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Author: Subject: Somewhat urgent nitric acid distillation issue
inspector071
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[*] posted on 16-6-2012 at 14:27
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]
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cyanureeves
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[*] posted on 16-6-2012 at 15:25


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.
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inspector071
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[*] posted on 16-6-2012 at 15:43


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.
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m1tanker78
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[*] posted on 16-6-2012 at 16:28


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




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inspector071
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[*] posted on 16-6-2012 at 16:38


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.
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m1tanker78
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[*] posted on 16-6-2012 at 22:17


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




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inspector071
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[*] posted on 16-6-2012 at 22:33


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?
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hissingnoise
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[*] posted on 17-6-2012 at 02:16


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.

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[*] posted on 17-6-2012 at 03:07


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.




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inspector071
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[*] posted on 17-6-2012 at 10:56


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?
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vmelkon
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[*] posted on 17-6-2012 at 11:15


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.
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watson.fawkes
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[*] posted on 17-6-2012 at 11:47


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.
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Endimion17
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[*] posted on 17-6-2012 at 12:11


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.




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inspector071
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[*] posted on 17-6-2012 at 12:34


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.
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DJF90
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[*] posted on 17-6-2012 at 15:43


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...).
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m1tanker78
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[*] posted on 17-6-2012 at 15:45


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




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inspector071
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[*] posted on 17-6-2012 at 16:25


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?
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Rogeryermaw
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[*] posted on 17-6-2012 at 16:35


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.
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inspector071
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[*] posted on 17-6-2012 at 17:39


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.
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Neil
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[*] posted on 18-6-2012 at 04:39


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.
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