Device for realizing photochemical reactions

Abstract

The present invention relates to an illumination device for a photoreactor comprising a tubular housing (40) having a longitudinal axis (41) and a plurality of individual light sources (30) mounted on an inner surface of the housing (40), the housing (40) comprising flow channels (46) for a heat transfer fluid, the flow channels (46) being disposed on the underside of the inner surface of the housing (40) behind the individual light sources to form conformal cooling passages for the individual light sources. The present invention further relates to a photoreactor comprising an illumination device and a reaction chamber having at least one tubular flow channel, the reaction chamber being disposed inside the illumination device, the channel walls being made of a material that is transparent to the light emitted by the light sources.

Description

[Technical field]

[0001] The present invention relates to an illumination device for a photoreactor comprising a tubular housing having a longitudinal axis and a plurality of individual light sources mounted on an inner surface of the housing. The present invention further relates to a photoreactor comprising an illumination device and a reaction chamber having at least one tubular flow channel, the reaction chamber being disposed inside the illumination device, the channel walls being made of a material transparent to the light emitted by the light source. [Background technology]

[0002] Photoreactors are reactors that make it possible to realize photoreactions, such as photocatalytic or photoinitiated reactions, and are well known in the art. Photoreactors are used for different types of reactions, such as bioreactions, chemical synthesis reactions or water treatment.

[0003] The most common light source for photochemical conversions on an industrial scale has by far been the medium pressure mercury lamp, which has been constructed for a wide range of applications from 150 W laboratory lamps to 60 kW burners. Industrial tubes typically have a diameter of 5 cm, producing an enormous amount of light in a small space; i.e., the light density is very high.

[0004] Basically, these lamps have the emission spectrum of mercury, which is characterized by several lines in the UV and visible range. To increase the intensity of the light in the visible range, it is possible, for example, to add thallium iodide to these lamps. Usually, medium pressure mercury lamps are of tubular construction and they operate either immersed in a stirred reactor as a submerged lamp or in a reactor in a pumping circuit where the reaction medium is continuously pumped past the lamp. Medium pressure mercury lamps emit light uniformly over a large part of the lamp body. The intensity of the light from the lamp can only be controlled to a very limited extent by the power supply. The main disadvantage of mercury lamps is their relatively low luminous efficiency, which is between 5% and 20% for the power consumed. A further disadvantage is the short useful life of the lamp, which is often only about one year. Another main disadvantage is the use of the toxic heavy metal mercury, which must be withdrawn from the tube after its useful life.

[0005] For several years now, high-brightness light-emitting diodes ("LEDs") have been built for the lighting sector, but also for applications in the chemical industry, where they usually produce quasi-monochromatic light in the desired range. In this case, monochromatic light means light with a full width at half maximum (FWHM) of ±10 nm to 30 nm relative to the emission maximum. The luminous efficiency of these diodes ranges from 10% to 60% relative to the power consumed.

[0006] Currently, LED flow-through reactors on the market (e.g. Corning photoreactors) make little consideration of the fact that for reactions with quantum efficiencies less than 100%, the amount of light absorbed decreases as the conversion increases. These reactors are essentially glass plates with serpentine channels inside. The channels cover only about 50%-80% of the surface of the glass plate. Each of the glass plates is uniformly illuminated from both sides. Thus, a significant amount of light does not enter the reaction chamber. In addition, as the conversion increases, the light generated is no longer completely absorbed.

[0007] Apart from the commercially available Corning photoreactor, several other types of photoreactors have been disclosed in the literature.

[0008] WO 2008 / 145719 A1 discloses a photoreactor for bioreactions, comprising an LED plastic moulded part in which at least one LED emitter as a radiation source is embedded in a plastic matrix. The radiation source is arranged inside the photoreactor.

[0009] DE 10 2010 014 712 B3 discloses a modular phototubular reactor for the photochemical treatment of fluidized media, comprising a central axial irradiation unit with at least one radiation source, which is coaxially surrounded by the reactor wall and encloses an annular gap, which provides an irradiation volume between the reactor wall and the irradiation unit.

[0010] DE 10 2014 012 217 A1, DE 10 2014 012 218 A1, DE 10 2014 012 219 A1 and WO 2020 / 228980 A1 disclose a lamp module for insertion into a photochemical reactor, which comprises a cooling body with at least one LED arranged on its exterior and with at least one support structure, at least two immersion tubes arranged one inside the other, and a head part for the electrical connection of the at least one LED and for mounting the lamp module inside the photoreactor.

[0011] China Patent No. 209393167U discloses a reaction tube for use as a photoreactor, which comprises an inner tube and an outer tube, forming a reaction chamber between the inner tube and the outer tube. An LED lamp bead is disposed on the inner tube facing the reaction chamber. A cooling medium can flow through the inner tube.

[0012] US 2015 / 0114912 A1 discloses a reactor that works with ultraviolet light emitting diodes (UV-LEDs) to achieve UV light reactions or UV light initiated reactions in a fluid stream for various applications including water purification. The UV-LED reactor is comprised of a conduit means for passing the fluid stream, an ultraviolet light emitting diode (UV-LED), and a radiation focusing element for focusing the UV-LED radiation onto the fluid along the length of the conduit. The UV-LED reactor may contain a photocatalyst or chemical oxidant that is activated by the UV emitted by the UV-LED for photocatalytic and photoinitiated reactions.

[0013] WO 2019 / 056135 A1 discloses a fluid flow conduit comprising a body having a longitudinally extending primary flow channel, an inlet for introducing a fluid into the primary flow channel, the inlet shaped such that an average velocity of the fluid entering the primary flow channel from the inlet is directed in an inlet flow direction that is non-parallel to the longitudinal direction, and an outlet for directing the fluid to be removed from the primary flow channel. The fluid conduit may be part of a photoreactor having at least one light source that illuminates the primary flow channel longitudinally. The light source may be a visible light LED or a UV-LED.

