Chemical reactions are not just chemistry

We often write chemical reactions as something like:

A + B → C

But this is an incomplete story.

For A and B to react, they first have to meet. How they mix, how quickly material moves, and how heat is transferred can all affect what actually happens.

A recent paper on mixing in synthetic chemistry made this point well. Two experiments can use the same chemicals, temperature and nominal conditions but behave differently because the mixing is different.

This becomes particularly important when reactions are fast, when several phases are present, or when local concentrations or hot spots appear. Under those conditions, what happens is governed by both chemistry and transport phenomena. This is relevant to CCS.

CO₂ streams can contain multiple impurities, and some of those species may react with each other. Knowing that a reaction is theoretically possible is not enough. We also need to ask whether the components actually come into contact, at what concentrations, and for how long. This can be the difference between a reaction being thermodynamically possible and operationally important.

It is also why treating pipelines or shipping systems as simple, predictable reactors can be misleading. Real systems are governed by the interaction of chemistry, mixing and transport phenomena.

Sometimes the interesting engineering starts after a reaction equation has been established.