JP2006231171A - Nitrogen-oxide removing catalyst, denitrification method and denitrification apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a nitrogen-oxide removing catalyst capable of keeping a denitrification efficiency with a simple constituent, to provide a denitrification method using it and to provide a denitrification apparatus. <P>SOLUTION: The nitrogen-oxide removing catalyst 10 is composed of urea 11 and a photocatalyst 12, and nitrogen oxide (NO) in a gas containing oxygen is reduced to nitrogen while being photooxidized to NO<SB>2</SB>by a photoirradiation 13 with ultraviolet to visible rays wherein urea 11 is supported on a carrier such as a quartz wool 14. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention uses a nitrogen oxide removal catalyst that efficiently purifies nitrogen oxide contained in an atmosphere gas in an intersection, a tunnel or a closed parking lot, an exhaust gas from an internal combustion engine, and an exhaust gas from an industrial facility. The present invention relates to a denitration method and apparatus.

  The purpose of ventilation equipment in road tunnels is to ensure a clear distance mainly due to dust and to reduce harmful substances such as carbon monoxide (CO) and nitrogen oxides (hereinafter also referred to as “NOx”) to below acceptable levels. Is installed. As a current ventilation method, a method is generally used in which fresh outside air is sucked from outside the tunnel, dust is removed as necessary, and forced ventilation is performed outside the tunnel. However, this method only diffuses ventilation gas containing harmful substances to the atmosphere, and does not fundamentally improve the environment. Especially in urban areas where air pollution due to automobile exhaust gas is serious, highly contaminated areas will be expanded, which may hinder tunneling and shelter installation in road planning. Therefore, development of a new ventilation system that saves energy and does not affect the surrounding environment is desired.

However, tunnel ventilation gas NOx concentration at room temperature and large volume is less and dilute 10 ppm, since the NOx concentration variation is particularity that heavy by traffic, NH ₃ which has already been put to practical use in the process of the boiler combustion exhaust gas It is impossible to apply the NOx purification method using NO as a reducing agent.

Accordingly, various dry methods and wet methods have been proposed as low-concentration NOx purification methods, but the wet methods are difficult to put into practical use because they require a wastewater treatment apparatus. As the dry method (1) adsorption to adsorb NOx on the adsorbent such as metal oxides in contaminated air, (2) adding NH ₃ to the contaminated air by irradiating an electron beam nitrate of NOx and SOx There is an electron beam irradiation method in which fine particles such as ammonium nitrate, ammonium sulfate, and a double salt of both are collected by an electrostatic precipitator or the like by reacting with NH ₃ by reacting with NH ₃ .
However, in the electron beam irradiation method of (2), it is difficult to uniformly mix a small amount of NH ₃ equivalent to that required for the reaction with NOx contained in a trace amount of 10 ppm or less in a large volume of contaminated air. There is a risk of secondary pollution such as outflow of ₃ (Non-patent Document 1).

In general, NOx in the tunnel exhaust gas has 80 to 90% NO and ₁₀ to 20% NO2, and the applicant of the present invention as an adsorbent that efficiently adsorbs NO by the method (1) An adsorbent carrying a noble metal (Pt, Pd, Ru, Rh, Ir) has been proposed (Patent Document 1).

  However, a large amount of NO adsorbent is required to be applied to large-capacity tunnel exhaust gas treatment, and the application of noble metal is considered to be economically unsatisfactory because it causes a rise in adsorbent and depletion of resources.

For this reason, polluted air containing low-concentration nitrogen oxides is adsorbed and removed at room temperature with an adsorbent to release clean gas into the atmosphere, and NO ₂ in the nitrogen oxides is adsorbed by the NO ₂ adsorption tower and NO is removed. Adsorbed in the NO adsorption tower, then the gas introduction and exhaust valves are closed, the other valve is opened, and the adsorption tower is heated by heating means to desorb nitrogen oxides, and contains concentrated nitrogen oxides It was previously proposed that nitrogen oxides be removed by adding ammonia to the desorption gas and decomposing it into nitrogen by a denitration catalyst (Patent Document 2).

