Bimodal HDPE from Ethylene and 1-Butene (Similar to BORSTAR)

The process under analysis comprises four major sections: (1) Feed Preparation; (2) Polymerization; (3) Separation; and (4) Finishing.

Feed Preparation. Fresh polymer grade (PG) ethylene provided via a pipeline from a nearby facility and butene are passed through fixed-bed adsorption systems, in which potential catalyst poisons such as water, oxygen and other polar impurities are removed from the monomers before feeding the reactors.

Polymerization. The prepolymerizer is a small loop reactor in which the catalyst mixture, part of the purified monomers and hydrogen are mixed to form a protective shell around the catalyst particles - this prevents the catalysts from breaking downstream. The prepolymerized catalyst is sent to the loop reactor, where the ethylene polymerization takes place in a propane-diluent slurry under supercritical conditions. The slurry is continuously discharged to a flash chamber, for removing unreacted monomers. The resulting slurry is transferred along with fresh ethylene, butene and hydrogen to a gas-phase reactor for further polymerization. The gas-phase reactor is a fluidized-bed reactor, which allows the production of heavy copolymers, with broader molecular-weight distribution.

Separation. The separated gaseous hydrocarbon stream from flash chamber is fed to three distillation columns in order to separate propane, unreacted butene and ethylene.

Finishing. The polymer powder is fed to a purge bin, where residual hydrocarbons are removed and the catalyst is deactivated by treatment with hot nitrogen and steam. The polymer powder from the degasser, additives and antiblocks are fed to a pelletizing system, where the mixture is melted, homogenized, and pelletized. The pellets are homogenized, packed and stored.