Liquefying Air

Air can be liquefied. The air mixture’s critical temperature is about −140.7 °C and its critical pressure about 37.7 bar: above the critical temperature, pressure alone cannot create a liquid phase. Industrial liquefaction uses cooling, compression, and expansion; liquid air boils near −194 °C at atmospheric pressure. Thus, −150 °C and 60 atmospheres are not a universal process condition. [1–3]