08-18-04 18:43
No 526088
I recently aquired some 3A molecular sieves, cause I need some "super-dry" MeOH. Then I UTFSE and came across this post Post 467135 (Rhodium: "Tips on drying organic solvents", Tryptamine Chemistry). Why does Rhodium say that he uses molecular sieves for drying every solvent except alcohols? As far as I know molecular sieves can be used for removing water from alcohols. Or maybe not?
(The Archetypical "Good Guy")
08-18-04 18:52
No 526090
Read this (../rhodium /equipm
If you are using 3A molecular sieves, they are good for drying ethanol and methanol. 4A and above are unsuitable for the lower alcohols, because they will suck up much of the solvent.
Regards
Bandil
Cocaine blows!
(Hive Addict)
08-18-04 19:33
No 526093
MOLECULAR SIEVES
Molecular sieves are crystalline metal aluminosilicates having a threedimensional interconnecting network of silica and alumina tetrahedra. Natural water of hydration is removed from this network by heating to produce uniform cavities which selectively adsorb molecules of a specific size.
A 4 to 8-mesh sieve is normally used in gasphase applications, while the 8 to 12-mesh type is common in liquidphase applications. The powder forms of the 3A, 4A, 5A and 13X sieves are suitable for specialized applications.
Long known for their drying capacity (even to 90°C), molecular sieves have recently demonstrated utility in synthetic organic procedures, frequently allowing isolation of desired products from condensation reactions that are governed by generally unfavorable equilibria. These synthetic zeolites have been shown to remove water, alcohols (including methanol and ethanol), and HCl from such systems as ketimine and enamine syntheses, ester condensations, and the conversion of unsaturated aldehydes to polyenals.
Type
3A
Composition
0.6 K2O: 0.40 Na2O : 1 Al2O3 : 2.0 ± 0.1SiO2 : x H2O
Description
The 3A form is made by substituting potassium cations for the inherent sodium ions of the 4A structure, reducing the effective pore size to ~3Å, excluding diameter >3Å, e.g., ethane.
Major Applications
Commercial dehydration of unsaturated hydrocarbon streams, including cracked gas, propylene, butadiene, acetylene; drying polar liquids such as methanol and ethanol. Adsorption of molecules such as NH3 and H2O from a N2/H2 flow. Considered a general-purpose drying agent in polar and nonpolar media.
.....read more,
http://www.sigmaaldrich.com/Brands/Aldri
It is better to die on your feet than to live on your knees.......
-Emiliano Zapata-
(Guardian)
08-21-04 02:36
No 526531
And for a quick little lesson that you will never forget regarding the heat of hydration, just take a handfull of 3Å sieves and introduce some H2O to the mix. This little experiment helped me obtain a bettter understanding of calorimetry.
Of course I wish I could remember what bee it was that informed me about this little experiment. I want to say barium, but I am unsure.
Please be advised that this will more than likely be very uncomfortable to you. But if you are the type that learns better when they have a "physical" understanding of the concept, this might be a rewarding avenue to explore...
regards,
methyl_ethyl
Unipolar Mania, It's good for life...
(The Archetypical "Good Guy")
08-21-04 08:29
No 526564
methyl_ethyl>
That was Hest
And he suggested taking a single sieve (can you even say "a sieve", or is that like saying "a pant"?) and holding firmly between two wetted fingers.No reason in overdoing things by using a handfull
Regards
Bandil
Cocaine blows!
(Hive Addict)
08-21-04 15:05
No 526585
I've never used a seive and do not properly understand what one is or what they are useful for but I do recall these well known Cheech & Chong lyrics from their famous song Earache My Eye.
my mama talkin' to me
try tell me how to live
but I don'y listen to her
'cause my head is like a sieve
I would now assume that a sieve might be somewhat like a filter in that certain things might have difficulty passing through it?
Is that in the ballpark?
edit - actually I just reread java's post and I get it now.
Without the existence of idiots geniuses would simply vaporize into thin air
(Guardian)
08-22-04 05:46
No 526717
(can you even say "a sieve", or is that like saying "a pant"?)
I have no problem saying "a sieve" I cannot however say "a pant" but that is beside the point. I may not have used a "handfull" of sieves per se, however I did use ~5-10 sieves and I introduced a steady stream of water to them, not a wetted hand as previously suggested. Of course I was just going on memory, and did not have his post in front of me at the time, hence the not remembering who posted it. It took ~3 seconds until I flung the little spherical bastards across the laboratory screaming. Fortunately I was alone at the time
.None the less thanks hive for a learning experience that will not be soon forgotten.
still intoxicated,
m_e
Unipolar Mania, It's good for life...