Editing Biofuel (section)

=== Liquid ===

==== Ethanol ====

{{Main|Ethanol fuel}}

Biologically produced [[alcohols]], most commonly ethanol, and less commonly [[Propan-1-ol|propanol]] and [[butanol fuel|butanol]], are produced by the action of [[microorganism]]s and [[enzyme]]s through the fermentation of sugars or starches (easiest to produce) or cellulose (more difficult to produce).The IEA estimates that ethanol production used 20% of sugar supplies and 13% of corn supplies in 2021.<ref name="Renewables 2022 Biofuels">{{Cite web |title=Is the biofuel industry approaching a feedstock crunch? – Analysis |url=https://www.iea.org/reports/is-the-biofuel-industry-approaching-a-feedstock-crunch |access-date=2023-01-02 |website=IEA |date=6 December 2022 |language=en-GB}}</ref>

Ethanol fuel is the most common biofuel worldwide, particularly [[Ethanol fuel in Brazil|in Brazil]]. [[Alcohol fuel]]s are produced by fermentation of sugars derived from [[wheat]], [[Maize|corn]], [[sugar beet]]s, [[sugar cane]], [[molasses]] and any sugar or starch from which [[alcoholic beverage]]s such as [[whiskey]], can be made (such as [[potato]] and [[fruit]] waste, etc.). Production methods used are [[digestive enzyme|enzyme digestion]] (to release sugars from stored starches), fermentation of the sugars, [[distillation]] and drying. The distillation process requires significant energy input to generate heat. Heat is sometimes generated with unsustainable [[natural gas]] fossil fuel, but cellulosic biomass such as [[bagasse]] is the most common fuel in Brazil, while pellets, wood chips and also [[waste heat]] are more common in Europe. Corn-to-ethanol and other food stocks has led to the development of [[cellulosic ethanol]].<ref>{{cite report |title=Breaking the biological barriers to cellulosic ethanol: a joint research agenda. |date=7 June 2006 |publisher=EERE Publication and Product Library |doi=10.2172/1218382 |location=Washington, DC (United States) |vauthors=Houghton J, Weatherwax S, Ferrell J}}</ref>

==== Other biofuels ====

Methanol is currently produced from [[natural gas]], a [[non-renewable]] fossil fuel. In the future it is hoped to be produced from biomass as [[biomethanol]]. This is technically feasible, but the production is currently being postponed for concerns that the economic viability is still pending.<ref>{{cite report |title=Dagens och framtidens hållbara biodrivmedel: underlagsrapport från f3 till utredningen om fossilfri fordonstrafik. |date=18 June 2013 |publisher=The Swedish Knowledge Centre for Renewable Transportation Fuels |volume=13 |page=170 |language=Swedish |vauthors=Börjesson P, Lundgren J, Ahlgren S, Nyström I |trans-title=Today's and the future's sustainable biofuels: background report from f3 to the inquiry into fossil-free vehicle traffic.}}</ref> The [[methanol economy]] is an alternative to the [[hydrogen economy]] to be contrasted with today's [[hydrogen]] production from natural gas.

