Materials and apparatus for hydrogen gas generation

Abstract

The present invention relates to a solid porous material for hydrogen gas generation, the material having a porosity of 20-75% by volume and a composition comprising, by weight of the material, 50-99% borohydride compound and 1-30% binder. Further aspects of the invention relate to gas generators comprising the material and its use in aerospace applications.

Description

Technical Field

[0001] The present invention is in the field of hydrogen gas generating devices. In particular, the present invention relates to solid porous materials for hydrogen gas generation and their use, for example, in aerospace applications.

Background Art

[0002] Hydrogen gas is a typical preferred gas for use in (expandable) aerospace applications because of its low specific weight. Supplying hydrogen gas to conventional containers such as pressurized bottles has certain drawbacks, namely, they are generally relatively heavy and prone to leakage. Weight is particularly a problem in space. Therefore, hydrogen generation chemical formulations are particularly suitable as alternatives to pressurized bottles. The supply of hydrogen gas from these hydrogen generation chemical formulations is based on the decomposition of compounds or chemical materials and the accompanying gas generation.

[0003] Hydrogen storage materials are disclosed in US Patent Application Publication No. 2006 / 0237688. This material includes active substance particles and a binder for sufficiently fixing the active particles to maintain the relative space between the active particles. These active substance particles can store hydrogen or can absorb and release hydrogen.

[0004] U.S. Patent Application Publication No. 2009 / 0078345 discloses an apparatus for generating, for example, hydrogen gas. The apparatus comprises an exothermic structure including a substrate of a first material and a coating of a second material. Furthermore, it includes a third material disposed adjacent to or inside the structure. By thermally activating the first and second materials, these materials react with each other, and an exothermic autocontinuous reaction propagates. This exothermic autocontinuous reaction thermally decomposes the third material. This third material may be, for example, ammonia borane or hydrogen boride for generating hydrogen gas. However, a drawback of this apparatus is that, when using ammonia borane, a thermite layer (particularly Fe2O3) is required, which is undesirable (see below). Further drawbacks include the high temperature of the generated gas and the presence of a considerable amount of material that does not directly contribute to the generation of hydrogen gas.

[0005] Another material is disclosed in International Publication No. 2007 / 098271, which describes a hydrogen fuel element comprising a heat-generating pyrotechnic charge with an ignition material and an ammonia borane encapsulation. The drawback is that this fuel element functions only at relatively low pressure differences between the inside and outside of the element. Similar to U.S. Patent Application Publication No. 2009 / 0078345, further drawbacks of the said fuel element include the high temperature of the gas produced and the presence of a considerable amount of material that does not directly contribute to the generation of hydrogen gas.

[0006] U.S. Patent Application Publication No. 2011 / 0033342 describes a hydrogen gas generator comprising a plurality of fuel pellets containing a hydrogen-producing compound. The pellets consist of ammonia borane and a thermal mixture which is a mixture of lithium aluminum hydride and ammonium chloride. Gas production can be initiated by heating the thermal mixture, which then generates enough heat to heat the ammonia borane and induce its decomposition. This system has several drawbacks, particularly relevant to aerospace applications. Firstly, because the decomposition temperature is much higher than the auto-ignition temperature (e.g., more than 480°C higher), individual pellets must be separated in an adiabatic space to prevent the decomposition of one pellet from leading to the ignition of an adjacent pellet. This empty adiabatic space is undesirable for scaling up the system to larger applications. Secondly, it is believed that the decomposition propagates with the help of gravity. At approximately 100°C, ammonia borane melts, and for further proper decomposition of ammonia borane, a system like the one described in U.S. Patent Application Publication 2011 / 0033342 is considered to require that the ammonia borane being decomposed be in good contact with the exothermic decomposition compound. This contact is lost in a microgravity or low-gravity environment. A further drawback of the system in U.S. Patent Application Publication 2011 / 0033342 is that the generated hydrogen gas is hot and generally requires cooling before use, adding weight and volume to the system. For this reason, conventional hydrogen gas generators are not well-suited for aerospace applications. [Overview of the project] [Problems that the invention aims to solve]

