laserlisa
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Coolant spray for controlling reaction temperature
Im attempting to run an exothermic reaction where temperature control is vital for success due to one of the intermediates being temperature
sensitive. Need to keep it below 10C during addition, but since its so exothermic is quite a challenge.
Ive tried using ice/brine bath but the addition takes forever because it simple doesn't cool enough, and unfortunately dry ice is not readily
available where I am located.
So I was thinking maybe it would be possible to cool the reaction further by bubbling coolant spray through my ice bath. The coolant spray I had in
mind consists of tetrafluoroethane and it is advertised to be able to cool down to -55C.
Would this work? Have I overlooked some major drawbacks with this technique? Any tips on what solvent mix I should use for the cooling bath to bubble
the coolant spray through?
Thanks 
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Elemental Phosphorus
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Have you considered immersing a glass coil with cold brine running through it into your reaction, for more efficient cooling?
Using coolant spray might work, but you will waste a lot of spray in the process. Usually acetone is used for very low temperature cooling, but
methanol, ethanol, or isopropanol can work as well. I have used a dry ice bath with isopropanol with no problems before.
Another good method for heat control, if you are not already using it, is to put the reagents in a freezer before the addition.
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brubei
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mixing reagent with exothermic reactions always take a long time.
Furthermore, if you complain about the time of addition, it's certainly because you have a big quantity of reagent... i don't think that the content
of a single bottle of spray would be enough if you are trying to mix over than a few grams of products.
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Sulaiman
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IF you have something like a peristatic pump using tubing compatible with your reagents,
then you could pump liquid from the reaction vessel through a water cooled heat exchanger
(e.g. http://www.scilabware.com/uploads/images_large/CX633SC.jpg) and back to the vessel,
providing cooling and mixing.
EDIT: one of the reagents can be added at the top of the heat exchanger, cooling the reaction as quickly as possible.
The entire heat exchanger will be liquid filled, either water or reagents.
[Edited on 17-5-2017 by Sulaiman]
CAUTION : Hobby Chemist, not Professional or even Amateur
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JJay
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I've had to do that before lots of times... I always just used a salted ice bath and an addition funnel with stirring and carefully monitored the
addition. It can take several hours, and you may have to change the ice bath. Sometimes you may see delayed temperature rises during addition, so it's
important to go slow, especially at first.
You might consider liquid nitrogen.
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laserlisa
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Thanks for the advice guys.
I really like the idea of immersing a glass coil into the reaction and run cold water through that. Any idea why one might purchase suitable glass
coils? Would need a fairly large one, a coil with the center diameter around 15 cm preferably. Im considering copper instead, that I could easily make
myself, but even though nothing in my reaction should react with copper as far as I know I dont really like the idea of introducing more sources of
potential errors than necessary.
Another idea, why not bubbling the coolant spray straight into the reaction mixture? The tetrafluoroethane should be inert to most conditions and it
will boil off right away, perhaps some will dissolve in the reaction solvent and affect the reaction somehow? Any opinions on this approach?
The price of the coolant spray is no issue, I found really cheap 0.5L bottles of this stuff at a local supermarket .
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