Styrene is an organic compound, formally known as ethenylbenzene, used to manufacture a vast range of synthetic materials, particularly plastics and synthetic rubbers. It is a monomer, a small molecule that chemically bonds with others to form large chain-like structures called polymers. Styrene is a chemical intermediate, produced in one process and then used as the primary raw material in another. Since it is not found in large, extractable quantities in nature, it is manufactured in industrial volumes to meet global polymer demand.
Foundational Chemical Components
The composition of styrene is derived from two simpler hydrocarbon feedstocks: benzene and ethylene. These molecules are extracted and refined from crude oil and natural gas during initial processing in petrochemical plants. Benzene is an aromatic hydrocarbon with a stable, six-carbon ring structure, while ethylene is a simple olefin (alkene) with a double bond between its two carbon atoms.
Styrene is essentially the benzene ring with a two-carbon vinyl group attached. The industrial process focuses on chemically linking the ethylene molecule to the benzene ring. This synthetic construction is necessary because the compound is not naturally abundant enough to sustain the millions of tons produced annually. The supply of these hydrocarbon precursors is closely tied to the global oil and gas sector.
Industrial Synthesis Process
The production of the styrene monomer from its components is a two-step process. The first step is alkylation, where benzene and ethylene react to create the intermediate compound, ethylbenzene. This reaction is carried out using a catalyst, such as aluminum chloride or zeolite catalysts, under controlled temperature and pressure in a specialized reactor.
The second step is the catalytic dehydrogenation of ethylbenzene to yield styrene. In this highly endothermic reaction, superheated steam, often reaching temperatures up to 600 degrees Celsius, is mixed with the ethylbenzene. This mixture is passed over a metal oxide catalyst, commonly iron oxide, which facilitates the removal of two hydrogen atoms. The removal of these hydrogen atoms creates the carbon-carbon double bond, converting the ethylbenzene into the styrene monomer.
Characteristics of the Styrene Monomer
Once synthesized, the styrene monomer exists as a clear, colorless liquid at room temperature. It possesses a sweet or aromatic odor, though higher concentrations are less pleasant. The molecule is highly reactive due to the presence of the vinyl group, which contains an unstable double bond.
This reactivity means that liquid styrene tends to spontaneously link with other styrene molecules, a process known as autopolymerization. This unintended polymerization can occur even at room temperature or when exposed to light, causing the liquid to become viscous. To prevent this during storage and transportation, chemical compounds known as polymerization inhibitors, such as tertiary butylcatechol, are added.
Transition to Commercial Polymers
The purpose of manufacturing the styrene monomer is to intentionally trigger its polymerization to create solid plastic and rubber materials. Polymerization is the chemical process where thousands of styrene monomer units link together to form long, repeating polymer chains. This transformation turns the liquid monomer into a solid material with entirely different properties.
The most common product is polystyrene (PS), formed when only styrene monomers are linked together. Polystyrene is a rigid, transparent plastic used for packaging and insulation foam. Styrene is also combined with other types of monomers to create copolymers with enhanced physical characteristics. Examples include Acrylonitrile Butadiene Styrene (ABS) plastic, valued for its impact resistance in electronics housings, and Styrene-Butadiene Rubber (SBR), used in tire manufacturing.