Crystallization of hydrogenated biodiesel–ethanol–diesel blend based on the solid–liquid equilibrium theory

Abstract

AbstractHydrogenated biodiesel–ethanol–diesel is a novel ternary fuel blend containing easily volatile, moderately volatile, and hardly volatile components. In this study, based on the thermodynamic phase equilibrium, a model was established to depict the phase transition under changeable pressure and temperature conditions. The crystallization behavior of hydrogenated biodiesel–ethanol–diesel ternary blends was estimated, and the influence of ethanol on the low temperature performance of ternary blends was interpreted in contrast to that of hydrogenated biodiesel–diesel binary blends. It was revealed that the crystallization points of ternary blends such as PHC5E5 (5% partially hydrogenated cottonseed biodiesel + 5% ethanol + 90% diesel), PHC10E10 (10% partially hydrogenated cottonseed biodiesel + 10% ethanol + 80% diesel), and PHC15E15 (15% partially hydrogenated cottonseed biodiesel + 15% ethanol + 70% diesel) were reduced by 4.5 K, 5.7 K and 6.1 K respectively as compared with their countering binary blends. Declines of 4.3 K, 5.3 K and 6.1 K in crystallization points were also demonstrated between partially hydrogenated soybean biodiesel ternary blends and binary blends. Meanwhile, apparent drops in crystallization quantities were perceived between ternary blends and binary blends under different temperatures. The role of ethanol affecting the crystallization of ternary blends was then comprehensively analyzed. At the onset of crystallization, ethanol was simultaneously precipitated in a eutectic manner with compositions of high melting point, impeding the tendency of nucleation and lagging the growth of solid crystals. In addition, most of non‐crystallized ethanol distributed in liquid fuel as well as the interstices of the network and the plate crystal. It beneficially increased the solubility of the crystalline composition in the base liquid to some extent. That is to say, the crystallization points and crystallization quantities were evaluated based on the solid–liquid equilibrium theory, which can provide an effective and reliable method for optimizing the low temperature performance of hydrogenated biodiesel.