Patent Application
20060210470
The present invention relates to systems and methods of generating hydrogen.
Combustion of solid mixtures is widely used for gas generation in various applications, e.g., in creating thrust in rocket engines or inflating air bags in case of car collisions. Hydrogen storage is considered a factor in the transition from fossil-fuel to hydrogen-based economy. Generation of hydrogen by combustion is of particular interest for fuel-cell based portable electronics and emergency power sources.
More specifically, hydrogen storage and generation systems are needed for lightweight, robust, cost effective fuel cell power sources. Hydrogen generation by combustion is of interest for portable power supplies to be used, for example, as chargers in various electronic devices. Thus, it is desired to identify systems that generate hydrogen during combustion and exhibit high hydrogen yield.
Moreover, as portable electronic devices, such as mobile phones, notebook computers, and other handheld device are becoming more widespread and power-demanding, fuel cell power sources are needed with higher specific energy (Wh/g) than batteries. In this context, direct methanol fuel cells (DMFC) have been suggested as power sources for small scale applications, but have drawbacks, including low power density, methanol crossover, electrode poisoning and methanol toxicity. Current hydrogen fuel cells do not have any methanol-related problems and provide higher power density and double conversion efficiency as compared to DMFCs. Hydrogen storage, however, is a challenge in the development of hydrogen fuel cell power sources. Compressed gas and reversible metal hydrides cannot provide sufficient hydrogen yield, while use of liquid hydrogen is currently not applicable in portable applications.
Some techniques call for using compounds with high content of hydrogen, released during chemical reaction with water. Many processes seem promising due to their relatively high theoretical hydrogen yield. However, the practical solution strengths are limited and, in turn, decrease maximum hydrogen yield to significantly less than the theoretical hydrogen yield. Further, reaction initiation typically requires introducing a catalyst to the mixture creating difficulty particularly for small scale applications.
Although hydrogen generation by combustion has been studied extensively for chemical laser applications since the 1970's, manufacturers continue to be challenged in avoiding the use of toxic components, poisonous gases to an anode catalyst, and expensive substances. The mixtures are typically based on compounds with high hydrogen content. However, many compounds are not suitable. For example, hydrazine, diborane and their derivatives, such as N2H4(BH3)2, are not suitable for fuel cell applications because of their extreme toxicity. Some other compositions generate gases, such as CO and NH3, poisonous for the anode catalyst.
Thus, there is a need to provide a way to generate hydrogen with sufficient hydrogen yield applicable on any suitable system including portable systems in a cost effective manner without requiring catalysts, toxic compounds, or poisonous substances.
The present invention generally provides examples of generating hydrogen with sufficient hydrogen yield applicable for any suitable system including portable systems in a cost effective matter. Examples of the present invention generate hydrogen in an efficient way that allows for hydrogen storage without requiring catalysts, toxicity, or poisonous or harmful components.
In one example, the present invention provides a method of generating hydrogen. The method comprises preparing a first mixture of a stabilizer and a gelling agent in water to define a resulting gel. The method further comprises mixing the resulting gel with metallic particles and metal borohydride to define a resulting mixture. The method further comprises igniting the resulting mixture to obtain hydrogen.
In another example, the present invention provides a method of generating hydrogen by combustion of a sodium borohydride-metal-water mixture. The method comprises preparing a first mixture of between about 1 and 10 percent weight sodium hydroxide and between about 1 and 10 percent weight polyacrylamide in distilled water to define a resulting gel. The method further comprises mixing the resulting gel with metal borohydride and metallic particles to define the sodium borohydride-metal-water mixture. The method further comprises heating the sodium borohydride-metal-water mixture to produce hydrogen from the sodium borohydride and the water by combustion.
In yet another example of the present invention, the method comprises a method of generating hydrogen. The method comprises mixing a reactant gel with a metallic powder and metal borohydride to define a resulting mixture. In this example, the reactant gel includes a stabilizer and a gelling agent in water. The method further comprises igniting the resulting mixture to produce hydrogen.
