Dictionary:

propane

  (prō'pān')

A colorless gas, C₃H₈, found in natural gas and petroleum and widely used as a fuel.

Background

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 chemistry—that 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.

Raw Materials

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 which accumulate in subterranean reservoirs made of porous layers of sandstone and carbonate rock. Petroleum is derived from various living organisms buried with sediments of early geological eras. The organisms were trapped between rock layers without oxygen and could not break down, or oxidize, completely. Instead, over tens of millions of years, the residual organic material was converted to propane-rich petroleum via two primary processes, diagenesis and catagenesis. Diagenesis occurs below 122°F (50°C) when the organic "soup" undergoes microbial action (and some chemical reactions) which result in dehydration, condensation, cyclization, and polymerization. Catagenesis, on the other hand, occurs under high temperatures of 122-424°F (50-200°C) and causes the organic materials to react via thermocatalytic cracking, decarboxylation, and hydrogen disproportionation. These complex reactions form petroleum in the sedimentary rocks.

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 ways—by separation from the natural gas phase of petroleum and by refinement of crude oil.

1. 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.
2. 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.)
3. 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.
4. 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.
5. 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.
6. 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 parts—butane, isobutane, and propane (about 5% of the total gas mixture).

Quality Control

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.

Byproducts/Waste

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.

The Future

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

Books

Clark, William, ed. Handbook of Butane! Propane Gases. Butane-Propane News, Inc., 1972.

Other

National Propane Gas Association. http://www.propanegas.com/npga/ (July 14,1997).

[Article by: Randy Schueller]

For more information on propane, visit Britannica.com.

Propane
General
Molecular formula	CH3CH2CH3 (g) C3H8 (g)
SMILES	CCC
Molar mass	44.096 g/mol
Appearance	Colorless gas
CAS number	[74-98-6]
Properties
Density and phase	1.83 kg/m3, gas
	0.5077 kg/L, liquid
Solubility in water	0.1 g/cm3 (37.8°C)
Melting point	−187.6 °C (85.5 K)
Boiling point	−42.09 °C (231.1 K)
Structure
Dipole moment	0.083 D
Symmetry group	C2v
Hazards
MSDS	External MSDS
EU classification	Extremely flammable (F+)
NFPA 704	4 1 0
R-phrases	R12
S-phrases	(S2), S9, S16
Flash point	-104 °C
Autoignition temperature	493-604 °C
Maximum burning temperature	2385°C
Explosive limits	2.37–9.5%
RTECS number	TX2275000
Supplementary data page
Structure and properties	n, εr, etc.
Thermodynamic data	Phase behaviour Solid, liquid, gas
Spectral data	UV, IR, NMR, MS
Related compounds
Related alkanes	Ethane Butane
Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa) Infobox disclaimer and references

Propane is a three-carbon alkane, normally a gas, but compressible to a liquid that is transportable. It is derived from other petroleum products during oil or natural gas processing. It is commonly used as a fuel for engines, barbecues, and home heating systems.

When sold as fuel, it is commonly known as liquified petroleum gas (LPG or LP-gas) which can be a mixture of propane along with small amounts of propylene, butane, and butylene. The odorant ethanethiol is also added so that people can easily smell the gas in case of a leak.

Properties and reactions

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.

C₃H₈ + 5O₂ → 3CO₂ + 4H₂O + heat

When not enough oxygen is present for complete combustion, propane burns to form water and carbon monoxide.

2C₃H₈ + 7O₂ → 6CO + 8H₂O + heat

Unlike natural gas, propane is heavier than air (1.5 times denser). In its raw state, propane sinks and pools at the floor. Liquid propane will flash to a vapor at atmospheric pressure and appears white due to moisture condensing from the air.

When properly combusted, propane produces about 2,500 BTU per cubic foot of gas.

Propane is nontoxic; however, when abused as an inhalant it poses a mild asphyxiation risk through oxygen deprivation. It must also be noted that commercial product contains hydrocarbons beyond propane, which may increase risk. Propane and its mixtures may cause mild frostbite during rapid expansion.

Propane combustion is much cleaner than gasoline, though not as clean as natural gas. The presence of C-C bonds, plus the multiple bonds of propylene and butylene, create organic exhausts besides carbon dioxide and water vapor during typical combustion. These bonds also cause propane to burn with a visible flame.

Uses

Retail sale of propane cylinders.