[[Butanol fuel|Butanol]] ({{chem|C|4|H|9|OH}}) is formed by [[Clostridium acetobutylicum|ABE fermentation]] (acetone, butanol, ethanol) and experimental modifications of the process show potentially high [[net energy gain]]s with [[biobutanol]] as the only liquid product. Biobutanol is often claimed to provide a direct replacement for gasoline, because it will produce more energy than ethanol and allegedly can be burned "straight" in existing gasoline engines (without modification to the engine or car),<ref>{{cite web |date=15 August 2005 |title=ButylFuel, LLC Main Page |url=http://www.butanol.com/ |url-status=live |archive-url=https://web.archive.org/web/20190710235804/http://www.butanol.com/ |archive-date=10 July 2019 |access-date=14 July 2010 |publisher=Butanol.com}}</ref> is less corrosive and less water-soluble than ethanol, and could be distributed via existing infrastructures. ''[[Escherichia coli]]'' strains have also been successfully engineered to produce butanol by modifying their [[protein metabolism|amino acid metabolism]].<ref name="butanol">{{Cite news |date=14 January 2008 |title=Biofuels aim higher |work=Biofuels, Bioproducts and Biorefining (BioFPR) |url=http://www.biofpr.com/details/feature/102347/Biofuels_aim_higher.html |url-status=live |access-date=3 December 2008 |archive-url=https://web.archive.org/web/20090810045124/http://www.biofpr.com/details/feature/102347/Biofuels_aim_higher.html |archive-date=10 August 2009 |vauthors=Evans J}}</ref> One drawback to butanol production in ''E.&nbsp;coli'' remains the high cost of [[Growth medium|nutrient rich media]], however, recent work has demonstrated ''E.&nbsp;coli'' can produce butanol with minimal nutritional supplementation.<ref>{{cite journal |vauthors=Pontrelli S, Fricke RC, Sakurai SS, Putri SP, Fitz-Gibbon S, Chung M, Wu HY, Chen YJ, Pellegrini M, Fukusaki E, Liao JC |date=September 2018 |title=Directed strain evolution restructures metabolism for 1-butanol production in minimal media |journal=Metabolic Engineering |volume=49 |pages=153–163 |doi=10.1016/j.ymben.2018.08.004 |pmid=30107263 |doi-access=free}}</ref> Biobutanol is sometimes called [[biogasoline]], which is incorrect as it is chemically different, being an alcohol and not a hydrocarbon like gasoline.

==== Biodiesel ====
[[File:Biofuel pumps DCA 07 2010 9834.JPG|thumb|upright=1.2|Biofuel pumps, 2010]]
{{Main|Biodiesel}}

{{Further|Biodiesel around the world}}

Biodiesel is the most common biofuel in Europe. It is produced from oils or fats using [[transesterification]] and is a liquid similar in composition to fossil/mineral diesel. Chemically, it consists mostly of fatty acid methyl (or ethyl) esters ([[Fatty acid methyl ester|FAMEs]]).<ref>{{cite journal |vauthors=Fukuda H, Kondo A, Noda H |date=January 2001 |title=Biodiesel fuel production by transesterification of oils |journal=Journal of Bioscience and Bioengineering |volume=92 |issue=5 |pages=405–416 |doi=10.1016/s1389-1723(01)80288-7 |pmid=16233120}}</ref> Feedstocks for biodiesel include animal fats, vegetable oils, [[soy]], [[rapeseed]], [[Jatropha curcas|jatropha]], [[Madhuca longifolia|mahua]], [[mustard plant|mustard]], [[flax]], [[sunflower]], [[palm oil]], [[hemp]], [[thlaspi arvense|field pennycress]], ''[[Pongamia pinnata]]'' and [[algae fuel|algae]]. Pure biodiesel (B100, also known as "neat" biodiesel) currently reduces emissions with up to 60% compared to diesel Second generation B100.<ref>{{Cite web |title=Perstop Press release: Verdis Polaris Aura – second generation B100 – The advanced green one |url=https://www.perstorp.com/en/Media/Pressreleases/2013/20130701_Verdis_Polaris_Aura_second_generation_B100/ |url-status=dead |archive-url=https://web.archive.org/web/20140804182248/https://www.perstorp.com/en/Media/Pressreleases/2013/20130701_Verdis_Polaris_Aura_second_generation_B100/ |archive-date=4 August 2014 |access-date=21 June 2014}}</ref> {{as of|2020}}, researchers at Australia's [[CSIRO]] have been studying [[safflower]] oil as an engine [[lubricant]], and researchers at [[Montana State University]]'s Advanced Fuels Center in the US have been studying the oil's performance in a large [[diesel engine]], with results described as a "breakthrough".<ref>{{cite web |date=7 June 2020 |title=Safflower oil hailed by scientists as possible recyclable, biodegradable replacement for petroleum |url=https://www.abc.net.au/news/2020-06-07/safflower-oil-new-biofuel-to-replace-petroleum/12321028 |url-status=live |archive-url=https://web.archive.org/web/20200607012058/https://www.abc.net.au/news/2020-06-07/safflower-oil-new-biofuel-to-replace-petroleum/12321028 |archive-date=7 June 2020 |access-date=7 June 2020 |website=ABC News |series=Landline |publisher=Australian Broadcasting Corporation |vauthors=Lee T}}</ref>

