Viscosities of Pure Ionic Liquids Using Combinations of Free Volume Theory or Friction Theory with the Cubic, the Cubic Plus Association, and the Perturbed-Chain Statistical Associating Fluid Theory Equations of State at High Pressures

Abstract

In this study, the behaviors of viscosities of nine ionic liquids (ILs) over wide ranges of pressures and temperatures were determined. The investigated ILs belonged to the three imidazolium-based families of tetrafluoroborate, hexafluorophosphate, and bis­[(trifluoromethyl)­sulfonyl]­imide. The two well-known cubic equations of state (EoS’s) of Peng–Robinson (PR) and the Soave–Redlich–Kwong (SRK), as well as the two more-sophisticated EoS’s of cubic plus association (CPA), and perturbed-chain statistical associating fluid theory (PC-SAFT), were each coupled with two well-known theoretical viscosity models, namely the friction theory and the free volume theory. Calculated results showed that the free volume model, coupled with PC-SAFT, has superior results in comparison to the free volume model with the CPA EoS. For the viscosity model of free volume, the studied cubic EoS’s did not give accurate results. When the friction model was used, the PC-SAFT EoS once more showed better accuracy than the CPA EoS; however, the CPA results in this model were quite close to that of the PC-SAFT, while the differences were great with the free volume model. One of the remarkable conclusions for the friction theory model was the unexpectedly reliable results that it gave with the cubic EoS’s. This suggests that when highly accurate results are not crucial, this combination can be the best choice because of the significantly greater simplicity of a cubic EoS over an association EoS.

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

“…In eq 1, a and b are the energy parameter and the covolume parameter of the SRK EoS, respectively. 44 The energy parameter follows exactly the Soave-type temperature-dependency, and is defined as 42…”

“…Such induced hydrogen-bonds occur only between inert and polar compounds and not as self-associating bonds between inert molecules. 44,50 In the case of solvation, only one association bond between the polar and inert compound has been considered, and the cross association volume parameter between the polar and inert compound (β ij ) must be fitted. The cross association energy parameter of ε ij is defined as the half of the association energy parameter of the polar compound (i).…”

“…In eq , a and b are the energy parameter and the covolume parameter of the SRK EoS, respectively . The energy parameter follows exactly the Soave-type temperature-dependency, and is defined as X Ai is the major term of the association part of CPA, which indicates the extent of association bonds occurring in the system and is defined as the fraction of A-sites of component i which are not bonded with other molecules’ sites.…”

Rheological Behavior of Mixtures of Ionic Liquids with Water

“…Haghbakhsh et al used a combination of different models (free volume theory, friction theory, and equations of state like perturbed‐chain statistical associating fluid theory (PC‐SAFT)) to study the viscosity behavior of nine pure ILs. They concluded that among the combinations tested the friction theory together with cubic equations of state gives the most reliable predictions.…”

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

“…In Equation (12), is the fraction of A -sites of molecule j that are not bonded to other substances. This parameter is calculated using Equations (15) and (16) [ 43 , 44 , 45 ]. and where is the association strength, is the association energy, and is the association volume parameter of the interactions between sites A j and B i .…”