Researchers at the University of Leeds have found an energy-efficient way to make hydrogen out of used vegetable oils discarded by restaurants and other establishments. The process generates some of the energy needed to make the hydrogen gas itself and is also essentially carbon-neutral.
"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," said Dr. Valerie Dupont, who is leading the project.
Hydrogen can be made 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. When much 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. The reactions could be run at lower temperatures but the catalysts would quickly become poisoned by residues left over from the dirty oil.
Dr. Dupont and colleagues have perfected a two-stage process that is essentially self-heating. 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.
The researchers also added a special sorbent material to trap all the carbon dioxide produced, leaving them with pure hydrogen gas. This trick 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," Dr. Dupont said. "So as well as the generation of heat, this is another way that makes the process very efficient."
The researchers have shown that the two-stage process works well in a small, test reactor. They 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," Dr. Dupont said. "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."