The condensed monomer is a good alternative to GPP processes because:
a) The condensed monomer is a liquid and, therefore, a good medium for transferring energy from the particles to a heat exchange device (high specific heat and heat transfer coefficient).
b) The density of pure liquid monomer is greater than that of pure gaseous monomer, so the concentration of polymerizing particles that the particles “encounter” is much higher in the former case.
These two reasons have been sufficient to drive the development of one of the most advanced technologies for PP: “bulk” processes. The most common types of processes for these technologies are:
- El Paso Petrochemicals' continuous stirred boiling reactor ("liquid pool/boiling reactor").
- Himont's closed-loop tubular reactor, without phase change.
Both processes use catalysts with high activity and stereospecificity.
The particles in which the reaction takes place are immersed in liquid propylene, forming a “slurry.” They are removed from the reactor as a slurry, and the monomer is recycled back into the process via flash evaporation. For some catalysts, it is possible to use petrochemical-grade propylene (95%) instead of the polymer-grade propylene (99.5%) normally required for polymerization.
In the BP process developed by El Paso Petrochemicals, a reactor known as a boiling reactor is used, in which the heat of reaction provides the latent heat of vaporization that produces propylene vapor. This vapor is recycled through a water-cooling and condensation system. In addition, the reactor has a water-jacketed heat exchanger.
EL PASO (BP) Polypropylene Production Process
HIMONT (BP) Polypropylene Production Process
