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.
Production and properties
MTBE is manufactured via the chemical reaction of
methanol and
isobutylene. Methanol is primarily derived from
natural gas,
where
steam reforming converts the various light hydrocarbons in natural gas (primarily methane) into carbon monoxide and hydrogen.
The resulting gases then further react in the presence of a catalyst to form methanol.
Isobutylene can be produced through a variety of methods.
Butane can be isomerized into
isobutane which can be dehydrogenated to isobutylene.
In the Halcon process,
t-Butyl hydroperoxide derived from isobutane oxygenation is treated with
propylene to produce
propylene oxide and
t-butanol. The
t-butanol can be dehydrated to isobutylene.
MTBE production across the globe has been steady because of its positive impact on engine performance.[Werner Dabelstein, Arno Reglitzky, Andrea Schütze and Klaus Reders "Automotive Fuels" in Ullmann's Encyclopedia of Industrial Chemistry 2007, Wiley-VCH, Weinheim. ] The global demand has been mainly driven by growing Asian markets.
US perspective
Production of MTBE in the U.S. peaked in 1999 at 260,000 barrels per day
before dropping down due to environmental and health concerns as well as pressure from the bioethanol lobby,
to about 50,000 barrels per day and holding steady,
mostly for the export market. After the purchase of
SABIC,
oil giant
Saudi Aramco is now considered to be the world's largest producer
with an estimated production capacity of 2.37 million metric tons per year (mt/yr).
Worldwide production capacity of MTBE in 2018 was estimated to be 35 million metric tons.
Uses
MTBE is used as a fuel component in fuel for
petrol engines. It is one of a group of chemicals commonly known as
because they raise the
oxygen content of gasoline.
As anti-knocking agent
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.
Oxygenates also help gasoline burn more completely, 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 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.
As a solvent
MTBE is sometimes used as a solvent,
although it is used less commonly than
diethyl ether. Although an ether, MTBE is a poor
Lewis base (due to
) and does not support formation of
. It reacts dangerously with strong acids or
bromine.
MTBE forms with water (52.6 °C; 96.5% MTBE)[ Zeon Corporation ] and methanol (51.3 °C; 68.6% MTBE).[ CRC Handbook of Chemistry and Physics, 90th edition] The solubility of water in MTBE is reported to be 1.5 g/100g at 23 °C.
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
| access-date = June 3, 2024
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.
Persistence and pervasiveness in the environment
MTBE gives water an unpleasant taste, even at very low concentrations of <30 μg/L (<30ppb).
MTBE often is introduced into water-supply
by leaking underground storage tanks (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.
[ San Francisco Bay Area Regional Water Quality Control Board Integrated Basin Management Plan (2004) ]
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,[ link text ] 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.
Health and safety
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Regulation and litigation in the U.S.
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.
[ http://www.cnn.com/2005/POLITICS/04/21/energy.bill.mtbe.ap/ ] This bill did include a provision that gave MTBE makers, including some major
oil industry, $2 billion in transition assistance while MTBE was phased out over the following nine years.
Due to opposition in the Senate,
[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).] the conference report dropped all MTBE provisions. The final bill was signed into law by President George W. Bush.
[United States. Energy Policy Act of 2005. . Approved 2005-08-08.] 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 billion
to US$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.
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.
[EPA (1998-03-02). "Announcement of the Drinking Water Contaminant Candidate List." Federal Register, ] The agency listed MTBE on its Contaminant Candidate List in 2022 but has not announced whether it will develop an MCL.
[EPA (2022-11-14). "Drinking Water Contaminant Candidate List 5―Final." Federal Register, ]
EPA uses toxicity data in developing MCLs for public water systems.
California established a state-level MCL for MTBE, 13 micrograms per liter, in 2000.
See also
-
Cyclopentyl methyl ether (CPME)
-
Di-tert-butyl ether
-
List of gasoline additives
-
tert-Amyl methyl ether (TAME)
External links
