Ethylene
Ethylene
Ethylene, also known by its IUPAC name ethene, is a hydrocarbon with the formula C₂H₄ or H₂C=CH₂. It is a colorless, flammable gas with a faint "sweet and musky" odor when pure. Ethylene has a multitude of applications in the chemical industry and is one of the most produced organic compounds worldwide, with production volumes exceeding 150 million tonnes annually as of 2016.
Chemical Structure and Properties
Ethylene is the simplest alkene, a hydrocarbon with carbon-carbon double bonds. This double bond gives ethylene its planar geometry, with all six atoms in the molecule lying in the same plane. The bond angles are approximately 117.4°, close to the ideal 120° for sp² hybridized carbon. The molecule's double bond also significantly lowers the energy required to rotate about the C-C bond, making ethylene relatively reactive.
Production
Ethylene is typically produced by the steam cracking of hydrocarbons, a process where larger hydrocarbon molecules are broken down into smaller ones using steam and heat. This process emits greenhouse gases, such as methane from feedstock production and carbon dioxide from non-sustainable energy sources.
Industrial Applications
Polyethylene
One of the primary uses of ethylene is in the production of polyethylene, the most commonly produced plastic. Polyethylene is a polymer consisting of repeated ethylene units, and it comes in several forms, including high-density polyethylene (HDPE) and low-density polyethylene (LDPE). HDPE is known for its strength and is used in products like plastic bottles and piping, while LDPE is more flexible and is used in plastic bags and films.
Ethylene Glycol
Ethylene is also a precursor to ethylene glycol, an organic compound with the formula (CH₂OH)₂. Ethylene glycol is produced via the intermediate ethylene oxide, which reacts with water to form the glycol. It is primarily utilized as an antifreeze in cooling systems and as a raw material in the production of polyester fibers and resins.
Ethylene Oxide
Ethylene oxide is another critical derivative, a cyclic ether and the simplest epoxide. It serves as an intermediary in producing various chemicals, including ethanolamines, ethylene glycol, and non-ionic surfactants. Despite its utility, ethylene oxide is hazardous, being both flammable and toxic.
Ethylene-Vinyl Acetate
Ethylene-vinyl acetate (EVA) is a copolymer of ethylene and vinyl acetate. It is widely used in applications such as foam sheets for cushioning, hot melt adhesives, and as a component in solar panel encapsulation due to its excellent adhesive properties and resistance to environmental degradation.
Ethylene as a Plant Hormone
Apart from its industrial applications, ethylene acts as a naturally occurring plant hormone. It plays a crucial role in regulating a wide range of plant processes, including fruit ripening, flower wilting, and leaf fall. The signaling pathway of ethylene involves complex interactions with other hormones like abscisic acid, jasmonic acid, and salicylic acid.
Agricultural Use
In agriculture, ethylene is used to induce the ripening of fruits, making it invaluable for the controlled ripening of climacteric fruits such as bananas, tomatoes, and apples. This application helps in synchronizing the ripening process, especially during storage and transport.
Ethylene Signaling Pathway
The ethylene signaling pathway is fundamental to many plant growth and developmental processes. Ethylene binds to its receptor in the plant cell membrane, initiating a cascade of molecular events that activate specific genes involved in growth regulation, stress responses, and senescence.