EP3894351A1

EP3894351A1 - Method and installation for releasing gas from a liquid medium

Info

Publication number: EP3894351A1
Application number: EP19816641.5A
Authority: EP
Inventors: Andreas BÖSMANN; Patrick PREUSTER; Peter Wasserscheid; Stephan MRUSEK
Original assignee: Hydrogenious LOHC Technologies GmbH
Current assignee: Hydrogenious Technologies GmbH
Priority date: 2018-12-11
Filing date: 2019-12-04
Publication date: 2021-10-20
Also published as: DE102018221447A1; WO2020120261A1; JP2022511475A; KR20210098987A

Abstract

The invention relates to a method for releasing gas form a liquid medium, comprising the method steps of: providing a reactor (2) for releasing the gas from the liquid medium, reducing a partial pressure (p_g) of the gas in the reactor (2) to less than 1 bar, releasing the gas from the liquid medium and discharging the released gas from the reactor (2).

Description

Process and installation for releasing gas from a liquid medium

This patent application claims priority from German patent application DE 10 2018 221 447.6, the content of which is incorporated herein by reference.

The invention relates to a method and a system for releasing gas from a liquid medium, in particular for releasing hydrogen gas from a liquid organic hydrogen storage medium.

Reactors for strongly exothermic and strongly endothermic reactions with high gas development are known. The reactions usually take place with short residence times in the reactor in order to achieve good heat transfers on the reactor wall by high axial flow velocities. Such reactors are suitable for two-phase reactions with gaseous reactants and solid catalysts. Such a reactor is in principle also suitable for a three-phase reaction in which a gaseous product is released from a liquid educt by means of a solid catalyst. If long residence times are realized in three-phase reactions, the low flow rate of the liquid educt makes heat transport and mass transport difficult. In particular, the heat transport is then essentially limited to heat conduction.

The invention has for its object to improve the release of a gaseous product from a liquid medium as a starting material, in particular in a chemical reaction with high gas development. In particular, the invention is also based on the object of releasing chemically bound hydrogen from a liquid, organic hydrogen storage medium, a so-called LOHC system, in a catalytic dehydrogenation reaction and removing the released hydrogen gas from a plant in high purity.

This object is achieved by a method with the features of claim 1 and by a system with the features of claim 10.

The essence of the invention is that by lowering a partial pressure of the gas in a reactor to less than 1 bar, the gas is released from the liquid medium, in particular is particularly favored by a catalytic gas release reaction. In particular, it has been found that the lowering of the partial pressure of the gas changes the driving force for the chemical reaction in such a way that the release of the gas is additionally promoted. A liquid organic hydrogen storage medium, which is also known as a liquid organic hydrogen carrier (LOHC), is used in particular as the liquid medium. The hydrogen storage medium can in particular be reversibly converted between an at least partially loaded, that is to say hydrogen-rich, form to an at least partially discharged, that is to say low-hydrogen, form. As a hydrogen-rich form, the hydrogen storage medium is present in particular as perhydro-dibenzyltoluene, in short H18-DBT, or as perhydro-benzyltoluene, in short H12-BT. As a low-hydrogen form, the hydrogen storage medium is present in particular as dibenzyltoluene, H0-DBT for short, or benzyltoluene, H0-BT for short.

When the hydrogen storage medium is transferred from the hydrogen-rich to the hydrogen-poor form, hydrogen is released as the gas. The release reaction is a dehydrogenation reaction, in particular a catalytic dehydrogenation reaction.

The hydrogen storage medium is a liquid. It is intended to provide a liquid, hydrogen-rich hydrogen storage compound or mixtures of liquid, hydrogen-rich hydrogen storage compounds in a storage container or tank, which is used for use in the facility and in particular for the release of hydrogen from the hydrogen carrier medium in a catalytic release reaction. In this catalytic release reaction, the liquid, hydrogen-rich hydrogen compound or the corresponding mixtures of such compounds are converted into a hydrogen-poor form. The liquid, hydrogen-rich hydrogen storage medium provides hydrogen in a bound form, in particular in a chemically bound form. The handling of molecular, gaseous hydrogen, the storage and handling of which is complicated and safety-related risky and therefore requires high equipment and associated costs to minimize safety-related risks can be avoided.

