Method of producing hydrogen

Abstract

The present invention relates to a method of producing hydrogen from ammonia, and in particular a method of producing hydrogen from ammonia for use in a fuel cell and/or in a prime mover. The method may be carried out in-situ in a vehicle. The invention also relates to an apparatus for producing hydrogen from ammonia.

Claims

1. A method of producing hydrogen from ammonia, the method comprising: (i) providing ammonia as a fuel source; (ii) introducing ammonia into a reactor; (iii) contacting at least some of the ammonia in the reactor with a metal-containing-compound to form hydrogen; (iv) removing at least some of the hydrogen formed in step (iii); and (v) contacting the metal-containing-compound with further ammonia; wherein the metal-containing-compound comprises one or more of Li, Be, Mg, Ca, Sr, Ba or alloys or mixtures of two or more thereof; wherein the metal-containing-compound is selected from a metal amide, metal imide, metal nitride or combinations thereof; and wherein the metal-containing-compound is regenerated prior to step (v).

2. The method according to claim 1, wherein the metal-containing-compound comprises one or more of Li, Be, Ca, Sr, Ba or alloys or mixtures of two or more thereof.

3. The method according to claim 1, wherein the metal-containing-compound comprises Li or alloys thereof.

4. The method of claim 1, wherein the metal-containing-compound comprises Be, Mg, Ca, Sr, Ba or alloys or mixtures of two or more thereof.

5. The method of claim 4, wherein the metal-containing-compound comprises Ca, Mg or alloys or mixtures of two or more thereof.

6. The method according to claim 1, wherein the metal-containing-compound is selected from a metal imide or metal nitride or combinations thereof.

7. The method according to claim 3, wherein the metal-containing-compound is a metal imide.

8. The method according to claim 1, wherein the metal-containing-compound comprises Li; and the metal-containing-compound is selected from a metal imide or metal nitride or combinations thereof.

9. The method according to claim 1, wherein the metal-containing-compound is provided by thermally decomposing a metal-containing-compound precursor.

10. The method according to claim 9, wherein the metal-containing-compound precursor is a metal amide.

11. The method according to claim 1, wherein step (iii) is carried out at a temperature in the range of from 30 to 800 C.

12. The method according to claim 1, wherein step (iii) is carried out at a temperature in the range of from 400 to 440 C.

13. The method according to claim 1, wherein step (iii) is carried out at a pressure in the range of from 0.05 to 20 MPa.

14. The method according to claim 1, wherein step (iii) is carried out at a pressure in the range of from 0.1 to 0.2 MPa.

15. The method according to claim 1, wherein ammonia is introduced into the reactor at a temperature in the range of from 30 to 800 C.

16. The method according to claim 1, wherein ammonia is introduced into the reactor at a temperature in the range of from 400 to 440 C.

17. The method according to claim 1, wherein ammonia is introduced into the reactor at a pressure in the range of from 0.05 to 20 MPa.

18. The method according to claim 1, wherein ammonia is introduced into the reactor at a pressure in the range of from 0.1 to 0.2 MPa.

19. The method according to claim 1, wherein the molar ratio of metal-containing-compound to ammonia is in the range of from 1:1 to 2:1.

20. The method according to claim 1 wherein the method is carried out in-situ in a vehicle.

21. The method according to claim 1, further comprising introducing the removed hydrogen into a fuel cell or a prime mover.

22. The method according to claim 1, further comprising combusting the removed hydrogen.

23. The method according to claim 1, wherein the ammonia is in a gaseous and/or liquid state.

24. The method according to claim 1, wherein ammonia is introduced into the reactor by injection, pumping, spraying and/or by mechanical means.

25. The method according to claim 1, further comprising refuelling the ammonia fuel source.

26. The method according to claim 1, wherein the metal-containing-compound is in the faun of a solid, liquid or dispersed form.

27. The method according to claim 1, wherein step (iii) is carried out in the absence of a catalyst.

28. The method according to claim 1, wherein step (iii) is carried out in the presence of a catalyst.

29. The method according to claim 28, wherein the catalyst comprises one or more transition metals, lanthanide metals and mixtures thereof.

