Research On Experiment And Molecular Simulation Of Vapor-liquid Equilibrium For Fatty Esters

Biodiesel is a renewable, clean-burning diesel substitute. The phase equilibrium data of the fatty esters which are the main components of biodiesel are important for the separation and simulation optimization of the production of biodiesel. At present, the experiment and molecular simulation about vapor liquid phase equilibrium of fatty acid methyl ester is insufficient. The research on vapor liquid phase equilibrium of fatty acid esters lay foundation of the separation and purification and the optimization of process conditions for high value of biodiesel refining,Isobaric vapor-liquid equilibrium(VLE) data for the binary system of methyl myristate + methyl palmitate at 0.5, 1.0 and 1.4 kPa were measured by a VLE modified Othmer still. The esters used in this paper are the major components of biodiesel. The experimental data in the vaccum conditions passed the Herington Test, Van Ness Test and Wisniak consistency test, which ensure the reliability of experimental data.These VLE data were correlated with Nonrandom Two-Liquid(NRTL) activity coefficient model and Wlison model, and predicted by UNIFAC and Dortmund(modified UNIFAC) models. The results indicate that the calculated values of these four models agree well with the experimental data. It is observed that the results simulated by the NRTL model are slight better than those of other models. The average mean deviations for NRTL model in vapor molar fraction, y, and temperature, T, are no more than 0.0063 and 0.50 K, respectively. Besides, it can be seen that the results calculated by Dortmund model showed the largest deviation for methyl myristate and methyl palmitate system at all studied pressures. The largest average mean deviations for Dortmund model in vapor molar fraction, y, and temperature, T, are 0.0220 and 1.42 K, respectively, In general, the results calculated by the four models at 0.5 kPa seemed slight worse than those at 1.0 and 1.4 kPa. From the view of industrial application, all the four models can be used to calculate the VLE of the binary system of methyl myristate and methyl palmitate.Molecular simulation was conducted for vapor-liquid equilibria of some fatty esters. The simulation was conducted through Towhee software while the TraPPE-UA force field was used. The simulation for pure components of methyl acetate, methyl propionate and methyl palmitate was under NVT-Gibbs ensemble. The liquid density and heat of vaporization was got to represent the pure substance's equilibrium. Then simulation of binary mixtures for the binary system of methyl acetate + methyl propionate and methyl myristate + methyl palmitate was conducted under NpT-Gibbs ensemble to get the T-x-y equilibria data. The results indicate that the calculated values of pure and binary components simulations agree well with the experimental data. which validate the accuracy and reliability of the TraPPE-UA force field and simulation methods that were used in the simulation of this paper.