Modelling and experimental checking of the influence of substrate concentration on the first order kinetic constant in photo-processes

•Methylene blue (MB) was efficiently degraded with a KrCl flow-through photoreactor.•A new and improved pseudo-first order kinetic model was validated.•The mass transfer of methylene blue is the rate determining step of the process.•The influence of the operational variables on the kinetic parameter was studied.

Most photoprocesses follow a pseudo first order kinetic law and, commonly, the kinetic parameter depends on the initial concentration of the substrate. In this work, a kinetic model, which explains this dependence on the substrate concentration and on the other operational variables, has been developed. In the model, mass transfer of substrate from the bulk solution to the wall of the photoreactor was assumed as the step determining the rate of the process. To check the model, methylene blue (MB) has been used as model substrate and photodegradation experiments have been carried out in an exciplex KrCl flow-through photoreactor, It was observed that the methylene blue conversion improved with a decrease in its initial concentration, in good agreement with the model. Also, by fitting the experimental data to the model, high correlation coefficients and a high degree of agreement between experimental and calculated conversion was obtained, which validates the model.