Estudos do equilíbrio e cinética de adsorção de aromáticos em zeólitos, utilizando o método gravimétrico.

Abstract

Adsorption has been a promising alternative to replace conventional separation process because it presents high efficiency and low energetic/environmental cost. The biggest petrochemical industrial interest is to separate and purificate xylene isomer using selective adsorption over type Y zeolites. The separation process occurs in liquid phase at high temperatures and generally utilizes a dessorbent to improve the separation (nowadays, /wra-diethylbenzene). In this work, studies of thermodynamic equilibrium and adsorption kinetics were accomplished for orfo-xylene, para-xylene, toluene and /?#ra-diethylbenzene over commercial Y zeolites pellets. The experimental data were obtained in gas phase by gravimetric method in temperatures between 150- 210°C. In the study of thermodynamic equilibrium, rectangular shape isotherms were obtained and adjusted by Langmuir model. At the same temperature, toluene showed the highest adsorption capacity, followed by para-xylene, orto-xy\ene and paradiethylbenzene. It was also observed that the increase of temperature reduces the sorbate retention for all substances studied. About adsorption kinetics, the uptake curves denoted that the diffusion rate rises when temperature increases. Two diffusional models (for micropore diffusion control and shrinking core) were proposed in order to predict the experimental behavior. Nevertheless the results pointed a more complex transport mechanism, probably involving the simultaneous effects of micropore and macropore resistences. In addition, preliminary experiments were made using xylenes over A1P04-11 molecular sieve at 60°C. The results revealed the existence of equilibrium selectivity for orto-xylene and kinetic selectivity for para-xilene.