greenyppols - 31-3-2006 at 10:15
Im sure I read something similar here, but cant find it.
Basically I think it was something like, 3a molecular sieves in a bottle (with whatever solvent you want dry) that had a disposing stopper of some
sort on it. It sat there upside down and basically you had anhydrous whatever-solvent-you-choose "on tap."
or can someone perhaps inform me where this information lies, or tell me Im freakin' nuts. 
runlabrun - 1-4-2006 at 00:11
Could be done... But molecular sieves arent meant to be exposed like that, just used in a normal fitration setup where they are exposed for short
amounts of time. Not to sure, give it a try and see how it turns out, sounds good in theory.
-rlr
greenyppols - 1-4-2006 at 03:54
rlr, by "in a normal filtration" did you mean pouring it through a column filled with the sieves? Not sure what you meant by exposing for a short
period of time, last I used 'em they sat for at least a couple days..of course now Im thinking it would be a permanent soak if left there...
would just pouring the solvent throught a column dry it sufficiently..for say, a grignard attempt?
Thanks
Drone - 1-4-2006 at 06:27
I cannot speak about the 'standard' lab procedure but I have had excellent results drying solvents by storing them over a few grams of molecular
sieves.
The sieves I used dried reagents/solvents sufficiently to perform grignard reactions easily.
The sole problem with the sieves was that they left small powder residues in the reagents, but these easily and speedily settled out.
Hope this helps.
runlabrun - 4-4-2006 at 05:10
I meant that the use of lab materials outside their design parameters may work, however u would need to test it. I thought u meant leaving the
apparatus as a permanent fixture ie very long times, not just a few days, few days even up to a month should be fine but i just would be wondering if
it were in place any longer than say a month...
Try it and see how u go... As for grignard, yes as its said its usually fine depending if the solvent is able to be adequatly dried by the type of
sieve your using, check the seive info and a solvent handbook for correct proceedures. As for this over a period of time, i would suggest testing it
first on something less expensive and hence expendable, say try a cheap grignard rxn with seive filtrate at 1 day, 5 days, 10 days, 20 days of sieve
exposure and determine the relative yield of the same repeated reaction to determine if there is any effect of the sieve sitting in place on the
solvent for use in grignards (thereby determine some sort of anhydrous vs sieve exposure relationship).... this takes into account your grignard
practice is great, hence repeatability is reliable. Give it a shot, id certainly like to hear if its viable over a period of say 2months...?
-rlr
DrP - 4-4-2006 at 07:41
How about distillation? For the higher boiling point solvents, we used to leave lengths of sodium wire in the bottle for a few days/weeks before
distillation - obviously takes out the water.
greenyppols - 5-4-2006 at 16:44
drone - I just thought of using a whitman cellulose extractor tube thingy..put some sieves in 'em and fold the end over tight to confine those little
particles..I know what you mean. It should fit in/out of the neck of a bottle too.
rlr- I should have been more specific. I cant imagine going beyond a month, max, for anything now that I think it thru more....unless I forget about
it. And yeah, I'll check the sieve info..I know 3a works drying ethanol, unless I check it for all I know it'll absorb ether, thf or whatnot...some
used for hydrocarbons and some not. Thanks for reminding me of that.
DrP- I do not have sodium nor means of acquiring it...currently anyway.
an unrelated doh: A small foundry was recently acquired, so calcium oxide can be used to dry ethanol now..but having sieves now I dont know...I'll
just put some slaked lime in a small alumina crucible and fire 'er up! and store it in a jar.
Is there a market here for CaO? lol.
runlabrun - 5-4-2006 at 18:27
well under those time limits i dont see any problem, try it out and let me know, its interesting... oh how are you goin to place the sieves in the
bottle? what type of bottle? i would imagine you would use a GP reagent bottle with a small piece of a sieve cut out to fit the squirt nozzel?
a pic or diagram of the setup once you get it sorted would be great.
