Method for releasing hydrogen from a hydrogen storage medium

Abstract

A method for releasing hydrogen from a hydrogen storage medium that is at least partially loaded comprises dehydrating the hydrogen storage medium that is at least partially loaded in a dehydration reactor (3) and thereby releasing hydrogen, providing heat by thermally utilizing hydrogen that has been released in the dehydration reactor (3) in a thermal utilization unit (9), and / or by utilizing a heating unit (11) operated by means of electricity from renewable energy sources, and / or by burning the hydrogen storage medium in a burner (13), controlling the heat supply by means of a control unit (15), wherein the CO2 emissions caused by the respective heat supply are used as input parameters for the control, and transferring the heat to the dehydration reactor (3).

Description

[0001] The invention relates to a method for releasing hydrogen from a hydrogen storage medium that is at least partially loaded.

[0002] It is known that hydrogen storage media are suitable for storing energy in the form of hydrogen through catalytic hydrogenation. Hydrogen is chemically bound to the hydrogen storage medium, thereby hydrogenating it. Energy can then be released in the form of hydrogen through catalytic dehydrogenation. The dehydrogenation process is endothermic, requiring an energy input, particularly in the form of heat. Due to this additional energy requirement, the dehydrogenation process has a larger CO2 footprint.

[0003] The invention is based on the objective of enabling the energy-efficient release of energy in the form of hydrogen by dehydrating a hydrogen storage medium and, in particular, of reducing the CO2 footprint of the process.

[0004] This problem is solved according to the invention by a method having the features of claim 1.

[0005] The core of the invention is that heat can be provided in various ways and transferred to a dehydration reactor in which at least partially loaded hydrogen storage medium is dehydrated to release hydrogen.

[0006] According to one approach, heat is supplied through the thermal utilization of hydrogen released in the dehydrogenation reactor. Thermal utilization of hydrogen means using hydrogen gas to generate heat. It has been found that this method provides heat directly and easily. In particular, additional energy sources are unnecessary. While the use of hydrogen from the dehydrogenation reaction does require additional energy for the hydrogen storage medium, especially since the amount of hydrogen transported to and from the dehydrogenation reactor is increased, it has been found that, overall, the process is more energy-efficient when considering the heat provided.

[0007] Additionally or alternatively, heat can be provided according to a second option by using electricity generated from renewable sources to operate an electric heating unit. Electricity from renewable energy sources is, in particular, CO2-free or at least CO2-reduced. The use of an electricity grid, especially a public grid, through which electricity from renewable energy sources is supplied is advantageous. The heating unit can, in particular, be connected directly to the electricity grid. Alternatively or additionally, it is conceivable to provide a power generation plant, especially a photovoltaic system, a wind turbine, and / or a hydroelectric power plant, for generating electricity for the heating unit.

[0008] According to a third option, heat can be provided additionally or alternatively by burning the hydrogen storage medium. Providing the heat is straightforward and immediate, as the hydrogen storage medium is already present. In particular, it is possible to burn the at least partially discharged hydrogen storage medium discharged from the dehydrogenation reactor. This does not affect the dehydrogenation performance. The amount of hydrogen storage medium that needs to be transported for re-hydrogenation is reduced, thus minimizing transport costs.

[0009] It is particularly advantageous if the combusted hydrogen storage medium has been produced regeneratively, i.e., in a CO2-neutral manner. Renewably produced toluene, which is used for the production of benzyltoluene, especially for benzyltoluene synthesis, is particularly suitable for this purpose.

[0010] Alternative processes exist that enable a particularly environmentally friendly supply of toluene as a raw material for the manufacturing facility. Compared to the current state of the art, in which toluene is obtained from petroleum as a fossil raw material through a refining process, the use of fossil energy sources can be reduced.

