Solubilities and diffusivities of R227ea, R236fa and R245fa in 1-hexyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide

doi:10.1016/j.jct.2018.04.004

The Journal of Chemical Thermodynamics

Volume 123, August 2018, Pages 158-164

https://doi.org/10.1016/j.jct.2018.04.004 Get rights and content

Highlights

•
Solubilities and diffusion coefficients of R227ea, R236fa and R245fa in [HMIM][Tf₂N] were reported.
•
Solubilities and diffusivities of HFCs in [HMIM][Tf₂N] were compared and analyzed.
•
Solubility and diffusion coefficient were well correlated with NRTL model and Wilke-Chang equation, respectively.

Abstract

The solubilities and diffusion coefficients of 1,1,1,3,3-pentafluoropropane (R245fa), 1,1,1,2,3,3,3-heptafluoropropane (R227ea) and 1,1,1,3,3,3-hexafluoropropane (R236fa) in 1-hexyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([HMIM][Tf₂N]) were determined experimentally along five isotherms (303.15, 313.15, 323.15, 333.15 and 343.15 K) with pressures from 0.01 to 0.50 MPa. The solubility measurements were carried out using the isochoric saturation method. A semi-infinite volume method was used to calculate diffusion coefficient via the time-dependent pressure-decay data. NRTL model was used to correlate the gas solubility data of R245fa, R227ea and R236fa in [HMIM][Tf₂N] with the average absolute relative deviations less than 1.0%, while Wilke-Chang equation was used to correlate the diffusion coefficient data with the average absolute relative deviations less than 9.7%.

Introduction

Absorption refrigeration appears to be one of the most promising cooling technologies because its driving force can be low-grade energies such as the geothermal energy [1]. Since the thermodynamic efficiency and reliability of absorption refrigeration system are strongly dependent on the working pair which contains one refrigerant and one absorbent. Traditional working pairs, lithium bromide-water and ammonia-water have some shortcomings such as crystallization, toxicity and corrosivity [2]. Therefore, developing new working pair is meaningful for improve the performance of the absorption refrigeration system.

In recent years, ionic liquid and hydrofluorocarbon (HFC) have been proposed to be the working pair of absorption refrigeration system [3], [4]. The dissolution behaviour of hydrofluorocarbon in ionic liquid is necessary for the design of absorption refrigeration system [5], [6]. However, there is a lack of studies on the solubilities and diffusivities of hydrofluorocarbons (HFCs) in ionic liquids, especially for fluorinated derivatives of propane [7] which show much higher solubility than fluorinated derivatives of ethane [5], [8], [9], [10], [11], [12], [13], [14], [15], [16]. High solubility results in lower circulating ratio and is helpful to improving the refrigeration efficiency of absorption refrigeration system [17], [18], [19].

In this work, we aim to investigate the solubilities and diffusivities of three potential working pairs for absorption refrigeration system. The refrigerants are 1,1,1,3,3-pentafluoropropane(R245fa), 1,1,1,2,3,3,3-heptafluoropropane (R227ea) and 1,1,1,3,3,3-hexafluoropropane (R236fa) while the absorbent is ionic liquid 1-hexyl-3-methyl-imidazolium bis (trifluoromethylsulfonyl) amide [HMIM][Tf₂N]. The temperature range is from 303 K to 343 K and the pressure range is from 0.01 MPa to 0.50 MPa. Moreover, we represented the solubility and diffusion coefficient data with NRTL model and Wilke-Chang equation, respectively.

Section snippets

Materials

R245fa (CAS# 460-73-1, mass fraction purity ≥ 0.999), R227ea (CAS# 431-89-0, mass fraction purity ≥0.999), R236fa (CAS# 690-39-1, mass fraction purity ≥0.999) were purchased from Zhejiang Sinoloong Refrigerant Co., Ltd. [HMIM][Tf₂N] (CAS# 382150-50-7, mass fraction purity ≥0.990) was purchased from Shanghai Cheng Jie Chemical CO., Ltd. [HMIM][Tf₂N] was put into vacuum oven for 48 h at 393 K to eliminate the water or other impurities before used. Table 1 provides the chemical names, suppliers,

Solubility model

NRTL model was selected to correlate the experimental solubility data. Vapour-liquid equilibrium of an N-component system is defined by [27], [28] $y_{i} p ϕ_{i} = x_{i} γ_{i} p_{i}^{S} (i = 1, \dots,N)$ Here x_i and y_i are the molar fractions for ith species in the liquid and vapour phase, respectively; p_i^S is the saturated vapour pressure for ith species which can be calculated by REFPROP 9.1 [20]; γ_i is the activity coefficient for ith species; Φ_i is the correction coefficient for ith species, it is given as $ϕ_{i} = \exp [\frac{(B_{i} - V_{i}^{L}) (p - p_{i}^{S})}{RT}]$

Results and discussion

The measured solubility values of R227ea, R236fa and R245fa in [HMIM][Tf₂N] at temperatures from 303.15 K to 343.15 K and pressures up to 0.50 MPa are summarized in Table 2. In order to investigate the effects of temperature and pressure on the solubility, the solubility data are plotted in Fig. 2, Fig. 3, Fig. 4. As expected, the solubilities of R227ea, R236fa and R245fa in [HMIM][Tf₂N] increase with the increasing pressure and decrease with the increasing temperature. Table 3 and Fig. 5 show

Conclusions

In this work, new experimental data for the solubilities and diffusion coefficients of R227ea, R236fa and R245fa in [HMIM][Tf₂N] at temperatures from 303 K to 343 K and pressures up to 0.50 MPa were presented. Solubilities of R227ea, R236fa and R245fa in [HMIM][Tf₂N] increase with the increasing pressure and decrease with the increasing of temperature. Diffusion coefficients of R227ea, R236fa and R245fa in [HMIM][Tf₂N] increase with the increasing temperature. The order of the solubilities of

Acknowledgements

The supports for the present work provided by the National Science Fund for Distinguished Young Scholars of China (No. 51525604), the Foundation for Innovative Research Groups of the National Natural Science Foundation of China (No. 51721004), the Science and Technology Research Project of Shaanxi Province, China (No. 2016GY-145) and 111 Project (No. B16038) are gratefully acknowledged.

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Solubilities and diffusivities of R227ea, R236fa and R245fa in 1-hexyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide

Highlights

Abstract

Introduction

Section snippets

Materials

Solubility model

Results and discussion

Conclusions

Acknowledgements

Geothermics

J. Chem. Thermodyn.

J. Renew. Sustain. Ener.

J. Mol. Liq.

Fluid Phase Equilib.

Fluid Phase Equilib.

Fluid Phase Equilib.

Fluid Phase Equilib.

Fluid Phase Equilib.

J. Chem. Thermodyn.

J. Chem. Thermodyn.

Energ. Convers. Manage.

Energ. Convers. Manage.

Int. J. Refrig.

J. Chem. Thermodyn.

J. Chem. Thermodyn.