METHOD FOR DEHYDROGENATING A HYDROGEN CARRIER MEDIUM

Description

[0001] The present patent application claims the priorities of the German patent applications DE 10 2018 210 337.2 and DE 10 2018 210 247.3.

[0002] The invention relates to a process for dehydrogenating a hydrogen carrier medium.

[0003] US 2018 / 0093889 A1 discloses a liquid hydrogen storage medium and a method for storing hydrogen.

[0004] JP 2015-030 653 A discloses a system and a method for energy utilization from carbon dioxide.

[0005] US 2017 / 0166496 A1 discloses a hydrogenation system for aromatic compounds.

[0006] Hydrogen release from a support material using a membrane is known from the articles Ferreira-Aparicio P. et al.: "On the Performance of Porous Vycor Membranes for Conversion Enhancement in the Dehydrogenation of Methylcyclohexane to Toluene", Journal of Catalysis, 212, 182-192 (2002) and Gang Li et al.: "Highly enhanced ammonia decomposition in a bimodal catalytic membrane reactor for CO-free hydrogen production", Catalytics Communications, 15 (2011) 60-63.

[0007] The chemical utilization of hydrogen from fluctuating energy sources is known from the article Geburtig, D. et al.: "Chemical utilization of hydrogen from fluctuating energy sources - Catalytic transfer hydrogenation from charged Liquid Organic Hydrogen Carrier Systems", International Journal of Hydrogen Energy, 41 (2016) 1010 to 1017.

[0008] A carrier medium for chemically binding hydrogen is known from EP 1 475 349 A2.

[0009] The hydrogen carrier medium is a liquid organic hydride known as a liquid organic hydrogen carrier (LOHC). LOHC can be loaded with hydrogen, i.e., hydrogenated. In its hydrogenated form, the hydrogen is chemically bonded to the hydrogen carrier medium. The carrier medium is in a loaded state. In particular, LOHC can be reversibly loaded with hydrogen and unloaded from hydrogen. The physicochemical properties of LOHC are highly similar to conventional liquid fuels, allowing pumps and tank vehicles to be used for transport, and containers to be used for storage of LOHC in the field of fuel logistics. Hydrogen storage in chemically bonded form in an organic liquid allows pressureless storage under normal conditions over long periods of time without significant hydrogen loss.LOHCs are aromatic compounds with at least one π-electron system that are converted into the corresponding saturated, alicyclic compounds through catalytic hydrogenation. Examples of LOHCs include dibenzyltoluene and benzyltoluene as pure substances, isomeric mixtures, or mixtures of these substances. Polycyclic, heteroaromatic compounds with at least one π-electron system that are converted into the corresponding saturated, polycyclic compounds containing heteroatoms such as nitrogen or oxygen through hydrogenation can also serve as LOHCs. In particular, N-ethylcarbazole, N-propylcarbazole, N-isopropylcarbazole, N-butylcarbazole, or mixtures of these substances serve as LOHCs. Oligomers or polymers with extended π-conjugated electron systems that are converted into the corresponding saturated compounds through hydrogenation are also possible as LOHCs.To release hydrogen, the hydrogen carrier medium, i.e., LOHC, is dehydrogenated with the addition of heat and in the presence of a catalyst, converting the LOHC into its discharged form. During the discharge of the LOHC, hydrogen is released from an organic molecule or from a mixture of organic molecules through a catalyzed dehydrogenation reaction. This means that the hydrogen is released through a material conversion of the at least partially loaded hydrogen carrier medium in a reaction vessel by means of a catalyzed dehydrogenation reaction.

[0010] It has been shown that the release rate, i.e., the amount of hydrogen released per unit of time, is limited with the state-of-the-art processes. Dehydrogenation of the hydrogen carrier medium according to the state-of-the-art is therefore uneconomical at temperatures below 250 °C. A technically viable release rate of at least 10 standard liters of hydrogen per liter of catalyst volume per minute can only be achieved with the state-of-the-art processes if the reaction temperature exceeds 250 °C.

[0011] The invention is based on the object of improving the release of hydrogen from a hydrogen carrier medium from an economic point of view, so that hydrogen is released in particular with an increased release rate and in particular at reduced temperatures.

[0012] The object is achieved by the features of claim 1. The core of the invention is that, in addition to a metal-containing catalyst material, a metal-free reaction accelerator substance is used to dehydrogenate an at least partially loaded hydrogen carrier medium. The hydrogen carrier medium is, in particular, LOHC and, in particular, heteroatom-free. The LOHC consists, in particular, exclusively of carbon atoms and hydrogen atoms. It has been found that heteroatom-free LOHC substances are advantageous over substances with heteroatoms such as nitrogen or boron. Heteroatom-free LOHC substances are chemically very similar to the fuels used today, so that the infrastructure for fuel transport, storage, and distribution can be used for the transport, storage, and distribution of the LOHC substance.In particular, heteroatom-free LOHC substances are more readily available and cost-effective, as these substances can be obtained directly from petrochemical feedstocks. Heteroatom-free carrier media do not have the disadvantage that the melting point in the hydrogen-depleted form is above room temperature, which would otherwise hamper the use of LOHC systems for technical applications.

[0013] For example, the heteroatom-free LOHC substance dibenzyltoluene has a melting point below -35 °C. The heteroatom-containing LOHC substance N-ethylcarbazole has a melting point of 70 °C.

[0014] The thermal stability of heteroatom-free hydrogen carrier media is increased compared to heteroatom-containing carrier media due to the comparatively more stable carbon-carbon bonds. Undesirable thermal decomposition reactions are reduced in the heteroatom-free hydrogen carrier media.

