Petroleum Substances Terminology

Petroleum (crude oil) and raw natural gas are naturally occurring substances, sometimes containing thousands of individual chemicals called hydrocarbons. In order to make finished petroleum products, they must be separated into different fractions (i.e., gases, naphtha, distillates). Each of these fractions often requires additional processing before they can be sold or blended into finished petroleum products like gasoline, jet fuel, diesel fuel, etc.

The separated fractions are individual substances often referred to as "petroleum process streams" and are defined according to the last processing step that they have undergone. Typically, there is no set chemical composition for most petroleum substances. They usually are TSCA Class II substances (Chemical Substances of Unknown or Variable Composition, Complex Reaction Products, and Biological Material or "UVCBs"). They are described generically in EPA’s Chemical Substances Inventory, and have a unique Chemical Abstracts Service (CAS) registry number. 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. For example:

Distillates¹ (petroleum²), heavy catalytic cracked³
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 C15 through C35⁴ and boiling in the range of approximately 260 °C to 500°C (500°F to 932°F)⁵. This stream is likely to contain 5 wt. % or more of 4- to 6-membered condensed ring aromatic hydrocarbons.

The substance name and definition usually contains the following information:

1. The primary hydrocarbon fraction such as Gases, Naphtha, Distillate/Gas Oil, or Residuum. Other nomenclature such as Extracts, Wax, etc. may be used for specific refinery processes.
2. The hydrocarbon source. The hydrocarbon source here is "petroleum" as opposed to "shale" or "coal".
3. The last refining step.
4. The carbon number range
5. The boiling point range.

This particular definition includes some information on specific components in the substance, although this is typically not the case.

Product Categories
Petroleum substances are often organized and evaluated according to product categories. Use of categories facilitates coordination of efforts to summarize existing data and develop new hazard data which will be appropriate for hazard and risk characterization worldwide and therefore, avoid unnecessary duplication of testing. Below is a comparision of the categories used by the Petroleum HPV Testing Group for the EPA’s High Production Volume Chemical (HPV) Challenge with the categories used for REACH registration in Europe by CONCAWE and the Lower Olefins & Aromatics Consortium (LOA).

(The number of substances sponsored is in the parenthesis.)

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