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stanfield
December 24th, 2002, 12:46 PM
I don't know if someone got this problem before but I guess 'cause it bugs myself each time I distill my HNO3 !

So, whatever the method I choose (nitrate+sulfuric or low concentrated HNO3+sulfuric), before the end of the distillation, there are always lot of red fumes in my boiling flask and no more HNO3 comes into the receiver flask ! In other words, I maybe loose 100 or 200 more mL of HNO3 !!! and I cannot accept that !

I think a vacuum pump could solve the "problem" but it's a bit expensive and I have another project...

what could I do ? heat the flask harder ? it's a bad idea...

see ya !

<small>[ December 24, 2002, 11:47 AM: Message edited by: stanfield ]</small>

nbk2000
December 24th, 2002, 01:48 PM
Less heat, more patience.

vulture
December 24th, 2002, 03:04 PM
Vacuum aspirator, just uses alot of water but works well.
Very cheap also.

stanfield
December 24th, 2002, 05:50 PM
"Less heat, more patience", hehehehe... The other problem is I have a 5L boiling flask ! so, at the end of the reaction, I already heated 6 or 7 hours the boiling flask, I'm not gonna wait for another 5 hours to complete !

yeah, the only solution is a vacuum. As you said, vacuum aspirator uses lot of water and "electric" pump is expensive... that's not easy !

But I'm lucky, I wanna bought the 10L boiling flask ! imagine : 10 or 12 hours for a complete distillation !

thanx !

ALENGOSVIG1
December 24th, 2002, 06:20 PM
If youre distilling a small amount (1/3 full flask) in a 5 or 10L flask, then theres gonna be lots of refluxing on the walls of the flask. Unless your using a nice heating mantle or you fully immerse the flask ofcourse. Mabe this is why your distillations are taking so long. Perhaps you should use some insulation around the flask etc if thats the problem. Oh, and why dont you just use a refrigerator compressor for vacuum? You could get one for free most likely.

stanfield
December 24th, 2002, 07:22 PM
refrigerator compressor for vacuum ?

this is for "freezer", right ? if no, what's it ?
where could it be found ? because I think this is going to be hard to find this one...

thanx !

EDIT : but, you're right, most of the time, I don't fill the boiling flask until the bottom (correct english?), so, there is a "reflux" effect...

<small>[ December 24, 2002, 06:27 PM: Message edited by: stanfield ]</small>

kingspaz
December 24th, 2002, 07:52 PM
stanfield, just go down to the dump and rip one off the back of a refrigerator with a crow bar or somthing. or even if there is some waste land people use to dump stuff on there will be one lying round there to exploit.

photonic
December 24th, 2002, 11:28 PM
I recently tried to use a refrigerator pump to pump water and it shorted. Is there anyway to prevent this from happening? Also, how do you keep the fumes out of the pump? I remember something about dropping the line into water but this seems like it would suck water into my vacuum pump and short it again.
Thanks.

nbk2000
December 25th, 2002, 12:43 AM
You're not going to be using a fridge compressor for pumping water.

A refrigerator COMPRESSOR isn't intended to pump fluids like water. It's purpose is to take freon GAS, and COMPRESS it till it liquifies. Freon is non-conductive, unlike water.

<small>[ December 24, 2002, 11:44 PM: Message edited by: nbk2000 ]</small>

megalomania
December 25th, 2002, 04:27 AM
I think there is probably plenty of information about using a fridge compresser over at The Hive if I am not mistaken. Perhaps Rhodium's site as well.

rikkitikkitavi
December 25th, 2002, 05:45 AM
if you use a frige/freezer compressor as a vacuum pump it will pump HNO3 vapour and it is definiately not made for such a corrosive media.
Problem is that any HNO3 will condense at the pressure side and the compression heats the gas being compressed , giving a very warm high-conc HNO3.

Before the pump you need a cold trap (LN2 filled) to fully condense any HNO3 or a stack of free compressors to replace the ones that gets corroded away.

but since they most likely are free from the junkyard it can be worth a try..easiy to replace and a lot safer handling than LN2. experience will show how long they last.

I have a slight memory of this being covered in old topics?
/rickard

<small>[ December 25, 2002, 04:54 AM: Message edited by: rikkitikkitavi ]</small>

BrAiNFeVeR
December 25th, 2002, 07:09 AM
Not only is it made to pump a non-corrosive gas, it also relies on the cold gas to cool the copper windings in it's engine !!

