Sidmadra
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Molecular Sieve dehydration efficiency, how effective is letting it sit without stirring?
I often see people say they dehydrate solvents by just letting them sit sealed with the molecular sieves for some period of time. How effective is
this, compared to stirring? How long is ideal to sit for?
I want to dehydrate a few gallons of cheap solvent I have that is just too much to stir and was wondering if just letting it sit with the sieves for a
few days would suffice.
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violet sin
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Well, I don't know what the prescribed length of time is by any accepted standard of drying, but it seems logical to assume you could stir a lesser
ammount for more immediate use while letting the lions share sit in another container with occasional hand stir.
Though I have sieves, I haven't used them yet. So cannot offer anything from first hand experience.
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Sidmadra
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I've heard people around these forums claim that just throwing some sieves in the solvent bottle and letting it sit for a few days was sufficient
enough to dry it almost completely.
I can see how this might be possible, but I my intuition leads me to think that the limiting aspect is the rate of brownian motion mixing and that
inevitable homogeneous equilibrium. I'm just skeptical that a few days is sufficient time to allow for that equilibrium mixing to take place for total
absorption, if the water is only gradually being absorbed at the sieves.
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JJay
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It only takes a few hours. Molecular sieves give off heat when they absorb water, so it's not just Brownian motion moving the water and ethanol
around; there are convection currents circulating as well.
You can test your ethanol for dryness by adding more dry sieves and checking for a temperature change.
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violet sin
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https://www.google.com/url?sa=t&source=web&rct=j&...
- VI. Standard Operating Procedures (SOPs) C. Drying Solvents - Joy Reseach ...
From Google search of "standard procedure for drying solvents with molecular sieves". But it covers more than just sieves.
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-Drying of Organic Solvents: Quantitative Evaluation of the Efficiency of Several Desiccants
D. Bradley G. Williams* and Michelle Lawton
https://www.google.com/url?sa=t&source=web&rct=j&...
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https://youtu.be/NMfs3e9OdZQ
Drying Alcohol Using Magnesium and Molecular Sieves
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Information, lots of it if you look.
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Dr.Bob
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If you wait a few days, they will work fine. The water will find them eventually, it moves around just fine. The final water level will depend on
how much water and sieves you started with.
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JJay
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It's not a bad idea to store dried solvents over fresh molecular sieves, assuming that they don't react with the sieves (like acetone and glacial
acetic acid). I keep most of my alcohols stored that way.
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