Oxygenates are hydrocarbons that contain one or more oxygen atoms.
When added to gasoline, oxygenates promote cleaner burning of the fuel in engines, thereby reducing tailpipe emissions, particularly carbon monoxide. The use of oxygenates dilutes or displaces less desirable gasoline components such as sulfur and aromatics (e.g. benzene, toluene). The primary oxygenates are ethers and alcohols. Ethers include methyl tertiary butyl ether (MTBE), ethyl tertiary butyl ether (ETBE), and tertiary amyl methyl ether (TAME) while alcohols include ethanol, methanol and tert‐butyl alcohol (TBA).
MTBE is an acronym for methyl tertiary butyl ether, a compound manufactured through the reaction of methanol and isobutylene. Today, it is most commonly used as a clean fuel component to boost the octane levels of unleaded gasoline due to its superior technical and blending properties. MTBE is also used to make other compounds used in the production of consumer goods and it is employed as a solvent and extractant.
QUESTIONS ABOUT THE USE OF MTBE
WHY IS MTBE USED IN MOTOR FUELS?
- MTBE is a high octane oxygenate that provides substantial, tangible air quality benefits in a cost‐effective and efficient manner.
- MTBE’s high octane rating makes it an ideal substitute for other octane components such as lead, a toxic compound that has been phased out around the world.
- MTBE lowers the Reid Vapor Pressure (RVP) of gasoline resulting in dramatically lower evaporative emissions from the fuel itself.
- MTBE enhances many of the properties of gasoline that improve the vehicle performance, while reducing combustion-related emissions of carbon monoxide, unburned hydrocarbons and other pollutants from most engines.
- By reducing the Ozone Forming Potential (OFP) of volatile organic compounds, MTBE performs significantly better than other octane blending components. It generates about half of the ozone when compared to iso/alkylates and one‐tenth that of aromatics.
- MTBE has been safely and successfully used around the world for more than 40 years.
WHAT IMPACT DOES MTBE HAVE ON AIR QUALITY?
- MTBE has an immediate impact in improving air quality.
- Adding MTBE to gasoline allows for a more complete combustion of the fuel, reducing harmful exhaust emissions including carbon monoxide, benzene, nitrogen oxides, particulate matter and unburned hydrocarbons.
- MTBE also significantly reduces evaporative emissions from the fuel itself and thus reduces the formation of ground level ozone or smog.
- MTBE reduces emissions from all types of gasoline vehicles, regardless of their emission‐control technology.
WHAT IMPACT DOES MTBE HAVE ON GREENHOUSE GASES?
- Studies have shown that MTBE has net benefits on CO2 emissions. MTBE is made from combining methanol and isobutylene. Isobutylene can be derived from refinery processes and natural gas, whilst methanol can also be derived from natural gas. Hence, MTBE is, in part, a derivative of natural gas.
ARE THERE ANY ALTERNATIVES TO MTBE AS A CLEAN FUEL COMPONENT AND OCTANE BOOSTER IN GASOLINE?
- Potential alternatives include oxygenates such as other ethers or alcohols, as well as aromatics, alkylates and isomerates.
- Each of the alternatives has advantages and disadvantages which need to be considered in relation to local conditions such as climate, altitude, season, age of vehicle fleet and fuel distribution infrastructure among many others.
WHAT IMPACT DOES MTBE-BLENDED GASOLINE HAVE ON VEHICLES AND THEIR COMPONENTS?
- Automobile and engine manufacturers worldwide support the use of MTBE in gasoline due to its ability to improve gasoline quality and in turn, engine performance. The Global Automobile Alliance has found no evidence to suggest that MTBE is harmful to engine performance.
In fact, in their worldwide fuel charter, the Global Automobile Alliance clearly states that “on the basis of emissions benefits, vehicle performance and existing regulations, when oxygenates are used, ethers are preferred [to ethanol]”.