Production of Materials > 1. Fossil Fuel Products >
Identify the industrial source of ethylene from the cracking of some of the fractions from the refining of petroleum
- Petroleum is made up of many different hydrocarbons, some of which are in far greater demand than others.
- In order to obtain more of the hydrocarbons in greater demand (which are general small molecules), hydrocarbons in lesser demand are broken down through a process known as catalytic cracking.
- Catalytic Cracking: The process in which high molecular weight (high boiling point) fractions from crude oil are broken into lower molecular weight (lower boiling point) substances in the presence of high temperatures and a catalyst.
- Zeolites: The inorganic compounds (aluminosilicates) used as catalysts for cracking alkanes.
- In catalytic cracking:
- Alkanes with 15 to 25 carbon atoms per molecule are broken into two smaller molecules, one an alkane and the other an alkene.
- The alkene further splits into smaller alkenes until ethylene, propene, or a combination of both is formed.
- Thus, ethylene is a major by-product of catalytic cracking.
- Catalytic cracking is not sufficient to meet demands for ethylene, and therefore some fractions of petroleum are decomposed completely to produce ethylene through steam thermal cracking.
- Steam Thermal Cracking: The process in which ethane gas or larger hydrocarbons are mixed with steam and passed through hot metal coils, producing ethylene.