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Author: Subject: Can you only dry 3A Molecular Sieves in the Microwave? (OTC)
LuckyWinner
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[*] posted on 5-9-2020 at 06:39
Can you only dry 3A Molecular Sieves in the Microwave? (OTC)


Ive been trying to find a clear answer but could not.

quote from article:
https://chemtips.wordpress.com/2014/12/01/how-to-activate-mo...

'Unfortunately, sieves are shipped saturated with water and must be dried before use. Sieves actually absorb water at 120 degC, so a conventional drying oven is not up to the task.

Conventional wisdom is that heating to 300 degC or greater at atmospheric pressure will dry sieves, and this temperature can be reduced somewhat under vacuum [3]. Experimentally I had some success heating to ~200 degC overnight in a vacuum oven, but was never quite sure that the sieves were fully active [4].'




this means your mol sieves can not be dried in a cheap pizza oven from the supermarket that goes up to 220C max?

or is this article false.

all videos usually recommend to nuke your 3A mol sieves in a microwave for 3x5 min with frequent vents to avoid superheated water exploding your microwave.

then immediately put in vacuum desiccator till its at room temperture and seal airtight after.


no way to dry it in a regular pizza 220C oven?
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[*] posted on 5-9-2020 at 07:13


Yes, you can dry in a conventional oven -- this is how I always do it. Spread sieves in a thin layer on a baking sheet, heat at 200 - 250 C for several hours while mixing the sieves around every now and then. Obviously don't put sieves in an oven if they smell like solvent or you could have an explosion. I rinse them several times with tap water and let them air dry, until they no longer smell like solvent, before placing them in an oven.

You test if the sieves are activated by placing a few in your palm and then dropping 1-2 drops of water on them. You should feel them heat up quickly, almost painfully hot.

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[*] posted on 5-9-2020 at 14:22


Be careful when heating things in the microwave when there isn't something like food/water in it. I think there needs to be a place for the energy to go and some materials do not absorb microwaves very well, IDK if the sieves do or not. I destroyed a magnatron and transformer when a glass beaker of water boiled away and then when there was no more water, the whole thing ended up cooking itself.
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[*] posted on 5-9-2020 at 15:20


You can always put a beaker(or plain drinking glass) filled with water in one of the edges, not on the rotating plate, this will absorb excessive heat.
Even better, two of them.
This is some key knowledge how to avoid your microwave exploding from solvent vapours and in consequence banging the door into your watching face with force :D

I wish I had done this when I heated that cherry stone pillow for my back in it that one time... for too long... but in my food microwave, keep that in mind!!!
Not the good ol chemistry microwave, which always has some chemical odour.
Now I can't get the smell of burnt cherry stones out of it :(
Pfui!
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[*] posted on 15-9-2020 at 13:16


Quote: Originally posted by karlos³  
Y
Now I can't get the smell of burnt cherry stones out of it :(
Pfui!


As with many things, getting stuff a little bit wet before the action is the key to an enjoyable outcome :D

Seriously, wet the cherry pits from time to time. That's what carries the heat after all!
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[*] posted on 15-9-2020 at 14:05


Quote: Originally posted by RogueRose  
Be careful when heating things in the microwave when there isn't something like food/water in it. I think there needs to be a place for the energy to go and some materials do not absorb microwaves very well, IDK if the sieves do or not. I destroyed a magnatron and transformer when a glass beaker of water boiled away and then when there was no more water, the whole thing ended up cooking itself.


I believe the sieves will take the heat protecting the microwave. Clay is a poor insulator even if it is filled with air pockets so it should have no issues taking the in the energy, though that is a very good thing to point out.

Ultimately I would just use an oven, get a cheap toaster oven and use it as your lab oven, also that way if a person is careless one day and blows up their oven, it was a cheap counter top toaster lol.

