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Petroleum '''asphalt''' is a sticky, black and highly [[viscosity|viscous]] liquid or semi-solid that is present in most [[petroleum]] [[crude oil]]s and in some natural deposits. Petroleum crude oil is a complex mixture of a great many different [[hydrocarbon]]s. Petroleum asphalt is defined as that part of crude oil which is separated from the higher-[[Boiling point|boiling]] hydrocarbons in crude oil by [[precipitation]] upon the addition of lower-boiling hydrocarbon [[solvent]]s such as [[propane]], [[pentane]], [[hexane]] or [[heptane]]. The precipitated material consists of ''asphaltenes'' which have an average [[molecular weight]] of about (800 - 2500 [[Kilogram|g]]/[[mole]])<ref>{{cite book|author=Oliver Mullins and Eric Sheu (Editors)|title=Structure & Dynamics of Asphaltenes|edition=1st Edition|publisher=Springer|year=1999|id=ISBN 0-306-45930-2}} (See Chapter 1, page 17)</ref><ref>Note: There are many other values in the technical literature for the molecular weight of asphaltenes and there does not appear to be a concensus as to which values are more correct.</ref> and  exist in the form of flat sheets of [[polyaromatic]] [[condensed ring]]s with short [[aliphatic]] chains.<ref>[http://www.ripi.ir/index.php?option=content&task=view&id=71 Experimental Investigation of Asphaltene Precipitation] From website of the [[Research Institute of Petroleum Industry]] in [[Tehran]], [[Iran]].</ref>


Over the years, petroleum asphalt has been referred to as ''bitumen'', ''asphaltum'' or ''pitch''. The terminology varies from country to country and from individual to individual. Asphalt is often confused with ''coal tar'' (or ''coal pitch'') derived from the [[pyrolosis]] of [[coal]] and which has a different chemical structure than asphalt.
When petroleum asphalt is combined with [[construction aggregate]] (sand, gravel, crushed stone, etc.) for use in road construction or paving, it has often been referred to as ''[[asphaltic concrete]]'', ''[[asphaltic cement]]'', ''[[bituminous concrete]]'', ''blacktop'' or ''road tar''.
The natural deposits of asphalt (often referred to as ''tar'') include asphaltic lakes such as [[Bermudez Lake]] in [[Venezuela]], and [[Pitch Lake]] in [[Trinidad]]. Other natural deposits include [[oil sands]] (often called ''tar sands'') and the two largest deposits of oil sands are such as in [[Alberta]], [[Canada]] and the [[Orinoco Oil Belt]] area of Venezuela.
== History of asphalt ==
The documented use of naturally occurring asphalt dates back almost to 4000 B.C.:<ref name=Speight>{{cite book|author=James G. Speight and Baki Ozum|title=Petroleum Refining Processes|edition=|publisher=Marcel Dekker|year=2002|id=ISBN 0-8247-0599-8}}</ref><ref name=Beyond>[http://www.beyondroads.com/index.cfm?fuseaction=page&filename=history.html The History of Asphalt] From the website of beyondRoads.com.</ref><ref name=NAPA>[http://www.hotmix.org/index.php?option=com_contents&task=view&id=21&Itemid=57 History of Asphalt] From the website of the [[National Asphalt Pavement Association]].</ref><ref name=Harper>[http://www.etymonline.com/index.php? Online Etymology Dictionary] by Douglas Harper</ref>
* 3800 B.C.: Asphalt used for caulking boats made of reeds.
* 3500 B.C.: Asphalt used as cement for jewelry.
* 3000 B.C.: Asphalt used as construction cement by the [[Sumerians]] of ancient [[Mesopotamia]] (now known as [[Iraq]]). Also used to seal a bathing pool or water tank in the city of [[Mohenjo-Daro]] in the [[Indus Valley Civilization]] located in what is now [[Pakistan]].
