(155b) Effect of Phase-Equilibrium Uncertainties on the Separation of Azeotropes Using Entrainers

Alejandro Cuevas,¹ Henry Z. Kister, Paul M. Mathias²

Fluor Corporation, Aliso Viejo, California 92698, USA

¹Presenting Author: Alex.Cuevas@Fluor.com

²Corresponding Author: Paul.Mathias@Fluor.com

Many papers have been written highlighting the need to estimate process-design uncertainties that result from the uncertainties in correlated physical properties. The most significant source of property uncertainties on process design is from the correlations of phase equilibrium. However, uncertainty analysis is not a routine element of todayâ??s industrial process-design practice, mainly because education and awareness are lacking, and the proposed methods are difficult and cumbersome to apply. 

In order to help rectify the situation, Mathias [1] developed an intuitive and easy-to-apply method based upon treating the mixture, for the purpose of activity-coefficient perturbation, as a set of pseudobinaries described by the Margules equation. Mathias [1] first applied his method to two case studies â?? (1) a propylene-propane superfractionator for which small changes in correlated relative volatilities have a large effect on the design of the distillation column; and (2) a dehexanizer column that separates a mixture containing many close-boiling hydrocarbon components â?? and demonstrated that the proposed approach provides quantitative insight into the effect of property uncertainties for both these diverse process designs, and helps to quantify the safety factors that need to be imposed upon the design. Mathias [2] also applied the methodology to a distillation train that separates the acetone-chloroform-benzene ternary mixture, which contains one maximum-boiling azeotrope, and showed that the approach quantifies the effect of property uncertainties on utility consumption and also identifies limits on operating variables (specifically recycle flow). In a third work, Mathias [3] applied the method to the separation of the water/1-butanol mixture, and demonstrated the use of the methodology to systems that exhibit liquid-liquid equilibrium, and for a case where the acivity-coefficient model cannot adequately describe the complex phase equilibrium. 

In this presentation, the Margules perturbation method is applied to the separation of the ethyl acetate/ethanol binary mixture, which forms an azeotrope and hence requires an entrainer to break the azeotrope. Other papers have used process modeling to compare the performance of different entrainers. This publication demonstrates the added value of employing uncertainty analysis to the relative performance of azeotropic entrainers, and highlights the manner in which uncertainty analysis can improve distillation technology. 

References

[1] Mathias, P. M., â??Sensitivity of Process Design to Phase Equilibrium â?? A New Perturbation Method Based Upon the Margules Equation,â? J. Chem. Eng. Data, 2014, 59, 1006-1015.

[2] Mathias, P. M., â??Effect of VLE Uncertainties on the Design of Separation Sequences by Distillation â?? Study of the Benzene-Chloroform-Acetone System,â? Fluid Phase Equilibria, 2016, 408, 265-272.

[3] Mathias, P. M., â??Effect of Phase-Equilibrium Uncertainties on the Separation of Heterogeneous Azeotropes â?? Application to the Water/1-Butanol System,â? presented at PPEPPD-2016, Porto, Portugal, May 22-26, 2016.