Search

• 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]

• Large nanotubular TiO 2 photocatalytic membranes prepared by anodization. • Galvanostatic anodization improves the process over potentiostatic conditions. • Confirmed activity for photocatalytic methanol oxidation and E.coli inactivation. • Hybrid process proved synergism between filtration and photocatalysis. • Nanotubular TiO 2 do not significantly improve activity of nanoparticulate TiO 2. Hybrid photocatalysis/membrane processes constitute promising alternatives for water and wastewater treatment because they combine the efficiencies of filtration membranes technology and the oxidative effect of the photocatalytic process, increasing the lifetime of the membranes. The main challenge of these systems is the incorporation of the titanium dioxide (TiO 2) catalyst without altering the filtration properties of the membrane and the photocatalytic activity of the catalyst. One way to achieve this goal is generating the TiO 2 layer by direct anodization of titanium supports under controlled conditions to form titanium dioxide nanotubes (TiO 2 -NTs). This work reports the development of novel photocatalytic titanium membranes based on the formation of TiO 2 -NT arrays by anodization under both potentiostatic and galvanostatic conditions, and the scaling-up of the most promising systems to operational membrane photoreactors. The results demonstrated that the galvanostatic method displays more controlled tuneability to obtain NTs formation than the potentiostatic method on porous surfaces. However, despite the formation of TiO 2 -NTs structures, the observed photocatalytic activity is lower than that exhibited by TiO 2 nanoparticles deposited directly on the membrane, although in this case the transmembrane pressure is significantly higher, and therefore the operational pumping costs are greater. Synergistic effects of photocatalysis and microfiltration are clearly demonstrated in the application of the hybrid system to the removal of bacteria for water disinfection processes, showing a significant improvement in the inactivation of E. coli bacteria in water with respect to the bare membrane. [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]

This work describes the procedure for the simulation of the operation of a photocatalytic reactor by using a multiphysics computational fluid dynamics (CFD) model based on the determination of the intrinsic kinetics parameters in an optically differential photoreactor. The model includes the rigorous description of the hydrodynamics, radiation transfer, mass transport and chemical reaction rate based on a mechanistic kinetic model. Possible existence of dead and recirculation zones has been identified from the flow field, showing a non-uniform flow through the reactor domain. The theoretical laminar profile is not reached due to the short length of the annular core and the departure from the ideal models has been quantified. The predicted velocity field has been experimentally validated with good agreement by injecting a tracer. The radiation field was simulated for slurry TiO 2 suspensions with concentrations between 0.005 and 5 g·L −1 , showing an optimum catalyst loading around 0.1–0.2 g·L −1 . Above this value, the increase in the absorption of radiation is negligible, whereas a more non-uniform radiation profile develops, keeping the most external regions of the reactor in the dark. The results of photocatalytic activity, using methanol oxidation as test reaction, showed good agreement between model predictions and experimental data, with errors between 2% and 10% depending on the catalyst concentration. The successful validation confirms not only the scientific background of the model, but also supports its applicability for engineering purposes in the design and optimization of large scale photocatalytic reactor to overcome some of limitations hindering the industrial development of this technology. [ABSTRACT FROM AUTHOR]

• Enhanced radiation transport model validated in commonly used photoreactors. • Isotropic, parallel and cone-shaped emission tested, representing common UV sources. • Increase of precision reached for sun direct light simulations. • Great improvement in LEDs simulations, from finer cone radiation and power cosine. This work presents the enhanced numerical simulation of the radiation transport in three different types of photocatalytic reactor using a novel Discrete Ordinate Method model recently developed for the open-source Computational Fluid Dynamics (CFD) platform OpenFOAM. The photoreactors represent commonly used geometries and illumination sources in the field of heterogeneous photocatalysis: an annular reactor illuminated by a mercury fluorescent lamp, a tubular reactor coupled to a compound parabolic collector illuminated by sunlight, and a tubular reactor illuminated by LEDs. Simulations were carried out for different photocatalyst concentrations, considering absorption and anisotropic scattering, showing differences smaller than 2.4% with respect to the results obtained by commercial CFD software for systems with isotropic emission, such as fluorescent lamps. Moreover, the model was able to improve the simulation of solar reactors and dramatically outperformed the simulation of LED sources, due to the combined effect of quadrature rotation and cone-limit fitting for cone-shaped sources, as well as a LED-specific power-cosine light distribution. The developed model has been thoroughly validated and is now available to the open-source CFD community. It allows a comprehensive numerical simulation of radiation transport using any type of light source, with applications in numerous engineering fields where optical phenomena affect the performance of the process. [ABSTRACT FROM AUTHOR]