Solid–Liquid Phase Behaviors of Binary Mixtures of Various Partial Acylglycerols by Differential Scanning Calorimetry

Abstract

Monoacylglycerol (MAG), diacylglycerol (DAG), and triacylglycerol (TAG) are impurities in biodiesel and a major cause of precipitation. Understanding the behavior of such acylglycerols is essential for predicting biodiesel cold flow properties (CFPs). The previous study on MAG/MAG binary mixtures shows that they tend to solidify by forming molecular compounds. In contrast, TAG/TAG mixtures, which have been studied extensively, are commonly eutectic or monotectic systems, in which each component solidifies separately. The present study focuses on binary mixtures of DAG/DAG and different acylglycerol pairs (MAG/DAG, TAG/MAG, and DAG/TAG), and determination of their solid-liquid phase behavior by differential scanning calorimetry. These mixtures are found to behave as eutectic or monotectic systems with no sign of compound formation. As DAG and TAG have lower contents than MAG in biodiesel and they are unlikely to form molecular compounds with MAG, it is suggested that DAG and TAG have little effect on the biodiesel CFPs. Practical Applications: Biodiesel has attracted much interest because its blending with conventional fossil diesel has become more standard with biofuel mandates. From an energy perspective, the solid-liquid phase behavior of acylglycerols will contribute to building prediction models for biodiesel CFPs.

Prediction of solidification behavior of biodiesel containing monoacylglycerols above the solubility limit

“…In addition, MAGs are generally present in higher concentration and have slightly higher melting points than DAGs and TAGs, meaning that MAGs will generally determine the liquidus temperature of biodiesel. Therefore, it is suggested that only the compound formation of MAG/MAG should be considered to predict the liquidus temperature of biodiesel [27]. This suggestion was supported even for multicomponent systems by the results of Figure 4, which shows no significant difference in liquidus temperature with the presence of DAG in the mixture.…”

“…In the CF model, not only MAG/MAG but also, for example, MAG/DAG or DAG/DAG may form compounds. However, our previous studies of acylglycerol binary systems showed that all combinations of acylglycerols except MAG/MAG mixtures tended to follow the NSS model [27], meaning that DAGs and TAGs do not interact with MAGs and solidify independently as pure components. In addition, MAGs are generally present in higher concentration and have slightly higher melting points than DAGs and TAGs, meaning that MAGs will generally determine the liquidus temperature of biodiesel.…”

“…Nevertheless, the experimental data are on one curve of the CF model, suggesting that the effect of DAG is minor, as discussed in Section 3.2. Our previous paper [27] showed that DAG tended not to form molecular compounds with MAG, suggesting that DAG does not affect the liquidus temperature of MAG.…”

Crystallization behavior and compatibility analysis of palm kernel stearin/anhydrous milk fat blends and application

“…In the melting process of binary blends containing 50%–90% PKS, a crystallization peak appeared, signifying solid–liquid–solid or melt‐mediated transformations in the binary blends. Initially, a polymorphic crystal form melted, recrystallized into a more stable form around 15°C, and then melted once again (Joshi et al., 2020; Seniorita et al., 2022). This phenomenon was consistent with the presence of eutectic systems when components in binary blends possessed significantly different molecular volumes, shapes, and polymorphic forms, yet similar melting points, as indicated by the iso‐solid diagram.…”