PROCESS AND APPARATUS FOR SYNTHESIS OF AMMONIA

Abstract

A process and system for synthesis of ammonia includes an electrochemical main cell and an electrochemical preliminary cell upstream of the main cell. A voltage is applied between the anode and cathode of the preliminary cell and the main cell. The anodic half-cell of the preliminary cell is supplied with water, and the cathodic half-cell of the preliminary cell with nitrogen and oxygen. Oxygen is in the anodic half-cell of the preliminary cell, and nitrogen and water are in the cathodic half-cell of the preliminary cell. The anodic half-cell of the main cell is supplied with water, and the cathodic half-cell of the main cell with nitrogen that has been obtained in the cathodic half-cell of the preliminary cell. Oxygen is in the anodic half-cell of the main cell, and ammonia in the cathodic half-cell of the main cell.

Claims

1. Method for synthesis of ammonia, wherein an electrochemical main cell (2) comprising an anodic half-cell (4) with an anode (5) and a cathodic half-cell (6) with a cathode (7) is provided, wherein a membrane (8), in particular a cation exchange membrane, is arranged between the anodic (4) and the cathodic half-cell (6), through which protons can pass from the anodic (4) into the cathodic half-cell (6), and wherein the anode (5) comprises at least one catalyst material, in particular iridium and/or ruthenium and/or platinum, and the cathode (7) comprises at least one catalyst material, in particular ruthenium and/or titanium and/or iron, preferably ruthenium and titanium and iron, wherein an electrochemical pre-cell (3), which is connected upstream of the main cell (2) and which comprises an anodic half-cell (4) with an anode (5) and a cathodic half-cell (6) with a cathode (7), is provided, wherein a membrane (8), in particular a cation exchange membrane, is arranged between the anodic half-cell (4) and the cathodic half-cell (6), through which protons can pass from the anodic (4) into the cathodic half-cell (6), and wherein the anode (5) comprises at least one catalyst material, in particular iridium and/or ruthenium, and the cathode (7) comprises at least one catalyst material, in particular platinum, a voltage is applied between the anode (5) and cathode (7) of the pre-cell (3), pre-cell voltage (UV), and a voltage is applied between the anode (5) and cathode (7) of the main cell (2), main cell voltage (UH), water is supplied to the anodic half-cell (4) of the pre-cell (3) and nitrogen and oxygen, in particular air, are supplied to the cathodic half-cell (6) of the pre-cell (3), oxygen is obtained in the anodic half-cell (4) of the pre-cell (3) and nitrogen and water are obtained in the cathodic half-cell (6) of the pre-cell (3), water, in particular vaporous water, is supplied to the anodic half-cell (4) of the main cell (2), and nitrogen obtained in the cathodic half-cell (6) of the pre-cell (3) is supplied to the cathodic half-cell (6) of the main cell (2), and oxygen is obtained in the anodic half-cell (4) of the main cell (2), and ammonia is obtained in the cathodic half-cell (6) of the main cell (2).

2. Method according to claim 1, wherein water taken from the anodic half-cell (4) of the pre-cell (3) is supplied to the anodic half-cell (4) of the main cell (2).

3. Method according to claim 1, wherein the anode (5) of the main cell (2) preferably comprises platinum as catalyst material, and in that an intermediate cell (18), which is connected downstream of the pre-cell (3) and upstream of the main cell (2) and which comprises an anodic half-cell (4) with an anode (5) and a cathodic half-cell (6) with a cathode (7), is provided, wherein a membrane (8), in particular a cation exchange membrane, is arranged between the anodic half-cell (4) and the cathodic half-cell (6), through which protons can pass from the anodic (4) into the cathodic half-cell (6), and wherein the anode (5) comprises at least one catalyst material, in particular iridium and/or ruthenium, and the cathode (7) comprises at least one catalyst material, in particular platinum, and a voltage is applied between the anode (5) and cathode (7) of the intermediate cell (18), intermediate cell voltage (UZ), and water is supplied to the anodic half-cell (4) of the intermediate cell (18), in particular water which was obtained in the anodic half-cell (4) of the pre-cell (3), and preferably no substances are supplied to the cathodic half-cell (6) of the intermediate cell (18), and oxygen is obtained in the anodic half-cell (4) of the intermediate cell (18), and hydrogen and permeating water are obtained in the cathodic half-cell (6) of the intermediate cell (18), and hydrogen and water obtained in the cathodic half-cell (6) of the intermediate cell (18) are supplied to the anodic half-cell (4) of the main cell (2), the water particularly being supplied in the vaporized state.

