Search results for "polymerization of ethylene"
showing 10 items of 13 documents
Transition metal chlorides complexes with tetrahydrofuran [MtCl(4)(THF)(2)] used as precursors of ethylene polymerization
2002
Otrzymano trzy kompleksy chlorków metali przejściowych z THF - [TiCl4(THF)2] (I), [ZrCl4(THF)2] (II), oraz [HfCWTHF),] (III) i zastosowano je jako prekursory katalizatorów tytanowo-magnezowych w niskociśnieniowej polimeryzacji (0,5 MPa, 323 K) etylenu przy użyciu AlEt3 (najkorzystniej), AlEt2Cl lub Al(z'-Bu)3 jako kokatalizatora (rys. 1, tabela 1). Zmierzono gęstość, gęstość nasypową, stopień krystaliczno-ści, ciężary cząsteczkowe i ich rozkład oraz temperaturę topnienia uzyskanego PE-HD (tabela 1). Aktywność katalizatorów wzrastała w szeregu (III) < (II) < (I), tzn. ze wzrostem elektroujemności pierwiastka metalu i ze spadkiem wartości ładunku cząstkowego na atomie metalu grupy przejściowe…
Rola chlorku magnezu jako nośnika katalizatorów Zieglera-Natty
2000
Structural examination data are presented for various supports. Porosimetry (Table 2) and particle size distribution studies on MgCl 2, MgCl 2(THF) 2, Al 2O 3 as supports, carried out prior to and after ball-milling (Figs. 1, 3), suggest that MgCl 2 is beneficial as carrier because it is more liable to pretreatment (ball-milling, presence of a Lewis base) and allows its mass to be better utilized and its surface to produce catalytically active centers. Prolonged ball-milling of MgCl 2 was found to result not only in comminuted particles but also in increased specific area and larger pore volume. Studies on synthesis conditions of a vanadium precursor supported on MgCl 2(THF) 2 showed prolon…
Synthesis of oxide-supported vanadium catalysts and their activity in ethylene polymerization
1999
The activity of oxide-supported vanadium-based catalyst systems (VOCl 3/Et 2AlCl) in low-pressure ethylene polymerization and the properties of the resulting polyethylenes were studied in relation to the type and mode of modification of the oxide support. Alumina, silica and an un"conventional silica-type material prepared by the sol-gel process were used as supports. Results are compared with those obtained earlier with a catalyst supported on MgCl 2(THF) 2. Of the oxides studied, the silica-type sol-gel material dehydrated and subsequently modified with Et 2AlCl proved to be the best carrier for a vanadium catalyst. The polyethylene prepared by using this catalyst support was found to exh…
Kompleksy metali przejściowych z zasadami Lewisa jako prekursory katalizatorów polimeryzacji olefin. Cz. I. Postęp w komputerowym modelowaniu procesu…
2001
A review with 35 references covering molecular modeling in coordination polymerization over homogeneous and heterogeneous Ziegler-Natta catalysts. The study includes supports, cocatalysts, Lewis bases and solvents. Recent progress in elucidating the mechanisrn of elementary polymerization steps is presented against the background of rapidly deveIoping computational methods and available computational power. Theoretical studies on polymerization mcchanisms and structure of active centers are described (egns. 1-4). Authors own calculations are used to compare [MtC14(THF)2] complex-based (Mt = Ti, Hf or Zr) heterogeneous catalysts. The geometrical characteristics of precursors is presented (Ta…
Studies on ethylene/1-hexene copolymerization over the zirconocene catalyst supported on MAO-modified MgCl2(THF)2. The effect of copolymerization con…
2002
Badania dotyczą układu katalitycznego MgCl2(THF)2/MAO/Cp2ZrCl2/MAO (MAO — metyloaluminoksan). Stwierdzono, że zarówno aktywność tego układu katalitycznego, jak i właściwości kopolimerów w znacznym stopniu zależą od stosunku molowego Al:Zr (zmienianego w przedziae 1500—7000) i od temperatury kopolimeryzacji (tabele 1 i 2), natomiast wpływ czasu kopolimeryzacji jest mniejszy (tabela 3). Aktywność katalizatora oraz zawartość 1-heksenu wbudowanego do kopolimeru zwiększają się ze wzrostem temperatury i stosunku Al:Zr, a jednocześnie maleje ciężar cząsteczkowy i temperatura topnienia produktów. Ustalono także, że osadzenie katalizatora cyrkonocenowego na stosowanym nośniku powoduje zwiększenie je…