30. The method according to claim 29, wherein the catalyst is selected from the group consisting of transition metal calogenides, lanthanide metal calogenides, transition metal halides, lanthanide metal halides, transition metal pnictides, lanthanide metal pnictides, transition metal tetrels, lanthanide metal tetrels and mixtures of two or more thereof.

31. The method according to claim 1, wherein the metal-containing-compound and/or a precursor thereof is introduced into the reactor.

32. The method according to claim 31, wherein the metal-containing-compound and/or a precursor thereof is introduced into the reactor by pumping (preferably electromotively), spraying, or is mechanically introduced.

33. The method according to claim 1, further comprising removing hydrogen formed by the contacting of ammonia with the metal-containing-compound from the reactor.

34. The method according to claim 1, wherein the metal imide includes stoichiometric and/or non-stoichiometric imides of the formula M(3-a)NHa where 1a <2 when M is Li and of the formula M(NHb)b where 1b<2 when M is one or more of Be, Mg, Ca, Sr, Ba.

Description

(1) These and other aspects of the invention will now be described with reference to the accompanying Figures, in which:

(2) FIG. 1: is a schematic diagram of an apparatus for carrying out an embodiment of the method of the present invention.

(3) FIG. 2: is a schematic diagram of a reactor for carrying out the process of the present invention.

(4) FIG. 3: shows an alternative design of a reactor for carrying out the method of the present invention where ammonia is fed through the molten metal-containing-compound.

(5) FIGS. 4 and 5: are schematic diagrams of reactors for carrying out an embodiment of the method of the present invention.

(6) FIG. 6: is a graph showing the conversion of flowing ammonia (NH.sub.3, 60 sccm) to nitrogen (N.sub.2) and hydrogen (H.sub.2) as a function of temperature.

(7) FIG. 7: is a graph showing the conversion of ammonia to hydrogen at different flow rates of ammonia at different temperatures.

(8) FIG. 8: is a graph showing the conversion of ammonia to hydrogen at different masses of metal-containing-compound at different temperatures.

(9) FIG. 9: is a graph showing the conversion of ammonia to hydrogen at different temperatures.

(10) FIG. 10: is a graph comparing the conversion of ammonia to hydrogen by thermolysis (no metal-containing-compound present), by reaction with sodium amide or by reaction with lithium imide (with lithium amide precursor).

(11) FIGS. 11, 12 and 13: are cross-sectional diagrams of a reactor for carrying out an embodiment of the present invention.

(12) FIG. 14: is a graph comparing the conversion of ammonia to hydrogen by thermolysis (no metal-containing-compound present), by reaction with sodium amide, by reaction with lithium imide (with lithium amide precursor), or by catalysis by ruthenium or nickel.

(13) FIG. 15: shows corresponding graphs and a chart which show the results from a neutron powder diffraction experiment on the decomposition of ammonia by lithium imide, showing a) the temperature (black) and gas flow (grey), b) the gas species used during the experiment, c) the ammonia conversion efficiency and d) a contour plot of a section of the diffraction data, showing characteristic (111) and (002) diffraction peaks for lithium imide, with the colour bar to the right indicating the intensity of the diffraction signal.

(14) FIG. 16: is a graph showing a comparison of ammonia conversion as a function of reaction temperature (between 250 C. and 600 C.) for the blank 46.9 cm3 nickel-coated stainless steel reactor and 0.5 g of Li.sub.2Mg(NH).sub.2, Li.sub.2Ca(NH).sub.2, LiNH.sub.2, NaNH.sub.2, at an ammonia flow rate of 60 sccm.

(15) As outlined above, FIG. 1 is a schematic diagram of an apparatus for carrying out an embodiment of the process of the present invention.

(16) The apparatus comprises a reactor (1) containing a metal-containing-compound (2); a fuel source reservoir (3) containing ammonia (4) as a fuel. A flowline (5) connects the reservoir (3) to the reactor (1) for introducing the fuel into the reactor (1). An energy source (6) is coupled to the reactor (1) and is arranged to input energy into the reactor (1) in order to promote the reaction of ammonia (4) and metal-containing-compound (2) to form hydrogen. The apparatus also comprises a hydrogen outlet (7) from the reactor (1) for removing hydrogen from the reactor (1).

