Sorption of volatile organic compounds on hydrophobic zeolites

Sorption measurements with ZSM-5, mordenite and faujasite zeolites were performed with single solvents as well as with a mixture of five solvents in the presence and absence of water. Thereby, the origins of hydrophilicity were rationalized and the selectivity of the sorbents determined. Because of their larger pores, faujasites and dealuminated mordenite are more suitable than ZSM-5 for separating mixtures with several components. Dealumination of mordenite generates sorption behavior typical of sorbents with a three-dimensional pore system due to the newly formed secondary pores and the removal of amorphous non-framework species. While the breakthrough of hydrophobic sorbents follows in the same order as their vapor pressures, sorption of hydrophilic molecules is influenced not only by the aluminum content in the framework, but also by the content of non-framework aluminum species and the concentration of silanol groups. Zeolites in the sodium form are more hydrophilic and need higher regeneration temperatures. On the other hand, zeolites in the H-form have a higher activity for catalytic conversion during thermal regeneration. Consequently, highly dealuminated zeolites are preferred for applications aiming at solvent recovery. (C) 2000 Elsevier Science B.V. All rights reserved.