A Study Of Molecular Simulation On Screening Solvent To Separate Benzene And Thiophene

As one of the most commonly used means of separation, extractive distillation have been widely used in dealing with close boiling and azeotropic system. By means of adding the solvent to the system, the relative volatility between key components be changed from 1 that make the separation more feasible. Choosing the proper solvent not only can greatly improve the purity of the product, but also can reduce the energy consumption. The traditional methods of screening optimal solvent yet remain on measuring the thermodynamic properties of fluids and assembling the functional groups, the extractive mechanic of solvent have not been adequately explored, which is more important for searching and designing a new good solvent, even improved the operation environment. To investigate the extractive mechanism of solvent, we choose benzene/thiophene system as the representative. The molecular simulation methods,computational quantum chemistry and GEMC, have been used to explore the interaction between solvent and solute and predicted the relative vapor-liquid equilibrium data.Density Function Theory, M062X method has been used to calculate the stable interaction conformations between solutes (benzene and thiophene) and solvents (NMP,Sulfolane, DMSO and DMF). The interaction energy and other properties have been analyzed, respectively. The AIM and RDG results indicate that NMP and Sulfolane can form the stable hydrogen bonding with thiophene, but not with benzene, which should be accounted for the good performance of those solvents. Due to the ESP distribution of DMSO and DMF, they are opting to accept electron of the π bond of benzene and thiophene. Additionally, the richer electron on benzene ring than that of thiophene can be seen from the analyzation of ESP. Thus, DMSO and DMF are more likely to interact with benzene that result in worse performance of DMSO and DMF. From this view,the optimal solvent should have more negative potential and little positive potential on the molecular surface.In addition, GEMC simulations have been performed to obtain the VEL data of the system, including benzene, thiophene and DMF. Because the bad performance of OPLS-CS2 for DMF and polarization interaction between DMF and solutes, the adjustable parameter λ=1.06 in LB mixture rule has been used to improve the results.Compared with the literature, the predicted VEL data is accurate. By means of analyzing RDFs, the difference of interaction between DMF/benzene and DMF/thiophene is the more stable hydrogen bonding between DMF and thiophene than DMF and benzene. The conclusions of GEMC were consistent with that of DFT.TraPPE-UA has been expanded to DMF and DMSO, but the simulation results indicated that the parameters of DMSO should be adjusted further. TraPPE-UA of DMF has been tested with predicting atmosphere VEL of DMF and methanol at atmosphere conditions and good results have been obtained.