The liquid, hydrogen-rich hydrogen storage medium used is in particular the hydrogen-rich compound of an FOHC system as is known from the prior art from Accounts of Chemical Research, 2017, 50 (1), 74-85. The provision of hydrogen in the form A hydrogen-rich LOHC compound has the particular advantage that LOHC hydrogen storage compounds are available as an organic compound in liquid form under the storage and process conditions used. In particular, the LOHC hydrogen storage media enable them to be reversibly loaded with hydrogen and to be discharged from hydrogen. The liquid, hydrogen-rich hydrogen storage medium and in particular a hydrogen-loaded LOHC-hydrogen storage medium and mixtures of such compounds represent a suitable form of transport and storage for the chemically bound hydrogen. The physicochemical properties of the LOHC hydrogen storage media are very similar to conventional liquid fuels, so that Tanks, pumps and tank vehicles can be used for transport and as storage containers for the fuel and fuel logistics sector. Hydrogen storage in a chemically bound form in an organic liquid allows pressure-free storage under normal conditions over long periods of time without significant loss of hydrogen.

Suitable liquid, hydrogen-rich FOHC hydrogen storage media are, in particular, saturated, cyclic hydrocarbons with one or more six-membered rings which, when hydrogen is released, are converted into aromatic compounds with one p-electron system or several p-electron systems and again catalytically hydrogenated from this low-hydrogen form can be won. Perhydro-dibenzyltoluenes and perhydro-benzyltoluenes, in particular, can be used as pure substances, isomeric mixtures or mixtures of these substances as the liquid, hydrogen-rich FOHC hydrogen storage media. It is also possible to use, as liquid, hydrogen-rich FOHC hydrogen storage media, heteroatom-containing, cyclic compounds which, when hydrogen is released, are converted into low-hydrogen, heteroaromatic compounds with one p-electron system or several p-electron stars. Perhydro-N-ethyl carbazole, perhydro-N-propyl carbazole, perhydro-N-isopropyl carbazole, perhydro-N-butyl carbazole, perhydro-N-ethyl indole or mixtures of these substances are particularly suitable.

Surprisingly, it was found that the lowering of the partial pressure of the gas increases the driving force for the release reaction, which is a dehydrogenation reaction, in such a way that the release of the hydrogen gas at temperatures below 250 ° C., in particular at temperatures tures below 220 ° C, especially at temperatures below 180 ° C and in particular at about 170 ° C. In particular, at the temperatures mentioned, hydrogen gas can be released from the at least partially loaded LOHC liquid at a technically usable release rate. A technically usable release rate is at least 0.0001 g hydrogen per gram of catalytically active metal and minute, in particular at least 0.0005 g hydrogen per gram of catalytically active metal and minute, and in particular at least 0.001 g hydrogen per gram of catalytically active metal and minute.

The released gas is removed from the reactor. Evaporated portions of the LOHC hydrogen storage medium can be removed from the reactor together with the released hydrogen gas. A partial evaporation of the LOHC hydrogen storage medium takes place in particular in the negative pressure mode of the reactor and at elevated temperatures in the reactor and / or the pipelines connected to it. The evaporated portions of the LOHC hydrogen storage medium which are discharged from the reactor can be separated off in a subsequent cleaning step, in particular in a condensation unit.

In particular, a solid catalyst is arranged in the reactor, which in particular has pores and is in particular porous. The catalyst contains in particular a metal component on which the gas release reaction, in particular the dehydrogenation reaction, takes place.

The metal component is in particular platinum or a mixture of platinum and at least one other metal such as nickel, cobalt, copper, iron, gallium, palladium, rhodium, ruthenium or iridium. Alternatively, it is possible to use nickel, cobalt, copper, iron, gallium, palladium, rhodium, ruthenium and / or iridium as the metal component.

Where the catalytically active metal component is located, the porous catalyst has an inner surface area of at least 5 m ² per gram of catalyst. The average pore diameter is in particular more than 0.5 nm.

The lowering of the partial pressure of the gas in the reactor favors the discharge of the added hydrogen gas from the catalyst pores and causes a faster introduction of fresh, at least partially loaded, liquid or vaporized LOHC into the catalyst pores. The simplified inflow of hot, at least partially laden hydrogen storage medium into the catalyst core means that latent heat can be introduced.

In a method according to claim 2, the release of the gas, in particular the hydrogen gas, is additionally favored.

