The Catalyst Review November 2019 - 10

SPECIAL FEATURE
chromium oxide catalyst) and increasing the capability of its Prodigy metallocene catalyst. Other Univation developments are based
on the combination of a metallocene for the low-MW (LMW) and an LTM for the high-MW (HMW) PE, di (1-ethylindenyl) zirconium
dimethyl and bis (n-propylcyclopentadienyl) hafnium dimethyl, to produce respectively the LMW and the HMW fractions. The high
MW catalyst is added as a trim. A new family of LTM is very active and can produce UHMWPE. Univation has bet on this type of
catalyst to make multimodal and bimodal PE in its single gas phase reactor process to compete with multi reactors processes.
Chevron Phillips Chemical (CPChem) is very focused on its PE slurry loop process; all the developments (in catalyst and process) are
made around the MarTECH process technology (single and advanced double loop or ADL technology), selectively licensed in the
market. CPChem has the coming challenge to produce economically (compared to a gas phase single reactor process) LLDPE and
HDPE in a slurry process. CPChem is one of the rare companies still developing improved chromium catalyst and new metallocenes.
CPChem is actively working on metallocene catalyst (generally bi metallocene) that will extend the density range of the PE made
in the loop and provide processability similar to chromium-based product. CPChem is looking for alternative ways to increase the
activity of the catalyst, which could indicate that there is still some need to decrease the catalyst cost. In recent years, CPChem has
been actively developing some new metallocene and unique LTM, as follows:
A. Bridge metallocene where a boron is in the bridge (the boron allows lower
densities to be produced and higher melt flow index (MFI));
B. Catalyst containing two metallocenes for the production of a medium density PE
with improved stress cracking resistance with processability similar to chromium
based MDPE (the metallocenes to make the low and high MW are depicted in
Figure 2);
C. Increased the number of different metallocenes on the catalyst support to three
in order to produce broad MWD PE having a reverse comonomer distribution
(meaning that the comonomer is located in the high molecular weight fraction);
and
D. Synthesis of bis (phenol) ligand compounds and transition metal bis (phenolate)
compounds. These LTMs supported on a fluoride silica coated alumina give PE
with very high MW (>2,500,000), a narrow MWD (Mw/m 2.5-3.0) and low density
(0.93-0.94); see Figure 2 for an example of their structures.

Figure 2: CPChem new metallocene/LTM PE
catalyst structures.

Source: TCGR 2018

PP is a versatile semi-crystalline thermoplastic with properties ranging from hard and stiff to flexible and elastomeric, controlled
by variations in composition and molecular stereostructure. The polymerization catalyst in turn controls the stereostructure, with
highly regular isotactic structures contributing crystallinity, stiffness and hardness, and random stereo-structure contributing
flexibility, softness and some impact resistance. Major global players in the PP market include LyondellBasell, Sinopec, Petrochina,
Braskem, Sabic, Total, Borealis, ExxonMobil, and Ineos. Mainly bulk and gas-phase process types produce PP primarily with the use
of Ziegler-Natta catalysts and in a limited extent through metallocene catalysts. Because of the threats from REACH and the growing
pressure from catalyst purchasers, the major global PP catalyst
Figure 3: ZN Catalysts vs. PP application fields.
producers (i.e., LyondellBasell, Grace, Ineos, Mitsui, Sinopec,
McDermott-Novolen, Clariant, and Toho) now have phthalatefree PP catalysts in their commercial product offerings. Basell
first developed and commercialized in the '90s di-ether-based
catalysts (high mileage and PP with narrow MWD), and in the
2000s' succinate-based catalysts (high isotacticity and PP with
broad MWD) 5th generation, phthalate free, ZN PP catalysts
that improved significantly the previous phthalate generation.
Currently LyondellBasell, that together with Sinopec, the
world's top producer of PP, also commercializes a generalpurpose (GP) phthalate-free catalyst including a mixed
di-ether/succinate internal donor, delivering good mileage
and high isotacticity. See in Figure 3 LyondellBasell's complete
phthalate-free catalyst offerings (diether, succinates and
Source: Covezzi 2017
mix) covering all the PP applications from PP commodities to
specialities.

The Catalyst Review

November 2019

The Catalyst Review November 2019

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