Propane is used as fuel in cooking on many barbecues, portable stoves and in motor vehicles. The ubiquitous 4.73-gallon (20 Lb.) steel container is often dubbed a "barbecue bottle". Propane powers some locomotives, buses, forklifts, and taxis and is used for heat and cooking in recreational vehicles and campers. In many rural areas of North America, propane is used in furnaces, cooking stoves, water heaters, laundry dryers, and other heat-producing appliances. As of 2000, 6.9 million American households use propane as their primary heating fuel.^[1]

Commercially-available "propane" fuel, or LPG, is not pure. Typically in the USA and Canada, it is primarily propane (at least 90%), with the rest mostly butane and propylene, plus odorants. This is the HD5 standard, written for vehicle fuels; note that not all products labeled "propane" conform to this standard. In Mexico, for example, the butane content is much higher.

Domestic and industrial fuel

In North America, local delivery trucks called "bobtails" fill up large tanks that are permanently installed on the property (sometimes called pigs), or other service trucks exchange empty cylinders of propane with filled cylinders. The bobtail is not unique to the North American market, though the practice is not as common elsewhere, and the vehicles are generally referred to as tankers. In many countries, propane is delivered to consumers via small or medium-sized individual tanks.

Propane is the fastest growing fuel source in the Third World, especially in China and India. Its use frees up the huge rural populations from time-consuming ancient chores such as wood gathering and allows them more time to pursue other activities, such as increased farming or educational opportunities. Hence it is sometimes referred to as "cooking gas."

As an aside, North American barbecue grills powered by propane cannot be used overseas. The "propane" sold overseas is actually a mixture of propane and butane. The warmer the country, the higher the butane content, commonly 50/50 and sometimes reaching 75% butane. Usage is calibrated to the different-sized nozzles found in non-U.S. grills. Americans who take their grills overseas — such as military personnel — can find U.S.-specification propane at AAFES military post exchanges.

Retail sale of propane in Monmouth, Oregon

North American industries using propane include glass makers, brick kilns, poultry farms, and other industries that need portable heat.

Propane risks and alternate gas fuels

Propane is heavier than air. If a leak in a propane fuel system occurs, the gas will have a tendency to sink into any enclosed area and thus poses a risk of explosion and fire. Compressed Natural Gas (CNG) is another gas used as fuel but is lighter than air and thus less risky. Propane is bought and stored in a liquid form (LPG) and thus more fuel energy can usually be stored in the same space than CNG.

Refrigeration

Propane is also instrumental in providing off-the-grid refrigeration, also called gas absorption refrigerators. Made popular by the Servel company, propane-powered refrigerators are highly efficient, do not require electricity, and have no moving parts. Refrigerators built in the 1930s are still in regular use, with little or no maintenance. However, certain Servel refrigerators are subject to a recall for CO poisoning. [1]

In highly purified form, propane (R-290) can serve as a direct replacement in mechanical refrigeration systems designed to use R-12, R-22 or R-134a chloro- or fluorocarbon based refrigerants. Today, the Unilever Ice Cream company and others are exploring the use of environmentally friendly propane as a refrigerant. As an added benefit, users are finding that refrigerators converted to use propane are 9-15% more energy efficient.

Vehicle fuel

Main article: Autogas

Propane is also being used increasingly for vehicle fuels. In the U.S., 190,000 on-road vehicles use propane, and 450,000 forklifts use it for power. It is the third most popular vehicle fuel in America, behind gasoline and diesel. In other parts of the world, propane used in vehicles is known as autogas. About 9 million vehicles worldwide use autogas.

The advantage of propane is its liquid state at room temperature and moderate pressure. This allows fast refill times, affordable fuel tank construction, and ranges comparable to (though still less than) gasoline. Meanwhile it is noticeably cleaner (both in handling, and in combustion), results in less engine wear (due to carbon deposits) without diluting engine oil (often extending oil-change intervals), and until recently was a relative bargain in North America. Octane rating is noticeably higher, which could result in more power, though exploiting this extra "octane" requires significant engine modification. However, public filling stations are still rare. Many converted vehicles have provisions for topping off from "barbecue bottles." Purpose-built vehicles are often in commercially-owned fleets, and have private fueling facilities.

Propane is generally stored and transported in steel cylinders as a liquid with a vapour space above the liquid. The vapour 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 extreme cases this may cause such a large reduction in pressure that the process can no longer be supported. In addition, the lightweight, high-octane compounds vaporize before the heavier, low-octane ones. Thus the ignition properties change as the tank empties. For these reasons, the liquid is often withdrawn using a dip tube.

