Avaliação de catalisadores zeolíticos bifuncionais na conversão de hidrocarbonetos leves em hidrocarbonetos maiores, visando a produção de querosene de aviação sustentável

Abstract

The need to curb global warming makes the use of carbon dioxide (CO₂) for the production of sustainable fuels an important issue. One sector that is responsible for approximately 2% of global CO₂ emissions is the aviation sector, which is quite high. The study of CO₂ hydrogenation seeking to obtain hydrocarbons in the range of aviation kerosene is a good strategy to reduce the environmental impact of this fuel. A zeolite that stands out for its high selectivity in catalytic reactions, thermal stability and acidity is the ZSM-5 zeolite. In addition to these characteristics, it is one of the most used zeolites in industry. Ferrierite zeolite (FER) is another zeolite with potential for hydrocarbon conversion that has a two-dimensional microporous structure and high stability. The doping of metals such as gallium, zinc and molybdenum in zeolites has shown good capacity in catalytic activities in the aromatization of hydrocarbons. The study proposes to verify the effect of bifunctional zeolitic catalysts in the conversion of light hydrocarbons into longer chain hydrocarbons (C5+), which helps in the development of low environmental impact aviation fuel. These bifunctional catalysts were prepared from the acidic supports H-ZSM-5 and H-Ferrierite and incorporated into the metals gallium, zinc and molybdenum through wet impregnation. Different techniques were used to characterize the textural properties, chemical composition and acidity of the bifunctional catalysts. The catalyst activity was evaluated in an automated continuous flow unit and two sequential fixed bed reactors: the first containing a CO₂ hydrogenation catalyst, based on iron and/or cobalt and the second with the zeolitic catalysts prepared with the aim of increasing the production of C5+ chain hydrocarbons from the products generated in the first reactor. The products were analyzed by in-line coupled gas chromatography. Different bifunctional zeolitic catalysts were evaluated, considering the acidic supports (HZSM-5 and HFER) and the metals Ga, Zn and Mo. It was possible to verify the favoring of cracking over oligomerization at temperatures between 250 oC and 450 oC, while at medium temperature (200 oC), there was a better distribution of C5+ chain hydrocarbons. The best result was observed in the presence of Ga(5)/ZSM-5, which demonstrated activity lower than 10% and an increase in the fraction of C5+ hydrocarbons, in relation to the first reactor, of 5%.