Optimal catalyst thickness in titanium dioxide fixed film reactors: Mathematical modelling and experimental validation

Abstract

h i g h l i g h t sExperimental results show an optimal catalyst thickness for sprayed TiO 2 of 5 lm.Liquid-side and catalyst-side illumination produce different behaviour. Model for diffusion, advection and rate of reaction in porous media is proposed. First principle model shows very good agreement with experimental results. Results can be used for optimisation of large-scale reactors. a b s t r a c tThe use of immobilised TiO 2 for the purification of polluted water streams introduces the necessity to evaluate the effect of mechanisms such as the transport of pollutants from the bulk of the liquid to the catalyst surface and the transport phenomena inside the porous film. Experimental results of the effects of film thickness on the observed reaction rate for both liquid-side and support-side illumination are here compared with the predictions of a one-dimensional mathematical model of the porous photocatalytic slab. Good agreement was observed between the experimentally obtained photodegradation of phenol and its by-products, and the corresponding model predictions. The results have confirmed that an optimal catalyst thickness exists and, for the films employed here, is 5 lm. Furthermore, the modelling results have highlighted the fact that porosity, together with the intrinsic reaction kinetics are the parameters controlling the photocatalytic activity of the film. The former by influencing transport phenomena and light absorption characteristics, the latter by naturally dictating the rate of reaction.

From the design to the development of a continuous fixed bed photoreactor for photocatalytic degradation of organic pollutants in wastewater

“…With respect to the annular photoreactors, a flat plate geometry is scalable, and these types of reactors can be easily used with solar radiation, so they are very attractive and also provide an excellent configuration for efficient excitation of the visible light active photocatalysts (Otálvaro-Marín et al, 2014). The flat plate reactor design possesses: (i) a fluid flow free from any dead or recirculation zones, obtaining a plug flow reactor; (ii) ability to operate under a wide range of liquid flow rates (flow regime should also be chosen carefully in order to avoid excessive velocities, turbulences and shear stresses that might damage the surface of the catalysts); (iii) ability to be easily and efficiently integrated with an illumination system, in order to obtain the maximum model simplicity (the design of the reactor and the illumination system is aimed to deliver a high uniformity of the radiation field on the photocatalytic surface); (iv) possibility to be configured for both liquid and structured catalyst side illumination (Vezzoli et al, 2013).…”

Main parameters influencing the design of photocatalytic reactors for wastewater treatment: a mini review

“…A photoreactor having flat plate geometry can gather: (i) a fluid flow without dead or recirculation zones, giving a plug flow regime; (ii) the ability to operate at different liquid flow rates and the regime for the liquid flow should be selected in order to avoid shear stresses, which may damage the photocatalysts surface; (iii) easy and efficient coupling with an irradiation system to obtain the maximum model simplicity; and (iv) the possibility to realize an illumination at the external walls of the photocatalytic reactor 63 …”

Influence of TiO2-based photocatalytic coating road on traffic-related NOx pollutants in urban street canyon by CFD modeling

“…CFD has been used to model flat plate photo reactor (Passalía et al, 2011) (Salvado, 2007) (Salvado and Hargreaves, 2007), multi-tube reactor (Jelle Roegiers, 2018) (Alpert et al, 2010), impeller reactor (Tokode et al, 2017) and rectangular reactor (Einaga et al, 2015). The effects of film thickness (Vezzoli et al, 2013) and gas flow rate (Alpert et al, 2010) (Einaga et al, 2015) have also been investigated. However, there are few studies on CFD simulations of the effect of NOx photocatalytic oxidation in street canyon with TiO2 photocatalytic nanoparticles as pavement coating.…”