Catalytic Polymerization of Liquid Propylene: Effect of Low‐Yield Hexene Prepolymerization on Kinetics and Morphology

Abstract

Summary: A Ziegler‐Natta‐catalyst was used in ultra low‐yield slurry prepolymerization followed by liquid propylene (main) polymerizations. Complete catalyst disintegration down to 1.5–2 µm particle size is observed at prepolymerization yields of 10 g per g cat. The initial (main) polymerization rate increased up to 55% and the final average particle diameter can be controlled between 50 and 1 500 µm at main polymerization yields of 20 kg PP per g cat · hr−1. Tension generation within the particle and the absence of a polymer layer explains these results.Surface SEM. Top: Catalyst surface covered with polyhexene. Bottom: Cracks on catalyst surface after washing with hexane.imageSurface SEM. Top: Catalyst surface covered with polyhexene. Bottom: Cracks on catalyst surface after washing with hexane.

1‐Hexene Polymerization over Supported Titanium–Magnesium Catalyst: The Effect of Composition of the Catalytic System and Polymerization Conditions on Temperature Dependence of the Polymerization Rate

“…It is unclear whether the supported catalyst is fragmented by amorphous polyhexene that is soluble in the reaction medium. Meanwhile, it was demonstrated that when polyhexene is formed over spherical particles of titanium–magnesium catalyst with a low yield, the spherical catalyst particles are partially degraded. Hence, it can be expected that upon hexene polymerization over supported catalysts, the porous catalyst particle also undergoes fragmentation under the influence of the polymer being produced.…”

Investigations of the initial state polymerization of propylene with Ziegler–Natta catalysts in slurry

“…To ensure thermally controlled initial state polymerizations, the effect of the ultra low-yield slurry prepolymerization of hexene followed by a liquid propylene polymerization by Ziegler-Natta catalysts on kinetics and morphology has been investigated. 3 Observing the fragmentation process in the initial slurry polymerization of propylene in hexane by Ziegler-Natta catalysts it was found that this process is controlled by the formation of a protective polymer layer around the fragmented catalyst particles preventing these particles from disintegrating. During the formation of this polymer layer the polymerization rate is high, decreases and reaches a constant activity at low polymerization yields of 2-3 g polypropylene/gram of catalyst at its completion, probably controlled by the monomer diffusion rate through the polymer layer.…”

Comparison of catalytic ethylene polymerization in slurry and gas phase

“…Does the higher growth stress [66] at higher pressure lead to particle disintegration and fines generation? Or is the strength of the skin around the particles [82] sufficiently high to keep the fragments together without disintegration under these conditions? Figure 5.6 shows the effect of ethylene pressure on cumulative particle size distribution normalized with the yield of the polymer extracted from the two experiments as described in Table 5.1.…”

“…Although reached the critical high crystallinity, the particles did not disintegrate too much if there is some ductile PE formed before H 2 addition. It is not completely clear how much the ductile skin [82] formed around the growing particle contributes to this effect. We assume that the ductile skin keeps the fragments inside the growing catalyst/polymer particle without disintegration even if the 2 nd step polymer shows a very high crystallinity.…”