Polyethylene (PE) is the most common polymer in the world, produced 85mt / year. This is mainly due to the wide range of possible uses. Depending on its melting point, the PE is divided into several categories: low, medium and high density, each class with specific industrial applications. It occurs in the following forms: high density polyethylene (HDPE), ULDPE (ultra low density polyethylene), LLDPE (linear low density polyethylene), MDPE (medium density polyethylene) HMWPE polyethylene (high molecular weight) and UHMWPE (ultra high molecular weight).
Traditionally, the polymerization was taking place under high pressure (several hundred bars) and high temperature (up to 300°C) but over the years the energy input has been reduced by using catalytic systems. The Ziegler and metallocene catalyst families have proven to be very flexible at copolymerizing ethylene with other olefins and have become the basis for the wide range of polyethylene resins available today, including very low density polyethylene and linear low-density polyethylene.
Polyethylene is mostly produced in slurry, gas-phase fluidized bed reactor or combination of both processes in series (such as like Spherilene and Borstar processes). Either double-tube loop reactors or autoclaves (stirred-tank reactors) are commercially employed for slurry-phase polymerization, in the presence of a catalyst system and a diluent.
The following image illustrates one of the slurry process configurations using a Double-Tube Loop Reactor followed by a gas phase reactor (Borstar process).