Vapor Liquid Equilibria for Acetic Acid-Acetaldehyde-Crotonaldehyde System: Gibbs Ensemble Molecular Simulation for Pure Components and Binary Systems and NRTL Model Prediction for Ternary System

The vapor-liquid equilibrium (VLE) for the system acetic acid, acetaldehyde, and crotonaldehyde was investigated by combining the Gibbs ensemble Monte Carlo (GEMC) method and activity coefficient models prediction. The VLE of above pure components and their binary systems were first studied using GEMC method. Based on the strong association characteristics of acetic acid, the revised TraPPE-UA-D force field was developed with quantum chemistry methods for the VLE calculation of the acetic acid system. The original and mixed TraPPE-UA force field was introduced for the VLE calculation of the acetaldehyde and crotonaldehyde system, respectively. The results showed that the predictions agreed fairly well with the average relative deviations of the saturated densities smaller than 4:60%. Moreover, the binary VLE diagram was calculated using the above force fields. The simulation results of the mole composition were in good agreement with the experimental values, which verified the high simulation accuracy of the adopted force fields. On this basis, the VLE of the ternary system was predicted with the NRTL (nonrandom two-liquid) and NRTL-HOC (Hayden-O'Connell) models, and binary interaction parameters of the models were obtained by fitting the VLE simulation results of the above binary systems. The simulation results were in accordance with the predictions obtained by the parameters from the Aspen data source. This work also provided a new and feasible way to obtain the VLE values of mixtures.