[0014] Although the use of LEDs in industry already brings many advantages over traditional medium pressure mercury lamps, known reactors still have some drawbacks. For example, the design of many reactors is complicated, for example with regard to sealing, power supplies, and cooling of the immersion lamps. Uniform energy input over the length of the reactor or targeted selective energy input to specific parts of the reactor is hardly possible with known reactors. Thus, targeted reaction control, for example with regard to conversion over the length of the reactor, becomes more difficult. Summary of the Invention [Problem to be solved by the invention]

[0015] It is an object of the present invention to provide a photoreactor that allows complete reaction control in terms of deposit conversion and is easy to build and maintain. [Means for solving the problem]

[0016] This task is solved according to the invention by an illumination device for a photoreactor according to claim 1 and by a photoreactor according to claim 10. Advantageous variants of the illumination device and the photoreactor are presented in claims 2 to 9 and 11 to 13. A further subject of the invention is a process for realizing a photoreaction according to claims 14 and 15.

[0017] A first subject of the invention relates to an illumination device for a photoreactor comprising a tubular housing having a longitudinal axis and a number of individual light sources mounted on the inner surface of the housing. According to the invention, the housing comprises a flow channel for a heat transfer fluid, which is arranged on the rear side of the inner surface of the housing behind the individual light sources to form a conformal cooling passage for the individual light sources. The provision of a conformal cooling passage on the rear side of the individual light sources allows efficient and rapid cooling of the light sources. Compared to the prior art, light sources with a higher energy release are possible, which expands the expected application area for the photoreaction. As a further advantage, the provision of a conformal channel allows thin walls of the housing, which offers the possibility of realizing a lightweight photoreactor with small dimensions.

[0018] The individual light sources can be individually mounted on the inner surface of the housing. Alternatively, the individual light sources can be grouped on a rack, with the rack mounted on the inner surface of the housing. A combination of mounting of individual light sources and mounting of racks or groups of light sources is also possible.

[0019] According to the invention, the lighting device comprises a plurality of individual light sources. In a preferred embodiment, the light sources are light emitting diodes (LEDs). The individual light sources may be any LEDs suitable for enabling the realization of a photoreaction, for example a photocatalytic or photoinitiated reaction. Depending on the reaction to be carried out in the photoreactor comprising the lighting device, the number, size and shape of the individual light sources can be appropriately adapted. Preferably, light emitting diodes are used that emit light in the wavelength range of 250 nm to 800 nm. Most preferably, the light emitted by the LEDs is in the near ultraviolet range (300 nm to 400 nm) or in the visible range (400 nm to 800 nm).

[0020] In a preferred embodiment of the lighting device according to the invention, a tubular protective shell made of a material transparent to the light emitted by the light source and having a longitudinal axis is placed inside the tubular housing, the outer surface of the protective shell and the inner surface of the housing forming an annular channel. Preferably, the longitudinal axis of the protective shell is coaxial or identical with the longitudinal axis of the housing. It is an advantage of this embodiment that the light source is shielded by the protective shell and thus separated from the reactor inside the tubular housing. In case of leakage or failure of the reactor, potentially dangerous components, e.g. volatile components such as reactants, products or solvents, are prevented from coming into contact with the light source.

[0021] It is further preferred for this embodiment that both ends of the annular channel are closed by covers sealingly attached to the housing and protective shell.

[0022] In a preferred variant of the lighting device with covers, at least one cover is provided with a sealable opening for the power cable. In a preferred variant of the lighting device without covers, the tubular housing is provided with a sealable opening for the power cable. These preferred variants can also be combined, for example such that the tubular housing as well as the at least one cover are provided with a sealable opening for the power cable. The sealable opening allows for a simple and safe supply of power to the individual light sources or to a rack of individual light sources.

[0023] The individual light sources or racks of light sources may be attached to the inner surface of the housing by known methods such as a positive lock or friction connection, for example by gluing, screwing or riveting.

[0024] In a preferred embodiment, the housing comprises a passageway through the flow channel between the inner and outer surfaces of the housing at the location where the light source is attached to the inner surface, the passageway being sealed against the flow channel. In this embodiment, individual light sources or racks of light sources can be easily mounted to the inner surface of the housing, for example by bolts inserted through the passageway. Furthermore, it has been found that the walls of the passageway, which extend into the flow channel and are surrounded by the heat transfer fluid during operation, increase the heat transfer from the hot backside of the light source to the cooler heat transfer fluid.

[0025] In another preferred embodiment, the housing comprises receptacles in the form of blind holes in the flow channel between the inner and outer surfaces of the housing, the receptacles being provided with threads for fixing the individual light sources and sealed against the flow channel. The receptacles are equivalent to the passages of the previous embodiment, with the difference that they do not extend outside the outer surface of the housing. In this embodiment, the individual light sources or racks of light sources can be easily mounted on the inner surface of the housing, for example by means of bolts which are screwed into the threads of the receptacles. Moreover, it has been found that the walls of the receptacles, which extend into the flow channel and are surrounded by the heat transfer fluid during operation, increase the heat transfer from the hot backside of the light source to the cold heat transfer fluid.

[0026] Embodiments using a combination of passages through the flow channel and receptacles in the form of blind holes in the flow channel are also possible.

