The Battle for Octane: Ethanol or Aromatics?

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July 24, 2018

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by Steve Vander Griend (Urban Air Initiative) After learning about the clean octane benefits of ethanol, you may wonder why oil refineries still choose the toxic octane source of aromatics. A big reason is due to the fact that aromatics are considered the highest octane value for any given hydrocarbon produced at an oil refinery. And since aromatics are a product refiners own they prefer to use it over increasing levels of ethanol. On average, a gallon of gas contains 25% aromatics, which is any chemical built on a benzene structure.

Aromatics also have the highest emission rate per any hydrocarbon found in gasoline. In several studies
that identify specific tailpipe emissions, aromatics can have three times the emission rate as compared to ethanol. For example, in a fuel that contains 10% ethanol and 10% toluene which is the most common aromatic in gasoline, testing shows 3X’s the amount of toluene coming out the tailpipe compared to
ethanol. In addition, toluene, and aromatics in general have three times the ozone forming potential.

The problem doesn’t stop there because aromatics are the building blocks for Polycyclic Aromatic
Hydrocarbons (PAH’s) which then create Ultra-Fine Particulates (UFP’s).

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(T)he true octane benefit of ethanol comes into play when it is blended with gasoline.

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(I)f you add 30% ethanol to E0 gasoline, you have a higher octane than if you add 30% toluene to the same fuel. Note that toluene needs to increase nearly 20 percent to meet the same increase in octane compared to just 10% ethanol. This has been a key economic driver for the E10 market since there was nothing in the oil refineries production that could beat ethanol’s octane based on volume. READ MORE

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