JPH11104461A - Treatment of hazardous gas by using photocatalyst - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enable a treatment wherein an operation for separation and recovery of a photocatalyst is unnecessary by a method wherein purification treatment of a gas to be treated contg. odorants such as sulfur compd., nitrogen compd. and aldehydes and hazardous ingredients such as org. chlorine compd. is performed by bringing it into contact with a suspension liq. contg. photocatalyst particles under irradiation with light. SOLUTION: A gas to be treated contg. hazardous ingredients is fed from the bottom of a cleaning tower 2 through a line 1 for the gas to be treated and, on the other hand, a suspension liq. 3 suapended with photocatalyst particles is fed from the top of the cleaning tower 2 to bring it into contact with the gas to be treated. Then, the suspension liq. 3 is discharged from the bottom of the cleaning tower 2 and is circulated to the top of the cleaning tower 2 by means of a pump. In this instance, in the intermediate part of the cleaning tower 2, it is irradiated with light by means of a light irradiating lamp 4 and the hazardous ingredients in the gas to be treated are absorbed into the suspension liq. 3 under this irradiation with light and, at the same time, photocatalytic reaction is performed on the surface or the photocatalyst particles in the suspension liq. 3 to decompose the hazardous ingredients. Water is used as the suspension liq. and the hazardous ingredients absorbed in the suspension liq. 3 are decomposed or transformed into carbon dioxide or acids and are dissolved into the suspension liq. 3.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a harmful gas treatment method for decomposing and removing harmful components in a gas to be treated by photocatalytic action of photocatalytic particles.

[0002]

2. Description of the Related Art Harmful components present in a gas to be treated, such as sulfur compounds (hydrogen sulfide, methyl mercaptan, methyl sulfide, methyl disulfide, dimethyl disulfide, etc.), nitrogen compounds (ammonia, amines, etc.), aldehydes Removes many odorous components such as aldehydes (formaldehyde, acetaldehyde, etc.), ketones (acetone, etc.), alcohols (methanol, ethanol, etc.), organic chlorine compounds and other harmful components which have recently become a problem due to carcinogenicity. As a method of performing the method, a method of adsorbing and removing harmful components with activated carbon or a washing method of absorbing harmful components with an absorbing solution containing an acid, an alkali, or an oxidizing agent is typically known.

In the above-mentioned method using activated carbon, the adsorbing ability is lost when the amount of adsorption approaches saturation, so that the activated carbon needs to be regenerated. Further, in the cleaning method using the absorbing solution, the absorption rate decreases when the gas is dissolved and approaches the saturation, and eventually the absorbing ability is lost. Therefore, there is a problem that the replenishment of the absorbing solution and the post-treatment of the absorbing solution are required. is there.

On the other hand, in recent years, there has been proposed a method of decomposing and removing harmful components in a gas to be treated using a photocatalyst. In this method, the gas to be treated containing harmful components is brought into direct contact with the photocatalyst while irradiating the photocatalyst with light, and the harmful components are decomposed (mainly oxidatively decomposed) on the catalyst surface. There is a processing method.

[0005] The first treatment method using a photocatalyst is a method in which a gas to be treated is brought into contact with a gas to be treated under light irradiation in a form in which the photocatalyst is fixed on the surface of the carrier so as to eliminate the operation of recovering the photocatalyst.

In a second treatment method using a photocatalyst, a particulate photocatalyst is filled in a light-transmissive container (reactor) such as quartz glass, and a gas to be treated is introduced into the reactor while irradiating light from the outside. Is supplied and processed.

In the first processing method, photocatalyst fine particles (for example, TiO ₂ ) are used as a plate-like, honeycomb-like, or fiber-like support material (for example, a glass material such as quartz glass, ceramic, etc.) using a binder such as water glass. The immobilized catalyst obtained by applying to the surface of the above (2) and then firing is used. As described above, in the first treatment method, there is a disadvantage that the operation of supporting the photocatalyst is complicated and the cost for the photocatalyst is expensive. In addition, the surface area of the obtained photocatalyst is reduced as compared with the particle form. Thus, there is a problem that the decomposition efficiency is remarkably reduced. In addition, there is a problem of a lifetime such that the photocatalyst component is separated from the support material.

