Implementation of CP-PC-SAFT for Predicting Thermodynamic Properties and Gas Solubility in 1-Alkyl-3-methylimidazolium Bis(trifluoromethylsulfonyl)imide Ionic Liquids without Fitting Binary Parameters

Abstract

In this study, simple molecular-weight-based correlations for the CP-PC-SAFT parameters for [C n mim][NTf 2 ] ionic liquids have been developed. These correlations allow a nearly precise modeling of densities, including at elevated pressures and at temperatures up to ∼400 K, as well as accurate predictions of the isobaric heat capacities, velocities of sound, and compressibilities. The accuracy of these predictions is superior to that of ePC-SAFT. The available data reveal that solubilities of gases are directly related to their critical temperatures. As the critical temperatures increase, the gas−IL systems become more symmetric, and the solubilities increase. The intrinsic robustness of the CP-PC-SAFT model, along with its agreement with the pure-compound critical temperatures, give this model the capability to accurately predict VLE in [C n mim][NTf 2 ] systems of various gases, such as CO, O 2 , CH 4 , Kr, N 2 O, H 2 S, SO 2 , R134a, R1234ze(E), and CO 2 , without prior consideration of any mixture data or adjustment of binary parameters. At the same time, the entirely predictive implementation of the model poses unavoidable compromises in its accuracy. In particular, it overestimates LLE in the system R134a− [C 6 mim][NTf 2 ] and substantially underestimates the extent of phase splits in CO 2 solutions above ∼50 bar. The latter flaw can be corrected by implementing a universal set of binary adjustable parameters. Similar accuracy of modeling can also be achieved with this set of binary parameters and with their zero values in the cases of additional CO 2 −[NTf 2 − ] IL systems.

Comparison of CP-PC-SAFT and SAFT-VR-Mie in Predicting Phase Equilibria of Binary Systems Comprising Gases and 1-Alkyl-3-methylimidazolium Ionic Liquids

“…Following the Lennard-Jones potential, the SAFT-VR-Mie parameters λ a and λ r were set to 6 and 12. The estimations of densities in wide range of T and P yielded by both models are particularly accurate, and the deviations from data are typically comparable with experimental uncertainties [39,42]. As seen, SAFT-VR-Mie yields the higher values of T c and P c versus CP-PC-SAFT.…”

“…The resulting values for the considered ILs, along with the predicted values of T c and P c , are listed in Table 2. The CP-PC-SAFT parameters of ILs belonging to the [C n mim][NTf 2 ] homologies series were generalized by molecular weight (M w ) [39]. Following the Lennard-Jones potential, the SAFT-VR-Mie parameters λ a and λ r were set to 6 and 12.…”

“…Table 2. The molecular parameters and critical constants of pure ILs yielded by SAFT-VR-Mie and CP-PC-SAFT [39,42].…”

“…Although such practice substantially improves an agreement between the experimental and calculated data, it affects the predictive character of the models and hinders evaluation of their overall robustness and reliability. At the same time, some studies [38][39][40][41][42] have applied the EoS approaches to the systems of ILs in the predictive manner, while keeping zero or universal substance-independent values of the binary parameter k 12 . The basic principle of EoS models is utilizing an input of available experimental data to produce an output of predicted data.…”

Heat Capacities of Fluids: The Performance of Various Equations of State

“…For 1-alcohols, PC-SAFT with both 2B and 3B schemes shows high accuracy of Cp data but low accuracy for u, with the AAD lower than 3% and higher than 6%, respectively. 28,29 For water, the model shows satisfactory accuracy for density and speed of sound and acceptable performance for heat capacities, while it substantially underestimates these properties at the saturated conditions. For ionic liquids at the atmospheric pressure, CP-PC-SAFT gives higher deviations of heat capacities (≤7.5%) than speed of sound (≤4.3%) and density (≤0.3%).…”