inspector071
Hazard to Self
Posts: 69
Registered: 20-2-2012
Member Is Offline
Mood: No Mood
|
|
Somewhat urgent nitric acid distillation issue
I recently got a 24/40 distillation set in hopes to distill some nitric acid more efficiently than a retort. I just got my pump in today and got all
of my glass set up. This is my first time working with this setup, and I'm getting joint leakage at my heated flask and still head joint, spewing out
some NO2 and nitric acid vapors, which started to dissolve my Keck clamp there. I am using some silicone dielectric grease at all of my joints. I've
read not to use too much grease, but I may have not used enough. What can I do now to try and salvage this experiment safely?
Edit: I decided to let the apparatus cool down a little, and donning some leather and butyl gloves, I cleaned off the ground glass joint, reapplied
more silicone grease and wrapped the outside of the joint in teflon tape before putting on the Keck clip. I"m also resting the bottom of my round
bottomed flask on the bottom of the oil bath/hot plate so as to not pull the joint apart at all but to keep pressure on it holding it together.
[Edited on 16-6-2012 by inspector071]
|
|
cyanureeves
National Hazard
Posts: 744
Registered: 29-8-2010
Location: Mars
Member Is Offline
Mood: No Mood
|
|
same thing happened to me and i just let it go since i thought the acid wasnt worth saving but boy was i wrong.i did lose a keck clip but the acid was
super strong i only gave it a half twist and separated the flask that was catching the acid from the rest of the set up so it would not build
pressure.
|
|
inspector071
Hazard to Self
Posts: 69
Registered: 20-2-2012
Member Is Offline
Mood: No Mood
|
|
That was exactly my problem. The system was building too much pressure. I did the same thing: loosened my receiving flask and immediately the vapor
column rose and started stilling over.
|
|
m1tanker78
National Hazard
Posts: 685
Registered: 5-1-2011
Member Is Offline
Mood: No Mood
|
|
What type of condenser are you using and in what configuration? You shouldn't perform distillations in a closed system. A vacuum takeoff adapter
allows some venting to take place and in some situations can simply be fitted with a suitable hose to vent outside.
One other thing, why do you all use Keck clips on the heating flask?? My understanding is that for higher temp stuff, a K-clip should not be used at
all except on the vac takeoff joint and receiving flask joint. In other words, all joints that are 'downstream' from the condenser can be clipped.
I've seen some use springs to secure the high temp section(s). Sturdy stands and clamps probably help tremendously and negate the need to clip every
single joint.
I do clip all joints when working with low-boiling organics and such although it may not be necessary at the boiling flask and still head.
Tank
Chemical CURIOSITY KILLED THE CATalyst.
|
|
inspector071
Hazard to Self
Posts: 69
Registered: 20-2-2012
Member Is Offline
Mood: No Mood
|
|
It's a one piece Liebig/still head with a 10/30 thermometer joint. I didn't even realize that a simple distillation like this couldn't be performed in
a closed system. I assumed my ice bath for my receiving flask would negate the pressure formed from the heated end. I've got my receiving flask
slightly loose to relieve the pressure, but next distillation I'll use my curved vacuum adapter at the end and vent it.
My oil bath is only at 115 C, so it's not terribly hot. I just assumed "better be safe than sorry" and use Kecks on all of my joints. I've got two
stands and two clamps on my apparatus right now. One clamp is about halfway up my condenser and the other is affixed to my receiving flask. My boiling
flask is being supported by my oil bath and hot plate now. Thanks for the tips.
|
|
m1tanker78
National Hazard
Posts: 685
Registered: 5-1-2011
Member Is Offline
Mood: No Mood
|
|
The vac adapter would be a vast improvement IMO. You may get away with simply bubbling the excess gas in water to help neutralize. A basic solution
may prove more effective.
Good luck,
Tank
Chemical CURIOSITY KILLED THE CATalyst.
|
|
inspector071
Hazard to Self
Posts: 69
Registered: 20-2-2012
Member Is Offline
Mood: No Mood
|
|
Yep, I've already fitted the vacuum adapter. My next learning experience will be to try and vacuum distill some acid. I have a vacuum pump (which is
actually a medical stomach pump, which is handy because I can use it's reservoir to store a sodium bicarb solution and have the vacuumed gas bubble
through it) and will try to distill under vacuum tomorrow. Are there any tips I should know before trying to run a nitric acid distillation under
vacuum?
|
|
hissingnoise
International Hazard
Posts: 3940
Registered: 26-12-2002
Member Is Offline
Mood: Pulverulescent!
|
|
Knowing little of stomach pumps, I can't say if it's suitable or not but under vacuum HNO<sub>3</sub> vapours need a very low temperature
to effect condensation.
Ice-water in the condenser and a cooled (below 0°C ) receiver is recommended.
|
|
Endimion17
International Hazard
Posts: 1468
Registered: 17-7-2011
Location: shores of a solar sea
Member Is Offline
Mood: speeding through time at the rate of 1 second per second
|
|
Quote: Originally posted by inspector071 | That was exactly my problem. The system was building too much pressure. I did the same thing: loosened my receiving flask and immediately the vapor
column rose and started stilling over. |
Please don't say you were trying to distill nitric acid in a closed system.
