Liquefied petroleum gas (LPG) is one of the petrochemical products, which refers to the petroleum gas that can be liquefied or stored and transported in liquid phase under appropriate ambient temperature and pressure. LPG mainly comes from the by-product gas from various devices in petroleum processing, and some comes from natural gas (including oil-associated gas). Obtained from refinery gas, LPG is mainly composed of propane, propylene, butane, butene, a small amount of pentane, pentene and traces of sulfur compound impurities. The liquefied gas obtained from natural gas (including oil-associated gas) basically doesn’t contain olefins.