Hydrogenation process and dehydrogenation process for a carrier medium for hydrogen and system for carrying out processes of this kind

Abstract

A system (1) for hydrogenating a carrier medium for hydrogen comprises a reactor (2) for catalytically hydrogenating the carrier medium for hydrogen, having an input degree of hydrogenation, at least one delivery means (10) for delivering the carrier medium for hydrogen to the reactor (2), and a control unit (17) which is in signal communication (18) with the at least one delivery means (10) and which is designed to control the catalytic hydrogenation in the reactor (2) by adapting the input degree of hydrogenation of the carrier medium for hydrogen.

Description

[0001] Hydrogenation process and dehydrogenation process for a hydrogen carrier medium and plant for carrying out such processes

[0002] This patent application claims priority from German patent application DE 10 2022 205 290.0, the contents of which are incorporated herein by reference.

[0003] The invention relates to a hydrogenation process and a dehydrogenation process for hydrogen carrier media and to a plant for carrying out such processes.

[0004] DE 10 2020 215 444 A1 discloses a process and a plant for the material use of hydrogen.

[0005] CN 101 993 721 A discloses a plant and a process for hydrogenating a carrier material.

[0006] DE 10 2021 203 883 A1 discloses a method and a system for providing hydrogen gas.

[0007] EP 1 081 780 A2 discloses a hydrogen supply system for a fuel cell.

[0008] Hydrogen carrier media, especially liquid organic hydrogen carriers (LOHC), can be reversibly hydrogenated (loaded) and dehydrogenated (unloaded) with hydrogen in catalytic processes. Special process conditions, particularly pressure and temperature, are required for the hydrogenation or dehydrogenation processes. To ensure the most efficient and thus economical implementation of the processes, the goal is to maximize the utilization of water absorption capacity, i.e., almost complete hydrogenation in the hydrogenation process or almost complete dehydrogenation in the dehydrogenation process. This can reduce logistics effort and costs.

[0009] In addition to the technical optimum, real boundary conditions must be taken into account, whereby load flexibility is particularly important for hydrogenation and / or dehydrogenation plants. If, for example, fluctuating hydrogen sources are used for hydrogenation, the supply of hydrogen gas is volatile. For example, when green hydrogen is produced from renewable energies using wind turbines and / or photovoltaic systems, their power generation profiles cause fluctuations. A downstream electrolyzer can follow these power fluctuations. However, this results in a fluctuating fluid flow of hydrogen gas, whereby the process dynamics of the hydrogenation process are sluggish and the process itself is inflexible, especially when operated at part load. Part load means that the plant operates at a power output below a nominal load orbelow a design point, the so-called normal operating point. The dynamics of the process refer to the speed of a load change. The limited partial load capacity essentially results from the system components that are designed for nominal load, such as pumps, lines, and / or filters.

[0010] Accordingly, volatile hydrogen sources such as industrial processes and / or mobility applications, especially filling stations, can cause fluctuations in the hydrogen demand to be met by a dehydrogenation process. Similar challenges arise for the dehydrogenation reaction and the associated plant.

[0011] Fikrt, A. et al.: "Dynamic power supply by hydrogen bound to a liquid organic hydrogen carrier", 194 (2017) 1-8, discloses a power control system for a dehydrogenation reaction of LOHC. The power control system is based on the input parameters of pressure, temperature, and reactant mass flow. The reactant mass flow is the mass flow fed into a reactor, i.e., the sum of all starting materials, i.e., reactants, fed into the reactor. It has been shown that power control using temperature is fundamentally possible. Due to the inertia of the hydrogenation and dehydrogenation processes, temperature has proven unsuitable as a control parameter for volatile hydrogen sources or volatile hydrogen sinks, i.e., for highly dynamic operation. Power control using pressure is also fundamentally possible, but has disadvantages in the lower partial load range.Power control using reactant mass flow is fundamentally possible and particularly conceivable for small power fluctuations in systems, which today are usually designed at load points of 80%, 100%, and 120%. However, it has been shown that for larger power fluctuations, i.e., in the lower partial load range (i.e., at a load of less than 80% of the nominal load), and in the peak load range (i.e., at a load of more than 120% of the nominal load), significant changes in the reactant mass flow would be necessary, resulting in significantly altered fluid dynamics of the overall system. The consequence would be that not all operating conditions can be realized, and the design of system components, especially pumps, in a high load range would become very complex and, in particular, costly.

[0012] The invention is based on the object of improving the hydrogenation and dehydrogenation of hydrogen carrier medium under volatile conditions, in particular when coupled to volatile hydrogen sources and / or volatile hydrogen sinks, and in particular of providing a flexible power control for a hydrogenation process and / or a dehydrogenation process.

[0013] This object is achieved by a hydrogenation process having the features of claim 1, by a dehydrogenation process having the features of claim 9 and by a plant having the features of claim 16.

[0014] The core of the invention is that power control in a hydrogenation or dehydrogenation process is based on the initial hydrogenation degree of the provided hydrogen carrier medium. In particular, it was recognized that the reactant, i.e., the hydrogen carrier medium, can be advantageously and directly used for power control. The power control according to the invention is thus based on an inherent component of the process. The additional effort required to implement the power control according to the invention is minimized and, in particular, unnecessary. In particular, it is possible to easily retrofit the power control according to the invention to existing plants.

[0015] In particular, it was recognized that the performance control of the chemical reaction, i.e., the hydrogenation reaction and / or the dehydrogenation reaction, is possible dynamically and flexibly by adjusting the initial degree of hydrogenation. The performance control is simplified compared to the prior art, in which a performance map is defined, for example, based on the reaction temperature, the reaction pressure, and / or the hydrogenation or dehydrogenation stroke. The process engineering design of the plant components used is straightforward, particularly since the reactant mass flows remain essentially unchanged. In particular, it was recognized that the process according to the invention can be operated stably even under significant changes in the reaction conditions. Neither the catalyst material nor the hydrogen carrier medium are adversely affected.No stability problems arise, and in particular, the quality, i.e., the purity, of the released hydrogen gas is unaffected. Because the process according to the invention enables an expanded performance map, savings in hydrogen gas buffer storage capacity are possible. Such a process results in reduced investment costs and is economically viable. In particular, such a process can also be operated at low partial loads, especially at loads of up to 0%.

