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• Spectral band discretization of multiphysics model of solar photoreactors operation. • Novel numerical approach for modelling photoreactors of any spectral distribution. • Small differences in light spectra play a critical role on photocatalytic activity. • Model predictions successfully validated with solar simulator and natural sunlight. • Successful explanation for disagreement of natural and simulated solar experiments. This work describes the critical role of the matching between the spectral distribution of the incident light and the absorption spectra of the semiconductor material on the accuracy of the simulation of solar photocatalytic reactors. In silico results have been generated by a multiphysics model including the rigorous description of the hydrodynamics, radiation transfer, mass transport and chemical reaction rate, with the particular feature of using a spectral band discretization approach for the resolution of the radiation balance and the estimation of the spectral local volumetric rate of photon absorption. Model predictions with a mechanistic kinetic model have been experimentally validated using a solar reactor based on a tubular reactor coupled to a compound parabolic collector (CPC) under illumination with a solar simulator (xenon lamp) and natural sunlight. Small differences in the spectral distribution of both light sources led to significantly different predictions for the reaction rate, explaining the higher efficiency experimentally achieved with natural sunlight in comparison with the solar simulator for equivalent total UV-A irradiances. The developed model is able to explain the discrepancies between experimental results in solar simulators and under natural sunlight, usually reported in the literature, offering a novel numerical approach for rigorous modelling of photoreactors using light sources with any spectral distribution. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • New mechanistic kinetic model proposed for NO x photocatalytic oxidation. • Intrinsic kinetic parameters for NO x removal determined in the ISO 22197-1 reactor. • Radiation homogeneity validated by numerical simulation. • Plug flow hypothesis confirmed by computational fluid dynamics simulation. • Successful model validation with prediction errors in the conversion below 13%. Abstract An air purification reactor working under the standard ISO 22197-1 is studied and used for the determination of the intrinsic kinetic parameters of the NOx photocatalytic removal. A new mechanistic kinetic model considering explicitly the radiation step is proposed. The derived reaction rate expressions for NO and NO 2 include the dependence on the concentration of NO, NO 2 and the local superficial rate of photon absorption. The air purification reactor was modelled using a numerical simulation methodology to validate homogeneity of the light distribution reaching the catalyst surface and go deep in the knowledge of fluid dynamic behaviour. Based on these results, general guidelines of the reactor behaviour working under the ISO 22197-1 standard can be stablished, being the first time that this reactor is modelled with a global predictive approach. Radiation intensity over the catalyst surface was confirmed to reach the specified value of 10 ± 0.5 W m−2. Plug flow can be applied in the studied reactor with an axial dispersion module lower than 0.001. However, the diffusion of chemical species in the reactor was also studied, as well as the impact of mass transfer phenomena on the accuracy of the calculated kinetic parameters. A comprehensive simulation model of the ISO reactor, including fluid dynamics, radiation, photochemical reaction and mass transfer was developed. The simulation results confirm that the kinetic parameters obtained without considering mass transfer limitation fail to reproduce the experimental data, whereas a global error lower than a 17% was achieved including the diffusion of the species in the reactor. The proposed methodology, experimentally validated, could be successfully applied to the prediction of the performance of different type of photocatalytic reactors or even open systems for NOx pollutants. [ABSTRACT FROM AUTHOR]