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Crude oil]]
Petroleum (from Latin petra – rock and oleum – oil), crude oil, sometimes colloquially called black gold, is a thick, dark brown or greenish liquid. A widely believed myth is that the oil itself is flammable; however, it is actually the gas that evaporates from the oil that is flammable. Petroleum exists in the upper strata of some areas of the Earth's crust. Another name is naphtha, from Persian naft or nafátá (to flow). It consists of a complex mixture of various hydrocarbons, largely of the alkane series, but may vary much in appearance, composition, and purity. Petroleum is used mostly, by volume, for producing fuel oil, which is an important "primary energy" source ([http://www.iea.org/bookshop/add.aspx?id=144 IEA Key World Energy Statistics]). Petroleum is also the raw material for many chemical products, including solvents, fertilizers, pesticides, and plastics.
Origin
Biogenic theory
Most geologists view crude oil, like coal and natural gas, as the product of compression and heating of ancient vegetation over geological time scales. According to this theory, it is formed from the decayed remains of prehistoric marine animals and terrestrial plants. Over many centuries this organic matter, mixed with mud, is buried under thick sedimentary layers of material. The resulting high levels of heat and pressure cause the remains to metamorphose, first into a waxy material known as kerogen, and then into liquid and gaseous hydrocarbons in a process known as catagenesis. These then migrate through adjacent rock layers until they become trapped underground in porous rocks called reservoirs, forming an oil field, from which the liquid can be extracted by drilling and pumping.
150 °C is generally considered the "oil window". Though this corresponds to different depths for different locations around the world, a 'typical' depth for an oil window might be 4 - 5 km. Three conditions must be present for oil reservoirs to form: a rich source rock, a migration conduit, and a trap (seal) that forms the reservoir.
The reactions that produce oil and natural gas are often modeled as first order breakdown reactions, where kerogen breaks down to oil and natural gas by a large set of parallel reactions, and oil eventually breaks down to natural gas by another set of reactions.
Abiogenic Theory
The idea of abiogenic petroleum origin was championed in the Western world by Thomas Gold based on thoughts from Russia, mainly on studies of Nikolai Kudryavtsev. The idea proposes that large amounts of carbon exist naturally in the planet, some in the form of hydrocarbons. Hydrocarbons are less dense than aqueous pore fluids, and migrate upward through deep fracture networks. Thermophilic, rock-dwelling microbial life-forms are in part responsible for the biomarkers found in petroleum. However, their role in the formation, alteration, or contamination of the various hydrocarbon deposits is not yet understood. Thermodynamic calculations and experimental studies confirm that n-alkanes (common petroleum components) do not spontaneously evolve from methane at pressures typically found in sedimentary basins, and so the theory of an abiogenic origin of hydrocarbons suggests deep generation (below 200 km) (see results [http://www.gasresources.net/]).
As with any petroleum, the idea goes, these hydrocarbons would migrate upwards with methane, sometimes bearing helium and nitrogen and frequently heavy metals such as Nickel, Vanadium, Arsenic, Lead, Cadmium, Copper, Zinc, Mercury and others. Diamondoids are common in oil and gas and its nature probably is related to natural diamonds that come from earth's mantle. The proponents of abiogenic petroleum claim that reserves are never exhausted because they are filled from below. This idea has not been supported by any critically reviewed research. It has been widely discredited by scientists and geologists alike. Also, even if oil fields can be replenished from abiotic deposits that exist deeper within the earth, it would be very near impossible that they could be replenished at current rates of depletion, future rates aside. It would certainly take many thousands if not millions of years for oil fields to regain original levels.
Composition
In refining, the component chemicals of petroleum are separated by fractional distillation, which is a separation based on relative boiling points (or equivalently relative volatility). The different products (in order of boiling points) include light gases (e.g. methane, ethane, propane), gasoline, jet fuel, kerosene, diesel, gasoil, paraffin wax, and asphalt. Subtler techniques, such as gas chromatography, HPLC, and GC-MS, can separate some fractions of petroleum into individual compounds; these are analytical chemistry methods used mainly in quality control in refineries.
Strictly speaking, petroleum consists of hydrocarbons (compounds of hydrogen and carbon) and non-hydrocarbon fractions, which might also include nitrogen, sulfur, oxygen, or traces of metals such as vanadium or nickel, such elements often constituting less than 1% of the whole.
The four lightest alkanes — CH4 (methane), C2H6 (ethane), C3H8
(propane) and C4H10 (butane) — are all gases, boiling at -161.6 °C, -88.6 °C, -42 °C, and -0.5 °C, respectively (-258.9°, -127.5°, -43.6°, and +31.1° F). Crude oil is non-polar.
The chains in the C5-7 range are all light, easily vaporized, clear naphthas. They are used as solvents, dry cleaning fluids, and other quick-drying products. The chains from C6H14 through C12H26 are blended together and used for gasoline. Kerosene is made up of chains in the C10 to C15 range, followed by diesel fuel/heating oil (C10 to C20) and heavier fuel oils as the ones used in ship engines. These petroleum compounds are all liquid at room temperature.
Lubricating oils and semi-solid greases (including Vaseline®) range from C16 up to C20.
Chains above C20 form solids, starting with paraffin wax, then tar and asphaltic bitumen.
Boiling ranges of petroleum atmospheric pressure distillation fractions in degrees Celsius:
- petrol ether: 40 - 70 °C (used as solvent)
- light petrol: 60 - 100 °C (gasoline)
- heavy petrol: 100 - 150 °C (automobile fuel)
- light kerosene: 120 - 150 °C (household solvent and fuel)
- kerosene: 150 - 300 °C (jet fuel)
- gasoil: 250 - 350 °C (diesel fuel/heating oil)
- lubrication oil: > 300 °C (engine oil)
- remaining fractions: tar, asphalt, residual fuel
Extraction
Generally the first stage in the extraction of crude oil is to drill a well into the underground reservoir. Historically, in the USA some oil fields existed where the oil rose naturally to the surface, but most of these fields have long since been depleted, except for certain remote locations in Alaska. Often many wells (called multilateral wells) will be drilled into the same reservoir, to ensure that the extraction rate will be economically viable. Also, some wells (secondary wells) may be used to pump water, steam, acids or various gas mixtures into the reservoir to raise or maintain the reservoir pressure, and so maintain an economic extraction rate.
If the underground pressure in the oil reservoir is sufficient, then the oil will be forced to the surface under this pressure. Gaseous fuels or natural gas are usually present, which also supplies needed underground pressure. In this situation it is sufficient to place a complex arrangement of valves (the Christmas tree) on the well head to connect the well to a pipeline network for storage and processing. This is called primary oil recovery. Usually, only about 20% of the oil in a reservoir can be extracted this way.
Over the lifetime of the well the pressure will fall, and at some point there will be insufficient underground pressure to force the oil to the surface. If economical, and it often is, the remaining oil in the well is extracted using secondary oil recovery methods (see: energy balance and net energy gain). Secondary oil recovery uses various techniques to aid in recovering oil from depleted or low-pressure reservoirs. Sometimes pumps, such as beam pumps and electrical submersible pumps (ESPs), are used to bring the oil to the surface. Other secondary recovery techniques increase the reservoir's pressure by water injection, natural gas reinjection and gas lift, which injects air, carbon dioxide or some other gas into the reservoir. Together, primary and secondary recovery allow 25% to 35% of the reservoir's oil to be recovered.
Tertiary oil recovery reduces the oil's viscosity to increase oil production. Tertiary recovery is started when secondary oil recovery techniques are no longer enough to sustain production, but only when the oil can still be extracted profitably. This depends on the cost of the extraction method and the current price of crude oil. When prices are high, previously unprofitable wells are brought back into production and when they are low, production is curtailed. Thermally-enhanced oil recovery methods (TEOR) are tertiary recovery techniques that heat the oil and make it easier to extract. Steam injection is the most common form of TEOR, and is often done with a cogeneration plant. In this type of cogeneration plant, a gas turbine is used to generate electricity and the waste heat is used to produce steam, which is then injected into the reservoir. This form of recovery is used extensively to increase oil production in the San Joaquin Valley, which has very heavy oil, yet accounts for 10% of the United States' oil production. In-situ burning is another form of TEOR, but instead of steam, some of the oil is burned to heat the surrounding oil. Occasionally, detergents are also used to decrease oil viscosity. Tertiary recovery allows another 5% to 15% of the reservoir's oil to be recovered.