[0016] It was also recognized that the state of the hydrogen carrier medium, i.e. its initial hydrogenation level, can advantageously be used as a basis for power control.

[0017] This makes it possible, in particular, to keep the reactant mass flow essentially constant, and in particular completely constant. The design of plant components for the liquid phase, especially pumps and lines, is thus straightforward. The driving force for the required chemical reactions can be defined and, in particular, specifically influenced by the initial hydrogenation degree of the hydrogen carrier medium. If the initial hydrogenation degree is reduced, the performance in the hydrogenation process is increased and in the dehydrogenation process is reduced.

[0018] The initial degree of hydrogenation is understood to be the degree of hydrogenation that the hydrogen carrier medium has when it is fed into a reactor required for the hydrogenation process or the dehydrogenation process, i.e. a hydrogenation reactor or a dehydrogenation reactor.

[0019] The initial degree of hydrogenation is understood to be the degree of hydrogenation exhibited by the hydrogen carrier medium when it is discharged from the required reactor after the hydrogenation or dehydrogenation process, i.e., after the respective reaction has been completed. In hydrogenation, the initial degree of hydrogenation is greater than the initial degree of hydrogenation. In dehydrogenation, the initial degree of hydrogenation is greater than the initial degree of hydrogenation. The difference between the initial degree of hydrogenation and the initial degree of hydrogenation indicates the hydrogenation or dehydrogenation stroke.

[0020] The degree of hydrogenation is defined as the molar balance, i.e., the percentage of a carrier molecule or a mixture of carrier molecules that has already bound hydrogen. It has proven useful to define threshold values ​​for different degrees of hydrogenation.

[0021] For example, the degree of hydrogenation after the hydrogenation process for the hydrogen carrier medium is more than 95%. Such a loaded hydrogen carrier medium is designated LOHC-H. The degree of hydrogenation after the dehydrogenation process is, in particular, less than 15%. Such a hydrogen carrier medium is designated LOHC-D. Partially hydrogenated hydrogen carrier medium or mixtures of different hydrogen carrier media can have a degree of hydrogenation between 15% and 95%. Such a hydrogen carrier medium is designated LOHC-X. Hydrogen carrier media with a comparatively higher degree of hydrogenation than LOHC-D can be used to increase the initial degree of hydrogenation. An increased initial degree of hydrogenation results in a reduction in the performance of the hydrogenation process. An increased initial degree of hydrogenation results in an increase in the performance of the dehydrogenation process.

[0022] Power control based on the inlet hydrogenation degree is based on the realization that the inlet hydrogenation degree serves as the thermodynamic driving force for the respective reaction, particularly at the inlet to the respective reactor. If a reactant, i.e. a hydrogen carrier medium, with a comparatively low inlet hydrogenation degree, particularly relative to a normal operating point, is fed into the hydrogenation process, the thermodynamic driving force and thus the power in the hydrogenation process increases. Conversely, if the inlet hydrogenation degree is greater than that of the hydrogen carrier medium at the normal operating point, the thermodynamic driving force and thus the power in the hydrogenation process decreases. Conversely, the power in the dehydrogenation process decreases if the inlet hydrogenation degree of the hydrogen carrier medium is lower than at the normal operating point. Accordingly, the power in the dehydrogenation process increases if the inlet hydrogenation degree of the hydrogen carrier medium is greater than at the normal operating point.The reason for this is that the changed driving force results in a different performance for the same residence time of the hydrogen carrier medium in the respective reactor, i.e., a different hydrogen uptake in the hydrogenation process or a different water gas release in the dehydrogenation process. The initial degree of hydrogenation is a result of the initial degree of hydrogenation and the performance achieved in the respective process.

[0023] A particularly suitable hydrogen carrier medium is a carrier material that is present in the at least partially loaded form (LOHC-H) as perhydrodibenzyltoluene (HisDBT), as perhydrobenzyltoluene (HnBT), as methylcyclohexane (C7H14), which can be at least partially discharged to toluene (CTHS), and / or as dicyclohexane. It is also possible to use a mixture of carrier material (LOHC-H) of perhydrodiphenylmethane and perhydrobiphenyl. These compounds can be dehydrogenated to diphenylmethane and biphenyl. A mixture of biphenyl to diphenylmethane in a ratio of 30:70, in particular 35:65, and especially 40:60 is particularly advantageous.

[0024] Both the hydrogenation process and the dehydrogenation process each use a catalyst material. The catalyst material comprises a metal, in particular platinum, palladium, nickel, rhodium, and / or ruthenium. The catalyst material is arranged on a catalyst support and in particular secured thereto. The catalyst support is a ceramic material, in particular aluminum oxide, silicon oxide, titanium oxide, and / or zirconium oxide, and / or activated carbon. In particular, the catalyst support is a porous oxide support. The material of the catalyst support has, in particular, pores with a diameter of at least 2 nm, in particular of at least 10 nm, in particular of at least 20 nm, in particular of at least 50 nm, and in particular of at least 100 nm. The weight fraction of the catalyst material, based on the catalyst support, is between 0.1% and 10%.

[0025] The catalyst material comprises, in particular, a plurality of catalyst particles, in particular catalyst support particles, which are in particular present as pellets. The catalyst particles are arranged, in particular, in the form of a fixed bed through which the hydrogen carrier medium, which is in particular liquid, flows. In the hydrogenation process according to the invention, hydrogen gas is stored, in particular on the hydrogen carrier medium. For this purpose, the hydrogen carrier medium and hydrogen gas are fed into a hydrogenation reactor, in particular via separate lines. The supplied hydrogen carrier medium is at least partially discharged and has the initial degree of hydrogenation. Through the catalytic hydrogenation, hydrogen is bound to the hydrogen carrier medium. The hydrogenated hydrogen carrier medium leaving the hydrogenation reactor has an initial degree of hydrogenation that is greater than its initial degree of hydrogenation.

