I recently put together a small refrigeration system capable of cooling a highly insulated SS cylinder of acetone to around -25C. It basically consisted of a small refrigerator compressor, 1/4" copper tubing for the evaporator/heat exchanger along with a little warm water to aid in evaporation, small dia. copper capillary tubing was used in place of a thermal expansion valve, and 1/4" copper tubing was also used for the condenser. I have used 134a, R22, and propane as refrigerants with little or no difference between any of them in terms of temperature. This little system works damn good for what it is, (basically a solvent chiller) I just can't get it down to the -35C or so required for NH3 liquefaction. I was wondering if anyone knew of any good cryogenic/ultra-low temp refrigeration schematics, or design information floating around on the net. Swic has done a lot of searching, and has found several pages dealing with this subject, but they all stop short of giving detailed schematics for their "proprietary" systems. They all work on vapor pressure refrigeration principles, although some do utilize multiple compressors, and I think this may be the key to actually reaching super low temps. I do happen to be an electrical tech, and a refrigeration mech, so I should have no problems putting together any system I want, given the proper schematics, and design details. Also, I am licensed, and have special EPA certification (don't even ask) so I am able to get any refrigerant I may need, no questions asked, to to make this happen. "Well if that's the case, why don't you just go buy a tank of NH3?" you ask. I could do that, and I have done that in the past, for refrigeration purposes. Basically it's just something I want to do. And once I get it up and working to efficiently condense NH3, I'll do a write up, and include the details of the rest of my generator system, which will produce 100ml of liquid ammonia in about 10 minutes using dry ice. I personally think that performing a Birch reduction of pseudoephedrine is, on orders of magnitude, easier, and more OTC than all the tedious, meticulous cleaning and detail work required for success in any HI/I2 reduction. (It is also much more dangerous and shouldn't be attempted by anyone who hasn't studied the procedure thoroughly) I've also been doing some reading lately on the electrolytic production of solvated electrons in NH3, which DOES NOT require any sort of special divided cell, so should be totally doable if I (or someone else) can come up with a suitable electrolyte that doesn't snatch up so many electrons. Anyhow, if anyone has any comments or suggestions please don't hesitate to post them.
CN