[[File:Targray Biodiesel Railcar.png|thumb|upright=1.2|Targray Biofuels Division railcar transporting Biodiesel.]]Biodiesel can be used in any diesel engine and modified equipment when mixed with mineral diesel. It can also be used in its pure form (B100) in diesel engines, but some maintenance and performance problems may occur during wintertime utilization, since the fuel becomes somewhat more [[viscosity|viscous]] at lower temperatures, depending on the feedstock used.<ref>{{Cite web |title=Alternative Fuels Data Center: Biodiesel Blends |url=https://afdc.energy.gov/fuels/biodiesel_blends.html |access-date=2022-03-31 |website=afdc.energy.gov}}</ref>

Electronically controlled '[[common rail]]' and '[[Unit Injector]]' type systems from the late 1990s onwards can only use biodiesel blended with conventional diesel fuel. These engines have finely metered and atomized multiple-stage injection systems that are very sensitive to the viscosity of the fuel. Many current-generation diesel engines are designed to run on B100 without altering the engine itself, although this depends on the [[fuel rail]] design. Since biodiesel is an effective [[solvent]] and cleans residues deposited by mineral diesel, [[oil filter|engine filters]] may need to be replaced more often, as the biofuel dissolves old deposits in the fuel tank and pipes. It also effectively cleans the engine [[combustion chamber]] of carbon deposits, helping to maintain efficiency.

Biodiesel is an [[oxygenate]]d fuel, meaning it contains a reduced amount of carbon and higher hydrogen and oxygen content than fossil diesel. This improves the [[combustion]] of biodiesel and reduces the particulate emissions from unburnt carbon. However, using pure biodiesel may increase NO<sub>x</sub>-emissions<ref>{{cite report |url=http://www.vtt.fi/inf/pdf/technology/2012/T46.pdf |title=Fuel and Technology Alternatives for Buses. Overall Energy Efficiency and Emission Performance. IEA Bioenergy Task 46 |date=2012 |publisher=VTT Technical Research Centre of Finland |archive-url=https://web.archive.org/web/20200216193457/https://www.vtt.fi/inf/pdf/technology/2012/T46.pdf |archive-date=16 February 2020 |vauthors=Nylund NO, Koponen K}}. Possibly the new emission standards Euro VI/EPA 10 will lead to reduced NO<sub>x</sub>-levels also when using B100.</ref> Biodiesel is also safe to handle and transport because it is non-toxic and [[biodegradable]], and has a high [[flash point]] of about 300&nbsp;°F (148&nbsp;°C) compared to petroleum diesel fuel, which has a flash point of 125&nbsp;°F (52&nbsp;°C).<ref>{{cite web |title=Biofuels Facts |url=http://www.hempcar.org/biofacts.shtml |url-status=dead |archive-url=https://web.archive.org/web/20110520231032/http://hempcar.org/biofacts.shtml |archive-date=20 May 2011 |access-date=14 July 2010 |publisher=Hempcar.org}}</ref>

In many European countries, a 5% biodiesel blend is widely used and is available at thousands of gas stations.<ref>{{cite web |title=ADM Biodiesel: Hamburg, Leer, Mainz |url=http://www.biodiesel.de/ |url-status=live |archive-url=https://web.archive.org/web/20090802071245/http://www.biodiesel.de/ |archive-date=2 August 2009 |access-date=14 July 2010 |publisher=Biodiesel.de}}</ref><ref>{{cite web |author=RRI Limited for Biodiesel Filling Stations |title=Welcome to Biodiesel Filling Stations |url=http://www.biodieselfillingstations.co.uk |url-status=dead |archive-url=https://web.archive.org/web/20180714031730/http://www.biodieselfillingstations.co.uk/ |archive-date=14 July 2018 |access-date=14 July 2010 |publisher=Biodieselfillingstations.co.uk}}</ref> In France, biodiesel is incorporated at a rate of 8% in the fuel used by all French diesel vehicles.<ref name="RA29">{{Harvsp|Avril Group : Activity Report|2014|p=58}}</ref> [[Avril Group]] produces under the brand [[Diester]], a fifth of 11&nbsp;million tons of biodiesel consumed annually by the [[European Union]].<ref name="EurObserv’ER">{{Harvsp|EurObserv|2014|p=4}}</ref> It is the leading European producer of biodiesel.<ref name="RA29" />

