Method for producing hydrogen from ammonia

Abstract

The present invention relates to a method of producing hydrogen from ammonia, and in particular a method of producing hydrogen from ammonia by reacting it with a Group I metal, particularly with sodium, 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 and reacting at least some of the ammonia with a metal and/or a metal-containing-compound to form at least one intermediate and optionally hydrogen; (iii) decomposing at least some of the intermediate produced in step (ii) to form hydrogen and to regenerate the metal and/or the metal-containing-compound; (iv) removing at least some of the hydrogen formed in step (iii); and (v) reacting the regenerated metal and/or the regenerated metal-containing-compound with further ammonia; wherein the metal and/or the metal-containing-compound comprises or is selected from the group consisting of Group I metals; wherein the Group I metal is selected from the group consisting of Na, Li, K, Rb, Cs, alloys and mixtures of two or more thereof; wherein the reaction of the at least some ammonia with the metal and/or the metal-containing-compound to form the at least one intermediate is carried out at a temperature in the range of from 450 to 800 C. and at a pressure of 0.01 to 20 MPa.

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

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

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

5. The method according to claim 1 wherein the at least one intermediate is a stable, isolatable intermediate.

6. The method according to claim 1 wherein the at least one intermediate is a metal amide.

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

8. The method according to claim 1 wherein the Group I metal is Na.

9. The method according to claim 1 wherein the reaction of the at least some ammonia with a metal and/or metal containing compound to form at least one intermediate is carried out in the presence of a catalyst.

10. The method according to claim 9 wherein the catalyst comprises one or more transition metals, lanthanide metals and mixtures thereof.

11. The method according to claim 10 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.

12. The method according to claim 1 wherein the at least some ammonia is introduced into the reactor such that the molar ratio of ammonia to metal and/or metal-containing-compound is in the range of from 1:1 to 1:2.

13. The method according to claim 1 further comprising removing hydrogen formed by the reaction of ammonia with the metal and/or the metal-containing-compound from the reactor.

14. The method according to claim 1 wherein at least some of the intermediate formed in step (ii) is decomposed to form hydrogen and to regenerate at least some of the metal and/or the metal-containing-compound by electrochemical, thermal, microwave, mechanical, impact, combustion, detonation and/or ultrasound means.

15. The method according to claim 1 wherein hydrogen is provided at the point of use or into a distributed network.

16. A method of producing hydrogen from ammonia the method comprising: (i) providing ammonia as a fuel source; (ii) introducing ammonia into a reactor and reacting at least some of the ammonia with a metal and/or a metal-containing-compound to form at least one intermediate and optionally hydrogen; (iii) decomposing at least some of the intermediate produced in step (ii) to form hydrogen and to regenerate the metal and/or the metal-containing-compound; (iv) removing at least some of the hydrogen formed in step (iii); and (v) reacting the regenerated metal and/or the regenerated metal-containing-compound with further ammonia; and wherein the reaction of the at least some ammonia with a metal and/or metal containing compound to form at least one intermediate is carried out in the presence of a catalyst; and 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.

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 the process according to the present invention.

(3) FIG. 2: is a schematic diagram of an apparatus for carrying out an embodiment of the process of the present invention. In this embodiment only one reactor is used in the hydrogen production.

(4) FIG. 3: is a schematic diagram of an apparatus for carrying out an embodiment of the process of the present invention. In this embodiment two reactors are used in the hydrogen production. In the first reactor the intermediate, preferably a metal amide is formed. The intermediate is then transferred to a second reactor where the intermediate is decomposed to release hydrogen and to regenerate the metal and/or the metal-containing compound.

(5) FIG. 4: is a schematic diagram of a reactor for carrying out the process of the present invention. In this embodiment only one reactor is used in the hydrogen production.

(6) FIG. 5: shows an alternative design of a reactor where ammonia is fed through the molten sodium.

(7) FIGS. 6 and 7: are schematic diagrams of reactors for carrying out an embodiment of the process of the present invention. In these embodiments only one reactor is used in the hydrogen production.