[0027] In a preferred embodiment of the lighting device, the housing is made from a material having a thermal conductivity of more than 8 W / (m·K), preferably selected from the group consisting of nickel, nickel alloys, stainless steel, copper, copper alloys, aluminum and aluminum alloys. These favorable heat transfer properties allow efficient heat transfer from the light source to the heat transfer fluid flowing in the flow channel.

[0028] According to the invention, the flow channels form conformal cooling passages for the individual light sources. The term "conformal" means that in the area where the light sources are arranged, the channel walls of the flow channels leading towards the light sources essentially follow the shape of the inner surface of the tubular housing. Preferably, the channel walls of the flow channels are arranged parallel to the inner surface of the tubular housing. This advantageous design ensures an essentially constant wall thickness between the light sources and the flow channels and therefore a uniform heat transfer from the individual light sources to the heat transfer fluid.

[0029] In a preferred embodiment, the conformal cooling passage comprises at least two flow channels oriented along a longitudinal axis having an inlet for a heat transfer fluid at one end of the passage and an outlet for the heat transfer fluid at the other end of the passage, the at least two flow channels being in fluid communication, In this embodiment, the cooling passage comprises at least two flow channels connected in series.

[0030] Preferably, the conformal cooling passage comprises 2-100, more preferably 6-50, in particular 8-36 flow channels oriented along a longitudinal axis having an inlet for a heat transfer fluid at one end of the first passage and an outlet for the heat transfer fluid at the other end of the passage, each flow channel being in fluid communication with its adjacent flow channels. The series connection of flow channels has the advantage that a heat exchange with a large total volume can be realized with little manufacturing effort. In particular, only a small number of inlets and outlets for the flow channels are required.

[0031] In another preferred embodiment, the conformal cooling passage comprises an inlet for the heat transfer fluid at one end of the passage and an outlet for the heat transfer fluid at the other end of the passage and at least two parallel flow channels oriented along the longitudinal axis, each flow channel being in fluid communication with the inlet and the outlet for the heat transfer fluid. In this embodiment, the cooling passage comprises at least two flow channels connected in parallel. The parallel connection of the flow channels has the advantage that the heat exchange can be achieved with a small pressure drop along the flow channels. A further advantage is the possibility of providing symmetrical flow channels, for example on different sides of the housing.

[0032] A combination of serially connected and parallel connected flow channels is also possible.

[0033] The conformal cooling passages are preferably designed to provide efficient cooling of the individual light sources, which results in an axially and radially uniform temperature profile of the lighting device.

[0034] The flow channels are conveniently used to remove heat generated by the light source by flowing a low temperature heat transfer fluid through the flow channels, which may be selected from, for example, water, demineralized water, glycol-water solutions, salt water, and thermal oils.

[0035] The tubular housing may have any shape suitable for mounting a light source thereon. Preferably, the inner surface of the tubular housing is formed as an n-polygon, n being the number of flat portions of the inner surface. Preferably, the number n is between 3 and 700, preferably between 3 and 350, in particular between 6 and 36.

[0036] In a preferred embodiment of the lighting device, at least at the location where the individual light sources are mounted, the wall thickness of the inner surface of the housing, between the back side of the light source and the inner wall of the corresponding cooling channel, is 0.3-2.5 mm, preferably 0.7-1.5 mm. It has been found that a wall thickness in the preferred range promotes good heat transfer from the hot light source to the cold heat transfer fluid while ensuring the stability of the housing.

[0037] The tubular housing may be produced by any known manufacturing process. Preferred processes for producing the tubular housing are additive manufacturing processes such as selective laser melting (SLM), laser beam powder bed fusion, electron beam melting, electron beam powder bed fusion, binder jetting, FDM processes or FDM-like processes. These processes make it possible to realize rather complex geometric shapes that are hardly or not possible at all with conventional production processes.

[0038] Depending on the roughness of the inner surface of the flow channel, it is preferred that the inner surface is post-treated by an abrasive method, for example by hydroerosive grinding, to reduce the roughness and therefore the possibility of deposits within the channel that can lead to reduced efficiency due to lower thermal conductivity.

[0039] It is further preferred that the inner surface of the tubular housing is polished after its production, the polished surface allowing a perfect connection between the surface and the light source, thereby allowing efficient heat transfer from the light source through the surface of the housing, through its wall, and to the heat exchange fluid flowing within the flow channels.

[0040] The tubular housing may be made in one piece, or may be comprised of multiple pieces which are later assembled to form the tubular housing, In a preferred embodiment, the tubular housing is made in one piece.

[0041] In another preferred embodiment, the tubular housing is made of two shells, each shell forming a longitudinal section of the housing. In this case, the tubular housing is preferably made of two half shells, each of which encompasses an angular range of 180°. Preferably, each shell comprises one or more flow channels that have no fluid connection to the other shell.

[0042] The tubular housing is preferably made from a material that has high thermal conductivity and can be processed by additive manufacturing techniques, preferably the material is selected from the group consisting of nickel, nickel alloys, stainless steel, copper, copper alloys, aluminum and aluminum alloys.

[0043] A second subject of the present invention is a photoreactor comprising an illumination device according to the invention and a reaction chamber arranged inside the illumination device, the reaction chamber having at least one tubular flow channel with a longitudinal axis, a gap being formed between the outer surface of the reaction chamber and the inner surface of the housing of the illumination device, the channel walls of the flow channel being made of a material that is transparent to the light emitted by the light sources, the individual light sources being light emitting diodes (LEDs) arranged around the reaction chamber in a radial direction relative to the longitudinal axis of the flow channel.

