Methyl tert-butyl ether: Difference between revisions

| Watchedfields = changed

| verifiedrevid = 451874187

| Name = {{nobr|Methyl ''tert''-butyl ether}}

| ImageFile = MTBE-2D.svg

| ImageSize = 150

| ImageAlt = Skeletal formula of MTBE

| ImageFile1 = Methyl tert-butyl ether 3D ball.png

| ImageSize1 = 150

| ImageAlt1 = Ball-and-stick model of the MTBE molecule

| PIN = 2-Methoxy-2-methylpropane

| OtherNames = {{ubl|Methyl ''tertiary''-butyl ether|Methyl ''t''-butyl ether|MTBE|''tert''-Butyl methyl ether|tBME|''tert''-BuOMe}}

| Section1 = {{Chembox Identifiers

| UNII_Ref = {{fdacite|correct|FDA}}

| UNII = 29I4YB3S89

| Section2 = {{Chembox Properties

| C=5|H=12|O=1

| Density = 0.7404 g/cm³

| Appearance = colourless liquid

| VaporPressure = 27kPa (20ºC)

| Viscosity = 3.4·10^-4 Pa·s (at 25ºC)

| MeltingPtC = -108.6

| BoilingPtC = 55.5

| Solubility = 26 g/L (20 °C)<ref name=GESTIS>{{GESTIS|ZVG=40480|Name=Methyl tert-butyl ether}}</ref>

| Section7 = {{Chembox Hazards

| NFPA-H = 2

| NFPA-F = 3

| NFPA-I = 0

| FlashPtC = -32.78

| AutoignitionPtC = 435

'''Methyl ''tert''-butyl ether''' ('''MTBE'''), also known as '''''tert''-butyl methyl ether''', is an [[organic compound]] with a structural formula (CH₃)₃COCH₃. MTBE is a volatile, flammable, and colorless liquid that is sparingly soluble in water.<ref name=GESTIS /> Primarily used as a fuel additive, MTBE is blended into [[gasoline]] to increase its [[octane rating]] and knock resistance, and reduce unwanted [[Exhaust gas|emissions]].<ref>{{Cite web |title=Methyl tertiary butyl ether prices, markets & analysis |url=https://www.icis.com/explore/commodities/chemicals/methyl-tertiary-butyl-ether/ |access-date=2020-06-28 |website=ICIS Explore |language=en-US}}</ref><ref>{{Cite web |title=Oxygenates |url=https://www.api.org:443/oil-and-natural-gas/environment/clean-water/ground-water/oxygenates |access-date=2020-06-28 |website=www.api.org |language=en}}</ref>

MTBE is manufactured via the [[chemical reaction]] of [[methanol]] and [[isobutylene]]. Methanol is primarily derived from [[natural gas]],<ref>{{Cite web |title=How is Methanol Produced |url=https://www.methanol.org/methanol-production/ |access-date=2020-06-29 |website=METHANOL INSTITUTE |language=en-US}}</ref> where [[steam reforming]] converts the various light hydrocarbons in natural gas (primarily methane) into carbon monoxide and hydrogen.<ref>{{Cite journal |last1=Anzelmo |first1=Bryce |last2=Wilcox |first2=Jennifer |last3=Liguori |first3=Simona |title=Hydrogen production via natural gas steam reforming in a Pd-Au membrane reactor. Investigation of reaction temperature and GHSV effects and long-term stability |url=https://users.wpi.edu/~jlwilcox/documents/bryce_hpv.pdf |journal=Journal of Membrane Science |pages=25–32 }}{{Dead link|date=October 2023 |bot=InternetArchiveBot |fix-attempted=yes }}</ref> The resulting gases then further react in the presence of a catalyst to form methanol.<ref>{{Cite web |title=methanol {{!}} Properties, Production, Uses, & Poisoning |url=https://www.britannica.com/science/methanol |access-date=2020-06-29 |website=Encyclopedia Britannica|language=en}}</ref> Isobutylene can be produced through a variety of methods. [[Butane|''n''-butane]] can be isomerized into [[isobutane]] which can be dehydrogenated to isobutylene.<ref>{{Cite web |title=Methyl Tertiary Butyl Ether (MTBE) Production and Manufacturing Process |url=https://www.icis.com/explore/resources/news/2007/11/05/9076055/methyl-tertiary-butyl-ether-mtbe-production-and-manufacturing-process |access-date=2020-06-29 |website=ICIS Explore |language=en-US}}</ref> In the Halcon process, ''t''-Butyl hydroperoxide derived from isobutane oxygenation is treated with [[propylene]] to produce [[propylene oxide]] and [[Tert-Butyl alcohol|''t''-butanol]]. The ''t''-butanol can be dehydrated to isobutylene.