  There is also a proposal for a nitrogen oxide removing agent in which an amine such as morpholine is supported on a porous carrier (Patent Document 3).

  Therefore, the present inventors have previously proposed a nitrogen oxide removal catalyst composed of urea and a carbon material (Patent Document 4).

Industrial Pollution Prevention Association: "Survey and research on automobile exhaust gas treatment technology" (Commissioned by Japan Highway Public Corporation) March 1984, p. 49 JP-A-5-31357 JP-A-8-299756 JP-A-9-262430 JP 2004-322004 A

  However, the proposal as disclosed in Patent Document 2 requires an adsorption tower that is an adsorption means for nitrogen oxides and a heating means for increasing the temperature in order to desorb the nitrogen oxides adsorbed by the adsorption tower. In desorption, it is necessary to stop the processing of contaminated air, and there is a problem that nitrogen oxides cannot be processed continuously.

  Further, the proposal as in Patent Document 3 has a problem that morpholine is designated as a dangerous substance because it has an explosion limit and is not suitable for denitration treatment equipment at an intersection or the like. In addition, in the proposal of Patent Document 3, the denitration action of the removal agent is an adsorption / absorption action in the presence of moisture, and the denitration effect lasts only for a few hours. There is a problem that it is not suitable for maintaining the denitration effect and treatment of the absorbent is required.

  Moreover, in the proposal like patent document 4, the denitration rate is about 80-90%, and the further improvement of the denitration rate is calculated | required.

  Moreover, in recent years, regulations on environmental exhaust gas have increased, and it is desired to further purify the nitrogen oxide concentration reduced by existing ammonia denitration in exhaust gas from industrial equipment such as boiler flue gas treatment equipment. For this reason, the advent of a simple yet efficient processing apparatus attached to existing facilities is eagerly desired.

  In view of the above problems, an object of the present invention is to provide a nitrogen oxide removal catalyst capable of maintaining denitration efficiency with a simple configuration, and a denitration method and apparatus using the same.

The first invention of the present invention for solving the above-mentioned problems comprises urea and a photocatalyst, and photooxidizes nitrogen oxide (NO) in a gas containing oxygen to NO ₂ with ultraviolet or visible light. The nitrogen oxide removing catalyst is characterized by being reduced to nitrogen.

  A second invention is the nitrogen oxide removal catalyst according to the first invention, wherein urea is supported on a carrier.

  A third invention is the nitrogen oxide removal catalyst according to the second invention, wherein the supported amount of urea is 4.5% by weight or more.

  A fourth invention is the invention according to the second or third invention, wherein the carrier is activated carbon, activated carbon fiber, titanium oxide, alumina, silica gel, quartz wool, or a composite of two or more thereof. A nitrogen oxide removal catalyst characterized by

  A fifth invention is the nitrogen oxide removal catalyst according to the fourth invention, wherein the activated carbon fiber is subjected to high-temperature heat treatment in an inert gas atmosphere.

  A sixth invention is the nitrogen oxide removal catalyst according to the first invention, wherein the photocatalyst is titanium oxide.

  A seventh invention is the nitrogen oxide removal catalyst according to any one of the fourth to sixth inventions, wherein the ratio of the photocatalyst to the activated carbon fiber is 1: 0.5 to 2.0. It is in.

  According to an eighth aspect of the present invention, there is provided a denitration method characterized in that the nitrogen oxide in the gas is reduced using any one of the first to seventh nitrogen oxide removing catalysts.

  A ninth invention comprises a nitrogen oxide purifying unit having any one of the first to seventh nitrogen oxide removing catalysts and an ultraviolet or visible light irradiation unit, and denitrating nitrogen oxides in the gas. In a denitration apparatus characterized by

  A tenth aspect of the invention is the denitration apparatus according to the ninth aspect of the invention, wherein the nitrogen oxide purification unit is a mixture of a photocatalyst unit and a carrier unit supporting urea.