[0044] The photoreactor according to the invention comprises at least: (a) an illumination device having a tubular housing having a longitudinal axis and a plurality of individual light sources mounted on an inner surface of the housing, the housing including flow channels for a heat transfer fluid, the flow channels being disposed on an inner surface of the housing behind the individual light sources to form conformal cooling passages for the individual light sources; and (b) a reaction chamber having at least one tubular flow channel having a longitudinal axis and disposed within the illumination device, wherein a gap is formed between an outer surface of the reaction chamber and an inner surface of a housing of the illumination device, the channel walls of the flow channel are made of a material that is transparent to light emitted by the light sources, and the individual light sources are light emitting diodes (LEDs) disposed radially around the reaction chamber relative to the longitudinal axis of the flow channel.

[0045] Arranging the light sources around and therefore outside the reaction chamber has the advantage that the intensity of the light emitted towards the reaction chamber can be controlled individually, which may be more flexible than in the photoreactor concepts known from the prior art. Furthermore, the heat generated by the light sources can be removed in an easier, more efficient and more flexible manner than in the case of a light source inside the reaction chamber.

[0046] Within the scope of the present invention, the term "photoreactor" means a flow reactor having at least one inlet for a reactant and at least one outlet for a product. The reactants flow through a reaction chamber where they chemically react under the influence of light emitted on them to form a product.

[0047] According to the invention, the reaction chamber comprises at least one tubular flow channel through which the reactants and resulting products flow. A tubular flow channel is to be understood as an elongated hollow channel whose length is greater than its diameter, e.g. a tube or pipe. The tubular flow channel has a longitudinal axis.

[0048] Preferably, the longitudinal axis of the housing is coaxial or identical to the longitudinal axis of the flow channel. The term "coaxial" means that the longitudinal axes of the housing and the flow channel are parallel and / or identical.

[0049] In a first embodiment of the photoreactor, the reaction chamber comprises a single tubular flow channel. In that case, the tubular flow channel represents the reaction chamber. This embodiment is particularly suitable for reaction systems in which the reactants have high light absorption. In such cases, a single tubular flow operating in one path may be sufficient to obtain high conversion and yield of the desired product.

[0050] In a second embodiment of the photoreactor, the reaction chamber comprises a number of tubular flow channels arranged coaxially in the reaction chamber and fluidly connected to each other. In this context, the term "coaxial" means that the longitudinal axes of the tubular flow channels are parallel and / or identical. This embodiment is particularly suitable for reaction systems in which the reactants have moderate to low light absorption. In such cases, providing a number of tubular flow channels as reaction space allows optimal use of the amount of light provided.

[0051] In a preferred variant of the second embodiment, the tubular flow channels are connected in series, meaning that the outlet of a flow channel is connected to the inlet of another flow channel. Depending on the arrangement of the tubular flow channels relative to one another, the connection can be realized by directly connecting the inlet to the outlet, for example for flow channels arranged in series, or by using a u-shaped bend, for example for flow channels arranged next to one another in parallel. Combinations of flow channels are also possible.

[0052] In another preferred variant of the second embodiment, the tubular flow channels are connected in parallel, meaning that their inlets are connected to an inlet manifold and their outlets are connected to an outlet manifold.

[0053] In another preferred variant of the second embodiment, the tubular flow channels are partly connected in series and partly connected in parallel.

[0054] In another preferred variation of the second embodiment, the multiple tubular flow channels comprise at least one inner tube open at both ends and at least one outer tube open at one end and closed at an opposite end, the inner tube being concentrically disposed within the outer tube with an axial distance between the one open end of the inner tube and the closed end of the outer tube.

[0055] Depending on the reaction to be carried out in the photoreactor, the number, size and shape of the tubular flow channels can be appropriately adapted.

[0056] In a preferred embodiment, the tubular flow channel is axially symmetrical with respect to its corresponding longitudinal axis, meaning that for each cross-section perpendicular to the longitudinal axis, the inner wall of the channel is point-symmetrical with respect to the longitudinal axis.

[0057] In a further preferred embodiment, the tubular flow channel is rotationally symmetric about its corresponding longitudinal axis, meaning that the inner wall of the flow channel has a circular cross-section.

[0058] The cross section of the tubular flow channel may be constant or may vary over the length of the flow channel. In one embodiment, the tubular flow channel has a conical shape with a cross section that widens in the flow direction. This embodiment can be advantageously used for reactions where the conversion of reactants depends on light absorption. With an increase in the cross section of the inner wall of the tubular flow channel, the flow rate decreases and the residence time of the reaction mixture inside the channel increases, thus compensating for the lower light absorption in the products than in the reactants.

[0059] In one embodiment, the cross-sections of the inner and outer walls of the tubular flow channel are identical, preferably circular, elliptical, or polygonal.

[0060] In a further embodiment, the cross-sections of the inner and outer walls of the tubular flow channel are different in shape. In a preferred variant of this embodiment, the inner wall has a circular cross-section and the outer wall has a polygonal cross-section. Using this variant, it may be advantageous to arrange the individual light sources on the surface of the polygon, with the effect that the emitted light strikes the surface perpendicularly, leading to efficient use of the light sources.

[0061] For thermal management or safety measures, it may be advantageous to use a gap between the outer surface of the reaction chamber and the inner surface of the housing. For thermal management, the gap can be empty or filled with an insulating material. A heat carrier medium, preferably transparent to the light emitted by the light source, preferably silicone oil, water or a mixture containing water and ethylene glycol, flows through the gap. For safety measures, the gap is filled with or allows the flow of an inert medium, preferably nitrogen.

[0062] In one embodiment of the photoreactor, the wall of the tubular flow channel is a double jacket. It may be advantageous to use the annular space between the inner and outer walls of the jacket for thermal management or safety measures. In the case of thermal management, the annular space may be empty or filled with an insulating material. A heat carrier medium, preferably transparent to the light emitted by the light source, preferably silicone oil, water or a mixture containing water and ethylene glycol, flows through the annular space. In the case of safety measures, the annular space is filled with or flows through an inert medium, preferably nitrogen.