* 2500 B.C.: Asphalt and other petroleum oils used in ancient [[Egypt]] for embalming [[Mummy|mummies]]. (The [[Persian language|Persian]] word for asphalt is ''mumiyah'' which may be related to the [[English language|English]] word for ''mummy'').
* 1000 B.C.: Asphalt used for waterproofing  by lake dwellers in what is now [[Switzerland]].
* 625 – 650 B.C.: The first recorded use of asphalt as a road-building material was in [[Babylon]] during the reigns of [[King Nabopolassar]] and his son, [[King Nebuchadnezzar]].
* 500 B.C.: Asphalt mixed with sulfur was used as an incendiary device in the [[Greece|Greek]] wars. (The word asphalt comes from the [[Greek language|Greek word]] ''asphaltos'', meaning ''secure'' in English.)
* 300 B.C. – A.D. 250: Reported occurrences of asphalt and oil seepages in Mesopotamia and the use of liquid asphalt as an illuminant in lamps.
* A.D. 750: First reported use in [[Italy]] of asphalt as a coloring material in paintings.
[[Europeans]] exploring the [[America]]s discovered natural deposits of asphalt. Writing in 1595, [[Sir Walter Raleigh]] described a lake of asphalt on the island of Trinidad, near Venezuela. He used it to recaulk his ships.<ref name=Beyond/><ref name=NAPA/>
In the late 1700s and early 1800s, first [[Pierre-Marie-Jérôme Trésaguet]] of [[France]], then [[Thomas Telford]] and subsequently [[John Loudon McAdam]] (both of [[Scotland]]) perfected the leveling, draining and construction of roads using layers of broken stones and gravel. In the period of 1860 – 1880, to reduce road dust and road maintenance, builders began using hot coal tar to bond the stones together. Such roads became named after McAdam and known as ''tarmacadam'' roads, later shortened to ''tarmac''.<ref name=Beyond/><ref name=NAPA/><ref name=Harper/><ref name=Lay>{{cite book|author=Maxwell G. Lay|title=Handbook of Road Technology|edition=3rd edition|publisher=Taylor&Francis|year=1999|id=ISBN 90-5699-157-4}}</ref>
In 1870, [[Belgium|Belgian]] chemist Edmond J. DeSmedt laid the first true asphalt pavement in the [[United States]] in [[Newark]], [[New Jersey]]. He also paved [[Pennsylvania Avenue]] in [[Washington, D.C.]] in 1876 using 54,000 [[U.S. customary units|square yards]] (45,140 square [[metre]]s) of sheet asphalt from Pitch Lake in Trinidad.<ref name=Beyond/><ref name=NAPA/>
During the early 1900s, [[coal gasification]] was being widely used to produce ''town gas'' and the by-product tar produced during coal gasification was a readily available product.<ref name=Lay/> That tar was extensively used in the construction of ''tarmacadam'' (or, more simply, ''tarmac'') roads.