So it won't last long anyway if you'd just pump normal air with it.

How can you maximise the useful life of this compressor:
-filter out the corrosive gasses (bubble it up through water)
-cool the air it sucks up in some way (use ice water in the above step ?)
-make sure there is no water coming into the pump (lead the vapor over some dessicant)

Basicly the only things that can enter ANY compressor is oil vapor (final oil bath ?) and dry cool air.

lucifer
December 25th, 2002, 08:24 AM
I also did use a freezer compressor but after it sucked up some water from the wash bottle it got shorted.

A freezer compressor also isn't designed to continue to run for hours and it did get very hot.

Now I use a vacuum aspirator connected to a pump and a big can of water, where the water is recycled.

This way I don't use any water (except for filling the can once) and water is quite expensive.

The drawback is, I can only create vacuum to 200mBar (or look for a pump with a higher pressure). But it works fine enough for me.

<small>[ December 25, 2002, 09:08 AM: Message edited by: nbk2000 ]</small>

nbk2000
December 25th, 2002, 10:12 AM
Since the compressor is being used to create a vacuum, you need to keep the nitric vapor from getting in it.

The easiest way to do this would be a scrubber tower. First the nitric fumes (after passing through the condenser into the receiving flask) are bubbled through water to get it wet.

These wet fumes are then passed over hydroxide pellets. This absorbs the water, and reacts with the nitric to form a solution of nitrate in water. This remains in the tower. As the gases continue up the tower, they are dried by the unreacted hydroxide, till finally the (now) dry and non-corrosive air gets exhausted.

rikkitikkitavi
December 25th, 2002, 07:51 PM
stanfield, have you tried to insulate the flask? I had similar troubles, but I couldnt get any HNO3 at all until I heated so hard that I had severe decomposition. Insulation took down heat loss and more came over at lower temperature.

the major problem with a compressor is that pressure can get very low, so low that the condensation point of HNO3 gets below what you can cool, which of course depends on your water temperature.

the lower the temperature difference between boiling point-cooling water the slower you must perform your distillation so that the condenser has enough capacity to fully condense all HNO3.

Thus you need some sort of pressure reglutation( a small bleeder for air into the system) . I m not sure , but I would guess that the boiling point of HNO3 is so low at 0,2 atm that it can be distilled witout much decomposition.

If you have a scrubber system, it will not wash out much HNO3 at low pressures, since the efficency of these suffers greatly from reduced pressure. It will probably have to be very tall too, increasing contacting surface to compensate for less molecules in the gas phase at low pressures.
Using a chemical absorbent like sodium hydroxide is much more efficient under this conditions.

Remember that water also has a vapour pressure, it will slowly evaporate too!

At proffesional labs cold traps filled with LN2 (for components &lt; boiling point 100C ) or dry ice is the only option to protect the very expensive vacuum pumps. I have never seen any other method used in vacuum distillation.

stanfield
December 26th, 2002, 06:53 PM
don't worry, when I will buy and use my vacuum, I will put an "erlenmeyer trap" with saturated solution of sodium carbonate to avoid injuries in the pump...

They are "all teflon" type vacuum... but a bit expensive :)

ALENGOSVIG1
December 27th, 2002, 04:01 PM
I wouldnt use an erlenmeyer flask. Most cant take high vacuum. Some can, but most wont. Be sure to house the flask in a wooden box or something for protection incase it implodes.

stanfield
December 27th, 2002, 05:38 PM
they are special erlenmeyer flask designed especially for vacuum ! :)
I will buy one when ready...

zylion
January 13th, 2003, 08:08 AM
Vacuum distilling with a aspirator and a jetpump/reservoir setup works very well for me, but keep in mind that the water needs to be cold to get the highest vacuum. Also the vacuum hose should be as short as can be. I always throw a bag with icecubes into the reservoir to keep it very cold.
In order to prevent the breakdown of the nitric acid I collect the nitric acid into a flask wich is supercooled with a mixture of dry-ice and rubbing alcohol. The nitic acid will freeze into the collecting flask. Nitric acid contracts on freezing, there is no danger of breaking the flask. Store the nitric acid in the freezer and in the dark.(still wondering if the light in the freezer goes off when I close the door. :D <img border="0" title="" alt="[Wink]" src="wink.gif" /> )

stanfield
January 13th, 2003, 03:13 PM
ok thanx for the tips !
Furthermore, I have won 500€ in some hazard games, wonderful, no ? so, shortly, I will buy a vacuum... I just need to choose one because it's not an easy task (lot of models!)

bye!

megalomania
January 13th, 2003, 11:53 PM
Ooh, I just threw away my latest issue of American Laboratory which had an article about picking a vacuum pump for the lab.

nbk2000
January 14th, 2003, 01:36 AM
I saw at least three vacuum pumps small enough to to fit in a small duffel bag while I was visiting a friend (non-pyro related) at the hospital today. Not bolted down or anything, just sitting there.