MTBE production in the U.S. peaked in 1999 at 260,000 barrels per day<ref name=":0">{{Cite web |title=The United States continues to export MTBE, mainly to Mexico, Chile, and Venezuela - Today in Energy - U.S. Energy Information Administration (EIA)|url=https://www.eia.gov/todayinenergy/detail.php?id=36614 |access-date=2020-06-28 |website=www.eia.gov}}</ref> before dropping down to about 50,000 barrels per day and holding steady,<ref>{{Cite web |title=United States {{!}} Methyl Tertiary Butyl Ether (MTBE): Production {{!}} Economic Indicators |url=https://www.ceicdata.com/en/united-states/production/methyl-tertiary-butyl-ether-mtbe-production |access-date=2020-06-28 |website=www.ceicdata.com}}</ref> mostly for the export market. After the purchase of [[SABIC]],<ref>{{Cite web |title=Aramco completes its acquisition of a 70% stake in SABIC from the Public Investment Fund (PIF) |url=https://www.saudiaramco.com/en/news-media/news/2020/saudi-aramco-completes-acquisition-of-70-percent-stake-in-sabic |access-date=2020-06-29 |website=www.saudiaramco.com |date=17 June 2020 |language=en}}</ref><ref>{{Cite news |date=2020-06-14 |title=Saudi Aramco buys SABIC shares on market as it completes acquisition |language=en |work=Reuters |url=https://www.reuters.com/article/us-saudi-sabic-deals-idUSKBN23L0EQ |access-date=2020-06-29}}</ref> oil giant [[Saudi Aramco]] is now considered to be the world's largest producer<ref>{{Cite web |title=Saudi Aramco to have largest MTBE capacity in Middle East and Asia |url=https://www.nsenergybusiness.com/news/saudi-aramco-mtbe-capacity-middle-east-asia/ |access-date=2020-06-29 |language=en-US}}</ref> with an estimated production capacity of 2.37 million metric tons per year (mt/yr).<ref>{{Cite web |date=2019-04-09 |title=Saudi Aramco's MTBE trading volume likely to rise after Sabic purchase {{!}} S&P Global Platts |url=https://www.spglobal.com/platts/en/market-insights/latest-news/oil/040919-saudi-aramcos-mtbe-trading-volume-likely-to-rise-after-sabic-purchase |access-date=2020-06-29 |website=www.spglobal.com |language=en}}</ref> Worldwide production capacity of MTBE in 2018 was estimated to be 35 million metric tons.<ref>{{Cite web |title=MTBE annual production capacity globally 2023 |url=https://www.statista.com/statistics/1067431/mtbe-production-capacity-globally/ |access-date=2020-06-28 |website=Statista |language=en}}</ref>

MTBE is used as a fuel component in fuel for [[petrol|gasoline]] engines. It is one of a group of chemicals commonly known as [[oxygenate]]s because they raise the [[oxygen]] content of gasoline.

In the U.S. MTBE has been used in gasoline at low levels since 1979, replacing [[tetraethyllead]] (TEL) as an antiknock (octane rating) additive to prevent [[engine knocking]].<ref>{{Cite web |title=Overview {{!}} Methyl Tertiary Butyl Ether (MTBE) {{!}} US EPA |url=https://archive.epa.gov/mtbe/web/html/faq.html |access-date=2021-04-07 |website=archive.epa.gov |language=en}}</ref> Oxygenates also help gasoline burn more completely, [[Automobile emissions control|reducing tailpipe emissions]]. Oxygenates also dilute or displace gasoline components such as aromatics (e.g., [[benzene]]). Before the introduction of other oxygenates and octane enhancers, refiners chose MTBE for its blending characteristics and low cost.

===Alternatives to MTBE as an anti-knock agent===

Other oxygenates are available as additives for gasoline including [[alcohol fuel|ethanol]] and other ethers such as [[ETBE]].

Ethanol has been advertised as a safe alternative by agricultural and other interest groups in the U.S. and Europe. In 2003, California was the first U.S. state to start replacing MTBE with ethanol.

An alternative to ethanol is ETBE, which is manufactured from ethanol and isobutene. Its performance as an additive is similar to MTBE, but due to the higher price of ethanol compared to methanol, it is more expensive.

