Avaliação dos catalisadores ziegler-natta mistos à base de Ti e V em reações de polimerização de etileno e copolimerização com alfa-olefinas

Sistemas mistos catalíticos Ziegler-Natta constituídos de VOCl3 e TiCl4 foram avaliados em reações de homopolimerização de etileno e co-polimerização de etileno com alfa-olefinas. O efeito da temperatura (30 a 200ºC), da pressão (2 a 15 bar) e da natureza do alquilalumínio (TEA, DEAC,TIBA,DEAL-E ,MAO,IPRA e DNBM) foram estudados. O comportamento do sistema catalítico juntamente com o alquilalumínio foi investigado através da caracterização por espectroscopia molecular no UV-visível. Os polímeros obtidos foram caracterizados por DSC, GPC e os copolímeros, também por C13-NMR. Nesse sistema catalítico, ainda foi avaliado a possibilidade da utilização de uma adição subseqüente do catalisador e cocatalisador no meio reacional. Catalisadores suportados sobre sílica funcionalizada com Mg(OEt)2 foram sintetizados, variando a razão entre VOCl3 e TiCl4. Teores de metal, determinados por ICP OES e RBS ficaram na faixa de 1% de titânio e 0,05% de vanádio. Os sistemas mais ativos foram aqueles, cujo sistema catalítico utilizado foi Ti + 2V e razão Al/M = 100.Ziegler-Natta catalyst systems consisting of VOCl3 and TiCl4 have been evaluated in ethylene homopolimerization reactions and co-polymerization of ethylene with alpha-olefins. The effect of the temperature (30- 200ºC), of the reaction pressure (2 - 15 bar) and of the nature of the alkylaluminum (TEA, DEAC, TIBA, DEAL-E, MAO, IPRA and DNBM) was studied. The behavior of the catalytic system together with the alkylaluminium was investigated through molecular spectroscopy in the UV-visible. The resulting polymers have been characterized by DSC, GPC and the copolymers, also by C13-NMR. Supported catalysts on silica chemically modified with Mg(OEt)2 have been synthetized, varying the ratio between VOCl3 and TiCl4. Metal content, determined by ICP OES and RBS laid in the range of 1 wt.-% of titanium and 0.05 wt.-% of vanadium. The most active system was shown to be that resulting of the combination Ti + 2V and Al/M ratio of 100

Avaliação dos catalisadores ziegler-natta mistos à base de Ti e V em reações de polimerização de etileno e copolimerização com alfa-olefinas

Sistemas mistos catalíticos Ziegler-Natta constituídos de VOCl3 e TiCl4 foram avaliados em reações de homopolimerização de etileno e co-polimerização de etileno com alfa-olefinas. O efeito da temperatura (30 a 200ºC), da pressão (2 a 15 bar) e da natureza do alquilalumínio (TEA, DEAC,TIBA,DEAL-E ,MAO,IPRA e DNBM) foram estudados. O comportamento do sistema catalítico juntamente com o alquilalumínio foi investigado através da caracterização por espectroscopia molecular no UV-visível. Os polímeros obtidos foram caracterizados por DSC, GPC e os copolímeros, também por C13-NMR. Nesse sistema catalítico, ainda foi avaliado a possibilidade da utilização de uma adição subseqüente do catalisador e cocatalisador no meio reacional. Catalisadores suportados sobre sílica funcionalizada com Mg(OEt)2 foram sintetizados, variando a razão entre VOCl3 e TiCl4. Teores de metal, determinados por ICP OES e RBS ficaram na faixa de 1% de titânio e 0,05% de vanádio. Os sistemas mais ativos foram aqueles, cujo sistema catalítico utilizado foi Ti + 2V e razão Al/M = 100.Ziegler-Natta catalyst systems consisting of VOCl3 and TiCl4 have been evaluated in ethylene homopolimerization reactions and co-polymerization of ethylene with alpha-olefins. The effect of the temperature (30- 200ºC), of the reaction pressure (2 - 15 bar) and of the nature of the alkylaluminum (TEA, DEAC, TIBA, DEAL-E, MAO, IPRA and DNBM) was studied. The behavior of the catalytic system together with the alkylaluminium was investigated through molecular spectroscopy in the UV-visible. The resulting polymers have been characterized by DSC, GPC and the copolymers, also by C13-NMR. Supported catalysts on silica chemically modified with Mg(OEt)2 have been synthetized, varying the ratio between VOCl3 and TiCl4. Metal content, determined by ICP OES and RBS laid in the range of 1 wt.-% of titanium and 0.05 wt.-% of vanadium. The most active system was shown to be that resulting of the combination Ti + 2V and Al/M ratio of 100

Paleoenvironmental evolution of the Aptian Romualdo Formation, Araripe Basin, Northeastern Brazil

The tectonic evolution of the Equatorial Atlantic Gateway (EAG) throughout the early Cretaceous had global implications. This break-up of western Gondwana has played a significant role in causing, or amplifying, environmental changes due to its influence on ocean chemistry, nutrient distribution, water mass circulation, and bottom waters ventilation. However, the timing of its establishment and the areal extent of this oceanic gateway is still poorly constrained. Marine settings were recorded by the black shales of the Romualdo Formation (Late Aptian), Araripe Basin - Northeastern Brazil, which are known worldwide for their fossil content and importance for paleogeographic reconstructions of Gondwana. In this contribution, we present multiproxy analyses, combining macro- and micropaleontological, as well as sediment compositional data to evaluate paleoenvironmental conditions during the deposition of sedimentary strata assigned to the Romualdo Formation. We investigate the ~100-m-thick succession of the Sobradinho Section, which is the most complete exposure of the Romualdo Formation. Increased abundances of ostracods, the occurrence of agglutinated benthic foraminifera, bakevelliid bivalves, and cassiopid gastropods coincide with levels of relatively high paleosalinity estimates based on the Sr/Ba (strontium/barium) and S/TOC (sulfur/total organic carbon) ratios. These levels correspond to a transgressive system tract and the lower interval of a highstand systems tract. Throughout the section, black shales occur intercalated with sparse sandstone and calcarenite levels, and the deposition of these black shales is associated with dysoxic to anoxic bottom water conditions, as suggested by the V/Cr (vanadium/chrome) ratio. The occurrence of stagnant bottom water conditions may explain the mass mortality of ostracods in the lower interval of the succession. The upper part of the highstand system tract in the studied section was deposited in coastal environments and is characterized by coarser-grained siliciclastic-dominated facies (high log(Zr/Rb) (zirconium/rubidium) ratio), as well as increased phytoclasts and terrigenous (high magnetic susceptibility) contents