The one I hefted weighed about 15-20 pounds and had a gauge and everything. :) Didn't snag any, but it'd have been easy if that's what I wanted to do.

Eliteforum
January 14th, 2003, 06:26 AM
What's this nbk? You? Friends? I smell a RTPB violation here!

nbk2000
January 14th, 2003, 07:04 AM
Stuff it up your ass 'cause I'm not interested in hearing your shit.

Flake2m
January 15th, 2003, 01:55 AM
@ Eliteforum:
Their is no RTBP that says you can't have friends. I also know that when you are hospital and you feel like shit because of the drugs they put you on. That their is nothing more comforting (other then being told you can leave :) ) then friends/family coming around to visit you. So Eliteforum go to HED hell if you you are going to piss of the velox Mortifer.

I think their might be a way to create a vacuum without needing a vacuum pump. I dont know if this would work though:
You will need 2 flasks and a heat source aswell as some tubing a valve.

In flask 1 you have your nitrate/H<sub>2</sub>SO<sub>4</sub> or HNO<sub>3</sub> + H<sub>2</sub>SO<sub>4</sub> mix.
Flask 2 contains some water for the gases to disolve into.

Flask 1 is conected to flask 2 with tubing. Flask 2 also contains a valve that is connected to the tubing, flask 2 and the outside air.

You heat up flask 2 with valve open to the outside air. The idea is that you are trying to create a lower pressure in the flask. Once you have lowered the pressure enough, the valve is closed and flask to is cooled. Flask 1 now has the gasses in it. You then open the valve to flask 1 and because of the difference in air pressure, the gasses should go into flask 2.

BASF
January 15th, 2003, 02:27 PM
Stanfield

"So, whatever the method I choose (nitrate+sulfuric or low concentrated HNO3+sulfuric), before the end of the distillation, there are always lot of red fumes in my boiling flask and no more HNO3 comes into the receiver flask !"

Preparative chemistry books describing absolute HNO3-distillation call this "vorlauf"/"nachlauf"(german; donŽt know the damn word..).
It means, the batch generally tends to develop nitrous oxides both at the beginning and towards the end of distillation, the procedures recommend to drop these fractions(nitrous oxides will often cause your nitrations to yield sensitive by-products).

nbk2000
January 15th, 2003, 04:27 PM
It's just good lab technique to discard the forerun and to NOT finish the distillation to completion.

Also, there is no RTPB against friends...just one saying you can't trust them. <img border="0" title="" alt="[Wink]" src="wink.gif" /> Hence none of them know about my time in the clink, or my "hobbies". :)

<small>[ January 15, 2003, 03:30 PM: Message edited by: nbk2000 ]</small>

zylion
January 27th, 2003, 08:18 AM
Question: In order to distill my own nitric acid, I was planning to use sulphric acid(&gt;98%) and NaNO3(fertilizer grade a.k.a chilisalpeter) of which I happend to have a 50kg bag. De reading on the bag is as follows CHILISALPETER N total 16%
Na2O total 35%
and then some kind of additive Boruim (B) 0.2%
IŽam wondering, does this additive have any effect on the distillation or the purity of the nitric acid.
I think the Borium is ment to prevent sucking up moisture from the air, the stuf does come in little prills.Or is it better to use KNO3 anyway. phew!!!! 50 kg, thats a lot of distilling and a shipload of nitric acid!!!!!

thanks

stanfield
January 27th, 2003, 10:06 AM
no, I don't think it'll fuck up your distillation
Like you my NaNO3 isn't pure and it works damn well dor distillation.

mongo blongo
January 27th, 2003, 11:00 AM
Well if it's only 0.2% then you have good NaNO3 and should not have anything to worry about. 50 kg!.. you lucky bastard!! :)