A method according to claim 3 enables the partial pressure to be influenced directly. The gas, in particular the hydrogen gas, is drawn off from the reactor in particular by means of a technical unit such as a membrane pump, a piston compressor, an electrochemical converter, a Venturi nozzle, a turbo compressor and / or a fuel cell, in particular a high temperature - Polymer electrolyte membrane fuel cell.

Alternatively or additionally, the partial pressure of the gas can be reduced in accordance with claim 4 in that a volatile in the reactor

or evaporating compound is added. It is advantageous if the volatile or evaporating compound does not convert into a poorly volatile compound under the conditions of the dehydrogenation reaction. Volatile compounds are avoided.

By avoiding low-volatility compounds, the hydrogen partial pressure can advantageously be reduced. Contamination of the hydrogen storage medium is prevented.

Suitable volatile or vaporizing compounds are linear or branched alkanes whose boiling point is at least 20 ° C. below that of the discharged hydrogen storage medium, such as n-octane, 2-methylheptane, 3-methylheptane, 2,3-dimethylhexane, decane or dodecane. Mixtures of suitable volatile or vaporizable compounds can also be used before.

In a method according to claim 5, the released gas can be used immediately. It is advantageous if the recovery unit works with the release of heat, that is, an exothermic process takes place in the recovery unit. Such a recycling unit is particularly in particular a fuel cell, in particular a high temperature polymer electrolyte membrane fuel cell, if the gas released is hydrogen. Alternatively, the utilization unit can be designed as an electrochemical compressor, in which hydrogen gas in particular is used as the released gas.

In particular, the recovery unit also serves to suck the gas out of the reactor. The use of the hydrogen gas in the recovery unit creates a pressure drop in such a way that the partial pressure of the gas in the reactor is reduced, so that the release of hydrogen gas in the reactor is promoted. In particular, a fuel cell is directly and directly linked to the reactor, so that the consumption of the hydrogen gas in the fuel cell leads to an immediate reduction in the partial pressure of the gas in the reactor. There is a direct connection between the fuel cell and the reactor, for example, if no further pressure-regulating components are arranged along a connecting line between the reactor and the fuel cell. The released hydrogen gas can be led directly from the reactor through the connecting line into the fuel cell.

In a method according to claim 6, waste heat from the recycling unit, in particular from the high-temperature polymer electrolyte membrane fuel cell, leads back to the reactor and can be used there for the release reaction, in particular for the release of hydrogen gas from perhydro-dibenzyltoluene or perhydro-benzyltoluene. It is possible to use the heat loss from the fuel cell to release hydrogen from perhydro-dibenzyltoluene or perhydro-benzyltoluene. In addition, the utilization of the hydrogen gas in the fuel cell brings about the reduced partial pressure of the gas required in the reactor. The heat transfer from the high-temperature polymer electrolyte membrane fuel cell to the reactor results in a particularly desired cooling of the fuel cell. The heat is returned from the recovery unit to the reactor, for example by a heat exchanger, a heat-conducting wall and / or a heat-conducting liquid line.

In a method according to claim 7 it is ensured that the waste heat from the recovery unit is sufficient to provide the heat for the release reaction in the reactor in whole or in part. For example, the required temperature in the reactor is at least 170 ° C. The temperature of the utilization of the released gas in the utilization unit, in particular in the high-temperature polymer electrolyte membrane fuel cell, is approximately 180 ° C.

In a method according to claim 8, the quality, in particular the purity, of the released hydrogen gas is improved before it is fed to the processing unit. The improved, ie increased, purity of the hydrogen gas results from the use of a cleaning unit, in particular in the form of a condenser or an adsorption unit. The utilization of the released hydrogen gas is more effective. The efficiency of the recovery unit is increased.

An increased purity of the hydrogen gas released can additionally or alternatively also be achieved in that a dehydrogenation catalyst is arranged in the dehydrogenation reactor above the liquid phase of the hydrogen storage medium. With the dehydrogenation catalyst, low-boiling, hydrogen-rich LOHC components in the gas phase are converted to hydrogen and low-boiling, low-hydrogen components, which condense more easily. The proportion of vaporized LOHC components that are removed from the reactor together with the released hydrogen gas is reduced. Evaporated LOHC fractions are still condensed and liquefied again in the reactor and remain in the reactor. The effectiveness and economy of the reactor is increased. The cleaning of the hydrogen gas is also improved, especially in connection with a downstream condenser.

