Reactor for molecular splitting and use thereof

Abstract

The invention relates to a reactor for molecular splitting, wherein the reactor has a double-walled reactor body having an interior with an inner wall and an outer wall made of a radiation-permeable material, and wherein a photocatalyst and an electrolyte are located between the inner wall and the outer wall.

Description

[0001] Reactor for molecular splitting and its use

[0002] The invention relates to a reactor for molecular splitting and its use.

[0003] To provide energy carriers in a resource-efficient manner, it would be desirable to produce hydrogen by electrolysis of water, with the energy input being directly provided by solar radiation, hereinafter also referred to as solar water splitting and also known as photoelectrochemical (PEC) water splitting.

[0004] Other molecules can also be split through molecular fission, such as CO2 into carbon monoxide and oxygen. If a mixture of water and CO2 is split, further or different fission products containing carbon and hydrogen, such as methane, can be formed. It is also possible to directly produce synthesis gas, i.e., a mixture of hydrogen and carbon monoxide, which can be used in a variety of applications, for example, in the chemical industry.

[0005] The object of the invention is to provide an inexpensive and simply constructed reactor for molecular fission, for example solar molecular fission, for the design of which, for example, existing commercial reactors can be easily modified. Preferably, the reactor should also enable a high efficiency.

[0006] This problem is solved by the subject matter of the independent claims. The dependent claims concern specific configurations.

[0007] A first aspect of the invention relates to a reactor for molecular splitting, for example, for solar molecular splitting, in particular for splitting water and / or CO2. The reactor has a double-walled reactor body with an interior, an inner wall, and an outer wall. At least the outer wall consists of a transparent material, e.g., glass such as quartz glass. Optionally, the inner wall can also consist of a radiation-transmitting material, for example, a solar radiation-transmitting material. The term "radiation" here refers to electromagnetic radiation that can be photocatalytically converted by the photocatalyst, for example, UV radiation, visible light, and / or IR radiation. The term "solar radiation" here refers to electromagnetic radiation emitted by the sun.

[0008] A material is described as "radiation-transparent" if it is transparent or permeable to at least a portion of the electromagnetic radiation spectrum, e.g., visible light with a wavelength between 380 nm and 780 nm, i.e., if it has a transmittance of at least 80%, preferably at least 90%, more preferably at least 95%, and particularly preferably at least 99%. Similarly, a material is described as "solar-transparent" if it is transparent or permeable or permeable to at least a portion of solar radiation, e.g., visible light with a wavelength between 380 nm and 780 nm, i.e., if it has a transmittance of at least 80%, preferably at least 90%, more preferably at least 95%, and particularly preferably at least 99%.

[0009] Preferably, the outer wall should be transparent to visible light and at least partially to infrared radiation. Infrared radiation, in this context, refers to radiation with a wavelength between 780 nm and 1 mm. Additionally, the outer wall may also be at least partially transparent to ultraviolet radiation. Ultraviolet radiation, in this context, refers to radiation with a wavelength between 200 nm and 380 nm.

[0010] The inner and outer walls are spaced apart, creating a gap. This gap can be, for example, between 0.2 mm and 3 mm and is preferably constant. Spacers or placeholders can be positioned between the inner and outer walls to maintain this gap.

[0011] A photocatalyst and an electrolyte, for example in the form of a photocatalyst-electrolyte mixture, such as an electrolyte-photocatalyst suspension, are arranged between the inner and outer walls, or in the space between them. The density of the photocatalyst in the space should preferably be as high as possible to ensure high efficiency. Replacing or replenishing the photocatalyst during the reactor's service life is not intended; that is, the reactor is static. Replenishing the electrolyte is also only intended to a limited extent, namely to replace electrolyte lost through molecular splitting. For example, when water is used as the electrolyte for water splitting, a small amount of water should be added from time to time.

[0012] The photocatalyst catalyzes the electrolysis or splitting of electrolyte components by absorbing electromagnetic radiation, e.g. solar radiation, and releasing electrons that cause the desired molecular splitting.

