Sulaiman
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Disappointing results with 3A molecular sieves
Over the span of several weeks I have been fermenting sugar
and distilling the ethanol/water produced using a Vigreux column.
After four levels of distillation I finally produced some reasonably concentrated ethanol,
five jars of about 500g each with %ABV ranging from 92.2 to 90.2.
I want some anhydrous ethanol so I took a jar with 487g 92.2 %ABV,
which I calculated to be 88.6 %ABW, 431.5g ethanol + 55.5g water.
I had 531g 3A molecular sieves available so I decided to use all of the sieves,
fresh from a sealed packet from China.
I guessed that the sieves should easily absorb 10.5% of their weight in water.
This meant that the liquid level was only a little above the level of the sieves, when combined.
Addition of the sieves was done over about an hour due to the heat released.
I left the sieves in the liquid for over 24 hours.
I had previously watched a YT video by NurdRage https://www.youtube.com/watch?v=MduzjhRHBFY
so I was expecting a little loss of ethanol.
Result ... 209g of 98.8% ethanol, full of dust from the sieves 
Maybe the ethanol is nearer to 100 %ABV, the suspended particles increasing density,
I will find out when the dust settles.
BUT
This means that the sieves absorbed/adsorbed most of the 55.5g water,
AND 222.5g of my ethanol 
Not the result that I was hoping for
I also lost about 10g of liquid during the filtration through cotton
- which obviously did not remove the dust from the sieves.
Overall ... quite a disappointing day.
CAUTION : Hobby Chemist, not Professional or even Amateur
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Ubya
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mh yeah that's too much dust, some is normal, but that is excessive.
about the loss of ethanol, they absorb water but being porous they get wet by the
solvent you are using. You could recover that ethanol by putting the sieves in a flask and then heating it so that the ethanol distills over, it won't
be dry but you can add it back to the ethanol you are going to distill to 90%
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Sulaiman
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Good idea, I will add the wet sieves to my next distillation ... thanks.
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Assuming that I recover ethanol from the sieves, wash and dry them,
then dehydrate them in an oven;
could '3A' molecular sieves be useful as a packing medium for a Hempel column for distilling more ethanol ?
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S.C. Wack
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You'll have to do the experiment. Drying is not fast as liquid.
I have to wonder if some of the color is due to reaction of fermentation products with sites on the zeolite.
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brubei
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Why don't you distill it ?
I'm French so excuse my language
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Sulaiman
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I'll leave it for a day or two to see if the dust settles out.
but yes, it looks likely that I will have to distill it.
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monolithic
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You might find this paper interesting: https://sci-hub.tw/10.1021/jo101589h
Fines can be an issue with low quality sieves. I purchased mine from an industrial supply company on Amazon. They're geared more toward drying of
process gases but it makes no difference. I still had to wash them a half dozen times with water to get out most of the fines and then activate them
in an 250 C oven for a few hours, spreading them in a thin layer across a baking sheet. Just make sure you wash all the solvent out of them because
you don't want an oven explosion. 
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unionised
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Drying alcohol soaked sieve in an oven is likely to lead to an explosion.
The sieves are fairly temperature resistant.
You can distill the alcohol from them until they are essentially "dry"-i.e. the alcohol has gone.
(It will be a bit slow, because the heat transfer through the beads is slow.)
Or you can take the used beads and leave them exposed to the air.
They will absorb moisture, and that will displace the alcohol (which evaporates).
You lose some product, but you don't end up with an explosion.
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violet sin
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If you covered them in low ethanol% wash, from say washing some glasswares up after distillation, you might be able to upgrade the wash water and
downgrade the potential explosion of your beads when drying. And at the same time, avoid getting them gummed up with fermentation organic leavings
likely in any non distilled low % wash.
I purchased some 3°A, 4°A and color shift gell beads years back in a group buy here, still in the bags lol, never used, for shame, I know. My
experience with them has been all reading so ... Probably not the best idea.
The thought of loosing 225g out of 431g run... Ouch. So this question may be more for me than practical.
[Edited on 21-6-2020 by violet sin]
[Edited on 21-6-2020 by violet sin]
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DavidJR
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My sieves are nowhere near that dusty.
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Deathunter88
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Most molecular sieves from China are fake - they are not designed to dry liquids, rather they are placed between window panes to absorb moisture. Buy
some quality sieves.
