Best desiccating agent

[rooster]

What is the best OTC desiccating agent around? I do not think of P2O5 as OTC(if it is, enlighten me).

Im believe these are some of the most important points of the "best" desiccating agent:

1: Has to suck up water pretty fast.

2: Has to be able to suck up a lot of water.

3: Short time of dehydrating (for re-use), f.ex. in an oven.

4: That it is a solid (or a liquid).

5: Not too reactive (should not react with the products you are trying to dry).

There are probably also many more...

Any suggestions?

[Arthis]

P2O5 is a common fertilizer, at least in France. I remember having seen 5 kg bags at the garden store, while looking for what they had (especially salpeter they happened to have (25 kg only, jeez !, it takes place near my bed) ). It may (probably) not be pure, I think a few 1% of shit coming with. Not too bad though.

Good dessicants usually suck up a lot of water, pretty fastly, but may not always be re-used.

CaO is often used, and pretty common. Anyway, you can go to your local homestore, and they have some. It may not be a pure compound, but in your case you just want a efficient dessicant.
It is used in climatization I think. Anyway it exists but is often a little expensive: 20$ for a kg. -> If you use a lot it will happen to be annoying.

In all case, the dessicant must not be in contact with the stuff dessicated. As an example you can put a beaker in a bath of CaO, in an airtight container (to avoid moisture from air ).

[Nihilist]

Ammonium nitrate is a good dessicant, though I don't know how it compares to the others. Also "Silica gel" packets come in beef jerky and other dry products, but I don't know exactly what "silica gel" is.

[kingspaz]

silica gel is an amorphous form of silicon dioxide. it can be easily reused and is unreactive. all you need to do is cook the moisture off and its ready to go again. i believe it works by trapping water molecules in its structure rather than reacting like CaO would.

[irish]

I find Silica gel the easyst one to use, no mess nonreactive and free I've been saving it for ten years so I've got a lot :D .
I also use copper sulfate, dry it at 200 c in an oven until it turns from blue to green/brown.

[vurr]

good stuff,easily refreshable:1kW microwave,~5minutes& 120g bag of granules->100g bag.+20g of steam...
P2O5 in fertilizer bags!!!: formula for calculations only!!!. never free phosphor oxide,(mostly ~calcium phosphate).exept when there is lake of H3PO4 around it :)

[Arthis]

I don't understand, are you saying that P2O5 never comes pure ? What's the link then with free phoshorus oxyde ? P2O5 is pentoxyde

[rooster]

What about sulfuric acid? Is it too reactive to take away water from, say, organic liquids? It is very easy to dehydrate again, so its good that way. How much water is it able to suck up?

Another thing I've been wondering about is the need of vacuum. Is it really necessay, or does it just speed up the process?

[knowledgehungry]

I havent used dessicants really but when i heat my copper sulfate i heat it till it is white. Also i think vacuum gets rid of moisture in the air allowing you to use less dessicant,not sure though.

EDIT: I'm a researcher now!:cool:

[Sparky]

I have used calcium chloride as a dessicant. It is handy because it comes from the store (for melting ice) ready to use.

Sulfuric acid is a good dessicant. In a normal dessicator setup the fact that sulfuric acid is reactive doesn't really matter since the chemicals never come into contact. All the sulfuric acid does is dry out the air inside the dessicator. Personally I wouldn't say it's very easy to dehydrate again at least not to high concentration but I suppose that's not really needed. Concentration certainly simple but boiling sulfuric is not something that is pleasant to do/be around and it tends to break it's container IMHE. My question is what will dry out sulfuric acid, since I would like to try concentrating it without boiling it if possible.