====Green diesel====

{{Main|Biodiesel production}}

[[Hydrotreated vegetable oil|Green diesel]] can be produced from a combination of biochemical and thermochemical processes. Conventional green diesel is produced through hydroprocessing biological oil feedstocks, such as vegetable oils and animal fats.<ref>{{cite web |title=Fast Pyrolysis and Bio-Oil Upgrading |url=http://www.ascension-publishing.com/BIZ/HD50.pdf |url-status=live |archive-url=https://web.archive.org/web/20120105183213/http://www.ascension-publishing.com/BIZ/HD50.pdf |archive-date=5 January 2012 |access-date=15 March 2012 |vauthors=Brown R, Holmgren J}}</ref><ref name="seven">{{cite web |title=Alternative & Advanced Fuels |url=http://www.afdc.energy.gov/fuels/emerging_green.html |url-status=live |archive-url=https://web.archive.org/web/20121027183202/http://www.afdc.energy.gov/fuels/emerging_green.html |archive-date=27 October 2012 |access-date=7 March 2012 |publisher=US Department of Energy}}</ref> Recently, it is produced using series of thermochemical processes such as pyrolysis and hydroprocessing. In the thermochemical route, syngas produced from gasification, bio-oil produced from pyrolysis or biocrude produced from hydrothermal liquefaction is upgraded to green diesel using hydroprocessing.<ref name=":2">{{Cite web |title=Technology {{!}} Comsyn |url=https://www.comsynproject.eu/technology/ |access-date=2024-04-19 |website=www.comsynproject.eu}}</ref><ref name=":3">{{Cite journal |last1=Lilonfe |first1=Sylvanus |last2=Dimitriou |first2=Ioanna |last3=Davies |first3=Ben |last4=Abdul-Manan |first4=Amir F. N. |last5=McKechnie |first5=Jon |date=2024-01-01 |title=Comparative techno-economic and life cycle analyses of synthetic "drop-in" fuel production from UK wet biomass |journal=Chemical Engineering Journal |volume=479 |pages=147516 |doi=10.1016/j.cej.2023.147516 |issn=1385-8947|doi-access=free |bibcode=2024ChEnJ.47947516L }}</ref><ref name=":4">{{Cite journal |last1=Lilonfe |first1=Sylvanus |last2=Davies |first2=Ben |last3=Abdul-Manan |first3=Amir F. N. |last4=Dimitriou |first4=Ioanna |last5=McKechnie |first5=Jon |date=2024-04-17 |title=A review of techno-economic analyses and life cycle greenhouse gas emissions of biomass-to-hydrocarbon "drop-in" fuels |journal=Sustainable Production and Consumption |volume=47 |pages=425–444 |doi=10.1016/j.spc.2024.04.016 |issn=2352-5509|doi-access=free |bibcode=2024SusPC..47..425L }}</ref> Hydroprocessing is the process of using hydrogen to reform a molecular structure. For example, [[hydrocracking]] which is a widely used hydroprocessing technique in refineries is used at elevated temperatures and pressure in the presence of a catalyst to break down larger [[molecules]], such as those found in [[vegetable oil]]s, into shorter [[hydrocarbon]] chains used in [[diesel fuel|diesel]] engines.<ref name="alpha">{{cite journal |vauthors=Knothe G |date=June 2010 |title=Biodiesel and renewable diesel: a comparison. |url=http://naldc.nal.usda.gov/download/39385/PDF |url-status=live |journal=Progress in Energy and Combustion Science |volume=36 |issue=3 |pages=364–373 |doi=10.1016/j.pecs.2009.11.004 |bibcode=2010PECS...36..364K |archive-url=https://web.archive.org/web/20121106063626/http://naldc.nal.usda.gov/download/39385/PDF |archive-date=6 November 2012 |access-date=23 August 2012|url-access=subscription }}</ref> Green diesel may also be called renewable diesel, drop-in biodiesel, hydrotreated vegetable oil (HVO fuel)<ref name="alpha" /> or hydrogen-derived renewable diesel.<ref name="seven" /> Unlike biodiesel, green diesel has exactly the same chemical properties as petroleum-based diesel.<ref name="alpha" /><ref>{{Cite web |title=Green Diesel v. Biodiesel |url=https://www.uop.com/processing-solutions/renewables/green-diesel/biodiesel/ |url-status=live |archive-url=https://web.archive.org/web/20180805143224/https://www.uop.com/processing-solutions/renewables/green-diesel/biodiesel/ |archive-date=5 August 2018 |access-date=5 August 2018}}</ref> It does not require new engines, pipelines or infrastructure to distribute and use, but has not been produced at a cost that is competitive with [[petroleum]].<ref name="seven" /> Gasoline versions are also being developed.<ref>{{cite news |title=Breakthroughs in Green Gasoline Production |newspaper=Biomass Magazine |url=http://biomassmagazine.com/articles/1731/breakthroughs-in-green-gasoline-production/ |url-status=live |access-date=14 August 2012 |archive-url=https://web.archive.org/web/20120311135648/http://biomassmagazine.com/articles/1731/breakthroughs-in-green-gasoline-production |archive-date=11 March 2012 |vauthors=Jessica E}}</ref> Green diesel is being developed in [[Louisiana]] and [[Singapore]] by [[ConocoPhillips]], [[Neste Oil]], [[Valero Energy Corporation|Valero]], Dynamic Fuels, and [[UOP LLC|Honeywell UOP]]<ref name="seven" /><ref>{{Cite report |url=http://www.pnnl.gov/main/publications/external/technical_reports/PNNL-20279.pdf |title=A Brief Literature Overview of Various Routes to Biorenewable Fuels from Lipids for the National Alliance of Advanced Biofuels and Bio-products NAAB Consortium |date=March 2011 |publisher=Prepared by the US Department of Energy |access-date=23 August 2012 |archive-url=https://web.archive.org/web/20120712170606/http://www.pnnl.gov/main/publications/external/technical_reports/PNNL-20279.pdf |archive-date=12 July 2012 |url-status=live |vauthors=Albrecht KO, Hallen RT |journal=}}</ref> as well as Preem in Gothenburg, Sweden, creating what is known as Evolution Diesel.<ref>{{cite web |date=August 2014 |title=Preem makes major investment in green diesel at the Port of Gothenburg – Port of Gothenburg |url=http://www.portofgothenburg.com/News-desk/Press-releases/Preem-makes-major-investment-in-green-diesel-at-the-Port-of-Gothenburg/ |url-status=dead |archive-url=https://web.archive.org/web/20140801105736/http://www.portofgothenburg.com/News-desk/Press-releases/Preem-makes-major-investment-in-green-diesel-at-the-Port-of-Gothenburg/ |archive-date=1 August 2014}}</ref>