(17) Optionally an additional flowline may be provided into reactor (1) for introducing the metal-containing-compound into the reactor (1).

(18) FIG. 2 shows a schematic diagram of a reactor for carrying out an embodiment of the process of the present invention. In this embodiment, one or more metal-containing-compounds (260) is placed in the reactor. Ammonia gas is introduced via flowline (250). Cool nitrogen may be introduced via flowline (210) and/or (220). An energy source (270), which may be for example a furnace, heater, electromagnetic pump and/or electrochemical cell is arranged to input energy into the reactor. Metal-containing-compound vapour (240) may be produced from a molten metal-containing-compound which reacts with the ammonia to form hydrogen (230) and the metal-containing-compound is recycled to react with further ammonia. Hydrogen is removed via flowline 200. The hydrogen removed may be transferred to a mass spectrometry machine for detecting hydrogen and any ammonia present.

(19) FIG. 3 shows an alternative design of a reactor where ammonia is fed through the molten metal-containing-compound. Such a design may be preferred as it reduces or potentially eliminates the problem of surface tarnishing of the molten metal-containing-compound. It may also simplify the reactor design. Preferably, the ammonia in-pipe has a swan neck or straight ammonia feed line that lies below the surface level of the liquid metal-containing-compound, to keep the metal-containing-compound molten within the hot zone but allow ammonia to bubble through the molten metal-containing-compound. In this embodiment one or more metal-containing-compounds (360) is placed in the reactor. Ammonia gas is introduced via flowline (350). Cool nitrogen may be introduced via flowline (310) and/or (320). An energy source (370), which may be for example a furnace, heater, electromagnetic pump and/or electrochemical cell is arranged to input energy into the reactor in order to promote the reaction of ammonia (4) and metal-containing-compound (2) to form hydrogen (330), and the metal-containing-compound is recycled to react with further ammonia. Hydrogen is removed via flowline 300. The hydrogen removed may be transferred to a mass spectrometry machine for detecting hydrogen and any ammonia present.

(20) The key for FIG. 4 is given below: 400: To mass spec detecting N.sub.2, H.sub.2 and NH.sub.3 405: Hot ammonia gas (Furnace temperature) Inlet 410: Cool N.sub.2 in 415: 316 stainless steel 420: Metal-containing-compound comprising Li, Be, Mg, Ca, Sr, Ba 425: RT (room temperature) to 800 C., 0.1 MPa NH.sub.3/N.sub.2 430: 300 mm 435: Cu gasket 440: Thermocouple 445: Wells 450: 100 mm 455: N.sub.2 and H.sub.2 460: External Tube Furnace 465: 20 mm 470: Molten metal-containing-compound 475: Metal-containing-compound vapour

(21) The key for FIG. 5 is given below: 500: To mass spec detecting N.sub.2, H.sub.2 and NH.sub.3 505: Hot ammonia gas (Furnace temperature) Inlet 510: Cool N.sub.2 in 515: 316 stainless steel 520: Metal-containing-compound comprising Li, Be, Mg, Ca, Sr, Ba 525: RT to 800 C., 0.1 MPa NH.sub.3/N.sub.2 530: 300 mm 535: Cu gasket 540: Thermocouple 545: Wells 550: 100 mm 555: N.sub.2 and H.sub.2 560: External Tube Furnace 565: 20 mm 570: Molten metal-containing-compound 575: Metal-containing-compound vapour

(22) The key for FIG. 11 is given below: 600: Thermal Couple Housing 605: 100 CF Top Blank 610: 100 CF Furnace Vessel Flanges 615: Large Furnace Tube (258.5 mm long) 620: Long Thermal Couple Pocket (280 mm long) 625: Short Thermal Couple Pocket (70 mm long) 630: Furnace Base 635: Parker Buttweld 640: Parker Buttweld 645: Minimise Trapped Volumes 650: Flush Fit to Minimise Trapped Volumes 655: 47.0 mm 660: 95.0 mm 665: 250.0 mm

