Design considerations for photocatalytic structured packed bed reactors

Abstract

Translucent photocatalytic reactor structures are interesting for the design of small and large scale photocatalytic reactors. Altering the base element size of the structure impacts the packing parameters. Decreasing the base element size increases the available surface area which increases the potential catalyst load per volume. However, a smaller base element increases the number of light scattering boundaries, resulting in a higher energy loss. This work elaborates on the influence of the base structure on absorption efficiency and mass transfer limitations. The varied parameters are the base structure size, light intensity and catalyst load. The base structure used in this work is a borosilicate glass sphere with a diameter of 1 mm, 2 mm or 3 mm. To assess the absorption efficiency, a two flux light model was validated and used. It was shown that, for the same catalyst load, 1 mm beads absorb less energy than 2 and 3 mm beads. Furthermore, for equal rates of energy absorption, the spheres with a diameter of 1 and 2 mm behave equally while the 3 mm spheres show a lower bed activity. This is partly attributed to mass transport resistances towards the catalytic surface and light distribution. Using the model and the principles in this study, a design strategy is proposed for cross-current illuminated photocatalytic packed bed reactors.