[mountainlion]

I took a “Power and Energy” course decades ago and liquified gas was part of the coursework. It seems that it took something like 3,500 PSI to to liquify natural gas. It was quite expensive compared to propane which may have been the point of the exercise. That was 35-40 years ago.

[thackney]

I took a “Power and Energy” course decades ago and liquified gas was part of the coursework. It seems that it took something like 3,500 PSI to to liquify natural gas.

You remember it incorrectly. No amount of pressure at atmospheric temperatures will liquefy methane. The critical temperature -116.7°F.

http://encyclopedia.airliquide.com/Encyclopedia.asp?GasID=41#VaporPressureGraph