Drying hygroscopic chemicals

[Smoakie]

Not sure where to put this so I'll put it here so I don't get in trouble.

I was curious about the best way to dry out hygroscopic chemicals.

I live in a very humid climate and my ammonium nitrate can absorb enough water in a day to turn into a puddle if left open to the atmosphere.

I can lay it in the sun on a hot day and it will dry out and look dry but when put into a container will turn hard, which I interpret as still having a fair amount of water.

I would rather not put it in my oven for safety reasons. While I'm sure it would be fine and not get too hot, I do not like the idea of chemicals in the same place as my food.

I have a 5 lb bag of silica gel. Would the silica gel pull the water out if both chems were seperated and put into a closed container? Or would they reach an equilibrium? Or would the AN pull the water out of the silica gel? I took some basic chemistry classes but nothing was ever mentioned about the affinity of water and such.

I guess I can go down to goodwill and get a cheap toaster oven but the cycling of the thermostat can cause some pretty drastic temperature spikes.

Just curious what others think.

Thanks

[Diabolique]

AN prill is manufactured by spraying hot, saturated AN solution at the top of a shot tower, and forcing hot, dry air into the bottom in a counter-flow. Not practicle for us.

The explosives labs, where they make nukes and design new weapons, they dry materials by warming them in a vacuum chamber. If you have a vacuum pump (or compressor that can be used as one), you might try vacuum drying.

You may try waming the AN in an oven (don't melt it) with a tray of silica gel or heat-dried calcium sulfate (plaster of Paris). It may or may not work.

If the AN has fused from water absorption, you will have to pulverize it first. That can be a task, as rock-hard is a good description.

It may be worth the money to purchase a surplus, steel, air tight, ammunition box to store the anhydrous AN in (add a silica gel pack for insurance). Put the AN in a plastic bag to prevent any interaction with the paint on the box.

The fertilizer codes are:
AN - 34-0-0
Ammonium Sulfate - Urea - 33.5-0-0
Urea - 46-0-0

[Sausagemit]

You should probabbly get some anhydrous magnesium sulfate or you could get some magnesium sulfate heptahydrate (epsom salt) and dry it out your self. It absorbs so much more water than silica gel it's freakin crazy.

Put some of that stuff in an airtight container with your AN and it will keep it super dry.

As for drying it out, You could get a heat gun (http://www.mpja.com/productview.asp?product=15857+TL). They acctually work fairly well for drying hydroscopic chemicals out in a hurry because they apply heat and moving air. They just don't work well for large amounts of chemicals because you can only apply so much heat to a specific spot at one time.

And you are present and have to be there for the whole process. And AN will start smoking long before it combusts so you won't really have to worry about AN exploding in your face.

I would try a heat gun before I put it in my oven that I cook my food in. That's what I use for everything except those highly temperature sensitive materials where drying it out is dangerously close to combustion. I have not used a heat gun on AN though as I have never made an AN based explosive.

[bipolar]

One thing about the use of silica gel, epsom salt, or other dessicants, is that they must be activated by heating in the oven for a long time to remove all the moisture from them.

In my opinion, that would be the best bet to remove all the moisture. Seal in an air tight container with the chemicals to be dried, but seperate.

It will achieve equillibium, which will significantly dry the chemical out. How much it dries out depends on the ratio of dessicant to material.

If you use dessicant frequently, you may want to purchase specialty resusable dessicant rocks that changes color depending on how much water has been absorbed. If I remember right, they also have shorter reactivation times.

[nbk2000]

Use the fucking oven, for God's sake, and keep it simple.

Spread it out in a clean glass casserole pan, or steel cookie sheet, with another sheet or aluminum foil between it and the heating elements.

Set the oven for 300 degrees F, and open it up and give it a quick raking (be quick!) with a spatula every 1/2 hour to break up clumps.

When it stops steaming, it's done. It might turn tan, but that's OK.

[megalomania]

I use a lot of Dririte in the lab; the color changing variety. You just shovel a scoop into the oven and let it dry for an hour just as nbk said. There is not much too it. The color changing product is used in sealed glove boxes and desiccant chambers so it can be observed at a glance when it is time to replace.

Don’t use a heat gun for anything critical unless you really know what you are doing. It is a lot harder than it looks to keep something from burning. Hold it a bit too close for a few seconds too long and you burn what you are heating. It takes practice to use a heat gun in the lab.

[Sausagemit]

It takes practice to use a heat gun in the lab.

