Theoretical Study on Molten Alkali Carbonate Interfaces

Abstract

The properties and structure of relevant interfaces involving molten alkali carbonates are studied using molecular dynamics simulations. Lithium carbonate and the Li/Na/K carbonate eutectic mixture are considered. Gas phase composed of pure CO 2 or a model flue gas mixture are analysed. Likewise, the adsorption of these gas phases on graphene are studied, showing competitive CO 2 and N 2 adsorption that develops liquid-like layers and damped oscillation behaviour for density. The interaction of the studied carbonates with graphene is also characterized by development of adsorption layers through strong graphene-carbonate interactions and the development of hexagonal lattice arrangements, especially for lithium carbonate. The development of molten salts-vacuum interfaces is also considered, analysing the ionic rearrangement in the interfacial region. The behaviour of the selected gas phases on top of molten alkyl carbonate is also studied, showing the preferential adsorption of CO 2 molecules when flue gases are considered.

Structure and diffusion of molten alkali carbonate salts at the liquid-vacuum interface

“…Additionally, the error would be estimated to be even smaller than depicted because of agreement between the left and right sides of the interface, which are independent from each other. These findings are similar to those reported by Gutiérrez et al who also showed ionic structuring near the Gibbs dividing surface (Gutiérrez et al, 2018). Next, these ionic arrangements will be examined further using a local definition of the interface.…”

“…1). This study uses the interaction parameters developed by Tissen and Janssen , sometimes called the JT model, which have been employed for many similar studies of molten alkali carbonate salts and as such provides a robust body of literature for validation and reference Tissen, Janssen & Eerden, 1994;(Koishi et al, 2000;Ottochian et al, 2016;Wilding et al, 2016;Roest et al, 2017;Du et al, 2017;Du et al, 2019;Ding et al, 2018;Gutiérrez et al, 2018). The JT model employs coulombic interactions with long-ranged interactions described by Ewald summation and Born-type repulsion parameterized from quantum mechanical calculations .…”

“…The performance of such devices have been studied in addition to the bulk behavior of individual components of relevant systems, but the thermodynamics and dynamics of alkali carbonate electrolytes near the relevant interfaces are not as well understood. The behavior of interfaces generally, and ions at liquid-vacuum interfaces, have received significant attention as regions featuring interesting manifestations of physical principles and as domains where distinct chemistries can occur (Allara, 2005;Kumar, Knight & Voth, 2013;Soniat, Kumar & Rick, 2015;Tse et al, 2015;Bastos-González et al, 2016;Gutiérrez et al, 2018). The purpose of this work is to apply similar methods to characterize the liquid-vacuum interface of three molten alkali carbonate electrolytes.…”

“…Interfacial behavior of these molten alkali carbonate salts has been considered in a few studies (Roest et al, 2017;Gutiérrez et al, 2018;Gutiérrez et al, 2019). Roest and coworkers studied the behavior of Li, Na, and K carbonate salts at charged and neutral interfaces (Roest et al, 2017).…”

“…They have identified distinct mass and charge profiles in the molten liquid near the interface and the ions are found to diffuse more slowly in close vicinity of the interface. Gutiérrez et al (2018) and Gutiérrez et al (2019) have studied molten LiCO 3 and a eutectic mixture of LiNaKCO 3 at an interface with carbon solids, gases, and vacuum. They find that the ions do arrange at the interface as defined by the Gibbs dividing surface.…”