[0011] Toluene can be produced enzymatically, for example, from phenyl acetate by an enzyme or enzyme system, in particular by decarboxylation of phenyl acetate with at least one enzyme of the glycyl radical enzyme (GRE) family, especially phenylacetate decarboxylase (PhdB) and the associated phenylacetate decarboxylase-activating enzyme (PhdA). This enzymatic toluene synthesis allows the use of various renewable carbon sources from which phenylacetic acid of non-fossil origin can be produced, especially glucose from cellulose-containing mass. Toluene synthesis can be carried out in vitro with isolated enzymes or in vivo with the microorganisms themselves. Microorganisms of the family Acidobacteria, especially the strain Tolsyn, are particularly suitable for this purpose. The production of the enzymes by protein engineering is also conceivable. Furthermore, a further conversion to BT using other enzymes or...Microorganisms are conceivable, especially genetically modified microorganisms. Direct synthesis from biomass to BT using genetically modified microorganisms is also conceivable.

[0012] Alternatively, lignin, due to its aromatic structure, can serve as a starting material for the direct production of aromatic-based chemicals. Like cellulose and hemicellulose, lignin belongs to the class of biopolymers that primarily comprise biomass. Lignocellulose biomass, especially from agricultural waste, forestry waste, and waste from the paper industry, is a potentially suitable starting material due to its comparatively high lignin content. Toluene (BT) can then be produced from the toluene thus obtained from renewable resources. It is also conceivable to catalytically produce phenazine from lignin in an intermediate step.

[0013] Another alternative is the use of biogas, which can be obtained through the fermentation of biogenic materials such as organic waste and plant and / or animal residues. Biogas consists primarily of methane (CH4) and carbon dioxide (CO2) and also contains smaller amounts of nitrogen (N2), oxygen (O2), hydrogen sulfide (H2S), hydrogen (H2), and ammonia (NH3). The carbon monoxide (CO) and hydrogen gas (H2) contained in the biogas can serve as synthesis gas, for example, to produce BT via catalytic synthesis. In this variant, toluene would not be required as a starting material for BT production. Alternatively, it is possible to produce toluene from the biogas as an intermediate product, which can then be used for BT synthesis. It is also conceivable to first produce methanol from the synthesis gas, then polyol, and finally BT from that.Furthermore, synthesis gas can be obtained from the methane contained in biogas by partial catalytic oxidation to carbon monoxide and by reacting methane with carbon dioxide. Likewise, in the case of mixed gas hydrogenation, particularly hydrogenation with biogas, the unreacted gas can be made available again for synthesis gas production and thus for BT production.

[0014] According to the invention, it was also found that the heat supply is controlled by a control unit, wherein the CO2 emissions caused by the respective heat supply are used as input parameters for the control. It was found that the different variants for heat supply cause CO2 emissions to varying degrees. The control system according to the invention enables optimization of the overall process, particularly with regard to the integral CO2 footprint.

[0015] The hydrogen storage medium is, in particular, a liquid organic hydrogen carrier, also referred to as LOHC (liquid organic hydrogen carrier). The LOHC is, in particular, a hydrocarbon compound, especially toluene, benzyltoluene, and / or dibenzyltoluene. The at least partially discharged form of the hydrogen storage medium is referred to, in particular, as LOHC-, and the at least partially charged form of the hydrogen storage medium is referred to, in particular, as LOHC+. The partially discharged hydrogen storage medium has a first degree of hydrogenation h1, which is, in particular, at most 15%, 10%, 8%, 5%, 3%, 2%, and 1%. The at least partially charged hydrogen storage medium has a second degree of hydrogenation h2, which is greater than the first degree of hydrogenation h1.The second degree of hydrogenation h2 is at least 85%, in particular at least 90%, in particular at least 93%, in particular at least 95%, in particular at least 98%, and in particular at least 99%. Non-LOHC hydrogen carriers, in particular ammonia (NH3), siloxanes, borohydrides, and / or carbazoles, can also serve as hydrogen storage media.

[0016] For the sake of simplicity, LOHC, LOHC- and LOHC+ are used below for all hydrogen storage media, especially also for non-organic and particularly non-liquid organic hydrogen carriers.

