The thermodynamics of alcohols-hydrocarbons mixtures

Abstract

Alcohols/hydrocarbons blends represent important products in the industry and remarkable systems from the thermodynamic standpoint, especially in presence of traces of water. In automotive applications, ethanol is incorporated in increasing proportions into car fuel formulations for environmental and economic reasons. From a thermodynamic viewpoint, the strongly polar nature of ethanol versus the rather apolar character of hydrocarbons makes the study of such blends particularly interesting in terms of vapor pressure and miscibility behavior. A long term collaboration between GE EnergyEurope (Belfort, France) and the Thermodynamics Team of the LRGP laboratory (Nancy, France) has been conducted to improve the knowledge of these systems, using the UNIFAC thermodynamic theory. First, blends of anhydrous ethanol and naphtha class hydrocarbons have been studied in terms of volatility: a strong liquid/vapor non-ideality effect has been put in evidence and numerically characterized. In a further step, blends of hydrated ethanol and hydrocarbons featuring diverse compositions have been the matter of a thermodynamic modeling that confirmed the paramount role played by the moisture content of ethanol on the miscibility, using the Maximum Miscibility Temperature (“TMM”) concept; this study also pointed out the non-negligible influence of the PONA data and sulfur species of the hydrocarbon cut. Later on, other alcohols namely methanol, isopropanol and n-butanol, that may play an important role in future “green fuel” formulations, were included in this study that showed an interesting chain length effect. Recently, the team has started a study of the effect of biodiesel additions on the TMM of hydrated alcoholhydrocarbon mixtures. This paper summarizes the methodology and the results of the multi-step, collaborative modeling study developed in the field of ethanol/hydrocarbon thermodynamics.