  An eleventh invention is characterized in that, in the ninth invention, the nitrogen oxide purifying part separates the photocatalyst part and the carrier part supporting urea and has a urea addition part in the carrier part. It is in the denitration equipment.

  A twelfth aspect of the invention is a denitration apparatus according to any one of the ninth to eleventh aspects, wherein a plurality of the nitrogen oxide purification units are provided.

  A thirteenth aspect of the invention is the denitration apparatus according to any one of the ninth to twelfth aspects, wherein dust removal means is provided on the upstream side of the nitrogen oxide purification unit.

  A fourteenth aspect of the invention is a denitration apparatus according to any one of the ninth to thirteenth aspects, wherein a desulfurization means is provided on the upstream side or the downstream side of the nitrogen oxide purification unit.

  According to a fifteenth aspect, in any one of the ninth to fourteenth aspects, the gas containing nitrogen oxide is from an atmosphere gas of a road, an intersection, a tunnel or a closed parking lot, an exhaust gas from an internal combustion engine, or an industrial facility. In the denitration apparatus, the exhaust gas is any one of the exhaust gases.

  According to the present invention, it is possible to provide a nitrogen oxide removal catalyst, a denitration method, and a denitration apparatus in a gas having good denitration efficiency.

  Hereinafter, the present invention will be described in detail with reference to the drawings. In addition, this invention is not limited by this embodiment and an Example. In addition, constituent elements in the following embodiments and examples include those that can be easily assumed by those skilled in the art or those that are substantially the same.

[Embodiment]
FIG. 1 is a schematic view of a nitrogen oxide removal catalyst. As shown in FIG. 1, a nitrogen oxide removing catalyst 10 according to the present invention includes urea 11 and a photocatalyst 12, and nitrogen oxide (NO) in a gas containing oxygen is irradiated with ultraviolet to visible light 13. Thus, it is reduced to nitrogen while being photooxidized to NO ₂ .

Here, the urea 11 may be in powder form, but is more preferably supported on a carrier such as quartz wool or activated carbon fiber (ACF). As the carrier, the activated carbon fiber is more preferable because it exhibits oxidation ability. In addition to activated carbon fiber and quartz wool, the carrier is activated carbon, titanium oxide, alumina and silica gel, or a combination of two or more of these, and further, activated carbon fiber and quartz wool. A combination is preferred.
The carrier has high urea dispersion or urea activity. Furthermore, these include those having an adsorptivity to NOx.

Here, the effect | action which purifies NO to nitrogen is demonstrated.
In FIG. 1, titanium oxide (TiO ₂ ) is used as the photocatalyst 12, and the titanium oxide uses oxygen due to the action of ultraviolet or visible light irradiation 13 to change NO to NO ₂ . This NO ₂ becomes nitrogen by the reducing action of urea 11. In FIG. 1, urea 11 is carried on quartz wool 14.

In addition, as shown in FIG. 2, when activated carbon fiber (ACF) 15 is used as a carrier, urea (CO (NH ₂ ) ₂ ) is formed in the area where micropores on the surface of activated carbon fiber are directly opened. When the support is activated and the interaction between urea and activated carbon fibers occurs, NO of nitrogen oxides reacts with urea in the presence of oxygen on the surface of activated carbon fibers and is reduced to N _2. The Alternatively, NO is oxidized to NO ₂ and reacted with urea to be reduced to N ₂ . On the other hand, NO ₂ present in the gas reacts directly with urea and is reduced to N ₂ .

Here, the amount of urea supported on the carrier is 4.5% by weight or more, preferably 10 to 40% by weight or more. This is because the denitration effect is not good at less than 4.5% by weight.
On the other hand, the upper limit of the supported amount of urea is not particularly limited, and the denitration duration increases as the supported amount increases. However, if the supported amount is too large, the surface of the activated carbon fiber is coated, resulting in an oxidation reaction (NO → NO ₂ ). About 40% by weight.