[0063] It is further preferred that a tubular protective shell, made of a material transparent to the light emitted by the light source and having a longitudinal axis, is disposed in the gap between the outer surface of the reaction chamber and the inner surface of the housing of the illumination device to form an annular channel between the outer surface of the reaction chamber and the protective shell, the longitudinal axis of the protective shell being preferably coaxial or identical to the longitudinal axis of the flow channel.

[0064] For thermal management or safety measures, it may be advantageous to use an annular channel between the outer surface of the reaction chamber and the protective shell. For thermal management, the annular channel can be empty or filled with an insulating material. A heat carrier medium, preferably transparent to the light emitted by the light source, preferably silicone oil, water or a mixture containing water and ethylene glycol, flows through the annular channel. For safety measures, the annular channel is filled with or flows through an inert medium, preferably nitrogen.

[0065] The tubular flow channels may include internal structures such as baffles or deflectors.

[0066] According to the invention, the walls of the flow channel, and in a preferred embodiment the protective shell, are made of a material that is transparent to the light emitted by the light source. The term "transparent" means that a large part of the light emitted by the light source passes through the material. Preferably, this material does not act as a filter in the incident wavelength range of the emitted light. Preferably, this material is translucent or transparent, in particular transparent.

[0067] Preferably, the material is selected from the group of substances including glass ceramics, quartz glass, borosilicate glass, plexiglass (acrylic glass), polycarbonate (PC), polyvinyl chloride (PVC), polystyrene (PS), cycloolefin copolymers (COC), microcrystalline polyamide (PA), polyethers, polyethylene terephthalate (PET), polyethylene 2,5-furandicarboxylate (PEF) or fluorine-containing polymers, such as FEP. The material may also be a mixture or composite of at least two of the above-mentioned substances. Fluorine-containing polymers are preferred among the polymers.

[0068] Plexiglas (acrylic glass) includes polymethylmethacrylate (PMMA) of different stereoregularities, polymethylmethacrylate fluoride of different stereoregularities, and polymethylmethacrylimide (PMMI) of different stereoregularities. Polycarbonate (PC) is a thermoplastic that is formally a polyester of carbonic acid. Polyvinyl chloride (PVC) is a polymer obtained by emulsion polymerization (E-PVC), suspension polymerization (S-PVC), or bulk polymerization from vinyl chloride itself (M-PVC). Polystyrene (PS) is an atactic, syndiotactic, or isotactic polymer produced from styrene. Cycloolefin copolymers (COC) are amorphous polyolefins obtained from monomeric olefins with cyclohexene rings and the monomer ethene. Microcrystalline polyamides (PA) are polymers prepared from aminocarboxylic acids (AS type) or from mixtures of dicarboxylic acids with diamond (ASSA type) that form crystalline domains. Polyethers are long chain, mostly aromatic ethers, such as polyetheretherketone. Polyethylene terephthalate (PET) is a polymer made from ethylene glycol and terephthalic acid. Polyethylene 2,5-furandicarboxylate (PEF) is a polymer prepared from 2,5-furandicarboxylic acid and ethylene glycol. FEP stands for tetrafluoroethylene-hexafluoropropylene copolymer.

[0069] Depending on the number and arrangement of the tubular flow channels, the reaction chamber can have different sizes and shapes. In the case of a single tubular flow channel or multiple tubular flow channels arranged concentrically, the outer wall of the outermost tubular flow channel represents the outer surface of the reaction chamber. In the case of multiple tubular flow channels arranged next to each other, the outer surface of the reaction chamber is formed by a portion of the outer wall of the outermost flow channel.

[0070] In a preferred embodiment of the photoreactor, the outer surface of the reaction chamber comprises flat or concave channel wall sections. It is an advantage of this embodiment that the coupling energy for the light emitted by the light source is higher in areas with flat or concave sections.

[0071] In a further preferred embodiment of the photoreactor, the outer surface of the reaction chamber is coated with an anti-reflective coating. The advantage of this embodiment is that the light transmission and therefore the efficiency of the photoreactor is increased.

[0072] In a further preferred embodiment of the photoreactor, the outer surface of the reaction chamber comprises a portion of the channel wall having a depression that is dome-shaped, cone-shaped or pyramid-shaped.

[0073] In this embodiment, it is further preferred that the light source comprises a number of individual light sources, which are assigned to the depressions and emit light in the direction of the depressions. In this embodiment, the energy loss due to reflection of the light emitted by the light source can be minimized.

[0074] The reaction chamber can be produced by any known manufacturing technique, for example by hot forming, machining, or additive manufacturing.

[0075] According to the invention, the photoreactor comprises LEDs as individual light sources, which are arranged radially with respect to the longitudinal axis of the flow channel and around the reaction chamber.

[0076] In a further preferred embodiment of the photoreactor, the light sources are arranged around the reaction chamber with axial symmetry of the light sources with respect to the longitudinal axis of the reaction chamber, meaning that for each cross section perpendicular to the longitudinal axis, the light emitting surface of the light sources is point symmetric with respect to the longitudinal axis.

[0077] In a preferred embodiment, the cross-section of the inner surface of the tubular housing perpendicular to the longitudinal axis of the flow channel has the shape of an n-polygon, n being the number of flat portions of the inner surface. Preferably, the number n is between 3 and 700, preferably between 3 and 350, in particular between 6 and 36. The flat inner surfaces of the n-polygon are well suited for mounting individual light sources or racks or groups of light sources.