Higher quality gasoline is also an alternative, so that additives such as MTBE are unnecessary. [[Iso-octane]] itself is used. MTBE plants can be retrofitted to produce iso-octane from isobutylene.<ref name=nesteengineering>{{cite web |url=http://www.nesteengineering.com/default.asp?path=111,360,362,477 |title= NExOCTANE™ - Neste Jacobs |website=www.nesteengineering.com |archive-url=https://web.archive.org/web/20060106041047/http://www.nesteengineering.com/default.asp?path=111%2C360%2C362%2C477 |archive-date=January 6, 2006}}</ref><ref name=halliburton>{{Cite web |url=http://www.halliburton.com/kbr/hydroChem/petroChem/nexoctane.jsp |title=KBR - NExOCTANE™ |access-date=2006-01-31 |archive-url=https://web.archive.org/web/20060106003915/http://www.halliburton.com/kbr/hydroChem/petroChem/nexoctane.jsp |archive-date=2006-01-06 |url-status=dead }}</ref>

MTBE is sometimes used as a solvent,<ref>{{cite journal |doi = 10.1194/jlr.D700041-JLR200 |doi-access=free |pmid = 18281723 |title = Lipid extraction by methyl-tert-butyl ether for high-throughput lipidomics |journal = [[The Journal of Lipid Research]]| volume = 49 |issue = 5 |pages = 1137–1146 |year = 2008 |last1 = Matyash |first1 = V. |last2 = Liebisch |first2 = G. |last3 = Kurzchalia |first3 = T. V. |last4 = Shevchenko |first4 = A. |last5 = Schwudke |first5 = D. |pmc = 2311442}}</ref><ref>{{Cite journal |title = Sorption of methanol, dimethyl carbonate, methyl acetate, and acetone vapors in CTA and PTMSP: General findings from the GAB Analysis |journal = [[Journal of Polymer Science Part B: Polymer Physics]] |date = 2016-03-01 |issn = 1099-0488 |pages = 561–569 |volume = 54 |issue = 5 |doi = 10.1002/polb.23945 |language = en |first1 = Ondřej |last1 = Vopička |first2 = Kryštof |last2 = Pilnáček |first3 = Petr |last3 = Číhal |first4 = Karel |last4 = Friess |bibcode = 2016JPoSB..54..561V}}</ref><ref>{{Cite journal |title = Sorption of vapour mixtures of methanol and dimethyl carbonate in PTMSP: Cooperative and competitive sorption in one system |journal = [[European Polymer Journal]] |date = 2016-02-01 |pages = 243–250 |volume = 75 |doi = 10.1016/j.eurpolymj.2015.12.015 |first1 = Ondřej |last1 = Vopička |first2 = Daniel |last2 = Radotínský |first3 = Karel |last3 = Friess}}</ref> although it is used less commonly than diethyl ether. Although an ether, MTBE is a poor [[Lewis base]] and does not support formation of [[Grignard reagent]]s. It is also unstable toward strong acids. It reacts dangerously with [[bromine]].<ref>{{cite web |url=http://www.crhf.org.uk/incident09.html |title=Interaction between bromine and tert-butyl methyl ether |publisher=UK Chemical Reaction Hazards Forum |access-date=13 May 2010 |archive-url=https://web.archive.org/web/20110313064840/http://www.crhf.org.uk/incident09.html |archive-date=13 March 2011}}</ref>

MTBE forms [[azeotrope]]s with water (52.6&nbsp;°C; 96.5% MTBE)<ref name=":1">[http://www.zeon.co.jp/business_e/enterprise/spechemi/cpme_tec_sup_e_200906.pdf Zeon Corporation] {{webarchive |url=https://web.archive.org/web/20110722102229/http://www.zeon.co.jp/business_e/enterprise/spechemi/cpme_tec_sup_e_200906.pdf |date=2011-07-22 }}</ref> and methanol (51.3&nbsp;°C; 68.6% MTBE).<ref>''[[CRC Handbook of Chemistry and Physics]]'', 90th edition</ref> The solubility of water in MTBE is reported to be 1.5 g/100g at 23 °C.<ref name=":1" />

In an investigational medical procedure called contact dissolution therapy, MTBE is injected directly into the gallbladder to dissolve cholesterol [[gallstones]]. Due to concerns of MTBE toxicity and potentially serious side effects in the event of solvent draining into the [[duodenum]], and the advent of [[laparoscopic surgery]] techniques, this procedure is considered obsolete. <ref>{{cite journal |vauthors=Schoenfield LJ, Marks JW |title=Oral and contact dissolution of gallstones |journal=[[Am. J. Surg.]] |volume=165 |issue=4 |pages=427–30 |year=1993 |pmid=8480875 |doi=10.1016/S0002-9610(05)80934-1 }}</ref><ref>{{cite news |url = https://www.nytimes.com/health/guides/disease/gallstones/treatment.html |title = Health Guide: Gallstones |newspaper = New York Times}}</ref><ref>https://www.aetna.com/cpb/medical/data/500_599/0509.html | access-date = June 3, 2024</ref>

MTBE is used in organic chemistry as a relatively inexpensive solvent with properties comparable to diethyl ether, but with a higher boiling point and less solubility in water. As a solvent, MTBE has one distinct advantage over most ethers - it has a much lower tendency to form explosive organic peroxides. It is widely used as a solvent in industry where, for safety and regulatory reasons, handling diethyl ether or other ethers is much more difficult and expensive. MTBE as a solvent is used in the oil refining industry as a method for dewaxing waxy petroleum fractions.

