Photochemical reactor

Abstract

This photochemical reactor comprises: a reaction tank in which an inflow port into which a raw material solution in which a gas necessary for a catalytic reaction is dissolved flows and a discharge port from which a photocatalytic reaction product after the photocatalytic reaction is discharged are formed, the reaction tank having a light intake surface for taking in light and an opposite surface on the opposite side from the light intake surface; and a porous carrier in which, in the interior of the reaction tank, an intake-side flow path is formed between the porous carrier and the light intake surface, an opposite-side flow path is formed between the porous carrier and the opposite surface, and the photocatalyst is immobilized.

Description

Photochemical Reactor

[0001] The present disclosure relates to photochemical reactors for use in photocatalytic reactions.

[0002] In recent years, in order to realize a carbon-neutral society, attention has been focused on "artificial photosynthesis," which reduces carbon dioxide using a photocatalyst and sunlight to extract energy in the form of formic acid, etc. Currently, photochemical reactors used for photocatalytic reactions employ a system in which a photocatalyst carrier is installed inside a tubular reactor and the liquid used in the reaction is circulated through it. Patent Document 1 discloses a water-repellent photocatalytic reaction device that increases the reaction surface area by suspending a granular photocatalyst carrier in an aqueous solution with carbon dioxide bubbles to improve reaction efficiency. Patent Document 2 also discloses a methanol synthesis device that provides a baffle plate in a reactor with a photocatalyst film on the wall, thereby increasing the contact time between the photocatalyst and the aqueous solution.

[0003] JP-A-4-59037 JP-A-7-33697

[0004] However, in Patent Document 1, when suspending particles carrying a photocatalyst, it is necessary to separate the raw material solution containing the product from the photocatalyst. Also, in Patent Document 2, the catalyst layer and the aqueous solution come into contact only with the wall surface of the reactor, resulting in low reaction efficiency.

[0005] The present disclosure has been made to solve the above-mentioned problems, and aims to provide a photochemical reactor that does not require a separation step between the raw material solution and the photocatalyst and achieves high reaction efficiency.

[0006] The photochemical reactor according to the present disclosure comprises a reaction vessel having an inlet through which a raw material solution dissolving a gas necessary for the catalytic reaction flows in and an outlet through which a photocatalytic reaction product is discharged after the photocatalytic reaction, the reaction vessel having a light-capturing surface for capturing light and an opposite surface opposite the light-capturing surface, and a porous carrier having an intake-side flow path formed between the reaction vessel and the light-capturing surface and an opposite-side flow path formed between the reaction vessel and the opposite surface, and having a photocatalyst immobilized thereon.

[0007] According to the present disclosure, a photocatalyst is immobilized on a porous carrier. Therefore, a separation process between the raw solution and the photocatalyst is not required. In addition, an intake-side flow path is formed between the porous carrier and the light-intake surface. In the intake-side flow path, a photocatalytic reaction occurs when light is irradiated onto the contact area between the raw solution and the photocatalyst. In addition, in the opposite flow path, a portion of the raw solution passes through the inside of the porous carrier and moves to the intake-side flow path, causing a photocatalytic reaction. In this way, the raw solution is supplied to the photocatalyst from other sides than the light-intake surface side of the porous carrier, thereby increasing the efficiency of the photocatalytic reaction. As described above, the photochemical reactor does not require a separation process between the raw solution and the photocatalyst and can achieve high reaction efficiency.

[0008] Fig. 1 is a perspective view showing a photochemical reactor according to embodiment 1. Fig. 2 is a cross-sectional view showing a photochemical reactor according to embodiment 1. Fig. 3 is a cross-sectional view showing a photochemical reactor according to embodiment 2. Fig. 4 is a cross-sectional view showing a photochemical reactor according to embodiment 3. Fig. 5 is a cross-sectional view showing a photochemical reactor according to embodiment 4.

[0009] Hereinafter, embodiments of the photochemical reactor of the present disclosure will be described with reference to the drawings. Note that the present disclosure is not limited to the embodiments described below. Furthermore, in the following drawings, including FIG. 1, the dimensional relationships between the components may differ from the actual ones. Furthermore, in the following description, terms indicating directions will be used as appropriate to facilitate understanding of the present disclosure, but these terms are for the purpose of explaining the present disclosure and do not limit the present disclosure. Examples of terms indicating directions include "up," "down," "right," "left," "front," and "rear."

