Styrene: properties, production and applications / Articles

Styrene (phenylethylene, vinylbenzene, ethenylbenzene) is an aromatic hydrocarbon of the alkenylbenzene series and one of the most important large-tonnage monomers of the modern petrochemical industry. Under normal conditions, it is a colourless, transparent liquid with a characteristic sweetish odour. Styrene is practically insoluble in water but readily soluble in organic solvents and is itself an effective solvent for many polymers. Its molecular formula is C₈H₈, with a molecular mass of 104.15 g/mol. Due to the presence of a vinyl group, styrene readily undergoes radical, anionic and cationic polymerisation, as well as copolymerisation with a wide range of comonomers, making it a versatile basis for the production of plastics, elastomers and resins.

Chemical Nature and Physicochemical Properties

Styrene belongs to the class of vinyl aromatic compounds. Its molecule combines a reactive vinyl group with an aromatic ring, which imparts rigidity, transparency and heat resistance to polymers based on it. The key physical characteristics of styrene determine its industrial application:

Boiling point: about 145 °C.
Melting point: minus 30.6 °C.
Density: 0.909 g/cm³ at 20 °C.
Refractive index: 1.543 at 25 °C.
Flash point: about 31 °C (closed cup). Styrene is classified as a flammable liquid, and its vapours form explosive mixtures with air.
Solubility: insoluble in water, miscible with ethanol, acetone, diethyl ether, benzene and other organic solvents.

Styrene is prone to spontaneous polymerisation, especially when heated, under the action of light and oxygen. To prevent this, inhibitors (e.g., para-tert-butylcatechol) are introduced during storage, and storage is carried out at reduced temperatures and for a limited time. In terms of impact on the body, styrene belongs to hazard class 3; its vapours have an irritating effect on the eyes and respiratory tract, and long-term exposure can adversely affect the nervous system.

Production Technology

Industrial production of styrene is almost entirely based on two technological routes, with ethylbenzene acting as the key intermediate.

Catalytic dehydrogenation of ethylbenzene. This method is dominant and accounts for about 85–90% of global styrene output. The process is carried out in the gas phase at a temperature of 600–650 °C and atmospheric pressure, diluting the reaction mixture with superheated steam 3–10 times to reduce partial pressure and suppress side reactions. Oxide iron-chromium systems with potassium carbonate additives are used as catalysts. Ethylbenzene, in turn, is obtained by alkylation of benzene with ethylene. After the dehydrogenation reaction, crude styrene is subjected to multi-stage vacuum distillation to separate unreacted ethylbenzene, which is recycled, and to isolate commercial high-purity styrene.

Coproduct with propylene oxide (SMPO process). This route accounts for about 10–15% of global production. Ethylbenzene is oxidised with air to form ethylbenzene hydroperoxide, which then reacts with propylene to give propylene oxide and methyl phenyl carbinol. The latter is dehydrated to form styrene. This method is economically advantageous when there is demand for both target products — styrene and propylene oxide.

Alternative methods are being developed, including catalytic cyclodimerisation of butadiene followed by dehydrogenation, oxidative coupling of toluene and olefin metathesis, but they have not yet gained wide industrial distribution.

Regulatory Framework and Grades

Requirements for styrene in Russia and CIS countries are regulated by GOST 10003-90 "Styrene. Specifications". The standard applies to styrene, a colourless liquid with a weak specific odour, insoluble in water, and establishes requirements for the product intended for national economy needs and export. Depending on the production method, two main grades are distinguished: SDEB (styrene obtained by catalytic dehydrogenation of ethylbenzene) and SDMFK (styrene obtained by dehydration of methyl phenyl carbinol in the coproduction of styrene and propylene oxide).

For both grades, the mass fraction of styrene must be at least 99.80%. The mass fractions of phenylacetylene, methyl ethyl acrolein, divinylbenzene, acetophenone, carbonyl compounds, peroxide compounds and polymer are also standardised. The colour by the platinum-cobalt scale (Hazen) must not exceed 10 units. To prevent polymerisation, a stabiliser — para-tert-butylcatechol — is introduced into the commercial product in an amount of 0.0005–0.0010%. Styrene is transported in railway tank cars or barrels in compliance with the requirements for the transport of flammable liquids.

