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| CATEGORIES ABOUT METHYL TERT-BUTYL ETHER | |
| ethers | |
| hazardous air pollutants | |
| ether solvents | |
| pollutants | |
| petroleum | |
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| water pollution | |
| oxygenates | |
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Methyl ''tertiary''-butyl ether (MTBE) is a Chemical compound with molecular formula C5H12O. MTBE is a volatile, flammable and colorless liquid that is highly soluble in water. MTBE has a minty odour vaguely reminiscent of Diethyl Ether , leading to unpleasant taste and odour in water. MTBE is a Gasoline additive, used as an Oxygenate and to raise the Octane Number , although its use has declined in the United States in response to environmental and health concerns. It has been found to easily Pollute large quantities of Groundwater when gasoline with MTBE is spilled or leaked at gas stations. MTBE is also used in Organic Chemistry as a relatively inexpensive Solvent with properties comparable to diethyl ether but with a higher Boiling Point and lower Solubility in Water . It is also used medically to dissolve Gallstones . PRODUCTION MTBE is manufactured by the Chemical Reaction of Methanol and Isobutylene . Methanol is a derived from natural gas, and isobutylene is made from Crude Oil or Natural Gas , thus MTBE, as used in motor gasoline, is a fossil fuel. In the United States, it was produced in very large quantities (more than 200,000 Barrel s per day in the United States in 1999 ) when it was being used widely as a fuel additive there. Because of widespread releases of MTBE-containing gasoline from Underground Storage Tanks all over the US, various jurisdictions banned the use of MTBE and production was reduced. MTBE contamination in drinking water Aquifers is a serious concern in many states (most famous cases are Lake Tahoe and Santa Monica). By late 2006, most American gasoline retailers had ceased using MTBE as an oxygenate, and accordingly, US production had declined. Similarly, lack of growth or even decline of MTBE production has been seen in Western Europe. This not because of environmental reasons; on the contrary, it is because the alternative ethanol-derived ether ETBE has been given more favorable tax treatment. Nevertheless, in other parts of the world, which account for about a half of 2004 production, the use of MTBE will continue and even grow.Michael Malveda, Hossein Janshekar, Masahiro Yoneyama. Gasoline Octane Improvers/Oxygenates. SRI Consulting. http://www.sriconsulting.com/CEH/Public/Reports/543.7500/ PHYSICAL PROPERTIES MTBE forms Azeotrope s with water (52.6 °C) and methanol (51.3 °C). USES MTBE is almost exclusively used as a fuel component in motor Gasoline . It is one of a group of chemicals commonly known as Oxygenate s because they raise the Oxygen content of gasoline. As anti-knocking agent In the US it has been used in gasoline at low levels since 1979 to replace Tetra-ethyl Lead to increase its Octane rating and help prevent Engine Knocking . Oxygen helps gasoline burn more completely, Reducing Tailpipe Emissions from pre-1984 motor vehicles. In more modern vehicles, the emissions reduction is negligible. In one respect, the oxygen dilutes or displaces gasoline components such as aromatics (e.g., Benzene ) and sulfur. In another, oxygen optimizes the oxidation during combustion. Most refiners have chosen to use MTBE over other oxygenates primarily for its blending characteristics and for economic reasons. It is produced from natural gas, which is less expensive than oil. Since 1992 , MTBE has been used at higher concentrations in some gasoline to fulfill the oxygenate requirements set by the United States Congress in Clean Air Act amendments; however, since 1999, in California and other locations MTBE has begun to be phased out because of groundwater contamination (California Air Resources Board, 2004). Due to its higher solubility in water MTBE moves more quickly than other fuel components (California Air Resources Board, 2004). The Energy Policy Act of 2005 reduces the federal requirement for oxygen content in reformulated gasoline http://www.epa.gov/otaq/rfg regs.htm#usage . In 1995 high levels of MTBE were unexpectedly discovered in the in drinking water has not yet been established by the EPA. The leakage problem is partially attributed to the lack of effective regulations for underground storage tanks, but spillage