The (p, ρ, T, x) properties of (x1 propane + x2 n-butane) with x1 = (0.0000, 0.2729, 0.5021, and 0.7308) over the temperature range from (280 to 440) K at pressures from (1 to 200) MPa

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Abstract

The (p, ρ, T, x) properties for (x1 propane + x2 n-butane) with x1 = (0.0000, 0.2729, 0.5021, and 0.7308) in the compressed liquid phase were measured by means of a metal-bellows variable volumometer over the temperature range from (280 to 440) K at pressures from (1 to 200) MPa. The mole fraction purities of the propane and n-butane used in the measurements were 0.9999 and 0.9997, respectively. The expanded uncertainties (k = 2) in temperature, pressure, density, and composition measurements have been estimated to be less than ±3 mK; 1.4 kPa (p  7 MPa), 0.06% (7 MPa < p  50 MPa), 0.1% (50 MPa < p  150 MPa), and 0.2% (p > 150 MPa); 0.09%; and 4.4 · 10−4, respectively. In the region above 100 MPa at T = (280 and 440) K, the uncertainty in density measurements increases from 0.09% to 0.13% and 0.22%, respectively. Comparisons of the available equation of state with the present measurements are reported. On the basis of the present results, the excess molar volume vmE of the mixtures was calculated and illustrated as a function of temperature and pressure.

Introduction

We reported various thermodynamic property measurements for isobutane [1], [2], propane [3], [4], n-butane [5], [6], and propane/isobutane binary mixture [7] using a metal-bellows variable volumometer. In this study, we measured (p, ρ, T, x) property data for (x1 propane + x2 n-butane) with x1 = (0.0000, 0.2729, 0.5021, and 0.7308) over a wide range of temperatures from (280 to 440) K at pressures from (1 to 200) MPa using the same apparatus.

Several sets of (p, ρ, T, x) data for propane/n-butane binary mixtures have been published previously. A detailed evaluation of data available prior to 1995 has also been published [8]. Kahre [9] measured a total 20 points of (p, ρ, T, x) data at T = (289 to 328) K with x1 = (0.1487 to 0.8441), including the data at pressures up to 1.6 MPa. Parrish [10] also measured total 513 points of data by means of vibrating tube densimeter at T = (283 to 333) K below p = 9.7 MPa and with x1 = (0.0990 to 0.7518). In recent years, Holcomb et al. [11] have obtained 23 points of (p, ρ, T, x) data at T = (339 to 374) K and with x1 = 0.61364 by means of a vibrating tube densimeter. Magee [12] has also reported 106 points of data at T = (244 to 400) K with x1 = 0.61364 in the high pressure range up to 35 MPa using the isochoric method. In 2005, Kayukawa et al. [13] have reported 271 points of (p, ρ, T, x) data at T = (239 to 380) K with x1 = (0.250, 0.500, and 0.750) in the pressure range up to 7.1 MPa by means of vibrating tube densimeter.

Section snippets

Experimental

The measurements were carried out using the same apparatus employed in the previous work [1], [2], [3], [4], [5], [6], [7]. The experimental procedures are described in detail elsewhere [2], [14].

A sample mixture of known mass and composition was prepared gravimetrically, and was loaded into a bellows container in a pressure vessel, which was immersed in a thermostatted oil bath. The temperature was measured with a 25 Ω platinum resistance thermometer (Tinsley: 5187SASS) by a thermometer bridge

Results

We carried out density, ρ, measurements of (x1 propane + x2 n-butane) with x1 = (0.0000, 0.2729, 0.5021, and 0.7308) over a wide range of temperatures from (280 to 440) K at pressures (1 to 200) MPa. The experimental results are given in table 1 for (x1 propane + x2 n-butane) with x1 = 0.0000, in table 2 with x1 = 0.2729, in table 3 with x1 = 0.5021, in table 4 with x1 = 0.7308. The measurements with x1 = 0.0000 were conducted for the purpose of calculation of the excess molar volumes vmE for (x1 propane + x2 n

Discussion

Figure 1 shows comparisons of the present data with our previous data [5] for n-butane at T = 380 K and at pressures (3 to 200) MPa. In this figure, the baseline represents the present data. Although the sample filling procedure and the calibration equations of the inner volume of the bellows are different, the differences are within their error bars which are the sum of the uncertainty in density measurements of 0.09% for the present data and of 0.09% for the previous data [5].

FIGURE 2, FIGURE 3,

Acknowledgement

The present work is supported through the Postdoctoral Fellowship in 2005–2007 (Project No. 8042) by Japan Society for the Promotion of Science.

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