[0078] A third subject of the invention is a process for achieving a photoreaction in a photoreactor according to the invention, comprising the steps of flowing at least one reactant through a reaction chamber and irradiating the reactant with light emitted from a light source.

[0079] In a preferred embodiment of the process for carrying out a photoreaction, the light source comprises a number of individual light sources, the intensity of light emitted by the individual light sources being adapted depending on the conversion rate of the photoreaction along the flow channel.

[0080] It is further preferred that at least one product of the photoreaction is vitamin A.

[0081] The invention will now be explained in more detail with reference to the drawings, which should be interpreted as a representation of the principles, and which do not constitute any limitation of the invention, for example with regard to specific dimensions or design variants. [Brief description of the drawings]

[0082] [Figure 1] 1 shows longitudinal and cross-sectional cut views of a photoreactor with a single flow channel as a first embodiment according to the present invention. [Diagram 2] 2A-2D show cross-sectional cutaway views of four different variations of the photoreactor of FIG. 1. [Diagram 3] 2 shows longitudinal and cross-sectional cut views of a photoreactor having a flow channel with an inner and outer tube as a second embodiment according to the invention. [Figure 4] 1 shows a three-dimensional view of a shell of a tubular housing for a first embodiment of a lighting device according to the invention. [Diagram 5] 5 shows a cutaway view of the shell of FIG. 4. [Figure 6] 2 shows a three-dimensional view of a second embodiment of a lighting device according to the invention; [Figure 7] 7 shows a longitudinal cut view of the lighting device of FIG. 6. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0083] List of reference numbers used 10 Reaction chamber 11 Annular Space 20 Flow Channel 21 Longitudinal axis 22 Wall 23 Inner tube 24 Outer tube 30 light source 40 Housing 41 Longitudinal axis 42 Wearing elements 43 Passage 44 Inlet for heat transfer fluid 45 Outlet for heat transfer fluid 46 Flow Channel 47 Flow channel deflection 48 Power supply opening 49 Underbite 50 Protective Shell 51 Longitudinal axis 52 Annular Channel 53 Sealing 54 Sealing 60 Cover EXAMPLES

[0084] Example 1 FIG. 1 shows a longitudinal cut (left) and a cross-sectional cut (right) of a photoreactor with a single flow channel as a first embodiment according to the invention. The photoreactor comprises an illumination device and a reaction chamber 10. The illumination device comprises a tubular housing 40 with a longitudinal axis 41 and a plurality of individual light sources 30 mounted on the inner surface of the housing 40. The reaction chamber 10 comprises a tubular flow channel 20 through which the reaction mixture flows from bottom to top (arrows). The flow channel 20 is a hollow cylinder with a circular cross section and a symmetrical alignment of the channel walls 22 around the longitudinal axis 21. The inner and outer surfaces of the channel walls 22 are therefore convex when viewed from the light source 30. In this first embodiment, the reaction chamber 10 is identical to the flow channel 20. The channel walls 22 are made of a material that is transparent to the light emitted by the light source 30. The individual light sources 30 are light emitting diodes (LEDs) and are arranged around the reaction chamber 10 radially relative to the longitudinal axis 21 of the flow channel 20. The tubular flow channel 20 is arranged inside the illumination device to form a gap 11 between the outer surface of the reaction chamber 10 and the inner surface of a housing 40 of the illumination device. The gap 11 may be filled or flowed with a heat transfer fluid, preferably silicone oil, that is transparent to the light emitted by the light sources 30. The longitudinal axis 41 of the housing 40 is the same as the longitudinal axis 21 of the flow channel 20.

[0085] Figures 2A-2D show cross-sectional cutaway views of four different variants of the photoreactor according to Figure 1. These variants differ from each other and from the variant according to Figure 1 in the cross-section of the channel wall 22 and the cross-section of the tubular housing with respect to the LEDs as light sources 30 surrounding the channel wall 22. In all variants, the channel wall 22 and the light sources 30 are symmetrical with respect to the longitudinal axis (indicated as "+" in the drawings).

[0086] In the variation of the photoreactor according to Figure 2A, the channel wall 22 and the tubular housing for the light source 30 are square in cross section. The LED is arranged on the inner surface of the tubular housing such that its light is emitted perpendicularly onto the flat outer surface of the channel wall 22. The inner surface of the channel wall 22 is also flat.

[0087] In the photoreactor variant according to Fig. 2B, the channel wall 22 and the tubular housing for the light source 30 are triangular in cross section. The LED is arranged on the inner surface of the tubular housing such that its light is emitted perpendicularly onto the flat outer surface of the channel wall 22. The inner surface of the channel wall 22 is also flat.

[0088] In the photoreactor variant according to Fig. 2C, the reaction chamber is formed by four sections of the channel wall 22, which are curved inwards and connected at their edges, which in cross section form a square. The four wall segments of the channel wall 22 have concave inner and outer surfaces when viewed from the light source 30. The tubular housing for the light source 30 is square in cross section. The LED as the light source 30 is mounted flat on the inner wall of the tubular housing and emits its light onto the concave outer surface of the channel wall 22.

[0089] In the variation of the photoreactor according to Fig. 2D, the cross-section of the outer surface of the channel wall 22 and of the outer surface of the tubular housing for the light source 30 are regular dodecagons. The LEDs are arranged on the inner surface of the tubular housing such that their light is emitted vertically onto 12 flat segments of the outer surface of the channel wall 22. The inner surface of the channel wall 22 is circular in cross-section.