[0007] The present invention aims to solve at least some of the aforementioned drawbacks and to provide a gas generator and chemical materials for hydrogen gas generation that can produce low-temperature hydrogen gas in a compact system. [Means for solving the problem]

[0008] Surprisingly, the inventors have found that approaches such as those described in Russian Patent Application Publication No. 2108282 and International Publication No. 0123327 can be suitably used. Russian Patent Application Publication No. 2108282 describes a cryogenic gas generator comprising a housing having a solid, porous gas-generating composition, arranged such that the generated gas is cooled by passing the gas through the porous composition in the same direction as the decomposition front moves. A similar approach is described in European Patent Application Publication No. 2070870 for generating nitrogen gas. Because the gas is cooled by passing through the porous composition, the amount of heat released to the outside of the generator and the amount of heat that can be transferred is low, and multiple gas generators can be arranged adjacent to each other without empty isolation spaces. Another advantage of this approach is that the flow of the generated gas is gravity-independent, and therefore the propagation of decomposition is also gravity-independent. [Brief explanation of the drawing]

[0009] [Figure 1] This figure shows a general layout of the gas generating apparatus of the present invention. [Modes for carrying out the invention]

[0010] Accordingly, the present invention relates to a gas generator for hydrogen gas generation, comprising a housing for a gas generating material and an igniter. The gas generating material is a solid porous material for hydrogen gas generation, having a porosity of 20-75% based on the volume of the material, and having a composition comprising 50-99% boron hydride compound and 1-30% binder based on the weight of the material. Preferably, the material contains 60-99%, more preferably 70-99%, and most preferably 80-99% boron hydride compound based on the weight of the material.

[0011] The porosity of the material ensures that the generated gas can pass through the pores of the material, thereby effectively cooling the gas and ensuring that the material is sufficiently heated for decomposition propagation. The porosity should preferably not be too high, as this would result in the loss of valuable space, which is particularly undesirable for aerospace applications. On the other hand, the porosity should not be too low, as this could lead to poor propagation or pressure increases within the generating apparatus, thus hindering gas flow. Therefore, a porosity of 30–60% is preferred based on the volume of the material, although slightly higher and slightly lower porosities, such as around 20–75%, may still be appropriate.

[0012] Using borane compounds over other hydrogen gas-producing compounds is advantageous for several reasons. For example, the use of metal hydrides (e.g., lithium aluminum hydride), as described in U.S. Patent Application Publication 2011 / 0033342 and Russian Patent Application Publication 2108282, requires reagents such as Fe2O3 that can react with the metal hydride to produce hydrogen gas. That is, metal hydrides are not self-degrading. The presence of additional reagents is undesirable because it reduces the amount of available space for the hydrogen gas-producing compound, and is particularly undesirable for aerospace applications. Furthermore, by-products such as water may be produced, which can lead to unpredictable system behavior. Water can be solid, liquid, or gaseous, for example, depending on the environment, and the physical state of water affects the final gas composition. By changing the environment, for example, by changes in exposure to sunlight or re-entry into the Earth's atmosphere in aerospace applications (see below), water can significantly affect the desired effect and use of hydrogen gas (e.g., pressure or volume of the gas produced).

[0013] Suitable borane compounds for the present invention include ammonia borane, magnesium borane, sodium borohydride, lithium borohydride, and combinations thereof. Ammonia borane (NH3BH3) is particularly preferred over other borane compounds due to its higher ratio of hydrogen gas production to weight. Under optimal conditions, each NH3BH3 molecule decomposes into three molecules of hydrogen (3×H2) and one molecule of boron nitride (BN). Thus, 19.6% by weight of ammonia borane can potentially be converted into hydrogen gas. This is far higher than the potential of metal hydrides, and for this reason, ammonia borane is preferred over metal hydrides.

