Modeling the Phase Behavior of Carbon Dioxide Solubility in Deep Eutectic Solvents with the Cubic Plus Association Equation of State

Abstract

The thermodynamic modeling of a new generation of solvents, deep eutectic solvents (DESs) is investigated. Because hydrogen bonding is a dominant molecular interaction, the cubic plus association (CPA) equation of state (EoS) was chosen for modeling. This is the first study to model DES density and carbon dioxide solubility using CPA. Fifteen different DESs were chosen which have density data, as well as CO2 solubility data, available in the literature over wide temperature and pressure ranges. To date, this is the most extended and global databank of DESs which has been employed in relation to a complex EoS. The density data were used to optimize the CPA parameters. The CPA EoS proved to be capable of accurately modeling pure DES densities. The validity of the optimized CPA parameters was further validated with literature density data of mixtures of DES + water, which were estimated successfully by a purely predictive procedure. To calculate CO2 solubility in DES, all the possible association schemes of CO2 were investigated. It was concluded that the inert (no-association) scheme for CO2 was the most accurate (AARD% = 6.2), while at the same time being the simplest with fewer fitting parameters. The induced association (solvation) scheme (AARD% = 7.1) is also suitable.

Energy Conservation in Absorption Refrigeration Cycles Using DES as a New Generation of Green Absorbents

“…The cubic-plus-association equation of state (CPA EoS) is among the most powerful equations of state that can handle associating compounds. Because of this, the CPA has been used in different studies involving physical property estimations or phase equilibrium calculations of DESs and their mixtures [ 36 , 37 , 38 , 39 ]. Viscosity, which is a challenging thermophysical property to model, was modeled successfully for a range of DES families using the CPA EoS coupled to theoretical models such as the free volume or the friction theory [ 36 , 38 ].…”

“…Viscosity, which is a challenging thermophysical property to model, was modeled successfully for a range of DES families using the CPA EoS coupled to theoretical models such as the free volume or the friction theory [ 36 , 38 ]. In other studies, the solubilities of CO 2 and SO 2 in different types of DESs were modeled successfully using the CPA EoS [ 37 , 38 ].…”

“…They categorized a number of compounds within general groups such as water, alcohols, amines, glycols, acids, etc., proposing specific association schemes for each [ 46 ]. The pseudo-pure component approach is commonly used for DESs, meaning that the combination of the HBA and HBD in the mixture is considered as one pseudo-component [ 36 , 37 , 38 , 39 ]. For the DES pseudo-component, the association scheme of 2B [ 46 ] is considered, while water is represented by the 4C scheme [ 37 , 47 , 48 ].…”

“…The pseudo-pure component approach is commonly used for DESs, meaning that the combination of the HBA and HBD in the mixture is considered as one pseudo-component [ 36 , 37 , 38 , 39 ]. For the DES pseudo-component, the association scheme of 2B [ 46 ] is considered, while water is represented by the 4C scheme [ 37 , 47 , 48 ]. This means that a water molecule has four sites on its molecule for possible hydrogen bonding, while a DES has the potential for making hydrogen bonds at two sites.…”

Effects of Electrolyte Additives on Nonaqueous Redox Flow Batteries

“…The results indicate that when the concentration of SO 2 increases, the viscosity of conventional ionic liquids will decrease sharply. Also, some studies have shown that the adoption of high-pressure CO 2 in DES can certainly improve the physical properties of the RFB system, and this can also increase its electrical conductivity [28][29][30][31][32]. However, there are not too much literature about how the gas additives influence on the electrochemical performance of nonaqueous flow batteries.…”