Patent Application
20110020215
The invention relates generally to fuel cells. More particularly, the invention relates to chemical hydride liquid reactant distribution mixtures for reducing caking and precipitation while promoting liquid reactant distribution.
Fuel cells, as an alternative source of electric energy, have been explored extensively. However, due to the lack of proper storage means of a fuel, hydrogen in most cases, applications of fuel cell systems for commercial products have been limited. In particular, for mobile applications such as laptops, mp3 players, or cellular phones, demand for portable hydrogen storage that is safe and high in energy density has grown significantly. Among many chemical hydride systems, sodium borohydride (SBH) as a source of hydrogen has been the most studied and understood. SBH reacts with water and becomes hydrolyzed releasing molecular hydrogen gas. This SBH hydrolysis is typically accelerated using catalytic materials or acids.
SBH-based hydrogen generator systems are known. A system has been described that generates hydrogen by feeding an alkaline-buffered SBH solution into catalytic beads. Although this system has an advantage in improved control of hydrogen reaction, the system energy density is relatively low due to its low solubility in a solvent (water mainly) and long-term stability. The low solubility of SBH allows only a fraction of solid SBH to dissolve in water, in the range of 10 and 20% concentration at best, at a room temperature. In addition, need for extra materials (e.g. sodium hydroxide) to stabilize the fuel leads to increased complexity of the system and a decrease in overall energy density. In addition, it is possible that fuel reactants or products may change its phase from a liquid to solid by precipitation under varying temperature and pressure conditions. This phase change may result in precipitation at unwanted locations, leading to the failure of the entire system.
Another hydrogen generator system has been described that uses a solid form of the chemical hydride. One example is a system that contains micro-particles of sodium borohydride mixed with catalyst materials. In this system, a fuel chamber is connected to a separate chamber that provides water as a liquid reactant to the fuel chamber. Another example is a cartridge system containing a substantially anhydrous chemical hydride reactant and liquid conduits. A liquid reactant is delivered to the chemical hydride via the liquid conduits. Although this method intends to provide control of the reactant liquid using spatial and form-factor variation of the conduits, construction of such a system may become complex and also lead to decrease in total energy density of the system. In addition, this system has not addressed serious issues such as the caking and precipitation of reaction products, which are detrimental to the performance of any hydrogen system based on solid chemical hydride. Furthermore, despite the high energy density of SBH material itself, the energy density of a hydrogen generator system using the SBH often decreases due to added components or increased volume of the system for reaction control and product filtration. Thus, it is also important to miniaturize these additional components and related system architecture without sacrificing the reliable performance of a SBH-based hydrogen system.
What is needed is a hydrogen system that suffices to meet goals of high energy density, controllability, and no risk of caking and precipitation at the same time.
The present invention provides a chemical hydride liquid reactant distribution mixture. The mixture includes a fuel mixture having at least one hydride and at least one activating agent. The invention further includes a liquid-distributing agent (LDA), a form-stabilizing agent, and at least one anti-caking agent. The liquid reactant distribution mixture reduces caking and precipitation while promoting liquid reactant distribution, where the chemical hydride liquid reactant distribution mixture generates hydrogen via hydrolysis.
According to one aspect of the invention, the LDA can include hydrophilic polymers, carbohydrates or sugar alcohols.
In one aspect the hydrophilic polymer includes poly alkyl (acrylic) acid and its salt, where the poly alkyl (acrylic) acid and its salt can include poly(acrylic acid), poly(α-ethylacrylic acid), poly(α-propylacrylic acid), poly(methacrylic acid), poly(sodium acrylate), poly(sodium methacrylate), poly(2-hydroxyethyl methacrylate), or polyacrylamide.
