Also see equipment
Also see equipment
This is more things I tried than a firm recommendation, take what you will out of it. Any e-mails related to explosives won't be honored with an answer.
In high school before I got good at ordering things online and such I managed to acquire a vacuum flask, some Bull Dozer brand drain cleaner, and some stump out. I added the chemicals to the flask and added a rubber stopper to keep things inside and keep temperature. A plastic acquire hose dripped acid out the side while it was heated with a wok I got at a thrift store. The receiving flask was placed in ice water to help condense and hat some cotton in top to try to slow its escape. It basically formed a crude retort. At the end of the day though, it did work to produce reasonably strong nitric acid.
The acid was unkind to the hose and turned it really hard. However, it did seem to hold up okay. On the other hand, the rubber stopper did not fair so well. Looking back, I should have covered it in aluminum foil which is pretty resistant to nitric acid. I think the above picture was taken much later, sometime during college when I didn't yet have proper distillation equipment but knew better than to use a rubber stopper.
This is more of a procedure of desperation, I suggest the RFNA procedure if you are looking for best work to product payoff
Having learned a little more about chemistry equipment and no longer making minimum wage, I was able to afford some jointed glassware.
Terrible picture (camera was dying) but it gives the idea. The second was a later very similar setup after I got a new camera. A ring stand holds a flask of KNO3 and H2SO4 in an oil bath. A thermometer allows me to check the oil bath temperature. Hot acid fumes go up through a Vigreux condenser and then at the top transfer to a Liebig condenser. The primary reason for using this was that I got it at the MIT flea market for a dollar. The condenser is passively cooled by circulating through an old freezer radiator and pumped by a diaphragm pump I found in the RPI dumpsters. The receiving flask is in an icewater bath.
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.
Starting to heat up (from a later run).
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.
Above: also the system got algae when I didn't drain it. Added some bleach and it stopped growing.
With my current equipment I'd do something like this.
Above: doubled ingredients for a 1 L flask
The next major advancement was switching the oil bath for a heating mantle. While I didn't think it was likely that a flask would break, if it did it would fail catastrophically.
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.
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.
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.
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.
Collected distillate. During distillation this is submerged in ice water. The feed to the right runs to the vacuum trap.
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.
With my current equipment I'd do something like this. Similar to the RFNA procedure with the following modifications
Above: doubled ingredients for a 1 L flask
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.
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.