Other

• It is also used as a feedstock for the production of base petrochemicals in steam cracking.
• Propane is used in some flamethrowers, as the fuel, or as the pressurizing gas.
• Some propane becomes a feedstock for propyl alcohol, a common solvent.
• It is used as fuel in hot air balloons.
• It is used in semiconductor manufacture to deposit silicon carbide

Sources

Propane is produced as a byproduct of two other processes: natural gas processing and petroleum refining.

The processing of natural gas involves removal of butane, propane, and large amounts of ethane from the raw gas, to prevent condensation of these volatiles in natural gas pipelines. Additionally, oil refineries produce some propane as a by-product of production of cracking petroleum into gasoline or heating oil.

The supply of propane cannot be easily adjusted to account for increased demand because of the by-product nature of propane production. About 85% of U.S. propane is domestically produced.

The United States imports about 10-15% of the propane consumed each year. Propane is imported into the United States via pipeline and rail from Canada, and by tankers from Algeria, Saudi Arabia, Venezuela, Norway and the United Kingdom.

After it is produced, North American propane is stored in huge salt caverns located in Fort Saskatchewan, Alberta, Canada, Mont Belvieu, Texas, and Conway, Kansas. These salt caverns were hollowed out in the 1940s and can store up to 80 million barrels of propane, if not more. When the propane is needed, most of it is shipped by pipelines to other areas of the Midwest, the North, and the South, for use by customers. Propane is also shipped by barge and rail car to selected U.S. areas.^{[citation needed]}

History

Propane was first identified as a volatile component in gasoline by Dr. Walter O. Snelling of the U.S. Bureau of Mines in 1910. Car owners had complained of disappearing fuel, between the time they had filled up and the time they arrived home.

See also

• Alkanes
• Hydrocarbons
• Gasoline

References

1. ^ U. S. Census Bureau, U.S. Departments of Energy and Transportation statistics (2000). General U.S. Industry Statistics and Characteristics of Propane. Retrieved on 2007-09-06.

External links

Wikimedia Commons has media related to:

Propane

• Propane Education & Research Council (U.S.)
• World LP Gas Association (WLPGA)
• International Chemical Safety Card 0319
• NIOSH Pocket Guide to Chemical Hazards
• Molview from bluerhinos.co.uk See Propane in 3D
• National Propane Gas Association (U.S.)

• Propane Gas Association of Canada
• European Chemicals Bureau
• LP Gas Association: Propane and Butane in the UK
• Computational Chemistry Wiki

 

Alkanes
Methane CH4	|		Ethane C2H6	|		Propane C3H8	|		Butane C4H10	|		Pentane C5H12	|		Hexane C6H14
Heptane C7H16	|		Octane C8H18	|		Nonane C9H20	|		Decane C10H22	|		Undecane C11H24	|		Dodecane C12H26

E numbers

Colors (E100–199) • Preservatives (E200–299) • Antioxidants & Acidity regulators (E300–399) • Thickeners, stabilisers & emulsifiers (E400–499) • pH regulators & anti-caking agents (E500–599) • Flavour enhancers (E600–699) • Miscellaneous (E900–999) • Additional chemicals (E1100–1599) Waxes (E900–909) • Synthetic glazes (E910–919) • Improving agents (E920–929) • Packaging gases (E930–949) • Sweeteners (E950–969) • Foaming agents (E990–999) Calcium peroxide (E930) • Argon (E938) • Helium (E939) • Dichlorodifluoromethane (E940) • Nitrogen (E941) • Nitrous oxide (E942) • Butane (E943a) • Isobutane (E943b) • Propane (E944) • Oxygen (E948) • Hydrogen (E949)

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Dansk (Danish)
n. - propan

Nederlands (Dutch)
propaan

Français (French)
n. - propane

Deutsch (German)
n. - (Chem.) Propan

Ελληνική (Greek)
n. - (χημ.) προπάνιο

Italiano (Italian)
propano

Português (Portuguese)
n. - propano (m)

Русский (Russian)
пропан

Español (Spanish)
n. - propano

Svenska (Swedish)
n. - propan

中文（简体） (Chinese (Simplified))
丙烷

中文（繁體） (Chinese (Traditional))
n. - 丙烷

한국어 (Korean)
n. - 프로판(메탄계 탄화수소의 하나)

日本語 (Japanese)
n. - プロパン

العربيه (Arabic)
‏(الاسم) غاز البروبين‏

עברית (Hebrew)
n. - ‮פרופן (גז)‬

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