In particular, the dehydrogenation catalyst attached above the liquid hydrogen storage medium to support the cleaning action of the downstream capacitor is at a higher temperature level than the capacitor, in particular at least 5 ° C. higher, in particular at least 10 ° C. higher and in particular at least 20 ° C. higher. The dehydrogenation catalyst attached above the liquid phase of the hydrogen storage medium preferably operates at the temperature level of the dehydrogenation reactor. This dehydrogenation catalyst is in particular additionally provided. This additional dehydrogenation catalyst is a cleaning catalyst to remove low-boiling hydrogen-rich LOHC fractions in the gas phase by dehydrogenation in the gas phase. This also releases hydrogen gas ff. A method according to claim 9 enables an additionally improved heat transfer in the reactor. By lowering a reactor outlet pressure to a reduced plant pressure, the partial pressure of the gas is also reduced, which regulates spontaneous outgassing of the gas from the liquid mixture of the liquid medium with the gas. Lowering the partial pressure also causes the rising gas bubbles to increase. The combination of these effects, that is, the outgassing and the enlargement of the mean bubble diameter, results in an improved local mixing of the reaction medium. A convective heat exchange between the inner wall of the reactor, the solid catalyst and the mixture of liquid medium and gas is improved. A subsequent increase in the pressure in the reactor to the reactor outlet pressure is made possible in that a gas discharge opening for discharging the released gas from the reactor housing is closed. The pressure in the reactor builds up again through the chemical release reaction, in particular automatically and automatically. When the system pressure is reached, it is spontaneously reduced to the reduced system pressure. In particular, there is a periodic change between the system pressure and the reactor outlet pressure. Due to the increase in pressure in the reactor, gaseous liquid components condense. The increase in pressure also causes coke precursors to dissolve on the catalyst and be discharged from the reactor. As a result, the catalyst is reprocessed during operation. This increases the life of the catalytic converter. The operating costs for plant operation are reduced. Inert components that have accumulated in the connecting line between the dehydrogenation reactor and the recovery unit can also be flushed out of the system by the pressure change process. Such a process is particularly economical.

A system according to claim 10 enables the method according to the invention to be carried out. The advantages that can be achieved with the system correspond to those of the method, to which reference is hereby made.

A system according to claim 11 favors the heat recovery from the recovery unit in the reactor.

An embodiment of the reactor housing according to claim 12 on the one hand enables large quantities of gas to be released in the reactor housing and on the other hand ensures that the driving with repeated pressure changes. It is advantageous if a reaction space volume is larger than a head space volume. The reaction chamber volume is a liquid volume. The headspace volume is in particular a gas volume. In order to avoid fluid surges during a pressure change, it is advantageous if the head space volume is not too small and in particular amounts to at least 10% of the reaction space volume.

Alternatively, it is also conceivable for the head volume to be greater than the liquid volume through which a liquid flows, in particular continuously. In particular, the headspace volume is at least ten percent larger than the liquid volume, in particular at least thirty percent larger than the liquid volume and in particular at least fifty percent larger than the liquid volume.

A system according to claim 13 enables an increase in the quality of the released hydrogen gas and thus an improvement in the recovery of the released gas in the recovery unit.

A system according to claim 14, on the one hand, enables suction of the hydrogen gas released from the reactor through the consumption of the hydrogen gas in the fuel cell itself. At the same time, the waste heat of the fuel cell can be used for the endothermic release reaction in the reactor, the waste heat of the high-temperature polymer - Electrolyte membrane fuel cell is particularly sufficient to carry out the dehydrogenation reaction in the reactor.

Further advantages, features and details of the invention result from the description of two exemplary embodiments with reference to the drawing. Show it:

1 shows a schematic representation of a system according to a first exemplary embodiment for carrying out the method according to the invention,

Fig. 2 is a Fig. 1 corresponding representation of a system according to a second embodiment, for example for performing the method with periodic pressure changes. A plant marked as 1 as a whole in FIG. 1 comprises a reactor 2 for releasing hydrogen gas from an at least partially loaded hydrogen storage medium. According to the exemplary embodiment shown, the reactor 2 is a dehydrogenation reactor for dehydrating at least partially laden hydrogen storage medium as the liquid medium.

