U. LEEDS (UK)—Researchers have found an energy efficient way to make hydrogen-based fuel out of used vegetable oil discarded by restaurants and pubs.

The process not only generates some of the energy needed to make the hydrogen gas itself, but is also essentially carbon-neutral, researchers say.

“We are working towards a vision of the hydrogen economy,” says Valerie Dupont of the University of Leeds.

“Hydrogen -based fuel could potentially be used to run our cars or even drive larger scale power plants, generating the electricity we need to light our buildings, run our kettles, and fridges, and power our computers.

“But hydrogen does not occur naturally, it has to be made. With this process, we can do that in a sustainable way by recycling waste materials, such as used cooking oil.”

To make hydrogen from simple fossil fuels, such as natural gas, the fuel is mixed with steam in the presence of a metal catalyst then heated to above 800 degrees centigrade to form hydrogen and carbon dioxide.

However when more complex fuels are used, such as waste vegetable oil, it is difficult to make very much hydrogen using this method without raising the temperature even further, Dupont says.

The reactions could be run at lower temperatures but the catalysts would quickly become poisoned by residues left over from the dirty oil.  In short, the process is not only expensive but also environmentally unsound.

Dupont and colleagues developed a two-stage self-heating process. To begin, the nickel catalyst is blasted with air to form nickel oxide—an ‘exothermic’ process that can raise the starting temperature of 650 degrees by another 200 degrees. The fuel and steam mixture then reacts with the hot nickel oxide to make hydrogen and carbon dioxide.

A material to trap the carbon dioxide was added, leaving pure hydrogen gas that eliminated the greenhouse gas emissions and also forced the reaction to keep running, increasing the amount of hydrogen made.

“The hydrogen starts to be made almost straight away, you don’t have to wait for all of the catalyst to be turned into pure nickel,” Dupont says.  “So as well as the generation of heat, this is another way that makes the process very efficient.”

The two-stage process has proved to work well in a small, test reactor. Dupont and colleagues now want to scale-up the trials and make larger volumes of hydrogen gas over longer periods of time.

“The beauty of this technology is that it can be operated at any scale. It is just as suitable for use at a filling station as at a small power plant,” Dupont explains.

“If we could create more of our electricity locally using hydrogen-powered fuel cells, then we could cut the amount of energy lost during transmission down power lines.”

Details of the work, funded by  the Engineering and Physical Sciences Research Council (EPSRC), will be published in the journal Bioresource Technology.

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