The Borstar polypropylene (PP) process can produce homopolymers, random copolymers, heterophasic copolymers, and very
high-rubber-content heterophasic copolymers. It is a modular process; consisting of a loop reactor/gas-phase reactor combination.
PP with a melt flowrate ranging from 0.1 to 1,200 can be produced. Borstar PP uses a Ziegler Natta catalyst, but single-site catalysts can be used in the future. When producing homopolymers and random copolymers, the process consists of a loop reactor and a gasphase reactor in series. One or two gas-phase reactors are combined to manufacture heterophasic copolymers.
Propylene, catalyst, cocatalyst, donor, hydrogen, and comonomer (for random copolymers) are fed into the loop reactor; propylene is used as the polymerization medium (bulk polymerization). The loop reactor is designed for supercritical conditions and operates at 80–100°C and 50–60 bar. The propylene/polymer mixture exits the loop reactor and is sent to a fluidized-bed, gas-phase reactor, where propylene is consumed in polymerization. This reactor operates at 80–100°C and 25–35 bar. Fresh propylene, hydrogen and comonomer (in case of random copolymers) are fed into the reactor. After removing hydrocarbon residuals, the polymer powder is transferred to extrusion.
For heterophasic copolymers, polymer from the gas-phase reactor is transferred to another, smaller gas-phase reactor where the rubbery copolymer is made. After this processing step, hydrocarbon residuals are removed, and the powder is transferred for extrusion.
The basic module, loop/gas-phase reactor combination, enables high once-through conversion (minimized recycle), since unreacted monomer from loop reactor is consumed in the gas-phase reactor. Polymerization conditions in each reactor can be independently controlled, enabling production of both standard unimodal and broad-molecularweight multimodal grades. The production rate ratio between the reactors can be adjusted to meet the targeted product properties.
Products: A wide range of polypropylenes with varying melt flowrates from 0.1 to 1,200, and from very stiff to very soft polymers are produced and can be tailored to customer needs. The products have reactor-made basic properties, thus minimizing additional compounding or other post-reactor treatment. Grades suitable for molding, film, fiber, thermoforming and pipe, as well as for engineering applications, are produced.
Licensor: Borealis A/S