Object-Oriented Modeling of a Capacitive Deionization Process

Magdalena Lenz,Robin Wagner,Ellen Hack,Matthias Franzreb

doi:10.3389/fceng.2020.00003

Magdalena Lenz, Robin Wagner + Show 2 more

Open Access

https://doi.org/10.3389/fceng.2020.00003

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Abstract

The process of capacitive deionization (CDI) is a cost effective and energy efficient method that offers many opportunities in terms of desalination of brackish water and the removal of ionic contaminants. Current research focusses on evaluating different influence parameters to make the CDI process more competitive to other commercially available methods like reverse osmosis, direct distillation or ion exchange. CDI is based on the adsorption of ions to highly porous electrodes by applying an external voltage difference. Although, remarkable progress in CDI modeling has been achieved during the past decade, so far, only few models exist which fully describe the CDI process and which predict the cell behavior in all its aspects, including e.g. performance under constant voltage and/or constant current control or pH effects including water dissociation. However, in this paper a new approach to CDI modeling is presented, which opens a path to fast and easy implementation of a digital depiction of complex CDI setups having e.g. multiple cells. The model is based on the object-oriented modeling language Modelica that enables the simulation and prediction of the behavior of complete CDI cells by combining chemical, electrochemical and electrical components. Furthermore, there is the possibility to predict complex setups with e.g. complex electrolytes, concentration or voltage fluctuations as they appear due to environmental influences outside laboratory experiments. Besides detailed time courses of species concentrations in the bulk and the electrodes or local electrical potentials, the model enables the prediction of important sum parameters such as the salt adsorption capacity, current efficiency and power consumption. The results of the developed CDI model are validated by using parameter settings from literature and comparing the resulting predictions of equilibrium and kinetics. In addition, the agreement between our own experimental results and the respective model predictions is discussed

Highlights

In recent years Capacitive Deionization (CDI) has become a commonly known technique for deionization of brackish water, as it is an energy efficient and cost effective technology (Oren, 2008; Zou et al, 2008; Anderson et al, 2010; Cohen et al, 2013; Porada et al, 2013; Han et al, 2014; Biesheuvel et al, 2015; Suss et al, 2015; Gude, 2016; Dykstra et al, 2018; Ma et al, 2018)
A physics-based model was presented by Dykstra et al (2017) showing the effect of pH changes in Membrane Capacitive Deionization (MCDI)
In Equations 8, 9 the electrosorption of the substances Xi to the electrode looks like a redox reaction, which seems to be in contrast to the principle of capacitive deionization (CDI) where there is no charge transfer between the electrode and the ions accumulated in the micropores (Biesheuvel and Bazant, 2010; Porada et al, 2013; Suss et al, 2015)

Summary

Introduction

In recent years Capacitive Deionization (CDI) has become a commonly known technique for deionization of brackish water, as it is an energy efficient and cost effective technology (Oren, 2008; Zou et al, 2008; Anderson et al, 2010; Cohen et al, 2013; Porada et al, 2013; Han et al, 2014; Biesheuvel et al, 2015; Suss et al, 2015; Gude, 2016; Dykstra et al, 2018; Ma et al, 2018). This shows that the Modelica model includes exactly the same relationship of the potential-dependent ratio between the ion concentration in the micro- and macropores as the modified Donnan model introduced previously (Biesheuvel et al, 2011a,b; Zhao et al, 2012).

Results

Conclusion