[0015] Particularly suitable metal-containing catalysts are catalysts containing the elements platinum, palladium, and / or nickel. Catalysts containing other or additional elements such as rhodium, iridium, gallium, chromium, iron, cobalt, and / or copper are also possible. It is essential that the metal-containing catalysts used have the ability to activate LOHC-bound hydrogen, transfer it to the metal-free reaction accelerator substance, and release it from there as elemental hydrogen. The metal-containing catalyst is suitable for both transfer hydrogenation and dehydrogenation. For dehydrogenation, the at least partially loaded hydrogen carrier medium is brought into direct contact with the metal-containing catalyst and the metal-free reaction accelerator substance.Contacting can take place in a single reaction vessel containing the three components—the hydrogen carrier medium, the catalyst, and the reaction accelerator substance. Contacting can also take place stepwise in several reaction vessels, particularly those connected in series. Hydrogen is transferred directly from the hydrogen carrier medium to the reaction accelerator substance, in particular. Alternatively, the hydrogen can also be transferred in atomic form from the hydrogen carrier medium to the reaction accelerator substance. The metal-free reaction accelerator substance has the ability to absorb hydrogen in the presence of a metal-containing catalyst. The metal-free reaction accelerator substance also has the ability to rapidly release the absorbed hydrogen at comparatively low temperatures, thereby releasing hydrogen gas.

[0016] The metal-free reaction accelerator substance is, in particular, initially present in a hydrogen-depleted form. By reacting with the loaded hydrogen carrier medium in the presence of the metal-containing catalyst, the metal-free reaction accelerator substance is converted into a hydrogen-enriched form. In particular, the hydrogen-enriched form of the metal-free reaction accelerator substance differs from the at least partially loaded hydrogen carrier medium. In particular, the hydrogen-depleted form of the metal-free reaction accelerator substance differs from the at least partially discharged hydrogen carrier medium. In particular, the metal-free reaction accelerator substance and the hydrogen carrier medium are two different and, in particular, two separate material systems.In the process according to the invention, hydrogen is transferred from the at least partially loaded hydrogen carrier medium, i.e., from a first material system, to the hydrogen-depleted form of the metal-free reaction accelerator substance, i.e., to a second material system that differs from the first material system. Subsequently, hydrogen gas, which has in particular previously been transferred to the metal-free reaction accelerator substance in the hydrogen-depleted form, is released from the hydrogen-enriched form of the reaction accelerator substance. The reaction accelerator substance differs from the hydrogen carrier medium.

[0017] It is essential that the hydrogen-enriched form of the reaction accelerator substance can release hydrogen as elemental hydrogen gas at lower temperatures and / or higher pressures than the hydrogen carrier medium with the same type and quantity of metal-containing catalyst. The intermediate step according to the invention, whereby hydrogen is first transferred from the hydrogen carrier medium to the reaction accelerator substance before release, reduces the overall energy consumption in the hydrogen release process, since the release of hydrogen gas can occur at a lower temperature.

[0018] According to the invention, it was recognized that the additional use of the metal-free reaction accelerator substance enables the release of hydrogen at reduced reaction temperatures with an increased release rate, i.e. an increased reaction rate.

[0019] It was recognized that the reaction rate during the dehydrogenation of a hydrogen carrier medium is essential for the economic viability of the process, since a target amount of hydrogen to be released at a low release rate would require a larger reaction vessel. This would result in additional space requirements and additional costs. This can be avoided with the invention.

[0020] If the reaction accelerator substance is present in the reaction vessel in the hydrogen-enriched form, the hydrogen is initially released as elemental hydrogen gas from the hydrogen-enriched reaction accelerator substance in intensive contact with the at least partially loaded hydrogen carrier medium and the metal-containing catalyst. In the process, the reaction accelerator substance is converted into the hydrogen-depleted form. Subsequently, hydrogen is transferred from the hydrogen carrier medium in contact with the metal-containing catalyst to the hydrogen-depleted form of the reaction accelerator substance, forming the hydrogen-enriched form of the reaction accelerator substance. Elemental hydrogen gas is again released from the hydrogen-enriched form of the reaction accelerator substance.This process is ideally repeated until all of the releasable hydrogen from the loaded hydrogen carrier medium is present in gaseous form as elemental hydrogen.

[0021] In particular, the processes described all take place simultaneously in the reaction vessel. They result in the hydrogen being converted from the hydrogen carrier medium to elemental hydrogen gas at much lower temperatures and / or much faster, i.e., with an increased release rate, compared to hydrogen release without a reaction accelerator.

[0022] The use of a reaction accelerator substance having at least one functional group containing oxygen and / or nitrogen has proven particularly suitable.

[0023] Processes according to claims 2 and 3 enable advantageous reaction conditions. In particular, the reaction temperature in the reaction vessel is reduced compared to the processes known from the prior art. Additionally or alternatively, the hydrogen can be obtained at a higher release rate at a given temperature.

[0024] A process according to claim 4 ensures a technically usable discharge rate at reduced reaction temperatures. In particular, the technically usable release rate of more than 10 standard liters of hydrogen per liter of catalyst volume per minute is possible at temperatures of less than 250°C, in particular less than 220°C, in particular less than 200°C, in particular less than 180°C, and in particular less than 150°C.

[0025] A reaction accelerator substance which in the hydrogen-enriched form produces secondary alcohols in the general form has proven advantageous. In particular, R 1 and R 2 are, independently of one another, linear or branched alkyl, aryl, or aralkyl groups having one, more than one, or, in polymer structures, a very large number of carbon atoms, which in turn may contain further alcohol functions, but also other functional groups such as nitrogen-containing groups, phosphorus-containing groups, or halogen atoms. In addition, R 1 and R 2 can, in particular, be bonded to one another in a ring shape, so that the hydrogen-enriched form of the metal-free reaction accelerator substance is a cycloalkanol compound. The ring-shaped compound may contain further alcohol functions, but also other functional groups such as nitrogen-containing groups, phosphorus-containing groups, or halogen atoms.

