ethanol drying

[Rene]

Hi guys, I'm using ethanol from a bottle with molecular sieve ('clay', zeolite I think) in it for drying, which I keep topped up from a bottle with 'absolute' ethanol. Does anyone know of an easy way to test whether the stuff in my bottle is still working?

Thanks, René

PS, replies in Deutsch welcome!

[Reinhard]

Hi Rene,

what does "still working" mean?
I suppose you don't think of the capability to get drunken.
The concentration of your Ethanol could be estimated for ex. with a
"hydrometer (?)", in German: "Spindel".

Reinhard

[Jürgen H.]

Hallo Rene,

Nimm eine kleine Menge Xylol und tropfe Dein Ethanol langsam zu. Wenn sich Trübungen ergeben ist der Alkohol nicht wasserfrei. Alternativ kann man getrocknetes Kupfersulfat verwenden. Bei Gegenwart von Wasser wird das getrocknete weiße Kupfersulfat blau.

Ein Körnchen Kaliumpermaganat in den Alkohol schmeißen müsste nach meiner Erinnerung auch funktionieren. Bilden sich violette Schlieren, ist Wasser vorhanden.

Schöne Grüße

Jürgen

[Thomas M]

Dear Rene,

I'm not sure of an "easy and quick test" as it will depend on the limit of residual water in the solvent you are targetting. In case of doubts I would replace the drying agent by a fresh sample or take a grade with indicator (e.g. see the following web page. You will find a link to a brochure with some helpful information for drying different kinds of solvents just scroll down).

https://www.merckmillipore.com/DE/de/product/Molekularsieb-0%2C3-nm,MDA_CHEM-105734#anchor_BRO

This should only be an example, I have nothing to do with this company.

For ethanol and methanol I recommend mole sieve with pore size of 3 Angstroem to limit competitive adsorption of the alcohol. Maybe you are using this already.

Don't if this of help.

Kind regards
Thomas

[JB]

Hi Rene,

That's a very interesting question. Not many hard numbers out there. This is what I found:

Limit of detection for water in absolute ethanol:

anhydrous copper sulfate test: 0.8%
potassium permanganate test: 0.4%
aluminium ethoxide test (produces "voluminous precipitate"): 0.05%

The right molecular sieve can dry ethanol to < 0.01%. So it really depends on how dry your ethanol has to be. if it has to be very dry, it might be easiest to calculate the capacity of the molecular sieve and regenerate the sieve accordingly and regularly (backing at 250C).

Beste Gruesse,

Jon

[Thomas M]

Hi Jon,

and regenerate the sieve accordingly and regularly (backing at 250C)

... I agree and would just like to mention that it necessary to additionally run the drying procedure under vacuum condition, if you really want to dry it. Water is bond extremely tight to the zeolite surface and only under these conditions we could really regenerate mole sieves. However, at home these conditions might not exist. Therefore my recommendation to replace it by fresh material.


@Rene,

Additional remark for a possible test (although I do not have a number for a detection limit, yet):

Titanates could give an indication about the status of your alcohol. These materials are very sensitive to traces of water. They give a clear solution in alcohol but are bery sensitive to water. They will hydrolyse and finally build insoluble Titaniumdioxid.

If you have access to these products and if you are a bit familiar in handling chemicals you can try the following (please always use safety glasses and suitable gloves!):

- Put a sample of your alcohol into a dry and closable glass container
- Add a drop of Titanate to the alcohol and reclose the container (to avoid humidity desturbing your test)
- Check if the solution will become hazy or develop an opalescence (wait a bit to allow agglomeration of the initial hydrolysis products, so that they can grow to a size to scatter light)

Suitable Titanates are Tetraethyl orthotitanate, or Tertaisopropyl orthotitanate or Tetrabutyl orthotitanate.


Best regards
Thomas

[JB]

... I agree and would just like to mention that it necessary to additionally run the drying procedure under vacuum condition, if you really want to dry it. Water is bond extremely tight to the zeolite surface and only under these conditions we could really regenerate mole sieves. However, at home these conditions might not exist. Therefore my recommendation to replace it by fresh material.

Hi Tom,

Good point. Thanks for correcting this!

[Rene]

Thanks guys, very helpful!

Yes, I've got size 3A. I didn't expect it to come shipped ready to use, so have baked it at 250oC beforehand. No vacuum stove around, I'm afraid.

What level of water-free ethanol do I need, is a good question. I suppose not clouding xylol is probably about right as a general guideline for general microscopy. I'm using it now mostly to dehydrate plankton before transfer into Pleurax. 

Now, I only use it occasionally and top up the bottle once a year with absolute alcohol (<0.5% according to the label), so it's hard to say when it's time again to regenerate the stuff. I'll try the permanganate method (also because that's what I have in the lab ;-), but I'll keep the comments on the other indicators in mind.

best wishes,
René

[momotaro]

Hi Rene,

Hünig, et al., Arbeitsmethoden in der Organischen Chemie, Berlin 2014, 279, 280.

Trocknen mit Molekularsieben:

https://www.magentacloud.de/lnk/9yM1httM
https://www.magentacloud.de/lnk/kvMVhdbu

Drying seems to be possible in the microwave:

https://www.youtube.com/watch?v=T9hPvmjftAg

Kind Regards

Helmut

[Christian3000]

Hi all,

thank you for this thread, I recently got a 0.3nm molecular sieve for drying acetone and ethanol. Your hints here helped me much to understand more details.

Maybe it is worth to mention that the book Helmut cited in his last post is freely available as pdf in German:

Arbeitsmethoden der organischen Chemie
http://www.ioc-praktikum.de/methoden/skript.html

Best regards and happy drying,
Christian

[Thomas M]

Hello Helmut,

Drying seems to be possible in the microwave

... yes, but this needs monitoring and careful adjustment of the set-up. We did it and the heat generated was so high that the glass started to melt locally.

Greetings
Thomas

[Rene]

Thank you all,
I'll stick for the moment to drying overnight at 250oC, and cooling down in the stove, I'm sure that will leave plenty of capacity for waterabsorption (or adsorption?).

Best wishes,
René