Alternate means of producing oil
As oil prices continue to escalate, other alternatives to producing oil have been gaining importance. The most viable of these is the coal to oil process, known as the Fischer-Tropsch process, that aims to convert coal into crude oil. It was a concept pioneered in Nazi Germany when imports of petroleum were restricted due to war and Germany found a method to extract oil from coal. It was known as Ersatz ("substitute" in German), and accounted for nearly half the total oil used in WWII by Germany. However, the process was used only as a last resort as naturally occurring oil was much cheaper. As crude oil prices increase, the cost of coal to oil conversion becomes comparatively cheaper.
The method involves converting high ash coal into synthetic oil in a multistage process. Ideally, a ton of coal produces nearly 200 liters of crude, with by-products ranging from tar to rare chemicals.
Currently, two companies have commercialised their Fischer-Tropsch technology. [http://www.shell.com.my/smds Shell] in Bintulu, Malaysia, uses natural gas as a feedstock, and produces primarily low-sulfur diesel fuels. [http://www.sasol.com Sasol] in South Africa uses coal as a feedstock, and produces a variety of synthetic petroleum products.
The process is today used in South Africa to produce most of the country's diesel fuel from coal by the company Sasol. The process was used in South Africa to meet its energy needs during its isolation under Apartheid. This process has received renewed attention in the quest to produce low sulfur diesel fuel in order to minimize the environmental impact from the use of diesel engines.
History
The first oil wells were drilled in China in the 4th century or earlier. They had depth of up to 800 feet and were drilled using bits attached to bamboo poles. The oil was burned to evaporate brine and produce salt. By the 10th century, extensive bamboo pipelines connected oil wells with salt springs.
Ancient Persian tablets indicate the medicinal and lighting uses of petroleum in the upper echelons of their society.
In the 8th century, the streets of the newly-constructed Baghdad were paved with tar, derived from easily-accessible petroleum from natural fields in the region. In the 9th century, oil fields were exploited in Baku, Azerbaijan, to produce naphtha. These fields were described by the geographer Masudi in the 10th century, and by Marco Polo in the 13th century, who described the output of those wells as hundreds of shiploads. (See also: Timeline of Islamic science and technology.)
The modern history of oil began in 1853, with the discovery of the process of oil distillation. Crude oil was distilled into kerosene by Ignacy Lukasiewicz, a Polish scientist. The first "rock oil" ("petr-oleum") mine was created in Bobrka, near Krosno in southern Poland in the following year and the first refinery (actually a distillery) was built in Ulaszowice, also by Lukasiewicz. These discoveries rapidly spread around the world, and Meerzoeff built the first Russian refinery in the mature oil fields at Baku in 1861.
1861 by Russian engineer F.N. Semyenov, on the Aspheron Peninsula north-east of Baku.38]]
The first commercial oil well drilled in North America was in Oil Springs, Ontario, Canada in 1858, dug by James Miller Williams. The American petroleum industry began with Edwin Drake's discovery of oil in 1859, near Titusville, Pennsylvania. The industry grew slowly in the 1800s, driven by the demand for kerosene and oil lamps. It became a major national concern in the early part of the 20th century; the introduction of the internal combustion engine provided a demand that has largely sustained the industry to this day. Early "local" finds like those in Pennsylvania and Ontario were quickly exhausted, leading to "oil booms" in Texas, Oklahoma, and California.
By 1910, significant oil fields had been discovered in Canada (specifically, in the province of Alberta), the Dutch East Indies (1885, in Sumatra), Persia (1901, in Masjed Soleiman), Peru, Venezuela, and Mexico, and were being developed at an industrial level.
Even until the mid-(1950s), coal was still the world's foremost fuel, but oil quickly took over. Following the 1973 energy crisis and the 1979 energy crisis there was significant media coverage of oil supply levels. This brought to light the concern that oil is a limited resource that will eventually run out, at least as an economically viable energy source. At the time, the most common and popular predictions were always quite dire, and when they did not come true, many dismissed all such discussion. The future of petroleum as a fuel remains somewhat controversial. USA Today news (2004) reports that there are 40 years of petroleum left in the ground. Some would argue that because the total amount of petroleum is finite, the dire predictions of the 1970s have merely been postponed. Others argue that technology will continue to allow for the production of cheap hydrocarbons and that the earth has vast sources of unconventional petroleum reserves in the form of tar sands, bitumen fields and oil shale that will allow for petroleum use to continue for an extremely long period in the future.
Today, about 90% of vehicular fuel needs are met by oil. Petroleum also makes up 40% of total energy consumption in the United States, but is responsible for only 2% of electricity generation. Petroleum's worth as a portable, dense energy source powering the vast majority of vehicles and as the base of many industrial chemicals makes it one of the world's most important commodities. Access to it was a major factor in several military conflicts, including World War II and the Persian Gulf War. About 80% of the world's readily accessible reserves are located in the Middle East, with 62.5% coming from the Arab 5: Saudi Arabia (12.5%), UAE, Iraq, Qatar and Kuwait. The USA has less than 3%.
Environmental effects
The presence of oil has significant social and environmental impacts, from accidents and routine activities such as seismic exploration, drilling, and generation of polluting wastes. Oil extraction is costly and sometimes environmentally damaging, although Dr. John Hunt from Woods Hole pointed out in a 1981 paper that over 70% of the reserves in the world are associated with visible macroseepages, and many oil fields are found due to natural leaks. Offshore exploration and extraction of oil disturbs the surrounding marine environment. Extraction may involve dredging, which stirs up the seabed, killing the sea plants that marine creatures need to survive. Crude oil and refined fuel spills from tanker ship accidents have damaged fragile ecosystems in Alaska, the Galapagos Islands, Spain, and many other places.
Burning oil releases carbon dioxide into the atmosphere, which contributes to global warming. Per energy unit, oil produces less CO2 than coal, but more than natural gas. However, oil's unique role as a transportation fuel makes reducing its CO2 emissions a particularly thorny problem; amelioration strategies such as carbon sequestering are generally geared for large power plants, not individual tailpipes.
Renewable energy source alternatives do exist, although the degree to which they can replace petroleum and the possible environmental damage they may cause are uncertain and controversial. Sun, wind, geothermal, and other renewable electricity sources cannot directly replace high energy density liquid petroleum for transportation use; instead automobiles and other equipment must be altered to allow using electricity (in batteries) or hydrogen (via fuel cells or internal combustion) which can be produced from renewable sources. Other options include using biomass-origin liquid fuels (ethanol, biodiesel). Any combination of solutions to replace petroleum as a liquid transportation fuel will be a very large undertaking.
Future of oil
Main article: Hubbert Peak
The Hubbert peak theory, also known as peak oil, is a theory concerning the long-term rate of production of conventional oil and other fossil fuels. It assumes that oil reserves are not replenishable (i.e. that abiogenic replenishment is negligible), and predicts that future world oil production must inevitably reach a peak and then decline as these reserves are exhausted. Controversy surrounds the theory, as predictions for when the global peak will actually take place are highly dependent on the past production and discovery data used in the calculation.
The issue can be considered from the point of view of individual regions or of the world as a whole. Originally M. King Hubbert noticed that the discoveries in the United States had peaked in the early 1930s, and concluded that production would then peak in the early 1970s. His prediction turned out to be correct, and after the US peaked in 1971 - and thus lost its excess production capacity - OPEC was finally able to manipulate oil prices, which led to the oil crisis in 1973. Since then, most other countries have also peaked: Britain's North Sea, for example in late 1990s. China has confirmed that two of its largest producing regions are in decline, and Mexico's national oil company, Pemex, has announced that Cantarell Field, one of the world's largest offshore fields, is expected to peak in 2006, and then decline 14% per annum.
