In organic chemistry, a hydrocarbon is an organic compound consisting entirely of hydrogen and carbon.: 620 Hydrocarbons are examples of group 14 hydrides. Hydrocarbons are generally colourless and hydrophobic with only weak odours. Because of their diverse molecular structures, it is difficult to generalize further. In the oil & gas industry, hydrocarbon is a generalised term, which combines petroleum and natural gas as the two naturally occurring phases of hydrocarbon commoditised by the sector. Most anthropogenic emissions of greenhouse gases are from the burning of fossil fuels including fuel production and combustion. Natural sources of hydrocarbons such as ethylene, isoprene, and monoterpenes come from the emissions of vegetation.
As defined by IUPAC nomenclature of organic chemistry, the classifications for hydrocarbons are:
- Saturated hydrocarbons are the simplest of the hydrocarbon types. They are composed entirely of single bonds and are saturated with hydrogen. The formula for acyclic saturated hydrocarbons (i.e., alkanes) is CnH2n+2.: 623 The most general form of saturated hydrocarbons is CnH2n+2(1-r), where r is the number of rings. Those with exactly one ring are the cycloalkanes. Saturated hydrocarbons are the basis of petroleum fuels and are found as either linear or branched species. Substitution reaction is their characteristics property (like chlorination reaction to form chloroform). Hydrocarbons with the same molecular formula but different structural formulae are called structural isomers.: 625 As given in the example of 3-methylhexane and its higher homologues, branched hydrocarbons can be chiral.: 627 Chiral saturated hydrocarbons constitute the side chains of biomolecules such as chlorophyll and tocopherol.
- Unsaturated hydrocarbons have one or more double or triple bonds between carbon atoms. Those with double bond are called alkenes. Those with one double bond have the formula CnH2n (assuming non-cyclic structures).: 628 Those containing triple bonds are called alkyne. Those with one triple bond have the formula CnH2n−2.: 631
- Aromatic hydrocarbons, also known as arenes, are hydrocarbons that have at least one aromatic ring. 10% of total nonmethane organic carbon emission are aromatic hydrocarbons from the exhaust of gasoline-powered vehicles.
Hydrocarbons can be gases (e.g. methane and propane), liquids (e.g. hexane and benzene), waxes or low melting solids (e.g. paraffin wax and naphthalene) or polymers (e.g. polyethylene, polypropylene and polystyrene).
The term 'aliphatic' refers to non-aromatic hydrocarbons. Saturated aliphatic hydrocarbons are sometimes referred to as 'paraffins'. Aliphatic hydrocarbons containing a double bond between carbon atoms are sometimes referred to as 'olefins'.
|Alkane (single bond)||Alkene (double bond)||Alkyne (triple bond)||Cycloalkane||Alkadiene|
|2||Ethane||Ethene (ethylene)||Ethyne (acetylene)||—||—|
|3||Propane||Propene (propylene)||Propyne (methylacetylene)||Cyclopropane||Propadiene (allene)|
The predominant use of hydrocarbons is as a combustible fuel source. Methane is the predominant component of natural gas. The C6 through C10 alkanes, alkenes and isomeric cycloalkanes are the top components of gasoline, naphtha, jet fuel and specialized industrial solvent mixtures. With the progressive addition of carbon units, the simple non-ring structured hydrocarbons have higher viscosities, lubricating indices, boiling points, solidification temperatures, and deeper color. At the opposite extreme from methane lie the heavy tars that remain as the lowest fraction in a crude oil refining retort. They are collected and widely utilized as roofing compounds, pavement composition (bitumen), wood preservatives (the creosote series) and as extremely high viscosity shear-resisting liquids.
Some large-scale non-fuel applications of hydrocarbons begins with ethane and propane, which are obtained from petroleum and natural gas. These two gases are converted either to syngas or to ethylene and propylene. These two alkenes are precursors to polymers, including polyethylene, polystyrene, acrylates, polypropylene, etc. Another class of special hydrocarbons is BTX, a mixture of benzene, toluene, and the three xylene isomers. Global consumption of benzene in 2021 is estimated at more than 58 million metric tons, which will increase to 60 million tons in 2022.
Hydrocarbons are also prevalent in nature. Some eusocial arthropods, such as the Brazilian stingless bee, Schwarziana quadripunctata, use unique cuticular hydrocarbon "scents" in order to determine kin from non-kin. This hydrocarbon composition varies between age, sex, nest location, and hierarchal position.