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Sulaiman
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Quote: Originally posted by Deathunter88  | | Most molecular sieves from China are fake - they are not designed to dry liquids, rather they are placed between window panes to absorb moisture. Buy
some quality sieves. |
Sounds reasonable.
After I've ried to recover ethanol from them, washed, sun dried and roasted them,
I'll keep them as a simple dessicant, as used in a dessicator.
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The bulk of the dust settled but some very fine stuff is still in suspension.
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outer_limits
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I wouldn't consider China as a reliable source of everything. They are acceptable for cheap glassware and equipment but in my opinion not for reagents
and other stuff. It of course depend on the supplier that you work with but is is very hard to find a good quality. Instead I would consider buying
sieves from reliable source.
That's how my sieves look - no dust.
[Edited on 22-6-2020 by outer_limits]
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Refinery
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I would not buy sieves or other stuff that are not easily observable as functional from china. Better save than sorry and buy only reputable glass and
simple things they can't mess up.
AFAIK sieves will last for quite a long if used properly.
I'm not sure if sieves can be reactivated the same way as activated carbon. It is boiled in water and then dried in oven. I've done this multiple
times when I've polished alcohol.
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Keras
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I agree with the two last posts. I've ordered molecular sieves from a well established, reputed chemical broker and never was letdown. Their sieves do
not produce any dust, I use it to bone-dry ether I use for Grignard reactions and it works fine.
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Refinery
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If I were to sell expanded clay aggregate as molecular sieves, people would buy it without knowing it has nothing to do with sieves, especially if
they never handled the real ones.
I've even faced faked silica gel and activated carbon.
Welcome to china.
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unionised
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| Quote: Originally posted by Deathunter88 | | Most molecular sieves from China are fake - they are not designed to dry liquids, rather they are placed between window panes to absorb moisture. Buy
some quality sieves. |
It's easy enough to check.
Bake some (thoroughly), let it cool in a closed container, weigh it, leave it open to the air for a while, weigh it again.
Should pick up water equal to about 20% of its dry mass.
https://www.sorbentsystems.com/desiccants_charts.html
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Ubya
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probably it is a luck game, but if you aren't in a hurry keep an eye on ebay, sometimes some quality stuff pops for cheap.
a guy sold me this https://www.difanmax.com/productinfo/247233.html for $8+free shipping
chinese stuff could be good stuff sold for cheap, or shitty stuff sold for cheap, it's risky but if you can find the right clues you can usually get
it right.
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SplendidAcylation
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I tried the same thing with sieves bought from China
Something like:
Sieves were first weighed
Sieves added to azeotropic alcohol, left to sit for a while, then strained out, and dried with a paper towel, then reweighed
The sieves were then dried in the oven (a few almost explosions occurred but nothing too bad)
Then the process was repeated
After a few cycles, the sieves were still gaining a lot of weight, more than expected given the amount of water that should have been present.
Also they seemed to be soaking up a lot of alcohol too, enough to make a nice fireball
I then checked the density of the alcohol, and it wasn't any lower than it was to begin with, but I had lost about half of it (100mL or so)
So I guess Chinese molecular sieves are no good at all
I did have some success drying pyridine with them, but generally disappointing too
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woelen
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I have varying experience with cheap reagents from China.
- good quality lithium
- good quality potassium iodide
- good quality iodine
- bad quality antimony (Was sold as 5N. After purchase I wrote that I would test the antimony and if it indeed was 5N, then I would order much more of
it. I immediately got a reply that it was not that pure, that it would be 3N, m,aybe 3N5 but not better than that and they also immediately gave a
refund. I asked them to change the text at the eBay auction and they did, they changed the 5N to 3N. I never tested it ).
- bad quality ampouled sulphur sample (lot of dust inside, while the picture showed nice granules inside the ampoule)
- bad quality ampouled lithium sample: shiny pieces of lithium, but lots of ugly looking grease inside the ampoule. After complaining I received a new
one, and that one is really good looking, it is a very nice and shiny lithium sample.
- fake vanadium powder (was sold as 3N vanadium, in reality it was zinc dust). I got a refund.
- fantastic shiny non-oxidized ampouled samples of calcium, dendritic samarium, barium.
- good quality ferrocene for a very good price.
- many cheap samples of As2S3 of good purity
- nice sample of HgS (red vermillion, the real stuff, very dense/heavy).
[Edited on 23-6-20 by woelen]
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