BBQ Propane Distillation Redux

[buffalobillpatrick]

From Wikipedia:

"Commercially available "propane" fuel, or LPG, is not pure. Typically in the United States and Canada, it is primarily propane (at least 90%), with the rest mostly ethane, propylene, butane, and odorants including ethyl mercaptan.[12][13] This is the HD-5 standard, (Heavy Duty-5% maximum allowable propylene content, and no more than 5% butanes and ethane) defined by the American Society for Testing and Materials by its Standard 1835 for internal combustion engines."


Originally Posted by Vlad
"
1 You can distill propane like I did. It is very easy just like making vodka. Old Russian tradition.

a. I put propane tank in freezer overnight. Low temperature will keep many additives frozen or liquid.

b. I connected refrigerant recovery unit and started pulling vapor propane from tank. Evaporating propane will keep tank even colder.

c. I used filter drier before recovery unit. There are some filters driers with male/female flares.

d. Condense propane to second tank.

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. "


From BradC

To Vlad, "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."


This seems correct for leaving Butane & isobutane in bottle

BUT, what about lower mass & more volatile Ethane?

Propane: Molecular Mass = 44.1, @1 atmosphere boil = -42.1C

Butane: Molecular Mass = 58.1, @1 atmosphere boil = 0C
Isobutane: Molecular Mass = 58.1, @1 atmosphere boil = -11.7C

Propylene: Molecular Mass = 42.1, @1 atmosphere boil = -47.6C
Ethane: Molecular Mass = 30.07, @1 atmosphere boil = -88.6C

[buffalobillpatrick]

Ethane @ 31.85C (89.33F) = 50 Bar (725 psi)

"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"

Would the Ethane come out then?

[NiHaoMike]

Apparently the blue torch bottles are more pure than the BBQ tanks.

[jeff5may]

If you need 99.99% pure propane, buy a bottle of r-290. It costs way more than bbq gas because of its high purity. For research projects at a university, the added cost and quality is worth the certainty of the results in a published paper. You don't need a refrigeration license to purchase it.

For hobby or personal use, I have found that the Worthington or Bernzomatic blowtorch bottles are of higher than 95% purity. Water is kept below 20 ppm at the refinery, because it accumulates and freezes in valves and orifices during distillation. Further downstream, the water would freeze up in pump stations and in fork trucks and regulators and such. Methane, ethane are distilled out as natural gas before the propane at the refinery. Butane and butylene are refined out after the propane.

The major contaminants in bbq propane are stink oil and propylene. The stink oil you can filter out, the propylene helps the propane act more like r-22.

[buffalobillpatrick]

Propane Butane Mix - Evaporation Pressure