Molecular Simulations of Fatty‐Acid Methyl Esters and Representative Biodiesel Mixtures

Abstract

Despite the importance of fatty-acid methyl esters (FAMEs) as key components of various green solvents, detergents, plasticizers, and biodiesels, our understanding of these systems at the molecular level is limited. An enhanced molecular-level perspective of FAMEs will enable a detailed analysis of the polymorph and crystallization phenomena that adversely impact flow properties at low temperatures. Presented here, is the parameterization and validation of a charge-modified generalized amber force field (GAFF) for eight common FAMEs and two representative biodiesel mixtures. Our simulations accurately reproduce available experimental data (e.g. densities and self-diffusivity coefficients) and their trends, with respect to temperature and degree of unsaturation. Structural analyses from our simulations provide a more detailed picture of liquid-phase molecular ordering in FAMEs and confirm recent experimental hypotheses. This study provides a firm foundation to initiate further studies into the mechanisms that drive crystallization phenomena at the molecular level.

Transport and Morphology of a Proton Exchange Membrane Based on a Doubly Functionalized Perfluorosulfonic Imide Side Chain Perflourinated Polymer

“…The classical hydronium cations (H 3 O + ) were modeled based on the force field used in previous work, − while a charge modified generalized AMBER force field was used to describe the polymer. , To calculate the charges, the PFIA monomer was optimized at the B3LYP/6-311G­(2d,d,p) level of theory and basis set using the Gaussian 09 program, followed by a single point calculation at the HF/6-311G­(2d,d,p) level of theory and basis set. The charges were then calculated using RESP and antechamber in accordance with previous publications. ,− Initial construction of the entangled polymer systems was performed using an in-house Monte Carlo chain-growing algorithm that allowed for precise specification of the length, number, and composition of polymer chains. , The entangled systems were then solvated with the program Packmol to insert the classical hydronium molecules (one for each acid group in the system) and the appropriate number of water molecules to obtain the desired hydration level. Systems were subjected to an initial minimization of 10 000 steps using the steepest descent algorithm followed by 10 000 steps of conjugated gradient geometry optimization.…”

Impact of Water-Dilution on the Solvation Properties of the Ionic Liquid 1-Methyltriethoxy-3-ethylimidazolium Acetate for Model Biomass Molecules

“…The water molecules were defined by the TIP3P force field while the glucose and cellobiose molecules used the Glycam06h force field. TIP3P was chosen as the water model because it was used during the validation of Glycam06h and also to allow direct comparison with previously published studies which also use TIP3P. ,, The [Me-(OEt) 3 -Et-IM + ] [OAc – ] IL used GAFF for the bond, angle, dihedral, and VDW terms while the charges were recalculated using the RESP method, Gaussian09, and antechamber in accordance with previous publications. ,,− Other groups have reported on the benefits of scaling the charges by 80% for increased accuracy in the prediction of ionic liquid properties; , however, they used the Hartree–Fock level of theory which does not account for electron correlation. For this study the charges were calculated using a level of theory, and basis set (MP2/cc-pVTZ), same as the OPLS method, which includes the first electron correlation terms and has been demonstrated to predict liquid dynamics of ILs very well .…”

Thermodynamics, Dynamics, and Rheology of Fuel Surrogates: Application of the Time–Temperature Superposition Principle in Molecular Dynamics Simulations

“…L-OPLS was also recently used in modeling surrogate fuel mixtures of n -hexadecane, n -alkylbenzene, and n -alkylcyclohexane. , Force field parameters have also been tuned and optimized in recent years for the AMBER force field. For example, the general AMBER force field (GAFF) originally developed for drug design has been successfully used in simulations of large organic molecules and polymers. ,,,, Bharadwaj et al successfully applied the GAFF to model various fatty acid methyl esters and biodiesel mixtures. Recently, Khabaz and Khare , implemented this force field in predicting the rheological properties of asphalt, which is a complex mixture of hydrocarbons.…”

“…For example, the general AMBER force field (GAFF) 32 originally developed for drug design has been successfully used in simulations of large organic molecules and polymers. 16,22,23,29,33 Bharadwaj et al 34 successfully applied the GAFF to model various fatty acid methyl esters and biodiesel mixtures. Recently, Khabaz and Khare 16,23 implemented this force field in predicting the rheological properties of asphalt, which is a complex mixture of hydrocarbons.…”