Working Pair Selection of Compression and Absorption Hybrid Cycles through Predicting the Activity Coefficients of Hydrofluorocarbon + Ionic Liquid Systems by the UNIFAC Model

Abstract

Hydrofluorocarbon (HFC) + ionic liquid (IL) systems can be adopted as working pairs for compression/absorption hybrid cycles. A method of selecting novel working pairs has been proposed in this paper, that the infinite dilution activity coefficients (γ1 ∞) of working pair system need to be obtained, and the UNIFAC model is implemented to predict the activity coefficients of the working pair system. With the help of published experimental vapor–liquid equilibrium (VLE) data of 18 HFC + IL systems, 16 new group interaction parameters for four anion ILs and nine HFCs have been fitted to extend the evaluating and predicting range of HFC + IL systems for developing alternative working pairs. To validate the reliability of the method, the model parameters have been used to calculate the VLE data with the average relative deviations (ARDs) of pressures less than 8.5%. The prediction of the γ1 ∞ shows that the solubility and affinity between HFCs and ILs increase with the decrease of the γ1 ∞, which is in agreement with the experimental results. It is found by the prediction that the combinations of R32/R134 and [Tf2N]-based ILs may be two kinds of potential working pairs to improve the performances of compression/absorption hybrid cycles.

Vapor liquid equilibrium prediction of methanol–ionic liquid systems using UNIFAC model to select alternative working fluids of absorption cycle

“…Because the methyl group has a positive contribution to the formation of hydrogen‐bonding interactions between the IL and CH 3 OH . This affinity law is consistent with the hydrofluorocarbon–IL system …”

“…It shows that values follow the law of CH 3 OH‐[Dmim]DMP > CH 3 OH‐[Emim]DMP > CH 3 OH‐[Pmim]DMP > CH 3 OH‐[Bmim]DMP > CH 3 OH‐[Hmim]DMP. Good working fluids should show highly negative . The affinity between CH 3 OH and ILs follows the law of CH 3 OH‐[Hmim]DMP > CH 3 OH‐[Bmim]DMP > CH 3 OH‐[Pmim]DMP > CH 3 OH‐[Emim]DMP > CH 3 OH‐[Dmim]DMP.…”

“…17 This affinity law is consistent with the hydrofluorocarbon-IL system. 33 Then change the anion, the vapor pressure data of four CH 3 OH-[Hmim]X (X = DMP, DEP, DBP, and ES) systems are compared in Figure 5. When the cation remains the same, the vapor pressure of the CH 3 17,[41][42][43] show that the hydrogen bonding between anions and CH 3 OH is much higher than that between cations and CH 3 OH.…”

“…Sun et al calculated and compared the absorption potential and the infinite dilution activity coefficient of 16 ammonia–IL working fluids through the UNIFAC model. Dong et al calculated the activity coefficient of hydrofluorocarbon–IL working fluids by the UNIFAC model and correlated the infinite dilution activity coefficient as a criterion in compression or absorption hybrid cycles to select the best working fluids.…”

Gaseous absorption of fluorinated ethanes by ionic liquids

“…Most of them have negligible vapor pressure, high thermal and chemical stability, and high solubilities for gases [1]. Recently, lots of work have been carried out on the solubility behaviors of hydrofluorocarbons (HFCs) in ionic liquids which are important for applying ionic liquids + HFCs as working pairs for the absorption refrigeration cycles [2][3][4] or using ionic liquids as solvents for separation of hydrofluorocarbon mixtures [5]. Most of these work are on the solubilities of HFCs in imidazolium-based ionic liquids [6][7][8][9][10][11][12][13][14][15][16][17][18][19][20][21][22].…”