Characterization of adsorptive and hydrophobic properties of silicalite-1, ZSM-5, TS-1 and Beta zeolites by TPD techniques

The adsorption properties of different zeolites (silicalite, ZSM-5, TS-1 and pure silica Beta) have been investigated by thermal programmed desorption (TPD) techniques. Toluene, isopentane and ethanol were used as adsorbates in order to check the ability of these zeolites for the adsorption of different volatile organic compounds (VOCs), whereas water was also used as adsorbate to study their hydrophobic properties. ZSM-5 zeolite probed to be a good adsorbent for the three organic compounds, although the presence of A1 species in its framework provides this material with a strong hydrophilic character, hindering its use as a useful adsorbent in humid atmospheres, whereas they catalyze ethanol dehydration reactions during the TPD tests. On the other hand, pure silica Beta zeolite, prepared by the fluoride route, showed to be a highly inert material establishing very weak interactions with all the adsorbates. Silicalite-1 presents interesting properties for the adsorption of ethanol, while exhibiting hydrophobic features. However, only weak interactions of the silicalite-1 surface take place with hydrocarbons. TS-1 zeolite behaviour is especially remarkable, since this material combines strong hydrophobic properties, similar to those of pure silica zeolites, with the adsorption of significant amounts of toluene and isopentane, as it occurred with ZSM-5 zeolite. Accordingly, TS-1 shows a great potential for the adsorption of hydrocarbons in water-containing streams. These unique properties of TS-1 are probably due to the presence of titanium atoms in tetrahedral positions of the MFI structure, which interact preferentially with hydrocarbon molecules rather than with polar molecules. (C) 2006 Elsevier B.V. All rights reserved.