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

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

Polymerization. In the first area, a catalyst suspension for the polymerization is prepared. Fresh and recovered monomers (ethylene and 1-butene), magnesium and titanium chloride, used as catalyst, suspended in hexane are continuously fed to the first reactors, forming a slurry which is homogenized by the agitators. Hydrogen is also used, as the chain terminator. The monomer molecules get in contact with the catalyst suspended in the slurry and form the polymer particles. As the particles precipitate, they do not dissolve in the slurry. Most of the polymerization reaction occurs continuously in the first two reactors. The suspension from the first reactor is pumped to the second reactor and subsequently, from the second reactor to the post-reactor, where the rest of the ethylene is converted into HDPE.

Purification. The slurry is directed to a decanter centrifuge where it is separated into a liquid and a solid fraction. The hexane moist HDPE powder is fed to a fluidized-bed dryer operated with hot nitrogen, in which the hexane is evaporated. The powder flow is passed through a silo, countercurrently to hot nitrogen and slightly superheated steam, in such a way that the residual hexane is removed, and catalysts residues are destroyed. Hexane and butene from off-gases are recovered and recycled to the Reactors.

Finishing. The dried polymer powder and a mix of stabilizers and other additives pass through an extrusion and pelletizing system, is packed and sent to storage facilities.