Asphaltene

Last updated

Asphaltenes are molecular substances that are found in crude oil, along with resins, aromatic hydrocarbons, and saturates (i.e. saturated hydrocarbons such as alkanes). [1] [2] The word "asphaltene" was coined by Boussingault in 1837 when he noticed that the distillation residue of some bitumens had asphalt-like properties. [ citation needed ] Asphaltenes in the form of asphalt or bitumen products from oil refineries are used as paving materials on roads, shingles for roofs, and waterproof coatings on building foundations.

Contents

An example of possible structure for an asphaltene molecule. Possible asphaltene molecule.svg
An example of possible structure for an asphaltene molecule.

Composition

Asphaltenes consist primarily of carbon, hydrogen, nitrogen, oxygen, and sulfur, as well as trace amounts of vanadium and nickel. The C:H ratio is approximately 1:1.2, depending on the asphaltene source. Asphaltenes are defined operationally as the n-heptane (C
7H
16)-insoluble, toluene (C
6H
5CH
3)-soluble component of a carbonaceous material such as crude oil, bitumen, or coal. Asphaltenes have been shown to have a distribution of molecular masses in the range of 400 u to 1500 u, but the average and maximum values are difficult to determine due to aggregation of the molecules in solution. [3]

Analysis

The molecular structure of asphaltenes is difficult to determine because the molecules tend to stick together in solution. [4] These materials are extremely complex mixtures containing hundreds or even thousands of individual chemical species. Asphaltenes do not have a specific chemical formula: individual molecules can vary in the number of atoms contained in the structure, and the average chemical formula can depend on the source. Although they have been subjected to modern analytical methods, including SARA, mass spectrometry, electron paramagnetic resonance and nuclear magnetic resonance, the exact molecular structures are difficult to determine. Given this limitation, asphaltenes are composed mainly of polyaromatic carbon ring units with oxygen, nitrogen, and sulfur heteroatoms, combined with trace amounts of heavy metals, particularly chelated vanadium and nickel, and aliphatic side chains of various lengths. [5] Many asphaltenes from crude oils around the world contain similar ring units, as well as polar and non-polar groups, which are linked together to make highly diverse large molecules. [6] [7]

Asphaltene after heating [8] have been subdivided as: nonvolatile (heterocyclic N and S species), and, volatile (paraffin + olefins, benzenes, naphthalenes, phenanthrenes, several others). Speight [9] reports a simplified representation of the separation of petroleum into the following six major fractions: volatile saturates, volatile aromatics, nonvolatile saturates, nonvolatile aromatics, resins and asphaltenes. He also reports arbitrarily defined physical boundaries for petroleum using carbon-number and boiling point.

Geochemistry

Asphaltenes are today widely recognised as dispersed, chemically altered fragments of kerogen, which migrated out of the source rock for the oil, during oil catagenesis. Asphaltenes had been thought to be held in solution in oil by resins (similar structure and chemistry, but smaller), but recent data shows that this is incorrect. Indeed, it has recently been suggested that asphaltenes are nanocolloidally suspended in crude oil and in toluene solutions of sufficient concentrations. In any event, for low surface tension liquids, such as alkanes and toluene, surfactants are not necessary to maintain nanocolloidal suspensions of asphaltenes.

The nickel to vanadium ratio of asphaltenes reflect the pH and Eh conditions of the paleo-depositional environment of the source rock for oil (Lewan, 1980;1984)[ full citation needed ], and this ratio is, therefore, in use in the petroleum industry for oil-oil correlation and for identification of potential source rocks for oil exploration.

Occurrence

Heavy oils, oil sands, bitumen and biodegraded oils (as bacteria cannot assimilate asphaltenes, but readily consume saturated hydrocarbons and certain aromatic hydrocarbon isomers – enzymatically controlled) contain much higher proportions of asphaltenes than do medium-API oils or light oils. Condensates are virtually devoid of asphaltenes.

Measurement

Because the ratio of electron spins per gram is constant for a particular species of asphaltene [10] then the quantity of asphaltene in an oil can be determined by measuring its paramagnetic signature (EPR). Measuring the EPR signature of the oil at the wellhead as the oil is produced then gives a direct indication of whether the amount of asphaltene is changing (e.g. because of precipitation or sloughing in the tubing below). [11]

In addition, asphaltene aggregation, precipitation or deposition can sometimes be predicted by modeling [12] [13] or machine learning [14] methods and can be measured in the laboratory using imaging methods or filtration.

