Separation of ethanol and water by extractive distillation with salt and solvent as entrainer: process simulation

TLDR

The study simulates and analyzes an extractive distillation process for azeotropic ethanol dehydration using an ethylene glycol–calcium chloride entrainer. Using Aspen Plus 11.1, the authors modeled the ethanol–water–ethylene glycol–calcium chloride system with NRTL‑E activity coefficients, designing a two‑column extractive distillation with a solvent‑to‑feed ratio of 0.3, reflux ratio 0.35, 18 theoretical stages, and feed conditions (Sf = 12, SS = 3, TS = 80 °C) to produce a distillate containing at least 99.5 % ethanol. The simulation predicts a substantial reduction in energy consumption compared with conventional processes.

Abstract

The aim of this work is to simulate and analyze an extractive distillation process for azeotropic ethanol dehydration with ethylene glycol and calcium chloride mixture as entrainer. The work was developed with Aspen Plus® simulator version 11.1. Calculation of the activity coefficients employed to describe vapor liquid equilibrium of ethanol - water - ethylene glycol - calcium chloride system was done with the NRTL-E equation and they were validated with experimental data. The dehydration process used two columns: the main extractive column and the recovery column. The solvent to feed molar ratio S/F=0.3, molar reflux ratio RR=0.35, number of theoretical stages Ns=18, feed stage Sf=12, feed solvent stage SS=3, and feed solvent temperature TS=80 ºC, were determined to obtain a distillate with at least 99.5 % mole of ethanol. A substantial reduction in the energy consumption, compared with the conventional processes, was predicted by using ethylene glycol and calcium chloride as entrainer.