Styrene is a liquid hydrocarbon known for its incredible capability to undergo polymerization — a process in which individual molecules react with each other to form large, three-dimensional networks or polymer chains.
Styrene is primarily used to produce a thermoplastic polymer called polystyrene, and several other plastics and synthetic rubbers. This lightweight and inexpensive material provides a high-quality finish appearance that can be cut into custom shapes.
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Chemical formula: C6H5CH=CH2
Molecular weight: 104.15 g/mol
Melting point: −30 °C
Boiling point: 145 °C
Density: 0.909 g/cm3
Solubility in water: 300 mg/L at 25 °C
Styrene is a member of the hydrocarbon vinyl group (CH2=CH-), whose molecules consist of a double bond between two carbon atoms.
Under the influence of initiators and catalysts, this double bond can be split into two single bonds linking a carbon atom of another styrene molecule. This is how polystyrene forms, in which thousands of styrene compounds are attached along a carbon backbone.
Physical and Chemical Properties
Styrene is a colorless oily liquid that evaporates easily. The old sample may appear slightly yellowish. Although it has a sweet smell, other chemicals can give it a sharp, unpleasant order.
While styrene doesn’t dissolve well in water, it is highly soluble in ethanol, ether, and acetone, and slightly soluble in carbon tetrachloride. Also, it forms a homogenous mixture with benzene.
Styrene is less dense than water, but its vapors are heavier than air and irritating to the eyes. If it polymerizes inside a closed container, the container might burst into pieces.
Viscosity: 0.696 cP at 25 °C
Polymerization: Gradually at room temperature and readily at above 65 °C.
Polymerization may also take place due to the presence of peroxides, oxidizers, or sunlight. To prevent this, styrene is usually mixed with inhibitors. However, it doesn’t prevent styrene from corroding copper and copper alloys.
How Is Styrene Produced?
Natural styrene is found (in very small quantities) in some foods and plants, such as coffee beans, peanuts, cinnamon, and balsam trees. It also occurs in coal tar.
However, large amounts of styrene are synthetically created from ethylbenzene. In fact, more than 99% of ethylbenzene made globally is intended for styrene production. Ethylbenzene is a highly flammable, colorless liquid created in Friedel–Crafts reactions between ethylene and benzene in the presence of zeolites.
At present, two processes are used to produce styrene from ethylbenzene:
1. Dehydrogenation of ethylbenzene
About 75% of styrene is made by removing hydrogen from ethylbenzene (C6H5CH2CH). This process involves heating ethylbenzene up to 600 °C in the presence of a catalyst, which is usually iron(III) oxide.
The reaction absorbs a significant amount of heat (from the external environment) and is reversible. It yields 88-94% of styrene, which is then purified via distillation.
Since styrene can undergo thermally induced polymerization during the process, an inhibitor is continuously added to the system.
2. Treating ethylbenzene with oxygen
The reaction between ethylbenzene and oxygen produces ethylbenzene hydroperoxide. This product is then treated with propylene to produce propylene oxide and 1-phenylethanol. Finally, the dehydration of 1-phenylethanol gives styrene.
Styrene can also be made by using inexpensive raw materials: methanol (the simplest alcohol) and toluene (an aromatic hydrocarbon).
The reaction between these compounds at 425 °C and in the presence of zeolitic catalyst gives a 9:1 mixture of styrene and ethylbenzene. The yield of the styrene is more than 60%.
From cinnamic acid
In laboratories, it is prepared by removing a carboxyl group from cinnamic acid, a white crystalline compound. Styrene was first produced using this technique.
Billions of kilograms of styrene are industrially produced every year to make products such as food containers, disposable cups, plastic, rubber, pipes, fiberglass, automobile components, and various chemicals.
While styrene is primarily used for the production of polystyrene plastics and resins, it also serves as an intermediate in the synthesis of compounds used for ion exchange resins.
More specifically, styrene is used to produce:
Solid polystyrene, which is used for making rigid foodservice containers, kitchen appliances, toys, and medical and optical instruments.