In the second processing method, since light is supplied from the outside of the reactor, light cannot reach the inside of a large-sized apparatus (reactor), and it is difficult to supply light to the inside of the reactor. Therefore, it is naturally limited to a very small reactor, and is not practical.

[0009]

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to solve the above-mentioned problems. Specifically, the present invention does not require an operation of separating and recovering a photocatalyst, and furthermore, does not need to carry a photocatalyst. Another object of the present invention is to provide a method for treating harmful gases using a photocatalyst having a high catalytic activity, which enables the photocatalyst to be used as fine particles having a large surface area.

[0010]

Means for Solving the Problems In order to solve the above-mentioned problems, a first method for treating harmful gas of the present invention comprises:
Purification treatment is performed by bringing a gas to be treated containing harmful components into contact with a suspension containing photocatalyst particles under light irradiation.

In the second method for treating harmful gases of the present invention, the gas to be treated containing harmful components is brought into contact with a suspension containing photocatalyst particles to absorb the harmful components, and then the suspension is subjected to light irradiation. And performing a purification treatment.

In each of the above-mentioned inventions, the gas to be treated containing the harmful component is brought into contact with the suspension containing the photocatalyst particles so that the gas to be treated containing the harmful component is brought into contact with the suspension during the contact with the suspension. The harmful components migrate into the suspension and become clean gas. On the other hand, the harmful components are detoxified by being absorbed in the suspension and simultaneously undergoing a photocatalytic reaction, or the harmful components are detoxified by the photocatalytic reaction after being absorbed by the suspension.

In the above method of treating harmful gases according to the present invention, the suspension is treated as a clean gas and the gas treated by contact with the gas containing harmful components is immediately separated, so that the remaining suspension is removed. The liquid is again available for absorption of the gas to be treated containing harmful components and for photocatalytic reactions. Therefore, by circulating the separated suspension and reusing it, efficient harmful gas treatment becomes possible.

In the method for treating a harmful gas according to the first aspect of the present invention, the form in which the suspension is subjected to light irradiation is a droplet, so that the light irradiation efficiency is increased, and therefore, the catalytic reaction efficiency is increased. Desirable in point.

In each of the above-described harmful gas treatment methods of the present invention, the suspension contains a chemical for absorbing harmful components in the gas to be treated, a chemical for promoting a photocatalytic reaction, or a chemical for cleaning the inside of the apparatus. The addition promotes the transfer of the harmful components in the gas to be treated to the suspension in the contact between the suspension and the gas containing the harmful components, and purifies the gas to be treated. Alternatively, it is preferable to enhance the cleaning effect of the light irradiation device and perform efficient light irradiation.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG.
And a conceptual diagram of the harmful gas treatment apparatus shown in FIG.

FIG. 1 is a conceptual diagram of a harmful gas processing apparatus for performing a first method of the present invention relating to a method of processing harmful gases. In the harmful gas treatment apparatus shown in FIG. 1, a gas to be treated containing a harmful component is supplied from a lower portion of the washing tower 2 through a gas line 1 to be treated. On the other hand, the suspension 3 in which the photocatalyst particles are suspended is supplied from the upper portion of the washing tower 2, falls as droplets, and comes into contact with the gas to be treated supplied from the lower portion in a flowing state. The washing tower 2 can be, for example, any of a spray tower, a perforated plate tower, a packed tower, a Venturi scrubber tower, or a combination thereof. It is discharged and supplied to the upper part of the washing tower 2 by a pump and circulated.