For various reasons (perhaps most importantly the lack of transparency in accounting of global oil reserves), it is difficult to predict the oil peak in any given region. Based on available production data, proponents have previously (and incorrectly) predicted the peak for the world to be in years 1989, 1995, or 1995-2000. However these predictions date from before the recession of the early 1980s, and the consequent reduction in global consumption, the effect of which was to delay the date of any peak by several years. A new prediction by Goldman Sachs picks 2007 for oil and some time later for natural gas. Just as the 1971 U.S. peak in oil production was only clearly recognized after the fact, a peak in world production will be difficult to discern until production clearly drops off.
One signal is that 2005 saw a dramatic fall in announced new oil projects coming to production from 2008 onwards. Since it takes on average four to six years for a new project to start producing oil, in order to avoid the peak, these new projects would have to not only make up for the depletion of current fields, but increase total production annually to meet increasing demand.
Classification
The oil industry classifies "crude" by the location of its origin (e.g., "West Texas Intermediate, WTI" or "Brent") and often by its relative weight (API gravity) or viscosity ("light", "intermediate" or "heavy"); refiners may also refer to it as "sweet", which means it contains relatively little sulfur, or as "sour", which means it contains substantial amounts of sulfur and requires more refining in order to meet current product specifications.
The world reference barrels are:
- Brent Blend, comprising 15 oils from fields in the Brent and Ninian systems in the East Shetland Basin of the North Sea. The oil is landed at Sullom Voe terminal in the Shetlands. Oil production from Europe, Africa and Middle Eastern oil flowing West tends to be priced off the price of this oil, which forms a benchmark. See also Brent crude.
- West Texas Intermediate (WTI) for North American oil.
- Dubai used as benchmark for the Asia-Pacific region for Middle East Oil
- Tapis (from Malaysia, used as a reference for light Far East oil)
- Minas (from Indonesia, used as a reference for heavy Far East oil)
- The OPEC Basket consisting of
- Arab Light Saudi Arabia
- Bonny Light Nigeria
- Fateh Dubai
- Isthmus Mexico (non-OPEC)
- Minas Indonesia
- Saharan Blend Algeria
- Tia Juana Light Venezuela
OPEC attempts to keep the price of the Opec Basket between upper and lower limits, by increasing and decreasing production. This makes the measure important for market analysts. The OPEC Basket, including a mix of light and heavy crudes, is heavier than both Brent and WTI.
See also [http://tonto.eia.doe.gov/ask/crude_types1.html]
Pricing
Venezuela
References to the oil price are usually either references to the spot price of either WTI/Light Crude as traded on New York Mercantile Exchange (NYMEX) for delivery in Cushing, Oklahoma; or the price of Brent as traded on the International Petroleum Exchange (IPE) for delivery at Sullom Voe. The price of a barrel of oil is highly dependent on both its grade (which is determined by factors such as its specific gravity or API and its sulphur content) and location. The vast majority of oil will not be traded on an exchange but on a over-the-counter basis, typically with reference to a marker crude oil grade that is typically quoted via the pricing agency Platts. For example in Europe a particular grade of oil, say Fulmar, might be sold at a price of "Brent plus US$0.25/barrel".or as an intra-company transaction. IPE claim that 65% of traded oil is priced off their Brent benchmarks. Other important benchmarks include Dubai, Tapis, and the OPEC basket. The Energy Information Administration (EIA) uses the Imported Refiner Acquisition Cost, the weighted average cost of all oil imported into the US as their "world oil price".
It is often claimed that OPEC sets the oil price and the true cost of a barrel of oil is around $2, which is equivalent to the cost of extraction of a barrel in the Middle East. These estimates of costs ignore the cost of finding and developing oil reserves. Furthermore the important cost as far as price is concerned, is not the price of the cheapest barrel but the cost of producing the marginal barrel. By limiting production OPEC has caused more expensive areas of production such as the North Sea to be developed before the Middle East has been exhausted. OPEC's power is also often overstated. Investing in spare capacity is expensive and the low oil price environment in the late 90s led to cutbacks in investment. This has meant during the oil price rally seen between 2003-2005, OPEC's spare capacity has not been sufficient to stabilise prices.
Energy Information Administration
Oil demand is highly dependent on global macroeconomic conditions, so this is also an important determinant of price. Some economists claim that high oil prices have a large negative impact on the global growth. This means that the relationship between the oil price and global growth is not particularly stable although a high oil price is often thought of as being a late cycle phenomenon.
A recent low point was reached in January 1999, after increased oil production from Iraq coincided with the Asian financial crisis, which reduced demand. The prices then rapidly increased, more than doubling by September 2000, then fell until the end of 2001 before steadily increasing, reaching US $40 to US $50 per barrel by September 2004. [http://futures.tradingcharts.com/chart/CO/M]
In October 2004, light crude futures contracts on the NYMEX for November delivery exceeded US $53 per barrel and for December delivery exceeded US $55 per barrel. Crude oil prices surged to a record high above $60 a barrel in June 2005, sustaining a rally built on strong demand for gasoline and diesel and on concerns about refiners' ability to keep up. This trend continued into early August 2005, as NYMEX crude oil futures contracts surged past the $65 mark as consumers kept up the demand for gasoline despite its high price. (see Oil price increases of 2004 and 2005).)
The New York Mercantile Exchange (NYMEX) trades crude oil (including futures contracts) and provides the basis of US crude oil pricing via WTI (West Texas Intermediate). Other exchanges also trade crude oil futures, eg the International Petroleum Exchange (IPE) in London trades contracts in Brent crude.
International Petroleum Exchange
See also [http://www.wtrg.com/prices.htm History and Analysis of Crude Oil Prices]
Top petroleum-producing countries
Source: [http://www.eia.doe.gov/emeu/cabs/topworldtables1_2.html Energy Statistics from the U.S. Government]
(Ordered by amount (barrels per day) produced in 2004):
- Saudi Arabia (OPEC)
- Russia
- United States 1
- Iran (OPEC)
- Mexico 1
- China 1
- Norway 1
- Canada 1
- Venezuela (OPEC) 1
- United Arab Emirates (OPEC)
- Kuwait (OPEC)
- Nigeria (OPEC)
- United Kingdom 1
- Iraq
1 peak production already passed in this state
peak production already passed in this state
(Ordered by amount exported in 2003):
- Saudi Arabia (OPEC)
- Russia
- Norway 1
- Iran (OPEC)
- United Arab Emirates (OPEC)
- Venezuela (OPEC) 1
- Kuwait (OPEC)
- Nigeria (OPEC)
- Mexico 1
- Algeria (OPEC)
- Libya (OPEC) 1
1 peak production already passed in this state
Note that the USA consumes almost all of its own production.
Total world production/consumption (as of 2005) is approximately 84 million barrels per day.
See also: Organization of Petroleum Exporting Countries.
See also
- Abiogenic petroleum origin
- List of oil fields
- List of oil-producing states
- List of oil-consuming states
- List of Countries that have already passed their production peak
- List of petroleum companies
- Energy crisis: 1973 energy crisis, 1979 energy crisis
- Fossil fuel
- Greenhouse gases
- History of the Petroleum Industry
- Hubbert peak (aka peak oil)
- Future energy development
- 1990 spike in the price of oil
- Non-conventional oil
- Oil imperialism
- Oil price increases of 2004 and 2005
- Oil refinery
- Oil supplies
- Oil well
- Olduvai theory (not strictly about oil, but it basically assumes that oil and gas are the only significant energy sources)
- Petroleum disasters
- Petroleum geology
- Petroleum politics
- Renewable energy
- Soft energy path
- Thermal depolymerization
- Thomas Gold
- Irish Sea
External links
- [http://www.longemergency.blogspot.com Long Emergency Blog] - A site with Peak Oil news and discussion, regarding how our world will never be the same.
- [http://www.api.org/ American Petroleum Institute] - A site run by the American Petroleum Institute, the trade association of the US oil industry.
- [http://futures.tradingcharts.com/chart/CO Crude Oil Commodity Charts] - Price charts for crude oil
- [http://www.eia.doe.gov/oil_gas/petroleum/info_glance/petroleum.html US Energy Information Administration] - Part of the informative website of the US Government's Energy Information Administration.
