Kinetics and mechanism of ethylene polymerization with TiCl4/MgCl2 model catalysts: Effects of titanium content

Jiang, Baiyu; Weng, Yuhong; Zhang, Shuangjie; Zhang, Zhen; Fu, Zhisheng; Fan, Zhiqiang

doi:10.1016/j.jcat.2018.01.008

Cited by 48 publications

(45 citation statements)

References 55 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…From Figure 10 we can see linear correlations between lg(k p ) and m p /m cat (mass ratio of polymer to catalyst) in m p /m cat range of 0 to 5 for the three groups of active centers of both catalysts. As proposed in our previous works, [32,37] decline of propagation rate constant with time can be attributed to time-dependent rise of mass transfer hindrance in the polymer/catalyst particles, where the monomer must pass through the polymer layer surrounding the catalyst fragments to reach at the active centers. When the rate of mass transfer in the particle is smaller than the potential polymerization rate, a gradient of monomer concentration along the particle radius will be formed.…”

Section: Active Center Fraction and Kinetic Parametersmentioning

confidence: 59%

“…In ethylene polymerization with Cat-1/TEA, we have observed [C*]/[Ti] fraction of 25 % after 30 s reaction. [32] However, in propylene polymerization with the same catalyst, only about 8 % of Ti species became active centers that produced PP products. This large difference between the two monomers is unlikely attributable to more efficient activation of Ti species in ethylene than propylene polymerization, since plenty of evidences have proven that activation of the Ti species (alkylation and reduction of supported TiCl 4 to the active center precursor TiCl 2 R) by AlR 3 takes less than one second.…”

Section: Active Center Models and Mechanistic Discussionmentioning

confidence: 99%

“…Contents of Mg, Cl and organics in the catalysts can be found in supplementary data of our previous work. [32]…”

Section: Preparation Of Mgcl 2 -Supported Ziegler-natta Catalystsmentioning

confidence: 99%

“…Similar phenomenon has been found in ethylene polymerization with the same model catalysts as reported in our previous work. [32] This difference could be explained by the presence of more clustered Ti species in supported Ziegler-Natta catalysts with higher Ti content. It seems that a high proportion of Ti atoms in the clustered Ti species cannot be activated into catalytical centers.…”

Section: Active Center Fraction and Kinetic Parametersmentioning

confidence: 99%

See 3 more Smart Citations

Effects of titanium dispersion state on distribution and reactivity of active centers in propylene polymerization with MgCl₂‐supported Ziegler‐Natta catalysts: A kinetic study based on active center counting

et al. 2020

Self Cite

View full text Add to dashboard Cite

Kinetics of propylene polymerization with two TiCl 4 /MgCl 2 model catalysts of different Ti load (Cat-1: Ti 0.1 wt%; Cat-2: Ti 1.0 wt%) was investigated in this work. Time-dependent variations of active centers fraction ([C*]/[Ti]) and active center distribution of the two catalysts were compared. In propylene polymerization with Cat-1, [C*]/[Ti] was only 7.8 % in the initial stage, but increased for more than three times in reaction period of 600 s. Propylene polymerization with Cat-2 had much lower [C*]/[Ti]. Active center distributions of the two catalysts were markedly different. Cat-1 has evidently higher proportion of aspecific active centers and less isospecific ones than that of Cat-2. These catalysts also showed different time-dependent variations of active center distribution. The chain propagation rate constant of isospecific centers in Cat-2 was evidently higher than that in Cat-1, but propagation rate constants of either aspecific and medium-isospecific centers were only slightly changed by enhancing Ti content of the catalyst. The results suggest that isospecific centers are mainly originated from clustered Ti species, but non-clustered Ti species are the main source of active centers with lower stereoselectivity. By considering factors like dispersion states of Ti species and release of shielded active species through disintegration of catalyst particles, active center models have been proposed to explain the different kinetic behaviors of the two model catalysts.

