Methyl tert-butyl ether (MTBE) has been used since 1979 in the United States. This compound is totally miscible with the gasoline, has a similar volatility, and does not absorb water, which confers a low susceptibility to the water-gasoline phase separation. MTBE was the main oxygenating compound and was added to the gasoline up to 15% (by volume), which is equivalent to 2.7% oxygen. Its uti­lization causes the reduction of ozone concentrations at ground level during sea­sons with high smog and CO formation as well as the decrease in benzene usage for gasoline, which led to the reduction of this powerful carcinogenic substance (Braids, 2001).

The production pace of MTBE has increased remarkably since the begin­ning of a reformulated gasoline program in the United States from 12,000 bar — rels/day in 1970 to 250,000 barrels/day in 1998 (Braids, 2001). In fact, it was the chemical with the greatest growth during the 1990s with annual increments in its production of 10 to 20%. The worldwide MTBE production reached 30 million ton/year at the end of the twentieth century (Oudshoorn et al., 1999). MTBE is produced by the reaction of isobutene with methanol. Both isobutene and methanol are from fossil origins, although the latter can be produced from natural gas and even from renewable sources through biomass gasification to methane followed by its oxidation toward methanol. The isobutene is obtained from fractions with four atoms of carbon (C4 fractions) from the catalytic crack­ing process in oil refineries as well as from processing of ethylene (Ancillotti and Fattore, 1998).

The solubility of MTBE in water is in the range of 50,000 ppm or 50 g/L, which makes this compound the most soluble compared to any other gasoline component. When gasoline contacts water, MTBE has a tendency to be dissolved in water but also continues to be dissolved in gasoline. In addition, MTBE is resistant to degradation by chemical or biological means. These two features suggest that MTBE presents a high mobility in natural water streams, especially in groundwater where it can migrate as a result of leakages in the storage and transport systems of gasoline. Furthermore, MTBE at low concentrations can alter the taste and odor of potable water (Nadim et al., 2001). Numerous cases of water sources contaminated with MTBE without the presence of the remaining gasoline hydrocarbons have been reported. One of the most effective methods for MTBE removal is by means of adsorption using granulated activated coal obtained from coconut peels (Braids, 2001). Due to these negative features, the use of MTBE was banned in California in 2004 and its total prohibition is pro­jected by 2010.