4. Method according to claim 3, wherein an intermediate cell voltage (UZ) in the range of 1.2 to 2.5 volts, preferably in the range of 1.48 to 2 volts, is applied.

5. Method according to claim 3, wherein solar energy is used to provide the intermediate cell voltage (UZ), in particular, wherein the intermediate cell voltage (UZ) is provided by means of at least one photovoltaic cell (9).

6. Method according to claim 1, wherein a pre-cell voltage (UV) of less than 1.7 volts, preferably of less than 1.48 volts, particularly preferably of less than 1.23 volts, is applied, and/or in that a main cell voltage (UH) in the range of 1 to 3 volts, preferably in the range of 1.7 to 2.7 volts, particularly preferably 1.2 to 1.3 volts, is applied.

7. Method according to claim 1, wherein solar energy is used for providing the pre-cell voltage (UV) and/or for providing the main cell voltage (UH), in particular, wherein the pre-cell voltage (UV) and/or the main cell voltage (UH) is provided by means of at least one photovoltaic cell (9), preferably, wherein the pre-cell voltage (UV) is provided by a photovoltaic cell (9) associated with the pre-cell (3) and the main cell voltage (UH) is provided by a further photovoltaic cell (9) associated with the main cell (2).

8. Method according to claim 1, wherein the water is separated from the nitrogen and water obtained in the cathodic half-cell (4) of the pre-cell (3), in particular by means of a cooling and/or separating device (17) provided between the pre-cell (3) and the main cell (2).

9. Method according to claim 1, wherein vaporous water is supplied to the anodic half-cell (4) of the main cell (2), in particular, wherein an evaporation device (13) connected upstream of the main cell (2) is used to obtain the vaporous water, preferably, wherein the evaporation device (13) comprises at least one solar thermal collector (14) or is coupled to at least one solar thermal collector (14).

10. Method according to claim 1, wherein nitrogen exiting from the cathodic half-cell (6) of the main cell (2) is supplied again to the cathodic half-cell (6) of the main cell (2).

11. Apparatus (1) for synthesis of ammonia, comprising an electrochemical main cell (2) comprising an anodic half-cell (4) with an anode (5) and a cathodic half-cell (6) with a cathode (7), wherein a membrane (8), in particular a cation exchange membrane, is arranged between the anodic half-cell (4) and the cathodic half-cell (6), through which protons can pass from the anodic (4) into the cathodic half-cell (6), and wherein the anode (5) comprises at least one catalyst material, in particular iridium and/or ruthenium and/or platinum, and the cathode (7) comprises at least one catalyst material, in particular ruthenium and/or titanium and/or iron, preferably ruthenium and titanium and iron, main cell voltage means (9) for providing a voltage (UH) between the anode (5) and the cathode (7), wherein the apparatus further comprises an electrochemical pre-cell (3) connected upstream of the main cell (2), which comprises an anodic half-cell (4) with an anode (5) and a cathodic half-cell (6) with a cathode (7), wherein a membrane (8), in particular a cation-exchange membrane, is arranged between the anodic half-cell (4) and the cathodic half-cell (6), through which protons can pass from the anodic (4) into the cathodic half-cell (6), and wherein the anode (5) comprises at least one catalyst material, in particular iridium and/or ruthenium, and the cathode (7) comprises at least one catalyst material, in particular platinum, pre-cell voltage means (9) for providing a voltage (UV) between the anode (5) and cathode (7) of the pre-cell (3), and fluid connection means (11) for fluidically connecting the cathodic half-cell (6) of the pre-cell (3) to the cathodic half-cell (6) of the main cell (2).

