Propylene, also known as propene, is an unsaturated organic compound with the chemical formula . It has one double bond, and is the second simplest member of the alkene class of hydrocarbons. It is a colorless gas with a faint petroleum-like odor. Production Steam cracking The dominant technology for producing propylene is steam cracking. The same technology is used to produce ethylene from ethane. Cracking propane yields a mixture of ethylene, propylene, methane, hydrogen, etc. The yield of propylene is about 15%. The other principal feedstock is naphtha, especially in the Middle East and Asia. Propylene can be separated by fractional distillation from hydrocarbon mixtures obtained from cracking and other refining processes; refinery-grade propene is about 50 to 70%. In the United States, shale gas is a major source of propane. Olefin conversion technology In the Phillips Triolefin or Olefin conversion technology propylene is interconverted with ethylene and 2-butenes. Rhenium and molybdenum catalysts are used: CH2=CH2{} + CH3CH=CHCH3 ->[][\text{Re, Mo} \atop \text{catalyst}] 2 CH2=CHCH3 The technology is founded on an olefin metathesis reaction discovered at Phillips Petroleum Company. Propylene yields of about 90 wt% are achieved. Related is the Methanol-to-Olefins/Methanol-to-Propene process. It converts synthesis gas (syngas) to methanol, and then converts the methanol to ethylene and/or propene. The process produces water as by-product. Synthesis gas is produced from |the reformation of natural gas or by the steam-induced reformation of petroleum products such as naphtha, or by gasification of coal. Fluid catalytic cracking High severity fluid catalytic cracking (FCC) uses traditional FCC technology under severe conditions (higher catalyst-to-oil ratios, higher steam injection rates, higher temperatures, etc.) in order to maximize the amount of propene and other light products. A high severity FCC unit is usually fed with gas oils (paraffins) and residues, and produces about 20–25 m% propene on feedstock together with greater volumes of motor gasoline and distillate byproducts. These high temperature processes are expensive and have a high carbon footprint. For these reasons, alternative routes to propylene continue to attract attention. Market and research Propene production has remained static at around 35 million tonnes (Europe and North America only) from 2000 to 2008, but it has been increasing in East Asia, most notably Singapore and China. Total world production of propene is currently about half that of ethylene. The use of engineered enzymes has been explored but has not been commercialized. Uses Propene is the second most important starting