Propane
Propane is a three-carbon chain alkane with the molecular formula. It is a gas at standard temperature and pressure, but becomes liquid when compressed for transportation and storage. A by-product of natural gas processing and petroleum refining, it is often a constituent of liquefied petroleum gas, which is commonly used as a fuel in domestic and industrial applications and in low-emissions public transportation; other constituents of LPG may include propylene, butane, butylene, butadiene, and isobutylene. Discovered in 1857 by the French chemist Marcellin Berthelot, it became commercially available in the US by 1911. Propane has lower volumetric energy density than gasoline or coal, but has higher gravimetric energy density than them and burns more cleanly.
Propane gas has become a popular choice for barbecues and portable stoves because its low −42 °C boiling point makes it vaporise inside pressurised liquid containers. It retains its ability to vaporise even in cold weather, making it better-suited for outdoor use in cold climates than alternatives with higher boiling points like butane. LPG powers buses, forklifts, automobiles, outboard boat motors, and ice resurfacing machines, and is used for heat and cooking in recreational vehicles and campers. Propane is also becoming popular as a replacement refrigerant for heatpumps as it offers greater efficiency than the current refrigerants: R410A / R32, higher temperature heat output and less damage to the atmosphere for escaped gases—at the expense of high gas flammability.
History
Propane was first synthesized by the French chemist Marcellin Berthelot in 1857 during his researches on hydrogenation. Berthelot made propane by heating propylene dibromide with potassium iodide and water. Propane was found dissolved in Pennsylvanian light crude oil by Edmund Ronalds in 1864. Walter O. Snelling of the U.S. Bureau of Mines highlighted it as a volatile component in gasoline in 1910, which marked the "birth of the propane industry" in the United States. The volatility of these lighter hydrocarbons caused them to be known as "wild" because of the high vapor pressures of unrefined gasoline. On March 31, 1912, The New York Times reported on Snelling's work with liquefied gas, saying "a steel bottle will carry enough gas to light an ordinary home for three weeks".It was during this time that Snelling—in cooperation with Frank P. Peterson, Chester Kerr, and Arthur Kerr—developed ways to liquefy the LP gases during the refining of gasoline. Together, they established American Gasol Co., the first commercial marketer of propane. Snelling had produced relatively pure propane by 1911, and on March 25, 1913, his method of processing and producing LP gases was issued patent #1,056,845. A separate method of producing LP gas through compression was developed by Frank Peterson and its patent was granted on July 2, 1912.
The 1920s saw increased production of LP gases, with the first year of recorded production totaling in 1922. In 1927, annual marketed LP gas production reached, and by 1935, the annual sales of LP gas had reached. Major industry developments in the 1930s included the introduction of railroad tank car transport, gas odorization, and the construction of local bottle-filling plants. The year 1945 marked the first year that annual LP gas sales reached a billion gallons. By 1947, 62% of all U.S. homes had been equipped with either natural gas or propane for cooking.
In 1950, 1,000 propane-fueled buses were ordered by the Chicago Transit Authority, and by 1958, sales in the U.S. had reached annually. In 2004, it was reported to be a growing $8-billion to $10-billion industry with over of propane being used annually in the U.S.
During the COVID-19 pandemic, propane shortages were reported in the United States due to increased demand.
Etymology
The prop- root found in propane and names of other compounds with three-carbon chains was derived from propionic acid, which in turn was derived from the Ancient Greek words πρῶτος,, "first" and πίων,, "fat", as it was the "first" member of the series of fatty acids.Properties and reactions
Propane is a colorless, odorless gas. Ethyl mercaptan is added as a safety precaution as an odorizer, and is commonly called a "rotten egg" smell. At normal pressure it liquifies below its boiling point at −42 °C and solidifies below its melting point at −187.7 °C. Propane crystallizes in the space group P21/n. The low space-filling of 58.5%, due to the bad stacking properties of the molecule, is the reason for the particularly low melting point.Propane undergoes combustion reactions in a similar fashion to other alkanes. In the presence of excess oxygen, propane burns to form water and carbon dioxide.
