In the hydrogen economy, automobiles would be powered by the simplest element on the periodic table, leveraging the element's abundance. But as the Hindenburg disaster demonstrated, hydrogen is also the most difficult element to compress into a safe, usable form. Why not instead synthesize a hydrocarbon-based fuel, such as methanol or even gasoline?
Sandia National Laboratories is building such a fuel synthesizer in a bid to harness sunlight to reverse the process of combustion. The reactor would use reclaimed carbon dioxide emissions to create renewable synthetic fuel by combining the CO2 with water.
"Rather than make hydrogen for people to use in fuel cells, we think it might make more sense to make a synthetic fuel that is already compatible with our existing [gasoline engine] infrastructure," said Rich Diver, inventor of the Counter Rotating Ring Receiver Reactor Recuperator (CR5). "Others are working on ways to make liquid synthetic fuels from natural gas, but we are going back a step further and looking at ways of thermochemically making the precursors for synthetic fuel using solar energy, carbon dioxide and water."
Unbelievable as it sounds, Diver claims that his solar-powered reactor could help clean up the planet by making internal combustion a reversible process. His team calls the project Sunshine to Petrol (S2P) and the envisioned synthesized product Liquid Solar Fuel.
"One way to look at it is as reverse combustiontaking heat from the sun, adding it to carbon dioxide and water, and making a synthetic fuel from them," said Diver. "We were originally just looking at ways of using solar energy to make hydrogen from water, but some of the same principles can be used to upgrade carbon dioxide to carbon monoxide. And with the right combination of carbon monoxide and hydrogen, you can make synthetic liquid fuel."
The conventional fuels with which we are familiargasoline, propane, butane, methane, natural gasare all just various types of hydrocarbon bondings. When enough hydrogen and carbon atoms are bonded together, they become heavy enough to exist as liquid at room temperature. For example, 100 octane gasoline is just 8 atoms of carbon bonded to 18 atoms of hydrogen: C8H18.
"Combining hydrogen and carbon monoxide gives you a fuel which you can use similarly to natural gas; and using a few chemical processing steps, you can make methanol and other liquid fuels that you can burn in engines designed for gasoline," said Diver.
Right now, it's cheaper to drill for oil and refine it, according to Diver; but in 20 years, as oil grows scarcer, synthesizing fuels for traditional gasoline and diesel engines will become an increasingly attractive alternative. That's when "our work will start to look very attractive," said Diver. "When the fossil fuels run out, you either have to go to solar energy or nuclear energy; there are no other choices."