Arthis, the label on the fertilizer bag may say it contains P205 but that's just a way to represent how much phosphorous it has. Just like if the potassium nitrate says it has 46% K20 in it, that doesn't mean that there is actually any K20 in there. It's kind of confusing and arcane, and every once in a while people post about it on rec.pyrotechnics. Here is an example of someone explaining it:
http://www.google.ca/groups?q=fertilizer+k20+group:rec.pyrotechnics&hl=en&lr=&ie=UTF-8&oe=UTF-8&safe=off&selm=388b2cd9.77325469%40news.toast.net&rnum=3

Magnesium sulphate is very cheap and handy but I have read that it is relatively difficult to dry out, that is it takes a long time in the oven.

[kingspaz]

knowledgehungry, 'Also i think vacuum gets rid of moisture in the air allowing you to use less dessicant,not sure though.'

a vacuum is a lowering of pressure. pressure is what keeps liquids liquid. without it they would be a gas. so, if you lower the pressure you lower the liquids boiling point so increase its rate of evapouration at a given temperature.

[frogfot]

What about ZnCl2? I made some and couldnt dehydrate it at 300*C for several hours, though solid formed in most of baker. CaCl2 couldnt dry it eather. On standing outside volume increased pretty fast..

Oh, some data on dehydrators from a book:
Dehydrator | Resting humidity of air mg/l
CaCl2 0,34
H2SO4 (95%) 0,3
CaO 0,20
NaOH 0,15
B2O3 0,14
MgO 0,008
H2SO4 (100%) 0,0027-0,003
Mg(ClO4)*3H2O 0,002
KOH 0,0018-0,002
Mg(ClO4)2 5E-4
Silicagel 3E-4
BaO 8,5E-5
P2O5 1E-5 - 2E-5
Trap with liquid air (?) 16E-23

Maby one can dehydrate H2SO4 without boiling, with, say.. KOH (longshot..) or even throwing some silicagel into dilute H2SO4?

[Arthis]

That wouldn't be suitable for more than a few mL. Even if silicagel is efficient, how would you concentrate 1L H2SO4 ? Unless you make your explosives gm by gm ;)

Forget about KOH, they have too close efficiency to make its use really interesting.

Anyway, diluted sulfuric acid is not a problem to concentrate to 90%. After it becomes more hazardous. But we try to be chemists, aren't we ? If one cannot concentrate sulfuric acid, when is he going to make some explosives ?

[knowledgehungry]

KOH is a strong base H2SO4 is a strong Acid the reaction you get is thus, H2SO4(aq)+2 KOH--> 2H2O+K2SO4.In no way will it dehydrate unless you were talking about using KOH as a dessicant. If you meant that sorry.

[frogfot]

But what if one fills a 15l bucket to 1/4 with silicagel, places 3l ~80% sulfuric in a glass jar and closes bucket airtight. Leaving this for couple of months :) Silicagel is about 1000 times better at dehydrating than 95% sulfuric (the final goal)
The 80% sulfuric can be probably ubtained by dehydrating 30% in oven without any evul SOx and further dangers..

Do anyone knows whats this "trap with liquid air" is? It wasn't described in book..

EDIT: sure i meant KOH as dessicant :) Btw, i just thoat that silicagel in acid would connect acid as effectively as water.. cause its thicker

[Tuatara]

A 'trap with liquid air' is merely a cold trap. liquid air at 77K will freeze or condense out any vapours present in the gas you are trying to dry. Most commonly used in high vacuum systems to prevent oil backflow from diffusion pumps.

[Chade]

I just use CaCl2, as it's a great dehydrator, and easy as hell to get hold of. Those chemical room dehydrators are just trays with bags of calcium chloride in. You can even get refills, which are just bags of calcium chloride. Easier and cheaper to get in bulk than slica gel and conc sulphuric acid. It's deliquescent too, which means it'll keep sucking water out of the air, until you end up with a tray of calcium chloride solution. When I first started using it, I left some out on a desk. It sucked up moisture from the air and made itself into calcium chloride solution, which, by the time I got back to it, had drained off, all over the floor.

