JP2001029946A - Photocatalytic reaction tube - Google Patents

Abstract

(57) [Problem] To improve oxidative decomposition efficiency while suppressing fluid resistance of a photocatalytic reaction tube. SOLUTION: Inside a reaction tube case 1, a partition wall 13a fixed to the inner wall of the reaction tube case 1 and arranged at a distance from the protection tube 7; Partition wall 13 arranged at an interval from inner wall 1
b are arranged. The partition walls 13a and 13b are arranged alternately, and their surfaces are coated with titanium dioxide as a photocatalyst. For the fluid sample, the sample inlet 3
And flows through the inside of the reaction tube case 1 while meandering by the partition walls 13a and 13b, during which it is oxidized by a photocatalyst.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a flow-type photocatalytic reaction tube in which a light source is disposed at the center of a cylindrical reaction tube case, and a fluid flows between the reaction tube case and the light source. Such a photocatalyst reaction tube is applied to the purification of the environment such as air, water, and soil, and is used to purify a contaminated fluid by oxidizing the fluid with a photocatalyst. It is important for the action of the photocatalyst that the photocatalyst is effectively irradiated with light and that the surface area of the photocatalyst to be irradiated with light is large.

[0002]

2. Description of the Related Art In recent years, photocatalysts have been developed around the world for the purpose of pollution, sterilization, deodorization, purification, etc. due to their strong oxidizing power. The shape of titanium dioxide often used as a photocatalyst is powdery in nature. However, since the application range is limited in the form of powder, a technique for applying the powder to an object has been rapidly developed. For example, there are a technique of applying or kneading a photocatalyst to the surface of beads or fibers made of glass or ceramic and baking it, a technique of applying a photocatalyst to the surface of metal or resin, and microencapsulation of the photocatalyst with paint or resin. These technologies include deodorizing honeycomb filters for air purifiers, partition walls for removing NOx on highways, indoor tiles and paints for antibacterial use,
It is used and realized in new markets such as fibers. These applications are consumer applications that utilize the natural contact of the contaminated fluid with the photocatalyst, and do not specifically use reaction tubes.

[0003] However, in business applications that require forcible purification, a photocatalytic reaction tube is required. And, a structural design with good reaction efficiency is an important factor in reducing the apparatus cost and the running cost. Conventionally, a photocatalyst is applied to the surface of a carrier such as a glass cloth or ceramic sphere, and the carrier is filled in a reaction tube case in which a light source is arranged in the center,
Fluid was flowing through the gap between the photocatalysts filled around the light source. Further, a powdery photocatalyst is circulated around a light source together with a fluid, and after the reaction, the photocatalyst is removed by a filter.

[0004]

In the above prior art,
Light from a light source is absorbed by a carrier such as glass, ceramic, or metal, and the photocatalyst is not effectively irradiated with light. As a result, a photocatalytic reaction tube with low efficiency of oxidative decomposition by the photocatalyst has been configured. In addition, a photocatalytic reaction tube filled with a carrier such as a powdery photocatalyst or a glass bead having a photocatalyst coated on the surface has a problem that the fluid resistance is large and a load is imposed on the pump and the piping. Due to these inconveniences, when a photocatalytic reaction tube is provided for application to environmental purification, the apparatus is expensive and has not been widely used. Therefore, an object of the present invention is to provide a photocatalytic reaction tube capable of improving oxidative decomposition efficiency while suppressing fluid resistance in the photocatalytic reaction tube.

[0005]

According to a first aspect of the present invention, there is provided:
A flow-type photocatalytic reaction tube in which a light source is disposed at a central portion of a cylindrical reaction tube case, and a fluid flows between the reaction tube case and the light source. A plurality of partitions are arranged in a direction perpendicular to the axis of the reaction tube case so as to alternately flow from the inside to the inner wall side of the reaction case in a stepped manner, and a photocatalyst is formed on the surface of the partition.

A second aspect of the present invention is a flow-type photocatalytic reaction tube in which a light source is arranged at the center of a cylindrical reaction tube case, and a fluid flows between the reaction tube case and the light source. A spiral partition is arranged around the light source so as to flow spirally around the light source, and a photocatalyst is formed on the surface of the partition.

