Antiknock Agent - Tetraethyllead

Tetraethyllead

In the U.S., where lead was blended with gasoline (primarily to boost octane levels) since the early 1920s, standards to phase out leaded gasoline were first implemented in 1973. In 1995, leaded fuel accounted for only 0.6% of total gasoline sales and less than 2,000 tons of lead per year. From January 1, 1996, the Clean Air Act banned the sale of leaded fuel for use in on-road vehicles. Possession and use of leaded gasoline in a regular on-road vehicle now carries a maximum $10,000 fine in the United States. However, fuel containing lead may continue to be sold for off-road uses, including aircraft, racing cars, farm equipment, and marine engines . The ban on leaded gasoline led to thousands of tons of lead not being released in the air by automobiles. Similar bans in other countries have resulted in lowering levels of lead in people's bloodstreams.

A side effect of the lead additives was protection of the valve seats from erosion. Many classic cars' engines have needed modification to use lead-free fuels since leaded fuels became unavailable. However, "Lead substitute" products are also produced and can sometimes be found at auto parts stores.

Gasoline, as delivered at the pump, also contains additives to reduce internal engine carbon buildups, improve combustion, and to allow easier starting in cold climates.

In some parts of South America, Asia and the Middle East, leaded gasoline is still in use. Leaded gasoline was phased out in sub-Saharan Africa with effect from 1 January 2006. A growing number of countries have drawn up plans to ban leaded gasoline in the near future.

To avoid deposits of lead inside the engine, lead scavengers are added to the gasoline together with tetraethyllead. The most common ones are:

• Tricresyl phosphate
• 1,2-Dibromoethane
• 1,2-Dichloroethane