The Influence of Bridge Type on the Activity of Supported Metallocene Catalysts in Ethylene Polymerization (original) (raw)
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In Situ Silica Supported Metallocene Catalysts for Ethylene Polymerization
2014
Bis(2-R-ind)ZrCl2 (R: H or phenyl) was supported on different types of silica by in situ impregnation method and used for ethylene polymerization. In this method, the step of catalyst loading on support was eliminated and common alkyl aluminum (triisobutylaluminum, TiBA) cocatalyst was used instead of expensive methyl aluminiumoxane (MAO) cocatalyst in the polymerization. The effect of surface area of silica on the performance of the supported catalysts using three different types of silica including EP12 (390 m 2 /gr.), PQ3060 (570 m 2 /gr.) and MCM-41 (1100 m 2 /gr.) was investigated. The surface area had a more critical role relative to other characteristics of the support in the performance of catalysts. By using MCM-41 as support, the kinetic stability was enhanced. The activity of the supported catalysts was increased by increasing the surface area of silica in the order of MCM-41 > PQ3060 > EP12. The morphology of polymer particles was improved and reactor fouling was e...
Polymer-Supported Metallocene Catalysts for Gas-Phase Ethylene Polymerization
The use of hydroxylated chloromethylated-styrene/divinylbenzene copolymer as a support for three different catalysts, Cp 2 ZrCl 2 , [Ind] 2 ZrCl 2 and (CH 3 ) 2 Si[Ind] 2 ZrCl 2 has been examined for the polymerization of ethylene in gas phase. The gas phase polymerization experiments were performed in a horizontal reactor by using Box-Behnken experimental design to study the effects of temperature, ethylene partial pressure, and MAO cocatalyst level on polymerization. The measured average catalyst activities were empirically correlated with these three factors. Temperature appears to be the most important factor, which shows a first and second order effect on activity and also interacts with pressure and MAO. The kinetic study shows that these supported catalysts might contain two types of active sites, and the deactivation of sites follows a first order kinetic.
Journal of Molecular Catalysis A: Chemical, 2003
In the present work Et(IndH 4 ) 2 ZrCl 2 was immobilized on silica previously modified with different chemical compounds, namely VOCl 3 , SnCl 4 , Bu 3 SnH, Me 2 SiHCl, polymethylhydrosiloxane (PMHS) and such systems were compared to methylaluminoxane (MAO) pretreated systems. Bu 3 SnH-modified silica led to the highest zirconocene grafted content. Zr 3d 5/2 binding energy determined by X-ray spectroscopy (XPS) was shown to increase for Et(IndH 4 ) 2 ZrCl 2 supported on silica modified with VOCl 3 , MAO and Bu 3 SnH, suggesting the generation of more electron deficient surface species. All systems were shown to be active in ethylene-propylene copolymerization, presenting higher activity than those prepared by grafting the zirconocene on bare silica. Aging test with MAO-mediated systems showed that the catalyst bearing 2.0 wt.% Al/SiO 2 kept its catalyst activity at least for 3 months after preparation.
Applied Catalysis A: General, 2007
The effects of support calcination temperature, an important catalyst synthesis parameter, on the overall performance of the supported catalyst [silica ES70-n BuSnCl 3 /MAO/(n BuCp) 2 ZrCl 2 ], polymerizing ethylene without separately feeding the MAO cocatalyst, were studied. The silica was calcined at 250, 450, 600, and 800 8C for 4 h. n BuSnCl 3 was used to functionalize the silica. Ethylene was polymerized using the synthesized catalysts at 8.5 bar(g) in hexane for 1 h. No reactor fouling was observed. Free-flowing polymer particles with bulk density (0.23-0.27 g/ml) and a fairly spherical morphology similar to that of the catalyst particles were obtained. Also, the particle size distribution of the polymer resembled that of the catalyst. Therefore, the replication phenomenon from catalyst to polymer took place. The narrow PSD span (1.41) indicates that the resulting polyethylenes are suitable for various mixing-intensive polymer applications. The MAO cocatalyst-free ethylene polymerization instantaneously formed a polymer film around the catalyst particle, which coated/immobilized the catalyst constituents; this is how leaching was in situ prevented which favored heterogeneous catalysis to occur. The catalysts showed fairly stable polymerization kinetics. The catalyst activity, as a function of the silica calcination temperature, varied as follows: 250 8C > 600 8C > 800 8C > 450 8C. This finding has been explained considering the relevant surface chemistry phenomena. The calcination temperature did not significantly affect the bulk density and the PDI (3.4 PDI 3.8) of the resulting polyethylenes. The low PDI substantiates the retention of single-site catalytic behavior of the experimental supported catalysts.