(8) FIG. 8: is a graph showing the incomplete conversion of ammonia to nitrogen and hydrogen at 250 C., ammonia flow rate 10 sccm.

(9) FIG. 9: is a graph showing that increasing the flow of ammonia to 40 sccm decreases the relative partial pressure of nitrogen and hydrogen.

(10) FIG. 10: is a graph showing that when the temperature is raised to 450 C., total conversion of ammonia to nitrogen and hydrogen may be observed.

(11) FIG. 11: is a graph showing that the rate of ammonia conversion to nitrogen and hydrogen may be controlled through temperature.

(12) FIGS. 12, 13 and 14: are cross-sectional diagrams of a reactor for carrying out an embodiment of the present invention. In these embodiments only one reactor is used in the hydrogen production.

(13) As outlined above, FIG. 2 is a schematic diagram of an apparatus for carrying out an embodiment of the process of the present invention. In this embodiment only one reactor is used in the hydrogen production.

(14) The apparatus comprises a reactor (1) containing metal and/or 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 produce decomposition of intermediate formed in the reactor (1) by reaction of the metal and/or a metal-containing-compound (2) with ammonia (4). The apparatus also comprises a hydrogen outlet (7) from the reactor (1) for removing hydrogen from the reactor (1).

(15) Optionally an additional flowline may be provided into reactor (1) for introducing the metal and/or a metal-containing-compound into the reactor (1).

(16) As outlined above, FIG. 3 is a schematic diagram of an apparatus for carrying out an embodiment of the process of the present invention. In this embodiment two reactors are used in the hydrogen production. In the first reactor (10) the intermediate, preferably a metal amide is formed. The intermediate is then transferred to a second reactor (80) where the intermediate is decomposed to release hydrogen and to regenerate the metal and/or the metal-containing compound.

(17) In FIG. 3 the apparatus comprises a first reactor (10) containing metal and/or a metal-containing-compound (20) and a second reactor (80). A fuel source reservoir (30) containing ammonia (40) as a fuel is connected to reactor (10) by a flowline (50) for introducing the fuel into the reactor (10) in order to produce the reaction of the ammonia (40) and the metal and/or a metal-containing-compound (20) to form the intermediate, which is preferably a metal amide. The apparatus optionally comprises a hydrogen outlet (70) from the reactor (10) for removing hydrogen from the reactor (10). A second flowline (90) connects the first (10) and second reactor (80) for transferring intermediate formed in the first reactor (10) to the second reactor (80). The energy source (100) is arranged to input energy into the reactor (80) in order to produce decomposition of the intermediate, which is preferably a metal amide, formed in the first reactor (10) by reaction of the metal and/or metal-containing-compound (20) with ammonia (40). At least one hydrogen outlet (110) is connected to the second reactor (80) for removing hydrogen from the reactor (80). The apparatus further comprises a recycle flowline (120) from the second reactor (80) to the first reactor (10) for transferring metal and/or the metal-containing-compound regenerated from the decomposition of the intermediate to the first reactor (10).

(18) Optionally an additional flowline may be provided into reactor (10) for introducing the metal and/or a metal-containing-compound into the reactor.

(19) Optionally an additional energy source may be coupled to the first reactor (10) and arranged to input energy into the first reactor (10).

(20) FIG. 4 shows a schematic diagram of a reactor for carrying out an embodiment of the process of the present invention. In this embodiment only one reactor is used in the hydrogen production. In this embodiment sodium (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. Sodium vapour (240) may be produced from molten sodium which reacts with the ammonia. An intermediate is formed which decomposes to provide nitrogen and hydrogen (230) and the sodium 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.

(21) Preferably the reactor is operated at a temperature of from 150 to 500 C., or from 220 C. to 500 C., or from 250 to 500 C.

(22) FIG. 5 shows an alternative design of a reactor where ammonia is fed through the molten sodium. Such a design may be preferred as it allows a higher intermediate formation:NH.sub.3 ratio to be formed and reduces or potentially eliminates the problem of surface tarnishing of the molten sodium. It may also simplify the reactor design.

