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--- chemical:hno3:distillation [2012/08/24 04:16] – [Cooled vacuum trap] mcmaster
+++ chemical:hno3:distillation [2018/09/05 17:00] (current) – [References] mcmaster
@@ Line 55: / Line 55: @@
 As the KNO3 and H2SO4 are mixed it puts off some NOx (sulfuric reacting with water?).  KNO3 sticking to the side will come down soon as vapors begin to rise and condense.
+{{:chemical:hno3:distillation:nobubbler_reactor_warming0.jpg.jpg?300|}}
+Starting to heat up (from a later run).
 {{:chemical:hno3:distillation:healthy_bubbles.jpg?300|}}
-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 83: / Line 87: @@
   * 14/20 Liebig condenser
   * 14/20 distillation head (connects reactor to condenser)
-  * Thermometer or plug if no thermometer is availible for distillation head.  10/18 is common
+  * Thermometer or plug if no thermometer is available for distillation head.  10/18 is common
   * 14/20 right angle vacuum adapter: allows good connection to receiving flask and to drip down and vent excess gas.  I haven't tried a straight adapter for a closed system, it might work as well but I am unsure about pressure buildup concerns
   * Condenser cooling source (ex: pump + ice water or faucet water)
@@ Line 93: / 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 110: / 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
   * Initially once distillation comes over expect about 1 drop per second.  It will slow down and its up to you what an acceptable rate is before you stop.  However, if you use up all the water you should notice that you are getting considerably less than before suddenly.  At this point you should stop as otherwise the flask will simply heat up and you'll eventually be boiling H2SO4
+  * 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
@@ Line 124: / Line 133: @@
 ====== Vacuum distillation (WFNA) ======
-While the above system works it takes a long time to heat up.  Vacuum distillation on the other hand quickly draws the fumes forward.  Additionally, the pressure regulation allows more accurate flow control and also lowers the working temperature.
+{{:chemical:hno3:distillation:bubbler_overview_warm.jpg?300|}}
+{{:chemical:hno3:distillation:bubbler_overview_cold1.jpg?300|}}
-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.
+While the above system works it takes a long time to heat up.  Vacuum distillation on the other hand quickly draws the fumes forward.  Additionally, the pressure regulation allows more accurate flow control and also lowers the working temperature.  Also note that I now lab jacks instead of stacking stuff up to put things into position against the ring stand.  I have also eliminated the oil bath / hotplate as noted above in favor of a heating mantle and a Variac to control its heat.  It works much better and is much safer.
-Some people suggested injecting air into the reactor to reduce bumping.  I didn't have a problem with bumping and didn't find that it aided the system.  More than likely it hurt as drawing in air increases the moisture in the system.
+{{:chemical:hno3:distillation:bubbler_chilled_beaker.jpg?300|}}
+{{:chemical:hno3:distillation:bubbler_chilled_beaker_inside0.jpg?300|}}
+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.
-====== Cooled vacuum trap ======
+{{:chemical:hno3:distillation:bubbler_head.jpg?300|}}
+Some people suggested injecting air into the reactor to reduce bumping.  I didn't have a problem with bumping and didn't find that it aided the system.  More than likely it hurt as drawing in air increases the moisture in the system.  The first pictures show the use of a vacuum inlet instead of a thermometer on the distillation head.  Part of it can be seen above.  It originally had a glass rod in the middle, I guess I removed it and was just playing with pressure regulation by the time that picture was taken.
+{{:chemical:hno3:distillation:nobubbler_overview1.jpg?300|}}
+{{:chemical:hno3:distillation:nobubbler_overview0.jpg?300|}}
+As the breathing tube wasn't helping it was removed in the next round as seen above.  The vacuum inlet is now simply capped off.  This worked much better.
+{{:chemical:hno3:distillation:distillate_cooled.jpg?300|}}
+{{:chemical:hno3:distillation:nobubbler_distillate.jpg?300|}}
+Collected distillate.  During distillation this is submerged in ice water.  The feed to the right runs to the vacuum trap.
+{{:chemical:hno3:distillation:nobubbler_pump_infection.jpg?200|}}
+The biggest problem with this approach is making sure the vacuum trap stays cool enough.  Although it still had some dry ice in it it was no longer iced over and so obviously had risen in temperature.  It evidently wasn't cool enough anymore as the pump got NOX in it.  I'm not sure if it sustained any noticeable damage, it seems to still work fine.
+===== Procedure =====
+With my current equipment I'd do something like this.  Similar to the RFNA procedure with the following modifications
+Additional chemicals:
+  * 10 lbs dry ice.  This should allow several batches
+  * 500 mL acetone or denatured alcohol
+{{:chemical:hno3:distillation:ingredients.jpg?300|}}
+Above: doubled ingredients for a 1 L flask
+Equipment:
+  * Tubing between vacuum adapter and cold trap
+  * Cold trap
+  * Cold trap container.  Dewar is ideal, a beaker will also work but will leak heat
+  * Tubing between cold trap and pump
+  * Vacuum valve.  I use a Swagelock valve because its stainless is chemically resistant and wedges into the tubing nicely
+  * Vacuum pump
+Procedure:
+  - Setup vacuum trap
+    - Place vacuum trap in container
+    - Pour in acetone until sufficiently covered
+    - Put dry ice into acetone
+  - Setup main glassware.  Use previous setup and then do the following
+    - Seal collecting flask to vacuum adapter with PTFE tape
+  - Start cooling as previously directed
+  - Connect tubing between vacuum adapter and cold trap.  I connect on the shell to avoid freezing in the column, I'm not sure which polarity is technically better
+  - Open vacuum valve
+  - Connect vacuum adapter to vacuum valve
+  - Connect vacuum valve to pump
+  - Mix ingredients as previously directed and connect reactor
+  - Turn on vacuum
+  - Apply heat
+  - 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
+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
+====== Continuously cooled vacuum trap ======
 {{:chemical:hno3:distillation:cryo_cooler_overview.jpg?200|}}
 {{:chemical:hno3:distillation:cryo_cooler_payload.jpg?300|}}
-The dry ice works okay but I wanted to look into alternatives.  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.
+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