[0026] Accordingly, the dehydrogenation process releases hydrogen gas from the water carrier medium. For this purpose, a hydrogen carrier medium that is at least partially loaded and has the initial hydrogenation degree is fed to a dehydrogenation reactor. Dehydrogenation releases hydrogen gas from the hydrogen carrier medium, so that the dehydrogenated hydrogen carrier medium discharged from the dehydrogenation reactor has an initial hydrogenation degree that is lower than its initial hydrogenation degree.

[0027] For example, a hydrogen carrier medium of technical quality (LOHC-V) can also be used. LOHC-V refers in particular to fresh hydrogen carrier medium that originates from a production process and, in particular, has not yet been hydrogenated. LOHC-V is, in particular, completely aromatic, i.e., it contains exclusively aromatic hydrocarbon compounds. The degree of hydrogenation of the LOHC-V is less than 10%, in particular less than 5%, in particular less than 3%, in particular less than 2%, in particular less than 1%, in particular less than 0.5%, and is, in particular, 0%. LOHC-V acts as an inert component to specifically reduce the initial degree of hydrogenation.

[0028] Additionally or alternatively, a hydrogen carrier medium that is at least partially oxidized (LOHC-OX) can be used to adjust the initial hydrogenation degree. The initial hydrogenation degree of LOHC-OX is in particular at least 20%, in particular at least 30%, in particular at least 40%, in particular at least 50%, and in particular at most 95%. The at least partially oxidized hydrogen carrier medium LOHC-OX enables an increase in the performance of the hydrogenation reaction because the uptake of hydrogen gas by LOHC-OX is increased. LOHC-OX is first reduced with hydrogen gas and then additionally hydrogenated. This can create increased performance in the hydrogenation process by adding LOHC-OX, particularly in a time-flexible and particularly temporary manner. This is particularly advantageous when, for example, more hydrogen gas is made available from a source temporarily and particularly spontaneously.This additional hydrogen gas can be utilized by adding LOHC-OX.

[0029] Processes according to claim 2 or 10 enable particularly uncomplicated adjustment of the initial hydrogenation degree. In particular, additional media are not required. The hydrogen carrier medium discharged from the hydrogenation reactor or dehydrogenation reactor can be directly recycled and fed back into the respective reactor. Depending on the mixing ratio of newly supplied, so-called fresh, hydrogen carrier medium and previously used, recycled hydrogen carrier medium, the initial hydrogenation degree for this mixture can be specifically adjusted.

[0030] It has been recognized that the catalytic reaction in the hydrogenation reactor or dehydrogenation reactor results in the hydrogen carrier medium not having a single, uniform initial degree of hydrogenation, but rather having various initial degrees of hydrogenation. The number of possible initial degrees of hydrogenation depends on the respective hydrogen carrier medium. For example, benzyltoluene as a hydrogen carrier medium exhibits twelve discrete hydrogenation states. The hydrogenation state H12, in which twelve hydrogen atoms are bonded to benzyltoluene, exhibits maximum loading. Accordingly, in the intermediate hydrogenation state H6, half of the maximum possible hydrogen atoms are bonded to benzyltoluene, and in HO, no additional hydrogen atom is bonded. These three hydrogenation states H12, H6, and HO are particularly important in practice. Intermediate states such as H3 or H9 also exist, but these occur rather rarely.The hydrogen carrier medium leaving the hydrogenation reactor or dehydrogenation reactor can be understood as a mixture of the hydrogen carrier medium with different initial degrees of hydrogenation. It is advantageous to separate the hydrogen carrier medium into several fractions in a separation unit, depending on the initial degree of hydrogenation. The fractions comprise the hydrogen carrier medium with a specific degree of hydrogenation or with a specific degree of hydrogenation range. A degree of hydrogenation range exists in particular when several degrees of hydrogenation are combined in one fraction, for example, H12 and H6. A mixture of hydrogen carrier medium with a defined initial degree of hydrogenation can be specifically adjusted from the various fractions. For example, a hydrogen carrier medium with a degree of hydrogenation of 90% can be mixed from 80% H12 and 20% H6 or from 90% H12 and 0% HO.The different fractions can be temporarily stored in separate storage containers.

[0031] By selectively recycling hydrogen carrier medium with a specific degree of hydrogenation or with a specific degree of hydrogenation range, it is possible to adjust the input degree of hydrogenation in a targeted manner by recycling the hydrogenated or dehydrogenated hydrogen carrier medium. Control is more targeted and, in particular, is not limited by the fact that the output degree of hydrogenation has a wide range of degrees of hydrogenation. Such a process is efficient.

[0032] Adjusting the initial hydrogenation level according to claim 3 or 11 allows for increased flexibility with regard to adjusting the initial hydrogenation level. In particular, it has been found that additional hydrogen carrier media can be used and, in particular, admixed to influence the initial hydrogenation level.

[0033] Processes according to claim 4 or 12 enable a more stable process implementation. By mixing the various material streams in a mixing unit before feeding them into the respective reactor, inhomogeneous material properties of the material stream are avoided.

[0034] Alternatively, it is possible to feed the different hydrogen carrier media streams into the respective reactor via a separate line and, in particular, unmixed.

[0035] A method according to claim 5 enables the oversizing of a plant, so that flexible power control is improved, in particular in a partial load range and in a peak load range of the hydrogenation reactor. In particular, the increased absolute reactant mass flow is selected such that the plant power at a new operating point is identical to the normal operating point. Methods according to claim 6 or 14 enable, in particular, stable implementation. Failures, in particular of pumps, lines and / or filters, are thereby avoided. A mass flow is considered constant if deviations of at most + / - 20% of a nominal mass flow occur, in particular of at most + / - 15%, in particular of at most + / - 10%, in particular of at most + / - 5%, in particular of at most + / - 3%, in particular of at most + / - 2%, in particular of at most + / - 1% and in particular no deviations, i.e. 0%.

