Photoreactors

Abstract

The present invention relates to photoreactors in particular for sun-supported photosynthesis, comprising a concentrator and a cavity, in particular configured as a continuous-flow reactor, wherein the cavity has a deformation such that the beam reflected from the point of incidence is not directly reflected back out of the cavity.

Description

[0001] Photoreactors

[0002] All documents cited in the present application are incorporated by reference in their entirety into the present disclosure.

[0003] The present invention relates to photoreactors, in particular for solar-assisted photosynthesis, comprising a concentrator and an optical cavity, in particular configured as a flow reactor, wherein the optical cavity has a geometry such that the beam reflected from the point of incidence is not directly reflected back out of the cavity.

[0004] Photoreactors are known from the state of the art. Various designs exist, for example, panel-type photoreactors without significant manipulation of the incident light, or concentrating photoreactors that concentrate the incident light using optical components before coupling it into the reaction volume. The latter typically comprise a concentrator to collect the light and an optical cavity into which the collected light is directed, forming the reaction volume. The optical cavities can have a wide variety of shapes, for example, tubular. The concentrators can also have a wide variety of shapes, but it must be ensured that the collected light is directed into the optical cavity.For example, the concentrators can be parabolic mirrors that reflect the light into the optical cavity in a concentrated manner; for example, the focus of the light rays is then at the entrance to the optical cavity.

[0005] EP 1 848 528 B1 describes a panel-like photoreactor that resembles a tube bundle composed of a multitude of parallel glass tubes. The wall thickness of the glass tubes is chosen to be so "high" (at least 10% of the inner diameter) that light incident on the tube bundle from one side also penetrates deeper tubes. The tube walls therefore serve, in addition to conducting the fluid, the function of "optical" dilution. The tubes are arranged in the bundle in such a way that a panel-like overall structure results. It is argued that the proposed arrangement also offers advantages with regard to light scattering in the reaction zone. Scattered light from one of the tubes would, with a high probability, hit the reaction zone in one of the neighboring tubes in the system. This ensures sufficient photocatalytic efficiency.To avoid "self-shadowing" of the reaction zone due to intense light absorption and / or scattering, the inner diameter of the tubes must be less than 10 mm. The concept of EP 1 848 528 B1 addresses the challenge of scattering losses through a suitable arrangement of several reaction zones next to each other. However, this requires considerable material expenditure. A large number of glass tubes must be arranged next to each other and fluidically connected. To meet the challenge of optically connecting larger catalyst volumes, the use of thick-walled glass tubes is proposed, which further reinforces the argument regarding material expenditure. Furthermore, the arrangement of "parasitically" absorbing volumes—in the case of EP 1 848 528 B1, large glass volumes—in the illuminated reaction volume always leads to absorption losses, which should be avoided.

[0006] EP 2 194 117 A1 discloses a channel-like photoreactor characterized by a trapezoidal cross-section. This cross-section is proposed to ensure homogeneous illumination of the reaction zone in photoreactions. The application focus of EP 2 194 117 A1 is biological photosynthesis by algae.

[0007] From an economic perspective, photosynthesis, especially in the case of photosynthesis of energy carriers, can only be viable if a sufficient photocatalytic efficiency is achieved and the reaction technology used can be deployed cost-effectively over large areas. To maintain the economic viability of energy carrier synthesis, an energy efficiency of at least 5-10% appears reasonable. This value would be similar to the system efficiency achieved by technically more advanced power-to-fuel technologies (electricity-based synthetic chemical energy carriers).

[0008] There is still room for improvement based on the current state of the art, particularly the utilization rate of the incident light or the radiation transport efficiency from the photoreactor aperture into the reaction volume, and the use of materials in the construction of photoreactors for solar-assisted photosynthesis still need to be improved.

[0009] The object of the present invention was therefore to provide improved photoreactors with regard to the state of the art, with which the disadvantages of the state of the art can be avoided and particularly good results can be achieved with a reduced use of materials.

[0010] Further tasks for the specialist arise from the following description.

[0011] These and other objects are achieved within the scope of the present invention by the subject matter of the independent claims.

[0012] Preferred embodiments emerge from the dependent claims and the following description.

[0013] Within the scope of the present invention, the term "comprise" also includes "consisting of" as a particularly preferred embodiment; this means that a corresponding list may contain (=comprise) further elements in addition to the explicitly mentioned elements, or it may contain precisely these elements (=consist of) (whereby non-essential elements such as screws, markings, etc. are not taken into account).

[0014] For relative information such as top, bottom, left, right or similar, the reference system used in the present invention is an observer standing upright on the ground in front of the object in question.

[0015] In the context of the present invention, the term "and / or" means that both elements mentioned in the context are included individually as well as the combination of the elements mentioned in the context.

[0016] In the context of the present invention, all quantities are to be understood as weights unless otherwise stated.

[0017] In the context of the present invention, the term "ambient temperature" means a temperature of 20°C. Temperatures are in degrees Celsius (°C), unless otherwise stated. Unless otherwise stated, the reactions or

[0018] Process steps carried out at atmospheric pressure, ie at about 1013 kPa.

[0019] In the context of the present invention, the term "aperture width" (or aperture width of the concentrator or line concentrator (also indicated as dl)) means the distance between the layers of the two legs of the concentrator that reflect the incident light (in the case of reflective metallic surfaces, this means between the two inner sides; in the case of transparent surfaces coated with a reflective coating on one side, this means between the coated sides) at the point of the concentrator with the widest cross-section, i.e. at the end of the concentrator that is furthest from the cavity.

[0020] In the context of the present invention, the term "width of the entrance into the cavity" (also indicated as d2) means the distance between the layers of the two legs of the concentrator that reflect the incident light (in the case of reflective metallic surfaces, this means between the two inner sides; in the case of transparent surfaces coated with a reflective coating on one side, this means between the coated sides) at the opening to the cavity (at the point where the concentrator and the cavity are connected to each other).

[0021] In the context of the present invention, the term "length of the concentrator" (also indicated as d4) means the height of the concentrator sides measured from the top tip of the incident light reflecting layer to the contact point of the incident light reflecting layer on the cavity outer wall.

[0022] In the context of the present invention, the term "diameter of the cavity" (also indicated as d3) means the inner diameter of the cavity, i.e. the width measured at the widest point of the cavity between the inner walls of the cavity, in the case of an ellipsoidal configuration, the largest inner diameter.