Reference numeral 5 denotes a power supply for the light irradiation lamp 4, which is irradiated with light from the light irradiation lamp 4 in an intermediate portion of the washing tower 2. Under this light irradiation, the harmful components in the gas to be treated are absorbed by the suspension 3 in the form of droplets, and at the same time, a photocatalytic reaction is performed on the surface of the photocatalyst particles in the suspension 3 to decompose the harmful components.

Water can be usually used for the suspension 3, but it may be used for the purpose of absorbing harmful components in the gas to be treated, promoting the photocatalytic reaction, or cleaning the inside of the apparatus if necessary. Then, an agent such as an acid, an alkali, and hydrogen peroxide may be added.

The processing gas from which the harmful components have been removed is discharged into the atmosphere via a processing gas line 6 directly or, if necessary, via an activated carbon adsorption tower (not shown). The harmful components absorbed in the suspension 3 are mainly decomposed or converted into carbon dioxide or acid and dissolved in the suspension 3, so that the regeneration of the suspension 3 usually requires only a neutralization operation. Although no operation is required, the water to be treated has a large amount of water and condenses to form a suspension 3
When the amount of water increases or when the suspension 3 becomes contaminated, it is supplied to the catalyst recovery unit 8 through the suspension treatment line 7 and purified by sedimentation, centrifugation or membrane separation.

FIG. 2 is a conceptual diagram of a harmful gas treatment apparatus for performing a second method of the present invention relating to a method of treating harmful gases. In the harmful gas treatment apparatus shown in FIG. 1, an example is shown in which light is supplied to the gas to be treated and droplets falling in the washing tower 2, but the harmful gas treatment apparatus shown in FIG. (Catalyst suspension), and the harmful gas can be treated in the same manner as in FIG. 1 except that light irradiation is performed in the suspension 3. That is, the gas to be treated is the gas line 1 to be treated.
The washing tower 2 is supplied to the lower part of the washing tower 2 through the washing tower 2 (the washing tower 2 is shown as an example of a packed tower type). 9, irradiated with light, and decomposed by a photocatalytic reaction.

The light irradiation reactor 9 contains an acid, an alkali, and
A chemical such as hydrogen peroxide may be added, or air or ozone may be supplied. The treated gas is released directly to the atmosphere via the treatment gas line 6 or, if necessary, via an activated carbon adsorption tower (not shown). Although the light irradiation reactor 9 is installed separately from the washing tower 2 in the harmful gas treatment apparatus of FIG. 2, the light irradiation reactor 9 may be provided continuously at the bottom in the washing tower 2.

The photocatalyst used in the harmful gas treatment method of the present invention includes oxides such as titanium dioxide, zinc oxide and tungsten trioxide; metal sulfides such as cadmium sulfide and zinc sulfide; and platinum, gold and palladium. And the like can be used. Alternatively, a porous material having a large specific surface area, such as alumina, silica, or activated carbon, having an adsorptive power and having the photocatalytic component such as titanium dioxide supported on the surface thereof may be used.

In general, titanium dioxide fine particles which are relatively inexpensive and easy to handle without toxicity are preferably used as a photocatalyst in the present invention. The finer the particle size of the photocatalyst, the larger the surface area and the greater the catalytic activity. Usually, a photocatalyst having a particle size of 0.01 μm to several mm is used. The amount of the photocatalyst in the dispersion is 0.1 to 50 g / l, preferably about 0.5 to 10 g / l.

The light irradiated in the harmful gas treatment method of the present invention can be used as long as it contains a wavelength (visible and / or ultraviolet light) that excites a semiconductor substance (a photocatalytic component such as titanium dioxide) to be used. As a typical light source, a low-pressure mercury lamp, a high-pressure mercury lamp, a xenon lamp, sunlight, excimer laser light, or the like can be used.

[0026]

【Example】

[Example] Air containing 5 ppm of hydrogen sulfide was supplied from a lower part of a spray tower type washing tower (made of quartz glass, an inner diameter of 100 mm, a tower height of 2 m) as shown in FIG. Titanium dioxide (particle size: about 10 μm) 5
Water having a pH of about 6 containing g / l was circulated and supplied at a rate of 0.3 liter per minute, and the water was continuously treated for 10 days.

