Obtaining magnesium and vanadium catalysts supported on activated carbon for the production of styrene. / Obtenção de catalisadores de vanádio e magnésio suportados em carvão ativado para a produção de estireno.

AUTOR(ES)
DATA DE PUBLICAÇÃO

2008

RESUMO

The main route industrially used for styrene production is the ethylbenzene catalytic dehydrogenation, responsible for more than 90% of its worldwide capacity. The industrial process is performed at the temperature range of 550-700 C with an excess of heated steam over potassium and chromium-promoted iron oxide catalysts, which are toxic and have 2-year lifetime. In this context, there is a demand for catalysts which are active and selective in this reaction, showing increasing lifetime besides not being toxic. In order to find alternative systems, the synthesis of vanadium and magnesium oxides supported on activated carbon, produced by pyrolysis of sulfonated styrene-divinylbenzene copolymer, in non-oxidative atmosphere was described in this work. The catalysts were characterized by specific surface area, pore size distribution and X-ray diffraction measurements, termogravimetry, differential thermal analysis, atomic absorption spectrophotometry and scanning electron microscopy coupled to quantification system by energy dispersive spectroscopy. The catalysts were evaluated in the ethylbenzene dehydrogenation in steam absence, at 530 C and 1 atm for styrene production. It was found the presence of vanadium trioxide and of clusters of vanadium and magnesium at different sizes on the solids. The materials showed Type II or IV nitrogen adsorption/desorption isotherms, typical of mesoporous and macroporouos solids with associate micropores and Type I hysteresis, characteristic of materials with cilindric pores. These solids showed specific surface areas between 378 and 611 m2/g. The catalysts with vanadium and magnesium showed a loss of specific surface area lower than the activated carbon during the ethylbenzene dehydrogenation. The addition of magnesium and vanadium caused an increase of catalytic activity of activated carbon and styrene selectivity. All catalysts were more active than a commercial catalyst. The catalyst containing 5% vanadium was the most promising one. This catalyst led to, in the absence of steam, to 35% of ethylbenzene conversion, about three times the value for the commercial catalyst evaluated in steam presence. It was attributed to vanadium catalytic activity and the presence of oxigenated groups in activated carbon surface which are active on the ethylbenzene dehydrogenation.

ASSUNTO(S)

vanádio styrene carvão ativado activated carbon ethylbenzene dehydrogenation desidrogenação do etilbenzeno quimica vanadium estireno

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