Photocatalytic oxidation of ethanol using paper-based nano-TiO2 immobilized on porous silica: A modelling study

A new model coupling the convection-diffusion equations for mass transfer and the Kubelka-Munk model for UV penetration is presented for describing the photocatalytic degradation of volatile organic compounds in titania-loaded papers. The model has been validated using a broad collection of ethanol degradation data measured on 10 different paper sheets incorporating titania-anchored hollow silica into the cellulose fibers with a wide spectra of basis weights and TiO2/SiO2 loadings, and operated at different ethanol concentrations, superficial velocities, UV intensities and configuration modes (i.e. counter- and co-current). Only two parameters were fitted, namely the intensity-independent kinetic constant and the adsorption constant of ethanol over TiO2. The simulated UV intensity profiles suggest a strong UV attenuation within the paper thickness, limiting the irradiated TiO2 to less than 30% of the available loading. Both the counter- and co-current configuration modes show comparable results in terms of photocatalytic activity, but with marked differences in terms of concentration and diffusive flow patterns. As a result, matching the general assumptions in the literature, mass transfer in co-current configuration approaches to a continuous stirred-tank reactor under Perfect Mixture, most of the photocatalytic activity being localized near the paper inlet. Our simulations reflect potential improvements in terms of activity by mitigating UV attenuation (especially UV scattering) in the papers.