When insufficient oxygen is present for complete combustion, carbon monoxide, soot, or both, are formed as well:
The complete combustion of propane produces about 50 MJ/kg of heat.
Propane combustion is much cleaner than that of coal or unleaded gasoline. Propane's per-BTU production of CO2 is almost as low as that of natural gas. Propane burns hotter than home heating oil or diesel fuel because of the very high hydrogen content. The presence of C–C bonds, plus the multiple bonds of propylene and butylene, produce organic exhausts besides carbon dioxide and water vapor during typical combustion. These bonds also cause propane to burn with a visible flame.
Energy content
The enthalpy of combustion of propane gas where all products return to standard state, for example where water returns to its liquid state at standard temperature, is kJ/mol, or MJ/kg.The enthalpy of combustion of propane gas where products do not return to standard state, for example where the hot gases including water vapor exit a chimney, is 2,043.455 kJ/mol. The lower heat value is the amount of heat available from burning the substance where the combustion products are vented to the atmosphere; for example, the heat from a fireplace when the flue is open.
Density
The density of propane gas at 25 °C is 1.808 kg/m3, about 1.5× the density of air at the same temperature. The density of liquid propane at 25 °C is 0.493 g/cm3, which is equivalent to 4.11 pounds per U.S. liquid gallon or 493 g/L. Propane expands at 1.5% per 10 °F. Thus, liquid propane has a density of approximately 4.2 pounds per gallon at 60 °F.As the density of propane changes with temperature, this fact must be considered every time when the application is connected with safety or custody transfer operations. If enough headspace is not left in a tank when filling, the tank could rupture when it heats up.
Uses
Portable stoves
Propane is a popular choice for barbecues and portable stoves because the low boiling point of 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.Refrigerant
Blends of pure, dry "isopropane" can be used as the circulating refrigerant in suitably constructed compressor-based refrigeration. Compared to fluorocarbons, propane has a negligible ozone depletion potential and very low global warming potential, or GWP and can serve as a functional replacement for R-12, R-22, R-134a, and other chlorofluorocarbon or hydrofluorocarbon refrigerants in conventional stationary refrigeration and air conditioning systems. Because its global warming effect is far less than current refrigerants, propane was chosen as one of five replacement refrigerants approved by the EPA in 2015, for use in systems specially designed to handle its flammability.Such substitution is widely prohibited or discouraged in motor vehicle air conditioning systems, on the grounds that using flammable hydrocarbons in systems originally designed to carry non-flammable refrigerant presents a significant risk of fire or explosion.
Vendors and advocates of hydrocarbon refrigerants argue against such bans on the grounds that there have been very few such incidents relative to the number of vehicle air conditioning systems filled with hydrocarbons.
Propane is also instrumental in providing off-the-grid refrigeration, as the energy source for a gas absorption refrigerator, and is commonly used for camping and recreational vehicles.
It has also been proposed to use propane as a refrigerant in heat pumps.
Domestic and industrial fuel
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. In June 2023, Stanford researchers found propane combustion emitted detectable and repeatable levels of benzene that in some homes raised indoor benzene concentrations above well-established health benchmarks. The research also shows that gas and propane fuels appear to be the dominant source of benzene produced by cooking.In rural areas of North America, as well as northern Australia, propane is used to heat livestock facilities, in grain dryers, and other heat-producing appliances. When used for heating or grain drying it is usually stored in a large, permanently-placed cylinder which is refilled by a propane-delivery truck., 6.2 million American households use propane as their primary heating fuel.
In North America, local delivery trucks with an average cylinder size of, fill up large cylinders that are permanently installed on the property, or other service trucks exchange empty cylinders of propane with filled cylinders. Large tractor-trailer trucks, with an average cylinder size of, transport propane from the pipeline or refinery to the local bulk plant. The bobtail tank truck is not unique to the North American market, though the practice is not as common elsewhere, and the vehicles are generally called tankers. In many countries, propane is delivered to end-users via small or medium-sized individual cylinders, while empty cylinders are removed for refilling at a central location.
There are also community propane systems, with a central cylinder feeding individual homes.