In another aspect, the hydrophilic polymers can include poly(N,N-dimethyl acrylamide), poly(N-isopropyl acrylamide), poly(ethylene glycol) or poly(ethylene oxide). Here, the poly(ethylene glycol) and poly(ethylene oxide) can include poly(ethylene glycol) methylether (initiator based on methoxy ethanol), poly(ethylene glycol) with disulfide linkage, poly(ethylene glycol) methylether (initiator based on 2-methoxy propanol), poly(ethylene glycol) monoethyl ether (nitiator based on ethoxy ethanol), poly(ethylene glycol) dimethyl ether, poly(ethylene glycol) mono-benzylether, poly(ethylene glycol) dibenzylmethylene terminated (initiator based on diphenyl methylene), poly(ethylene glycol) dimethylamine and hydroxy terminated, poly(ethylene glycol) dimethylamine or methoxy terminated.
In a further aspect, the hydrophilic polymers can include poly(methyl vinyl ether), poly(2-vinyl N-methylpyridinium iodide), poly(4-vinyl N-methylpyridinium iodide), poly(N-vinyl imidazole-quaternized with CH3I), poly(ethylene imine), poly(vinylamine) with poly(vinyl carboxylic acid amide), or poly(styrene sulfonic acid) and its salt. Here, the poly(styrene sulfonic acid) and its salt can include poly(styrene sulfonic acid) dialysed, poly(styrene sulfonic acid), undialysed, poly(styrene sulfonic acid cesium salt), dialysed, poly(styrene sulfonic acid cesium salt), undialysed, poly(styrene sulfonic acid sodium salt), dialysed, poly(styrene sulfonic acid sodium salt), or undialysed poly(vinyl alcohol). Further, the poly(vinylamine) and poly(vinyl carboxylic acid amide) can include poly(N-vinylamine), poly(N-vinyl formamide), poly(N-vinyl isobutyramide), or poly(N-vinyl pyrrolidone).
In another aspect of the invention, the carbohydrates can include monosaccharides such as glucose, fructose, galactose, xylose, ribose disaccharides such as sucrose or polysaccharides such as cellulose, starch, chitin, dextran (dextrin), or maltodextrin.
In another aspect of the invention, the sugar alcohols can include glycol, glycerol, erythritol, threitol, arabitol, xylitol, ribitol, mannitol, sorbitol, dulcitol, iditol, isomalt, maltitol, lactitol, or polyglycitol.
According to one aspect of the invention, the LDA further has material that can include microcrystalline cellulose, carboxymethyl cellulose, methyl cellulose, alginic acid, dibasic calcium phosphate, dextrates, calcium sulfate dehydrate, or compressible sucrose.
In a further aspect, the LDA includes a weight percentage of the liquid reactant distribution mixture in a range from 0.1 to 50 percent.
In another aspect of the invention, the form-stabilizing agent can include starch, methyl cellulose, hypromellose, microcrystalline cellulose, dibasic calcium phosphate, dextrate, sucrose, or polyethylene glycol.
In yet another aspect, the at least one anti-caking agent can include magnesium carbonate, calcium carbonate, silica (silicon dioxide), sodium bicarbonate, sodium ferrocyanide, potassium ferrocyanide, calcium ferrocyanide, bone phosphate, sodium silicate, calcium silicate, magnesium trisilicate, talcum powder, sodium aluminosilicate, potassium aluminium silicate, calcium aluminosilicate, bentonite, aluminium silicate, stearic acid, or polydimethylsiloxane.
In another aspect, the at least one anti-caking agent has a weight percentage of the liquid reactant distribution mixture in a range from 0.1 to 10 percent.
According to another aspect of the invention, the at least one hydride can include sodium borohydride, lithium borohydride, lithium aluminum hydride, lithium hydride, sodium hydride, magnesium hydride, or calcium hydride.
In a further aspect, the at least one activating agent comprises a acidic catalyst wherein the acidic catalyst can include boric acid, malic acid, succinic acid, oxalic acid, citric acid, tartaric acid, malonic acid, boric oxide, mucic acid, calcium chloride, sodium borofluoride, phthalic acid, salicylic acid, alum, benzoic acid, phthalic anahydride, sulfamic acid, ammonium alum, ammonium chloride, maleic anahyrdride, sodium acid sulfate, sodium diacid phosphate, aluminum sulfate, maleic acid, calcium chloride or ammonium carbonate.
