Propylene is a colorless gas that is a byproduct of oil refining and natural gas processing. It is also produced by the cracking of hydrocarbons, such as propane and ethylene. Propylene is an important building block for the petrochemical industry, as it is used to produce a variety of chemicals and materials, mainly for the production of polypropylene. The dominant technology for producing propylene is steam cracking, using propane as the feedstock. Another frequently used process for propylene production is fluid catalytic cracking. This process involves the use of a fluidized bed reactor, which is a vessel that contains a bed of catalyst particles suspended in a stream of hot gas. The feedstock, which is typically a heavy oil or gas oil, is injected into the reactor, where it reacts with the hot catalyst particles. The reaction produces a mixture of lighter hydrocarbons, including propylene, which is separated from the other products using a series of distillation and fractionation steps.