The Catalyst Review - May 2015 - 8

SPECIal fEaTuRE
The described innovation path is valid for any PO catalyst developer-either it is an integrated process technology and catalyst
supplier or is an independent catalyst supplier. Of course in the former case the innovation process is played internally to the same
company while in the latter a strong cooperation is needed between the catalyst supplier and its customer, which is heavily involved
in the innovation path and has to carry out some critical steps like the pilot or industrial plant trials, the PO samples market tests, etc.
Intellectual property is the foundation on which the businesses of industry-leading technology providers rest. Without continuous
focus on innovation and development of their patent portfolios, their customers will not have access to evergreen products
and technologies with the ultimate risk of falling behind and losing their competitive standing. It is therefore essential that any
stakeholder in the polyolefin value chain retain core research as a fundamental business objective. This is the only path to continued
growth and profitability, and ultimately to a sustainable business.
A fascinating and exciting innovation story regards the developments during the years of the diverse generations of innovative
Ziegler-Natta (ZN) PP catalysts since the inception of the industry
until the present (Pasqini 2005). A brief description of main
characteristics of these catalyst generations is given below (see a
summary in Figure 3).
At Natta's discovery of PP in 1954, the TiCl3-AlEt2Cl catalyst used
in the earlier industrial PP process showed a low productivity and
stereo-specificity, the II being only around 90% (this is first PP
catalyst generation). Consequently, both removal of the catalytic
residues (de-ashing) and separation of the atactic polymer fraction
were required. In the early 1970s, efforts by Solvay led to the
development of a TiCl3 catalyst having a much higher productivity
(about 10 tons PP/kg catalyst) and an II around 95%; the so called
Solvay PP catalyst constituted the second PP catalyst generation.

figure 3. PP ZN catalyst generations.

Source: Author

Attempts to develop supported catalysts started very early in the 1960s by making use of conventional high surface supports (e.g.,
silica, alumina). These attempts, however, though in some cases leading to highly active catalysts for PE, were not very successful
for PP because of the low activity, until in the late 1960s when it was discovered that catalysts based on "activated" MgCl2 were very
active for PP as well as PE. Due to their low stereospecificity, the use of these catalysts was initially limited to PE. In a few years,
however, this problem was overcome by the addition of appropriate Lewis bases, which made it possible to obtain highly-active and
stereospecific PP catalysts by co-milling MgCl2, TiCl4 and a Lewis base, usually referred to as internal donor, combined with an Altrialkyl as co-catalyst and a second Lewis base called external donor (usually a benzoic acid ester). Though sufficiently active to avoid
the need for de-ashing, these catalysts constituting the 3rd PP catalyst generation, generally still require the removal of the atactic
polymer.
The internal donor is a catalyst ingredient particularly important because it determines the catalyst main features-e.g., the yield,
polymerization decay characteristics, polymer MWD, isotacticity range, hydrogen response (hydrogen is added to the reactor as a
chain transfer agent to regulate the MW of the polymer produced), and oligomer (low MW polymer) content. In the early 1980s a
new combination of electron donors was discovered-alkyl-phthalates as internal donors and alkoxysilanes as external donors-able
to afford a much better productivity (yields up to 40 tons PP/kg
figure 4. Internal donor catalyst components
catalysts) and isotacticity balance (II about 99%) than benzoic
acid esters. These catalyst systems of the fourth PP catalyst
generation are currently used in most of the modern industrial
PP manufacturing process technologies.
At the end of the 1980s a new type of electron donor (1-3
diethers) was discovered by Basell, which, if used as internal
donor, provided extremely high activities (yield up to 100 tons PP/
kg catalyst) and good stereospecificity, even in the absence
of external Lewis base.
Around 2000, another development was made by Basell with the
discovery and use of succinate internal donors and alkylsilanes
as external donor; this catalytic system led to the production
of PP having a much broader MWD. These improved catalysts
constituted the fifth PP catalyst generation (see in Figure 4 the
structure of different internal donors).
8

The Catalyst Review

Source: Author
May 2015

The Catalyst Review - May 2015

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