Research On Vapor-liquid Equilibrium Properties Of Multi-components System Using Molecular Simulation

The boiling points of benzene and thiophene are close, which is difficult forseparation through conventional distillation method. Extractive distillation is acommon way in industry to solve this problem. The desired separation effects couldbe achieved because of the addition of an extractant with high boiling point which canincrease the relative volatility of the components. The vapor-liquid equilibration datafor the corresponding binary and ternary system is vital to chemical production anddesign work.Compared with traditional method including experiments and empirical model,molecular simulation is a competitive new way to obtain thermodynamic dataefficiently and economically. In this work, simulations for benzene/thiophene binarysystem and benzene/thiophene/NMP ternary system at101.3KPa and varioustemperatures were carried out using GEMC method and TraPPE-UA force field. Thecalculated VLE properties were compared with the experimental data and discussed.Besides, radial distribution functions (RDFs) for the condensed phase wereinvestigated as well. Besides, contrast simulations were performed to study theinfluence of the partial charges of thiophene molecule on the VLE data. The primeresults of this research were as follows:(1)In general, the simulation results for both benzene/thiophene binary systemand benzene/thiophene/NMP ternary system agree well with the experimental data,indicating the good transferability of TraPPE-UA, TraPPE-EH and OPLS-AA forcefields. The results from ternary simulation also prove the compatibility of applyingTraPPE-EH and OPLS-AA force field in one simulation, demonstrating that thearithmetic and geometric mixing rules have little differences in calculating thenonbonded interactions between different molecules.(2)The study on the radial distribution functions shows that in benzene/thiophenebinary system, interactions between any two molecules are similar. Neither kind ofmolecule shows the tendency to gathering in one phase. The relative volatility wasthus low in this system and increased slightly with the increment of temperature. Internary equilibrium liquid phase, the interactions between NMP and thiophenemolecules were observed to be stronger than that between NMP and benzene, illustrating that benzene molecules are relatively easy to get rid of the benzene andNMP molecules and move into the vapor phase. As a result, the relative volatilitybetween benzene and thiophene molecules increased, which is consistent with ourformer knowledge in chemical engineering field.(3)The contrast simulation shows a similar results, meaning the partial chargeson thiophene molecule could be ignored in simulation.(4)Both T-x,y curves are slightly wider than the experimental results because ofthe underestimation of the interactions between benzene and thiophene molecules.