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 phillipsiteand chabazite, were studied. The adsorption isotherms of both compounds on a tuff sample with a grain size ranging from 120 to 60 meshand having a total zeolite content of 40% were determined at temperatures of 20, 40, 60 and 80 C and furthermore the same isothermswere determined at T = 20 C and T = 80 C on two other samples of the same tuff, having zeolite contents of 18% and 68% and grainsize distributions in the ranges >120 mesh and 60 · 35 mesh, respectively. The experimental results were satisfactorily interpreted in termsof the pore filling Dubinin–Astakhov model. The model used allowed to estimate the micropore volume of the three grain size fractionsconsidered (ranging from 36 to 121 ml/kg) and the characteristic energy of adsorbate–tuff interaction (about 20 kJ/mol for water andabout 25 kJ/mol for ethanol). Furthermore, the binary (water–ethanol) adsorption isotherms were predicted. The overall results indicatedthat a strong correlation between zeolitic content of the tuff and adsorption capacity exists and that the selected tuff is very selectivetowards water, with a molar separation factor in the order of 6–7 if the azeotropic mixture is considered.