[0017] Energy is released in the form of hydrogen through the catalytic dehydrogenation of LOHC+. This process converts LOHC+ into LOHC-. The dehydrogenation takes place at a secondary location, which is particularly energy-poor. This means that energy is required at this secondary location. The hydrogen gas released at this secondary location is then used, for example, in a fuel cell to generate electricity. Additionally or alternatively, the hydrogen gas can also be used as a raw material, particularly in industrial applications, such as steel production or the chemical industry.

[0018] The second location is spatially separated from the first location. In particular, the distance between the first and second locations is several kilometers, especially several tens of kilometers, especially several hundred kilometers, and especially several thousand kilometers. It is particularly possible that the first and second locations are in different countries, especially on different continents.

[0019] It was particularly recognized that avoiding long transport routes between locations is advantageous. The overall energy expenditure for providing the hydrogen carrier medium is reduced. In particular, transport costs are reduced. Pollutant emissions from transport vehicles are also reduced.

[0020] It is understood that various combinations of heat sources are possible, particularly proportional ones. It is conceivable that only one, several, or all heat sources are used for heat supply. In particular, the respective share of each heat source in the total heat quantity can be variably determined, especially continuously.

[0021] A method according to claim 2 enables the straightforward and, in particular, efficient thermal utilization of hydrogen. By generating electricity from hydrogen in a fuel cell, not only heat but also electricity is provided, which can be used, at least partially, to operate the system. This increases the overall efficiency of the process, i.e., its efficiency. When using a high-temperature fuel cell, the temperature level of the waste heat is increased, which can then be used to operate the dehydrogenation reactor.

[0022] Additionally or alternatively, hydrogen gas can be burned in a hydrogen burner. Additionally or alternatively, the hydrogen gas can be used in a hydrogen combustion engine to provide additional kinetic energy.

[0023] The thermal use of hydrogen is flexible and opens up alternative applications that can be individually adapted to the specific requirements profile of a plant.

[0024] A method according to claim 3 enables further optimization with regard to a reduced CO2 footprint. It has been recognized, in particular, that CO2-neutral or CO2-reduced heat sources can be used preferentially to reduce the overall CO2 footprint. For example, it has been recognized that hydrogen released in the dehydrogenation reactor can be used thermally if the other heat sources cannot provide heat or cannot provide it in sufficient quantity. This means, for example, that the dehydrogenation capacity can be increased to provide additional hydrogen gas if there is insufficient electricity from renewable energy sources and / or LOHC combustion is not possible to a sufficient extent. Accordingly, electricity from CO2-neutral or CO2-reduced sources can be used preferentially, and in particular exclusively, if it is available.In this case, the thermal use of hydrogen and LOHC combustion can be dispensed with in order to avoid burdening the LOHC cycle system.

[0025] A method according to claim 4 enables further optimization of the control method from a cost perspective. It has been recognized, in particular, that the purchase prices for energy carriers, and especially for electricity, fluctuate, particularly daily, hourly, minutely, or secondly. If the current electricity price is used as an input parameter for the control system, the purchase of electricity for heat generation can be regulated in a cost-optimized manner. In the event of a particularly high price for electricity from renewable energy sources, for example at night and / or in winter, LOHC can additionally be combusted and / or hydrogen can be used for thermal purposes.

[0026] A process according to claim 5 enables a further reduction of CO2 emissions during dehydrogenation. It has been found that it is advantageous to use a mixture as the hydrogen storage medium, particularly one enriched with an isomer and having an isomer as its main component. For example, benzyltoluene (BT), which is available as a mixture of the isomers ortho-benzyltoluene, para-benzyltoluene, and meta-benzyltoluene following industrial production, serves as the hydrogen storage medium. The Greek prefixes ortho, meta, and para denote the arrangement of the second substituent relative to the first substituent on the aromatic ring. It has been found in particular that para-benzyltoluene is especially suitable for dehydrogenation because it has a favorable reaction enthalpy compared to the other two isomers, ortho and meta.The dehydrogenation of para-benzyltoluene can be achieved with reduced energy input, thus lowering the required energy input in the form of heat. This reduces the overall energy consumption and therefore the CO2 footprint.

