HNO3 your way

[Swede]

How can you tell if the glass will handle vacuum or not?

 

I got this parts from a friend and I want to distill some HNO3 under vacuum.

 

http://img179.imageshack.us/img179/6088/bild007rd6.jpg

 

Do you think it will handle it or brake?

 

Very grateful for any help!

Dear Christian

 

They APPEAR to be quality glassware components. Can you try a run with water or some material other than acid(s), even though the temps will be different? At leat it would give you a bit of an idea.

[tentacles]

I would definitely recommend a "dry run" with water before you attempt to distill nitric in that. It looks like a fairly standard set of 24/40 glassware, it ought to handle the vacuum fine, but do a test run and make sure it will - there could be flaws in the glass or something.. Last thing you want is for a joint to come off during the distillation!

[Swede]

Tentacles, what temp differences are we talking about when doing a water run vs HNO3? Is there a safer material that would more closely resemble the actual process?

[Boomer]

You can separate those, first try a heating test, and then evacuate while FULL of water at room temp. If it fails there is not implosion risk.

 

And use only round bottom flasks with vacuum. Remember on a 4x4 inch bottom there's 220 pounds of air pressure, no matter what pump (crappy fridge compressors still reach 210).

 

Why the hassle? Using AN+ excess sulfuric, and going s l o w l y (2 drops/sec for a liter flask with 500g AN + 600ml SA), discarding the first and last 10% (that contain by far most of the NOx), plus some careful purging, gives 97-98% without vacuum. A 74-82% RDX yield says it all.

[tentacles]

Swede: The temp differences won't be all that great under vacuum, but you do in fact want to run a test like boomer recommends - basically a hydrostat test, but with vacuum instead of pressure.

 

Boomer: Are you suggesting to drip the sulfuric on top of the AN or something? I'm not getting the picture here. I mix the nitrate salt and the sulfuric as best I can quickly, and then use a water bath and my hotplate to heat the RBF.

 

Vacuum does speed up the process CONSIDERABLY, as well as increasing efficiency.. Less NOx created per volume of HNO3 distilled. What I do is start with cold nitrate/sulfuric/water and then apply vacuum slowly, as the initial reaction will be somewhat vigorous. I've toyed with distilling at atmospheric pressure, and quite frankly it sucks. I can distill 300-500ml of 98% HNO3 in like 4 hours with vacuum. How long does it take you without?

[superman1451]

Tentacles: How are you creating your vacuum?

[tentacles]

superman:

 

crazy: A vacuum aspirator, I bought a cheap LDPE (might actualy be PP) one from ebay a while back.. There's info on it in this thread somewhere, I had to fabricate a nozzle for it, though. You can find them on ebay for cheap. I made a faucet adaptor for mine as well, but that's because I wasn't willing to spend Home Depot kind of money on one. I've only measured up to about 28" of vacuum through it, but that's certainly good enough. I haven't even bothered drying my H2SO4 or nitrate first, and the last batch came out about 99%. Granted, I did do it in the winter, and it's so dry up here that everything is dessicated just by the air. Anhydrous copper sulfate? Just put it on the counter for a week and you'll have those nice white crystals.

[superman1451]

whoops forgot about that. For some reason I couldn't pull a vacuum with my metal aspirator. I hooked it up to a water hose and held the aspirator every which way but still no vacuum. Any suggestion?

[tentacles]

Is there a nozzle of some kind in the aspirator? What you want is a small stream/jet of water coming out right next to the vacuum inlet of the body - on my plastic one I had to fabricate a nozzle on my lathe - it didn't work for crap stock. I don't know if mine was missing the nozzle or what. I tried several different nozzle sizes and settled on one that provided good vacuum without blasting away 2-3 GPM. I think the one on there requires like 1 GPM, which is still a considerable amount of water.

 

I want to say the nozzle I ended up with was like .062" or 1/16", but I can't remember for certain. A good source of aspirators is those waterbed drain and fill kits, or at pet stores for "gravel vacs". Should run between 10 and 20, and they pull a pretty good vacuum. Their design may permit modification of the nozzle (heat and reshape or plug with hot glue and drill/carve with a hot wire) so that you can modify the water usage. You could probably try the hot glue thing on your metal aspirator, but be sure to get the metal good and hot before applying the glue (unless there's a ridge in there to stop it from being shot out) so that the glue sticks to the metal.

 

You could viably reheat and reglue the nozzle as much as you wanted with the hot glue method - hopefully there's some sort of ridge for you to work with to keep it in place.

Edited December 16, 2008 by tentacles

[Aristocles]

My way of distilling HNO3

 

Glass:

 

2000ml RBF

Ace Glass Thermometer Adapter

300mm Pyrex West Condenser

1000ml Pyrex RBF

(All joints are 24/40 ground glass and are 'sealed' with a thin layer of vaseline, then taped heavily with Teflon tape)

 

Heat:

Single burner hotplate

 

Dispersion/Control of Temp:

Aluminum Pan filled ~2/3 with cooking oil into which the 2000ml RBF is suspended just slightly from the bottom

Salt/Ice bath for the 1000ml RBF

 

Siphon Setup:

H20 container above and below the apparatus, above goes to the water in valve on condenser and below goes to the out valve

 

Vacuum:

Mityvac Pump with a TNF between it and the apparatus... it pulls between 26 and 28 if one is willing to pump it once in a while

 

I work out the amount of reactants via Stoichiometry.

 

All in all, I have found it best to keep the temp down as much as possible (not too low) while keeping the vacuum at close to 28.

 

As for a slight yellow look, I have found Urea/bubbling air through works well.

Edited December 23, 2008 by Aristocles

[Steps]

I guess i must be lucky my mate got me a tub of Fuming white nitric with no questions asked. Wish Perc was this easy