Effects of Diacetinmonoglycerides and Triacetin on Biodiesel Quality

Triacetin offers a higher added value compared to glycerol and can be obtained during the interesterification reaction between methyl acetate and triglycerides. In the same reaction, diacetinmonoglyceride is produced as an intermediate compound. The objective of this study was to assess whether the biodiesel produced, with varying concentrations of these compounds, meets the requirements established by the EN 14214 and ASTM D6751 standards. To achieve this, several properties were measured, including density, kinematic viscosity, cloud point, pour point, cold filter plugging point, methyl ester content, mono-, di-, triglyceride and total glycerol content, as well as the vacuum distillation curve. These measurements were conducted on mixtures of triacetin, diacetinmonoglyceride, and biodiesel, using different types of biodiesel such as palm, soybean, sunflower and rapeseed. Additionally, the solubility of these ternary mixtures in conventional diesel was evaluated. The results indicated that the EN 14214 standard imposes limits on the density and viscosity of biodiesel, restricting the content of triacetin (up to 5-10% by weight) and diacetinmonoglyceride (up to 3-4% by weight). However, the content of monoglycerides presents the most restrictive condition, as the chromatographic technique used cannot differentiate between monoglycerides and diacetinmonoglycerides. Consequently, their content is limited to a range of 0.15% to 0.70% by weight, depending on the prevailing climate conditions. Similarly, the ASTM D6751 standard sets a limitation of 0.40% by weight for monoglycerides to three out of six grades of biodiesel. Based on the findings of this study, which demonstrate that diacetinmonoglycerides do not have adverse effects on the cold performance of biodiesel, the inclusion of diacetinmonoglycerides in biodiesel production would still necessitate the development of standard test methods capable of differentiating between monoglycerides and diacetinmonoglycerides.