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The Molecular Simulation Of The Association Of Acetic Acid And Vapor-liquid Phase Equilibrium For Acetic Acid-ethylene

Posted on:2014-04-02Degree:MasterType:Thesis
Country:ChinaCandidate:X J ShaFull Text:PDF
GTID:2181330422468376Subject:Chemical processes
Abstract/Summary:PDF Full Text Request
The fluid phase equilibrium has always been a very important issue in the ofchemical production process. It is the theoretical basis of the development and designfor separation technology and separation equipment. Molecular simulation hasgradually become an important mean of access to the data of phase equilibrium, inaddition to the way of experimental, equation of state and activity coefficient. Gibbsensemble Monte Carlo simulation method has been the main method for fluid phaseequilibrium because of not considering the phase boundary conditions and notcalculating the chemical potential. The force field is a key factor in determining theaccuracy of the phase equilibrium data in this method. The data of vapor-liquidequilibrium for acetate-ethylene system is one of the basic data in the vapor-phaseproduction of vinyl acetate. However, the vapor-liquid data of the acetate-ethylene isvery lacking. As to as the acetic acid associating system, the structure of the system iscomplicated, and the dimmer, trimmers or even the multi-dimmer can be found in thesystem besides the molecular acetate monomer. So the association of acetic acidshould be studied in order to get an accurate description for the intermolecularpotential energy function.Molecular dynamics simulation is occupied to studying the association of aceticacid in the saturated vapor in this work. Through the analysis of radial distributionfunction for the acetic acid vapor at different temperature, the four different dimmersand the proportion in the vapor phase are obtained. At the same time, the proportionof the most stable configuration which is formed by the two hydrogen bonding ring ofdimer with carbonyl oxygen and hydroxyl hydrogen is the most, up to50%.In order to obtain the special force field for acetic acid, the associating of aceticacid is considered to optimize the initial TraPPE force field parameters of acetic acidby using the first-principle quantum chemical method. The intermolecular interactionenergy of different dimmers is calculated by applying the DNP basis set which is suitfor calculating the hydrogen bond system. LJ12-6potential model is chose to fit thecalculated energy and the proportion of the different acetic acid dimmers are takeninto account. At last, the optimization parameters of acetic acid are obtained. Vapor-liquid equilibrium of acetic acid-ethylene is studied by using the optimizedforce field and NPT-GEMC simulation method. It can be found that the accuracy issignificantly improved in comparison to the original force field by using theoptimized force field to predict the phase equilibrium for the binary system. The errorfor the solubility of ethylene in acetic acid is decreased from34.83%to11.46%. Thedata of vapor-liquid phase equilibrium for the acetic acid-ethylene system wascalculated at P=100KPa and T=283.15~373.15K using the optimized force field.
Keywords/Search Tags:Acetic acid, Ethylene, Phase equilibrium, Force field, Firstprinciple, GEMC
PDF Full Text Request
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