Photocatalytic oxidation of 2,4,6-trichlorophenol in water using a cocurrent downflow contactor reactor (CDCR)

The heterogeneous photocatalytic oxidation of aqueous solutions of 2,4,6-trichlorophenol (2,4,6-TCP) as a model pollutant in industrial wastewater has been carried out in a pilot scale cocurrent downflow contactor reactor (CDCR). The reactions were carried out in the presence of Ultra-Violet radiation, O2 and TiO2 photocatalyst (VP Aeroperl P25/20). The TiO2 was characterized by Dynamic Vapour Sorption (DVS) technique giving specific surface area and surface energy of 46.06 m2 g-1 and 80.12 mJ m-2, respectively. The CDC reactor was fitted with an internally and vertically mounted 1.0 kW or 2.0 kW UV lamp. The reactions were carried out at 50 deg. C and 1 bar, with the reactor being operated in closed loop recycle mode and suspended photocatalyst being re-circulated. The CDC reactor, a device of very high mass transfer efficiency giving unusually large gas hold-up of approximately 50%, was operated with oxygen mass transfer and dissolution in the zone above the UV lamp (high mass transfer zone) and along and around the UV lamp housing (reaction zone). Under optimized reaction conditions, 100% conversion of 2,4,6-TCP was achieved in 180 min using 15 dm3 solutions with initial concentration of 120 mg dm-3. A combination of TiO2 photocatalyst, UV irradiation and oxidant was observed to give the most rapid photodegradation and photomineralization of the 2,4,6-TCP in comparison with irradiation only. Using the 1 kW or 2 kW UV lamps, conversion of 100 mg dm-3 of 2,4,6-TCP after 30 min was 62.51% and 90.71%, respectively, with initial reaction rates of 1.33 x 10-5 and 4.22 x 10-5 mol min-1, respectively, and rate constants 0.0046 and 0.29 min-1, respectively