The reactor 2 is connected to a recycling unit 3 via a connecting line 4. According to the exemplary embodiment shown, the utilization unit 3 is designed as a fuel cell, in particular as a high-temperature polymer electrolyte membrane fuel cell. The connecting line 4 serves to transport released hydrogen gas from the reactor 2 into the recycling unit 3.

Along the connecting line 4, a condenser 5 for condensing gaseous constituents of the liquid medium are provided between the reactor 2 and the utilization unit 3 and are carried in the hydrogen gas stream used. The condenser 5 is connected to the reactor 2 via a return line 6 for the condensed liquid medium.

A cleaning unit 7 is arranged between the condenser 5 and the recycling unit 3 along the connecting line 4 in order to clean contaminants from the hydrogen gas stream which is to be fed to the fuel cell 3. In particular, the cleaning unit 7 is designed as an adsorption unit. The system 1 can also be performed without a cleaning unit 7.

The condenser 5 is designed with an upstream dehydrogenation catalytic converter 28, the dehydrogenation catalytic converter 28 being at a higher temperature level than the condenser 5. In the condenser 5, the FOHC components in the gas phase are removed from the hydrogen gas stream and separated. In addition, low-boiling aromatic compounds or cycloalkanes, which can form in small amounts due to thermal decomposition of the FOHC carrier material, can be deposited.

The dehydrogenation catalyst 28 serves as a cleaning catalyst for the gas phase. The dehydrogenation catalyst 28 is seen in addition to the dehydrogenation catalyst 30 in the FOHC support material. The dehydrogenation catalyst 28 is in the reactor 2 by means of a suitable holder 29 held. The holder 29 is particularly fastened to an inner wall of the reactor 2. A plurality of holders 29, in particular spaced apart from one another along the longitudinal axis 12 of the reactor 2, can be provided.

From the cleaning unit 7, the separated impurities can be discharged via a separating line 8 and can be disposed of and / or further processed.

The condenser 5 and the cleaning unit 7 are not pressure-regulating components. According to the exemplary embodiment in FIG. 1, the reactor 2 is directly connected to the utilization unit 3 via the connecting line 4.

Furthermore, the recycling unit 3 is connected to the reactor 2 in a heat-transferring manner in order to discharge waste heat from the recycling unit 3 to the reactor 2. The heat-transferring connection between the recycling unit 3 and the reactor 2 is realized according to the exemplary embodiment shown by a heat-conducting liquid line 9, which connects a recycling unit heat exchanger 10 to a reactor heat exchanger 11.

Instead of the heat-conducting liquid line 9, the connection can also be carried out in a heat-transferring manner by a heat exchanger which couples the utilization unit 3 to the reactor 2 directly. In particular, a heat-conducting wall can be provided in order to dissipate the heat from the utilization unit 3 directly to the reactor 2.

The reactor 2 has a reactor housing, which in particular has a vertically oriented longitudinal axis 12. The reactor housing has a medium supply line 13 in order to supply the liquid medium, in particular at least partially loaded LOHC, into the reactor housing. A medium supply line 14 is connected to the medium supply opening 13, in particular with a first medium storage tank 15 is connected.

The return line 6 is connected in particular to the medium supply line 14. The return line 6 can also be fed directly into the medium feed opening 13. A separate return opening can also be provided in the reactor housing for the return line 6. The reactor housing also has a medium discharge opening 16 in order to discharge liquid medium from the reactor housing. In particular, at least partially discharged LOHC is discharged from the reactor housing via the medium discharge opening 16. A medium discharge line 17, which leads to a second medium storage tank 18, is connected to the medium discharge opening 16. The medium supply line 14 and the medium discharge line 17 are advantageously mounted so that heat exchange between the two lines 14, 17 is possible.

The reactor housing comprises a liquid-filled reaction space 19 in which the liquid medium is arranged. The liquid-filled reaction space 19 has a liquid volume VR.

A gas-filled head space 20, which has a head space volume V _K , is arranged in the reactor housing above the liquid-filled reaction space 19. In particular, the head space volume V _{K is} smaller than the liquid volume V _R.

According to the exemplary embodiment shown, the additional dehydrogenation catalyst 28 is located in the head space 20, that is to say within the head space volume V _K. A sieve tray is used in particular as the holder 29. With the additional dehydrogenation catalyst 28 attached to the sieve plate, hydrogen-rich LOHC components which pass into the gas phase at reduced pressure can be dehydrated in the gas phase and thereby converted into the high-boiling, low-hydrogen LOHC components, which can be condensed more easily.