In another aspect, the at least one activating agent includes a metallic catalyst, where the metallic catalyst can include colloidal platinum, platinized asbestose, platinum oxidation catalyst, copper-chromic oxide, activated charcoal, Raney nickel, manganese(II) chloride, iron(II) chloride, cobalt(II) chloride, nickel(II) chloride, or copper(II) chloride.
In yet another aspect, the at least one activating agent includes at least one salt such as alkaline earth metals, alkali metals or halides.
In another aspect of the invention, the halides can include MgCl2, BeF2, BeCl2, BeBr2, BeI2, MgF2, MgBr2, MgCl2, MgI2, CaF2, CaCl2, CaBr2, CaI2, LiF, LiCl, LiBr, LiI, NaF, NaCl, NaBr, NaI, KF, KCl, KBr, KI, Li2S, or Li2Se. Finally, other candidates of activating agents include at least one of Cu, Co, Ni, Pt, Pd, Fe, Ru, Mn, and Cr.
According to one embodiment, the invention is liquid reactant distribution mixture that includes a fuel, at least one accelerator, at least one liquid distributing agent (LDA), and at least one form-stabilizing agent or binder.
According to one aspect of the current embodiment, the at least one accelerator can include an acid accelerator, a metallic catalyst, a mixture of acidic and metallic accelerators, an acidic accelerator dissolved in a liquid reactant, a metallic accelerator dissolved in a liquid reactant, an acidic accelerator partially mixed in solid mixture and partially dissolved in liquid reactant, or a metallic accelerator partially mixed in solid mixture and partially dissolved in liquid reactant.
According to one aspect, the fuel is sodium borohydride.
In a further aspect, the at least one acidic accelerator can include oxalic acid, succinic acid, malonic acid, citric acid, tartic acid, malic acid, boric acid mucic acid, calcium chloride sodium borofluoride phthalic acid, salicylic acid, alum, bezoic acid, phthalic anhydride, sulfamic acid ammonium alum, ammonium chloride, maleic anhydride, sodium acid sulfate, sodium diacid phosphate, aluminum sulfate, or ammonium carbonate.
In another aspect of the invention, the at least one LDA can include hydrophilic polymers, carbohydrates, or sugar alcohols.
In a further aspect of the invention, the at least one form-stabilizing agent can include starch, methyl cellulose, hypromellose, microcrystalline cellulose, dibasic calcium phosphate, dextrate, sucrose, or polyethylene glycol.
According to another aspect, the liquid distribution mixture is compacted to form a solid structure, where the solid structure has a shape that can include a rod, a cylinder, a tube, a plate, a thin sheet, a block, micro-spheres, macro-spheres or powder form.
In another aspect, the liquid distribution mixture is uniformly mixed into a gel or paste.
In a further aspect of the invention, the liquid reactant distribution mixture further includes an anti-foam agent, where the anti-foam agent includes alcohols such as butyl alcohol, hexyl alcohol, or organosilicon compounds.
In another aspect, the organosilicon compounds can include polydimethylsiloxane, polyhydrosiloxane, and silica particles.
The objectives and advantages of the present invention will be understood by reading the following detailed description in conjunction with the drawing, in which:
a-2b show a prior art schematic diagram of liquid distribution in a fuel mixture with liquid blocked by caking layer, and an enhanced liquid distribution in a fuel mixture containing anti-caking agents and LDA according to the present invention, respectively.
a-3d show exemplary moving boundary interface (MBI) designs according to the present invention.
a-4d show examples of product-guide design in a solid fuel mixture (cylindrical shape), according to the present invention.
a-5c show examples of engineered guides for product disposal according to the present invention.
a-6c show schematic diagrams of layout variations of product separation media according to the present invention.
a-8b show a schematic diagram and a CAD model, respectively of a hydrogen generation system having a liquid reactant chamber, fuel chamber, filter chamber, and pump according to the present invention.
a-9c show schematic diagrams of a preferred assembly of an LDM and fuel mixture in a form of a nozzle, plane, or envelope, respectively according to the present invention.