[0014] The binder in the composition provides the binding of the boron compound and the structural integrity and solid properties of the composition. In certain embodiments, the binder is an inert binder that remains intact before, during, and after the decomposition of the boron hydride compound. In certain applications of the present invention (e.g., use of gas generators and materials as fuel cells), it may be desirable to produce high-purity hydrogen gas. In these cases, the decomposition of the binder leads to impurities in the hydrogen gas. For example, hydrocarbon binders such as resins may decompose into volatile hydrocarbon compounds and / or oxygen-containing compounds, which may then cause water formation. As mentioned above, water formation can also be undesirable, especially for aerospace applications. Therefore, the use of an inert binder such as an alkali metal silicate may be preferred. Examples of suitable alkali metal silicates include potassium silicate, lithium silicate, and sodium silicate. Potassium silicate is particularly preferred because of its lower hygroscopicity compared to other inert binders. Low hygroscopicity is preferable because it facilitates maintaining a low water content in the composition.

[0015] In another specific embodiment, the binder preferably comprises an energetic binder that decomposes exothermally. Thus, the binder provides several additional functions in addition to providing bonding and structural integrity. Exothermic decomposition can aid in the propagation of the decomposition of boron hydride compounds, and if a suitable energetic binder is selected, additional gases useful in the end use of the material and gas generator can be produced. In this regard, it is particularly preferable that the binder comprises energetic binders such as vinyltetrazole-based polymers (PVT), polyvinyltetrazoles and their salts, glycidyl azide polymers (GAP), poly(3-nitratomethyl-3-methyloxetane) (Poly(NiMMo)), poly(glycidyl nitrate) (Poly(GLyN)), nitroxyethyl nitramine (NENA), alkyl nitroxyethyl nitramines such as ethyl nitroxyethyl nitramine and n-butyl nitroxyethyl nitramine (BuNENA), and nitro-hydroxyl-terminated polybutadiene (NHTPB). Preferred active binders have a relatively large number of NN bonds or tetrazole groups (e.g., polyvinyltetrazole (e.g., poly-5-vinyltetrazole or its sodium salt)), produce a relatively large amount of nitrogen gas upon decomposition, and produce minimal or no water or other condensable compounds. Nitrogen gas is a clean gas and does not typically condense in aerospace applications where the present invention can be used. Furthermore, the additional gas produced by the above-mentioned active binders can help create a gas-filled volume and may therefore be beneficial for devices with inflatable structures (see below). While it is preferable that binders do not produce water or other condensable compounds upon decomposition, certain binders may actually produce small amounts of them, in which case it is preferable to maintain small amounts of these binders in the composition so that the amount of water produced is not detrimental to the composition's intended use. Accordingly, in certain embodiments of the present invention, one or more combinations of the active and inactive binders described herein may be included in the composition.

[0016] Furthermore, the composition may contain an energizer. This energizer can be advantageously used to provide the initial activation energy that enables the decomposition of the boron hydride compound. Additionally or as an alternative, the energizer may be further used to maintain the propagation of the decomposition front. The energizer preferably does not result in the production of water, particularly for the reasons mentioned above. Therefore, a suitable energizer is typically oxygen-free. A suitable energizer preferably contains an ammonium halide, such as ammonium chloride and / or ammonium fluoride. The energizer may be present in the composition in an amount of 5 to 25%, preferably 5 to 10% by weight, based on the weight of the material. The energizer content is preferably relatively low so that more ammonium borane can be included in the formulation.

