Method and system for releasing hydrogen gas from an at least partially loaded carrier material

Abstract

The invention relates to a method for releasing hydrogen gas from an at least partially loaded carrier material, having the steps of dehydrogenating the carrier material from a starting degree of hydrogenation to a first degree of hydrogenation in a first dehydrogenation reactor (2) by bringing the carrier material into contact with a catalyst material and thereby releasing hydrogen gas, wherein the carrier material leaves the first dehydrogenation reactor (2) with a liquid phase proportion of at least 5%; transferring the carrier material with the first degree of hydrogenation from the first dehydrogenation reactor (2) to a second dehydrogenation reactor (3, 4); dehydrogenating the carrier material in the second dehydrogenation reactor (3, 4) from the first degree of hydrogenation to a second degree of hydrogenation; and removing auxiliary products from the carrier material.

Description

[0001] Method and system for releasing hydrogen gas from at least partially loaded carrier material

[0002] This patent application claims priority from German patent application DE 10 2022 210 822.1, the contents of which are incorporated herein by reference.

[0003] The invention relates to a method and a plant for releasing hydrogen gas from at least partially loaded carrier material.

[0004] Support materials are known that can chemically bind and release hydrogen in catalytic reactions. These catalytic reactions are, in particular, completely reversible. Such support materials are, in particular, liquid organic hydrogen carriers, also known as LOHCs. In a release reaction, which is a dehydrogenation reaction, hydrogen is separated from the organic support material. This produces byproducts that are, in particular, liquid and have a higher boiling point than the support material. These byproducts are undesirable. The byproducts can deposit on a catalyst material required for the dehydrogenation reaction and reduce its activity. The overall efficiency of the dehydrogenation process is reduced.In particular, catalyst activity is reduced by the byproducts adsorbing onto the catalyst material and, in particular, competing with the support material itself for active reaction sites. It has been found that the byproducts can react further to form polymers and / or coke-like, solid byproducts, which, on the one hand, coat the catalytically active material, in particular a noble metal, and / or clog pore structures of a catalyst support. It has also been recognized that, upon evaporation of the support material during the dehydrogenation reaction, byproducts accumulate on the catalyst material and can lead to a further reduction in catalyst activity. Reactivation of the catalyst material is complex.

[0005] The invention is based on the object of improving the overall efficiency of dehydration, particularly in continuous operation. This object is achieved according to the invention by a method having the features of claim 1 and by a system having the features of claim 12.

[0006] The core of the invention is that by-product deposits on the catalyst material are avoided, in particular from the outset, and / or removed inexpensively by suitable process control of the dehydrogenation reaction. The by-products, which are higher-boiling compounds, are removed from the support material. Permanent deposits that lead to deactivation of the catalyst material are avoided. The dehydrogenation of support material takes place in several stages. The support material is at least partially loaded, in particular predominantly loaded, and in particular fully loaded. The degree of loading is described by the so-called degree of hydrogenation. The support material to be dehydrogenated has an initial degree of hydrogenation of at least 85%, in particular at least 90%, in particular at least 95%, in particular at least 98%, in particular at least 99%, and in particular at least 99.9%.

[0007] A further key finding is that the dehydrogenation reaction is carried out in multiple stages, with several dehydrogenation reactors arranged in series. Additionally or alternatively, further dehydrogenation reactors can be connected in parallel. By carrying out the dehydrogenation reaction in stages over several dehydrogenation stages, the reaction conditions in the respective dehydrogenation reactors can be individually adapted so that they are optimized for the respective dehydrogenation stage. In particular, the reaction conditions can be adjusted so that the support material is present with a sufficient liquid phase fraction in at least one dehydrogenation reactor, in particular in several, and especially in all dehydrogenation reactors.

[0008] In a first dehydrogenation reactor, the support material is dehydrogenated from the initial hydrogenation level to a first hydrogenation level. The support material is brought into contact with a catalyst material, thereby releasing hydrogen gas. It is essential that the support material leaves the first dehydrogenation reactor with a liquid phase fraction of at least 5%. Due to the dependence of the vapor fraction of the support material on the ratio of hydrogen gas to the support material fraction in the dehydrogenation reactor, the liquid phase fraction of the support material can vary along the dehydrogenation reactor. In particular, the liquid phase fraction of the support material can be greater at the inlet of the dehydrogenation reactor than at the outlet of the dehydrogenation reactor, since the support material increasingly transitions into the gas phase with increasing hydrogen gas release, in particular with increasing hydrogen gas fraction as a result of the dehydrogenation reaction.If the carrier material leaves the first dehydrogenation reactor with a minimum liquid phase content, it is ensured that a complete liquid phase is reliably maintained over the entire length of the first dehydrogenation reactor.

[0009] In particular, the liquid phase fraction is at least 25% and especially at least 50%. Complete evaporation of the support material during dehydrogenation is prevented. By ensuring that the support material has a liquid phase fraction in the first dehydrogenation reactor, byproducts formed during the dehydrogenation reaction are flushed out of the first dehydrogenation reactor, in particular continuously. Byproducts flushed out by the liquid phase fraction of the support material can be separated from the support material in a removal unit. This prevents the accumulation of byproducts. Impairment of catalyst performance when using support material contaminated by byproducts is also avoided.

[0010] By-products are, in particular, aromatic and / or unsaturated molecules, which are particularly large. Large molecules are, in particular, planar, aromatic, pi-conjugated hydrocarbon compounds with at least 16 carbon atoms and, in particular, at least 20 carbon atoms in the carbon skeleton. The by-products are, in particular, multiply condensed ring systems, in particular polycyclic aromatic hydrocarbons (PAHs), especially pyrene or chrysene. Other by-products can be methylfluorenes or oligomerized hydrocarbon compounds, in particular ring systems with several aromatic rings, in particular with four or six aromatic rings.