[blindreeper]

Calcium chloride (http://www.geocities.com/blindreeper_chemistry/Calcium_Chloride.jpg) (copy and paste into browser)

Thats the Australian brand of Calcium Chloride. I have seen others, this particular one doesn't list that CaCl2 is an accual ingredient but it's snow white pellets and they turn out brick red with a flame test :)

[FlaAlchemist]

Anhydrous Magnesium sulfate is the best OTC drying agent for the home lab.

Purchase some Epsom Salt (magnesium sulfate heptahydrate) then dry it in a oven @ 140'C
for a few hours. Cool and store in a air tight container.

Another OTC Drying agent is Damp Rid. It is anhydrous Calcium Chloride..
Transfer it to a air tight container since the cardboard box its in is crap once it is opened.

I mostly use the homemade anhydrous magnesium sulfate for my experiments.
Seems to work great , can even dry Diethyl ether for grignard reagent.

[ChemHacker]

Originally posted by frogfot
What about ZnCl2? I made some and couldnt dehydrate it at 300*C for several hours . . .
Hydrated ZnCl2 hydrolyses in its own water of crystallization forming a basic zinc chloride and HCl and finally zinc oxide and more HCl when strongly heated. (IIRC)

[vulture]

Anhydrous Magnesium sulfate is the best OTC drying agent for the home lab.


Not really, MgSO4 takes much longer to absorb moisture than CaCl2. Also, recycling MgSO4 often passivates it.

[CommonScientist]

Cynmar Corp. sells Calcium Sulfate , although you cant really get it OTC, it is a very powerful dessicating agent. 8 mesh granules ; 500g : $9.95. Their website is www.cynmar.com

[vulture]

Trouble is that CaSO4 has a rather low drying capacity, although it does dry stuff quickly.

[CommonScientist]

I dont have any experience with it though. I am using my basement's dehumidifier to remove water from bleach so I can get relativly pure sodium hypochlorite, and it is working very good. although it is slow, it is the only resource that I have to remove the water. Im sure my mom wouldnt want me boiling bleach and making the house smell like chlorine.

[Mumble]

Boiling bleach would also thermally decompose the hypochlorite. It might not go to completion, but I doubt you'd be left with any sort of a pure product.

[CommonScientist]

I am pouring 10mL of 6% sodium hypochlorite bleach solution into a watch glass, then setting it in front of my dehumidifier. I let it sit for about 12 hours or more until crystals form on the watch glass. I then scrape them up and put them into a container for further use. But with my lacking knowledge, I do not know what to use the crystals for , I did a flammability test and they just poped and smoked a little bit. Does anyone have a use for them? I would appreciate further enlightenment.

[vulture]

One acronym for you:

UTFSE!!!!

This has been covered millions of times.

[CommonScientist]

What I ment was : can I use the chem as it is for use in pyro? I didnt think I could.

[tmp]

I like plain old rock salt because it's cheap and easy to dry. I use it
to make anhydrous ethanol. It won't dissolve but sucks up the water
in the mix. It'll also dry out in sunlight.

CommonScientist, sodium hypochlorite doesn't exist in solid form -
aqueous solutions only. If you dry it out you could have 3 different
compounds in there: NaCl, NaClO3, NaOH

If you boil it dry, the sodium hypochlorite will thermally decompose
into NaCl and NaClO3.

3NaClO --> NaClO3 + 2 NaCl

To anybody: If my equation is wrong, please feel free to correct.

[CommonScientist]

Thank you TMP for correcting me, I appreciate it.
I have never used rock salt before, does it suck up the water relativly fast?

[tmp]

In all honesty, I've never compared absorption rates for any compound.
Some work better than others to be sure. It would also depend on what
you're trying to absorb the water from. For example, I wouldn't dry
ammonia gas with compounds of copper because ammonia would bond
to the copper atom as tetramine. There's probably very little that could
draw water out of sulphuric acid because it reacts with many compounds.

The best advice is to use the search engine or google to find the
information you're looking for.