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Chemistry In Pictures

Chemistry in Pictures: Soot

by Craig Bettenhausen
June 7, 2022


Two petri dishes are on fire. Just the one on the right is putting off a lot of soot.
Credit: Neste

Sustainable aviation fuel (SAF), which is made from waste oils and other biomass by various chemical routes, is attracting a lot of attention and investment because of its lower net carbon emissions. SAF is the central pillar of the aggressive carbon reduction goals set by cargo and passenger airlines. One under-heralded benefit of SAF is that it burns much cleaner than petroleum jet fuel does. That’s because about 20% of petroleum jet fuel is made up of small aromatic compounds such as naphthalene and ethyl benzene, which burn less completely and form more soot than typically happens with straight, branched, and cyclical alkanes. Those types of compounds each make up 20–30% of petroleum jet fuel.

Most ways of making SAF don’t produce any aromatics, with the exception of catalytic hydrothermolysis. Unfortunately, aromatics cause gaskets and other rubber or plastic parts to swell, so engines and fueling infrastructure are sized to expect that swelling. As a result, SAF needs to have aromatics added in, usually by blending it with petroleum jet fuel—at least for now.

To read more about sustainable aviation fuel, check out the June 13 issue of C&EN.

Credit: Neste

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