[0017] In addition to the boron hydride compound, binder, and optional activator, the composition may also contain additives to adjust specific properties of the composition. However, for reasons particularly mentioned above, it is preferable that such additives do not react with boron hydride or the resulting hydrogen gas to produce water. Therefore, modifiers such as iron oxide (Fe2O3) or sodium carbonate (Na2CO3) are undesirable, and the composition is essentially free of them. Accordingly, the materials of the present invention are preferably substantially free of compounds or additives that react with the boron hydride compound to produce water directly or indirectly. Direct and indirect means that the production of water is prevented, including indirect production through the reaction of reaction products between the additive and the boron hydride compound. Substantially free as used herein means that the amount of modifier is sufficiently small so as not to adversely affect the use of the composition. In certain embodiments, the composition contains less than 15% Fe2O3, more preferably less than 5% Fe2O3, and most preferably less than 1% Fe2O3, based on the weight of the material. Therefore, typically, the material of the present invention contains a compound or additive that reacts with a boron hydride compound to produce water directly or indirectly, in an amount of less than 20%, more preferably less than 10%, more preferably less than 2%, and most preferably less than 1%, based on the weight of the material.

[0018] The solid gas-generating material is in the form of one or more porous charge having a porosity of 20–75 volume%. If there are two or more gas-generating charge materials, the first charge is started by an ignition device (igniter), and the other charge materials are successively ignited by the preceding one or more charge materials. The reaction (decomposition) front moves at a controlled rate so that the high-temperature decomposition gas moves away from the igniter as it passes through one or more porous charge materials, thereby exchanging heat with one or more charge materials so that one or more charge materials are warmed and the gas cools to the initial charge material temperature.

[0019] Therefore, the generated hydrogen gas is typically at a low temperature (e.g., the initial packing temperature, or similar to the ambient temperature). This low temperature can be advantageous because the hydrogen gas is typically less reactive compared to high-temperature hydrogen gas. Furthermore, the low temperature allows the gas to be used directly for several purposes (see below).

[0020] One or more fillers are manufactured separately and are installed within the housing of the gas generator such that the majority of the generated gas, preferably more than 90%, and more specifically more than 95%, of the decomposition gas passes through the pores of one or more porous fillers.

[0021] One or more fillers may have a composition that varies along the length and / or width of the filler.

[0022] The igniter may be a classic ignition type, but other (conventional) igniters can also be used.

[0023] (The first) filler is ignited at the position of the filler away from the gas generator outlet. Ignition is performed at the top of the first porous filler. In this way, the housing passes the pyrolysis gas through one solid porous filler or a plurality of solid porous fillers. Thereby, the gas generated while one filler or a plurality of fillers are being heated is cooled. By raising the temperature of one porous filler or a plurality of porous fillers, controlled decomposition is maintained. At the outlet of the last filler, generally, the gas reaches the (initial) temperature of the last porous filler and completely exchanges its heat with the unburned portion of the filler.

[0024] To ensure that the gas generator does not emit reaction products such as boron nitride and the gas does not contain particulate matter or undesirable chemical contaminants, the gas generator can include a special filter that removes boron hydride residues such as boron nitride, other undesirable contaminants, and solid or liquid substances. Suitable filters contain particulate materials such as activated carbon, sand, zeolite, metal oxides, and combinations thereof, mixed with each other or continuously.

[0025] The present invention will be described with reference to FIG. 1 which shows a general layout of the gas generator of the present invention.

[0026] Note that since the figure is mainly shown as an aid for understanding the present invention and its preferred embodiments, the following description is not limited to the specific embodiments of the figure.

[0027] The gas generation device shown in FIG. 1 includes an igniter (1) and one or more porous gas generation fillers (2). It is essential that the one or more fillers are porous and allow decomposition gas to pass through the one or more fillers. Further, the gas generation device may include one or more filters (3). The gas generation device has a housing (4) and a vent (5), and can have a second igniter, which is optional. Further, the gas generation device may have a neutralizing charge, which is also optional. The neutralizing charge can be used, for example, to neutralize or activate the remaining species of the non-fully decomposed boron hydride compound, converting these species into less harmful species or hydrogen gas so that hydrogen gas generation can be further increased.

[0028] Although not preferred, the filler may have any suitable shape, may have a diameter smaller than the main filler, or may have a perforated shape. Also, a layout is possible in which the neutralizing charge is ignited (with a certain delay) by the main igniter.