[0011] In particular, the byproducts are compounds that differ from the support material, especially from the support material in the at least partially loaded and / or partially unloaded form. Undesired deposition of the byproducts on the catalyst material is reduced and, in particular, prevented. A reduction in catalyst performance is prevented. The effectiveness of the catalyst material is improved. The service life of the catalyst material, i.e., the service life of the catalyst material, is increased.

[0012] The liquid phase fraction of the support material can be adjusted according to the vapor-liquid equilibrium, also known as VLE (vapor-liquid equilibrium), in which the support material is in thermodynamic equilibrium as a liquid and as vapor and / or gas. The liquid phase fraction is directly related to the amount of hydrogen gas released in the respective dehydrogenation reactor. The greater the proportion of hydrogen gas released in the dehydrogenation reactor, the greater the proportion of vaporous support material and, accordingly, the smaller the liquid phase fraction of the support material. The equilibrium position depends essentially on the reaction conditions, in particular pressure and temperature, in the respective dehydrogenation reactor. In principle, the higher the pressure and / or the lower the temperature, the greater the liquid phase fraction.A relevant temperature range is between 250 °C and 350 °C. A relevant pressure is greater than 0 barg and up to 8 barg. The proportion of the support material in the vapor phase depends on these parameters, the amount of catalyst, and the amount of hydrogen gas released during dehydrogenation.

[0013] One finding of the invention is that the reaction conditions in the first dehydrogenation reactor are controlled and, in particular, regulated in such a way that the liquid phase fraction is ensured. In particular, a comparatively small dehydrogenation stroke is accepted to avoid complete evaporation of the support material in the first dehydrogenation reactor.

[0014] The support material dehydrogenated in the first dehydrogenation reactor is transferred to a second dehydrogenation reactor, where it is further dehydrogenated, i.e., from the first degree of hydrogenation to a second degree of hydrogenation. In particular, additional dehydrogenation reactors may be present, arranged parallel to the second dehydrogenation reactor and / or in series, in particular upstream of the second dehydrogenation reactor, and interconnected accordingly. The second dehydrogenation reactor is, in particular, the last dehydrogenation reactor in the series arrangement of several dehydrogenation reactors. The reaction conditions, in particular temperature and pressure, in the second dehydrogenation reactor may be identical to or different from those in the first dehydrogenation reactor.

[0015] The support material is in an at least partially hydrogen-loaded form perhydrodibenzyltoluene (HixDBT), perhydrobenzyltoluene (H12BT), dicyclohexane (C12H22), and / or methylcyclohexane (C7H14). Additionally or alternatively, a mixture of support material in the at least partially hydrogen-loaded form of perhydrodiphenylmethane and perhydrobiphenyl can be used.

[0016] The catalyst material comprises a metal, in particular a noble metal, in particular platinum, palladium, nickel, rhodium, rhenium and / or ruthenium, in particular mixtures and / or alloys of these elements. The metal is catalytically active and is referred to as the active material. The active material is in particular arranged on a catalyst support and in particular attached thereto. The catalyst support is in particular an oxidic material, in particular aluminum oxide, silicon oxide, titanium oxide, zirconium oxide, cerium oxide, and / or activated carbon. In particular, the catalyst support is a porous material. The pores of the catalyst support have a diameter of at least 10 nm, in particular at least 20 nm, in particular at least 50 nm and in particular at least 100 nm. The weight fraction of the catalyst material based on the catalyst support is between 0.1% and 10%.

[0017] The catalyst material comprises a plurality of catalyst particles, in particular catalyst support particles, which are present in particular as pellets. The catalyst particles have an average particle size of 0.5 mm to 10 mm, in particular of 1 mm to 8 mm, and in particular of 2 mm to 4 mm.

[0018] Because the dehydrogenation process is carried out in several stages, optimization of the overall process is possible, primarily in that the respective dehydrogenation reactors and the catalyst material contained therein can be specified so that they meet the specific requirements of the expected reaction and, in particular, the dehydrogenation stroke range to be covered. This is based on the finding that in a first stroke range, in which the initial degree of hydrogenation is at least 95%, in particular at least 98%, in particular at least 99%, and in particular up to 100%, and the first degree of hydrogenation HG1 is at most 80%, in particular at most 70%, and in particular at most 60%, the dehydrogenation reaction is limited, in particular, by the heat input.An improvement in the reaction conditions can be achieved in particular by reducing the diameter of a reaction tube in order to increase the heat transfer area per catalyst mass, by increasing a flow velocity, for example by LOHC circulation, in order to increase tube-side heat transfer, by reducing the loading of the catalyst material with active material in order to increase the efficiency of the active material, in particular of the noble metal, by diluting the catalyst bed with inert material, in particular heat-conducting, in order to increase catalyst utilization and / or to reduce the heat requirement per volume element of the dehydrogenation reactor, and by using specific catalysts, wherein the catalysts have high activities, in particular in the first stroke range, such as platinum / rhenium catalyst systems.

[0019] In the dehydrogenation reactors in which the low stroke ranges are represented, the degree of hydrogenation with which the support material is fed into the respective dehydrogenation reactor, in particular the first degree of hydrogenation, is at most 70%, in particular at most 50%, in particular at most 40%, in particular at most 30%, in particular at most 25%, and in particular at most 20%. The final degree of hydrogenation with which the support material leaves the plant, in particular the second degree of hydrogenation, is in particular at most 20%, in particular at most 10%, in particular at most 5%, in particular at most 2%, and in particular 0%. In this low degree of hydrogenation range, the dehydrogenation reaction is particularly kinetically limited and exhibits higher by-product formation rates. The following measures are possible to improve the reaction conditions:

[0020] Increasing the pipe diameter in the dehydrogenation reactor, since there is no limiting heat input.

