Aromatics are hydrocarbons containing a benzene ring of six unsaturated carbon atoms. Benzene is the the smallest, most basic aromatic compound, but other common ones include toluene and xylene.

Aromatics in petroleum products

Aromatics are an important element in gasoline blending because they are a key source of highly valued octane. However, some aromatics are also toxic to humans and a contributor to smog when released into the atmosphere. As a result, refiners typically try to maximize the aromatics content of gasoline up to a maximum limit set by environmental concerns.

Regulations typically limit both the overall volume percent of aromatics, and the volume percent of benzene in particular.

Aromatics are very undesirable in distillates such as jet fuel and diesel, where they tend to lower smoke point and cetane, respectively.

Aromatics such as benzene, toluene and xylene are also important refined products in their own right. All of these are important feed stocks to petrochemicals. Consequently, many refiners will extract these products from reformate and sell them as final products.

Aromatics in refinery feed stocks

Aromatics content also has an effect on how well a hydrocarbon performs in some conversion units. In particular, highly-aromatic compounds tend to crack very poorly in an FCC unit.