Azeotropic Trends in Oxygenated Fuel Mixtures: Linking Molecular Architecture to Volatility Behavior

The use of alcohols, ethers, and other oxygenated compounds as fuel blend components continues to generate substantial interest due to their renewable sourcing and positive impact on various fuel performance properties. Of unique importance, when blending these oxygenates into hydrocarbon fuels, is their characteristic effect on phase equilibrium. It is well-known that certain oxygenates can promote nonideal vapor–liquid equilibrium (VLE) effects, such as azeotropic behavior, when blended in fuel. In gasoline, this phenomenon has been well studied; however, the azeotropic behavior resulting from the individual underlying structural classes that comprise gasoline (i.e., n-paraffins, iso-paraffins, naphthenes, olefins, aromatics) has been largely unexplored. Herein, experimental ASTM D86 distillation and statistical associating fluid theory (SAFT) calculations to model phase phenomena are employed to elucidate these fundamental contributions. The use of these simple techniques will be highlighted to demonstrate the ease of access to such information and the implications of the results will provide useful insight into how these components offer tunability of fuel properties and performance.