Method and apparatus for the reversible catalytic hydration of carbazole using proton-conducting membranes

Abstract

Method for loading and unloading carbazole or its derivatives with hydrogen, wherein the loading and unloading takes place in three separate steps, namely a loading of the carbazole with hydrogen, an intermediate storage and a discharge of the hydrogen-loaded carbazole, wherein: the loading is carried out by a carbazole loading cell (2) which includes a PEM membrane electrolyzer or an electrochemical hydrogen pump, the intermediate storage of the carbazole in a carbazole storage container (5) serving as an intermediate carbazole storage container, and The discharge of the hydrogen-loaded carbazole is carried out by a carbazole discharge cell (8) which includes a fuel cell in which the hydrogen-loaded carbazole is converted into electrical and thermal energy, wherein the carbazole storage container (5) is arranged between the PEM membrane electrolyzer or the electrochemical hydrogen pump and the fuel cell.

Description

[0001] The invention relates to a method and an apparatus for the reversible hydrogenation of carbazole and its derivatives with the features of the preamble of independent claim 1.

[0002] The cost-effective storage of hydrogen for use, e.g., in fuel cells in combined heat and power plants, heating systems, stationary and mobile systems, etc., is one of the most important challenges in fuel cell technology. Several methods are currently known: volumetric storage, pressure storage, storage of liquefied hydrogen, storage using metal hydrides, etc. The storage and release of hydrogen in carbazole is also state of the art, but only on a laboratory scale. A fully functional, closed-loop system is not yet known.

[0003] From WO 2005 / 000 457 A2 it is generally known to store and release hydrogen in carbazole.

[0004] AutoBild, No. 26, July 1, 2011, pages 26 and 27, reveals the use of carbazole as an energy carrier in electric cars.

[0005] US 2008 / 0248 345 A1 and US 2010 / 0055513A1 each teach a principle of a combined fuel cell which can be operated in an electrolysis or a fuel cell mode.

[0006] DE 10 2005 061 137 A1 discloses a method for providing compressed hydrogen gas.

[0007] The invention therefore aims to provide a method that enables the storage and release of hydrogen in a liquid by means of catalytic hydrogenation. N-Ethylcarbazole (C14H13N) is preferably used as the starting liquid.

[0008] This task is solved by the subject matter of the independent claims. The various possibilities of practical application of this membrane are described in Fig. 2 shown.

[0009] It can be deduced from this that a wide variety of tasks can be solved by using a proton-conducting membrane. The catalyst used in each case supports the necessary reactions and enables them to proceed even at lower temperature and pressure levels. The four most important applications are summarized here as the so-called "basic processes" of the proton-conducting membrane: • Membrane electrolysis, in which deionized water is electrochemically split into hydrogen and oxygen • Fuel cell in which hydrogen and (atmospheric) oxygen are electrochemically combusted to produce water, releasing electrical energy in a "cold" process. • Oxygen generator in which pure oxygen is produced electrochemically from water; the hydrogen formed is recombined with atmospheric oxygen in a half-cell in its initial stages. This achieves a significant energy advantage because the decomposition voltage of the electrolysis, normally 1.6 volts, begins at only 0.6 volts, as the (atmospheric) oxygen-hydrogen potential can be utilized. • Electrochemical hydrogen compressor (H2 pump), in which hydrogen can be “pumped” through the membrane via the ionic path at very low voltages.

[0010] For the application according to the invention, membrane electrolysis or an electrochemical compressor and a fuel cell are connected together as a system in a suitable form.

[0011] It is assumed that the storage of hydrogen in the carbazole, in particular, is especially rapid and easy due to the atomic hydrogen briefly generated in status nascendi during electrolysis, as well as in the electrochemical pump.

[0012] The method for storing and releasing hydrogen differs from known methods insofar as the storage of hydrogen by absorbing the hydrogen into a liquid and the release of the hydrogen from the same liquid are reversible.

[0013] The invention consists of three process steps that are implemented in one system: a) the partial or complete storage of hydrogen carbazole b) the intermediate storage of hydrogen-enriched carbazole and c) the subsequent release of hydrogen from the carbazole partially or completely charged with hydrogen. Process steps a), as well as c), are carried out in so-called electrochemical cells, which are combined as individual components to form a system according to this invention. Storage of hydrogen in carbazole

[0014] According to the invention, the storage process of hydrogen in carbazole is also represented by two possibilities: • By means of (membrane) electrolysis using a direct process and • by an electrochemical hydrogen pump Electrolyzer, membrane electrolysis

[0015] An alkaline electrolyzer or a membrane electrolyzer can be used as an electrolyzer. A membrane electrolyzer is described here because of its system compatibility with proton-conducting membranes (PEMs). Membrane electrolyzer

[0016] By means of an electrochemical cell which has electrodes on both sides and is divided by a catalyst-coated proton-conducting membrane (PEM), deionized water is split into hydrogen and oxygen, with the water being offered on one side (electrical positive pole) and carbazole (electrical negative pole) on the other side of the membrane.

