Production of Styrene Monomer

Chemical formula: C8H8

Shell companies have over 40 years' experience in producing and supplying styrene monomer around the globe. Today, the Shell Group is the second largest producer of styrene monomer in the world and has a strong global manufacturing base. Shell companies are recognized as technology leaders in operating co-product SM/PO (styrene monomer/propylene oxide) plants and conventional styrene monomer plants.

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Styrene monomer is an aromatic hydrocarbon which, under normal conditions, is a clear, colourless, flammable liquid. The conventional method for producing styrene monomer is the alkylation of benzene with ethylene followed by dehydrogenation to produce styrene monomer. Also, it can be produced via the ‘SMPO’ process, which co-produces styrene monomer and propylene oxide via the oxidation of propylene by ethylbenzene hydroperoxide. An alternative would be producing it through the DOW process.

Process:

1. The energy needed for the reaction is supplied by superheated steam (at about 720 degree Celcius) that is injected into a vertically mounted fixed bed catalytic reactor with vaporized ethylbenzene.
   
2. The catalyst is iron oxide based and contains Cr2O3 and a potassium compound (KOH or K2CO3) which act as reaction promoters.


3. Typically, 2.5-3 kg steam are required for each kilogram of ethylbenzene to ensure sufficiently high temperatures throughout the reactor. The superheated steam supplies the necessary reaction temperature of 550-620 0C throughout the reactor.


4. Ethylbenzene conversion is typically 60-65%. Styrene selectivity is greater than 90%. The three significant byproducts are toluene, benzene, and hydrogen.


5. After the reaction, the products are cooled rapidly to prevent polymerization.


6. The product stream (containing styrene, toulene, benzene, and unreacted ethylbenzene) is fractionally condensed after the hydrogen is flashed from the stream.


7. The hydrogen from the reaction is used as fuel to heat the steam (boiler fuel).


8. After adding a polymerization inhibitor (usually a phenol), the styrene is vacuum distilled in a series of four columns (often times packed columns) to reach the required 99.8% purity.

Industrial Safety Precautions:

Styrene monomer can affect you when breathed and by passing through the skin. It is a flammable and reactive chemical thus being a fire and explosion hazard. Good work practices in the production of styrene monomer can help to reduce hazardous exposures.

• Workers whose clothing has been contaminated by styrene monomer should change into clean clothing promptly, not taking contaminated work clothes home as family members could be exposed.


• No eating, drinking and smoking in the place where styrene monomer is handled / processed / stored as the chemical itself can be swallowed.


• Styrene monomer must be stored to avoid contact with oxidizing agents and catalysts for vinyl polymerization such as peroxides, strong acids, and aluminium chlorides since violent reactions will occur.


• Workers should use only non sparking tools and equipment, especially when opening and closing containers of styrene monomer. Due to the fact that it is highly reactive and flammable, styrene monomer should be stored with an inhibitor to prevent explosive reactions.