Development and simulation of annular flow photoreactors: integration of light-diffusing fibers as optical diffusers with laser diodes†

Continuous flow chemical photoreactors have emerged as a highly attractive platform, garnering considerable attention in both industry and academia. Utilizing thin channels, these reactors offer a promising solution for achieving more uniform irradiation in the reactor volume. While advancements have been enabled by the implementation of LEDs, significant limitations persist. These include managing the heat generated by light emitting diodes (LEDs), requiring proximity of electrical equipment and hot surfaces to flammable environments, ensuring operator safety amidst high levels of irradiating light, and addressing efficiency issues arising from irradiation of unintended areas, light scattering, and divergent photon emission. Herein, we introduce a novel approach that involves guiding photons emitted by a laser diode via total reflection optic fiber to an optical diffuser inside the reactor, specifically a light-diffusing fiber (LDF). This system capitalizes on the radial photon distribution capability of LDFs to irradiate the tubular annulus, enclosing all irradiation within it. The Continuous Annular Photoreactor (CAP-Flow system) effectively divorces photon generation from potentially explosive environments, enhancing safety, and operational convenience. The CAP-Flow system underwent testing via actinometry and a C–N coupling reaction across various flow rates and catalyst loadings. Our results found superior efficiency for the CAP-Flow system when compared to current LED configurations. The defined geometry, flow-field and photon absorption distribution facilitated mathematical modeling to de-convolute the reaction kinetics governing the photocatalytic process, offering valuable insights for optimizing operational parameters to enhance process understanding, productivity, and selectivity.