[0027] It is advantageous if the BT isomer, which serves as the main component, is present in the mixture with a mass fraction of at least 50% for ortho- or para-BT or at least 10% for meta-BT, thus exhibiting a higher mass fraction of at least one BT isomer compared to an industrially produced BT isomer mixture. If the BT isomer constitutes the main component of the mixture, this means that the BT isomer has the relatively largest mass fraction in the mixture. Should other BT isomers be present in the mixture, they each have a lower mass fraction than the main component.

[0028] In addition to the main component, other BT isomers may be present in the mixture, for example, 60% para-BT and 40% ortho-BT. Any mixing ratios are possible with a corresponding BT isomer as the main component. It is advantageous if the total mass fraction of the at least one or more BT isomers that do not constitute the main component is less than 50%, in particular not more than 40%, in particular not more than 30%, in particular not more than 25%, in particular not more than 20%, in particular not more than 15%, in particular not more than 10%, in particular not more than 5%, and in particular not more than 1%.

[0029] A mixture is considered isomerically pure if it contains only a single BT isomer. The mass fraction of this single BT isomer, in particular para-BT or ortho-BT, is less than 100% of the mixture. Due to the nature of the process, the mixture may contain unavoidable impurities and / or byproducts. However, isomerically pure means that, besides the BT isomer as the main component, no or essentially no other BT isomers are present in the mixture. In particular, due to the manufacturing process, other BT isomers besides the main isomeric component may be present in the mixture, provided that the total mass fraction of the other BT isomers is less than 5%, in particular less than 3%, in particular less than 2%, in particular less than 1%, in particular less than 0.5%, in particular less than 0.1%, in particular less than 0.01%, and in particular less than 0.001%.The mass fraction of the BT isomer as the main component in an isomerically pure mixture is in particular at least 95%, in particular at least 97%, in particular at least 98%, in particular at least 99%, in particular at least 99.5%, in particular at least 99.9%, in particular at least 99.99% and in particular at least 99.999%.

[0030] The mixture according to the invention is liquid at room temperature. Room temperature is understood to be a temperature of 20°C. A method according to claim 6 leads to a reduction in the CO2 footprint by taking into account waste heat from a hydrogenation process. It has been recognized that an LOHC cycle process, in addition to the dehydrogenation process, also comprises a hydrogenation process, in particular by catalytic hydrogenation, wherein at least partially discharged hydrogen storage medium, which has been dehydrogenated in particular in the dehydrogenation reactor, can be at least partially charged with hydrogen gas. The hydrogenation process is in particular a catalytic process.

[0031] Waste heat utilization does not mean, in particular, that the waste heat from the hydrogenation reactor is supplied as heat to the dehydrogenation reactor. Rather, the waste heat from the hydrogenation process is used in other processes, such as seawater desalination to provide water for hydrogen gas production via electrolysis and / or for integration into refinery or BT production processes. The utilization of waste heat from the hydrogenation process is generally possible for processes that have a similar heat demand to the heat output of the hydrogenation reactor at a similar temperature level, in particular at a temperature level of at least 150°C, at least 250°C, and at least 300°C.

[0032] A method according to claim 7 enables the integration of a further heat source, in particular an exothermic reaction, especially an exothermic oxidation of a hydrogen storage medium. It has been recognized in particular that the heat generated during the oxidation of a hydrogen storage medium can completely cover the heat requirement for endothermic dehydrogenation. The necessary equipment and a corresponding method are disclosed in DE 10 2021 203 883 A1, to which express reference is hereby made. The use of waste heat from an exothermic process to completely cover the heat requirement in the dehydrogenation reactor enables so-called autothermal dehydrogenation.

[0033] Both the features specified in the claims and those specified in the exemplary embodiment of a hydrogen release system are suitable, individually or in combination, for further developing the subject matter of the invention. The respective combinations of features do not constitute a limitation with regard to the further development of the subject matter of the invention, but are essentially merely exemplary.