By 1907, asphalt from [[Petroleum refining processes|petroleum refineries]] had outstripped the use of natural asphalt from Trinidad or elsewhere.<ref name=NAPA/>. Later in the 1900s, when [[natural gas]] replaced ''town gas'', asphalt from petroleum refineries dominated the asphalt paving market from that point on. By the early 1990s, asphalt paving mixture producers in the United States used more than 50 × 10<sup>6</sup> [[U.S. customary units|barrels]] (7.95 × 10<sup>6</sup> cubic metres) of petroleum asphalt per year. Of the 2.27 × 10<sup>6</sup> [[U.S. customary units|miles]] (3.65 × 10<sup>6</sup> kilometers) of paved road in the United States, 94 percent of them are surfaced with asphalt, including 65 percent of the interstate system. <ref>[http://www.referenceforbusiness.com/industries/Petroleum-Refining-Related/Asphalt-Paving-Mixtures-Blocks.html SIC 2951, Asphalt Paving Mixtures and Blocks]</ref>
== Asphalt production from petroleum crude oil ==
{{Image|Petroleum Asphalt Flow Diagram.png|right|216px|Schematic flow diagram of how petroleum asphalt is produced in petroleum refineries.}}
As mentioned earlier above, petroleum crude oil is essentially a complex mixture of a great many hydrocarbons. There are a great many different crude oil sources and each of the crude oils from those sources has its own unique mixture of hydrocarbons. Upon being fed into a [[Petroleum refining processes|petroleum refinery]], the crude oil is initially [[Continuous distillation|distilled]] (i.e., [[Boiling point|boiled]]) to remove and recover various products such as [[Petroleum naphtha|naphtha]] which is subsequently further refined to produce [[gasoline]]  ([[petrol]]), [[jet fuel]], [[diesel oil]], [[heating  oil]] and so-called ''[[vacuum oil]]s'' which may also be further refined to produce more gasoline.<ref name=Speight/><ref name=Jones>{{cite book|author=David S.J. Jones and Peter P.Pujado (Editors)|title=Handbook of Petroleum Processing|edition=First Edition|publisher=Springer|year=2006|id=ISBN 1-4020-2819-9}}</ref><ref name=Speight2>{{cite book|author=James G. Speight, Sunggyu Lee and Sudarshan K. Loyalka|title=Handbook of Alternative Fuel Technologies|edition=1st Edition|publisher=CRC Press|year=2007|id=ISBN 0-8247-4069-6}}</ref><ref name=Handwerk>{{cite book|author=Gary, J.H. and Handwerk, G.E.|title=Petroleum Refining Technology and Economics|edition=2nd Edition|publisher=Marcel Dekker, Inc|year=1984|id=ISBN 0-8247-7150-8}}</ref>
The initial distillation of the petroleum crude oil is done in two steps as shown in the adjacent diagram:
*The first step is [[Petroleum refining processes#The crude oil distillation unit|atmospheric distillation]], at an [[Pressure|absolute pressure]] slightly above atmospheric pressure, after heating the crude oil in a process [[furnace]] to a [[temperature]] of about 395 °[[Celsius|C]]. That temperature cannot be exceeded because, above that temperature, the hydrocarbon [[molecule]]s will ''crack'' (break) into smaller molecules and [[coke]] that is essentially solid [[carbon]] which would plug up the furnace tubes.<ref name=Speight/><ref name=Jones>{{cite book|author=David S.J. Jones and Peter P.Pujado (Editors)|title=Handbook of Petroleum Processing|edition=First Edition|publisher=Springer|year=2006|id=ISBN 1-4020-2819-9}}</ref><ref name=Speight2>{{cite book|author=James G. Speight, Sunggyu Lee and Sudarshan K. Loyalka|title=Handbook of Alternative Fuel Technologies|edition=1st Edition|publisher=CRC Press|year=2007|id=ISBN 0-8247-4069-6}}</ref><ref name=Handwerk>{{cite book|author=Gary, J.H. and Handwerk, G.E.|title=Petroleum Refining Technology and Economics|edition=2nd Edition|publisher=Marcel Dekker, Inc|year=1984|id=ISBN 0-8247-7150-8}}</ref>
*The second step is [[vacuum distillation]] at an absolute pressure of 10 – 40 [[Pressure|mmHg]]. The temperature must still be limited to being no higher than about 395 °C. However, under the vacuum of 10 – 40  mmHg, that is equivalent to a [[boiling point]] of about 565 °C at atmospheric pressure.<ref name=Speight/><ref name=Jones>{{cite book|author=David S.J. Jones and Peter P.Pujado (Editors)|title=Handbook of Petroleum Processing|edition=First Edition|publisher=Springer|year=2006|id=ISBN 1-4020-2819-9}}</ref><ref name=Speight2>{{cite book|author=James G. Speight, Sunggyu Lee and Sudarshan K. Loyalka|title=Handbook of Alternative Fuel Technologies|edition=1st Edition|publisher=CRC Press|year=2007|id=ISBN 0-8247-4069-6}}</ref><ref name=Handwerk>{{cite book|author=Gary, J.H. and Handwerk, G.E.|title=Petroleum Refining Technology and Economics|edition=2nd Edition|publisher=Marcel Dekker, Inc|year=1984|id=ISBN 0-8247-7150-8}}</ref>
