Effect of silica alumina ratio and thermal treatment of beta zeolites on the adsorption of toluene from aqueous solutions

The adsorption of toluene from aqueous solutions onto hydrophobic zeolites was studied by combining chromatographic, thermal and structural techniques. Three beta zeolites (notated BEAs, since they belong to BEA framework type), with different SiO/AlO ratios (i.e., 25, 38 and 360), before and after calcination, were tested as adsorbents of toluene from aqueous media. This was performed by measuring the adsorbed quantities of toluene onto zeolites in a wide concentration range of solute. The adsorption data were fitted with isotherms whose models are based on surface heterogeneity of the adsorbent, according to the defective structure of beta zeolites. The thermal treatment considerably increases the adsorption of toluene, in the low concentration range, on all BEAs, probably due to surface and structural modifications induced by calcination. Among the calcined BEAs, the most hydrophobic zeolite (i.e., that with SiO/AlO ratio of 360) showed the highest binding constant, probably due to its high affinity for an organophilic solute such as toluene. The high sorption capacity was confirmed by thermogravimetric analyses on BEAs, before and after saturation with toluene.