The Borstar polyethylene (PE) process can produce a broad range of bimodal and unimodal linear-low-density polyethylenes (LLDPE), medium-density polyethylenes (MDPE) and high-density polyethylenes (HDPE). The Borstar PE consists of a loop reactor and a gas-phase reactor in series.
PEs with densities of 918–970 kg/m3 and melt flowrate of 0.1–100 can be produced. Ziegler Natta catalysts are used, but singlesite catalysts will be introduced for PE processing.
Catalyst is mixed with a propane diluent and fed to the compact prepolymerization reactor. Cocatalyst, ethylene and hydrogen are also fed into this reactor. The pre-polymerized slurry is sent to the loop reactor, which is designed for supercritical conditions and operates at 75–100°C and 55–65 bar. Typically, lower molecular weight and higher density components of the bimodal polymers are produced in the loop reactor.
Diluent and unreacted components are separated from the polymer produced in the loop reactor in a flash tank. The loop reactor and gas-phase reactor are fully independent from each other, which enables easy control of reactor conditions and the flexibility to process a wide product range.
Polymer from the flash tank polymerizes further in a fluidized-bed gas-phase reactor. No fresh catalyst is needed. The polymer continues to grow on the same catalyst particles, resulting in a homogeneous polymer. The gas-phase reactor operates at 75–100°C and 20 bar. Fresh ethylene, comonomer and hydrogen are fed into the reactor.
Typically, high molecular weight components are produced in this step, thus broadening the molecular weight distribution (MWD) and providing strength to the polymer. The production rate ratio between the reactors can be adjusted to meet the targeted product properties. After removing hydrocarbon residuals, the polymer powder is transferred to extrusion.
A wide range of bimodal and unimodal products with a full control of comonomer distribution, can be produced, with densities ranging from 918 kg/m3 to 970 kg/m3 and melt flowrate from less than 0.1 to over 100. The MWD can be controlled from narrow to broad. Advanced properties are tailor-made for different applications such as pipe strength, film-bubble stability as well as high ESCR and stiffness in blow molding. Other special applications include extrusion coating and wire and cable.
Licensor: Borealis A/S