(23) Preferably, the ammonia in-pipe has a swan neck or straight ammonia feed line that lies below the surface level of the liquid metal M, to keep the sodium molten within the hot zone but allow ammonia to bubble through the molten sodium. In this embodiment sodium (360) is placed in the reactor.

(24) 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. An intermediate is formed which decomposes to provide nitrogen and hydrogen (330) and the sodium 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.

(25) Preferably the reactor is operated at a temperature of from 150 to 500 C., or from 220 to 500 C., or from 250 to 500 C.

(26) The key for FIG. 6 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 420: 18.54 g (20 cm.sup.3) molten sodium 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 sodium 475: Na Vapour

(27) The key for FIG. 7 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 520: 18.54 g (20 cm.sup.3) molten sodium 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 sodium 575: Na Vapour

(28) The key for FIG. 12 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

(29) The key for FIG. 13 is given below: 700: Details AS DN100 CF Flange 705: Details AS DN100 CF Flange 710: M855 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

(30) The key for FIG. 14 is given below: 800: Reactor

(31) 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.

(32) The following non-limiting example further illustrates the present invention.

EXAMPLE 1

(33) A stainless steel reactor (100 mm OD, 300 mm in height) is pre-loaded with 18.54 g (20 cm.sup.3 when liquid) of pristine sodium metal in an inert (N2, Ar or He) atmosphere. The reactor is isolated from the atmosphere and connected to a gas handling panel and then evacuated to a pressure of 0.6-1 kPa. The sodium may be cleaned/pre-reacted in 100 kPa flowing (60 sccm (Standard Cubic Centimeters per Minute)) hydrogen gas at 300 C. to reduce the surface of the sodium metal and/or create NaH for reaction initiation on the surface of the sodium metal, although this step is not essential. If the system is pre-treated with hydrogen, the apparatus is then evacuated again to a pressure of 0.6-1 kPa before the introduction of ammonia. The bottom half of the reactor is then heated to 500 C. and the top half continuously flushed with room temperature, high purity, dry nitrogen buffer gas (100 kPa). A 1 cm.sup.3/sec (60 sccm) flow of high purity, dry ammonia gas (H.sub.2O<1 ppm), controlled by a mass flow controller, is heated to 500 C. and then delivered into the sodium reactor either into the volatilised vapour of sodium above the molten metal (Reactor 1) or below the level of the liquid sodium and bubbled through the liquid sodium (Reactor 2). The ammonia and sodium react, resulting in the formation of NaNH2, which then decomposes to produce Na metal (which is returned to the molten reservoir), N.sub.2 and H.sub.2 according to Equations 1, 2, 2a and 2b.
2NH.sub.3+2Na=2NaNH.sub.2+H.sub.2Equation 1
2NaNH.sub.2=2Na+N.sub.2+2H.sub.2Equation 2
2NaNH.sub.2=2NaH+N.sub.2+H.sub.2Equation 2a
2NaH=2Na+H.sub.2Equation 2b

(34) Equations 2 and 2a may occur in competition, but at the temperature of reaction (500 C.) both occur spontaneously, as does Equation 2b.

(35) H.sub.2 is evolved at a rate of 1.5 times the flow rate of ammonia (thus 90 sccm) and N.sub.2 evolved at the same rate as the flow rate of ammonia (60 sccm). Reaction will continue at this rate for as long as the ammonia feed stock is added at a rate of 60 sccm. The rate of H.sub.2 and N.sub.2 production varies linearly with the rate of addition of ammonia.

EXAMPLE 2

(36) A mass of precursor material(s) (Na, NaH, NaNH.sub.2 or some combination thereof) is loaded, under inert atmosphere, into the reactor which is then sealed and connected to an inert gas supply. Inert gas (typically Ar) is flowed through the reactor to maintain the inert atmosphere within the reactor and over the precursor material(s). The precursor materials may be heated under inert atmosphere to decompose them and create a pristine Na metallic surface for reaction. Alternatively, where an appropriate mixture of Na, NaH and NaNH.sub.2 is used the decomposition step is not necessary. When a pristine Na surface has been produced, the sample is heated under flowing inert atmosphere or under flowing NH.sub.3 atmosphere until the appropriate temperature for hydrogen generation has been reached. This temperature is between 100 and 800 C., preferably between 100 and 500 C. and optimally between 150 and 450 C. Flow rates of Ar and/or NH.sub.3 between 1 sccm and 500 sccm are appropriate depending on the flow of hydrogen required.

