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--- chemical:hno3:distillation [2012/08/24 05:52] – mcmaster
+++ chemical:hno3:distillation [2025/08/04 21:23] (current) – external edit 127.0.0.1
@@ Line 62: / Line 62: @@
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-Once it gets hot enough the KNO3 will completely dissolve in the H2SO4.  It should give a healthy bubble like above.  Try not to let the level exceed halfway.
+Once it gets hot enough the KNO3 will completely dissolve in the H2SO4.  It should give a healthy bubble like above.  Try not to let the level exceed halfway.  Its fine if the mixture is only bubbling at top and is liquid at bottom (ie just at the boiling point).
 This works okay but takes a while to heat up (30-45 minutes typical IIRC).  Helped a little to put aluminum foil over the still.  Overall, the probably was that the Vireux condenser was overkill for the level of purity I require.
@@ Line 97: / Line 97: @@
 Procedure:
-  - Setup main glassware.  Use PTFE tape on all joints, vacuum grease will likely get eaten too quickly
+  - Setup main glassware
     - Connect/clamp 14/20-24/40 adapter to distillation head
     - Plug distillation head or attach thermometer
@@ Line 114: / Line 114: @@
 Tips:
   * Yields maybe 50 or 60 mL of RFNA
+  * You can make 70% by adding some water.  The H2SO4 will keep water from boiling off and instead favor dilute HNO3.  Wikipedia says 70% boils at 121C.
   * Use a fume hood if available / do in a well ventilated area.  I do this outside and use a 3M full face respirator with acid gas cartridges.  I'm looking into building a gas scrubber system, possibly using a catalytic converter
   * Use excess H2SO4.  The more you use the easier the reactor will be to clean and the less you have to worry about moisture contamination
+  * Seal all joints.  I used PTFE tape on all joints, mostly because it was available from the hardware store.  I haven't tried vacuum grease, maybe would get eaten, maybe not
   * Probably best not to exceed a 1L flask.  At the very least, the self heating must be watched which gets worse as the batch is larger.  I'd start with a 500 mL flask
   * Depending on ambient temperature, I've had it take as long as 45 before distillate forms
@@ Line 121: / Line 123: @@
   * If more than a few mL of acid accumulates in the vacuum trap decrease flow rate or cool collection flask more
   * Might be able to put fiberglass or similar in the vacuum trap to help it condense / increase surface area
+  * Once solution is dissolved / under vacuum do not let it solidify on the surface (its fine if its bubbling on top and slushy under).  If you do it will form an insoluble layer that will considerably slow down distillation.  Try to rapidly drop pressure (rapidly increase vacuum), in some situations this can shatter it and bring back normal distillation.  Thus, if the solution level is getting too high favor decreasing pressure and increasing temperature over simply decreasing vacuum
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-However, I didn't want to damage the vacuum pump so I bought a cold trap.  It was cooled by a dry ice acetone bath.
+However, I didn't want to damage the vacuum pump so I bought a cold trap.  It was cooled by a dry ice acetone bath.  This is when it was just poured, the bath freezes over from collecting moisture in the air.
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   - Turn on vacuum
   - Apply heat
-  - Adjust vacuum as heat increases by adjusting vacuum valve.  Required heat should be lower than RFNA distillation
+  - Adjust vacuum as heat increases by adjusting vacuum valve.  Try to maintain a healthy bubble as shown earlier.  Required heat should be lower than RFNA distillation
-  - If / when changing collection flasks close the vacuum valve to let vapor bring the system up from vacuum.  The collection flask should then be removable reasonably easily
 Tips:
   * Watch vacuum trap temperature.  Even if there is dry ice left it might not be cold enough
   * Watch pump oil and interior for signs of NOx contamination.  Stop if begins to get contaminated
+  * If / when changing collection flasks close the vacuum valve to let vapor bring the system up from vacuum.  The collection flask should then be removable reasonably easily
+  * Because of the vacuum trap, this should put off little gas while running and really only some when disassembling
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 {{:chemical:hno3:distillation:cryo_cooler_payload.jpg?300|}}
 The dry ice works okay but I wanted to look into alternatives, in part to guarantee the temperature stays low.  I decided to try an electrically driven cooler.  While NO2 condenses at only 21C, lower temperatures condense things faster / more completely.  I found a -100C immersion cryocooler and will be using that for the next batch.  I'm out of FNA so it will likely be in the near future.  I have some dewar that fits both the cooling head and the vacuum trap meaning the system won't require a pump.  I also have a peltier cooler for cooling the condenser.
+Admittedly the vacuum pump only cost me $50 (although I think that was a good deal) while the cryocooler cost several hundred...but I like experimenting with different configurations.  In other words, if you are strapped for cash, this is not a good approach.  Dry ice costs me a few dollars a pound and you might be able to argue that its less expensive to buy old vacuum pumps and just let them burn out (if that's even easy to do so).  I've also considered using potassium permanganate in the vacuum trap as its very reactive with NOx and cheap.  Activated carbon would work fine as well but I'm not sure it can absorb as much.  I'm looking into a catalytic converter as another alternative which could also also help a lot.
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 {{:chemical:hno3:distillation:rfna_biproduct.jpg?300|}}
-Don't try to pour old the hot H2SO4 / KNO3 biproduct (KHSO4).  It will likely solidify on the cooler upper half of the flask and close it off.  This can cause pressure to build from the still hot bottom cooking off.  Instead, wait until its cool and then add water.  I blow it with a fan to help it cool down faster.  The more acid you use the more acid that will be leftover and keeping the mixture liquid.  Above: KHSO4 waste product.
+Don't try to pour old the hot H2SO4 / KNO3 biproduct (KHSO4).  It will likely solidify on the cooler upper half of the flask and close it off.  This can cause pressure to build from the still hot bottom cooking off.  Instead, wait until its cool and then add water.  It will likely take a number of washings to get it all out.  Warm water and sloshing it around so that it breaks up and not just dissolves helps.  I blow the flask with a fan to help it cool down faster.  The more acid you use the more acid that will be leftover and keeping the mixture liquid.  Above: KHSO4 waste product.
+====== References ======
+http://www.sciencemadness.org/talk/viewthread.php?tid=13090&page=2
+  * Persulfate to reduce NO2