Propane is a three-carbon alkane with the molecular formula C3H8, normally a gas, but compressible to a transportable liquid. A by-product of natural gas processing and petroleum refining, it is commonly used as a fuel forengines, oxy-gas torches, barbecues, portable stoves, and residential central heating. Propane is one of a group ofliquefled petroleum gases (LP gases). The others include butane, propylene, butadiene, butylene, isobutylene and mixtures thereof.
Propane is a popular choice for barbecues and portable stoves because the low boiling point of -42 °C (--44 °F) makes it vaporize as soon as it is released from its pressurized container. Therefore, no carburetor or other vaporizing device is required; a simple metering nozzle suffices. Propane powers some locomotives, buses, forklifts, taxis and ice resurfacing machines and is used for heat and cooking in recreational vehicles and campers. Since it can be transported easily, it is a popular fuel for home heat and backup electrical generation in sparsely populated areas that do not have natural gas pipelines.
Propane is generally stored and transported in steel cylinders as a liquid with a vapor space above the liquid. The vapor pressure in the cylinder is a function of temperature. When gaseous propane is drawn at a high rate, the latent heat of vaporisation required to create the gas will cause the bottle to cool. (This is why water often condenses on the sides of the bottle and then freezes). In addition, the lightweight, high-octane compounds vaporize before the heavier, low-octane ones. Thus, the ignition properties change as the cylinder empties. For these reasons, the liquid is often withdrawn using a dip tube. Propane is used as fuel in furnaces for heat, in cooking, as an energy source for water heaters, laundry dryers, barbecues, portable stoves, and motor vehicles.
Commercially available "propane" fuel, or L PG, is not pure. Typically in the United States and Canada, it is primarily propane (at least 90%), with the rest mostly ethane, propylene, butane, and odorants including ethyl mercaptan.This is the HD-5 standard, (Heavy Duty-5% maximum allowable propylene content, and no more than5% butanes and ethane) defined by the American Society for Testing and Materials by its Standard 1835 for internal combustion engines. Not all products labeled "propane" conform to this standard however. In Mexico, for example, where much of the bottled liquefied gas sold is, in fact, butane, gas labeled "propane" may actually consist of 60% propane and 40% butane.