[0026] A corresponding hydrogen-depleted form of this reaction accelerator substance is ketone compounds.

[0027] A reaction accelerator substance has proven particularly advantageous which, in the hydrogen-enriched form, contains oligovinyl alcohols in the general form and / or polyvinyl alcohols in the general form includes.

[0028] R 3 is in particular a linear or branched alkyl, aryl or aralkyl group with one, several or, in polymer structures, very many carbon atoms, which in turn may contain further alcohol functions, but also other functional groups such as nitrogen-containing groups, phosphorus-containing groups or halogen atoms.

[0029] R 4 is in particular a group of the general formula -(CH 2 -) n with n = 1 to 100.

[0030] R 5 is, in particular, independently of R 3, another linear or branched alkyl, aryl or aralkyl group with one, several or, in polymer structures, very many carbon atoms, which in turn may contain further alcohol functions, but also other functional groups such as nitrogen-containing groups, phosphorus-containing groups or halogen atoms.

[0031] Secondary amines in the general form proven.

[0032] In particular, R 6 and R 7 are independently linear or branched alkyl, aryl, or aralkyl groups with one, several, or, in polymer structures, very many carbon atoms, which in turn may contain further amine functions, but also other functional groups such as oxygen-containing groups, phosphorus-containing groups, or halogen atoms. Additionally or alternatively, R 6 and R 7 can be connected to one another in a ring-like manner, so that the hydrogen-enriched form of the reaction accelerator substance is a cycloamine compound. The ring-shaped compound may contain further amine functions, but also other functional groups such as oxygen-containing groups, phosphorus-containing groups, or halogen atoms.

[0033] R 8 can be another linear or branched alkyl, aryl or aralkyl group with one, several or, in polymer structures, very many carbon atoms, which in turn can contain further amine functions, but also other functional groups such as oxygen-containing groups, phosphorus-containing groups or halogen atoms.

[0034] The corresponding hydrogen-depleted form of this reaction accelerator substance is imine compounds.

[0035] Furthermore, a reaction accelerator substance has proven particularly preferred which, in the hydrogen-enriched form, contains oligovinylamines and / or polyvinylamines in the general form has.

[0036] In particular, R 9 is a linear or branched alkyl, aryl or aralkyl group with one, several or, in polymer structures, very many carbon atoms, which in turn may contain further amine functions, but also other functional groups such as oxygen-containing groups, phosphorus-containing groups or halogen atoms.

[0037] R 10 is in particular a group of the general formula -(CH 2 -) n with n = 1 to 100.

[0038] R 11 can in particular be another linear or branched alkyl, aryl or aralkyl group with one, several or, in polymer structures, very many carbon atoms, which in turn can contain further amine functions, but also other functional groups such as oxygen-containing groups, phosphorus-containing groups or halogen atoms.

[0039] R 12 and R 13 can each independently be another linear or branched alkyl, aryl or aralkyl group with one, several or, in polymer structures, very many carbon atoms, which in turn can contain further amine functions, but also other functional groups such as oxygen-containing groups, phosphorus-containing groups or halogen atoms.

[0040] A reaction accelerator substance has also proven suitable, which in the hydrogen-enriched form is a dehydrogenatable hetero-alicyclic compound in the general form or or or or represents.

[0041] In particular, R 14 and / or R 16 can be a hydrogen atom, a linear or branched alkyl, aryl or aralkyl group with one, several or, in polymer structures, very many carbon atoms, which in turn can contain further amine functions, but also other functional groups such as oxygen-containing groups, phosphorus-containing groups or halogen atoms.

[0042] R 15 can in particular be one or more linear or branched alkyl, aryl or aralkyl groups attached at any position on the ring with one, more or, in polymer structures, very many carbon atoms, which in turn can contain further amine functions, but also other functional groups such as oxygen-containing groups, phosphorus-containing groups or halogen atoms, or can contain an oxygen-, nitrogen- or phosphorus-containing functional group or a halogen atom.

[0043] A process using a reaction accelerator substance according to claim 10 has proven advantageous and, in particular, enables simplified separation of the reaction accelerator substance from the released hydrogen gas. It is essential that the vapor pressure of the reaction accelerator is higher, and in particular significantly higher, than the vapor pressure of the hydrogen carrier medium, particularly under the reaction conditions of hydrogen release, i.e., the reaction temperature and the reaction pressure. In this process, the reaction accelerator substance is fed into the reaction vessel in liquid and / or gaseous form and made available there. The reaction accelerator substance is discharged from the reaction vessel in gaseous form together with the released hydrogen. The reaction accelerator substance can be condensed from the exhaust gas stream and returned to the reaction vessel.When the metal-free reaction accelerator substance condenses, highly pure hydrogen remains in the gas phase. In particular, the vapor pressure of the reaction accelerator substance is more than twice, in particular more than five times, in particular more than ten times, in particular at least 50 times, in particular at least 100 times, and in particular at least 200 times the vapor pressure of the hydrogen carrier medium. The LOHC compounds have a vapor pressure of less than 1 mbar at room temperature. It is advantageous if the reaction accelerator substance has a vapor pressure of at least 10 mbar at room temperature. This is the case, for example, for the reaction accelerators acetone, 2-butanone, 2-pentanone, cyclopentanone, and / or cyclohexanone.

[0044] For example, the vapor pressure of the LOHC substance dibenzyltoluene is less than 1 mbar at room temperature. The vapor pressure of the reaction accelerator substance acetone is 246 mbar at room temperature.

