mrjeffy321
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Isopropanol – Dry Ice Bath
For a project I am planning I need to achieve very low temperatures so I would like to use an isopropanol – dry ice bath. Dry ice sublimes at -78
°C and the freezing point of (pure) isopropanol is -89 °C. I am not using pure isopropanol, though, I only have 91 v% , the rest being water.
What I would like to know is if the ~9 v% water in my alcohol will raise its freezing point enough so that it will freeze in the dry ice? What is the
freezing point of 91 v% isopropanol?
I was able to find 99 v% isopropanol at the drug store, but it is about 4 times the price as the 91% alcohol and I’d rather not use it.
If I do need a more-dehydrated form of the alcohol for my bath, is it practical to obtain it by “salting out” the 91% alcohol? What is the
practical limit of this method?
Of course, I could just try this out myself and see if it works, but I figure surely someone on this forum has done this before and would allow me to
benefit from their experience.
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per.y.ohlin
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This chart may be of use. From the blog, I gather that the data wasn't collected in a very precise manner. The last data point has the correct
temperature in fahrenheit, but it is off in celsius (They didn't even need to measure this point). From the chart, it appears as though your
isopropanol would freeze, but I don't know whether water freezes out preferentially, increasing the concentration of isopropanol, and preventing the
rest from freezing, or if isopropanol freezes out with the water, freezing the entire solution.
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Panache
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I run a freezer at -85 and 99.9% isopropanol will not freeze in it although NH3 will. Once i have used the isopropanol a few times (i run it as a
coolant) and it has picked up some water it gets very viscous when i drop its temperature to -85. I think you will be fine using the 91% as a bath, at
worst you will have a vert viscous bath, however it will not freeze into discrete crystals and there become hard and unsuitable as a heat transfer
medium.
If you have any ethanol/methano or acetone adding a small amount of this to your IPA will lessen the chances even further of runnin g into problems.
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entropy51
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I use 91% IPA and dry ice in a large cold trap on a vacuum system. It does indeed form a very thick semisolid mass, but it seems to work fine for
trapping oil vapors from a diffusion pump.
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mrjeffy321
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Well, as long as the mixture is still fluid enough to use as my cooling bath then it should work for my purposes.
Could you compare the consistency of the very thick IPA – dry ice mix to something common?
What about the “denatured alcohol” sold as solvents in hardware stores…that is generally a mixture of several alcohols. Might that be a better
option?
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Panache
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Quote: Originally posted by mrjeffy321  |
Could you compare the consistency of the very thick IPA – dry ice mix to something common?
What about the “denatured alcohol” sold as solvents in hardware stores…that is generally a mixture of several alcohols. Might that be a better
option?
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Nothing i can think of compares really, maybe like ice cream on the cusp of being totally liquid.
Definitely use the denatured alcohol.
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vulture
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Denatured alcohol, methanol, ethanol, IPA, acetone, they all work if you use enough dry ice. Acetone is a bit nasty because it has the tendency to
splatter with CO2.
One shouldn't accept or resort to the mutilation of science to appease the mentally impaired.
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mrjeffy321
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Calling something “denatured alcohol” is such a generic name that it made me uncertain about its precise contents and purity. I was not sure if,
perhaps, there might be enough water impurities in the alcohols that would make the freezing point sufficiently high that it would freeze in the dry
ice. Furthermore, I would like to use a Styrofoam box as the container for my dry ice bath in order to provide insulation. Therefore I cannot use
anything with acetone in it or it will dissolve the box, otherwise acetone would be been my first choice to use. But I tested my denatured alcohol
and it seems that it should work nicely.
[Edited on 1-1-2010 by mrjeffy321]
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vulture
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I've used both ethanol and acetone of questionable quality, which had been exposed to the atmosphere for quite some time and never had problems with
the bath freezing up. Also, the dry ice we have is usually in storage for a few days and accumulates quite some water ice on the outside, this has
never been a problem.
Isopropanol does increase quite a bit in viscosity at -78C, comparable to water/glycerol. Ethanol does not seem to do this, which is why it is
preferable for applications which require circulation, such as cryostats.
One shouldn't accept or resort to the mutilation of science to appease the mentally impaired.
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mrjeffy321
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The denatured alcohol worked splendidly; it remained very non-viscous throughout my usage of the dry ice – alcohol bath, without any signs of ice
crystals or degradation of my Styrofoam box container. Thanks.
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The WiZard is In
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Years ago when I worked in a radiocarbon (C14) lab
we used an dry ice in acetone cooled cold-trap, which
after a few months developed a strange odour!
In da line was also P2O4 and LN2.
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agorot
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I personally did this just a few weeks ago and used 91%. The alcohol took on a gelatinous sort of consistency, but it worked just fine.
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Panache
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| Quote: Originally posted by The WiZard is In | Years ago when I worked in a radiocarbon (C14) lab
we used an dry ice in acetone cooled cold-trap, which
after a few months developed a strange odour!
In da line was also P2O4 and LN2. |
man you guys really loved your vac pump, i'm surprised though that you had nothing for acidic vapours like NaOH pellets.
was it a synthetic lab or like a carbon dating lab?
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The WiZard is In
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Radiocarbon dating. Benzene from catalyzed CO2, very-very
dry CO2.
Radiocarbon, Vol. 18, No.2, 1976, P. 205-209
Queens College Radiocarbon Measurements I.
Speaking of LN2 ... when things were dull we froze stray cats
in LN2 dropped them from the second floor window onto the cement
patio and sold their shattered parts for shark bait.
Just ignore the fact that the International Game Fish
Association will not accept for world record and fish caught
using any mammal for bait/chum.
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stoichiometric_steve
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| Quote: Originally posted by The WiZard is In |
Speaking of LN2 ... when things were dull we froze stray cats
in LN2 dropped them from the second floor window onto the cement
patio and sold their shattered parts for shark bait.
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You are sick.
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peach
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| Quote: Originally posted by mrjeffy321 | | The denatured alcohol worked splendidly; it remained very non-viscous throughout my usage of the dry ice – alcohol bath, without any signs of ice
crystals or degradation of my Styrofoam box container. Thanks. |
Did you have the alcohol straight in your styrofoam box? What kind of ultimate temperature did it reach, if you know?
Does anyone have experience with smashing up blocks of dry ice? Praxair tell me not to do it, but I've seen people chopping it up in the kitchen with
a knife and tea towel, no problems.
I'd obviously much rather use pelletized, but the only place nearby sells 1kg blocks.
Has anyone ever used dry ice directly in the solvent of their workup? Specifically, DCM. If I'm the first to think of that I want a gold star.
[Edited on 8-5-2010 by peach]
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not_important
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I know some overclockers have tried DCM&DI, and there's this 1977 report in which the cold trap uses DXCM+DI http://pubs.acs.org/doi/abs/10.1021/es60129a002
Just put the dry ice in a heavy bag and whack it with a hammer.
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peach
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Ha ha, I was going to add to my question;
"Praxair also say not to smack it with a hammer"
PRAXAIR!?
Thanks for the DCM notes, domo origato not_important.
[Edited on 9-5-2010 by peach]
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not_important
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Well, don't whack it if it's not well wrapped up. Fine bits of flying dry ice are no fun, especially if one lands in an eye. I suspect over caution
on their part, just to avoid being blamed if something goes wrong.
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Panache
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a big spade bit (like 50mm) works great on both ice and dry ice, do it in a deep bucket to stop stuff flying everywhere and get some cryo gloves.
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