How is High Density Polyethylene Produced?
The most common method for producing high-density polyethylene innoplus is by slurry or gas-phase processing, and there are a few that are produced by solution processing. All these processes are exothermic reactions involving ethylene monomers, a-olefin monomers, catalyst systems (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 loop reactor in which the slurry can be circulated and stirred.
When ethylene and comonomer (as needed) come into contact with the catalyst, polyethylene particles are formed. After removing the diluent, the polyethylene particles or powder particles are dried and the additives are added in dosages to produce pellets. The modern production line for large reactors with twin-screw extruders can produce more than 40,000 pounds of PE per hour. The development of new catalysts has contributed to improving the performance of new grades of HDPE.
The two most commonly used catalyst types are chromium oxide-based catalysts and titanium compound monoalkylaluminum catalysts. The high-density polyethylene produced by the catalyst has a mid-width molecular weight distribution; the titanium-alkyl aluminum catalyst produces a narrow molecular weight distribution. The catalysts used to produce narrow MDW polymers in a double reactor can also be used to produce wide MDW grades. For example, two reactors in series that produce products of significantly different molecular weights can produce bimodal molecular weight polymers. This polymer has a broad molecular weight distribution.