I just think microwaves don't heat even enough and don't maintain a set temperature like an oven.
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[*] posted on 8-5-2021 at 23:45
Can't reactivate even with MW


Got some 3A sieves from a very popular seller on Amazon, Ebay, and they have their own website storefront.
Ordered 1 pound(456g). received 500g instead(This confused me for a long time:P)

Name and brand of product:
"HFS (R) Molecular Sieve Zeolite 3A 8X12 mesh (1lbs)"
Price - $15 USD


specs claimed by the vendor:

Quote:

8*12Mesh
Bead Size: 1.6~2.5
Bulk Density: ≥0.70~0.82 g/ml
Equilibrium Water Capacity @25℃: ≥ 19.0~20.0 wt%
Equilibrium Ethylene Capacity: ≤3.0mg/g
Heat of Adsorption: BTU/lb of H2O 1800
Point Contact: N≥20~58
Variation Coefficient: 0.3
Attrition Rate: wt%≤ 0.1
Size Qualification %≥ 98
Package Moisture: wt%≤ 1.5


I received the item 2 days later. It was vacuum-bag-sealed in a sturdy aluminum type ziplock bag.

First order of business, test them!

Quote: Originally posted by monolithic  


You test if the sieves are activated by placing a few in your palm and then dropping 1-2 drops of water on them. You should feel them heat up quickly, almost painfully hot.



It's odd to me that even the most nit-picking, pedantic, and vulcan/android like scientific journal publishers and bloggers all cite the above mentioned test.

Nurdrage to the rescue:
https://youtu.be/MduzjhRHBFY

Testing EBAY Molecular Sieves

Here's a screenshot that says it all:

NurdRage3A.JPG - 191kB

So I followed his exact procedure. High quality K type thermocouple
in the beaker with distilled water first. Dropped in the sieves. Hooray! My results matches those portrayed on the left side of the video. 4 - 5 seconds in the temp was crossing 45C.

I used them primarily for drying MeOH, EtOH, and isopropanol, they seemed to work slow but well.

Since then, I have tried everything to regenerate the used ones. Every time I perform the test portrayed in the video.
-No working oven, tried boro dish on frying pan on stove top
-Tried layering a bed straight onto SS pan on stove top
-Tried 1L RBF Clamped, vacuum pump directly attached pulling down to whatever my cranky rotary vane pump pulls(easily 100mmHg absolute, possibly much lower), and heating with a brushy propane torch

In all above cases, subsequent testing showed maybe 3 or 4 degrees Celsius of exothermia.

Finally I borrowed a friends microwave, haha.
1200 Watts. Left power setting on 10.
10 minutes. The best I got was 25C -> 35C, and that was without stopping to cool down , etc.
Weight loss was about 3 - 4 grams from ~ 175g

What if the sneaky vendor added some chemically exothermic reagent adsorbed into the sieves!?

In the questions section someone asked if they could be regenerated, and the vendor said no, these were meant to use and discard!

Great! I think NaOH/Na2CO3 -> reflux -> Distillation, a process I have grown very very sick of repeating, will remain as my only real means of drying lower alcohols=/

Any advice folks?
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[*] posted on 9-5-2021 at 10:23


CaO

What will it take for everyone saying (presumably Chinese) sieves and MgSO4 don't work to try lime? When a video is made?

Notice that real directions for sieve regeneration always specify hot, dry air flow-through or somewhat high vacuum. This is not to say that beads can't be dried in an oven at say 250C, but I suspect it doesn't work as well.

Who says that tossing sieves in the oven doesn't mess up the sieves and/or dries more than a portion that actually absorbs the microwaves? (i.e. hot/cold spots)

Is there such a thing as 3A sieves that only work once? Maybe the [pickaxes and shovels division of the] future4200 mafia has no clue? Does anyone still think ebay and amazon means quality goods? Maybe they're good sieves but need a hot stream of dry air...won't know until the experiment is done.

Bought a bag of dolomitic hydrated lime for mortar from Home Depot (Western type S "Miracle")...mucho carbonate through and through (plastic inner lining)...no wonder the roads are so crappy these days.

[Edited on 9-5-2021 by S.C. Wack]




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[*] posted on 9-5-2021 at 12:56


Quote: Originally posted by S.C. Wack  

CaO

What will it take for everyone saying (presumably Chinese) sieves and MgSO4 don't work to try lime? When a video is made?
[Edited on 9-5-2021 by S.C. Wack]


In my area, mostly based on what people say on this forum, CaO is no longer sold as 'quicklime' or similar. But various 'safe alternatives'.

I did a fair share of research, that was pretty well balanced, I'd like to imagine anyway. Balanced meaning, the Academia journal procedures, where things like inert gas supply, plentiful supply of shlenk flasks and so on are assumed. And then the creative kitchen chemists who understand the underlying principles to know which rules to break, and even tested their theories. (Somewhere inbetween lies the Fischer or Sigma official instructions, sometimes pretty surreal).

