Parameter assessment for scale-up of co- and counter-current photochemical reactors using non-collimated LEDs

Abstract

Common cross-currently illuminated photochemical reactors lack energy efficiency to make them competitive in industry. The use of co- and counter-current illumination was previously proven to increase reactor performance, but these approaches made use of a collimated LED module whereby the used LED module itself having a lower than typical optical efficiency. In this paper, we study the use of non-collimated LEDs for the use in co- and counter-currently illuminated reactors. A ray tracing model was implemented in COMSOL and was validated using experimental data. Via these experimental data, the regime of no kinetic limitations was observed as conversion is not hampered by increasing light flux. Via the model results, it was determined that the most suitable light source for optimal light absorption by the reagent was the most collimated LED possible, in this case with a total viewing angle of 10°. The optimal reactor set-up uses the most reflective material, preferably aluminium or silver, to recuperate diverging light rays of the used wavelength. Furthermore, the wall thickness of the glass reactor must not be excessively thick, with an optimum at 1.5 mm wall thickness for this case. Regarding reagents and absorbance, it is best to use a higher concentration and reduce reactor length as this increases reactor performance under the condition that quantum yield is stable. Via the use of non-collimated light, it was determined that the entrance efficiency can be increased compared to a fully collimated light source, at the cost of reflection losses that increase with path length.