Prediction of the Distillation Curve and Vapor Pressure of Alcohol-Gasoline Blends Using Pseudocomponents and an Equation of State

The use of alternative fuels that produce less pollutants and greenhouse gases is an intense area of research spanning across many disciplines. Currently, gasolines are blended with oxygenates in an attempt to make them less harmful to the environment. Ethanol is a commonly used compound for this purpose, although other alcohols have also been utilized. Understanding the effects oxygenate blending has on the properties of gasoline is essential for both the use of these mixtures as fuels and their processing in the refinery setting. In this work, we compare how one of two equations of state (Perturbed-Chain Statistical Associating Fluid Theory (PC-SAFT) or Predictive Soave-Redlich-Kwong (PSRK)) combined with a pseudocomponent characterization of gasoline can be used to accurately predict the change in distillation and volatility properties of a gasoline when mixed with alcohols. Specifically, we examine the effects of oxygenate blending on the D86 curve and the dry vapor pressure equivalent (DVPE). The methodology, regardless of the choice of the equation of state, only requires the D86 curve, the average specific gravity, and a measure of the vapor pressure of the base gasoline to fully characterize the stream as a mixture of pseudocomponents. After proper characterization, the equation of state can robustly predict the effect of mixing alcohols on the D86 and DVPE. It is demonstrated that PC-SAFT and PSRK perform similarly for most alcohol-gasoline blends; however, PC-SAFT is superior for methanol-gasoline blends and for predicting absolute liquid densities. The methodology outlined here sets the foundation for the development of predictive blending tools to be used in refineries.