[0023] In the context of the present invention, the term "wall thickness of the transparent material" (also indicated as d5) means the thickness of the walls of the concentrator or the cavity when the walls are made of optically transparent material (for the incident light rays, i.e., their wavelengths (fully or only partially)) and are preferably reflective (coated) on the outside. In general terms, the present invention relates to a photoreactor design which can be used in particular for solar-assisted photosynthesis, e.g., of energy sources from CO2 and water, or for water treatment. The present invention is therefore also located in the field of reaction engineering.

[0024] A particular subject of the present invention is a photoreactor, in particular for sun-assisted photosynthesis, in particular configured as a flow reactor, comprising a concentrator and a cavity, wherein the concentrator, seen in the flow direction, has a V-shaped cross-section which is open at the bottom (i.e. at the base of the cavity), or is designed as a Compound Parabolic Concentrator (CPC) (there doesn't seem to be a German term at the moment), which is in direct contact with the cavity at its lower end and forms an entrance area to the cavity there, and has an aperture width dl, a width of the entrance into the cavity d2 and a length d4;the cavity inner wall, viewed in the flow direction, has an ellipsoidal, preferably circular, cross-section with a diameter d3, which, in the region of the impact of the primary incident light beam, has at least one deformation such that the light beam reflected from the impact point is not directly reflected back out of the cavity; and wherein;

[0025] (1) the ratio of dl to d2 is in a range of 2 to 3,

[0026] (2) the ratio of d4 to dl is in the range of 0.5 to 2.5.

[0027] Optional is

[0028] (3)a for a single photoreactor configuration dl less than d3 or equal to d3, and

[0029] (3)b for a configuration as one of several interconnected photoreactors (as a photoreactor array) dl is greater than d3.

[0030] In this context, it should be noted that a single photoreactor can, of course, be set up / arranged with several other photoreactors in close proximity. "Single reactor" simply means that the reactors are not connected to each other, but rather operate independently, and the cavities do not form a connected flow channel.

[0031] The concentrator legs in the V-shaped cross-section variant do not have to be completely straight, but can be curved independently of each other, either over their entire length or partially. The curvature depends on the location and incidence of light and can be easily adjusted by a person skilled in the art based on their specialist knowledge. In a preferred variant of the present invention, the curvature corresponds to that of a Compound Parabolic Concentrator (CPC).

[0032] In the context of the present invention, a compound parabolic concentrator (CPC) is understood to be a reflective, non-imaging optical device that uses specially configured parabolic properties to maximize the concentration of light energy. The wide (upper or cavity-facing) end of the CPC collects divergent light or light coming from different incident directions throughout the day, which is then reflected in the CPC and concentrated at the narrow (lower or cavity-facing) output end or in the cavity. CPCs are defined by an acceptance angle, which specifies the angular range within which the CPC can collect light. In this respect, a CPC in the context of the present invention can be viewed as a variant derived from the V-shaped cross-section, in which the legs are not straight but curved.

[0033] In the context of the present invention, the term "ellipsoidal, preferably circular, cross-section" means that the inner wall, apart from the at least one deformation, corresponds to an ellipse (i.e., a unit circle stretched along the x- and y-axes) when viewed in the flow direction. Particularly preferably, the cross-section, apart from the at least one deformation, corresponds to a unit circle. In particular, the inner wall can be oval and deviate from the unit circle by a maximum of 20%, preferably a maximum of 10%, particularly preferably a maximum of 5%, and in particular a maximum of 2% (i.e., be stretched "in the direction" of an oval). This deviation refers to the basic shape, not to the deviations from the unit circle caused by the at least one deformation.Within the scope of the present invention, the concentrator can be formed integrally with the cavity or it can be placed on top of the cavity; in the latter case, care must be taken to ensure that the lower opening of the concentrator is adapted to the opening of the cavity, as this allows for optimal light transfer from the concentrator into the cavity (so that the entire size of the cavity entrance is used and part of the light is not blocked by the outer wall of the cavity).

[0034] The photoreactor according to the invention, and thus also the concentrator and the cavity, are preferably elongated and straight in shape, in other words, they have a depth, as seen in the flow direction, whose amount is greater, in particular significantly greater, than the height of the photoreactor (i.e. the sum of the heights of the cavity and the concentrator).

[0035] For example, the photoreactors according to the invention can have the following dimensions: a specific, successfully tested example of a single-channel reactor had the following characteristics: d1 = 5 mm; d2 = 2.3 mm; d3 = 7.8 mm; d4 = 11 mm. This example accordingly represents a particularly preferred embodiment of the present invention for use as a single-channel photoreactor.

[0036] Another example of a channel array, i.e., for the interconnection of several photoreactors according to the invention, had the following characteristics: d1 = 9 mm; d2 = 3.3 mm; d3 = 8 mm; d4 = 14.3 mm. This example accordingly represents a particularly preferred embodiment of the present invention for use in photoreactor arrays.

[0037] The latter example is particularly well suited, but by no means limited, for the photocatalytic reduction of 2 mM potassium trioxalatoferrate solution. The depth in the flow direction (i.e., the length of the path the medium flows through the reactor) varies greatly depending on the specific application (e.g., depending on the chemical reaction, the desired conversion, etc.). As a rule, it is significantly greater than the "height" of the channel cross-section, in this example (much) greater than 100 mm. As is known to those skilled in the art, the exact dimensions of the photoreactors according to the invention can be adapted by adhering to the above conditions (1), (2), and (3). The skilled person can therefore readily adapt this based on their general technical knowledge, if necessary with the aid of simple preliminary tests.

[0038] The photoreactors according to the invention are preferably used to capture and utilize sunlight. However, it is also possible to use the photoreactors according to the invention with other light, for example, UV light or infrared light, preferably UV light, or a combination of UV light, visible light, and / or infrared light in proportions different from sunlight. For this purpose, the surfaces or the reflective layers of the concentrator and / or cavity can, if necessary, be adapted to the wavelengths of the incident light, for example by changing the coating or coating composition of the reflective layer. This enables the use of the photoreactors according to the invention for a wide variety of applications.

[0039] In preferred embodiments of the present invention, the deformations are in each case indentations or bulges with respect to the ellipsoidal, preferably circular, cross-section of the cavity with deformation depths in the range between 1% and 20% of the diameter of the cavity (d3), wherein the deformations are preferably dent-shaped, i.e. smooth indentations and bulges or protrusions or depressions.

[0040] In further preferred embodiments, indentations or protrusions are also formed at other locations on the cavity surface to reflect the light further into the cavity. Preferably, a whole series of deformations are designed so that the light is reflected as often as possible within the cavity and thus radiates through the reaction volume as often as possible. Particularly preferably, the beams intersect as often as possible where a photocatalyst (if used) is arranged or where a reaction is taking place (or is intended to take place).

