Method for dehydrogenating a liquid hydrogen carrier material

Abstract

Method for dehydrogenating a liquid hydrogen carrier material in the form of a metal hydride or a liquid organic hydrogen carrier (LOHC) with the following steps: a. providing the metal hydride or LOHC to a thin-film evaporator (1), wherein the LOHC is brought into contact with a catalyst, the catalyst is mixed into the LOHC before entering the thin-film evaporator (1) and / or wherein the LOHC is brought into contact with the catalyst in the thin-film evaporator (1); b. mechanically producing a film of the liquid hydrogen carrier material on a heated, cylindrical or conical wall (7) by means of a rotor (3) in the thin-film evaporator (1), wherein the chemical bond of the hydrogen to the liquid hydrogen carrier material is broken by supplying heat through the wall (7), wherein the produced hydrogen is extracted from the thin-film evaporator (1) and the residual liquid hydrogen carrier material is captured.

Description

Technical Field

[0001] The present invention relates to a method for dehydrogenating a liquid hydrogen-carrying material according to the features described in claim 1. Background Technology

[0002] Gradual climate change necessitates a shift in energy towards CO2-neutral sources such as solar and wind power. In the case of solar power, production capacity depends on the day-night cycle. Production is significantly lower in the Northern Hemisphere winter than in summer. In the case of wind power, periods without wind must be considered. Ideally, excess electricity generated by solar or wind power facilities should be stored and supplied at a later time. Storing and buffering peak power generation requires large storage capacities.

[0003] Hydrogen can be used as a promising chemical energy storage material. It can be produced in an electrolyzer when the current is too high, transported, and converted back into electricity, for example, in connection with a fuel cell. Hydrogen has a very high calorific value by weight and produces no greenhouse gas emissions when burned. However, its storability is generally poor due to its low density. To achieve sufficiently high density, hydrogen must be compressed under sufficiently high pressure or liquefied at sufficiently low temperatures.

[0004] Due to the unfavorable properties of hydrogen when stored as an element, various novel hydrogen storage methods have been developed. Chemical storage in liquids or suspensions offers advantages in terms of handling and economics. Strictly speaking, the chemical conversion of hydrogen falls under hydrogen storage, where hydrogen is recaptured and irreversibly converted into other fuels. Such storage methods include, for example, storage in liquid organic hydrogen carriers (LOHCs). LOHCs are organic compounds that can accept and release hydrogen again through chemical reactions. Storage can be achieved using suspensions (such as hydrides), where hydrogen is chemically bonded to suspended metal particles. With such liquid hydrogen carrier materials, much of the existing infrastructure used for fossil fuel energy carriers can be utilized.

[0005] To store electrical energy using a LOHC (Loose-of-Hydrogen Capacitor), energy must be used, as hydrogen must first be produced through electrolysis. To store the hydrogen, that is, to hydrogenate the LOHC, the produced hydrogen is brought into contact with the storage medium and chemically bonded to it. The LOHC reacts with hydrogen in the presence of a catalyst at an increased pressure of approximately 30 to 50 bar and an increased temperature of approximately 150 to 200°C. The hydrogenation reaction is exothermic.

[0006] The hydrogen-loaded LOHC is stable under environmental conditions and can be stored or transported, for example. The hydrogen is then released again in a dehydrogenation device. Dehydrogenation is an exothermic reaction at elevated temperatures above 150°C, which is further carried out in the presence of a catalyst. Due to the elevated temperature, the portion of the LOHC that must be separated from the hydrogen also evaporates, and can then be reused, for example, to generate electricity in a fuel cell. The LOHC support medium can then be reused as a hydrogen storage medium.

[0007] Some metals, such as lithium, calcium, and magnesium, can store hydrogen in the form of metal hydrides. For example, suspending magnesium powder in a liquid creates a hydrogen storage material that is easy and safe to handle and inexpensive. Such a hydrogen storage material can be a suspension of magnesium powder in mineral oil (https: / / carbon280.com). This material is non-toxic and does not react under environmental conditions. Therefore, storage and transportation are particularly simple. No catalyst is required for hydrogenation and dehydrogenation. The hydrogen released through dehydrogenation is particularly pure and can be used without further purification. The energy requirements for hydrogenation and dehydrogenation are significantly lower compared to LOHC. Heat must be supplied to break the chemical bonds between the hydrogen and the metal hydride in order to release hydrogen from the suspension.