In still another example of the present invention, the method comprises preparing a first mixture of a stabilizer in water to define a resulting solution and mixing the resulting solution with metallic particles and metal borohydride to define a resulting mixture. The method further comprises igniting the resulting mixture to obtain hydrogen.
Further objects, features, and advantages of the present invention will become apparent from consideration of the following description and the appended claims when taken in connection with the accompanying drawings.
a-e are images of reaction wave propagation having a borohydride-aluminum-water mixture;
a-e are images of reaction wave propagation having a borohydride-magnesium-water mixture;
Examples of the present invention generate hydrogen in a relatively efficient manner without including any catalysts or toxic components. In one example, the method comprises using combustion of triple borohydride-metal-water mixtures, wherein relatively high-exothermic reactions between metal and water create conditions for hydrolysis of borohydride. The mixtures ignite and burn in inert atmosphere to produce hydrogen, sodium metaborate and metal oxides—all environmentally benign materials. The mixtures are independent of any catalysts or toxic components.
In one example, the method of generating hydrogen comprises preparing a first mixture of a stabilizer and a gelling agent in water to define a resulting gel. The method further comprises mixing the resulting gel with metallic particles and metal borohydride to define a resulting mixture. Preferably, the metal borohydride is sodium borohydride. The method further comprises igniting the resulting mixture to obtain hydrogen.
In this example, the stabilizer may be any suitable substance including an alkali, e.g., sodium hydroxide (NaOH). The stabilizer is prepared with the gelling agent to reduce or prevent hydrolysis of borohydride at room temperature. Preferably, the stabilizer comprises between about 1 and 10 percent weight sodium hydroxide and more preferably about 2 percent weight sodium hydroxide.
The gelling agent may include any suitable substance, e.g., polyacrylamide. Preferably, the gelling agent may comprise between about 1 and 10 percent weight polyacrylamide and more preferably about 3 percent weight polyacrylamide.
In this example of the present invention, the metallic particles comprise aluminum (Al), magnesium (Mg), or their alloy. Preferably, the aluminum particles comprise nanoscale aluminum particles and more preferably having an average particle size of between about 70 and 100 nanometers. In yet another example, the magnesium particles comprise microscale magnesium particles.
In this example of the present invention, the resulting mixture is the borohydride-metal-water mixture. The combustion of the resulting mixture is performed wherein high-exothermic reactions between metal and water create conditions for the hydrolysis of borohydride. Preferably, this is accomplished by performing the reactions as follows:
NaBH4+2 H2O→NaBO2+4 H2 (1)
Al+1.5 H2O→0.5 Al2O3+1.5 H2 (2)
or
NaBH4+2 H2O→NaBO2+4 H2 (1)
Mg+H2O→MgO+H2. (3)
By performing reaction (1) with either reaction (2) or (3) in one combustion process, higher hydrogen yields are reached than by performing reaction (2) or (3) alone and by performing reaction (1) without any catalyst. Moreover, the triple borohydride-metal-water mixtures are absent in producing any harmful compounds of Nitrogen, Chlorine, or Sulfur. The mixtures of sodium borohydride with water and metal (e.g., aluminum or magnesium powder) ignite relatively easily at about room temperature and burn in inert atmosphere, producing hydrogen, sodium metaborate (NaBO2) and alumina (Al2O3) or magnesia (MgO). Such products are environmentally benign materials. As mentioned above, the borohydride-metal-water mixtures include relatively small quantities of the resulting gel, including a gelling agent (e.g., polyacrylamide) and a stabilizer (e.g., NaOH), to prevent hydrolysis of borohydride at room temperature.
In reaction (1), water in this example is both a reactant and an additional source of hydrogen. As a result, borohydrides provide relatively high hydrogen yield making them attractive for applications. As will be shown below, the moderate exothermicity of the metal borohydrides hydrolysis welcomes the presence of either reactions (2) or (3) for the combustion-based hydrogen generation without any catalysts.
One of reactions (2) and (3) may be used in parallel with reaction (1) to generate hydrogen by way of combustion of metals with water. As mentioned above, such metals may include aluminum or magnesium, or their alloys. In each of reactions (2) and (3), water acts as an oxidizer for the metal and as the sole source of hydrogen. The adiabatic combustion temperature of the stoichiometric mixtures, e.g., Al/H2O and Mg/H2O, at pressure 1 atmosphere (atm) is about 2900 and 2750 K, respectively, indicating that the heat release is sufficient for self-sustained reaction of reactions (1) and (2) or reactions (1) and (3).