[0034] The essential features, advantages, and details of the invention will become apparent from the following description of an exemplary embodiment with reference to the drawing. The drawing shows: Fig. 1 a schematic representation of a system for releasing hydrogen from a hydrogen storage medium, Fig. 2 a schematic sketch of a control procedure of the plant according to Fig. 1.

[0035] One in Fig. One system, labelled with the letter 1, serves to release hydrogen, in particular hydrogen gas, from a hydrogen storage medium that is at least partially loaded. The hydrogen storage medium is, in particular, isomerically pure benzyltoluene.

[0036] The system 1 comprises a first storage tank 2, in which the hydrogen storage medium, at least partially loaded, is stored. The first storage tank 2 is connected to a dehydrogenation reactor 3 via a fluid system. A separation unit 4 is connected to the dehydrogenation reactor 3 via a fluid system. In the separation unit 4, the products from the dehydrogenation reactor 3 are separated from one another. In particular, the hydrogen storage medium and / or the released hydrogen gas are conditioned and / or purified, in particular independently of each other and in particular in separate conditioning and / or purification units.

[0037] The separation apparatus 4 is designed in a multi-stage manner, with the individual stages serving to perform specific separation tasks, in particular cooling, condensation, and / or separation of the product mixture. The individual stages are optimized for their respective separation tasks, ensuring that these tasks can be carried out efficiently in each stage. A hydrogen line 5 and a hydrogen storage medium line 6 are connected to the separation apparatus 4, leading to an optional hydrogen buffer storage tank 7 and a second storage container 8, respectively.

[0038] A thermal unit 9 is connected to the hydrogen buffer tank 7. According to the illustrated embodiment, this thermal unit 9 is designed as a fuel cell, in particular a high-temperature fuel cell. The thermal unit 9 is connected to the dehydrogenation reactor 3 via a heat transfer connection. The fuel cell is connected to an electric heating unit 11 via an electrical connection 10, which is also connected to the dehydrogenation reactor 3 via a heat transfer connection. The electric heating unit 11 is additionally or alternatively connected to a power grid 12, in particular to the public power supply, by means of a further power line 10. The power grid is, in particular, an electrical power source.

[0039] The second storage tank 8 is fluidically connected to a burner 13, which is connected to the dehydrogenation reactor 3 via heat transfer. Additionally or alternatively, the second storage tank 8 is connected to an oxidation reactor 14, which in turn is coupled to the dehydrogenation reactor 3 via heat transfer.

[0040] Plant 1 includes a control unit 15 to regulate the heat supply for the dehydration reactor 3, in particular based on at least one input parameter. One input parameter is the CO2 emissions caused by the respective heat supply.

[0041] The following section explains in more detail the procedure for operating Plant 1.

[0042] Partially loaded hydrogen storage medium, referred to as para-BT-H, is stored in the first storage container 2 and is transferred to the dehydrogenation reactor 3, where it is dehydrogenated. Since the dehydrogenation reaction is endothermic, the input of heat Q is required.

[0043] The heat is supplied, for example, from the thermal unit 9, in particular the fuel cell, from the electric heating unit 11, from the burner 13, and / or from the oxidation reactor 14. It is possible to operate only one, several, or all of these heat sources. Crucially, the heat supply is regulated by the control unit 15. For this purpose, the control unit 15 is in communication, particularly bidirectional communication, with the heat supply devices, namely the thermal unit, the electric heating unit 11, the burner 13, and the oxidation reactor 14. This communication can be wired and / or wireless.

[0044] The following will be based on Fig. 2 a regulatory procedure for Annex 1 according to Fig. 1 explained in more detail.

[0045] The aim of the control system is to minimize the integral CO2 emissions, i.e., to minimize the integral CO2 footprint. To this end, the control unit 15 takes into account various input parameters, in particular the CO2 emissions caused by the respective heat supply, the availability of the respective heat sources 9, 11, 13, 14, and / or the costs associated with the heat supply from the various heat sources.

