Determining photon flux and effective optical path length in intensified flow photoreactors

Photocatalysis for small-molecule activation has advanced considerably over the past decade, yet its scale-up remains challenging in part due to photon attenuation effects. One promising solution lies in combining high photonic intensities with continuous-flow reactor technology, requiring careful understanding of photon transport for successful implementation. Here, to address this, we introduce a characterization approach, starting with radiometric light source analysis, followed by three-dimensional reactor and light source simulation. This strategy, when followed up with chemical actinometry experiments, decouples photon flux quantification and path length determination, substantially curtailing the experimental process. The workflow proves versatile across various reactor systems, simplifying intricate light interactions into a single one-dimensional parameter—the effective optical path length. This parameter effectively characterizes photoreactor setups, irrespective of scale, geometry, light intensity or concentration. Additionally, the proposed workflow provides insight into light source positioning and reactor design, and facilitates experiments at lower concentrations, ensuring representative reactor operation. In essence, our approach provides a thorough, efficient and consistent framework for reactor irradiation characterization. The characterization of light irradiation for intensified flow reactors extends beyond the determination of photon fluxes, requiring the precise determination of optical path lengths. Here the authors introduce a systematic workflow that integrates radiometry, ray-tracing simulations and actinometry to obtain these system parameters.