[0036] Processes according to claim 7 or 15 increase the overall efficiency of the respective process, since, in particular, the energy required for preheating the hydrogen carrier medium to be supplied is reduced. In particular, the preheating of the hydrogen carrier medium to be supplied takes place in a heat exchanger, in particular by means of the hydrogen carrier medium recycled from the reactor. The heat exchanger is a so-called recuperator.

[0037] In particular, in the dehydrogenation process, a substream of the hot product stream, i.e., a mixture of at least partially dehydrogenated hydrogen carrier medium LOHC-D and released hydrogen gas, can be directly contacted with a reactant stream, i.e., fresh, at least partially hydrogenated hydrogen carrier medium LOHC-H. In the hot product stream, the at least partially dehydrogenated hydrogen carrier medium LOHC-D is present, in particular at least partially, in vapor form. The heat transfer from the hot product stream to the fresh reactant is improved because, in addition to sensible heat, condensation heat is also transferred as the vaporous LOHC-D at least partially condenses. Furthermore, a phase separation of the condensed LOHC-D from the hydrogen gas occurs.

[0038] A method according to claim 8 enables the advantageous use of hydrogen gas, which can in particular also be provided in fluctuating quantities. This makes the method suitable for using hydrogen gas generated using renewable energies, in particular wind power, photovoltaic systems, and hydropower. The method enables advantageous dynamics. A plant according to claim 16 essentially has the advantages of the aforementioned methods, to which reference is hereby made. A plant can be used for the catalytic hydrogenation or catalytic dehydrogenation of hydrogen carrier medium. It is essential that a control unit is designed to control the catalytic hydrogenation and / or catalytic dehydrogenation in the reactor by adjusting the initial degree of hydrogenation. For this purpose, the control unit is in signal communication with at least one conveying means.The at least one conveying means, in particular a pump, serves to convey the hydrogen carrier medium into the reactor. In particular, the at least one conveying means is arranged directly upstream of the reactor and in particular upstream of a mixing unit. It is understood that multiple conveying means can be provided, in particular if different hydrogen carrier medium streams are supplied to the reactor, in particular via separate lines. In particular, each line is assigned at least one conveying means.

[0039] A system according to claim 17 simplifies the direct recycling of the hydrogen carrier medium. The system simplifies a process according to claim 2 or 10. A separation unit for separating or enriching, i.e. only partially, not completely separating, the hydrogen carrier medium discharged from the hydrogenation reactor or the dehydrogenation reactor is particularly advantageous. The separation unit enables the separation of the hydrogen carrier medium. The separation takes place in particular according to the chemical and / or physical properties of the hydrogen carrier medium. In particular, the separation takes place by distillation due to boiling point differences and / or in a centrifuge due to density differences. The separation unit can be a separate unit. The separation unit can also comprise several components, in particular several devices.For example, a coarse separation based on density can be performed using a centrifuge, followed by a fine separation based on boiling point using a distillation column. The separation unit can also be integrated into a product buffer tank.

[0040] A system according to claim 18 enables the flexible provision of additional hydrogen carrier medium at the system.

[0041] A system according to claim 19 enables the direct mixing of various hydrogen carrier media before feeding them into the reactor. A system according to claim 20 enables the processes to be carried out with increased overall efficiency.

[0042] Both the features specified in the patent claims and the features specified in the exemplary embodiments of systems 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.

[0043] Further features, advantages, and details of the invention will become apparent from the following description of four exemplary embodiments with reference to the drawings. They show:

[0044] Fig. 1 is a schematic representation of a plant according to the invention for hydrogenating hydrogen carrier medium according to a first embodiment,

[0045] Fig. 2 is a diagram showing the dependence of a plant output on the inlet hydrogenation degree of the hydrogen carrier medium in the plant according to Fig. 1,

[0046] Fig. 3 is a representation corresponding to Fig. 1 of a plant according to the invention for dehydrogenating hydrogen carrier medium according to a second embodiment,

[0047] Fig. 4 is a diagram corresponding to Fig. 2 for the system in Fig. 3,

[0048] Fig. 5 is a diagram corresponding to Fig. 2 illustrating the power control for partial load conditions and peak load conditions,

[0049] Fig. 6 is a diagram illustrating the functional relationship between electrolyzer performance and the time of day when coupled with a renewable power generation source, Fig. 7 is a diagram corresponding to Fig. 6 illustrating the hydrogenation reactor performance in relation to a peak power of the electrolyzer,

[0050] Fig. 8 shows a representation of a buffer storage charge level corresponding to Fig. 6 in relation to a daily electrolysis production,

[0051] Fig. 9 is a representation corresponding to Fig. 1 of a plant for hydrogenating hydrogen carrier medium according to a third embodiment,

[0052] Fig. 10 is a representation corresponding to Fig. 3 of a plant for dehydrogenating hydrogen carrier medium according to a fourth embodiment.

[0053] A system, designated as a whole by 1 in Fig. 1, is used to hydrogenate a hydrogen carrier medium. The system 1 comprises a reactor 2, which is designed as a hydrogenation reactor. A hydrogen gas supply line 3, to which a hydrogen gas buffer storage 4 is connected, opens into the hydrogenation reactor 2. In the hydrogen gas buffer storage 4, hydrogen gas can be stored, i.e., buffered, in comparatively small quantities, particularly temporarily. For this purpose, the hydrogen gas buffer storage is pressurized.

[0054] The hydrogen gas buffer storage 4 is fed by an electrolyzer 5, in which water is separated into hydrogen gas and oxygen gas by electrolysis, i.e., using electrical current. The electrolyzer 5 is operated with electrical current provided by a power generation unit 6. The power generation unit 6 enables, in particular, the generation of electrical current from renewable energy sources such as wind power or solar radiation. The power generation unit 6 is, in particular, a photovoltaic system and / or a wind turbine. However, other designs of the power generation unit are also possible.

[0055] The plant 1 further comprises a first reactant storage tank 7 in which the hydrogen carrier medium LOHC, and in particular at least partially discharged hydrogen carrier medium LOHC-D, is stored, in particular without pressure and at room temperature. The first reactant storage tank 7 is connected via a liquid line 8 to a mixing unit 9, which is connected via a further liquid line 8 to the hydrogenation reactor 2.