Production problems

Asphaltenes impart high viscosity to crude oils, negatively impacting production. Furthermore, the variable asphaltene concentration in crude oils within individual reservoirs creates a myriad of production problems. [ example needed ]

Heat exchanger fouling

Asphaltenes are known to be one of the largest causes of fouling in the heat exchangers of the crude oil distillation preheat train. They are present within micelles in crude oil, which can be broken down by reaction with paraffins under high temperature. Once the protective micelle has been removed polar asphaltenes agglomerate and are transported to the tube walls, where they can stick and form a foulant layer.

Asphaltene removal

Chemical treatments for removing asphaltene include:

  1. Solvents
  2. Dispersants/solvents
  3. Oil/dispersants/solvents

The dispersant/solvent approach is used for removing asphaltenes from formation minerals. Continuous treating may be required to inhibit asphaltene deposition in the tubing. Batch treatments are common for dehydration equipment and tank bottoms. There are also asphaltene precipitation inhibitors that can be used by continuous treatment or squeeze treatments. [15]

See also

Related Research Articles

<span class="mw-page-title-main">Hydrocarbon</span> Organic compound consisting entirely of hydrogen and carbon

In organic chemistry, a hydrocarbon is an organic compound consisting entirely of hydrogen and carbon. Hydrocarbons are examples of group 14 hydrides. Hydrocarbons are generally colourless and hydrophobic; their odor is usually faint, and may be similar to that of gasoline or lighter fluid. They occur in a diverse range of molecular structures and phases: they can be gases, liquids, low melting solids or polymers.

A lubricant is a substance that helps to reduce friction between surfaces in mutual contact, which ultimately reduces the heat generated when the surfaces move. It may also have the function of transmitting forces, transporting foreign particles, or heating or cooling the surfaces. The property of reducing friction is known as lubricity.

<span class="mw-page-title-main">Kerogen</span> Solid organic matter in sedimentary rocks

Kerogen is solid, insoluble organic matter in sedimentary rocks. It consists of a variety of organic materials, including dead plants, algae, and other microorganisms, that have been compressed and heated by geological processes. All the kerogen on earth is estimated to contain 1016 tons of carbon. This makes it the most abundant source of organic compounds on earth, exceeding the total organic content of living matter 10,000-fold.

Naphtha is a flammable liquid hydrocarbon mixture. Generally, it is a fraction of crude oil, but it can also be produced from natural gas condensates, petroleum distillates, and the fractional distillation of coal tar and peat. In some industries and regions, the name naphtha refers to crude oil or refined petroleum products such as kerosene or diesel fuel.

<span class="mw-page-title-main">Oil refinery</span> Facility that processes crude oil

An oil refinery or petroleum refinery is an industrial process plant where petroleum is transformed and refined into useful products such as gasoline (petrol), diesel fuel, asphalt base, fuel oils, heating oil, kerosene, liquefied petroleum gas and petroleum naphtha. Petrochemical feedstock like ethylene and propylene can also be produced directly by cracking crude oil without the need of using refined products of crude oil such as naphtha. The crude oil feedstock has typically been processed by an oil production plant. There is usually an oil depot at or near an oil refinery for the storage of incoming crude oil feedstock as well as bulk liquid products. In 2020, the total capacity of global refineries for crude oil was about 101.2 million barrels per day.

<span class="mw-page-title-main">Petroleum jelly</span> Chemical substance used as a lubricating agent and topical ointment

Petroleum jelly, petrolatum, white petrolatum, soft paraffin, or multi-hydrocarbon, CAS number 8009-03-8, is a semi-solid mixture of hydrocarbons, originally promoted as a topical ointment for its healing properties. Vaseline has been an American brand of petroleum jelly since 1870.

A visbreaker is a processing unit in an oil refinery whose purpose is to reduce the quantity of residual oil produced in the distillation of crude oil and to increase the yield of more valuable middle distillates by the refinery. A visbreaker thermally cracks large hydrocarbon molecules in the oil by heating in a furnace to reduce its viscosity and to produce small quantities of light hydrocarbons.. The process name of "visbreaker" refers to the fact that the process reduces the viscosity of the residual oil. The process is non-catalytic.

<span class="mw-page-title-main">Catalytic reforming</span> Chemical process used in oil refining

Catalytic reforming is a chemical process used to convert petroleum refinery naphthas distilled from crude oil into high-octane liquid products called reformates, which are premium blending stocks for high-octane gasoline. The process converts low-octane linear hydrocarbons (paraffins) into branched alkanes (isoparaffins) and cyclic naphthenes, which are then partially dehydrogenated to produce high-octane aromatic hydrocarbons. The dehydrogenation also produces significant amounts of byproduct hydrogen gas, which is fed into other refinery processes such as hydrocracking. A side reaction is hydrogenolysis, which produces light hydrocarbons of lower value, such as methane, ethane, propane and butanes.