Comparative ethylene polymerization using FI-like zirconium based catalysts
Reaction Kinetics, Mechanisms and Catalysis, 2010
Three FI-like Zr-based catalysts, Bis[1-[(phenylimino)methyl]-2naphtholato]zirconium(IV) dichloride (1), Bis[1-[(mesitylimino)methyl]-2-naphtholato]zirconium(IV) dichloride (2) and Bis[1-[(2,6-diisopropylphenyl)imino] methyl-2-naphtholato]zirconium(IV) dichloride (3) were prepared by changing the ligand from salicylaldehyde imine ligand, which is a well known FI catalysts, to 2-hydroxynaphthalene-1-carbaldehyde imine ligand and used for polymerization of ethylene. Triisobutylaluminum (TIBA) and methylaluminoxane (MAO) were used as scavenger and cocatalyst, respectively. Introduction of the bulky substitution phenyl ring on the N of the phenoxy imine ligand enhanced the viscosity average molecular weight of the obtained polymer strongly. Catalyst 3 produced the highest viscosity average molecular weight (M v) of the obtained polyethylene, but showed the lowest catalytic activity. The activity of all the catalysts was increased with the increase of [Al]/[Zr] molar ratio to an optimum value followed by a slight decrease at higher [Al]/[Zr] molar ratios. Optimum activity of catalyst 1 was obtained at about 30°C while the highest activity of catalysts 2 and 3 was obtained at about 40°C following a sharp decrease at higher temperatures. The rate/time profile of the polymerization decayed with a short acceleration period for all of the catalysts. The polymerization activity was increased with increasing the hydrogen concentration due to the fast hydrogenation of sterically more hindered and less reactive intermediates such as those resulting from 2,1-insertions. It is noteworthy that the experimental results indicated that the hydrogen does not act as a chain transfer
Polymer-supported metallocene catalysts for gas-phase ethylene/1-hexene polymerization
Applied Catalysis A: General, 2005
The ethylene and ethylene/1-hexene polymerization activities of seven catalysts, consisting of (n-BuCp) 2 ZrCl 2 /MAO supported on five different types of spherical polymer beads, were determined for gas-phase polymerization at 1.4 MPa ethylene pressure and initial 1-hexene concentrations of up to 40 mol/m 3. The catalytic activity for all the catalysts was highest at 80-90 8C. Copolymerization activities were higher than homopolymerization activities; the average rates for 1 h runs ranged from 0.1 to 4.1 and from 2.4 to 13 kg PE/(mol Zr s MPa C 2 H 4) for homo-and copolymerization, respectively. Specific rates decreased with increasing Zr content for copolymerization (range of Zr concentration 0.21-0.39 mass%). The rates of 1-hexene incorporation decreased with increasing Al:Zr ratios (range of Al:Zr ratios 100-370). Most of the catalysts produced spherical copolymer particles without the production of fines. Molar masses of copolymers were lower than those of homopolymers, but they did not change appreciably with changes in 1-hexene concentration.
2006
Me 2 Si(Ind) 2 ZrCl 2 was in situ immobilized onto SMAO and used for ethylene and propylene polymerization in the presence of TEA or TIBA as cocatalyst. The catalytic system Me 2 Si(Ind) 2 ZrCl 2 /SMAO exhibited different behavior depending on theamount and nature of the alkylaluminum employed and on the monomer type. The catalyst activity was nearly 0.4 kg polymer ·g cat -1 · h -1 with both cocatalysts for propylene polymerization. Similar activities were observed for ethylene polymerization in the presence of TIBA. When ethylene was polymerized using TEA at an AVZr molar ratio of 250, the activity was 10 times higher. Polyethylenes made by in situ supported or homogeneous catalyst systems had practically the same melting point (T m ). On the other hand, poly(propylenes) made using in situ supported catalyst systems had a slightly lower T m than poly(propylenes) made using homogeneous catalyst systems. The nature and amount of the alkylaluminum also influenced the molar mass. The p...
Journal of Polymer Science Part A: Polymer Chemistry, 1999
The effects of polymerization conditions were evaluated on the production of polyethylene by silica-supported (n-BuCp) 2 ZrCl 2 grafted under optimized conditions and cocatalyzed by methylaluminoxane (MAO). The Al : Zr molar ratio, reaction temperature, monomer pressure, and the age and concentration of the catalyst were systematically varied. Most reactions were performed in toluene. Hexane, with the addition of triisobutilaluminum (TIBA) to MAO, was also tested as a polymerization solvent for both homogeneous and heterogeneous catalyst systems. Polymerization reactions in hexane showed their highest activities with MAO : TIBA ratios of 3 : 1 and 1 : 1 for the homogeneous and supported systems, respectively. Catalyst activity increased continuously as Al : Zr molar ratios increased from 0 to 2000, and remained constant up to 5000. The highest activity was observed at 333 K. High monomer pressures (Ϸ 4 atm) appeared to stabilize active species during polymerization, producing polyethylenes with high molecular weight (Ϸ 3 ϫ 10 5 g mol Ϫ1 ). Catalyst concentration had no significant effect on polymerization activity or polymer properties. Catalyst aging under inert atmosphere was evaluated over 6 months; a pronounced reduction in catalyst activity [from 20 to 13 ϫ 10 5 g PE (mol Zr h) Ϫ1 ] was observed only after the first two days following preparation.