- [http://www.geo.uw.edu.pl/BOBRKA/DATY/daty.htm Major dates of the Polish petroleum industry]
- [http://www.gasresources.net/DisposalBioClaims.htm Dismissal of the Claims of a Biological Connection for Natural Petroleum.]
- [http://www.aapg.org/explorer/2002/11nov/abiogenic.cfm Abiogenic Gas Debate 11:2002 (EXPLORER)]
- [http://www.gasresources.net/Introduction.htm An introduction to the modern petroleum science, and to the Russian-Ukrainian theory of deep, abiotic petroleum origins.]
- [http://www.spe.org/elibinfo/eLibrary_Papers/spe/1982/82UGR/00010836/00010836.htm Unconventional Ideas About Unconventional Gas (Society of Petroleum Engineers)]
- [http://www.bp.com/genericsection.do?categoryId=92&contentId=7005893 BP Statistical Revue of World Energy ]
- [http://www.nymex.com Nymex] - oil trading center of the US
- [http://www.bloomberg.com/energy/ Bloomberg Energy Prices] - current prices on world mercantile exchanges
- [http://www.oilmarketer.co.uk/ Oil Marketer] - oil news and market information
- [http://www.economist.com/surveys/displaystory.cfm?story_id=3884623 Oil in troubled waters] - Economist article on investor approaches to oil markets, supply, and future
- [http://www.pdvsa.com] - The site for the state-owned oil company of Venezuela, much of whose profits go to helping the poor of the country as well as others.
- [http://www.venezuelanalysis.com] - A site focusing on developments in Venezuela, with a big emphasis on the oil issue.
Articles
- [http://pr.caltech.edu/periodicals/CaltechNews/articles/v38/oil.html The End of the Age of Oil] - article adapted from a talk by Caltech vice provost and professor of physics David Goodstein
- [http://www.publicintegrity.org/oil/ The Politics of Oil] - A report on the oil industry's influence of lawmakers and public policy by the Center for Public Integrity.
- [http://news.bbc.co.uk/2/hi/business/3953907.stm BBC: Stability fears rise as oil reliance grows]
- [http://www.washingtonpost.com/wp-dyn/content/article/2005/06/09/AR2005060900148_pf.html Top Saudi Says Kingdom Has Plenty of Oil] "261 billion barrels in reserve..."
- [http://business.timesonline.co.uk/article/0,,16849-1733893,00.html Lee Raymond of Exxon Mobile believes oil supplies will rise]
- [http://www.arabnews.com/?page=6§ion=0&article=44011&d=29&m=4&y=2004 Known Saudi Arabian Oil Reserves Tripled]
- [http://www2.eluniversal.com.mx/pls/impreso/noticia.html?id_nota=6110&tabla=miami Pemex's oil estimates double:] Mexican Oil company's estimate of reserves doubled.
- [http://www.gasresources.net/DisposalBioClaims.htm Dismissal of the Claims of a Biological Connection for Natural Petroleum]
- [http://www.aapg.org/explorer/2002/11nov/abiogenic.cfm Abiogenic Gas Debate 11:2002 (EXPLORER)]
Data
- [http://www.eia.doe.gov/emeu/international/petroleu.html Department of Energy EIA - World supply and consumption]
- [http://www.eia.doe.gov/oil_gas/petroleum/info_glance/prices.html US petroleum prices]
References
# [http://www.pnas.org/cgi/content/full/99/17/10976 Article link]
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Books about the petroleum industry
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Films about petroleum
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Writers covering the petroleum industry
- Colin J. Campbell
- Jay Hanson
- Kenneth S. Deffeyes
- David Goodstein
- Daniel Yergin
- Thomas Gold
Category:Lubricants
Category:Petroleum
Category:Oils
ko:석유
ja:石油
Rock (geology), plutonic, metamorphic rock types of North America. ]]
Rock is a naturally occurring aggregate of minerals and/or mineraloids. Rocks are classified by mineral and chemical composition; the texture of the constituent particles; and also by the processes that formed them. These indicators separate rocks into igneous, sedimentary, and metamorphic.
Igneous rocks are formed from molten magma, and are divided into two main categories: Plutonic rock and Volcanic rock.
Plutonic rocks result when the magma cools and crystallises slowly within the Earth's crust, while Volcanic rocks result from the magma reaching the surface either as lava or fragmental ejecta.
Sedimentary rocks are formed by deposition of either detrital or organic matter, or chemical precipitates (evaporites), followed by compaction of the particulate matter and cementation. The latter can occur at or near the earth's surface, especially in the case of carbonate-rich sediments.
Metamorphic rocks are formed by subjecting any rock type (including previously-formed metamorphic rock) to different temperature and pressure conditions than those in which the original rock was formed. These temperatures and pressures are always higher than those at the earth's surface, and must be sufficiently high so as to change the original minerals into other mineral types or else into other forms of the same minerals (e.g. by recrystallisation).
The transformation of one rock type to another is described by the geological model called the rock cycle.
The Earth's crust (including the lithosphere) and mantle are formed of rock.
See also
- Geology
- Petrology
- List of minerals
- List of rocks
- List of stone
- Quarrying
- Rock formations
- Megalith
- Riprap
External links
- [http://www.geol.lsu.edu/henry/Geology3041/2IgneousClassify/IgneousClassFlow.htm Classification of Igneous Rocks]
Category:Geology
Category:Rocks
ja:岩石
ms:Batu
th:หิน
Oil:For the heavy metal band, see Oil (band). For the language family, see Langue d'oïl.
Oil is a generic term for organic liquids that are not miscible with water. The name comes from Latin oleum (olive oil).
Oil is frequently used to refer to petroleum (crude oil), the type of oil that is pumped up from the ground and currently serves as a major energy source and important part of the world economy. The term foreign oil is used in the United States to refer to imported petroleum, a major point of concern since the 1973 energy crisis.
Types of oil
- Cooking oil
- Essential oil
- Fish oil
- Gear oil
- Heating oil
- Mineral oil
- Motor oil
- Painting oil
- Petroleum (crude oil)
- Stomach oil
- Synthetic oil
- Tramp oil is the unwanted oil that becomes mixed with cutting fluids
- Vegetable oil
ja:油
simple:Oil
Liquid
A liquid (a phase of matter) is a fluid whose volume is fixed under conditions of constant temperature and pressure; and, whose shape is usually determined by the container it fills. Furthermore, liquids exert pressure on the sides of a container as well as on anything within the liquid itself; this pressure is transmitted undiminished in all directions.
If a liquid is at rest in a uniform gravitational field, the pressure at any point is given by
:
where is the density of the liquid (assumed constant) and is the depth of the point below the surface. Note that this formula assumes that the pressure at the free surface is zero, and that surface tension effects may be neglected.
Liquids have traits of surface tension and capillarity; they generally expand when heated, and contract when cooled. Objects immersed in liquids are subject to the phenomenon of buoyancy.
Liquids at their respective boiling point change to gases, and at their freezing points, change to a solids. Via fractional distillation, liquids can be separated from one another as they vaporise at their own individual boiling points. Cohesion between molecules of liquid is insufficient to prevent those at free surface from evaporating.
It should be noted that glass at normal temperatures is not a "supercooled liquid", but a solid. See the article on glass for more details.
See also
- List of phases of matter
- Cooling curve
- Ripple
- Specific gravity
- Liquid dancing
Category:Condensed matter physics
ko:액체
ms:Cecair
ja:液体
simple:Liquid
FlammableFlammability is the ease with which a substance will ignite, causing fire or combustion. Materials that will ignite at temperatures commonly encountered are considered flammable, with various specific definitions giving a temperature requirement. The flash point is the important characteristic. Flash points below 200 °F (93 °C) are regulated in the United States by OSHA as potential workplace hazards. Examples of flammable liquids are gasoline, ethanol, and acetone. Diesel fuel is in one of the less heavily regulated flammability categories, and biodiesel is considered nonflammable with a flash point usually over 300 °F (150 °C), even though biodiesel will combust inside of a diesel engine.
