Predicting Solid–Liquid Equilibrium of Fatty Acid Methyl Ester and Monoglyceride Mixtures as Biodiesel Model Fuels

An erratum to this article is available at https://doi.org/10.1007/s11746‐017‐3029‐4.Fatty acid methyl esters from plant oils are the main component of biodiesel and used as a substitute for petroleum diesel. Biodiesel generally contains a small amount of monoglycerides as intermediate compounds, which have high melting points and often solidify and clog fuel filters. The prediction of the cold‐flow property of biodiesel is of great importance for practical application. In this study, a thermodynamic study was conducted for mixtures of monoglycerides and fatty acid methyl esters. Temperatures of the solid–liquid equilibrium for the mixtures were measured by differential scanning calorimetry and visual observation, while the theoretical values were calculated using the modified Universal Quasi‐chemical Functional‐group Activity Coefficients (UNIFAC) model (Dortmund). The theoretical and experimental results were in good agreement, especially for binary mixtures of monoglycerides and methyl esters. The importance of monoglycerides on the cold‐flow properties of biodiesel was determined, and the effects could be well described by the modified UNIFAC model (Dortmund)

The Effect of Monoglyceride Polymorphism on Cold-Flow Properties of Biodiesel Model Fuel

The cloud point (CP) of biodiesel refers to the temperature at which crystallization begins on cooling. However, solid precipitates are often formed at a temperature higher than the CP during storage. Such precipitates are known to consist largely of monoglycerides (MGs) as intermediate compounds. MGs have high melting points, which are detrimental to the cold-flow properties of biodiesel. MGs have several polymorphic forms, including α, β′ and β, with different melting points (α < β′ < β), and this fact makes the behavior of biodiesel at low temperature complicated. In this study, the precipitation behavior of MGs in biodiesel is discussed focusing on polymorphism using 1-monopalmitin and methyl oleate mixtures as a model biodiesel fuel. The CPs measured were close to the calculated solid-liquid equilibrium curve for α-type 1-monopalmitin. However, precipitates formed at temperatures higher than the CP when the mixtures were held at temperatures lower than the equilibrium curve of the β′ form. This indicates that the β′ form causes a risk of precipitation at temperatures above the CP and that the CP is not a suitable indicator of the cold-flow properties of biodiesel