In this investigation we evaluated the feasibility and effectiveness of ozone-producing UV (254 + 185 nm) irradiation and a TiO2 photocatalyst for degradation of ethylene, which has strong hydrophobicity and does not decompose easily in a humid environment. Tests were performed in a photoreactor (V = 0.55 L) under UV irradiation at various wavelengths (365, 254 and 254 + 185 nm), relative humidities (RH < 1 % and RH > 86 %), atmospheres (pure N2 and air), residence times (11-33 sec), initial ethylene concentrations in the range of 25-105 ppmv and TiO2 contact areas (86.4-259 cm2) with presumably ambient pressure and temperature.
Experimental results demonstrated that the use of TiO2 under 254 + 185 nm UV irradiation significantly enhanced the photodegradation of ethylene compared to the case of UV irradiation alone, owing to the synergistic effect of photochemical oxidation in the gas phase and photocatalytic oxidation on the TiO2 surface. Photodegradation induced with 254 + 185 nm UV irradiation was compared with photodegradation induced with UV irradiation at wavelengths of 365 and 254 nm. The highest conversion and mineralization were obtained with 254 + 185 nm UV irradiation among the three tested UV sources. Moreover, irradiating the 254 +185 nm light generated secondary organic aerosols (SOA) via gas-to-particle conversion of organic compounds in air stream. Results indicate that the concentration of generated SOAs decreased in presence of the TiO2 catalyst and prove that TiO2 may be used to effectively control the emission of undesirable SOAs.
In an application test, for photocatalytic oxidation with 254 + 185 nm UV irradiation, corresponding to a flow rate of 0.5 L min-1, and an initial concentration of 34 ppmv, over 90 % of the inlet ethylene could be degraded.