show abstract

Section: Active Center Fraction and Kinetic Parametersmentioning

confidence: 59%

Section: Active Center Models and Mechanistic Discussionmentioning

confidence: 99%

“…Contents of Mg, Cl and organics in the catalysts can be found in supplementary data of our previous work. [32]…”

Section: Preparation Of Mgcl 2 -Supported Ziegler-natta Catalystsmentioning

confidence: 99%

Section: Active Center Fraction and Kinetic Parametersmentioning

confidence: 99%

See 2 more Smart Citations

Effects of titanium dispersion state on distribution and reactivity of active centers in propylene polymerization with MgCl₂‐supported Ziegler‐Natta catalysts: A kinetic study based on active center counting

et al. 2020

Self Cite

View full text Add to dashboard Cite

show abstract

“…The MgCl 2 support used for preparing the model catalysts was prepared by reacting Mg powder with 1‐chlorobutane. In our previous work, X‐ray diffraction analysis on MgCl 2 support prepared in this approach showed that it is a highly activated δ‐MgCl 2 composed of very small crystallites . A blank TiCl 4 /MgCl 2 catalyst (Cat‐1) and two TiCl 4 /Di/MgCl 2 type catalysts (Cat‐2, Di = DCPDMA and Cat‐3, Di = DBP) were prepared by treating the support with TiCl 4 (Cat‐1) or with Di before TiCl 4 (Cat‐2 and Cat‐3), respectively.…”

Section: Resultsmentioning

confidence: 99%

Mechanism of internal and external electron donor effects on propylene polymerization with MgCl₂‐supported Ziegler–Natta catalyst: New evidences based on active center counting

Weng

Jiang

et al. 2018

J of Applied Polymer Sci

Self Cite

View full text Add to dashboard Cite

Two TiCl 4 /Di/MgCl 2 type supported Ziegler-Natta catalysts were prepared by loading dibutylphthalate or dicyclopentyldimethoxysilane (DCPDMS) (internal donor, Di) and TiCl 4 on activated d-MgCl 2 in sequence, and a blank catalyst was prepared by loading TiCl 4 on the same d-MgCl 2 without adding Di. These catalysts have similar specific surface area and pore size distribution, thus form a suitable base for comparative studies. Propylene polymerization with the catalysts was conducted in n-heptane slurry using triethylaluminum (TEA) as cocatalyst, and the effects of Di as well as De (external donor, in this work it was DCPDMS) on the number of active centers, the distribution of active centers among three polypropylene (PP) fractions (isotactic, medium isotactic, and atactic PP chains), and chain propagation rate constants of the PP fractions were studied by counting the number of active centers in the PP fractions using a method based on selective quench-labeling of the propagation chains by 2-thiophenecarbonyl chloride. When De was not added in the polymerization, introducing a phthalate type Di in the catalyst evidently changed the active center distribution by enhancing the proportion of active centers producing isotactic PP (iPP) (C Ã i ), but scarcely changed reactivities of the three groups of active centers forming the three fractions. When the De was added in the polymerization system with TiCl 4 / phthalate/MgCl 2 catalyst, further shifting of active center distribution in favor of C Ã i took place, meanwhile reactivities of the three groups of active centers also remarkably changed in favor of C Ã i . Mutual effects of these changes led to overwhelming dominance of iPP production in the TiCl 4 /Di/MgCl 2 -TEA/De system (Di 5 phthalate, De 5 alkoxysilane). In contrast, though using alkoxysilane as Di also caused shifting of active center distribution in favor of C Ã i when De was not added, addition of alkoxysilane De caused reverse shifting of active center distribution in favor of those producing PP of lower stereoregularity. This unfavorable change largely counteracted the reactivity changes in favor of C Ã i caused by the De, rendering the catalytic system rather poor isospecificity. V C 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018, 135, 46605.

show abstract

Improvement of catalytic activity for α‐diimine nickel complex with active sites stabilized by bulky boron counterions at elevated temperature

