High density polyethylene is produced by polymerizing ethylene (HDPE) and in cases co-polymerizing with propylene and 1-butene to achieve the desired density and properties. Hydrogen is also used to control average molecular weight of the polymer. One industrial process for producing HDPE is slurry phase reactor. Hexane is used as the solvent for catalyst and co-catalyst and provides a medium for polymerization reaction and acts as an effective heat carrier to remove heat of reaction.
The reactor benefits from two/three mechanisms of heat removal based on the design. At low pressure (3-10 bar) hexane evaporation occurs. The vapor hexane is condensed and recycled back to the reactor. Another heat removal mechanism is provided by slurry coolers in which a fraction of hot reactor slurry is drawn out of the reactor, cooled and returned to the reactor. Jacket cooling also provides another heat removal mechanism.
The process contains two or three reactors working in parallel or series. These reactors may work at different operating conditions and material input. The use of two or three reactors leads to bi-modal or tri-modal chain size distribution, which gives the process to produce a wider range of HDPE grades.
Here you will learn how to use Aspen Plus to simulate such a reactor with full reaction mechanism. Only one reactor is simulated and the process is simplified to put the main focus of tutorial on the simulation of polymerization reactor only.
