Enhanced separation of azeotropic mixtures by ultrasound-assisted distillation process

Abstract

The main objective of this study is to develop an ultrasound-assisted distillation process that can break minimum boiling azeotropes under various operating conditions for enhancing the effectiveness of distillation processes in providing solution to high purity separation requirement. As a case study, ethanol/ethyl acetate (ETOH/ETAC) separation process was considered. The effect of both intensity and frequency of the ultrasonic waves on the vapor–liquid equilibrium (VLE) of this system was experimentally studied. The sonication was found to affect the VLE significantly in a way which led to an alteration in the relative volatility and a complete elimination of the azeotropic point, with the preference towards a combination of low frequency and high intensity operation. A mathematical model describing the system was developed based on conservation principles, VLE of the system and sonication effects. The model, which took into account a single-stage VLE system enhanced with ultrasonic waves, was coded using the Aspen Custom Modeler. The effects of ultrasonic waves on the relative volatility and azeotropic point were examined and the experimental data were successfully used in validating the model with a reasonable accuracy. The mathematical model was exported to the Aspen Plus to form a model that represents the sonication equilibrium stages, which were connected serially to configure an ultrasound-assisted distillation (UAD) process for separation of ETOH/ETAC mixture. The simulation results revealed that ETAC can be recovered from the azeotropic mixture with a purity of 99 mol% using 27 sonication stages. To validate the suitability of UAD process for separation of other minimum boiling azeotropes, separation of other mixtures were tested such as ethanol/water, methanol/methyl acetate and nbutanol/ water. The developed model was found to have some limitations with respect to separation of maximum boiling azeotropes.