ethene, copolymerization with 1-butene or other 1-olefins, and chain transfer
reactions especially with hydrogen are running in line with the reaction model as
published elsewhere [26]. The high activity is caused by the high number of active
sites and the particle structure of these super-active catalysts. The catalyst particle,
with a diameter in micrometer range (10–50 μm), is an agglomerate of nanosized
particles, called primary particles. It has been found that close to 100% of all
titanium complexes are involved in the polymerization process [52]. The catalyst
particle must fulfil the following conditions: It must be stable enough to be pumped
as a slurry with the hydrocarbon diluent into the polymerization vessel and, on the
other hand, it must be easily disrupted down to the primary particles by the polymer,
and these primary particles must then be evenly distributed over the whole polymer
grain.
3 Modeling the Slurry Polymerization Process
This polymerization process can be separated into three different levels as proposed
by Ray [22]. First this is the microscale level, modeling all processes at the surface
and inside the growing polymer particle. The next level is the mesoscale level,
describing all mass and heat transfer processes inside the three-phase slurry
containing gas bubbles, hydrocarbon diluent with the dissolved aluminumalkyl
compound, and the solid growing polymer particles loaded with the active sites.
Finally, there is the macroscale level comprising the polymerization vessel as a
whole, with sensors to control this slurry polymerization process. These three levels
are shown in Fig. 4.
3.1 The Microscale Level
A key process of the slurry polymerization is the particle-forming process, which
involves the transformation of a catalyst particle into a polymer grain. It has been
found that each catalyst particle is transferred into one polymer grain, as shown in
Fig. 5.
Figure 5 shows in a schematic way that the catalyst particle with a diameter in
the range of 10–50 μm is an agglomerate of nanosized particles called primary
particles. During the polymerization, these primary particles are separated by the
polymer. Then, each primary particle is enveloped by a polymer layer. These small
polymer grains are held together by the polymer to form a stable polymer particle.
The particle-forming process is not understood in all details, and it is also not
known which forces are responsible for the stability of both the catalyst particle
and the polymer grain. However, from experience with industrial catalysts it can
be concluded that the particle-forming process runs well without problems in a
technical plant.
All chemical reactions take place inside these microreactors. These chemical
reactions and the mass and heat transfer processes are regarded as the
The Slurry Polymerization Process with Super-Active Ziegler-Type Catalyst. . .
65
reactions especially with hydrogen are running in line with the reaction model as
published elsewhere [26]. The high activity is caused by the high number of active
sites and the particle structure of these super-active catalysts. The catalyst particle,
with a diameter in micrometer range (10–50 μm), is an agglomerate of nanosized
particles, called primary particles. It has been found that close to 100% of all
titanium complexes are involved in the polymerization process [52]. The catalyst
particle must fulfil the following conditions: It must be stable enough to be pumped
as a slurry with the hydrocarbon diluent into the polymerization vessel and, on the
other hand, it must be easily disrupted down to the primary particles by the polymer,
and these primary particles must then be evenly distributed over the whole polymer
grain.
3 Modeling the Slurry Polymerization Process
This polymerization process can be separated into three different levels as proposed
by Ray [22]. First this is the microscale level, modeling all processes at the surface
and inside the growing polymer particle. The next level is the mesoscale level,
describing all mass and heat transfer processes inside the three-phase slurry
containing gas bubbles, hydrocarbon diluent with the dissolved aluminumalkyl
compound, and the solid growing polymer particles loaded with the active sites.
Finally, there is the macroscale level comprising the polymerization vessel as a
whole, with sensors to control this slurry polymerization process. These three levels
are shown in Fig. 4.
3.1 The Microscale Level
A key process of the slurry polymerization is the particle-forming process, which
involves the transformation of a catalyst particle into a polymer grain. It has been
found that each catalyst particle is transferred into one polymer grain, as shown in
Fig. 5.
Figure 5 shows in a schematic way that the catalyst particle with a diameter in
the range of 10–50 μm is an agglomerate of nanosized particles called primary
particles. During the polymerization, these primary particles are separated by the
polymer. Then, each primary particle is enveloped by a polymer layer. These small
polymer grains are held together by the polymer to form a stable polymer particle.
The particle-forming process is not understood in all details, and it is also not
known which forces are responsible for the stability of both the catalyst particle
and the polymer grain. However, from experience with industrial catalysts it can
be concluded that the particle-forming process runs well without problems in a
technical plant.
All chemical reactions take place inside these microreactors. These chemical
reactions and the mass and heat transfer processes are regarded as the
The Slurry Polymerization Process with Super-Active Ziegler-Type Catalyst. . .
65