The Catalyst Review - May 2015 - 6

SPECIal fEaTuRE

Polyolefin Catalyst Technology Overview
By Salvatore Ali, PhD

Polyolefins (PO), with reference to polyethylene and polypropylene (PE/PP), have grown since its inception to become an industry
with global annual revenues of over USD $350 billion and installed annual capacity of about 190 million tons. The current trend
indicates that PE and PP global installed capacity growth is expected to continue at 4-5% over GDP in the coming years, with peak
growth rates in Asia, Middle East, North Africa, and the Americas, while Europe and Japan will maintain/restructure their current
capacity.
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 polyolefin resin demand is changing in favor of more sophisticated types.
Innovation in the PO industry is then necessary for more value-added profitability and materials substitution, which lead to the
enhancement of competitive strength. Thus, catalysts and processes will continue to play a vital role within all markets.
Within the broad activity areas of polyolefin catalysts and polymers, industry research efforts covered the full spectrum of traditional
Ziegler-Natta (ZN) and chromium oxide (CrO) catalysts through to advanced metallocene and single-site catalysts (SSC), to produce
innovative polymer products from traditional catalyzed PP homopolymers to unique new elastomeric polyolefins with structures
controlled on a nanoscale.
I have previously written an article titled, "Polyolefin Catalyst Market Overview," which appeared in the April 2014 issue of The
Catalyst Review (Ali 2014). I follow that up here with an overview of developments in polyolefin catalyst technology. In Section 1 of
this article, the PO catalyst technology innovation process from R&D to commercialization is deepened, and a description of the PP
catalyst innovation cycles is briefed. In Section 2, the most used PO catalyst systems are presented together with some of the recent
development trends in the catalyst technologies and related polyolefin products. In Section 3, the highly competitive environment of
the polyolefin catalyst market, possible new entrants, etc. are examined. Commentary is also made on the impact of regulations on
PO catalysts and the related implications for the industry.

1. PE & PP Catalyst Technology Cycles
The catalyst function is to activate and accelerate the polymerization reaction enabling the economical scale-up of the related
polyolefin production process from lab to industrial plant; the catalyst productivity or yield (tons of PO/kg of catalyst) is a key driver
of the PO process efficiency and product quality (a high yield renders the catalyst residues negligibly low, producing high purity
polymers). The catalyst controls:
*	

Polymer microstructure, thus controlling the molecular orientation and producing the desired specific isomer;
particularly important for PP is the isotacticity index (II) that measures the stereo-selectivity of the polymer as
fraction of isotactic PP;

*	

Polymer molecular weight (MW) by adjusting the polymer chain length and molecular weight distribution (MWD); and

*	

Polymer macrostructure and then the polymer morphology (including particle size, shape and porosity) and phase
distribution of co-monomers and/or bi-polymers.

The catalyst, therefore, effectively determines what polymers can be produced and how efficiently they can be produced. Polyolefin
catalysts, as ZN and chromium based systems, must be used in the polymerization together with co-catalysts or activators (aluminum
alkyls) to destroy catalyst poisons and increase catalytic productivity. For PP, an external donor (silanes, others) also has to be added
to the system to regulate the stereo-selectivity of the catalyst. With the advent of metallocene and single site catalysts (SSC) for PE/
PP in the early 1990s, new and more complex types of activators, such as aluminoxanes, fluorinated boron compounds, and similar
complex structures are used.
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