The condensed monomer represents a good alternative to the GPP process, because:
(a) The condensed monomer is liquid, and therefore a good medium to effect energy transfer from the particles to some heat exchange device (high specific heat and heat transfer coefficient).
b) The density of the pure liquid monomer is higher than that of the pure gaseous monomer, so that the concentration "seen" by polymerising particles is much higher in the former case.
These two reasons have been sufficient for the development of one of the most modern technologies for PP: bulk processes. The most widespread types of processes for these technologies are:
- El Paso Petrochemicals' continuous boiling agitated tank reactor (liquid pool/boiling reactor).
- The Himont closed-loop tubular reactor without phase change.
Both processes employ catalysts of high activity and stero-specificity.
The particles in which the reaction takes place are immersed in liquid propylene, forming a slurry. They are extracted as sludge from the reactor, and by flash evaporation the monomer is recycled to the process. For some catalysts it is possible to use petrochemical grade propylene (95%) instead of the polymer grade (99.5%) normally required for polymerisation.
In the BP developed by El Paso Petrochemicals, a so-called boiling reactor is used, in which the heat of reaction provides the latent heat of vaporisation that produces propylene vapour. This is recycled through a water cooling and condensation system. In addition, the reactor has a heat exchange jacket with water.
EL PASO (BP) Polypropylene production process
HIMONT (BP) process of Polypropylene production
