Measurement and correlation of the (p, ρ, T) behavior of liquid propylene glycol at temperatures from (272.7 to 393.0) K and pressures up to 91.4 MPa
Graphical abstract
Introduction
Propylene glycol (IUPAC name: propane-1,2-diol) is an important industrial substance across a variety of applications. It is generally used as an emulsifier and is an ingredient in antifreeze, cosmetics and pharmaceuticals [1]. Additionally, propylene glycol is commonly utilized as a pressure transmitting fluid [2]. Although propylene glycol has a large and diverse portfolio of applications, there is currently no fundamental equation of state (EOS) available to accurately calculate thermodynamic properties of this fluid over a wide range of temperature and pressure.
A literature review of the available experimental (p, ρ, T) data and vapour pressures ps for propylene glycol is summarized in Table 1, Table 2, respectively, and is illustrated in Fig. 1; here, the vapour-liquid phase boundary was calculated with the Wagner-type equation [3]:where TC = 676.40 K, pC = 6.3455 MPa, al = 2.60958, a2 = –37.8647, a3 = 32.84467, a4 = –15.2156, bl = 1.0, b2 = 1.5, b3 = 2.0, and b4 = 4.0. The critical point data (TC and pC) were acquired from literature [4], [5], and the parameters ai were obtained by correlating the available experimental data to Eq. (1) with fixed parameters bi. An obvious lack of experimental (p, ρ, T) data was observed. Therefore, the main purpose of this work is to extend the current experimental (p, ρ, T) data situation for propylene glycol.
Measurements were conducted with a commercially-available high-pressure vibrating-tube densimeter (VTD) in the homogeneous liquid phase over the temperature range from (272.7 to 393.0) K at pressures from (5.0 to 91.4) MPa. The measured (p, T) state points are depicted in Fig. 1. While the development of a fundamental EOS is outside the scope of the current work, a simpler correlation equation for liquid densities of propylene glycol is introduced here.
Section snippets
Apparatus description
The current measuring system was set up to enable density measurements between T = (263.15 and 393.15) K and from vacuum up to pressures of 100 MPa. A schematic diagram of the measuring system is shown in Fig. 2. The VTD (Anton Paar, Austria, type: DMA HPM), with its inlet and outlet tubes, is connected to a sample manifold, which also includes a pressure transducer (WIKA, Germany, type: P-30) and a rupture disc. The VTD is thermostated by a circulation thermostat (Huber, Germany, type:
Calibration
To determine the apparatus parameters A(p,T) and B(p,T) in Eq. (2), mathematical models and calibration measurements with reference fluids are necessary. There are various models available in the literature [7], [8], [9], [10]. To investigate the influence of the selected model on the results of the density determination and to estimate the uncertainty attributed from the model, two models were utilized in this work.
May et al. [7], [11] presented a physically-based model as:
Conclusion
The (p, ρ, T) behavior of propylene glycol was investigated over the temperature range from T = (272.7 to 393.0) K at pressures from (5.0 to 91.4) MPa utilizing a commercially-available high-pressure vibrating-tube densimeter. This work extends the current data situation for propylene glycol with respect to temperature and pressure range. The influence of the model for the vibrating-tube densimeter on the results of the density measurements was investigated, and the uncertainty in density
Notes
The authors declare no competing financial interest.
Acknowledgements
This work was financially supported through funds of the faculty of mechanical engineering at Ruhr-Universität Bochum (RUB). We thank our colleague Dr. Monika Thol of the thermodynamics group at RUB who has motivated the measurements presented here and who was always available for fruitful discussions. Also, we appreciate our laboratory engineer Malte Heine for his support in setting up the high-pressure measuring system in a short time and our colleague Christian Scholz for conducting part of
References (182)
- et al.
J. Chem. Thermodyn.
(2012) Cryogenics
(1973)- et al.
Fluid Phase Equilib.
(2001) - et al.
Fluid Phase Equilib.
(1998) - et al.
Fluid Phase Equilib.
(2007) - et al.
Fluid Phase Equilib.
(2014) - et al.
J. Chem. Thermodyn.
(2008) - et al.
Fluid Phase Equilib.
(2017) - et al.
J. Chem. Thermodyn.
(2013) - et al.
J. Chem. Thermodyn.
(2001)