The present invention relates to apparatus for synthesis of ammonia N¾ . The present invention also relates to processes for synthesis of ammonia N¾ .

Known approaches to the requirement for synthesis of ammonia include :

(1) Haber Bosch process - pressurization and heating of N2 and ¾ 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/j cat .2000.2877

[5] Lan, R., Irvine, J.T.S., and Tao, S. (2013). Synthesis of 30 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. The present invention seeks to provide alternative methods and apparatus for the synthesis of ammonia from hydrogen ¾ and nitrogen N ₂ .

Accordingly, the invention provides methods and apparatus as defined in the appended claims. 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 arrangement for synthesis of ammonia according to an embodiment of the present invention; and

Fig. 2 illustrates an alternative valve arrangement. Fig. 1 shows an embodiment of the present invention, illustrating a dual-piston reciprocal arrangement for synthesis of ammonia.

Cylinders 1 are each provided with a piston 2, which is preferably gas-tight, driven by an associated piston rod 6. The piston rods 6 are driven in anti-phase by linear electric motor 7. A controller 8 is provided to control operation of the linear electric motor 7. Within each cylinder is provided a catalyst 3, for promoting the reaction N2 + 3H ₂ => 2N¾, such as iron (Fe) or rhodium (Rh) . Preferably, the catalyst is provided in a porous form. A stoichiometric mixture of nitrogen and hydrogen is provided at inlet valve 4 for each cylinder. An outlet valve 5 is also provided for each cylinder, to enable the synthesised ammonia to be retrieved.

In operation, starting the cycle at an arbitrary location, the piston 2 is withdrawn and inlet valve 4 is opened. This may, for example, be by operation of an electrically-operated valve under control of controller 8, or may be a mechanical valve opening by mechanical interaction with the linear motor 7. Once the piston is withdrawn to its fullest extent, inlet valve 4 closes. The cylinder is then filled with the stoichiometric mixture of hydrogen and nitrogen. The piston 2 is then driven back into the cylinder 1 with inlet valve 4 closed and outlet valve 5 closed. The resulting compression of the gas mixture causes heating. The heated gas mixture, in contact with the catalyst 3, reacts to produce ammonia. The piston 2 is again withdrawn, cooling the synthesised ammonia. Outlet valve 5 is opened. This may, for example, be by operation of an electrically-operated valve under control of controller 8, or may be a mechanical valve opening by mechanical interaction with the linear motor 7. The synthesised ammonia is exhausted from the cylinder 1 by the piston 2 being driven back into the cylinder. As the piston 2 begins to withdraw again, inlet valve 4 opens to admit a new volume of stoichiometric mixture of nitrogen and hydrogen, and the process repeats. As shown in Fig. 2, there may be provided two cylinders operated in antiphase by a linear motor 7 under control of a controller 8. The valves may be electrically controlled by the controller, or may be mechanically controlled by mechanical interaction with the linear motor 7. The ammonia exhausted through outlet valve 5 may be directed to a storage arrangement.

Although two pistons, as illustrated, operated in anti-phase, provide a more regular flow of gases through the inlet and outlet valves 4, 5, the present invention may be embodied as a single piston operated by a linear motor.

The catalyst 3 is provided to ensure a suitable reaction rate which enables useful synthesis of ammonia during a piston cycle. The use of a piston provides a convenient and efficient means for applying heat to the gas mixture. The invention may be operated without the catalyst 3, although the rate of generation of the ammonia will fall accordingly.

The nitrogen and hydrogen raw materials may be provided from any convenient source. The hydrogen may be generated from electrolysis of water. The apparatus of the present invention may be employed to synthesise ammonia as an energy storage medium. For example, electrical generators in the form of renewable energy sources such as wind turbines or solar panels may generate electricity intermittently, out of synchronisation with demand for energy. Such electrical generators may be employed to generate ammonia by use of the equipment and method of the present invention, and the generated ammonia may later be combusted in an energy recovery step. Other valve arrangements, different from those shown in Figs. 1, 2 may be employed. For example, Fig. 2 illustrates an alternative valve arrangement in which inlet valve 4' and outlet valve 5' are uncontrolled unidirectional mechanical valves such as flap valves, and a controlled valve 10 is provided to allow access to and from the chamber 1. In an inlet phase, controlled valve 10 is open and the piston withdraws from the cylinder, reducing pressure in the cylinder. This reduced pressure keeps outlet valve 5' closed and causes inlet valve 4' to open, allowing the mixture of hydrogen gas ¾ and nitrogen gas 2 to enter the cylinder. During a compression phase, the controlled valve 10 is closed. During an expansion phase, the controlled valve 10 remains closed. During an exhaust phase, controlled valve 10 is opened. The piston is driven into the cylinder, causing an increase in gas pressure within the cylinder. This increased pressure holds inlet valve 4' closed and causes outlet valve 5' to open, allowing the synthesised ammonia to exhaust from the cylinder. Other valve arrangements may be provided, as will be apparent to those skilled in the art. Controlled valve 10 may be electrically controlled by a controller, or may be mechanically controlled by mechanical interaction with a motor driving the piston 2. The invention has been described with particular emphasis on introducing a nitrogen / hydrogen mixture in stoichiometric ratio. The invention may be operated with the mixture of gases in another ratio, in which case the ammonia exhausted from the ammonia synthesis apparatus of the present invention will include some unreacted gas. For safety considerations, it would be preferable if nitrogen were present in excess, rather than hydrogen. A later step, for example liquefaction of ammonia, may be employed to separate the synthesised ammonia from unreacted nitrogen or hydrogen.

Further modifications and variations are possible, within the scope of the invention as defined by the appended claims, as will be apparent to those skilled in the art.