So to answer your question:

Quote:

Notice that real directions for sieve regeneration always specify hot, dry air flow-through or somewhat high vacuum. This is not to say that beads can't be dried in an oven at say 250C, but I suspect it doesn't work as well.

Who says that tossing sieves in the oven doesn't mess up the sieves and/or dries more than a portion that actually absorbs the microwaves? (i.e. hot/cold spots)



Just as one cannot disprove the existence of God(s), no one has ever empirically challenged what you propose.
On the other hand, I never read one comment on any forum, blog, or youtube video where anyone reports that microwave or oven technique is inadequate in any way. The consensus is just that it's slower.

Actually regarding microwaves:
http://www.sciencemadness.org/talk/viewthread.php?tid=9710


Solo:
Quote:

The microwave technique: A new route for high dispersion of inorganic salts onto supports
F. -S. Xiao1, W. Xu1, S. Qiu1 and R. Xu
Journal of Materials Science Letters Volume 14, Number 8, page 598-599, January, 1995


Excerpt
.........In comparison with other methods such as ionexchange, impregnation and monolayer dispersion, the dispersion of inorganic salts onto the surface of supports by the microwave method exhibits the following features: (i) high loadings of inorganic salts may be dispersed onto the surface of supports;
(ii) microwave treatment time is very short; generally, treatment of 10 min can achieve high dispersion; (iii) the sample preparation is very simple, avoiding stirring of solution, drying and calcination; and (iv) inorganic salts can easily be dispersed in porous solids not having ion-exchange capacity, such as silicalite-I zeolite.

Attachment: The microwave technique-A new route for high dispersion of inorganic salts onto supports.pdf (236kB)
This file has been downloaded 851 times



But your conjecture is perfectly plausible.
Just as is mine, that Li metal or something that reacts ultra exothermically with water was impregnated into ball shaped zeolite, that was never engineered with uniform pores at all, just so they could pass the initial exothermia test.

OK there's more I can do. I have some of the still fresh and tightly vacuum bagged sieves left, just a little bit. I could weigh before and after on my 0.001g scale.

Honestly it's the MeOH, that's the only issue.
All references agree that 3A sieves should be pulverized to dry EtOH and larger alcohols. But because MeOH is just barely larger a molecule than H2O, methanol and water will just swim casually in and out of the pores, which makes it take far longer to dry, and won't get the MeOH as dry, if pulverized.


I have never been impressed by MgSO4. Maybe slightly for very non-polars. Pretty crazy to think it would work for alcohol.

Anyway, thanks for sharing your side of the story S.C. Wack, I will certainly consider it.
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[*] posted on 9-5-2021 at 13:45


> All references agree that 3A sieves should be pulverized to dry EtOH and larger alcohols
Dubious...it may be faster and give better drying by weight, but there's no need to do so.

The CaO has to be made yourself.

Kitchen chemists have a clue? Eh... I doubt that real chemists go through the trouble of punching holes in their microwaves and assembling that whole apparatus for no reason. How hot are sieves immediately after microwaving? Here, there, everywhere. How do sieves absorb microwaves with little water? How hot can they get at the pore level when very wet?

Impregnating/making sieves or working with sieves other than 3/4/5A in microwave ovens or doing it with vacuum or airflow is not particularly related to what happens when a pile or plate of damp zeolite A is microwaved. What people say about success or failure without analysis is sometimes closely related to the meaning of my sig. Few videos, blogs, and forums are reliable sources of science.

Many have tried MgSO4, IIRC their reports are as good as the negative amazon reviews for your sieves. AFAIK I'm the only person on the internet who's tried lime.

Sieves select the more polar molecule (not perfectly) when given a choice. (Grace Davison disagrees with Grain Processing Corp's US4319057 regeneration of sieves with methanol or acetone, specifically giving drying of methanol as an example)

edit: there are of course sieves designed to not be regenerated!!! For refrigerants and insulated windows! duh. That could very well be what people are selling.

[Edited on 9-5-2021 by S.C. Wack]




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[*] posted on 9-5-2021 at 14:51


Quote: Originally posted by S.C. Wack  
> All references agree that 3A sieves should be pulverized to dry EtOH and larger alcohols
Dubious...it may be faster and give better drying by weight, but there's no need to do so.