The word flammable is of relatively recent origin but has in many contexts, especially safety, taken the place of the word inflammable, an older term with the same meaning. Some find inflammable misleading, falsely concluding that the Latin prefix in- (here an intensifier) always means "not." [http://www.bartleby.com/61/47/F0164700.html Discussion] Hence gasoline trucks will doubtlessly continue to be labelled flammable, while for those in internet circles inflaming someone will continue to have a very different meaning from flaming them.
See Also
Fire
External link
- [http://www.osha.gov/SLTC/smallbusiness/sec8.html United States Occupational Safety & Health Administration (OSHA) regulations regarding flammability]
Category:Thermodynamics
Crust (geology) to exosphere. Partially to scale.]]
In geology, a crust is the outer layer of a planet, part of its lithosphere. Planetary crusts are generally composed of a less dense material than that of its deeper layers. The crust of the Earth is composed mainly of basalt and granite. It is cooler and more rigid than the deeper layers of the mantle and core.
On partially-molten planets, such as Earth, the lithosphere is floating on fluid interior layers. Because of the partially-fluid upper mantle, or asthenosphere, underneath, floating lithospheres can be broken into tectonic plates that move. Sea floor crust is different from that of the continents. The oceanic crust (sima) is 5 to 10 km thick and is composed primarily of a dark, dense rock called basalt. The continental crust (sial) is 20-70 km deep and is composed of a variety of less dense rocks.
See also
- Continental drift
- Plate tectonics
External links
- [http://quake.wr.usgs.gov/research/structure/CrustalStructure/ USGS Crust Thickness Map]
Category:Geology
Category:Plate tectonics
ms:Kerak bumi
ja:地殻
simple:Crust
th:เปลือกโลก
Persian language
Persian (فارسی = Fârsi ... پارسی = Pârsi), (local name in Iran, Afghanistan and Tajikistan: ‘Fârsi’), ‘Pârsi’ (older local name, but still used by some speakers), Tajik (a Central Asian dialect) or Dari (another local name in Tajikistan and Afghanistan), is a language spoken in Iran, Tajikistan, Afghanistan, Uzbekistan, Bahrain, and elsewhere. Prior to British colonization, Persian was also widely used as a second language in the Indian subcontinent; it took prominence as the language of culture and education in several Muslim courts in the subcontinent throughout the Middle Ages and became the official court language under the Mughal emperors. Evidence of its former rank in the region can still be seen by the extent of its influence on Hindi or Urdu, as well as the popularity that Persian literature still enjoys in the region. Persian or its dialects have official-language status in the countries of Iran, Afghanistan, and Tajikistan. There are 61-71 million native speakers [http://www.ethnologue.com/show_family.asp?subid=90035]. It belongs to the Indo-European language family, and is of the Subject Object Verb type.
History
Persian is a member of the Indo-European family of languages, and within that family it belongs to the Indo-Iranian (Aryan) branch. Scholars believe the Iranian sub-branch consists of the following chronological linguistic path: Old Persian (Avestan and Achaemenid Persian) → Middle Persian (Pahlavi, Parthian, and Sassanids Persian) → Modern Persian (Dari, c. 900 to present Persian).
Old Persian, the main language of the Achaemenid inscriptions, should not be confused with the non-Indo-European Elamite language (see Behistun inscription). Over this period, the morphology of the language was simplified from the complex conjugation and declension system of Old Persian to the almost completely regularized morphology and rigid syntax of Modern Persian, in a manner often described as paralleling the development of English. Additionally, many words were introduced from neighboring languages, including Aramaic and Greek in earlier times, and later Arabic and to a lesser extent Turkish. In more recent times, some Western European words have entered the language (notably from French and English).
The language itself has greatly developed during the centuries. Due to technological developments, new words and idioms are created and enter into Persian like any other language. In Tehran the Academy of Persian Language and Literature is a center that evaluates the new words in order to initiate and advise their Persian equivalents. In Afghanistan, the Academy of Sciences of Afghanistan does the same for Afghan Persian (among other languages).
Nomenclature
Persian, the more widely used name of the language in English, is an Anglicized form derived from Latin
- Persianus, < Latin Persia, < Greek Persis, a hellenized form of Old Persian Parsa. Farsi is the Arabicized form of Parsi, due to a lack of the /p/ phoneme in Standard Arabic. Its use in the English language is very recent (since the 1970s). Native Persian speakers typically call it "Fârsi" in modern usage. ISO, the Academy of Persian Language and Literature, and many other sources call the language Persian. The government of Afghanistan uses both "Dari" and "Persian" in English communications.
The Academy of Persian Language and Literature as well as many lexicographers have announced that "Farsi" is not the appropriate term to use for the Persian language in English. In the ISO 639-1, the local names form the basis for the language codes and for this reason "fa" is the designation for the Persian language in that system.
Dialects and close languages
ISO 639-1
Communication is generally mutually intelligible between Iranians, Tajiks, and Persian-speaking Afghans; however, by popular definition:
- Dari is the local name for the eastern dialect of Persian, one of the two official languages of Afghanistan, including Hazaragi — spoken by the Hazara people of central Afghanistan.
- Tajik could also be considered an eastern dialect of Persian, but, contrary to Iranian and Afghan Persian, it is written in the Cyrillic script.
The following are some of the closely related languages of various Iranian peoples within modern Iran proper:
- Mazerooni, or Mazandarani, spoken in northern Iran mainly in the province of Mazandaran.
- Guilaki, or Gilaki — spoken in the province of Guilan.
- Talysh, or Talishi — spoken in northern Iran and southern parts of the Republic of Azerbaijan.
- Luri, or Lori — spoken mainly in the southwestern Iranian province of Lorestan.
- (a.k.a. Tati, or Eshtehardi) — spoken in parts of the Iranian provinces of East Azarbaijan, Zanjan and Qazvin.
- Dari or Gabri — spoken originally in Yazd and Kerman by the Zoroastrians of Iran. Also called Yazdi by some.
- Dzhidi or Judæo-Persian — a collection of languages or dialects spoken by the many varied and ancient Jewish communities throughout the former greatest extent of the Persian Empire, one of the many Jewish languages of Persian Jews.
Orthography
The vast majority of modern Persian text is written in a form of the Arabic alphabet. In recent years the Latin alphabet has been used by some for technological or internationalization reasons.
Arabic Alphabet
Modern Persian is normally written using a modified variant of the Arabic alphabet.
The adoption of the Arabic script
After the conversion of Persia to Islam (see Islamic conquest of Iran), it took approximately one hundred and fifty years before Persians adopted the Arabic alphabet as a replacement for the older alphabet. Previously, two different alphabets were used for the Persian language (Middle Persian, or Pahlavi, at that time): one was also called Pahlavi and was a modified version of the Aramaic alphabet, and the other was a native Iranian alphabet called Dîndapirak (literally: religion script).
Note: "independence" of Arabic and Persian languages
One should note that despite their shared standard alphabet, Persian and Arabic are entirely different languages: they are not closely genetically related (they belong to separate genetic language families, namely, Indo-European and Afro-Asiatic) and naturally have different phonology and grammar.
The features of the Persian variant
The Persian variant adds four letters to the Arabic alphabet for its use, due to the fact that four sounds that exist in Persian do not exist in Arabic. Additionally, it changes the shape of another two. Some people call this modified alphabet the Perso-Arabic alphabet. The additional four letters are:
The letters different in shape are:
The diacritical marks used in the Arabic script, a.k.a. harakat, are also used in Persian, although some of them have different pronunciations. For example, an Arabic Damma is pronounced as /u/, while in Persian it is pronounced as /o/.
The Persian variant also adds the notion of a pseudo-space to the Arabic script, called a Zero-width non-joiner (ZWNJ) by the Unicode Standard. It acts like a space in disconnecting two otherwise-joining adjacent letters, but does not have a visual width.
Note: Spelling of Arabic words in Arabic and in Persian
It should also be noted that many Persian words with an Arabic root are spelled differently from the original Arabic word. Alef with hamza below ( إ ) always changes to alef ( ا ); teh marbuta ( ة ) usually, but not always, changes to teh ( ت ) or heh ( ه ); and words using various hamzas get spelled with yet another kind of hamza (so that مسؤول becomes مسئول).