[0090] Example 2 FIG. 3 shows a longitudinal cut (left) and a cross-sectional cut (right) of a photoreactor with a flow channel comprising an inner tube and an outer tube as a second embodiment according to the invention. The photoreactor comprises an illumination device and a reaction chamber 10. The illumination device comprises a tubular housing 40 having a longitudinal axis 41 and a plurality of individual light sources 30 mounted on the inner surface of the housing 40. The reaction chamber 10 comprises an inner tube 23 open at both ends and an outer tube 24 open at its lower end and closed at its upper end. The inner tube 23 is concentrically arranged inside the outer tube with an axial distance between the upper open end of the inner tube and the upper closed end of the outer tube 24. The inner tube 23 and the outer tube 24 form one tubular flow channel through which the reaction mixture flows from the bottom to the top of the inner tube 23 and from the top to the bottom of the outer tube 24 (arrows). The flow channel is a hollow cylinder having a circular cross-section with channel walls 22 symmetrically aligned about longitudinal axis 21. Thus, the inner and outer surfaces of channel walls 22 are convex when viewed from light source 30.

[0091] In this second embodiment, the reaction chamber 10 is identical to the flow channel 20. The channel walls 22 are made of a material that is transparent to the light emitted by the light sources 30. The individual light sources 30 are light emitting diodes (LEDs) and are arranged around the reaction chamber 10 radially relative to the longitudinal axis 21 of the flow channels 23, 24. The tubular flow channel is arranged inside the lighting device, forming a gap 11 between the outer surface of the reaction chamber 10 and the inner surface of the housing 40 of the lighting device. The gap 11 can be filled or flowed by a heat transfer fluid, preferably silicone oil, that is transparent to the light emitted by the light sources 30. The longitudinal axis 41 of the housing 40 is identical to the longitudinal axis 21 of the flow channel.

[0092] Example 3 Fig. 4 shows a three-dimensional view of a shell of a tubular housing 40 for a first embodiment of a lighting device according to the present invention. Fig. 5 shows a cutaway view of the shell of Fig. 4, without showing the outer wall of the tubular housing. In this exemplary embodiment, two shells as shown in Fig. 4 are assembled to form the tubular housing 40. The shells form the longitudinal section of the housing and encompass an angular range of 180°. The shells comprise a number of flanges for assembling two of the shells to form the tubular housing. Mounting elements 42 are provided on the outside of the tubular housing 40, allowing the housing to be mounted on a support.

[0093] The inner and outer surfaces of the shell are formed as polygons, each with eight flats. The inner surface of the assembled tubular housing is therefore formed as a polygon with 16 flats on the inner surface. The tubular housing 40 is constructed to allow a number of individual light sources (not shown in FIG. 4) to be attached to the inner surface of the housing 40. The individual light sources may be light emitting diodes (LEDs), either as individual LEDs or a rack with a number of LEDs. For this purpose, each section of the polygon is provided with a passage 43 between the inner and outer surfaces of the shell. The individual light sources or the rack of light sources can be easily mounted to the inner surface of the housing, for example by means of bolts inserted through the passages 43 and fixed from the outside.

[0094] A heat transfer fluid is configured to flow through the tubular housing 40. The housing 40 includes flow channels 46 for the heat transfer fluid, which are arranged on the back side of the inner surface of the housing 40 behind the individual light sources to form conformal cooling passages for the individual light sources. In the embodiment shown in FIG. 5, the conformal cooling passage includes eight flow channels 46 oriented along the longitudinal axis of the housing 40, one flow channel 46 for each of the eight parts of a polygon. The flow channels 46 are separated from one another by walls that extend from the back side of the inner wall of the housing to the back side of the outer wall of the housing. Each flow channel 46 is in fluid communication with its adjacent flow channel by a cutout in the separating wall that forms a flow channel deflection portion 47. The cooling passage has the shape of a labyrinth extending between an inlet for the heat transfer fluid 44 at one end of the passage and an outlet for the heat transfer fluid 45 at the other end of the passage.

[0095] A passage 43 for fixing the light source extends through the flow channel 46 between the inner and outer surfaces of the housing 40 at the location where the light source 30 is attached to the inner surface. In the embodiment shown, the passage 43 is formed by a channel that is radially closed and therefore sealed with respect to the flow channel 46. Besides sealing, it has been found that this configuration of the passage has the further advantage that the walls of the passage, which extend into the flow channel and are surrounded by the heat transfer fluid in operation, increase the heat transfer from the hot backside of the light source to the cold heat transfer fluid.

[0096] Example 4 Fig. 6 shows a three-dimensional view of a second embodiment of a lighting device according to the invention. Fig. 7 shows a longitudinal cut-away view of the lighting device of Fig. 6. The lighting device for a photoreactor comprises a tubular housing 40 having a longitudinal axis 41. In this exemplary embodiment, the tubular housing 40 is produced in one piece. On the outside of the tubular housing 40, mounting elements 42 are provided, allowing the housing to be mounted on a support. The LEDs, grouped on a longitudinal rack, are mounted on the inner surface of the housing 40 as individual light sources 30.

[0097] The housing 40 comprises flow channels 46 for the heat transfer fluid, which are arranged on the back side of the inner surface of the housing 40 behind the individual light sources 30 to form conformal cooling passages for the individual light sources 30. As in the previous embodiment, in the embodiment shown in Figs. 6 and 7, the conformal cooling passage comprises several flow channels 46 oriented along the longitudinal axis 41 of the housing 40. The flow channels 46 are separated from one another by walls that extend from the back side of the inner wall of the housing to the back side of the outer wall of the housing. Each flow channel 46 is in fluid communication with its neighboring flow channels by a cutout in the separating wall that constitutes a deflection of the flow channel. The cooling passage has the shape of a labyrinth extending between an inlet for the heat transfer fluid 44 at one end of the passage and an outlet for the heat transfer fluid 45 at the other end of the passage. In this example, the housing 40 has a receptacle 49 in the form of a blind hole in the flow channel 46 between the inner and outer surfaces of the housing 40, the receptacle 49 having a screw thread for fixing a rack of individual light sources and sealed against the flow channel 46.