Moreover, it is preferable that the said activated carbon fiber heat-processes the said activated carbon fiber in an inert gas atmosphere so that the oxidation activity function may be improved. This high-temperature heat treatment removes some or all of the hydrophilic oxygen functional groups present on the surface of the activated carbon fiber as CO and CO ₂ , increasing the oxidation active sites and urea active sites of NO. Compared with the surface having higher hydrophobicity. As a result, approach to the oxidation active point of NO occurs easily, and the oxidation rate to NO ₂ and the reduction rate by urea are improved.

  Here, the high temperature treatment temperature of the activated carbon fiber varies depending on the carbon material, but is preferably about 600 to 1300 ° C., for example. This is because a heat treatment effect does not appear at temperatures below 600 ° C., while no further effect is exhibited even when heat treatment is performed at temperatures above 1300 ° C.

  Table 1 shows the urea content according to the presence or absence of temperature treatment on activated carbon fiber using a 3% urea solution and a 6% urea solution. Tests 1 to 3 are pitch-based activated carbon fibers, and test 1 was not heat-treated. Further, heat treatment was performed at 800 ° C. for test 2 and 1100 ° C. for test 3. Furthermore, Tests 4 to 5 are polyacrylonitrile (PAN) activated carbon fibers, and Test 4 was not heat-treated. In Test 5, heat treatment was performed at 800 ° C.

  As shown in Table 1, it was confirmed that the hydrophobicity was increased by the heat treatment and the urea content was improved.

Here, an example of the activated carbon fiber used in the catalyst layer of the present invention and an example of its production are shown below.
Examples of the activated carbon fiber used in the present invention include pitch-based activated carbon fiber, polyacrylonitrile-based activated carbon fiber, phenol-based activated carbon fiber, and cellulose-based activated carbon fiber, but the present invention is limited to these. However, the activated carbon fibers exhibiting the above catalytic action are not limited in any way.

Specific production examples are shown below.
(Production Example 1)
A pitch-based activated carbon fiber (“OG-20A”, manufactured by Adol Co., Ltd.) is used, and this is fired in a nitrogen atmosphere at a temperature of 900 to 1200 ° C. for 1 hour.
(Production Example 2)
Polyacrylonitrile-based activated carbon fiber (“FE-300”, manufactured by Toho Linux Co., Ltd.) is used, and this is fired in a nitrogen atmosphere at a temperature range of 600 to 900 ° C. for 1 hour.
(Production Example 3)
Phenol-based activated carbon fiber (“Kractive-20”, manufactured by Kuraray Chemical Co., Ltd.) is used, and this is fired in a nitrogen atmosphere at a temperature range of 900 to 1200 ° C. for 1 hour.

  Moreover, it is preferable that the ratio of the said photocatalyst and activated carbon fiber shall be 1: 0.5-2.0. This is not preferable when the amount of activated carbon fiber is 0.5 or less with respect to the photocatalyst, and the amount of urea contained in the activated carbon fiber is also reduced, which is not preferable. On the other hand, the amount of activated carbon fiber is not preferable. This is because when the ratio is 2.0 or more, a catalyst such as titanium oxide that is not exposed to light increases and is wasted.

Next, FIG. 3 shows an example of a denitration apparatus.
As shown in FIG. 3, the denitration apparatus 30 according to the present embodiment includes a nitrogen oxide removal unit 32 in which a nitrogen oxide removal catalyst 10 is filled in a denitration vessel 31, and ultraviolet or visible light in the catalyst purification unit. And a light irradiation part 33 for irradiating the nitrogen gas, and efficiently denitrating nitrogen oxides in the introduced gas G.

  At this time, as shown in FIG. 3, the nitrogen oxide purification unit 32 in the denitration vessel 31 is a mixture of the photocatalyst 12 and the quartz wool 14 or the activated carbon fiber 15 as the carrier carrying the urea 11. is there.

As shown in FIG. 4, another denitration device 36 includes a first container 37-1 filled with the photocatalyst 12 and a second container 37-2 filled with a carrier carrying urea 11 (for example, ACF15). The photocatalytic reaction and the urea reaction may be separated, and a urea addition unit 39 for adding the urea solution 38 to the second container 37-2 may be provided.
By adding this urea, the denitration ability is regenerated.