Although the following detailed description contains many specifics for the purposes of illustration, anyone of ordinary skill in the art will readily appreciate that many variations and alterations to the following exemplary details are within the scope of the invention. Accordingly, the following preferred embodiment of the invention is set forth without any loss of generality to, and without imposing limitations upon, the claimed invention.
The present invention provides a hydrogen generator system optimized for portable applications with the emphasis on novel fuel mixture that enhances the energy density, controllability, low cost, safety, and environmental friendliness. In addition, for system miniaturization, this invention also presents system architectures, reaction control mechanisms and their appropriate materials, and filtration designs and their suitable materials. In particular, these inventions are optimized for the non-liquid fuel mixture described above.
The current invention further includes non-liquid hydrogen fuel mixtures optimized for the use of the system described above. The fuel mixtures were designed to enhance the distribution of a liquid reactant throughout the entire volume of the fuel mixture to minimize any caking or precipitation. The product of SBH reaction, sodium borate, is known to cause caking, which creates a thick and hard solid layer that eventually blocks liquid access to the unreacted portion of a fuel mixture.
According to the current invention, a non-liquid hydrogen fuel mixture is provided that includes at least one liquid-distributing agent (LDA) 210 that is mixed uniformly or non-uniformly in the fuel mixture to temporally or spatially control or enhance the delivery of a liquid reactant 208. The LDA 210 is preferably hydrophilic such that the agent attracts water and gets readily dissolved. The LDA 210 also prevents the local precipitation of any substance used in the fuel mixture by drawing enough water to prevent any precipitation of chemical substances used in the fuel mixture. The non-liquid fuel mixture also includes at least one anti-caking agent at a level of 0.1 and 10 weight percent of the total fuel mixture. The fuel mixture further includes at least one binder or form-stabilizing agent, at least one hydride, and at least one activating agent.
The LDA 210 can include hydrophilic polymers, carbohydrates or sugar alcohols. According to the current invention, the hydrophilic polymer includes poly alkyl (acrylic) acid and its salt, where the poly alkyl (acrylic) acid and its salt can include poly(acrylic acid), poly(α-ethylacrylic acid), poly(α-propylacrylic acid), poly(methacrylic acid), poly(sodium acrylate), poly(sodium methacrylate), poly(2-hydroxyethyl methacrylate), or polyacrylamide. The hydrophilic polymers can include poly(N,N-dimethyl acrylamide), poly(N-isopropyl acrylamide), poly(ethylene glycol) or poly(ethylene oxide). Here, the poly(ethylene glycol) and poly(ethylene oxide) can include poly(ethylene glycol) methylether (initiator based on methoxy ethanol), poly(ethylene glycol) with disulfide linkage, poly(ethylene glycol) methylether (initiator based on 2-methoxy propanol), poly(ethylene glycol) monoethyl ether (nitiator based on ethoxy ethanol), poly(ethylene glycol) dimethyl ether, poly(ethylene glycol) mono-benzylether, poly(ethylene glycol) dibenzylmethylene terminated (initiator based on diphenyl methylene), poly(ethylene glycol) dimethylamine and hydroxy terminated, poly(ethylene glycol) dimethylamine or methoxy terminated. The hydrophilic polymers can include poly(methyl vinyl ether), poly(2-vinyl N-methylpyridinium iodide), poly(4-vinyl N-methylpyridinium iodide), poly(N-vinyl imidazole-quaternized with CH3I), poly(ethylene imine), poly(vinylamine) with poly(vinyl carboxylic acid amide), or poly(styrene sulfonic acid) and its salt. Here, the poly(styrene sulfonic acid) and its salt can include poly(styrene sulfonic acid) dialysed, poly(styrene sulfonic acid), undialysed, poly(styrene sulfonic acid cesium salt), dialysed, poly(styrene sulfonic acid cesium salt), undialysed, poly(styrene sulfonic acid sodium salt), dialysed, poly(styrene sulfonic acid sodium salt), or undialysed poly(vinyl alcohol). Further, the poly(vinylamine) and poly(vinyl carboxylic acid amide) can include poly(N-vinylamine), poly(N-vinyl formamide), poly(N-vinyl isobutyramide), or poly(N-vinyl pyrrolidone). The carbohydrates can include monosaccharides such as glucose, fructose, galactose, xylose, ribose disaccharides such as sucrose or polysaccharides such as cellulose, starch, chitin, dextran (dextrin), or maltodextrin. The sugar alcohols can include glycol, glycerol, erythritol, threitol, arabitol, xylitol, ribitol, mannitol, sorbitol, dulcitol, iditol, isomalt, maltitol, lactitol, or polyglycitol.