[0041] The photoreactors according to the invention are not limited to use for light-induced or light-assisted reactions; they can also be used as a type of heat collector and use the captured (sun)light to heat liquids, preferably water, flowing through the cavity.

[0042] In preferred embodiments of the present invention, the inner sides of the concentrator or the cavity or of the concentrator and the cavity are highly reflective for the incident light, i.e. they have a high reflectance of >80%, preferably >90%, for the incident light.

[0043] This can be achieved, for example, by mirroring or polishing the surfaces.

[0044] "Mirroring" can be inherent in the material, for example, in some metals, or can be achieved by applying material to the concentrator or cavity surface. Possible methods for such application include dip coating, vapor deposition, PVD, and CVD (physical or chemical vapor deposition). Processing the surfaces of the structure, especially by polishing, can also lead to a reflective surface.

[0045] If the surfaces are made of metal, they can be post-processed using micro-milling, hand polishing, and / or electroplated silver plating to increase reflectivity. Furthermore, components manufactured using wire EDM, polymer extrusion, etc., can also be post-processed using other methods. For PMMA (polymethyl methacrylate), for example, flame polishing is recommended, and for wire-EDM components, suspension polishing, etc.

[0046] It is important to ensure that the optical coatings used for this invention (e.g., silver or aluminum) have the specified reflectivities in the relevant UV-VIS band. Reflectance values ​​below 80% lead to poorer results, as the proportion of absorbed light would become too large due to multiple reflections.

[0047] If the concentrator and / or cavity material is optically transparent (e.g., PMMA), either the inside or the outside can be coated. The latter is often simpler for purely practical reasons and is therefore preferred in some embodiments. If the materials are opaque, the reflective layer is naturally applied to the inside.

[0048] In variants of the present invention, the reflective coating may consist of or be based on aluminum or silver.

[0049] The coating can also contain materials that cause a wavelength shift of the incident light, if desired.

[0050] In this respect, in a preferred embodiment of the present invention, the concentrator and cavity are made of a transparent polymer, preferably polymethyl methacrylate, and the outer sides of the concentrator or cavity or concentrator and cavity are highly reflective for the incident light, in particular have a reflectance of at least 80%, and are preferably polished or mirrored.

[0051] In preferred embodiments of the present invention, one or more photocatalysts are arranged in the cavity, preferably on a light-permeable and / or (translucent) weakly light-absorbing support. "Light-permeable" here means that the absorption coefficient of the support must be significantly lower than that of the photocatalyst used, so that the proportion of light absorbed by the catalyst is large compared to the proportion absorbed by the support. The quantification of this property depends on the respective system—radiation belt, reflectivity in the cavity, type of catalyst, and type of reaction medium—and therefore cannot be generally determined. However, the skilled person can readily adapt this based on their general technical knowledge, if necessary with the aid of simple preliminary tests.In some embodiments of the present invention, it is particularly preferred if a translucent vessel, preferably a tube, in particular made of glass or plastic transparent to the incident light, is arranged in the cavity. In these embodiments, one or more photocatalysts can then be arranged, in particular also on a corresponding support. These supports can, in principle, be any desired structures and / or materials, as long as they allow sufficient incident light to pass through to the photocatalyst or cast as little shadow as possible. Materials transparent to the incident light are therefore preferred.

[0052] In the context of the present invention, "weakly light-absorbing" in the context of the carrier means a proportion of the light absorbed by the carrier of the light coupled into the system of less than 20%, preferably less than 10%, particularly preferably less than 5% (with a single beam passage, not cumulatively over multiple beam passages). Suitable materials for the carriers are, in particular, plastics (such as PMMA) or glass. These carriers can, for example, have the form of gratings. Aerogels are also suitable.

[0053] In some further embodiments of the present invention, cooling or heating structures, in particular cooling fins or heat transfer channels, are arranged outside the cavity.

[0054] In some preferred embodiments of the present invention, the photoreactor is externally surrounded by support structures, which may optionally have devices for connecting to other photoreactors, preferably click connections, slide-in connections, screw connections, or clamp connections. The cooling or heating structures mentioned can be incorporated into or integrated into these support structures.

[0055] In further preferred embodiments of the present invention, the photoreactors have, as seen in flow directions, connections at one or both ends of the respective cavities, via which liquid, for example the reaction medium, can be supplied and discharged.

[0056] Using appropriate connections, several photoreactors can also be connected in series to create a flow channel.

[0057] In some preferred variants of the present invention, the photoreactors are configured as individual reactors and have no connections. Filling with reaction medium then takes place through the concentrator. This configuration is particularly well-suited for laboratory experiments, mechanistic studies, and the like. Furthermore, the present invention provides a photoreaction array comprising a plurality of photoreactors according to the invention, optionally enclosed by a housing (closed at the bottom and on several, preferably all, sides and) open at the top (i.e., the light incident side) or an enclosure open at the bottom and top (i.e., the light incident side).

[0058] These arrays are particularly suitable when there is a lot of light and a large area, such as building roofs and sunlight.

[0059] When using the arrays according to the invention on roofs, in preferred embodiments of the present invention, the photoreactors in the arrays are aligned along an east-west axis, in particular such that the projection of the reaction channels into a horizontal plane is parallel to an east-west axis. This can be achieved on roofs of houses that are not aligned along an east-west axis by arranging the arrays at an angle. Furthermore, in some embodiments of the present invention, the aperture normal is preferably aligned with the sun's path at the equinox, which leads to a latitude-dependent inclination of the arrays.

[0060] Another particular subject of the present invention is a method for producing photoreactors, preferably the photoreactors according to the invention, comprising the steps a) producing the concentrator and cavity by additive manufacturing processes, in particular 3D printing or extrusion; b) if the surfaces of the concentrator and / or cavity do not already have a sufficiently high reflectance for the incident light due to the production in step a), treating the inner or outer surfaces of the concentrator and cavity by polishing or mirroring, in particular as described above by means of solution deposition, CVD, PVD; c) optionally inserting a reaction vessel, in particular a tube, preferably made of glass or plastic (as described above), into the cavity. In preferred variants of this subject of the present invention, the geometry of the cavity is previously (and in conjunction with a (suitable) concentrator),preferably determined using an algorithm, in particular based on MATLAB®, by the following steps: i) providing a cavity with a predetermined geometry, preferably ellipsoidal or in particular circular cross-section, ii) specifying deformation parameters that describe at least one deformation with regard to the location on the wall of the cavity, width and depth of the at least one deformation, iii) deforming the cavity geometry based on the deformation parameters, in particular at the location of the incidence of the primary light beam, iv) determining the reflection values, in particular the frequency of reflections, of the primary light beam within the cavity, reflection values, and optionally storing the determined values, or determining the functionality of the modified geometry with regard to the achieved photocatalytic efficiency, and optionally storing the determined values, va) repeating steps ii) to iv several times,wherein in step ii) modified deformation parameters are specified in each case, and comparison of the respectively determined reflection values ​​or photocatalytic efficiency with the previously determined reflection values ​​or values ​​of the photocatalytic efficiency, vb) terminating the repetition of steps ii) to iv) as soon as the reflection values ​​or the photocatalytic efficiency in a cavity geometry with one or more deformations have reached a desired quality, preferably when the optimal, in particular highest, frequency of reflections of the primary light beam within the cavity has been achieved, vi) output of the determined cavity geometry.