12. Apparatus (1) according to claim 11, wherein fluid connection means (11) are provided for the fluidic connection of the anodic half-cell (4) of the pre-cell (3) to the anodic half-cell (4) of the main cell (2).

13. Apparatus (1) according to claim 11, wherein the anode (5) of the main cell (2) preferably comprises platinum as catalyst material, and the apparatus (1) further comprises an intermediate cell (18), which is connected downstream of the pre-cell (3) and upstream of the main cell (2), and which comprises an anodic half-cell (4) with an anode (5) and a cathodic half-cell (6) with a cathode (7), wherein a membrane (8), in particular a cation exchange membrane, is arranged between the anodic half-cell (4) and the cathodic half-cell (6), through which protons can pass from the anodic (4) into the cathodic half-cell (6), and where the anode (5) comprises at least one catalyst material, in particular iridium and/or ruthenium, and the cathode (7) comprises at least one catalyst material, in particular platinum, and intermediate cell voltage means (9) for providing a voltage (UZ) between the anode (5) and cathode (7) of the intermediate cell (18), fluid connection means (11) for fluidically connecting the anodic half-cell (4) of the pre-cell (3) to the anodic half-cell (4) of the intermediate cell (18), fluid connection means (11) for fluidically connecting the cathodic half-cell (6) of the intermediate cell (18) to the anodic half-cell (4) of the main cell (2).

14. Apparatus (1) according to claim 13, wherein the intermediate cell voltage means (9) are designed to provide a voltage (UZ) in the range of 1.2 to 2.5 volts, preferably in the range of 1.48 to 2 volts.

15. Apparatus (1) according to claim 13, wherein the intermediate cell voltage means comprise at least one photovoltaic cell (9) or are provided by at least one photovoltaic cell (9).

16. Apparatus according to claim 11, wherein the pre-cell voltage means (9) are designed to provide a voltage (UV) of less than 1.7 volts, preferably of less than 1.48 volts, particularly preferably of less than 1.23 volts, and/or that the main cell voltage means (9) are designed to provide a voltage (UH) in the range of 1 to 3 volts, preferably in the range of 1.7 to 2.7 volts, particularly preferably 1.2 to 1.3 volts.

17. Apparatus according to claim 11, wherein the pre-cell voltage means comprise at least one photovoltaic cell (9) or are given by at least one photovoltaic cell (9), and/or that the main cell voltage means comprise at least one photovoltaic cell (9) or are given by at least one photovoltaic cell (9).

18. Apparatus according to claim 11, wherein a separating device (17) connected upstream of the cathodic half-cell (6) of the main cell (2) is provided, so that water can be separated before it reaches the cathodic half-cell (6) of the main cell (2).

19. Apparatus (1) according to claim 11, wherein an evaporation device (13) connected upstream of the anodic half-cell (4) of the main cell (2) is provided, preferably, wherein the evaporation device (13) on the input side is fluidically connected to the anodic half-cell (4) of the pre-cell (3), and/or wherein the evaporation device (13) comprises at least one solar thermal collector (14).

20. Apparatus (1) according to claim 11, wherein at least one circulation pipe (12) is provided, by means of which nitrogen emerging from the cathodic half-cell (6) of the main cell (2) can be fed back to the input side of the cathodic half-cell (6).

Description

[0066] FIG. 1 a purely schematic representation of a first exemplary embodiment of an apparatus according to the invention, comprising two electrochemical cells; and

[0067] FIG. 2 is a purely schematic representation of a second embodiment of an apparatus according to the invention, comprising three electrochemical cells.

[0068] In the figures, the same components are provided with the same reference signs.

[0069] FIG. 1 shows in purely schematic representation a first example of an apparatus 1 for ammonia synthesis according to the invention, which comprises a main electrochemical cell 2 and a electrochemical pre-cell 3 connected upstream thereof.

