Sulfur Dioxide Sorption Properties and Thermal Stability of Hydrophobic Zeolites

Adsorption isotherms of SO₂ in air on hydrophobic dealuminated Y (DAY) zeolite and silicalite at SO₂ partial pressures ranging from 0.5 to 5 kPa were measured by the gravimetric method. The SO₂ sorption isotherms on these two zeolites at different temperatures (25–100 °C) can be correlated by the Langmuir equation at low SO₂ pressures (<2 kPa) and by the Freundlich equation in the whole SO₂ pressure range studied. The sorption capacity of SO₂ 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 SO₂ sorption and desorption kinetic data obtained on these two zeolites show the dominant role of the reaction of SO₂ on the zeolite surface in the SO₂ sorption or desorption process. The simple Langmuir adsorption kinetic model provides a good description of SO₂ sorption and desorption kinetics on these two zeolites at low SO₂ partial pressures. The thermal stability of these two zeolites was studied by comparing the pore texture, crystalline structure, and SO₂ 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.