[0045] Alternatively, in a process according to claim 11, simplified hydrogen release can be achieved by making the vapor pressure of the reaction accelerator substance lower, and in particular significantly lower, than the vapor pressure of the hydrogen carrier medium, particularly under the conditions of the hydrogen release process. In this process, the metal-free reaction accelerator substance is initially added to the reaction vessel; the released hydrogen leaves the reaction vessel in gaseous form together with a certain amount of hydrogen carrier medium, which is condensed from the product stream, leaving hydrogen of high purity. In particular, a reaction accelerator substance with a high molecular weight has a low vapor pressure.The reaction accelerator substance is, for example, a high-molecular liquid or a high-molecular compound dissolved in the hydrogen carrier medium, for example a liquid or soluble polymer.

[0046] In particular, the vapor pressures in the reaction vessel vary under reaction conditions. This makes it possible for the hydrogen carrier medium to evaporate along with the released hydrogen, while the reaction accelerator substance remains in the reactor.

[0047] The hydrogen carrier medium, dibenzyltoluene, has a vapor pressure of 2.6 mbar at a reaction temperature of 210 °C. The reaction accelerator substance, in particular polyvinyl alcohol, has a vapor pressure of less than 0.2 mbar at a reaction temperature of 210 °C.

[0048] In particular, the vapor pressure of the reaction accelerator substance is less than 80% of the vapor pressure of the hydrogen carrier medium, in particular less than 60%, in particular less than 30% and in particular less than 10%.

[0049] A method according to claim 12 enables simplified separation of the reaction accelerator substance from the hydrogen carrier medium, particularly at the outlet of the reaction vessel. In particular, the reaction accelerator substance can be separated from the hydrogen carrier medium by decantation. This is achieved in particular by the reaction accelerator substance, both in the hydrogen-depleted form and in a mixture of hydrogen-enriched and hydrogen-depleted forms, and at reaction temperatures below 50 °C, exhibiting a miscibility gap with the hydrogen carrier medium. This means that the substance mixture decomposes into two immiscible liquid phases in this state space, i.e., it demixes independently. The separation of the reaction accelerator substance can be carried out easily, for example, in a separator.

[0050] It has been recognized that an intrinsic property of a mixture of the reaction accelerator substance, which particularly comprises alcohols and / or polyols, and the hydrogen carrier medium, which particularly comprises aromatics and / or cycloalkanes, is that it exhibits a liquid-liquid miscibility gap. In particular, the liquid-liquid miscibility gap is present in the mixture of dibenzyltoluene and acetone. This miscibility gap can be advantageously utilized for subsequent substance separation steps.

[0051] In a process using a reaction accelerator substance according to claim 13, this substance can be easily separated from the released hydrogen gas and from the hydrogen carrier medium. The reaction accelerator substance is in particular present as a solid. It is advantageous if the reaction accelerator substance is arranged as a solid in the immediate spatial proximity to the metal-containing catalyst. This can be achieved, for example, by depositing the catalyst directly onto a solid that acts as a reaction accelerator substance. It is particularly advantageous if the reaction accelerator substance has a membrane effect. A membrane effect exists when, for example, two reaction spaces are separated by the membrane in such a way that small molecules such as hydrogen gas can preferentially pass through the membrane at a high diffusion rate.Large molecules such as the hydrogen carrier medium are retained at the membrane and thus cannot pass through it. Solid reaction accelerators are particularly suitable polymers characterized by their high molecular weight structure containing a suitable number of oxygen- or nitrogen-containing functional groups that are reducible upon contact with an at least partially charged hydrogen carrier medium and are readily dehydrogenated in this reduced form.

[0052] Suitable reaction accelerator substances are polymers in which the numerical ratio of reducible groups and groups which are easily hydrogenated in reduced form to the carbon atoms present in the polymer is less than 100, in particular less than 20 and in particular less than 5.

[0053] Such polymer structures can be produced from oxygen- or nitrogen-containing monomers by polymerization. Other solid reaction accelerators can be inorganic particles, for example, solid metal oxide particles, to which oxygen- or nitrogen-containing organic groups are applied by covalent immobilization. This covalent immobilization is referred to as "grafting." A solid reaction accelerator can also be formed by pyrolysis of oxygen- or nitrogen-containing organic starting materials, such as sugars or amino sugars, other carbohydrates, or amino-functionalized carbohydrates. During pyrolysis, oxygen- or nitrogen-containing functional groups form in the pyrolyzate.

[0054] A device comprising at least one reaction vessel and a contacting unit arranged therein enables the process according to the invention to be carried out. The device ensures intensive contact between the loaded hydrogen carrier medium, the metal-containing catalyst, and the metal-free reaction accelerator substance. Intensive contact between the substances is essential for the efficiency, in particular the release rate of hydrogen, in the process according to the invention. Intensive contact between the substances takes place by means of a contacting unit arranged in the reaction vessel. Intensive contact can be achieved, for example, by a stirrer, static mixing elements, or a suitable flow guide for the substances in the reaction vessel. Flow guide elements can be provided in the reaction vessel to ensure suitable flow guidance.Examples of suitable reaction vessels include a stirred tank reactor, a loop reactor with static mixers, a trickle-bed reactor, a fixed-bed reactor with intensive flow, and / or a bubble column reactor. The reaction vessel can be linked to other process-related apparatus, containers, and units to form a hydrogen release apparatus. The hydrogen release apparatus has, in particular, a control unit for process control, which is in particular in bidirectional signal communication with heating units, pumps, and / or valves of the hydrogen release apparatus. According to the invention, the hydrogen release apparatus is operated at total pressures of less than 50 bar, in particular less than 20 bar, and in particular less than 3 bar.