[0013] If the proposed reactor is operated using solar radiation, this has the advantage that essentially no additional energy is required to operate the reactor, since solar energy is used as the energy source. If the proposed reactor is operated not with solar radiation, but with electromagnetic radiation from another radiation source, this has the advantage that the reactor can be used independently of the presence of solar radiation, e.g., in darkness. For this purpose, the reactor can incorporate suitable radiation sources. Using a radiation source other than the sun could, for example, enable CCh fission at the point of CO2 production.

[0014] When the reactor is used for water splitting, the electrolyte contains water. When the reactor is used for CCh splitting, the electrolyte contains CO2. The electrolyte may also contain agents for adjusting the pH value; that is, the electrolyte may be acidic or basic, for example.

[0015] The proposed reactor is similar to known vacuum tubes used in solar thermal applications. Therefore, the proposed reactor can be obtained through simple modifications of known reactors and is thus inexpensive to manufacture.

[0016] Depending on the design, the inner and outer walls can be curved. The radii of curvature can be chosen, for example, to maintain a constant distance between the inner and outer walls. For instance, the reactor body can be tubular. That is, the interior has the shape of a circular cylinder and is surrounded by an annular cylinder formed by the inner and outer walls.

[0017] This has the advantage of a large outer surface area, allowing a significant amount of electromagnetic radiation to pass into the space and achieving high efficiency. According to further embodiments, the inner and outer walls can be at least partially planar, meaning the reactor can be formed by a planar glass bilayer.

[0018] This represents a simpler and more cost-effective alternative compared to the tubular reactor.

[0019] According to further design variants, a reflector with a radiation-reflecting surface can be arranged outside the reactor body.

[0020] Preferably, the surface can be designed to reflect visible light, i.e., the reflectance for visible light can be at least 80%, preferably at least 90%, more preferably at least 95%, and particularly preferably at least 99%. In addition, the radiation-reflecting surface can also be designed to reflect at least parts of the IR radiation and / or UV radiation.

[0021] The radiation-reflecting surface can be curved, with the curvature being adapted to the curvature of the outer wall. The curvature can, for example, be a parabolic curve.

[0022] The reflector is preferably arranged with respect to the outer wall in such a way that as much electromagnetic radiation as possible is reflected towards the reactor body.

[0023] The reflector can increase efficiency, as a higher proportion of the electromagnetic radiation can be used for molecular splitting.

[0024] The reflector can preferably be a compound parabolic concentrator or a double parabolic reflector.

[0025] Such a reflector can contribute to a particularly high efficiency, as sufficient solar radiation is reflected even when the sun's position changes. Tracking the reflector according to the sun's position is not necessary.

[0026] The radiation-reflecting surface can preferably be oriented essentially perpendicular to the sun at its apex or to another radiation source. Depending on the specific design, the photocatalyst can be 3C-SiC. Here, "3C-SiC" refers to silicon carbide with a cubic crystal structure, also known as β-SiC. 3C-SiC has a band gap of 2.35 eV and therefore exhibits a band gap that is optimally matched to the electromagnetic spectrum of solar radiation. Among all semiconductor materials, 3C-SiC is the most chemically stable and best suited with respect to its band gap.

[0027] Preferably, the 3C-SiC can be in the form of microparticles. Microparticles are defined as objects with three external dimensions, wherein the dimension of the object in at least one dimension, preferably in at least two dimensions, and particularly preferably in all three dimensions, is smaller than 1000 pm. Furthermore, the dimension in none of the three dimensions is smaller than 100 nm. The term microparticles also includes aggregates of small particles, provided the above definition of microparticles applies to the particle aggregate. The microparticles can be crystalline.

[0028] Micrometer particles have the advantage that they can also absorb electromagnetic radiation with wavelengths greater than 380 nm and use it for (solar) molecular splitting, including, for example, the visible and infrared components of sunlight. Furthermore, light scattering by the particles can increase efficiency by allowing the absorption of not only direct but also scattered electromagnetic radiation. For example, this can increase the efficiency of solar water splitting to approximately 10%.

[0029] According to further embodiments, the reactor can have a co-catalyst arranged between the inner and outer walls. In other words, a mixture of electrolyte, photocatalyst, and co-catalyst can be present in the space between the walls.

