Titanium-based phenoxy-imine catalyst for selective ethylene trimerization: effect of temperature on the activity, selectivity and properties of polymeric side products
The reactivity of a phenoxy-imine-ether system (FI)TiCl 3 /MAO was studied toward selective ethylene trimerization. This system was shown to either trimerize or polymerize ethylene depending on the reaction temperature. Its selectivity switches from a significant production of the trimerization prod...
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Published in | Catalysis science & technology Vol. 1; no. 6; pp. 162 - 168 |
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Main Authors | , , , , , , , |
Format | Journal Article |
Language | English |
Published |
Cambridge
Royal Society of Chemistry
24.03.2020
|
Subjects | |
Online Access | Get full text |
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Summary: | The reactivity of a phenoxy-imine-ether system (FI)TiCl
3
/MAO was studied toward selective ethylene trimerization. This system was shown to either trimerize or polymerize ethylene depending on the reaction temperature. Its selectivity switches from a significant production of the trimerization product, 1-hexene (85 wt%, 520-450 kg
1-hexene
g
Ti
−1
h
−1
) between 30 and 40 °C, to a moderate polyethylene formation (70-80 wt%, 60-70 kg
polyethylene
g
Ti
−1
h
−1
) at a higher reaction temperature (
T
> 60 °C). Polymerization was investigated based on an original "polymer-to-catalyst" strategy aiming at identifying the active species responsible for this side reaction. Using DSC, SEC and high temperature
13
C NMR analyses, polyethylenes were found to exhibit high molar masses (>10
5
g mol
−1
) and a low 1-hexene content (<1 mol%) at any temperature. Kinetic studies support that trimerization and polymerization species are generated from the catalyst precursor at 40 °C but a parallel process may occur at a higher temperature. The increase of dispersity to 4.6 at 80 °C suggests a change from single to multi-site catalysis. The poor comonomer incorporation ability of the active species is reminiscent of a molecular Ziegler-Natta or a bulky post-metallocene catalyst.
A thermal switch of selectivity for a phenoxy-imine titanium catalyst was studied by combining kinetic studies and a "polymer-to-catalyst" approach. |
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Bibliography: | 10.1039/c9cy02056j Electronic supplementary information (ESI) available: Details of catalytic test data and kinetic fitting. See DOI |
ISSN: | 2044-4753 2044-4761 |
DOI: | 10.1039/c9cy02056j |