Quote:
Originally Posted by Vlad
If we cool bottle down to -5-10 Degree Celsius and start pulling propane as a vapor (bottle valve up) with recovery unit then propane will start evaporating (and it will help to keep bottle cold) but butane will stay as a liquid. Also this will keep water in original bottle as well.
We will get some non condensables but it is easy to get rid of them by purging and charging as a liquid.
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Your theory is sound, but you will want to start quite a bit lower than -10C as you are likely to have some iso-butane in there also.
Hydrocarbon gasses that you want to keep are very much more dense than any non-condensible you are likely to find in the bottle. Leaving the bottle overnight and then very slowly cracking the valve to purge out the top part of the bottle will likely rid you of 99.9% of them before you even start decanting. The trick is to make sure you don't disturb the bottle so the layers can stratify.
You will need to limit the rate you pull the propane from the bottle, but certainly the theory is sound. What you are doing is effectively fractional distillation. The R290 for heatpumps thread has quite a bit of information on water and propane. It's not quite as easy to separate as you might think, particularly if you live in a country like mine where negative temperatures only happen in deep freeze units.