Styrene . Organic compound of molecular form C 8 H 8 , consisting of a benzene ring with an ethylene substituent. Also known as vinylbenzene, ethenylbenzene, cinnamene, and phenylethylene. Very important for the production of polystyrene .
Summary
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- 1 Physical properties
- 2 Structure and chemical properties
- 3 Obtaining styrene
- 4 Production of styrene from ethylbenzene
- 5 Applications
- 6 Sources
Physical properties
- Colorless liquid with a sweet aroma that evaporates easily.
- Systematic name Ethenylbenzene
- Molecular formula C 8H 8
- Density: 909.00 kg / m³
- Molar mass: 104.15 g / mol
- CAS number 100-42-5
- Melting point -30 ° C
- Boiling point at normal temperature: 145ºC.
- Solubility: Practically insoluble in water(1%), and soluble in some liquids.
- Density: 0.909 g / cm³, in water
- Viscosity 0,762 cP at 20 ° C
Structure and chemical properties
Styrene has a structure formed by an ethene molecule (CH 2 = CH 2 ) in which one of the hydrogens has been replaced by a phenyl group (C 6 H 5 ); the carbon- carbon double bond of ethene is preserved . This double bond is an electron-rich area that makes the molecule especially reactive.
The phenyl group is described as aromatic: it has a symmetrical hexagonal ring of carbon atoms that contains a special type of bond that gives it unusual stability.
Styrene gives rise to most of the ethene reactions, in particular, the addition reactions in which the double bond is broken and the reagents are attached to the atoms that formed it.
Styrene is apolar, and therefore dissolves in some organic liquids, but does not dissolve very easily in water.
Obtaining styrene
Styrene is manufactured by the chemical industry, it is obtained from ethylene and benzene by the following process:
Obtaining styrene
Polymerization occurs slowly at room temperature. Its polymerization rate increases with increasing temperature. The polystyrene is a product resulting from the polymerization of styrene. Millions of tons are produced annually to make products such as rubber , plastics , insulating material, plumbing, auto parts , food packaging, and carpet coating . Most of these products contain long chain styrene (polystyrene) as well as non-chain styrene. Low levels of styrene are naturally obtained in a variety of foods such as fruits, vegetables , nuts , drinks and meats .
Production of styrene from ethylbenzene
Ethylbenzene undergoes a catalytic dehydrogenation reaction to styrene in the presence of steam. This process is done through the following reaction:
It is obtained from benzene (C 6 H 6 ). Industrially, the most important application of styrene is as a starting product of polystyrene, which is the result of its polymerization. Styrene is manufactured mainly by the method of dehydrogenation of ethylbenzene. This process is simple in concept:
C 6 H 5 CH 2 CH 3 = C 6 H 5 CHCH 2 + H 2
The dehydrogenation of ethylbenzene to styrene takes place with a catalyst of iron oxide and other potassium oxide in a fixed bed reactor at a temperature between 550-680 ° C in steam and low pressure (0.41 Ata) given that low pressures favor the progress of the reaction. The main by-products obtained in the dehydrogenation reactor are toluene and benzene.
The figure shows a typical dehydrogenation unit.
Styrene Dehydrogenation
Ethylbenzene and ethylbenzene recycle are combined with steam and preheated by heat exchange with the product at the reactor outlet. Before entering the reactor it is mixed with more steam that comes out of a superheater that raises the steam temperature to 800 ° C. This mixture is fed to the reactors where the reaction occurs. The effluent from the reactor passes through a heat exchanger where it is cooled.
The condensate is separated into vent gas (mostly hydrogen ), process water, and organic phase. The vent gas is removed by a compressor to be used as fuel or for hydrogen recovery. Process water is separated from organic materials and reused. The organic phase is pumped with polymerization inhibitors to a distillation train .
A: Superheater
B: Reactor
C: Exchanger
D: Capacitor
E: Drum
In the distillation train , the benzene and toluene by-products are recovered at the top of the benzene-toluene column. The bottoms of the benzene toluene column are distilled in an ethylbenzene recycling column where the separation of ethylbenzene from styrene is carried out.
The ethylbenzene containing more than 3% styrene is led to the dehydrogenation section where it is recycled. Glues containing styrene, by-products heavier than styrene, polymers, inhibitor, and above 1000 ppm ethylbenzene are pumped to the styrene finish column.
The product leaving the top of the distillation column is pure styrene. The bottoms are processed in a waste recovery system (flash distillation or a small distillation column) to separate it from the heavy products, polymers and inhibitor. The residue is used as fuel.
Applications
Styrene is a monomer used in the manufacture of a wide range of polymers (such as polystyrene) and elastomeric copolymers such as styrene-butadiene rubber or acrylonitrile butadiene styrene (ABS), which are obtained by copolymerizing styrene with 1,3-butadiene and acrylonitrile.
The vast majority of production is via ethylbenzene, that is, using benzene and ethylene as raw materials.
It is used in the production of transparent plastics.
Ethylbenzene is an intermediate in organic synthesis, especially in the production of styrene and synthetic rubber. It is used as a solvent or diluent, as a component of automotive and airplane fuels, and in the manufacture of cellulose acetate .
Styrene has good mechanical and impact resistance. They are used in automobiles (bumpers, dashboards, …) in household appliances, etc.