Light was supplied from a low-pressure mercury lamp (20 W, four tubes) installed on the outer wall in the middle of the quartz glass washing tower. As a result, the removal rate of hydrogen sulfide in the processing gas discharged from the outlet of the washing tower was 95% or more in all the test periods.

Comparative Example A treatment was performed under the same conditions as in the above example except that no catalyst was added and no light irradiation was performed. As a result, the removal rate of hydrogen sulfide in the processing gas discharged from the outlet of the washing tower was 70 to 80% at the beginning of the test, but decreased with time, and decreased to 20% or less after 10 days.

[0029]

According to the method for treating harmful gas using a photocatalyst of the present invention, the following effects are obtained. Since the photocatalytic component is used as suspension particles in a suspension without immobilization, that is, the photocatalytic component is used while exposing the surface having catalytic activity, the catalytic activity is high, and the photocatalytic Since there is no need for processing for fixing, the cost can be reduced. In addition, since the photocatalyst is not fixed, there is no problem such as peeling or deterioration of the photocatalyst from the support material.

Since the photocatalyst is circulated as suspended particles in the suspension, the photocatalyst does not usually need to be separated and recovered.

In the conventional method of irradiating light by filling a packed tower with a photocatalyst, there is a problem that the irradiated light does not reach the inside only on the outermost surface of the packed tower and the catalytic reaction is not uniformly performed. However, when irradiating the droplets of the suspension containing the photocatalyst particles of the present invention with light, the light can reach the inside and the photocatalytic reaction can be efficiently performed.

Since the photocatalyst particles are used in droplets or in a liquid, the gas to be treated or a poisoning component which is a decomposition product of the gas to be treated does not come into direct contact with the photocatalyst. As compared with the conventional method of treating harmful gas which comes into direct contact with the harmful gas, the photocatalyst is prevented from being poisoned, and there is no problem of lowering the catalytic activity.

The harmful components in the gas to be treated absorbed by the suspension containing the photocatalyst particles are converted into harmless components such as carbon dioxide by photocatalysis and released into the gas phase, or converted into another substance such as an acid. As it is converted, the suspension is constantly capable of absorbing harmful components in the fresh gas to be treated. Therefore, the absorption speed of the harmful component is high, and the suspension which has absorbed the harmful component is constantly regenerated. Therefore, the operation of regenerating the suspension is not usually required.

[Brief description of the drawings]

FIG. 1 is a conceptual diagram of a harmful gas treatment apparatus for performing a first method of the present invention relating to a method of treating harmful gases.

FIG. 2 is a conceptual diagram of a harmful gas treatment apparatus for performing a second method of the present invention relating to a method of treating harmful gases.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Gas line to be processed 2 Cleaning tower 3 Suspension 4 Light irradiation lamp 5 Power supply 6 Processing gas line 7 Suspension processing line 8 Catalyst recovery device 9 Light irradiation reactor

Claims (5)

[Claims] 1. A method for treating harmful gas, comprising purifying a gas to be treated containing harmful components by bringing it into contact with a suspension containing photocatalyst particles under light irradiation. 2. A gas to be treated containing a harmful component is brought into contact with a suspension containing photocatalyst particles to absorb the harmful component,
Thereafter, the suspension is irradiated with light for purification treatment. 3. The harmful gas treatment method according to claim 1, wherein the suspension used for purifying the gas to be treated containing harmful components is circulated and used again for purification treatment. 4. The harmful gas processing method according to claim 1, wherein the suspension is subjected to light irradiation in the form of droplets. 5. The suspension according to claim 1, wherein an agent for absorbing harmful components in the gas to be treated and / or an agent for promoting a photocatalytic reaction are added to the suspension. The harmful gas treatment method described in the above.