Vapor-phase chemical equilibrium and combined chemical and vapor-liquid equilibrium for the ternary system ethylene plus water plus ethanol from reaction-ensemble and reactive Gibbs-ensemble molecular simulations

摘要

Combined chemical and vapor-liquid equilibrium (ChVLE) data for the ternary system ethylene + water + ethanol are required for the conceptual design of a reactive separation process to obtain ethanol by the hydration of ethylene. Due to the absence of experimental data for the combined ChVLE of the reacting system, molecular simulation looks appealing to predict such data. In this work, the reaction-ensemble Monte Carlo (RxMC) method was used to calculate the chemical equilibrium of the ternary system in the vapor phase, and the reactive Gibbs-ensemble Monte Carlo (RxGEMC) method was used to calculate its combined ChVLE. A set of previously validated Lennard-Jones plus point-charge potential models were employed for ethylene, water, and ethanol. The RxMC predictions for the vapor-phase chemical equilibrium composition of the ternary system and the equilibrium conversion of ethylene to ethanol, at 200 degrees C and pressures of 30, 40, 50, and 60 atm, were found to be in good agreement with predictions made by use of a previously proposed thermodynamic model that combines the Peng-Robinson-Stryjek-Vera equation of state, the Wong-Sandler mixing rules, and the UNIQUAC activity coefficient model. The RxGEMC simulations were used to predict the reactive phase diagram (twodimensional graph of pressure versus transformed liquid and vapor-phase ethylene mole fractions) at 200 degrees C. In contrast to the thermodynamic model, molecular simulation predicts a wider reactive phase diagram (due to a reactive dew-point line much richer in ethylene). However, these two independent approaches were found to be in very good agreement with regard to the predicted bubble-point line of the reactive phase diagram and the approximate location of the reactive critical point. (C) 2015 Elsevier B.V. All rights reserved.