[0008] Different reactor concepts have been followed in the past to release hydrogen from liquid storage materials. To provide the largest possible contact area between the loaded LOHC and the catalyst required for release, mesh structures and microstructured reactors can be used. The catalyst can be introduced into the structure or applied as a layer to the surface of the structured assembly. Structured plates coated with catalyst can be introduced into the tubes. Other construction forms consist of stainless steel tubes filled with catalyst, heated externally by heat transfer oil. Hydrogen is separated, for example, after passing through the reactor. The residual load is released and deposited in a separate stage. (https: / / d-nb.info / 1227451172 / 34, Simonte, M.: Reactor Concept for Cycloalkanes Dehydrogenation to Store Heat and Hydrogen, Dissertation, Department of Chemical Engineering and Process Engineering, Karlsruhe Institute of Technology (KIT), Karlsruhe 2020).

[0009] In all concepts of gas-liquid systems, it has been shown that the necessary process heat transfer and the contact between the LOHC and the catalyst are of particular importance to the dehydrogenation power of the reactor. If a large amount of hydrogen is released, a portion of the device is filled with hydrogen rather than LOHC, leaving only a portion of the catalyst-coated surface available for reaction. This can be an advantage of metal hydride suspensions, as hydrogen can be released without a catalyst. In summary, the following essential requirements for reactors used for hydrogen release can be derived: heat should be efficiently transferred to the liquid hydrogen storage material (LOHC or metal hydride suspension) to provide the necessary heat of reaction. Additionally, hydrogen should be efficiently removed after release. Furthermore, it should be operable with solid particles in the liquid hydrogen carrier and should be able to operate under overpressure to prevent evaporation of the hydrogen carrier.

[0010] To date, reactors used for dehydrogenating liquid hydrogen storage materials cannot meet these requirements due to system limitations. Summary of the Invention

[0011] Therefore, the basic objective of this invention is to demonstrate a method for dehydrogenating liquid hydrogen-carrying materials (i.e., LOHC or metal hydrides in suspension) that avoids these drawbacks.

[0012] This objective is achieved in a method having the features described in claim 1.

[0013] Advantageous improvements of the present invention are the subject of the dependent claims.

[0014] In the context of this invention, the term "liquid hydrogen-carrying material" refers to a LOHC and metal hydride suspension (hereinafter referred to as metal hydride) loaded with hydrogen (i.e., hydrogenated) and in which the chemical bonds between the LOHC and hydrogen can be broken (i.e., dehydrogenated). The support material can be reused, that is, it can be re-hydrogenated after dehydrogenation. Dehydrogenation of LOHC includes the presence of a catalyst, while dehydrogenation of metal hydrides does not require a catalyst. The term "dehydrogenation" is based on the assumption that the required boundary conditions are satisfied.

[0015] In the method for dehydrogenating a liquid hydrogen carrier according to the invention, LOHC or a metal hydride is used as the hydrogen carrier. If LOHC is used, a catalyst is mixed into the LOHC. The mixture of catalyst and LOHC is introduced into a thin-film evaporator. The thin-film evaporator serves as a reactor. The thin-film evaporator can also be called a thin-film dehydrogenator, or, due to its high efficiency, a high-efficiency thin-film dehydrogenator. The working principle of the thin-film evaporator is based on the mechanical generation of a film of the liquid mixture on a columnar or conical heated wall by means of a rotor. Here, in the presence of a catalyst, the chemical bonds between hydrogen and the liquid organic hydrogen carrier are broken by heating via the wall. Hydrogen is extracted from the thin-film evaporator. The remaining liquid organic carrier and catalyst are collected. Alternatively or additionally, the surfaces inside the thin-film evaporator that come into contact with the LOHC are coated with a catalyst. In this case, pre-mixing the catalyst is optional or redundant. When the metal hydride is to be dehydrogenated, the presence of the catalyst can be omitted.

[0016] Using the method of this invention, heat can be efficiently transferred to the hydrogen carrier to provide the desired heat of reaction. Simultaneously, the thin-film evaporator, in its function as a highly efficient thin-film dehydrogenator, can efficiently remove hydrogen after release. Furthermore, the thin-film evaporator can also be used to operate with solid particles in a liquid hydrogen carrier. Because the thin-film evaporator operates in a sealed environment, overpressure operation is also possible to prevent the evaporation of the hydrogen carrier.

