Free Temperature vs Vapour Pressure Chart
Why do I need to know this data ?
Because reactions are pressurised, the Flow Chemistry approach enables reactions to be carried out at elevated temperatures, (which would result in solvents boiling away if they were still at atmospheric pressure). This means reactions can proceed faster, and this gives flow a significant advantage over simple batch chemistry in many situations.
However, it is important to know just how much pressure is required for a given solvent at a given pressure.
What happens if I don't have enough pressure ?
With insufficient pressure, a volatile solvent at an elevated temperature may boil, leaving behind a solid precipitate which will then block the flow reactor. At best this is massively inconvenient, at worst it can result in a reactor being permanently rendered unusable.
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Can't I simply calculate these values ? You'd think so. In fact there are some well known formulae that can give crude answers for a given solvent at a given temperature, but as you'll see below these can be quite risky. (There are websites you can go to that allow you to type in values and calculate an answer, but they are only as accurate as the rule or formula they use.) One example of this is the Trouton-Hildebrand-Everett rule. Though this can give relatively accurate results at pressures near atmospheric pressure, it becomes less accurate at pressures significantly above atmospheric pressure. To show how inaccurate this approach is, here's an example. Solvent : Ethanol Working Temperature : 170 oC Website answer (using Trouton-Hildebrand-Everett rule) : 7.0 bar
Put another way, provided you have more than 7 bar pressure, you can heat ethanol to 170oC and it will stay in the liquid state. Which seems fine, except that it is completely wrong ! The correct pressure answer is approximately twice that. If you were to pressurise to only 7 bar, you'd boil off the solvent, and possible block the reactor.
So what data can I use ? Vapourtec have produced a handy chart that shows the pressure required for common solvents across the complete range of typical flow chemistry temperatures. And we'll send you a copy of the chart for free. Simply fill in the request form.. |
Where does the Vapourtec data come from ?
The data that has been compiled on the Vapourtec chart is actual measured experimental data from a range of reputable published sources, interpolated using a tailor-made curve fitting formula known as the Antoine equation. For example, the data quoted in the ethanol example above was measured by Ambrose, Sprake, et al., and published in 1975.
If you'd like a copy of this chart, fill in the form and press "Request Chart". We'll send you a single confirmation email so that you know the request has been received. Requesting the chart will not sign you up for any other newsletters or mailing lists.