[0010] Embodiment 1. FIG. 1 is a perspective view showing a photochemical reactor 10 according to embodiment 1. The photochemical reactor 10 is used for photocatalytic reactions. A photocatalyst carrier is placed inside a tubular reactor, and a liquid used in the reaction is circulated through the reactor. As shown in FIG. 1, the photochemical reactor 10 includes a reaction vessel 11 and a porous carrier 20. The reaction vessel 11 has a hexagonal shape that is elongated in one direction and has a hollow interior. The reaction vessel 11 is formed with an inlet 13 and an outlet 14. The inlet 13 is an opening through which a raw material solution containing dissolved gases necessary for the catalytic reaction flows. Since the gas is dissolved in the raw material solution before flowing in, there is no need to install a gas generator in the reaction vessel 11. This eliminates the need for a gas generator in the reaction vessel 11. This reduces the diffusion and reflection of incident light due to bubbles continuously generated in the reaction vessel 11. The raw material solution is, for example, water or triethanolamine. The outlet 14 is an opening through which the reaction product and raw material solution are discharged. The photocatalytic reaction product 30 generated is a liquid, such as formic acid or ethanol.

[0011] The upper surface of the reaction vessel 11 is a light-intake surface 12. The light-intake surface 12 is a surface that takes in light 40 into the reaction vessel 11. The light-intake surface 12 is a member for introducing light 40 of a wavelength required for a photocatalytic reaction to a photocatalyst in the reaction vessel 11. The light-intake surface 12 is made of, for example, a material that has high transparency to visible light, such as glass, or a material that has high transparency to ultraviolet light, such as quartz. The opposite side of the light-intake surface 12 of the reaction vessel 11 is an opposite surface 16. The opposite surface 16 may be a surface through which the light 40 passes, or a surface through which the light 40 does not pass.

[0012] The porous carrier 20 is a plate-shaped substrate on which a photocatalyst is immobilized. Because the porous carrier 20 is porous, the surface area on which the photocatalyst is supported is large, allowing the solution to pass through the interior of the carrier. The porous carrier 20 is, for example, porous glass. The diameter of each pore in the porous carrier 20 is preferably 1 μm to 1000 μm. However, the diameter of the pores in the porous carrier 20 may be smaller than 1 μm to increase the surface area. The diameter of the pores in the porous carrier 20 may be larger than 1000 μm to increase the permeation rate of the raw solution. By immobilizing the photocatalyst in the porous carrier 20, it is not necessary to separate the photocatalyst from the reaction product at the outlet 14.

[0013] The porous carrier 20 is provided in a position inside the reaction vessel 11 where an intake-side flow path 12a is formed between the porous carrier 20 and the light capture surface 12. The porous carrier 20 is also provided in a position inside the reaction vessel 11 where an opposite-side flow path 16a is formed between the porous carrier 20 and the opposite surface 16. In this way, the porous carrier 20 is fixed to the side of the reaction vessel 11 in a state where it is floating above the light 40 capture layer and the opposite surface 16.

[0014] Figure 2 is a cross-sectional view showing the photochemical reactor 10 according to the first embodiment, taken along the line A-A in Figure 1. As shown in Figure 2, the porous carrier 20 is disposed with the light-collecting surface 12 tilted from the horizontal plane. Specifically, the reaction vessel 11 is tilted so that its height increases from the inlet 13 toward the outlet 14.

[0015] (Photocatalytic Reaction) Next, the mechanism of the photocatalytic reaction in the photochemical reactor 10 will be described. In an environment where the light intake surface 12 of the reaction vessel 11 is irradiated with light 40, a raw material solution in which gases such as carbon dioxide necessary for the photocatalytic reaction are dissolved is introduced into the reaction vessel 11 from the inlet 13. In the first embodiment, sunlight is used as the light 40, but light 40 from an artificial light source containing light 40 of a wavelength used in the photocatalytic reaction may also be used. Examples of artificial light sources include a metal halide lamp, a halogen lamp, a fluorescent lamp, an incandescent lamp, a mercury lamp, and an LED (Light Emitting Diode).

[0016] The raw material solution flowing into the reaction tank 11 from the inlet 13 is branched by the plate-shaped porous carrier 20 into two paths: an inlet side flow path 12a running from the light-collecting surface 12 side to the outlet 14, and an opposite side flow path 16a running from the opposite side 16 of the light-collecting surface 12 to the outlet 14.

[0017] Along the way in the inlet flow path 12a, light 40 is irradiated onto the contact area between the raw solution and the photocatalyst immobilized on the porous carrier 20. This causes a photocatalytic reaction, and the generated photocatalytic reaction product 30 is discharged together with the raw solution from the outlet 14. Furthermore, the water flow sweeps away any air bubbles remaining on the light-intake surface 12 and the porous carrier 20.