The residual bottoms product from the atmospheric distillation is referred to as ''atmospheric resid'' or ''atmospheric residuum''. Similarly, the residual bottoms product from the vacuum distillation is referred to as ''vacuum resid'' or ''vacuum residuum''. In some refineries that process very heavy crude oils (i.e., crude oil with a higher than average crude oil [[density]]), the atmospheric resid may be suitable for further processing to obtain a petroleum asphalt end-product. However, again as shown in the adjacent diagram, it is more generally the vacuum resid that is further processed to derive an end-product of petroleum asphalt.<ref name=Speight/><ref name=Jones>{{cite book|author=David S.J. Jones and Peter P.Pujado (Editors)|title=Handbook of Petroleum Processing|edition=First Edition|publisher=Springer|year=2006|id=ISBN 1-4020-2819-9}}</ref><ref name=Speight2>{{cite book|author=James G. Speight, Sunggyu Lee and Sudarshan K. Loyalka|title=Handbook of Alternative Fuel Technologies|edition=1st Edition|publisher=CRC Press|year=2007|id=ISBN 0-8247-4069-6}}</ref>
The vacuum resid may be used as: a [[heavy fuel oil]] blending stock; for further processing in a [[delayed coker]] to produce hydrocarbon [[gas]]es, [[coker naphtha]], [[coker gas oil]] and [[petroleum coke]]; as a feed stock for processing into lubricating oil; or routed through a de-asphalting process to produce petroleum asphalt. The adjacent diagram depicts a portion of the vacuum resid being routed to use as a heavy fuel oil blending stock and a portion being routed through a de-asphalting process.
There are a number of de-asphalting processes. Perhaps the most common one is known as ''propane de-asphalting'' which uses [[Supercritical fluid|supercritical]] [[propane]] (meaning the propane is at temperature and pressure conditions above its [[critical point]]) as a [[solvent]] to separate the lower-boiling, lower-density hydrocarbon oil molecules from the asphaltene molecules. Any propane solvent remaining in the separated deasphalted oil is then stripped out and recycled for re-use as the de-asphalting solvent. The solvent-free, deasphalted oil may then be used as a feedstock component in other petroleum refinery processes such as a [[fluid catalytic cracker]] or a [[hydrocracker]] to produce a gasoline blending component. The asphalt product from the de-asphalter may be marketed as end-product petroleum asphalt. Alternatively, all or some of the asphalt product from the de-asphalter may be processed in an air-blowing process to produce what is known as ''air-blown'' or ''oxidized'' asphalt.<ref name=Speight/><ref name=Jones>{{cite book|author=David S.J. Jones and Peter P.Pujado (Editors)|title=Handbook of Petroleum Processing|edition=First Edition|publisher=Springer|year=2006|id=ISBN 1-4020-2819-9}}</ref><ref name=Speight2>{{cite book|author=James G. Speight, Sunggyu Lee and Sudarshan K. Loyalka|title=Handbook of Alternative Fuel Technologies|edition=1st Edition|publisher=CRC Press|year=2007|id=ISBN 0-8247-4069-6}}</ref>
As shown in the adjacent diagram, an air-blowing process consists of using an air [[compressor]] to blow air through the liquid asphalt at a temperature ranging from 235 to 290 °C and being careful to avoid any [[combustion]] of the asphalt by remaining about 25 °C below the [[flash point]] of the feedstock asphalt.  In brief, the asphalt fed into an air-blowing process is [[oxidized]] by the [[oxygen]] in the air. The air-blown product asphalt has a higher temperature softening point than asphalt which has not been air-blown and that is a desirable property for certain uses of petroleum asphalt.<ref name=Speight/><ref name=Jones>{{cite book|author=David S.J. Jones and Peter P.Pujado (Editors)|title=Handbook of Petroleum Processing|edition=First Edition|publisher=Springer|year=2006|id=ISBN 1-4020-2819-9}}</ref><ref name=Speight2>{{cite book|author=James G. Speight, Sunggyu Lee and Sudarshan K. Loyalka|title=Handbook of Alternative Fuel Technologies|edition=1st Edition|publisher=CRC Press|year=2007|id=ISBN 0-8247-4069-6}}</ref>
The end-product petroleum asphalt is typically maintained at a temperature of about 150 °C during storage at the petroleum refinery as well as during transportation to the asphalt end-users.
