Cold Trap Augmentation with Molecular Sieves

We all know that when sugars char in your short path/wiper, problems can arise. One of the unanticipated issues that I never thought about was water (along with aldehydes, alcohols and other crap) being generated by the dehydration of sugars at higher temperatures. Not only is this a great way to gunk up your still and vacuum pump, but it can also ruin your vacuum pressure. I’ve found that even profusely washed starting material can cause this issue.

A solution I’m yet to try is packing a cold trap or secondary condenser with molecular sieves (4-5A to catch alcohols). My hesitancy is that under such a high vacuum, the sieves won’t hold the things I’m trying to catch.

Has anybody tried this, or does anyone know if a mol-sieves retain their adsorptive properties under high vacuum?

I’m sure it’s a tug of war between the positive interactions between the surface of the sieve and the vapor pressure, so it’s going to vary compound by compound. Maybe using something besides sieves like a CRC material that absorbs rather than adsorbs the targeted material? Obviously not a powder…

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Interesting. I suppose that’s the balance I though of. I have a -50 mechanical cold trap, so maybe putting them in the cold trap will help, since there is the absorbance and the temperature helping tug back.

There are some that go to -110 they work great. That helps solve this problem.i tried runnin the sieve beads in a custom made pipe but like you stated that don’t stay there and will cause problems with you vac.

Using the glass bubbler type cold trap from across international sells, those could easily be filled all the way since they catch on the bottom.

It wasn’t an AI cold trap it was another brand I am trying to remember to remember the brand.

molecular sieve get hot when they are working


Maybe sh-scientific or labconoco

Following this because I have also thought about this in a different application.

After some thought, I actually plan on just getting a simple liquid nitrogen setup as an Uber cold trap, should stop those pesky volatile compounds :smiling_imp:

I still think this has its applications though, perhaps in a vacuum terp strip application

You can fill that bubbler with vac pump oil and catch quite a bit of impurities


profusely washed starting material will not cause this issue. you’re wrong.

lol you’re suggesting to plug up the vapor stream with media?

I have once cleaned a vac pump filled with clay.

it was horriffic.

dont let it happen to you

toss in $150 worth of diffusion pump oil and heat it up… if you boil the diff pump oil and can find a way to condense and recirculate it the oil mist will catch basically anything that comes thro- oh wait thats literally how a diffusion pump works

I was suggesting something with the particle size of a mol sieve but made of a material that adsorbs whatever the fuck you want to trap.

Whats that?

That’s going to take some R&D.

A google scholar search for ‘monolithic adsorbent’ would be a good place to start.