Photolytic and photocatalytic degradation of micro pollutants in a tubular reactor and the reaction kinetic models

The photocatalytic decomposition and mineralization of p-chlorobenzoic acid (p-CBA), 4-chlorophenol (4-CP), hydroquinone and 4-nitrophenol (4-NP) in aqueous solution were investigated using two kinds of low-pressure mercury lamps: one was UV (ultraviolet) lamp emitting at 254 nm and the other was VUV (vacuum ultraviolet) lamp emitting at both 254 and 185 nm. VUV irradiation led to the most efficient degradation of the organics. The validation of calculation shows the effect of bubble on radiation scattering was little. The evolution of the radiation absorbance of the reaction solutions suggests the radiation adsorption of the intermediates was negligible. Based on these results simple reaction kinetic models were established with the pseudo-first order reaction rate constants relating to incident radiation intensity. The reaction rate constants of photolysis and photocatalysis (kPD and KPCD) were calculated through the numerical simulation of the models. Using the calculated kPD and KPCD of p-CBA (0.1 and 11.0 min−1, respectively), the removals of p-CBA in TiO2/UV photocatalysis were predicted, which were almost the same as the measured removals. With the calculated kPD and KPCD of 4-NP (0.011 and 4.8 min−1, respectively), the removals of 4-NP in TiO2/UV photocatalysis process in a big reactor under the different gas flow rates were also predicated, which agreed well with the measured results.