At the recent 17th International Process Development Conference in Baltimore there was an excellent session discussing continuous flow chemistry. The desire to develop new and improved chemical processes that optimize the use of resources has facilitated a large amount of work in the development of Continuous Flow Reactor (CFR) technologies in recent years.
Modern flow reactors can deliver a number of distinct advantages over more traditional batch reactor technology. For example, reaction conditions that may be challenging to achieve in a batch reactor can be easier to achieve in a flow reactor. A good example is a reaction in which the temperature of the reaction far exceeds the boiling point of the solvent. This type of reaction can be easily run due to the flow reactor’s ability to contain pressure. (The ThalesNano’s H-Cube pictured above is a widely used CFR designed specifically to simplify screening and development of continuous hydrogenation reactions.)
Another instance would be reactions which involve the use of dissolved gases as reagents. These can be more easily handled in a flow reactor as compared to a batch process, enabling the use of those reagents. These types of factors, coupled with the improved mixing properties of a flow reactor, give chemists and engineers a greater choice of conditions and reagents, meaning that flow reactors can be used to deliver products with better yields and fewer impurities.
The thermal mass of the reactants is typically significantly lower than the thermal mass of the system itself. This means controlling the temperature of the reaction mass is faster and easier than in a batch process, meaning more exothermic reactions can be chosen. These reactions can have more favorable reaction times, and so synthetic pathways can be chosen that are faster to complete in flow compared to batch mode. This, combined with the ability to arrange multi-step reactions in sequence, can lead to a dramatic reduction in the total cycle time of the operation.
If you are interested in learning more about the benefits of flow chemistry, I invite you to view the online presentation given by Professor Steven Ley of the University of Cambridge, UK: The Application of the ReactIR Flow Cell to Continuous Processing Technology or read the post regarding the challenges of continuous flow chemistry.