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Bitumen

Bitumen is a mixture of organic liquids that are highly

viscous, black, sticky, entirely soluble in carbon disulfide,and composed primarily of highly condensed polycyclicaromatic hydrocarbons.

Naturally occurring or crude bitumen is a sticky, tar-like form of petroleum which is so thick and heavy that it must be heated ordiluted before it will flow. At room temperature, it has aconsistency much like cold molasses. Refined bitumen is theresidual (bottom) fraction obtained by fractional distillation of crude oil. It is the heaviest fraction and the one with the highestboiling point, boiling at 525 °C (977 °F).

History

The use of natural asphalt or mixtures thereof forwaterproofing and as an adhesive dates at least to thefourth millennium B.C., when the Sumerians used it instatuary, mortaring brick walls, waterproofing baths anddrains, in stair treads, and for shipbuilding. Other cultures

such as Babylon, India, Persia, Egypt, and ancient Greeceand Rome continued these uses, and in several cases theasphalt has continued to hold components securelytogether to this day. Though the existence of thestructures have not been confirmed, it was reported thatasphalt was used to bind the bricks of the Tower of Babel,and in a one-kilometer tunnel beneath the river Euphrates at Babylon in the time of Queen Semiramis (ca. 700 B.C.),where burnt bricks were covered with asphalt as a

waterproofing agent.[2]The Greek name for the substance was άσπηαλτος(asphaltos). Approximately 40 A.D. Dioscorides describedproduction of asphalt (as distinguished from pissasphaltand naphtha): (1655 Goodyer translation)

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"The Judaicum Bitumen is better than others; that isreckoned the best, which doth shine like purple, being of astrong scent & weightie, but the black and fowle is naughtfor it is adulterated with Pitch mixed with it. It growes inPhoenice also, and in Sidon, & in Babylon, & in Zacynthum.It is found also moyst swimming upon wells in the countrieof the Agrigentines of Sicilie, which they use for lampsinstead of oyle, and which they call falsely Sicilian oyle, forit is a kinde of moyst Bitumen."[3]

The Judaicum Bitumen is a famous deposit of native asphaltseeping through diapirs at the bottom of the Dead Sea,which comes occasionally to the surface through seismicactivity in blocks of up to 100 tons in weight which aremore than 99.99% pure. It was the object of the first known

battle for a hydrocarbon deposit, between the Seleucids and the Nabateans in 312 B.C.[4]

Modern usage

In British English, the word 'asphalt' refers to a mixture of mineral aggregate and bitumen (or tarmac in commonparlance). The word 'tar' refers to the black viscousmaterial obtained from the destructive distillation of coal 

and is chemically distinct from bitumen. In AmericanEnglish, bitumen is referred to as 'asphalt' or 'asphaltcement' in engineering  jargon. In Australian English,bitumen is sometimes used as the generic term for roadsurfaces. In Canadian English, the word bitumen is used torefer to the vast Canadian deposits of extremely heavycrude oil,[5] while asphalt is used for the oil refinery product used to pave roads and manufacture roof shingles.Diluted bitumen (diluted with naphtha to make it flow inpipelines) is known as dilbit in the Canadian petroleum

industry, while bitumen "upgraded" to synthetic crude oil isknown as syncrude and syncrude blended with bitumen assynbit.[6]

Most bitumens contain sulfur and several heavy metalssuch as nickel, vanadium, lead, chromium, mercury and

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also arsenic, selenium, and other toxic elements. Bitumenscan provide good preservation of plants and animal fossils.

Uses

The University of Queensland Pitch drop experiment,demonstrating the viscosity of bitumen.

Bitumen is primarily used for paving roads.

Its other uses are for bituminous waterproofing products, including the use of bitumen in the production of roofing felt and for sealing flat roofs.

Naturally occurring crude bitumen is the prime feed stock 

for petroleum production from tar sands currently underdevelopment in Alberta, Canada. Canada has most of theworld's supply of natural bitumen, covering 140,000 squarekilometres[5] (an area larger than England), giving it thesecond largest proven oil reserves in the world. TheAthabasca oil sands is the largest bitumen deposit inCanada and the only one accessible to surface mining,although recent technological breakthroughs have resultedin deeper deposits becoming producible by in-situ methods.Because of oil price increases since 2003, upgrading

bitumen to synthetic crude oil has become highlyprofitable. As of 2006 Canadian crude bitumen productionaveraged about 1.1 million barrels (170,000 m3) per dayand was projected to rise to 4.4 million barrels(700,000 m3) per day by 2020.[6] The total amount of crude bitumen in Alberta which could be extracted isestimated to be about 310 billion barrels (50×10^9 m3),[7] which at a rate of 4.4 million barrels per day would lastabout 200 years.

In the past, bitumen was used to waterproof boats, andeven as a coating for buildings with some additives. TheGreek historian Herodotus said hot bitumen was used as

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mortar in the walls of Babylon.[8] It is also possible thatthe city of Carthage was easily burnt due to extensive useof bitumen in construction.

Vessels for the heating of bitumen or bituminouscompounds are usually subject to specific conditions in

public liability insurance policies, similar to those requiredfor blow torches, welders, and flame-cutting equipment.[9]

Bitumen was also used in early photographic technology. Itwas most notably used by French scientist JosephNicéphore Niépce in the first picture ever taken. Thebitumen used in his experiments were smeared on pewter plates and then exposed to light, thus making a black andwhite image. It was similarly used to print millions of 

photochrom postcards.

Thin bitumen plates are sometimes used by computerenthusiasts for silencing computer cases or noisy computerparts such as the hard drive. Bitumen layers are bakedonto the outside of high end dishwashers to provide soundinsulation.

Bitumen also is used in paint and marker inks by somegraffiti supply companies (primarily Molotow) to increase

the weather resistance and permanence of the paint and/orink, and to make the color much darker.

Bitumen was the nemesis of many artists during the 19thcentury. Although widely used for a time, it ultimatelyproved unstable for use in oil painting, especially whenmixed with the most common dilutents, such as linseed oil,varnish and turpentine. Unless thoroughly diluted, bitumennever fully solidifies and will in time corrupt the other

pigments with which it comes into contact. The use of bitumen as a glaze to set in shadow or mixed with othercolors to render a darker tone resulted in the eventualdeterioration of a good many paintings, those of Delacroixbeing just one notable example.

Bitumen alternatives

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Bitumen can now be made from non-petroleum based renewableresources such as sugar, molasses and rice, corn and potatostarches. Bitumen can also be made from waste material by fractional distillation of used motor oils, which is sometimes disposed byburning or dumping into land fills. Non-petroleum based bitumenbinders can be made light-colored. Roads made with lighter-coloredpitch absorb less heat from solar radiation, and become less hot thandarker surfaces, reducing their contribution to the urban heat island effect.[10]

Geologic origin

Bituminous outcrop of the Puy de la Poix, Clermont-Ferrand, France

Naturally occurring deposits of bitumen are formed from the remainsof ancient, microscopic algae and other once-living things. Whenthese organisms died, their remains were deposited in the mud onthe bottom of the ocean or lake where they lived. Under the heat andpressure of burial deep in the earth, the remains were transformedinto materials such as bitumen, kerogen, or petroleum.

As bitumen are also found in meteorites and Archean rocks it ispossible that some bitumen are primordial material formed during

accretion of the Earth and reworked by bacteria that consumehydrocarbons.

Grades of bitumen

The Paving Grades of bitumen are 30/40, 60/70 and 80/100. The grade80/100 is commonly used in India and Bangladesh but for lowertemperatures other grades are preferable.