The LDA 210 further has material that can include microcrystalline cellulose, carboxymethyl cellulose, methyl cellulose, alginic acid, dibasic calcium phosphate, dextrates, calcium sulfate dehydrate, or compressible sucrose.
The hydride is at least one chosen from any chemical hydrides such as sodium borohydride, lithium borohydride, lithium aluminum hydride, lithium hydride, sodium hydride, magnesium hydride, and calcium hydride.
The activating agent can include an acidic catalyst where the acidic catalyst can include boric acid, malic acid, succinic acid, oxalic acid, citric acid, tartaric acid, malonic acid, boric oxide, mucic acid, calcium chloride, sodium borofluoride, phthalic acid, salicylic acid, alum, benzoic acid, phthalic anahydride, sulfamic acid, ammonium alum, ammonium chloride, maleic anahyrdride, sodium acid sulfate, sodium diacid phosphate, aluminum sulfate, maleic acid, calcium chloride or ammonium carbonate.
The activating agent can further include a metallic catalyst, where the metallic catalyst can include colloidal platinum, platinized asbestose, platinum oxidation catalyst, copper-chromic oxide, activated charcoal, Raney nickel, manganese(II) chloride, iron(II) chloride, cobalt(II) chloride, nickel(II) chloride, or copper(II) chloride.
Further, the activating agent can include at least one salt such as alkaline earth metals, alkali metals or halides. The halides can include MgCl2, BeF2, BeCl2, BeBr2, BeI2, MgF2, MgBr2, MgCl2, MgI2, CaF2, CaCl2, CaBr2, CaI2, LiF, LiCl, LiBr, LiI, NaF, NaCl, NaBr, NaI, KF, KCl, KBr, KI, Li2S, or Li2Se. Finally, other candidates of activating agents include at least one of Cu, Co, Ni, Pt, Pd, Fe, Ru, Mn, and Cr.
According to one embodiment, the invention is liquid reactant distribution mixture that includes a fuel (such as sodium borohydride), at least one accelerator, at least one LDA, at least one anti-caking agent, and at least one form-stabilizing agent or binder. The at least one accelerator can include a metallic catalyst, a mixture of acidic and metallic accelerators, an acidic accelerator dissolved in a liquid reactant, a metallic accelerator dissolved in a liquid reactant, an acidic accelerator partially mixed in solid mixture and partially dissolved in liquid reactant, or a metallic accelerator partially mixed in solid mixture and partially dissolved in liquid reactant.
According to the current invention, the acidic accelerator can include oxalic acid, succinic acid, malonic acid, citric acid, tartic acid, malic acid, boric acid mucic acid, calcium chloride sodium borofluoride phthalic acid, salicylic acid, alum, bezoic acid, phthalic anhydride, sulfamic acid ammonium alum, ammonium chloride, maleic anhydride, sodium acid sulfate, sodium diacid phosphate, aluminum sulfate, or ammonium carbonate.
The form-stabilizing agent can include starch, methyl cellulose, hypromellose, microcrystalline cellulose, dibasic calcium phosphate, dextrate, sucrose, or polyethylene glycol. The liquid distribution mixture is compacted to form a solid structure, where the solid structure has a shape that can include a rod, a cylinder, a tube, a plate, a thin sheet, a block, micro-spheres, macro-spheres or powder form. The liquid distribution mixture is uniformly mixed into a gel or paste.
