What MTBE Is
Methyl tert-butyl ether, normally abbreviated MTBE, is an oxygenated ether with the CAS number 1634-04-4 and the molecular formula C5H12O. It is produced commercially by reacting methanol with isobutylene over an acid catalyst. Blended into gasoline it raises octane number and adds oxygen, while its low latent heat of vaporisation and favourable distillation behaviour improve vaporisation and cold starting. MTBE can also be cracked back to isobutylene, which links fuel-grade production to the rubber and chemical industries.
| Parameter | Typical value |
|---|---|
| CAS number | 1634-04-4 |
| Molecular formula | C5H12O |
| Molecular weight | 88.15 g/mol |
| Appearance | Clear, colourless liquid with ether odour |
| Boiling point | About 55 °C |
| Density | About 0.74 g/cm3 at 20 °C |
| Water solubility | High for a fuel component, commonly reported near 42 g/L at 20 °C |
Is MTBE Still Used in Gasoline?
The answer depends on the market. MTBE has been withdrawn from United States gasoline and has been substantially phased out across most other developed economies, yet it remains a mainstream blending component in several Asian and Middle Eastern markets.
In the United States, the reformulated gasoline programme of the Clean Air Act originally encouraged oxygenates, and MTBE became the preferred choice. California banned it in 2003 because of groundwater contamination, and the 2005 Energy Policy Act removed the federal oxygenate requirement, after which American gasoline use fell sharply in favour of ethanol. Within the European Union, MTBE use was restricted and most member states moved to ethanol or other oxygenates, while Canada and Australia reduced MTBE blending on similar grounds.
Where MTBE Is Still Used Today
China, where it is produced at scale and blended as an octane enhancer and oxygenate.
India and several Southeast Asian markets, where refinery configurations and feedstock economics favour ether oxygenates.
Parts of the Middle East, where ethanol supply can be limited and existing infrastructure is designed around ether blending.
Non-fuel applications, including use as a chemical intermediate and as a reaction solvent in some processes.
Quality and Specification Considerations
Fuel-grade MTBE is traded against tight specifications, and blending value depends on consistent purity. Purchasers normally review the assay, the distillation range, water content, acidity and the level of heavier ethers or sulphur-bearing impurities, because these determine both octane contribution and blend stability. A certificate of analysis for each lot allows blenders to model the finished gasoline against the applicable national fuel standard rather than relying on nominal figures.
Safety, Storage and Environmental Protection
MTBE is a flammable liquid and must be stored away from ignition sources with proper bonding and grounding, flame arresters where required and adequate ventilation. Vapour is heavier than air and can travel to distant ignition points. The liquid irritates the eyes and skin, and breathing high vapour concentrations must be avoided; suitable gloves, eye protection and, where necessary, respiratory protection should be provided.
Because MTBE is far more mobile in soil and groundwater than most gasoline hydrocarbons, storage and handling systems should incorporate leak detection, impermeable secondary containment and regular integrity testing of tanks, pipelines and loading arms. Spill response procedures, absorbent materials and a documented inspection schedule form part of basic environmental protection.
Frequently Asked Questions
Q: Is MTBE still used in gasoline?
It is no longer used in United States gasoline and has been largely phased out in the European Union, but it remains in use across parts of Asia and the Middle East.
Q: Why was MTBE withdrawn in the United States?
California banned it in 2003 over groundwater contamination concerns, and the 2005 Energy Policy Act removed the federal oxygenate requirement, which ended its main use.
Q: What replaced MTBE in United States gasoline?
Ethanol became the principal oxygenate and octane-enhancing blending component after MTBE was phased out.
Q: Is MTBE still used in China?
Yes. It continues to be produced and blended as a gasoline component in China, alongside several other Asian and Middle Eastern markets.
Q: Is MTBE hazardous?
It is a flammable liquid that irritates eyes and skin, high vapour exposure must be avoided, and a release creates a groundwater risk because of its mobility.
Q: What is MTBE made from?
It is produced by the reaction of methanol with isobutylene, and it can be cracked back to isobutylene for chemical use.