  For example, as shown in FIG. 5, the denitration devices 36A and 36B shown in FIG. 4 are provided in parallel so that the introduction of the gas G is alternately switched by the shutoff valves 40A and 40B, and the shutoff valves 40A and 40B are used. Then, the gas is purified by one denitration device 36A, and the urea solution 38 is supplied from the urea addition unit 39 to the nitrogen oxide purification unit of the denitration device 36B that does not allow the other gas to pass, so that regeneration is performed. You can do it.

  As shown in FIG. 6, the denitration apparatus 42 according to the present embodiment is provided with a plurality of denitration apparatuses (three in this embodiment) shown in FIG. 4 to denitrate nitrogen oxide in the gas G continuously. You may do it.

The nitrogen oxide in the gas can be reduced using the nitrogen oxide removing catalyst.
Furthermore, in the present embodiment, desulfurization means may be provided on the upstream side or the downstream side of the denitration apparatus so that denitration and desulfurization are performed simultaneously. Thereby, not only nitrogen oxide (NOx) but also sulfur oxide (SOx) in the gas can be efficiently purified.
Moreover, you may make it provide the soot removal apparatus which removes soot.

  Such a denitration apparatus 10 can be installed on the ground or underground such as roads (general roads and highways) and intersections, and the vicinity of the intersections can be purified.

  According to this exhaust gas treatment facility, a large amount of nitrogen oxide contained in the exhaust gas from the vehicle floating near the intersection can be efficiently and continuously denitrated. Further, since denitration can be performed at room temperature, power consumption is extremely small.

  The denitration apparatus according to the present invention is not limited to the purification of gas at the roads and intersections described above, but other than the intersections, for example, atmospheric gas in tunnels or closed parking lots, exhaust gas from internal combustion engines, industrial equipment Nitrogen oxides in the exhaust gas can be efficiently denitrated.

Examples illustrating the effects of the present invention will be described below.
<Example 1>
In this test example, 0.5 g of quartz wool (diameter 2 to 6 μm) loaded with 0.05 g of urea and 0.5 g of titanium oxide as a photocatalyst are mixed and filled into a cylindrical tube, as a simulated gas. NO was supplied at 100 ppm (flow rate: 100 ml / min). Oxygen was 21% and nitrogen was balanced. The temperature was 30 ° C. and the humidity was 0%.
For light irradiation, 352 nm black light was used.
The NO concentration in the gas discharged from the other end of the cylindrical tube was measured.

<Example 2>
In this test example, 0.5 g of activated carbon fiber with 0.116 g of urea (urea: 33.2%) and 0.5 g of titanium oxide as a photocatalyst are mixed and filled into the cylindrical tube. As a simulation gas, 100 ppm of NO was supplied (flow rate: 100 ml / min). The other conditions are the same as in Example 1.
The NO concentration in the gas discharged from the other end of the cylindrical tube was measured.
The activated carbon fiber used is pitch-based (fiber diameter: 16 to 20 μm) “OG-20A” (product name: manufactured by Adol), and is heat-treated at a high temperature (1100 ° C.) during manufacture.

<Comparative Examples 1-3>
When Comparative Example 1 uses only photocatalyst titanium oxide, and Comparative Example 2 uses “0%” that does not support urea in “Example 2”, only activated carbon fiber and urea are used. Each case was tested.

These results are shown in FIGS.
When only the photocatalyst of Comparative Example 1 was used, 100% denitration could be continued only for 6 hours as shown in FIG. Further, in the case of the photocatalyst and the activated carbon fiber of Comparative Example 2, 100% denitration could only be performed for 14 hours as shown in FIG. Furthermore, in the case of only the activated carbon fiber and urea of Comparative Example 3, as shown in FIG. 11, it could only be continued for 42 hours with 80% denitration.

