Understanding the interactions between triolein and co-solvent binary mixtures using molecular dynamics simulations

Biodiesel is one of the emerging renewable sources of energy to replace fossil-fuel-based resources. It is produced by a transesterification reaction in which a triglyceride reacts with methanol in the presence of a catalyst. The reaction is slow because of the low solubility of methanol in triglycerides, which results in low concentrations of methanol available to react with triglyceride. To speed up the reaction, cosolvents are added to create a single phase which helps to improve the concentration of methanol in the triglyceride phase. In this study, molecular dynamics simulations are used to help understand the role of cosolvents in the solvation of triglyceride (triolein). Six binary mixtures of triolein/cosolvent were used to study the solvation of triolein at 298.15 K. Results of 100 ns simulations at constant temperature and pressure to simulate mixing experiments show that in the first 10 ns all the binary mixtures remain largely unmixed. However, for the cosolvents that are fully miscible with triolein, the partial densities across the simulation boxes show that the systems are fully mixed in the final 10 ns. Some solvents were found to interact strongly with the polar part of triolein, while others interacted with the aliphatic part. The radial distribution functions and clustering of the solvents around triolein were also used as indicators for solvation. The presence of cosolvents also influenced the conformation of triolein molecules. In the presence of solvents that solubilize it, triolein preferred a propeller conformation but took up a trident conformation when there is less or no solubilization. The results show that tetrahydrofuran is the best solvent at solubilizing triolein, followed by cyclopentyl methyl ether, diethyl ether, and hexane. With 1,4-dioxane, the solubility improves with an increase in temperature. The miscibility of a solvent in triolein is aided by its ability to interact with both the polar and nonpolar parts of triolein.