Hydrogenation of olefins and polymerization of ethene over chromium oxide/silica catalysts IV. Kinetics of the polymerization reaction

Groeneveld, C.; Wittgen, P.P.M.M.; Lavrijsen, J.P.M.; Schuit, G.C.A.

doi:10.1016/0021-9517(83)90119-7

Cited by 24 publications

(4 citation statements)

References 5 publications

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“…On the other hand, Δ G i1 ‡ was as high as 21.1 kcal/mol for C(OH)*, indicating its much lower propagation rate. The reaction enthalpy barriers between 4 TS[6X-7X] and 4 6X were in the range of 12–14 kcal/mol, which was consistent with the values reported by Groeneveld et al and Blom et al, who, respectively reported activation energies of 12.7 and 17.9 kcal/mol for C 2 H 4 polymerization over CrO x /SiO 2 . , However, as shown in Figure , F modification causes the energies of 4 TS[6X-7X] for C(FOH)* and C(F)* to be 4–5 kcal/mol lower than that for C(OH)*, while those for A(F)*, B(FOH)*, and B(F)* were slightly lower than or almost the same as those of the unmodified counterparts. Therefore, the Δ G i1 ‡ for C(FOH)* and C(F)* decreased to 17 and 16 kcal/mol, implying the major promotion effect of F modification on the propagation rate of the sites comprising 8CR .…”

Section: Resultssupporting

confidence: 89%

Computational Insights into the Multisite Nature of the Phillips CrO_x/SiO₂ Catalyst for Ethylene Polymerization: The Perspective of Chromasiloxane Ring Size and F Modification

Huang

Liu

et al. 2022

ACS Catal.

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The famous Phillips CrO x /SiO2 catalyst is characterized by its multisite nature and the resulting broad molecular weight distribution (MWD) of its polyethylene (PE) products. However, the multiplicity of active sites and their catalytic behavior relating to the broad MWD have scarcely been studied. Given the high and comparable efficiency of calcination and F modification in regulating the active site multiplicity of this catalyst, eight polyhedral oligomeric silsesquioxane (POSS)-based cluster models comprising four-, six-, and eight-membered chromasiloxane rings (4CR, 6CR, and 8CR) were partially or fully capped by OH or F and employed for density functional theory (DFT) calculations related to C2H4 polymerization. For the OH-capped models, the results emphasized the dominant size effect of the chromasiloxane ring (CR), where the model with a smaller CR was less abundant but could produce higher-molecular-weight (MW) PE with a higher activity. The predicted MW indicated the very broad MWD of the PE products, consistent with that of the products generated from low-temperature calcinated CrO x /SiO2. However, depending on the size of the CR, these models responded unequally to F modification. Specifically, the more abundant sites with 8CR were promoted more obviously, and the MW of their PE products was increased. This makes the polymerization rate higher and the MWD of the PE narrower, which agrees with those of the PE products synthesized by F-modified CrO x /SiO2 calcined at a low temperature. Furthermore, the origin of the effects of CR size and F modification was properly illustrated in terms of both steric and electronic variations.

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Section: Resultssupporting

confidence: 89%

Computational Insights into the Multisite Nature of the Phillips CrO_x/SiO₂ Catalyst for Ethylene Polymerization: The Perspective of Chromasiloxane Ring Size and F Modification

Huang

Liu

et al. 2022

ACS Catal.

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“…Rate Law and Activity. First-order behavior with respect to monomer pressure has previously been observed for polymerizations by heterogeneous Cr/silica catalysts, ,, although reports of other orders ranging from zero , to second have also appeared; it has further been observed that the reaction order is pressure dependent . Polymerizations initiated by 2 at low pressures are cleanly pseudo-first-order in monomer for the entire course of the reaction.…”

Section: Discussionmentioning

confidence: 84%

A Kinetic Study of Ethylene and 1-Hexene Homo- and Copolymerization Catalyzed by a Silica-Supported Cr(IV) Complex: Evidence for Propagation by a Migratory Insertion Mechanism