[0018] In the opposite flow path 16a, a portion of the raw solution passes through the inside of the porous carrier 20 and flows toward the light collecting surface 12. The raw solution that has flowed toward the light collecting surface 12 reacts with the photocatalyst to produce a photocatalytic reaction product 30. The produced photocatalytic reaction product 30 passes through the intake side flow path 12a, which runs from the light collecting surface 12 side toward the outlet 14, and is discharged from the outlet 14 together with the raw solution. This allows the raw solution to be supplied to the photocatalyst from places other than the surface of the opposing carrier, and the photocatalytic reaction occurs with high efficiency.

[0019] As described above, according to the first embodiment, the photocatalyst is immobilized on the porous carrier 20. Therefore, a separation process between the raw solution and the photocatalyst is not required. Furthermore, an intake-side flow path 12a is formed between the porous carrier 20 and the light-intake surface 12. In the intake-side flow path 12a, a photocatalytic reaction occurs when light 40 is irradiated onto the contact portion between the raw solution and the photocatalyst. Furthermore, in the opposite flow path 16a, a portion of the raw solution passes through the interior of the porous carrier 20 and moves to the intake-side flow path 12a, causing a photocatalytic reaction. In this way, the raw solution is supplied to the photocatalyst from other sides of the porous carrier 20 than the light-intake surface 12, thereby increasing the efficiency of the photocatalytic reaction. As described above, the photochemical reactor 10 does not require a separation process between the raw solution and the photocatalyst and can achieve high reaction efficiency.

[0020] Conventionally, water-repellent photocatalytic reaction devices have been known that enlarge the reaction surface area by suspending granular photocatalyst carriers in aqueous solution with carbon dioxide bubbles. However, in practice, the particle size must be very small to suspend the particles with bubbles, which inevitably requires the pore size of the filter that separates the particles to be very small. This reduces the filtration rate, making this difficult to achieve. In contrast, the present embodiment 1 is easy to achieve because it does not require suspension with bubbles.

[0021] Furthermore, the water temperature in the reaction vessel 11 is raised by the light 40, causing the gas dissolved in the raw material solution to turn into bubbles. The bubbles move upward in the reaction vessel 11. In the first embodiment, after the bubbles reach the light-intake surface 12 on the upper side of the reaction vessel 11, they move along the inclined light-intake surface 12 and remain at the end of the light-intake surface 12 on the outlet 14 side. Therefore, the light-intake surface 12 is not covered with bubbles. Therefore, the reflection or diffusion of incident light by the bubbles is suppressed, and the efficiency of irradiating the photocatalyst with the light 40 is improved.

[0022] As described above, conventionally, water-repellent photocatalytic reaction devices have been known in which the reaction surface area is increased by suspending granular photocatalyst carriers in aqueous solution with carbon dioxide bubbles. However, the carbon dioxide bubbles that are constantly generated can reflect or diffuse incident light, potentially reducing the efficiency of irradiation of the photocatalyst. In contrast, in the present embodiment 1, the light-receiving surface 12 is not covered with bubbles, thereby suppressing the reflection or diffusion of incident light by the bubbles and improving the efficiency of irradiation of light 40 onto the photocatalyst.

[0023] It is also possible that the amount of bubbles generated in the reaction vessel 11 increases, or that bubbles adhere to and remain on the light-collecting surface 12. In this case, if the bubbles are carbon dioxide, the bubbles can be removed by allowing a basic solution to flow in from the inlet 13.

[0024] Embodiment 2. Figure 3 is a cross-sectional view showing a photochemical reactor 10 according to embodiment 2. This embodiment 2 differs from embodiment 1 in that it includes a flow straightening member 50. In this embodiment 2, parts that are common to embodiment 1 are given the same reference numerals and their description will be omitted, and the description will focus on the differences from embodiment 1.

[0025] The flow rectifying member 50 is provided between the opposite surface 16 and the porous carrier 20 and guides the water flow toward the porous carrier 20. As shown in FIG. 3 , the end of the flow rectifying member 50 on the inlet 13 side abuts against the opposite surface 16 of the reaction vessel 11, and the end of the flow rectifying member 50 on the outlet 14 side abuts against the end of the porous carrier 20 on the outlet 14 side. That is, the flow rectifying member 50 is inclined from the bottom to the top of the reaction vessel 11 as it moves from the inlet 13 side to the outlet 14 side. The flow rectifying member 50 reflects the water flow in the opposite flow path 16a toward the porous carrier 20, and introduces the raw solution into the porous carrier 20. This allows the photocatalyst and the raw solution to react with each other with high efficiency. Although the first embodiment illustrates a case in which the flow rectifying member 50 has a linear shape when viewed from the side, the flow rectifying member 50 may have a bent or curved shape.

