Search results for "vanadium"
showing 10 items of 260 documents
Vanadium complex with tetradentate [O,N,N,O] ligand supported on magnesium type carrier for ethylene homopolymerization and copolymerization
2010
Immobilization of 1,2‐cyclohexylenebis(5‐chlorosalicylideneiminato)vanadium dichloride on the magnesium support obtained in the reaction of MgCl2·3.4EtOH with Et2AlCl gives a highly active precursor for ethylene homopolymerization and its copolymerization with 1‐octene. This catalyst exhibits the highest activity in conjunction with MAO, but it is also highly active with AlMe3 as a cocatalyst. On the other hand, when combined with chlorinated alkylaluminum compounds, Et2AlCl and EtAlCl2, it gives traces of polyethylene. Moreover, its catalytic activity is strongly affected by the reaction temperature: it increased with rising polymerization temperature from 20 °C to 60 °C. The kinetic curve…
Ethylenebis(5‐chlorosalicylideneiminato)vanadium dichloride immobilized on MgCl2‐based supports as a highly effective precursor for ethylene polymeri…
2009
Ethylenebis(5‐chlorosalicylideneiminato)vanadium dichloride supported on MgCl2(THF)2 or on the same carrier modified by EtnAlCl3−n, where n = 1–3, was used in ethylene polymerization in the presence of MAO or a common alkylaluminium compounds as a cocatalyst. The support type alter vanadium loading and also change the characteristic of the catalytic active sites. Et2AlCl is the best activator for a catalyst which has been immobilized on a nonmodified support, whereas the systems which contain a carrier which has been modified by an organoaluminium compound reveal the highest activity in conjunction with MAO. That difference, together with different temperature effects on polymerization effi…
Dichlorovanadium (IV) complexes with salen‐type ligands for ethylene polymerization
2008
Vanadium complexes with tetradentate salen‐type ligands were first time explored in ethylene polymerizations. The effects of the vanadium complex structure, the alkyl aluminum cocatalysts type (EtAlCl2, Et2AlCl, Et3Al, and MAO), and the polymerization conditions (Al/V molar ratio, temperature) on polyethylene yield were explored. It was found that EtAlCl2 in conjunction with investigated vanadium complexes produced the most efficient catalytic systems. It was shown, moreover, that the structural changes of the tetradentate salen ligand (type of bridge which bond donor nitrogen atoms and type of substituent on aryl rings) affected activity of the catalytic system. The complexes containing li…
Ethylene polymerization using vanadium catalyst supported on silica modified by pyridinium ionic liquid
2016
Vanadium catalyst systems (SIL1–3A(B)/V) for ethylene polymerization were obtained by immobilization of the Cp2VCl2precursor (V) in the ionic liquid -[3-(triethoxysilyl)propyl]pyridinium chloride (IL), modified by AlCl3 and AlEtCl2(A) or AlEt2Cl (B), and supported on three types of silica carrier S1–3. The properties of the ionic liquid supports were determined using Fourier transform infrared spectroscopy, Brunauer–Emmett–Teller measurements, scanning electron microscopy and elemental analysis. The best results (above 2 tons PE (mol V)−1(0.5 h)−1) were obtained using the catalyst system SIL3B/V. Addition of ethyl trichloroacetate is possible in the ionic liquid medium and it further increas…
Effect of hydrogen on the ethylene polymerization process over Ziegler–Natta catalysts supported on MgCl2(THF)2. II. Kinetic studies
2001
This article reports on a study of the effects of hydrogen on the activity of vanadium and titanium catalysts supported on MgCl2(THF)2 in ethylene polymerization. It was found that hydrogen did not change the stable nature of the active sites and the polydispersity index of the polyethylene obtained. The propagation rate, expressed as kp, was found to be independent of the presence and concentration of hydrogen, indicating that this reacting agent does not modify the reactivity of the active sites. However, the presence of hydrogen in the polymerization medium is responsible for partial deactivation of the active sites just before polymerization is initiated.
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 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…
Rainwater-induced leaching of selenium, arsenic and vanadium from Etnean volcanic soils
2009
Active volcanoes emit considerable amounts of contaminants such as As, Se and V. Mount Etna is the biggest volcano of Europe and an excellent geochemical site to study water-soil processes. Due to its volcanic activity, the rainwater has a strong compositional gradient, both in time and space. At present, the behaviour of trace elements in the soils around Mt Etna is poorly understood. To determine the influence of the rainwater pH on the potential mobilization of geogenic pollutants, batch experiments have been performed with synthetic rainwater for 25 soils collected along the flanks of the volcano. Our results show that: i) The maximum concentrations in the leaching solutions are higher …
Silica powder obtained by sol-gel method as a support of organometallic vanadium catalyst for ethylene polymerization
2004
Sol-gel technique was employed to obtain the silica-type powder, which after modification procedure was applied as asupport of organometallic catalytic system for ethylene polymerization. The powder product was synthesized using hydrolysis and condensation of TEOS, catalyzed by ammonia. Obtained material and a reference support (commercial silica Davisil) were characterized to determine their particle size distributions, BET surface area, pore volume and diameter. Gas-phase adsorption of vanadium catalyst on analyzed support materials as well as adsorption from the solution in hexane were carried out. Both carrier materials were thermally pretreated prior catalytic systems syntheses and the…
Optical limiters relying on VO2 phase transition in thin multilayer films
2022
We propose a self-activating optical limiter device based on phase transition of vanadium dioxide in thin multilayer films. The optimal geometry reduces the transmitted power by ~ 70% and shows a recovery time of 10 ns.