Ozone and oxygen permeation behavior of silicone capillary membranes employed in membrane ozonators

The permeabilities and selectivities of O₃,O₂, and N₂ through silicone capillary membranes employed to degrade organic pollutants in water or air have been experimentally determined. These characteristics have been studied for silicone membranes used in membrane reactors having the following conditions: O₃ in O₂ on one side of the membrane, and either water containing pollutants or a perfluorocarbon (FC) phase containing pollutants on the other side. The permeability of O₃ (8.8 e-13 kgmol·m/m²·s· kPa) is four times that of O₂ through virgin silicone rubber. Exposure to O₃ modifies the polymer and alters the permeabilities of O₃ and O₂. The presence of water with O₃ leads to an increase in O₃ and O₂ permeability (∼ 30%) and an increase in the selectivity, αo₂-N₂ (∼ 10%). The increased permeabilities are likely to be due to the formation of peroxides on the surface and possibly in the polymer. When the silicone capillary membranes were exposed to a perfluorocarbon (FC), the permeabilities of O₃ and O₂ decreased (∼ 9%) due to an increase in crosslinking in the polymer matrix; there was also a slight increase in αo₂-N₂ ( ∼ 2%), which can be ascribed to the smaller molecular sieving radius of O₂ compared to N₂.