The liquid reactant distribution mixture can further include an anti-foam agent, where the anti-foam agent includes alcohols such as butyl alcohol, hexyl alcohol, or organosilicon compounds.
In another aspect, the organosilicon compounds can include polydimethylsiloxane, polyhydrosiloxane, and silica particles.
The invention further includes reaction control mechanisms to ensure the stable and repeatable performance of a hydrogen system for both continuous and on/off operation. Stable hydrogen generation relies on how uniform and constant reaction interface is maintained between a fuel and liquid reactant. Most of SBH-based hydrogen systems use an alkaline-stabilized SBH solution as its fuel. The reaction control of such a liquid fuel is achieved by pumping a designated amount of the fuel to catalysts. However, the solution type SBH fuel is less favored due to its low energy density. While solid fuels have higher energy density, their further development has been hampered by difficulty in achieving reliable reaction control. The reaction control of a solid SBH system relies on both the pumping rate of liquid reactants and the size of a reaction interface. In practical cases, volatile hydrolysis reaction at the interface leaves cavities or voids when the generated products flow away from the interface. This results in a non-contact between a fuel surface and liquid delivery medium such as a nozzle or wick. When this occurs, the performance of hydrogen generation system degrades over time. The performance of the fuel system becomes unpredictable when it is restarted after a stop period from the previous run. Typically, when the fuel system is investigated after its operation for a certain period, large gaps or voids are observed between the non-reacted surface of the solid fuel and the liquid delivery medium (LDM) such as a nozzle, wick, or membrane. This lack of control in maintaining constant and intact boundary between a solid fuel and liquid delivery medium has been the largest obstacle to achieving reliable performance of a solid fuel system.
To address these issues, a moving boundary interface (MBI) is provided that ensures a constant contact between a solid fuel and LDM. The MBI includes either physically bringing the reacting surface of a solid fuel in contact with a stationary LDM, or bringing an LDM in contact with the varying contour of the reacting surface of a solid fuel. Physically moving one boundary to another includes, but is not limited to spring force, gas (preferably H2) pressure, or elastic membrane.
When a non-liquid fuel is employed and the hydrolysis reaction is induced at any surface of the solid fuel, the hydrolysis products need to be continuously removed from a reaction zone to ensure a clean contact between an LDM and the unreacted surface of the solid fuel. Providing clear and engineered pathways for product removal prevents any unexpected failure such as uncontrolled pressure buildup due to the product clogging, the entry disruption of liquid reactants, or the uncontrolled form-factor dismantling of a solid fuel. According to the current invention, for product removal of a non-liquid fuel is provided.
The detailed dimension and pattern of this product guide can be further engineered for the operation conditions of each fuel system.
Orientation-dependent consumption at a certain location of a fuel, in particular of solid type SBH fuels, due to gravity, often causes the uncontrolled dismantling of the fuel form factor, resulting in uncontrolled hydrogen generation. Even when the pumping rate of a liquid reactant is maintained constant, orientation change of the system causes sudden change in hydrogen generation rate. This typically occurs when there is a surplus of a liquid reactant or the reactant is not contained properly at the desired reaction zone of a system. The surplus or leaking reactant is typically pooled at the bottom of the fuel by gravity. This pooled reactant starts unwanted SBH hydrolysis at a location away from the reaction zone, resulting in the uncontrolled fuel consumption. This orientation-dependency issue is the best overcome by combining the embodiment of the MBI 308 (see
According to another aspect of the invention designs and materials for multi-step filtration of highly viscous products are provided, where the highly viscous products result from hydrolysis of a sodium borohydride reaction. Hydrogen gas needs separation from other products of SBH hydrolysis but the separation, i.e filtration, becomes more challenging with the highly viscous SBH product. The hydrolysis of SBH generates hydrogen and boron oxides that have relatively low solubility in most liquid reactants (such as water). There are also additives typically included in a fuel mixture for facilitation of the SBH hydrolysis as explained in the previous section. Furthermore, since a non-liquid fuel mixture reacts at a near-stoichiometric ratio of the fuel and a liquid reactant (e.g. water), the SBH hydrolysis generates highly viscous products. This highly viscous product is likely to result in a high-pressure drop across filters or even clogging in the filters.