Further expansion of the Persian variant
The features of the Persian variant have been taken for other languages, such as Pashto or Urdu, and have sometimes been further extended with new letters or punctuation.
Latin Alphabet
The Universal Persian (UniPers / Pârsiye Jahâni) Alphabet is a Latin-based alphabet created over 50 years ago in Iran and popularized by Mohamed Keyvan, who had used it in a number of Persian textbooks for foreigners and travellers. It sidesteps the difficulties of the traditional Arabic-based alphabet, with its multiple letter shapes and ambiguous spellings, and fits particularly well in contemporary electronically written media.
Fingilish is the name given to texts written in Persian using the Basic Latin alphabet. It is most commonly used in chat, emails and SMS applications.
Phonology
:Main article: Persian phonology
The Persian language has six vowels and twenty-three consonants, including two affricates /ʧ/ (ch) and /ʤ/ (j).
Historically, Persian distinguished length: the long vowels , , contrasting with the short vowels , , respectively. Modern spoken Persian, however, generally does not make this distinction anymore.
Persian phonology
Consonants
| | labial |
alveolars |
post-alveolars |
velars |
glottals |
| voiceless stops | |
| |
| |
| voiced stops | |
| |
| |
| voiceless fricatives | |
| |
| |
| voiced fricatives | |
|
|
| |
| nasals | |
| | | |
| liquids | | , |
| | |
| glides | | |
|
| |
Note that and are affricates, not stops.
Grammar
:Main article: Persian grammar
Suffixes predominate Persian morphology, though there are a small number of prefixes. Verbs can express tense and aspect, and they agree with the subject in person and number. There is no grammatical gender for nouns, nor are pronouns marked for natural gender.
Normal sentences are structured as "(S) (PP) (O) V". If the object is definite, then the order is "(S) (O + "rɑ:") (PP) V".
Vocabulary
There are many loanwords in the Persian language, mostly coming from Arabic, English, French, and the Turkic languages.
Persian has likewise influenced the vocabularies of other languages, especially Indo-Iranian languages and Turkic languages. Many Persian words have also found their way into the English language. See List of English words of Persian origin.
See also
- Academy of Persian Language and Literature
- Arabic numerals
- Dzhidi language
- History of Urdu
- List of English words of Persian origin
- List of Persian poets and authors
- Middle Persian literature
- Persian grammar
- Persian literature
- Persian mythology
- Persian phonology
- Persian or Farsi? - The announcement of the Academy of Persian Language and Literature
References
- Mace, J. (2003). Persian Grammar: For reference and revision. Routledge-Curzon, London.
- Mahootian, S. (1997). Persian. Descriptive Grammars. Routledge, London.
- Windfuhr, G. L. (1987). Persian. In Comrie, B., editor, The World’s Major Languages, pages 523–546. Oxford University Press, Oxford.
External links
- [http://www.ethnologue.org/show_language.asp?code=PRS Ethnologue report for Eastern Persian]
- [http://www.ethnologue.org/show_language.asp?code=PES Ethnologue report for Western Persian]
- [http://www.easypersian.com/ Easypersian.com]
- [http://www.websters-online-dictionary.org/translation/Farsi/ Dictionary] with Farsi - English Translations from [http://www.websters-online-dictionary.org Webster's Online Dictionary] - the Rosetta Edition
- [http://www.aryanpour.com/ Aryanpour Persian-English English-Persian Dictionary]
- [http://www.lmp.ucla.edu/Profile.aspx?LangID=63 UCLA Language Materials Project: Persian]
- [http://www.unipers.com/ UniPers.com A proposed Latin-based writing system designed specifically for the Persian language.]
- [http://www.persiandirect.com Persian Linguistics Association]
- [http://homepages.nyu.edu/%7Emmk4/AATP.htm American Association of Teachers of Persian (AATP)]
- [http://www.apersian.org The Centre for Promotion of Persian Language and Literature]
- [http://www.voanews.com/persian VOA’s Persian Language Service]
- [http://www.bbc.co.uk/persian BBC’s Persian Language Service]
- [http://www.dwelle.de/persian Deutche Welle’s Persian Service]
- [http://iran-heritage.org/interestgroups/language-articles.htm An Online Persian Language Forum]
Category:Classical languages
Category:Iranian culture
Category:Iranian languages
Category:Languages of Afghanistan
Category:Languages of Iran
Category:Languages of Tajikistan
Category:Languages of Uzbekistan
Category:Languages of Pakistan
Category:Languages of Russia
ko:페르시아어
ja:ペルシア語
th:ภาษาเปอร์เซีย
Alkane:For saturated hydrocarbons containing one or more rings, see Cycloalkane.
An alkane in organic chemistry is a saturated hydrocarbon without cycles, that is, an acyclic hydrocarbon in which the molecule has the maximum possible number of hydrogen atoms and so has no double bonds.
Alkanes are also often known as paraffins, or collectively as the paraffin series; these terms, however, are also used to apply only to alkanes whose carbon atoms form a single, unbranched chain; when this is done, branched-chain alkanes are called isoparaffins.
Alkanes are aliphatic compounds.
The general formula for alkanes is CnH2n+2; the simplest possible alkane is therefore methane, CH4. The next simplest is ethane, C2H6; the series continues indefinitely. Each carbon atom in an alkane has sp3 hybridization.
Isomerism
The atoms in alkanes with more than three carbon atoms can be arranged in multiple ways, forming different isomers. "Normal" alkanes have a linear, unbranched configuration. The number of isomers increases rapidly with the number of carbon atoms; for alkanes with 1 to 12 carbon atoms, the number of isomers equals 1, 1, 1, 2, 3, 5, 9, 18, 35, 75, 159, and 355, respectively .
Nomenclature of alkanes
The names of all alkanes end with -ane.
Alkanes with unbranched carbon chains
The first four members of the series (in terms of number of carbon atoms) are named as follows:
:methane, CH4
:ethane, C2H6
:propane, C3H8
:butane, C4H10
Alkanes with five or more carbon atoms are named by adding the suffix -ane to the appropriate numerical multiplier with elision of a terminal -a- from the basic numerical term. Hence, pentane, C5H12; hexane, C6H14; heptane, C7H16; octane, C8H18; etc. For a more complete list, see List of alkanes.
Straight-chain alkanes are sometimes indicated by the prefix n- (for normal) to distinguish them from branched-chain alkanes having the same number of carbon atoms. Although this is not strictly necessary, the usage is still common in cases where there is an important difference in properties between the straight-chain and branched-chain isomers: e.g. n-hexane is a neurotoxin while its branched-chain isomers are not.
Alkanes with branched carbon chains
Branched alkanes are named as follows:
- Identify the longest straight chain of carbon atoms.
- Number the atoms in this chain, starting from 1 at one end and counting upwards to the other end.
- Examine the groups attached to the chain in order and form their names.
- Form the name by looking at the different attached groups, and writing, for each group, the following:
- The number, or numbers, of the carbon atom, or atoms, where it is attached.
- The prefixes di-, tri-, tetra-, etc. if the group is attached in 2, 3, 4, etc. places, or nothing if it is attached in only one place.
- The name of the attached group.
- The formation of the name is finished by writing down the name of the longest straight chain.
To carry out this algorithm, we must know how to name the substituent groups. This is done by the same method, except that instead of the longest chain of carbon atoms, the longest chain starting from the attachment point is used; also, the numbering is done so that the carbon atom next to the attachment point has the number 1.
For example, the compound
image:isobutane.png
is the only 4-carbon alkane possible, apart from butane. Its formal name is 2-methylpropane.
Pentane, however, has two branched isomers, in addition to its linear, normal form:
image:dimethylpropane.png
2,2-dimethylpropane
and
image:2-methylbutane.png
2-methylbutane.
Trivial names
The following nonsystematic names are retained in the IUPAC system:
:isobutane for 2-methylpropane
:isopentane for 2-methylbutane
:neopentane for 2,2-dimethylpropane
The name isooctane is very widely used in the petrochemical industry to refer to 2,2,4-trimethylpentane.