In any of the embodiments, light from a light source is applied to the surfaces of all the photocatalysts formed on the surface of the partition. Thereby, the light from the light source is irradiated on the photocatalyst without being absorbed by the carrier or the like, and the photocatalytic effect is improved. Further, the fluid sample flows along the step-like partition or the spiral partition while contacting the photocatalyst formed on the surface of the partition, so that the contact area between the fluid sample and the photocatalyst increases. Furthermore, since there is no filler such as a carrier even when the flow path in the reaction tube case becomes long, the fluid resistance is small, the specifications of the pump and piping are loosened, and the cost is reduced.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A preferred example of the photocatalyst is titanium dioxide, and the light source preferably emits ultraviolet light having a wavelength of 400 nm or less. The light source that generates such ultraviolet light may be a black light widely used for a photocatalyst, but a more efficient low-pressure mercury lamp capable of generating ozone is preferable. When the fluid sample is irradiated with ultraviolet rays, the following reaction occurs, and oxygen atoms and ozone are generated in the fluid sample. The oxygen atoms and ozone promote the oxidation of pollutants together with the action of the photo-oxidation catalyst comprising titanium dioxide. O ₂ + UV (185 nm) → 2O O + O ₂ → O ₃ O ₃ + UV (254 nm) → O + O ₂ Oxygen atoms and ozone have oxidizing power together with the oxidizing action of the photocatalyst, so that the photochemical oxidative decomposition efficiency can be further improved. .

At least a part of the inner wall of the reaction tube case is
It is preferably a light reflecting surface. As a result, the light from the light source is effectively used until it is absorbed by the photocatalyst, and the photocatalytic effect is maximized. It is preferable that the surface of the partition is formed in an uneven shape. As a result, the surface area of the photocatalyst increases, and the photocatalytic effect is further improved.

[0010]

FIG. 1 shows an embodiment of the first aspect (embodiment 1).
FIG. A cylindrical reaction tube case 1 made of stainless steel and sealed at both ends is provided so that the axial direction is vertical. A sample inlet 3 is provided at the lower end of the side wall of the reaction tube case 1, and a sample inlet 3 is provided at the upper end. A sample outlet 5 is provided on the side. The dimensions of the reaction tube case 1 are as follows:
The length is 250 mm. A protective tube 7 made of quartz glass is arranged around the central axis of the reaction tube case 1, and a low-pressure mercury lamp 9 is arranged on the central axis inside the protective tube 7. The output of the low-pressure mercury lamp 9 is 20 W and is electrically connected to a 100 V AC power supply via the ballast 11.
The low-pressure mercury lamp 9 emits ultraviolet light having wavelengths of 185 nm and 254 nm, and generates ozone from oxygen using the ultraviolet light.

Inside the reaction tube case 1, a plurality of disk-shaped partitions 13a and 13b are arranged. Partition wall 13a
An opening having a size larger than the outer diameter of the protection tube 7 is formed at the center thereof, is fixed to the inner wall of the reaction tube case 1, and is arranged at a distance from the protection tube 7.
The partition wall 13b is formed with a size smaller than the inner diameter of the reaction tube case 1, is fixed around the protective tube 7, and is arranged at an interval from the inner wall of the reaction tube case 1. The partitions 13a and 13b are arranged alternately, and
The distance between a and 13b is 6 mm.

The fluid sample introduced into the reaction tube case 1 from the sample inlet 3 is guided to the protection tube 7 side along the partition 13a, and is turned back by the protection tube 7 to pass the space between the partitions 13a and 13b into the reaction tube case 1. The reaction tube case 1 is guided to the inner wall side.
And the space between the next partition 13a and 13b is guided to the protective tube 7 side. In this way, the fluid sample is
After flowing while meandering inside the reaction tube case 1 along the stepped flow path formed by the steps a and b, the sample is discharged from the sample outlet 5.

The partition walls 13a and 13b have a wire diameter of 0.3 m.
The titanium dioxide mesh having a m and a pitch of 0.5 mm is coated with titanium dioxide as a photocatalyst. Partition 13
As a method for producing a and 13b, a titanium wire mesh is baked in a heating furnace at 800 ° C. for 30 minutes to form a titanium oxide thin film on the surface of the titanium wire mesh, and then an anatase type titanium dioxide having high photocatalytic activity. Was applied. When the photocatalyst is directly applied to the titanium wire mesh, the photocatalyst may peel off. However, the peeling of the photocatalyst can be prevented by forming a titanium oxide thin film having a high adhesion on the surface of the titanium wire mesh. The surfaces of the partition walls 13a and 13b formed in this manner have irregularities.