In order to avoid this filter failure, the invention provides a filter set having single or multiple layers of product separation media installed between a fuel mixture and gas separating membrane.
In addition to the layout variations 600 provided above, the current invention provides specific design and selection of filter materials for the highly viscous products from SBH hydrolysis. Products from the current sodium borohydride (SBH) mixture consist of precipitated particulates (mostly boron oxide salts), hydrogen gas, and highly viscous paste (mixture of boron oxide salts, acid accelerators, surplus of water, and other additives). These products of different physical properties need to be filtered out using multiple steps. According to another embodiment,
In a preferred embodiment of the invention, a fuel mixture includes a fuel (sodium borohydride), acidic accelerators (acids such as malic acid, boric acid, succinic acid, or oxalic acid), a liquid distributing agent (polyethylene glycols, compressible sugars, poly saccharides, or glass fibers), and a binder (polyethylene glycol, poly saccharides, alginic acid, or cellulose). This mixture can either be compacted to form a solid structure such as a rod, cylinder, rectangle, micro-/macro-spheres or other forms, or be in its powder form, when the powder mixture is packaged in a fuel pack. Acid accelerators for this mixture are discussed above. Table I shows some exemplary compositions fuel mixtures and their mixing ratios.
a-8b show a schematic and a CAD model, respectively, of the current embodiment of a hydrogen generator system 800 that includes a liquid chamber 802, a fuel chamber 804, a filter chamber 806, and a pump 808. The liquid chamber 802 contains a plastic bag made out of polyethylene/BON material that stores deionized water. The DI water is pumped into the fuel chamber 804 and reaches an LDM (not shown). Hydrogen reaction occurs in the fuel chamber 804 at a defined reaction zone, then the resulting products flow into the filter chamber 806. The products are filtered out and only hydrogen gas exits the hydrogen generator system 800.
In a further embodiment, hydrogen generation is regulated by pumping of a liquid reactant, preferably clean filtered water. One pump, according to the current invention, is a diaphragm pump and the delivery of liquid is controlled by on/off, stroke volume, and pumping frequency. With a pre-determined stroke volume, the rate of hydrogen generation is mainly controlled by pumping frequency. In order to increase a hydrogen generation rate, the fuel cell sends a signal for an increased pumping frequency for accelerated hydrogen generation. Other types of pumps suitable for a hydrogen generator system include peristaltic pumps, and electro-osmotic (EO) pumps.
According to the current invention, a liquid-delivery medium (LDM) can be porous media, wicking fibers, wicking foams, or wicking fabrics such that any liquid flowing into the LDM can spread out uniformly to the fuel mixture.
According to another embodiment, a multi-stage filter for product separation can include a stiff hydrophobic material with high porosity (filter #1), a stiff hydrophobic material with medium porosity (filter #2), and a soft hydrophilic material with the least porosity (filter #3). Preferably, the filter #1 is placed at a product entrance to filter large particulates, then the filter #2 to filter viscous pasty components of products, and the filter #3 is placed at the last place to absorb any liquid. Typically, a gas separation membrane (e.g. silicone, PTFE, or ePTFE based materials) is placed after the filter #3. Preferred choice of hydrophobic porous materials includes, but is not limited to, synthetic nylon wools, silicone foams, rubber foams, polyethylene foams, viton foams, polyurethane foams, neoprene foams, or vinyl foams. Preferred choice of hydrophilic materials includes, but is not limited to, acryl yarns, polyimide foams, carbon felts, polypropylene felts. A preferred set of filters can include about 10˜20% (w/w) of a synthetic nylon wool (grade #2 coarse, McMaster Carr, CA) as a filter #1, about 10˜40% (w/w) of another synthetic nylon wool (grade #1 medium, McMaster Carr, CA), and about 40˜80% (w/w) synthetic acryl yarn (4 medium, Lion Brand Yarn Company, NY).