[0021] Increasing the carrier material residence time in the dehydrogenation reactor by reducing the volume flow, in particular by prior separation of the hydrogen gas.

[0022] Increasing the power density in the dehydrogenation reactor by increasing the active material concentration, in particular the precious metal loading on the catalyst material.

[0023] Reduction of the by-product formation rate by using highly selective catalysts, in particular highly selective catalysts such as sulfided platinum catalysts and / or sulfided platinum-rhenium catalysts.

[0024] A method according to claim 2 simplifies the guarantee of the liquid phase content of the support material. It has been found that a dehydrogenation stroke in the first dehydrogenation reactor must not be too large in order to ensure a sufficiently large minimum liquid phase content of the support material as a result of the VLE. The dehydrogenation stroke is understood to be the difference between the initial degree of hydrogenation and the first degree of hydrogenation, i.e. before and after dehydrogenation in the first dehydrogenation reactor. It has been found that it is advantageous for maintaining the liquid phase if the dehydrogenation reaction in the first dehydrogenation reactor is deliberately incomplete, in particular only partially, wherein the first dehydrogenation stroke is at most 50%, in particular at most 40%, in particular at most

[0025] 30% and in particular at most 25%. Additionally or alternatively, the first degree of hydrogenation, i.e. after the dehydrogenation reaction, is at least 50%, in particular at least 60%, in particular at least 70% and in particular at least 75%.

[0026] Further dehydrogenation, i.e., discharging the carrier material, in particular until complete discharging, can take place in further dehydrogenation reactors, i.e., in further dehydrogenation stages. The efficiency of the overall process is ensured. A process according to claim 3 enables reliable and efficient separation of the material streams, in particular of the released hydrogen gas, from the carrier material. A separation apparatus provided for this purpose is arranged, in particular, downstream of the first and / or second dehydrogenation reactor. The separation apparatus is designed, in particular, as a removal unit and, in particular, as a carrier material purification apparatus, in particular, as an LOHC purification apparatus. The removal unit simplifies the removal of by-products from the liquid carrier material. The removal unit is, in particular, a liquid-liquid separation apparatus.

[0027] A process according to claim 4 enables the uncomplicated removal of byproducts deposited on the catalyst material. In particular, it has been found that the dehydrogenation reactors can be efficiently flushed with a flushing medium, with the support material itself serving as the flushing medium. It is particularly advantageous that the support material can efficiently detach byproduct deposits from the catalyst material. In particular, the first dehydrogenation reactor, the second dehydrogenation reactor, and / or further dehydrogenation reactors can be flushed simultaneously or at different times.

[0028] A process according to claim 5 enables similar and, in particular, identical reaction conditions in the second dehydrogenation reactor to those in the first dehydrogenation reactor. By ensuring a liquid phase content of at least 5% in several, and in particular in all, dehydrogenation reactors, unwanted deposition of by-products on the catalyst material can be prevented. The by-products are reliably flushed out of the respective dehydrogenation reactor with the liquid phase and can subsequently be removed. Complex reactivation measures for the catalyst material are unnecessary. It is understood that more than two dehydrogenation reactors can be arranged in series. In particular, the support material can be present with a liquid phase content of at least 5% in several, and in particular in all, dehydrogenation reactors.

[0029] A removal unit simplifies the removal of by-products from the liquid carrier material and, in particular, a corresponding separation of the liquids, namely the by-products from the carrier material. The removal unit is arranged, in particular, downstream of the dehydrogenation reactors. It is particularly conceivable for such a removal unit to be spatially separated and, in particular, arranged remotely from the dehydrogenation reactors. The dehydrogenation reactors can be arranged at a first, low-energy location. Low-energy means that there is a demand for electrical energy or that electrical energy is available at comparatively high prices. Electrical energy is to be provided at this first location, in particular by releasing hydrogen gas.

[0030] The distance unit is located, in particular, at a second location remote from the first location. The second location is, in particular, energy-rich. Energy-rich means that electrical energy is available, in particular, at low cost and / or can be generated inexpensively using renewable energy sources, for example, photovoltaic systems and / or wind turbines.

[0031] In particular, there is no direct fluid connection between the dehydrogenation reactor and the removal unit. An indirect fluid connection from the at least one dehydrogenation reactor to the removal unit can be established, for example, by means of transport vehicles, in particular transport trucks.

[0032] A method according to claim 6 enables an increase in the overall efficiency of the dehydrogenation process, in particular in several stages. It has been recognized in particular that the second dehydrogenation reactor can be used as a removal unit. In the second dehydrogenation reactor, in particular, essentially complete dehydrogenation takes place. A dehydrogenation stroke DH, which corresponds to the difference between the first degree of hydrogenation and the second degree of hydrogenation, is at least 30%, in particular at least 50%, in particular at least 60%, in particular at least 70%, in particular at least 80%, in particular at least 85%, and in particular at least 90%. The temperature in the second dehydrogenation reactor is in a range from 300°C to 350°C and in particular from 300°C to 320°C. A pressure in the second dehydrogenation reactor is in a range between 0.5 barg and 8.0 barg, in particular between 0.5 barg and 2.0 barg.Under the reaction conditions mentioned, the support material leaves the second dehydrogenation reactor essentially completely and in particular exclusively in gaseous and / or vaporous form. In particular, the support material is not present in the liquid phase in the second dehydrogenation reactor. The liquid phase fraction is less than 5%, in particular at most 3%, in particular at most 1%, in particular at most 0.1%, and in particular 0%.