[0056] A liquid pump 10 is arranged on the liquid line 8 upstream and / or downstream of the mixing unit 9 to convey the liquid hydrogen carrier medium into the hydrogenation reactor 2. For illustrative purposes only, in Fig. 1, the pump 10 is arranged between the first reactant storage container 7 and the mixing unit 9. The pump 10 forms a conveying means for conveying the hydrogen carrier medium along the liquid lines 8, in particular into the hydrogenation reactor 2 and out of the hydrogenation reactor 2. In principle, a pump or a comparable conveying means can be arranged along each line shown in Fig. 1.

[0057] A discharge line 11 is connected to the hydrogenation reactor 2, which opens into a product buffer tank 12. A product storage tank 13 is connected to the product buffer tank 12 via a further liquid line 8. A return line 14, which opens into the mixing unit 9, is also connected to the product buffer tank 12. It is also conceivable for the return line 14 to open directly into the liquid line 8 connected to the hydrogenation reactor 2 or, alternatively, to open directly into the hydrogenation reactor 2, similar to the liquid line 8 connected to the hydrogenation reactor 2, and in particular adjacent to the liquid line 8 in the hydrogenation reactor 2.

[0058] The product buffer container 12 is particularly optional.

[0059] A separation unit 25 is arranged downstream of the hydrogenation reactor 2. In the separation unit 25, the hydrogen carrier medium discharged from the hydrogenation reactor 2 can be separated and, in particular, stored in the separation unit 25. It is also conceivable for the hydrogen carrier medium to be temporarily stored partly in the separation unit 25 and partly in the product buffer tank 12. It is also conceivable to arrange a plurality of product buffer tanks 12 in order to temporarily store the hydrogen carrier medium depending on the initial degree of hydrogenation. It is also conceivable for the degree-dependent temporary storage to take place in a single product buffer tank 12, which can be designed, in particular, according to DE 10 2016 206 106 A1. The separation unit 25 can also be arranged downstream of the product buffer tank 12.

[0060] The separation unit 25 can also be arranged along the return line 14.

[0061] The hydrogenation reactor 2, the upstream mixing unit 9 and the downstream product buffer tank 12 form a hydrogenation module 15. The hydrogenation module 15 can also include the separation unit 25.

[0062] The plant 1 has a second reactant storage tank 16, which is essentially identical to the first reactant storage tank 7 and is connected to the mixing unit 9 via a liquid line 8. A pump, also not shown in detail, can be arranged along this liquid line 8. The second reactant storage tank stores a hydrogen carrier medium that differs in particular from the hydrogen carrier medium stored in the first reactant storage tank 7. In particular, this is LOHC-V, LOHC-X or LOHC-OX. It can also be LOHC-D, whose initial degree of hydrogenation differs from the LOHC-D in the first reactant storage tank 7.

[0063] The system 1 comprises a control unit 17, which is in particular in a bidirectional signal connection with the pump 10. The signal connection can be wired or wireless, in particular via a radio connection. The radio connection is indicated by symbol 18 in Fig. 1.

[0064] In addition, the control unit 17 can also be in signal connection, in particular bidirectional, with the hydrogenation reactor 2.

[0065] In particular, the plant 1 has a sensor device 19, shown purely schematically in Fig. 1, which is suitable for detecting the inlet hydrogenation degree before the hydrogen carrier medium is fed into the hydrogenation reactor 2. In particular, the sensor device 19 is in signal communication with the control unit 17. In particular, the measured inlet hydrogenation degree serves as a feedback variable for the control loop of the control unit 17. In particular, the sensor device 19 is arranged downstream of the mixing unit 9 and in particular immediately upstream of the hydrogenation reactor 2. The mode of operation of the plant 1 is explained in more detail below with reference to Fig. 2 and Figs. 5 to 8. For hydrogenation, the hydrogen carrier medium, in particular in at least partially discharged LOHC-D form, is fed from the first reactant storage tank 7 to the hydrogenation reactor 2.In addition, hydrogen, in particular hydrogen gas, which has been generated by the electrolyzer 5 and temporarily stored in the hydrogen gas buffer storage 4, is provided. Since the electrical power required for this purpose is generated from renewable energies, the supply of hydrogen gas can be volatile.

[0066] In order to counteract the temporally variable and, in particular, unpredictable supply of hydrogen gas in the hydrogenation reactor 2, the performance of the hydrogenation reaction in the hydrogenation reactor 2 is regulated by specifically changing the initial hydrogenation degree of the supplied hydrogen carrier medium. For this purpose, for example, hydrogen carrier medium already hydrogenated in the hydrogenation reactor 2 with an initial hydrogenation degree that is greater than the initial hydrogenation degree can be returned to the mixing unit 9 via the return line 14 and mixed with hydrogen carrier medium LOHC-D from the first reactant storage tank 7. This mixture then has a higher initial hydrogenation degree than LOHC-D. This makes it possible to reduce the driving force for the hydrogenation reaction in the hydrogenation reactor 2.

[0067] To adjust the initial hydrogenation level, it is possible to mix LOHC-D from the first reactant storage tank 7 with LOHC-H from the product buffer tank 12. Depending on the mixing ratio, the resulting initial hydrogenation level can be specifically adjusted. Additionally or alternatively, it is possible to mix LOHC-D from the first reactant storage tank 7 with LOHC-V and / or LOHC-OX from at least one second reactant storage tank 16.

[0068] As can be seen in particular from Fig. 2, the hydrogenation process carried out with plant 1 enables a reduction in plant output by increasing the input hydrogenation degree through a targeted adjustment of the input hydrogenation degree, which was measured in particular by means of the sensor device 19. For example, for the characteristic curve of a constant reactant mass flow (mReduct, abs = 100%), a reduction in plant output from 100%, which corresponds to the normal operating point (BPNormai), to a partial load range and in particular to a standby range (BPstand-By) with a plant output of 0% is possible. In this case, the input hydrogenation degree is approximately 100%.