== Uses of petroleum asphalt==
=== Road construction ===
{{main|Asphalt (paving)}}
The largest use of petroleum asphalt is for making asphaltic concrete for road constrFuction and accounts for approximately 80% of the petroleum asphalt consumed in the United States. The asphalt is used as the binder or glue  that holds together the aggregate of sand, gravel, crushed stone, slag or other material.
There are various mixtures of asphalt with other materials that are used in road construction and other paving applications:
*''Rolled asphaltic concrete'' that contains about 95% aggregate and 5% petroleum asphalt binder.
*''Mastic asphalt'' that contains about 90–93% aggregate and 7–10% petroleum asphalt binder.
*''Asphalt emulsions'' that contain about 70% petroleum asphalt and 30% water plus a small amount of chemical additives.
*''Cutback asphalt'' that contains petroleum solvents (referred to as ''cutbacks'').
Only rarely, if ever, are air-blown asphalts used in asphalt-aggregate mixtures for paving purposes.<ref>[http://www.e-asfalto.com/ingles/oxidador/pilot.htm Air-blown Asphalt: Pilot Plant]</ref>
=== Roofing shingles ===
[[Asphalt shingle|Roofing shingle]]s account for most of the remaining 20% of asphalt consumption in the United States. Asphalt roofing shingles are the dominant roofing material in the United States, representing more than three-fifths of the total installed shingle.<ref>[http://www.thefreelibrary.com/US+roofing+demand+to+reach+$11+billion+in+2007-a098694830 Research Studies: Freedonia Group, Febraury 2003]</ref> They are a very economical roofing choice, especially so for house with sloping roofs.<ref name=EETD>[http://eetd.lbl.gov/coolroof/asshingl.htm Asphalt shingles]</ref>
There are two basic types of asphalt shingles, those with an ''organic'' base and those with a ''fiberglass'' base:<ref>[http://www.nationmaster.com/encyclopedia/Asphalt-shingle Types of Asphalt Shingles]</ref>
*[[Fiberglass shingles]] have a glass fiber reinforced mat coated with asphalt that contains [[mineral]] fillers. The glass fiber mat is not waterproof by itself, but the asphalt coating makes it waterproof.
*Organic base shingles are generally paper saturated with asphalt for waterproofing. Then a top coating of asphalt is applied and [[ceramic]] granules are imbedded in that top coating. Organic shingles contain about 40% more asphalt than fiberglass shingles which makes them heavier and more resistant to being blown off in windy conditions.