====Straight vegetable oil====
[[File:Walmart’s Grease Fuel Truck (2).jpg|thumb|upright=1.2|A biofuel truck in 2009<ref>{{cite web |date=3 February 2009 |title=Wal-Mart To Test Hybrid Trucks |url=https://www.sustainablebusiness.com/index.cfm/go/news.display/id/17599 |url-status=live |archive-url=https://web.archive.org/web/20140508095041/https://www.sustainablebusiness.com/index.cfm/go/news.display/id/17599 |archive-date=8 May 2014 |access-date=8 May 2014 |publisher=Sustainable Business}}</ref>]]
{{Main|Vegetable oil fuel}}

Straight unmodified [[Eating|edible]] vegetable oil is generally not used as fuel, but lower-quality oil has been used for this purpose. Used vegetable oil is increasingly being processed into biodiesel, or (more rarely) cleaned of water and particulates and then used as a fuel. The IEA estimates that biodiesel production used 17% of global vegetable oil supplies in 2021.<ref name="Renewables 2022 Biofuels" />

Oils and fats reacted with 10 pounds of a short-chain alcohol (usually methanol) in the presence of a catalyst (usually sodium hydroxide [NaOH] can be [[hydrogenated]] to give a diesel substitute.<ref>{{Cite web |title=Alternative Fuels Data Center: Biodiesel Production and Distribution |url=https://afdc.energy.gov/fuels/biodiesel_production.html#:~:text=Biodiesel%20is%20produced%20from%20vegetable,and%20glycerin%20(a%20coproduct). |access-date=2022-03-31 |website=afdc.energy.gov}}</ref> The resulting product is a straight-chain hydrocarbon with a high [[cetane number]], low in [[aromatics]] and [[sulfur]] and does not contain oxygen. [[Hydrogenated oil]]s can be blended with diesel in all proportions. They have several advantages over biodiesel, including good performance at low temperatures, no storage stability problems and no susceptibility to microbial attack.<ref name="evans">{{cite report |url=http://www.nnfcc.co.uk/metadot/index.pl?id=6597%3Bisa%3DDBRow%3Bop%3Dshow%3Bdbview_id%3D2457 |title=Liquid Transport Biofuels – Technology Status Report |date=14 April 2008 |publisher=[[National Non-Food Crops Centre]] |archive-url=https://web.archive.org/web/20080611062858/http://www.nnfcc.co.uk/metadot/index.pl?id=6597%3Bisa%3DDBRow%3Bop%3Dshow%3Bdbview_id%3D2457 |archive-date=11 June 2008 |vauthors=Evans G}}</ref>

==== Biogasoline ====
{{Main|Biogasoline}}

Biogasoline can be produced biologically and thermochemically. Using biological methods, a study led by Professor Lee Sang-yup at the Korea Advanced Institute of Science and Technology ([[KAIST]]) and published in the international science journal ''[[Nature (journal)|Nature]]'' used modified ''E.&nbsp;coli'' fed with glucose found in plants or other non-food crops to produce biogasoline with the produced enzymes. The enzymes converted the sugar into fatty acids and then turned these into hydrocarbons that were chemically and structurally identical to those found in commercial gasoline fuel.<ref name="fuels">{{cite report |url=https://www.fuelsandlubes.com/knowledge-base/south-korean-scientists-use-e-coli-to-make-gasoline/ |title=Liquid Transport Fuels&Lubes - South Korean scientists use E. coli to make gasoline |date=2013-11-04 |publisher=Fuels&Lubes Daily |archive-url=https://web.archive.org/web/20220907102013/https://www.fuelsandlubes.com/knowledge-base/south-korean-scientists-use-e-coli-to-make-gasoline/ |archive-date=2022-09-07}}</ref> The thermochemical approach of producing biogasoline are similar to those used to produce biodiesel.<ref name=":2" /><ref name=":3" /><ref name=":4" /> Biogasoline may also be called drop-in gasoline or renewable gasoline.

