Ethylene is a colorless, odorless gas, composition C2H4, it being the simplest of the alkene hydrocarbons having a double bond, therefore it is classified as an unsaturated hydrocarbon. It is found in trace amounts in Nature (biosynthesis) and plays an important role in the ripening of certain fruits.
Ethylene production is the economic indicator of the organic chemical industry. It is made by steam cracking of petroleum, usually with co-production of propylene, and both hydrocarbons are primary feedstocks of the petrochemical industry that makes polymers, plastics, rubber, fibers, resins and solvents. Global production of ethylene was about 110 million tonnes in 2009 and is forecast to grow by 4% per year up to 2014.
Important major industrial reactions involving ethylene are in order of importance (a) polymerization (b) oxidation (c) halogenation and (d) alkylation
About 60% of ethylene goes to making polyethylene (PE). Processes involving heat and compression cause ethylene gas to polymerize into liquid polyethylene, a valuable thermoplastic material. A low density form 0.92g/cm3 (LDPE) and a high density 0.97g/cm3 form (HDPE) of polyethylene is made for different end uses. LDPE is mainly used for film applications in packaging of goods and making plastic bags, whereas HDPE is used for injection molded products such as buckets, dustbins, outdoor furniture, and extruding pipes for water, gas and irrigation.
Ethylene is used to make three important chemicals, viz., ethylene oxide, ethylene dichloride and ethylbenzene, which are precursors to the manufacture of many commonly used materials.
The main use of ethylene oxide is to make ethylene glycol used for anti-freeze for car cooling systems. Other glycol ethers and acetates are widely used as solvents. Polyethylene oxides are used in pharmaceuticals, cosmetics and lubricants.
Ethylene dichloride (EDC) is made by chlorination of ethylene. EDC can be cracked to give vinyl chloride monomer (VCM) which is used to make polyvinyl chloride (PVC) plastic used in the construction industry.
Ethylene chloride is made by reaction of hydrogen chloride with ethylene. Its main use was to produce tetraethyl lead which was added to gasoline to reduce “knocking” and improve the octane number, but now is in reduced demand.
Ethylene reacts with benzene to give ethyl benzene, which is a precursor to the formation of Styrene and Styrene-Butadiene rubbers. Styrene can be polymerized to form polystyrene which is one of the cheapest thermoplastics used for bottle making.
Ethylene is a high volume product of the petrochemical industry and is used to make a huge number of products having diverse end uses. It is therefore viewed as an indicator of the economic well being of the chemical industry in particular and industrial development in general.