Homopolymer HDPE from Ethylene (Similar to Advanced SCLAIRTECH)

The process under analysis comprises three major sections: (1) Polymerization; (2) Finishing; and (3) Chemicals Recovery.

Polymerization. The methylpentane solvent and ethylene monomer recycled from distillation columns are mixed with fresh streams and sent to fixed-bed adsorption systems to remove potential catalyst poisons, such as water and oxygen. The reaction temperature is a major determinant of polymer molecular weight, so the solution is sent to a cooler before being fed to the reactors. The exothermic polymerization reaction is carried out in two adiabatic continuous-stirred-tank reactors (CSTR) operating in series. Under the process conditions, the polymer is dissolved in the solvent. The catalyst employed in the process is an advanced Ziegler-Natta catalyst. Since a small amount of the catalyst remains active, a deactivating solution is added to the mixture to terminate the polymerization process.

Finishing. The deactivated solution is first heated by using high pressure steam, and then flashed into an intermediate pressure separator and in a second low pressure separator. In the separators, the unreacted ethylene, impurities, reaction solvent, deactivator solvent and any other volatile matter are separated from the Polyethylene. The resin leaving the low-pressure separator is fed into an extruder, which is used to incorporate the required additives, as well as to pelletize the polymer. The pellets are then stripped with steam to remove any remaining solvent or comonomer. Finally, they are homogenized in blending silos and stored.

Chemicals Recovery. The gas stream from the separators is mixed with the recovered solvent from finishing area and pumped to two distillation columns. There, ethylene and methylpentane solvent are recovered and recycled to purification. Low process steam is generated to be used in the process and heavy impurities are eliminated.