Where Found (Encyclopedia of Global Resources)
Propane occurs in natural gas, to the extent of up to 6 percent, as well as with crude oil. It is commercially available after its separation from natural gas or the gases formed when heavy oil is broken down (cracked) to produce gasoline. The principal gas deposits are in the United States, Canada, the former Soviet bloc, and the Middle East.
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Primary Uses (Encyclopedia of Global Resources)
Technical Definition (Encyclopedia of Global Resources)
Propane’s condensed chemical formula is C3H8 or CH3CH2CH3, and it is a colorless, odorless, and nontoxic gas. It has a density of 0.58 gram per cubic meter at -450° Celsius, a melting point of -187° Celsius, and a boiling point of -42.2° Celsius. Its heat of combustion (the energy released when a hydrocarbon is burned in the presence of oxygen to produce carbon dioxide and water) is relatively high and is equal to 531 kilocalories per mole, or 2,220 kilojoules per mole.
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Description, Distribution, and Forms (Encyclopedia of Global Resources)
Propane is the third-lightest alkane of the hydrocarbon family after methane and ethane. Propane is almost insoluble in water, moderately soluble in alcohol, and very soluble in ether.
In 2007, the proven world reserves of natural gas (most of which is methane) were estimated to be well over 6,000 trillion cubic feet. This figure suggests that there are ample supplies of propane gas for the near future. Such sources include ultradeep gas, which is in the form of sedimentary deposits as deep as 15,000 meters, the hydrated gas that exists in the Arctic regions, and the reserves beneath the oceans.
Unlike coal and petroleum products, such as diesel fuel, which create environmental problems when burned, propane and natural gas are clean fuels. Pollution-control equipment is generally unnecessary. Incomplete combustion of propane, however, yields carbon monoxide (instead of carbon dioxide) and water. Carbon monoxide is particularly toxic to humans, since it has an excellent binding ability to the iron of hemoglobin and displaces oxygen during the breathing process. As a result, the tissues die from oxygen starvation. Incomplete propane combustion takes place in areas that do not have sufficient oxygen, such as closed garages and relatively airtight rooms. Because of this danger the use of camping stoves indoors to heat water is highly discouraged. Another area of great concern is the deliberate inhaling...
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History (Encyclopedia of Global Resources)
In 1910, Walter O. Snelling discovered propane while working for the U.S. Bureau of Mines. Snelling and others started the American Gasol Company to sell propane. The product reached its peak in the post-World War II era, when many houses were equipped with propane stoves. In the 1960’s, Chevrolet built and marketed propane trucks. In 1990, propane was designated a clean fuel.
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Obtaining Propane (Encyclopedia of Global Resources)
Propane is not a common starting reagent in industrial synthetic processes. Nevertheless, more than 20 percent of the propane obtained from natural gas sources is converted to its unsaturated derivative, propylene. This process involves its decomposition in hot tubes. Propane is also used in the synthesis of the colorless, flammable gas ethylene, which serves as the monomer of the useful polymer polyethylene. Polyethylene is the essential ingredient of many household plastics (such as plastic wraps for food items). Ethylene is formed via cracking, a process that involves high temperatures of about 500° Celsius and several atmospheres of pressure. Isopropyl alcohol, also known as rubbing alcohol, was the first petrochemical synthesized via propane in the 1920’s. The high-temperature oxidation of propane to acetaldehyde is also of commercial importance.
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Uses of Propane (Encyclopedia of Global Resources)
Propane and the next higher alkane, butane, are the main components of liquefied petroleum gas (LPG), which may be carried in tanks or cylinders and used as camping gas and in portable cooking stoves. In certain areas LPG is transported via pipelines, and it may also be used for internal combustion engines. In many agricultural areas propane and butane are more cost-effective tractor fuels than are gasoline and diesel fuel. Commercially, the clean-burning fuel is maintained in the liquid state, which is obtained under conditions of elevated pressures, in a steel container. It converts spontaneously to the gas state upon exposure to the normal atmospheric pressure. Unlike propane, butane condenses to a liquid at 0° Celsius and thus cannot be used for camping under cold conditions. As a result butane tends to be used in the southern United States, while propane (which condenses at -42° Celsius under normal pressure conditions is used in the North.
As noted previously, propane has a high heat of combustion, which, combined with its ease of transport, makes it a convenient fuel. Another way of measuring the fuel capacity of propane is its “heating value,” which measures the amount of heat evolved when a gram of propane is burned. Propane’s value is about 6,098 kilocalories per liter. Overall the fuel capacity of propane is about 2.5 times that of natural gas.
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Further Reading (Encyclopedia of Global Resources)
Atkins, Peter. Atkins’ Molecules. 2d ed. New York: Cambridge University Press, 2003.