[0055] Both the features specified in the patent claims and the features specified in the following exemplary embodiments of the device and method according to the invention are suitable, either individually or in combination with one another, for further developing the subject matter of the invention. The respective combinations of features do not represent any limitation with regard to further developments of the subject matter of the invention, but are essentially merely exemplary in nature.

[0056] Further features, advantages, and details of the invention will become apparent from the following description of exemplary embodiments with reference to the drawings. They show: Fig. 1 a schematic representation of a device according to a first embodiment with a reaction vessel as a stirred tank reactor for dehydrogenating a hydrogen carrier medium, Fig. 2 a Fig. 1 corresponding representation of a device according to a second embodiment with a bubble column reactor as reaction vessel, Fig. 3 a Fig. 1 corresponding representation of a device according to a third embodiment with a fixed bed reactor as reaction vessel, Fig. 4 a Fig. 1 corresponding representation of a device according to a fourth embodiment with a reaction-accelerating membrane in a reaction vessel, Fig. 5 with two separate reaction vessels arranged in series.

[0057] Details of the exemplary embodiments explained in more detail below may also constitute an invention in themselves or be part of an inventive subject matter.

[0058] A whole in Fig. 1 The hydrogen release apparatus, designated 1, comprises a reaction vessel 2, which, according to the illustrated embodiment, is designed as a stirred tank reactor. The reaction vessel 2 has a closed housing 3 having a bottom 4, a lid 5, and a side wall 6 connecting the bottom 4 to the lid 5.

[0059] A metal-containing catalyst material 7, in particular as a particle bed, is arranged in the reaction vessel 2, particularly in the region of the bottom 4. Also provided in the reaction vessel 2 are a liquid, metal-free reaction accelerator substance 8 and an at least partially loaded hydrogen carrier medium 9, in particular heteroatom-free LOHC.

[0060] The reaction vessel 2 has a contacting unit 10, which, according to the illustrated embodiment, is designed as a stirrer. The stirrer is rotatable about a rotational axis 11, which is oriented in particular parallel to the longitudinal axis of the housing 3 and in particular parallel to the, in particular cylindrical, side wall 6 of the housing 3. The stirrer, with its stirring elements 12, is arranged below the level 13 of the mixture of reaction accelerator substance 8 and hydrogen carrier medium 9. The direction of rotation of the stirrer about the rotational axis 11 is symbolized by the arrow 14.

[0061] The reaction vessel 2 has, particularly on the lid 5, a hydrogen discharge line 15 through which the gaseous hydrogen 16 released in the reaction vessel 2 can be supplied for further use, for example, for generating electricity in a fuel cell or for thermal utilization. The hydrogen discharge line 15 can also be connected to a different position on the housing 3. It is advantageous if the hydrogen discharge line 15 is arranged at a point on the housing 3 that is above the level 13.

[0062] Furthermore, a liquid discharge line 17 is connected to the reaction vessel 2, which leads to a separator 18. The separator 18 is connected to the reaction vessel 2 via a return line 19. According to the exemplary embodiment shown, the connection for the liquid discharge line 17 on the reaction vessel 2 is provided on the bottom 4, in particular at a lowest point of the housing 3. This ensures a particularly advantageous removal of liquid from the reaction vessel 2. The liquid discharge line 17 can also be connected to the reaction vessel 2 at a different point on the housing 3. It is advantageous if the connection point for the liquid discharge line 17 is arranged at a point on the housing 3 that is below the level 13.

[0063] The connection point for the return line 19 on the reaction vessel 2 is provided in particular in the area of ​​the stirring elements 12. This improves the mixing of the returned reaction accelerator substance 8 with the liquid mixture already present in the reaction vessel 2.

[0064] The separator 18 is further connected via a fluid line 20 to a first storage container 21 for discharged hydrogen carrier medium 9.

[0065] A second storage tank 22 for loaded hydrogen carrier medium 9 is connected to the reaction tank 2 via a hydrogen carrier medium supply line 23. The hydrogen carrier medium supply line 23 is arranged on the housing 3, particularly in an area of ​​the stirring elements 12. This improves the mixing of the supplied, loaded hydrogen carrier medium 9 with the liquid mixture present in the reaction tank 2.

[0066] The hydrogen release apparatus 1 has a control unit 24, which is in signal communication with the individual components of the hydrogen release apparatus 1, in particular the reaction vessel 2, the separator 18, the first storage vessel 21, and the second storage vessel 22. In particular, the control unit 24 is connected to further Fig. 1 Units not shown in detail, such as heating units, pumps, and / or valves, are in signal communication, which are arranged in particular along lines 15, 17, 19, 20, and 23. By means of the control unit 24, it is possible to actively control the process for releasing hydrogen gas, for example, to monitor and influence the reaction conditions in the reaction vessel 2, in particular the reaction temperature and / or reaction pressure, as well as the water level 13.

[0067] For monitoring purposes, corresponding sensors are arranged in or on the components mentioned, which are also connected to the control unit 24. The signal connections can, as shown in Fig. 1 As indicated by symbol 25, the signal connections may be wireless, particularly as a radio connection. The signal connections may additionally or alternatively be wired.

[0068] The operation of the hydrogen release apparatus 1 for the use of a polyvinyl alcohol with a molecular weight of more than 10,000 g / mol as reaction accelerator substance 8 and perhydrodibenzyltoluene as hydrogen-loaded hydrogen carrier medium 9 is explained in more detail below.