Wang

Feng

Guo

et al. 2022

Applied Organom Chemis

Self Cite

View full text Add to dashboard Cite

Three α‐diimine Ni (II) catalysts (Cat.1, Cat.2 and Cat.3) were synthesized and investigated for ethylene polymerization using alkyl aluminum and organoboron compounds as binary cocatalyst. The effects of different alkyl aluminum and boron complexes on ethylene polymerization catalyzed by Cat.1, Cat.2, and Cat.3 were studied. The sodium tetrakis[3,5‐bis (trifluoromethyl)phenyl]borate (NaBArF) was found to have best promotion for the catalytic activity of Cat.1, compared to negative effect of dimethylanilinium tetrakis (pentafluorophenyl)borate (TTB) and trityl tetrakis (pentafluorophenyl)borate (AB). All the three catalysts showed higher catalytic activity when NaBArF was introduced into the catalytic system, especially for Cat.3 (increased by 41.3% at 70°C). There was still minor increase of the catalytic activity for Cat.2 which have much better thermostability than Cat.3. The charging sequence of NaBArF and the [B]/[Ni] ratio have significant effects on the catalytic activity. The better catalytic performance of Cat.1/AlEt2Cl/NaBArF could be explained by its ability to raise the number of active centers. Namely, the molar percentage of active centers of Cat.1/AlEt2Cl/NaBArF was still above 30%, which was 1.7 times that of Cat.1/AlEt2Cl even if polymerization ran up to 30 min based on 2‐thiophenecarbonyl chloride (TPCC) quench‐labeling method. Lower [Al]/[Ni] ratio but more active centers and longer active centers lifetime of this binary cocatalyst is promising for improving the activity of ethylene polymerization industrially at elevated temperature.

show abstract

Kinetics and mechanism of ethylene polymerization with TiCl4/MgCl2 model catalysts: Effects of titanium content

Cited by 48 publications

References 55 publications

Effects of titanium dispersion state on distribution and reactivity of active centers in propylene polymerization with MgCl₂‐supported Ziegler‐Natta catalysts: A kinetic study based on active center counting

Effects of titanium dispersion state on distribution and reactivity of active centers in propylene polymerization with MgCl₂‐supported Ziegler‐Natta catalysts: A kinetic study based on active center counting

Mechanism of internal and external electron donor effects on propylene polymerization with MgCl₂‐supported Ziegler–Natta catalyst: New evidences based on active center counting

Improvement of catalytic activity for α‐diimine nickel complex with active sites stabilized by bulky boron counterions at elevated temperature

Contact Info

Product

Resources

About

Kinetics and mechanism of ethylene polymerization with TiCl4/MgCl2 model catalysts: Effects of titanium content

Cited by 48 publications

References 55 publications

Effects of titanium dispersion state on distribution and reactivity of active centers in propylene polymerization with MgCl2‐supported Ziegler‐Natta catalysts: A kinetic study based on active center counting

Effects of titanium dispersion state on distribution and reactivity of active centers in propylene polymerization with MgCl2‐supported Ziegler‐Natta catalysts: A kinetic study based on active center counting

Mechanism of internal and external electron donor effects on propylene polymerization with MgCl2‐supported Ziegler–Natta catalyst: New evidences based on active center counting

Improvement of catalytic activity for α‐diimine nickel complex with active sites stabilized by bulky boron counterions at elevated temperature

Contact Info

Product

Resources

About

Effects of titanium dispersion state on distribution and reactivity of active centers in propylene polymerization with MgCl₂‐supported Ziegler‐Natta catalysts: A kinetic study based on active center counting

Effects of titanium dispersion state on distribution and reactivity of active centers in propylene polymerization with MgCl₂‐supported Ziegler‐Natta catalysts: A kinetic study based on active center counting

Mechanism of internal and external electron donor effects on propylene polymerization with MgCl₂‐supported Ziegler–Natta catalyst: New evidences based on active center counting