Berger, Bill D., and Kenneth E. Anderson. Modern Petroleum: A Basic Primer of the Industry. 3d ed. Tulsa, Okla.: PennWell Books, 1992.
Erjavec, Jack, and Jeff Arias. “Propane/LPG Vehicles.” In Hybrid, Electric, and Fuel-Cell Vehicles. Clifton Park, N.Y.: Thomson Delmar Learning, 2007.
Gibilisco, Stan. “Propulsion with Methane, Propane, and Biofuels.” In Alternative Energy Demystified. New York: McGraw-Hill, 2007.
Myers, Richard L. “Propane.” In The One Hundred Most Important Chemical Compounds: A Reference Guide. Westport, Conn.: Greenwood Press, 2007.
Mushrush, George W., and James G. Speight. Petroleum Products: Instability and Incompatibility. Washington, D.C.: Taylor & Francis, 1995.
Royal Dutch/Shell Group of Companies, comp. The Petroleum Handbook. 6th ed. New York: Elsevier, 1983.
Speight, James G. The Chemistry and Technology of Petroleum. 4th ed. Boca Raton, Fla.: CRC Press/Taylor & Francis, 2007.
Weininger, Stephen J., and Frank R. Stermitz. Organic Chemistry. Orlando, Fla.: Academic Press, 1984.
U.S. Department of Energy. Alternative and Advanced Fuels: Propane. http://www.afdc.energy.gov/afdc/fuels/propane.html
U.S. Department of...
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Propane (How Products are Made)
Propane is a naturally occurring gas composed of three carbon atoms and eight hydrogen atoms. It is created along with a variety of other hydrocarbons (such as crude oil, butane, and gasoline) by the decomposition and reaction of organic matter over long periods of time. After it is released from oil fields deep within Earth, propane is separated from other petrochemicals and refined for commercial use. Propane belongs to a class of materials known as liquefied petroleum gases (LPGs), which are known for their ability to be converted to liquid under relatively low pressures. As a liquid, propane is 270 times more compact than it is as a gas, which allows it to be easily transported and stored as a liquid until ready for use. Approximately 15 billion gal (57 billion L) of propane are consumed annually in the United States as a fuel gas. The greatest consumers are the chemical and manufacturing industries, which use propane as chemical intermediates and aerosol propellants, followed by residential homes and commercial establishments, who use propane for heating and in dryers and portable grills.
The value of petroleum products has long been recognized by the civilized world, with documented examples of their use stretching back more than 5,000 years. The ancient Mesopotamians used petroleum-derived tar-like compounds for many applications, including caulking for masonry and bricks and adhesives for jewelry. About 2,000 years ago Arabian scientists learned one of the basic tenets of petroleum chemistryhat it can be distilled or separated into different parts, or fractions, based on their boiling points, and that each fraction has its own distinctive properties.
The modern era of refining is considered to have begun in 1859, when petroleum was found in Pennsylvania and the Sennaca Oil Company drilled the first oil well there. From a depth of 70 ft (21.2 m) the world's first oil well produced nearly 300 tons (305 metric tons) of oil in its first year, and thus an entire industry was born. Propane was first recognized as an important component of petroleum in 1910, when a Pittsburgh motor car owner asked chemist Dr. Walter Snelling why the gallon of gasoline he had purchased was half gone by the time he got home. The car owner thought the government should investigate why consumers were being cheated, because the gasoline was evaporating at a rapid and expensive rate. Snelling discovered a large part of liquid gasoline was actually composed of propane, butane, and other hydrocarbons. Using coils from an old hot water heater and other miscellaneous pieces of laboratory equipment, Snelling built a still that could separate the gasoline into its liquid and gaseous components. Since the days of Snelling, chemists have made tremendous advances in techniques for processing propane and other LPGs. Today, the manufacture of propane gas is an $8 billion industry in the United States.
Because propane has natural origins, it is not "made" of other raw materials; instead, it is "found" in petroleum chemical mixtures deep within the earth. These petroleum mixtures are literally rock oil, combinations of various hydrocarbon-rich fluids
The Manufacturing Process
Propane manufacture involves separation and collection of the gas from its petroleum sources. Propane and other LPGs are isolated from petrochemical mixtures in one of two waysy separation from the natural gas phase of petroleum and by refinement of crude oil.
- Both processes begin when underground oil fields are tapped by drilling oil wells. The gas/oil hydrocarbon mixture is piped out of the well and into a gas trap, which separates the stream into crude oil and "wet" gas, which contains natural gasoline, liquefied petroleum gases, and natural gas.
