PP Homopolymer from Propylene (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) propylene and propylene recycle provided via a pipeline from a nearby facility 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, reducing the occurrence of fouling. The prepolymerized catalyst, propylene and hydrogen are sent to the loop reactor, where the propylene polymerization takes place in bulk propylene under supercritical conditions. The resulting slurry is transferred along with propylene 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 polymer powder is fed to a degasser, where residual hydrocarbons are removed and the catalyst is deactivated by treatment with hot nitrogen and steam. The separated gaseous hydrocarbon stream from degasser is fed to a molecular sieve and a distillation column in order to recover propylene. Part of it is sent to a petrochemical complex for treatment. The second part is directly fed back to the gas-phase reactor.

Finishing. 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.