In their efforts to reduce carbon emissions, some airlines and aircraft makers are pivoting towards biofuels to power airplanes. But jet fuel made from wasted food could slash emissions from flying much more dramatically, researchers report in the journal Proceedings of the National Academy of Sciences.
In the paper, they detail a way to convert organic waste into paraffin, a kerosene-like fuel that can be used in jet engines. Such food waste-derived fuel could cut aviation emission levels by 165 percent compared to fossil fuels.
The aviation industry produces about 2.5 percent of global carbon emissions. Some airlines have recently committed to reduce their carbon footprint by half before 2050. Hybrid and electric airplanes are one way to do that, but biofuels are a more near-term solution. Boeing, for instance, plans to make commercial airplanes that can fly solely on biofuels by 2030. United Airlines is already powering some of its flights with a biofuel blend, which the company says reduces greenhouse gas emissions by over 60 percent.
Until now, sustainable aviation fuel in the U.S. has been produced from virgin vegetable oils or waste fats and oils. But using food waste achieves two goals: it gives a cleaner fuel, and also diverts organic matter from the landfill, avoiding the methane emissions created as it sits and rots. Plus you could also potentially use other wastes like wastewater sludge and manure.
The challenge is that the high water content in this wet waste makes it difficult to process using traditional methods used to make biofuels. So the team led by researchers at the National Renewable Energy Laboratory used a technique to interrupt the fermentation process of the organic matter into methane.
The process generates acids that have either short chains of carbon atoms or long ones. Petroleum is used today to make such short-chain acids, while the long-chain acids are made from coconut and palm oil.
Next, the researchers used a process called ketonization to convert the acids into paraffins that are identical to those found in petroleum. They were also able to make a slightly different type of paraffin called isoparaffin, which has a much lower freezing point for jet fuel applications, and produces less soot.
A cost analysis showed that the fuel could be produced for a minimum selling price of $2.50 per gallon. The researchers say that this conversion process has the potential to replace 20 percent of the U.S.’s jet fuel consumption, providing a path towards net-zero carbon emissions aviation fuel.
Source: Nabila A. Huq et al. Toward net-zero sustainable aviation fuel with wet waste–derived volatile fatty acids. PNAS, 2021.