[0070] The main cell 2 has an anodic half-cell 4 with an anode 5 and a cathodic half-cell 6 with a cathode 7. The two half-cells 4, 6 each define a reaction space in their interior and each have at least one inlet and at least one outlet, which are not visible in the purely schematic figure.

[0071] A cation exchange membrane 8 is arranged between the anodic 4 and the cathodic half-cell 6 of the main cell 2, which separates the two half-cells 4, 6 from each other and through which protons can pass from the anodic 4 into the cathodic half-cell 6 of the main cell 2 during operation. The anode 5 and cathode 7 are each pressed onto opposite sides of the membrane 8. The membrane 8 is a polymer membrane comprising nafion.

[0072] Both the anode 5 and the cathode 7 each have at least one catalyst material. In the embodiment shown, the anode 5 has Iridium Ir as the catalyst material, and the cathode 7 has Ruthenium Ru and Titanium Ti and Iron Fe.

[0073] Main cell voltage means for providing a main cell voltage U.sub.H between the anode 5 and the cathode 7 of the main cell 2 are further provided, which in the present case are given by a photovoltaic cell 9. The photovoltaic cell 9 is connected to the anode 5 and the cathode 7 via electrical conductors 10.

[0074] The electrochemical pre-cell 3 of the apparatus 1, which is connected upstream of the electrochemical main cell 2, is constructed completely analogously to the main cell 2, and accordingly also comprises an anodic half-cell 4 with an anode 5 and a cathodic half-cell 6 with a cathode 7, and a cation exchange membrane 8, which is arranged between the anodic and the cathodic half-cells 4, 6 and separates the two half-cells 4, 6 from one another. The two half-cells 4, 6 of the pre-cell 3 also each define a reaction space in their interior and each have at least one inlet and at least one outlet, which cannot be seen in the purely schematic figure. The membrane 8 of the pre-cell 3 also comprises nafion.

[0075] The anode 5 and the cathode 7 of the pre-cell 3 each have at least one catalyst material. The catalyst material of the anode 4 is iridium, again analogous to the main cell 2. A difference between the main and pre-cells 2, 3 exists in the catalyst material of the cathode 5. The cathode 5 of the pre-cell has only one catalyst material, specifically platinum.

[0076] Associated with the pre-cell 3 is another photovoltaic cell 9 of the apparatus 1, which forms pre-cell voltage means for providing a pre-cell voltage U.sub.V between the anode 5 and cathode 7 of the pre-cell 3. The associated electrical connection is provided via conductors 10.

[0077] The apparatus of FIG. 1 further comprises fluid connection means 11 for fluidically connecting the anodic half-cell 4 of the pre-cell 3 to the anodic half-cell 4 of the main cell 2, which in the example shown comprise or are provided by at least one fluid conduit, specifically at least one tube. Fluid connection means 11 are also provided for fluidically connecting the cathodic half-cell 6 of the pre-cell 3 with the cathodic half-cell 6 of the main cell 2, which here likewise comprise or are given by at least one fluid line, specifically at least one tube.

[0078] A circulation conduit 12 is associated with the main cell 2, which fluidically connects the outlet of its cathodic half-cell 6 with the inlet of its cathodic half-cell 6 to enable circulation.

[0079] In the shown example, the apparatus 1 also comprises an evaporation device 13 connected upstream of the anodic half-cell 4 of the main cell 2, which is fluidically connected on the input side to the anodic half-cell 4 of the pre-cell 3 and on the output side to the anodic half-cell 4 of the main cell 2. The evaporation device 13 comprises a solar thermal collector 14, a heat exchanger unit 15 and a heat transfer medium circuit 16. Heat transfer medium circulating through the circuit 16 during operation can be heated by means of the solar thermal collector 14 and release heat in the heat exchanger unit 15 in order to evaporate a liquid flowing through.

[0080] Furthermore, a separator unit 17 is provided downstream of the cathodic half-cell 4 of the pre-cell 3 and upstream of the cathodic half-cell 4 of the main cell 2. In the purely schematic FIG. 1, only a highly simplified representation of this is shown by a conduit for the drain of separated liquid which runs from the fluid connection means 11 connecting the two cathodic half-cells 6.