Applications

Production of polystyrene (PS). This is the largest consumption area for styrene, accounting for about 65% of global demand. Styrene is the monomer for producing general-purpose polystyrene (GPPS), high-impact polystyrene (HIPS) and expandable polystyrene (EPS). Polystyrene is widely used in packaging, household appliances, electronics, construction thermal insulation materials, toys and consumer goods. Transparency, rigidity and low cost make it one of the most in-demand polymers.

Production of ABS plastics and SAN. Styrene is copolymerised with acrylonitrile and butadiene to form high-impact ABS plastic (acrylonitrile-butadiene-styrene), which is used in the automotive industry, production of household appliance housings, pipes and electronics parts. The copolymer of styrene with acrylonitrile (SAN) is used for transparent products, tableware and battery cases.

Production of synthetic rubbers and latices. Styrene is a key comonomer in the production of styrene-butadiene rubbers (SBR), which are used in the tyre industry, production of conveyor belts and footwear. Styrene-butadiene latices are used for textile impregnation, production of adhesives and coatings. Styrene-based thermoplastic elastomers (SBS, styrene-butadiene-styrene) are also produced, used in road construction and footwear production.

Unsaturated polyester resins. Styrene acts as a solvent and crosslinking agent in unsaturated polyester resins, which are used in the production of fibreglass, gelcoats, artificial stone, pipes, boats and construction panels. During curing, styrene copolymerises with the polyester chain, providing a three-dimensional structure of the material.

Other applications. Styrene is used for the production of ion-exchange resins, styrene-butadiene block copolymers, oil additives, and in small volumes — as an intermediate in the synthesis of pharmaceuticals and flavourings.

Safety and Storage

Styrene belongs to hazard class 3 substances (moderately hazardous substances). Styrene vapours have an irritating effect on the mucous membranes of the eyes and upper respiratory tract, and at high concentrations — a narcotic effect. The maximum allowable concentration (MAC) of styrene vapours in the working area air is 30 mg/m³ (according to GOST 12.1.005-88). When working with styrene, personal protective equipment must be used: respirators, safety goggles, rubber gloves and protective clothing. Premises must be equipped with effective supply and exhaust ventilation.

Styrene is highly flammable, and its vapours form explosive mixtures with air. The flash point is about 31 °C, so strict fire safety measures must be observed when handling styrene. Storage is carried out in hermetically sealed containers made of stainless steel or with an internal coating, in a cool, light-protected place, away from ignition sources and oxidisers. Due to its tendency to polymerise, styrene is stored with an added inhibitor and at reduced temperature, and storage periods are limited. Before use, the inhibitor can be removed or neutralised.

Market and Trends

The global styrene market demonstrates steady development, driven by demand for polystyrene, ABS plastics, synthetic rubbers and construction materials. The Asia-Pacific region is the largest producer and consumer of styrene, due to large-scale production of polymers and packaging. Key industry trends include the modernisation of existing capacities, the introduction of more energy-efficient ethylbenzene dehydrogenation catalysts, and the development of technologies that reduce the formation of by-products and waste. Requirements for production safety and reducing emissions of volatile organic compounds are tightening. Supplies of styrene, including grade selection (SDEB, SDMFK), quality confirmation and logistics arrangements taking into account temperature conditions and dangerous goods requirements, require an individual approach and a reliable partner.

Conclusion

Styrene remains one of the key monomers of the global petrochemical industry, providing for the production of polystyrene, ABS plastics, synthetic rubbers and polyester resins. Its unique properties — the ability to polymerise and copolymerise, the transparency of polymers and the availability of feedstock — make it indispensable in modern industry. Organising supplies of styrene, including grade selection, quality confirmation and logistics, requires an individual approach that takes into account specific technological requirements and operating conditions.