Olefins are a class of organic compounds found throughout nature, but they are most recognizable as the building blocks of modern synthetic materials. An olefin refers to any hydrocarbon that contains at least one carbon-carbon double bond within its structure. While they are produced biologically by plants and animals, the vast majority encountered in commerce are synthetically manufactured for industrial purposes.
What Defines an Olefin?
Olefins belong to the broader family of hydrocarbons, compounds composed solely of hydrogen and carbon atoms. They are also known as alkenes, and their defining feature is the presence of a carbon-carbon double bond (C=C). This double bond means the molecule is “unsaturated,” containing fewer hydrogen atoms than a corresponding saturated alkane. The simplest example is ethylene, which consists of two carbon atoms connected by a double bond, each bonded to two hydrogen atoms.
The inclusion of the double bond significantly alters the chemical behavior of the molecule compared to its saturated counterparts. The C=C bond represents a site of high electron density, making the olefin highly reactive. This inherent reactivity allows olefins to readily undergo addition reactions, where the double bond breaks to form two new single bonds. This ability to easily react and link together is the primary reason for their industrial utility as chemical feedstocks.
Olefins in the Natural World
Despite the dominance of synthetic olefins in industry, these compounds function as biological molecules with specific roles in living organisms. The most widely known natural olefin is ethylene, a simple two-carbon molecule that acts as a gaseous hormone in plants. Ethylene regulates numerous processes, including fruit ripening, leaf shedding, and flower opening.
Many characteristic scents and flavors produced by plants are due to a large group of natural olefins called terpenes. These compounds, such as alpha-pinene found in turpentine and limonene in citrus rinds, are hydrocarbons built from repeating five-carbon isoprene units. Terpenes serve various ecological roles, including attracting pollinators and repelling herbivores. Furthermore, many insect pheromones, used for communication between members of the same species, are mono- or bis-olefinic fatty acid derivatives.
Synthetic Manufacturing and Industrial Use
The scale of synthetic olefin production dwarfs natural amounts, making them the most voluminous organic chemicals produced globally. Synthetic olefins are derived from fossil fuel sources, primarily natural gas liquids like ethane and propane, or heavier petroleum fractions like naphtha. The foundational step in industrial manufacturing is thermal or steam cracking. This high-temperature process breaks the strong carbon-carbon single bonds in the larger, saturated hydrocarbon feedstocks.
The intense heat and pressure involved in cracking sever these bonds, creating smaller, unsaturated, and highly reactive olefin monomers. Ethylene and propylene are the two most heavily produced olefins, serving as the primary building blocks for the petrochemical industry. Global production of ethylene alone is in the hundreds of millions of tons annually, a testament to its industrial significance. These small molecules are then channeled into reactors for polymerization.
In polymerization, the reactive double bonds open up, allowing thousands of individual olefin monomers to link end-to-end, forming long molecular chains called polymers. This process converts ethylene and propylene into the globally ubiquitous plastics polyethylene and polypropylene. Polyethylene is used in a vast array of products, from packaging film to durable containers, while polypropylene is found in fibers, automotive parts, and various consumer goods. Other synthetic olefins, such as butenes and butadiene, are produced for the manufacture of synthetic rubbers and specialty chemicals.