The Effect of Ethanol on Gasoline Oxidation Stability

The motor gasoline on which Brazilian vehicles run is in fact a “gasohol” composed of gasoline and a variable amount of 19 to 25 % volume of anhydrous ethanol. The oxidation of the hydrocarbon portion of this mixture is accelerated by the presence of oxygen, light and temperature, but its speed is primarily dependent on its composition. This paper examines the ethanol effect on gasoline oxidation stability, based on experimental work carried out in PETROBRAS laboratories to evaluate gasolines with and without ethanol. The chemical composition of the collected samples were analysed by GC/MS for hydrocarbon types (PIANO), sulfur and nitrogen content by X-ray fluorescence and other properties. The effect of the oxygenate on gasoline stability was evaluated by measuring the washed gum, color degradation and insolubles formed during aging up to 24 weeks at ambient temperature (Rio de Janeiro, 13 to 41 °C, average 25°C) and 43°C, as well as by the 4-hour potential gum test.