[0061] The changed deformation parameters can represent other, alternative deformations and / or superpositions of the first at least one deformation with further deformations.

[0062] In preferred embodiments, the location of the at least one deformation is randomly predetermined during the first pass of step ii). In further preferred embodiments, the location of at least one deformation is selected during the first pass of step ii) such that it corresponds to the location of the impingement of the primary light beam or includes this location.

[0063] In some preferred embodiments of this subject matter of the present invention, the repetition of steps ii) to iv) is stopped as soon as a deformation or a number of deformations results in an improvement in the reflection values ​​(increase in the reflection frequency) or an increase in the photocatalytic efficiency.

[0064] In other preferred embodiments of this subject matter of the present invention, the modified deformation parameter(s) for step ii) are obtained by optimizing deformation parameters that have led to an improvement in the reflection values ​​(increase in reflection frequency) or an increase in photocatalytic efficiency, in an optimization process, for example, a "pattern search" process. These parameters are preferably then stored. In a subsequent run (repetition of steps ii) to iv)), these improved deformation parameters are then used as a basis for comparison; an improvement in the reflection values ​​(increase in reflection frequency) or an increase in photocatalytic efficiency is then assessed against these already improved parameters and not against the original parameters. This can be repeated until no further improvement can be achieved.

[0065] The improved deformation parameters can be completely new deformations that are set instead of the first deformation, whereby at least one deformation from the first run of the method is / are replaced.

[0066] In other, often preferred, variants, the deformation parameters are assumed to be the deformation or deformations from the first run, and in the subsequent runs, additional deformations are added; the resulting geometry is usually (but not necessarily - it may also be the case that the first deformation parameters provide the best results) a geometry with numerous (even superimposed) deformations. Yet another particular subject of the present invention is a method for optimizing the cavity geometry of a photoreactor, preferably a photoreactor according to the invention, preferably using an algorithm, in particular based on MATLAB®, comprising the steps of i) providing a cavity with a predetermined geometry, preferably ellipsoidal or in particular circular cross-section, ii) specifying deformation parameters that define at least one deformation with regard to location on the wall of the cavity,Describe the width and depth of at least one deformation, iii) deforming the cavity geometry based on the deformation parameters, in particular at the location of the impact of the primary light beam, iv) determining the reflection values, in particular the frequency of reflections, of the primary light beam within the cavity, reflection values, and optionally storing the determined values, or determining the functionality of the modified geometry with regard to the achieved photocatalytic efficiency, and optionally storing the determined values, va) repeating steps ii) to iv several times, wherein in step ii) modified deformation parameters are specified in each case, and comparing the respectively determined reflection values ​​or photocatalytic efficiency with the previously determined reflection values ​​or values ​​of the photocatalytic efficiency,vb) terminating the repetition of steps ii) to iv) as soon as the reflection values ​​or the photocatalytic efficiency in a cavity geometry with one or more deformations has reached a desired quality, preferably when the optimal, in particular highest, frequency of reflections of the primary light beam within the cavity has been reached, vi) outputting the determined cavity geometry.

[0067] In preferred embodiments, the location of the at least one deformation is randomly predetermined during the first run of step ii).

[0068] In further preferred embodiments, during the first pass of step ii), the location of at least one deformation is selected such that it corresponds to the location of the primary light beam's impact or includes this location. In some preferred embodiments of this subject matter of the present invention, the repetition of steps ii) to iv) is terminated as soon as a deformation or a number of deformations results in an improvement in the reflection values ​​(increase in the reflection frequency) or an increase in the photocatalytic efficiency.

[0069] In other preferred embodiments of this subject matter of the present invention, the modified deformation parameter(s) for step ii) are obtained by optimizing deformation parameters that have led to an improvement in the reflection values ​​(increase in reflection frequency) or an increase in photocatalytic efficiency, in an optimization process, for example, a "pattern search" process. These parameters are preferably then stored. In a subsequent run (repetition of steps ii) to iv)), these improved deformation parameters are then used as a basis for comparison; an improvement in the reflection values ​​(increase in reflection frequency) or an increase in photocatalytic efficiency is then assessed against these already improved parameters and not against the original parameters. This can be repeated until no further improvement can be achieved.

[0070] The improved deformation parameters can be completely new deformations that are set instead of the first deformation, whereby at least one deformation from the first run of the method is / are replaced.

[0071] In other, often preferred, variants, the deformation parameters are assumed to be the deformation or deformations from the first run, and additional deformations are added in the subsequent runs; the resulting geometry is usually (but not necessarily - it may also be that the first deformation parameters provide the best results) a geometry with numerous (also superimposed) deformations.

[0072] Finally, a particular subject of the present invention is the use of the photoreactors according to the invention and / or the photoreaction array according to the invention for photocatalytic reactions, preferably photosynthesis processes, for use on areas of 5 cm 2 up to several hectares, preferably open areas or exterior building surfaces, especially on roofs, or for heating and / or disinfecting liquids flowing through the cavity, preferably water, or for the (catalytic) conversion of CO2 and H2O to chemical energy sources.

[0073] In the context of the present invention, the concentrator is preferably designed symmetrically, ie both sides or both walls are of the same height.

[0074] In other preferred embodiments of the present invention, the concentrator is designed asymmetrically. This variant can be used particularly in lighting situations where alignment of the aperture normal to the sun's path is not possible at equinoxes.

[0075] In further embodiments of the present invention, the coatings on the walls of the concentrator and / or cavity can be designed in such a way that they cause a shift in the wavelengths of the incident light. This can be useful and preferred in some variants in order to adapt the incident light, which is preferably sunlight, to the absorption properties of the photocatalyst (or catalyst system) arranged in the reaction space (in the cavity) and / or the reactant(s).

[0076] In further embodiments of the present invention, instead of a photocatalyst, a thermally activatable catalyst (or catalyst system) can be used, which is heated and activated by the light rays incident and reflected in the cavity.