When the low-pressure mercury lamp 9 is turned on, the partition walls 13a, 13
When the photocatalyst applied to b is irradiated with ultraviolet rays, the contaminants in the fluid sample are oxidized, and ozone is generated from oxygen in the fluid sample, and the contaminants are also oxidized by the ozone. Further, ozone also oxidizes reduced species formed on the surface of the photocatalyst, thereby promoting the oxidizing action of the photocatalyst. In this way, contaminants in the fluid sample can be decomposed.

FIG. 2 is a sectional view showing an embodiment (Embodiment 2) of the second mode. As in FIG. 1, a sample inlet 3 is provided at the lower end of the side wall, and a protective tube 7 is disposed at the center of the reaction tube case 1 provided with a sample outlet 5 at the upper end. A mercury lamp 9 is provided. The low-pressure mercury lamp 9 is electrically connected to a 100 V AC power supply via a ballast 11.

In this embodiment, a spiral partition 15 is provided in the space between the reaction tube case 1 and the protection tube 7.
The fluid sample introduced from the sample inlet 3 into the reaction tube case 1 is guided to the fluid outlet 5 while traveling around the low-pressure mercury lamp 9 along the partition 15. Reaction case 1
The distance between the surfaces of the partition walls 15 in the axial direction is 6 mm. The partition 15 has a wire diameter of 0.3 mm and a pitch of 0.5 m.
m is coated with titanium dioxide as a photocatalyst on the surface of a titanium wire mesh. The partition 15 is the partition 13 of the first embodiment.
By the same manufacturing method as in a and 13b, the surface is formed in an uneven shape, and peeling of the photocatalyst is suppressed.
When the low pressure mercury lamp 9 is turned on and the photocatalyst applied to the partition 15 is irradiated with ultraviolet rays, contaminants in the fluid sample can be decomposed in the same manner as in the first embodiment.

Next, in order to evaluate the oxidative decomposition efficiency of Examples 1 and 2, a liquid sample (sample water) was introduced into the reaction tube case 1 and circulated, and its TOC (total organic carbon) removal rate was examined. . As sample water, 2.5 pp of C ₆ H ₁₂ O ₆ was added to distilled water.
at a concentration of mC, at a concentration of 2.5ppmC the C ₆ H ₅ NaPO _4, and a NH ₄ Cl was used an aqueous solution containing a concentration of 0.5PpmN. As comparative examples, three types of reaction tube cases were prepared. 3A and 3B are cross-sectional views showing a comparative example thereof. FIG. 3A is a photocatalytic reaction tube in which a photocatalyst powder 17 is suspended in sample water (Comparative Example 1), and FIG. (C) shows a photocatalytic reaction tube in which a ceramic foam 19 is arranged (Comparative Example 2), (C) shows a photocatalytic reaction tube in which an aluminum lattice plate 21 coated with a photocatalyst is arranged, and (D) shows a photocatalytic reaction tube in (C). It is sectional drawing along CC 'position. In Comparative Examples 1, 2, and 3, the same reaction tube case 1, protective tube 7, and low-pressure mercury lamp 9 as those in Example 2 were used, and illustration was omitted. It is electrically connected to an AC power supply. In Comparative Example 1, the powdery photocatalyst 17 is introduced from the sample inlet 3 together with the sample water and discharged from the sample outlet 5 (see (A)). In Comparative Example 2, a porous ceramic foam 19 coated with a photocatalyst is disposed in a space between the reaction tube case 1 and the protective tube 7 (see (B)). Comparative Example 3
In the space between the reaction tube case 1 and the protection tube 7, 36 aluminum grids 21 coated with a photocatalyst are radially arranged around the low-pressure mercury lamp 9 (see (C)).

