An efficient, super-fast new method of turning waste biomass into hydrogen has been developed by scientists in Minnesota, US. The researchers say it could help significantly reduce many nations’ dependence on fossil fuels.
Hydrogen represents a cleaner alternative to fossil fuels but is both costly and dangerous to transport, leading many to argue that it must be generated in distributed fashion, rather than in centralised facilities. Anything that could lead to smaller and more portable hydrogen generation is likely to be welcomed by proponents of green energy.
The new process, developed by Lanny Schmidt, Brandon Dreyer and colleagues at the University of Minnesota’s Department of Chemical Engineering and Material Science, is known as “flash volatilisation”.
It relies on a simple but highly reactive chemical catalyst to break down biomass, such as agricultural waste, with heat. Not only does the process avoid the need to expend extra energy generating the heat needed, it also takes place up to 100 times more rapidly than existing techniques allow, the researchers claim.
Chemical trick
Droplets of oil and sugar taken from biomass are sprayed into a small chamber containing a foam catalyst of rhodium and cerium. As the droplets hit the foam, volatile compounds within them oxidise (combust) to produce heat. This breaks down larger non-volatile compounds into a combination of hydrogen and carbon monoxide – a synthesis gas, or “syngas”.
The deceptively simple process relies on a complex chemical trick. Normally, when a volatile droplet hits a hot surface it vaporises so rapidly that an insulating layer of gas emerges between itself and the surface, preventing it from being heated. Here, however, the porous nature of the foam used causes heat to be transferred to the droplets, while also drawing syngas down through the catalyst.
Syngas can then either be used to make fuels like gasoline, or its hydrogen can be separated in order to power fuel cells. The biomass required can come from anything from cooking oil to glucose-rich cornstalks, Schmidt says.
Sustained temperatures
Using flash volatilisation the Minnesota scientists were able to generate one megawatt of heat per square metre of biomass. A sustained temperature of 800°C was produced by the reaction.
A key advantage of the approach is that it should scale up easily, Dreyer says. “The simplicity of the process makes it easily scaled to both small and very large systems,” he told New Scientist.
Soren Kaer, a combustion expert at Aalborg University’s Institute of Energy Technology in Denmark, agrees that scalability will be important to making domestic hydrogen generation possible. “The combination of the combustion process and use of catalysts in this way is a new idea,” he notes.
Journal reference: Science (vol 314, p 801)
