GAS GENERATOR WITH BUOYANT CATALYST CARRIER
FIELD OF TOE INVENTION
[0001] This invention generally relates to a gas generator and more particularly to a hydrogen generator with a catalyst carrier that is suspended within the generator. The gas generator is passively controlled, i.e., it automatically stops generating gas when the internal pressure reaches a certain level, and vice versa.
BACKGROUND OF THE INVENTION [0002] Fuel cells arc devices that directly convert chemical energy of reactants, i.e., fuel and oxidant, into direct current (DC) electricity. For an increasing number of applications, fuel cells are more efficient than conventional power generation, such as the combustion of fossil fuels, as well as portable power storage, such as lithium-ion batteries. In particular, one use of fuel cells is as a mobile power source for portable or mobile consumer electronic devices, such as cell phones, smart phones, personal digital assistants, personal gaming devices, global positioning devices, rechargeable batteries, computer tablets, laptop computers, etc.
[0003] Known fuel cells include alkali fuel cells, polymer electrolyte fuel cells, phosphoric acid fuel cells, molten carbonate fuel cells, solid oxide fuel cells, and enzyme fuel cells. Fuel cells generally run on hydrogen (H2) fuel, and they can also consume non pure hydrogen fuel. Non pure hydrogen fuel cells include direct oxidation fuel cells, such as direct methanol fuel cells (DMFC). which use methanol, or solid oxide fuel cells (SOFC). which use hydrocarbon at high temperature. Hydrogen fuel can be stored in compressed form or within compounds, such as alcohols or hydrocarbons or other hydrogen containing materials, that can be reformed or converted into hydrogen fuel and byproducts. Hydrogen can also be stored in chemical hydrides, such as sodium borohydride (NaBH.i), that react with water or an alcohol to produce hydrogen and byproducts. Hydrogen can also be adsorbed or absorbed in metal hydrides, such as lanthanum pentanickel (LaNts), at a first pressure and temperature and released to a fuel cell at a second pressure and temperature. Hydrogen can also be released via thermolysis reaction of a metal hydride, such as magnesium hydride (MgH'2).
[0004] Most low temperature hydrogen fuel cells have a proton exchange membrane, or polymer electrolyte membrane (PEM), which allows the hydrogen's protons to pass through, but forces the electrons to pass through an external circuit, which advantageously can be a smart phone, a personal digital assistant. (PDA), a computer, a power tool, or any device that uses electron flow or electrical current. The fuel cell reaction can be represented as follows:
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Half-reaction at the anode of the fuel cell:
H2 -> 2H+ + 2e~; Half-reaction at the cathode of the fuel cell:
2(2H+ + 2e") I O2-^2H20.
[0005] Generally, the PEM is made from a proton exchange polymer that acts as the electrolyte, such as Nation*1 available from DuPont, which is a perfluorinated sulfonic acid polymer, or other suitable membranes. The anode is typically made from a Teflonized carbon paper support with a thin layer of catalyst, such as platinum-ruthenium, deposited thereon. The cathode is typically a gas diffusion electrode in which platinum particles are bonded to one side of the membrane.
[0006] The patent and scientific literatures disclose few gas or hydrogen gas generation systems that automatically separate the catalyst from the reactants when a predetermined pressure is reached. However, there remains a need for additional designs.
SUMMARY OF THE INVENTION [0007] The invention is directed to a gas generation system that automatically separates the catalyst system from the reactants when a predetermined pressure is reached and automatically brings the catalyst system into chemical contact with the reactants when the pressure drops below the predetermined pressure. [0008| The present invention relates to a gas generation apparatus comprising:
a housing containing a liquid reactant that reacts to produce a gas in the presence of a catalyst, wherein the catalyst is contained in a carrier disposed within the housing and wherein the carrier has an overall density lower than that of the liquid reactant,
at least one carrier movement restraining member adapted to selectively control the location of the carrier, and
at least one compressible body containing a volume of gas,
wherein, in a first configuration, an internal pressure of the gas generator is lower than an internal pressure of the compressible body and the compressible body increases in volume and, in a second configuration, the internal pressure of the gas generator is higher than the internal pressure of the compressible body and the compressible body decreases in volume, and
wherein the at least one carrier restraining member restricts the earner's movement in the first configuration,

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[0009] The carrier movement restraining member may comprise at least one porous
containment member that allows the liquid reactant to flow therethrough and at least partially
encloses the carrier. In the first configuration, the at least one porous containment member
prevents the carrier from floating on top of the liquid reactant. In some embodiments, the at
least one carrier restraining member can be affixed relative to the housing of the gas
generator.