[0077] The cavity entrance, through which the light collected by the concentrator enters the cavity, can be a simple window or, when using reaction tubes in the cavity, a simple hole. These are the typical cases and therefore preferred embodiments of the present invention.

[0078] In other preferred embodiments of the present invention, an optical lens or lens group can be arranged in this entrance, making it possible to precisely control the incident light, for example, to focus it on a desired location or to distribute the incident rays. In yet other preferred embodiments of the present invention, an optical element can be arranged in this entrance that selectively reflects or transmits light of certain wavelengths. This, particularly in the case of wavelength shifts in the cavity (for example, due to corresponding coatings of the cavity's inner walls or reaction media, supports, and / or catalysts arranged in the cavity), allows the incident light of the corresponding wavelengths to pass through but prevents light of corresponding other wavelengths from escaping, thus preventing or reducing loss due to re-emerging light rays.

[0079] Furthermore, the following can be stated regarding the present invention:

[0080] The inventive panel-like, microstructured, and cost-effectively manufactured photoreactor design is characterized by a clever optical layout that, among other things, ensures high photocatalytic efficiency in photosynthesis throughout the year without mechanically aligning the reactor panels to the current position of the sun. This is particularly true with a preferred east-west orientation and a latitude-adapted inclination of the inventive photoreactors.

[0081] Expensive and maintenance-intensive solar tracking, such as is often required in CSP (concentrated solar power) power plants or in the field of solar fuels, is eliminated. Operating costs are significantly reduced by eliminating solar tracking. The geometry of the microstructure allows for cost-effective production, for example, via additive manufacturing processes such as 3D printing or extrusion of polymers (for example, with subsequent vapor deposition of aluminum). The photoreactor design according to the invention can also minimize the amount of expensive photocatalysts used through high catalyst utilization. The homogeneous illumination of the reaction zone ensured by the specific design ensures that a photocatalyst can be operated at its optimal operating point.

[0082] The core element of the photoreactor design is a microstructured reaction channel that directs incident light from various directions into a mirrored cavity. The microstructuring is achieved or represented by the deformations described above. Many photoreactors arranged in parallel (array) allow (arbitrarily) large areas to be covered. In some embodiments of the present invention, a photocatalyst supported on a transparent, preferably porous, structure is located in the cavity. This photocatalyst absorbs the introduced light and uses it to convert, for example, CO2 and water into an energy carrier. Light that is not absorbed during an initial passage through the reaction zone or is scattered by the catalyst is preferentially guided back to the catalyst by the mirrored walls of the cavity.

[0083] In preferred embodiments of the present invention, the geometry of the cavity is optimized with regard to the ability to guide incident, transmitted and scattered light into the reaction zone.

[0084] The latter property of the cavity ensures high radiation transport efficiency despite optical dilution of the catalyst. The optical dilution of the catalyst and the resulting good optical connection guarantee optimal operating conditions for the entire photocatalyst in the system. In this context, "optimal" means that the catalyst is operated at high catalyst utilization and, at the same time, without any loss in the achieved quantum yield. Both properties combined—high radiation transport efficiency and the most optimal operating conditions possible—guarantee high photocatalytic efficiency of the overall system.

[0085] In one embodiment of the present invention, the arrays of photoreactors can be manufactured by cost-effective extrusion of plastics with subsequent optical coating, for example by physical vapor deposition (PVD) of aluminum or silver.

[0086] The photocatalyst can be introduced into these polymer-based and optically coated molded extrudates, for example, by gelation of catalyst-loaded silica alcogels followed by supercritical drying and the concomitant formation of a translucent aerogel.

[0087] In some embodiments of the present invention, the photocatalytically active panels (i.e., the photoreactor arrays according to the invention or a plurality of photoreactors according to the invention) are integrated into a housing and statically aligned at the installation site to optimally match the local lighting conditions. Optimal alignment in this context means that the annual average photocatalytic efficiency achieved is maximized through appropriate panel inclination and orientation. For different roof surface orientations (compass direction and inclination) and different installation locations (latitude), the best possible radiation transport efficiency can be achieved by optimizing the geometry of the mirrored walls of the photoreactors.Thus, variants of the present invention can be produced in an economically viable number of different geometries, each optimized for a range of roof orientations, slopes, and latitudes. The modular design of the present invention enables uncomplicated expansion of existing systems and simple replacement of panels whose photocatalytic efficiency has declined over time due to possible aging of the catalyst or the optical coating.

[0088] The photoreactor panels (arrays) according to the invention are characterized by a clever optical design that ensures high photocatalytic efficiency and good catalyst utilization over a wide range of incidence angles. The materials used for their manufacture also enable cost-effective production.

[0089] What is new about the present invention is the geometry of the reaction channel, which only slightly concentrates light (concentration factor C = 2 - 3, in particular 2.5) and guides it into the actual reaction zone in the mirrored cavity. The appropriately selected dimensions of the reaction zone and a suitably selected optical layer thickness – the latter in the case where the walls of the cavity and / or concentrator are optically transparent to the incident light and coated with a mirror on the outside – further ensure that just two to ten beam passes lead to significant absorption in the reaction volume, while still illuminating the entire reaction volume. The low concentration ratio of the concentrating optics and the channel-like geometry ensure efficient operation even without solar tracking.

[0090] Since photocatalyst systems, despite optical dilution, generally allow very shallow light penetration depths (ranging from a few micrometers to hundreds of micrometers), the appropriate dimensions mentioned above range from a few hundred micrometers to a maximum of a few centimeters. Therefore, it is fundamentally impossible to effectively illuminate larger bulk volumes directly, and micro- to microstructuring of the reaction zone is ultimately unavoidable.

[0091] The new photoreactor design combines the advantages of photoreaction technology with sophisticated tracking optics that efficiently guide incident light to the photocatalyst at all angles of incidence, with the simple construction of a simple photoreactor panel (array) that is easily expandable, cost-effective to produce, and straightforward to operate and maintain. The microstructuring ensures homogeneous illumination of the reaction zone, high catalyst utilization, and ideal operating conditions for the entire catalyst volume.

[0092] The photoreactor design according to the invention essentially consists of a concentrator and an optical cavity. The reaction volume is located in the cavity. The two main components—concentrator and cavity—perform the following functions:

[0093] The concentrator "captures" light in the relevant angle of incidence range and directs it into the cavity.

[0094] The cavity ensures multiple passages of coupled beams through the reaction volume through the deformation of the circular basic geometry.

[0095] In particular embodiments of the present invention, the photoreactors according to the present invention have the following five properties (in particular with which they enable efficient, cost-effective, sunlight-assisted photosynthesis):

[0096] 1. They ensure that the largest possible proportion of the incident light is absorbed in the reaction zone (= have a high radiation transport efficiency in the relevant wavelength range - C|T,A-).