MTBE gives water an unpleasant taste at very low concentrations. MTBE often is introduced into water-supply [[aquifer]]s by leaking [[underground storage tank]]s (USTs) at gasoline stations or spills of gasoline. The higher water solubility and persistence of MTBE cause it to travel faster and farther than many other components of gasoline when released into an aquifer.<ref>[http://www.swrcb.ca.gov/rwqcb2/download/WMI%202004%20Executive%20Summary.pdf San Francisco Bay Area Regional Water Quality Control Board Integrated Basin Management Plan (2004)] {{webarchive |url=https://web.archive.org/web/20080229160231/http://www.swrcb.ca.gov/rwqcb2/download/WMI%202004%20Executive%20Summary.pdf |date=2008-02-29 }}</ref>

MTBE is biodegraded by the action of bacteria. In the proper type of [[bioreactor]], such as a [[fluidized bed]] bioreactor, MTBE may be removed rapidly and economically from water to undetectable levels. [[Activated carbon]] produced from coconut shells and optimized for MTBE adsorption may reduce MTBE to undetectable levels,<ref name="Carbon: Optimized Activated Carbons for MTBE Removal in POU/POE Systems"> [http://www.wcponline.com/pdf/spotlight.pdf link text] {{webarchive |url=https://web.archive.org/web/20110728081446/http://www.wcponline.com/pdf/spotlight.pdf |date=2011-07-28 }}</ref> although this level of reduction is likely to occur only in the most ideal circumstances. There are currently no known published cases of any in-situ treatment method that has been capable of reducing contaminant concentrations to baseline (pre-development) conditions within the aquifer soil matrix.

According to the [[International Agency for Research on Cancer]] (IARC), a branch of the [[World Health Organization]], MTBE is not classified as a human [[carcinogen]]. MTBE may be tasted in water at concentrations of 5–15&nbsp;μg/L (5-15ppb).<ref>{{cite journal |journal = Environ Sci Pollut Res Int |year = 2005 |volume = 12 |issue = 6 |pages = 381–6 |title = Biotic and abiotic transformations of methyl tertiary butyl ether (MTBE) |vauthors = Fischer A, Oehm C, Selle M, Werner P |pmid = 16305145 |doi = 10.1065/espr2005.08.277 |s2cid = 97168152}}</ref>

==Regulation and litigation in the U.S.==

{{main article|MTBE controversy}}

===Restrictions on MTBE manufacturing and use===

The [[Energy Policy Act of 2005]], as approved by the U.S. House of Representatives, did not include a provision for shielding MTBE manufacturers from [[water contamination]] lawsuits. This provision was first proposed in 2003 and had been thought by some to be a priority of [[Tom DeLay]] and Rep. [[Joe Barton]], then chairman of the Energy and Commerce Committee.<ref>[http://www.cnn.com/2005/POLITICS/04/21/energy.bill.mtbe.ap/ http://www.cnn.com/2005/POLITICS/04/21/energy.bill.mtbe.ap/] {{webarchive|url=https://web.archive.org/web/20050422043436/http://www.cnn.com/2005/POLITICS/04/21/energy.bill.mtbe.ap/ |date=2005-04-22 }}</ref> This bill did include a provision that gave MTBE makers, including some major [[oil industry|oil companies]], $2 billion in transition assistance while MTBE was phased out over the following nine years.<ref>{{Cite web | url=https://www.nbcnews.com/id/wbna7574562 |title = House approves $12 billion energy package|website = [[NBC News]]|date = 2005-04-22}}</ref> Due to opposition in the Senate,<ref>Charles Babington, House Again Passes GOP Energy Measures, Washington Post, June 16, 2004, at A4 (House passes Energy Bill, but Senate opponents of MTBE provision in House Bill have the votes to prevent its enactment).</ref> the conference report dropped all MTBE provisions. The final bill was signed into law by President [[George W. Bush]].<ref>United States. Energy Policy Act of 2005. {{uspl|109|58}}. Approved 2005-08-08.</ref> The lack of MTBE liability protection is resulting in a switchover to the use of ethanol as a gasoline additive.