[0030] In this context, a co-catalyst can mean that it provides a combined catalytic effect with the photocatalyst, e.g., the 3C-SiC microparticles, which can be considered the "main catalyst," and / or an additional catalytic effect. The co-catalyst can, for example, be a noble metal catalyst, where the noble metal could be, for instance, gold and / or platinum. Alternatively or additionally, other co-catalysts, e.g., iron-based or based on organic compounds such as carbonitrides, can be used. The co-catalyst can advantageously improve charge separation.

[0031] According to further design variations, the reactor can have a heat transfer medium located inside. This heat transfer medium can, for example, be a solar thermal fluid, i.e., a heat transfer medium commonly used in solar thermal systems.

[0032] The function of the heat transfer medium is to store thermal energy and to heat the substances in the interstitial space—i.e., the electrolyte, photocatalyst, and, if applicable, co-catalyst—as uniformly as possible, while maintaining the achieved temperature for as long as possible. A temperature of at least 80 °C would be desirable, as photocatalysis is preferentially carried out at higher temperatures.

[0033] The proposed reactor can therefore also be used for solar thermal applications, for example simultaneously with molecular fission or during a period in which no molecular fission takes place.

[0034] According to further design variants, the inner wall can have a coating.

[0035] The coating can be arranged on the inside of the inner walls, i.e., on the side facing the interior, and / or on the outside of the inner wall, i.e., on the side facing the space between.

[0036] The coating can be a radiation-absorbing coating, e.g., a solar radiation-absorbing coating, and / or a radiation-reflecting coating, e.g., a solar radiation-reflecting coating.

[0037] For example, the coating can be designed to absorb IR radiation. Remaining IR radiation, i.e., IR radiation not used for photocatalysis, can be converted into heat energy by the absorbing coating, thereby contributing to a further temperature increase of the heat transfer medium and / or the electrolyte-photocatalyst mixture.

[0038] Alternatively or additionally, a reflective coating can cause electromagnetic radiation to be reflected into the space between the electrolytes and photocatalysts, so that this reflected radiation can also be used for photocatalysis, thereby increasing the efficiency. In this case, the heating of the heat transfer medium can be achieved through heat transfer from the electrolyte-photocatalyst mixture.

[0039] Another aspect of the invention relates to the use of a reactor according to the above description for molecular splitting, in particular for water splitting and / or CCh splitting. The molecular splitting can, for example, be solar molecular splitting.

[0040] The aspects and advantages of the reactor explained above also apply analogously to the proposed use, so reference is made to the above statements.

[0041] The invention is explained in more detail below with reference to the accompanying figures. These show:

[0042] Fig. 1 shows a schematic cross-sectional representation of an exemplary reactor;

[0043] Fig. 2 is a schematic representation of the reactor from Fig. 1 in longitudinal section;

[0044] Fig. 3 shows a diagram illustrating the operating principle of a double parabolic reflector;

[0045] Fig. 4a shows a representation to illustrate the usable absorption area without a reflector;

[0046] Fig. 4b is a representation to illustrate the usable absorption area with reflector.

[0047] Figures 1 and 2 show an exemplary reactor 1 with a tubular reactor body 2 formed by an inner wall 4 and an outer wall 5, which are concentric and enclose an interior space 3 containing a heat transfer medium. Between the inner wall 4 and the outer wall 5 is a space 6 in which a photocatalyst 7, an electrolyte 8, and a co-catalyst 11 are arranged. In this embodiment, the reactor 1 is for solar water splitting; that is, the main component of the electrolyte is water. 3C-SiC microparticles are used as the photocatalyst. Alternatively, a radiation source other than the sun can be used for molecular splitting.

[0048] The outer surface of the inner wall 4 can optionally be provided with a reflective and / or absorbent coating 13. Alternatively, the coating 13 can also be arranged on the inner surface of the inner wall 4.

[0049] During operation, reactor 1 is exposed to solar radiation 14, which, in the example shown, strikes the reactor body 2 perpendicularly from above. A reflector 9, designed as a double parabolic reflector, is arranged on the side of the reactor body 2 opposite the sun. The reflector 9 has a radiation-reflecting surface 10 that reflects the incident solar radiation 14 towards the reactor body 2.

