Photodegradation of tebuconazole in a fluidized bed reactor mediated by phenalenone supported on sand

Abstract This study reports on the photodegradation of tebuconazole (TEB) within a fluidized bed pilot unit mediated by phenalenone (PN) grafted on sand (PN-sand). The photodegradation experiments were conducted in both a cylindrical laboratory-scale reactor and a fluidized bed pilot unit equipped with a lit LED strip, for reactional volumes of 0.4 L and 38.7 L, respectively. The lab reactor study showed that TEB removal was slightly affected by the LED emission type, i.e. purple LEDs (380 nm–440 nm) and blue LEDs (435 nm–465 nm). The PN-sand loading also affected TEB removal, with a maximum rate of 79% at a loading of 30 g.L−1, corresponding to a PN/TEB molar ratio of 1800. TEB photodegradation could be described by a first-order kinetic constant of (1.1 ± 0.2) × 10−3 min−1 with a first step where photodegradation was coupled to a rapid sorption. Similar kinetic constants were observed in both reactors. A recirculation flow of 440 L.h−1 made it possible to assimilate the fluidized bed reactor into a perfectly stirred reactor. Experiments were conducted with this recycling flow and an inlet flow of 1.1 L.h−1 and 4.2 L.h−1, respectively. The use of the first-order kinetic constant of 1.0 × 10−3 min−1 in a CSTR reactor served to propose a reactional model for the TEB solution photodegradation. A drift towards the model was detected after a contact time of 33 h and independently of the residence time. A degradation of phenalenone or a decrease in active phenalenone took place by photobleaching or ungrafting from the support.