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A Modification of UNIQUAC Model for Electrolyte Solutions Based on the Local Composition Concept Hamid Bakhshi1   · Poorya Mobalegholeslam1 Received: 15 September 2019 / Accepted: 14 April 2020 © Springer Science+Business Media, LLC, part of Springer Nature 2020

Abstract In the present study, a thermodynamic model is developed to predict the phase equilibrium of electrolyte solutions. In this model the Pitzer–Debye–Hückel equation was used to calculate the long-range contribution of the activity coefficient. To take into account the shortrang part of activity coefficient a new modified UNIQUAC-based model was developed. The model was applied for 18 binary electrolyte solutions. Results show that the model presented reproduces the osmotic coefficients of electrolyte solutions accurately to high concentration levels of salt. Comparison of standard deviation of the model and E-NRTL and E-UNIQUAC-NRF models was performed in the manuscript. Keywords  Electrolyte · Thermodynamic modeling · Osmotic coefficient · Phase equilibrium · UNIQUAC​

1 Introduction Electrolyte solutions are widely found in gas sweetening, extractive distillation, crystallization-desalination, separation, purification of biological materials, etc. Determination of the properties and phase behavior of electrolyte solutions is very important in the design and optimization of industrial processes [1]. Strongly non-ideal behavior of electrolytes is one of the main problems in the prediction of phase equilibria in chemical processes [2]. As a result, accurate thermodynamic models are necessary to predict the equilibrium behavior of electrolytes for design, control and optimization of related industries [3]. The activity of the solvent in an electrolyte solution is a key parameter, which can be regressed through thermodynamic modeling and an expression of the excess Gibbs energy. Several excess Gibbs energy and activity coefficient models have been proposed for electrolyte solutions. Such models usually contain two terms for the excess Gibbs energy, one responsible for long rage and the other for short range forces between the available species in the mixture. In most cases the Debye–Hückel theory has been used to calculate the long-range interactions between species [4]. Recently, Kontogeorgis et al. [5] wrote a vast review on importance of Debye–Hückel theory and its application for electrolyte solutions. Different * Hamid Bakhshi [email protected] 1



Faculty of Chemical Engineering, Babol Noshirvani University of Technology, Babol, Iran

13

Vol.:(0123456789)



Journal of Solution Chemistry

groups of equations have been proposed for short-range contribution to the excess Gibbs energy. The first are models which apply a term of osmotic virial expansion to excess Gibbs energy, such as models proposed by Pitzer and by Bromley [6, 7]. Also, new extensions of this group of models have been presented by others [8]. Another group of short range interaction term are based on the local composition concept. E-NRTL [9], NRTL-NRF [10], Wilson-NRF [2], an