You are correct, dubious nails it. It's actually the inverse that I read. MeOH specifically, cannot* be dried with pulverized zeolite 3A sieves.
*cannot, was a paraphrasing for simplicity. Indeed, they can be, but the best possible PPM of H2O that can be achieved is a few orders of magnitude larger than for the higher alcohols. But if left as beads, it's about equal.


Quote:

The CaO has to be made yourself.


This is the closest I'll come to the edge of spoonfead requesting, I promise. Could you recommend a ref. or resource for your favorite procedure?


Quote:

Kitchen chemists have a clue? Eh... I doubt that real chemists go through the trouble of punching holes in their microwaves and assembling that whole apparatus for no reason. How hot are sieves immediately after microwaving? Here, there, everywhere. How do sieves absorb microwaves with little water? How hot can they get at the pore level when very wet?


I see what you mean about relying on heat alone to displace water with dry....atmosphere.... Since a microwave only excites water molecules, the activation would approach a negative asymptote. However, let's not forget to factor in that of course the additional steps and specialized equipment used in a lab i done for a reason, but such a lab would have much stricter requirements for dryness, then little ol' me and my racing car methanol.

3A sieves are mostly a mixture of a certain lattice of silica and alumina. Essentially, tiny little kilns.

What I'm saying is that your challenge based on thermal H2O, vaporization, if correct, would be applicable to all dessicants, no?

One thing that does come to mind is the official purpose of my big rotary vane vacuum pump. It's meant to remove all of the humidity in a house/building sized closed A/C system by slowly but surely bringing the whole system down to sub-torr vacuum, thus all the humidity that's floating about boils away.

When I heated a 1L RBF under pretty strong vacuum, I never even saw any condensation appearing or blowing around as it would normally under similar circumstances.


Quote:

Sieves select the more polar molecule (not perfectly) when given a choice. (Grace Davison disagrees with Grain Processing Corp's US4319057 regeneration of sieves with methanol or acetone, specifically giving drying of methanol as an example)

edit: there are of course sieves designed to not be regenerated!!! For refrigerants and window insulation! duh. That could very well be what people are selling.


Interesting. And Interesting!!
You know, I think I'm going to openly challenge the vendor on the amazon questions/answers page. Just with a simple "Why not" when they proclaim that these sieves are to be tossed away, and more ordered, from them.

I'll do some reading to figure out the difference between the refrigerant(some A/C systems use dessicant towers, a two tower system, when one is drying the stream of air/gas, the other tower is being regenerated. ) and window insulation sieves, vs. every other '3A molecular sieves' anyone ever speaks of.

Thanks again kindly for the very helpful information!
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[*] posted on 9-5-2021 at 19:39


I bought inexpensive 3A sieves through Amazon and received them vacuum packed but deactivated. Dried them for two hours in a toaster oven at 450F and found they lost near the theoretical capacity of water - I forget the measurement - and got hot when wetted. Very pleased. Give it a try, it's easy.
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[*] posted on 9-5-2021 at 19:41


Quote: Originally posted by earpain  
This is the closest I'll come to the edge of spoonfead requesting, I promise. Could you recommend a ref. or resource for your favorite procedure?


Quote: Originally posted by earpain  
What I'm saying is that your challenge based on thermal H2O, vaporization, if correct, would be applicable to all dessicants, no?


These are related in a way...one can look at it from a vapor pressure perspective, but I'm not sure that it's entirely accurate in practice; some things may dehydrate better than others when heated to whatever temp is given for 760 mm. CaCO3 is said to require 850C to become CaO, but the degree to which this happens depends on how fast the CO2 is removed; a flow of not-CO2 greatly improves the situation. I should test the same weight of precipitated carbonate against white marble or chalk and see if the form makes a difference. It is said that 450C is needed to dehydrate the hydroxide, but I heat the Hi-Yield product to 600C (gradually to not stress the crucible FWIW). A tall crucible is fine and nearly the theoretical weight is lost after a few hours in a furnace packed with it, it's a matter of economics on how complete you want it to be, because it's soon mostly complete. I do have older 3A sieves of unknown make but have not tested that in the same fashion, i.e. done good science.

