Photo-Oxidation in Three-Phase Flow with Continuous Photosensitizer Recycling

Abstract

Microreactors have emerged as a promising platform for conducting photo-oxidations, offering green routes to facilitate significant chemical transformations. In this study, the sustainability of photooxidations is improved by a three-phase gas/liquid/liquid flow reaction in a photo-microreactor with continuous recycling, which is applied to a model reaction. Recycling is enabled by the photosensitizer and the substrate, which are in immiscible phases. The effect of various operational parameters on the reaction and the contact pattern among phases is explored, and the interplay between the flow pattern and photo-oxidation is discussed. The highest conversion is detected for flow conditions that display significantly lower diffusion distance between the dispersed photosensitizer slug and the oxygen bubble, highlighting the link between the flow pattern and mass transfer. Furthermore, phase separation was automated using a liquid−liquid separator where the photosensitizer and organic substrate were recycled continuously to achieve full conversion. The proposed approach eliminates the downstream purification step and provides a sustainable pathway toward photooxidations in microreactors.

Photo‐induced Multiphasic Reactions in Flow Process: A Decade of Progress

“…In 2023, the Kuhn group published a study on a purificationfree photo-oxidation process employing microreactors with continuous recycling and adjustable contact patterns (Scheme 23). [57] The model reaction involves the singlet oxygenmediated oxidation of the substrate, 1,3-diphenylisobenzofuran (DPBF) 43, using Rose Bengal (RB) as a photosensitizer under green light (526 nm). DPBF resides in the organic phase (toluene), RB is in the aqueous phase, and pure oxygen gas is employed in the gas phase.…”

Photo Microreactor with Luminescent Fluid Mediating Solar Photochemical Synthesis

“…As early as in 1834, solar light was used to activate photochemical reactions . To date, with the emergence of visible-light photocatalysis, solar photochemical synthesis has exhibited good prospects for practical application. , Meanwhile, new discoveries or concepts in photocatalysis, e.g., photocatalysts absorbing red light that afford high efficiency at ppb loadings and three-phase flow to enable continuous recycling of the photocatalyst, are continually springing up, which will aid in enhancing the sustainability of solar photochemical synthesis. Also, with regard to new technologies, the application of microreactor technology provides a more photon-efficient and scalable way to conduct solar photochemical synthesis, and the luminescent solar concentrator photo microreactor (LSC-PM) stands out among the current solar photochemical reactors for converting the photons of higher energy to those that can match the wavelength demands of photoreactions and exhibiting the potential of using sunlight as the sole energy source …”

Continuous Flow Approach for Benzylic Photo-oxidations Using Compressed Air

“…Benzylic photooxidations have been performed using a range of metal-containing catalysts such as tetra-butylammonium decatungstate (TBADT), which can oxidize both activated and unactivated C–H bonds. Organic dyes such as Eosin Y and Rose Bengal have also been shown to facilitate photooxidations. Typically, these methods use pure O 2 .…”