(37) The reaction corresponds to the creation and decomposition of NaNH.sub.2, evolving hydrogen. The evolution of hydrogen begins after the evolution of nitrogen which suggests that hydrogen evolved in the initial reaction/decomposition of ammonia is trapped by metallic sodium. Once the temperature plateaus, the rate of nitrogen evolution also plateaus.

(38) As the temperature is lowered, hydrogen and nitrogen continue to be evolved but if the temperature is lowered sufficiently, not all of the ammonia is converted and the concentration of ammonia in the exhaust flow increases. The conversion or partial conversion of ammonia to nitrogen and hydrogen depends on i) the mass of Na/NaH, NaNH.sub.2 reactant ii) the flow rate of ammonia and iii) the temperature.

(39) The reactor is then flushed with argon and allowed to cool. Once at room temperature, the reactor is heated to between 250 C. and 260 C. under argon and, once at temperature, exposed to a flow of 10 sccm ammonia. As soon as the ammonia is introduced (at a temperature corresponding to 260 C.) the evolution of N.sub.2 is observed, followed shortly after by the evolution of N.sub.2H.sub.4 and subsequently H.sub.2.

(40) FIG. 8 shows the incomplete conversion of ammonia to nitrogen and hydrogen at 250 C., ammonia flow rate 10 sccm.

(41) The flow rate is then increased to 40 sccm and a decrease in the partial pressure of nitrogen and hydrogen is observed (at time=0, FIG. 9), consistent with the increased concentration of ammonia. The temperature is slightly increased and only the hydrogen signal is seen to increase, which suggests an increase in the rate of formation of amide with respect to the rate of decomposition

(42) FIG. 9 shows that increasing the flow of ammonia to 40 sccm decreases the relative partial pressure of nitrogen and hydrogen. The subsequent increase in temperature causes an increase in rate of amide formation with respect to the rate of decomposition and thus a gradual conversion of the material to the amide.

(43) The temperature is then raised to 450 C. and the total conversion of ammonia to nitrogen and hydrogen is observed (FIG. 10). This conversion continues for as long as the flow and temperature remains constant.

(44) FIG. 11 shows the influence of temperature. As the temperature is lowered, the rate of amide formation increases above that of amide decomposition, and the partial pressure of hydrogen increases, while that of nitrogen decreases. The ammonia concentration also increases which indicates the relative rates of the two processes and the amount of Na/NaH available for conversion to amide. Conversion of ammonia to nitrogen and hydrogen continues even below 300 C., but at a rate insufficient to convert all the incoming ammonia. As the temperature is raised, the rate of amide decomposition/ammonia conversion increases accordingly.

(45) FIGS. 8 to 11 show that: 1) Ammonia may be converted to nitrogen and hydrogen, for example within the temperature range of 220-450 C. 2) The total conversion efficiency of ammonia is thought to be dependent on mass of reactants, ammonia flow rate, temperature and the position of the Na/NaH/NaNH.sub.2 reactants within the reactor and with respect to the ammonia flow. Without wishing to be bound by any particular theory, temperature is thought to be the most significant variable in controlling the rate of ammonia conversion, as expected for exothermic (Na/NaH+NH.sub.3.fwdarw.NaNH.sub.2+0.5/1.0H.sub.2) and endothermic (NaNH.sub.2.fwdarw.Na+0.5N.sub.2+H.sub.2) processes, with higher temperatures favouring the endothermic process and thus increasing the conversion rate. At no stage is the temperature too high to prevent the formation of amide. 3) Preferably, conversion of ammonia continues without abatement once the process has begun as long as ammonia continues to flow. Changing the temperature may change the rate of those processes. There does not appear to be any reduction in the ability of the system to convert ammonia as a function of time. 4) The system may be cooled and heated, even with gas changes, without any impairment to its ability to convert ammonia.