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Predictive models for the phase behaviour and solution properties of weak electrolytes: nitric, sulfuric and carbonic acid.

Abstract

The distribution of ionic species in electrolyte systems is important in many fields of science and engineering, ranging from the study of degradation mechanisms to the design of systems for electrochemical energy storage. Often, other phenomena closely related to the ionic speciation, such as ion pairing, clustering and hydrogen bonding, which are difficult to investigate experimentally, are also of interest. Here, we develop an accurate molecular approach, accounting for reactions as well as association and ion pairing, to deliver a predictive framework that helps validate experiment and guides future modelling of speciation phenomena of weak electrolytes. We extend the \SAFT equation of state [D.~K.~Eriksen \textit{et al., Mol.~Phys.}, 2016, \textbf{114}, 2724--2749] to study aqueous solutions of nitric, sulphuric and carbonic acid, considering complete and partially dissociated models. In order to incorporate the dissociation equilibria, correlations to experimental data for the relevant thermodynamic equilibrium constants of the dissociation reactions are taken from the literature and are imposed as a boundary condition in the calculations. The models for water, the hydronium ion, and carbon dioxide are treated as transferable and are taken from our previous work. Here we present new molecular models for nitric acid, and the nitrate, bisulfate, sulfate, and bicarbonate anions. The resulting framework is used to predict a range of phase behaviour and solution properties of the aqueous acids over wide ranges of concentration and temperature, including the degree of dissociation, as well as the activity coefficients of the ionic species, and the activity of water and osmotic coefficient, density, and vapour pressure. The \SAFT models obtained in this manner provide a means of elucidating the mechanisms of association and ion pairing in the systems studied, complementing the experimental observations reported in the literature.

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Article information


Submitted
17 Dec 2019
Accepted
17 Mar 2020
First published
23 Mar 2020

Phys. Chem. Chem. Phys., 2020, Accepted Manuscript
Article type
Paper

Predictive models for the phase behaviour and solution properties of weak electrolytes: nitric, sulfuric and carbonic acid.

M. Kohns, G. Lazarou, E. Forte, F. A. Perdomo, S. Kournopoulos, G. Jackson, C. Adjiman and A. Galindo, Phys. Chem. Chem. Phys., 2020, Accepted Manuscript , DOI: 10.1039/C9CP06795G

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