[0097] 2. They ensure that the ideal conditions for synthesis prevail throughout the reaction volume. This applies in particular to the local volumetric photon absorption rate - -, the measure of how much light is absorbed per unit of time and volume at a location in the reaction volume (= local process intensity). 3. Criterion 1. is valid over the entire range of angles of incidence, which results from the daily and annual cycle of the sun.

[0098] 4. Criterion 3 is met without tracking to the sun.

[0099] 5. The geometry of the reactor can be manufactured using inexpensive materials and known mass production processes.

[0100] (Additional information: The daily course of the sun in the sky results in a required acceptance angle of ±90° in the plane of the sun's orbit, and the annual course results in an acceptance angle of ±23.5° in a plane perpendicular to the plane of the ecliptic.)

[0101] (a) Criterion 2 can only be met if the reaction volume can be "transmitted," i.e., is not optically dense. The illumination becomes more homogeneous if only a small portion of the beam's energy (= photons) is absorbed during a beam passage. This has the consequence that a large portion of the light directed onto the reaction volume "transmits" it and is not absorbed. This, in turn, means that the portion of the light directed onto the reaction volume that is absorbed in the reaction volume is small (= r). T ,A is small).

[0102] Furthermore, criteria 1 and (a), and thus also criteria 1 and 2, are only compatible if light that "transmits" the reaction volume without being absorbed is deflected and passed through the reaction volume again.

[0103] Taking criterion 4 into account, this results in a photoreactor design that can ensure "multiple passages" of incident light through the reaction volume at variable angles of incidence.

[0104] In order to ensure that criteria 1 to 5 are met, it is therefore important in the context of the present invention:

[0105] That the ratio of the aperture width of the concentrator (dl) to the width of the entrance into the cavity (d2) is in a range of 2 to 3.

[0106] That the ratio of the length of the concentrator (d4) to the aperture width of the concentrator is in a range of 0.5 to 2.5.

[0107] That the aperture width (dl) is larger than the diameter of the cavity (d3).

[0108] In some specific embodiments of the present invention, the characteristic diameter of the cavity d3 can be determined as a function of the reaction volume as follows: i) The characteristic diameter of the cavity is determined such that the reaction volume can be illuminated with a given absorption coefficient. ii) The characteristic diameter of the cavity is simultaneously determined such that a "reasonable" number of passages of the light beam ensures the absorption of the majority (>90%) of the coupled radiation.

[0109] Furthermore, the absorption coefficient of the reaction volume is set such that a significant fraction of the light absorbed in the cavity is absorbed in the reaction volume (and not in a possibly transparent, but still slightly absorbing, wall or optical coating). iii) In other words, the absorption coefficient of the reaction volume is set (by appropriate optical dilution of the photocatalyst system used) such that, despite parasitic absorption (if any) in the cavity wall and the optical coating of the cavity, C|T,A is at least 60% (= fulfillment of criterion (1)).

[0110] These considerations i) to iii) represent a coupled system. In all three considerations, the optical transport properties of the reaction volume and the reactor components, as well as their characteristic dimensions, play a role. This challenge can be addressed as follows:

[0111] What is needed is the (dimensionless) absorbance of the reaction volume (A RV ) defined according to equation (1), such that the (dimensionless) radiative transport efficiency I-| T ,A has a maximum value, but at least 60% AND the (dimensionless) number of passages of a beam (Nmin) necessary to absorb at least 90% of the coupled light lies in a range from 2 to 10. The given boundary conditions are the (dimensionless) reflectivity of the optical coating (R) and the (dimensionless) absorbance of the cavity wall (A w ), defined according to equation (2).

[0112] The desired absorbance of the reaction volume can be estimated using equation (3). The required number of passages follows from equations (4) and (5). fi = R exp(-2 iy) exp(- Rlz ) (5)

[0113] In order to meet considerations i) to iii), the absorbance of the reaction volume is typically in a range from 0.2 to 1.1. Accordingly, if the walls of the cavity are made of a material that is transparent to the incident light and are treated to be mirror-like on the outside, then in preferred variants of the present invention the diameter of the cavity (d3) and the absorption coefficient of the reaction volume (ORV) are determined as a function of the reflectivity of the optical coating of the cavity (R) and the absorption coefficient (ow) of the wall of the cavity and its wall thickness (d5), so that a number of 2 to 10 passages of an injected beam leads to an absorption of the beam energy of at least 90% and the radiation transport efficiency I-| T ,A is maximum, but at least 60%. This is for relevant material systems and wall thicknesses of the cavity wall (R>90% and A w<<0.2) with an absorbance of the reaction volume (üRvd3) in the range of 0.2 to 1.1.

[0114] Ideal beam paths (in the cavities of the photoreactors according to the invention) are characterized by two properties:

[0115] The ratio between the beam segment length in the reaction volume and in the cavity wall is maximized. This minimizes losses due to parasitic absorption in the cavity wall.

[0116] The length of the beam segment in the reaction volume is maximized. This minimizes the number of necessary passes and thus the losses due to parasitic absorption by the optical coating.

[0117] In a circle-like geometry, i.e. a circular geometry with corresponding deformations, ideal ray paths pass through the center of the geometry.

[0118] Accordingly, in some embodiments of the present invention, it is preferred if the optical elements at the entrance to the cavity or on the wall of the cavity are designed so that coupled beams are guided through the center of the reaction volume as often as necessary (approximately 2 to 10 times, see above). Suitable geometries can be derived using (free-form) optimization tailored to the respective material system, for example, as described above, using algorithms, preferably based on MATLAB®, C++, Python, and especially MATLAB®.

[0119] In the present invention, deformations are particularly preferred such that the majority of incident rays are guided through the reaction volume in as many passes as possible, such that, on the one hand, a high proportion of the incident radiation energy is absorbed in the reaction volume and, on the other hand, the entire reaction volume is illuminated as homogeneously as possible. Accordingly, an incident beam, in particular the primary incident light beam, is not immediately reflected back from the cavity. This leads to high radiation transport efficiency and homogeneous illumination of the reaction volume. Both of these together ensure high photocatalytic efficiency in photosynthesis.

[0120] Within the scope of the present invention, it is possible to achieve a high photocatalytic efficiency with low system costs due to the geometry and the specific design of the photoreactors:

[0121] 1) no tracking of the sun's position is required;

[0122] 2) optimal operating conditions for a catalyst are ensured;

[0123] 3) the catalyst utilization (efficiency), if used, is high;

[0124] 4) a high radiation transport efficiency is ensured.