====Bioethers====
[[File:Sao Paulo ethanol pump 04 2008 74 zoom.jpg|thumb|upright=1.2|[[Common ethanol fuel mixtures#E100|Neat ethanol]] on the left&nbsp;(A), [[gasoline]] on the right (G) at a [[filling station]] in Brazil in 2008|alt=]]
Bioethers (also referred to as fuel [[ether]]s or oxygenated fuels) are cost-effective [[Chemical compound|compounds]] that act as [[octane rating]] enhancers. "Bioethers are produced by the reaction of reactive iso-olefins, such as iso-butylene, with bioethanol."<ref>{{cite web |year=2007 |title=Bioethers Impact on the Gasoline Pool |url=http://www.digitalrefining.com/article/1000210,Bioethers_impact_on_the_gasoline_pool.html |url-status=live |archive-url=https://web.archive.org/web/20161114001438/http://www.digitalrefining.com/article/1000210,Bioethers_impact_on_the_gasoline_pool.html |archive-date=14 November 2016 |access-date=15 February 2014 |publisher=Digital Refining |vauthors=Rock K, Korpelshoek M}}</ref>{{attribution needed|date=October 2022}} Bioethers are created from wheat or sugar beets, and also be produced from the waste glycerol that results from the production of biodiesel.<ref>{{Cite web |title=Biofuels - Types of Biofuels - Bioethers |url=http://biofuel.org.uk/bioethers.html |url-status=live |archive-url=https://web.archive.org/web/20160201004223/http://biofuel.org.uk/bioethers.html |archive-date=1 February 2016 |website=biofuel.org.uk}}</ref> They also enhance [[engine]] performance, while significantly reducing engine wear and [[toxic]] [[exhaust gas|exhaust emissions]]. By greatly reducing the amount of ground-level [[ozone]] emissions, they contribute to improved air quality.{{refn|{{CELEX|id=31985L0536|text=Council Directive 85/536/EEC of 5 December 1985 on crude-oil savings through the use of substitute fuel components in petrol}}. No longer in force, Date of end of validity: 31/12/1999; Repealed by 31998L0070.<ref>{{CELEX|id=01998L0070-20231120|text=Consolidated text: Directive 98/70/EC of the European Parliament and of the Council of 13 October 1998 relating to the quality of petrol and diesel fuels and amending Council Directive 93/12/EEC}}</ref>}}<ref>{{cite web |date=2007-01-31 |title=Impact Assessment of the Proposal for a Directive of the European Parliament and of the Council modifying Directive 98/70/EC relating to the quality of petrol and diesel fuels |url=http://www.europarl.europa.eu/registre/docs_autres_institutions/commission_europeenne/sec/2007/0055/COM_SEC(2007)0055_EN.pdf |url-status=live |archive-url=https://web.archive.org/web/20110715105028/http://www.europarl.europa.eu/registre/docs_autres_institutions/commission_europeenne/sec/2007/0055/COM_SEC(2007)0055_EN.pdf |archive-date=15 July 2011 |access-date=14 July 2010 |publisher=Commission of the European Communities |location=Brussels}}</ref>

