WHY THE LIQUID LPG TURNING TO GAS IS NOT AGAIN TURNING BACK TO LIQUID IN THE ATMOSPHERE??

CRITICAL TEMPERATURE

The critical point is the highest pressure and highest temperature at which a pure chemical species is observed to exist in vapor/liquid equilibrium. Insight into the nature of the critical point is gained from a description of the changes that occur when a pure substance is heated in a sealed upright tube of constant volume. In other words, the critical temperature is the highest temperature, a gas can be liquefied by means of applying pressure. At or above the critical point, it is impossible to liquefy a pure gas by increasing pressure.

DAILY LIFE EXAMPLE

• Household gas distribution

HOUSEHOLD GAS DISTRIBUTION

In the early 1900s, town gas produced by the pyrolysis of mineral coal was supplied for household use. For the distribution of town gas, underground pipelines were constructed. Because the critical temperature of the town gas, containing hydrogen, carbon monoxide, and nitrogen, is below the daily temperatures, thus it cannot be liquefied to be sold in tubes. In the 1950s, LPG was supplied for household use instead of town gas. But due to the high critical temperature of LPG, consisting of propane and butane, it was possible to distribute in tubes instead of pipelines. In the 1990s, natural gas supplied for household use. Similar to town gas, primarily methane mixture of natural gas was distributed with pipelines due to its low critical temperature.