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Essay on Global Effects of the MTBE Additive in Gasoline and Ethanol as a Solution
Over the last five years, a significant debate has developed surrounding the use of oxygen-bearing chemicals as additives for automotive fuels. The increase in the use of MTBE from a minor component to 11% by volume to meet the requirements of the Clean Air Act Amendments of 1990 resulted in widespread contamination of ground and surface waters and, thus, has adversely affected drinking water supplies. The subsequent phase-out of MTBE as a gasoline additive in California and several other states has placed renewed interest in the use of ethanol as a gasoline oxygenate. Ethanol is generally used at ~8% in oxyfuel or 6% in reformulated gasoline by volume. It is also sometimes used at 10% volume in gasoline, even in areas that are not required to use RFG, because there is a federal subsidy to promote markets for fuel-grade ethanol. Gasoline with ethanol added as an oxygenate at 10% or less by volume is generally referred to as "gasohol."
Methyl tert-butyl ether (MTBE) is produced by the reaction of methanol with isobutylene using an acid catalyst. Some 95% of global demand for MTBE is as a fuel blend stock. The chemical demand is for production of methacrolein and methacrlyic acid. Every tonne of MTBE produced therefore uses around 0.36 tonnes of methanol. Until the 1990s, global demand for MTBE was relatively modest. However, its use, and hence that of methanol, mushroomed due to the passing of the Clean Air Act Amendment in the United States, which mandated the use of oxygenates in so-called 'reformulated' gasoline (RFG), in order to make the fuel burn more cleanly in engines and reduce carbon monoxide levels in built-up areas in winter. RFG had to be 2.7% oxygen by weight. Initially it was anticipated that this would be met by blending ethanol into the fuel.......