There is also potential to harvest hydrocarbons from plants like Euphorbia lathyris and Euphorbia tirucalli as an alternative and renewable energy source for vehicles that use diesel. Furthermore, endophytic bacteria from plants that naturally produce hydrocarbons have been used in hydrocarbon degradation in attempts to deplete hydrocarbon concentration in polluted soils.
The noteworthy feature of hydrocarbons is their inertness, especially for saturated members. Otherwise, three main types of reactions can be identified:
Substitution reactions only occur in saturated hydrocarbons (single carbon–carbon bonds). Such reactions require highly reactive reagents, such as chlorine and fluorine. In the case of chlorination, one of the chlorine atoms replaces a hydrogen atom. The reactions proceed via free-radical pathways.
- CH4 + Cl2 → CH3Cl + HCl
- CH3Cl + Cl2 → CH2Cl2 + HCl
all the way to CCl4 (carbon tetrachloride)
- C2H6 + Cl2 → C2H5Cl + HCl
- C2H4Cl2 + Cl2 → C2H3Cl3 + HCl
all the way to C2Cl6 (hexachloroethane)
Of the classes of hydrocarbons, aromatic compounds uniquely (or nearly so) undergo substitution reactions. The chemical process practiced on the largest scale is an example: the reaction of benzene and ethene to give ethylbenzene.
Addition reactions apply to alkenes and alkynes. In this reaction a variety of reagents add "across" the pi-bond(s). Chlorine, hydrogen chloride, water, and hydrogen are illustrative reagents. Alkenes and some alkynes also undergo polymerization, alkene metathesis, and alkyne metathesis.
Hydrocarbons are currently the main source of the world's electric energy and heat sources (such as home heating) because of the energy produced when they are combusted. Often this energy is used directly as heat such as in home heaters, which use either petroleum or natural gas. The hydrocarbon is burnt and the heat is used to heat water, which is then circulated. A similar principle is used to create electrical energy in power plants.
Common properties of hydrocarbons are the facts that they produce steam, carbon dioxide and heat during combustion and that oxygen is required for combustion to take place. The simplest hydrocarbon, methane, burns as follows:
- CH4 + 2 O2 → 2 H2O + CO2 + energy
- 2 CH4 + 3 O2 → 2 CO + 4 H2O
Another example is the combustion of propane:
- C3H8 + 5 O2 → 4 H2O + 3 CO2 + energy
And finally, for any linear alkane of n carbon atoms,
- CnH2n+2 + 3n + 1/2 O2 → (n + 1) H2O + n CO2 + energy.
The vast majority of hydrocarbons found on Earth occur in crude oil, petroleum, coal, and natural gas. Petroleum (literally "rock oil" – petrol for short) and coal are generally thought to be products of decomposition of organic matter. Coal, in contrast to petroleum, is richer in carbon and poorer in hydrogen. Natural gas is the product of methanogenesis.
A seemingly limitless variety of compounds comprise petroleum, hence the necessity of refineries. These hydrocarbons consist of saturated hydrocarbons, aromatic hydrocarbons, or combinations of the two. Missing in petroleum are alkenes and alkynes. Their production requires refineries. Petroleum-derived hydrocarbons are mainly consumed for fuel, but they are also the source of virtually all synthetic organic compounds, including plastics and pharmaceuticals. Natural gas is consumed almost exclusively as fuel. Coal is used as a fuel and as a reducing agent in metallurgy.
Some hydrocarbons also are widespread and abundant in the solar system. Lakes of liquid methane and ethane have been found on Titan, Saturn's largest moon, confirmed by the Cassini-Huygens Mission. Hydrocarbons are also abundant in nebulae forming polycyclic aromatic hydrocarbon (PAH) compounds.
Bioremediation of hydrocarbon from soil or water contaminated is a formidable challenge because of the chemical inertness that characterize hydrocarbons (hence they survived millions of years in the source rock). Nonetheless, many strategies have been devised, bioremediation being prominent. The basic problem with bioremediation is the paucity of enzymes that act on them. Nonetheless the area has received regular attention. Bacteria in the gabbroic layer of the ocean's crust can degrade hydrocarbons; but the extreme environment makes research difficult. Other bacteria such as Lutibacterium anuloederans can also degrade hydrocarbons.Mycoremediation or breaking down of hydrocarbon by mycelium and mushrooms is possible.
