oxygen or an organic peroxide such as dibutyl peroxide, benzoyl peroxide or diethyl peroxide as initiator.
An initiator is a substance which is added in small quantities and is decomposed by light or heat to produce a free radical (R.). A free radical is formed when a covalent bond is broken and a bonding electron is left on each part of the broken molecule. Since the O-O covalent bond is weak, free radicals are easily formed from oxygen or peroxides.
benzene or chlorobenzene used as the solvent since both polymer (polythene) and monomer (ethene) dissolve in these compounds at the temperature and pressure used.
Water or other liquids may be added to dissipate the heat of reaction as the polymerization reaction is highly exothermic.
Process continues to form polythene (polyethylene) [-CH2-CH2-]n
aluminium-based metal oxide catalyst (metallocene catalyst)
The catalyst can be used in a variety of operating modes including fixed-bed, moving-bed, fluid-bed or slurry processes
The ethene (ethylene) monomer is fed with a paraffin or cycloparaffin diluent (diluting agent).
After polymerization the polymer (polythene) is recovered by cooling or by solvent evaporation.
Production of HDPE by coordination polymerization requires:
a coordination catalyst is prepared as a colloidal suspension by reacting an aluminium alkyl and titanium chloride (TiCl4) in a solvent such as heptane (C7H16).
The polymer (polythene) forms as a powder or granules which are insoluble in the reaction mixture. When the polymerization is completed, the catalyst is destroyed by adding water or alcohol to the reaction mixture. The polymer (polythene) is then filtered or centrifuged off, washed and dried.