Síntese da ZSM-5 de alto teor de sílica com sementes na presença de etanol e aminas

Abstract

In this study, it was evaluated the crystallization of ZSM-5 with high Si/Al ratio (100 and 150) through combined use of crystallization seeds and addition of organic compounds which are not conventional templates of ZSM-5 (ethanol, methylamine, ethylamine, propylamine, butylamine, isopropylamine and diethylamine), intending to establish a route of synthesis with less environmental impact and low cost. In the first stage, it was verified the effect of ethanol and amines added to the synthesis gel, as well as the time of hydrothermal and ratios codirecting/silica and OH/silica in static crystallization conditions. In the second stage, it was analyzed the influence of agitation during the crystallization upon the ZSM-5’s proprieties obtained in optimized conditions on static experiments from the past stage. The zeolites formed were analyzed by X-ray diffractometry to comprehend the effects of template types and further studied parameters about this material’s formation, whilst for the most crystalline samples were realized additional characterizations for: desorption at the programmed temperature, nitrogen adsorption, scanning electronic microscopy, dispersive X-Ray energy spectroscopy and thermogravimetric analysis. Through these data, it was observed that the crystallinity decreased, due to the formation of the magadiite phase with increasement of the synthesis time. It was verified that the magadiite phase is thermally instable, disappearing after the stage of calcination at 550 °C. On synthesis under agitation, it was observed ZSM-5/magadiite/cristobalita composites. The cristobalite phase occurred due to prolonged times of hydrothermal treatment and the system agitation, making necessaire to adjust the synthesis parameters to establish a methodology able to produce the ZSM-5 with high crystallinity. This procedure was successfully obtained to the synthesis of ZSM-5, using propylamine as template agent of alternative structure, under static conditions. The material formed through this method showed a superior crystallinity rate over the standard commercial sample and average crystal size between 23 and 24 nm. Its superficial specific area was superior to 300 m2.g-1, and the microporous volume reached 0,09 cm3.g-1. The biggest accessibility to the catalyzer porous with propylamine led to superior catalytic results over further evaluated material, with low ratio of coke formation, showing high stability on n-hexane cracking.