from overfilling remains an important upset scenario. As an ingredient in unleaded gasoline, MTBE is the most soluble part. When dissolved in groundwater, MTBE will lead the contaminant plume with the remaining components such as Benzene , Toluene , etc. to follow. Thus the discovery of MTBE in public groundwater wells indicates that the contaminant source was a gasoline release. The MTBE concentrations used in the EU (usually 1.0–1.6%) and allowed (maximum 5%) in Europe are lower than in California. European Commission . MTBE and the Requirements for Underground Storage Tank Construction and Operation in Member States. Alternatives Other compounds are available as oxygenate additives for gasoline, for example Ethanol and related ethers, e.g. Tert-amyl Methyl Ether (TAME). Reasons for using MTBE include economic considerations, as some of the production is obtained by adding Methanol to Isobutylene produced as a by-product of other processes. However, most MTBE facilities have to manufacture the methanol and isobutylene required to produce MTBE. Ethanol has been advertised as a safe alternative by the agricultural interest groups in the USA and Europe. Its lack of toxicity is not different from MTBE, but as a polar solvent, it drives off nonpolar hydrocarbons from the gasoline, a problem that MTBE does not cause. Volatile hydrocarbons from gasoline are known (and severe) carcinogens and the main contributor to Photochemical Smog . EU's agricultural subsidies have produced an oversupply of wine, and the excess low-quality wine is being refined to ethanol fuel in Europe. This gives rise to political motives for supporting ethanol over MTBE. However, the political stability of the supply is a major advantage for ethanol and other biofuels. Advocates of both sides of the debate in the United States sometimes claim that gasoline manufacturers have been forced to add MTBE to gasoline by law. It might be more correct to say they have been induced to do so, although any Oxygenate would fulfill the law. In 2003, California was the first state to start replacing the MTBE with ethanol. Several other states started switching soon afterward. Higher quality gasoline is also an alternative, i.e. so that additives such as MTBE are unnecessary. . In the long run, Diesel fuel is also an alternative, although it requires a major switchover to diesel-run cars. There are several varieties of Biodiesel ; both oxygen-containing esters and oxygen-free alkyl biodiesels are available. In chemistry Being an ether, MTBE is a Lewis Base . However, unlike other ethers such as Diethyl Ether or THF , it does not coordinate well enough with magnesium to be used for making Grignard Reagent s. The ''tert''- Butyl group is easily cleaved off under strongly acidic conditions (forming a moderately stable Carbocation ), particularly if heated ( Isobutylene is lost), something which can limit the use of MTBE as a solvent. However it possesses one distinct advantage over most ethers- it has a much lower tendency to form explosive Organic Peroxide s than most ethers. Opened bottles of Diethyl Ether or THF can build up dangerous levels of these peroxides in months, whereas samples of MTBE are usually safe for years (but they should still be tested periodically). PERSISTENCE AND PERVASIVENESS IN THE ENVIRONMENT MTBE is often introduced into water-supply aquifers by leaking Underground Storage Tanks (USTs) at gasoline stations. Although USTs are much better constructed now than in the 1980s, accidental releases still take place because of the very large number of USTs. The high solubility and persistence of MTBE cause it to travel faster and farther than many other gasoline components when released into an aquifer. It is also released whenever gasoline with MTBE is spilled on the ground. Because it is so water soluable, it easily moves through soil, polluting both surface and groundwater. Sierra Club on Gasoline Additive: MTBE MTBE has widespread occurrences in the Aquifer s of North America , where the majority of groundwater chemistry data has been acquired. As one regional example, the San Francisco Bay Area Regional Water Quality Control Board has indicated MTBE is one of the groundwater pollutants of most widespread concern in this major metropolitan region of the USA . San Francisco Bay Area Regional Water Quality Control Board Integrated Basin Management Plan (2004) HEALTH RISKS |
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