[0081] The apparatus shown in FIG. 1 can be used to carry out a first example of the method according to the invention. For this purpose, a pre-cell voltage U.sub.V of less than 1.23 V is applied between the anode 5 and cathode 7 of the pre-cell 3 and a main cell voltage U.sub.H in the range of 1.7 V to 2.7 V is applied between the anode 5 and cathode 7 of the main cell 2. The voltage is provided in an environmentally friendly and sustainable manner by means of the photovoltaic cells 9.

[0082] Water is supplied to the anodic half-cell 4 of the pre-cell 3 and, at the same time, nitrogen and oxygen in the form of air are supplied to the cathodic half-cell 6 of the pre-cell 3 by means of suitable conveying devices, such as pumps and/or blowers and/or compressors. In the shown example, water is supplied in liquid form. In the figure, this is indicated by a subscripted (f) after the H.sub.2O. The fact that the water is in a vapor state is indicated by H.sub.2O.sub.(d) in corresponding places. In the anodic half-cell 4 of the pre-cell 3, water is supplied in excess and oxygen is obtained, and in the cathodic half-cell 6 of the pre-cell 3, nitrogen and oxygen are supplied and the oxygen is reduced with protons and electrons to water. The cathode 7 of the pre-cell 3 serves as an oxygen-consuming cathode. The operating temperature in the pre-cell 3 can in particular be up to 90° C.

[0083] From the liquid water and oxygen leaving the anodic half-cell 4, the gaseous oxygen is separated, which is indicated by a branching arrow in FIG. 1, and the remaining water is evaporated in the evaporation device 13 and fed in vaporous state to the anodic half-cell 4 of the main cell 2. The evaporation is carried out using the solar thermal collector 14, i.e. by using solar energy, and is therefore also particularly environmentally friendly and sustainable.

[0084] From the nitrogen and water obtained in the cathodic half-cell 6 of the pre-cell 3, the liquid water is separated, which can be done very easily by means of the separation device 17, and the remaining nitrogen is fed to the cathodic half-cell 6 of the main cell 2, thus serving, in other words, as input for this half-cell 6. Water is fed to the anodic half-cell 4 of the main cell 2 and in an electrochemical reaction split into oxygen, protons and electrons. Water is fed in excess, therefore water and oxygen leave the half-cell 4 and in the cathodic half-cell 6 of the main cell 2 the nitrogen fed in excess reacts with protons and electrons to form ammonia. The operating temperature in the main cell 2 can in particular be about 30° C., which has proven to be especially suitable, since a particularly good performance of the cell can then be observed and the ammonia yield increases.

[0085] The ammonia produced is available for further use then. It can be fed to a storage facility.

[0086] Via the circulation pipe 12, nitrogen obtained in the cathodic half-cell 6 of the main cell 2 can be fed back to the input side of the cathodic half-cell 6 of the main cell 2 and used again as input for the latter.

[0087] FIG. 2 shows a second embodiment of an apparatus for the synthesis of ammonia according to the invention, which differs from that according to FIG. 1 essentially in that it comprises an intermediate cell 18 downstream of the pre-cell 3 and upstream of the main cell 2, i.e. another third cell, and in that the anode 5 in the anodic half-cell 6 of the main cell 2 of this apparatus is characterized by a catalyst material other than iridium, namely platinum.

[0088] The pre-cell 3 of the apparatus of FIG. 2 is identical in construction to the pre-cell 3 of the apparatus of FIG. 1, and the catalyst materials of anode 5 and cathode 7 of the latter are also identical to those of the pre-cell 3 of FIG. 1. They are identically designed cells.

[0089] The intermediate cell 18 of the apparatus of FIG. 2 is identical in construction to the pre-cell 3 of this apparatus—and thus also to the pre-cell 3 of FIG. 1—and has the same catalyst materials, namely iridium, as far as the anode 5 is concerned, and platinum, as far as the cathode 7 is concerned. In other words, the apparatus 1 of FIG. 2 has two identical electrochemical cells, which are used differently, which will be discussed in more detail below.

