Modeling and simulation of saline extractive distillation columns for the production of absolute ethanol

A steady-state equilibrium-stage model. based on normalized MESH equations is proposed to simulate saline extractive distillation columns and applied to the production of absolute ethanol, using CaCl2 to break the ethanol-water azeotrope. Among the activity coefficient models available for mixed solvent/salt systems, the NRTL-E model (with refitted parameters), is shown to be the most accurate to correlate the experimental vapor-liquid equilibrium (VLE) data available for the ethanol/water/CaCl2 system. A model is proposed and implemented to calculate the salt contribution to the liquid phase enthalpy by combining calorimetric quantities of the solute such as its relative apparent enthalpy and the infinite dilution values of its integral heat of solution and partial isobaric heat capacity. The column model is solved by use of the Newton-Raphson method with a damping factor found by minimizing the Euclidean norm of the vector of discrepancy functions associated with the MESH equations. (C) 2002 Elsevier Science-Ltd. All rights reserved.