1 was 18.8 Nm ³ / Hr (1.0% of the theoretical oxygen demand).
(5 times).

At this time, ammonia in the exhaust gas was not detected, and NOx was 10,000 ppm.

Example 2 The following experiment was performed using the apparatus schematically shown in FIG. That is, high-concentration ammonia-containing gas 10 Nm ³ / Hr (NH 3 ³⁾ generated from the steam stripping device.
0vol%, H2O 70vol%) and recycled gas 40.6Nm ³ / H
r, and air 9.7 Nm ³ / Hr (the theoretical oxygen demand of 0.9
Times) to 250 ° C. This mixed gas 60.3
Nm ³ / Hr was introduced into the first reactor 1 filled with 1.2 liters of the catalyst obtained in Catalyst Preparation Example 1. Oxygen and NOx in the gas discharged from the reactor 1 were not detected. Of this gas, 40.6 Nm ³ / Hr was cooled in the heat exchanger 2 and used as recycle. 18.4Nm air for the remaining gas
³ / Hr (large excess of oxygen)
After lowering to 0 ° C., the catalyst obtained in Catalyst Preparation Example 2 7.
It was introduced into the second reactor 3 filled with 7 liters. At this time, ammonia in the exhaust gas was not detected, and NOx was 3p
pm.

[Brief description of the drawings]

FIG. 1 is a diagram of an apparatus used in a purification method according to the present invention. (FIG. 2) One embodiment of an apparatus used in the purification method according to the present invention, which is an apparatus provided with a heater. (FIG. 3) An embodiment of the purification method according to the present invention, in which a pre-stage gas is heated by a heat exchanger using a gas after the reaction. (FIG. 4) One embodiment of the purification method according to the present invention, which is an apparatus for exchanging heat of a part of the gas after the first-stage reaction and further recycling the gas to the first-stage gas. (FIG. 5) This is an apparatus used in a conventional purification method.

──────────────────────────────────────────────────の Continued on the front page Examiner Yoshihisa Seki (58) Field surveyed (Int.Cl. ⁷ , DB name) B01D 53/86 B01D 53/94 B01D 53/34 B01J 21/00-38/74

Claims (6)

(57) [Claims] (1) When treating an ammonia-containing exhaust gas using a plurality of reactors filled with a catalyst, a reactor at a stage preceding the flow of the exhaust gas is required to decompose ammonia into nitrogen and water. The gas is treated with less than the stoichiometric oxygen amount, and the gas after passing through the pre-reactor is more than the stoichiometric oxygen amount with respect to the ammonia contained in the gas after the treatment in the former reactor in the latter-stage reactor. A method for purifying an ammonia-containing exhaust gas, which comprises treating. 2. The method according to claim 1, wherein the ammonia concentration in the ammonia exhaust gas is 1% by volume or more. 3. The method of claim 1, wherein said plurality of reactors is two. 4. The method according to claim 1, wherein a gas obtained by extracting a part of a gas after said first reactor is mixed with a gas before said reaction and introduced into said first reactor. The method of claim 1, wherein 5. The method according to claim 1, wherein the pre-catalyst comprises aluminum, titanium,
Oxides of at least one element selected from the group consisting of silicon, zirconium, cerium and iron; and / or
The method according to claim 1, further comprising a metal and / or oxide of at least one element selected from the group consisting of platinum, palladium, rhodium, ruthenium, iridium, manganese, and copper. 6. The post-catalyst comprising aluminum, titanium,
Oxide of at least one element selected from the group consisting of silicon and zirconium, and / or at least one oxide selected from the group consisting of vanadium, tungsten, cesium, and iron, and / or platinum, palladium, rhodium, ruthenium ,iridium,
The method according to claim 1, further comprising a metal and / or oxide of at least one element selected from the group consisting of manganese, chromium, and copper.