In hot climate areas, the amount of sunlight reflectance provided by the shingles is an important property in evaluating the performance of a specific brand of shingle. Reflectance is provide by the embedded granules and by colored shingle coatings.<ref name=EETD/><ref>[http://hes.lbl.gov/hes/makingithappen/no_regrets/coolroofs.html Cool Roofs for Hot Climates]</ref>
According to the [[U.S. Census Bureau]], asphalt shingles accounted for more than half of the residential roofing market during the early 2000s.<ref>[http://www.referenceforbusiness.com/industries/Petroleum-Refining-Related/Asphalt-Felts-Coatings.html NAICS CODE 324122: Asphalt Shingle and Coating Materials Manufacturing]</ref>
=== Other uses ===
*Asphaltic concrete is widely used for paving vehicle parking lots and aircraft landing and take-off runways in airports around the world
*Canal and reservoir linings as well as dam facings
*Floor tiles
*Battery casings
*Waterproofing of fabrics and various other materials
*Treatment of fence posts and other wooden objects
*Cattle sprays
==Asphalt production from oil sands==
{| class = "wikitable" align="right"
|+ Athabasca Oil Sands<br>Operating facilities (February 2009)<ref name=QuarterlyReport>[http://www.albertacanada.com/documents/AOSID_QuarterlyUpdate.pdf Alberta Oil Sands Industry, Quarterly Update, February 2, 2009]</ref>
! Type of project!! Number<br>of projects!![[U.S. customary units|bbl]]/day<br>of asphalt
|-
| In situ extraction || align="center" | 12 || align="right" | 595,000
|-
| Surface mining || align="center" | 4 || align="right" | 1,018,000
|-
| Upgrading || align="center" | 3 || align="right" | 1,002,000
|-
| colspan="3"|<small>Note: 1 bbl/day = 158.987 [[Litre|L]]/day = 0.159 m<sup>3</sup>/day</small>
|}
{{main|Athabasca oil sands}}
There are three large natural deposits of asphalt (or ''bitumen'') in Alberta, Canada that are known as the ''Athabasca oil sands'' and their total surface area is about 54,000 square miles (141,000 square [[kilometre]]s).<ref>[http://www.canadasoilsands.ca/en/issues/land_use.aspx Canada's Oil Sands] a website of the [[Canadian Association of Petroleum Producers]] (CAPP).</ref> The oil sands consist of about 83% sand, 3% clay, 4% water and 10% asphalt.
The proven reserves of asphalt in those deposits are about 1.7 × 10<sup>12</sup> barrels (270 Gm<sup>3 </sup>). About 10% of that is recoverable by current (2009) technology and it is estimated that, with new technologies, the recoverable amount could be about 18-19% which would be about 315 × 10<sup>9</sup> barrels (50 Gm<sup>3 </sup>).<ref name=QuarterlyReport/> For comparison, the estimated reserves of petroleum crude oil in Saudi Arabia (as of early 2008) are about 265 × 10<sup>9</sup> barrels (42 Gm<sup>3 </sup>).<ref>''Oil& Gas Journal'', December 24, 2007</ref>
Asphalt is currently being extracted from the Athabasca oil sands and being converted into synthetic petroleum crude oil (referred to as ''[[Syncrude|syncrude]]''). About 20% of the Athabasca oil sands can be and is being extracted by surface mining techniques. In addition, in situ techniques are being used to extract asphalt from various depths beneath the surface of the oil sands deposits. After extraction, the asphalt is converted into synthetic petroleum crude oil in refining facilities that are referred to as ''upgraders''.<ref name=QuarterlyReport/><ref name=EROI>[http://www.theoildrum.com/node/3839 Unconventional Oil: Tar Sands and Shale Oil] Part 3 of 6 parts of a series entitled ''Energy Return on Investment (EROI) on the Web'' contributed by Professor Charles Hall of the State University of New York (SUNY) and his students (of whom, the authors of this Part 3 were M.C. Herweyer and A. Gupta)</ref> Currently, about 1,000,000 barrels (159,000 m<sup>3 </sup>) of the asphalt are being converted into synthetic crude oil (see adjacent table).
On average, upgrading of about 1.16 barrels of asphalt is required to produce 1 barrel of syncrude.<ref name=EROI/><ref>[http://www.eia.doe.gov/oiaf/aeo/otheranalysis/aeo_2006analysispapers/nlf.html Nonconventional Liquid fuels] From a [[U.S. Department of Energy]] website.</ref> The synthetic crude oil is subsequently transported to conventional petroleum refineries for processing.
Very little, if any, of the extracted asphalt is used for road construction because the Athabasca oil sands are far from the major markets for road construction asphalt and the transportation costs would be too high.
== References ==
{{reflist}}

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