The Catalyst Review November 2019 - 7

SPECIAL FEATURE

Polymerization Catalysts: Technology Advances and Markets
By Salvatore Ali, PhD
Introduction
Polymers are an industry with a huge global market of over $900 billion that includes rubbers, synthetic fiber products, functional
polymers and structural polymers (plastics). Plastics are the largest polymer domain, including such commodity high volume
thermoplastics as polyethylene (PE), polypropylene (PP), polyvinyl chloride (PVC), polystyrene (PS), polyethylene terephthalate (PET),
engineering and high-performance resins and so on. Within plastics, polyolefins (PE and PP), are the largest market with an estimated
global consumption of about 160 million tons/yr in 2017 (TCGR 2018). The rapidly growing car industry has enabled the growth of
rubber products in recent years. Styrene-butadiene rubber (SBR), polybutadiene (PBR) and polymers of ethylene, propylene and a
non-conjugated diene (EPDM) are, respectively, the most produced synthetic rubbers by volume. Current trends indicate that the
global market for plastics will continue to exceed GDP growth in the coming years. Due to the increasing massive investments in
automotive, packaging and medical application markets, also in the less developed regions, the ratio of commodity versus advanced
materials in polymer demand is changing in favor of the more sophisticated types. Technology innovation in the polymer industry
is necessary for more value-added profitability and materials substitution, which lead to the enhancement of competitive strength.
Thus, polymerization catalysts and process technologies will continue to play a vital role in all markets. Within the broad activity
areas of polymers, industry research efforts cover the full spectrum of catalysts from traditional Ziegler-Natta through to advanced
metallocene and single-site catalysts and so on, to produce innovative polymer products from traditional catalyzed PP homopolymers
to unique new elastomeric materials with structures controlled on a nano-scale. The catalyst function is to activate and accelerate
the polymerization reaction enabling the economical scale-up of the related polymer production process from lab to industrial plant.
Catalyst productivity is a key driver of the polymer process efficiency and product quality. In general, the catalyst system may control
three things:
1. Polymer microstructure, thereby controlling the molecular orientation;
2. Polymer molecular weight (MW) by adjusting the polymer chain length and molecular weight distribution (MWD); and
3. Polymer macrostructure and then the polymer morphology and phase distribution of co-monomers and/or co-polymers. The
catalyst therefore effectively determines what polymers can be produced and how efficiently they can be produced.
More specifically, commercial polymerization catalysts can be broadly classified as follows:
1. Oxygen or nitrogen containing initiators, such as peroxides and azo-compounds, for free radical polymerization and
organometallic complexes for anionic or cationic polymerization, used in the production of some volume polymers (e.g., LDPE,
PVC, PS & ABS), engineering plastics and rubbers;
2. Ziegler Natta (ZN), metallocene and single site catalysts (SSC) or supported metal oxide catalysts (as chromium oxide catalysts)
for coordination and stereo specific polymerization mainly used in the production of polyolefins (PP, PE) and advanced
elastomers (e.g., EPR/EPDM, POE); and
3. Speciality acids, bases, metal ion compounds and organometallic complexes for step-chain (condensation) polymerization for
the production of polyesters, polyamides and so on.
The author has previously written several articles (Ali 2018 a/b; 2019) focused on polymerization initiators (peroxides and azocompounds together with cationic and anionic polymerization initiators), catalyst systems for engineering plastics (PET, PA, PC, etc.),
and some rubbers including the catalyst systems for the condensation polymerization, the ring opening polymerization. In this article
the author focuses his analysis on certain selected high value polymerization catalyst's families, not reviewed in the aforementioned
articles.
Recent Technology Advances
The technologies used for the polymer production can be classified generally according to the type of polymer they produce, the
basic catalyst family used, and the polymerization process used as slurry, bulk, gas phase, solution process, and so on. Table 1
summarizes polymerization routes, main catalyst and process technologies related to the polymers of interest for this article. In the
following sections the main features of the ZN, SSC (metallocene and post-metallocene) and chromium oxide catalyst technologies
are addressed.
The Catalyst Review 										

	

November 2019

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The Catalyst Review November 2019

Table of Contents for the Digital Edition of The Catalyst Review November 2019

The Catalyst Review November 2019 - cover
The Catalyst Review November 2019 - contents
The Catalyst Review November 2019 - 1
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