In a further embodiment of the invention, a local heating and cooling of a fuel or reaction chamber can assist faster start and stop function of hydrogen generation is provided. Application to the system 1000 (see
As shown in
According to another embodiment of the invention, provided is an apparatus disposed for the pre-heating of a liquid reactant before it reaches the reaction chamber can accelerate hydrogen generation after a system was off. As shown in
In one exemplary embodiment of the invention, a fuel mixture was prepared by grinding and mixing each component at a pre-determined mixing ratio. In this example, 15 gram of succinic acid, 1 gram of compressible sugar, 0.3 gram of silica, and 15 gram of sodium borohydride were weighed and poured into a grinding bowl. After uniform mixing under a dry condition, preferably in a humidity-controlled glove box, the powder mixture was poured into a compaction mold. Then, the powder mixture was compressed under a pressure of around 1,000˜2,000 psi to form a compacted cylinder with a conduit at its center. This compacted fuel pill was assembled with a nozzle type LDM 902 (see
According to another exemplary embodiment of the invention, fuel mixture contained 20 gram of sodium borohydride, 10 gram of malic acid, 1 gram of PEG6000 (Polyethylene Glycol, Mw=6,000), and 0.3 gram of silica was used. Other conditions were the same as the previous example.
According to a further exemplary embodiment of the current invention, the fuel mixture contains 20 gram of sodium borohydride, 10 gram of malic acid, 1 gram of PEG6000 (Polyethylene Glycol, Mw=6,000), and 0.3 gram of silica. Other conditions were the same as the previous example. The orientation of the fuel bag was changed at multiple time points, such as 1 hr 20 min, 2 hr 32 min, and 3 hr.
According to another exemplary embodiment of the invention, a synthetic polypropylene felt (McMaster Carr, CA) was used as a planar LDM 902 and placed in one side of a cylindrical fuel pill 904 (see
In yet another exemplary embodiment of the invention, a cylindrical solid fuel 306 is placed in an elastic balloon membrane 308 that has an inlet for liquid reactants 310a and outlet for products to exit 310b (see
According to another exemplary embodiment of the invention, a hydrogen generation system described in the previous example was tested under a dynamic condition where a liquid reactant pumping into the system was on for 20 min and off for 20 min. The dynamic performance of the stop/start is shown in
The present invention has now been described in accordance with several exemplary embodiments, which are intended to be illustrative in all aspects, rather than restrictive. Thus, the present invention is capable of many variations in detailed implementation, which may be derived from the description contained herein by a person of ordinary skill in the art. For example acid accelerators can be replaced or combined with metal catalysts. The presented invention can be applied to any chemical hydride reacting with any liquid reactant. Multi-stage filter set can be configured in serial, parallel, or combination of serial and parallel steps. Assembly sequence of each filter material can be altered for optimal performance. Physical form of a fuel mixture can be cylindrical, planar, annular, cubic, rectangular, particles, microspheres, beads, pallets, powder, or paste. Acid accelerators can be incorporated in a fuel mixture, or dissolved in the solution of a liquid reactant. Liquid delivery medium (LDM) can be in contact or proximate to the unreacted surface of a fuel mixture. LDM can be hydrophilic or lipophilic. LDM can have relatively large pores or small pores. A hydrogen generation system has a single or multiple LDMs at single or multiple locations. LDM can have a variety of form factors. Solubility modifying agents for hydrolysis products of sodium borohydride can be included in a fuel mixture, filter set, or saturated in the solution of liquid reactants. Liquid reactants can be preheated to assist the resuming function of the system after being turned off. Reaction zone or interface can be preheated to assist the resuming function of the system after being turned off. Heat generated from the exothermic reaction of sodium borohydride reaction can be stored and utilized to assist resuming function after the system being turned off. Heat generated from the exothermic reaction of sodium borohydride reaction can be utilized to preheat liquid reactants. Heat generated from the exothermic reaction of sodium borohydride reaction can be utilized to heat filtration area to lower viscosity of product flowing through filer materials.
All such variations are considered to be within the scope and spirit of the present invention as defined by the following claims and their legal equivalents.
