Why Is Mtbe Added To Gasoline?

Since the 1980s, flammable liquid methyl tert-butyl ether (MTBE) has been used as an additive for unleaded gasoline. MTBE raises the octane and oxygen content of gasoline while lowering pollutant emissions. MTBE has been prohibited or restricted in numerous states due to concerns about groundwater contamination and water quality. In limited amounts, MTBE is also employed as a laboratory solvent and in some medical applications.

What is the purpose of MTBE in motor fuel?

This material is no longer updated by the EPA, but it may be useful as a reference or resource.

NOTE: To see any of the files on this page, you’ll need Adobe Acrobat Reader, which is a free download. Learn more about PDF on the EPA’s PDF page, which also includes a link to the free Acrobat Reader.

MTBE in Fuels

The Energy Policy Act of 2005 repealed the requirement for oxygenates in reformulated gasoline (RFG). Congress also enacted a renewable fuel mandate at the same time. Refineries responded by eliminating MTBE from petrol and mixing it with ethanol. MTBE has not been utilized in large quantities in RFG areas since 2005, according to the EPA’s RFG Survey Data. In locations where conventional gasoline is used, a similar drop in MTBE use has been seen.

The chemical compound MTBE (methyl tertiary-butyl ether) is created by the reaction of methanol with isobutylene. MTBE is manufactured in enormous amounts (about 200,000 barrels per day in the United States in 1999) and is almost solely utilized as a fuel additive in gasoline. Because it raises the oxygen content of gasoline, it is one among a group of compounds known as “oxygenates.” MTBE is a volatile, flammable, colorless liquid that dissolves readily in water at ambient temperature.

Since 1979, MTBE has been used as an octane enhancer in U.S. gasoline at low levels to replace lead (helps prevent the engine from “knocking”). MTBE was used at higher amounts in some gasoline between 1992 and 2005 to meet the oxygenate criteria set by Congress in the 1990 Clean Air Act Amendments. (At the late 1980s, a few cities, including Denver, used oxygenates (MTBE) in higher concentrations during the winter.)

Oxygen aids in the complete combustion of fuel, lowering hazardous tailpipe emissions from automobiles. In one way, oxygen dilutes or displaces gasoline constituents like aromatics (benzene, for example) and sulfur. Oxygen, on the other hand, optimizes oxidation during burning. Most refiners prefer MTBE to other oxygenates because of its blending properties and cost.

In places with dangerous levels of air pollution, the Clean Air Act Amendments of 1990 (CAA) required the use of oxygenated gasoline. The CAA did not specify that MTBE be used. Other oxygenates, such as ethanol, could be used by refiners. The following were the two oxygenated gasoline programs:

During the winter months, the CAA requires oxygenated fuel (gasoline containing 2.7 percent oxygen by weight) in cities, which was first implemented in 1992. (PDF)

Is MTBE still present in gasoline?

In 2017, the United States exported 38,000 barrels per day (b/d) of methyl tert-butyl ether (MTBE), a motor gasoline additive, principally to Mexico, Chile, and Venezuela. In the United States, MTBE was once widely utilized, but it was phased out in the late 2000s due to worries about water contamination. Fuel ethanol has since supplanted MTBE as a gasoline additive.

MTBE is a fuel oxygenate that helps gasoline engines achieve more complete combustion by increasing octane ratings. Since 2005, the majority of MTBE exports from the United States have gone to Mexico and Venezuela, with exports to Chile growing. Mexico accounted for two-thirds (66%) of US MTBE exports in 2017. Venezuela’s economic instability may have contributed to a drop in MTBE shipments from the United States in recent years. Overall, MTBE exports from the United States make up a modest percentage of total petroleum product exports, averaging 0.7 percent in 2017.

In those countries, MTBE is utilized as an oxygenate instead of gasoline ethanol since it emits fewer evaporative emissions, can be delivered in pipelines alongside finished petroleum products, and does not necessitate the infrastructure investments that ethanol does.

MTBE exports from the United States almost entirely come from the Gulf Coast, where production is concentrated. In the United States, MTBE can be combined with motor gasoline blendstock to create a completed product that can then be shipped to Mexico.

What is the reason that MTBE isn’t used in gasoline?

Following the passage of the Clean Air Act in 1990, MTBE began to be widely used in gasoline. MTBE can be found in gasoline in concentrations ranging from 10% to 15%.

The biggest issue with MTBE is that it is suspected of being carcinogenic and that it dissolves quickly in water. If MTBE-containing gasoline leaks from a gas station’s underground tank, it can damage groundwater and wells. Of course, MTBE isn’t the only item that leaks into the groundwater; gasoline and a variety of other gasoline additives do as well, but MTBE has been singled out in recent years.

When did MTBE become illegal to use in gasoline?

Governor Gary Davis declared that the chemical must be phased out by December 31, 2002, citing “a major risk to California’s environment” linked with its ongoing use in gasoline. The need for reformulated gasoline was implemented in January 1995.

Is ethanol preferable to MTBE?

For the same volume, ethanol has a larger oxygen concentration than MTBE, roughly 35 wt percent vs. 18 wt percent for MTBE. While MTBE supplies are roughly quadruple those of ethanol in volumetric terms, MTBE produces around double the amount of oxygen in the US gasoline pool.

Is MTBE dangerous to people?

Nervous system symptoms, dizziness, headaches, nausea, and throat irritation could be short-term health impacts from high amounts of MTBE in water. In experimental animals given high doses of MTBE over lengthy periods of time, kidney and liver consequences, including cancer, have been observed.

Is MTBE a safe substance?

* Contact with the skin and eyes can cause irritation. The nose and throat can be irritated by breathing Methyl-tert-Butyl Ether. Concentration problems, headaches, nausea, dizziness, weakness, and lightheadedness are all possible side effects of exposure to Methyl-tert-Butyl Ether. The liver and kidneys may be affected by Methyl-tert-Butyl Ether.

How much gas is added by MTBE?

When averaging, reformulated gasoline must have at least 2.1 percent oxygen by weight, which equates to approximately 11.7 volume percent MTBE or 5.8 volume percent ethanol.