You see, that's why wer can't have nice things. Because of this.
|
|
inspector071
Hazard to Self
Posts: 69
Registered: 20-2-2012
Member Is Offline
Mood: No Mood
|
|
Quote: Originally posted by Endimion17 | Quote: Originally posted by inspector071 | That was exactly my problem. The system was building too much pressure. I did the same thing: loosened my receiving flask and immediately the vapor
column rose and started stilling over. |
Please don't say you were trying to distill nitric acid in a closed system.
You see, that's why wer can't have nice things. Because of this. |
It had been established in previous posts that I had started with a closed distillation. Your snarky reply doesn't really accomplish much. As my first
post said, this is my first time working with ground glass equipment. I'm a recently changed chemistry major from chemical engineering but haven't
taken any organic classes yet, and have been enjoying trying to learn how to use some of the equipment I'll see in the next 2 years.
When is a distillation in a closed system preferred over an open one? Does distilling nitric acid in a closed system not work because of the
production of nitrogen oxides generating too much pressure?
|
|
vmelkon
National Hazard
Posts: 669
Registered: 25-11-2011
Location: Canada
Member Is Offline
Mood: autoerotic asphyxiation
|
|
For nitric acid, it is preferred to keep a low pressure to avoid decomp of the nitric acid to NO2.
If you make it a closed system, pressure builds up and it pushes out the silicone grease at the joints. I am an amateur and I have wondered what
people do if they want positive pressure in their distillation apparatus or reactor or whatever.
|
|
watson.fawkes
International Hazard
Posts: 2793
Registered: 16-8-2008
Member Is Offline
Mood: No Mood
|
|
Quote: Originally posted by vmelkon | I am an amateur and I have wondered what people do if they want positive pressure in their distillation apparatus or reactor or whatever.
| They use something other than tapered-joint glassware. There's a whole range of pressure reactors and the
like out there.
|
|
Endimion17
International Hazard
Posts: 1468
Registered: 17-7-2011
Location: shores of a solar sea
Member Is Offline
Mood: speeding through time at the rate of 1 second per second
|
|
Quote: Originally posted by inspector071 | It had been established in previous posts that I had started with a closed distillation. Your snarky reply doesn't really accomplish much. As my first
post said, this is my first time working with ground glass equipment. I'm a recently changed chemistry major from chemical
engineering but haven't taken any organic classes yet, and have been enjoying trying to learn how to use some of the equipment I'll see in
the next 2 years.
When is a distillation in a closed system preferred over an open one? Does distilling nitric acid in a closed system not work because of the
production of nitrogen oxides generating too much pressure? |
My snarky reply is the exact thing you need!
If I understood you correctly, you have a degree? Or you've passed at least one chemistry subject? Nevermind. You want to know when is a distillation
in a closed system preferred over an open one? Always!
Dude, lack of experience with organic chemistry laboratory is not an excuse for not knowing this. This is basic laboratory knowledge. Laboratory
distillations with glass apparatuses are always made in an opened system. If the air/moisture needs to be kept out, the end of the system is closed
with a bubbler or a drying tube.
You obviously have no idea about the danger you were in. Hot, concentrated nitric acid in a pressurized system means "if possible, remove the source
of heat immediately and get the fuck out of the room".
If your Keck clips were stronger, or if the joints were more stuck, upon sudden releasing of the pressure your corrosive acid would've come out
shooting like a jet, similar to a shaked can of Coke. Have you seen the victims of nitric acid attacks in India? You better google it.
And learn to accept criticism, especially if the person criticizing you would hate to see you get hurt.
Next time you try to do something, take a peek into the lab manual. Forget fucking YouTube.
|
|
inspector071
Hazard to Self
Posts: 69
Registered: 20-2-2012
Member Is Offline
Mood: No Mood
|
|
Quote: Originally posted by Endimion17 | Quote: Originally posted by inspector071 | It had been established in previous posts that I had started with a closed distillation. Your snarky reply doesn't really accomplish much. As my first
post said, this is my first time working with ground glass equipment. I'm a recently changed chemistry major from chemical
engineering but haven't taken any organic classes yet, and have been enjoying trying to learn how to use some of the equipment I'll see in
the next 2 years.
When is a distillation in a closed system preferred over an open one? Does distilling nitric acid in a closed system not work because of the
production of nitrogen oxides generating too much pressure? |
My snarky reply is the exact thing you need!
If I understood you correctly, you have a degree? Or you've passed at least one chemistry subject? Nevermind. You want to know when is a distillation
in a closed system preferred over an open one? Always!
Dude, lack of experience with organic chemistry laboratory is not an excuse for not knowing this. This is basic laboratory knowledge. Laboratory
distillations with glass apparatuses are always made in an opened system. If the air/moisture needs to be kept out, the end of the system is closed
with a bubbler or a drying tube.