[0033] The second dehydrogenation reactor is, in particular, the last dehydrogenation reactor in a series connection of several dehydrogenation reactors along the flow direction. If further dehydrogenation reactors are present in addition to the first dehydrogenation reactor and the second dehydrogenation reactor, they are arranged parallel to the second dehydrogenation reactor or upstream of the second dehydrogenation reactor. These further dehydrogenation reactors can be operated in a manner similar to the first dehydrogenation reactor with a minimum liquid phase content of 5% of the support material, or analogously to the second dehydrogenation reactor such that the support material is present essentially entirely and, in particular, exclusively in gaseous and / or vaporous form.

[0034] It is particularly advantageous if the second dehydrogenation reactor operated in this way is the last dehydrogenation reactor. The last dehydrogenation reactor forms a final dehydrogenation stage. In particular, it has been found that such a final dehydrogenation stage can be used as a removal unit. It has been found that, due to the high vapor content of the support material, the removal of byproducts from the support material by adsorption on the catalyst material is favored. This means that both dehydrogenation of the support material and removal of byproducts from the support material take place in the last dehydrogenation reactor. The thus deactivated last dehydrogenation reactor can be returned to its original activity by suitable regeneration measures, in particular by oxidative regeneration.

[0035] It is particularly advantageous if several final dehydrogenation reactors are arranged in parallel, which are operated, in particular alternately, in regeneration mode and dehydrogenation mode. This ensures a continuous and, in particular, uninterrupted supply of hydrogen gas. Alternatively or additionally, the removal unit can be arranged immediately downstream of a dehydrogenation reactor, in particular the second dehydrogenation reactor. For particularly efficient removal of the by-products from the support material by adsorption on the catalyst material, it is advantageous if the dehydrogenation stroke in the dehydrogenation reactor used as the removal unit is large and, in particular, amounts to at least 20%, in particular at least 30%, in particular at least 40%, and in particular at least 50%.

[0036] A process according to claim 7 enables the advantageous removal of byproducts deposited on the catalyst material. In particular, it has been found that the second dehydrogenation reactor can be efficiently flushed with a flushing medium, the support material itself serving as the flushing medium. It has been found that the support material is suitable for flushing byproduct deposits from the catalyst material. In particular, no dehydrogenation operation takes place in the second dehydrogenation reactor during flushing.

[0037] A process according to claim 8 enables dehydrogenation with an overall improved overall efficiency. It has been found that the reaction conditions in the first dehydrogenation reactor and in the second dehydrogenation reactor can be alternated. The dehydrogenation reactors are operated, in particular, alternately in liquid-phase mode and in gas-phase mode. The equipment required for a particularly continuous implementation of the dehydrogenation process is reduced. In particular, the reaction conditions in the first dehydrogenation reactor and in the second dehydrogenation reactor can be adjusted cyclically. It is particularly conceivable to alternate the reaction conditions in the first and second dehydrogenation reactor when a decrease in catalyst activity is detected in the reactor, in particular due to a decrease in the hydrogen release rate.Additionally or alternatively, changes in the reaction conditions in the dehydrogenation reactors can also be applied at fixed time intervals, in particular after a specified operating period.

[0038] A process according to claim 9 enables additional or alternative removal of the byproducts from the catalyst material in the second dehydrogenation reactor. It has been found that the catalyst material can be reactivated, in particular, by oxidative regeneration. Oxidative regeneration efficiently and reliably removes the byproducts from the catalyst material.

[0039] A method according to claim 10 enables advantageous implementation of oxidative regeneration. A temperature advantageous for this purpose is between 250°C and 600°C, and in particular between 300°C and 500°C. A reaction pressure is in particular between 0 barg and 3 barg, in particular between 0 barg and 1 barg, in particular between 0 barg and 0.5 barg, and in particular between 0 barg and 0.1 barg. Additionally or alternatively, an oxygen concentration between 0.1 vol.% and 20 vol.% is advantageous for oxidative regeneration.

[0040] A process according to claim 11 enables an improvement in overall efficiency, in particular also with regard to the hydrogen gas release performance, when the catalyst material is oxidatively regenerated in the second dehydrogenation reactor. The presence of two second dehydrogenation reactors, which are operated alternately for dehydrogenation and oxidative regeneration, ensures efficient dehydrogenation on the one hand and reliable reactivation of the catalyst material on the other. It is understood that more than two second dehydrogenation reactors can be used to further increase the overall efficiency of the process and, in particular, the flexibility in carrying out the process.

[0041] A system according to claim 12 essentially has the advantages of the method according to the invention, to which reference is hereby made.

[0042] A plant according to claim 13 enables independent and reliable removal of by-products from the liquid carrier material. Separation of by-products, in particular liquid ones, from the carrier material, in particular liquid ones, is inexpensive and possible in a separate removal unit. The removal unit is arranged in particular downstream of the last dehydrogenation reactor. The separation of the, in particular liquid, streams of carrier material and by-products is in particular independent of the dehydrogenation reaction. A plant according to claim 14 enables the use of regeneration, in particular oxidative regeneration, for the catalyst material, thereby avoiding downtimes due to alternating operation.

[0043] A plant according to claim 15 enables increased flexibility in the implementation of the overall process. Multiple dehydrogenation reactors, which can be flexibly interconnected, enable, in particular, scaling of the process through parallel connection and / or additional cascading through series connection of several dehydrogenation reactors. The respective reaction conditions in the dehydrogenation reactors connected in series can be more precisely adjusted to the expected degree of hydrogenation of the support material.

[0044] 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.