[0010] Alternatively, the carrier movement restraining member may comprise at least one
flexible string or strip connected at one end to the carrier and to the housing of the gas
generator at the other end.
[0011] Alternatively, the carrier movement restraining member may comprise at least one
substantially nonflexible rod connected at one end to the carrier and pivotally to the housing
of the generator at the other end.
[0012] In some embodiments, the at least one porous containment member is movable
relative to the housing of the gas generator. In one example, the at least one porous
containment member may be connected to the compressible body. In the first configuration,
the at least one porous containment member moves to immerse the carrier in the liquid
reactant.
[0013] The catalyst carrier may comprise at least one buoyant member and/or at least one
ballast.
[0014] The present invention also relates to a method of operating a gas generator comprising
the steps of:
providing a housing containing a liquid reactant and a catalyst carrier, wherein the catalyst carrier is more buoyant than the liquid reactant;
providing within the housing a compressible body containing a volume of gas. wherein, in a first configuration, an internal pressure of the gas generator is lower than an internal pressure of the compressible body so the compressible body increases in volume, and. in a second configuration, the internal pressure of the gas generator is higher than the internal pressure of the compressible body so the compressible body decreases in volume; and
restricting movement of the catalyst carrier in the first configuration.
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BRIEF DESCRIPTION OF THE DRAWINGS
[0015] In the accompanying drawings, which form a part of the specification and are to be read in conjunction therewith and in which like reference numerals are used to indicate like parts in the various views:
[0016] FIGURE 1 is a schematic drawing of the inventive gas generator;
[0017] FIGURE 2A is a perspective view of one embodiment of the inventive catalyst float; and FIGURE 2B is a cross-sectional view of the catalyst float of Figure 2A;
[0018] FIGURES 3A-3C are cross-sectional views of another embodiment of the inventive gas generator in various configurations;
[0019] FIGURES 4A-4B are cross-sectional views of another embodiment of the inventive gas generator;
[0020] FIGURES 5A-5B are cross-sectional vicw^ of another embodiment of the inventive gas generator; and
[0021] Figures 6A-6B are cross-sectional views of another embodiment of the inventive gas generator.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0022] The present invention is directed to a gas generator with a catalyst earner that has restricted movements within the gas generator. Preferably., the catalyst carrier comprises a catalyst float that has an overall density that is lower than that of the liquid reactant(s) within the gas generator to provide the catalyst sufficient buoyancy to float on top of the liquid reactant(s), thereby lifting or otherwise separating the catalyst from the liquid reactant(s) to slop the reaction by the reactants to produce a gas. The catalyst carrier, or float, in some embodiments is unattached to the gas generator and is contained within a cage or an open/porous containment system that allows the liquid reactani(s) lo flow there through and that allows the generated gas to exit. In other embodiments, the catalyst carrier is attached to the housing of the gas generator via a flexible attachment means, such as a string or a strip. During operation, in one embodiment the containment system remains substantially stationary relative to a housing of the gas generator. The gas generator further comprises at least one expanding or compressible member. 'ITie volume of this expanding member depends on the internal pressure of the gas generator. In this embodiment, when the internal pressure is low the volume of the expanding member increases to raise the level of the liquid
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reactants to substantially cover the catalyst float, whose movement is restricted by the open containment system, in order to allow the liquid reactants to reach the catalyst in the catalyst float. When the internal pressure is high, the volume of the expanding member decreases to lower the level of the liquid reactants, and die catalyst float floats to the top of the liquid reactants without restriction by the open containment system, which lifts the catalyst above the level of the liquid reactants. In another embodiment, the porous containment system comprises at least one movable porous member that moves in response to the internal pressure of the gas generator to move the catalyst carrier to be immersed in the liquid reactant(s).
[0023] The catalyst float may have buoyancy member(s) and/or ballast(s) to control its buoyancy or overall density, and the float may have ingress channel(s) to allow the liquid reactant to enter the float and egress channel(s) for the produced gas to exit through. Preferably, the catalyst within the catalyst float is located away from the inlet end of the ingress channel(s) and toward the center of the float, so that the catalyst is spaced apart from the surface of the liquid reactants when the catalyst float floats on top of the liquid reactant. The present inventive gas generator may have one or more preferred specific orientations, or range of orientations, to operate, or it can operate independent of the orientation of the gas generator.