On the other hand, in the case of titanium oxide and urea of Example 1, 90% denitration could be continued for 28 hours as shown in FIG.
Further, in the case of the titanium oxide and urea / activated carbon fiber of Example 2, as shown in FIG. 8, 100% denitration could continue for 100 hours and 90% denitration could continue for 170 hours.
The reason why the denitration rate is 90% or less is that the surface of titanium oxide is covered with urea and light irradiation is blocked, or the contact between titanium oxide and urea is poor.

  As described above, the nitrogen oxide removal catalyst according to the present invention efficiently removes nitrogen oxides in the gas, thereby improving the denitration efficiency and reacting at room temperature, thereby reducing the power consumption of the denitration equipment. For example, it is suitable for use at an intersection or the like to prevent environmental pollution.

It is a schematic diagram of the nitrogen oxide removal catalyst concerning this embodiment. It is a schematic diagram of the other nitrogen oxide removal catalyst concerning this embodiment. It is the schematic of the denitration apparatus concerning this embodiment. It is the schematic of the other denitration apparatus concerning this embodiment. It is the schematic of the other denitration apparatus concerning this embodiment. It is the schematic of the other denitration apparatus concerning this embodiment. 3 is a graph showing the denitration result of Example 1. 6 is a graph showing the denitration result of Example 2. 6 is a graph showing the denitration result of Comparative Example 1. 5 is a graph showing the denitration result of Comparative Example 2. 10 is a graph showing the denitration result of Comparative Example 3.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Nitrogen oxide removal catalyst 11 Urea 12 Photocatalyst 13 Light irradiation 14 Quartz wool 15 Activated carbon fiber

Claims (15)

A nitrogen oxide removal catalyst comprising urea and a photocatalyst, wherein nitrogen oxide (NO) in a gas containing oxygen is reduced to nitrogen while being photooxidized to NO ₂ by ultraviolet or visible light. In claim 1,
A catalyst for removing nitrogen oxide, wherein urea is supported on a carrier. In claim 2,
A supported catalyst for removing nitrogen oxide, wherein the supported amount of urea is 4.5% by weight or more. In claim 2 or 3,
The nitrogen oxide removal catalyst, wherein the carrier is activated carbon, activated carbon fiber, titanium oxide, alumina, silica gel, quartz wool, or a composite of two or more thereof. In claim 4,
A nitrogen oxide removing catalyst, wherein the activated carbon fiber is subjected to a high temperature heat treatment in an inert gas atmosphere. In claim 1,
A nitrogen oxide removing catalyst, wherein the photocatalyst is titanium oxide. In any one of Claims 4 thru | or 6,
The ratio of the said photocatalyst and activated carbon fiber is 1: 0.5-2.0, The nitrogen oxide removal catalyst characterized by the above-mentioned.   A denitration method comprising reducing the nitrogen oxide in the gas using the nitrogen oxide removing catalyst according to any one of claims 1 to 7.   A denitration system comprising: a nitrogen oxide purification unit having the nitrogen oxide removal catalyst according to any one of claims 1 to 7; and an ultraviolet ray or visible light irradiation unit, wherein the nitrogen oxide in the gas is denitrated. apparatus. In claim 9,
A denitration apparatus, wherein the nitrogen oxide purification unit is a mixture of a photocatalyst unit and a carrier unit supporting urea. In claim 9,
A denitration apparatus, wherein the nitrogen oxide purifying part separates the photocatalyst part and the carrier part supporting urea and has a urea addition part in the carrier part. In any one of Claims 9 thru | or 11,
A denitration apparatus comprising a plurality of the nitrogen oxide purification sections. In any one of claims 9 to 12,
A denitration apparatus comprising dust removal means provided on the upstream side of the nitrogen oxide purification unit. In any one of Claims 9 thru | or 13,
A denitration apparatus characterized in that a desulfurization means is provided on the upstream or downstream side of the nitrogen oxide purification unit. In any one of Claims 9 thru | or 14,
The denitration apparatus, wherein the gas containing nitrogen oxide is any one of an atmosphere gas in a road, an intersection, a tunnel or a closed parking lot, an exhaust gas from an internal combustion engine, and an exhaust gas from an industrial facility.

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