Kinetic Analysis of the Photocatalytic Degradation of Ethylene over TiO₂ Thin Films in a Batch Reactor

The photocatalytic oxidation process has been recognized as an environmental friendly, sustainable and low-cost technology for air treatment. A photocatalytic batch reactor has been employed to assess the kinetics of the oxidation of ethylene (C₂H₄) over immobilized titanium dioxide (TiO₂) and the effect of initial pollutant concentration on the kinetics. The rate model based on the simplified mono-molecular Langmuir-Hinshelwood (LH) kinetic model was found to represent the degradation satisfactorily, however with numerical constrains. These were overcome by employing two different approaches. On one hand the Langmuir-Hinshelwood model was solved by means of the Lambert W-function and on the other hand it was reduced to a pseudo-first order rate law, both resulting in a good fit to the experimental data, thus proving that the photodegradation of C₂H₄ over TiO₂ can be modelled by a first order rate law under low concentration conditions. Moreover, both models give a linear dependence between the reaction rate and the initial C₂H₄ concentration, making an estimation of reaction rate as a function of concentration possible, for a larger interval of C₂H₄ concentrations.
To derive a mathematical dependence of kinetics on UV irradiance, experiments are conducted at varying values of irradiance, from 38 to 50 W/m². Based on the results, the relation can be assumed to be linear, where increasing irradiance speeds up the reaction, up to a limit dictated by the catalyst.