[0098] The lighting device according to this embodiment further comprises a tubular protective shell 50 made of a material transparent to the light emitted by the light source 30, having a longitudinal axis 51 and arranged inside the tubular housing 40. The outer surface of the protective shell 50 and the inner surface of the housing 40 form an annular channel 52. The longitudinal axis 51 of the protective shell 50 is identical to the longitudinal axis 41 of the housing 40. Both ends of the annular channel 52 are closed by covers 60 sealingly attached to the housing 40 and to the protective shell 50. At the upper end of the tubular housing 40 openings 48 for the power cable are provided. These openings are sealed against the flow channel 46.

Claims

Claim 1 An illumination device for a photoreactor comprising a tubular housing (40), said tubular housing having a longitudinal axis (41) and a plurality of individual light sources (30) mounted on the inner surface of said housing (40), said housing (40) comprising a flow channel (46) for a heat transfer fluid, the channel wall of said flow channel (46) directed towards said light source (30) being arranged on the back side of the inner surface of said tubular housing (40) behind said individual light sources such that the flow channel (46) substantially follows the shape of the inner surface of said tubular housing (40) in the region where said light source (30) is arranged, forming a conformal cooling passage for said individual light sources. An illumination device characterized by this. Claim 2 The illumination device according to claim 1, characterized in that said light source (30) is a light emitting diode (LED) having a wavelength of 250 nm to 800 nm. Claim 3 A tubular protective shell (50) made of a material having transparency to the light emitted by said light source (30) and having a longitudinal axis (51) is arranged inside said tubular housing, the outer surface of said protective shell (50) and the inner surface of said housing (40) forming an annular channel (52), the longitudinal axis (51) of said protective shell (50) preferably being coaxial or identical to the longitudinal axis (41) of said housing (40). The illumination device according to claim 1, characterized by this. Claim 4 The illumination device according to claim 3, characterized in that both ends of said annular channel (52) are closed by a cover (60) attached to said housing (40) and said protective shell (50) in a sealed state. Claim 5 The housing (40) comprises a passage (43) passing through said flow channel (46) between the inner surface and the outer surface of said housing (40) at the position where said light source (30) is attached to the inner surface, said passage (43) being sealed with respect to said flow channel (46). The illumination device according to claim 1, characterized by this. Claim 6 The housing (40) comprises a receptacle (49) in the form of a blind hole in the flow channel (46) between the inner surface and the outer surface of the housing (40), the receptacle (49) comprising a thread for fixing the individual light sources, and being sealed with respect to the flow channel (46). The lighting device according to claim 1, characterized in that.

7. The housing (40) is made of a material having a thermal conductivity exceeding 8 W / (m·K), and the material is preferably selected from the group consisting of nickel, nickel alloys, stainless steel, copper, copper alloys, aluminum and aluminum alloys. The lighting device according to claim 1, characterized in that.

8. The conformal cooling passage has at least two flow channels (46) directed along the longitudinal axis (41), having an inlet (44) for the heat transfer fluid at one end of the passage and an outlet (45) for the heat transfer fluid at the other end of the passage, and the at least two flow channels (46) being in fluid communication. The lighting device according to claim 1, characterized in that.

9. The conformal cooling passage comprises an inlet (44) for the heat transfer fluid at one end of the passage, an outlet (45) for the heat transfer fluid at the other end of the passage, and at least two flow channels (46) parallel to each other directed along the longitudinal axis (41), each flow channel (46) being in fluid communication with the inlet (44) and the outlet (45) for the heat transfer fluid. The lighting device according to claim 1, characterized in that.

10. An illumination device according to any one of claims 1 to 9, and a reaction chamber (10) having at least one tubular flow channel (20) with a longitudinal axis (21), the reaction chamber being disposed inside the illumination device, wherein a gap (11) is formed between the outer surface of the reaction chamber (10) and the inner surface of the housing (40) of the illumination device, the channel wall (22) of the flow channel (20) is made of a material that is transparent to the light emitted by the light source (30), and the individual light sources (30) are light-emitting diodes (LEDs) arranged radially around the reaction chamber (10) with respect to the longitudinal axis (21) of the flow channel (20). A photoreactor comprising the reaction chamber (10).

11. The photoreactor according to claim 10, wherein the longitudinal axis (41) of the housing (40) is coaxial with or the same as the longitudinal axis (21) of the flow channel (20).

12. A tubular protective shell (50) made of a material that is transparent to the light emitted by the light source (30) and having a longitudinal axis (51) is disposed in the gap (11) to form an annular channel between the outer surface of the reaction chamber (10) and the protective shell (50), and the longitudinal axis (51) of the protective shell (50) is preferably coaxial with or the same as the longitudinal axis (21) of the flow channel (20). The photoreactor according to claim 10.

13. The cross-section of the inner surface of the housing (40) perpendicular to the longitudinal axis (21) of the flow channel (20) has an n-sided polygon shape, where n is the number of flat portions of the inner surface, and the number n is from 3 to 700, more preferably from 6 to 350. The photoreactor according to claim 10.

14. A process for realizing a photoreaction in the photoreactor according to claim 10, the process comprising the steps of flowing at least one reactant through the reaction chamber and irradiating the reactant with the light emitted from the light source.

15. The process according to claim 14, wherein at least one product of the photoreaction is vitamin A.

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