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

Due to the special energy structure in our country, the preparation of vinyl acetate by acetylene obtain a great development. Vapor-liquid equilibrium data of acetic acid-crotonaldehyde system is one of the basis of the process design. However, the phase equilibrium data are very scarce in the low concentration scope of crotonaldehyde in the system. With the rapid development of computer simulation and hardware, molecular simulation became an effective way to obtain equilibrium data other than experimental, the equation of state and activity coefficient method. As the basis of molecular simulation, force field become the key factor to improve the simulation accuracy. Due to the particularity of acetic acid, the association character for vapor and liquid need to be described accurate by force field. In order to obtain more accurate phase equilibrium data, the article researched association of acetic acid by molecular dynamics methods, and the phase equilibrium of acetic acidcrotonaldehyde was calculated by GEMC method.Firstly, acetic acid were studied using molecular dynamics method in the vapor phase, liquid phase and acetic acid-crotonaldehyde system. Through the radial distribution function, the association character were investigated with the temperature, pressure and concentration. Research results show that the acetic acid are mainly exists in the form of dimers in vapor and chain segments in liquid. Based on TraPPE-UA force field, the force field parameters of acetic acid were optimized by quantum chemistry, and a double acetate model were built through force field and input file.At the same time, the lack parameters of crotonaldehyde in force field were obtained by quantum chemical method and the force field of crotonaldehyde were built. By calculating the phase equilibrium data of pure crotonaldehyde components and crotonaldehyde-acetaldehyde binary system, the applicability of the force field were verified.Using the original TraPPE-UA and optimized force field, vapor-liquid equilibrium data of pure acetic acid and acetic acid-crotonaldehyde mixture were calculated. Compared with experiment data, simulated results show that the deviation of pure acetic acid was decreased from 1.1~13.5% to 1.3~6.2% in vapor, and decreased from 0.3~8.3% to 0.1~5.9% in liquid. For acetic acid-crotonaldehyde mixture, the deviation was decreased from 0.9~10.0% to 0.6~6.7% in vapor, and decreased from 0.2~13.3% to 0.4~8.3% in liquid, which certified the accuracy of the optimized force field.