The aviation industry has spent the past decade looking for ways to reduce its global carbon footprint, such as buying so-called carbon offsets – such as tree planting projects or wind farms – to offset the carbon dioxide emitted by high-flying jets. At the same time, airports in San Francisco, Chicago and Los Angeles, along with a dozen in Europe, are powering planes with greener alternative fuels to help meet carbon reduction goals.
Now, a team from Oxford University in the UK has devised an experimental process that converts carbon dioxide – a greenhouse gas emitted by all gas-fired engines – into jet fuel. If successful, the process, which uses an iron-based chemical reaction, can result in “net zero” emissions from aircraft.
The experiment, reported today in the journal Nature Communications, was conducted in a laboratory and has yet to be replicated more widely. But the chemical engineers who designed and executed the process are hopeful it could be a climate game changer.
“Climate change is accelerating, and we have massive carbon dioxide emissions,” said Tiancun Xiao, a senior research fellow at Oxford’s Department of Chemistry and an author of the paper. “The hydrocarbon fuel infrastructure is already there. This process could help mitigate climate change and use the current carbon infrastructure for sustainable development. “
When fossil fuels such as oil or natural gas burn, their hydrocarbons are converted into carbon dioxide and water and energy are released. This experiment reverses the process of converting carbon dioxide back into fuel using the so-called organic combustion method (OCM). By adding heat (350 degrees Celsius, which is 662 degrees Fahrenheit) to citric acid, hydrogen, and a catalyst made of iron, manganese and potassium to the carbon dioxide, the team was able to produce liquid fuel that would work in a jet engine. The experiment was done in a stainless steel reactor and produced only a few grams of the substance.
In the lab, the carbon dioxide came from a canister. But the idea of adapting the concept for the real world would be to capture large amounts of greenhouse gas from a factory or directly from the air to remove it from the environment. Carbon dioxide is the most abundant of the planet’s warming greenhouse gases and is produced by factories, automobiles and wood burning, including wildfires and slash-and-burn agriculture. Keeping it out of the atmosphere can reduce global warming, although global carbon emissions have risen in recent decades and are on track to heat the planet by 2 degrees Celsius by the end of the century.
Xiao and colleagues say the new method would also be cheaper than existing methods that turn hydrogen and water into a fuel, a process called hydrogenation, mainly because it would use less electricity. Xiao plans to install a jet fuel plant next to a steel or cement plant or a coal-fired power plant, capturing the excess carbon dioxide to make the fuel. The process can also include sucking up carbon dioxide from the atmosphere, something called direct air intake. The catalyst that does the trick is plentiful on Earth, and it requires fewer steps than other methods of synthesizing high-value-added chemicals, the authors say.
An expert not involved in the experiment says the concept looks promising as long as the authors can figure out how to go from producing miniscule amounts of jet fuel in the lab to larger amounts in a pilot plant. “This looks different, and it looks like it could work,” said Joshua Heyne, associate professor of mechanical and chemical engineering at the University of Dayton. “Scaling up is always a problem, and there are new surprises when you move to a larger scale. But in terms of a longer term solution, the idea of a circular carbon economy is certainly something that could be the future. “