[0024] Referring to Figure 1. gas generator 10 contains a liquid reactant that may comprise a mixture 12 of sodium borohydride or potassium borohydride. water, and a preservative, such as sodium hydroxide or potassium hydroxide. This mixture reacts in the presence of a catalyst to produce hydrogen. The present invention is not limited to any particular fuel mixtures that react to produce hydrogen. Other suitable fuels are described in US 8.636,961 and US 8,636,826. Furthermore, other fuel mixtures can be used with gas generator 10 to produce other gases, such as oxygen carbonic acid gas, etc. Non-limiting examples of a non-hydrogen gas generator arc disclosed in US Patent Nos. K, 142,726 and 1 50,995, which are incorporated herein by reference in (heir entireties. The top level of the liquid reactant 12 is controlled by the internal pressure of gas generator 10 and the internal pressure of a compressible body 14, which preferably contains a fixed volume of gas. When the internal pressure (PJO) within gas generator 10 is higher than the internal pressure (P14) of compressible body 14, first this relative pressure (PJO > PH) compresses the compressible body 14 to lower the liquid level. On the other hand, when the internal pressure (P]0) within gas generator 10 is lower Lhan the internal pressure (P]4) of compressible body 14. this second
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relative pressure (P14 > P10) allows the compressible body 14 to expand to raise the liquid level. Hence. Pj4 can be thought of as a reference pressure, which may have any value including the value of atmospheric pressure. The volume of compressible body 14 determines the amount of level rise experienced by liquid reactant 12. [0025] Gas generator 10 further comprises a catalyst carrier/system or a catalyst float 16, which contains catalyst 18, optional buoyant member 20 and optional ballast 22. Liquid reactant 12 reacts in the presence of catalyst 18 to produce gas. preferably hydrogen 24. Buoyant member 20 and/or ballast 22 are used to tune the density of catalyst float 16 so that float 16 preferably would float on top of the surface of liquid reactant 12, if the movements of catalyst float 16 is unconstrained. As illustrated in Figure 1, the movement of catalyst float 16 is limited to within a boundary, such may be a provided by a earner movement restraining members, such as. for example, a porous enclosure 26, e.g., a cage or a screen enclosure, etc. Preferably, porous enclosure 26 is relatively fixed to housing 27 of gas generator 10. For example, porous enclosure 26 may be attached directly or indirectly to housing 27. [0026] In operation, liquid reactant 12 reacts in the presence of catalyst 18 to produce gas 24. If gas 24 remains within gas generator 10, or if gas 24 is withdrawn at a rate thai is less than the rate of gas generation, then the internal pressure Pm of gas generator 10 would increase. When PJO is greater than the internal pressure Pi4 of compressible body 14, the first pressure differential (PJO - PM) compresses body 14 and, thereby, lowers the level of liquid reactant 12. When the liquid level drops below porous enclosure 26, e.g., at level 30 shown in Figure 1, liquid reactant 12 no longer contacts catalyst 18, and the reaction that produces gas 24 stops. On the other hand, if gas 24 exits gas generator 10 and is consumed by a device, such as a fuel cell(s), Pio decreases and when PJO is lower than PM, this second pressure differential (Pr-i - PJO) allows compressible body 14 to expand to raise the liquid level of liquid reactant 12 until the liquid level rises above porous enclosure 26, thereby allowing liquid reactant 12 access into catalyst float 16 and to catalyst 18. It is noted that since catalyst float 16 floats on top of liquid reactant 12, reaction should not occur until after catalyst float 16.'s motion is arrested by the top of porous enclosure 26.
[0027] Gas generator 10 may also have liquid reactant inlet 32 and liquid reactant outlet 34 to replace spent liquid reactant 12 with fresh supplies, and gas outlet 36 to remove the produce gas from the gas generator. Additionally, gas generator 10 may have a gas separator or a gas separator composite, such as those described and claimed in US 8,636,826 and US
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2011/0212374 to separate and remove the produced gas from liquid rcactant 12 and byproducts.
