CO2 Bottle Impurity

[tripeland]

I see a lot of recent threads talking about the purity of commercial CO2 bottles, especially in regard to the O2 impurity level (around <0.02% depending on supplier) and it’s potential for oxidation when used to carbonate beer.
The critical temperature of oxygen is around -118C, above this temperature it cannot be compressed into liquid phase. CO2 on the other hand has a critical temperature of around +31C, and is supplied in a gas/liquid phase at around 800-1100psi depending on ambient temperature. This means that any O2 impurity exists only as a mixture with CO2 in gas phase inside the pressurised bottle
Wouldn’t then the gaseous O2 simply be flushed from the bottle with the gaseous CO2 within the first few moments of use, such as purging a line? Then there would be no further O2 impurity to be concerned with for force carbonation.
Or does the O2 diffuse into the liquid CO2 and reintroduce itself in the CO2 gas as it is boiled during depressurisation.

 

[Vale71]

Or does the O2 diffuse into the liquid CO2 and reintroduce itself in the CO2 gas as it is boiled during depressurisation.

This. Liquid CO2 is an excellent solvent.