[0045] 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:

[0046] Fig. 1 is a schematic representation of a plant according to the invention with several dehydrogenation reactors, in each of which a carrier material is present with a minimum liquid phase content,

[0047] Fig. 2 is a representation corresponding to Fig. 1 of a plant according to a second embodiment with two dehydrogenation reactors which are operated alternately with different reaction conditions,

[0048] Fig. 3 is a representation of the functional relationship of the vapor-liquid equilibrium VLE as a function of pressure and temperature for various dehydrogenation strokes with a minimum liquid content of the carrier material benzyltoluene of 10%. Fig. 4 is a representation corresponding to Fig. 1 of a further embodiment with three dehydrogenation reactors, wherein an oxidative regeneration of catalyst material takes place in one dehydrogenation reactor, in particular in alternating operation with another dehydrogenation reactor.

[0049] A plant, designated overall by 1 in Fig. 1, serves to release hydrogen gas from an at least partially loaded carrier material. In the at least partially loaded state, the carrier material is referred to as LOHC-H. Plant 1 comprises a first dehydrogenation reactor 2, a second dehydrogenation reactor 4 arranged in series therewith, and a third dehydrogenation reactor 3 arranged upstream of the second dehydrogenation reactor 4. The second dehydrogenation reactor 4 is the final dehydrogenation reactor.

[0050] The first dehydrogenation reactor 2 and the second dehydrogenation reactor 4 are fluidly connected by a first fluid line 5. The second dehydrogenation reactor 4 and the third dehydrogenation reactor 3 are fluidly connected by a second fluid line 6. A first separation apparatus 7 is arranged along the first fluid line 5 between the first dehydrogenation reactor 2 and the second dehydrogenation reactor 4. Accordingly, a second separation apparatus 8 is arranged between the second dehydrogenation reactor 4 and the third dehydrogenation reactor 3. A third separation apparatus 9 is arranged downstream of the third dehydrogenation reactor 3. The separation apparatuses 7, 8, and 9 are each connected to a hydrogen gas buffer tank 11 via a hydrogen gas line 10.A hydrogen delivery line 12 is connected to the hydrogen gas buffer tank 11 and serves to deliver hydrogen gas to a hydrogen consumer, in particular a fuel cell and / or a hydrogen combustion engine.

[0051] Each dehydrogenation reactor 2, 3, 4 and the corresponding separation apparatus 7, 8, 9 form a partial dehydrogenation system 13 of plant 1. Plant 1 has several, in particular three, partial dehydrogenation systems 13 which are connected to one another in series.

[0052] The carrier material to be dehydrogenated in plant 1, particularly in the partial dehydrogenation systems 13, is stored in a first storage tank 14, which is connected to the first dehydrogenation reactor 2 via a supply line 15. LOHC-H is stored in the first storage tank 14. It is also conceivable in principle for the first storage tank 14 to be directly fluidically connected to the second dehydrogenation reactor 4 and / or to the third dehydrogenation reactor 3.

[0053] The third separation apparatus 9 is connected to a second storage tank 17 via a discharge line 16. At least partially dehydrated LOHC-D carrier material is stored in the second storage tank 17 in the partial dehydration systems 13.

[0054] A first return line 18 is connected to the first fluid line 5. At least partially dehydrated carrier material can be returned to the first dehydrogenation reactor 2 via the first return line 18. Correspondingly, a second return line 19 is connected to the second fluid line 6, and a third return line 20 is connected to the discharge line 16. To direct the fluid flow along the respective fluid line 5, 6, 16, a switchable valve arrangement 21 is arranged in the region of the branch to the return line 18, 19, 20. By means of the valve arrangements 21, a variably definable portion of the fluid flow in the respective fluid line 5, 6, 16 can be independently returned to the respective dehydrogenation reactor 2, 3, 4. The portion is between 0% and 100%.

[0055] A removal unit 22 is arranged downstream of the second storage container 17 and is in fluid communication with the second storage container 17. In the removal unit 22, unwanted byproducts can be removed from the liquid carrier material.

[0056] A method for operating plant 1 is explained in more detail below. The at least partially loaded support material LOHC-H is conveyed from the first storage vessel 14 via the feed line 15 into the first dehydrogenation reactor 2, where it comes into contact with a catalyst material. The supplied support material LOHC-H has an initial degree of hydrogenation HG0 of at least 90%, in particular at least 95%, in particular at least 98%, in particular 99%, and in particular 99.9%. The dehydrogenation reaction releases hydrogen gas from the support material. The support material is at least partially dehydrogenated. The at least partially dehydrogenated support material has a first degree of hydrogenation HG1 that is lower than the initial degree of hydrogenation HGO, and which, according to the exemplary embodiment shown, is 70% for the support material upon leaving the first dehydrogenation reactor 2.The first dehydrogenation stroke, which corresponds to the difference between the initial degree of hydrogenation HGO and the first degree of hydrogenation HG1, is therefore at most 20%, in particular at most 25%, in particular at most 28%, in particular at most.

[0057] 29% and in particular a maximum of 29.9%.

[0058] In the first dehydrogenation reactor 2, the carrier material is at least partially liquid. A minimum liquid phase fraction of the carrier material is 5%. The minimum liquid phase fraction is ensured in particular by maintaining a comparatively high pressure, in particular at least 3 barg, in particular at least 4 barg, and in particular at least 5 barg, and / or comparatively reduced temperatures of at most 310°C, in particular at most 300°C, in particular at most 290°C, and in particular at most 285°C.

[0059] In the first dehydrogenation reactor 2, complete evaporation of the support material is avoided. This prevents unwanted byproducts that may be formed from the support material during the dehydrogenation reaction, and in particular, those that have a higher boiling point than the support material, from settling on the catalyst material and / or bonding there. The unwanted byproducts are flushed out of the first dehydrogenation reactor 2 together with the liquid support material.