(23) The key for FIG. 12 is given below: 700: Details AS DN100 CF Flange 705: Details AS DN100 CF Flange 710: M8x55 Hex Bolts 715: 2 Off Welded in Thermocouple pockets for Top and Bottom Level Sensing. Internal Diameter 1.8 mm 720: Parker Hannifin ZHBW2 6 Buttweld Connector 725: Parker Hannifin ZHBW2 4 Buttweld Connector. 3 Off. 730: DN100 CF Copper Gasket 735: 250 mm 740: 95 mm 745: 5 mm 750: 152 mm 755: 47 mm 760: 20 mm 765: Reactor

(24) The key for FIG. 13 is given below: 800: Reactor

(25) The foregoing detailed description has been provided by way of explanation and illustration, and is not intended to limit the scope of the appended claims. Many variations in the presently preferred embodiments illustrated herein will be apparent to one of ordinary skill in the art, and remain within the scope of the appended claims and their equivalents.

(26) The following non-limiting examples further illustrate the present invention.

EXAMPLES

Example 1

(27) Ammonia decomposition reactions were performed in a cylindrical stainless steel (316 L) reactor with an internal volume of 46.93 cm.sup.3, with a gas-in pipe running to approximately 0.5 cm from the base of the reactor, gas outlet from the lid, and a thermocouple monitoring the internal temperature at the point of gas inlet. Ammonia gas (0.1 MPa (1 bar), 99.999%) supply to the reactor was via a custom-designed gas control panel where the inlet flow was controlled using a mass flow controller (Hastings Instruments) and the outlet gas flow is measured using a mass flow meter (Hastings Instruments); the flow is recorded in standard cubic centimetres per minute (sccm). The gas species leaving the reactor were characterised using a Hiden Analytical HPR-20 R&D Mass Spectrometer System.

(28) The solid sample was loaded into a reactor under an argon atmosphere. The reactor was then sealed and transferred to a standard upright furnace and connected to the gas control panel. The panel and reactor were first flushed with argon, then ammonia, prior to heating. Decomposition experiments were performed under 1 bar of flowing ammonia, at flow rates set by the mass flow controller. The percentage conversion of ammonia is calculated by expressing the NH.sub.3 signal as a percentage of the sum of the partial pressures for NH.sub.3, H.sub.2 and N.sub.2 (corrected for baseline levels). The percentage conversion of ammonia is then calculated as 100% minus the calculated ammonia percentage.

(29) FIG. 6 shows mass spectroscopy data showing that at all temperatures the amide/imide converts the flowing ammonia to nitrogen and hydrogen. Above 320 C. the conversion becomes very rapid and reaches 100% efficiency at approximately 480 C.

(30) FIG. 7 shows the variable-flow ammonia decomposition performance for six temperatures, using 0.5 g of lithium amide and 0.1 MPa (1 bar) of ammonia.

(31) FIG. 8 shows a comparison of the variable-temperature ammonia decomposition performance for different starting masses of lithium amide, under 60 sccm ammonia flow at 0.1 MPa (1 bar).

(32) FIG. 9 shows the variation in percentage ammonia decomposition with temperature for 0.5 g lithium amide under 60 sccm of ammonia flow at 0.1 MPa (1 bar). The system was allowed to equilibrate at each temperature for 2 hours.

(33) FIG. 10 shows the variation in percentage ammonia decomposition with temperature for 0.5 g sodium amide, 0.5 g lithium amide (precursor of lithium imide) and an empty reactor (thermolysis). These data are compared with the theoretical conversion values calculated using the standard thermodynamic parameters for the decomposition of ammonia/sodium amide. FIG. 10 shows that ammonia decomposes to produce hydrogen in the presence of lithium amide/imide at a lower temperature than in the presence of sodium amide.

