Kinetic modelling of paracetamol degradation by photocatalysis: Incorporating the competition for photons by the organic molecule and the photocatalyst

The design of a photoreactor is a complex task due to the different involved parameters. These parameters are mainly included in the kinetic model and its robustness directly impacts the photoreactor design. In this context, it is a common practice to assume that the reagents, i.e. organic molecules, are transparent to radiation. There are many cases, however, when this is not accurate. In such circumstances, the photons absorbed by the organic molecule should be accounted for in the corresponding kinetic model. This work aimed to achieve so in the Paracetamol oxidation photocatalyzed by TiO2 at 254 nm. At this wavelength both, TiO2 and Paracetamol, absorb energy. A kinetic model was developed, and this includes a local volumetric rate of energy absorption function (LVREA) that takes into account that the reagent is capable of interact with radiation thus modifying the radiant field. To simulate the radiant field, the Monte Carlo method described in the literature was modified to consider the competition for energy absorption between the catalyst and Paracetamol. The resulting model allows to predict the effect on Paracetamol degradation of catalyst concentration, initial Paracetamol concentration, intensity of emitted radiation and thickness of the reaction space. The results of computer simulation are in good agreement with experimental data for both, photolytic and photocatalytic degradation using the commercial DP25 catalyst.