New Paradigm in Electrolyte Thermodynamics

Project Information

ElectroThermo

Grant agreement ID: 832460

DOI

10.3030/832460

Project closed

EC signature date 10 April 2019

Start date 1 September 2019

End date 31 August 2025

Funded under

• EXCELLENT SCIENCE - European Research Council (ERC)

Total cost

€ 2 500 000,00

EU contribution

€ 2 500 000,00

Coordinated by

DANMARKS TEKNISKE UNIVERSITET
Denmark

Periodic Reporting for period 4 - ElectroThermo (New Paradigm in Electrolyte Thermodynamics)

Reporting period: 2024-03-01 to 2025-08-31

Summary of the context and overall objectives of the project

The project’s overall target is to arrive at a fundamental understanding of electrolyte thermodynamics and thus enable the engineering of a new generation of useful, physically sound models for electrolyte solutions. These models should be general and applicable to a very wide range of conditions so that they can be potentially used for a wide range of applications. The aim is both to achieve a fundamental understanding of electrolyte thermodynamics but also to ensure contact with stakeholders (industry, etc) where electrolyte thermodynamics is expected to be relevant and useful.

Moreover, as water is inherently present in numerous electrolyte solutions, the study of water properties and interrelation with its structure is also a major target of the work.

Electrolyte solutions are present almost anywhere and find numerous applications in physical sciences including chemistry, geology, material science, medicine, biochemistry and physiology as well as in many engineering fields especially chemical & biochemical, electrical and petroleum engineering. In all these applications thermodynamics plays a crucial role over wide ranges of temperature, pressure and composition. As the subject is important, a relatively large body of knowledge has been accumulated with lots of data and models. However, disappointingly the state-of-the-art thermodynamic models used today in engineering practice are semi-empirical and require numerous experimental data. They lack generality and have not enhanced our understanding of electrolyte thermodynamics. Going beyond the current state of the art, we create a scientific foundation for studying, at their extremes, various approaches for electrolyte solutions and we identify strengths and limitations.

We make new advances which clarify major questions and misunderstandings in electrolyte thermodynamics, some remaining for over 100 years, which currently prevent real progress from being made, thus creating a new paradigm that may potentially pave the way for the development of new engineering models for electrolyte solutions. We expect significant benefits in many industrial sectors as well as in environmental studies and potentially also biotechnology.

Work performed from the beginning of the project to the end of the period covered by the report and main results achieved so far

The work can be divided into the following phases (some of them clearly interconnected):
1. Fundamental studies of the Debye-Hückel (DH) equation and the Born equation for ion-ion and ion-water solvation. This included the study of the role of the relative study permittivity and its concentration dependency and the overall importance of these phenomena in studying electrolyte solutions.
2. The study of ion-pairing via theories, equations of state and electrical conductivity studies. This included the full solution of the Poisson-Boltzmann equation, comparison to DH theory and the development of a binding-version of the DH theory.
3. The study of solvation phenomena via quantum chemistry, including a novel method to estimate the monomer fraction of associating compounds.
4. The development of predictive methods for obtaining solid-state properties using quantum chemistry and machine learning.
5. The study of water properties and connection to water structure via molecular simulation and equations of state.
6. The development of machine learning methods for predicting properties of complex aqueous electrolyte solutions with biomolecules.
7. The use of molecular simulation for studying individual ion activity coefficients (IIAC). This included the use of these data for estimating parameters of equations of state as well as evaluating the relative contributions of the various terms of such models (physical, solvation, ion-ion forces).
8. The development and comparison of advanced equations of state for electrolytes (e-CPA, e-PC-SAFT and e-SAFT-FV Mie) over a wide range of systems and properties, including mixed solvents, and mixed salts. We have compared the DH and MSA ion-ion interaction theories for electrolytes.
9. The collection and open publication of extensive databases of model parameters and experimental data for electrolyte solutions for various properties.
10. The discussion of the results with industry and other stakeholders, permitting further exploration and dissemination.

We have concluded that IIAC can be very useful in the study of electrolyte systems. We have demonstrated that the full version of the Debye-Hückel theory is a powerful model for developing engineering models for electrolytes in the form of equations of state, but future studies may need to include ion pairing. The studies for water demonstrated that new fundamentals are needed and possibly the two-state theory for water can provide new insights towards an improved understanding of water-structure properties and connection. We have demonstrated that e-SAFT VR Mie is a powerful model for engineering applications and we plan to further develop it in a forthcoming ERC PoC project.

Progress beyond the state of the art and expected potential impact (including the socio-economic impact and the wider societal implications of the project so far)

Significant developments beyond the current state of the art include:

1.The molecular simulation studies (both individual ion activity coefficients for water-salts and hydrogen bonding of water) and the demonstration that IIAC data from simulation validate qualitatively previous, often considered controversial, measurements for electrolytes. Moreover, that such IIAC data can be used in the development and validation of equations of state.
2. Revealing the true value of the Debye-Hückel theory, similarity to other theories for ion-ion interactions (MSA) and comprehensive evaluation of a variety of associated phenomena in electrolyte thermodynamics (charging processes involved in the derivation of the models, solvation - Born equation, the concentration dependency of the relative static permittivity, ion-pairing).
3. A thorough evaluation of water structure-properties connection, both for pure water as well as aqueous electrolytes.
4. The development of a binding version of the DH theory which is implemented in electrolyte models for accounting for ion-pairing.
5. The development of a novel theory for the electrical conductivity based on the Debye-Hückel-Onsager approach in a new formulation.
6. The use of machine learning and quantum chemistry for a-priori prediction of solid-state properties for electrolytes as well as the use of ML for aqueous electrolyte systems containing biomolecules.
7. The development as well as the systematic and on equal basis comparison of different electrolyte equations of state considering a wide range of systems/conditions but also diverse development (parameter estimation) methods.

At the dissemination level, in addition to publications/conferences, workshops on electrolyte thermodynamics have been organized as well as an extensive survey on industrial needs for thermodynamic properties which revealed the need for much better electrolyte models and understanding. Both of these studies have been carried out under the auspices of the European Federation of Chemical Engineering.

It is also intended to proceed with more systematic dissemination of the results, beyond the scientific ones, to key stakeholders in the industry and academia.

Finally, four pending manuscripts will be published after the completion of the project; on ion-pairing theories, on a new method to analyze the different contributions (physical, electrostatic, etc) of electrolyte models, a new analysis of the complete Debye-Hückel theory and finally a major review on the Debye-Hückel and Born equations.

Journal Cover for Paper Water−Hydrocarbon Phase Equilibria with SAFT-VR Mie Equation of State

Journal Cover for Paper Modeling of Gas Solubility in Aqueous Electrolyte Solutions with the eSAFTVR