[0069] In Fig. 2, for the different degrees of hydrogenation of the product stream HG pro d of 99% and 95%. The product stream after hydrogenation reactor 2 therefore primarily comprises LOHC-H.

[0070] In particular, Plant 1 allows the definition of a new operating point BPoptioni, at which a higher reactant mass flow mEduct,abs = 150% and an initial hydrogenation degree of 40% are present. This new design operating point BPoptioni is marked in Fig. 5. This design therefore assumes that hydrogen carrier medium with an initial hydrogenation degree of 40% is already provided at the normal operating point, i.e., a mixture of LOHC-D and LOHC-H, i.e., LOHC-X. However, the design of Plant 1 is selected such that the relative plant performance P reicompared to the initial normal operating point BPNormai. Since the mass flow remains essentially constant during power control, the modified operating point moves along the now steeper characteristic curve for mEduct,abs = 150%. Because the modified operating point BPoptioni is shifted toward higher hydrogenation degrees, peak loads can be covered more easily by lowering the input hydrogenation degree. Accordingly, partial load conditions can also be achieved here by further increasing the hydrogenation degree, i.e., by adding additional LOHC-H.

[0071] Fig. 6 shows a standardized profile of hydrogen gas production using electrical power provided by the power generation unit 6 in the form of a photovoltaic system. Relative to the time of day, there is a peak power in the early afternoon. Based on this volatile hydrogen gas source, various operating modes of a hydrogenation plant are explained below using Figs. 7 and 8. According to a first operating mode, the plant is operated at constant power. The corresponding curve for constant operation is marked KB in Figs. 7 and 8.

[0072] A second operating mode considers power control in a power range from 40% to 120%, i.e., with partial load and peak load ranges. Power control is achieved by adjusting the mass flow. The corresponding graphs are labeled MS in Figs. 7 and 8.

[0073] A third operating mode corresponds to the hydrogenation process according to the invention, i.e., dynamic power control in a power range from 0% to 145%, whereby a modified normal operating point is defined as shown in Fig. 5 at an initial hydrogenation level of 40%, and power control is achieved by adjusting the initial hydrogenation level. The corresponding graphs are marked HG in Figs. 7 and 8.

[0074] One finding is that constant operation (CV) cannot even begin to represent the volatile hydrogen gas source in terms of hydrogenation output, resulting in a large buffer storage requirement (see Fig. 8). The process of power control via the reactant mass flow (MS) is improved compared to constant operation (CV), but still has deficiencies. In contrast, the process according to the invention shows that the volatile profile of hydrogen gas production using the photovoltaic system can be ideally represented due to the highly dynamic control, and the buffer storage requirement is minimized and, in particular, is zero.

[0075] A comparison of the key figures is summarized in Table 1.

[0076] The various systems differ in their basic design, i.e., their nominal load relative to the peak power of electrolyzer 5. Since KB operates constantly throughout the day, a significantly smaller design is possible compared to electrolyzer 5, amounting to approximately 28%. However, approximately 56% of the daily hydrogen gas production must be temporarily stored in hydrogen gas buffer storage 4. A large hydrogen gas buffer storage 4 is expensive and disadvantageous.

[0077] In the MS plant, which is more load-flexible and therefore requires less buffer storage, the overall system size is 42% larger than that of electrolyzer 5.

[0078] As already mentioned, due to the high dynamic nature of the HG plant, no hydrogen gas buffer storage is required, or at most, a minimal one. In particular, the plant allows for peak loads of up to 145%. In terms of daily balance, the plant's utilization is minimal compared to the two aforementioned plants, amounting to less than half that of the plant in constant operation.

[0079] The process according to the invention enables, in particular, a continuous reduction in power down to partial load conditions and, in particular, down to 0% power. During the hydrogenation reaction, to reduce power, the initial hydrogenation degree is increased, in particular continuously, i.e., in particular, LOHC-H and / or LOHC-OX and / or LOHC-X are added, i.e., in the borderline case, fully hydrogenated LOHC. 0% power corresponds to a so-called hot standby state. In this hot standby state, hydrogen carrier medium continues to flow through the hydrogenation reactor 2, but it does not output any power or absorb any load, i.e., a hydrogenation reaction takes place. By changing the initial hydrogenation degree, i.e., by lowering the initial hydrogenation degree, the hydrogenation reactor can go back into operation directly.

[0080] A further embodiment of the invention is described below with reference to Figs. 3 and 4. Structurally identical parts have the same reference numerals as in the first embodiment, to the description of which reference is hereby made. Structurally different but functionally similar parts have the same reference numerals with a suffix "a."

[0081] In plant 1a, reactor 2a is a dehydrogenation reactor. Accordingly, at least partially loaded hydrogen carrier medium LOHC-X and / or LOHC-H is stored in the first reactant storage container 7. In dehydrogenation reactor 2a, hydrogen gas is released from the hydrogen carrier medium, which can be removed from dehydrogenation reactor 2a via a hydrogen gas removal line 20 and temporarily stored in an optional hydrogen gas buffer storage 4 before the hydrogen gas is made available to a hydrogen gas consumer 21. Hydrogen gas consumer 21 is, in particular, an electricity generation unit and, in particular, a fuel cell. Hydrogen gas consumer 21 can be a stationary plant. However, it is also conceivable in principle for hydrogen gas consumer 21 to be a mobile unit, for example, in a motor vehicle.In particular, the hydrogen gas consumer 21 is a hydrogen gas interface, such as at a hydrogen gas filling station. Hydrogen gas is made available to a consumer, in particular to a hydrogen gas tank in a vehicle, via the hydrogen gas interface. The consumption of hydrogen gas via the hydrogen gas interface is particularly volatile, so that power control of the dehydrogenation reaction in the dehydrogenation reactor 2a is required. The control unit 17 serves this purpose.

[0082] It is fundamentally conceivable that the hydrogen gas from the dehydrogenation reactor 2a is discharged together with the at least partially dehydrogenated hydrogen carrier medium via a common discharge line and the two material streams are separated from each other in a separation unit.

