Methyl tert-butyl ether

Methyl tert-butyl ether (MTBE) is an organic compound with the chemical formula C5H12O. MTBE is a volatile, flammable, and colorless liquid that is sparingly soluble in water. It is used primarily as a fuel additive in motor gasoline to increase octane rating and reduce engine knocking and air pollution. MTBE is produced by the chemical reaction of methanol and isobutylene. Methanol is derived from natural gas, and isobutylene is a byproduct of petroleum refining or through the butane isomerization process.

Production

The production of MTBE involves the acid-catalyzed reaction of methanol and isobutylene. The process typically uses a strong acid, such as sulfuric acid or hydrofluoric acid, as a catalyst. The reaction is highly exothermic, and the MTBE produced is separated from the reactants and byproducts through distillation.

Uses

The primary use of MTBE is as an oxygenate in gasoline. By adding oxygen to gasoline, MTBE helps to increase the fuel's octane rating and reduce the emissions of unburned hydrocarbons and carbon monoxide from automobiles. This has made MTBE a popular choice for improving air quality and complying with environmental regulations, such as the Clean Air Act in the United States.

Environmental and Health Concerns

Despite its benefits in reducing air pollution, MTBE has been found to contaminate groundwater and drinking water supplies when gasoline spills or leaks from underground storage tanks. MTBE is more soluble in water than other gasoline components, making it more likely to contaminate water sources. The presence of MTBE in water can lead to unpleasant taste and odor issues.

Health effects associated with exposure to MTBE include headaches, dizziness, nausea, and irritation of the respiratory tract. Long-term exposure to high levels of MTBE may have more serious health effects, although the research is not conclusive.

Regulation and Phase-out

Due to concerns about water contamination and health risks, the use of MTBE has been phased out in many parts of the world. In the United States, the Energy Policy Act of 2005 removed the federal requirement for oxygenates in gasoline, leading to a significant decrease in the use of MTBE. Many states have banned or restricted the use of MTBE in gasoline.

Alternatives

As MTBE has been phased out, ethanol has become the most common replacement as a gasoline oxygenate. Ethanol serves a similar function in increasing octane ratings and reducing emissions but is considered to be more environmentally friendly because it is biodegradable and less likely to contaminate groundwater.

See Also

• Gasoline
• Ethanol fuel
• Environmental impact of the petroleum industry
• Water pollution