===Cleanup costs and litigation===

MTBE removal from groundwater and [[soil contamination]] in the U.S. was estimated to cost from $1 [[1000000000 (number)|billion]]<ref>{{cite web |url=http://www.sigma.org/wr/reports/05/050523.html |title=MTBE Cleanup Estimates |author=<!--Not stated--> |date=2005-05-23 |website=SIGMA Weekly Report |publisher=Society of Independent Gasoline Marketers of America (SIGMA) |location=Fairfax, VA |archive-url=https://web.archive.org/web/20091009071418/http://www.sigma.org/wr/reports/05/050523.html |archive-date=2009-10-09}}</ref> to US$30 [[billion]],<ref>{{cite web |url=http://www.mtbe-eresource.com/liu.cfm |title=Long Island Utility Fighting to Defeat MTBE Safe Harbor |author=<!--Not stated--> |date=2004-03-16 |website=The MTBE e-Resource |publisher=Napoli Bern, LLP |location=New York, NY |archive-url=https://web.archive.org/web/20071020072714/http://www.mtbe-eresource.com/liu.cfm |archive-date=2007-10-20}}</ref> including removing the compound from aquifers and municipal water supplies and replacing leaky underground oil tanks. In one case, the cost to oil companies to clean up the MTBE in wells belonging to the city of [[Santa Monica, California]] was estimated to exceed $200 million.<ref>{{cite web |url=http://www.ens-newswire.com/ens/feb2005/2005-02-17-09.html |title=Oil Companies Pay Santa Monica MTBE Cleanup Costs |author=<!--Not stated--> |date=2005-02-17 |website=Environment News Service |publisher=Ecology Prime Media, Inc.}}</ref> In another case, [[New York City]] estimated a $250 million cost for cleanup of a single wellfield in the borough of [[Queens, New York|Queens]] in 2009.<ref>{{cite news| url=https://www.nytimes.com/2009/10/20/science/earth/20exxon.html |work=The New York Times |title=City Awarded $105 Million in Exxon Mobil Lawsuit |first=Mireya |last=Navarro |date=2009-10-20 | access-date=2010-05-12}}</ref> In 2013 a jury awarded the State of [[New Hampshire]] $236 million in damages in order to treat groundwater contaminated by MTBE.<ref>{{cite news |url=https://www.bloomberg.com/news/2013-04-09/exxon-mobile-is-found-neligent-in-new-hampshire-mtbe-use.html |work=Bloomberg |title=Exxon Mobil is Found Negligent in New Hampshire MTBE Use |first=Sarah |last=Earle |date=2013-04-09}}</ref>

Many lawsuits are still pending regarding MTBE contamination of public and private drinking water supplies.

===Drinking water regulations===

EPA first listed MTBE in 1998 as a candidate for development of a national [[Maximum Contaminant Level]] (MCL) standard in drinking water.<ref>EPA (1998-03-02). "Announcement of the Drinking Water Contaminant Candidate List." ''Federal Register'', {{usfr|63|10274}}</ref> The agency listed MTBE on its [[Safe Drinking Water Act#Unregulated contaminants|Contaminant Candidate List]] in 2022 but has not announced whether it will develop an MCL.<ref>EPA (2022-11-14). "Drinking Water Contaminant Candidate List 5―Final." ''Federal Register,'' {{USFR|87|68060}}</ref>

EPA uses toxicity data in developing MCLs for [[public water system]]s.<ref>{{cite web |url=https://www.epa.gov/dwregdev/how-epa-regulates-drinking-water-contaminants |title=How EPA Regulates Drinking Water Contaminants |author=<!--Not stated--> |date=2017-05-03 |publisher=EPA}}</ref>

California established a state-level MCL for MTBE, 13 micrograms per liter, in 2000.<ref>{{cite web |url=https://www.waterboards.ca.gov/drinking_water/certlic/drinkingwater/MTBE.html |title=MTBE: Regulations and Drinking Water Monitoring Results |author=<!--Not stated--> |date=2014-08-04 |publisher=California State Water Resources Control Board |location=Sacramento, CA}}</ref>

*[[Cyclopentyl methyl ether]] (CPME)

*[[Di-tert-butyl ether]]

*[[List of gasoline additives]]

*[[tert-Amyl methyl ether|''tert''-Amyl methyl ether]] (TAME)

* [http://www.efoa.eu/ MTBE in Europe]

[[Category:Dialkyl ethers]]

[[Category:Tert-butyl compounds]]