[0017] In a vertically arranged thin-film evaporator, meaning its longitudinal axis is vertical, hydrogenated liquid hydrogen carrier is fed into the upper part of the evaporator and distributed, for example, into the thin film on the heated wall using a liquid distributor. After passing through the liquid distributor, the film is vigorously and thoroughly mixed by means of a wiping element. This thorough mixing ensures a very high heat flux density, thereby achieving a high hydrogen release rate. Under these conditions, without the intervention of a wiping element or wiping blades, an air cushion forms beneath the liquid film, which could potentially lead to a significant reduction in heat transfer. The wiping element of the rotor, especially the wiping blades, fixes the film to the heated wall, thus preventing a reduction in heat flux density due to the insulating effect of the air cushion.

[0018] As a result, the liquid film migrates downwards through the thin-film evaporator and is exposed to a strong heat flow. Along its downward path through the thin-film evaporator, hydrogen is released and exits at the upper end.

[0019] To facilitate hydrogen flow in the thin-film evaporator, a rotor with wiping elements is configured to expose a sufficiently large free cross-section for hydrogen flow. The partially or completely unloaded liquid hydrogen carrier is removed at the lower end of the thin-film evaporator.

[0020] The catalyst required to release hydrogen from the LOHC can be added to the liquid hydrogen storage material or applied as a thin layer to the heated walls and / or the wiping elements of the rotor before being fed into the device in powder or granular form.

[0021] The thin-film evaporator dehydrogenator can theoretically be implemented vertically or horizontally. The advantages of this invention can also be obtained when the thin-film evaporator is arranged at an angle deviating from the vertical axis or when it is arranged completely horizontally.

[0022] The wiping element of the rotor can be implemented as a rigid element, a movable flap, or a wiper loaded with spring force or restoring force. This implementation depends particularly on whether the feed mass flow rate, consisting of liquid hydrogen carrier, contains particles, for example, due to catalyst added to the LOHC. The number of wiping blades depends on the desired hydrogen release rate. The greater the number of wiping blades, the greater the heat flux and the higher the hydrogen release rate can be.

[0023] The reaction for releasing hydrogen is carried out at elevated temperatures, for example, in the temperature range of 250°C to 320°C. Even higher temperatures are possible. At these temperatures, at least a portion of the liquid hydrogen carrier evaporates even at atmospheric pressure, and this must be removed from the hydrogen as an impurity before use. The thin-film evaporator used as a reactor according to the invention can also operate under overpressure, particularly in a pressure range of at least 1 bar overpressure. Preferably, this range is 1 to 10 bar overpressure, thereby releasing hydrogen that can be used without further treatment if the amount of impurities is very small.

[0024] The use of a thin-film evaporator as a reactor for dehydrogenating LOHC according to the present invention allows for the separation of residual liquid organic hydrogen-carrying material from the catalyst and enables both the catalyst and LOHC to be fed for rehydrogenation. The catalyst is, in particular, a finely dispersed solid mixed with LOHC, wherein the resulting suspension is introduced into the thin-film evaporator. The catalyst can also be introduced separately from the LOHC into the thin-film evaporator and mixed therewith. When a catalyst-coated area exists within the thin-film evaporator, it is not necessary to separate the dehydrogenated LOHC from the catalyst.

[0025] The invention will now be explained with the aid of a thin-film evaporator, which is shown schematically only in the accompanying drawings. This embodiment relates to the dehydrogenation of LOHC. The thin-film evaporator can be operated using metal hydrides in the same manner without the need for pre-addition of a catalyst. Attached Figure Description

[0026] Figure 1A thin-film evaporator 1 with a vertical orientation is shown in cross-section. The thin-film evaporator 1 has a generally cylindrical shell 2. Inside the shell 2, there is a rotor 3 with a rotation axis 4, which is centrally oriented in the longitudinal direction within the cylindrical shell. The rotor 3 is driven by a drive unit 5 located at the upper end of the shell 2. The drive unit 5 includes a motor and an optional transmission unit. The rotor 3 rotates in the direction of arrow P1. Detailed Implementation

[0027] In the upper region of rotor 3, a pre-mixed, hydrogenated liquid organic hydrogen carrier, along with the catalyst, is introduced into housing 2 in the direction of arrow P2. The liquid LOHC reaches the liquid distributor 6 and is distributed as evenly as possible onto the inner wall 7 of housing 2. The inner wall 7 is heated radially from the outside. For this purpose, a heating medium 8 is guided in the direction of arrow P3 through the gap between the inner wall 7 and the outer wall 9. At the lower end of housing 2, the heating medium 8 is again discharged from the gap 10 between the inner wall 7 and the outer wall 9 in the direction of arrow P4. The temperature of the inner wall 7 is in the range of 150 to 320°C. Higher temperatures can also be set to provide a sufficiently high heat flux density. Thus, in the presence of the catalyst, the chemical bonds between hydrogen and LOHC are broken. Hydrogen gas (H2) leaves the LOHC and flows radially inward from the inner wall 7, rising upwards. Hydrogen is extracted at outlet 11 at the top of the thin-film evaporator 1 in the direction of arrow P5. For example, hydrogen can be used in fuel cells to generate electricity.