In one example, the use of nanoscale aluminum particles or microscale magnesium particles decreases the ignition temperature of the metal, while the gelling agent inhibits water evaporation during the process. Hence, the borohydride-metal-water mixture ignites easily and reacts in inert atmosphere, producing hydrogen. Alumina and magnesia, produced also in reactions (2) and (3), are environmentally benign materials.
In one example, about 2 percent weight NaOH and 3 percent weight polyacrylamide (Mw=5×106) are prepared in preferably distilled water to define a resulting gel. The resulting gel is mixed with NaBH4 and aluminum powders, preferably nanoscale aluminum particles having an average particle size of about 80 nm. The resulting mixture is then ignited to generate hydrogen.
Thermodynamic calculations for NaBH4/Al/H2O and NaBH4/Mg/H2O systems were performed. This was accomplished by using Thermo™ software version 4.3 (Feb. 20, 1995) manufactured by the Institute of Structural Macrokinetics and Materials Science, Russian Academy of Sciences (Chernogolovka, Russia), Copyright 1993 Dr. A. Shiryaev, E. Petrova. As shown in
As depicted in
In yet another example, the applicants have found that if the metallic particles comprise nanoscale aluminum particles, then the first mixture may not necessarily comprise a gelling agent. Thus, in this example, first mixture is free of a gelling agent and comprises the stabilizer in water to define a resulting solution. The resulting solution is then mixed with the metallic particles and metal borohydride to define the resulting mixture. The resulting mixture is then ignited to generate hydrogen.
This example provides a method of generating hydrogen. In this example, experiments on combustion of the NaBH4/Al/H2O mixtures were conducted.
The resulting mixture was placed in a quartz cylinder (height 3 cm, inner diameter 1 cm) represented by reference numeral 22 in
The experiments for various metal/NaBH4 ratios at stoichiometric water contents show that mixtures with relatively coarser Al powder do not burn while those with Mg and nanoscale Al powders are combustible. This is associated with the desire to ignite metal particles in the combustion front.
Increasing metal fuel loading significantly stimulates combustion. Specifically, reaction with no metal fuel addition requires permanent heating by the igniter, while metal fuel-rich mixtures burn vigorously as depicted in
In the second stage of the process, the gradual pressure growth corresponds to hydrogen generation during uniform propagation of the combustion front, while the final decrease is caused by cooling. The dependence of combustion front velocity on the metal fuel content is shown in
Powder XRD analysis of condensed products shows sodium metaborate (NaBO2), metal oxide (Al2O3 or MgO) and, in the case of Al, some amount of unreacted metal. Gas chromatography indicates that the evolved gas is essentially hydrogen (about 99%). It is to be noted that vapors of unreacted water and formed NaBO2 (likely to be present during combustion) condense readily upon cooling and hence are not present in the gaseous products.
Furthermore, the triple sodium borohydride/metal/water mixtures with polyacrylamide and NaOH additives are combustible and exhibit higher hydrogen yield than theoretically achievable for either reaction (2) or (3) alone. In these mixtures, the highly exothermic combustion reaction (2) or (3) assists sodium borohydride hydrolysis (1). This eliminates the use of catalyst, one of the challenges for portable fuel cell applications. The proposed mixtures provide self-sustained generation of hydrogen with relatively high hydrogen yield.
While the present invention has been described in terms of preferred embodiments, it will be understood, of course, that the invention is not limited thereto since modifications may be made to those skilled in the art, particularly in light of the foregoing teachings.
This application claims the benefit of U.S. Provisional Application Ser. No. 60/663,238, filed on Mar. 18, 2005, entitled “SYSTEM AND METHOD OF GENERATING HYDROGEN,” the entire contents of which are incorporated herein by reference.
| Number | Date | Country | |
|---|---|---|---|
| 60663238 | Mar 2005 | US |