[0069] The reaction vessel 2 contains palladium from activated carbon as the metal-containing catalyst material 7, polyvinyl alcohol as the metal-free reaction accelerator substance 8, and perhydrodibenzyltoluene as the hydrogen carrier medium 9. The reaction accelerator substance 8 is in liquid form and, according to the illustrated embodiment, exhibits thermomorphic behavior. This means that the reaction accelerator substance 8 is at least partially dissolved in the hydrogen carrier medium 9 under the reaction conditions of 200 °C and a total pressure of less than 2 mbar in the reaction vessel 2.

[0070] Due to the intensive contact resulting from the stirring of the liquid mixture 8, 9 and the catalyst material 7, hydrogen gas is initially released from the polyvinyl acetone, forming a corresponding polyketone or corresponding enol. Subsequently, hydrogen is transferred from the hydrogen carrier medium 9 to the at least partially hydrogen-depleted reaction accelerator substance 8. The hydrogen-rich form of the reaction accelerator substance 8 thus formed, i.e., the corresponding polyvinyl alcohol, is dehydrated under the same reaction conditions in the reaction vessel 2, releasing hydrogen. The liquid mixture 8, 9 is discharged from the reaction vessel 2 via the liquid discharge line 17 and fed to the separator 18.

[0071] The temperature in the separator 18 is at most 50 °C. It is particularly advantageous that the reaction accelerator substance 8 has a miscibility gap with the hydrogen carrier medium 9 at a temperature of at most 50 °C. As in Fig. 1 As shown schematically, two separate, mutually distinct liquid layers form independently in the separator 18, with the reaction accelerator substance 8 at the bottom and the comparatively less dense hydrogen carrier medium 9 at the top of the separator 18. In particular, the density of the polyvinyl alcohols is more than 1.1 g / cm 3 . The density of dibenzyltoluene is approximately 1.05 g / cm 3 . The reaction accelerator substance 8 is easily separated from the hydrogen carrier medium 9 and can be fed to the reaction vessel 2 via the return line 19 for reuse.

[0072] The discharged hydrogen carrier medium 9 is conveyed from the separator 18 via the fluid line 20 into the first storage vessel 21. The discharged hydrogen carrier medium 9 can be re-enriched with hydrogen, i.e., recharged, using a charging station. The charging station can be located at the location of the hydrogen release apparatus 1 or remotely therefrom. The charged or recharged hydrogen carrier medium 9 is stored in the second storage vessel 22 and supplied to the reaction vessel 2 via the hydrogen carrier supply line 23.

[0073] Hydrogen 16, which in particular passes directly or in atomic form from the hydrogen carrier medium 9 to the reaction accelerator substance 8, can be released from the reaction accelerator substance 8 as hydrogen gas 16 and discharged from the reaction vessel 2 via the hydrogen discharge line 15.

[0074] In the following, with reference to Fig. 2 A second embodiment of the invention is described. Structurally identical parts are given the same reference numerals as in the first embodiment, to the description of which reference is hereby made. Structurally different but functionally similar parts are given the same reference numerals with an a suffix.

[0075] The key difference compared to the first embodiment is that the reaction vessel 2a is designed as a bubble column reactor. The catalyst material 7, the liquid hydrogen carrier medium 9, and the reaction accelerator substance 8, which is present in liquid and / or gaseous form, are arranged in the reaction vessel 2a. What is important in this embodiment is that, under the conditions in the reaction vessel 2a, the reaction accelerator substance has a vapor pressure p R that is significantly higher than the vapor pressure p W of the hydrogen carrier medium 9. Acetone, in particular, serves as the reaction accelerator substance 8. Perhydrodibenzyltoluene serves as the hydrogen carrier medium 9. Under the reaction conditions exemplified, with a reaction temperature of 210 °C and a total pressure of less than 2 bar, perhydrodibenzyltoluene is in liquid form. The vapor pressure p R is around 2 mbar.Acetone, on the other hand, is present in gaseous form under these reaction conditions, especially the reaction temperature and the total pressure.

[0076] The bubble column reactor is a process engineering apparatus for gas / liquid processes. The bubble column reactor is characterized by a liquid, in this case, hydrogen carrier medium 9, into which gas, in this case, the reaction accelerator substance 8, is introduced and bubbles through the liquid, thereby creating a phase interface between the reaction accelerator substance 8 and the liquid hydrogen carrier medium 9. Gassing occurs, in particular, through a perforated distributor plate, an evaporator element, or an injection tube as distributor element 26, which is connected to the return line 19. According to the illustrated embodiment, the distributor element 26 is arranged approximately centrally on the side wall 6 between the base 4 and the cover 5.

[0077] The hydrogen carrier medium supply line 23 is provided on the housing 3 below the connection point for the return line 19. According to the illustrated embodiment, the hydrogen carrier medium 9 and the reaction accelerator substance 8 are supplied in a cocurrent process, and the bubble column reactor is operated in a cocurrent process. It is also conceivable to carry out the process in a countercurrent process.

[0078] Via the liquid discharge line 17, which is located particularly in the upper region of the housing 3, adjacent to the cover 5, a mixture of reaction accelerator substance 8 and hydrogen carrier medium 9 is drawn from the reaction vessel 2a and fed to the separator 18a. Due to the significantly higher vapor pressure of the reaction accelerator substance 8 compared to the hydrogen carrier medium 9, the two substances are easily separated in the separator 18a, which is designed as an air- or water-cooled condenser. The condenser 18a can contain internal components to increase the surface area in the condenser 18a and thus improve the condensation effect.

[0079] In the following, with reference to Fig. 3 A third embodiment of the invention is described. Structurally identical parts are given the same reference numerals as in the first embodiment, to the description of which reference is hereby made. Structurally different but functionally similar parts are given the same reference numerals with a suffix "b."

