Chemical engineers know better than anyone the difficulties in turning a promising lab curiosity into an actual product. Consider, for example, aluminum-water reactions as a means for generating hydrogen gas. For decades, researchers have been trying to tap the commercial potential of these reactions, which have the potential to produce hydrogen without the high costs and energy inefficiency of steam reforming and electrolysis techniques and systems. Over the years, there have been scores of patents and technical papers documenting efforts to harness the hydrogen-generating power of aluminum-water reactions.

By and large, these efforts have remained in the lab because of the thorny chemistry and engineering development challenges associated with the commercialization and “productization” of the technology.

Until now. AlumiFuel Power, Inc., this month introduced a new aluminum-water reactor system called the Portable Balloon Inflation System, or PBIS-1000 (Figure 1). Unlike other hydrogen generation technologies, this portable hydrogen generator requires no external energy whatsoever.  All it needs is freshwater or salt water in its tank and a pair of AlumiFuel 32-ounce cartridges containing aluminum powder along with proprietary additives and packing materials. To initiate the reaction and start generating hydrogen, users open the cartridge and insert it into the unit’s stainless-steel reaction chamber, where it is punctured by a needle that allows the water to be pumped in by hand. A two-cartridge PBIS system fits in a two-foot cube with room to spare and can generate 1,000 liters of hydrogen in about 20 minutes; this is enough lift gas to launch a 5-foot-diameter weather balloon. Yields for the system typically exceed 95%.

Though initially developed for inflating weather balloons in the field, this reactor technology can generate hydrogen for use in fuel cells. The current sweet spot for technology is portable, supplying backup and remote power in the range of 100 W to 5kW. Energy densities for the fuel are 9.2 kWh/L or 8.9 kWh/kg, or about four times the amount offered by current state-of-the-art battery technologies. The system also can produce hydrogen for a variety of niche applications that currently rely on hydrogen supplied in bulky, expensive K cylinders.

The aluminum-water-additive reaction isn’t just about hydrogen. Similar reactor designs can be used to harness the superheated steam from this highly exothermic reaction. In one promising class of applications, the steam can be used to drive turbines that power unmanned underwater vehicles (UUVs) and other submersibles for naval and commercial customers.

To make the aluminum-water reaction commercially viable in such a broad spectrum of applications,   AlumiFuel’s team of engineers and material scientists had to overcome challenges related to both the reaction chemistry and the physical design of the system.

Details about the chemistry are proprietary and are part of a growing intellectual property portfolio that currently consists of several patents pending and disclosures that cover application-specific reactions involving powders, solid aluminum, and gels. Suffice it to say that the key to the technology is not a single, one-size-fits-all formulation of aluminum and reaction promoters. Instead, AlumiFuel material scientists have developed the ability to tailor formulations to specific application requirements.

In all, they draw on about a half dozen proprietary reaction promoters, adjusting the ratios of each as needed, as shown in the following equation:

2 Al(s) + proprietary reactants/initiators + 6 H₂O(l) → 2 Al(OH)₃(s) + 3 H₂(g) + heat

One invaluable tool in gaining mastery over the aluminum-water reaction has been AlumiFuel’s investment in nanotechnology techniques and testing equipment through its membership in the Drexel Nanotechnology Consortium. AlumiFuel materials scientists routinely employ scanning electron microscopy to analyze aluminum powder feedstocks before and after the reaction (Figure 2).

These engineers also can fine-tune process conditions in the reactor and account for the particle size distribution and the shape of different aluminum powders.  The result of all this control over all the process inputs is that the reaction can be optimized for the application at hand. Filling a 5-foot-diameter weather balloon in 20 minutes, for example, may require a different reaction profile than does generating heat for a small steam-powered turbine  (Figure 3).

Aside from the chemistry, the engineers were charged with developing production and packaging methods that would keep the cost of all consumables low and make the system easy to use. One way they did that was to build the entire system around readily available items of commerce. The aluminum powder, for example, is nothing exotic, just a low-cost commercial grade. The cartridges, to take another important example, are based on 32-ounce aluminum beverage cans that lend themselves to high-volume manufacturing techniques.  Initially, the cans, the same kind used for Monster Energy Drinks, could not withstand the temperatures associated with the aluminum-water reactions. Therefore, the engineers developed proprietary packing methods and packing materials that preserve the integrity of the can once the reaction begins.

AlumiFuel’s engineers also made the hydrogen generation system modular, scalable, and flexible, in keeping with the diverse group of applications that the technology targets. For example, the reactor design used for balloon inflation comes in one-cartridge and two-cartridge versions, depending on the desired hydrogen generation capabilities. AlumiFuel engineers can scale the reactor technology even further, adding cartridges or groups of reactors to increase the capacity of the system beyond the 1,000 liters of gas produced in 20 minutes by the current system. On the other end of the capacity spectrum, they are ironing out the details on a small lab-scale reactor for use in educational or research settings.

AlumiFuel engineers also are working on other form factors, including some that do not make use of the current reactor hardware. UUV power plants using turbines, thermoelectric converters, and/or fuel cells are one example. To take another example, the aluminum-water reaction technology could see use in flameless heater pouches for military rations or even hand warmers, applications that AlumiFuel is pursuing aggressively.

These heater applications may seem like a departure from balloon inflation or portable power, but a common thread runs through all these applications: Tailor the reaction chemistry to the job at hand and find  clever ways to package that chemistry for the user.

The Problem with Aluminum-Water Reactions

In a generic aluminum-water reaction, a layer of aluminum oxide forms on the aluminum surface and prevents direct contact with the water:

2Al + 6H₂O → 2Al(OH)₃ + 3H₂

A variety of reaction promoters, catalysts, and initiators can help keep the reaction going by disrupting the formation of the aluminum oxide layer. Researchers have demonstrated, for example, that various hydroxide, oxide, and salt promoters can help maintain aluminum-water reactions. Other research has focused on reactions of water with molten aluminum alloys whose molten state inherently prevents oxide formation. Still other research has delved into the use of solid aluminum immersed in a solution of water and additives. Although the reaction-promotion chemistry is well understood by some experts, no one has been able to translate that knowledge into a commercial-scale hydrogen generator.

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