Advantages of Flow Chemistry
A lot of these advantages derive from the small size of the reactor allowing rate promoting, elevated conditions to be safely applied – the enhancement then brings about the productivity required to run a reaction in the small reactor. A particular feature is the ability to run under high pressures, which in turn allows the temperature to be increased above the normal (atmospheric) boiling point of the solvent. This allows significant rate enhancement. Since the volume within the reactor (the hold-up volume) is small, then, subject to proper management of risks, it can become feasible to carry this out in a laboratory where a batch process may not be possible.
Increasing Reaction Rate
This modeller uses the Arrhenius equation to determine the effect of the temperature on the rate constant. For short predicted reaction times, mixing may well dominate and control your reactions. With active mixing (e.g. stirrers within the fReactor-Classic or static mixing elements in tubes) the time at which mixing starts to dominate will be lower than for unmixed systems, allowing you to intensify your reaction.
If you don't have a value for the activation energy, use a value of 50 kJ/mol.
Small reactor size → low inventory → safely run under high T and P → enhanced reaction rates → high productivity
Small reactor size → high stirring power per unit volume → fast micro-mixing → good reaction control → reaction selectivity
Small reactor size → high surface area per unit volume → good heat transfer and control → ability to run under high temperatures → high productivity
Flow transport of material → ability to telescope reactions → inline workup → high productivity
Well defined conditions at steady state → characteristics defined fundamentally → route to scale-up
Disadvantages of Flow Chemistry
The disadvantages of flow chemistry are that more specialised equipment is required. The choice and cost of this equipment can make flow chemistry difficult to access. Since flow chemistry is part-engineering and part-chemistry there isn’t always the broad skillset required to make the leap to this very powerful technique.
It is exactly for this reason that the fReactor-Classic platform was created. We recognise that chemists want to incorporate existing equipment (for example stirrers, hotplates, measurement equipment, pumps) into their flow process and to have the flexibility for multiphasic flow chemistry. The fReactor-Classic allows you to do just this.
Notes
The approach using Arrhenius' is a small extension to the rule of thumb that a reaction rate doubles for every 10°C rise in temperature. For some reactions - e.g. acid/base neutralisations, the activation energy is so low that the reaction is always diffusion / mixing limited. Arrhenius isn't universal in describing reaction rates.