[0060] The liquids, along with the released hydrogen gas, are fed into the first separation apparatus 7. In the first separation apparatus, the released hydrogen gas is separated from the liquid stream. The hydrogen gas is transported via the hydrogen gas line 10 into the hydrogen gas buffer tank 11, where it can be temporarily stored until it is released to a hydrogen consumer via the hydrogen release line 12. The liquid stream separated in the first separation apparatus 7 is fed to the second dehydrogenation reactor 4 via the first fluid line 5. The first separation apparatus 7 can additionally be used as a removal unit, for example in the form of a distillation column. In the first separation apparatus 7, hydrogen gas, in particular, can be separated from the carrier material and / or, in particular, carrier materials of different qualities can be separated from one another and processed separately.

[0061] A portion of the fluid stream can be returned to the first dehydrogenation reactor 2 via the first return line 18. The return of at least a partial stream of the support material serves, in particular, to maintain the liquid phase fraction in the first dehydrogenation reactor 2. In particular, a liquid excess can be deliberately provided in the first dehydrogenation reactor 2, i.e., a mass flow of the support material that is greater than the mass flow that reacts with the catalyst material in the first dehydrogenation reactor 2.

[0062] The valve assemblies 21 are controllable, in particular, via a central control unit (not shown in detail). In particular, the valve assemblies 21 are controllable independently of one another, in particular continuously.

[0063] Because the first dehydrogenation stroke in the first dehydrogenation reactor 2 is comparatively short, the maintenance of the liquid phase of the carrier material is simplified.

[0064] By connecting three dehydrogenation reactors 2, 3, 4 in series, a total dehydrogenation stroke of at least 70%, in particular at least 80%, in particular 90% and in particular up to

[0065] 100% can be achieved. In particular, the total dehydrogenation stroke is distributed essentially evenly between the three dehydrogenation reactors 2, 3, and 4.

[0066] The amount of hydrogen gas released in the respective dehydrogenation reactors 2, 3, 4 and separated in the respective separation devices 7, 8, 9 is in each case smaller than the total amount of hydrogen gas discharged via the hydrogen discharge line 12. Plant 1 can have one or more conditioning units for conditioning the hydrogen gas and / or for conditioning the carrier material. Alternatively or additionally, one or more compression stages can be present to compress the released hydrogen gas.

[0067] Depending on the operating mode of Plant 1, it is also conceivable that—at least temporarily—a partial dehydrogenation system 13 is not operated, meaning that no hydrogen gas is released by the respective partial dehydrogenation system 13. Plant 1 has corresponding bypass lines to ensure fluid flows when a partial dehydrogenation system 13 is not operating.

[0068] In the separation apparatuses 7, 8, 9, in particular at least 50%, in particular at least 75%, in particular at least 90%, in particular at least 95% and in particular at least 99% of the LOHC stream from the respective separation apparatus 7, 8, 9 is released in liquid phase back into the respectively connected fluid line 5, 6, 16.

[0069] The separation apparatus 7, 8, 9 is designed in particular as a membrane separation unit, in particular with a palladium membrane. The separation apparatus 7, 8, 9 can additionally or alternatively have a condenser and / or a scrubber. Additionally or alternatively, the separation apparatus 7, 8, 9 can be designed as a reactor with a separation function according to DE 10 2021 200 978 A1 and / or as a compression vessel according to DE 10 2021 201 368 A1.

[0070] Surprisingly, it was found that a, in particular continuous, liquid phase flow through the respective dehydrogenation reactor 2, 3, 4 for flushing out the higher-boiling by-products can be achieved by the ratio of the amount of vaporous carrier material to the gaseous carrier material being less than 1. The following applies: From equation (1), it is immediately clear that the liquid phase fraction of the support material depends on the amount of hydrogen gas released and, in particular, is smaller the larger the amount of hydrogen gas released. Therefore, the smallest possible dehydrogenation stroke is advantageous for the first dehydrogenation reactor.

[0071] Accordingly, the ratio of vaporized carrier material to the total flow of LOHC material within a partial dehydrogenation system 13 can be specified. This also shows that maintaining the liquid phase flow tends to be achieved by reducing the amount of released hydrogen FE, by reducing the dehydrogenation stroke, by increasing the total system pressure p gesby lowering the temperature-dependent LOHC vapor pressure (PLOHC, vapor) by lowering the temperature, and by increasing the LOHC flow (ULOHC, total) by increasing the recycle rate in the respective dehydrogenation reactor 2, 3, 4.

[0072] Surprisingly, it was discovered that the transition of the reaction from the gas phase to the liquid phase, through a combination of all the aforementioned measures, results in an increase in the reaction rate and thus, in particular, a reduction in the specific catalyst material requirement. In particular, it was found that a higher average reaction rate can be achieved within the liquid phase.

[0073] The LOHC-D carrier material fed to the second storage vessel 17 and at least partially discharged comprises undesired byproducts that can be removed from the liquid stream in the removal unit 22. The removal in the removal unit 22 is carried out, for example, by thermal processes, in particular rectification and / or distillation, by membrane separation processes and / or by absorptive processes. The removal step, i.e., the feeding of the discharged LOHC-D carrier material into the removal unit 22, can be carried out cyclically, i.e., each time before the discharged LOHC-D carrier material is rehydrogenated to LOHC-H in a hydrogenation reactor (not shown). For reasons of efficiency, the removal step can be deliberately omitted and, in particular, only carried out when the concentration of byproducts in the carrier material reaches a certain threshold.Suitable measurements can be performed to determine the concentration of by-products in the carrier material. Such measurements are described, for example, in WO 2006 / 127439 A1.

[0074] A second embodiment is described below with reference to Fig. 2. Structurally identical parts are given the same reference numerals as in the previous 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 "a."