[0017] The temperature conditions are designed such that the carbazole is in liquid form and is continuously or intermittently pumped through the cell half. According to the invention, a reservoir is provided from which the pump draws carbazole and can return it to the reservoir through the cell half. The reservoir also allows the necessary temperature conditions to be established by incorporating a heater. Alternatively, the cell can be heated directly for this purpose.

[0018] The electrochemical process of the reaction can be simplified as follows: On the water side, the catalyst and the electrode split the water into hydrogen and oxygen in such a way that the hydrogen produced is separated from its electron in atomic form and transported through the membrane as a hydrogen ion (proton). On the other side (carbazole side), the hydrogen ion is recombined to form atomic / molecular hydrogen by gaining an electron and can be immediately and directly absorbed by the carbazole. An external power source, e.g., a photovoltaic system, wind turbine, etc., ensures the necessary electron and ion transport into and through the cell by drawing electrons from the positive electrical side (water side) and supplying them to the negative electrical side. The resulting ion current through the membrane is always in equilibrium with the electron current. Membrane electrolysis requires a minimum decomposition voltage (approx.The voltage must exceed 1.6V (=) to allow current to flow. Due to electroosmosis and the fact that hydrogen ions can only migrate across the membrane with a hydration shell, etc., the water carried across the membrane on the carbazole side must be separated by a water separator and can then be reintroduced into the process. Since carbazole is water-insoluble, no solution can form. Electrochemical hydrogen pump (electrolysis of hydrogen)

[0019] The second method applied according to the invention in a system represents the use and operation of an electrochemical hydrogen pump, which is briefly explained below. In an electrochemical cell, which is divided by a catalyst-coated proton-conducting membrane (PEM) and has electrodes on both sides, hydrogen is supplied on one side and carbazole on the other side of the membrane.

[0020] The temperature conditions are designed such that the carbazole is in liquid form and is continuously or intermittently pumped through the cell half. According to the invention, a storage vessel is provided from which the pump draws carbazole and returns it to the storage vessel through the cell half. The storage vessel also allows the necessary temperature conditions to be established by incorporating a heater. Alternatively, the cell can be heated directly for this purpose.

[0021] By applying a low voltage to the electrodes, hydrogen is electrochemically transported across the membrane. First, on the hydrogen side, the hydrogen is broken down from its molecular form (H₂) to its atomic form at the catalyst. Then, due to the applied voltage (external power source, positive electrode) and the concentration difference, it is transported as hydrogen ions (protons) across the proton-conducting membrane. The electrons released in this process are extracted by the external power source. On the carbazole side, the protons are converted back into atomic hydrogen at the catalyst by accepting electrons from the external power source (negative electrode).

[0022] In the two alternative process steps, which can also be switched sequentially: electrolyzer and electrochemical hydrogen pump, carbazole is able to absorb the hydrogen either atomically or molecularly immediately and directly, resulting in hydrogen-enriched carbazole (perhydrocarbazole) according to the following system of equations:

[0023] The enrichment process continues steadily until 100% of the solution is saturated with hydrogen. The electric current flowing in the electrolyzer or hydrogen pump, as well as in a series connection of both processes, due to the applied voltage and the internal electrical resistance of the cells (electron resistance and ion resistance), is in each case an exact measure of the hydrogen transport (Faraday reaction). The rise in the hydrogen level due to the increase in volume of carbazole in the storage vessel is a measure of the degree of hydrogenation of the carbazole.

[0024] For the electrochemical hydrogen pump, either a low-temperature PEM (sulfuric acid membrane) or a high-temperature PEM (phosphoric acid membrane) can be used as the cell membrane. The latter has the advantage that its process temperatures are compatible with those of carbazole. Hydrogen release from carbazole (perhydrocarbazole)

[0025] The release of hydrogen can be catalytically achieved in various ways. According to the invention, the release is accomplished by a second cell, which operates as a PEM fuel cell. Perhydrocarbazole is pumped through the cell via a pump and storage vessel, similar to the storage of hydrogen in carbazole. Molecular / atomic hydrogen is produced at the catalyst. If an electric current is applied via an external circuit, protons flow through the proton-conducting membrane. The electrode then becomes the negative pole, meaning it has an excess of electrons, which are drawn off by an electrical load. An oxidizer, such as oxygen, air, or other substances (e.g., chlorine), is supplied to the other side of the membrane. Using air, which consists of approximately 20% oxygen, water (H₂O) is produced by the uptake of electrons from the hydrogen ions and the oxygen.The electron circuit is closed via the external electrical load - current will flow as long as hydrogen from the perhydrocarbazole is available.

