Diffusion coefficients and Henry’s constants of hydrofluorocarbons in [HMIM][Tf2N], [HMIM][TfO], and [HMIM][BF4]

https://doi.org/10.1016/j.jct.2017.04.009Get rights and content

Highlights

  • D and H of hydrofluorocarbons in RTILs were measured.

  • The influence factors of D and H were investigated.

  • The Wilke-Chang correlation was proposed to fit the experiment data.

Abstract

A semi-infinite volume technique was used to measure the diffusion coefficients of six hydrofluorocarbons in three room-temperature ionic liquids in the temperature range from 303.2 K to 343.2 K. The Henry’s constants were also determined at the same time. The hydrofluorocarbons are difluoromethane (R-32), pentafluoroethane (R-125), fluoroethane (R-161), 1,1,1-trifluoroethane (R-143a), 2,3,3,3-tetrafluoropropene (R-1234yf), and 1,1-difluoroethane (R-152a). The room-temperature ionic liquids are 1-hexyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([HMIM][Tf2N]), 1-hexyl-3-methylimidazolium trifluoromethanesulfonate ([HMIM][TfO]), and 1-hexyl-3-methylimidazolium tetrafluoroborate ([HMIM][BF4]). The diffusion coefficients and the Henry’s constants of hydrofluorocarbons in the three RTILs all increase with the increasing temperature, but the orders of them are different. In addition, the relationship between the diffusion coefficient and the Henry’s constant was investigated. Finally, the Wilke-Chang equation was successfully applied to correlate the diffusion coefficients of hydrofluorocarbons in room-temperature ionic liquids.

Introduction

Room-temperature ionic liquids (RTILs) are a class of salts, which are liquid near ambient temperature. Due to their peculiar properties of high solubility, non-flammability, good electrical conductivity and negligible vapor pressure, they have been widely used in many industrial fields [1], [2], [3], [4]. Recently, RTILs and hydrofluorocarbons are proposed to be used together as working fluid in absorption refrigeration system to overcome the disadvantages of traditional working fluids such as toxicity, crystallization and corrosivity [5], [6], [7].

The reliable thermophysical property data of RTILs + hydrofluorocarbons binary mixtures are required for the design of the refrigeration process, especially the solubility and diffusion coefficient of refrigerant in absorbent because they influence the performance of absorption refrigeration system from the thermodynamic and kinetic aspects.

In recent years, a large amount of solubility data of hydrofluorocarbons in RTILs have been reported [8], [9], [10], [11], [12], [13], [14], [15], [16], [17], [18], [19], [20], [21], [22], [23], [24], [25], [26], [27], [28]. For example, Ren and Scurto [11] studied the solubilities of R134a in [HMIM][Tf2N]; Sousa et al. [12], [13] investigated the solubilities of R-23, R-32 and R-41 in several phosphonium-based RTILs; Shiflett et al. [14], [15], [16], [17], [18], [19], [20], [21], [22], [23], [24] reported the solubility data of R-1141, R-134, R-161, R-32, R-23, R-125, R-134a, R143a, and R-152a in different RTILs; Our group [25], [26], [27], [28] also investigated vapor-liquid equilibrium of R-32, R125, R-134a, R-161, R-143a, R-1234yf, R-1234ze(E) and R-152a in [P(14)666][TMPP] and [HMIM][Tf2N]. But the diffusion coefficient data of hydrofluorocarbons in RTILs were scarce. Only Shiflett group [15], [16], [17] studied the diffusion coefficients of R-32, R-23, R-125, R-134a, R143a and R-152a in several RTILs.

In this work, the diffusion coefficients of R-32, R125, R-161, R-143a, R-1234yf and R-152a in [HMIM][Tf2N], [HMIM][TfO] and [HMIM][BF4] were presented in the temperature range from 303.2 K to 343.2 K. The Henry’s constants of R-32, R125, R-161, R-143a, R-1234yf and R-152a in [HMIM][TfO] and [HMIM][BF4] were also measured at the same temperature. The influences of temperature and viscosity on the diffusion coefficients and Henry’s constants were evaluated. The relationship between diffusion coefficient and Henry’s constant was investigated. Finally, the Wilke-Chang equation was used to correlate the diffusion coefficients of hydrofluorocarbons in RTILs.

Section snippets

Materials

All hydrofluorocarbons (R-32, R125, R-161 R-143a, R-1234yf and R-152a) used in this work were purchased from Zhejiang Sinoloong Refrigerant CO., LTD with purities higher than 99.9 wt%. Carbon dioxide was purchased from Praxair with a purity higher than 99.999 wt%. They were used without further purification. [HMIM][Tf2N], [HMIM][TfO] and [HMIM][BF4] were purchased from Shanghai Cheng Jie Chemical CO., LTD with purities higher than 99.0 wt%. Before used, RTILs was dried at 393 K for 24 h in a vacuum

Results and discussion

The diffusion coefficient of CO2 in [HMIM][Tf2N] at 283.2 K was measured to describe the experimental method. During the experiment, the pressure in diffusion cell varied from 98.6 kPa to 91.3 kPa. Because the measurement was performed at low pressure, the gas slightly dissolved in RTIL. The measured value was considered to be the infinite dilution diffusion coefficient. The surface concentration, Cz=0, was calculated using the measured pressure at time t and the Henry’s constant with Eq. (4). The

Conclusion

The diffusion coefficients of six hydrofluorocarbons in [HMIM][Tf2N], [HMIM][TfO] and [HMIM][BF4] and the Henry’s constants of hydrofluorocarbons in [HMIM][TfO] and [HMIM][BF4] were measured at low pressure and in the temperature range from 303.2 K to 343.2 K. The diffusion coefficients of hydrofluorocarbons in RTILs are an order of magnitude smaller than those of gases in traditional solvents due to the high viscosity of RTILs. The effect of temperature on the absorption rate of

Acknowledgements

This work was supported by the National Science Fund for Distinguished Young Scholars of China (No. 51525604), Science and Technology Research Project of Shaanxi Province, China (No. 2016GY-145), and 111 Project (No. B16038). The authors gratefully acknowledge for financial support.

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