ARRANGEMENT AND METHOD FOR PRODUCING A GAS-FORMED PRODUCT CONSISTING AMMONIA

Description

[0001] The present invention relates to an arrangement for producing a gaseous product being ammonia from first and second material, and a method for production of a gaseous product being ammonia by use of such arrangement, see claims 1 and 6.

[0002] Known approaches to the requirement for synthesis of ammonia include: (1) Haber Bosch process - pressurization and heating of N 2 and H2 over an iron catalyst; (2) Electrochemical synthesis with a molten salt electrolyte and gas electrodes [1-3]; and (3) Electrochemical synthesis with a solid electrolyte and eletrocatalytic electrodes [4-6]. [1] Murakami T., T. Nishikiori, T. Nohira, and Y. Ito, "Electrolytic Synthesis of Ammonia in Molten Salts Under Atmospheric Pressure", J. Amer. Chem. Soc. 125 (2) , pp. 334-335 (2003). [2] Murakami T. et al., "Electrolytic Ammonia Synthesis from Water and Nitrogen Gas in Molten Salt Under Atmospheric Pressure", Electrochim. Acta 50 (27), pp. 5423-5426 (2005). [3] US Patent 6,881,308 B2 [4] Marnellos,G., Zisekas,S., and Stoukides,M. (2000). Synthesis of ammonia at atmospheric pressure with the use of solid state proton conductors. J. Catal. 193, 80-88. doi:10.1006 / jcat.2000.2877 [5] Lan, R., Irvine, J.T.S., and Tao, S. (2013). Synthesis of ammonia directly from air and water at ambient temperature and pressure. Sci.Rep. 3, 1145. doi:10.1038 / srep01145 [6] Skodra, A., and Stoukides, M. (2009). Electrocatalytic synthesis of ammonia from steam and nitrogen at atmospheric pressure. Solid State Ionics 180, 1332-1336.

[0003] KR 101 392 828 B1, describes also such arrangement for producing a gaseous product from first and second material, and a method for production of a gaseous product being ammonia by use of such arrangement.

[0004] The present invention seeks to provide alternative methods and apparatus for the synthesis of ammonia from water and nitrogen N 2 .

[0005] Accordingly, the present invention provides an arrangement for producing a gaseous product being ammonia from first and second material, and a method for production of a gaseous product being ammonia by use of such arrangement as defined in claims 1 and 6.

[0006] Further preferred embodiments of the present invention are defined in the dependent claims.

[0007] The above, and further, objects, characteristics and advantages of the present invention will become more apparent from the following description of certain embodiments thereof, in conjunction with the appended claims wherein: Fig. 1 illustrates an exemplary electrochemical cell as provided by an embodiment of the present invention.

[0008] The embodiment of the invention shown in Fig. 1 comprises an electrochemical cell 10 with three porously partitioned volumes 1-3.

[0009] The first volume 1 contains a nitride conductor 20 such as a molten salt eutectic, for example LiCl / KCl / Li 3 N. In use, steam H 2 O is introduced into this first volume through a steam inlet 5. A steam diffuser 22 may be provided to ensure wide distribution of inlet steam.

[0010] The second volume 2 is a cathode gas electrode. Nitrogen gas N 2 26 is introduced into this gas electrode, on a surface of the porous electrode 24 away from the nitride conductor 20.

[0011] The third volume 3 is an anode gas electrode. A porous electrode 28 is in contact with the nitride conductor 20 on one side.

[0012] A DC power supply 7 applies a potential difference between the two porous electrodes 24, 28, with the more positive voltage +V being applied to the anode gas electrode 3 and the more negative voltage -V being applied to the cathode gas electrode 2. Typically, the applied potential difference may be in the region of 0.5 V to 2 V.

[0013] In use, nitrogen gas is reduced to nitride ions at the gas cathode 2: N2 + 6 e − = > 2 N 3 −

[0014] Within the nitride conductor 20, the nitride ions migrate towards the anode under the influence of the voltage gradient between the anode and the cathode. Within the nitride conductor 20, the nitride ions encounter and react with steam (water) to produce ammonia: 2 N 3 − + 3 H 2 O = > 2 NH 3 + 3 O 2 −

[0015] Ammonia is accordingly produced from nitrogen gas and steam. The ammonia diffuses through the nitride conductor 20 to be evolved at the surface of the nitride conductor. An enclosure 6 traps the evolved ammonia gas and allows it to be harvested. The resulting oxide ions migrate towards the anode under the potential gradient between the electrodes. The anode reaction returns electrons to the DC power supply and generates oxygen into the gas anode electrode: 2 O 2 − = > O 2 + 4 e − .

[0016] According to the present invention, a layer of solid oxide conducting material 4, such as yttria stabilised zirconia, is placed between the porous anode 28 and the nitride conductor 20. The layer of solid oxide conducting material may be bonded to the porous anode 28 or may simply be immersed in the nitride conductor. Oxide ions O 2-< diffuse through the electrically insulating porous material 4 to the anode 28 under the influence of the potential gradient between the anode 28 and the cathode 24. The O 2-< ions are able to diffuse through the layer of solid oxide conducting material, but water molecules cannot pass through this layer. Examples of suitable solid oxide conducting materials include yttria-stabilized zirconia (YSZ) (often the 8% form Y8SZ), scandia stabilized zirconia (ScSZ) (usually 9 mol% Sc 2 O 3 - 9ScSZ) and gadolinium doped ceria (GDC). Other options include perovskite materials such as La1-xSrxGa1-yMgyO3-δ (LSGM).

