Speciality Chemicals Magazine SEP / OCT 2024 | Page 49

FLOW CHEMISTRY

This boosted interest from other segments , including pharmaceuticals , in adopting a cheaper , multi-purpose approach , using one reactor to run several flow campaigns with proper changeover procedures in place .

Initial focus

Initial demand mainly focused on chemical reactions , with the idea of achieving safer , cheaper , purer , greener synthesis . The ideal candidate would be an energetic , fast and exothermic reaction , if possible , with a liquid / liquid ( L / L ) biphasic reaction media , which would fit nicely into static mixers with efficient heat exchange and mass transfer capacities .

Common chemistries were nitrations , fluorinations , azidations and oxidations . 1 , 2 Biphasic enzymecatalysed reactions were also investigated , with enhanced mixing playing a significant role . 3 More recently , the need appeared to enlarge the field towards more efficient liquid / gas and liquid / solid flow reactors to accompany the growth of flow .

In this field , MEPI ( Maison Européenne des Procédés Innovants ) a Toulouse-based academicindustrial partnership that promotes eco-friendly and cost-competitive processes to cut traditional sourcing routes short and encourage the return of local manufacture , started a partnership with a French flow reactor company , Khimod , focusing on continuous scalable hydrogenations .

Here the technology not only involves reactor design , but also specific catalysis know-how , delivered via several options , including catalytic static mixers or trickle-bed options . In collaboration with Toulouse University , MEPI has also developed a specific metalbased catalytic solution using a liquid matrix , avoiding deadly clogging issues in flow reactors . 4

Issues with solids

If the introduction of solids into a flow reactor remains very challenging , the need to address solid generation in flow reactors without causing clogging issues is definitively there . A common way of achieving this is to use continuous stirred tank reactors . However , these involve larger reaction volumes and poorer heat exchange control , which could lead to some limitations . For this reason , MEPI formed a collaboration with the South Korean flow reactor maker Laminar and developed a specific Taylor Couette active reactor for chemical purposes .

It should be noted that this technology allows solid formation inside the reactor and slower chemistries , thus potentially opening doors to reactions that have not been eligible for flow synthesis so far . We may also think of running L / L reaction in less diluted conditions to increase concentration and cost-efficiency . Reactions with several temperature zones and multi-injection strategies are also possible .

The equipment also shows interesting performances in crystallisation with specific narrow particle size distributions . In addition , other crystallization tools , and continuous filtration , washing and drying units , from AWL DEC Group , among others , are now available offering a wide panel of technologies to address downstream processing steps .

Last but not least , the intrinsic reactor volume reduction gained when switching from batch to flow makes it particularly attractive to photochemistry and electrochemistry options . 5 This not only makes it possible to revive old chemistries , but also opens our minds towards reaching targeted structures through alternative synthetic pathways . The flexibility and the inventive DNA of the flow chemistry players are definitively paving the way to a promising ecofriendly chemical future . ●

Laurent Pichon

PRESIDENT

SEP / OCT 2024 SPECCHEMONLINE . COM

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