Estudo da dinâmica de adsorção do etanol e a coadsorção do metanol-etanol com zeólitas 4A em uma coluna de leito fixo.

Abstract

The use of adsorption as separation process has become more attractive the last years, mainly after the discovery of new adsorbents such as zeolites and other molecular sieves. In order to project and optimize adsorption equipment, the knowledge of the dynamics of adsorption of the components in experimental systems is very important. In this work, a study of the dynamics of adsorption of ethanol and the co-adsorption of methanol-ethanol solutions in a fixed bed column of 4A zeolite pellets has been made. Breakthrough curves were obtained by means o f analysis o f ethanol and methanol-ethanol concentrations in the effluents at the top of the bed. The column o f 2.94cm internal diameter had temperature sensors at the inlet and outlet of the fixed bed, to observe the thermal evolution during the process of adsorption and co-adsorption. In the order to get a more detailed study of the input variables, a 23 factorial experimental planning, plus star configuration with three experiments in the central point was employed. Influence o f input concentration of the solution, operational flow rate and height of the fixed bed on the dynamic behavior of the experimental runs was investigated. The experimental conditions were: (a) input concentrations ranging from 2.5 to 12.0% (w/w) ethanol in toluene and 2.5 to 5.7% method in ethanol; (b) flow rates ranging from 2.5cm3/s to 12.0cm3/s and (c) height of the fixed bed ranging from 6.6 to 23.4cm. The breakthrough curves of ethanol adsorption were analyzed by Thomas model, valid for isothermal systems and Langmuir equilibrium. The experimental data showed a good fitting with the model, in spite of the inherent simplifications o f the model. The values o f adsorption capacity of the 4A zeolites at the equilibrium calculated from the breakthrough curves showed a good agreement with those found in previous works, obtained by the static method, except for those obtained with smaller fixed bed heights. The breakthrough curves obtained for the methanol-ethanol system presented characteristic format of the co-adsorption without inert and strong isothermal deviation as expected. The methanol adsorption capacity was higher than that obtained for ethanol. Statistic analysis of the results showed that, under the employed experimental conditions, fixed bed height is the main parameter affecting ethanol adsorption while co-adsorption is mainly influenced by the input methanol concentration.