[0125] In addition, the costs of the present invention are low because:

[0126] 5) can be manufactured from polymers using cost-effective processes, preferably additive manufacturing methods, in particular 3D printing and / or extrusion.

[0127] Furthermore, the present invention is advantageous because the system

[0128] 6) is modularly expandable and easy to maintain.

[0129] The individual parts of the devices according to the invention are operatively connected to one another in a manner customary and known in the art. The various embodiments of the present invention, for example—but not exclusively—those of the various dependent claims or individual embodiments described in the figures, can be combined with one another in any desired manner, provided such combinations do not contradict one another.

[0130] The embodiments of the present invention explained in more detail below with reference to the figures represent various preferred embodiments. Many of the features or embodiments shown in individual figures below can be combined with features and embodiments shown in other figures or the rest of the description, particularly where the features are described accordingly. Furthermore, the figures are not to be interpreted in a limiting manner and are not true to scale. Furthermore, the figures do not contain all features that conventional devices / systems have, but are reduced to the features essential to the present invention and its understanding. For example, screws, hoses, etc. are not shown or not shown in detail.

[0131] The same reference symbols / numbers mean the same or equivalent device parts.

[0132] Figure 1 shows a schematic cross-sectional view of a photoreactor 1 according to the invention. The concentrator KO and the (optical) cavity KA are each enclosed in curly brackets. Furthermore, the figure shows the characteristic parameters of the aperture width dl, the width of the entrance to the cavity d2, the characteristic diameter of the cavity d3 (= largest inner diameter), the length of the concentrator d4, and the wall thickness of the cavity wall d5. Furthermore, various regions are shown: firstly, as I, the entrance to the cavity, and as II, the region of the cavity in which, after an initial beam passage through the cavity (the reaction volume), light beams strike the (mirrored) inner wall of the cavity in the center of the cavity. The dashed lines in Figure 1 indicate how the walls can be designed in variants of the present invention.On the one hand, it is indicated that the concentrator's legs can be curved (deviating from the ideal V-shape or as a cross-section of a CPC). On the other hand, various deformations of the cavity wall are indicated, which can be used to influence the reflection directions of incoming rays.

[0133] It should be expressly noted that this figure serves to illustrate which elements of the photoreactors according to the invention are arranged where and how; the ratios (1), (2) and (3) required according to the invention and the dimensions of the wall variations are not intended to be correctly represented by the schematic Figure 1.

[0134] In Figure 1, the walls of concentrator KO and cavity KA are shown as hatched, outlined areas. This illustrates that, in this example, they are made of a material that is optically transparent to the incident light. In this example, the outer surfaces of concentrator KO and cavity KA are also coated with a reflective layer, which is represented by a thicker line. It can be seen from this figure that the quantities d1, d2, and d4 act on the respective "ends" of the coatings and not on the inner walls (they would act on the inner walls if they were coated or if the walls were made of reflective metal). Quantity d3, on the other hand, acts on the inner walls of the cavity.

[0135] Figure 2 illustrates, likewise not to scale, a possible embodiment of a photoreactor according to the invention. It should be expressly noted that Figure 2 is also not intended to correctly represent the conditions (1), (2), and (3) required according to the invention. In Figure 2, the photoreactor 1 according to the invention is surrounded by a support structure 2. This can contain cooling or heating structures (not shown). III denotes an area with schematic deformations for deflecting the reflection of incident light. Shown here on both sides are optional connecting devices (or connecting areas) IV, with which several photoreactors can be connected to one another, for example to construct photoreactor arrays according to the invention.

[0136] Figure 3 illustrates, for a photoreactor 1 according to the invention, which is surrounded by a support structure 2, the beam path of an incident primary light beam 3, which is redirected by deformation onto a wall of the cavity. This figure also shows a tube 4 (made of glass or plastic, for example), which contains a photocatalyst in its center and through which the reaction medium is passed. It is clearly visible how the light beam 3 is redirected multiple times, thus providing a much better utilization of the light beam than if it were directly reflected back out of the cavity.

[0137] Figure 4 shows a schematic representation (of one use) of a photoreaction array 5 according to the invention, comprising a plurality of photoreactors 1 according to the invention, on a rooftop. The section shows the milli / microstructure of a panel-like photoreaction technology within the scope of the present invention, in which hundreds of parallel-arranged photoreactors 1 according to the invention each enclose small reaction volumes.

[0138] List of reference symbols:

[0139] 1 photoreactor

[0140] 2 Support structure (for example, in a 3D-printed photoreactor)

[0141] 3 primary light beam

[0142] 4 tubes (e.g. made of glass or plastic)

[0143] 5 Photoreactor array

[0144] KO concentrator

[0145] KA (optical) cavity dl aperture width d2 width of the entrance into the cavity d3 characteristic diameter of the cavity (inner diameter) d4 length of the concentrator d5 wall thickness of the transparent material

[0146] I Entrance area into the cavity

[0147] II Area in which the primary light beam hits the mirrored inner wall of the cavity

[0148] III Area with schematic deformations for redirecting the reflection of incident light

[0149] IV Connecting device (connecting area)

[0150] The invention will now be further illustrated with reference to the following non-limiting examples. Example 1:

[0151] The photoreactor design was demonstrated in a laboratory reactor for a photocatalytic model reaction. The geometric dimensions were scaled for ease of handling. The reactor's characteristics were: d1 = 5 mm; d2 = 2.3 mm; d3 = 7.8 mm; and d4 = 11 mm.

[0152] The photoreactor was modelled in a MATLAB®-based simulation environment and its geometry was optimized using optimization algorithms developed specifically for the application. The goal of the optimization was to achieve the highest possible photocatalytic efficiency with perpendicular light incidence into the concentrator. The optimized geometry was 3D printed in stainless steel. The optical surfaces were subsequently post-processed using micro-milling, hand polishing, and electroplating with silver to ensure high reflectivity in the relevant wavelength range.

[0153] The resulting optics were used in a solar-assisted, photocatalytic example reaction (photocatalytic reduction of iron(III) oxalate to iron(II) oxalate). A comparison of simulated and experimentally determined photocatalytic efficiencies showed good agreement between simulation and reality. Varying the angle of incidence of the light in the experiment and the simulation further demonstrated that the tested (inventive) geometry reliably coupled light into the reaction zone within an angle of incidence range of plus / minus 20° to the vertical. Therefore, alignment to the sun was not necessary.

[0154] Example 2:

[0155] Another example was conducted, this time arranging the reactors as a channel array. The reactors each had the following characteristics: d1 = 9 mm; d2 = 3.3 mm; d3 = 8 mm; d4 = 14.3 mm.

