The_Catalyst_Review_January_2024 - 10

SPECIAL FEATURE
technique. Control of melt index ratio (MIR) and melt strength (MS) are crucial to maintaining good PE processability, and it
is difficult to enhance both.
* ExxonMobil claims to achieve this by having two metallocenes on the same fluroided silica support and adjusting the ratio
within the catalyst and the process conditions. In another novel disclosure, ExxonMobil describes in a patent the use of a
group 4 metallocene compounds with an activator, using hydrogen to control the MW. In another unusual claim, ExxonMobil
discloses an iron-containing catalyst with bisiminopyridyl ligands, which does not incorporate comonomers in copolymer
synthesis, so that in a mixed catalyst system they can control the broad orthogonal composition distribution (BOCD) because
the iron catalyst is asymmetric, whereas the other is symmetric.
PP Ziegler-Natta Catalysts
From the beginning, the development of ZN
catalysts has been aimed at improving catalyst
yield and sterospecificity to achieve substantial
simplifications of the polymerization technologies,
so as to reduce manufacturing costs and improve
overall efficiency and product quality. Advances
such as the discovery of steroregulating agents
(electron donors) and of the advantage of complete
control over the morphology of both catalyst and
resulting polymer particle have already brought
these technologies to a high level. However, the
catalyst yield or the yield/cost balance continues to
be a subject of investigation for economic reasons.
* Because of REACH (European Union
Regulator) push, all the major global PP
catalyst producers offer today phthalate-free
(PF) PP catalysts in their commercial product
offerings. The market penetration of PF PP
catalyst in Europe is evaluated to be greater
than 75%, demonstrating an increase year
by year. Also in North America, Asia and the
Middle East the PF catalysts are regularly
requested for suited applications like food
contact. In response to competitive pressure,
Clariant has recently developed new PF PP
catalysts, known as PolyMax 600/610. These
catalysts demonstrate a significantly higher
activity and an excellent hydrogen response
compared to phthalate-based catalysts,
allowing the production of high melt flow
products with lower energy consumption.
The lower hydrogen concentration during
production allows operations with up to
a 25% smaller recycle compressor load.
Further, this structure allows for an excellent
incorporation of ethylene into the polymer
matrix. With PolyMax 600/610, many PP
grades are produced with a very low amount
of external donor, or even without an external
donor. You can see in Figure 5 the broad
range of achievable xylene solubles (XS) and
the excellent H2
response and in Figure 6
and Figure 7 respectively the higher flexural
modulus and better elongation properties
shown by PolyMax 600/610 vs benchmark
phthalate-free catalysts (Richter Lukesova,
2022).
Figure 6. Clariant Polymax 600/610 phthalate free PP catalyst features.
Source: Richter Lukesova, 2022
Figure 5. Clariant Polymax 600/610 phthalate free PP catalyst features.
Source: Richter Lukesova, 2022
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The Catalyst Review
January 2024

The_Catalyst_Review_January_2024

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