5. Conclusions

The responses to the environmental challenges require development and application of new environmentally friendly working media. As one of the promising media for chemical and refrigeration industry, the mixtures of conventional refrigerants with ionic liquids are considered. This requires reliable data on thermophysical properties and phase behavior of the mixture.

Tremendously growing amount of data and development of the data science provides new basis for estimation of the model parameters which influence the description and further prediction of the different physical processes.

The information on breaking of azeotrope is crucial for the separation of different industrial mixtures and is intensively discussed in the literature. The proposed existing expressions for identification of azeotrope behavior generally are empirical. To describe and predict the phase behavior of the mixture, the equation of state

The calculations of phase equilibria for system imidazolium-based ionic liquid and refrigerants R134a and R1234yf are performed. The Redlich-Kwong one-fluid model equation of state was selected due to simplicity, few parameters to be estimated, existing robust computational algorithms for obtaining the derivations of different thermodynamic features, as well as a large amount of existing data on

The phase behavior of imidazolium-based ionic liquids С8H11N3F6S2O4 ([EMIm] [Tf2N]) and C10H19N2BF4 ([HMIm][BF4]) with refrigerants R134а and R1234yf was evaluated using the parameters regressed at the low-pressure experimental data. It is noted that the variation of anionic group leads to the shift of critical point of ILs and obviously impact intermolecular interactions between ionic liquids and molecules of refrigerants. To this end the phase behavior pattern is also impacted. Variation in the k12 interaction coefficient shifts the position of a specific point on the global phase diagram. For R1234yf-[HMIm][BF4] system, the position of the specific point at different values k12 = 0.1, 0, + 0.1 demonstrates a tendency to transition from azeotrope to zeotrope state or vice versa. The binary

models is more suitable for calculation of the thermodynamic properties.

Critical point temperatures and molar volumes of representative components from [25–29].

interaction parameters k12 and l12 for R134a-Il blends were restored from experimental data provided by Ren et al. [28, 29] with Pareto-based method

[BF4] + refrigerants R134a (R1234yf) systems is also provided in Figure 11. It is considered that the azeotrope definitely appears in the R134a-R1234yf system. The literature search provides lack of experimental data for this system. The boundaries presented in Figure 11 for the R1234yf-[HMIm][BF4] mixture practically coincide. The addition of the ionic liquid to azeotropic mixture leads to azeotrope-breaking that is demonstrated by a change of phase envelope for the

In case a specific point is located in the northern or southern quadrants of the diagrams depicted in Figure 11, the azeotropic phenomenon is expected to appear in the binary mixture. The pattern of specific point location for ionic liquid [HMIm]

binary interacting parameters in the existing literature.

Distillation - Modelling, Simulation and Optimization

R134a-R1234yf-[HMIm][BF4] mixture in Figure 12.

described in Section 3.

84

Figure 10.

In this study we present new approach which does not require vapor–liquid equilibrium calculations for binary mixtures. This approach is based on synergetic combination of global phase diagram technique and Pareto-based regression to reduce the uncertainty level caused by different sources of the data.

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The global phase diagram is used to determine the type of phase behavior and derive analytical expressions to predict azeotrope and double azeotrope phenomena in terms of critical parameters of pure components.

To restore the EoS model parameters under uncertainty, the Pareto-optimality concept with fuzzy convolution scheme is applied. This approach is quite general and can be applied to other mathematical models, which describe a wide spectrum of phenomena of thermodynamic and phase behavior.

The azeotrope and double azeotrope criteria were elaborated and assessed for the imidazolium (IL)-based ionic liquids and industrial refrigerant mixtures. It was shown that IL doping leads to the breaking of azeotrope in binary refrigerant mixtures that open the way for the azeotrope refrigerant mixture separation technologies in order to remove the environmentally harmful substances.

The azeotrope phenomena in the refrigerant-IL mixtures are discussed, and conclusion about the highly improbable azeotrope blend formation for these systems is given. Azeotrope-breaking in the R134a-R1234yf mixture at IL doping is considered as an illustration of zeotrope behavior in the refrigerant-IL mixtures. Global phase behavior of ionic liquid-industrial refrigerant mixture is analyzed, and possible types of phase behavior according to the classification scheme of Scott and Van Konynenburg are established.
