Photooxygenation in an advanced led-driven flow reactor module: Experimental investigations and modelling

Abstract

The photooxygenation of α-terpinene was investigated as a benchmark reaction in an advanced LED-driven flow reactor module, both from an experimental and modelling point of view. Ethanol was used as a green solvent and rose Bengal was chosen as a cheap sensitizer of industrial importance. Firstly, the kinetic law based on all mechanistic steps was established for the chosen photooxygenation. From this, the set of operating parameters potentially influencing the photoreaction rate were identified. Subsequently, experiments were carried out under continuous-flow conditions to screen these operating parameters, namely concentration of α-terpinene, concentration of photosensitizer, residence time, structure of the segmented gas-liquid flow and nature of the reagent gas phase (air versus pure oxygen). Finally, the conditions enabling minimization of sensitizer bleaching were established. It was also shown that the hydrodynamic characteristics of the gas-liquid flow can have an effect on the conversion levels. From this, a simplified model was proposed to predict the conversion at the reactor's outlet when pure oxygen was used.

Continuous Flow Photochemistry for the Preparation of Bioactive Molecules

“…In addition, photochemical flow approaches have been developed with great success for functionalization reactions, such as halogenations [66][67][68][69], trifluoromethylations [70][71][72], oxygenations [73][74][75] and C-H activations [76][77][78]. All these applications showcase how continuous set-ups help to overcome limitations commonly encountered with classical photochemistry, and it is apparent that a variety of light sources as well as reactor configurations are exploited to best serve the intended chemical route.…”

A method to determine the correct photocatalyst concentration for photooxidation reactions conducted in continuous flow reactors

“…Further, when considering an industrial process, the concentration of the photocatalyst will have not only an economic impact but could also impact the downstream process or subsequent synthetic steps. It may be noted that in typical studies on photooxidation reactions, the concentration of the reactants is usually varied, while the catalyst concentration is rarely addressed [24][25][26].…”

Hydrodynamics of Gas–Liquid Slug Flows in a Long In-Plane Spiral Shaped Milli-Reactor

“…However, the mass transfer between phases is often the limiting step for implementing chemical reactions with high yield and selectivity. This is the case, for example, in the fine chemistry and pharmaceutical industries, for catalytic hydrogenations, sensitized photo-oxygenations, photo-redox reactions, or fluorinations [1][2][3]. With respect to safety, compactness, quality and ecoimpact issues, some cutting-edge technologies for process intensification, such as continuous-flow micro-structured technologies (heat-exchanger-reactor, monolith reactor, micro-reactor, etc.…”

“…This work will constitute the preliminary step required for investigating gas-liquid mass transfer inside such a reactor. The knowledge gained on both gas-liquid hydrodynamics and mass transfer characteristics in the spiral shaped milli-reactors will finally be used to provide guidelines to optimize multiphase micro/milli-reactors [3].…”