[0083] The product buffer tank 12 is connected to the product storage tank 13 via the liquid line 8 in the manner described.

[0084] The plant 1a also has a separation unit 25 arranged downstream of the dehydrogenation reactor 2a. The separation unit 25 can be arranged upstream and / or downstream of the product buffer tank 12 and in particular along the return line 14.

[0085] The mixing unit 9, the dehydrogenation reactor 2a, and the product buffer tank 12 form a dehydrogenation module 22. The dehydrogenation module 22 can also include the separation unit 25. The dehydrogenation process functions analogously to the hydrogenation process. In particular, the power control in the dehydrogenation reactor 2a is achieved by adjusting the initial hydrogenation level. In particular, it has been shown that a reduction in plant power towards partial load ranges is possible by reducing the initial hydrogenation level of the hydrogen carrier medium, especially at a constant reactant mass flow. The initial hydrogenation level can be reduced in particular by adding at least partially dehydrogenated hydrogen carrier medium LOHC-X or LOHC-D. This can be achieved either via the return from the product buffer tank 12 via the return line 14 and / or via the second reactant storage tank 16, in which appropriate material is stored.

[0086] With regard to the hot standby state already described, this is achieved in the dehydrogenation process by adding increasingly more dehydrogenated hydrogen carrier material, and in particular completely dehydrogenated hydrogen carrier material LOHC-D.

[0087] To restart the dehydrogenation reactor 2a, the initial degree of hydrogenation must be increased again. Furthermore, the dehydrogenation reactor 2a must be heated. Unlike hydrogenation processes, the dehydrogenation process requires heating, so the dehydrogenation reactor 2a must be maintained at a temperature in hot standby mode while absorbing heat. This means that the heating of the dehydrogenation reactor must be separately controlled by the control unit 17 using a heating unit 23, which provides a heat flow Q from the heating unit 23 to the dehydrogenation reactor 2a. The control unit 17 is in a signal connection, in particular a bidirectional one, with the heating unit 23.

[0088] If no hydrogen gas demand is reported by the hydrogen gas consumer 21 or the corresponding hydrogen gas interface, the dehydrogenation reactor 2a can be operated in hot standby mode or in a so-called self-sustaining mode by releasing a minimal amount of hydrogen gas to keep the dehydrogenation reactor 2a at a minimum operating temperature. In particular, the minimal amount of released hydrogen gas can be used exclusively to heat the dehydrogenation reactor 2a. In this case, the heating unit 23 is designed as a hydrogen gas burner and / or as a fuel cell, wherein in particular a branch of the hydrogen gas discharge line 20 is directly connected to the heating unit 23. A renewed change to a load state of the dehydrogenation reactor 2a, i.e. a hydrogen gas demand at the hydrogen gas consumer 21, could be realized more quickly and quickly and thus more dynamically from the hot standby mode.

[0089] A further embodiment of the invention is described below with reference to Fig. 9. Structurally identical parts are given the same reference numerals as in the previous embodiments, to whose description reference is hereby made. Structurally different and functionally similar parts are given the same reference numerals with a suffix "b."

[0090] Plant 1b comprises a hydrogenation reactor 2 and essentially corresponds to the first exemplary embodiment. One difference from the first exemplary embodiment is that the hydrogenation module 15 additionally has a heat exchanger 24, which serves to preheat the reactant. The heat exchanger 24 is arranged, in particular, upstream of the mixing unit 9. In particular, the heat exchanger is designed as a liquid-liquid heat exchanger. The comparatively warm hydrogen carrier medium LOHC-H, i.e., the product, which is at least partially hydrogenated in the hydrogenation reactor 2, serves to preheat the product, i.e., the at least partially dehydrogenated hydrogen carrier medium, in particular LOHC-D, LOHC-V, or LOHC-X. Accordingly, the return line 14 is connected to both the mixing unit 9 and the heat exchanger 24.The product, which has been at least partially cooled in the heat exchanger 24, is fed from the heat exchanger 24 via a liquid line 8 to the product storage container 13.

[0091] This also results in advantages with regard to the storage of the cooled product.

[0092] A further embodiment of the invention is described below with reference to Fig. 10. Structurally identical parts are given the same reference numerals as in the previous embodiments, to whose description reference is hereby made. Structurally different but functionally similar parts are given the same reference numerals with a suffix c. The system 1c comprises the dehydrogenation reactor 2a and the heat exchanger 24, which, as in the previous embodiment, serves to preheat the reactant stream from the first reactant storage tank 7.

[0093] It was surprisingly found that the heat exchanger 24 in this exemplary embodiment has the additional function of a separation unit. The material stream discharged from the dehydrogenation reactor 2a and returned via the return line 14 comprises, on the one hand, the product, i.e., LOHC-D, and the released hydrogen gas, both of which are present in particular as vapor or in the gas phase. This hot mixture of LOHC-D and hydrogen gas can, on the one hand, be fed to the mixing unit 9, wherein the mixer 9 could function as a scrubbing unit and as a preheater. For example, the hot mixture of LOHC-D vapor and hydrogen gas could be introduced into fresh LOHC-H, i.e., starting material, by means of a distribution plate. Since LOHC-H has a comparatively lower temperature, the mixture of LOHC-D and hydrogen gas would cool down and, in particular, LOHC-D would condense.Both the sensible heat generated by steam cooling and the condensation enthalpy could be used to preheat the LOHC-H. The cooled hydrogen gas could be selectively removed at the top of the mixing unit 9. The mixture of LOHC-D and LOHC-H, i.e., LOHC-X, could be fed to the dehydrogenation reactor 2a. Additionally or alternatively, the hot mixture of LOHC-D and hydrogen gas can be fed to the heat exchanger 24, whereby condensation of the product, i.e., LOHC-D, can also take place in the heat exchanger.