[0028] The rotor 3 has multiple wiping elements 12, 13, and 14 arranged sequentially along the longitudinal direction of the rotation axis 4, which distribute the LOHC film onto the heated wall 7. The dehydrogenated liquid organic hydrogen carrier collects in a funnel 15 at the bottom of the thin-film evaporator 1 and is drawn downwards in the direction of arrow P6. The dehydrogenated LOHC can then be rehydrogenated. This involves a closed loop.

[0029] List of reference numerals in the attached diagram:

[0030] 1 - Thin Film Evaporator

[0031] 2-1 housing

[0032] Rotor in 3-1

[0033] 4 - 3 axis of rotation

[0034] 5 - Drive unit

[0035] 6 - Liquid Dispenser

[0036] 7-2 heated wall

[0037] 8 - Heating medium

[0038] 9-2 outer wall

[0039] 10 - The gap between 7 and 9

[0040] 11 - 2 Exit

[0041] 12 - 3 wiping elements

[0042] 13 - 3 wiping element

[0043] 14 - 3 wiping elements

[0044] 15 - 2 funnel

[0045] P1 - Arrow / Rotation Direction

[0046] P2 - Arrow / (hydrogenated) LOHC with catalyst

[0047] P3 - Arrow / Heating Medium

[0048] P4 - Arrow / Heating Medium

[0049] P5 - Arrow / Hydrogen

[0050] P6 - Arrow / Dehydrogenated LOHC

Claims

1. A method for dehydrogenating a liquid hydrogen carrier material in the form of a metal hydride or a liquid organic hydrogen carrier (LOHC), comprising the following steps: a. Providing the metal hydride or LOHC to the thin-film evaporator (1), wherein the LOHC is contacted with the catalyst, the catalyst is mixed into the LOHC before entering the thin-film evaporator (1), and / or wherein the LOHC is contacted with the catalyst in the thin-film evaporator (1); b. In the thin film evaporator (1), a film of the liquid hydrogen-carrying material is mechanically generated on a columnar or conical heated wall (7) by means of a rotor (3), wherein the chemical bond between the hydrogen and the liquid hydrogen-carrying material is broken by heating via the wall (7), wherein the generated hydrogen is extracted from the thin film evaporator (1) and the residual liquid hydrogen-carrying material is captured.

2. The method according to claim 1, characterized in that, The residual liquid hydrogen-carrying material is separated from the catalyst and sent for rehydrogenation.

3. The method according to claim 1 or 2, characterized in that, The catalyst is mixed with the LOHC as a finely dispersed solid and the resulting suspension is introduced into the thin-film evaporator (1).

4. The method according to any one of claims 1 to 3, characterized in that, The LOHC and the catalyst separated from the LOHC are introduced into the thin-film evaporator (1) and mixed in the thin-film evaporator (1).

5. The method according to any one of claims 1 to 4, characterized in that, The surface of the thin-film evaporator (1) that comes into contact with the LOHC is at least partially coated with a catalyst.

6. The method according to claim 5, characterized in that, The heated wall (7) is coated with the catalyst.

7. The method according to claim 5 or 6, characterized in that, The rotor (3) is at least partially coated with the catalyst.

8. The method according to any one of claims 1 to 7, characterized in that, The hydrogenated liquid hydrogen-carrying material is heated in the thin-film evaporator (1) to a temperature exceeding 150°C, particularly in the range of 150°C to 400°C, and preferably in the range of 200°C to 300°C.

9. The method according to any one of claims 1 to 5, characterized in that, The working pressure of 1 to 10 bar overpressure is set in the thin film evaporator (1).

10. The method according to any one of claims 1 to 9, characterized in that, The LOHC is selected from the group consisting of toluene, N-ethylcarbazole, dibenzyltoluene, and benzyltoluene.

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