High density polyethylene production process

The most common production method of PE is through slurry or gas phase processing, and a few are produced by solution phase processing. All of these processes are exothermic reactions involving ethylene monomer, alpha-olefin monomer, a catalyst system (which may be more than one compound) and various types of hydrocarbon diluents. Hydrogen and some catalysts are used to control molecular weight. The slurry reactor is generally a stirred tank or a more commonly used large-scale annular reactor in which the slurry can be circulated and stirred. Polyethylene particles are formed when ethylene and comonomer (if required) come into contact with a catalyst. After removing the diluent, the polyethylene granules or powder are dried and additives are dosed to produce pellets. A modern production line with large reactors with twin-screw extruders capable of producing over 40,000 pounds of PE per hour. The development of new catalysts contributes to improving the performance of new grades of HDPE. The two most commonly used catalyst types are Philips' chromium oxide-based catalysts and titanium compound-alkyl aluminum catalysts. HDPE produced with Phillips-type catalysts has a medium-wide molecular weight distribution; titanium-alkylaluminum catalysts produce narrow molecular weight distribution. The same catalysts used to produce narrow MDW polymers in duplex reactors can also be used to produce broad MDW grades. For example, two reactors in series producing products of significantly different molecular weights can produce bimodal molecular weight polymers with a full range of molecular weight distributions.