Continuous-flow integrated processes for photo-oxygenations with solid-supported sensitizers for the safe and sustainable production of fine chemicals and pharmaceuticals – PICPOSS

PICPOSS involves 4 scientific tasks, supported by task 0 (coordination).
Task 1 aims at studying two benchmark photo-oxygenations (alpha-terpinene, furfural) in different batch reactors (ICMR Reims. M1-M18).
Fed by Task 1, Task 2 (LGC. M6-M24) is devoted to the transfer of the benchmark photo-oxygenations to microreactors using solubilized sensitizers.
Task 3 concerns the preparation and characterization of various sensitizing materials for implementation in microreactors (IPREM. M6-M36)..
In Task 4 (LGC/JCU. M12-M42), benchmark photo-oxygenations will be carried out in LED-driven microreactors using sensitizing materials.

Task 1 studied both benchmark photo-oxygenations in batch reactors with ethanol as green solvent. Analytical conditions were firstly optimized and the optimal reaction conditions found by varying different parameters. The reactions were performed in Pyrex tubes using a halogen lamp as visible light source, and then with using the 600 mL photoreactor from Peschl Ultraviolet GmbH..
Task 2 studied the transfer of the photo-oxygenation of alpha-terpinene using solubilized Rose Bengal in 2 types of LED-driven microreactors. The first results showed that high yields were achieved in few minutes in residence times, with more concentrated starting material and with significantly reduced concentration in PS. The impurity profile was found to be significantly cleaner than with batch reactors irradiated with a mercury lamp.
In Task 3, original photosensitizers (PS)-supported colloids for singlet oxygen production were developed. Two different types of RB-supporting materials were investigated: silica core-shell nanoparticles and polymer submicronic particles and nanoparticles. Up to now, several samples were prepared and fully characterized. The stability of the polymer colloids in water was demonstrated, as well as their singlet oxygen production.

Task 1 is now almost finished; the results obtained are currently valorised as scientific articles.
In Task 2, complementary experiments should be carried out to confirm the trends observed when implementing photooxygenations with solubilized sensitizer in LED-driven microreactors, especially with the second reaction (furfural). Modelling tools (including a kinetic model) are also currently developed to better understand the coupling between the phenomena involved and to try to predict the performances.
In Task 3, additional studies to increase the RB loading on the polymer microgels will be undertaken in the next months. Their efficiency in ethanol will be also increased. Further investigations on their recovery from the solvent have to be carried out to implement a recycling procedure.
In Task 4, the first step will concern the characterisation of the “slurry Taylor” flow in the spiral-shaped microreactor with using the colloidal particles sent by IPREM. Then, the photooxygenations will be implemented using these sensitizing materials.

R. Radjagobalou, J-F Blanco, S. Elgue., O. Dechy-Cabaret, K. Loubière (2017), Study of sensitized photooxygenations in LED-driven spiral-shaped microreactors, 10th World Congress of Chemical Engineering, Joint Event IPIC1/EPIC6/APSPI3 , October 1st-5th, 2017, Barcelone (Spain)

K. Loubière, R. Radjagobalou, J-F Blanco, S. Elgue, O. Dechy-Cabaret, C. Michelin, N. Hoffmann, L. Petrizza, M. Save, S. Lacombe and M. Oelgemöller, Integrated continuous-flow photooxygenation processes with solid-supported sensitizers for
the safe and sustainable production of fine chemicals and pharmaceuticals (PICPOSS), EPA Newsletter, June 2017, 92 14-21

L. Petrizza, M. Le Bechec, S. Blanc, T. Pigot, M. Save, S. Lacombe, Design of photoactive colloids for singlet oxygen production, 28th International Conference on Photochemistry (ICP 2017), July 16 – 21 2017, Strasbourg (France)

PICPOSS seeks to develop a continuous flow process for the sustainable production of fine chemicals and pharmaceuticals through sensitized photo-oxygenations. Various LED-driven microreactors will be constructed: due to their dimensions, mass, heat and light transfer phenomena are enhanced, thus enabling yields and selectivity to be increased, and safe and photon-efficient conditions to be possible. Contrary to conventionally studies reported in the literature, the sensitizer will not be solubilized in the reaction medium, but supported on silica/polymer beads or inside colloid systems instead. The advantage is to reduce downstream separation processes and to develop a new photochemical synthesis concept. Gas-liquid-solid “slurry Taylor” flows will be generated in flow reactors which can be readily adopted for industrial application using meso-scale continuous equipment. PICPOSS will focus on two benchmark reactions of industrial relevance: the photo-oxygenation of alpha-terpinene, a common essential oil component, and of furfural obtained from hemicelluloses contacting waste from agriculture. PICPOSS combines chemical engineering & process intensification (LGC-Toulouse. K. Loubière), mechanistic photochemistry (ICMR-Reims, N. Hoffmann), solid-supported sensitizer development (IPREM-Pau, S. Lacombe), organic chemistry and trioxane preparation (LCC-Toulouse, O. Dechy-Cabaret), and applied flow photochemistry (JCU-Australia, M. Oelgemoeller). PICPOSS involves four scientific tasks, supported by task 0 (coordination). Task 1 aims at studying benchmark photo-oxygenations in batch reactors. Eco-friendly solvents will be studied and various sensitizers investigated (commercially available, advanced sensitizers synthesized in Task 3). Side reactions (including sensitizer decomposition) will be determined, and analytical conditions for an easy reaction monitoring in microreactors will be established. Task 2 is devoted to the transfer of the benchmark photo-oxygenations to microreactors using solubilized photosensitizers. It also includes the characterization of gas-liquid mass transfer in microreactors and the determination of the incident photon flux. Task 3 concerns the preparation and characterization of various sensitizing materials. Commercial and advanced lab-made sensitizers will be firstly surface-fixed on commercial silica/polymer beads. Then, sensitizing colloids systems (polymer particle, microgel) will be synthetized as they offer higher surface area and/or enable core-functionalization. These materials will be characterized and their stability, photobleaching, turnover frequency and quantum yields of singlet oxygen production will be evaluated. The most efficient and stable sensitizing materials will be tested in batch reactors in view of their implementation in microreactors. In Task 4, photo-oxygenations will be carried out in microreactors using sensitizing materials. For each reaction, a screening of operating conditions will be performed to define an operating domain and to maximize the reaction’s outputs. Experiments will be also implemented in meso-scale flow-equipment to demonstrate proof-of-concept for scale-up. Finally, the performances of the different batch and microreactors will be compared depending on the sensitizing materials. Likewise, the effectiveness of the advanced solid-supported sensitizers will be demonstrated by comparison with their solubilized counterparts. Combining experiments and modelling tools, guidelines will be established to assess the feasibility of flow photochemistry with sensitizing materials, and to address smart scale-up issues. The breakthroughs developed will overcome safety and cost concerns of currently available technologies (batch reactors, energy-demanding mercury lamps), and thus open new opportunities for industrial synthesis of valuable fine chemicals via sensitized photo-oxygenation.