Polyethylene, HDPE Process by LyondellBasell

To produce bimodal and multimodal high-density polyethylene (HDPE) using the stirred-tank, heavy-diluent Hostalen ACP process.

The Hostalen ACP process is a slurry polymerization method with three reactors in series. The reaction in cascade enables producing top quality unimodal, bimodal and multimodal polyethylene (PE) from narrow to broad molecular weight distribution (MWD) with the same catalyst family.

Polymerization occurs in a dispersing medium, such as n-hexane, using a very high-activity Ziegler catalyst. No deactivation and catalyst removal is necessary because a very low level of catalyst residue remains in the polymer. For HDPE production the catalyst, the dispersing medium, monomer and hydrogen are fed to the reactor (1, ) where the first polymerisation step occurs.

The second and third step polymerization occurs under different reaction conditions with respect to each reactor. No further catalyst only ethylene, butene and further dispersing medium are fed to the second (2) and third reactor (3). Reactor conditions are controlled continuously, thus HDPE with very high properties is manufactured. Finally, the HDPE slurry from the third reactor is sent to the decanter (4) and the polymer is separated from the dispersing medium. The polymer containing the remaining hexane is dried in a fluidized bed dryer (5) and catalyst/cocatalyst residuals are removed in the powder treatment vessel (7).

The powder is then pelletized in the extrusion section. The separated and collected dispersing medium of the fluid separation step (6) with the dissolved co-catalyst and comonomer is recycled to the polymerization reactors. A small part of the dispersing medium is distilled to maintain the composition of the diluent.

The advanced cascade technology enables the manufacturing of tailor-made products with a definite MWD from narrow to broad MWD, including bimodal and multimodal molecular design. The melt flow index may vary from below 0.2 (multimodal product) to over 50 (unimodal product). Homopolymers and copolymers are used in various applications such as blow-molding (large containers, small bottles), extrusion molding (film, pipes, tapes and monofilaments, functional packaging), and injection molding (crates, waste bins, transport containers).

Licensor: LyondellBasell