Hydrocarbons are generally of low toxicity, hence the widespread use of gasoline and related volatile products. Aromatic compounds such as benzene are narcotic and chronic toxins and are carcinogenic. Certain rare polycyclic aromatic compounds are carcinogenic. Hydrocarbons are highly flammable.
Burning hydrocarbons as fuel, which produces carbon dioxide and water, is a major contributor to anthropogenic global warming. Hydrocarbons are introduced into the environment through their extensive use as fuels and chemicals as well as through leaks or accidental spills during exploration, production, refining, or transport of fossil fuels. Anthropogenic hydrocarbon contamination of soil is a serious global issue due to contaminant persistence and the negative impact on human health.
When soil is contaminated by hydrocarbons, it can have a significant impact on its microbiological, chemical, and physical properties. This can serve to prevent, slow down or even accelerate the growth of vegetation depending on the exact changes that occur. Crude oil and natural gas are the two largest sources of hydrocarbon contamination of soil.
- Silberberg, Martin (2004). Chemistry: The Molecular Nature Of Matter and Change. New York: McGraw-Hill Companies. ISBN 0-07-310169-9.
- IUPAC Goldbook hydrocarbyl groups Archived 7 January 2010 at the Wayback Machine
- Dewulf, Jo. "Hydrocarbons in the Atmosphere" (PDF). Retrieved 26 October 2020.
- Meierhenrich, Uwe. Amino Acids and the Asymmetry of Life Archived 2 March 2017 at the Wayback Machine. Springer, 2008. ISBN 978-3-540-76885-2
- Barnes, I. "TROPOSPHERIC CHEMISTRY AND COMPOSITION (Aromatic Hydrocarbons)". Retrieved 26 October 2020.
- Liu, Shenglin; Xiong, Guoxing; Yang, Weisheng; Xu, Longya (1 July 2000). "Partial Oxidation of Ethane to Syngas over Supported Metal Catalysts". Reaction Kinetics and Catalysis Letters. 70 (2): 311–317. doi:10.1023/A:1010397001697. ISSN 1588-2837. S2CID 91569579.
- Ge, Meng; Chen, Xingye; Li, Yanyong; Wang, Jiameng; Xu, Yanhong; Zhang, Lihong (1 June 2020). "Perovskite-derived cobalt-based catalyst for catalytic propane dehydrogenation". Reaction Kinetics, Mechanisms and Catalysis. 130 (1): 241–256. doi:10.1007/s11144-020-01779-8. ISSN 1878-5204. S2CID 218496057.
- Li, Qian; Yang, Gongbing; Wang, Kang; Wang, Xitao (2020). "Preparation of carbon-doped alumina beads and their application as the supports of Pt–Sn–K catalysts for the dehydrogenation of propane". Reaction Kinetics, Mechanisms and Catalysis. 129 (2): 805–817. doi:10.1007/s11144-020-01753-4. S2CID 212406355.
- Naumann d'Alnoncourt, Raoul; Csepei, Lénárd-István; Hävecker, Michael; Girgsdies, Frank; Schuster, Manfred E.; Schlögl, Robert; Trunschke, Annette (2014). "The reaction network in propane oxidation over phase-pure MoVTeNb M1 oxide catalysts". J. Catal. 311: 369–385. doi:10.1016/j.jcat.2013.12.008. hdl:11858/00-001M-0000-0014-F434-5.
- Hävecker, Michael; Wrabetz, Sabine; Kröhnert, Jutta; Csepei, Lenard-Istvan; Naumann d'Alnoncourt, Raoul; Kolen'Ko, Yury V.; Girgsdies, Frank; Schlögl, Robert; Trunschke, Annette (2012). "Surface chemistry of phase-pure M1 MoVTeNb oxide during operation in selective oxidation of propane to acrylic acid". J. Catal. 285: 48–60. doi:10.1016/j.jcat.2011.09.012. hdl:11858/00-001M-0000-0012-1BEB-F.
- Kinetic studies of propane oxidation on Mo and V based mixed oxide catalysts (PDF). TU Berlin. 2011.
- Li, Guixian; Wu, Chao; Ji, Dong; Dong, Peng; Zhang, Yongfu; Yang, Yong (1 April 2020). "Acidity and catalyst performance of two shape-selective HZSM-5 catalysts for alkylation of toluene with methanol". Reaction Kinetics, Mechanisms and Catalysis. 129 (2): 963–974. doi:10.1007/s11144-020-01732-9. ISSN 1878-5204. S2CID 213601465.
- "Benzene global market volume 2015-2026". Statista. Retrieved 5 December 2021.
