The Vapor-Liquid Equilibrium Research On Medium-Chain Fatty Acid Esters

Medium-chain fatty acid esters are a series of important chemicals.And the vapor-liquid equilibrium(VLE)data of them are the vital theoretical fundament for their separation in distillation.Currently,the study related to medium-chain fatty acid esters is far from enough.The VLE data of them are rather scarce.Therefore,in this work,we carry out VLE experimental research on medium-chain fatty acid esters.On the basis of the acquired VLE data,we try to apply the theoretical method to compute the VLE.All the work will definitely make great contribution to the theoretical research and the application of medium-chain fatty acid esters.First of all,three kinds of representative medium-chain fatty acid esters were chosen as our objects.The modified Othmer still was used to measure the VLE data of their binaries methyl caprylate(1)+ methyl caprate(2)at 2,6 and 10 kPa and methyl caprate(1)+ methyl laurate(2)at 2,4,and 6 kPa.The point consistency test of Van Ness method was applied to check the thermodynamic consistency of all the experimental values,which guaranteed the reliability of our measurements.Then the Wilson model and the NRTL model were used to regress the experimental values.And the UNIFAC model was applied to make the data prediction.The results provided by the three models are in good agreement with the experimental data.Thereinto,the NRTL model reproduced the experimental values best,with the absolute deviations of the vapor composition and the equilibrium temperature less than 0.0173 and 0.95 K,respectively;the data reproduction provided by the Wilson model was a little worse and the results obtained by the UNIFAC model were the worst of the three models,with the absolute deviations of the vapor compostion and the equilibrium temperature less than 0.0386 and 2.08 K,respectively.Secondly,the simulation code Towhee was used for all the Gibbs ensemble Monte Carlo simulations,which were based on the statistical mechanics.The TraPPE-UA force field was chosen for all the calculations.Both the thermodynamic properties of pure compounds and the VLE data of binaries were calculated.The saturated liquid-phase densities,vapor-phase pressures and heats of vaporization of ethyl propionate,methyl butyrate and methyl palmitate were simulated by the NVT-Gibbs ensemble simulations.While the VLE data of the binary systems of methyl caprylate(1)+ methyl caprate(2)at 10 kPa and methyl caprate(1)+ methyl laurate(2)at 6 kPa were computed by the NPT-Gibbs simulations.The results obtained showed that the simulations agreed with the experimental data basically.Hence,we conclude that the TraPPE-UA force field is suitable for the VLE simulation of fatty acid esters and the simulation methods that we used are feasible and effective.Finally,the COSMO-SAC model,which was based on statistical mechanics and quantum mechanics,was used to predict all the VLE data of the binaries of methyl myristate(1)+ methyl palmitate(2)at 0.5,1.0 and 1.4 kPa,ethyl myristate(1)+ ethyl palmitate(2)at 0.5,1.0 and 1.5 kPa,methyl caprylate(1)+ methyl caprate(2)at 2,6 and 10 kPa and methyl caprate(1)+ methyl laurate(2)at 2,4 and 6 kPa.The results presented by the COSMO-SAC model were reasonable,with a maximum average relative deviation of 5.82%.And the COSMO-SAC model has the advantage of using much fewer parameters than the other models.And more importantly,it can compute very fast.Therefore,it can be used for the prediction of phase-equilbrium of fatty acid esters.