[0050] The incident solar radiation 14, after catalysis by means of the photocatalyst 7 and the co-catalyst 11, causes solar water splitting, i.e., water present as electrolyte 8 is split into H2 and O2 and removed from the space 6, as indicated by block arrows in Fig. 2.

[0051] Figure 3 illustrates the operation of the double parabolic reflector. This ensures that, even with changing solar position, the incident solar radiation 14 is delivered to the photocatalyst as completely as possible. A change in the position of the reflector 9 depending on the sun's position is not necessary for this. The efficiency can be further increased by carefully selecting the distance between the reflector 9 and the reactor body 2.

[0052] Figure 4a illustrates the usable absorption area of ​​reactors 1 without a reflector 9 under oblique incident solar radiation 14, e.g., at sunrise or sunset. Since a reflector 9 is omitted, the reactor bodies 2 can advantageously be arranged close together, e.g., with a distance of 70 mm. Under oblique incident solar radiation 14, approximately 50% of the area of ​​the outer wall 5 is used as an absorption surface; however, for subsequent reactor bodies 2, due to the shadowing effect of the preceding reactor body 2, this is reduced to approximately 30%.

[0053] In contrast, the arrangement of reflectors 9, as shown in Figure 4b, results in almost 100% utilization of the surface of the outer wall 5 as an absorption surface. Even though the arrangement of the reflectors 9 requires a certain amount of space and the reactor bodies 2 consequently have to be arranged with a greater distance between them, e.g., a distance of 110 mm, the overall efficiency is still significantly higher than without the use of a reflector 9.

[0054] Reference symbol list: Reactor 9 Reflector Reactor body 10 radiation-reflecting interior surface inner wall 11 Co-catalyst outer wall 12 Heat transfer medium space 13 Coating Photocatalyst 14 Solar radiation Electrolyte

Claims

Patent claims:

1. Reactor (1 ) for molecular splitting, the reactor (1 ) comprising: a double-walled reactor body (2) with an interior (3), an inner wall (4) and an outer wall (5) made of a radiolucent material, a photocatalyst (7) arranged between the inner wall and the outer wall, and an electrolyte (8) arranged between the inner wall and the outer wall.

2. Reactor (1) according to claim 1, wherein the inner wall (4) and the outer wall (5) are curved.

3. Reactor (1) according to claim 2, wherein the reactor body (2) is tubular.

4. Reactor (1) according to one of the preceding claims, wherein the inner wall (4) and the outer wall (5) are at least partially planar.

5. Reactor (1) according to one of the preceding claims, comprising: a reflector (9) arranged outside the reactor body (1) with a radiation-reflecting surface (10).

6. Reactor (1 ) according to one of the preceding claims, wherein the radiation-reflecting surface (10) is curved.

7. Reactor (1) according to claim 6, wherein the curvature is a parabolic curvature.

8. Reactor (1) according to any one of claims 5 to 7, wherein the reflector (9) is a composite parabolic concentrator.

9. Reactor (1) according to one of the preceding claims, wherein the photocatalyst (7) is 3C-SiC.

10. Reactor (1 ) according to claim 9, wherein the 3C-SiC is in the form of microparticles.

11. Reactor (1 ) according to one of the preceding claims, comprising: a co-catalyst (11) arranged between the inner wall (4) and the outer wall (5).

12. Reactor (1) according to one of the preceding claims, comprising: a heat transfer medium (12) arranged in the interior (3).

13. Reactor (1) according to one of the preceding claims, wherein the inner wall (4) has a coating (13).

14. Reactor (1 ) according to claim 13, wherein the coating (13) is a radiation-absorbing and / or radiation-reflecting coating.

15. Use of a reactor (1 ) according to any of the preceding claims for molecular cleavage.

16. Use according to claim 15, wherein the molecular cleavage is water cleavage and / or CCh cleavage.

17. Use according to claim 15 or 16, wherein the molecular cleavage is solar molecular cleavage.

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