[0026] Both low-temperature PEM (sulfuric acid membrane) and high-temperature PEM (phosphoric acid membrane) membranes can be used as fuel cell membranes. The latter has the advantage of compatible process temperatures. Reversible process

[0027] The reversible process of hydrogenation and dehydrogenation of carbazole is described in the literature as follows: Each carbazole molecule either gains or loses 6 hydrogen molecules, i.e., 12 H atoms. C14H13N (N-ethylcarbazole) is converted to C14H25N (perhydrocarbazole), as can be seen from... Fig. 1 equals 1. Reverse operation

[0028] From a system perspective, reversibility can be demonstrated by a single cell operating in alternating mode or by two cells connected in series. Furthermore, and not only in reverse operation, multiple cells can be combined into stacks, as is common in fuel cell technology. The electrical circuitry used in this configuration requires special attention and technical solutions due to the specific characteristics of the hydrogen pump.

[0029] In pure reverse operation, one and the same cell is operated first as an electrochemical H2 pump and then as a fuel cell. Initially, following the principle of the electrochemical H2 pump, hydrogen is introduced into the carbazole by applying a low voltage, resulting in an electric current. The duration of the H2 supply and the amount of carbazole in the reservoir determine the total amount of hydrogen stored in the carbazole during recirculation.

[0030] Once the charging process is complete, which can also happen after a partial charge, the hydrogen is switched off and atmospheric oxygen is offered instead of the hydrogen from the same cell.

[0031] The hydrogen-charged carbazole now releases its hydrogen again, and electrical power, as well as heat, can be extracted from the same cell in fuel cell operation.

[0032] The basic process with the proton-conducting membrane results from Fig. 2.

[0033] The invention is explained and described in more detail below with reference to the accompanying drawings. These show: Fig. 1 a reversible process, Fig. 2 a basic process with the proton-conducting membrane, Fig. 3. A schematic diagram of the entire energy chain, Fig. 4. The mode of operation of the charging process using a (membrane) electrolyzer, Fig. 5. The operating principle of the charging process using an electrochemical hydrogen pump, Fig. 6. The mode of operation of the discharge process using the fuel cell principle, Fig. 7 a 2-cell arrangement with charge and discharge cells and in Fig. 8 different combination possibilities of the system units to form a complete system.

[0034] At the in Fig. The entire energy chain is depicted in the process shown in Figure 3. An external electrical power supply 1 provides the necessary electrical energy. A cell 2 is used for the catalytic loading of the carbazole. This cell can be configured as either an electroroyer (direct loading cell) or as an electrochemical H2 pump if hydrogen is supplied by another means. A carbazole circulation pump 3 ensures the intermittent contact of the carbazole during the unloading process to prevent overcharging. The water separator 4 separates water from the hydrogen-enriched carbazole. The carbazole is stored in a reservoir 5. The carbazole temperature is set by a heater 6. This heater can also be integrated into the loading cell 2. The carbazole reservoir 5 must be vented; this is done by the vent 7.The carbazole discharge takes place in cell 8. A second carbazole circulation pump 9 enables continuous discharge of the carbazole by flowing through it. The electrical power supplied by cell 8 is used by the consumer 10.

[0035] The Fig. Figure 4 represents the hydrogen supply for the hydrogenation of the carbazole by a membrane electrolyzer. Upon water inlet, the cell, which is compressed gas-tight by two end plates 13, is supplied with demineralized water 11. The electrolysis that occurs as a result of the interaction of the power supply 17, the electron-conducting electrodes 14a and 14b, the catalyst 15, and the proton-conducting membrane (PEM) 16, which acts as a solid electrolyte, produces current-proportional hydrogen on the carbazole side of the cell facing away from the water and oxygen 12 on the water side of the cell, which is released to the environment in a closed loop. The carbazole is pumped through the cell and to the carbazole reservoir 19 by pump 18 via lines 22a and 22b. Since the carbazole 20 experiences a significant increase in volume due to hydrogen uptake, a ventilation device 23 is required.A regulated heating element 21 brings and keeps the carbazole in a liquid state.