[0080] The key difference from the previous embodiments is that the reaction vessel 2b is designed as a fixed-bed reactor. A solid is filled into the fixed-bed reactor. The solid is the metal-free reaction accelerator substance 8, which simultaneously serves as a porous support material for the metal-containing catalyst 7. This solid can provide both the function of the metal-free reaction accelerator 8 and the function of the metal-containing catalyst 7 at spatially separate locations within its structure. According to the embodiment shown, the solid metal-free reaction accelerator substance 8 is a porous sugar pyrolysis product containing alcohol functionalities, which serves as a support material for the metal-containing catalyst 7, here, for example, platinum nanoparticles.

[0081] The reaction vessel 2b is, for example, filled with the loaded hydrogen carrier medium 9 at a temperature of 240 °C and a total pressure of 1 bar, according to the embodiment shown in Fig. 3 from bottom to top along the flow direction 27. As a result, the reaction accelerator substance 8 is first hydrogenated, with hydrogen in elemental form being subsequently released as a gas from the reaction accelerator substance 8 in a dehydrogenation reaction and being discharged from the reaction vessel 2b via a mixing line 28 together with evaporated hydrogen carrier medium 9.

[0082] A condenser 29 is connected to the mixing line 28, in which the discharged gaseous hydrogen carrier medium 9 condenses. The condensed hydrogen carrier medium 9 is returned to the reaction vessel 2b via a heat exchanger 30 and the return line 19. Pure gaseous hydrogen 16 is discharged from the condenser 29 via the hydrogen discharge line 15. The at least partially discharged hydrogen carrier medium 9 leaves the reaction vessel 2b via the liquid discharge line 17 predominantly in liquid form and is fed in particular to the first storage vessel 21.

[0083] The return line 19 and the hydrogen carrier medium supply line 23 are each located in a lower region of the reaction vessel 2b. The reaction accelerator substance 8 and the loaded hydrogen carrier medium 9 flow through the fixed-bed reactor together along the flow direction 27, i.e., in a cocurrent process. The fixed-bed reactor can also be operated in a countercurrent process.

[0084] In the following, with reference to Fig. 4 A fourth embodiment of the invention is described. Structurally identical parts are given the same reference numerals as in the first embodiment, to the description of which reference is hereby made. Structurally different but functionally similar parts are given the same reference numerals with a suffix "c."

[0085] The key difference from the previous embodiment is that the container 2c has a reaction-accelerating membrane 31, which divides the reaction container into a first sub-chamber 32 and a second sub-chamber 33. The reaction-accelerating membrane 31 is made from the solid reaction accelerator substance 8. The reaction accelerator substance 8 forms a structural framework of the membrane 31 and also serves as a support for the metal-containing catalyst 7 applied thereto. It is advantageous if the membrane material has a reaction-accelerating effect and possesses proton conductivity and / or selective hydrogen permeability, in particular from the first sub-chamber 32 into the second sub-chamber 33. In this way, pure hydrogen gas can be obtained on the permeate side, i.e., in the second sub-chamber 33.The released hydrogen is removed from equilibrium by transport through membrane 31, so that equilibrium limitations in the dehydrogenation reaction can be overcome.

[0086] According to the embodiment shown in Fig. 4 A fuel cell 34 is arranged adjacent to the reaction vessel 2c. Heat generated during the exothermic fuel cell operation can be used directly, and in particular without the use of a heat exchanger, to operate the reaction-accelerating membrane 31. This is achieved by a direct heat transfer line 35 that connects the fuel cell 34 to the reaction vessel 2c, in particular to the membrane 31 arranged therein. A heat exchanger attached to the fuel cell 34 is used for heat transfer, which heats a heat transfer medium, in particular the hydrogen carrier medium 9 that can be used as a heat transfer medium. The heated heat transfer medium is supplied to the reaction vessel 2c in order to heat it with the aid of a heat exchanger.

[0087] Alternatively, heat transfer can be particularly advantageously achieved by locating the fuel cell 34 and the reaction vessel 2c in a thermally insulated container. Thus, the heat generated by the fuel cell 34 can be directly utilized for hydrogen release in the reaction vessel 2c.

[0088] For heat transfer, a heat pipe can be used additionally or alternatively, which connects the fuel cell, which is arranged next to each other, with the reaction vessel isothermally and particularly efficiently.

[0089] The fuel cell 34 further comprises a supply line 36 for supplying oxygen, in particular ambient air, to the fuel cell 34. A power line 37 is connected to the fuel cell 34 for extracting electrical energy from the fuel cell 34.

[0090] A further advantage is that the hydrogen consumption in the fuel cell 34 creates a steeper gradient of hydrogen concentration across the hydrogen release apparatus 1. Overall, this increases the thermodynamic driving force for hydrogen release, so that the release rate is further increased.

[0091] In the following, with reference to Fig. 5 A fifth embodiment of the invention is described. Structurally identical parts are given the same reference numerals as in the first embodiment, to the description of which reference is hereby made. Structurally different but functionally similar parts are given the same reference numerals with a suffix "d."

[0092] The essential difference compared to the third embodiment is that in addition to the reaction vessel 2d, which is designed as a fixed bed reactor, a second reaction vessel 38 is provided.

[0093] In the first reaction vessel 2d, the hydrogen transfer from the loaded hydrogen carrier medium 9 to the reaction accelerator substance 8 takes place in the manner described. The enriched form of the reaction accelerator substance 8 is fed to the second reaction vessel 38, where the hydrogen release occurs. It is essential that the metal-containing catalyst 7 is contained in both the first reaction vessel 2d and the second reaction vessel 38.

[0094] The catalysts in the reaction vessels 2d, 38 may be identical or different.

[0095] According to this embodiment, the partial reactions are divided into different reaction vessels 2d, 38. This allows the reaction conditions to be better adapted for each partial reaction.

