Continuous-flow photochemistry: a need for chemical engineering

The present paper aims to illustrate that chemical engineering enables to address some of the current challenges and issues in continuous-flow photochemistry. For that, some common limitations encountered in industrial photochemistry are firstly highlighted and a general overview on flow photochemistry equipment is presented. The main challenges linked to photochemical (micro)reactor engineering are subsequently stated. By considering only the case of a purely direct photochemical reactions A->B in homogenous medium, the key factors to consider when implementing such photochemical reactions in microstructured technologies are outlined. Their influence on the outputs (conversion, productivity, photonic efficiency) of this simple type of photochemical reaction is then discussed. The significance of chemical engineering frameworks is finally demonstrated using several examples concerning the understanding of the coupling between the different phenomena involved, the predictions of the performances obtained, the acquisition of kinetics data and the elaboration of strategies for photochemical process intensification and smart scale-up. In the future, the challenge will be to integrate the complexity of photochemistry (e.g. heterogeneous phase reactions) into the present modelling tools so as to enlarge the spectrum of strategies devoted to photochemical process intensification