1 – Fractionation

Large fractionation

The first stage in the petroleum refining process is separating the crude oil into various components called “fractions”.

Petroleum Refining Process Map


Petroleum Products

Fractionation Process

The crude oil is fed into a distillation column, shown below, where the differences in boiling points of the different components within the crude oil drive the separation of the hydrocarbons into heavy and light streams. The lighter products such as butane, naphtha, kerosene, distillate, and gas oil are sent onto additional process units for further processing (treatment/conversion). The remaining heavy product (reduced crude/residuum) is sent to a vacuum column for further separation.

vacuum column
(Copyright Sulzer Chemtech Ltd., Switzerland)

The reduced crude can be further separated at a reduced pressure requiring a vacuum distillation tower. The vacuum column removes any remaining gas oil from the reduced crude, leaving behind a heavy material (vacuum bottoms) that can be used as asphalt or charged to a conversion unit (Coker).



  • “Petroleum Refining Process.” OSHA Technical Manual. Section IV: Chapter 2. United States Department of Labor, Occupational Safety & Health Administration, n.d. Web. 24 February 2016.
  • Catalano, Salvatore, Marathon Oil Corporation, Industry Consultant, personal communication, 2015


  • Matthew Posh