[0029] The igniter (1) ignites the main gas generation filler (2). The igniter can be any suitable and classical ignition type when there are no strict requirements on the purity of the gas provided by the gas generation device. The igniter can include an initiator, which can be an electrical initiator, an impact-activated initiator, or a laser-ignited initiator.

[0030] The main gas generation filler may have different shapes or may be composed of a stack of fillers of suitable shapes.

[0031] Each stack may also have different compositions to change the decomposition rate or gas composition, and / or the composition may vary along the length and / or width of the filler.

[0032] In the diagram, the packing material is cylindrical, which results in a relatively constant mass flow rate of the generated gas. However, the mass flow rate of the gas may be pre-programmed for its specific application by making the packing material one (frustum of a cone), two frustums of cones, a sphere, or other suitable shape. The hot gas passes through one or more porous packing materials, thereby exchanging heat with the initial (first) cold packing material and cooling the gas.

[0033] Next, the decomposition products may be passed through a filter after they have left the packing material to purify the gas. The secondary function of the filter is to cool the gas produced by the very last portion of the porous packing material.

[0034] The filler material can be cast inside the container, or it can be cast separately and later installed inside the housing using a liner as needed.

[0035] The gas generator is laid out so that the decomposition gas constantly passes through the porous packing material (2) to exchange heat with the main packing material. Any bypass of the packing material is generally avoided by proper sealing, or by the packing material being bonded to or case-bonded to the housing, or tightly housed within the housing. This serves two purposes: to heat the packing material to maintain the decomposition reaction, while cooling the decomposition gas to ambient temperature.

[0036] Gas generators and materials can be used in a variety of applications, including fuel cells and energy delivery, but may be particularly suitable for aerospace applications. In aerospace, the generated gas can be used, for example, to inflate a device and increase its surface area. This may be particularly suitable for landing gear, which is expected to reduce speed early when re-entering the atmosphere of a celestial body such as a planet or moon. Currently, landing gear re-enters the Earth's atmosphere at high speed, simultaneously accompanied by high frictional forces that generate a large amount of heat. By increasing the outer surface area of ​​the landing gear (especially its re-entry shield) early in atmospheric re-entry, speed can be reduced at an earlier stage before the frictional forces result in such high heat generation. Due to the low atmospheric pressure at high altitudes (e.g., at an altitude of 20 km, the atmospheric pressure is approximately 5 pKa or less), a relatively small amount of hydrogen gas can already provide a considerable volume and associated surface area.

[0037] Therefore, a further aspect of the present invention is an aerospace module, such as a breaking system, which is preferably suitable for aerospace landing gear. The vent can be connected to an inflatable structure adapted so that its outer surface area increases when inflated.

[0038] As used herein, the singular forms “a,” “an,” and “the” are intended to include the plural form unless the context explicitly indicates otherwise. The terms “and / or” include any and all combinations of one or more of the related enumerated items. The terms “comprises” and / or “comprising” are understood to identify the presence of the described feature but not to exclude the presence or addition of one or more other features.