[0028] Figures 2A and 2B illustrate one embodiment of catalyst float 16, which has two half-shells that form housing 28 of the float 16. The two half-shells are joined at ccnterline 38. Catalyst 18 is preferably stored proximate to the center of catalyst float 16. Buoyant member 20 is provided to ensure that catalyst float 16 floats on top of the surface of liquid reactant 12. Ballast 22 (shown in Figure 1) can also be added. Catalyst float 16 has at least one inlet 40 and one outlet 42. Typically, in the orientation shown in Figures 2A and 2B, liquid reactant 3 2 enters catalyst float 16 at inlet 40 and the gas produced exits catalyst float 16 at outlet 42. Since this embodiment of catalyst float 16 is symmetrical, it remains operational when turned upside down and the inlet becomes the outlet, and vice versa. It is also preferred that catalyst 18 is spaced apart from the outer edge of inlet/outlet 40, 42, so that when catalyst float 16 sits on top of liquid reactant 12 catalyst 18 is not in contact with liquid reactant 12. Porous enclosure 26 may be provided to enclose the catalyst float 16 and forces catalyst float 16 to immerse into liquid rcactant 12, as the level of liquid rcactant 12 rises when compressible body 14 expands when (P14 > P10).
[0029] Figure 3 A shows another embodiment of gas generator 10 in operation and producing gas. Catalyst float 16 is immersed within liquid reactants 12 and compressible body 14 is inflated. Porous enclosure 26 keeps catalyst float 16 immersed in liquid reactant 12. Porous enclosure 26 in this embodiment at least partially encloses catalyst float 163 although it may also fully enclose the catalyst float 16. Figure 3B shows gas generator 10 in operation but with compressible body 14 deflated, and the surface level of liquid reactant 12 has fallen below the top of porous enclosure 26 sufficiently for catalyst float 16 to float on top of liquid reactant 12, thereby lifting catalyst 18 away from Liquid reactant 12. It is noted that, as shown in Figures 3A and 3B, while gas generator is in operation, porous enclosure 26 is fixed relative to housing 28 of gas generator 10,
[0030] Figure 3C illustrates one possible way to keep catalyst float 16 away from liquid reactant 12 during storage and before first use by moving porous enclosure 26 upward relative to housing 28 so that catalyst float 16 always remains above liquid rcactant 32. Another way of storing gas generator before the first use, or the first sale, is to keep separate and unmixed the two or more components of liquid reactant 12, e.g., keep the water unmixed with the sodium borohydride until just before the first use.
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|0031 [ As shown in Figures 1 and 3 A and 3B, gas generator 10 operates in the orientation shown. However, gas generator 10 can be made operational in any orientation if shapes of the housing 27 and the porous enclosure 26 are substantially similar and with porous enclosure 26 placed within housing 28 so their geometric centers coincide with each other. For example, housing 27 and porous enclosure 26 may have spherical shapes with their centers located at substantially the same point. The distance between porous enclosure 26 and housing 27 would substantially be the same in this case. In another example, housing 27 and porous enclosure 26 have a cubic shape with their geometrical centers coinciding with each other. The distance between cubic porous enclosure 26 and cubic housing 28 is substantially the same except at the corners.
[0032] In another embodiment, porous enclosure 26 is simplified to be a porous piston 44 attached to compressible body 14, as shown in Figures 4A and 4B. As (?u> Pio), compressible body 14 expands and pushes porous piston 44 and catalyst float 16 into liquid reactant 12. As (Pi4 PIO, one or more compressible bodies 14 in the liquid reactant 11 expand to an expanded state and, as a result.
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the level of liquid reactant in the housing 27 rises to level L[. As evident from Figure 6B, when P|4 < P]o, the one or more compressible bodies 34 in the liquid reactant 12 contract to a contracted state and, as a result the level of liquid reactant in housing 27 Mis to level L2, which is lower than level L). String/strip 50 is Figure 6B may be slacked and not taught/tight. As evident from Figures 6A and 6B, level L5 is higher than level L2. [0035] Alternatively, member 50 can be a substantially nonflexible rod or link 50 that is connected at one end to catalyst float 16 and pivotally connected at end 55 to housing 27. such that as the reactant level drops to level L2 as shown in Figure 6B. rod 50 can pivot to maintain catalyst float 16 on top of the surface of the reactant.
[0036] Wliile it is apparent that the illustrative embodiments of the invention disclosed herein fulfil] the objectives stated above, it is appreciated that numerous modifications and other embodiments may be devised by those skilled in the art. Features from one embodiment can be used with other embodiments. Therefore, it will be understood that the appended claims are intended to cover all such modifications and embodiments, which would come within the spirit and scope of the present invention.
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