Borstar® Technology - Process Overview
Borstar® was developed by Borealis from scratch because no commercially available bimodal PE technology met the demands of the next generation of PE technology.
With a proprietary catalyst, Borstar® can produce the whole range of PE from linear low density (LLDPE) to high density (HDPE), all in one production campaign.
Polymers can be produced with widely ranging molecular weights, molecular weight distribution and comonomer distribution.
The Borstar® process is illustrated above. It combines a loop reactor using supercritical propane as the polymerisation medium, placed in series with a gas-phase reactor where the second stage of the reaction takes place.
The process starts when catalyst is fed into the loop reactor. With Borstar®, no further addition of catalyst is required for the gas-phase reactor.
The loop reactor can be run in a stable manner due to the use of supercritical propane as the polymerisation medium. The special conditions also significantly reduce reactor fouling. This key advantage comes from reduced polymer solubility above the critical point.
With isobutane, as used in other processes, polymer solubility is higher. This increases the risk of reactor fouling and limits the density range that can be achieved.
Separate control of the two reactors is at the very heart of Borstar® benefits. The resin's modality is easily controlled, whether unimodal or bimodal.
For bimodal polymers, low molecular weights are formed in the loop, while high molecular weights are formed in the gas-phase reactor and the same high production rates are possible with unimodal resins.
It is also possible to manipulate the comonomer content between the two reactors for bimodal polymers. Increasing this content in the gas phase reactor - where the high molecular weight fraction is produced - provides softness, higher impact resistance and improved sealability.