The additional dehydrogenation catalyst 28 arranged in the head space 20 is typically at a temperature level of the liquid-filled reaction space 19, but at least above the temperature level of the cleaning unit 7.

It is advantageous if the medium feed opening 13 and the medium discharge opening 16 are arranged in the region of the liquid-filled reaction chamber 19, that is to say in particular below half the liquid level in the reactor housing. The reactor housing also has a gas discharge opening 21 to which the connecting line 4 is connected. In particular, the gas discharge opening 21 is arranged in the head space 20.

The gas discharge opening 21 is arranged above the liquid level.

It is advantageous if the heat recovery from the recycling unit 3 to the reactor 2 opens at the liquid-filled reaction chamber 19 in order to introduce the waste heat from the recycling unit 3 directly into the liquid medium. According to the embodiment shown, the reactor heat exchanger 11 is arranged in the region of the liquid-filled reaction space 19.

A catalyst 30 is also arranged in the reactor housing in order to promote the release of the hydrogen gas. The catalyst 30 is arranged in particular below the liquid level, that is to say in the liquid-filled reaction space 19, above the liquid level, that is to say in the gas-filled head space 20, or above and below the liquid level. The catalyst 30 arranged above the liquid level in particular forms the additional dehydrogenation catalyst 28. A noble metal catalyst 30, in particular a platinum catalyst 30, has proven to be particularly suitable for the release of hydrogen gas from LOHC, in particular from perhydro-dibenzyltoluene or perhydro-benzyltoluene. In particular, the catalyst 30 is a dehydrogenation catalyst 30, which has platinum supported on aluminum oxide or carbon.

A pressure sensor 22 can be arranged on the reactor housing in order to measure the gas pressure in the head space 20, which is also referred to as the reactor outlet pressure pi.

A power line 23 is connected to the fuel cell in order to remove electrical current, in particular to an electrical consumer. Electric current can also be fed into a local or external power network via the power line 23. The fuel cell also has a supply line, not shown, for oxygen and / or air. Furthermore, a discharge line, not shown, is provided in order to discharge water and / or water vapor which are produced when hydrogen gas is converted into electricity. A heat exchanger on the discharge line for water and / or water vapor can be used for heat recirculation, in particular for thermal energy which is present in the water and / or emerging from the fuel cell 3 Steam is located to use. For example, the material flows within the plant 1 can be preheated and / or the hydrogen release in the reactor 2 can be driven.

A method for releasing gas, in particular what is hydrogen gas from a liquid medium, in particular at least partially loaded LOHC, is explained below with reference to FIG. 1.

At least partially loaded LOHC is conveyed from the first medium storage tank 15 via the medium supply line 14 and the medium supply opening 13 into the reactor housing of the reactor 2. A dehydrogenation catalyst is present in the reactor 2. As a result of a dehydrogenation reaction, hydrogen gas is released from the at least partially loaded LOHC and passes from the liquid medium in the reaction space 19 into the head space 20 arranged above it. The at least partially discharged LOHC is discharged from the reactor 2 through the medium discharge opening 16 in the reactor housing and the medium discharge line 17 is fed to the second medium storage tank 18.

The release of the hydrogen gas from the at least partially loaded LOHC is favored in that a partial pressure p _{g of} the gas, that is to say the hydrogen gas, is lowered in the reactor 2, in particular to a value of less than 1 bar. The partial pressure p _g of the gas prevails in the head space 20. The lowering of the partial pressure p _g is realized by the utilization unit 3 in the form of the fuel cell. Hydrogen gas is consumed in the fuel cell and converted into electrical current.

By lowering the partial pressure p _{g of} the gas in the reactor 2, the driving force for the dehydrogenation reaction increases.

The generation of electricity from the hydrogen gas in the fuel cell is exothermic. Heat generated there is released by means of the recovery unit heat exchanger 10, the heat-carrying liquid line 9 and the reactor heat exchanger 11 to the reactor 2. In particular, the temperature level of the fuel cell of approximately 180 ° C. is sufficient to provide the heat required for the dehydrogenation reaction in the reactor 2, which in particular can already take place at 170 ° C. In the hydrogen gas stream entrained vaporous portions of the LOHC are condensed in the condenser 5 and fed back to the reactor 2 via the return line 6. Impurities from the hydrogen gas can be cleaned in the cleaning unit 7.

