MTBE

MTBE, or methyl tert-butyl ether, is a colorless, volatile liquid used primarily as an oxygenate additive in gasoline. Its main purpose is to raise the octane rating and promote cleaner combustion, helping to reduce certain air pollutants. MTBE is produced industrially by acid-catalyzed reaction of methanol with isobutylene, yielding the chemical formula C5H12O.

Historically, MTBE gained widespread use in reformulated gasoline starting in the 1980s, particularly in the United States, to meet clean-air standards. It replaced some earlier oxygenates and was valued for its high solubility and quick vaporization, which aided uniform distribution in fuels.

Environmental and health concerns have limited MTBE’s popularity. It is relatively soluble in water and can migrate through soil to groundwater, leading to contamination of drinking-water sources and odor issues at low concentrations. Its degradation is slower under anaerobic conditions, though aerobic biodegradation can occur. Cleanup methods for contaminated water or soil include air stripping, activated carbon adsorption, and in situ oxidation, among others. Public health guidance emphasizes taste and odor concerns and potential exposure impacts, with higher risk associated with inhalation or ingestion of contaminated water.

Regulatory status varies by region. Many jurisdictions have restricted or banned MTBE in gasoline, opting to replace it with ethanol-based oxygenates or ethers such as ETBE (ethyl tert-butyl ether) or TAME (tert-amyl methyl ether). In some places MTBE remains in limited use or persists in legacy fuel supplies. MTBE remains a notable case study in gasoline additives and groundwater protection.