- Nunes, T.M.; Turatti, I.C.C.; Mateus, S.; Nascimento, F.S.; Lopes, N.P.; Zucchi, R. (2009). "Cuticular Hydrocarbons in the Stingless Bee Schwarziana quadripunctata (Hymenoptera, Apidae, Meliponini): Differences between Colonies, Castes and Age" (PDF). Genetics and Molecular Research. 8 (2): 589–595. doi:10.4238/vol8-2kerr012. PMID 19551647. Archived (PDF) from the original on 26 September 2015.
- Calvin, Melvin (1980). "Hydrocarbons from plants: Analytical methods and observations". Naturwissenschaften. 67 (11): 525–533. Bibcode:1980NW.....67..525C. doi:10.1007/BF00450661. S2CID 40660980.
- Pawlik, Malgorzata (2017). "Hydrocarbon degradation potential and plant growth-promoting activity of culturable endophytic bacteria of Lotus corniculatus and Oenothera biennis from a long-term polluted site". Environmental Science and Pollution Research International. 24 (24): 19640–19652. doi:10.1007/s11356-017-9496-1. PMC 5570797. PMID 28681302.
- "Generating Electricity". Canadian Electricity Association. Retrieved 5 December 2021.
- Zou, Caineng; Zhao, Qun; Zhang, Guosheng; Xiong, Bo (1 January 2016). "Energy revolution: From a fossil energy era to a new energy era". Natural Gas Industry B. 3 (1): 1–11. doi:10.1016/j.ngib.2016.02.001. ISSN 2352-8540.
- Clayden, J., Greeves, N., et al. (2001) Organic Chemistry Oxford ISBN 0-19-850346-6 p. 21
- McMurry, J. (2000). Organic Chemistry 5th ed. Brooks/Cole: Thomson Learning. ISBN 0-495-11837-0 pp. 75–81
- Sephton, M. A.; Hazen, R. M. (2013). "On the Origins of Deep Hydrocarbons". Reviews in Mineralogy and Geochemistry. 75 (1): 449–465. Bibcode:2013RvMG...75..449S. doi:10.2138/rmg.2013.75.14.
- NASA's Cassini Spacecraft Reveals Clues About Saturn Moon Archived 2 September 2014 at the Wayback Machine. NASA (12 December 2013)
- Guzman-Ramirez, L.; Lagadec, E.; Jones, D.; Zijlstra, A. A.; Gesicki, K. (2014). "PAH formation in O-rich planetary nebulae". Monthly Notices of the Royal Astronomical Society. 441 (1): 364–377. arXiv:1403.1856. Bibcode:2014MNRAS.441..364G. doi:10.1093/mnras/stu454. S2CID 118540862.
- Lim, Mee Wei; Lau, Ee Von; Poh, Phaik Eong (2016). "A comprehensive guide of remediation technologies for oil contaminated soil — Present works and future directions". Marine Pollution Bulletin. 109 (1): 14–45. doi:10.1016/j.marpolbul.2016.04.023. PMID 27267117.
- Mason OU, Nakagawa T, Rosner M, Van Nostrand JD, Zhou J, Maruyama A, Fisk MR, Giovannoni SJ (2010). "First investigation of the microbiology of the deepest layer of ocean crust". PLOS ONE. 5 (11): e15399. Bibcode:2010PLoSO...515399M. doi:10.1371/journal.pone.0015399. PMC 2974637. PMID 21079766.
- Yakimov, M. M.; Timmis, K. N.; Golyshin, P. N. (2007). "Obligate oil-degrading marine bacteria". Curr. Opin. Biotechnol. 18 (3): 257–266. CiteSeerX 10.1.1.475.3300. doi:10.1016/j.copbio.2007.04.006. PMID 17493798.
- Stamets, Paul (2008). "6 ways mushrooms can save the world" (video). TED Talk. Archived from the original on 31 October 2014.
- Stamets, Paul (2005). "Mycoremediation". Mycelium Running: How Mushrooms Can Help Save the World. Ten Speed Press. p. 86. ISBN 9781580085793.
- "Microbial Degradation of Alkanes (PDF Download Available)". ResearchGate. Archived from the original on 24 February 2017. Retrieved 23 February 2017.
- "Additives Affecting the Microbial Degradation of Petroleum Hydrocarbons", Bioremediation of Contaminated Soils, CRC Press, pp. 353–360, 9 June 2000, doi:10.1201/9781482270235-27, ISBN 978-0-429-07804-0