[0090] Associated with the intermediate cell 18 is yet another photovoltaic cell 9, which forms intermediate cell voltage means for providing an intermediate cell voltage U.sub.Z between the anode 5 and cathode 7 of the intermediate cell 18. Here, too, the associated electrical connection is established via electrical conductors 10.

[0091] The apparatus of FIG. 2 further comprises fluid connection means for the fluid connection of the anodic half-cell 4 of the pre-cell 3 with the anodic half-cell 4 of the intermediate cell 18 and fluid connection means for the fluid connection of the cathodic half-cell 6 of the intermediate cell 18 with the anodic half-cell 4 of the main cell 2. The fluid connection means here likewise comprise at least one fluid line, specifically at least one tube, or are provided thereby.

[0092] With the apparatus of FIG. 2, a second exemplary embodiment of the method according to the invention can be carried out. For this purpose, an intermediate cell voltage U.sub.Z in the range of 1.48 to 2 V is applied between the anode 5 and cathode 7 of the intermediate cell 18. The voltage is provided in an environmentally friendly and sustainable manner by means of the photovoltaic cell 9 associated with the intermediate cell 18.

[0093] Regarding the pre-cell 3, the procedure is exactly the same as in the first embodiment described above. That is, water H.sub.2O is supplied to the anodic half-cell 4 of the pre-cell 3 and, at the same time, nitrogen N.sub.2 and oxygen O.sub.2 in the form of air are supplied to the cathodic half-cell 6 of the pre-cell 3. In the shown example, water is supplied in liquid form. Oxygen is obtained in the anodic half-cell 4 of the pre-cell 3 and nitrogen and water in the cathodic half-cell 6 of the pre-cell 3. The cathode 7 of the pre-cell 3 of the apparatus shown in FIG. 2 thus also serves as an oxygen-consuming cathode.

[0094] Oxygen is separated from the water and oxygen leaving the anodic half-cell 4 of the pre-cell 3, which is again indicated by a branching arrow in FIG. 2, and the remaining water is fed in liquid state to the anodic half-cell 4 of the intermediate cell 18. In contrast, nothing is fed to the cathodic half-cell 6 of the intermediate cell 18.

[0095] In the anodic half-cell 4 of the intermediate cell 18, water is fed and oxygen is created in the electrochemical reaction, and in the cathodic half-cell 6 of the intermediate cell 18, hydrogen is created in an electrochemical reaction. At the same time, water permeates through the membrane and accumulates in the half-cell 6. The operating temperature in the intermediate cell 18 can in particular be up to 90° C.

[0096] Hydrogen obtained in the cathodic half-cell 6 of the intermediate cell 18 and water obtained therein are fed to the anodic half-cell 4 of the main cell 2. On the way to the main cell 2, any liquid water can be separated or evaporated in an evaporation device.

[0097] Exactly as in FIG. 1, the cathodic half-cell 6 of the main cell is supplied with nitrogen which was obtained in the cathodic half-cell 6 of the pre-cell 3. The nitrogen can pass from the cathodic half-cell 6 of the pre-cell 3 to the cathodic half-cell 6 of the main cell 2 via the fluidic connection means 11 between these two half-cells 6. Since the intermediate cell 18 plays no role on the cathode side, one can also say that it is connected between the pre-cell and the main cell 2 on the anode side.

[0098] In the example according to FIG. 2—again in accordance with FIG. 1—oxygen is obtained in the anodic half-cell 4 of the main cell 2 and ammonia in the cathodic half-cell 6 of the main cell 2. Here, the ammonia produced is then also available for further use. It can be supplied to a storage facility.

[0099] Via the circulation pipe 12, nitrogen exiting the cathodic half-cell 6 of the main cell 2 can be fed back to the input side of the cathodic half-cell 6 of the main cell 2 and used again as input for the latter.

[0100] The illustrated embodiments of apparatuses 1 according to the invention and the embodiments of methods according to the invention carried out therein enable the solar production of ammonia from air and water. They are characterized by sustainability and environmental friendliness.