I only really have high school level knowledge of chemistry, and also I don't really own any lab equipment.

I'm using 3A zeolite molecular sieves to dry ethanol (and sometimes isopropanol) and they seem to be working great.

However, I'm always left with a bunch of dust.

I can let the dust settle over night and then pour off the top in the morning, but it's still got an orange tint to it. I can keep repeating that process but it starts to take a really long time.

I tried running it through a coffee filter but the particles are too small for the coffee filter to catch.

What should I look for in a filter paper / what other material could I use to filter the remaining dust out of the ethanol?

I don't want to distill it, I don't have the setup for that.

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    $\begingroup$ Better filter paper. Whatman #1? Of course you will be picking up moisture as you filter. $\endgroup$
    – user55119
    Aug 9 '20 at 16:23
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    $\begingroup$ If you have a lot of dust it may mean that your zeolite is degrading because of excess water in your ethanol. Was the dust present before drying? What is the source of the ethanol? In research labs, sieves are often flame-dried in a flask under vacuum. They do pick up water sitting around in a can that is continually opened and closed. $\endgroup$
    – user55119
    Aug 9 '20 at 16:41
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    $\begingroup$ I think it is too much to ask for the sieves to remove 5% water. One way to do this in a lab is to add some sodium to 95% ethanol and diethyl phthalate. The mixture is heated to to allow hydroxide from water saponify diethyl phthalate. Then 100% ethanol is distilled out. Not to be attempted in your kitchen. Good Luck! $\endgroup$
    – user55119
    Aug 9 '20 at 19:54
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    $\begingroup$ Most lab-used molecular sieves come with very little dust and are usually supplied as small spherical lumps. If you handle them well you don't get a lot of dust. Perhaps you have cheap sives that are very dusty. $\endgroup$
    – matt_black
    Aug 10 '20 at 14:02
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    $\begingroup$ You can use a sintered funnel with a small bed of celite. $\endgroup$ Aug 10 '20 at 19:36

Since this never got a proper answer I thought I'd come back with a follow-up.

Essentially the root cause was low quality sieves (I had just picked the cheapest I could find on the internet). There are probably other things that work but all of the following captured the dust when used alone:

  • Whatman #6 filters do a decent job. I have #597 too but I don't recall if they worked here. (Whatman filter grade chart).
  • A bed of sodium bentonite over a #597, which I was using to filter other stuff, also incidentally captured the sieve dust.
  • I never actually tried celite; but it was recommended in the comments so that could be a solution, too.

And the following also helped with the issue:

  • Simply letting the solutions sit for a day then pouring off the top left a significant portion of the dust settled at the bottom. I'd do this anyways before running it through a filter, to lighten the filter load.
  • More importantly, they were just cheap sieves. The second time I used them after baking them there was significantly less dust, and by the third time the issue was basically solved.

The next time I get cheap sieves I think I might wash them in the solvent first just to get the initial dust load out, recharge them, and then use them for their intended purpose. Although I suspect that if I balance the time, cost, and energy of doing this with the extra cost of better sieves, it's probably a good idea just to pay for the better sieves.

Pretty obvious in retrospect but maybe a fellow non-chemist will find it useful some day.

  • 1
    $\begingroup$ This is a great answer (and your original question was a great question). Thanks for taking the time to post it. $\endgroup$
    – Curt F.
    Mar 11 at 0:52

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