On the Effect of Pulsing Conditions on Reaction Rates in a Pulsed Baffled Tube Photoreactor (PBTPR)

Heterogeneous photocatalysis has emerged as a viable tool for the treatment of wastewaters, since it allows for the mineralization of a wide range of organic materials. Photocatalysts can be utilized either in the immobilized form, in which case the catalyst particles are bound to the walls of the reactor vessel or to other suitable supports, or as a powder dispersion (slurry phase). Using a Pulsed Baffied Tube Photochemical Reactor (PBTPR), we have investigated the effect of the oscillatory Reynolds number on the rate of reaction in slurry type photocatalysed systems, as well as the case where the catalyst (TiO 2) is coated onto polystyrene beads using a heat treatment procedure. While reduction in reaction rates is observed with increasing pulsing conditions in the slurry phase, the opposite effect is observed for the same mass concentration of particles in the immobilized (coated) catalyst system, i.e. an increase in rates is observed with increase in pulsing conditions. In the slurry phase, the use of the PBTPR is optimized when it is operated at the threshold of conditions necessary for the uniform suspension and distribution of catalyst. Any further increases in mixing intensity served to enhance the scattering effects, therefore leading to a reduction in average reaction rates. The viability of the PBTPR as an efficient reactor for the treatment of wastewaters via heterogeneous photocatalysis is demonstrated. The particular suitability of the PBTPR to handle naturally buoyant particulates with ease is highlighted as one of its other attractions. For the slurry system, the critical catalyst concentration for the reactor system is 140mg l −1. Further work is being carried out in the immobilized catalyst phase to determine the conditions of optimal operation.