You obviously have no idea about the danger you were in. Hot, concentrated nitric acid in a pressurized system means "if possible, remove the source
of heat immediately and get the fuck out of the room".
If your Keck clips were stronger, or if the joints were more stuck, upon sudden releasing of the pressure your corrosive acid would've come out
shooting like a jet, similar to a shaked can of Coke. Have you seen the victims of nitric acid attacks in India? You better google it.
And learn to accept criticism, especially if the person criticizing you would hate to see you get hurt.
Next time you try to do something, take a peek into the lab manual. Forget fucking YouTube. |
That snarky reply was not what was needed. This reply is perfect, though. It explains why what I did was incorrect and why it doesn't work.
I'm a junior that just switched from a chemical engineering major to chemistry. I have had no prior experience using ground glass apparatus. I had a
misconception that the cooled condenser would keep the pressure in the system constant, but as we've established, that is not correct. It appears I am
not the only one with this misconception, so I hope this thread makes it clear to others also. I believe that I handled my situation as safely as
possible. Given that the system was venting through a leak in the boiling flask joint, I undid my receiving flask and proceeded to have a successful
distillation.
I can take criticism just fine, but a reply that says "this is why we can't have nice things" and makes no other effort to address my original
question is not constructive. I appreciate the thoughtful reply, and your concern for my well-being.
|
|
DJF90
International Hazard
Posts: 2266
Registered: 15-12-2007
Location: At the bench
Member Is Offline
Mood: No Mood
|
|
I was always taught growing up in science NEVER to heat a closed system. While there are certainly exceptions (pressure reactions/reactions in sealed
tube), this is generally the case. I'm glad the situation has been resolved, but something else has caught my eye - it sounds as if you're keck
clipping between the boiling flask and whatever it is connected to (column/stillhead). It also sounds as if this keck clip is the only real support
the flask is receiving. Please ensure that all distilling flasks are CLAMPED (you may be doing this, but its hard to tell...). Recieving flasks should
also be supported if they're sizable (100mls or bigger perhaps?), and keck clips should only be used where needed (i.e. NOT on vertical joints! Clamps
should deal with this. The one exception I can think of right now is for flash chromatography, but lets not go there...).
|
|
m1tanker78
National Hazard
Posts: 685
Registered: 5-1-2011
Member Is Offline
Mood: No Mood
|
|
Luckily, your distillation didn't result in a catastrophe but don't rely on luck! I have ZERO classroom training/experience in organic chemistry,
glassware, etc. so I do a great deal of online and book research before I venture into an unknown (to me) experiment. If I can't find the answers in
literature or in a reliable forum (like this one), I try the experiment on a small scale first.
I agree with Endimion17; careful with Youtube. Check this video made by hkparker:
http://www.youtube.com/watch?v=CzKwyCIkUEQ
A good example of a proper setup and procedure for distilling HNO3..
Tank
Chemical CURIOSITY KILLED THE CATalyst.
|
|
inspector071
Hazard to Self
Posts: 69
Registered: 20-2-2012
Member Is Offline
Mood: No Mood
|
|
Thanks for the help. I appreciate the replies. I did end up removing the Keck clip from the joint between the boiling blask and still head. The flask
is now properly clamped and supported.
Are there any preferred greases for ground glass when working with concentrated nitric acid? The dielectric silicone grease I'm using holds up
decently well, but it leaves a rather hard to remove residue at the end of the distillation.
I'm wanting to perform a vacuum distillation of nitric acid. My pump has an operating vacuum of 650 mmHg. Using a boiling point calculator and the
enthalpy of evaporation of nitric acid, I believe it should boil at around 34 C. I've taken the time to read about the setup and use of a vacuum
distillation (and also watch a MIT video lab manual about it), but are there any other nuances or tips I should know before proceeding?
|
|
Rogeryermaw
National Hazard
Posts: 656
Registered: 18-8-2010
Member Is Offline
Mood: No Mood
|
|
when i distill nitric i use a vacuum adapter as the drip tube and lead a hose from it outside. no pressure buildup and no fumes to breathe. your pump
may not stand up well to nitric fumes unless it is made with teflon internal parts. also, you may want to consider a water cooled condenser. you may
have better yield as less nitric vapor will escape.
|
|
inspector071
Hazard to Self
Posts: 69
Registered: 20-2-2012
Member Is Offline
Mood: No Mood
|
|
I have the pump pulling air through a gas washing bottle filled with a sodium bicarbonate solution in hopes to neutralize any nitrogen oxides. My
condenser has ice water flowing through it, and my receiving flask has a salt/ice solution.
|
|
Neil
National Hazard
Posts: 556
Registered: 19-3-2008
Member Is Offline
Mood: No Mood
|
|
Nitrogen oxides are very hard to fully absorb, check out scrubbers designed for such fumes. One bottle will not do it, that stuff is pernicious. Your
pump will likely suffer.
|
|