Claims

Patent claims 1. Hydrogenation process for a hydrogen carrier medium comprising the process steps Feeding the hydrogen carrier medium into a hydrogenation reactor (2), wherein the supplied hydrogen carrier medium is at least partially discharged and has an initial degree of hydrogenation, Supply of hydrogen to the hydrogenation reactor (2), catalytic hydrogenation of the hydrogen carrier medium in the hydrogenation reactor (2) such that the hydrogen carrier medium has an initial degree of hydrogenation that is greater than the initial degree of hydrogenation, Control the hydrogenation reaction by adjusting the initial degree of hydrogenation.

2. Hydrogenation process according to claim 1, characterized in that the adjustment of the input degree of hydrogenation is carried out by returning hydrogenated hydrogen carrier medium with the output degree of hydrogenation to the hydrogenation reactor (2).

3. Hydrogenation process according to one of the preceding claims, characterized in that the adjustment of the incoming degree of hydrogenation is carried out by supplying further hydrogen carrier medium to the hydrogenation reactor (2), wherein the further hydrogen carrier medium has a further degree of hydrogenation which differs from the incoming degree of hydrogenation.

4. Hydrogenation process according to claim 2 or 3, characterized in that the hydrogen carrier medium is mixed with the recycled hydrogen carrier medium and / or with the further hydrogen carrier medium in a mixing unit (9) before being fed into the hydrogenation reactor (2).

5. Hydrogenation process according to one of claims 2 to 4, characterized by operating the process at an operating point (BPoption i) with a higher absolute feed mass flow rate mEdukt,abs and / or with an increased degree of input hydrogenation, wherein mEdukt,abs > 100%, in particular mEdukt,abs > 150%, and wherein in particular the degree of input hydrogenation is at least 20% and in particular at least 40%.

6. Hydrogenation process according to one of the preceding claims, characterized in that the mass flow rate of the hydrogen carrier medium supplied to the hydrogenation reactor (2) is constant.

7. Hydrogenation process according to one of the preceding claims, characterized by preheating the hydrogen carrier medium, in particular in a heat exchanger (24) upstream of the hydrogenation reactor (2) and in particular the mixing unit (9), wherein the preheating is carried out in particular by means of the recycled hydrogen carrier medium.

8. Hydrogenation process according to one of the preceding claims, characterized in that the amount of hydrogen supplied to the hydrogenation reactor (2), in particular the dynamically changing amount, is taken into account as an input variable for controlling the hydrogenation reaction.

9. Dehydrogenation process for a hydrogen carrier medium comprising the process steps Feeding the hydrogen carrier medium into a dehydrogenation reactor (2a), wherein the supplied hydrogen carrier medium is at least partially loaded and has an initial degree of hydrogenation, catalytic dehydrogenation of the hydrogen carrier medium in the dehydrogenation reactor (2a) such that hydrogen gas is released from the hydrogen carrier medium and the hydrogen carrier medium has an initial degree of hydrogenation that is lower than the initial degree of hydrogenation, removal of the released hydrogen gas from the dehydrogenation reactor (2a), control of the dehydrogenation reaction by adjusting the initial degree of hydrogenation.

10. Dehydration process according to claim 9, characterized in that the adjustment of the input degree of hydrogenation is carried out by returning dehydrated hydrogen carrier medium with the output degree of hydrogenation to the dehydration reactor (2a).

11. Dehydration process according to claim 9 or 10, characterized in that the adjustment of the incoming degree of hydrogenation is carried out by adding further hydrogen carrier medium to the dehydrogenation reactor (2a) takes place, wherein the further hydrogen carrier medium has a further degree of hydrogenation that differs from the initial degree of hydrogenation.

12. Dehydrogenation process according to claim 10 or 11, characterized in that the hydrogen carrier medium is mixed with the recycled hydrogen carrier medium and / or with the further hydrogen carrier medium in a mixing unit (9) before being fed into the dehydrogenation reactor (2a).

13. Dehydration process according to one of claims 9 to 12, characterized by operating the process at an operating point (BPoption i) with a higher absolute feed mass flow rate mEdukt,abs and / or with an increased degree of input hydrogenation, wherein mEdukt,abs > 100%, in particular mEdukt,abs > 150%, and wherein in particular the degree of input hydrogenation is at most 80% and in particular at most 60%.

14. Dehydrogenation process according to one of claims 9 to 13, characterized in that the mass flow rate of the hydrogen carrier medium supplied to the dehydrogenation reactor (2a) is constant.

15. Dehydration process according to one of claims 9 to 14, characterized by preheating the hydrogen carrier medium, in particular in a heat exchanger (24) upstream of the dehydration reactor (2a) and in particular the mixing unit (9), wherein the preheating is carried out in particular by means of the recycled hydrogen carrier medium.

16. Plant for carrying out a process according to one of the preceding claims, wherein the plant comprises: a. a reactor (2; 2a) for the catalytic hydrogenation and / or catalytic dehydrogenation of a hydrogen carrier medium having an inlet degree of hydrogenation; b. at least one conveying means (10) for conveying the hydrogen carrier medium into the reactor (2; 2a); c. a control unit (17) in signal communication (18) with the at least one conveying means (10), which is configured to control the catalytic hydrogenation and / or dehydrogenation. The catalytic dehydration in the reactor (2; 2a) is controlled by adjusting the inlet degree of hydrogenation of the hydrogen carrier medium. The system according to claim 16 is characterized by a return line (14) for returning hydrogen carrier medium to the reactor (2; 2a). The system according to claim 16 or 17 is characterized by an additional storage tank (16) in which further hydrogen carrier medium is stored, having a degree of hydrogenation different from that of the inlet hydrogenation. The system according to claim 17 or 18 is characterized by a mixing unit (9) for mixing the hydrogen carrier medium with the recirculated hydrogen carrier medium and / or with the further hydrogen carrier medium.Plant according to one of claims 17 to 19, characterized by a heat exchanger (24) for preheating the hydrogen carrier medium to be supplied to the reactor (2; 2a), wherein the heat exchanger (24) is arranged in particular upstream of the mixing unit (9), and wherein in particular the return line (14) connects the reactor (2; 2a) to the heat exchanger (24), in particular directly.

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