Occurrence
:de:Alkane
Alkanes occur both on Earth and in the solar system, however only the first hundred or so, and even then mostly only in traces. The light hydrocarbons, especially methane and ethane are of great importance for other heavenly bodies: they are found, for example, both in the tail of the comet Hyakutake and in some meteorites such as carbonaceous chondrites. They also form an important portion of the atmospheres of the outer gas planets Jupiter, Saturn, Uranus and Neptune. On Titan, the satellite of Saturn, it is believed that there were once large oceans of these and longer chain alkanes: smaller seas of liquid ethane are thought still to exist there.
Traces of methane (about 0.0001% or 1 ppm) occur in the Earth's atmosphere, produced primarily by forms of Archaea. The content in the oceans is negligible due to the low solubility in water: however, at high pressures and low temperatures, methane can co-crystallize with water to form a solid methane hydrate. Although they cannot be commercially exploited at the present time, the calorific value of the known methane hydrate fields exceeds the energy content of all the natural gas and oil deposits put together—methane extracted from methane hydrate is considered therefore a candidate for future fuels.
methane hydrate
Today, the most important commercial sources for alkanes are clearly natural gas and oil, which are the only organic compounds to occur as minerals in nature. Natural gas contains primarily methane and ethane, with some propane and butane: oil is a mixture of liquid alkanes and other hydrocarbons. Both developed when dead sea animals were covered with sediments to the exclusion of oxygen and converted over many millions years at high temperatures and high pressure to the respective natural substances. Natural gas resulted thereby for example from the following reaction:
:C6H12O6 → 3CH4 + 3CO2
They collected themselves in porous rocks, which were sealed by impermeable layers above. In contrast to methane, which is constantly reformed in large quantities, higher alkanes rarely develop to a considerable extent in nature. The present deposits will not be reformed once they are exhausted.
Solid alkanes occur as evaporation residues from oil, known as tar. One of the largest natural deposits of solid alkanes is in the bitumen lake known as La Brea on the Caribbean island of Trinidad.
Purification and use
:de:Alkane, California]]
Alkanes are both important raw materials of the chemical industry and the most important fuels of the world economy.
The starting materials for the processing are always natural gas and crude oil. The latter is separated in an oil refinery by fractional distillation and processed into many different products, for example gasoline. The different "fractions" of crude oil have different boiling points and can be isolated and separated quite easily: within the individual fractions the boiling points lie closely together.
The domain of usage of a certain alkane can be determined quite well according to the number of carbon atoms, although the following demarcation is idealized and not perfect. The first four alkanes are used mainly for heating and cooking purposes, and in some countries for electricity generation. Methane and ethane are the main componants of natural gas; they are normally stored as gases under pressure. It is however easier to transport them as liquids: this requires both compression and cooling of the gas.
Propane and butane can be liquefied at fairly low pressures, and are well known as liquified petroleum gas (LPG). Propane, for example, is used in the propane gas burner, butane in disposable cigarette lighters (where the pressure is a mere 2 bar). The two alkanes are used as propellants in aerosol sprays.
From pentane to octane the alkanes are highly volatile liquids. They are used as fuels in internal combustion engines, as the vaporise easily on entry into the combustion chamber without forming droplets which would impair the unifomity of the combustion. Branched-chain alkanes are preferred, as they are much less prone to premature ignition which causes knocking than their straight-chain homologues. This propensity to premature ignition is measured by the octane number of the fuel, where 2,2,4-trimethylpentane (isooctane) has an arbitrary value of 100 and heptane has a value of zero. Apart from their use as fuels, the middle alkanes are also good solvents for nonpolar substances.
Alkanes from nonane to, for instance, hexadecane (an alkane with sixteen carbon atoms) are liquids of higher viscosity, less and less suitable for use in gasoline. They form instead the major part of diesel and aviation fuel. Diesel fuels are charaterised by their cetane nember, cetane being an old name for hexadecane. However the higher melting points of these alkanes can cause problems at low temperatures and in polar regions, where the fuel becomes too thick to flow correctly
Alkanes from hexadecane upwards form the most important components of fuel oil and lubricating oil. In latter function they work at the same time as anti-corrosive agents, as their hydrophobic nature means that water cannot reach the metal surface. Many solid alkanes find use as paraffin wax, for example in candles. This should not be confused however with true wax, which consists primarily of esters.
Alkanes with a chain length of approximately 35 or more carbon atoms are found in bitumen, used for example in road surfacing. However the higher alkanes have little value and are usually split into lower alkanes by cracking.
Preparation
Numerous ways exist to prepare alkanes in the laboratory. The most well known methods are hydrogenation of alkenes and hydrolysis of Grignard reagents. Alkanes can also be prepared directly from alkyl halides in the Corey-House-Posner-Whitesides reaction. The Barton-McCombie deoxygenation removes hydroxyl groups from alcohols and the Clemmensen reduction removes carbonyl groups from aldehydes and ketones to form alkanes.
Molecular geometry
Clemmensen reduction
The molecular structure of the alkanes directly affects their physical and chemical characteristics. It is derived from the electron configuration of carbon, which has four valence electrons. The carbon atoms in alkanes are always sp3-hybridised, that is to say that the valence electrons are said to be in four equivalent orbitals derived from the combination of the 2s-orbital and the three 2p-orbitals. These orbitals, which have identical energies, are arranged spatially in the form of a tetrahedron, the angle of 109.47° between them.
Bond lengths and bond angles
sp3-hybridised
An alkane molecule has only C–H and C–C single bonds. The former result from the overlap of an sp3-orbital of carbon with the 1s-orbital of a hydrogen; the latter by the overlap of two sp3-orbitals on different carbon atoms. The bond lengths amount to 1.09×10−10 m for a C–H bond and 1.54×10−10 m for a C–C bond.
The spatial arrangement of the bonds is similar to that of the four sp3-orbitals—they are tetrahedrally arranged, with an angle of 109.47° between them. Structural formulae which represent the bonds as being at right angles to one another, while both common and useful, do not correspond with the reality.
Conformation
The structural formula and the bond angles are not usually sufficient to completely describe the geometry of a molecule. There is a further degree of freedom for each carbon–carbon bond: the torsion angle between the atoms or groups bound to the atoms at each end of the bond. The spatial arrangement described by the torsion angles of the molecule is known as its conformation.
Ethane
conformation
Ethane forms the simplest case for studying the conformation of alkanes, as there is only one C–C bond. If one looks down the axis of the C–C bond, then one will see the so-called Newman projection: The circle represents the two carbon atoms, one behind the other, and the bonds to hydrogen are represented by the straight lines. The hydrogen atoms on both the front and rear carbon atoms have an angle of 120° between them, resulting from the projection of the base of the tetrahedron onto a flat plane. However the torsion angle between a given hydrogen atom attached to the front carbon and a given hydrogen atom attached to the rear carbon can vary freely between 0° and 360°. This is a consequence of the free rotation about a carbon–carbon single bond. Despite this apparent freedom, only two limiting conformations are important:
- In the eclipsed conformation, corresponding to a torsion angle of 0°, 120° or 240°, the hydrogen atoms attached to the front carbon are directly in front of those attached to the rear carbon.
- In the staggered conformation, corresponding to a torsion angle of 60°, 180° or 300°, the hydrogen atoms attached to the front carbon are exactly in between those attached to the rear carbon.
The two conformations, also known as rotomers, differ in energy: The staggered conformation is 12.6 kJ/mol lower in energy (more stable) than the eclipsed conformation. The explanation for this difference in energy has been the subject of debate, with two main theories predominating:
- in the eclipsed conformation, the electrostatic repulsion between the electrons in the carbon–hydrogen bonds is maximised.
- in the staggered conformation, the hyperconjugation (a form of delocalisation) of the valence electrons is maximised.
These two explanations are not contradictory or exclusive; the latter is thought to be the more important for ethane itself.