In Examples 1 and 2 and Comparative Examples 1, 2 and 3, 50 liters of the above sample water was circulated at 20 liters / minute. FIG. 4 is a graph showing the photochemical oxidative decomposition efficiencies of Examples 1 and 2 and Comparative Examples 1, 2 and 3. The vertical axis is T
The OC loss rate (%) is shown, and the horizontal axis is time (unit is time h)
Is shown. It can be seen from the graph of FIG. 4 that Examples 1 and 2 of the present invention have the highest TOC oxidative decomposition efficiency. Further, the oxidative decomposition efficiencies of Comparative Examples 2 and 3 were lower than those of Comparative Example 1 because the ceramic foam 19 or the aluminum grid plate 21 shielded the light of the low-pressure mercury lamp 9 from the photocatalyst. It can be said that the light is not effectively utilized even if is applied. As described above, according to the present invention, the light from the light source can be effectively irradiated to the photocatalyst surface, and the contact area between the sample water and the photocatalyst is increased, so that the efficiency of oxidative decomposition can be improved. Further, since no packing is required, the fluid resistance in the reaction tube case does not increase.

The present invention is not limited to the embodiments, and the shape and configuration of the partition may be any as long as the flow path formed by the partition has a stepped or spiral shape. The measurement object of the present invention is not limited to a liquid sample,
It can be applied to gas samples, solid samples or even mixed phases. Further, in the embodiment, the titanium wire mesh is used as the partition wall, but the partition wall is not limited to this, and the shape may be a plate shape, a porous shape, a thin film shape, or the like. Ceramics, fibers, etc. are not particularly limited. For example, a structure in which a partition wall having a honeycomb structure is formed of a nonwoven fabric, activated carbon is applied to the surface thereof, and a photocatalyst is further formed on the surface is preferable because of high activity and high practicability.

[0020]

According to the first aspect of the present invention, a plurality of partition walls are arranged so that the fluid alternately flows from the inner wall side of the reaction tube case to the light source side and from the light source side to the inner wall side of the reaction case in steps. Since photocatalysts were formed on the surfaces of the partition walls, and in the second embodiment, the spiral partition walls were arranged so that the fluid spirally flowed around the light source, and the photocatalyst was formed on the surface of the partition walls.
Since there is no filler such as a carrier, the fluid resistance in the reaction tube case can be suppressed, and the surface of all the photocatalysts formed on the partition wall surface can be irradiated with light from a light source, thereby reducing the contact area between the fluid sample and the photocatalyst. Oxidation decomposition efficiency can be increased.

[Brief description of the drawings]

FIG. 1 is a sectional view showing an example (Example 1) of a first mode.

FIG. 2 is a cross-sectional view illustrating an example (Example 2) of the second aspect.

FIG. 3 is a cross-sectional view showing a comparative example, in which (A) is a photocatalytic reaction tube in which a photocatalytic powder is suspended in sample water (Comparative Example 1),
(B) shows a photocatalytic reaction tube in which a porous ceramic foam coated with a photocatalyst is disposed (Comparative Example 2), and (C) shows a photocatalytic reaction tube in which an aluminum lattice plate coated with a photocatalyst is disposed (Comparative Example 3). (D) is a sectional view taken along the line CC ′ of (C).

FIG. 4 is a graph showing photochemical oxidative decomposition efficiencies of Example 2, Comparative Examples 1, 2 and 3.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Reaction tube case 3 Sample inlet 5 Sample outlet 7 Protective tube 9 Low pressure mercury lamp 11 Ballast 13a, 13b, 15 Partition wall

Claims (5)

[Claims] 1. A flow-type photocatalytic reaction tube in which a light source is disposed at a central portion of a cylindrical reaction tube case and a fluid flows between the reaction tube case and the light source, wherein the fluid is on an inner wall side of the reaction tube case. From the light source side and the light source side, a plurality of partitions are arranged in a direction perpendicular to the axis of the reaction tube case so as to alternately flow from the light source side to the inner wall side of the reaction case, and a photocatalyst is provided on the surface of the partition. A photocatalytic reaction tube characterized by being formed. 2. A flow-type photocatalytic reaction tube in which a light source is arranged at a central portion of a cylindrical reaction tube case and a fluid flows between the reaction tube case and the light source, wherein the fluid spirals around the light source. A helical partition wall is arranged around the light source so as to flow through the light source, and a photocatalyst is formed on the surface of the partition wall. 3. The photocatalytic reaction tube according to claim 1, wherein the photocatalyst is titanium dioxide, and the light source emits ultraviolet light having a wavelength of 400 nm or less. 4. The photocatalytic reaction tube according to claim 1, wherein at least a part of an inner wall of the reaction tube case is a light reflecting surface. 5. The photocatalytic reaction tube according to claim 1, wherein the surface of the partition wall is formed in an uneven shape.