- Crude oil is heavier and sinks to the bottom of the trap; it is then pumped into an oil storage tank for later refinement. (Although propane is most easily isolated from the "wet gas" mixture, it can be produced from crude oil. Crude oil undergoes a variety of complex chemical processes, including catalytic cracking, crude distillation, and others. While the amount of propane produced by refinery processing is small compared to the amount separated from natural gas, it is still important because propane produced in this manner is commonly used as a fuel for refineries or to make LPG or ethylene.)
- The "wet" gas comes off the top of the trap and is piped to a gasoline absorption plant, where it is cooled and pumped through an absorption oil to remove the natural gasoline and liquefied petroleum gases. The remaining dry gas, about 90% methane, comes off the top of the trap and is piped to towns and cities for distribution by gas utility companies.
- The absorbing oil, saturated with hydrocarbons, is piped to a still where the hydrocarbons are boiled off. This petroleum mixture is known as "wild gasoline." The clean absorbing oil is then returned to the absorber, where it repeats the process.
- The "wild gasoline" is pumped to stabilizer towers, where the natural liquid gasoline is removed from the bottom and a mixture of liquefied petroleum gases is drawn off the top.
- This mixture of LP gases, which is about 10% of total gas mixture, can be used as a mixture or further separated into its three partsutane, isobutane, and propane (about 5% of the total gas mixture).
As described above, propane must be carefully isolated from a complex mixture of petrochemicals which includes methane, ethane, ethene, propene, isobutane, isobutene, butadiene, pentane, and pentene, to name a few. If such impurities are not removed, the propane or propane and butane mixture will not liquefy properly. Liquefaction at appropriate temperature and pressure is critical for the gas to be economically useful. The liquefied gas industry has established standardized specifications that LPG mixtures must conform to in order to be considered acceptable for use as fuel gas. Standardized test methodologies for evaluating these specifications are approved and published by the American Society for Testing and Materials (ASTM). For example, the LPG known as "commercial propane" must have a maximum vapor pressure of 200 psig at 100°F (38°C) and can have no more than 0.0017 ounces (0.05 ml) of residual matter. Furthermore, the allowed amount of volatile residue is strictly limited, and the gas must meet established guidelines for corrosivity to copper, volatile sulfur content, and moisture. Other mixtures of propane and butane are commercially available which have slightly different target values.
These tightly held quality standards make propane an environmentally attractive fuel. In fact, to meet pipeline standards, nearly all pollutants are removed from propane before it is allowed to enter pipelines. When used in properly adjusted and maintained burners, propane's emissions easily meet the standards for clean air set by the Environmental Protection Agency (EPA). Their testing has proven that propane is environmentally safer than other hydrocarbon energy sources, and that properly processed propane can be used as a motor fuel which is significantly cleaner than gasoline. Studies have shown that, compared to gasoline, propane engines have as much as 45% less ozone-forming potential. Results of another recent EPA study show propane reduces total hydrocarbon emissions by 29% according to the new Federal Clean Air Standards. Furthermore, carbon monoxide emissions are 93% below the standard, hydrocarbon emissions are 73% below the standard, and nitrogen oxide emissions are 57% below the standard.
As detailed above, the manufacture of propane produces a variety of byproducts that are economically useful. Actually, it is more accurate to think of these not as byproducts but as co-products, since they are produced along with propane as part of petroleum refinement. These co-products may be in the form of solids, gases, or liquids. Solids (or semisolids) include bitumes, hydrogen sulfide, and carbon dioxide and are sold for fuel purposes. The liquid fractions include crude oil, which is further refined to give a variety of products. These oils vary dramatically in appearance and physical properties like boiling point, density, odor, and viscosity. The different fractions of crude oil are referred to as "light" or "heavy" depending on their density. Light crude is rich in low-boiling and paraffinic hydrocarbons; heavy crudes are higher-boiling and more viscous. They yield a variety of asphalt-like molecules. Many of the co-products of propane production, such as propylene and butylene, are useful in gasoline refining, synthetic rubber manufacture, and the production of petrochemicals.
As the field of petroleum chemistry evolves, propane chemistry will continue to advance. Improvements will be made in the way propane is separated from petroleum. One area that offers opportunity for advancement is in the area of oil well production. Much natural gas is burned at remote oil wells because the extensive piping system required to transport it is prohibitively expensive. There are efforts underway to convert more of this wasted gas to condensable gases, which could be easily stored and transported. It is also important to note that propane is likely to become increasingly popular as a fuel gas based on economic factors and enviromnental concerns. In fact, in the Clean Air Act of 1990 Congress named LPGs as one of the clean-burning alternative fuels designated to take national air quality into the twenty-first century.
Where to Learn More
Clark, William, ed. Handbook of Butane! Propane Gases. Butane-Propane News, Inc., 1972.
National Propane Gas Association. http://www.propanegas.com/npga/ (July 14,1997).