Example 2

(34) The ammonia decomposition activity of lithium amide/imide was tested in an identical manner to that described in Example 1, with flowing ammonia gas passing over the amide/imide in a stainless steel Dreschel bottle design. The variable-temperature ammonia decomposition efficiency of 0.5 g lithium amide compared with an equivalent mass of sodium amide, supported nickel and ruthenium catalysts, and the empty reactor is shown in FIG. 14. The ammonia flow rate was constant at 60 sccm for all of the samples. Lithium amide/imide gives high conversion at moderate temperatures, reaching 90.7% conversion at 458 C., compared with 54.9% for sodium amide, 53.7% for ruthenium on alumina, and 34.0% for the blank reactor. At low temperatures, sodium amide and ruthenium catalyst show superior performance. However, lithium amide/imide shows a steeper conversion curve than the other systems in FIG. 14. It is clear that lithium amide displays superior ammonia decomposition activity (high conversion) at higher temperatures.

(35) The superior properties of the lithium amide/imide may be attributable to the reaction mechanism. This was investigated and a summary of the results shown in FIG. 15. FIG. 15 shows a section of Neutron Powder Diffraction (NPD) data showing the (111) and (002) reflections of Li.sub.2ND, along with the temperature, gas flow, input gas species and the ammonia conversion efficiency over the course of the reaction. At 550 C., the sample remains crystalline throughout the ammonia decomposition experiment. The ammonia conversion efficiency was around 75%, compared with 39% using the same reaction conditions with the blank sample cell. Clearly the sample was involved in the enhanced decomposition of the ammonia in this experiment. Interestingly, the efficiencies for both the empty reactor and the catalyst are lower than those presented in FIG. 14. This may be as a result of the different geometry of the reaction zone and/or the difference in the reaction kinetics between using NH.sub.3 or ND.sub.3.

(36) The lithium amide/imide system is thought to form a continuum of non-stoichiometric intermediates (Li.sub.(1+x)NH.sub.(2x), 0x1) which have the same average cubic structure as high-temperature lithium imide, but with an increased cubic lattice parameter as the stoichiometry approaches that of lithium amide. Therefore, the lattice parameter is a good guide to the stoichiometry of the sample when measured under isothermal conditions. As the temperature of the ammonia decomposition reaction is lowered, the stoichiometry of the sample moves towards more amide-like stoichiometry. As this occurs, the sample will eventually melt. However, as shown by FIG. 15, at higher temperatures, lithium imide remains solid while decomposing ammonia.

(37) From the perspective of practicality, the ability to keep the metal-containing-compound solid at high temperatures has important implications, potentially giving a lithium-based amide/imide an additional advantage over the sodium system, along with the higher conversion efficiency. Working with a solid metal-containing-compound may allow for traditional methods used in catalysis to be applied in order to achieve higher turnover frequency, e.g. nanosizing and complex support structures. The task of containing the metal-containing-compound is also significantly simpler.

(38) For instance, a typical experimental run with sodium amide (99.75% conversion, 600 C., 100 sccm NH.sub.3) results in material recoveries as low as 0.1%, as the sodium amide ends up coating the reactor and outlet tubing with a fine coating of powder. In contrast, lithium imide, which is heated to 500 C. under argon before switching to ammonia in order to avoid amide formation, shows material recoveries in excess of 80% after similar reaction conditions (99.85% conversion, 590 C., 100 sccm NH.sub.3).

Example 3

(39) Lithium magnesium imide (Li.sub.2Mg(NH).sub.2) and lithium calcium imide (Li.sub.2Ca(NH).sub.2) were formed by the reaction of lithium amide and the magnesium/calcium hydride:
2LiNH.sub.2+(Mg/Ca)H.sub.2Li.sub.2(Mg/Ca)(NH).sub.2+2H.sub.2

(40) The variable-temperature ammonia decomposition efficiency of 0.5 g of the lithium-calcium and lithium-magnesium imides were tested in the same manner as that described for each of Examples 1 and 2. The results are shown in FIG. 16 and show that the performance of both ternary imides is superior at low temperatures compared to sodium amide. Above 430 C. the lithium-calcium imide tracks the performance of lithium amide-imide quite closely.

(41) The recovery of the lithium-calcium imide was almost quantitative (96%). This is significant in light of the fact that the decomposition performance was equivalent to lithium amide-imide, making it particularly advantageous.

(42) The results indicate that calcium imide is also likely to show good ammonia decomposition performance.