[0075] Plant 1a differs from the previous plant in that it has only two dehydrogenation reactors 2a, 4a. The second dehydrogenation reactor 4a forms the final dehydrogenation reactor. In the second dehydrogenation reactor 4a, the reaction conditions are selected such that even low final hydrogenation degrees between 0% and 20% are easily achievable. In particular, the reaction conditions in the second dehydrogenation reactor 4a are such that the temperature is in the range between 300°C and 340°C, in particular between 300°C and 330°C and in particular between 300°C and 320°C, and the pressure is between 0.5 barg and 5 barg, in particular between 0.5 barg and 3 barg and in particular between 0.5 barg and 2.0 barg.

[0076] The corresponding dependence of the gas-liquid equilibrium VLE is shown in Fig. 3 for a dehydrogenation such that the carrier material leaves the dehydrogenation reactor with a minimum liquid fraction of 10%. Fundamentally, it can be deduced from this that the retention of the liquid phase of the carrier material at higher dehydrogenation strokes DH can be ensured by increasing the pressure p and / or lowering the temperature T. As a result of the reaction conditions selected for the second dehydrogenation reactor 4a, the carrier material in the second dehydrogenation reactor 4a is essentially and in particular completely evaporated. The liquid phase fraction of the carrier material in the second dehydrogenation reactor 4a is less than 5% and in particular at most 3%, in particular at most

[0077] 2%, in particular a maximum of 1%, in particular a maximum of 0.1% and in particular a maximum of 0.01%.

[0078] It is particularly advantageous that the operation of the dehydrogenation reactors 2a and 4a can be variably adjusted, and in particular, cyclically interchanged. This is indicated by the double arrow 23 in Fig. 2. This improves the overall economic efficiency of the plant 1a. The hydrogen output stream 12 does not need to be reduced.

[0079] If a cyclical change takes place between the partial dehydrogenation systems 13, the dehydrogenation reactor, which was previously operated with the support material in the vapor phase, can subsequently be operated with the support material in the liquid phase. It has surprisingly been found that, during regular dehydrogenation operation with the support material in the liquid phase, the catalyst material can be regenerated. In particular, the deactivating by-products are separated from the catalyst material by the liquid phase portion of the support material and flushed out. Additional, particularly separate, flushing measures are unnecessary. The overall utilization and thus the overall efficiency of plant 1a is increased.

[0080] With the plant la shown in Fig. 2, it is particularly possible to realize a total dehydrogenation stroke of 90% in a two-stage dehydrogenation process with equally dimensioned dehydrogenation reactors 2a, 4a, wherein a continuous liquid phase of the carrier material is ensured in one of the two reactors 2a, 4a.

[0081] It is understood that plant 1a may contain multiple dehydrogenation reactors. Accordingly, it is possible to cyclically change the operating modes of the dehydrogenation reactors, so that a different dehydrogenation reactor is always operated with the liquid phase portion of the support material. A cyclical change takes place, in particular, at least monthly, in particular at least every two weeks, in particular at least weekly, in particular at least every three days, and in particular at least daily. The change can also be carried out, in particular, depending on the catalyst activity. The catalyst activity is determined, in particular, based on the hydrogen gas release rate.If the hydrogen gas release rate falls below a minimum value, particularly within a specified operating window, i.e., particularly at a specified reaction pressure and / or specified reaction temperature, a change in operating mode can be initiated. A minimum value for catalyst activity is defined as a decrease in catalyst activity of no more than 50%, in particular no more than 30%, in particular no more than 10%, and in particular no more than 1%.

[0082] It is essential that at least one dehydrogenation reactor has the carrier material in the liquid phase and at least one further dehydrogenation reactor has the carrier material in the gas phase or vapor phase.

[0083] To enable flexible fluid flow into and out of the dehydrogenation reactors 2a, 4a, these are each connected independently of one another via corresponding fluid lines to the storage tanks 14, 17 and / or the separation devices 7, 8. Corresponding valves can be used for this purpose, but are not shown in Fig. 2 for illustrative reasons.

[0084] A third embodiment is described below with reference to Fig. 4. 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 "b."

[0085] The key difference compared to the second embodiment is that plant 1b additionally includes a third dehydrogenation reactor 3b, which is operated cyclically with the second dehydrogenation reactor 4b. A regenerative measure, in particular oxidative regeneration, takes place in the second dehydrogenation reactor 4b. Other regenerative processes and / or a replacement of the catalyst material are also possible. The second dehydrogenation reactor 4b is a final dehydrogenation reactor. It has been found that the by-product deposits on the catalyst material can be advantageously burned off by oxidative regeneration by supplying an oxygen-containing gas stream via an oxygen supply line 24 and discharging a carbon dioxide-containing exhaust gas via an exhaust line 25.It was therefore recognized that the higher-boiling byproducts deposited on the catalyst material do not need to be flushed out, but rather the catalyst material itself can be regenerated through oxidation. Temperatures between 250°C and 600°C, a pressure between 0 barg and 1 barg, and an oxygen concentration between 0.1 and 20 vol% are advantageous for oxidative regeneration.

[0086] By applying the oxidative regeneration process only to a portion of Plant 1b, specifically to a partial dehydrogenation system, energy consumption is reduced and, in particular, limited to only a portion of the total catalyst inventory. Furthermore, hydrogen gas availability is improved. The reliability of the hydrogen gas supply is increased. In particular, a failure of a dehydrogenation reactor can be compensated for.

[0087] To minimize downtime, it is advantageous to operate dehydrogenation reactors 3b and 4b cyclically, with one dehydrogenation reactor 3b operating under dehydrogenating, LOHC-removing conditions and the other dehydrogenation reactor 4b operating under oxidatively regenerating conditions. It is also conceivable that dehydrogenation reactors 3b and 4b are operated simultaneously for dehydrogenation, at least temporarily, in order to increase the absolute dehydrogenation capacity. This enables straightforward scaling of the dehydrogenation process.

