Flow vs. batch chemistry: how the reactor design affects the reaction

As one of the most important components in a chemist’s fume hood, the chemical reactor is designed to allow the chemist to utilize the best possible conditions for their reaction. With the introduction of flow chemistry systems, chemists now have more choice available to them for performing their chemistry, and it’s important to understand whether batch or flow techniques are best for their specific applications.

Traditional batch chemistry reactors

Traditional batch chemistry techniques are great; they’ve been around for hundreds of years and remained virtually unchanged in that time, aside from obvious improvements such as the introduction of jacketed reactors, complex software automation, and automated syringe pumps.

In a complex batch chemistry system it could be argued that the most important component – the reactor vessel – can be the least interesting. The reaction vessel is where the chemist will systematically feed in reagents and wait for something to happen based on a set of reaction conditions.

Though the chemistry purists among us will remind us that a batch reactor can come in various shapes (round bottom/torispherical), types (jacketed/vacuum jacketed) and sizes (100 mL – 50 L in Syrris’ case), when it boils down to it – like solvent in an unoptimized batch reaction – they all perform the same basic function.

Flow chemistry: a modern alternative to batch chemistry techniques

In more recent years, continuous flow chemistry techniques (also known as plug flow or segmented flow) have become popular because, for certain types of chemistry, they offer significant advantages.

Read our recent blog post – “why perform your chemistry in continuous flow” – for a detailed breakdown of the 9 main reasons your chemistry may be better performed in flow

In a flow chemistry system, the reactor can be the most interesting and most intricate component. This the point where two or more reagents synchronize their flow and navigate a network of tubing in a glass microreactor chip or tube reactor to mix and then react.

“In continuous flow, fundamentally; tube A meets tube B to give us a single tube C which will output the product.”

A typical flow chemistry microreactor designed for 2 input-1 output reactions

Why flow chemistry may be a better choice for your reactions

Continuous flow chemistry techniques may be a better choice for your chemistry and is well worth investigating if you’re interested in producing consistent, fast, and safer chemistry.

A caveat here: flow chemistry is not always the right choice and its use very much depends on the application(s) you’re performing. For some applications, continuous flow will produce faster, safer reactions with higher yields at a faster rate than is possible in batch, and opens up new chemistries not possible in batch. However, there are some reactions where batch techniques will be best. Speak to the Syrris chemistry team to discuss your specific applications to determine if continuous flow chemistry is for you.

There are many designs of continuous flow reactors that allow you to have more control over your experiment parameters and prevent them from being a limiting factor in the same way that can happen in a batch reactor:

Point of reaction

With flow chemistry, accurate reactor geometry means that you can have multiple inputs which meet at the same junction and at the same time. This, alongside precisely defined dimensions across each channel, ultimately means there is less opportunity for variation downstream and increased batch to batch consistency.

Fast-mixing

As mixing is done by the diffusion of reagents across a concentration gradient in flow, the size of the channels has a large effect on the mixing efficiency.

Decreasing the size of the channel can see more efficient mixing, and the size of the channels is simply limited by the volume of fluid that you are looking to flow through.

Additionally, you can modify your channel geometry to include fast mixing regions which can be thought of as analogous to using baffles in a batch reactor.

Residence time

Whilst reactions in a flow reactor are typically faster than their batch equivalent, it is still beneficial in many reactions to allow the reagents time to sufficiently react to obtain a good yield of product before they exit the system.

Syrris Tube reactors are available in 4 mL and 16 mL depending on the desired residence time of the reaction

The amount of time reagents remain reacting within the channel can be influenced by its length. Long serpentine channels will give greater residence times which maximize the amount of time reagents are left to react.

Temperature control

As fluid is flowing through small channels, heat transfer from a heating/cooling source is substantially more efficient than in batch where often large temperature gradients are present. In continuous flow, smaller channels promote more efficient heat transfer.

The benefits of flow chemistry are clear, however, understanding how components such as a reactor in a flow chemistry system work individually and how to maximize their potential based on the chemistry is important in further understanding how an application can be developed in continuous flow.

Discover flow chemistry basics and applications

Click the button below to discover more about the basics of flow chemistry and the various applications chemists are performing using Asia Flow Chemistry systems.

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