HDPE Granules

Production process

 

PE is most commonly produced by slurry or gas-phase processing, and to a lesser extent by solution-phase processing. All of these processes are exothermic reactions involving ethylene monomer, a-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 typically a stirred kettle or one of the more commonly used large ring reactors in which the slurry can be circulated and stirred. Upon contact between the ethylene and copolymer monomers (as required) and the catalyst, polyethylene pellets are formed. After removing the diluent, the polyethylene pellets or powder are dried and additives are dosed to produce pellets. Modern lines with large reactors with twin-screw extruders can produce more than 40,000 pounds of PE per hour. The development of new catalysts contributes to the improved performance of new grades of HDPE Granules. The two most commonly used catalyst types are Philips' chromium oxide-based catalysts and titanium compound monoalkyl aluminum catalysts. The Philips type catalyst produces HDPE Granules with a medium-width molecular weight distribution; the titanium-alkyl-aluminum catalyst produces a narrow molecular weight distribution. The catalysts used to produce polymers with a narrow MDW in a complex reactor can also be used to produce wide MDW grades. For example, two tandem reactors producing products with significantly different molecular weights can produce bimodal molecular weight polymers with a full-width molecular weight distribution.