and

Scott

2000

J. Am. Chem. Soc.

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The surface organometallic fragment (tSiO) 2 CrdCHCMe 3 initiates the polymerization of ethylene and 1-hexene at room temperature in the absence of organoaluminum or other activators. The kinetics at the gas-solid interface were studied by in situ IR spectroscopy in a constant volume, variable pressure reactor. At low pressures, the reaction is first order in P(C 2 H 4 ), first order in the number of moles of chromium, and linearly dependent on the Cr loading on silica. The second-order rate constant for polymerization is (177 ( 3) s -1 (mol Cr) -1 at 21 °C, and is virtually unchanged upon subsequent additions of ethylene to the catalyst. The kinetic isotope effect, k(C 2 H 4 )/k(C 2 D 4 ), is a meagre 1.29. The temperature dependence of the second-order rate constants yields ∆H ‡ obs ) (30.2 ( 0.9) kJ/mol and ∆S ‡ obs ) (-99 ( 3) J/(K‚mol). These values are consistent with a propagation mechanism of agostically assisted migratory insertion at an alkylchromium(IV) active site. They are inconsistent with an alternating alkylidene/metallacycle mechanism requiring ratedetermining C-H cleavage. The rate of polymerization is accelerated by a factor of 3.2 in the presence of 18 mol % H 2 . Homopolymerization of 1-hexene is only 4.7 times slower than that of ethylene, an effect attributed to weaker preequilibrium binding of the substituted olefin which is partially compensated by faster migratory insertion. Copolymerization of ethylene and 1-hexene is random. It results in slower incorporation of ethylene but faster incorporation of 1-hexene relative to their respective homopolymerization rates.

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“…It is known that chromium has the ability to selectively catalyze olefin trimerization, 25 as well as olefin oligomerization and polymerization. 26 The oil product showed good lubricating oil properties (Table 5) when compared with oil derived from oligomerization of 1-hexene by other catalysts. 3,12,[27][28][29] The high viscosity index of the product indicates that the oligomers from Cr/H-MCM-41 were mostly obtained from 1-hexene and that the 1-hexene was not isomerized prior to oligomerization.…”

Section: Discussionmentioning

confidence: 91%

“…The oil fraction constituted about 60% of the product. It is known that chromium has the ability to selectively catalyze olefin trimerization, as well as olefin oligomerization and polymerization . The oil product showed good lubricating oil properties (Table ) when compared with oil derived from oligomerization of 1-hexene by other catalysts. ,,− …”

Section: Discussionmentioning

confidence: 99%

Oligomerization of 1-Hexene and 1-Octene over Solid Acid Catalysts

Klerk

2005

Ind. Eng. Chem. Res.

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Oligomerization of hexene and heavier olefins is important for synthetic fuel producers to reduce refinery complexity, as well as to produce good quality middle distillates and lubricating oils. Conversion of such olefins with homogeneous catalysts is much easier than with solid acid catalysts, which are prone to deactivation and are limited to middle distillate production. Solid phosphoric acid, amorphous silica-alumina, sulfated zirconia, MCM-41, ZSM-5, zeolite-Y, and zeolite-omega heterogeneous catalysts were evaluated in fixed-bed reactors with 1-hexene and 1-octene to determine the key catalyst properties required. The influence of added chromium and nickel was also evaluated. It was found that solid acids with average pore size of more than 10 nm had consistently better catalyst lifetime, because heavy oligomers were less readily trapped in the catalyst. It was also found that in large-pore catalysts chromium improved selectivity to lubricating oil significantly by changing the oligomerization mechanism.

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Hydrogenation of olefins and polymerization of ethene over chromium oxide/silica catalysts IV. Kinetics of the polymerization reaction

Cited by 24 publications

References 5 publications

Computational Insights into the Multisite Nature of the Phillips CrO_x/SiO₂ Catalyst for Ethylene Polymerization: The Perspective of Chromasiloxane Ring Size and F Modification

Computational Insights into the Multisite Nature of the Phillips CrO_x/SiO₂ Catalyst for Ethylene Polymerization: The Perspective of Chromasiloxane Ring Size and F Modification

A Kinetic Study of Ethylene and 1-Hexene Homo- and Copolymerization Catalyzed by a Silica-Supported Cr(IV) Complex: Evidence for Propagation by a Migratory Insertion Mechanism

Oligomerization of 1-Hexene and 1-Octene over Solid Acid Catalysts

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Hydrogenation of olefins and polymerization of ethene over chromium oxide/silica catalysts IV. Kinetics of the polymerization reaction

Cited by 24 publications

References 5 publications

Computational Insights into the Multisite Nature of the Phillips CrOx/SiO2 Catalyst for Ethylene Polymerization: The Perspective of Chromasiloxane Ring Size and F Modification

Computational Insights into the Multisite Nature of the Phillips CrOx/SiO2 Catalyst for Ethylene Polymerization: The Perspective of Chromasiloxane Ring Size and F Modification

A Kinetic Study of Ethylene and 1-Hexene Homo- and Copolymerization Catalyzed by a Silica-Supported Cr(IV) Complex: Evidence for Propagation by a Migratory Insertion Mechanism

Oligomerization of 1-Hexene and 1-Octene over Solid Acid Catalysts

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Computational Insights into the Multisite Nature of the Phillips CrO_x/SiO₂ Catalyst for Ethylene Polymerization: The Perspective of Chromasiloxane Ring Size and F Modification

Computational Insights into the Multisite Nature of the Phillips CrO_x/SiO₂ Catalyst for Ethylene Polymerization: The Perspective of Chromasiloxane Ring Size and F Modification