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CAMD for entrainer screening of extractive distillation process based on new thermodynamic criteria

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Abstract

This paper presents a preliminary design framework for finding suitable homogeneous entrainers E to separate minimum boiling azeotropic mixtures AB by extractive distillation. The framework incorporates techniques such as Computer Aided Molecular Design (CAMD), addressing process needs and targeted thermodynamic properties. New thermodynamic criteria are considered for the entrainer design based on both, the thermodynamic properties of the binary mixtures AE and BE and the isovolatility curves in the ternary mixture ABE. In the CAMD problem, energy related property constraints on the boiling point and the vaporization enthalpy are also considered, leading to a mixed integer non-linear programming problem. Entrainer candidates are ranked by the maximization of the driving force of separation of A and B from their respective mixtures AE and BE under constraints limiting the entrainer composition for fixed values of the relative volatility. Further process optimization is done for validating the entrainer ranking by using Aspen plus V7.3, which minimizes the energy consumption and computes the total annual cost to compare different designs. The new thermodynamic criteria perform better than selectivity alone or a combined selectivity — capacity criterion, as proposed in the literature. The framework is illustrated through an entrainer problem design for the separation of acetone–methanol. Ethylene glycol is obtained as the best design solution. Comparison with conventional entrainers water and DMSO is carried out to validate the performance of the new criteria based on optimal process design study.