Polymerization of ethylene by oxide-supported titanium halide catalyst: kinetic model with a deactivation of active species
2000
Abstract The effect of the calcination temperature of alumina, which was then used as a support for a titanium halide catalyst [TiCl4/Et2AlCl], on the catalyst activity in ethylene polymerization was investigated. α-Al2O3 was found to make a more advantageous catalyst support as compared to γ-Al2O3 despite the fact that the former offered a clearly lower specific surface area and its content of surface OH groups was inferior. The ethylene polymerization in the presence of the catalytic system on different alumina supports was investigated on the basis of a proposed kinetic model, taking into consideration the deactivation of active sites in the process. The improved activity was found to re…
Organometallic VCl4-based catalyst supported on MgCl2(THF)2 for ethylene polymerization
1997
A Ziegler-Natta catalyst was obtained by milling VCl4 with the magnesium support in the from of the MgCl2(THF)2 complex, followed by activation with an organoaluminum compound. This catalyst was employed in low-pressure polymerization of ethylene. The system was found to offer a very high activity and to polymerize ethylene at a rate of a few hundred kg PE/(g Vh) with the resulting molecular weight of the product very high. The kinetic investgation of the polymerization process revealed over 80 % of the transition metal atoms to be involved in the forming catalytic active sites, undergoing virtually no deactivation over the period of time studied.
Weryfikacja kinetycznego modelu polimeryzacji etylenu wobec metaloorganicznych katalizatorów wanadowych na nośniku magnezowym
1998
The kinetic studies are reviewed on low-pressure polymerization of ethylene over two types of organovanadium catalysts, viz., MgCl 2(THF) 2/VCl 4/Et 2AlCl and MgCl 2(THF) 2VOCl 3Et 2AlCl, each deposited on a magnesium carrier. The polymerization rate was found to be directly related to the catalyst and monomer concentrations (Figs. 2 and 3), unless when the access of the monomer to the reactive V-C bond is restricted by diffusion. Polymer chain termination step was found to result from the reaction of the transfer onto the monomer and to be associated with the regeneration of the active site on which a new macromolecule can be formed. A kinetic model was developed for the ethylene polymeriz…
Synthesis and characterization of ethylene-1-hexene copolymers prepared by using MgCl2(THF)2-supported Ziegler-Natta catalysts
2000
Ethylene was copolymerized with 1-hexene over vanadium (VOCl3 and VCl4) and titanium (TiCl4) catalysts supported on MgCl2(THF)2 and activated with Et2AlCl. So far these catalyst systems have not been known as initiators of ethylene-1-hexene copolymerization. The vanadium catalysts were more active than the titanium catalyst and, at identical comonomer concentrations in the feed, gave rise to a greater incorporation of 1-hexene into the copolymer. Even at relatively low fractions of 1-hexene, the MgCl2(THF)2-supported catalysts affected much the copolymer properties like density, melting point and crystallinity.
The effect of the comonomer on the copolymerization of ethylene with long chain α-olefins using Ziegler–Natta catalysts supported on MgCl2(THF)2
2000
Abstract The effect of the type of the comonomer (1-pentene, 1-hexene, 1-octene, 1-decene and 1-dodecene) on the copolymerization of ethylene with α-olefin over vanadium (VOCl3 and VCl4) and titanium (TiCl4) catalysts supported on MgCl2(THF)2 and activated by Et2AlCl was studied. The results show that the introduction of a longer α-olefin in the ethylene polymerization feed depresses the catalytic activity of all investigated catalysts. The catalyst activity does not depend on the type of the comonomer applied but changes with the comonomer concentration in the feed. The incorporation of α-olefin in the polymer chain was found to be dependent on the type and concentration of the comonomer i…