<span class="mw-page-title-main">Petroleum coke</span> Solid carbon-rich material

Petroleum coke, abbreviated coke, pet coke or petcoke, is a final carbon-rich solid material that derives from oil refining, and is one type of the group of fuels referred to as cokes. Petcoke is the coke that, in particular, derives from a final cracking process—a thermo-based chemical engineering process that splits long chain hydrocarbons of petroleum into shorter chains—that takes place in units termed coker units. Stated succinctly, coke is the "carbonization product of high-boiling hydrocarbon fractions obtained in petroleum processing ". Petcoke is also produced in the production of synthetic crude oil (syncrude) from bitumen extracted from Canada's tar sands and from Venezuela's Orinoco oil sands.

Heavy crude oil is highly viscous oil that cannot easily flow from production wells under normal reservoir conditions.

<span class="mw-page-title-main">Bonny Light oil</span>

Bonny Light oil was found at Oloibiri in the Niger delta region of Nigeria in 1956 for its commercial use. Due to its features of generating high profit, it is highly demanded by refiners. Bonny light oil has an API of 32.9, classified as light oil. It is regarded as more valuable than the other oils with lower API as more high-value products are produced in the refinement. However, in Nigeria, problems due to oil spillage caused by vandalism, affects both human and the ecosystem in detrimental ways. Some experiments on animals and soil are done to figure out those impacts on organisms.

A crude oil assay is the chemical evaluation of crude oil feedstocks by petroleum testing laboratories. Each crude oil type has unique molecular and chemical characteristics. No two crude oil types are identical and there are crucial differences in crude oil quality. The results of crude oil assay testing provide extensive detailed hydrocarbon analysis data for refiners, oil traders and producers. Assay data help refineries determine if a crude oil feedstock is compatible for a particular petroleum refinery or if the crude oil could cause yield, quality, production, environmental and other problems.

Crude oil is extracted from the bedrock before being processed in several stages, removing natural contaminants and undesirable hydrocarbons. This separation process produces mineral oil, which can in turn be denoted as paraffinic, naphthenic or aromatic. The differences between these different types of oils are not clear-cut, but mainly depend on the predominant hydrocarbon types in the oil. Paraffinic oil, for example, contains primarily higher alkanes, whereas naphthenic oils have a high share of cyclic alkanes in the mixture.

Petroleum naphtha is an intermediate hydrocarbon liquid stream derived from the refining of crude oil with CAS-no 64742-48-9. It is most usually desulfurized and then catalytically reformed, which rearranges or restructures the hydrocarbon molecules in the naphtha as well as breaking some of the molecules into smaller molecules to produce a high-octane component of gasoline.

Saturate, Aromatic, Resin and Asphaltene (SARA) is an analysis method that divides crude oil components according to their polarizability and polarity. The saturate fraction consists of nonpolar material including linear, branched, and cyclic saturated hydrocarbons (paraffins). Aromatics, which contain one or more aromatic rings, are slightly more polarizable. The remaining two fractions, resins and asphaltenes, have polar substituents. The distinction between the two is that asphaltenes are insoluble in an excess of heptane whereas resins are miscible with heptane.

<span class="mw-page-title-main">Alkylbenzene</span> Family of organic compounds

An alkylbenzene is a chemical compound that contains a monocyclic aromatic ring attaching to one or more saturated hydrocarbon chains. Alkylbenzenes are derivatives of benzene, in which one or more hydrogen atoms are replaced by alkyl groups. The simplest member, toluene, has the hydrogen atom of the benzene ring replaced by a methyl group. The chemical formula of alkylbenzenes is CnH2n-6.

Bitumen froth treatment is a process used in the Athabasca oil sands (AOS) bitumen recovery operations to remove fine inorganics—water and mineral particles—from bitumen froth, by diluting the bitumen with a light hydrocarbon solvent—either naphthenic or paraffinic—to reduce the viscosity of the froth and to remove contaminants that were not removed in previous water-based gravity recovery phases. Bitumen with a high viscosity or with too many contaminants, is not suitable for transporting through pipelines or refining. The original and conventional naphthenic froth treatment (NFT) uses a naphtha solvent with the addition of chemicals. Paraffinic Solvent Froth Treatment (PSFT), which was first used commercially in the Albian Sands in the early 2000s, results in a cleaner bitumen with lower levels of contaminates, such as water and mineral solids. Following froth treatments, bitumen can be further upgraded using "heat to produce synthetic crude oil by means of a coker unit."

