Modeling of water and ethanol adsorption data on a commercial zeolite-rich tuff and prediction of the relevant binary isotherms

Adsorption equilibria of water and ethanol vapors on a zeolitized tuff from Campania (Southern Italy), containing both phillipsite and chabazite, were studied. The adsorption isotherms of both compounds on a tuff sample with a grain size ranging from 120 to 60 mesh and having a total zeolite content of 40% were determined at temperatures of 20, 40, 60 and 80 degrees C and furthermore the same isotherms were determined at T = 20 degrees C and T = 80 degrees C on two other samples of the same tuff, having zeolite contents of 18% and 68% and grain size distributions in the ranges > 120 mesh and 60 x 35 mesh, respectively. The experimental results were satisfactorily interpreted in terms of the pore filling Dubinin-Astakhov model. The model used allowed to estimate the micropore volume of the three grain size fractions considered (ranging from 36 to 121 ml/kg) and the characteristic energy of adsorbate-tuff interaction (about -20 kJ/mol for water and about -25 kJ/mol for ethanol). Furthermore, the binary (water-ethanol) adsorption isotherms were predicted. The overall results indicated that a strong correlation between zeolitic content of the tuff and adsorption capacity exists and that the selected tuff is very selective towards water, with a molar separation factor in the order of 6-7 if the azeotropic mixture is considered. (c) 2007 Elsevier Inc. All rights reserved.