[0039] For the sake of clarity and concise description, features are described herein as part of the same embodiment or as part of a separate embodiment, but the scope of the invention is understood to include embodiments having all or some combinations of the described features. (Note) This disclosure includes the following aspects. <1> A solid porous material for hydrogen gas generation, wherein the material has a porosity of 20 to 75 volume percent and a composition comprising 50 to 99% boron hydride compound and 1 to 30% binder, based on the weight of the material. <2> The boron hydride compound is selected from the group consisting of ammonia borane, magnesium borane, sodium borohydride, lithium borohydride, and combinations thereof, and is preferably ammonia borane. <1> The materials listed. <3> The binder comprises an energetic binder, preferably an energetic binder selected from the group consisting of vinyltetrazole-based polymers (PVT), polyvinyltetrazole and their salts, glycidyl azide polymers (GAP), poly(3-nitratomethyl-3-methyloxetane) (Poly(NiMMo)), poly(glycidyl nitrate) (Poly(GLyN)), nitroxyethyl nitramine (NENA), alkyl nitroxyethyl nitramines such as ethyl nitroxyethyl nitramine and n-butyl nitroxyethyl nitramine (BuNENA), nitro-hydroxyl-terminated polybutadiene (NHTPB), and more preferably polyvinyltetrazole such as poly-5-vinyltetrazole sodium. <1> or <2> The materials listed. <4> The binder comprises an inert binder, preferably an alkali metal silicate such as potassium silicate. <1> ~ <3> The materials listed in any one of the items. <5> Substantially free of compounds or additives that react with the boron hydride compound to directly or indirectly produce water, <1> ~ <4> The materials listed in any one of the items. <6> The activator further comprises an activator, preferably one containing ammonium halide, more preferably one containing ammonium chloride and / or ammonium fluoride. <1> ~ <5> The materials listed in any one of the items. <7> A gas generator for hydrogen gas production comprising a housing for a gas generating material and an igniter, wherein the gas generating material is <1> ~ <6> A gas generating apparatus characterized by being made of any one of the materials described in item 1. <8> During the operation, at least 90% of the generated gas passes through the material. <1> ~ <6> Includes materials as described in any one of the items, <7> The gas generating apparatus described above. <9> An aerospace module such as a re-entry shield, preferably suitable for a landing gear, wherein the aerospace module is <1> ~ <6> The materials described in any one of the items or <7> or <8> An aerospace module equipped with the gas generator described above. <10> The gas generator comprises a vent for the generated gas, and the vent is connected to an inflatable structure adapted such that its outer surface area increases when it expands. <9> Aerospace modules as described above. <11> To increase the surface area of ​​the landing gear, <1> ~ <10> Use of any of the materials, gas generators, or aerospace modules described in any one of the paragraphs.

Claims

1. A solid porous material for hydrogen gas generation, wherein the material has a porosity of 20 to 75 volume percent, and has a composition comprising 50 to 99% of a boron hydride compound, 1 to 30% of a binder, and an activator (energizer) containing ammonium halide, based on the weight of the material.

2. The material according to claim 1, wherein the boron hydride compound is selected from the group consisting of ammonia borane, magnesium borane, sodium borohydride, lithium borohydride, and combinations thereof.

3. The material according to claim 1 or 2, wherein the binder comprises an energetic binder selected from the group consisting of vinyltetrazole-based polymers (PVT), polyvinyltetrazole and salts thereof, glycidyl azide polymers (GAP), poly(3-nitratomethyl-3-methyloxetane) (Poly(NiMMo)), poly(glycidyl nitrate) (Poly(GLyN)), nitroxyethylnitramine (NENA), and nitro-hydroxyl-terminated polybutadiene (NHTPB).

4. The material according to any one of claims 1 to 3, wherein the binder contains an alkali metal silicate.

5. The material according to any one of claims 1 to 4, which substantially does not contain any compounds or additives that react with the boron hydride compound to directly or indirectly produce water.

6. The material according to any one of claims 1 to 5, wherein the activator comprises ammonium chloride and / or ammonium fluoride.

7. The material according to any one of claims 1 to 6, wherein the composition contains 5 to 25% of the activator based on the weight of the material.

8. The material according to any one of claims 1 to 7, wherein the composition contains 5 to 10% of the activator based on the weight of the material.

9. The material according to any one of claims 1 to 8, wherein the boron hydride compound is ammonia borane.

10. A gas generating apparatus for generating hydrogen gas, comprising a housing for a gas generating material, an igniter, and a hydrogen gas generating material according to any one of claims 1 to 9.

11. The gas generator according to claim 10, wherein the hydrogen gas generating material is installed in the housing such that at least 90% of the generated gas passes through the material during operation of the gas generator and during gas generation.

12. A braking system suitable for an aerospace landing device, wherein the braking system comprises a gas generator according to claim 10 or claim 11, wherein the gas generator comprises a vent for the generated gas, and the vent is connected to an inflatable structure of the braking system that is adapted to increase its outer surface area when expanded.

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