[0026] Embodiment 3. Figure 4 is a cross-sectional view showing a photochemical reactor 10 according to embodiment 3. This embodiment 3 differs from embodiment 1 in that the reaction vessel 11 is equipped with a recovery section 15. In this embodiment 3, parts common to embodiments 1 and 2 are given the same reference numerals and description thereof will be omitted, and the following description will focus on the differences from embodiments 1 and 2.

[0027] The recovery unit 15 is provided on the light-intake surface 12 side of the reaction vessel 11 and recovers bubbles generated inside the reaction vessel 11. As shown in FIG. 4 , the recovery unit 15 is provided at the end of the light-intake surface 12 on the exhaust port 14 side. As described in the first embodiment, the water temperature in the reaction vessel 11 is increased by the light 40, causing gas dissolved in the raw material solution to turn into bubbles. The bubbles move upward in the reaction vessel 11. After reaching the light-intake surface 12, which is the upper side of the reaction vessel 11, the bubbles move along the inclined light-intake surface 12 and reach the end of the light-intake surface 12 on the exhaust port 14 side. The recovery unit 15 recovers bubbles remaining at the end of the light-intake surface 12 on the exhaust port 14 side and discharges them to the outside of the reaction vessel 11. This prevents bubbles from accumulating inside the reaction vessel 11. Furthermore, separating the gas recovered by the recovery unit 15 allows the raw material solution to be reused.

[0028] Fourth Embodiment Figure 5 is a cross-sectional view showing a photochemical reactor 10 according to a fourth embodiment. This fourth embodiment differs from the first embodiment in that the porous carrier 20 is inclined. In this fourth embodiment, the same parts as those in the first to third embodiments are denoted by the same reference numerals and their description will be omitted, and the following description will focus on the differences from the first to third embodiments.

[0029] As shown in Figure 5, the porous carrier 20 is inclined toward the opposite surface 16 from the inlet 13 toward the outlet 14. The end of the porous carrier 20 on the outlet 14 side abuts against the opposite surface 16 of the reaction vessel 11. That is, the opposite-side flow path 16a dead ends at the end of the porous carrier 20 on the outlet 14 side. Therefore, the raw material solution flowing in the opposite-side flow path 16a is introduced into the porous carrier 20 with high efficiency and reacts with the photocatalyst. Therefore, this fourth embodiment can further increase the efficiency of the photocatalytic reaction.

[0030] REFERENCE SIGNS LIST 10 Photochemical reactor, 11 Reaction tank, 12 Light intake surface, 12a Intake side flow path, 13 Inlet, 14 Outlet, 15 Recovery section, 16 Opposite surface, 16a Opposite side flow path, 20 Porous carrier, 30 Photocatalytic reaction product, 40 Light, 50 Straightening member.

Claims

1. A photochemical reactor that uses a photocatalytic reaction in which a photocatalyst is irradiated with light and discharges a photocatalytic reaction product, a reaction vessel having an inlet through which a raw material solution having a gas necessary for the photocatalytic reaction is introduced and an outlet through which a photocatalytic reaction product is discharged after the photocatalytic reaction, the reaction vessel having a light-introducing surface for capturing the light and an opposite surface opposite to the light-introducing surface; In the reaction vessel, an intake side flow path is formed between the light intake surface and the opposite surface, and an opposite side flow path is formed between the opposite surface and a porous carrier on which the photocatalyst is immobilized; A photochemical reactor comprising:

2. The reaction vessel comprises: The light-collecting surface is disposed in a state inclined from a horizontal plane. The photochemical reactor of claim 1.

3. The water supply device further includes a flow straightening member provided between the opposite surface and the porous carrier, for guiding the water flow toward the porous carrier.

3. The photochemical reactor of claim 1 or 2.

4. The reaction vessel comprises: A recovery section is provided on the light receiving surface side and recovers bubbles generated inside the reaction vessel.

3. The photochemical reactor of claim 1 or 2.

5. The porous carrier is The inlet is inclined toward the opposite surface from the outlet.

3. The photochemical reactor of claim 1 or 2.