-rlr
evil_lurker - 5-4-2006 at 20:57
Use 4a's over ether to absorb any ethanol.
unitednuclear.com is now selling sodium metal (30 grams for $25... ouch!)
There are also listings on ebay for it.
greenyppols - 6-4-2006 at 07:14
rlr- Its just an amber bottle with green teflon cap. The bottle anyway. As for putting the sieves in the bottle, I was going to place #grams in a
whitman cellulose extractor, but it wont fit in the neck of the bottle. It'll fit though a 2l erlenmeyer, but dayum, I wont need that much of anything
I dont think. A smaller extractor tube..or place the sieves in something like a bean-bag bag. (sew it in a piece of cotton pillowcase, shaped maybe
like a cigarcase to fit in the neck of the bottle?)
I figure 1000 ml 95% etoh will have 50ml of H20 in it, so I'd hafta figure how many g's of sieve will absorb 50ml of H20, then just add some extra
sieves. Id be able to recover the sieves, take 'em out of the pouch thingy to put 'em in an oven to dry 'em out for use again.
Its the dispensor thing thats got me now. Originally I thought of something like whats used in a bar to dispense booze, ya know? Thats not airtight
though....gonna hafta search, I think I read/saw something awhile back but since my 'puter drive died and Im on a laptop, alotta info and sources went
poof. Until I motivate to hook the dead drive to my laptop and extract the files that are still there....
evil - yeah, I know those..but Im to paranoid to order that. I dont want black helicopters or big, jackbooted, heavily-armed brutish thugs kicking my
door down, and then my ass. ....not directly order anyway. hm, now ya got me thinkin'.
greenyppols - 6-4-2006 at 07:56
Some molecular sieve info. This courtesy of sigma aldrich
Molecule Critical diam. (Å) Molecule Critical diam.(Å)
Helium 2.0 Propylene 5.0
Hydrogen 2.4 Ethyl mercaptan 5.1
Acetylene 2.4 1-Butene 5.1
Oxygen 2.8 trans-2-Butene 5.1
Carbon monoxide 2.8 1,3-Butadiene 5.2
Carbon dioxide 2.8 Chlorodi fluoromethane (Freon 22®) 5.3
Nitrogen 3.0 Thiophene 5.3
Water 3.2 Isobutane to isodocosane 5.6
Ammonia 3.6 Cyclohexane 6.1
Hydrogen sulfide 3.6 Benzene 6.7
Argon 3.8 Toluene 6.7
Methane 4.0 p-Xylene 6.7
Ethylene 4.2 Carbon tetrachloride 6.9
Ethylene oxide 4.2 Chloroform 6.9
Ethane 4.4 Neopentane 6.9
Methanol 4.4 m-Xylene 7.1
Methyl mercaptan 4.5 o-Xylene 7.4
Propane 4.9 Triethylamine 8.4
n-Butane to n-docosane 4.9
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.
Type 4A
Composition 1 Na2O: 1 Al2O3: 2.0 ± 0.1 SiO2 : x H2O
Description This sodium form represents the type A family of molecular sieves. Effective pore opening is 4Å, thus excluding molecules of effective
diameter >4Å, e.g., propane.
Major Applications Preferred for static dehydration in closed liquid or gas systems, e.g., in packaging of drugs, electric components and perishable
chemicals; water scavenging in printing and plastics systems and drying saturated hydrocarbon streams.Adsorbed species include SO2, CO2, H2S, C2H4,
C2H6, and C3H6. Generally considered a universal drying agent in polar and nonpolar media.
Type 5A
Composition 0.80 CaO : 0.20 Na2O : 1 Al2O3: 2.0 ± 0.1 SiO2: x H2O
Description Divalent calcium ions in place of sodium cations give apertures of ~5Å which exclude molecules of effective diameter >5Å, e.g., all
4-carbon rings, and iso-compounds.
Major Applications Separation of normal paraffins frombranched-chain and cyclic hydrocarbons; removal of H2S, CO2 and mercaptans from natural gas.
