Various situations observed when oxidizing organic compounds via ozone in a semi-batch reactor are illustrated. The resistance to the transfer of ozone from gas to liquid is accounted for using the film model. The mass balances are numerically solved simultaneously within the reactor and within the film to produce time dependent profiles of concentrations, Hatta, enhancement and depletion factors. Firstly, theoretical profiles are exemplified for various kinetic regimes from slow to fast; reaction occurs either in the bulk, in the film or in both. This shows the drastic importance of the shapes of the gas concentration profiles - both at the exit of the reactor and in the liquid phase - in determining the regime. Then, a typical example dealing with fumaric acid ozonation is shown. Firstly, the acid itself oxidizes rapidly producing an intermediate regime: part of the reaction occurs within the film, part within the bulk and the rate constant can be determined. Then, the by-products oxidize more slowly producing a typical regime: reaction occurs within the bulk, the concentration of dissolved ozone is almost 0 and the mass transfer coefficient can be determined. Finally, when all organics have oxidized, the self-decomposition of ozone governs a slow kinetic regime: the concentration of dissolved ozone is close to equilibrium.
Jet aeration as alternative to overcome mass transfer limitation of stirred bioreactors
