Accurate Measurement of the Photon Flux Received Inside Two Continuous Flow Microphotoreactors by Actinometry

In this study, the photon flux received in two continuous flow microphotoreactors was measured by actinometry (potassium ferrioxalate). The microphotoreactors had two different geometries and were irradiated by either a polychromatic or a monochromatic light source. A model considering the partial absorption of photons through the reactor depth and, if required, the polychromatic character of the light source and the dependence of the actinometer properties on the wavelength were formulated to describe the variation of the actinometer conversion with the irradiation time. The photon flux received in the microphotoreactors could be thus accurately calculated as a function of the emitted wavelength. The same methodology was then applied to measure the photon flux received in a batch immersion well photoreactor. The radiant power received in each photoreactor was compared to that emitted by the lamp and major differences were found, thus confirming the need for this kind of in situ measurement. Finally, some guidelines based on a knowledge of the photon flux were proposed to compare various photoreactors. They revealed in particular that the choice of the most efficient photoreactor depended on the criteria chosen to evaluate the performances (i.e. productivity, Space Time Yield).