Base oils are used to manufacture products including lubricating greases, motor oil and metal processing fluids. Different products require different compositions and properties in the oil. One of the most important factors is the liquid’s viscosity at various temperatures. Whether or not a crude oil is suitable to be made into a base oil is determined by the concentration of base oil molecules as well as how easily these can be extracted.

Maltenes are the n-alkane -soluble molecular components of asphalt, which is the residue remaining after petroleum refiners remove other useful derivatives such as gasoline and kerosene from crude oil. Asphaltene compounds are the other primary component of asphalt.

Hydrocarbonoclastic bacteria are a heterogeneous group of prokaryotes which can degrade and utilize hydrocarbon compounds as source of carbon and energy. Despite being present in most of environments around the world, several of these specialized bacteria live in the sea and have been isolated from polluted seawater.

References

  1. ↑ Mullins, O. C. et al. (eds.) (2007) Asphaltenes, Heavy Oils and Petroleomics, Springer, New York.
  2. ↑ Asphaltene. uic.edu
  3. ↑ Podgorski, D. C. (2013). "Heavy Petroleum Composition. 5. Compositional and Structural Continuum of Petroleum Revealed". Energy & Fuels. 27 (3): 1268–1276. doi:10.1021/ef301737f.
  4. ↑ McKenna, A. M. (2013). "Heavy Petroleum Composition. 3. Asphaltene Aggregation". Energy & Fuels. 27 (3): 1246–1256. doi:10.1021/ef3018578.
  5. ↑ Asomaning, S. (1997). Heat exchanger fouling by petroleum asphaltenes. Ph.D. Thesis, University of British Columbia
  6. ↑ G.A. Mansoori, (2009). Int. J. Oil, Gas and Coal Technology 2 141.
  7. ↑ Rueda-Velasquez, R. I. (2013). "Characterization of Asphaltene Building Blocks by Cracking under Favorable Hydrogenation Conditions". Energy & Fuels. 27 (4): 1817–1829. doi:10.1021/ef301521q.
  8. ↑ J.H. Pacheco-Sánchez, and G.A.Mansoori, (2013) Revista Mexicana de Física 59, 584-593.
  9. ↑ J.G. Speight, (1994). in the book Asphaltenes and Asphalts, 1, Developments in Petroleum Science, 40 edited by Yen T. F. and G. V. Chilingarian, (Elsevier Science, New York ). Chapter: Chemical and physical studies of petroleum asphaltenes
  10. ↑ Yen, T.G.; Erdman, J.G.; Saraceno, A.J. (1962). "Investigation of the nature of free radicals in petroleum asphaltenes and related substances by Electron Spin Resonance". Analytical Chemistry. 34 (6): 694–700. doi:10.1021/ac60186a034.
  11. ↑ Abdallah, D.; Punnapalla, S.; Kulbrandstad, O.; Godoy, M.; Madem, S.; Babakhani, A.; Lovell, J. (2018). Asphaltene studies in on-shore Abu Dhabi fields, Part IV: Development of a surface sensor. SPE ATCE. Vol. SPE-191676. Dallas. doi:10.2118/191676-MS.
  12. ↑ Yang, Z.; Ma, C. -F.; Lin, X. -S.; Yang, J. -T.; Guo, T. -M. (1999). "Experimental and modeling studies on the asphaltene precipitation in degassed and gas-injected reservoir oils". Fluid Phase Equilibria. 157: 143–158. doi:10.1016/S0378-3812(99)00004-7.
  13. ↑ Lei, H.; Pingping, S.; Ying, J.; Jigen, Y.; Shi, L.; Aifang, B. (2010). "Prediction of asphaltene precipitation during CO2 injection". Petroleum Exploration and Development. 37 (3): 349. Bibcode:2010PEDO...37..349L. doi: 10.1016/S1876-3804(10)60038-9 .
  14. ↑ Rasuli Nokandeh, N.; Khishvand, M.; Naseri, A. (2012). "An artificial neural network approach to predict asphaltene deposition test result". Fluid Phase Equilibria. 329: 32–41. doi:10.1016/j.fluid.2012.06.001.
  15. ↑ Understanding paraffin and asphaltene problems in oil and gas wells Archived August 3, 2008, at the Wayback Machine , Petroleum Technology Transfer Council, South Midcontinent Region, July 16, 2003 Workshop in Smackover, Arkansas at the Arkansas Natural Resources Museum
This page is based on this Wikipedia article
Text is available under the CC BY-SA 4.0 license; additional terms may apply.
Images, videos and audio are available under their respective licenses.