This difference in energy between the two conformations, known as the torsion energy, is low compared to the thermal energy of an ethane molecule at ambient temperature. There is constant rotation about the C–C bond, albeit with short "pauses" at each staggered conformation. The time taken for an ethane molecule to pass from one staggered conformation to the next, equivalent to the rotation of one CH3-group by 120° relative to the other, is of the order of 10−11 seconds.
Higher alkanes
torsion energy
The situation with respect to the two C–C bonds in propane is qualitatively similar to that of ethane: it is more complex, however, for butane and higher alkanes.
If one takes the central C–C bond of butane as the reference axis, each of the two central carbon atoms is bound to two hydrogen atoms and a methyl group. Four different conformations can be defined by the torsion angle between the two methyl groups and, as in the case of ethane, each has its characteristic energy.
- The fully eclipsed or synperiplanar conformation has a torsion angle of 0°. It is the configuration with the highest energy.
- The inclined conformation has a torsion angle of 60° (or 300°). It is a local energy minimum.
- The partially eclipsed conformation has a torsion angle of 120° (or 240°). It is a local energy maximum.
- The antiperiplanar conformation has a torsion angle of 180°. The two methyl groups are as far from each other as is possible, and this configuration has the lowest energy.
The difference in energy between the fully eclipsed conformation and the antiperiplanar conformation is about 19 kJ/mol, and is therefore still relatively small at ambient temperature.
The case of higher alaknes is similar: the antiperiplanar conformation is always the most favoured around each carbon–carbon bond. For this reason, alkanes are usually shown in a zigzag arrangement in diagrams or in models. The actual structure will always differ somewhat from these idealised forms, as the differences in energy between the conformations are small compared to the thermal energy of the molecules: alkane molecules have no fixed structural form, whatever the models may suggest.
The conformations of other organic molecules are based on those of alkanes, and are discussed in the relevant articles.
Properties
Physical properties
butane
The molecular structure, particularly the surface area of the molecule, determines the boiling point of the alkane: the smaller the surface, the lower the boiling point, as the van der Waals forces between the molecules are weaker. A reduction of the surface area can be achieved by chain-branching or by a circular structure. This means in practice that alkanes with higher number of carbon atoms usually have higher boiling points than those with lower numbers of carbon atoms, and that branched-chain alkanes and cycloalkanes have lower boiling points than their straight-chain homologues. Under standard conditions, from CH4 to C4H10 alkanes are gaseous; from C5H12 to C17H36 they are liquids; and after C18H38 they are solids. The boiling point increases between 20 and 30 °C per CH2-group.
The melting points of the alkanes also rise with the increase in the number of carbon atoms (with only one exception, propane). However the melting points rise more slowly than the boiling points, in particular for the higher alkanes. In addition, the melting points of alkanes with an odd number of carbon atoms increase faster than the melting points of alkanes with an even number of carbon atoms (see figure): the cause of this phenomenon is the higher packing density of the alkanes with an even number of carbon atoms. The melting points of branched-chain alkanes can be either higher or lower than those of the corresponding straight-chain alkanes, depending on the efficiency of molecular packing: this is particularly true for isoalkanes (2-methyl isomers), which often have melting points higher than those of their normal analogues.
Alkanes do not conduct electricity, nor are they substantially polarized by an electric field. For this reason they do not form hydrogen bonds and are insoluble in polar solvents such as water. Since the hydrogen bonds between individual water molecules are aligned away from an alkane molecule, the coexistance of an alkane and water leads to an increase in molecular order (a reduction in entropy). As there is no significant bonding between water molecules and alkane molecules, the second law of thermodynamics suggests that this reduction in entropy should be minimised by minimising the contact between alkane and water: alkanes are said to be hydrophobic in that they repel water.
Their solubility in nonpolar solvents is relatively good, a property which is called lipophilicity. Different alkanes are, for example, miscible in all proportions among themselves.
The density of the alkanes usually increases with increasing number of carbon atoms, but remains less than that of water. Hence, alkanes form the upper layer in an alkane-water mixture.
Chemical properties
Alkanes generally show a relatively low reactivity, because their C–H and C–C bonds are relatively stable and cannot be easily broken. Unlike all other organic compounds, they possess no functional groups.
They react only very poorly with ionic or other polar substances. The pKa values of all alkanes are above 60, and so they are practically inert to acids and bases. This inertness is the source of the term paraffins (Latin para + affinis, with the meaning here of "lacking affinity"). In crude oil the alkane molecules have remained chemically unchanged for millions of years.
However redox reactions of alkanes, in particular with oxygen and the halogens, are possible as the carbon atoms are in a strongly reduced condition; in the case of methane, the lowest possible oxidation state for carbon (−4) is reached. Reaction with oxygen leads to combustion; with halogens, substitution.
Free radicals, molecules with unpaired electrons, play a large role in most reactions of alkanes, such as cracking and reformation where long-chain alknes are converted into shorter-chain alkanes and straight-chain alknaes into branched-chain isomers.
In highly brached alkanes, the bond angles may differ significantly from the optimal value (109.5°) in order to allow the different groups sufficient space. This causes a tension in the molecule, known as steric hinderance, and can substantially increase the reactivity.
Thermochemistry
Alkanes are stable molecules relative to their constituent elements, which is manifested as a negative heat of formation. For linear alkanes, each methylene (CH2) unit contributes -5 kcal/mol to the overal heat of formation. Branched alkanes are always a little bit more stable than their linear isomers; for example, 2-methylbutane is more stable than n-pentane by 1.8 kcal/mol, and 2,2-methylpropane is more stable than n-pentane by 5 kcal/mol.
See the alkane heat of formation table for detailed data.
Spectroscopic properties
Virtually all organic compounds contain carbon–carbon and carbon–hydrogen bonds, and so show some of the features of alkanes in their spectra. Alkanes are notable for having no other groups, and therefore for the absence of other characreistic spectroscopic features.
Infrared spectroscopy
The carbon–hydrogen stretching mode gives a strong absorption between 2850 and 2960 cm−1, while the carbon–carbon stretching mode absorbes between 800 and 1300 cm−1. The carbon–hydrogen bending modes depend on the nature of the group: methyl groups show bands at 1450 cm−1 and 1375 cm−1, while methylene groups show bands at 1465 cm−1 and 1450 cm−1. Carbon chains with more than four carbon atoms show a weak absorption at around 725 cm−1.
NMR spectroscopy
The proton resonances of alkanes are usually found at δH = 0–1. The carbon-13 resonances depend on the number of hydrogen atoms attached to the carbon: δC = 8–30 (methyl), 15–55 (methylene), 20–60 (methyne). The carbon-13 resonance of quaternary carbon atoms is characteristically weak, due to the lack of nuclear Overhauser enhancement and the long relaxation time: it can be missed in routine spectra.
Mass spectrometry
Alkanes have a high ionisation energy, and the molecular ion is usually weak. The fragmentation pattern can be difficult to interpret, but, in the case of branched chain alkanes, the carbon chain is preferentially cleaved at tertiary or quaternary carbons due to the relative stability of the resulting free radicals. The fragment resulting from the loss of a single methyl group (M−15) is often absent, and other fragment are often spaced by intervals of fourteen mass units, corresponding to sequential loss of CH2-groups.
Reactions
Reactions with oxygen
All alkanes react with oxygen in a combustion reaction, although they become increasing difficult to ignite as the number of carbon atoms increases. The general equation for complete combustion is:
:2CnH2n+2 + (3n+1)O2 → 2(n+1)H2O + 2nCO2
In the absence of sufficient oxygen, carbon monoxide or even soot can be formed, as shown below for methane:
:2CH4 + 3O2 → 2CO + 4H2O
:CH4 + O2 → C + 2H2O
Alkanes usually burn with a non-luminous flame with very little soot formation.
The standard enthalpy change of combustion, ΔcHo, for alkanes increases by about 650 kJ/mol per CH2 group. Branched-chain alkanes have lower values of ΔcHo than straight-chain alkanes of the same number of carbon atoms, and so can be seen to be somewhat more stable.
Reactions with halogens
Alkanes react with halogens in a so-called halogenation reaction. The hydrogen atoms of the alkane are progressively re | | |