[0036] Fig. Figure 5 shows the loading of the carbazole with hydrogen 24, which is supplied externally and electrically "pumped" from the hydrogen inlet side to the carbazole side using the principle of an electrochemical hydrogen pump. The hydrogen is converted from its molecular to its atomic form at the catalysts 27, its electrons are carried away via the electrode 26a and through the consumer 25, and are then reabsorbed on the carbazole side by the H ions flowing through the membrane and bound within the carbazole. The end plates 29 allow for gas-tight compression of the cell. The subsequent pump 30 allows the carbazole 32 to be recirculated to facilitate hydrogen uptake within the cell. The container 33 holds the carbazole supply, and a venting device 35 ensures pressure-neutral compensation for the volume increase caused by the hydrogen uptake of the carbazole.A regulated heating element 34 brings and keeps the carbazole in a liquid state.

[0037] Fig. Section 6 deals with hydrogen storage from the charged carbazole. A fuel cell, either a low-temperature PEM fuel cell (sulfuric acid PEM) or a high-temperature PEM fuel cell (phosphoric acid PEM), is used for storage. The fuel cell requires hydrogen and oxygen to operate. It obtains the oxygen 36 from the environment (fan, compressor, etc.). The end products and reaction products are water 37 and oxygen-depleted air 37. The required hydrogen is extracted from the enriched carbazole 45, which is circulated by a pump 43, within the cell by a catalytic reaction (storage). Lines 44a and 44b are required for the supply and return flow. The cell itself is equipped with catalysts 39, where the oxygen-hydrogen reaction takes place.

[0038] Ion conduction occurs through the proton-conducting membrane (PEM) 40; the electrodes 41a (positive electrode), 41b (negative electrode) attached on both sides enable the electron flow, which can perform technical work on the consumer 42.

[0039] The carbazole supply 45 is provided in a storage vessel 46; a ventilation unit enables the pressure-neutral volume loss of the charged carbazole as a result of the desorption of hydrogen.

[0040] In the Fig. Figure 7 shows a two-cell overall unit consisting of a carbazole loading unit, a carbazole storage container (carbazole storage 50) and a carbazole discharge unit.

[0041] In Fig. Eight possible combinations of the system units to form a complete system are shown in a table.

Claims

[1] Method for loading and unloading carbazole or its derivatives with hydrogen, wherein the loading and unloading takes place in three separate steps, namely loading the carbazole with hydrogen, intermediate storage and unloading the hydrogen-loaded carbazole, wherein: the loading is carried out by a carbazole loading cell (2) which includes a PEM membrane electrolyzer or an electrochemical hydrogen pump, the intermediate storage of the carbazole in a carbazole storage container (5) serving as an intermediate carbazole storage container, and The discharge of the hydrogen-loaded carbazole is carried out by a carbazole discharge cell (8) which includes a fuel cell in which the hydrogen-loaded carbazole is converted into electrical and thermal energy, wherein the carbazole storage container (5) is arranged between the PEM membrane electrolyzer or the electrochemical hydrogen pump and the fuel cell. [2] Method according to claim 1, characterized by , that the PEM membrane electrolyzer is an electrochemical cell divided by a catalyst-coated proton-conducting membrane (PEM) and has electrodes (14, 14a, 14b) on both sides, with water being offered on one side and carbazole on the other side of the membrane. [3] Method according to any of the preceding claims, characterized by , that the carbazole storage container (5) has a controlled heating system (34) which brings the carbazole into a liquid state and keeps it there. [4] Method according to any of the preceding claims, characterized by that the PEM membrane electrolyzer has an integrated heater for adjusting the temperature of the carbazole. [5] Method according to any of the preceding claims, characterized by that the electrochemical hydrogen pump has a low-temperature PEM (sulfuric acid membrane) or a high-temperature PEM (phosphoric acid membrane). [6] Method according to any of the preceding claims, characterized by that the fuel cell has a low-temperature PEM (sulfuric acid membrane) or a high-temperature PEM (phosphoric acid membrane) as its fuel cell membrane. [7] Apparatus for carrying out the method according to any one of the preceding claims, characterized by a carbazole loading cell (2) comprising a PEM membrane electrolyzer or an electrochemical hydrogen pump for loading the carbazole with hydrogen, a carbazole storage container (5) serving as an intermediate storage container for the carbazole, and a carbazole discharge cell (8) comprising a fuel cell for discharging the hydrogen-loaded carbazole, in which the hydrogen-loaded carbazole can be converted into electrical and thermal energy, wherein the carbazole storage container is arranged between the PEM membrane electrolyzer or the electrochemical hydrogen pump and the fuel cell.

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