Or just practice stripping paint or bending giant 1/2" thick sheets of acrylic with a heat gun. And I do have a lot of experience with that.

But your right, if you don't have any experience with a heat gun you can burn stuff easily. But once you get it figured out you can maintain a constant temp and moving air very efficiently with a heat gun.

[Diabolique]

For me, oven = microwave. That may not be wise to use for dehydrating.

Others may have the same problem. Will a toaster oven work?

[Lewis]

It seems like a microwave might be a fairly good option, if the power level was low enough. Seeing as the microwave only heats the water molecules, and not other substances.

Am I completley out to lunch on this one?

[nbk2000]

Toaster oven would work for non-combustible materials.

I wouldn't use it for something like AN, though, because the heating element is so close to where the pan would be, that radiant heat could cause localized overheating of the material, leading to an 'undesireable' event. ;)

[Diabolique]

The problem with a microwave is that there is no way to read the temperature of the material you are heating while you are heating it, just like the toaster oven.

You're right, nbk, a miniature recreation of the Texas City disaster (1949) in one's kitchen wouldn't be fun. Do you think an asbestos paper shield between the heating elements and material would help make this safer?

[nbk2000]

As long as there's a barrier between the tray and the radiant heating elements, than it should be OK.

In fact, you could simply fill the bottom of the toaster oven with fine dry sand, covering the elements. Then your toaster oven becomes an air bath. :)

[megalomania]

There is a way to determine the temperature of a material being microwaved, which they do in laboratory experiments. I believe the technique is infrared thermographic analysis. Of course that might be expensive. I have run across the technique being used to evaluate microwave catalytic hydrogenations to monitor metallic catalyst hot-spots.

An exposed element for this sort of heating of a potentially explosive compound is bad. There are always plenty of auctions around the Internet for small lab ovens that can more precisely maintain a temperature of 100-110 degrees C. That is the only temperature range you need. You are more than likely to decompose ammonium nitrate into nitrous oxide by overheating it, but who would want to take the chance?

[nitram3000]

I have tried using a toaster oven to dry my AN. It started out white, then I came back an hour later(by the way I was drying at 90 degrees C). The AN has slightly brown and black. Also it seemed more wet than before the drying process. I then turned up the temperature to 120 degrees C. I came back a half hour later and it was even browner and it was steaming a lot. It still seemed very damp. I turned the temperature back down to 190 degrees C. There is about 300 grams of AN in the oven on a metal pan laying uncovered. Has any one experienced this problem? I thought that it should only take an hour to dry the AN. For 300 grams, I suppose a heat gun would work better. Any opinions?

[megalomania]

Unless you are using a reagent grade ammonium nitrate, there is probably some sort of impurity causing the brown color. You may have to heat a large quantity of material for several hours, or even overnight to get rid of all the moisture. You must also keep the heat above 100 degrees C for drying to be effective. About 110 degrees C works fine, no need to go higher because then you run into trouble. Also, make sure whatever material you are drying can handle sustained temperatures of 100 C...

A heat gun is very tricky unless you are experienced with it. It causes hot spots that can easily lead to burning and decomposition of chemicals. Unless your heat gun only puts out 110 C air, it may be too much.

A toaster oven also may not be the best thing for heating chemicals. The close proximity of the heating element can easily cause hot spots directly beneath or above them. Not to mention the possibility of fumes that close to the element could be a fire or explosion hazard. Toaster ovens are not exactly built to the same standards as real convection ovens, but even those are not exactly well suited to chemical drying. The temperature calibration of a toaster oven leaves a lot to be desired. They may be off by 25-50 degrees or more depending on the make, model, age, and condition.

You really can't beat an actual lab oven for this sort of thing. Notice real lab oven do not have exposed elements, and they have a thermometer port for accurate temperature regulation.

[Evolutionist]

I treated filter paper with a colbalt chloride solution (which turns blue in the absence of humidity and pink in humid conditions) and I put a strip in the container that I use as a dessicator so I know when to change the dessicant.

[c4goesbang]

I have been wondering if a food dehydrator would work. I have a large one, about the size of a microwave oven.

I will try it and post the results.

[nitram3000]

I actually continued using the toaster oven to dry my AN and it dried the AN enough to make APAN. It was very brown, but the AN provided a very good detonation. (there was almost no smoke after the blast, which I assume is a good thing). I just had to grind the AN again cause it hardened and stuck to the pan. I conclude that toaster ovens are usable, but the AN must be observed carefully.