Methyl tert-butyl ether
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. It has a minty smell vaguely reminiscent of diethyl ether, leading to unpleasant taste and odor in water. MTBE is a blending component of gasoline, used as an oxygenate to raise the octane number and to replace tetraethyllead (TEL). Its use is controversial in some parts of the world, such as the US, because of contamination of groundwater, which was followed by legislation favoring ethanol. However, worldwide production of MTBE has been constant owing to growth in Asian markets.
Methyl tertiary-butyl ether; Methyl tert-butyl ether; Methyl t-butyl ether; MTBE; tert-Butyl methyl ether; tBME; tert-BuOMe
3D model (JSmol)
CompTox Dashboard (EPA)
|Molar mass||88.150 g·mol−1|
|Melting point||−109 °C (−164 °F; 164 K)|
|Boiling point||55.2 °C (131.4 °F; 328.3 K)|
|42 g/L (20 °C)|
|Viscosity||0.36 cP at 25 °C|
|NFPA 704 (fire diamond)|
|Flash point||−33.0 °C (−27.4 °F; 240.2 K)|
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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- 1 Production and properties
- 2 Uses
- 3 Persistence and pervasiveness in the environment
- 4 Regulation and litigation in the U.S.
- 5 See also
- 6 References
- 7 External links
Production and propertiesEdit
MTBE is manufactured via the chemical reaction of methanol and isobutylene. Methanol is derived from natural gas, and isobutylene is derived from butane obtained from crude oil or natural gas, thus MTBE is derived from fossil fuels. In the United States, it was produced in very large quantities (more than 200,000 barrels (32,000 m3) per day in 1999) during its use as a fuel additive.
As anti-knocking agentEdit
In the US it has been used in gasoline at low levels since 1979, replacing tetraethyllead (TEL) as an antiknock (octane rating) additive to prevent engine knocking. Oxygenates also help gasoline burn more completely, reducing tailpipe emissions and 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 agentEdit
Ethanol has been advertised as a safe alternative by agricultural and other interest groups in the US and Europe. In 2003, California was the first US 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.
As a solventEdit
MTBE is extensively used in industry as a safer alternative to diethyl ether (which is commonly used in academic research) as the tert-butyl group prevents MTBE from forming potentially explosive peroxides. It is also used as a solvent in academic research, although it is less commonly used than diethyl ether. Although an ether, MTBE is a poor Lewis base and does not support formation of Grignard reagents. It is also unstable toward strong acids. It reacts dangerously with bromine.
Persistence and pervasiveness in the environmentEdit
MTBE gives water an unpleasant taste at very low concentrations. MTBE is often introduced into water-supply aquifers by leaking underground storage tanks (USTs) at gasoline stations or by gasoline containing MTBE spilled onto the ground. 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.
MTBE is biodegraded by the action of bacteria. In the proper type of bioreactor, such as a fluidized bed bioreactor, MTBE can be rapidly and economically removed from water to undetectable levels. Activated carbon produced from coconut shells and optimized for MTBE adsorption may reduce MTBE to undetectable levels, although this level of reduction is likely only in the most ideal circumstances. There are currently no known published cases of any in-situ treatment method which has been capable of reducing contaminant concentrations to baseline (pre-development) conditions within the aquifer soil matrix itself.
As of 2007, researchers have limited data about the health effects of ingestion of MTBE. The United States Environmental Protection Agency (EPA) has concluded that available data are inadequate to quantify health risks of MTBE at low exposure levels in drinking water, but the data support the conclusion that MTBE is a potential human carcinogen at high doses.
Regulation and litigation in the U.S.Edit
The examples and perspective in this article deal primarily with the United States and do not represent a worldwide view of the subject. (April 2018) (Learn how and when to remove this template message)
Restrictions on MTBE manufacturing and usageEdit
In 2000, EPA drafted plans to phase out the use of MTBE nationwide over four years. Some states enacted MTBE prohibitions without waiting for federal restrictions. California banned MTBE as a gasoline additive in 2002. The State of New York banned the use of MTBE as a "fuel additive", effective in 2004. MTBE is still legal in the state for other industrial uses.
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. This bill did include a provision that gives MTBE makers, including some major oil companies, $2 billion in transition assistance while MTBE was phased out over the next nine years. Due to opposition in the Senate, the conference report dropped all MTBE provisions. The final bill was signed into law by President George W. Bush. The lack of MTBE liability protection is resulting in a switchover to the use of ethanol as a gasoline additive.
Cleanup costs and litigationEdit
MTBE removal from groundwater and soil contamination in the U.S. was estimated to cost from $1 billion to $30 billion, 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. In another case, New York City estimated a $250 million cost for cleanup of a single wellfield in the borough of Queens in 2009. In 2013 a jury awarded the State of New Hampshire $236 million in damages in order to treat groundwater contaminated by MTBE.
As of 2016, hundreds of lawsuits are still pending regarding MTBE contamination of public and private drinking water supplies.
Drinking water regulationsEdit
EPA first listed MTBE in 1998 as a candidate for development of a national Maximum Contaminant Level (MCL) standard in drinking water. As of 2018 the agency has not announced whether it will develop an MCL. EPA uses toxicity data in developing MCLs for public water systems.
California established a state-level MCL for MTBE in 2000.
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- 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).
- United States. Energy Policy Act of 2005. Pub.L. 109–58. Approved 2005-08-08.
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- Navarro, Mireya (2009-10-20). "City Awarded $105 Million in Exxon Mobil Lawsuit". The New York Times. Retrieved 2010-05-12.
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- EPA (1998-03-02). "Announcement of the Drinking Water Contaminant Candidate List." Federal Register, 63 FR 10274
- "Drinking Water Regulations Under Development or Review". EPA. 2017-01-27. Retrieved 2018-04-06.
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- "MTBE: Regulations and Drinking Water Monitoring Results". Sacramento, CA: California State Water Resources Control Board. 2014-08-04.