Sulfur Dioxide Sorption Properties and Thermal Stability of Hydrophobic Zeolites

Adsorption isotherms of SO{sub 2} in air on hydrophobic dealuminated Y (DAY) zeolite and silicalite at SO{sub 2} partial pressures ranging from 0.5 to 5 kPa were measured by the gravimetric method. The SO{sub 2} sorption isotherms on these two zeolites at different temperatures (25--100 C) can be correlated by the langmuir equation at low SO{sub 2} pressures (< 2 kPa) and by the Freundlich equation in the whole SO{sub 2} pressure range studied. The sorption capacity of SO{sub 2} on silicalite is larger than that of the DAY zeolite. Selective surface adsorption rather than the pore-filling mechanism was observed on adsorption equilibrium in these two zeolites. The SO{sub 2} sorption and desorption kinetic data obtained on these two zeolites show the dominant role of the reaction of SO{sub 2} on the zeolite surface in the SO{sub 2} sorption or desorption process. The simple Langmuir adsorption kinetic model provides a good description of SO{sub 2} sorption and desorption kinetics on these two zeolites at low SO{sub 2} partial pressures. The thermal stability of these two zeolites was studied by comparing the pore texture, crystalline structure, and SO{sub 2} adsorption ability of the fresh samples with those of the thermally treated samples at 550 or 850 C under various caustic conditions. It was found that these two zeolites are thermally and chemically stable under the studied conditions.