Study On The Construction Of United-atom Force Field And The Molecular Simulation For Vapor-liquid Phase Equilibrium Of Vinyl Acetate

As an important organic chemical material,vinyl acetate is widely used in chemical industry and is mainly synthesized using acetylene as the main raw material in China.But the necessary vapor-liquid equilibrium?VLE?data for the system are very scarce,which is important to the process development.Using molecular simulation to calculate VLE data has become an important method,which can avoid the restrictment under extreme experiment conditions.The combination of quantum chemistry and molecular dynamics method are performed in this paper to build the specific force field for vinyl acetate,which can accurately describe the thermodynamic properties of vinyl acetate.The specific force field is used to calculate the VLE of the systems concerning vinyl acetate,to provide basic data for the synthesis and separation process in manufacturing vinyl acetate.The accuracy of simulation results depends on the force field used in the calculation of phase equilibrium properties.The parameters of vinyl acetate in the TraPPE-UA force field are rather lack,which could be obtained by the migration of force field parameters and quantum chemistry method,in order to calculate the VLE data of vinyl acetate.Compared with experimental data,the average relative errors are 12.4% and 7.3%,respectively.The results show that original TraPPE-UA force field parameters can't accurately describe the intramolecular and intermolecular interaction for vinyl acetate.The characteristic electronic properties of vinyl acetate are deeply analyzed by the quantum chemistry method to guide the development of the specific force field for vinyl acetate.Inspired by the building method of coarse-grained force field,the bond parameters of vinyl acetate are obtained by investigating the influence of adjacent molecules on the middle molecules in the equilibrium system.In addition,the center of mass?COM?of the UA group is taken as the center of UA,to further optimize the force field parameters.The charge parameters are obtained in the molecular cluster configuration,the average polarization of charge in the balanced system is considered to obtain the charge parameters.The specific force field for vinyl acetate is constructed and used to calculate the VLE data of vinyl acetate,the average relative error is lowered to 4.8%.The results show that the specific force field for vinyl acetate developed by the combination of quantum chemistry and molecular dynamics method can describe the actual interaction of balance system more accurately,and show higher accuracy to prediction of the VLE of vinyl acetate.The new-developed force field in calculating phase equilibrium properties could be extended to the binary systems.The NPT-GEMC method is applied to calculate the VLE data of some binary mixtures such as acetylene-vinyl acetate,CO₂-vinyl acetate,acetaldehyde-vinyl acetate and nitrogen-vinyl acetate,the average relative errors between simulation results and the experimental data are all less than 10%.The reliability of the new-developed force field is tested and the applicable systems could be expanded.