jharmon12
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Absorption of Nitric Acid Vapors
Hi Group,
Have a vacuum and cold trap and want to pull said vacuum on my glass distillation set. Plan to start with cold acid/nitrate mix to minimize
pre-vapor. Want to know if it is better to use something cold in the cold trap jar or something absorbent like calcium chloride to remove/scrub the
vapors. What is best?
Please help.
Thanks.
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Fantasma4500
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ammonia works well and it should be commonly available
but perhaps bicarbonate + cold water would do the job aswell?
but if were talking HNO3 vapours then it should dissolve pretty fast in water, put a small beaker of ammonia above the trap to detect any HNO3 vapours
and turn them into NH4NO3 smoke..
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chemcam
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Quote: Originally posted by Antiswat  | ...but perhaps bicarbonate + cold water would do the job aswell?
but if were talking HNO3 vapours then it should dissolve pretty fast in water...
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Running the HNO3 vapor into bicarbonate solution makes A LOT of foam so use a large beaker.
Running HNO3 vapor into water works okay, as long as it is a tall container like a graduated cylinder so more vapor will be absorbed. Using hydrogen
peroxide is better than water, even 3% works, but, higher percentage is preferred. You can even recycle the recovered acid, I try not to waste
anything.
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Oscilllator
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I wouldn't use bicarbonate because as chemcam said, it would produce lots of foam because of the evolution of carbon dioxide. Just pass it through a
solution of sodium hydroxide or other cheap base, that'll absorb the vapors no problem.
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jharmon12
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Keep in mind that this is a container between the vacuum pump and the glass distillation apparatus. I cannot immerse any of the tubes from this
intermediary container into a solution of water or it will get sucked up into the vacuum. Other suggestions?
Are there any salts that will absorb the nitric acid vapor? If not, I am thinking I might have to go with a cold trap. And I am just not clear on
how cold it needs to be to keep the vapor from going from the glassware and into the vacuum.
Thanks.
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Fantasma4500
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| Quote: Originally posted by jharmon12 | Keep in mind that this is a container between the vacuum pump and the glass distillation apparatus. I cannot immerse any of the tubes from this
intermediary container into a solution of water or it will get sucked up into the vacuum. Other suggestions?
Are there any salts that will absorb the nitric acid vapor? If not, I am thinking I might have to go with a cold trap. And I am just not clear on
how cold it needs to be to keep the vapor from going from the glassware and into the vacuum.
Thanks. |
ammonia, that is the question
but be ready for shittonnes of smoke
looks nice tho
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chemcam
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What about using NaOH? That will remove acid vapor.
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watson.fawkes
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| Quote: Originally posted by jharmon12 | | Have a vacuum and cold trap and want to pull said vacuum on my glass distillation set. Plan to start with cold acid/nitrate mix to minimize
pre-vapor. Want to know if it is better to use something cold in the cold trap jar or something absorbent like calcium chloride to remove/scrub the
vapors. What is best? |
What is best is to start with an acknowledgment that you have a gas washing train,
and that those are generally not best done as a single stage. Even though you're pulling vacuum, you don't have vacuum, but rather a gas flow system
with mass transport.
Your vapor source is some combination of the condenser and the receiving flask. If the receiving flask is warmer than the condenser, it will be the
dominant source of vapor. You can minimize source emissions by insulating and chilling your receiver flask. The condenser temperature might drive the
vapor pressure in that case. Much depends on how whether the vapor off the condenser passes past the condensed liquid surface or not.
A cold trap has the property that the dew point of the exhaust is at or near (a bit higher than) the temperature of the trap. Look up partial pressure
in a table for the substance to see how much is present in the vapor. No cold trap eliminates vapor, but it will can knock it down enough so that
either it can be dealt with in a subsequent stage or its harm is negligible.
It sounds like a two stage train may be adequate: a cold trap to trap and recover most of the acid vapor and then a reactive trap to eliminate the
remainder.
Incidentally, you can use a liquid gas washing stage as a trap, but you need to precede it with a suckback trap in case vacuum is removed from the
system in the wrong order.
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S.C. Wack
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recommended HNO3 liquid gas washing stage with suckback trap
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Rosco Bodine
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Tried and true on the nalgene aspirators, decades old standby that works like a charm. For a chemically active scrubber I would say urea would be
just what the doctor ordered. It will neutralize the nitric forming the salt of urea, and will decompose the nitrous to nitrogen and water and
carbon dioxide.
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