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styrene

Product name styrene
Synonyms vinyl benzene
phenylethene
phenylethylene
styrol
GOST 10003-90
CAS 100-42-5

Styrene is a clear, colorless, flammable liquid with an unpleasant odor. It is miscible with benzene, toluene, hexane, diethyl ether, chloroform and most organic solvents. It dissolves different organic compounds including polystyrene, polyester resins and other polymers. Styrene is slightly soluble in water (~0.032% vol at 20°C). It forms an azeotrope with water (44% wt of water, b.p. 34.8°C).

Styrene displays chemical properties both aromatic compounds and olefins. Chlorine or bromine act into side chain to form dihalogenated adducts:

C6H5CH=CH2 + Br2 → C6H5CHBrCH2Br

Hydrogen chloride HCl, hydrogen bromide HBr or hydrogen cyanide HCN interact with styrene according to Markovnikov rule:

C6H5CH=CH2 + HCN → C6H5CH(CN)CH3

Styrene can be hydrated in the presence of mercury(II) salts to give after subsequent treatment with sodium borohydride NaBH4 α-phenylethanol:

phenethyl alcohol synthesis from styrene


Styrene is quite reactive compound. It readily oxidizes resulting in different adducts. The nature of product depends on oxidizing agent and reaction conditions:

Products in reaction of styrene oxidation


Styrene is one of most important industrial monomers. It polymerizes itself in the presence of initiators to form polystyrene:

nPhCH=CH2 → -(CH(Ph)-CH2-)n

It can be also copolymerized with number of monomers such as acrylonitrile, α-methyl styrene, vinyl chloride, vinyl acetate, maleic anhydride, methylmethacrylate.

Styrene has a low ignition point 34.4°C and burns with smoking flame. It is moderately toxic compound, a potential carcinogen. It irritates mucous membranes of upper airways, causes headache and disorders of central nervous system.

Production.

  • More than 90% of total world styrene production is carried out via ethylbenzene dehydration. Process is conducted in gaseous phase at 580-650°C in vacuum in the presence of catalyst (Fe2O3 promoted with CrO3, V2O5 or KOH). The reaction is endothermic (ΔH=124KJ/mol).

    C6H5CH2CH2 ⇄ C6H5CH=CH2 + H2

    The steam is used in this process for several purposes. It is the source for compensation of heat used by endothermic reaction. It continuously clean the catalyst surface from the coke that tends to form during reaction. Water interact with carbon deposition to give gaseous carbon oxides. The promoter on the catalyst is present to increase decoking reaction. The steam addition is also shifting the position of chemical equilibrium towards products due to dilution of reactants and products concentration in the reaction mixture. A typical styrene plant consists of two or three reactors in series. A per-pass conversions are about 65% if two reactors were used and 70-75% for three reactors plant. The selectivity to styrene varies in range 93-97% and depends on reactor operating pressure, temperature, catalyst and conversion. The main by-products are benzene and toluene which can be easily removed by distillation. The separation of styrene from the ethylbenzene is carried out on tall distillation towers with high reflux ratios because styrene and ethylbenzene boil very close to each other (145°C and 136°C respectively). Also distillation is complicated by the fact that styrene polymerizes at high temperature. To prevent a spontaneous polymerization upon purification process the mixture is doped with free radical inhibitor prior distillation.
  • Styrene is a co-product in propylene oxide manufacturing (SM/PO process - styrene monomer/propylene oxide). This process is based on oxidation of ethylbenzene and consists of three steps. At the first stage ethylbenzene is oxidized with oxygen of air at 130°C to form hydroperoxide. Then hydroperoxide reacts with propylene at 90-100°C and pressure 1.6-6.5 MPa in the presence of molibdenum catalyst to give propylene oxide and α-phenylethanol. After the separation of this mixture the phenylethanol is dehydrated at 180-280°C in the presence of titanium(IV) oxide resulting in styrene:

    C6H5CH2CH3 + O2 → C6H5CH(OOH)CH3

    C6H5CH(OOH)CH3 + CH3CH=CH2 → C6H5CH(OH)CH3 + CH3CHCH2O

    C6H5CH(OH)CH3 → C6H5CH=CH2 + H2O

Uses.

  • as a raw material for different types of polystyrene making;
  • as a comonomer in ABS plastics production (ABS is acrylonitrile, butadiene and styrene copolymer);
  • in butadiene-styrene (BS) latex and resins manufacturing;
  • in thermoplastic elastomers production;
  • the copolymer of styrene with divinylbenzene is a feedstock in ion-exchange resins making;
  • to produce copolymers with vinyl chloride, acrylonitrile, methylmethacrylate, maleic anhydryde and others;
  • as a reactive solvent for polyester resins;
  • as an alkyd resins modifier;
  • as a parent compound in α-phenylethanol synthesis. This compound is used in perfumery;

Manufacturer(s) JSC "Nizhnekamskneftekhim" Inc.
JSC Salavatnefteorgsintez
SIBUR-CHEMPROM
Chemical structure of styrene

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