[0088] The respective dehydrogenation reactors 3b and 4b are dimensioned identically. The first dehydrogenation reactor 2b can be dimensioned independently.

[0089] In particular, it was recognized that LOHC evaporation in the dehydrogenation reactor 3b can be accelerated if the first separation apparatus 7 is deliberately operated inefficiently. In particular, evaporation can be further accelerated if the fluid flow from the first dehydrogenation reactor 2b is bypassed past the first separation apparatus 7 via the bypass line 26. To enable the optional feeding of the support material into the second dehydrogenation reactor 4b or the third dehydrogenation reactor 3b, both reactors 3b, 4b are connected to the first fluid line 5.

[0090] Since the byproducts in plant 1b are removed through oxidative regeneration, a downstream removal unit 22 is not required. The second dehydrogenation reactor 4b forms the removal unit, which is designed as an integrated unit.

Claims

Patent claims 1. A process for releasing hydrogen gas from at least partially loaded support material, comprising the process steps of, in a first dehydrogenation reactor (2; 2a; 2b), dehydrogenating the support material from an initial degree of hydrogenation (HGO) to a first degree of hydrogenation (HG1) by contacting the support material with a catalyst material and thereby releasing hydrogen gas, wherein (2; 2a; 2b) the support material leaves the first dehydrogenation reactor with a liquid phase fraction of at least 5%, Transferring the support material having the first degree of hydrogenation (HG1) from the first dehydrogenation reactor (2; 2a; 2b) to a second dehydrogenation reactor (3, 4; 4a; 3b, 4b), Dehydrogenating the support material in the second dehydrogenation reactor (3, 4; 4a; 3b, 4b) from the first degree of hydrogenation (HG1) to a second degree of hydrogenation (HG2), Removal of by-products from the carrier material.

2. Process according to claim 1, characterized in that the dehydrogenation in the first dehydrogenation reactor (2; 2a; 2b) is carried out with a first dehydrogenation stroke of at most 50% and / or the first degree of hydrogenation (HG1) is at least 50%.

3. Process according to one of the preceding claims, characterized by separating the released hydrogen gas from the carrier material in at least one separation apparatus (7, 8, 9) arranged downstream of the first dehydrogenation reactor (2; 2a; 2b) and / or downstream of the second dehydrogenation reactor (3, 4; 4a; 3b, 4b).

4. Process according to one of the preceding claims, characterized by flushing the first dehydrogenation reactor (2; 2a; 2b) and / or the second dehydrogenation reactor (3, 4; 4a; 3b, 4b), in particular with carrier material as flushing medium, for flushing out by-product deposits on the catalyst material.

5. Process according to one of the preceding claims, characterized in that the carrier material supplies the second dehydrogenation reactor (3, 4; 4a) with a liquid phase fraction of at least 5% leaves, wherein in particular the removal of the by-products takes place in a removal unit (22) which is arranged in particular downstream of the dehydrogenation reactors (2, 3, 4; 2a, 4a).

6. Process according to one of claims 1 to 4, characterized in that the dehydrogenation in the second dehydrogenation reactor (4a; 3b, 4b) is carried out with a second dehydrogenation stroke of at least 30% and / or at a temperature in the range from 300 °C to 350 °C and / or at a pressure of from 0.5 barg to 2.0 barg.

7. The method according to claim 6, characterized by rinsing the second dehydrogenation reactor (4a; 3b, 4b), in particular with carrier material as rinsing medium, in particular during a dehydrogenation break.

8. The process according to claim 6 or 7, characterized in that the reaction conditions are alternated between the first dehydrogenation reactor (2a) and the second dehydrogenation reactor (4a), in particular cyclically.

9. The process according to any one of claims 6 to 8, characterized by regenerating the catalyst material in the second dehydrogenation reactor (3b, 4b) to remove by-product deposits on the catalyst material, in particular by oxidative regeneration.

10. The process according to claim 9, characterized in that the oxidative regeneration is carried out at a temperature of 250 °C to 600 °C, at a pressure greater than 0 barg and less than 1 barg, and / or at an oxygen concentration of 0.1 vol% to 20 vol%.

11. Process according to claim 9 or 10, characterized in that two second dehydrogenation reactors (3b, 4b) are present, which are operated in particular cyclically, alternately for dehydrogenation and for oxidative regeneration.

12. Plant for releasing hydrogen gas from at least partially loaded carrier material (LOHC-H) comprising a. a first dehydrogenation reactor (2; 2a; 2b) for dehydrogenating the carrier material from an initial degree of hydrogenation (HGO) to a first degree of hydrogenation (HG1) by contacting the carrier material with a catalyst material arranged in the first dehydrogenation reactor (2; 2a; 2b), b. a second dehydrogenation reactor (3, 4; 4a; 3b, 4b) which is fluidically downstream of the first dehydrogenation reactor (2; 2a; 2b), c. a removal unit (22; 22; 4b, 3b) for removing by-products from the carrier material.

13. Plant according to claim 12, characterized in that the removal unit (22) is arranged downstream of the second dehydrogenation reactor (3, 4; 4a).

14. Plant according to claim 12 or 13, characterized in that the removal unit is formed by the second dehydrogenation reactor (3b, 4b), in which the catalyst material is regenerated, in particular oxidatively, in alternating operation with a further second dehydrogenation reactor (4b, 3b).

15. Plant according to one of claims 12 to 14, characterized in that further dehydrogenation reactors are present, which are arranged in particular parallel and / or in series to the second dehydrogenation reactor and in particular upstream of the second dehydrogenation reactor.

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