The method is carried out in particular by means of a central control unit 27, which is in signal connection with the essential components of the system 1, in particular in a wired signal connection and / or in a wireless signal connection, for example by radio signal transmission, which is indicated schematically in FIG. 1.

A second exemplary embodiment of the invention is described below with reference to FIG. 2. Structurally identical parts are given the same reference numerals as in the first exemplary embodiment. Structurally different, but functionally similar parts are given the same reference numerals followed by a.

An essential difference compared to the first exemplary embodiment is that the system 1 a additionally has a pressure reducer 24. The pressure reducer 24 is arranged along the connecting line 4 between the reactor 2 and the utilization unit 3. In particular, the pressure reducer 24 is arranged along the connecting line 4 between the reactor 2 and the condenser 5.

Another difference from the first exemplary embodiment is that the gas discharge opening 21 in the reactor housing of the reactor 2 can be closed by means of a closing element (not shown). The closing element is adjustable between an open position, in which the gas discharge opening 21 is released, and a closed position, in which the gas discharge opening is closed, in particular automatically and in particular regulatedly adjustable. The adjustment of the closing element takes place in particular via the control unit 27, in particular as a function of the reactor outlet pressure pi.

Another difference from the first exemplary embodiment is that an expansion tank 25 is arranged along the connecting line 4. The expansion tank 25 is designed in particular in the form of a wind boiler. In particular, the expansion tank 25 along the connecting line 4 between the cleaning unit 7 and the Verwertungsein unit 3. The plant la is used to carry out the process with repeated pressure changes, in particular between the reactor outlet pressure pi and a plant pressure p ₂ .

In particular, the reactor outlet pressure pi is less than the atmospheric pressure. In particular, the reactor outlet pressure pi is less than 1 bar. In particular, a system pressure p _{2 is} lower than the reactor outlet pressure pi. In particular, system pressure is less than atmospheric pressure. In particular, the system pressure is less than 1 bar.

In particular, a second pressure sensor 26 is provided in order to measure the system pressure p ₂ . The second pressure sensor 26 is arranged in particular along the connecting line 4 behind the pressure reducer 24, in particular between the expansion tank 25 and the Verwertungsein unit 3.

The function of the system 1 a is explained in more detail below with reference to FIG. 2.

Starting from the operating mode of the plant according to the first exemplary embodiment, the reactor outlet pressure pi and thus the partial pressure p _{g of} the gas in the reactor 2 can be increased. The reactor outlet pressure pi represents the total pressure of all gases in the reactor 2, in particular a mixture of hydrogen gas and with vaporized LOHC. The reactor outlet pressure pi and the partial pressure p _g are different from each other.

The system pressure p ₂ is increased by at least partially opening the pressure reducing valve 24, which is designed in particular as a pressure regulator, throttle and / or valve.

Sudden lowering of the reactor outlet pressure pi results in a spontaneous outgassing of the product gas with an enlarged mean bubble diameter of the ascending bubbles, which improves the local mixing of the reaction medium and results in an improved convective heat exchange between the reactor wall, catalyst and liquid. The sudden drop in the reactor outlet pressure pi takes place within a fixed time interval, which is in particular less than 5 s, in particular less than 3 s, in particular less than 1 s, in particular less than 0.5 s, in particular less than 0.1 s and in particular less than 0.01 s.

After the pressure in the expansion tank 25 has been reduced to the system pressure p2, the gas discharge opening 21 is closed by means of the closing element. Due to the chemical reaction in the reactor 2, the pressure in the reactor 2 rises again until it is suddenly reduced again to the system pressure p2 by opening the closing element and / or the pressure reducer 23. The initialization of the renewed pressure build-up from the reactor outlet pressure pi to the system pressure p2 takes place in particular with the aid of sensors and in particular automatically. A signal can be used for this purpose, which is triggered by the pressure sensor 22 and measures the reactor outlet pressure pi in the head space 20. The pressure pi is preferably greater than 1 bar before the sudden drop in pressure. In this way, inert gases that have accumulated in the connecting line can be released from the system 1 via the separating line 8. In particular, the reactor outlet pressure pi is greater than 1 bar before the sudden drop in pressure and less than 1 bar after the sudden drop in pressure.

