(440g) Thermodynamic Modeling of CO2 Absorption in Aqueous Amino Acid Salt Solutions with Symmetric Electrolyte NRTL Model

Development and large-scale deployment of renewable energy is the need of the hour, but it is still desirable to mitigate the increased CO₂ emissions as we make a transition from fossil fuel-based energy sources to renewable energy sources. In this perspective, many separation technologies have been designed for the large-scale removal of CO₂ from industrial sources. The most developed technology for CO₂ removal is the solvent based absorption using monoethanolamine (MEA)¹. However, alkanolamines suffer from volatility, oxidative degradation and toxicity making them less suitable for solvent-based absorption^2,4. Recently, aqueous solutions of amino acid salts (AAS) have gained considerable attention as alternative solvents for carbon capture because the inherent ionic nature of the system makes it non-volatile² which is advantageous at the stripper conditions. Also, their higher oxidative stability is favorable for oxygen-rich flue gas streams⁴. They also have comparable absorption kinetics to alkanolamines². Thus, it is desirable to develop an extensive thermodynamic model of AAS-H₂O-CO₂ system to support process development and optimization. However, scarcity of extensive experimental data on thermodynamic aspects of the binary (AAS-H₂O) and ternary (AAS-H₂O-CO₂) systems² as well as the dissociation of salt to zwitterion, anion and cation³ add to the complexity of modeling the liquid phase chemical equilibrium. Limited work has been reported for the experimental determination of CO₂ solubility in aqueous solutions of potassium salts of Glycine⁴ (KGly), Sarcosine² (KSar), Proline⁵ (KPro) and Taurine⁶ (KTau). Prior models using extended UNIQUAC framework² and Deshmukh-Mather mehtodology⁴ have been developed for potassium salts of sarcosine and glycine respectively.

In this study, we develop a symmetric electrolyte NRTL model to represent liquid phase non-idealities in conjunction with Redlich-Kwong equation of state to model vapor phase fugacity. Solubility data and pH data is used to identify eNRTL binary interaction parameters for one binary system (KSar-H₂O) and three ternary (KSar-H₂O-CO₂), (KGly-H₂O-CO₂), (KPro-H₂O-CO₂) systems. The models accurately represent the VLE behavior and liquid phase speciation in the three AAS-H₂O-CO₂ systems, covering a temperature range of 313-353 K and CO₂ loading of 0.2-1. The models can be further advanced upon the availability of more extensive experimental data on the absorption enthalpy for the three AAS-H₂O-CO₂ systems.

References:

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