chemical process is a method or means of somehow changing one or more chemicals or chemical compounds. Such a chemical process can occur by itself or be caused by an outside force, and involves a chemical reaction of some sort. In an “engineering” sense, a chemical process is a method intended to be used in manufacturing or on an industrial scale (see Industrial process) to change the composition of chemical(s) or material(s), usually using technology similar or related to that used in chemical plants or the chemical industry.

In an oil refinery, there are many chemical processes that converts crude oil into various petroleum products. For each chemical process, various units are installed. Some of the chemical processing units involved in refineries are:

  • Crude Distillation Unit (CDU) – In CDU, crude oil is heated and further divided into various fractions for further distillation.
  • Vacuum Distillation Unit (VDU) – In VDU, the heavy residual oil obtained from CDU is processed and broken down into lighter molecules.
  • Naphtha Hydrotreater Unit – In this unit, hydrogen is used to desulfurize naphtha from CDU and other chemical process units.
  • Catalytic Reforming unit – In this unit, high octane molecules are produced by chemically reacting desulfurized naphtha with the catalyst. It is called reformate which is a component of end product motor spirit (or gasoline).
  • Alkylation Unit – Here butylenes and isobutenes are converted into alkylates which again serve as high octane components of end product motor spirit (or gasoline).
  • Isomerization Unit – Converts normal pentane, butane and isobutene into high octane molecules.
  • Merox unit – Here undesired mercaptan in LPG, kerosene, Jet fuel is oxidized to organic desulfides.
  • Amine gas treater unit – This process is used to convert hydrogen sulfide gas into elemental sulfur.
  • Fluidized Catalytic Converter unit (FCCU) – In FCCU, high-boiling fractions from CDU are converted into lighter and more valuable products.
  • Hydrocracker Unit – It makes use of hydrogen to convert thick residual oil from CDU and VDU into lighter and more valuable products.
  • Delayed coker unit – Converts thick residual oil into lighter components such as naphtha and diesel oil by products.


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