In particular, a periodic pressure change takes place in the reactor 2. The comparatively larger reactor outlet pressure pi relaxes to the system pressure p2 by at least partially opening the pressure reducer 24. Then there is an increase in pressure in the reactor 2 by closing the closing element and / or by closing or at least partially closing the pressure reducer 24, in particular spontaneously.

As a result, the positive effects of outgassing in particular can be used for the release of hydrogen. On average, the reactor outlet pressure pi in the reactor 2 is less than 1 bar. This results in an advantageously accelerated release of the hydrogen gas. It is advantageous if the pressure peaks, which are reached shortly before the sudden drop in pressure, are greater than 1 bar, in particular are slightly greater than 1 bar, in particular between 1.01 bar and 1.3 bar and in particular between 1 , 05 bar and 1.2 bar. With these pressure peaks, the discharge of inert gases from system 1 against atmospheric pressure is improved. By increasing the pressure in the head space 20, gaseous liquid constituents condense and return to the liquid-filled reaction space 19. In addition, the catalyst is reprocessed because coke precursors are detached from the catalyst and discharged from the reactor 2 via the medium discharge line 17 .

Claims

1. A method for releasing gas from a liquid medium, in particular for releasing hydrogen gas from a liquid organic hydrogen storage medium (LOHC), comprising the method steps

Providing a reactor (2) for releasing the gas from the liquid medium, lowering a partial pressure (p _g ) of the gas in the reactor (2) to less than 1 bar, releasing the gas from the liquid medium,

Removing the released gas from the reactor (2).

2. The method according to claim 1, characterized by lowering the partial pressure (p _g ) of the gas to less than 700 mbar, in particular to less than 500 mbar, in particular to less than 300 mbar and in particular to less than 100 mbar.

3. The method according to any one of the preceding claims, characterized in that the lowering of the partial pressure (p _g ) is carried out by sucking off the gas from the reactor (2).

4. The method according to any one of the preceding claims, characterized in that the lowering of the partial pressure (p _g ) is carried out by adding a volatile or evaporative compound in the reactor (2).

5. The method according to any one of the preceding claims, characterized in that the gas discharged from the reactor (2) is fed to a processing unit (3), in particular a fuel cell or an electrochemical compressor.

6. The method according to claim 5, characterized in that waste heat from the recovery unit (3) is returned to the reactor (2).

7. The method according to any one of claims 5 or 6, characterized in that the temperature level for the utilization of the gas in the utilization unit (3) is at least 5 ° K higher than the temperature level for the release of the gas in the reactor (2) .

8. The method according to any one of claims 5 to 7, characterized in that the gas discharged from the reactor (2) is cleaned in a cleaning unit (7), in particular an adsorption unit, before it is fed to the utilization unit (3).

9. The method according to any one of the preceding claims, characterized in that repeated, in particular periodic, pressure changes take place between a reactor outlet pressure (pi) and a system pressure (p2), where: p2 <pi, in particular p2 <0.9 · pi, in particular p2 <0.7 · pi, in particular p2 <0.5 · pi, in particular p2 <0.3 · pi and in particular p2 <0.1 · pi, pi> 1 bar and in particular p2 <1 bar in particular .

10. Plant for releasing gas from a liquid medium comprising

a. a reactor (2) with a reactor housing, which has

i. a medium feed opening (13) for feeding the loaded liquid medium into the reactor housing,

ii. a medium discharge opening (16) for discharging the discharged liquid medium from the reactor housing,

iii. a gas discharge opening (21) for discharging the released gas from the reactor housing,

b. a catalyst (28, 30) arranged in the reactor housing, which promotes the release of the gas from the liquid medium,

c. a utilization unit (3) in fluid communication with the reactor (2) for

Utilization of the gas released in the reactor (2).

11. Plant according to claim 10, characterized in that the recovery unit (3) with the reactor (2) is connected in a heat transfer manner.

12. Plant according to claim 10 or 11, characterized in that the reactor housing has a, in particular liquid-filled, reaction space (19) and a, in particular gas-filled, head space (20), the head space volume (V _K ) being in particular smaller than the reaction space volume (V _R ).

13. Plant according to one of claims 10 to 12, characterized in that a cleaning unit (7) is arranged along the fluid connection between the reactor (2) and the utilization unit (3).

14. Plant according to one of claims 10 to 13, characterized in that the utilization unit (3) is designed as a fuel cell, in particular as a high-temperature polymer electrolyte membrane fuel cell.