[0017] In oxide ion conductors, current flow occurs by the movement of oxide ions through the crystal lattice. This movement is a result of thermally-activated movement of the oxide ions, moving from crystal lattice site to crystal lattice site, with a superimposed drift in the direction of the electric field. The ionic conductivity of an oxide ion conductor is consequently strongly temperature dependent. At high temperatures, this conductivity can approach values close to 1 S.cm -1< , which is comparable to the levels of ionic conductivity found in liquid electrolytes.

[0018] The layer of solid oxide conducting material 4 shields the porous anode from the water molecules (steam) within the nitride conductor. In the absence of such an electrically insulating porous material shield, the following unwanted reduction would take place at the anode and would contaminate the evolved ammonia NH3 with hydrogen H2 as well as providing a competing side reaction thereby reducing the efficiency: 3 H 2 O = > 3 / 2 O 2 + 6 H + + 6 e −

[0019] Ammonia gas diffuses through nitride conductor 20 and is trapped in enclosure 6. It may be dried and cleaned as necessary, and may be stored for later use.

[0020] The structure of the electrochemical cell of the present invention allows steam H 2 O to be used as the source of hydrogen in the ammonia product, rather than hydrogen H 2 as was commonly the case in conventional methods and apparatus for synthesising ammonia. This enables the electrochemical synthesis of ammonia NH 3 without requiring a separate electrolysis stage to generate hydrogen H 2 , or the need to buy and store hydrogen H 2 , resulting in a much simpler system design.

[0021] A particular feature of the present invention is the layer of solid oxide conducting material 4 which acts as an electrode protector, preventing steam from reaching the anode. The layer of solid oxide conducting material should allow the passage of oxide ions O2- under the influence of the applied potential gradient, but not the diffusion of water molecules H2O.

[0022] In general, means are provided for introducing a first source material 5 (steam H 2 O) into the first volume 1 and means are provided for introducing a second source material 26 (nitrogen N 2 ) to a cathode 24. An electrolyte (in the form of the nitride conductor) is provided between anode 28 and cathode 24. Voltages +V and -V are applied respectively to the anode and cathode. At the cathode, a first ionic component (N 3-< ) is produced from the second source material. The first ionic component traverses the electrolyte under the influence of the voltage gradient between the anode and the ground electrode, towards the anode. Within the electrolyte, the first ionic component encounters the first source material, and a reaction takes place to generate a product (ammonia NH3) and an ionic by-product oxide ions O2-). The ionic by-product continues to traverse the electrolyte under the influence of the voltage gradient between the anode and the ground electrode, towards the anode. On reaching the anode, the ionic by-product gives up its charge and becomes an evolved by-product (oxagen O 2 ).

[0023] Means are provided to collect the product and preferably also the evolved by-product. Means may also be provided to collect any by-products generated at the anode or cathode.

Claims

1. An arrangement for producing a gaseous product from first and second source materials, wherein the first source material is steam H2O, the second source material is nitrogen N2, and the gaseous product is ammonia NH3, comprising: - an electrochemical cell comprising a first volume, a second volume and a third volume; wherein the second volume is a cathode gas electrode (24) and the third volume is an anode gas electrode (28); the electrochemical cell also being provided with an inlet (5) to allow the first source material into the first volume, wherein a layer of solid oxide conducting material (4) is positioned to impede the first source material from the inlet (5) from reaching the anode (28); - means (5, 22), including the inlet (5), for introducing the first source material into the first volume (1); - means (2, 24) for introducing a second source material (26) into the first volume (1); and - an electrolyte (20) provided in the first volume (1), the arrangement further comprising: - a power supply (7), arranged to apply a positive voltage +V to the anode (28), and to apply a negative voltage -V to the cathode (24); and - an enclosure (6) to trap the gaseous product.

2. An arrangement according to claim 1, wherein the layer of solid oxide conducting material comprises yttria stabilised zirconia.

3. An arrangement according to claim 1, wherein the layer of solid oxide conducting material comprises scandia stabilized zirconia (ScSZ), or gadolinium doped ceria.

4. An arrangement according to claim 1, wherein the layer of solid oxide conducting material comprises a perovskite material.

5. An arrangement according to any preceding claim wherein the inlet (5) is provided with a steam diffuser (22).

6. A method for production of a gaseous product, the gaseous product being ammonia, by use of an arrangement according to any preceding claim, wherein the cathode (24) is a gas electrode, and being a porous cathode and the second volume (2), the method comprising the steps of: - applying a positive voltage +V to the anode (28); - applying a negative voltage -V to the cathode (24); - introducing the first source material being steam H2O into the first volume (1); - introducing the second source material being nitrogen N2 into the second volume (2), said second source material reacting at the cathode to provide a first ionic component in the electrolyte in the first volume (1), wherein the first ionic component is nitride ions N3+; - generating the gaseous product being ammonia NH3 by reaction between the first ionic component and the first source material; and - collecting (6) the gaseous product produced in the first volume.

7. A method according to claim 6, further comprising the step of collecting a by-product generated at the anode.