How well CaO works with methanol no one seems to say, but for ethanol 99.9% dryness is very possible, despite what Vogel says about 99.5...because it all depends on how much is used or how many times it's repeated, plus how much care is taken in the distillation (I use a drying tube and no vacuum adapter) and handling; the anhydrous alcohols suck up air-water just like fresh-dried sieves, but worse probably.

[Edited on 10-5-2021 by S.C. Wack]




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[*] posted on 11-5-2021 at 04:19


Here's a pic of the 3A molecular sieves (still wet with methanol) I've been using and re-using for years to dry methanol. I usually dry them at 200°C for a few hours, and ideally zap them a short while in the microwave afterwards (although the latter is optional).

3A mol sieves.png - 621kB




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[*] posted on 16-5-2021 at 09:28


Quote: Originally posted by S.C. Wack  
Quote: Originally posted by earpain  
This is the closest I'll come to the edge of spoonfead requesting, I promise. Could you recommend a ref. or resource for your favorite procedure?


Quote: Originally posted by earpain  
What I'm saying is that your challenge based on thermal H2O, vaporization, if correct, would be applicable to all dessicants, no?


These are related in a way...one can look at it from a vapor pressure perspective, but I'm not sure that it's entirely accurate in practice; some things may dehydrate better than others when heated to whatever temp is given for 760 mm. CaCO3 is said to require 850C to become CaO, but the degree to which this happens depends on how fast the CO2 is removed; a flow of not-CO2 greatly improves the situation. I should test the same weight of precipitated carbonate against white marble or chalk and see if the form makes a difference. It is said that 450C is needed to dehydrate the hydroxide, but I heat the Hi-Yield product to 600C (gradually to not stress the crucible FWIW). A tall crucible is fine and nearly the theoretical weight is lost after a few hours in a furnace packed with it, it's a matter of economics on how complete you want it to be, because it's soon mostly complete. I do have older 3A sieves of unknown make but have not tested that in the same fashion, i.e. done good science.

How well CaO works with methanol no one seems to say, but for ethanol 99.9% dryness is very possible, despite what Vogel says about 99.5...because it all depends on how much is used or how many times it's repeated, plus how much care is taken in the distillation (I use a drying tube and no vacuum adapter) and handling; the anhydrous alcohols suck up air-water just like fresh-dried sieves, but worse probably.

[Edited on 10-5-2021 by S.C. Wack]


Much obliged!
This sounds like one of the first things I'll try once i finish building my forced air/propane burner, my compressed air/propane burner. Probably overkill for the H2 pencil torch.

Also, update:
I tried again. S.C. Wack I think this supports your theory. I didn't really give it much thought, but the used sieves I was microwaving this time, I had experimentally attempted to dry 91% isopropanol, which doesn't really work. But this meant there was plenty of water absorbed. I had them in an open jar, to allow any flammable volatiles to evaporate(this seemed more appealing than washing the sieves with water before re-activation)

And from here an all-too-familiar story:
I was excited to see that there was lots of steam and water vapor inbetween 1 or 2 minute zaps. I had a clip fan, and would just blow the moist air out of the microwave and turn it back on.

I was also doing something else at the time, heh, and after not that long, maybe a total of 15min, with stops inbetween, I come to see that the beaker had molten lava inside of it. Yes the sieves had formed a globe, it was glowing bright red, and I counted to 5 in my head and:
tada! the beaker cracks. however the glowing molten sieves were resting on a bunch of not glowing sieves. So I decided to just sit and watch it cool down.

It took a VERY long time to cool down wow.

When the not-destroyed sieves from this batch were used to dry methanol again, they lost their most celebrated property of allowing simple decanting or filtration. The methanol was tinted orange. I even sucked it through my VWR fine porosity sintered funnel, the sort you hate, because anything takes forever to filter through it.
Still discolored. So now distillation is the only option.

That being said, I think maybe after another cycle, or some intentional washing(HERE a Soxlet would be very handy), all the ultra fine zeolite dust would be washed off and they could be used as normal again.

Jenks and dicyanin thanks for the reassurance, and the pic.
Those are a much much smaller size than mine are.
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[*] posted on 17-5-2021 at 15:29


BTW it would be unsurprising if a different clay binder had the effect of causing changes with an identical zeolite base in a microwave. FWIW my sieves (also from ebay IIRC), after heating in crucibles in a 250C furnace for a few hours, increased their weight by 18.3% from exposure to room air, in a single bead layer.



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