Vapor–liquid equilibria of the 1,1-difluoroethane (HFC-152a) + isobutene system
Introduction
Recently, there has been growing interest in environmental problems because of the potential to seriously damage entire world. Especially, ozone depletion and climate change are considered as critical challenges. Chlorofluorocarbons (CFCs) have been widely used as working fluid in various refrigeration-based industries. To prevent ozone depletion, however, the production and use of CFCs were regulated under the 1987 Montreal Protocol. Although hydrofluorocarbons (HFCs) have been considered as possible candidates due to zero ozone depletion potentials (ODPs), some of them have been banned by Kyoto Protocol because of high global warming potentials (GWPs). Since hydrocarbons(HCs), such as propane, n-butane, isobutene, and propylene, have zero ODPs and near zero GWPs, they have also been used as possible alternatives. However, HCs’ low flammability level increases the risk of fires in case of leakage. These problems of pure HFCs and HCs can be solved by mixing them. Thus many studies of various mixtures of HFCs and HCs have been investigated [1], [2], [3], [4], [5], [6], [7], [8].
Vapor–liquid equilibrium (VLE) data for HFCs and HCs are essential to decide the optimal composition of the mixtures and to design refrigeration process. Although many binary VLE data for the mixture have been measured, more data are still needed in order to seek alternative refrigerants and to evaluate the efficiency of the refrigerant cycle. In this paper, we present isothermal VLE data of the HFC-152a + isobutene system in the temperature range from 273.15 K to 348.15 K at 15 K intervals. The experimental data were correlated by the Peng–Robinson–Stryjek–Vera equation of state (PRSV EOS) [9], [10] with the Wong–Sandler mixing rules [11] involving NRTL model [12].
Section snippets
Materials
HFC-152a was purchased from Ulsan Chemical Co with a guaranteed purity higher than 99.9%. Isobutene was supplied by Korean Industrial Gases with a guaranteed purity higher than 99.5%. All components were used without further purification in these experiments.
Experimental apparatus
The measurement of the VLE data was conducted in a circulation type apparatus. The details of this apparatus were given in our previous studies [8]. The equilibrium cell was made of 316-stainless steel and equipped with two windows for
Correlations
In this work, the experimental VLE data were correlated with the Peng–Robinson–Stryjek–Vera equation of state (PRSV EOS) [10] using the Wong–Sandler mixing rules [11]. The PRSV EOS and the Wong–Sandler mixing rules are expressed as follows:where Tc is the critical temperature, Pc is the critical pressure, Tr is the reduced temperature,
Results and discussion
Isothermal VLE data for the binary system, HFC-152a (1) + isobutene (2), were measured at temperatures from 273.15 K to 348.15 K. Experimental and calculated data are given in Table 2. The Simplex algorithm was used to minimize the following objective function:where N is the number of data points, Pexp is the measured pressures and Pcal is the calculated pressures. As can be seen in Fig. 1, the calculated results represent a good agreement with the measured data at each
Conclusions
In this work, VLE data for the HFC-152a (1) + isobutene (2) system were measured in a temperature range from 273.15 K to 348.15 K at 15 K interval. The Peng–Robinson–Stryjek–Vera equation of state with the Wong–Sandler mixing rules involving NRTL model was used to correlate experimental data. The results indicate that this system shows a positive azeotrope at each temperature. Overall, the values of the deviations of pressure and vapor composition were less than 0.385% and 0.0282, and the calculated
Acknowledgements
This work was supported by the Brain Korea 21 Program supported by the Ministry of Education and by the National Research Laboratory (NRL) Program supported by Korea Institute of S&T Evaluation and Planning.
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