[0156] In this example, the photocatalytic reduction of 2 mM potassium trioxalatoferrate solution was investigated. The photoreactors according to the invention were also very effective, demonstrating that they also achieve excellent results as flow reactors. The examples demonstrate that advantageous effects can be achieved with the reactors according to the invention and the process according to the invention, and that the objectives underlying the present invention can be achieved.

Claims

Claims:

1. A photoreactor, in particular for solar photosynthesis, comprising a concentrator and a cavity configured as a flow reactor, wherein the concentrator, viewed in the flow direction, has a V-shaped cross-section open at the bottom or is designed as a compound parabolic concentrator, which is in direct contact with the cavity at its lower end and forms an entrance area to the cavity there, has an aperture width dl, a width of the entrance into the cavity d2 and a height d4; the cavity inner wall, viewed in the flow direction, has an ellipsoidal cross-section with a diameter d3, which, in the area of ​​incidence of the primary incident light beam, has at least one deformation such that the light beam reflected from the point of incidence is not directly reflected back out of the cavity; and wherein (1) the ratio of dl to d2 is in a range of 2 to 3, (2) the ratio of d4 to dl is in the range of 0.5 to 2.

5.

2. Photoreactor according to claim 1, characterized in that (3)a for a single photoreactor configuration dl is less than d3 or equal to d3, or (3)b for a configuration as one of several interconnected photoreactors dl is greater than d3.

3. Photoreactor according to claim 1 or 2, characterized in that the deformations are in the form of indentations or bulges with respect to the ellipsoidal, preferably circular, cross-section of the cavity, wherein the deformation depths are in the range between 1% and 20% of the diameter of the cavity d3 and wherein the deformations are preferably dent-shaped.

4. Photoreactor according to one of the preceding claims, in particular according to claim 1, characterized in that the inner sides of the concentrator or cavity or concentrator and cavity are highly reflective for the incident light, that is to say having a reflectance of at least 80%, preferably polished or mirrored.

5. Photoreactor according to one of the preceding claims, in particular according to claim 1, characterized in that the concentrator and cavity are made of a transparent polymer, preferably polymethyl methacrylate, and the outer sides of the concentrator or cavity or concentrator and cavity are highly reflective for the incident light, in particular have a reflectance of at least 80%, and are preferably polished or mirrored.

6. Photoreactor according to one of the preceding claims, in particular according to claim 1, characterized in that one or more photocatalysts are arranged in the cavity, preferably on a light-permeable support, more preferably in a light-permeable vessel, in particular a tube, arranged in the cavity.

7. Photoreactor according to one of the preceding claims, in particular according to claim 1, characterized in that cooling or heating structures, in particular cooling fins or heat transfer channels, are arranged outside the cavity.

8. Photoreactor according to one of the preceding claims, in particular according to claim 1, characterized in that the photoreactor is surrounded externally by support structures which can optionally have devices for connecting to further photoreactors, preferably click connections, slide-in connections, screw connections or clamp connections.

9. Photoreaction array comprising a plurality of photoreactors according to one of the preceding claims, in particular according to claim 1 or claim 8, optionally enclosed by a housing or an enclosure open at the bottom. Process for the production of photoreactors according to one of claims 1 to 8, in particular according to claim 1, comprising the steps a) producing the concentrator and the cavity by additive manufacturing processes, in particular 3D printing or extrusion; b) if the surfaces of the concentrator and / or the cavity do not already have a sufficiently high degree of reflection for the incident light due to the production in step a), treating the inner or outer surfaces of the concentrator and the cavity by polishing or mirroring, in particular by means of solution deposition, CVD, PVD; c) optionally inserting a reaction vessel into the cavity. Method according to claim 10, characterized in that the geometry of the cavity was previously determined, preferably with the aid of an algorithm, by the following steps: i) providing a cavity with a predetermined geometry, ellipsoidal or, in particular, circular cross-section, ii) specifying deformation parameters that determine at least one deformation with regard to location on the wall of the cavity,Describe the width and depth of at least one deformation, iii) deforming the cavity geometry on the basis of the deformation parameters, in particular at the location of the impact of the primary light beam, iv) determining the reflection values, in particular the frequency of reflections, of the primary light beam within the cavity, reflection values, and optionally storing the determined values, or determining the functionality of the modified geometry with regard to the achieved photocatalytic efficiency, and optionally storing the determined values, va) repeating steps ii) to iv several times, wherein in step ii) modified deformation parameters are specified in each case, and comparing the respectively determined reflection values ​​or photocatalytic, efficiency with the previously determined reflection values ​​or photocatalytic efficiency values, vb) stopping the repetition of steps ii) to iv) as soon as the reflection values ​​or photocatalytic efficiency in a The cavity geometry with one or more deformations has achieved a desired quality, preferably when the optimal, in particular highest, frequency of reflections of the primary light beam within the cavity has been achieved, vi) outputting the determined cavity geometry. Method for optimizing the cavity geometry of a photoreactor according to one of claims 1 to 8, in particular according to claim 1, preferably using an algorithm, comprising the steps of i) providing a cavity with a predetermined geometry, ellipsoidal or, in particular, circular cross-section, ii) specifying deformation parameters that describe at least one deformation with regard to the location on the wall of the cavity, the width, and the depth of the at least one deformation, iii) deforming the cavity geometry based on the deformation parameters, in particular at the location of the impingement of the primary light beam, iv) determining the reflection values, in particular the frequency of the reflections,of the primary light beam within the cavity, reflection values, and optionally saving the determined values, or determining the functionality of the modified geometry with regard to the achieved photocatalytic efficiency, and optionally saving the determined values, va) repeating steps ii) to iv several times, wherein in step ii) modified deformation parameters are specified in each case, and comparing the respectively determined reflection values ​​or photocatalytic efficiency with the previously determined reflection values ​​or values ​​of the photocatalytic efficiency, vb) terminating the repetition of steps ii) to iv) as soon as the reflection values ​​or the photocatalytic efficiency in a, Cavity geometry with one or more deformations has achieved a desired quality, preferably when the optimal, in particular highest, frequency of reflections of the primary light beam within the cavity has been achieved, vi) outputting the determined cavity geometry. Use of the photoreactors according to any one of claims 1 to 8 or of the photoreaction array according to claim 9 or of the photoreactors produced by the method according to claim 10 or claim 11 for photocatalytic reactions, preferably photosynthesis processes, for use on open surfaces, preferably open terrain or building exterior surfaces, in particular on roofs, or for converting CO2 and H2O into chemical energy carriers, or for water treatment.

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