Influence of post-synthesis treatment on BEA zeolites hydrophobicity assessed under static and dynamic conditions

A series of BEA samples were dealuminated from a parent sample (Cal) by steaming and acid leaching. The hydrophobicity of these samples was compared to the hydrophobicity of a purely siliceous BEA. The hydrophobicity was assessed by Weitkamp original or modified relation for water and toluene competitive and non-competitive adsorption under static or dynamic conditions. According to sample dealumination method, water adsorption sites were identified to be Brønsted acidic sites, silanols nests, extra-framework aluminum species (EFAl), microporous and mesoporous available volume. Toluene molecules were mainly physisorbed by capillary condensation in microporous and mesoporous volume. Hydrophobicity indexes achieved by non-competitive adsorption under static or dynamic conditions were not a good assessment of zeolites hydrophobicity in operating industrial conditions. On the other hand water and toluene competitive adsorption under dynamic conditions as described by Weitkamp remains an appropriate method to estimate the hydrophobicity of zeolites. According to the nature of treatment, hydrophobicity index (HI) increases when aluminum content decreases. This increase is moderate for acid leached samples and pronounced for steamed samples.