In transportation fuel there are six ether additives: dimethyl ether (DME), [[diethyl ether]] (DEE), [[Methyl tert-butyl ether|methyl ''tert''-butyl ether]] (MTBE), [[Ethyl tert-butyl ether|ethyl ''tert''-butyl ether]] (ETBE), [[tert-Amyl methyl ether|''tert''-amyl methyl ether]] (TAME), and [[tert-Amyl ethyl ether|''tert''-amyl ethyl ether]] (TAEE).<ref>{{cite web |title=Bio-Ethers as Transportation Fuel: A Review |url=http://www.ascension-publishing.com/BIZ/DMEoverview.pdf |url-status=live |archive-url=https://web.archive.org/web/20111014172515/http://www.ascension-publishing.com/BIZ/DMEoverview.pdf |archive-date=14 October 2011 |access-date=15 February 2014 |publisher=Indian Institute of Petroleum Dehradun |vauthors=Sukla MK, Bhaskar T, Jain AK, Singal SK, Garg MO}}</ref>

The European Fuel Oxygenates Association identifies MTBE and ETBE as the most commonly used ethers in fuel to replace lead. Ethers were introduced in Europe in the 1970s to replace the highly toxic compound.<ref>{{cite web |title=What are Bio-Ethers? |url=http://www.petrochemistry.eu/ftp/pressroom/EFOA_2008_def.pdf |url-status=dead |archive-url=https://web.archive.org/web/20140306082952/http://www.petrochemistry.eu/ftp/pressroom/EFOA_2008_def.pdf |archive-date=6 March 2014 |publisher=. The European Fuel Oxygenates Association}}</ref> Although Europeans still use bioether additives, the U.S. [[Energy Policy Act of 2005]] lifted a requirement for [[reformulated gasoline]] to include an oxygenate, leading to less MTBE being added to fuel.<ref>{{cite web |title=Gasoline |url=http://www.epa.gov/mtbe/gas.htm |url-status=dead |archive-url=https://web.archive.org/web/20131206222912/http://www.epa.gov/mtbe/gas.htm |archive-date=6 December 2013 |access-date=6 March 2014 |publisher=Environmental Protection Agency}}</ref> Although bioethers are likely to replace ethers produced from petroleum in the UK, it is highly unlikely they will become a fuel in and of itself due to the low energy density.<ref>{{cite web |title=Biofuels – Types of Biofuels – Bioethers |url=http://biofuel.org.uk/bioethers.html |url-status=live |archive-url=https://web.archive.org/web/20160201004223/http://biofuel.org.uk/bioethers.html |archive-date=1 February 2016 |access-date=30 May 2015}}</ref>

====Aviation biofuel====
{{excerpt|Aviation biofuel}}