Fiber-reinforced polymer composites, which are used for manufacturing corrosion-resistant pipes and tanks, sporting goods, wind turbine components, military and commercial aircraft, and automobile parts.
Polystyrene foam and films, which are used for making food-service containers, lightweight protective packaging, and laminating and printing applications.
The most popular styrene-based materials are:
- ABS (Acrylonitrile Butadiene Styrene) Plastic: used for making small household items, toys, and refrigerator liners.
- SBL (Styrene Butadiene Latex): used as a coating in paper products, such as magazines and catalogs, to achieve high gloss and good printability.
- SAN (Styrene Acrylonitrile) Plastic: used in bathroom fittings, optical fibers, and food containers.
- SBR (Styrene Butadiene Rubber): is a general-purpose rubber used in tires, conveyor belts, and gaskets.
Styrene is a storage hazard above 32 °C. When it is decomposed (by heating), it releases acrid smoke and irritating fumes.
Styrene vapor is quite irritating to the throat, nose, eyes, and lungs. Workers exposed to high levels of styrene vapor may develop degenerative disorders of the nervous system.
Prolonged exposure could result in tiredness, hearing loss, compromised color vision, reduced concentration, slowed reaction time, and psychiatric problems. Some workers have experienced asthma, allergic skin reactions, changes in immune function, and even blood clotting.
The United States Department of Health and Human Services classifies styrene as a carcinogen (a substance capable of causing cancer), while the International Agency for Research on Cancer considers it to be “probably carcinogenic to humans.”
In 2019, the global styrene market was valued at $48 billion. This figure is projected to reach $70 billion by 2026, at a compound annual growth rate (CAGR) of 4.6% from 2020 to 2026.
Styrene production plant in Iran
The ever-increasing demand for electronics and automotive components are a few of the major factors driving the growth of the market. The automotive industry, for example, has been a major end-user of SBR (Styrene Butadiene Rubber is mostly used to manufacture tires).
However, increasing health and environmental concerns of styrene usage will hamper market growth. Various industrial accidents have been reported in the past decade. Recently, in May 2020, the styrene gas leak killed thirteen workers at the LG Chem plant in Visakhapatnam, India.
Despite its ill effects, styrene will have a significant demand due to the applications of polystyrene. Asian countries will continue dominating the market during the forecast period.
China, in particular, is expected to witness consistent growth over the coming years because of the rising demand for packaged goods in the food segment.
Europe and North America are the next two largest markets for styrene. There is a high demand for Expanded Polystyrene (EPS) and Acrylonitrile Butadiene Styrene (ABS) but low for polystyrene in these mature markets.
Frequently Asked Questions
How are people exposed to styrene?
Styrene can get into the human body via either breathing (in vapor form) or direct skin contact. The general population may be exposed by drinking water, eating food, smoking cigarettes, breathing indoor air, or using consumer products that contain styrene.
When released into the environment, styrene moves into the air from water surfaces and moist soil. Low amounts of styrene have been detected in both air-breathing organisms (sea birds, carnivores, humans) and water respiring organisms (predatory fish).
How dangerous is styrene?
Styrene oxide can be carcinogenic in both humans and animals. It causes liver cancer in animals. There may be no safe level of exposure to this gas, so any form of contact should be reduced to the lowest possible level.
How fast styrene enters the body?
In many controlled studies, the pulmonary retention of styrene is found to be up to 70% of the inhaled dose. In ambient air, it can be absorbed through the skin at 4% of the dose absorbed in the respiratory tract. Furthermore, liquid styrene can penetrate the skin at a rate of 1 µg/m2 per minute.
How to protect yourself from styrene gas?
Workers can use protective equipment and follow emergency procedures to keep themselves safe. This includes ensuring adequate ventilation and removing all sources of ignition in the plant.
Keep vapors from accumulating in small areas and prevent any kind of leakage or spillage. Also, the discharge of product into the environment must be avoided.