Molecules adsorbed include nC4H10, nC4H9OH, C3H8 to C22H46, and dichlorodifluoro-methane (Freon 12®).
Type 13X
Composition 1 Na2O: 1 Al2O3 : 2.8 ± 0.2 SiO2 : xH2O
Description The sodium form represents the basicstructure of the type X family, with an effective pore opening in the 910¼ range. Will not
adsorb(C4F9)3N, for example.
Major Applications Commercial gas drying, air plantfeed purification (simultaneous H2O and CO2 removal) and liquid hydrocarbon/natural gas sweetening
(H2S and mercaptan removal).
Hope this helps, sorry if its somewhere else here.
so if Im using 4a molecular sieves, anything larger than 4.0 will not be absorbed, right? I can use sieves to remove water from anything above 4.0,
including toluene.
[Edited on 6-4-2006 by greenyppols]
This is the best thread I found for this
BromicAcid - 10-5-2006 at 18:34
http://news.uns.purdue.edu/UNS/html3month/820611.Ladisch.cor...
"Corn Grits Spark Money-Saving, Octane-Boosting Idea At Purdue"
It's an older news article revolving around using corn grits to remove the last of the water from azeotropic ethanol. Supposedly there is a patent
involved and the process was widely implemented. I have to wonder how simple it would be for the home chemist to pull it off. Strange that this is
the first I've heard of it.
More info:
http://journeytoforever.org/biofuel_library/ethanol_grits.ht...
[Edited on 5/11/2006 by BromicAcid]
Nixie - 25-12-2006 at 01:00
That article talks about drying vapors with the grits. I read elsewhere that it's possible to dry it while liquid. Has anyone here tried that? How
would I prepare the grits? Wash them of dust and heat them in the oven at __ degrees?
Sauron - 25-12-2006 at 06:19
As you know some reactions just don't go well with any water around. The Grignard. Even more so lithiation. The Claisen. Acetoacetic ester reactions.
Aldol condensations. etc etc. The basics of procedures to dry the solvents are to be found in Vogel, Gatterman, etc., with more contemporary mods and
variations in Org.Syn. usually in the Notes section. You will often want to bake out your glassware in a drying oven overnight before working. Use a
freshly opened bottle of absolute alcohol, distill it over sodium directly into rxn flask. Using a freshly opened container of ether or THF reduces
peroxide hazards; if in doubt peroxides are destroyed with base. Distilling from a little Na is a good idea, again directly into your predried,
flamed-out flask. THF is particularly prone to peroxide formation (more so than Et2O). The worst ether I can think of from this standpoint is
di-2-propyl ether. Formy peroxides in a NY minute.
Once again a thorough review of the classics like Vogel and then updating with Org.Syn. is a must. Org.Syn. has several warnings regarding hazards in
the purification of THF. Just as an example.
Molecular sieves are better for storing already dried solvents over than they are at removing gross contamination with water.
DMF is a nightmare to dry as it is always breaking down and forming water in the process. So it is a good one to store over zeolites (molecular
sieves.)
Nixie - 25-12-2006 at 16:05
Well, the corn grit sieve is used to dry ethanol for fuel uses, and the source does have gross contamination with water -- at least several percent.
You didn't really answer my question. It was whether the grits are useful for drying liquid ethanol; the article only mentioned its use for drying
ethanol vapors.
Fleaker - 25-12-2006 at 20:01
"Use a freshly opened bottle of absolute alcohol, distill it over sodium directly into rxn flask. "
You mean sodium sulfate, not sodium metal? Sodium metal will react with ethanol (albeit not that quickly).
Nixie - 25-12-2006 at 20:33
I came across copper sulfate used to dry ethanol, but the problem is it would have to be distilled afterwards as the CuSO4 is slightly soluble in the
ethanol.
I wonder if anything in the corn grits is soluble in ethanol. Or perhaps they can be prewashed with hot ethanol to remove soluble contents, and then
oven-dried.
[Edited on 26-12-2006 by Nixie]