Preparação e testes cataliticos com o catalisador do tipo Ziegler TiCl4/TiO2red. suportado em silica gel

AUTOR(ES)
DATA DE PUBLICAÇÃO

2001

RESUMO

The reduced form of anatase (titanium dioxide) was used by our research group as alternative support to TiCI4, showing good results in ethylene and propylene polymerization, producing polypropylene with 80 % of isotaticity. However, there was only a very small concentration of active sites in this catalyst, nearly 1% of titanium atoms of the support, and this catalytic system show low productivity. To increase the number of the sites and the productivity, a new catalytic system was developed with a higher surface area by depositing anatase on the silica gel surface. This was possible by the Atomic Layer Epitaxy method (ALE) using TiCI4 vapor at high temperatures. To obtain the anatase form, the thermal treatment of the silica was carried out at 500°C and the deposition of TiCI4 at 300°C. The process was completed by chemical reduction using n-butil-Lithiun and finally the heterogenization with TiCI4. The amount of TiO2 supported was nearly 13 mgTiO2.gSiO2. The average concentration of Ti(lll) was 23 mmoITi(III).gcat. The productivity of ethylene in liquid and gas phase polymerization was 140 and 120 gPE.gcat., respectively. The polyethylene showed a melting point of 137°C, molar mass around 300 kg.mol and cristalinity index beetwen 49 and 69%. In polypropylene reactions, the productivity was 6 gPP.gcat., giving a polymer with melting point of 154°C and isotaticity index about 60%. Two kinds of active sites probably co-exist on the catalyst surface, The evidences that support this hypotesis are low isotaticity index, polidispersity (2,2) and an EPR spectra with two resonance signals for Ti(lll) (g=1,98 and g=1,96). This catalysts have a life time which is long enough to produce statistic co-polymer in an elastomer form, with two melting points at 132 and 142°C.

ASSUNTO(S)

silica gel dioxido de titanio polimerização etileno deposição quimica de vapor

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