The_Catalyst_Review_January_2024 - 7

SPECIAL FEATURE
co-catalysts, metals, supports and energy have been associated with production cost pressures and reduced margins. The prices
of polyolefin catalysts have increased to compensate for these inflationary pressures. In the global marketplace, we are currently
observing a multiplicity of factors, some exacerbated by the pandemic and the Ukraine war, which continue to affect activities and
plans in the plastic value chain:
* high interest rates, inflation and an ongoing risk of economic recession;
* shifting patterns of supply/demand, critical material supply shortages and geopolitical events that may significantly affect
global trade;
* increasingly demanding regulatory environments and a growing practice of ESG drivers; and
* consolidation/ownership changes, including the important variables of venture capital and start-ups.
The global polymer market is projected to have an average annual growth rate at 3.4% across the major polymer resins from 2023 to
2029 (TCGR, 2023).
Polyolefins (PO), including PE (high-density PE [HDPE], low-density PE [LDPE] and linear low-density PE [LLDPE]) and polypropylene
(PP), represent about one-half of the entire global polymer demand. Of the four different polyolefin resins, PP is the single largest
volume resin, with global demand reaching about 85 million tons in 2022, while the global demand for the three PE resins in the same
year was about 116 million tons (TCGR, 2023).
Commercial polyolefin catalysts can be broadly classified as follows: Ziegler Natta (ZN), metallocene and single-site catalysts (SSC)
and supported metal oxide catalysts (as chromium oxide catalysts) for coordination and stereo specific polymerization, mainly used in
the production of PP and linear PE as HD/MDPE and LLDPE. A summary of the polyolefin catalyst technologies is shown in Table 1,
including PP and linear PE (HDPE and LLDPE). LDPE is excluded because it is produced using initiators.
Table 1. Polyolefins production technologies using catalysts.
Source: Author
Coordination catalysts such as ZN and chromium
oxide called pro-catalysts must be used in the
polymerization together with co-catalysts activators
(aluminum alkyls) to destroy catalyst poisons and
increase catalytic productivity. For isotactic PP, also
stereo-regulators, internal (phthalates or others
phthalate-free) and external electron donors (e.g.,
silanes), have to be added to the catalyst system
for tuning the polymer chain stereo-regularity, the
molecular mass distribution and the co-monomer
incorporation. Metallocene/SSC are complexes
of biscyclopentadienyl (Cp) ligands or other Cptype
ligands on a transition metal of group 4
such as titanium, zirconium or hafnium, with an
organoaluminum activator compound suitable to
polymerize both propylene and ethylene to PP or
PE. Metallocene and SSC require complex types of
activators, such as aluminoxanes (MAO), fluorinated
boron compounds and similar complex structures, to
form the metallocene-SSC catalyst. Table 2 provides a
list of the most used Al Alkyls applied as co-catalysts/
activators.
Table 2. Commercial al-alkyls activators.
Source: Author
Most olefin polymerization processes operate with
heterogeneous catalysts in two-phase or threephase
(suspension or gas phase) reactors. Either
Ziegler-Natta or Chrome Phillips and metallocene
catalysts used for such productions are supported
heterogeneous catalysts. Inorganic materials are
widely used as catalyst supports. Silica, alumina,
magnesium dichloride and mixtures thereof are
The Catalyst Review
January 2024
7

The_Catalyst_Review_January_2024

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