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Petroleum Streams Terminology

Crude oil is a naturally occurring mixture of thousands of chemicals called hydrocarbons. In order to make petroleum products from crude oil, it must be heated to separate the oil into different fractions (gases, naphthas, gas oils, residual materials). Each of these fractions requires additional processing before they can be blended into petroleum products like gasoline, diesel fuel, motor oil, candle wax, asphalt, etc.

These fractions are referred to as petroleum process streams and are labeled according to the processing that they have undergone. If it has undergone multiple processing steps, it is labeled by the last process step it underwent. These process streams include gases, liquids and solids and most are complex mixtures of hydrocarbons. The chemical composition for any one stream can vary from refinery to refinery, and can also vary with different sources of crude oil. There is no set chemical composition for a petroleum stream. The streams are described generically in EPA’s Chemical Substances Inventory, and have a unique Chemical Abstracts Service (CAS) registry number. Accordingly, each of these "complex mixtures" is considered a unique chemical substance. The EPA Inventory listing typically provides a brief description of the stream, with the approximate carbon number range of the hydrocarbons present, and the approximate boiling range.

Shown below are several examples of refinery stream listings in the EPA inventory.

Distillates (petroleum), light crude oil  CAS 68410-05-9

A complex combination of hydrocarbons produced by the distillation of crude oil. It consists of hydrocarbons having carbon numbers predominantly in the range of C2 through C7 and boiling in the range of approximately –127 degrees F to 200 degrees F.

Naphtha (petroleum), light catalytic cracked  CAS 64741-55-5

A complex combination of hydrocarbons produced by the distillation of products from a catalytic cracking process. It consists of hydrocarbons having carbon numbers predominantly in the range of approximately minus 20 degrees C to 190 degrees C (-4 degrees F to 374 degrees F). It contains a relatively large proportion of unsaturated hydrocarbons.

Distillates (petroleum), light distillate hydrotreating process, low boiling CAS 68410-97-9

A complex combination of hydrocarbons obtained by the distillation of products from the light distillate hydrotreating process. It consists of hydrocarbons having carbon numbers predominantly in the range of C6 through C9 and boiling in the range of approximately 37 degrees F to 382 degrees F.

For more information on EPA’s TSCA Inventory of Chemical Substances, visit

http://www.epa.gov/opptintr/newchems/invntory.htm.