The catalyst–cocatalyst system must be managed as described above in such
a way that, at the beginning of the polymerization process at the virgin catalyst
particle there is a balance between heat production by the polymerization process
and heat removal via the particle surface to avoid overheating of the polymerizing
particle. Heat removal must always be higher than heat production. This is
achieved by low activity in the start-up phase of the polymerization, achieved by
optimized catalyst design in combination with a controlled activation process by
the aluminumalkyl compound. With increasing reaction time, the catalyst becomes
more active and must hold this high activity over a long time, in the range of the
heat production
T 0
Q
.
temperature temperature
kinetically controlled
range
T min min
T max max
diffusion controlled
range
heat removal
lower stable
reaction point
upper stable
reaction point
Fig. 6 Stable reaction points at the microreactor
c(r)
T(r)
T c
R
r
Δr
lower stable reaction point
upper stable reaction point
R polymer particle radius
Fig. 7 Temperature (T) and concentration (c) profiles at the microreactor
The Slurry Polymerization Process with Super-Active Ziegler-Type Catalyst. . .
67