[0096] According to the fifth exemplary embodiment, advantages arise in particular from the fact that the reaction temperature and reaction pressure for the hydrogen transfer from the hydrogen carrier medium 9 to the reaction accelerator substance 8, on the one hand, and for the release of hydrogen gas from the thus hydrogen-enriched reaction accelerator substance 8, on the other hand, can be selected independently of one another. For example, the hydrogen transfer from the hydrogen carrier medium 9 to the reaction accelerator substance can be carried out at a reaction pressure of 1 bar and a temperature of only 180 °C. With the aim of an increased hydrogen gas pressure, the hydrogen gas release from the reaction accelerator substance 8 can be carried out, for example, at 240 °C and a total pressure of 5 bar.

[0097] Pure hydrogen gas 16 is generated by condensing the hydrogen-depleted reaction accelerator substance 8 in the second reaction vessel 38. The condensed reaction accelerator substance is returned as a liquid to the first reaction vessel 2d via the return line 19.

[0098] In an example of a process according to the invention, 290 g of perhydrodibenzyltoluene as a loaded hydrogen carrier medium with a degree of hydrogenation of 99% and 5.3 g of a commercial Pd-on-carbon catalyst with 5 wt% Pd and 58 g of acetone as a reaction accelerator substance were mixed in an autoclave.

[0099] The autoclave contains 0.265 g of Pd, which corresponds to 0.25 mol% based on the perhydrodibenzyltoluene used. The autoclave also contains equimolar amounts of perhydrodibenzyltoluene and acetone. The autoclave is heated to 210 °C and maintained at this temperature with stirring for five hours. The autoclave is then cooled back to room temperature, and the autoclave pressure is determined at room temperature. The autoclave is then depressurized, opened, and a liquid sample is taken. It is found that a significant amount of hydrogen gas was formed. The pressure in the autoclave after complete cooling to room temperature was over 16 bar. Gas chromatographic analysis of the gas phase revealed that the gas phase consists exclusively of hydrogen. The liquid sample revealed a decrease in the degree of hydrogenation of the hydrogen carrier medium of more than 10%, i.e., to less than 90%.

[0100] When conducting a comparable hydrogen release according to the state of the art, i.e., without the use of acetone, and under otherwise identical reaction conditions, only a negligible amount of hydrogen was detected. The pressure in the autoclave after cooling to room temperature was less than 1.5 bar. A decrease in the degree of hydrogenation of less than 1%, i.e., to approximately 98%, was observed.

Claims

1. A method for dehydrogenating a hydrogen carrier medium, comprising the method steps of - providing -- a metal-containing catalyst material (7), -- an at least partially loaded hydrogen carrier medium (9), -- a metal-free reaction accelerator substance (8), - transferring hydrogen from the hydrogen carrier medium (9) to the reaction accelerator substance (8) by means of the metal-containing catalyst material (7), - releasing hydrogen gas (16) from the reaction accelerator substance (8) by means of the metal-containing catalyst material (7), wherein the reaction accelerator substance (8) has at least one functional group which contains oxygen and / or nitrogen.

2. The method as claimed in claim 1, characterized by a reaction pressure (p) of from 0.001 bar to 50 bar, in particular of from 0.3 bar to 20 bar, in particular of from 0.8 bar to 3 bar and in particular of less than 0.1 bar.

3. The method as claimed in either of the preceding claims, characterized by a reaction temperature (T) of from 25°C to 400°C, in particular of from 60°C to 250°C, in particular of from 80°C to 220°C and in particular of less than 100°C.

4. The method as claimed in any of the preceding claims, characterized by a release rate of at least 10 standard liters of hydrogen per liter of catalyst volume and per minute at a reaction temperature (T) of less than 250°C.

5. The method as claimed in any of the preceding claims, characterized in that the reaction accelerator substance (8) in the hydrogen-enriched form comprises secondary alcohols of the form 6. The method as claimed in any of the preceding claims, characterized in that the reaction accelerator substance (8) in the hydrogen-enriched form comprises oligovinyl alcohols of the form and / or polyvinyl alcohols of the form 7. The method as claimed in any of the preceding claims, characterized in that the reaction accelerator substance (8) in the hydrogen-enriched form comprises secondary amines of the form 8. The method as claimed in any of the preceding claims, characterized in that the reaction accelerator substance (8) in the hydrogen-enriched form comprises oligovinylamines and / or polyvinylamines of the form 9. The method as claimed in any of the preceding claims, characterized in that the reaction accelerator substance (8) in the hydrogen-enriched form comprises a dehydro-genatable heteroalicyclic compound of the form or of the form or of the form or of the form or of the form 10. The method as claimed in any of the preceding claims, characterized in that the reaction accelerator substance (8) has a vapor pressure (pR) which is greater than the vapor pressure (pw) of the hydrogen carrier medium (9), wherein in particular pR > 1.5 pW, in particular pR > 2.0 pW, in particular pR > 5.0 pW, in particular pR > 10.0 pW.

11. The method as claimed in any of claims 1 to 9, characterized in that the reaction accelerator substance (8) has a vapor pressure (pR) which is lower than the vapor pressure (pW) of the hydrogen carrier medium (9), wherein in particular pR < 0.8 pW, in particular pR < 0.6 pW, in particular pR < 0.3 pW, in particular pR < 0.1 pW.

12. The method as claimed in any of the preceding claims, characterized in that the reaction accelerator substance (8) has a miscibility gap with the hydrogen carrier medium at a temperature of at most 50°C.

13. The method as claimed in any of the preceding claims, characterized in that the reaction accelerator substance (8) is present as a solid, the catalyst material (7) in particular having been deposited directly onto the reaction accelerator substance (8).