[0046] The system can be operated in various scenarios. According to the first scenario, designated A, energy, in particular heat for dehydration in the dehydration reactor 3, is used from waste heat 16, which is provided in particular by the thermal utilization unit 9, especially the fuel cell 9. Additionally or alternatively, the waste heat, especially when the dehydration reactor 3 has an increased power demand, can be provided by heat 17 generated by electricity, which has been produced by the electric heating unit 11, and / or by combustion heat 18, which has been generated by burning hydrogen gas, in particular in the burner 13.

[0047] In scenario B, instead of hydrogen combustion, LOHC is combusted to generate the corresponding heat of combustion 19. It is also possible to utilize the heat of combustion 19 if there is a corresponding heat demand. The burner 13, which is also used for the combustion of hydrogen gas, can be used to provide the heat of combustion 19. Alternatively, an additional, separate LOHC burner can be used. Scenario B is particularly advantageous if the LOHC, especially benzyltoluene, has been produced in a CO2-neutral manner and is available as a CO2-neutral raw material.

[0048] In scenario C, oxidation heat 20 can be utilized, which is generated by the oxidation of LOHC via oxidation reactor 14. Specifically, the dehydrogenation reactor 3 is heated exclusively by oxidation heat 20 according to scenario C. Therefore, the operation of the alternative energy sources 16 to 19 according to scenario C may be unnecessary. If the heat demand in the dehydrogenation reactor 3 cannot be fully met by the oxidation heat 20, additional heat sources 16 to 19 can be added, particularly considering the CO2 footprint of each heat source.

[0049] According to the regulation in Fig.2. Hydrogen gas can be fed not only directly into the thermal utility unit 9, i.e., the fuel cell, but also, in particular, into a consumer unit 21. The consumer unit 21 serves, in particular, to generate electricity from the hydrogen gas, especially in the form of a fuel cell, and / or for the direct use of the hydrogen gas in chemical processes. QUOTES INCLUDED IN THE DESCRIPTION

[0000] This list of documents cited by the applicant was automatically generated and is included solely for the reader's convenience. The list is not part of the German patent or utility model application. The DPMA accepts no liability for any errors or omissions. Cited patent literature

[0000] DE 10 2021 203 883 A1

[0032]

Claims

[1] Method for releasing hydrogen from an at least partially loaded hydrogen storage medium comprising the method steps - dehydrogenating the at least partially loaded hydrogen storage medium in a dehydrogenation reactor (3) and thereby releasing hydrogen, - Providing heat through -- thermal utilization of hydrogen released in the dehydrogenation reactor (3) in a thermal utilization unit (9), and / or -- Use of a heating unit (11) powered by electricity from renewable energy sources, and / or -- burning the hydrogen storage medium in a burner (13), - controlling the heat supply by means of a control unit (15), wherein the CO2 emissions caused by the respective heat supply are used as input parameters for the control, - Transferring the heat to the dehydrogenation reactor (3). [2] Method according to claim 1, characterized by that the thermal use of hydrogen includes generating electricity in a fuel cell, burning in a hydrogen burner and / or using it in a hydrogen combustion engine. [3] Method according to one of the preceding claims, characterized by that when controlling the heat supply, the availability of the heat sources (9, 11, 13, 14) is used as an input parameter for the control, with particular priority being given to CO2-neutral or CO2-reduced heat sources (9, 11, 13, 14). [4] Method according to one of the preceding claims, characterized by that when controlling the heat supply, the costs of the heat sources (9, 11, 13, 14) are used as input parameters for the control. [5] Method according to one of the preceding claims, characterized bythat benzyltoluene (BT) is used as a hydrogen storage medium, in particular a mixture of substances enriched with para-benzyltoluene isomer. [6] Method according to one of the preceding claims, characterized by that waste heat from the hydrogenation of an at least partially discharged hydrogen storage medium is used to reduce the CO2 footprint of the energy supply. [7] Method according to one of the preceding claims, characterized by that waste heat from a process, in particular a reaction of the hydrogen storage medium, is used to dehydrogenate the at least partially loaded hydrogen storage medium.

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